14 CFR 23.471 - General.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false General. 23.471 Section 23.471 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... forces that act upon an airplane structure. In each specified ground load condition, the external...

14 CFR 23.471 - General.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false General. 23.471 Section 23.471 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... forces that act upon an airplane structure. In each specified ground load condition, the external...

14 CFR 23.471 - General.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false General. 23.471 Section 23.471 Aeronautics and Space FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION AIRCRAFT AIRWORTHINESS... forces that act upon an airplane structure. In each specified ground load condition, the external...

Different elution modes and field programming in gravitational field-flow fractionation. III. Field programming by flow-rate gradient generated by a programmable pump.

PubMed

Plocková, J; Chmelík, J

2001-05-25

Gravitational field-flow fractionation (GFFF) utilizes the Earth's gravitational field as an external force that causes the settlement of particles towards the channel accumulation wall. Hydrodynamic lift forces oppose this action by elevating particles away from the channel accumulation wall. These two counteracting forces enable modulation of the resulting force field acting on particles in GFFF. In this work, force-field programming based on modulating the magnitude of hydrodynamic lift forces was implemented via changes of flow-rate, which was accomplished by a programmable pump. Several flow-rate gradients (step gradients, linear gradients, parabolic, and combined gradients) were tested and evaluated as tools for optimization of the separation of a silica gel particle mixture. The influence of increasing amount of sample injected on the peak resolution under flow-rate gradient conditions was also investigated. This is the first time that flow-rate gradients have been implemented for programming of the resulting force field acting on particles in GFFF.

Adaptation of Porter’s Five Forces Model to Risk Management

DTIC Science & Technology

2010-07-01

The external forces—new entrants, bargaining power of buyers and suppliers, and substitutes—are shown as the threats acting on the industry. FIGURE 2...Planned Actual FIGURE 3. PORTER’S FIVE FORCES MODEL Industry Competitors Intensity of Rivalry Suppliers Buyers Bargaining Power of Suppliers Bargaining... Power of Buyers New Entrants Threat of New Entrants Substitutes Threat of Substitutes 3 7 9 | A Publication of the Defense Acquisition

Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma

NASA Astrophysics Data System (ADS)

Brower, D. L.; Ding, W. X.; Lin, L.; Almagri, A. F.; den Hartog, D. J.; Sarff, J. S.

2012-10-01

Magnetic fluctuations have been long observed in various magnetic confinement configurations. These perturbations may arise naturally from plasma instabilities such as tearing modes and energetic particle driven modes, but they can also be externally imposed by error fields or external magnetic coils. It is commonly observed that large MHD modes lead to plasma locking (no rotation) due to torque produced by eddy currents on the wall, and it is predicted that stochastic field induces flow damping where the radial electric field is reduced. Flow generation is of great importance to fusion plasma research, especially low-torque devices like ITER, as it can act to improve performance. Here we describe new measurements in the MST reversed field pinch (RFP) showing that the coherent interaction of magnetic and particle density fluctuations can produce a turbulent fluctuation-induced kinetic force, which acts to drive intrinsic plasma rotation. Key observations include; (1) the average kinetic force resulting from density fluctuations, ˜ 0.5 N/m^3, is comparable to the intrinsic flow acceleration, and (2) between sawtooth crashes, the spatial distribution of the kinetic force is directed to create a sheared parallel flow profile that is consistent with the measured flow profile in direction and amplitude, suggesting the kinetic force is responsible for intrinsic plasma rotation.

Dikin-type algorithms for dextrous grasping force optimization

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

Buss, M.; Faybusovich, L.; Moore, J.B.

1998-08-01

One of the central issues in dextrous robotic hand grasping is to balance external forces acting on the object and at the same time achieve grasp stability and minimum grasping effort. A companion paper shows that the nonlinear friction-force limit constraints on grasping forces are equivalent to the positive definiteness of a certain matrix subject to linear constraints. Further, compensation of the external object force is also a linear constraint on this matrix. Consequently, the task of grasping force optimization can be formulated as a problem with semidefinite constraints. In this paper, two versions of strictly convex cost functions, onemore » of them self-concordant, are considered. These are twice-continuously differentiable functions that tend to infinity at the boundary of possible definiteness. For the general class of such cost functions, Dikin-type algorithms are presented. It is shown that the proposed algorithms guarantee convergence to the unique solution of the semidefinite programming problem associated with dextrous grasping force optimization. Numerical examples demonstrate the simplicity of implementation, the good numerical properties, and the optimality of the approach.« less

The Rural Community College as an Administrative Labor Market

ERIC Educational Resources Information Center

Allen, Nathan T.; Cejda, Brent D.

2007-01-01

External culture acts as a powerful force on rural community colleges and the presidents that lead them. This article examines whether rural community colleges comprise an administrative labor market, based on the careers of 69 chief academic officers employed in rural community colleges. Findings indicate the characteristics of both an…

The Ontology of Determination: From Descartes to Spinoza.

PubMed

Sangiacomo, Andrea

2015-12-01

This paper argues that Spinoza's notions of "conatus" and "power of acting" are derived by means of generalization from the notions of "force of motion" and "force of determination" that Spinoza discussed in his Principles of Cartesian Philosophy to account for interactions among bodies (impacts) on the basis of their degrees of contrariety. I argue that in the Ethics, Spinoza's ontology entails that interactions must always be accounted for in terms of degrees of "agreement or disagreement in nature" among interacting things. The notion of "power of acting" is used to express the extent to which a thing's conatus is aided or restrained by external causes on the basis of its degree of agreement or disagreement in nature with them. "Power of acting" generalizes the same approach and method of resolution at the basis of the notion of "force of determination" in order to account for causal interactions not only among the simplest bodies but also among more complex individuals.

Structural and rheological relaxation upon flow cessation in colloidal dispersions: Transient, nonlinear microrheology

NASA Astrophysics Data System (ADS)

Mohanty, Ritesh P.; Zia, Roseanna N.

2017-11-01

We theoretically study the impact of particle roughness, Brownian motion, and hydrodynamic interactions on the relaxation of colloidal dispersions by examining the structural and rheological relaxation after microrheological flow cessation. In particular, we focus on the disparity in timescales over which hydrodynamic and entropic forces act and influence colloidal relaxation. To do this, we employ the active microrheology framework, in which a colloidal probe, driven by an arbitrarily strong external force, interacts with many surrounding particle configurations before reaching steady-state motion. We utilize the steady-state structure around the probe as the initial condition in a Smoluchowski equation that we solve to obtain the structural evolution upon flow cessation. We systematically tune the strength of hydrodynamic and entropic forces, and study their influence on structural and rheological relaxation. Upon cessation, the non-Newtonian behavior arising directly from hydrodynamic forces dissipates instantaneously, while the entropic contributions decay over longer times. We find that increasing pre-cessation external flow strength enhances the relaxation rate, while hydrodynamic interactions slow down the relaxation.

Load response of shape-changing microswimmers scales with their swimming efficiency

NASA Astrophysics Data System (ADS)

Friedrich, Benjamin M.

2018-04-01

External forces acting on a microswimmer can feed back on its self-propulsion mechanism. We discuss this load response for a generic microswimmer that swims by cyclic shape changes. We show that the change in cycle frequency is proportional to the Lighthill efficiency of self-propulsion. As a specific example, we consider Najafi's three-sphere swimmer. The force-velocity relation of a microswimmer implies a correction for a formal superposition principle for active and passive motion.

Theory of interacting dislocations on cylinders.

PubMed

Amir, Ariel; Paulose, Jayson; Nelson, David R

2013-04-01

We study the mechanics and statistical physics of dislocations interacting on cylinders, motivated by the elongation of rod-shaped bacterial cell walls and cylindrical assemblies of colloidal particles subject to external stresses. The interaction energy and forces between dislocations are solved analytically, and analyzed asymptotically. The results of continuum elastic theory agree well with numerical simulations on finite lattices even for relatively small systems. Isolated dislocations on a cylinder act like grain boundaries. With colloidal crystals in mind, we show that saddle points are created by a Peach-Koehler force on the dislocations in the circumferential direction, causing dislocation pairs to unbind. The thermal nucleation rate of dislocation unbinding is calculated, for an arbitrary mobility tensor and external stress, including the case of a twist-induced Peach-Koehler force along the cylinder axis. Surprisingly rich phenomena arise for dislocations on cylinders, despite their vanishing Gaussian curvature.

Charge-Spot Model for Electrostatic Forces in Simulation of Fine Particulates

NASA Technical Reports Server (NTRS)

Walton, Otis R.; Johnson, Scott M.

2010-01-01

The charge-spot technique for modeling the static electric forces acting between charged fine particles entails treating electric charges on individual particles as small sets of discrete point charges, located near their surfaces. This is in contrast to existing models, which assume a single charge per particle. The charge-spot technique more accurately describes the forces, torques, and moments that act on triboelectrically charged particles, especially image-charge forces acting near conducting surfaces. The discrete element method (DEM) simulation uses a truncation range to limit the number of near-neighbor charge spots via a shifted and truncated potential Coulomb interaction. The model can be readily adapted to account for induced dipoles in uncharged particles (and thus dielectrophoretic forces) by allowing two charge spots of opposite signs to be created in response to an external electric field. To account for virtual overlap during contacts, the model can be set to automatically scale down the effective charge in proportion to the amount of virtual overlap of the charge spots. This can be accomplished by mimicking the behavior of two real overlapping spherical charge clouds, or with other approximate forms. The charge-spot method much more closely resembles real non-uniform surface charge distributions that result from tribocharging than simpler approaches, which just assign a single total charge to a particle. With the charge-spot model, a single particle may have a zero net charge, but still have both positive and negative charge spots, which could produce substantial forces on the particle when it is close to other charges, when it is in an external electric field, or when near a conducting surface. Since the charge-spot model can contain any number of charges per particle, can be used with only one or two charge spots per particle for simulating charging from solar wind bombardment, or with several charge spots for simulating triboelectric charging. Adhesive image-charge forces acting on charged particles touching conducting surfaces can be up to 50 times stronger if the charge is located in discrete spots on the particle surface instead of being distributed uniformly over the surface of the particle, as is assumed by most other models. Besides being useful in modeling particulates in space and distant objects, this modeling technique is useful for electrophotography (used in copiers) and in simulating the effects of static charge in the pulmonary delivery of fine dry powders.

Using Enthalpy as a Prognostic Variable in Atmospheric Modelling with Variable Composition

DTIC Science & Technology

2016-04-14

the first place. It then becomes clear that specific enthalpy provides a viable alternative to account for the effects of composi- tional changes on...forces. It is also assumed that external forces acting on a molecule are proportional to its mass, mi , as is the case with the gravity or Coriolis ...relative humidity and is introduced into Equation (11) to account for the effects of water vapour on the gas constant R and, consequently, on the

Assessing the industry using Porter's five forces.

PubMed

2014-01-01

To develop a business and plan for the future, there is a need to assess the current situation. One way of doing this is to use Porter's five forces framework. This was the brainchild of Harvard Business School's Michael Porter and developed in 1979. Looking at the competitive intensity of an industry, the model assesses internal and external factors that act together to determine the direction of the business; taken together, this gives an indication of the attractiveness of the industry.

Characterization of the biomechanical properties of T4 pili expressed by Streptococcus pneumoniae--a comparison between helix-like and open coil-like pili.

PubMed

Castelain, Mickaël; Koutris, Efstratios; Andersson, Magnus; Wiklund, Krister; Björnham, Oscar; Schedin, Staffan; Axner, Ove

2009-07-13

Bacterial adhesion organelles, known as fimbria or pili, are expressed by gram-positive as well as gram-negative bacteria families. These appendages play a key role in the first steps of the invasion and infection processes, and they therefore provide bacteria with pathogenic abilities. To improve the knowledge of pili-mediated bacterial adhesion to host cells and how these pili behave under the presence of an external force, we first characterize, using force measuring optical tweezers, open coil-like T4 pili expressed by gram-positive Streptococcus pneumoniae with respect to their biomechanical properties. It is shown that their elongation behavior can be well described by the worm-like chain model and that they possess a large degree of flexibility. Their properties are then compared with those of helix-like pili expressed by gram-negative uropathogenic Escherichia coli (UPEC), which have different pili architecture. The differences suggest that these two types of pili have distinctly dissimilar mechanisms to adhere and sustain external forces. Helix-like pili expressed by UPEC bacteria adhere to host cells by single adhesins located at the distal end of the pili while their helix-like structures act as shock absorbers to dampen the irregularly shear forces induced by urine flow and to increase the cooperativity of the pili ensemble, whereas open coil-like pili expressed by S. pneumoniae adhere to cells by a multitude of adhesins distributed along the pili. It is hypothesized that these two types of pili represent different strategies of adhering to host cells in the presence of external forces. When exposed to significant forces, bacteria expressing helix-like pili remain attached by distributing the external force among a multitude of pili, whereas bacteria expressing open coil-like pili sustain large forces primarily by their multitude of binding adhesins which presumably detach sequentially.

Mathematical model for gyroscope effects

NASA Astrophysics Data System (ADS)

Usubamatov, Ryspek

2015-05-01

Gyroscope effects are used in many engineering calculations of rotating parts, and a gyroscope is the basic unit of numerous devices and instruments used in aviation, space, marine and other industries. The primary attribute of a gyroscope is a spinning rotor that persists in maintaining its plane of rotation, creating gyroscope effects. Numerous publications represent the gyroscope theory using mathematical models based on the law of kinetic energy conservation and the rate of change in angular momentum of a spinning rotor. Gyroscope theory still attracts many researchers who continue to discover new properties of gyroscopic devices. In reality, gyroscope effects are more complex and known mathematical models do not accurately reflect the actual motions. Analysis of forces acting on a gyroscope shows that four dynamic components act simultaneously: the centrifugal, inertial and Coriolis forces and the rate of change in angular momentum of the spinning rotor. The spinning rotor generates a rotating plane of centrifugal and Coriols forces that resist the twisting of the spinning rotor with external torque applied. The forced inclination of the spinning rotor generates inertial forces, resulting in precession torque of a gyroscope. The rate of change of the angular momentum creates resisting and precession torques which are not primary one in gyroscope effects. The new mathematical model for the gyroscope motions under the action of the external torque applied can be as base for new gyroscope theory. At the request of the author of the paper, this corrigendum was issued on 24 May 2016 to correct an incomplete Table 1 and errors in Eq. (47) and Eq. (48).

Scale-dependent Ocean Wave Turbulence

NASA Technical Reports Server (NTRS)

Glazman, R. E.

1995-01-01

Wave turbulence is a common feature of nonlinear wave motions observed when external forcing acts during a long period of time, resulting in developed spectral cascades of energy, momentum, and other conserved integrals. In the ocean, wave turbulence occurs on various scales from capillary ripples, and those of baroclinic inertia-gravity, to Rossby waves. Oceanic wave motions are discussed.

Spool-Valve Pressure-Difference Regulator

NASA Technical Reports Server (NTRS)

Grasso, A. P.

1983-01-01

Valves maintain preset pressure difference between gas flows. Two spool valves connected by shaft move back and forth in response to changes in pressure in oxygen and hydrogen chambers. Spool-valve assembly acts to restore pressures to preset difference. By eliminating diaphragms, pressure exerted directly on external end of spool valve; however, forces and therefore sensitivity of assembly are reduced.

Magneto-motive detection of tissue-based macrophages by differential phase optical coherence tomography.

PubMed

Oh, Junghwan; Feldman, Marc D; Kim, Jihoon; Kang, Hyun Wook; Sanghi, Pramod; Milner, Thomas E

2007-03-01

A novel method to detect tissue-based macrophages using a combination of superparamagnetic iron oxide (SPIO) nanoparticles and differential phase optical coherence tomography (DP-OCT) with an external oscillating magnetic field is reported. Magnetic force acting on iron-laden tissue-based macrophages was varied by applying a sinusoidal current to a solenoid containing a conical iron core that substantially focused and increased magnetic flux density. Nanoparticle motion was detected with DP-OCT, which can detect tissue movement with nanometer resolution. Frequency response of iron-laden tissue movement was twice the modulation frequency since the magnetic force is proportional to the product of magnetic flux density and gradient. Results of our experiments indicate that DP-OCT can be used to identify tissue-based macrophage when excited by an external focused oscillating magnetic field. (c) 2007 Wiley-Liss, Inc

Development of magnetic separation system of magnetoliposomes

NASA Astrophysics Data System (ADS)

Nakao, R.; Matuo, Y.; Mishima, F.; Taguchi, T.; Maenosono, S.; Nishijima, S.

2009-10-01

The magnetic separation technology using sub-microsized ferromagnetic particle is indispensable in many areas of medical biosciences. For example, ferromagnetic particles (200-500 nm) are widely used for cell sorting in stem cell research with the use of cell surface-specific antigens. Nanosized ferromagnetic particles (10-20 nm) have been suggested as more suitable in drug delivery studies given their efficiency of tissue penetration, however, the magnetic separation method for them has not been established. One of the major reasons is that magnetic force acting on the object particles decreases drastically as a particle diameter becomes small. In this study, magnetic force acting on the targets was enhanced by the combination of superconducting magnet and the filter consisting of ferromagnetic particle. By doing so, we confirmed that Fe 3O 4 of 20 nm in diameter was trapped in the magnetic filter under an external magnetic field of 0.5 T. Fe 3O 4 encapsulated with phospholipid liposomes of 200 nm in diameter was also shown to be trapped as external magnetic field of 1.5 T, but not of 0.5 T. We also showed the result of particle trajectory calculation which emulated well the experimental data.

Design of responsive materials using topologically interlocked elements

NASA Astrophysics Data System (ADS)

Molotnikov, A.; Gerbrand, R.; Qi, Y.; Simon, G. P.; Estrin, Y.

2015-02-01

In this work we present a novel approach to designing responsive structures by segmentation of monolithic plates into an assembly of topologically interlocked building blocks. The particular example considered is an assembly of interlocking osteomorphic blocks. The results of this study demonstrate that the constraining force, which is required to hold the blocks together, can be viewed as a design parameter that governs the bending stiffness and the load bearing capacity of the segmented structure. In the case where the constraining forces are provided laterally using an external frame, the maximum load the assembly can sustain and its stiffness increase linearly with the magnitude of the lateral load applied. Furthermore, we show that the segmented plate with integrated shape memory wires employed as tensioning cables can act as a smart structure that changes its flexural stiffness and load bearing capacity in response to external stimuli, such as heat generated by the switching on and off an electric current.

Unstable footwear as a speed-dependent noise-based training gear to exercise inverted pendulum motion during walking.

PubMed

Dierick, Frédéric; Bouché, Anne-France; Scohier, Mikaël; Guille, Clément; Buisseret, Fabien

2018-05-15

Previous research on unstable footwear has suggested that it may induce mechanical noise during walking. The purpose of this study was to explore whether unstable footwear could be considered as a noise-based training gear to exercise body center of mass (CoM) motion during walking. Ground reaction forces were collected among 24 healthy young women walking at speeds between 3 and 6 km h -1 with control running shoes and unstable rocker-bottom shoes. The external mechanical work, the recovery of mechanical energy of the CoM during and within the step cycles, and the phase shift between potential and kinetic energy curves of the CoM were computed. Our findings support the idea that unstable rocker-bottom footwear could serve as a speed-dependent noise-based training gear to exercise CoM motion during walking. At slow speed, it acts as a stochastic resonance or facilitator that reduces external mechanical work; whereas at brisk speed it acts as a constraint that increases external mechanical work and could mimic a downhill slope.

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

The use of electromagnetic body forces to enhance the quality of laser welds

NASA Astrophysics Data System (ADS)

Ambrosy, Guenter; Berger, P.; Huegel, H.; Lindenau, D.

2003-11-01

The use of electromagnetic body forces in laser beam welding of aluminum alloys is a new method to shape the geometry and to enhance the quality of the weld seams. In this new approach, electromagnetic volume forces are utilized by applying magnetic fields and electric currents of various origins. Acting in the liquid metal, they directly affect the flow field and can lead to favourable conditions for the melt dynamics and energy coupling. Numerous welds with full and partial penetration using both CO2 and Nd:YAG lasers demonstrate that this method directly influences the seam geometry and top-bead topography as well as the penetration depth and the evolution of pores and cracks. In the case of full penetration, it is also possible to lift or to lower the weld pool. The method, therefore, can be used to shape the geometry and to enhance the quality of the weld seam. Depending on the orientation of an external magnetic field, significant impacts are achieved in CO2 welding, even without an external current: the shape of the cross-sectional area can be increased of up to 50% and also the seam width is changed. Whereas for such conditions with Nd:YAG lasers no significant effect could be observed, it turned out that, when an external electric current is applied, similar effects are present with both wavelengths. In further investigations, the effect of electromagnetic body forces resulting from the interaction of an external current and its self-induced magnetic field was studied. Hereby, the current was fed into the workpiece via a tungsten electrode or a filler wire. The resulting phenomena are the same independent from wavelength and means of current feed.

Proceedings and Minutes of the National Interagency Coordination Group Meeting - Low Altitude Direct Strike Lightning Characterization Program Held in Saint Louis, Missouri on 28-29 January 1985.

DTIC Science & Technology

1985-09-01

Gallon External Fuel Tank. a. This is a filament-wound fuel tank with nomex honeycomb core, inner layers of Kevlar and glass , outer layers of...MD 20910 Dr. A. Carro FAA Technical Center Mr. Jack Lippert ACT-340 AFWAL/FIEA Atlantic City Airport, NJ 08405 Air Force Wright Aeronautical Lab

Non-exponential kinetics of unfolding under a constant force.

PubMed

Bell, Samuel; Terentjev, Eugene M

2016-11-14

We examine the population dynamics of naturally folded globular polymers, with a super-hydrophobic "core" inserted at a prescribed point in the polymer chain, unfolding under an application of external force, as in AFM force-clamp spectroscopy. This acts as a crude model for a large class of folded biomolecules with hydrophobic or hydrogen-bonded cores. We find that the introduction of super-hydrophobic units leads to a stochastic variation in the unfolding rate, even when the positions of the added monomers are fixed. This leads to the average non-exponential population dynamics, which is consistent with a variety of experimental data and does not require any intrinsic quenched disorder that was traditionally thought to be at the origin of non-exponential relaxation laws.

Non-exponential kinetics of unfolding under a constant force

NASA Astrophysics Data System (ADS)

Bell, Samuel; Terentjev, Eugene M.

2016-11-01

We examine the population dynamics of naturally folded globular polymers, with a super-hydrophobic "core" inserted at a prescribed point in the polymer chain, unfolding under an application of external force, as in AFM force-clamp spectroscopy. This acts as a crude model for a large class of folded biomolecules with hydrophobic or hydrogen-bonded cores. We find that the introduction of super-hydrophobic units leads to a stochastic variation in the unfolding rate, even when the positions of the added monomers are fixed. This leads to the average non-exponential population dynamics, which is consistent with a variety of experimental data and does not require any intrinsic quenched disorder that was traditionally thought to be at the origin of non-exponential relaxation laws.

Nature of the electromagnetic force between classical magnetic dipoles

NASA Astrophysics Data System (ADS)

Mansuripur, Masud

2017-09-01

The Lorentz force law of classical electrodynamics states that the force 𝑭𝑭 exerted by the magnetic induction 𝑩𝑩 on a particle of charge 𝑞𝑞 moving with velocity 𝑽𝑽 is given by 𝑭𝑭 = 𝑞𝑞𝑽𝑽 × 𝑩𝑩. Since this force is orthogonal to the direction of motion, the magnetic field is said to be incapable of performing mechanical work. Yet there is no denying that a permanent magnet can readily perform mechanical work by pushing/pulling on another permanent magnet or by attracting pieces of magnetizable material such as scrap iron or iron filings. We explain this apparent contradiction by examining the magnetic Lorentz force acting on an Amperian current loop, which is the model for a magnetic dipole. We then extend the discussion by analyzing the Einstein-Laub model of magnetic dipoles in the presence of external magnetic fields.

Understanding force-generating microtubule systems through in vitro reconstitution

PubMed Central

Kok, Maurits; Dogterom, Marileen

2016-01-01

ABSTRACT Microtubules switch between growing and shrinking states, a feature known as dynamic instability. The biochemical parameters underlying dynamic instability are modulated by a wide variety of microtubule-associated proteins that enable the strict control of microtubule dynamics in cells. The forces generated by controlled growth and shrinkage of microtubules drive a large range of processes, including organelle positioning, mitotic spindle assembly, and chromosome segregation. In the past decade, our understanding of microtubule dynamics and microtubule force generation has progressed significantly. Here, we review the microtubule-intrinsic process of dynamic instability, the effect of external factors on this process, and how the resulting forces act on various biological systems. Recently, reconstitution-based approaches have strongly benefited from extensive biochemical and biophysical characterization of individual components that are involved in regulating or transmitting microtubule-driven forces. We will focus on the current state of reconstituting increasingly complex biological systems and provide new directions for future developments. PMID:27715396

Note: Effect of the parasitic forced vibration in an atom gravimeter

NASA Astrophysics Data System (ADS)

Chen, Le-Le; Luo, Qin; Zhang, Heng; Duan, Xiao-Chun; Zhou, Min-Kang; Hu, Zhong-Kun

2018-06-01

The vibration isolator usually plays an important role in atom interferometry gravimeters to improve their sensitivity. We show that the parasitic forced vibration of the Raman mirror, which is induced by external forces acting on the vibration isolator, can cause a bias in atom gravimeters. The mechanism of how this effect induces an additional phase shift in our interferometer is analyzed. Moreover, modulation experiments are performed to measure the dominant part of this effect, which is caused by the magnetic force between the passive vibration isolator and the coil of the magneto-optic trap. In our current apparatus, this forced vibration contributes a systematic error of -2.3(2) × 10-7 m/s2 when the vibration isolator works in the passive isolation mode. Even suppressed with an active vibration isolator, this effect can still contribute -6(1) × 10-8 m/s2; thus, it should be carefully considered in precision atom gravimeters.

Identity transformation in medical students.

PubMed

Cohen, Mitchell J M; Kay, Abigail; Youakim, James M; Balaicuis, John M; Balacius, John M

2009-03-01

This paper reviews the literature on the impact of medical school on personal development and consolidation of core identity. The limited literature relies on reports from medical students' journaling exercises, discussion groups, post-graduation surveys, and repeated personality testing. We review forces acting on medical students, with potential transforming effects. These forces include high external expectations and internal fear of superficial knowledge and skills, entry into the culture of medicine with its insider jargon and hierarchy, high academic workload, and the emotional burdens of confronting cadavers and death as well as bearing witness to patients' suffering. Potential developmental delay, emergence of substance abuse and hedonic acting out, cynicism, and loss of individual core values are possible consequences. Protections against these adverse outcomes include identification of strong mentors and role models, developing post-conventional morality and relativistic thinking, finding healthy coping strategies such as peer support, and remaining intellectually creative and personally reflective.

Robust tilt and lock mechanism for hopping actuator

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

Salton, Jonathan R.; Buerger, Stephen; Dullea, Kevin J.

A tilt and lock apparatus that includes a tilt servomechanism, a spiral torsion spring, a lock wheel, and a lock hook is described herein. The spiral torsion spring is mechanically coupled to the tilt servomechanism and the lock wheel (which includes an opening). When a shaft is positioned through the opening, rotation of the lock wheel is in unison with rotation of the shaft. An external surface of the lock wheel includes one or more grooves. The lock hook includes a head that engages and disengages the grooves. The lock wheel is stationary when the head engages one of themore » grooves and is rotatable when the head disengages the grooves. The head and the grooves are geometrically aligned when engaged to prevent creation of a force that acts to disengage the head responsive to an applied force acting on the shaft.« less

α-Helix Unwinding as Force Buffer in Spectrins.

PubMed

Takahashi, Hirohide; Rico, Felix; Chipot, Christophe; Scheuring, Simon

2018-03-27

Spectrins are cytoskeletal proteins located at the inner face of the plasma membrane, making connections between membrane anchors and the actin cortex, and between actin filaments. Spectrins share a common structure forming a bundle of 3 α-helices and play a major role during cell deformation. Here, we used high-speed force spectroscopy and steered molecular dynamics simulations to understand the mechanical stability of spectrin, revealing a molecular force buffering function. We find that spectrin acts as a soft spring at short extensions (70-100 Å). Under continuous external stretching, its α-helices unwind, leading to a viscous mechanical response over larger extensions (100-300 Å), represented by a constant-force plateau in force/extension curves. This viscous force buffering emerges from a quasi-equilibrium competition between disruption and re-formation of α-helical hydrogen bonds. Our results suggest that, in contrast to β-sheet proteins, which unfold in a catastrophic event, α-helical spectrins dominantly unwind, providing a viscous force buffer over extensions about 5 times their folded length.

Optical forces, torques, and force densities calculated at a microscopic level using a self-consistent hydrodynamics method

NASA Astrophysics Data System (ADS)

Ding, Kun; Chan, C. T.

2018-04-01

The calculation of optical force density distribution inside a material is challenging at the nanoscale, where quantum and nonlocal effects emerge and macroscopic parameters such as permittivity become ill-defined. We demonstrate that the microscopic optical force density of nanoplasmonic systems can be defined and calculated using the microscopic fields generated using a self-consistent hydrodynamics model that includes quantum, nonlocal, and retardation effects. We demonstrate this technique by calculating the microscopic optical force density distributions and the optical binding force induced by external light on nanoplasmonic dimers. This approach works even in the limit when the nanoparticles are close enough to each other so that electron tunneling occurs, a regime in which classical electromagnetic approach fails completely. We discover that an uneven distribution of optical force density can lead to a light-induced spinning torque acting on individual particles. The hydrodynamics method offers us an accurate and efficient approach to study optomechanical behavior for plasmonic systems at the nanoscale.

The effect of climatic forcing on population synchrony and genetic structuring of the Canadian lynx

PubMed Central

Stenseth, Nils Chr.; Ehrich, Dorothee; Rueness, Eli Knispel; Lingjærde, Ole Chr.; Chan, Kung-Sik; Boutin, Stan; O'Donoghue, Mark; Robinson, David A.; Viljugrein, Hildegunn; Jakobsen, Kjetill S.

2004-01-01

The abundance of Canadian lynx follows 10-year density fluctuations across the Canadian subcontinent. These cyclic fluctuations have earlier been shown to be geographically structured into three climatic regions: the Atlantic, Continental, and Pacific zones. Recent genetic evidence revealed an essentially similar spatial structuring. Introducing a new population model, the “climate forcing of ecological and evolutionary patterns” model, we link the observed ecological and evolutionary patterns. Specifically, we demonstrate that there is greater phase synchrony within climatic zones than between them and show that external climatic forcing may act as a synchronizer. We simulated genetic drift by using data on population dynamics generated by the climate forcing of ecological and evolutionary patterns model, and we demonstrate that the observed genetic structuring can be seen as an emerging property of the spatiotemporal ecological dynamics. PMID:15067131

Are external knee load and EMG measures accurate indicators of internal knee contact forces during gait?

PubMed

Meyer, Andrew J; D'Lima, Darryl D; Besier, Thor F; Lloyd, David G; Colwell, Clifford W; Fregly, Benjamin J

2013-06-01

Mechanical loading is believed to be a critical factor in the development and treatment of knee osteoarthritis. However, the contact forces to which the knee articular surfaces are subjected during daily activities cannot be measured clinically. Thus, the ability to predict internal knee contact forces accurately using external measures (i.e., external knee loads and muscle electromyographic [EMG] signals) would be clinically valuable. We quantified how well external knee load and EMG measures predict internal knee contact forces during gait. A single subject with a force-measuring tibial prosthesis and post-operative valgus alignment performed four gait patterns (normal, medial thrust, walking pole, and trunk sway) to induce a wide range of external and internal knee joint loads. Linear regression analyses were performed to assess how much of the variability in internal contact forces was accounted for by variability in the external measures. Though the different gait patterns successfully induced significant changes in the external and internal quantities, changes in external measures were generally weak indicators of changes in total, medial, and lateral contact force. Our results suggest that when total contact force may be changing, caution should be exercised when inferring changes in knee contact forces based on observed changes in external knee load and EMG measures. Advances in musculoskeletal modeling methods may be needed for accurate estimation of in vivo knee contact forces. Copyright © 2012 Orthopaedic Research Society.

Designing an experiment to measure cellular interaction forces

NASA Astrophysics Data System (ADS)

McAlinden, Niall; Glass, David G.; Millington, Owain R.; Wright, Amanda J.

2013-09-01

Optical trapping is a powerful tool in Life Science research and is becoming common place in many microscopy laboratories and facilities. The force applied by the laser beam on the trapped object can be accurately determined allowing any external forces acting on the trapped object to be deduced. We aim to design a series of experiments that use an optical trap to measure and quantify the interaction force between immune cells. In order to cause minimum perturbation to the sample we plan to directly trap T cells and remove the need to introduce exogenous beads to the sample. This poses a series of challenges and raises questions that need to be answered in order to design a set of effect end-point experiments. A typical cell is large compared to the beads normally trapped and highly non-uniform - can we reliably trap such objects and prevent them from rolling and re-orientating? In this paper we show how a spatial light modulator can produce a triple-spot trap, as opposed to a single-spot trap, giving complete control over the object's orientation and preventing it from rolling due, for example, to Brownian motion. To use an optical trap as a force transducer to measure an external force you must first have a reliably calibrated system. The optical trapping force is typically measured using either the theory of equipartition and observing the Brownian motion of the trapped object or using an escape force method, e.g. the viscous drag force method. In this paper we examine the relationship between force and displacement, as well as measuring the maximum displacement from equilibrium position before an object falls out of the trap, hence determining the conditions under which the different calibration methods should be applied.

Prehension Synergies in Three Dimensions

PubMed Central

Shim, Jae Kun; Latash, Mark L.; Zatsiorsky, Vladimir M.

2010-01-01

The goal of this study was to investigate the conjoint changes of digit forces/moments in 3 dimensions during static prehension under external torques acting on the object in one plane. The experimental paradigm was similar to holding a book vertically in the air where the center of mass of the book is located farther from the hand than the points of digit contacts. Three force and 3 moment components from each digit were recorded during static prehension of a customized handle. Subjects produced forces and moments in all 3 directions, although the external torques were exerted on the handheld object about only the Z-axis. The 3-dimensional response to a 2-dimensional task was explained by the cause– effect chain effects prompted by the noncollinearity of the normal forces of the thumb and the 4 fingers (represented by the “virtual finger”). Because the forces are not collinear (not along the same line), they generate moments of force about X- and Y-axes that are negated by the finger forces along the Y- and X-directions. The magnitudes of forces produced by lateral fingers (index and little) with longer moment arms were larger compared with the central fingers (middle and ring). At the virtual finger (an imaginary digit whose mechanical action is equivalent to the summed action of the 4 fingers) level, the relative contribution of different fractions of the resistive moment produced by subjects did not depend on the torque magnitude. We conclude that the CNS 1) solves a planar prehension task by producing forces and moments in all 3 directions, 2) uses mechanical advantage of fingers, and 3) shares the total torque among finger forces and moments in a particular way disregarding the torque magnitude. PMID:15456799

Long range transport of colloids in aqueous solutions

NASA Astrophysics Data System (ADS)

Florea, Daniel; Musa, Sami; Huyghe, Jacques M. R. J.; Wyss, Hans M.

2013-03-01

Colloids in aqueous suspensions can experience strong, extremely long range repulsive forces near interfaces such as biological tissues, gels, ion exchange resins or metals. As a result exclusion zones extending over several millimeters can be formed. While this phenomenon has been previously described, a physical understanding of this process is still lacking. This exclusion zone formation is puzzling because the typical forces acting on colloidal particles are limited to much shorter distances and external fields that could drive the particles are absent. Here we study the exclusion zone formation in detail by following the time and distance-dependent forces acting on the particles. We present a simple model that accounts for our experimental data and directly links the exclusion zone formation to an already known physical transport phenomenon. We show that the effect can be tuned by changing the zeta potential of the particles or by varying the species present in the aqueous solution. We thus provide a direct physical explanation for the intriguing exclusion zone formation and we illustrate how this effect can be exploited in a range of industrial applications.

Mechanical rigidity of the Ortho-SUV frame compared to the Ilizarov frame in the correction of femoral deformity.

PubMed

Skomoroshko, Petr V; Vilensky, Victor A; Hammouda, Ahmed I; Fletcher, Matt D A; Solomin, Leonid N

2015-04-01

The Ortho-SUV frame (OSF) is a novel hexapod circular external fixator which draws upon the innovation of the Ilizarov method and the advantages of hexapod construction in the three-dimensional control of bone segments. Stability of fixation is critical to the success or failure of an external circular fixator for fracture or osteotomy healing. In vitro biomechanical modelling study was performed comparing the stability of the OSF under load in both original form and after dynamisation to the Ilizarov fixator in all zones of the femur utilising optimal frame configuration. A superior performance of the OSF in terms of resistance to deforming forces in both original and dynamised forms over that of the original Ilizarov fixator was found. The OSF shows higher rigidity than the Ilizarov in the control of forces acting upon the femur. This suggests better stabilisation of femoral fractures and osteotomies and thus improved healing with a reduced incidence of instability-related bone segment deformity, non-union and delayed union.

Bungee force level, stiffness, and variation during treadmill locomotion in simulated microgravity.

PubMed

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

2014-04-01

Crewmembers performing treadmill exercise on the International Space Station must wear a harness with an external gravity replacement force that is created by elastomer bungees. The quantification of the total external force, displacement, stiffness, and force variation is important for understanding the forces applied to the crewmember during typical exercise. Data were collected during static trials in the laboratory from a single subject and four subjects were tested while walking at 1.34 m x s(-1) and running at 2.24 m x s(-1) and 3.13 m x s(-1) on a treadmill during simulated microgravity in parabolic flight. The external force was provided by bungees and carabiner clips in configurations commonly used by crewmembers. Total external force, displacement, and force variation in the bungee system were measured, from which stiffness was computed. Mean external force ranged from 431 to 804 N (54-131% bodyweight) across subjects and conditions. Mean displacement was 4 to 8 cm depending upon gait speed. Mean stiffness was affected by bungee configuration and ranged from 1.73 to 29.20 N x cm(-1). Force variation for single bungee configurations was 2.61-4.48% of total external force and between 4.30-57.5% total external force for two-bungee configurations. The external force supplied to crewmembers by elastomer bungees provided a range of loading levels with variations that occur throughout the gait cycle. The quantification of bungee-loading characteristics is important to better define the system currently used by crewmembers during exercise.

Mechanically induced alterations in cultured skeletal muscle growth

NASA Technical Reports Server (NTRS)

Vandenburgh, H. H.; Hatfaludy, S.; Karlisch, P.; Shansky, J.

1991-01-01

Model systems are available for mechanically stimulating cultured skeletal muscle cells by passive tensile forces which simulate those found in vivo. When applied to embryonic muscle cells in vitro these forces induce tissue organogenesis, metabolic adaptations, and muscle cell growth. The mechanical stimulation of muscle cell growth correlates with stretch-induced increases in the efflux of prostaglandins PGE2 and PGF2(alpha) in a time and frequency dependent manner. These prostaglandins act as mechanical 'second messengers' regulating skeletal muscle protein turnover rates. Since they also effect bone remodelling in response to tissue loading and unloading, secreted prostaglandins may serve as paracrine growth factors, coordinating the growth rates of muscle and bone in response to external mechanical forces. Cell culture model systems will supplement other models in understanding mechanical transduction processes at the molecular level.

Scramjet exhaust simulation technique for hypersonic aircraft nozzle design and aerodynamic tests

NASA Technical Reports Server (NTRS)

Hunt, J. L.; Talcott, N. A., Jr.; Cubbage, J. M.

1977-01-01

Current design philosophy for scramjet-powered hypersonic aircraft results in configurations with the entire lower fuselage surface utilized as part of the propulsion system. The lower aft-end of the vehicle acts as a high expansion ratio nozzle. Not only must the external nozzle be designed to extract the maximum possible thrust force from the high energy flow at the combustor exit, but the forces produced by the nozzle must be aligned such that they do not unduly affect aerodynamic balance. The strong coupling between the propulsion system and aerodynamics of the aircraft makes imperative at least a partial simulation of the inlet, exhaust, and external flows of the hydrogen-burning scramjet in conventional facilities for both nozzle formulation and aerodynamic-force data acquisition. Aerodynamic testing methods offer no contemporary approach for such vehicle design requirements. NASA-Langley has pursued an extensive scramjet/airframe integration R&D program for several years and has recently developed a promising technique for simulation of the scramjet exhaust flow for hypersonic aircraft. Current results of the research program to develop a scramjet flow simulation technique through the use of substitute gas blends are described in this paper.

STS-51 preparation: ACTS, ORFEUS, Discovery in VAB

NASA Technical Reports Server (NTRS)

1993-01-01

In NASA's building AM on Cape Canaveral Air Force Station, STS-51 mission specialist Carl Walz (right) and Deutsche Aerospace technician Gregor Dawidowitsch check over the scientific instruments mounted on the Shuttle Pallet Satellite (SPAS) carrier (38573); The Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (ORFEUS) and SPAS is readied for hoisting into a test cell at the Vertical Processing Facility (VPF) (38574); Mating of the Advanced Communications Technology Satellite (ACTS) with the Transfer Orbit Stage (TOS) booster is under way in the Payload Hazardous Servicing Facility (PHSF) (38575); The mated ACTS and TOS are ready to be moved from the PHSF to the Vertical Processsing Facility (VPF) (38576); The orbiter Discovery is rolled into the Vehicle Assembly Building (VAB) for mating with the external tank and twin solid rocket boosters (38577-8).

Dynamic inversion enables external magnets to concentrate ferromagnetic rods to a central target.

PubMed

Nacev, A; Weinberg, I N; Stepanov, P Y; Kupfer, S; Mair, L O; Urdaneta, M G; Shimoji, M; Fricke, S T; Shapiro, B

2015-01-14

The ability to use magnets external to the body to focus therapy to deep tissue targets has remained an elusive goal in magnetic drug targeting. Researchers have hitherto been able to manipulate magnetic nanotherapeutics in vivo with nearby magnets but have remained unable to focus these therapies to targets deep within the body using magnets external to the body. One of the factors that has made focusing of therapy to central targets between magnets challenging is Samuel Earnshaw's theorem as applied to Maxwell's equations. These mathematical formulations imply that external static magnets cannot create a stable potential energy well between them. We posited that fast magnetic pulses could act on ferromagnetic rods before they could realign with the magnetic field. Mathematically, this is equivalent to reversing the sign of the potential energy term in Earnshaw's theorem, thus enabling a quasi-static stable trap between magnets. With in vitro experiments, we demonstrated that quick, shaped magnetic pulses can be successfully used to create inward pointing magnetic forces that, on average, enable external magnets to concentrate ferromagnetic rods to a central location.

Hebbian Plasticity in CPG Controllers Facilitates Self-Synchronization for Human-Robot Handshaking.

PubMed

Jouaiti, Melanie; Caron, Lancelot; Hénaff, Patrick

2018-01-01

It is well-known that human social interactions generate synchrony phenomena which are often unconscious. If the interaction between individuals is based on rhythmic movements, synchronized and coordinated movements will emerge from the social synchrony. This paper proposes a plausible model of plastic neural controllers that allows the emergence of synchronized movements in physical and rhythmical interactions. The controller is designed with central pattern generators (CPG) based on rhythmic Rowat-Selverston neurons endowed with neuronal and synaptic Hebbian plasticity. To demonstrate the interest of the proposed model, the case of handshaking is considered because it is a very common, both physically and socially, but also, a very complex act in the point of view of robotics, neuroscience and psychology. Plastic CPGs controllers are implemented in the joints of a simulated robotic arm that has to learn the frequency and amplitude of an external force applied to its effector, thus reproducing the act of handshaking with a human. Results show that the neural and synaptic Hebbian plasticity are working together leading to a natural and autonomous synchronization between the arm and the external force even if the frequency is changing during the movement. Moreover, a power consumption analysis shows that, by offering emergence of synchronized and coordinated movements, the plasticity mechanisms lead to a significant decrease in the energy spend by the robot actuators thus generating a more adaptive and natural human/robot handshake.

Effect of forearm axially rotated posture on shoulder load and shoulder abduction / flexion angles in one-armed arrest of forward falls.

PubMed

Hsu, Hsiu-Hao; Chou, You-Li; Lou, Shu-Zon; Huang, Ming-Jer; Chou, Paul Pei-Hsi

2011-03-01

Falling onto the outstretched hand is the most common cause of upper extremity injury. This study develops an experimental model for evaluating the shoulder load during a simulated forward fall onto one hand with three different forearm axially rotated postures, and examines the shoulder abduction angle and shoulder flexion angle in each case. Fifteen healthy young male subjects with an average age of 23.7 years performed a series of one-armed arrests from a height of 5 cm onto a force plate. The kinematics and kinetics of the upper extremity were analyzed for three different forearm postures, namely 45° externally rotated, non-rotated, and 45° internally rotated. The shoulder joint load and shoulder abduction/flexion angles were significantly dependent on the rotational posture of the forearm. The shoulder medio-lateral shear forces in the externally rotated group were found to be 1.61 and 2.94 times higher than those in the non-rotated and internally rotated groups, respectively. The shoulder flexion angles in the externally rotated, non-rotated and internally rotated groups were 0.6°, 8.0° and 19.2°, respectively, while the corresponding shoulder abduction angles were 6.1°, 34.1° and 46.3°, respectively. In falls onto the outstretched hand, an externally rotated forearm posture should be avoided in order to reduce the medio-lateral shear force acting on the shoulder joint. In falls of this type, a 45° internally rotated forearm posture represents the most effective fall strategy in terms of minimizing the risk of upper extremity injuries. Copyright © 2010 Elsevier Ltd. All rights reserved.

Effect of External Loading on Force and Power Production During Plyometric Push-ups.

PubMed

Hinshaw, Taylour J; Stephenson, Mitchell L; Sha, Zhanxin; Dai, Boyi

2018-04-01

Hinshaw, TJ, Stephenson, ML, Sha, Z, and Dai, B. Effect of external loading on force and power production during plyometric push-ups. J Strength Cond Res 32(4): 1099-1108, 2018-One common exercise to train upper-body strength and power is the push-up. Training at the loads that would produce the greatest power is an effective way to increase peak power. The purpose of the current study was to quantify the changes in peak force, peak power, and peak velocity among a modified plyometric push-up and plyometric push-ups with or without external loading in physically active young adults. Eighteen male and 17 female participants completed 4 push-ups: (a) modified plyometric push-up on the knees, (b) plyometric push-up without external loading, (c) plyometric push-up with an external load of 5% of body weight, and (d) plyometric push-up with an external load of 10% of body weight. Two force platforms were set up to collect vertical ground reaction forces at the hands and feet. The modified plyometric push-up demonstrated the lowest force, power, and velocity (5.4≥ Cohen's dz ≥1.2). Peak force and force at peak velocity increased (3.8≥ Cohen's dz ≥0.3) and peak velocity and velocity at peak power decreased (1.4≥ Cohen's dz ≥0.8) for the push-up without external loading compared with the 2 push-ups with external loading. No significant differences were observed for peak power among the push-ups with or without external loading (0.4≥ Cohen's dz ≥0.1). Although peak power is similar with or without external loading, push-ups without external loading may be more beneficial for a quick movement, and push-ups with external loading may be more beneficial for a greater force production.

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.

A Progression of Static Equilibrium Laboratory Exercises

NASA Astrophysics Data System (ADS)

Kutzner, Mickey; Kutzner, Andrew

2013-10-01

Although simple architectural structures like bridges, catwalks, cantilevers, and Stonehenge have been integral in human societies for millennia, as have levers and other simple tools, modern students of introductory physics continue to grapple with Newton's conditions for static equilibrium. As formulated in typical introductory physics textbooks, these two conditions appear as ΣF=0(1) and Στ=0,(2) where each torque τ is defined as the cross product between the lever arm vector r and the corresponding applied force F, τ =r×F,(3) having magnitude, τ =Frsinθ.(4) The angle θ here is between the two vectors F and r. In Eq. (1), upward (downward) forces are considered positive (negative). In Eq. (2), counterclockwise (clockwise) torques are considered positive (negative). Equation (1) holds that the vector sum of the external forces acting on an object must be zero to prevent linear accelerations; Eq. (2) states that the vector sum of torques due to external forces about any axis must be zero to prevent angular accelerations. In our view these conditions can be problematic for students because a) the equations contain the unfamiliar summation notation Σ, b) students are uncertain of the role of torques in causing rotations, and c) it is not clear why the sum of torques is zero regardless of the choice of axis. Gianino5 describes an experiment using MBL and a force sensor to convey the meaning of torque as applied to a rigid-body lever system without exploring quantitative aspects of the conditions for static equilibrium.

Intradiscal pressure variation under spontaneous ventilation

NASA Astrophysics Data System (ADS)

Roriz, Paulo; Ferreira, J.; Potes, J. C.; Oliveira, M. T.; Santos, J. L.; Simões, J. A.; Frazão, O.

2014-05-01

The pressure measured in the intervertebral discs is a response to the loads acting on the spine. External loads, such as the reaction forces resulting from locomotion, manual handling and collisions are probably the most relevant in studying spine trauma. However, the physiological functions such as breathing and hearth rate also participate in subtle variations of intradiscal pressure that can be observed only in vivo at resting. Present work is an effort to measure the effect of breathing on intradiscal pressure of an anesthetized sheep.

Ultrafast single molecule technique for the study of force dependent kinetics and conformational changes of actin-protein interaction involved in mechanotransduction

NASA Astrophysics Data System (ADS)

Sergides, M.; Arbore, C.; Pavone, F. S.; Capitanio, M.

2018-02-01

Mechanical signals occurring at the interface between cell membrane and extracellular matrix and at intercellular junctions trigger biochemical signals that are fundamental for cell growth, development and regulation. Adaptor proteins, which link the cell membrane to the actin cytoskeleton, seem to partake in this process of mechanotransduction. In particular, catenins play a key role in intercellular junctions, where they act as a bridge between the cell membrane and actin. Studies suggest that α-catenin contains a domain that normally masks vinculin binding sites, which can become accessible after a conformational change induced by an external force. Here we demonstrate a single-molecule technique for investigating actin-protein interactions at different forces (up to 17 pN) with adequate temporal resolution (sub-ms). This system is based on the ultrafast force-clamp spectroscopy technique that has been recently developed by our group and is adapted to study and measure force-dependent kinetics of the catenin-actin interaction, as well as the amplitude of the expected conformational changes such as force-induced protein unfolding.

The effect of muscle stiffness and damping on simulated impact force peaks during running.

PubMed

Nigg, B M; Liu, W

1999-08-01

It has been frequently reported that vertical impact force peaks during running change only minimally when changing the midsole hardness of running shoes. However, the underlying mechanism for these experimental observations is not well understood. An athlete has various possibilities to influence external and internal forces during ground contact (e.g. landing velocity, geometrical alignment, muscle tuning, etc.). The purpose of this study was to discuss one possible strategy to influence external impact forces acting on the athlete's body during running, the strategy to change muscle activity (muscle tuning). The human body was modeled as a simplified mass-spring-damper system. The model included masses of the upper and the lower bodies with each part of the body represented by a rigid and a non-rigid wobbling mass. The influence of mechanical properties of the human body on the vertical impact force peak was examined by varying the spring constants and damping coefficients of the spring-damper units that connected the various masses. Two types of shoe soles were modeled using a non-linear force deformation model with two sets of parameters based on the force-deformation curves of pendulum impact experiments. The simulated results showed that the regulation of the mechanical coupling of rigid and wobbling masses of the human body had an influence on the magnitude of the vertical impact force, but not on its loading rate. It was possible to produce the same impact force peaks altering specific mechanical properties of the system for a soft and a hard shoe sole. This regulation can be achieved through changes of joint angles, changes in joint angular velocities and/or changes in muscle activation levels in the lower extremity. Therefore, it has been concluded that changes in muscle activity (muscle tuning) can be used as a possible strategy to affect vertical impact force peaks during running.

Conditions for Destabilizing Pickering emulsions using external electric fields

NASA Astrophysics Data System (ADS)

Hwang, Kyuho; Singh, Pushpendra; Aubry, Nadine

2009-11-01

Fine particles are readily adsorbed at fluid-fluid interfaces, and can be used as stabilizers in emulsion technology by preventing adjacent drops from coalescing with each other. We investigate a new technique to destabilize such emulsions, or Pickering emulsions, by applying an external electric field. Experiments show that the latter has two effects: (i) the drops elongate in the direction of the electric field, (ii) the local particle density varies on the drop surface due to the dielectrophoretic (DEP) force acting on the particles. It is shown that the latter is the dominant factor in the destabilization process. Particularly, the success of the method depends on the values of certain dimensionless parameters; specifically, the ratio of the work done by the dielectrophoretic force must be larger than the work done by the buoyant force. Moreover, drops do not coalesce through the regions where the particles locally cluster, whether those are gathered at the poles or at the equator of the drops. As particles move, particle-free openings form on the drop's surface, which allow for adjacent drops to merge. This process takes place even if the particles are fully packed on the drops' surfaces as particles get ejected from the clustering areas due to a buckling phenomenon.

Precession of the Earth as the Cause of Geomagnetism: Experiments lend support to the proposal that precessional torques drive the earth's dynamo.

PubMed

Malkus, W V

1968-04-19

I have proposed that the precessional torques acting on the earth can sustain a turbulent hydromagnetic flow in the molten core. A gross balance of the Coriolis force, the Lorentz force, and the precessional force in the core fluid provided estimates of the fluid velocity and the interior magnetic field characteristic of such flow. Then these numbers and a balance of the processes responsible for the decay and regeneration of the magnetic field provided an estimate of the magnetic field external to the core. This external field is in keeping with the observations, but its value is dependent upon the speculative value for the electrical conductivity of core material. The proposal that turbulent flow due to precession can occur in the core was tested in a study of nonmagnetic laboratory flows induced by the steady precession of fluid-filled rotating spheroids. It was found that these flows exhibit both small wavelike instabilities and violent finite-amplitude instability to turbulent motion above critical values of the precession rate. The observed critical parameters indicate that a laminar flow in the core, due to the earth's precession, would have weak hydrodynamic instabilities at most, but that finite-amplitude hydromagnetic instability could lead to fully turbulent flow.

Trapping Phenomenon Attenuates the Consequences of Tipping Points for Limit Cycles

NASA Astrophysics Data System (ADS)

Medeiros, Everton S.; Caldas, Iberê L.; Baptista, Murilo S.; Feudel, Ulrike

2017-02-01

Nonlinear dynamical systems may be exposed to tipping points, critical thresholds at which small changes in the external inputs or in the system’s parameters abruptly shift the system to an alternative state with a contrasting dynamical behavior. While tipping in a fold bifurcation of an equilibrium is well understood, much less is known about tipping of oscillations (limit cycles) though this dynamics are the typical response of many natural systems to a periodic external forcing, like e.g. seasonal forcing in ecology and climate sciences. We provide a detailed analysis of tipping phenomena in periodically forced systems and show that, when limit cycles are considered, a transient structure, so-called channel, plays a fundamental role in the transition. Specifically, we demonstrate that trajectories crossing such channel conserve, for a characteristic time, the twisting behavior of the stable limit cycle destroyed in the fold bifurcation of cycles. As a consequence, this channel acts like a “ghost” of the limit cycle destroyed in the critical transition and instead of the expected abrupt transition we find a smooth one. This smoothness is also the reason that it is difficult to precisely determine the transition point employing the usual indicators of tipping points, like critical slowing down and flickering.

Impact of external forcing on simulated hydroclimate from interannual to multicentennial timescales

NASA Astrophysics Data System (ADS)

Roldán, Pedro; Fidel González-Rouco, Jesús; Melo-Aguilar, Camilo

2017-04-01

During the last millennium, external forcing experienced important changes in different timescales. It has been demostrated that these changes had an impact on climate. In particular, changes in solar activity, volcanic eruptions and emissions of greenhouse gases are related to short-term and long-term changes in global temperatures, with situations of higher total external forcing generally related with higher global and hemispherical temperatures, and conversely with situations of lower forcing. This connection is clearly observed in climate simulations from different models and in proxy-based reconstructions. The changes in external forcing can also explain certain changes in atmospheric dynamics and hydroclimate, although in this case it is in general more difficult to trace causality arguments. Analyses based on simulations from two different models (ECHO-G and CESM-LME) have been performed, to assess the impact of external forcing on climate in timescales ranging from interannual to multicentennial. Various climatic variables have been analysed, including temperature, sea level pressure, surface wind, precipitation and soil moisture. For interannual timescales, composites have been defined with the years before and after the main volcanic eruptions of the last millennium as well as the minima of solar activity during this period. For longer timescales, a Principal Component analysis has been performed, to try to separate the signal of external forcing from that of internal variability. This has been done for the whole millennium and for the pre-industrial period, to assess the difference between natural and anthropogenic forcing. For multicentennial timescales, composites for the Medieval Climate Anomaly (MCA; ca. 950-1250), the Little Ice Age (LIA; ca. 1450-1850) and the 20th Century have been compared. These three periods were respectively characterised by higher, lower and higher forcing. This allows to assess the contribution of external forcing to the evolution of climate over longer time intervals. These analyses have shown that external forcing is an important factor in the evolution of the simulated hydroclimate of the last millennium. In the short-term, it has been observed that volcanic eruptions and other situations of extreme forcing significantly alter the global precipitation in the subsequent years. In the long-term, variations of external forcing can be related to changes in atmospheric dynamics and in hydroclimate. However, this impact is not homogeneously distributed. There are areas where hydroclimate is mainly influenced by the external forcing and other areas more influenced by internal variability, with spatial decorrelation being higher in precipitation or drought related variables than in temperature. The regional sensitivity to external forcing of hydroclimate is model and, to a lesser degree, simulation dependent.

A nucleotide binding rectification Brownian ratchet model for translocation of Y-family DNA polymerases

PubMed Central

2011-01-01

Y-family DNA polymerases are characterized by low-fidelity synthesis on undamaged DNA and ability to catalyze translesion synthesis over the damaged DNA. Their translocation along the DNA template is an important event during processive DNA synthesis. In this work we present a Brownian ratchet model for this translocation, where the directed translocation is rectified by the nucleotide binding to the polymerase. Using the model, different features of the available structures for Dpo4, Dbh and polymerase ι in binary and ternary forms can be easily explained. Other dynamic properties of the Y-family polymerases such as the fast translocation event upon dNTP binding for Dpo4 and the considerable variations of the processivity among the polymerases can also be well explained by using the model. In addition, some predicted results of the DNA synthesis rate versus the external force acting on Dpo4 and Dbh polymerases are presented. Moreover, we compare the effect of the external force on the DNA synthesis rate of the Y-family polymerase with that of the replicative DNA polymerase. PMID:21699732

A Novel Approach to Apply Gait Synchronized External Forces on the Pelvis using A-TPAD to Reduce Walking Effort

PubMed Central

Vashista, Vineet; Khan, Moiz; Agrawal, Sunil K.

2017-01-01

In this paper, we develop an intervention to apply external gait synchronized forces on the pelvis to reduce the user’s effort during walking. A cable-driven robot was used to apply the external forces and an adaptive frequency oscillator scheme was developed to adapt the timing of force actuation to the gait frequency during walking. The external forces were directed in the sagittal plane to assist the trailing leg during the forward propulsion and vertical deceleration of the pelvis during the gait cycle. A pilot experiment with five healthy subjects was conducted. The results showed that the subjects applied lower ground reaction forces in the vertical and anterior-posterior directions during the late stance phase. In summary, the current work provides a novel approach to study the role of external pelvic forces in altering the walking effort. These studies can provide better understanding for designing exoskeletons and prosthetic devices to reduce the overall walking effort. PMID:29623294

Mechanics of deformations in terms of scalar variables

NASA Astrophysics Data System (ADS)

Ryabov, Valeriy A.

2017-05-01

Theory of particle and continuous mechanics is developed which allows a treatment of pure deformation in terms of the set of variables "coordinate-momentum-force" instead of the standard treatment in terms of tensor-valued variables "strain-stress." This approach is quite natural for a microscopic description of atomic system, according to which only pointwise forces caused by the stress act to atoms making a body deform. The new concept starts from affine transformation of spatial to material coordinates in terms of the stretch tensor or its analogs. Thus, three principal stretches and three angles related to their orientation form a set of six scalar variables to describe deformation. Instead of volume-dependent potential used in the standard theory, which requires conditions of equilibrium for surface and body forces acting to a volume element, a potential dependent on scalar variables is introduced. A consistent introduction of generalized force associated with this potential becomes possible if a deformed body is considered to be confined on the surface of torus having six genuine dimensions. Strain, constitutive equations and other fundamental laws of the continuum and particle mechanics may be neatly rewritten in terms of scalar variables. Giving a new presentation for finite deformation new approach provides a full treatment of hyperelasticity including anisotropic case. Derived equations of motion generate a new kind of thermodynamical ensemble in terms of constant tension forces. In this ensemble, six internal deformation forces proportional to the components of Irving-Kirkwood stress are controlled by applied external forces. In thermodynamical limit, instead of the pressure and volume as state variables, this ensemble employs deformation force measured in kelvin unit and stretch ratio.

GO-DEVILS

DOEpatents

Jefferson, S.

1958-01-28

This patent relates to a device normally termed a godevil for use in clearing pipes of sludge, and in particular describes an arrangement for housing a radioactive source within a go-devil whereby the source is removed from a radioactivity shield for detection purposes only when the go-devil is in use. In the described go-devil the radioactive source is housed in a member attached to a piston. Under normal pressure conditions the piston is forced in a direction to position the source within a lead shield. A bellows senses the pressure external to the go-devil and acts through a hydraulic line to force the piston in a direction to remove the source from the shield as long as the pressure is above a pre-set value.

Patterning in systems driven by nonlocal external forces.

PubMed

Luneville, L; Mallick, K; Pontikis, V; Simeone, D

2016-11-01

This work focuses on systems displaying domain patterns resulting from competing external and internal dynamics. To this end, we introduce a Lyapunov functional capable of describing the steady states of systems subject to external forces, by adding nonlocal terms to the Landau Ginzburg free energy of the system. Thereby, we extend the existing methodology treating long-range order interactions, to the case of external nonlocal forces. By studying the quadratic term of this Lyapunov functional, we compute the phase diagram in the temperature versus external field and we determine all possible modulated phases (domain patterns) as a function of the external forces and the temperature. Finally, we investigate patterning in chemical reactive mixtures and binary mixtures under irradiation, and we show that the last case opens the path toward micro-structural engineering of materials.

