Science.gov

Sample records for forced driven disk-ridging

  1. Impact Forces from Tsunami-Driven Debris

    NASA Astrophysics Data System (ADS)

    Ko, H.; Cox, D. T.; Riggs, H.; Naito, C. J.; Kobayashi, M. H.; Piran Aghl, P.

    2012-12-01

    Debris driven by tsunami inundation flow has been known to be a significant threat to structures, yet we lack the constitutive equations necessary to predict debris impact force. The objective of this research project is to improve our understanding of, and predictive capabilities for, tsunami-driven debris impact forces on structures. Of special interest are shipping containers, which are virtually everywhere and which will float even when fully loaded. The forces from such debris hitting structures, for example evacuation shelters and critical port facilities such as fuel storage tanks, are currently not known. This research project focuses on the impact by flexible shipping containers on rigid columns and investigated using large-scale laboratory testing. Full-scale in-air collision experiments were conducted at Lehigh University with 20 ft shipping containers to experimentally quantify the nonlinear behavior of full scale shipping containers as they collide into structural elements. The results from the full scale experiments were used to calibrate computer models and used to design a series of simpler, 1:5 scale wave flume experiments at Oregon State University. Scaled in-air collision tests were conducted using 1:5 scale idealized containers to mimic the container behavior observed in the full scale tests and to provide a direct comparison to the hydraulic model tests. Two specimens were constructed using different materials (aluminum, acrylic) to vary the stiffness. The collision tests showed that at higher speeds, the collision became inelastic as the slope of maximum impact force/velocity decreased with increasing velocity. Hydraulic model tests were conducted using the 1:5 scaled shipping containers to measure the impact load by the containers on a rigid column. The column was instrumented with a load cell to measure impact forces, strain gages to measure the column deflection, and a video camera was used to provide the debris orientation and speed. The

  2. A measurable force driven by an excitonic condensate

    SciTech Connect

    Hakioğlu, T.; Özgün, Ege; Günay, Mehmet

    2014-04-21

    Free energy signatures related to the measurement of an emergent force (≈10{sup −9}N) due to the exciton condensate (EC) in Double Quantum Wells are predicted and experiments are proposed to measure the effects. The EC-force is attractive and reminiscent of the Casimir force between two perfect metallic plates, but also distinctively different from it by its driving mechanism and dependence on the parameters of the condensate. The proposed experiments are based on a recent experimental work on a driven micromechanical oscillator. Conclusive observations of EC in recent experiments also provide a strong promise for the observation of the EC-force.

  3. Spin motive force driven by skyrmion dynamics in magnetic nanodisks

    NASA Astrophysics Data System (ADS)

    Shimada, Yuhki; Ohe, Jun-ichiro

    2015-05-01

    The spin motive force driven by the dynamics of the skyrmion structure formed in a nanomagnetic disk is numerically investigated. Due to the existence of the magnetic structure along the disk edge, the collective mode of the magnetization is modified from that of the bulk skyrmion lattice obtained by using the periodic boundary condition. For a single-skyrmion disk, the dynamics of the skyrmion core and the edge magnetization induce the spin motive force, and a measurable AC voltage is obtained by two probes on the disk. For a multi-skyrmions disk, the phase-locked collective mode of skyrmions is found in the lowest resonant frequency where the amplitude of the AC voltage is enhanced by the cascade effect of the spin motive force. We also investigate the effect of the Rashba spin-orbit coupling on the spin motive force.

  4. Note: A novel piezoelectrically driven pipette using centrifugal force

    NASA Astrophysics Data System (ADS)

    Deng, Zhi Sen; Ma, Yu Ting; Feng, Zhi Hua

    2014-05-01

    This paper proposes a novel piezoelectrically driven pipette, which utilizes centrifugal force in swing motion of a vibrating tube as the driving force, to input and output liquid at first bending resonant frequency. Control circuit capable of frequency tracking is designed. Pulse volume changing with different driving voltage amplitude, driving frequency, tip size, and target reagents are studied in experiments. The output pulse volume of a prototype pipette driven by voltage of 560 Vpp at 175.9 Hz is 43.2 μl with a variation of ±3.5%. Minimum water spots of 3 μl can be deposited in this manner. This pipette represents an alternative to standard liquid transfer techniques in chemical or biological experiments.

  5. Electron Force Balance in Steady Collisionless-Driven Reconnection

    SciTech Connect

    Li Bin; Horiuchi, Ritoku

    2008-11-21

    Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfven velocity averaged over the electron dissipation region.

  6. Force-Driven Polymerization and Turgor-Induced Wall Expansion.

    PubMed

    Ali, Olivier; Traas, Jan

    2016-05-01

    While many molecular players involved in growth control have been identified in the past decades, it is often unknown how they mechanistically act to induce specific shape changes during development. Plant morphogenesis results from the turgor-induced yielding of the extracellular and load-bearing cell wall. Its mechanochemical equilibrium appears as a fundamental link between molecular growth regulation and the effective shape evolution of the tissue. We focus here on force-driven polymerization of the cell wall as a central process in growth control. We propose that mechanical forces facilitate the insertion of wall components, in particular pectins, a process that can be modulated through genetic regulation. We formalize this idea in a mathematical model, which we subsequently test with published experimental results.

  7. Depletion force induced collective motion of microtubules driven by kinesin

    NASA Astrophysics Data System (ADS)

    Inoue, Daisuke; Mahmot, Bulbul; Kabir, Arif Md. Rashedul; Farhana, Tamanna Ishrat; Tokuraku, Kiyotaka; Sada, Kazuki; Konagaya, Akihiko; Kakugo, Akira

    2015-10-01

    Collective motion is a fascinating example of coordinated behavior of self-propelled objects, which is often associated with the formation of large scale patterns. Nowadays, the in vitro gliding assay is being considered a model system to experimentally investigate various aspects of group behavior and pattern formation by self-propelled objects. In the in vitro gliding assay, cytoskeletal filaments F-actin or microtubules are driven by the surface immobilized associated biomolecular motors myosin or dynein respectively. Although the F-actin/myosin or microtubule/dynein system was found to be promising in understanding the collective motion and pattern formation by self-propelled objects, the most widely used biomolecular motor system microtubule/kinesin could not be successfully employed so far in this regard. Failure in exhibiting collective motion by kinesin driven microtubules is attributed to the intrinsic properties of kinesin, which was speculated to affect the behavior of individual gliding microtubules and mutual interactions among them. In this work, for the first time, we have demonstrated the collective motion of kinesin driven microtubules by regulating the mutual interaction among the gliding microtubules, by employing a depletion force among them. Proper regulation of the mutual interaction among the gliding microtubules through the employment of the depletion force was found to allow the exhibition of collective motion and stream pattern formation by the microtubules. This work offers a universal means for demonstrating the collective motion using the in vitro gliding assay of biomolecular motor systems and will help obtain a meticulous understanding of the fascinating coordinated behavior and pattern formation by self-propelled objects.Collective motion is a fascinating example of coordinated behavior of self-propelled objects, which is often associated with the formation of large scale patterns. Nowadays, the in vitro gliding assay is being

  8. Depletion force induced collective motion of microtubules driven by kinesin.

    PubMed

    Inoue, Daisuke; Mahmot, Bulbul; Kabir, Arif Md Rashedul; Farhana, Tamanna Ishrat; Tokuraku, Kiyotaka; Sada, Kazuki; Konagaya, Akihiko; Kakugo, Akira

    2015-11-21

    Collective motion is a fascinating example of coordinated behavior of self-propelled objects, which is often associated with the formation of large scale patterns. Nowadays, the in vitro gliding assay is being considered a model system to experimentally investigate various aspects of group behavior and pattern formation by self-propelled objects. In the in vitro gliding assay, cytoskeletal filaments F-actin or microtubules are driven by the surface immobilized associated biomolecular motors myosin or dynein respectively. Although the F-actin/myosin or microtubule/dynein system was found to be promising in understanding the collective motion and pattern formation by self-propelled objects, the most widely used biomolecular motor system microtubule/kinesin could not be successfully employed so far in this regard. Failure in exhibiting collective motion by kinesin driven microtubules is attributed to the intrinsic properties of kinesin, which was speculated to affect the behavior of individual gliding microtubules and mutual interactions among them. In this work, for the first time, we have demonstrated the collective motion of kinesin driven microtubules by regulating the mutual interaction among the gliding microtubules, by employing a depletion force among them. Proper regulation of the mutual interaction among the gliding microtubules through the employment of the depletion force was found to allow the exhibition of collective motion and stream pattern formation by the microtubules. This work offers a universal means for demonstrating the collective motion using the in vitro gliding assay of biomolecular motor systems and will help obtain a meticulous understanding of the fascinating coordinated behavior and pattern formation by self-propelled objects. PMID:26260025

  9. Kinetic theory of a confined polymer driven by an external force and pressure-driven flow

    NASA Astrophysics Data System (ADS)

    Butler, Jason E.; Usta, O. Berk; Kekre, Rahul; Ladd, Anthony J. C.

    2007-11-01

    Kinetic theory is used to investigate the mechanisms causing cross-stream migration of confined polymers and polyelectrolytes under the influence of external forces and flow fields. Numerical simulations and experiments have demonstrated that confined polymers migrate towards the center of the channel in response to both external forces and uniaxial flows. Yet, migration towards the walls has been observed with combinations of external force and flow. In this paper, the kinetic theory for an elastic dumbbell developed by Ma and Graham [Phys. Fluids 17, 083103 (2005)] has been extended to account for the effects of an external force. Further modifications account for counterion screening within a Debye-Hückel approximation. This enables qualitative comparison with experimental results [Zheng and Yeung, Anal. Chem. 75, 3675 (2003)] on DNA migration under combined electric and pressure-driven flow fields. The comparison supports the contention [Long et al., Phys. Rev. Lett. 76, 3858 (1996)] that the hydrodynamic interactions in polyelectrolytes decay algebraically, as 1/r3, rather than exponentially. The theory qualitatively reproduces results of both simulations and experiments for the migration of neutral polymers and polyelectrolytes. Concentration profiles similar to those found in numerical simulations are observed, but the Peclet numbers differ by factors of 2-3.

  10. Avalanches and force drops in displacement-driven compression of porous glasses

    NASA Astrophysics Data System (ADS)

    Navas-Portella, Víctor; Corral, Álvaro; Vives, Eduard

    2016-09-01

    Similarities between force-driven compression experiments of porous materials and earthquakes have been recently proposed. In this paper, we measure the acoustic emission during displacement-driven compression of a porous glass. The energy of acoustic-emission events shows that the failure process exhibits avalanche scale-invariance and therefore follows the Gutenberg-Richter law. The resulting exponents do not exhibit significant differences with respect the force-driven case. Furthermore, the force exhibits an avalanche-type behavior for which the force drops are power-law distributed and correlated with the acoustic emission events.

  11. Control of force through feedback in small driven systems.

    PubMed

    Dieterich, E; Camunas-Soler, J; Ribezzi-Crivellari, M; Seifert, U; Ritort, F

    2016-07-01

    Controlling a time-dependent force applied to single molecules or colloidal particles is crucial for many types of experiments. Since in optical tweezers the primary controlled variable is the position of the trap, imposing a target force requires an active feedback process. We analyze this feedback process for the paradigmatic case of a nonequilibrium steady state generated by a dichotomous force protocol, first theoretically for a colloidal particle in a harmonic trap and then with both simulations and experiments for a long DNA hairpin. For the first setup, we find there is an optimal feedback gain separating monotonic from oscillatory response, whereas a too strong feedback leads to an instability. For the DNA molecule, reaching the target force requires substantial feedback gain since weak feedback cannot overcome the tendency to relax towards the equilibrium force. PMID:27575077

  12. Control of force through feedback in small driven systems.

    PubMed

    Dieterich, E; Camunas-Soler, J; Ribezzi-Crivellari, M; Seifert, U; Ritort, F

    2016-07-01

    Controlling a time-dependent force applied to single molecules or colloidal particles is crucial for many types of experiments. Since in optical tweezers the primary controlled variable is the position of the trap, imposing a target force requires an active feedback process. We analyze this feedback process for the paradigmatic case of a nonequilibrium steady state generated by a dichotomous force protocol, first theoretically for a colloidal particle in a harmonic trap and then with both simulations and experiments for a long DNA hairpin. For the first setup, we find there is an optimal feedback gain separating monotonic from oscillatory response, whereas a too strong feedback leads to an instability. For the DNA molecule, reaching the target force requires substantial feedback gain since weak feedback cannot overcome the tendency to relax towards the equilibrium force.

  13. Control of force through feedback in small driven systems

    NASA Astrophysics Data System (ADS)

    Dieterich, E.; Camunas-Soler, J.; Ribezzi-Crivellari, M.; Seifert, U.; Ritort, F.

    2016-07-01

    Controlling a time-dependent force applied to single molecules or colloidal particles is crucial for many types of experiments. Since in optical tweezers the primary controlled variable is the position of the trap, imposing a target force requires an active feedback process. We analyze this feedback process for the paradigmatic case of a nonequilibrium steady state generated by a dichotomous force protocol, first theoretically for a colloidal particle in a harmonic trap and then with both simulations and experiments for a long DNA hairpin. For the first setup, we find there is an optimal feedback gain separating monotonic from oscillatory response, whereas a too strong feedback leads to an instability. For the DNA molecule, reaching the target force requires substantial feedback gain since weak feedback cannot overcome the tendency to relax towards the equilibrium force.

  14. Force-Driven Separation of Short Double-Stranded DNA

    PubMed Central

    Ho, Dominik; Zimmermann, Julia L.; Dehmelt, Florian A.; Steinbach, Uta; Erdmann, Matthias; Severin, Philip; Falter, Katja; Gaub, Hermann E.

    2009-01-01

    Abstract Short double-stranded DNA is used in a variety of nanotechnological applications, and for many of them, it is important to know for which forces and which force loading rates the DNA duplex remains stable. In this work, we develop a theoretical model that describes the force-dependent dissociation rate for DNA duplexes tens of basepairs long under tension along their axes (“shear geometry”). Explicitly, we set up a three-state equilibrium model and apply the canonical transition state theory to calculate the kinetic rates for strand unpairing and the rupture-force distribution as a function of the separation velocity of the end-to-end distance. Theory is in excellent agreement with actual single-molecule force spectroscopy results and even allows for the prediction of the rupture-force distribution for a given DNA duplex sequence and separation velocity. We further show that for describing double-stranded DNA separation kinetics, our model is a significant refinement of the conventionally used Bell-Evans model. PMID:20006953

  15. Force-driven aggregation of specific bonds on compliant substrates.

    PubMed

    Sarvestani, Alireza S

    2013-07-26

    A thermodynamic model was employed to understand the underlying physics of the force-dependent size of cell's focal adhesions. The model describes the specific adhesion of an elastic membrane to a compliant substrate such that the adhesion site is subjected to the force of a constant pulling traction. The membrane contains mobile adhesion receptors with specific energetic affinities for complimentary ligands on the substrate. The adhesion is resisted by a disjoining pressure induced by a squeezed layer of glycocalyx. The model demonstrates that the enlargement of adhesion area with increasing pulling traction is possible due to a spontaneous response of the adhesion site to attain the state of minimum free energy. The correlation between the force and the adhesion area strongly depends on the rigidity of the substrate. PMID:23764177

  16. Force Model for Control of Tendon Driven Hands

    NASA Technical Reports Server (NTRS)

    Pena, Edward; Thompson, David E.

    1997-01-01

    Knowing the tendon forces generated for a given task such as grasping via a model, an artificial hand can be controlled. A two-dimensional force model for the index finger was developed. This system is assumed to be in static equilibrium, therefore, the equations of equilibrium were applied at each joint. Constraint equations describing the tendon branch connectivity were used. Gaussian elimination was used to solve for the unknowns of the Linear system. Results from initial work on estimating tendon forces in post-operative hands during active motion therapy were discussed. The results are important for understanding the effects of hand position on tendon tension, elastic effects on tendon tension, and overall functional anatomy of the hand.

  17. "Magic" surface clustering of borazines driven by repulsive intermolecular forces.

    PubMed

    Kervyn, Simon; Kalashnyk, Nataliya; Riello, Massimo; Moreton, Ben; Tasseroul, Jonathan; Wouters, Johan; Jones, Tim S; De Vita, Alessandro; Costantini, Giovanni; Bonifazi, Davide

    2013-07-15

    It's a kind of magic: Hydroxy pentaaryl borazine molecules self-assemble into small clusters (see structure) on Cu(111) surfaces, whereas with symmetric hexaaryl borazine molecules large islands are obtained. Simulations indicate that the observed "magic" cluster sizes result from long-range repulsive Coulomb forces arising from the deprotonation of the B-OH groups of the hydroxy pentaaryl borazine.

  18. Interface dynamics of a two-component Bose-Einstein condensate driven by an external force

    SciTech Connect

    Kobyakov, D.; Bychkov, V.; Lundh, E.; Bezett, A.; Marklund, M.; Akkerman, V.

    2011-04-15

    The dynamics of an interface in a two-component Bose-Einstein condensate driven by a spatially uniform time-dependent force is studied. Starting from the Gross-Pitaevskii Lagrangian, the dispersion relation for linear waves and instabilities at the interface is derived by means of a variational approach. A number of diverse dynamical effects for different types of driving force is demonstrated, which includes the Rayleigh-Taylor instability for a constant force, the Richtmyer-Meshkov instability for a pulse force, dynamic stabilization of the Rayleigh-Taylor instability and onset of the parametric instability for an oscillating force. Gaussian Markovian and non-Markovian stochastic forces are also considered. It is found that the Markovian stochastic force does not produce any average effect on the dynamics of the interface, while the non-Markovian force leads to exponential perturbation growth.

  19. CDW-Exciton Condensate Competition and a Condensate Driven Force

    NASA Astrophysics Data System (ADS)

    Özgün, Ege; Hakioğlu, Tuğrul

    2016-08-01

    We examine the competition between the charge-density wave (CDW) instability and the excitonic condensate (EC) in spatially separated layers of electrons and holes. The CDW and the EC order parameters (OPs), described by two different mechanisms and hence two different transition temperatures TcCDW and TcEC, are self-consistently coupled by a microscopic mean field theory. We discuss the results in our model specifically focusing on the transition-metal dichalcogenides which are considered as the most typical examples of strongly coupled CDW/EC systems with atomic layer separations where the electronic energy scales are large with the critical temperatures in the range TcEC ˜ TcCDW ˜ 100-200 K. An important consequence of this is that the excitonic energy gap, hence the condensed free energy, vary with the layer separation resulting in a new type of force FEC. We discuss the possibility of this force as the possible driver of the structural lattice deformation observed in some TMDCs with a particular attention on the 1T-TiSe2 below 200 K.

  20. Molecular Self-Assembly Driven by London Dispersion Forces

    SciTech Connect

    Li, Guo; Cooper, Valentino R; Cho, Jun-Hyung; Du, Shixuan; Gao, Hongjun; Zhang, Zhenyu

    2011-01-01

    The nature and strength of intermolecular interactions are crucial to a variety of kinetic and dynamic processes at surfaces. Whereas strong chemisorption bonds are known to facilitate molecular binding, the importance of the weaker yet ubiquitous van der Waals (vdW) interactions remains elusive in most cases. Here we use first-principles calculations combined with kinetic Monte Carlo simulations to unambiguously demonstrate the vital role that vdW interactions play in molecular self-assembly, using styrene nanowire growth on silicon as a prototypical example. We find that, only when the London dispersion forces are included, accounting for the attractive parts of vdW interactions, can the effective intermolecular interaction be reversed from being repulsive to attractive. Such attractive interactions, in turn, ensure the preferred growth of long wires under physically realistic conditions as observed experimentally. We further propose a cooperative scheme, invoking the application of an electric field and the selective creation of Si dangling bonds, to drastically improve the ordered arrangement of the molecular structures. The present study represents a significant step forward in the fundamental understanding and precise control of molecular self-assembly guided by London dispersion forces.

  1. Cold ablation driven by localized forces in alkali halides.

    PubMed

    Hada, Masaki; Zhang, Dongfang; Pichugin, Kostyantyn; Hirscht, Julian; Kochman, Michał A; Hayes, Stuart A; Manz, Stephanie; Gengler, Regis Y N; Wann, Derek A; Seki, Toshio; Moriena, Gustavo; Morrison, Carole A; Matsuo, Jiro; Sciaini, Germán; Miller, R J Dwayne

    2014-01-01

    Laser ablation has been widely used for a variety of applications. Since the mechanisms for ablation are strongly dependent on the photoexcitation level, so called cold material processing has relied on the use of high-peak-power laser fluences for which nonthermal processes become dominant; often reaching the universal threshold for plasma formation of ~1 J cm(-2) in most solids. Here we show single-shot time-resolved femtosecond electron diffraction, femtosecond optical reflectivity and ion detection experiments to study the evolution of the ablation process that follows femtosecond 400 nm laser excitation in crystalline sodium chloride, caesium iodide and potassium iodide. The phenomenon in this class of materials occurs well below the threshold for plasma formation and even below the melting point. The results reveal fast electronic and localized structural changes that lead to the ejection of particulates and the formation of micron-deep craters, reflecting the very nature of the strong repulsive forces at play. PMID:24835317

  2. Knudsen torque: A rotational mechanism driven by thermal force

    NASA Astrophysics Data System (ADS)

    Li, Qi; Liang, Tengfei; Ye, Wenjing

    2014-09-01

    Thermally induced mechanical loading has been shown to have significant effects on micro- and nano-objects immersed in a gas with a nonuniform temperature field. While the majority of existing studies and related applications focus on forces, we investigate the torque, and thus the rotational motion, produced by such a mechanism. Our study has found that a torque can be induced if the configuration of the system is asymmetric. In addition, both the magnitude and the direction of the torque depend highly on the system configuration, indicating the possibility of manipulating the rotational motion via geometrical design. Based on this feature, two types of rotational micromotor that are of practical importance, namely pendulum motor and unidirectional motor, are designed. The magnitude of the torque at Kn =0.5 can reach to around 2nN×μm for a rectangular microbeam with a length of 100μm.

  3. A silicon-nanowire memory driven by optical gradient force induced bistability

    SciTech Connect

    Dong, B.; Cai, H. Gu, Y. D.; Kwong, D. L.; Chin, L. K.; Ng, G. I.; Ser, W.; Huang, J. G.; Yang, Z. C.; Liu, A. Q.

    2015-12-28

    In this paper, a bistable optical-driven silicon-nanowire memory is demonstrated, which employs ring resonator to generate optical gradient force over a doubly clamped silicon-nanowire. Two stable deformation positions of a doubly clamped silicon-nanowire represent two memory states (“0” and “1”) and can be set/reset by modulating the light intensity (<3 mW) based on the optical force induced bistability. The time response of the optical-driven memory is less than 250 ns. It has applications in the fields of all optical communication, quantum computing, and optomechanical circuits.

  4. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences.

  5. Aggregation of PEGylated liposomes driven by hydrophobic forces.

    PubMed

    Bozó, Tamás; Mészáros, Tamás; Mihály, Judith; Bóta, Attila; Kellermayer, Miklós S Z; Szebeni, János; Kálmán, Benedek

    2016-11-01

    Polyethylene glycol (PEG) is widely used to sterically stabilize liposomes and improve the pharmacokinetic profile of drugs, peptides and nanoparticles. Here we report that ammonium sulfate (AS) can evoke the aggregation of PEGylated vesicles in a concentration-dependent manner. Liposomes with 5mol% PEG were colloidally stable at AS concentrations up to 0.7mM, above which they precipitated and formed micron-size aggregates with irregular shape. While aggregation was reversible up to 0.9M of AS, above 1M fusion occurred, which irreversibly distorted the size distribution. Zeta potential of liposomes markedly increased from -71±2.5mV to 2±0.5mV upon raising the AS concentration from 0 to 0.1M, but no considerable increase was seen during further AS addition, showing that the aggregation is independent of surface charge. There was no aggregation in the absence of the PEG chains, and increasing PEG molar% shifted the aggregation threshold to lower AS concentrations. Changes in the FTIR spectral features of PEGylated vesicles suggest that AS dehydrates PEG chains. Other kosmotropic salts also led to aggregation, while chaotropic salts did not, which indicates a general kosmotropic phenomenon. The driving force behind aggregation is likely to be the hydrophobic effect due to salting out the polymer similarly to what happens during protein purification or Hydrophobic Interaction Chromatography. Since liposome aggregation and fusion may result in difficulties during formulation and adverse reaction upon application, the phenomena detailed in this paper may have both technological and therapeutical consequences. PMID:27588427

  6. Path integral approach to Brownian motion driven with an ac force

    NASA Astrophysics Data System (ADS)

    Chen, L. Y.; Nash, P. L.

    2004-09-01

    Brownian motion in a periodic potential driven by an ac (oscillatory) force is investigated for the full range of damping constant from the overdamped limit to the underdamped limit. The path (functional) integral approach is advanced to produce formulas for the probability distribution function and for the current of the Brownian particle in response to an ac driving force. The negative friction Langevin dynamics technique is employed to evaluate the dc current for various parameters without invoking the overdamped or the underdamped approximation. The dc current is found to have nonlinear dependence upon the damping constant, the potential parameter, and the ac force magnitude and frequency.

  7. Minimum detectable change for knee joint contact force estimates using an EMG-driven model

    PubMed Central

    Gardinier, Emily S.; Manal, Kurt; Buchanan, Thomas S.; Snyder-Mackler, Lynn

    2013-01-01

    Adequate test–retest reliability of model estimates is a necessary precursor to examining treatment effects or longitudinal changes in individuals. Purpose The purpose of this study was to establish thresholds for minimal detectable change (MDC) for joint contact forces obtained using a patient specific EMG-driven musculoskeletal model of the knee. Design A sample of young, active individuals was selected for this study, and subjects were tested on 2 separate days. Three-dimensional motion analysis with electromyography (EMG) was used to obtain data from each subject during gait for model input. An EMG-driven modeling approach was used to estimate joint contact forces at each session. Results MDC’s for contact force variables ranged from 0.30 to 0.66 BW. The lowest MDC was for peak medial compartment force (0.30 BW) and the highest was for peak tibiofemoral contact force (0.66 BW). Test–retest reliability coefficients were also reported for comparison with previous work. Conclusions Using the present model, changes in joint contact forces between baseline and subsequent measurements that are greater than these MDCs are greater than typical day-to-day variation and can be identified as real change. PMID:23601782

  8. The electromechanical behavior of a micro-ring driven by traveling electrostatic force.

    PubMed

    Ye, Xiuqian; Chen, Yibao; Chen, Da-Chih; Huang, Kuo-Yi; Hu, Yuh-Chung

    2012-01-01

    There is no literature mentioning the electromechanical behavior of micro structures driven by traveling electrostatic forces. This article is thus the first to present the dynamics and stabilities of a micro-ring subjected to a traveling electrostatic force. The traveling electrostatic force may be induced by sequentially actuated electrodes which are arranged around the flexible micro-ring. The analysis is based on a linearized distributed model considering the electromechanical coupling effects between electrostatic force and structure. The micro-ring will resonate when the traveling speeds of the electrostatic force approach some critical speeds. The critical speeds are equal to the ratio of the natural frequencies to the wave number of the correlative natural mode of the ring. Apart from resonance, the ring may be unstable at some unstable traveling speeds. The unstable regions appear not only near the critical speeds, but also near some fractions of some critical speeds differences. Furthermore the unstable regions expand with increasing driving voltage. This article may lead to a new research branch on electrostatic-driven micro devices.

  9. Force-velocity relation for actin-polymerization-driven motility from Brownian dynamics simulations.

    PubMed

    Lee, Kun-Chun; Liu, Andrea J

    2009-09-01

    We report numerical simulation results for the force-velocity relation for actin-polymerization-driven motility. We use Brownian dynamics to solve a physically consistent formulation of the dendritic nucleation model with semiflexible filaments that self-assemble and push a disk. We find that at small loads, the disk speed is independent of load, whereas at high loads, the speed decreases and vanishes at a characteristic stall pressure. Our results demonstrate that at small loads, the velocity is controlled by the reaction rates, whereas at high loads the stall pressure is determined by the mechanical properties of the branched actin network. The behavior is consistent with experiments and with our recently proposed self-diffusiophoretic mechanism for actin-polymerization-driven motility. New in vitro experiments to measure the force-velocity relation are proposed.

  10. Velocity-Force characteristics of a driven interface in a periodic potential

    NASA Astrophysics Data System (ADS)

    Ettouhami, A. M.; Radzihovsky, Leo

    2002-03-01

    We study the nonequilibrium creep dynamics of a two-dimensional interface driven through a periodic potential, using dynamical renormalization group methods. We find that the nature of transport depends qualitatively on whether the temperature, T, is above or below the equilibrium roughening transition temperature T_c. In the rough phase, the velocity-force characteristics is Ohmic, with linear mobility exhibiting a jump discontinuity across the transition. In contrast, in the smooth phase (T <= T_c), the transport is a strongly nonlinear function of the applied force, exhibiting a rich universal crossover in temperature and applied force, with an intermediate regime where v(f) ~ exp(-1/f^μ), with μ=2(1-T/T_c).

  11. Biased Brownian stepping rotation of FoF1-ATP synthase driven by proton motive force.

    PubMed

    Watanabe, Rikiya; Tabata, Kazuhito V; Iino, Ryota; Ueno, Hiroshi; Iwamoto, Masayuki; Oiki, Shigetoshi; Noji, Hiroyuki

    2013-01-01

    FoF1-ATP synthase (FoF1) produces most of the ATP in cells, uniquely, by converting the proton motive force (pmf) into ATP production via mechanical rotation of the inner rotor complex. Technical difficulties have hampered direct investigation of pmf-driven rotation, which are crucial to elucidating the chemomechanical coupling mechanism of FoF1. Here we develop a novel supported membrane system for direct observation of the rotation of FoF1 driven by pmf that was formed by photolysis of caged protons. Upon photolysis, FoF1 initiated rotation in the opposite direction to that of the ATP-driven rotation. The step size of pmf-driven rotation was 120°, suggesting that the kinetic bottleneck is a catalytic event on F1 with threefold symmetry. The reaction equilibrium was slightly biased to ATP synthesis like under physiological conditions, and FoF1 showed highly stochastic behaviour, frequently making a 120° backward step. This new experimental system would be applicable to single-molecule study of other membrane proteins.

  12. The response of subsurface oceans in icy satellites to tidally driven forcing

    NASA Astrophysics Data System (ADS)

    Chen, E. M.; Glatzmaier, G. A.; Nimmo, F.

    2009-12-01

    Observations from the Galileo and Cassini spacecraft suggest that subsurface global water oceans are likely present on multiple icy satellites of Jupiter and Saturn. However, the dynamics of these oceans, under the influence of a time-varying tidal potential and buoyancy and coriolis forces, have not been investigated in detail. We have investigated the large scale ocean flow in two ways. First, we simulate the 3-D global circulation of the subsurface oceans on Europa and Titan driven primarily by a time-varying tidal potential and secondarily by heating at the base of the ocean. Second, we analyze the behavior of tidally-forced subsurface oceans in two-dimensions using quasi-nonlinear shallow water theory. These approaches allow us to predict potentially observable effects, in particular non-synchronous rotation of the ice shell driven by ocean torques and spatial variations in the heat flow supplied to the base of the ice shell, and magnetic induction effects due to the ocean circulation. Time-series analyses suggest that the ocean responds primarily at the tidal frequency; however, there are responses at lower frequencies as well. Preliminary results of full 3-D simulations will be presented, and comparisons will be made to the forced shallow water model.

  13. Transmission of Force Sensations by Hand of Multi-DOF Master-Slave Robot Using Tendon-Driven Mechanism

    NASA Astrophysics Data System (ADS)

    Nozaki, Takahiro; Suzuki, Yusuke; Ohnishi, Kouhei

    In this study, a bilateral control system for tendon-driven robots is proposed. The rotation angle and torque of the robot joints are controlled by the proposed control system. In addition, a tendon-driven robot hand for haptic applications is developed. The proposed control system is employed by the robot hand to transmit force sensations.

  14. Cascaded spin motive force driven by the dynamics of the skyrmion lattice

    SciTech Connect

    Ohe, Jun-ichiro; Shimada, Yuhki

    2013-12-09

    We numerically investigate the spin motive force (SMF) driven by the dynamics of a Skyrmion lattice. The rotating mode of the Skyrmion core excited by the AC magnetic field induces the large spin-dependent electric field near the core. Due to the collective dynamics of Skyrmion lattice, the measurable voltage is enhanced by the cascade effect of the SMF. The amplitude of the AC voltage is estimated to 30 μV in a macroscopic sample, where 100 Skyrmions exist between two probes. We also investigate the SMF due to the dynamics of the helical magnetic state, where the enhancement of the SMF does not occur.

  15. The effect of power-law body forces on a thermally driven flow between concentric rotating spheres

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.

    1986-01-01

    A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

  16. The effect of power law body forces on a thermally-driven flow between concentric rotating spheres

    NASA Technical Reports Server (NTRS)

    Macaraeg, M. G.

    1985-01-01

    A numerical study is conducted to determine the effect of power-law body forces on a thermally-driven axisymmetric flow field confined between concentric co-rotating spheres. This study is motivated by Spacelab geophysical fluid-flow experiments, which use an electrostatic force on a dielectric fluid to simulate gravity; this force exhibits a (1/r)sup 5 distribution. Meridional velocity is found to increase when the electrostatic body force is imposed, relative to when the body force is uniform. Correlation among flow fields with uniform, inverse-square, and inverse-quintic force fields is obtained using a modified Grashof number.

  17. Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, S. H.; Hashi, S.; Ishiyama, K.

    2011-01-01

    This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.

  18. Modeling the mechanics of cells in the cell-spreading process driven by traction forces

    NASA Astrophysics Data System (ADS)

    Fang, Yuqiang; Lai, King W. C.

    2016-04-01

    Mechanical properties of cells and their mechanical interaction with the extracellular environments are main factors influencing cellular function, thus indicating the progression of cells in different disease states. By considering the mechanical interactions between cell adhesion molecules and the extracellular environment, we developed a cell mechanical model that can characterize the mechanical changes in cells during cell spreading. A cell model was established that consisted of various main subcellular components, including cortical cytoskeleton, nuclear envelope, actin filaments, intermediate filaments, and microtubules. We demonstrated the structural changes in subcellular components and the changes in spreading areas during cell spreading driven by traction forces. The simulation of nanoindentation tests was conducted by integrating the indenting force to the cell model. The force-indentation curve of the cells at different spreading states was simulated, and the results showed that cell stiffness increased with increasing traction forces, which were consistent with the experimental results. The proposed cell mechanical model provides a strategy to investigate the mechanical interactions of cells with the extracellular environments through the adhesion molecules and to reveal the cell mechanical properties at the subcellular level as cells shift from the suspended state to the adherent state.

  19. Modeling the mechanics of cells in the cell-spreading process driven by traction forces.

    PubMed

    Fang, Yuqiang; Lai, King W C

    2016-04-01

    Mechanical properties of cells and their mechanical interaction with the extracellular environments are main factors influencing cellular function, thus indicating the progression of cells in different disease states. By considering the mechanical interactions between cell adhesion molecules and the extracellular environment, we developed a cell mechanical model that can characterize the mechanical changes in cells during cell spreading. A cell model was established that consisted of various main subcellular components, including cortical cytoskeleton, nuclear envelope, actin filaments, intermediate filaments, and microtubules. We demonstrated the structural changes in subcellular components and the changes in spreading areas during cell spreading driven by traction forces. The simulation of nanoindentation tests was conducted by integrating the indenting force to the cell model. The force-indentation curve of the cells at different spreading states was simulated, and the results showed that cell stiffness increased with increasing traction forces, which were consistent with the experimental results. The proposed cell mechanical model provides a strategy to investigate the mechanical interactions of cells with the extracellular environments through the adhesion molecules and to reveal the cell mechanical properties at the subcellular level as cells shift from the suspended state to the adherent state. PMID:27176326

  20. Velocity-force characteristics of an interface driven through a periodic potential

    NASA Astrophysics Data System (ADS)

    Ettouhami, A. M.; Radzihovsky, Leo

    2003-03-01

    We study creep dynamics of a two-dimensional interface driven through a periodic potential using dynamic renormalization-group methods. We find that the nature of weak-drive transport depends qualitatively on whether the temperature T is above or below the equilibrium roughening transition temperature Tc. Above Tc, the velocity-force characteristics are Ohmic, with linear mobility exhibiting a jump discontinuity across the transition. For T⩽Tc, the transport is highly nonlinear, exhibiting an interesting crossover in temperature and weak external force F. For intermediate drive, F>F*, we find near T-c a power-law velocity-force characteristics v(F)˜Fσ, with σ-1∝t˜, and well below Tc, v(F)˜e-(F*/F)2t˜, with t˜=(1-T/Tc). In the limit of vanishing drive (F≪F*), the velocity-force characteristics cross over to v(F)˜e-(F0/F), and are controlled by soliton nucleation.

  1. Pattern formation, social forces, and diffusion instability in games with success-driven motion

    NASA Astrophysics Data System (ADS)

    Helbing, Dirk

    2009-02-01

    A local agglomeration of cooperators can support the survival or spreading of cooperation, even when cooperation is predicted to die out according to the replicator equation, which is often used in evolutionary game theory to study the spreading and disappearance of strategies. In this paper, it is shown that success-driven motion can trigger such local agglomeration and may, therefore, be used to supplement other mechanisms supporting cooperation, like reputation or punishment. Success-driven motion is formulated here as a function of the game-theoretical payoffs. It can change the outcome and dynamics of spatial games dramatically, in particular as it causes attractive or repulsive interaction forces. These forces act when the spatial distributions of strategies are inhomogeneous. However, even when starting with homogeneous initial conditions, small perturbations can trigger large inhomogeneities by a pattern-formation instability, when certain conditions are fulfilled. Here, these instability conditions are studied for the prisoner’s dilemma and the snowdrift game. Furthermore, it is demonstrated that asymmetrical diffusion can drive social, economic, and biological systems into the unstable regime, if these would be stable without diffusion.

  2. Robust Operation of Tendon-Driven Robot Fingers Using Force and Position-Based Control Laws

    NASA Technical Reports Server (NTRS)

    Abdallah, Muhammad E (Inventor); Platt, Jr., Robert J. (Inventor); Reiland, Matthew J (Inventor); Hargrave, Brian (Inventor); Diftler, Myron A (Inventor); Strawser, Philip A (Inventor); Ihrke, Chris A. (Inventor)

    2013-01-01

    A robotic system includes a tendon-driven finger and a control system. The system controls the finger via a force-based control law when a tension sensor is available, and via a position-based control law when a sensor is not available. Multiple tendons may each have a corresponding sensor. The system selectively injects a compliance value into the position-based control law when only some sensors are available. A control system includes a host machine and a non-transitory computer-readable medium having a control process, which is executed by the host machine to control the finger via the force- or position-based control law. A method for controlling the finger includes determining the availability of a tension sensor(s), and selectively controlling the finger, using the control system, via the force or position-based control law. The position control law allows the control system to resist disturbances while nominally maintaining the initial state of internal tendon tensions.

  3. Turbulent Flows Driven by the Mechanical Forcing of an Ellipsoidal Container

    NASA Astrophysics Data System (ADS)

    Favier, Benjamin; Le Bars, Michael; Grannan, Alexander; Ribeiro, Adolfo; Aurnou, Jonathan; Irphe Team; Spinlab Team

    2015-11-01

    We present a combination of laboratory experiments and numerical simulations modelling geophysically relevant mechanical forcings. Libration and tides correspond to the periodic perturbation of a body's rotation rate and shape, and are both due to gravitational interactions with orbiting companions. Such mechanical forcings can convey a fraction of the rotational energy available and generate intense turbulence in the fluid interior of satellites and planets. We investigate the fluid motions inside a librating or tidally deformed triaxial ellipsoidal container filled with an incompressible fluid. In both cases, the turbulent flow is driven by the elliptic instability which is a triadic resonance between two inertial modes and the base flow. We characterize the transition to turbulence as triadic resonances develop while also investigating both intermittent and sustained regimes. It is shown that the flow is largely independent of the properties of the mechanical forcing, hinting at a possible universal behaviour of the saturated elliptical instability. The existence of such intense flows may play an important role in understanding the thermal and magnetic evolution of celestial bodies. This work was funded by the French Agence Nationale pour la Recherche and the National Science Foundation Geophysics Program.

  4. Numerical investigations of the force experienced by a wall subject to granular lid-driven flows: regimes and scaling of the mean force

    NASA Astrophysics Data System (ADS)

    Kneib, François; Faug, Thierry; Dufour, Frédéric; Naaim, Mohamed

    2016-07-01

    Discrete element simulations are used to model a two-dimensional gravity-free granular sample, which is trapped between two smooth sidewalls and one bottom rough wall while being subject to a constant shearing velocity at the top under a given confinement pressure. This system, inspired by conventional fluid mechanics, is called a granular lid-driven cavity. Attention is firstly paid to the time-averaged dynamics of the grains once a steady-state is reached. Strong spatial heterogeneities associated with a large-scale vortex formed within the whole volume of the lid-driven cavity are observed. The mean steady force on the sidewall facing the shearing velocity is then investigated in detail for different cavity lengths, shearing velocities and confinement pressures at the top. The ratio of the force on the latter wall to the top confinement pressure force is not constant but depends on both the shearing velocity and the confinement pressure. Above a critical value of the cavity length relative to the wall height and over a wide range of both shearing velocity and top confinement pressure, all data merge into a one-to-one relation between the mean force scaled by the top pressure force and the macroscopic inertial number of the lid-driven cavity. This result reveals the key role played by the inertial rheology of the granular material in the granular force transmission.

  5. Direct force wall shear measurements in pressure-driven three-dimensional turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Mcallister, J. E.; Tennant, M. H.; Pierce, F. J.

    1982-01-01

    Unique, simultaneous direct measurements of the magnitude and direction of the local wall shear stress in a pressure-driven three-dimensional turbulent boundary layer are presented. The flow is also described with an oil streak wall flow pattern, a map of the wall shear stress-wall pressure gradient orientations, a comparison of the wall shear stress directions relative to the directions of the nearest wall velocity as measured with a typical, small boundary layer directionally sensitive claw probe, as well as limiting wall streamline directions from the oil streak patterns, and a comparison of the freestream streamlines and the wall flow streamlines. A review of corrections for direct force sensing shear meters for two-dimensional flows is presented with a brief discussion of their applicability to three-dimensional devices.

  6. An EMG-driven Model to Estimate Muscle Forces and Joint Moments in Stroke Patients

    PubMed Central

    Shao, Qi; Bassett, Daniel N.; Manal, Kurt; Buchanan, Thomas S.

    2009-01-01

    Individuals following stroke exhibit altered muscle activation and movement patterns. Improving the efficiency of gait can be facilitated by knowing which muscles are affected and how they contribute to the pathological pattern. In this paper we present an electromyographically (EMG) driven musculoskeletal model to estimate muscle forces and joint moments. Subject specific EMG for the primary ankle plantar and dorsiflexor muscles, and joint kinematics during walking for four subjects following stroke were used as inputs to the model to predict ankle joint moments during stance. The model’s ability to predict the joint moment was evaluated by comparing the model output with the moment computed using inverse dynamics. The model did predict the ankle moment with acceptable accuracy, exhibiting an average R2 value ranging between 0.87 and 0.92, with RMS errors between 9.7% and 14.7%. The values are in line with previous results for healthy subjects, suggesting that EMG-driven modeling in this population of patients is feasible. It is our hope that such models can provide clinical insight into developing more effective rehabilitation therapies and to assess the effects of an intervention. PMID:19818436

  7. Capillary Force-Driven, Hierarchical Co-Assembly of Dandelion-Like Peptide Microstructures.

    PubMed

    Wang, Yuefei; Huang, Renliang; Qi, Wei; Xie, Yanyan; Wang, Mengfan; Su, Rongxin; He, Zhimin

    2015-06-24

    The wetting and drying of drops on flexible fibers occurs ubiquitously in nature, and the capillary force underlying this phenomenon has motivated our great interest in learning how to direct supramolecular self-assembly. Here, the hierarchical co-assembly of two aromatic peptides, diphenylalanine (FF) and ferrocene-diphenylalanine (Fc-FF), is reported via sequential, combinatorial assembly. The resulting dandelion-like microstructures have highly complex architectures, where FF microtube arrays serve as the scapes and the Fc-FF nanofibers serve as the flower heads. Homogeneous FF microtubes with diameters tailored between 1 and 9 μm and wall thickness ranging from 70 to 950 nm are initially formed by controlling the degree of supersaturation of the FF and the water content. Once the FF microtubes are formed, the growth of the dandelion-like microstructures is then driven by the capillary force, derived from the wetting and drying of the Fc-FF solution on the FF microtubes. This simple and ingenious strategy offers many opportunities to develop new and creative methods for controlling the hierarchical self-assembly of peptides and thus building highly complex nano and microstructures. PMID:25759325

  8. Sea surface temperature anomalies driven by oceanic local forcing in the Brazil-Malvinas Confluence

    NASA Astrophysics Data System (ADS)

    da Silveira, Isabel Porto; Pezzi, Luciano Ponzi

    2014-03-01

    Sea surface temperature (SST) anomaly events in the Brazil-Malvinas Confluence (BMC) were investigated through wavelet analysis and numerical modeling. Wavelet analysis was applied to recognize the main spectral signals of SST anomaly events in the BMC and in the Drake Passage as a first attempt to link middle and high latitudes. The numerical modeling approach was used to clarify the local oceanic dynamics that drive these anomalies. Wavelet analysis pointed to the 8-12-year band as the most energetic band representing remote forcing between high to middle latitudes. Other frequencies observed in the BMC wavelet analysis indicate that part of its variability could also be forced by low-latitude events, such as El Niño. Numerical experiments carried out for the years of 1964 and 1992 (cold and warm El Niño-Southern Oscillation (ENSO) phases) revealed two distinct behaviors that produced negative and positive sea surface temperature anomalies on the BMC region. The first behavior is caused by northward cold flow, Río de la Plata runoff, and upwelling processes. The second behavior is driven by a southward excursion of the Brazil Current (BC) front, alterations in Río de la Plata discharge rates, and most likely by air-sea interactions. Both episodes are characterized by uncoupled behavior between the surface and deeper layers.

  9. Translocation dynamics of a short polymer driven by an oscillating force.

    PubMed

    Pizzolato, Nicola; Fiasconaro, Alessandro; Adorno, Dominique Persano; Spagnolo, Bernardo

    2013-02-01

    We study the translocation dynamics of a short polymer moving in a noisy environment and driven by an oscillating force. The dynamics is numerically investigated by solving a Langevin equation in a two-dimensional domain. We consider a phenomenological cubic potential with a metastable state to model the polymer-pore interaction and the entropic free energy barrier characterizing the translocation process. The mean first translocation time of the center of inertia of polymers shows a nonmonotonic behavior, with a minimum, as a function of the number of the monomers. The dependence of the mean translocation time on the polymer chain length shows a monotonically increasing behavior for high values of the number of monomers. Moreover, the translocation time shows a minimum as a function of the frequency of the oscillating forcing field for all the polymer lengths investigated. This finding represents the evidence of the resonant activation phenomenon in the dynamics of polymer translocation, whose occurrence is maintained for different values of the noise intensity.

  10. Capillary Force-Driven, Hierarchical Co-Assembly of Dandelion-Like Peptide Microstructures.

    PubMed

    Wang, Yuefei; Huang, Renliang; Qi, Wei; Xie, Yanyan; Wang, Mengfan; Su, Rongxin; He, Zhimin

    2015-06-24

    The wetting and drying of drops on flexible fibers occurs ubiquitously in nature, and the capillary force underlying this phenomenon has motivated our great interest in learning how to direct supramolecular self-assembly. Here, the hierarchical co-assembly of two aromatic peptides, diphenylalanine (FF) and ferrocene-diphenylalanine (Fc-FF), is reported via sequential, combinatorial assembly. The resulting dandelion-like microstructures have highly complex architectures, where FF microtube arrays serve as the scapes and the Fc-FF nanofibers serve as the flower heads. Homogeneous FF microtubes with diameters tailored between 1 and 9 μm and wall thickness ranging from 70 to 950 nm are initially formed by controlling the degree of supersaturation of the FF and the water content. Once the FF microtubes are formed, the growth of the dandelion-like microstructures is then driven by the capillary force, derived from the wetting and drying of the Fc-FF solution on the FF microtubes. This simple and ingenious strategy offers many opportunities to develop new and creative methods for controlling the hierarchical self-assembly of peptides and thus building highly complex nano and microstructures.

  11. A systematic review of resilience and mental health outcomes of conflict-driven adult forced migrants

    PubMed Central

    2014-01-01

    Background The rising global burden of forced migration due to armed conflict is increasingly recognised as an important issue in global health. Forced migrants are at a greater risk of developing mental disorders. However, resilience, defined as the ability of a person to successfully adapt to or recover from stressful and traumatic experiences, has been highlighted as a key potential protective factor. This study aimed to review systematically the global literature on the impact of resilience on the mental health of adult conflict-driven forced migrants. Methodology Both quantitative and qualitative studies that reported resilience and mental health outcomes among forcibly displaced persons (aged 18+) by way of exploring associations, links, pathways and causative mechanisms were included. Fourteen bibliographic databases and seven humanitarian study databases/websites were searched and a four stage screening process was followed. Results Twenty three studies were included in the final review. Ten qualitative studies identified highlighted family and community cohesion, family and community support, individual personal qualities, collective identity, supportive primary relationships and religion. Thirteen quantitative studies were identified, but only two attempted to link resilience with mental disorders, and three used a specific resilience measure. Over-reliance on cross-sectional designs was noted. Resilience was generally shown to be associated with better mental health in displaced populations, but the evidence on this and underlying mechanisms was limited. Discussion The review highlights the need for more epidemiological and qualitative evidence on resilience in forcibly displaced persons as a potential avenue for intervention development, particularly in resource-poor settings. PMID:25177360

  12. ACOUSTIC RADIATION FORCE-DRIVEN ASSESSMENT OF MYOCARDIAL ELASTICITY USING THE DISPLACEMENT RATIO RATE (DRR) METHOD

    PubMed Central

    Bouchard, Richard R.; Hsu, Stephen J.; Palmeri, Mark L.; Rouze, Ned C.; Nightingale, Kathryn R.; Trahey, Gregg E.

    2011-01-01

    A noninvasive method of characterizing myocardial stiffness could have significant implications in diagnosing cardiac disease. Acoustic radiation force (ARF)–driven techniques have demonstrated their ability to discern elastic properties of soft tissue. For the purpose of myocardial elasticity imaging, a novel ARF-based imaging technique, the displacement ratio rate (DRR) method, was developed to rank the relative stiffnesses of dynamically varying tissue. The basis and performance of this technique was demonstrated through numerical and phantom imaging results. This new method requires a relatively small temporal (<1 ms) and spatial (tenths of mm2) sampling window and appears to be independent of applied ARF magnitude. The DRR method was implemented in two in vivo canine studies, during which data were acquired through the full cardiac cycle by imaging directly on the exposed epicardium. These data were then compared with results obtained by acoustic radiation force impulse (ARFI) imaging and shear wave velocimetry, with the latter being used as the gold standard. Through the cardiac cycle, velocimetry results portray a range of shear wave velocities from 0.76–1.97 m/s, with the highest velocities observed during systole and the lowest observed during diastole. If a basic shear wave elasticity model is assumed, such a velocity result would suggest a period of increased stiffness during systole (when compared with diastole). Despite drawbacks of the DRR method (i.e., sensitivity to noise and limited stiffness range), its results predicted a similar cyclic stiffness variation to that offered by velocimetry while being insensitive to variations in applied radiation force. PMID:21645966

  13. Elephant overflows: Multi-annual variability in Weddell Sea Deep Water driven by surface forcing

    NASA Astrophysics Data System (ADS)

    Meijers, Andrew; Meredith, Michael; Abrahamsen, Povl; Naviera-Garabato, Alberto; Ángel Morales Maqueda, Miguel; Polzin, Kurt

    2015-04-01

    The volume of the deepest and densest water mass in Drake Passage, Lower Weddell Sea Deep Water (LWSDW), is shown to have been decreasing over the last 20 years of observations, with an associated reduction in density driven by freshening. Superimposed on this long term trend is a multi-annual oscillation with a period of 3-5 years. This variability only appears in Drake Passage; observations in the east of the Scotia Sea show a similar long term trend, but with no apparent multi-annual variability. Clues as to the source of this variability may be found on the continental slope at approximately 1000 m immediately north of Elephant Island on the northern tip of the Antarctic Peninsula. Here there is an intermittent westward flowing cold/fresh slope current whose volume and properties are strongly correlated with the LWSDW multi-annual variability, although leading the LWSDW by around one year. As the slope current and LWSDW are separated from each other both geographically and in water mass characteristics, their co-variability implies that they are responding to a common forcing, while the lag between deep LWSDW and shallow slope current provides information on the timescale of this response. A newly available high resolution temperature and salinity multi-year time series from the Elephant Island slope at 1000 m is compared with reanalysis and model derived surface fluxes, sea ice extent and wind stress. We find that there are strong positive relationships between the surface wind stress and heat flux over the shelf at the tip of the Antarctic Peninsula and the properties of the slope current at 1000 m on seasonal to annual timescales. We use tracer release experiments in the Southern Ocean State Estimate (SOSE) model to investigate the lag between the slope current and LWSDW timeseries and hypothesise that the observed multi-annual variability in both water masses is driven by surface forcing over the shelf and the overflow of modified water from the slope in

  14. An EMG-driven musculoskeletal model to estimate muscle forces and knee joint moments in vivo.

    PubMed

    Lloyd, David G; Besier, Thor F

    2003-06-01

    This paper examined if an electromyography (EMG) driven musculoskeletal model of the human knee could be used to predict knee moments, calculated using inverse dynamics, across a varied range of dynamic contractile conditions. Muscle-tendon lengths and moment arms of 13 muscles crossing the knee joint were determined from joint kinematics using a three-dimensional anatomical model of the lower limb. Muscle activation was determined using a second-order discrete non-linear model using rectified and low-pass filtered EMG as input. A modified Hill-type muscle model was used to calculate individual muscle forces using activation and muscle tendon lengths as inputs. The model was calibrated to six individuals by altering a set of physiologically based parameters using mathematical optimisation to match the net flexion/extension (FE) muscle moment with those measured by inverse dynamics. The model was calibrated for each subject using 5 different tasks, including passive and active FE in an isokinetic dynamometer, running, and cutting manoeuvres recorded using three-dimensional motion analysis. Once calibrated, the model was used to predict the FE moments, estimated via inverse dynamics, from over 200 isokinetic dynamometer, running and sidestepping tasks. The inverse dynamics joint moments were predicted with an average R(2) of 0.91 and mean residual error of approximately 12 Nm. A re-calibration of only the EMG-to-activation parameters revealed FE moments prediction across weeks of similar accuracy. Changing the muscle model to one that is more physiologically correct produced better predictions. The modelling method presented represents a good way to estimate in vivo muscle forces during movement tasks.

  15. Hydro-climatic fluctuations driven by natural and anthropogenic forcing in China

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Yang, D.

    2014-12-01

    Hydrological change is one of the most profound parts of global change which is associated with freshwater resources, food security and balance of ecosystem. Its driving factors in the past need to be understood and quantified for projection of future changes and management of water available. Here by applying the Budyko water-energy balance framework, we analyse the hydro-climatic fluctuations at annual scale and their natural and anthropogenic drivers during past fifty years in six major Chinese drainage basins, from south to north, and from natural basins to human-modified basins. Natural forcing here means the fluctuations in precipitation and temperature, and the shift of precipitation from snow towards rain. And we focus on the impact of change in vegetational coverage, agricultural irrigation and water division as anthropogenic effect. By cross-regional comparison and within-region comparison, we explore the spatial variability of the hydro-climatic change and the type and contribution of different driven factors, especially various human modifications, throughout China. This study shows how the complex coupled system of climate, human and eco-hydrology can be described and explored by an effective and simple model and how the water balance constraints of hydrological basins affect water available throughout China and their spatial variability in the past half century.

  16. A Low Voltage Driven Digital-Droplet-Transporting-Chip by Electrostatic Force

    NASA Astrophysics Data System (ADS)

    Gao, An-Ran; Liu, Xiang; Gao, Xiu-Li; Li, Tie; Gao, Hua-Min; Zhou, Ping; Wang, Yue-Lin

    2011-08-01

    A low-voltage-driven digital-droplet-transporting chip with an open structure is designed, fabricated and characterized. The digital microfluidic chip is fabricated by the silicon planar process. Using only a single electrode panel, the droplet on the chip can be manipulated by electrostatic force under a dc driving voltage. The actuation principle is proposed and verified by the experiment. The experimental results show that the minimum driving voltage decreases as the thickness of the dielectric layer decreases. The driving voltage for a 3 μL deionized (DI) water droplet is reduced to 15 V in air and 13.5 V in oil by employing a thin dielectric layer of 600 nm with a high dielectric constant and a coating hydrophobic layer on the top. The DI water droplets are also demonstrated to be transported in two dimensions smoothly in a programmable manner, and the maximum transport speed reaches 96 mm/s. The droplets of normal saline, a solution of 0.9 wt% NaCl, are also successfully manipulated on the chip.

  17. The dynamics of capillary-driven two-phase flow: the role of nanofluid structural forces.

    PubMed

    Nikolov, Alex; Zhang, Hua

    2015-07-01

    Capillary-driven flows are fundamental phenomena and are involved in many key technological processes, such as oil recovery through porous rocks, ink-jet printing, the bubble dynamics in a capillary, microfluidic devices and labs on chips. Here, we discuss and propose a model for the oil displacement dynamics from the capillary by the nanofluid (which is composed of a liquid suspension of nanoparticles); we elucidate the physics of the novelty of the phenomenon and its application. The oil displacement by the nanofluid flow is a multi-stage phenomenon, first leading to the oil film formation on the capillary wall, its break-up, and retraction over the capillary wall; this lead to the formation of the oil double concave meniscus. With time, the process repeats itself, leading to the formation of a regular "necklace" of oil droplets inside the capillary. Finally, the oil droplets are separated by the nanofluid film from the capillary wall. The light reflected differential interferometry technique is applied to investigate the nanofluid interactions with the glass wall. We find nanoparticles tend to self-structure into multiple layers close to the solid wall, which cause the structural forces to arise that lead to the oil displacement from the capillary. This research is expected to benefit the understanding of nanofluid phenomena in a capillary and promote their use in technological applications. PMID:25465201

  18. 1D self-assembly of chemisorbed thymine on Cu(110) driven by dispersion forces

    NASA Astrophysics Data System (ADS)

    Temprano, I.; Thomas, G.; Haq, S.; Dyer, M. S.; Latter, E. G.; Darling, G. R.; Uvdal, P.; Raval, R.

    2015-03-01

    Adsorption of thymine on a defined Cu(110) surface was studied using reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and scanning tunnelling microscopy (STM). In addition, density functional theory (DFT) calculations were undertaken in order to further understand the energetics of adsorption and self-assembly. The combination of RAIRS, TPD, and DFT results indicates that an upright, three-point-bonded adsorption configuration is adopted by the deprotonated thymine at room temperature. DFT calculations show that the upright configuration adopted by individual molecules arises as a direct result of strong O-Cu and N-Cu bonds between the molecule and the surface. STM data reveal that this upright thymine motif self-assembles into 1D chains, which are surprisingly oriented along the open-packed [001] direction of the metal surface and orthogonal to the alignment of the functional groups that are normally implicated in H-bonding interactions. DFT modelling of this system reveals that the molecular organisation is actually driven by dispersion interactions, which cause a slight tilt of the molecule and provide the major driving force for assembly into dimers and 1D chains. The relative orientations and distances of neighbouring molecules are amenable for π-π stacking, suggesting that this is an important contributor in the self-assembly process.

  19. Delineating the Barotropic and Baroclinic Mechanisms in the Midlatitude Eddy-Driven Jet Response to Lower-Tropospheric Thermal Forcing

    NASA Astrophysics Data System (ADS)

    Nie, Yu; Zhang, Yang; Chen, Gang; Yang, Xiuqun

    2016-04-01

    Observations and climate models have shown that the midlatitude eddy-driven jet can exhibit an evident latitudinal shift in response to lower-tropospheric thermal forcing (e.g., the tropical SST warming during El Niño or extratropical SST anomalies associated with the atmosphere-ocean-sea ice coupling). In addition to the direct thermal wind response, the eddy feedbacks - including baroclinic mechanisms, such as lower-level baroclinic eddy generation, and barotropic mechanisms, such as upper-level wave propagation and breaking - can all contribute to the atmospheric circulation response to lower-level thermal forcing, but their individual roles have not been well explained. In this study, using a nonlinear beta-plane multilevel quasigeostrophic channel model, the mechanisms through which the lower-level thermal forcing induces the jet shift are investigated. By diagnosing the finite-amplitude wave activity (FAWA) budget, the baroclinic and barotropic eddy feedbacks to the lower-level thermal forcing are delineated. Particularly, by examining the transient circulation response after thermal forcing is switched on, it is shown that the lower-level thermal forcing affects the eddy-driven jet rapidly by modifying the upper-level zonal thermal wind distribution and the associated meridional wave propagation and breaking. The anomalous baroclinic eddy generation, however, acts to enhance the latitudinal shift of the eddy-driven jet only in the later stage of transient response. Furthermore, the barotropic mechanism is explicated by overriding exper- iments in which the barotropic flow in the vorticity advection is prescribed. Unlike the conventional baroclinic view, the barotropic eddy feedback, particularly the irreversible PV mixing through barotropic vorticity advection and deformation, plays a major role in the atmospheric circulation response to the lower-level thermal forcing.

