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Sample records for fluctuation induced forces

  1. Constraints on Stable Equilibria with Fluctuation-Induced (Casimir) Forces

    SciTech Connect

    Rahi, Sahand Jamal; Kardar, Mehran; Emig, Thorsten

    2010-08-13

    We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in space is unstable to small perturbations in position. This extends Earnshaw's theorem for electrostatics by including thermal fluctuations of internal charges. Quantum fluctuations of the electromagnetic field are responsible for Casimir or van der Waals interactions. Neglecting permeabilities, we find that any equilibrium position of items subject to such forces is also unstable if the permittivities of all objects are higher or lower than that of the enveloping medium, the former being the generic case for ordinary materials in vacuum.

  2. Fluctuation-induced forces between rings threaded around a polymer chain under tension.

    PubMed

    Gilles, F M; Llubaroff, R; Pastorino, C

    2016-09-01

    We characterize the fluctuation properties of a polymer chain under external tension and the fluctuation-induced forces between two ring molecules threaded around the chain. The problem is relevant in the context of fluctuation-induced forces in soft-matter systems, features of liquid interfaces, and to describe the properties of polyrotaxanes and slide-ring materials. We perform molecular-dynamics simulations of the Kremer-Grest bead-spring model for the polymer and a simple ring-molecule model in the canonical ensemble. We study transverse fluctuations of the stretched chain as a function of chain stretching and in the presence of ring-shaped threaded molecules. The fluctuation spectra of the chains are analyzed in equilibrium at constant temperature, and the differences in the presence of two-ring molecules are compared. For the rings located at fixed distances, we find an attractive fluctuation-induced force between the rings, proportional to the temperature and decaying with the ring distance. We characterize this force as a function of ring distance, chain stretching, and ring radius, and we measure the differences between the free chain spectrum and the fluctuations of the chain constrained by the rings. We also compare the dependence and range of the force found in the simulations with theoretical models coming from different fields.

  3. Electron fluctuation induced resonance broadening in nano electromechanical systems: the origin of shear force in vacuum.

    PubMed

    Siria, A; Barois, T; Vilella, K; Perisanu, S; Ayari, A; Guillot, D; Purcell, S T; Poncharal, P

    2012-07-11

    This article presents a study of the poorly understood "shear-force" used in an important class of near-field instruments that use mechanical resonance feedback detection. In the case of a metallic probe near a metallic surface in vacuum, we show that in the 10-60 nm range there is no such a thing as a shear-force in the sense of the nonconservative friction force. Fluctuations of the oscillator resonance frequency, likely induced by local charge variations, could account for the reported effects in the literature without introducing a dissipative force.

  4. Fluctuating Pressure Environments and Hydrodynamic Radial Force Mitigation for a Two Blade Unshrouded Inducer

    NASA Technical Reports Server (NTRS)

    Mulder, Andrew; Skelley, Stephen

    2011-01-01

    Fluctuating pressure data from water flow testing of an unshrouded two blade inducer revealed a cavitation induced oscillation with the potential to induce a radial load on the turbopump shaft in addition to other more traditionally analyzed radial loads. Subsequent water flow testing of the inducer with a rotating force measurement system confirmed that the cavitation induced oscillation did impart a radial load to the inducer. After quantifying the load in a baseline configuration, two inducer shroud treatments were selected and tested to reduce the cavitation induced load. The first treatment was to increase the tip clearance, and the second was to introduce a circumferential groove near the inducer leading edge. Increasing the clearance resulted in a small load decrease along with some steady performance degradation. The groove greatly reduced the hydrodynamic load with little to no steady performance loss. The groove did however generate some new, relatively high frequency, spatially complex oscillations to the environment.

  5. Fluctuating Pressure Environments and Hydrodynamic Radial Force Mitigation for a Two Blade Unshrouded Inducer

    NASA Technical Reports Server (NTRS)

    Mulder, Andrew; Skelley, Stephen

    2011-01-01

    Fluctuating pressure data from water flow testing of an unshrouded two blade inducer revealed a cavitation induced oscillation with the potential to induce a radial load on the turbopump shaft in addition to other more traditionally analyzed radial loads. Subsequent water flow testing of the inducer with a rotating force measurement system confirmed that the cavitation induced oscillation did impart a radial load to the inducer. After quantifying the load in a baseline configuration, two inducer shroud treatments were selected and tested to reduce the cavitation induced load. The first treatment was to increase the tip clearance, and the second was to introduce a circumferential groove near the inducer leading edge. Increasing the clearance resulted in a small decrease in radial load along with some steady performance degradation. The groove greatly reduced the hydrodynamic load with little to no steady performance loss. The groove did however generate some new, relatively high frequency, spatially complex oscillations to the flow environment.

  6. Fluctuation-induced forces in nematics with a foreign anisotropy in the bulk

    NASA Astrophysics Data System (ADS)

    Karimi Pour Haddadan, Fahimeh

    2017-02-01

    Within a linear coupling between orientational order of nematic liquid crystal and anisotropic mesoscopic particles immeresed in the nematic, the pseudo-Casimir effect is investigated. A quenched disorder in the alignment of the particles, which is on average in the direction of the nematic director, induces an inter-substrate force as this composite is confined by two flat parallel surfaces a distance d apart. The disorder-induced force decays as -d -1 in the weak coupling regime. The force magnitude increases with the variance of the disorder and decreases on increasing the correlation length of the disorder. If the disorder is considered to be annealed, the disorder effects are not decoupled from the thermal effects and thus the form of the nematic fluctuation-induced force does not alter. The force is affected by the disorder only through a re-normalization of the mean particles’ pinning strength. The trend for this modified thermal-induced force with respect to the variance and the correlation length of the disorder remains as in the quenched case, where the pseudo-Casimir force was decomposed into two distinct thermal- and disorder-induced components.

  7. Depletion-induced forces and crowding in polymer-nanoparticle mixtures: Role of polymer shape fluctuations and penetrability.

    PubMed

    Lim, Wei Kang; Denton, Alan R

    2016-01-14

    Depletion forces and macromolecular crowding govern the structure and function of biopolymers in biological cells and the properties of polymer nanocomposite materials. To isolate and analyze the influence of polymer shape fluctuations and penetrability on depletion-induced interactions and crowding by nanoparticles, we model polymers as effective penetrable ellipsoids, whose shapes fluctuate according to the probability distributions of the eigenvalues of the gyration tensor of an ideal random walk. Within this model, we apply Monte Carlo simulation methods to compute the depletion-induced potential of mean force between hard nanospheres and crowding-induced shape distributions of polymers in the protein limit, in which polymer coils can be easily penetrated by smaller nanospheres. By comparing depletion potentials from simulations of ellipsoidal and spherical polymer models with predictions of polymer field theory and free-volume theory, we show that polymer depletion-induced interactions and crowding depend sensitively on polymer shapes and penetrability, with important implications for bulk thermodynamic phase behavior.

  8. Effects of local and core body temperature on grip force modulation during movement-induced load force fluctuations.

    PubMed

    Cheung, Stephen S; Reynolds, Luke F; Macdonald, Mark A B; Tweedie, Constance L; Urquhart, Robin L; Westwood, David A

    2008-05-01

    Impaired manual functioning often occurs when the hands are exposed to cold temperatures, but the underlying mechanism is not clearly understood. Tactile feedback is thought to provide important information during object manipulations in order to scale and regulate grip forces; however, topical anaesthetic-induced tactile sensation impairments may not realistically simulate the systemic neuromuscular impairment of the whole hand that could occur during cold temperature exposure. In two experiments, we studied the impact of (1) local hand cooling [thermoneutral finger skin temperature, cold (<8 degrees C)] and (2) core body temperature (thermoneutral core body temperature, pre-heated by 0.5 degrees C, pre-cooled by 0.5 degrees C) with cold hands on manual dexterity and the ability to control and co-ordinate grip forces during a cyclical load-lifting task. In Experiment 1 (n = 10), hand cooling significantly decreased Purdue Pegboard performance (P = 0.002), while increasing grip force by approximately 5 N during the cyclical load-lifting task compared to thermoneutral (P = 0.037). The temporal co-ordination of grip and load forces was unaffected by hand cooling. In Experiment 2 (n = 11), pegboard performance was impaired following hand cooling (P < 0.001), and to a greater extent when the body was pre-cooled (p < 0.001). However, neither grip force (P = 0.99) nor the temporal co-ordination of grasping and lifting forces (P = 0.85) were affected by core body temperature. These data support the existence of a robust centrally controlled feedforward system able to anticipate the dynamics of manual manipulations and accordingly regulate the temporal co-ordination of fingertip forces during object manipulation. This centrally controlled mechanism appears to differ from the mechanisms governing other aspects of manual dexterity.

  9. Force fluctuations in stretching a tethered polymer

    NASA Astrophysics Data System (ADS)

    Varghese, Anoop; Vemparala, Satyavani; Rajesh, R.

    2013-08-01

    The recently proposed fluctuation relation in unfolding forces [Phys. Rev. E1539-375510.1103/PhysRevE.84.060101 84, 060101(R) (2011)] is reexamined taking into account the explicit time dependence of the force distribution. The stretching of a tethered Rouse polymer is exactly solved and the ratio of the probabilities of positive to negative forces is shown to be an exponential in force. Extensive steered molecular dynamics simulations of unfolding of deca alanine peptide confirm the form of fluctuation relation proposed earlier, but with explicit correct time dependence of unfolding forces taken into account. From exact calculations and simulations, a linear dependence of the constant in the exponential of the fluctuation relation on average unfolding forces and inverse temperature is proposed.

  10. Friction forces arising from fluctuating thermal fields

    NASA Astrophysics Data System (ADS)

    Zurita-Sánchez, Jorge R.; Greffet, Jean-Jacques; Novotny, Lukas

    2004-02-01

    We calculate the damping of a classical oscillator induced by the electromagnetic field generated by thermally fluctuating currents in the environment. The fluctuation-dissipation theorem is applied to derive the linear-velocity damping coefficient γ. It turns out that γ is the result of fourth-order correlation functions. The theory is applied to a particle oscillating parallel to a flat substrate and numerical values for γ are evaluated for particle and substrate materials made of silver and glass. We find that losses are much higher for dielectric materials than for metals because of the higher resistivity. We predict that measurements performed on metal films are strongly affected by the underlying dielectric substrate and we show that our theory reproduces existing theoretical results in the nonretarded limit. The theory provides an explanation for the observed distance-dependent damping in shear-force microscopy and it gives guidance for future experiments. Also, the theory should be of importance for the design of nanoscale mechanical systems and for understanding the trade-offs of miniaturization.

  11. FLUCTUATING MOTOR FORCES BEND GROWING MICROTUBULES

    PubMed Central

    Shekhar, Nandini; Neelam, Srujana; Wu, Jun; Ladd, Anthony JC; Dickinson, Richard B.; Lele, Tanmay P.

    2013-01-01

    Despite their rigidity, microtubules in living cells bend significantly during polymerization resulting in greater curvature than can be explained by thermal forces alone. However, the source of the non-thermal forces that bend growing microtubules remains obscure. We analyzed the motion of microtubule tips in NIH-3T3 fibroblasts expressing EGFP-EB1, a fluorescent +TIP protein that specifically binds to the growing ends of microtubules. We found that dynein inhibition significantly reduced the deviation of the growing tip from its initial trajectory. Inhibiting myosin modestly reduced tip fluctuations, while simultaneous myosin and dynein inhibition caused no further decrease in fluctuations compared to dynein inhibition alone. Our results can be interpreted with a model in which dynein linkages play a key role in generating and transmitting fluctuating forces that bend growing microtubules. PMID:24039637

  12. 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.

  13. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, {le}{approximately}{ovr J} {times} {approximately}{ovr B}{ge}, has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  14. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, [le][approximately][ovr J] [times] [approximately][ovr B][ge], has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  15. Response of Brownian Fluctuations to External Forces

    NASA Astrophysics Data System (ADS)

    Laub, Jeffrey William

    Millikan's law of particle fall is an empirical result which shows the dependence of particle fall rate in a gas on particle radius and host gas density. The size of submicron particles in gases has long been determined by Millikan's law. The dominant factor is Stokes' law with a correction added to account for the physics of slip. However, it was recently shown by Kim and Fedele that Brownian fluctuations affect the fall rate while showing no anomalies in the density dependence of the rms displacement. The effect was an enhancement of the fall rate of small particles as the density of the host gas is increased. This enhancement showed a size dependence in the form of a smooth transition from the one of decreasing fall rate with increasing density for large particles (~0.4 μm radius) to another of increasing fall rate with increasing gas density for small particles ( ~0.15mum radius). The magnitude of the anomaly is determined by how the rms Brownian velocity compares with its fall rate. In an effort to understand the effect of Brownian fluctuations coupling with gravity, a new experiment has been carried out where an AC field was applied to force particles to fluctuate more in the vertical direction on one hand and where a constant DC field was applied to change the effective force of gravity on the other. These fields were applied to a charged oil drop in the 0.2 to 0.3 μm radius range falling in a nitrogen environment. Displacements over a 4 second time interval were repeatedly measured in both the vertical and horizontal directions. The original experimental apparatus was used with some modifications. The modifications included computer automation of particle control and data taking to allow for longer use of the same particle, up to 120 hours, and to facilitate application of the additional fields. The objective was to make large particles appear to be smaller via forced oscillations and make them fall faster or slower via the DC bias to effect the change in

  16. Noncontact Friction and Force Fluctuations between Closely Spaced Bodies

    SciTech Connect

    Stipe, B. C.; Mamin, H. J.; Stowe, T. D.; Kenny, T. W.; Rugar, D.

    2001-08-27

    Noncontact friction between a Au(111) surface and an ultrasensitive gold-coated cantilever was measured as a function of tip-sample spacing, temperature, and bias voltage using observations of cantilever damping and Brownian motion. The importance of the inhomogeneous contact potential is discussed and comparison is made to measurements over dielectric surfaces. Using the fluctuation-dissipation theorem, the force fluctuations are interpreted in terms of near-surface fluctuating electric fields interacting with static surface charge.

  17. Dielectric fluctuations in force microscopy: noncontact friction and frequency jitter.

    PubMed

    Yazdanian, Showkat M; Marohn, John A; Loring, Roger F

    2008-06-14

    Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe's motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell's equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement.

  18. Dielectric fluctuations in force microscopy: Noncontact friction and frequency jitter

    PubMed Central

    Yazdanian, Showkat M.; Marohn, John A.; Loring, Roger F.

    2008-01-01

    Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe’s motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell’s equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement. PMID:18554042

  19. Force fluctuations in three-dimensional suspended fibroblasts.

    PubMed

    Schlosser, Florian; Rehfeldt, Florian; Schmidt, Christoph F

    2015-02-05

    Cells are sensitive to mechanical cues from their environment and at the same time generate and transmit forces to their surroundings. To test quantitatively forces generated by cells not attached to a substrate, we used a dual optical trap to suspend 3T3 fibroblasts between two fibronectin-coated beads. In this simple geometry, we measured both the cells' elastic properties and the force fluctuations they generate with high bandwidth. Cell stiffness decreased substantially with both myosin inhibition by blebbistatin and serum-starvation, but not with microtubule depolymerization by nocodazole. We show that cortical forces generated by non-muscle myosin II deform the cell from its rounded shape in the frequency regime from 0.1 to 10 Hz. The amplitudes of these forces were strongly reduced by blebbistatin and serum starvation, but were unaffected by depolymerization of microtubules. Force fluctuations show a spectrum that is characteristic for an elastic network activated by random sustained stresses with abrupt transitions.

  20. The medial gastrocnemius muscle attenuates force fluctuations during plantar flexion.

    PubMed

    Shinohara, Minoru; Yoshitake, Yasuhide; Kouzaki, Motoki; Fukunaga, Tetsuo

    2006-02-01

    Force fluctuations during steady contractions of multiple agonist muscles may be influenced by the relative contribution of force by each muscle. The purpose of the study was to compare force fluctuations during steady contractions performed with the plantar flexor muscles in different knee positions. Nine men (25.8+/-5.1 years) performed steady contractions of the plantar flexor muscles in the knee-flexed and knee-extended (greater involvement of the gastrocnemii muscles) positions. The maximal voluntary contraction (MVC) force was 32% greater in the knee-extended position compared with the knee-flexed position. The target forces were 2.5-10% MVC force in the respective position. The amplitude of electromyogram in the medial gastrocnemius muscle was greater in the knee-extended position (10.50+/-9.80%) compared with the knee-flexed position (1.26+/-1.15%, P<0.01). The amplitude of electromyogram in the soleus muscle was not influenced by the knee position. The amplitude of electromyogram in the lateral gastrocnemius and tibialis anterior muscles was marginal and unaltered with knee position. At the same force (in Newtons), the standard deviation of force was lower in the knee-extended position compared with the knee-flexed position. These results indicate that force fluctuations during plantar flexion are attenuated with greater involvement of the medial gastrocnemius muscle.

  1. Fluctuating magnetic field induced resonant activation

    SciTech Connect

    Mondal, Shrabani; Das, Sudip; Baura, Alendu; Bag, Bidhan Chandra

    2014-12-14

    In this paper, we have studied the properties of a Brownian particle at stationary state in the presence of a fluctuating magnetic field. Time dependence of the field makes the system thermodynamically open. As a signature of that the steady state distribution function becomes function of damping strength, intensity of fluctuations and constant parts of the applied magnetic field. It also depends on the correlation time of the fluctuating magnetic field. Our another observation is that the random magnetic field can induce the resonant activation phenomenon. Here correlation time is increased under the fixed variance of the fluctuating field. But if the correlation time (τ) increases under the fixed field strength then the mean first passage time rapidly grows at low τ and it almost converges at other limit. This is sharp contrast to the usual colored noise driven open system case where the mean first passage time diverges exponentially. We have also observed that a giant enhancement of barrier crossing rate occurs particularly at large strength of constant parts of the applied magnetic field even for very weak fluctuating magnetic field. Finally, break down of the Arrhenius result and disappearance of the Kramers’ turn over phenomenon may occur in the presence of a fluctuating magnetic field.

  2. Force fluctuations in three-dimensional suspended fibroblasts

    PubMed Central

    Schlosser, Florian; Rehfeldt, Florian; Schmidt, Christoph F.

    2015-01-01

    Cells are sensitive to mechanical cues from their environment and at the same time generate and transmit forces to their surroundings. To test quantitatively forces generated by cells not attached to a substrate, we used a dual optical trap to suspend 3T3 fibroblasts between two fibronectin-coated beads. In this simple geometry, we measured both the cells' elastic properties and the force fluctuations they generate with high bandwidth. Cell stiffness decreased substantially with both myosin inhibition by blebbistatin and serum-starvation, but not with microtubule depolymerization by nocodazole. We show that cortical forces generated by non-muscle myosin II deform the cell from its rounded shape in the frequency regime from 0.1 to 10 Hz. The amplitudes of these forces were strongly reduced by blebbistatin and serum starvation, but were unaffected by depolymerization of microtubules. Force fluctuations show a spectrum that is characteristic for an elastic network activated by random sustained stresses with abrupt transitions. PMID:25533089

  3. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

    DOE PAGES

    Squire, J.; Bhattacharjee, A.

    2015-11-02

    Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is nomore » strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.« less

  4. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

    SciTech Connect

    Squire, J.; Bhattacharjee, A.

    2015-11-02

    Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.

  5. Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence.

    PubMed

    Squire, J; Bhattacharjee, A

    2015-11-01

    This article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of α effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of α, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.

  6. Force Fluctuations in a 2D Granular Drag Experiment

    NASA Astrophysics Data System (ADS)

    Geng, Junfei; Behringer, R. P.

    2002-11-01

    We study fluctuations in the drag force experienced by an object slowly moving through a 2D granular material consisting of bidisperse disks. Slow drag experiments provide a useful way to understand the nature of stress propagation, fluctuations, and slow dynamics in granular materials. Unlike in a liquid, the drag force in a granular material is largely due to the resistance of inhomogeneous and anisotropic ``force chains'', and thus exhibits strong fluctuations. Experiments were carried out in an apparatus similar in spirit to the one by Albert et al.(R. Albert, M.A. Pfeifer, A.L. Barabasi and P. Schiffer, Phys. Rev. Lett. 82), 205 (1999). and we varied the rotation rate (ω=6.3× 10-6 ˜ 8.7× 10-4Hz), the object size (0.744, 0.876, 1.250,1.610,1.930 cm), and the packing fraction of the system. We observed a weak dependence of the mean force on the medium velocity, a rate-invariant power spectrum decaying as ω-2 for large ω (a remarkable resemblance to results by Miller et al.(B. Miller, C. O'Hern and R.P. Behringer, Phys. Rev. Lett. 77), 3110 (1996).), an exponential distribution of avalanche sizes, and a well defined ``Stress Chain Force Constant''. We also show that a simple model adapted after Kahng. et al.(B. Kahng, I. Albert, P. Schiffer and A.L. Barabasi, Phys. Rev. E. 64), 051303 (2001). reproduces many of experimental observations.

  7. Traction force and tension fluctuations in growing axons

    NASA Astrophysics Data System (ADS)

    Urbach, Jeffrey; Polackwich, Jamie; Koch, Daniel; McAllister, Ryan; Geller, Herbert

    Actively generated mechanical forces play a central role in axon growth and guidance during nervous system development. We describe the dynamics of traction stresses from growth cones of actively advancing axons from postnatal rat DRG neurons. By tracking the movement of the growth cone and analyzing the traction stresses in a co-moving reference frame, we show that there is a clear and consistent average stress field underlying the complex spatial stresses present at any one time. The average stress field has strong maxima on the sides of the growth cone, directed inward toward the growth cone neck. This pattern represents a Contractile stress contained within the growth cone, and a net force that is balanced by the axon tension. In addition, using high time-resolution measurements, we show that the stress field is composed of fluctuating local stress peaks, with a population of peaks whose lifetime distribution follows an exponential decay, and a small number of very long-lived peaks. We also find that the tension appears to vary randomly over short time scales, roughly consistent with the lifetime of the stress peaks, suggesting that the tension fluctuations originate from stochastic adhesion dynamics.

  8. Imperceptible electrical noise attenuates isometric plantar flexion force fluctuations with correlated reductions in postural sway.

    PubMed

    Magalhães, Fernando Henrique; Kohn, André Fabio

    2012-03-01

    Optimal levels of noise stimulation have been shown to enhance the detection and transmission of neural signals thereby improving the performance of sensory and motor systems. The first series of experiments in the present study aimed to investigate whether subsensory electrical noise stimulation applied over the triceps surae (TS) in seated subjects decreases torque variability during a force-matching task of isometric plantar flexion and whether the same electrical noise stimulation decreases postural sway during quiet stance. Correlation tests were applied to investigate whether the noise-induced postural sway decrease is linearly predicted by the noise-induced torque variability decrease. A second series of experiments was conducted to investigate whether there are differences in torque variability between conditions in which the subsensory electrical noise is applied only to the TS, only to the tibialis anterior (TA) and to both TS and TA, during the force-matching task with seated subjects. Noise stimulation applied over the TS muscles caused a significant reduction in force variability during the maintained isometric force paradigm and also decreased postural oscillations during quiet stance. Moreover, there was a significant correlation between the reduction in force fluctuation and the decrease in postural sway with the electrical noise stimulation. This last result indicates that changes in plantar flexion force variability in response to a given subsensory random stimulation of the TS may provide an estimate of the variations in postural sway caused by the same subsensory stimulation of the TS. We suggest that the decreases in force variability and postural sway found here are due to stochastic resonance that causes an improved transmission of proprioceptive information. In the second series of experiments, the reduction in force variability found when noise was applied to the TA muscle alone did not reach statistical significance, suggesting that TS

  9. Electric force microscopy of semiconductors: theory of cantilever frequency fluctuations and noncontact friction.

    PubMed

    Lekkala, Swapna; Marohn, John A; Loring, Roger F

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

  10. Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction

    SciTech Connect

    Lekkala, Swapna; Marohn, John A.; Loring, Roger F.

    2013-11-14

    An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

  11. Influence of the Basset force on the resonant behavior of an oscillator with fluctuating frequency

    SciTech Connect

    Rekker, A. Mankin, R.

    2015-10-28

    The influence of hydrodynamic interactions, such as Stokes and Basset forces, on the dynamics of a harmonically trapped Brownian tracer is considered. A generalized Langevin equation is used to describe the tracer’s response to an external periodic force and to dichotomous fluctuations of the stiffness of the trapping potential. Relying on the Shapiro-Loginov formula, exact expressions for the complex susceptibility and for the response function are presented. On the basis of these exact formulas, it is demonstrated that interplay of a multiplicative colored noise and the Basset force induced memory effects can generate a variety of cooperation effects, such as multiresonance versus the driving frequency, as well as stochastic resonance versus noise parameters. In particular, in certain parameter regions the response function exhibits a resonance-like enhancement at intermediate values of the intensity of the Basset force. Conditions for the appearance of these effects are also discussed.

  12. Solar wind thermally induced magnetic fluctuations.

    PubMed

    Navarro, R E; Moya, P S; Muñoz, V; Araneda, J A; F-Viñas, A; Valdivia, J A

    2014-06-20

    A kinetic description of Alfvén-cyclotron magnetic fluctuations for anisotropic electron-proton quasistable plasmas is studied. An analytical treatment, based on the fluctuation-dissipation theorem, consistently shows that spontaneous fluctuations in plasmas with stable distributions significantly contribute to the observed magnetic fluctuations in the solar wind, as seen, for example, in [S. D. Bale et al., Phys. Rev. Lett. 103, 211101 (2009)], even far below from the instability thresholds. Furthermore, these results, which do not require any adjustable parameters or wave excitations, are consistent with the results provided by hybrid simulations. It is expected that this analysis contributes to our understanding of the nature of magnetic fluctuations in the solar wind.

  13. Structural fluctuation of proteins induced by thermodynamic perturbation

    SciTech Connect

    Hirata, Fumio; Akasaka, Kazuyuki

    2015-01-28

    A theory to describe structural fluctuations of protein induced by thermodynamic perturbations, pressure, temperature, and denaturant, is proposed. The theory is formulated based on the three methods in the statistical mechanics: the generalized Langevin theory, the linear response theory, and the three dimensional interaction site model (3D-RISM) theory. The theory clarifies how the change in thermodynamic conditions, or a macroscopic perturbation, induces the conformational fluctuation, which is a microscopic property. The theoretical results are applied, on the conceptual basis, to explain the experimental finding by Akasaka et al., concerning the NMR experiment which states that the conformational change induced by pressure corresponds to structural fluctuations occurring in the ambient condition. A method to evaluate the structural fluctuation induced by pressure is also suggested by means of the 3D-RISM and the site-site Kirkwood-Buff theories.

  14. Laser-Based Faraday-Effect Measurement of Magnetic Fluctuations and Fluctuation-Induced Transport

    NASA Astrophysics Data System (ADS)

    Lin, L.; Brower, D. L.; Ding, W. X.; Sarff, J. S.

    2013-10-01

    A multichord far-infrared laser-based Faraday-effect polarimetry diagnostic has been well developed on MST. Combined polarimetry-interferometry capability permits simultaneous measurement of internal structure of density and magnetic field with fast time response (~ 4 μs) and low phase noise (< 0 .01°) . With this diagnostic, the impact on toroidal current profile from a tangentially injected neutral beam is directly measured, allowing evaluation of non-inductive current drive. In addition, 0 .05° Faraday-effect fluctuations associated with global tearing modes are resolved with an uncertainty below 0 .01° . For physics investigations, these Faraday-effect fluctuations are complicated by contributions from both density and magnetic fluctuations. In our analysis, the local density fluctuations are obtained by inverting the line-integrated interferometry data after resolving the mode helicity through correlation techniques. The local magnetic fluctuations are then reconstructed using a parameterized fit of the polarimetry data, accounting for both the density and magnetic contributions. For the same mode, density and radial magnetic fluctuations exhibit very different spatial structure. In this process, their relative phase is also determined, thereby allowing the determination of magnetic-fluctuation-induced transport. Work supported by US DoE.

  15. Diastolic scattered light fluctuation, resting force and twitch force in mammalian cardiac muscle

    PubMed Central

    Lakatta, E. G.; Lappé, D. L.

    1981-01-01

    1. When coherent light was passed through isolated isometric cardiac muscles during the diastolic or resting period, intensity fluctuations were observed in the scattered field. The frequency of these intensity fluctuations (f½) varied with many experimental interventions known to enhance Ca2+ flux into the cell. 2. In rat muscles stimulated at low frequencies (0.1 ± 2.0 min-1) stepwise increases (0.4-10 mm) of [Ca2+] in the bathing fluid ([Ca2+]e), or addition of ouabain (10-6-6 × 10-4 m) to the perfusate caused stepwise increases in f½. These were paralleled by increments in resting force (RF) such that the changes in f½ and RF were highly correlated. Substitution of K+ for Na+ in the perfusate resulted in parallel transients in RF and f½. 3. In contrast to the rat, most cat muscles stimulated at low frequencies in the steady state exhibited neither diastolic intensity fluctuations nor Ca2+-dependent changes in RF in [Ca2+]e of 10 mm or less; when [Ca2+]e was increased to 12-32 mm, however, steady-state Ca2+-dependent f½ and RF were observed. In a given [Ca2+]e reduction of [Na+]e increased f½. In the transient state following cessation of regular stimulation at more rapid rates (12-96 min-1) intensity fluctuations were present in all [Ca2+]e and decayed with time (seconds to minutes); the f½ and time course of the decay of the fluctuations were determined by the rate of prior stimulation and [Ca2+]e. 4. Maximum potentiation of twitch force in response to the above inotropic interventions was associated with an optimal level of f½ which was similar in both species; when higher levels of f½ were produced by more intense inotropic intervention, twitch force declined. Over the range of inotropic intervention up to and including that at which maximum twitch potentiation occurred, the increase in diastolic f½ predicted the extent of twitch potentiation with a high degree of accuracy (r > 0.97) both in the transient and steady states. 5. In contrast to the

  16. Portfolio theory of optimal isometric force production: Variability predictions and nonequilibrium fluctuation dissipation theorem

    NASA Astrophysics Data System (ADS)

    Frank, T. D.; Patanarapeelert, K.; Beek, P. J.

    2008-05-01

    We derive a fundamental relationship between the mean and the variability of isometric force. The relationship arises from an optimal collection of active motor units such that the force variability assumes a minimum (optimal isometric force). The relationship is shown to be independent of the explicit motor unit properties and of the dynamical features of isometric force production. A constant coefficient of variation in the asymptotic regime and a nonequilibrium fluctuation-dissipation theorem for optimal isometric force are predicted.

  17. Parameter Fluctuation-Induced Pattern Transition in the Complex Ginzburg-Landau Equation

    NASA Astrophysics Data System (ADS)

    Ma, Jun; Ja, Ya; Tang, Jun; Chen, Yong

    Parameter fluctuation, which is often induced by the noise, temperature, deformation of the media etc., plays an important role in changing the dynamics of the system. In this paper, the problem of parameter fluctuation-induced pattern transition in the Complex Ginzburg-Landau equation (CGLE) is investigated. At first, the perpendicular-gradient initial values are used to generate spiral wave and spiral turbulence under appropriate parameters. At second, the parameter is perturbed with the periodical and/or random signal to simulate the parameter fluctuation, respectively. Then a class of linear error feedback is used to induce transition of the spiral wave and spiral turbulence. It is found that target waves can be induced by the complete feedback forcing, while the local feedback forcing seldom induce a target wave. In the case of spiral turbulence, spiral wave is generated and the spiral turbulence is removed by the new appeared spiral wave as the linear error feedback began to work on the whole media. Finally, the common negative feedback is also used to control the parameter-fluctuated CGLE, and the results are compared with the linear error feedback control, it is found that the whole system become homogeneous when the negative feedback is imposed on the whole media, and the local negative feedback can induce new target wave to remove the spiral wave while it is in vain to generate new target or spiral wave to overcome and eliminate the spiral turbulence.

  18. Robustness of networks against fluctuation-induced cascading failures.

    PubMed

    Heide, Dominik; Schäfer, Mirko; Greiner, Martin

    2008-05-01

    Fluctuating fluxes on a complex network lead to load fluctuations at the vertices, which may cause them to become overloaded and to induce a cascading failure. A characterization of the one-point load fluctuations is presented, revealing their dependence on the nature of the flux fluctuations and on the underlying network structure. Based on these findings, an alternate robustness layout of the network is proposed. Taking load correlations between the vertices into account, an analytical prediction of the probability for the network to remain fully efficient is confirmed by simulations. Compared to previously proposed mean-flux layouts, the alternate layout comes with significantly less investment costs in the high-confidence limit.

  19. Comment on ``Gravity as a zero-point-fluctuation force''

    NASA Astrophysics Data System (ADS)

    Carlip, S.

    1993-04-01

    A paper by H. Puthoff [Phys. Rev. A 39, 2333 (1989)], which claims to derive Newtonian gravity from stochastic electrodynamics, contains a serious computational error. When the calculation is corrected, the resulting force is shown to be nongravitational and negligible.

  20. Vacuum Fluctuation Force on a Rigid Casimir Cavity in de Sitter and Schwarzschild-De Sitter Space-Time

    NASA Astrophysics Data System (ADS)

    Chen, Xiang

    2012-11-01

    We investigate the net force on a rigid Casimir cavity generated by vacuum fluctuations of electromagnetic field in three cases: de Sitter space-time, de Sitter space-time with weak gravitational field and Schwarzschild-de Sitter space-time. In de Sitter space-time the resulting net force follows the square inverse law but unfortunately it is too weak to be measurable due to the large universe radius. By introducing a weak gravitational field into the de Sitter space-time, we find that the net force can now be split into two parts, one is the gravitational force due to the induced effective mass between the two plates and the other one is generated by the metric structure of de Sitter space-time. In order to investigate the vacuum fluctuation force on the rigid cavity under strong gravitational field, we perform a similar analysis in Schwarzschild-de Sitter space-time and results are obtained in three different limits. The most interesting one is when the cavity gets closer to the horizon of a blackhole, square inverse law is recovered and the repulsive force due to negative energy/mass of the cavity now has an observable strength. More importantly the force changes from being repulsive to attractive when the cavity crosses the event horizon, so that the energy/mass of the cavity switches the sign, which suggests the unusual time direction inside the event horizon.

  1. Laser-detected lateral muscle displacement is correlated with force fluctuations during voluntary contractions in humans.

    PubMed

    Yoshitake, Yasuhide; Masani, Kei; Shinohara, Minoru

    2008-08-30

    Fluctuations in muscle force during steady voluntary contractions result from the summation of twitch forces produced by asynchronous activation of multiple motor units. We hypothesized that oscillatory lateral muscle displacement, measured with a non-contact high-resolution laser displacement sensor, is correlated with force fluctuations during steady, voluntary contractions with a human muscle. Eight healthy young adults (20-33 yrs) performed steady isometric contractions with the first dorsal interosseus muscle. Contraction intensity ranged from 2.5% to 60% of the maximal voluntary contraction force. Oscillatory lateral displacement of the muscle surface was measured with a high-resolution laser displacement sensor (0.5 microm resolution), concurrently with abduction force of the index finger. In the time-domain analysis, there was a significant positive peak in the cross-correlation function between lateral muscle displacement and force fluctuations. In addition, the amplitude increased linearly with contraction intensity in both signals. In the frequency-domain analysis, frequency content was similar in both signals, and there was significant coherence between signals for the major frequency range of the signals (<5 Hz). In conclusion, laser-detected lateral displacement of a hand muscle is correlated with force fluctuations across a wide range of contraction intensity during steady voluntary contractions in humans.

  2. Short-term climatic fluctuations forced by thermal anomalies

    NASA Technical Reports Server (NTRS)

    Hanna, A. F.

    1982-01-01

    A two level, global, spectral model using pressure as a vertical coordinate was developed. The system of equations describing the model is nonlinear and quasi-geostrophic (linear balance). Static stability is variable in the model. A moisture budget is calculated in the lower layer only. Convective adjustment is used to avoid supercritical temperature lapse rates. The mechanical forcing of topography is introduced as a vertical velocity at the lower boundary. Solar forcing is specified assuming a daily mean zenith angle. The differential diabatic heating between land and sea is paramterized. On land and sea ice surfaces, a steady state thermal energy equation is solved to calculate the surface temperature. On the oceans, the sea surface temperature is specified as the climatological average for January. The model is used to simulate the January, February and March circulations.

  3. Fluctuations of the proton-electromotive force across the inner mitochondrial membrane

    NASA Astrophysics Data System (ADS)

    Procopio, Joaquim; Fornés, José A.

    1997-05-01

    The intermembrane mitochondrial space (IMMS) is delimited by the inner and outer mitochondrial membranes and defines a region of molecular dimension where fluctuations of the number of free protons and of transmembrane voltage can give rise to fluctuations in the proton-electromotive force EPMF across the inner mitochondrial membrane (IMM). We have applied the fluctuation-dissipation theorem to an electrical equivalent circuit consisting of a resistor Rm in parallel with a capacitor Cm representing the passive electrical properties of the IMM, in series with another capacitor Cb representing the proton-buffering power of the IMMS fluid. An access resistance Ra was defined as a link between the capacitor Cb and the membrane. Average EPMF fluctuations across the IMM were calculated for different assumptions concerning the intermembrane space dimensions. The calculated average EPMF fluctuations were in the vicinity of 100 mV for relaxation times in the few-microseconds range. The corresponding fluctuational protonic free energy is about 10 kJ/mole, which is comparable to the binding energy for protons in different transporters. This suggests that fluctuations in EPMF can be of relevance in the universe of forces influencing the molecular machinery embedded in the IMM.

  4. Branching influences force-velocity curves and length fluctuations in actin networks

    NASA Astrophysics Data System (ADS)

    Hansda, Deepak Kumar; Sen, Shamik; Padinhateeri, Ranjith

    2014-12-01

    We investigate collective dynamics of branched actin networks growing against a rigid movable wall constrained by a resistive force. Computing the force velocity relations, we show that the stall force of such networks depends not only on the average number of filaments touching the wall, but also on the amount of fluctuation of the leading edge of the network. These differences arise due to differences in the network architecture, namely, distance between two adjacent branching points and the initial distance of the starting filament from the wall, with their relative magnitudes influencing the nature of the force velocity curves (convex versus concave). We also show that the introduction of branching results in nonmonotonic diffusion constant, a quantity that measures the growth in length fluctuation of the leading edge of the network, as a function of externally applied force. Together our results demonstrate how the collective dynamics of a branched network differs from that of a parallel filament network.

  5. Fluctuation forces and wetting layers in colloid-polymer mixtures.

    PubMed

    Hennequin, Y; Aarts, D G A L; Indekeu, J O; Lekkerkerker, H N W; Bonn, D

    2008-05-02

    We present confocal microscopy experiments on the wetting of phase-separated colloid-polymer mixtures. We observe that an unusually thick wetting layer of the colloid-rich phase forms at the walls of the glass container that holds the mixture. Because of the ultralow interfacial tension between the colloid-rich and the polymer-rich phases, the thermally activated roughness of the interfaces becomes very big and measurable. We observe that close to the critical point the roughness of the interface between the wetting layer and the polymer-rich phase decreases with decreasing layer thickness: large excursions of the interface are confined in the wetting layer. The measured relationship between the roughness and the thickness of the wetting layer is in qualitative agreement with the predictions of renormalization group theory for short-range forces and complete wetting.

  6. Giant Amplification of Noise in Fluctuation-Induced Pattern Formation

    NASA Astrophysics Data System (ADS)

    Biancalani, Tommaso; Jafarpour, Farshid; Goldenfeld, Nigel

    2017-01-01

    The amplitude of fluctuation-induced patterns might be expected to be proportional to the strength of the driving noise, suggesting that such patterns would be difficult to observe in nature. Here, we show that a large class of spatially extended dynamical systems driven by intrinsic noise can exhibit giant amplification, yielding patterns whose amplitude is comparable to that of deterministic Turing instabilities. The giant amplification results from the interplay between noise and nonorthogonal eigenvectors of the linear stability matrix, yielding transients that grow with time, and which, when driven by the ever-present intrinsic noise, lead to persistent large amplitude patterns. This mechanism shows that fluctuation-induced Turing patterns are observable, and are not strongly limited by the amplitude of demographic stochasticity nor by the value of the diffusion coefficients.

  7. Subthreshold electrical stimulation reduces motor unit discharge variability and decreases the force fluctuations of plantar flexion.

    PubMed

    Kouzaki, Motoki; Kimura, Tetsuya; Yoshitake, Yasuhide; Hayashi, Tatsuya; Moritani, Toshio

    2012-04-04

    The purpose of this study was to examine the influence of subthreshold electrical stimulation on the force fluctuations and motor-unit discharge variability during low-level, steady contraction of the plantar flexor muscles. Seven subjects performed a force-matching task of isometric plantar flexion at 5% of maximal voluntary contraction with and without random electrical stimulation applied to the tibial nerve. During the task, the motor unit action potential was continuously recorded with fine-wire electrodes, and the inter-spike intervals of a single motor unit were calculated. The coefficient of variation (CV) of the force fluctuations and the inter-spike intervals of the motor unit discharge were significantly decreased by the intervention of subthreshold electrical stimulation, although there were no changes in the mean values. These results suggest that subthreshold stimulation reduced the motor-unit discharge variability, which in turn, increased the steadiness of the force.

  8. Pressure Fluctuations Induced by a Hypersonic Turbulent Boundary Layer

    NASA Technical Reports Server (NTRS)

    Duan, Lian; Choudhari, Meelan M.; Zhang, Chao

    2016-01-01

    Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially-developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analyzed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean velocity pro les and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from the Taylor's hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The freestream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the freestream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

  9. Structure Formation in the Universe from Texture Induced Fluctuations

    NASA Astrophysics Data System (ADS)

    Durrer, Ruth; Zhou, Zhi-Hong

    1995-03-01

    We discuss structure formation with topological defects. First we present a partially new, local, and gauge invariant system of perturbation equations to treat microwave background and dark matter fluctuations induced by topological defects or any other type of seeds. We show that this system is well suited for numerical analysis of structure formation by applying it to the texture scenario. Our numerical results cover a larger dynamical range than previous investigations and are complementary to them since we use substantially different methods.

  10. OH* imager response to turbulence-induced temperature fluctuations

    NASA Astrophysics Data System (ADS)

    Gardner, Chester S.; Vargas, Fabio A.

    2016-12-01

    The layer of the excited state hydroxyl radical (OH*) is formed in the mesopause region by the reaction of ozone (O3) and atomic hydrogen (H). We derive the theoretical expressions for the OH* brightness and rotational temperature (T*) responses to high-frequency atmospheric temperature perturbations. The theory is used to calculate the 1-D and 2-D horizontal wave number spectra of the OH* and T* image fluctuations induced by atmospheric turbulence. By applying the theory to images of a breaking gravity wave packet, acquired by the Utah State University Advanced Mesospheric Temperature Mapper, we show that existing infrared OH* imager technology can observe the evolution of gravity wave breakdown and characterize the resulting turbulent eddies in the source region and in the inertial subrange of the turbulence spectrum. For the example presented here, the RMS OH* brightness fluctuations induced by the gravity wave packet was 2.90% and by the associated turbulence was 1.07%. Unfortunately, the T* fluctuations induced by turbulence are usually too small to be observed in the OH* rotational temperature maps.

  11. Endpoint Force Fluctuations Reveal Flexible Rather Than Synergistic Patterns of Muscle Cooperation

    PubMed Central

    Kutch, Jason J.; Kuo, Arthur D.; Bloch, Anthony M.; Rymer, William Z.

    2008-01-01

    We developed a new approach to investigate how the nervous system activates multiple redundant muscles by studying the endpoint force fluctuations during isometric force generation at a multi-degree-of-freedom joint. We hypothesized that, due to signal-dependent muscle force noise, endpoint force fluctuations would depend on the target direction of index finger force and that this dependence could be used to distinguish flexible from synergistic activation of the musculature. We made high-gain measurements of isometric forces generated to different target magnitudes and directions, in the plane of index finger metacarpophalangeal joint abduction–adduction/flexion–extension. Force fluctuations from each target were used to calculate a covariance ellipse, the shape of which varied as a function of target direction. Directions with narrow ellipses were approximately aligned with the estimated mechanical actions of key muscles. For example, targets directed along the mechanical action of the first dorsal interosseous (FDI) yielded narrow ellipses, with 88% of the variance directed along those target directions. It follows the FDI is likely a prime mover in this target direction and that, at most, 12% of the force variance could be explained by synergistic coupling with other muscles. In contrast, other target directions exhibited broader covariance ellipses with as little as 30% of force variance directed along those target directions. This is the result of cooperation among multiple muscles, based on independent electromyographic recordings. However, the pattern of cooperation across target directions indicates that muscles are recruited flexibly in accordance with their mechanical action, rather than in fixed groupings. PMID:18799603

  12. Net force on an asymmetrically excited two-atom system from vacuum fluctuations

    NASA Astrophysics Data System (ADS)

    Donaire, M.

    2016-12-01

    A net force on a system of two dissimilar atoms, one of which is excited, is shown to result from their van der Waals interaction. It is accompanied by a net transfer of linear momentum to the quantum fluctuations of the electromagnetic field. This momentum results from the asymmetric interference of the virtual photons scattered off each atom along the interatomic direction, which is in itself a manifestation of the optical theorem. Ultimately, the virtual photons' momentum, of equal strength and opposite direction to the momentum gained by the two-atom system while excited, is released through directional spontaneous emission, which allows for an indirect measure, a posteriori, of the total force on the excited system. A quantitative prediction is made in a two-alkali atom system. It is conjectured that a net force and hence a nonzero momentum of quantum fluctuations take place in any asymmetrically excited system.

  13. Thermoelectricity in polymer composites due to fluctuation-induced tunneling.

    PubMed

    Stedman, T; Wei, K; Nolas, G S; Woods, L M

    2015-11-07

    Transport in heavily-doped polymer composites, characterized by localized charge regions, is examined in light of the recent interest in polymers for thermoelectric applications. The developed fundamental transport theory describes carrier tunneling between charged localizations by taking into account thermally induced fluctuations of the applied potential. A range of characteristic behaviors corresponding to experimental data are described. Deviations from the Wiedemann-Franz law are also identified. This novel theory enables the determination of factors dominating the transport in polymers and a comparison to tunneling without thermal fluctuations is also provided. The obtained asymptotic expressions for the conductivity, Seebeck coefficient, and carrier thermal conductivity are particularly useful for elucidating possible routes for thermoelectric transport control and optimization.

  14. Geometry-induced fluctuations of olfactory searches in bounded domains

    NASA Astrophysics Data System (ADS)

    Rodríguez, Juan Duque; Gómez-Ullate, David; Mejía-Monasterio, Carlos

    2014-04-01

    In olfactory search an immobile target emits chemical molecules at constant rate. The molecules are transported by the medium, which is assumed to be turbulent. Considering a searcher able to detect such chemical signals and whose motion follows the infotaxis strategy, we study the statistics of the first-passage time to the target when the searcher moves on a finite two-dimensional lattice of different geometries. Far from the target, where the concentration of chemicals is low, the direction of the searcher's first movement is determined by the geometry of the domain and the topology of the lattice, inducing strong fluctuations on the average search time with respect to the initial position of the searcher. The domain is partitioned in well-defined regions characterized by the direction of the first movement. If the search starts over the interface between two different regions, large fluctuations in the search time are observed.

  15. Eustatic sea level fluctuations induced by polar wander

    NASA Technical Reports Server (NTRS)

    Sabadini, Roberto; Doglioni, Carlo; Yuen, David A.

    1990-01-01

    It is shown here that polar wander of a viscoelastic, stratified earth can induce global sea level fluctuations comparable to the short-term component in eustatic sea-level curves. The sign of these fluctuations, which are very sensitive to the rheological stratification, depends on the geographical location of the observation point; rises and falls in sea level can thus be coeval in different parts of the world. This finding is a distinct contrast to the main assumption underlying the reconstruction of eustatic curves, namely that global sea-level events produce the same depositional sequence everywhere. It is proposed that polar wander should be added to the list of geophysical mechanisms that can control the third-order cycles in sea level.

  16. Geometry-induced fluctuations of olfactory searches in bounded domains.

    PubMed

    Rodríguez, Juan Duque; Gómez-Ullate, David; Mejía-Monasterio, Carlos

    2014-04-01

    In olfactory search an immobile target emits chemical molecules at constant rate. The molecules are transported by the medium, which is assumed to be turbulent. Considering a searcher able to detect such chemical signals and whose motion follows the infotaxis strategy, we study the statistics of the first-passage time to the target when the searcher moves on a finite two-dimensional lattice of different geometries. Far from the target, where the concentration of chemicals is low, the direction of the searcher's first movement is determined by the geometry of the domain and the topology of the lattice, inducing strong fluctuations on the average search time with respect to the initial position of the searcher. The domain is partitioned in well-defined regions characterized by the direction of the first movement. If the search starts over the interface between two different regions, large fluctuations in the search time are observed.

  17. Dynamic Runner Forces and Pressure Fluctuations on the Draft Tube Wall of a Model Pump-Turbine

    NASA Astrophysics Data System (ADS)

    Kirschner, O.; Ruprecht, A.; Göde, E.; Riedelbauch, S.

    2016-11-01

    When Francis-turbines and pump-turbines operate at off-design conditions, typically a vortex rope develops. The vortex rope causes pressure oscillations leading to fluctuations of the forces affecting the runner. The presence of dynamic runner forces over a long period of time might damage the bearings and possibly the runner. In this experimental investigation, the fluctuating part of the runner forces and the pressure oscillations on the draft tube wall were measured on a model pump-turbine with a simplified straight cone draft tube in different operating conditions. The investigation focuses on the correlation of the pressure fluctuations frequency measured at the draft tube wall with the frequency of the fluctuating forces on the runner. The comparison between pressure fluctuations and dynamic forces shows a significant correlation in all operating points. For the comparison of different components in the spatial directions of the forces, the pressure fluctuations were separated in a synchronous part and a rotating part for operating points with higher amplitudes. The rotating pressure fluctuations correlate with the radial forces especially in the operating points with a rotating vortex rope. At frequencies with higher amplitudes in the pressure fluctuations caused by the vortex rope movement, there are also higher amplitudes in the radial forces at the same frequencies.

  18. Electromagnetic fluctuation-induced interactions in randomly charged slabs

    NASA Astrophysics Data System (ADS)

    Rezvani, Vahid; Sarabadani, Jalal; Naji, Ali; Podgornik, Rudolf

    2012-09-01

    Randomly charged net-neutral dielectric slabs are shown to interact across a featureless dielectric continuum with long-range electrostatic forces that scale with the statistical variance of their quenched random charge distribution and inversely with the distance between their bounding surfaces. By accounting for the whole spectrum of electromagnetic field fluctuations, we show that this long-range disorder-generated interaction extends well into the retarded regime where higher order (non-zero) Matsubara frequencies contribute significantly. This occurs even for highly clean samples with only a trace amount of charge disorder and shows that disorder effects can be important down to the nanoscale. As a result, the previously predicted non-monotonic behavior for the total force between dissimilar slabs as a function of their separation distance is substantially modified by higher order contributions, and in almost all cases of interest, we find that the equilibrium inter-surface separation is shifted to substantially larger values compared to predictions based solely on the zero-frequency component. This suggests that the ensuing non-monotonic interaction is more easily amenable to experimental detection. The presence of charge disorder in the intervening dielectric medium between the two slabs is shown to lead to an additional force that can be repulsive or attractive depending on the system parameters and can, for instance, wash out the non-monotonic behavior of the total force when the intervening slab contains a sufficiently large amount of disorder charges.

  19. Mean and Fluctuating Force Distribution in a Random Array of Spheres

    NASA Astrophysics Data System (ADS)

    Akiki, Georges; Jackson, Thomas; Balachandar, Sivaramakrishnan

    2015-11-01

    This study presents a numerical study of the force distribution within a cluster of mono-disperse spherical particles. A direct forcing immersed boundary method is used to calculate the forces on individual particles for a volume fraction range of [0.1, 0.4] and a Reynolds number range of [10, 625]. The overall drag is compared to several drag laws found in the literature. As for the fluctuation of the hydrodynamic streamwise force among individual particles, it is shown to have a normal distribution with a standard deviation that varies with the volume fraction only. The standard deviation remains approximately 25% of the mean streamwise force on a single sphere. The force distribution shows a good correlation between the location of two to three nearest upstream and downstream neighbors and the magnitude of the forces. A detailed analysis of the pressure and shear forces contributions calculated on a ghost sphere in the vicinity of a single particle in a uniform flow reveals a mapping of those contributions. The combination of the mapping and number of nearest neighbors leads to a first order correction of the force distribution within a cluster which can be used in Lagrangian-Eulerian techniques. We also explore the possibility of a binary force model that systematically accounts for the effect of the nearest neighbors. This work was supported by the National Science Foundation (NSF OISE-0968313) under Partnership for International Research and Education (PIRE) in Multiphase Flows at the University of Florida.

  20. Fluctuation and synchronization of gait intervals and gait force profiles distinguish stages of Parkinson's disease

    PubMed Central

    Bartsch, Ronny; Plotnik, Meir; Kantelhardt, Jan W.; Havlin, Shlomo; Giladi, Nir; Hausdorff, Jeffrey M.

    2007-01-01

    We study the effects of Parkinson's disease (PD) on the long-term fluctuation and phase synchronization properties of gait timing (series of interstride intervals) as well as gait force profiles (series characterizing the morphological changes between the steps). We find that the fluctuations in the gait timing are significantly larger for PD patients and early PD patients, who were not treated yet with medication, compared to age-matched healthy controls. Simultaneously, the long-term correlations and the phase synchronization of right and left leg are significantly reduced in both types of PD patients. Surprisingly, long-term correlations of the gait force profiles are relatively weak for treated PD patients and healthy controls, while they are significantly larger for early PD patients. The results support the idea that timing and morphology of recordings obtained from a complex system can contain complementary information. PMID:18163154

  1. Fluctuation and synchronization of gait intervals and gait force profiles distinguish stages of Parkinson's disease

    NASA Astrophysics Data System (ADS)

    Bartsch, Ronny; Plotnik, Meir; Kantelhardt, Jan W.; Havlin, Shlomo; Giladi, Nir; Hausdorff, Jeffrey M.

    2007-09-01

    We study the effects of Parkinson's disease (PD) on the long-term fluctuation and phase synchronization properties of gait timing (series of interstride intervals) as well as gait force profiles (series characterizing the morphological changes between the steps). We find that the fluctuations in the gait timing are significantly larger for PD patients and early PD patients, who were not treated yet with medication, compared to age-matched healthy controls. Simultaneously, the long-term correlations and the phase synchronization of right and left leg are significantly reduced in both types of PD patients. Surprisingly, long-term correlations of the gait force profiles are relatively weak for treated PD patients and healthy controls, while they are significantly larger for early PD patients. The results support the idea that timing and morphology of recordings obtained from a complex system can contain complementary information.