Patterning in systems driven by nonlocal external forces

NASA Astrophysics Data System (ADS)

Luneville, L.; Mallick, K.; Pontikis, V.; Simeone, D.

2016-11-01

This work focuses on systems displaying domain patterns resulting from competing external and internal dynamics. To this end, we introduce a Lyapunov functional capable of describing the steady states of systems subject to external forces, by adding nonlocal terms to the Landau Ginzburg free energy of the system. Thereby, we extend the existing methodology treating long-range order interactions, to the case of external nonlocal forces. By studying the quadratic term of this Lyapunov functional, we compute the phase diagram in the temperature versus external field and we determine all possible modulated phases (domain patterns) as a function of the external forces and the temperature. Finally, we investigate patterning in chemical reactive mixtures and binary mixtures under irradiation, and we show that the last case opens the path toward micro-structural engineering of materials.

Interfacial fluid instabilities and Kapitsa pendula.

PubMed

Krieger, Madison S

2017-07-01

The onset and development of instabilities is one of the central problems in fluid mechanics. Here we develop a connection between instabilities of free fluid interfaces and inverted pendula. When acted upon solely by the gravitational force, the inverted pendulum is unstable. This position can be stabilized by the Kapitsa phenomenon, in which high-frequency low-amplitude vertical vibrations of the base creates a fictitious force which opposes the gravitational force. By transforming the dynamical equations governing a fluid interface into an appropriate pendulum-type equation, we demonstrate how stability can be induced in fluid systems by properly tuned vibrations. We construct a "dictionary"-type relationship between various pendula and the classical Rayleigh-Taylor, Kelvin-Helmholtz, Rayleigh-Plateau and the self-gravitational instabilities. This makes several results in control theory and dynamical systems directly applicable to the study of tunable fluid instabilities, where the critical wavelength depends on the external forces or the instability is suppressed entirely. We suggest some applications and instances of the effect ranging in scale from microns to the radius of a galaxy.

A novel free floating accelerometer force balance system for shock tunnel applications

NASA Astrophysics Data System (ADS)

Joarder, R.; Mahaptra, D. R.; Jagadeesh, G.

In order to overcome the interference of the model mounting system with the external aerodynamics of the body during shock tunnel testing, a new free floating internally mountable balance system that ensures unrestrained model motion during testing has been designed, fabricated and tested. Minimal friction ball bearings are used for ensuring the free floating condition of the model during tunnel testing. The drag force acting on a blunt leading edge flat plate at hypersonic Mach number has been measured using the new balance system. Finite element model (FEM) and CFD are exhaustively used in the design as well as for calibrating the new balance system. The experimentally measured drag force on the blunt leading edge flat plate at stagnation enthalpy of 0.7 and 1.2 MJ/kg and nominal Mach number of 5.75 matches well with FEM results. The concept can also be extended for measuring all the three fundamental aerodynamic forces in short duration test facilities like free piston driven shock tunnels.

Reentry aerodynamics forces and moments on the engine nozzle of the 146-inch solid rocket booster model 473 tested in MSFC 14 by 14 inch trisonic wind tunnel (SA30F)

NASA Technical Reports Server (NTRS)

Johnson, J. D.; Braddock, W. F.

1975-01-01

A test of a model of the Space Shuttle Solid Rocket Boosters (SRB's) was performed in a 14 x 14 inch Trisonic Wind Tunnel to determine the aerodynamic forces and moments imposed on the nozzle of the SRB during reentry. The model, with scale dimensions equal to 0.5479 of the actual SRB dimensions, was instrumented with a six-component force balance attached to the model nozzle so that only forces and moments acting on the nozzle were measured. A total of 137 runs (20 deg pitch polars) were performed during this test. The angle of attack ranged from 60 to 185 deg, the Reynolds number from 5.2 million to 7.6 million. The Mach numbers investigated were 1.96, 2.74, and 3.48. Five external protuberances were simulated. The effective roll angle simulated was 180 deg. The effects of three different heat shield configurations were investigated.

77 FR 26046 - Agency Information Collection Activities; Submission for OMB Review; Comment Request; Affordable...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-02

... for OMB Review; Comment Request; Affordable Care Act Internal Claims and Appeals and External Review...) titled, ``Affordable Care Act Internal Claims and Appeals and External Review Procedures for Non... provisions of the Affordable Care Act pertaining to internal claims and appeals, and the external review...

A Bidirectional Brain-Machine Interface Algorithm That Approximates Arbitrary Force-Fields

PubMed Central

Semprini, Marianna; Mussa-Ivaldi, Ferdinando A.; Panzeri, Stefano

2014-01-01

We examine bidirectional brain-machine interfaces that control external devices in a closed loop by decoding motor cortical activity to command the device and by encoding the state of the device by delivering electrical stimuli to sensory areas. Although it is possible to design this artificial sensory-motor interaction while maintaining two independent channels of communication, here we propose a rule that closes the loop between flows of sensory and motor information in a way that approximates a desired dynamical policy expressed as a field of forces acting upon the controlled external device. We previously developed a first implementation of this approach based on linear decoding of neural activity recorded from the motor cortex into a set of forces (a force field) applied to a point mass, and on encoding of position of the point mass into patterns of electrical stimuli delivered to somatosensory areas. However, this previous algorithm had the limitation that it only worked in situations when the position-to-force map to be implemented is invertible. Here we overcome this limitation by developing a new non-linear form of the bidirectional interface that can approximate a virtually unlimited family of continuous fields. The new algorithm bases both the encoding of position information and the decoding of motor cortical activity on an explicit map between spike trains and the state space of the device computed with Multi-Dimensional-Scaling. We present a detailed computational analysis of the performance of the interface and a validation of its robustness by using synthetic neural responses in a simulated sensory-motor loop. PMID:24626393

Direct Numerical Simulation of Oscillatory Flow Over a Wavy, Rough, and Permeable Bottom

NASA Astrophysics Data System (ADS)

Mazzuoli, Marco; Blondeaux, Paolo; Simeonov, Julian; Calantoni, Joseph

2018-03-01

The results of a direct numerical simulation of oscillatory flow over a wavy bottom composed of different layers of spherical particles are described. The amplitude of wavy bottom is much smaller in scale than typical bed forms such as sand ripples. The spherical particles are packed in such a way to reproduce a bottom profile observed during an experiment conducted in a laboratory flow tunnel with well-sorted coarse sand. The amplitude and period of the external forcing flow as well as the size of the particles are set equal to the experimental values and the computed velocity field is compared with the measured velocity profiles. The direct numerical simulation allows for the evaluation of quantities, which are difficult to measure in a laboratory experiment (e.g., vorticity, seepage flow velocity, and hydrodynamic force acting on sediment particles). In particular, attention is focused on the coherent vortex structures generated by the vorticity shed by both the spherical particles and the bottom waviness. Results show that the wavy bottom triggers transition to turbulence. Moreover, the forces acting on the spherical particles are computed to investigate the mechanisms through which they are possibly mobilized by the oscillatory flow. It was found that forces capable of mobilizing surface particles are strongly correlated with the particle position above the mean bed elevation and the passage of coherent vortices above them.

Relative contributions of external forcing factors to circulation and hydrographic properties in a micro-tidal bay

NASA Astrophysics Data System (ADS)

Yoon, Seokjin; Kasai, Akihide

2017-11-01

The dominant external forcing factors influencing estuarine circulation differ among coastal environments. A three-dimensional regional circulation model was developed to estimate external influence indices and relative contributions of external forcing factors such as external oceanic forcing, surface heat flux, wind stress, and river discharge to circulation and hydrographic properties in Tango Bay, Japan. Model results show that in Tango Bay, where the Tsushima Warm Current passes offshore of the bay, under conditions of strong seasonal winds and river discharge, the water temperature and salinity are strongly influenced by surface heat flux and river discharge in the surface layer, respectively, while in the middle and bottom layers both are mainly controlled by open boundary conditions. The estuarine circulation is comparably influenced by all external forcing factors, the strong current, surface heat flux, wind stress, and river discharge. However, the influence degree of each forcing factor varies with temporal variations in external forcing factors as: the influence of open boundary conditions is higher in spring and early summer when the stronger current passes offshore of the bay, that of surface heat flux reflects the absolute value of surface heat flux, that of wind stress is higher in late fall and winter due to strong seasonal winds, and that of river discharge is higher in early spring due to snow-melting and summer and early fall due to flood events.

Chiral drag force

DOE PAGES

Rajagopal, Krishna; Sadofyev, Andrey V.

2015-10-05

Here, we provide a holographic evaluation of novel contributions to the drag force acting on a heavy quark moving through strongly interacting plasma. The new contributions are chiral in the sense that they act in opposite directions in plasmas containing an excess of left- or right-handed quarks. The new contributions are proportional to the coefficient of the axial anomaly, and in this sense also are chiral. These new contributions to the drag force act either parallel to or antiparallel to an external magnetic field or to the vorticity of the fluid plasma. In all these respects, these contributions to themore » drag force felt by a heavy quark are analogous to the chiral magnetic effect (CME) on light quarks. However, the new contribution to the drag force is independent of the electric charge of the heavy quark and is the same for heavy quarks and antiquarks, meaning that these novel effects do not in fact contribute to the CME current. We show that although the chiral drag force can be non-vanishing for heavy quarks that are at rest in the local fluid rest frame, it does vanish for heavy quarks that are at rest in a suitably chosen frame. In this frame, the heavy quark at rest sees counterpropagating momentum and charge currents, both proportional to the axial anomaly coefficient, but feels no drag force. This provides strong concrete evidence for the absence of dissipation in chiral transport, something that has been predicted previously via consideration of symmetries. Along the way to our principal results, we provide a general calculation of the corrections to the drag force due to the presence of gradients in the flowing fluid in the presence of a nonzero chemical potential. We close with a consequence of our result that is at least in principle observable in heavy ion collisions, namely an anticorrelation between the direction of the CME current for light quarks in a given event and the direction of the kick given to the momentum of all the heavy quarks and antiquarks in that event.« less

Combined passive magnetic bearing element and vibration damper

DOEpatents

Post, Richard F.

2001-01-01

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium and dampen transversely directed vibrations. Mechanical stabilizers are provided to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. In a improvement over U.S. Pat. No. 5,495,221, a magnetic bearing element is combined with a vibration damping element to provide a single upper stationary dual-function element. The magnetic forces exerted by such an element, enhances levitation of the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations, and suppresses the effects of unbalance or inhibits the onset of whirl-type rotor-dynamic instabilities. Concurrently, this equilibrium is made stable against displacement-dependent drag forces of the rotating object from its equilibrium position.

Theoretical Model for Cellular Shapes Driven by Protrusive and Adhesive Forces

PubMed Central

Kabaso, Doron; Shlomovitz, Roie; Schloen, Kathrin; Stradal, Theresia; Gov, Nir S.

2011-01-01

The forces that arise from the actin cytoskeleton play a crucial role in determining the cell shape. These include protrusive forces due to actin polymerization and adhesion to the external matrix. We present here a theoretical model for the cellular shapes resulting from the feedback between the membrane shape and the forces acting on the membrane, mediated by curvature-sensitive membrane complexes of a convex shape. In previous theoretical studies we have investigated the regimes of linear instability where spontaneous formation of cellular protrusions is initiated. Here we calculate the evolution of a two dimensional cell contour beyond the linear regime and determine the final steady-state shapes arising within the model. We find that shapes driven by adhesion or by actin polymerization (lamellipodia) have very different morphologies, as observed in cells. Furthermore, we find that as the strength of the protrusive forces diminish, the system approaches a stabilization of a periodic pattern of protrusions. This result can provide an explanation for a number of puzzling experimental observations regarding cellular shape dependence on the properties of the extra-cellular matrix. PMID:21573201

Effect of tibial positioning on the diagnosis of posterolateral rotatory instability in the posterior cruciate ligament-deficient knee.

PubMed

Strauss, Eric J; Ishak, Charbel; Inzerillo, Christopher; Walsh, Michael; Yildirim, Gokce; Walker, Peter; Jazrawi, Laith; Rosen, Jeffrey

2007-08-01

To determine whether positioning of the tibia affects the degree of tibial external rotation seen during a dial test in the posterior cruciate ligament (PCL)-posterolateral corner (PLC)-deficient knee. Laboratory investigation. Biomechanics laboratory. An anterior force applied to the tibia in the combined PCL-PLC-deficient knee will yield increased tibial external rotation during a dial test. The degree of tibial external rotation was measured with 5 Nm of external rotation torque applied to the tibia at both 30 degrees and 90 degrees of knee flexion. Before the torque was applied, an anterior force, a posterior force, or neutral (normal, reduced control) force was applied to the tibia. External rotation measurements were repeated after sequential sectioning of the PCL, the posterolateral structures and the fibular collateral ligament (FCL). Baseline testing of the intact specimens demonstrated a mean external rotation of 18.6 degrees with the knee flexed to 30 degrees (range 16.1-21.0 degrees ), and a mean external rotation of 17.3 degrees with the knee flexed to 90 degrees (range 13.8-20.0 degrees ). Sequential sectioning of the PCL, popliteus and popliteofibular ligament, and the FCL led to a significant increase in tibial external rotation compared with the intact knee for all testing scenarios. After sectioning of the popliteus and popliteofibular ligament, the application of an anterior force during testing led to a mean tibial external rotation that was 5 degrees greater than during testing in the neutral position and 7.5 degrees greater than during testing with a posterior force. In the PCL, popliteus/popliteofibular ligament and FCL-deficient knee, external rotation was 9 degrees and 12 degrees greater with the application of an anterior force during testing compared with neutral positioning and the application of a posterior force, respectively. An anterior force applied to the tibia during the dial test in a combined PCL-PLC-injured knee increased the overall amount of observed tibial external rotation during the dial test. The anterior force reduced the posterior tibial subluxation associated with PCL injury, which is analogous to what is observed when the dial test is performed with the patient in the prone position. Reducing the tibia with either an anterior force when the patient is supine or performing the dial test with the patient in the prone position increases the ability of an examiner to detect a concomitant PLC injury in the setting of a PCL-deficient knee.

Correlation of Shoulder and Elbow Kinetics With Ball Velocity in Collegiate Baseball Pitchers.

PubMed

Post, Eric G; Laudner, Kevin G; McLoda, Todd A; Wong, Regan; Meister, Keith

2015-06-01

Throwing a baseball is a dynamic and violent act that places large magnitudes of stress on the shoulder and elbow. Specific injuries at the elbow and glenohumeral joints have been linked to several kinetic variables throughout the throwing motion. However, very little research has directly examined the relationship between these kinetic variables and ball velocity. To examine the correlation of peak ball velocity with elbow-valgus torque, shoulder external-rotation torque, and shoulder-distraction force in a group of collegiate baseball pitchers. Cross-sectional study. Motion-analysis laboratory. Sixty-seven asymptomatic National Collegiate Athletic Association Division I baseball pitchers (age = 19.5 ± 1.2 years, height = 186.2 ± 5.7 cm, mass = 86.7 ± 7.0 kg; 48 right handed, 19 left handed). We measured peak ball velocity using a radar gun and shoulder and elbow kinetics of the throwing arm using 8 electronically synchronized, high-speed digital cameras. We placed 26 reflective markers on anatomical landmarks of each participant to track 3-dimensional coordinate data. The average data from the 3 highest-velocity fastballs thrown for strikes were used for data analysis. We calculated a Pearson correlation coefficient to determine the associations between ball velocity and peak elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque (P < .05). A weak positive correlation was found between ball velocity and shoulder-distraction force (r = 0.257; 95% confidence interval [CI] = 0.02, 0.47; r(2) = 0.066; P = .018). However, no significant correlations were noted between ball velocity and elbow-valgus torque (r = 0.199; 95% CI = -0.043, 0.419; r(2) = 0.040; P = .053) or shoulder external-rotation torque (r = 0.097; 95% CI = -0.147, 0.329; r(2) = 0.009; P = .217). Although a weak positive correlation was present between ball velocity and shoulder-distraction force, no significant association was seen between ball velocity and elbow-valgus torque or shoulder external-rotation torque. Therefore, other factors, such as improper pitching mechanics, may contribute more to increases in joint kinetics than peak ball velocity.

Correlation of Shoulder and Elbow Kinetics With Ball Velocity in Collegiate Baseball Pitchers

PubMed Central

Post, Eric G.; Laudner, Kevin G.; McLoda, Todd A.; Wong, Regan; Meister, Keith

2015-01-01

Context Throwing a baseball is a dynamic and violent act that places large magnitudes of stress on the shoulder and elbow. Specific injuries at the elbow and glenohumeral joints have been linked to several kinetic variables throughout the throwing motion. However, very little research has directly examined the relationship between these kinetic variables and ball velocity. Objective To examine the correlation of peak ball velocity with elbow-valgus torque, shoulder external-rotation torque, and shoulder-distraction force in a group of collegiate baseball pitchers. Design Cross-sectional study. Setting Motion-analysis laboratory. Patients or Other Participants Sixty-seven asymptomatic National Collegiate Athletic Association Division I baseball pitchers (age = 19.5 ± 1.2 years, height = 186.2 ± 5.7 cm, mass = 86.7 ± 7.0 kg; 48 right handed, 19 left handed). Main Outcome Measure(s) We measured peak ball velocity using a radar gun and shoulder and elbow kinetics of the throwing arm using 8 electronically synchronized, high-speed digital cameras. We placed 26 reflective markers on anatomical landmarks of each participant to track 3-dimensional coordinate data. The average data from the 3 highest-velocity fastballs thrown for strikes were used for data analysis. We calculated a Pearson correlation coefficient to determine the associations between ball velocity and peak elbow-valgus torque, shoulder-distraction force, and shoulder external-rotation torque (P < .05). Results A weak positive correlation was found between ball velocity and shoulder-distraction force (r = 0.257; 95% confidence interval [CI] = 0.02, 0.47; r2 = 0.066; P = .018). However, no significant correlations were noted between ball velocity and elbow-valgus torque (r = 0.199; 95% CI = −0.043, 0.419; r2 = 0.040; P = .053) or shoulder external-rotation torque (r = 0.097; 95% CI = −0.147, 0.329; r2 = 0.009; P = .217). Conclusions Although a weak positive correlation was present between ball velocity and shoulder-distraction force, no significant association was seen between ball velocity and elbow-valgus torque or shoulder external-rotation torque. Therefore, other factors, such as improper pitching mechanics, may contribute more to increases in joint kinetics than peak ball velocity. PMID:25756790

Delayed-feedback chimera states: Forced multiclusters and stochastic resonance

NASA Astrophysics Data System (ADS)

Semenov, V.; Zakharova, A.; Maistrenko, Y.; Schöll, E.

2016-07-01

A nonlinear oscillator model with negative time-delayed feedback is studied numerically under external deterministic and stochastic forcing. It is found that in the unforced system complex partial synchronization patterns like chimera states as well as salt-and-pepper-like solitary states arise on the route from regular dynamics to spatio-temporal chaos. The control of the dynamics by external periodic forcing is demonstrated by numerical simulations. It is shown that one-cluster and multi-cluster chimeras can be achieved by adjusting the external forcing frequency to appropriate resonance conditions. If a stochastic component is superimposed to the deterministic external forcing, chimera states can be induced in a way similar to stochastic resonance, they appear, therefore, in regimes where they do not exist without noise.

Object Imaging Accomplished with an Integrated Circuit Robotic Tactile Sensor Incorporating a Piezoelectric Polyvinylidene Fluoride Thin Film

DTIC Science & Technology

1993-12-01

sensor response. That is, the tactile sensor’s response to a temperature change could be interpreted as the sensor’s response solely to an externally...is a vector quantity. A force acting on a surface can be interpreted in terms of a normal and a tangential component. Often, these components are...polarization [12]: 3-16 h K" + (3.34) Similarly, the stress in a material due to an applied strain and polarization is [12]: T = cS- hTP (3.35) The electric

A vector-dyadic development of the equations of motion for N-coupled rigid bodies and point masses

NASA Technical Reports Server (NTRS)

Frisch, H. P.

1974-01-01

The equations of motion are derived, in vector-dyadic format, for a topological tree of coupled rigid bodies, point masses, and symmetrical momentum wheels. These equations were programmed, and form the basis for the general-purpose digital computer program N-BOD. A complete derivation of the equations of motion is included along with a description of the methods used for kinematics, constraint elimination, and for the inclusion of nongyroscope forces and torques acting external or internal to the system.

Nonlinear dynamical model of human gait

NASA Astrophysics Data System (ADS)

West, Bruce J.; Scafetta, Nicola

2003-05-01

We present a nonlinear dynamical model of the human gait control system in a variety of gait regimes. The stride-interval time series in normal human gait is characterized by slightly multifractal fluctuations. The fractal nature of the fluctuations becomes more pronounced under both an increase and decrease in the average gait. Moreover, the long-range memory in these fluctuations is lost when the gait is keyed on a metronome. Human locomotion is controlled by a network of neurons capable of producing a correlated syncopated output. The central nervous system is coupled to the motocontrol system, and together they control the locomotion of the gait cycle itself. The metronomic gait is simulated by a forced nonlinear oscillator with a periodic external force associated with the conscious act of walking in a particular way.

Self-organizing magnetic beads for biomedical applications

NASA Astrophysics Data System (ADS)

Gusenbauer, Markus; Kovacs, Alexander; Reichel, Franz; Exl, Lukas; Bance, Simon; Özelt, Harald; Schrefl, Thomas

2012-03-01

In the field of biomedicine magnetic beads are used for drug delivery and to treat hyperthermia. Here we propose to use self-organized bead structures to isolate circulating tumor cells using lab-on-chip technologies. Typically blood flows past microposts functionalized with antibodies for circulating tumor cells. Creating these microposts with interacting magnetic beads makes it possible to tune the geometry in size, position and shape. We developed a simulation tool that combines micromagnetics and discrete particle dynamics, in order to design micropost arrays made of interacting beads. The simulation takes into account the viscous drag of the blood flow, magnetostatic interactions between the magnetic beads and gradient forces from external aligned magnets. We developed a particle-particle particle-mesh method for effective computation of the magnetic force and torque acting on the particles.

Contact-force distribution optimization and control for quadruped robots using both gradient and adaptive neural networks.

PubMed

Li, Zhijun; Ge, Shuzhi Sam; Liu, Sibang

2014-08-01

This paper investigates optimal feet forces' distribution and control of quadruped robots under external disturbance forces. First, we formulate a constrained dynamics of quadruped robots and derive a reduced-order dynamical model of motion/force. Consider an external wrench on quadruped robots; the distribution of required forces and moments on the supporting legs of a quadruped robot is handled as a tip-point force distribution and used to equilibrate the external wrench. Then, a gradient neural network is adopted to deal with the optimized objective function formulated as to minimize this quadratic objective function subjected to linear equality and inequality constraints. For the obtained optimized tip-point force and the motion of legs, we propose the hybrid motion/force control based on an adaptive neural network to compensate for the perturbations in the environment and approximate feedforward force and impedance of the leg joints. The proposed control can confront the uncertainties including approximation error and external perturbation. The verification of the proposed control is conducted using a simulation.

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age

PubMed Central

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-01-01

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400–1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO. PMID:24567051

Evidence for external forcing of the Atlantic Multidecadal Oscillation since termination of the Little Ice Age.

PubMed

Knudsen, Mads Faurschou; Jacobsen, Bo Holm; Seidenkrantz, Marit-Solveig; Olsen, Jesper

2014-02-25

The Atlantic Multidecadal Oscillation (AMO) represents a significant driver of Northern Hemisphere climate, but the forcing mechanisms pacing the AMO remain poorly understood. Here we use the available proxy records to investigate the influence of solar and volcanic forcing on the AMO over the last ~450 years. The evidence suggests that external forcing played a dominant role in pacing the AMO after termination of the Little Ice Age (LIA; ca. 1400-1800), with an instantaneous impact on mid-latitude sea-surface temperatures that spread across the North Atlantic over the ensuing ~5 years. In contrast, the role of external forcing was more ambiguous during the LIA. Our study further suggests that the Atlantic Meridional Overturning Circulation is important for linking external forcing with North Atlantic sea-surface temperatures, a conjecture that reconciles two opposing theories concerning the origin of the AMO.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

NASA Astrophysics Data System (ADS)

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-01

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces.

PubMed

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian; Cremer, Johannes; Chasovskikh, Egor; Signorell, Ruth

2015-04-21

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance for the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.

Wartime Transitions: Historical Case Analyses Applied to the US Campaign in Afghanistan (2001 to Present)

DTIC Science & Technology

2017-05-25

operate independently without external nation support; (3) a custom approach is necessary in security forces development based on political requirements...independently without external nation support; (3) a custom approach is necessary in security forces development based on political requirements...interventions both successful and unsuccessful, that an external country must craft a custom approach to develop local security forces based on the

Mechanical Failure in Colloidal Gels

NASA Astrophysics Data System (ADS)

Kodger, Thomas Edward

When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form them.

Monitoring the degrafting of polyelectrolyte brushes by using surface gradients

NASA Astrophysics Data System (ADS)

Ko, Yeongun; Genzer, Jan

Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. Based on previous experiments conducted in our group and by others, we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. The kinetic of hydrolysis is affected by mechanical forces acting on the initiator. Those forces depend on the molecular weight and the grafting density of the brush, and the concentration and distribution of charges along the macromolecule (tuned by pH - for weak electrolytes - and concentration of external salt). In this work, we study the stability of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes in two solvents (ethanol and water) at various pH values in water and under different levels of external salt concentration. National Science Foundation.

Ballistic induced pumping of hypersonic heat current in DNA nano wire

NASA Astrophysics Data System (ADS)

Behnia, Sohrab; Panahinia, Robabe

2016-12-01

Heat shuttling properties of DNA nano-wire driven by an external force against the spontaneous heat current direction in non-zero temperature bias (non averaged) have been studied. We examined the valid region of driving amplitude and frequency to have pumping state in terms of temperature bias and the system size. It was shown that DNA could act as a high efficiency thermal pump in the hypersonic region. Amplitude-dependent resonance frequencies of DNA indicating intrinsic base pair internal vibrations have been detected. Nonlinearity implies that by increasing the driven amplitude new vibration modes are detected. To verify the results, an analytical parallel investigation based on multifractal concept has been done. By using the geometric properties of the strange attractor of the system, the threshold value to transition to the pumping state for given external amplitude has been identified. It was shown that the system undergoes a phase transition in sliding point to the pumping state. Fractal dimension demonstrates that the ballistic transport is responsible for energy pumping in the system. In the forbidden band gap, DNA could transmit the energy by exceeding the threshold amplitude. Despite of success in energy pumping, in this framework, DNA could not act as a real cooler.

Calcaneal loading during walking and running

NASA Technical Reports Server (NTRS)

Giddings, V. L.; Beaupre, G. S.; Whalen, R. T.; Carter, D. R.

2000-01-01

PURPOSE: This study of the foot uses experimentally measured kinematic and kinetic data with a numerical model to evaluate in vivo calcaneal stresses during walking and running. METHODS: External ground reaction forces (GRF) and kinematic data were measured during walking and running using cineradiography and force plate measurements. A contact-coupled finite element model of the foot was developed to assess the forces acting on the calcaneus during gait. RESULTS: We found that the calculated force-time profiles of the joint contact, ligament, and Achilles tendon forces varied with the time-history curve of the moment about the ankle joint. The model predicted peak talocalcaneal and calcaneocuboid joint loads of 5.4 and 4.2 body weights (BW) during walking and 11.1 and 7.9 BW during running. The maximum predicted Achilles tendon forces were 3.9 and 7.7 BW for walking and running. CONCLUSIONS: Large magnitude forces and calcaneal stresses are generated late in the stance phase, with maximum loads occurring at approximately 70% of the stance phase during walking and at approximately 60% of the stance phase during running, for the gait velocities analyzed. The trajectories of the principal stresses, during both walking and running, corresponded to each other and qualitatively to the calcaneal trabecular architecture.

Effects of load on ground reaction force and lower limb kinematics during concentric squats.

PubMed

Kellis, Eleftherios; Arambatzi, Fotini; Papadopoulos, Christos

2005-10-01

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1 +/- 0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67 +/- 0.20 to 3.21 +/- 0.29 times body weight and increased significantly as external load increased (P < 0.05). Bar linear velocity ranged from 0.54 +/- 0.11 to 2.50 +/- 0.50 m x s(-1) and decreased significantly with increasing external load (P < 0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P < 0.05). The force-barbell velocity curves were fitted using linear models with coefficients (r2) ranging from 0.59 to 0.96. The results suggest that maximal force exertion during squat exercises is not achieved at the same position of the lower body as external load is increased. In contrast, joint velocity coordination does not change as load is increased. The force-velocity relationship was linear and independent from the set of data used for its determination.

Particles with nonlinear electric response: Suppressing van der Waals forces by an external field.

PubMed

Soo, Heino; Dean, David S; Krüger, Matthias

2017-01-01

We study the classical thermal component of Casimir, or van der Waals, forces between point particles with highly anharmonic dipole Hamiltonians when they are subjected to an external electric field. Using a model for which the individual dipole moments saturate in a strong field (a model that mimics the charges in a neutral, perfectly conducting sphere), we find that the resulting Casimir force depends strongly on the strength of the field, as demonstrated by analytical results. For a certain angle between the external field and center-to-center axis, the fluctuation force can be tuned and suppressed to arbitrarily small values. We compare the forces between these particles with those between particles with harmonic Hamiltonians and also provide a simple formula for asymptotically large external fields, which we expect to be generally valid for the case of saturating dipole moments.

Studying Climate Response to Forcing by the Nonlinear Dynamical Mode Decomposition

NASA Astrophysics Data System (ADS)

Mukhin, Dmitry; Gavrilov, Andrey; Loskutov, Evgeny; Feigin, Alexander

2017-04-01

An analysis of global climate response to external forcing, both anthropogenic (mainly, CO2 and aerosol) and natural (solar and volcanic), is needed for adequate predictions of global climate change. Being complex dynamical system, the climate reacts to external perturbations exciting feedbacks (both positive and negative) making the response non-trivial and poorly predictable. Thus an extraction of internal modes of climate system, investigation of their interaction with external forcings and further modeling and forecast of their dynamics, are all the problems providing the success of climate modeling. In the report the new method for principal mode extraction from climate data is presented. The method is based on the Nonlinear Dynamical Mode (NDM) expansion [1,2], but takes into account a number of external forcings applied to the system. Each NDM is represented by hidden time series governing the observed variability, which, together with external forcing time series, are mapped onto data space. While forcing time series are considered to be known, the hidden unknown signals underlying the internal climate dynamics are extracted from observed data by the suggested method. In particular, it gives us an opportunity to study the evolution of principal system's mode structure in changing external conditions and separate the internal climate variability from trends forced by external perturbations. Furthermore, the modes so obtained can be extrapolated beyond the observational time series, and long-term prognosis of modes' structure including characteristics of interconnections and responses to external perturbations, can be carried out. In this work the method is used for reconstructing and studying the principal modes of climate variability on inter-annual and decadal time scales accounting the external forcings such as anthropogenic emissions, variations of the solar activity and volcanic activity. The structure of the obtained modes as well as their response to external factors, e.g. forecast their change in 21 century under different CO2 emission scenarios, are discussed. [1] Mukhin, D., Gavrilov, A., Feigin, A., Loskutov, E., & Kurths, J. (2015). Principal nonlinear dynamical modes of climate variability. Scientific Reports, 5, 15510. http://doi.org/10.1038/srep15510 [2] Gavrilov, A., Mukhin, D., Loskutov, E., Volodin, E., Feigin, A., & Kurths, J. (2016). Method for reconstructing nonlinear modes with adaptive structure from multidimensional data. Chaos: An Interdisciplinary Journal of Nonlinear Science, 26(12), 123101. http://doi.org/10.1063/1.4968852

Spaceborne gravity gradiometry characterizing the data type

NASA Technical Reports Server (NTRS)

Sonnabend, D.

1987-01-01

Satellite gravity gradiometers, particularly the two stage drag free carrier vehicle are discussed. An inner stage, carrying the tracking antenna(s), measures the relative position of the internal free proof mass, and feeds this to a set of magnetic forcers, acting against the outer or main vehicle. As the external forces on the inner stage are low, and as the position relative to the proof mass is tightly controlled, carrier phase disturbances are greatly reduced. The arrangement lowers instantaneous accelerations. It is stressed that gravity gradiometers do not measure gradients, they measure components of an intrinsic tensor.

New Trends in Medical Libraries in Hospitals *

PubMed Central

Gartland, Henry J.

1971-01-01

External and internal forces affecting medical library services are examined. Public Law 89-239, the Heart, Cancer and Stroke Amendments of 1965, and Public Law 89-291, the Medical Library Assistance Act of 1965 which was extended by Public Law 91-212 have an impact on medical libraries. The Veterans Administration relationships with primary beneficiaries of these laws are explained. Internally, effort has been expended through automation, networking, and extension of resources by amalgamation of books and audiovisuals to evolve responsive concepts with emphasis on independence through interdependence. The Veterans Administration Library Service plans and accomplishments in these areas are reviewed. PMID:4932204

Stability of aerosol droplets in Bessel beam optical traps under constant and pulsed external forces

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

David, Grégory; Esat, Kıvanç; Hartweg, Sebastian

We report on the dynamics of aerosol droplets in optical traps under the influence of additional constant and pulsed external forces. Experimental results are compared with simulations of the three-dimensional droplet dynamics for two types of optical traps, the counter-propagating Bessel beam (CPBB) trap and the quadruple Bessel beam (QBB) trap. Under the influence of a constant gas flow (constant external force), the QBB trap is found to be more stable compared with the CPBB trap. By contrast, under pulsed laser excitation with laser pulse durations of nanoseconds (pulsed external force), the type of trap is of minor importance formore » the droplet stability. It typically needs pulsed laser forces that are several orders of magnitude higher than the optical forces to induce escape of the droplet from the trap. If the droplet strongly absorbs the pulsed laser light, these escape forces can be strongly reduced. The lower stability of absorbing droplets is a result of secondary thermal processes that cause droplet escape.« less

Dynamically stable magnetic suspension/bearing system

DOEpatents

Post, R.F.

1996-02-27

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw`s Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements. 32 figs.

Dynamically stable magnetic suspension/bearing system

DOEpatents

Post, Richard F.

1996-01-01

A magnetic bearing system contains magnetic subsystems which act together to support a rotating element in a state of dynamic equilibrium. However, owing to the limitations imposed by Earnshaw's Theorem, the magnetic bearing systems to be described do not possess a stable equilibrium at zero rotational speed. Therefore, mechanical stabilizers are provided, in each case, to hold the suspended system in equilibrium until its speed has exceeded a low critical speed where dynamic effects take over, permitting the achievement of a stable equilibrium for the rotating object. A state of stable equilibrium is achieved above a critical speed by use of a collection of passive elements using permanent magnets to provide their magnetomotive excitation. The magnetic forces exerted by these elements, when taken together, levitate the rotating object in equilibrium against external forces, such as the force of gravity or forces arising from accelerations. At the same time, this equilibrium is made stable against displacements of the rotating object from its equilibrium position by using combinations of elements that possess force derivatives of such magnitudes and signs that they can satisfy the conditions required for a rotating body to be stably supported by a magnetic bearing system over a finite range of those displacements.

Molecular Dynamics Investigation of Cl− and Water Transport through a Eukaryotic CLC Transporter

PubMed Central

Cheng, Mary Hongying; Coalson, Rob D.

2012-01-01

Early crystal structures of prokaryotic CLC proteins identified three Cl– binding sites: internal (Sint), central (Scen), and external (Sext). A conserved external GLU (GLUex) residue acts as a gate competing for Sext. Recently, the first crystal structure of a eukaryotic transporter, CmCLC, revealed that in this transporter GLUex competes instead for Scen. Here, we use molecular dynamics simulations to investigate Cl– transport through CmCLC. The gating and Cl–/H+ transport cycle are inferred through comparative molecular dynamics simulations with protonated and deprotonated GLUex in the presence/absence of external potentials. Adaptive biasing force calculations are employed to estimate the potential of mean force profiles associated with transport of a Cl– ion from Sext to Sint, depending on the Cl– occupancy of other sites. Our simulations demonstrate that protonation of GLUex is essential for Cl– transport from Sext to Scen. The Scen site may be occupied by two Cl– ions simultaneously due to a high energy barrier (∼8 Kcal/mol) for a single Cl– ion to translocate from Scen to Sint. Binding two Cl– ions to Scen induces a continuous water wire from Scen to the extracellular solution through the side chain of the GLUex gate. This may initiate deprotonation of GLUex, which then drives the two Cl– ions out of Scen toward the intracellular side via two putative Cl– transport paths. Finally, a conformational cycle is proposed that would account for the exchange stoichiometry. PMID:22455919

Role of spin-transfer torques on synchronization and resonance phenomena in stochastic magnetic oscillators

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

Accioly, Artur; Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay; Locatelli, Nicolas

2016-09-07

A theoretical study on how synchronization and resonance-like phenomena in superparamagnetic tunnel junctions can be driven by spin-transfer torques is presented. We examine the magnetization of a superparamagnetic free layer that reverses randomly between two well-defined orientations due to thermal fluctuations, acting as a stochastic oscillator. When subject to an external ac forcing, this system can present stochastic resonance and noise-enhanced synchronization. We focus on the roles of the mutually perpendicular damping-like and field-like torques, showing that the response of the system is very different at low and high frequencies. We also demonstrate that the field-like torque can increase themore » efficiency of the current-driven forcing, especially at sub-threshold electric currents. These results can be useful for possible low-power, more energy efficient applications.« less

Investigation of a relationship between external force to shoulder and chest injury of WorldSID and THUMS in 32 km/h oblique pole side impact.

PubMed

Tanaka, Shinobu; Hayashi, Shigeki; Fukushima, Satoshi; Yasuki, Tsuyoshi

2013-01-01

This article describes the chest injury risk reduction effect of shoulder restraints using finite element (FE) models of the worldwide harmonized side impact dummy (WorldSID) and Total Human Model for Safety (THUMS) in an FE model 32 km/h oblique pole side impact. This research used an FE model of a mid-sized vehicle equipped with various combinations of curtain shield air bags, torso air bags, and shoulder restraint air bags. As occupant models, AM50 WorldSID and THUMS AM50 Version 4 were used for comparison. The research investigated the effect of shoulder restraint air bag on chest injury by comparing cases with and without a shoulder side air bag. The maximum external force to the chest was reduced by shoulder restraint air bag in both WorldSID and THUMS, reducing chest injury risk as measured by the amount of rib deflection, number of the rib fractures, and rib deflection ratio. However, it was also determined that the external force to shoulder should be limited to the chest injury threshold because the external shoulder force transmits to the chest via the arm in the case of WorldSID and via the scapula in the case of THUMS. Because these results show the shoulder restraint air bag effect on chest injury risk, the vent hole size of the shoulder restraint air bag was changed for varying reaction forces to investigate the relationship between the external force to the shoulder and the risk of chest injury. In the case of THUMS, an external shoulder force of 1.8 kN and more force from the shoulder restraint air bag was necessary to help prevent rib fracture. Increasing external force applied to shoulder up to 6.2 kN (the maximum force used in this study) did not induce any rib or clavicle fractures in the THUMS. When the shoulder restraint air bag generated external force to the shoulder from 1.8 to 6.2 kN in THUMS, which were applied to the WorldSID, the shoulder deflection ranged from 35 to 68 mm, and the shoulder force ranged from 1.8 to 2.3 kN. In the test configuration used, a shoulder restraint using the air bag helps reduce chest injury risk by lowering the maximum magnitude of external force to the shoulder and chest. To help reduce rib fracture risk in the THUMS, the shoulder restraint air bag was expected to generate a force of 3.7 kN with a minimum rib deflection ratio. This corresponds to a shoulder rib deflection of 60 mm and a shoulder load of 2.2 kN in WorldSID. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Effect of externally applied periodic force on ion acoustic waves in superthermal plasmas

NASA Astrophysics Data System (ADS)

Chowdhury, Snigdha; Mandi, Laxmikanta; Chatterjee, Prasanta

2018-04-01

Ion acoustic solitary waves in superthermal plasmas are investigated in the presence of trapped electrons. The reductive perturbation technique is employed to obtain a forced Korteweg-de Vries-like Schamel equation. An analytical solution is obtained in the presence of externally applied force. The effect of the external applied periodic force is also observed. The effect of the spectral index (κ), the strength ( f 0 ) , and the frequency ( ω ) on the amplitude and width of the solitary wave is obtained. The result may be useful in laboratory plasma as well as space environments.

Electrophoresis of concentrically and eccentrically positioned cylindrical particles in a long tube.

PubMed

Liu, Hui; Bau, Haim H; Hu, Howard H

2004-03-30

We study analytically and numerically the electrophoretic motion of cylindrical particles translating slowly in long tubes filled with an electrolyte solution and subjected to axial electric fields. Both thin and thick double layers are considered. Of particular interest is the case when the particle's and tube's radii are of the same order of magnitude. The model accounts for the flow induced by the particle's motion (the particle acts as a leaky piston) and the electroosmotic flow in the tube. The electrophoretic velocity of the particle and the forces and torques acting on it are determined as functions of the particle's radius, length, and position, the particle's and tube's zeta potentials, the tube's length, and the externally imposed pressures. When the particle is positioned off center, it rotates and its trajectory traces an oscillatory path.

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External Forces Affecting Higher Education. NACUBO Professional File. Vol. 7, No. 5.

ERIC Educational Resources Information Center

Bailey, Stephen K.

Out of the many external forces that influence college campuses, there are four that have had (or are likely to have) a major impact on the fortunes of higher education. The ways in which college and university officials and friends react to these forces can make an enormous difference to the future of higher education. The forces are: (1) Federal…

Anharmonic 1D actuator model including electrostatic and Casimir forces with fractional damping perturbed by an external force

NASA Astrophysics Data System (ADS)

Mansoori Kermani, Maryam; Dehestani, Maryam

2018-06-01

We modeled a one-dimensional actuator including the Casimir and electrostatic forces perturbed by an external force with fractional damping. The movable electrode was assumed to oscillate by an anharmonic elastic force originated from Murrell-Mottram or Lippincott potential. The nonlinear equations have been solved via the Adomian decomposition method. The behavior of the displacement of the electrode from equilibrium position, its velocity and acceleration were described versus time. Also, the changes of the displacement have been investigated according to the frequency of the external force and the voltage of the electrostatic force. The convergence of the Adomian method and the effect of the orders of expansion on the displacement versus time, frequency, and voltage were discussed. The pull-in parameter was obtained and compared with the other models in the literature. This parameter was described versus the equilibrium position and anharmonicity constant.

Anharmonic 1D actuator model including electrostatic and Casimir forces with fractional damping perturbed by an external force

NASA Astrophysics Data System (ADS)

Mansoori Kermani, Maryam; Dehestani, Maryam

2018-03-01

We modeled a one-dimensional actuator including the Casimir and electrostatic forces perturbed by an external force with fractional damping. The movable electrode was assumed to oscillate by an anharmonic elastic force originated from Murrell-Mottram or Lippincott potential. The nonlinear equations have been solved via the Adomian decomposition method. The behavior of the displacement of the electrode from equilibrium position, its velocity and acceleration were described versus time. Also, the changes of the displacement have been investigated according to the frequency of the external force and the voltage of the electrostatic force. The convergence of the Adomian method and the effect of the orders of expansion on the displacement versus time, frequency, and voltage were discussed. The pull-in parameter was obtained and compared with the other models in the literature. This parameter was described versus the equilibrium position and anharmonicity constant.

A novel torsional exciter for modal vibration testing of large rotating machinery

NASA Astrophysics Data System (ADS)

Sihler, Christof

2006-10-01

A novel exciter for applying a dynamic torsional force to a rotating structure is presented in this paper. It has been developed at IPP in order to perform vibration tests with shaft assemblies of large flywheel generators (synchronous machines). The electromagnetic exciter (shaker) needs no fixture to the rotating shaft because the torque is applied by means of the stator winding of an electrical machine. Therefore, the exciter can most easily be applied in cases where a three-phase electrical machine (a motor or generator) is part of the shaft assembly. The oscillating power for the shaker is generated in a separate current-controlled DC circuit with an inductor acting as a buffer storage of magnetic energy. An AC component with adjustable frequency is superimposed on the inductor current in order to generate pulsating torques acting on the rotating shaft with the desired waveform and frequency. Since this torsional exciter does not require an external power source, can easily be installed (without contact to the rotating structure) and provides dynamic torsional forces which are sufficient for multi-megawatt applications, it is best suited for on-site tests of large rotating machinery.

Diffusion of Brownian particles in a tilted periodic potential under the influence of an external Ornstein-Uhlenbeck noise

NASA Astrophysics Data System (ADS)

Bai, Zhan-Wu; Zhang, Wei

2018-01-01

The diffusion behaviors of Brownian particles in a tilted periodic potential under the influence of an internal white noise and an external Ornstein-Uhlenbeck noise are investigated through numerical simulation. In contrast to the case when the bias force is smaller or absent, the diffusion coefficient exhibits a nonmonotonic dependence on the correlation time of the external noise when bias force is large. A mechanism different from locked-to-running transition theory is presented for the diffusion enhancement by a bias force in intermediate to large damping. In the underdamped regime and the presence of external noise, the diffusion coefficient is a monotonically decreasing function of low temperature rather than a nonmonotonic function when external noise is absent. The diffusive process undergoes four regimes when bias force approaches but is less than its critical value and noises intensities are small. These behaviors can be attributed to the locked-to-running transition of particles.

Force adaptation transfers to untrained workspace regions in children: evidence for developing inverse dynamic motor models.

PubMed

Jansen-Osmann, Petra; Richter, Stefanie; Konczak, Jürgen; Kalveram, Karl-Theodor

2002-03-01

When humans perform goal-directed arm movements under the influence of an external damping force, they learn to adapt to these external dynamics. After removal of the external force field, they reveal kinematic aftereffects that are indicative of a neural controller that still compensates the no longer existing force. Such behavior suggests that the adult human nervous system uses a neural representation of inverse arm dynamics to control upper-extremity motion. Central to the notion of an inverse dynamic model (IDM) is that learning generalizes. Consequently, aftereffects should be observable even in untrained workspace regions. Adults have shown such behavior, but the ontogenetic development of this process remains unclear. This study examines the adaptive behavior of children and investigates whether learning a force field in one hemifield of the right arm workspace has an effect on force adaptation in the other hemifield. Thirty children (aged 6-10 years) and ten adults performed 30 degrees elbow flexion movements under two conditions of external damping (negative and null). We found that learning to compensate an external damping force transferred to the opposite hemifield, which indicates that a model of the limb dynamics rather than an association of visited space and experienced force was acquired. Aftereffects were more pronounced in the younger children and readaptation to a null-force condition was prolonged. This finding is consistent with the view that IDMs in children are imprecise neural representations of the actual arm dynamics. It indicates that the acquisition of IDMs is a developmental achievement and that the human motor system is inherently flexible enough to adapt to any novel force within the limits of the organism's biomechanics.

Radiation reaction on a classical charged particle: a modified form of the equation of motion.

PubMed

Alcaine, Guillermo García; Llanes-Estrada, Felipe J

2013-09-01

We present and numerically solve a modified form of the equation of motion for a charged particle under the influence of an external force, taking into account the radiation reaction. This covariant equation is integro-differential, as Dirac-Röhrlich's, but has several technical improvements. First, the equation has the form of Newton's second law, with acceleration isolated on the left hand side and the force depending only on positions and velocities: Thus, the equation is linear in the highest derivative. Second, the total four-force is by construction perpendicular to the four-velocity. Third, if the external force vanishes for all future times, the total force and the acceleration automatically vanish at the present time. We show the advantages of this equation by solving it numerically for several examples of external force.

Radiation reaction on a classical charged particle: A modified form of the equation of motion

NASA Astrophysics Data System (ADS)

Alcaine, Guillermo García; Llanes-Estrada, Felipe J.

2013-09-01

We present and numerically solve a modified form of the equation of motion for a charged particle under the influence of an external force, taking into account the radiation reaction. This covariant equation is integro-differential, as Dirac-Röhrlich's, but has several technical improvements. First, the equation has the form of Newton's second law, with acceleration isolated on the left hand side and the force depending only on positions and velocities: Thus, the equation is linear in the highest derivative. Second, the total four-force is by construction perpendicular to the four-velocity. Third, if the external force vanishes for all future times, the total force and the acceleration automatically vanish at the present time. We show the advantages of this equation by solving it numerically for several examples of external force.

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Effect of the External Lubrication Method for a Rotary Tablet Press on the Adhesion of the Film Coating Layer.

PubMed

Kondo, Hisami; Toyota, Hiroyasu; Kamiya, Takayuki; Yamashita, Kazunari; Hakomori, Tadashi; Imoto, Junko; Kimura, Shin-Ichiro; Iwao, Yasunori; Itai, Shigeru

2017-01-01

External lubrication is a useful method which reduces the adhesion of powder to punches and dies by spraying lubricants during the tableting process. However, no information is available on whether the tablets prepared using an external lubrication system can be applicable for a film coating process. In this study, we evaluated the adhesion force of the film coating layer to the surface of tablets prepared using an external lubrication method, compared with those prepared using internal lubrication method. We also evaluated wettability, roughness and lubricant distribution state on the tablet surface before film coating, and investigated the relationship between peeling of the film coating layer and these tablet surface properties. Increasing lubrication through the external lubrication method decreased wettability of the tablet surface. However, no change was observed in the adhesion force of the film coating layer. On the other hand, increasing lubrication through the internal lubrication method, decreased both wettability of the tablet surface and the adhesion force of the film coating layer. The magnesium stearate distribution state on the tablet surface was assessed using an X-ray fluorescent analyzer and lubricant agglomerates were observed in the case of the internal lubrication method. However, the lubricant was uniformly dispersed in the external lubrication samples. These results indicate that the distribution state of the lubricant affects the adhesion force of the film coating layer, and external lubrication maintained sufficient lubricity and adhesion force of the film coating layer with a small amount of lubricant.

Priors Engaged in Long-Latency Responses to Mechanical Perturbations Suggest a Rapid Update in State Estimation

PubMed Central

Crevecoeur, Frédéric; Scott, Stephen H.

2013-01-01

In every motor task, our brain must handle external forces acting on the body. For example, riding a bike on cobblestones or skating on irregular surface requires us to appropriately respond to external perturbations. In these situations, motor predictions cannot help anticipate the motion of the body induced by external factors, and direct use of delayed sensory feedback will tend to generate instability. Here, we show that to solve this problem the motor system uses a rapid sensory prediction to correct the estimated state of the limb. We used a postural task with mechanical perturbations to address whether sensory predictions were engaged in upper-limb corrective movements. Subjects altered their initial motor response in ∼60 ms, depending on the expected perturbation profile, suggesting the use of an internal model, or prior, in this corrective process. Further, we found trial-to-trial changes in corrective responses indicating a rapid update of these perturbation priors. We used a computational model based on Kalman filtering to show that the response modulation was compatible with a rapid correction of the estimated state engaged in the feedback response. Such a process may allow us to handle external disturbances encountered in virtually every physical activity, which is likely an important feature of skilled motor behaviour. PMID:23966846

[Adhesive properties and related phenomena for powdered pharmaceuticals].

PubMed

Otsuka, A

1998-04-01

This report deals with adhesive properties and related phenomena of powdered materials including pharmaceuticals. The adhesive force between a powder particle and substrate as well as the tensile strength of a powder bed and tablet was measured. Various factors were found to affect powder adhesion. Physical properties such as the size, shape and surface roughness were examined. The adhesive force between a particle and substrate decreased remarkably in the presence of ultrafine particles, which is of interest since the addition of adequate amount of "glidant" causes an increase in powder fluidity. From a pharmaceutical point of view, temperature and humidity were essential to particle adhesion. For several organic substances, the adhesive force increased significantly at homologous temperatures more than ca. 0.7, suggesting the sintering mechanism to be operative. The adhsive force between polymer films and glass beads varied according to polymer and relative humidity. A close correlation of water sorbed by the polymer film with adhesive force was noted. In connection with powder fluidity, compaction properties were studied by the centrifugal and tapping methods. Apparent adhesion defined as the ratio of the adhesive force between two contacting particles to the external force acting on a particle was noted to be the primary determinant of the void fraction or the porosity of the powder bed, indicating that the probability of particle displacement essentially depended on apparent adhesion.

Reactive granular optics for passive tracking of the sun

NASA Astrophysics Data System (ADS)

Frenkel, I.; Niv, A.

2017-08-01

The growing need for cost-effective renewable energy sources is hampered by the stagnation in solar cell technology, thus preventing a substantial reduction in the module and energy-production price. Lowering the energy-production cost could be achieved by using modules with efficiency. One of the possible means for increasing the module efficiency is concentrated photovoltaics (CPV). CPV, however, requires complex and accurate active tracking of the sun that reduces much of its cost-effectiveness. Here, we propose a passive tracking scheme based on a reactive optical device. The optical reaction is achieved by a new kind of light activated mechanical force that acts on micron-sized particles. This optical force allows the formation of granular disordered optical media that can be switched from being opaque to become transparent based on the intensity of light it interacts with. Such media gives rise to an efficient passive tracking scheme that when combined with an external optical cavity forms a new solar power conversion approach. Being external to the cell itself, this approach is indifferent to the type of semiconducting material that is used, as well as to other aspects of the cell design. This, in turn, liberates the cell layout from its optical constraints thus paving the way to higher efficiencies at lower module price.

Direct numerical simulation of the effect of an electric field on flame stability

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

Belhi, Memdouh; Domingo, Pascale; Vervisch, Pierre

2010-12-15

The role of electric fields in stabilising combustion is a well-known phenomenon. Among the possible mechanisms favouring the anchorage of the flame base, the ion-driven wind acting directly on flow momentum ahead of the flame base could be the leading one. Direct numerical simulation has been used to verify this hypothesis and lead to a better understanding of diffusion flame base anchoring in the presence of an externally applied voltage. In this context, a simplified modelling approach is proposed to describe combustion in the presence of electric body forces. The model reproduces the tendencies of experimental observations found in themore » literature. The sensitivity of the flame lift-off height to the applied voltage is studied and the modification of the velocity field ahead of the flame base induced by the electric volume forces is highlighted. (author)« less

Natural Curvature as Effective Confinement in Elastic Sheets

NASA Astrophysics Data System (ADS)

Albarran, Octavio; Katifori, Eleni; Goehring, Lucas

The wrinkling and folding transitions of thin elastic sheets have been extensively studied in the last decade. The exchange of energy from stretching to bending acts as a paradigm for a wide range of elastic instabilities, including the wrinkling of the gut, and the crinkling of leaves. In two dimensions this type of problem is typically considered by the model of an Euler-elastica in compressive confinement. We show that, even without any external forces, an elastic surface supported by a fluid can bend and wrinkle when it acquires a non-zero natural curvature. Locally, we will demonstrate how a preferential curvature can be related to an effective compression, and hence a confining force that can vary spatially. This suggests a simple experimental setup, where we have characterised a variety of wrinkle patterns that can be generated for different mechanical properties and natural curvatures.

Effect of attentional focus strategies on peak force and performance in the standing long jump.

PubMed

Wu, Will F W; Porter, Jared M; Brown, Lee E

2012-05-01

Significant benefits in standing long jump performance have been demonstrated when subjects were provided verbal instructions that promoted an external focus of attention compared with an internal focus of attention, suggesting differences in ground reaction forces. The purpose of the present study was to evaluate peak force and jump performance between internal and external focus of attention strategies. Untrained subjects were assigned to both experimental conditions in which verbal instructions were provided to promote either an external or internal focus of attention. All subjects completed a total number of 5 standing long jumps. The results of the study demonstrated that the external focus of attention condition elicited significantly greater jump distance (153.6 ± 38.6 cm) than the internal focus of attention condition (139.5 ± 46.7 cm). There were no significant differences observed between conditions in peak force (1429.8 ± 289.1 N and 1453.7 ± 299.7 N, respectively). The results add to the growing body of literature describing the training and learning benefits of an external focus of attention. Practitioners should create standardized verbal instructions using an external focus of attention to maximize standing long jump performance.

Proprioception Is Robust under External Forces

PubMed Central

Kuling, Irene A.; Brenner, Eli; Smeets, Jeroen B. J.

2013-01-01

Information from cutaneous, muscle and joint receptors is combined with efferent information to create a reliable percept of the configuration of our body (proprioception). We exposed the hand to several horizontal force fields to examine whether external forces influence this percept. In an end-point task subjects reached visually presented positions with their unseen hand. In a vector reproduction task, subjects had to judge a distance and direction visually and reproduce the corresponding vector by moving the unseen hand. We found systematic individual errors in the reproduction of the end-points and vectors, but these errors did not vary systematically with the force fields. This suggests that human proprioception accounts for external forces applied to the hand when sensing the position of the hand in the horizontal plane. PMID:24019959

Examining the Impact of External Influences on Police Use of Deadly Force over Time.

ERIC Educational Resources Information Center

White, Michael D.

2002-01-01

Used interrupted time-series analysis (ARIMA) to study the impact of legislation and judicial intervention on the use of deadly force by police officers in Philadelphia, Pennsylvania. Findings generally suggest that dynamic changes in the internal working environment can outweigh the influence of external mechanisms on deadly force use. Findings…

Force sharing and other collaborative strategies in a dyadic force perception task

PubMed Central

Tatti, Fabio

2018-01-01

When several persons perform a physical task jointly, such as transporting an object together, the interaction force that each person experiences is the sum of the forces applied by all other persons on the same object. Therefore, there is a fundamental ambiguity about the origin of the force that each person experiences. This study investigated the ability of a dyad (two persons) to identify the direction of a small force produced by a haptic device and applied to a jointly held object. In this particular task, the dyad might split the force produced by the haptic device (the external force) in an infinite number of ways, depending on how the two partners interacted physically. A major objective of this study was to understand how the two partners coordinated their action to perceive the direction of the third force that was applied to the jointly held object. This study included a condition where each participant responded independently and another one where the two participants had to agree upon a single negotiated response. The results showed a broad range of behaviors. In general, the external force was not split in a way that would maximize the joint performance. In fact, the external force was often split very unequally, leaving one person without information about the external force. However, the performance was better than expected in this case, which led to the discovery of an unanticipated strategy whereby the person who took all the force transmitted this information to the partner by moving the jointly held object. When the dyad could negotiate the response, we found that the participant with less force information tended to switch his or her response more often. PMID:29474433

Spin-oscillator model for the unzipping of biomolecules by mechanical force.

PubMed

Prados, A; Carpio, A; Bonilla, L L

2012-08-01

A spin-oscillator system models unzipping of biomolecules (such as DNA, RNA, or proteins) subject to an external force. The system comprises a macroscopic degree of freedom, represented by a one-dimensional oscillator, and internal degrees of freedom, represented by Glauber spins with nearest-neighbor interaction and a coupling constant proportional to the oscillator position. At a critical value F(c) of an applied external force F, the oscillator rest position (order parameter) changes abruptly and the system undergoes a first-order phase transition. When the external force is cycled at different rates, the extension given by the oscillator position exhibits a hysteresis cycle at high loading rates, whereas it moves reversibly over the equilibrium force-extension curve at very low loading rates. Under constant force, the logarithm of the residence time at the stable and metastable oscillator rest position is proportional to F-F(c) as in an Arrhenius law.

75 FR 56601 - Privacy Act of 1974: New System of Records

Federal Register 2010, 2011, 2012, 2013, 2014

2010-09-16

...The Patient Protection and Affordable Care Act (the Affordable Care Act), Public Law 111-148, was enacted on March 23, 2010; the Health Care and Education Reconciliation Act (the Reconciliation Act), Public Law 111-152, was enacted on March 30, 2010. The Affordable Care Act and implementing regulations (codified in HHS interim final rules (IFR) at 45 CFR Part 147) require that non-grandfathered health insurance plans and issuers offering group and individual coverage have effective internal claims and appeals and external review processes. The effective date for these requirements is plan or policy years beginning on or after September 23, 2010. Regarding external review, the statute requires that health plans and issuers must comply with either a state external review process or a process meeting standards issued by the Secretary of Health and Human Services (HHS) that is ``similar to'' a state process meeting requirements in section 2719 (a ``federal external review process''). The IFR includes a transition period prior to July 1, 2011, during which time HHS will work with states to assist in making any necessary changes so that the state process will meet the minimum consumer protections identified in 45 CFR 147.136 that must be met in order for the state process to apply. During this interim period, health insurance issuers in states with external review laws in effect prior to September 23, 2010 will follow that state's external review law to the extent applicable. In states that have not passed an external review law that is in effect on September 23, 2010, a health insurance issuer must follow an interim federal external review process that will be administered by the Office of Personnel Management (OPM). The system of records will be created as OPM assists HHS by providing external reviews of adverse benefit determinations and final internal adverse benefit determinations as requested by eligible claimants and their authorized representatives (``claimants''). The system of records will include any data relevant to these external reviews, and OPM proposes to add this new system of records to its inventory of records systems subject to the Privacy Act of 1974 (5 U.S.C. 552a), as amended. This action is necessary to meet the requirements of the Privacy Act to publish in the Federal Register notice of the existence and character of records maintained by the agency (5 U.S.C. 552a(e)(4)).

The Fundamental Solutions for the Stress Intensity Factors of Modes I, II And III. The Axially Symmetric Problem

NASA Astrophysics Data System (ADS)

Rogowski, B.

2015-05-01

The subject of the paper are Green's functions for the stress intensity factors of modes I, II and III. Green's functions are defined as a solution to the problem of an elastic, transversely isotropic solid with a penny-shaped or an external crack under general axisymmetric loadings acting along a circumference on the plane parallel to the crack plane. Exact solutions are presented in a closed form for the stress intensity factors under each type of axisymmetric ring forces as fundamental solutions. Numerical examples are employed and conclusions which can be utilized in engineering practice are formulated.