  20. Irrelevance of the Power Stroke for the Directionality, Stopping Force, and Optimal Efficiency of Chemically Driven Molecular Machines

    PubMed Central

    Astumian, R. Dean

    2015-01-01

    A simple model for a chemically driven molecular walker shows that the elastic energy stored by the molecule and released during the conformational change known as the power-stroke (i.e., the free-energy difference between the pre- and post-power-stroke states) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Further, the apportionment of the dependence on the externally applied force between the forward and reverse rate constants of the power-stroke (or indeed among all rate constants) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Arguments based on the principle of microscopic reversibility demonstrate that this result is general for all chemically driven molecular machines, and even more broadly that the relative energies of the states of the motor have no role in determining the directionality, stopping force, or optimal efficiency of the machine. Instead, the directionality, stopping force, and optimal efficiency are determined solely by the relative heights of the energy barriers between the states. Molecular recognition—the ability of a molecular machine to discriminate between substrate and product depending on the state of the machine—is far more important for determining the intrinsic directionality and thermodynamics of chemo-mechanical coupling than are the details of the internal mechanical conformational motions of the machine. In contrast to the conclusions for chemical driving, a power-stroke is very important for the directionality and efficiency of light-driven molecular machines and for molecular machines driven by external modulation of thermodynamic parameters. PMID:25606678

  1. Irrelevance of the power stroke for the directionality, stopping force, and optimal efficiency of chemically driven molecular machines.

    PubMed

    Astumian, R Dean

    2015-01-20

    A simple model for a chemically driven molecular walker shows that the elastic energy stored by the molecule and released during the conformational change known as the power-stroke (i.e., the free-energy difference between the pre- and post-power-stroke states) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Further, the apportionment of the dependence on the externally applied force between the forward and reverse rate constants of the power-stroke (or indeed among all rate constants) is irrelevant for determining the directionality, stopping force, and efficiency of the motor. Arguments based on the principle of microscopic reversibility demonstrate that this result is general for all chemically driven molecular machines, and even more broadly that the relative energies of the states of the motor have no role in determining the directionality, stopping force, or optimal efficiency of the machine. Instead, the directionality, stopping force, and optimal efficiency are determined solely by the relative heights of the energy barriers between the states. Molecular recognition--the ability of a molecular machine to discriminate between substrate and product depending on the state of the machine--is far more important for determining the intrinsic directionality and thermodynamics of chemo-mechanical coupling than are the details of the internal mechanical conformational motions of the machine. In contrast to the conclusions for chemical driving, a power-stroke is very important for the directionality and efficiency of light-driven molecular machines and for molecular machines driven by external modulation of thermodynamic parameters.

  2. A computational model of cerebrospinal fluid production and reabsorption driven by Starling forces.

    PubMed

    Buishas, Joel; Gould, Ian G; Linninger, Andreas A

    2014-10-01

    Experimental evidence has cast doubt on the classical model of river-like cerebrospinal fluid (CSF) flow from the choroid plexus to the arachnoid granulations. We propose a novel model of water transport through the parenchyma from the microcirculation as driven by Starling forces. This model investigates the effect of osmotic pressure on water transport between the cerebral vasculature, the extracellular space (ECS), the perivascular space (PVS), and the CSF. A rigorous literature search was conducted focusing on experiments which alter the osmolarity of blood or ventricles and measure the rate of CSF production. Investigations into the effect of osmotic pressure on the volume of ventricles and the flux of ions in the blood, choroid plexus epithelium, and CSF are reviewed. Increasing the osmolarity of the serum via a bolus injection completely inhibits nascent fluid flow production in the ventricles. A continuous injection of a hyperosmolar solution into the ventricles can increase the volume of the ventricle by up to 125%. CSF production is altered by 0.231 μL per mOsm in the ventricle and by 0.835 μL per mOsm in the serum. Water flux from the ECS to the CSF is identified as a key feature of intracranial dynamics. A complete mathematical model with all equations and scenarios is fully described, as well as a guide to constructing a computational model of intracranial water balance dynamics. The model proposed in this article predicts the effects the osmolarity of ECS, blood, and CSF on water flux in the brain, establishing a link between osmotic imbalances and pathological conditions such as hydrocephalus and edema. PMID:25358881

  3. The two-phase flow at gas-evolving electrodes: Bubble-driven and Lorentz-force-driven convection

    NASA Astrophysics Data System (ADS)

    Weier, T.; Landgraf, S.

    2013-03-01

    We observe electrolysis with gas evolution, a phenomenon occurring in a number of industrial scale electrochemical processes. Here, water electrolysis takes place in a small undivided electrolysis cell consisting of vertical electrodes embedded in a larger glass vessel which contains a dilute NaOH solution. Fluid flow velocities are measured by particle image velocimetry with fluorescent tracers, while size distribution and velocities of the bubbles are determined from bubble shadow images obtained with a high speed camera. Coalescence phenomena are observed in the flow and explain the relatively wide distribution of bubble sizes. Depending on the gap width and the current density, bubbles ascending near the electrodes form two discernible bubble curtains (low average void fraction, wide gaps) or a flow profile more akin to a channel flow (high average void fraction, small gaps). If the flow consists of separate bubble curtains, instabilities develop not unlike to those of a single phase wall jet. Finally, the influence of different wall parallel Lorentz force configurations on the velocity distribution in the cell is investigated. These Lorentz forces are generated by permanent magnets mounted behind the electrodes. Depending on gap width, current density, and magnet configuration, liquid phase velocities can be increased by several times compared to the baseline case.

  4. A Three-Dimensional Shape-Based Force and Stiffness-Sensing Platform for Tendon-Driven Catheters.

    PubMed

    Kouh Soltani, Minou; Khanmohammadi, Sohrab; Ghalichi, Farzan

    2016-01-01

    This paper presents an efficient shape-based three-axial force and stiffness estimator for active catheters commonly implemented in cardiac ablation. The force-sensing capability provides important feedback for catheterization procedures including real-time control and catheter steering in autonomous navigation systems. The proposed platform is based on the introduced accurate and computationally efficient Cosserat rod model for tendon-driven catheters. The proposed nonlinear Kalman filter formulation for contact force estimation along with the developed catheter model provides a real-time force observer robust to nonlinearities and noise covariance uncertainties. Furthermore, the proposed platform enables stiffness estimation in addition to tip contact force sensing in different operational circumstances. The approach incorporates pose measurements which can be achieved using currently developed pose-sensing systems or imaging techniques. The method makes the approach compatible with the range of forces applied in clinical applications. The simulation and experimental results verify the viability of the introduced force and stiffness-sensing technique. PMID:27367685

  5. A Three-Dimensional Shape-Based Force and Stiffness-Sensing Platform for Tendon-Driven Catheters

    PubMed Central

    Kouh Soltani, Minou; Khanmohammadi, Sohrab; Ghalichi, Farzan

    2016-01-01

    This paper presents an efficient shape-based three-axial force and stiffness estimator for active catheters commonly implemented in cardiac ablation. The force-sensing capability provides important feedback for catheterization procedures including real-time control and catheter steering in autonomous navigation systems. The proposed platform is based on the introduced accurate and computationally efficient Cosserat rod model for tendon-driven catheters. The proposed nonlinear Kalman filter formulation for contact force estimation along with the developed catheter model provides a real-time force observer robust to nonlinearities and noise covariance uncertainties. Furthermore, the proposed platform enables stiffness estimation in addition to tip contact force sensing in different operational circumstances. The approach incorporates pose measurements which can be achieved using currently developed pose-sensing systems or imaging techniques. The method makes the approach compatible with the range of forces applied in clinical applications. The simulation and experimental results verify the viability of the introduced force and stiffness-sensing technique. PMID:27367685

  6. Tooth eruption results from bone remodelling driven by bite forces sensed by soft tissue dental follicles: a finite element analysis.

    PubMed

    Sarrafpour, Babak; Swain, Michael; Li, Qing; Zoellner, Hans

    2013-01-01

    Intermittent tongue, lip and cheek forces influence precise tooth position, so we here examine the possibility that tissue remodelling driven by functional bite-force-induced jaw-strain accounts for tooth eruption. Notably, although a separate true 'eruptive force' is widely assumed, there is little direct evidence for such a force. We constructed a three dimensional finite element model from axial computerized tomography of an 8 year old child mandible containing 12 erupted and 8 unerupted teeth. Tissues modelled included: cortical bone, cancellous bone, soft tissue dental follicle, periodontal ligament, enamel, dentine, pulp and articular cartilage. Strain and hydrostatic stress during incisive and unilateral molar bite force were modelled, with force applied via medial and lateral pterygoid, temporalis, masseter and digastric muscles. Strain was maximal in the soft tissue follicle as opposed to surrounding bone, consistent with follicle as an effective mechanosensor. Initial numerical analysis of dental follicle soft tissue overlying crowns and beneath the roots of unerupted teeth was of volume and hydrostatic stress. To numerically evaluate biological significance of differing hydrostatic stress levels normalized for variable finite element volume, 'biological response units' in Nmm were defined and calculated by multiplication of hydrostatic stress and volume for each finite element. Graphical representations revealed similar overall responses for individual teeth regardless if incisive or right molar bite force was studied. There was general compression in the soft tissues over crowns of most unerupted teeth, and general tension in the soft tissues beneath roots. Not conforming to this pattern were the unerupted second molars, which do not erupt at this developmental stage. Data support a new hypothesis for tooth eruption, in which the follicular soft tissues detect bite-force-induced bone-strain, and direct bone remodelling at the inner surface of the

  7. Chaotic phase synchronization in bursting-neuron models driven by a weak periodic force.

    PubMed

    Ando, Hiroyasu; Suetani, Hiromichi; Kurths, Jürgen; Aihara, Kazuyuki

    2012-07-01

    We investigate the entrainment of a neuron model exhibiting a chaotic spiking-bursting behavior in response to a weak periodic force. This model exhibits two types of oscillations with different characteristic time scales, namely, long and short time scales. Several types of phase synchronization are observed, such as 1:1 phase locking between a single spike and one period of the force and 1:l phase locking between the period of slow oscillation underlying bursts and l periods of the force. Moreover, spiking-bursting oscillations with chaotic firing patterns can be synchronized with the periodic force. Such a type of phase synchronization is detected from the position of a set of points on a unit circle, which is determined by the phase of the periodic force at each spiking time. We show that this detection method is effective for a system with multiple time scales. Owing to the existence of both the short and the long time scales, two characteristic phenomena are found around the transition point to chaotic phase synchronization. One phenomenon shows that the average time interval between successive phase slips exhibits a power-law scaling against the driving force strength and that the scaling exponent has an unsmooth dependence on the changes in the driving force strength. The other phenomenon shows that Kuramoto's order parameter before the transition exhibits stepwise behavior as a function of the driving force strength, contrary to the smooth transition in a model with a single time scale.

  8. Flow in complex domains simulated by Dissipative Particle Dynamics driven by geometry-specific body-forces

    NASA Astrophysics Data System (ADS)

    Yazdani, Alireza; Deng, Mingge; Caswell, Bruce; Karniadakis, George Em

    2016-01-01

    We demonstrate how the quality of simulations by Dissipative Particle Dynamics (DPD) of flows in complex geometries is greatly enhanced when driven by body forces suitably tailored to the geometry. In practice, the body force fields are most conveniently chosen to be the pressure gradient of the corresponding Navier-Stokes (N-S) flow. In the first of three examples, the driving-force required to yield a stagnation-point flow is derived from the pressure field of the potential flow for a lattice of counter-rotating line vortices. Such a lattice contains periodic squares bounded by streamlines with four vortices within them. Hence, the DPD simulation can be performed with periodic boundary conditions to demonstrate the value of a non-uniform driving-force without the need to model real boundaries. The second example is an irregular geometry consisting of a 2D rectangular cavity on one side of an otherwise uniform channel. The Navier-Stokes pressure field for the same geometry is obtained numerically, and its interpolated gradient is then employed as the driving-force for the DPD simulation. Finally, we present a third example, where the proposed method is applied to a complex 3D geometry of an asymmetric constriction. It is shown that in each case the DPD simulations closely reproduce the Navier-Stokes solutions. Convergence rates are found to be much superior to alternative methods; in addition, the range of convergence with respect to Reynolds number and Mach number is greatly extended.

  9. Viscoelastic properties of single polysaccharide molecules determined by analysis of thermally driven oscillations of an atomic force microscope cantilever.

    PubMed

    Kawakami, Masaru; Byrne, Katherine; Khatri, Bhavin; McLeish, Tom C B; Radford, Sheena E; Smith, D Alastair

    2004-10-12

    We report on single molecule measurements of the viscoelastic properties of the polysaccharide dextran using a new approach which involves acquiring the power spectral density of the thermal noise of an atomic force microscope cantilever while holding the single molecule of interest under force-clamp conditions. The attractiveness of this approach when compared with techniques which use forced oscillations under constant loading rate conditions is that it is a near-equilibrium measure of mechanical response which provides a more relevant probe of thermally driven biomolecular dynamics. Using a simple harmonic oscillator model of the cantilever-molecule system and by subtracting the response of the free cantilever taking into account hydrodynamic effects, the effective damping zetamol and elastic constant kmol of a single molecule are obtained. The molecular elasticity measured by this new technique shows a dependence on applied force that reflects the chair-boat conformational transition of the pyranose rings of the dextran molecule which is in good agreement with values obtained directly from the gradient of a conventional constant loading rate force-extension curve. The molecular damping is also seen to follow a nontrivial dependence on loading which we suggest indicates that it is internal friction and not work done on the solvent that is the dominant dissipative process. PMID:15461521

  10. Tooth Eruption Results from Bone Remodelling Driven by Bite Forces Sensed by Soft Tissue Dental Follicles: A Finite Element Analysis

    PubMed Central

    Sarrafpour, Babak; Swain, Michael; Li, Qing; Zoellner, Hans

    2013-01-01

    Intermittent tongue, lip and cheek forces influence precise tooth position, so we here examine the possibility that tissue remodelling driven by functional bite-force-induced jaw-strain accounts for tooth eruption. Notably, although a separate true ‘eruptive force’ is widely assumed, there is little direct evidence for such a force. We constructed a three dimensional finite element model from axial computerized tomography of an 8 year old child mandible containing 12 erupted and 8 unerupted teeth. Tissues modelled included: cortical bone, cancellous bone, soft tissue dental follicle, periodontal ligament, enamel, dentine, pulp and articular cartilage. Strain and hydrostatic stress during incisive and unilateral molar bite force were modelled, with force applied via medial and lateral pterygoid, temporalis, masseter and digastric muscles. Strain was maximal in the soft tissue follicle as opposed to surrounding bone, consistent with follicle as an effective mechanosensor. Initial numerical analysis of dental follicle soft tissue overlying crowns and beneath the roots of unerupted teeth was of volume and hydrostatic stress. To numerically evaluate biological significance of differing hydrostatic stress levels normalized for variable finite element volume, ‘biological response units’ in Nmm were defined and calculated by multiplication of hydrostatic stress and volume for each finite element. Graphical representations revealed similar overall responses for individual teeth regardless if incisive or right molar bite force was studied. There was general compression in the soft tissues over crowns of most unerupted teeth, and general tension in the soft tissues beneath roots. Not conforming to this pattern were the unerupted second molars, which do not erupt at this developmental stage. Data support a new hypothesis for tooth eruption, in which the follicular soft tissues detect bite-force-induced bone-strain, and direct bone remodelling at the inner surface of

  11. Force.

    ERIC Educational Resources Information Center

    Gamble, Reed

    1989-01-01

    Discusses pupil misconceptions concerning forces. Summarizes some of Assessment of Performance Unit's findings on meaning of (1) force, (2) force and motion in one dimension and two dimensions, and (3) Newton's second law. (YP)

  12. Motion of an atom in a weakly driven fiber-Bragg-grating cavity: Force, friction, and diffusion

    SciTech Connect

    Le Kien, Fam; Hakuta, K.

    2010-06-15

    We study the translational motion of an atom in the vicinity of a weakly driven nanofiber with two fiber-Bragg-grating mirrors. We calculate numerically and analytically the force, the friction coefficients, and the momentum diffusion. We find that the spatial dependences of the force, the friction coefficients, and the momentum diffusion are very complicated due to the evanescent-wave nature of the atom-field coupling as well as the effect of the van der Waals potential. We show that the time development of the mean number of photons in the cavity closely follows the translational motion of the atom through the nodes and antinodes of the fiber-guided cavity standing-wave field even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.

  13. Force-driven evolution of mesoscale structure in engineered 3D microtissues and the modulation of tissue stiffening

    PubMed Central

    Zhao, Ruogang; Chen, Christopher S.; Reich, Daniel H.

    2014-01-01

    The complex structures of tissues determine their mechanical strength. In engineered tissues formed through self-assembly in a mold, artificially imposed boundary constraints have been found to induce anisotropic clustering of the cells and the extracellular matrix in local regions. To understand how such tissue remodeling at the intermediate length-scale (mesoscale) affects tissue stiffening, we used a novel microtissue mechanical testing system to manipulate the remodeling of the tissue structures and to measure the subsequent changes in tissue stiffness. Microtissues were formed through cell driven self-assembly of collagen matrix in arrays of micro-patterned wells, each containing two flexible micropillars that measured the microtissues’ contractile forces and also their elastic moduli via magnetic actuation. We manipulated tissue remodeling by inducing myofibroblast differentiation with TGF-β1, by varying the micropillar spring constants or by blocking cell contractility with blebbistatin and collagen cross-linking with BAPN. We showed that increased anisotropic compaction of the collagen matrix, caused by increased micropillar spring constant or elevated cell contraction force, contributed to tissue stiffening. Conversely, collagen matrix and tissue stiffness were not affected by inhibition of cell-generated contraction forces.. Together, these measurements showed that mesoscale tissue remodeling is an important middle step linking tissue compaction forces and tissue stiffening. PMID:24630092

  14. The role of turbulent dissipation in planetary fluid interiors driven by tidal and librational forcing

    NASA Astrophysics Data System (ADS)

    Grannan, Alex; Favier, Benjamin; Bills, Bruce; Lemasquerier, Daphne; Le Bars, Michael; Aurnou, Jonathan

    2016-10-01

    The turbulent fluid motions generated in the liquid metal cores and oceans of planetary bodies can have profound effects on energy dissipation and magnetic field generation. An important driver of such fluid motions is mechanical forcing from precession, libration, and tidal forcing. On Earth, the dissipation of energy through tidal forcing occurs primarily in the oceans and may be due, in part, to nonlinear tidally forced resonances. However, the role that such nonlinear resonances play are not generally considered for other planetary bodies also possessing oceans and liquid metal cores.Recent laboratory experimental and numerical studies of Grannan et al. 2014 and Favier et al. 2015 have shown that nonlinear fluid resonances generated by sufficiently strong librational forcing can drive turbulent flows in ellipsoidal containers that mimic gravitational deformations. In Grannan et al. 2016, similar results were found for strong tidal forcing. Thus, a generalized scaling law for the turbulent r.m.s. velocity is derived, U~ɛβE-α, where ɛ is the dimensionless amplitude of the tidal or librational forcing, β is the dimensionless tidal deformation of the body, E is the dimensionless Ekman number characterizing the ratio of viscous to Coriolis forces, and α is a varying exponent.Using planetary values for tidal and librational forcing parameters, the turbulent dissipation is estimated for multiple bodies. For the subsurface oceans of Europa and Enceladus, the amount of nonlinear dissipation is comparable to the dissipation generated from linear resonances of the fluid layer and from upper bounding estimates of the tidal dissipation in the solid icy shell. In addition, our estimates of this turbulent dissipation provide bounds for the stratification in these subsurface oceans. Finally we find that dissipation from these nonlinear resonances in the liquid metal cores of the the early and present Earth, Io, and several exoplanets may help drive the dynamos in these

  15. Mapping of force fields in a capacitively driven radiofrequency plasma discharge

    NASA Astrophysics Data System (ADS)

    Dropmann, Michael; Chen, M.; Sabo, H.; Laufer, R.; Herdrich, G.; Matthews, L. S.; Hyde, T. W.

    2016-08-01

    > In this paper a method is described that allows mapping of the forces acting on dust particles in a GEC reference cell. Monodisperse particles are dropped into the plasma environment and their trajectories are tracked using a high-speed camera system to determine local accelerations and respective forces. Collecting data from a large number of particle drops allows the identification of three-dimensional vector fields for the acting forces. The procedure is described and multiple examples in which the method has been applied are given. These examples include a simple plasma sheath, plasmas perturbed by a horizontal and vertical dipole magnet, an array of multiple magnets mimicking the fields found at a lunar swirl, and the fields inside a glass box used for particle confinement. Further applicability in other plasma environments will be discussed shortly.

  16. Interplay of RhoA and mechanical forces in collective cell migration driven by leader cells.

    PubMed

    Reffay, M; Parrini, M C; Cochet-Escartin, O; Ladoux, B; Buguin, A; Coscoy, S; Amblard, F; Camonis, J; Silberzan, P

    2014-03-01

    The leading front of a collectively migrating epithelium often destabilizes into multicellular migration fingers where a cell initially similar to the others becomes a leader cell while its neighbours do not alter. The determinants of these leader cells include mechanical and biochemical cues, often under the control of small GTPases. However, an accurate dynamic cartography of both mechanical and biochemical activities remains to be established. Here, by mapping the mechanical traction forces exerted on the surface by MDCK migration fingers, we show that these structures are mechanical global entities with the leader cells exerting a large traction force. Moreover, the spatial distribution of RhoA differential activity at the basal plane strikingly mirrors this force cartography. We propose that RhoA controls the development of these fingers through mechanical cues: the leader cell drags the structure and the peripheral pluricellular acto-myosin cable prevents the initiation of new leader cells.

  17. Macrophage motility is driven by frontal-towing with a force magnitude dependent on substrate stiffness.

    PubMed

    Hind, Laurel E; Dembo, Micah; Hammer, Daniel A

    2015-04-01

    The ability of macrophages to properly migrate is crucial to their success as early responders during the innate immune response. Furthermore, improper regulation of macrophage migration is known to contribute to several pathologies. The signaling mechanisms underlying macrophage migration have been previously studied but to date the mechanical mechanism of macrophage migration has not been determined. In this study, we have created the first traction maps of motile primary human macrophages by observing their migration on compliant polyacrylamide gels. We find that the force generated by migrating macrophages is concentrated in the leading edge of the cell - so-called frontal towing - and that the magnitude of this force is dependent on the stiffness of the underlying matrix. With the aid of chemical inhibitors, we show that signaling through the RhoA kinase ROCK, myosin II, and PI3K is essential for proper macrophage force generation. Finally, we show that Rac activation by its GEF Vav1 is crucial for macrophage force generation while activation through its GEF Tiam1 is unnecessary.

  18. Forced desorption of semiflexible polymers, adsorbed and driven by molecular motors.

    PubMed

    Chaudhuri, Abhishek; Chaudhuri, Debasish

    2016-02-21

    We formulate and characterize a model to describe the dynamics of semiflexible polymers in the presence of activity due to motor proteins attached irreversibly to a substrate, and a transverse pulling force acting on one end of the filament. The stochastic binding-unbinding of the motor proteins and their ability to move along the polymer generate active forces. As the pulling force reaches a threshold value, the polymer eventually desorbs from the substrate. Performing underdamped Langevin dynamics simulation of the polymer, and with stochastic motor activity, we obtain desorption phase diagrams. The correlation time for fluctuations in the desorbed fraction increases as one approaches complete desorption, captured quantitatively by a power law spectral density. We present theoretical analysis of the phase diagram using mean field approximations in the weakly bending limit of the polymer and performing linear stability analysis. This predicts an increase in the desorption force with the polymer bending rigidity, active velocity and processivity of the motor proteins to capture the main features of the simulation results. PMID:26750537

  19. Longitudinal oscillations and flights of the string pendulum driven by a periodic force.

    PubMed

    Arinstein, A

    2009-05-01

    The longitudinal oscillations of a string pendulum are discussed. The regime in which the oscillating bob executes free flight under gravity is studied. This regime arises if, during the motion in the upward direction, bob reaches a height at which no elastic force acts on bob, and its further motion occurs only under gravity. Thus, the string pendulum executes a motion of two types: the harmonic oscillations under the action of elastic force and free flights under gravity. In doing so, the height of flights can considerably exceed the amplitude of the forced oscillations, i.e., a noticeable amplitude amplification in the longitudinal oscillations of a string pendulum takes place. A mechanism of a resonance phenomenon related to the excitation of free oscillations is described. These free oscillations arising after each bob flight are the channel for energy pumping into the system in question. It turns out that the frequency of the above resonance is equal to the fundamental frequency of the string, and the resonance amplitude of the flights is proportional to the square of amplitude of regular forced oscillations.

  20. Longitudinal oscillations and flights of the string pendulum driven by a periodic force

    NASA Astrophysics Data System (ADS)

    Arinstein, A.

    2009-05-01

    The longitudinal oscillations of a string pendulum are discussed. The regime in which the oscillating bob executes free flight under gravity is studied. This regime arises if, during the motion in the upward direction, bob reaches a height at which no elastic force acts on bob, and its further motion occurs only under gravity. Thus, the string pendulum executes a motion of two types: the harmonic oscillations under the action of elastic force and free flights under gravity. In doing so, the height of flights can considerably exceed the amplitude of the forced oscillations, i.e., a noticeable amplitude amplification in the longitudinal oscillations of a string pendulum takes place. A mechanism of a resonance phenomenon related to the excitation of free oscillations is described. These free oscillations arising after each bob flight are the channel for energy pumping into the system in question. It turns out that the frequency of the above resonance is equal to the fundamental frequency of the string, and the resonance amplitude of the flights is proportional to the square of amplitude of regular forced oscillations.

  1. Optical remote sensing of penetration into the lower thermosphere of neutral wind and composition perturbations driven by magnetospheric forcing

    NASA Astrophysics Data System (ADS)

    Conde, M. G.; Anderson, C.; Hecht, J. H.

    2011-12-01

    Numerous observations of thermospheric neutral winds at altitudes of 240 km and higher clearly show wind structures occurring at auroral latitudes in response to magnetospheric forcing. It is also known from observations that magnetospheric forcing is not a major driver of winds down at mesopause heights and below. Because it is difficult to measure winds in the intervening "transition region" between these height regimes, very little is known about how deeply the magnetospherically driven neutral wind structures penetrate into the lower thermosphere, what factors affect this penetration, and what consequences it may have for transport of chemical species. Here we will show neutral wind maps obtained at F-region and E-region heights in the auroral zone using Fabry-Perot Doppler spectroscopy of the 630 nm and 558 nm optical emissions. Although thermospheric neutral winds are smoothed by viscosity and inertia, observed responses to magnetospheric forcing still include wind responses on time scales as short as 10 minutes or less, and on length scales shorter than 100 km horizontally and 5 km vertically. The data also show that the degree of penetration of magnetospheric forcing into the lower thermospheric wind field is highly variable from day to day. Signatures of magnetospheric forcing are sometimes seen at altitudes as low as 120 km, whereas at other times the E-region does not seem to respond at all. Possible links will be explored between this variability and the day to day differences seen in the column integrated thermospheric [O]/[N2] ratio over Alaska.

  2. Observation of the saturation of Langmuir waves driven by ponderomotive force in a large scale plasma

    SciTech Connect

    Kirkwood, R. K.; Moody, J. D.; MacGowan, B. J.; Glenzer, S. H.; Kruer, W. L.; Estabrook, K. G.; Wharton, K. B.; Williams, E. A.; Berger, R. L.

    1997-06-22

    We report the observation of amplification of a probe laser beam (I {le} 1 {times} 10{sup 14} W/cm{sup 2}) in a large scale ({approximately} 1 mm) plasma by interaction with a pumping laser beam (I = 2 {times} 10{sup 15} W/cm{sup 2}) and a stimulated Langmuir wave. When the plasma density is adjusted to allow the Langmuir wave dispersion to match the difference frequency and wave number of the two beams, amplification factors as high as {times} 2.5 result. Interpretation of this amplification as scattering of pump beam energy by the Langmuir wave that is produced by the ponderomotive force of the two beams, allows the dependence of Langmuir wave amplitude on ponderomotive force to be measured. It is found that the Langmuir wave amplitude saturates at a level that depends on ion wave damping, and is generally consistent with secondary ion wave instabilities limiting its growth. 20 refs., 4 figs.

  3. Approach and Coalescence of Gold Nanoparticles Driven by Surface Thermodynamic Fluctuations and Atomic Interaction Forces.

    PubMed

    Wang, Jiadao; Chen, Shuai; Cui, Kai; Li, Dangguo; Chen, Darong

    2016-02-23

    The approach and coalescence behavior of gold nanoparticles on a silicon surface were investigated by experiments and molecular dynamics simulations. By analyzing the behavior of the atoms in the nanoparticles in the simulations, it was found that the atoms in a single isolated nanoparticle randomly fluctuated and that the surface atoms showed greater fluctuation. The fluctuation increased as the temperature increased. When there were two or more neighboring nanoparticles, the fluctuating surface atoms of the nanoparticles "flowed" toward the neighboring nanoparticle because of atomic interaction forces between the nanoparticles. With the surface atoms "flowing", the gold nanoparticles approached and finally coalesced. The simulation results were in good agreement with the experimental results. It can be concluded that surface thermodynamic fluctuations and atomic interaction forces are the causes of the approach and coalescence behavior of the gold nanoparticles. PMID:26756675

  4. Heinrich events driven by feedback between ocean forcing and glacial isostatic adjustment

    NASA Astrophysics Data System (ADS)

    Bassis, J. N.; Petersen, S. V.; Cathles, L. M. M., IV

    2015-12-01

    One of the most puzzling glaciological features of the past ice age is the episodic discharge of large volumes of icebergs from the Laurentide Ice Sheet, known as Heinrich events. It has been suggested that Heinrich events are caused by internal instabilities in the ice sheet (e.g. the binge-purge oscillation). A purely ice dynamic cycle, however, is at odds with the fact that every Heinrich event occurs during the cold phase of a DO cycle, implying some regional climate connection. Recent work has pointed to subsurface water warming as a trigger for Heinrich events through increased basal melting of an ice shelf extending across the Hudson Strait and connecting with the Greenland Ice Sheet. Such a large ice shelf, spanning the deepest part of the Labrador Sea, has no modern analog and limited proxy evidence. Here we use a width averaged "flowline" model of the Hudson Strait ice stream to show that Heinrich events can be triggered by ocean forcing of a grounded terminus without the need for an ice shelf. At maximum ice extent, bed topography is depressed and the terminus is more sensitive to a subsurface thermal forcing. Once triggered, the retreat is rapid, and continues until isostatic rebound of the bed causes local sea level to drop sufficiently to arrest retreat. Topography slowly rebounds, decreasing the sensitivity to ocean forcing and the ice stream re-advances at a rate that is an order of magnitude slower than collapse. This simple feedback cycle between a short-lived ocean trigger and slower isostatic adjustment can reproduce the periodicity and timing of observed Heinrich events under a range of glaciological and solid earth parameters. Our results suggest that not only does the solid Earth play an important role in regulating ice sheet stability, but that grounded marine terminating portions of ice sheets may be more sensitive to ocean forcing than previously thought.

  5. A full analytical solution for the force-driven compressible Poiseuille gas flow based on a nonlinear coupled constitutive relation

    NASA Astrophysics Data System (ADS)

    Myong, R. S.

    2011-01-01

    The compressible Poiseuille gas flow driven by a uniform force is analytically investigated using a phenomenological nonlinear coupled constitutive relation model. A new fully analytical solution in compact tangent (or hyperbolic tangent in the case of diatomic gases) functional form explains the origin behind the central temperature minimum and a heat transfer from the cold region to the hot region. The solution is not only proven to satisfy the conservation laws exactly but also well-defined for all physical conditions (the Knudsen number and a force-related dimensionless parameter). It is also shown that the non-Fourier law associated with the coupling of force and viscous shear stress in the constitutive relation is responsible for the existence of the central temperature minimum, while a kinematic constraint on viscous shear and normal stresses identified in the velocity shear flow is the main source of the nonuniform pressure distribution. In addition, the convex pressure profile with a maximum at the center is theoretically predicted for diatomic gases. Finally, the existence of the Knudsen minimum in the mass flow rate is demonstrated by developing an exact analytical formula for the average temperature of the bulk flow.

  6. Onset of deglacial warming in West Antarctica driven by local orbital forcing.

    PubMed

    2013-08-22

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  7. Onset of deglacial warming in West Antarctica driven by local orbital forcing

    USGS Publications Warehouse

    WAIS Divide Project Members,; Steig, Eric J.; Markle, Bradley R.; Schoenemann, Spruce W.; Ding, Qinghua; Taylor, Kendrick C.; McConnell, Joseph R.; Brook, Edward J.; Sowers, Todd; White, James W. C.; Alley, Richard B.; Chen, Hai; Clow, Gary D.; Cole-Dai, Jihong; Conway, Howard; Fitzpatrick, Joan J.; Hargreaves, Geoffrey; ,

    2013-01-01

    The cause of warming in the Southern Hemisphere during the most recent deglaciation remains a matter of debate. Hypotheses for a Northern Hemisphere trigger, through oceanic redistributions of heat, are based in part on the abrupt onset of warming seen in East Antarctic ice cores and dated to 18,000 years ago, which is several thousand years after high-latitude Northern Hemisphere summer insolation intensity began increasing from its minimum, approximately 24,000 years ago. An alternative explanation is that local solar insolation changes cause the Southern Hemisphere to warm independently. Here we present results from a new, annually resolved ice-core record from West Antarctica that reconciles these two views. The records show that 18,000 years ago snow accumulation in West Antarctica began increasing, coincident with increasing carbon dioxide concentrations, warming in East Antarctica and cooling in the Northern Hemisphere associated with an abrupt decrease in Atlantic meridional overturning circulation. However, significant warming in West Antarctica began at least 2,000 years earlier. Circum-Antarctic sea-ice decline, driven by increasing local insolation, is the likely cause of this warming. The marine-influenced West Antarctic records suggest a more active role for the Southern Ocean in the onset of deglaciation than is inferred from ice cores in the East Antarctic interior, which are largely isolated from sea-ice changes.

  8. Dehydration-Driven Solvent Exposure of Hydrophobic Surfaces as a Driving Force in Peptide Folding

    SciTech Connect

    Daidone, Isabella; Ulmschneider, Martin; DiNola, Alfredo; Amadei, Andrea; Smith, Jeremy C

    2007-09-01

    Recent work has shown that the nature of hydration of pure hydrophobic surfaces changes with the length scale considered: water hydrogen-bonding networks adapt to small exposed hydrophobic species, hydrating or 'wetting' them at relatively high densities, whereas larger hydrophobic areas are 'dewetted' [Chandler D (2005), Nature 29:640-647]. Here we determine whether this effect is also present in peptides by examining the folding of a {beta}-hairpin (the 14-residue amyloidogenic prion protein H1 peptide), using microsecond time-scale molecular dynamics simulations. Two simulation models are compared, one explicitly including the water molecules, which may thus adapt locally to peptide configurations, and the other using a popular continuum approximation, the generalized Born/surface area implicit solvent model. The results obtained show that, in explicit solvent, peptide conformers with high solvent-accessible hydrophobic surface area indeed also have low hydration density around hydrophobic residues, whereas a concomitant higher hydration density around hydrophilic residues is observed. This dewetting effect stabilizes the fully folded {beta}-hairpin state found experimentally. In contrast, the implicit solvent model destabilizes the fully folded hairpin, tending to cluster hydrophobic residues regardless of the size of the exposed hydrophobic surface. Furthermore, the rate of the conformational transitions in the implicit solvent simulation is almost doubled with respect to that of the explicit solvent. The results suggest that dehydration-driven solvent exposure of hydrophobic surfaces may be a significant factor determining peptide conformational equilibria.

  9. Electrothermally driven high-frequency piezoresistive SiC cantilevers for dynamic atomic force microscopy

    SciTech Connect

    Boubekri, R.; Cambril, E.; Couraud, L.; Bernardi, L.; Madouri, A.; Portail, M.; Chassagne, T.; Moisson, C.; Zielinski, M.; Jiao, S.; Michaud, J.-F.; Alquier, D.; Bouloc, J.; Nony, L.; Bocquet, F.; Loppacher, C.

    2014-08-07

    Cantilevers with resonance frequency ranging from 1 MHz to 100 MHz have been developed for dynamic atomic force microscopy. These sensors are fabricated from 3C-SiC epilayers grown on Si(100) substrates by low pressure chemical vapor deposition. They use an on-chip method both for driving and sensing the displacement of the cantilever. A first gold metallic loop deposited on top of the cantilever is used to drive its oscillation by electrothermal actuation. The sensing of this oscillation is performed by monitoring the resistance of a second Au loop. This metallic piezoresistive detection method has distinct advantages relative to more common semiconductor-based schemes. The optimization, design, fabrication, and characteristics of these cantilevers are discussed.

  10. An EMG-driven Modeling Approach to Muscle Force and Joint Load Estimations: Case Study in Knee Osteoarthritis

    PubMed Central

    Kumar, Deepak; Rudolph, Katherine S.; Manal, Kurt T.

    2011-01-01

    Summary It is important to know the magnitude and patterns of joint loading in people with knee osteoarthritis (OA), since altered loads are implicated in onset and progression of the disease. We used an EMG-driven forward dynamics model to estimate joint loads during walking in a subject with knee OA and a healthy control subject. Kinematic, kinetic, and surface EMG data were used to predict muscle forces using a Hill-type muscle model. The muscle forces were used to balance the frontal plane moment to obtain medial and lateral condylar loads. Loads were normalized to body weight (BWs) and the mean of three trials taken. The OA subject had greater medial and lower lateral loads compared to the control subject. 75 to 80% of the total load was borne on the medial compartment in the control subject, compared to 90 to 95% in the OA subject. In fact, complete lateral unloading occurred during midstance for the OA subject. Loading for the healthy subject was consistent with the data from instrumented knee studies. In the future, the model can be used to analyze the impact of various interventions to reduce the loads on the medial compartment in people with knee OA. PMID:21901754

  11. Indian and African plate motions driven by the push force of the Réunion plume head.

    PubMed

    Cande, Steven C; Stegman, Dave R

    2011-07-01

    Mantle plumes are thought to play an important part in the Earth's tectonics, yet it has been difficult to isolate the effect that plumes have on plate motions. Here we analyse the plate motions involved in two apparently disparate events--the unusually rapid motion of India between 67 and 52 million years ago and a contemporaneous, transitory slowing of Africa's motion--and show that the events are coupled, with the common element being the position of the Indian and African plates relative to the location of the Réunion plume head. The synchroneity of these events suggests that they were both driven by the force of the Réunion plume head. The recognition of this plume force has substantial tectonic implications: the speed-up and slowdown of India, the possible cessation of convergence between Africa and Eurasia in the Palaeocene epoch and the enigmatic bends of the fracture zones on the Southwest Indian Ridge can all be attributed to the Réunion plume. PMID:21734702

  12. Viscoelastic measurements of single molecules on a millisecond time scale by magnetically driven oscillation of an atomic force microscope cantilever.

    PubMed

    Kawakami, Masaru; Byrne, Katherine; Khatri, Bhavin S; Mcleish, Tom C B; Radford, Sheena E; Smith, D Alastair

    2005-05-10

    The dynamical nature of biomolecular systems means that knowledge of their viscoelastic behavior is important in fully understanding function. The linear viscoelastic response can be derived from an analysis of Brownian motion. However, this is a slow measurement and technically demanding for many molecular systems of interest. To address this issue, we have developed a simple method for measuring the full linear viscoelastic response of single molecules based on magnetically driven oscillations of an atomic force microscope cantilever. The cantilever oscillation frequency is periodically swept through the system resonance in less than 200 ms allowing the power spectrum to be obtained rapidly and analyzed with a suitable model. The technique has been evaluated using dextran, a polysaccharide commonly used as a test system for single molecule mechanical manipulation experiments. The monomer stiffness and friction constants were compared with those derived from other methods. Excellent agreement is obtained indicating that the new method accurately and, most importantly, rapidly provides the viscoelastic response of a single molecule between the tip and substrate. The method will be a useful tool for studying systems that change their structure and dynamic response on a time scale of 100-200 ms, such as protein folding and unfolding under applied force. PMID:16032901

  13. Indian and African plate motions driven by the push force of the Réunion plume head.

    PubMed

    Cande, Steven C; Stegman, Dave R

    2011-07-06

    Mantle plumes are thought to play an important part in the Earth's tectonics, yet it has been difficult to isolate the effect that plumes have on plate motions. Here we analyse the plate motions involved in two apparently disparate events--the unusually rapid motion of India between 67 and 52 million years ago and a contemporaneous, transitory slowing of Africa's motion--and show that the events are coupled, with the common element being the position of the Indian and African plates relative to the location of the Réunion plume head. The synchroneity of these events suggests that they were both driven by the force of the Réunion plume head. The recognition of this plume force has substantial tectonic implications: the speed-up and slowdown of India, the possible cessation of convergence between Africa and Eurasia in the Palaeocene epoch and the enigmatic bends of the fracture zones on the Southwest Indian Ridge can all be attributed to the Réunion plume.

  14. Dielectrophoresis-magnetophoresis force driven magnetic nanoparticle movement in transformer oil based magnetic fluids.

    PubMed

    Lee, Jong-Chul; Lee, Sangyoup

    2013-09-01

    Magnetic fluid is a stable colloidal mixture contained magnetic nanoparticles coated with a surfactant. Recently, it was found that the fluid has properties to increase heat transfer and dielectric characteristics due to the added magnetic nanoparticles in transformer oils. The magnetic nanoparticles in the fluid experience an electrical force directed toward the place of maximum electric field strength when the electric field is applied. And when the external magnetic field is applied, the magnetic nanoparticles form long chains oriented along the direction of the field. The behaviors of magnetic nanoparticles in both the fields must play an important role in changing the heat transfer and dielectric characteristics of the fluids. In this study, we visualized the movement of magnetic nanoparticles influenced by both the fields applied in-situ. It was found that the magnetic nanoparticles travel in the region near the electrode by the electric field and form long chains along the field direction by the magnetic field. It can be inferred that the movement of magnetic nanoparticles appears by both the fields, and the breakdown voltage of transformer oil based magnetic fluids might be influenced according to the dispersion of magnetic nanoparticles. PMID:24205624

  15. A new model for biological effects of radiation and the driven force of molecular evolution

    NASA Astrophysics Data System (ADS)

    Wada, Takahiro; Manabe, Yuichiro; Nakajima, Hiroo; Tsunoyama, Yuichi; Bando, Masako

    We proposed a new mathematical model to estimate biological effects of radiation, which we call Whack-A-Mole (WAM) model. A special feature of WAM model is that it involves the dose rate of radiation as a key ingredient. We succeeded to reproduce the experimental data of various species concerning the radiation induced mutation frequencies. From the analysis of the mega-mouse experiments, we obtained the mutation rate per base-pair per year for mice which is consistent with the so-called molecular clock in evolution genetics, 10-9 mutation/base-pair/year. Another important quantity is the equivalent dose rate for the whole spontaneous mutation, deff. The value of deff for mice is 1.1*10-3 Gy/hour which is much larger than the dose rate of natural radiation (10- (6 - 7) Gy/hour) by several orders of magnitude. We also analyzed Drosophila data and obtained essentially the same numbers. This clearly indicates that the natural radiation is not the dominant driving force of the molecular evolution, but we should look for other factors, such as miscopy of DNA in duplication process. We believe this is the first quantitative proof of the small contribution of the natural radiation in the molecular evolution.

  16. A self-stabilized coherent phonon source driven by optical forces

    PubMed Central

    Navarro-Urrios, D.; Capuj, N. E.; Gomis-Bresco, J.; Alzina, F.; Pitanti, A.; Griol, A.; Martínez, A.; Sotomayor Torres, C. M.

    2015-01-01

    We report a novel injection scheme that allows for “phonon lasing” in a one-dimensional opto-mechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10−2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermo-optical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications. PMID:26503448

  17. A self-stabilized coherent phonon source driven by optical forces

    NASA Astrophysics Data System (ADS)

    Navarro-Urrios, D.; Capuj, N. E.; Gomis-Bresco, J.; Alzina, F.; Pitanti, A.; Griol, A.; Martínez, A.; Sotomayor Torres, C. M.

    2015-10-01

    We report a novel injection scheme that allows for “phonon lasing” in a one-dimensional opto-mechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10-2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermo-optical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.

  18. Dielectrophoresis-magnetophoresis force driven magnetic nanoparticle movement in transformer oil based magnetic fluids.

    PubMed

    Lee, Jong-Chul; Lee, Sangyoup

    2013-09-01

    Magnetic fluid is a stable colloidal mixture contained magnetic nanoparticles coated with a surfactant. Recently, it was found that the fluid has properties to increase heat transfer and dielectric characteristics due to the added magnetic nanoparticles in transformer oils. The magnetic nanoparticles in the fluid experience an electrical force directed toward the place of maximum electric field strength when the electric field is applied. And when the external magnetic field is applied, the magnetic nanoparticles form long chains oriented along the direction of the field. The behaviors of magnetic nanoparticles in both the fields must play an important role in changing the heat transfer and dielectric characteristics of the fluids. In this study, we visualized the movement of magnetic nanoparticles influenced by both the fields applied in-situ. It was found that the magnetic nanoparticles travel in the region near the electrode by the electric field and form long chains along the field direction by the magnetic field. It can be inferred that the movement of magnetic nanoparticles appears by both the fields, and the breakdown voltage of transformer oil based magnetic fluids might be influenced according to the dispersion of magnetic nanoparticles.

  19. EMG-Driven Forward-Dynamic Estimation of Muscle Force and Joint Moment about Multiple Degrees of Freedom in the Human Lower Extremity

    PubMed Central

    Sartori, Massimo; Reggiani, Monica; Farina, Dario; Lloyd, David G.

    2012-01-01

    This work examined if currently available electromyography (EMG) driven models, that are calibrated to satisfy joint moments about one single degree of freedom (DOF), could provide the same musculotendon unit (MTU) force solution, when driven by the same input data, but calibrated about a different DOF. We then developed a novel and comprehensive EMG-driven model of the human lower extremity that used EMG signals from 16 muscle groups to drive 34 MTUs and satisfy the resulting joint moments simultaneously produced about four DOFs during different motor tasks. This also led to the development of a calibration procedure that allowed identifying a set of subject-specific parameters that ensured physiological behavior for the 34 MTUs. Results showed that currently available single-DOF models did not provide the same unique MTU force solution for the same input data. On the other hand, the MTU force solution predicted by our proposed multi-DOF model satisfied joint moments about multiple DOFs without loss of accuracy compared to single-DOF models corresponding to each of the four DOFs. The predicted MTU force solution was (1) a function of experimentally measured EMGs, (2) the result of physiological MTU excitation, (3) reflected different MTU contraction strategies associated to different motor tasks, (4) coordinated a greater number of MTUs with respect to currently available single-DOF models, and (5) was not specific to an individual DOF dynamics. Therefore, our proposed methodology has the potential of producing a more dynamically consistent and generalizable MTU force solution than was possible using single-DOF EMG-driven models. This will help better address the important scientific questions previously approached using single-DOF EMG-driven modeling. Furthermore, it might have applications in the development of human-machine interfaces for assistive devices. PMID:23300725

  20. Generation of Nonlinear Force Driven Blocks from Skin Layer Interaction of Petawatt-Picosecond Laser Pulses for ICF

    NASA Astrophysics Data System (ADS)

    Heinrich, Hora; Cang, Yu; He, Xiantu; Zhang, Jie; F, Osman; J, Badziak; F, P. Boody; S, Gammino; R, Höpfl; K, Jungwirth; B, Kralikova; J, Kraska; L, Laska; Liu, Hong; G, H. Miley; P, Parys; Peng, Hansheng; M, Pfeifer; K, Rohlena; J, Skala; Z, Skladanowski; L, Torrisi; J, Ullschmied; J, Wolowski; Zhang, Weiyan

    2004-02-01

    The discovery of the essential difference of maximum ion energy for TW - ps laser plasma interaction compared with the 100 ns laser pulses [1] led to the theory of a skin layer model [2] where the control of prepulses suppressed the usual relativistic self-focusing. The subsequent generation of two nonlinear force driven blocks has been demonstrated experimentally and in extensive numerical studies where one block moves against the laser light and the other block into the irradiated target. These blocks of nearly solid state density DT plasma correspond to ion beam current densities [3] exceeding 1010 A/cm2 where the ion velocity can be chosen up to highly relativistic values. Using the results of the expected ignition of DT fuel by light ion beams, a self-sustained fusion reaction front may be generated even into uncompressed solid DT fuel similar to the Nuckolls-Wood [4] scheme where 10 kJ laser pulses produce 100 MJ fusion energy. This new and simplified scheme of laser-ICF needs and optimisation of the involved parameters.

  1. General circulation driven by baroclinic forcing due to cloud layer heating: Significance of planetary rotation and polar eddy heat transport

    NASA Astrophysics Data System (ADS)

    Yamamoto, Masaru; Takahashi, Masaaki

    2016-04-01

    A high significance of planetary rotation and poleward eddy heat fluxes is determined for general circulation driven by baroclinic forcing due to cloud layer heating. In a high-resolution simplified Venus general circulation model, a planetary-scale mixed Rossby-gravity wave with meridional winds across the poles produces strong poleward heat flux and indirect circulation. This strong poleward heat transport induces downward momentum transport of indirect cells in the regions of weak high-latitude jets. It also reduces the meridional temperature gradient and vertical shear of the high-latitude jets in accordance with the thermal wind relation below the cloud layer. In contrast, strong equatorial superrotation and midlatitude jets form in the cloud layer in the absence of polar indirect cells in an experiment involving Titan's rotation. Both the strong midlatitude jet and meridional temperature gradient are maintained in the situation that eddy horizontal heat fluxes are weak. The presence or absence of strong poleward eddy heat flux is one of the important factors determining the slow or fast superrotation state in the cloud layer through the downward angular momentum transport and the thermal wind relation. For fast Earth rotation, a weak global-scale Hadley circulation of the low-density upper atmosphere maintains equatorial superrotation and midlatitude jets above the cloud layer, whereas multiple meridional circulations suppress the zonal wind speed below the cloud layer.

  2. Towards all-optical quantification of force- and power-based performance metrics in cilia-driven fluid flow physiology (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Huang, Brendan K.; Khokha, Mustafa K.; Loewenberg, Michael; Choma, Michael A.

    2016-03-01

    In pulmonary ciliary physiology, most tissue-level measures of performance focus on flow velocity. However, as with the heart, fluid transport performance requires an understanding of force and power generation under various loading conditions. Here, we present our initial work in quantifying shearing force and net power dissipation from OCT-based cilia-driven fluid flow velocimetry. Typical measurements of force require invasive contact with the ciliated surface, while measurements of power rely on metabolic consumption that reflect energy consumption not just from cilia, but from the entirety of cellular processes. We will present two different approaches to non-contact, all-optical shear force and power dissipation physiology. First, we developed a lumped-parameter model of flow driven by a ciliated surface. The lumped-parameter model yields semi-quantitative, Ohm's law-type relationships (F=U*R and P=U*F) between flow velocity (U), shear force (F), viscous resistance (R), and power dissipation (P). This model allows a lumped (spatially averaged) approach to evaluate force and power performance under viscous loading, an approach we demonstrated using ciliated Xenopus embryos. Second, we numerically estimate shear force and power dissipation using flow velocity fields acquired using OCT. Specifically, the velocity gradient tensor estimated from the flow velocity field contains the required information to estimate both shear force and net power dissipation. We have preliminary data using this numerical approach in Xenopus. Our results support the feasibility of an all-optical approach to estimating mesoscopic measures of force and power in ciliary physiology.

  3. Eddy permitting simulation of the global ocean model COCO4.3 driven by the CORE inter- annual forcing

    NASA Astrophysics Data System (ADS)

    Suzuki, T.; Hasumi, H.; Komuro, Y.; Sakamoto, T. T.

    2008-12-01

    We are developing ocean component of the CCSR/NIES/FRCGC climate model to conduct high-resolution global warming simulations under IPCC scenarios. This presentation focuses on the performance and the behavior and role of eddies in the global ocean. The Ocean model is CCSR Ocean Component Model (COCO) version 4.3, which is a z-coordinate, free-surface primitive equation ocean model with multi-category sea ice model. The geographical North Pole is moved to 40W, 77N on Greenland and the geographical South Pole is moved to 40E, 77S. The computational domain covers global ocean, with zonal grid spacing of 0.28125 degree and meridional grid spacing of 0.1875 degree. There are 50 vertical levels excluding the bottom boundary layer, and 7 of which are within the sigma-coordinate (~42m). The model employs the momentum advection algorithm of Ishizaki and Motoi (1991), which is a pseudo-enstrophy preserving scheme with a consideration for up-/down-sloping advection. The model's tracer advection is based on the second-order moment (SOM) advection scheme of Prather, M. J. (1986). The vertical mixing of momentum and tracers is represented by a harmonic form. The coefficients are calculated by the parameterization of Noh and Kim (1999), but the formulation is slightly modified (see K1-developers, 2004). As background diffusivity, a minimum value is set for each level, suggested by Tsujino et al. (2000). The Smagorinsky's (1963) biharmonic viscosity is applied for the lateral momentum mixing, and its coefficient is dependent on the grid width and the strain rate, and its controlled by a single non- dimensional parameter whose values is taken to be 2.5. The constant coefficient biharmonic diffusion is applied with the coefficient value of 1.0E9 m4/s. The model is driven by the inter-annual forcing data set adopted by common ocean-ice reference experiments (CORE). The results are reported by focusing on heat transport in strong eddy activity regions, such as the Kuroshio

  4. EMGD-FE: an open source graphical user interface for estimating isometric muscle forces in the lower limb using an EMG-driven model

    PubMed Central

    2014-01-01

    Background This paper describes the “EMG Driven Force Estimator (EMGD-FE)”, a Matlab® graphical user interface (GUI) application that estimates skeletal muscle forces from electromyography (EMG) signals. Muscle forces are obtained by numerically integrating a system of ordinary differential equations (ODEs) that simulates Hill-type muscle dynamics and that utilises EMG signals as input. In the current version, the GUI can estimate the forces of lower limb muscles executing isometric contractions. Muscles from other parts of the body can be tested as well, although no default values for model parameters are provided. To achieve accurate evaluations, EMG collection is performed simultaneously with torque measurement from a dynamometer. The computer application guides the user, step-by-step, to pre-process the raw EMG signals, create inputs for the muscle model, numerically integrate the ODEs and analyse the results. Results An example of the application’s functions is presented using the quadriceps femoris muscle. Individual muscle force estimations for the four components as well the knee isometric torque are shown. Conclusions The proposed GUI can estimate individual muscle forces from EMG signals of skeletal muscles. The estimation accuracy depends on several factors, including signal collection and modelling hypothesis issues. PMID:24708668

  5. Trunk active response and spinal forces in sudden forward loading: analysis of the role of perturbation load and pre-perturbation conditions by a kinematics-driven model.

    PubMed

    Shahvarpour, Ali; Shirazi-Adl, Aboulfazl; Larivière, Christian; Bazrgari, Babak

    2015-01-01

    Understanding the central nervous system (CNS) response strategy to trunk perturbations could help in prevention of back injuries and development of rehabilitation and treatment programs. This study aimed to investigate biomechanical response of the trunk musculoskeletal system under sudden forward loads, accounting for pre-perturbation conditions (preloading, initial posture and abdominal antagonistic coactivation) and perturbation magnitudes. Using a trunk kinematics-driven iterative finite element (FE) model, temporal profiles of measured kinematics and external load along with subjects' weights were prescribed to predict thoracolumbar muscle forces/latencies and spinal loads for twelve healthy subjects when tested in six conditions during pre- and post-perturbation periods. Results demonstrated that preloading the trunk significantly (i.e., p<0.05) increased pre-perturbation back muscle forces but significantly decreased post-perturbation peak muscle active forces and muscle latencies. Initial trunk flexion significantly increased muscle active and passive forces before the perturbation and their peak values after the perturbation, which in turn caused much larger spinal loads. Abdominal muscles antagonistic pre-activation did not alter the internal variables investigated in this study. Increase in sudden applied load increased muscle reflex activities and spinal forces; a 50 N increase in sudden load (i.e., when comparing 50 N to 100 N) increased the L5-S1 compression force by 1327 N under 5 N preload and by 1374 N under 50 N preload. Overall, forces on the spine and hence risk of failure substantially increased in sudden forward loading when the magnitude of sudden load increased and when the trunk was initially in a flexed posture. In contrast, a higher initial preload diminished reflex latencies and compression forces.

  6. Estimation of broadband acoustic power radiated from a turbulent boundary layer-driven reinforced finite plate section due to rib and boundary forces.

    PubMed

    Rumerman, M L

    2002-03-01

    Previous papers considered an infinite fluid-loaded plate with parallel line attachments, driven by a wave-number-white pressure excitation invariant in the direction of an attachment, and established the conditions and procedure for estimating the broadband radiated power by assuming the ribs to radiate independently. This paper applies those results to a finite rectangular ribbed plate, and extends the methodology to include the contribution of the plate's boundary support forces to the radiation and the consideration of excitation that varies in the direction parallel to the ribs. The approach is relevant to problems of sound radiation by underwater stiffened steel plates driven by turbulent boundary layer (TBL) pressures, and is also applicable to stiffened circular cylindrical shells when the response is dominated by bending. Comparisons of sample calculations with results of rigorous models validate the approximation.

  7. Fo-driven Rotation in the ATP Synthase Direction against the Force of F1 ATPase in the FoF1 ATP Synthase.

    PubMed

    Martin, James; Hudson, Jennifer; Hornung, Tassilo; Frasch, Wayne D

    2015-04-24

    Living organisms rely on the FoF1 ATP synthase to maintain the non-equilibrium chemical gradient of ATP to ADP and phosphate that provides the primary energy source for cellular processes. How the Fo motor uses a transmembrane electrochemical ion gradient to create clockwise torque that overcomes F1 ATPase-driven counterclockwise torque at high ATP is a major unresolved question. Using single FoF1 molecules embedded in lipid bilayer nanodiscs, we now report the observation of Fo-dependent rotation of the c10 ring in the ATP synthase (clockwise) direction against the counterclockwise force of ATPase-driven rotation that occurs upon formation of a leash with Fo stator subunit a. Mutational studies indicate that the leash is important for ATP synthase activity and support a mechanism in which residues aGlu-196 and cArg-50 participate in the cytoplasmic proton half-channel to promote leash formation. PMID:25713065

  8. Convective flow patterns in an eight-box cube driven by combined wind stress, thermal and saline forcing. (Reannouncement with new availability information). Technical report

    SciTech Connect

    Huang, R.X.; Stommel, H.M.

    1992-02-15

    An eight-box cube model ocean, simulating the subpolar gyre in the North Atlantic, is formulated in order to understand how the wind-induced horizontal gyre affects the thermohaline circulation and its catastrophe. The model is forced from above by thermal conduction and freshwater flux. The structure of the thermohaline circulation and its catastrophe during the process of gradually increasing or reducing the evaporation/precipitation are examined. The results indicate that, although adding the third dimension and a wind-driven horizontal gyre of medium strength splits the catastrophe into several separate ones, only some of these catastrophes remain of significant amplitude. With choice of parameters appropriate for the North Atlantic, the model predicts a single stable state, circulating in the thermal sense (sinking at the pole). This can be driven smoothly to a reversed saline sense (sinking at the equator), without catastrophe, by increasing the precipitation/evaporation rate beyond 3 times the present-day value.

  9. Interplay between Switching Driven by the Tunneling Current and Atomic Force of a Bistable Four-Atom Si Quantum Dot.

    PubMed

    Yamazaki, Shiro; Maeda, Keisuke; Sugimoto, Yoshiaki; Abe, Masayuki; Zobač, Vladimír; Pou, Pablo; Rodrigo, Lucia; Mutombo, Pingo; Pérez, Ruben; Jelínek, Pavel; Morita, Seizo

    2015-07-01

    We assemble bistable silicon quantum dots consisting of four buckled atoms (Si4-QD) using atom manipulation. We demonstrate two competing atom switching mechanisms, downward switching induced by tunneling current of scanning tunneling microscopy (STM) and opposite upward switching induced by atomic force of atomic force microscopy (AFM). Simultaneous application of competing current and force allows us to tune switching direction continuously. Assembly of the few-atom Si-QDs and controlling their states using versatile combined AFM/STM will contribute to further miniaturization of nanodevices.

  10. Effects of eddy viscosity and thermal conduction and Coriolis force in the dynamics of gravity wave driven fluctuations in the OH nightglow

    NASA Technical Reports Server (NTRS)

    Hickey, M. P.