  2. Cosmological implications of modified gravity induced by quantum metric fluctuations

    NASA Astrophysics Data System (ADS)

    Liu, Xing; Harko, Tiberiu; Liang, Shi-Dong

    2016-08-01

    We investigate the cosmological implications of modified gravities induced by the quantum fluctuations of the gravitational metric. If the metric can be decomposed as the sum of the classical and of a fluctuating part, of quantum origin, then the corresponding Einstein quantum gravity generates at the classical level modified gravity models with a non-minimal coupling between geometry and matter. As a first step in our study, after assuming that the expectation value of the quantum correction can be generally expressed in terms of an arbitrary second order tensor constructed from the metric and from the thermodynamic quantities characterizing the matter content of the Universe, we derive the (classical) gravitational field equations in their general form. We analyze in detail the cosmological models obtained by assuming that the quantum correction tensor is given by the coupling of a scalar field and of a scalar function to the metric tensor, and by a term proportional to the matter energy-momentum tensor. For each considered model we obtain the gravitational field equations, and the generalized Friedmann equations for the case of a flat homogeneous and isotropic geometry. In some of these models the divergence of the matter energy-momentum tensor is non-zero, indicating a process of matter creation, which corresponds to an irreversible energy flow from the gravitational field to the matter fluid, and which is direct consequence of the non-minimal curvature-matter coupling. The cosmological evolution equations of these modified gravity models induced by the quantum fluctuations of the metric are investigated in detail by using both analytical and numerical methods, and it is shown that a large variety of cosmological models can be constructed, which, depending on the numerical values of the model parameters, can exhibit both accelerating and decelerating behaviors.

  3. Decoherence in current induced forces: Application to adiabatic quantum motors

    NASA Astrophysics Data System (ADS)

    Fernández-Alcázar, Lucas J.; Bustos-Marún, Raúl A.; Pastawski, Horacio M.

    2015-08-01

    Current induced forces are not only related with the discrete nature of electrons but also with its quantum character. It is natural then to wonder about the effect of decoherence. Here, we develop the theory of current induced forces including dephasing processes and we apply it to study adiabatic quantum motors (AQMs). The theory is based on Büttiker's fictitious probe model, which here is reformulated for this particular case. We prove that it accomplishes the fluctuation-dissipation theorem. We also show that, in spite of decoherence, the total work performed by the current induced forces remains equal to the pumped charge per cycle times the voltage. We find that decoherence affects not only the current induced forces of the system but also its intrinsic friction and noise, modifying in a nontrivial way the efficiency of AQMs. We apply the theory to study an AQM inspired by a classical peristaltic pump where we surprisingly find that decoherence can play a crucial role by triggering its operation. Our results can help to understand how environmentally induced dephasing affects the quantum behavior of nanomechanical devices.

  4. Forces and mechanical energy fluctuations during diagonal stride roller skiing; running on wheels?

    PubMed

    Kehler, Alyse L; Hajkova, Eliska; Holmberg, Hans-Christer; Kram, Rodger

    2014-11-01

    Mechanical energy can be conserved during terrestrial locomotion in two ways: the inverted pendulum mechanism for walking and the spring-mass mechanism for running. Here, we investigated whether diagonal stride cross-country roller skiing (DIA) utilizes similar mechanisms. Based on previous studies, we hypothesized that running and DIA would share similar phase relationships and magnitudes of kinetic energy (KE), and gravitational potential energy (GPE) fluctuations, indicating elastic energy storage and return, as if roller skiing is like 'running on wheels'. Experienced skiers (N=9) walked and ran at 1.25 and 3 m s(-1), respectively, and roller skied with DIA at both speeds on a level dual-belt treadmill that recorded perpendicular and parallel forces. We calculated the KE and GPE of the center of mass from the force recordings. As expected, the KE and GPE fluctuated with an out-of-phase pattern during walking and an in-phase pattern during running. Unlike walking, during DIA, the KE and GPE fluctuations were in phase, as they are in running. However, during the glide phase, KE was dissipated as frictional heat and could not be stored elastically in the tendons, as in running. Elastic energy storage and return epitomize running and thus we reject our hypothesis. Diagonal stride cross-country skiing is a biomechanically unique movement that only superficially resembles walking or running.

  5. Coherent control of quantum fluctuations using cavity electromagnetically induced transparency.

    PubMed

    Souza, J A; Figueroa, E; Chibani, H; Villas-Boas, C J; Rempe, G

    2013-09-13

    We study the all-optical control of the quantum fluctuations of a light beam via a combination of single-atom cavity quantum electrodynamics (CQED) and electromagnetically induced transparency (EIT). Specifically, the EIT control field is used to tune the CQED transition frequencies in and out of resonance with the probe light. In this way, photon blockade and antiblockade effects are employed to produce sub-Poissonian and super-Poissonian light fields, respectively. The achievable quantum control paves the way towards the realization of a prototype of a novel quantum transistor which amplifies or attenuates the relative intensity noise of a light beam. Its feasibility is demonstrated by calculations using realistic parameters from recent experiments.

  6. Velocity Measurement by Scattering from Index of Refraction Fluctuations Induced in Turbulent Flows

    NASA Technical Reports Server (NTRS)

    Lading, Lars; Saffman, Mark; Edwards, Robert

    1996-01-01

    Induced phase screen scattering is defined as scatter light from a weak index of refraction fluctuations induced by turbulence. The basic assumptions and requirements for induced phase screen scattering, including scale requirements, are presented.

  7. Bubble mass center and fluid feedback force fluctuations activated by constant lateral impulse with variable thrust

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    Sloshing dynamics within a partially filled rotating dewar of superfluid helium 2 are investigated in response to constant lateral impulse with variable thrust. The study, including how the rotating bubble of superfluid helium 2 reacts to the constant impulse with variable time period of thrust action in microgravity, how amplitudes of bubble mass center fluctuates with growth and decay of disturbances, and how fluid feedback forces fluctuates in activating on the rotating dewar through the dynamics of sloshing waves are investigated. The numerical computation of sloshing dynamics is based on the non-inertial frame spacecraft bound coordinate with lateral impulses actuating on the rotating dewar in both inertial and non-inertial frames of thrust. Results of the simulations are illustrated.

  8. Measurement on the Fluid Forces Induced by Rotor-Stator Interaction in a Centrifugal Pump

    NASA Astrophysics Data System (ADS)

    Guo, Shijie; Okamoto, Hidenobu; Maruta, Yoshiyuki

    The pressure fluctuations and the radial fluid forces induced by rotor-stator interaction in a centrifugal pump were measured and their relationship was investigated. Experiments were done for various guide vanes, flow rates, and rotating speeds. It was demonstrated that both the blade pressure fluctuations and the volute static pressures are non-uniform circumferentially (not axisymmetric) under off-design operating conditions and that the two have a strong relationship. At high flow rates, the interaction-induced blade pressure fluctuations are large in areas where the volute static pressure is low. The propagating directions of the pressure fluctuations, the whirling directions of the radial fluid forces acting on the impeller and the dominant frequency components of both the fluctuations and the fluid forces are discussed. When measuring the fluid forces in the rotating frame, other frequency components, in addition to those related to the products of the number of guide vanes and the rotating frequency, may occur due to the circumferential unevenness of the pressure fluctuations.

  9. Characterization of base pressure fluctuations in a blunt trailing edge wake with three-dimensional forcing

    NASA Astrophysics Data System (ADS)

    Clark, Heather; Lavoie, Philippe

    2015-11-01

    The wakes of many nominally two-dimensional bluff bodies exhibit multiple intrinsic three-dimensional instabilities whose spatiotemporal structure and growth rate depend on geometry and Reynolds number. Here, these features are investigated experimentally for a blunt trailing edge profiled body using simultaneous measurements of velocity and fluctuating surface pressure on the model rear face near separation. Passive three-dimensional forcing of the wake is implemented with an array of vortex generators that are distributed according to the characteristic spanwise wavelength of the dominant secondary instability. For a Reynolds number of 8000 based on model thickness, the control strategy is found to increase the base pressure coefficient by 26% while globally reducing the amplitude of base pressure fluctuations, relative to the unforced flow. Additionally, amplitude modulation of the pressure signals that is observed in the natural wake decreases in strength with distributed forcing as a result of the modified three-dimensional flow structure. The spanwise distribution of pressure will be further examined for the baseline and controlled flows via temporal spectral analysis and spatial modal decomposition.

  10. Fluctuations-induced coexistence in public goods dynamics

    NASA Astrophysics Data System (ADS)

    Behar, H.; Brenner, N.; Ariel, G.; Louzoun, Y.

    2016-10-01

    Cooperative interactions between individuals in a population and their stability properties are central to population dynamics and evolution. We introduce a generic class of nonlinear dynamical systems describing such interactions between producers and non-producers of a rapidly equilibrating common resource extracted from a finite environment. In the deterministic mean field approximation, fast-growing non-producers drive the entire population to extinction. However, the presence of arbitrarily small perturbations destabilizes this fixed point into a stochastic attractor where both phenotypes can survive. Phase space arguments and moment closure are used to characterize the attractor and show that its properties are not determined by the noise amplitude or boundary conditions, but rather it is stabilized by the stochastic nonlinear dynamics. Spatial Monte Carlo simulations with demographic fluctuations and diffusion illustrate a similar effect, supporting the validity of the two-dimensional stochastic differential equation as an approximation. The functional distribution of the noise emerges as the main factor determining the dynamical outcome. Noise resulting from diffusion between different regions, or additive noise, induce coexistence while multiplicative or local demographic noise do not alter the outcome of deterministic dynamics. The results are discussed in a general context of the effect of noise on phase space structure.

  11. Spin jam induced by quantum fluctuations in a frustrated magnet

    PubMed Central

    Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P.; Huang, Q.; Copley, John R. D.; Lee, Seung-Hun

    2015-01-01

    Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr3+ (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga3+ impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p>0.8) and a cluster spin glass for lower magnetic concentration (p<0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood. PMID:26324917

  12. Spin jam induced by quantum fluctuations in a frustrated magnet.

    PubMed

    Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P; Huang, Q; Copley, John R D; Lee, Seung-Hun

    2015-09-15

    Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood.

  13. Multifield measurement of magnetic fluctuation-induced particle flux in a high-temperature toroidal plasma

    NASA Astrophysics Data System (ADS)

    Lin, L.; Ding, W. X.; Brower, D. L.

    2016-12-01

    Magnetic fluctuation-induced particle transport is explored in the high-temperature, high-beta interior of the Madison symmetric torus (MST) reversed-field pinch by performing a multifield measurement of the correlated product of magnetic and density fluctuations associated with global resistive tearing modes. Local density fluctuations are obtained by inverting the line-integrated interferometry data after resolving the mode helicity through correlation techniques. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of Faraday-effect polarimetry measurements. Reconstructed 2D images of density and current density perturbations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particle transport flux and its spatial distribution are resolved. The convective magnetic fluctuation-induced particle flux profile is measured for both standard and high-performance plasmas in MST with tokamak-like confinement, showing large reduction in the flux during improved confinement.

  14. Estimating Transmissivity from the Water Level Fluctuations of a Sinusoidally Forced Well

    USGS Publications Warehouse

    Mehnert, E.; Valocchi, A.J.; Heidari, M.; Kapoor, S.G.; Kumar, P.

    1999-01-01

    The water levels in wells are known to fluctuate in response to earth tides and changes in atmospheric pressure. These water level fluctuations can be analyzed to estimate transmissivity (T). A new method to estimate transmissivity, which assumes that the atmospheric pressure varies in a sinusoidal fashion, is presented. Data analysis for this simplified method involves using a set of type curves and estimating the ratio of the amplitudes of the well response over the atmospheric pressure. Type curves for this new method were generated based on a model for ground water flow between the well and aquifer developed by Cooper et al. (1965). Data analysis with this method confirmed these published results: (1) the amplitude ratio is a function of transmissivity, the well radius, and the frequency of the sinusoidal oscillation; and (2) the amplitude ratio is a weak function of storativity. Compared to other methods, the developed method involves simpler, more intuitive data analysis and allows shorter data sets to be analyzed. The effect of noise on estimating the amplitude ratio was evaluated and found to be more significant at lower T. For aquifers with low T, noise was shown to mask the water level fluctuations induced by atmospheric pressure changes. In addition, reducing the length of the data series did not affect the estimate of T, but the variance of the estimate was higher for the shorter series of noisy data.

  15. Spectroscopic observation of fluctuation-induced dynamo in the edge of the reversed-field pinch.

    PubMed

    Fontana, P W; Den Hartog, D J; Fiksel, G; Prager, S C

    2000-07-17

    The fluctuation-induced dynamo has been investigated by direct measurement of v and b in the edge of a reversed-field pinch and is found to be significant in balancing Ohm's law. The velocity fluctuations producing the dynamo emf have poloidal mode number m = 0, consistent with MHD calculations and in contrast with the core m = 1 dynamo. The velocity fluctuations exhibit the parity relative to their resonant surface predicted by linear MHD theory.

  16. Developments of the theory of spin fluctuations and spin fluctuation-induced superconductivity

    PubMed Central

    Moriya, Tôru

    2006-01-01

    Theory of spin fluctuations as developed in the past 30 years have played important roles in the theory of magnetism in metals, particularly in elucidating the properties around the magnetic instability or quantum critical points. Recently the theory has been extended to deal with the spin fluctuaion-mediated superconductivity with anisotropic order parameters in strongly correlated electron systems. These theoretical developments are briefly reviewed and the high temperature superconductivity of cuprates and organic and heavy electron superconductors are discussed in the light of these theories. PMID:25792765

  17. Orbital forced sea level fluctuations during the Middle Eocene (ODP site 1172, East Tasman Plateau)

    NASA Astrophysics Data System (ADS)

    Warnaar, J.; Stickley, C.; Jovane, L.; Roehl, U.; Brinkhuis, H.; Visscher, H.

    2004-12-01

    Ocean Drilling Program leg 189 was undertaken to test and refine the hypothesis (by Kennett et al., 1975), that the reconfiguration of continents around Antarctica (e.g.: the opening of the Tasmanian Gateway and Drake passage) led to the onset of the Antarctic Circumpolar Current that, in turn, would cause thermal isolation and hence cooling of Antarctica. This would possibly even cause global cooling, as suggested by the 33.3 Ma Oi1 event. The cores of leg 189, site 1172 on the eastern side of the Tasmanian Gateway provided a nearly complete succession of Eocene and Oligocene sediments. Cyclostratigraphic analysis based on XRF derived Ca and Fe records indicates distinct Milankovitch cyclicity between 40 and 36 Ma. (Röhl et al, in press). In the core-section representing magnetochron 18n-1n, the Ca record shows precession cycles in combination with obliquity, suggested to reflect sea level fluctuations (Röhl et al, in press). New datasets include microfossil data (organic-walled dinoflagellate cysts, pollen/spores and diatoms), loss-on-ignition measurements, magnetic data (environmental magnetics - ARM). Here, we aim to further investigate the proposed relationship between astronomical forcing and sea-level fluctuations. Additionally, we aim to obtain insight in the palaeoecology of the distinct endemic circum-Antarctic late Middle to Late Eocene dinoflagellate cyst assemblages. Results corroborate the concept that the cyclicity recorded by Ca and Fe measurements is the result of sea-level fluctuations. This implies that during late Middle Eocene times, astronomical forcing has modulated sea level - most likely through Antarctic ice buildup and meltdown. In turn, this would indicate the presence of significant, though probably modest, ice masses already ~40 Ma ago, well before the onset of the Antarctic Circumpolar Current. Kennett, J. P., R. E. Houtz, et al. (1975). Development of the circum-Antarctic current. Science 186: 144-147. Röhl, U.; H. Brinkhuis, C

  18. Syringe-pump-induced fluctuation in all-aqueous microfluidic system implications for flow rate accuracy.

    PubMed

    Li, Zida; Mak, Sze Yi; Sauret, Alban; Shum, Ho Cheung

    2014-02-21

    We report a new method to display the minute fluctuations induced by syringe pumps on microfluidic flows by using a liquid-liquid system with an ultralow interfacial tension. We demonstrate that the stepper motor inside the pump is a source of fluctuations in microfluidic flows by comparing the frequencies of the ripples observed at the interface to that of the pulsation of the stepper motor. We also quantify the fluctuations induced at different flow rates, using syringes of different diameters, and using different syringe pumps with different advancing distances per step. Our work provides a way to predict the frequency of the fluctuation that the driving syringe pump induces on a microfluidic system and suggests that syringe pumps can be a source of fluctuations in microfluidic flows, thus contributing to the polydispersity of the resulting droplets.

  19. Nonmonotoic fluctuation-induced interactions between dielectric slabs carrying charge disorder

    NASA Astrophysics Data System (ADS)

    Sarabadani, Jalal; Naji, Ali; Dean, David S.; Horgan, Ron R.; Podgornik, Rudolf

    2010-11-01

    We investigate the effect of monopolar charge disorder on the classical fluctuation-induced interactions between randomly charged net-neutral dielectric slabs and discuss various generalizations of recent results [A. Naji et al., Phys. Rev. Lett. 104, 060601 (2010)] to highly inhomogeneous dielectric systems with and without statistical disorder correlations. We shall focus on the specific case of two generally dissimilar plane-parallel slabs, which interact across vacuum or an arbitrary intervening dielectric medium. Monopolar charge disorder is considered to be present on the bounding surfaces and/or in the bulk of the slabs, may be in general quenched or annealed and may possess a finite lateral correlation length reflecting possible "patchiness" of the random charge distribution. In the case of quenched disorder, the bulk disorder is shown to give rise to an additive long-range contribution to the total force, which decays as the inverse distance between the slabs and may be attractive or repulsive depending on the dielectric constants of the slabs. By contrast, the force induced by annealed disorder in general combines with the underlying van der Waals forces in a nonadditive fashion, and the net force decays as an inverse cube law at large separations. We show, however, that in the case of two dissimilar slabs, the net effect due to the interplay between the disorder-induced and the pure van der Waals interactions can lead to a variety of unusual nonmonotonic interaction profiles between the dielectric slabs. In particular, when the intervening medium has a larger dielectric constant than the two slabs, we find that the net interaction can become repulsive and exhibit a potential barrier, while the underlying van der Waals force is attractive. On the contrary, when the intervening medium has a dielectric constant between that of the two slabs, the net interaction can become attractive and exhibit a free energy minimum, while the pure van der Waals force is

  20. Effective cosmological constant induced by stochastic fluctuations of Newton's constant

    NASA Astrophysics Data System (ADS)

    de Cesare, Marco; Lizzi, Fedele; Sakellariadou, Mairi

    2016-09-01

    We consider implications of the microscopic dynamics of spacetime for the evolution of cosmological models. We argue that quantum geometry effects may lead to stochastic fluctuations of the gravitational constant, which is thus considered as a macroscopic effective dynamical quantity. Consistency with Riemannian geometry entails the presence of a time-dependent dark energy term in the modified field equations, which can be expressed in terms of the dynamical gravitational constant. We suggest that the late-time accelerated expansion of the Universe may be ascribed to quantum fluctuations in the geometry of spacetime rather than the vacuum energy from the matter sector.

  1. Low frequency modes and instability analysis in non-thermal dusty magnetoplasma considering dust charge fluctuation and polarization force

    NASA Astrophysics Data System (ADS)

    Sharma, Prerana; Jain, Shweta; Patidar, Archana

    2017-01-01

    The effect of non-thermal ion population on self-gravitational instability of magnetized dusty plasma considering electrons are in Maxwell-Boltzmann distribution has been investigated. The dust dynamics is described including polarization force, thermal velocity, and charge fluctuation dust. The modified general dispersion relation has been derived including non-thermal ion population, polarization force, and dust charge fluctuation for self-gravitating dusty plasma system, using the normal mode analysis method. The obtained general dispersion relation is discussed in parallel and perpendicular modes of propagation. The population of non-thermal ion, polarization force and dust charge fluctuation affect the self-gravitational instability criteria in both the modes of propagation while the magnetic field affects the instability criterion only in perpendicular mode of propagation. The domains of instability has been discussed analytically to signify the importance of considered parameters. The stability of the self-gravitating dusty plasma system has been analyzed using Routh-Hurwitz stability criterion. Numerical calculations have been performed to analyze the effects of non-thermal ion population, polarization force, and dust charge fluctuation on the growth rate of self-gravitational instability. The results of the present work can be useful in self-gravitating dusty plasma found in space and the interstellar medium such as the interstellar molecular clouds where non-thermally distributed ions are the species of the plasma matter.

  2. Fluctuation-induced pair density wave in itinerant ferromagnets

    NASA Astrophysics Data System (ADS)

    Conduit, G. J.; Pedder, C. J.; Green, A. G.

    2013-03-01

    Magnetic fluctuations near to quantum criticality can have profound effects. They lead to characteristic scaling at high temperature which may ultimately give way to a reconstruction of the phase diagram and the formation of new phases at low temperatures. The ferromagnet UGe2 is unstable to p-wave superconducting order—an effect presaged by the superfluidity in 3He—whereas in CeFePO fluctuations drive the formation of spiral magnetic order. Here we develop a general quantum order-by-disorder description of these systems that encompasses both of these instabilities within a unified framework. This allows us to demonstrate that in fact these instabilities intertwine to form a pair density wave.

  3. Star polymers rupture induced by constant forces.

    PubMed

    García, N A; Febbo, M; Vega, D A; Milchev, A

    2014-10-28

    In this work, we study the breakage process of an unknotted three-arm star-shaped polymer when it is pulled from its free ends by a constant force. The star polymer configuration is described through an array of monomers coupled by anharmonic bonds, while the rupture process is tracked in three-dimensional space by means of Langevin Molecular Dynamics simulations. The interaction between monomers is described by a Morse potential, while a Weeks-Chandler-Anderson energetic contribution accounts for the excluded volume interaction. We explore the effect of the molecular architecture on the distributions of rupture times over a broad interval of pulling forces and star configurations. It was found that the rupture time distribution of the individual star arms is strongly affected by the star configuration imposed by the pulling forces and the length of the arms. We also observed that for large pulling forces the rupture time distributions resemble the dominant features observed for linear polymer chains. The model introduced here provides the basic ingredients to describe the effects of tensile forces on stress-induced degradation of branched macromolecules and polymer networks.

  4. Calibration of Atmospherically Induced Delay Fluctuations Due to Water Vapor

    NASA Technical Reports Server (NTRS)

    Resch, George; Jacobs, Christopher; Keihm, Steve; Lanyi, Gabor; Naudet, Charles; Riley, Abraham; Rosenberger, Hans; Tanner, Alan

    2000-01-01

    We have completed a new generation of water vapor radiometers (WVR), the A- series, in order to support radio science experiments with the Cassini spacecraft. These new instruments sense three frequencies in the vicinity of the 22 GHz emission line of atmospheric water vapor within a 1 degree beamwidth from a clear aperture antenna that is co-pointed with the radio telescope down to 10 degree elevation. The radiometer electronics features almost an order of magnitude improvement in temperature stability compared with earlier WVR designs. For many radio science experiments, the error budget is likely to be dominated by path delay fluctuations due to variable atmospheric water vapor along the line-of-sight to the spacecraft. In order to demonstrate the performance of these new WVRs we are attempting to calibrate the delay fluctuations as seen by a radio interferometer operating over a 21 km baseline with a WVR near each antenna. The characteristics of these new WVRs will be described and the results of our preliminary analysis will be presented indicating an accuracy of 0.2 to 0.5 mm in tracking path delay fluctuations over time scales of 10 to 10,000 seconds.

  5. Force Spectroscopy with Dual-Trap Optical Tweezers: Molecular Stiffness Measurements and Coupled Fluctuations Analysis

    PubMed Central

    Ribezzi-Crivellari, M.; Ritort, F.

    2012-01-01

    Dual-trap optical tweezers are often used in high-resolution measurements in single-molecule biophysics. Such measurements can be hindered by the presence of extraneous noise sources, the most prominent of which is the coupling of fluctuations along different spatial directions, which may affect any optical tweezers setup. In this article, we analyze, both from the theoretical and the experimental points of view, the most common source for these couplings in dual-trap optical-tweezers setups: the misalignment of traps and tether. We give criteria to distinguish different kinds of misalignment, to estimate their quantitative relevance and to include them in the data analysis. The experimental data is obtained in a, to our knowledge, novel dual-trap optical-tweezers setup that directly measures forces. In the case in which misalignment is negligible, we provide a method to measure the stiffness of traps and tether based on variance analysis. This method can be seen as a calibration technique valid beyond the linear trap region. Our analysis is then employed to measure the persistence length of dsDNA tethers of three different lengths spanning two orders of magnitude. The effective persistence length of such tethers is shown to decrease with the contour length, in accordance with previous studies. PMID:23199920

  6. Prediction of fluctuating pressure environments associated with plume-induced separated flow fields

    NASA Technical Reports Server (NTRS)

    Plotkin, K. J.

    1973-01-01

    The separated flow environment induced by underexpanded rocket plumes during boost phase of rocket vehicles has been investigated. A simple semi-empirical model for predicting the extent of separation was developed. This model offers considerable computational economy as compared to other schemes reported in the literature, and has been shown to be in good agreement with limited flight data. The unsteady pressure field in plume-induced separated regions was investigated. It was found that fluctuations differed from those for a rigid flare only at low frequencies. The major difference between plume-induced separation and flare-induced separation was shown to be an increase in shock oscillation distance for the plume case. The prediction schemes were applied to PRR shuttle launch configuration. It was found that fluctuating pressures from plume-induced separation are not as severe as for other fluctuating environments at the critical flight condition of maximum dynamic pressure.

  7. AMBER-DYES: Characterization of Charge Fluctuations and Force Field Parameterization of Fluorescent Dyes for Molecular Dynamics Simulations.

    PubMed

    Graen, Timo; Hoefling, Martin; Grubmüller, Helmut

    2014-12-09

    Recent advances in single molecule fluorescence experiments and theory allow a direct comparison and improved interpretation of experiment and simulation. To this end, force fields for a larger number of dyes are required which are compatible with and can be integrated into existing biomolecular force fields. Here, we developed, characterized, and implemented AMBER-DYES, a modular fluorescent label force field, for a set of 22 fluorescent dyes and their linkers from the Alexa, Atto, and Cy families, which are in common use for single molecule spectroscopy experiments. The force field is compatible with the AMBER protein force fields and the GROMACS molecular dynamics simulation program. The high electronic polarizability of the delocalized π-electron orbitals, as found in many fluorescent dyes, poses a particular challenge to point charge based force fields such as AMBER. To quantify the charge fluctuations due to the electronic polarizability, we simulated the 22 dyes in explicit solvent and sampled the charge fluctuations using QM/MM simulations at the B3LYP/6-31G*//TIP3P level of theory. The analysis of the simulations enabled us to derive ensemble fitted RESP charges from the solvated charge distributions of multiple trajectories. We observed broad, single peaked charge distributions for the conjugated ring atoms with well-defined mean values. The charge fitting procedure was validated against published charges of the dyelike amino acid tryptophan, which showed good agreement with existing tryptophan parameters from the AMBER, CHARMM, and OPLS force field families. A principal component analysis of the charge fluctuations revealed that a small number of collective coordinates suffices to describe most of the in-plane dye polarizability. The AMBER-DYES force field allows the rapid preparation of all atom molecular dynamics simulations of fluorescent systems for state of the art multi microsecond trajectories.

  8. Characterization of syringe-pump-driven induced pressure fluctuations in elastic microchannels.

    PubMed

    Zeng, Wen; Jacobi, Ian; Beck, David J; Li, Songjing; Stone, Howard A

    2015-02-21

    We study pressure and flow-rate fluctuations in microchannels, where the flow rate is supplied by a syringe pump. We demonstrate that the pressure fluctuations are induced by the flow-rate fluctuations coming from mechanical oscillations of the pump motor. Also, we provide a mathematical model of the effect of the frequency of the pump on the normalized amplitude of pressure fluctuations and introduce a dimensionless parameter incorporating pump frequency, channel geometry and mechanical properties that can be used to predict the performance of different microfluidic device configurations. The normalized amplitude of pressure fluctuations decreases as the frequency of the pump increases and the elasticity of the channel material decreases. The mathematical model is verified experimentally over a range of typical operating conditions and possible applications are discussed.

  9. Spectroscopic Observation of Fluctuation-Induced Dynamo in the Edge of the Reversed-Field Pinch

    SciTech Connect

    Fontana, P. W.; Den Hartog, D. J.; Fiksel, G.; Prager, S. C.

    2000-07-17

    The fluctuation-induced dynamo has been investigated by direct measurement of v(tilde sign) and b(tilde sign) in the edge of a reversed-field pinch and is found to be significant in balancing Ohm's law. The velocity fluctuations producing the dynamo emf have poloidal mode number m=0 , consistent with MHD calculations and in contrast with the core m=1 dynamo. The velocity fluctuations exhibit the parity relative to their resonant surface predicted by linear MHD theory. (c) 2000 The American Physical Society.

  10. Transconductance fluctuations as a probe for interaction-induced quantum Hall states in graphene.

    PubMed

    Lee, Dong Su; Skákalová, Viera; Weitz, R Thomas; von Klitzing, Klaus; Smet, Jurgen H

    2012-08-03

    Transport measurements normally provide a macroscopic, averaged view of the sample so that disorder prevents the observation of fragile interaction-induced states. Here, we demonstrate that transconductance fluctuations in a graphene field effect transistor reflect charge localization phenomena on the nanometer scale due to the formation of a dot network which forms near incompressible quantum states. These fluctuations give access to fragile broken symmetry and fractional quantum Hall states even though these states remain hidden in conventional magnetotransport quantities.

  11. Force on a slow moving impurity due to thermal and quantum fluctuations in a 1D Bose-Einstein condensate

    SciTech Connect

    Roberts, David; Sykes, Andrew

    2009-01-01

    We study the drag force acting on an impurity moving through a 1D Bose-Einstein condensate in the presence of both quantum and thermal fluctuations. We are able to find exact analytical solutions of the partial differential equations to the level of the Bogoliubov approximation. At zero temperature, we find a nonzero force is exerted on the impurity at subcritical velocities, due to the scattering of quantum fluctuations. We make the following explicit assumptions: far from the impurity the system is in a quantum state given by that of a zero (or finite) temperature Bose-Einstein condensate, and the scattering process generates only causally related reflection/transmission. The results raise unanswered questions in the quantum dynamics associated with the formation of persistent currents.

  12. Density Fluctuation Induced Kinetic Dynamo and Tearing Mode Nonlinear Saturation in the MST Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Ding, Weixing; Lin, Liang; Duff, J. R.; Brower, D. L.; Sarff, J. S.

    2014-10-01

    In the MST reversed field pinch (RFP), the evolution of core tearing mode nonlinear evolution is partially determined by the electron current density profile along with nonlinear interactions among multiple tearing modes. Density fluctuations driven by intrinsic magnetic perturbations are usually large, approximately 1%, in RFP plasmas. These density fluctuations can modify the current density profile via the kinetic dynamo effect, defined as the correlated product of parallel electron pressure and radial magnetic field fluctuations, which alters the temporal dynamics of tearing modes in MST. A component of the kinetic dynamo originating from the correlated product of density and radial magnetic fluctuations has been measured using a high-speed, low phase noise polarimetry-interferometry diagnostic. Between sawtooth crashes it is found that the measured kinetic dynamo has finite amplitude that generates an anti-dynamo in the plasma core, which would tend to flatten the current density profile. These measurements suggest that density fluctuations passively driven by magnetic fluctuations can actively alter tearing modes via fluctuation-induced current transport. Work supported by US DOE and NSF.

  13. Puerarin may protect against Schwann cell damage induced by glucose fluctuation.

    PubMed

    Xue, Bing; Wang, Lin; Zhang, Zhe; Wang, Rui; Xia, Xin-Xin; Han, Ping-Ping; Cao, Li-Jun; Liu, Yong-Hui; Sun, Lian-Qing

    2017-02-08

    Puerarin is one of the major active ingredients in Gegen, a traditional Chinese herb that has been reported to have a wide variety of beneficial pharmacology functions. Previous studies have implicated that the damaging effects of hyperglycemia resulting from oxidative stress and glucose fluctuation may be more dangerous than constant high glucose in the development of diabetes-related complications. The present study focuses on the effects of puerarin on glucose fluctuation-induced oxidative stress-induced Schwann cell (SC) apoptosis in vitro. Primarily cultured SCs were exposed to different conditions and the effect of puerarin on cell viability was determined by MTT assays. Intracellular reactive oxygen species (ROS) generation and mitochondrial transmembrane potential were detected by flow cytometry analysis. Apoptosis was confirmed by the Annexin V-FITC/PI and TUNEL method. Quantitative real-time reverse transcriptase polymerase chain reaction was performed to analyze the expression levels of bax and bcl-2. Western blot was performed to analyze the expression levels of some important transcription factors and proteins. The results showed that incubating SCs with intermittent high glucose for 48 h decreased cell viability and increased the number of apoptotic cells whereas treating with puerarin protected SCs against glucose fluctuation-induced cell damage. Further study demonstrated that puerarin suppressed activation of apoptosis-related proteins including PARP and caspase-3, downregulation of bcl-2, and upregulation of intracellular distribution of bax from cytosol to mitochondria, which was induced by glucose fluctuation. Moreover, puerarin inhibited the elevation of intracellular ROS and mitochondrial depolarization induced by glucose fluctuation. These results suggest that puerarin may protect SCs against glucose fluctuation-induced cell injury through inhibiting apoptosis as well as oxidative stress.

  14. Numerical study on the partitioning of the molecular polarizability into fluctuating charge and induced atomic dipole contributions

    SciTech Connect

    Mei, Ye; Simmonett, Andrew C.; Pickard, IV, Frank C.; DiStasio, Jr., Robert A.; Brooks, Bernard R.; Shao, Yihan

    2015-05-06

    In order to carry out a detailed analysis of the molecular static polarizability, which is the response of the molecule to a uniform external electric field, the molecular polarizability was computed in this study using the finite-difference method for 21 small molecules, using density functional theory. Within nine charge population schemes (Lowdin, Mulliken, Becke, Hirshfeld, CM5, Hirshfeld-I, NPA, CHELPG, MK-ESP) in common use, the charge fluctuation contribution is found to dominate the molecular polarizability, with its ratio ranging from 59.9% with the Hirshfeld or CM5 scheme to 96.2% with the Mulliken scheme. The Hirshfeld-I scheme is also used to compute the other contribution to the molecular polarizability coming from the induced atomic dipoles, and the atomic polarizabilities in eight small molecules and water pentamer are found to be highly anisotropic for most atoms. In conclusion, the overall results suggest that (a) more emphasis probably should be placed on the charge fluctuation terms in future polarizable force field development and (b) an anisotropic polarizability might be more suitable than an isotropic one in polarizable force fields based entirely or partially on the induced atomic dipoles.

  15. Numerical Study on the Partitioning of the Molecular Polarizability into Fluctuating Charge and Induced Atomic Dipole Contributions

    PubMed Central

    Mei, Ye; Simmonett, Andrew C.; Pickard, Frank C.; DiStasio, Robert A.; Brooks, Bernard R.; Shao, Yihan

    2015-01-01

    In order to carry out a detailed analysis of the molecular static polarizability, which is the response of the molecule to a uniform external electric field, the molecular polarizability was computed using the finite-difference method for 21 small molecules, using density functional theory. Within nine charge population schemes (Löwdin, Mulliken, Becke, Hirshfeld, CM5, Hirshfeld-I, NPA, CHELPG, MK-ESP) in common use, the charge fluctuation contribution is found to dominate the molecular polarizability, with its ratio ranging from 59.9% with the Hirshfeld or CM5 scheme to 96.2% with the Mulliken scheme. The Hirshfeld-I scheme is also used to compute the other contribution to the molecular polarizability coming from the induced atomic dipoles, and the atomic polarizabilities in 8 small molecules and water pentamer are found to be highly anisotropic for most atoms. Overall, the results suggest that (a) more emphasis probably should be placed on the charge fluctuation terms in future polarizable force field development; (b) an anisotropic polarizability might be more suitable than an isotropic one in polarizable force fields based entirely or partially on the induced atomic dipoles. PMID:25945749

  16. Numerical study on the partitioning of the molecular polarizability into fluctuating charge and induced atomic dipole contributions

    DOE PAGES

    Mei, Ye; Simmonett, Andrew C.; Pickard, IV, Frank C.; ...

    2015-05-06

    In order to carry out a detailed analysis of the molecular static polarizability, which is the response of the molecule to a uniform external electric field, the molecular polarizability was computed in this study using the finite-difference method for 21 small molecules, using density functional theory. Within nine charge population schemes (Lowdin, Mulliken, Becke, Hirshfeld, CM5, Hirshfeld-I, NPA, CHELPG, MK-ESP) in common use, the charge fluctuation contribution is found to dominate the molecular polarizability, with its ratio ranging from 59.9% with the Hirshfeld or CM5 scheme to 96.2% with the Mulliken scheme. The Hirshfeld-I scheme is also used to computemore » the other contribution to the molecular polarizability coming from the induced atomic dipoles, and the atomic polarizabilities in eight small molecules and water pentamer are found to be highly anisotropic for most atoms. In conclusion, the overall results suggest that (a) more emphasis probably should be placed on the charge fluctuation terms in future polarizable force field development and (b) an anisotropic polarizability might be more suitable than an isotropic one in polarizable force fields based entirely or partially on the induced atomic dipoles.« less

  17. Decoherence induced by a fluctuating Aharonov-Casher phase

    SciTech Connect

    Lombardo, Fernando C.; Mazzitelli, Francisco D.; Villar, Paula I.

    2005-10-15

    Dipole interference is studied when atomic systems are coupled to classical electromagnetic fields. The interaction between the dipoles and the classical fields induces a time-varying Aharonov-Casher phase. Averaging over the phase generates a suppression of fringe visibility in the interference pattern. We show that, for suitable experimental conditions, the loss of contrast for dipoles can be observable and almost as large as the corresponding one for coherent electrons. We analyze different trajectories in order to show the dependence of the decoherence factor with the velocity of the particles.

  18. Current-induced forces in mesoscopic systems: A scattering-matrix approach.

    PubMed

    Bode, Niels; Kusminskiy, Silvia Viola; Egger, Reinhold; von Oppen, Felix

    2012-01-01

    Nanoelectromechanical systems are characterized by an intimate connection between electronic and mechanical degrees of freedom. Due to the nanoscopic scale, current flowing through the system noticeably impacts upons the vibrational dynamics of the device, complementing the effect of the vibrational modes on the electronic dynamics. We employ the scattering-matrix approach to quantum transport in order to develop a unified theory of nanoelectromechanical systems out of equilibrium. For a slow mechanical mode the current can be obtained from the Landauer-Büttiker formula in the strictly adiabatic limit. The leading correction to the adiabatic limit reduces to Brouwer's formula for the current of a quantum pump in the absence of a bias voltage. The principal results of the present paper are the scattering-matrix expressions for the current-induced forces acting on the mechanical degrees of freedom. These forces control the Langevin dynamics of the mechanical modes. Specifically, we derive expressions for the (typically nonconservative) mean force, for the (possibly negative) damping force, an effective "Lorentz" force that exists even for time-reversal-invariant systems, and the fluctuating Langevin force originating from Nyquist and shot noise of the current flow. We apply our general formalism to several simple models that illustrate the peculiar nature of the current-induced forces. Specifically, we find that in out-of-equilibrium situations the current-induced forces can destabilize the mechanical vibrations and cause limit-cycle dynamics.

  19. A stochastic mechanism for signal propagation in the brain: Force of rapid random fluctuations in membrane potentials of individual neurons.

    PubMed

    Hong, Dawei; Man, Shushuang; Martin, Joseph V

    2016-01-21

    There are two functionally important factors in signal propagation in a brain structural network: the very first synaptic delay-a time delay about 1ms-from the moment when signals originate to the moment when observation on the signal propagation can begin; and rapid random fluctuations in membrane potentials of every individual neuron in the network at a timescale of microseconds. We provide a stochastic analysis of signal propagation in a general setting. The analysis shows that the two factors together result in a stochastic mechanism for the signal propagation as described below. A brain structural network is not a rigid circuit rather a very flexible framework that guides signals to propagate but does not guarantee success of the signal propagation. In such a framework, with the very first synaptic delay, rapid random fluctuations in every individual neuron in the network cause an "alter-and-concentrate effect" that almost surely forces signals to successfully propagate. By the stochastic mechanism we provide analytic evidence for the existence of a force behind signal propagation in a brain structural network caused by rapid random fluctuations in every individual neuron in the network at a timescale of microseconds with a time delay of 1ms.

  20. Inducer Hydrodynamic Forces in a Cavitating Environment

    NASA Technical Reports Server (NTRS)

    Skelley, Stephen E.

    2004-01-01

    Marshall Space Flight Center has developed and demonstrated a measurement device for sensing and resolving the hydrodynamic loads on fluid machinery. The device - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining the amplitude and frequency content associated with operating in various cavitation modes. The rotating balance was calibrated statically using a dead-weight load system in order to generate the 6 x 12 calibration matrix later used to convert measured voltages to engineering units. Structural modeling suggested that the rotating assembly first bending mode would be significantly reduced with the balance s inclusion. This reduction in structural stiffness was later confirmed experimentally with a hammer-impact test. This effect, coupled with the relatively large damping associated with the rotating balance waterproofing material, limited the device s bandwidth to approximately 50 Hertz Other pre-test validations included sensing the test article rotating assembly built-in imbalance for two configurations and directly measuring the assembly mass and buoyancy while submerged under water. Both tests matched predictions and confirmed the device s sensitivity while stationary and rotating. The rotating balance was then demonstrated in a water test of a full-scale Space Shuttle Main Engine high-pressure liquid oxygen pump inducer. Experimental data was collected a scaled operating conditions at three flow coefficients across a range of cavitation numbers for the single inducer geometry and radial clearance. Two distinct cavitation modes were observed symmetric tip vortex cavitation and alternate-blade cavitation. Although previous experimental tests on the same inducer demonstrated two additional

  1. New spreading law of thin film liquids controlled by gravity and vdW forces under thermal fluctuations

    NASA Astrophysics Data System (ADS)

    Nesic, Svetozar; Cuerno Rejado, Rodolfo; Moro Egido, Esteban

    2013-11-01

    It has been shown that, in the regime controlled by surface tension, the spreading dynamics of a thin viscous fluid droplet changes significantly when it is subjected to thermal fluctuations. Technically, this has been accomplished through the incorporation of appropriate stochastic terms into the standard lubrication equation. In practice, it leads to a modification of the classic Tanner's law for spreading, with implications for Micro and Nanofluidic systems. We have recently found a new law of spreading for the same kind of systems, but in the gravity-dominated regime. Moreover, in the deteministic case a finite contact angle is formed when a van der Waals attractive force is introduced to the system and we show that there is a slight change in contact angle when thermal fluctuations are taken into account. Ph.D student and a member of GISC (http://matematicas.uc3m.es/index.php/gisc).

  2. Protein Denaturants at Aqueous–Hydrophobic Interfaces: Self-Consistent Correlation between Induced Interfacial Fluctuations and Denaturant Stability at the Interface

    PubMed Central

    2015-01-01

    The notion of direct interaction between denaturing cosolvent and protein residues has been proposed in dialogue relevant to molecular mechanisms of protein denaturation. Here we consider the correlation between free energetic stability and induced fluctuations of an aqueous–hydrophobic interface between a model hydrophobically associating protein, HFBII, and two common protein denaturants, guanidinium cation (Gdm+) and urea. We compute potentials of mean force along an order parameter that brings the solute molecule close to the known hydrophobic region of the protein. We assess potentials of mean force for different relative orientations between the protein and denaturant molecule. We find that in both cases of guanidinium cation and urea relative orientations of the denaturant molecule that are parallel to the local protein–water interface exhibit greater stability compared to edge-on or perpendicular orientations. This behavior has been observed for guanidinium/methylguanidinium cations at the liquid–vapor interface of water, and thus the present results further corroborate earlier findings. Further analysis of the induced fluctuations of the aqueous–hydrophobic interface upon approach of the denaturant molecule indicates that the parallel orientation, displaying a greater stability at the interface, also induces larger fluctuations of the interface compared to the perpendicular orientations. The correlation of interfacial stability and induced interface fluctuation is a recurring theme for interface-stable solutes at hydrophobic interfaces. Moreover, observed correlations between interface stability and induced fluctuations recapitulate connections to local hydration structure and patterns around solutes as evidenced by experiment (Cooper et al., J. Phys. Chem. A2014, 118, 5657.) and high-level ab initio/DFT calculations (Baer et al., Faraday Discuss2013, 160, 89). PMID:25536388

  3. Electrostatic potential fluctuation induced by charge discreteness in a nanoscale trench

    SciTech Connect

    Lee, Taesang; Kim, S. S.; Jho, Y. S.; Park, Gunyoung; Chang, C. S.

    2007-10-15

    A simplified two-dimensional Monte Carlo simulation is performed to estimate the charging potential fluctuations caused by strong binary Coulomb interactions between discrete charged particles in nanometer scale trenches. It is found that the discrete charge effect can be an important part of the nanoscale trench research, inducing scattering of ion trajectories in a nanoscale trench by a fluctuating electric field. The effect can enhance the ion deposition on the side walls and disperse the material contact energy of the incident ions, among others.

  4. Photo-induced conductance fluctuations in mesoscopic Ge/Si systems with quantum dots

    SciTech Connect

    Stepina, N. P.; Dvurechenskii, A. V.; Nikiforov, A. I.; Moers, J.; Gruetzmacher, D.

    2014-08-20

    We study the evolution of electron transport in strongly localized mesoscopic system with quantum dots under small photon flux. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photo-induced fluctuations on the light intensity and the step-like response of conductance on the pulse excitation. The effect of the light wavelength, measurement temperature, size of the conductive channel on the device efficiency are considered.

  5. Shock induced ignition and DDT in the presence of mechanically driven fluctuations

    NASA Astrophysics Data System (ADS)

    Wang, Wentian; McDonald, James G.; Radulescu, Matei I.

    2015-11-01

    The present study addresses the problem of shock induced ignition and transition to detonation in the presence of mechanical and thermal fluctuations. These departures from a homogeneous medium are of significant importance in practical situations, where such fluctuations may promote hot-spot ignition and favor the flame transition to detonation. The problem is studied in 1D, where a piston-induced shock ignites the gas. The fluctuations in the shock-compressed medium are controlled by allowing the piston's speed to oscillate around a mean, with controllable frequency and amplitude. A Lagrangian numerical formulation is used, which allows to treat exactly the transient boundary condition at the piston head. The hydrodynamic solver is coupled with the reactive dynamics of the gas using Cantera. The code was verified by comparison with steady state ZND solutions and previous shock induced ignition results in homogeneous media. Results obtained for different fuels illustrate the strong relation of the DDT amplification length to mechanical fluctuations in systems with a high effective activation energy and fast rate of energy deposition, consistent with experiments performed on fast flame acceleration in the presence of strong mechanical perturbations. Financial support from NSERC and Shell, with A. Pekalski and M. Levin as technical monitors, are greatly acknowledged.

  6. Fluctuations induced extinction and stochastic resonance effect in a model of tumor growth with periodic treatment

    NASA Astrophysics Data System (ADS)

    Li, Dongxi; Xu, Wei; Guo, Yongfeng; Xu, Yong

    2011-01-01

    We investigate a stochastic model of tumor growth derived from the catalytic Michaelis-Menten reaction with positional and environmental fluctuations under subthreshold periodic treatment. Firstly, the influences of environmental fluctuations on the treatable stage are analyzed numerically. Applying the standard theory of stochastic resonance derived from the two-state approach, we derive the signal-to-noise ratio (SNR) analytically, which is used to measure the stochastic resonance phenomenon. It is found that the weak environmental fluctuations could induce the extinction of tumor cells in the subthreshold periodic treatment. The positional stability is better in favor of the treatment of the tumor cells. Besides, the appropriate and feasible treatment intensity and the treatment cycle should be highlighted considered in the treatment of tumor cells.

  7. Force fluctuations while pressing and moving against high- and low-friction touch screen surfaces.

    PubMed

    Joshi, Mukta N; Keenan, Kevin G

    2016-07-01

    The purpose of this study was to identify the influence of a high- and low-friction surface on the ability to maintain a steady downward force during an index finger pressing and moving task. Fifteen right-handed subjects (24-48 years) performed a static force pressing task and a hybrid pressing and moving task on the surface of an iPad mini while holding a steady 2-N force on high- and low-friction surfaces. Variability of force was quantified as the standard deviation (SD) of normal force (F z) and shear force (F xy) across friction conditions and tasks. The SD of F z was 227 % greater during the hybrid task as compared to the static task (p < .001) and was 19 % greater for the high- versus low-friction condition (p = .033). There were positive correlations between SD of F z and F xy during the hybrid force/motion tasks on the high- and low-friction conditions (r (2) = 0.5 and 0.86, respectively), suggesting significant associations between normal and shear forces for this hybrid task. The correlation between the SD of F z for static and hybrid tasks was r (2) = 0.44, indicating that the common practice of examining the control of static tasks may not sufficiently explain performance during hybrid tasks, at least for the young subjects tested in the current study. As activities of daily living frequently require hybrid force/motion tasks (e.g., writing, doing the dishes, and cleaning counters), the results of this study emphasize the need to study motor performance during hybrid tasks in addition to static force tasks.

  8. Including Thermal Fluctuations in Actomyosin Stable States Increases the Predicted Force per Motor and Macroscopic Efficiency in Muscle Modelling.

    PubMed

    Marcucci, Lorenzo; Washio, Takumi; Yanagida, Toshio

    2016-09-01

    Muscle contractions are generated by cyclical interactions of myosin heads with actin filaments to form the actomyosin complex. To simulate actomyosin complex stable states, mathematical models usually define an energy landscape with a corresponding number of wells. The jumps between these wells are defined through rate constants. Almost all previous models assign these wells an infinite sharpness by imposing a relatively simple expression for the detailed balance, i.e., the ratio of the rate constants depends exponentially on the sole myosin elastic energy. Physically, this assumption corresponds to neglecting thermal fluctuations in the actomyosin complex stable states. By comparing three mathematical models, we examine the extent to which this hypothesis affects muscle model predictions at the single cross-bridge, single fiber, and organ levels in a ceteris paribus analysis. We show that including fluctuations in stable states allows the lever arm of the myosin to easily and dynamically explore all possible minima in the energy landscape, generating several backward and forward jumps between states during the lifetime of the actomyosin complex, whereas the infinitely sharp minima case is characterized by fewer jumps between states. Moreover, the analysis predicts that thermal fluctuations enable a more efficient contraction mechanism, in which a higher force is sustained by fewer attached cross-bridges.

  9. Including Thermal Fluctuations in Actomyosin Stable States Increases the Predicted Force per Motor and Macroscopic Efficiency in Muscle Modelling

    PubMed Central

    2016-01-01

    Muscle contractions are generated by cyclical interactions of myosin heads with actin filaments to form the actomyosin complex. To simulate actomyosin complex stable states, mathematical models usually define an energy landscape with a corresponding number of wells. The jumps between these wells are defined through rate constants. Almost all previous models assign these wells an infinite sharpness by imposing a relatively simple expression for the detailed balance, i.e., the ratio of the rate constants depends exponentially on the sole myosin elastic energy. Physically, this assumption corresponds to neglecting thermal fluctuations in the actomyosin complex stable states. By comparing three mathematical models, we examine the extent to which this hypothesis affects muscle model predictions at the single cross-bridge, single fiber, and organ levels in a ceteris paribus analysis. We show that including fluctuations in stable states allows the lever arm of the myosin to easily and dynamically explore all possible minima in the energy landscape, generating several backward and forward jumps between states during the lifetime of the actomyosin complex, whereas the infinitely sharp minima case is characterized by fewer jumps between states. Moreover, the analysis predicts that thermal fluctuations enable a more efficient contraction mechanism, in which a higher force is sustained by fewer attached cross-bridges. PMID:27626630

  10. Retinal Changes Induced by Epiretinal Tangential Forces

    PubMed Central

    Romano, Mario R.; Comune, Chiara; Ferrara, Mariantonia; Cennamo, Gilda; De Cillà, Stefano; Toto, Lisa; Cennamo, Giovanni

    2015-01-01

    Two kinds of forces are active in vitreoretinal traction diseases: tangential and anterior-posterior forces. However, tangential forces are less characterized and classified in literature compared to the anterior-posterior ones. Tangential epiretinal forces are mainly due to anomalous posterior vitreous detachment (PVD), vitreoschisis, vitreopapillary adhesion (VPA), and epiretinal membranes (ERMs). Anomalous PVD plays a key role in the formation of the tangential vectorial forces on the retinal surface as consequence of gel liquefaction (synchysis) without sufficient and fast vitreous dehiscence at the vitreoretinal interface. The anomalous and persistent adherence of the posterior hyaloid to the retina can lead to vitreomacular/vitreopapillary adhesion or to a formation of avascular fibrocellular tissue (ERM) resulting from the proliferation and transdifferentiation of hyalocytes resident in the cortical vitreous remnants after vitreoschisis. The right interpretation of the forces involved in the epiretinal tangential tractions helps in a better definition of diagnosis, progression, prognosis, and surgical outcomes of vitreomacular interfaces. PMID:26421183

  11. Current-induced forces: a simple derivation

    NASA Astrophysics Data System (ADS)

    Todorov, Tchavdar N.; Dundas, Daniel; Lü, Jing-Tao; Brandbyge, Mads; Hedegård, Per

    2014-11-01

    We revisit the problem of forces on atoms under current in nanoscale conductors. We derive and discuss the five principal kinds of force under steady-state conditions from a simple standpoint that—with the help of background literature—should be accessible to physics undergraduates. The discussion aims at combining methodology with an emphasis on the underlying physics through examples. We discuss and compare two forces present only under current—the non-conservative electron wind force and a Lorentz-like velocity-dependent force. It is shown that in metallic nanowires both display significant features at the wire surface, making it a candidate for the nucleation of current-driven structural transformations and failure. Finally we discuss the problem of force noise and the limitations of Ehrenfest dynamics.

  12. Piston slap induced pressure fluctuation in the water coolant passage of an internal combustion engine

    NASA Astrophysics Data System (ADS)

    Ohta, Kazuhide; Wang, Xiaoyu; Saeki, Atsushi

    2016-02-01

    Liner cavitation is caused by water pressure fluctuation in the water coolant passage (WCP). When the negative pressure falls below the saturated vapor pressure, the impulsive pressure following the implosion of cavitation bubbles causes cavitation erosion of the wet cylinder liner surface. The present work establishes a numerical model for structural-acoustic coupling between the crankcase and the acoustic field in the WCP considering their dynamic characteristics. The coupling effect is evaluated through mutual interaction terms that are calculated from the mode shapes of the acoustic field and of the crankcase vibration on the boundary. Water pressure fluctuations in the WCP under the action of piston slap forces are predicted and the contributions of the uncoupled mode shapes of the crankcase and the acoustic field to the pressure waveform are analyzed. The influence of sound speed variations on the water pressure response is discussed, as well as the pressure on the thrust sides of the four cylinders.

  13. Homotopy Perturbation Method-Based Analytical Solution for Tide-Induced Groundwater Fluctuations.

    PubMed

    Munusamy, Selva Balaji; Dhar, Anirban

    2016-05-01

    The groundwater variations in unconfined aquifers are governed by the nonlinear Boussinesq's equation. Analytical solution for groundwater fluctuations in coastal aquifers under tidal forcing can be solved using perturbation methods. However, the perturbation parameters should be properly selected and predefined for traditional perturbation methods. In this study, a new dimensional, higher-order analytical solution for groundwater fluctuations is proposed by using the homotopy perturbation method with a virtual perturbation parameter. Parameter-expansion method is used to remove the secular terms generated during the solution process. The solution does not require any predefined perturbation parameter and valid for higher values of amplitude parameter A/D, where A is the amplitude of the tide and D is the aquifer thickness.