Model-Based Heterogeneous Data Fusion for Reliable Force Estimation in Dynamic Structures under Uncertainties

PubMed Central

Khodabandeloo, Babak; Melvin, Dyan; Jo, Hongki

2017-01-01

Direct measurements of external forces acting on a structure are infeasible in many cases. The Augmented Kalman Filter (AKF) has several attractive features that can be utilized to solve the inverse problem of identifying applied forces, as it requires the dynamic model and the measured responses of structure at only a few locations. But, the AKF intrinsically suffers from numerical instabilities when accelerations, which are the most common response measurements in structural dynamics, are the only measured responses. Although displacement measurements can be used to overcome the instability issue, the absolute displacement measurements are challenging and expensive for full-scale dynamic structures. In this paper, a reliable model-based data fusion approach to reconstruct dynamic forces applied to structures using heterogeneous structural measurements (i.e., strains and accelerations) in combination with AKF is investigated. The way of incorporating multi-sensor measurements in the AKF is formulated. Then the formulation is implemented and validated through numerical examples considering possible uncertainties in numerical modeling and sensor measurement. A planar truss example was chosen to clearly explain the formulation, while the method and formulation are applicable to other structures as well. PMID:29149088

Modelling cell motility and chemotaxis with evolving surface finite elements

PubMed Central

Elliott, Charles M.; Stinner, Björn; Venkataraman, Chandrasekhar

2012-01-01

We present a mathematical and a computational framework for the modelling of cell motility. The cell membrane is represented by an evolving surface, with the movement of the cell determined by the interaction of various forces that act normal to the surface. We consider external forces such as those that may arise owing to inhomogeneities in the medium and a pressure that constrains the enclosed volume, as well as internal forces that arise from the reaction of the cells' surface to stretching and bending. We also consider a protrusive force associated with a reaction–diffusion system (RDS) posed on the cell membrane, with cell polarization modelled by this surface RDS. The computational method is based on an evolving surface finite-element method. The general method can account for the large deformations that arise in cell motility and allows the simulation of cell migration in three dimensions. We illustrate applications of the proposed modelling framework and numerical method by reporting on numerical simulations of a model for eukaryotic chemotaxis and a model for the persistent movement of keratocytes in two and three space dimensions. Movies of the simulated cells can be obtained from http://homepages.warwick.ac.uk/∼maskae/CV_Warwick/Chemotaxis.html. PMID:22675164

Foraging at the Edge of Chaos: Internal Clock versus External Forcing

NASA Astrophysics Data System (ADS)

Nicolis, S. C.; Fernández, J.; Pérez-Penichet, C.; Noda, C.; Tejera, F.; Ramos, O.; Sumpter, D. J. T.; Altshuler, E.

2013-06-01

Activity rhythms in animal groups arise both from external changes in the environment, as well as from internal group dynamics. These cycles are reminiscent of physical and chemical systems with quasiperiodic and even chaotic behavior resulting from “autocatalytic” mechanisms. We use nonlinear differential equations to model how the coupling between the self-excitatory interactions of individuals and external forcing can produce four different types of activity rhythms: quasiperiodic, chaotic, phase locked, and displaying over or under shooting. At the transition between quasiperiodic and chaotic regimes, activity cycles are asymmetrical, with rapid activity increases and slower decreases and a phase shift between external forcing and activity. We find similar activity patterns in ant colonies in response to varying temperature during the day. Thus foraging ants operate in a region of quasiperiodicity close to a cascade of transitions leading to chaos. The model suggests that a wide range of temporal structures and irregularities seen in the activity of animal and human groups might be accounted for by the coupling between collectively generated internal clocks and external forcings.

Unfolding DNA condensates produced by DNA-like charged depletants: A force spectroscopy study

NASA Astrophysics Data System (ADS)

Lima, C. H. M.; Rocha, M. S.; Ramos, E. B.

2017-02-01

In this work, we have measured, by means of optical tweezers, forces acting on depletion-induced DNA condensates due to the presence of the DNA-like charged protein bovine serum albumin (BSA). The stretching and unfolding measurements performed on the semi-flexible DNA chain reveal (1) the softening of the uncondensed DNA contour length and (2) a mechanical behavior strikingly different from those previously observed: the force-extension curves of BSA-induced DNA condensates lack the "saw-tooth" pattern and applied external forces as high as ≈80 pN are unable to fully unfold the condensed DNA contour length. This last mechanical experimental finding is in agreement with force-induced "unpacking" detailed Langevin dynamics simulations recently performed by Cortini et al. on model rod-like shaped condensates. Furthermore, a simple thermodynamics analysis of the unfolding process has enabled us to estimate the free energy involved in the DNA condensation: the estimated depletion-induced interactions vary linearly with both the condensed DNA contour length and the BSA concentration, in agreement with the analytical and numerical analysis performed on model DNA condensates. We hope that future additional experiments can decide whether the rod-like morphology is the actual one we are dealing with (e.g. pulling experiments coupled with super-resolution fluorescence microscopy).

The Role of Contact Line (Pinning) Forces on Bubble Blockage in Microchannels.

PubMed

Mohammadi, Mahshid; Sharp, Kendra V

2015-03-01

This paper highlights the influence of contact line (pinning) forces on the mobility of dry bubbles in microchannels. Bubbles moving at velocities less than the dewetting velocity of liquid on the surface are essentially dry, meaning that there is no thin liquid film around the bubbles. For these "dry" bubbles, contact line forces and a possible capillary pressure gradient induced by pinning act on the bubbles and resist motion. Without sufficient driving force (e.g., external pressure), a dry bubble is brought to stagnation. For the first time, a bipartite theoretical model that estimates the required pressure difference across the length of stagnant bubbles with concave and convex back interfaces to overcome the contact line forces and stimulate motion is proposed. To validate our theory, the pressure required to move a single dry bubble in square microchannels exhibiting contact angle hysteresis has been measured. The working fluid was deionized water. The experiments have been conducted on coated glass channels with different surface hydrophilicities that resulted in concave and convex back interfaces for the bubbles. The experimental results were in agreement with the model's predictions for square channels. The predictions of the concave and convex back models were within 19% and 27% of the experimental measurements, respectively.

Solar and atmospheric forcing on mountain lakes.

PubMed

Luoto, Tomi P; Nevalainen, Liisa

2016-10-01

We investigated the influence of long-term external forcing on aquatic communities in Alpine lakes. Fossil microcrustacean (Cladocera) and macrobenthos (Chironomidae) community variability in four Austrian high-altitude lakes, determined as ultra-sensitive to climate change, were compared against records of air temperature, North Atlantic Oscillation (NAO) and solar forcing over the past ~400years. Summer temperature variability affected both aquatic invertebrate groups in all study sites. The influence of NAO and solar forcing on aquatic invertebrates was also significant in the lakes except in the less transparent lake known to have remained uniformly cold during the past centuries due to summertime snowmelt input. The results suggest that external forcing plays an important role in these pristine ecosystems through their impacts on limnology of the lakes. Not only does the air temperature variability influence the communities but also larger-scale external factors related to atmospheric circulation patterns and solar activity cause long-term changes in high-altitude aquatic ecosystems, through their connections to hydroclimatic conditions and light environment. These findings are important in the assessment of climate change impacts on aquatic ecosystems and in greater understanding of the consequences of external forcing on lake ontogeny. Copyright © 2016 Elsevier B.V. All rights reserved.

An allosterically regulated reversible mechanical molecular switch: A de novo protein maquette functions as a redox/ionic strength sensor coupling chemical binding energy or charge interactions to conformational change

NASA Astrophysics Data System (ADS)

Grosset, Anne Marie

2000-10-01

Switch-like structural rearrangements of subunits due to charge-interactions are common in the basic biological action of proteins that couple and transfer chemical and ionic signals, sensing and regulation, mechanical force and electrochemical free energy. A simple synthetic protein model (maquette) has been designed to better understand the engineering of natural switches. Basic thermodynamic principles define the two key elements required for biological or chemical function of a switch. First, there must be two well-defined states. In this case, the two conformational states must have an energetic difference (DeltaDeltaG°) that is spanned by the applied driving force. Second, there must be an external stimulus, which preferentially interacts with one of the two states. The external stimulus provides the driving force that shifts the equilibrium from the first state to the second state (≥10:1 shifting towards ≤1:10). The energetic difference between the states must be the same order of magnitude as the driving force. In this synthetic protein, the two conformational states correspond to parallel (syn) and antiparallel (anti) assembly of the two identical helix-ss-helix subunits that bind heme close to the di-sulfide loop region. Charge interactions between two ferric hemes bound to histidines provide a driving force on the order of 2 kcal/mol (corresponding in the syn-topology to the 75--100 mV split in the heme redox potentials, or the 25--80 times weaker binding for the second ferric heme). The tetra-alpha-helix bundle has been modified to have a DeltaG around 1.8--2.5 kcal/mol (a 50--80 fold difference in the anti/syn ratio). Therefore, oxidation and reduction of the heme, or the binding of a second charged ferric heme can reversibly switch between syn- and anti-topologies, providing a sensitive detector of redox state or heme concentration. External solution conditions (e.g. ionic composition) can act on the protein remotely from the primary internal switch action and confer a secondary level of allosteric regulation. Bifunctional ligands can link subunits to shift topology. Scanning redox potentiometry can monitor the kinetics of topological change. Point amino acid substitutions and computer repacking of the hydrophobic core can modulate both the kinetics and the energetics.

Dynamic force signal processing system of a robot manipulator

NASA Technical Reports Server (NTRS)

Uchiyama, M.; Kitagaki, K.; Hakomori, K.

1987-01-01

If dynamic noises such as those caused by the inertia forces of the hand can be eliminated from the signal of the force sensor installed on the wrist of the robot manipulator and if the necessary information of the external force can be detected with high sensitivity and high accuracy, a fine force feedback control for robots used in high speed and various fields will be possible. As the dynamic force sensing system, an external force estimate method with the extended Kalman filter is suggested and simulations and tests for a one axis force were performed. Later a dynamic signal processing system of six axes was composed and tested. The results are presented.

Thermal Noise Reduction of Mechanical Oscillators by Actively Controlled External Dissipative Forces

NASA Technical Reports Server (NTRS)

Liang, Shoudan; Medich, David; Czajkowsky, Daniel M.; Sheng, Sitong; Yuan, Jian-Yang; Shao, Zhifeng

1999-01-01

We show that the thermal fluctuations of very soft mechanical oscillators, such as the cantilever in an atomic force microscope (AFM), can be reduced without changing the stiffness of the spring or having to lower the environment temperature. We derive a theoretical relationship between the thermal fluctuations of an oscillator and an actively external-dissipative force. This relationship is verified by experiments with an AFM cantilever where the external active force is coupled through a magnetic field. With simple instrumentation, we have reduced the thermal noise amplitude of the cantilever by a factor of 3.4, achieving an apparent temperature of 25 K with the environment at 295K. This active noise reduction approach can significantly improve the accuracy of static position or static force measurements in a number of practical applications.

The nature of the laning transition in two dimensions

NASA Astrophysics Data System (ADS)

Glanz, T.; Löwen, H.

2012-11-01

If a binary colloidal mixture is oppositely driven by an external field, a transition towards a laned state occurs at sufficiently large drives, where particles driven alike form elongated structures (‘lanes’) characterized by a large correlation length ξ along the drive. Here we perform extensive Brownian dynamics computer simulations on a two-dimensional equimolar binary Yukawa system driven by a constant force that acts oppositely on the two species. We systematically address finite-size effects on lane formation by exploring large systems up to 262 144 particles under various boundary conditions. It is found that the correlation length ξ along the field depends exponentially on the driving force (or Peclet number). Conversely, in a finite system, ξ reaches a fraction of the system size at a driving force which is logarithmic in the system size, implying massive finite-size corrections. For a fixed finite drive, ξ does not diverge in the thermodynamic limit. Therefore, though laning has a signature as a sharp transition in a finite system, it is a smooth crossover in the thermodynamic limit.

Modeling mechanical properties of a shear thickening fluid damper based on phase transition theory

NASA Astrophysics Data System (ADS)

Wei, Minghai; Lin, Kun; Guo, Qian

2018-03-01

Shear thickening fluids (STFs) are highly concentrated colloidal suspensions consisting of monodisperse nano-particles suspended in a carrying fluid, and have the capacity to display both flowable and rigid behaviors, when subjected to sudden stimuli. In that process, the external energy that acts on an STF can be dissipated quickly. The aim of this study is to present a dynamic model of a damper filled with STF that can be directly used in control engineering fields. To this end, shear stress during phase transition of the STF material is chosen as an internal variable. A non-convex function with bifurcation behavior is used to describe the phase transitioning of STF by determining the relationship between the behavioral characteristics of the microscopic phase and macroscopic damping force. This model is able to predict force-velocity and force-displacement relationships as functions of the loading frequency. Efficacy of the model is demonstrated via comparison with experimental results from previous studies. In addition, the results confirm the hypothesis regarding the occurrence of STF phase transitioning when subject to shear stress.

Dispersion of aerosol particles undergoing Brownian motion

NASA Astrophysics Data System (ADS)

Alonso, Manuel; Endo, Yoshiyuki

2001-12-01

The variance of the position distribution for a Brownian particle is derived in the general case where the particle is suspended in a flowing medium and, at the same time, is acted upon by an external field of force. It is shown that, for uniform force and flow fields, the variance is equal to that for a free particle. When the force field is not uniform but depends on spatial location, the variance can be larger or smaller than that for a free particle depending on whether the average motion of the particles takes place toward, respectively, increasing or decreasing absolute values of the field strength. A few examples concerning aerosol particles are discussed, with especial attention paid to the mobility classification of charged aerosols by a non-uniform electric field. As a practical application of these ideas, a new design of particle-size electrostatic classifier differential mobility analyser (DMA) is proposed in which the aerosol particles migrate between the electrodes in a direction opposite to that for a conventional DMA, thereby improving the resolution power of the instrument.

Sequence-encoded colloidal origami and microbot assemblies from patchy magnetic cubes

PubMed Central

Han, Koohee; Shields, C. Wyatt; Diwakar, Nidhi M.; Bharti, Bhuvnesh; López, Gabriel P.; Velev, Orlin D.

2017-01-01

Colloidal-scale assemblies that reconfigure on demand may serve as the next generation of soft “microbots,” artificial muscles, and other biomimetic devices. This requires the precise arrangement of particles into structures that are preprogrammed to reversibly change shape when actuated by external fields. The design and making of colloidal-scale assemblies with encoded directional particle-particle interactions remain a major challenge. We show how assemblies of metallodielectric patchy microcubes can be engineered to store energy through magnetic polarization and release it on demand by microscale reconfiguration. The dynamic pattern of folding and reconfiguration of the chain-like assemblies can be encoded in the sequence of the cube orientation. The residual polarization of the metallic facets on the microcubes leads to local interactions between the neighboring particles, which is directed by the conformational restrictions of their shape after harvesting energy from external magnetic fields. These structures can also be directionally moved, steered, and maneuvered by global forces from external magnetic fields. We illustrate these capabilities by examples of assemblies of specific sequences that can be actuated, reoriented, and spatially maneuvered to perform microscale operations such as capturing and transporting live cells, acting as prototypes of microbots, micromixers, and other active microstructures. PMID:28798960

Designing the Army’s Future Active Duty Weapons of Mass Destruction Response: Is the Defense Chemical, Biological, Radiological, Nuclear and High-Yield Explosives Response Force (DCRF) the Right Force at the Right Time?

DTIC Science & Technology

2013-06-14

ever-evolving contemporary nature of external and internal threats to the safety and security of the American homeland, it becomes increasingly...Major Justin P. Hurt, 146 pages. With the ever-evolving contemporary nature of external and internal threats to the safety and security of the American...HAZMAT Hazardous Materials HRF Homeland Response Force HSPD Homeland Security Presidential Directive JFHQ Joint Force

Midsole material-related force control during heel-toe running.

PubMed

Kersting, Uwe G; Brüggemann, Gert-Peter

2006-01-01

The impact maximum and rearfoot eversion have been used as indicators of load on internal structures in running. The midsole hardness of a typical running shoe was varied systematically to determine the relationship between external ground reaction force (GRF), in-shoe force, and kinematic variables. Eight subjects were tested during overground running at 4 m/s. Rearfoot movement as well as in-shoe forces and external GRF varied nonsystematically with midsole hardness. Kinematic parameters such as knee flexion and foot velocity at touchdown (TD), also varied nonsystematically with altered midsole hardness. Results demonstrate that considerable variations of in-shoe loading occur that were not depicted by external GRF measurements alone. Individuals apparently use different strategies of mechanical and neuromuscular adaptation in response to footwear modifications. In conclusion, shoe design effects on impact forces or other factors relating to injuries depend on the individual and therefore cannot be generalized.

Self-similar solutions of stationary Navier-Stokes equations

NASA Astrophysics Data System (ADS)

Shi, Zuoshunhua

2018-02-01

In this paper, we mainly study the existence of self-similar solutions of stationary Navier-Stokes equations for dimension n = 3 , 4. For n = 3, if the external force is axisymmetric, scaling invariant, C 1 , α continuous away from the origin and small enough on the sphere S2, we shall prove that there exists a family of axisymmetric self-similar solutions which can be arbitrarily large in the class Cloc3 , α (R3 0). Moreover, for axisymmetric external forces without swirl, corresponding to this family, the momentum flux of the flow along the symmetry axis can take any real number. However, there are no regular (U ∈ Cloc3 , α (R3 0)) axisymmetric self-similar solutions provided that the external force is a large multiple of some scaling invariant axisymmetric F which cannot be driven by a potential. In the case of dimension 4, there always exists at least one self-similar solution to the stationary Navier-Stokes equations with any scaling invariant external force in L 4 / 3 , ∞ (R4).

Muscle contributions to propulsion and braking during walking and running: insight from external force perturbations.

PubMed

Ellis, Richard G; Sumner, Bonnie J; Kram, Rodger

2014-09-01

There remains substantial debate as to the specific contributions of individual muscles to center of mass accelerations during walking and running. To gain insight, we altered the demand for muscular propulsion and braking by applying external horizontal impeding and aiding forces near the center of mass as subjects walked and ran on a treadmill. We recorded electromyographic activity of the gluteus maximus (superior and inferior portions), the gluteus medius, biceps femoris, semitendinosus/membrinosus, vastus medialis, lateral and medial gastrocnemius and soleus. We reasoned that activity in a propulsive muscle would increase with external impeding force and decrease with external aiding force whereas activity in a braking muscle would show the opposite. We found that during walking the gastrocnemius and gluteus maximus provide propulsion while the vasti are central in providing braking. During running, we found that the gluteus maximus, vastus medialis, gastrocnemius and soleus all contribute to propulsion. Copyright © 2014 Elsevier B.V. All rights reserved.

Defects formation and wave emitting from defects in excitable media

NASA Astrophysics Data System (ADS)

Ma, Jun; Xu, Ying; Tang, Jun; Wang, Chunni

2016-05-01

Abnormal electrical activities in neuronal system could be associated with some neuronal diseases. Indeed, external forcing can cause breakdown even collapse in nervous system under appropriate condition. The excitable media sometimes could be described by neuronal network with different topologies. The collective behaviors of neurons can show complex spatiotemporal dynamical properties and spatial distribution for electrical activities due to self-organization even from the regulating from central nervous system. Defects in the nervous system can emit continuous waves or pulses, and pacemaker-like source is generated to perturb the normal signal propagation in nervous system. How these defects are developed? In this paper, a network of neurons is designed in two-dimensional square array with nearest-neighbor connection type; the formation mechanism of defects is investigated by detecting the wave propagation induced by external forcing. It is found that defects could be induced under external periodical forcing under the boundary, and then the wave emitted from the defects can keep balance with the waves excited from external forcing.

A better way of fitting clips? A comparative study with respect to physical workload.

PubMed

Gaudez, Clarisse; Wild, Pascal; Aublet-Cuvelier, Agnès

2015-11-01

The clip fitting task is a frequently encountered assembly operation in the car industry. It can cause upper limb pain. During task laboratory simulations, upper limb muscular activity and external force were compared for 4 clip fitting methods: with the bare hand, with an unpowered tool commonly used at a company and with unpowered and powered prototype tools. None of the 4 fitting methods studied induced a lower overall workload than the other three. Muscle activity was lower at the dominant limb when using the unpowered tools and at the non-dominant limb with the bare hand or with the powered tool. Fitting clips with the bare hand required a higher external force than fitting with the three tools. Evaluation of physical workload was different depending on whether external force or muscle activity results were considered. Measuring external force only, as recommended in several standards, is insufficient for evaluating physical workload. Copyright © 2015 Elsevier Ltd and The Ergonomics Society. All rights reserved.

Motor Control of Landing from a Jump in Simulated Hypergravity.

PubMed

Gambelli, Clément N; Theisen, Daniel; Willems, Patrick A; Schepens, Bénédicte

2015-01-01

On Earth, when landing from a counter-movement jump, muscles contract before touchdown to anticipate imminent collision with the ground and place the limbs in a proper position. This study assesses how the control of landing is modified when gravity is increased above 1 g. Hypergravity was simulated in two different ways: (1) by generating centrifugal forces during turns of an aircraft (A300) and (2) by pulling the subject downwards in the laboratory with a Subject Loading System (SLS). Eight subjects were asked to perform counter-movement jumps at 1 g on Earth and at 3 hypergravity levels (1.2, 1.4 and 1.6 g) both in A300 and with SLS. External forces applied to the body, movements of the lower limb segments and muscular activity of 6 lower limb muscles were recorded. Our results show that both in A300 and with SLS, as in 1 g: (1) the anticipation phase is present; (2) during the loading phase (from touchdown until the peak of vertical ground reaction force), lower limb muscles act like a stiff spring, whereas during the second part (from the peak of vertical ground reaction force until the return to the standing position), they act like a compliant spring associated with a damper. (3) With increasing gravity, the preparatory adjustments and the loading phase are modified whereas the second part does not change drastically. (4) The modifications are similar in A300 and with SLS, however the effect of hypergravity is accentuated in A300, probably due to altered sensory inputs. This observation suggests that otolithic information plays an important role in the control of the landing from a jump.

Power, muscular work, and external forces in cycling.

PubMed

de Groot, G; Welbergen, E; Clijsen, L; Clarijs, J; Cabri, J; Antonis, J

1994-01-01

Cycling performance is affected by the interaction of a number of variables, including environment, mechanical, and human factors. Engineers have focused on the development of more efficient bicycles. Kinesiologists have examined cycling performance from a human perspective. This paper summarizes only certain aspects of human ergonomics of cycling, especially those which are important for the recent current research in our departments. Power is a key to performance of physical work. During locomotion an imaginary flow of energy takes place from the metabolism to the environment, with some efficiency. The 'useful' mechanical muscle power output might be used to perform movements and to do work against the environment. The external power is defined as the sum of joint powers, each calculated as the product of the joint (net) moment and angular velocity. This definition of external power is closely related to the mean external power as applied to exercise physiology: the sum of joint powers reflects all mechanical power which in principle can be used to fulfil a certain task. In this paper, the flow of energy for cycling is traced quantitatively as far as possible. Studies on the total lower limb can give insight into the contribution of individual muscles to external power. The muscle velocity (positive or negative) is obtained from the positions and orientations of body segments and a bar linkage model of the lower limb. The muscle activity can be measured by electromyography. In this way, positive and negative work regions in individual muscles are identified. Synergy between active agonistic/antagonistic muscle groups occurs in order to deliver external power. Maximum power is influenced by body position, geometry of the bicycle and pedalling rate. This has to be interpreted in terms of the length-tension and force-velocity-power relationships of the involved muscles. Flat road and uphill cycling at different saddle-tube angles is simulated on an ergometer. The measured pedal forces (magnitude and direction) are only dependent on the intersegmental orientation of saddle tube, crank position, upper and lower leg, and foot. The changed direction of the gravitational force with respect to the saddle-tube does not interfere with the co-ordinated force production pattern. During locomotory cycling at constant speed the external power is mainly used to overcome the aerodynamic friction force. This force and the rolling resistance are determined by coasting down experiments, yielding the external power.(ABSTRACT TRUNCATED AT 400 WORDS)

Meandering Brownian Donkeys

NASA Astrophysics Data System (ADS)

Eichhorn, R.; Reimann, P.

2004-04-01

We consider a Brownian particle whose motion is confined to a ``meandering'' pathway and which is driven away from thermal equilibrium by an alternating external force. This system exhibits absolute negative mobility, i.e. when an external static force is applied the particle moves in the direction opposite to that force. We reveal the physical mechanism behind this ``donkey-like'' behavior, and derive analytical approximations that are in excellent agreement with numerical results.

A Comparison of Male and Female Assistant Superintendents and Their Descriptions of Internal Barriers, External Barriers, Motivators, Stressors, and Discriminatory Acts They Anticipate Encountering on the Route to the Superintendency

ERIC Educational Resources Information Center

Hunter, Tanesha N.

2013-01-01

The purpose of this research study was to compare male and female assistant superintendents and their descriptions of Internal Barriers, External Barriers, Internal Motivators, External Motivators, Stressors, and Discriminatory Acts they anticipated encountering on the route to the superintendency in Suffolk and Nassau Counties on Long Island, New…

Tibiofemoral contact forces during walking, running and sidestepping.

PubMed

Saxby, David J; Modenese, Luca; Bryant, Adam L; Gerus, Pauline; Killen, Bryce; Fortin, Karine; Wrigley, Tim V; Bennell, Kim L; Cicuttini, Flavia M; Lloyd, David G

2016-09-01

We explored the tibiofemoral contact forces and the relative contributions of muscles and external loads to those contact forces during various gait tasks. Second, we assessed the relationships between external gait measures and contact forces. A calibrated electromyography-driven neuromusculoskeletal model estimated the tibiofemoral contact forces during walking (1.44±0.22ms(-1)), running (4.38±0.42ms(-1)) and sidestepping (3.58±0.50ms(-1)) in healthy adults (n=60, 27.3±5.4years, 1.75±0.11m, and 69.8±14.0kg). Contact forces increased from walking (∼1-2.8 BW) to running (∼3-8 BW), sidestepping had largest maximum total (8.47±1.57 BW) and lateral contact forces (4.3±1.05 BW), while running had largest maximum medial contact forces (5.1±0.95 BW). Relative muscle contributions increased across gait tasks (up to 80-90% of medial contact forces), and peaked during running for lateral contact forces (∼90%). Knee adduction moment (KAM) had weak relationships with tibiofemoral contact forces (all R(2)<0.36) and the relationships were gait task-specific. Step-wise regression of multiple external gait measures strengthened relationships (0.20

Comparisons Between Experimental and Semi-theoretical Cutting Forces of CCS Disc Cutters

NASA Astrophysics Data System (ADS)

Xia, Yimin; Guo, Ben; Tan, Qing; Zhang, Xuhui; Lan, Hao; Ji, Zhiyong

2018-05-01

This paper focuses on comparisons between the experimental and semi-theoretical forces of CCS disc cutters acting on different rocks. The experimental forces obtained from LCM tests were used to evaluate the prediction accuracy of a semi-theoretical CSM model. The results show that the CSM model reliably predicts the normal forces acting on red sandstone and granite, but underestimates the normal forces acting on marble. Some additional LCM test data from the literature were collected to further explore the ability of the CSM model to predict the normal forces acting on rocks of different strengths. The CSM model underestimates the normal forces acting on soft rocks, semi-hard rocks and hard rocks by approximately 38, 38 and 10%, respectively, but very accurately predicts those acting on very hard and extremely hard rocks. A calibration factor is introduced to modify the normal forces estimated by the CSM model. The overall trend of the calibration factor is characterized by an exponential decrease with increasing rock uniaxial compressive strength. The mean fitting ratios between the normal forces estimated by the modified CSM model and the experimental normal forces acting on soft rocks, semi-hard rocks and hard rocks are 1.076, 0.879 and 1.013, respectively. The results indicate that the prediction accuracy and the reliability of the CSM model have been improved.

Effect of lateral offset center of rotation in reverse total shoulder arthroplasty: a biomechanical study.

PubMed

Henninger, Heath B; Barg, Alexej; Anderson, Andrew E; Bachus, Kent N; Burks, Robert T; Tashjian, Robert Z

2012-09-01

Lateral offset center of rotation (COR) reduces the incidence of scapular notching and potentially increases external rotation range of motion (ROM) after reverse total shoulder arthroplasty (rTSA). The purpose of this study was to determine the biomechanical effects of changing COR on abduction and external rotation ROM, deltoid abduction force, and joint stability. A biomechanical shoulder simulator tested cadaveric shoulders before and after rTSA. Spacers shifted the COR laterally from baseline rTSA by 5, 10, and 15 mm. Outcome measures of resting abduction and external rotation ROM, and abduction and dislocation (lateral and anterior) forces were recorded. Resting abduction increased 20° vs native shoulders and was unaffected by COR lateralization. External rotation decreased after rTSA and was unaffected by COR lateralization. The deltoid force required for abduction significantly decreased 25% from native to baseline rTSA. COR lateralization progressively eliminated this mechanical advantage. Lateral dislocation required significantly less force than anterior dislocation after rTSA, and both dislocation forces increased with lateralization of the COR. COR lateralization had no influence on ROM (adduction or external rotation) but significantly increased abduction and dislocation forces. This suggests the lower incidence of scapular notching may not be related to the amount of adduction deficit after lateral offset rTSA but may arise from limited impingement of the humeral component on the lateral scapula due to a change in joint geometry. Lateralization provides the benefit of increased joint stability, but at the cost of increasing deltoid abduction forces. Copyright © 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

Numerical and experimental study of the effect of the induced electric potential in Lorentz force velocimetry

NASA Astrophysics Data System (ADS)

Hernández, Daniel; Boeck, Thomas; Karcher, Christian; Wondrak, Thomas

2018-01-01

Lorentz force velocimetry (LFV) is a contactless velocity measurement technique for electrically conducting fluids. When a liquid metal or a molten glass flows through an externally applied magnetic field, eddy currents and a flow-braking force are generated inside the liquid. This force is proportional to the velocity or flow rate of the fluid and, due to Newton’s third law, a force of the same magnitude but in opposite direction acts on the source of the applied magnetic field which in our case are permanent magnets. According to Ohm’s law for moving conductors at low magnetic Reynolds numbers, an electric potential is induced which ensures charge conservation. In this paper, we analyze the contribution of the induced electric potential to the total Lorentz force by considering two different scenarios: conducting walls of finite thickness and aspect ratio variation of the cross-section of the flow. In both the cases, the force component generated by the electric potential is always in the opposite direction to the total Lorentz force. This force component is sensitive to the electric boundary conditions of the flow of which insulating and perfectly conducting walls are the two limiting cases. In the latter case, the overall electric resistance of the system is minimized, resulting in a considerable increase in the measured Lorentz force. Additionally, this force originating from the electric potential also decays when the aspect ratio of the cross-section of the flow is changed. Hence, the sensitivity of the measurement technique is enhanced by either increasing wall conductivity or optimizing the aspect ratio of the cross-section of the flow.

Conversion of neurons and glia to external-cell fates in the external sensory organs of Drosophila hamlet mutants by a cousin-cousin cell-type respecification.

PubMed

Moore, Adrian W; Roegiers, Fabrice; Jan, Lily Y; Jan, Yuh-Nung

2004-03-15

The Drosophila external sensory organ forms in a lineage elaborating from a single precursor cell via a stereotypical series of asymmetric divisions. HAMLET transcription factor expression demarcates the lineage branch that generates two internal cell types, the external sensory neuron and thecogen. In HAMLET mutant organs, these internal cells are converted to external cells via an unprecedented cousin-cousin cell-fate respecification event. Conversely, ectopic HAMLET expression in the external cell branch leads to internal cell production. The fate-determining signals NOTCH and PAX2 act at multiple stages of lineage elaboration and HAMLET acts to modulate their activity in a branch-specific manner.

An analytical approach to the external force-free motion of pendulums on surfaces of constant curvature

NASA Astrophysics Data System (ADS)

Rubio, Rafael M.; Salamanca, Juan J.

2018-07-01

The dynamics of external force free motion of pendulums on surfaces of constant Gaussian curvature is addressed when the pivot moves along a geodesic obtaining the Lagrangian of the system. As an application it is possible the study of elastic and quantum pendulums.

Investigation of certain wing shapes with sections varying progressively along the span

NASA Technical Reports Server (NTRS)

Arsandaux, L

1931-01-01

This investigation has a double object: 1) the calculation of the general characteristics of certain wings with progressively varying sections; 2) the determination of data furnishing, in certain cases, some information on the actual distribution of the external forces acting on a wing. We shall try to show certain advantages belonging to the few wing types of variable section which we shall study and that, even if the general aerodynamic coefficients of these wings are not often clearly superior to those of certain wings of uniform section, the wings of variable section nevertheless have certain advantages over those of uniform section in the distribution of the attainable stresses.

Skyrmions Driven by Intrinsic Magnons

NASA Astrophysics Data System (ADS)

Psaroudaki, Christina; Loss, Daniel

2018-06-01

We study the dynamics of a Skyrmion in a magnetic insulating nanowire in the presence of time-dependent oscillating magnetic field gradients. These ac fields act as a net driving force on the Skyrmion via its own intrinsic magnetic excitations. In a microscopic quantum field theory approach, we include the unavoidable coupling of the external field to the magnons, which gives rise to time-dependent dissipation for the Skyrmion. We demonstrate that the magnetic ac field induces a super-Ohmic to Ohmic crossover behavior for the Skyrmion dissipation kernels with time-dependent Ohmic terms. The ac driving of the magnon bath at resonance results in a unidirectional helical propagation of the Skyrmion in addition to the otherwise periodic bounded motion.

Design and Analysis of an Electromagnetic Thrust Bearing

NASA Technical Reports Server (NTRS)

Banerjee, Bibhuti; Rao, Dantam K.

1996-01-01

A double-acting electromagnetic thrust bearing is normally used to counter the axial loads in many rotating machines that employ magnetic bearings. It essentially consists of an actuator and drive electronics. Existing thrust bearing design programs are based on several assumptions. These assumptions, however, are often violated in practice. For example, no distinction is made between maximum external loads and maximum bearing forces, which are assumed to be identical. Furthermore, it is assumed that the maximum flux density in the air gap occurs at the nominal gap position of the thrust runner. The purpose of this paper is to present a clear theoretical basis for the design of the electromagnetic thrust bearing which obviates such assumptions.

Poverty, global health, and infectious disease: lessons from Haiti and Rwanda.

PubMed

Alsan, Marcella M; Westerhaus, Michael; Herce, Michael; Nakashima, Koji; Farmer, Paul E

2011-09-01

Poverty and infectious diseases interact in complex ways. Casting destitution as intractable, or epidemics that afflict the poor as accidental, erroneously exonerates us from responsibility for caring for those most in need. Adequately addressing communicable diseases requires a biosocial appreciation of the structural forces that shape disease patterns. Most health interventions in resource-poor settings could garner support based on cost/benefit ratios with appropriately lengthy time horizons to capture the return on health investments and an adequate accounting of externalities; however, such a calculus masks the suffering of inaction and risks eroding the most powerful incentive to act: redressing inequality. Copyright © 2011 Elsevier Inc. All rights reserved.

Acceleration and holographic studies on different types of dynamization of external fixators of the bones

NASA Astrophysics Data System (ADS)

Podbielska, Halina; Kasprzak, Henryk T.; Voloshin, Arkady S.; Pennig, Dietmar; von Bally, Gert

1992-08-01

The unilateral axially dynamic fixator (Orthofix) was mounted on a sheep tibial shaft. Three fixation modes: static, dynamic controlled, and dynamic free were examined by means of double exposure holographic interferometry. Simultaneously, the acceleration was measured by an accelerometer and displayed on the monitor together with loading characteristics. The first exposure was made before the acting force was applied to the tibia plateau. The second one after the moment when the acceleration wave started to propagate through the specimen. We stated that in the case of dynamization less torsion occurs at the fracture site. So far, we have not been able to determine any correlation between results of holographic and accelerometric measurements.

Computing Gravitational Fields of Finite-Sized Bodies

NASA Technical Reports Server (NTRS)

Quadrelli, Marco

2005-01-01

A computer program utilizes the classical theory of gravitation, implemented by means of the finite-element method, to calculate the near gravitational fields of bodies of arbitrary size, shape, and mass distribution. The program was developed for application to a spacecraft and to floating proof masses and associated equipment carried by the spacecraft for detecting gravitational waves. The program can calculate steady or time-dependent gravitational forces, moments, and gradients thereof. Bodies external to a proof mass can be moving around the proof mass and/or deformed under thermoelastic loads. An arbitrarily shaped proof mass is represented by a collection of parallelepiped elements. The gravitational force and moment acting on each parallelepiped element of a proof mass, including those attributable to the self-gravitational field of the proof mass, are computed exactly from the closed-form equation for the gravitational potential of a parallelepiped. The gravitational field of an arbitrary distribution of mass external to a proof mass can be calculated either by summing the fields of suitably many point masses or by higher-order Gauss-Legendre integration over all elements surrounding the proof mass that are part of a finite-element mesh. This computer program is compatible with more general finite-element codes, such as NASTRAN, because it is configured to read a generic input data file, containing the detailed description of the finiteelement mesh.

Measurement of external forces and torques on a large pointing system

NASA Technical Reports Server (NTRS)

Morenus, R. C.

1980-01-01

Methods of measuring external forces and torques are discussed, in general and as applied to the Large Pointing System wind tunnel tests. The LPS tests were in two phases. The first test was a preliminary test of three models representing coelostat, heliostat, and on-gimbal telescope configurations. The second test explored the coelostat configuration in more detail. The second test used a different setup for measuring external loads. Some results are given from both tests.

Bubble Dynamics, Two-Phase Flow, and Boiling Heat Transfer in Microgravity

NASA Technical Reports Server (NTRS)

Chung, Jacob N.

1996-01-01

The objective of the research is to study the feasibility of employing an external force to replace the buoyancy force in order to maintain nucleate boiling in microgravity. We have found that a bulk velocity field, an electric field and an acoustic field could each play the role of the gravity field in microgravity. Nucleate boiling could be maintained by any one of the three external force fields in space.

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion

PubMed Central

Daszkiewicz, Karol; Witkowski, Wojciech; Chróścielewski, Jacek; Ferenc, Tomasz; Baczkowski, Boguslaw

2018-01-01

Objective The purpose of this study was to evaluate the influence of a change in the meniscus cross sectional shape on its position and on the biomechanics of a knee joint. Methods One main finite element model of a left knee joint was created on the basis of MRI images. The model consisted of bones, articular cartilages, menisci and ligaments. Eight variants of this model with an increased or decreased meniscus height were then prepared. Nonlinear static analyses with a fixed flexion/extension movement for a compressive load of 1000 N were performed. The additional analyses for those models with a constrained medio-lateral relative bone translation allowed for an evaluation of the influence of this translation on a meniscus external shift. Results It was observed that a decrease in the meniscus height caused a decrease in the contact area, together with a decrease in the contact force between the flattened meniscus and the cartilage. For the models with an increased meniscus height, a maximal value of force acting on the meniscus in a medio-lateral direction was obtained. The results have shown that the meniscus external shift was approximately proportional to the meniscus slope angle, but that relationship was modified by a medio-lateral relative bone translation. It was found that the translation of the femur relative to the tibia may be dependent on the geometry of the menisci. Conclusions The results have suggested that a change in the meniscus geometry in the cross sectional plane can considerably affect not only the meniscal external shift, but also the medio-lateral translation of the knee joint as well as the congruency of the knee joint. PMID:29447236

The influence of a change in the meniscus cross-sectional shape on the medio-lateral translation of the knee joint and meniscal extrusion.

PubMed

Luczkiewicz, Piotr; Daszkiewicz, Karol; Witkowski, Wojciech; Chróścielewski, Jacek; Ferenc, Tomasz; Baczkowski, Boguslaw

2018-01-01

The purpose of this study was to evaluate the influence of a change in the meniscus cross sectional shape on its position and on the biomechanics of a knee joint. One main finite element model of a left knee joint was created on the basis of MRI images. The model consisted of bones, articular cartilages, menisci and ligaments. Eight variants of this model with an increased or decreased meniscus height were then prepared. Nonlinear static analyses with a fixed flexion/extension movement for a compressive load of 1000 N were performed. The additional analyses for those models with a constrained medio-lateral relative bone translation allowed for an evaluation of the influence of this translation on a meniscus external shift. It was observed that a decrease in the meniscus height caused a decrease in the contact area, together with a decrease in the contact force between the flattened meniscus and the cartilage. For the models with an increased meniscus height, a maximal value of force acting on the meniscus in a medio-lateral direction was obtained. The results have shown that the meniscus external shift was approximately proportional to the meniscus slope angle, but that relationship was modified by a medio-lateral relative bone translation. It was found that the translation of the femur relative to the tibia may be dependent on the geometry of the menisci. The results have suggested that a change in the meniscus geometry in the cross sectional plane can considerably affect not only the meniscal external shift, but also the medio-lateral translation of the knee joint as well as the congruency of the knee joint.

The effect of external ankle support on knee and ankle joint movement and loading in netball players.

PubMed

Vanwanseele, Benedicte; Stuelcken, Max; Greene, Andrew; Smith, Richard

2014-09-01

External ankle support has been successfully used to prevent ankle sprains. However, some recent studies have indicated that reducing ankle range of motion can place larger loads on the knee. The aim of this study was to investigate the effect of external ankle support (braces and high-top shoes) on the ankle and knee joint loading during a netball specific landing task. A repeated measure design. High performance netball players with no previously diagnosed severe ankle or knee injury (n=11) were recruited from NSW Institute of Sport netball programme. The kinematic and kinetic data were collected simultaneously using a 3-D Motion Analysis System and one Kistler force plate to measure ground reaction forces. Players performed a single leg landing whilst receiving a pass while wearing a standard netball shoe, the same shoe with a lace-up brace and a high-top shoe. Only the brace condition significantly reduced the ankle range of motion in the frontal plane (in/eversion) by 3.95 ± 3.74 degrees compared to the standard condition. No changes were found for the knee joint loading in the brace condition. The high-top shoes acted to increase the peak knee internal rotation moment by 15%. Both the brace and high-top conditions brought about increases in the peak ankle plantar flexion moment during the landing phase. Lace-up braces can be used by netball players to restrict ankle range of motion during a single leg landing while receiving a pass without increasing the load on the knee joint. Copyright © 2013 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

On radiation forces acting on a transparent nanoparticle in the field of a focused laser beam

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

Afanas'ev, A A; Rubinov, A N; Gaida, L S

2015-10-31

Radiation forces acting on a transparent spherical nanoparticle in the field of a focused Gaussian laser beam are studied theoretically in the Rayleigh scattering regime. Expressions are derived for the scattering force and Cartesian components of the gradient force. The resultant force acting on a nanoparticle located in the centre of a laser beam is found. The parameters of the focused beam and optical properties of the nanoparticle for which the longitudinal component of the gradient force exceeds the scattering force are determined. Characteristics of the transverse gradient force are discussed. (nanophotonics)

Model of the discrete destruction process of a solid body

NASA Astrophysics Data System (ADS)

Glagolev, V. V.; Markin, A. A.

2018-03-01

Destruction is considered as a discrete thermomechanical process, in which the deformation of a solid body is achieved by changing the boundary stresses acting on the part of the volume being destroyed with the external load unchanged. On the basis of the proposed concept, a model for adhesive stratification of a composite material is constructed. When adhesive stratification is used, the stress state of one or two boundaries of the adhesive layer changes to zero if the bonds with the joined body are broken. As a result of the stratification, the interaction between the part of the composite, which may include an adhesive layer and the rest of the body stops. When solving the elastoplastic problem of cohesive stratification, the region in which the destruction criterion is achieved is identified. With the help of a repeated solution of the problem of subcritical deformation with the known law of motion of the boundary of the region, the distribution of the load (nodal forces) acting from the region to the body is located. The next step considers the change in the stress–strain state of the body in the process of destruction of the selected area. The elastoplastic problem is solved with a simple unloading of the formed surface of the body and preservation of the external load corresponding to the beginning of the process of destruction.

Localization of adhesins on the surface of a pathogenic bacterial envelope through atomic force microscopy

NASA Astrophysics Data System (ADS)

Arnal, L.; Longo, G.; Stupar, P.; Castez, M. F.; Cattelan, N.; Salvarezza, R. C.; Yantorno, O. M.; Kasas, S.; Vela, M. E.

2015-10-01

Bacterial adhesion is the first and a significant step in establishing infection. This adhesion normally occurs in the presence of flow of fluids. Therefore, bacterial adhesins must be able to provide high strength interactions with their target surface in order to maintain the adhered bacteria under hydromechanical stressing conditions. In the case of B. pertussis, a Gram-negative bacterium responsible for pertussis, a highly contagious human respiratory tract infection, an important protein participating in the adhesion process is a 220 kDa adhesin named filamentous haemagglutinin (FHA), an outer membrane and also secreted protein that contains recognition domains to adhere to ciliated respiratory epithelial cells and macrophages. In this work, we obtained information on the cell-surface localization and distribution of the B. pertussis adhesin FHA using an antibody-functionalized AFM tip. Through the analysis of specific molecular recognition events we built a map of the spatial distribution of the adhesin which revealed a non-homogeneous pattern. Moreover, our experiments showed a force induced reorganization of the adhesin on the surface of the cells, which could explain a reinforced adhesive response under external forces. This single-molecule information contributes to the understanding of basic molecular mechanisms used by bacterial pathogens to cause infectious disease and to gain insights into the structural features by which adhesins can act as force sensors under mechanical shear conditions.Bacterial adhesion is the first and a significant step in establishing infection. This adhesion normally occurs in the presence of flow of fluids. Therefore, bacterial adhesins must be able to provide high strength interactions with their target surface in order to maintain the adhered bacteria under hydromechanical stressing conditions. In the case of B. pertussis, a Gram-negative bacterium responsible for pertussis, a highly contagious human respiratory tract infection, an important protein participating in the adhesion process is a 220 kDa adhesin named filamentous haemagglutinin (FHA), an outer membrane and also secreted protein that contains recognition domains to adhere to ciliated respiratory epithelial cells and macrophages. In this work, we obtained information on the cell-surface localization and distribution of the B. pertussis adhesin FHA using an antibody-functionalized AFM tip. Through the analysis of specific molecular recognition events we built a map of the spatial distribution of the adhesin which revealed a non-homogeneous pattern. Moreover, our experiments showed a force induced reorganization of the adhesin on the surface of the cells, which could explain a reinforced adhesive response under external forces. This single-molecule information contributes to the understanding of basic molecular mechanisms used by bacterial pathogens to cause infectious disease and to gain insights into the structural features by which adhesins can act as force sensors under mechanical shear conditions. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04644k

Implementing the Small Business Innovation Development Act--The First 2 Years.

DTIC Science & Technology

1985-10-25

GENERAL Report To The Congress OF THE UNITED STATES , Implementing The Small Business Innovation Development Act--The First 2 Years (AD I The 1982 act...seeks to encourage innovation and small business participation in federal Sresearch. Among other requirements, agen- cies spending more than $100...million annu- !* ally for external research must award por- tions of their external research dollars to small businesses . This first of several

The paradox of moral focus.

PubMed

Young, Liane; Phillips, Jonathan

2011-05-01

When we evaluate moral agents, we consider many factors, including whether the agent acted freely, or under duress or coercion. In turn, moral evaluations have been shown to influence our (non-moral) evaluations of these same factors. For example, when we judge an agent to have acted immorally, we are subsequently more likely to judge the agent to have acted freely, not under force. Here, we investigate the cognitive signatures of this effect in interpersonal situations, in which one agent ("forcer") forces another agent ("forcee") to act either immorally or morally. The structure of this relationship allowed us to ask questions about both the "forcer" and the "forcee." Paradoxically, participants judged that the "forcer" forced the "forcee" to act immorally (i.e. X forced Y), but that the "forcee" was not forced to act immorally (i.e. Y was not forced by X). This pattern obtained only for human agents who acted intentionally. Directly changing participants' focus from one agent to another (forcer versus forcee) also changed the target of moral evaluation and therefore force attributions. The full pattern of judgments may provide a window into motivated moral reasoning and focusing bias more generally; participants may have been motivated to attribute greater force to the immoral forcer and greater freedom to the immoral forcee. Copyright © 2011 Elsevier B.V. All rights reserved.

Coupled loads analysis for Space Shuttle payloads

NASA Technical Reports Server (NTRS)

Eldridge, J.

1992-01-01

Described here is a method for determining the transient response of, and the resultant loads in, a system exposed to predicted external forces. In this case, the system consists of four racks mounted on the inside of a space station resource node module (SSRNMO) which is mounted in the payload bay of the space shuttle. The predicted external forces are forcing functions which envelope worst case forces applied to the shuttle during liftoff and landing. This analysis, called a coupled loads analysis, is used to couple the payload and shuttle models together, determine the transient response of the system, and then recover payload loads, payload accelerations, and payload to shuttle interface forces.

Stride length: the impact on propulsion and bracing ground reaction force in overhand throwing.

PubMed

Ramsey, Dan K; Crotin, Ryan L

2018-03-26

Propulsion and bracing ground reaction force (GRF) in overhand throwing are integral in propagating joint reaction kinetics and ball velocity, yet how stride length effects drive (hind) and stride (lead) leg GRF profiles remain unknown. Using a randomised crossover design, 19 pitchers (15 collegiate and 4 high school) were assigned to throw 2 simulated 80-pitch games at ±25% of their desired stride length. An integrated motion capture system with two force plates and radar gun tracked each throw. Vertical and anterior-posterior GRF was normalised then impulse was derived. Paired t-tests identified whether differences between conditions were significant. Late in single leg support, peak propulsion GRF was statistically greater for the drive leg with increased stride. Stride leg peak vertical GRF in braking occurred before acceleration with longer strides, but near ball release with shorter strides. Greater posterior shear GRF involving both legs demonstrated increased braking with longer strides. Conversely, decreased drive leg propulsion reduced both legs' braking effects with shorter strides. Results suggest an interconnection between normalised stride length and GRF application in propulsion and bracing. This work has shown stride length to be an important kinematic factor affecting the magnitude and timing of external forces acting upon the body.

Effect of stern hull shape on turning circle of ships

NASA Astrophysics Data System (ADS)

Jaswar, Maimun, A.; Wahid, M. A.; Priyanto, A.; Zamani, Pauzi, Saman

2012-06-01

Many factors such as: stern hull shape, length, draught, trim, propulsion system and external forces affecting the drift angle influence rate of turn and size of turning circle of ships. This paper discusses turning circle characteristics of U and V stern hull shape of Very Large Crude Oil Carrier (VLCC) ships. The ships have same principal dimension such as length, beam, and draught. The turning circle characteristics of the VLCC ships are simulated at 35 degree of rudder angle. In the analysis, firstly, turning circle performance of U-type VLCC ship is simulated. In the simulation, initial ship speed is determined using given power and rpm. Hydrodynamic derivatives coefficients are determined by including effect of fullness of aft run. Using the obtained, speed and hydrodynamic coefficients, force and moment acting on hull, force and moment induced by propeller, force and moment induced by rudder are determined. Finally, ship trajectory, ratio of speed, yaw angle and drift angle are determined. Results of simulation results of the VLCC ship are compared with the experimental one as validation. Using the same method, V-type VLCC is simulated and the simulation results are compared with U-type VLCC ship. Results shows the turning circle of U-type is larger than V-type due to effect stern hul results of simulation are.

Malaria vaccine development and how external forces shape it: an overview.

PubMed

Lorenz, Veronique; Karanis, Gabriele; Karanis, Panagiotis

2014-06-30

The aim of this paper is to analyse the current status and scientific value of malaria vaccine approaches and to provide a realistic prognosis for future developments. We systematically review previous approaches to malaria vaccination, address how vaccine efforts have developed, how this issue may be fixed, and how external forces shape vaccine development. Our analysis provides significant information on the various aspects and on the external factors that shape malaria vaccine development and reveal the importance of vaccine development in our society.

Characterization of magnetic force microscopy probe tip remagnetization for measurements in external in-plane magnetic fields

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

Weis, Tanja; Engel, Dieter; Ehresmann, Arno

2008-12-15

A quantitative analysis of magnetic force microscopy (MFM) images taken in external in-plane magnetic fields is difficult because of the influence of the magnetic field on the magnetization state of the magnetic probe tip. We prepared calibration samples by ion bombardment induced magnetic patterning with a topographically flat magnetic pattern magnetically stable in a certain external magnetic field range for a quantitative characterization of the MFM probe tip magnetization in point-dipole approximation.

Structural phase transitions in isotropic magnetic elastomers

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

Meilikhov, E. Z., E-mail: meilikhov@yandex.ru; Farzetdinova, R. M.

Magnetic elastomers represent a new type of materials that are “soft” matrices with “hard” magnetic granules embedded in them. The elastic forces of the matrix and the magnetic forces acting between granules are comparable in magnitude even under small deformations. As a result, these materials acquire a number of new properties; in particular, their mechanical and/or magnetic characteristics can depend strongly on the polymer matrix filling with magnetic particles and can change under the action of an external magnetic field, pressure, and temperature. To describe the properties of elastomers, we use a model in which the interaction of magnetic granulesmore » randomly arranged in space with one another is described in the dipole approximation by the distribution function of dipole fields, while their interaction with the matrix is described phenomenologically. A multitude of deformation, magnetic-field, and temperature effects that are described in this paper and are quite accessible to experimental observation arise within this model.« less

Analysis of operational limit of an aircraft: An aeroelastic approach

NASA Astrophysics Data System (ADS)

Hasan, Md. Mehedi; Hassan, M. D. Mehedi; Sarrowar, S. M. Bayazid; Faisal, Kh. Md.; Ahmed, Sheikh Reaz, Dr.

2017-06-01

In classical theory of elasticity, external loading acting on the body is independent of deformation of the body. But, in aeroelasticity, aerodynamic forces depend on the attitude of the body relative to the flow. Aircraft's are subjected to a range of static loads resulting from equilibrium or steady flight maneuvers such as coordinated level turn, steady pitch and bank rate, steady and level flight. Interaction of these loads with elastic forces of aircraft structure creates some aeroelastic phenomena. In this paper, we have summarized recent developments in the area of aeroelasticity. A numerical approach has been applied for finding divergence speed, a static aeroelastic phenomena, of a typical aircraft. This paper also involves graphical representations of constraints on load factor and bank angle during different steady flight maneuvers taking flexibility into account and comparing it with the value without flexibility. Effect of wing skin thickness, spar web thickness and position of flexural axis of wing on this divergence speed as well as load factor and bank angle has also been observed using MATLAB.

Solitary waves in the nonlinear Dirac equation in the presence of external driving forces

DOE PAGES

Mertens, Franz G.; Cooper, Fred; Quintero, Niurka R.; ...

2016-01-05

In this paper, we consider the nonlinear Dirac (NLD) equation in (1 + 1) dimensions with scalar–scalar self interaction g 2/κ + 1 (Ψ¯Ψ) κ + 1 in the presence of external forces as well as damping of the form f(x) - iμγ 0Ψ, where both f and Ψ are two-component spinors. We develop an approximate variational approach using collective coordinates (CC) for studying the time dependent response of the solitary waves to these external forces. This approach predicts intrinsic oscillations of the solitary waves, i.e. the amplitude, width and phase all oscillate with the same frequency. The translational motionmore » is also affected, because the soliton position oscillates around a mean trajectory. For κ = 1 we solve explicitly the CC equations of the variational approximation for slow moving solitary waves in a constant external force without damping and find reasonable agreement with solving numerically the CC equations. Finally, we then compare the results of the variational approximation with no damping with numerical simulations of the NLD equation for κ = 1, when the components of the external force are of the form f j = r j exp(–iΚx) and again find agreement if we take into account a certain linear excitation with specific wavenumber that is excited together with the intrinsic oscillations such that the momentum in a transformed NLD equation is conserved.« less

Upriver transport of dissolved substances in an estuary and sub-estuary system of the lower James River, Chesapeake Bay

NASA Astrophysics Data System (ADS)

Hong, Bo; Shen, Jian; Xu, Hongzhou

2018-01-01

The water exchange between the James River and the Elizabeth River, an estuary and sub-estuary system in the lower Chesapeake Bay, was investigated using a 3D numerical model. The conservative passive tracers were used to represent the dissolved substances (DS) discharged from the Elizabeth River. The approach enabled us to diagnose the underlying physical processes that control the expansion of the DS, which is representative of potential transport of harmful algae blooms, pollutants from the Elizabeth River to the James River without explicitly simulating biological processes. Model simulations with realistic forcings in 2005, together with a series of processoriented numerical experiments, were conducted to explore the correlations of the transport process and external forcing. Model results show that the upriver transport depends highly on the freshwater discharge on a seasonal scale and maximum upriver transport occurs in summer with a mean transport time ranging from 15-30 days. The southerly/easterly wind, low river discharge, and neap tidal condition all act to strengthen the upriver transport. On the other hand, the northerly/westerly wind, river pulse, water level pulse, and spring tidal condition act to inhibit the upriver transport. Tidal flushing plays an important role in transporting the DS during spring tide, which shortens the travel time in the lower James River. The multivariable regression analysis of volume mean subtidal DS concentration in the mesohaline portion of the James River indicates that DS concentration in the upriver area can be explained and well predicted by the physical forcings (r = 0.858, p = 0.00001).

Dynamic Stability and Gravitational Balancing of Multiple Extended Bodies

NASA Technical Reports Server (NTRS)

Quadrelli, Marco

2008-01-01

Feasibility of a non-invasive compensation scheme was analyzed for precise positioning of a massive extended body in free fall using gravitational forces influenced by surrounding source masses in close proximity. The N-body problem of classical mechanics is a paradigm used to gain insight into the physics of the equivalent N-body problem subject to control forces. The analysis addressed how a number of control masses move around the proof mass so that the proof mass position can be accurately and remotely compensated when exogenous disturbances are acting on it, while its sensitivity to gravitational waves remains unaffected. Past methods to correct the dynamics of the proof mass have considered active electrostatic or capacitive methods, but the possibility of stray capacitances on the surfaces of the proof mass have prompted the investigation of other alternatives, such as the method presented in this paper. While more rigorous analyses of the problem should be carried out, the data show that, by means of a combined feedback and feed-forward control approach, the control masses succeeded in driving the proof mass along the specified trajectory, which implies that the proof mass can, in principle, be balanced via gravitational forces only while external perturbations are acting on it. This concept involves the dynamic stability of a group of massive objects interacting gravitationally under active control, and can apply to drag-free control of spacecraft during missions, to successor gravitational wave space borne sensors, or to any application requiring flying objects to be precisely controlled in position and attitude relative to another body via gravitational interactions only.

Trends and projections of Southern Hemisphere baroclinicity: the role of external forcing and impact on Australian rainfall

NASA Astrophysics Data System (ADS)

Frederiksen, Carsten S.; Frederiksen, Jorgen S.; Sisson, Janice M.; Osbrough, Stacey L.

2017-05-01

Changes in the characteristics of Southern Hemisphere (SH) storms, in all seasons, during the second half of the twentieth century, have been related to changes in the annual cycle of SH baroclinic instability. In particular, significant negative trends in baroclinic instability, as measured by the Phillips Criterion, have been found in the region of the climatological storm tracks; a zonal band of significant positive trends occur further poleward. Corresponding to this decrease/increase in baroclinic instability there is a decrease/increase in the growth rate of storm formation at these latitudes over this period, and in some cases a preference for storm formation further poleward than normal. Based on model output from a multi-model ensemble (MME) of coupled atmosphere-ocean general circulation models, it is shown that these trends are the result of external radiative forcing, including anthropogenic greenhouse gases, ozone, aerosols and land-use change. The MME is used in an analysis of variance method to separate the internal (natural) variability in the Phillips Criterion from influences associated with anomalous external radiative forcing. In all seasons, the leading externally forced mode has a significant trend and a loading pattern highly correlated with the pattern of trends in the Phillips Criterion. The covariance between the externally forced component of SH rainfall and the leading external mode strongly resembles the MME pattern of SH rainfall trends. A comparison between similar analyses of MME simulations using the second half of the twenty-first century of the Representative Concentration Pathways (RCP) RCP8.5 and RCP4.5 scenarios show that trends in the Phillips Criterion and rainfall are projected to continue and intensify under increasing anthropogenic greenhouse gas concentrations.

Capillary-Physics Mechanism of Elastic-Wave Mobilization of Residual Oil

NASA Astrophysics Data System (ADS)

Beresnev, I. A.; Pennington, W. D.; Turpening, R. M.

2003-12-01

Much attention has been given to the possibility of vibratory mobilization of residual oil as a method of enhanced recovery. The common features of the relevant applications have nonetheless been inconsistency in the results of field tests and the lack of understanding of a physical mechanism that would explain variable experiences. Such a mechanism can be found in the physics of capillary trapping of oil ganglia, driven through the pore channels by an external pressure gradient. Entrapping of ganglia occurs due to the capillary pressure building on the downstream meniscus entering a narrow pore throat. The resulting internal-pressure imbalance acts against the external gradient, which needs to exceed a certain threshold to carry the ganglion through. The ganglion flow thus exhibits the properties of the Bingham (yield-stress) flow, not the Darcy flow. The application of vibrations is equivalent to the addition of an oscillatory forcing to the constant gradient. When this extra forcing acts along the gradient, an instant "unplugging" occurs, while, when the vibration reverses direction, the flow is plugged. This asymmetry results in an average non-zero flow over one period of vibration, which explains the mobilization effect. The minimum-amplitude and maximum-frequency thresholds apply for the mobilization to occur. When the vibration amplitude exceeds a certain "saturation" level, the flow returns to the Darcy regime. The criterion of the mobilization of a particular ganglion involves the parameters of both the medium (pore geometry, interfacial and wetting properties, fluid viscosity) and the oscillatory field (amplitude and frequency). The medium parameters vary widely under natural conditions. It follows that an elastic wave with a given amplitude and frequency will always produce a certain mobilization effect, mobilizing some ganglia and leaving others intact. The exact macroscopic effect is hard to predict, as it will represent a response of the populations of ganglia with unknown parameter distributions. The variability of responses to vibratory stimulation should thus be expected.

32 CFR 842.110 - Claims not payable.

Code of Federal Regulations, 2011 CFR

2011-07-01

... National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE CLAIMS AND LITIGATION... International Agreements Claims Act. (4) The Air Force Admiralty Claims Act and the Admiralty Extensions Act. (5...) Claims from the combat activities of the armed forces during war or armed conflict. (c) Claims for...

Internalizing and externalizing problems in adolescence: general and dimension-specific effects of familial loadings and preadolescent temperament traits.