    1988-01-01

    The chemical-dynamical model of Walterscheid et al. (1987), which describes wave-driven fluctuations in OH nightglow, was modified to include the effects of both eddy thermal conduction and viscosity, as well as the Coriolis force (with the shallow atmosphere approximation). Using the new model, calculations were performed for the same nominal case as used by Walterscheid et al. but with only wave periods considered. For this case, the Coriolis force was found to be unimportant at any wave period. For wave periods greater than 2 or 3 hours, the inclusion of thermal conduction alone greatly modified the results (in terms of a complex ratio 'eta' which expresses the relationship between the intensity oscillation about the time-averaged intensity and the temperature oscillation about the time-averaged temperature); this effect was reduced with the further inclusion of the eddy viscosity.

  11. Wavelength dependence of eddy dissipation and Coriolis force in the dynamics of gravity wave driven fluctuations in the OH nightglow

    NASA Technical Reports Server (NTRS)

    Hickey, M. P.

    1988-01-01

    This paper examines the effect of inclusion of Coriolis force and eddy dissipation in the gravity wave dynamics theory of Walterscheid et al. (1987). It was found that the values of the ratio 'eta' (where eta is a complex quantity describing the ralationship between the intensity oscillation about the time-averaged intensity, and the temperature oscillation about the time-averaged temperature) strongly depend on the wave period and the horizontal wavelength; thus, if comparisons are to be made between observations and theory, horizontal wavelengths will need to be measured in conjunction with the OH nightglow measurements. For the waves with horizontal wavelengths up to 1000 km, the eddy dissipation was found to dominate over the Coriolis force in the gravity wave dynamics and also in the associated values of eta. However, for waves with horizontal wavelengths of 10,000 km or more, the Coriolis force cannot be neglected; it has to be taken into account along with the eddy dissipation.

  12. Numerical Study of Convection in the Directional Solidification of a Binary Alloy Driven by the Combined Action of Buoyancy, Surface Tension, and Electromagnetic Forces

    NASA Astrophysics Data System (ADS)

    Sampath, Rajiv; Zabaras, Nicholas

    2001-04-01

    Directional solidification of a dilute electrically conducting binary alloy driven by the combined action of buoyancy, surface-tension, and electromagnetic forces is considered. A numerical methodology using a moving finite element technique is proposed for the simulation of the above phase change process. The melt is modeled as a Boussinesq fluid and the transient Navier-Stokes equations are solved simultaneously with the transient heat and solute transport equations. The location of the advancing solid-liquid interface is numerically determined using an energy preserving weak form of the Stefan condition. The standard SUPG/PSPG method for the simulation of incompressible fluid flow is here extended to flows driven by the combination of buoyancy, surface tension, and electromagnetic forces. A reference problem of directional solidification of a dilute germanium alloy in a horizontal open-boat configuration is considered. The relative influence of thermocapillary convection and buoyancy-driven convection on the solidification process is investigated by varying the Bond number. Thermocapillary convection is shown to have a significant influence on various solidification parameters, such as the shape of the solid-liquid interface and the solute segregation, especially under low gravity conditions. The influence of an external magnetic field on the reference solidification problem is investigated both in a normal and a reduced gravity environment. It is demonstrated that the application of an appropriate strong magnetic field significantly damps the melt flow and improves the solute segregation pattern. The relative influence of an external magnetic field on the solidification process is also studied by independently varying the orientation and magnitude of the applied magnetic field.

  13. Anomalous pinch of turbulent plasmas driven by the magnetic-drift-induced Lorentz force through the Stokes-Einstein relation

    NASA Astrophysics Data System (ADS)

    Wang, Shaojie

    2016-07-01

    It is found that the Lorentz force generated by the magnetic drift drives a generic plasma pinch flux of particle, energy and momentum through the Stokes-Einstein relation. The proposed theoretical model applies for both electrons and ions, trapped particles, and passing particles. An anomalous parallel current pinch due to the electrostatic turbulence with long parallel wave-length is predicted.

  14. Floating chip mounting system driven by repulsive force of permanent magnets for multiple on-site SPR immunoassay measurements.

    PubMed

    Horiuchi, Tsutomu; Tobita, Tatsuya; Miura, Toru; Iwasaki, Yuzuru; Seyama, Michiko; Inoue, Suzuyo; Takahashi, Jun-ichi; Haga, Tsuneyuki; Tamechika, Emi

    2012-10-17

    We have developed a measurement chip installation/removal mechanism for a surface plasmon resonance (SPR) immunoassay analysis instrument designed for frequent testing, which requires a rapid and easy technique for changing chips. The key components of the mechanism are refractive index matching gel coated on the rear of the SPR chip and a float that presses the chip down. The refractive index matching gel made it possible to optically couple the chip and the prism of the SPR instrument easily via elastic deformation with no air bubbles. The float has an autonomous attitude control function that keeps the chip parallel in relation to the SPR instrument by employing the repulsive force of permanent magnets between the float and a float guide located in the SPR instrument. This function is realized by balancing the upward elastic force of the gel and the downward force of the float, which experiences a leveling force from the float guide. This system makes it possible to start an SPR measurement immediately after chip installation and to remove the chip immediately after the measurement with a simple and easy method that does not require any fine adjustment. Our sensor chip, which we installed using this mounting system, successfully performed an immunoassay measurement on a model antigen (spiked human-IgG) in a model real sample (non-homogenized milk) that included many kinds of interfering foreign substances without any sample pre-treatment. The ease of the chip installation/removal operation and simple measurement procedure are suitable for frequent on-site agricultural, environmental and medical testing.

  15. Forces driven by morphogenesis modulate Twist Expression to determine Anterior Mid-gut Differentiation in Drosophila embryos

    NASA Astrophysics Data System (ADS)

    Farge, Emmanuel

    2008-03-01

    By combining magnetic tweezers to in vivo laser ablation, we locally manipulate Drosophila embryonic tissues with physiologically relevant forces. We demonstrate that high level of Twist expression in the stomodeal primordium is mechanically induced in response to compression by the 60±20 nN force developed during germ-band extension (GBE). We find that this force triggers the junctional release and nuclear translocation of Armadillo involved in Twist mechanical induction in the stomodeum in a Src42A dependent way. Finally, stomodeal-specific RNAi-mediated silencing of Twist during compression impairs the differentiation of midgut cells, as revealed by strong defects in Dve expression and abnormal larval lethality. Thus, mechanical induction of Twist overexpression in stomodeal cells is necessary for subsequent midgut differentiation. In collaboration with Nicolas Desprat, Willy Supatto, and Philippe-Alexandre Pouille, MGDET, UMR168 CNRS, Institut Curie11 rue Pierre et Marie Curie, F-75005, Paris, France; and Emmanuel Beaurepaire, LOB, Ecole Polytechnique, CNRS and INSERM U 696, 91128 Palaiseau, France.

  16. Magnetic force driven six degree-of-freedom active vibration isolation system using a phase compensated velocity sensor

    SciTech Connect

    Kim, Yongdae; Park, Kyihwan; Kim, Sangyoo

    2009-04-15

    A six-axis active vibration isolation system (AVIS) is developed using voice coil actuators. Point contact configuration is employed to have an easy assembly of eight voice coil actuators to an upper and a base plates. The velocity sensor, using an electromagnetic principle that is commonly used in the vibration control, is investigated since its phase lead characteristic causes an instability problem for a low frequency vibration. The performances of the AVIS are investigated in the frequency domain and finally validated by comparing with the passive isolation system using the atomic force microscope images.

  17. Magnetic force driven six degree-of-freedom active vibration isolation system using a phase compensated velocity sensor.

    PubMed

    Kim, Yongdae; Kim, Sangyoo; Park, Kyihwan

    2009-04-01

    A six-axis active vibration isolation system (AVIS) is developed using voice coil actuators. Point contact configuration is employed to have an easy assembly of eight voice coil actuators to an upper and a base plates. The velocity sensor, using an electromagnetic principle that is commonly used in the vibration control, is investigated since its phase lead characteristic causes an instability problem for a low frequency vibration. The performances of the AVIS are investigated in the frequency domain and finally validated by comparing with the passive isolation system using the atomic force microscope images.

  18. Wavelength dependence of eddy dissipation and Coriolis force in the dynamics of gravity wave driven fluctuations in the OH nightglow

    SciTech Connect

    Hickey, M.P. )

    1988-05-01

    The theory of Walterscheid et al. (1987) to explain internal gravity wave induced oscillations in the emission intensity I and rotational temperature T of the OH nightglow was modified by Hickey (1988) to include the effects of eddy dissipation and Coriolis force. In the theory of Walterscheid et al. (1987) the ratio {eta} = ({delta}I/I{sub 0})/({delta}T/T{sub 0}) ({delta} refers to a perturbation quantity, and a zero subscript refers to an average) was found to be independent of horizontal wavelength at long periods, while in the extended theory of Hickey (1988) some such dependence was inferred. In the present paper the horizontal wavelength dependence of {eta} is examined. It is found that values of {eta} will be dependent on both wave period and horizontal wavelength, meaning that in order to compare measurement with theory, horizontal wavelengths will need to be measured in conjunction with the OH nightglow measurements. At long periods the modifications to {eta} by the inclusion of eddy dissipation are much larger for the shorter horizontal wavelength waves, although such modifications may be more observable for some of the longer horizontal wavelength waves. The Coriolis force is important only for waves of very large horizontal wavelength.

  19. In vitro study of ultrasound radiation force-driven twinkling sign using PVA-H gel and glass beads tissue-mimicking phantom.

    PubMed

    Liu, Lei; Funamoto, Kenichi; Ozawa, Kei; Ohta, Makoto; Hayase, Toshiyuki; Ogasawara, Masafumi

    2013-07-01

    The twinkling sign observed in ultrasound coded-excitation imaging (e.g., GE B-Flow) has been reported in previous research as a potential phenomenon to detect micro calcification in soft tissue. However, the mechanism of the twinkling sign has not been clearly understood yet. We conducted an in vitro experiment to clarify the mechanism of the twinkling sign by measuring a soft tissue-mimicking phantom with ultrasonic and optical devices. A soft tissue-mimicking phantom was made of poly(vinyl alcohol) hydro (PVA-H) gel and 200-μm-diameter glass beads. We applied ultrasound to the phantom using medical ultrasound diagnostic equipment to observe the twinkling sign of glass beads. Optical imaging with a laser sheet and a high-speed camera was performed to capture the scatter lights of the glass beads with and without ultrasound radiation. The scatter lights from the glass beads were quantified and analyzed to evaluate their oscillations driven by the ultrasound radiation force. The twinkling sign from the glass beads embedded in the PVA-H gel soft tissue phantom was observed in ultrasound B-Flow color imaging. The intensity and oscillation of the scattered lights from the glass beads showed significant difference between the cases with and without ultrasound radiation. The results showed a close relationship between the occurrence of the twinkling sign and the variations of the scatter lights of glass beads, indicating that ultrasound radiation force-driven micro oscillation causes the twinkling sign of micro calcification in soft tissue.

  20. Individual-specific muscle maximum force estimation using ultrasound for ankle joint torque prediction using an EMG-driven Hill-type model.

    PubMed

    de Oliveira, Liliam Fernandes; Menegaldo, Luciano Luporini

    2010-10-19

    EMG-driven models can be used to estimate muscle force in biomechanical systems. Collected and processed EMG readings are used as the input of a dynamic system, which is integrated numerically. This approach requires the definition of a reasonably large set of parameters. Some of these vary widely among subjects, and slight inaccuracies in such parameters can lead to large model output errors. One of these parameters is the maximum voluntary contraction force (F(om)). This paper proposes an approach to find F(om) by estimating muscle physiological cross-sectional area (PCSA) using ultrasound (US), which is multiplied by a realistic value of maximum muscle specific tension. Ultrasound is used to measure muscle thickness, which allows for the determination of muscle volume through regression equations. Soleus, gastrocnemius medialis and gastrocnemius lateralis PCSAs are estimated using published volume proportions among leg muscles, which also requires measurements of muscle fiber length and pennation angle by US. F(om) obtained by this approach and from data widely cited in the literature was used to comparatively test a Hill-type EMG-driven model of the ankle joint. The model uses 3 EMGs (Soleus, gastrocnemius medialis and gastrocnemius lateralis) as inputs with joint torque as the output. The EMG signals were obtained in a series of experiments carried out with 8 adult male subjects, who performed an isometric contraction protocol consisting of 10s step contractions at 20% and 60% of the maximum voluntary contraction level. Isometric torque was simultaneously collected using a dynamometer. A statistically significant reduction in the root mean square error was observed when US-obtained F(om) was used, as compared to F(om) from the literature.

  1. Superfluid helium sloshing dynamics induced oscillations and fluctuations of angular momentum, force and moment actuated on spacecraft driven by gravity gradient or jitter acceleration associated with slew motion

    NASA Technical Reports Server (NTRS)

    Hung, R. J.

    1994-01-01

    The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by the gravity gradient and jitter accelerations associated with slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with the Advanced X-Ray Astrophysics Facility-Spectroscopy (AXAF-S) for slew motion which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid-vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers have also been derived. Examples are also given for cases applicable to the AXAF-S spacecraft sloshing dynamics associated with slew motion.

  2. A size-dependent model for beam-like MEMS driven by electrostatic and piezoelectric forces: A variational approach

    NASA Astrophysics Data System (ADS)

    Yin, Tenghao; Wang, Binglei; Zhou, Shenjie; Zhao, Moli

    2016-10-01

    A size-dependent model of a micro-electromechanical system (MEMS) actuated by both electrostatic and piezoelectric forces is proposed based on the modified couple stress. The governing equation and boundary conditions are derived with the help of the Hamilton principle and solved numerically by employing the Galerkin method and Newton downhill method. A material length scale parameter (MLSP) is incorporated in the model to capture the size effect in microstructures. An excellent agreement is found between the results of the present model and the experimental data, providing the validity of this model. The results reveal that the introduction of the MLSP stiffens the system and increases the pull-in voltage. The size-effect is significant when the dimension of the beam is comparable to the MLSP but it becomes smaller as the beam size increases. Besides, the static characteristic of the micro-switch is studied. It is found that the piezoelectric material attached on the beam can reduce the pull-in voltage remarkably, which may guide the design of the micro-structure when the system is on the order of micron or submicron.

  3. High sensitive space electric field sensing based on micro fiber interferometer with field force driven gold nanofilm

    PubMed Central

    Zhu, Tao; Zhou, Liming; Liu, Min; Zhang, Jingdong; Shi, Leilei

    2015-01-01

    The traditional electrical field sensing can be realized by utilizing electro-optic materials or liquid crystals, and has limitations of easy breakdown, free assembly and difficult measurement of low-frequency. Here, we propose a new method to realize safe measurement of spatial dynamic electric field by using a micro fiber interferometer integrated with gold nanofilm. The energy of the electric charge received through antenna forms the intrinsic electric field with two micro electrodes, one of which is the 120 nm gold film vibration beam micromachined by femtosecond lasers and integrated with the micro fiber. The change of the intrinsic electric field force due to the spatial electric field will cause the vibration of the film beam. By demodulating the output signal of the micro fiber interferometer, the electric field can be measured. We demonstrate the detectable frequency ranges from tens of Hz to tens of KHz, and the minimum electric field intensity is ~200 V/m at 1 KHz. Our electric field measurement technology combining optical fiber interference with gold nanostructures shows the advantages of security, high sensitivity, compact size, and multiplexed multi-point and remote detection. PMID:26507680

  4. Dynamics driven by lipophilic force in Langmuir monolayers: In-plane and out-of-plane growth

    NASA Astrophysics Data System (ADS)

    Basak, Uttam Kumar; Datta, Alokmay

    2015-04-01

    While monolayer area fraction versus time (An-t ) curves obtained from surface pressure-area (π -A ) isotherms for desorption-dominated (DD) processes in Langmuir monolayers of fatty acids represent continuous loss, those from Brewster angle microscopy (BAM) also show a two-dimensional (2D) coalescence. For nucleation-dominated (ND) processes both techniques suggest competing processes, with BAM showing 2D coalescence alongside multilayer formation. π enhances both DD and ND processes with a lower cutoff for ND processes, while temperature has a lower cutoff for DD but negligible effect on ND processes. Hydrocarbon chain length has the strongest effect, causing a crossover from DD to ND dynamics. Imaging ellipsometry of horizontally transferred films onto Si(100) shows Stranski-Krastanov-like growth for ND process in an arachidic acid monolayer resulting in successive stages of monolayer, trilayer, and multilayer islands, ridges from lateral island coalescence, and shallow wavelike structures from ridge coalescence on the film surface. These studies show that lipophilic attraction between hydrocarbon chains is the driving force at all stages of long-term monolayer dynamics.

  5. Derivation of governing equation describing time-dependent penetration length in channel flows driven by non-mechanical forces.

    PubMed

    Bhattacharya, Sukalyan; Gurung, Dilkumar

    2010-05-01

    Several past attempts were made to describe the penetration length in microchannels as a function of time for electroosmotic or capillary flow. In all of these studies, a complex governing equation is derived by taking into account the inertial contributions along with other forces. The system being unsteady, this derivation requires the consideration of proper unsteady flow-profile inside the channel. However, the past theories introduced an inconsistency by using parabolic velocity-field valid only for steady systems. This discrepancy creates an error of the same order as the inertial contribution leading to two consequences. Firstly, the inherent inaccuracy makes the past theories inapplicable when Reynolds number is greater than unity. Secondly, it renders the inclusion of inertial terms pointless for low Reynolds number systems-the additional complexity due to inertia does not serve any purpose because error of similar order is already present in the formulation. In this paper, we address this problem by rectifying the mathematical derivation where instead of the parabolic velocity-profile, proper analytical expression for unsteady flow is used. As a result, the correct governing equation is derived for the penetration length for any laminar system with arbitrary Reynolds number. We also simplify the equation for low Reynolds number cases by considering appropriate limiting conditions. The equation for low Reynolds number flow, while being as accurate as the ones obtained in the earlier studies, is much simpler than the previous versions.

  6. High sensitive space electric field sensing based on micro fiber interferometer with field force driven gold nanofilm

    NASA Astrophysics Data System (ADS)

    Zhu, Tao; Zhou, Liming; Liu, Min; Zhang, Jingdong; Shi, Leilei

    2015-10-01

    The traditional electrical field sensing can be realized by utilizing electro-optic materials or liquid crystals, and has limitations of easy breakdown, free assembly and difficult measurement of low-frequency. Here, we propose a new method to realize safe measurement of spatial dynamic electric field by using a micro fiber interferometer integrated with gold nanofilm. The energy of the electric charge received through antenna forms the intrinsic electric field with two micro electrodes, one of which is the 120 nm gold film vibration beam micromachined by femtosecond lasers and integrated with the micro fiber. The change of the intrinsic electric field force due to the spatial electric field will cause the vibration of the film beam. By demodulating the output signal of the micro fiber interferometer, the electric field can be measured. We demonstrate the detectable frequency ranges from tens of Hz to tens of KHz, and the minimum electric field intensity is ~200 V/m at 1 KHz. Our electric field measurement technology combining optical fiber interference with gold nanostructures shows the advantages of security, high sensitivity, compact size, and multiplexed multi-point and remote detection.

  7. Aerosol size distribution and radiative forcing response to anthropogenically driven historical changes in biogenic secondary organic aerosol formation

    NASA Astrophysics Data System (ADS)

    D'Andrea, S. D.; Acosta Navarro, J. C.; Farina, S. C.; Scott, C. E.; Rap, A.; Farmer, D. K.; Spracklen, D. V.; Riipinen, I.; Pierce, J. R.

    2015-03-01

    Emissions of biogenic volatile organic compounds (BVOCs) have changed in the past millennium due to changes in land use, temperature, and CO2 concentrations. Recent reconstructions of BVOC emissions have predicted that global isoprene emissions have decreased, while monoterpene and sesquiterpene emissions have increased; however, all three show regional variability due to competition between the various influencing factors. In this work, we use two modeled estimates of BVOC emissions from the years 1000 to 2000 to test the effect of anthropogenic changes to BVOC emissions on secondary organic aerosol (SOA) formation, global aerosol size distributions, and radiative effects using the GEOS-Chem-TOMAS (Goddard Earth Observing System; TwO-Moment Aerosol Sectional) global aerosol microphysics model. With anthropogenic emissions (e.g., SO2, NOx, primary aerosols) turned off and BVOC emissions changed from year 1000 to year 2000 values, decreases in the number concentration of particles of size Dp > 80 nm (N80) of > 25% in year 2000 relative to year 1000 were predicted in regions with extensive land-use changes since year 1000 which led to regional increases in the combined aerosol radiative effect (direct and indirect) of > 0.5 W m-2 in these regions. We test the sensitivity of our results to BVOC emissions inventory, SOA yields, and the presence of anthropogenic emissions; however, the qualitative response of the model to historic BVOC changes remains the same in all cases. Accounting for these uncertainties, we estimate millennial changes in BVOC emissions cause a global mean direct effect of between +0.022 and +0.163 W m-2 and the global mean cloud-albedo aerosol indirect effect of between -0.008 and -0.056 W m-2. This change in aerosols, and the associated radiative forcing, could be a largely overlooked and important anthropogenic aerosol effect on regional climates.

  8. Aerosol size distribution and radiative forcing response to anthropogenically driven historical changes in biogenic secondary organic aerosol formation

    NASA Astrophysics Data System (ADS)

    D'Andrea, S. D.; Acosta Navarro, J. C.; Farina, S. C.; Scott, C. E.; Rap, A.; Farmer, D. K.; Spracklen, D. V.; Riipinen, I.; Pierce, J. R.

    2014-10-01

    and the global mean cloud-albedo aerosol indirect effect of between -0.008 and -0.056 W m-2. This change in aerosols, and the associated radiative forcing, could be a~largely overlooked and important anthropogenic aerosol effect on regional climates.

  9. Testing the validity of the Ehrenfest theorem beyond simple static systems: Caldirola-Kanai oscillator driven by a time-dependent force

    NASA Astrophysics Data System (ADS)

    Medjber, Salim; Bekkar, Hacene; Menouar, Salah; Ryeol Choi, Jeong

    2016-08-01

    The relationship between quantum mechanics and classical mechanics is investigated by taking a Gaussian-type wave packet as a solution of the Schrödinger equation for the Caldirola-Kanai oscillator driven by a sinusoidal force. For this time-dependent system, quantum properties are studied by using the invariant theory of Lewis and Riesenfeld. In particular, we analyze time behaviors of quantum expectation values of position and momentum variables and compare them to those of the counterpart classical ones. Based on this, we check whether the Ehrenfest theorem which was originally developed in static quantum systems can be extended to such time-varying systems without problems. Project supported by Fund from the Algerian Ministry of Higher Education and Scientific Research (Grant No. CNEPRU/ D01220120010) and the Basic Science Research Program of the year 2015 through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant No. NRF-2013R1A1A2062907).

  10. Testing the validity of the Ehrenfest theorem beyond simple static systems: Caldirola–Kanai oscillator driven by a time-dependent force

    NASA Astrophysics Data System (ADS)

    Medjber, Salim; Bekkar, Hacene; Menouar, Salah; Ryeol Choi, Jeong

    2016-08-01

    The relationship between quantum mechanics and classical mechanics is investigated by taking a Gaussian-type wave packet as a solution of the Schrödinger equation for the Caldirola–Kanai oscillator driven by a sinusoidal force. For this time-dependent system, quantum properties are studied by using the invariant theory of Lewis and Riesenfeld. In particular, we analyze time behaviors of quantum expectation values of position and momentum variables and compare them to those of the counterpart classical ones. Based on this, we check whether the Ehrenfest theorem which was originally developed in static quantum systems can be extended to such time-varying systems without problems. Project supported by Fund from the Algerian Ministry of Higher Education and Scientific Research (Grant No. CNEPRU/ D01220120010) and the Basic Science Research Program of the year 2015 through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (Grant No. NRF-2013R1A1A2062907).

  11. Intercellular Adhesion-Dependent Cell Survival and ROCK-Regulated Actomyosin-Driven Forces Mediate Self-Formation of a Retinal Organoid.

    PubMed

    Lowe, Albert; Harris, Raven; Bhansali, Punita; Cvekl, Ales; Liu, Wei

    2016-05-10

    In this study we dissected retinal organoid morphogenesis in human embryonic stem cell (hESC)-derived cultures and established a convenient method for isolating large quantities of retinal organoids for modeling human retinal development and disease. Epithelialized cysts were generated via floating culture of clumps of Matrigel/hESCs. Upon spontaneous attachment and spreading of the cysts, patterned retinal monolayers with tight junctions formed. Dispase-mediated detachment of the monolayers and subsequent floating culture led to self-formation of retinal organoids comprising patterned neuroretina, ciliary margin, and retinal pigment epithelium. Intercellular adhesion-dependent cell survival and ROCK-regulated actomyosin-driven forces are required for the self-organization. Our data supports a hypothesis that newly specified neuroretina progenitors form characteristic structures in equilibrium through minimization of cell surface tension. In long-term culture, the retinal organoids autonomously generated stratified retinal tissues, including photoreceptors with ultrastructure of outer segments. Our system requires minimal manual manipulation, has been validated in two lines of human pluripotent stem cells, and provides insight into optic cup invagination in vivo. PMID:27132890

  12. Tectonically driven late Paleocene (57.9-54.7 Ma) transgression and climatically forced latest middle Eocene (41.3-38.0 Ma) regression on the Indian subcontinent

    NASA Astrophysics Data System (ADS)

    Singh, B. P.; Singh, Y. Raghumani; Andotra, D. S.; Patra, A.; Srivastava, V. K.; Guruaribam, Venus; Sijagurumayum, Umarani; Singh, G. P.

    2016-01-01

    Cenozoic era was the turning point in the geological history of the Indian subcontinent when India experienced maximum isolation before it collided with Asia and there occurred a great mountain building activity shaping the Himalaya. In the Cenozoic era, the sedimentation commenced in the late Paleocene (∼57.9 Ma) in the pericratonic basins of the western India as well as the foreland basins of the Himalaya that marks the beginning of a major transgression on the Indian subcontinent. Till now, it is not sure whether this transgression was forced by tectonics or climate. We have interpreted that the primary driver for this transgression was the tectonics that marks the beginning of the India-Asia convergence. A major regression of similar magnitude occurred during latest middle Eocene (41.3-38.0 Ma) that corresponds to global sea-level fall. This regression is global and can be identified even in the Cenozoic basins developed within the African plate. It is interpreted that this regression was driven by the global cooling during latest middle Eocene/late Eocene possibly associated with the nucleation of the Antarctica ice-sheets coupled with the uplift of the Himalaya.

  13. 2D simulations of the line-driven instability in hot-star winds. II. Approximations for the 2D radiation force

    NASA Astrophysics Data System (ADS)

    Dessart, L.; Owocki, S. P.

    2005-07-01

    We present initial attempts to include the multi-dimensional nature of radiation transport in hydrodynamical simulations of the small-scale structure that arises from the line-driven instability in hot-star winds. Compared to previous 1D or 2D models that assume a purely radial radiation force, we seek additionally to treat the lateral momentum and transport of diffuse line-radiation, initially here within a 2D context. A key incentive is to study the damping effect of the associated diffuse line-drag on the dynamical properties of the flow, focusing particularly on whether this might prevent lateral break-up of shell structures at scales near the lateral Sobolev angle of ca. 1^o. Based on 3D linear perturbation analyses that show a viscous diffusion character for the damping at these scales, we first explore nonlinear simulations that cast the lateral diffuse force in the simple, local form of a parallel viscosity. We find, however, that the resulting strong damping of lateral velocity fluctuations only further isolates azimuthal zones, leading again to azimuthal incoherence down to the grid scale. To account then for the further effect of lateral mixing of radiation associated with the radial driving, we next explore models in which the radial force is azimuthally smoothed over a chosen scale, and thereby show that this does indeed translate to a similar scale for the resulting density and velocity structure. Accounting for both the lateral line-drag and the lateral mixing in a more self-consistent way thus requires a multi-ray computation of the radiation transport. As a first attempt, we explore further a method first proposed by Owocki (1999), which uses a restricted 3-ray approach that combines a radial ray with two oblique rays set to have an impact parameter p < Rast within the stellar core. From numerical simulations with various grid resolutions (and p), we find that, compared to equivalent 1-ray simulations, the high-resolution 3-ray models show

  14. Simulation of sloshing dynamics induced forces and torques actuated on dewar container driven by gravity gradient and jitter accelerations in microgravity

    NASA Technical Reports Server (NTRS)

    Hung, R. J.; Pan, H. L.

    1993-01-01

    three levels of gravity jitter (10(exp -6), 10(exp -7), and 10(exp -8) g(sub 0)) each at three predominant frequencies (0.1, 1.0, and 10 Hz), combined with a gravity gradient appropriate for the GP-B orbit. Dynamical evolution of sloshing dynamics excited fluid forces and torque fluctuations exerted on the dewar container driven by the combined gravity gradient and jitter accelerations are also investigated and simulated.

  15. Time-Dependent Measure of a Nano-Scale Force-Pulse Driven by the Axonemal Dynein Motors in Individual Live Sperm Cells

    SciTech Connect

    Allen, M J; Rudd, R E; McElfresh, M W; Balhorn, R

    2009-04-23

    Nano-scale mechanical forces generated by motor proteins are crucial to normal cellular and organismal functioning. The ability to measure and exploit such forces would be important to developing motile biomimetic nanodevices powered by biological motors for Nanomedicine. Axonemal dynein motors positioned inside the sperm flagellum drive microtubule sliding giving rise to rhythmic beating of the flagellum. This force-generating action makes it possible for the sperm cell to move through viscous media. Here we report new nano-scale information on how the propulsive force is generated by the sperm flagellum and how this force varies over time. Single cell recordings reveal discrete {approx}50 ms pulses oscillating with amplitude 9.8 {+-} 2.6 nN independent of pulse frequency (3.5-19.5 Hz). The average work carried out by each cell is 4.6 x 10{sup -16} J per pulse, equivalent to the hydrolysis of {approx}5,500 ATP molecules. The mechanochemical coupling at each active dynein head is {approx}2.2 pN/ATP, and {approx}3.9 pN per dynein arm, in agreement with previously published values obtained using different methods.

  16. Fluctuations of a Greenlandic tidewater glacier driven by changes in atmospheric forcing: observations and modelling of Kangiata Nunaata Sermia, 1859-present

    NASA Astrophysics Data System (ADS)

    Lea, J. M.; Mair, D. W. F.; Nick, F. M.; Rea, B. R.; van As, D.; Morlighem, M.; Nienow, P. W.; Weidick, A.

    2014-11-01

    Many tidewater glaciers in Greenland are known to have undergone significant retreat during the last century following their Little Ice Age maxima. Where it is possible to reconstruct glacier change over this period, they provide excellent records for comparison to climate records, as well as calibration/validation for numerical models. These glacier change records therefore allow for tests of numerical models that seek to simulate tidewater glacier behaviour over multi-decadal to centennial timescales. Here we present a detailed record of behaviour from Kangiata Nunaata Sermia (KNS), SW Greenland, between 1859 and 2012, and compare it against available oceanographic and atmospheric temperature data between 1871 and 2012. We also use these records to evaluate the ability of a well-established one-dimensional flow-band model to replicate behaviour for the observation period. The record of terminus change demonstrates that KNS has advanced/retreated in phase with atmosphere and ocean climate anomalies averaged over multi-annual to decadal timescales. Results from an ensemble of model runs demonstrate that observed dynamics can be replicated. Model runs that provide a reasonable match to observations always require a significant atmospheric forcing component, but do not necessarily require an oceanic forcing component. Although the importance of oceanic forcing cannot be discounted, these results demonstrate that changes in atmospheric forcing are likely to be a primary driver of the terminus fluctuations of KNS from 1859 to 2012. We propose that the detail and length of the record presented makes KNS an ideal site for model validation exercises investigating links between climate, calving rates, and tidewater glacier dynamics.

  17. Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation.

    PubMed

    Staton, Sarah J R; Terray, Alex; Collins, Greg E; Hart, Sean J

    2013-04-01

    Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high-throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods. PMID:23404174

  18. Capillary Force Driven Self-Assembly of Anisotropic Hierarchical Structures Prepared by Femtosecond Laser 3D Printing and Their Applications in Crystallizing Microparticles.

    PubMed

    Lao, Zhaoxin; Hu, Yanlei; Zhang, Chenchu; Yang, Liang; Li, Jiawen; Chu, Jiaru; Wu, Dong

    2015-12-22

    The hierarchical structures are the derivation of various functionalities in the natural world and have inspired broad practical applications in chemical systhesis and biological manipulation. However, traditional top-down fabrication approaches suffered from low complexity. We propose a laser printing capillary-assisted self-assembly (LPCS) strategy for fabricating regular periodic structures. Microscale pillars are first produced by the localized femtosecond laser polymerization and are subsequently self-assembled into periodic hierarchical architectures with the assistance of controlled capillary force. Moreover, based on anisotropic assemblies of micropillars, the LPCS method is further developed for the preparation of more complicated and advanced functional microstructures. Pillars cross section, height, and spatial arrangement can be tuned to guide capillary force, and diverse assemblies with different configurations are thus achieved. Finally, we developed a strategy for growing micro/nanoparticles in designed spatial locations through solution-evaporation self-assembly induced by morphology. Due to the high flexibility of LPCS method, the special arrangements, sizes, and distribution density of the micro/nanoparticles can be controlled readily. Our method will be employed not only to fabricate anisotropic hierarchical structures but also to design and manufacture organic/inorganic microparticles.

  19. Experimental approach for selecting the excitation frequency for maximum compositional contrast in viscous environments for piezo-driven bimodal atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Eslami, Babak; Solares, Santiago D.

    2016-02-01

    We propose a method for guiding the selection of the microcantilever excitation frequencies in low-quality-factor (liquid) bimodal amplitude-modulation atomic force microscopy (AFM). Within the proposed method, the compositional contrast frequency is selected based on maximizing the derivative of the phase shift with respect to the drive frequency, observed during a tuning curve. This leads to different frequency choices and significant differences in the observables with respect to the customary practice of selecting the drive frequencies based on the amplitude peaks in the tuning curve. We illustrate the advantages and disadvantages of our approach by imaging an atomically flat calcite surface with single-eigenmode tapping-mode AFM in water, but driving a higher eigenmode instead of the fundamental eigenmode, and by imaging a polytetrafluoroethylene thin film with bimodal AFM, also in water.

  20. Climate-driven increase in the variability and multi-year mean level of severe thunderstorm-related losses and thunderstorm forcing environments in the U.S. since 1970

    NASA Astrophysics Data System (ADS)

    Sander, Julia; Eichner, Jan; Faust, Eberhard; Steuer, Markus

    2013-04-01

    In the year 2011, direct losses from thunderstorms reached US 26 billion (insured) and US 47 billion (economic), thus equalling the dimension of losses caused by Hurricane Sandy in the New York area 2012. Beyond doubt the 2011 damages had outlier characteristics due to two cities hit by tornadoes. Nonetheless a substantial increase in the variability of normalised direct economic and insured severe thunderstorm-related losses in the U.S. east of the Rocky Mountains over the period 1970-2009 (March - September) has been detected. Besides the annual variability, also the multi-year mean level of losses has strongly increased. Our study focused on sizeable severe thunderstorm events causing at least US 250 million in normalized economic losses. The high threshold guarantees homogeneity over time, because those events regularly covered several states and thus are very unlikely to have been missed at any time due to reporting variability. To shed light on the question whether the strong increase was driven by an external climate driver, the time series of normalized losses (annual counts and annual loss aggregate) was correlated with the time series of thunderstorm forcing environments. The latter were inferred from NCEP/NCAR reanalysis data and comprise 6-hourly CAPE and vertical wind shear data combined to form a variable called Thunderstorm Severity Potential (TSP). From the notable correlation found between the time series of normalized thunderstorm-related losses and meteorologically registered thunderstorm forcing environments (TSP) it could be inferred that climate was the dominant driver for the increase in variability and average level of thunderstorm-related losses over the period 1970-2009. An important component in the rise of TSP over time could be identified in CAPE, as we found a substantial rise in the annual number of exceedances of a high CAPE threshold in the reanalysis data. Recent studies imply that the changes observed in our study, particularly

  1. Century-long increasing trend and variability of dissolved organic carbon export from the Mississippi River basin driven by natural and anthropogenic forcing

    NASA Astrophysics Data System (ADS)

    Ren, Wei; Tian, Hanqin; Cai, Wei-Jun; Lohrenz, Steven E.; Hopkinson, Charles S.; Huang, Wei-Jen; Yang, Jia; Tao, Bo; Pan, Shufen; He, Ruoying

    2016-09-01

    There has been considerable debate as to how natural forcing and anthropogenic activities alter the timing and magnitude of the delivery of dissolved organic carbon (DOC) to the coastal ocean, which has ramifications for the ocean carbon budget, land-ocean interactions, and coastal life. Here we present an analysis of DOC export from the Mississippi River to the Gulf of Mexico during 1901-2010 as influenced by changes in climate, land use and management practices, atmospheric CO2, and nitrogen deposition, through the integration of observational data with a coupled hydrologic/biogeochemical land model. Model simulations show that DOC export in the 2000s increased more than 40% since the 1900s. For the recent three decades (1981-2010), however, our simulated DOC export did not show a significant increasing trend, which is consistent with observations by U.S. Geological Survey. Our factorial analyses suggest that land use and land cover change, including land management practices (LMPs: i.e., fertilization, irrigation, tillage, etc.), were the dominant contributors to the century-scale trend of rising total riverine DOC export, followed by changes in atmospheric CO2, nitrogen deposition, and climate. Decadal and interannual variations of DOC export were largely attributed to year-to-year climatic variability and extreme flooding events, which have been exacerbated by human activity. LMPs show incremental contributions to DOC increase since the 1960s, indicating the importance of sustainable agricultural practices in coping with future environmental changes such as extreme flooding events. Compared to the observational-based estimate, the modeled DOC export was 20% higher, while DOC concentrations were slightly lower. Further refinements in model structure and input data sets should enable reductions in uncertainties in our prediction of century-long trends in DOC.

  2. Affinity driven social networks

    NASA Astrophysics Data System (ADS)

    Ruyú, B.; Kuperman, M. N.

    2007-04-01

    In this work we present a model for evolving networks, where the driven force is related to the social affinity between individuals of a population. In the model, a set of individuals initially arranged on a regular ordered network and thus linked with their closest neighbors are allowed to rearrange their connections according to a dynamics closely related to that of the stable marriage problem. We show that the behavior of some topological properties of the resulting networks follows a non trivial pattern.

  3. Current-driven atomic waterwheels.

    PubMed

    Dundas, Daniel; McEniry, Eunan J; Todorov, Tchavdar N

    2009-02-01

    A current induces forces on atoms inside the conductor that carries it. It is now possible to compute these forces from scratch, and to perform dynamical simulations of the atomic motion under current. One reason for this interest is that current can be a destructive force--it can cause atoms to migrate, resulting in damage and in the eventual failure of the conductor. But one can also ask, can current be made to do useful work on atoms? In particular, can an atomic-scale motor be driven by electrical current, as it can be by other mechanisms? For this to be possible, the current-induced forces on a suitable rotor must be non-conservative, so that net work can be done per revolution. Here we show that current-induced forces in atomic wires are not conservative and that they can be used, in principle, to drive an atomic-scale waterwheel. PMID:19197311

  4. Force feedback in limb lengthening.

    PubMed

    Wee, Jinyong; Rahman, Tariq; Seliktar, Rahamim; Akins, Robert; Levine, David; Richardson, Dean; Dodge, George R; Thabet, Ahmed M; Holmes, Lauren; Mackenzie, William G

    2010-01-01

    A new variable-rate distraction system using a motorized distractor driven by feedback from the distraction force was designed. The distractor was mounted on a unilateral fixator and attached to the tibiae of 6 sheep that underwent distraction osteogenesis. The sheep were divided equally into 3 groups. In group 1, the forces were recorded but were not used to drive the lengthening rate. In group 2, force feedback was used and the desired distraction force level was set to 300 N and the initial rate was 1 mm/day. Group 3 also underwent force feedback with the desired force limit at 300 N, but the rate change was initiated earlier, at 200 N. The distraction force was recorded at 15 second intervals throughout the distraction phase and stored onboard the distractor.

  5. Nuclear forces

    SciTech Connect

    Machleidt, R.

    2013-06-10

    These lectures present an introduction into the theory of nuclear forces. We focus mainly on the modern approach, in which the forces between nucleons emerge from low-energy QCD via chiral effective field theory.

  6. Qplus AFM driven nanostencil.

    PubMed

    Grévin, B; Fakir, M; Hayton, J; Brun, M; Demadrille, R; Faure-Vincent, J

    2011-06-01

    We describe the development of a novel setup, in which large stencils with suspended silicon nitride membranes are combined with atomic force microscopy (AFM) regulation by using tuning forks. This system offers the possibility to perform separate AFM and nanostencil operations, as well as combined modes when using stencil chips with integrated tips. The flexibility and performances are demonstrated through a series of examples, including wide AFM scans in closed loop mode, probe positioning repeatability of a few tens of nanometer, simultaneous evaporation of large (several hundred of micron square) and nanoscopic metals and fullerene patterns in static, multistep, and dynamic modes. This approach paves the way for further developments, as it fully combines the advantages of conventional stenciling with the ones of an AFM driven shadow mask. PMID:21721701

  7. Labor Force

    ERIC Educational Resources Information Center

    Occupational Outlook Quarterly, 2012

    2012-01-01

    The labor force is the number of people ages 16 or older who are either working or looking for work. It does not include active-duty military personnel or the institutionalized population, such as prison inmates. Determining the size of the labor force is a way of determining how big the economy can get. The size of the labor force depends on two…

  8. Heat driven pulse pump

    NASA Technical Reports Server (NTRS)

    Benner, Steve M (Inventor); Martins, Mario S. (Inventor)

    2000-01-01

    A heat driven pulse pump includes a chamber having an inlet port, an outlet port, two check valves, a wick, and a heater. The chamber may include a plurality of grooves inside wall of the chamber. When heated within the chamber, a liquid to be pumped vaporizes and creates pressure head that expels the liquid through the outlet port. As liquid separating means, the wick, disposed within the chamber, is to allow, when saturated with the liquid, the passage of only liquid being forced by the pressure head in the chamber, preventing the vapor from exiting from the chamber through the outlet port. A plurality of grooves along the inside surface wall of the chamber can sustain the liquid, which is amount enough to produce vapor for the pressure head in the chamber. With only two simple moving parts, two check valves, the heat driven pulse pump can effectively function over the long lifetimes without maintenance or replacement. For continuous flow of the liquid to be pumped a plurality of pumps may be connected in parallel.

  9. One Force

    NASA Astrophysics Data System (ADS)

    Kotas, Ronald R.

    2002-04-01

    There is only one entity that can extend force and couple through space; and it should be apparent that Electromagnetism is that entity. In the cases of the nuclear strong force and the nuclear weak force, this is the same fundamental Electromagnetism manifesting itself in two different ways in the nucleus. It remains the same basic Electromagnetism. On the other hand, General Relativity fails to produce force at a distance, fails the Cavendish experiment, and does not allow an apple to fall to the ground. The result shows there is only Electromagnetism that functions through physical nature providing gravity, actions in the nucleus, as well as all other physical actions universally, including Gravity and Gravitation. There are many direct proofs of this, the same proofs as in NUCLEAR QUANTUM GRAVITATION. In contrast, General Relativity plainly relies on fallacy abstract and incoherent proofs; proofs which have now been mostly disproved. In the past it was deemed necessary by some to have an "ether" to propagate Electromagnetic waves. The fallacy concept of time space needs "space distortions" in order to cause gravity. However, Electromagnetic gravity does not have this problem. Clearly there is only ONE FORCE that causes Gravity, Electromagnetism, the Nuclear Strong Force, and the Nuclear Weak Force, and that ONE FORCE is Electromagnetism.

  10. Labor Force

    ERIC Educational Resources Information Center

    Occupational Outlook Quarterly, 2010

    2010-01-01

    The labor force is the number of people aged 16 or older who are either working or looking for work. It does not include active-duty military personnel or institutionalized people, such as prison inmates. Quantifying this total supply of labor is a way of determining how big the economy can get. Labor force participation rates vary significantly…

  11. Active and driven hydrodynamic crystals.

    PubMed

    Desreumaux, N; Florent, N; Lauga, E; Bartolo, D

    2012-08-01

    Motivated by the experimental ability to produce monodisperse particles in microfluidic devices, we study theoretically the hydrodynamic stability of driven and active crystals. We first recall the theoretical tools allowing to quantify the dynamics of elongated particles in a confined fluid. In this regime hydrodynamic interactions between particles arise from a superposition of potential dipolar singularities. We exploit this feature to derive the equations of motion for the particle positions and orientations. After showing that all five planar Bravais lattices are stationary solutions of the equations of motion, we consider separately the case where the particles are passively driven by an external force, and the situation where they are self-propelling. We first demonstrate that phonon modes propagate in driven crystals, which are always marginally stable. The spatial structures of the eigenmodes depend solely on the symmetries of the lattices, and on the orientation of the driving force. For active crystals, the stability of the particle positions and orientations depends not only on the symmetry of the crystals but also on the perturbation wavelengths and on the crystal density. Unlike unconfined fluids, the stability of active crystals is independent of the nature of the propulsion mechanism at the single-particle level. The square and rectangular lattices are found to be linearly unstable at short wavelengths provided the volume fraction of the crystals is high enough. Differently, hexagonal, oblique, and face-centered crystals are always unstable. Our work provides a theoretical basis for future experimental work on flowing microfluidic crystals. PMID:22864543

  12. Entropic forces in Brownian motion

    NASA Astrophysics Data System (ADS)

    Roos, Nico

    2014-12-01

    Interest in the concept of entropic forces has risen considerably since Verlinde proposed in 2011 to interpret the force in Newton's second law and gravity as entropic forces. Brownian motion—the motion of a small particle (pollen) driven by random impulses from the surrounding molecules—may be the first example of a stochastic process in which such forces are expected to emerge. In this article, it is shown that at least two types of entropic force can be identified in three-dimensional Brownian motion. This analysis yields simple derivations of known results of Brownian motion, Hooke's law, and—applying an external (non-radial) force—Curie's law and the Langevin-Debye equation.

  13. Force sensor

    DOEpatents

    Grahn, A.R.

    1993-05-11

    A force sensor and related method for determining force components is described. The force sensor includes a deformable medium having a contact surface against which a force can be applied, a signal generator for generating signals that travel through the deformable medium to the contact surface, a signal receptor for receiving the signal reflected from the contact surface, a generation controller, a reception controller, and a force determination apparatus. The signal generator has one or more signal generation regions for generating the signals. The generation controller selects and activates the signal generation regions. The signal receptor has one or more signal reception regions for receiving signals and for generating detections signals in response thereto. The reception controller selects signal reception regions and detects the detection signals. The force determination apparatus measures signal transit time by timing activation and detection and, optionally, determines force components for selected cross-field intersections. The timer which times by activation and detection can be any means for measuring signal transit time. A cross-field intersection is defined by the overlap of a signal generation region and a signal reception region.

  14. Force sensor

    DOEpatents

    Grahn, Allen R.

    1993-01-01

    A force sensor and related method for determining force components. The force sensor includes a deformable medium having a contact surface against which a force can be applied, a signal generator for generating signals that travel through the deformable medium to the contact surface, a signal receptor for receiving the signal reflected from the contact surface, a generation controller, a reception controller, and a force determination apparatus. The signal generator has one or more signal generation regions for generating the signals. The generation controller selects and activates the signal generation regions. The signal receptor has one or more signal reception regions for receiving signals and for generating detections signals in response thereto. The reception controller selects signal reception regions and detects the detection signals. The force determination apparatus measures signal transit time by timing activation and detection and, optionally, determines force components for selected cross-field intersections. The timer which times by activation and detection can be any means for measuring signal transit time. A cross-field intersection is defined by the overlap of a signal generation region and a signal reception region.

  15. Radiative forcing and climate response

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Sato, M.; Ruedy, R.

    1997-03-01

    -50% of the positive forcing due to the increase of well-mixed greenhouse gases in the same period. As the net ozone change includes halogen-driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen-driven ozone depletion has counterbalanced more than half of the radiative forcing due to well-mixed greenhouse gases since 1979.

  16. Micromechanism linear actuator with capillary force sealing

    DOEpatents

    Sniegowski, Jeffry J.

    1997-01-01

    A class of micromachine linear actuators whose function is based on gas driven pistons in which capillary forces are used to seal the gas behind the piston. The capillary forces also increase the amount of force transmitted from the gas pressure to the piston. In a major subclass of such devices, the gas bubble is produced by thermal vaporization of a working fluid. Because of their dependence on capillary forces for sealing, such devices are only practical on the sub-mm size scale, but in that regime they produce very large force times distance (total work) values.

  17. Work in the Knowledge-Driven Economy.

    ERIC Educational Resources Information Center

    Bayliss, Valerie

    2001-01-01

    The knowledge-driven economy has become a "given," yet there is disagreement over what it entails and who is helped or harmed. The aging of the work force, disappearance of unskilled jobs, and changes in business and social organization suggest that the social, economic, and infrastructural problems of the knowledge economy will not solve…

  18. Wind driven air pump

    SciTech Connect

    Beisel, V.A.

    1983-05-31

    An improved pump for lifting water from an underground source utilizes a wind motor for driving an oil-less air compressor eliminating oil contamination of ground water which is forced to the surface. The wind motor is movable to face the wind by means of a novel swivel assembly which also eliminates the formation and freezing of condensate within the airline from the compressor. The propeller blades of the wind motor and the tail section are formed from a pair of opposed convex air foil shaped surfaces which provide the propeller blades and the tail section with fast sensitivity to slight changes in wind direction and speed. A novel well tower for supporting the wind motor and compressor and for lifting the water from the underground source is an optional modification which requires no welding and eliminates the problem of condensate freezing in the airline going to the well. The wind driven air pump disclosed is lightweight, can be easily installed, is relatively inexpensive to produce and is virtually maintenance-free and capable of operating in winds exceeding 100 miles per hour.

  19. Inter-daily variability of a strong thermally-driven wind system over the Atacama Desert of South America: synoptic forcing and short-term predictability using the GFS global model

    NASA Astrophysics Data System (ADS)

    Jacques-Coper, Martín; Falvey, Mark; Muñoz, Ricardo C.

    2015-07-01

    Crucial aspects of a strong thermally-driven wind system in the Atacama Desert in northern Chile during the extended austral winter season (May-September) are studied using 2 years of measurement data from the Sierra Gorda 80-m meteorological mast (SGO, 22° 56' 24″ S; 69° 7' 58″ W, 2,069 m above sea level (a.s.l.)). Daily cycles of atmospheric variables reveal a diurnal (nocturnal) regime, with northwesterly (easterly) flow and maximum mean wind speed of 8 m/s (13 m/s) on average. These distinct regimes are caused by pronounced topographic conditions and the diurnal cycle of the local radiative balance. Wind speed extreme events of each regime are negatively correlated at the inter-daily time scale: High diurnal wind speed values are usually observed together with low nocturnal wind speed values and vice versa. The associated synoptic conditions indicate that upper-level troughs at the coastline of southwestern South America reinforce the diurnal northwesterly wind, whereas mean undisturbed upper-level conditions favor the development of the nocturnal easterly flow. We analyze the skill of the numerical weather model Global Forecast System (GFS) in predicting wind speed at SGO. Although forecasted wind speeds at 800 hPa do show the diurnal and nocturnal phases, observations at 80 m are strongly underestimated by the model. This causes a pronounced daily cycle of root-mean-squared error (RMSE) and bias in the forecasts. After applying a simple Model Output Statistics (MOS) post-processing, we achieve a good representation of the wind speed intra-daily and inter-daily variability, a first step toward reducing the uncertainties related to potential wind energy projects in the region.

  20. Impulse-driven Micromechanism Capsule

    NASA Astrophysics Data System (ADS)

    Ito, Takahiro; Ishimori, Shohei; Hayashi, Teru

    We have developed a traveling small capsule, which has a smooth outer surface and is driven by inertia force and friction force. Measuring only 7 mm in diameter and 12 mm in length, it is sufficiently small to be placed in the human gullet or intestines. The capsule contains a small magnet and a coil, and an electric pulse drives the magnet to move the capsule. We performed an experimental investigation on making our capsule travel on a plastic material, which has similar elasticity characteristics to the living body. We also showed that it can travel on the surface of a pig's intestine. Our capsule may be useful for medical treatments such as inspection, drug delivery and operation.

  1. Vacuum force

    NASA Astrophysics Data System (ADS)

    Han, Yongquan

    2015-03-01

    To study on vacuum force, we must clear what is vacuum, vacuum is a space do not have any air and also ray. There is not exist an absolute the vacuum of space. The vacuum of space is relative, so that the vacuum force is relative. There is a certain that vacuum vacuum space exists. In fact, the vacuum space is relative, if the two spaces compared to the existence of relative vacuum, there must exist a vacuum force, and the direction of the vacuum force point to the vacuum region. Any object rotates and radiates. Rotate bend radiate- centripetal, gravity produced, relative gravity; non gravity is the vacuum force. Gravity is centripetal, is a trend that the objects who attracted wants to Centripetal, or have been do Centripetal movement. Any object moves, so gravity makes the object curve movement, that is to say, the radiation range curve movement must be in the gravitational objects, gravity must be existed in non vacuum region, and make the object who is in the region of do curve movement (for example: The earth moves around the sun), or final attracted in the form gravitational objects, and keep relatively static with attract object. (for example: objects on the earth moves but can't reach the first cosmic speed).

  2. Molecular Force Spectroscopy on Cells

    NASA Astrophysics Data System (ADS)

    Liu, Baoyu; Chen, Wei; Zhu, Cheng

    2015-04-01

    Molecular force spectroscopy has become a powerful tool to study how mechanics regulates biology, especially the mechanical regulation of molecular interactions and its impact on cellular functions. This force-driven methodology has uncovered a wealth of new information of the physical chemistry of molecular bonds for various biological systems. The new concepts, qualitative and quantitative measures describing bond behavior under force, and structural bases underlying these phenomena have substantially advanced our fundamental understanding of the inner workings of biological systems from the nanoscale (molecule) to the microscale (cell), elucidated basic molecular mechanisms of a wide range of important biological processes, and provided opportunities for engineering applications. Here, we review major force spectroscopic assays, conceptual developments of mechanically regulated kinetics of molecular interactions, and their biological relevance. We also present current challenges and highlight future directions.

  3. Strategic forces

    SciTech Connect

    Not Available

    1990-10-01

    The Air Force now plans to retain the Minuteman II and III missile force through fiscal year 2008. Introduced about 25 years ago, these missiles have served as a nuclear deterrence for longer than initially envisioned. Over the extended lives of the systems, questions have arisen over their continued reliability and operational effectiveness, particularly the Minuteman II system. Limited flight testing, due to a shortage of test missiles, and reduced reliability caused by age-related deterioration of guidance computers and propulsion motors are two factors undermining confidence in the Minuteman II. GAO believes that the Minuteman II could be retired before 1998 as presently contemplated under an assumption of a Strategic Arms Reduction Talks agreement. An alternative would be to reinstate the Air Force's plans to replace deteriorated missile components and acquire the assets needed to resume flight testing at rates necessary to restore and sustain confidence in the system's performance through fiscal year 2008. However, on the basis of current test schedules, GAO is concerned that components to test the missile's warheads will be depleted by about 1999.

  4. Design Considerations for Plasma Accelerators Driven by Lasers or Particle Beams

    SciTech Connect

    Schroeder, C. B.; Esarey, E.; Benedetti, C.; Toth, Cs.; Geddes, C. G. R.; Leemans, W.P.

    2010-06-01

    Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space-charge force of a charged particle beam. The implications for accelerator design and the different physical mechanisms of laser-driven and beam-driven plasma acceleration are discussed. Driver propagation is examined, as well as the effects of the excited plasma wave phase velocity. The driver coupling to subsequent plasma accelerator stages for high-energy physics applications is addressed.

  5. Self-driven jamming in growing microbial populations

    NASA Astrophysics Data System (ADS)

    Delarue, Morgan; Hartung, Jörn; Schreck, Carl; Gniewek, Pawel; Hu, Lucy; Herminghaus, Stephan; Hallatschek, Oskar

    2016-08-01

    In natural settings, microbes tend to grow in dense populations where they need to push against their surroundings to accommodate space for new cells. The associated contact forces play a critical role in a variety of population-level processes, including biofilm formation, the colonization of porous media, and the invasion of biological tissues. Although mechanical forces have been characterized at the single-cell level, it remains elusive how collective pushing forces result from the combination of single-cell forces. Here, we reveal a collective mechanism of confinement, which we call self-driven jamming, that promotes the build-up of large mechanical pressures in microbial populations. Microfluidic experiments on budding yeast populations in space-limited environments show that self-driven jamming arises from the gradual formation and sudden collapse of force chains driven by microbial proliferation, extending the framework of driven granular matter. The resulting contact pressures can become large enough to slow down cell growth, to delay the cell cycle in the G1 phase, and to strain or even destroy the micro-environment through crack propagation. Our results suggest that self-driven jamming and build-up of large mechanical pressures is a natural tendency of microbes growing in confined spaces, contributing to microbial pathogenesis and biofouling.

  6. ISOTROPICALLY DRIVEN VERSUS OUTFLOW DRIVEN TURBULENCE: OBSERVATIONAL CONSEQUENCES FOR MOLECULAR CLOUDS

    SciTech Connect

    Carroll, Jonathan J.; Frank, Adam; Blackman, Eric G.

    2010-10-10

    Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.

  7. Forces driving epithelial wound healing

    PubMed Central

    Veldhuis, Jim H.; Gupta, Mukund; Colombelli, Julien; Muñoz, José J.; Brodland, G. Wayne; Ladoux, Benoit; Trepat, Xavier

    2015-01-01

    A fundamental feature of multicellular organisms is their ability to self-repair wounds through the movement of epithelial cells into the damaged area. This collective cellular movement is commonly attributed to a combination of cell crawling and “purse-string” contraction of a supracellular actomyosin ring. Here we show by direct experimental measurement that these two mechanisms are insufficient to explain force patterns observed during wound closure. At early stages of the process, leading actin protrusions generate traction forces that point away from the wound, showing that wound closure is initially driven by cell crawling. At later stages, we observed unanticipated patterns of traction forces pointing towards the wound. Such patterns have strong force components that are both radial and tangential to the wound. We show that these force components arise from tensions transmitted by a heterogeneous actomyosin ring to the underlying substrate through focal adhesions. The structural and mechanical organization reported here provides cells with a mechanism to close the wound by cooperatively compressing the underlying substrate. PMID:27340423

  8. Cosmic ray driven Galactic winds

    NASA Astrophysics Data System (ADS)

    Recchia, S.; Blasi, P.; Morlino, G.

    2016-11-01

    The escape of cosmic rays from the Galaxy leads to a gradient in the cosmic ray pressure that acts as a force on the background plasma, in the direction opposite to the gravitational pull. If this force is large enough to win against gravity, a wind can be launched that removes gas from the Galaxy, thereby regulating several physical processes, including star formation. The dynamics of these cosmic ray driven winds is intrinsically non-linear in that the spectrum of cosmic rays determines the characteristics of the wind (velocity, pressure, magnetic field) and in turn the wind dynamics affects the cosmic ray spectrum. Moreover, the gradient of the cosmic ray distribution function causes excitation of Alfvén waves, that in turn determines the scattering properties of cosmic rays, namely their diffusive transport. These effects all feed into each other so that what we see at the Earth is the result of these non-linear effects. Here, we investigate the launch and evolution of such winds, and we determine the implications for the spectrum of cosmic rays by solving together the hydrodynamical equations for the wind and the transport equation for cosmic rays under the action of self-generated diffusion and advection with the wind and the self-excited Alfvén waves.

  9. Cosmic ray driven Galactic winds

    NASA Astrophysics Data System (ADS)

    Recchia, S.; Blasi, P.; Morlino, G.

    2016-08-01

    The escape of cosmic rays from the Galaxy leads to a gradient in the cosmic ray pressure that acts as a force on the background plasma, in the direction opposite to the gravitational pull. If this force is large enough to win against gravity, a wind can be launched that removes gas from the Galaxy, thereby regulating several physical processes, including star formation. The dynamics of these cosmic ray driven winds is intrinsically non-linear in that the spectrum of cosmic rays determines the characteristics of the wind (velocity, pressure, magnetic field) and in turn the wind dynamics affects the cosmic ray spectrum. Moreover, the gradient of the cosmic ray distribution function causes excitation of Alfvén waves, that in turn determine the scattering properties of cosmic rays, namely their diffusive transport. These effects all feed into each other so that what we see at the Earth is the result of these non-linear effects. Here we investigate the launch and evolution of such winds, and we determine the implications for the spectrum of cosmic rays by solving together the hydrodynamical equations for the wind and the transport equation for cosmic rays under the action of self-generated diffusion and advection with the wind and the self-excited Alfvén waves.

  10. Torque Control of Underactuated Tendon-driven Robotic Fingers

    NASA Technical Reports Server (NTRS)

    Abdallah, Muhammad E. (Inventor); Ihrke, Chris A. (Inventor); Reiland, Matthew J. (Inventor); Wampler, Charles W. (Inventor); Diftler, Myron A. (Inventor); Platt, Robert (Inventor); Bridgwater, Lyndon (Inventor)

    2013-01-01

    A robotic system includes a robot having a total number of degrees of freedom (DOF) equal to at least n, an underactuated tendon-driven finger driven by n tendons and n DOF, the finger having at least two joints, being characterized by an asymmetrical joint radius in one embodiment. A controller is in communication with the robot, and controls actuation of the tendon-driven finger using force control. Operating the finger with force control on the tendons, rather than position control, eliminates the unconstrained slack-space that would have otherwise existed. The controller may utilize the asymmetrical joint radii to independently command joint torques. A method of controlling the finger includes commanding either independent or parameterized joint torques to the controller to actuate the fingers via force control on the tendons.