  14. Fluctuation-induced transport of two coupled particles: Effect of the interparticle interaction

    NASA Astrophysics Data System (ADS)

    Makhnovskii, Yurii A.; Rozenbaum, Viktor M.; Sheu, Sheh-Yi; Yang, Dah-Yen; Trakhtenberg, Leonid I.; Lin, Sheng Hsien

    2014-06-01

    We consider a system of two coupled particles fluctuating between two states, with different interparticle interaction potentials and particle friction coefficients. An external action drives the interstate transitions that induces reciprocating motion along the internal coordinate x (the interparticle distance). The system moves unidirectionally due to rectification of the internal motion by asymmetric friction fluctuations and thus operates as a dimeric motor that converts input energy into net movement. We focus on how the law of interaction between the particles affects the dimer transport and, in particular, the role of thermal noise in the motion inducing mechanism. It is argued that if the interaction potential behaves at large distances as xα, depending on the value of the exponent α, the thermal noise plays a constructive (α > 2), neutral (α = 2), or destructive (α < 2) role. In the case of α = 1, corresponding piecewise linear potential profiles, an exact solution is obtained and discussed in detail.

  15. Fluctuation-Induced Particle Transport and Density Relaxation in a Stochastic Magnetic Field

    NASA Astrophysics Data System (ADS)

    Brower, David L.

    2009-11-01

    Particle transport and density relaxation associated with electromagnetic fluctuations is an unresolved problem of long standing in plasma physics and magnetic fusion research. In toroidal fusion plasmas, magnetic field fluctuations can arise spontaneously from global MHD instabilities, e.g., tearing fluctuations associated with sawtooth oscillations. Resonant magnetic perturbations (RMP) have also been externally imposed to mitigate the effect of edge localized modes (ELMs) by locally enhancing edge transport in Tokamaks. Understanding stochastic-field-driven transport processes is thus not only of basic science interest but possibly critical to ELM control in ITER. We report on the first direct measurement of magnetic fluctuation-induced particle transport in the core of a high-temperature plasma, the MST reversed field pinch. Measurements focus on the sawtooth crash, when the stochastic field resulting from tearing reconnection is strongest, and are accomplished using newly developed, laser-based, differential interferometry and Faraday rotation techniques. The measured electron particle flux, resulting from the correlated product of electron density (δn) and radial magnetic fluctuations (δbr), accounts for density profile relaxation during these magnetic reconnection events. Surprisingly, the electron diffusion is 30 times larger than estimates of ambipolarity-constrained transport in a stochastic magnetic field. A significant ion flux associated with parallel ion flow velocity fluctuations (δvi,//) correlated with δbr appears responsible for transport larger than predictions from the quasi-linear test particle model. These results indicate the need for improved understanding of particle transport in a stochastic magnetic field. Work performed in collaboration with W.X. Ding, W.F. Bergerson, T.F. Yates, UCLA; D.J. Den Hartog, G. Fiksel, S.C. Prager, J.S. Sarff and the MST Group, University of Wisconsin-Madison.

  16. Memory effect in the upper bound of the heat flux induced by quantum fluctuations

    NASA Astrophysics Data System (ADS)

    Koide, T.

    2016-10-01

    Thermodynamic behaviors in a quantum Brownian motion coupled to a classical heat bath is studied. We then define a heat operator by generalizing the stochastic energetics and show the energy balance (first law) and the upper bound of the expectation value of the heat operator (second law). We further find that this upper bound depends on the memory effect induced by quantum fluctuations and hence the maximum extractable work can be qualitatively modified in quantum thermodynamics.

  17. Memory effect in the upper bound of the heat flux induced by quantum fluctuations.

    PubMed

    Koide, T

    2016-10-01

    Thermodynamic behaviors in a quantum Brownian motion coupled to a classical heat bath is studied. We then define a heat operator by generalizing the stochastic energetics and show the energy balance (first law) and the upper bound of the expectation value of the heat operator (second law). We further find that this upper bound depends on the memory effect induced by quantum fluctuations and hence the maximum extractable work can be qualitatively modified in quantum thermodynamics.

  18. Critical Casimir force and its fluctuations in lattice spin models: exact and Monte Carlo results.

    PubMed

    Dantchev, Daniel; Krech, Michael

    2004-04-01

    We present general arguments and construct a stress tensor operator for finite lattice spin models. The average value of this operator gives the Casimir force of the system close to the bulk critical temperature T(c). We verify our arguments via exact results for the force in the two-dimensional Ising model, d -dimensional Gaussian, and mean spherical model with 2force F(C) in a slab geometry confining a critical substance in-between is k(b) TD(T) (A/ a(d-1) )(1/2), where A is the surface area of the plates, a is the lattice spacing, and D(T) is a slowly varying nonuniversal function of the temperature T. The numerical calculations demonstrate that at the critical temperature T(c) the force possesses a Gaussian distribution centered at the mean value of the force = k(b) T(c) (d-1)Delta/ (L/a)(d), where L is the distance between the plates and Delta is the (universal) Casimir amplitude.

  19. QED vacuum fluctuations and induced electric dipole moment of the neutron

    SciTech Connect

    Dominguez, C. A.; Falomir, H.; Ipinza, M.; Loewe, M.; Kohler, S.; Rojas, J. C.

    2009-08-01

    Quantum fluctuations in the QED vacuum generate nonlinear effects, such as peculiar induced electromagnetic fields. In particular, we show here that an electrically neutral particle, possessing a magnetic dipole moment, develops an induced electric dipole-type moment with unusual angular dependence, when immersed in a quasistatic, constant external electric field. The calculation of this effect is done in the framework of the Euler-Heisenberg effective QED Lagrangian, corresponding to the weak field asymptotic expansion of the effective action to one-loop order. It is argued that the neutron might be a good candidate to probe this signal of nonlinearity in QED.

  20. Transcription upregulation via force-induced direct stretching of chromatin

    NASA Astrophysics Data System (ADS)

    Tajik, Arash; Zhang, Yuejin; Wei, Fuxiang; Sun, Jian; Jia, Qiong; Zhou, Wenwen; Singh, Rishi; Khanna, Nimish; Belmont, Andrew S.; Wang, Ning

    2016-12-01

    Mechanical forces play critical roles in the function of living cells. However, the underlying mechanisms of how forces influence nuclear events remain elusive. Here, we show that chromatin deformation as well as force-induced transcription of a green fluorescent protein (GFP)-tagged bacterial-chromosome dihydrofolate reductase (DHFR) transgene can be visualized in a living cell by using three-dimensional magnetic twisting cytometry to apply local stresses on the cell surface via an Arg-Gly-Asp-coated magnetic bead. Chromatin stretching depended on loading direction. DHFR transcription upregulation was sensitive to load direction and proportional to the magnitude of chromatin stretching. Disrupting filamentous actin or inhibiting actomyosin contraction abrogated or attenuated force-induced DHFR transcription, whereas activating endogenous contraction upregulated force-induced DHFR transcription. Our findings suggest that local stresses applied to integrins propagate from the tensed actin cytoskeleton to the LINC complex and then through lamina-chromatin interactions to directly stretch chromatin and upregulate transcription.

  1. Blade Section Design of Marine Propellers with Minimum Cavitation Induced Pressure Fluctuations

    NASA Astrophysics Data System (ADS)

    Zeng, Zhibo; Kuiper, Gert

    2015-12-01

    To minimize cavitation induced pressure fluctuations by marine propellers with minimum efficiency loss, the paper presents a new design and optimization method using a blade section design method. The sheet cavity volume variation on a two-dimensional blade section in quasi-steady condition has been simplified to a relation with only a limited number of non-dimensional parameters. This results in a fast prediction method of the cavity volume of a blade section passing a wake peak, using a pre-calculated database. This makes optimization feasible. The optimization method was applied to the propeller of a container ship. Extensive tests in a towing tank and a cavitation channel validated the reduction of pressure fluctuations: 33% reduction in the first blade frequency amplitude and 18% reduction in the second blade frequency amplitude, with the same open water efficiency.

  2. Stochastic transport in the presence of spatial disorder: Fluctuation-induced corrections to homogenization

    NASA Astrophysics Data System (ADS)

    Russell, Matthew J.; Jensen, Oliver E.; Galla, Tobias

    2016-10-01

    Motivated by uncertainty quantification in natural transport systems, we investigate an individual-based transport process involving particles undergoing a random walk along a line of point sinks whose strengths are themselves independent random variables. We assume particles are removed from the system via first-order kinetics. We analyze the system using a hierarchy of approaches when the sinks are sparsely distributed, including a stochastic homogenization approximation that yields explicit predictions for the extrinsic disorder in the stationary state due to sink strength fluctuations. The extrinsic noise induces long-range spatial correlations in the particle concentration, unlike fluctuations due to the intrinsic noise alone. Additionally, the mean concentration profile, averaged over both intrinsic and extrinsic noise, is elevated compared with the corresponding profile from a uniform sink distribution, showing that the classical homogenization approximation can be a biased estimator of the true mean.

  3. Fluctuation-induced shear flow and energy transfer in plasma interchange turbulence

    SciTech Connect

    Li, B.; Sun, C. K.; Wang, X. Y.; Zhou, A.; Wang, X. G.; Ernst, D. R.

    2015-11-15

    Fluctuation-induced E × B shear flow and energy transfer for plasma interchange turbulence are examined in a flux-driven system with both closed and open magnetic field lines. The nonlinear evolution of interchange turbulence shows the presence of two confinement regimes characterized by low and high E × B flow shear. In the first regime, the large-scale turbulent convection is dominant and the mean E × B shear flow is at a relatively low level. By increasing the heat flux above a certain threshold, the increased turbulent intensity gives rise to the transfer of energy from fluctuations to mean E × B flows. As a result, a transition to the second regime occurs, in which a strong mean E × B shear flow is generated.

  4. Gravity effects on Soret-induced non-equilibrium fluctuations in ternary mixtures.

    PubMed

    Martínez Pancorbo, Pablo; Ortiz de Zárate, José M; Bataller, Henri; Croccolo, Fabrizio

    2017-02-01

    We discuss the gravity effects on the dynamics of composition fluctuations in a ternary mixture around the non-equilibrium quiescent state induced by thermodiffusion when subjected to a stationary temperature gradient. We found that the autocorrelation matrix of concentration fluctuations can be expressed as the sum of two exponentially decaying concentration modes. Without accounting for confinement, we obtained exact analytical expressions for the two decay rates which, as a consequence of gravity, display a wave-number-dependent mixing. The stability of the quiescent solution is also examined, as a function of the two solutal Rayleigh numbers used to express the decay rates. After having discussed the dynamics of the two concentration modes, we calculate the corresponding amplitudes. Consequences for optical experiments are discussed.

  5. Motor Proteins as Nanomachines: The Roles of Thermal Fluctuations in Generating Force and Motion

    NASA Astrophysics Data System (ADS)

    Howard, Jonathon

    Motor proteins are enzymes that convert chemical energy derived from the hydrolysis of a small molecule called ATP into mechanical work used to power directed movement along cytoskeletal filaments inside cells. Motor proteins have essential biological functions such as driving the contraction of muscle, the beating of sperm and cilia, and the transport of intracellular cargoes. Motor proteins are also interesting from a physical point of view because they do what no man-made engines do: they transduce chemical energy directly to mechanical work without using heat or electrical energy as an intermediate. A central issue in the mechanism of this chemomechanical transduction by motor proteins concerns the roles played by thermal fluctuations, diffusion and Brownian motion. In this lecture I discuss several molecular models for motor proteins, including so-called ratchet models, and compare predictions of these models to experimental results for the microtubule-based motor protein kinesin. I argue that kinesin, which has two motor domains or "heads," walks using a "hand-over-hand" mechanism such that at least one head is bound to the microtubule. Diffusion likely plays an essential role by facilitating the search of the unbound head for the next binding site, a distance 8 nm away. During this diffusive phase, the bound head supports the load ensuring that forward motion can still take place even against loads up to several piconewtons.

  6. Flow-induced agitations create a granular fluid: effective viscosity and fluctuations.

    PubMed

    Nichol, Kiri; van Hecke, Martin

    2012-06-01

    We fluidize a granular medium with localized stirring in a split-bottom shear cell. We probe the mechanical response of quiescent regions far from the main flow by observing the vertical motion of cylindrical probes rising, sinking, and floating in the grains. First, we find that the probe motion suggests that the granular material behaves in a liquid-like manner: high-density probes sink and low-density probes float at the depth given by Archimedes' law. Second, we observe that the drag force on moving probes scales linearly with their velocity, which allows us to define an effective viscosity for the system. This effective viscosity is inversely proportional to the rotation rate of the disk which drives the split bottom flow. Moreover, the apparent viscosity depends on radius and mass of the probe: despite the linear dependence of the drag forces on sinking speed of the probe, the granular medium is not simply Newtonian, but exhibits a more complex rheology. The decrease of viscosity with filling height of the cell, combined with the poor correlation between local strain rate and viscosity, suggests that the fluid-like character of the material is set by agitations generated in the stirred region: the relation between applied stress and observed strain rate in one location depends on the strain rate in another location. We probe the nature of the granular fluctuations that we believe mediates these nonlocal interactions by characterizing the small and random up and down motion that the probe experiences. These Gaussian fluctuations exhibit a mix of diffusive and subdiffusive behavior at short times and saturate at a value of roughly 1/10th of a grain diameter longer times, consistent with the picture of a random walker in a potential well. The product of crossover time and effective viscosity is constant, evidencing a direct link between fluctuations and viscosity.

  7. Transient violations of the second law of thermodynamics in protein unfolding examined using synthetic atomic force microscopy and the fluctuation theorem.

    PubMed

    Paramore, Sterling; Ayton, Gary S; Voth, Gregory A

    2007-09-14

    The synthetic atomic force microscopy (AFM) method is developed to simulate a periodically replicated atomistic system subject to force and length fluctuations characteristic of an AFM experiment. This new method is used to examine the forced-extension and subsequent rupture of the alpha-helical linker connecting periodic images of a spectrin protein repeat unit. A two-dimensional potential of mean force (PMF) along the length and a reaction coordinate describing the state of the linker was calculated. This PMF reveals that the basic material properties of the spectrin repeat unit are sensitive to the state of linker, an important feature that cannot be accounted for in a one-dimensional PMF. Furthermore, nonequilibrium simulations were generated to examine the rupture event in the context of the fluctuation theorem. These atomistic simulations demonstrate that trajectories which are in apparent violation of the second law can overcome unfolding barriers at significantly reduced rupture forces.

  8. Geometry and Excitation Energy Fluctuations of NMA in Aqueous Solution with CHARMM, AMBER, OPLS, and GROMOS Force Fields: Implications for Protein Ultraviolet Spectra Simulation.

    PubMed

    Li, Zhenyu; Yu, Haibo; Zhuang, Wei; Mukamel, Shaul

    2008-02-04

    Molecular dynamics (MD) simulations are performed for N-methylamide (NMA) in water at 300 K with different force fields. Compared to the three all-atom force fields (CHARMM22, AMBER03, and OPLS-AA), the united-atom force field (GROMOS96) predicts a broader distribution of the peptide OCNH dehedral angle. A map constructed by fitting the npi* and pipi* transition energies as quadratic functions of the NMA geometric variables is used to simulate the excitation energy fluctuations. GROMOS96 predicts blue-shifted npi* and pipi* energies and stronger fluctuations compared to the other three force fields, which indicates that different force fields may predict different spectral lineshapes for proteins.

  9. Geometry and excitation energy fluctuations of NMA in aqueous solution with CHARMM, AMBER, OPLS, and GROMOS force fields: Implications for protein ultraviolet spectra simulation

    NASA Astrophysics Data System (ADS)

    Li, Zhenyu; Yu, Haibo; Zhuang, Wei; Mukamel, Shaul

    2008-02-01

    Molecular dynamics (MD) simulations are performed for N-methylacetamide (NMA) in water at 300 K with different force fields. Compared to the three all-atom force fields (CHARMM22, AMBER03, and OPLS-AA), the united-atom force field (GROMOS96) predicts a broader distribution of the peptide OCNH dehedral angle. A map constructed by fitting the nπ∗ and ππ∗ transition energies as quadratic functions of the NMA geometric variables is used to simulate the excitation energy fluctuations. GROMOS96 predicts blue shifted nπ∗ and ππ∗ energies and stronger fluctuations compared to the other three force fields, which indicates that different force fields may predict different spectral lineshapes for proteins.

  10. Orbitally Forced Climatic Fluctuations in Snowball Earth: Compelling Evidence from a Data-Model Study

    NASA Astrophysics Data System (ADS)

    Benn, D.; Fairchild, I. J.; Le Hir, G.; Fleming, E.; Ramstein, G.; Stevenson, C.; Donnadieu, Y.; Bao, H.; Hambrey, M.; Petronis, M. S.; Wynn, P.

    2014-12-01

    The Snowball Earth model provides a powerful conceptual framework for understanding the causes and demise of the extreme global glaciations that occurred during the Neoproterozoic, and can be refined through creative interactions between geological, geochemical and modeling studies. We present unequivocal evidence for oscillating glacier extent and varying hydrological conditions during the Marinoan, the second major Cryogenian glaciation (~650-635 Ma), from the Wilsonbreen Formation of NE Svalbard. Extensive exposures record (1) a possibly long arid periglacial phase; (2) multiple switches between subglacial, glaciolacustrine, carbonate lacustrine and non-glacial terrestrial deposition; and (3) rapid deglaciation. Oxygen and sulfur isotopes of sulfate in carbonate facies indicate persistently high pCO2 consistent with deposition of the Formation on a 105-year timescale. Using an ice sheet model (GRISLI) coupled to a General Circulation Model (LMDz), the response of the continental ice-sheet to insolation changes (i.e. orbital forcing) and pCO2 is investigated. We show that land-ice cover waxes and wanes over the course of a precession cycle for pCO2 levels from 0.01 to 0.05 bar. Growth and retreat of ice reflect shifts in the balance between precipitation and evaporation (P-E), in response to migration of the tropical Hadley Cell. In cold conditions (<0.01bar), the weakness of the hydrological cycle makes the system insensitive to precession changes, explaining relatively stable ice-sheets during the earlier stages of the Snowball Earth. With 0.01forcing) produces advances/retreats of the ice sheet in <10 kyr. With pCO2>0.05bar, the albedo effect is overcome and air temperatures rise in ice free regions in low latitudes and deglaciation occurs. The results show that the Snowball Earth model can be reconciled with evidence for prolonged, pulsed glacial deposition. The main, longest

  11. 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.

  12. Geometry-induced modification of fluctuation spectrum in quasi-two-dimensional condensates

    NASA Astrophysics Data System (ADS)

    Roy, Arko; Angom, D.

    2016-08-01

    We report the structural transformation of the low-lying spectral modes, especially the Kohn mode, from radial to circular topology as harmonic confining potential is modified to a toroidal one, and this corresponds to a transition from simply to multiply connected geometry. For this we employ the Hartree-Fock-Bogoliubov theory to examine the evolution of low energy quasiparticles. We, then, use the Hartree-Fock-Bogoliubov theory with the Popov approximation to demonstrate the two striking features of quantum and thermal fluctuations. At T = 0, the non-condensate density due to interaction induced quantum fluctuations increases with the transformation from pancake to toroidal geometry. The other feature is, there is a marked change in the density profile of the non-condensate density at finite temperatures with the modification of trapping potential. In particular, the condensate and non-condensate density distributions have overlapping maxima in the toroidal condensate, which is in stark contrast to the case of pancake geometry. The genesis of this difference lies in the nature of the thermal fluctuations.

  13. Mean and fluctuating components of drag and lift forces on an isolated finite-sized particle in turbulence

    NASA Astrophysics Data System (ADS)

    Kim, Jungwoo; Balachandar, S.

    2012-01-01

    We perform fully resolved direct numerical simulations of an isolated particle subjected to free-stream turbulence in order to investigate the effect of turbulence on the drag and lift forces at the level of a single particle, following Bagchi and Balachandar's work (Bagchi and Balachandar in Phys Fluids 15:3496-3513, 2003). The particle Reynolds numbers based on the mean relative particle velocity and the particle diameter are Re = 100, 250 and 350, which covers three different regimes of wake evolution in a uniform flow: steady axisymmetric wake, steady planar symmetric wake, and unsteady planar symmetric vortex shedding. At each particle Reynolds number, the turbulent intensity is 5-10% of the mean relative particle velocity, and the corresponding diameter of the particle is comparable to or larger than the Kolmogorov scale. The simulation results show that standard drag values determined from uniform flow simulations can accurately predict the drag force if the turbulence intensity is sufficiently weak (5% or less compared to the mean relative velocity). However, it is shown that for finite-sized particles, flow non-uniformity, which is usually neglected in the case of the small particles, can play an important role in determining the forces as the relative turbulence intensity becomes large. The influence of flow non-uniformity on drag force could be qualitatively similar to the Faxen correction. In addition, finite-sized particles at sufficient Reynolds number are inherently subjected to stochastic forces arising from their self-induced vortex shedding in addition to lift force arising from the local ambient flow properties (vorticity and strain rate). The effect of rotational and strain rate of the ambient turbulence seen by the particle on the lift force is explored based on the conditional averaging using the generalized representation of the quasi-steady force proposed by Bagchi and Balachandar (J Fluid Mech 481:105-148, 2003). From the present study, it

  14. Materials for damping the PTC-induced thermal fluctuations of the cold-head

    NASA Astrophysics Data System (ADS)

    Catarino, I.; Martins, D.; Sudiwala, R.

    2015-12-01

    The cold head on mechanical Pulse Tube Cryocoolers (PTCs) is subject to substantially less mechanical vibration and electromagnetic interference compared to that typically found in Gifford MacMahon coolers. However, thermal fluctuations at the PTC frequency are still present at the cold-head, typically at a level of 200 mK peak-to-peak at 1.4 Hz for a Cryomech Model PT405 cooler running at 4 K. It is highly desirable to damp out these fluctuations if PTCs are to be used successfully for running systems sensitive to such thermal fluctuations, for example, bolometeric detectors. We report here the characterization over the temperature range 2.5 K to 6 K of two materials, GOS (Gd2O2S) and GAP (GdAlO3), for use as low-pass thermal filters. These materials have antiferromagnetic transitions at around 4 K giving rise to an enhanced heat capacity and have a high thermal conductance. These are two highly desirable properties for thermal dampers in this application. Those materials were fired as ceramic discs to be tested as thermal dumpers. Thermal filter assemblies with discs of diameter 75 mm and thickness 2.5 mm and 1.6 mm (GOS and GAP, respectively) mounted in a PTC show thermal attenuation levels of x0.12 (GOS) and x0.11 (GAP) at 0.01Hz with a clean-side temperature of 4 K; the PTC induced fluctuations at 1.48 Hz are damped completely to within the noise limits (0.2 mK) of the thermometers. Experimentally determined thermal conductance and heat capacity data are reported. For this system, with a PTC cold-head (dirty-side) temperature of 3.3 K, a clean-side power dissipation of up to 30 mW is realized before its temperature rises above 4.2 K.

  15. Corticosterone influences forced swim-induced immobility.

    PubMed

    Báez, M; Volosin, M

    1994-11-01

    The effect of corticosterone (CS) synthesis inhibition with metyrapone-a blocker of the 11 beta-hydroxylase (150 mg/kg IP)-on immobility time during the forced swim test was recorded. Immobility time was measured during a 15-min forced swim (test). Twenty-four hours later rats were subjected to an additional 5 min forced swim (retest). In one experiment, metyrapone or vehicle was administered 3 h before the initial test, while CS (0, 5, 10, or 20 mg/kg SC) was administered 1 h prior to the initial test. Metyrapone significantly reduced immobility time during both test and retest. This effect was reverted in a dose-dependent fashion by CS. In a second experiment, animals exposed to the initial test 24 h before were injected with metyrapone or vehicle 3 h before the retest, while CS (0, 10, or 20 mg/kg SC) was administered 1 h prior the retest. Metyrapone, administered before the retest, reduced immobility time and CS partially reverted metyrapone effect. In another group of animals, serum CS concentrations were evaluated before and after test and retest. In vehicle groups, the high immobility time during test and retest was associated with high CS serum concentrations poststress. In animals receiving metyrapone prior to the initial test, the reduced immobility time was related to low levels of CS after the test and an attenuated secretion following the retest. Moreover, CS (20 mg/kg) and metyrapone+CS groups had high CS levels before the test, which remained high 2 h after the test, although after the retest, both groups showed a pattern of CS secretion similar to that observed in vehicle animals.(ABSTRACT TRUNCATED AT 250 WORDS)

  16. Visualization of thermally fluctuating surface structure in noncontact atomic-force microscopy and tip effects on fluctuation: theoretical study of Si(111)-(square root[3] x square root[3])-Ag surface.

    PubMed

    Sasaki, Naruo; Watanabe, Satoshi; Tsukada, Masaru

    2002-01-28

    We investigated noncontact atomic-force microscopy (NC-AFM) images of a thermally fluctuating surface structure together with tip effects based on the first-principles electronic state calculation. As an example the Si(111)-(square root[3] x square root[3])-Ag (square root[3]-Ag) surface is studied. We have succeeded in theoretically visualizing the thermal fluctuation of the square root[3]-Ag surface at room temperature, and in reproducing the observed NC-AFM image for the first time. Further, the pinning effect of the thermal fluctuation of the square root[3]-Ag surface by the tip is clarified, which shows a novel ability of NC-AFM to modify the surface structure.

  17. Measurement of laterally induced optical forces at the nanoscale

    NASA Astrophysics Data System (ADS)

    Huang, Fei; Tamma, Venkata Ananth; Rajaei, Mohsen; Almajhadi, Mohammad; Kumar Wickramasinghe, H.

    2017-02-01

    We demonstrate the measurement of laterally induced optical forces using an Atomic Force Microscope (AFM). The lateral electric field distribution between a gold coated AFM probe and a single nano-aperture in a gold film is mapped by measuring the lateral optical force between the apex of the AFM probe and the nano-aperture. The fundamental torsional eigen-mode of an AFM cantilever probe was used to detect the laterally induced optical forces. We engineered the cantilever shape using focused ion beam milling to improve the detected signal to noise ratio. The measured distributions of lateral optical force agree well with electromagnetic simulations of the metal coated AFM probe interacting with the nano-aperture. This technique can be extended to simultaneously detect both lateral and longitudinal optical forces at the nanoscale by using an AFM cantilever as a multi-channel detector. This will enable simultaneous Photon Induced Force Microscopy detection of molecular responses with different incident field polarizations. The technique can be implemented on both cantilever and tuning fork based AFMs.

  18. Locomotive and reptation motion induced by internal force and friction

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Hidetsugu; Ishihara, Taisuke

    2011-06-01

    We propose a simple mechanical model of locomotion induced by internal force and friction. We first construct a system of two elements as an analog of the bipedal motion. The internal force does not induce a directional motion by itself because of the action-reaction law, but a directional motion becomes possible by the control of the frictional force. The efficiency of these model systems is studied using an analogy to the heat engine. As a modified version of the two-element model, we construct a model that exhibits a bipedal motion similar to kinesin’s motion of molecular motor. Next, we propose a linear chain model and a ladder model as an extension of the original two-element model. We find a transition from a straight to a snake-like motion in a ladder model by changing the strength of the internal force.

  19. Force-induced tautomerization in a single molecule

    NASA Astrophysics Data System (ADS)

    Ladenthin, Janina N.; Frederiksen, Thomas; Persson, Mats; Sharp, John C.; Gawinkowski, Sylwester; Waluk, Jacek; Kumagai, Takashi

    2016-10-01

    Heat transfer, electrical potential and light energy are common ways to activate chemical reactions. Applied force is another way, but dedicated studies for such a mechanical activation are limited, and this activation is poorly understood at the single-molecule level. Here, we report force-induced tautomerization in a single porphycene molecule on a Cu(110) surface at 5 K, which is studied by scanning probe microscopy and density functional theory calculations. Force spectroscopy quantifies the force needed to trigger tautomerization with submolecular spatial resolution. The calculations show how the reaction pathway and barrier of tautomerization are modified in the presence of a copper tip and reveal the atomistic origin of the process. Moreover, we demonstrate that a chemically inert tip whose apex is terminated by a xenon atom cannot induce the reaction because of a weak interaction with porphycene and a strong relaxation of xenon on the tip as contact to the molecule is formed.

  20. Locomotive and reptation motion induced by internal force and friction.

    PubMed

    Sakaguchi, Hidetsugu; Ishihara, Taisuke

    2011-06-01

    We propose a simple mechanical model of locomotion induced by internal force and friction. We first construct a system of two elements as an analog of the bipedal motion. The internal force does not induce a directional motion by itself because of the action-reaction law, but a directional motion becomes possible by the control of the frictional force. The efficiency of these model systems is studied using an analogy to the heat engine. As a modified version of the two-element model, we construct a model that exhibits a bipedal motion similar to kinesin's motion of molecular motor. Next, we propose a linear chain model and a ladder model as an extension of the original two-element model. We find a transition from a straight to a snake-like motion in a ladder model by changing the strength of the internal force.

  1. Image reconstruction with acoustic radiation force induced shear waves

    NASA Astrophysics Data System (ADS)

    McAleavey, Stephen A.; Nightingale, Kathryn R.; Stutz, Deborah L.; Hsu, Stephen J.; Trahey, Gregg E.

    2003-05-01

    Acoustic radiation force may be used to induce localized displacements within tissue. This phenomenon is used in Acoustic Radiation Force Impulse Imaging (ARFI), where short bursts of ultrasound deliver an impulsive force to a small region. The application of this transient force launches shear waves which propagate normally to the ultrasound beam axis. Measurements of the displacements induced by the propagating shear wave allow reconstruction of the local shear modulus, by wave tracking and inversion techniques. Here we present in vitro, ex vivo and in vivo measurements and images of shear modulus. Data were obtained with a single transducer, a conventional ultrasound scanner and specialized pulse sequences. Young's modulus values of 4 kPa, 13 kPa and 14 kPa were observed for fat, breast fibroadenoma, and skin. Shear modulus anisotropy in beef muscle was observed.

  2. Light-Induced Pulling and Pushing by the Synergic Effect of Optical Force and Photophoretic Force

    NASA Astrophysics Data System (ADS)

    Lu, Jinsheng; Yang, Hangbo; Zhou, Lina; Yang, Yuanqing; Luo, Si; Li, Qiang; Qiu, Min

    2017-01-01

    Optical force, coming from momentum exchange during light-matter interactions, has been widely utilized to manipulate microscopic objects, though mostly in vacuum or in liquids. By contrast, due to the light-induced thermal effect, photophoretic force provides an alternative and effective way to transport light-absorbing particles in ambient gases. However, in most cases these forces work independently. Here, by employing the synergy of optical force and photophoretic force, we propose and experimentally demonstrate a configuration which can drive a micron-size metallic plate moving back and forth on a tapered fiber with supercontinuum light in ambient air. Optical pulling and oscillation of the metallic plate are experimentally realized. The results might open exhilarating possibilities in applications of optical driving and energy conversion.

  3. Thermal-induced force release in oxyhemoglobin

    PubMed Central

    Gevorkian, S. G.; Allahverdyan, A. E.; Gevorgyan, D. S.; Hu, Chin-Kun

    2015-01-01

    Oxygen is released to living tissues via conformational changes of hemoglobin from R-state (oxyhemoglobin) to T-state (desoxyhemoglobin). The detailed mechanism of this process is not yet fully understood. We have carried out micromechanical experiments on oxyhemoglobin crystals to determine the behavior of the Young’s modulus and the internal friction for temperatures between 20 °C and 70 °C. We have found that around 49 °C oxyhemoglobin crystal samples undergo a sudden and strong increase of their Young’s modulus, accompanied by a sudden decrease of the internal friction. This sudden mechanical change (and the ensuing force release) takes place in a partially unfolded state and precedes the full denaturation transition at higher temperatures. After this transformation, the hemoglobin crystals have the same mechanical properties as their initial state at room temperatures. We conjecture that it can be relevant for explaining the oxygen-releasing function of native oxyhemoglobin when the temperature is increased, e.g. due to active sport. The effect is specific for the quaternary structure of hemoglobin, and is absent for myoglobin with only one peptide sequence. PMID:26277901

  4. Effects of mixing-induced irradiance fluctuations on nitrogen uptake in size-fractionated coastal phytoplankton communities

    NASA Astrophysics Data System (ADS)

    Maguer, Jean-François; L'Helguen, Stéphane; Waeles, Matthieu

    2015-03-01

    In coastal waters subjected to strong tidal forcing, phytoplankton populations are exposed to highly variable light regimes. To grow under such fluctuating light environments, phytoplankton adjust their physiological properties. Here, we investigated nitrogen (N) uptake patterns in the western English Channel to determine whether phytoplankton modify their physiological processes involved in N uptake in response to changing irradiance conditions induced by spring-neap tidal cycles. Nitrate (NO3-) and ammonium (NH4+) uptake kinetics as a function of irradiance (VN-E curves) were assessed using 15N tracer techniques on two size fractions (<10 and >10 μm) of phytoplankton collected at 50% and 1% of surface irradiance during two spring-neap tidal cycles. Overall, the results showed that both small and large phytoplankton, whatever their vertical position in the water column, increased their maximum uptake capacity and their light utilization efficiency for the two N substrates following the decrease in vertical mixing intensity. Moreover, the improvement of irradiance conditions at neap tides was of greater benefit for the larger cells than for the smaller ones and was more favorable for NO3- uptake than for NH4+ uptake. These findings show that the light regime fluctuation resulting from the relaxation of tidal mixing during spring-neap tidal cycle leads to profound physiological adjustments of N uptake processes in phytoplankton communities. They suggest that the changes in NO3- uptake by large phytoplankton associated with the fortnightly spring-neap tidal cycle can account for most of the deviation in background productivity in the western English Channel which is based on NH4+ and is dominated by small cells. The dynamic light regime inherent to macrotidal coastal ecosystems could therefore determine, to a large extent, the importance of new vs. regenerated production as well as the size structure of the phytoplankton community.

  5. Wave-Induced Fluctuations in Underwater Light Field: Analysis of Data from RaDyO Experiments

    DTIC Science & Technology

    2011-09-30

    special instrument, an Underwater Porcupine Radiometer System, which provides a capability to measure wave-induced fluctuations in downward irradiance...fluctuations with the Porcupine system at various depths within the near-surface ocean, typically at depths from about 0.5 or 1 m to 10 m under sunny...conditions. Typical 10-min time-series obtained with the Porcupine system using the sampling frequency of 1 kHz includes 600,000 data points for each of

  6. Thermal gradient-induced forces on geodesic reference masses for LISA

    SciTech Connect

    Carbone, L.; Ciani, G.; Dolesi, R.; Hueller, M.; Tombolato, D.; Vitale, S.; Weber, W. J.; Cavalleri, A.

    2007-11-15

    The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodesic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the Laser Interferometer Space Antenna (LISA) gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensor that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the current LISA noise estimate, which assumes a maximum net force per degree of temperature difference of 100(pN/K) for the overall thermal gradient-induced effects.

  7. Probability distribution analysis of force induced unzipping of DNA

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Giri, Debaprasad

    2006-07-01

    We present a semimicroscopic model of dsDNA by incorporating the directional nature of hydrogen bond to describe the force induced unzipping transition. Using exact enumeration technique, we obtain the force-temperature and the force-extension curves and compare our results with the other models of dsDNA. The model proposed by us is rich enough to describe the basic mechanism of dsDNA unzipping and predicts the existence of an "eye phase." We show oscillations in the probability distribution function during unzipping. Effects of stacking energies on the melting profile have also been studied.

  8. Ion-specific induced fluctuations and free energetics of aqueous protein hydrophobic interfaces: toward connecting to specific-ion behaviors at aqueous liquid-vapor interfaces.

    PubMed

    Cui, Di; Ou, Shuching; Peters, Eric; Patel, Sandeep

    2014-05-01

    We explore anion-induced interface fluctuations near protein-water interfaces using coarse-grained representations of interfaces as proposed by Willard and Chandler ( J. Phys. Chem. B 2010 , 114 , 1954 - 1958 ). We use umbrella sampling molecular dynamics to compute potentials of mean force along a reaction coordinate bridging the state where the anion is fully solvated and one where it is biased via harmonic restraints to remain at the protein-water interface. Specifically, we focus on fluctuations of an interface between water and a hydrophobic region of hydrophobin-II (HFBII), a 71 amino acid residue protein expressed by filamentous fungi and known for its ability to form hydrophobically mediated self-assemblies at interfaces such as a water/air interface. We consider the anions chloride and iodide that have been shown previously by simulations as displaying specific-ion behaviors at aqueous liquid-vapor interfaces. We find that as in the case of a pure liquid-vapor interface, at the hydrophobic protein-water interface, the larger, less charge-dense iodide anion displays a marginal interfacial stability compared with that of the smaller, more charge-dense chloride anion. Furthermore, consistent with the results at aqueous liquid-vapor interfaces, we find that iodide induces larger fluctuations of the protein-water interface than chloride.

  9. Statistics of fluctuation induced transport in the scrape-off layer of Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Kube, Ralph; Garcia, Odd Erik; Theodorsen, Audun; Labombard, Brian; Terry, James

    2016-10-01

    The fluctuation induced transport in the scrape-off layer of Alcator C-Mod is investigated in an ohmically heated lower single-null discharge using Mirror Langmuir Probes. The probes are connected to a horizontal scanning probe which dwells at the outboard mid plane limiter radius and to electrodes in the outer divertor baffle. At the limiter radius the electron density, electron temperature and plasma potential are correlated with linear correlation coefficients r of approximately r=0.8. The bursts show a steep rise and a decay on a time scales of approximately 5 and 10 microseconds respectively. Amplitudes of bursts in the density, temperature, and plasma potential time series are correlated with r approximately 0.7-0.8. Conditionally averaged bursts in the radial particle and heat flux time series are less coherent and less reproducible, their amplitudes are correlated to the amplitude of bursts in the density time series with r=0.4. Statistics of the fluctuating plasma parameters at the outer divertor baffle are qualitatively similar to those at outboard midplane. Histograms, as well as statistics for level crossings and excess times spent above a given threshold for the time series compare favorably to a stochastic model for time series of scrape-off layer plasmas.

  10. Solvent induced conformational fluctuation of alanine dipeptide studied by using vibrational probes

    NASA Astrophysics Data System (ADS)

    Cai, Kaicong; Du, Fenfen; Liu, Jia; Su, Tingting

    2015-02-01

    The solvation effect on the three dimensional structure and the vibrational feature of alanine dipeptide (ALAD) was evaluated by applying the implicit solvents from polarizable continuum solvent model (PCM) through ab initio calculations, by using molecular dynamic (MD) simulations with explicit solvents, and by combining these two approaches. The implicit solvent induced potential energy fluctuations of ALAD in CHCl3, DMSO and H2O are revealed by means of ab initio calculations, and a global view of conformational and solvation environmental dependence of amide I frequencies is achieved. The results from MD simulations with explicit solvents show that ALAD trends to form PPII, αL, αR, and C5 in water, PPII and C5 in DMSO, and C5 in CHCl3, ordered by population, and the demonstration of the solvated structure, the solute-solvent interaction and hydrogen bonding is therefore enhanced. Representative ALAD-solvent clusters were sampled from MD trajectories and undergone ab initio calculations. The explicit solvents reveal the hydrogen bonding between ALAD and solvents, and the correlation between amide I frequencies and the Cdbnd O bond length is built. The implicit solvents applied to the ALAD-solvent clusters further compensate the solvation effect from the bulk, and thus enlarge the degree of structural distortion and the amide I frequency red shift. The combination of explicit solvent in the first hydration shell and implicit solvent in the bulk is helpful for our understanding about the conformational fluctuation of solvated polypeptides through vibrational probes.

  11. Solvent induced conformational fluctuation of alanine dipeptide studied by using vibrational probes.

    PubMed

    Cai, Kaicong; Du, Fenfen; Liu, Jia; Su, Tingting

    2015-02-25

    The solvation effect on the three dimensional structure and the vibrational feature of alanine dipeptide (ALAD) was evaluated by applying the implicit solvents from polarizable continuum solvent model (PCM) through ab initio calculations, by using molecular dynamic (MD) simulations with explicit solvents, and by combining these two approaches. The implicit solvent induced potential energy fluctuations of ALAD in CHCl3, DMSO and H2O are revealed by means of ab initio calculations, and a global view of conformational and solvation environmental dependence of amide I frequencies is achieved. The results from MD simulations with explicit solvents show that ALAD trends to form PPII, αL, αR, and C5 in water, PPII and C5 in DMSO, and C5 in CHCl3, ordered by population, and the demonstration of the solvated structure, the solute-solvent interaction and hydrogen bonding is therefore enhanced. Representative ALAD-solvent clusters were sampled from MD trajectories and undergone ab initio calculations. The explicit solvents reveal the hydrogen bonding between ALAD and solvents, and the correlation between amide I frequencies and the CO bond length is built. The implicit solvents applied to the ALAD-solvent clusters further compensate the solvation effect from the bulk, and thus enlarge the degree of structural distortion and the amide I frequency red shift. The combination of explicit solvent in the first hydration shell and implicit solvent in the bulk is helpful for our understanding about the conformational fluctuation of solvated polypeptides through vibrational probes.

  12. Quantum decoherence of a single ion qubit induced by photon-number fluctuations

    NASA Astrophysics Data System (ADS)

    Lee, Moonjoo; Friebe, Konstantin; Ong, Florian R.; Fioretto, Dario A.; Schüppert, Klemens; Blatt, Rainer; Northup, Tracy E.

    2016-09-01

    Quantum measurement is based on the interaction between a quantum object and a meter entangled with the object. While information about the object is being extracted by the interaction, the quantum fluctuations of the object are imprinted onto the meter as a form of decoherence. Here, we study the nondestructive reconstruction of the photon number in an optical cavity, harnessing the quantum decoherence. We consider a single 40Ca+ ion that is dispersively coupled to a high-finesse cavity. While the cavity is populated with weak coherent states, Ramsey spectroscopy is performed on the qubit transition to identify the shift and the broadening of the atomic energy levels. The shift is due to the ac Stark effect induced by cavity photons, and the broadening is attributed to the photon-number fluctuations of the cavity field. We show theoretically that photon-number distributions of the intracavity fields can be reconstructed in a basis of up to eleven Fock states with the maximum likelihood method. Furthermore, we show that the photon number of each polarization component can also be reconstructed, taking advantage of the rich energy-level structure of the ion. In combination with currently available mirror-coating technology, quantum non-demolition (QND) measurement of cavity photons will make it possible to create and manipulate nonclassical cavity-field states in the optical domain.

  13. Tip-bias-induced domain evolution in PMN-PT transparent ceramics via piezoresponse force microscopy

    NASA Astrophysics Data System (ADS)

    Zhao, K. Y.; Zhao, W.; Zeng, H. R.; Yu, H. Z.; Ruan, W.; Xu, K. Q.; Li, G. R.

    2015-05-01

    Piezoresponse force microscopy (PFM) was employed to investigate ferroelectric domain structures and their dynamic behavior of lead magnesium niobate-lead titanate [Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT)] transparent ceramics under an tip-bias-induced electric field. A remarkable effect of fluctuation of PT content on the domain configurations and domain dynamic response in PMN-PT transparent ferroelectric ceramics were found by PFM. Comparing with PMN-10%PT and PMN-20%PT, the reversed polarization of macrodomain area in PMN-35%PT and PMN-25%PT exhibits a relatively higher response behavior and better polarization retention performance under the PFM tip-bias-induced electric field, which correspond to their unique macroscopic electro-optic properties.

  14. Fluctuation analysis of nonselective cation currents induced by AIF complex in guinea-pig chromaffin cells.

    PubMed

    Inoue, M; Imanaga, I

    1996-11-11

    Properties of aluminium fluoride (AIF) complex-activated nonselective cation (NS) channels in guinea-pig chromaffin cells were investigated using the patch clamp technique. As the membrane potential was hyperpolarized from the holding potential of -55 mV, the AIF-induced nonselective cation current (INS) diminished progressively. With hyperpolarizations to -100 mV or more negative potentials, the AIF.INS almost instantaneously disappeared. The apparent unit conductance of AIF INS was estimated to be 3 pS by fluctuation analysis. The open state probability of AIF-activated NS channels became large with a decrease in concentration of free Mg2+ ions inside the cell and was less than 0.5 at 12 microM Mg2+. It is concluded that NS channels in the chromaffin cell apparently differ from those in smooth muscle cells.

  15. Quantum dots in InAs nanowires induced by surface potential fluctuations.

    PubMed

    Weis, Karl; Wirths, Stephan; Winden, Andreas; Sladek, Kamil; Hardtdegen, Hilde; Lüth, Hans; Grützmacher, Detlev; Schäpers, Thomas

    2014-04-04

    Back-gated InAs nanowire field-effect transistors are studied focusing on the formation of intrinsic quantum dots, i.e. dots not intentionally defined by electrodes. Such dots have been studied before, but the suggested explanations for their origin leave some open questions, which are addressed here. Stability diagrams of samples with different doping levels are recorded at electron temperatures below 200 mK, allowing us to estimate the number and size of the dots as well as the type of connection, i.e. in series or in parallel. We discuss several potential physical origins of the dots and conclude that they are most probably induced by potential fluctuations at the nanowire surface. Additionally, we show that via gate voltage and doping, the samples can be tuned to different regimes of Coulomb blockade.

  16. Glassiness and exotic entropy scaling induced by quantum fluctuations in a disorder-free frustrated magnet.

    PubMed

    Klich, I; Lee, S-H; Iida, K

    2014-04-01

    When spins are arranged in a lattice of triangular motif, the phenomenon of frustration leads to numerous energetically equivalent ground states, and results in exotic states such as spin liquid and spin ice. Here we report an alternative situation: a system, classically a liquid, freezes in the clean limit into a glassy state induced by quantum fluctuations. We call such glassy state a spin jam. The case in point is a frustrated magnet, where spins are arranged in a triangular network of bipyramids. Quantum corrections break the classical degeneracy into a set of aperiodic spin configurations forming local minima in a rugged energy landscape. This is established by mapping the problem into tiling with hexagonal tiles. The number of tessellations scales with the boundary length rather than its volume, showing the absence of local zero-energy modes. Low-temperature thermodynamics is discussed to compare it with other glassy materials.

  17. Transcription upregulation via force-induced direct stretching of chromatin

    PubMed Central

    Tajik, Arash; Zhang, Yuejin; Wei, Fuxiang; Sun, Jian; Jia, Qiong; Zhou, Wenwen; Singh, Rishi; Khanna, Nimish; Belmont, Andrew S.; Wang, Ning

    2016-01-01

    Mechanical forces play critical roles in the function of living cells. However, the underlying mechanisms of how forces influence nuclear events remain elusive. Here, we show that chromatin deformation as well as force-induced transcription of a green-fluorescent-protein (GFP) tagged bacterial-chromosome dihydrofolate reductase (DHFR) transgene can be visualized in a living cell by using three-dimensional magnetic twisting cytometry to apply local stresses on the cell surface via an Arg-Gly-Asp-coated magnetic bead. Chromatin stretching depended on loading direction. DHFR transcription upregulation was sensitive to load direction and proportional to the magnitude of chromatin stretching. Disrupting filamentous actin or inhibiting actomyosin contraction abrogated or attenuated force-induced DHFR transcription, whereas activating endogenous contraction upregulated force-induced DHFR transcription. Our findings suggest that local stresses applied to integrins propagate from the tensed actin cytoskeleton to the LINC complex and then through lamina-chromatin interactions to directly stretch chromatin and upregulate transcription. PMID:27548707

  18. Lorentz-force-induced motion in conductive media.

    PubMed

    Basford, Alexandra T; Basford, Jeffrey R; Kugel, Jennifer; Ehman, Richard L

    2005-06-01

    This project was designed to assess whether MRI imaging could detect Lorentz-force-induced motion in conductive samples. Experiments were performed by applying alternating voltages across 2% agar and 18% bovine gels placed in the field of a 1.5-T MRI scanner. Motion-sensitized time-gated MRI images that were obtained and analyzed with custom-developed software used in previous studies revealed the production of movement in both agar and gel samples. Motion was most pronounced in the plane vertical to the sample and had the greatest amplitude when the current path was perpendicular to the scanner's magnetic field. These findings are compatible with the vector cross product nature of the Lorentz force and suggest that the imaging of Lorentz-force-induced motion in conductive samples is feasible. Whether this approach can be extended to study electrically active tissues such as the peripheral nerves, brain and heart remains to be seen.

  19. Water's role in the force-induced unfolding of ubiquitin.

    PubMed

    Li, Jingyuan; Fernandez, Julio M; Berne, B J

    2010-11-09

    In atomic force spectroscopic studies of the elastomeric protein ubiquitin, the β-strands 1-5 serve as the force clamp. Simulations show how the rupture force in the force-induced unfolding depends on the kinetics of water molecule insertion into positions where they can eventually form hydrogen bonding bridges with the backbone hydrogen bonds in the force-clamp region. The intrusion of water into this region is slowed down by the hydrophobic shielding effect of carbonaceous groups on the surface residues of β-strands 1-5, which thereby regulates water insertion prior to hydrogen bond breakage. The experiments show that the unfolding of the mechanically stressed protein is nonexponential due to static disorder. Our simulations show that different numbers and/or locations of bridging water molecules give rise to a long-lived distribution of transition states and static disorder. We find that slowing down the translational (not rotational) motions of the water molecules by increasing the mass of their oxygen atoms, which leaves the force field and thereby the equilibrium structure of the solvent unchanged, increases the average rupture force; however, the early stages of the force versus time behavior are very similar for our "normal" and fictitious "heavy" water models. Finally, we construct six mutant systems to regulate the hydrophobic shielding effect of the surface residues in the force-clamp region. The mutations in the two termini of β-sheets 1-5 are found to determine a preference for different unfolding pathways and change mutant's average rupture force.

  20. Tokamak Plasma Flows Induced by Local RF Forces

    NASA Astrophysics Data System (ADS)

    Chen, Jiale; Gao, Zhe

    2015-10-01

    The tokamak plasma flows induced by the local radio frequency (RF) forces in the core region are analyzed. The effective components of local RF forces are composed of the momentum absorption term and the resonant parallel momentum transport term (i.e. the parallel component of the resonant ponderomotive forces). Different momentum balance relations are employed to calculate the plasma flows depending on different assumptions of momentum transport. With the RF fields solved from RF simulation codes, the toroidal and poloidal flows by these forces under the lower hybrid current drive and the mode conversion ion cyclotron resonance heating on EAST-like plasmas are evaluated. supported by National Natural Science Foundation of China (Nos. 11405218, 11325524, 11375235 and 11261140327), in part by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB111002, 2013GB112001 and 2013GB112010), and the Program of Fusion Reactor Physics and Digital Tokamak with the CAS “One-Three-Five” Strategic Planning

  1. Quantum Mechanical Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations and Lowering in Sub 0.1 Micron MOSFETs

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, Subhash

    1999-01-01

    A detailed study of the influence of quantum effects in the inversion layer on the random dopant induced threshold voltage fluctuations and lowering in sub 0.1 micron MOSFETs has been performed. This has been achieved using a full 3D implementation of the density gradient (DG) formalism incorporated in our previously published 3D 'atomistic' simulation approach. This results in a consistent, fully 3D, quantum mechanical picture which implies not only the vertical inversion layer quantisation but also the lateral confinement effects manifested by current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical fluctuations, is an increase in both threshold voltage fluctuations and lowering.

  2. Market forces and technological substitutes cause fluctuations in the value of bat pest-control services for cotton.

    PubMed

    López-Hoffman, Laura; Wiederholt, Ruscena; Sansone, Chris; Bagstad, Kenneth J; Cryan, Paul; Diffendorfer, Jay E; Goldstein, Joshua; Lasharr, Kelsie; Loomis, John; McCracken, Gary; Medellín, Rodrigo A; Russell, Amy; Semmens, Darius

    2014-01-01

    Critics of the market-based, ecosystem services approach to biodiversity conservation worry that volatile market conditions and technological substitutes will diminish the value of ecosystem services and obviate the "economic benefits" arguments for conservation. To explore the effects of market forces and substitutes on service values, we assessed how the value of the pest-control services provided by Mexican free-tailed bats (Tadarida brasiliensis mexicana) to cotton production in the southwestern U.S. has changed over time. We calculated service values each year from 1990 through 2008 by estimating the value of avoided crop damage and the reduced social and private costs of insecticide use in the presence of bats. Over this period, the ecosystem service value declined by 79% ($19.09 million U.S. dollars) due to the introduction and widespread adoption of Bt (Bacillus thuringiensis) cotton transgenically modified to express its own pesticide, falling global cotton prices and the reduction in the number of hectares in the U.S. planted with cotton. Our results demonstrate that fluctuations in market conditions can cause temporal variation in ecosystem service values even when ecosystem function--in this case bat population numbers--is held constant. Evidence is accumulating, however, of the evolution of pest resistance to Bt cotton, suggesting that the value of bat pest-control services may increase again. This gives rise to an economic option value argument for conserving Mexican free-tailed bat populations. We anticipate that these results will spur discussion about the role of ecosystem services in biodiversity conservation in general, and bat conservation in particular.

  3. Market forces and technological substitutes cause fluctuations in the value of bat pest-control services for cotton

    USGS Publications Warehouse

    López-Hoffman, Laura; Wiederholt, Ruscena; Sansone, Chris; Bagstad, Kenneth J.; Cryan, Paul M.; Diffendorfer, James E.; Goldstein, Joshua; LaSharr, Kelsie; Loomis, John; McCracken, Gary; Medellin, Rodrigo A.; Russell, Amy; Semmens, Darius J.

    2014-01-01

    Critics of the market-based, ecosystem services approach to biodiversity conservation worry that volatile market conditions and technological substitutes will diminish the value of ecosystem services and obviate the “economic benefits” arguments for conservation. To explore the effects of market forces and substitutes on service values, we assessed how the value of the pest-control services provided by Mexican free-tailed bats (Tadarida brasiliensis mexicana) to cotton production in the southwestern U.S. has changed over time. We calculated service values each year from 1990 through 2008 by estimating the value of avoided crop damage and the reduced social and private costs of insecticide use in the presence of bats. Over this period, the ecosystem service value declined by 79% ($19.09 million U.S. dollars) due to the introduction and widespread adoption of Bt (Bacillus thuringiensis) cotton transgenically modified to express its own pesticide, falling global cotton prices and the reduction in the number of hectares in the U.S. planted with cotton. Our results demonstrate that fluctuations in market conditions can cause temporal variation in ecosystem service values even when ecosystem function – in this case bat population numbers – is held constant. Evidence is accumulating, however, of the evolution of pest resistance to Bt cotton, suggesting that the value of bat pest-control services may increase again. This gives rise to an economic option value argument for conserving Mexican free-tailed bat populations. We anticipate that these results will spur discussion about the role of ecosystem services in biodiversity conservation in general, and bat conservation in particular.