PubMed

Ormel, J; Oldehinkel, A J; Ferdinand, R F; Hartman, C A; De Winter, A F; Veenstra, R; Vollebergh, W; Minderaa, R B; Buitelaar, J K; Verhulst, F C

2005-12-01

We investigated the links between familial loading, preadolescent temperament, and internalizing and externalizing problems in adolescence, hereby distinguishing effects on maladjustment in general versus dimension-specific effects on either internalizing or externalizing problems. In a population-based sample of 2230 preadolescents (10-11 years) familial loading (parental lifetime psychopathology) and offspring temperament were assessed at baseline by parent report, and offspring psychopathology at 2.5-years follow-up by self-report, teacher report and parent report. We used purified measures of temperament and psychopathology and partialled out shared variance between internalizing and externalizing problems. Familial loading of internalizing psychopathology predicted offspring internalizing but not externalizing problems, whereas familial loading of externalizing psychopathology predicted offspring externalizing but not internalizing problems. Both familial loadings were associated with Frustration, low Effortful Control, and Fear. Frustration acted as a general risk factor predicting severity of maladjustment; low Effortful Control and Fear acted as dimension-specific risk factors that predicted a particular type of psychopathology; whereas Shyness, High-Intensity Pleasure, and Affiliation acted as direction markers that steered the conditional probability of internalizing versus externalizing problems, in the event of maladjustment. Temperament traits mediated one-third of the association between familial loading and psychopathology. Findings were robust across different composite measures of psychopathology, and applied to girls as well as boys. With regard to familial loading and temperament, it is important to distinguish general risk factors (Frustration) from dimension-specific risk factors (familial loadings, Effortful Control, Fear), and direction markers that act as pathoplastic factors (Shyness, High-Intensity Pleasure, Affiliation) from both types of risk factors. About one-third of familial loading effects on psychopathology in early adolescence are mediated by temperament.

Asymmetric adaptation in human walking using the Tethered Pelvic Assist Device (TPAD).

PubMed

Vashista, Vineet; Reisman, Darcy S; Agrawal, Sunil K

2013-06-01

Human nervous system is capable of modifying motor commands in response to alterations in walking conditions. Previous research has shown that external perturbations that induce gait asymmetry can lead to adaptation in gait parameters. Such strategies have also been shown to temporarily restore gait symmetry in subjects with post stroke hemiparesis. This work aims to develop an experimental paradigm to induce gait asymmetry in human subjects by applying external asymmetric forces on the pelvis through the Tethered Pelvic Assist Device (TPAD). These external forces on the pelvis have the potential to influence the swing and the stance phases of both legs. Eight healthy subjects participated in the experiment where a higher resistive force was applied on the pelvis during the swing phase of the left leg as compared to the right leg. We hypothesized that such asymmetrically applied forces on the pelvis will lead to asymmetric adaptation in the human walking.

Surface effects on friction-induced fluid heating in nanochannel flows.

PubMed

Li, Zhigang

2009-02-01

We investigate the mechanism of friction-induced fluid heating under the influence of surfaces. The temperature distributions of liquid argon and helium in nanoscale Poiseuille flows are studied through molecular dynamics simulations. It is found that the fluid heating is mainly caused by the viscous friction in the fluid when the external force is small and there is no slip at the fluid-solid interface. When the external force is larger than the fluid-surface binding force, the friction at the fluid-solid interface dominates over the internal friction of the fluid and is the major contribution to fluid heating. An asymmetric temperature gradient in the fluid is developed in the case of nonidentical walls and the general temperature gradient may change sign as the dominant heating factor changes from internal to interfacial friction with increasing external force. The effect of temperature on the fluid heating is also discussed.

Force-extension behavior of DNA in the presence of DNA-bending nucleoid associated proteins

NASA Astrophysics Data System (ADS)

Dahlke, K.; Sing, C. E.

2018-02-01

Interactions between nucleoid associated proteins (NAPs) and DNA affect DNA polymer conformation, leading to phenomena such as concentration dependent force-extension behavior. These effects, in turn, also impact the local binding behavior of the protein, such as high forces causing proteins to unbind, or proteins binding favorably to locally bent DNA. We develop a coarse-grained NAP-DNA simulation model that incorporates both force- and concentration-dependent behaviors, in order to study the interplay between NAP binding and DNA conformation. This model system includes multi-state protein binding and unbinding, motivated by prior work, but is now dependent on the local structure of the DNA, which is related to external forces acting on the DNA strand. We observe the expected qualitative binding behavior, where more proteins are bound at lower forces than at higher forces. Our model also includes NAP-induced DNA bending, which affects DNA elasticity. We see semi-quantitative matching of our simulated force-extension behavior to the reported experimental data. By using a coarse-grained simulation, we are also able to look at non-equilibrium behaviors, such as dynamic extension of a DNA strand. We stretch a DNA strand at different rates and at different NAP concentrations to observe how the time scales of the system (such as pulling time and unbinding time) work in concert. When these time scales are similar, we observe measurable rate-dependent changes in the system, which include the number of proteins bound and the force required to extend the DNA molecule. This suggests that the relative time scales of different dynamic processes play an important role in the behavior of NAP-DNA systems.

Selective effects of weight and inertia on maximum lifting.

PubMed

Leontijevic, B; Pazin, N; Kukolj, M; Ugarkovic, D; Jaric, S

2013-03-01

A novel loading method (loading ranged from 20% to 80% of 1RM) was applied to explore the selective effects of externally added simulated weight (exerted by stretched rubber bands pulling downward), weight+inertia (external weights added), and inertia (covariation of the weights and the rubber bands pulling upward) on maximum bench press throws. 14 skilled participants revealed a load associated decrease in peak velocity that was the least associated with an increase in weight (42%) and the most associated with weight+inertia (66%). However, the peak lifting force increased markedly with an increase in both weight (151%) and weight+inertia (160%), but not with inertia (13%). As a consequence, the peak power output increased most with weight (59%), weight+inertia revealed a maximum at intermediate loads (23%), while inertia was associated with a gradual decrease in the peak power output (42%). The obtained findings could be of importance for our understanding of mechanical properties of human muscular system when acting against different types of external resistance. Regarding the possible application in standard athletic training and rehabilitation procedures, the results speak in favor of applying extended elastic bands which provide higher movement velocity and muscle power output than the usually applied weights. © Georg Thieme Verlag KG Stuttgart · New York.

Development of a multi-degree-of-freedom micropositioning, vibration isolation and vibration suppression system

NASA Astrophysics Data System (ADS)

Jaensch, M.; Lampérth, M. U.

2007-04-01

This paper describes the design and performance testing of a micropositioning, vibration isolation and suppression system, which can be used to position a piece of equipment with sub-micrometre accuracy and stabilize it against various types of external disturbance. The presented demonstrator was designed as part of a novel extremely open pre-polarization magnetic resonance imaging (MRI) scanner. The active control system utilizes six piezoelectric actuators, wide-bandwidth optical fibre displacement sensors and a very fast digital field programmable gate array (FPGA) controller. A PID feedback control algorithm with emphasis on a very high level of integral gain is employed. Due to the high external forces expected, the whole structure is designed to be as stiff as possible, including a novel hard mount approach with parallel passive damping for the suspension of the payload. The performance of the system is studied theoretically and experimentally. The sensitive equipment can be positioned in six degrees of freedom with an accuracy of ± 0.2 µm. External disturbances acting on the support structure or the equipment itself are attenuated in three degrees of freedom by more than -20 dB within a bandwidth of 0-200 Hz. Excellent impulse rejection and input tracking are demonstrated as well.

Flutter Analysis for Turbomachinery Using Volterra Series

NASA Technical Reports Server (NTRS)

Liou, Meng-Sing; Yao, Weigang

2014-01-01

The objective of this paper is to describe an accurate and efficient reduced order modeling method for aeroelastic (AE) analysis and for determining the flutter boundary. Without losing accuracy, we develop a reduced order model based on the Volterra series to achieve significant savings in computational cost. The aerodynamic force is provided by a high-fidelity solution from the Reynolds-averaged Navier-Stokes (RANS) equations; the structural mode shapes are determined from the finite element analysis. The fluid-structure coupling is then modeled by the state-space formulation with the structural displacement as input and the aerodynamic force as output, which in turn acts as an external force to the aeroelastic displacement equation for providing the structural deformation. NASA's rotor 67 blade is used to study its aeroelastic characteristics under the designated operating condition. First, the CFD results are validated against measured data available for the steady state condition. Then, the accuracy of the developed reduced order model is compared with the full-order solutions. Finally the aeroelastic solutions of the blade are computed and a flutter boundary is identified, suggesting that the rotor, with the material property chosen for the study, is structurally stable at the operating condition, free of encountering flutter.

A metabolic basis for impaired muscle force production and neuromuscular compensation during sprint cycling.

PubMed

Bundle, Matthew W; Ernst, Carrie L; Bellizzi, Matthew J; Wright, Seth; Weyand, Peter G

2006-11-01

For both different individuals and modes of locomotion, the external forces determining all-out sprinting performances fall predictably with effort duration from the burst maximums attained for 3 s to those that can be supported aerobically as trial durations extend to roughly 300 s. The common time course of this relationship suggests a metabolic basis for the decrements in the force applied to the environment. However, the mechanical and neuromuscular responses to impaired force production (i.e., muscle fatigue) are generally considered in relation to fractions of the maximum force available, or the maximum voluntary contraction (MVC). We hypothesized that these duration-dependent decrements in external force application result from a reliance on anaerobic metabolism for force production rather than the absolute force produced. We tested this idea by examining neuromuscular activity during two modes of sprint cycling with similar external force requirements but differing aerobic and anaerobic contributions to force production: one- and two-legged cycling. In agreement with previous studies, we found greater peak per leg aerobic metabolic rates [59% (+/-6 SD)] and pedal forces at VO2 peak [30% (+/-9)] during one- vs. two-legged cycling. We also determined downstroke pedal forces and neuromuscular activity by surface electromyography during 15 to 19 all-out constant load sprints lasting from 12 to 400 s for both modes of cycling. In support of our hypothesis, we found that the greater reliance on anaerobic metabolism for force production induced compensatory muscle recruitment at lower pedal forces during two- vs. one-legged sprint cycling. We conclude that impaired muscle force production and compensatory neuromuscular activity during sprinting are triggered by a reliance on anaerobic metabolism for force production.

A nonlinear Fokker-Planck equation approach for interacting systems: Anomalous diffusion and Tsallis statistics

NASA Astrophysics Data System (ADS)

Marin, D.; Ribeiro, M. A.; Ribeiro, H. V.; Lenzi, E. K.

2018-07-01

We investigate the solutions for a set of coupled nonlinear Fokker-Planck equations coupled by the diffusion coefficient in presence of external forces. The coupling by the diffusion coefficient implies that the diffusion of each species is influenced by the other and vice versa due to this term, which represents an interaction among them. The solutions for the stationary case are given in terms of the Tsallis distributions, when arbitrary external forces are considered. We also use the Tsallis distributions to obtain a time dependent solution for a linear external force. The results obtained from this analysis show a rich class of behavior related to anomalous diffusion, which can be characterized by compact or long-tailed distributions.

Effect of deltoid tension and humeral version in reverse total shoulder arthroplasty: a biomechanical study.

PubMed

Henninger, Heath B; Barg, Alexej; Anderson, Andrew E; Bachus, Kent N; Tashjian, Robert Z; Burks, Robert T

2012-04-01

No clear recommendations exist regarding optimal humeral component version and deltoid tension in reverse total shoulder arthroplasty (TSA). A biomechanical shoulder simulator tested humeral versions (0°, 10°, 20° retroversion) and implant thicknesses (-3, 0, +3 mm from baseline) after reverse TSA in human cadavers. Abduction and external rotation ranges of motion as well as abduction and dislocation forces were quantified for native arms and arms implanted with 9 combinations of humeral version and implant thickness. Resting abduction angles increased significantly (up to 30°) after reverse TSA compared with native shoulders. With constant posterior cuff loads, native arms externally rotated 20°, whereas no external rotation occurred in implanted arms (20° net internal rotation). Humeral version did not affect rotational range of motion but did alter resting abduction. Abduction forces decreased 30% vs native shoulders but did not change when version or implant thickness was altered. Humeral center of rotation was shifted 17 mm medially and 12 mm inferiorly after implantation. The force required for lateral dislocation was 60% less than anterior and was not affected by implant thickness or version. Reverse TSA reduced abduction forces compared with native shoulders and resulted in limited external rotation and abduction ranges of motion. Because abduction force was reduced for all implants, the choice of humeral version and implant thickness should focus on range of motion. Lateral dislocation forces were less than anterior forces; thus, levering and inferior/posterior impingement may be a more probable basis for dislocation (laterally) than anteriorly directed forces. Copyright © 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

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

Krasnobaeva, L. A., E-mail: kla1983@mail.ru; Siberian State Medical University Moscowski Trakt 2, Tomsk, 634050; Shapovalov, A. V.

Within the formalism of the Fokker–Planck equation, the influence of nonstationary external force, random force, and dissipation effects on dynamics local conformational perturbations (kink) propagating along the DNA molecule is investigated. Such waves have an important role in the regulation of important biological processes in living systems at the molecular level. As a dynamic model of DNA was used a modified sine-Gordon equation, simulating the rotational oscillations of bases in one of the chains DNA. The equation of evolution of the kink momentum is obtained in the form of the stochastic differential equation in the Stratonovich sense within the frameworkmore » of the well-known McLaughlin and Scott energy approach. The corresponding Fokker–Planck equation for the momentum distribution function coincides with the equation describing the Ornstein–Uhlenbek process with a regular nonstationary external force. The influence of the nonlinear stochastic effects on the kink dynamics is considered with the help of the Fokker– Planck nonlinear equation with the shift coefficient dependent on the first moment of the kink momentum distribution function. Expressions are derived for average value and variance of the momentum. Examples are considered which demonstrate the influence of the external regular and random forces on the evolution of the average value and variance of the kink momentum. Within the formalism of the Fokker–Planck equation, the influence of nonstationary external force, random force, and dissipation effects on the kink dynamics is investigated in the sine–Gordon model. The equation of evolution of the kink momentum is obtained in the form of the stochastic differential equation in the Stratonovich sense within the framework of the well-known McLaughlin and Scott energy approach. The corresponding Fokker–Planck equation for the momentum distribution function coincides with the equation describing the Ornstein–Uhlenbek process with a regular nonstationary external force. The influence of the nonlinear stochastic effects on the kink dynamics is considered with the help of the Fokker–Planck nonlinear equation with the shift coefficient dependent on the first moment of the kink momentum distribution function. Expressions are derived for average value and variance of the momentum. Examples are considered which demonstrate the influence of the external regular and random forces on the evolution of the average value and variance of the kink momentum.« less

Modes of interannual variability in northern hemisphere winter atmospheric circulation in CMIP5 models: evaluation, projection and role of external forcing

NASA Astrophysics Data System (ADS)

Frederiksen, Carsten S.; Ying, Kairan; Grainger, Simon; Zheng, Xiaogu

2018-04-01

Models from the coupled model intercomparison project phase 5 (CMIP5) dataset are evaluated for their ability to simulate the dominant slow modes of interannual variability in the Northern Hemisphere atmospheric circulation 500 hPa geopotential height in the twentieth century. A multi-model ensemble of the best 13 models has then been used to identify the leading modes of interannual variability in components related to (1) intraseasonal processes; (2) slowly-varying internal dynamics; and (3) the slowly-varying response to external changes in radiative forcing. Modes in the intraseasonal component are related to intraseasonal variability in the North Atlantic, North Pacific and North American, and Eurasian regions and are little affected by the larger radiative forcing of the Representative Concentration Pathways 8.5 (RCP8.5) scenario. The leading modes in the slow-internal component are related to the El Niño-Southern Oscillation, Pacific North American or Tropical Northern Hemisphere teleconnection, the North Atlantic Oscillation, and the Western Pacific teleconnection pattern. While the structure of these slow-internal modes is little affected by the larger radiative forcing of the RCP8.5 scenario, their explained variance increases in the warmer climate. The leading mode in the slow-external component has a significant trend and is shown to be related predominantly to the climate change trend in the well mixed greenhouse gas concentration during the historical period. This mode is associated with increasing height in the 500 hPa pressure level. A secondary influence on this mode is the radiative forcing due to stratospheric aerosols associated with volcanic eruptions. The second slow-external mode is shown to be also related to radiative forcing due to stratospheric aerosols. Under RCP8.5 there is only one slow-external mode related to greenhouse gas forcing with a trend over four times the historical trend.

In situ forces and length patterns of the fibular collateral ligament under controlled loading: an in vitro biomechanical study using a robotic system.

PubMed

Liu, Ping; Wang, Jianquan; Xu, Yan; Ao, Yingfang

2015-04-01

The aim of this study was to determine the in situ forces and length patterns of the fibular collateral ligament (FCL) and kinematics of the knee under various loading conditions. Six fresh-frozen cadaveric knees were used (mean age 46 ± 14.4 years; range 20-58). In situ forces and length patterns of FCL and kinematics of the knee were determined under the following loading conditions using a robotic/universal force-moment sensor testing system: no rotation, varus (10 Nm), external rotation (5 Nm), and internal rotation (5 Nm) at 0°, 15°, 30°, 60º, 90°, and 120° of flexion, respectively. Under no rotation loading, the distances between the centres of the FCL attachments decreased as the knee flexed. Under varus loading, the force in FCL peaked at 15° of flexion and decreased with further knee flexion, while distances remained nearly constant and the varus rotation increased with knee flexion. Using external rotation, the force in the FCL also peaked at 15° flexion and decreased with further knee flexion, the distances decreased with flexion, and external rotation increased with knee flexion. Using internal rotation load, the force in the FCL was relatively small across all knee flexion angles, and the distances decreased with flexion; the amount of internal rotation was fairly constant. FCL has a primary role in preventing varus and external rotation at 15° of flexion. The FCL does not perform isometrically following knee flexion during neutral rotation, and tibia rotation has significant effects on the kinematics of the FCL. Varus and external rotation laxity increased following knee flexion. By providing more realistic data about the function and length patterns of the FCL and the kinematics of the intact knee, improved reconstruction and rehabilitation protocols can be developed.

Lower extremity control during turns initiated with and without hip external rotation.

PubMed

Zaferiou, Antonia M; Flashner, Henryk; Wilcox, Rand R; McNitt-Gray, Jill L

2017-02-08

The pirouette turn is often initiated in neutral and externally rotated hip positions by dancers. This provides an opportunity to investigate how dancers satisfy the same mechanical objectives at the whole-body level when using different leg kinematics. The purpose of this study was to compare lower extremity control strategies during the turn initiation phase of pirouettes performed with and without hip external rotation. Skilled dancers (n=5) performed pirouette turns with and without hip external rotation. Joint kinetics during turn initiation were determined for both legs using ground reaction forces (GRFs) and segment kinematics. Hip muscle activations were monitored using electromyography. Using probability-based statistical methods, variables were compared across turn conditions as a group and within-dancer. Despite differences in GRFs and impulse generation between turn conditions, at least 90% of each GRF was aligned with the respective leg plane. A majority of the net joint moments at the ankle, knee, and hip acted about an axis perpendicular to the leg plane. However, differences in shank alignment relative to the leg plane affected the distribution of the knee net joint moment when represented with respect to the shank versus the thigh. During the initiation of both turns, most participants used ankle plantar flexor moments, knee extensor moments, flexor and abductor moments at the push leg׳s hip, and extensor and abductor moments at the turn leg׳s hip. Representation of joint kinetics using multiple reference systems assisted in understanding control priorities. Copyright © 2017 Elsevier Ltd. All rights reserved.

Evaluation of Load Analysis Methods for NASAs GIII Adaptive Compliant Trailing Edge Project

NASA Technical Reports Server (NTRS)

Cruz, Josue; Miller, Eric J.

2016-01-01

The Air Force Research Laboratory (AFRL), NASA Armstrong Flight Research Center (AFRC), and FlexSys Inc. (Ann Arbor, Michigan) have collaborated to flight test the Adaptive Compliant Trailing Edge (ACTE) flaps. These flaps were installed on a Gulfstream Aerospace Corporation (GAC) GIII aircraft and tested at AFRC at various deflection angles over a range of flight conditions. External aerodynamic and inertial load analyses were conducted with the intention to ensure that the change in wing loads due to the deployed ACTE flap did not overload the existing baseline GIII wing box structure. The objective of this paper was to substantiate the analysis tools used for predicting wing loads at AFRC. Computational fluid dynamics (CFD) models and distributed mass inertial models were developed for predicting the loads on the wing. The analysis tools included TRANAIR (full potential) and CMARC (panel) models. Aerodynamic pressure data from the analysis codes were validated against static pressure port data collected in-flight. Combined results from the CFD predictions and the inertial load analysis were used to predict the normal force, bending moment, and torque loads on the wing. Wing loads obtained from calibrated strain gages installed on the wing were used for substantiation of the load prediction tools. The load predictions exhibited good agreement compared to the flight load results obtained from calibrated strain gage measurements.

Orientational ordering of colloidal dispersions by application of time-dependent external forces.

PubMed

Moths, Brian; Witten, T A

2013-08-01

We discuss a method of organizing incoherent motion of a colloidal suspension to produce synchronized, coherent motion, extending the discussion of our recent Letter [Moths and Witten, Phys. Rev. Lett. 110, 028301 (2013)]. The method does not require interaction between the objects. Instead, the effect is controlled by the "twist matrix" which gives the angular velocity of an asymmetric object in a fluid resulting from a weak external force. We analyze the two types of forcing considered in the Letter: a force alternating between two directions and a continuously rotating force. For the alternating force, we justify the claim of the Letter that under appropriate forcing conditions, the orientational entropy of the objects decreases indefinitely with time, on average. We provide a bound on that rate in terms of the twist matrix. For the case of rotating force, we derive conditions for phased-locked motion of the objects to the force and prove that there is only one stable phase-locked orientation under these conditions. We find numerically that the fastest alignment typically occurs for tilt angles of order unity. We discuss how the alignment effect scales with the object size for external forcing caused by gravity or an electric field. Under practical forcing conditions we estimate that the alignment should persist despite rotational diffusion for objects larger than about 10 microns. Potential misalignment owing to hydrodynamic interaction of the objects is estimated to be negligible at volume fractions smaller than about 10(-4.5) (10(-3)) when the forcing is gravitational (electrophoretic).

Characterization of the modified nickel-zinc ferrite nanoparticles coated with APTES by salinization reaction

NASA Astrophysics Data System (ADS)

Zainal, Israa G.; Al-Shammari, Ahmed Majeed; Kachi, Wjeah

2018-05-01

Surface functionalization of magnetic iron oxide nanoparticles (NPs) is a kind of functional materials, which have been widely used in the biotechnology and catalysis. In this study, Nickel-Zinc ferrite nanoparticles was functionalized with amino propyl triethoxy silane (APTES) by silanization reaction and both non coated and organosilane-coated magnetite characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry, Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy. Basic groups of amino anchored on the external surface of the coated magnetite were observed. Our study procedure nanoparticles which have surface with free - NH2 groups which can carry out ionic interaction with carboxylic groups and act as a carrier of biological molecules, drugs and metals.

External Influences on Modeled and Observed Cloud Trends

NASA Technical Reports Server (NTRS)

Marvel, Kate; Zelinka, Mark; Klein, Stephen A.; Bonfils, Celine; Caldwell, Peter; Doutriaux, Charles; Santer, Benjamin D.; Taylor, Karl E.

2015-01-01

Understanding the cloud response to external forcing is a major challenge for climate science. This crucial goal is complicated by intermodel differences in simulating present and future cloud cover and by observational uncertainty. This is the first formal detection and attribution study of cloud changes over the satellite era. Presented herein are CMIP5 (Coupled Model Intercomparison Project - Phase 5) model-derived fingerprints of externally forced changes to three cloud properties: the latitudes at which the zonally averaged total cloud fraction (CLT) is maximized or minimized, the zonal average CLT at these latitudes, and the height of high clouds at these latitudes. By considering simultaneous changes in all three properties, the authors define a coherent multivariate fingerprint of cloud response to external forcing and use models from phase 5 of CMIP (CMIP5) to calculate the average time to detect these changes. It is found that given perfect satellite cloud observations beginning in 1983, the models indicate that a detectable multivariate signal should have already emerged. A search is then made for signals of external forcing in two observational datasets: ISCCP (International Satellite Cloud Climatology Project) and PATMOS-x (Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmospheres - Extended). The datasets are both found to show a poleward migration of the zonal CLT pattern that is incompatible with forced CMIP5 models. Nevertheless, a detectable multivariate signal is predicted by models over the PATMOS-x time period and is indeed present in the dataset. Despite persistent observational uncertainties, these results present a strong case for continued efforts to improve these existing satellite observations, in addition to planning for new missions.

A thermostatted kinetic theory model for event-driven pedestrian dynamics

NASA Astrophysics Data System (ADS)

Bianca, Carlo; Mogno, Caterina

2018-06-01

This paper is devoted to the modeling of the pedestrian dynamics by means of the thermostatted kinetic theory. Specifically the microscopic interactions among pedestrians and an external force field are modeled for simulating the evacuation of pedestrians from a metro station. The fundamentals of the stochastic game theory and the thermostatted kinetic theory are coupled for the derivation of a specific mathematical model which depicts the time evolution of the distribution of pedestrians at different exits of a metro station. The perturbation theory is employed in order to establish the stability analysis of the nonequilibrium stationary states in the case of a metro station consisting of two exits. A general sensitivity analysis on the initial conditions, the magnitude of the external force field and the number of exits is presented by means of numerical simulations which, in particular, show how the asymptotic distribution and the convergence time are affected by the presence of an external force field. The results show how, in evacuation conditions, the interaction dynamics among pedestrians can be negligible with respect to the external force. The important role of the thermostat term in allowing the reaching of the nonequilibrium stationary state is stressed out. Research perspectives are underlined at the end of paper, in particular for what concerns the derivation of frameworks that take into account the definition of local external actions and the introduction of the space and velocity dynamics.

Non-cooperative Brownian donkeys: A solvable 1D model

NASA Astrophysics Data System (ADS)

Jiménez de Cisneros, B.; Reimann, P.; Parrondo, J. M. R.

2003-12-01

A paradigmatic 1D model for Brownian motion in a spatially symmetric, periodic system is tackled analytically. Upon application of an external static force F the system's response is an average current which is positive for F < 0 and negative for F > 0 (absolute negative mobility). Under suitable conditions, the system approaches 100% efficiency when working against the external force F.

Regularity in an environment produces an internal torque pattern for biped balance control.

PubMed

Ito, Satoshi; Kawasaki, Haruhisa

2005-04-01

In this paper, we present a control method for achieving biped static balance under unknown periodic external forces whose periods are only known. In order to maintain static balance adaptively in an uncertain environment, it is essential to have information on the ground reaction forces. However, when the biped is exposed to a steady environment that provides an external force periodically, uncertain factors on the regularity with respect to a steady environment are gradually clarified using learning process, and finally a torque pattern for balancing motion is acquired. Consequently, static balance is maintained without feedback from ground reaction forces and achieved in a feedforward manner.

Propagation of the state change induced by external forces in local interactions

NASA Astrophysics Data System (ADS)

Lu, Jianjun; Tokinaga, Shozo

2016-10-01

This paper analyses the propagation of the state changes of agents that are induced by external forces applied to a plane. In addition, we propose two models for the behavior of the agents placed on a lattice plane, both of which are affected by local interactions. We first assume that agents are allowed to move to another site to maximise their satisfaction. Second, we utilise a model in which the agents choose activities on each site. The results show that the migration (activity) patterns of agents in both models achieve stability without any external forces. However, when we apply an impulsive external force to the state of the agents, we then observe the propagation of the changes in the agents' states. Using simulation studies, we show the conditions for the propagation of the state changes of the agents. We also show the propagation of the state changes of the agents allocated in scale-free networks and discuss the estimation of the agents' decisions in real state changes. Finally, we discuss the estimation of the agents' decisions in real state temporal changes using economic and social data from Japan and the United States.

Movement: How the Brain Communicates with the World.

PubMed

Schwartz, Andrew B

2016-03-10

Voluntary movement is a result of signals transmitted through a communication channel that links the internal world in our minds to the physical world around us. Intention can be considered the desire to effect change on our environment, and this is contained in the signals from the brain, passed through the nervous system to converge on muscles that generate displacements and forces on our surroundings. The resulting changes in the world act to generate sensations that feed back to the nervous system, closing the control loop. This Perspective discusses the experimental and theoretical underpinnings of current models of movement generation and the way they are modulated by external information. Movement systems embody intentionality and prediction, two factors that are propelling a revolution in engineering. Development of movement models that include the complexities of the external world may allow a better understanding of the neuronal populations regulating these processes, as well as the development of solutions for autonomous vehicles and robots, and neural prostheses for those who are motor impaired. Copyright © 2016 Elsevier Inc. All rights reserved.

The Dynamics of Oblate Drop Between Heterogeneous Plates Under Alternating Electric Field. Non-uniform Field

NASA Astrophysics Data System (ADS)

Kashina, M. A.; Alabuzhev, A. A.

2018-02-01

The dynamics of the incompressible fluid drop under the non-uniform electric field are considered. The drop is bounded axially by two parallel solid planes and the case of heterogeneous plates is investigated. The external electric field acts as an external force that causes motion of the contact line. We assume that the electric current is alternative current and the AC filed amplitude is a spatially non-uniform function. In equilibrium, the drop has the form of a circular cylinder. The equilibrium contact angle is 0.5 π. In order to describe this contact line motion the modified Hocking boundary condition is applied: the velocity of the contact line is proportional to the deviation of the contact angle and the speed of the fast relaxation processes, which frequency is proportional to twice the frequency of the electric field. The Hocking parameter depends on the polar angle, i.e. the coefficient of the interaction between the plate and the fluid (the contact line) is a function of the plane coordinates. This function is expanded in a series of the Laplace operator eigenfunctions.

Modeling of combustion processes of stick propellants via combined Eulerian-Lagrangian approach

NASA Technical Reports Server (NTRS)

Kuo, K. K.; Hsieh, K. C.; Athavale, M. M.

1988-01-01

This research is motivated by the improved ballistic performance of large-caliber guns using stick propellant charges. A comprehensive theoretical model for predicting the flame spreading, combustion, and grain deformation phenomena of long, unslotted stick propellants is presented. The formulation is based upon a combined Eulerian-Lagrangian approach to simulate special characteristics of the two phase combustion process in a cartridge loaded with a bundle of sticks. The model considers five separate regions consisting of the internal perforation, the solid phase, the external interstitial gas phase, and two lumped parameter regions at either end of the stick bundle. For the external gas phase region, a set of transient one-dimensional fluid-dynamic equations using the Eulerian approach is obtained; governing equations for the stick propellants are formulated using the Lagrangian approach. The motion of a representative stick is derived by considering the forces acting on the entire propellant stick. The instantaneous temperature and stress fields in the stick propellant are modeled by considering the transient axisymmetric heat conduction equation and dynamic structural analysis.

U.S. hospitals mired in bureaucracy: 10 roadblocks to change.

PubMed

Thompson, R E

2000-01-01

Given the dot.com revolution in health care, advancing medical technology, and dissatisfaction with managed care, fundamental change is the order of the day in U.S. hospitals. Some hospital leaders are responding effectively to these new century challenges. But too many only tinker with existing systems, hoping to get by with choices that are comfortable, conventional, and convenient. Meanwhile, the sharks of dwindling public confidence and lost political support circle ever closer. The vice president of medical affairs (VPMA) is positioned at the vertex of disparate organizational, interpersonal, and external forces and can lead the way in recognizing and removing common roadblocks delaying needed change. External obstacles include: (1) Too much regulation; (2) too many attorneys; and (3) theatrical local TV newscasts. Internal factors include: (4) A natural fear of change; (5) arguing when we do not really disagree; (6) Cake Committee management mentality; (7) over-aggressive downsizing; (8) natural conflict in choosing a health care ethic; (9) the past; and (10) lack of trust. Hospital leaders need to effectively act, not just think, "outside the box."

Analyzing the Long Term Cohesive Effect of Sector Specific Driving Forces.

PubMed

Berman, Yonatan; Ben-Jacob, Eshel; Zhang, Xin; Shapira, Yoash

2016-01-01

Financial markets are partially composed of sectors dominated by external driving forces, such as commodity prices, infrastructure and other indices. We characterize the statistical properties of such sectors and present a novel model for the coupling of the stock prices and their dominating driving forces, inspired by mean reverting stochastic processes. Using the model we were able to explain the market sectors' long term behavior and estimate the coupling strength between stocks in financial markets and the sector specific driving forces. Notably, the analysis was successfully applied to the shipping market, in which the Baltic dry index (BDI), an assessment of the price of transporting the major raw materials by sea, influences the shipping financial market. We also present the analysis of other sectors-the gold mining market and the food production market, for which the model was also successfully applied. The model can serve as a general tool for characterizing the coupling between external forces and affected financial variables and therefore for estimating the risk in sectors and their vulnerability to external stress.

Analyzing the Long Term Cohesive Effect of Sector Specific Driving Forces

PubMed Central

Berman, Yonatan; Zhang, Xin; Shapira, Yoash

2016-01-01

Financial markets are partially composed of sectors dominated by external driving forces, such as commodity prices, infrastructure and other indices. We characterize the statistical properties of such sectors and present a novel model for the coupling of the stock prices and their dominating driving forces, inspired by mean reverting stochastic processes. Using the model we were able to explain the market sectors’ long term behavior and estimate the coupling strength between stocks in financial markets and the sector specific driving forces. Notably, the analysis was successfully applied to the shipping market, in which the Baltic dry index (BDI), an assessment of the price of transporting the major raw materials by sea, influences the shipping financial market. We also present the analysis of other sectors—the gold mining market and the food production market, for which the model was also successfully applied. The model can serve as a general tool for characterizing the coupling between external forces and affected financial variables and therefore for estimating the risk in sectors and their vulnerability to external stress. PMID:27031230

Nonstationary time series prediction combined with slow feature analysis

NASA Astrophysics Data System (ADS)

Wang, G.; Chen, X.

2015-01-01

Almost all climate time series have some degree of nonstationarity due to external driving forces perturbations of the observed system. Therefore, these external driving forces should be taken into account when reconstructing the climate dynamics. This paper presents a new technique of combining the driving force of a time series obtained using the Slow Feature Analysis (SFA) approach, then introducing the driving force into a predictive model to predict non-stationary time series. In essence, the main idea of the technique is to consider the driving forces as state variables and incorporate them into the prediction model. To test the method, experiments using a modified logistic time series and winter ozone data in Arosa, Switzerland, were conducted. The results showed improved and effective prediction skill.

Nonlinear modeling of forced magnetic reconnection in slab geometry with NIMROD

NASA Astrophysics Data System (ADS)

Beidler, M. T.; Callen, J. D.; Hegna, C. C.; Sovinec, C. R.

2017-05-01

The nonlinear, extended-magnetohydrodynamic (MHD) code NIMROD is benchmarked with the theory of time-dependent forced magnetic reconnection induced by small resonant fields in slab geometry in the context of visco-resistive MHD modeling. Linear computations agree with time-asymptotic, linear theory of flow screening of externally applied fields. The inclusion of flow in nonlinear computations can result in mode penetration due to the balance between electromagnetic and viscous forces in the time-asymptotic state, which produces bifurcations from a high-slip state to a low-slip state as the external field is slowly increased. We reproduce mode penetration and unlocking transitions by employing time-dependent externally applied magnetic fields. Mode penetration and unlocking exhibit hysteresis and occur at different magnitudes of applied field. We also establish how nonlinearly determined flow screening of the resonant field is affected by the square of the magnitude of the externally applied field. These results emphasize that the inclusion of nonlinear physics is essential for accurate prediction of the reconnected field in a flowing plasma.

Linear response and correlation of a self-propelled particle in the presence of external fields

NASA Astrophysics Data System (ADS)

Caprini, Lorenzo; Marini Bettolo Marconi, Umberto; Vulpiani, Angelo

2018-03-01

We study the non-equilibrium properties of non interacting active Ornstein-Uhlenbeck particles (AOUP) subject to an external nonuniform field using a Fokker-Planck approach with a focus on the linear response and time-correlation functions. In particular, we compare different methods to compute these functions including the unified colored noise approximation (UCNA). The AOUP model, described by the position of the particle and the active force acting on it, is usually mapped into a Markovian process, describing the motion of a fictitious passive particle in terms of its position and velocity, where the effect of the activity is transferred into a position-dependent friction. We show that the form of the response function of the AOUP depends on whether we put the perturbation on the position and keep unperturbed the active force in the original variables or perturb the position and maintain unperturbed the velocity in the transformed variables. Indeed, as a result of the change of variables the perturbation on the position becomes a perturbation both on the position and on the fictitious velocity. We test these predictions by considering the response for three types of convex potentials: quadratic, quartic and double-well potential. Moreover, by comparing the response of the AOUP model with the corresponding response of the UCNA model we conclude that although the stationary properties are fairly well approximated by the UCNA, the non equilibrium properties are not, an effect which is not negligible when the persistence time is large.

Application of largest Lyapunov exponent analysis on the studies of dynamics under external forces

NASA Astrophysics Data System (ADS)

Odavić, Jovan; Mali, Petar; Tekić, Jasmina; Pantić, Milan; Pavkov-Hrvojević, Milica

2017-06-01

Dynamics of driven dissipative Frenkel-Kontorova model is examined by using largest Lyapunov exponent computational technique. Obtained results show that besides the usual way where behavior of the system in the presence of external forces is studied by analyzing its dynamical response function, the largest Lyapunov exponent analysis can represent a very convenient tool to examine system dynamics. In the dc driven systems, the critical depinning force for particular structure could be estimated by computing the largest Lyapunov exponent. In the dc+ac driven systems, if the substrate potential is the standard sinusoidal one, calculation of the largest Lyapunov exponent offers a more sensitive way to detect the presence of Shapiro steps. When the amplitude of the ac force is varied the behavior of the largest Lyapunov exponent in the pinned regime completely reflects the behavior of Shapiro steps and the critical depinning force, in particular, it represents the mirror image of the amplitude dependence of critical depinning force. This points out an advantage of this technique since by calculating the largest Lyapunov exponent in the pinned regime we can get an insight into the dynamics of the system when driving forces are applied. Additionally, the system is shown to be not chaotic even in the case of incommensurate structures and large amplitudes of external force, which is a consequence of overdampness of the model and the Middleton's no passing rule.

Human influence on Canadian temperatures

NASA Astrophysics Data System (ADS)

Wan, Hui; Zhang, Xuebin; Zwiers, Francis

2018-02-01

Canada has experienced some of the most rapid warming on Earth over the past few decades with a warming rate about twice that of the global mean temperature since 1948. Long-term warming is observed in Canada's annual, winter and summer mean temperatures, and in the annual coldest and hottest daytime and nighttime temperatures. The causes of these changes are assessed by comparing observed changes with climate model simulated responses to anthropogenic and natural (solar and volcanic) external forcings. Most of the observed warming of 1.7 °C increase in annual mean temperature during 1948-2012 [90% confidence interval (1.1°, 2.2 °C)] can only be explained by external forcing on the climate system, with anthropogenic influence being the dominant factor. It is estimated that anthropogenic forcing has contributed 1.0 °C (0.6°, 1.5 °C) and natural external forcing has contributed 0.2 °C (0.1°, 0.3 °C) to the observed warming. Up to 0.5 °C of the observed warming trend may be associated with low frequency variability of the climate such as that represented by the Pacific decadal oscillation (PDO) and North Atlantic oscillation (NAO). Overall, the influence of both anthropogenic and natural external forcing is clearly evident in Canada-wide mean and extreme temperatures, and can also be detected regionally over much of the country.

Stability diagram for the forced Kuramoto model.

PubMed

Childs, Lauren M; Strogatz, Steven H

2008-12-01

We analyze the periodically forced Kuramoto model. This system consists of an infinite population of phase oscillators with random intrinsic frequencies, global sinusoidal coupling, and external sinusoidal forcing. It represents an idealization of many phenomena in physics, chemistry, and biology in which mutual synchronization competes with forced synchronization. In other words, the oscillators in the population try to synchronize with one another while also trying to lock onto an external drive. Previous work on the forced Kuramoto model uncovered two main types of attractors, called forced entrainment and mutual entrainment, but the details of the bifurcations between them were unclear. Here we present a complete bifurcation analysis of the model for a special case in which the infinite-dimensional dynamics collapse to a two-dimensional system. Exact results are obtained for the locations of Hopf, saddle-node, and Takens-Bogdanov bifurcations. The resulting stability diagram bears a striking resemblance to that for the weakly nonlinear forced van der Pol oscillator.

Force approach to radiation reaction

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

López, Gustavo V., E-mail: gulopez@udgserv.cencar.udg.mx

The difficulty of the usual approach to deal with the radiation reaction is pointed out, and under the condition that the radiation force must be a function of the external force and is zero whenever the external force be zero, a new and straightforward approach to radiation reaction force and damping is proposed. Starting from the Larmor formula for the power radiated by an accelerated charged particle, written in terms of the applied force instead of the acceleration, an expression for the radiation force is established in general, and applied to the examples for the linear and circular motion ofmore » a charged particle. This expression is quadratic in the magnitude of the applied force, inversely proportional to the speed of the charged particle, and directed opposite to the velocity vector. This force approach may contribute to the solution of the very old problem of incorporating the radiation reaction to the motion of the charged particles, and future experiments may tell us whether or not this approach point is in the right direction.« less

Safety evaluation of large external fixation clamps and frames in a magnetic resonance environment.

PubMed

Luechinger, Roger; Boesiger, Peter; Disegi, John A

2007-07-01

Large orthopedic external fixation clamps and related components were evaluated for force, torque, and heating response when subjected to the strong electromagnetic fields of magnetic-resonance (MR) imaging devices. Forces induced by a 3-Tesla (T) MR scanner were compiled for newly designed nonmagnetic clamps and older clamps that contained ferromagnetic components. Heating trials were performed in a 1.5 and in a 3 T MR scanner with two assembled external fixation frames. Forces of the newly designed clamps were more than a factor 2 lower as the gravitational force on the device whereas, magnetic forces on the older devices showed over 10 times the force induced by earth acceleration of gravity. No torque effects could be found for the newly designed clamps. Temperature measurements at the tips of Schanz screws in the 1.5 T MR scanner showed a rise of 0.7 degrees C for a pelvic frame and of 2.1 degrees C for a diamond knee bridge frame when normalized to a specific absorption rate (SAR) of 2 W/kg. The normalized temperature increases in the 3 T MR scanner were 0.9 degrees C for the pelvic frame and 1.1 degrees C for the knee bridge frame. Large external fixation frames assembled with the newly designed clamps (390 Series Clamps), carbon fiber reinforced rods, and implant quality 316L stainless steel Schanz screws met prevailing force and torque limits when tested in a 3-T field, and demonstrated temperature increase that met IEC-60601 guidelines for extremities. The influence of frame-induced eddy currents on the risk of peripheral nerve stimulation was not investigated. Copyright 2006 Wiley Periodicals, Inc.

32 CFR 806b.1 - Summary of revisions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... for the Air Force Privacy Program from Air Force Communications and Information Center to the Air Force Chief Information Officer; prescribes Air Force Visual Aid 33-276, Privacy Act Label as optional; adds the E-Gov Act of 2002 requirement for a Privacy Impact Assessment for all information systems that...

32 CFR 806b.1 - Summary of revisions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... for the Air Force Privacy Program from Air Force Communications and Information Center to the Air Force Chief Information Officer; prescribes Air Force Visual Aid 33-276, Privacy Act Label as optional; adds the E-Gov Act of 2002 requirement for a Privacy Impact Assessment for all information systems that...

32 CFR 806b.1 - Summary of revisions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... for the Air Force Privacy Program from Air Force Communications and Information Center to the Air Force Chief Information Officer; prescribes Air Force Visual Aid 33-276, Privacy Act Label as optional; adds the E-Gov Act of 2002 requirement for a Privacy Impact Assessment for all information systems that...

Correlates of Romantic Love

ERIC Educational Resources Information Center

Dion, Kenneth L.; Dion, Karen K.

1973-01-01

Relationships between internal-external control and romantic love were hypothesized on the basis of a social influence interpretation and the view that romantic love is culturally stereotyped as an external force. Consistent with these perspectives, proportionally fewer internals than externals reported having been romantically attached. (Author)

Molecular dynamics study of response of liquid N,N-dimethylformamide to externally applied electric field using a polarizable force field

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

Gao, Weimin; Niu, Haitao; Lin, Tong

2014-01-28

The behavior of Liquid N,N-dimethylformamide subjected to a wide range of externally applied electric fields (from 0.001 V/nm to 1 V/nm) has been investigated through molecular dynamics simulation. To approach the objective the AMOEBA polarizable force field was extended to include the interaction of the external electric field with atomic partial charges and the contribution to the atomic polarization. The simulation results were evaluated with quantum mechanical calculations. The results from the present force field for the liquid at normal conditions were compared with the experimental and molecular dynamics results with non-polarizable and other polarizable force fields. The uniform externalmore » electric fields of higher than 0.01 V/nm have a significant effect on the structure of the liquid, which exhibits a variation in numerous properties, including molecular polarization, local cluster structure, rotation, alignment, energetics, and bulk thermodynamic and structural properties.« less

Blades Forced Vibration Under Aero-Elastic Excitation Modeled by Van der Pol

NASA Astrophysics Data System (ADS)

Pust, Ladislav; Pesek, Ludek

This paper employs a new analytical approach to model the influence of aerodynamic excitation on the dynamics of a bladed cascade at the flutter state. The flutter is an aero-elastic phenomenon that is linked to the interaction of the flow and the traveling deformation wave in the cascade when only the damping of the cascade changes. As a case study the dynamic properties of the five-blade-bunch excited by the running harmonic external forces and aerodynamic self-excited forces are investigated. This blade-bunch is linked in the shroud by means of the viscous-elastic damping elements. The external running excitation depends on the ratio of stator and rotor blade numbers and corresponds to the real type of excitation in the steam turbine. The aerodynamic self-excited forces are modeled by two types of Van der Pol nonlinear models. The influence of the interaction of both types of self-excitation with the external running excitation is investigated on the response curves.

78 FR 47016 - Submission for Review: Request for External Review

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-02

... OFFICE OF PERSONNEL MANAGEMENT Submission for Review: Request for External Review AGENCY: U.S... External Review. As required by the Paperwork Reduction Act of 1995, (Pub. L. 104-13, 44 U.S.C. chapter 35... the Multi-State Plan Program (MSPP) on March 11, 2013, 78 FR 15560, which outlined an external review...

Viscous/Inviscid Interaction Analysis of the Aerodynamic Performance of the NACA 65-213 Airfoil.

DTIC Science & Technology

1987-03-01

flows . The principal forces that act on the body are those which act directly on the mass of the fluid element, the bodi’ forces , and those which act...shall again consider a 2-D flow , as indicated in Figure.2-. The resultant force in the x- direction, for one unit length in z is F= ph.r~u + a(𔃼.10...x,+.a. Where fx is the body force per-unit mass in the x direction. The most conmmon body force for the flow fields is that of gravity. Equation 2.10

Physical therapy students' willingness to report misconduct to protect the patient's interests.

PubMed

Mansbach, Abraham; Bachner, Yaacov G; Melzer, Itzik

2010-12-01

This article presents a study on the ethical dilemma of whistleblowing in physical therapy, and suggests some lines for further research on this topic as well as ways for integrating it in the physical therapy curriculum. The study examines the self-reported willingness of physical therapy students to report misconduct, whether internally or externally, to protect the patient's interests. Internal disclosure entails reporting the wrongdoing to an authority within the organisation. External disclosure entails reporting the offence to an outside agency, such as the police, professional organisation, or press. The findings indicate that the students view the acts that are detrimental or cause injustice to the patient in a very serious light. In dilemma situations such as these, the students reported a willingness to act. The students also report considerably greater likelihood of whistleblowing internally than externally. The pattern reveals a desire to correct the misconduct coupled with a marked decline in the willingness to blow the whistle as this act moved from the workplace to an external authority.

Nonstationary time series prediction combined with slow feature analysis

NASA Astrophysics Data System (ADS)

Wang, G.; Chen, X.

2015-07-01

Almost all climate time series have some degree of nonstationarity due to external driving forces perturbing the observed system. Therefore, these external driving forces should be taken into account when constructing the climate dynamics. This paper presents a new technique of obtaining the driving forces of a time series from the slow feature analysis (SFA) approach, and then introduces them into a predictive model to predict nonstationary time series. The basic theory of the technique is to consider the driving forces as state variables and to incorporate them into the predictive model. Experiments using a modified logistic time series and winter ozone data in Arosa, Switzerland, were conducted to test the model. The results showed improved prediction skills.

Environmental And Quality Management System In The Context Of Sustainable Development

NASA Astrophysics Data System (ADS)

Rusko, Miroslav

2015-06-01

Growing load and deterioration of the environment can be interpreted as a result of some external effects interventions. While the positive externalities influence the positive productional and utilizational functions of other subjects, the negative externalities influence the negative ones. Both types of external effects can act as parcial or global externalities. Linking of environmental issues to economy and finance is an important sphere.

Advances in Quantum Mechanochemistry: Electronic Structure Methods and Force Analysis.

PubMed

Stauch, Tim; Dreuw, Andreas

2016-11-23

In quantum mechanochemistry, quantum chemical methods are used to describe molecules under the influence of an external force. The calculation of geometries, energies, transition states, reaction rates, and spectroscopic properties of molecules on the force-modified potential energy surfaces is the key to gain an in-depth understanding of mechanochemical processes at the molecular level. In this review, we present recent advances in the field of quantum mechanochemistry and introduce the quantum chemical methods used to calculate the properties of molecules under an external force. We place special emphasis on quantum chemical force analysis tools, which can be used to identify the mechanochemically relevant degrees of freedom in a deformed molecule, and spotlight selected applications of quantum mechanochemical methods to point out their synergistic relationship with experiments.

Every Mass or Mass Group When Created Will have No Motion, Linear, Rotational or Vibratory Motion, Singly or in Some Combination, Which May Be Later Modified by External Forces--A Natural Law

NASA Astrophysics Data System (ADS)

Brekke, Stewart

2010-03-01

Every mass or mass group, from atoms and molecules to stars and galaxies,has no motion, is vibrating, rotating,or moving linearly, singularly or in some combination. When created, the excess energy of creation will generate a vibration, rotation and/or linear motion besides the mass or mass group. Curvilinear or orbital motion is linear motion in an external force field. External forces, such as photon, molecular or stellar collisions may over time modify the inital rotational, vibratory or linear motions of the mass of mass group. The energy equation for each mass or mass group is E=mc^2 + 1/2mv^2 + 1/2I2̂+ 1/2kx0^2 + WG+ WE+ WM.

Response to a small external force and fluctuations of a passive particle in a one-dimensional diffusive environment

NASA Astrophysics Data System (ADS)

Huveneers, François

2018-04-01

We investigate the long-time behavior of a passive particle evolving in a one-dimensional diffusive random environment, with diffusion constant D . We consider two cases: (a) The particle is pulled forward by a small external constant force and (b) there is no systematic bias. Theoretical arguments and numerical simulations provide evidence that the particle is eventually trapped by the environment. This is diagnosed in two ways: The asymptotic speed of the particle scales quadratically with the external force as it goes to zero, and the fluctuations scale diffusively in the unbiased environment, up to possible logarithmic corrections in both cases. Moreover, in the large D limit (homogenized regime), we find an important transient region giving rise to other, finite-size scalings, and we describe the crossover to the true asymptotic behavior.

Unbinding Transition of Probes in Single-File Systems

NASA Astrophysics Data System (ADS)

Bénichou, Olivier; Démery, Vincent; Poncet, Alexis

2018-02-01

Single-file transport, arising in quasi-one-dimensional geometries where particles cannot pass each other, is characterized by the anomalous dynamics of a probe, notably its response to an external force. In these systems, the motion of several probes submitted to different external forces, although relevant to mixtures of charged and neutral or active and passive objects, remains unexplored. Here, we determine how several probes respond to external forces. We rely on a hydrodynamic description of the symmetric exclusion process to obtain exact analytical results at long times. We show that the probes can either move as a whole, or separate into two groups moving away from each other. In between the two regimes, they separate with a different dynamical exponent, as t1 /4. This unbinding transition also occurs in several continuous single-file systems and is expected to be observable.

Internal phase transition induced by external forces in Finsler geometric model for membranes

NASA Astrophysics Data System (ADS)

Koibuchi, Hiroshi; Shobukhov, Andrey

2016-10-01

In this paper, we numerically study an anisotropic shape transformation of membranes under external forces for two-dimensional triangulated surfaces on the basis of Finsler geometry. The Finsler metric is defined by using a vector field, which is the tangential component of a three-dimensional unit vector σ corresponding to the tilt or some external macromolecules on the surface of disk topology. The sigma model Hamiltonian is assumed for the tangential component of σ with the interaction coefficient λ. For large (small) λ, the surface becomes oblong (collapsed) at relatively small bending rigidity. For the intermediate λ, the surface becomes planar. Conversely, fixing the surface with the boundary of area A or with the two-point boundaries of distance L, we find that the variable σ changes from random to aligned state with increasing of A or L for the intermediate region of λ. This implies that an internal phase transition for σ is triggered not only by the thermal fluctuations, but also by external mechanical forces. We also find that the frame (string) tension shows the expected scaling behavior with respect to A/N (L/N) at the intermediate region of A (L) where the σ configuration changes between the disordered and ordered phases. Moreover, we find that the string tension γ at sufficiently large λ is considerably smaller than that at small λ. This phenomenon resembles the so-called soft-elasticity in the liquid crystal elastomer, which is deformed by small external tensile forces.

The Effects of Partial Mechanical Loading and Ibandronate on Skeletal Tissues in the Adult Rat Hindquarter Suspension Model for Microgravity

NASA Technical Reports Server (NTRS)

Schultheis, Lester W.

1999-01-01

We report initial data from a suspended rat model that quantitatively relates chronic partial weightbearing to bone loss. Chronic partial weightbearing is our simulation of the effect of limited artificial gravity aboard spacecraft or reduced planetary gravity. Preliminary analysis of bone by PQCT, histomorphometry, mechanical testing and biochemistry suggest that chronic exposure to half of Earth gravity is insufficient to prevent severe bone loss. The effect of episodic full weightbearing activity (Earth Gravity) on rats otherwise at 50% weightbearing was also explored. This has similarity to treatment by an Earth G-rated centrifuge on a spacecraft that normally maintained artificial gravity at half of Earth G. Our preliminary evidence, using the above techniques to analyze bone, indicate that 2 hours daily of full weightbearing was insufficient to prevent the bone loss observed in 50% weightbearing animals. The effectiveness of partial weightbearing and episodic full weightbearing as potential countermeasures to bone loss in spaceflight was compared with treatment by ibandronate. Ibandronate, a long-acting potent bisphosphonate proved more effective in preventing bone loss and associated functionality based upon structure than our first efforts at mechanical countermeasures. The effectiveness of ibandronate was notable by each of the testing methods we used to study bone from gross structure and strength to tissue and biochemistry. These results appear to be independent of generalized systemic stress imposed by the suspension paradigm. Preliminary evidence does not suggest that blood levels of vitamin D were affected by our countermeasures. Despite the modest theraputic benefit of mechanical countermeasures of partial weightbearing and episodic full weightbearing, we know that some appropriate mechanical signal maintains bone mass in Earth gravity. Moreover, the only mechanism that correctly assigns bone mass and strength to oppose regionally specific force applied to bone is mechanical, a process based upon bone strain. Substantial evidence indicates that the specifics of dynamic loading i.e. time-varying forces are critical. Bone strain history is a predictor of the effect that mechanical conditions have on bone structure mass and strength. Using servo-controlled force plates on suspended rats with implanted strain gauges we manipulated impact forces of ambulation in the frequency (Fourier) domain. Our results indicate that high frequency components of impact forces are particularly potent in producing bone strain independent of the magnitude of the peak force or peak energy applied to the leg. Because a servo-system responds to forces produced by the rat's own muscle activity during ambulation, the direction of ground-reaction loads act on bone through the rat's own musculature. This is in distinction to passive vibration of the floor where forces reach bone through the natural filters of soft tissue and joints. Passive vibration may also be effective, but it may or may not increase bone in the appropriate architectural pattern to oppose the forces of normal ambulatory activity. Effectiveness of high frequency mechanical stimulation in producing regional (muscle directed) bone response will be limited by 1. the sensitivity of bone to a particular range of frequencies and 2. the inertia of the muscles, limiting their response to external forces by increasing tension along insertions. We have begun mathematical modeling of normal ambulatory activity. Effectiveness of high frequency mechanical stimulation in producing regional (muscle directed) bone response will be limited by 1. the sensitivity of bone to a particular range of frequencies and 2. the inertia of the muscles, limiting their response to external forces by increasing tension along insertions. We have begun mathematical modeling of the rat forelimb as a transfer function between impact force and bone strain to predict optimal dynamic loading conditions for this system. We plan additional studies of mechanical counter-measures that incorporate improved dynamic loading, features relevant to anticipated evaluation of artificial gravity, exercise regimens and exposure to Martian gravity, The combination of mechanical countermeasures with ibandronate will also be investigated for signs of synergy.

Magnetic assembly route to colloidal responsive photonic nanostructures.

PubMed

He, Le; Wang, Mingsheng; Ge, Jianping; Yin, Yadong

2012-09-18

Responsive photonic structures can respond to external stimuli by transmitting optical signals. Because of their important technological applications such as color signage and displays, biological and chemical sensors, security devices, ink and paints, military camouflage, and various optoelectronic devices, researchers have focused on developing these functional materials. Conventionally, self-assembled colloidal crystals containing periodically arranged dielectric materials have served as the predominant starting frameworks. Stimulus-responsive materials are incorporated into the periodic structures either as the initial building blocks or as the surrounding matrix so that the photonic properties can be tuned. Although researchers have proposed various versions of responsive photonic structures, the low efficiency of fabrication through self-assembly, narrow tunability, slow responses to the external stimuli, incomplete reversibility, and the challenge of integrating them into existing photonic devices have limited their practical application. In this Account, we describe how magnetic fields can guide the assembly of superparamagnetic colloidal building blocks into periodically arranged particle arrays and how the photonic properties of the resulting structures can be reversibly tuned by manipulating the external magnetic fields. The application of the external magnetic field instantly induces a strong magnetic dipole-dipole interparticle attraction within the dispersion of superparamagnetic particles, which creates one-dimensional chains that each contains a string of particles. The balance between the magnetic attraction and the interparticle repulsions, such as the electrostatic force, defines the interparticle separation. By employing uniform superparamagnetic particles of appropriate sizes and surface charges, we can create one-dimensional periodicity, which leads to strong optical diffraction. Acting remotely over a large distance, magnetic forces drove the rapid formation of colloidal photonic arrays with a wide range of interparticle spacing. They also allowed instant tuning of the photonic properties because they manipulated the interparticle force balance, which changed the orientation of the colloidal assemblies or their periodicity. This magnetically responsive photonic system provides a new platform for chromatic applications: these colloidal particles assemble instantly into ordered arrays with widely, rapidly, and reversibly tunable structural colors, which can be easily and rapidly fixed in a curable polymer matrix. Based on these unique features, we demonstrated many applications of this system, such as structural color printing, the fabrication of anticounterfeiting devices, switchable signage, and field-responsive color displays. We also extended this idea to rapidly organize uniform nonmagnetic building blocks into photonic structures. Using a stable ferrofluid of highly charged magnetic nanoparticles, we created virtual magnetic moments inside the nonmagnetic particles. This "magnetic hole" strategy greatly broadens the scope of the magnetic assembly approach to the fabrication of tunable photonic structures from various dielectric materials.

Towards Subject-Specific Strength Training Design through Predictive Use of Musculoskeletal Models.

PubMed

Plüss, Michael; Schellenberg, Florian; Taylor, William R; Lorenzetti, Silvio

2018-01-01

Lower extremity dysfunction is often associated with hip muscle strength deficiencies. Detailed knowledge of the muscle forces generated in the hip under specific external loading conditions enables specific structures to be trained. The aim of this study was to find the most effective movement type and loading direction to enable the training of specific parts of the hip muscles using a standing posture and a pulley system. In a novel approach to release the predictive power of musculoskeletal modelling techniques based on inverse dynamics, flexion/extension and ab-/adduction movements were virtually created. To demonstrate the effectiveness of this approach, three hip orientations and an external loading force that was systematically rotated around the body were simulated using a state-of-the art OpenSim model in order to establish ideal designs for training of the anterior and posterior parts of the M. gluteus medius (GM). The external force direction as well as the hip orientation greatly influenced the muscle forces in the different parts of the GM. No setting was found for simultaneous training of the anterior and posterior parts with a muscle force higher than 50% of the maximum. Importantly, this study has demonstrated the use of musculoskeletal models as an approach to predict muscle force variations for different strength and rehabilitation exercise variations.

Towards Subject-Specific Strength Training Design through Predictive Use of Musculoskeletal Models

PubMed Central

Plüss, Michael; Schellenberg, Florian

2018-01-01

Lower extremity dysfunction is often associated with hip muscle strength deficiencies. Detailed knowledge of the muscle forces generated in the hip under specific external loading conditions enables specific structures to be trained. The aim of this study was to find the most effective movement type and loading direction to enable the training of specific parts of the hip muscles using a standing posture and a pulley system. In a novel approach to release the predictive power of musculoskeletal modelling techniques based on inverse dynamics, flexion/extension and ab-/adduction movements were virtually created. To demonstrate the effectiveness of this approach, three hip orientations and an external loading force that was systematically rotated around the body were simulated using a state-of-the art OpenSim model in order to establish ideal designs for training of the anterior and posterior parts of the M. gluteus medius (GM). The external force direction as well as the hip orientation greatly influenced the muscle forces in the different parts of the GM. No setting was found for simultaneous training of the anterior and posterior parts with a muscle force higher than 50% of the maximum. Importantly, this study has demonstrated the use of musculoskeletal models as an approach to predict muscle force variations for different strength and rehabilitation exercise variations. PMID:29796082

Hydrodynamic interactions induce movement against an external load in a ratchet dimer Brownian motor.

PubMed

Fornés, José A

2010-01-15

We use the Brownian dynamics with hydrodynamic interactions simulation in order to describe the movement of a elastically coupled dimer Brownian motor in a ratchet potential. The only external forces considered in our system were the load, the random thermal noise and an unbiased thermal fluctuation. For a given set of parameters we observe direct movement against the load force if hydrodynamic interactions were considered.

Effect of flow oscillations on cavity drag and a technique for their control

NASA Technical Reports Server (NTRS)

Gharib, M.; Roshko, A.; Sarohia, V.