  11. Glacial cycles and astronomical forcing

    SciTech Connect

    Muller, R.A.; MacDonald, G.J.

    1997-07-11

    Narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces. Two million years ago, the cycles match the 41,000-year period of Earth`s obliquity. This supports the Croll/Milankovitch theory, which attributes the cycles to variations in insolation. But for the past million years, the spectrum is dominated by a single 100,000-year feature and is a poor match to the predictions of insolation models. The spectrum can be accounted for by a theory that derives the cycles of glaciation from variations in the inclination of Earth`s orbital plane.

  12. Quantum thermodynamics of the driven resonant level model

    NASA Astrophysics Data System (ADS)

    Bruch, Anton; Thomas, Mark; Viola Kusminskiy, Silvia; von Oppen, Felix; Nitzan, Abraham

    2016-03-01

    We present a consistent thermodynamic theory for the resonant level model in the wide-band limit, whose level energy is driven slowly by an external force. The problem of defining "system" and "bath" in the strong-coupling regime is circumvented by considering as the system everything that is influenced by the externally driven level. The thermodynamic functions that are obtained to first order beyond the quasistatic limit fulfill the first and second law with a positive entropy production, successfully connect to the forces experienced by the external driving, and reproduce the correct weak-coupling limit of stochastic thermodynamics.

  13. Manipulating bubbles with secondary Bjerknes forces

    SciTech Connect

    Lanoy, Maxime; Derec, Caroline; Leroy, Valentin; Tourin, Arnaud

    2015-11-23

    Gas bubbles in a sound field are submitted to a radiative force, known as the secondary Bjerknes force. We propose an original experimental setup that allows us to investigate in detail this force between two bubbles, as a function of the sonication frequency, as well as the bubbles radii and distance. We report the observation of both attractive and, more interestingly, repulsive Bjerknes force, when the two bubbles are driven in antiphase. Our experiments show the importance of taking multiple scatterings into account, which leads to a strong acoustic coupling of the bubbles when their radii are similar. Our setup demonstrates the accuracy of secondary Bjerknes forces for attracting or repealing a bubble, and could lead to new acoustic tools for noncontact manipulation in microfluidic devices.

  14. The driven spinning top

    NASA Astrophysics Data System (ADS)

    Grosu, Ioan; Featonby, David

    2016-05-01

    This driven top is quite a novelty and can, with some trials, be made using the principles outlined here. This new top has many applications in developing both understanding and skills and these are detailed in the article. Depending on reader’s available time and motivation they may feel an urge to make one themselves, or simply invest a few pounds in the one that has been designed, tested and manufactured to a high standard. Either way the unique design of the driven top can provide several hours of interesting experimentation. Our aim here is simply to inform and inspire readers to further investigation and experimentation.

  15. Plasma sheath driven targets

    NASA Astrophysics Data System (ADS)

    Brownell, J. H.; Freeman, B. L.

    1980-02-01

    Plasma focus driven target implosions are simulated using hydrodynamic-burn codes. Support is given to the idea that the use of a target in a plasma focus should allow 'impedance matching' between the fuel and gun, permitting larger fusion yields from a focus-target geometry than the scaling laws for a conventional plasma focus would predict.

  16. Data Driven Teachers

    ERIC Educational Resources Information Center

    Tech & Learning, 2009

    2009-01-01

    Data-driven decision-making (DDDM) is a system of teaching and management practices that gets better information about students into the hands of classroom teachers. This article discusses the five major elements: (1) good baseline data; (2) measurable instructional goals; (3) frequent formative assessment; (4) professional learning communities;…

  17. The Driven Spinning Top

    ERIC Educational Resources Information Center

    Grosu, Ioan; Featonby, David

    2016-01-01

    This driven top is quite a novelty and can, with some trials, be made using the principles outlined here. This new top has many applications in developing both understanding and skills and these are detailed in the article. Depending on reader's available time and motivation they may feel an urge to make one themselves, or simply invest a few…

  18. Argument-Driven Inquiry

    ERIC Educational Resources Information Center

    Sampson, Victor; Grooms, Jonathon; Walker, Joi

    2009-01-01

    Argument-Driven Inquiry (ADI) is an instructional model that enables science teachers to transform a traditional laboratory activity into a short integrated instructional unit. To illustrate how the ADI instructional model works, this article describes an ADI lesson developed for a 10th-grade chemistry class. This example lesson was designed to…

  19. Data-Driven Districts.

    ERIC Educational Resources Information Center

    LaFee, Scott

    2002-01-01

    Describes the use of data-driven decision-making in four school districts: Plainfield Public Schools, Plainfield, New Jersey; Palo Alto Unified School District, Palo Alto, California; Francis Howell School District in eastern Missouri, northwest of St. Louis; and Rio Rancho Public Schools, near Albuquerque, New Mexico. Includes interviews with the…

  20. Atomic Force Microscope Mediated Chromatography

    NASA Technical Reports Server (NTRS)

    Anderson, Mark S.

    2013-01-01

    The atomic force microscope (AFM) is used to inject a sample, provide shear-driven liquid flow over a functionalized substrate, and detect separated components. This is demonstrated using lipophilic dyes and normal phase chromatography. A significant reduction in both size and separation time scales is achieved with a 25-micron-length column scale, and one-second separation times. The approach has general applications to trace chemical and microfluidic analysis. The AFM is now a common tool for ultra-microscopy and nanotechnology. It has also been demonstrated to provide a number of microfluidic functions necessary for miniaturized chromatography. These include injection of sub-femtoliter samples, fluidic switching, and sheardriven pumping. The AFM probe tip can be used to selectively remove surface layers for subsequent microchemical analysis using infrared and tip-enhanced Raman spectroscopy. With its ability to image individual atoms, the AFM is a remarkably sensitive detector that can be used to detect separated components. These diverse functional components of microfluidic manipulation have been combined in this work to demonstrate AFM mediated chromatography. AFM mediated chromatography uses channel-less, shear-driven pumping. This is demonstrated with a thin, aluminum oxide substrate and a non-polar solvent system to separate a mixture of lipophilic dyes. In conventional chromatographic terms, this is analogous to thin-layer chromatography using normal phase alumina substrate with sheardriven pumping provided by the AFM tip-cantilever mechanism. The AFM detection of separated components is accomplished by exploiting the variation in the localized friction of the separated components. The AFM tip-cantilever provides the mechanism for producing shear-induced flows and rapid pumping. Shear-driven chromatography (SDC) is a relatively new concept that overcomes the speed and miniaturization limitations of conventional liquid chromatography. SDC is based on a

  1. Position Control of Tendon-Driven Fingers

    NASA Technical Reports Server (NTRS)

    Abdallah, Muhammad E.; Platt, Robert, Jr.; Hargrave, B.; Pementer, Frank

    2011-01-01

    Conventionally, tendon-driven manipulators implement some force control scheme based on tension feedback. This feedback allows the system to ensure that the tendons are maintained taut with proper levels of tensioning at all times. Occasionally, whether it is due to the lack of tension feedback or the inability to implement sufficiently high stiffnesses, a position control scheme is needed. This work compares three position controllers for tendon-driven manipulators. A new controller is introduced that achieves the best overall performance with regards to speed, accuracy, and transient behavior. To compensate for the lack of tension feedback, the controller nominally maintains the internal tension on the tendons by implementing a two-tier architecture with a range-space constraint. These control laws are validated experimentally on the Robonaut-2 humanoid hand. I

  2. Measurements of gravity driven granular channel flows

    NASA Astrophysics Data System (ADS)

    Facto, Kevin

    This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

  3. The swim force as a body force

    NASA Astrophysics Data System (ADS)

    Yan, Wen; Brady, John

    2015-11-01

    Net (as opposed to random) motion of active matter results from an average swim (or propulsive) force. It is shown that the average swim force acts like a body force - an internal body force [Yan and Brady, Soft Matter, DOI:10.1039/C5SM01318F]. As a result, the particle-pressure exerted on a container wall is the sum of the swim pressure [Takatori et al., Phys. Rev. Lett., 2014, 113, 028103] and the `weight' of the active particles. A continuum mechanical description is possible when variations occur on scales larger than the run length of the active particles and gives a Boltzmann-like distribution from a balance of the swim force and the swim pressure. Active particles may also display `action at a distance' and accumulate adjacent to (or be depleted from) a boundary without any external forces. In the momentum balance for the suspension - the mixture of active particles plus fluid - only external body forces appear.

  4. Parametric resonance induced chaos in magnetic damped driven pendulum

    NASA Astrophysics Data System (ADS)

    Khomeriki, Giorgi

    2016-07-01

    A damped driven pendulum with a magnetic driving force, appearing from a solenoid, where ac current flows is considered. The solenoid acts on the magnet, which is located at a free end of the pendulum. In this system the existence and interrelation of chaos and parametric resonance is theoretically examined. Derived analytical results are supported by numerical simulations and conducted experiments.

  5. Energy-beam-driven rapid fabrication system

    DOEpatents

    Keicher, David M.; Atwood, Clinton L.; Greene, Donald L.; Griffith, Michelle L.; Harwell, Lane D.; Jeantette, Francisco P.; Romero, Joseph A.; Schanwald, Lee P.; Schmale, David T.

    2002-01-01

    An energy beam driven rapid fabrication system, in which an energy beam strikes a growth surface to form a molten puddle thereon. Feed powder is then injected into the molten puddle from a converging flow of feed powder. A portion of the feed powder becomes incorporated into the molten puddle, forcing some of the puddle contents to freeze on the growth surface, thereby adding an additional layer of material. By scanning the energy beam and the converging flow of feed powder across the growth surface, complex three-dimensional shapes can be formed, ready or nearly ready for use. Nearly any class of material can be fabricated using this system.

  6. Laser driven radiography

    SciTech Connect

    Perry, M.D.; Sefcik, J.; Cowan, T.

    1997-12-20

    Intense laser (> 1021 W/cm{sup 3}) driven hard x-ray sources offer a new alternative to conventional electron accelerator Bremsstrahlung sources. These laser driven sources offer considerable simplicity in design and potential cost advantage for multiple axis views. High spatial and temporal resolution is achievable as a result of the very small source size (<100 um) and short-duration of the laser pulse. We have begun a series of experiments with the Petawatt laser at LLNL to determine the photon flux achievable with these sources and assess their potential for Stewardship applications. Additionally, we are developing a conceptual design and cost estimate of a multi-pulse, multi-axis (up to five) radiographic facility utilizing the Contained Firing Facility at site 300 and existing laser hardware.

  7. Test-driven programming

    NASA Astrophysics Data System (ADS)

    Georgiev, Bozhidar; Georgieva, Adriana

    2013-12-01

    In this paper, are presented some possibilities concerning the implementation of a test-driven development as a programming method. Here is offered a different point of view for creation of advanced programming techniques (build tests before programming source with all necessary software tools and modules respectively). Therefore, this nontraditional approach for easier programmer's work through building tests at first is preferable way of software development. This approach allows comparatively simple programming (applied with different object-oriented programming languages as for example JAVA, XML, PYTHON etc.). It is predictable way to develop software tools and to provide help about creating better software that is also easier to maintain. Test-driven programming is able to replace more complicated casual paradigms, used by many programmers.

  8. Stochastically driven genetic circuits

    NASA Astrophysics Data System (ADS)

    Tsimring, L. S.; Volfson, D.; Hasty, J.

    2006-06-01

    Transcriptional regulation in small genetic circuits exhibits large stochastic fluctuations. Recent experiments have shown that a significant fraction of these fluctuations is caused by extrinsic factors. In this paper we review several theoretical and computational approaches to modeling of small genetic circuits driven by extrinsic stochastic processes. We propose a simplified approach to this problem, which can be used in the case when extrinsic fluctuations dominate the stochastic dynamics of the circuit (as appears to be the case in eukaryots). This approach is applied to a model of a single nonregulated gene that is driven by a certain gating process that affects the rate of transcription, and to a simplified version of the galactose utilization circuit in yeast.

  9. Sparsity driven ultrasound imaginga)

    PubMed Central

    Tuysuzoglu, Ahmet; Kracht, Jonathan M.; Cleveland, Robin O.; C¸etin, Müjdat; Karl, W. Clem

    2012-01-01

    An image formation framework for ultrasound imaging from synthetic transducer arrays based on sparsity-driven regularization functionals using single-frequency Fourier domain data is proposed. The framework involves the use of a physics-based forward model of the ultrasound observation process, the formulation of image formation as the solution of an associated optimization problem, and the solution of that problem through efficient numerical algorithms. The sparsity-driven, model-based approach estimates a complex-valued reflectivity field and preserves physical features in the scene while suppressing spurious artifacts. It also provides robust reconstructions in the case of sparse and reduced observation apertures. The effectiveness of the proposed imaging strategy is demonstrated using experimental data. PMID:22352501

  10. Gas-driven microturbine

    SciTech Connect

    Sniegowski, J.J.; Rodgers, M.S.; McWhorter, P.J.; Aeschliman, D.P.; Miller, W.M.

    1996-06-27

    This paper describes an invention which relates to microtechnology and the fabrication process for developing microelectrical systems. It describes a means for fabricating a gas-driven microturbine capable of providing autonomous propulsion in which the rapidly moving gases are directed through a micromachined turbine to power devices by direct linkage or turbo-electric generators components in a domain ranging from tenths of micrometers to thousands of micrometers.

  11. Data-Driven Objectness.

    PubMed

    Hongwen Kang; Hebert, Martial; Efros, Alexei A; Kanade, Takeo

    2015-01-01

    We propose a data-driven approach to estimate the likelihood that an image segment corresponds to a scene object (its "objectness") by comparing it to a large collection of example object regions. We demonstrate that when the application domain is known, for example, in our case activity of daily living (ADL), we can capture the regularity of the domain specific objects using millions of exemplar object regions. Our approach to estimating the objectness of an image region proceeds in two steps: 1) finding the exemplar regions that are the most similar to the input image segment; 2) calculating the objectness of the image segment by combining segment properties, mutual consistency across the nearest exemplar regions, and the prior probability of each exemplar region. In previous work, parametric objectness models were built from a small number of manually annotated objects regions, instead, our data-driven approach uses 5 million object regions along with their metadata information. Results on multiple data sets demonstrates our data-driven approach compared to the existing model based techniques. We also show the application of our approach in improving the performance of object discovery algorithms. PMID:26353218

  12. Driven superconducting quantum circuits

    NASA Astrophysics Data System (ADS)

    Nakamura, Yasunobu

    2014-03-01

    Driven nonlinear quantum systems show rich phenomena in various fields of physics. Among them, superconducting quantum circuits have very attractive features such as well-controlled quantum states with design flexibility, strong nonlinearity of Josephson junctions, strong coupling to electromagnetic driving fields, little internal dissipation, and tailored coupling to the electromagnetic environment. We have investigated properties and functionalities of driven superconducting quantum circuits. A transmon qubit coupled to a transmission line shows nearly perfect spatial mode matching between the incident and scattered microwave field in the 1D mode. Dressed states under a driving field are studied there and also in a semi-infinite 1D mode terminated by a resonator containing a flux qubit. An effective Λ-type three-level system is realized under an appropriate driving condition. It allows ``impedance-matched'' perfect absorption of incident probe photons and down conversion into another frequency mode. Finally, the weak signal from the qubit is read out using a Josephson parametric amplifier/oscillator which is another nonlinear circuit driven by a strong pump field. This work was partly supported by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST), Project for Developing Innovation Systems of MEXT, MEXT KAKENHI ``Quantum Cybernetics,'' and the NICT Commissioned Research.

  13. A compact high field magnetic force microscope.

    PubMed

    Zhou, Haibiao; Wang, Ze; Hou, Yubin; Lu, Qingyou

    2014-12-01

    We present the design and performance of a simple and compact magnetic force microscope (MFM), whose tip-sample coarse approach is implemented by the piezoelectric tube scanner (PTS) itself. In brief, a square rod shaft is axially spring-clamped on the inner wall of a metal tube which is glued inside the free end of the PTS. The shaft can thus be driven by the PTS to realize image scan and inertial stepping coarse approach. To enhance the inertial force, each of the four outer electrodes of the PTS is driven by an independent port of the controller. The MFM scan head is so compact that it can easily fit into the 52mm low temperature bore of a 20T superconducting magnet. The performance of the MFM is demonstrated by imaging a manganite thin film at low temperature and in magnetic fields up to 15T. PMID:25189114

  14. Dissipation and oscillatory solvation forces in confined liquids studied by small-amplitude atomic force spectroscopy.

    PubMed

    de Beer, Sissi; van den Ende, Dirk; Mugele, Frieder

    2010-08-13

    We determine conservative and dissipative tip-sample interaction forces from the amplitude and phase response of acoustically driven atomic force microscope (AFM) cantilevers using a non-polar model fluid (octamethylcyclotetrasiloxane, which displays strong molecular layering) and atomically flat surfaces of highly ordered pyrolytic graphite. Taking into account the base motion and the frequency-dependent added mass and hydrodynamic damping on the AFM cantilever, we develop a reliable force inversion procedure that allows for extracting tip-sample interaction forces for a wide range of drive frequencies. We systematically eliminate the effect of finite drive amplitudes. Dissipative tip-sample forces are consistent with the bulk viscosity down to a thickness of 2-3 nm. Dissipation measurements far below resonance, which we argue to be the most reliable, indicate the presence of peaks in the damping, corresponding to an enhanced 'effective' viscosity, upon expelling the last and second-last molecular layer. PMID:20639584

  15. Coalescence cascade of dissipative solitons in parametrically driven systems.

    PubMed

    Clerc, M G; Coulibaly, S; Gordillo, L; Mujica, N; Navarro, R

    2011-09-01

    Parametrically driven spatially extended systems exhibit uniform oscillations which are modulationally unstable. The resulting periodic state evolves to the creation of a gas of dissipative solitons. Driven by the interaction of dissipative solitons, the multisoliton state undergoes a cascade of coalescence processes, where the average soliton separation distance obeys a temporal self-similar law. Starting from the soliton pair interaction law, we have derived analytically and characterized the law of this multisoliton coarsening process. A comparison of numerical results obtained with different models such as the parametrically driven damped nonlinear Schrödinger equation, a vertically driven chain of pendula, and a parametrically forced magnetic wire, shows remarkable agreement. Both phenomena, the pair interaction law and the coarsening process, are also observed experimentally in a quasi-one-dimensional layer of Newtonian fluid which is oscillated vertically. PMID:22060473

  16. Volcanic forcing in decadal forecasts

    NASA Astrophysics Data System (ADS)

    Ménégoz, Martin; Doblas-Reyes, Francisco; Guemas, Virginie; Asif, Muhammad; Prodhomme, chloe

    2016-04-01

    Volcanic eruptions can significantly impact the climate system, by injecting large amounts of particles into the stratosphere. By reflecting backward the solar radiation, these particles cool the troposphere, and by absorbing the longwave radiation, they warm the stratosphere. As a consequence of this radiative forcing, the global mean surface temperature can decrease by several tenths of degrees. However, large eruptions are also associated to a complex dynamical response of the climate system that is particularly tricky do understand regarding the low number of available observations. Observations seem to show an increase of the positive phases of the Northern Atlantic Oscillation (NAO) the two winters following large eruptions, associated to positive temperature anomalies over the Eurasian continent. The summers following large eruptions are generally particularly cold, especially over the continents of the Northern Hemisphere. Overall, it is really challenging to forecast the climate response to large eruptions, as it is both modulated by, and superimposed to the climate background conditions, largely driven themselves by internal variability at seasonal to decadal scales. This work describes the additional skill of a forecast system used for seasonal and decadal predictions when it includes observed volcanic forcing over the last decades. An idealized volcanic forcing that could be used for real-time forecasts is also evaluated. This work consists in a base for forecasts that will be performed in the context of the next large volcanic eruption.

  17. Nanonet Force Microscopy for Measuring Cell Forces.

    PubMed

    Sheets, Kevin; Wang, Ji; Zhao, Wei; Kapania, Rakesh; Nain, Amrinder S

    2016-07-12

    The influence of physical forces exerted by or felt by cells on cell shape, migration, and cytoskeleton arrangement is now widely acknowledged and hypothesized to occur due to modulation of cellular inside-out forces in response to changes in the external fibrous environment (outside-in). Our previous work using the non-electrospinning Spinneret-based Tunable Engineered Parameters' suspended fibers has revealed that cells are able to sense and respond to changes in fiber curvature and structural stiffness as evidenced by alterations to focal adhesion cluster lengths. Here, we present the development and application of a suspended nanonet platform for measuring C2C12 mouse myoblast forces attached to fibers of three diameters (250, 400, and 800 nm) representing a wide range of structural stiffness (3-50 nN/μm). The nanonet force microscopy platform measures cell adhesion forces in response to symmetric and asymmetric external perturbation in single and cyclic modes. We find that contractility-based, inside-out forces are evenly distributed at the edges of the cell, and that forces are dependent on fiber structural stiffness. Additionally, external perturbation in symmetric and asymmetric modes biases cell-fiber failure location without affecting the outside-in forces of cell-fiber adhesion. We then extend the platform to measure forces of (1) cell-cell junctions, (2) single cells undergoing cyclic perturbation in the presence of drugs, and (3) cancerous single-cells transitioning from a blebbing to a pseudopodial morphology. PMID:27410747

  18. Drag in a resonantly driven polariton fluid

    NASA Astrophysics Data System (ADS)

    Berceanu, A. C.; Cancellieri, E.; Marchetti, F. M.

    2012-06-01

    We study the linear response of a coherently driven polariton fluid in the pump-only configuration scattering against a point-like defect and evaluate analytically the drag force exerted by the fluid on the defect. When the system is excited near the bottom of the lower polariton dispersion, the sign of the interaction-renormalised pump detuning classifies the collective excitation spectra into three different categories (Ciuti and Carusotto 2005 Phys. Status Solidi b 242 2224): linear for zero, diffusive-like for positive and gapped for negative detuning. We show that both cases of zero and positive detuning share a qualitatively similar crossover of the drag force from the subsonic to the supersonic regime as a function of the fluid velocity, with a critical velocity given by the speed of sound found for the linear regime. In contrast, for gapped spectra, we find that the critical velocity exceeds the speed of sound. In all cases, the residual drag force in the subcritical regime depends on the polariton lifetime only. Also, well below the critical velocity, the drag force varies linearly with the polariton lifetime, in agreement with previous work (Cancellieri et al 2010 Phys. Rev. B 82 224512), where the drag was determined numerically for a finite-size defect.

  19. Drag in a resonantly driven polariton fluid.

    PubMed

    Berceanu, A C; Cancellieri, E; Marchetti, F M

    2012-06-13

    We study the linear response of a coherently driven polariton fluid in the pump-only configuration scattering against a point-like defect and evaluate analytically the drag force exerted by the fluid on the defect. When the system is excited near the bottom of the lower polariton dispersion, the sign of the interaction-renormalised pump detuning classifies the collective excitation spectra into three different categories (Ciuti and Carusotto 2005 Phys. Status Solidi b 242 2224): linear for zero, diffusive-like for positive and gapped for negative detuning. We show that both cases of zero and positive detuning share a qualitatively similar crossover of the drag force from the subsonic to the supersonic regime as a function of the fluid velocity, with a critical velocity given by the speed of sound found for the linear regime. In contrast, for gapped spectra, we find that the critical velocity exceeds the speed of sound. In all cases, the residual drag force in the subcritical regime depends on the polariton lifetime only. Also, well below the critical velocity, the drag force varies linearly with the polariton lifetime, in agreement with previous work (Cancellieri et al 2010 Phys. Rev. B 82 224512), where the drag was determined numerically for a finite-size defect.

  20. Chemically Driven Hydrodynamic Instabilities

    NASA Astrophysics Data System (ADS)

    Almarcha, C.; Trevelyan, P. M. J.; Grosfils, P.; de Wit, A.

    2010-01-01

    In the gravity field, density changes triggered by a kinetic scheme as simple as A+B→C can induce or affect buoyancy-driven instabilities at a horizontal interface between two solutions containing initially the scalars A and B. On the basis of a general reaction-diffusion-convection model, we analyze to what extent the reaction can destabilize otherwise buoyantly stable density stratifications. We furthermore show that, even if the underlying nonreactive system is buoyantly unstable, the reaction breaks the symmetry of the developing patterns. This is demonstrated both numerically and experimentally on the specific example of a simple acid-base neutralization reaction.

  1. System Driven Workarounds

    NASA Technical Reports Server (NTRS)

    Connell, Linda; Wichner, David; Jakey, Abegael Marie

    2013-01-01

    The Aviation Safety Reporting System (ASRS) in a partnership between the National Aeronautics and Space Administration (NASA), the Federal Aviation Administration (FAA), participating carriers, and labor organizations. It is designed to improve the National Airspace System by collecting and studying reports detailing unsafe conditions and events in the aviation industry. Employees are able to report safety issues or concerns with confidentiality and without fear of discipline. Safety reports highlighting system driven workarounds for the aviation community highlight the human workaround for the complex aviation system.

  2. Dissipative adaptation in driven self-assembly

    NASA Astrophysics Data System (ADS)

    England, Jeremy L.

    2015-11-01

    In a collection of assembling particles that is allowed to reach thermal equilibrium, the energy of a given microscopic arrangement and the probability of observing the system in that arrangement obey a simple exponential relationship known as the Boltzmann distribution. Once the same thermally fluctuating particles are driven away from equilibrium by forces that do work on the system over time, however, it becomes significantly more challenging to relate the likelihood of a given outcome to familiar thermodynamic quantities. Nonetheless, it has long been appreciated that developing a sound and general understanding of the thermodynamics of such non-equilibrium scenarios could ultimately enable us to control and imitate the marvellous successes that living things achieve in driven self-assembly. Here, I suggest that such a theoretical understanding may at last be emerging, and trace its development from historic first steps to more recent discoveries. Focusing on these newer results, I propose that they imply a general thermodynamic mechanism for self-organization via dissipation of absorbed work that may be applicable in a broad class of driven many-body systems.

  3. Magnetic Control of Solutal Buoyancy Driven Convection

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.; Leslie, F. W.

    2003-01-01

    Volumetric forces resulting from local density variations and gravitational acceleration cause buoyancy induced convective motion in melts and solutions. Solutal buoyancy is a result of concentration differences in an otherwise isothermal fluid. If the fluid also exhibits variations in magnetic susceptibility with concentration then convection control by external magnetic fields can be hypothesized. Magnetic control of thermal buoyancy induced convection in ferrofluids (dispersions of ferromagnetic particles in a carrier fluid) and paramagnetic fluids have been demonstrated. Here we show the nature of magnetic control of solutal buoyancy driven convection of a paramagnetic fluid, an aqueous solution of Manganese Chloride hydrate. We predict the critical magnetic field required for balancing gravitational solutal buoyancy driven convection and validate it through a simple experiment. We demonstrate that gravity driven flow can be completely reversed by a magnetic field but the exact cancellation of the flow is not possible. This is because the phenomenon is unstable. The technique can be applied to crystal growth processes in order to reduce convection and to heat exchanger devices for enhancing convection. The method can also be applied to impose a desired g-level in reduced gravity applications.

  4. Micro-force sensing mobile microrobots

    NASA Astrophysics Data System (ADS)

    Jing, Wuming; Cappelleri, David J.

    2015-06-01

    This paper presents the first microscale micro force sensing mobile microrobot. The design consists of a planar, vision-based micro force sensor end-effector, while the microrobot body is made from photoresist mixed with nickel particles that is driven by an exterior magnetic field. With a known stiffness, the manipulation forces can be determined from observing the deformation of the end-effector through a camera attached to an optical microscope. After analyzing and calibrating the stiffness of a micromachined prototype, proof of concept tests are conducted to verify this microrobot prototype possessing the mobility and in-situ force sensing capabilities. This microscale micro-Force Sensing Mobile Microrobot (μFSMM) is able to translate with the speed up to 10 mm=s in a fluid environment. The calibrated stiffness of the micro force sensor end-effector of the μFSMM is on the order of 10-2 N=m. The force sensing resolution with the current vision system is approximately 100 nN.

  5. Lorentz Body Force Induced by Traveling Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Volz, M. P.; Mazuruk, K.

    2003-01-01

    The Lorentz force induced by a traveling magnetic field (TMF) in a cylindrical container has been calculated. The force can be used to control flow in dectrically conducting melts and the direction of the magnetic field and resulting flow can be reversed. A TMF can be used to partially cancel flow driven by buoyancy. The penetration of the field into the cylinder decreases as the frequency increases, and there exists an optimal value of frequency for which the resulting force is a maximum. Expressions for the Lorentz force in the limiting cases of low frequency and infinite cylinder are also given and compared to the numerical calculations.

  6. Phase contrast and operation regimes in multifrequency atomic force microscopy

    SciTech Connect

    Santos, Sergio

    2014-04-07

    In amplitude modulation atomic force microscopy the attractive and the repulsive force regimes induce phase shifts above and below 90°, respectively. In the more recent multifrequency approach, however, multiple operation regimes have been reported and the theory should be revisited. Here, a theory of phase contrast in multifrequency atomic force microscopy is developed and discussed in terms of energy transfer between modes, energy dissipation and the kinetic energy and energy transfer associated with externally driven harmonics. The single frequency virial that controls the phase shift might undergo transitions in sign while the average force (modal virial) remains positive (negative)

  7. Forced wetting and hydrodynamic assist

    NASA Astrophysics Data System (ADS)

    Blake, Terence D.; Fernandez-Toledano, Juan-Carlos; Doyen, Guillaume; De Coninck, Joël

    2015-11-01

    Wetting is a prerequisite for coating a uniform layer of liquid onto a solid. Wetting failure and air entrainment set the ultimate limit to coating speed. It is well known in the coating art that this limit can be postponed by manipulating the coating flow to generate what has been termed "hydrodynamic assist," but the underlying mechanism is unclear. Experiments have shown that the conditions that postpone air entrainment also reduce the apparent dynamic contact angle, suggesting a direct link, but how the flow might affect the contact angle remains to be established. Here, we use molecular dynamics to compare the outcome of steady forced wetting with previous results for the spontaneous spreading of liquid drops and apply the molecular-kinetic theory of dynamic wetting to rationalize our findings and place them on a quantitative footing. The forced wetting simulations reveal significant slip at the solid-liquid interface and details of the flow immediately adjacent to the moving contact line. Our results confirm that the local, microscopic contact angle is dependent not simply only on the velocity of wetting but also on the nature of the flow that drives it. In particular, they support an earlier suggestion that during forced wetting, an intense shear stress in the vicinity of the contact line can assist surface tension forces in promoting dynamic wetting, thus reducing the velocity-dependence of the contact angle. Hydrodynamic assist then appears as a natural consequence of wetting that emerges when the contact line is driven by a strong and highly confined flow. Our theoretical approach also provides a self-consistent model of molecular slip at the solid-liquid interface that enables its magnitude to be estimated from dynamic contact angle measurements. In addition, the model predicts how hydrodynamic assist and slip may be influenced by liquid viscosity and solid-liquid interactions.

  8. Ultrasensitive hysteretic force sensing with parametric nonlinear oscillators.

    PubMed

    Papariello, Luca; Zilberberg, Oded; Eichler, Alexander; Chitra, R

    2016-08-01

    We propose a method for linear detection of weak forces using parametrically driven nonlinear resonators. The method is based on a peculiar feature in the response of the resonator to a near resonant periodic external force. This feature stems from a complex interplay among the parametric drive, external force, and nonlinearities. For weak parametric drive, the response exhibits the standard Duffing-like single jump hysteresis. For stronger drive amplitudes, we find a qualitatively new double jump hysteresis which arises from stable solutions generated by the cubic Duffing nonlinearity. The additional jump exists only if the external force is present and the frequency at which it occurs depends linearly on the amplitude of the external force, permitting a straightforward ultrasensitive detection of weak forces. With state-of-the-art nanomechanical resonators, our scheme should permit force detection in the attonewton range. PMID:27627292

  9. Collisional effects on nonlinear ion drag force for small grains

    SciTech Connect

    Hutchinson, I. H.; Haakonsen, C. B.

    2013-08-15

    The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

  10. Ultrasensitive hysteretic force sensing with parametric nonlinear oscillators

    NASA Astrophysics Data System (ADS)

    Papariello, Luca; Zilberberg, Oded; Eichler, Alexander; Chitra, R.

    2016-08-01

    We propose a method for linear detection of weak forces using parametrically driven nonlinear resonators. The method is based on a peculiar feature in the response of the resonator to a near resonant periodic external force. This feature stems from a complex interplay among the parametric drive, external force, and nonlinearities. For weak parametric drive, the response exhibits the standard Duffing-like single jump hysteresis. For stronger drive amplitudes, we find a qualitatively new double jump hysteresis which arises from stable solutions generated by the cubic Duffing nonlinearity. The additional jump exists only if the external force is present and the frequency at which it occurs depends linearly on the amplitude of the external force, permitting a straightforward ultrasensitive detection of weak forces. With state-of-the-art nanomechanical resonators, our scheme should permit force detection in the attonewton range.

  11. Market Driven Space Exploration

    NASA Astrophysics Data System (ADS)

    Gavert, Raymond B.

    2004-02-01

    Market driven space exploration will have the opportunity to develop to new levels with the coming of space nuclear power and propulsion. NASA's recently established Prometheus program is expected to receive several billion dollars over the next five years for developing nuclear power and propulsion systems for future spacecraft. Not only is nuclear power and propulsion essential for long distance Jupiter type missions, but it also important for providing greater access to planets and bodies nearer to the Earth. NASA has been working with industrial partners since 1987 through its Research Partnerships Centers (RPCs) to utilize the attributes of space in Low Earth Orbit (LEO). Plans are now being made to utilize the RPCs and industrial partners in extending the duration and boundaries of human space flight to create new opportunities for exploration and discovery. Private investors are considering setting up shops in LEO for commercial purposes. The trend is for more industrial involvement in space. Nuclear power and propulsion will hasten the progress. The objective of this paper is to show the progression of space market driven research and its potential for supporting space exploration given nuclear power and propulsion capabilities.

  12. THERMALLY DRIVEN ATMOSPHERIC ESCAPE

    SciTech Connect

    Johnson, Robert E.

    2010-06-20

    Accurately determining the escape rate from a planet's atmosphere is critical for determining its evolution. A large amount of Cassini data is now available for Titan's upper atmosphere and a wealth of data is expected within the next decade on escape from Pluto, Mars, and extra-solar planets. Escape can be driven by upward thermal conduction of energy deposited well below the exobase, as well as by nonthermal processes produced by energy deposited in the exobase region. Recent applications of a model for escape driven by upward thermal conduction, called the slow hydrodynamic escape model, have resulted in surprisingly large loss rates for the atmosphere of Titan, Saturn's largest moon. Based on a molecular kinetic simulation of the exobase region, these rates appear to be orders of magnitude too large. Therefore, the slow hydrodynamic model is evaluated here. It is shown that such a model cannot give a reliable description of the atmospheric temperature profile unless it is coupled to a molecular kinetic description of the exobase region. Therefore, the present escape rates for Titan and Pluto must be re-evaluated using the atmospheric model described here.

  13. Forced obliquity variations of Mercury

    NASA Astrophysics Data System (ADS)

    Bills, Bruce G.; Comstock, Robert L.

    2005-04-01

    The spin pole of Mercury is very nearly, but not quite, aligned with its orbit pole. Tidal dissipation has driven the free obliquity to very small values, and the high rate of spin pole precession allows the forced obliquity variations to remain small despite significant variations in orbital inclination and eccentricity. We present calculations of the obliquity for a 10 million year time span, centered on the present. The obliquity remains small, with typical values of 2-4 minutes of arc. The dominant period of obliquity oscillations is 895 kyr, which is also the main period at which the orbital inclination varies. If the orbit pole precession rate were uniform, dissipation would have driven Mercury into a Cassini state, in which the spin pole and orbit pole remain coplanar with the invariable pole, as the spin pole precesses about the moving orbit pole. However, due to the nonuniform orbit precession rate, this simple coplanar configuration is not maintained, except on a mode-by-mode basis. That is, when the orbit pole motion is represented as a sum of normal modes of the coupled oscillations of the planetary system, the spin pole coprecesses with the orbit pole at each modal frequency. This is a generalization of Cassini's second and third laws of lunar rotation to the case of nonuniform orbit precession. We compare results of a linearized obliquity model with a numerical integration of the equations of motion. The two solutions agree at the level of a few seconds of arc.

  14. Force propagation and force generation in cells.

    PubMed

    Jonas, Oliver; Duschl, Claus

    2010-09-01

    Determining how forces are produced by and propagated through the cytoskeleton (CSK) of the cell is of great interest as dynamic processes of the CSK are intimately correlated with many molecular signaling pathways. We are presenting a novel approach for integrating measurements on cell elasticity, transcellular force propagation, and cellular force generation to obtain a comprehensive description of dynamic and mechanical properties of the CSK under force loading. This approach uses a combination of scanning force microscopy (SFM) and Total Internal Reflection Fluorescence (TIRF) microscopy. We apply well-defined loading schemes onto the apical cell membrane of fibroblasts using the SFM and simultaneously use TIRF microscopy to image the topography of the basal cell membrane. The locally distinct changes of shape and depth of the cytoskeletal imprints onto the basal membrane are interpreted as results of force propagation through the cytoplasm. This observation provides evidence for the tensegrity model and demonstrates the usefulness of our approach that does not depend on potentially disturbing marker compounds. We confirm that the actin network greatly determines cell stiffness and represents the substrate that mediates force transduction through the cytoplasm of the cell. The latter is an essential feature of tensegrity. Most importantly, our new finding that, both intact actin and microtubule networks are required for enabling the cell to produce work, can only be understood within the framework of the tensegrity model. We also provide, for the first time, a direct measurement of the cell's mechanical power output under compression at two femtowatts. PMID:20607861

  15. Six axis force feedback input device

    NASA Technical Reports Server (NTRS)

    Ohm, Timothy (Inventor)

    1998-01-01

    The present invention is a low friction, low inertia, six-axis force feedback input device comprising an arm with double-jointed, tendon-driven revolute joints, a decoupled tendon-driven wrist, and a base with encoders and motors. The input device functions as a master robot manipulator of a microsurgical teleoperated robot system including a slave robot manipulator coupled to an amplifier chassis, which is coupled to a control chassis, which is coupled to a workstation with a graphical user interface. The amplifier chassis is coupled to the motors of the master robot manipulator and the control chassis is coupled to the encoders of the master robot manipulator. A force feedback can be applied to the input device and can be generated from the slave robot to enable a user to operate the slave robot via the input device without physically viewing the slave robot. Also, the force feedback can be generated from the workstation to represent fictitious forces to constrain the input device's control of the slave robot to be within imaginary predetermined boundaries.

  16. Stochastic regimes in the driven oscillator with a step-like nonlinearity

    SciTech Connect

    Bulanov, S. V.; Esirkepov, T. Zh.; Koga, J. K.; Kondo, K.; Kando, M.; Yogo, A.; Bulanov, S. S.

    2015-06-15

    A nonlinear oscillator with an abruptly inhomogeneous restoring force driven by an uniform oscillating force exhibits stochastic properties under specific resonance conditions. This behaviour elucidates the elementary mechanism of the electron energization in the strong electromagnetic wave interaction with thin targets.

  17. Aerodynamic Lifting Force.

    ERIC Educational Resources Information Center

    Weltner, Klaus

    1990-01-01

    Describes some experiments showing both qualitatively and quantitatively that aerodynamic lift is a reaction force. Demonstrates reaction forces caused by the acceleration of an airstream and the deflection of an airstream. Provides pictures of demonstration apparatus and mathematical expressions. (YP)

  18. Climate-driven regime shift of a temperate marine ecosystem.

    PubMed

    Wernberg, Thomas; Bennett, Scott; Babcock, Russell C; de Bettignies, Thibaut; Cure, Katherine; Depczynski, Martial; Dufois, Francois; Fromont, Jane; Fulton, Christopher J; Hovey, Renae K; Harvey, Euan S; Holmes, Thomas H; Kendrick, Gary A; Radford, Ben; Santana-Garcon, Julia; Saunders, Benjamin J; Smale, Dan A; Thomsen, Mads S; Tuckett, Chenae A; Tuya, Fernando; Vanderklift, Mathew A; Wilson, Shaun

    2016-07-01

    Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests. PMID:27387951

  19. Liquid mixing driven motions of floating macroscopic objects

    NASA Astrophysics Data System (ADS)

    Su, Ming

    2007-04-01

    Dropping miscible and low-density organic solvents into water generates translational and rotational motions of floating objects including oil droplets, polymer half spheres, and model boats. The moving speed of the boat at different loads and the force produced by solvent drops are measured. In contrast to motions driven by surface tension of monolayer, the liquid mixing driven motion can be dynamically steered without restriction and continued provided the supply is maintained and the amount of water is large enough. Such motions are the result of Marangoni instability in binary liquid-liquid systems with intentionally produced concentration gradients behind the floating objects.

  20. Climate-driven regime shift of a temperate marine ecosystem.

    PubMed

    Wernberg, Thomas; Bennett, Scott; Babcock, Russell C; de Bettignies, Thibaut; Cure, Katherine; Depczynski, Martial; Dufois, Francois; Fromont, Jane; Fulton, Christopher J; Hovey, Renae K; Harvey, Euan S; Holmes, Thomas H; Kendrick, Gary A; Radford, Ben; Santana-Garcon, Julia; Saunders, Benjamin J; Smale, Dan A; Thomsen, Mads S; Tuckett, Chenae A; Tuya, Fernando; Vanderklift, Mathew A; Wilson, Shaun

    2016-07-01

    Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests.

  1. Optically driven actuators using poly(vinylidene difluoride)

    NASA Astrophysics Data System (ADS)

    Mizutani, Yasuhiro; Otani, Yukitoshi; Umeda, Norihiro

    2008-05-01

    Optically driven actuators have a feature of a non-contact method supplied by light energy. A new method is proposed with three poly(vinylidene difluoride) (PVDF) cantilevers as the legs and a polymer film as the body. The PVDF cantilevers are coated with silver on one surface. When one side of the cantilever is irradiated by a laser beam, an electric field is produced along a cross-section of the cantilever by the pyroelectric effect and a mechanical displacement occurs by the piezoelectric effect. Its response time and its generated force are measured experimentally. Two types of optically driven actuators using PVDF film are proposed to move using different characteristics.

  2. Dynamo Driven By Inertial Instabilities, Application to the Moon

    NASA Astrophysics Data System (ADS)

    Cebron, D.; Hollerbach, R.; Vantieghem, S.; Noir, J.; Schaeffer, N.

    2014-12-01

    Large-scale planetary or stellar magnetic fields generated by a dynamo effect are mostly attributed to flows forced by buoyancy forces in electrically conducting fluid layers. However, large-scale, turbulent flows may also be driven by the combined action of boundary topography (i.e. departure from spherical geometry), and mechanical forcings (e.g. libration, tides). This has been previously proposed to explain the magnetic data we have on the star τ-boo, Mars, or the early Moon. In this work, we use theoretical analysis and global magneto-hydrodynamic simulations to show, for the first time, that: (i) the tidal forcing can generate a (dipole-dominated) large-scale magnetic field in global simulations, an hypothesis previously assumed by Le Bars et al. (2011) in their model of lunar magnetic history. (ii) latitudinal libration (i.e. an oscillation of the figure axis with respect to the mean rotation axis) can excite inertial instabilities, which may have driven dynamos in telluric bodies such as the Early Moon. We discuss our results in the light of magnetic observations. In particular, we propose here a new possible mechanism for the early Moon dynamo, based on latitudinal libration driven instabilities. This new scenario is evaluated by comparing the associated estimates of the surface magnetic field strength with the recent paleo-magnetic lunar measurements.

  3. Microprocessor controlled force actuator

    NASA Technical Reports Server (NTRS)

    Zimmerman, D. C.; Inman, D. J.; Horner, G. C.

    1986-01-01

    The mechanical and electrical design of a prototype force actuator for vibration control of large space structures (LSS) is described. The force actuator is an electromagnetic system that produces a force by reacting against a proof-mass. The actuator has two colocated sensors, a digital microcontroller, and a power amplifier. The total weight of actuator is .998 kg. The actuator has a steady state force output of approximately 2.75 N from approximately 2 Hz to well beyond 1000 Hz.

  4. Fluid force transducer

    DOEpatents

    Jendrzejczyk, Joseph A.

    1982-01-01

    An electrical fluid force transducer for measuring the magnitude and direction of fluid forces caused by lateral fluid flow, includes a movable sleeve which is deflectable in response to the movement of fluid, and a rod fixed to the sleeve to translate forces applied to the sleeve to strain gauges attached to the rod, the strain gauges being connected in a bridge circuit arrangement enabling generation of a signal output indicative of the magnitude and direction of the force applied to the sleeve.

  5. Steady Capillary Driven Flow

    NASA Technical Reports Server (NTRS)

    Weislogel, Mark M.

    1996-01-01

    A steady capillary driven flow is developed for a liquid index in a circular tube which is partially coated with a surface modifier to produce a discontinuous wetting condition from one side of the tube to the other. The bulk flow is novel in that it is truly steady, and controlled solely by the physics associated with dynamic wetting. The influence of gravity on the flow is minimized through the use of small diameter tubes approximately O(1 mm) tested horizontally in a laboratory and larger tubes approximately O(10 mm) tested in the low gravity environment of a drop tower. Average steady velocities are predicted and compared against a large experimental data set which includes the effects of tube dimensions and fluid properties. The sensitivity of the velocity to surface cleanliness is dramatic and the advantages of experimentation in a microgravity environment are discussed.

  6. Muscle-driven nanogenerators

    DOEpatents

    Wang, Zhong L.; Yang, Rusen

    2011-03-01

    In a method of generating electricity, a plurality of living cells are grown on an array of piezoelectric nanowires so that the cells engage the piezoelectric nanowires. Induced static potentials are extracted from at least one of the piezoelectric nanowires when at least one of the cells deforms the at least one of the piezoelectric nanowires. A cell-driven electrical generator that includes a substrate and a plurality of spaced-apart piezoelectric nanowires disposed on the substrate. A plurality of spaced-apart conductive electrodes interact with the plurality of piezoelectric nanowires. A biological buffer layer that is configured to promote growth of cells is disposed on the substrate so that cells placed on the substrate will grow and engage the piezoelectric nanowires.

  7. Soliton driven angiogenesis

    PubMed Central

    Bonilla, L. L.; Carretero, M.; Terragni, F.; Birnir, B.

    2016-01-01

    Angiogenesis is a multiscale process by which blood vessels grow from existing ones and carry oxygen to distant organs. Angiogenesis is essential for normal organ growth and wounded tissue repair but it may also be induced by tumours to amplify their own growth. Mathematical and computational models contribute to understanding angiogenesis and developing anti-angiogenic drugs, but most work only involves numerical simulations and analysis has lagged. A recent stochastic model of tumour-induced angiogenesis including blood vessel branching, elongation, and anastomosis captures some of its intrinsic multiscale structures, yet allows one to extract a deterministic integropartial differential description of the vessel tip density. Here we find that the latter advances chemotactically towards the tumour driven by a soliton (similar to the famous Korteweg-de Vries soliton) whose shape and velocity change slowly. Analysing these collective coordinates paves the way for controlling angiogenesis through the soliton, the engine that drives this process. PMID:27503562

  8. Soliton driven angiogenesis

    NASA Astrophysics Data System (ADS)

    Bonilla, L. L.; Carretero, M.; Terragni, F.; Birnir, B.

    2016-08-01

    Angiogenesis is a multiscale process by which blood vessels grow from existing ones and carry oxygen to distant organs. Angiogenesis is essential for normal organ growth and wounded tissue repair but it may also be induced by tumours to amplify their own growth. Mathematical and computational models contribute to understanding angiogenesis and developing anti-angiogenic drugs, but most work only involves numerical simulations and analysis has lagged. A recent stochastic model of tumour-induced angiogenesis including blood vessel branching, elongation, and anastomosis captures some of its intrinsic multiscale structures, yet allows one to extract a deterministic integropartial differential description of the vessel tip density. Here we find that the latter advances chemotactically towards the tumour driven by a soliton (similar to the famous Korteweg-de Vries soliton) whose shape and velocity change slowly. Analysing these collective coordinates paves the way for controlling angiogenesis through the soliton, the engine that drives this process.

  9. Consistent model driven architecture

    NASA Astrophysics Data System (ADS)

    Niepostyn, Stanisław J.

    2015-09-01

    The goal of the MDA is to produce software systems from abstract models in a way where human interaction is restricted to a minimum. These abstract models are based on the UML language. However, the semantics of UML models is defined in a natural language. Subsequently the verification of consistency of these diagrams is needed in order to identify errors in requirements at the early stage of the development process. The verification of consistency is difficult due to a semi-formal nature of UML diagrams. We propose automatic verification of consistency of the series of UML diagrams originating from abstract models implemented with our consistency rules. This Consistent Model Driven Architecture approach enables us to generate automatically complete workflow applications from consistent and complete models developed from abstract models (e.g. Business Context Diagram). Therefore, our method can be used to check practicability (feasibility) of software architecture models.

  10. Soliton driven angiogenesis.

    PubMed

    Bonilla, L L; Carretero, M; Terragni, F; Birnir, B

    2016-01-01

    Angiogenesis is a multiscale process by which blood vessels grow from existing ones and carry oxygen to distant organs. Angiogenesis is essential for normal organ growth and wounded tissue repair but it may also be induced by tumours to amplify their own growth. Mathematical and computational models contribute to understanding angiogenesis and developing anti-angiogenic drugs, but most work only involves numerical simulations and analysis has lagged. A recent stochastic model of tumour-induced angiogenesis including blood vessel branching, elongation, and anastomosis captures some of its intrinsic multiscale structures, yet allows one to extract a deterministic integropartial differential description of the vessel tip density. Here we find that the latter advances chemotactically towards the tumour driven by a soliton (similar to the famous Korteweg-de Vries soliton) whose shape and velocity change slowly. Analysing these collective coordinates paves the way for controlling angiogenesis through the soliton, the engine that drives this process. PMID:27503562

  11. Estimates of biomechanical forces in Magnaporthe grisea.

    PubMed

    Goriely, Alain; Tabor, Michael

    2006-07-01

    The mechanical actions of the fungus Magnaporthe grisea raise many intriguing questions concerning the forces involved. These include: (1) the material properties of the appressorial wall; (2) the strength of the adhesive that keeps the appressorium anchored to the rice leaf surface; and (3) the forces involved in the penetration process whereby a peg is driven through the host cell wall. In this paper we give order of magnitude estimates for all three of these quantities. A simple Young-Laplace law type argument is used to show that the appressorial wall elastic modulus is of order 10-100 MPa; and an adaptation of standard adhesion theory indicates a lower bound on the strength of the appressorial adhesive to be of the order 500 J/m(2). Drawing on ideas from plasticity theory and ballistics, estimates of the penetration force raise interesting questions about experiments performed on the penetration of inert substrates by the fungus.

  12. Forces in General Relativity

    ERIC Educational Resources Information Center

    Ridgely, Charles T.

    2010-01-01

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

  13. Turkish Students' Force Meanings

    ERIC Educational Resources Information Center

    Menekse, Muhsin; Clark, Douglas B.; Ozdemir, Gokhan; D'angelo, Cynthia; Scheligh, Sharon

    2009-01-01

    What are Turkish pre, elementary, middle, and high school students' force ideas? And, how do Turkish students' non-normative force ideas differ or be similar to the well-known force misconceptions reported in the literature? Students have false and persistent beliefs about the physical world and they struggle with challenging misconceptions based…

  14. Debunking Coriolis Force Myths

    ERIC Educational Resources Information Center

    Shakur, Asif

    2014-01-01

    Much has been written and debated about the Coriolis force. Unfortunately, this has done little to demystify the paradoxes surrounding this fictitious force invoked by an observer in a rotating frame of reference. It is the purpose of this article to make another valiant attempt to slay the dragon of the Coriolis force! This will be done without…

  15. Crossflow force transducer. [LMFBR

    SciTech Connect

    Mulcahy, T M

    1982-05-01

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

  16. Effect of Forcing Function on Nonlinear Acoustic Standing Waves

    NASA Technical Reports Server (NTRS)

    Finkheiner, Joshua R.; Li, Xiao-Fan; Raman, Ganesh; Daniels, Chris; Steinetz, Bruce

    2003-01-01

    Nonlinear acoustic standing waves of high amplitude have been demonstrated by utilizing the effects of resonator shape to prevent the pressure waves from entering saturation. Experimentally, nonlinear acoustic standing waves have been generated by shaking an entire resonating cavity. While this promotes more efficient energy transfer than a piston-driven resonator, it also introduces complicated structural dynamics into the system. Experiments have shown that these dynamics result in resonator forcing functions comprised of a sum of several Fourier modes. However, previous numerical studies of the acoustics generated within the resonator assumed simple sinusoidal waves as the driving force. Using a previously developed numerical code, this paper demonstrates the effects of using a forcing function constructed with a series of harmonic sinusoidal waves on resonating cavities. From these results, a method will be demonstrated which allows the direct numerical analysis of experimentally generated nonlinear acoustic waves in resonators driven by harmonic forcing functions.

  17. Varying the effective buoyancy of cells using magnetic force

    NASA Astrophysics Data System (ADS)

    Guevorkian, Karine; Valles, James M.

    2004-06-01

    We introduce a magnetic force buoyancy variation (MFBV) technique that employs intense inhomogeneous magnetic fields to vary the effective buoyancy of cells and other diamagnetic systems in solution. Nonswimming Paramecia have been suspended, forced to sediment and driven to rise in solution using MFBV. Details of their response to MFBV have been used to determine the magnetic susceptibility of a single Paramecium. The use of MFBV as a means by which to suspend cell cultures indefinitely is also described.

  18. Efficacy of climate forcings

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Sato, M.; Ruedy, R.; Nazarenko, L.; Lacis, A.; Schmidt, G. A.; Russell, G.; Aleinov, I.; Bauer, M.; Bauer, S.; Bell, N.; Cairns, B.; Canuto, V.; Chandler, M.; Cheng, Y.; Del Genio, A.; Faluvegi, G.; Fleming, E.; Friend, A.; Hall, T.; Jackman, C.; Kelley, M.; Kiang, N.; Koch, D.; Lean, J.; Lerner, J.; Lo, K.; Menon, S.; Miller, R.; Minnis, P.; Novakov, T.; Oinas, V.; Perlwitz, Ja.; Perlwitz, Ju.; Rind, D.; Romanou, A.; Shindell, D.; Stone, P.; Sun, S.; Tausnev, N.; Thresher, D.; Wielicki, B.; Wong, T.; Yao, M.; Zhang, S.

    2005-09-01

    We use a global climate model to compare the effectiveness of many climate forcing agents for producing climate change. We find a substantial range in the "efficacy" of different forcings, where the efficacy is the global temperature response per unit forcing relative to the response to CO2 forcing. Anthropogenic CH4 has efficacy ˜110%, which increases to ˜145% when its indirect effects on stratospheric H2O and tropospheric O3 are included, yielding an effective climate forcing of ˜0.8 W/m2 for the period 1750-2000 and making CH4 the largest anthropogenic climate forcing other than CO2. Black carbon (BC) aerosols from biomass burning have a calculated efficacy ˜58%, while fossil fuel BC has an efficacy ˜78%. Accounting for forcing efficacies and for indirect effects via snow albedo and cloud changes, we find that fossil fuel soot, defined as BC + OC (organic carbon), has a net positive forcing while biomass burning BC + OC has a negative forcing. We show that replacement of the traditional instantaneous and adjusted forcings, Fi and Fa, with an easily computed alternative, Fs, yields a better predictor of climate change, i.e., its efficacies are closer to unity. Fs is inferred from flux and temperature changes in a fixed-ocean model run. There is remarkable congruence in the spatial distribution of climate change, normalized to the same forcing Fs, for most climate forcing agents, suggesting that the global forcing has more relevance to regional climate change than may have been anticipated. Increasing greenhouse gases intensify the Hadley circulation in our model, increasing rainfall in the Intertropical Convergence Zone (ITCZ), Eastern United States, and East Asia, while intensifying dry conditions in the subtropics including the Southwest United States, the Mediterranean region, the Middle East, and an expanding Sahel. These features survive in model simulations that use all estimated forcings for the period 1880-2000. Responses to localized forcings, such

  19. Cell adhesion force microscopy

    PubMed Central

    Sagvolden, G.; Giaever, I.; Pettersen, E. O.; Feder, J.

    1999-01-01

    The adhesion forces of cervical carcinoma cells in tissue culture were measured by using the manipulation force microscope, a novel atomic force microscope. The forces were studied as a function of time and temperature for cells cultured on hydrophilic and hydrophobic polystyrene substrates with preadsorbed proteins. The cells attached faster and stronger at 37°C than at 23°C and better on hydrophilic than on hydrophobic substrates, even though proteins adsorb much better to the hydrophobic substrates. Because cell adhesion serves to control several stages in the cell cycle, we anticipate that the manipulation force microscope can help clarify some cell-adhesion related issues. PMID:9892657

  20. Shear-Driven Reconnection in Kinetic Models

    NASA Astrophysics Data System (ADS)

    Black, C.; Antiochos, S. K.; Germaschewski, K.; Karpen, J. T.; DeVore, C. R.; Bessho, N.

    2015-12-01

    The explosive energy release in solar eruptive phenomena is believed to be due to magnetic reconnection. In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field countered by a downward tension due to overlying unsheared field. Magnetic reconnection disrupts this force balance; therefore, it is critical for understanding CME/flare initiation, to model the onset of reconnection driven by the build-up of magnetic shear. In MHD simulations, the application of a magnetic-field shear is a trivial matter. However, kinetic effects are dominant in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is challenging, however, and indicates the necessity of a true multiscale model for such processes in the solar environment. The field must be sheared self-consistently and indirectly to prevent the generation of waves that destroy the desired system. Plasma instabilities can arise nonetheless. In the work presented here, we show that we can control this instability and generate a predicted out-of-plane magnetic flux. This material is based upon work supported by the National Science Foundation under Award No. AGS-1331356.

  1. Hydrodynamically driven colloidal assembly in dip coating.

    PubMed

    Colosqui, Carlos E; Morris, Jeffrey F; Stone, Howard A

    2013-05-01

    We study the hydrodynamics of dip coating from a suspension and report a mechanism for colloidal assembly and pattern formation on smooth substrates. Below a critical withdrawal speed where the coating film is thinner than the particle diameter, capillary forces induced by deformation of the free surface prevent the convective transport of single particles through the meniscus beneath the film. Capillary-induced forces are balanced by hydrodynamic drag only after a minimum number of particles assemble within the meniscus. The particle assembly can thus enter the thin film where it moves at nearly the withdrawal speed and rapidly separates from the next assembly. The interplay between hydrodynamic and capillary forces produces periodic and regular structures below a critical ratio Ca(2/3)/sqrt[Bo] < 0.7, where Ca and Bo are the capillary and Bond numbers, respectively. An analytical model and numerical simulations are presented for the case of two-dimensional flow with circular particles in suspension. The hydrodynamically driven assembly documented here is consistent with stripe pattern formations observed experimentally in dip coating.

  2. Hydrodynamically Driven Colloidal Assembly in Dip Coating

    NASA Astrophysics Data System (ADS)

    Colosqui, Carlos E.; Morris, Jeffrey F.; Stone, Howard A.

    2013-05-01

    We study the hydrodynamics of dip coating from a suspension and report a mechanism for colloidal assembly and pattern formation on smooth substrates. Below a critical withdrawal speed where the coating film is thinner than the particle diameter, capillary forces induced by deformation of the free surface prevent the convective transport of single particles through the meniscus beneath the film. Capillary-induced forces are balanced by hydrodynamic drag only after a minimum number of particles assemble within the meniscus. The particle assembly can thus enter the thin film where it moves at nearly the withdrawal speed and rapidly separates from the next assembly. The interplay between hydrodynamic and capillary forces produces periodic and regular structures below a critical ratio Ca2/3/Bo<0.7, where Ca and Bo are the capillary and Bond numbers, respectively. An analytical model and numerical simulations are presented for the case of two-dimensional flow with circular particles in suspension. The hydrodynamically driven assembly documented here is consistent with stripe pattern formations observed experimentally in dip coating.

  3. Entropic force between biomembranes

    NASA Astrophysics Data System (ADS)

    Li, Long; Song, Fan

    2016-08-01

    Undulation force, an entropic force, stems from thermally excited fluctuations, and plays a key role in the essential interactions between neighboring surfaces of objects. Although the characteristics of the undulation force have been widely studied theoretically and experimentally, the distance dependence of the force, which constitutes its most fundamental characteristic, remains poorly understood. In this paper, first, we obtain a novel expression for the undulation force by employing elasticity and statistical mechanics and prove it to be in good agreement with existing experimental results. Second, we clearly demonstrate that the two representative forms of the undulation force proposed by Helfrich and Freund were respectively the upper and lower bounds of the present expression when the separation between membranes is sufficiently small, which was intrinsically different from the existing results where Helfrich's and Freund's forms of the undulation force were only suitable for the intermediate and small separations. The investigations show that only in a sufficiently small separation does Helfrich's result stand for the undulation force with a large wave number and Freund's result express the force with a small wave number. Finally, a critical acting distance of the undulation force, beyond which the entropic force will rapidly decay approaching zero, is presented.