  4. Market Forces and Technological Substitutes Cause Fluctuations in the Value of Bat Pest-Control Services for Cotton

    PubMed Central

    López-Hoffman, Laura; Wiederholt, Ruscena; Sansone, Chris; Bagstad, Kenneth J.; Cryan, Paul; Diffendorfer, Jay E.; Goldstein, Joshua; LaSharr, Kelsie; Loomis, John; McCracken, Gary; Medellín, Rodrigo A.; Russell, Amy; Semmens, Darius

    2014-01-01

    Critics of the market-based, ecosystem services approach to biodiversity conservation worry that volatile market conditions and technological substitutes will diminish the value of ecosystem services and obviate the “economic benefits” arguments for conservation. To explore the effects of market forces and substitutes on service values, we assessed how the value of the pest-control services provided by Mexican free-tailed bats (Tadarida brasiliensis mexicana) to cotton production in the southwestern U.S. has changed over time. We calculated service values each year from 1990 through 2008 by estimating the value of avoided crop damage and the reduced social and private costs of insecticide use in the presence of bats. Over this period, the ecosystem service value declined by 79% ($19.09 million U.S. dollars) due to the introduction and widespread adoption of Bt (Bacillus thuringiensis) cotton transgenically modified to express its own pesticide, falling global cotton prices and the reduction in the number of hectares in the U.S. planted with cotton. Our results demonstrate that fluctuations in market conditions can cause temporal variation in ecosystem service values even when ecosystem function – in this case bat population numbers – is held constant. Evidence is accumulating, however, of the evolution of pest resistance to Bt cotton, suggesting that the value of bat pest-control services may increase again. This gives rise to an economic option value argument for conserving Mexican free-tailed bat populations. We anticipate that these results will spur discussion about the role of ecosystem services in biodiversity conservation in general, and bat conservation in particular. PMID:24498400

  5. Theory of spin-fluctuation induced superconductivity in iron-based superconductors

    SciTech Connect

    Zhang, Junhua

    2011-01-01

    In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum

  6. Force-Induced Craniosynostosis in the Murine Sagittal Suture

    PubMed Central

    Oppenheimer, Adam J.; Rhee, Samuel T.; Goldstein, Steven A.; Buchman, Steven R.

    2010-01-01

    BACKGROUND The etiology of non-syndromic craniosynostosis remains elusive. While compressive forces have been implicated in premature suture fusion, conclusive evidence of force-induced craniosynostosis is lacking. The purpose of this study was to determine if cyclical loading of the murine calvarium could induce suture fusion. METHODS Calvarial coupons from post-natal day 21, B6CBA wild-type mice (n = 18) were harvested and cultured. A custom appliance capable of delivering controlled, cyclical, compressive loads was applied perpendicular to the sagittal suture within the coupon in vitro. Nine coupons were subjected to 0.3g of force for 30 minutes each day for a total of 14 days. A control group of nine coupons was clamped in the appliance without loading. Analysis of suture phenotype was performed using alkaline phosphatase and H&E staining techniques, as well as in situ hybridization analysis using Bone Sialoprotein (BSP). RESULTS Control group sagittal sutures—which normally remain patent in mice—showed their customary histological appearance. In contradistinction, sagittal sutures subjected to cyclic loading showed histological evidence of premature fusion (craniosynostosis). In addition, alkaline phosphatase activity and BSP expression was observed to be increased in the experimental group when compared to matched controls. CONCLUSIONS An in vitro model of forced-induced craniosynostosis has been devised. Premature fusion of the murine sagittal suture was induced with the application of controlled, cyclical, compressive loads. These results implicate abnormal forces in the development of non-syndromic craniosynostosis, which supports our global hypothesis that epigenetic phenomena have a crucial role in the pathogenesis of craniosynostosis. PMID:19952640

  7. Earthquake-induced water-level fluctuations at Yucca Mountain, Nevada, June 1992

    SciTech Connect

    O`Brien, G.M.

    1993-07-01

    This report presents earthquake-induced water-level and fluid-pressure data for wells in the Yucca Mountain area, Nevada, during June 1992. Three earthquakes occurred which caused significant water-level and fluid-pressure responses in wells. Wells USW H-5 and USW H-6 are continuously monitored to detect short-term responses caused by earthquakes. Two wells, monitored hourly, had significant, longer-term responses in water level following the earthquakes. On June 28, 1992, a 7.5-magnitude earthquake occurred near Landers, California causing an estimated maximum water-level change of 90 centimeters in well USW H-5. Three hours later a 6.6-magnitude earthquake occurred near Big Bear Lake, California; the maximum water-level fluctuation was 20 centimeters in well USW H-5. A 5.6-magnitude earthquake occurred at Little Skull Mountain, Nevada, on June 29, approximately 23 kilometers from Yucca Mountain. The maximum estimated short-term water-level fluctuation from the Little Skull Mountain earthquake was 40 centimeters in well USW H-5. The water level in well UE-25p {number_sign}1, monitored hourly, decreased approximately 50 centimeters over 3 days following the Little Skull Mountain earthquake. The water level in UE-25p {number_sign}1 returned to pre-earthquake levels in approximately 6 months. The water level in the lower interval of well USW H-3 increased 28 centimeters following the Little Skull Mountain earthquake. The Landers and Little Skull Mountain earthquakes caused responses in 17 intervals of 14 hourly monitored wells, however, most responses were small and of short duration. For several days following the major earthquakes, many smaller magnitude aftershocks occurred causing measurable responses in the continuously monitored wells.

  8. Derivation of Aero-Induced Fluctuating Pressure Environments for Ares I-X

    NASA Technical Reports Server (NTRS)

    Yang, Michael Y.; Wilby, John F.

    2008-01-01

    A description is given of the external aero-inducted fluctuating pressure model which was fit and anchored to wind tunnel data from the past 40 years. This model is based upon the assumption that the flow around a vehicle can be divided into discrete flow zones with independent fluctuating pressure properties. The model is then used to derive fluctuating pressure environments during ascent for the Ares I-X test vehicle. A sensitivity study of the structural response to the spatial correlation of the fluctuating pressures is also performed.

  9. Stratospheric Annular Modes Induced By Stationary Wave Forcing

    NASA Astrophysics Data System (ADS)

    Körnich, H.; Schmitz, G.

    The variability of the winter stratosphere shows distinguishable features in the north- ern and southern hemisphere. Since these differences are based on the different plan- etary waves of the underlying atmosphere, we explore the mechanism how stationary wave forcing in the troposphere can induce a stratospheric Annular Mode using a simple GCM. The model KMCM (Kühlungsborn Mechanistic Circulation Model) extends from the ground up to 60 km height and produces a reasonable winter climate. It takes into account the different large-scale wave forcings in the troposphere as prescribed pro- cesses. This allows us to examine the stratospheric Annular-Mode generation depend- ing on different wave forcings under perpetual January conditions. Principal com- ponent analysis is applied to identify the variability patterns of the geopotential and of the zonally averaged zonal wind. By this way, it is shown that the amplitude and composition of the orographic and thermal eddy forcing determines the stratospheric Annular Mode and the related downward propagation in the temperature field. Further model simplifications are introduced in order to understand the mechanism of the stratospheric AM-generation. Using a linear model version we illuminate the influence of the different wave forcing processes on the Annular Modes. Addition- ally, a constant-troposphere model is used to clarify the importance of transient and stationary waves. Finally, the Annular Mode is interpreted in terms of the dynamical coupling of the troposphere and stratosphere.

  10. Asymmetrical, agonist-induced fluctuations in local extracellular [Ca2+] in intact polarized epithelia

    PubMed Central

    Caroppo, Rosa; Gerbino, Andrea; Debellis, Lucantonio; Kifor, Olga; Soybel, David I.; Brown, Edward M.; Hofer, Aldebaran M.; Curci, Silvana

    2001-01-01

    We recently proposed that extracellular Ca2+ ions participate in a novel form of intercellular communication involving the extracellular Ca2+-sensing receptor (CaR). Here, using Ca2+-selective microelectrodes, we directly measured the profile of agonist-induced [Ca2+]ext changes in restricted domains near the basolateral or luminal membranes of polarized gastric acid-secreting cells. The Ca2+-mobilizing agonist carbachol elicited a transient, La3+-sensitive decrease in basolateral [Ca2+] (average ≈250 µM, but as large as 530 µM). Conversely, carbachol evoked an HgCl2-sensitive increase in [Ca2+] (average ≈400 µM, but as large as 520 µM) in the lumen of single gastric glands. Both responses were significantly reduced by pre-treatment with sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) pump inhibitors or with the intracellular Ca2+ chelator BAPTA-AM. Immunofluores cence experiments demonstrated an asymmetric localization of plasma membrane Ca2+ ATPase (PMCA), which appeared to be partially co-localized with CaR and the gastric H+/K+-ATPase in the apical membrane of the acid-secreting cells. Our data indicate that agonist stimulation results in local fluctuations in [Ca2+]ext that would be sufficient to modulate the activity of the CaR on neighboring cells. PMID:11707403

  11. Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

    PubMed Central

    Chekhovich, E.A.; Hopkinson, M.; Skolnick, M.S.; Tartakovskii, A.I.

    2015-01-01

    Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2–4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

  12. Spatiotemporal patterns of water table fluctuations and evapotranspiration induced by riparian vegetation in a semiarid area

    NASA Astrophysics Data System (ADS)

    Yue, Weifeng; Wang, Tiejun; Franz, Trenton E.; Chen, Xunhong

    2016-03-01

    Groundwater evapotranspiration (ETg) links various ecohydrological processes and is an important component in regional water budgets. In this study, an extensive monitoring network was established in a semiarid riparian area to investigate various controls on the spatiotemporal pattern of water table fluctuations (WTFs) and ETg induced by riparian vegetation. Along a vegetation gradient (˜1200 m), diurnal WTFs were observed during a growing season in areas covered by woody species (Populus sect. Aigeiros and Juniperus virginiana) and wet slough vegetation (Panicum virgatum and Bromus inermis) with deeper root systems; whereas, no diurnal WTFs were found in the middle section with shallower-rooted grasses (Poa pratensis and Carex sp.). The occurrence of diurnal WTFs was related to temperature-controlled plant phenology at seasonal scales and to radiation at subdaily scales. Daily ETg in the mid-growing season was calculated using the White method. The results revealed that depth to water table (DTWT) was the dominant control on ETg, followed by potential evapotranspiration (ETp). By combining the effects of DTWT and ETp, it was found that at shallower depths, ETg was more responsive to changes in ETp, due to the closer linkage of land surface processes with shallower groundwater. Finally, exponential relationships between ETg/ETp and DTWT were obtained at the study site, although those relationships varied considerably across the sites. This study demonstrates the complex interactions of WTFs and ETg with surrounding environmental variables and provides further insight into modeling ETg over different time scales and riparian vegetation.

  13. Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain.

    PubMed

    Chekhovich, E A; Hopkinson, M; Skolnick, M S; Tartakovskii, A I

    2015-02-23

    Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2-4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging.

  14. The key event in force-induced unfolding of Titin's immunoglobulin domains.

    PubMed

    Lu, H; Schulten, K

    2000-07-01

    Steered molecular dynamics simulation of force-induced titin immunoglobulin domain I27 unfolding led to the discovery of a significant potential energy barrier at an extension of approximately 14 A on the unfolding pathway that protects the domain against stretching. Previous simulations showed that this barrier is due to the concurrent breaking of six interstrand hydrogen bonds (H-bonds) between beta-strands A' and G that is preceded by the breaking of two to three hydrogen bonds between strands A and B, the latter leading to an unfolding intermediate. The simulation results are supported by Angstrom-resolution atomic force microscopy data. Here we perform a structural and energetic analysis of the H-bonds breaking. It is confirmed that H-bonds between strands A and B break rapidly. However, the breaking of the H-bond between strands A' and G needs to be assisted by fluctuations of water molecules. In nanosecond simulations, water molecules are found to repeatedly interact with the protein backbone atoms, weakening individual interstrand H-bonds until all six A'-G H-bonds break simultaneously under the influence of external stretching forces. Only when those bonds are broken can the generic unfolding take place, which involves hydrophobic interactions of the protein core and exerts weaker resistance against stretching than the key event.

  15. SNW 2000 Proceedings. Oxide Thickness Variation Induced Threshold Voltage Fluctuations in Decanano MOSFETs: a 3D Density Gradient Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Kaya, S.; Davies, J. H.; Saini, S.

    2000-01-01

    We use the density gradient (DG) simulation approach to study, in 3D, the effect of local oxide thickness fluctuations on the threshold voltage of decanano MOSFETs in a statistical manner. A description of the reconstruction procedure for the random 2D surfaces representing the 'atomistic' Si-SiO2 interface variations is presented. The procedure is based on power spectrum synthesis in the Fourier domain and can include either Gaussian or exponential spectra. The simulations show that threshold voltage variations induced by oxide thickness fluctuation become significant when the gate length of the devices become comparable to the correlation length of the fluctuations. The extent of quantum corrections in the simulations with respect to the classical case and the dependence of threshold variations on the oxide thickness are examined.

  16. A field investigation of phreatophyte-induced fluctuations in the water table

    USGS Publications Warehouse

    Butler, J.J.; Kluitenberg, G.J.; Whittemore, D.O.; Loheide, S.P.; Jin, W.; Billinger, M.A.; Zhan, X.

    2007-01-01

    Hydrographs from shallow wells in vegetated riparian zones frequently display a distinctive pattern of diurnal water table fluctuations produced by variations in plant water use. A multisite investigation assessed the major controls on these fluctuations and the ecohydrologic insights that can be gleaned from them. Spatial and temporal variations in the amplitude of the fluctuations are primarily a function of variations in (1) the meteorological drivers of plant water use, (2) vegetation density, type, and vitality, and (3) the specific yield of sediments in the vicinity of the water table. Past hydrologic conditions experienced by the riparian zone vegetation, either in previous years or earlier within the same growing season, are also an important control. Diurnal water table fluctuations can be considered a diagnostic indicator of groundwater consumption by phreatophytes at most sites, so the information embedded within these fluctuations should be more widely exploited in ecohydrologic studies. Copyright 2007 by the American Geophysical Union.

  17. Fluctuation amplitude and local synchronization of brain activity in the ultra-low frequency band: An fMRI investigation of continuous feedback of finger force.

    PubMed

    Zhang, Hang; Zhang, Lijuan; Zang, Yufeng

    2015-12-10

    Functional magnetic resonance imaging (fMRI) studies of motor feedback have suggested that brain activity in the ultra-low frequency band (0-0.01Hz) may be physiologically significant for various feedback conditions, i.e., real and sham feedback. However, the functional role of the ultra-low frequency band of brain activity during the feedback procedure remains unclear. Here, we carried out an fMRI study of continuous feedback (8min) of finger force and assessed two important properties of brain activity: the fluctuation amplitude and local synchronization in the ultra-low frequency band. Two intriguing results were obtained: (1) real feedback recruited a stronger fluctuation amplitude and local synchronization in the basal ganglia compared with sham feedback; however, no significant correlation was found between the two properties across subjects; and (2) the behavioral performance was significantly correlated with the fluctuation amplitude but was not correlated with local synchronization in the basal ganglia. These findings contribute to characterization of the functional role of brain activity in the ultra-low frequency band and further suggest that the fluctuation amplitude and local synchronization in the basal ganglia may contribute differently to motor feedback.

  18. Wave-induced mass transport affects daily Escherichia coli fluctuations in nearshore water

    USGS Publications Warehouse

    Ge, Zhongfu; Whitman, Richard L.; Nevers, Meredith B.; Phanikumar, Mantha S.

    2012-01-01

    Characterization of diel variability of fecal indicator bacteria concentration in nearshore waters is of particular importance for development of water sampling standards and protection of public health. Significant nighttime increase in Escherichia coli (E. coli) concentration in beach water, previously observed at marine sites, has also been identified in summer 2000 from fixed locations in waist- and knee-deep waters at Chicago 63rd Street Beach, an embayed, tideless, freshwater beach with low currents at night (approximately 0.015 m s–1). A theoretical model using wave-induced mass transport velocity for advection was developed to assess the contribution of surface waves to the observed nighttime E. coli replenishment in the nearshore water. Using average wave conditions for the summer season of year 2000, the model predicted an amount of E. coli transported from water of intermediate depth, where sediment resuspension occurred intermittently, that would be sufficient to have elevated E. coli concentration in the surf and swash zones as observed. The nighttime replenishment of E. coli in the surf and swash zones revealed here is an important phase in the cycle of diel variations of E. coli concentration in nearshore water. According to previous findings in Ge et al. (Environ. Sci. Technol. 2010, 44, 6731–6737), enhanced current circulation in the embayment during the day tends to displace and deposit material offshore, which partially sets up the system by the early evening for a new period of nighttime onshore movement. This wave-induced mass transport effect, although facilitating a significant base supply of material shoreward, can be perturbed or significantly influenced by high currents (orders of magnitude larger than a typical wave-induced mass transport velocity), current-induced turbulence, and tidal forcing.

  19. Wave-induced mass transport affects daily Escherichia coli fluctuations in nearshore water.

    PubMed

    Ge, Zhongfu; Whitman, Richard L; Nevers, Meredith B; Phanikumar, Mantha S

    2012-02-21

    Characterization of diel variability of fecal indicator bacteria concentration in nearshore waters is of particular importance for development of water sampling standards and protection of public health. Significant nighttime increase in Escherichia coli (E. coli) concentration in beach water, previously observed at marine sites, has also been identified in summer 2000 from fixed locations in waist- and knee-deep waters at Chicago 63rd Street Beach, an embayed, tideless, freshwater beach with low currents at night (approximately 0.015 m s(-1)). A theoretical model using wave-induced mass transport velocity for advection was developed to assess the contribution of surface waves to the observed nighttime E. coli replenishment in the nearshore water. Using average wave conditions for the summer season of year 2000, the model predicted an amount of E. coli transported from water of intermediate depth, where sediment resuspension occurred intermittently, that would be sufficient to have elevated E. coli concentration in the surf and swash zones as observed. The nighttime replenishment of E. coli in the surf and swash zones revealed here is an important phase in the cycle of diel variations of E. coli concentration in nearshore water. According to previous findings in Ge et al. (Environ. Sci. Technol. 2010, 44, 6731-6737), enhanced current circulation in the embayment during the day tends to displace and deposit material offshore, which partially sets up the system by the early evening for a new period of nighttime onshore movement. This wave-induced mass transport effect, although facilitating a significant base supply of material shoreward, can be perturbed or significantly influenced by high currents (orders of magnitude larger than a typical wave-induced mass transport velocity), current-induced turbulence, and tidal forcing.

  20. Fluctuations induced transition of localization of granular objects caused by degrees of crowding

    NASA Astrophysics Data System (ADS)

    Oda, Soutaro; Kubo, Yoshitsugu; Shew, Chwen-Yang; Yoshikawa, Kenichi

    2016-12-01

    Fluctuations are ubiquitous in both microscopic and macroscopic systems, and an investigation of confined particles under fluctuations is relevant to how living cells on the earth maintain their lives. Inspired by biological cells, we conduct the experiment through a very simple fluctuating system containing one or several large spherical granular particles and multiple smaller ones confined on a cylindrical dish under vertical vibration. We find a universal behavior that large particles preferentially locate in cavity interior due to the fact that large particles are depleted from the cavity wall by small spheres under vertical vibration in the actual experiment. This universal behavior can be understood from the standpoint of entropy.

  1. Field-induced quantum fluctuations in the heavy fermion superconductor CeCu(2)Ge(2).

    PubMed

    Singh, D K; Thamizhavel, A; Lynn, J W; Dhar, S; Rodriguez-Rivera, J; Herman, T

    2011-01-01

    Quantum-mechanical fluctuations in strongly correlated electron systems cause unconventional phenomena such as non-Fermi liquid behavior, and arguably high temperature superconductivity. Here we report the discovery of a field-tuned quantum critical phenomenon in stoichiometric CeCu(2)Ge(2), a spin density wave ordered heavy fermion metal that exhibits unconventional superconductivity under ≃10 GPa of applied pressure. Our finding of the associated quantum critical spin fluctuations of the antiferromagnetic spin density wave order, dominating the local fluctuations due to single-site Kondo effect, provide new information about the underlying mechanism that can be important in understanding superconductivity in this novel compound.

  2. Tissue deformation induced by radiation force from Gaussian transducers.

    PubMed

    Myers, Matthew R

    2006-05-01

    Imaging techniques based upon the tissue mechanical response to an acoustic radiation force are being actively researched. In this paper a model for predicting steady-state tissue displacement induced by a radiation force arising from the absorption of Gaussian ultrasound beams is presented. A simple analytic expression is derived that agrees closely with the numerical quadrature of the displacement convolution integrals. The analytic result reveals the dependence of the steady-state axial displacement upon the operational parameters, e.g., an inverse proportional relationship to the tissue shear modulus. The derivation requires that the transducer radius be small compared to the focal length, but accurate results were obtained for transducer radii comparable to the focal length. Favorable comparisons with displacement predictions for non-Gaussian transducers indicate that the theory is also useful for a broader range of transducer intensity profiles.

  3. Fluctuations of fresh-saline water interface and of water table induced by sea tides in unconfined aquifers

    NASA Astrophysics Data System (ADS)

    Levanon, Elad; Shalev, Eyal; Yechieli, Yoseph; Gvirtzman, Haim

    2016-10-01

    This study examines effects of tides on fluctuations of the fresh-saline water interface and the groundwater level in unconfined coastal aquifers using a two-dimensional numerical model. The time-lags of the simulated hydraulic heads and salinities fluctuations compared to sea level fluctuations are analyzed using cross-correlation analysis. The results show that both the fresh-saline water interface and the groundwater level are affected harmonically by sea tide fluctuations. However, significantly different time-lags are obtained between the hydraulic head in the deeper and upper parts of the aquifer, and between head and salinity in the fresh-saline water interface. The hydraulic head in the deeper part of the aquifer responses much faster to sea level fluctuations than in the upper part. Surprisingly, a similar difference is detected between the time-lag of the hydraulic head in the fresh-saline water interface and the time-lag of the salinity at the same location. Furthermore, the time-lag of the salinity in the fresh-saline water interface is similar to the time-lag of the water table. We suggest a comprehensive mechanism for tidal influence on the coastal groundwater system, in which two main processes act simultaneously. First, sea tide causes a pressure head wave which propagates into the saturated zone of the aquifer, governed by the diffusivity of the aquifer (Ks/Ss). Second, this pressure head wave is attenuated at the water table due to the unsaturated flow within the capillary fringe which occurs during groundwater level oscillations. Because the tidal forcing acts on the sea-floor boundary and the attenuation of the groundwater level due to capillary effect acts on the groundwater table, two dimensional distributions of time-lag and hydraulic head amplitude are created. The capillary effect in the unsaturated zone plays a key role not only in the water table fluctuations as shown previously, but also on the salinity fluctuations in the fresh

  4. Moist Greenhouse states with solar and CO2-induced forcing

    NASA Astrophysics Data System (ADS)

    Popp, Max; Schmidt, Hauke; Marotzke, Jochem

    2016-04-01

    Water-rich planets such as Earth are expected to become eventually uninhabitable, because liquid water does not remain stable at the surface as surface temperatures increase with the solar luminosity over time. It is conceivable that a large increase in atmospheric greenhouse-gas concentrations could also destroy the habitability of water-rich planets, but previous studies could not clearly establish this. Here we use for the first time a state-of-the-art atmospheric general circulation model, namely a modified version of ECHAM6, to compare the potential of both solar and CO2-induced forcing to render a water-rich planet uninhabitable. We find that CO2-induced forcing as readily destabilizes a present-day Earth-like climate as does solar forcing. This climate instability is caused by a positive cloud feedback, which is in turn caused by the weakening large-scale circulation with increasing surface temperature. The climate does not run away, but instead attains a new steady state with global-mean sea-surface temperatures above 330 K. The upper atmosphere is considerably moister in this warm steady state than in the reference climate. The upper-atmospheric mixing ratio of water exceeds the so-called Moist-Greenhouse limit, which implies that the planet would be subject to substantial loss of water to space. For either a certain range of elevated CO2 concentrations or solar irradiation, we find both cold and warm equilibrium states. Therefore the transition to the warm state may not simply be reversed by removing the additional forcing.

  5. Comparison of theories for gravity wave induced fluctuations in airglow emissions

    NASA Technical Reports Server (NTRS)

    Walterscheid, R. L.; Schubert, G.; Hickey, M. P.

    1994-01-01

    A comparison is undertaken of theories for the gravity wave induced fluctuations in the intensity of airglow emissions and the associated temperature of the source region. The comparison is made in terms of Krassovsky's ratio eta(sub E) for a vertically extended emission region (eta(sub E) is the ratio of the vertically integrated normalized intensity perturbation to the vertically integrated intensity-weighted temperature perturbation). It is shown that the formulas for eta(sub E) in the works by Tarasick and Hines (1990) and Schubert et al. (1991) are in agreement for the case of an inviscid atmosphere. The calculation of eta(sub E) using the theory of Tarasick and Hines (1990) requires determination of their function chi; we show that chi is simply related to the 'single-level' Krassovsky's ratio eta of Schubert et al. (1991). The general relationship between chi and eta is applied to a simple chemical-dynamical model of the O2 atmospheric airglow and the altitude dependence of these quantities is evaluated for nonsteady state chemistry. Though the Tarasick and Hines (1990) formula for eta(sub E) does not explicitly depend on the scale heights of the minor constituents involved in airglow chemistry, eta(sub E) implicitly depends upon these scale heights through its dependences on chemical production and loss contained in chi. We demonstrate this dependence of eta(sub E) for the OH nightglow on atomic oxygen scale height by direct numerical evaluation of eta(sub E) in this case the dependence originates in the chemical production of perturbed ozone.

  6. Measurement of energetic-particle-driven core magnetic fluctuations and induced fast-ion transport

    NASA Astrophysics Data System (ADS)

    Lin, L.; Ding, W. X.; Brower, D. L.; Koliner, J. J.; Eilerman, S.; Reusch, J. A.; Anderson, J. K.; Nornberg, M. D.; Sarff, J. S.; Waksman, J.; Liu, D.

    2013-03-01

    Internal fluctuations arising from energetic-particle-driven instabilities, including both density and radial magnetic field, are measured in a reversed-field-pinch plasma. The fluctuations peak near the core where fast ions reside and shift outward along the major radius as the instability transits from the n = 5 to n = 4 mode. During this transition, strong nonlinear three-wave interaction among multiple modes accompanied by enhanced fast-ion transport is observed.

  7. Current-induced forces and hot spots in biased nanojunctions.

    PubMed

    Lü, Jing-Tao; Christensen, Rasmus B; Wang, Jian-Sheng; Hedegård, Per; Brandbyge, Mads

    2015-03-06

    We investigate theoretically the interplay of current-induced forces (CIFs), Joule heating, and heat transport inside a current-carrying nanoconductor. We find that the CIFs, due to the electron-phonon coherence, can control the spatial heat dissipation in the conductor. This yields a significant asymmetric concentration of excess heating (hot spot) even for a symmetric conductor. When coupled to the electrode phonons, CIFs drive different phonon heat flux into the two electrodes. First-principles calculations on realistic biased nanojunctions illustrate the importance of the effect.

  8. Interferometric fiber-optic gyroscope performance owing to temperature-induced index fluctuations in the fiber: effect on bias modulation

    NASA Astrophysics Data System (ADS)

    Knudsen, Sverre; Bløtekjær, Kjell

    1995-06-01

    An analysis of the noise floor owing to temperature-induced index fluctuations in the fiber of a dynamically biased interferometric fiber-optic gyroscope is presented. A comparison with shot noise indicates that, for a harmonic bias modulation, thermal noise in the fiber dominates for fiber lengths longer than \\similar 1 - 2km when practical source power levels are considered. The noise can be reduced or eliminated by the proper choice of modulation frequency or waveform.

  9. Optical measurements of fluctuating temperatures in a supersonic turbulent flow using one- and two-photon, laser-induced fluorescence

    NASA Technical Reports Server (NTRS)

    Gross, K. P.; Mckenzie, R. L.

    1984-01-01

    A laser-induced fluorescence technique has been developed that provides a practical means of nonintrusively measuring the instantaneous temperatures in low-temperature turbulent flows. The capabilities of the method are reviewed, and its application to a simple, two-dimensional, turbulent boundary-layer flow at Mach 2 is reported. Measurements of the average temperature distribution through the boundary layer and the magnitudes of temperature fluctuations about their average values are presented.

  10. Optical measurements of fluctuating temperatures in a supersonic turbulent flow using one- and two-photon, laser-induced fluorescence

    NASA Technical Reports Server (NTRS)

    Gross, K. P.; Mckenzie, R. L.

    1984-01-01

    A laser-induced fluorescence technique was developed that provides a practical means of nonintrusively measuring the instantaneous temperatures in low-temperature turbulent flows. The capabilities of the method are reviewed, and its application to a simple, two-dimensional, turbulent boundary-layer flow at Mach 2 is reported. Measurements of the average temperature distribution through the boundary layer and the magnitudes of temperature fluctuations about their average values are presented.

  11. Finite-difference analysis of plasmon-induced forces of metal nano-clusters by the Lorentz force formulation.

    PubMed

    Fujii, Masafumi

    2010-12-20

    We analyze light-induced forces on metal nano-spheres by using the three-dimensional finite-difference time-domain method with the Lorentz force formulation. Convergent analysis of the force on metal nano-particle clusters has been achieved by integrating the Lorentz and the Coulomb forces over the volume of the metal particles. Comparison to the Mie theory of radiation pressure on metal spheres under a plane wave illumination has verified rigorously the accuracy of the numerical method. We also analyze separate two metal spheres in close proximity and the results of the induced forces are compared to those in previous publications. The present method allows analysis of forces on various irregular structures; we apply the method to touching metal spheres, forming a simple cluster with a slight deformation at the contact point, to analyze the forces induced by the plasmonic resonance of the clusters. We show that the fundamental resonance modes, which newly appear in an infrared range when spheres are touching, exhibit strong binding forces within the clusters. Based on the numerical analyses we identify the resonance modes and evaluate quantitatively the infrared-induced forces on metal nano-sphere clusters.

  12. A 3D CFD Simulation and Analysis of Flow-Induced Forces on Polymer Piezoelectric Sensors in a Chinese Liquors Identification E-Nose

    PubMed Central

    Gu, Yu; Wang, Yang-Fu; Li, Qiang; Liu, Zu-Wu

    2016-01-01

    Chinese liquors can be classified according to their flavor types. Accurate identification of Chinese liquor flavors is not always possible through professional sommeliers’ subjective assessment. A novel polymer piezoelectric sensor electric nose (e-nose) can be applied to distinguish Chinese liquors because of its excellent ability in imitating human senses by using sensor arrays and pattern recognition systems. The sensor, based on the quartz crystal microbalance (QCM) principle is comprised of a quartz piezoelectric crystal plate sandwiched between two specific gas-sensitive polymer coatings. Chinese liquors are identified by obtaining the resonance frequency value changes of each sensor using the e-nose. However, the QCM principle failed to completely account for a particular phenomenon: we found that the resonance frequency values fluctuated in the stable state. For better understanding the phenomenon, a 3D Computational Fluid Dynamics (CFD) simulation using the finite volume method is employed to study the influence of the flow-induced forces to the resonance frequency fluctuation of each sensor in the sensor box. A dedicated procedure was developed for modeling the flow of volatile gas from Chinese liquors in a realistic scenario to give reasonably good results with fair accuracy. The flow-induced forces on the sensors are displayed from the perspective of their spatial-temporal and probability density distributions. To evaluate the influence of the fluctuation of the flow-induced forces on each sensor and ensure the serviceability of the e-nose, the standard deviation of resonance frequency value (SDF) and the standard deviation of resultant forces (SDFy) in y-direction (Fy) are compared. Results show that the fluctuations of Fy are bound up with the resonance frequency values fluctuations. To ensure that the sensor's resonance frequency values are steady and only fluctuate slightly, in order to improve the identification accuracy of Chinese liquors using

  13. A 3D CFD Simulation and Analysis of Flow-Induced Forces on Polymer Piezoelectric Sensors in a Chinese Liquors Identification E-Nose.

    PubMed

    Gu, Yu; Wang, Yang-Fu; Li, Qiang; Liu, Zu-Wu

    2016-10-20

    Chinese liquors can be classified according to their flavor types. Accurate identification of Chinese liquor flavors is not always possible through professional sommeliers' subjective assessment. A novel polymer piezoelectric sensor electric nose (e-nose) can be applied to distinguish Chinese liquors because of its excellent ability in imitating human senses by using sensor arrays and pattern recognition systems. The sensor, based on the quartz crystal microbalance (QCM) principle is comprised of a quartz piezoelectric crystal plate sandwiched between two specific gas-sensitive polymer coatings. Chinese liquors are identified by obtaining the resonance frequency value changes of each sensor using the e-nose. However, the QCM principle failed to completely account for a particular phenomenon: we found that the resonance frequency values fluctuated in the stable state. For better understanding the phenomenon, a 3D Computational Fluid Dynamics (CFD) simulation using the finite volume method is employed to study the influence of the flow-induced forces to the resonance frequency fluctuation of each sensor in the sensor box. A dedicated procedure was developed for modeling the flow of volatile gas from Chinese liquors in a realistic scenario to give reasonably good results with fair accuracy. The flow-induced forces on the sensors are displayed from the perspective of their spatial-temporal and probability density distributions. To evaluate the influence of the fluctuation of the flow-induced forces on each sensor and ensure the serviceability of the e-nose, the standard deviation of resonance frequency value (SDF) and the standard deviation of resultant forces (SDFy) in y-direction (Fy) are compared. Results show that the fluctuations of Fy are bound up with the resonance frequency values fluctuations. To ensure that the sensor's resonance frequency values are steady and only fluctuate slightly, in order to improve the identification accuracy of Chinese liquors using

  14. Limitations to photosynthesis by proton motive force-induced photosystem II photodamage

    PubMed Central

    Davis, Geoffry A; Kanazawa, Atsuko; Schöttler, Mark Aurel; Kohzuma, Kaori; Froehlich, John E; Rutherford, A William; Satoh-Cruz, Mio; Minhas, Deepika; Tietz, Stefanie; Dhingra, Amit; Kramer, David M

    2016-01-01

    The thylakoid proton motive force (pmf) generated during photosynthesis is the essential driving force for ATP production; it is also a central regulator of light capture and electron transfer. We investigated the effects of elevated pmf on photosynthesis in a library of Arabidopsis thaliana mutants with altered rates of thylakoid lumen proton efflux, leading to a range of steady-state pmf extents. We observed the expected pmf-dependent alterations in photosynthetic regulation, but also strong effects on the rate of photosystem II (PSII) photodamage. Detailed analyses indicate this effect is related to an elevated electric field (Δψ) component of the pmf, rather than lumen acidification, which in vivo increased PSII charge recombination rates, producing singlet oxygen and subsequent photodamage. The effects are seen even in wild type plants, especially under fluctuating illumination, suggesting that Δψ-induced photodamage represents a previously unrecognized limiting factor for plant productivity under dynamic environmental conditions seen in the field. DOI: http://dx.doi.org/10.7554/eLife.16921.001 PMID:27697149

  15. 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.

  16. Analysis of Numerical Simulation Database for Pressure Fluctuations Induced by High-Speed Turbulent Boundary Layers

    NASA Technical Reports Server (NTRS)

    Duan, Lian; Choudhari, Meelan M.

    2014-01-01

    Direct numerical simulations (DNS) of Mach 6 turbulent boundary layer with nominal freestream Mach number of 6 and Reynolds number of Re(sub T) approximately 460 are conducted at two wall temperatures (Tw/Tr = 0.25, 0.76) to investigate the generated pressure fluctuations and their dependence on wall temperature. Simulations indicate that the influence of wall temperature on pressure fluctuations is largely limited to the near-wall region, with the characteristics of wall-pressure fluctuations showing a strong temperature dependence. Wall temperature has little influence on the propagation speed of the freestream pressure signal. The freestream radiation intensity compares well between wall-temperature cases when normalized by the local wall shear; the propagation speed of the freestream pressure signal and the orientation of the radiation wave front show little dependence on the wall temperature.

  17. Stochastic Faraday rotation induced by the electric current fluctuations in nanosystems

    NASA Astrophysics Data System (ADS)

    Smirnov, D. S.; Glazov, M. M.

    2017-01-01

    We demonstrate theoretically that in gyrotropic semiconductors and semiconductor nanosystems the Brownian motion of electrons results in temporal fluctuations of the polarization plane of light passing through or reflected from the structure, i.e., in stochastic Faraday or Kerr rotation effects. The theory of the effects is developed for a number of prominent gyrotropic systems such as bulk tellurium, ensembles of chiral carbon nanotubes, and GaAs-based quantum wells of different crystallographic orientations. We show that the power spectrum of these fluctuations in thermal equilibrium is proportional to the a c conductivity of the system. We evaluate contributions resulting from the fluctuations of the electric current, as well as of spin, valley polarization, and the spin current to the noise of the Faraday/Kerr rotation. Hence all-optical measurements of the Faraday and Kerr rotation noise provide an access to the transport properties of the semiconductor systems.

  18. Experimental investigation of lateral forces induced by flow through model labyrinth glands

    NASA Technical Reports Server (NTRS)

    Leong, Y. M. M. S.; Brown, R. D.

    1984-01-01

    The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients.

  19. Geographic variation in the flood-induced fluctuating temperature requirement for germination in Setaria parviflora seeds.

    PubMed

    Mollard, F P O; Insausti, P

    2011-07-01

    Our aim was to search for specific seed germinative strategies related to flooding escape in Setaria parviflora, a common species across the Americas. For this purpose, we investigated induction after floods, in relation to fluctuating temperature requirements for germination in seeds from mountain, floodplain and successional grasslands. A laboratory experiment was conducted in which seeds were imbibed or immersed in water at 5°C. Seeds were also buried in flood-prone and upland grasslands and exhumed during the flooding season. Additionally, seeds were buried in flooded or drained grassland mesocosms. Germination of exhumed seeds was assayed at 25°C or at 20°C/30°C in the dark or in the presence of red light pulses. After submergence or soil flooding, a high fraction (>32%) of seeds from the floodplain required fluctuating temperatures to germinate. In contrast, seeds from the mountains showed maximum differences in germination between fluctuating and constant temperature treatment only after imbibition (35%) or in non-flooded soil conditions (40%). The fluctuating temperature requirement was not clearly related to the foregoing conditions in the successional grassland seeds. Maximum germination could also be attained with red light pulses to seeds from mountain and successional grasslands. Results show that the fluctuating temperature requirement might help floodplain seeds to germinate after floods, indicating a unique feature of the dormancy of S. parviflora seeds from floodplains, which suggests an adaptive advantage aimed at postponing emergence during inundation periods. In contrast, the fluctuating temperature required for germination among seeds from mountain and successional grasslands show its importance for gap detection.

  20. Microwave-induced excess quasiparticles in superconducting resonators measured through correlated conductivity fluctuations

    NASA Astrophysics Data System (ADS)

    de Visser, P. J.; Baselmans, J. J. A.; Yates, S. J. C.; Diener, P.; Endo, A.; Klapwijk, T. M.

    2012-04-01

    We have measured the number of quasiparticles and their lifetime in aluminium superconducting microwave resonators. The number of excess quasiparticles below 160 mK decreases from 72 to 17 μm-3 with a 6 dB decrease of the microwave power. The quasiparticle lifetime increases accordingly from 1.4 to 3.5 ms. These properties of the superconductor were measured through the spectrum of correlated fluctuations in the quasiparticle system and condensate of the superconductor, which show up in the resonator amplitude and phase, respectively. Because uncorrelated noise sources vanish, fluctuations in the superconductor can be studied with a sensitivity close to the vacuum noise.

  1. Fluctuating plasma phosphorus level by changes in dietary phosphorus intake induces endothelial dysfunction.

    PubMed

    Watari, Eriko; Taketani, Yutaka; Kitamura, Tomoyo; Tanaka, Terumi; Ohminami, Hirokazu; Abuduli, Maerjianghan; Harada, Nagakatsu; Yamanaka-Okumura, Hisami; Yamamoto, Hironori; Takeda, Eiji

    2015-01-01

    High serum phosphorus (P) impairs endothelial function by increasing oxidative stress and decreasing nitric oxide production. Serum P levels fluctuate due to circadian rhythms or dietary P intake in healthy people and due to dialysis in end-stage chronic kidney disease patients. Here we examined whether fluctuating plasma P caused by changes in dietary P intake may be involved in endothelial dysfunction, resulting in increased cardiovascular risk. Rats were fed a diet containing 0.6% P for 16 days (control group), or a diet alternating between 0.02% P and 1.2% P (LH group) or between 1.2% P and 0.02% P (HL group) every 2 days; the total amount of P intake among the groups during the feeding period was similar. In the LH and HL groups, endothelial-dependent vasodilation significantly decreased plasma 8-(OH)dG level significantly increased, and the expression of inflammatory factors such as MCP-1 increased in the endothelium as compared with the control group. These data indicate that repetitive fluctuations of plasma P caused by varying dietary P intake can impair endothelial function via increased oxidative stress and inflammatory response. Taken together, these results suggest that habitual fluctuation of dietary P intake might be a cause of cardiovascular disease through endothelial dysfunction, especially in chronic kidney disease patients.

  2. 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.

  3. Fluctuations in isometric muscle force can be described by one linear projection of low-frequency components of motor unit discharge rates.

    PubMed

    Negro, Francesco; Holobar, Ales; Farina, Dario

    2009-12-15

    The aim of the study was to investigate the relation between linear transformations of motor unit discharge rates and muscle force. Intramuscular (wire electrodes) and high-density surface EMG (13 x 5 electrode grid) were recorded from the abductor digiti minimi muscle of eight healthy men during 60 s contractions at 5%, 7.5% and 10% of the maximal force. Spike trains of a total of 222 motor units were identified from the EMG recordings with decomposition algorithms. Principal component analysis of the smoothed motor unit discharge rates indicated that one component (first common component, FCC) described 44.2 +/- 7.5% of the total variability of the smoothed discharge rates when computed over the entire contraction interval and 64.3 +/- 10.2% of the variability when computed over 5 s intervals. When the FCC was computed from four or more motor units per contraction, it correlated with the force produced by the muscle (62.7 +/- 10.1%) by a greater degree (P < 0.001) than the smoothed discharge rates of individual motor units (41.4 +/- 7.8%). The correlation between FCC and the force signal increased up to 71.8 +/- 13.1% when the duration and the shape of the smoothing window for discharge rates were similar to the average motor unit twitch force. Moreover, the coefficients of variation (CoV) for the force and for the FCC signal were correlated in all subjects (R(2) range = 0.14-0.56; P < 0.05) whereas the CoV for force was correlated to the interspike interval variability in only one subject (R(2) = 0.12; P < 0.05). Similar results were further obtained from measures on the tibialis anterior muscle of an additional eight subjects during contractions at forces up to 20% of the maximal force (e.g. FCC explained 59.8 +/- 11.0% of variability of the smoothed discharge rates). In conclusion, one signal captures most of the underlying variability of the low-frequency components of motor unit discharge rates and explains large part of the fluctuations in the motor output

  4. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    DOE PAGES

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; ...

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It ismore » found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.« less

  5. Fluctuation-induced conductivity of superconductors above the transition temperature - Regularization of the Maki diagram.

    NASA Technical Reports Server (NTRS)

    Keller, J.; Korenman, V.

    1972-01-01

    The Maki contribution to the conductivity above the superconducting transition temperature is regularized within the framework of the BCS theory. This is achieved through the renormalization of the impurity-scattering vertex by inclusion of the effects of pair fluctuations. The conductivity is evaluated for a thin film. It depends only on the reduced temperature and the normal resistance per square. Fair agreement is found with Al films over a wide temperature range. Agreement is not found with experiments on Bi, Pb, and Ga films, which apparently contain a strong additional pair-breaking effect. The temperature range in which interactions among fluctuations become important in the Maki conductivity is generally larger than that given by the Ginzburg criterion.

  6. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    SciTech Connect

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; Lu, Zhaoping; George, Easo P.; Gao, Yanfei

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It is found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.

  7. Structure-fluctuation-induced abnormal thermoelectric properties in semiconductor copper selenide

    SciTech Connect

    Liu, Huili; Shi, Xun; Kirkham, Melanie J; Wang, Hsin; Li, Qiang; Uher, Ctirad; Zhang, Wenqing; Chen, Lidong

    2013-01-01

    Thermoelectric effects and related technologies have attracted a great interest due to the world-wide energy harvesting. Thermoelectricity has usually been considered in the context of stable material phases. Here we report that the fluctuation of structures during the second-order phase transition in Cu2Se semiconductor breaks the conventional trends of thermoelectric transports in normal phases, leading to a critically phase-transition-enhanced thermoelectric figure of merit zT above unity at 400K, a three times larger value than for the normal phases. Dynamic structural transformations introduce intensive fluctuations and extreme complexity, which enhance the carrier entropy and thus the thermopower, and strongly scatter carriers and phonons as well to make their transports behave critically.

  8. Computational Investigation of Block Copolymer Surfactants for Stabilizing Fluctuation-Induced Polymeric Microemulsions

    NASA Astrophysics Data System (ADS)

    Delaney, Kris; Fredrickson, Glenn

    2013-03-01

    High molecular weight diblock copolymers introduced into a blend of immiscible homopolymers can act as a surfactant to suppress macroscopic two-fluid phase separation. With variation of block copolymer composition, the crossover between low-temperature ordering into microphase or macrophase separated states is marked by a mean-field isotropic Lifshitz multi-critical point. Strong fluctuations close to the Lifshitz point are observed to suppress the low-temperature ordering; a microemulsion state emerges, with large, co-continuous domains of segregated fluid lacking any long-range order. We study this phenomenon with fully fluctuating field-theoretic simulations based on complex Langevin sampling, and we attempt to design new block polymer surfactants that can produce the microemulsion state with a wider composition tolerance.

  9. Possible weakly first-order superconducting transition induced by magnetic excitations in the YBCO system: A fluctuation conductivity study

    NASA Astrophysics Data System (ADS)

    Hneda, Marlon Luiz; da Silva Berchon, Luciano; Pureur, Paulo; das Neves Vieira, Valdemar; Jaeckel, Sandra Teixeira; Dias, Fábio Teixeira; Menegotto Costa, Rosângela

    2017-04-01

    Fluctuation conductivity is experimentally studied in the genuine critical region near the superconducting transition of YBa2Cu3O7 - δ, YBa2Cu2.985Fe0.015O7 - δ and Y0.95Ca0.05Ba2Cu3O7 - δ single crystal samples. Two fluctuation regimes where the electrical conductivity diverges as a power-law of the reduced temperature were systematically observed. In the first regime, farther from the critical temperature Tc, the transition behaves as predicted by the thermodynamics of the three dimensional-XY (3D-XY) universality class characteristic of a second-order phase transition. In the asymptotic regime closer to Tc a power-law regime characterized by a much smaller exponent is observed. The smallest value ever reported for the fluctuation conductivity exponent in the high-Tc superconductors is obtained for the Fe- and Ca-doped systems. We suggest that the regime beyond 3D-XY is a crossover towards a weakly first-order transition induced by internal magnetic excitations.

  10. 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)

  11. Spatial mobility fluctuation induced giant linear magnetoresistance in multilayered graphene foam

    NASA Astrophysics Data System (ADS)

    Li, Peng; Zhang, Qiang; He, Xin; Ren, Wencai; Cheng, Hui-Ming; Zhang, Xi-xiang

    2016-07-01

    Giant, positive, and near-temperature-independent linear magnetoresistance (LMR), as large as 340%, was observed in graphene foam with a three-dimensional flexible network. Careful analysis of the magnetoresistance revealed that Shubnikov-de Haas (SdH) oscillations occurred at low temperatures and decayed with increasing temperature. The average classical mobility ranged from 300 (2 K) to 150 (300 K) c m2V-1s-1 , which is much smaller than that required by the observed SdH oscillations. To understand the mechanism behind the observation, we performed the same measurements on the microsized graphene sheets that constitute the graphene foam. Much more pronounced SdH oscillations superimposed on the LMR background were observed in these microscaled samples, which correspond to a quantum mobility as high as 26 ,500 c m2V-1s-1 . Moreover, the spatial mobility fluctuated significantly from 64 ,200 c m2V-1s-1 to 1370 c m2V-1s-1 , accompanied by a variation of magnetoresistance from near 20,000% to less than 20%. The presence of SdH oscillations actually excludes the possibility that the observed LMR originated from the extreme quantum limit, because this would demand all electrons to be in the first Landau level. Instead, we ascribe the large LMR to the second case of the classical Parish and Littlewood model, in which spatial mobility fluctuation dominates electrical transport. This is an experimental confirmation of the Parish and Littlewood model by measuring the local mobility randomly (by measuring the microsized graphene sheets) and finding the spatial mobility fluctuation.

  12. Exercise-induced metabolic fluctuations influence AMPK, p38-MAPK and CaMKII phosphorylation in human skeletal muscle

    PubMed Central

    Combes, Adrien; Dekerle, Jeanne; Webborn, Nick; Watt, Peter; Bougault, Valérie; Daussin, Frédéric N

    2015-01-01

    During transition from rest to exercise, metabolic reaction rates increase substantially to sustain intracellular ATP use. These metabolic demands activate several kinases that initiate signal transduction pathways which modulate transcriptional regulation of mitochondrial biogenesis. The purpose of this study was to determine whether metabolic fluctuations per se affect the signaling cascades known to regulate peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α). On two separate occasions, nine men performed a continuous (30-min) and an intermittent exercise (30 × 1-min intervals separated by 1-min of recovery) at 70% of . Skeletal muscle biopsies from the vastus lateralis were taken at rest and at +0 h and +3 h after each exercise. Metabolic fluctuations that correspond to exercise-induced variation in metabolic rates were determined by analysis of VO2 responses. During intermittent exercise metabolic fluctuations were 2.8-fold higher despite identical total work done to continuous exercise (317 ± 41 vs. 312 ± 56 kJ after intermittent and continuous exercise, respectively). Increased phosphorylation of AMP-activated protein kinase (AMPK) (˜2.9-fold, P < 0.01), calcium/calmodulin-dependent protein kinase II (CaMKII) (˜2.7-fold, P < 0.01) and p38-mitogen-activated protein kinase (MAPK) (˜4.2-fold, P < 0.01) occurred immediately in both exercises and to a greater extent after the intermittent exercise (condition x time interaction, P < 0.05). A single bout of intermittent exercise induces a greater activation of these signaling pathways regulating PGC-1α when compared to a single bout of continuous exercise of matched work and intensity. Chronic adaptations to exercise on mitochondria biogenesis are yet to be investigated. PMID:26359238

  13. Berry-phase-induced heat pumping and its impact on the fluctuation theorem.

    PubMed

    Ren, Jie; Hänggi, Peter; Li, Baowen

    2010-04-30

    Applying adiabatic, cyclic two-parameter modulations we investigate quantum heat transfer across an anharmonic molecular junction contacted with two heat baths. We demonstrate that the pumped heat typically exhibits a Berry-phase effect in providing an additional geometric contribution to heat flux. Remarkably, a robust fractional quantized geometric phonon response is identified as well. The presence of this geometric phase contribution in turn causes a breakdown of the fluctuation theorem of the Gallavotti-Cohen type for quantum heat transfer. This can be restored only if (i) the geometric phase contribution vanishes and if (ii) the cyclic protocol preserves the detailed balance symmetry.

  14. Berry-Phase-Induced Heat Pumping and Its Impact on the Fluctuation Theorem

    NASA Astrophysics Data System (ADS)

    Ren, Jie; Hänggi, Peter; Li, Baowen

    2010-04-01

    Applying adiabatic, cyclic two-parameter modulations we investigate quantum heat transfer across an anharmonic molecular junction contacted with two heat baths. We demonstrate that the pumped heat typically exhibits a Berry-phase effect in providing an additional geometric contribution to heat flux. Remarkably, a robust fractional quantized geometric phonon response is identified as well. The presence of this geometric phase contribution in turn causes a breakdown of the fluctuation theorem of the Gallavotti-Cohen type for quantum heat transfer. This can be restored only if (i) the geometric phase contribution vanishes and if (ii) the cyclic protocol preserves the detailed balance symmetry.

  15. Feasibility of measuring temperature and density fluctuations in air using laser-induced O2 fluorescence

    NASA Technical Reports Server (NTRS)

    Massey, G. A.; Lemon, C. J.

    1984-01-01

    A tunable line-narrowed ArF laser can selectively excite several rotation al lines of the Schumann-Runge band system of O2 in air. The resulting ultraviolet fluorescence can be monitored at 90 deg to the laser beam axis, permitting space and time resolved observation of density and temperature fluctuations in turbulence. Experiments and calculations show that + or - 1 K, + or - 1 percent density, 1 cu mm spatial, and 1 microsecond temporal resolution can be achieved simultaneously under some conditions.

  16. Conductance fluctuations and disorder induced ν =0 quantum Hall plateau in topological insulator nanowires

    NASA Astrophysics Data System (ADS)

    Xypakis, Emmanouil; Bardarson, Jens H.

    2017-01-01

    Clean topological insulators exposed to a magnetic field develop Landau levels accompanied by a nonzero Hall conductivity for the infinite slab geometry. In this work we consider the case of disordered topological insulator nanowires and find, in contrast, that a zero Hall plateau emerges within a broad energy window close to the Dirac point. We numerically calculate the conductance and its distribution for a statistical ensemble of disordered nanowires, and use the conductance fluctuations to study the dependence of the insulating phase on system parameters, such as the nanowire length, disorder strength, and the magnetic field.

  17. Directivity of a Sparse Array in the Presence of Atmospheric-Induced Phase Fluctuations for Deep Space Communications

    NASA Technical Reports Server (NTRS)

    Nessel, James A.; Acosta, Robert J.

    2010-01-01

    Widely distributed (sparse) ground-based arrays have been utilized for decades in the radio science community for imaging celestial objects, but have only recently become an option for deep space communications applications with the advent of the proposed Next Generation Deep Space Network (DSN) array. But whereas in astronomical imaging, observations (receive-mode only) are made on the order of minutes to hours and atmospheric-induced aberrations can be mostly corrected for in post-processing, communications applications require transmit capabilities and real-time corrections over time scales as short as fractions of a second. This presents an unavoidable problem with the use of sparse arrays for deep space communications at Ka-band which has yet to be successfully resolved, particularly for uplink arraying. In this paper, an analysis of the performance of a sparse antenna array, in terms of its directivity, is performed to derive a closed form solution to the expected array loss in the presence of atmospheric-induced phase fluctuations. The theoretical derivation for array directivity degradation is validated with interferometric measurements for a two-element array taken at Goldstone, California. With the validity of the model established, an arbitrary 27-element array geometry is defined at Goldstone, California, to ascertain its performance in the presence of phase fluctuations. It is concluded that a combination of compact array geometry and atmospheric compensation is necessary to ensure high levels of availability.

  18. Brevity of haptic force perturbations induces heightened adaptive sensitivity.

    PubMed

    Wanda, Paul A; Fine, Michael S; Weeks, Heidi M; Gross, Andrew M; Macy, Jenny L; Thoroughman, Kurt A

    2013-05-01

    We have exposed human participants to both full-movement and pulsatile viscous force perturbations to study the effect of force duration on the incremental transformation of sensation into adaptation. Traditional views of movement biomechanics could suggest that pulsatile forces would largely be attenuated as stiffness and viscosity act as a natural low-pass filter. Sensory transduction, however, tends to react to changes in stimuli and therefore could underlie heightened sensitivity to briefer, pulsatile forces. Here, participants adapted within perturbation duration conditions in a manner proportionate to sensed force and positional errors. Across perturbation conditions, we found participants had greater adaptive sensitivity when experiencing pulsatile forces rather than full-movement forces. In a follow-up experiment, we employed error-clamped, force channel trials to determine changes in predictive force generation. We found that while participants learned to closely compensate for the amplitude and breadth of full-movement forces, they exhibited a persistent mismatch in amplitude and breadth between adapted motor output and experienced pulsatile forces. This mismatch could generate higher salience of error signals that contribute to heightened sensitivity to pulsatile forces.