1985-01-01

Experiments to relate the state of the shear layer to cavity drag have been performed in a water channel using a 4" axisymmetric cavity model. Detailed flow measurements in various cavity flow oscillation phases, amplitude amplification along the flow direction, distribution of shear stress, and other momentum flux obtained by laser Doppler velocimeter are presented. Measurements show exponential dependence of cavity drag on the length of the cavity. A jump in the cavity drag coefficient is observed as the cavity flow shows a bluff body wake type behavior. Natural and forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of the gap. For a large gap, self-sustained periodic oscillations are observed, while for smaller gaps, which do not oscillate naturally, periodical oscillations can be obtained by external forcing through the strip heater. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. Also, it is possible to completely eliminate mode switching by external forcing. For the first time, it is demonstrated that amplitude of cavity flow Kelvin-Helmholtz wave is dampened or cancelled by introduction of external perturbation of natural flow frequency but different phase.

Permeability of continental crust influenced by internal and external forcing

USGS Publications Warehouse

Rojstaczer, S.A.; Ingebritsen, S.E.; Hayba, D.O.

2008-01-01

The permeability of continental crust is so highly variable that it is often considered to defy systematic characterization. However, despite this variability, some order has been gleaned from globally compiled data. What accounts for the apparent coherence of mean permeability in the continental crust (and permeability-depth relations) on a very large scale? Here we argue that large-scale crustal permeability adjusts to accommodate rates of internal and external forcing. In the deeper crust, internal forcing - fluxes induced by metamorphism, magmatism, and mantle degassing - is dominant, whereas in the shallow crust, external forcing - the vigor of the hydrologic cycle - is a primary control. Crustal petrologists have long recognized the likelihood of a causal relation between fluid flux and permeability in the deep, ductile crust, where fluid pressures are typically near-lithostatic. It is less obvious that such a relation should pertain in the relatively cool, brittle upper crust, where near-hydrostatic fluid pressures are the norm. We use first-order calculations and numerical modeling to explore the hypothesis that upper-crustal permeability is influenced by the magnitude of external fluid sources, much as lower-crustal permeability is influenced by the magnitude of internal fluid sources. We compare model-generated permeability structures with various observations of crustal permeability. ?? 2008 The Authors Journal compilation ?? 2008 Blackwell Publishing Ltd.

Volumetric flow rate in simulations of microfluidic devices+

NASA Astrophysics Data System (ADS)

Kovalčíková, KristÍna; Slavík, Martin; Bachratá, Katarína; Bachratý, Hynek; Bohiniková, Alžbeta

2018-06-01

In this work, we examine the volumetric flow rate of microfluidic devices. The volumetric flow rate is a parameter which is necessary to correctly set up a simulation of a real device and to check the conformity of a simulation and a laboratory experiments [1]. Instead of defining the volumetric rate at the beginning as a simulation parameter, a parameter of external force is set. The proposed hypothesis is that for a fixed set of other parameters (topology, viscosity of the liquid, …) the volumetric flow rate is linearly dependent on external force in typical ranges of fluid velocity used in our simulations. To confirm this linearity hypothesis and to find numerical limits of this approach, we test several values of the external force parameter. The tests are designed for three different topologies of simulation box and for various haematocrits. The topologies of the microfluidic devices are inspired by existing laboratory experiments [3 - 6]. The linear relationship between the external force and the volumetric flow rate is verified in orders of magnitudes similar to the values obtained from laboratory experiments. Supported by the Slovak Research and Development Agency under the contract No. APVV-15-0751 and by the Ministry of Education, Science, Research and Sport of the Slovak Republic under the contract No. VEGA 1/0643/17.

Dynamical diagnostics of the SST annual cycle in the eastern equatorial Pacific: part I a linear coupled framework

NASA Astrophysics Data System (ADS)

Chen, Ying-Ying; Jin, Fei-Fei

2018-03-01

The eastern equatorial Pacific has a pronounced westward propagating SST annual cycle resulting from ocean-atmosphere interactions with equatorial semiannual solar forcing and off-equatorial annual solar forcing conveyed to the equator. In this two-part paper, a simple linear coupled framework is proposed to quantify the internal dynamics and external forcing for a better understanding of the linear part of the dynamics annual cycle. It is shown that an essential internal dynamical factor is the SST damping rate which measures the coupled stability in a similar way as the Bjerknes instability index for the El Niño-Southern Oscillation. It comprises three major negative terms (dynamic damping due to the Ekman pumping feedback, mean circulation advection, and thermodynamic feedback) and two positive terms (thermocline feedback and zonal advection). Another dynamical factor is the westward-propagation speed that is mainly determined by the thermodynamic feedback, the Ekman pumping feedback, and the mean circulation. The external forcing is measured by the annual and semiannual forcing factors. These linear internal and external factors, which can be estimated from data, determine the amplitude of the annual cycle.

Tight junctions negatively regulate mechanical forces applied to adherens junctions in vertebrate epithelial tissue.

PubMed

Hatte, Guillaume; Prigent, Claude; Tassan, Jean-Pierre

2018-02-05

Epithelia are layers of polarised cells tightly bound to each other by adhesive contacts. Epithelia act as barriers between an organism and its external environment. Understanding how epithelia maintain their essential integrity while remaining sufficiently plastic to allow events such as cytokinesis to take place is a key biological problem. In vertebrates, the remodelling and reinforcement of adherens junctions maintains epithelial integrity during cytokinesis. The involvement of tight junctions in cell division, however, has remained unexplored. Here, we examine the role of tight junctions during cytokinesis in the epithelium of the Xenopus laevis embryo. Depletion of the tight junction-associated proteins ZO-1 and GEF-H1 leads to altered cytokinesis duration and contractile ring geometry. Using a tension biosensor, we show that cytokinesis defects originate from misregulation of tensile forces applied to adherens junctions. Our results reveal that tight junctions regulate mechanical tension applied to adherens junctions, which in turn impacts cytokinesis.This article has an associated First Person interview with the first author of the paper. © 2018. Published by The Company of Biologists Ltd.

Observations reveal external driver for Arctic sea-ice retreat

NASA Astrophysics Data System (ADS)

Notz, Dirk; Marotzke, Jochem

2012-04-01

The very low summer extent of Arctic sea ice that has been observed in recent years is often casually interpreted as an early-warning sign of anthropogenic global warming. For examining the validity of this claim, previously IPCC model simulations have been used. Here, we focus on the available observational record to examine if this record allows us to identify either internal variability, self-acceleration, or a specific external forcing as the main driver for the observed sea-ice retreat. We find that the available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration. Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.

3D Printed Anchoring Sutures for Permanent Shaping of Tissues.

PubMed

Wei, Wei; Li, Yuxiao; Yang, Huazhe; Nassab, Reza; Shahriyari, Fatemeh; Akpek, Ali; Guan, Xiaofei; Liu, Yanhui; Taranejoo, Shahrouz; Tamayol, Ali; Zhang, Yu Shrike; Khademhosseini, Ali; Jang, Hae Lin

2017-12-01

Sutures are one of the most widely used devices for adhering separated tissues after injury or surgery. However, most sutures require knotting, which can create a risk of inflammation, and can act as mechanically weak points that often result in breakage and slipping. Here, an anchoring suture is presented with a design that facilitates its propagation parallel to the suturing direction, while maximizing its resistive force against the opposite direction of external force to lock its position in tissues. Different microstructures of suture anchors are systematically designed using orthogonal arrays, and selected based on shape factors associated with mechanical strength. 3D printing is used to fabricate different types of hollow microstructured suture anchors, and optimize their structure for the effective shaping of tissues. To define the structural design for fixing tissues, the maximum force required to pull 3D printed anchors in different directions is examined with tissues. The tissue reshaping function of suture anchors is further simulated ex vivo by using swine ear, nose, and skin, and bovine muscle tendon. This study provides advantages for building functional sutures that can be used for permanently reshaping tissues with enhanced mechanical strength, eliminating the need for knotting to improve surgical efficiency. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Low Piconewton Towing of CNS Axons against Diffusing and Surface-Bound Repellents Requires the Inhibition of Motor Protein-Associated Pathways

NASA Astrophysics Data System (ADS)

Kilinc, Devrim; Blasiak, Agata; O'Mahony, James J.; Lee, Gil U.

2014-11-01

Growth cones, dynamic structures at axon tips, integrate chemical and physical stimuli and translate them into coordinated axon behaviour, e.g., elongation or turning. External force application to growth cones directs and enhances axon elongation in vitro; however, direct mechanical stimulation is rarely combined with chemotactic stimulation. We describe a microfluidic device that exposes isolated cortical axons to gradients of diffusing and substrate-bound molecules, and permits the simultaneous application of piconewton (pN) forces to multiple individual growth cones via magnetic tweezers. Axons treated with Y-27632, a RhoA kinase inhibitor, were successfully towed against Semaphorin 3A gradients, which repel untreated axons, with less than 12 pN acting on a small number of neural cell adhesion molecules. Treatment with Y-27632 or monastrol, a kinesin-5 inhibitor, promoted axon towing on substrates coated with chondroitin sulfate proteoglycans, potent axon repellents. Thus, modulating key molecular pathways that regulate contractile stress generation in axons counteracts the effects of repellent molecules and promotes tension-induced growth. The demonstration of parallel towing of axons towards inhibitory environments with minute forces suggests that mechanochemical stimulation may be a promising therapeutic approach for the repair of the damaged central nervous system, where regenerating axons face repellent factors over-expressed in the glial scar.

Development of a Passive Liquid Valve (PLV) Utilizing a Pressure Equilibrium Phenomenon on the Centrifugal Microfluidic Platform

PubMed Central

Al-Faqheri, Wisam; Ibrahim, Fatimah; Thio, Tzer Hwai Gilbert; Bahari, Norulain; Arof, Hamzah; Rothan, Hussin A.; Yusof, Rohana; Madou, Marc

2015-01-01

In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger. PMID:25723143

Development of a passive liquid valve (PLV) utilizing a pressure equilibrium phenomenon on the centrifugal microfluidic platform.

PubMed

Al-Faqheri, Wisam; Ibrahim, Fatimah; Thio, Tzer Hwai Gilbert; Bahari, Norulain; Arof, Hamzah; Rothan, Hussin A; Yusof, Rohana; Madou, Marc

2015-02-25

In this paper, we propose an easy-to-implement passive liquid valve (PLV) for the microfluidic compact-disc (CD). This valve can be implemented by introducing venting chambers to control the air flow of the source and destination chambers. The PLV mechanism is based on equalizing the main forces acting on the microfluidic CD (i.e., the centrifugal and capillary forces) to control the burst frequency of the source chamber liquid. For a better understanding of the physics behind the proposed PLV, an analytical model is described. Moreover, three parameters that control the effectiveness of the proposed valve, i.e., the liquid height, liquid density, and venting chamber position with respect to the CD center, are tested experimentally. To demonstrate the ability of the proposed PLV valve, microfluidic liquid switching and liquid metering are performed. In addition, a Bradford assay is performed to measure the protein concentration and evaluated in comparison to the benchtop procedure. The result shows that the proposed valve can be implemented in any microfluidic process that requires simplicity and accuracy. Moreover, the developed valve increases the flexibility of the centrifugal CD platform for passive control of the liquid flow without the need for an external force or trigger.

Performance Analysis of a Self-Propelling Flat Plate Fin with Joint Compliance

NASA Astrophysics Data System (ADS)

Reddy, N. Srinivasa; Sen, Soumen; Pal, Sumit; Shome, Sankar Nath

2017-12-01

Fish fin muscles are compliant and they regulate the stiffness to suit different swimming conditions. This article attempts to understand the significance of presence of compliance in fin muscle with help of a flexible joint flat plate fin model. Blade element method is employed to model hydrodynamics and to compute the forces of interaction during motion of the plate within fluid. The dynamic model of self-propelling fin is developed through multi-body dynamics approach considering the hydrodynamic forces as external forces acting on the fin. The derived hydrodynamic model is validated with experiments on rigid flat plate fin. The effect of the joint stiffness and flapping frequency on the propulsion speed and efficiency is investigated through simulations using the derived and validated model. The propulsion efficiency is found to be highly influenced by the joint stiffness at a given flapping frequency. The fin attained maximum propulsion efficiency when the joint stiffness is tuned to a value at which flapping frequency matches near natural frequency of the fin. At this tuned joint stiffness and flapping frequency, the resulted Strouhal numbers are observed to fall within the optimum range (0.2 to 0.4) for maximized propulsion efficiency of flying birds and swimming aquatic animals reported in literature.

Amplitude and phase fluctuations of Van der Pol oscillator under external random forcing

NASA Astrophysics Data System (ADS)

Singh, Aman K.; Yadava, R. D. S.

2018-05-01

The paper presents an analytical study of noise in Van der Pol oscillator output subjected to an external force noise assumed to be characterized by delta function (white noise). The external fluctuations are assumed to be small in comparison to the average response of the noise free system. The autocorrelation function and power spectrum are calculated under the condition of weak nonlinearity. The latter ensures limit cycle oscillations. The total spectral power density is dominated by the contributions from the phase fluctuations. The amplitude fluctuations are at least two orders of magnitude smaller. The analysis is shown to be useful to interpretation microcantilever based biosensing data.

Inducing and destruction of chimeras and chimera-like states by an external harmonic force

NASA Astrophysics Data System (ADS)

Shepelev, I. A.; Vadivasova, T. E.

2018-03-01

We study the phenomena of chimera destruction and inducing of chimera-like states in an ensemble of nonlocally coupled chaotic Rössler oscillators under an external harmonic force. The localized harmonic influence can lead to both destruction and changing of the spatial topology of chimeras. At the same time this influence can cause the emergence of stable chimera-like states (induced chimeras) for the regime of partial coherent chaos. Induced chimeras are also observed for the global influence. We show the possibility of controlling the chimera-like state topology by varying the parameters of localized external harmonic influence.

Caught between the global economy and local bureaucracy: the barriers to good waste management practice in South Africa.

PubMed

Godfrey, Linda; Scott, Dianne; Trois, Cristina

2013-03-01

Empirical research shows that good waste management practice in South Africa is not always under the volitional control of those tasked with its implementation. While intention to act may exist, external factors, within the distal and proximal context, create barriers to waste behaviour. In addition, these barriers differ for respondents in municipalities, private industry and private waste companies. The main barriers to implementing good waste management practice experienced by respondents in municipalities included insufficient funding for waste management and resultant lack of resources; insufficient waste knowledge; political interference in decision-making; a slow decision-making process; lack of perceived authority to act by waste staff; and a low priority afforded to waste. Barriers experienced by respondents in private industry included insufficient funding for waste and the resultant lack of resources; insufficient waste knowledge; and government bureaucracy. Whereas, barriers experienced in private waste companies included increasing costs; government bureaucracy; global markets; and availability of waste for recycling. The results suggest that respondents in public and private waste organizations are subject to different structural forces that shape, enable and constrain waste behaviour.

Force measuring valve assemblies, systems including such valve assemblies and related methods

DOEpatents

DeWall, Kevin George [Pocatello, ID; Garcia, Humberto Enrique [Idaho Falls, ID; McKellar, Michael George [Idaho Falls, ID

2012-04-17

Methods of evaluating a fluid condition may include stroking a valve member and measuring a force acting on the valve member during the stroke. Methods of evaluating a fluid condition may include measuring a force acting on a valve member in the presence of fluid flow over a period of time and evaluating at least one of the frequency of changes in the measured force over the period of time and the magnitude of the changes in the measured force over the period of time to identify the presence of an anomaly in a fluid flow and, optionally, its estimated location. Methods of evaluating a valve condition may include directing a fluid flow through a valve while stroking a valve member, measuring a force acting on the valve member during the stroke, and comparing the measured force to a reference force. Valve assemblies and related systems are also disclosed.

The capsular ligaments provide more hip rotational restraint than the acetabular labrum and the ligamentum teres

PubMed Central

van Arkel, R. J.; Amis, A. A.; Cobb, J. P.; Jeffers, J. R. T.

2015-01-01

In this in vitro study of the hip joint we examined which soft tissues act as primary and secondary passive rotational restraints when the hip joint is functionally loaded. A total of nine cadaveric left hips were mounted in a testing rig that allowed the application of forces, torques and rotations in all six degrees of freedom. The hip was rotated throughout a complete range of movement (ROM) and the contributions of the iliofemoral (medial and lateral arms), pubofemoral and ischiofemoral ligaments and the ligamentum teres to rotational restraint was determined by resecting a ligament and measuring the reduced torque required to achieve the same angular position as before resection. The contribution from the acetabular labrum was also measured. Each of the capsular ligaments acted as the primary hip rotation restraint somewhere within the complete ROM, and the ligamentum teres acted as a secondary restraint in high flexion, adduction and external rotation. The iliofemoral lateral arm and the ischiofemoral ligaments were primary restraints in two-thirds of the positions tested. Appreciation of the importance of these structures in preventing excessive hip rotation and subsequent impingement/instability may be relevant for surgeons undertaking both hip joint preserving surgery and hip arthroplasty. Cite this article: Bone Joint J 2015; 97-B:484–91. PMID:25820886

The Veterans Administration library program.

PubMed

Gartland, H J

1968-01-01

The Veterans Administration Library Service is continuously responsive to the information requirements of the agency's policies which provide for the improved care and treatment of veterans through research, education, and clinical programs. At the same time, it participates in the planning of the federal government as a whole in providing library support for health care for the American people. There are both internal and external forces influencing VA hospitals and their libraries. Retirements and consequent recruitment of new people will necessitate a rethinking of the VA library program at the same time as external forces will be affecting the program. These external forces include the application of machines to library services through the development of in-house capabilities coupled with joint-use participation and P.L. 89-785 which provides for the exchange of medical information, sharing of facilities, and cooperative training programs. A conceptual rearrangement of information resources will facilitate attainment of our goals.

Transient Reactivation of a Deep-Seated Landslide by Undrained Loading Captured With Repeat Airborne and Terrestrial Lidar

NASA Astrophysics Data System (ADS)

Booth, Adam M.; McCarley, Justin; Hinkle, Jason; Shaw, Susan; Ampuero, Jean-Paul; Lamb, Michael P.

2018-05-01

Landslides reactivate due to external environmental forcing or internal mass redistribution, but the process is rarely documented quantitatively. We capture the three-dimensional, 1-m resolution surface deformation field of a transiently reactivated landslide with image correlation of repeat airborne lidar. Undrained loading by two debris flows in the landslide's head, rather than external forcing, triggered reactivation. After that loading, the lower 2 km of the landslide advanced by up to 14 m in 2 years before completely stopping. The displacement field over those 2 years implies that the slip surface gained 1 kPa of shear strength, which was likely accomplished by a negative dilatancy-pore pressure feedback as material deformed around basal roughness elements. Thus, landslide motion can be decoupled from external environmental forcing in cases, motivating the need to better understand internal perturbations to the stress field to predict hazards and sediment fluxes as landscapes evolve.

Quantization and instability of the damped harmonic oscillator subject to a time-dependent force

NASA Astrophysics Data System (ADS)

Majima, H.; Suzuki, A.

2011-12-01

We consider the one-dimensional motion of a particle immersed in a potential field U(x) under the influence of a frictional (dissipative) force linear in velocity ( -γẋ) and a time-dependent external force ( K(t)). The dissipative system subject to these forces is discussed by introducing the extended Bateman's system, which is described by the Lagrangian: ℒ=mẋẏ-U(x+{1}/{2}y)+U(x-{1}/{2}y)+{γ}/{2}(xẏ-yẋ)-xK(t)+yK(t), which leads to the familiar classical equations of motion for the dissipative (open) system. The equation for a variable y is the time-reversed of the x motion. We discuss the extended Bateman dual Lagrangian and Hamiltonian by setting U(x±y/2)={1}/{2}k( specifically for a dual extended damped-amplified harmonic oscillator subject to the time-dependent external force. We show the method of quantizing such dissipative systems, namely the canonical quantization of the extended Bateman's Hamiltonian ℋ. The Heisenberg equations of motion utilizing the quantized Hamiltonian ℋ̂ surely lead to the equations of motion for the dissipative dynamical quantum systems, which are the quantum analog of the corresponding classical systems. To discuss the stability of the quantum dissipative system due to the influence of an external force K(t) and the dissipative force, we derived a formula for transition amplitudes of the dissipative system with the help of the perturbation analysis. The formula is specifically applied for a damped-amplified harmonic oscillator subject to the impulsive force. This formula is used to study the influence of dissipation such as the instability due to the dissipative force and/or the applied impulsive force.

Tibiofemoral Contact Forces in the Anterior Cruciate Ligament-Reconstructed Knee.

PubMed

Saxby, David John; Bryant, Adam L; Modenese, Luca; Gerus, Pauline; Killen, Bryce A; Konrath, Jason; Fortin, Karine; Wrigley, Tim V; Bennell, Kim L; Cicuttini, Flavia M; Vertullo, Christopher; Feller, Julian A; Whitehead, Tim; Gallie, Price; Lloyd, David G

2016-11-01

To investigate differences in anterior cruciate ligament-reconstructed (ACLR) and healthy individuals in terms of the magnitude of the tibiofemoral contact forces, as well as the relative muscle and external load contributions to those contact forces, during walking, running, and sidestepping gait tasks. A computational EMG-driven neuromusculoskeletal model was used to estimate the muscle and tibiofemoral contact forces in those with single-bundle combined semitendinosus and gracilis tendon autograft ACLR (n = 104, 29.7 ± 6.5 yr, 78.1 ± 14.4 kg) and healthy controls (n = 60, 27.5 ± 5.4 yr, 67.8 ± 14.0 kg) during walking (1.4 ± 0.2 m·s), running (4.5 ± 0.5 m·s) and sidestepping (3.7 ± 0.6 m·s). Within the computational model, the semitendinosus of ACLR participants was adjusted to account for literature reported strength deficits and morphological changes subsequent to autograft harvesting. ACLR had smaller maximum total and medial tibiofemoral contact forces (~80% of control values, scaled to bodyweight) during the different gait tasks. Compared with controls, ACLR were found to have a smaller maximum knee flexion moment, which explained the smaller tibiofemoral contact forces. Similarly, compared with controls, ACLR had both a smaller maximum knee flexion angle and knee flexion excursion during running and sidestepping, which may have concentrated the articular contact forces to smaller areas within the tibiofemoral joint. Mean relative muscle and external load contributions to the tibiofemoral contact forces were not significantly different between ACLR and controls. ACLR had lower bodyweight-scaled tibiofemoral contact forces during walking, running, and sidestepping, likely due to lower knee flexion moments and straighter knee during the different gait tasks. The relative contributions of muscles and external loads to the contact forces were equivalent between groups.

Empirical model of TEC response to geomagnetic and solar forcing over Balkan Peninsula

NASA Astrophysics Data System (ADS)

Mukhtarov, P.; Andonov, B.; Pancheva, D.

2018-01-01

An empirical total electron content (TEC) model response to external forcing over Balkan Peninsula (35°N-50°N; 15°E-30°E) is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 17 years, January 1999 - December 2015. The external forcing includes geomagnetic activity described by the Kp-index and solar activity described by the solar radio flux F10.7. The model describes the most probable spatial distribution and temporal variability of the externally forced TEC anomalies assuming that they depend mainly on latitude, Kp-index, F10.7 and LT. The anomalies are expressed by the relative deviation of the TEC from its 15-day mean, rTEC, as the mean value is calculated from the 15 preceding days. The approach for building this regional model is similar to that of the global TEC model reported by Mukhtarov et al. (2013a) however it includes two important improvements related to short-term variability of the solar activity and amended geomagnetic forcing by using a "modified" Kp index. The quality assessment of the new constructing model procedure in terms of modeling error calculated for the period of 1999-2015 indicates significant improvement in accordance with the global TEC model (Mukhtarov et al., 2013a). The short-term prediction capabilities of the model based on the error calculations for 2016 are improved as well. In order to demonstrate how the model is able to reproduce the rTEC response to external forcing three geomagnetic storms, accompanied also with short-term solar activity variations, which occur at different seasons and solar activity conditions are presented.

Electromagnetic Radiation Reaction in General Relativity.

NASA Astrophysics Data System (ADS)

O'Donnell, Nuala

Available from UMI in association with The British Library. This thesis examines the electromagnetic radiation reaction felt by a charged body falling freely in an external gravitational field in general relativity. The original objective was to find a new derivation of the radiation reaction force F^{i} of DeWitt and DeWitt^1 which was calculated for the special case of a point charge falling in slow motion in a weak, static gravitational field: F ^{i} = {2over 3}e^2R^{i}_{0j0 }v^{j}. This may be thought of as a local expression since it involves the particle's velocity v^{j } and the local Riemann curvature tensor R ^{i}_{0j0}. Its derivation involves integrals over the whole history of the particle, covering distances of approximately the length scale on which R^{i}_{0j0 } changes. This is different from calculations of the Abraham-Lorentz force of flat space-time involving integrals over distances only a few times the size of the charge. This work was motivated by the wish to find a "local" derivation of the local reaction force. Using Schutz's^2 local initial value method to solve the problem of a charged, rigid, spherically symmetric body moving in an external gravitational field of arbitrary metric. Calculations are done in a Riemann normal coordinate system ^3 and are only valid in a normal neighbourhood of the origin, where geodesics have not begun to cross one another. We solve Maxwell's equations for the self -force by making a slow-motion approximation and keeping terms to first order only in the Riemann tensor and velocity. It is surprising that we find no local radiation reaction. Consider two particles in a static spacetime with the same initial conditions at t = 0. Particle A is that of DeWitt and DeWitt; it feels a reaction force F^{i} = {2over 3}e^2R^{i }_{0j0}v^{j}. Particle B is accelerated from rest to the same small velocity; it feels no reaction force. The two particles therefore follow different trajectories. We conclude that there is a certain amount of history dependence in curved spacetime which is absent in flat spacetime where the Abraham-Lorentz reaction force acts equally on both particles. ftn ^1C. M. DeWitt and B. S. Brehme, Falling Charges, Phys., 1, 3 (1964). ^2B. F. Schutz, Statistical Formulation of Gravitational Radiation Reaction, Phys. Rev. D., 22, 249 (1980). ^3See for example A. Z. Petrov, Einstein Spaces, p.33, Pergamon Press (1969).

Assessing the Impact of Earth Radiation Pressure Acceleration on Low-Earth Orbit Satellites

NASA Astrophysics Data System (ADS)

Vielberg, Kristin; Forootan, Ehsan; Lück, Christina; Kusche, Jürgen; Börger, Klaus

2017-04-01

The orbits of satellites are influenced by several external forces. The main non-gravitational forces besides thermospheric drag, acting on the surface of satellites, are accelerations due to the Earth and Solar Radiation Pres- sure (SRP and ERP, respectively). The sun radiates visible and infrared light reaching the satellite directly, which causes the SRP. Earth also emits and reflects the sunlight back into space, where it acts on satellites. This is known as ERP acceleration. The influence of ERP increases with decreasing distance to the Earth, and for low-earth orbit (LEO) satellites ERP must be taken into account in orbit and gravity computations. Estimating acceler- ations requires knowledge about energy emitted from the Earth, which can be derived from satellite remote sensing data, and also by considering the shape and surface material of a satellite. In this sensitivity study, we assess ERP accelerations based on different input albedo and emission fields and their modelling for the satellite missions Challenging Mini-Satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE). As input fields, monthly 1°x1° products of Clouds and the Earth's Radiant En- ergy System (CERES), L3 are considered. Albedo and emission models are generated as latitude-dependent, as well as in terms of spherical harmonics. The impact of different albedo and emission models as well as the macro model and the altitude of satellites on ERP accelerations will be discussed.

Observed and Projected Changes to the Precipitation Annual Cycle

DOE PAGES

Marvel, Kate; Biasutti, Michela; Bonfils, Celine; ...

2017-06-08

Anthropogenic climate change is predicted to cause spatial and temporal shifts in precipitation patterns. These may be apparent in changes to the annual cycle of zonal mean precipitation P. Trends in the amplitude and phase of the P annual cycle in two long-term, global satellite datasets are broadly similar. Model-derived fingerprints of externally forced changes to the amplitude and phase of the P seasonal cycle, combined with these observations, enable a formal detection and attribution analysis. Observed amplitude changes are inconsistent with model estimates of internal variability but not attributable to the model-predicted response to external forcing. This mismatch betweenmore » observed and predicted amplitude changes is consistent with the sustained La Niña–like conditions that characterize the recent slowdown in the rise of the global mean temperature. However, observed changes to the annual cycle phase do not seem to be driven by this recent hiatus. Furthermore these changes are consistent with model estimates of forced changes, are inconsistent (in one observational dataset) with estimates of internal variability, and may suggest the emergence of an externally forced signal.« less

Dynamics of molecular motors with finite processivity on heterogeneous tracks.

PubMed

Kafri, Yariv; Lubensky, David K; Nelson, David R

2005-04-01

The dynamics of molecular motors which occasionally detach from a heterogeneous track like DNA or RNA is considered. Motivated by recent single-molecule experiments, we study a simple model for a motor moving along a disordered track using chemical energy while an external force opposes its motion. The motors also have finite processivity, i.e., they can leave the track with a position-dependent rate. We show that the response of the system to disorder in the hopping-off rate depends on the value of the external force. For most values of the external force, strong disorder causes the motors which survive for long times on the track to be localized at preferred positions. However, near the stall force, localization occurs for any amount of disorder. To obtain these results, we study the complex eigenvalue spectrum of the time evolution operator. Existence of localized states near the top of the band implies a stretched exponential contribution to the decay of the survival probability. A similar spectral analysis also provides a very efficient method for studying the dynamics of motors with infinite processivity.

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

Marvel, Kate; Biasutti, Michela; Bonfils, Celine

Anthropogenic climate change is predicted to cause spatial and temporal shifts in precipitation patterns. These may be apparent in changes to the annual cycle of zonal mean precipitation P. Trends in the amplitude and phase of the P annual cycle in two long-term, global satellite datasets are broadly similar. Model-derived fingerprints of externally forced changes to the amplitude and phase of the P seasonal cycle, combined with these observations, enable a formal detection and attribution analysis. Observed amplitude changes are inconsistent with model estimates of internal variability but not attributable to the model-predicted response to external forcing. This mismatch betweenmore » observed and predicted amplitude changes is consistent with the sustained La Niña–like conditions that characterize the recent slowdown in the rise of the global mean temperature. However, observed changes to the annual cycle phase do not seem to be driven by this recent hiatus. Furthermore these changes are consistent with model estimates of forced changes, are inconsistent (in one observational dataset) with estimates of internal variability, and may suggest the emergence of an externally forced signal.« less

32 CFR 842.110 - Claims not payable.

Code of Federal Regulations, 2013 CFR

2013-07-01

... International Agreements Claims Act. (4) The Air Force Admiralty Claims Act and the Admiralty Extensions Act. (5... National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE CLAIMS AND LITIGATION... providing employee benefits through insurance, local law, or custom and the United States pays for such...

32 CFR 842.110 - Claims not payable.

Code of Federal Regulations, 2010 CFR

2010-07-01

... International Agreements Claims Act. (4) The Air Force Admiralty Claims Act and the Admiralty Extensions Act. (5... National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE CLAIMS AND LITIGATION... providing employee benefits through insurance, local law, or custom and the United States pays for such...

32 CFR 842.110 - Claims not payable.

Code of Federal Regulations, 2012 CFR

2012-07-01

... International Agreements Claims Act. (4) The Air Force Admiralty Claims Act and the Admiralty Extensions Act. (5... National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE CLAIMS AND LITIGATION... providing employee benefits through insurance, local law, or custom and the United States pays for such...

32 CFR 842.110 - Claims not payable.

Code of Federal Regulations, 2014 CFR

2014-07-01

... International Agreements Claims Act. (4) The Air Force Admiralty Claims Act and the Admiralty Extensions Act. (5... National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE CLAIMS AND LITIGATION... providing employee benefits through insurance, local law, or custom and the United States pays for such...

Stabilization of the total force in multi-finger pressing tasks studied with the ‘inverse piano’ technique

PubMed Central

Martin, J.R.; Budgeon, M.K.; Zatsiorsky, V.M.; Latash, M.L.

2010-01-01

When one finger changes its force, other fingers of the hand can show unintended force changes in the same direction (enslaving) and in the opposite direction (error compensation). We tested a hypothesis that externally imposed changes in finger force predominantly lead to error compensation effects in other fingers thus stabilizing the total force. A novel device, the “inverse piano”, was used to impose controlled displacements to one of the fingers over different magnitudes and at different rates. Subjects (n =10) pressed with four fingers at a constant force level and then one of the fingers was unexpectedly raised. The subjects were instructed not to interfere with possible changes in the finger forces. Raising a finger caused an increase in its force and a drop in the force of the other three fingers. Overall, total force showed a small increase. Larger force drops were seen in neighbors of the raised finger (proximity effect). The results show that multi-finger force stabilizing synergies dominate during involuntary reactions to externally imposed finger force changes. Within the referent configuration hypothesis, the data suggest that the instruction “not to interfere” leads to adjustments of the referent coordinates of all the individual fingers. PMID:21450360

Interactions between kinematics and loading during walking for the normal and ACL deficient knee.

PubMed

Andriacchi, Thomas P; Dyrby, Chris O

2005-02-01

The relationships between extrinsic forces acting at the knee and knee kinematics were examined with the purpose of identifying specific phases of the walking cycle that could cause abnormal kinematics in the anterior cruciate ligament (ACL) deficient knee. Intersegmental forces and moments in directions that would produce anterior-posterior (AP) translation, internal-external (IE) rotation and flexion-extension (FE) at the knee were compared with the respective translation and rotations of the tibia relative to the femur during four selected phases (heel strike, weight acceptance, terminal extension and swing) of the walking cycle. The kinematic changes associated with loss of the ACL occurred primarily during the terminal portion of swing phase of the walking cycle where, for the ACL deficient knee, the tibia had reduced external rotation and anterior translation as the knee extended prior to heel strike. The kinematic changes during swing phase were associated with a rotational offset relative to the contralateral knee in the average position of the tibia towards internal rotation. The offset was maintained through the entire gait cycle. The abnormal offsets in the rotational position were correlated with the magnitude of the flexion moment (balanced by a net quadriceps moment) during weight acceptance. These results suggest that adaptations to the patterns of muscle firing during walking can compensate for kinematic changes associated with the loss of the ACL. The altered rotational position would cause changes in tibiofemoral contact during walking that could cause the type of degenerative changes reported in the meniscus and the articular cartilage following ACL injury.

Dynamic mechanical control of local vacancies in NiO thin films

NASA Astrophysics Data System (ADS)

Seol, Daehee; Yang, Sang Mo; Jesse, Stephen; Choi, Minseok; Hwang, Inrok; Choi, Taekjib; Park, Bae Ho; Kalinin, Sergei V.; Kim, Yunseok

2018-07-01

The manipulation of local ionic behavior via external stimuli in oxide systems is of great interest because it can help in directly tuning material properties. Among external stimuli, mechanical force has attracted intriguing attention as novel stimulus for ionic modulation. Even though effectiveness of mechanical force on local ionic modulation has been validated in terms of static effect, its real-time i.e., dynamic, behavior under an application of the force is barely investigated in spite of its crucial impact on device performance such as force or pressure sensors. In this study, we explore dynamic ionic behavior modulated by mechanical force in NiO thin films using electrochemical strain microscopy (ESM). Ionically mediated ESM hysteresis loops were significantly varied under an application of mechanical force. Based on these results, we were able to investigate relative relationship between the force and voltage effects on ionic motion and, further, control effectively ionic behavior through combination of mechanical and electrical stimuli. Our results can provide comprehensive information on the effect of mechanical forces on ionic dynamics in ionic systems.

Dynamic mechanical control of local vacancies in NiO thin films.

PubMed

Seol, Daehee; Yang, Sang Mo; Jesse, Stephen; Choi, Minseok; Hwang, Inrok; Choi, Taekjib; Park, Bae Ho; Kalinin, Sergei V; Kim, Yunseok

2018-07-06

The manipulation of local ionic behavior via external stimuli in oxide systems is of great interest because it can help in directly tuning material properties. Among external stimuli, mechanical force has attracted intriguing attention as novel stimulus for ionic modulation. Even though effectiveness of mechanical force on local ionic modulation has been validated in terms of static effect, its real-time i.e., dynamic, behavior under an application of the force is barely investigated in spite of its crucial impact on device performance such as force or pressure sensors. In this study, we explore dynamic ionic behavior modulated by mechanical force in NiO thin films using electrochemical strain microscopy (ESM). Ionically mediated ESM hysteresis loops were significantly varied under an application of mechanical force. Based on these results, we were able to investigate relative relationship between the force and voltage effects on ionic motion and, further, control effectively ionic behavior through combination of mechanical and electrical stimuli. Our results can provide comprehensive information on the effect of mechanical forces on ionic dynamics in ionic systems.

Dynamic Scaling Theory of the Forced Translocation of a Semi-flexible Polymer Through a Nanopore

NASA Astrophysics Data System (ADS)

Lam, Pui-Man; Zhen, Yi

2015-10-01

We present a theoretical description of the dynamics of a semi-flexible polymer being pulled through a nanopore by an external force acting at the pore. Our theory is based on the tensile blob picture of Pincus in which the front of the tensile force propagates through the backbone of the polymer, as suggested by Sakaue and recently applied to study a completely flexible polymer with self-avoidance, by Dubbledam et al. For a semi-flexible polymer with a persistence length P, its statistics is self-avoiding for a very long chain. As the local force increases, the blob size starts to decrease. At the blob size , where a is the size of a monomer, the statistics becomes that of an ideal chain. As the blob size further decreases to below the persistence length P, the statistics is that of a rigid rod. We argue that semi-flexible polymer in translocation should include the three regions: a self-avoiding region, an ideal chain region and a rigid rod region, under uneven tension propagation, instead of a uniform scaling picture as in the case of a completely flexible polymer. In various regimes under the effect of weak, intermediate and strong driving forces we derive equations from which we can calculate the translocation time of the polymer. The translocation exponent is given by , where is an effective exponent for the end-to-end distance of the semi-flexible polymer, having a value between 1/2 and 3/5, depending on the total contour length of the polymer. Our results are of relevance for forced translocation of biological polymers such as DNA through a nanopore.

Force measurements of a magnetic micro actuator proposed for a microvalve array

NASA Astrophysics Data System (ADS)

Chang, Pauline J.; Chang, Frank W.; Yuen, Michelle C.; Otillar, Robert; Horsley, David A.

2014-03-01

Low-cost, easily-fabricated and power-efficient microvalves are necessary for many microfluidic lab-on-a-chip applications. In this study, we present a simple, low-power, scalable, CMOS-compatible magnetic actuator for microvalve applications composed of a paramagnetic bead as the ball valve over a picoliter reaction well etched into a silicon substrate. The paramagnetic bead, composed of either pure FeSi or magnetite in a SiO2 matrix, is actuated by the local magnetic field gradient generated by a microcoil in an aqueous environment, and the reaction well is situated at the microcoil center. A permanent magnet beneath the microvalve device provides an external magnetic biasing field that magnetizes the bead, enabling bidirectional actuation and reducing the current required to actuate the bead to a level below 10 mA. The vertical and radial magnetic forces exerted on the bead by the microcoil were measured for both pure FeSi and composite beads and agree well with the predictions of 2D axisymmetric finite element method models. Vertical forces were within a range of 13-80 nN, and radial forces were 11-60 nN depending on the bead type. The threshold current required to initiate bead actuation was measured as a function of bead diameter and is found to scale inversely with volume for small beads, as expected based on the magnetic force model. To provide an estimate of the stiction force acting between the bead and the passivation layer on the substrate, repeated actuation trials were used to study the bead throw distance for substrates coated with silicon dioxide, Parylene-C, and photoresist. The stiction observed was lowest for a photoresist-coated substrate, while silicon dioxide and Parylene-C coated substrates exhibited similar levels of stiction.

Coordinated, multi-joint, fatigue-resistant feline stance produced with intrafascicular hind limb nerve stimulation.

PubMed

Normann, R A; Dowden, B R; Frankel, M A; Wilder, A M; Hiatt, S D; Ledbetter, N M; Warren, D A; Clark, G A

2012-04-01

The production of graceful skeletal movements requires coordinated activation of multiple muscles that produce torques around multiple joints. The work described herein is focused on one such movement, stance, that requires coordinated activation of extensor muscles acting around the hip, knee and ankle joints. The forces evoked in these muscles by external stimulation all have a complex dependence on muscle length and shortening velocities, and some of these muscles are biarticular. In order to recreate sit-to-stand maneuvers in the anesthetized feline, we excited the hind limb musculature using intrafascicular multielectrode stimulation (IFMS) of the muscular branch of the sciatic nerve, the femoral nerve and the main branch of the sciatic nerve. Stimulation was achieved with either acutely or chronically implanted Utah Slanted Electrode Arrays (USEAs) via subsets of electrodes (1) that activated motor units in the extensor muscles of the hip, knee and ankle joints, (2) that were able to evoke large extension forces and (3) that manifested minimal coactivation of the targeted motor units. Three hind limb force-generation strategies were investigated, including sequential activation of independent motor units to increase force, and interleaved or simultaneous IFMS of three sets of six or more USEA electrodes that excited the hip, knee and ankle extensors. All force-generation strategies evoked stance, but the interleaved IFMS strategy also reduced muscle fatigue produced by repeated sit-to-stand maneuvers compared with fatigue produced by simultaneous activation of different motor neuron pools. These results demonstrate the use of interleaved IFMS as a means to recreate coordinated, fatigue-resistant multi-joint muscle forces in the unilateral hind limb. This muscle activation paradigm could provide a promising neuroprosthetic approach for the restoration of sit-to-stand transitions in individuals who are paralyzed by spinal cord injury, stroke or disease.

Coordinated, multi-joint, fatigue-resistant feline stance produced with intrafascicular hind limb nerve stimulation

NASA Astrophysics Data System (ADS)

Normann, R. A.; Dowden, B. R.; Frankel, M. A.; Wilder, A. M.; Hiatt, S. D.; Ledbetter, N. M.; Warren, D. A.; Clark, G. A.

2012-04-01

The production of graceful skeletal movements requires coordinated activation of multiple muscles that produce torques around multiple joints. The work described herein is focused on one such movement, stance, that requires coordinated activation of extensor muscles acting around the hip, knee and ankle joints. The forces evoked in these muscles by external stimulation all have a complex dependence on muscle length and shortening velocities, and some of these muscles are biarticular. In order to recreate sit-to-stand maneuvers in the anesthetized feline, we excited the hind limb musculature using intrafascicular multielectrode stimulation (IFMS) of the muscular branch of the sciatic nerve, the femoral nerve and the main branch of the sciatic nerve. Stimulation was achieved with either acutely or chronically implanted Utah Slanted Electrode Arrays (USEAs) via subsets of electrodes (1) that activated motor units in the extensor muscles of the hip, knee and ankle joints, (2) that were able to evoke large extension forces and (3) that manifested minimal coactivation of the targeted motor units. Three hind limb force-generation strategies were investigated, including sequential activation of independent motor units to increase force, and interleaved or simultaneous IFMS of three sets of six or more USEA electrodes that excited the hip, knee and ankle extensors. All force-generation strategies evoked stance, but the interleaved IFMS strategy also reduced muscle fatigue produced by repeated sit-to-stand maneuvers compared with fatigue produced by simultaneous activation of different motor neuron pools. These results demonstrate the use of interleaved IFMS as a means to recreate coordinated, fatigue-resistant multi-joint muscle forces in the unilateral hind limb. This muscle activation paradigm could provide a promising neuroprosthetic approach for the restoration of sit-to-stand transitions in individuals who are paralyzed by spinal cord injury, stroke or disease.

Effect of coating on properties of esthetic orthodontic nickel-titanium wires.

PubMed

Iijima, Masahiro; Muguruma, Takeshi; Brantley, William; Choe, Han-Cheol; Nakagaki, Susumu; Alapati, Satish B; Mizoguchi, Itaru

2012-03-01

To determine the effect of coating on the properties of two esthetic orthodontic nickel-titanium wires. Woowa (polymer coating; Dany Harvest) and BioForce High Aesthetic Archwire (metal coating; Dentsply GAC) with cross-section dimensions of 0.016 × 0.022 inches were selected. Noncoated posterior regions of the anterior-coated Woowa and uncoated Sentalloy were used for comparison. Nominal coating compositions were determined by x-ray fluorescence (JSX-3200, JOEL). Cross-sectioned and external surfaces were observed with a scanning electron microscope (SEM; SSX-550, Shimadzu) and an atomic force microscope (SPM-9500J2, Shimadzu). A three-point bending test (12-mm span) was carried out using a universal testing machine (EZ Test, Shimadzu). Hardness and elastic modulus of external and cross-sectioned surfaces were obtained by nanoindentation (ENT-1100a, Elionix; n  =  10). Coatings on Woowa and BioForce High Aesthetic Archwire contained 41% silver and 14% gold, respectively. The coating thickness on Woowa was approximately 10 µm, and the coating thickness on BioForce High Aesthetic Archwire was much smaller. The surfaces of both coated wires were rougher than the noncoated wires. Woowa showed a higher mean unloading force than the noncoated Woowa, although BioForce High Aesthetic Archwire showed a lower mean unloading force than Sentalloy. While cross-sectional surfaces of all wires had similar hardness and elastic modulus, values for the external surface of Woowa were smaller than for the other wires. The coating processes for Woowa and BioForce High Aesthetic Archwire influence bending behavior and surface morphology.

A many-body dissipative particle dynamics study of forced water-oil displacement in capillary.

PubMed

Chen, Chen; Zhuang, Lin; Li, Xuefeng; Dong, Jinfeng; Lu, Juntao

2012-01-17

The forced water-oil displacement in capillary is a model that has important applications such as the groundwater remediation and the oil recovery. Whereas it is difficult for experimental studies to observe the displacement process in a capillary at nanoscale, the computational simulation is a unique approach in this regard. In the present work, the many-body dissipative particle dynamics (MDPD) method is employed to simulate the process of water-oil displacement in capillary with external force applied by a piston. As the property of all interfaces involved in this system can be manipulated independently, the dynamic displacement process is studied systematically under various conditions of distinct wettability of water in capillary and miscibility between water and oil as well as of different external forces. By analyzing the dependence of the starting force on the properties of water/capillary and water/oil interfaces, we find that there exist two different modes of the water-oil displacement. In the case of stronger water-oil interaction, the water particles cannot displace those oil particles sticking to the capillary wall, leaving a low oil recovery efficiency. To minimize the residual oil content in capillary, enhancing the wettability of water and reducing the external force will be beneficial. This simulation study provides microscopic insights into the water-oil displacement process in capillary and guiding information for relevant applications. © 2011 American Chemical Society

Validation of a scenario-based assessment of critical thinking using an externally validated tool.

PubMed

Buur, Jennifer L; Schmidt, Peggy; Smylie, Dean; Irizarry, Kris; Crocker, Carlos; Tyler, John; Barr, Margaret

2012-01-01

With medical education transitioning from knowledge-based curricula to competency-based curricula, critical thinking skills have emerged as a major competency. While there are validated external instruments for assessing critical thinking, many educators have created their own custom assessments of critical thinking. However, the face validity of these assessments has not been challenged. The purpose of this study was to compare results from a custom assessment of critical thinking with the results from a validated external instrument of critical thinking. Students from the College of Veterinary Medicine at Western University of Health Sciences were administered a custom assessment of critical thinking (ACT) examination and the externally validated instrument, California Critical Thinking Skills Test (CCTST), in the spring of 2011. Total scores and sub-scores from each exam were analyzed for significant correlations using Pearson correlation coefficients. Significant correlations between ACT Blooms 2 and deductive reasoning and total ACT score and deductive reasoning were demonstrated with correlation coefficients of 0.24 and 0.22, respectively. No other statistically significant correlations were found. The lack of significant correlation between the two examinations illustrates the need in medical education to externally validate internal custom assessments. Ultimately, the development and validation of custom assessments of non-knowledge-based competencies will produce higher quality medical professionals.

Ballistic Impact Resistance of Multi-Layer Textile Fabrics

DTIC Science & Technology

1981-10-01

REBOT (NNOLA, NVAR). the first array contains the vector of forces externally applied to the ’ top surface of the layer under consideration, while the...array REBOT (NNOLA, NVAR) contains the forces externally applied to the lower surface of the array. Initially all the elements of each of the two arrays...Qodes in a layer, the contents of array REBOT are now replaced with those of array RETOP in preparation for the repetition of the same calculations for

EEO External Relevant Labor Force Analysis

DTIC Science & Technology

1980-09-01

N 04 .- . / Washington. D.C. 20350 If. CONTROLLING OFFICE NAME AND ADDRESS Navy Personnel Research and Development Center,/, Sentber 1 8 Code 303 N-i...8217Mn. RESEARCH REPORT NO. 37 EEO EXTERNAL RELEVANT LABOR FORCE ANALYSIS D.M. ATWATER R. J. NIEHAUS’ N BY J. A. SHERIDAN ii OFFICE OF THE ASSISTANT...San Diego. CA 92152 86 I4. MONITORING AGENCY NAME & AOORESS(I diflerent ham Controlling ONce.) IS. SECURITY CLASS. (of Ihis report) oA SN (/#/F

Characterisation of acoustic energy content in an experimental combustion chamber with and without external forcing

NASA Astrophysics Data System (ADS)

Webster, S.; Hardi, J.; Oschwald, M.

2015-03-01

The influence of injection conditions on rocket engine combustion stability is investigated for a sub-scale combustion chamber with shear coaxial injection elements and the propellant combination hydrogen-oxygen. The experimental results presented are from a series of tests conducted at subcritical and supercritical pressures for oxygen and for both ambient and cryogenic temperature hydrogen. The stability of the system is characterised by the root mean squared amplitude of dynamic combustion chamber pressure in the upper part of the acoustic spectrum relevant for high frequency combustion instabilities. Results are presented for both unforced and externally forced combustion chamber configurations. It was found that, for both the unforced and externally forced configurations, the injection velocity had the strongest influence on combustion chamber stability. Through the use of multivariate linear regression the influence of hydrogen injection temperature and hydrogen injection mass flow rate were best able to explain the variance in stability for dependence on injection velocity ratio. For unforced tests turbulent jet noise from injection was found to dominate the energy content of the signal. For the externally forced configuration a non-linear regression model was better able to predict the variance, suggesting the influence of non-linear behaviour. The response of the system to variation of injection conditions was found to be small; suggesting that the combustion chamber investigated in the experiment is highly stable.

76 FR 77498 - Privacy Act of 1974; System of Records

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-13

... Force's notices for systems of records subject to the Privacy Act of 1974 (5 U.S.C. 552a), as amended... (HQ USAF/SG), Air Force Medical Service Chief Information Officer's Office (AFMS CIO's office), 5201... Air Force medical facilities. Documentation includes: Patient's medical history, physical examination...

75 FR 48954 - Arbitration Panel Decision Under the Randolph-Sheppard Act

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-12

... and its implementing regulations concerning the food services at Wright-Patterson Air Force Base in... permit to operate snack and beverage vending machines throughout the Wright-Patterson Air Force Base, and... income from the vending machines at the Wright-Patterson Air Force Base pursuant to the Act and...

ESB Clinical Biomechanics Award 2008: Complete data of total knee replacement loading for level walking and stair climbing measured in vivo with a follow-up of 6-10 months.

PubMed

Heinlein, Bernd; Kutzner, Ines; Graichen, Friedmar; Bender, Alwina; Rohlmann, Antonius; Halder, Andreas M; Beier, Alexander; Bergmann, Georg

2009-05-01

Detailed information about the loading of the knee joint is required for various investigations in total knee replacement. Up to now, gait analysis plus analytical musculo-skeletal models were used to calculate the forces and moments acting in the knee joint. Currently, all experimental and numerical pre-clinical tests rely on these indirect measurements which have limitations. The validation of these methods requires in vivo data; therefore, the purpose of this study was to provide in vivo loading data of the knee joint. A custom-made telemetric tibial tray was used to measure the three forces and three moments acting in the implant. This prosthesis was implanted into two subjects and measurements were obtained for a follow-up of 6 and 10 months, respectively. Subjects performed level walking and going up and down stairs using a self-selected comfortable speed. The subjects' activities were captured simultaneously with the load data on a digital video tape. Customized software enabled the display of all information in one video sequence. The highest mean values of the peak load components from the two subjects were as follows: during level walking the forces were 276%BW (percent body weight) in axial direction, 21%BW (medio-lateral), and 29%BW (antero-posterior). The moments were 1.8%BW*m in the sagittal plane, 4.3%BW*m (frontal plane) and 1.0%BW*m (transversal plane). During stair climbing the axial force increased to 306%BW, while the shear forces changed only slightly. The sagittal plane moment increased to 2.4%BW*m, while the frontal and transversal plane moments decreased slightly. Stair descending produced the highest forces of 352%BW (axial), 35%BW (medio-lateral), and 36%BW (antero-posterior). The sagittal and frontal plane moments increased to 2.8%BW*m and 4.6%BW*m, respectively, while the transversal plane moment changed only slightly. Using the data obtained, mechanical simulators can be programmed according to realistic load profiles. Furthermore, musculo-skeletal models can be validated, which until now often lacked the ability to predict properly the non-sagittal load values, e.g. varus-valgus and internal-external moments.

A Basic Study on Countermeasure Against Aerodynamic Force Acting on Train Running Inside Tunnel Using Air Blowing

NASA Astrophysics Data System (ADS)

Suzuki, Masahiro; Nakade, Koji

A basic study of flow controls using air blowing was conducted to reduce unsteady aerodynamic force acting on trains running in tunnels. An air blowing device is installed around a model car in a wind tunnel. Steady and periodic blowings are examined utilizing electromagnetic valves. Pressure fluctuations are measured and the aerodynamic force acting on the car is estimated. The results are as follows: a) The air blowing allows reducing the unsteady aerodynamic force. b) It is effective to blow air horizontally at the lower side of the car facing the tunnel wall. c) The reduction rate of the unsteady aerodynamic force relates to the rate of momentum of the blowing to that of the uniform flow. d) The periodic blowing with the same frequency as the unsteady aerodynamic force reduces the aerodynamic force in a manner similar to the steady blowing.

Regionally dependent summer heat wave response to increased surface temperature in the US

NASA Astrophysics Data System (ADS)

Lopez, H.; Dong, S.; Kirtman, B. P.; Goni, G. J.; Lee, S. K.; Atlas, R. M.; West, R.

2017-12-01

Climate projections for the 21st Century suggest an increase in the occurrence of heat waves. However, the time it takes for the externally forced signal of climate change to emerge against the background of natural variability (i.e., Time of Emergence, ToE) particularly on the regional scale makes reliable future projection of heat waves challenging. Here, we combine observations and model simulations under present and future climate forcing to assess internal variability versus external forcing in modulating US heat waves. We characterized the most common heat wave patterns over the US by the use of clustering of extreme events by their spatial distribution. For each heat wave cluster, we assess changes in the probability density function (PDF) of summer temperature extremes by modeling the PDF as a stochastically generated skewed (SGS) distribution. The probability of necessary causation for each heat wave cluster was also quantified, allowing to make assessments of heat extreme attribution to anthropogenic climate change. The results suggest that internal variability will dominate heat wave occurrence over the Great Plains with ToE occurring in the 2050s (2070s) and of occurrence of ratio of warm-to-cold extremes of 1.7 (1.7) for the Northern (Southern) Plains. In contrast, external forcing will dominate over the Western (Great Lakes) region with ToE occurring as early as in the 2020s (2030s) and warm-to-cold extremes ratio of 6.4 (10.2), suggesting caution in attributing heat extremes to external forcing due to their regional dependence.

Influences of load characteristics on impaired control of grip forces in patients with cerebellar damage.

PubMed

Brandauer, B; Timmann, D; Häusler, A; Hermsdörfer, J

2010-02-01

Various studies showed a clear impairment of cerebellar patients to modulate grip force in anticipation of the loads resulting from movements with a grasped object. This failure corroborated the theory of internal feedforward models in the cerebellum. Cerebellar damage also impairs the coordination of multiple-joint movements and this has been related to deficient prediction and compensation of movement-induced torques. To study the effects of disturbed torque control on feedforward grip-force control, two self-generated load conditions with different demands on torque control-one with movement-induced and the other with isometrically generated load changes-were directly compared in patients with cerebellar degeneration. Furthermore the cerebellum is thought to be more involved in grip-force adjustment to self-generated loads than to externally generated loads. Consequently, an additional condition with externally generated loads was introduced to further test this hypothesis. Analysis of 23 patients with degenerative cerebellar damage revealed clear impairments in predictive feedforward mechanisms in the control of both self-generated load types. Besides feedforward control, the cerebellar damage also affected more reactive responses when the externally generated load destabilized the grip, although this impairment may vary with the type of load as suggested by control experiments. The present findings provide further support that the cerebellum plays a major role in predictive control mechanisms. However, this impact of the cerebellum does not strongly depend on the nature of the load and the specific internal forward model. Contributions to reactive (grip force) control are not negligible, but seem to be dependent on the physical characteristics of an externally generated load.

Propulsion of Active Colloids by Self-Induced Field Gradients.

PubMed

Boymelgreen, Alicia; Yossifon, Gilad; Miloh, Touvia

2016-09-20

Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

Pelvic rotation torque during fast-pitch softball hitting under three ball height conditions.

PubMed

Iino, Yoichi; Fukushima, Atsushi; Kojima, Takeji

2014-08-01

The purpose of this study was to investigate the relevance of hip joint angles to the production of the pelvic rotation torque in fast-pitch softball hitting and to examine the effect of ball height on this production. Thirteen advanced female softball players hit stationary balls at three different heights: high, middle, and low. The pelvic rotation torque, defined as the torque acting on the pelvis through the hip joints about the pelvic superior-inferior axis, was determined from the kinematic and force plate data using inverse dynamics. Irrespective of the ball heights, the rear hip extension, rear hip external rotation, front hip adduction, and front hip flexion torques contributed to the production of pelvic rotation torque. Although the contributions of the adduction and external rotation torques at each hip joint were significantly different among the ball heights, the contributions of the front and rear hip joint torques were similar among the three ball heights owing to cancelation of the two torque components. The timings of the peaks of the hip joint torque components were significantly different, suggesting that softball hitters may need to adjust the timings of the torque exertions fairly precisely to rotate the upper body effectively.

Position and attitude tracking control for a quadrotor UAV.

PubMed

Xiong, Jing-Jing; Zheng, En-Hui

2014-05-01

A synthesis control method is proposed to perform the position and attitude tracking control of the dynamical model of a small quadrotor unmanned aerial vehicle (UAV), where the dynamical model is underactuated, highly-coupled and nonlinear. Firstly, the dynamical model is divided into a fully actuated subsystem and an underactuated subsystem. Secondly, a controller of the fully actuated subsystem is designed through a novel robust terminal sliding mode control (TSMC) algorithm, which is utilized to guarantee all state variables converge to their desired values in short time, the convergence time is so small that the state variables are acted as time invariants in the underactuated subsystem, and, a controller of the underactuated subsystem is designed via sliding mode control (SMC), in addition, the stabilities of the subsystems are demonstrated by Lyapunov theory, respectively. Lastly, in order to demonstrate the robustness of the proposed control method, the aerodynamic forces and moments and air drag taken as external disturbances are taken into account, the obtained simulation results show that the synthesis control method has good performance in terms of position and attitude tracking when faced with external disturbances. Copyright © 2014 ISA. Published by Elsevier Ltd. All rights reserved.

The Financial Sector and Sustainable Development

NASA Astrophysics Data System (ADS)

Rusko, Miroslav; Korauš, Anton

2010-01-01

Growing load and deterioration of the environment can be interpreted as a result of some external effects interventions. While the positive externalities influence the positive productional and utilizational functions of other subjects, the negative externalities influence the negative ones. Both types of external effects can act as parcial or global externalities. Linking the environmental issues to economy and finance is an important sphere. Coimplementation of both marketing and environmental audits is an important element of this sphere too.

Experimental study of forced convective heat transfer from a vertical tube conveying dilute Ag/DI water nanofluids in a cross flow of air

NASA Astrophysics Data System (ADS)

Mohammadian, Shahabeddin Keshavarz; Layeghi, Mohammad; Hemmati, Mansor

2013-03-01

Forced convective heat transfer from a vertical circular tube conveying deionized (DI) water or very dilute Ag-DI water nanofluids (less than 0.02% volume fraction) in a cross flow of air has been investigated experimentally. Some experiments have been performed in a wind tunnel and heat transfer characteristics such as thermal conductance, effectiveness, and external Nusselt number has been measured at different air speeds, liquid flow rates, and nanoparticle concentrations. The cross flow of air over the tube and the liquid flow in the tube were turbulent in all cases. The experimental results have been compared and it has been found that suspending Ag nanoparticles in the base fluid increases thermal conductance, external Nusselt number, and effectiveness. Furthermore, by increasing the external Reynolds number, the external Nusselt number, effectiveness, and thermal conductance increase. Also, by increasing internal Reynolds number, the thermal conductance and external Nusselt number enhance while the effectiveness decreases.

Homodyne detection of short-range Doppler radar using a forced oscillator model

NASA Astrophysics Data System (ADS)

Kittipute, Kunanon; Saratayon, Peerayudh; Srisook, Suthasin; Wardkein, Paramote

2017-03-01

This article presents the homodyne detection in a self-oscillation system, which represented by a short-range radar (SRR) circuit, that is analysed using a multi-time forced oscillator (MTFO) model. The MTFO model is based on a forced oscillation perspective with the signal and system theory, a second-order differential equation, and the multiple time variable technique. This model can also apply to analyse the homodyne phenomenon in a difference kind of the oscillation system under same method such as the self-oscillation system, and the natural oscillation system with external forced. In a free oscillation system, which forced by the external source is represented by a pendulum with an oscillating support experiment, and a modified Colpitts oscillator circuit in the UHF band with input as a Doppler signal is a representative of self-oscillation system. The MTFO model is verified with the experimental result, which well in line with the theoretical analysis.

Recurrence plots revisited

NASA Astrophysics Data System (ADS)

Casdagli, M. C.

1997-09-01

We show that recurrence plots (RPs) give detailed characterizations of time series generated by dynamical systems driven by slowly varying external forces. For deterministic systems we show that RPs of the time series can be used to reconstruct the RP of the driving force if it varies sufficiently slowly. If the driving force is one-dimensional, its functional form can then be inferred up to an invertible coordinate transformation. The same results hold for stochastic systems if the RP of the time series is suitably averaged and transformed. These results are used to investigate the nonlinear prediction of time series generated by dynamical systems driven by slowly varying external forces. We also consider the problem of detecting a small change in the driving force, and propose a surrogate data technique for assessing statistical significance. Numerically simulated time series and a time series of respiration rates recorded from a subject with sleep apnea are used as illustrative examples.