  4. Forces in molecules.

    PubMed

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

    2007-01-01

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

  5. Forces in molecules.

    PubMed

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

    2007-01-01

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

  6. Force-Measuring Clamps

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark

    2003-01-01

    Force-measuring clamps have been invented to facilitate and simplify the task of measuring the forces or pressures applied to clamped parts. There is a critical need to measure clamping forces or pressures in some applications for example, while bonding sensors to substrates or while clamping any sensitive or delicate parts. Many manufacturers of adhesives and sensors recommend clamping at specific pressures while bonding sensors or during adhesive bonding between parts in general. In the absence of a force-measuring clamp, measurement of clamping force can be cumbersome at best because of the need for additional load sensors and load-indicating equipment. One prior method of measuring clamping force involved the use of load washers or miniature load cells in combination with external power sources and load-indicating equipment. Calibrated spring clamps have also been used. Load washers and miniature load cells constitute additional clamped parts in load paths and can add to the destabilizing effects of loading mechanisms. Spring clamps can lose calibration quickly through weakening of the springs and are limited to the maximum forces that the springs can apply. The basic principle of a force-measuring clamp can be implemented on a clamp of almost any size and can enable measurement of a force of almost any magnitude. No external equipment is needed because the component(s) for transducing the clamping force and the circuitry for supplying power, conditioning the output of the transducers, and displaying the measurement value are all housed on the clamp. In other words, a force-measuring clamp is a complete force-application and force-measurement system all in one package. The advantage of unitary packaging of such a system is that it becomes possible to apply the desired clamping force or pressure with precision and ease.

  7. Force Limited Vibration Testing

    NASA Technical Reports Server (NTRS)

    Scharton, Terry; Chang, Kurng Y.

    2005-01-01

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

  8. Global Plate Driving Forces at 50Ma

    NASA Astrophysics Data System (ADS)

    Butterworth, N. P.; Quevedo, L. E.; Müller, R. D.

    2011-12-01

    We apply a novel workflow utilising the BEM-Earth geodynamic software to analyse the global coupled plate-mantle dynamics at 50 Ma. A subduction history model based on kinematic data going as far back as 80 Ma was developed using the GPlates software. Advection of the plates into the mantle takes into account the absolute plate motions and lithospheric thickness derived from its age to produce an estimated density heterogeneity initial model condition in the upper mantle. The resulting global model consists of regions of a mantle viscosity and density structure that is post-processed to ensure smooth non-overlapping 3D surfaces. BEM-Earth is then free to evolve the model toward the 50 Ma solution. The evolution of the model is driven by self-consistent buoyancy driven mantle dynamics. We use the model velocity output to quantify changes in forces driving the plates before and after 50 Ma. We analyse the rapid change in plate motion of India, Africa and plates in the Pacific Ocean basin by considering slab-pull, ridge-push and mantle drag/suction forces that naturally result from such top-down driven mantle flow. We compare the results with plate kinematic reconstructions and other geological observations.

  9. Flow enhancement of deformable self-driven objects by countercurrent

    NASA Astrophysics Data System (ADS)

    Mashiko, Takashi; Fujiwara, Takashi

    2016-10-01

    We report numerical simulations of the mixed flows of two groups of deformable self-driven objects. The objects belonging to the group A (B) have drift coefficient D =DA (DB), where a positive (negative) value of D denotes the rightward (leftward) driving force. For co-current flows (DA ,DB > 0), the result is rather intuitive: the net flow of one group (QA) increases if the driving force of the other group is stronger than its own driving force (i.e., DB >DA), and decreases otherwise (DB force of the other group (|DB |), and the net flow with a stronger countercurrent can be larger than the net flow with a weaker co-current. This phenomenon is observed only for deformable objects and results from the entanglement of objects, which in turn is caused by their deformability.

  10. Fluid driven reciprocating apparatus

    DOEpatents

    Whitehead, J.C.

    1997-04-01

    An apparatus is described comprising a pair of fluid driven pump assemblies in a back-to-back configuration to yield a bi-directional pump. Each of the pump assemblies includes a piston or diaphragm which divides a chamber therein to define a power section and a pumping section. An intake-exhaust valve is connected to each of the power sections of the pump chambers, and function to direct fluid, such as compressed air, into the power section and exhaust fluid therefrom. At least one of the pistons or diaphragms is connected by a rod assembly which is constructed to define a signal valve, whereby the intake-exhaust valve of one pump assembly is controlled by the position or location of the piston or diaphragm in the other pump assembly through the operation of the rod assembly signal valve. Each of the pumping sections of the pump assemblies are provided with intake and exhaust valves to enable filling of the pumping section with fluid and discharging fluid therefrom when a desired pressure has been reached. 13 figs.

  11. Compositionally Driven Dynamos

    NASA Astrophysics Data System (ADS)

    Soderlund, K. M.; Schubert, G.

    2014-12-01

    It is generally believed that compositional convection driven by inner core solidification is the main driver of the geodynamo. Thermal evolution considerations make it likely that compositional convection is also behind the present dynamos of Mercury and Ganymede as well as the early dynamos in the Moon, Mars and smaller solar system bodies. Compositional buoyancy can arise in several different ways, for example, through inner core solidification and FeS flotation with upward mixing and through freezing out and sinking of iron snow near the core-mantle boundary or deeper within the core. The mode of core cooling and freezing depends on conditions of temperature and pressure in the core and the concentration of light elements such as sulfur. Different distributions of compositional buoyancy will give rise to different patterns of core convection and dynamo magnetic fields. We report here the first results of a systematic study of the distribution of compositional buoyancy on the dynamo-generated magnetic fields, with an emphasis on Mars' core evolution due to iron rain.

  12. Fluid driven recipricating apparatus

    DOEpatents

    Whitehead, John C.

    1997-01-01

    An apparatus comprising a pair of fluid driven pump assemblies in a back-to-back configuration to yield a bi-directional pump. Each of the pump assemblies includes a piston or diaphragm which divides a chamber therein to define a power section and a pumping section. An intake-exhaust valve is connected to each of the power sections of the pump chambers, and function to direct fluid, such as compressed air, into the power section and exhaust fluid therefrom. At least one of the pistons or diaphragms is connected by a rod assembly which is constructed to define a signal valve, whereby the intake-exhaust valve of one pump assembly is controlled by the position or location of the piston or diaphragm in the other pump assembly through the operation of the rod assembly signal valve. Each of the pumping sections of the pump assemblies are provided with intake and exhaust valves to enable filling of the pumping section with fluid and discharging fluid therefrom when a desired pressure has been reached.

  13. Invention-driven marketing

    NASA Technical Reports Server (NTRS)

    Carlson, William E.

    1994-01-01

    Suppose you have just created a revolutionary bicycle suspension which allows a bike to be ridden over rough terrain at 60 miles per hour. In addition, suppose that you are deeply concerned about the plight of hungry children. Which should you do: be sure all hungry children have bicycles; transfer the technology for your new suspension to bicycle manufacturers worldwide; or start a company to supply premium sports bicycle based on your patented technology, and donate the profits to a charity which feeds hungry children? Woven through this somewhat trivial example is the paradox of technology transfer - the supplier (owner) may want to transfer technology; but to succeed, he or she must reformulate the problem as a user need for which there is a new and better solution. Successful technology transfer is little more than good marketing applied to an existing invention, process, or capability. You must identify who needs the technology, why they need it, why the new technology is better than alternatives, how much the customers are willing and able to pay for these benefits, and how to distribute products based on the technology tc the target customers. In market-driven development, the term 'technology transfer' is rarely used. The developers focus on studying user needs and designing solution They may have technology needs, but they don't have technology in search of a use.

  14. Pressure-driven flow in a channel with porous walls

    NASA Astrophysics Data System (ADS)

    Liu, Qianlong; Prosperetti, Andrea

    2010-11-01

    The finite-Reynolds-number three-dimensional flow in a channel bounded by one and two parallel porous walls is studied numerically. The porous medium is modelled by spheres in a simple cubic arrangement. The results for the slip velocity at the surface of the porous layers are compared with the phenomenological Beavers-Joseph model. It is found that the value of the slip coefficient is different for pressure-driven and shear-driven flow. A modification of the relation is suggested to deal with this feature. Furthermore, detailed results on the flow structure and the hydrodynamic forces and couple acting on the sphere layer bounding the porous medium are reported and their dependence on the Reynolds number illustrated. It is shown that, at finite Reynolds numbers, a lift force acts on the spheres, which may be expected to contribute to the the mobilization of bottom sediments.

  15. A photon-driven micromotor can direct nerve fibre growth

    NASA Astrophysics Data System (ADS)

    Wu, Tao; Nieminen, Timo A.; Mohanty, Samarendra; Miotke, Jill; Meyer, Ronald L.; Rubinsztein-Dunlop, Halina; Berns, Michael W.

    2012-01-01

    Axonal path-finding is important in the development of the nervous system, nerve repair and nerve regeneration. The behaviour of the growth cone at the tip of the growing axon determines the direction of axonal growth and migration. We have developed an optical-based system to control the direction of growth of individual axons (nerve fibres) using laser-driven spinning birefringent spheres. One or two optical traps position birefringent beads adjacent to growth cones of cultured goldfish retinal ganglion cell axons. Circularly polarized light with angular momentum causes the trapped bead to spin. This creates a localized microfluidic flow generating an estimated 0.17 pN shear force against the growth cone that turns in response to the shear. The direction of axonal growth can be precisely manipulated by changing the rotation direction and position of this optically driven micromotor. A physical model estimating the shear force density on the axon is described.

  16. Coulomb force as an entropic force

    SciTech Connect

    Wang Tower

    2010-05-15

    Motivated by Verlinde's theory of entropic gravity, we give a tentative explanation to the Coulomb's law with an entropic force. When trying to do this, we find the equipartition rule should be extended to charges and the concept of temperature should be reinterpreted. If one accepts the holographic principle as well as our generalizations and reinterpretations, then Coulomb's law, the Poisson equation, and the Maxwell equations can be derived smoothly. Our attempt can be regarded as a new way to unify the electromagnetic force with gravity, from the entropic origin. Possibly some of our postulates are related to the D-brane picture of black hole thermodynamics.

  17. Coulomb force as an entropic force

    NASA Astrophysics Data System (ADS)

    Wang, Tower

    2010-05-01

    Motivated by Verlinde’s theory of entropic gravity, we give a tentative explanation to the Coulomb’s law with an entropic force. When trying to do this, we find the equipartition rule should be extended to charges and the concept of temperature should be reinterpreted. If one accepts the holographic principle as well as our generalizations and reinterpretations, then Coulomb’s law, the Poisson equation, and the Maxwell equations can be derived smoothly. Our attempt can be regarded as a new way to unify the electromagnetic force with gravity, from the entropic origin. Possibly some of our postulates are related to the D-brane picture of black hole thermodynamics.

  18. Mechanically driven centrifugal pyrolyzer

    DOEpatents

    Linck, Martin Brendan; Bush, Phillip Vann

    2012-03-06

    An apparatus for fast pyrolysis of biomass and other solid organic materials including a vertically oriented cylindrical vessel having a solids outlet proximate the bottom thereof, a vapor outlet, a top wall forming at least one opening, and an adjacent heated side wall. Disposed within the cylindrical vessel and extending through the at least one opening in the top wall is a rotor having a rotatable shaft coincident with the longitudinal axis of the cylindrical vessel to which is attached at least one substantially vertically oriented blade having one edge connected directly or indirectly with the rotatable shaft and having an opposite edge spaced apart from the heated side wall, whereby a non-radial, preferably tangential, force is imparted on the feedstock in the cylindrical vessel. Also disclosed is a method for fast pyrolysis of biomass and other solid organic materials.

  19. A damped pendulum forced with a constant torque

    NASA Astrophysics Data System (ADS)

    Coullet, P.; Gilli, J. M.; Monticelli, M.; Vandenberghe, N.

    2005-12-01

    The dynamics of a damped pendulum driven by a constant torque is studied experimentally and theoretically. We use this simple device to demonstrate some generic dynamical behavior including the loss of equilibrium or saddle node bifurcation with or without hysteresis and the homoclinic bifurcation. A qualitative analysis is developed to emphasize the role of two dimensionless parameters corresponding to damping and forcing.

  20. Quantum Fictitious Forces

    NASA Astrophysics Data System (ADS)

    Białynicki-Birula, I.; Cirone, M. A.; Dahl, J. P.; Seligman, T. H.; Straub, F.; Schleich, W. P.

    2003-09-01

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

  1. Relaxation of a qubit measured by a driven Duffing oscillator

    SciTech Connect

    Serban, I.; Dykman, M. I.; Wilhelm, F. K.

    2010-02-15

    We investigate the relaxation of a superconducting qubit for the case when its detector, the Josephson bifurcation amplifier, remains latched in one of its two (meta)stable states of forced vibrations. The qubit relaxation rates are different in different states. They can display strong dependence on the qubit frequency and resonant enhancement, which is due to quasienergy resonances. Coupling to the driven oscillator changes the effective temperature of the qubit.

  2. Entropic forces drive contraction of cytoskeletal networks.

    PubMed

    Braun, Marcus; Lansky, Zdenek; Hilitski, Feodor; Dogic, Zvonimir; Diez, Stefan

    2016-05-01

    The cytoskeleton is a network of interconnected protein filaments, which provide a three-dimensional scaffold for cells. Remodeling of the cytoskeleton is important for key cellular processes, such as cell motility, division, or morphogenesis. This remodeling is traditionally considered to be driven exclusively by processes consuming chemical energy, such as the dynamics of the filaments or the action of molecular motors. Here, we review two mechanisms of cytoskeletal network remodeling that are independent of the consumption of chemical energy. In both cases directed motion of overlapping filaments is driven by entropic forces, which arise from harnessing thermal energy present in solution. Entropic forces are induced either by macromolecular crowding agents or by diffusible crosslinkers confined to the regions where filaments overlap. Both mechanisms increase filament overlap length and lead to the contraction of filament networks. These force-generating mechanisms, together with the chemical energy-dependent mechanisms, need to be considered for the comprehensive quantitative picture of the remodeling of cytoskeletal networks in cells. PMID:26996935

  3. Edge convection driven by externally applied potentials

    SciTech Connect

    D'Ippolito, D. A.; Myra, J. R.

    2000-08-01

    A theoretical model of convection in collisional tokamak edge and scrape-off-layer plasmas is described. In the linear theory, any mechanism for poloidal and toroidal symmetry breaking of the equilibrium will drive ExB flows; this result stems from the parallel thermal and pressure forces in Ohm's law. In the nonlinear theory, the quadratic coupling of the perturbations leads to quasilinear-type fluxes in the vorticity, density, and temperature equations. If the convection is strong enough, these fluxes lead to an ambipolarity constraint on the equilibrium electric field and to increased transport of particles and energy. The theory shows qualitative agreement with some tokamak experiments in which potential perturbations are externally driven by radio frequency antennas. (c) 2000 American Institute of Physics.

  4. Bistability in a Driven-Dissipative Superfluid.

    PubMed

    Labouvie, Ralf; Santra, Bodhaditya; Heun, Simon; Ott, Herwig

    2016-06-10

    We experimentally study a driven-dissipative Josephson junction array, realized with a weakly interacting Bose-Einstein condensate residing in a one-dimensional optical lattice. Engineered losses on one site act as a local dissipative process, while tunneling from the neighboring sites constitutes the driving force. We characterize the emerging steady states of this atomtronic device. With increasing dissipation strength γ the system crosses from a superfluid state, characterized by a coherent Josephson current into the lossy site, to a resistive state, characterized by an incoherent hopping transport. For intermediate values of γ, the system exhibits bistability, where a superfluid and an incoherent branch coexist. We also study the relaxation dynamics towards the steady state, where we find a critical slowing down, indicating the presence of a nonequilibrium phase transition. PMID:27341243

  5. Bistability in a Driven-Dissipative Superfluid

    NASA Astrophysics Data System (ADS)

    Labouvie, Ralf; Santra, Bodhaditya; Heun, Simon; Ott, Herwig

    2016-06-01

    We experimentally study a driven-dissipative Josephson junction array, realized with a weakly interacting Bose-Einstein condensate residing in a one-dimensional optical lattice. Engineered losses on one site act as a local dissipative process, while tunneling from the neighboring sites constitutes the driving force. We characterize the emerging steady states of this atomtronic device. With increasing dissipation strength γ the system crosses from a superfluid state, characterized by a coherent Josephson current into the lossy site, to a resistive state, characterized by an incoherent hopping transport. For intermediate values of γ , the system exhibits bistability, where a superfluid and an incoherent branch coexist. We also study the relaxation dynamics towards the steady state, where we find a critical slowing down, indicating the presence of a nonequilibrium phase transition.

  6. Arnold diffusion in a driven optical lattice.

    PubMed

    Boretz, Yingyue; Reichl, L E

    2016-03-01

    The effect of time-periodic forces on matter has been a topic of growing interest since the advent of lasers. It is known that dynamical systems with 2.5 or more degrees of freedom are intrinsically unstable. As a consequence, time-periodic driven systems can experience large excursions in energy. We analyze the classical and quantum dynamics of rubidium atoms confined to a time-periodic optical lattice with 2.5 degrees of freedom. When the laser polarizations are orthogonal, the system consists of two 1.5 uncoupled dynamical systems. When laser polarizations are turned away from orthogonal, an Arnold web forms and the dynamics undergoes a fundamental change. For parallel polarizations, we find huge random excursions in the rubidium atom energies and significant entanglement of energies in the quantum dynamics. PMID:27078351

  7. Laser-Driven Mini-Thrusters

    SciTech Connect

    Sterling, Enrique; Lin Jun; Sinko, John; Kodgis, Lisa; Porter, Simon; Pakhomov, Andrew V.; Larson, C. William; Mead, Franklin B. Jr.

    2006-05-02

    Laser-driven mini-thrusters were studied using Delrin registered and PVC (Delrin registered is a registered trademark of DuPont) as propellants. TEA CO2 laser ({lambda} = 10.6 {mu}m) was used as a driving laser. Coupling coefficients were deduced from two independent techniques: force-time curves measured with a piezoelectric sensor and ballistic pendulum. Time-resolved ICCD images of the expanding plasma and combustion products were analyzed in order to determine the main process that generates the thrust. The measurements were also performed in a nitrogen atmosphere in order to test the combustion effects on thrust. A pinhole transmission experiment was performed for the study of the cut-off time when the ablation/air breakdown plasma becomes opaque to the incoming laser pulse.

  8. Relativistic Linear Restoring Force

    ERIC Educational Resources Information Center

    Clark, D.; Franklin, J.; Mann, N.

    2012-01-01

    We consider two different forms for a relativistic version of a linear restoring force. The pair comes from taking Hooke's law to be the force appearing on the right-hand side of the relativistic expressions: d"p"/d"t" or d"p"/d["tau"]. Either formulation recovers Hooke's law in the non-relativistic limit. In addition to these two forces, we…

  9. Debunking Coriolis Force Myths

    NASA Astrophysics Data System (ADS)

    Shakur, Asif

    2014-11-01

    Much has been written and debated about the Coriolis force.1-8 Unfortunately, this has done little to demystify the paradoxes surrounding this fictitious force invoked by an observer in a rotating frame of reference. It is the purpose of this article to make another valiant attempt to slay the dragon of the Coriolis force! This will be done without unleashing the usual mathematical apparatus, which we believe is more of a hindrance than a help.

  10. Fluid flows and forces in development: functions, features and biophysical principles

    PubMed Central

    Freund, Jonathan B.; Goetz, Jacky G.; Hill, Kent L.; Vermot, Julien

    2012-01-01

    Throughout morphogenesis, cells experience intracellular tensile and contractile forces on microscopic scales. Cells also experience extracellular forces, such as static forces mediated by the extracellular matrix and forces resulting from microscopic fluid flow. Although the biological ramifications of static forces have received much attention, little is known about the roles of fluid flows and forces during embryogenesis. Here, we focus on the microfluidic forces generated by cilia-driven fluid flow and heart-driven hemodynamics, as well as on the signaling pathways involved in flow sensing. We discuss recent studies that describe the functions and the biomechanical features of these fluid flows. These insights suggest that biological flow determines many aspects of cell behavior and identity through a specific set of physical stimuli and signaling pathways. PMID:22395739

  11. Electrodynamic force law controversy.

    PubMed

    Graneau, P; Graneau, N

    2001-05-01

    Cavalleri et al. [Phys. Rev. E 52, 2505 (1998); Eur. J. Phys. 17, 205 (1996)] have attempted to resolve the electrodynamic force law controversy. This attempt to prove the validity of either the Ampère or Lorentz force law by theory and experiment has revealed only that the two are equivalent when predicting the force on part of a circuit due to the current in the complete circuit. However, in our analysis of internal stresses, only Ampère's force law agrees with experiment. PMID:11415053

  12. Salinity driven oceanographic upwelling

    DOEpatents

    Johnson, David H.

    1986-01-01

    The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water.

  13. Salinity driven oceanographic upwelling

    DOEpatents

    Johnson, D.H.

    1984-08-30

    The salinity driven oceanographic upwelling is maintained in a mariculture device that includes a long main duct in the general shape of a cylinder having perforated cover plates at each end. The mariculture device is suspended vertically in the ocean such that one end of the main duct is in surface water and the other end in relatively deep water that is cold, nutrient rich and relatively fresh in comparison to the surface water which is relatively warm, relatively nutrient deficient and relatively saline. A plurality of elongated flow segregating tubes are disposed in the main duct and extend from the upper cover plate beyond the lower cover plate into a lower manifold plate. The lower manifold plate is spaced from the lower cover plate to define a deep water fluid flow path to the interior space of the main duct. Spacer tubes extend from the upper cover plate and communicate with the interior space of the main duct. The spacer tubes are received in an upper manifold plate spaced from the upper cover plate to define a surface water fluid flow path into the flow segregating tubes. A surface water-deep water counterflow is thus established with deep water flowing upwardly through the main duct interior for discharge beyond the upper manifold plate while surface water flows downwardly through the flow segregating tubes for discharge below the lower manifold plate. During such counterflow heat is transferred from the downflowing warm water to the upflowing cold water. The flow is maintained by the difference in density between the deep water and the surface water due to their differences in salinity. The upwelling of nutrient rich deep water is used for marifarming by fertilizing the nutrient deficient surface water. 1 fig.

  14. Climate forcings and feedbacks

    NASA Technical Reports Server (NTRS)

    Hansen, James

    1993-01-01

    Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption

  15. Gravity Driven Universe

    NASA Astrophysics Data System (ADS)

    Masters, Roy

    2010-03-01

    Flowing global gravitation initially produced space without time or mass. Space-time and mass are properties of flowing global gravitation. From its fabric, primal mass spins spontaneously giving rise to local gravitational space-time curvatures. Global gravity is the unifying background field. Gravity began flowing from its singularity with a big whoosh. It curves with angular rotational precession, creating a spatial geometry similar to the windings of a ball of string. Three-dimensional global gravity swirls locally into massive densities. Concurrently with these densities, local gravity curvatures of space-time arise. The expanse between celestial objects is not completely empty, void space as generally believed; it is antecedent gravity, a prerequisite associated field necessary for originating the first quantum particles. Gravity is dark energy; gravity's spin, as the second fundamental force, is electromagnetic dark matter. Electromagnetic masses attract then gravity compresses hot, dense and small---then bang, the first hydrogen star of which there are many. There may have been many big bangs, but no Big Bang that ultimately created the universe.

  16. Comments on event driven animation

    NASA Technical Reports Server (NTRS)

    Gomez, Julian E.

    1987-01-01

    Event driven animation provides a general method of describing controlling values for various computer animation techniques. A definition and comments are provided on genralizing motion description with events. Additional comments are also provided about the implementation of twixt.

  17. Elementary Particles and Forces.

    ERIC Educational Resources Information Center

    Quigg, Chris

    1985-01-01

    Discusses subatomic particles (quarks, leptons, and others) revealed by higher accelerator energies. A connection between forces at this subatomic level has been established, and prospects are good for a description of forces that encompass binding atomic nuclei. Colors, fundamental interactions, screening, camouflage, electroweak symmetry, and…

  18. Polarizable force fields.

    PubMed

    Antila, Hanne S; Salonen, Emppu

    2013-01-01

    This chapter provides an overview of the most common methods for including an explicit description of electronic polarization in molecular mechanics force fields: the induced point dipole, shell, and fluctuating charge models. The importance of including polarization effects in biomolecular simulations is discussed, and some of the most important achievements in the development of polarizable biomolecular force fields to date are highlighted.

  19. Forces in yeast flocculation.

    PubMed

    El-Kirat-Chatel, Sofiane; Beaussart, Audrey; Vincent, Stéphane P; Abellán Flos, Marta; Hols, Pascal; Lipke, Peter N; Dufrêne, Yves F

    2015-02-01

    In the baker's yeast Saccharomyces cerevisiae, cell-cell adhesion ("flocculation") is conferred by a family of lectin-like proteins known as the flocculin (Flo) proteins. Knowledge of the adhesive and mechanical properties of flocculins is important for understanding the mechanisms of yeast adhesion, and may help controlling yeast behaviour in biotechnology. We use single-molecule and single-cell atomic force microscopy (AFM) to explore the nanoscale forces engaged in yeast flocculation, focusing on the role of Flo1 as a prototype of flocculins. Using AFM tips labelled with mannose, we detect single flocculins on Flo1-expressing cells, showing they are widely exposed on the cell surface. When subjected to force, individual Flo1 proteins display two distinct force responses, i.e. weak lectin binding forces and strong unfolding forces reflecting the force-induced extension of hydrophobic tandem repeats. We demonstrate that cell-cell adhesion bonds also involve multiple weak lectin interactions together with strong unfolding forces, both associated with Flo1 molecules. Single-molecule and single-cell data correlate with microscale cell adhesion behaviour, suggesting strongly that Flo1 mechanics is critical for yeast flocculation. These results favour a model in which not only weak lectin-sugar interactions are involved in yeast flocculation but also strong hydrophobic interactions resulting from protein unfolding.

  20. Forces in yeast flocculation

    NASA Astrophysics Data System (ADS)

    El-Kirat-Chatel, Sofiane; Beaussart, Audrey; Vincent, Stéphane P.; Abellán Flos, Marta; Hols, Pascal; Lipke, Peter N.; Dufrêne, Yves F.

    2015-01-01

    In the baker's yeast Saccharomyces cerevisiae, cell-cell adhesion (``flocculation'') is conferred by a family of lectin-like proteins known as the flocculin (Flo) proteins. Knowledge of the adhesive and mechanical properties of flocculins is important for understanding the mechanisms of yeast adhesion, and may help controlling yeast behaviour in biotechnology. We use single-molecule and single-cell atomic force microscopy (AFM) to explore the nanoscale forces engaged in yeast flocculation, focusing on the role of Flo1 as a prototype of flocculins. Using AFM tips labelled with mannose, we detect single flocculins on Flo1-expressing cells, showing they are widely exposed on the cell surface. When subjected to force, individual Flo1 proteins display two distinct force responses, i.e. weak lectin binding forces and strong unfolding forces reflecting the force-induced extension of hydrophobic tandem repeats. We demonstrate that cell-cell adhesion bonds also involve multiple weak lectin interactions together with strong unfolding forces, both associated with Flo1 molecules. Single-molecule and single-cell data correlate with microscale cell adhesion behaviour, suggesting strongly that Flo1 mechanics is critical for yeast flocculation. These results favour a model in which not only weak lectin-sugar interactions are involved in yeast flocculation but also strong hydrophobic interactions resulting from protein unfolding.

  1. Force Concept Inventory.

    ERIC Educational Resources Information Center

    Hestenes, David; And Others

    1992-01-01

    Reports the rationale, design, validation, and uses of the "Force Concept Inventory," an instrument to assess the students' beliefs on force. Includes results and implications of two studies that compared the inventory with the "Mechanics Baseline." Includes a copy of the instrument. (MDH)

  2. SCM-Forcing Data

    DOE Data Explorer

    Xie, Shaocheng; Tang,Shuaiqi; Zhang,Yunyan; Zhang,Minghua

    2016-07-01

    Single-Column Model (SCM) Forcing Data are derived from the ARM facility observational data using the constrained variational analysis approach (Zhang and Lin 1997 and Zhang et al., 2001). The resulting products include both the large-scale forcing terms and the evaluation fields, which can be used for driving the SCMs and Cloud Resolving Models (CRMs) and validating model simulations.

  3. Nuclear mechanotransduction: forcing the nucleus to respond.

    PubMed

    Guilluy, Christophe; Burridge, Keith

    2015-01-01

    Cell phenotype and fate are driven by the mechanical properties of their surrounding environment. Changes in matrix rigidity or application of force have been shown to impact profoundly cell behavior and phenotype, demonstrating that the molecular mechanisms which "sense" and transduce these signals into biochemical pathways are central in cell biology. In this commentary, we discuss recent evidence showing that mechanotransduction mechanisms occur in the nucleus, allowing dynamic regulation of the nucleoskeleton in response to mechanical stress. We will review this nucleoskeletal response and its impact on both nuclear structure and function.

  4. Lorentz force velocimetry.

    PubMed

    Thess, A; Votyakov, E V; Kolesnikov, Y

    2006-04-28

    We describe a noncontact technique for velocity measurement in electrically conducting fluids. The technique, which we term Lorentz force velocimetry (LFV), is based on exposing the fluid to a magnetic field and measuring the drag force acting upon the magnetic field lines. Two series of measurements are reported, one in which the force is determined through the angular velocity of a rotary magnet system and one in which the force on a fixed magnet system is measured directly. Both experiments confirm that the measured signal is a linear function of the flow velocity. We then derive the scaling law that relates the force on a localized distribution of magnetized material to the velocity of an electrically conducting fluid. This law shows that LFV, if properly designed, has a wide range of potential applications in metallurgy, semiconductor crystal growth, and glass manufacturing. PMID:16712237

  5. Conservative entropic forces

    NASA Astrophysics Data System (ADS)

    Visser, Matt

    2011-10-01

    Entropic forces have recently attracted considerable attention as ways to reformulate, retrodict, and perhaps even "explain" classical Newtonian gravity from a rather specific thermodynamic perspective. In this article I point out that if one wishes to reformulate classical Newtonian gravity in terms of an entropic force, then the fact that Newtonian gravity is described by a conservative force places significant constraints on the form of the entropy and temperature functions. (These constraints also apply to entropic reinterpretations of electromagnetism, and indeed to any conservative force derivable from a potential.) The constraints I will establish are sufficient to present real and significant problems for any reasonable variant of Verlinde's entropic gravity proposal, though for technical reasons the constraints established herein do not directly impact on either Jacobson'sor Padmanabhan's versions of entropic gravity. In an attempt to resolve these issues, I will extend the usual notion of entropic force to multiple heat baths with multiple "temperatures" and multiple "entropies".

  6. Numerical study of thermal driven buoyancy flow effect on solidification process of continuous slab caster

    NASA Astrophysics Data System (ADS)

    JAMBHULKAR, ROHIT Y.; SINGH, V.; MISHRA, P.; KRISHNAMURTHY, R.

    2016-09-01

    The main aim of the present research is to study the role of thermal driven buoyancy flow in solidification process of continues slab caster. A 3-D fluid flow, heat transfer and solidification model was developed. The result from the model combined with nondimensional number to study the effect of thermal driven buoyancy flow on fluid flow and temperature distribution. For mushy region Kozeny-Carman is applicable. Observations show the relative strength between thermal driven buoyancy flow and forced flow and steel flow through mushy region. It is observed that buoyancy force in mould and sub mould region depend on the characteristic flow velocity, temperature difference and porosity of mushy zone. The most effect zone of thermal driven buoyancy flow is mushy zone and centre of mould where inertial flow is inferior. The convection flow creates by thermal buoyancy cause appearance of local turbulence.

  7. Directly Driven Ion Outflow

    NASA Technical Reports Server (NTRS)

    Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Moore, T. E.; Russell, C. T.; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    We examine ionospheric outflows in the high altitude magnetospheric polar cap during the POLAR satellite's apogee on April 19, 1996 using the Thermal Ion Dynamics Experiment (TIDE) instrument. The elevated levels of O(+) observed in this pass may be due to the geophysical conditions during and prior to the apogee pass. In addition to the high abundance of O(+) relative to H(+), several other aspects of this data are noteworthy. We observe relationships between the density, velocity, and temperature which appear to be associated with perpendicular heating and the mirror force, rather than adiabatic expansion. The H(+) outflow is at a fairly constant flux which is consistent with being source limited by charge exchange at lower altitudes. Local centrifugal acceleration in the polar cap is found to be insufficient to account for the main variations we observe in the outflow velocity. The solar wind speed is high during this pass approximately 700 kilometers per second, and there are Alfve'n waves present in the solar wind such that the solar wind speed and IMF Bx are correlated. In this pass both the H(+) and O(+) outflow velocities correlate with both the solar wind speed and IMF fluctuations. Polar cap magnetometer and Hydra electron data show the same long period wave structure as found in the solar wind and polar cap ion outflow. In addition, the polar cap Poynting flux along the magnetic field direction correlates well with the H(+) temperature (R=0.84). We conclude that the solar wind can drive polar cap ion outflow particularly during polar squalls by setting up a parallel drop that is tens of eV which then causes the ion outflow velocity of O(+) and H(+), the electrons, and magnetic perturbations to vary in a similar fashion.

  8. Stable electroosmotically driven actuators

    NASA Astrophysics Data System (ADS)

    Sritharan, Deepa; Motsebo, Mylene; Tumbic, Julia; Smela, Elisabeth

    2013-04-01

    We have previously presented "nastic" actuators based on electroosmotic (EO) pumping of fluid in microchannels using high electric fields for potential application in soft robotics. In this work we address two challenges facing this technology: applying EO to meso-scale devices and the stability of the pumping fluid. The hydraulic pressure achieved by EO increases with as 1/d2, where d is the depth of the microchannel, but the flow rate (which determines the stroke and the speed) is proportional to nd, where n is the number of channels. Therefore to get high force and high stroke the device requires a large number of narrow channels, which is not readily achievable using standard microfabrication techniques. Furthermore, for soft robotics the structure must be soft. In this work we present a method of fabricating a three-dimensional porous elastomer to serve as the array of channels based on a sacrificial sugar scaffold. We demonstrate the concept by fabricating small pumps. The flexible devices were made from polydimethylsiloxane (PDMS) and comprise the 3D porous elastomer flanked on either side by reservoirs containing electrodes. The second issue addressed here involves the pumping fluid. Typically, water is used for EO, but water undergoes electrolysis even at low voltages. Since EO takes place at kV, these systems must be open to release the gases. We have recently reported that propylene carbonate (PC) is pumped at a comparable rate as water and is also stable for over 30 min at 8 kV. Here we show that PC is, however, degraded by moisture, so future EO systems must prevent water from reaching the PC.

  9. Thermal motion of athermal driven grains

    NASA Astrophysics Data System (ADS)

    Ojha, Rajesh; Durian, D. J.; Dixon, P. K.

    2001-03-01

    The uniform upward gas flow in a gas-fluidized bed provides a homogeneous driving force. This allows a controlled study of the transition of a granular material from a static to a fluid-like state. Macroscopic properties of gas-fluidized beds, such as bed height, volume fraction, and gas pressure drop have been well-studied. However, experimental research on the dynamics of individual grains is lacking. Here, we use a scaled-up fluidized bed to observe grain motion. Our bed consists of a monolayer of ping-pong balls fluidized with air. High-speed photography allows us to track ball motions with high temporal resolution. From the images, we extract ball positions, velocities, and net forces due to the air turbulence. In the case of a lone ball, we find that a simple statistical mechanics model accurately describes its position, velocity, and energy distributions. Namely, it behaves exactly like a thermally-excited particle in a harmonic potential well. If such behavior holds for multiple balls, we will be able to develop a statistical mechanics description of grain interactions in an athermal driven system.

  10. Diffusion Driven Combustion Waves in Porous Media

    NASA Technical Reports Server (NTRS)

    Aldushin, A. P.; Matkowsky, B. J.

    2000-01-01

    Filtration of gas containing oxidizer, to the reaction zone in a porous medium, due, e.g., to a buoyancy force or to an external pressure gradient, leads to the propagation of Filtration combustion (FC) waves. The exothermic reaction occurs between the fuel component of the solid matrix and the oxidizer. In this paper, we analyze the ability of a reaction wave to propagate in a porous medium without the aid of filtration. We find that one possible mechanism of propagation is that the wave is driven by diffusion of oxidizer from the environment. The solution of the combustion problem describing diffusion driven waves is similar to the solution of the Stefan problem describing the propagation of phase transition waves, in that the temperature on the interface between the burned and unburned regions is constant, the combustion wave is described by a similarity solution which is a function of the similarity variable x/square root of(t) and the wave velocity decays as 1/square root of(t). The difference between the two problems is that in the combustion problem the temperature is not prescribed, but rather, is determined as part of the solution. We will show that the length of samples in which such self-sustained combustion waves can occur, must exceed a critical value which strongly depends on the combustion temperature T(sub b). Smaller values of T(sub b) require longer sample lengths for diffusion driven combustion waves to exist. Because of their relatively small velocity, diffusion driven waves are considered to be relevant for the case of low heat losses, which occur for large diameter samples or in microgravity conditions, Another possible mechanism of porous medium combustion describes waves which propagate by consuming the oxidizer initially stored in the pores of the sample. This occurs for abnormally high pressure and gas density. In this case, uniformly propagating planar waves, which are kinetically controlled, can propagate, Diffusion of oxidizer decreases

  11. Wave Forced Normal Modes on Fringing Reefs

    NASA Astrophysics Data System (ADS)

    Pequignet, A. N.; Becker, J. M.; Merrifield, M. M.; Aucan, J.

    2008-12-01

    In an effort to assess wave-driven coastal inundation at the shoreline of fringing reefs, pressure and current observations were collected at reefs on Guam (Ipan) and Oahu, Hawaii (Mokuleia) as part of the PILOT (Pacific Island Land-Ocean Typhoon) experiment. Similar to dissipative sandy beaches, nearshore surface elevation at both reefs is dominated by energy in the infragravity frequency band. Coherent infragravity oscillations across the reef tend to occur at discrete frequencies and with standing wave cross-shore structures that are consistent with open basin resonant modes. The modes are forced by swell wave groups, similar to a time-dependent setup. The resonant modes are most apparent during energetic wave events, in part because wave setup over the reef increases the low mode resonant frequencies to a range that is conducive to wave group forcing. Evidence of the excitation of resonant modes during tropical storm Man-Yi at Ipan, Guam is presented.

  12. Direct Cytoskeleton Forces Cause Membrane Softening in Red Blood Cells

    PubMed Central

    Rodríguez-García, Ruddi; López-Montero, Iván; Mell, Michael; Egea, Gustavo; Gov, Nir S.; Monroy, Francisco

    2015-01-01

    Erythrocytes are flexible cells specialized in the systemic transport of oxygen in vertebrates. This physiological function is connected to their outstanding ability to deform in passing through narrow capillaries. In recent years, there has been an influx of experimental evidence of enhanced cell-shape fluctuations related to metabolically driven activity of the erythroid membrane skeleton. However, no direct observation of the active cytoskeleton forces has yet been reported to our knowledge. Here, we show experimental evidence of the presence of temporally correlated forces superposed over the thermal fluctuations of the erythrocyte membrane. These forces are ATP-dependent and drive enhanced flickering motions in human erythrocytes. Theoretical analyses provide support for a direct force exerted on the membrane by the cytoskeleton nodes as pulses of well-defined average duration. In addition, such metabolically regulated active forces cause global membrane softening, a mechanical attribute related to the functional erythroid deformability. PMID:26083919

  13. Non-equilibrium Casimir force between vibrating plates.

    PubMed

    Hanke, Andreas

    2013-01-01

    We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed. PMID:23326401

  14. Apparatus for controlling an engine in a hydraulically driven vehicle

    SciTech Connect

    Kitada, T.

    1987-01-27

    An apparatus is described for controlling the internal combustion engine of a hydraulically driven vehicle comprising: a transmission mechanism for transmitting the operation of a fuel control lever to a governor control lever and having a loose spring mechanism with a loose spring therein: a hydraulic decelerator cylinder connected to the transmission mechanism and having a spring and piston therein. The deceleration cylinder spring has a slightly larger spring force than the loose spring in the loose spring mechanism and applies a force absorbing action, in the absence of hydraulic force acting on the piston, to set the governor control lever in its deceleration position when the fuel control lever is moved to its full engine speed position and for moving the governor control lever to its full engine speed position when hydraulic force is applied to the piston; an electromagnetic valve for applying fluid pressure from a control pump driven by the engine to the piston in the decelerator cylinder and releasing the fluid pressure; and an electric circuit including switches operationally associated with levers for operating a hydraulic valve.

  15. Traceable periodic force calibration

    NASA Astrophysics Data System (ADS)

    Schlegel, Ch; Kieckenap, G.; Glöckner, B.; Buß, A.; Kumme, R.

    2012-06-01

    A procedure for dynamic force calibration using sinusoidal excitations of force transducers is described. The method is based on a sinusoidal excitation of force transducers equipped with an additional top mass excited with an electrodynamic shaker system. The acting dynamic force can in this way be determined according to Newton's law as mass times acceleration, whereby the acceleration is measured on the surface of the top mass with the aid of laser interferometers. The dynamic sensitivity, which is the ratio of the electrical output signal of the force transducer and the acting dynamic force, is the main point of interest of such a dynamic calibration. In addition to the sensitivity, the parameter stiffness and damping of the transducer can also be determined. The first part of the paper outlines a mathematical model to describe the dynamic behaviour of a transducer. This is followed by a presentation of the traceability of the measured quantities involved and their uncertainties. The paper finishes with an example calibration of a 25 kN strain gauge force transducer.

  16. Turbomachinery rotor forces

    NASA Technical Reports Server (NTRS)

    Arndt, Norbert

    1988-01-01

    The fluid-induced forces, both steady and unsteady, acting upon an impeller of a centrifugal pump, and impeller blade-diffuser vane interaction in centrifugal pumps with vaned radial diffusers were evaluated experimentally and theoretically. Knowledge of the steady and unsteady forces, and the associated rotordynamic coefficients are required to effectively model the rotor dynamics of the High Pressure Fuel Turbopump (HPFTP) of the Space Shuttle Main Engine (SSME). These forces and rotordynamic coefficients were investigated using different impellers in combination with volutes and vaned diffusers, and axial inducers. These rotor forces are global. Local forces and pressures are also important in impeller-diffuser interaction, for they may cause cavitation damage and even vane failures. Thus, in a separate investigation, impeller wake, and impeller blade and diffuser vane pressure measurements were made. The nature of the rotordynamic forces is discussed, the experimental facility is described, and the measurements of unsteady forces and pressure are reported together with a brief and incomplete attempt to calculate these flows.

  17. OOTW Force Design Tools

    SciTech Connect

    Bell, R.E.; Hartley, D.S.III; Packard, S.L.

    1999-05-01

    This report documents refined requirements for tools to aid the process of force design in Operations Other Than War (OOTWs). It recommends actions for the creation of one tool and work on other tools relating to mission planning. It also identifies the governmental agencies and commands with interests in each tool, from whom should come the user advisory groups overseeing the respective tool development activities. The understanding of OOTWs and their analytical support requirements has matured to the point where action can be taken in three areas: force design, collaborative analysis, and impact analysis. While the nature of the action and the length of time before complete results can be expected depends on the area, in each case the action should begin immediately. Force design for OOTWs is not a technically difficult process. Like force design for combat operations, it is a process of matching the capabilities of forces against the specified and implied tasks of the operation, considering the constraints of logistics, transport and force availabilities. However, there is a critical difference that restricts the usefulness of combat force design tools for OOTWs: the combat tools are built to infer non-combat capability requirements from combat capability requirements and cannot reverse the direction of the inference, as is required for OOTWs. Recently, OOTWs have played a larger role in force assessment, system effectiveness and tradeoff analysis, and concept and doctrine development and analysis. In the first Quadrennial Defense Review (QDR), each of the Services created its own OOTW force design tool. Unfortunately, the tools address different parts of the problem and do not coordinate the use of competing capabilities. These tools satisfied the immediate requirements of the QDR, but do not provide a long-term cost-effective solution.

  18. Manual discrimination of force

    NASA Technical Reports Server (NTRS)

    Pang, Xiao-Dong; Tan, HONG-Z.; Durlach, Nathaniel I.

    1991-01-01

    Optimal design of human-machine interfaces for teleoperators and virtual-environment systems which involve the tactual and kinesthetic modalities requires knowledge of the human's resolving power in these modalities. The resolution of the interface should be appropriately matched to that of the human operator. We report some preliminary results on the ability of the human hand to distinguish small differences in force under a variety of conditions. Experiments were conducted on force discrimination with the thumb pushing an interface that exerts a constant force over the pushing distance and the index finger pressing against a fixed support. The dependence of the sensitivity index d' on force increment can be fit by a straight line through the origin and the just-noticeable difference (JND) in force can thus be described by the inverse of the slope of this line. The receiver operating characteristic (ROC) was measured by varying the a priori probabilities of the two alternatives, reference force and reference force plus an increment, in one-interval, two-alternative, forced-choice experiments. When plotted on normal deviate coordinates, the ROC's were roughly straight lines of unit slope, thus supporting the assumption of equal-variance normal distributions and the use of the conventional d' measure. The JND was roughly 6-8 percent for reference force ranging from 2.5 to 10 newtons, pushing distance from 5 to 30 mm, and initial finger-span from 45 to 125 mm. Also, the JND remained the same when the subjects were instructed to change the average speed of pushing from 23 to 153 mm/sec. The pushing was terminated by reaching either a wall or a well, and the JND's were essentially the same in both cases.

  19. Dilatonic Entropic Force

    NASA Astrophysics Data System (ADS)

    Sakalli, I.

    2011-08-01

    We show in detail that the entropic force of the static spherically symmetric spacetimes with unusual asymptotics can be calculated through the Verlinde's arguments. We introduce three different holographic screen candidates, which are first employed thoroughly by Myung and Kim [Phys. Rev. D 81, 105012 (2010)] for Schwarzschild black hole solutions, in order to identify the entropic force arising between a charged dilaton black hole and a test particle. The significance of the dilaton parameter on the entropic force is highlighted, and shown graphically.

  20. Parameterization of the Lorentz to Coriolis Force Ratio in Planetary Dynamos

    NASA Astrophysics Data System (ADS)

    Soderlund, K. M.; Sheyko, A. A.; King, E. M.; Aurnou, J. M.

    2015-12-01

    The Lorentz to Coriolis force ratio is an important parameter for the dynamics of planetary cores: it is expected that dynamos with dominant Coriolis forces will be driven by fundamentally different archetypes of fluid motions than those with co-dominant Lorentz forces. Using a suite of geodynamo simulations, we have tested several parameterizations of the Lorentz to Coriolis force ratio against direct calculations and developed a scaling estimate to predict this ratio for planetary cores. Our results suggest that the Earth's core is likely to be in magnetostrophic balance where the Lorentz and Coriolis forces are comparable. The Lorentz force may also be significant in Jupiter's core, where it is predicted to be approximately a factor of ten less than the Coriolis force. Magnetic fields become increasingly sub-dominant for the other planets: the Coriolis force is predicted to exceed the Lorentz force by at least two orders of magnitude within the cores of Saturn, Uranus/Neptune, Ganymede, and Mercury.

  1. Causal reasoning with forces

    PubMed Central

    Wolff, Phillip; Barbey, Aron K.

    2015-01-01

    Causal composition allows people to generate new causal relations by combining existing causal knowledge. We introduce a new computational model of such reasoning, the force theory, which holds that people compose causal relations by simulating the processes that join forces in the world, and compare this theory with the mental model theory (Khemlani et al., 2014) and the causal model theory (Sloman et al., 2009), which explain causal composition on the basis of mental models and structural equations, respectively. In one experiment, the force theory was uniquely able to account for people's ability to compose causal relationships from complex animations of real-world events. In three additional experiments, the force theory did as well as or better than the other two theories in explaining the causal compositions people generated from linguistically presented causal relations. Implications for causal learning and the hierarchical structure of causal knowledge are discussed. PMID:25653611

  2. Forces in Motion.

    ERIC Educational Resources Information Center

    Goodsell, David; And Others

    1995-01-01

    Describes an activity to give students experience with the variables and forces impacting a moving body on an inclined plane by observing a ball as it rolls down an inclined PVC pipe of fixed length. Includes a student worksheet. (MKR)

  3. Metamaterials enhancing optical forces

    NASA Astrophysics Data System (ADS)

    Ginis, Vincent; Tassin, Philippe; Soukoulis, Costas M.; Veretennicoff, Irina

    2014-05-01

    The interaction between light and matter involves not only an energy transfer, but also the transfer of linear momentum. In everyday life applications this linear momentum of light is too small to play any significant role. However, in nanoscale dimensions, the associated optical forces start to play an increasingly important role. These forces are, e.g., large enough for exiting experiments in the fields of cavity-optomechanics, laser cooling and optical trapping of small particles. Recently, it has been suggested that optical gradient forces can also be employed for all-optical actuation in micro- and nanophotonic systems. The typical setup consists of two slab waveguides positioned in each others vicinity such that they are coupled through the interaction of the evanescent tails. Although the gradient forces between these waveguides can be enhanced considerably using electromagnetic resonators or slow-light techniques, the resulting displacements remain relatively small. In this contribution, we present an alternative approach to enhance optical gradient forces between waveguides using a combination of transformation optics and metamaterials. Our design starts from the observation that gradient forces exponentially decay with the separation distance between the waveguides. Therefore, we employ transformation optics to annihilate the apparent distance for light between the waveguides. Analytical calculations confirm that the resulting forces indeed increase when such an annihilating cladding is inserted. Subsequently, we discuss the metamaterial implementation of this annihilating medium. Such lensing media automatically translate into anisotropic metamaterials with negative components in the permittivity and permeability tensors. Our full-wave numerical simulations show that the overall amplification is highly limited by the loss-tangent of the metamaterial cladding. However, as this cladding only needs to operate in the near-field for a specific polarization

  4. Strategic forces briefing

    SciTech Connect

    Bing, G.; Chrzanowski, P.; May, M.; Nordyke, M.

    1989-04-06

    The Strategic Forces Briefing'' is our attempt, accomplished over the past several months, to outline and highlight the more significant strategic force issues that must be addressed in the near future. Some issues are recurrent: the need for an effective modernized Triad and a constant concern for force survivability. Some issues derive from arms control: the Strategic Arms Reduction Talks (SALT) are sufficiently advanced to set broad numerical limits on forces, but not so constraining as to preclude choices among weapon systems and deployment modes. Finally, a new administration faced with serious budgetary problems must strive for the most effective strategic forces limited dollars can buy and support. A review of strategic forces logically begins with consideration of the missions the forces are charged with. We begin the briefing with a short review of targeting policy and implementation within the constraints of available unclassified information. We then review each element of the Triad with sections on SLBMs, ICBMs, and Air-Breathing (bomber and cruise missile) systems. A short section at the end deals with the potential impact of strategic defense on offensive force planning. We consider ABM, ASAT, and air defense; but we do not attempt to address the technical issues of strategic defense per se. The final section gives a brief overview of the tritium supply problem. We conclude with a summary of recommendations that emerge from our review. The results of calculation on the effectiveness of various weapon systems as a function of cost that are presented in the briefing are by Paul Chrzanowski.

  5. Force-Measuring Clamp

    NASA Technical Reports Server (NTRS)

    Nunnelee, Mark (Inventor)

    2004-01-01

    A precision clamp that accurately measures force over a wide range of conditions is described. Using a full bridge or other strain gage configuration. the elastic deformation of the clamp is measured or detected by the strain gages. Thc strain gages transmit a signal that corresponds to the degree of stress upon the clamp. Thc strain gage signal is converted to a numeric display. Calibration is achieved by ero and span potentiometers which enable accurate measurements by the force-measuring clamp.

  6. Optical ``Bernoulli'' forces

    NASA Astrophysics Data System (ADS)

    Movassagh, Ramis; Johnson, Steven

    2015-03-01

    By Bernoulli's law, an increase in the relative speed of a fluid around a body is accompanies by a decrease in the pressure. Therefore, a rotating body in a fluid stream experiences a force perpendicular to the motion of the fluid because of the unequal relative speed of the fluid across its surface. It is well known that light has a constant speed irrespective of the relative motion. Does a rotating body immersed in a stream of photons experience a Bernoulli-like force? We show that, indeed, a rotating dielectric cylinder experiences such a lateral force from an electromagnetic wave. In fact, the sign of the lateral force is the same as that of the fluid-mechanical analogue as long as the electric susceptibility is positive (ɛ >ɛ0), but for negative-susceptibility materials (e.g. metals) we show that the lateral force is in the opposite direction. Because these results are derived from a classical electromagnetic scattering problem, Mie-resonance enhancements that occur in other scattering phenomena also enhance the lateral force. [This talk is based on Phys. Rev. A 88, 023829 (2013).] Supported in part by the U.S. Army Research Office under contract W911NF-13-D-0001.

  7. The Missing Climate Forcing

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Sato, M.; Lacis, A.; Ruedy, R.

    1997-02-01

    Observed climate change is consistent with radiative forcings on several time scales for which the dominant forcings are known, ranging from the few years after a large volcanic eruption to glacial-to-interglacial changes. In the period with most detailed data, 1979 to the present, climate observations contain clear signatures of both natural and anthropogenic forcings. But in the full period since the industrial revolution began, global warming is only about half of that expected due to the principal forcing, increasing greenhouse gases. The direct radiative effect of anthropogenic aerosols contributes only little towards resolving this discrepancy. Unforced climate variability is an unlikely explanation. We argue on the basis of several lines of indirect evidence that aerosol effects on clouds have caused a large negative forcing, at least -1 Wm-2, which has substantially offset greenhouse warming. The tasks of observing this forcing and determining the microphysical mechanisms at its basis are exceptionally difficult, but they are essential for the prognosis of future climate change.

  8. Van der Waals Forces

    NASA Astrophysics Data System (ADS)

    Parsegian, V. Adrian

    2006-03-01

    This should prove to be the definitive work explaining van der Waals forces, how to calculate them and take account of their impact under any circumstances and conditions. These weak intermolecular forces are of truly pervasive impact, and biologists, chemists, physicists and engineers will profit greatly from the thorough grounding in these fundamental forces that this book offers. Parsegian has organized his book at three successive levels of mathematical sophistication, to satisfy the needs and interests of readers at all levels of preparation. The Prelude and Level 1 are intended to give everyone an overview in words and pictures of the modern theory of van der Waals forces. Level 2 gives the formulae and a wide range of algorithms to let readers compute the van der Waals forces under virtually any physical or physiological conditions. Level 3 offers a rigorous basic formulation of the theory. Author is among the most highly respected biophysicists Van der Waals forces are significant for a wide range of questions and problems in the life sciences, chemistry, physics, and engineering, ranging up to the macro level No other book that develops the subject vigorously, and this book also makes the subject intuitively accessible to students who had not previously been mathematically sophisticated enough to calculate them

  9. Foot force production and asymmetries in elite rowers.

    PubMed

    Buckeridge, Erica M; Bull, Anthony M J; McGregor, Alison H

    2014-03-01

    The rowing stroke is a leg-driven action, in which forces developed by the lower limbs provide a large proportion of power delivered to the oars. In terms of both performance and injury, it is important to initiate each stroke with powerful and symmetrical loading of the foot stretchers. The aims of this study were to assess the reliability of foot force measured by footplates developed for the Concept2 indoor ergometer and to examine the magnitude and symmetry of bilateral foot forces in different groups of rowers. Five heavyweight female scullers, six heavyweight female sweep rowers, and six lightweight male (LWM) rowers performed an incremental step test on the Concept2 ergometer. Vertical, horizontal, and resultant forces were recorded bilaterally, and asymmetries were quantified using the absolute symmetry index. Foot force was measured with high consistency (coefficient of multiple determination > 0.976 +/- 0.010). Relative resultant, vertical, and horizontal forces were largest in LWM rowers, whilst average foot forces significantly increased across stroke rates for all three groups of rowers. Asymmetries ranged from 5.3% for average resultant force to 28.9% for timing of peak vertical force. Asymmetries were not sensitive to stroke rate or rowing group, however, large inter-subject variability in asymmetries was evident.

  10. Data-driven batch schuduling

    SciTech Connect

    Bent, John; Denehy, Tim; Arpaci - Dusseau, Remzi; Livny, Miron; Arpaci - Dusseau, Andrea C

    2009-01-01

    In this paper, we develop data-driven strategies for batch computing schedulers. Current CPU-centric batch schedulers ignore the data needs within workloads and execute them by linking them transparently and directly to their needed data. When scheduled on remote computational resources, this elegant solution of direct data access can incur an order of magnitude performance penalty for data-intensive workloads. Adding data-awareness to batch schedulers allows a careful coordination of data and CPU allocation thereby reducing the cost of remote execution. We offer here new techniques by which batch schedulers can become data-driven. Such systems can use our analytical predictive models to select one of the four data-driven scheduling policies that we have created. Through simulation, we demonstrate the accuracy of our predictive models and show how they can reduce time to completion for some workloads by as much as 80%.

  11. Buoyancy-Driven Polymerase Chain Reaction (PCR) Devices

    SciTech Connect

    Ness, K D; Wheeler, E K; Benett, W; Stratton, P; Christian, A; Chen, A; Ortega, J; Weisgraber, T H; Goodson, K E

    2004-09-28

    Polymerase chain reaction (PCR) facilitates DNA detection by significantly increasing the concentration of specific DNA segments. A new class of PCR instruments uses a buoyancy-driven re-circulating flow to thermally cycle the DNA sample and benefits from reduced cycle times, low sample volumes, a miniaturized format, and low power consumption. This paper analyzes a specific buoyancy PCR device in a micro-channel ''race-track'' geometry to determine key parameters about PCR cycle times and other figures of merit as functions of device dimensions. The 1-D model balances the buoyancy driving force with frictional losses. A hydrostatic pressure imbalance concept is used between the left and right sides of the fluid loop to calculate the buoyancy driving force. Velocity and temperature distributions within the channels are determined from two-dimensional analysis of the channel section, with developing region effects included empirically through scaled values of the local Nusselt number. Good agreement between four independent verification steps validate the 1-D simulation approach: (1) analytical expressions for the thermal entrance length are compared against, (2) comparison with a full 3-D finite element simulation, (3) comparison with an experimental flow field characterization, and (4) calculation of the minimum PCR runtime required to get a positive PCR signal from the buoyancy-driven PCR device. The 1-D approach closely models an actual buoyancy-driven PCR device and can further be used as a rapid design tool to simulate buoyancy PCR flows and perform detailed design optimizations studies.

  12. Flow Field Measurement of Mixing Driven by Buoyancy

    NASA Technical Reports Server (NTRS)

    Batur, C.; Zhong, H.

    2003-01-01

    Mixing driven by buoyancy-induced flows inside a cavity consists of stretching and folding of an interface. Measurement of the flow field using particle imaging velocimetry shows that during stretching the flow field has a single elliptic point, thus dominated by a single vortex. However, global bifurcation that results in folding introduces a hyperbolic point whereby the flow field degenerates to multiple vortex interactions. The short-lived coherent structure observed during mixing which results in the Rayleigh- Taylor morphology is attributed to vortex interactions. The mixing characteristics of non-homogeneous fluids driven by buoyancy are important towards understanding transport phenomenon in a microgravity environment. Mixing consists of stretching and folding of an interface due to a flow field whose intensity depends on the body force. For miscible liquids, the characteristic of the flow field determines whether mass transport is governed by diffusion or bulk stirring which induces mixing. For technologically important processes, transport of mass is governed by the coupling of the body force to scalar gradients such as concentration and or temperature' 2 3 . In order to lend insight into these classes of problems we consider a model experimental system to study mixing driven by buoyancy-induced flows. The characteristics of mixing is addressed from detail measurements of the flow field using particle imaging velocimetry (PIV), and its corresponding interface dynamics using image processing techniques.

  13. Magnetically driven quantum heat engine.

    PubMed

    Muñoz, Enrique; Peña, Francisco J

    2014-05-01

    We studied the efficiency of two different schemes for a magnetically driven quantum heat engine, by considering as the "working substance" a single nonrelativistic particle trapped in a cylindrical potential well, in the presence of an external magnetic field. The first scheme is a cycle, composed of two adiabatic and two isoenergetic reversible trajectories in configuration space. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity. The second scheme is a variant of the former, where the isoenergetic trajectories are replaced by isothermal ones, along which the system is in contact with macroscopic thermostats. This second scheme constitutes a quantum analog of the classical Carnot cycle.

  14. Design, fabrication and testing of laterally driven electrostatic motors employing walking motion and mechanical leverage

    NASA Astrophysics Data System (ADS)

    Tas, N. R.; Sonnenberg, T.; Molenaar, R.; Elwenspoek, M.

    2003-01-01

    Laterally driven linear electrostatic micromotors have been fabricated by standard surface micromachining. We attempt to employ mechanical leverage with the aim to increase the force from the order of 1 μN up to the order of 0.1 mN, in combination with walking motion to increase the stroke to virtually unlimited. Three designs have been made and tested. We conclude that mechanical levers with proper stiffness characteristics to be driven by electrostatic actuators are feasible. Friction as a function of the applied electrostatic clamp force has been measured, showing that there is a significant adhesion in the clamps. Walking motion has been successfully generated in one of the designs, generating a stroke of 15 μm and a force of 3 μN. Improvement of the clamping is needed to benefit from the implemented levers to increase the generated force.