  19. Detection of Non-Equilibrium Fluctuations in Active Gels

    NASA Astrophysics Data System (ADS)

    Bacanu, Alexandru; Broedersz, Chase; Gladrow, Jannes; Mackintosh, Fred; Schmidt, Christoph; Fakhri, Nikta

    Active force generation at the molecular scale in cells can result in stochastic non-equilibrium dynamics on mesoscpopic scales. Molecular motors such as myosin can drive steady-state stress fluctuations in cytoskeletal networks. Here, we present a non-invasive technique to probe non-equilibrium fluctuations in an active gel using single-walled carbon nanotubes (SWNTs). SWNTs are semiflexible polymers with intrinsic fluorescence in the near infrared. Both thermal and active motor-induced forces in the network induce transverse fluctuations of SWNTs. We demonstrate that active driven shape fluctuations of the SWNTs exhibit dynamics that reflect the non-equilibrium activity, in particular the emergence of correlations between the bending modes. We discuss the observation of breaking of detailed balance in this configurational space of the SWNT probes. Supported by National Defense Science and Engineering Graduate Student Fellowship (NDSEG).

  20. Dynamic interactions between a membrane binding protein and lipids induce fluctuating diffusivity

    PubMed Central

    Yamamoto, Eiji; Akimoto, Takuma; Kalli, Antreas C.; Yasuoka, Kenji; Sansom, Mark S. P.

    2017-01-01

    Pleckstrin homology (PH) domains are membrane-binding lipid recognition proteins that interact with phosphatidylinositol phosphate (PIP) molecules in eukaryotic cell membranes. Diffusion of PH domains plays a critical role in biological reactions on membrane surfaces. Although diffusivity can be estimated by long-time measurements, it lacks information on the short-time diffusive nature. We reveal two diffusive properties of a PH domain bound to the surface of a PIP-containing membrane using molecular dynamics simulations. One is fractional Brownian motion, attributed to the motion of the lipids with which the PH domain interacts. The other is temporally fluctuating diffusivity; that is, the short-time diffusivity of the bound protein changes substantially with time. Moreover, the diffusivity for short-time measurements is intrinsically different from that for long-time measurements. This fluctuating diffusivity results from dynamic changes in interactions between the PH domain and PIP molecules. Our results provide evidence that the complexity of protein-lipid interactions plays a crucial role in the diffusion of proteins on biological membrane surfaces. Changes in the diffusivity of PH domains and related membrane-bound proteins may in turn contribute to the formation/dissolution of protein complexes in membranes. PMID:28116358

  1. Increase in the Random Dopant Induced Threshold Fluctuations and Lowering in Sub 100 nm MOSFETs Due to Quantum Effects: A 3-D Density-Gradient Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, S.

    2000-01-01

    In this paper we present a detailed simulation study of the influence of quantum mechanical effects in the inversion layer on random dopant induced threshold voltage fluctuations and lowering in sub 100 nm MOSFETs. The simulations have been performed using a 3-D implementation of the density gradient (DG) formalism incorporated in our established 3-D atomistic simulation approach. This results in a self-consistent 3-D quantum mechanical picture, which implies not only the vertical inversion layer quantisation but also the lateral confinement effects related to current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical dopant fluctuations, is an increase in both threshold voltage fluctuations and lowering. At the same time, the random dopant induced threshold voltage lowering partially compensates for the quantum mechanical threshold voltage shift in aggressively scaled MOSFETs with ultrathin gate oxides.

  2. Ground state energy fluctuations in the nuclear shell model

    NASA Astrophysics Data System (ADS)

    Velázquez, Víctor; Hirsch, Jorge G.; Frank, Alejandro; Barea, José; Zuker, Andrés P.

    2005-05-01

    Statistical fluctuations of the nuclear ground state energies are estimated using shell model calculations in which particles in the valence shells interact through well-defined forces, and are coupled to an upper shell governed by random 2-body interactions. Induced ground-state energy fluctuations are found to be one order of magnitude smaller than those previously associated with chaotic components, in close agreement with independent perturbative estimates based on the spreading widths of excited states.

  3. The Risk of Noise-Induced Hearing Loss During Simulated Dives in Canadian Forces Hyperbaric Facilities

    DTIC Science & Technology

    2012-10-01

    The risk of noise-induced hearing loss during simulated dives in Canadian Forces hyperbaric facilities Sharon M...2012-084 October 2012 The risk of noise-induced hearing loss during simulated dives in Canadian Forces hyperbaric ...transferred into the dive chamber of a hyperbaric facility. The mechanism is audible and sufficiently high in level in adjacent areas to warrant the

  4. Harmonic tracking of acoustic radiation force-induced displacements.

    PubMed

    Doherty, Joshua R; Dahl, Jeremy J; Trahey, Gregg E

    2013-11-01

    Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse-inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse-inversion techniques. The method is implemented with acoustic radiation force impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8-MHz harmonic images created using a band-pass filter approach and the fully sampled pulse-inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower- and higher-frequency methods suggests that any improvement resulting from the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse-inversion harmonic ARFI images. Within the lumen, the harmonic tracking

  5. Harmonic Tracking of Acoustic Radiation Force Induced Displacements

    PubMed Central

    Doherty, Joshua R.; Dahl, Jeremy J.; Trahey, Gregg E.

    2014-01-01

    Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse inversion techniques. The method is implemented with Acoustic Radiation Force Impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8 MHz harmonic images created using a bandpass filter approach and the fully sampled pulse inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower and higher frequency methods suggests that any improvement due to the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse inversion harmonic ARFI images. Within the lumen, the harmonic tracking methods

  6. Computational Catalysis Using the Artificial Force Induced Reaction Method.

    PubMed

    Sameera, W M C; Maeda, Satoshi; Morokuma, Keiji

    2016-04-19

    The artificial force induced reaction (AFIR) method in the global reaction route mapping (GRRM) strategy is an automatic approach to explore all important reaction paths of complex reactions. Most traditional methods in computational catalysis require guess reaction paths. On the other hand, the AFIR approach locates local minima (LMs) and transition states (TSs) of reaction paths without a guess, and therefore finds unanticipated as well as anticipated reaction paths. The AFIR method has been applied for multicomponent organic reactions, such as the aldol reaction, Passerini reaction, Biginelli reaction, and phase-transfer catalysis. In the presence of several reactants, many equilibrium structures are possible, leading to a number of reaction pathways. The AFIR method in the GRRM strategy determines all of the important equilibrium structures and subsequent reaction paths systematically. As the AFIR search is fully automatic, exhaustive trial-and-error and guess-and-check processes by the user can be eliminated. At the same time, the AFIR search is systematic, and therefore a more accurate and comprehensive description of the reaction mechanism can be determined. The AFIR method has been used for the study of full catalytic cycles and reaction steps in transition metal catalysis, such as cobalt-catalyzed hydroformylation and iron-catalyzed carbon-carbon bond formation reactions in aqueous media. Some AFIR applications have targeted the selectivity-determining step of transition-metal-catalyzed asymmetric reactions, including stereoselective water-tolerant lanthanide Lewis acid-catalyzed Mukaiyama aldol reactions. In terms of establishing the selectivity of a reaction, systematic sampling of the transition states is critical. In this direction, AFIR is very useful for performing a systematic and automatic determination of TSs. In the presence of a comprehensive description of the transition states, the selectivity of the reaction can be calculated more accurately

  7. Doping-Induced Universal Conductance Fluctuations in GaN Nanowires.

    PubMed

    Elm, Matthias T; Uredat, Patrick; Binder, Jan; Ostheim, Lars; Schäfer, Markus; Hille, Pascal; Müßener, Jan; Schörmann, Jörg; Eickhoff, Martin; Klar, Peter J

    2015-12-09

    The transport properties of Ge-doped single GaN nanowires are investigated, which exhibit a weak localization effect as well as universal conductance fluctuations at low temperatures. By analyzing these quantum interference effects, the electron phase coherence length was determined. Its temperature dependence indicates that in the case of highly doped nanowires electron-electron scattering is the dominant dephasing mechanism, while for the slightly doped nanowires dephasing originates from Nyquist-scattering. The change of the dominant scattering mechanism is attributed to a modification of the carrier confinement caused by the Ge-doping. The results demonstrate that the phase coherence length can be tuned by the donor concentration making Ge-doped GaN nanowires an ideal model system for studying the influence of impurities on quantum-interference effects in mesoscopic and nanoscale systems.

  8. Cholesterol-induced suppression of membrane elastic fluctuations at the atomistic level.

    PubMed

    Molugu, Trivikram R; Brown, Michael F

    2016-09-01

    Applications of solid-state NMR spectroscopy for investigating the influences of lipid-cholesterol interactions on membrane fluctuations are reviewed in this paper. Emphasis is placed on understanding the energy landscapes and fluctuations at an emergent atomistic level. Solid-state (2)H NMR spectroscopy directly measures residual quadrupolar couplings (RQCs) due to individual C-(2)H labeled segments of the lipid molecules. Moreover, residual dipolar couplings (RDCs) of (13)C-(1)H bonds are obtained in separated local-field NMR spectroscopy. The distributions of RQC or RDC values give nearly complete profiles of the order parameters as a function of acyl segment position. Measured equilibrium properties of glycerophospholipids and sphingolipids including their binary and tertiary mixtures with cholesterol show unequal mixing associated with liquid-ordered domains. The entropic loss upon addition of cholesterol to sphingolipids is less than for glycerophospholipids and may drive the formation of lipid rafts. In addition relaxation time measurements enable one to study the molecular dynamics over a wide time-scale range. For (2)H NMR the experimental spin-lattice (R1Z) relaxation rates follow a theoretical square-law dependence on segmental order parameters (SCD) due to collective slow dynamics over mesoscopic length scales. The functional dependence for the liquid-crystalline lipid membranes is indicative of viscoelastic properties as they emerge from atomistic-level interactions. A striking decrease in square-law slope upon addition of cholesterol denotes stiffening relative to the pure lipid bilayers that is diminished in the case of lanosterol. Measured equilibrium properties and relaxation rates infer opposite influences of cholesterol and detergents on collective dynamics and elasticity at an atomistic scale that potentially affects lipid raft formation in cellular membranes.

  9. X-ray polarization fluctuations induced by cloud eclipses in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Marin, F.; Dovčiak, M.

    2015-01-01

    Context. A fraction of active galactic nuclei (AGN) show dramatic X-ray spectral changes on the day-to-week time scales associated with variation in the line of sight of the cold absorber. Aims: We intend to model the polarization fluctuations arising from an obscuration event, thereby offering a method of determining whether flux variations are due to occultation or extreme intrinsic emission variability. Methods: Undertaking 1-100 keV polarimetric simulations with the Monte Carlo code Stokes, we simulated the journey of a variety of cold gas clouds in front of an extended primary source. We varied the hydrogen column density nH and size of the absorber, as well as the initial polarization state of the emitting source, to cover a wide range of scenarios. Results: Simulations indicate that different results are expected according to the initial polarization of the extended continuum source. For unpolarized primary fluxes, large (~50°) variations of the polarization position angle ψ are expected before and after an occultation event, which is associated with very low residual polarization degrees (P ≪ 1%). In the case of an emitting disk with intrinsic, position-independent polarization, and for a given range of parameters, X-ray eclipses significantly alter the observed polarization spectra, with most of the variations seen in ψ. Finally, non-uniformly polarized emitting regions produce very distinctive polarization variations due to the successive covering and uncovering of different portions of the disk. Plotted against time, variations in P and ψ form detectable P Cygni type profiles that are distinctive signatures of non-axisymmetric emission. Conclusions: We find that X-ray polarimetry is particularly adapted to probing X-ray eclipses due to Compton-thin and Compton-thick gas clouds. Polarization measurements would distinguish between intrinsic intensity fluctuations and external eclipsing events, constrain the geometry of the covering medium, and test

  10. Cholesterol-Induced Suppression of Membrane Elastic Fluctuations at the Atomistic Level

    PubMed Central

    Molugu, Trivikram R.

    2017-01-01

    Applications of solid-state NMR spectroscopy for investigating the influences of lipid-cholesterol interactions on membrane fluctuations are reviewed in this paper. Emphasis is placed on understanding the energy landscapes and fluctuations at an emergent atomistic level. Solid-state 2H NMR spectroscopy directly measures residual quadrupolar couplings (RQCs) due to individual C–2H labeled segments of the lipid molecules. Moreover, residual dipolar couplings (RDCs) of 13C–1H bonds are obtained in separated local-field NMR spectroscopy. The distributions of RQC or RDC values give nearly complete profiles of the order parameters as a function of acyl segment position. Measured equilibrium properties of glycerophospholipids and sphingolipids including their binary and tertiary mixtures with cholesterol show unequal mixing associated with liquid-ordered domains. The entropic loss upon addition of cholesterol to sphingolipids is less than for glycerophospholipids and may drive the formation of lipid rafts. In addition relaxation time measurements enable one to study the molecular dynamics over a wide time-scale range. For 2H NMR the experimental spin-lattice (R1Z) relaxation rates follow a theoretical square-law dependence on segmental order parameters (SCD) due to collective slow dynamics over mesoscopic length scales. The functional dependence for the liquid-crystalline lipid membranes is indicative of viscoelastic properties as they emerge from atomistic-level interactions. A striking decrease in square-law slope upon addition of cholesterol denotes stiffening relative to the pure lipid bilayers that is diminished in the case of lanosterol. Measured equilibrium properties and relaxation rates infer opposite influences of cholesterol and detergents on collective dynamics and elasticity at an atomistic scale that potentially affects lipid raft formation in cellular membranes. PMID:27154600

  11. Fluctuating Hydrodynamics of Electrolytes Solutions

    NASA Astrophysics Data System (ADS)

    Peraud, Jean-Philippe; Nonaka, Andy; Chaudhri, Anuj; Bell, John B.; Donev, Aleksandar; Garcia, Alejandro L.

    2016-11-01

    In this work, we develop a numerical method for multicomponent solutions featuring electrolytes, in the context of fluctuating hydrodynamics as modeled by the Landau-Lifshitz Navier Stokes equations. Starting from a previously developed numerical scheme for multicomponent low Mach number fluctuating hydrodynamics, we study the effect of the additional forcing terms induced by charged species. We validate our numerical approach with additional theoretical considerations and with examples involving sodium-chloride solutions, with length scales close to Debye length. In particular, we show how charged species modify the structure factors of the fluctuations, both in equilibrium and non-equilibrium (giant fluctuations) systems, and show that the former is consistent with Debye-Huckel theory. We also discuss the consistency of this approach with the electroneutral approximation in regimes where characteristic length scales are significantly larger than the Debye length. Finally, we use this method to explore a type of electrokinetic instability. This work was supported by the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research,.

  12. Force-Induced H2S by PDLSCs Modifies Osteoclastic Activity during Tooth Movement.

    PubMed

    Liu, F; Wen, F; He, D; Liu, D; Yang, R; Wang, X; Yan, Y; Liu, Y; Kou, X; Zhou, Y

    2017-02-01

    Hydrogen sulfide (H2S), a gasotransmitter, has been recently linked to mesenchymal stem cell (MSC) function and bone homeostasis. Periodontal ligament stem cells (PDLSCs) are the main MSCs in PDL, which respond to mechanical force to induce physiological activities during orthodontic tooth movement (OTM). However, it is unknown whether mechanical force might induce endogenous H2S production by PDLSCs to regulate alveolar bone homeostasis. Here, we used a mouse OTM model to demonstrate that orthodontic force-induced endogenous H2S production in PDL tissue was associated with macrophage accumulation and osteoclastic activity in alveolar bone. Then, we showed that mechanical force application induced cystathionine β-synthase (CBS) expression and endogenous H2S production by PDLSCs. Moreover, blocking endogenous H2S or systemically increasing H2S levels could decrease or enhance force-induced osteoclastic activities to control tooth movement. We further revealed how force-induced H2S production by PDLSCs contributed to the secretion of monocyte chemoattractant protein-1 (MCP-1) and the expression of receptor activator of nuclear factor-κB ligand/osteoprotegerin (RANKL/OPG) system by PDLSCs. The secretion and expression of these factors controlled macrophage migration and osteoclast differentiation. This study demonstrated that PDLSCs produced H2S to respond to and transduce force signals. Force-induced gasotransmitter H2S production in PDLSCs therefore regulated osteoclastic activities in alveolar bone and controlled the OTM process through the MCP-1 secretion and RANKL/OPG system.

  13. Seismic wave attenuation and dispersion due to wave-induced fluid flow in rocks with strong permeability fluctuations.

    PubMed

    Germán Rubino, J; Monachesi, Leonardo B; Müller, Tobias M; Guarracino, Luis; Holliger, Klaus

    2013-12-01

    Oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy. The resulting seismic signature depends not only on the rock compressibility distribution, but also on a statistically averaged permeability. This so-called equivalent seismic permeability does not, however, coincide with the respective equivalent flow permeability. While this issue has been analyzed for one-dimensional (1D) media, the corresponding two-dimensional (2D) and three-dimensional (3D) cases remain unexplored. In this work, this topic is analyzed for 2D random medium realizations having strong permeability fluctuations. With this objective, oscillatory compressibility simulations based on the quasi-static poroelasticity equations are performed. Numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow, while the frequency range where these effects are significant gets broader. By comparing the acoustic responses obtained using different permeability averages, it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability, while for very high frequencies this parameter approaches the arithmetic average of the permeability field. These seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data.

  14. Fluctuating Arctic Sea ice thickness changes estimated by an in situ learned and empirically forced neural network model

    USGS Publications Warehouse

    Belchansky, G.I.; Douglas, D.C.; Platonov, N.G.

    2008-01-01

    Sea ice thickness (SIT) is a key parameter of scientific interest because understanding the natural spatiotemporal variability of ice thickness is critical for improving global climate models. In this paper, changes in Arctic SIT during 1982-2003 are examined using a neural network (NN) algorithm trained with in situ submarine ice draft and surface drilling data. For each month of the study period, the NN individually estimated SIT of each ice-covered pixel (25-km resolution) based on seven geophysical parameters (four shortwave and longwave radiative fluxes, surface air temperature, ice drift velocity, and ice divergence/convergence) that were cumulatively summed at each monthly position along the pixel's previous 3-yr drift track (or less if the ice was <3 yr old). Average January SIT increased during 1982-88 in most regions of the Arctic (+7.6 ?? 0.9 cm yr-1), decreased through 1996 Arctic-wide (-6.1 ?? 1.2 cm yr-1), then modestly increased through 2003 mostly in the central Arctic (+2.1 ?? 0.6 cm yr-1). Net ice volume change in the Arctic Ocean from 1982 to 2003 was negligible, indicating that cumulative ice growth had largely replaced the estimated 45 000 km3 of ice lost by cumulative export. Above 65??N, total annual ice volume and interannual volume changes were correlated with the Arctic Oscillation (AO) at decadal and annual time scales, respectively. Late-summer ice thickness and total volume varied proportionally until the mid-1990s, but volume did not increase commensurate with the thickening during 1996-2002. The authors speculate that decoupling of the ice thickness-volume relationship resulted from two opposing mechanisms with different latitudinal expressions: a recent quasi-decadal shift in atmospheric circulation patterns associated with the AO's neutral state facilitated ice thickening at high latitudes while anomalously warm thermal forcing thinned and melted the ice cap at its periphery. ?? 2008 American Meteorological Society.

  15. Can the Gulf Stream induce coherent short-term fluctuations in sea level along the US East Coast? A modeling study

    NASA Astrophysics Data System (ADS)

    Ezer, Tal

    2016-02-01

    Much attention has been given in recent years to observations and models that show that variations in the transport of the Atlantic Meridional Overturning Circulation (AMOC) and in the Gulf Stream (GS) can contribute to interannual, decadal, and multi-decadal variations in coastal sea level (CSL) along the US East Coast. However, less is known about the impact of short-term (time scales of days to weeks) fluctuations in the GS and their impact on CSL anomalies. Some observations suggest that these anomalies can cause unpredictable minor tidal flooding in low-lying areas when the GS suddenly weakens. Can these short-term CSL variations be attributed to changes in the transport of the GS? An idealized numerical model of the GS has been set up to test this proposition. The regional model uses a 1/12° grid with a simplified coastline to eliminate impacts from estuaries and small-scale coastal features and thus isolate the GS impact. The GS in the model is driven by inflows/outflows, representing the Florida Current (FC), the Slope Current (SC), and the Sargasso Sea (SS) flows. Forcing the model with an oscillatory FC transport with a period of 2, 5, and 10 days produced coherent CSL variations from Florida to the Gulf of Maine with similar periods. However, when imposing variations in the transports of the SC or the SS, they induce CSL variations only north of Cape Hatteras. The suggested mechanism is that variations in GS transport produce variations in sea level gradient across the entire GS length and this large-scale signal is then transmitted into the shelf by the generation of coastal-trapped waves (CTW). In this idealized model, the CSL variations induced by variations of ˜10 Sv in the transport of the GS are found to resemble CSL variations induced by ˜5 m s-1 zonal wind fluctuations, though the mechanisms of wind-driven and GS-driven sea level are quite different. Better understanding of the relation between variations in offshore currents and CSL will help

  16. Optical forces on metallic nanoparticles induced by a photonic nanojet.

    PubMed

    Cui, Xudong; Erni, Daniel; Hafner, Christian

    2008-09-01

    We investigate the optical forces acting on a metallic nanoparticle when the nanoparticle is introduced within a photonic nanojet (PNJ). Optical forces at resonance and off-resonance conditions of the microcylinder or nanoparticle are investigated. Under proper polarization conditions, the whispering gallery mode can be excited in the microcylinder, even at off resonance provided that scattering from the nanoparticle is strong enough. The optical forces are enhanced at resonance either of the single microcylinder or of the nanoparticle with respect to the forces under off-resonant illuminations. We found that the optical forces acting on the nanoparticle depend strongly on the dielectric permittivity of the nanoparticle, as well as on the intensity and the beam width of the PNJ. Hence, metallic sub-wavelength nanoparticle can be efficiently trapped by PNJs. Furthermore, the PNJ's attractive force can be simply changed to a repulsive force by varying the polarization of the incident beam. The changed sign of the force is related to the particle's polarizability and the excitation of localized surface plasmons in the nanoparticle.

  17. Force-induced remodelling of proteins and their complexes

    PubMed Central

    Chen, Yun; Radford, Sheena E; Brockwell, David J

    2015-01-01

    Force can drive conformational changes in proteins, as well as modulate their stability and the affinity of their complexes, allowing a mechanical input to be converted into a biochemical output. These properties have been utilised by nature and force is now recognised to be widely used at the cellular level. The effects of force on the biophysical properties of biological systems can be large and varied. As these effects are only apparent in the presence of force, studies on the same proteins using traditional ensemble biophysical methods can yield apparently conflicting results. Where appropriate, therefore, force measurements should be integrated with other experimental approaches to understand the physiological context of the system under study. PMID:25710390

  18. Cholesterol-induced variations in the volume and enthalpy fluctuations of lipid bilayers.

    PubMed Central

    Halstenberg, S; Heimburg, T; Hianik, T; Kaatze, U; Krivanek, R

    1998-01-01

    The sound velocity and density of suspensions of large unilamellar liposomes from dimyristoylphosphatidylcholine with admixed cholesterol have been measured as a function of temperature around the chain melting temperature of the phospholipid. The cholesterol-to-phospholipid molar ratio xc has been varied over a wide range (0 fluctuations within the samples. A theoretical relation between the compressibility and the excess heat capacity of the bilayer system has been derived. Comparison of the compressibilities (and sound velocity numbers) with heat capacity traces display the close correlation between these quantities for bilayer systems. This correlation appears to be very useful as it allows some of the mechanical properties of membrane systems to be calculated from the specific heat capacity data and vice versa. PMID:9649386

  19. Manganese oxidation induced by water table fluctuations in a sand column.

    PubMed

    Farnsworth, Claire E; Voegelin, Andreas; Hering, Janet G

    2012-01-03

    On-off cycles of production wells, especially in bank filtration settings, cause oscillations in the local water table, which can deliver significant amounts of dissolved oxygen (DO) to the shallow groundwater. The potential for DO introduced in this manner to oxidize manganese(II) (Mn(II)), mediated by the obligate aerobe Pseudomonas putida GB-1, was tested in a column of quartz sand fed with anoxic influent solution and subject to 1.3 m water table changes every 30-50 h. After a period of filter ripening, 100 μM Mn was rapidly removed during periods of low water table and high dissolved oxygen concentrations. The accumulation of Mn in the column was confirmed by XRF analysis of the sand at the conclusion of the study, and both measured net oxidation rates and XAS analysis suggest microbial oxidation as the dominant process. The addition of Zn, which inhibited GB-1 Mn oxidation but not its growth, interrupted the Mn removal process, but Mn oxidation recovered within one water table fluctuation. Thus transient DO conditions could support microbially mediated Mn oxidation, and this process could be more relevant in shallow groundwater than previously thought.

  20. Carrier-Number-Fluctuation Induced Ultralow 1/f Noise Level in Top-Gated Graphene Field Effect Transistor.

    PubMed

    Peng, Songang; Jin, Zhi; Zhang, Dayong; Shi, Jingyuan; Mao, Dacheng; Wang, Shaoqing; Yu, Guanghui

    2017-03-01

    A top-gated graphene FET with an ultralow 1/f noise level of 1.8 × 10(-12) μm(2)Hz(1-) (f = 10 Hz) has been fabricated. The noise has the least value at Dirac point, it then increases fast when the current deviates from that at Dirac point, the noise slightly decreases at large current. The phenomenon can be understood by the carrier-number-fluctuation induced low frequency noise, which caused by the trapping-detrapping processes of the carriers. Further analysis suggests that the effect trap density depends on the location of Fermi level in graphene channel. The study has provided guidance for suppressing the 1/f noise in graphene-based applications.

  1. Synchronization transitions induced by the fluctuation of adaptive coupling strength in delayed Newman-Watts neuronal networks.

    PubMed

    Wang, Qi; Gong, Yubing; Wu, Yanan

    2015-11-01

    Introducing adaptive coupling in delayed neuronal networks and regulating the dissipative parameter (DP) of adaptive coupling by noise, we study the effect of fluctuations of the changing rate of adaptive coupling on the synchronization of the neuronal networks. It is found that time delay can induce synchronization transitions for intermediate DP values, and the synchronization transitions become strongest when DP is optimal. As the intensity of DP noise is varied, the neurons can also exhibit synchronization transitions, and the phenomenon is delay-dependent and is enhanced for certain time delays. Moreover, the synchronization transitions change with the change of DP and become strongest when DP is optimal. These results show that randomly changing adaptive coupling can considerably change the synchronization of the neuronal networks, and hence could play a crucial role in the information processing and transmission in neural systems.

  2. Endogenous insulin fluctuations during glucose-induced paralysis in patients with familial periodic hypokalemia.

    PubMed

    Johnsen, T

    1977-11-01

    Endogenous insulin production in patients with familial periodic hypokalemia has not previously been studied during induced attacks. The serum insulin, serum potassium, and blood glucose concentrations were measured in six patients with familial periodic hypokalemia during six attacks of paralysis induced by long-lasting glucose stimulation. The same parameters were measured in four normal subjects under the same conditions. There was no difference in insulin response or in blood glucose between the two groups. Basal insulin levels showed no difference. There was no correlation between the occurrence of the attack and the serum insulin level in the patients. All the patients responded by severe paralysis and hypokalemia.

  3. Polarization force-induced changes in the dust sheath formation

    SciTech Connect

    Mayout, Saliha; Bentabet, Karima; Tribeche, Mouloud

    2015-09-15

    The modifications arising in the dusty plasma sheath structure due to the presence of polarization forces acting on the dust grains are investigated. The corresponding appropriate Bohm criterion for sheath formation is obtained. It is found that the critical Mach number, beyond which the dusty plasma electrostatic sheath sets in, decreases whenever the polarization effects become important. In addition, when the polarization force dominates over the electrical one, the dust plasma sheath cannot set in. This happens whenever the dust grain size exceeds a critical threshold. Moreover, the sheath electrostatic potential-gradient becomes abruptly steep, and the sheath thickness becomes broader as the polarization force effects strengthen.

  4. Chemotherapy Drug Induced Discoordination of Mitochondrial Life Cycle Detected by Cardiolipin Fluctuation

    PubMed Central

    Chao, Yu-Jen; Chan, Jui-Fen; Hsu, Yuan-Hao Howard

    2016-01-01

    Chemotherapy drugs have been prescribed for the systemic treatment of cancer. We selected three chemotherapy drugs, including methotrexate, mitomycine C and vincristine to inhibit the proliferation of HT1080 human fibrosarcoma cells in S, G2 and M phases of the cell cycle respectively. These chemotherapy drugs showed significant toxicity and growth inhibition to the cancer cells measured by MTT assay. After treated with a 50% inhibitory dosage for 48 hours, these cancer cells showed significant accumulation of cardiolipin (CL), which was a reverse trend of the nutritional deficiency induced arrest at G1 phase. The quantity of each CL species was further semi-quantitated by HPLC-ion trap mass spectrometer. Methotraxate treatment caused unique increases of acyl chain length on CL, which were the opposite of the serum starvation, mitomycine C and vincristine treatments. Although mitomycine C and vincristine have different mechanisms to induce cell cycle arrest, these two drugs displayed similar effects on decreasing chain length of CL. Continuation of CL synthesis during cell cycle arrest indicated the chemotherapy drugs resulting in the discoordination of the mitochondrial life cycle from the cell cycle and thus caused the accumulation of CL. These finding reveals that the pre-remodeling nascent CL accumulates during the methotraxate induced arrest; however, the post-remodeling mature CL accumulates during the mitomycine C and vincristine induced arrest after the synthesis phase. PMID:27627658

  5. Cold induces micro- and nano-scale reorganization of lipid raft markers at mounds of T-cell membrane fluctuations.

    PubMed

    Chen, Yong; Qin, Jie; Cai, Jiye; Chen, Zheng W

    2009-01-01

    Whether and how cold causes changes in cell-membrane or lipid rafts remain poorly characterized. Using the NSOM/QD and confocal imaging systems, we found that cold caused microscale redistribution of lipid raft markers, GM1 for lipid and CD59 for protein, from the peripheral part of microdomains to the central part on Jurkat T cells, and that cold also induced the nanoscale size-enlargement (1/3- to 2/3-fold) of the nanoclusters of lipid raft markers and even the colocalization of GM1 and CD59 nanoclusters. These findings indicate cold-induced lateral rearrangement/coalescence of raft-related membrane heterogeneity. The cold-induced re-distribution of lipid raft markers under a nearly-natural condition provide clues for their alternations, and help to propose a model in which raft lipids associate themselves or interact with protein components to generate functional membrane heterogeneity in response to stimulus. The data also underscore the possible cold-induced artifacts in early-described cold-related experiments and the detergent-resistance-based analyses of lipid rafts at 4 degrees C, and provide a biophysical explanation for recently-reported cold-induced activation of signaling pathways in T cells. Importantly, our fluorescence-topographic NSOM imaging demonstrated that GM1/CD59 raft markers distributed and re-distributed at mounds but not depressions of T-cell membrane fluctuations. Such mound-top distribution of lipid raft markers or lipid rafts provides spatial advantage for lipid rafts or contact molecules interacting readily with neighboring cells or free molecules.

  6. EMG and peak force responses to PNF stretching and the relationship between stretching-induced force deficits and bilateral deficits

    PubMed Central

    Cengiz, Asim

    2015-01-01

    [Purpose] The aim of the present study was to investigate the possibility of an interaction between stretching induced deficit (SFD) and bilateral deficits (BLD) during maximal voluntary isometric hand flexion under PNF stretch and no-stretch conditions through measurement of EMG and force production. [Subjects and Methods] Ten physically active male Caucasian students (age, 24.1±2.38 years; body mass, 79.48±11.40 kg; height, 174.15±0.8 cm) volunteered to participate in this study. EMG and force measurements of the subjects were recorded during either unilateral or bilateral 3-second maximal voluntary isometric hand flexion (MVC) against a force transducer. The paired sample t-test was used to examine the significance of differences among several conditions. Pearson product-moment correlation was used to evaluate the associations between different parameters. [Results] Stretching-induced deficits correlated with bilateral deficits in both force (r=0.85) and iEMG (r=0.89). PNF stretching caused significant decrements in the bilateral and unilateral conditions for both the right and left sides. [Conclusion] Since both force and iEMG decreases were observed in most measurements; it suggests there is a neural mechanism behinnd both the BLD and the SFD. PMID:25931696

  7. A magnetic gradient induced force in NMR restricted diffusion experiments

    SciTech Connect

    Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

    2014-03-28

    We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested.

  8. Effect of baclofen, a GABAB-agonist, on forced swimming-induced immobility in mice.

    PubMed

    Aley, K O; Kulkarni, S K

    1990-01-01

    The effect of baclofen, a GABAB-agonist, was studied on both forced swimming-induced immobility and isoprenaline-induced enhancement of forced swimming-induced immobility in mice. (+/-) Baclofen (0.5 and 1 mg/kg), and (-) baclofen (0.5, 1 and 2 mg/kg) attenuated forced swimming-induced immobility. The effect of baclofen was not reversed by bicuculline, a GABAA-antagonist. Baclofen also reduced isoprenaline-induced enhancement of forced swimming-induced immobility. On concomitant administration of a subeffective dose of baclofen with a subeffective dose of propranolol, desipramine and amitriptyline, a potentiating effect was observed. These results are corroborative of our previous finding that GABAergic agents, particularly GABAB-receptors, play a role in the modulation of despair behavior in mice and in the action of antidepressant drugs. Baclofen (5 mg/kg) did not produce any significant effect on forced swimming-induced immobility, but reduced significantly the locomotor activity of the animals. Lower doses (0.5 and 1 mg/kg) of baclofen, which reduced the forced swimming-induced immobility, did not affect the locomotor activity. At higher and lower tissue concentrations of the drug, involvement of different receptor populations is suggested.

  9. A new motor model representing the stretch-induced force enhancement and shortening-induced force depression in skeletal muscle.

    PubMed

    Tamura, Youjiro; Saito, Masami; Nagato, Rie

    2005-04-01

    A motor model that consists of two Maxwell elements with a force generator and one Voigt element is proposed in this paper. The motor model can achieve a hyperbolic force-velocity relation when we alter weight functions applied to the Maxwell elements and the force generator. Rate coefficients are introduced to determine the weight function and to improve the motor performance and the time course of the motor force. The weight functions are used as a controller of the motor. We assume that the mechanical impulse applied to the motor affects the rate coefficients and found that the amount of the mechanical impulse is related to the amount of force depression following motor shortening and to the amount of force enhancement following motor stretching. The time courses of the motor force following shortening and stretching quantitatively resemble those in other muscle experiments. The maximum energy efficiency of the motor that we obtained was 50% with an ATP hydrolysis type and 25% with an AC-DC motor type.

  10. Residual force enhancement following eccentric induced muscle damage.

    PubMed

    Power, Geoffrey A; Rice, Charles L; Vandervoort, Anthony A

    2012-06-26

    During lengthening of an activated skeletal muscle, the force maintained following the stretch is greater than the isometric force at the same muscle length. This is termed residual force enhancement (RFE), but it is unknown how muscle damage following repeated eccentric contractions affects RFE. Using the dorsiflexors, we hypothesised muscle damage will impair the force generating sarcomeric structures leading to a reduction in RFE. Following reference maximal voluntary isometric contractions (MVC) in 8 young men (26.5±2.8y) a stretch was performed at 30°/s over a 30° ankle excursion ending at the same muscle length as the reference MVCs (30° plantar flexion). Surface electromyography (EMG) of the tibialis anterior and soleus muscles was recorded during all tasks. The damage protocol involved 4 sets of 25 isokinetic (30°/s) lengthening contractions. The same measures were collected at baseline and immediately post lengthening contractions, and for up to 10min recovery. Following the lengthening contraction task, there was a 30.3±6.4% decrease in eccentric torque (P<0.05) and 36.2±9.7% decrease in MVC (P<0.05) compared to baseline. Voluntary activation using twitch interpolation and RMS EMG amplitude of the tibialis anterior remained near maximal without increased coactivation for MVC. Contrary to our hypothesis, RFE increased (∼100-250%) following muscle damage (P<0.05). It appears stretch provided a mechanical strategy for enhanced muscle function compared to isometric actions succeeding damage. Thus, active force of cross-bridges is decreased because of impaired excitation-contraction coupling but force generated during stretch remains intact because force contribution from stretched sarcomeric structures is less impaired.

  11. Magnetic field induced enlargement of the regime of critical fluctuations in the classical superconductor V3Si from high-resolution specific heat experiments

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Liu, Y.; Toyota, N.; Lortz, R.

    2015-02-01

    We present high-resolution specific heat data from a high-purity single crystal of the classical superconductor V3Si, which reveal tiny lambda-shape anomalies at the superconducting transition superimposed onto the BCS specific heat jump in magnetic fields of 2 T and higher. The appearance of these anomalies is accompanied by a magnetic-field-induced broadening of the superconducting transition. We demonstrate, using scaling relations predicted by the fluctuation models of the 3d-XY and the 3d-lowest-Landau-level (3d-LLL) universality class that the effect of critical fluctuations becomes experimentally observable due to of a magnetic field-induced enlargement of the regime of critical fluctuations. The scaling indicates that a reduction of the effective dimensionality due to the confinement of quasiparticles into low Landau levels is responsible for this effect.

  12. APPLICATIONS OF LASERS AND OTHER TOPICS IN LASER PHYSICS AND TECHNOLOGY: Influence of atmospheric fluctuations of the induced temperature on the characteristics of laser radiation

    NASA Astrophysics Data System (ADS)

    Banakh, Viktor A.; Smalikho, I. N.

    1987-10-01

    The expression for the function representing the second-order mutual coherence of a laser beam propagating in a turbulent atmosphere under thermal self-interaction conditions is derived in the aberration-free approximation. An analysis is made of the width of a beam, its wind refraction, and the radius of coherence as a function of the initial coherence of the radiation, of conditions of diffraction on the transmitting aperture, and of fluctuations of the wind velocity. It is shown that on increase in the power the coherence radius of cw laser radiation first increases because of thermal defocusing and then decreases due to the appearance (because of fluctuations of the wind velocity) of induced temperature inhomogeneities in air in the beam localization region. The conditions under which fluctuations of the induced temperature have a significant influence on the coherence of the radiation are determined.

  13. The 4-Dimensional Plant: Effects of Wind-Induced Canopy Movement on Light Fluctuations and Photosynthesis

    PubMed Central

    Burgess, Alexandra J.; Retkute, Renata; Preston, Simon P.; Jensen, Oliver E.; Pound, Michael P.; Pridmore, Tony P.; Murchie, Erik H.

    2016-01-01

    Physical perturbation of a plant canopy brought about by wind is a ubiquitous phenomenon and yet its biological importance has often been overlooked. This is partly due to the complexity of the issue at hand: wind-induced movement (or mechanical excitation) is a stochastic process which is difficult to measure and quantify; plant motion is dependent upon canopy architectural features which, until recently, were difficult to accurately represent and model in 3-dimensions; light patterning throughout a canopy is difficult to compute at high-resolutions, especially when confounded by other environmental variables. Recent studies have reinforced the expectation that canopy architecture is a strong determinant of productivity and yield; however, links between the architectural properties of the plant and its mechanical properties, particularly its response to wind, are relatively unknown. As a result, biologically relevant data relating canopy architecture, light- dynamics, and short-scale photosynthetic responses in the canopy setting are scarce. Here, we hypothesize that wind-induced movement will have large consequences for the photosynthetic productivity of our crops due to its influence on light patterning. To address this issue, in this study we combined high resolution 3D reconstructions of a plant canopy with a simple representation of canopy perturbation as a result of wind using solid body rotation in order to explore the potential effects on light patterning, interception, and photosynthetic productivity. We looked at two different scenarios: firstly a constant distortion where a rice canopy was subject to a permanent distortion throughout the whole day; and secondly, a dynamic distortion, where the canopy was distorted in incremental steps between two extremes at set time points in the day. We find that mechanical canopy excitation substantially alters light dynamics; light distribution and modeled canopy carbon gain. We then discuss methods required for

  14. The 4-Dimensional Plant: Effects of Wind-Induced Canopy Movement on Light Fluctuations and Photosynthesis.

    PubMed

    Burgess, Alexandra J; Retkute, Renata; Preston, Simon P; Jensen, Oliver E; Pound, Michael P; Pridmore, Tony P; Murchie, Erik H

    2016-01-01

    Physical perturbation of a plant canopy brought about by wind is a ubiquitous phenomenon and yet its biological importance has often been overlooked. This is partly due to the complexity of the issue at hand: wind-induced movement (or mechanical excitation) is a stochastic process which is difficult to measure and quantify; plant motion is dependent upon canopy architectural features which, until recently, were difficult to accurately represent and model in 3-dimensions; light patterning throughout a canopy is difficult to compute at high-resolutions, especially when confounded by other environmental variables. Recent studies have reinforced the expectation that canopy architecture is a strong determinant of productivity and yield; however, links between the architectural properties of the plant and its mechanical properties, particularly its response to wind, are relatively unknown. As a result, biologically relevant data relating canopy architecture, light- dynamics, and short-scale photosynthetic responses in the canopy setting are scarce. Here, we hypothesize that wind-induced movement will have large consequences for the photosynthetic productivity of our crops due to its influence on light patterning. To address this issue, in this study we combined high resolution 3D reconstructions of a plant canopy with a simple representation of canopy perturbation as a result of wind using solid body rotation in order to explore the potential effects on light patterning, interception, and photosynthetic productivity. We looked at two different scenarios: firstly a constant distortion where a rice canopy was subject to a permanent distortion throughout the whole day; and secondly, a dynamic distortion, where the canopy was distorted in incremental steps between two extremes at set time points in the day. We find that mechanical canopy excitation substantially alters light dynamics; light distribution and modeled canopy carbon gain. We then discuss methods required for

  15. Attosecond Electro-Magnetic Forces Acting on Metal Nanospheres Induced By Relativistic Electrons

    NASA Astrophysics Data System (ADS)

    Lagos, M. J.; Batson, P. E.; Reyes-Coronado, A.; Echenique, P. M.; Aizpurua, J.

    2014-03-01

    Swift electron scattering near nanoscale materials provides information about light-matter behavior, including induced forces. We calculate time-dependent electromagnetic forces acting on 1-1.5 nm metal nanospheres induced by passing swift electrons, finding both impulse-like and oscillatory response forces. Initially, impulse-like forces are generated by a competition between attractive electric forces and repulsive magnetic forces, lasting a few attoseconds (5-10 as). Oscillatory, plasmonic response forces take place later in time, last a few femtoseconds (1- 5 fs), and apparently rely on photon emission by decay of the electron-induced surface plasmons. A comparison of the strength of these two forces suggests that the impulse-like behavior dominates the process, and can transfer significant linear momentum to the sphere. Our results advance understanding of the physics behind the observation of both attractive and repulsive behavior of gold nano-particles induced by electron beams in aberration-corrected electron microscopy. Work supported under DOE, Award # DE-SC0005132, Basque Gov. project ETORTEK inano, Spanish Ministerio de Ciencia e Innovacion, No. FIS2010-19609-C02-01.

  16. Force Responses and Sarcomere Dynamics of Cardiac Myofibrils Induced by Rapid Changes in [Pi].

    PubMed

    Stehle, Robert

    2017-01-24

    The second phase of the biphasic force decay upon release of phosphate from caged phosphate was previously interpreted as a signature of kinetics of the force-generating step in the cross-bridge cycle. To test this hypothesis without using caged compounds, force responses and individual sarcomere dynamics upon rapid increases or decreases in concentration of inorganic phosphate [Pi] were investigated in calcium-activated cardiac myofibrils. Rapid increases in [Pi] induced a biphasic force decay with an initial slow decline (phase 1) and a subsequent 3-5-fold faster major decay (phase 2). Phase 2 started with the distinct elongation of a single sarcomere, the so-called sarcomere "give". "Give" then propagated from sarcomere to sarcomere along the myofibril. Propagation speed and rate constant of phase 2 (k+Pi(2)) had a similar [Pi]-dependence, indicating that the kinetics of the major force decay (phase 2) upon rapid increase in [Pi] is determined by sarcomere dynamics. In contrast, no "give" was observed during phase 1 after rapid [Pi]-increase (rate constant k+Pi(1)) and during the single-exponential force rise (rate constant k-Pi) after rapid [Pi]-decrease. The values of k+Pi(1) and k-Pi were similar to the rate constant of mechanically induced force redevelopment (kTR) and Ca(2+)-induced force development (kACT) measured at same [Pi]. These results indicate that the major phase 2 of force decay upon a Pi-jump does not reflect kinetics of the force-generating step but results from sarcomere "give". The other phases of Pi-induced force kinetics that occur in the absence of "give" yield the same information as mechanically and Ca(2+)-induced force kinetics (k+Pi(1) ∼ k-Pi ∼ kTR ∼ kACT). Model simulations indicate that Pi-induced force kinetics neither enable the separation of Pi-release from the rate-limiting transition f into force states nor differentiate whether the "force-generating step" occurs before, along, or after the Pi-release.

  17. Earth-tide-induced fluctuations in the salinity of an inland river, New South Wales, Australia: a short-term study.

    PubMed

    Jasonsmith, J F; Macdonald, B C T; White, I

    2017-04-01

    Wybong Creek discharges salts into the agriculturally and industrially important Hunter River in New South Wales, Australia. Abrupt increases in salinity occur periodically in the mid-Wybong Creek catchment. In order to understand the processes which cause these abrupt increases, changes in surface and groundwater were investigated. It is shown that salinity increases can be attributed to highly discrete groundwater discharge directly into the river from below. Hourly electrical conductivity data measured in the river showed regular, diurnal electrical conductivity fluctuations of up to 350 μS cm(-1). These fluctuations could not be attributed to barometric pressure, temperature, or evapotranspiration. Instead, a similar periodicity in surface water electrical conductivity and groundwater height in nearby groundwater wells was found. Fluctuations were of similar periodicity to the orthotides which cause fluctuations in surface water height and are induced by Earth tides. The geology in the mid-catchment area indicates conditions are optimal for Earth tides to impact groundwater. The reporting of orthotidal changes in water chemistry in this article is believed to be the first of its kind in the scientific literature, with the large fluctuations noted having important implications for water monitoring and management in the catchment. Further research investigating Earth-tide-induced phases of groundwater heights will better constrain the relationships between surface water chemistry and groundwater height.

  18. Anomalous transport and diffusion phenomena induced by biharmonic forces in deformable potential systems

    NASA Astrophysics Data System (ADS)

    Mbemmo, André Marie Fopossi; Kenmoé, Germaine Djuidjé; Kofané, Timoléon Crépin

    2016-09-01

    We study transport properties of an inertial Brownian motor which moves in a deformable Remoissenet-Peyrad periodic potential and is subjected to both a static bias force and time periodic driving biharmonic force. By modifying the shape of the potential, the anomalous transport is identified for a particular set of the system parameters. For a particular potential shape, the mean velocity of a particle is modified by going from negative to positive values according to the external bias force. These features also depend on both the biharmonic parameter and the phase-lag of two signals. A remarkable transition of the negative velocity depending on the shape of the potential is observed. We also focus on the efficiency of the motor and discuss velocity fluctuation. In addition, within selected system parameters, different types of diffusion particle such as subdiffusion, superdiffusion, normal diffusion, ballistic diffusion, hyperdiffusion and dispersionless transport phenomena are generated in the system.

  19. Revisiting detrended fluctuation analysis

    PubMed Central

    Bryce, R. M.; Sprague, K. B.

    2012-01-01

    Half a century ago Hurst introduced Rescaled Range (R/S) Analysis to study fluctuations in time series. Thousands of works have investigated or applied the original methodology and similar techniques, with Detrended Fluctuation Analysis becoming preferred due to its purported ability to mitigate nonstationaries. We show Detrended Fluctuation Analysis introduces artifacts for nonlinear trends, in contrast to common expectation, and demonstrate that the empirically observed curvature induced is a serious finite-size effect which will always be present. Explicit detrending followed by measurement of the diffusional spread of a signals' associated random walk is preferable, a surprising conclusion given that Detrended Fluctuation Analysis was crafted specifically to replace this approach. The implications are simple yet sweeping: there is no compelling reason to apply Detrended Fluctuation Analysis as it 1) introduces uncontrolled bias; 2) is computationally more expensive than the unbiased estimator; and 3) cannot provide generic or useful protection against nonstationaries. PMID:22419991

  20. Fluctuations of electrical and mechanical properties of diamond induced by interstitial hydrogen

    NASA Astrophysics Data System (ADS)

    Zhuang, Chun-Qiang; Liu, Lei

    2015-01-01

    While experimental evidence demonstrates that the presence of hydrogen (H) impurities in diamond films plays a significant role in determining their physical properties, the small radius of the H atom makes detecting such impurities quite a challenging task. In the present work, first-principles calculations were employed to provide an insight into the effects of the interstitial hydrogen on the electrical and mechanical properties of diamond crystals at the atomic level. The migrated pathways of the interstitial hydrogen are dictated by energetic considerations. Some new electronic states are formed near the Fermi level. The interstitial hydrogen markedly narrows the bandgap of the diamond and weakens the diamond crystal. The obvious decrement of the critical strain clearly implies the presence of an H-induced embrittlement effect. Project supported by the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality, China (Grant No. IDHT20140504), the National Natural Science Foundation of China (Grant No. 51402009), and the Foundation for Young Scholars of Beijing University of Technology, China.

  1. Synergistic Modification Induced Specific Recognition between Histone and TRIM24 via Fluctuation Correlation Network Analysis

    PubMed Central

    Zhang, Jinmai; Luo, Huajie; Liu, Hao; Ye, Wei; Luo, Ray; Chen, Hai-Feng

    2016-01-01

    Histone modification plays a key role in gene regulation and gene expression. TRIM24 as a histone reader can recognize histone modification. However the specific recognition mechanism between TRIM24 and histone modification is unsolved. Here, systems biology method of dynamics correlation network based on molecular dynamics simulation was used to answer the question. Our network analysis shows that the dynamics correlation network of H3K23ac is distinctly different from that of wild type and other modifications. A hypothesis of “synergistic modification induced recognition” is then proposed to link histone modification and TRIM24 binding. These observations were further confirmed from community analysis of networks with mutation and network perturbation. Finally, a possible recognition pathway is also identified based on the shortest path search for H3K23ac. Significant difference of recognition pathway was found among different systems due to methylation and acetylation modifications. The analysis presented here and other studies show that the dynamic network-based analysis might be a useful general strategy to study the biology of protein post-translational modification and associated recognition. PMID:27079666

  2. Synergistic Modification Induced Specific Recognition between Histone and TRIM24 via Fluctuation Correlation Network Analysis

    NASA Astrophysics Data System (ADS)

    Zhang, Jinmai; Luo, Huajie; Liu, Hao; Ye, Wei; Luo, Ray; Chen, Hai-Feng

    2016-04-01

    Histone modification plays a key role in gene regulation and gene expression. TRIM24 as a histone reader can recognize histone modification. However the specific recognition mechanism between TRIM24 and histone modification is unsolved. Here, systems biology method of dynamics correlation network based on molecular dynamics simulation was used to answer the question. Our network analysis shows that the dynamics correlation network of H3K23ac is distinctly different from that of wild type and other modifications. A hypothesis of “synergistic modification induced recognition” is then proposed to link histone modification and TRIM24 binding. These observations were further confirmed from community analysis of networks with mutation and network perturbation. Finally, a possible recognition pathway is also identified based on the shortest path search for H3K23ac. Significant difference of recognition pathway was found among different systems due to methylation and acetylation modifications. The analysis presented here and other studies show that the dynamic network-based analysis might be a useful general strategy to study the biology of protein post-translational modification and associated recognition.

  3. Zero field splitting fluctuations induced phase relaxation of Gd3+ in frozen solutions at cryogenic temperatures

    PubMed Central

    Raitsimring, A.; Dalaloyan, A.; Collauto, A.; Feintuch, A.; Meade, T.; Goldfarb, D.

    2015-01-01

    Distance measurements using double electron–electron resonance (DEER) and Gd3+ chelates for spin labels (GdSL) have been shown to be an attractive alternative to nitroxide spin labels at W-band (95 GHz). The maximal distance that can be accessed by DEER measurements and the sensitivity of such measurements strongly depends on the phase relaxation of Gd3+ chelates in frozen, glassy solutions. In this work, we explore the phase relaxation of Gd3+-DOTA as a representative of GdSL in temperature and concentration ranges typically used for W-band DEER measurements. We observed that in addition to the usual mechanisms of phase relaxation known for nitroxide based spin labels, GdSL are subjected to an additional phase relaxation mechanism that features an increase in the relaxation rate from the center to the periphery of the EPR spectrum. Since the EPR spectrum of GdSL is the sum of subspectra of the individual EPR transitions, we attribute this field dependence to transition dependent phase relaxation. Using simulations of the EPR spectra and its decomposition into the individual transition subspectra, we isolated the phase relaxation of each transition and found that its rate increases with |ms|. We suggest that this mechanism is due to transient zero field splitting (tZFS), where its magnitude and correlation time are scaled down and distributed as compared with similar situations in liquids. This tZFS induced phase relaxation mechanism becomes dominant (or at least significant) when all other well-known phase relaxation mechanisms, such as spectral diffusion caused by nuclear spin diffusion, instantaneous and electron spin spectral diffusion, are significantly suppressed by matrix deuteration and low concentration, and when the temperature is sufficiently low to disable spin lattice interaction as a source of phase relaxation. PMID:25442776

  4. Zero field splitting fluctuations induced phase relaxation of Gd3+ in frozen solutions at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Raitsimring, A.; Dalaloyan, A.; Collauto, A.; Feintuch, A.; Meade, T.; Goldfarb, D.

    2014-11-01

    Distance measurements using double electron-electron resonance (DEER) and Gd3+ chelates for spin labels (GdSL) have been shown to be an attractive alternative to nitroxide spin labels at W-band (95 GHz). The maximal distance that can be accessed by DEER measurements and the sensitivity of such measurements strongly depends on the phase relaxation of Gd3+ chelates in frozen, glassy solutions. In this work, we explore the phase relaxation of Gd3+-DOTA as a representative of GdSL in temperature and concentration ranges typically used for W-band DEER measurements. We observed that in addition to the usual mechanisms of phase relaxation known for nitroxide based spin labels, GdSL are subjected to an additional phase relaxation mechanism that features an increase in the relaxation rate from the center to the periphery of the EPR spectrum. Since the EPR spectrum of GdSL is the sum of subspectra of the individual EPR transitions, we attribute this field dependence to transition dependent phase relaxation. Using simulations of the EPR spectra and its decomposition into the individual transition subspectra, we isolated the phase relaxation of each transition and found that its rate increases with |ms|. We suggest that this mechanism is due to transient zero field splitting (tZFS), where its magnitude and correlation time are scaled down and distributed as compared with similar situations in liquids. This tZFS induced phase relaxation mechanism becomes dominant (or at least significant) when all other well-known phase relaxation mechanisms, such as spectral diffusion caused by nuclear spin diffusion, instantaneous and electron spin spectral diffusion, are significantly suppressed by matrix deuteration and low concentration, and when the temperature is sufficiently low to disable spin lattice interaction as a source of phase relaxation.