Scattering of accelerated wave packets

NASA Astrophysics Data System (ADS)

Longhi, S.; Horsley, S. A. R.; Della Valle, G.

2018-03-01

Wave-packet scattering from a stationary potential is significantly modified when the wave packet is subject to an external time-dependent force during the interaction. In the semiclassical limit, wave-packet motion is simply described by Newtonian equations, and the external force can, for example, cancel the potential force, making a potential barrier transparent. Here we consider wave-packet scattering from reflectionless potentials, where in general the potential becomes reflective when probed by an accelerated wave packet. In the particular case of the recently introduced class of complex Kramers-Kronig potentials we show that a broad class of time-dependent forces can be applied without inducing any scattering, while there is a breakdown of the reflectionless property when there is a broadband distribution of initial particle momentum, involving both positive and negative components.

Elasto-dynamic analysis of a gear pump-Part IV: Improvement in the pressure distribution modelling

NASA Astrophysics Data System (ADS)

Mucchi, E.; Dalpiaz, G.; Fernàndez del Rincòn, A.

2015-01-01

This work concerns external gear pumps for automotive applications, which operate at high speed and low pressure. In previous works of the authors (Part I and II, [1,2]), a non-linear lumped-parameter kineto-elastodynamic model for the prediction of the dynamic behaviour of external gear pumps was presented. It takes into account the most important phenomena involved in the operation of this kind of machine. The two main sources of noise and vibration are considered: pressure pulsation and gear meshing. The model has been used in order to foresee the influence of working conditions and design modifications on vibration generation. The model experimental validation is a difficult task. Thus, Part III proposes a novel methodology for the validation carried out by the comparison of simulations and experimental results concerning forces and moments: it deals with the external and inertial components acting on the gears, estimated by the model, and the reactions and inertial components on the pump casing and the test plate, obtained by measurements. The validation is carried out by comparing the level of the time synchronous average in the time domain and the waterfall maps in the frequency domain, with particular attention to identify system resonances. The validation results are satisfactory global, but discrepancies are still present. Moreover, the assessed model has been properly modified for the application to a new virtual pump prototype with helical gears in order to foresee gear accelerations and dynamic forces. Part IV is focused on improvements in the modelling and analysis of the phenomena bound to the pressure distribution around the gears in order to achieve results closer to the measured values. As a matter of fact, the simulation results have shown that a variable meshing stiffness has a notable contribution on the dynamic behaviour of the pump but this is not as important as the pressure phenomena. As a consequence, the original model was modified with the aim at improving the calculation of pressure forces and torques. The improved pressure formulation includes several phenomena not considered in the previous one, such as the variable pressure evolution at input and output ports, as well as an accurate description of the trapped volume and its connections with high and low pressure chambers. The importance of these improvements are highlighted by comparison with experimental results, showing satisfactory matching.

Elasto-dynamic analysis of a gear pump-Part III: Experimental validation procedure and model extension to helical gears

NASA Astrophysics Data System (ADS)

Mucchi, E.; Dalpiaz, G.

2015-01-01

This work concerns external gear pumps for automotive applications, which operate at high speed and low pressure. In previous works of the authors (Part I and II, [1,2]), a non-linear lumped-parameter kineto-elastodynamic model for the prediction of the dynamic behaviour of external gear pumps was presented. It takes into account the most important phenomena involved in the operation of this kind of machine. The two main sources of noise and vibration are considered: pressure pulsation and gear meshing. The model has been used in order to foresee the influence of working conditions and design modifications on vibration generation. The model's experimental validation is a difficult task. Thus, Part III proposes a novel methodology for the validation carried out by the comparison of simulations and experimental results concerning forces and moments: it deals with the external and inertial components acting on the gears, estimated by the model, and the reactions and inertial components on the pump casing and the test plate, obtained by measurements. The validation is carried out comparing the level of the time synchronous average in the time domain and the waterfall maps in the frequency domain, with particular attention to identify system resonances. The validation results are satisfactory globally, but discrepancies are still present. Moreover, the assessed model has been properly modified for the application to a new virtual pump prototype with helical gears in order to foresee gear accelerations and dynamic forces. Part IV is focused on improvements in the modelling and analysis of the phenomena bound to the pressure evolution around the gears in order to achieve results closer to the measured values. As a matter of fact, the simulation results have shown that a variable meshing stiffness has a notable contribution on the dynamic behaviour of the pump but this is not as important as the pressure phenomena. As a consequence, the original model was modified with the aim at improving the calculation of pressure forces and torques. The improved pressure formulation includes several phenomena not considered in the previous one, such as the variable pressure evolution at input and output ports, as well as an accurate description of the trapped volume and its connections with high and low pressure chambers. The importance of these improvements are highlighted by comparison with experimental results, showing satisfactory matching.

Characterizing the mechanics of cultured cell monolayers

PubMed Central

Peter, Loic; Bellis, Julien; Baum, Buzz; Kabla, Alexandre J.; Charras, Guillaume T.

2012-01-01

One-cell-thick monolayers are the simplest tissues in multicellular organisms, yet they fulfill critical roles in development and normal physiology. In early development, embryonic morphogenesis results largely from monolayer rearrangement and deformation due to internally generated forces. Later, monolayers act as physical barriers separating the internal environment from the exterior and must withstand externally applied forces. Though resisting and generating mechanical forces is an essential part of monolayer function, simple experimental methods to characterize monolayer mechanical properties are lacking. Here, we describe a system for tensile testing of freely suspended cultured monolayers that enables the examination of their mechanical behavior at multi-, uni-, and subcellular scales. Using this system, we provide measurements of monolayer elasticity and show that this is two orders of magnitude larger than the elasticity of their isolated cellular components. Monolayers could withstand more than a doubling in length before failing through rupture of intercellular junctions. Measurement of stress at fracture enabled a first estimation of the average force needed to separate cells within truly mature monolayers, approximately ninefold larger than measured in pairs of isolated cells. As in single cells, monolayer mechanical properties were strongly dependent on the integrity of the actin cytoskeleton, myosin, and intercellular adhesions interfacing adjacent cells. High magnification imaging revealed that keratin filaments became progressively stretched during extension, suggesting they participate in monolayer mechanics. This multiscale study of monolayer response to deformation enabled by our device provides the first quantitative investigation of the link between monolayer biology and mechanics. PMID:22991459

On the autonomous motion of active drops or bubbles.

PubMed

Ryazantsev, Yuri S; Velarde, Manuel G; Guzman, Eduardo; Rubio, Ramón G; Ortega, Francisco; Montoya, Juan-Jose

2018-05-19

Thermo-capillary stresses on the surface of a drop can be the result of a non-isothermal surface chemical conversion of a reactant dissolved in the host fluid. The strength of heat production (with e.g. absorption) on the surface is ruled by the diffusion of the reactant and depends on the state of motion of the drop. Such thermo-capillary stresses can provoke the motion of the drop or its motionless state in the presence of an external body force. If in the balance of forces, including indeed viscous drag, the net resultant force vanishes there is the possibility of autonomous motion with constant velocity of the drop. Focusing on drops with radii in the millimeter range provided here is a quantitative study of the possibility of such autonomous motion when the drop, considered as active unit, is seat of endo- or exo-thermic reactive processes that dominate its motion. The framework is restricted to Stokes flows in the hydrodynamics, negligible heat Peclet number while the solute Peclet number is considered very high. A boundary layer approximation is used in the description of reactant diffusion. Those processes eventually end up in the action being expressed by surface tension gradients and the Marangoni effect. Explicit expressions of the force acting on the drop and the velocity fields inside and outside the drop are provided. Some significant particular cases are discussed to illustrate the usefulness of the theory. Copyright © 2018. Published by Elsevier Inc.

Muscles that do not cross the knee contribute to the knee adduction moment and tibiofemoral compartment loading during gait.

PubMed

Sritharan, Prasanna; Lin, Yi-Chung; Pandy, Marcus G

2012-10-01

The aims of this study were to evaluate and explain the individual muscle contributions to the medial and lateral knee compartment forces during gait, and to determine whether these quantities could be inferred from their contributions to the external knee adduction moment. Gait data from eight healthy male subjects were used to compute each individual muscle contribution to the external knee adduction moment, the net tibiofemoral joint reaction force, and reaction moment. The individual muscle contributions to the medial and lateral compartment forces were then found using a least-squares approach. While knee-spanning muscles were the primary contributors, non-knee-spanning muscles (e.g., the gluteus medius) also contributed substantially to the medial compartment compressive force. Furthermore, knee-spanning muscles tended to compress both compartments, while most non-knee-spanning muscles tended to compress the medial compartment but unload the lateral compartment. Muscle contributions to the external knee adduction moment, particularly those from knee-spanning muscles, did not accurately reflect their tendencies to compress or unload the medial compartment. This finding may further explain why gait modifications may reduce the knee adduction moment without necessarily decreasing the medial compartment force. Copyright © 2012 Orthopaedic Research Society.

A Managerial Approach to Compensation

ERIC Educational Resources Information Center

Wolfe, Arthur V.

1975-01-01

The article examines the major external forces constraining equitable employee compensation, sets forth the classical employee compensation assumptions, suggests somewhat more realistic employee compensation assumptions, and proposes guidelines based on analysis of these external constraints and assumptions. (Author)

Transition of torque pattern in undulatory locomotion due to wave number variation in resistive force dominated media

NASA Astrophysics Data System (ADS)

Ding, Yang; Ming, Tingyu

2016-11-01

In undulatory locomotion, torque (bending moment) is required along the body to overcome the external forces from environments and bend the body. Previous observations on animals using less than two wavelengths on the body showed such torque has a single traveling wave pattern. Using resistive force theory model and considering the torque generated by external force in a resistive force dominated media, we found that as the wave number (number of wavelengths on the locomotor's body) increases from 0.5 to 1.8, the speed of the traveling wave of torque decreases. When the wave number increases to 2 and greater, the torque pattern transits from a single traveling wave to a two traveling waves and then a complex pattern that consists two wave-like patterns. By analyzing the force distribution and its contribution to the torque, we explain the speed decrease of the torque wave and the pattern transition. This research is partially supported by the Recruitment Program of Global Young Experts (China).

The role of external forcing and Pacific trade winds in recent changes of the global climate system

NASA Astrophysics Data System (ADS)

Friedman, Andrew; Gastineau, Guillaume; Khodri, Myriam

2017-04-01

The Pacific trade winds experienced an unprecedented strengthening since the mid 1990s. Several studies have proposed that the increased Pacific trade winds were associated with the reduced rate of global mean surface temperature warming in the first decade of the 21st century, as well as far-reaching atmospheric teleconnections. We designed a set of ensemble partial coupling experiments using the IPSL-CM5A-LR coupled model that allow us to cleanly distinguish the influence of Pacific trade wind variability from that of external forcing over the past few decades. In this study, we quantify the respective impacts of these processes on surface temperature, ocean heat content, and atmospheric teleconnections. We designed two ensembles of coupled simulations using partial coupling with the IPSL-CM5A-LR model to separate the Pacific internal variability and that of external radiative forcing. We prescribe surface wind stress in the tropical Pacific (20°S to 20°N) from 1979-2014 in two ensembles of 30 members each: (1) Prescribed climatological model wind stress, which allows us to estimate the influence of external radiative forcing in the absence of variability within the Pacific Ocean. (2) Wind stress anomalies from ERA-Interim reanalysis added to the model wind stress climatology, which accounts for the effects of both external radiative forcing and the wind stress variability. We find that the observed wind stress anomalies account for the pattern of eastern tropical Pacific cooling when compared to the climatology experiment, so that it resembles the observed trends from 1992-2011. The tropical Pacific shows dominant heat uptake in the western Pacific above the 20°C isotherm, which contributed to slow the warming of tropical SST during the 2000s. The trade wind increase is associated with a strengthening of the Pacific Walker circulation, and zonal shifts in tropical rainfall. Despite tropical SST biases which affect the response of tropical rainfall and the location of deep convection, the wind stress anomaly forcing effectively simulates the wave train pattern emanating from the tropical Pacific, and associated extratropical teleconnections such as a weakening of the Aleutian Low and drought in North America.

Femoral Component External Rotation Affects Knee Biomechanics: A Computational Model of Posterior-stabilized TKA.

PubMed

Kia, Mohammad; Wright, Timothy M; Cross, Michael B; Mayman, David J; Pearle, Andrew D; Sculco, Peter K; Westrich, Geoffrey H; Imhauser, Carl W

2018-01-01

The correct amount of external rotation of the femoral component during TKA is controversial because the resulting changes in biomechanical knee function associated with varying degrees of femoral component rotation are not well understood. We addressed this question using a computational model, which allowed us to isolate the biomechanical impact of geometric factors including bony shapes, location of ligament insertions, and implant size across three different knees after posterior-stabilized (PS) TKA. Using a computational model of the tibiofemoral joint, we asked: (1) Does external rotation unload the medial collateral ligament (MCL) and what is the effect on lateral collateral ligament tension? (2) How does external rotation alter tibiofemoral contact loads and kinematics? (3) Does 3° external rotation relative to the posterior condylar axis align the component to the surgical transepicondylar axis (sTEA) and what anatomic factors of the femoral condyle explain variations in maximum MCL tension among knees? We incorporated a PS TKA into a previously developed computational knee model applied to three neutrally aligned, nonarthritic, male cadaveric knees. The computational knee model was previously shown to corroborate coupled motions and ligament loading patterns of the native knee through a range of flexion. Implant geometries were virtually installed using hip-to-ankle CT scans through measured resection and anterior referencing surgical techniques. Collateral ligament properties were standardized across each knee model by defining stiffness and slack lengths based on the healthy population. The femoral component was externally rotated from 0° to 9° relative to the posterior condylar axis in 3° increments. At each increment, the knee was flexed under 500 N compression from 0° to 90° simulating an intraoperative examination. The computational model predicted collateral ligament forces, compartmental contact forces, and tibiofemoral internal/external and varus-valgus rotation through the flexion range. The computational model predicted that femoral component external rotation relative to the posterior condylar axis unloads the MCL and the medial compartment; however, these effects were inconsistent from knee to knee. When the femoral component was externally rotated by 9° rather than 0° in knees one, two, and three, the maximum force carried by the MCL decreased a respective 55, 88, and 297 N; the medial contact forces decreased at most a respective 90, 190, and 570 N; external tibial rotation in early flexion increased by a respective 4.6°, 1.1°, and 3.3°; and varus angulation of the tibia relative to the femur in late flexion increased by 8.4°, 8.0°, and 7.9°, respectively. With 3° of femoral component external rotation relative to the posterior condylar axis, the femoral component was still externally rotated by up to 2.7° relative to the sTEA in these three neutrally aligned knees. Variations in MCL force from knee to knee with 3° of femoral component external rotation were related to the ratio of the distances from the femoral insertion of the MCL to the posterior and distal cuts of the implant; the closer this ratio was to 1, the more uniform were the MCL tensions from 0° to 90° flexion. A larger ratio of distances from the femoral insertion of the MCL to the posterior and distal cuts may cause clinically relevant increases in both MCL tension and compartmental contact forces. To obtain more consistent ligament tensions through flexion, it may be important to locate the posterior and distal aspects of the femoral component with respect to the proximal insertion of the MCL such that a ratio of 1 is achieved.

A Parametric Approach to Numerical Modeling of TKR Contact Forces

PubMed Central

Lundberg, Hannah J.; Foucher, Kharma C.; Wimmer, Markus A.

2009-01-01

In vivo knee contact forces are difficult to determine using numerical methods because there are more unknown forces than equilibrium equations available. We developed parametric methods for computing contact forces across the knee joint during the stance phase of level walking. Three-dimensional contact forces were calculated at two points of contact between the tibia and the femur, one on the lateral aspect of the tibial plateau, and one on the medial side. Muscle activations were parametrically varied over their physiologic range resulting in a solution space of contact forces. The obtained solution space was reasonably small and the resulting force pattern compared well to a previous model from the literature for kinematics and external kinetics from the same patient. Peak forces of the parametric model and the previous model were similar for the first half of the stance phase, but differed for the second half. The previous model did not take into account the transverse external moment about the knee and could not calculate muscle activation levels. Ultimately, the parametric model will result in more accurate contact force inputs for total knee simulators, as current inputs are not generally based on kinematics and kinetics inputs from TKR patients. PMID:19155015

Biased and flow driven Brownian motion in periodic channels

NASA Astrophysics Data System (ADS)

Martens, S.; Straube, A.; Schmid, G.; Schimansky-Geier, L.; Hänggi, P.

2012-02-01

In this talk we will present an expansion of the common Fick-Jacobs approximation to hydrodynamically as well as by external forces driven Brownian transport in two-dimensional channels exhibiting smoothly varying periodic cross-section. We employ an asymptotic analysis to the components of the flow field and to stationary probability density for finding the particles within the channel in a geometric parameter. We demonstrate that the problem of biased Brownian dynamics in a confined 2D geometry can be replaced by Brownian motion in an effective periodic one-dimensional potential ψ(x) which takes the external bias, the change of the local channel width, and the flow velocity component in longitudinal direction into account. In addition, we study the influence of the external force magnitude, respectively, the pressure drop of the fluid on the particle transport quantities like the averaged velocity and the effective diffusion coefficient. The critical ratio between the external force and pressure drop where the average velocity equals zero is identified and the dependence of the latter on the channel geometry is derived. Analytic findings are confirmed by numerical simulations of the particle dynamics in a reflection symmetric sinusoidal channel.

Effects of vertically ribbed surface roughness on the forced convective heat losses in central receiver systems

NASA Astrophysics Data System (ADS)

Uhlig, Ralf; Frantz, Cathy; Fritsch, Andreas

2016-05-01

External receiver configurations are directly exposed to ambient wind. Therefore, a precise determination of the convective losses is a key factor in the prediction and evaluation of the efficiency of the solar absorbers. Based on several studies, the forced convective losses of external receivers are modeled using correlations for a roughened cylinder in a cross-flow of air. However at high wind velocities, the thermal efficiency measured during the Solar Two experiment was considerably lower than the efficiency predicted by these correlations. A detailed review of the available literature on the convective losses of external receivers has been made. Three CFD models of different level of detail have been developed to analyze the influence of the actual shape of the receiver and tower configuration, of the receiver shape and of the absorber panels on the forced convective heat transfer coefficients. The heat transfer coefficients deduced from the correlations have been compared to the results of the CFD simulations. In a final step the influence of both modeling approaches on the thermal efficiency of an external tubular receiver has been studied in a thermal FE model of the Solar Two receiver.

76 FR 53421 - Privacy Act of 1974; System of Records

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Two for the Price of One: Integration of NEPA and NHPA Procedures

DTIC Science & Technology

2013-09-01

Air Force Base AFI Air Force Instruction AFPD Air Force Policy Directive AR Army Regulation AT/FP Anti-Terrorism/Force Protection BLM Bureau of...Magnuson-Stevens Fishery Conservation and Management Act NASA National Aeronautics and Space Administration NEPA National Environmental Policy Act...example, the US Forest Service (USFS), US Fish and Wildlife Service (FWS), and Bureau of Land Management ( BLM ) have programs which create military

Multipoles and Force on External Points for a Two-layered Spheroidal Liquid Mass Rotating Differentialy

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

Cisneros-Parra, Joel U.; Martinez-Herrera, Francisco J.; Montalvo-Castro, J. Daniel

We recently reported on a series of equilibrium figures for a self-gravitating heterogeneous liquid body, consisting of two concentric distorted spheroids, “nucleus” and “atmosphere,” each endowed with its own internal motion of differential rotation. In our current work, we calculate the body’s force at external points and obtain a multipolar expansion of the potential. We also give an account of figures with prolate nuclei, which remained unnoticed by us in our former paper.

Nanoscale Mechanism of Composite Reinforcement by Fibers and Filler, Theoretical Computation and Experimental Validation of the Theory Using Rubber/Short Carbon Fiber Compounds

DTIC Science & Technology

2005-06-24

for an adhesion-active surface. 2.8.2 Dupre’s equation Let adhesive interaction between two bodies take place. Dupre’s equation defines the...connection between work of external forces on system of two bodies with adhesive interaction contact, the potential energies these bodies and the energy...Lagrangian of system of two bodies with adhesion interaction is equal half of work of external forces enclosed to this system” With the help of

8 CFR 216.5 - Waiver of requirement to file joint petition to remove conditions by alien spouse.

Code of Federal Regulations, 2013 CFR

2013-01-01

... act or threatened act of violence, including any forceful detention, which results or threatens to..., molestation, incest (if the victim is a minor) or forced prostitution shall be considered acts of violence... from police, judges, medical personnel, school officials and social service agency personnel. The...

8 CFR 216.5 - Waiver of requirement to file joint petition to remove conditions by alien spouse.

Code of Federal Regulations, 2012 CFR

2012-01-01

... act or threatened act of violence, including any forceful detention, which results or threatens to result in physical or mental injury. Psychological or sexual abuse or exploitation, including rape, molestation, incest (if the victim is a minor) or forced prostitution shall be considered acts of violence...

8 CFR 216.5 - Waiver of requirement to file joint petition to remove conditions by alien spouse.

Code of Federal Regulations, 2014 CFR

2014-01-01

... act or threatened act of violence, including any forceful detention, which results or threatens to result in physical or mental injury. Psychological or sexual abuse or exploitation, including rape, molestation, incest (if the victim is a minor) or forced prostitution shall be considered acts of violence...

Visco-Resistive MHD Modeling Benchmark of Forced Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Beidler, M. T.; Hegna, C. C.; Sovinec, C. R.; Callen, J. D.; Ferraro, N. M.

2016-10-01

The presence of externally-applied 3D magnetic fields can affect important phenomena in tokamaks, including mode locking, disruptions, and edge localized modes. External fields penetrate into the plasma and can lead to forced magnetic reconnection (FMR), and hence magnetic islands, on resonant surfaces if the local plasma rotation relative to the external field is slow. Preliminary visco-resistive MHD simulations of FMR in a slab geometry are consistent with theory. Specifically, linear simulations exhibit proper scaling of the penetrated field with resistivity, viscosity, and flow, and nonlinear simulations exhibit a bifurcation from a flow-screened to a field-penetrated, magnetic island state as the external field is increased, due to the 3D electromagnetic force. These results will be compared to simulations of FMR in a circular cross-section, cylindrical geometry by way of a benchmark between the NIMROD and M3D-C1 extended-MHD codes. Because neither this geometry nor the MHD model has the physics of poloidal flow damping, the theory of will be expanded to include poloidal flow effects. The resulting theory will be tested with linear and nonlinear simulations that vary the resistivity, viscosity, flow, and external field. Supported by OFES DoE Grants DE-FG02-92ER54139, DE-FG02-86ER53218, DE-AC02-09CH11466, and the SciDAC Center for Extended MHD Modeling.

Infrastructure Task Force National Environmental Policy Act Requirements - February 2011

EPA Pesticide Factsheets

This document summarizes in a matrix format the federal regulations requirements and guidance for complying with the National Environmental Policy Act for the Infrastructure Task Force federal partner agencies.

Experimental studies of protozoan response to intense magnetic fields and forces

NASA Astrophysics Data System (ADS)

Guevorkian, Karine

Intense static magnetic fields of up to 31 Tesla were used as a novel tool to manipulate the swimming mechanics of unicellular organisms. It is shown that homogenous magnetic fields alter the swimming trajectories of the single cell protozoan Paramecium caudatum, by aligning them parallel to the applied field. Immobile neutrally buoyant paramecia also oriented in magnetic fields with similar rates as the motile ones. It was established that the magneto-orientation is mostly due to the magnetic torques acting on rigid structures in the cell body and therefore the response is a non-biological, passive response. From the orientation rate of paramecia in various magnetic field strengths, the average anisotropy of the diamagnetic susceptibility of the cell was estimated. It has also been demonstrated that magnetic forces can be used to create increased, decreased and even inverted simulated gravity environments for the investigation of the gravi-responses of single cells. Since the mechanisms by which Earth's gravity affects cell functioning are still not fully understood, a number of methods to simulate different strength gravity environments, such as centrifugation, have been employed. Exploiting the ability to exert magnetic forces on weakly diamagnetic constituents of the cells, we were able to vary the gravity from -8 g to 10 g, where g is Earth's gravity. Investigations of the swimming response of paramecia in these simulated gravities revealed that they actively regulate their swimming speed to oppose the external force. This result is in agreement with centrifugation experiments, confirming the credibility of the technique. Moreover, the Paramecium's swimming ceased in simulated gravity of 10 g, indicating a maximum possible propulsion force of 0.7 nN. The magnetic force technique to simulate gravity is the only earthbound technique that can create increased and decreased simulated gravities in the same experimental setup. These findings establish a general technique for applying continuously variable forces to cells or cell populations suitable for exploring their force transduction mechanisms.

A Study on the Effects of J2 Perturbations on a Drag-Free Control System for Spacecraft in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Vess, Melissa Fleck; Starin, Scott R.

2003-01-01

Low Earth Orbit (LEO) missions provide a unique means of gathering information about many of Earth s aspects such as climate, atmosphere, and gravitational field. Among the greatest challenges of LEO missions are designing, predicting, and maintaining the spacecraft orbit. The predominant perturbative forces acting on a spacecraft in LEO are J2 and higher order gravitational components, the effects of which are fairly easy to predict, and atmospheric drag, which causes the greatest uncertainty in predicting spacecraft ephemeris. The continuously varying atmospheric drag requires increased spacecraft tracking in order to accurately predict spacecraft location. In addition, periodic propulsive maneuvers typically must be planned and performed to counteract the effects of drag on the spacecraft orbit. If the effects of drag could be continuously and autonomously counteracted, the uncertainty in ephemeris due to atmospheric drag would essentially be eliminated from the spacecraft dynamics. One method of autonomous drag compensation that has been implemented on some missions is drag-free control. Drag-free control of a spacecraft was initially proposed in the 1960's and is discussed extensively by Lange. His drag-free control architecture consists of a free-floating proof mass enclosed within a spacecraft, isolating it from external disturbance forces such as atmospheric drag and solar radiation pressure. Under ideal conditions, internal disturbance forces can be ignored or mitigated, and the orbit of the proof mass depends only on gravitational forces. A sensor associated with the proof mass senses the movement of the spacecraft relative to the proof mass. Using the sensor measurements, the spacecraft is forced to follow the orbit of the proof mass by using low thrust propulsion, thus counteracting any non-gravitational disturbance forces. If the non-gravitational disturbance forces are successfully removed, the spacecraft s orbit will be affected only by well-known gravitational forces and will thus be easier to predict.

Ponderomotive forces in electrodynamics of moving media: The Minkowski and Abraham approaches

NASA Astrophysics Data System (ADS)

Nesterenko, V. V.; Nesterenko, A. V.

2016-09-01

In the general setting of the problem, the explicit compact formulae are derived for the ponderomotive forces in the macroscopic electrodynamics of moving media in the Minkowski and Abraham approaches. Taking account of the Minkowski constitutive relations and making use of a special representation for the Abraham energy-momentum tensor enable one to obtain a compact expression for the Abraham force in the case of arbitrary dependence of the medium velocity on spatial coordinates and the time and for nonstationary external electromagnetic field. We term the difference between the ponderomotive forces in the Abraham and Minkowski approaches as the Abraham force not only under consideration of media at rest but also in the case of moving media. The Lorentz force is found which is exerted by external electromagnetic field on the conduction current in a medium, the covariant Ohm law, and the constitutive Minkowski relations being taken into account. The physical argumentation is traced for the definition of the 4-vector of the ponderomotive force as the 4-divergence of the energy-momentum tensor of electromagnetic field in a medium.

Locomotor Adaptation to an Asymmetric Force on the Human Pelvis Directed Along the Right Leg.

PubMed

Vashista, Vineet; Martelli, Dario; Agrawal, Sunil

2015-09-11

In this work, we study locomotor adaptation in healthy adults when an asymmetric force vector is applied to the pelvis directed along the right leg. A cable-driven Active Tethered Pelvic Assist Device (A-TPAD) is used to apply an external force on the pelvis, specific to a subject's gait pattern. The force vector is intended to provide external weight bearing during walking and modify the durations of limb supports. The motivation is to use this paradigm to improve weight bearing and stance phase symmetry in individuals with hemiparesis. An experiment with nine healthy subjects was conducted. The results show significant changes in the gait kinematics and kinetics while the healthy subjects developed temporal and spatial asymmetry in gait pattern in response to the applied force vector. This was followed by aftereffects once the applied force vector was removed. The adaptation to the applied force resulted in asymmetry in stance phase timing and lower limb muscle activity. We believe this paradigm, when extended to individuals with hemiparesis, can show improvements in weight bearing capability with positive effects on gait symmetry and walking speed.

Dynamical AdS strings across horizons

DOE PAGES

Ishii, Takaaki; Murata, Keiju

2016-03-01

We examine the nonlinear classical dynamics of a fundamental string in anti-deSitter spacetime. The string is dual to the flux tube between an external quark-antiquark pair in $N = 4$ super Yang-Mills theory. We perturb the string by shaking the endpoints and compute its time evolution numerically. We find that with sufficiently strong perturbations the string continues extending and plunges into the Poincare´ horizon. In the evolution, effective horizons are also dynamically created on the string worldsheet. The quark and antiquark are thus causally disconnected, and the string transitions to two straight strings. The forces acting on the endpoints vanishmore » with a power law whose slope depends on the perturbations. Lastly, the condition for this transition to occur is that energy injection exceeds the static energy between the quark-antiquark pair.« less

Bending and buckling of viscoplastic threads

NASA Astrophysics Data System (ADS)

Hewitt, Ian; Balmforth, Neil

2012-11-01

We use a slender body theory to describe the dynamics of a thin viscoplastic thread undergoing extrusion, such as occurs when squeezing toothpaste from a tube. The theory adopts the Bingham model for a yield stress fluid, together with an asymptotic approximation for the stress and strain-rate profiles across the narrow width of the thread, which imply that the thread must either be rigid or fully yielded across its entire width. A compact description of the resultant longitudinal stress and moment acting on the thread allows these yielded and unyielded regions to be identified for given external forces. The theory is applied to extrusion flows; the yield stress prevents any deformation until a critical length of extrusion is reached, after which the dynamically evolving yielded regions mediate a distinctive drooping of a horizontal beam, or a catastrophic collapse of an upright beam.

Requirements of titanium alloys for aeronautical industry

NASA Astrophysics Data System (ADS)

Ghiban, Brânduşa; Bran, Dragoş-Teodor; Elefterie, Cornelia Florina

2018-02-01

The project presents the requirements imposed for aeronatical components made from Titanium based alloys. Asignificant portion of the aircraft pylons are manufactured from Titanium alloys. Strength, weight, and reliability are the primary factors to consider in aircraft structures. These factors determine the requirements to be met by any material used to construct or repair the aircraft. Many forces and structural stresses act on an aircraft when it is flying and when it is static and this thesis describes environmental factors, conditions of external aggression, mechanical characteristics and loadings that must be satisfied simultaneously by a Ti-based alloy, compared to other classes of aviation alloys (as egg. Inconel super alloys, Aluminum alloys). For this alloy class, the requirements are regarding strength to weight ratio, reliability, corrosion resistance, thermal expansion and so on. These characteristics additionally continue to provide new opportunities for advanced manufacturing methods.

Aeronautical Industry Requirements for Titanium Alloys

NASA Astrophysics Data System (ADS)

Bran, D. T.; Elefterie, C. F.; Ghiban, B.

2017-06-01

The project presents the requirements imposed for aviation components made from Titanium based alloys. A significant portion of the aircraft pylons are manufactured from Titanium alloys. Strength, weight, and reliability are the primary factors to consider in aircraft structures. These factors determine the requirements to be met by any material used to construct or repair the aircraft. Many forces and structural stresses act on an aircraft when it is flying and when it is static and this thesis describes environmental factors, conditions of external aggression, mechanical characteristics and loadings that must be satisfied simultaneously by a Ti-based alloy, compared to other classes of aviation alloys (as egg. Inconel super alloys, Aluminum alloys).For this alloy class, the requirements are regarding strength to weight ratio, reliability, corrosion resistance, thermal expansion and so on. These characteristics additionally continue to provide new opportunities for advanced manufacturing methods.

Spontaneous mentalizing predicts the fundamental attribution error.

PubMed

Moran, Joseph M; Jolly, Eshin; Mitchell, Jason P

2014-03-01

When explaining the reasons for others' behavior, perceivers often overemphasize underlying dispositions and personality traits over the power of the situation, a tendency known as the fundamental attribution error. One possibility is that this bias results from the spontaneous processing of others' mental states, such as their momentary feelings or more enduring personality characteristics. Here, we use fMRI to test this hypothesis. Participants read a series of stories that described a target's ambiguous behavior in response to a specific social situation and later judged whether that act was attributable to the target's internal dispositions or to external situational factors. Neural regions consistently associated with mental state inference-especially, the medial pFC-strongly predicted whether participants later made dispositional attributions. These results suggest that the spontaneous engagement of mentalizing may underlie the biased tendency to attribute behavior to dispositional over situational forces.

Macroscopic self-reorientation of interacting two-dimensional crystals

PubMed Central

Woods, C. R.; Withers, F.; Zhu, M. J.; Cao, Y.; Yu, G.; Kozikov, A.; Ben Shalom, M.; Morozov, S. V.; van Wijk, M. M.; Fasolino, A.; Katsnelson, M. I.; Watanabe, K.; Taniguchi, T.; Geim, A. K.; Mishchenko, A.; Novoselov, K. S.

2016-01-01

Microelectromechanical systems, which can be moved or rotated with nanometre precision, already find applications in such fields as radio-frequency electronics, micro-attenuators, sensors and many others. Especially interesting are those which allow fine control over the motion on the atomic scale because of self-alignment mechanisms and forces acting on the atomic level. Such machines can produce well-controlled movements as a reaction to small changes of the external parameters. Here we demonstrate that, for the system of graphene on hexagonal boron nitride, the interplay between the van der Waals and elastic energies results in graphene mechanically self-rotating towards the hexagonal boron nitride crystallographic directions. Such rotation is macroscopic (for graphene flakes of tens of micrometres the tangential movement can be on hundreds of nanometres) and can be used for reproducible manufacturing of aligned van der Waals heterostructures. PMID:26960435

From strings to coils: Rotational dynamics of DNA-linked colloidal chains

NASA Astrophysics Data System (ADS)

Kuei, Steve; Garza, Burke; Biswal, Sibani Lisa

2017-10-01

We investigate the dynamical behavior of deformable filaments experimentally using a tunable model system consisting of linked paramagnetic colloidal particles, where the persistence length lp, the contour length lc, and the strength and frequency of the external driving force are controlled. We find that upon forcing by an external magnetic field, a variety of structural and conformational regimes exist. Depending on the competition of forces and torques on the chain, we see classic rigid rotator behavior, as well as dynamically rich wagging, coiling, and folding behavior. Through a combination of experiments, computational models, and theoretical calculations, we are able to observe, classify, and predict these dynamics as a function of the dimensionless Mason and magnetoelastic numbers.

Stress Response of Granular Systems

NASA Astrophysics Data System (ADS)

Ramola, Kabir; Chakraborty, Bulbul

2017-10-01

We develop a framework for stress response in two dimensional granular media, with and without friction, that respects vector force balance at the microscopic level. We introduce local gauge degrees of freedom that determine the response of contact forces between constituent grains on a given, disordered, contact network, to external perturbations. By mapping this response to the spectral properties of the graph Laplacian corresponding to the underlying contact network, we show that this naturally leads to spatial localization of forces. We present numerical evidence for localization using exact diagonalization studies of network Laplacians of soft disk packings. Finally, we discuss the role of other constraints, such as torque balance, in determining the stability of a granular packing to external perturbations.

Decreased knee adduction moment does not guarantee decreased medial contact force during gait.

PubMed

Walter, Jonathan P; D'Lima, Darryl D; Colwell, Clifford W; Fregly, Benjamin J

2010-10-01

Excessive contact force is believed to contribute to the development of medial compartment knee osteoarthritis. The external knee adduction moment (KAM) has been identified as a surrogate measure for medial contact force during gait, with an abnormally large peak value being linked to increased pain and rate of disease progression. This study used in vivo gait data collected from a subject with a force-measuring knee implant to assess whether KAM decreases accurately predict corresponding decreases in medial contact force. Changes in both quantities generated via gait modification were analyzed statistically relative to the subject's normal gait. The two gait modifications were a "medial thrust" gait involving knee medialization during stance phase and a "walking pole" gait involving use of bilateral walking poles. Reductions in the first (largest) peak of the KAM (32-33%) did not correspond to reductions in the first peak of the medial contact force. In contrast, reductions in the second peak and angular impulse of the KAM (15-47%) corresponded to reductions in the second peak and impulse of the medial contact force (12-42%). Calculated reductions in both KAM peaks were highly sensitive to rotation of the shank reference frame about the superior-inferior axis of the shank. Both peaks of medial contact force were best predicted by a combination of peak values of the external KAM and peak absolute values of the external knee flexion moment (R(2) = 0.93). Future studies that evaluate the effectiveness of gait modifications for offloading the medial compartment of the knee should consider the combined effect of these two knee moments. Published by Wiley Periodicals, Inc. J Orthop Res 28:1348-1354, 2010.

On the discrepancy between observed and CMIP5 multi-model simulated Barents Sea winter sea ice decline

NASA Astrophysics Data System (ADS)

Li, Dawei; Zhang, Rong; Knutson, Thomas R.

2017-04-01

This study aims to understand the relative roles of external forcing versus internal climate variability in causing the observed Barents Sea winter sea ice extent (SIE) decline since 1979. We identify major discrepancies in the spatial patterns of winter Northern Hemisphere sea ice concentration trends over the satellite period between observations and CMIP5 multi-model mean externally forced response. The CMIP5 externally forced decline in Barents Sea winter SIE is much weaker than that observed. Across CMIP5 ensemble members, March Barents Sea SIE trends have little correlation with global mean surface air temperature trends, but are strongly anti-correlated with trends in Atlantic heat transport across the Barents Sea Opening (BSO). Further comparison with control simulations from coupled climate models suggests that enhanced Atlantic heat transport across the BSO associated with regional internal variability may have played a leading role in the observed decline in winter Barents Sea SIE since 1979.

The QBO and weak external forcing by solar activity: A three dimensional model study

NASA Technical Reports Server (NTRS)

Dameris, M.; Ebel, A.

1989-01-01

A better understanding is attempted of the physical mechanisms leading to significant correlations between oscillations in the lower and middle stratosphere and solar variability associated with the sun's rotation. A global 3-d mechanistic model of the middle atmosphere is employed to investigate the effects of minor artificially induced perturbations. The aim is to explore the physical mechanisms of the dynamical response especially of the stratosphere to weak external forcing as it may result from UV flux changes due to solar rotation. First results of numerical experiments dealing about the external forcing of the middle atmosphere by solar activity were presented elsewhere. Different numerical studies regarding the excitation and propagation of weak perturbations have been continued since then. The model calculations presented are made to investigate the influence of the quasi-biennial oscillation (QBO) on the dynamical response of the middle atmosphere to weak perturbations by employing different initial wind fields which represent the west and east phase of the QBO.

Regimes of Flow over Complex Structures of Endothelial Glycocalyx: A Molecular Dynamics Simulation Study.

PubMed

Jiang, Xi Zhuo; Feng, Muye; Ventikos, Yiannis; Luo, Kai H

2018-04-10

Flow patterns on surfaces grafted with complex structures play a pivotal role in many engineering and biomedical applications. In this research, large-scale molecular dynamics (MD) simulations are conducted to study the flow over complex surface structures of an endothelial glycocalyx layer. A detailed structure of glycocalyx has been adopted and the flow/glycocalyx system comprises about 5,800,000 atoms. Four cases involving varying external forces and modified glycocalyx configurations are constructed to reveal intricate fluid behaviour. Flow profiles including temporal evolutions and spatial distributions of velocity are illustrated. Moreover, streamline length and vorticity distributions under the four scenarios are compared and discussed to elucidate the effects of external forces and glycocalyx configurations on flow patterns. Results show that sugar chain configurations affect streamline length distributions but their impact on vorticity distributions is statistically insignificant, whilst the influence of the external forces on both streamline length and vorticity distributions are trivial. Finally, a regime diagram for flow over complex surface structures is proposed to categorise flow patterns.

78 FR 5789 - Privacy Act of 1974; System of Records

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-28

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Passive levitation in alternating magnetic fields

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

Romero, Louis; Christenson, Todd; Aronson, Eugene A.

2010-09-14

Stable levitation of an object in an alternating magnetic field can be achieved by eliminating coupling between the rotational and translational forces acting on the object. Stable levitation can also be achieved by varying the coupling between the rotational and translational forces acting on the object, while maintaining one or more of the rotational and translational forces steady in time.

Passive levitation in alternating magnetic fields

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

Romero, Louis; Christenson, Todd; Aronson, Eugene A

2009-06-16

Stable levitation of an object in an alternating magnetic field can be achieved by eliminating coupling between the rotational and translational forces acting on the object. Stable levitation can also be achieved by varying the coupling between the rotational and translational forces acting on the object, while maintaining one or more of the rotational and translational forces steady in time.

76 FR 11213 - Privacy Act of 1974; System of Records

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2011-03-01

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Self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers.

PubMed

Wittkowski, Raphael; Löwen, Hartmut

2012-02-01

Recently the Brownian dynamics of self-propelled (active) rodlike particles was explored to model the motion of colloidal microswimmers, catalytically driven nanorods, and bacteria. Here we generalize this description to biaxial particles with arbitrary shape and derive the corresponding Langevin equation for a self-propelled Brownian spinning top. The biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low Reynolds numbers, to fluctuating random forces and torques as well as to an external and an internal (effective) force and torque. The latter quantities control its self-propulsion. Due to biaxiality and hydrodynamic translational-rotational coupling, the Langevin equation can only be solved numerically. In the special case of an orthotropic particle in the absence of external forces and torques, the noise-free (zero-temperature) trajectory is analytically found to be a circular helix. This trajectory is confirmed numerically to be more complex in the general case of an arbitrarily shaped particle under the influence of arbitrary forces and torques involving a transient irregular motion before ending up in a simple periodic motion. By contrast, if the external force vanishes, no transient regime is found, and the particle moves on a superhelical trajectory. For orthotropic particles, the noise-averaged trajectory is a generalized concho-spiral. We furthermore study the reduction of the model to two spatial dimensions and classify the noise-free trajectories completely finding circles, straight lines with and without transients, as well as cycloids and arbitrary periodic trajectories. © 2012 American Physical Society

76 FR 10010 - Privacy Act of 1974; System of Records

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-23

... inventory of records systems subject to the Privacy Act of 1974, (5 U.S.C. 552a), as amended. DATES: The...: The Department of the Air Force systems of records notices subject to the Privacy Act of 1974, (5 U.S... 78150-7412 and at Military Personnel Sections at Air Force Installations. Official mailing addresses are...

Impact of internal variability on projections of Sahel precipitation change

NASA Astrophysics Data System (ADS)

Monerie, Paul-Arthur; Sanchez-Gomez, Emilia; Pohl, Benjamin; Robson, Jon; Dong, Buwen

2017-11-01

The impact of the increase of greenhouse gases on Sahelian precipitation is very uncertain in both its spatial pattern and magnitude. In particular, the relative importance of internal variability versus external forcings depends on the time horizon considered in the climate projection. In this study we address the respective roles of the internal climate variability versus external forcings on Sahelian precipitation by using the data from the CESM Large Ensemble Project, which consists of a 40 member ensemble performed with the CESM1-CAM5 coupled model for the period 1920-2100. We show that CESM1-CAM5 is able to simulate the mean and interannual variability of Sahel precipitation, and is representative of a CMIP5 ensemble of simulations (i.e. it simulates the same pattern of precipitation change along with equivalent magnitude and seasonal cycle changes as the CMIP5 ensemble mean). However, CESM1-CAM5 underestimates the long-term decadal variability in Sahel precipitation. For short-term (2010-2049) and mid-term (2030-2069) projections the simulated internal variability component is able to obscure the projected impact of the external forcing. For long-term (2060-2099) projections external forcing induced change becomes stronger than simulated internal variability. Precipitation changes are found to be more robust over the central Sahel than over the western Sahel, where climate change effects struggle to emerge. Ten (thirty) members are needed to separate the 10 year averaged forced response from climate internal variability response in the western Sahel for a long-term (short-term) horizon. Over the central Sahel two members (ten members) are needed for a long-term (short-term) horizon.

Cytoplasmic motion induced by cytoskeleton stretching and its effect on cell mechanics.

PubMed

Zhang, T

2011-09-01

Cytoplasmic motion assumed as a steady state laminar flow induced by cytoskeleton stretching in a cell is determined and its effect on the mechanical behavior of the cell under externally applied forces is demonstrated. Non-Newtonian fluid is assumed for the multiphase cytoplasmic fluid and the analytical velocity field around the macromolecular chain is obtained by solving the reduced nonlinear momentum equation using homotopy technique. The entropy generation by the fluid internal friction is calculated and incorporated into the entropic elasticity based 8-chain constitutive relations. Numerical examples showed strengthening behavior of cells in response to externally applied mechanical stimuli. The spatial distribution of the stresses within a cell under externally applied fluid flow forces were also studied.

Load identification approach based on basis pursuit denoising algorithm

NASA Astrophysics Data System (ADS)

Ginsberg, D.; Ruby, M.; Fritzen, C. P.

2015-07-01

The information of the external loads is of great interest in many fields of structural analysis, such as structural health monitoring (SHM) systems or assessment of damage after extreme events. However, in most cases it is not possible to measure the external forces directly, so they need to be reconstructed. Load reconstruction refers to the problem of estimating an input to a dynamic system when the system output and the impulse response functions are usually the knowns. Generally, this leads to a so called ill-posed inverse problem, which involves solving an underdetermined linear system of equations. For most practical applications it can be assumed that the applied loads are not arbitrarily distributed in time and space, at least some specific characteristics about the external excitation are known a priori. In this contribution this knowledge was used to develop a more suitable force reconstruction method, which allows identifying the time history and the force location simultaneously by employing significantly fewer sensors compared to other reconstruction approaches. The properties of the external force are used to transform the ill-posed problem into a sparse recovery task. The sparse solution is acquired by solving a minimization problem known as basis pursuit denoising (BPDN). The possibility of reconstructing loads based on noisy structural measurement signals will be demonstrated by considering two frequently occurring loading conditions: harmonic excitation and impact events, separately and combined. First a simulation study of a simple plate structure is carried out and thereafter an experimental investigation of a real beam is performed.

Relationship of forces acting on implant rods and degree of scoliosis correction.

PubMed

Salmingo, Remel Alingalan; Tadano, Shigeru; Fujisaki, Kazuhiro; Abe, Yuichiro; Ito, Manabu

2013-02-01

Adolescent idiopathic scoliosis is a complex spinal pathology characterized as a three-dimensional spine deformity combined with vertebral rotation. Various surgical techniques for correction of severe scoliotic deformity have evolved and became more advanced in applying the corrective forces. The objective of this study was to investigate the relationship between corrective forces acting on deformed rods and degree of scoliosis correction. Implant rod geometries of six adolescent idiopathic scoliosis patients were measured before and after surgery. An elasto-plastic finite element model of the implant rod before surgery was reconstructed for each patient. An inverse method based on Finite Element Analysis was used to apply forces to the implant rod model such that it was deformed the same after surgery. Relationship between the magnitude of corrective forces and degree of correction expressed as change of Cobb angle was evaluated. The effects of screw configuration on the corrective forces were also investigated. Corrective forces acting on rods and degree of correction were not correlated. Increase in number of implant screws tended to decrease the magnitude of corrective forces but did not provide higher degree of correction. Although greater correction was achieved with higher screw density, the forces increased at some level. The biomechanics of scoliosis correction is not only dependent to the corrective forces acting on implant rods but also associated with various parameters such as screw placement configuration and spine stiffness. Considering the magnitude of forces, increasing screw density is not guaranteed as the safest surgical strategy. Copyright © 2012 Elsevier Ltd. All rights reserved.

Is the thumb a fifth finger? A study of digit interaction during force production tasks

PubMed Central

Olafsdottir, Halla; Zatsiorsky, Vladimir M.; Latash, Mark L.

2010-01-01

We studied indices of digit interaction in single- and multi-digit maximal voluntary contraction (MVC) tests when the thumb acted either in parallel or in opposition to the fingers. The peak force produced by the thumb was much higher when the thumb acted in opposition to the fingers and its share of the total force in the five-digit MVC test increased dramatically. The fingers showed relatively similar peak forces and unchanged sharing patterns in the four-finger MVC task when the thumb acted in parallel and in opposition to the fingers. Enslaving during one-digit tasks showed relatively mild differences between the two conditions, while the differences became large when enslaving was quantified for multi-digit tasks. Force deficit was pronounced when the thumb acted in parallel to the fingers; it showed a monotonic increase with the number of explicitly involved digits up to four digits and then a drop when all five digits were involved. Force deficit all but disappeared when the thumb acted in opposition to the fingers. However, for both thumb positions, indices of digit interaction were similar for groups of digits that did or did not include the thumb. These results suggest that, given a certain hand configuration, the central nervous system treats the thumb as a fifth finger. They provide strong support for the hypothesis that indices of digit interaction reflect neural factors, not the peripheral design of the hand. An earlier formal model was able to account for the data when the thumb acted in parallel to the fingers. However, it failed for the data with the thumb acting in opposition to the fingers. PMID:15322785

78 FR 8193 - Sunshine Act Meeting; Audit Committee Meeting of the Board of Directors

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-05

... Corporate Secretary (202) 220-2376; [email protected] . AGENDA: I. Call to Order II. External Auditors' Presentation III. Executive Session with External Auditors IV. Executive Session: Audit Committee V. Executive...

Internal or external whistleblowing: nurses' willingness to report wrongdoing.

PubMed

Mansbach, Abraham; Bachner, Yaacov G

2010-07-01

In Israel, whistleblowing in the nursing profession has been largely ignored. This topic is neither part of the professional-ethical discourse nor a subject for research. Focusing on the divide between internal and external whistleblowing, this article presents a study that explores nurses' willingness to disclose an act that could jeopardize the rights or safety of patients. Internal disclosure entails reporting wrongdoing to an authority within the organization. External disclosure involves reporting the offense to an outside agency, such as a professional organization or the press. The study's findings indicate that the nurse respondents viewed both the harmful misconduct of a colleague and that of a manager as being very serious. In such dilemmas the nurses reported a desire to correct the wrongdoing and a concomitant willingness to act. They were, however, much more likely to whistleblow internally rather than externally. This study revealed a pattern of nurses' progressive retraction as the circle of disclosure widened.

The Association Between Callous-Unemotional Traits, Externalizing Problems, and Gender in Predicting Cognitive and Affective Morality Judgments in Adolescence.

PubMed

Fragkaki, Iro; Cima, Maaike; Meesters, Cor

2016-09-01

Morality deficits have been linked to callous-unemotional traits and externalizing problems in response to moral dilemmas, but these associations are still obscure in response to antisocial acts in adolescence. Limited evidence on young boys suggested that callous-unemotional traits and externalizing problems were associated with affective but not cognitive morality judgments. The present study investigated these associations in a community sample of 277 adolescents (M age  = 15.35, 64 % females). Adolescents with high callous-unemotional traits showed deficits in affective but not cognitive morality, indicating that they can identify the appropriate moral emotions in others, but experience deviant moral emotions when imagining themselves committing antisocial acts. Externalizing problems and male gender were also strongly related to deficits in affective morality, but they had smaller associations with deficits in cognitive morality too. Implications for treatment and the justice system are discussed.

Magnetic Torque in Single Crystal Ni-Mn-Ga

NASA Astrophysics Data System (ADS)

Hobza, Anthony; Müllner, Peter

2017-06-01

Magnetic shape memory alloys deform in an external magnetic field in two distinct ways: by axial straining—known as magnetic-field-induced strain—and by bending when exposed to torque. Here, we examine the magnetic torque that a magnetic field exerts on a long Ni-Mn-Ga rod. A single crystal specimen of Ni-Mn-Ga was constrained with respect to bending and subjected to an external magnetic field. The torque required to rotate the specimen in the field was measured as a function of the orientation of the sample with the external magnetic field, strain, and the magnitude of the external magnetic field. The torque was analyzed based on the changes in the free energy with the angle between the field and the sample. The contributions of magnetocrystalline anisotropy and shape anisotropy to the Zeeman energy determine the net torque. The torque is large when magneotcrystalline and shape anisotropies act synergistically and small when these anisotropies act antagonistically.

A dynamic load estimation method for nonlinear structures with unscented Kalman filter

NASA Astrophysics Data System (ADS)

Guo, L. N.; Ding, Y.; Wang, Z.; Xu, G. S.; Wu, B.

2018-02-01

A force estimation method is proposed for hysteretic nonlinear structures. The equation of motion for the nonlinear structure is represented in state space and the state variable is augmented by the unknown the time history of external force. Unscented Kalman filter (UKF) is improved for the force identification in state space considering the ill-condition characteristic in the computation of square roots for the covariance matrix. The proposed method is firstly validated by a numerical simulation study of a 3-storey nonlinear hysteretic frame excited by periodic force. Each storey is supposed to follow a nonlinear hysteretic model. The external force is identified and the measurement noise is considered in this case. Then a case of a seismically isolated building subjected to earthquake excitation and impact force is studied. The isolation layer performs nonlinearly during the earthquake excitation. Impact force between the seismically isolated structure and the retaining wall is estimated with the proposed method. Uncertainties such as measurement noise, model error in storey stiffness and unexpected environmental disturbances are considered. A real-time substructure testing of an isolated structure is conducted to verify the proposed method. In the experimental study, the linear main structure is taken as numerical substructure while the one of the isolations with additional mass is taken as the nonlinear physical substructure. The force applied by the actuator on the physical substructure is identified and compared with the measured value from the force transducer. The method proposed in this paper is also validated by shaking table test of a seismically isolated steel frame. The acceleration of the ground motion as the unknowns is identified by the proposed method. Results from both numerical simulation and experimental studies indicate that the UKF based force identification method can be used to identify external excitations effectively for the nonlinear structure with accurate results even with measurement noise, model error and environmental disturbances.

Internal-external malalignment of the femoral component in kinematically aligned total knee arthroplasty increases tibial force imbalance but does not change laxities of the tibiofemoral joint.

PubMed

Riley, Jeremy; Roth, Joshua D; Howell, Stephen M; Hull, Maury L

2018-06-01

The purposes of this study were to quantify the increase in tibial force imbalance (i.e. magnitude of difference between medial and lateral tibial forces) and changes in laxities caused by  2° and 4° of internal-external (I-E) malalignment of the femoral component in kinematically aligned total knee arthroplasty. Because I-E malalignment would introduce the greatest changes to the articular surfaces near 90° of flexion, the hypotheses were that the tibial force imbalance would be significantly increased near 90° flexion and that primarily varus-valgus laxity would be affected near 90° flexion. Kinematically aligned TKA was performed on ten human cadaveric knee specimens using disposable manual instruments without soft tissue release. One 3D-printed reference femoral component, with unmodified geometry, was aligned to restore the native distal and posterior femoral joint lines. Four 3D-printed femoral components, with modified geometry, introduced I-E malalignments of 2° and 4° from the reference component. Medial and lateral tibial forces were measured from 0° to 120° flexion using a custom tibial force sensor. Bidirectional laxities in four degrees of freedom were measured from 0° to 120° flexion using a custom load application system. Tibial force imbalance increased the greatest at 60° flexion where a regression analysis against the degree of I-E malalignment yielded sensitivities (i.e. slopes) of 30 N/° (medial tibial force > lateral tibial force) and 10 N/° (lateral tibial force > medial tibial force) for internal and external malalignments, respectively. Valgus laxity increased significantly with the 4° external component with the greatest increase of 1.5° occurring at 90° flexion (p < 0.0001). With the tibial component correctly aligned, I-E malalignment of the femoral component caused significant increases in tibial force imbalance. Minimizing I-E malalignment lowers the increase in the tibial force imbalance. By keeping the resection thickness of each posterior femoral condyle to within ± 0.5 mm of the thickness of the respective posterior region of the femoral component, the increase in imbalance can be effectively limited to 38 N. Generally laxities were unaffected within the ± 4º range tested indicating that instability is not a clinical concern and that manual testing of laxities is not useful to detect I-E malalignment.

Hydrodynamic investigation of a self-propelled robotic fish based on a force-feedback control method.

PubMed

Wen, L; Wang, T M; Wu, G H; Liang, J H

2012-09-01

We implement a mackerel (Scomber scombrus) body-shaped robot, programmed to display the three most typical body/caudal fin undulatory kinematics (i.e. anguilliform, carangiform and thunniform), in order to biomimetically investigate hydrodynamic issues not easily tackled experimentally with live fish. The robotic mackerel, mounted on a servo towing system and initially at rest, can determine its self-propelled speed by measuring the external force acting upon it and allowing for the simultaneous measurement of power, flow field and self-propelled speed. Experimental results showed that the robotic swimmer with thunniform kinematics achieved a faster final swimming speed (St = 0.424) relative to those with carangiform (St = 0.43) and anguilliform kinematics (St = 0.55). The thrust efficiency, estimated from a digital particle image velocimetry (DPIV) flow field, showed that the robotic swimmer with thunniform kinematics is more efficient (47.3%) than those with carangiform (31.4%) and anguilliform kinematics (26.6%). Furthermore, the DPIV measurements illustrate that the large-scale characteristics of the flow pattern generated by the robotic swimmer with both anguilliform and carangiform kinematics were wedge-like, double-row wake structures. Additionally, a typical single-row reverse Karman vortex was produced by the robotic swimmer using thunniform kinematics. Finally, we discuss this novel force-feedback-controlled experimental method, and review the relative self-propelled hydrodynamic results of the robot when utilizing the three types of undulatory kinematics.

Effects of comprehensive function of factors on retention behavior of microparticles in gravitational field-flow fractionation.

PubMed

Guo, Shuang; Qiu, Bai-Ling; Zhu, Chen-Qi; Yang, Ya-Ya Gao; Wu, Di; Liang, Qi-Hui; Han, Nan-Yin

2016-09-15

Gravitational field-flow fractionation (GrFFF) is a useful technique for separation and characterization for micrometer-sized particles. Elution behavior of micrometer-sized particles in GrFFF was researched in this study. Particles in GrFFF channel are subject to hydrodynamic lift forces (HLF), fluid inertial forces and gravity, which drive them to different velocities by carrier flow, resulting in a size-based separation. Effects of ionic strength, flow rate and viscosity as well as methanol were investigated using polystyrene latex beads as model particles. This study is devoted to experimental verification of the effect of every factor and their comprehensive function. All experiments were performed to show isolated influence of every variable factor. The orthogonal design test was used to evaluate various factors comprehensively. Results suggested that retention ratio of particles increases with increasing flow rate or the viscosity of carrier liquid by adjusting external forces acting on particles. In addition, retention ratio increases as ionic strength decreases because of decreased electrostatic repulsion between particles and channel accumulation wall. As far as methanol, there is no general trend due to the change of both density and viscosity. On the basis of orthogonal design test it was found that viscosity of carrier liquid plays a significant role in determining resolution of micrometer-sized particles in GrFFF. Copyright © 2016 Elsevier B.V. All rights reserved.

Validation of a dynamic linked segment model to calculate joint moments in lifting.

PubMed

de Looze, M P; Kingma, I; Bussmann, J B; Toussaint, H M

1992-08-01

A two-dimensional dynamic linked segment model was constructed and applied to a lifting activity. Reactive forces and moments were calculated by an instantaneous approach involving the application of Newtonian mechanics to individual adjacent rigid segments in succession. The analysis started once at the feet and once at a hands/load segment. The model was validated by comparing predicted external forces and moments at the feet or at a hands/load segment to actual values, which were simultaneously measured (ground reaction force at the feet) or assumed to be zero (external moments at feet and hands/load and external forces, beside gravitation, at hands/load). In addition, results of both procedures, in terms of joint moments, including the moment at the intervertebral disc between the fifth lumbar and first sacral vertebra (L5-S1), were compared. A correlation of r = 0.88 between calculated and measured vertical ground reaction forces was found. The calculated external forces and moments at the hands showed only minor deviations from the expected zero level. The moments at L5-S1, calculated starting from feet compared to starting from hands/load, yielded a coefficient of correlation of r = 0.99. However, moments calculated from hands/load were 3.6% (averaged values) and 10.9% (peak values) higher. This difference is assumed to be due mainly to erroneous estimations of the positions of centres of gravity and joint rotation centres. The estimation of the location of L5-S1 rotation axis can affect the results significantly. Despite the numerous studies estimating the load on the low back during lifting on the basis of linked segment models, only a few attempts to validate these models have been made. This study is concerned with the validity of the presented linked segment model. The results support the model's validity. Effects of several sources of error threatening the validity are discussed. Copyright © 1992. Published by Elsevier Ltd.

Extracting Leading Nonlinear Modes of Changing Climate From Global SST Time Series

NASA Astrophysics Data System (ADS)

Mukhin, D.; Gavrilov, A.; Loskutov, E. M.; Feigin, A. M.; Kurths, J.

2017-12-01

Data-driven modeling of climate requires adequate principal variables extracted from observed high-dimensional data. For constructing such variables it is needed to find spatial-temporal patterns explaining a substantial part of the variability and comprising all dynamically related time series from the data. The difficulties of this task rise from the nonlinearity and non-stationarity of the climate dynamical system. The nonlinearity leads to insufficiency of linear methods of data decomposition for separating different processes entangled in the observed time series. On the other hand, various forcings, both anthropogenic and natural, make the dynamics non-stationary, and we should be able to describe the response of the system to such forcings in order to separate the modes explaining the internal variability. The method we present is aimed to overcome both these problems. The method is based on the Nonlinear Dynamical Mode (NDM) decomposition [1,2], but takes into account external forcing signals. An each mode depends on hidden, unknown a priori, time series which, together with external forcing time series, are mapped onto data space. Finding both the hidden signals and the mapping allows us to study the evolution of the modes' structure in changing external conditions and to compare the roles of the internal variability and forcing in the observed behavior. The method is used for extracting of the principal modes of SST variability on inter-annual and multidecadal time scales accounting the external forcings such as CO2, variations of the solar activity and volcanic activity. The structure of the revealed teleconnection patterns as well as their forecast under different CO2 emission scenarios are discussed.[1] Mukhin, D., Gavrilov, A., Feigin, A., Loskutov, E., & Kurths, J. (2015). Principal nonlinear dynamical modes of climate variability. Scientific Reports, 5, 15510. [2] Gavrilov, A., Mukhin, D., Loskutov, E., Volodin, E., Feigin, A., & Kurths, J. (2016). Method for reconstructing nonlinear modes with adaptive structure from multidimensional data. Chaos: An Interdisciplinary Journal of Nonlinear Science, 26(12), 123101.