  15. Low frequency driven oscillations of cantilevers in viscous fluids at very low Reynolds number

    NASA Astrophysics Data System (ADS)

    Cranch, G. A.; Lane, J. E.; Miller, G. A.; Lou, J. W.

    2013-05-01

    The motion of submerged cantilevers driven by viscous fluids is experimentally investigated and a previously published theoretical model is verified over a broad range of Reynolds number covering 4×10-3≤Re≤2000 at frequencies up to 1 kHz. Both planar and cylindrical cantilevers are implemented using short length (few centimeters) fiber lasers, which are also used to measure the deflections. The driving forces are analyzed in detail illustrating how the dominant force transitions from a pressure related force to a viscous force depending on the Reynolds number of the fluid flow around the cantilever. Simplified, approximate expressions for the tip displacement of cantilevers oscillating in the highly viscous regime are also presented. These results will enable accurate, a priori, calculation of the motion of driven cantilevers over a range of dimensions, geometries, and fluid properties.

  16. Lenz's Law: Feel the Force.

    ERIC Educational Resources Information Center

    Sawicki, Charles A.

    1996-01-01

    Describes a simple, inexpensive system that allows students to have hands-on contact with simple experiments involving forces generated by induced currents. Discusses the use of a dynamic force sensor in making quantitative measurements of the forces generated. (JRH)

  17. Surgical force detection probe

    NASA Technical Reports Server (NTRS)

    Tcheng, Ping; Roberts, Paul; Scott, Charles; Prass, Richard

    1991-01-01

    The development progress of a precision electro-mechanical instrument which allows the detection and documentation of the forces and moment applied to human tissue during surgery (under actual operation room conditions), is reported. The pen-shaped prototype probe which measures 1/2 inch in diameter and 7 inches in length was fabricated using an aerodynamic balance. The aerodynamic balance, a standard wind tunnel force and moment sensing transducer, measures the forces and the moments transmitted through the surgeon's hand to the human tissue during surgery. The prototype probe which was fabricated as a development tool was tested successfully. The final version of the surgical force detection probe will be designed based on additional laboratory tests in order to establish the full scale loads. It is expected that the final product will require a simplified aerodynamic balance with two or three force components and one moment component with lighter full scale loads. A signal conditioner was fabricated to process and display the outputs from the prototype probe. This unit will be interfaced with a PC-based data system to provide automatic data acquisition, data processing, and graphics display. The expected overall accuracy of the probe is better than one percent full scale.

  18. Radiative Forcing by Contrails

    NASA Technical Reports Server (NTRS)

    Meerkoetter, R.; Schumann, U.; Doelling, D. R.; Nakajima, T.; Tsushima, Y.

    1999-01-01

    A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmospheres The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 W/m(exp 2)a daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

  19. A combined Event-Driven/Time-Driven molecular dynamics algorithm for the simulation of shock waves in rarefied gases

    NASA Astrophysics Data System (ADS)

    Valentini, Paolo; Schwartzentruber, Thomas E.

    2009-12-01

    A novel combined Event-Driven/Time-Driven (ED/TD) algorithm to speed-up the Molecular Dynamics simulation of rarefied gases using realistic spherically symmetric soft potentials is presented. Due to the low density regime, the proposed method correctly identifies the time that must elapse before the next interaction occurs, similarly to Event-Driven Molecular Dynamics. However, each interaction is treated using Time-Driven Molecular Dynamics, thereby integrating Newton's Second Law using the sufficiently small time step needed to correctly resolve the atomic motion. Although infrequent, many-body interactions are also accounted for with a small approximation. The combined ED/TD method is shown to correctly reproduce translational relaxation in argon, described using the Lennard-Jones potential. For densities between ρ=10-4 kg/m and ρ=10-1 kg/m, comparisons with kinetic theory, Direct Simulation Monte Carlo, and pure Time-Driven Molecular Dynamics demonstrate that the ED/TD algorithm correctly reproduces the proper collision rates and the evolution toward thermal equilibrium. Finally, the combined ED/TD algorithm is applied to the simulation of a Mach 9 shock wave in rarefied argon. Density and temperature profiles as well as molecular velocity distributions accurately match DSMC results, and the shock thickness is within the experimental uncertainty. For the problems considered, the ED/TD algorithm ranged from several hundred to several thousand times faster than conventional Time-Driven MD. Moreover, the force calculation to integrate the molecular trajectories is found to contribute a negligible amount to the overall ED/TD simulation time. Therefore, this method could pave the way for the application of much more refined and expensive interatomic potentials, either classical or first-principles, to Molecular Dynamics simulations of shock waves in rarefied gases, involving vibrational nonequilibrium and chemical reactivity.

  20. A combined Event-Driven/Time-Driven molecular dynamics algorithm for the simulation of shock waves in rarefied gases

    SciTech Connect

    Valentini, Paolo Schwartzentruber, Thomas E.

    2009-12-10

    A novel combined Event-Driven/Time-Driven (ED/TD) algorithm to speed-up the Molecular Dynamics simulation of rarefied gases using realistic spherically symmetric soft potentials is presented. Due to the low density regime, the proposed method correctly identifies the time that must elapse before the next interaction occurs, similarly to Event-Driven Molecular Dynamics. However, each interaction is treated using Time-Driven Molecular Dynamics, thereby integrating Newton's Second Law using the sufficiently small time step needed to correctly resolve the atomic motion. Although infrequent, many-body interactions are also accounted for with a small approximation. The combined ED/TD method is shown to correctly reproduce translational relaxation in argon, described using the Lennard-Jones potential. For densities between {rho}=10{sup -4}kg/m{sup 3} and {rho}=10{sup -1}kg/m{sup 3}, comparisons with kinetic theory, Direct Simulation Monte Carlo, and pure Time-Driven Molecular Dynamics demonstrate that the ED/TD algorithm correctly reproduces the proper collision rates and the evolution toward thermal equilibrium. Finally, the combined ED/TD algorithm is applied to the simulation of a Mach 9 shock wave in rarefied argon. Density and temperature profiles as well as molecular velocity distributions accurately match DSMC results, and the shock thickness is within the experimental uncertainty. For the problems considered, the ED/TD algorithm ranged from several hundred to several thousand times faster than conventional Time-Driven MD. Moreover, the force calculation to integrate the molecular trajectories is found to contribute a negligible amount to the overall ED/TD simulation time. Therefore, this method could pave the way for the application of much more refined and expensive interatomic potentials, either classical or first-principles, to Molecular Dynamics simulations of shock waves in rarefied gases, involving vibrational nonequilibrium and chemical reactivity.

  1. Database Driven 6-DOF Trajectory Simulation for Debris Transport Analysis

    NASA Technical Reports Server (NTRS)

    West, Jeff

    2008-01-01

    Debris mitigation and risk assessment have been carried out by NASA and its contractors supporting Space Shuttle Return-To-Flight (RTF). As a part of this assessment, analysis of transport potential for debris that may be liberated from the vehicle or from pad facilities prior to tower clear (Lift-Off Debris) is being performed by MSFC. This class of debris includes plume driven and wind driven sources for which lift as well as drag are critical for the determination of the debris trajectory. As a result, NASA MSFC has a need for a debris transport or trajectory simulation that supports the computation of lift effect in addition to drag without the computational expense of fully coupled CFD with 6-DOF. A database driven 6-DOF simulation that uses aerodynamic force and moment coefficients for the debris shape that are interpolated from a database has been developed to meet this need. The design, implementation, and verification of the database driven six degree of freedom (6-DOF) simulation addition to the Lift-Off Debris Transport Analysis (LODTA) software are discussed in this paper.

  2. Light driven microactuators: Design, fabrication, and mathematical modeling

    NASA Astrophysics Data System (ADS)

    Han, Li-Hsin

    This dissertation is concerned with design, fabrication, and mathematical modeling of three different microactuators driven by light. Compared to electricity, electromagnetic wave is a wireless source of power. A distant light source can be delivered, absorbed, and converted to generate a driving force for a microactuator. The study of light-driven microsystems, still at its early stage, is already expanding the horizon for the research of microsystems. The microactuators of this dissertation include micro-cantilevers driven by pulsed laser, photo-deformable microshells coated with gold nanospheres, and a nano-particles coated micro-turbine driven by visible light. Experimental investigation and theoretical analysis of these microactuators showed interesting results. These microactuators were functioned based on cross-linked, multiple physics phenomenon, such as photo-heating, thermal expansion, photo-chemistry effect, plasomonics enhancement, and thermal convection in rarefied gas. These multiple physics effects dominate the function of a mechanical system, when the system size becomes small. The modeling results of the microactuators suggest that, to simulate a microscale mechanical system accurately, one has to take account the minimum dimension of the system and to consider the validity of a theoretical model. Examples of the building of different microstructures were shown to demonstrate the capacity of a digital-micromirror-device (DMD) based apparatus for three-dimensional, heterogeneous fabrication of polymeric microstructures.

  3. Joint entropy and decoherence without dissipation in a driven harmonic oscillator

    NASA Astrophysics Data System (ADS)

    Fotue, A. J.; Wirngo, A. V.; Keumo Tsiaze, R. M.; Hounkonnou, M. N.

    2016-09-01

    The joint entropy of a non-dissipative driven harmonic oscillator for both the single and the double Gaussian states is determined. It is shown that, a non-random driving force does not influence the evolution of the system's joint entropy. For a random driving force however, the joint entropy increases almost monotonically with time, while exhibiting oscillatory behavior. The increase is a further proof of the decoherence mechanism in the system, for which we determine the duration and other characteristics.

  4. Development of a miniature motor-driven pulsatile LVAD driven by a fuzzy controller.

    PubMed

    Okamoto, Eiji; Makino, Tsutomu; Tanaka, Shuji; Yasuda, Takahiko; Akasaka, Yuta; Tani, Makiko; Inoue, Yusuke; Mitoh, Ayumu; Mitamura, Yoshinori

    2007-01-01

    We have been developing a small, lightweight motor-driven pulsatile left ventricular assist device (LVAD) with a ball screw. The motor-driven LVAD consists of a brushless DC motor and a ball screw. The attractive magnetic force between Nd-Fe-B magnets (with a diameter of 5 mm and a thickness of 1.5 mm) mounted in holes in a silicone rubber sheet (thickness 2 mm) and an iron plate adhered onto the a diaphragm of the blood pump can provide optimum active blood filling during the pump filling phase. The LVAD has a stroke volume of 55 ml and an overall volume of 285 ml; it weighs 360 g. The controller mainly consists of a fuzzy logic position and velocity controller to apply doctors' and engineers' knowledge to control the LVAD. Each unit of the controller consists of a functionally independent program module for easy improvement of the controller's performance. The LVAD was evaluated in in vitro experiments using a mock circulation. A maximum pump outflow of 5.1 l/min was obtained at a drive rate of 95 bpm against an afterload of 95 mmHg, and active filling using the attractive magnetic force provided a pump output of 3.6 l/min at a drive rate of 75 bpm under a preload of 0 mmHg. The operating efficiency of the LVAD was measured at between 8% and 10.5%. While the LVAD can provide adequate pump outflow for cardiac assistance, further upgrading of the software and improvement of the blood pump are required to improve pump performance and efficiency. PMID:17846714

  5. Pattern Formation in Driven Systems

    NASA Astrophysics Data System (ADS)

    Klymko, Katherine

    Model colloidal particles of two types, driven in opposite directions, will in two dimensions segregate into lanes, a phenomenon studied extensively by Lowen and co-workers [Dzubiella et al. Phys. Rev. E 65, 021402 (2002)]. We have simulated mixtures of oppositely-driven particles using three numerical protocols. We find that laning results from enhanced diffusion, in the direction perpendicular to the drive, of particles surrounded by particles of the opposite type, consistent with the observation of Vissers et al. [Soft Matter 7, 6, 2352 (2011)]. By comparing protocols we find that enhanced diffusion follows from a simple geometrical constraint: oppositely-driven particles must, in the time taken to encounter each other in the direction of the drive, diffuse in the perpendicular direction by about one particle diameter. This constraint implies that the effective lateral diffusion constant grows linearly with drive speed and as the square root of the packing fraction, a prediction supported by our numerics. By invoking an analogy between hard particles with environment-dependent mobilities and mutually attractive particles we argue that there exists an equilibrium system whose pattern-forming properties are similar to those of the driven system. Katherine Klymko acknowledges support from the NSF Graduate Research Fellowship.

  6. Driven shielding capacitive proximity sensor

    NASA Technical Reports Server (NTRS)

    Vranish, John M. (Inventor); McConnell, Robert L. (Inventor)

    2000-01-01

    A capacitive proximity sensing element, backed by a reflector driven at the same voltage as and in phase with the sensor, is used to reflect the field lines away from a grounded robot arm towards an intruding object, thus dramatically increasing the sensor's range and sensitivity.

  7. Data-Driven Proficiency Profiling

    ERIC Educational Resources Information Center

    Mostafavi, Behrooz; Liu, Zhongxiu; Barnes, Tiffany

    2015-01-01

    Deep Thought is a logic tutor where students practice constructing deductive logic proofs. Within Deep Thought is a data-driven mastery learning system (DDML), which calculates student proficiency based on rule scores weighted by expert-decided weights in order to assign problem sets of appropriate difficulty. In this study, we designed and tested…

  8. Rectified Forces in Rubidium

    NASA Astrophysics Data System (ADS)

    Grove, Timothy Todd

    The forces exerted on a three-level atom by a bichromatic standing-wave field are investigated. A theoretical analysis shows that the standing-wave dipole force can be rectified, i.e., maintain its sign over many optical wavelengths. Three systems in particular are studied: the lambda, the vee, and the cascade. Experimental results for the rubidium 5S --> 5P --> 5D cascade system are used to confirm the theory. The nearly coincident transition wavelengths for this system (780.0 nm and 776.0 nm) provide potential wells repeating at the beat wavelength (71 μm) which can accumulate laser cooled atoms. This force may have future applications in forming deep neutral atom traps as well as in the creation of new elements for atom optics. Two-color, two-photon spectroscopy of the 5D_{5/2}<=vel using the same cascade system (5S --> 5P --> 5D) was also performed.

  9. Linear force device

    NASA Technical Reports Server (NTRS)

    Clancy, John P.

    1988-01-01

    The object of the invention is to provide a mechanical force actuator which is lightweight and manipulatable and utilizes linear motion for push or pull forces while maintaining a constant overall length. The mechanical force producing mechanism comprises a linear actuator mechanism and a linear motion shaft mounted parallel to one another. The linear motion shaft is connected to a stationary or fixed housing and to a movable housing where the movable housing is mechanically actuated through actuator mechanism by either manual means or motor means. The housings are adapted to releasably receive a variety of jaw or pulling elements adapted for clamping or prying action. The stationary housing is adapted to be pivotally mounted to permit an angular position of the housing to allow the tool to adapt to skewed interfaces. The actuator mechanisms is operated by a gear train to obtain linear motion of the actuator mechanism.

  10. Carbohydrate force fields

    PubMed Central

    Foley, B. Lachele; Tessier, Matthew B.; Woods, Robert J.

    2014-01-01

    Carbohydrates present a special set of challenges to the generation of force fields. First, the tertiary structures of monosaccharides are complex merely by virtue of their exceptionally high number of chiral centers. In addition, their electronic characteristics lead to molecular geometries and electrostatic landscapes that can be challenging to predict and model. The monosaccharide units can also interconnect in many ways, resulting in a large number of possible oligosaccharides and polysaccharides, both linear and branched. These larger structures contain a number of rotatable bonds, meaning they potentially sample an enormous conformational space. This article briefly reviews the history of carbohydrate force fields, examining and comparing their challenges, forms, philosophies, and development strategies. Then it presents a survey of recent uses of these force fields, noting trends, strengths, deficiencies, and possible directions for future expansion. PMID:25530813

  11. Self-repairing symmetry in jellyfish through mechanically driven reorganization

    PubMed Central

    Abrams, Michael J.; Basinger, Ty; Yuan, William; Guo, Chin-Lin; Goentoro, Lea

    2015-01-01

    What happens when an animal is injured and loses important structures? Some animals simply heal the wound, whereas others are able to regenerate lost parts. In this study, we report a previously unidentified strategy of self-repair, where moon jellyfish respond to injuries by reorganizing existing parts, and rebuilding essential body symmetry, without regenerating what is lost. Specifically, in response to arm amputation, the young jellyfish of Aurelia aurita rearrange their remaining arms, recenter their manubria, and rebuild their muscular networks, all completed within 12 hours to 4 days. We call this process symmetrization. We find that symmetrization is not driven by external cues, cell proliferation, cell death, and proceeded even when foreign arms were grafted on. Instead, we find that forces generated by the muscular network are essential. Inhibiting pulsation using muscle relaxants completely, and reversibly, blocked symmetrization. Furthermore, we observed that decreasing pulse frequency using muscle relaxants slowed symmetrization, whereas increasing pulse frequency by lowering the magnesium concentration in seawater accelerated symmetrization. A mathematical model that describes the compressive forces from the muscle contraction, within the context of the elastic response from the mesoglea and the ephyra geometry, can recapitulate the recovery of global symmetry. Thus, self-repair in Aurelia proceeds through the reorganization of existing parts, and is driven by forces generated by its own propulsion machinery. We find evidence for symmetrization across species of jellyfish (Chrysaora pacifica, Mastigias sp., and Cotylorhiza tuberculata). PMID:26080418

  12. Flows driven by libration, precession, and tides, in planetary cores

    NASA Astrophysics Data System (ADS)

    Le Bars, Michael

    2015-11-01

    Because of gravitational interactions with their companions, the rotational dynamics of planets involve periodic perturbations of their shape, the direction of their rotational vector, and their rotation rate. These perturbations correspond in planetary terms to tides, precession, and longitudinal libration. I will review the flows driven by those mechanical forcings in the liquid iron core of planets, as well as their possible consequences on the planetary dynamics. Special focus will be placed on the associated instabilities and on the various routes toward turbulence recently studied, combining laboratory experiments and numerical simulations. The key point is that mechanical forcings do not provide the energy to the excited flows: They convey part of the available rotational energy and generate intense fluid motions through the excitation of localized jets, shear layers, and resonant inertial modes. Hence, even very small forcings - as it is the case in planets - may have large scale consequences. Mechanically driven flows thus play a fundamental role in planets, providing for instance alternative mechanisms to the standard convective models in explaining the puzzling past magnetic fields recorded on Moon and Mars, and in rationalizing the variety of shapes and rotational states observed in exoplanets.

  13. [Forced spirometry procedure].

    PubMed

    Cortés Aguilera, Antonio Javier

    2008-11-01

    Forced spirometry consists in a complementary test which is carried out in a health office in a workplace in order to determine the lung capacity of workers exposed to determined professional risks or those susceptible to determined working conditions which could lead to the development of respiratory problems. This test has been developed based on health vigilance laws under Article 22 of the Law for Prevention of Risks in the Workplace and requires that the technician, a nurse in a workplace, who performs it have some knowledge and skills regarding its use, following the norms for forced spirometry set by the Spanish Association for Pneumatology and Thoracic Surgery (SEPAR). PMID:19203116

  14. A real-time EMG-driven virtual arm.

    PubMed

    Manal, Kurt; Gonzalez, Roger V; Lloyd, David G; Buchanan, Thomas S

    2002-01-01

    An EMG-driven virtual arm is being developed in our laboratories for the purposes of studying neuromuscular control of arm movements. The virtual arm incorporates the major muscles spanning the elbow joint and is used to estimate tension developed by individual muscles based on recorded electromyograms (EMGs). It is able to estimate joint moments and the corresponding virtual movements, which are displayed in real-time on a computer screen. In addition, the virtual arm offers artificial control over a variety of physiological and environmental conditions. The virtual arm can be used to examine how the neuromuscular system compensates for the partial or total loss of a muscle's ability to generate force as might result from trauma or pathology. The purpose of this paper is to describe the design objectives, fundamental components and implementation of our real-time, EMG-driven virtual arm. PMID:11738638

  15. Noise spectroscopy and decoherence mitigation during free and driven evolution

    NASA Astrophysics Data System (ADS)

    Oliver, William

    2014-03-01

    Gate operations in a quantum information processor are generally realized by tailoring specific periods of free and driven evolution of a quantum system. Unwanted environmental noise, which may be distinct during these two periods, acts to decohere the system and increase the gate error rate. In this talk, we review our work on noise spectroscopy of superconducting qubits (persistent-current qubits, transmons) undergoing both free and driven evolution, and we present dynamical decoupling methods that can mitigate coherent errors in both cases. We discuss these results in the context of our present work and future directions. This research was funded in part by the Intelligence Advanced Research Projects Activity (IARPA), and by the Assistant Secretary of Defense for Research & Engineering, under Air Force Contract FA8721-05-C-0002.

  16. Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind

    NASA Technical Reports Server (NTRS)

    Alexander, M. J.; Rosenlof, K. H.

    1996-01-01

    The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.

  17. Radiative Forcing of Climate Change

    SciTech Connect

    Ramaswamy, V.; Boucher, Olivier; Haigh, J.; Hauglustaine, D.; Haywood, J.; Myhre, G.; Nakajima, Takahito; Shi, Guangyu; Solomon, S.; Betts, Robert E.; Charlson, R.; Chuang, C. C.; Daniel, J. S.; Del Genio, Anthony D.; Feichter, J.; Fuglestvedt, J.; Forster, P. M.; Ghan, Steven J.; Jones, A.; Kiehl, J. T.; Koch, D.; Land, C.; Lean, J.; Lohmann, Ulrike; Minschwaner, K.; Penner, Joyce E.; Roberts, D. L.; Rodhe, H.; Roelofs, G.-J.; Rotstayn, Leon D.; Schneider, T. L.; Schumann, U.; Schwartz, Stephen E.; Schwartzkopf, M. D.; Shine, K. P.; Smith, Steven J.; Stevenson, D. S.; Stordal, F.; Tegen, I.; van Dorland, R.; Zhang, Y.; Srinivasan, J.; Joos, Fortunat

    2001-10-01

    Chapter 6 of the IPCC Third Assessment Report Climate Change 2001: The Scientific Basis. Sections include: Executive Summary 6.1 Radiative Forcing 6.2 Forcing-Response Relationship 6.3 Well-Mixed Greenhouse Gases 6.4 Stratospheric Ozone 6.5 Radiative Forcing By Tropospheric Ozone 6.6 Indirect Forcings due to Chemistry 6.7 The Direct Radiative Forcing of Tropospheric Aerosols 6.8 The Indirect Radiative Forcing of Tropospheric Aerosols 6.9 Stratospheric Aerosols 6.10 Land-use Change (Surface Albedo Effect) 6.11 Solar Forcing of Climate 6.12 Global Warming Potentials hydrocarbons 6.13 Global Mean Radiative Forcings 6.14 The Geographical Distribution of the Radiative Forcings 6.15 Time Evolution of Radiative Forcings Appendix 6.1 Elements of Radiative Forcing Concept References.

  18. Kinetochore-independent chromosome segregation driven by lateral microtubule bundles

    PubMed Central

    Muscat, Christina C; Torre-Santiago, Keila M; Tran, Michael V; Powers, James A; Wignall, Sarah M

    2015-01-01

    During cell division, chromosomes attach to spindle microtubules at sites called kinetochores, and force generated at the kinetochore-microtubule interface is the main driver of chromosome movement. Surprisingly, kinetochores are not required for chromosome segregation on acentrosomal spindles in Caenorhabditis elegans oocytes, but the mechanism driving chromosomes apart in their absence is not understood. In this study, we show that lateral microtubule–chromosome associations established during prometaphase remain intact during anaphase to facilitate separation, defining a novel form of kinetochore-independent segregation. Chromosome dynamics during congression and segregation are controlled by opposing forces; plus-end directed forces are mediated by a protein complex that forms a ring around the chromosome center and dynein on chromosome arms provides a minus-end force. At anaphase onset, ring removal shifts the balance between these forces, triggering poleward movement along lateral microtubule bundles. This represents an elegant strategy for controlling chromosomal movements during cell division distinct from the canonical kinetochore-driven mechanism. DOI: http://dx.doi.org/10.7554/eLife.06462.001 PMID:26026148

  19. Shadow-driven 4D haptic visualization.

    PubMed

    Zhang, Hui; Hanson, Andrew

    2007-01-01

    Just as we can work with two-dimensional floor plans to communicate 3D architectural design, we can exploit reduced-dimension shadows to manipulate the higher-dimensional objects generating the shadows. In particular, by taking advantage of physically reactive 3D shadow-space controllers, we can transform the task of interacting with 4D objects to a new level of physical reality. We begin with a teaching tool that uses 2D knot diagrams to manipulate the geometry of 3D mathematical knots via their projections; our unique 2D haptic interface allows the user to become familiar with sketching, editing, exploration, and manipulation of 3D knots rendered as projected imageson a 2D shadow space. By combining graphics and collision-sensing haptics, we can enhance the 2D shadow-driven editing protocol to successfully leverage 2D pen-and-paper or blackboard skills. Building on the reduced-dimension 2D editing tool for manipulating 3D shapes, we develop the natural analogy to produce a reduced-dimension 3D tool for manipulating 4D shapes. By physically modeling the correct properties of 4D surfaces, their bending forces, and their collisions in the 3D haptic controller interface, we can support full-featured physical exploration of 4D mathematical objects in a manner that is otherwise far beyond the experience accessible to human beings. As far as we are aware, this paper reports the first interactive system with force-feedback that provides "4D haptic visualization" permitting the user to model and interact with 4D cloth-like objects.

  20. Radiation-Driven Astrophysical Jets

    NASA Astrophysics Data System (ADS)

    Fukue, Jun

    2000-10-01

    Radiative winds and jets from luminous accretion disks/tori are reviewed. Among various models of astrophysical jets, plasma outflows emanating from accretion disks/tori and accelerated by the radiation pressure is the most promising one. Here explained are the roles of radiation pressure force and radiation drag force. Rise and fall of a torus model are also discussed, following its revenge. Finally, the millennium jet model, where the multistage acceleration takes place, is proposed.

  1. Lorentz force particle analyzer

    NASA Astrophysics Data System (ADS)

    Wang, Xiaodong; Thess, André; Moreau, René; Tan, Yanqing; Dai, Shangjun; Tao, Zhen; Yang, Wenzhi; Wang, Bo

    2016-07-01

    A new contactless technique is presented for the detection of micron-sized insulating particles in the flow of an electrically conducting fluid. A transverse magnetic field brakes this flow and tends to become entrained in the flow direction by a Lorentz force, whose reaction force on the magnetic-field-generating system can be measured. The presence of insulating particles suspended in the fluid produce changes in this Lorentz force, generating pulses in it; these pulses enable the particles to be counted and sized. A two-dimensional numerical model that employs a moving mesh method demonstrates the measurement principle when such a particle is present. Two prototypes and a three-dimensional numerical model are used to demonstrate the feasibility of a Lorentz force particle analyzer (LFPA). The findings of this study conclude that such an LFPA, which offers contactless and on-line quantitative measurements, can be applied to an extensive range of applications. These applications include measurements of the cleanliness of high-temperature and aggressive molten metal, such as aluminum and steel alloys, and the clean manufacturing of semiconductors.

  2. The Force of Ideas

    ERIC Educational Resources Information Center

    Ascher, Carol

    2005-01-01

    "The Force of Ideas" describes a little-known aspect of both educational history and Viennese psychoanalysis during the interwar years: the movement for psychoanalytic pedagogy. The author traces her father's own story, beginning with his application to the Vienna Psychoanalytic Society for training as a psychoanalytic pedagogue, as a way to…

  3. Force limited vibration testing

    NASA Technical Reports Server (NTRS)

    Scharton, Terry D.

    1991-01-01

    A new method of conducting lab vibration tests of spacecraft equipment was developed to more closely simulate the vibration environment experienced when the spacecraft is launched on a rocket. The improved tests are tailored to identify equipment design and workmanship problems without inducing artificial failures that would not have occurred at launch. These new, less destructive types of vibration tests are essential to JPL's protoflight test approach in which lab testing is conducted using the flight equipment, often one of a kind, to save time and money. In conventional vibration tests, only the input vibratory motion is specified; the feedback, or reaction force, between the test item and the vibration machine is ignored. Most test failures occur when the test item goes into resonance, and the reaction force becomes very large. It has long been recognized that the large reaction force is a test artifact which does not occur with the lightweight, flexible mounting structures characteristic of spacecraft and space vehicles. In new vibration tests, both the motion and the force provided to the test item by the vibration machine are controlled, so that the vibration ride experienced by the test item is as in flight.

  4. Measuring Your Force

    ERIC Educational Resources Information Center

    Gee, David E.

    2005-01-01

    This article talks about the force behind education leaders. With all the challenges facing public education today, it is difficult to remain focused and to remember why one chartered this particular leadership course. Perhaps someone respected encouraged one to take this path long ago. Perhaps this kind of service to the nation and its future…

  5. Unification of Fundamental Forces

    NASA Astrophysics Data System (ADS)

    Salam, Abdus; Taylor, Foreword by John C.

    2005-10-01

    Foreword John C. Taylor; 1. Unification of fundamental forces Abdus Salam; 2. History unfolding: an introduction to the two 1968 lectures by W. Heisenberg and P. A. M. Dirac Abdus Salam; 3. Theory, criticism, and a philosophy Werner Heisenberg; 4. Methods in theoretical physics Paul Adrian Maurice Dirac.

  6. The Dynamic Force Table

    ERIC Educational Resources Information Center

    Geddes, John B.; Black, Kelly

    2008-01-01

    We examine an experimental apparatus that is used to motivate the connections between the basic properties of vectors, potential functions, systems of nonlinear equations, and Newton's method for nonlinear systems of equations. The apparatus is an adaptation of a force table where we remove the center-pin and allow the center-ring to move freely.…

  7. Perpendicular-Force Latch

    NASA Technical Reports Server (NTRS)

    Mattei, John P.; Buck, Peter A.; Williams, Michael D.

    1990-01-01

    Latching mechanism simultaneously applies force in two perpendicular directions to install or remove electronic-equipment modules. Used to simplify installation and removal of modular equipment where movement restricted by protective clothing as in hazardous environments or where installation and removal to be performed by robots or remote manipulators. Concept adaptable to hydraulic, pneumatic, and mechanical systems.

  8. Direct Aerosol Forcing Uncertainty

    DOE Data Explorer

    Mccomiskey, Allison

    2008-01-15

    Understanding sources of uncertainty in aerosol direct radiative forcing (DRF), the difference in a given radiative flux component with and without aerosol, is essential to quantifying changes in Earth's radiation budget. We examine the uncertainty in DRF due to measurement uncertainty in the quantities on which it depends: aerosol optical depth, single scattering albedo, asymmetry parameter, solar geometry, and surface albedo. Direct radiative forcing at the top of the atmosphere and at the surface as well as sensitivities, the changes in DRF in response to unit changes in individual aerosol or surface properties, are calculated at three locations representing distinct aerosol types and radiative environments. The uncertainty in DRF associated with a given property is computed as the product of the sensitivity and typical measurement uncertainty in the respective aerosol or surface property. Sensitivity and uncertainty values permit estimation of total uncertainty in calculated DRF and identification of properties that most limit accuracy in estimating forcing. Total uncertainties in modeled local diurnally averaged forcing range from 0.2 to 1.3 W m-2 (42 to 20%) depending on location (from tropical to polar sites), solar zenith angle, surface reflectance, aerosol type, and aerosol optical depth. The largest contributor to total uncertainty in DRF is usually single scattering albedo; however decreasing measurement uncertainties for any property would increase accuracy in DRF. Comparison of two radiative transfer models suggests the contribution of modeling error is small compared to the total uncertainty although comparable to uncertainty arising from some individual properties.

  9. On the Transition from Thermally-driven to Ponderomotively-driven Stimulated Brillouin Scattering and Filamentation of Light in Plasma

    SciTech Connect

    R.L. Berger; E.J. Valeo; S. Brunner

    2005-04-04

    The dispersion properties of ion acoustic waves and their nonlinear coupling to light waves through ponderomotive and thermal forces are sensitive to the strength of electron-ion collisions. Here, we consider the growth rate of stimulated Brillouin scattering (SBS) when the driven acoustic wave frequency and wavelength span the range of small to large compared to electron-ion collision frequency and mean free path respectively. We find in all cases the thermal contributions to the SBS growth rate are insignificant if the ion acoustic wave frequency is greater than the electron-ion collision frequency and the wavelength is much shorter than the electron-ion mean free path. On the other hand, the purely growing filamentation instability remains thermally driven for shorter wavelengths than SBS even when the growth rate is larger than the acoustic frequency.

  10. Chiral drag force

    NASA Astrophysics Data System (ADS)

    Rajagopal, Krishna; Sadofyev, Andrey V.

    2015-10-01

    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 the 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

  11. Propulsive Forces of a Biomimetic Undulating Fin

    NASA Astrophysics Data System (ADS)

    Kalumuck, Kenneth; Brandt, Alan; Armand, Mehran

    2007-11-01

    Understanding gained from much recent work on force production mechanisms of aquatic organisms holds great promise for improved undersea vehicle propulsion and maneuvering. One class of fish locomotion is that of the median fin utilized by animals such as squid, cuttlefish, knifefish, and seahorse. It is characterized by undulatory motion that creates traveling waves along the fin. Results of experiments conducted on a submerged mechanical underwater undulating fin test bed are presented. The 0.5 m long fin is mounted to a cylindrical body and consists of a flexible skin attached to ribs driven by an adjustable cam mechanism and variable speed motor that enables changing the characteristics of the undulating wave(s). Forces produced were measured in a captive mode under quiescent conditions as well in the presence of an ambient current. Propulsive forces are characterized as a function of the fin width, oscillation frequency, amplitude, and wavelength. Free swimming experiments were also conducted to determine the point of self propulsion. Flow field structure visualization using dye tracers is presented for selected cases. Estimates of performance and applications for use with larger scale vehicles are discussed.

  12. Frictional Force Behavior in the Elastic Regime

    NASA Astrophysics Data System (ADS)

    Crawford, P. J.; Hammerberg, J. E.

    2005-07-01

    The friction force between materials in explosively driven events is an important constitutive relationship, even though defining the friction coefficient in the presence of large bulk deformations is difficult. Measuring the force at an interface near deformations, without significantly modifying the interface in the process, proves difficult as well. Few studies (the pressure-shear plate experiments originally performed by Clifton et al. being one) have investigated the nature of the friction force at the small time-scales and the very high sliding speeds and pressures involved in explosive events. In order to approach the study of such combinations, we have developed a novel experimental apparatus (the rotating barrel gas gun, or RBGG) that gives us independent control of sliding speed and pressure at the interface while keeping the impact elastic, allowing us to make measurements away from the interface and to interpret the results without resorting to a simulation. We measure the axial and torsional strain in an annular target rod produced by the impact of a spinning, translating annular projectile. Experiments performed using Cu/Cu, Cu/Stainless and Cu/Al tribopairs provide some insight into the kinetic coefficient of friction behavior at various sliding speeds and loads.

  13. Amplification of actin polymerization forces

    PubMed Central

    Dmitrieff, Serge; Nédélec, François

    2016-01-01

    The actin cytoskeleton drives many essential processes in vivo, using molecular motors and actin assembly as force generators. We discuss here the propagation of forces caused by actin polymerization, highlighting simple configurations where the force developed by the network can exceed the sum of the polymerization forces from all filaments. PMID:27002174

  14. Artificial cognitive memory—changing from density driven to functionality driven

    NASA Astrophysics Data System (ADS)

    Shi, L. P.; Yi, K. J.; Ramanathan, K.; Zhao, R.; Ning, N.; Ding, D.; Chong, T. C.

    2011-03-01

    Increasing density based on bit size reduction is currently a main driving force for the development of data storage technologies. However, it is expected that all of the current available storage technologies might approach their physical limits in around 15 to 20 years due to miniaturization. To further advance the storage technologies, it is required to explore a new development trend that is different from density driven. One possible direction is to derive insights from biological counterparts. Unlike physical memories that have a single function of data storage, human memory is versatile. It contributes to functions of data storage, information processing, and most importantly, cognitive functions such as adaptation, learning, perception, knowledge generation, etc. In this paper, a brief review of current data storage technologies are presented, followed by discussions of future storage technology development trend. We expect that the driving force will evolve from density to functionality, and new memory modules associated with additional functions other than only data storage will appear. As an initial step toward building a future generation memory technology, we propose Artificial Cognitive Memory (ACM), a memory based intelligent system. We also present the characteristics of ACM, new technologies that can be used to develop ACM components such as bioinspired element cells (silicon, memristor, phase change, etc.), and possible methodologies to construct a biologically inspired hierarchical system.

  15. People Get Ready...A Call for Data-Driven Instruction

    ERIC Educational Resources Information Center

    Dyck, Brenda A.

    2006-01-01

    Fueled by a culture fascinated by numbers and increased accountability, data-driven instruction has become a mighty force as it joins with the tools of technology to handle the mammoth task of gathering, sorting, analyzing, and synthesizing data. Success stories from districts all over the country attest to the positive results of implementing…

  16. Incompressible Limit for Compressible Fluids with Stochastic Forcing

    NASA Astrophysics Data System (ADS)

    Breit, Dominic; Feireisl, Eduard; Hofmanová, Martina

    2016-11-01

    We study the asymptotic behavior of the isentropic Navier-Stokes system driven by a multiplicative stochastic forcing in the compressible regime, where the Mach number approaches zero. Our approach is based on the recently developed concept of a weak martingale solution to the primitive system, uniform bounds derived from a stochastic analogue of the modulated energy inequality, and careful analysis of acoustic waves. A stochastic incompressible Navier-Stokes system is identified as the limit problem.

  17. Buckling-driven delamination of carbon nanotube forests

    NASA Astrophysics Data System (ADS)

    Pour Shahid Saeed Abadi, Parisa; Hutchens, Shelby B.; Greer, Julia R.; Cola, Baratunde A.; Graham, Samuel

    2013-06-01

    We report buckling-driven delamination of carbon nanotube (CNT) forests from their growth substrates when subjected to compression. Macroscale compression experiments reveal local delamination at the CNT forest-substrate interface. Results of microscale flat punch indentations indicate that enhanced CNT interlocking at the top surface of the forest accomplished by application of a metal coating causes delamination of the forest from the growth substrate, a phenomenon not observed in indentation of as-grown CNT forests. We postulate that the post-buckling tensile stresses that develop at the base of the CNT forests serve as the driving force for delamination.

  18. Designing and operating electrostatically driven microengines

    SciTech Connect

    Rodgers, M.S.; Sniegowski, J.J.; Miller, S.L.; LaVigne, G.F.

    1998-02-01

    Microelectromechanical engines that convert the linear outputs from dual orthogonal electrostatic actuators to rotary motion were first developed in 1993. Referred to as microengines, these early devices demonstrated the potential of microelectromechanical technology, but, as expected from any first-of-its-kind device, were not yet optimized. Yield was relatively low, and the 10 micronewtons of force generated by the actuators was not always enough to ensure reliable operation. Since initial development, these engines have undergone a continuous series of significant improvements on three separate fronts: design, fabrication, and electrical activation. Although all three areas will be discussed, emphasis will be on aspects related to mechanical design and generation of the electrical waveforms used to drive these devices. Microtransmissions that dramatically increase torque will also be discussed. Electrostatically driven microengines can be operated at hundreds of thousands of revolutions per minute making large gear reduction ratios feasible; overall ratios of 3,000,000:1 have been successfully demonstrated. Today`s microengines have evolved into high endurance (one test device has seen over 7,000,000,000 revolutions), high yield, robust devices that have become the primary actuation source for MicroElectroMechanical Systems (MEMS) at Sandia National Laboratories.

  19. Computational dynamics of acoustically driven microsphere systems.

    PubMed

    Glosser, Connor; Piermarocchi, Carlo; Li, Jie; Dault, Dan; Shanker, B

    2016-01-01

    We propose a computational framework for the self-consistent dynamics of a microsphere system driven by a pulsed acoustic field in an ideal fluid. Our framework combines a molecular dynamics integrator describing the dynamics of the microsphere system with a time-dependent integral equation solver for the acoustic field that makes use of fields represented as surface expansions in spherical harmonic basis functions. The presented approach allows us to describe the interparticle interaction induced by the field as well as the dynamics of trapping in counter-propagating acoustic pulses. The integral equation formulation leads to equations of motion for the microspheres describing the effect of nondissipative drag forces. We show (1) that the field-induced interactions between the microspheres give rise to effective dipolar interactions, with effective dipoles defined by their velocities and (2) that the dominant effect of an ultrasound pulse through a cloud of microspheres gives rise mainly to a translation of the system, though we also observe both expansion and contraction of the cloud determined by the initial system geometry. PMID:26871188

  20. Transient Mixing Driven by Buoyancy Flows

    NASA Technical Reports Server (NTRS)

    Duval, W. M. B.; Batur, C.; Zhong, H.

    2002-01-01

    Mixing driven by buoyancy-induced flows is of particular interest to microgravity processes, as the body force that governs the intensity of flow fields can be directly controlled. We consider a model experimental system to explore the dynamics of mixing which employs two miscible liquids inside a cavity separated initially by a divider. The two liquids are oriented vertically inside a rectangular cavity with constant width and height, and varying depths to span the range of a Hele-Shaw cell to a 3-D configuration. The two miscible liquids can be sufficiently diluted and died, for example water and deuterium oxide, such that a distinct interface exists across the divider. The transient mixing characteristic of the two fluids is addressed by following the Lagrangian history of the interface for various aspect ratios in the z-plane (depth variation) as well as a range of pulling velocities of the divider. The mixing characteristics of the two fluids are quantified from measurement of the length stretch of the interface and its flow field using respectively image processing techniques and Particle Imaging Velocimetry. Scaling analysis shows that the length stretch depends on four governing parameters, namely the Grashof number (Gr), Schmidt number (Sc), aspect ratio (Ar), and Reynolds number (Re). Variation of the Schmidt number is taken into account through thermophysical property variation. Thus our problem reduces to a codimension three bifurcation in parametric space for Gr, Ar, and Re.

  1. A quasilinear formulation of turbulence driven current

    SciTech Connect

    McDevitt, C. J.; Tang, Xian-Zhu; Guo, Zehua

    2014-02-15

    Non-inductive current drive mechanisms, such as the familiar neoclassical bootstrap current correspond to an essential component to the realization of steady state tokamak operation. In this work, we discuss a novel collisionless mechanism through which a mean plasma current may be driven in the presence of microturbulence. In analogy with the traditional neoclassical bootstrap current drive mechanism, in which the collisional equilibrium established between trapped and passing electrons results in the formation of a steady state plasma current, here we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons. The resulting collisionless equilibrium is shown to result in the formation of an equilibrium current whose magnitude is a function of the thermodynamic forces. A mean field formulation is utilized to incorporate the above components into a unified framework through which both collisional as well as collisionless current drive mechanisms may be self-consistently treated. Utilizing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions as well as turbulent stresses is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.

  2. STREAMER WAVES DRIVEN BY CORONAL MASS EJECTIONS

    SciTech Connect

    Chen, Y.; Song, H. Q.; Li, B.; Xia, L. D.; Wu, Z.; Fu, H.; Li Xing

    2010-05-01

    Between 2004 July 5 and July 7, two intriguing fast coronal mass ejection (CME)-streamer interaction events were recorded by the Large Angle and Spectrometric Coronagraph. At the beginning of the events, the streamer was pushed aside from its equilibrium position upon the impact of the rapidly outgoing and expanding ejecta; then, the streamer structure, mainly the bright streamer belt, exhibited elegant large-scale sinusoidal wavelike motions. The motions were apparently driven by the restoring magnetic forces resulting from the CME impingement, suggestive of magnetohydrodynamic kink mode propagating outward along the plasma sheet of the streamer. The mode is supported collectively by the streamer-plasma sheet structure and is therefore named 'streamer wave' in the present study. With the white light coronagraph data, we show that the streamer wave has a period of about 1 hr, a wavelength varying from 2 to 4 solar radii, an amplitude of about a few tens of solar radii, and a propagating phase speed in the range 300-500 km s{sup -1}. We also find that there is a tendency for the phase speed to decline with increasing heliocentric distance. These observations provide good examples of large-scale wave phenomena carried by coronal structures and have significance in developing seismological techniques for diagnosing plasma and magnetic parameters in the outer corona.

  3. Computational dynamics of acoustically driven microsphere systems.

    PubMed

    Glosser, Connor; Piermarocchi, Carlo; Li, Jie; Dault, Dan; Shanker, B

    2016-01-01

    We propose a computational framework for the self-consistent dynamics of a microsphere system driven by a pulsed acoustic field in an ideal fluid. Our framework combines a molecular dynamics integrator describing the dynamics of the microsphere system with a time-dependent integral equation solver for the acoustic field that makes use of fields represented as surface expansions in spherical harmonic basis functions. The presented approach allows us to describe the interparticle interaction induced by the field as well as the dynamics of trapping in counter-propagating acoustic pulses. The integral equation formulation leads to equations of motion for the microspheres describing the effect of nondissipative drag forces. We show (1) that the field-induced interactions between the microspheres give rise to effective dipolar interactions, with effective dipoles defined by their velocities and (2) that the dominant effect of an ultrasound pulse through a cloud of microspheres gives rise mainly to a translation of the system, though we also observe both expansion and contraction of the cloud determined by the initial system geometry.

  4. Parasitic driven heliostat mirror declinator

    SciTech Connect

    Rhodes, W.A.

    1983-09-06

    An automatic parasitically driven declinator is disclosed for changing the tilt angle of the mirror of a heliostat to provide solar declination tracking by the heliostat. The declinator includes an axial gear drive train coupled to the polar axial shaft of the heliostat, which shaft is rotated. A pendulum arrangement coupled via an input shaft to the axial gear drive train is substantially held in plumb position by gravity wherein the gear drive train is driven as it is rotated about the polar axis by the polar axial shaft. An output shaft coupled to the gear train is rotated to drive a skew bar linkage assembly that is connected to the mirror mounting assembly of the heliostat. The gear ratio of the gear drive train assembly is made 365:1 so that the mirror angle is annually nutated a predetermined number of degrees corresponding to the cyclic variations of solar declination.

  5. Electrically driven environmental control system

    SciTech Connect

    Mcnamara, J.E.

    1984-05-01

    An environmental control system (ECS) being developed under the title of energy efficient environmental control system is described. The ECS is a closed-loop, electrically driven, vapor cycle system. The vapor cycle will have a compressor driven by a variable speed, high-voltage dc motor. The reasons for selecting this type of system are discussed here. Breadboard testing of a variable speed compressor to demonstrate the feasibility of such an approach has been completed. The testing results were used to develop a preliminary design of a prototype compressor. In future phases of the program, the prototype compressor will be developed a prototype system will be constructed and laboratory tested and finally the prototype system will be flight demonstrated.

  6. Pulsed Power Driven Fusion Energy

    SciTech Connect

    SLUTZ,STEPHEN A.

    1999-11-22

    Pulsed power is a robust and inexpensive technology for obtaining high powers. Considerable progress has been made on developing light ion beams as a means of transporting this power to inertial fusion capsules. However, further progress is hampered by the lack of an adequate ion source. Alternatively, z-pinches can efficiently convert pulsed power into thermal radiation, which can be used to drive an inertial fusion capsule. However, a z-pinch driven fusion explosion will destroy a portion of the transmission line that delivers the electrical power to the z-pinch. They investigate several options for providing standoff for z-pinch driven fusion. Recyclable Transmission Lines (RTLs) appear to be the most promising approach.

  7. Kaehler-driven tribrid inflation

    SciTech Connect

    Antusch, Stefan; Nolde, David E-mail: david.nolde@unibas.ch

    2012-11-01

    We discuss a new class of tribrid inflation models in supergravity, where the shape of the inflaton potential is dominated by effects from the Kaehler potential. Tribrid inflation is a variant of hybrid inflation which is particularly suited for connecting inflation with particle physics, since the inflaton can be a D-flat combination of charged fields from the matter sector. In models of tribrid inflation studied so far, the inflaton potential was dominated by either loop corrections or by mixing effects with the waterfall field (as in 'pseudosmooth' tribrid inflation). Here we investigate the third possibility, namely that tribrid inflation is dominantly driven by effects from higher-dimensional operators of the Kaehler potential. We specify for which superpotential parameters the new regime is realized and show how it can be experimentally distinguished from the other two (loop-driven and {sup p}seudosmooth{sup )} regimes.

  8. Quantum dynamics of light-driven chiral molecular motors.

    PubMed

    Yamaki, Masahiro; Nakayama, Shin-ichiro; Hoki, Kunihito; Kono, Hirohiko; Fujimura, Yuichi

    2009-03-21

    The results of theoretical studies on quantum dynamics of light-driven molecular motors with internal rotation are presented. Characteristic features of chiral motors driven by a non-helical, linearly polarized electric field of light are explained on the basis of symmetry argument. The rotational potential of the chiral motor is characterized by a ratchet form. The asymmetric potential determines the directional motion: the rotational direction is toward the gentle slope of the asymmetric potential. This direction is called the intuitive direction. To confirm the unidirectional rotational motion, results of quantum dynamical calculations of randomly-oriented molecular motors are presented. A theoretical design of the smallest light-driven molecular machine is presented. The smallest chiral molecular machine has an optically driven engine and a running propeller on its body. The mechanisms of transmission of driving forces from the engine to the propeller are elucidated by using a quantum dynamical treatment. The results provide a principle for control of optically-driven molecular bevel gears. Temperature effects are discussed using the density operator formalism. An effective method for ultrafast control of rotational motions in any desired direction is presented with the help of a quantum control theory. In this method, visible or UV light pulses are applied to drive the motor via an electronic excited state. A method for driving a large molecular motor consisting of an aromatic hydrocarbon is presented. The molecular motor is operated by interactions between the induced dipole of the molecular motor and the electric field of light pulses. PMID:19290336

  9. Heterogeneity in motor driven transport

    NASA Astrophysics Data System (ADS)

    Tabei, Ali

    2015-03-01

    I will discuss quantitative analysis of particle tracking data for motor driven vesicles inside an insulin secreting cell. We use this method to study the dynamical and structural heterogeneity inside the cell. I will discuss our effort to explain the origin of observed heterogeneity in intracellular transport. Finally, I will explain how analyzing directional correlations in transport trajectories reveals self-similarity in the diffusion media.

  10. Mission Driven Science at Argonne

    SciTech Connect

    Thackery, Michael; Wang, Michael; Young, Linda

    2012-01-01

    Mission driven science at Argonne means applying science and scientific knowledge to a physical and "real world" environment. Examples include testing a theoretical model through the use of formal science or solving a practical problem through the use of natural science. At the laboratory, our materials scientists are leading the way in producing energy solutions today that could help reduce and remove the energy crisis of tomorrow.

  11. Kinetics of accelerator driven devices

    SciTech Connect

    Perry, R.T.; Buksa, J.; Houts, M.

    1994-09-01

    Kinetic calculations were made to show that subcritical accelerator driven devices are robust and stable. The calculations show that large changes in reactivity that would lead to an uncontrollable excursion in a reactor would lead only to a new power level in subcritical device. Calculations were also made to show the rate of power changes resulting from startup and shutdown, and that methods also exist for continuously monitoring the reactivity of a subcritical system.

  12. The universal response of fluid interiors to end-member models of mechanical forcing

    NASA Astrophysics Data System (ADS)

    Grannan, A. M.; Favier, B.; Ribeiro, A.; Le Bars, M.; Aurnou, J. M.

    2015-12-01

    Turbulence generated in electrically conductive liquid interiors of planetary bodies may be due, in part, to mechanical forcing through geophysically relevant mechanisms of precession/nutation, librations, tidal forcing, and collisions. Using experimental particle image velocimetry techniques accompanied by selected high-resolution numerical simulations, we show, for the first time, the generation of bulk-filling turbulence driven by high frequency tidal forcing. The transition to sustained turbulence is characterized by a succession of resonances first between the tidally forced ellipsoidal base flow with two primary inertial modes and subsequently between secondary inertial modes and the primary inertial modes. Furthermore, deviations in the amplitude of the time-averaged retrograde zonal flow suggest an as yet unseen secondary flow transition that may promote additional turbulence. The turbulence generated by high frequency, low amplitude tidal forcing is similar to the libration-driven turbulent flows studied by Grannan et al. [2014] and Favier et al. [2015]. These works reveal the universal fluid response to elliptical instability driven by separate models that correspond, in geophysical terms, to two end member types of mechanical forcing. In the first, non-synchronous satellites possess elastically deformable boundaries such that shape of the distortion has a non-zero mean motion. In the second, the core-mantle boundary of a body possesses an inherently rigid or tidally frozen-in ellipsoidal shape in a synchronous orbit such that the mean motion of the elliptically deformed boundary is zero. Although the strength of the mechanical forcing is much weaker at planetary settings, the corresponding viscous dissipation is also weaker and thus may still permit the generation of the same turbulent flow found in both experiments and numerical simulations. The efficacy of such turbulent flows in magnetic field generation and dissipation is currently being pursued

  13. Investigation of Calibrating Force Transducer Using Sinusoidal Force

    SciTech Connect

    Zhang Li; Wang Yu; Zhang Lizhe

    2010-05-28

    Sinusoidal force calibration method was studied several years before at Physikalisch-Technische Bundesanstalt (PTB). A similar dynamic force calibration system is developed at Changcheng Institute of Metrology and Measurement (CIMM). It uses electro-dynamic shakers to generate dynamic force in the range from 1 N to 20 kN, and heterodyne laser interferometers are used for acceleration measurement. The force transducer to be calibrated is mounted on the shaker, and a mass block is screwed on the top of force transducer, the sinusoidal forces realized by accelerated load masses are traceable to acceleration and mass according to the force definition. The methods of determining Spatial-dependent acceleration on mass block and measuring the end mass of force transducer in dynamic force calibration are discussed in this paper.

  14. Edge-driven microplate kinematics

    USGS Publications Warehouse

    Schouten, Hans; Klitgord, Kim D.; Gallo, David G.

    1993-01-01

    It is known from plate tectonic reconstructions that oceanic microplates undergo rapid rotation about a vertical axis and that the instantaneous rotation axes describing the microplate's motion relative to the bounding major plates are frequently located close to its margins with those plates, close to the tips of propagating rifts. We propose a class of edge-driven block models to illustrate how slip across the microplate margins, block rotation, and propagation of rifting may be related to the relative motion of the plates on either side. An important feature of these edge-driven models is that the instantaneous rotation axes are always located on the margins between block and two bounding plates. According to those models the pseudofaults or traces of disrupted seafloor resulting from the propagation of rifting between microplate and major plates may be used independently to approximately trace the continuous kinematic evolution of the microplate back in time. Pseudofault geometries and matching rotations of the Easter microplate show that for most of its 5 m.y. history, block rotation could be driven by the drag of the Nazca and Pacific plates on the microplate's edges rather than by a shear flow of mantle underneath.

  15. Wind driven power generating apparatus

    SciTech Connect

    Andruszkiw, W.; Andrushkiw, R.

    1986-10-14

    A vertically adjustable wind driven power generating apparatus comprised of, in combination, a well in which is vertically movably mounted a wind driven power generating apparatus comprised of: (i) a wind driven power generating means comprised of a tubular housing having rotatably mounted therein a horizontally extending shaft. The shaft has a centrally disposed bevel gear fixedly attached thereto and helical vanes disposed longitudinally on both sides of the bevel gear; (ii) means for vertical movement of the tubular housing within the well comprised of (a) a hollow vertical support column having a circular cross section and having one end thereof attached to the bottom of the tubular housing and (b) a vertically extending hollow tubular member having a hollow interior fixedly mounted at its bottom end in the floor of the well and being open at its other end, the tubular member adapted to telescopically receive the vertical support column in its open end; (iii) vertical movement control means comprised of (a) downward movement control means comprising an inverted wing system generating inverse-lift mounted on the tubular housing, and (b) upward movement control means comprising a cylinder having an axially movable piston therein; (iv) power transmission means comprising a vertically extending power transmitting shaft that drives a power generator.

  16. DSMC Simulation of Microstructure Actuation by Knudsen Thermal Force

    NASA Astrophysics Data System (ADS)

    Pikus, Aaron; Sebastiao, Israel; Strongrich, Andrew; Alexeenko, Alina

    2015-11-01

    Compact, low-power and highly accurate vacuum sensors are needed for emerging applications such as high-altitude communication platforms, small satellites and in-vacuum manufacturing processes. A novel MEMS-based pressure and gas sensor - Microelectromechanical In-plane Knudsen Radiometric Actuator (MIKRA) - has been developed at Purdue. MIKRA is based on Knudsen thermal force generated by rarefied flow driven by thermal gradients within the microstructure. The goal of this work is to model the rarefied gas flow in the MIKRA sensor to validate the numerical modeling of rarefied thermally-driven flows and gain insights for sensor design. The Direct Simulation Monte Carlo (DSMC) solver SPARTA is employed to numerically calculate the distribution of the flowfield and surface properties. The resulting forces on the colder shuttle beam are calculated and compared to the available experimental data as well as other numerical solvers. Both DSMC and experimental results suggest that the maximum forces occur at a Knudsen number of approximately 1. The streamlines indicate the presence of two small vortexes between the heated beam and the colder shuttle beam, and a larger one above these two beams. The DSMCsimulations, validated by experimental measurements, help understand the unique flow behaviors encountered in rarefied thermally-driven flows. NSF CBET grant #1055453.

  17. The Myths of Data-Driven Schools

    ERIC Educational Resources Information Center

    Jones, Alan

    2005-01-01

    The most recent attempt by educators to emulate the "sound principles" and methods of business and science is to become data-driven. The leaders in a data-driven school are able to demonstrate how some number, preferably scores on standardized tests, has moved upward as a result of some program they have initiated. Data-driven schools also possess…

  18. Is "Market-Driven" Good Enough?

    ERIC Educational Resources Information Center

    Kaufman, Roger

    1995-01-01

    Discusses marketing and management strategies and evaluates the path most traveled; going beyond market-driven; proactive and reactive organizational positioning; ways to manage human and physical resources to make both market-driven and market-making contributions; and values necessary for an organization to move from market-driven to…

  19. Force Feedback Joystick

    NASA Technical Reports Server (NTRS)

    1997-01-01

    I-FORCE, a computer peripheral from Immersion Corporation, was derived from virtual environment and human factors research at the Advanced Displays and Spatial Perception Laboratory at Ames Research Center in collaboration with Stanford University Center for Design Research. Entrepreneur Louis Rosenberg, a former Stanford researcher, now president of Immersion, collaborated with Dr. Bernard Adelstein at Ames on studies of perception in virtual reality. The result was an inexpensive way to incorporate motors and a sophisticated microprocessor into joysticks and other game controllers. These devices can emulate the feel of a car on the skid, a crashing plane, the bounce of a ball, compressed springs, or other physical phenomenon. The first products incorporating I-FORCE technology include CH- Products' line of FlightStick and CombatStick controllers.

  20. Suicide and Forced Marriage

    PubMed Central

    Pridmore, Saxby; Walter, Garry

    2013-01-01

    Background: The prevailing view that the vast majority of those who complete suicide have an underlying psychiatric disorder has been recently challenged by research on the contribution of “predicaments”, in the absence of mental illness, to suicide. In this paper, we sought data to support the notion that forced marriage may lead to suicide without the presence of psychiatric disorder. Methods: Historical records, newspapers, and the electronic media were searched for examples. Results: Two examples from ancient times and six from the last hundred years were located and described. Conclusion: These cases suggest that forced marriage may lead to suicide and complements earlier findings that loss of fortune, health, liberty, and reputation may lead to suicide in the absence of mental disorder. PMID:23983577

  1. Forces Driving Chaperone Action.

    PubMed

    Koldewey, Philipp; Stull, Frederick; Horowitz, Scott; Martin, Raoul; Bardwell, James C A

    2016-07-14

    It is still unclear what molecular forces drive chaperone-mediated protein folding. Here, we obtain a detailed mechanistic understanding of the forces that dictate the four key steps of chaperone-client interaction: initial binding, complex stabilization, folding, and release. Contrary to the common belief that chaperones recognize unfolding intermediates by their hydrophobic nature, we discover that the model chaperone Spy uses long-range electrostatic interactions to rapidly bind to its unfolded client protein Im7. Short-range hydrophobic interactions follow, which serve to stabilize the complex. Hydrophobic collapse of the client protein then drives its folding. By burying hydrophobic residues in its core, the client's affinity to Spy decreases, which causes client release. By allowing the client to fold itself, Spy circumvents the need for client-specific folding instructions. This mechanism might help explain how chaperones can facilitate the folding of various unrelated proteins. PMID:27293188

  2. Force Modulator System

    SciTech Connect

    Redmond Clark

    2009-04-30

    Many metal parts manufacturers use large metal presses to shape sheet metal into finished products like car body parts, jet wing and fuselage surfaces, etc. These metal presses take sheet metal and - with enormous force - reshape the metal into a fully formed part in a manner of seconds. Although highly efficient, the forces involved in forming metal parts also damage the press itself, limit the metals used in part production, slow press operations and, when not properly controlled, cause the manufacture of large volumes of defective metal parts. To date, the metal-forming industry has not been able to develop a metal-holding technology that allows full control of press forces during the part forming process. This is of particular importance in the automotive lightweighting efforts under way in the US automotive manufacturing marketplace. Metalforming Controls Technology Inc. (MC2) has developed a patented press control system called the Force Modulator that has the ability to control these press forces, allowing a breakthrough in stamping process control. The technology includes a series of hydraulic cylinders that provide controlled tonnage at all points in the forming process. At the same time, the unique cylinder design allows for the generation of very high levels of clamping forces (very high tonnages) in very small spaces; a requirement for forming medium and large panels out of HSS and AHSS. Successful production application of these systems testing at multiple stamping operations - including Ford and Chrysler - has validated the capabilities and economic benefits of the system. Although this technology has been adopted in a number of stamping operations, one of the primary barriers to faster adoption and application of this technology in HSS projects is system cost. The cost issue has surfaced because the systems currently in use are built for each individual die as a custom application, thus driving higher tooling costs. This project proposed to better

  3. Air Force seal activities

    NASA Astrophysics Data System (ADS)

    Mayhew, Ellen R.