  5. A complex social-ecological disaster: Environmentally induced forced migration

    PubMed Central

    Rechkemmer, Andreas; O'Connor, Ashley; Rai, Abha; Decker Sparks, Jessica L.; Mudliar, Pranietha; Shultz, James M.

    2016-01-01

    ABSTRACT In the 21st century, global issues are increasingly characterized by inter-connectedness and complexity. Global environmental change, and climate change in particular, has become a powerful driver and catalyst of forced migration and internal displacement of people. Environmental migrants may far outnumber any other group of displaced people and refugees in the years to come. Deeper scientific integration, especially across the social sciences, is a prerequisite to tackle this issue.

  6. A complex social-ecological disaster: Environmentally induced forced migration.

    PubMed

    Rechkemmer, Andreas; O'Connor, Ashley; Rai, Abha; Decker Sparks, Jessica L; Mudliar, Pranietha; Shultz, James M

    2016-01-01

    In the 21(st) century, global issues are increasingly characterized by inter-connectedness and complexity. Global environmental change, and climate change in particular, has become a powerful driver and catalyst of forced migration and internal displacement of people. Environmental migrants may far outnumber any other group of displaced people and refugees in the years to come. Deeper scientific integration, especially across the social sciences, is a prerequisite to tackle this issue.

  7. Influence of the Polysilicon Gate on the Random Dopant Induced Threshold Voltage Fluctuations in Sub 100 nm MOSFETS with Thin Gate Oxides

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Saini, S.

    2000-01-01

    In this paper for the first time we study the influence of the polysilicon gate on the random dopant induced threshold voltage fluctuations in sub 100 nm MOSFETs with tunnelling gate oxides. This is done by using an efficient 3D 'atomistic' simulation technique described elsewhere. Devices with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveale that the polysilicon gate is responsible for a substantial fraction of the threshold voltage fluctuations in both devices when the gate oxide is scaled to tunnelling thickness in the range of 1 - 2 nm.

  8. Effect of disorder on temporal fluctuations in drying-induced cracking.

    PubMed

    Villalobos, Gabriel; Kun, Ferenc; Muñoz, José D

    2011-10-01

    We investigate by means of computer simulations the effect of structural disorder on the statistics of cracking for a thin layer of material under uniform and isotropic drying. For this purpose, the layer is discretized into a triangular lattice of springs with a slightly randomized arrangement. The drying process is captured by reducing the natural length of all springs by the same factor, and the amount of quenched disorder is controlled by varying the width ξ of the distribution of the random breaking thresholds for the springs. Once a spring breaks, the redistribution of the load may trigger an avalanche of breaks, not necessarily as part of the same crack. Our computer simulations revealed that the system exhibits a phase transition with the amount of disorder as control parameter: at low disorders, the breaking process is dominated by a macroscopic crack at the beginning, and the size distribution of the subsequent breaking avalanches shows an exponential form. At high disorders, the fracturing proceeds in small-sized avalanches with an exponential distribution, generating a large number of microcracks, which eventually merge and break the layer. Between both phases, a sharp transition occurs at a critical amount of disorder ξ(c)=0.40±0.01, where the avalanche size distribution becomes a power law with exponent τ=2.6±0.08, in agreement with the mean-field value τ=5/2 of the fiber bundle model. Moreover, good quality data collapses from the finite-size scaling analysis show that the average value of the largest burst ⟨Δ(max)⟩ can be identified as the order parameter, with β/ν=1.4 and 1/ν≃1.0, and that the average ratio ⟨m(2)/m(1)⟩ of the second m(2) and first moments m(1) of the avalanche size distribution shows similar behavior to the susceptibility of a continuous transition, with γ/ν=1, 1/ν≃0.9. These results suggest that the disorder-induced transition of the breakup of thin layers is analogous to a continuous phase transition.

  9. Investigation on flow and mixing characteristics of supersonic mixing layer induced by forced vibration of cantilever

    NASA Astrophysics Data System (ADS)

    Zhang, Dongdong; Tan, Jianguo; Lv, Liang

    2015-12-01

    The mixing process has been an important issue for the design of supersonic combustion ramjet engine, and the mixing efficiency plays a crucial role in the improvement of the combustion efficiency. In the present study, nanoparticle-based planar laser scattering (NPLS), particle image velocimetry (PIV) and large eddy simulation (LES) are employed to investigate the flow and mixing characteristics of supersonic mixing layer under different forced vibration conditions. The indexes of fractal dimension, mixing layer thickness, momentum thickness and scalar mixing level are applied to describe the mixing process. Results show that different from the development and evolution of supersonic mixing layer without vibration, the flow under forced vibration is more likely to present the characteristics of three-dimensionality. The laminar flow region of mixing layer under forced vibration is greatly shortened and the scales of rolled up Kelvin-Helmholtz vortices become larger, which promote the mixing process remarkably. The fractal dimension distribution reveals that comparing with the flow without vibration, the turbulent fluctuation of supersonic mixing layer under forced vibration is more intense. Besides, the distribution of mixing layer thickness, momentum thickness and scalar mixing level are strongly influenced by forced vibration. Especially, when the forcing frequency is 4000 Hz, the mixing layer thickness and momentum thickness are 0.0391 m and 0.0222 m at the far field of 0.16 m, 83% and 131% higher than that without vibration at the same position, respectively.

  10. Aerodynamic forces induced by controlled transitory flow on a body of revolution

    NASA Astrophysics Data System (ADS)

    Rinehart, Christopher S.

    The aerodynamic forces and moments on an axisymmetric body of revolution are controlled in a low-speed wind tunnel by induced local flow attachment. Control is effected by an array of aft-facing synthetic jets emanating from narrow, azimuthally segmented slots embedded within an axisymmetric backward facing step. The actuation results in a localized, segmented vectoring of the separated base flow along a rear Coanda surface and induced asymmetric aerodynamic forces and moments. The observed effects are investigated in both quasi-steady and transient states, with emphasis on parametric dependence. It is shown that the magnitude of the effected forces can be substantially increased by slight variations of the Coanda surface geometry. Force and velocity measurements are used to elucidate the mechanisms by which the synthetic jets produce asymmetric aerodynamic forces and moments, demonstrating a novel method to steer axisymmetric bodies during flight.

  11. Contact force measurements and stress-induced anisotropy in granular materials.

    PubMed

    Majmudar, T S; Behringer, R P

    2005-06-23

    Interparticle forces in granular media form an inhomogeneous distribution of filamentary force chains. Understanding such forces and their spatial correlations, specifically in response to forces at the system boundaries, represents a fundamental goal of granular mechanics. The problem is of relevance to civil engineering, geophysics and physics, being important for the understanding of jamming, shear-induced yielding and mechanical response. Here we report measurements of the normal and tangential grain-scale forces inside a two-dimensional system of photoelastic disks that are subject to pure shear and isotropic compression. Various statistical measures show the underlying differences between these two stress states. These differences appear in the distributions of normal forces (which are more rounded for compression than shear), although not in the distributions of tangential forces (which are exponential in both cases). Sheared systems show anisotropy in the distributions of both the contact network and the contact forces. Anisotropy also occurs in the spatial correlations of forces, which provide a quantitative replacement for the idea of force chains. Sheared systems have long-range correlations in the direction of force chains, whereas isotropically compressed systems have short-range correlations regardless of the direction.

  12. Fluctuations between multiple EF-G-induced chimeric tRNA states during translocation on the ribosome

    NASA Astrophysics Data System (ADS)

    Adio, Sarah; Senyushkina, Tamara; Peske, Frank; Fischer, Niels; Wintermeyer, Wolfgang; Rodnina, Marina V.

    2015-06-01

    The coupled translocation of transfer RNA and messenger RNA through the ribosome entails large-scale structural rearrangements, including step-wise movements of the tRNAs. Recent structural work has visualized intermediates of translocation induced by elongation factor G (EF-G) with tRNAs trapped in chimeric states with respect to 30S and 50S ribosomal subunits. The functional role of the chimeric states is not known. Here we follow the formation of translocation intermediates by single-molecule fluorescence resonance energy transfer. Using EF-G mutants, a non-hydrolysable GTP analogue, and fusidic acid, we interfere with either translocation or EF-G release from the ribosome and identify several rapidly interconverting chimeric tRNA states on the reaction pathway. EF-G engagement prevents backward transitions early in translocation and increases the fraction of ribosomes that rapidly fluctuate between hybrid, chimeric and posttranslocation states. Thus, the engagement of EF-G alters the energetics of translocation towards a flat energy landscape, thereby promoting forward tRNA movement.

  13. Differential equations governing slip-induced pore-pressure fluctuations in a water-saturated granular medium

    USGS Publications Warehouse

    Iverson, R.M.

    1993-01-01

    Macroscopic frictional slip in water-saturated granular media occurs commonly during landsliding, surface faulting, and intense bedload transport. A mathematical model of dynamic pore-pressure fluctuations that accompany and influence such sliding is derived here by both inductive and deductive methods. The inductive derivation shows how the governing differential equations represent the physics of the steadily sliding array of cylindrical fiberglass rods investigated experimentally by Iverson and LaHusen (1989). The deductive derivation shows how the same equations result from a novel application of Biot's (1956) dynamic mixture theory to macroscopic deformation. The model consists of two linear differential equations and five initial and boundary conditions that govern solid displacements and pore-water pressures. Solid displacements and water pressures are strongly coupled, in part through a boundary condition that ensures mass conservation during irreversible pore deformation that occurs along the bumpy slip surface. Feedback between this deformation and the pore-pressure field may yield complex system responses. The dual derivations of the model help explicate key assumptions. For example, the model requires that the dimensionless parameter B, defined here through normalization of Biot's equations, is much larger than one. This indicates that solid-fluid coupling forces are dominated by viscous rather than inertial effects. A tabulation of physical and kinematic variables for the rod-array experiments of Iverson and LaHusen and for various geologic phenomena shows that the model assumptions commonly are satisfied. A subsequent paper will describe model tests against experimental data. ?? 1993 International Association for Mathematical Geology.

  14. Study of Elastin Sequences with Solvent Induced Force Field

    NASA Astrophysics Data System (ADS)

    Arkin, Handan

    Conformational structures of two common repeat motifs Val1-Pro2-Gly3-Val4-Gly5 and Gly1-Leu2-Gly3-Gly4 of tropoelastin are investigated by using the multicanonical simulation procedure with solvation effects included energy force field. The effects of solvation energy term on the conformations are determined by analyzing Ramachandran plots. By minimizing the energy structures along the trajectory, the thermodynamically most stable low-energy microstates of the molecule in aqueous solution are determined and the root mean square deviations of these structures with respect to the global minimum are calculated.

  15. Comparison of various approaches to the calculation of optically induced forces

    SciTech Connect

    Torchigin, V.P. Torchigin, A.V.

    2012-09-15

    Various approaches used for the calculation of optically induced forces applied to a transparent optical medium imbedded in a close plane optical resonator are analyzed. The forces are calculated by means of analysis of a change in the eigen frequency and energy stored in the resonator at various positions of the medium. It is shown that results obtained are identical to those calculated by means of approaches based on the Maxwell stress tensor, based on an analysis of a change in the momentum of light. An exception is for results obtained on the base of last versions of the Lorentz density force. - Highlights: Black-Right-Pointing-Pointer There are no Lorentz forces in a homogeneous optical medium. Black-Right-Pointing-Pointer A net force produced by an inhomogeneous electrostriction pressure is equal to zero. Black-Right-Pointing-Pointer Any distributions of the Lorentz force in a homogeneous optical medium are misleading.

  16. Force-induced selective dissociation of noncovalent antibody-antigen bonds.

    PubMed

    Yao, Li; Xu, Shoujun

    2012-08-23

    Specific noncovalent binding between antibody and antigen molecules is the basis for molecular recognition in biochemical processes. Quantitative investigation of the binding forces could lead to molecular specific analysis and potentially mechanical manipulation of these processes. Using our force-induced remnant magnetization spectroscopy, we revealed a well-defined binding force for the bonds between mouse immunoglobulin G and magnetically labeled α-mouse immunoglobulin G. The force was calibrated to be 120 ± 15 pN. In comparison, the binding force was only 17 ± 3 pN for physisorption and much higher than 120 pN for biotin-streptavidin bonds. A unique rebinding method was used to confirm the dissociation of the antibody-antigen bonds. A well-defined and molecule-specific binding force opens a new avenue for distinguishing different noncovalent bonds in biochemical processes.

  17. Depletion forces on circular and elliptical obstacles induced by active matter

    NASA Astrophysics Data System (ADS)

    Leite, L. R.; Lucena, D.; Potiguar, F. Q.; Ferreira, W. P.

    2016-12-01

    Depletion forces exerted by self-propelled particles on circular and elliptical passive objects are studied using numerical simulations. We show that a bath of active particles can induce repulsive and attractive forces which are sensitive to the shape and orientation of the passive objects (either horizontal or vertical ellipses). The resultant force on the passive objects due to the active particles is studied as a function of the shape and orientation of the passive objects, magnitude of the angular noise, and distance between the passive objects. By increasing the distance between obstacles the magnitude of the repulsive depletion force increases, as long as such a distance is less than one active particle diameter. For longer distances, the magnitude of the force always decreases with increasing distance. We also found that attractive forces may arise for vertical ellipses at high enough area fraction.

  18. Enhancement of vortex induced forces and motion through surface roughness control

    DOEpatents

    Bernitsas, Michael M [Saline, MI; Raghavan, Kamaldev [Houston, TX

    2011-11-01

    Roughness is added to the surface of a bluff body in a relative motion with respect to a fluid. The amount, size, and distribution of roughness on the body surface is controlled passively or actively to modify the flow around the body and subsequently the Vortex Induced Forces and Motion (VIFM). The added roughness, when designed and implemented appropriately, affects in a predetermined way the boundary layer, the separation of the boundary layer, the level of turbulence, the wake, the drag and lift forces, and consequently the Vortex Induced Motion (VIM), and the fluid-structure interaction. The goal of surface roughness control is to increase Vortex Induced Forces and Motion. Enhancement is needed in such applications as harnessing of clean and renewable energy from ocean/river currents using the ocean energy converter VIVACE (Vortex Induced Vibration for Aquatic Clean Energy).

  19. The response of short-scale density fluctuations to the activity of beta-induced Alfvén eigenmodes during strong tearing modes on EAST tokamak

    NASA Astrophysics Data System (ADS)

    Cao, G. M.; Li, Y. D.; Li, Q.; Sun, P. J.; Wu, G. J.; Hu, L. Q.; the EAST Team

    2015-08-01

    Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes (TMs) have been frequently observed in fast-electron plasmas of EAST tokamak. The dynamics of the short-scale ({k}\\perp {ρ }s~{1.5-4.3}) density fluctuations during the activity of BAEs with strong TMs has been preliminarily investigated by a tangential CO2 laser collective scattering system. The results suggest the active, but different, response of short-scale density fluctuations to the TMs and BAEs. In the low-frequency (0-10 kHz) part of density fluctuations, there are harmonic oscillations totally corresponding to those of TMs. In the medium-high frequency (10-250 kHz) part of density fluctuations, with the appearance of the BAEs, the medium-high frequency density fluctuations begin to be dominated by several quasi-coherent (QC) modes, and the frequencies of the QC modes seem to be related to the changes of both TMs and BAEs. These results would shed some light on the understanding of the multi-scale interaction physics.

  20. Correlative atomic force and confocal fluorescence microscopy: single molecule imaging and force induced spectral shifts (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Basché, Thomas; Hinze, Gerald; Stöttinger, Sven

    2016-09-01

    A grand challenge in nanoscience is to correlate structure or morphology of individual nano-sized objects with their photo-physical properties. An early example have been measurements of the emission spectra and polarization of single semiconductor quantum dots as well as their crystallographic structure by a combination of confocal fluorescence microscopy and transmission electron microscopy.[1] Recently, the simultaneous use of confocal fluorescence and atomic force microscopy (AFM) has allowed for correlating the morphology/conformation of individual nanoparticle oligomers or molecules with their photo-physics.[2, 3] In particular, we have employed the tip of an AFM cantilever to apply compressive stress to single molecules adsorbed on a surface and follow the effect of the impact on the electronic states of the molecule by fluorescence spectroscopy.[3] Quantum mechanical calculations corroborate that the spectral changes induced by the localized force can be associated to transitions among the different possible conformers of the adsorbed molecule.

  1. Mechanical force-induced midpalatal suture remodeling in mice

    PubMed Central

    Hou, Bo; Fukai, Naomi; Olsen, Bjorn R.

    2007-01-01

    Mechanical stress is an important epigenetic factor for regulating skeletal remodeling, and application of force can lead to remodeling of both bone and cartilage. Chondrocytes, osteoblasts and osteoclasts all participate and interact with each other in this remodeling process. To study cellular responses to mechanical stimuli in a system that can be genetically manipulated, we used mouse midpalatal suture expansion in vivo. 6-weeks-old male C57BL/6 mice were subjected to palatal suture expansion by opening loops with an initial force of 0.56N for periods of 1, 3, 7, 14 or 28 days. Periosteal cells in expanding sutures showed increased proliferation, with Ki67 positive cells representing 1.8±0.1% to 4.5±0.4% of total suture cells in control groups and 12.0±2.6% to 19.9±1.2% in experimental/expansion groups (p<0.05). Starting at day 1, cells expressing alkaline phosphatase and type I collagen were seen. New cartilage and bone formation was observed at the oral edges of the palatal bones at day 7; at the nasal edges only bone formation without cartilage appeared to occur. An increase in osteoclast numbers suggested increased bone remodeling, ranging from 60 to 160% throughout the experimental period. Decreased Saffranin O staining after day 3 suggested decreased proteoglycan content in the secondary cartilage. MicroCT showed a significant increase in maxillary width at days 14 and 28 (from 2334±4μm to 2485±3μm at day 14 and from 2383±5μm to 2574±7μm at day 28, p<0.001). The suture width was increased at days 14 and 28, except in the oral third region at day 28 (from 48±5μm to 36±4μm, p<0.05). Bone volume/total volume was significantly reduced at days 14 and 28 (50.2±0.7% vs. 68.0±3.7% and 56.5±1.0%vs. 60.9±1.3%, respectively, p<0.05), indicative of increased bone marrow space. These findings demonstrate that expansion forces across the midpalatal suture promote bone resorption through activation of osteoclasts and bone and cartilage formation via

  2. Structural changes in precipitated silica induced by external forces

    NASA Astrophysics Data System (ADS)

    Schneider, Gerald Johannes; Göritz, Dietmar

    2010-04-01

    The morphology of pure precipitated silica, silica filled in polydimethylsiloxane rubber, and silica filled in styrene butadiene rubber was studied by means of small-angle X-ray scattering experiments. The silica at a length scale of a few nanometers consists of primary particles, which form aggregates, and clusters with aggregates as basic units. It is evidenced that the aggregate branching, represented by the mass fractal dimension, and the aggregate diameter are different if pure silica and silica in rubber are compared. Contrary, the size of the primary particles and their surface are not influenced. It is demonstrated that the change in the aggregate morphology is due to the external mechanical forces appearing during the mixing process. This is achieved by model experiments using a pistil and a mortar and a composite with different silica fractions. By that means, a systematic change in the morphology with grinding time is observed. Then, the experiments on the composite demonstrate that the major contributions to the mass fractal dimensions are due to the external mechanical forces. In order to test reproducibility and universal validity in the case of precipitated silicas, independent experiments on one silica and further silicas are performed. Several important conclusions are obtained from the study. First, it is shown that a comparison of different pure silica samples without knowing their history may be difficult or questionable. Second, it becomes evident that it is not sufficient to provide only a description of the materials, rather than the details of the sample treatment have to be reported. Therefore, solely the characterization of the morphology of the pure silica is not sufficient to be compared to the mechanical properties of the composites.

  3. 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.

  4. Microrheology of highly crosslinked microtubule networks is dominated by force-induced crosslinker unbinding

    PubMed Central

    Yang, Yali; Bai, Mo; Klug, William S.; Levine, Alex J.

    2012-01-01

    We determine the time- and force-dependent viscoelastic responses of reconstituted networks of microtubules that have been strongly crosslinked by biotin-streptavidin bonds. To measure the microscale viscoelasticity of such networks, we use a magnetic tweezers device to apply localized forces. At short time scales, the networks respond nonlinearly to applied force, with stiffening at small forces, followed by a reduction in the stiffening response at high forces, which we attribute to the force-induced unbinding of crosslinks. At long time scales, force-induced bond unbinding leads to local network rearrangement and significant bead creep. Interestingly, the network retains its elastic modulus even under conditions of significant plastic flow, suggesting that crosslinker breakage is balanced by the formation of new bonds. To better understand this effect, we developed a finite element model of such a stiff filament network with labile crosslinkers obeying force-dependent Bell model unbinding dynamics. The coexistence of dissipation, due to bond breakage, and the elastic recovery of the network is possible because each filament has many crosslinkers. Recovery can occur as long as a sufficient number of the original crosslinkers are preserved under the loading period. When these remaining original crosslinkers are broken, plastic flow results. PMID:23577042

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

    PubMed Central

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

    2012-01-01

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

  6. Transient Casimir Forces from Quenches in Thermal and Active Matter.

    PubMed

    Rohwer, Christian M; Kardar, Mehran; Krüger, Matthias

    2017-01-06

    We compute fluctuation-induced (Casimir) forces for classical systems after a temperature quench. Using a generic coarse-grained model for fluctuations of a conserved density, we find that transient forces arise even if the initial and final states are force free. In setups reminiscent of Casimir (planar walls) and van der Waals (small inclusions) interactions, we find comparable exact universal expressions for the force. Dynamical details only scale the time axis of transient force curves. We propose that such quenches can be achieved, for instance, in experiments on active matter, employing tunable activity or interaction protocols.

  7. Transient Casimir Forces from Quenches in Thermal and Active Matter

    NASA Astrophysics Data System (ADS)

    Rohwer, Christian M.; Kardar, Mehran; Krüger, Matthias

    2017-01-01

    We compute fluctuation-induced (Casimir) forces for classical systems after a temperature quench. Using a generic coarse-grained model for fluctuations of a conserved density, we find that transient forces arise even if the initial and final states are force free. In setups reminiscent of Casimir (planar walls) and van der Waals (small inclusions) interactions, we find comparable exact universal expressions for the force. Dynamical details only scale the time axis of transient force curves. We propose that such quenches can be achieved, for instance, in experiments on active matter, employing tunable activity or interaction protocols.

  8. Magnetic Fluctuation-Driven Intrinsic Flow in a Toroidal Plasma

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  9. Induced Voltage Linear Extraction Method Using an Active Kelvin Bridge for Disturbing Force Self-Sensing.

    PubMed

    Yang, Yuanyuan; Wang, Lei; Tan, Jiubin; Zhao, Bo

    2016-05-20

    This paper presents an induced voltage linear extraction method for disturbing force self-sensing in the application of giant magnetostrictive actuators (GMAs). In this method, a Kelvin bridge combined with an active device is constructed instead of a conventional Wheatstone bridge for extraction of the induced voltage, and an additional GMA is adopted as a reference actuator in the self-sensing circuit in order to balance the circuit bridge. The linear fitting of the measurement data is done according to the linear relationship between the disturbing forces and the integral of the induced voltage. The experimental results confirm the good performance of the proposed method, and the self-sensitivity of the disturbing forces is better than 2.0 (mV·s)/N.

  10. Reduction of vortex induced forces and motion through surface roughness control

    DOEpatents

    Bernitsas, Michael M; Raghavan, Kamaldev

    2014-04-01

    Roughness is added to the surface of a bluff body in a relative motion with respect to a fluid. The amount, size, and distribution of roughness on the body surface is controlled passively or actively to modify the flow around the body and subsequently the Vortex Induced Forces and Motion (VIFM). The added roughness, when designed and implemented appropriately, affects in a predetermined way the boundary layer, the separation of the boundary layer, the level of turbulence, the wake, the drag and lift forces, and consequently the Vortex Induced Motion (VIM), and the fluid-structure interaction. The goal of surface roughness control is to decrease/suppress Vortex Induced Forces and Motion. Suppression is required when fluid-structure interaction becomes destructive as in VIM of flexible cylinders or rigid cylinders on elastic support, such as underwater pipelines, marine risers, tubes in heat exchangers, nuclear fuel rods, cooling towers, SPAR offshore platforms.

  11. Imaging of Shear Waves Induced by Lorentz Force in Soft Tissues

    NASA Astrophysics Data System (ADS)

    Grasland-Mongrain, P.; Souchon, R.; Cartellier, F.; Zorgani, A.; Chapelon, J. Y.; Lafon, C.; Catheline, S.

    2014-07-01

    This study presents the first observation of elastic shear waves generated in soft solids using a dynamic electromagnetic field. The first and second experiments of this study showed that Lorentz force can induce a displacement in a soft phantom and that this displacement was detectable by an ultrasound scanner using speckle-tracking algorithms. For a 100 mT magnetic field and a 10 ms, 100 mA peak-to-peak electrical burst, the displacement reached a magnitude of 1 μm. In the third experiment, we showed that Lorentz force can induce shear waves in a phantom. A physical model using electromagnetic and elasticity equations was proposed. Computer simulations were in good agreement with experimental results. The shear waves induced by Lorentz force were used in the last experiment to estimate the elasticity of a swine liver sample.

  12. The nature of the force-induced conformation transition of dsDNA studied by using single molecule force spectroscopy.

    PubMed

    Liu, Ningning; Bu, Tianjia; Song, Yu; Zhang, Wei; Li, Jinjing; Zhang, Wenke; Shen, Jiacong; Li, Hongbin

    2010-06-15

    Single-stranded DNA binding proteins (SSB) interact with single-stranded DNA (ssDNA) specifically. Taking advantage of this character, we have employed Bacillus subtilis SSB protein to investigate the nature of force-induced conformation transition of double-stranded DNA (dsDNA) by using AFM-based single molecule force spectroscopy (SMFS) technique. Our results show that, when a dsDNA is stretched beyond its contour length, the dsDNA is partially melted, producing some ssDNA segments which can be captured by SSB proteins. We have also systematically investigated the effects of stretching length, waiting time, and salt concentration on the conformation transition of dsDNA and SSB-ssDNA interactions, respectively. Furthermore, the effect of proflavine, a DNA intercalator, on the SSB-DNA interactions has been investigated, and the results indicate that the proflavine-saturated dsDNA can be stabilized to the extent that the dsDNA will no longer melt into ssDNA under the mechanical force even up to 150 pN, and no SSB-DNA interactions are detectable.

  13. Divergent global precipitation changes induced by natural versus anthropogenic forcing.

    PubMed

    Liu, Jian; Wang, Bin; Cane, Mark A; Yim, So-Young; Lee, June-Yi

    2013-01-31

    As a result of global warming, precipitation is likely to increase in high latitudes and the tropics and to decrease in already dry subtropical regions. The absolute magnitude and regional details of such changes, however, remain intensely debated. As is well known from El Niño studies, sea-surface-temperature gradients across the tropical Pacific Ocean can strongly influence global rainfall. Palaeoproxy evidence indicates that the difference between the warm west Pacific and the colder east Pacific increased in past periods when the Earth warmed as a result of increased solar radiation. In contrast, in most model projections of future greenhouse warming this gradient weakens. It has not been clear how to reconcile these two findings. Here we show in climate model simulations that the tropical Pacific sea-surface-temperature gradient increases when the warming is due to increased solar radiation and decreases when it is due to increased greenhouse-gas forcing. For the same global surface temperature increase the latter pattern produces less rainfall, notably over tropical land, which explains why in the model the late twentieth century is warmer than in the Medieval Warm Period (around AD 1000-1250) but precipitation is less. This difference is consistent with the global tropospheric energy budget, which requires a balance between the latent heat released in precipitation and radiative cooling. The tropospheric cooling is less for increased greenhouse gases, which add radiative absorbers to the troposphere, than for increased solar heating, which is concentrated at the Earth's surface. Thus warming due to increased greenhouse gases produces a climate signature different from that of warming due to solar radiation changes.

  14. Thermally induced chronic developmental stress in coho salmon: Integrating measures of mortality, early growth and fluctuating asymmetry

    USGS Publications Warehouse

    Campbell, W.B.; Emlen, J.M.; Hershberger, W.K.

    1998-01-01

    Developmental stability, or homeostasis, facilitates the production of consistent phenotypes by buffering against stress. Fluctuating asymmetry is produced by developmental instability and is manifested as small random departures from bilateral symmetry. Increased fluctuating asymmetry is thought to parallel compromised fitness, in part, because stress promotes energy dissipation. Compensatory energy expenditures within the organism are required to complete development, thus promoting instability through reductions in homeostasis. Increased heterozygosity may enhance developmental stability by reducing energy dissipation from stress through increased metabolic efficiency, possibly by providing greater flexibility in metabolic pathways. Traditionally, fluctuating asymmetry has been used as a bioindicator of chronic stress, provided that selective mortality of less fit individuals did not reduce stress-mediated increases in fluctuating asymmetry to background levels produced by natural developmental error, or create data inconsistencies such as higher asymmetry in groups exposed to lower stress. Unfortunately, absence of selective mortality and its effects, while often assumed, can be difficult to substantiate. We integrated measures of early growth, mortality, fluctuating asymmetry (mandibular pores, pectoral finrays, pelvic finrays, and gillrakers on the upper and lower arms of the first branchial arch) and directional asymmetry (branchiostegal rays) to assess chronic thermal stress (fluctuating temperatures as opposed to ambient temperatures) in developing eggs from two different coho salmon (Oncorhynchus kisutch) stocks and their reciprocal hybrids. Hybridization provided insight on the capacity of heterozygosity to reduce stress during development. Although egg losses were consistently higher in crosses exposed to fluctuating temperatures, egg mortality was predominantly a function of maternal stock of origin. Post-hatch losses were higher in crosses exposed to

  15. Environmental forcing does not induce diel or synoptic variation in carbon isotope content of forest soil respiration

    NASA Astrophysics Data System (ADS)

    Bowling, D. R.; Egan, J. E.; Hall, S. J.; Risk, D. A.

    2015-04-01

    Recent studies have examined temporal fluctuations in the amount and carbon isotope content (δ13C) of CO2 produced by respiration of roots and soil organisms. These changes have been correlated with diel cycles of environmental forcing (e.g., sunlight and soil temperature) and with synoptic-scale atmospheric motion (e.g., rain events and pressure-induced ventilation). We used an extensive suite of measurements to examine soil respiration over two months in a subalpine forest in Colorado, USA (the Niwot Ridge AmeriFlux forest). Observations included automated measurements of CO2 and δ13C of CO2 in the soil efflux, the soil gas profile, and forest air. There was strong diel variability in soil efflux, but no diel change in the δ13C of the soil efflux (δR) or the CO2 produced by biological activity in the soil (δJ). Following rain, soil efflux increased significantly, but δR and δJ did not change. Temporal variation in the δ13C of the soil efflux was unrelated to measured environmental variables. Measurements of the δ13C of the soil efflux with chambers agreed closely with independent observations of the isotopic composition of soil CO2 production derived from soil gas well measurements. Deeper in the soil profile and at the soil surface, results confirmed established theory regarding diffusive soil gas transport and isotopic fractionation. Deviation from best-fit diffusion model results at the shallower depths illuminated a pump-induced ventilation artifact that should be anticipated and avoided in future studies. There was no evidence of natural pressure-induced ventilation of the deep soil. However, higher variability of δ13C of the soil efflux relative to δ13C of production derived from soil profile measurements was likely caused by transient pressure-induced transport with small horizontal length scales.

  16. Environmental forcing does not induce diel or synoptic variation in the carbon isotope content of forest soil respiration

    NASA Astrophysics Data System (ADS)

    Bowling, D. R.; Egan, J. E.; Hall, S. J.; Risk, D. A.

    2015-08-01

    Recent studies have examined temporal fluctuations in the amount and carbon isotope content (δ13C) of CO2 produced by the respiration of roots and soil organisms. These changes have been correlated with diel cycles of environmental forcing (e.g., sunlight and soil temperature) and with synoptic-scale atmospheric motion (e.g., rain events and pressure-induced ventilation). We used an extensive suite of measurements to examine soil respiration over 2 months in a subalpine forest in Colorado, USA (the Niwot Ridge AmeriFlux forest). Observations included automated measurements of CO2 and δ13C of CO2 in the soil efflux, the soil gas profile, and forest air. There was strong diel variability in soil efflux but no diel change in the δ13C of the soil efflux (δR) or the CO2 produced by biological activity in the soil (δJ). Following rain, soil efflux increased significantly, but δR and δJ did not change. Temporal variation in the δ13C of the soil efflux was unrelated to measured environmental variables, and we failed to find an explanation for this unexpected result. Measurements of the δ13C of the soil efflux with chambers agreed closely with independent observations of the isotopic composition of soil CO2 production derived from soil gas well measurements. Deeper in the soil profile and at the soil surface, results confirmed established theory regarding diffusive soil gas transport and isotopic fractionation. Deviation from best-fit diffusion model results at the shallower depths illuminated a pump-induced ventilation artifact that should be anticipated and avoided in future studies. There was no evidence of natural pressure-induced ventilation of the deep soil. However, higher variability in δ13C of the soil efflux relative to δ13C of production derived from soil profile measurements was likely caused by transient pressure-induced transport with small horizontal length scales.

  17. Akt activation prevents the force drop induced by eccentric contractions in dystrophin-deficient skeletal muscle.

    PubMed

    Blaauw, Bert; Mammucari, Cristina; Toniolo, Luana; Agatea, Lisa; Abraham, Reimar; Sandri, Marco; Reggiani, Carlo; Schiaffino, Stefano

    2008-12-01

    Skeletal muscles of the mdx mouse, a model of Duchenne Muscular Dystrophy, show an excessive reduction in the maximal tetanic force following eccentric contractions. This specific sign of the susceptibility of dystrophin-deficient muscles to mechanical stress can be used as a quantitative test to measure the efficacy of therapeutic interventions. Using inducible transgenesis in mice, we show that when Akt activity is increased the force drop induced by eccentric contractions in mdx mice becomes similar to that of wild-type mice. This effect is not correlated with muscle hypertrophy and is not blocked by rapamycin treatment. The force drop induced by eccentric contractions is similar in skinned muscle fibers from mdx and Akt-mdx mice when stretch is applied directly to skinned fibers. However, skinned fibers isolated from mdx muscles exposed to eccentric contractions in vivo develop less isometric force than wild-type fibers and this force depression is completely prevented by Akt activation. These experiments indicate that the myofibrillar-cytoskeletal system of dystrophin-deficient muscle is highly susceptible to a damage caused by eccentric contraction when elongation is applied in vivo, and this damage can be prevented by Akt activation. Microarray and PCR analyses indicate that Akt activation induces up-regulation of genes coding for proteins associated with Z-disks and costameres, and for proteins with anti-oxidant or chaperone function. The protein levels of utrophin and dysferlin are also increased by Akt activation.

  18. Active shortening protects against stretch-induced force deficits in human skeletal muscle.

    PubMed

    Saripalli, Anjali L; Sugg, Kristoffer B; Mendias, Christopher L; Brooks, Susan V; Claflin, Dennis R

    2017-02-23

    Skeletal muscle contraction results from molecular interactions of myosin "crossbridges" with adjacent actin filament binding sites. The binding of myosin to actin can be "weak" or "strong", and only strong binding states contribute to force production. During active shortening, the number of strongly-bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences whereas stretch of an isometrically (fixed-length) contracting muscle causes ultrastructural damage and a decline in force-generating capability. Our working hypothesis is that stretch-induced damage is uniquely attributable to the population of crossbridges that are strongly-bound. We tested the hypothesis that stretch-induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and either allowed to generate maximum isometric force (Fo), or to shorten at velocities that resulted in force maintenance of ≈50% Fo or ≈2% Fo. For each test condition, a rapid stretch equivalent to 0.1 x optimal fiber length was applied. Relative to pre-stretch Fo, force deficits resulting from stretches applied during force maintenance of 100%, ≈50%, and ≈2% Fo were 23.2 ± 8.6%, 7.8 ± 4.2% and 0.3 ± 3.3%, respectively (mean ± SD, n=20). We conclude that stretch-induced damage declines with increasing shortening velocity, consistent with the working hypothesis that the fraction of strongly-bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch-induced damage.

  19. Mechanical force-induced polymerization and depolymerization of F-actin at water/solid interfaces

    NASA Astrophysics Data System (ADS)

    Zhang, Xueqiang; Hu, Xiuyuan; Lei, Haozhi; Hu, Jun; Zhang, Yi

    2016-03-01

    Actin molecules are among the three main cytoskeleton proteins of cells and undergo rapid cycling to regulate critical processes such as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. Although extensive studies have been carried out on the dynamics as well as biological functions of actin polymerization and depolymerization both in vivo and in vitro, the molecular mechanisms by which cells sense and respond to mechanical signals are not fully understood. In particular, little attention has been paid to the effect of a physical force that is exerted directly on the actin cytoskeleton. In this paper, we have explored how the mechanical force affects the actin polymerization and depolymerization behaviors at water/solid interfaces using an atomic force microscope (AFM) operated in liquid. By raster scanning an AFM probe on a substrate surface with a certain load, it was found that actin monomers could polymerize into filaments without the help of actin related proteins (ARPs). Further study indicated that actin monomers were inclined to form filaments only under a small scanning load. The polymerized actin filaments would be depolymerized when the mechanical force was stronger. A possible mechanism has been suggested to explain the mechanical force induced actin polymerization.Actin molecules are among the three main cytoskeleton proteins of cells and undergo rapid cycling to regulate critical processes such as endocytosis, cytokinesis, cell polarity, and cell morphogenesis. Although extensive studies have been carried out on the dynamics as well as biological functions of actin polymerization and depolymerization both in vivo and in vitro, the molecular mechanisms by which cells sense and respond to mechanical signals are not fully understood. In particular, little attention has been paid to the effect of a physical force that is exerted directly on the actin cytoskeleton. In this paper, we have explored how the mechanical force affects the actin

  20. Hole-s± State Induced by Coexisting Ferro- and Antiferromagnetic and Antiferro-orbital Fluctuations in Iron Pnictides

    NASA Astrophysics Data System (ADS)

    Ishizuka, Jun; Yamada, Takemi; Yanagi, Yuki; Ōno, Yoshiaki

    2016-11-01

    The five-orbital Hubbard model for iron-based superconductors is investigated using the dynamical mean-field theory combined with the Eliashberg equation to clarify the local correlation effects on the electronic states and the superconductivity. In the specific case where the antiferromagnetic (AFM) and antiferro-orbital (AFO) fluctuations are comparably enhanced, the orbital dependence of the vertex function is significantly large, while that of the self-energy is small, in contrast to the AFM fluctuation-dominated case where the vertex function (the self-energy) shows a small (large) orbital dependence. The orbital-dependent vertex function together with the nesting between the inner and outer hole Fermi surfaces results in the enhancement of the inter-orbital ferromagnetic (FM) fluctuation in addition to the AFM and AFO fluctuations. In this case, the hole-s±-wave pairing with the sign change of the two hole Fermi surfaces is mediated by the coexisting three fluctuations as expected to be observed in the specific compound LiFeAs.

  1. Measurements of drift-wave-induced density and velocity fluctuations using high-speed passive impurity spectroscopy

    NASA Astrophysics Data System (ADS)

    Nishizawa, Takashi; Craig, D.; den Hartog, D. J.; Nornberg, M. D.

    2016-10-01

    Passive impurity spectroscopy is used to study high frequency ( 100 kHz) electron density and ion velocity fluctuations in the edge of MST reversed field pinch plasmas. When tearing modes are suppressed, stochastic transport is greatly reduced and microturbulence is anticipated to become important. Gyrokinetic simulations predict unstable trapped electron modes (TEM) in the edge region of these improved-confinement MST plasmas. Interferometry measurements reveal electron density fluctuations with wavenumbers, propagation direction, and a density-gradient threshold in good agreement with predictions for TEMs. These density fluctuations are also observed as emission fluctuations using a recently upgraded Ion Dynamics Spectrometer (IDS II) through edge passive C +2 measurements. The particle transport associated with TEMs will be evaluated directly by correlating the IDS-measured ion velocity and density fluctuations. The measurement is localized to the C +2 emission shell in the edge of the plasma, which is determined by a coronal charge-state balance model using ADAS. We used a large-throughput spectrometer originally developed for fast CHERS measurements and PMTs for light detection to achieve high time resolution. This work is supported by the US DOE.

  2. Irrigation Induced Surface Cooling in the Context of Modern and Increased Greenhouse Gas Forcing

    NASA Technical Reports Server (NTRS)

    Cook, Benjamin I.; Puma, Michael J.; Krakauer, Nir Y.

    2010-01-01

    There is evidence that expected warming trends from increased greenhouse gas (GHG) forcing have been locally masked by irrigation induced cooling, and it is uncertain how the magnitude of this irrigation masking effect will change in the future. Using an irrigation dataset integrated into a global general circulation model, we investigate the equilibrium magnitude of irrigation induced cooling under modern (Year 2000) and increased (A1B Scenario, Year 2050) GHG forcing, using modern irrigation rates in both scenarios. For the modern scenario, the cooling is largest over North America, India, the Middle East, and East Asia. Under increased GHG forcing, this cooling effect largely disappears over North America, remains relatively unchanged over India, and intensifies over parts of China and the Middle East. For North America, irrigation significantly increases precipitation under modern GHG forcing; this precipitation enhancement largely disappears under A1B forcing, reducing total latent heat fluxes and the overall irrigation cooling effect. Over India, irrigation rates are high enough to keep pace with increased evaporative demand from the increased GHG forcing and the magnitude of the cooling is maintained. Over China, GHG forcing reduces precipitation and shifts the region to a drier evaporative regime, leading to a relatively increased impact of additional water from irrigation on the surface energy balance. Irrigation enhances precipitation in the Middle East under increased GHG forcing, increasing total latent heat fluxes and enhancing the irrigation cooling effect. Ultimately, the extent to which irrigation will continue to compensate for the warming from increased GHG forcing will primarily depend on changes in the background evaporative regime, secondary irrigation effects (e.g. clouds, precipitation), and the ability of societies to maintain (or increase) current irrigation rates.

  3. Direct Measurement of Optical Force Induced by Near-Field Plasmonic Cavity Using Dynamic Mode AFM

    PubMed Central

    Guan, Dongshi; Hang, Zhi Hong; Marcet, Zsolt; Liu, Hui; Kravchenko, I. I.; Chan, C. T.; Chan, H. B.; Tong, Penger

    2015-01-01

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. The experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures. PMID:26586455

  4. Fano resonance-induced negative optical scattering force on plasmonic nanoparticles.

    PubMed

    Chen, Huajin; Liu, Shiyang; Zi, Jian; Lin, Zhifang

    2015-02-24

    We demonstrate theoretically that Fano resonance can induce a negative optical scattering force acting on plasmonic nanoparticles in the visible light spectrum when an appropriate manipulating laser beam is adopted. Under the illumination of a zeroth-order Bessel beam, the plasmonic nanoparticle at its Fano resonance exhibits a much stronger forward scattering than backward scattering and consequently leads to a net longitudinal backward optical scattering force, termed Fano resonance-induced negative optical scattering force. The extinction spectra obtained based on the Mie theory show that the Fano resonance arises from the interference of simultaneously excited multipoles, which can be either a broad electric dipole mode and a narrow electric quadrupole mode, or a quadrupole and an octupole mode mediated by the broad electric dipole. Such Fano resonance-induced negative optical scattering force is demonstrated to occur for core-shell, homogeneous, and hollow metallic particles and can therefore be expected to be universal for many other nanostructures exhibiting Fano resonance, adding considerably to the flexibility of optical micromanipulation on the plasmonic nanoparticles. More interestingly, the flexible tunability of the Fano resonance by particle morphology opens up the possibility of tailoring the optical scattering force accordingly, offering an additional degree of freedom to optical selection and sorting of plasmonic nanoparticles.

  5. Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

    DOE PAGES

    Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; ...

    2015-11-20

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength goldmore » disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.« less

  6. Direct measurement of optical force induced by near-field plasmonic cavity using dynamic mode AFM

    SciTech Connect

    Guan, Dongshi; Hang, Zhi Hong; Marset, Zsolt; Liu, Hui; Kravchenko, Ivan I.; Chan, Ho Bun; Chan, C. T.; Tong, Penger

    2015-11-20

    Plasmonic nanostructures have attracted much attention in recent years because of their potential applications in optical manipulation through near-field enhancement. Continuing experimental efforts have been made to develop accurate techniques to directly measure the near-field optical force induced by the plasmonic nanostructures in the visible frequency range. In this work, we report a new application of dynamic mode atomic force microscopy (DM-AFM) in the measurement of the enhanced optical force acting on a nano-structured plasmonic resonant cavity. The plasmonic cavity is made of an upper gold-coated glass sphere and a lower quartz substrate patterned with an array of subwavelength gold disks. In the near-field when the sphere is positioned close to the disk array, plasmonic resonance is excited in the cavity and the induced force by a 1550 nm infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. Lastly, the experiment demonstrates that DM-AFM is a powerful tool for the study of light induced forces and their enhancement in plasmonic nanostructures.

  7. The effect of heating and cooling on the velocity fluctuations in the ISM induced by the system of stars

    NASA Astrophysics Data System (ADS)

    Deiss, B. M.; Kegel, W. H.

    1986-06-01

    Dissipative thermal effects are taken into account in the expressions for interstellar gas velocity fluctuations (due to the gravitational interaction with stars) derived by Kegel and Volk (1983), with application to the interpretation of interstellar lines, the large scale flow of the interstellar matter, and the collapse of interstellar clouds. Results indicate a decrease in the critical wavelength for gravitational instability, which value is prevented by thermal effects from becoming zero when the relative velocity approaches the velocity of sound, in contradiction with the results of Kegel and Volk, and of Niimi (1970). The velocity fluctuations in the gas derived by Kegel and Volk are shown to be reduced considerably, though velocity fluctuations many times the velocity of sound, which increase with increasing relative motion between gas and stars, are found, principally in molecular clouds.

  8. Modeling of wall-induced force for wall-bounded bubbly flow

    NASA Astrophysics Data System (ADS)

    Kim, Dongjoo; Kim, Jungwoo; Park, Hyungmin; Lee, Jun Ho

    2014-11-01

    The two-fluid model based on Eulerian-Eulerian approach has been widely used for simulating two-phase flow in industrial applications due to much less CPU time compared with interface tracking methods. However, the two-fluid approach requires accurate modeling of mass and momentum transfers between phases. The interfacial momentum exchange terms include drag, shear-induced lift, and wall-induced force. The last one is particularly important in order to correctly predict ``wall peaking'' and ``core peaking'' phenomena observed in bubbly pipe flows. However, the wall-induced force is not fully understood yet and the wall force coefficient used in previous studies has a wide range of values, probably tuned to match experiment. Therefore, we propose a new wall-induced force model in the present study. To verify the accuracy of present model, numerical simulations are performed for several laminar bubbly flows available in the literature. The spatial distributions of void fraction, liquid velocity, and bubble velocity are compared with those with previous models as well as experimental results. Supported by the NRF Programs (NRF-2012M2A8A4055647) of Korean government.

  9. GRADFLEX: Fluctuations in Microgravity

    NASA Technical Reports Server (NTRS)

    Vailati, A.; Cerbino, R.; Mazzoni, S.; Giglio, M.; Nikolaenko, G.; Cannell, D. S.; Meyer, W. V.; Smart, A. E.

    2004-01-01

    We present the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single-component fluid with a temperature gradient. We also describe the experimental apparatus being developed to carry out similar measurement under microgravity conditions.

  10. A programmable DNA origami nanospring that reveals force-induced adjacent binding of myosin VI heads.

    PubMed

    Iwaki, M; Wickham, S F; Ikezaki, K; Yanagida, T; Shih, W M

    2016-12-12

    Mechanosensitive biological nanomachines such as motor proteins and ion channels regulate diverse cellular behaviour. Combined optical trapping with single-molecule fluorescence imaging provides a powerful methodology to clearly characterize the mechanoresponse, structural dynamics and stability of such nanomachines. However, this system requires complicated experimental geometry, preparation and optics, and is limited by low data-acquisition efficiency. Here we develop a programmable DNA origami nanospring that overcomes these issues. We apply our nanospring to human myosin VI, a mechanosensory motor protein, and demonstrate nanometre-precision single-molecule fluorescence imaging of the individual motor domains (heads) under force. We observe force-induced transitions of myosin VI heads from non-adjacent to adjacent binding, which correspond to adapted roles for low-load and high-load transport, respectively. Our technique extends single-molecule studies under force and clarifies the effect of force on biological processes.

  11. A programmable DNA origami nanospring that reveals force-induced adjacent binding of myosin VI heads

    PubMed Central

    Iwaki, M.; Wickham, S. F.; Ikezaki, K.; Yanagida, T.; Shih, W. M.

    2016-01-01

    Mechanosensitive biological nanomachines such as motor proteins and ion channels regulate diverse cellular behaviour. Combined optical trapping with single-molecule fluorescence imaging provides a powerful methodology to clearly characterize the mechanoresponse, structural dynamics and stability of such nanomachines. However, this system requires complicated experimental geometry, preparation and optics, and is limited by low data-acquisition efficiency. Here we develop a programmable DNA origami nanospring that overcomes these issues. We apply our nanospring to human myosin VI, a mechanosensory motor protein, and demonstrate nanometre-precision single-molecule fluorescence imaging of the individual motor domains (heads) under force. We observe force-induced transitions of myosin VI heads from non-adjacent to adjacent binding, which correspond to adapted roles for low-load and high-load transport, respectively. Our technique extends single-molecule studies under force and clarifies the effect of force on biological processes. PMID:27941751

  12. Residual force depression in single sarcomeres is abolished by MgADP-induced activation.

    PubMed

    Trecarten, Neal; Minozzo, Fabio C; Leite, Felipe S; Rassier, Dilson E

    2015-06-03

    The mechanisms behind the shortening-induced force depression commonly observed in skeletal muscles remain unclear, but have been associated with sarcomere length non-uniformity and/or crossbridge inhibition. The purpose of this study was twofold: (i) to evaluate if force depression is present in isolated single sarcomeres, a preparation that eliminates sarcomere length non-uniformities and (ii) to evaluate if force depression is inhibited when single sarcomeres are activated with MgADP, which biases crossbridges into a strongly-bound state. Single sarcomeres (n = 16) were isolated from rabbit psoas myofibrils using two micro-needles (one compliant, one rigid), piercing the sarcomere externally adjacent to the Z-lines. The sarcomeres were contracted isometrically and subsequently shortened, in both Ca(2+)- and MgADP-activating solutions. Shortening in Ca(2+)-activated samples resulted in a 27.44 ± 9.04% force depression when compared to isometric contractions produced at similar final sarcomere lengths (P < 0.001). There was no force depression in MgADP-activated sarcomeres (force depression = -1.79 ± 9.69%, P =  0.435). These results suggest that force depression is a sarcomeric property, and that is associated with an inhibition of myosin-actin interactions.

  13. Spatially correlated fluctuations and coherence dynamics in photosynthesis.

    PubMed

    Yu, Z G; Berding, M A; Wang, Haobin

    2008-11-01

    Recent multicolor photon-echo experiments revealed a long-lasting quantum coherence between excitations on the donor and acceptor in photosynthetic systems. Identifying the origin of the quantum coherence is essential to fully understand photosynthesis. Here we present a generic model in which a strong intermolecular steric restoring force in densely packed pigment-protein complexes results in a spatial correlation in conformational (static) variations of chromophores, which in turn induces an effective coupling between high-frequency (dynamic) fluctuations in donor and acceptor. The spatially correlated static and dynamic fluctuations provide a favorable environment to maintain quantum coherence, which can consistently explain the photon-echo measurements.

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

    NASA Astrophysics Data System (ADS)

    Koibuchi, Hiroshi; Shobukhov, Andrey

    2016-10-01

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

  15. Vorticity Fluctuations in Plane Couette Flow

    NASA Astrophysics Data System (ADS)

    Ortiz de Zarate, Jose; Sengers, Jan V.

    2010-11-01

    In this presentation we evaluate the flow-induced amplification of the thermal noise in plane Couette configuration. The physical origin of the noise is the random nature of molecular collisions, that contribute with a stochastic component to the stress tensor (Landau's fluctuating hydrodynamics). This intrinsic stochastic forcing is then amplified by the mode- coupling mechanisms associated to shear flow. In a linear approximation, noise amplification can be studied by solving stochastic Orr-Sommerfeld and Squire equations. We compare the efficiency of the different mechanisms, being the most important the direct coupling between Squire and Orr-Sommerfed equations. The main effect is to amplify wall-normal vorticity fluctuations with an spanwise modulation at wave number around 1.5, a configuration that resembles the streaks that have been proposed as precursors of the flow instability.

  16. Anisotropic spin fluctuations in Sr2RuO4 : Role of spin-orbit coupling and induced strain

    NASA Astrophysics Data System (ADS)

    Cobo, Sergio; Ahn, Felix; Eremin, Ilya; Akbari, Alireza

    2016-12-01

    We analyze the spin anisotropy of the magnetic susceptibility of Sr2RuO 4 in the presence of spin-orbit coupling and anisotropic strain using quasi-two-dimensional tight-binding parametrization fitted to the angle-resolved photoemission spectroscopy results. Similar to the previous observations we find the in-plane polarization of the low-q magnetic fluctuations and the out-of-plane polarization of the incommensurate magnetic fluctuation at the nesting wave-vector Q1=(2 /3 π ,2 /3 π ) but also nearly isotropic fluctuations near Q2=(π /6 ,π /6 ) . Furthermore, one finds that, apart from the high-symmetry direction of the tetragonal Brillouin zone, the magnetic anisotropy is maximal, i.e., χx x≠χy y≠χz z reflected in the x polarization of the intraband nesting wave-vector Q3=(π /2 ,π ) . This is a consequence of the orbital anisotropy of the t2 g orbitals in momentum space. We also study how the magnetic anisotropy evolves in the presence of the strain and find strong Ising-like ferromagnetic fluctuations near the Lifshitz transition for the x y band.

  17. Dimethyl sulfoxide induced structural transformations and non-monotonic concentration dependence of conformational fluctuation around active site of lysozyme.

    PubMed

    Roy, Susmita; Jana, Biman; Bagchi, Biman

    2012-03-21

    Experimental studies have observed significant changes in both structure and function of lysozyme (and other proteins) on addition of a small amount of dimethyl sulfoxide (DMSO) in aqueous solution. Our atomistic molecular dynamic simulations of lysozyme in water-DMSO reveal the following sequence of changes on increasing DMSO concentration. (i) At the initial stage (around 5% DMSO concentration) protein's conformational flexibility gets markedly suppressed. From study of radial distribution functions, we attribute this to the preferential solvation of exposed protein hydrophobic residues by the methyl groups of DMSO. (ii) In the next stage (10-15% DMSO concentration range), lysozome partially unfolds accompanied by an increase both in fluctuation and in exposed protein surface area. (iii) Between 15-20% concentration ranges, both conformational fluctuation and solvent accessible protein surface area suddenly decrease again indicating the formation of an intermediate collapse state. These results are in good agreement with near-UV circular dichroism (CD) and fluorescence studies. We explain this apparently surprising behavior in terms of a structural transformation which involves clustering among the methyl groups of DMSO. (iv) Beyond 20% concentration of DMSO, the protein starts its final sojourn towards the unfolding state with further increase in conformational fluctuation and loss in native contacts. Most importantly, analysis of contact map and fluctuation near the active site reveal that both partial unfolding and conformational fluctuations are centered mostly on the hydrophobic core of active site of lysozyme. Our results could offer a general explanation and universal picture of the anomalous behavior of protein structure-function observed in the presence of cosolvents (DMSO, ethanol, tertiary butyl alcohol, dioxane) at their low concentrations.