Measuring Air Force Contracting Customer Satisfaction

DTIC Science & Technology

2015-12-01

NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA MBA PROFESSIONAL REPORT MEASURING AIR FORCE CONTRACTING CUSTOMER SATISFACTION ...... satisfaction elements should be included in a standardized tool that measures the level of customer satisfaction for AF Contracting’s external and

Distribution of sup 3 H-proline within transseptal fibers of the rat following release of orthodontic forces

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

Row, K.L.; Johnson, R.B.

1990-10-01

Maxillary right first molar teeth of rats were tipped mesially with an orthodontic appliance for 2 weeks (experimental group), {sup 3}H-proline was injected, and orthodontic forces were removed 6 hr later (time 0). The contralateral molar teeth of treated (internal control group) and age- and weight-matched untreated animals (external control group) were also studied. Diastemata were created between the molar teeth by the orthodontic appliance, and transseptal fibers between first and second (P less than 0.001) and second and third molars (P less than 0.005) were significantly lengthened as compared to external and internal controls at time 0. Diastemata betweenmore » molar teeth were closed 5 days after removal of orthodontic force. Transseptal fibers adjacent to the source of the orthodontic force (mesial region) had the highest mean number of {sup 3}H-proline-labeled proteins at time 0 and at all times following removal of the force (P less than 0.001), and had the highest rate of labeled protein removal (P less than 0.001). Half-lives for removal of 3H-proline-labeled transseptal fiber proteins were significantly greater in mesial and distal regions and significantly less in middle regions of experimentals than in corresponding regions of external controls (P less than 0.001).« less

Cross-field diffusion in Hall thrusters and other plasma thrusters

NASA Astrophysics Data System (ADS)

Boeuf, J. P.

2012-10-01

Understanding and quantifying electron transport perpendicular to the magnetic field is a challenge in many low temperature plasma applications. Hall effect thrusters (HETs) provide an excellent example of cross-field transport. The HET is a very successful concept that can be considered both as a gridless ion source and an electromagnetic thruster. In HETs, the electric field E accelerating the ions is a consequence of the Lorentz force due to an external magnetic field B acting on the ExB Hall electron current. An essential aspect of HETs is that the ExB drift is closed, i.e. is in the azimuthal direction of a cylindrical channel. In the first part of this presentation we will discuss the physics of cross-field electron transport in HETs, and the current understanding (or non-understanding) of the possible role of turbulence and wall collisions on cross-field diffusion. We will also briefly comment on alternative designs of ion sources based on the same principles as the conventional HET (Anode Layer Thruster, Diverging Cusp Field Thrusters, End-Hall ion sources). In a second part of the presentation we show that the Lorentz force acting on diamagnetic currents (associated with the ∇PexB term in the electron momentum equation) can also provide thrust. This is the case for example in helicon thrusters where the plasma expands in a magnetic nozzle. We will report and discuss recent work on helicon thrusters and other devices where the diamagnetic current is dominant (with some examples where the ∇PexB current is not closed and is directed toward a wall!).

The optimal neural strategy for a stable motor task requires a compromise between level of muscle cocontraction and synaptic gain of afferent feedback

PubMed Central

Dideriksen, Jakob L.; Negro, Francesco

2015-01-01

Increasing joint stiffness by cocontraction of antagonist muscles and compensatory reflexes are neural strategies to minimize the impact of unexpected perturbations on movement. Combining these strategies, however, may compromise steadiness, as elements of the afferent input to motor pools innervating antagonist muscles are inherently negatively correlated. Consequently, a high afferent gain and active contractions of both muscles may imply negatively correlated neural drives to the muscles and thus an unstable limb position. This hypothesis was systematically explored with a novel computational model of the peripheral nervous system and the mechanics of one limb. Two populations of motor neurons received synaptic input from descending drive, spinal interneurons, and afferent feedback. Muscle force, simulated based on motor unit activity, determined limb movement that gave rise to afferent feedback from muscle spindles and Golgi tendon organs. The results indicated that optimal steadiness was achieved with low synaptic gain of the afferent feedback. High afferent gains during cocontraction implied increased levels of common drive in the motor neuron outputs, which were negatively correlated across the two populations, constraining instability of the limb. Increasing the force acting on the joint and the afferent gain both effectively minimized the impact of an external perturbation, and suboptimal adjustment of the afferent gain could be compensated by muscle cocontraction. These observations show that selection of the strategy for a given contraction implies a compromise between steadiness and effectiveness of compensations to perturbations. This indicates that a task-dependent selection of neural strategy for steadiness is necessary when acting in different environments. PMID:26203102

Collaborating with EPA through the Federal Technology Transfer Act

EPA Pesticide Factsheets

Under the Federal Technology Transfer Act (FTTA), EPA can collaborate with external parties on research projects, and share research materials. Learn more about the types of partnerships the EPA offers.

Externalizing disorders: cluster 5 of the proposed meta-structure for DSM-V and ICD-11.

PubMed

Krueger, R F; South, S C

2009-12-01

The extant major psychiatric classifications DSM-IV and ICD-10 are purportedly atheoretical and largely descriptive. Although this achieves good reliability, the validity of a medical diagnosis is greatly enhanced by an understanding of the etiology. In an attempt to group mental disorders on the basis of etiology, five clusters have been proposed. We consider the validity of the fifth cluster, externalizing disorders, within this proposal. We reviewed the literature in relation to 11 validating criteria proposed by the Study Group of the DSM-V Task Force, in terms of the extent to which these criteria support the idea of a coherent externalizing spectrum of disorders. This cluster distinguishes itself by the central role of disinhibitory personality in mental disorders spread throughout sections of the current classifications, including substance dependence, antisocial personality disorder and conduct disorder. Shared biomarkers, co-morbidity and course offer additional evidence for a valid cluster of externalizing disorders. Externalizing disorders meet many of the salient criteria proposed by the Study Group of the DSM-V Task Force to suggest a classification cluster.

Newton's Law: Not so Simple after All

ERIC Educational Resources Information Center

Robertson, William C.; Gallagher, Jeremiah; Miller, William

2004-01-01

One of the most basic concepts related to force and motion is Newton's first law, which essentially states, "An object at rest tends to remain at rest unless acted on by an unbalanced force. An object in motion in a straight line tends to remain in motion in a straight line unless acted upon by an unbalanced force." Judging by the time and space…

Physical driving force of actomyosin motility based on the hydration effect.

PubMed

Suzuki, Makoto; Mogami, George; Ohsugi, Hideyuki; Watanabe, Takahiro; Matubayasi, Nobuyuki

2017-12-01

We propose a driving force hypothesis based on previous thermodynamics, kinetics and structural data as well as additional experiments and calculations presented here on water-related phenomena in the actomyosin systems. Although Szent-Györgyi pointed out the importance of water in muscle contraction in 1951, few studies have focused on the water science of muscle because of the difficulty of analyzing hydration properties of the muscle proteins, actin, and myosin. The thermodynamics and energetics of muscle contraction are linked to the water-mediated regulation of protein-ligand and protein-protein interactions along with structural changes in protein molecules. In this study, we assume the following two points: (1) the periodic electric field distribution along an actin filament (F-actin) is unidirectionally modified upon binding of myosin subfragment 1 (M or myosin S1) with ADP and inorganic phosphate Pi (M.ADP.Pi complex) and (2) the solvation free energy of myosin S1 depends on the external electric field strength and the solvation free energy of myosin S1 in close proximity to F-actin can become the potential force to drive myosin S1 along F-actin. The first assumption is supported by integration of experimental reports. The second assumption is supported by model calculations utilizing molecular dynamics (MD) simulation to determine solvation free energies of a small organic molecule and two small proteins. MD simulations utilize the energy representation method (ER) and the roughly proportional relationship between the solvation free energy and the solvent-accessible surface area (SASA) of the protein. The estimated driving force acting on myosin S1 is as high as several piconewtons (pN), which is consistent with the experimentally observed force. © 2017 Wiley Periodicals, Inc.

Extended state observer-based motion synchronisation control for hybrid actuation system of large civil aircraft

NASA Astrophysics Data System (ADS)

Wang, Xingjian; Shi, Cun; Wang, Shaoping

2017-07-01

Hybrid actuation system with dissimilar redundant actuators, which is composed of a hydraulic actuator (HA) and an electro-hydrostatic actuator (EHA), has been applied on modern civil aircraft to improve the reliability. However, the force fighting problem arises due to different dynamic performances between HA and EHA. This paper proposes an extended state observer (ESO)-based motion synchronisation control method. To cope with the problem of unavailability of the state signals, the well-designed ESO is utilised to observe the HA and EHA state variables which are unmeasured. In particular, the extended state of ESO can estimate the lumped effect of the unknown external disturbances acting on the control surface, the nonlinear dynamics, uncertainties, and the coupling term between HA and EHA. Based on the observed states of ESO, motion synchronisation controllers are presented to make HA and EHA to simultaneously track the desired motion trajectories, which are generated by a trajectory generator. Additionally, the unknown disturbances and the coupling terms can be compensated by using the extended state of the proposed ESO. Finally, comparative simulation results indicate that the proposed ESO-based motion synchronisation controller can achieve great force fighting reduction between HA and EHA.

Deformations of a pre-stretched and lubricated finite elastic membrane driven by non-uniform external forcing

NASA Astrophysics Data System (ADS)

Boyko, Evgeniy; Gat, Amir; Bercovici, Moran

2017-11-01

We study viscous-elastic dynamics of a fluid confined between a rigid plate and a finite pre-stretched circular elastic membrane, pinned at its boundaries. The membrane is subjected to forces acting either directly on the membrane or through a pressure distribution in the fluid. Under the assumptions of strong pre-stretching and small deformations of the elastic sheet, and by applying the lubrication approximation for the flow, we derive the Green's function for the resulting linearized 4th order diffusion equation governing the deformation field in cylindrical coordinates. In addition, defining an asymptotic expansion with the ratio of the induced to prescribed tension serving as the small parameter, we reduce the coupled Reynolds and non-linear von-Karman equations to a set of three one-way coupled linear equations. The solutions to these equations provide insight onto the effects of induced tension, and enable simplified prediction of the correction for the deformation field. Funded by the European Research Council (ERC) under the European Union'sHorizon 2020 Research and Innovation Programme, Grant Agreement No. 678734 (MetamorphChip). E.B. is supported by the Adams Fellowship Program.

Stretch-induced contraction in pulmonary arteries.

PubMed

Kulik, T J; Evans, J N; Gamble, W J

1988-12-01

Stretch stimulates contraction of systemic blood vessels, but the response has not been described in pulmonary vessels. To determine whether pulmonary arteries contract when stretched, isolated cylindrical segments of pulmonary arteries were suspended between two parallel wires, stretched, and the active force was generated in response to stretch measured. Eighty-nine percent of segments from small (in situ diameter less than 1,000 microns) feline pulmonary arteries contracted when stretched, and in 65% of these the magnitude of stretch was related to the magnitude of contraction. Large (in situ diameter greater than or equal to 1,000 microns) feline pulmonary arteries did not contract with stretch. Multiple, rapidly repeated stretches resulted in a diminution of active force development. Stretch-induced contraction required external Ca2+ and was abolished by diltiazem (10 microns), but it was not affected by phenoxybenzamine, phentolamine, diethylcarbamazine, or mechanical removal of endothelium. Indomethacin blunted but did not abolish stretch-induced contraction, an effect that may have been nonspecific. This study suggests that stretch can act, probably directly, on smooth muscle in small feline pulmonary arteries to elicit contraction and that it may be a determinant of pulmonary vascular tone. In addition, feline pulmonary arteries are suitable for the in vitro study of stretch-induced contraction.

Lumbar spinal loads and muscle activity during a golf swing.

PubMed

Lim, Young-Tae; Chow, John W; Chae, Woen-Sik

2012-06-01

This study estimated the lumbar spinal loads at the L4-L5 level and evaluated electromyographic (EMG) activity of right and left rectus abdominis, external and internal obliques, erector spinae, and latissimus dorsi muscles during a golf swing. Four super VHS camcorders and two force plates were used to obtain three-dimensional (3D) kinematics and kinetics of golf swings performed by five male collegiate golfers. Average EMG levels for different phases of golf swing were determined. An EMG-assisted optimization model was applied to compute the contact forces acting on the L4-L5. The results revealed a mean peak compressive load of over six times the body weight (BW) during the downswing and mean peak anterior and medial shear loads approaching 1.6 and 0.6 BW during the follow-through phases. The peak compressive load estimated in this study was high, but less than the corresponding value (over 8 BW) reported by a previous study. Average EMG levels of different muscles were the highest in the acceleration and follow-through phases, suggesting a likely link between co-contractions of paraspinal muscles and lumbar spinal loads.

77 FR 6595 - Notice of Sunshine Act Meeting; Audit Committee of the Board of Directors

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-08

..., Assistant Corporate Secretary (202) 220-2376; [email protected] . AGENDA: I. CALL TO ORDER II. External Auditor's Presentation III. Executive Session with External Auditors IV. Executive Session with Internal Audit Director V...

Balancing a force on the fingertip of a two-dimensional finger model without intrinsic muscles.

PubMed

Spoor, C W

1983-01-01

A slightly flexed human middle finger can balance an external force on the fingertip. Internal stabilization is also possible, which means that the externally unloaded finger can be kept stiff. We want to analyse whether in these situations the intrinsic hand muscles are needed. Distances from tendons to flexion axes are taken from the literature and are substituted in the moment equilibrium equations of a two-dimensional finger model. Diagrams illustrate the statically indeterminate problem of solving tendon forces. The possibilities for equilibrium without intrinsics appear to depend mainly on four tendon-to-joint distances. These distances determine to which of two groups a finger belongs: (1) one in which intrinsics are not necessary for internal stabilization nor for balancing a force on the fingertip in any direction in the sagittal plane; (2) one in which, without intrinsics, internal stabilization is impossible and only dorso-distally directed forces on the fingertip can be balanced.

Corporate funding and conflicts of interest: a primer for psychologists.

PubMed

Pachter, Wendy S; Fox, Ronald E; Zimbardo, Philip; Antonuccio, David O

2007-12-01

A presidential task force on external funding was established by the American Psychological Association (APA) in 2003 to review APA policies, procedures, and practices regarding the acceptance of funding and support from private corporations for educational and training programs; continuing education offerings; research projects; publications; advertising; scientific and professional meetings and conferences; and consulting, practice, and advocacy relationships. This article, based on the Executive Summary of the APA Task Force on External Funding Final Report, presents the findings and unanimous recommendations of the task force in the areas of association income, annual convention, research and journals, continuing education, education, practice, and conflicts of interest and ethics. The task force concluded that it is important for both APA and individual psychologists to become familiar with the challenges that corporate funding can pose to their integrity. The nature and extent of those challenges led the task force to recommend that APA develop explicit policies, educational materials, and continuing education programs to preserve the independence of psychological science, practice, and education. (Copyright) 2007 APA.

Stress Transmission in Granular Packings: Localization and Cooperative Response

NASA Astrophysics Data System (ADS)

Ramola, Kabir

We develop a framework for stress transmission in two dimensional granular media that respects vector force balance at the microscopic level. For a packing of grains interacting via pairwise contact forces, we introduce local gauge degrees of freedom that determine the response of the system to external perturbations. This allows us to construct unique force-balanced solutions that determine the change in contact forces as a response to external stress. By mapping this response to diffusion in the underlying contact network, we show that this naturally leads to spatial localization of forces. We present numerical evidence for stress localization using exact diagonalization studies of network Laplacians associated with soft disk packings. We use this formalism to characterize the deviation from elastic behaviour as the amount of disorder in the underlying network is varied. We discuss generalizations to systems with large friction between grains and other networks that display topological disorder. This work has been supported by NSF-DMR 1409093 and the W. M. Keck Foundation.

Combination of Universal Mechanical Testing Machine with Atomic Force Microscope for Materials Research

PubMed Central

Zhong, Jian; He, Dannong

2015-01-01

Surface deformation and fracture processes of materials under external force are important for understanding and developing materials. Here, a combined horizontal universal mechanical testing machine (HUMTM)-atomic force microscope (AFM) system is developed by modifying UMTM to combine with AFM and designing a height-adjustable stabilizing apparatus. Then the combined HUMTM-AFM system is evaluated. Finally, as initial demonstrations, it is applied to analyze the relationship among macroscopic mechanical properties, surface nanomorphological changes under external force, and fracture processes of two kinds of representative large scale thin film materials: polymer material with high strain rate (Parafilm) and metal material with low strain rate (aluminum foil). All the results demonstrate the combined HUMTM-AFM system overcomes several disadvantages of current AFM-combined tensile/compression devices including small load force, incapability for large scale specimens, disability for materials with high strain rate, and etc. Therefore, the combined HUMTM-AFM system is a promising tool for materials research in the future. PMID:26265357

Combination of Universal Mechanical Testing Machine with Atomic Force Microscope for Materials Research.

PubMed

Zhong, Jian; He, Dannong

2015-08-12

Surface deformation and fracture processes of materials under external force are important for understanding and developing materials. Here, a combined horizontal universal mechanical testing machine (HUMTM)-atomic force microscope (AFM) system is developed by modifying UMTM to combine with AFM and designing a height-adjustable stabilizing apparatus. Then the combined HUMTM-AFM system is evaluated. Finally, as initial demonstrations, it is applied to analyze the relationship among macroscopic mechanical properties, surface nanomorphological changes under external force, and fracture processes of two kinds of representative large scale thin film materials: polymer material with high strain rate (Parafilm) and metal material with low strain rate (aluminum foil). All the results demonstrate the combined HUMTM-AFM system overcomes several disadvantages of current AFM-combined tensile/compression devices including small load force, incapability for large scale specimens, disability for materials with high strain rate, and etc. Therefore, the combined HUMTM-AFM system is a promising tool for materials research in the future.

Homodyne detection of short-range Doppler radar using a forced oscillator model

PubMed Central

Kittipute, Kunanon; Saratayon, Peerayudh; Srisook, Suthasin; Wardkein, Paramote

2017-01-01

This article presents the homodyne detection in a self-oscillation system, which represented by a short-range radar (SRR) circuit, that is analysed using a multi-time forced oscillator (MTFO) model. The MTFO model is based on a forced oscillation perspective with the signal and system theory, a second-order differential equation, and the multiple time variable technique. This model can also apply to analyse the homodyne phenomenon in a difference kind of the oscillation system under same method such as the self-oscillation system, and the natural oscillation system with external forced. In a free oscillation system, which forced by the external source is represented by a pendulum with an oscillating support experiment, and a modified Colpitts oscillator circuit in the UHF band with input as a Doppler signal is a representative of self-oscillation system. The MTFO model is verified with the experimental result, which well in line with the theoretical analysis. PMID:28252000

Study of hydrodynamic characteristics of a Sharp Eagle wave energy converter

NASA Astrophysics Data System (ADS)

Zhang, Ya-qun; Sheng, Song-wei; You, Ya-ge; Huang, Zhen-xin; Wang, Wen-sheng

2017-06-01

According to Newton's Second Law and the microwave theory, mechanical analysis of multiple buoys which form Sharp Eagle wave energy converter (WEC) is carried out. The movements of every buoy in three modes couple each other when they are affected with incident waves. Based on the above, mechanical models of the WEC are established, which are concerned with fluid forces, damping forces, hinge forces, and so on. Hydrodynamic parameters of one buoy are obtained by taking the other moving buoy as boundary conditions. Then, by taking those hydrodynamic parameters into the mechanical models, the optimum external damping and optimal capture width ratio are calculated out. Under the condition of the optimum external damping, a plenty of data are obtained, such as the displacements amplitude of each buoy in three modes (sway, heave, pitch), damping forces, hinge forces, and speed of the hydraulic cylinder. Research results provide theoretical references and basis for Sharp Eagle WECs in the design and manufacture.

Tug of war in motility assay experiments

NASA Astrophysics Data System (ADS)

Hexner, Daniel; Kafri, Yariv

2009-09-01

The dynamics of two groups of molecular motors pulling in opposite directions on a rigid filament is studied theoretically. To this end we first consider the behavior of one set of motors pulling in a single direction against an external force using a new mean-field approach. Based on these results we analyze a similar setup with two sets of motors pulling in opposite directions in a tug of war in the presence of an external force. In both cases we find that the interplay of fluid friction and protein friction leads to a complex phase diagram where the force-velocity relations can exhibit regions of bistability and spontaneous symmetry breaking. Finally, motivated by recent work, we turn to the case of motility assay experiments where motors bound to a surface push on a bundle of filaments. We find that, depending on the absence or the presence of bistability in the force-velocity curve at zero force, the bundle exhibits anomalous or biased diffusion on long-time and large-length scales.

Single molecule force measurements of perlecan/HSPG2: A key component of the osteocyte pericellular matrix.

PubMed

Wijeratne, Sithara S; Martinez, Jerahme R; Grindel, Brian J; Frey, Eric W; Li, Jingqiang; Wang, Liyun; Farach-Carson, Mary C; Kiang, Ching-Hwa

2016-03-01

Perlecan/HSPG2, a large, monomeric heparan sulfate proteoglycan (HSPG), is a key component of the lacunar canalicular system (LCS) of cortical bone, where it is part of the mechanosensing pericellular matrix (PCM) surrounding the osteocytic processes and serves as a tethering element that connects the osteocyte cell body to the bone matrix. Within the pericellular space surrounding the osteocyte cell body, perlecan can experience physiological fluid flow drag force and in that capacity function as a sensor to relay external stimuli to the osteocyte cell membrane. We previously showed that a reduction in perlecan secretion alters the PCM fiber composition and interferes with bone's response to a mechanical loading in vivo. To test our hypothesis that perlecan core protein can sustain tensile forces without unfolding under physiological loading conditions, atomic force microscopy (AFM) was used to capture images of perlecan monomers at nanoscale resolution and to perform single molecule force measurement (SMFMs). We found that the core protein of purified full-length human perlecan is of suitable size to span the pericellular space of the LCS, with a measured end-to-end length of 170±20 nm and a diameter of 2-4 nm. Force pulling revealed a strong protein core that can withstand over 100 pN of tension well over the drag forces that are estimated to be exerted on the individual osteocyte tethers. Data fitting with an extensible worm-like chain model showed that the perlecan protein core has a mean elastic constant of 890 pN and a corresponding Young's modulus of 71 MPa. We conclude that perlecan has physical properties that would allow it to act as a strong but elastic tether in the LCS. Copyright © 2015 International Society of Matrix Biology. Published by Elsevier B.V. All rights reserved.

Rotor vibration caused by external excitation and rub

NASA Technical Reports Server (NTRS)

Matsushita, O.; Takagi, M.; Kikuchi, K.; Kaga, M.

1982-01-01

For turbomachinery with low natural frequencies, considerations have been recently required for rotor vibrations caused by external forces except unbalance one, such as foundation motion, seismic wave, rub and so forth. Such a forced vibration is investigated analytically and experimentally in the present paper. Vibrations in a rotor-bearing system under a harmonic excitation are analyzed by the modal technique in the case of a linear system including gyroscopic effect. For a nonlinear system a new and powerful quasi-modal technique is developed and applied to the vibration caused by rub.

75 FR 70160 - Affordable Care Act; Federal External Review Process; Request for Information

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-17

...-9986-NC] DEPARTMENT OF LABOR Employee Benefits Security Administration 29 CFR Part 2590 Affordable Care... Affordable Care Act, and its implementing regulations. DATES: Submit written or electronic comments by... processes under the Affordable Care Act; those comments are being collected and evaluated on a separate...

Biomechanical Comparison of External Fixation and Compression Screws for Transverse Tarsal Joint Arthrodesis.

PubMed

Latt, L Daniel; Glisson, Richard R; Adams, Samuel B; Schuh, Reinhard; Narron, John A; Easley, Mark E

2015-10-01

Transverse tarsal joint arthrodesis is commonly performed in the operative treatment of hindfoot arthritis and acquired flatfoot deformity. While fixation is typically achieved using screws, failure to obtain and maintain joint compression sometimes occurs, potentially leading to nonunion. External fixation is an alternate method of achieving arthrodesis site compression and has the advantage of allowing postoperative compression adjustment when necessary. However, its performance relative to standard screw fixation has not been quantified in this application. We hypothesized that external fixation could provide transverse tarsal joint compression exceeding that possible with screw fixation. Transverse tarsal joint fixation was performed sequentially, first with a circular external fixator and then with compression screws, on 9 fresh-frozen cadaveric legs. The external fixator was attached in abutting rings fixed to the tibia and the hindfoot and a third anterior ring parallel to the hindfoot ring using transverse wires and half-pins in the tibial diaphysis, calcaneus, and metatarsals. Screw fixation comprised two 4.3 mm headless compression screws traversing the talonavicular joint and 1 across the calcaneocuboid joint. Compressive forces generated during incremental fixator foot ring displacement to 20 mm and incremental screw tightening were measured using a custom-fabricated instrumented miniature external fixator spanning the transverse tarsal joint. The maximum compressive force generated by the external fixator averaged 186% of that produced by the screws (range, 104%-391%). Fixator compression surpassed that obtainable with screws at 12 mm of ring displacement and decreased when the tibial ring was detached. No correlation was found between bone density and the compressive force achievable by either fusion method. The compression across the transverse tarsal joint that can be obtained with a circular external fixator including a tibial ring exceeds that which can be obtained with 3 headless compression screws. Screw and external fixator performance did not correlate with bone mineral density. This study supports the use of external fixation as an alternative method of generating compression to help stimulate fusion across the transverse tarsal joints. The findings provide biomechanical evidence to support the use of external fixation as a viable option in transverse tarsal joint fusion cases in which screw fixation has failed or is anticipated to be inadequate due to suboptimal bone quality. © The Author(s) 2015.

Kinetics of molecular transitions with dynamic disorder in single-molecule pulling experiments

NASA Astrophysics Data System (ADS)

Zheng, Yue; Li, Ping; Zhao, Nanrong; Hou, Zhonghuai

2013-05-01

Macromolecular transitions are subject to large fluctuations of rate constant, termed as dynamic disorder. The individual or intrinsic transition rates and activation free energies can be extracted from single-molecule pulling experiments. Here we present a theoretical framework based on a generalized Langevin equation with fractional Gaussian noise and power-law memory kernel to study the kinetics of macromolecular transitions to address the effects of dynamic disorder on barrier-crossing kinetics under external pulling force. By using the Kramers' rate theory, we have calculated the fluctuating rate constant of molecular transition, as well as the experimentally accessible quantities such as the force-dependent mean lifetime, the rupture force distribution, and the speed-dependent mean rupture force. Particular attention is paid to the discrepancies between the kinetics with and without dynamic disorder. We demonstrate that these discrepancies show strong and nontrivial dependence on the external force or the pulling speed, as well as the barrier height of the potential of mean force. Our results suggest that dynamic disorder is an important factor that should be taken into account properly in accurate interpretations of single-molecule pulling experiments.

Influence of radius of cylinder HTS bulk on guidance force in a maglev vehicle system

NASA Astrophysics Data System (ADS)

Longcai, Zhang

2014-07-01

Bulk superconductors had great potential for various engineering applications, especially in a high-temperature superconducting (HTS) maglev vehicle system. In such a system, the HTS bulks were always exposed to AC external magnetic field, which was generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, it was observed that the guidance force of the YBCO bulk over the NdFeB guideway used in the HTS maglev vehicle system was decayed by the application of the AC external magnetic field. In this paper, we investigated the influence of the radius of the cylinder HTS bulk exposed to an AC magnetic field perturbation on the guidance force in the maglev vehicle system. From the results, it was found that the guidance force was stronger for the bulk with bigger radius and the guidance force decay rates of the bulks were approximately equal despite of the different radius in the maglev vehicle system. Therefore, in order to obtain higher guidance force in the maglev vehicle system, we could use the cylinder HTS bulks with the bigger radius.

Molecular crowding at microtubule plus-ends acts as a physical barrier to microtubule sliding for the organization of stable anti-parallel overlaps by PRC1 and Kif4A

NASA Astrophysics Data System (ADS)

Wijeratne, Sitara; Subramanian, Radhika

The relative sliding of microtubules by motor proteins is important for the organization of specialized cellular microtubule networks. In cells, sliding filaments are likely to encounter crowded regions of microtubules, such as the plus-ends, which are densely occupied by motor and non-motor proteins. How molecular crowding impacts microtubule sliding is not well understood. Here, we reconstitute the collective activities of the non-motor protein PRC1 and the motor protein Kif4A on anti-parallel microtubules to address this question. We find that the accumulation of PRC1 and Kif4A at microtubule-plus ends (`end-tags') can act as a physical barrier to Kif4A-mediated microtubule sliding. This enables the formation of stable microtubule overlaps that persist even after the deactivation of the motor protein. Our data suggest that while end-tags stabilize anti-parallel overlaps by inhibiting relative sliding, they permit the remodeling of the microtubule bundles by external forces, as may be required for the reorganization of microtubule networks during dynamic cellular processes.

Instabilities of conducting fluid flows in cylindrical shells under external forcing

NASA Astrophysics Data System (ADS)

Burguete, Javier; Miranda, Montserrat

2010-11-01

Flows created in neutral conducting flows remain one of the less studied topics of fluid dynamics, in spite of their relevance both in fundamental research (dynamo action, turbulence suppression) and applications (continuous casting, aluminium production, biophysics). Here we present the effect of a time-dependent magnetic field parallel to the axis of circular cavities. Due to the Lenz's law, the time-dependent magnetic field generates an azymuthal current, that produces a radial force. This force produces the destabilization of the static fluid layer, and a flow is created. The geommetry of the experimental cell is a disc layer with external diameter smaller than 94 mm, with or without internal hole. The layer is up to 20mm depth, and we use as conducting fluid an In-Ga-Sn alloy. There is no external current applied on the problem, only an external magnetic field. This field evolves harmonically with a frequency up to 10Hz, small enough to not to observe skin depth effects. The magnitude ranges from 0 to 0.1 T. With a threshold of 0.01T a dynamical behaviour is observed, and the main characteristics of this flow have been determined: different temporal resonances and spatial patterns with differents symmetries (squares, hexagonal, triangles,...).

The equation of motion for a radiating charged particle without self-interaction term

NASA Astrophysics Data System (ADS)

Herrera, L.

1990-03-01

The motion of a radiating charged particle is studied from the point of view of relativistic classical mechanics. Thus, the resulting equation of motion emerges from equating the total rate of change of momentum to the external force, without the introduction of a “self-force” term. Doing so, one is forced to abandon either one, or both, of the following restrictions: (a) the external force is non-dissipative, (b) the proper mass of the particle is constant. By abandoning (a) we obtain the Mo and Papas equation of motion, whereas allowing variations in the proper mass one is led, uniquely, to the Bonnor equation. A new equation of motion is proposed by abandoning both (a) and (b).

Energy and nutrient flows connecting coastal wetland food webs to land and lake

EPA Science Inventory

Both landscape character and hydrologic forces (principally, tributary discharge and seiches) can influence utilization of externally-derived energy and nutrients in coastal wetland food webs. We quantified the contribution of internal vs external energy and nutrients among wetla...

Monsoonal Responses to External Forcings over the Past Millennium: A Model Study (Invited)

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, B.

2009-12-01

The climate variations related to Global Monsoon (GM) and East Asian summer monsoon (EASM) rainfall over the past 1000 years were investigated by analysis of a pair of millennium simulations with the coupled climate model named ECHO-G. The free run was generated using fixed external (annual cycle) forcing, while the forced run was obtained using time-varying solar irradiance variability, greenhouse gases (CO2 and CH4) concentration and estimated radiative effect of volcanic aerosols. The model results indicate that the centennial-millennial variation of the GM and EASM is essentially a forced response to the external radiative forcings (insolation, volcanic aerosols, and greenhouse gases). The GM strength responds more directly to the effective solar forcing (insolation plus radiative effect of the volcanoes) when compared to responses of the global mean surface temperature on centennial timescale. The simulated GM precipitation in the forced run exhibits a significant quasi-bi-centennial oscillation. Weak GM precipitation was simulated during the Little Ice Age (1450-1850) with three weakest periods concurring with the Spörer, Maunder, and Dalton Minimum of solar activity. Conversely, strong GM was simulated during the model Medieval Warm Period (ca. 1030-1240). Before the industrial period, the natural variation in effective solar forcing reinforces the thermal contrasts both between the ocean and continent and between the northern and southern hemispheres, resulting in millennium-scale variation and the quasi-bi-centennial oscillation of the GM. The prominent upward trend in the GM precipitation occurring in the last century and the remarkably strengthening of the global monsoon in the period of 1961-1990 appear unprecedented and owed possibly in part to the increase of atmospheric carbon dioxide concentration. The EASM has the largest meridional extent (5oN-55oN) among all the regional monsoons on globe. Thus, the EASM provides an unique opportunity for understanding the latitudinal differences of the monsoonal responses to external forcings and internal feedback processes. The strength of the forced response depends on latitude. On centennial-millennial time scales, the variation of the extratropical and subtropical rainfall tends to follow the effective solar radiation forcing closely; the tropical rainfall is less sensitive to the effective solar radiation forcing but responds significantly to the modern anthropogenic CO2 forcing. The spatial patterns and structures of the forced response differ from the internal mode (i.e., interannual variability that arises primarily from the internal feedback processes within the climate system). Further, the behavior of the internal mode is effectively modulated by changes in the mean state on the centennial to millennial time scales. These findings have important ramification in understanding the differences and linkages between the forced and internal modes of variability as well as in promoting communication between scientists studying modern- and paleo-monsoon variations.

Information driving force and its application in agent-based modeling

NASA Astrophysics Data System (ADS)

Chen, Ting-Ting; Zheng, Bo; Li, Yan; Jiang, Xiong-Fei

2018-04-01

Exploring the scientific impact of online big-data has attracted much attention of researchers from different fields in recent years. Complex financial systems are typical open systems profoundly influenced by the external information. Based on the large-scale data in the public media and stock markets, we first define an information driving force, and analyze how it affects the complex financial system. The information driving force is observed to be asymmetric in the bull and bear market states. As an application, we then propose an agent-based model driven by the information driving force. Especially, all the key parameters are determined from the empirical analysis rather than from statistical fitting of the simulation results. With our model, both the stationary properties and non-stationary dynamic behaviors are simulated. Considering the mean-field effect of the external information, we also propose a few-body model to simulate the financial market in the laboratory.

Characterization of structural and electrical properties of ZnO tetrapods

NASA Astrophysics Data System (ADS)

Gu, Yu-Dong; Mai, Wen-Jie; Jiang, Peng

2011-12-01

ZnO tetrapods were synthesized by a typical thermal vapor-solid deposition method in a horizontal tube furnace. Structural characterization was carried out by transmission electron microscopy (TEM) and select-area electron diffraction (SAED), which shows the presence of zinc blende nucleus in the center of tetrapods while the four branches taking hexagonal wurtzite structure. The electrical transport property of ZnO tetrapods was investigated through an in-situ nanoprobe system. The three branches of a tetrapod serve as source, drain, and "gate", respectively; while the fourth branch pointing upward works as the force trigger by vertically applying external force downward. The conductivity of each branch of ZnO-tetrapods increases 3-4 times under pressure. In such situation, the electrical current through the branches of ZnO tetrapods can be tuned by external force, and therefore a simple force sensor based on ZnO tetrapods has been demonstrated for the first time.

Compression asphyxia from a human pyramid.

PubMed

Tumram, Nilesh Keshav; Ambade, Vipul Namdeorao; Biyabani, Naushad

2015-12-01

In compression asphyxia, respiration is stopped by external forces on the body. It is usually due to an external force compressing the trunk such as a heavy weight on the chest or abdomen and is associated with internal injuries. In present case, the victim was trapped and crushed under the falling persons from a human pyramid formation for a "Dahi Handi" festival. There was neither any severe blunt force injury nor any significant pathological natural disease contributing to the cause of death. The victim was unable to remove himself from the situation because his cognitive responses and coordination were impaired due to alcohol intake. The victim died from asphyxia due to compression of his chest and abdomen. Compression asphyxia resulting from the collapse of a human pyramid and the dynamics of its impact force in these circumstances is very rare and is not reported previously to the best of our knowledge. © The Author(s) 2015.

Modelling of deformation process for the layer of elastoviscoplastic media under surface action of periodic force of arbitrary type

NASA Astrophysics Data System (ADS)

Mikheyev, V. V.; Saveliev, S. V.

2018-01-01

Description of deflected mode for different types of materials under action of external force plays special role for wide variety of applications - from construction mechanics to circuits engineering. This article con-siders the problem of plastic deformation of the layer of elastoviscolastic soil under surface periodic force. The problem was solved with use of the modified lumped parameters approach which takes into account close to real distribution of normal stress in the depth of the layer along with changes in local mechanical properties of the material taking place during plastic deformation. Special numeric algorithm was worked out for computer modeling of the process. As an example of application suggested algorithm was realized for the deformation of the layer of elasoviscoplastic material by the source of external lateral force with the parameters of real technological process of soil compaction.

Error-enhancing robot therapy to induce motor control improvement in childhood onset primary dystonia.

PubMed

Casellato, Claudia; Pedrocchi, Alessandra; Zorzi, Giovanna; Rizzi, Giorgio; Ferrigno, Giancarlo; Nardocci, Nardo

2012-07-23

Robot-generated deviating forces during multijoint reaching movements have been applied to investigate motor control and to tune neuromotor adaptation. Can the application of force to limbs improve motor learning? In this framework, the response to altered dynamic environments of children affected by primary dystonia has never been studied. As preliminary pilot study, eleven children with primary dystonia and eleven age-matched healthy control subjects were asked to perform upper limb movements, triangle-reaching (three directions) and circle-writing, using a haptic robot interacting with ad-hoc developed task-specific visual interfaces. Three dynamic conditions were provided, null additive external force (A), constant disturbing force (B) and deactivation of the additive external force again (C). The path length for each trial was computed, from the recorded position data and interaction events. The results show that the disturbing force affects significantly the movement outcomes in healthy but not in dystonic subjects, already compromised in the reference condition: the external alteration uncalibrates the healthy sensorimotor system, while the dystonic one is already strongly uncalibrated. The lack of systematic compensation for perturbation effects during B condition is reflected into the absence of after-effects in C condition, which would be the evidence that CNS generates a prediction of the perturbing forces using an internal model of the environment.The most promising finding is that in dystonic population the altered dynamic exposure seems to induce a subsequent improvement, i.e. a beneficial after-effect in terms of optimal path control, compared with the correspondent reference movement outcome. The short-time error-enhancing training in dystonia could represent an effective approach for motor performance improvement, since the exposure to controlled dynamic alterations induces a refining of the existing but strongly imprecise motor scheme and sensorimotor patterns.

Error-enhancing robot therapy to induce motor control improvement in childhood onset primary dystonia

PubMed Central

2012-01-01

Background Robot-generated deviating forces during multijoint reaching movements have been applied to investigate motor control and to tune neuromotor adaptation. Can the application of force to limbs improve motor learning? In this framework, the response to altered dynamic environments of children affected by primary dystonia has never been studied. Methods As preliminary pilot study, eleven children with primary dystonia and eleven age-matched healthy control subjects were asked to perform upper limb movements, triangle-reaching (three directions) and circle-writing, using a haptic robot interacting with ad-hoc developed task-specific visual interfaces. Three dynamic conditions were provided, null additive external force (A), constant disturbing force (B) and deactivation of the additive external force again (C). The path length for each trial was computed, from the recorded position data and interaction events. Results The results show that the disturbing force affects significantly the movement outcomes in healthy but not in dystonic subjects, already compromised in the reference condition: the external alteration uncalibrates the healthy sensorimotor system, while the dystonic one is already strongly uncalibrated. The lack of systematic compensation for perturbation effects during B condition is reflected into the absence of after-effects in C condition, which would be the evidence that CNS generates a prediction of the perturbing forces using an internal model of the environment. The most promising finding is that in dystonic population the altered dynamic exposure seems to induce a subsequent improvement, i.e. a beneficial after-effect in terms of optimal path control, compared with the correspondent reference movement outcome. Conclusions The short-time error-enhancing training in dystonia could represent an effective approach for motor performance improvement, since the exposure to controlled dynamic alterations induces a refining of the existing but strongly imprecise motor scheme and sensorimotor patterns. PMID:22824547

Analysis and Modeling of the Arctic Oscillation Using a Simple Barotropic Model with Baroclinic Eddy Forcing.

NASA Astrophysics Data System (ADS)

Tanaka, H. L.

2003-06-01

In this study, a numerical simulation of the Arctic Oscillation (AO) is conducted using a simple barotropic model that considers the barotropic-baroclinic interactions as the external forcing. The model is referred to as a barotropic S model since the external forcing is obtained statistically from the long-term historical data, solving an inverse problem. The barotropic S model has been integrated for 51 years under a perpetual January condition and the dominant empirical orthogonal function (EOF) modes in the model have been analyzed. The results are compared with the EOF analysis of the barotropic component of the real atmosphere based on the daily NCEP-NCAR reanalysis for 50 yr from 1950 to 1999.According to the result, the first EOF of the model atmosphere appears to be the AO similar to the observation. The annular structure of the AO and the two centers of action at Pacific and Atlantic are simulated nicely by the barotropic S model. Therefore, the atmospheric low-frequency variabilities have been captured satisfactorily even by the simple barotropic model.The EOF analysis is further conducted to the external forcing of the barotropic S model. The structure of the dominant forcing shows the characteristics of synoptic-scale disturbances of zonal wavenumber 6 along the Pacific storm track. The forcing is induced by the barotropic-baroclinic interactions associated with baroclinic instability.The result suggests that the AO can be understood as the natural variability of the barotropic component of the atmosphere induced by the inherent barotropic dynamics, which is forced by the barotropic-baroclinic interactions. The fluctuating upscale energy cascade from planetary waves and synoptic disturbances to the zonal motion plays the key role for the excitation of the AO.

Multidigit force control during unconstrained grasping in response to object perturbations

PubMed Central

Haschke, Robert; Ritter, Helge; Santello, Marco; Ernst, Marc O.

2017-01-01

Because of the complex anatomy of the human hand, in the absence of external constraints, a large number of postures and force combinations can be used to attain a stable grasp. Motor synergies provide a viable strategy to solve this problem of motor redundancy. In this study, we exploited the technical advantages of an innovative sensorized object to study unconstrained hand grasping within the theoretical framework of motor synergies. Participants were required to grasp, lift, and hold the sensorized object. During the holding phase, we repetitively applied external disturbance forces and torques and recorded the spatiotemporal distribution of grip forces produced by each digit. We found that the time to reach the maximum grip force during each perturbation was roughly equal across fingers, consistent with a synchronous, synergistic stiffening across digits. We further evaluated this hypothesis by comparing the force distribution of human grasping vs. robotic grasping, where the control strategy was set by the experimenter. We controlled the global hand stiffness of the robotic hand and found that this control algorithm produced a force pattern qualitatively similar to human grasping performance. Our results suggest that the nervous system uses a default whole hand synergistic control to maintain a stable grasp regardless of the number of digits involved in the task, their position on the objects, and the type and frequency of external perturbations. NEW & NOTEWORTHY We studied hand grasping using a sensorized object allowing unconstrained finger placement. During object perturbation, the time to reach the peak force was roughly equal across fingers, consistently with a synergistic stiffening across fingers. Force distribution of a robotic grasping hand, where the control algorithm is based on global hand stiffness, was qualitatively similar to human grasping. This suggests that the central nervous system uses a default whole hand synergistic control to maintain a stable grasp. PMID:28228582

Forced Atlantic Multidecadal Variability Over the Past Millennium

NASA Astrophysics Data System (ADS)

Halloran, P. R.; Reynolds, D.; Scourse, J. D.; Hall, I. R.

2016-02-01

Paul R. Halloran, David J. Reynolds, Ian R. Hall and James D. Scourse Multidecadal variability in Atlantic sea surface temperatures (SSTs) plays a first order role in determining regional atmospheric circulation and moisture transport, with major climatic consequences. These regional climate impacts range from drought in the Sahel and South America, though increased hurricane activity and temperature extremes, to modified monsoonal rainfall. Multidecadal Atlantic SST variability could arise through internal variability in the Atlantic Meridional Overturning Circulation (AMOC) (e.g., Knight et al., 2006), or through externally forced change (e.g. Booth et al., 2012). It is critical that we know whether internal or external forcing dominates if we are to provide useful near-term climate projections in the Atlantic region. A persuasive argument that internal variability plays an important role in Atlantic Multidecadal Variability is that periodic SST variability has been observed throughout much of the last millennium (Mann et al., 2009), and the hypothesized external forcing of historical Atlantic Multidecadal Variability (Booth et al., 2012) is largely anthropogenic in origin. Here we combine the first annually-resolved millennial marine reconstruction with multi-model analysis, to show that the Atlantic SST variability of the last millennium can be explained by a combination of direct volcanic forcing, and indirect, forced, AMOC variability. Our results indicate that whilst climate models capture the timing of both the directly forced SST and forced AMOC-mediated SST variability, the models fail to capture the magnitude of the forced AMOC change. Does this mean that models underestimate the 21st century reduction in AMOC strength? J. Knight, C. Folland and A. Scaife., Climate impacts of the Atlantic Multidecadal Oscillation, GRL, 2006 B.B.B Booth, N. Dunstone, P.R. Halloran et al., Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability, Nature, 2012 M.E. Mann, Z. Zhang, S. Rutherford et al., Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly, Science, 2009

Theory and computation of general force balance in non-axisymmetric tokamak equilibria

NASA Astrophysics Data System (ADS)

Park, Jong-Kyu; Logan, Nikolas; Wang, Zhirui; Kim, Kimin; Boozer, Allen; Liu, Yueqiang; Menard, Jonathan

2014-10-01

Non-axisymmetric equilibria in tokamaks can be effectively described by linearized force balance. In addition to the conventional isotropic pressure force, there are three important components that can strongly contribute to the force balance; rotational, anisotropic tensor pressure, and externally given forces, i.e. ∇ --> p + ρv-> . ∇ --> v-> + ∇ --> . <-->Π + f-> = j-> × B-> , especially in, but not limited to, high β and rotating plasmas. Within the assumption of nested flux surfaces, Maxwell equations and energy minimization lead to the modified-generalized Newcomb equation for radial displacements with simple algebraic relations for perpendicular and parallel displacements, including an inhomogeneous term if any of the forces are not explicitly dependent on displacements. The general perturbed equilibrium code (GPEC) solves this force balance consistent with energy and torque given by external perturbations. Local and global behaviors of solutions will be discussed when ∇ --> . <-->Π is solved by the semi-analytic code PENT and will be compared with MARS-K. Any first-principle transport code calculating ∇ --> . <-->Π or f-> , e.g. POCA, can also be incorporated without demanding iterations. This work was supported by DOE Contract DE-AC02-09CH11466.

Minimization of extracellular space as a driving force in prokaryote association and the origin of eukaryotes.

PubMed

Hooper, Scott L; Burstein, Helaine J

2014-11-18

Internalization-based hypotheses of eukaryotic origin require close physical association of host and symbiont. Prior hypotheses of how these associations arose include chance, specific metabolic couplings between partners, and prey-predator/parasite interactions. Since these hypotheses were proposed, it has become apparent that mixed-species, close-association assemblages (biofilms) are widespread and predominant components of prokaryotic ecology. Which forces drove prokaryotes to evolve the ability to form these assemblages are uncertain. Bacteria and archaea have also been found to form membrane-lined interconnections (nanotubes) through which proteins and RNA pass. These observations, combined with the structure of the nuclear envelope and an energetic benefit of close association (see below), lead us to propose a novel hypothesis of the driving force underlying prokaryotic close association and the origin of eukaryotes. Respiratory proton transport does not alter external pH when external volume is effectively infinite. Close physical association decreases external volume. For small external volumes, proton transport decreases external pH, resulting in each transported proton increasing proton motor force to a greater extent. We calculate here that in biofilms this effect could substantially decrease how many protons need to be transported to achieve a given proton motor force. Based as it is solely on geometry, this energetic benefit would occur for all prokaryotes using proton-based respiration. This benefit may be a driving force in biofilm formation. Under this hypothesis a very wide range of prokaryotic species combinations could serve as eukaryotic progenitors. We use this observation and the discovery of prokaryotic nanotubes to propose that eukaryotes arose from physically distinct, functionally specialized (energy factory, protein factory, DNA repository/RNA factory), obligatorily symbiotic prokaryotes in which the protein factory and DNA repository/RNA factory cells were coupled by nanotubes and the protein factory ultimately internalized the other two. This hypothesis naturally explains many aspects of eukaryotic physiology, including the nuclear envelope being a folded single membrane repeatedly pierced by membrane-bound tubules (the nuclear pores), suggests that species analogous or homologous to eukaryotic progenitors are likely unculturable as monocultures, and makes a large number of testable predictions. This article was reviewed by Purificación López-García and Toni Gabaldón.

Unlocking higher harmonics in atomic force microscopy with gentle interactions.

PubMed

Santos, Sergio; Barcons, Victor; Font, Josep; Verdaguer, Albert

2014-01-01

In dynamic atomic force microscopy, nanoscale properties are encoded in the higher harmonics. Nevertheless, when gentle interactions and minimal invasiveness are required, these harmonics are typically undetectable. Here, we propose to externally drive an arbitrary number of exact higher harmonics above the noise level. In this way, multiple contrast channels that are sensitive to compositional variations are made accessible. Numerical integration of the equation of motion shows that the external introduction of exact harmonic frequencies does not compromise the fundamental frequency. Thermal fluctuations are also considered within the detection bandwidth of interest and discussed in terms of higher-harmonic phase contrast in the presence and absence of an external excitation of higher harmonics. Higher harmonic phase shifts further provide the means to directly decouple the true topography from that induced by compositional heterogeneity.

On the stiffness analysis of a cable driven leg exoskeleton.

PubMed

Sanjeevi, N S S; Vashista, Vineet

2017-07-01

Robotic systems are being used for gait rehabilitation of patients with neurological disorder. These devices are externally powered to apply external forces on human limbs to assist the leg motion. Patients while walking with these devices adapt their walking pattern in response to the applied forces. The efficacy of a rehabilitation paradigm thus depends on the human-robot interaction. A cable driven leg exoskeleton (CDLE) use actuated cables to apply external joint torques on human leg. Cables are lightweight and flexible but can only be pulled, thus a CDLE requires redundant cables. Redundancy in CDLE can be utilized to appropriately tune a robot's performance. In this work, we present the stiffness analysis of CDLE. Different stiffness performance indices are established to study the role of system parameters in improving the human-robot interaction.

Effect of attractive interactions between polymers on the effective force acting between colloids immersed in a polymer system: Analytic liquid-state theory.

PubMed

Chervanyov, A I

2016-12-28

By making use of the polymer reference interaction site model, we analytically study the effect of attractive interactions between polymers on the effective forces acting between colloids immersed in a polymer system. The performed theoretical analysis has no restrictions with respect to the polymer density and relative sizes of the colloids and polymers. The polymer mediated (PM) potential acting between colloids is shown to significantly depend on the strength and range of the polymer-polymer interactions. In the nano-particle limit, where the colloid radius is much smaller than the polymer gyration radius, the presence of attractive polymer-polymer interactions causes only quantitative changes to the PM potential. In the opposite limit of relatively large colloids, the polymer-polymer interactions revert the sign of the total effective force acting between colloids so that this force becomes attractive at sufficiently large polymer densities. With the objective to study an intricate interplay between the attractive PM forces and steric repulsion in different polymer density regimes, we calculate the second virial coefficient B of the total effective potential acting between colloids. The dependence of B on the polymer density is discussed in detail, revealing several novel features of the PM interactions caused by the presence of attractive polymer-polymer interactions.

Microgravity Experiments to Evaluate Electrostatic Forces in Controlling Cohesion and Adhesion of Granular Materials

NASA Technical Reports Server (NTRS)

Marshall, J.; Weislogel, M.; Jacobson, T.

1999-01-01

The bulk behavior of dispersed, fluidized, or undispersed stationary granular systems cannot be fully understood in terms of adhesive/cohesive properties without understanding the role of electrostatic forces acting at the level of the grains themselves. When grains adhere to a surface, or come in contact with one another in a stationary bulk mass, it is difficult to measure the forces acting on the grains, and the forces themselves that induced the cohesion and adhesion are changed. Even if a single gain were to be scrutinized in the laboratory, it might be difficult, perhaps impossible, to define the distribution and character of surface charging and the three- dimensional relationship that charges (electrons, holes) have to one another. The hypothesis that we propose to test in microgravity (for dielectric materials) is that adhesion and cohesion of granular matter are mediated primarily by dipole forces that do not require the presence of a net charge; in fact, nominally electrically neutral materials should express adhesive and cohesive behavior when the neutrality results from a balance of positive and negative charge carriers. Moreover, the use of net charge alone as a measure of the electrical nature of grain-to-grain relationships within a granular mass may be misleading. We believe that the dipole forces arise from the presence of randomly-distributed positive and negative fixed charge carriers on grains that give rise to a resultant dipole moment. These dipole forces have long-range attraction. Random charges are created whenever there is triboelectrical activity of a granular mass, that is, whenever the grains experience contact/separation sequences or friction. Electrostatic forces are generally under-estimated for their role in causing agglomeration of dispersed grains in particulate clouds, or their role in affecting the internal frictional relationships in packed granular masses. We believe that electrostatic, in particular dipole-mediated processes, are pervasive and probably affect, at some level, everything from astrophysical-scale granular systems such as interstellar nebulae, protoplanetary dust and debris disks, planetary-scale systems such as debris palls from meteorite impact, volcanic eruptions, and aeolian dust storms, all the way to industrial-scale systems in mining, powder and grain processing, pharmaceuticals, and smoke-stack technologies. NASA must concern itself with the electrostatic behavior of dust and sand on Mars because of its potentially critical importance to human exploration. The motion and adhesion of martian surface materials will affect the design and performance of spacesuits, habitats, processing plants, solar panels, and any externally exposed equipment such as surface rovers or communication and weather stations. Additionally, the adhesion of dust and sand could greatly enhance contact with the potentially toxic components of the martian soil.

Forced synchronization of thermoacoustic oscillations in a ducted flame

NASA Astrophysics Data System (ADS)

Guan, Yu; Gupta, Vikrant; Kashinath, Karthik; Li, Larry K. B.

2016-11-01

Forced synchronization is a process in which a self-excited system subjected to external forcing starts to oscillate at the forcing frequency ff in place of its own natural frequency fn. There are two motivations for studying this in thermoacoustics: (i) to determine how external forcing could be used to control thermoacoustic oscillations, which are harmful to many combustors; and (ii) to better understand the nonlinear interactions between self-excited hydrodynamic and thermoacoustic oscillations. In this experimental study, we examine the response of a ducted premixed flame to harmonic acoustic forcing, for two natural states of the system: (1) a state with periodic oscillations at f1 and a marginally stable mode at f2; and (2) a state with quasiperiodic oscillations at two incommensurate frequencies f1 and f2. When forcing the periodic state, we find that the forcing amplitude required for lock-in increases linearly with | ff -f1 | and that the marginally stable mode becomes excited when ff f2 . When forcing the quasiperiodic state, we find that the system locks into the forcing when ff f1 or f2 or 1 / 2 (f1 +f2) . These findings should lead to improved control of periodic and aperiodic thermoacoustic oscillations in combustors. This work was supported by the Research Grants Council of Hong Kong (Project No. 16235716 and 26202815).

External foam layers to football helmets reduce head impact severity.

PubMed

Nakatsuka, Austin S; Yamamoto, Loren G

2014-08-01

Current American football helmet design has a rigid exterior with a padded interior. Softening the hard external layer of the helmet may reduce the impact potential of the helmet, providing extra head protection and reducing its use as an offensive device. The objective of this study is to measure the impact reduction potential provided by external foam. We obtained a football helmet with built-in accelerometer-based sensors, placed it on a boxing mannequin and struck it with a weighted swinging pendulum helmet to mimic the forces sustained during a helmet-to-helmet strike. We then applied layers of 1.3 cm thick polyolefin foam to the exterior surface of the helmets and repeated the process. All impact severity measures were significantly reduced with the application of the external foam. These results support the hypothesis that adding a soft exterior layer reduces the force of impact which may be applicable to the football field. Redesigning football helmets could reduce the injury potential of the sport.

External Foam Layers to Football Helmets Reduce Head Impact Severity

PubMed Central

Nakatsuka, Austin S

2014-01-01

Current American football helmet design has a rigid exterior with a padded interior. Softening the hard external layer of the helmet may reduce the impact potential of the helmet, providing extra head protection and reducing its use as an offensive device. The objective of this study is to measure the impact reduction potential provided by external foam. We obtained a football helmet with built-in accelerometer-based sensors, placed it on a boxing mannequin and struck it with a weighted swinging pendulum helmet to mimic the forces sustained during a helmet-to-helmet strike. We then applied layers of 1.3 cm thick polyolefin foam to the exterior surface of the helmets and repeated the process. All impact severity measures were significantly reduced with the application of the external foam. These results support the hypothesis that adding a soft exterior layer reduces the force of impact which may be applicable to the football field. Redesigning football helmets could reduce the injury potential of the sport. PMID:25157327

Time-dependent computational studies of flames in microgravity

NASA Technical Reports Server (NTRS)

Oran, Elaine S.; Kailasanath, K.

1989-01-01

The research performed at the Center for Reactive Flow and Dynamical Systems in the Laboratory for Computational Physics and Fluid Dynamics, at the Naval Research Laboratory, in support of the NASA Microgravity Science and Applications Program is described. The primary focus was on investigating fundamental questions concerning the propagation and extinction of premixed flames in Earth gravity and in microgravity environments. The approach was to use detailed time-dependent, multispecies, numerical models as tools to simulate flames in different gravity environments. The models include a detailed chemical kinetics mechanism consisting of elementary reactions among the eight reactive species involved in hydrogen combustion, coupled to algorithms for convection, thermal conduction, viscosity, molecular and thermal diffusion, and external forces. The external force, gravity, can be put in any direction relative to flame propagation and can have a range of values. A combination of one-dimensional and two-dimensional simulations was used to investigate the effects of curvature and dilution on ignition and propagation of flames, to help resolve fundamental questions on the existence of flammability limits when there are no external losses or buoyancy forces in the system, to understand the mechanism leading to cellular instability, and to study the effects of gravity on the transition to cellular structure. A flame in a microgravity environment can be extinguished without external losses, and the mechanism leading to cellular structure is not preferential diffusion but a thermo-diffusive instability. The simulations have also lead to a better understanding of the interactions between buoyancy forces and the processes leading to thermo-diffusive instability.

Swarm- Validation of Star Tracker and Accelerometer Data

NASA Astrophysics Data System (ADS)

Schack, Peter; Schlicht, Anja; Pail, Roland; Gruber, Thomas

2016-08-01

The ESA Swarm mission is designed to advance studies in the field of magnetosphere, thermosphere and gravity field. To be fortunate on this task precise knowledge of the orientation of the Swarm satellites is required together with knowledge about external forces acting on the satellites. The key sensors providing this information are the star trackers and the accelerometers. Based on star tracker studies conducted by the Denmark Technical University (DTU), we found interesting patterns in the interboresight angles on all three satellites, which are partly induced by temperature alterations. Additionally, structures of horizontal stripes seem to be caused by the unique distribution of observed stars on the charge-coupled device of the star trackers. Our accelerometer analyses focus on spikes and pulses in the observations. Those short term events on Swarm might originate from electrical processes introduced by sunlight illuminating the nadir foil. Comparisons to GOCE and GRACE are included.

IR thermography for dynamic detection of laminar-turbulent transition

NASA Astrophysics Data System (ADS)

Simon, Bernhard; Filius, Adrian; Tropea, Cameron; Grundmann, Sven

2016-05-01

This work investigates the potential of infrared (IR) thermography for the dynamic detection of laminar-turbulent transition. The experiments are conducted on a flat plate at velocities of 8-14 m/s, and the transition of the laminar boundary layer to turbulence is forced by a disturbance source which is turned on and off with frequencies up to 10 Hz. Three different heating techniques are used to apply the required difference between fluid and structure temperature: a heated aluminum structure is used as an internal structure heating technique, a conductive paint acts as a surface bounded heater, while an IR heater serves as an example for an external heating technique. For comparison of all heating techniques, a normalization is introduced and the frequency response of the measured IR camera signal is analyzed. Finally, the different heating techniques are compared and consequences for the design of experiments on laminar-turbulent transition are discussed.

A novel open-loop tracking strategy for photovoltaic systems.

PubMed

Alexandru, Cătălin

2013-01-01

This paper approaches a dual-axis equatorial tracking system that is used to increase the photovoltaic efficiency by maximizing the degree of use of the solar radiation. The innovative aspect in the solar tracker design consists in considering the tracking mechanism as a perturbation for the DC motors. The goal is to control the DC motors, which are perturbed with the motor torques whose computation is based on the dynamic model of the mechanical structure on which external forces act. The daily and elevation angles of the PV module represent the input parameters in the mechanical device, while the outputs transmitted to the controller are the motor torques. The controller tuning is approached by a parametric optimization process, using design of experiments and response surface methodology techniques, in a multiple regression. The simulation and experimental results demonstrate the operational performance of the tracking system.

A Novel Open-Loop Tracking Strategy for Photovoltaic Systems

PubMed Central

Alexandru, Cătălin

2013-01-01

This paper approaches a dual-axis equatorial tracking system that is used to increase the photovoltaic efficiency by maximizing the degree of use of the solar radiation. The innovative aspect in the solar tracker design consists in considering the tracking mechanism as a perturbation for the DC motors. The goal is to control the DC motors, which are perturbed with the motor torques whose computation is based on the dynamic model of the mechanical structure on which external forces act. The daily and elevation angles of the PV module represent the input parameters in the mechanical device, while the outputs transmitted to the controller are the motor torques. The controller tuning is approached by a parametric optimization process, using design of experiments and response surface methodology techniques, in a multiple regression. The simulation and experimental results demonstrate the operational performance of the tracking system. PMID:24327803

Pressure gradients fail to predict diffusio-osmosis

NASA Astrophysics Data System (ADS)

Liu, Yawei; Ganti, Raman; Frenkel, Daan

2018-05-01

We present numerical simulations of diffusio-osmotic flow, i.e. the fluid flow generated by a concentration gradient along a solid-fluid interface. In our study, we compare a number of distinct approaches that have been proposed for computing such flows and compare them with a reference calculation based on direct, non-equilibrium molecular dynamics simulations. As alternatives, we consider schemes that compute diffusio-osmotic flow from the gradient of the chemical potentials of the constituent species and from the gradient of the component of the pressure tensor parallel to the interface. We find that the approach based on treating chemical potential gradients as external forces acting on various species agrees with the direct simulations, thereby supporting the approach of Marbach et al (2017 J. Chem. Phys. 146 194701). In contrast, an approach based on computing the gradients of the microscopic pressure tensor does not reproduce the direct non-equilibrium results.