    1994-07-01

    Seal technology development is an important part of the Air Force's participation in the Integrated High Performance Turbine Engine Technology (IHPTET) initiative, the joint DOD, NASA, ARPA, and industry endeavor to double turbine engine capabilities by the turn of the century. Significant performance and efficiency improvements can be obtained through reducing internal flow system leakage, but seal environment requirements continue to become more extreme as the engine thermodynamic cycles advance towards these IHPTET goals. Brush seal technology continues to be pursued by the Air Force to reduce leakage at the required conditions. Likewise, challenges in engine mainshaft air/oil seals are also being addressed. Counter-rotating intershaft applications within the IHPTET initiative involve very high rubbing velocities. This viewgraph presentation briefly describes past and current seal research and development programs and gives a summary of seal applications in demonstrator and developmental engine testing.

  4. Ultrasonic Force Microscopies

    NASA Astrophysics Data System (ADS)

    Kolosov, Oleg; Briggs, Andrew

    Ultrasonic Force Microscopy, or UFM, allows combination of two apparently mutually exclusive requirements for the nanomechanical probe—high stiffness for the efficient indentation and high mechanical compliance that brings force sensitivity. Somewhat inventively, UFM allows to combine these two virtues in the same cantilever by using indention of the sample at high frequency, when cantilever is very rigid, but detecting the result of this indention at much lower frequency. That is made possible due to the extreme nonlinearity of the nanoscale tip-surface junction force-distance dependence, that acts as "mechanical diode" detecting ultrasound in AFM. After introducing UFM principles, we discuss features of experimental UFM implementation, and the theory of contrast in this mode, progressing to quantitative measurements of contact stiffness. A variety of UFM applications ranging from semiconductor quantum nanostructures, graphene, very large scale integrated circuits, and reinforced ceramics to polymer composites and biological materials is presented via comprehensive imaging gallery accompanied by the guidance for the optimal UFM measurements of these materials. We also address effects of adhesion and topography on the elasticity imaging and the approaches for reducing artifacts connected with these effects. This is complemented by another extremely useful feature of UFM—ultrasound induced superlubricity that allows damage free imaging of materials ranging from stiff solid state devices and graphene to biological materials. Finally, we proceed to the exploration of time-resolved nanoscale phenomena using nonlinear mixing of multiple vibration frequencies in ultrasonic AFM—Heterodyne Force Microscopy, or HFM, that also include mixing of ultrasonic vibration with other periodic physical excitations, eg. electrical, photothermal, etc. Significant section of the chapter analyzes the ability of UFM and HFM to detect subsurface mechanical inhomogeneities, as well as

  5. Dynamic nanoindentation by instrumented nanoindentation and force microscopy: a comparative review

    PubMed Central

    Kalfon-Cohen, Estelle

    2013-01-01

    Summary Viscoelasticity is a complex yet important phenomenon that drives material response at different scales of time and space. Burgeoning interest in nanoscale dynamic material mechanics has driven, and been driven by two key techniques: instrumented nanoindentation and atomic force microscopy. This review provides an overview of fundamental principles in nanoindentation, and compares and contrasts these two techniques as they are used for characterization of viscoelastic processes at the nanoscale. PMID:24367751

  6. ``Force,'' ontology, and language

    NASA Astrophysics Data System (ADS)

    Brookes, David T.; Etkina, Eugenia

    2009-06-01

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

  7. Force Fluctuations and Correlations

    NASA Astrophysics Data System (ADS)

    Behringer, Robert

    1998-03-01

    Granular materials exhibit a rich array of dynamic and static phenomena which are only partly understood. Here, I focus on fluctuations in kinetic properties and in forces for slowly sheared granular materials. We have carried out a series of experiments in both 2D and in 3D. For 2D, we use a novel apparatus which allows us to quantify the forces, positions and orientations associated with individual grains. For slow to moderate shear rates, we find rate independence except for small random deviations which are associated with very long time changes in the system. The system evolves to a nearly steady average flow profile in which the velocity falls off approximately exponentially with distance from the shearing surface. The particle rotation shows systematic oscillations near the shearing surface. Velocity profiles show a complicated non-gaussian structure. Force measurements in both the 2D and 3D system are approximately exponentially distributed, but there are also some systematic deviations. Companion calculations by S. Schoellmann, S. Luding and H. Herrmann capture a number of these features. The experimental work has been carried out partially at Duke and partially at the E.S.P.C.I. Paris in collaboration with D. Howell, B. Miller, S. Tennakoon, and C. Veje.

  8. The task force process

    SciTech Connect

    Applegate, J.S.

    1995-01-31

    This paper focuses on the unique aspects of the Fernald Citizens Task Force process that have contributed to a largely successful public participation effort at Fernald. The Fernald Citizens Task Force passed quickly by many procedural issues. Instead, the Task Force concentrated on (a) educating itself about the site, its problems, and possible solutions, and (b) choosing a directed way to approach its mandate: To make recommendations on several {open_quotes}big picture{close_quotes} issues, including future use of the site, cleanup levels, waste disposition, and cleanup priorities. This paper presents the approach used at Fernald for establishing and running a focused site-specific advisory board, the key issues that have been faced, and how these issues were resolved. The success of Fernald in establishing a strong and functioning site-specific advisory board serves as a useful model for other DOE facilities, although the Fernald model is just one of many approaches that can be taken. However, the approach presented here has worked extremely well for Fernald.

  9. Modified entropic force

    SciTech Connect

    Gao Changjun

    2010-04-15

    The theory of statistical thermodynamics tells us the equipartition law of energy does not hold in the limit of very low temperatures. It is found the Debye model is very successful in explaining the experimental results for most of the solid objects. Motivated by this fact, we modify the entropic force formula which is proposed very recently. Since the Unruh temperature is proportional to the strength of the gravitational field, so the modified entropic force formula is an extension of the Newtonian gravity to the weak field. On the contrary, general relativity extends Newtonian gravity to the strong field case. Corresponding to Debye temperature, there exists a Debye acceleration g{sub D}. It is found the Debye acceleration is g{sub D}=10{sup -15} N kg{sup -1}. This acceleration is very much smaller than the gravitational acceleration 10{sup -4} N kg{sup -1} which is felt by Neptune and the gravitational acceleration 10{sup -10} N kg{sup -1} felt by the Sun. Therefore, the modified entropic force can be very well approximated by the Newtonian gravity in the Solar System and in the Galaxy. With this Debye acceleration, we find the current cosmic speeding up can be explained without invoking any kind of dark energy.

  10. The competition between Lorentz and Coriolis forces in planetary dynamos

    NASA Astrophysics Data System (ADS)

    Soderlund, Krista M.; Sheyko, Andrey; King, Eric M.; Aurnou, Jonathan M.

    2015-12-01

    Fluid motions within planetary cores generate magnetic fields through dynamo action. These core processes are driven by thermo-compositional convection subject to the competing influences of rotation, which tends to organize the flow into axial columns, and the Lorentz force, which tends to inhibit the relative movement of the magnetic field and the fluid. It is often argued that these forces are predominant and approximately equal in planetary cores; we test this hypothesis using a suite of numerical geodynamo models to calculate the Lorentz to Coriolis force ratio directly. Our results show that this ratio can be estimated by ( Λ i is the traditionally defined Elsasser number for imposed magnetic fields and Rm is the system-scale ratio of magnetic induction to magnetic diffusion). Best estimates of core flow speeds and magnetic field strengths predict the geodynamo to be in magnetostrophic balance where the Lorentz and Coriolis forces are comparable. The Lorentz force may also be significant, i.e., within an order of magnitude of the Coriolis force, in the Jovian interior. In contrast, the Lorentz force is likely to be relatively weak in the cores of Saturn, Uranus, Neptune, Ganymede, and Mercury.

  11. Finger force perception during ipsilateral and contralateral force matching tasks

    PubMed Central

    Park, Woo-Hyung; Leonard, Charles T.; Li, Sheng

    2010-01-01

    The aims of the present study were to compare matching performance between ipsilateral and contralateral finger force matching tasks and to examine the effect of handedness on finger force perception. Eleven subjects were instructed to produce reference forces by an instructed finger (index – I or little – L finger) and to reproduce the same amount force by the same or a different finger within the hand (i.e., ipsilateral matching task), or by a finger of the other hand (i.e., contralateral matching task). The results of the ipsilateral and contralateral tasks in the present study commonly showed that 1) the reference and matching forces were matched closely when the two forces were produced by the same or homologous finger(s) such as I/I task; 2) the weaker little finger underestimated the magnitude of reference force of the index finger (I/L task), even with the higher level of effort (relative force), but the two forces were matched when considering total finger forces; 3) the stronger index finger closely matched the reference force of the little finger with the lower level of relative force (i.e., L/I task); 4) when considering the constant errors, I/L tasks showed an underestimation and L/I tasks showed an overestimation compared to I/I tasks. There was no handedness effect during ipsilateral tasks. During the contralateral task, the dominant hand overestimated the force of the non-dominant hand, while the non-dominant hand attempted to match the absolute force of the dominant hand. The overall results support the notion that the absolute, rather than relative, finger force is perceived and reproduced during ipsilateral and contralateral finger force matching tasks, indicating the uniqueness of finger force perception. PMID:18488212

  12. Force control compensation method with variable load stiffness and damping of the hydraulic drive unit force control system

    NASA Astrophysics Data System (ADS)

    Kong, Xiangdong; Ba, Kaixian; Yu, Bin; Cao, Yuan; Zhu, Qixin; Zhao, Hualong

    2016-05-01

    Each joint of hydraulic drive quadruped robot is driven by the hydraulic drive unit (HDU), and the contacting between the robot foot end and the ground is complex and variable, which increases the difficulty of force control inevitably. In the recent years, although many scholars researched some control methods such as disturbance rejection control, parameter self-adaptive control, impedance control and so on, to improve the force control performance of HDU, the robustness of the force control still needs improving. Therefore, how to simulate the complex and variable load characteristics of the environment structure and how to ensure HDU having excellent force control performance with the complex and variable load characteristics are key issues to be solved in this paper. The force control system mathematic model of HDU is established by the mechanism modeling method, and the theoretical models of a novel force control compensation method and a load characteristics simulation method under different environment structures are derived, considering the dynamic characteristics of the load stiffness and the load damping under different environment structures. Then, simulation effects of the variable load stiffness and load damping under the step and sinusoidal load force are analyzed experimentally on the HDU force control performance test platform, which provides the foundation for the force control compensation experiment research. In addition, the optimized PID control parameters are designed to make the HDU have better force control performance with suitable load stiffness and load damping, under which the force control compensation method is introduced, and the robustness of the force control system with several constant load characteristics and the variable load characteristics respectively are comparatively analyzed by experiment. The research results indicate that if the load characteristics are known, the force control compensation method presented in this

  13. Foundational Forces & Hidden Variables in Technology Commercialization

    NASA Astrophysics Data System (ADS)

    Barnett, Brandon

    2011-03-01

    The science of physics seems vastly different from the process of technology commercialization. Physics strives to understand our world through the experimental deduction of immutable laws and dependent variables and the resulting macro-scale phenomenon. In comparison, the~goal of business is to make a profit by addressing the needs, preferences, and whims of individuals in a market. It may seem that this environment is too dynamic to identify all the hidden variables and deduct the foundational forces that impact a business's ability to commercialize innovative technologies. One example of a business ``force'' is found in the semiconductor industry. In 1965, Intel co-founder Gordon Moore predicted that the number of transistors incorporated in a chip will approximately double every 24 months. Known as Moore's Law, this prediction has become the guiding principle for the semiconductor industry for the last 40 years. Of course, Moore's Law is not really a law of nature; rather it is the result of efforts by Intel and the entire semiconductor industry. A closer examination suggests that there are foundational principles of business that underlie the macro-scale phenomenon of Moore's Law. Principles of profitability, incentive, and strategic alignment have resulted in a coordinated influx of resources that has driven technologies to market, increasing the profitability of the semiconductor industry and optimizing the fitness of its participants. New innovations in technology are subject to these same principles. So, in addition to traditional market forces, these often unrecognized forces and variables create challenges for new technology commercialization. In this talk, I will draw from ethnographic research, complex adaptive theory, and industry data to suggest a framework with which to think about new technology commercialization. Intel's bio-silicon initiative provides a case study.

  14. Forcing continuous reconnection in hybrid simulations

    SciTech Connect

    Laitinen, T. V. Janhunen, P.; Jarvinen, R.; Kallio, E.

    2014-07-15

    We have performed hybrid simulations of driven continuous reconnection with open boundary conditions. Reconnection is started by a collision of two subsonic plasma fronts with opposite magnetic fields, without any specified magnetic field configuration as initial condition. Due to continued forced plasma inflow, a current sheet co-located with a dense and hot plasma sheet develops. The translational symmetry of the current sheet is broken by applying a spatial gradient in the inflow speed. We compare runs with and without localized resistivity: reconnection is initiated in both cases, but localized resistivity stabilizes it and enhances its efficiency. The outflow speed reaches about half of Alfvén speed. We quantify the conversion of magnetic energy to kinetic energy of protons and to Joule heating and show that with localized resistivity, kinetic energy of protons is increased on average five-fold in the reconnection in our simulation case.

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

    NASA Technical Reports Server (NTRS)

    Bents, D. J.

    1981-01-01

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

  16. Passive Joint Forces Are Tuned to Limb Use in Insects and Drive Movements without Motor Activity

    PubMed Central

    Ache, Jan M.; Matheson, Thomas

    2013-01-01

    Summary Background Limb movements are generally driven by active muscular contractions working with and against passive forces arising in muscles and other structures. In relatively heavy limbs, the effects of gravity and inertia predominate, whereas in lighter limbs, passive forces intrinsic to the limb are of greater consequence. The roles of passive forces generated by muscles and tendons are well understood, but there has been little recognition that forces originating within joints themselves may also be important, and less still that these joint forces may be adapted through evolution to complement active muscle forces acting at the same joint. Results We examined the roles of passive joint forces in insect legs with different arrangements of antagonist muscles. We first show that passive forces modify actively generated movements of a joint across its working range, and that they can be sufficiently strong to generate completely passive movements that are faster than active movements observed in natural behaviors. We further demonstrate that some of these forces originate within the joint itself. In legs of different species adapted to different uses (walking, jumping), these passive joint forces complement the balance of strength of the antagonist muscles acting on the joint. We show that passive joint forces are stronger where they assist the weaker of two antagonist muscles. Conclusions In limbs where the dictates of a key behavior produce asymmetry in muscle forces, passive joint forces can be coadapted to provide the balance needed for the effective generation of other behaviors. PMID:23871240

  17. On transition from Alfvén resonance to forced magnetic reconnection

    SciTech Connect

    Luan, Q.; Wang, X.

    2014-07-15

    We revisit the transition from Alfvén resonance to forced magnetic reconnection with a focus on the property of their singularities. As the driven frequency tends to zero, the logarithmic singularity of Alfvén resonance shifts to the power-law singularity of forced reconnection, due to merging of the two resonance layers. The transition criterion depends on either kinetic effects or dissipations that resolve the singularity. As an example, a small but finite resistivity η is introduced to investigate the transition process. The transition threshold is then obtained as the driven frequency reaches a level of ∼O((η/k){sup 1/3})

  18. Catastrophe-driven vs what?

    SciTech Connect

    Stever, H.G.

    1995-12-31

    The author notes that much has been accomplished by catastrophe-driven scientific effort. Examples include World War II and the social wars against crime, poverty and hunger and famine. A positive approach is suggested to be more appropriate as the drivers of science. Three tables are presented and outline a positive base for justifying scientific endeavor: (1) Examples of Major Societal Goals to Which Science and Technology Contribute. (2) Policy Areas That Would Benefit from the Articulation of Long-Term S&T Goals; and (3) Major Components of the Science and Technology Base.

  19. Actively driven thermal radiation shield

    DOEpatents

    Madden, Norman W.; Cork, Christopher P.; Becker, John A.; Knapp, David A.

    2002-01-01

    A thermal radiation shield for cooled portable gamma-ray spectrometers. The thermal radiation shield is located intermediate the vacuum enclosure and detector enclosure, is actively driven, and is useful in reducing the heat load to mechanical cooler and additionally extends the lifetime of the mechanical cooler. The thermal shield is electrically-powered and is particularly useful for portable solid-state gamma-ray detectors or spectrometers that dramatically reduces the cooling power requirements. For example, the operating shield at 260K (40K below room temperature) will decrease the thermal radiation load to the detector by 50%, which makes possible portable battery operation for a mechanically cooled Ge spectrometer.

  20. Ontology-Driven Information Integration

    NASA Technical Reports Server (NTRS)

    Tissot, Florence; Menzel, Chris

    2005-01-01

    Ontology-driven information integration (ODII) is a method of computerized, automated sharing of information among specialists who have expertise in different domains and who are members of subdivisions of a large, complex enterprise (e.g., an engineering project, a government agency, or a business). In ODII, one uses rigorous mathematical techniques to develop computational models of engineering and/or business information and processes. These models are then used to develop software tools that support the reliable processing and exchange of information among the subdivisions of this enterprise or between this enterprise and other enterprises.

  1. Electromagnetically driven, fast opening and closing gas jet valve

    NASA Astrophysics Data System (ADS)

    Krishnan, Mahadevan; Elliott, Kristi Wilson; Geddes, C. G. R.; van Mourik, R. A.; Leemans, W. P.; Murphy, H.; Clover, M.

    2011-03-01

    The design and performance are presented of an electromagnetically driven gas valve [M. Krishnan, J. Wright, and T. Ma, Proceedings of the 13th Advanced Accelerator Concepts Workshop, Santa Cruz, CA, AIP Conf. Proc. No. 1086 (AIP, New York, 2008)] that opens in <100μs, closes in <500μs, and can operate at pressures of ˜1000psia to drive supersonic nozzles. Such a valve has applications to laser-plasma accelerators, where the fast opening and closing would allow sharper edges to the flow and also allow higher rep-rate operation without loading the vacuum chamber. The valve action is effected by a flyer plate accelerated by the electromagnetic impulse of a low inductance, spiral wound, strip-line coil driven by a capacitor. Gas flows out of the valve when the seal between this flyer plate and the valve seat is broken. The electromagnetic force greatly exceeds the restoring forces provided by a spring and the gas pressure against the valve seat. Piezoresistive sensor and laser interferometer measurements of flow show that the valve opens in ˜100μs for all pressures up to 800 psia. The closing time is 500μs, set by the spring constant and mass. The prototype valve has been operated with helium at 0.5 Hz and at 500 psia for ˜1 hour at a time with no cooling.

  2. Photochemically driven redox chemistry induces protocell membrane pearling and division.

    PubMed

    Zhu, Ting F; Adamala, Katarzyna; Zhang, Na; Szostak, Jack W

    2012-06-19

    Prior to the evolution of complex biochemical machinery, the growth and division of simple primitive cells (protocells) must have been driven by environmental factors. We have previously demonstrated two pathways for fatty acid vesicle growth in which initially spherical vesicles grow into long filamentous vesicles; division is then mediated by fluid shear forces. Here we describe a different pathway for division that is independent of external mechanical forces. We show that the illumination of filamentous fatty acid vesicles containing either a fluorescent dye in the encapsulated aqueous phase, or hydroxypyrene in the membrane, rapidly induces pearling and subsequent division in the presence of thiols. The mechanism of this photochemically driven pathway most likely involves the generation of reactive oxygen species, which oxidize thiols to disulfide-containing compounds that associate with fatty acid membranes, inducing a change in surface tension and causing pearling and subsequent division. This vesicle division pathway provides an alternative route for the emergence of early self-replicating cell-like structures, particularly in thiol-rich surface environments where UV-absorbing polycyclic aromatic hydrocarbons (PAHs) could have facilitated protocell division. The subsequent evolution of cellular metabolic processes controlling the thiol:disulfide redox state would have enabled autonomous cellular control of the timing of cell division, a major step in the origin of cellular life. PMID:22665773

  3. Intense Flows in Librationally Driven Non-Axisymmetric Systems

    NASA Astrophysics Data System (ADS)

    Grannan, A. M.; Le Bars, M.; Cebron, D.; Aurnou, J. M.

    2013-12-01

    We present laboratory experimental results that demonstrate that librational forcing can drive intense motions of interior, low viscosity fluid layers. Longitudinal libration refers to small periodic changes in a satellite's mean rotation rate as it orbits a primary body. These libration studies are conducted using ellipsoidal acrylic containers filled with water. Particle image velocimetry (PIV) methods are used to measure the 2D velocity field in the equatorial plane over hundreds and thousands of libration cycles. In doing so we determine the coupled modes of the triadic resonance responsible for the instability that produces both intermittent and persistent turbulent motions in the bulk fluid. Additionally, we measure the amplitude and the growth rate for the instability and compare it with previous studies [1][2]. Excitation of global turbulence by librational forcing provides a mechanism for transferring rotational energy into fluid turbulence and thus may play an important role in the thermal evolution, interior dynamics, and magneto-hydrodynamics of librating bodies. [1] Cébron, D., M. Le Bars, J. Noir, J.M. Aurnou. (2012). Libration driven elliptical instability. Physics of Fluids 24, 061703. [2] Noir J., D. Cébron, M. Le Bars, A. Sauret, J.M. Aurnou (2012). Experimental study of libration-driven flows in non-axisymmetric containers, Physics of the Earth and Planetary Interiors 204-205, 1-10.

  4. Dynamo-driven plasmoid ejections above a spherical surface

    NASA Astrophysics Data System (ADS)

    Warnecke, J.; Brandenburg, A.; Mitra, D.

    2011-10-01

    Aims: We extend earlier models of turbulent dynamos with an upper, nearly force-free exterior to spherical geometry, and study how flux emerges from lower layers to the upper ones without being driven by magnetic buoyancy. We also study how this affects the possibility of plasmoid ejection. Methods: A spherical wedge is used that includes northern and southern hemispheres up to mid-latitudes and a certain range in longitude of the Sun. In radius, we cover both the region that corresponds to the convection zone in the Sun and the immediate exterior up to twice the radius of the Sun. Turbulence is driven with a helical forcing function in the interior, where the sign changes at the equator between the two hemispheres. Results: An oscillatory large-scale dynamo with equatorward migration is found to operate in the turbulence zone. Plasmoid ejections occur in regular intervals, similar to what is seen in earlier Cartesian models. These plasmoid ejections are tentatively associated with coronal mass ejections (CMEs). The magnetic helicity is found to change sign outside the turbulence zone, which is in agreement with recent findings for the solar wind. Movie is available in electronic form at http://www.aanda.org

  5. Computations of wind-driven ocean-induced magnetic fields

    NASA Astrophysics Data System (ADS)

    Sachl, Libor; Einspigel, David; Martinec, Zdenek

    2016-04-01

    We present the results of computations of the secondary magnetic field induced by ocean motions. Ocean velocities are computed using the baroclinic ocean model LSOMG. The velocities are then used to determine the Lorentz force which is plugged into the magnetic induction code TLAM as a principal forcing. The TLAM is a 2D magnetic induction code based on the thin-shell approximation (Vivier et al., 2004; Tyler et al., 1997). In this approximation, the equation of magnetic induction simplifies significantly, time derivatives of main and induced magnetic fields are neglected as well as the self-induction term. The price for simplification of governing equations is the limited applicability of the resulting system. It is only suitable for slowly evolving processes. In order to meet the condition, we restrict ourselves to the wind (buoyancy) driven ocean circulation, although the LSOMG model is able to model both tidally- and wind-driven circulations. We assess the accuracy of thin-shell approximation in our setup by comparing the results with the Swarm satellite magnetic data. References Tyler, R. H., Mysak, L. A., and Oberhuber, J. M, 1997. Electromagnetic fields generated by a three dimensional global ocean circulation. J. Geophys. Res., 102, 5531-5551. Vivier, F., Meier-Reimer, E., and Tyler, R. H., 2004. Simulations of magnetic fields generated by the Antarctic Circumpolar Current at satellite altitude: Can geomagnetic measurements be used to monitor the flow? Geophys. Res. Lett., 31, L10306, doi:10.1029/2004GL019804.

  6. Consumer control of salt marshes driven by human disturbance.

    PubMed

    Bertness, Mark D; Silliman, Brian R

    2008-06-01

    Salt marsh ecosystems are widely considered to be controlled exclusively by bottom-up forces, but there is mounting evidence that human disturbances are triggering consumer control in western Atlantic salt marshes, often with catastrophic consequences. In other marine ecosystems, human disturbances routinely dampen (e.g., coral reefs, sea grass beds) and strengthen (e.g., kelps) consumer control, but current marsh theory predicts little potential interaction between humans and marsh consumers. Thus, human modification of top-down control in salt marshes was not anticipated and was even discounted in current marsh theory, despite loud warnings about the potential for cascading human impacts from work in other marine ecosystems. In spite of recent experiments that have challenged established marsh dogma and demonstrated consumer-driven die-off of salt marsh ecosystems, government agencies and nongovernmental organizations continue to manage marsh die-offs under the old theoretical framework and only consider bottom-up forces as causal agents. This intellectual dependency of many coastal ecologists and managers on system-specific theory (i.e., marsh bottom-up theory) has the potential to have grave repercussions for coastal ecosystem management and conservation in the face of increasing human threats. We stress that marine vascular plant communities (salt marshes, sea grass beds, mangroves) are likely more vulnerable to runaway grazing and consumer-driven collapse than is currently recognized by theory, particularly in low-diversity ecosystems like Atlantic salt marshes. PMID:18577090

  7. Eastern Indian Ocean microcontinent formation driven by plate motion changes

    NASA Astrophysics Data System (ADS)

    Whittaker, J. M.; Williams, S. E.; Halpin, J. A.; Wild, T. J.; Stilwell, J. D.; Jourdan, F.; Daczko, N. R.

    2016-11-01

    The roles of plate tectonic or mantle dynamic forces in rupturing continental lithosphere remain controversial. Particularly enigmatic is the rifting of microcontinents from mature continental rifted margins, with plume-driven thermal weakening commonly inferred to facilitate calving. However, a role for plate tectonic reorganisations has also been suggested. Here, we show that a combination of plate tectonic reorganisation and plume-driven thermal weakening were required to calve the Batavia and Gulden Draak microcontinents in the Cretaceous Indian Ocean. We reconstruct the evolution of these two microcontinents using constraints from new paleontological samples, 40Ar/39Ar ages, and geophysical data. Calving from India occurred at 101-104 Ma, coinciding with the onset of a dramatic change in Indian plate motion. Critically, Kerguelen plume volcanism does not appear to have directly triggered calving. Rather, it is likely that plume-related thermal weakening of the Indian passive margin preconditioned it for microcontinent formation but calving was triggered by changes in plate tectonic boundary forces.

  8. Consumer control of salt marshes driven by human disturbance.

    PubMed

    Bertness, Mark D; Silliman, Brian R

    2008-06-01

    Salt marsh ecosystems are widely considered to be controlled exclusively by bottom-up forces, but there is mounting evidence that human disturbances are triggering consumer control in western Atlantic salt marshes, often with catastrophic consequences. In other marine ecosystems, human disturbances routinely dampen (e.g., coral reefs, sea grass beds) and strengthen (e.g., kelps) consumer control, but current marsh theory predicts little potential interaction between humans and marsh consumers. Thus, human modification of top-down control in salt marshes was not anticipated and was even discounted in current marsh theory, despite loud warnings about the potential for cascading human impacts from work in other marine ecosystems. In spite of recent experiments that have challenged established marsh dogma and demonstrated consumer-driven die-off of salt marsh ecosystems, government agencies and nongovernmental organizations continue to manage marsh die-offs under the old theoretical framework and only consider bottom-up forces as causal agents. This intellectual dependency of many coastal ecologists and managers on system-specific theory (i.e., marsh bottom-up theory) has the potential to have grave repercussions for coastal ecosystem management and conservation in the face of increasing human threats. We stress that marine vascular plant communities (salt marshes, sea grass beds, mangroves) are likely more vulnerable to runaway grazing and consumer-driven collapse than is currently recognized by theory, particularly in low-diversity ecosystems like Atlantic salt marshes.

  9. Atomic Force Microscope

    SciTech Connect

    Day, R.D.; Russell, P.E.

    1988-12-01

    The Atomic Force Microscope (AFM) is a recently developed instrument that has achieved atomic resolution imaging of both conducting and non- conducting surfaces. Because the AFM is in the early stages of development, and because of the difficulty of building the instrument, it is currently in use in fewer than ten laboratories worldwide. It promises to be a valuable tool for obtaining information about engineering surfaces and aiding the .study of precision fabrication processes. This paper gives an overview of AFM technology and presents plans to build an instrument designed to look at engineering surfaces.

  10. Causal Entropic Forces

    NASA Astrophysics Data System (ADS)

    Wissner-Gross, A. D.; Freer, C. E.

    2013-04-01

    Recent advances in fields ranging from cosmology to computer science have hinted at a possible deep connection between intelligence and entropy maximization, but no formal physical relationship between them has yet been established. Here, we explicitly propose a first step toward such a relationship in the form of a causal generalization of entropic forces that we find can cause two defining behaviors of the human “cognitive niche”—tool use and social cooperation—to spontaneously emerge in simple physical systems. Our results suggest a potentially general thermodynamic model of adaptive behavior as a nonequilibrium process in open systems.

  11. Turbulent forced diffusion flames

    SciTech Connect

    Arpaci, V.S.; Li, C.Y.

    1995-07-01

    It is the purpose of this study to introduce a turbulent microscale appropriate for forced diffusion flames and to propose models for fuel consumption and skin friction in terms of this scale. The study consists of four sections. Following the introduction, Section 2 recapitulates the laminar theories of reacting boundary layers in terms of dimensional arguments and proposes models for fuel consumption and skin friction. Section 3 extends these arguments by introducing a microscale appropriate for turbulent flames and, in terms of this scale, develops models for fuel consumption and skin friction, correlates the experimental data on skin friction, and Section 4 concludes the study.

  12. Radiative forcing of climate

    NASA Technical Reports Server (NTRS)

    Ramanswamy, V.; Shine, Keith; Leovy, Conway; Wang, Wei-Chyung; Rodhe, Henning; Wuebbles, Donald J.; Ding, M.; Lelieveld, Joseph; Edmonds, Jae A.; Mccormick, M. Patrick

    1991-01-01

    An update of the scientific discussions presented in Chapter 2 of the Intergovernmental Panel on Climate Change (IPCC) report is presented. The update discusses the atmospheric radiative and chemical species of significance for climate change. There are two major objectives of the present update. The first is an extension of the discussion on the Global Warming Potentials (GWP's), including a reevaluation in view of the updates in the lifetimes of the radiatively active species. The second important objective is to underscore major developments in the radiative forcing of climate due to the observed stratospheric ozone losses occurring between 1979 and 1990.

  13. Force measurements reveal how small binders perturb the dissociation mechanisms of DNA duplex sequences

    NASA Astrophysics Data System (ADS)

    Burmistrova, Anastasia; Fresch, Barbara; Sluysmans, Damien; de Pauw, Edwin; Remacle, Françoise; Duwez, Anne-Sophie

    2016-06-01

    The force-driven separation of double-stranded DNA is crucial to the accomplishment of cellular processes like genome transactions. Ligands binding to short DNA sequences can have a local stabilizing or destabilizing effect and thus severely affect these processes. Although the design of ligands that bind to specific sequences is a field of intense research with promising biomedical applications, so far, their effect on the force-induced strand separation has remained elusive. Here, by means of AFM-based single molecule force spectroscopy, we show the co-existence of two different mechanisms for the separation of a short DNA duplex and demonstrate how they are perturbed by small binders. With the support of Molecular Dynamics simulations, we evidence that above a critical pulling rate one of the dissociation pathways becomes dominant, with a dramatic effect on the rupture forces. Around the critical threshold, we observe a drop of the most probable rupture forces for ligand-stabilized duplexes. Our results offer a deep understanding of how a stable DNA-ligand complex behaves under force-driven strand separation.The force-driven separation of double-stranded DNA is crucial to the accomplishment of cellular processes like genome transactions. Ligands binding to short DNA sequences can have a local stabilizing or destabilizing effect and thus severely affect these processes. Although the design of ligands that bind to specific sequences is a field of intense research with promising biomedical applications, so far, their effect on the force-induced strand separation has remained elusive. Here, by means of AFM-based single molecule force spectroscopy, we show the co-existence of two different mechanisms for the separation of a short DNA duplex and demonstrate how they are perturbed by small binders. With the support of Molecular Dynamics simulations, we evidence that above a critical pulling rate one of the dissociation pathways becomes dominant, with a dramatic effect

  14. The stiffness variation of a micro-ring driven by a traveling piecewise-electrode.

    PubMed

    Li, Yingjie; Yu, Tao; Hu, Yuh-Chung

    2014-01-01

    In the practice of electrostatically actuated micro devices; the electrostatic force is implemented by sequentially actuated piecewise-electrodes which result in a traveling distributed electrostatic force. However; such force was modeled as a traveling concentrated electrostatic force in literatures. This article; for the first time; presents an analytical study on the stiffness variation of microstructures driven by a traveling piecewise electrode. The analytical model is based on the theory of shallow shell and uniform electrical field. The traveling electrode not only applies electrostatic force on the circular-ring but also alters its dynamical characteristics via the negative electrostatic stiffness. It is known that; when a structure is subjected to a traveling constant force; its natural mode will be resonated as the traveling speed approaches certain critical speeds; and each natural mode refers to exactly one critical speed. However; for the case of a traveling electrostatic force; the number of critical speeds is more than that of the natural modes. This is due to the fact that the traveling electrostatic force makes the resonant frequencies of the forward and backward traveling waves of the circular-ring different. Furthermore; the resonance and stability can be independently controlled by the length of the traveling electrode; though the driving voltage and traveling speed of the electrostatic force alter the dynamics and stabilities of microstructures. This paper extends the fundamental insights into the electromechanical behavior of microstructures driven by electrostatic forces as well as the future development of MEMS/NEMS devices with electrostatic actuation and sensing. PMID:25230308

  15. The Stiffness Variation of a Micro-Ring Driven by a Traveling Piecewise-Electrode

    PubMed Central

    Li, Yingjie; Yu, Tao; Hu, Yuh-Chung

    2014-01-01

    In the practice of electrostatically actuated micro devices; the electrostatic force is implemented by sequentially actuated piecewise-electrodes which result in a traveling distributed electrostatic force. However; such force was modeled as a traveling concentrated electrostatic force in literatures. This article; for the first time; presents an analytical study on the stiffness variation of microstructures driven by a traveling piecewise electrode. The analytical model is based on the theory of shallow shell and uniform electrical field. The traveling electrode not only applies electrostatic force on the circular-ring but also alters its dynamical characteristics via the negative electrostatic stiffness. It is known that; when a structure is subjected to a traveling constant force; its natural mode will be resonated as the traveling speed approaches certain critical speeds; and each natural mode refers to exactly one critical speed. However; for the case of a traveling electrostatic force; the number of critical speeds is more than that of the natural modes. This is due to the fact that the traveling electrostatic force makes the resonant frequencies of the forward and backward traveling waves of the circular-ring different. Furthermore; the resonance and stability can be independently controlled by the length of the traveling electrode; though the driving voltage and traveling speed of the electrostatic force alter the dynamics and stabilities of microstructures. This paper extends the fundamental insights into the electromechanical behavior of microstructures driven by electrostatic forces as well as the future development of MEMS/NEMS devices with electrostatic actuation and sensing. PMID:25230308

  16. Forces for Morphogenesis Investigated with Laser Microsurgery and Quantitative Modeling

    NASA Astrophysics Data System (ADS)

    Hutson, M. Shane; Tokutake, Yoichiro; Chang, Ming-Shien; Bloor, James W.; Venakides, Stephanos; Kiehart, Daniel P.; Edwards, Glenn S.

    2003-04-01

    We investigated the forces that connect the genetic program of development to morphogenesis in Drosophila. We focused on dorsal closure, a powerful model system for development and wound healing. We found that the bulk of progress toward closure is driven by contractility in supracellular ``purse strings'' and in the amnioserosa, whereas adhesion-mediated zipping coordinates the forces produced by the purse strings and is essential only for the end stages. We applied quantitative modeling to show that these forces, generated in distinct cells, are coordinated in space and synchronized in time. Modeling of wild-type and mutant phenotypes is predictive; although closure in myospheroid mutants ultimately fails when the cell sheets rip themselves apart, our analysis indicates that βPS integrin has an earlier, important role in zipping.

  17. Drag force on two disks moving in a granular bed

    NASA Astrophysics Data System (ADS)

    Kuwabara, A.; Yoshioka, N.; Shimada, T.; Ito, N.

    2016-09-01

    The drag forces acting on a disk and two disks dragged at constant speeds in a two-dimensional granular bed are measured by an event-driven molecular dynamics simulation. The normal drag force on a disk in case of two disks are dragged in parallel, F2x , is almost the same with the drag force on a disk in case of a single disk is dragged, F1x , when they are apart enough. As the distance between the disks D decreases, F2x increases until it has the maximum at a certain point, D*, and after that it decreases. When D is small enough, whether F2x is larger than F1x or not depends on the ratio of the average radius of the granular prticles to the one of the dragged objects.

  18. Resonant difference-frequency atomic force ultrasonic microscope

    NASA Technical Reports Server (NTRS)

    Cantrell, John H. (Inventor); Cantrell, Sean A. (Inventor)

    2010-01-01

    A scanning probe microscope and methodology called resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM), employs an ultrasonic wave launched from the bottom of a sample while the cantilever of an atomic force microscope, driven at a frequency differing from the ultrasonic frequency by one of the contact resonance frequencies of the cantilever, engages the sample top surface. The nonlinear mixing of the oscillating cantilever and the ultrasonic wave in the region defined by the cantilever tip-sample surface interaction force generates difference-frequency oscillations at the cantilever contact resonance. The resonance-enhanced difference-frequency signals are used to create images of nanoscale near-surface and subsurface features.

  19. Forces stabilizing proteins.

    PubMed

    Nick Pace, C; Scholtz, J Martin; Grimsley, Gerald R

    2014-06-27

    The goal of this article is to summarize what has been learned about the major forces stabilizing proteins since the late 1980s when site-directed mutagenesis became possible. The following conclusions are derived from experimental studies of hydrophobic and hydrogen bonding variants. (1) Based on studies of 138 hydrophobic interaction variants in 11 proteins, burying a -CH2- group on folding contributes 1.1±0.5 kcal/mol to protein stability. (2) The burial of non-polar side chains contributes to protein stability in two ways: first, a term that depends on the removal of the side chains from water and, more importantly, the enhanced London dispersion forces that result from the tight packing in the protein interior. (3) Based on studies of 151 hydrogen bonding variants in 15 proteins, forming a hydrogen bond on folding contributes 1.1±0.8 kcal/mol to protein stability. (4) The contribution of hydrogen bonds to protein stability is strongly context dependent. (5) Hydrogen bonds by side chains and peptide groups make similar contributions to protein stability. (6) Polar group burial can make a favorable contribution to protein stability even if the polar group is not hydrogen bonded. (7) Hydrophobic interactions and hydrogen bonds both make large contributions to protein stability.

  20. Magnetic force microscopy

    PubMed Central

    Passeri, Daniele; Dong, Chunhua; Reggente, Melania; Angeloni, Livia; Barteri, Mario; Scaramuzzo, Francesca A; De Angelis, Francesca; Marinelli, Fiorenzo; Antonelli, Flavia; Rinaldi, Federica; Marianecci, Carlotta; Carafa, Maria; Sorbo, Angela; Sordi, Daniela; Arends, Isabel WCE; Rossi, Marco

    2014-01-01

    Magnetic force microscopy (MFM) is an atomic force microscopy (AFM) based technique in which an AFM tip with a magnetic coating is used to probe local magnetic fields with the typical AFM spatial resolution, thus allowing one to acquire images reflecting the local magnetic properties of the samples at the nanoscale. Being a well established tool for the characterization of magnetic recording media, superconductors and magnetic nanomaterials, MFM is finding constantly increasing application in the study of magnetic properties of materials and systems of biological and biomedical interest. After reviewing these latter applications, three case studies are presented in which MFM is used to characterize: (i) magnetoferritin synthesized using apoferritin as molecular reactor; (ii) magnetic nanoparticles loaded niosomes to be used as nanocarriers for drug delivery; (iii) leukemic cells labeled using folic acid-coated core-shell superparamagnetic nanoparticles in order to exploit the presence of folate receptors on the cell membrane surface. In these examples, MFM data are quantitatively analyzed evidencing the limits of the simple analytical models currently used. Provided that suitable models are used to simulate the MFM response, MFM can be used to evaluate the magnetic momentum of the core of magnetoferritin, the iron entrapment efficiency in single vesicles, or the uptake of magnetic nanoparticles into cells. PMID:25050758

  1. Pairing forces in nuclei

    SciTech Connect

    Chasman, R.R.

    1996-12-31

    In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.

  2. Forces Stabilizing Proteins

    PubMed Central

    Pace, C. Nick; Scholtz, J. Martin; Grimsley, Gerald R.

    2014-01-01

    The goal of this article is to summarize what has been learned about the major forces stabilizing proteins since the late 1980s when site-directed mutagenesis became possible. The following conclusions are derived from experimental studies of hydrophobic and hydrogen bonding variants. 1. Based on studies of 138 hydrophobic interaction variants in 11 proteins, burying a –CH2– group on folding contributes 1.1 ± 0.5 kcal/mol to protein stability. 2. The burial of nonpolar side chains contributes to protein stability in two ways: first, a term that depends on the removal of the side chains from water and, more importantly, the enhanced London dispersion forces that result from the tight packing in the protein interior. 3. Based on studies of 151 hydrogen bonding variants in 15 proteins, forming a hydrogen bond on folding contributes 1.1 ± 0.8 kcal/mol to protein stability. 4. The contribution of hydrogen bonds to protein stability is strongly context dependent. 5. Hydrogen bonds by side chains and peptide groups make similar contributions to protein stability. 6. Polar group burial can make a favorable contribution to protein stability even if the polar group is not hydrogen bonded. 7. Hydrophobic interactions and hydrogen bonds both make large contributions to protein stability. PMID:24846139

  3. Environmental Crack Driving Force

    NASA Astrophysics Data System (ADS)

    Hall, M. M.

    2013-03-01

    The effect of environment on the crack driving force is considered, first by assuming quasistatic extension of a stationary crack and second, by use of stress corrosion cracking (SCC) crack growth rate models developed previously by this author and developed further here. A quasistatic thermodynamic energy balance approach, of the Griffith-Irwin type, is used to develop stationary crack threshold expressions, tilde{J}_c , which represent the conjoint mechanical and electrochemical conditions, below which stationary cracks are stable. Expressions for the electrochemical crack driving force (CDF) were derived using an analysis that is analogous to that used by Irwin to derive his "strain energy release rate," G, which Rice showed as being equivalent to his mechanical CDF, J. The derivations show that electrochemical CDFs both for active path dissolution (APD) and hydrogen embrittlement (HE) mechanisms of SCC are simply proportional to Tafel's electrochemical anodic and cathodic overpotentials, η a and η c, respectively. Phenomenological SCC models based on the kinetics of APD and HE crack growth are used to derive expressions for the kinetic threshold, J scc, below which crack growth cannot be sustained. These models show how independent mechanical and environmental CDFs may act together to drive SCC crack advance. Development of a user-friendly computational tool for calculating Tafel's overpotentials is advocated.

  4. Force normalization in paraplegics.

    PubMed

    Serra-Añó, P; García-Massó, X; Pellicer, M; González, L-M; López-Pascual, J; Giner-Pascual, M; Toca-Herrera, J L

    2012-06-01

    The principal aim of our study was the determination of the effectiveness of a standardized ratio, allometric scaling model and a gamma function model in normalizing the isometric torque data of spinal cord patients and healthy subjects. For this purpose we studied a sample of 21 healthy males and 23 spinal cord injury males. The experiment consisted of the measurement of the force of the upper limb movement executed by all the subjects. We also determined anthropometric variables with dual-energy x-ray absorptiometry. The experimental data were analyzed with 3 force normalization methods. Our results indicate that the most important confounding variable was the fat free mass of the dominant upper limb (r>0.36, p<0.05). With the standardization by body mass and allometric scaling model, the normalized torque was influenced by body size variables. However, the normalized torque by the gamma function model was independent of body size measures. Paraplegics were weaker (p<0.05) in extension movements when the data were normalized by the gamma function model. In summary, this study shows that the gamma function model with fat free mass of the dominant upper limb was more effective than the standardized ratio in removing the influence of body size variables. PMID:22377940

  5. Forced emigration, favourable outcomes.

    PubMed

    Pearn, J

    2001-10-01

    The discipline of public health and preventive medicine in Australia and New Zealand had its genesis in the advocacy of 18th and 19th century military pioneers. Military (Royal Navy and British Army) surgeons were posted to Australia as part of their non-discretionary duty. Civilian doctors emigrated variously for adventure, escapism and gold fever. One group, a particularly influential group disproportionate to their numbers, came in one sense as forced emigrants because of chronic respiratory disease in general, and tuberculosis in particular. Tuberculosis was an occupational hazard of 19th century medical and surgical practice throughout western Europe. This paper analyses six examples of such emigration which had, perhaps unforeseen at the time, significant results in the advancement of public health. Such emigration was in one sense voluntary, but in another was forced upon the victims in their quest for personal survival. In Australia, such medical individuals became leading advocates and successful catalysts for change in such diverse fields as social welfare, public health, the preventive aspects of medical practice, child health, nutrition and medical education. A number of such public health pioneers today have no physical memorials; but their influence is to be seen in the ethos of medical practice in Australia and New Zealand today. Their memory is further perpetuated in the names of Australian native wildflowers and trees that symbolise not only a healthy environment but the long-term investment, accrued with interest, of the institution of public health measures for which their advocacy achieved much success.

  6. Force reflecting hand controller

    NASA Technical Reports Server (NTRS)

    Mcaffee, Douglas A. (Inventor); Snow, Edward R. (Inventor); Townsend, William T. (Inventor)

    1993-01-01

    A universal input device for interfacing a human operator with a slave machine such as a robot or the like includes a plurality of serially connected mechanical links extending from a base. A handgrip is connected to the mechanical links distal from the base such that a human operator may grasp the handgrip and control the position thereof relative to the base through the mechanical links. A plurality of rotary joints is arranged to connect the mechanical links together to provide at least three translational degrees of freedom and at least three rotational degrees of freedom of motion of the handgrip relative to the base. A cable and pulley assembly for each joint is connected to a corresponding motor for transmitting forces from the slave machine to the handgrip to provide kinesthetic feedback to the operator and for producing control signals that may be transmitted from the handgrip to the slave machine. The device gives excellent kinesthetic feedback, high-fidelity force/torque feedback, a kinematically simple structure, mechanically decoupled motion in all six degrees of freedom, and zero backlash. The device also has a much larger work envelope, greater stiffness and responsiveness, smaller stowage volume, and better overlap of the human operator's range of motion than previous designs.

  7. Force reflecting hand controller

    NASA Astrophysics Data System (ADS)

    McAffee, Douglas A.; Snow, Edward R.; Townsend, William T.

    1993-03-01

    A universal input device for interfacing a human operator with a slave machine such as a robot or the like includes a plurality of serially connected mechanical links extending from a base. A handgrip is connected to the mechanical links distal from the base such that a human operator may grasp the handgrip and control the position thereof relative to the base through the mechanical links. A plurality of rotary joints is arranged to connect the mechanical links together to provide at least three translational degrees of freedom and at least three rotational degrees of freedom of motion of the handgrip relative to the base. A cable and pulley assembly for each joint is connected to a corresponding motor for transmitting forces from the slave machine to the handgrip to provide kinesthetic feedback to the operator and for producing control signals that may be transmitted from the handgrip to the slave machine. The device gives excellent kinesthetic feedback, high-fidelity force/torque feedback, a kinematically simple structure, mechanically decoupled motion in all six degrees of freedom, and zero backlash. The device also has a much larger work envelope, greater stiffness and responsiveness, smaller stowage volume, and better overlap of the human operator's range of motion than previous designs.

  8. Assessing respondent-driven sampling.

    PubMed

    Goel, Sharad; Salganik, Matthew J

    2010-04-13

    Respondent-driven sampling (RDS) is a network-based technique for estimating traits in hard-to-reach populations, for example, the prevalence of HIV among drug injectors. In recent years RDS has been used in more than 120 studies in more than 20 countries and by leading public health organizations, including the Centers for Disease Control and Prevention in the United States. Despite the widespread use and growing popularity of RDS, there has been little empirical validation of the methodology. Here we investigate the performance of RDS by simulating sampling from 85 known, network populations. Across a variety of traits we find that RDS is substantially less accurate than generally acknowledged and that reported RDS confidence intervals are misleadingly narrow. Moreover, because we model a best-case scenario in which the theoretical RDS sampling assumptions hold exactly, it is unlikely that RDS performs any better in practice than in our simulations. Notably, the poor performance of RDS is driven not by the bias but by the high variance of estimates, a possibility that had been largely overlooked in the RDS literature. Given the consistency of our results across networks and our generous sampling conditions, we conclude that RDS as currently practiced may not be suitable for key aspects of public health surveillance where it is now extensively applied. PMID:20351258

  9. Piezoelectrically-driven Thermoacoustic Refrigerator

    NASA Astrophysics Data System (ADS)

    Chinn, Daniel George

    Thermoacoustic refrigeration is an emerging refrigeration technology which does not require any moving parts or harmful refrigerants in its operation. This technology uses acoustic waves to pump heat across a temperature gradient. The vast majority of thermoacoustic refrigerators to date have used electromagnetic loudspeakers to generate the acoustic input. In this thesis, the design, construction, operation, and modeling of a piezoelectrically-driven thermoacoustic refrigerator are detailed. This refrigerator demonstrates the effectiveness of piezoelectric actuation in moving 0.3 W of heat across an 18 degree C temperature difference with an input power of 7.6 W. The performance characteristics of this class of thermoacoustic-piezoelectric refrigerators are modeled by using DeltaEC software and the predictions are experimentally validated. The obtained results confirm the validity of the developed model. Furthermore, the potential of piezoelectric actuation as effective means for driving thermoacoustic refrigerators is demonstrated as compared to the conventional electromagnetic loudspeakers which are heavy and require high actuation energy. The developed theoretical and experimental tools can serve as invaluable means for the design and testing of other piezoelectrically-driven thermoacoustic refrigerator configurations.

  10. Magnetically driven quantum heat engine

    NASA Astrophysics Data System (ADS)

    Munoz, Enrique; Pena, Francisco

    2015-03-01

    In analogy with classical thermodynamics, a quantum heat engine generates useful mechanical work from heat, by means of a reversible sequence of transformations (trajectories), where the ``working substance'' is of quantum mechanical nature. Several theoretical implementations for a quantum heat engine have been discussed in the literature, such as entangled states in a qubit, quantum mechanical versions of the Otto cycle, and photocells. In this work, we propose yet a different alternative by introducing the concept of a magnetically driven quantum heat engine. We studied the efficiency of such system, by considering as the ``working substance'' a single nonrelativistic particle trapped in a cylindrical potential well, as a model for a semiconductor quantum dot, in the presence of an external magnetic field. The trajectories are driven by a quasistatic modulation of the external magnetic-field intensity, while the system is in contact with macroscopic thermostats. The external magnetic field modulation allows to modify the effective geometric confinement, in analogy with a piston in a classical gas. E. Munoz acknowledges financial support from Fondecyt under Contract 1141146.

  11. Force-Field Parameter Fitter

    SciTech Connect

    2015-05-27

    ParFit is a flexible and extendable framework and library of classes for fitting force-field parameters to data from high-level ab-initio calculations on the basis of deterministic and stochastic algorithms. Currently, the code is fitting MM3 and Merck force-field parameters but could easily extend to other force-field types.

  12. Investigating Reaction-Driven Cracking

    NASA Astrophysics Data System (ADS)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required

  13. Superdiffusion in dispersions of active colloids driven by an external field and their sedimentation equilibrium

    NASA Astrophysics Data System (ADS)

    Chen, Yen-Fu; Wei, Hsien-Hung; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2016-04-01

    The diffusive behaviors of active colloids with run-and-tumble movement are explored by dissipative particle dynamics simulations for self-propelled particles (force dipole) and external field-driven particles (point force). The self-diffusion of tracers (solvent) is investigated as well. The influences of the active force, run time, and concentration associated with active particles are studied. For the system of self-propelled particles, the normal diffusion is observed for both active particles and tracers. The diffusivity of the former is significantly greater than that of the latter. For the system of field-driven particles, the superdiffusion is seen for both active particles and tracers. In contrast, it is found that the anomalous diffusion exponent of the former is slightly less than that of the latter. The anomalous diffusion is caused by the many-body, long-range hydrodynamic interactions. In spite of the superdiffusion, the sedimentation equilibrium of field-driven particles can be acquired and the density profile is still exponentially decayed. The sedimentation length of field-driven particles is always greater than that of self-propelled particles.

  14. Superdiffusion in dispersions of active colloids driven by an external field and their sedimentation equilibrium.

    PubMed

    Chen, Yen-Fu; Wei, Hsien-Hung; Sheng, Yu-Jane; Tsao, Heng-Kwong

    2016-04-01

    The diffusive behaviors of active colloids with run-and-tumble movement are explored by dissipative particle dynamics simulations for self-propelled particles (force dipole) and external field-driven particles (point force). The self-diffusion of tracers (solvent) is investigated as well. The influences of the active force, run time, and concentration associated with active particles are studied. For the system of self-propelled particles, the normal diffusion is observed for both active particles and tracers. The diffusivity of the former is significantly greater than that of the latter. For the system of field-driven particles, the superdiffusion is seen for both active particles and tracers. In contrast, it is found that the anomalous diffusion exponent of the former is slightly less than that of the latter. The anomalous diffusion is caused by the many-body, long-range hydrodynamic interactions. In spite of the superdiffusion, the sedimentation equilibrium of field-driven particles can be acquired and the density profile is still exponentially decayed. The sedimentation length of field-driven particles is always greater than that of self-propelled particles. PMID:27176356

  15. Dynamics of a quantum two-state system in a linearly driven quantum bath

    NASA Astrophysics Data System (ADS)

    Reichert, J.; Nalbach, P.; Thorwart, M.

    2016-09-01

    When an open quantum system is driven by an external time-dependent force, the coupling of the driving to the central system is usually included, whereas the impact of the driving field on the bath is neglected. We investigate the effect of a quantum bath of linearly driven harmonic oscillators on the relaxation dynamics of a quantum two-level system which is not directly driven. In particular, we calculate the frequency-dependent response of the system when the bath is subject to Dirac and Gaussian driving pulses. We show that a time-retarded effective force on the system is induced by the driven bath which depends on the full history of the perturbation and the spectral characteristics of the underlying bath. In particular, when a structured Ohmic bath with a pronounced Lorentzian peak is considered, the dynamical response of the system to a driven bath is qualitatively different than that of the undriven bath. Specifically, additional resonances appear which can be directly associated with a Jaynes-Cummings-like effective energy spectrum.

  16. A comparison of fixed-base and driven-base modal testing of an electronics package

    SciTech Connect

    Carne, T.G.; Martinez, D.R.; Nord, A.R.

    1989-08-01

    This paper compares results for a fixed-base and a driven-base modal test of an electronics package. A fixed-base modal test uses the common testing procedure of attaching the structure to a large inertial mass which is freely suspended. The problem with this approach is that the input levels are typically limited by the strength of the structure and stinger attachment. An attractive alternative to fixed-base modal testing is to use high force shaker-tables to provide a driven-base input. Some of the issues of concern are: properly simulating the fixed boundary conditions, applying modal estimation algorithms to motion-to-motion frequency response functions vs. motion-to-force frequency response functions, non-linearity effects and testing at very low input levels vs. levels equal to those of the field environment, complications involved with shaker resonances, exciting the ''response-critical'' modes of the structure, and consistency of the modal parameters using driven-base tests vs. fixed-base modal tests. Experimental results are presented which demonstrate the adequacy of using vibration shake tables to excite the fixed-based modes of the system. A direct comparison of the modes acquired using fixed-base and driven-base excitation for the electronics package shows very close agreement. A discussion of the theory for driven-base testing is given, as well as a brief presentation of analytical predictions for the structure. 4 refs., 11 figs., 1 tab.

  17. Proximal arm kinematics affect grip force-load force coordination.

    PubMed

    Vermillion, Billy C; Lum, Peter S; Lee, Sang Wook

    2015-10-01

    During object manipulation, grip force is coordinated with load force, which is primarily determined by object kinematics. Proximal arm kinematics may affect grip force control, as proximal segment motion could affect control of distal hand muscles via biomechanical and/or neural pathways. The aim of this study was to investigate the impact of proximal kinematics on grip force modulation during object manipulation. Fifteen subjects performed three vertical lifting tasks that involved distinct proximal kinematics (elbow/shoulder), but resulted in similar end-point (hand) trajectories. While temporal coordination of grip and load forces remained similar across the tasks, proximal kinematics significantly affected the grip force-to-load force ratio (P = 0.042), intrinsic finger muscle activation (P = 0.045), and flexor-extensor ratio (P < 0.001). Biomechanical coupling between extrinsic hand muscles and the elbow joint cannot fully explain the observed changes, as task-related changes in intrinsic hand muscle activation were greater than in extrinsic hand muscles. Rather, between-task variation in grip force (highest during task 3) appears to contrast to that in shoulder joint velocity/acceleration (lowest during task 3). These results suggest that complex neural coupling between the distal and proximal upper extremity musculature may affect grip force control during movements, also indicated by task-related changes in intermuscular coherence of muscle pairs, including intrinsic finger muscles. Furthermore, examination of the fingertip force showed that the human motor system may attempt to reduce variability in task-relevant motor output (grip force-to-load force ratio), while allowing larger fluctuations in output less relevant to task goal (shear force-to-grip force ratio). PMID:26289460

  18. Proximal arm kinematics affect grip force-load force coordination

    PubMed Central

    Vermillion, Billy C.; Lum, Peter S.

    2015-01-01

    During object manipulation, grip force is coordinated with load force, which is primarily determined by object kinematics. Proximal arm kinematics may affect grip force control, as proximal segment motion could affect control of distal hand muscles via biomechanical and/or neural pathways. The aim of this study was to investigate the impact of proximal kinematics on grip force modulation during object manipulation. Fifteen subjects performed three vertical lifting tasks that involved distinct proximal kinematics (elbow/shoulder), but resulted in similar end-point (hand) trajectories. While temporal coordination of grip and load forces remained similar across the tasks, proximal kinematics significantly affected the grip force-to-load force ratio (P = 0.042), intrinsic finger muscle activation (P = 0.045), and flexor-extensor ratio (P < 0.001). Biomechanical coupling between extrinsic hand muscles and the elbow joint cannot fully explain the observed changes, as task-related changes in intrinsic hand muscle activation were greater than in extrinsic hand muscles. Rather, between-task variation in grip force (highest during task 3) appears to contrast to that in shoulder joint velocity/acceleration (lowest during task 3). These results suggest that complex neural coupling between the distal and proximal upper extremity musculature may affect grip force control during movements, also indicated by task-related changes in intermuscular coherence of muscle pairs, including intrinsic finger muscles. Furthermore, examination of the fingertip force showed that the human motor system may attempt to reduce variability in task-relevant motor output (grip force-to-load force ratio), while allowing larger fluctuations in output less relevant to task goal (shear force-to-grip force ratio). PMID:26289460

  19. Modeling of magnetic field driven simultaneous assembly

    NASA Astrophysics Data System (ADS)

    Rivero, Rene David

    The Magnetic Field Driven Simultaneous Assembly (MFDSA) is a method that offers a non-statistical and deterministic solution to the problem of assembly via batch processing; a hybrid of serial and parallel processing. The technique requires the use of electromagnets as well as soft and hard magnetic materials that are applied to devices and recesses respectively. The MFDSA approach offers the ability to check and correct errors in real-time and is capable of scalable, versatile, and high-yield integration. Devices, coated with a layer of soft magnetic material, are moved from initial to final positions along predetermined pathways through the action of an array of electromagnets. Various devices, of arbitrary geometries, with different physical and functional properties, are manipulated simultaneously toward specific desired locations and then dropped onto a template under the influence of gravity by weakening the local applied field. Locations on the template correspond to sites on a substrate that contain recesses. When a number of devices have been dropped onto the template, a substrate is pressed onto it and the soft magnetic layers on the devices adhere to the hard magnetic strips in the recesses, completing integration in a single step. The objectives of this dissertation are the following: to present the MFDSA method; comparing and contrasting it with other extant techniques employed by the semiconductor industry; to discuss key aspects of this solution with respect to the problem of assembly, and to model the calculations involved with determining both device pathways and field interactions that are required to implement the approach. The Fourier Series technique will be used to describe the force of attraction between the device's soft magnetic layer and the recess's hard magnetic strips. Methodology from finite element analysis will be employed to calculate the force exerted on a device by an array of electromagnets. The Swarm Algorithm, which was

  20. Buoyancy Driven Shear Flows of Bubble Suspensions

    NASA Technical Reports Server (NTRS)

    Koch, D. L.; Hill, R. J.; Chellppannair, T.; Zenit, R.; Zenit, R.; Spelt, P. D. M.