  18. Toward steering a jet of particles into an x-ray beam with optically induced forces

    NASA Astrophysics Data System (ADS)

    Eckerskorn, Niko; Bowman, Richard; Kirian, Richard A.; Awel, Salah; Wiedorn, Max; Küpper, Jochen; Padgett, Miles J.; Chapman, Henry N.; Rode, Andrei V.

    2015-08-01

    Optical trapping of light-absorbing particles in a gaseous environment is governed by a laser-induced photophoretic force, which can be orders of magnitude stronger than the force of radiation pressure induced by the same light intensity. In spite of many experimental studies, the exact theoretical background underlying the photophoretic force and the prediction of its influence on the particle motion is still in its infancy. Here, we report the results of a quantitative analysis of the photophoretic force and the stiffness of trapping achieved by levitating graphite and carbon-coated glass shells of calibrated sizes in an upright diverging hollow-core vortex beam, which we refer to as an `optical funnel'. The measurements of forces were conducted in air at various gas pressures in the range from 5 mbar to 2 bar. The results of these measurements lay the foundation for developing a touch-free optical system for precisely positioning sub-micrometer bioparticles at the focal spot of an x-ray free electron laser, which would significantly enhance the efficiency of studying nanoscale morphology of proteins and biomolecules in femtosecond coherent diffractive imaging experiments.

  19. Spin motive force induced by Rashba interaction in the strong sd coupling regime

    NASA Astrophysics Data System (ADS)

    Tatara, Gen; Nakabayashi, Noriyuki; Lee, Kyun-Jin

    2013-02-01

    Spin motive force induced by the Rashba interaction in the presence of strong sd interaction between conduction electron and localized spin is theoretically studied. The motive force is calculated by evaluating the time derivative of the current density on the basis of microscopic formalism. It is shown that there are two motive forces, one proportional to ER×ṅ, the other, perpendicular component proportional to ER×(n×ṅ), where ER and n are the Rashba electric field and localized spin direction, respectively. The second type arises in the strong sd coupling regime from the spin relaxation. The appearance of perpendicular component from the spin relaxation is understood from the analogy with the current-induced torques. In the case of domain wall motion, the two contributions to the spin motive force are the same order of magnitude, while the first term dominates in the case of precession of uniform magnetization. Our result explains the appearance of the perpendicular component in the weak sd coupling limit, recently discussed in the context of spin damping monopole. Detection of ac voltage induced by the precession of uniform magnetization serves as a experimental evidence of the Rashba interaction in films and wires.

  20. Does visually induced self-motion affect grip force when holding an object?

    PubMed

    Bringoux, Lionel; Lepecq, Jean-Claude; Danion, Frédéric

    2012-09-01

    Accurate control of grip force during object manipulation is necessary to prevent the object from slipping, especially to compensate for the action of gravitational and inertial forces resulting from hand/object motion. The goal of the current study was to assess whether the control of grip force was influenced by visually induced self-motion (i.e., vection), which would normally be accompanied by changes in object load. The main task involved holding a 400-g object between the thumb and the index finger while being seated within a virtual immersive environment that simulated the vertical motion of an elevator across floors. Different visual motions were tested, including oscillatory (0.21 Hz) and constant-speed displacements of the virtual scene. Different arm-loading conditions were also tested: with or without the hand-held object and with or without oscillatory arm motion (0.9 Hz). At the perceptual level, ratings from participants showed that both oscillatory and constant-speed motion of the elevator rapidly induced a long-lasting sensation of self-motion. At the sensorimotor level, vection compellingness altered arm movement control. Spectral analyses revealed that arm motion was entrained by the oscillatory motion of the elevator. However, we found no evidence that grip force used to hold the object was visually affected. Specifically, spectral analyses revealed no component in grip force that would mirror the virtual change in object load associated with the oscillatory motion of the elevator, thereby allowing the grip-to-load force coupling to remain unaffected. Altogether, our findings show that the neural mechanisms underlying vection interfere with arm movement control but do not interfere with the delicate modulation of grip force. More generally, those results provide evidence that the strength of the coupling between the sensorimotor system and the perceptual level can be modulated depending on the effector.

  1. 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.

  2. Biomechanical force induces the growth factor production in human periodontal ligament-derived cells.

    PubMed

    Ichioka, Hiroaki; Yamamoto, Toshiro; Yamamoto, Kenta; Honjo, Ken-Ichi; Adachi, Tetsuya; Oseko, Fumishige; Mazda, Osam; Kanamura, Narisato; Kita, Masakazu

    2016-01-01

    Although many reports have been published on the functional roles of periodontal ligament (PDL) cells, the mechanisms involved in the maintenance and homeostasis of PDL have not been determined. We investigated the effects of biomechanical force on growth factor production, phosphorylation of MAPKs, and intracellular transduction pathways for growth factor production in human periodontal ligament (hPDL) cells using MAPK inhibitors. hPDL cells were exposed to mechanical force (6 MPa) using a hydrostatic pressure apparatus. The levels of growth factor mRNA and protein were examined by real-time RT-PCR and ELISA. The phosphorylation of MAPKs was measured using BD™ CBA Flex Set. In addition, MAPKs inhibitors were used to identify specific signal transduction pathways. Application of biomechanical force (equivalent to occlusal force) increased the synthesis of VEGF-A, FGF-2, and NGF. The application of biomechanical force increased the expression levels of phosphorylated ERK and p38, but not of JNK. Furthermore, the levels of VEGF-A and NGF expression were suppressed by ERK or p38 inhibitor. The growth factors induced by biomechanical force may play a role in the mechanisms of homeostasis of PDL.

  3. Comparison of rotordynamic fluid forces in axial inducers and centrifugal turbopump impellers

    NASA Astrophysics Data System (ADS)

    d'Agostino, Luca

    2016-05-01

    The paper illustrates and compares the results of the experimental campaigns carried out in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at Alta, Italy, under ESA funding for the characterization of the lateral rotordynamic fluid forces acting on high-head axial inducers and centrifugal turbopump impellers for space propulsion applications. The configurations presented here refer to a three-bladed tapered-hub, variable-pitch, inducer (DAPROT3) and a single-stage centrifugal pump (VAMPIRE) with vaneless diffuser and single spiral volute. Both the centrifugal pump and the inducer have been designed by means of reduced order models specifically developed by the author and his collaborators for the geometric definition and performance prediction of this kind of hydraulic turbomachinery. Continuous spectra of the rotordynamic forces acting on the impellers as functions of the whirl frequency have been obtained by means of the novel technique recently developed and demonstrated at Alta. The influence of the rotor whirl motion, flow rate, cavitating conditions, and liquid temperature (thermal cavitation effects) on the rotordynamic fluid forces is illustrated and the observed differences in their behavior in axial inducers and centrifugal turbpumps are discussed and interpreted in the light of the outcome of recent cavitation visualization experiments carried out by the Chemical Propulsion Team at Alta.

  4. The Norton-Simon hypothesis and the onset of non-genetic resistance to chemotherapy induced by stochastic fluctuations

    NASA Astrophysics Data System (ADS)

    d'Onofrio, Alberto; Gandolfi, Alberto; Gattoni, Sara

    2012-12-01

    By studying a simple but realistic biophysical model of tumor growth in the presence of a constant continuous chemotherapy, we show that if an extended Norton-Simon hypothesis holds, the system may have multiple equilibria. Thus, the stochastic bounded fluctuations that affect both the tumor carrying capacity and/or the drug pharmacodynamics (and/or the drug pharmacokinetics) may cause the transition from a small equilibrium to a far larger one, not compatible with the life of the host. In particular, we mainly investigated the effects of fluctuations that involve parameters nonlinearly affecting the deterministic model. We propose to frame the above phenomena as a new and non-genetic kind of resistance to chemotherapy.

  5. Fluctuating shells under pressure

    PubMed Central

    Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.

    2012-01-01

    Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558

  6. Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems

    NASA Astrophysics Data System (ADS)

    Huo, Pengfei; Coker, David F.

    2012-03-01

    Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light

  7. Molecular stress relief through a force-induced irreversible extension in polymer contour length.

    PubMed

    Wu, Dong; Lenhardt, Jeremy M; Black, Ashley L; Akhremitchev, Boris B; Craig, Stephen L

    2010-11-17

    Single-molecule force spectroscopy is used to observe the irreversible extension of a gem-dibromocyclopropane (gDBC)-functionalized polybutadiene under tension, a process akin to polymer necking at a single-molecule level. The extension of close to 28% in the contour length of the polymer backbone occurs at roughly 1.2 nN (tip velocity of 3 μm/s) and is attributed to the force-induced isomerization of the gDBCs into 2,3-dibromoalkenes. The rearrangement represents a possible new mechanism for localized stress relief in polymers and polymer networks under load, and the quantification of the force dependency provides a benchmark value for further studies of mechanically triggered chemistry in bulk polymers.

  8. A Nonlinear Elasticity Model of Macromolecular Conformational Change Induced by Electrostatic Forces

    PubMed Central

    Zhou, Y. C.; Holst, Michael; McCammon, J. Andrew

    2008-01-01

    In this paper we propose a nonlinear elasticity model of macromolecular conformational change (deformation) induced by electrostatic forces generated by an implicit solvation model. The Poisson-Boltzmann equation for the electrostatic potential is analyzed in a domain varying with the elastic deformation of molecules, and a new continuous model of the electrostatic forces is developed to ensure solvability of the nonlinear elasticity equations. We derive the estimates of electrostatic forces corresponding to four types of perturbations to an electrostatic potential field, and establish the existance of an equilibrium configuration using a fixed-point argument, under the assumption that the change in the ionic strength and charges due to the additional molecules causing the deformation are sufficiently small. The results are valid for elastic models with arbitrarily complex dielectric interfaces and cavities, and can be generalized to large elastic deformation caused by high ionic strength, large charges, and strong external fields by using continuation methods. PMID:19461946

  9. A Nonlinear Elasticity Model of Macromolecular Conformational Change Induced by Electrostatic Forces.

    PubMed

    Zhou, Y C; Holst, Michael; McCammon, J Andrew

    2008-04-01

    In this paper we propose a nonlinear elasticity model of macromolecular conformational change (deformation) induced by electrostatic forces generated by an implicit solvation model. The Poisson-Boltzmann equation for the electrostatic potential is analyzed in a domain varying with the elastic deformation of molecules, and a new continuous model of the electrostatic forces is developed to ensure solvability of the nonlinear elasticity equations. We derive the estimates of electrostatic forces corresponding to four types of perturbations to an electrostatic potential field, and establish the existance of an equilibrium configuration using a fixed-point argument, under the assumption that the change in the ionic strength and charges due to the additional molecules causing the deformation are sufficiently small. The results are valid for elastic models with arbitrarily complex dielectric interfaces and cavities, and can be generalized to large elastic deformation caused by high ionic strength, large charges, and strong external fields by using continuation methods.

  10. Protective effects of forced exercise against methylphenidate-induced anxiety, depression and cognition impairment in rat

    PubMed Central

    Motaghinejad, Majid; Motevalian, Manijeh; Larijani, Setare Farokhi; Khajehamedi, Zohreh

    2015-01-01

    Background: Methylphenidate (MPH), a neural stimulant, can cause damages to brain; the chronic neurochemical and behavioral effects of MPH remain unclear. Exercise lowers stress and anxiety and can act as non-pharmacologic neuroprotective agent. In this study protective effects of exercise in MPH-induced anxiety, depression and cognition impairment were investigated. Materials and Methods: Seventy adult male rats were divided randomly into five groups. Group 1 served as negative control, received normal saline (0.2 ml/rat) for 21 days, group 2 and 3 (as positive controls) received MPH (10 and 20 mg/kg) for 21 days. Groups 4 and 5 concurrently were treated with MPH (10 and 20 mg/kg) and forced exercise for 21 days. On day 21, Elevated Plus Maze (EPM), Open Field Test (OFT), Forced Swim Test (FST) and Tail Suspension Test (TST) were used to investigate the level of anxiety and depression in animals. In addition between 17th and 21th days, Morris Water Maze (MWM) was applied to evaluate the effect of MPH on spatial learning and memory. Results: MPH-treated animals indicated a reflective depression and anxiety in a dose-dependent manner in FST, EPM and TST which were significantly different from the control group and also can significantly attenuate the motor activity and anxiety in OFT. Forced exercise by treadmill can attenuate MPH-induced anxiety, depression and motor activity alteration in OFT. MPH also can disturb learning and memory in MWM and forced exercise can neutralize this effect of MPH. Conclusion: We conclude that forced exercise can be protective in brain against MPH-induced anxiety, depression and cognition alteration. PMID:26322282

  11. Effects of wave-induced forcing on a circulation model of the North Sea

    NASA Astrophysics Data System (ADS)

    Staneva, Joanna; Alari, Victor; Breivik, Øyvind; Bidlot, Jean-Raymond; Mogensen, Kristian

    2017-01-01

    The effect of wind waves on water level and currents during two storms in the North Sea is investigated using a high-resolution Nucleus for European Modelling of the Ocean (NEMO) model forced with fluxes and fields from a high-resolution wave model. The additional terms accounting for wave-current interaction that are considered in this study are the Stokes-Coriolis force, the sea-state-dependent energy and momentum fluxes. The individual and collective role of these processes is quantified and the results are compared with a control run without wave effects as well as against current and water-level measurements from coastal stations. We find a better agreement with observations when the circulation model is forced by sea-state-dependent fluxes, especially in extreme events. The two extreme events, the storm Christian (25-27 October 2013), and about a month later, the storm Xaver (5-7 December 2013), induce different wave and surge conditions over the North Sea. Including the wave effects in the circulation model for the storm Xaver raises the modelled surge by more than 40 cm compared with the control run in the German Bight area. For the storm Christian, a difference of 20-30 cm in the surge level between the wave-forced and the stand-alone ocean model is found over the whole southern part of the North Sea. Moreover, the modelled vertical velocity profile fits the observations very well when the wave forcing is accounted for. The contribution of wave-induced forcing has been quantified indicating that this represents an important mechanism for improving water-level and current predictions.

  12. Schlieren High Speed Imaging on Fluid Flow in Liquid Induced by Plasma-driven Interfacial Forces

    NASA Astrophysics Data System (ADS)

    Lai, Janis; Foster, John

    2016-10-01

    Effective plasma-based water purification depends heavily on the transport of plasma-derived reactive species from the plasma into the liquid. Plasma interactions at the liquid-gas boundary are known to drive circulation in the bulk liquid. This forced circulation is not well understood. A 2-D plasma- in-liquid water apparatus is currently being investigated as a means to study the plasma-liquid interface to understand not only reactive species flows but to also understand plasma- driven fluid dynamic effects in the bulk fluid. Using Schlieren high speed imaging, plasma-induced density gradients near the interfacial region and into the bulk solution are measured to investigate the nature of these interfacial forces. Plasma-induced flow was also measured using particle imaging velocimetry. NSF CBET 1336375 and DOE DE-SC0001939.

  13. Aerodynamic design of a Coanda induced force and thruster anti-torque system

    NASA Technical Reports Server (NTRS)

    Velkoff, Henry R.; Tung, Chee

    1991-01-01

    A general method of analysis of the external and internal aerodynamics of a generic Coanda induced circulation anti-torque system is presented. The technique gives moment about the yaw axis and download induced on the boom as well as the force developed by an aft jet. The external flows including downwash, wake swirl and the boom circulation are considered. The internal flow and losses through the duct, fan, blown slots, cascades and nozzle are considered on a step-by-step basis. Limited comparison is made with open data where available.

  14. Nonvolatile data storage using mechanical force-induced polarization switching in ferroelectric polymer

    SciTech Connect

    Chen, Xin; Tang, Xin; Chen, Xiang-Zhong; Chen, Yu-Lei; Shen, Qun-Dong; Guo, Xu; Ge, Hai-Xiong

    2015-01-26

    Ferroelectric polymers offer the promise of low-cost and flexible electronic products. They are attractive for information storage due to their spontaneous polarization which is usually switched by electric field. Here, we demonstrate that electrical signals can be readily written on ultra-thin ferroelectric polymer films by strain gradient-induced polarization switching (flexoelectric effect). A force with magnitude as small as 64nN is enough to induce highly localized (40 nm feature size) change in the polarization states. The methodology is capable of realizing nonvolatile memory devices with miniaturized cell size and storage density of tens to hundreds Gbit per square inch.

  15. Orthodontic Forces Induce the Cytoprotective Enzyme Heme Oxygenase-1 in Rats

    PubMed Central

    Suttorp, Christiaan M.; Xie, Rui; Lundvig, Ditte M. S.; Kuijpers-Jagtman, Anne Marie; Uijttenboogaart, Jasper Tom; Van Rheden, René; Maltha, Jaap C.; Wagener, Frank A. D. T. G.

    2016-01-01

    Orthodontic forces disturb the microenvironment of the periodontal ligament (PDL), and induce craniofacial bone remodeling which is necessary for tooth movement. Unfortunately, orthodontic tooth movement is often hampered by ischemic injury and cell death within the PDL (hyalinization) and root resorption. Large inter-individual differences in hyalinization and root resorption have been observed, and may be explained by differential protection against hyalinization. Heme oxygenase-1 (HO-1) forms an important protective mechanism by breaking down heme into the strong anti-oxidants biliverdin/bilirubin and the signaling molecule carbon monoxide. These versatile HO-1 products protect against ischemic and inflammatory injury. We postulate that orthodontic forces induce HO-1 expression in the PDL during experimental tooth movement. Twenty-five 6-week-old male Wistar rats were used in this study. The upper three molars at one side were moved mesially using a Nickel-Titanium coil spring, providing a continuous orthodontic force of 10 cN. The contralateral side served as control. After 6, 12, 72, 96, and 120 h groups of rats were killed. On parasagittal sections immunohistochemical staining was performed for analysis of HO-1 expression and quantification of osteoclasts. Orthodontic force induced a significant time-dependent HO-1 expression in mononuclear cells within the PDL at both the apposition- and resorption side. Shortly after placement of the orthodontic appliance HO-1 expression was highly induced in PDL cells but dropped to control levels within 72 h. Some osteoclasts were also HO-1 positive but this induction was shown to be independent of time- and mechanical stress. It is tempting to speculate that differential induction of tissue protecting- and osteoclast activating genes in the PDL determine the level of bone resorption and hyalinization and, subsequently, “fast” and “slow” tooth movers during orthodontic treatment. PMID:27486402

  16. Calculation of the induced currents and forces for a hybrid magnetic levitation system

    SciTech Connect

    Albertz, D.; Dappen, S.; Henneberger, G.

    1997-03-01

    This paper presents the calculation of the induced currents and forces for a 3D non-linear eddy current field problem with ferromagnetic moving conductors. The {rvec A}, V-{rvec A} formulation is used in combination with four different gauging methods to stabilize the solution process. To consider non-rectangular shapes of geometries tetrahedral elements were employed. The computation procedure is applied to a hybrid magnetic levitation system of a contactless and frictionless conveyance system.

  17. The CB1 cannabinoid receptor agonist reduces L-DOPA-induced motor fluctuation and ERK1/2 phosphorylation in 6-OHDA-lesioned rats.

    PubMed

    Song, Lu; Yang, Xinxin; Ma, Yaping; Wu, Na; Liu, Zhenguo

    2014-01-01

    The dopamine precursor L-3,4-dihydroxyphenylalanine (L-DOPA) has been used as an effective drug for treating dopamine depletion-induced Parkinson's disease (PD). However, long-term administration of L-DOPA produces motor complications. L-DOPA has also been found to modify the two key signaling cascades, protein kinase A/dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32) and extracellular signal-regulated kinases 1 and 2 (ERK1/2), in striatal neurons, which are thought to play a pivotal role in forming motor complications. In the present study, we tested the possible effect of a CB1 cannabinoid receptor agonist on L-DOPA-stimulated abnormal behavioral and signaling responses in vivo. Intermittent L-DOPA administration for 3 weeks induced motor fluctuation in a rat model of PD induced by intrastriatal infusion of dopamine-depleting neurotoxin 6-hydroxydopamine (6-OHDA). A single injection of a CB1 cannabinoid receptor agonist WIN-55,212-2 had no effect on L-DOPA-induced motor fluctuation. However, chronic injections of WIN-55,212-2 significantly attenuated abnormal behavioral responses to L-DOPA in 6-OHDA-lesioned rats. Similarly, chronic injections of WIN-55,212-2 influence the L-DOPA-induced alteration of DARPP-32 and ERK1/2 phosphorylation status in striatal neurons. These data provide evidence for the active involvement of CB1 cannabinoid receptors in the regulation of L-DOPA action during PD therapy.

  18. System for measurement of small vibrations at material interfaces induced by electrostrictive forces

    SciTech Connect

    Ali, J.S.; Joines, W.T.

    1985-10-01

    The mechanisms of interaction of ELF and ELF-modulated RF fields with biological systems is presently an active area of research. Some models propose that field-induced forces may influence certain observed biological effects such as RF hearing and calcium ion efflux. To investigate the validity of the field-induced force model for the calcium-ion efflux effect, a system is needed which is capable of exposing samples to ELF fields or to ELF-modulated RF fields. At the same time the induced vibration caused by the forces of electrostriction must be monitored preferably by a noncontacting method. A microwave phase-sensitive receiver was designed to sense the small vibrations. Limitations on the receiver sensitivity imposed by phase noise is discussed. Phase noise measurement systems were designed and used to characterize the key receiver components. A limiting amplifier in the IF section of the receiver eliminates the need for knowledge of the reflection coefficient of the object of interest for quantitative vibration measurements.

  19. Optical interaction between small plasmonic nanowires: a perspective from induced forces and torques

    NASA Astrophysics Data System (ADS)

    Ekeroth, Ricardo M. Abraham

    2016-08-01

    This paper addresses a new numerical study of the near electromagnetic coupling between two small, metallic nanowires under plane-wave illumination. The forces and torques induced give a different point of view of the interaction. The analysis of these near-field, mechanical observables is based entirely on the plasmon hybridization model, with the help of an adequate correlation with far fields. Although several studies of the opto-mechanical inductions have been done, unexpected features of the movement are obtained. ‘Coordinated’ spin for the wires are found, in addition to binding or repulsion forces between the wires and scattering forces. For heterodimers, also orbital torques are obtained. The binding and rotation of the nanowires as well as orbital torques are strongly dependent on the plasmonic excitations of the system. They identify uniquely the surface plasmons. In particular, dark modes can be optically detected without using evanescent fields. The optical forces and torques are calculated exactly by Maxwell stress tensor. ‘Realistic’ infinite nanowires of silver and gold are simulated by a size correction in bulk dielectric function. Thus, the importance of this correction on the mechanical results is also studied. The results can contribute to the design of devices for real observation/detection of surface plasmons. The spectra of forces, and specially of torques, show more resolved resonances because overlapping effects are not as present as in far-field calculations. The spinning of wires found and the analysis made could open new directions of studies and applications of dimers.

  20. Fluctuation-induced anisotropic magnetoconductivity in oxygen-deficient YBa 2Cu 3O 7-δthin films

    NASA Astrophysics Data System (ADS)

    Göb, W.; Lang, W.; Kula, W.; Sobolewski, Roman

    1997-04-01

    We report on measurements of both the longitudinal and transverse magnetoresistivity (MR) of oxygen-reduced YBa2Cu3O7-δ(YBCO) thin films with critical temperatures betweenTc = 55 K andTc = 89 . We find the MR solely caused by the suppression of superconducting fluctuations by a magnetic field. In fully oxygenated samples both the Aslamazov-Larkin process (AL) and another, presumably the Maki-Thompson process (MT), contribute to the MR. In oxygen-deficient samples the MT process unambiguously is absent, thus indicating an unconventional (non-s-wave) pairing symmetry in YBCO.

  1. Correlation between intensity fluctuations induced by scattering of a partially coherent, electromagnetic wave from a quasi-homogeneous medium

    NASA Astrophysics Data System (ADS)

    Li, Jia; Chang, Liping; Chen, Feinan

    2016-12-01

    Based on the first-order Born approximation, the correlation between intensity fluctuations is derived for a partially coherent, electromagnetic plane wave scattering from a spatially quasi-homogeneous medium. Young's pinholes are utilized to control the degree of coherence of the incident field. For the electromagnetic scattering case, it is shown that the CIF of the scattered field strongly depends on the degree of polarization of the incident wave, Young's pinhole parameter, effective radius and correlation length of the medium. The influences of these parameters on the CIF distributions are revealed by numerical calculations.

  2. Topographic analysis of the skull vibration-induced nystagmus test with piezoelectric accelerometers and force sensors.

    PubMed

    Dumas, Georges; Lion, Alexis; Perrin, Philippe; Ouedraogo, Evariste; Schmerber, Sébastien

    2016-03-23

    Vibration-induced nystagmus is elicited by skull or posterior cervical muscle stimulations in patients with vestibular diseases. Skull vibrations delivered by the skull vibration-induced nystagmus test are known to stimulate the inner ear structures directly. This study aimed to measure the vibration transfer at different cranium locations and posterior cervical regions to contribute toward stimulus topographic optimization (experiment 1) and to determine the force applied on the skull with a hand-held vibrator to study the test reproducibility and provide recommendations for good clinical practices (experiment 2). In experiment 1, a 100 Hz hand-held vibrator was applied on the skull (vertex, mastoids) and posterior cervical muscles in 11 healthy participants. Vibration transfer was measured by piezoelectric sensors. In experiment 2, the vibrator was applied 30 times by two experimenters with dominant and nondominant hands on a mannequin equipped to measure the force. Experiment 1 showed that after unilateral mastoid vibratory stimulation, the signal transfer was higher when recorded on the contralateral mastoid than on the vertex or posterior cervical muscles (P<0.001). No difference was observed between the different vibratory locations when vibration transfer was measured on vertex and posterior cervical muscles. Experiment 2 showed that the force applied to the mannequin varied according to the experimenters and the handedness, higher forces being observed with the most experienced experimenter and with the dominant hand (10.3 ± 1.0 and 7.8 ± 2.9 N, respectively). The variation ranged from 9.8 to 29.4% within the same experimenter. Bone transcranial vibration transfer is more efficient from one mastoid to the other mastoid than other anatomical sites. The mastoid is therefore the optimal site for skull vibration-induced nystagmus test in patients with unilateral vestibular lesions and enables a stronger stimulation of the healthy side. In clinical practice

  3. Fatigue-induced changes in synergistic muscle force do not match tendon elongation.

    PubMed

    Mitsukawa, Naotoshi; Sugisaki, Norihide; Miyamoto, Naokazu; Yanai, Toshimasa; Kanehisa, Hiroaki; Fukunaga, Tetsuo; Kawakami, Yasuo

    2010-05-28

    This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min x 5 times: interval 30 s, intensity: 20-30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles. The tendon elongation of MG and SOL in post-fatigue ramp was similar, although evoked MG forces dropped nearly to zero. In addition, for a given torque output, the tendon elongation of SOL significantly decreased while that of LG did not, although the activation levels of both muscles had increased. Results suggest that the fatigue-induced changes in force of the triceps surae muscles do not match their tendon elongation. These results imply that the tendons of the triceps surae muscles are mechanically coupled even after selective fatigue of a single muscle.

  4. Fluctuations of tensile strength and hardness of c-BC₂N crystals induced by difference in atomic configuration.

    PubMed

    Zhuang, Chunqiang; Li, Xiaoqing; Zhao, Jijun; Samra, H Abu; Jiang, Xin

    2011-11-23

    At the atomistic level, the physical properties of a material are determined by its structure such as atomic arrangements. Here first-principles calculations were performed to investigate the effect of atomic configuration on the tensile strength and Vickers hardness of cubic-BC₂N (c-BC₂N) crystals. Depending on the degree of mixture between diamond and c-BN, the tensile strength of c-BC2N crystals can vary drastically from 27 to 77 GPa. The magnitude of the Vickers hardness fluctuations (~10 GPa) is also comparable to the experimental difference (~14 GPa). Thus, atomic-scale characterization of c-BC₂N crystal structures may unveil the discrepancy of the measured Vickers hardness in experiments, and uncover the obvious differences of tensile strength described in theoretical calculations.

  5. Fluctuations, Intermittency and Predictivity

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter considers the various mechanisms capable of producing amplitude and duration variations in the various dynamo models introduced in Chap. 3 (10.1007/978-3-642-32093-4_3). After a survey of observed and inferred fluctuation patterns of the solar cycle, the effects on the basic cycle of stochastic forcing, dynamical nonlinearities and time delay are considered in turn. The occurrence of intermittency in a subset of these models is then investigated, with an eye on explaining Grand Minima observed in the solar activity record. The chapter closes with a brief discussion of solar cycle prediction schemes based on dynamo models.

  6. Capillary-Force-Induced Cold Welding in Silver-Nanowire-Based Flexible Transparent Electrodes.

    PubMed

    Liu, Yuan; Zhang, Jianming; Gao, Heng; Wang, Yan; Liu, Qingxian; Huang, Siya; Guo, Chuan Fei; Ren, Zhifeng

    2017-02-08

    Silver nanowire (AgNW) films have been studied as the most promising flexible transparent electrodes for flexible photoelectronics. The wire-wire junction resistance in the AgNW film is a critical parameter to the electrical performance, and several techniques of nanowelding or soldering have been reported to reduce the wire-wire junction resistance. However, these methods require either specific facilities, or additional materials as the "solder", and often have adverse effects to the AgNW film or substrate. In this study, we show that at the nanoscale, capillary force is a powerful driving force that can effectively cause self-limited cold welding of the wire-wire junction for AgNWs. The capillary-force-induced welding can be simply achieved by applying moisture on the AgNW film, without any technical support like the addition of materials or the use of specific facilities. The moisture-treated AgNW films exhibit a significant decrease in sheet resistance, but negligible changes in transparency. We have also demonstrated that this method is effective to heal damaged AgNW films of wearable electronics and can be conveniently performed not only indoors but also outdoors where technical support is often unavailable. The capillary-force-based method may also be useful in the welding of other metal NWs, the fabrication of nanostructures, and smart assemblies for versatile flexible optoelectronic applications.

  7. A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

    NASA Technical Reports Server (NTRS)

    Alexander, M. J.; Holton, James R.

    1997-01-01

    A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.

  8. Examination of hydrodynamic force acting on a circular cylinder in vortex-induced vibrations in synchronization

    NASA Astrophysics Data System (ADS)

    Shen, Linwei; Chan, Eng-Soon; Sun, Zhilin

    2017-04-01

    An immersed boundary method is employed to simulate vortex-induced vibrations (VIV) of a circular cylinder in two dimensions. The Reynolds number is 150, and the cylinder mass ratios of 2 and 10 are considered. The synchronization regions for these two mass ratios are determined by the simulations. It is found that the cycle-averaged added mass is about zero at the reduced velocity of 6.1. The instantaneous frequency, which is obtained by Hilbert transformation of the cylinder oscillating displacement, exhibits an important feature whereby the cylinder oscillation in the VIV synchronization region is modulated with a frequency twice the displacement prevailing frequency. The cylinder displacement could still be well approximated by a sine function with a constant frequency and amplitude. However, the lift force acting on the cylinder cannot be estimated in the same manner. In fact, both the lift force amplitude and frequency are modulated. The suggested expression provides a better approximation of the lift force. Moreover, it reveals that the presence of the higher harmonics in the lift force is the result of the amplitude and frequency modulation.

  9. Frequency fluctuations in silicon nanoresonators

    PubMed Central

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C.; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K.; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L.; Jourdan, Guillaume; Hentz, Sébastien

    2016-01-01

    Frequency stability is key to performance of nanoresonators. This stability is thought to reach a limit with the resonator’s ability to resolve thermally-induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature, and found a similar discrepancy. We propose a new method to show this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices. PMID:26925826

  10. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    NASA Astrophysics Data System (ADS)

    Fujihashi, Yuta; Fleming, Graham R.; Ishizaki, Akihito

    2015-06-01

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  11. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra

    SciTech Connect

    Fujihashi, Yuta; Ishizaki, Akihito; Fleming, Graham R.

    2015-06-07

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  12. Impact of environmentally induced fluctuations on quantum mechanically mixed electronic and vibrational pigment states in photosynthetic energy transfer and 2D electronic spectra.

    PubMed

    Fujihashi, Yuta; Fleming, Graham R; Ishizaki, Akihito

    2015-06-07

    Recently, nuclear vibrational contribution signatures in two-dimensional (2D) electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted electronic coherence lifetime. As a plausible explanation for this long-lived spectral beating in 2D electronic spectra, quantum-mechanically mixed electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon electronic-vibrational quantum mixtures by calculating the electronic energy transfer dynamics and 2D electronic spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D electronic spectra. At physiological temperatures, however, the fluctuations eradicate the mixing, and hence, the beating in the 2D spectra disappears. Further, it is demonstrated that such electronic-vibrational quantum mixtures do not necessarily play a significant role in electronic energy transfer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D electronic spectra, contrary to speculations in recent publications.

  13. Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy.

    PubMed

    Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

    2014-08-07

    Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results.

  14. Energy losses of nanomechanical resonators induced by atomic force microscopy-controlled mechanical impedance mismatching

    NASA Astrophysics Data System (ADS)

    Rieger, Johannes; Isacsson, Andreas; Seitner, Maximilian J.; Kotthaus, Jörg P.; Weig, Eva M.

    2014-03-01

    Clamping losses are a widely discussed damping mechanism in nanoelectromechanical systems, limiting the performance of these devices. Here we present a method to investigate this dissipation channel. Using an atomic force microscope tip as a local perturbation in the clamping region of a nanoelectromechanical resonator, we increase the energy loss of its flexural modes by at least one order of magnitude. We explain this by a transfer of vibrational energy into the cantilever, which is theoretically described by a reduced mechanical impedance mismatch between the resonator and its environment. A theoretical model for this mismatch, in conjunction with finite element simulations of the evanescent strain field of the mechanical modes in the clamping region, allows us to quantitatively analyse data on position and force dependence of the tip-induced damping. Our experiments yield insights into the damping of nanoelectromechanical systems with the prospect of engineering the energy exchange in resonator networks.

  15. Energy losses of nanomechanical resonators induced by atomic force microscopy-controlled mechanical impedance mismatching

    PubMed Central

    Rieger, Johannes; Isacsson, Andreas; Seitner, Maximilian J.; Kotthaus, Jörg P.; Weig, Eva M.

    2014-01-01

    Clamping losses are a widely discussed damping mechanism in nanoelectromechanical systems, limiting the performance of these devices. Here we present a method to investigate this dissipation channel. Using an atomic force microscope tip as a local perturbation in the clamping region of a nanoelectromechanical resonator, we increase the energy loss of its flexural modes by at least one order of magnitude. We explain this by a transfer of vibrational energy into the cantilever, which is theoretically described by a reduced mechanical impedance mismatch between the resonator and its environment. A theoretical model for this mismatch, in conjunction with finite element simulations of the evanescent strain field of the mechanical modes in the clamping region, allows us to quantitatively analyse data on position and force dependence of the tip-induced damping. Our experiments yield insights into the damping of nanoelectromechanical systems with the prospect of engineering the energy exchange in resonator networks. PMID:24594876

  16. Photon-phonon Interaction in a Microfiber Induced by Optical and Electrostrictive Forces

    PubMed Central

    Shi, Yun-chao; Luo, Wei; Xu, Fei; Lu, Yan-qing

    2017-01-01

    Stimulated Brillouin scattering (SBS) via electrostrictive force is a fundamental interaction between light and sound which limits the power in conventional optical fibers. The emergence of optical microfibers with subwavelength diameter, ultralight mass and an intense light field, provides a new platform for photon–phonon coupling, resulting in the radiation pressure mediated contribution of SBS. This study examines the optomechanical system in cylindrical coordinates, reveals the theoretically radiation pressure induced analogous, and demonstrates contrary effect compared with electrostrictive force in solid or hollow silica microfibers. The finding shows that the photon-phonon coupling, which is related to SBS, can be suppressed in a solid microfiber, and even be completely cancelled in a hollow microfiber. PMID:28145514

  17. Photon-phonon Interaction in a Microfiber Induced by Optical and Electrostrictive Forces

    NASA Astrophysics Data System (ADS)

    Shi, Yun-Chao; Luo, Wei; Xu, Fei; Lu, Yan-Qing

    2017-02-01

    Stimulated Brillouin scattering (SBS) via electrostrictive force is a fundamental interaction between light and sound which limits the power in conventional optical fibers. The emergence of optical microfibers with subwavelength diameter, ultralight mass and an intense light field, provides a new platform for photon–phonon coupling, resulting in the radiation pressure mediated contribution of SBS. This study examines the optomechanical system in cylindrical coordinates, reveals the theoretically radiation pressure induced analogous, and demonstrates contrary effect compared with electrostrictive force in solid or hollow silica microfibers. The finding shows that the photon-phonon coupling, which is related to SBS, can be suppressed in a solid microfiber, and even be completely cancelled in a hollow microfiber.

  18. Force-Induced Unfolding of Fibronectin in the Extracellular Matrix of Living Cells

    PubMed Central

    Smith, Michael L; Gourdon, Delphine; Little, William C; Kubow, Kristopher E; Eguiluz, R. Andresen; Luna-Morris, Sheila; Vogel, Viola

    2007-01-01

    Whether mechanically unfolded fibronectin (Fn) is present within native extracellular matrix fibrils is controversial. Fn extensibility under the influence of cell traction forces has been proposed to originate either from the force-induced lengthening of an initially compact, folded quaternary structure as is found in solution (quaternary structure model, where the dimeric arms of Fn cross each other), or from the force-induced unfolding of type III modules (unfolding model). Clarification of this issue is central to our understanding of the structural arrangement of Fn within fibrils, the mechanism of fibrillogenesis, and whether cryptic sites, which are exposed by partial protein unfolding, can be exposed by cell-derived force. In order to differentiate between these two models, two fluorescence resonance energy transfer schemes to label plasma Fn were applied, with sensitivity to either compact-to-extended conformation (arm separation) without loss of secondary structure or compact-to-unfolded conformation. Fluorescence resonance energy transfer studies revealed that a significant fraction of fibrillar Fn within a three-dimensional human fibroblast matrix is partially unfolded. Complete relaxation of Fn fibrils led to a refolding of Fn. The compactly folded quaternary structure with crossed Fn arms, however, was never detected within extracellular matrix fibrils. We conclude that the resting state of Fn fibrils does not contain Fn molecules with crossed-over arms, and that the several-fold extensibility of Fn fibrils involves the unfolding of type III modules. This could imply that Fn might play a significant role in mechanotransduction processes. PMID:17914904

  19. Analysis of liquid sodium purity by laser-induced breakdown spectroscopy. Modeling and correction of signal fluctuation prior to quantitation of trace elements

    NASA Astrophysics Data System (ADS)

    Maury, Cécile; Sirven, Jean-Baptiste; Tabarant, Michel; L'Hermite, Daniel; Courouau, Jean-Louis; Gallou, Catherine; Caron, Nadège; Moutiers, Gilles; Cabuil, Valérie

    2013-04-01

    Liquid sodium is used as coolant in sodium-cooled fast nuclear reactors. Among many parameters to monitor to ensure the safe operation of the reactor, the coolant chemical purity is a relevant indicator of several undesirable situations, like corrosion of structural materials or sodium contamination, which may release different elements in the coolant. Several techniques have already been implemented to measure the sodium purity, but their response time is long and not suited for continuous monitoring. Therefore, as a complement to them, laser-induced breakdown spectroscopy (LIBS) is considered as a promising technique for real-time analysis of the coolant purity. In this paper we report on the first LIBS quantitative measurements performed in liquid sodium at 150 °C. Calibration curves were traced for lead and indium using the standard addition method. Important intensity drifts and fluctuations were observed, mostly due to pressure variations in the sodium oven. Background subtraction and/or normalization was used to compensate for those intensity fluctuations. To describe the effect of these corrections on the analytical signal noise, a simple model was proposed and its results were found to satisfactorily fit the experimental data. Using this approach, the best detection limits were obtained for the background-subtracted and normalized data, and were found to be 6 ppm for lead and 5 ppm for indium.

  20. Parameterization of Turbulent-Induced Correlated Phytoplankton and Nutrient Fluctuations in an Upwelling Sea Surface Mixed Layer and Their Effect on Mean Production

    NASA Astrophysics Data System (ADS)

    Robinson, A. R.; Goodman, L.

    2008-12-01

    Many fundamental biological dynamical processes in the sea are strongly non-linear. Thus, physical turbulence in the sea not only enhances advective transport processes by eddy diffusivity but also importantly induces turbulent fluctuations in biological state variables which can correlate in the mean and effect mean biological dynamics. Goodman and Robinson (Proc. Roy. Soc A, 2008, 484, 555-572; doi: 10.1098/rspa. 2007.0251) have formulated a theory of turbulent biological-physical interactions in terms of probability density functions (pdfs) and applied it to the simple example of nutrient (N) and seed phytoplankton (P) upwelling into a surface turbulent layer. The mean uptake is to the sum of the product of the means and the often neglected correlation fluctuations . and are positive, but is found to be negative and to significantly reduce . Here we parameterize by with a proportionality constant a function of two non-dimensional parameters: i) the ratio of the biological uptake time scale to the upwelling time, and ii) the ratio of the upwelling time scale to the turbulent diffusive time (Peclet number). An ADR (advective-diffusive-reactive) model is then formulated for the mean fields , and solved analytically for the intense turbulent limit of small Peclet number by perturbation methods. Agreement of , values in the mixed layer with the pdf theory is excellent. The ADR results provide useful insight into coupled turbulent physical-biological dynamical processes.

  1. Solvation force induced by short range, exact dissipative particle dynamics effective surfaces on a simple fluid and on polymer brushes.

    PubMed

    Goicochea, Armando Gama; Alarcón, Francisco

    2011-01-07

    The thermodynamic properties of a simple fluid confined by effective wall forces are calculated using Monte Carlo simulations in the grand canonical ensemble. The solvation force produced by polymer brushes of two different lengths is obtained also. For the particular type of model interactions used, known as the dissipative particle dynamics method, we find that it is possible to obtain an exact, simple expression for the effective force induced by a planar wall composed of identical particles that interact with those in the fluid. We show that despite the short range of all forces in the model, the solvation force can be finite at relatively large distances and therefore does not depend only on the range of the interparticle or solvent-surface forces. As for the polymer brushes, we find that the shape of the solvation force profiles is in fair agreement with scaling and self-consistent field theories. The applications and possible extensions of this work are discussed.

  2. Nonlinear Force-Length Relationship in the ADP-Induced Contraction of Skeletal Myofibrils

    PubMed Central

    Shimamoto, Yuta; Kono, Fumiaki; Suzuki, Madoka; Ishiwata, Shin'ichi

    2007-01-01

    The regulatory mechanism of sarcomeric activity has not been fully clarified yet because of its complex and cooperative nature, which involves both Ca2+ and cross-bridge binding to the thin filament. To reveal the mechanism of regulation mediated by the cross-bridges, separately from the effect of Ca2+, we investigated the force-sarcomere length (SL) relationship in rabbit skeletal myofibrils (a single myofibril or a thin bundle) at SL > 2.2 μm in the absence of Ca2+ at various levels of activation by exogenous MgADP (4–20 mM) in the presence of 1 mM MgATP. The individual SLs were measured by phase-contrast microscopy to confirm the homogeneity of the striation pattern of sarcomeres during activation. We found that at partial activation with 4–8 mM MgADP, the developed force nonlinearly depended on the length of overlap between the thick and the thin filaments; that is, contrary to the maximal activation, the maximal active force was generated at shorter overlap. Besides, the active force became larger, whereas this nonlinearity tended to weaken, with either an increase in [MgADP] or the lateral osmotic compression of the myofilament lattice induced by the addition of a macromolecular compound, dextran T-500. The model analysis, which takes into account the [MgADP]- and the lattice-spacing-dependent probability of cross-bridge formation, was successfully applied to account for the force-SL relationship observed at partial activation. These results strongly suggest that the cross-bridge works as a cooperative activator, the function of which is highly sensitive to as little as ≤1 nm changes in the lattice spacing. PMID:17890380

  3. Casimir effect, quantum fluctuations and related topics

    NASA Astrophysics Data System (ADS)

    Hushwater, Velvel Shaia

    Casimir forces are the very long-range (retarded) forces between electrically neutral systems. Such forces may be thought of as arising from the quantum fluctuations of the electromagnetic field. Contrary to popular opinion such forces need not be attractive. After giving a foundation of the method of the change in the 'zero-point energy' we show how other methods to compute Casimir forces follow from it. We consider the repulsion between electric and magnetic dipoles induced by vacuum fluctuations of electromagnetic field. The calculation are made by the use of the Heisenberg picture operators and by the stochastic electrodynamics approach. We present a purely geometrical proof of the image method, and use it to discuss the Casimir interaction between an atom and a plate. We study the Casimir repulsion between a perfectly conducting and an infinitely permeable plate with the radiation pressure approach. This example illustrates how a repulsive force arises as a consequence of the redistribution of vacuum-field modes corresponding to specific boundary conditions. We show that result is independent of a cutoff function. Discussing the connection with perturbation theory, we prove the negativity of the leading order shift in the ground state. The Casimir effect supports the reality of the 'zero- point energy.' To clarify this we present a novel approach to quantum theory, based on the principle of the quantization of the ensemble-averaged action variable. This quantization leads to the probabilistic description of coordinates and momentum as random variables, which satisfy the uncertainty relation. Using such variables we show that the 'quantum momentum function' must satisfy the Riccati differential equation, which can be converted to the Schrodinger equation for the Ψ function. We derive also the form of basic operators and the rule for probabilities in quantum mechanics. We show that the approach leads to a simple interpretation of gauge invariance, and discuss

  4. Evolution of magnetic fluctuations through the Fe-induced paramagnetic to ferromagnetic transition in Cr2B

    NASA Astrophysics Data System (ADS)

    Arčon, D.; Schoop, L. M.; Cava, R. J.; Felser, C.

    2016-03-01

    In itinerant ferromagnets, the quenched disorder is predicted to dramatically affect the ferromagnetic to paramagnetic quantum phase transition driven by external control parameters at zero temperature. Here we report a study on Fe-doped Cr2B , which, starting from the paramagnetic parent, orders ferromagnetically for Fe-doping concentrations x larger than xc=2.5 % . In parent Cr2B , 11B nuclear magnetic resonance data reveal the presence of both ferromagnetic and antiferromagnetic fluctuations. The latter are suppressed with Fe doping, before the ferromagnetic ones finally prevail for x >xc . Indications for non-Fermi-liquid behavior, usually associated with the proximity of a quantum critical point, were found for all samples, including undoped Cr2B . The sharpness of the ferromagneticlike transition changes on moving away from xc, indicating significant changes in the nature of the magnetic transitions in the vicinity of the quantum critical point. Our data provide some constraints for understanding quantum phase transitions in itinerant ferromagnets in the limit of weak quenched disorder.

  5. Loss of force induced by high extracellular [K+] in rat muscle: effect of temperature, lactic acid and beta2-agonist.

    PubMed

    Pedersen, Thomas Holm; Clausen, Torben; Nielsen, Ole Baekgaard

    2003-08-15

    Loss of K+ from active muscles, leading to increased [K+]o, has been proposed to cause muscle fatigue by reducing excitability. Since exercise increases muscle temperature, we investigated the influence of temperature on muscle [K+]o sensitivity. Intact rat soleus or extensor digitorum longus (EDL) muscles were mounted on force transducers and stimulated electrically to evoke short isometric tetani at regular intervals. In each experiment, control force at 4 mM K+ was initially determined at every temperature used. In soleus muscles at 20 degrees C, 9 mM K+ reduced force to 33 +/- 5 % of control force. Increasing the temperature to 30 degrees C restored force to 89 +/- 5 % of control force. Likewise, at 30 degrees C 11 mM K+ reduced force to 16 +/- 4 % and increasing the temperature to 35 degrees C restored force to 35 +/- 5 %. Similar results were obtained using EDL. The force recovery induced by elevating temperature, reflecting reduced [K+]o sensitivity, was associated with improved excitability assessed from compound action potentials. Force recovery induced by a temperature elevation from 20 to 30 degrees C was associated with hyperpolarization (5 mV), reduced [Na+]i and a 93 % increase in Na+-K+ pump activity. The force recovery was blocked by ouabain. Since intensive exercise leads to lactic acidosis and increased plasma catecholamines, the effect of these two factors was also investigated. At 11 mM K+, force was completely restored by combining temperature elevation (30 to 35 degrees C), L-lactic acid (10 mM) and the beta2-agonist salbutamol (10-5 M). We suggest an exercise scenario where the depressing action of exercise-induced hyperkalaemia is counteracted by elevated muscle temperature, lactic acidosis and catecholamines.

  6. Spin motive force induced in Fe3O4 thin films with negative spin polarization

    NASA Astrophysics Data System (ADS)

    Nagata, Masaki; Moriyama, Takahiro; Tanabe, Kenji; Tanaka, Kensho; Chiba, Daichi; Ohe, Jun-ichiro; Hisamatsu, Yuki; Niizeki, Tomohiko; Yanagihara, Hideto; Kita, Eiji; Ono, Teruo

    2015-12-01

    Spin motive force (SMF) is induced by a time and spatial derivative of magnetizations and is dependent on spin polarization. We compare the SMF in FeNi with positive spin polarization with that in a magnetite (Fe3O4) with negative spin polarization. We observe the SMF induced by a nonuniform ferromagnetic resonance in Fe3O4 and find that the SMF in Fe3O4 is opposite to that in FeNi. This result originates from the negative spin polarization of Fe3O4. Our clear observation of the SMF depending on the sign of the spin polarization agrees well with the framework of the SMF theory.

  7. A Microfluidic Approach for Inducing Cell Rotation by Means of Hydrodynamic Forces

    PubMed Central

    Torino, Stefania; Iodice, Mario; Rendina, Ivo; Coppola, Giuseppe; Schonbrun, Ethan

    2016-01-01

    Microfluidic technology allows to realize devices in which cells can be imaged in their three-dimensional shape. However, there are still some limitations in the method, due to the fact that cells follow a straight path while they are flowing in a channel. This can result in a loss in information, since only one side of the cell will be visible. Our work has started from the consideration that if a cell rotates, it is possible to overcome this problem. Several approaches have been proposed for cell manipulation in microfluidics. In our approach, cells are controlled by only taking advantages of hydrodynamic forces. Two different devices have been designed, realized, and tested. The first device induces cell rotation in a plane that is parallel (in-plane) to the observation plane, while the second one induce rotation in a plane perpendicular (out-of-plane) to the observation plane. PMID:27548187

  8. Synergistic effect of fluconazole and doxycycline against Candida albicans biofilms resulting from calcium fluctuation and downregulation of fluconazole-inducible efflux pump gene overexpression.

    PubMed

    Gao, Yuan; Li, Hui; Liu, Shuyuan; Zhang, Xiang; Sun, Shujuan

    2014-07-01

    Candida albicans biofilms are intrinsically resistant to antimicrobial agents. Previous work demonstrated that the antifungal activity of fluconazole against C. albicans biofilms is notably enhanced by doxycycline. In order to explore the synergistic mechanism of fluconazole and doxycycline, we investigated the changes of efflux pump gene expression, intracellular calcium concentration and cell cycle distribution after drug intervention in this study. The expression levels of CDR1, CDR2 and MDR1 were determined by real-time PCR, and the results showed that fluconazole alone could stimulate the high expression of CDR1, CDR2 and MDR1, and the combination of doxycycline and fluconazole downregulated the gene overexpression induced by fluconazole. Intracellular calcium concentration was determined using Fluo-3/AM by observing the fluorescence with flow cytometry. A calcium fluctuation, which started 4 h and peaked 8 h after the treatment with fluconazole, was observed. The combined drugs also initiated a calcium fluctuation after 4 h treatment and showed a peak at 16 h, and the peak was higher than that stimulated by fluconazole alone. The cell cycle was measured using flow cytometry. Fluconazole alone and the combined drugs both induced a reduction in the percentages of S-phase cells and an elevation in the percentages of cells in the G2/M phase. The results of this research showed that the synergism of fluconazole and doxycycline against C. albicans biofilms is associated with blockade of the efflux pump genes CDR1, CDR2 and MDR1, and stimulation of high intracellular calcium concentration. The findings of this study are of great significance in the search for new antifungal mechanisms.

  9. Fluctuations and Stimulus-Induced Changes in Blood Flow Observed in Individual Capillaries in Layers 2 through 4 of Rat Neocortex

    NASA Astrophysics Data System (ADS)

    Kleinfeld, David; Mitra, Partha P.; Helmchen, Fritjof; Denk, Winfried

    1998-12-01

    Cortical blood flow at the level of individual capillaries and the coupling of neuronal activity to flow in capillaries are fundamental aspects of homeostasis in the normal and the diseased brain. To probe the dynamics of blood flow at this level, we used two-photon laser scanning microscopy to image the motion of red blood cells (RBCs) in individual capillaries that lie as far as 600 μ m below the pia mater of primary somatosensory cortex in rat; this depth encompassed the cortical layers with the highest density of neurons and capillaries. We observed that the flow was quite variable and exhibited temporal fluctuations around 0.1 Hz, as well as prolonged stalls and occasional reversals of direction. On average, the speed and flux (cells per unit time) of RBCs covaried linearly at low values of flux, with a linear density of ≈ 70 cells per mm, followed by a tendency for the speed to plateau at high values of flux. Thus, both the average velocity and density of RBCs are greater at high values of flux than at low values. Time-locked changes in flow, localized to the appropriate anatomical region of somatosensory cortex, were observed in response to stimulation of either multiple vibrissae or the hindlimb. Although we were able to detect stimulus-induced changes in the flux and speed of RBCs in some single trials, the amplitude of the stimulus-evoked changes in flow were largely masked by basal fluctuations. On average, the flux and the speed of RBCs increased transiently on stimulation, although the linear density of RBCs decreased slightly. These findings are consistent with a stimulus-induced decrease in capillary resistance to flow.

  10. Atmospheric Teleconnection over Eurasia Induced by Aerosol Radiative Forcing during Boreal Spring

    NASA Technical Reports Server (NTRS)

    Kim, Maeng-Ki; Lau, William K. M.; Chin, Mian; Kim, Kyu-Myong; Sud, Y. C.; Walker, Greg K.