Lower extremity joint moments of collegiate soccer players differ between genders during a forward jump.

PubMed

Hart, Joseph M; Garrison, J Craig; Palmieri-Smith, Riann; Kerrigan, D Casey; Ingersoll, Christopher D

2008-05-01

Lower extremity kinetics while performing a single-leg forward jump landing may help explain gender biased risk for noncontact anterior cruciate ligament injury. Gender comparison of lower extremity joint angles and moments. Static groups comparison. Motion analysis laboratory. 8 male and 8 female varsity, collegiate soccer athletes. 5 single-leg landings from a 100cm forward jump. Peak and initial contact external joint moments and joint angles of the ankle, knee, and hip. At initial heel contact, males exhibited a adduction moment whereas females exhibited a abduction moment at the hip. Females also had significantly less peak hip extension moment and significantly less peak hip internal rotation moment than males had. Females exhibited greater knee adduction and hip internal rotation angles than men did. When decelerating from a forward jump, gender differences exist in forces acting at the hip.

Protecting vulnerable research participants: a Foucault-inspired analysis of ethics committees.

PubMed

Juritzen, Truls I; Grimen, Harald; Heggen, Kristin

2011-09-01

History has demonstrated the necessity of protecting research participants. Research ethics are based on a concept of asymmetry of power, viewing the researcher as powerful and potentially dangerous and establishing ethics committees as external agencies in the field of research. We argue in favour of expanding this perspective on relationships of power to encompass the ethics committees as one among several actors that exert power and that act in a relational interplay with researchers and participants. We employ Michel Foucault's ideas of power as an omnipresent force which is dynamic and unstable, as well as the notion that knowledge and power are inextricably intertwined. The article discusses how research ethics committees may affect academic freedom. In addition it is pointed out that research participants could be harmed - not only by unfortunate research practices, but also by being subjected to the protective efforts of ethics monitoring bodies.

Forces Acting on a Ball in an Air Jet

ERIC Educational Resources Information Center

Lopez-Arias, T.; Gratton, L. M.; Zendri, G.; Oss, S.

2011-01-01

The forces acting on a ball in an air jet have been measured using simple equipment. Such measurements allow quite a precise, non-ambiguous description and understanding of the physical mechanism which explains the famous levitating ball experiment. (Contains 7 figures.)

External force/velocity control for an autonomous rehabilitation robot

NASA Astrophysics Data System (ADS)

Saekow, Peerayuth; Neranon, Paramin; Smithmaitrie, Pruittikorn

2018-01-01

Stroke is a primary cause of death and the leading cause of permanent disability in adults. There are many stroke survivors, who live with a variety of levels of disability and always need rehabilitation activities on daily basis. Several studies have reported that usage of rehabilitation robotic devices shows the better improvement outcomes in upper-limb stroke patients than the conventional therapy-nurses or therapists actively help patients with exercise-based rehabilitation. This research focuses on the development of an autonomous robotic trainer designed to guide a stroke patient through an upper-limb rehabilitation task. The robotic device was designed and developed to automate the reaching exercise as mentioned. The designed robotic system is made up of a four-wheel omni-directional mobile robot, an ATI Gamma multi-axis force/torque sensor used to measure contact force and a microcontroller real-time operating system. Proportional plus Integral control was adapted to control the overall performance and stability of the autonomous assistive robot. External force control was successfully implemented to establish the behavioral control strategy for the robot force and velocity control scheme. In summary, the experimental results indicated satisfactorily stable performance of the robot force and velocity control can be considered acceptable. The gain tuning for proportional integral (PI) velocity control algorithms was suitably estimated using the Ziegler-Nichols method in which the optimized proportional and integral gains are 0.45 and 0.11, respectively. Additionally, the PI external force control gains were experimentally tuned using the trial and error method based on a set of experiments which allow a human participant moves the robot along the constrained circular path whilst attempting to minimize the radial force. The performance was analyzed based on the root mean square error (E_RMS) of the radial forces, in which the lower the variation in radial forces, the better the performance of the system. The outstanding performance of the tests as specified by the E_RMS of the radial force was observed with proportional and integral gains of Kp = 0.7 and Ki = 0.75, respectively.

Biomechanics of leukocyte rolling

PubMed Central

Sundd, Prithu; Pospieszalska, Maria K.; Cheung, Luthur Siu-Lun; Konstantopoulos, Konstantinos; Ley, Klaus

2011-01-01

Leukocyte rolling on endothelial cells and other P-selectin substrates is mediated by P-selectin binding to P-selectin glycoprotein ligand-1 expressed on the tips of leukocyte microvilli. Leukocyte rolling is a result of rapid, yet balanced formation and dissociation of selectin-ligand bonds in the presence of hydrodynamic shear forces. The hydrodynamic forces acting on the bonds may either increase (catch bonds) or decrease (slip-bonds) their lifetimes. The force-dependent ‘catch-slip’ bond kinetics are explained using the ‘two pathway model’ for bond dissociation. Both the ‘sliding-rebinding’ and the ‘allosteric’ mechanisms attribute ‘catch-slip’ bond behavior to the force-induced conformational changes in the lectin-EGF domain hinge of selectins. Below a threshold shear stress, selectins cannot mediate rolling. This ‘shear-threshold’ phenomenon is a consequence of shear-enhanced tethering and catch-bond enhanced rolling. Quantitative dynamic footprinting microscopy has revealed that leukocytes rolling at venular shear stresses (> 0.6 Pa) undergo cellular deformation (large footprint) and form long tethers. The hydrodynamic shear force and torque acting on the rolling cell are thought to be synergistically balanced by the forces acting on tethers and stressed microvilli, however, their relative contribution remains to be determined. Thus, improvement beyond the current understanding requires in silico models that can predict both cellular and microvillus deformation and experiments that allow measurement of forces acting on individual microvilli and tethers. PMID:21515934

Comparison of abdominal muscle activity and peak expiratory flow between forced vital capacity and fast expiration exercise.

PubMed

Ishida, Hiroshi; Suehiro, Tadanobu; Watanabe, Susumu

2017-04-01

[Purpose] The purpose of this investigation was to compare the activities of the abdominal muscles and peak expiratory flow between forced vital capacity and fast expiration exercise. [Subjects and Methods] Fifteen healthy male participated in this study. Peak expiratory flow and electromyographic activities of the rectus abdominis, external oblique, and internal oblique/transversus abdominis muscles were measured during forced vital capacity and fast expiration exercise and then peak amplitude and its appearance time were obtained. [Results] Peak expiratory flow values were significantly higher during fast expiration exercise than during forced vital capacity. The internal oblique/transversus abdominis muscles showed significantly higher peak amplitude during fast expiration exercise than during forced vital capacity. However, there were no significant differences between forced vital capacity and fast expiration exercise in the rectus abdominis and external oblique muscles. There was no difference in the appearance time of the peak amplitude between forced vital capacity and fast expiration exercise in any muscle. [Conclusion] Fast expiration exercise might be beneficial for increasing expiratory speed and neuromuscular activation of the internal oblique/transversus abdominis muscles compared to forced vital capacity. These findings could be considered when recommending a variation of expiratory muscle strength training as part of pulmonary rehabilitation programs.

Indian Ocean warming during 1958-2004 simulated by a climate system model and its mechanism

NASA Astrophysics Data System (ADS)

Dong, Lu; Zhou, Tianjun; Wu, Bo

2014-01-01

The mechanism responsible for Indian Ocean Sea surface temperature (SST) basin-wide warming trend during 1958-2004 is studied based on both observational data analysis and numerical experiments with a climate system model FGOALS-gl. To quantitatively estimate the relative contributions of external forcing (anthropogenic and natural forcing) and internal variability, three sets of numerical experiments are conducted, viz. an all forcing run forced by both anthropogenic forcing (greenhouse gases and sulfate aerosols) and natural forcing (solar constant and volcanic aerosols), a natural forcing run driven by only natural forcing, and a pre-industrial control run. The model results are compared to the observations. The results show that the observed warming trend during 1958-2004 (0.5 K (47-year)-1) is largely attributed to the external forcing (more than 90 % of the total trend), while the residual is attributed to the internal variability. Model results indicate that the anthropogenic forcing accounts for approximately 98.8 % contribution of the external forcing trend. Heat budget analysis shows that the surface latent heat flux due to atmosphere and surface longwave radiation, which are mainly associated with anthropogenic forcing, are in favor of the basin-wide warming trend. The basin-wide warming is not spatially uniform, but with an equatorial IOD-like pattern in climate model. The atmospheric processes, oceanic processes and climatological latent heat flux together form an equatorial IOD-like warming pattern, and the oceanic process is the most important in forming the zonal dipole pattern. Both the anthropogenic forcing and natural forcing result in easterly wind anomalies over the equator, which reduce the wind speed, thereby lead to less evaporation and warmer SST in the equatorial western basin. Based on Bjerknes feedback, the easterly wind anomalies uplift the thermocline, which is unfavorable to SST warming in the eastern basin, and contribute to SST warming via deeper thermocline in the western basin. The easterly anomalies also drive westward anomalous equatorial currents, against the eastward climatology currents, which is in favor of the SST warming in the western basin via anomalous warm advection. Therefore, both the atmospheric and oceanic processes are in favor of the IOD-like warming pattern formation over the equator.

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…

Correlational approach to study interactions between dust Brownian particles in a plasma

NASA Astrophysics Data System (ADS)

Lisin, E. A.; Vaulina, O. S.; Petrov, O. F.

2018-01-01

A general approach to the correlational analysis of Brownian motion of strongly coupled particles in open dissipative systems is described. This approach can be applied to the theoretical description of various non-ideal statistically equilibrium systems (including non-Hamiltonian systems), as well as for the analysis of experimental data. In this paper, we consider an application of the correlational approach to the problem of experimental exploring the wake-mediated nonreciprocal interactions in complex plasmas. We derive simple analytic equations, which allows one to calculate the gradients of forces acting on a microparticle due to each of other particles as well as the gradients of external field, knowing only the information on time-averaged correlations of particles displacements and velocities. We show the importance of taking dissipative and random processes into account, without which consideration of a system with a nonreciprocal interparticle interaction as linearly coupled oscillators leads to significant errors in determining the characteristic frequencies in a system. In the examples of numerical simulations, we demonstrate that the proposed original approach could be an effective instrument in exploring the longitudinal wake structure of a microparticle in a plasma. Unlike the previous attempts to study the wake-mediated interactions in complex plasmas, our method does not require any external perturbations and is based on Brownian motion analysis only.

Workplace health promotion and stakeholder positions: a Finnish case study.

PubMed

Auvinen, Ari-Matti; Kohtamäki, Kari; Ilvesmäki Msc, Antti

2012-01-01

Modern workplace health promotion (WHP) requires collaboration, partnerships, and alliances with both internal and external stakeholders. However, the identification of the key stakeholders as well as the systematic mapping of their views has barely been covered in the existing research literature. This article describes the stakeholders and stakeholder positions in WHP in Finland. In this study, the stakeholders were classified as internal, interface, and external stakeholders. Furthermore, based on the authors' research, stakeholders and their positions were represented on a stakeholder map as well as by the power-interest matrix of the stakeholders. The governmental authorities play a key role in driving the strategic change toward WHP by preparing the required legislation and regulatory measures. However, both active employers and active employees can through their own work accelerate the development of new WHP services. Close collaboration between employers and employees is required at the individual workplaces. Some stakeholders, such as pension funds and occupational health services (OHS) providers, can act as important driving forces and support the strategic implementation of WHP in the workplaces. However, alone they have only limited opportunities to organize the WHP activities. Understanding the various stakeholders and the systematic mapping of their positions is essential for the successful planning and implementation of WHP activities.

Bursting Regimes in a Reaction-Diffusion System with Action Potential-Dependent Equilibrium

PubMed Central

Meier, Stephen R.; Lancaster, Jarrett L.; Starobin, Joseph M.

2015-01-01

The equilibrium Nernst potential plays a critical role in neural cell dynamics. A common approximation used in studying electrical dynamics of excitable cells is that the ionic concentrations inside and outside the cell membranes act as charge reservoirs and remain effectively constant during excitation events. Research into brain electrical activity suggests that relaxing this assumption may provide a better understanding of normal and pathophysiological functioning of the brain. In this paper we explore time-dependent ionic concentrations by allowing the ion-specific Nernst potentials to vary with developing transmembrane potential. As a specific implementation, we incorporate the potential-dependent Nernst shift into a one-dimensional Morris-Lecar reaction-diffusion model. Our main findings result from a region in parameter space where self-sustaining oscillations occur without external forcing. Studying the system close to the bifurcation boundary, we explore the vulnerability of the system with respect to external stimulations which disrupt these oscillations and send the system to a stable equilibrium. We also present results for an extended, one-dimensional cable of excitable tissue tuned to this parameter regime and stimulated, giving rise to complex spatiotemporal pattern formation. Potential applications to the emergence of neuronal bursting in similar two-variable systems and to pathophysiological seizure-like activity are discussed. PMID:25823018

Deep wells integrated with microfluidic valves for stable docking and storage of cells.

PubMed

Jang, Yun-Ho; Kwon, Cheong Hoon; Kim, Sang Bok; Selimović, Seila; Sim, Woo Young; Bae, Hojae; Khademhosseini, Ali

2011-02-01

In this paper, we describe a microfluidic mechanism that combines microfluidic valves and deep wells for cell localization and storage. Cells are first introduced into the device via externally controlled flow. Activating on-chip valves was used to interrupt the flow and to sediment the cells floating above the wells. Thus, valves could be used to localize the cells in the desired locations. We quantified the effect of valves in the cell storage process by comparing the total number of cells stored with and without valve activation. We hypothesized that in deep wells external flows generate low shear stress regions that enable stable, long-term docking of cells. To assess this hypothesis we conducted numerical calculations to understand the influence of well depth on the forces acting on cells. We verified those predictions experimentally by comparing the fraction of stored cells as a function of the well depth and input flow rate upon activation of the valves. As expected, upon reintroduction of the flow the cells in the deep wells were not moved whereas those in shallow wells were washed away. Taken together, our paper demonstrates that deep wells and valves can be combined to enable a broad range of cell studies. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Letter to the editor concerning the article "Bar velocities capable of optimising the muscle power in strength-power exercises" by Loturco, Pereira, Abad, Tabares, Moraes, Kobal, Kitamura & Nakamura (2017).

PubMed

Jaric, Slobodan; Garcia Ramos, Amador

2018-05-01

Loturco and co-workers (2017) recently published data in the Journal of Sports Sciences to present the optimum loading magnitudes regarding the maximization of the "mean propulsive power" of the leg and arm muscles. Among the most important findings were that (1) the recorded power in the squat and squat jump exercises was markedly low, (2) the optimum external load that maximized the power in the same exercises was close to 100% of body weight, while (3) the ballistic bench press throw revealed smaller power than the regular bench press typically performed with relatively low level of muscle activation towards the end of the propulsive lifting phase. The findings are either counter-intuitive, or contradict the literature findings, or both, and we believe that they originate from apparent methodological flaws. The first one is neglecting the force acting against the body segments moved together with the external load that is particularly high in squat exercises. The second one is an erroneous calculation of the propulsive phase that included a part of the bar's flight time. Both of these methodological flaws are frequent in the literature and could be associated with the improper use and calculation of variables when utilizing linear position transducers.

Spin caloric effects in antiferromagnets assisted by an external spin current

NASA Astrophysics Data System (ADS)

Gomonay, O.; Yamamoto, Kei; Sinova, Jairo

2018-07-01

Searching for novel spin caloric effects in antiferromagnets, we study the properties of thermally activated magnons in the presence of an external spin current and temperature gradient. We predict the spin Peltier effect—generation of a heat flux by spin accumulation—in an antiferromagnetic insulator with cubic or uniaxial magnetic symmetry. This effect is related to the spin-current induced splitting of the relaxation times of the magnons with the opposite spin direction. We show that the Peltier effect can trigger antiferromagnetic domain wall motion with a force whose value grows with the temperature of a sample. At a temperature larger than the energy of the low-frequency magnons, this force is much larger than the force caused by direct spin transfer between the spin current and the domain wall. We also demonstrate that the external spin current can induce the magnon spin Seebeck effect. The corresponding Seebeck coefficient is controlled by the current density. These spin-current assisted caloric effects open new ways for the manipulation of the magnetic states in antiferromagnets.

Compression asphyxia in upright suspended position.

PubMed

Tumram, Nilesh Keshav; Ambade, Vipul Namdeorao; Dixit, Pradeep Gangadhar

2014-06-01

In compression asphyxia, the respiration is prevented by external pressure on the body. It is usually due to external force compressing the trunk due to heavy weight over chest/abdomen and is associated with internal injuries. In the present case, the victim was suspended in an upright position owing to wedging of the chest and the abdomen in the gap between 2 parallel bridges undergoing construction. There was neither any heavy weight over the body, nor was any external force applied over the trunk. Moreover, there was neither any severe blunt force injury nor any significant pathological natural disease contributing to the cause of death. The body was wedged in the gap between 2 static hard surfaces. The victim was unable to extricate himself from the position owing to impairment of cognitive responses and coordination due to influence of alcohol. The victim died as a result of "static" asphyxia due to compression of the chest and the abdomen. Compression asphyxia in upright suspended position under this circumstance is very rare and not reported previously to the best of our knowledge.

Tension, cell shape and triple-junction angle anisotropy in the Drosophila germband

NASA Astrophysics Data System (ADS)

Lacy, Monica; Hutson, M. Shane; Meyer, Christian; McDonald, Xena

In the field of tissue mechanics, the embryonic development of Drosophila melanogaster offers many opportunities for study. One of Drosophila's most crucial morphogenetic stages is the retraction of an epithelial tissue called the germband. During retraction, the segments of the retracting germband, as well as the individual germband cells, elongate in response to forces from a connected tissue, the amnioserosa. Modeling of this elongation, based on tissue responses to laser wounding, has plotted the internal germband tension against the external amnioserosa stress, creating a phase space to determine points and regions corresponding to stable elongation. Although the resulting fits indicate a necessary opposition of internal and external forces, they are inconclusive regarding the exact balance. We will present results testing the model predictions by measuring cell shapes and the correlations between cell-edge directions and triple-junction angles. These measures resolve the ambiguity in pinpointing the internal-external force balance for each germband segment. Research was supported by NIH Grant Numbers 1R01GM099107 and 1R21AR068933.

PDMS-based triboelectric and transparent nanogenerators with ZnO nanorod arrays.

PubMed

Ko, Yeong Hwan; Nagaraju, Goli; Lee, Soo Hyun; Yu, Jae Su

2014-05-14

Vertically-grown ZnO nanorod arrays (NRAs) on indium tin oxide (ITO)-coated polyethylene terephthalate (PET), as a top electrode of nanogenerators, were investigated for the antireflective property as well as an efficient contact surface in bare polydimethysiloxane (PDMS)-based triboelectric nanogenerators. Compared to conventional ITO-coated PET (i.e., ITO/PET), the ZnO NRAs considerably suppressed the reflectance from 20 to 9.7% at wavelengths of 300-1100 nm, creating a highly transparent top electrode, as demonstrated by theoretical analysis. Also, the interval time between the peaks of generated output voltage under external pushing forces was significantly decreased from 1.84 to 0.19 s because the reduced contact area of the PDMS by discrete surfaces of the ZnO NRAs on ITO/PET causes a rapid sequence for triboelectric charge generation process including rubbing and separating. Therefore, the use of this top electrode enabled to operate the transparent PDMS-based triboelectric nanogenerator at high frequency of external pushing force. Under different external forces of 0.3-10 kgf, the output voltage and current were also characterized.

Computational study of a self-cleaning process on superhydrophobic surface

NASA Astrophysics Data System (ADS)

Farokhirad, Samaneh

All substances around us are bounded by interfaces. In general, interface between different phases of materials are categorized as fluid-fluid, solid-fluid, and solid-solid. Fluid-fluid interfaces exhibit a distinct behavior by adapting their shape in response to external stimulus. For example, a liquid droplet on a substrate can undergo different wetting morphologies depending on topography and chemical composition of the surface. Fundamentally, interfacial phenomena arise at the limit between two immiscible phases, namely interface. The interface dynamic governs, to a great extent, physical processes such as impact and spreading of two immiscible media, and stabilization of foams and emulsions from break-up and coalescence. One of the recent challenging problems in the interface-driven fluid dynamics is the self-propulsion mechanism of droplets by means of different types of external forces such as electrical potential, or thermal Marangoni effect. Rapid removal of self-propelled droplet from the surface is an essential factor in terms of expense and efficiency for many applications including self-cleaning and enhanced heat and mass transfer to save energy and natural resources. A recent study on superhydrophobic nature of micro- and nanostructures of cicada wings offers a unique way for the self-propulsion process with no external force, namely coalescence-induced self-propelled jumping of droplet which can act effectively at any orientation. The biological importance of this new mechanism is associated with protecting such surfaces from long term exposure to colloidal particles such as microbial colloids and virus particles. Different interfacial phenomena can occur after out-of-plane jumping of droplet. If the departed droplet is landed back by gravity, it may impact and spread on the surface or coalesce with another droplet and again self-peopled itself to jump away from the surface. The complete removal of the propelled droplet to a sufficient distance beyond the boundary layer of the surface can be accomplished with a surface-parallel shear flow. This thesis presents an investigation of the physics involved in the mechanism of coalescence-induced self-propelled jumping of droplet with and without particle presence, through the use of numerical simulation. (Abstract shortened by ProQuest.).

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.

Depth-dependent resistance of granular media to vertical penetration.

PubMed

Brzinski, T A; Mayor, P; Durian, D J

2013-10-18

We measure the quasistatic friction force acting on intruders moving downwards into a granular medium. By utilizing different intruder geometries, we demonstrate that the force acts locally normal to the intruder surface. By altering the hydrostatic loading of grain contacts by a sub-fluidizing airflow through the bed, we demonstrate that the relevant frictional contacts are loaded by gravity rather than by the motion of the intruder itself. Lastly, by measuring the final penetration depth versus airspeed and using an earlier result for inertial drag, we demonstrate that the same quasistatic friction force acts during impact. Altogether this force is set by a friction coefficient, hydrostatic pressure, projectile size and shape, and a dimensionless proportionality constant. The latter is the same in nearly all experiments, and is surprisingly greater than one.

Vertical and lateral forces when a permanent magnet above a superconductor traverses in arbitrary directions

NASA Astrophysics Data System (ADS)

Yang, Yong

2008-12-01

In an actual levitation system composed of high temperature superconductors (HTSs) and permanent magnets (PMs), the levitating bodies may traverse in arbitrary directions. Many previous researchers assumed that the levitating bodies moved in a vertical direction or a lateral direction in order to simplify the problem. In this paper, the vertical and lateral forces acting on the PM are calculated by the modified frozen-image method when a PM above an HTS traverses in arbitrary directions. In order to study the effects of the movement directions on the vertical and lateral forces, comparisons of the forces that act on a PM traversing in a tilted direction with those that act on a PM traversing in a vertical direction or a lateral direction have been presented.

The Chinese Communist Armed Forces.

DTIC Science & Technology

1974-01-01

tepriorcosn \\ MAR 1 3 1981 C ~) AIR UNIVERSITY -4 MAXWELL AIR FORCE BASE, ALABAMA I z AU-I I "-- ’The Chinese Communist Armed Forces. Kenneth R. Whiting...AO-A096 28𔃾 DEPARTMENT OF STATE WASHINGTON DC OFFICE OF EXTERNAL--ETC F/6 S/ THE CH INESE C OMMUNIST ARMED FORCES. (U) vsif k.1974 K R WHITING FAR...1974 Directorate of Documentary Research Air University Institute for Professional Development Maxwell Air Force Base, Alabama "/" I;-) K II AIR

Mechanics and statistics of the worm-like chain

NASA Astrophysics Data System (ADS)

Marantan, Andrew; Mahadevan, L.

2018-02-01

The worm-like chain model is a simple continuum model for the statistical mechanics of a flexible polymer subject to an external force. We offer a tutorial introduction to it using three approaches. First, we use a mesoscopic view, treating a long polymer (in two dimensions) as though it were made of many groups of correlated links or "clinks," allowing us to calculate its average extension as a function of the external force via scaling arguments. We then provide a standard statistical mechanics approach, obtaining the average extension by two different means: the equipartition theorem and the partition function. Finally, we work in a probabilistic framework, taking advantage of the Gaussian properties of the chain in the large-force limit to improve upon the previous calculations of the average extension.

Qualitative analysis of a discrete thermostatted kinetic framework modeling complex adaptive systems

NASA Astrophysics Data System (ADS)

Bianca, Carlo; Mogno, Caterina

2018-01-01

This paper deals with the derivation of a new discrete thermostatted kinetic framework for the modeling of complex adaptive systems subjected to external force fields (nonequilibrium system). Specifically, in order to model nonequilibrium stationary states of the system, the external force field is coupled to a dissipative term (thermostat). The well-posedness of the related Cauchy problem is investigated thus allowing the new discrete thermostatted framework to be suitable for the derivation of specific models and the related computational analysis. Applications to crowd dynamics and future research directions are also discussed within the paper.

Controlling Force and Depth in Friction Stir Welding

NASA Technical Reports Server (NTRS)

Adams, Glynn; Loftus, Zachary; McCormac, Nathan; Venable, Richard

2005-01-01

Feedback control of the penetration force applied to a pin tool in friction stir welding has been found to be a robust and reliable means for controlling the depth of penetration of the tool. This discovery has made it possible to simplify depth control and to weld with greater repeatability, even on workpieces with long weld joints. Prior to this discovery, depths of penetration in friction stir welding were controlled by hard-tooled roller assemblies or by depth actuators controlled by feedback from such external sensors as linear variable-differential transformers or laser-based devices. These means of control are limited: A hard-tooled roller assembly confines a pin tool to a preset depth that cannot be changed easily during the welding process. A measurement by an external sensor is only an indirect indicative of the depth of penetration, and computations to correlate such a measurement with a depth of penetration are vulnerable to error. The present force-feedback approach exploits the proportionality between the depth and the force of penetration Unlike a depth measurement taken by an external sensor, a force measurement can be direct because it can be taken by a sensor coupled directly to the pin tool. The reading can be processed through a modern electronic servo control system to control an actuator to keep the applied penetration force at the desired level. In comparison with the older depth-control methods described above, this method offers greater sensitivity to plasticizing of the workpiece metal and is less sensitive to process noise, resulting in a more consistent process. In an experiment, a tapered panel was friction stir welded while controlling the force of penetration according to this method. The figure is a plot of measurements taken during the experiment, showing that force was controlled with a variation of 200 lb (890 N), resulting in control of the depth of penetration with a variation of 0.004 in. (0.1 mm).

The uncertainties and causes of the recent changes in global evapotranspiration from 1982 to 2010

NASA Astrophysics Data System (ADS)

Dong, Bo; Dai, Aiguo

2017-07-01

Recent studies have shown considerable changes in terrestrial evapotranspiration (ET) since the early 1980s, but the causes of these changes remain unclear. In this study, the relative contributions of external climate forcing and internal climate variability to the recent ET changes are examined. Three datasets of global terrestrial ET and the CMIP5 multi-model ensemble mean ET are analyzed, respectively, to quantify the apparent and externally-forced ET changes, while the unforced ET variations are estimated as the apparent ET minus the forced component. Large discrepancies of the ET estimates, in terms of their trend, variability, and temperature- and precipitation-dependence, are found among the three datasets. Results show that the forced global-mean ET exhibits an upward trend of 0.08 mm day-1 century-1 from 1982 to 2010. The forced ET also contains considerable multi-year to decadal variations during the latter half of the 20th century that are caused by volcanic aerosols. The spatial patterns and interannual variations of the forced ET are more closely linked to precipitation than temperature. After removing the forced component, the global-mean ET shows a trend ranging from -0.07 to 0.06 mm day-1 century-1 during 1982-2010 with varying spatial patterns among the three datasets. Furthermore, linkages between the unforced ET and internal climate modes are examined. Variations in Pacific sea surface temperatures (SSTs) are found to be consistently correlated with ET over many land areas among the ET datasets. The results suggest that there are large uncertainties in our current estimates of global terrestrial ET for the recent decades, and the greenhouse gas (GHG) and aerosol external forcings account for a large part of the apparent trend in global-mean terrestrial ET since 1982, but Pacific SST and other internal climate variability dominate recent ET variations and changes over most regions.

Oblique abdominal muscle activity in response to external perturbations when pushing a cart.

PubMed

Lee, Yun-Ju; Hoozemans, Marco J M; van Dieën, Jaap H

2010-05-07

Cyclic activation of the external and internal oblique muscles contributes to twisting moments during normal gait. During pushing while walking, it is not well understood how these muscles respond to presence of predictable (cyclic push-off forces) and unpredictable (external) perturbations that occur in pushing tasks. We hypothesized that the predictable perturbations due to the cyclic push-off forces would be associated with cyclic muscle activity, while external perturbations would be counteracted by cocontraction of the oblique abdominal muscles. Eight healthy male subjects pushed at two target forces and two handle heights in a static condition and while walking without and with external perturbations. For all pushing tasks, the median, the static (10th percentile) and the peak levels (90th percentile) of the electromyographic amplitudes were determined. Linear models with oblique abdominal EMGs and trunk angles as input were fit to the twisting moments, to estimate trunk stiffness. There was no significant difference between the static EMG levels in pushing while walking compared to the peak levels in pushing while standing. When pushing while walking, the additional dynamic activity was associated with the twisting moments, which were actively modulated by the pairs of oblique muscles as in normal gait. The median and static levels of trunk muscle activity and estimated trunk stiffness were significantly higher when perturbations occurred than without perturbations. The increase baseline of muscle activity indicated cocontraction of the antagonistic muscle pairs. Furthermore, this cocontraction resulted in an increased trunk stiffness around the longitudinal axis. Copyright 2010 Elsevier Ltd. All rights reserved.

Support for the existence of invertible maps between electronic densities and non-analytic 1-body external potentials in non-relativistic time-dependent quantum mechanics

NASA Astrophysics Data System (ADS)

Mosquera, Martín A.

2017-10-01

Provided the initial state, the Runge-Gross theorem establishes that the time-dependent (TD) external potential of a system of non-relativistic electrons determines uniquely their TD electronic density, and vice versa (up to a constant in the potential). This theorem requires the TD external potential and density to be Taylor-expandable around the initial time of the propagation. This paper presents an extension without this restriction. Given the initial state of the system and evolution of the density due to some TD scalar potential, we show that a perturbative (not necessarily weak) TD potential that induces a non-zero divergence of the external force-density, inside a small spatial subset and immediately after the initial propagation time, will cause a change in the density within that subset, implying that the TD potential uniquely determines the TD density. In this proof, we assume unitary evolution of wavefunctions and first-order differentiability (which does not imply analyticity) in time of the internal and external force-densities, electronic density, current density, and their spatial derivatives over the small spatial subset and short time interval.

Annular Internal-External-Expansion Rocket Nozzles for Large Booster Applications

NASA Technical Reports Server (NTRS)

Connors, James F.; Cubbison, Robert W.; Mitchell, Glenn A.

1961-01-01

For large-thrust booster applications, annular rocket nozzles employing both internal and external expansion are investigated. In these nozzles, free-stream air flows through the center as well as around the outside of the exiting jet. Flaps for deflecting the rocket exhaust are incorporated on the external-expansion surface for thrust-vector control. In order to define nozzle off-design performance, thrust vectoring effectiveness, and external stream effects, an experimental investigation was conducted on two annular nozzles with area ratios of 15 and 25 at Mach 0, 2, and 3 in the Lewis 10- by 10-foot wind tunnel. Air, pressurized to 600 pounds per square inch absolute, was used to simulate the exhaust flow. For a nozzle-pressure-ratio range of 40 to 1000, the ratio of actual to ideal thrust was essentially constant at 0.98 for both nozzles. Compared with conventional convergent-divergent configurations on hypothetical boost missions, the performance gains of the annular nozzle could yield significant orbital payload increases (possibly 8 to 17 percent). A single flap on the external-expansion surface of the area-ratio-25 annular nozzle produced a side force equal to 4 percent of the axial force with no measurable loss in axial thrust.

76 FR 32224 - Migratory Birds; Take of Migratory Birds by the Armed Forces

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-03

... DEPARTMENT OF THE INTERIOR Fish and Wildlife Service Migratory Birds; Take of Migratory Birds by... Forces to incidentally take migratory birds during approved military readiness activities without violating the Migratory Bird Treaty Act (MBTA). The Authorization Act provided this interim authority to...

Contracting out : benchmarking study : phase 1 : part 2 : external data collection

DOT National Transportation Integrated Search

2002-04-17

The planning provisions of the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) and the transportation provisions of the Clean Air Act Amendments of 1990 (CAAA) define the framework for the effective integration of transportation and ...

Child Trafficking and Formalisation: The Case of International Adoption from Ecuador

ERIC Educational Resources Information Center

Leifsen, Esben

2008-01-01

Child trafficking activity often draws on formal administrative and legal resources. Formalisation implies considerable cooperation between public functionaries, lawyers and external actors. I argue that child rights advocates are forceful policy formulators who tend to ignore the public-external link because they focus on the external…

The external amino acid signaling pathway promotes activation of Stp1 and Uga35/Dal81 transcription factors for induction of the AGP1 gene in Saccharomyces cerevisiae.

PubMed Central

Abdel-Sater, Fadi; Iraqui, Ismaïl; Urrestarazu, Antonio; André, Bruno

2004-01-01

Yeast cells respond to the presence of amino acids in their environment by inducing transcription of several amino acid permease genes including AGP1, BAP2, and BAP3. The signaling pathway responsible for this induction involves Ssy1, a permease-like sensor of external amino acids, and culminates with proteolytic cleavage and translocation to the nucleus of the zinc-finger proteins Stp1 and Stp2, the lack of which abolishes induction of BAP2 and BAP3. Here we show that Stp1-but not Stp2-plays an important role in AGP1 induction, although significant induction of AGP1 by amino acids persists in stp1 and stp1 stp2 mutants. This residual induction depends on the Uga35/Dal81 transcription factor, indicating that the external amino acid signaling pathway activates not only Stp1 and Stp2, but also another Uga35/Dal81-dependent transcriptional circuit. Analysis of the AGP1 gene's upstream region revealed that Stp1 and Uga35/Dal81 act synergistically through a 21-bp cis-acting sequence similar to the UAS(AA) element previously found in the BAP2 and BAP3 upstream regions. Although cells growing under poor nitrogen-supply conditions display much higher induction of AGP1 expression than cells growing under good nitrogen-supply conditions, the UAS(AA) itself is totally insensitive to nitrogen availability. Nitrogen-source control of AGP1 induction is mediated by the GATA factor Gln3, likely acting through adjacent 5'-GATA-3' sequences, to amplify the positive effect of UAS(AA). Our data indicate that Stp1 may act in combination with distinct sets of transcription factors, according to the gene context, to promote induction of transcription in response to external amino acids. The data also suggest that Uga35/Dal81 is yet another transcription factor under the control of the external amino acid sensing pathway. Finally, the data show that the TOR pathway mediating global nitrogen control of transcription does not interfere with the external amino acid signaling pathway. PMID:15126393

Force coordination in static manipulation tasks performed using standard and non-standard grasping techniques.

PubMed

de Freitas, Paulo B; Jaric, Slobodan

2009-04-01

We evaluated coordination of the hand grip force (GF; normal component of the force acting at the hand-object contact area) and load force (LF; the tangential component) in a variety of grasping techniques and two LF directions. Thirteen participants exerted a continuous sinusoidal LF pattern against externally fixed handles applying both standard (i.e., using either the tips of the digits or the palms; the precision and palm grasps, respectively) and non-standard grasping techniques (using wrists and the dorsal finger areas; the wrist and fist grasp). We hypothesized (1) that the non-standard grasping techniques would provide deteriorated indices of force coordination when compared with the standard ones, and (2) that the nervous system would be able to adjust GF to the differences in friction coefficients of various skin areas used for grasping. However, most of the indices of force coordination remained similar across the tested grasping techniques, while the GF adjustments for the differences in friction coefficients (highest in the palm and the lowest in the fist and wrist grasp) provided inconclusive results. As hypothesized, GF relative to the skin friction was lowest in the precision grasp, but highest in the palm grasp. Therefore, we conclude that (1) the elaborate coordination of GF and LF consistently seen across the standard grasping techniques could be generalized to the non-standard ones, while (2) the ability to adjust GF using the same grasping technique to the differences in friction of various objects cannot be fully generalized to the GF adjustment when different grasps (i.e., hand segments) are used to manipulate the same object. Due to the importance of the studied phenomena for understanding both the functional and neural control aspects of manipulation, future studies should extend the current research to the transient and dynamic tasks, as well as to the general role of friction in our mechanical interactions with the environment.

Brownian dynamics study of ion transport in the vestibule of membrane channels.

PubMed

Li, S C; Hoyles, M; Kuyucak, S; Chung, S H

1998-01-01

Brownian dynamics simulations have been carried out to study the transport of ions in a vestibular geometry, which offers a more realistic shape for membrane channels than cylindrical tubes. Specifically, we consider a torus-shaped channel, for which the analytical solution of Poisson's equation is possible. The system is composed of the toroidal channel, with length and radius of the constricted region of 80 A and 4 A, respectively, and two reservoirs containing 50 sodium ions and 50 chloride ions. The positions of each of these ions executing Brownian motion under the influence of a stochastic force and a systematic electric force are determined at discrete time steps of 50 fs for up to 2.5 ns. All of the systematic forces acting on an ion due to the other ions, an external electric field, fixed charges in the channel protein, and the image charges induced at the water-protein boundary are explicitly included in the calculations. We find that the repulsive dielectric force arising from the induced surface charges plays a dominant role in channel dynamics. It expels an ion from the vestibule when it is deliberately put in it. Even in the presence of an applied electric potential of 100 mV, an ion cannot overcome this repulsive force and permeate the channel. Only when dipoles of a favorable orientation are placed along the sides of the transmembrane segment can an ion traverse the channel under the influence of a membrane potential. When the strength of the dipoles is further increased, an ion becomes detained in a potential well, and the driving force provided by the applied field is not sufficient to drive the ion out of the well. The trajectory of an ion navigating across the channel mostly remains close to the central axis of the pore lumen. Finally, we discuss the implications of these findings for the transport of ions across the membrane.

A parametric experimental investigation of a scramjet nozzle at Mach 6 with Freon and argon or air used for exhaust simulation

NASA Technical Reports Server (NTRS)

Cubbage, James M.; Monta, William J.

1991-01-01

A parametric experimental investigation of a scramjet nozzle was conducted with a gas mixture used to simulate the scramjet engine exhaust flow at a free-stream Reynolds number of approximately 6.5 x 10(exp 6) per foot. External nozzle surface angles of 16, 20, and 24 deg were tested with a fixed-length ramp and for cowl internal surface angles of 6 and 12 deg. Pressure data on the external nozzle surface were obtained for mixtures of Freon and argon gases with a ratio of specific heats of about 1.23, which matches that of a scramjet exhaust. Forces and moments were determined by integration of the pressure data. Two nozzle configurations were also tested with air used to simulate the exhaust flow. On the external nozzle surface, lift and thrust forces for air exhaust simulation were approximately half of those for Freon-argon exhaust simulation and the pitching moment was approximately a third. These differences were primarily due to the difference in the ratios of specific heats between the two exhaust simulation gases. A 20 deg external surface angle produced the greatest thrust for a 6 deg cowl internal surface angle. A flow fence significantly increased lift and thrust forces over those for the nozzle without a flow fence.

75 FR 13095 - Privacy Act of 1974; System of Records

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32 CFR 806b.3 - Violation penalties.

Code of Federal Regulations, 2011 CFR

2011-07-01

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32 CFR 806b.3 - Violation penalties.

Code of Federal Regulations, 2010 CFR

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Federal Register 2010, 2011, 2012, 2013, 2014

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Maintaining rotational equilibrium during object manipulation: linear behavior of a highly non-linear system

PubMed Central

Gao, Fan; Latash, Mark L.

2010-01-01

We address issues of simultaneous control of the grasping force and the total moment of forces applied to a handheld object during its manipulation. Six young healthy male subjects grasped an instrumented handle and performed its cyclic motion in the vertical direction. The handle allowed for setting different clockwise (negative) or counterclockwise torques. Three movement frequencies: 1, 1.5 and 2 Hz, and five different torques: −1/3, −1/6, 0, 1/6 and 1/3 Nm, were used. The rotational equilibrium was maintained by two means: (1) Concerted changes of the moments produced by the normal and tangential forces, specifically anti-phase changes of the moments during the tasks with zero external torque and in-phase changes during the non-zero-torque tasks, and (2) Redistribution of the normal forces among individual fingers such that the agonist fingers—the fingers that resist external torque—increased the force in phase with the acceleration, while the forces of the antagonist fingers—those that assist the external torque—especially, the fingers with the large moment arms, the index and little fingers, stayed unchanged. The observed effects agree with the principle of superposition—according to which some complex actions, for example, prehension, can be decomposed into elemental actions controlled independently—and the mechanical advantage hypothesis according to which in moment production the fingers are activated in proportion to their moment arms with respect to the axis of rotation. We would like to emphasize the linearity of the observed relations, which was not prescribed by the task mechanics and seems to be produced by specific neural control mechanisms. PMID:16328302

Complexion of forces in an anisotropic self-gravitating system

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

Kandrup, H.E.

Chandrasekhar and von Neumann developed a completely stochastic formalism to analyze the complexion of forces acting upon a test star situated in an infinite, homogeneous distribution of field stars. This formalism is generalized here to allow for more realistic inhomogeneous and anisotropic systems. It is demonstrated that the forces acting upon a test star decompose ''naturally'' into the incoherent sum of a mean force associated with the average spatial inhomogeneity and a fluctuating force associated with stochastic deviations from these mean conditions. Moreover, as in the special case considered by Chandrasekhar and von Neumann, one can apparently associate the fluctuatingmore » forces with the effects of particularly proximate field stars, thereby motivating the ''nearest neighbor'' interpretation first introduced by Chandrasekhar.« less

Effects of anthropogenic activity emerging as intensified extreme precipitation over China

NASA Astrophysics Data System (ADS)

Li, Huixin; Chen, Huopo; Wang, Huijun

2017-07-01

This study aims to provide an assessment of the effects of anthropogenic (ANT) forcings and other external factors on observed increases in extreme precipitation over China from 1961 to 2005. Extreme precipitation is represented by the annual maximum 1 day precipitation (RX1D) and the annual maximum 5 day consecutive precipitation (RX5D), and these variables are investigated using observations and simulations from the Coupled Model Intercomparison Project phase 5. The analyses mainly focus on the probability-based index (PI), which is derived from RX1D and RX5D by fitting generalized extreme value distributions. The results indicate that the simulations that include the ANT forcings provide the best representation of the spatial and temporal characteristics of extreme precipitation over China. We use the optimal fingerprint method to obtain the univariate and multivariate fingerprints of the responses to external forcings. The results show that only the ANT forcings are detectable at a 90% confidence level, both individually and when natural forcings are considered simultaneously. The impact of the forcing associated with greenhouse gases (GHGs) is also detectable in RX1D, but its effects cannot be separated from those of combinations of forcings that exclude the GHG forcings in the two-signal analyses. Besides, the estimated changes of PI, extreme precipitation, and events with a 20 year return period under nonstationary climate states are potentially attributable to ANT or GHG forcings, and the relationships between extreme precipitation and temperature from ANT forcings show agreement with observations.

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.

DNA under Force: Mechanics, Electrostatics, and Hydration.

PubMed

Li, Jingqiang; Wijeratne, Sithara S; Qiu, Xiangyun; Kiang, Ching-Hwa

2015-02-25

Quantifying the basic intra- and inter-molecular forces of DNA has helped us to better understand and further predict the behavior of DNA. Single molecule technique elucidates the mechanics of DNA under applied external forces, sometimes under extreme forces. On the other hand, ensemble studies of DNA molecular force allow us to extend our understanding of DNA molecules under other forces such as electrostatic and hydration forces. Using a variety of techniques, we can have a comprehensive understanding of DNA molecular forces, which is crucial in unraveling the complex DNA functions in living cells as well as in designing a system that utilizes the unique properties of DNA in nanotechnology.

Self-oscillation

NASA Astrophysics Data System (ADS)

Jenkins, Alejandro

2013-04-01

Physicists are very familiar with forced and parametric resonance, but usually not with self-oscillation, a property of certain dynamical systems that gives rise to a great variety of vibrations, both useful and destructive. In a self-oscillator, the driving force is controlled by the oscillation itself so that it acts in phase with the velocity, causing a negative damping that feeds energy into the vibration: no external rate needs to be adjusted to the resonant frequency. The famous collapse of the Tacoma Narrows bridge in 1940, often attributed by introductory physics texts to forced resonance, was actually a self-oscillation, as was the swaying of the London Millennium Footbridge in 2000. Clocks are self-oscillators, as are bowed and wind musical instruments. The heart is a “relaxation oscillator”, i.e., a non-sinusoidal self-oscillator whose period is determined by sudden, nonlinear switching at thresholds. We review the general criterion that determines whether a linear system can self-oscillate. We then describe the limiting cycles of the simplest nonlinear self-oscillators, as well as the ability of two or more coupled self-oscillators to become spontaneously synchronized (“entrained”). We characterize the operation of motors as self-oscillation and prove a theorem about their limit efficiency, of which Carnot’s theorem for heat engines appears as a special case. We briefly discuss how self-oscillation applies to servomechanisms, Cepheid variable stars, lasers, and the macroeconomic business cycle, among other applications. Our emphasis throughout is on the energetics of self-oscillation, often neglected by the literature on nonlinear dynamical systems.

Locomotor variation and bending regimes of capuchin limb bones.

PubMed

Demes, Brigitte; Carlson, Kristian J

2009-08-01

Primates are very versatile in their modes of progression, yet laboratory studies typically capture only a small segment of this variation. In vivo bone strain studies in particular have been commonly constrained to linear locomotion on flat substrates, conveying the potentially biased impression of stereotypic long bone loading patterns. We here present substrate reaction forces (SRF) and limb postures for capuchin monkeys moving on a flat substrate ("terrestrial"), on an elevated pole ("arboreal"), and performing turns. The angle between the SRF vector and longitudinal axes of the forearm or leg is taken as a proxy for the bending moment experienced by these limb segments. In both frontal and sagittal planes, SRF vectors and distal limb segments are not aligned, but form discrepant angles; that is, forces act on lever arms and exert bending moments. The positions of the SRF vectors suggest bending around oblique axes of these limb segments. Overall, the leg is exposed to greater moments than the forearm. Simulated arboreal locomotion and turns introduce variation in the discrepancy angles, thus confirming that expanding the range of locomotor behaviors studied will reveal variation in long bone loading patterns that is likely characteristic of natural locomotor repertoires. "Arboreal" locomotion, even on a linear noncompliant branch, is characterized by greater variability of force directions and discrepancy angles than "terrestrial" locomotion (significant for the forearm only), partially confirming the notion that life in trees is associated with greater variation in long bone loading. Directional changes broaden the range of external bending moments even further.

Polymer translocation through a nanopore: a showcase of anomalous diffusion.

PubMed

Milchev, A; Dubbeldam, Johan L A; Rostiashvili, Vakhtang G; Vilgis, Thomas A

2009-04-01

We investigate the translocation dynamics of a polymer chain threaded through a membrane nanopore by a chemical potential gradient that acts on the chain segments inside the pore. By means of diverse methods (scaling theory, fractional calculus, and Monte Carlo and molecular dynamics simulations), we demonstrate that the relevant dynamic variable, the transported number of polymer segments, s(t), displays an anomalous diffusive behavior, both with and without an external driving force being present. We show that in the absence of drag force the time tau, needed for a macromolecule of length N to thread from the cis into the trans side of a cell membrane, scales as tauN(2/alpha) with the chain length. The anomalous dynamics of the translocation process is governed by a universal exponent alpha= 2/(2nu + 2 - gamma(1)), which contains the basic universal exponents of polymer physics, nu (the Flory exponent) and gamma(1) (the surface entropic exponent). A closed analytic expression for the probability to find s translocated segments at time t in terms of chain length N and applied drag force f is derived from the fractional Fokker-Planck equation, and shown to provide analytic results for the time variation of the statistical moments and . It turns out that the average translocation time scales as tau proportional, f(-1)N(2/alpha-1). These results are tested and found to be in perfect agreement with extensive Monte Carlo and molecular dynamics computer simulations.

Spinning optical resonator sensor for torsional vibrational applications measurements

NASA Astrophysics Data System (ADS)

Ali, Amir R.; Gatherer, Andrew; Ibrahim, Mariam S.

2016-03-01

Spinning spherical resonators in the torsional vibrational applications could cause a shift in its whispering gallery mode (WGM). The centripetal force acting on the spinning micro sphere resonator will leads to these WGM shifts. An analysis and experiment were carried out in this paper to investigate and demonstrate this effect using different polymeric resonators. In this experiment, centripetal force exerted by the DC-Motor on the sphere induces an elastic deformation of the resonator. This in turn induces a shift in the whispering gallery modes of the sphere resonator. Materials used for the sphere are polydimethylsiloxane (PDMS 60:1 where 60 parts base silicon elastomer to 1 part polymer curing agent by volume) with shear modulus (G≍1kPa), (PDMS 10:1) with shear modulus (G≍300kPa), polymethylmethacrylate (PMMA, G≍2.6×109GPa) and silica (G≍3×1010 GPa). The sphere size was kept constant with 1mm in diameter for all above materials. The optical modes of the sphere exit using a tapered single mode optical fiber that is coupled to a distributed feedback laser. The transmission spectrum through the fiber is monitored to detect WGM shifts. The results showed the resonators with smaller shear modulus G experience larger WGM shift due to the larger mechanical deformation induced by the applied external centripetal force. Also, the results show that angular velocity sensors used in the torsional vibrational applications could be designed using this principle.

Drag on a Satellite Moving across a Spherical Galaxy: Tidal and Frictional Forces in Short-lived Encounters

NASA Astrophysics Data System (ADS)

Colpi, Monica; Pallavicini, Andrea

1998-07-01

The drag force on a satellite of mass M moving with speed V in the gravitational field of a spherically symmetric background of stars is computed. During the encounter, the stars are subject to a time-dependent force that alters their equilibrium. The resulting distortion in the stellar density field acts back to produce a force FΔ that decelerates the satellite. This force is computed using a perturbative technique known as linear response theory. In this paper, we extend the formalism of linear response to derive the correct expression for the back-reaction force FΔ that applies when the stellar system is described by an equilibrium one-particle distribution function. FΔ is expressed in terms of a suitable correlation function that couples the satellite dynamics to the unperturbed dynamics of the stars. At time t, the force depends upon the whole history of the composite system. In the formalism, we account for the shift of the stellar center of mass resulting from linear momentum conservation. The self-gravity of the response is neglected since it contributes to a higher order in the perturbation. Linear response theory applies also to the case of a satellite orbiting outside the spherical galaxy. The case of a satellite moving on a straight line, at high speed relative to the stellar dispersion velocity, is explored. We find that the satellite during its passage raises (1) global tides in the stellar distribution and (2) a wake, i.e., an overdense region behind its trail. If the satellite motion is external to the galaxy, it suffers a dissipative force that is not exclusively acting along V but acquires a component along R, the position vector relative to the center of the spherical galaxy. We derive the analytical expression of the force in the impulse approximation. In penetrating short-lived encounters, the satellite moves across the stellar distribution and the transient wake excited in the density field is responsible for most of the deceleration. We find that dynamical friction arises from a memory effect involving only those stars perturbed along the path. The force can be written in terms of an effective Coulomb logarithm that now depends upon time. The value of ln Λ is computed for two simple equilibrium density distributions; it is shown that the drag increases as the satellite approaches the denser regions of the stellar distribution and attains a maximum after pericentric passage. When the satellite crosses the edge of the galaxy, the force does not vanish since the galaxy keeps memory of the perturbation induced and declines on a time comparable to the dynamical time of the stellar system. In the case of a homogeneous cloud, we compute the total energy loss. In evaluating the contribution resulting from friction, we derive self-consistently the maximum impact parameter, which is found to be equal to the length traveled by the satellite within the system. Tides excited by the satellite in the galaxy reduce the value of the energy loss by friction; in close encounters, this value is decreased by a factor of ~1.5.

Specific sine-Gordon soliton dynamics in the presence of external driving forces

NASA Astrophysics Data System (ADS)

Reinisch, Gilbert; Fernandez, Jean Claude

1981-07-01

We consider the acceleration of a single sine-Gordon (SG) soliton kink wave by an external time-dependent force χ(t), first without any dissipation, and then in the presence of a weak damping effect. We use the method of Fogel, Trullinger, Bishop, and Krumhansl [FTBK,

Adaptation of multijoint coordination during standing balance in healthy young and healthy old individuals

PubMed Central

Pasma, J. H.; Schouten, A. C.; Aarts, R. G. K. M.; Meskers, C. G. M.; Maier, A. B.; van der Kooij, H.

2015-01-01

Standing balance requires multijoint coordination between the ankles and hips. We investigated how humans adapt their multijoint coordination to adjust to various conditions and whether the adaptation differed between healthy young participants and healthy elderly. Balance was disturbed by push/pull rods, applying two continuous and independent force disturbances at the level of the hip and between the shoulder blades. In addition, external force fields were applied, represented by an external stiffness at the hip, either stabilizing or destabilizing the participants' balance. Multivariate closed-loop system-identification techniques were used to describe the neuromuscular control mechanisms by quantifying the corrective joint torques as a response to body sway, represented by frequency response functions (FRFs). Model fits on the FRFs resulted in an estimation of time delays, intrinsic stiffness, reflexive stiffness, and reflexive damping of both the ankle and hip joint. The elderly generated similar corrective joint torques but had reduced body sway compared with the young participants, corresponding to the increased FRF magnitude with age. When a stabilizing or destabilizing external force field was applied at the hip, both young and elderly participants adapted their multijoint coordination by lowering or respectively increasing their neuromuscular control actions around the ankles, expressed in a change of FRF magnitude. However, the elderly adapted less compared with the young participants. Model fits on the FRFs showed that elderly had higher intrinsic and reflexive stiffness of the ankle, together with higher time delays of the hip. Furthermore, the elderly adapted their reflexive stiffness around the ankle joint less compared with young participants. These results imply that elderly were stiffer and were less able to adapt to external force fields. PMID:26719084

External fixation using locking plate in distal tibial fracture: a finite element analysis.

PubMed

Zhang, Jingwei; Ebraheim, Nabil; Li, Ming; He, Xianfeng; Schwind, Joshua; Liu, Jiayong; Zhu, Limei

2015-08-01

External fixation of tibial fractures using a locking plate has been reported with favorable results in some selected patients. However, the stability of external plate fixation in this fracture pattern has not been previously demonstrated. We investigated the stability of external plate fixation with different plate-bone distances. In this study, the computational processing model of external fixation of a distal tibial metaphyseal fracture utilizing the contralateral femoral less invasive stabilization system plate was analyzed. The plate was placed on the anteromedial aspect of tibia with different plate-bone distances: 1, 10, 20, and 30 mm. Under axial load, the stiffness of construct in all groups was higher than intact tibia. Under axial load with an internal rotational force, the stiffness of construct with 1 and 10 mm plate-bone distances was similar to that of an intact tibia and the stiffness of the construct with 20 and 30 mm distances was lower than that of an intact tibia. Under axial load with an external rotational force, the stiffness of the construct in all groups was lower than that of an intact tibia. The maximum plate stresses were concentrated at the two most distal screws and were highest in the construct with the 10 mm plate-bone distance, and least in the construct with a 1 mm plate-bone distance. To guarantee a stable external plate fixation in distal tibial fracture, the plate-bone distance should be less than 30 mm.

Force Sensing Applications of DNA Origami Nanodevices

NASA Astrophysics Data System (ADS)

Hudoba, Michael William

Mechanical forces in biological systems vary in both length and magnitude by orders of magnitude making them difficult to probe and characterize with existing experimental methodologies. From molecules to cells, forces can act across length scales of nanometers to microns at magnitudes ranging from picoNewtons to nanoNewtons. Although single-molecule techniques such as optical traps, magnetic tweezers, and atomic force microscopy have improved the resolution and sensitivity of such measurements, inherent drawbacks exist in their capabilities due to the nature of the tools themselves. Specifically, these techniques have limitations in their ability to measure forces in realistic cellular environments and are not amenable to in vivo applications or measurements in mimicked physiological environments. In this thesis, we present a method to develop DNA force-sensing nanodevices with sub-picoNewton resolution capable of measuring forces in realistic cellular environments, with future applications in vivo. We use a design technique known as DNA origami to assemble devices with nanoscale geometric precision through molecular self-assembly via Watson-Crick base pairing. The devices have multiple conformational states, monitored by observing a Forster Resonance Energy Transfer signal that can change under the application of force. We expanded this study by demonstrating the design of responsive structural dynamics in DNA-based nanodevices. While prior studies have relied on external inputs to drive relatively slow dynamics in DNA nanostructures, here we developed DNA nanodevices with thermally driven dynamic function. The device was designed with an ensemble of conformations, and we establish methods to tune the equilibrium distribution of conformations and the rate of switching between states. We also show this nanodynamic behavior is responsive to physical interactions with the environment by measuring molecular crowding forces in the sub-picoNewton range, which are known to play a critical role in regulating molecular interactions and processes. Broadly, this work establishes a foundation for nanodevices with thermally driven dynamics that enable new measurement and control functions. We also examine the effect that forces have on the mechanical properties of DNA origami devices by developing a method to automate mesh generation for Finite Element Analysis. With this approach we are able to determine how defects that arise during assembly affect mechanical strain within structures during force application that can ultimately lead to device failure.

Developing a Magnetic Resonance Imaging measurement of the forces within 3D granular materials under external loads

NASA Astrophysics Data System (ADS)

Elrington, Stefan; Bertrand, Thibault; Frey, Merideth; Shattuck, Mark; O'Hern, Corey; Barrett, Sean

2014-03-01

Granular materials are comprised of an ensemble of discrete macroscopic grains that interact with each other via highly dissipative forces. These materials are ubiquitous in our everyday life ranging in scale from the granular media that forms the Earth's crust to that used in agricultural and pharmaceutical industries. Granular materials exhibit complex behaviors that are poorly understood and cannot be easily described by statistical mechanics. Under external loads individual grains are jammed into place by a network of force chains. These networks have been imaged in quasi two-dimensional and on the outer surface of three-dimensional granular materials. Our goal is to use magnetic resonance imaging (MRI) to detect contact forces deep within three-dimensional granular materials, using hydrogen-1 relaxation times as a reporter for changes in local stress and strain. To this end, we use a novel pulse sequence to narrow the line width of hydrogen-1 in rubber. Here we present our progress to date, and prospects for future improvements.

Brownian escape and force-driven transport through entropic barriers: Particle size effect.

PubMed

Cheng, Kuang-Ling; Sheng, Yu-Jane; Tsao, Heng-Kwong

2008-11-14

Brownian escape from a spherical cavity through small holes and force-driven transport through periodic spherical cavities for finite-size particles have been investigated by Brownian dynamic simulations and scaling analysis. The mean first passage time and force-driven mobility are obtained as a function of particle diameter a, hole radius R(H), cavity radius R(C), and external field strength. In the absence of external field, the escape rate is proportional to the exit effect, (R(H)R(C))(1-a2R(H))(32). In weak fields, Brownian diffusion is still dominant and the migration is controlled by the exit effect. Therefore, smaller particles migrate faster than larger ones. In this limit the relation between Brownian escape and force-driven transport can be established by the generalized Einstein-Smoluchowski relation. As the field strength is strong enough, the mobility becomes field dependent and grows with increasing field strength. As a result, the size selectivity diminishes.

United States Air Force Response to Problems of Child Abuse within the Military Community.

DTIC Science & Technology

1985-01-01

The Child Abuse Prevention and Treatment Act became national law in the United States. This act authorized a National Center on Child Abuse and...Neglect to compile information, operate a clearinghouse on programs showing promise of success in prevention, identification and treatment of child abuse , publish...Force base to investigate and evaluate suspected child abuse cases. This study focuses on child abuse in the Air Force community rather than in the

14 CFR 29.471 - General.

Code of Federal Regulations, 2011 CFR

2011-01-01

... equilibrium. For limit ground loads— (1) The limit ground loads obtained in the landing conditions in this part must be considered to be external loads that would occur in the rotorcraft structure if it were acting as a rigid body; and (2) In each specified landing condition, the external loads must be placed in...

Piano Students' Conceptions of Musical Scores as External Representations: A Cross-Sectional Study

ERIC Educational Resources Information Center

Bautista, Alfredo; Perez Echeverria, Ma del Puy; Pozo, J. Ignacio; Brizuela, Barbara M.

2009-01-01

Musical scores are some of the most important learning tools for musicians' acquisition of musical knowledge. However, despite their educational relevance, very little is known about how music students "conceive" of these cultural external representations. Given that these conceptions might act as mediators of students' learning…

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.

IS FREE REALLY FREE PALACE ACQUIRE AS AN EFFECTIVE FORCE RENEWAL SOURCE FOR AIR FORCE PUBLIC AFFAIRS

DTIC Science & Technology

2016-02-29

AU/ACSC/2016 AIR COMMAND AND STAFF COLLEGE AIR UNIVERSITY IS FREE REALLY FREE ? PALACE ACQUIRE AS AN EFFECTIVE FORCE RENEWAL SOURCE FOR AIR...transfer-eligible candidates, and external applicants. Ultimately, this research reveals, the cost – in both money and manpower – does not support...these employees provide to their sponsoring offices in “ free manning.” 5 CHAPTER 1 Introduction Public Affairs is key aspect of Air Force