    1999-01-01

    In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1a nd Re >> 1, for which comparisons are made with kinetic theory and numerical simulations. Here Re = gamma(a(exp 2)/nu is the Reynolds number and We = rho(gamma(exp 2))a(exp 3)/sigma is the Weber number; gamma is the shear rate, a is the bubble radius, nu is the kinematic viscosity of the liquid, rho is the density of the liquid, and sigma is the surface tension of the gas/liquid interface. Kang et al. calculated the bubble phase pressure and velocity variance of sheared bubble suspensions under conditions where the bubbles are spherical and the liquid phase velocity field can be approximated using potential flow theory, i.e. We= 0 and Re >> 1. Such conditions can be achieved in an experiment using gas bubbles, with a radius of O(0.5mm), in water. The theory requires that there be no average relative motion of the gas and liquid phases, hence the motivation for an experimental program in microgravity. The necessity of performing preliminary, Earth based experiments, however, requires performing experiments where the gas phase rises in the liquid, which significantly complicates the comparison of experiments with theory. Rather than comparing experimental results with theory for a uniform, homogeneous shear flow, experiments can be compared directly with solutions of the averaged equations of motion for bubble suspensions. This requires accounting for the significant lift force acting on the gas phase when the bubbles rise parallel to the average velocity of the sheared suspension. Shear flows can be produced in which the bubble phase pressure gradient, arising from shear induced collisions amongst the bubbles, balances a body force (centrifugal or gravitational) on the gas phase. A steady, non-uniform gas volume fraction

  1. Hydrogel Actuation by Electric Field Driven Effects

    NASA Astrophysics Data System (ADS)

    Morales, Daniel Humphrey

    the applied electric field. We extend the use of ionoprinting to develop multi-responsive bilayer gel systems capable of more complex shape transformation. The localized crosslinked regions determine the bending axis as the gel responds to the external environment. The bending can be tuned to reverse direction isothermally by changing the solvent quality or by changing the temperature at a fixed concentration. The multi-responsive behavior is caused by the volume transitions of a non-ionic, thermos-sensitive hydrogel coupled with a superabsorbent ionic hydrogel. Lastly, electric field driven microparticle assembly, using dielectrophoretic (DEP) forces, organized colloidal microparticles within a hydrogel matrix. The use of DEP forces enables rapid, efficient and precise control over the colloidal distribution. The resulting supracolloidal endoskeleton structures impart directional bending as the hydrogel shrinks. We compare the ordered particles structures to random particle distributions in affecting the hydrogel sheet bending response. This study demonstrates a universal technique for imparting directional properties in hydrogels towards new generations of hybrid soft materials.

  2. Erosion and basal forces in granular flow experiments

    NASA Astrophysics Data System (ADS)

    Sanvitale, Nicoletta; Bowman, Elisabeth

    2016-04-01

    Extreme mass wasting avalanche events such as rock, snow and ice avalanches, debris flows, and pyroclastic flows are among the most hazardous geological phenomena. These events driven by gravity, can travel for long distance and high speed, increasing their volumes as they can entertain material along their path. The erosion of material and its entrainment can greatly affect the overall dynamics of transportation, either enhancing or impeding the avalanche mobility depending on flow dynamics and characteristics of the substrate. However, the mechanisms and processes acting at the base as they travel over deformable or erodible substrates are still poor understood. Experiments, simulations and field measurements indicate that large fluctuations can occur in basal forces and stresses, which may be the result of non-uniform load transfer within the mass, and rolling, bouncing and sliding of the particles along the bed. In dense granular materials, force distributions can propagate through filamentary chain structures that carry a large fraction of the forces within the system. Photoelastic experiments on two-dimensional, monodisperse, gravity-driven flows have shown that force chains can transmit high localized forces to the boundary of dense granular flows. Here we describe the preliminary setup and results of 2D experiments on polydisperse granular flows of photoelastic disks down a small flume designed to acquire the forces exerted at the boundaries of the flow and to analyze their effects on an erodible bed. The intended outcome of this research is to provide better information on the complex mechanism of erosion and its effects on avalanche behaviour.

  3. Near and far-wall effects on the three-dimensional motion of bacteria-driven microbeads

    NASA Astrophysics Data System (ADS)

    Edwards, Matthew R.; Wright Carlsen, Rika; Sitti, Metin

    2013-04-01

    Bio-hybrid microrobots have been heavily studied due to their potential applications as minimally invasive medical microdevices. Though most researchers have focused on two-dimensional and near-wall motion, this letter uses a defocused optical tracking method to quantify the three-dimensional motion of 5 μm diameter polystyrene beads driven by attached Serratia marcescens bacteria. Away from walls the beads trace out helical trajectories, demonstrating kinematics produced by near-constant forces and torques. Near-wall motion is observed to be more stochastic. The motion of beads driven by single bacteria is analyzed in detail, providing an understanding of the forces and torques on the beads.

  4. Numerical modelling of iceberg calving force responsible for glacial earthquakes

    NASA Astrophysics Data System (ADS)

    Sergeant, Amandine; Yastrebov, Vladislav; Castelnau, Olivier; Mangeney, Anne; Stutzmann, Eleonore; Montagner, Jean-Paul

    2016-04-01

    Glacial earthquakes is a class of seismic events of magnitude up to 5, occurring primarily in Greenland, in the margins of large marine-terminated glaciers with near-grounded termini. They are caused by calving of cubic-kilometer scale unstable icebergs which penetrate the full-glacier thickness and, driven by the buoyancy forces, capsize against the calving front. These phenomena produce seismic energy including surface waves with dominant energy between 10-150 s of period whose seismogenic source is compatible with the contact force exerted on the terminus by the iceberg while it capsizes. A reverse motion and posterior rebound of the terminus have also been measured and associated with the fluctuation of this contact force. Using a finite element model of iceberg and glacier terminus coupled with simplified fluid-structure interaction model, we simulate calving and capsize of icebergs. Contact and frictional forces are measured on the terminus and compared with laboratory experiments. We also study the influence of geometric factors on the force history, amplitude and duration at the laboratory and field scales. We show first insights into the force and the generated seismic waves exploring different scenarios for iceberg capsizing.

  5. Critical Assessment of Current Force Fields. Short Peptide Test Case.

    PubMed

    Vymětal, Jiří; Vondrášek, Jiří

    2013-01-01

    The applicability of molecular dynamics simulations for studies of protein folding or intrinsically disordered proteins critically depends on quality of energetic functions-force fields. The four popular force fields for biomolecular simulations, CHARMM22/CMAP, AMBER FF03, AMBER FF99SB, and OPLS-AA/L, were compared in prediction of conformational propensities of all common proteinogenic amino acids. The minimalistic model of terminally block amino acids (dipeptides) was chosen for assessment of side chain effects on backbone propensities. The precise metadynamics simulations revealed striking inconsistency of trends in conformational preferences as manifested by investigated force fields for both backbone and side chains. To trace this disapproval between force fields, the two related AMBER force fields were studied more closely. In the cases of FF99SB and FF03, we uncovered that the distinct tends were driven by different charge models. Additionally, the effects of recent correction for side chain torsion (FF99SB-ILDN) were examined on affected amino acids and exposed significant coupling between free energy profiles and propensities of backbone and side chain conformers. These findings have important consequences for further force field development.

  6. Force generation by endocytic actin patches in budding yeast.

    PubMed

    Carlsson, Anders E; Bayly, Philip V

    2014-04-15

    Membrane deformation during endocytosis in yeast is driven by local, templated assembly of a sequence of proteins including polymerized actin and curvature-generating coat proteins such as clathrin. Actin polymerization is required for successful endocytosis, but it is not known by what mechanisms actin polymerization generates the required pulling forces. To address this issue, we develop a simulation method in which the actin network at the protein patch is modeled as an active gel. The deformation of the gel is treated using a finite-element approach. We explore the effects and interplay of three different types of force driving invagination: 1), forces perpendicular to the membrane, generated by differences between actin polymerization rates at the edge of the patch and those at the center; 2), the inherent curvature of the coat-protein layer; and 3), forces parallel to the membrane that buckle the coat protein layer, generated by an actomyosin contractile ring. We find that with optimistic estimates for the stall stress of actin gel growth and the shear modulus of the actin gel, actin polymerization can generate almost enough force to overcome the turgor pressure. In combination with the other mechanisms, actin polymerization can the force over the critical value.

  7. Force Generation by Endocytic Actin Patches in Budding Yeast

    PubMed Central

    Carlsson, Anders E.; Bayly, Philip V.

    2014-01-01

    Membrane deformation during endocytosis in yeast is driven by local, templated assembly of a sequence of proteins including polymerized actin and curvature-generating coat proteins such as clathrin. Actin polymerization is required for successful endocytosis, but it is not known by what mechanisms actin polymerization generates the required pulling forces. To address this issue, we develop a simulation method in which the actin network at the protein patch is modeled as an active gel. The deformation of the gel is treated using a finite-element approach. We explore the effects and interplay of three different types of force driving invagination: 1), forces perpendicular to the membrane, generated by differences between actin polymerization rates at the edge of the patch and those at the center; 2), the inherent curvature of the coat-protein layer; and 3), forces parallel to the membrane that buckle the coat protein layer, generated by an actomyosin contractile ring. We find that with optimistic estimates for the stall stress of actin gel growth and the shear modulus of the actin gel, actin polymerization can generate almost enough force to overcome the turgor pressure. In combination with the other mechanisms, actin polymerization can the force over the critical value. PMID:24739159

  8. Microfluidics, Chromatography, and Atomic-Force Microscopy

    NASA Technical Reports Server (NTRS)

    Anderson, Mark

    2008-01-01

    A Raman-and-atomic-force microscope (RAFM) has been shown to be capable of performing several liquid-transfer and sensory functions essential for the operation of a microfluidic laboratory on a chip that would be used to perform rapid, sensitive chromatographic and spectro-chemical analyses of unprecedentedly small quantities of liquids. The most novel aspect of this development lies in the exploitation of capillary and shear effects at the atomic-force-microscope (AFM) tip to produce shear-driven flow of liquids along open microchannels of a microfluidic device. The RAFM can also be used to perform such functions as imaging liquids in microchannels; removing liquid samples from channels for very sensitive, tip-localized spectrochemical analyses; measuring a quantity of liquid adhering to the tip; and dip-pen deposition from a chromatographic device. A commercial Raman-spectroscopy system and a commercial AFM were integrated to make the RAFM so as to be able to perform simultaneous topographical AFM imaging and surface-enhanced Raman spectroscopy (SERS) at the AFM tip. The Raman-spectroscopy system includes a Raman microprobe attached to an optical microscope, the translation stage of which is modified to accommodate the AFM head. The Raman laser excitation beam, which is aimed at the AFM tip, has a wavelength of 785 nm and a diameter of about 5 m, and its power is adjustable up to 10 mW. The AFM is coated with gold to enable tip-localized SERS.

  9. Buoyancy Driven Shear Flows of Bubble Suspensions

    NASA Astrophysics Data System (ADS)

    Hill, R. J.; Zenit, R.; Chellppannair, T.; Koch, D. L.; Spelt, P. D. M.; Sangani, A.

    1998-11-01

    In this work the gas volume fraction and the root-mean-squared fluid velocity are measured in buoyancy driven shear flows of bubble suspensions in a tall, inclined, rectangular channel. The experiments are performed under conditions where We << 1 and Re >> 1 , so that the bubbles are relatively undeformed and the flow is inviscid and approximately irrotational. Nitrogen is introduced through an array of capillaries at the base of a .2x.02x2 m channel filled with an aqueous electrolyte solution (0.06 molL-1 MgSO_4). The rising bubbles generate a unidirectional shear flow, where the denser suspension at the lower surface of the channel falls, while the less dense suspension at the upper surface rises. Hot-film anemometry is used to measure the resulting gas volume fraction and fluid velocity profiles. The bubble collision rate with the sensor is related to the gas volume fraction and the mean and variance of the bubble velocity using an experimentally measured collision surface area for the sensor. Bubble collisions with the sensor are identified by the characteristic slope of the hot-film anemometer signal when bubbles collide with the sensor. It is observed that the steady shear flow develops a bubble phase pressure gradient across the channel gap as the bubbles interchange momentum through direct collisions. The discrete phase presssure gradient balances the buoyancy force driving bubbles toward the upper surface resulting in a steady void fraction profile across the gap width. The strength of the shear flow is controlled by the extent of bubble segregation and by the effective viscosity of the bubble phase. The measurements are compared with solutions of the averaged equations of motion (Kang et al. 1997; Spelt and Sangani, 1998), for a range of gas volume fractions and channel inclination angles.

  10. Parallel computation with the force

    NASA Technical Reports Server (NTRS)

    Jordan, H. F.

    1985-01-01

    A methodology, called the force, supports the construction of programs to be executed in parallel by a force of processes. The number of processes in the force is unspecified, but potentially very large. The force idea is embodied in a set of macros which produce multiproceossor FORTRAN code and has been studied on two shared memory multiprocessors of fairly different character. The method has simplified the writing of highly parallel programs within a limited class of parallel algorithms and is being extended to cover a broader class. The individual parallel constructs which comprise the force methodology are discussed. Of central concern are their semantics, implementation on different architectures and performance implications.

  11. Updates on Force Limiting Improvements

    NASA Technical Reports Server (NTRS)

    Kolaini, Ali R.; Scharton, Terry

    2013-01-01

    The following conventional force limiting methods currently practiced in deriving force limiting specifications assume one-dimensional translation source and load apparent masses: Simple TDOF model; Semi-empirical force limits; Apparent mass, etc.; Impedance method. Uncorrelated motion of the mounting points for components mounted on panels and correlated, but out-of-phase, motions of the support structures are important and should be considered in deriving force limiting specifications. In this presentation "rock-n-roll" motions of the components supported by panels, which leads to a more realistic force limiting specifications are discussed.

  12. Adapting the Quesant Nomad atomic force microscope for biology and patch-clamp atomic force microscopy.

    PubMed

    Besch, S; Snyder, K V; Zhang, P C; Sachs, F

    2003-01-01

    The Quesant Nomad atomic force microscope (AFM) was modified to produce a reliable patch-clamp AFM for demanding biologic applications. The AFM's laser optics forms the basis of a condenser that allows simultaneous Köhler illumination and AFM imaging on an inverted optical microscope. The original AFM scan head was replaced with plastic and glass to make it biologically inert. A bevel cut in the new scan head permits clearance for patch clamp pipets. Cantilevers are attached to the scan head with a quick setting silicone rubber that is readily removable. Software was developed to (a) automate a gentle approach and set a specific feedback force, (b) provide a mouse-driven control of the X-Y position of the probe tip and recall of saved locations, and (c) measure force-distance curves over user defined paths. Additional modifications were made to minimize mechanical noise. The patch-clamp AFM achieves 600 fA (3 kHz bandwidth) and 1 A RMS noise levels (10 kHz bandwidth). The correlation of electrical and mechanical information allows signal averaging and measures sub-Angstrom, sub-millisecond electromotile responses from cells. PMID:14716076

  13. Forced to be right.

    PubMed

    Trout, J D

    2014-05-01

    In "Forced to be Free", Neil Levy surveys the raft of documented decision-making biases that humans are heir to, and advances several bold proposals designed to enhance the patient's judgment. Gratefully, Levy is moved by the psychological research on judgment and decision-making that documents people's inaccuracy when identifying courses of action will best promote their subjective well-being. But Levy is quick to favour the patient's present preferences, to ensure they get "final say" about their treatment. I urge the opposite inclination, raising doubts about whether the patient's "present preferences" are the best expression of their "final say". When there is adequate evidence that people, by their own lights, overemphasize their present preferences about the future, we should carefully depreciate those preferences, in effect biasing them to make the right decision by their own lights.

  14. [Galileo and centrifugal force].

    PubMed

    Vilain, Christiane

    This work intends to focus on Galileo's study of what is now called "centrifugal force," within the framework of the Second Day of his Dialogo written in 1632, rather than on the previously published commentaries on the topic. Galileo proposes three geometrical demonstrations in order to prove that gravity will always overcome centrifugalforce, and that the potential rotation of the Earth, whatever its speed, cannot in any case project objects beyond it. Each of these demonstrations must consequently contain an error and it has seemed to us that the first one had not been understood up until now. Our analysis offers an opportunity to return to Galileo's geometrical representation of dynamical questions; actually, we get an insight into the sophistication of Galileo's practices more than into his mistakes. Our second point, concerning the historiography of the problem, shows an evolution from anachronic critics to more contextual considerations, in the course of the second half of the twentieth century. PMID:25029818

  15. Silicon force sensor

    DOEpatents

    Galambos, Paul C.; Crenshaw, Thomas B.; Nishida, Erik E.; Burnett, Damon J.; Lantz, Jeffrey W.

    2016-07-05

    The various technologies presented herein relate to a sensor for measurement of high forces and/or high load shock rate(s), whereby the sensor utilizes silicon as the sensing element. A plate of Si can have a thinned region formed therein on which can be formed a number of traces operating as a Wheatstone bridge. The brittle Si can be incorporated into a layered structure comprising ductile and/or compliant materials. The sensor can have a washer-like configuration which can be incorporated into a nut and bolt configuration, whereby tightening of the nut and bolt can facilitate application of a compressive preload upon the sensor. Upon application of an impact load on the bolt, the compressive load on the sensor can be reduced (e.g., moves towards zero-load), however the magnitude of the preload can be such that the load on the sensor does not translate to tensile stress being applied to the sensor.

  16. [Galileo and centrifugal force].

    PubMed

    Vilain, Christiane

    This work intends to focus on Galileo's study of what is now called "centrifugal force," within the framework of the Second Day of his Dialogo written in 1632, rather than on the previously published commentaries on the topic. Galileo proposes three geometrical demonstrations in order to prove that gravity will always overcome centrifugalforce, and that the potential rotation of the Earth, whatever its speed, cannot in any case project objects beyond it. Each of these demonstrations must consequently contain an error and it has seemed to us that the first one had not been understood up until now. Our analysis offers an opportunity to return to Galileo's geometrical representation of dynamical questions; actually, we get an insight into the sophistication of Galileo's practices more than into his mistakes. Our second point, concerning the historiography of the problem, shows an evolution from anachronic critics to more contextual considerations, in the course of the second half of the twentieth century.

  17. Force Limit System

    NASA Technical Reports Server (NTRS)

    Pawlik, Ralph; Krause, David; Bremenour, Frank

    2011-01-01

    The Force Limit System (FLS) was developed to protect test specimens from inadvertent overload. The load limit value is fully adjustable by the operator and works independently of the test system control as a mechanical (non-electrical) device. When a test specimen is loaded via an electromechanical or hydraulic test system, a chance of an overload condition exists. An overload applied to a specimen could result in irreparable damage to the specimen and/or fixturing. The FLS restricts the maximum load that an actuator can apply to a test specimen. When testing limited-run test articles or using very expensive fixtures, the use of such a device is highly recommended. Test setups typically use electronic peak protection, which can be the source of overload due to malfunctioning components or the inability to react quickly enough to load spikes. The FLS works independently of the electronic overload protection.

  18. Forced Migration: Refugee Populations

    PubMed Central

    Boyle, Joyceen S.

    2015-01-01

    Undocumented migration is a global phenomenon that manifests in various contexts. This article describes the impact of the movement of large numbers of people in several African countries, producing a unique type of migrant—the refugee. We describe issues that refugee movements create on fragile health care systems, situations that precipitate refugee movements, certain human rights violations that are of particular concern such as gender based violence (GBV) and child soldiers, and lastly, implications for nursing practice and policy. We use examples from several countries in Sub-Saharan Africa, including the Democratic Republic of the Congo, Rwanda, Liberia, Sierra Leone, and Mozambique. Drawing on key documents from the United Nations High Commissioner for Refugees, current literature, as well as the international experience of the authors, this article presents an overview of forced migration and discusses opportunities for nurses to impact research, practice and policy related to refugee health. PMID:25645484

  19. Force protection: today's reality.

    PubMed

    Torgerson, Ron

    2004-11-11

    Most US infrastructure and major chemical manufacturing facilities as well as their supporting utility systems are inherently vulnerable to a terrorist attack. Force protection is a military and civilian term used to protect personnel and critical facilities and assets against would-be aggressors or terrorists. The war on terrorism is a 200-300-year war. Terrorist attacks on US soil could become as common-place as in the State of Israel. It is very easy to penetrate infrastructure or plants as evidenced by vulnerability assessments performed for states, cities, plants, and military facilities by Versar and others around the country. Chemical, biological, radiological, nuclear, and explosive weapons can be readily used to attack facilities in the US. This paper will explain some of those vulnerabilities, outline the current DoD standard as it relates to vulnerability assessments, and explain how this may be used in commercial applications to deter potential aggressors.

  20. Comparison between static maximal force and handbrake pulling force.

    PubMed

    Chateauroux, E; Wang, X

    2012-01-01

    The measurement of maximum pulling force is important not only for specifying force limit of industrial workers but also for designing controls requiring high force. This paper presents a comparison between maximal static handbrake pulling force (FST) and force exerted during normal handbrake pulling task (FDY). These forces were measured for different handle locations and subject characteristics. Participants were asked to pull a handbrake on an adjustable car mock-up as they would do when parking their own car, then to exert a force as high as possible on the pulled handbrake. Hand pulling forces were measured using a six-axes force sensor. 5 fixed handbrake positions were tested as well as a neutral handbrake position defined by the subject. FST and FDY were significantly correlated. Both were found to be dependent on handbrake position, age and gender. As expected, women and older subjects exerted lower forces. FST was significantly higher than FDY. The ratio FmR (FDY divided by FST) was also analyzed. Women showed higher FmR than men meaning that the task required a higher amount of muscle capability for women. FmR was also influenced by handbrake location. These data will be useful for handbrake design.

  1. Normal Force and Drag Force in Magnetorheological Finishing

    SciTech Connect

    Miao, C.; Shafrir, S.N.; Lambropoulos, J.C.; Jacobs, S.D.

    2010-01-13

    The material removal in magnetorheological finishing (MRF) is known to be controlled by shear stress, tau, which equals drag force, Fd, divided by spot area, As. However, it is unclear how the normal force, Fn, affects the material removal in MRF and how the measured ratio of drag force to normal force Fd/Fn, equivalent to coefficient of friction, is related to material removal. This work studies, for the first time for MRF, the normal force and the measured ratio Fd/Fn as a function of material mechanical properties. Experimental data were obtained by taking spots on a variety of materials including optical glasses and hard ceramics with a spot-taking machine (STM). Drag force and normal force were measured with a dual load cell. Drag force decreases linearly with increasing material hardness. In contrast, normal force increases with hardness for glasses, saturating at high hardness values for ceramics. Volumetric removal rate decreases with normal force across all materials. The measured ratio Fd/Fn shows a strong negative linear correlation with material hardness. Hard materials exhibit a low “coefficient of friction”. The volumetric removal rate increases with the measured ratio Fd/Fn which is also correlated with shear stress, indicating that the measured ratio Fd/Fn is a useful measure of material removal in MRF.

  2. Flow mechanotransduction regulates traction forces, intercellular forces, and adherens junctions

    PubMed Central

    Ting, Lucas H.; Jahn, Jessica R.; Jung, Joon I.; Shuman, Benjamin R.; Feghhi, Shirin; Han, Sangyoon J.; Rodriguez, Marita L.

    2012-01-01

    Endothelial cells respond to fluid shear stress through mechanotransduction responses that affect their cytoskeleton and cell-cell contacts. Here, endothelial cells were grown as monolayers on arrays of microposts and exposed to laminar or disturbed flow to examine the relationship among traction forces, intercellular forces, and cell-cell junctions. Cells under laminar flow had traction forces that were higher than those under static conditions, whereas cells under disturbed flow had lower traction forces. The response in adhesion junction assembly matched closely with changes in traction forces since adherens junctions were larger in size for laminar flow and smaller for disturbed flow. Treating the cells with calyculin-A to increase myosin phosphorylation and traction forces caused an increase in adherens junction size, whereas Y-27362 cause a decrease in their size. Since tugging forces across cell-cell junctions can promote junctional assembly, we developed a novel approach to measure intercellular forces and found that these forces were higher for laminar flow than for static or disturbed flow. The size of adherens junctions and tight junctions matched closely with intercellular forces for these flow conditions. These results indicate that laminar flow can increase cytoskeletal tension while disturbed flow decreases cytoskeletal tension. Consequently, we found that changes in cytoskeletal tension in response to shear flow conditions can affect intercellular tension, which in turn regulates the assembly of cell-cell junctions. PMID:22447948

  3. Microphotonic Forces from Superfluid Flow

    NASA Astrophysics Data System (ADS)

    McAuslan, D. L.; Harris, G. I.; Baker, C.; Sachkou, Y.; He, X.; Sheridan, E.; Bowen, W. P.

    2016-04-01

    In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly 1 order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces we demonstrate here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, while the ability to apply forces remotely, combined with the persistence of flow in superfluids, offers the prospect for new applications.

  4. Force oscillations simulating breathing maneuvers do not prevent force adaptation.

    PubMed

    Pascoe, Chris; Jiao, Yuekan; Seow, Chun Y; Paré, Peter D; Bossé, Ynuk

    2012-07-01

    Airway inflammation in patients with asthma exposes the airway smooth muscle (ASM) to a variety of spasmogens. These spasmogens increase ASM tone, which can lead to force adaptation. Length oscillations of ASM, which occur in vivo due to breathing maneuvers, can attenuate force adaptation. However, in the presence of tone, the force oscillations required to achieve these length oscillations may be unphysiologic (i.e., magnitude greater than the ones achieved due to the swings in transpulmonary pressure required for breathing). In the present study, we applied force oscillations simulating the tension oscillations experienced by the wall of a fourth-generation airway during tidal breathing with or without deep inspirations (DI) to ASM. The goal was to investigate whether force adaptation occurs in conditions mimicking breathing maneuvers. Tone was induced by carbachol (average, 20 nM), and the force-generating capacity of the ASM was assessed at 5-minute intervals before and after carbachol administration using electrical field stimulations (EFS). The results show that force oscillations applied before the introduction of tone had a small effect on the force produced by EFS (declined to 96.8% [P > 0.05] and 92.3% [P < 0.05] with and without DI, respectively). The tone induced by carbachol transiently decreased after a DI and declined significantly (P < 0.05) due to tidal breathing oscillations (25%). These force oscillations did not prevent force adaptation (gain of force of 11.2 ± 2.2 versus 13.5 ± 2.7 and 11.2 ± 3.0% in static versus dynamic conditions with or without DI, respectively). The lack of effect of simulated breathing maneuvers on force adaptation suggests that this gain in ASM force may occur in vivo and could contribute to the development of airway hyperresponsiveness. PMID:22323367

  5. Chin force in violin playing.

    PubMed

    Obata, Satoshi; Kinoshita, Hiroshi

    2012-06-01

    Force generated between the left mandible of violinists and the chinrest of the violin was examined using a force-sensing chinrest developed in this study. A strain-gauge force sensor was built, and it was fixed between the violin's top plate and a chin cup. Fifteen professional/amateur violinists held the violin statically, played musical scales with different sound properties and sounding techniques, as well as an excerpt from a Max Bruch concerto. Peak and mean forces were evaluated for each task. In a separate experiment, lateral movement of the lower teeth due to different levels of voluntary chin force exertion was measured. Static holding forces observed were 15 and 22 N with and without the help of the left hand, respectively. Peak force increased from 16 N at soft dynamics to 20 N at strong dynamics during scales. The force further increased to 29 N with the use of vibrato technique and 35 N during shifts. Tempo and hand position did not affect the force. Playing a Bruch concerto induced a mean peak force of 52 N, ranging from 31 to 82 N among the violinists. The developed force-sensing chinrest could accurately record the generated chin force. Typical chin force to stabilize the violin during ordinary musical performance was less than 30 N, but it could momentarily exceed 50 N when technically demanding musical pieces were performed. The lateral shift of the mandible was fairly small (<0.4 mm) even with high chin-force exertion, possibly due to clenching of the molars.

  6. Chin force in violin playing.

    PubMed

    Obata, Satoshi; Kinoshita, Hiroshi

    2012-06-01

    Force generated between the left mandible of violinists and the chinrest of the violin was examined using a force-sensing chinrest developed in this study. A strain-gauge force sensor was built, and it was fixed between the violin's top plate and a chin cup. Fifteen professional/amateur violinists held the violin statically, played musical scales with different sound properties and sounding techniques, as well as an excerpt from a Max Bruch concerto. Peak and mean forces were evaluated for each task. In a separate experiment, lateral movement of the lower teeth due to different levels of voluntary chin force exertion was measured. Static holding forces observed were 15 and 22 N with and without the help of the left hand, respectively. Peak force increased from 16 N at soft dynamics to 20 N at strong dynamics during scales. The force further increased to 29 N with the use of vibrato technique and 35 N during shifts. Tempo and hand position did not affect the force. Playing a Bruch concerto induced a mean peak force of 52 N, ranging from 31 to 82 N among the violinists. The developed force-sensing chinrest could accurately record the generated chin force. Typical chin force to stabilize the violin during ordinary musical performance was less than 30 N, but it could momentarily exceed 50 N when technically demanding musical pieces were performed. The lateral shift of the mandible was fairly small (<0.4 mm) even with high chin-force exertion, possibly due to clenching of the molars. PMID:21952980

  7. Molecular Mechanotransduction: how forces trigger cytoskeletal dynamics

    NASA Astrophysics Data System (ADS)

    Ehrlicher, Allen

    2012-02-01

    Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders, such as cardiac failure and pulmonary injury. Despite detailed knowledge of the cytoskeleton's structure, the specific molecular switches that convert mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein, filamin A (FLNa) as a central mechanotransduction element of the cytoskeleton by using Fluorescence Loss After photoConversion (FLAC), a novel high-speed alternative to FRAP. We reconstituted a minimal system consisting of actin filaments, FLNa and two FLNa-binding partners: the cytoplasmic tail of ß-integrin, and FilGAP. Integrins form an essential mechanical linkage between extracellular and intracellular environments, with ß integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FilGAP is a FLNa-binding GTPase-activating protein specific for Rac, which in vivo regulates cell spreading and bleb formation. We demonstrate that both externally-imposed bulk shear and myosin II driven forces differentially regulate the binding of integrin and FilGAP to FLNa. Consistent with structural predictions, strain increases ß-integrin binding to FLNa, whereas it causes FilGAP to dissociate from FLNa, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify the first molecular mechanotransduction element within the actin cytoskeleton, revealing that mechanical strain of key proteins regulates the binding of signaling molecules. Moreover, GAP activity has been shown to switch cell movement from mesenchymal to amoeboid motility, suggesting that mechanical forces directly impact the invasiveness of cancer.

  8. Asynchronous Event-Driven Particle Algorithms

    SciTech Connect

    Donev, A

    2007-02-28

    We present in a unifying way the main components of three examples of asynchronous event-driven algorithms for simulating physical systems of interacting particles. The first example, hard-particle molecular dynamics (MD), is well-known. We also present a recently-developed diffusion kinetic Monte Carlo (DKMC) algorithm, as well as a novel event-driven algorithm for Direct Simulation Monte Carlo (DSMC). Finally, we describe how to combine MD with DSMC in an event-driven framework, and discuss some promises and challenges for event-driven simulation of realistic physical systems.

  9. Asynchronous Event-Driven Particle Algorithms

    SciTech Connect

    Donev, A

    2007-08-30

    We present, in a unifying way, the main components of three asynchronous event-driven algorithms for simulating physical systems of interacting particles. The first example, hard-particle molecular dynamics (MD), is well-known. We also present a recently-developed diffusion kinetic Monte Carlo (DKMC) algorithm, as well as a novel stochastic molecular-dynamics algorithm that builds on the Direct Simulation Monte Carlo (DSMC). We explain how to effectively combine event-driven and classical time-driven handling, and discuss some promises and challenges for event-driven simulation of realistic physical systems.

  10. Photogated humidity-driven motility

    NASA Astrophysics Data System (ADS)

    Zhang, Lidong; Liang, Haoran; Jacob, Jolly; Naumov, Panče

    2015-06-01

    Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day-night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min-1. The element can lift objects ~85 times heavier and can transport cargos ~20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

  11. Light-driven phase shifter

    DOEpatents

    Early, James W.

    1990-01-01

    A light-driven phase shifter is provided for modulating a transmission light beam. A gaseous medium such as argon is provided with electron energy states excited to populate a metastable state. A tunable dye laser is selected with a wavelength effective to deplete the metastable electron state and may be intensity modulated. The dye laser is directed through the gaseous medium to define a first optical path having an index of refraction determined by the gaseous medium having a depleted metastable electron state. A transmission laser beam is also directed through the gaseous medium to define a second optical path at least partially coincident with the first optical path. The intensity of the dye laser beam may then be varied to phase modulate the transmission laser beam.

  12. Acoustically driven arrayed waveguide grating.

    PubMed

    Crespo-Poveda, A; Hernández-Mínguez, A; Gargallo, B; Biermann, K; Tahraoui, A; Santos, P V; Muñoz, P; Cantarero, A; de Lima, M M

    2015-08-10

    We demonstrate compact tunable phased-array wavelength-division multiplexers driven by surface acoustic waves (SAWs) in the low GHz range. The devices comprise two couplers, which respectively split and combine the optical signal, linked by an array of single-mode waveguides (WGs). Two different layouts are presented, in which multi-mode interference couplers or free propagating regions were separately employed as couplers. The multiplexers operate on five equally distributed wavelength channels, with a spectral separation of 2 nm. A standing SAW modulates the refractive index of the arrayed WGs. Each wavelength component periodically switches paths between the output channel previously asigned by the design and the adjacent channels, at a fixed applied acoustic power. The devices were monolithically fabricated on (Al,Ga)As. A good agreement between theory and experiment is achieved.

  13. Laser-driven fusion reactor

    DOEpatents

    Hedstrom, J.C.

    1973-10-01

    A laser-driven fusion reactor consisting of concentric spherical vessels in which the thermonuclear energy is derived from a deuterium-tritium (D + T) burn within a pellet'', located at the center of the vessels and initiated by a laser pulse. The resulting alpha -particle energy and a small fraction of the neutron energy are deposited within the pellet; this pellet energy is eventually transformed into sensible heat of lithium in a condenser outside the vessels. The remaining neutron energy is dissipated in a lithium blanket, located within the concentric vessels, where the fuel ingredient, tritium, is also produced. The heat content of the blanket and of the condenser lithium is eventually transferred to a conventional thermodynamic plant where the thermal energy is converted to electrical energy in a steam Rankine cycle. (Official Gazette)

  14. Multifunctionalities driven by ferroic domains

    SciTech Connect

    Yang, J. C.; Huang, Y. L.; Chu, Y. H.; He, Q.

    2014-08-14

    Considerable attention has been paid to ferroic systems in pursuit of advanced applications in past decades. Most recently, the emergence and development of multiferroics, which exhibit the coexistence of different ferroic natures, has offered a new route to create functionalities in the system. In this manuscript, we step from domain engineering to explore a roadmap for discovering intriguing phenomena and multifunctionalities driven by periodic domain patters. As-grown periodic domains, offering exotic order parameters, periodic local perturbations and the capability of tailoring local spin, charge, orbital and lattice degrees of freedom, are introduced as modeling templates for fundamental studies and novel applications. We discuss related significant findings on ferroic domain, nanoscopic domain walls, and conjunct heterostructures based on the well-organized domain patterns, and end with future prospects and challenges in the field.

  15. Photogated humidity-driven motility

    PubMed Central

    Zhang, Lidong; Liang, Haoran; Jacob, Jolly; Naumov, Panče

    2015-01-01

    Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day–night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min−1. The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids. PMID:26067649

  16. Photogated humidity-driven motility.

    PubMed

    Zhang, Lidong; Liang, Haoran; Jacob, Jolly; Naumov, Panče

    2015-06-11

    Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day-night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min(-1). The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

  17. Remarks on Tachyon Driven Cosmology

    NASA Astrophysics Data System (ADS)

    Sen, Ashoke

    2005-08-01

    We begin by reviewing the results on the decay of unstable D-branes in type II string theory, and the open-closed string duality proposal that arises from these studies. We then apply this proposal to the study of tachyon driven cosmology, namely cosmological solutions describing the decay of unstable space filling D-branes. This naturally gives rise to a time reversal invariant bounce solution with positive spatial curvature. In the absence of a bulk cosmological constant the universe always begins with a big bang and ends in a big crunch. In the presence of a bulk cosmological constant one may get non-singular cosmological solutions for some special range of initial conditions on the tachyon.

  18. Signal Processing in Periodically Forced Gradient Frequency Neural Networks

    PubMed Central

    Kim, Ji Chul; Large, Edward W.

    2015-01-01

    Oscillatory instability at the Hopf bifurcation is a dynamical phenomenon that has been suggested to characterize active non-linear processes observed in the auditory system. Networks of oscillators poised near Hopf bifurcation points and tuned to tonotopically distributed frequencies have been used as models of auditory processing at various levels, but systematic investigation of the dynamical properties of such oscillatory networks is still lacking. Here we provide a dynamical systems analysis of a canonical model for gradient frequency neural networks driven by a periodic signal. We use linear stability analysis to identify various driven behaviors of canonical oscillators for all possible ranges of model and forcing parameters. The analysis shows that canonical oscillators exhibit qualitatively different sets of driven states and transitions for different regimes of model parameters. We classify the parameter regimes into four main categories based on their distinct signal processing capabilities. This analysis will lead to deeper understanding of the diverse behaviors of neural systems under periodic forcing and can inform the design of oscillatory network models of auditory signal processing. PMID:26733858

  19. Conversion of rotational output to linear force-a transmission

    SciTech Connect

    Montalbano, P.J.

    1991-08-27

    This patent describes a transmission device for converting rotational torque into linear force. It comprises a combination large internally toothed annular gear and large flywheel rotatable within a housing by bearing means, in operative interconnection with a small externally toothed circular gear mounted within it annulus and provided with a source of variable rotary motion for driving the annular gear, a second large internally toothed annular gear, located above the first the annular gear, rotatable within a housing by bearing means and provided with a clutch connection to first annular gear, is in operative connection with three small externally toothed circular gears driven by the second annular gear, a member pivotably supported along the axis of the annular gear and rockable on the axis, the member having an upper and a lower arm, the upper arm in interconnection with two of the respective gears and the lower arm in interconnection with one of the respective gears, the gears driven by the second annular gear, in upper arm the gears causing the rocker element to move two off- centered weights, the first weight rotatable with one of the gears, the second weight rotatable in the opposite direction and mounted within the rocker element driven by an additional small externally toothed circular gear in mesh with one of the small gears, the weights generating centrifugal forces.

  20. Signal Processing in Periodically Forced Gradient Frequency Neural Networks.

    PubMed

    Kim, Ji Chul; Large, Edward W

    2015-01-01

    Oscillatory instability at the Hopf bifurcation is a dynamical phenomenon that has been suggested to characterize active non-linear processes observed in the auditory system. Networks of oscillators poised near Hopf bifurcation points and tuned to tonotopically distributed frequencies have been used as models of auditory processing at various levels, but systematic investigation of the dynamical properties of such oscillatory networks is still lacking. Here we provide a dynamical systems analysis of a canonical model for gradient frequency neural networks driven by a periodic signal. We use linear stability analysis to identify various driven behaviors of canonical oscillators for all possible ranges of model and forcing parameters. The analysis shows that canonical oscillators exhibit qualitatively different sets of driven states and transitions for different regimes of model parameters. We classify the parameter regimes into four main categories based on their distinct signal processing capabilities. This analysis will lead to deeper understanding of the diverse behaviors of neural systems under periodic forcing and can inform the design of oscillatory network models of auditory signal processing.

  1. Indirectly driven targets for ignition

    SciTech Connect

    Wilson, D.C.; Krauser, W.J.

    1994-12-31

    Both Los Alamos and Lawrence Livermore Laboratories have studied capsule and laser driven target designs for the National Ignition Facility. The current hohlraum design is a 2.76mm radius, 9.5mm long gold cylinder with 1.39mm radius laser entrance holes covered by 1{mu}m thick plastic foils. Laser beams strike the inside cylinder wall from two separate cones with a peak power less than 400 TW. The problem with a pressure pulse caused by wall plasma stagnating on axis has been overcome by filling the hohlraum with gas. Currently this is equi-molar hydrogen-helium gas at 0.83 mg/cc density. One capsule uses a 160 {mu}m plastic ablator doped with oxygen and bromine surrounding an 80 {mu}m thick DT ice layer with an inner radius of 0.87 mm. Los Alamos integrated calculations of the hohlraum and this capsule using 1.4 MJ of laser energy achieve yields of 4.9 MJ using LTE atomic physics, and 3.5 MJ with non-LTE. This confirms Livermore calculations of ignition. For radiation driven implosions, a beryllium ablator offers a viable alternative to plastic. It is strong enough to contain high DT pressures. Copper, soluble at required levels, is an excellent dopant to add opacity. A beryllium capsule with a 155 {mu}m thick ablator doped with 0.9 atom % copper, and the same inner dimensions as the plastic capsule, placed in a similar hohlraum , yields 6.9 MJ with LTE. Although these calculations show the designs are sensitive, they add to the confidence that NIF can achieve ignition. Using their best integrated calculations which are not yet fully optimized, they confirm Livermore calculations of ignition with a plastic capsule, and have added an alternate capsule design with a beryllium ablator.

  2. Development of a precision indentation and scratching system with a tool force and displacement control module.

    PubMed

    Park, Jae-Jun; Kwon, Kihwan; Bang, Jinhyeok; Cho, Nahmgyoo; Han, Chang-Soo; Choi, Nak-Sam

    2007-04-01

    This article presents a tip-based micropatterning system with a precision device for measuring the machine force and the tool path. The machine force is obtained by a tool control module with a leaf spring and a capacitive displacement sensor. It is controlled to provide a force that ranges from 80 microN to 8 N. The force sensing unit, which is part of the module, is mounted on a PZT (PbZrTi) driven in-feed motion stage with a resolution of 1 nm. The work piece is set on an X-Y motion stage, and the position can be controlled with a tool path accuracy of 5 nm. Micropatterning and precision indentation experiments were performed, while the machined surfaces were examined by atomic force microscopy. From these results, the feasibility of the system for precise force-displacement control was verified for application in tip-based precision machining.

  3. Mapping interaction forces with the atomic force microscope.

    PubMed Central

    Radmacher, M; Cleveland, J P; Fritz, M; Hansma, H G; Hansma, P K

    1994-01-01

    Force curves were recorded as the sample was raster-scanned under the tip. This opens new opportunities for imaging with the atomic force microscope: several characteristics of the samples can be measured simultaneously, for example, topography, adhesion forces, elasticity, van der Waals, and electrostatic interactions. The new opportunities are illustrated by images of several characteristics of thin metal films, aggregates of lysozyme, and single molecules of DNA. Images FIGURE 1 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 PMID:8075349

  4. An Integrated Higgs Force Theory

    NASA Astrophysics Data System (ADS)

    Colella, Antonio

    2016-03-01

    An Integrated Higgs force theory (IHFT) was based on 2 key requirement amplifications: a matter particle/Higgs force was one and inseparable; a matter particle/Higgs force bidirectionally condensed/evaporated from/to super force. These were basis of 5 theories: particle creation, baryogenesis, superpartner/quark decays, spontaneous symmetry breaking, and stellar black holes. Our universe's 129 matter/force particles contained 64 supersymmetric Higgs particles; 9 transient matter particles/Higgs forces decayed to 8 permanent matter particles/Higgs forces; mass was given to a matter particle by its Higgs force and gravitons; and sum of 8 Higgs force energies of 8 permanent matter particles was dark energy. An IHFT's essence is the intimate physical relationships between 8 theories. These theories are independent because physicists in one theory worked independently of physicists in the other seven. An IHFT's premise is without sacrificing their integrities, 8 independent existing theories are replaced by 8 interrelated amplified theories. Requirement amplifications provide interfaces between the 8 theories. Intimate relationships between 8 theories including the above 5 and string, Higgs forces, and Super Universe are described. The sorting category selected was F. PARTICLES AND FIELDS (e.g., F1 Higgs Physics, F10 Alternative Beyond the Standard Model Physics, F11 Dark Sector Theories and Searches, and F12 Particle Cosmology).

  5. Transverse migration of a polyelectrolyte driven by electric and pressure-driven flow fields

    NASA Astrophysics Data System (ADS)

    Ladd, Tony; Kekre, Rahul; Butler, Jason

    2010-03-01

    Capillary electrophoresis experiments show that a flexible polyelectrolyte migrates under the combined action of electric and pressure-driven-flow fields [1]. When the fields act in conjunction, the polymer migrates to the center of the channel, but when the pressure gradient and external force act in opposite directions, the polymer migrates towards the boundaries. We have previously proposed that this is caused by long-range dipolar interactions between segments of the polyelectrolyte chain [2]. Due to the stretching and orientation of the chain by the local shear flow, there is a net motion transverse to the flow and field lines. Here I will describe a coarse-grained simulation of polyelectrolyte migration, including hydrodynamic interactions from the imposed flow and electric fields. The effects of the no-slip condition on the walls are included by regularized Green's functions. Our results explain the experimentally observed migration under different combinations of flow and electric field. [1] J. Zheng and E. S. Yeung. Anal. Chem., 74:4536, 2002; 75:3675, 2003. [2] O. B. Usta, J. E. Butler and A. J. C. Ladd. Phys. Rev. Lett., 98:098301, 2007.

  6. Theory of Casimir Forces without the Proximity-Force Approximation.

    PubMed

    Lapas, Luciano C; Pérez-Madrid, Agustín; Rubí, J Miguel

    2016-03-18

    We analyze both the attractive and repulsive Casimir-Lifshitz forces recently reported in experimental investigations. By using a kinetic approach, we obtain the Casimir forces from the power absorbed by the materials. We consider collective material excitations through a set of relaxation times distributed in frequency according to a log-normal function. A generalized expression for these forces for arbitrary values of temperature is obtained. We compare our results with experimental measurements and conclude that the model goes beyond the proximity-force approximation. PMID:27035293

  7. Automated force controller for amplitude modulation atomic force microscopy.

    PubMed

    Miyagi, Atsushi; Scheuring, Simon

    2016-05-01

    Atomic Force Microscopy (AFM) is widely used in physics, chemistry, and biology to analyze the topography of a sample at nanometer resolution. Controlling precisely the force applied by the AFM tip to the sample is a prerequisite for faithful and reproducible imaging. In amplitude modulation (oscillating) mode AFM, the applied force depends on the free and the setpoint amplitudes of the cantilever oscillation. Therefore, for keeping the applied force constant, not only the setpoint amplitude but also the free amplitude must be kept constant. While the AFM user defines the setpoint amplitude, the free amplitude is typically subject to uncontrollable drift, and hence, unfortunately, the real applied force is permanently drifting during an experiment. This is particularly harmful in biological sciences where increased force destroys the soft biological matter. Here, we have developed a strategy and an electronic circuit that analyzes permanently the free amplitude of oscillation and readjusts the excitation to maintain the free amplitude constant. As a consequence, the real applied force is permanently and automatically controlled with picoNewton precision. With this circuit associated to a high-speed AFM, we illustrate the power of the development through imaging over long-duration and at various forces. The development is applicable for all AFMs and will widen the applicability of AFM to a larger range of samples and to a larger range of (non-specialist) users. Furthermore, from controlled force imaging experiments, the interaction strength between biomolecules can be analyzed. PMID:27250433

  8. Performance of different force fields in force probe simulations.

    PubMed

    Schlesier, Thomas; Diezemann, Gregor

    2013-02-14

    We present detailed force probe molecular dynamic simulations of mechanically interlocked dimeric calix[4]arene-catenanes, comparing the results obtained using three different commonly used force fields (GROMOS G53a5, OPLS-AA, and AMBER GAFF). The model system is well characterized as a two-state system consisting of a closed compact and an elongated structure. Both states are stabilized by a different hydrogen-bond network, and complete separation of the dimer is prevented by the mechanical lock of the entangled aliphatic loops. The system shows fully reversible rebinding meaning that after bond rupture the system rejoins when the external force is relaxed. We present a detailed study of quantities determined in simulations using a force ramp, like the rupture force and rejoin force distributions. Additionally, we analyze the dynamics of the hydrogen-bond network. We find that the results obtained from using the different force fields qualitatively agree in the sense that always the fully reversible behavior is found. The details, like the mean rupture forces, however, do depend on the particular force field. Some of the differences observed can be traced back to differences in the strength of the hydrogen-bond networks.

  9. General Purpose Data-Driven Monitoring for Space Operations

    NASA Technical Reports Server (NTRS)

    Iverson, David L.; Martin, Rodney A.; Schwabacher, Mark A.; Spirkovska, Liljana; Taylor, William McCaa; Castle, Joseph P.; Mackey, Ryan M.

    2009-01-01

    As modern space propulsion and exploration systems improve in capability and efficiency, their designs are becoming increasingly sophisticated and complex. Determining the health state of these systems, using traditional parameter limit checking, model-based, or rule-based methods, is becoming more difficult as the number of sensors and component interactions grow. Data-driven monitoring techniques have been developed to address these issues by analyzing system operations data to automatically characterize normal system behavior. System health can be monitored by comparing real-time operating data with these nominal characterizations, providing detection of anomalous data signatures indicative of system faults or failures. The Inductive Monitoring System (IMS) is a data-driven system health monitoring software tool that has been successfully applied to several aerospace applications. IMS uses a data mining technique called clustering to analyze archived system data and characterize normal interactions between parameters. The scope of IMS based data-driven monitoring applications continues to expand with current development activities. Successful IMS deployment in the International Space Station (ISS) flight control room to monitor ISS attitude control systems has led to applications in other ISS flight control disciplines, such as thermal control. It has also generated interest in data-driven monitoring capability for Constellation, NASA's program to replace the Space Shuttle with new launch vehicles and spacecraft capable of returning astronauts to the moon, and then on to Mars. Several projects are currently underway to evaluate and mature the IMS technology and complementary tools for use in the Constellation program. These include an experiment on board the Air Force TacSat-3 satellite, and ground systems monitoring for NASA's Ares I-X and Ares I launch vehicles. The TacSat-3 Vehicle System Management (TVSM) project is a software experiment to integrate fault

  10. Elementary Implantable Force Sensor

    PubMed Central

    Wachs, Rebecca A.; Ellstein, David; Drazan, John; Healey, Colleen P.; Uhl, Richard L.; Connor, Kenneth A.

    2014-01-01

    Implementing implantable sensors which are robust enough to maintain long term functionality inside the body remains a significant challenge. The ideal implantable sensing system is one which is simple and robust; free from batteries, telemetry, and complex electronics. We have developed an elementary implantable sensor for orthopaedic smart implants. The sensor requires no telemetry and no batteries to communicate wirelessly. It has no on-board signal conditioning electronics. The sensor itself has no electrical connections and thus does not require a hermetic package. The sensor is an elementary L-C resonator which can function as a simple force transducer by using a solid dielectric material of known stiffness between two parallel Archimedean coils. The operating characteristics of the sensors are predicted using a simplified, lumped circuit model. We have demonstrated sensor functionality both in air and in saline. Our preliminary data indicate that the sensor can be reasonably well modeled as a lumped circuit to predict its response to loading. PMID:24883335

  11. Tunneling magnetic force microscopy

    NASA Technical Reports Server (NTRS)

    Burke, Edward R.; Gomez, Romel D.; Adly, Amr A.; Mayergoyz, Isaak D.

    1993-01-01

    We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording.

  12. Maximum bow force revisited.

    PubMed

    Mores, Robert

    2016-08-01

    Schelleng [J. Acoust. Soc. Am. 53, 26-41 (1973)], Askenfelt [J. Acoust. Soc. Am. 86, 503-516 (1989)], Schumacher [J. Acoust. Soc. Am. 96, 1985-1998 (1994)], and Schoonderwaldt, Guettler, and Askenfelt [Acta Acust. Acust. 94, 604-622 (2008)] formulated-in different ways-how the maximum bow force relates to bow velocity, bow-bridge distance, string impedance, and friction coefficients. Issues of uncertainty are how to account for friction or for the rotational admittance of the strings. Related measurements at the respective transitions between regimes of Helmholtz motion and non-Helmholtz motion employ a variety of bowing machines and stringed instruments. The related findings include all necessary parameters except the friction coefficients, leaving the underlying models unconfirmed. Here, a bowing pendulum has been constructed which allows precise measurement of relevant bowing parameters, including the friction coefficients. Two cellos are measured across all strings for three different bow-bridge distances. The empirical data suggest that-taking the diverse elements of existing models as options-Schelleng's model combined with Schumacher's velocity term yields the best fit. Furthermore, the pendulum employs a bow driving mechanism with adaptive impedance which discloses that mentioned regimes are stable and transitions between them sometimes require a hysteresis on related parameters. PMID:27586745

  13. Forced air heater

    SciTech Connect

    Livezey, D.J.

    1980-09-23

    An air heating chamber is supported to project into a stove through an opening provided in the rear wall of the stove by a mounting plate mounted to the exterior of the stove rear wall. The mounting plate which forms the exterior end wall of the heating chamber, includes laterally spaced heating chamber inlet and outlet openings. A blower is detachably mounted to the exterior of the mounting plate in registration with the heating chamber inlet opening to deliver cool forced air into the heating chamber. After circulating therethrough, the air exits the heating chamber through the outlet opening and flows into a hot air manifold, which is also detachably mounted to the exterior of the mounting plate. The manifold includes an upwardly extending inlet chamber with a hot air inlet at its lower end aligned with the heating chamber outlet opening. A horizontal outlet chamber is attached to the top end of the inlet chamber to extend laterally along the back of the stove. Hot air outlets are provided at each end of the manifold outlet chamber to discharge the heated air horizontally over the top and towards the front of the stove.

  14. Deep atomic force microscopy

    SciTech Connect

    Barnard, H.; Drake, B.; Randall, C.; Hansma, P. K.

    2013-12-15

    The Atomic Force Microscope (AFM) possesses several desirable imaging features including the ability to produce height profiles as well as two-dimensional images, in fluid or air, at high resolution. AFM has been used to study a vast selection of samples on the scale of angstroms to micrometers. However, current AFMs cannot access samples with vertical topography of the order of 100 μm or greater. Research efforts have produced AFM scanners capable of vertical motion greater than 100 μm, but commercially available probe tip lengths are still typically less than 10 μm high. Even the longest probe tips are below 100 μm and even at this range are problematic. In this paper, we present a method to hand-fabricate “Deep AFM” probes with tips of the order of 100 μm and longer so that AFM can be used to image samples with large scale vertical topography, such as fractured bone samples.

  15. Use of magnetic forces to promote stem cell aggregation during differentiation, and cartilage tissue modeling.

    PubMed

    Fayol, D; Frasca, G; Le Visage, C; Gazeau, F; Luciani, N; Wilhelm, C

    2013-05-14

    Magnetic forces induce cell condensation necessary for stem cell differentiation into cartilage and elicit the formation of a tissue-like structure: Magnetically driven fusion of aggregates assembled by micromagnets results in the formation of a continuous tissue layer containing abundant cartilage matrix. PMID:23526452

  16. Force Limited Vibration Testing Monograph

    NASA Technical Reports Server (NTRS)

    Scharton, Terry D.

    1997-01-01

    The practice of limiting the shaker force in vibration tests was investigated at the NASA Jet Propulsion Laboratory (JPL) in 1990 after the mechanical failure of an aerospace component during a vibration test. Now force limiting is used in almost every major vibration test at JPL and in many vibration tests at NASA Goddard Space Flight Center (GSFC) and at many aerospace contractors. The basic ideas behind force limiting have been in the literature for several decades, but the piezo-electric force transducers necessary to conveniently implement force limiting have been available only in the last decade. In 1993, funding was obtained from the NASA headquarters Office of Chief Engineer to develop and document the technology needed to establish force limited vibration testing as a standard approach available to all NASA centers and aerospace contractors. This monograph is the final report on that effort and discusses the history, theory, and applications of the method in some detail.

  17. Non-conservative optical forces and Brownian vortexes

    NASA Astrophysics Data System (ADS)

    Sun, Bo

    Optical manipulation using optical tweezers has been widely adopted in physics, chemical engineering and biology. While most applications and fundamental studies of optical trapping have focused on optical forces resulting from intensity gradients, we have also explored the role of radiation pressure, which is directed by phase gradients in beams of light. Interestingly, radiation pressure turns out to be a non-conservative force and drives trapped objects out of thermodynamic equilibrium with their surrounding media. We have demonstrated the resulting nonequilibrium effects experimentally by tracking the thermally driven motions of optically trapped colloidal spheres using holographic video microscopy. Rather than undergoing equilibrium thermal fluctuations, as has been assumed for more than a quarter century, a sphere in an optical tweezer enters into a stochastic steady-state characterized by closed loops in its probability current density. These toroidal vortexes constitute a bias in the particle's otherwise random thermal fluctuations arising at least indirectly from a solenoidal component in the optical force. This surprising effect is a particular manifestation of a more general class of noise-driven machines that we call Brownian vortexes. This previously unrecognized class of stochastic heat engines operates on qualitatively different principles from such extensively studied nonequilibrium systems as thermal ratchets and Brownian motors. Among its interesting properties, a Brownian vortex can reverse its direction with changes in temperature or equivalent control parameters.

  18. Ice-Shelf Flexure and Tidal Forcing of Bindschadler Ice Stream, West Antarctica

    NASA Technical Reports Server (NTRS)

    Walker, Ryan T.; Parizek, Bryron R.; Alley, Richard B.; Brunt, Kelly M.; Anandakrishnan, Sridhar

    2014-01-01

    Viscoelastic models of ice-shelf flexure and ice-stream velocity perturbations are combined into a single efficient flowline model to study tidal forcing of grounded ice. The magnitude and timing of icestream response to tidally driven changes in hydrostatic pressure and/or basal drag are found to depend significantly on bed rheology, with only a perfectly plastic bed allowing instantaneous velocity response at the grounding line. The model can reasonably reproduce GPS observations near the grounding zone of Bindschadler Ice Stream (formerly Ice Stream D) on semidiurnal time scales; however, other forcings such as tidally driven ice-shelf slope transverse to the flowline and flexurally driven till deformation must also be considered if diurnal motion is to be matched

  19. Hemodynamics driven cardiac valve morphogenesis.

    PubMed

    Steed, Emily; Boselli, Francesco; Vermot, Julien

    2016-07-01

    Mechanical forces are instrumental to cardiovascular development and physiology. The heart beats approximately 2.6 billion times in a human lifetime and heart valves ensure that these contractions result in an efficient, unidirectional flow of the blood. Composed of endocardial cells (EdCs) and extracellular matrix (ECM), cardiac valves are among the most mechanically challenged structures of the body both during and after their development. Understanding how hemodynamic forces modulate cardiovascular function and morphogenesis is key to unraveling the relationship between normal and pathological cardiovascular development and physiology. Most valve diseases have their origins in embryogenesis, either as signs of abnormal developmental processes or the aberrant re-expression of fetal gene programs normally quiescent in adulthood. Here we review recent discoveries in the mechanobiology of cardiac valve development and introduce the latest technologies being developed in the zebrafish, including live cell imaging and optical technologies, as well as modeling approaches that are currently transforming this field. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

  20. High-speed adaptive contact-mode atomic force microscopy imaging with near-minimum-force

    SciTech Connect

    Ren, Juan; Zou, Qingze

    2014-07-15

    In this paper, an adaptive contact-mode imaging approach is proposed to replace the traditional contact-mode imaging by addressing the major concerns in both the speed and the force exerted to the sample. The speed of the traditional contact-mode imaging is largely limited by the need to maintain precision tracking of the sample topography over the entire imaged sample surface, while large image distortion and excessive probe-sample interaction force occur during high-speed imaging. In this work, first, the image distortion caused by the topography tracking error is accounted for in the topography quantification. Second, the quantified sample topography is utilized in a gradient-based optimization method to adjust the cantilever deflection set-point for each scanline closely around the minimal level needed for maintaining stable probe-sample contact, and a data-driven iterative feedforward control that utilizes a prediction of the next-line topography is integrated to the topography feeedback loop to enhance the sample topography tracking. The proposed approach is demonstrated and evaluated through imaging a calibration sample of square pitches at both high speeds (e.g., scan rate of 75 Hz and 130 Hz) and large sizes (e.g., scan size of 30 μm and 80 μm). The experimental results show that compared to the traditional constant-force contact-mode imaging, the imaging speed can be increased by over 30 folds (with the scanning speed at 13 mm/s), and the probe-sample interaction force can be reduced by more than 15% while maintaining the same image quality.