    2006-01-01

    The direct effects of aerosols on global and regional climate during boreal spring are investigated based on numerical simulations with the NASA Global Modeling and Assimilation Office finite-volume general circulation model (fvGCM) with Microphyics of Clouds with the Relaxed Arakawa Schubert Scheme (McRAS), using aerosol forcing functions derived from the Goddard Ozone Chemistry Aerosol Radiation and Transport model (GOCART). The authors find that anomalous atmospheric heat sources induced by absorbing aerosols (dust and black carbon) excite a planetary-scale teleconnection pattern in sea level pressure, temperature, and geopotential height spanning North Africa through Eurasia to the North Pacific. Surface cooling due to direct effects of aerosols is found in the vicinity and downstream of the aerosol source regions, that is, South Asia, East Asia, and northern and western Africa. Significant atmospheric heating is found in regions with large loading of dust (over northern Africa and the Middle East) and black carbon (over Southeast Asia). Paradoxically, the most pronounced feature in aerosol-induced surface temperature is an east west dipole anomaly with strong cooling over the Caspian Sea and warming over central and northeastern Asia, where aerosol concentrations are low. Analyses of circulation anomalies show that the dipole anomaly is a part of an atmospheric teleconnection pattern driven by atmospheric heating anomalies induced by absorbing aerosols in the source regions, but the influence was conveyed globally through barotropic energy dispersion and sustained by feedback processes associated with the regional circulations. The surface temperature signature associated with the aerosol-induced teleconnection bears striking resemblance to the spatial pattern of observed long-term trend in surface temperature over Eurasia. Additionally, the boreal spring wave train pattern is similar to that reported by Fukutomi et al. associated with the boreal summer

  11. Multivariate nonlinear regression analysis of trajectory tracking performance using force reflecting joystick in chronic stroke-induced hemiparesis.

    PubMed

    Feng, Xin; Winters, Jack M

    2011-01-01

    Individualizing a neurorehabilitation training protocol requires understanding the performance of subjects with various capabilities under different task settings. We use multivariate regression to evaluate the performance of subjects with stroke-induced hemiparesis in trajectory tracking tasks using a force-reflecting joystick. A nonlinear effect was consistently shown in both dimensions of force field strength and impairment level for selected kinematic performance measures, with greatest sensitivity at lower force fields. This suggests that the form of a force field may play a different "role" for subjects with various impairment levels, and confirms that to achieve optimized therapeutic benefit, it is necessary to personalize interfaces.

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

    NASA Astrophysics Data System (ADS)

    Lu, Jianjun; Tokinaga, Shozo

    2016-10-01

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

  13. Response of the Martian induced magnetosphere to variations in solar forcing

    NASA Astrophysics Data System (ADS)

    Woodson, Adam; Weber, Tristan; Andersson, Laila; Ergun, Robert; Andrews, David; Chamandy, Tiffany; Connerny, John; Delory, Greg; Eriksson, Anders; Fowler, Christopher; Halekas, Jasper; Mahaffy, Paul; Mitchell, David; Morooka, Michiko

    2015-11-01

    Solar forcing and compression of Mars' induced magnetosphere may play an important role in oxygen loss at Mars via enhanced ionization and heating of the lower atmosphere, and in the formation of ambipolar electric fields in the upper atmosphere. Steep electron temperature gradients in the upper atmosphere can produce strong ambipolar fields at altitudes where collisions are infrequent, leading to increased outflow of O+ and O2+. Such enhanced escape has been observed in simulations of Mars’ ionosphere where the ambipolar field was artificially varied to study its influence on escape. It is important, therefore, to understand how solar wind forcing modulates electron density- and temperature-versus-altitude profiles in Mars' ionosphere.During the first five days of May 2015, MAVEN’s Langmuir Probe and Waves Instrument (LPW) observed variations in the location and extent of the transition region between the shocked solar wind and the Martian ionosphere in the dayside hemisphere. Solar wind densities and velocities derived from MAVEN’s Solar Wind Ion Analyzer (SWIA) indicate that the solar wind dynamic pressure was also highly variable during this period. In this work we investigate how the shapes of the electron density- and temperature-versus-altitude profiles measured by LPW depend on the location and extent of the transition region as determined from Solar Wind Electron Analyzer (SWEA) spectra, and on solar wind forcing as determined from SWIA and MAVEN Magnetometer (MAG) measurements over this five-day period.

  14. Tension and drag forces of flexible risers undergoing vortex-induced vibration

    NASA Astrophysics Data System (ADS)

    Song, Lei-jian; Fu, Shi-xiao; Li, Man; Gao, Yun; Ma, Lei-xin

    2017-03-01

    This paper presents the results of an experimental investigation on the variation in the tension and the distribution of drag force coefficients along flexible risers under vortex-induced vibration (VIV) in a uniform flow for Reynolds numbers ( Re) up to 2.2×105. The results show that the mean tension is proportional to the square of the incoming current speed, and the tension coefficient of a flexible riser undergoing VIV can be up to 12. The mean drag force is uniformly and symmetrically distributed along the axes of the risers undergoing VIV. The corresponding drag coefficient can vary between 1.6 and 2.4 but is not a constant value of 1.2, as it is for a fixed cylinder in the absence of VIV. These experimental results are used to develop a new empirical prediction model to estimate the drag force coefficient for flexible risers undergoing VIV for Reynolds number on the order of 105, which accounts for the effects of the incoming current speed, the VIV dominant modal number and the frequency.

  15. Sensing nanometric displacement of a micro-/nano-fiber induced by optical forces by use of white light interferometry

    NASA Astrophysics Data System (ADS)

    Qiu, Weiqia; Huang, Hankai; Yu, Jianhui; Dong, Huazhuo; Chen, Zhe; Lu, Huihui

    2015-07-01

    Sensing the nanometric displacement of a micro-/nano-fiber induced by optical forces is a key technology to study optical forces and optical momentum. When the gap between a micro-/nano-fiber and glass substrate becomes down to micrometer scale or less, a white light interference was observed. The gap changes when optical force arising from the propagating pump light along the micro-/nano-fiber causes a transversal nanometric displacement of a micro-/nanofiber, resulting in movement of the interferometric fringes. Therefore this movement of the interferometric fringes can be used to sense the nanometric displacement of the micro-/nano-fiber induced by optical forces. Experimental results show that the resolutions of this method can reach 7.27nm/pixel for tilted angle 0.8o between the micro-/nano-fiber and substrate. It is concluded that the white light interferometry method is suitable for measuring the weak optical force.

  16. Force-induced bone growth and adaptation: A system theoretical approach to understanding bone mechanotransduction

    NASA Astrophysics Data System (ADS)

    Maldonado, Solvey; Findeisen, Rolf

    2010-06-01

    The modeling, analysis, and design of treatment therapies for bone disorders based on the paradigm of force-induced bone growth and adaptation is a challenging task. Mathematical models provide, in comparison to clinical, medical and biological approaches an structured alternative framework to understand the concurrent effects of the multiple factors involved in bone remodeling. By now, there are few mathematical models describing the appearing complex interactions. However, the resulting models are complex and difficult to analyze, due to the strong nonlinearities appearing in the equations, the wide range of variability of the states, and the uncertainties in parameters. In this work, we focus on analyzing the effects of changes in model structure and parameters/inputs variations on the overall steady state behavior using systems theoretical methods. Based on an briefly reviewed existing model that describes force-induced bone adaptation, the main objective of this work is to analyze the stationary behavior and to identify plausible treatment targets for remodeling related bone disorders. Identifying plausible targets can help in the development of optimal treatments combining both physical activity and drug-medication. Such treatments help to improve/maintain/restore bone strength, which deteriorates under bone disorder conditions, such as estrogen deficiency.

  17. Preventing probe induced topography correlated artifacts in Kelvin Probe Force Microscopy.

    PubMed

    Polak, Leo; Wijngaarden, Rinke J

    2016-12-01

    Kelvin Probe Force Microscopy (KPFM) on samples with rough surface topography can be hindered by topography correlated artifacts. We show that, with the proper experimental configuration and using homogeneously metal coated probes, we are able to obtain amplitude modulation (AM) KPFM results on a gold coated sample with rough topography that are free from such artifacts. By inducing tip inhomogeneity through contact with the sample, clear potential variations appear in the KPFM image, which correlate with the surface topography and, thus, are probe induced artifacts. We find that switching to frequency modulation (FM) KPFM with such altered probes does not remove these artifacts. We also find that the induced tip inhomogeneity causes a lift height dependence of the KPFM measurement, which can therefore be used as a check for the presence of probe induced topography correlated artifacts. We attribute the observed effects to a work function difference between the tip and the rest of the probe and describe a model for such inhomogeneous probes that predicts lift height dependence and topography correlated artifacts for both AM and FM-KPFM methods. This work demonstrates that using a probe with a homogeneous work function and preventing tip changes is essential for KPFM on non-flat samples. From the three investigated probe coatings, PtIr, Au and TiN, the latter appears to be the most suitable, because of its better resistance against coating damage.

  18. Combined depletion and electrostatic forces in polymer-induced membrane adhesion: A theoretical model

    NASA Astrophysics Data System (ADS)

    Raudino, Antonio; Pannuzzo, Martina; Karttunen, Mikko

    2012-02-01

    We develop a semi-quantitative analytical theory to describe adhesion between two identical planar charged surfaces embedded in a polymer-containing electrolyte solution. Polymer chains are uncharged and differ from the solvent by their lower dielectric permittivity. The solution mimics physiological fluids: It contains 0.1 M of monovalent ions and a small number of divalent cations that form tight bonds with the headgroups of charged lipids. The components have heterogeneous spatial distributions. The model was derived self-consistently by combining: (a) a Poisson-Boltzmann like equation for the charge densities, (b) a continuum mean-field theory for the polymer profile, (c) a solvation energy forcing the ions toward the polymer-poor regions, and (d) surface interactions of polymers and electrolytes. We validated the theory via extensive coarse-grained Molecular Dynamics (MD) simulations. The results confirm our analytical model and reveal interesting details not detected by the theory. At high surface charges, polymer chains are mainly excluded from the gap region, while the concentration of ions increases. The model shows a strong coupling between osmotic forces, surface potential and salting-out effects of the slightly polar polymer chains. It highlights some of the key differences in the behaviour of monomeric and polymeric mixed solvents and their responses to Coulomb interactions. Our main findings are: (a) the onset of long-ranged ion-induced polymer depletion force that increases with surface charge density and (b) a polymer-modified repulsive Coulomb force that increases with surface charge density. Overall, the system exhibits homeostatic behaviour, resulting in robustness against variations in the amount of charges. Applications and extensions of the model are briefly discussed.

  19. Bingham Canyon Landslide: Force History Analysis and Identification of Induced Earthquakes

    NASA Astrophysics Data System (ADS)

    Pankow, K. L.; Ford, S. R.; Kubacki, T.; Koper, K. D.; Whidden, K. M.; Moore, J. R.; McCarter, M. K.

    2013-12-01

    On 10 April 2013 two massive rock avalanches, separated in time by 1.5 hours, occurred at the Bingham Canyon copper mine located in the Oquirrh Mountains near Salt Lake City, UT. Following the first slide, small (ML ≤ 2.5) tectonic earthquakes began occurring beneath the mine area, suggesting the earthquakes were triggered by the rock avalanches. Seismic data from the landslide events and tectonic quakes were well recorded by the Utah Regional Seismic Network. Signals from the rock avalanches are broadband and have a duration approaching two minutes each. Magnitude estimates for the two slides vary considerably based on methodology (slide 1: ML 2.5, MC 4.2, MSW 5.0; slide 2: ML 2.4, MC 3.5, MSW 4.9), which is indicative of a non-earthquake source. Initial estimates from Kennecott Utah Copper show that the combined rock avalanches moved a total mass of ~150 billion kg, equivalent to a source volume of ~55 million m3, and preliminary analysis based on signal duration and peak amplitudes of the seismograms suggest that the two slides were roughly equal in volume. However, when using a time-varying point source to invert for the landslide force history, we find that the second slide was approximately half the volume and half the mass of the first slide. Using the force history, we are also able to track the path of each rock avalanche, with good match to field observations. Waveform template analysis using two weeks of data preceding the rock avalanches show that the induced seismic events began following the first slide. This analysis will be extended further back in time to better determine if these events were induced by the rock avalanches. Earthquakes identified by the template analysis will also be located using newly calculated station delays determined from ground-truth events and relative relocation. If possible, we will also determine first-motion focal mechanisms for the larger induced quakes. The Bingham Canyon rock avalanches are two of the best

  20. Current-induced forces: a new mechanism to induce negative differential resistance and current-switching effect in molecular junctions.

    PubMed

    Gu, Lei; Fu, Hua-Hua

    2015-12-04

    Current-induced forces can excite molecules, polymers and other low-dimensional materials, which in turn leads to an effective gate voltage through Holstein interaction. Here, by taking a short asymmetric DNA junction as an example, and using the Langevin approach, we find that when suppression of charge transport by the effective gate voltage surpasses the current increase from an elevated voltage bias, the current-voltage (I-V) curves display strong negative differential resistance (NDR) and perfect current-switching characteristics. The asymmetric DNA chain differs in mechanical stability under inverse voltages and the I-V curve is asymmetric about inverse biases, which can be used to understand recent transport experiments on DNA chains, and meanwhile provides a new strategy to realize NDR in molecular junctions and other low-dimensional quantum systems.

  1. Creatine supplementation enhances muscle force recovery after eccentrically-induced muscle damage in healthy individuals

    PubMed Central

    Cooke, Matthew B; Rybalka, Emma; Williams, Andrew D; Cribb, Paul J; Hayes, Alan

    2009-01-01

    Background Eccentric exercise-induced damage leads to reductions in muscle force, increased soreness, and impaired muscle function. Creatine monohydrate's (Cr) ergogenic potential is well established; however few studies have directly examined the effects of Cr supplementation on recovery after damage. We examined the effects of Cr supplementation on muscle proteins and force recovery after eccentrically-induced muscle damage in healthy individuals. Methods Fourteen untrained male participants (22.1 ± 2.3 yrs, 173 ± 7.7 cm, 76.2 ± 9.3 kg) were randomly separated into 2 supplement groups: i) Cr and carbohydrate (Cr-CHO; n = 7); or ii) carbohydrate (CHO; n = 7). Participants consumed their supplement for a period of 5 days prior to, and 14 days following a resistance exercise session. Participants performed 4 sets of 10 eccentric-only repetitions at 120% of their maximum concentric 1-RM on the leg press, leg extension and leg flexion exercise machine. Plasma creatine kinase (CK) and lactate dehydrogenase (LDH) activity were assessed as relevant blood markers of muscle damage. Muscle strength was examined by voluntary isokinetic knee extension using a Cybex dynamometer. Data were analyzed using repeated measures ANOVA with an alpha of 0.05. Results The Cr-supplemented group had significantly greater isokinetic (10% higher) and isometric (21% higher) knee extension strength during recovery from exercise-induced muscle damage. Furthermore, plasma CK activity was significantly lower (by an average of 84%) after 48 hrs (P < 0.01), 72 hrs (P < 0.001), 96 hrs (P < 0.0001), and 7 days (P < 0.001) recovery in the Cr-supplemented group. Conclusion The major finding of this investigation was a significant improvement in the rate of recovery of knee extensor muscle function after Cr supplementation following injury. PMID:19490606

  2. The NEUF-DIX space project - Non-EquilibriUm Fluctuations during DIffusion in compleX liquids.

    PubMed

    Baaske, Philipp; Bataller, Henri; Braibanti, Marco; Carpineti, Marina; Cerbino, Roberto; Croccolo, Fabrizio; Donev, Aleksandar; Köhler, Werner; Ortiz de Zárate, José M; Vailati, Alberto

    2016-12-01

    Diffusion and thermal diffusion processes in a liquid mixture are accompanied by long-range non-equilibrium fluctuations, whose amplitude is orders of magnitude larger than that of equilibrium fluctuations. The mean-square amplitude of the non-equilibrium fluctuations presents a scale-free power law behavior q(-4) as a function of the wave vector q, but the divergence of the amplitude of the fluctuations at small wave vectors is prevented by the presence of gravity. In microgravity conditions the non-equilibrium fluctuations are fully developed and span all the available length scales up to the macroscopic size of the systems in the direction parallel to the applied gradient. Available theoretical models are based on linearized hydrodynamics and provide an adequate description of the statics and dynamics of the fluctuations in the presence of small temperature/concentration gradients and under stationary or quasi-stationary conditions. We describe a project aimed at the investigation of Non-EquilibriUm Fluctuations during DIffusion in compleX liquids (NEUF-DIX). The focus of the project is on the investigation in micro-gravity conditions of the non-equilibrium fluctuations in complex liquids, trying to tackle several challenging problems that emerged during the latest years, such as the theoretical predictions of Casimir-like forces induced by non-equilibrium fluctuations; the understanding of the non-equilibrium fluctuations in multi-component mixtures including a polymer, both in relation to the transport coefficients and to their behavior close to a glass transition; the understanding of the non-equilibrium fluctuations in concentrated colloidal suspensions, a problem closely related with the detection of Casimir forces; and the investigation of the development of fluctuations during transient diffusion. We envision to parallel these experiments with state-of-the-art multi-scale simulations.

  3. Reducing chloride conductance prevents hyperkalaemia-induced loss of twitch force in rat slow-twitch muscle.

    PubMed

    van Emst, Maarten Geert; Klarenbeek, Sjoerd; Schot, Arend; Plomp, Jaap Jan; Doornenbal, Arie; Everts, Maria Elisabeth

    2004-11-15

    Exercise-induced loss of skeletal muscle K(+) can seriously impede muscle performance through membrane depolarization. Thus far, it has been assumed that the negative equilibrium potential and large membrane conductance of Cl(-) attenuate the loss of force during hyperkalaemia. We questioned this idea because there is some evidence that Cl(-) itself can exert a depolarizing influence on membrane potential (V(m)). With this study we tried to identify the possible roles played by Cl(-) during hyperkalaemia. Isolated rat soleus muscles were kept at 25 degrees C and twitch contractions were evoked by current pulses. Reducing [Cl(-)](o) to 5 mM, prior to introducing 12.5 mM K(o), prevented the otherwise occurring loss of force. Reversing the order of introducing these two solutions revealed an additional effect, i.e. the ongoing hyperkalaemia-related loss of force was sped up tenfold after reducing [Cl(-)](o). However, hereafter twitch force recovered completely. The recovery of force was absent at [K(+)](o) exceeding 14 mM. In addition, reducing [Cl(-)](o) increased membrane excitability by 24%, as shown by a shift in the relationship between force and current level. Measurements of V(m) indicated that the antagonistic effect of reducing [Cl(-)](o) on hyperkalaemia-induced loss of force was due to low-Cl(-)-induced membrane hyperpolarization. The involvement of specific Cl(-) conductance was established with 9-anthracene carboxylic acid (9-AC). At 100 microm, 9-AC reduced the loss of force due to hyperkalaemia, while at 200 microm, 9-AC completely prevented loss of force. To study the role of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) in this matter, we added 400 microm of the NKCC inhibitor bumetanide to the incubation medium. This did not affect the hyperkalaemia-induced loss of force. We conclude that Cl(-) exerts a permanent depolarizing influence on V(m). This influence of Cl(-) on V(m), in combination with a large membrane conductance, can apparently have two

  4. Pumping of electrolytes by electrical forces induced on the diffusion layer: A weakly nonlinear analysis.

    PubMed

    García-Sánchez, Pablo; Loucaides, Neophytos G; Ramos, Antonio

    2017-02-01

    Pumping of electrolytes in microchannels can be achieved with the use of microelectrodes subjected to AC potentials. Experiments have shown an influence of Faradaic currents in the pumping performance, and theoretical studies for asymmetric electrolytes suggest that induced charges in the diffusion layer play an important role. In this work we consider the case of a diffusion layer induced by an array of electrodes subjected to a traveling wave potential and we include Faradaic currents. Previous theoretical studies considered the case of very small applied voltages, which allowed for two major simplifications: (i) Butler-Volmer (B-V) equation was linearized, and (ii) the presence of gradients in ion concentration was neglected. We extend previous results and used the full nonlinear B-V equation. A comparison with the linear limit shows that the flow rate in both cases coincides for voltages around and below ≈0.25 V. For voltages larger than this, the nonlinear equations show that gradients in ion concentration appear and have an important influence, therefore, the predictions deviate from the linear model. We show that the electrical force in the diffusion layer can induce pumping either in the same or the opposite direction of the applied traveling-wave potential and it could be responsible for the reversal of the flow as observed in experiments.

  5. Cell patterning via diffraction-induced optoelectronic dielectrophoresis force on an organic photoconductive chip.

    PubMed

    Yang, Shih-Mo; Tseng, Sheng-Yang; Chen, Hung-Po; Hsu, Long; Liu, Cheng-Hsien

    2013-10-07

    A laser diffraction-induced dielectrophoresis (DEP) phenomenon for the patterning and manipulation of individual HepG2 cells and polystyrene beads via positive/negative DEP forces is reported in this paper. The optoelectronic substrate was fabricated using an organic photoconductive material, TiOPc, via a spin-coating process on an indium tin oxide glass surface. A piece of square aperture array grid grating was utilized to transform the collimating He-Ne laser beam into the multi-spot diffraction pattern which forms the virtual electrodes as the TiOPc-coating surface was illuminated by the multi-spot diffraction light pattern. HepG2 cells were trapped at the spot centers and polystyrene beads were trapped within the dim region of the illuminated image. The simulation results of light-induced electric field and a Fresnel diffraction image illustrated the distribution of trapped microparticles. The HepG2 morphology change, adhesion, and growth during a 5-day culture period demonstrated the cell viability through our manipulation. The power density inducing DEP phenomena, the characteristics of the thin TiOPc coating layer, the operating ac voltage/frequency, the sandwiched medium, the temperature rise due to the ac electric fields and the illuminating patterns are discussed in this paper. This concept of utilizing laser diffraction images to generate virtual electrodes on our TiOPc-based optoelectronic DEP chip extends the applications of optoelectronic dielectrophoretic manipulation.

  6. Pumping of electrolytes by electrical forces induced on the diffusion layer: A weakly nonlinear analysis

    NASA Astrophysics Data System (ADS)

    García-Sánchez, Pablo; Loucaides, Neophytos G.; Ramos, Antonio

    2017-02-01

    Pumping of electrolytes in microchannels can be achieved with the use of microelectrodes subjected to AC potentials. Experiments have shown an influence of Faradaic currents in the pumping performance, and theoretical studies for asymmetric electrolytes suggest that induced charges in the diffusion layer play an important role. In this work we consider the case of a diffusion layer induced by an array of electrodes subjected to a traveling wave potential and we include Faradaic currents. Previous theoretical studies considered the case of very small applied voltages, which allowed for two major simplifications: (i) Butler-Volmer (B-V) equation was linearized, and (ii) the presence of gradients in ion concentration was neglected. We extend previous results and used the full nonlinear B-V equation. A comparison with the linear limit shows that the flow rate in both cases coincides for voltages around and below ≈0.25 V. For voltages larger than this, the nonlinear equations show that gradients in ion concentration appear and have an important influence, therefore, the predictions deviate from the linear model. We show that the electrical force in the diffusion layer can induce pumping either in the same or the opposite direction of the applied traveling-wave potential and it could be responsible for the reversal of the flow as observed in experiments.

  7. Intracerebroventricular administration of neuronostatin induces depression-like effect in forced swim test of mice.

    PubMed

    Yang, Ai-min; Ji, Yue-ke; Su, Shu-fang; Yang, Shao-bin; Lu, Song-song; Mi, Ze-yun; Yang, Qing-zhen; Chen, Qiang

    2011-09-01

    Neuronostatin is a recently discovered endogenous bioactive peptide that is encoded by pro-mRNA of somatostatin. In the present study, we investigated the effect of neuronostatin on mood regulation in the forced swim test of mice. Our results showed intracerebroventricular (i.c.v.) administration of neuronostatin produced an increase in the immobility time, suggesting that neuronostatin induced depression-like effect. In order to rule out the possibility that neuronostatin had increased immobility time by a non-specific reduction in general activity, the effect of neuronostatin on locomotor activity was examined. Neuronostatin had no influence on locomotor activity in mice. In addition, the depression-like effect of neuronostatin was completely reversed by melanocortin 3/4 receptor antagonist SHU9119 or GABAA receptor antagonist bicuculline, but not by opioid receptor antagonist naloxone. These data suggested that the depression-like effect induced by i.c.v. administered neuronostatin was dependent upon the central melanocortin system and GABAA receptor. In conclusion, the results of this study report that neuronostatin induces depression-like effect. These findings reveal that neuronostatin is a new neuropeptide with an important role in regulating depressive behavior.

  8. Field Induced Phase Transition with Quadrupole Fluctuation in HoFe2Al10 with Orthorhombic Symmetry

    NASA Astrophysics Data System (ADS)

    Kamikawa, Shuhei; Ishii, Isao; Takezawa, Kohki; Sakami, Tatsuhiro; Nakagawa, Fumiya; Tanida, Hiroshi; Sera, Masafumi; Suzuki, Takashi

    2017-04-01

    To explore phase transitions in HoFe2Al10 with an orthorhombic structure, we performed ultrasonic measurements on transverse elastic moduli C55 and C66 under magnetic fields H. At zero magnetic field, C55 and C66 show an elastic softening down to 0.5 K without a clear anomaly, suggesting that no phase transition exists at zero magnetic field. However, in H along the a- and c-axes, the softening of C55 under 0.6 (0.4) T stops at TQ = 0.8 (0.75) K for H || a (c). Below TQ, C55 shows an elastic hardening. With further increasing H, we observed a remarkable softening of C55 toward TQ. C66 also shows a kink anomaly at TQ in H || a and c. From the results, we clarified the field induced phase transition for H || a and c in HoFe2Al10. The minimum point of C55 at TQ suggests that the field induced phase transition results from a quadrupolar ordering with the order parameter of quadrupole Ozx despite a singlet ground state under an orthorhombic crystal electric field in HoFe2Al10.

  9. Energy dissipation and switching delay in stress-induced switching of multiferroic nanomagnets in the presence of thermal fluctuations

    NASA Astrophysics Data System (ADS)

    Roy, Kuntal; Bandyopadhyay, Supriyo; Atulasimha, Jayasimha

    2012-07-01

    Switching the magnetization of a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress is known to dissipate very little energy (<1 aJ for a switching time of ˜0.5 ns) at 0 K temperature. Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that switching can be carried out with ˜100% probability in less than 1 ns while dissipating less than 1.5 aJ at room temperature. This makes nanomagnetic logic and memory systems, predicated on stress-induced magnetic reversal, one of the most energy-efficient computing hardware extant. We also study the dependence of energy dissipation, switching delay, and the critical stress needed to switch, on the rate at which stress on the nanomagnet is ramped up or down.

  10. High g-Force Rollercoaster Rides Induce Sinus Tachycardia but No Cardiac Arrhythmias in Healthy Children.

    PubMed

    Pieles, Guido E; Husk, Victoria; Blackwell, Teresa; Wilson, Deirdre; Collin, Simon M; Williams, Craig A; Stuart, A Graham

    2017-01-01

    Theme park operators and medical professionals advise children with heart conditions against using rollercoaster rides, but these recommendations are not evidence-based. The underlying assumption is that the combination of adrenergic stimulation through stress and acceleration might trigger arrhythmias in susceptible individuals. We conducted a cross-sectional observational study to assess heart rate and rhythm in healthy children during commercial rollercoaster rides. Twenty healthy children (9 male) aged 11-15 (mean 13.3 ± 1.4) years underwent continuous heart rate and rhythm monitoring (2-lead ECG) from 5 min before until 10 min after each of 4 high speed (>50 km h(-1)), high g-force (>4) commercial rollercoaster rides. Total recording time was 13 h 20 min. No arrhythmic events were detected. Resting heart rate was 81 ± 10 b min(-1) and increased to 158 ± 20 b·min(-1) during rides. The highest mean HR (165 ± 23 b min(-1)) was observed on the ride with the lowest g-force (4.5 g), but one of the highest speeds (100 km h(-1)). Anticipatory tachycardia (126 ± 15 b min(-1)) within 5 min was frequently observed. A 10 min recovery HR (124 ± 17 b min(-1)) was 56 % greater than resting HR. The speed and g-force experienced on roller coasters induce sinus tachycardia but do not elicit pathological arrhythmias in healthy children.

  11. Artificial Force Induced Reaction (AFIR) Method for Exploring Quantum Chemical Potential Energy Surfaces.

    PubMed

    Maeda, Satoshi; Harabuchi, Yu; Takagi, Makito; Taketsugu, Tetsuya; Morokuma, Keiji

    2016-10-01

    In this account, a technical overview of the artificial force induced reaction (AFIR) method is presented. The AFIR method is one of the automated reaction-path search methods developed by the authors, and has been applied extensively to a variety of chemical reactions, such as organocatalysis, organometallic catalysis, and photoreactions. There are two modes in the AFIR method, i.e., a multicomponent mode and a single-component mode. The former has been applied to bimolecular and multicomponent reactions and the latter to unimolecular isomerization and dissociation reactions. Five numerical examples are presented for an Aldol reaction, a Claisen rearrangement, a Co-catalyzed hydroformylation, a fullerene structure search, and a nonradiative decay path search in an electronically excited naphthalene molecule. Finally, possible applications of the AFIR method are discussed.

  12. Modulation of rotation-induced lift force for cell filtration in a low aspect ratio microchannel

    PubMed Central

    Zhou, Jian; Giridhar, Premkumar Vummidi; Kasper, Susan; Papautsky, Ian

    2014-01-01

    Cell filtration is a critical step in sample preparation in many bioapplications. Herein, we report on a simple, filter-free, microfluidic platform based on hydrodynamic inertial migration. Our approach builds on the concept of two-stage inertial migration which permits precise prediction of microparticle position within the microchannel. Our design manipulates equilibrium positions of larger microparticles by modulating rotation-induced lift force in a low aspect ratio microchannel. Here, we demonstrate filtration of microparticles with extreme efficiency (>99%). Using multiple prostate cell lines (LNCaP and human prostate epithelial tumor cells), we show filtration from spiked blood, with 3-fold concentration and >83% viability. Results of a proliferation assay show normal cell division and suggest no negative effects on intrinsic properties. Considering the planar low-aspect-ratio structure and predictable focusing, we envision promising applications and easy integration with existing lab-on-a-chip systems. PMID:25379097

  13. Light-induced dynamics in the Lorentz oscillator model with magnetic forces

    SciTech Connect

    Fisher, W. M.; Rand, S. C.

    2010-07-15

    The classical Lorentz oscillator model of bound electron motion ordinarily excludes magnetic forces at nonrelativistic intensities for the simple reason that their magnitude is small. However, perturbative and numerical results show that when the v-vectorxB-vector term is retained, dynamically enhanced terms give rise to large amplitude, magnetically induced charge displacements at zero frequency and at twice the driving frequency in the Cartesian laboratory frame. Numerical simulations of electron motion are in accord with the predictions of perturbative theory for steady-state motion in the classical picture. Direct integration shows that magnetic response which is comparable to electric dipole response can arise in transparent dielectrics at optical frequencies. Parametric instability in the equations of motion is implicated as the source of rapid energy transfer from electric to magnetic motions by reduction of the equations to a complex Mathieu equation.

  14. Artificial Force Induced Reaction Method for Systematic Determination of Complex Reaction Mechanisms.

    PubMed

    Sameera, W M C; Kumar Sharma, Akhilesh; Maeda, Satoshi; Morokuma, Keiji

    2016-10-01

    Nowadays, computational studies are very important for the elucidation of reaction mechanisms and selectivity of complex reactions. However, traditional computational methods usually require an estimated reaction path, mainly driven by limited experimental implications, intuition, and assumptions of stationary points. However, the artificial force induced reaction (AFIR) method in the global reaction route mapping (GRRM) strategy can be used for unbiased and automatic reaction path searches for complex reactions. In this account, we highlight applications of the AFIR method to a variety of reactions (organic, organometallic, enzymatic, and photochemical) of complex molecular systems. In addition, the AFIR method has been successfully used to rationalise the origin of stereo- and regioselectivity. The AFIR method can be applied from small to large molecular systems, and will be a very useful tool for the study of complex molecular problems in many areas of chemistry, biology, and material sciences.

  15. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule.

    PubMed

    Zheng, Peng; Arantes, Guilherme M; Field, Martin J; Li, Hongbin

    2015-06-25

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions.

  16. Evidence that bacteriophage λ lysogens may induce in response to the proton motive force uncoupler CCCP

    PubMed Central

    Thomason, Lynn C.; Court, Donald L.

    2015-01-01

    We describe a genetic β-galactoside reporter system using a disk diffusion assay on MacConkey Lactose agar petri plates to monitor maintenance of the bacteriophage λ prophage state and viral induction in Escherichia coli K-12. Evidence is presented that the phage λ major lytic promoters, pL and pR, are activated when cells containing the reporters are exposed to the energy poison carbonyl cyanide m-chlorophenyl hydrazine, CCCP. This uncoupler of oxidative phosphorylation inhibits ATP synthesis by collapsing the proton motive force. Expression of the λ lytic promoters in response to CCCP requires host RecA function and an autocleavable CI repressor, as does SOS induction of the λ prophage that occurs by a DNA damage-dependent pathway. λ Cro function is required for CCCP-mediated activation of the λ lytic promoters. CCCP does not induce an sfi-lacZ SOS reporter. PMID:26705574

  17. 63Cu nuclear magnetic resonance study of Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4): Ni-induced spin density oscillation and modification of the low energy spin fluctuations.

    PubMed

    Williams, G V M; Jurkutat, M; Rybicki, D; Haase, J

    2011-02-23

    We report the results from a (63)Cu nuclear magnetic resonance (NMR) study of the electron-doped high temperature superconducting cuprate (HTSC) Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4). We find that Ni induces a magnetic broadening of the (63)Cu NMR spectra that can be interpreted in terms of an induced spin density oscillation about the Ni site, similar to that reported from (63)Cu NMR measurements on the hole-doped HTSCs when Zn is partially substituted for Cu. There is also an additional temperature-dependent contribution to the (63)Cu spin-lattice relaxation rate that can be interpreted in terms of an Ni-induced modification of the low energy spin fluctuations. Furthermore, the spin fluctuations are intrinsically spatially inhomogeneous and additional inhomogeneities are induced by Ni.

  18. Simultaneous Knee Extensor Muscle Action Induces an Increase in Voluntary Force Generation of Plantar Flexor Muscles.

    PubMed

    Suzuki, Takahito; Shioda, Kohei; Kinugasa, Ryuta; Fukashiro, Senshi

    2017-02-01

    Suzuki, T, Shioda, K, Kinugasa, R, and Fukashiro, S. Simultaneous knee extensor muscle action induces an increase in voluntary force generation of plantar flexor muscles. J Strength Cond Res 31(2): 365-371, 2017-Maximum activation of the plantar flexor muscles is required for various sporting activities that involve simultaneous plantar flexion and knee extension. During a multi-joint movement, activation of the plantar flexor muscles is affected by the activity of the knee extensor muscles. We hypothesized that coactivation of the plantar flexor muscles and knee extensor muscles would result in a higher plantar flexion torque. To test this hypothesis, 8 male volunteers performed maximum voluntary isometric action of the plantar flexor muscles with and without isometric action of the knee extensor muscles. Surface electromyographic data were collected from 8 muscles of the right lower limb. Voluntary activation of the triceps surae muscles, evaluated using the interpolated twitch technique, significantly increased by 6.4 percentage points with intentional knee extensor action (p = 0.0491). This finding is in line with a significant increase in the average rectified value of the electromyographic activity of the vastus lateralis, fibularis longus, and soleus muscles (p = 0.013, 0.010, and 0.045, respectively). The resultant plantar flexion torque also significantly increased by 11.5% of the predetermined maximum (p = 0.031). These results suggest that higher plantar flexor activation coupled with knee extensor activation facilitates force generation during a multi-joint task.

  19. Effect of Polysaccharide from Cordyceps militaris (Ascomycetes) on Physical Fatigue Induced by Forced Swimming.

    PubMed

    Xu, Yan-Feng

    2016-01-01

    Cordyceps militaris is the one of the most important medicinal mushrooms, widely used in East Asian countries. Polysaccharide is considered to be the principal active component in C. militaris and has a wide range of biological and pharmacological properties. This study was undertaken to investigate the effect of polysaccharide from C. militaris (PCM) on physical fatigue induced in animals through a forced swimming test. The mice were divided into 4 groups receiving 28 days' treatment with drinking water (exercise control) or low-, medium-, and high-dose PCM (40, 80, and 160 mg/kg/day, respectively). After 28 days, the mice were subjected to the forced swimming test; the exhaustive swimming time was measured and fatigue-related biochemical parameters, including serum lactic acid, urea nitrogen, creatine kinase, alanine aminotransferase, aspartate aminotransferase, superoxide dismutase, glutathi- one peroxidase, catalase, malondialdehyde, liver glycogen, and muscle glycogen, were analyzed. The results showed that PCM could significantly prolong the exhaustive swimming time of mice; decrease concentrations of serum lactic acid, urea nitrogen, creatine kinase, aspartate aminotransferase, alanine aminotransferase, and malondialdehyde; and increase liver and muscle glycogen contents and the concentrations of serum superoxide dismutase, glutathione per- oxidase, and catalase. The data suggest that PCM has an antifatigue effect, and it might become a new functional food or medicine for fatigue resistance.

  20. The effect of solar forcing induced atmospheric perturbations on LEO satellites' nominal aerodynamic drag

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar; Weigel, Robert

    2016-07-01

    Atmospheric drag is the strongest force perturbing the motion of satellites in low Earth orbits LEO, and could cause re-entry of satellites, difficulty in identifying and tracking of the satellites and other space objects, manuvering and prediction of lifetime and re-entry. Solar activities influence the temperature, density and composition of the upper atmosphere. These effects thus strongly depend on the phase of a solar cycle. The frequency of intense flares and storms increase during solar maximum. Heating up of the atmosphere causes its expansion eventually leading to accelerated drag of orbiting satellites, especially those in LEO. In this paper, we present the model of the atmospheric drag effect on the trajectory of hypothetical LEO satellites of different ballistic coefficients. We investigate long-term trend of atmospheric drag on LEO satellites due to solar forcing induced atmospheric perturbations and heating at different phases of the solar cycle, and during interval of strong geomagnetic disturbances or storms. We show the dependence of orbital decay on severity of both the solar cycle and phase, and the extent of geomagnetic perturbations. The result of the model compares well with the observed decay profile of existing LEO satellites and provides a better understanding of the issue of the orbital decay. Our result may also be useful for selection of launch window of satellites for an extended lifetime in the orbit.

  1. Acoustic Radiation Force for Noninvasive Evaluation of Corneal Biomechanical Changes Induced by Cross-linking Therapy

    PubMed Central

    Urs, Raksha; Lloyd, Harriet O.; Silverman, Ronald H.

    2015-01-01

    Objectives To noninvasively measure changes in corneal biomechanical properties induced by ultraviolet-activated riboflavin cross-linking therapy using acoustic radiation force (ARF). Methods Cross-linking was performed on the right eyes of 6 rabbits, with the left eyes serving as controls. Acoustic radiation force was used to assess corneal stiffness before treatment and weekly for 4 weeks after treatment. Acoustic power levels were within US Food and Drug Administration guidelines for ophthalmic safety. Strain, determined from ARF-induced displacement of the front and back surfaces of the cornea, was fit to the Kelvin-Voigt model to determine the elastic modulus (E) and coefficient of viscosity (η). The stiffness factor, the ratio of E after treatment to E before treatment, was calculated for treated and control eyes. At the end of 4 weeks, ex vivo thermal shrinkage temperature analysis was performed for comparison with in vivo stiffness measurements. One-way analysis of variance and Student t tests were performed to test for differences in E, η, the stiffness factor, and corneal thickness. Results Biomechanical stiffening was immediately evident in cross-linking–treated corneas. At 4 weeks after treatment, treated corneas were 1.3 times stiffer and showed significant changes in E(P= .006) and η (P= .007), with no significant effect in controls. Corneal thickness increased immediately after treatment but did not differ significantly from the pretreatment value at 4 weeks. Conclusions Our findings demonstrate a statistically significant increase in stiffness in cross-linking–treated rabbit corneas based on in vivo axial stress/strain measurements obtained using ARF. The capacity to noninvasively monitor corneal stiffness offers the potential for clinical monitoring of cross-linking therapy. PMID:25063407

  2. Kinetic Defects Induced by Melittin in Model Lipid Membranes: A Solution Atomic Force Microscopy Study.

    PubMed

    Pan, Jianjun; Khadka, Nawal K

    2016-05-26

    Quantitative characterization of membrane defects (pores) is important for elucidating the molecular basis of many membrane-active peptides. We study kinetic defects induced by melittin in vesicular and planar lipid bilayers. Fluorescence spectroscopy measurements indicate that melittin induces time-dependent calcein leakage. Solution atomic force microscopy (AFM) is used to visualize melittin-induced membrane defects. After initial equilibration, the most probable defect radius is ∼3.8 nm in 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) bilayers. Unexpectedly, defects become larger with longer incubation, accompanied by substantial shape transformation. The initial defect radius is ∼4.7 nm in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayers. Addition of 30 mol % cholesterol to DOPC bilayers suppresses defect kinetics, although the inhibitory impact is negated by longer incubation. Overall, the kinetic rate of defect development follows DLPC > DOPC > DOPC/cholesterol. Kinetic defects are also observed when anionic lipids are present. Based on the observation that defects can occupy as large as 40% of the bilayer surface, we propose a kinetic defect growth model. We also study the effect of melittin on the phase behavior of DOPC/egg-sphingomyelin/cholesterol bilayers. We find that melittin initially suppresses or eliminates liquid-ordered (Lo) domains; Lo domains gradually emerge and become the dominant species with longer incubation; and defects in phase-coexisting bilayers have a most probable radius of ∼5 nm and are exclusively localized in the liquid-disordered (Ld) phase. Our experimental data highlight that melittin-induced membrane defects are not static; conversely, spontaneous defect growth is intrinsically associated with membrane permeabilization exerted by melittin.

  3. Impacts of cloud-induced mass forcing on the development of moist potential vorticity anomaly during torrential rains

    NASA Astrophysics Data System (ADS)

    Gao, Shouting; Zhou, Yushu; Cui, Xiaopeng; Dai, Guoping

    2004-12-01

    The impacts of cloud-induced mass forcing on the development of the moist potential vorticity (MPV) anomaly associated with torrential rains are investigated by using NCEP/NCAR 1° × 1° data. The MPV tendency equation with the cloud-induced mass forcing is derived, and applied to the torrential rain event over the Changjiang River-Huaihe River Valleys during 26 30 June 1999. The result shows that positive anomalies are located mainly between 850 hPa and 500 hPa, while the maximum MPV, maximum positive tendency of the MPV, and maximum surface rainfall are nearly collocated. The cloud-induced mass forcing contributes to the positive tendency of the moist potential vorticity anomaly. The results indicate that the MPV may be used to track the propagation of rain systems for operational applications.

  4. Coherent vortex model for surface pressure fluctuations induced by the wall region of a turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Dhanak, Manhar R.; Dowling, Ann P.; Si, Chao

    1997-09-01

    Exact solutions of the Navier-Stokes equations describing the interaction of streamwise vortices with a rigid surface are utilized to develop a conceptual model for the surface pressure spectrum associated with the wall region of a turbulent boundary layer. The evolution of single as well as pairs of coherent streamwise vortices, which principally govern the production of turbulence in the wall region, is considered in the presence of local straining flow induced by larger, outer-layer eddies. The surface pressure signatures of the coherent vortex motion and the associated power spectrum of the pressure are examined. Based on the results of the exact solutions, the surface pressure spectrum of an ensemble of independent coherent structures is modeled using the assumption of ergodicity in the manner described by Townsend and Lundgren for homogeneous turbulence. The free parameters in the model are estimated through comparison with available results from experiments and numerical simulations. The model, especially the one involving pairs of streamwise vortices, predicts the high frequency and high spanwise wave number range of the surface pressure spectrum quite well. Further, the probability density function of surface pressure associated with the model compares well with experimental results. Interestingly, the model also suggests that the contribution of the viscous interaction to low wave number spectral elements accounts for the discrepancy between experimental observations at such wave numbers and the prediction of the Kraichnan-Phillips theorem.

  5. Force-Induced Unfolding of Leucine-Rich Repeats of Glycoprotein Ibα Strengthens Ligand Interaction.

    PubMed

    Ju, Lining; Lou, Jizhong; Chen, Yunfeng; Li, Zhenhai; Zhu, Cheng

    2015-11-03

    Leucine-rich repeat (LRR) is a versatile motif widely present in adhesive proteins and signal-transducing receptors. The concave structure formed by a group of LRRs is thought to facilitate binding to globular protein domains with increased affinities. However, little is known about the conformational dynamics of LRRs in such a structure, e.g., whether and how force induces conformational changes in LRRs to regulate protein binding and signal transduction. Here we investigated the platelet glycoprotein Ibα (GPIbα), a demonstrated mechanoreceptor with known crystal structures for the N-terminal domain (GPIbαN), as a model for LRR-containing proteins using a combined method of steered molecular dynamics simulations and single-molecule force spectroscopy with a biomembrane force probe. We found that force-induced unfolding of GPIbαN starts with LRR2-4 and propagates to other LRRs. Importantly, force-dependent lifetimes of individual VWF-A1 bonds with GPIbα are prolonged after LRR unfolding. Enhancement of protein-protein interactions by force-induced LRR unfolding may be a phenomenon of interest in biology.

  6. Interactions of protons with single open L-type calcium channels. Location of protonation site and dependence of proton-induced current fluctuations on concentration and species of permeant ion

    PubMed Central

    1989-01-01

    We further investigated the rapid fluctuations between two different conductance levels promoted by protons when monovalent ions carry current through single L-type Ca channels. We tested for voltage dependence of the proton-induced current fluctuations and for accessibility of the protonation site from both sides of the membrane patch. The results strongly suggest an extracellular location of the protonation site. We also studied the dependence of the kinetics of the fluctuations and of the two conductance levels on the concentration of permeant ion and on external ionic strength. We find that saturation curves of channel conductance vs. [K] are similar for the two conductance levels. This provides evidence that protonation does not appreciably change the surface potential near the entry of the permeation pathway. The proton-induced conduction change must therefore result from an indirect interaction between the protonation site and the ion-conducting pathway. Concentration of permeant ion and ionic strength also affect the kinetics of the current fluctuations, in a manner consistent with our previous hypothesis that channel occupancy destabilizes the low conductance channel conformation. We show that the absence of measurable fluctuations with Li and Ba as charge carriers can be explained by significantly higher affinities of these ions for permeation sites. Low concentrations of Li reduce the Na conductance and abbreviate the lifetimes of the low conductance level seen in the presence of Na. We use whole-cell recordings to extrapolate our findings to the physiological conditions of Ca channel permeation and conclude that in the presence of 1.8 mM Ca no proton-induced fluctuations occur between pH 7.5 and 6.5. Finally, we propose a possible physical interpretation of the formal model of the protonation cycle introduced in the companion paper. PMID:2553858

  7. Dietary flavonoid fisetin induces a forced exit from mitosis by targeting the mitotic spindle checkpoint

    PubMed Central

    Salmela, Anna-Leena; Pouwels, Jeroen; Varis, Asta; Kukkonen, Anu M.; Toivonen, Pauliina; Halonen, Pasi K.; Perälä, Merja; Kallioniemi, Olli; Gorbsky, Gary J.; Kallio, Marko J.

    2009-01-01

    Fisetin is a natural flavonol present in edible vegetables, fruits and wine at 2–160 μg/g concentrations and an ingredient in nutritional supplements with much higher concentrations. The compound has been reported to exert anticarcinogenic effects as well as antioxidant and anti-inflammatory activity via its ability to act as an inhibitor of cell proliferation and free radical scavenger, respectively. Our cell-based high-throughput screen for small molecules that override chemically induced mitotic arrest identified fisetin as an antimitotic compound. Fisetin rapidly compromised microtubule drug-induced mitotic block in a proteasome-dependent manner in several human cell lines. Moreover, in unperturbed human cancer cells fisetin caused premature initiation of chromosome segregation and exit from mitosis without normal cytokinesis. To understand the molecular mechanism behind these mitotic errors, we analyzed the consequences of fisetin treatment on the localization and phoshorylation of several mitotic proteins. Aurora B, Bub1, BubR1 and Cenp-F rapidly lost their kinetochore/centromere localization and others became dephosphorylated upon addition of fisetin to the culture medium. Finally, we identified Aurora B kinase as a novel direct target of fisetin. The activity of Aurora B was significantly reduced by fisetin in vitro and in cells, an effect that can explain the observed forced mitotic exit, failure of cytokinesis and decreased cell viability. In conclusion, our data propose that fisetin perturbs spindle checkpoint signaling, which may contribute to the antiproliferative effects of the compound. PMID:19395653

  8. Force-induced melting of DNA--evidence for peeling and internal melting from force spectra on short synthetic duplex sequences.

    PubMed

    Bosaeus, Niklas; El-Sagheer, Afaf H; Brown, Tom; Åkerman, Björn; Nordén, Bengt

    2014-07-01

    Overstretching of DNA occurs at about 60-70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive.

  9. Atmospheric Teleconnection over Eurasia Induced by Aerosol Radiative Forcing During Boreal Spring

    NASA Technical Reports Server (NTRS)

    Kim, Maeng-Ki; Lau, K. M.; Chin, Mian; Kim, Kyu-Myong; Sud, Y. C.; Walker, Greg K.

    2005-01-01

    The direct effects of aerosols on global and regional climate during boreal spring are investigated based on simulations using the NASA Global Modeling and Assimilation Office (GMAO) finite-volume general circulation model (fvGCM) with Microphyics of clouds in Relaxed Arakawa Schubert Scheme (McRAS). The aerosol loading are prescribed from three-dimensional monthly distribution of tropospheric aerosols viz., sulfate, black carbon, organic carbon, soil dust, and sea salt from output of the Goddard Ozone Chemistry Aerosol Radiation and Transport model (GOCART). The aerosol extinction coefficient, single scattering albedo, and asymmetric factor are computed as wavelength-dependent radiative forcing in the radiative transfer scheme of the fvGCM, and as a function of the aerosol loading and ambient relative humidity. We find that anomalous atmospheric heat sources induced by absorbing aerosols (dust and black carbon) excites a planetary scale teleconnection pattern in sea level pressure, temperature and geopotential height spanning North Africa through Eurasia to the North Pacific. Surface cooling due to direct effects of aerosols is found in the vicinity and downstream of the aerosol source regions, i.e., South Asia, East Asia, and northern and western Africa. Additionally, atmospheric heating is found in regions with large loading of dust (over Northern Africa, and Middle East), and black carbon (over South-East Asia). Paradoxically, the most pronounced feature in aerosol-induced surface temperature is an east-west dipole anomaly with strong cooling over the Caspian Sea, and warming over central and northeastern Asia, where aerosol concentration are low. Analyses of circulation anomalies show that the dipole anomaly is a part of an atmospheric teleconnection driven by atmospheric heating anomalies induced by absorbing aerosols in the source regions, but the influence was conveyed globally through barotropic energy dispersion and sustained by feedback processes

  10. A stochastic model and Monte Carlo algorithm for fluctuation-induced H2 formation on the surface of interstellar dust grains

    NASA Astrophysics Data System (ADS)

    Sabelfeld, K. K.

    2015-09-01

    A stochastic algorithm for simulation of fluctuation-induced kinetics of H2 formation on grain surfaces is suggested as a generalization of the technique developed in our recent studies [1] where this method was developed to describe the annihilation of spatially separate electrons and holes in a disordered semiconductor. The stochastic model is based on the spatially inhomogeneous, nonlinear integro-differential Smoluchowski equations with random source term. In this paper we derive the general system of Smoluchowski type equations for the formation of H2 from two hydrogen atoms on the surface of interstellar dust grains with physisorption and chemisorption sites. We focus in this study on the spatial distribution, and numerically investigate the segregation in the case of a source with a continuous generation in time and randomly distributed in space. The stochastic particle method presented is based on a probabilistic interpretation of the underlying process as a stochastic Markov process of interacting particle system in discrete but randomly progressed time instances. The segregation is analyzed through the correlation analysis of the vector random field of concentrations which appears to be isotropic in space and stationary in time.

  11. Nanoscale patterning of chemical order induced by displacement cascades in irradiated L10 alloys: Scaling analysis of the fluctuations of order

    NASA Astrophysics Data System (ADS)

    Ye, Jia; Bellon, Pascal

    2006-06-01

    Atomistic kinetic Monte Carlo simulations are employed to analyze the dynamical stabilization of nanoscale patterning of L10 chemical order in a model binary alloy subjected to sustained irradiation. The effect of irradiation-induced displacement cascades on the chemical order is modeled by the introduction at a controlled rate of nearly fully disordered spherical zones, which compete with the reordering promoted by the thermally activated migration of vacancies. When the size of the disordered zones is small, the alloy reaches a steady state that is either long-range ordered at low irradiation-induced ballistic jump frequency, Γb , or disordered at high Γb , with a first-order dynamical transition between these two steady states at Γb=Γbc . Furthermore, in the disordered steady state, the intensity of order fluctuations scales with the reduced variable Γb/Γbc , a scaling that is consistent with an effective temperature approach. For larger cascade sizes, however, an additional steady state is stabilized at intermediate ballistic jump frequency, with a microstructure comprised of well-ordered nanoscale domains. In this patterning-of-order steady state, the above rescaling breaks down but we show that, after deconvolution of the structure factor into Gaussian and Lorentzian components, scaling of the Gaussian component is recovered by introducing a new reduced variable, Γb/Γbp , where 1/Γbp is interpreted as the characteristic time for new domains to form in a disordered zone. This new scaling relationship provides a rigorous definition of the regime of patterning of order. This regime corresponds to the steady states stabilized by cascade sizes and ballistic jump frequencies satisfying Γbc≤Γb≤Γbp . A dynamical phase diagram based on this new criterion is constructed and it agrees well with direct visualization of atomic configurations. Extensions to nonstoichiometric compositions are investigated. Consequences for the direct synthesis of functional

  12. The impact of flow-induced forces on the morphogenesis of the outflow tract

    PubMed Central

    Biechler, Stefanie V.; Junor, Lorain; Evans, Ashlie N.; Eberth, John F.; Price, Robert L.; Potts, Jay D.; Yost, Michael J.; Goodwin, Richard L.

    2014-01-01

    One percent of infants are born with congenital heart disease (CHD), which commonly involves outflow tract (OFT) defects. These infants often require complex surgeries, which are associated with long term adverse remodeling effects, and receive replacement valves with limited strength, biocompatibility, and growth capability. To address these problematic issues, researchers have carried out investigations in valve development and valve mechanics. A longstanding hypothesis is that flow-induced forces regulate fibrous valve development, however, the specific mechanisms behind this mechanotransduction remain unclear. The purpose of this study was to implement an in vitro system of outflow tract development to test the response of embryonic OFT tissues to fluid flow. A dynamic, three-dimensional bioreactor system was used to culture embryonic OFT tissue under different levels of flow as well as the absence of flow. In the absence of flow, OFT tissues took on a more primitive phenotype that is characteristic of early OFT cushion development where widely dispersed mesenchymal cells are surrounded by a sparse, disorganized extracellular matrix (ECM). Whereas OFT tissues subjected to physiologically matched flow formed compact mounds of cells, initated, fibrous ECM development, while prolonged supraphysiological flow resulted in abnormal tissue remodeling. This study indicates that both the timing and magnitude of flow alter cellular processes that determine if OFT precursor tissue undergoes normal or pathological development. Specifically, these experiments showed that flow-generated forces regulate the deposition and localization of fibrous ECM proteins, indicating that mechanosensitive signaling pathways are capable of driving pathological OFT development if flows are not ideal. PMID:24987377

  13. Cloud radiative forcing induced by layered clouds and associated impact on the atmospheric heating rate

    NASA Astrophysics Data System (ADS)

    Lü, Qiaoyi; Li, Jiming; Wang, Tianhe; Huang, Jianping

    2015-10-01

    A quantitative analysis of cloud fraction, cloud radiative forcing, and cloud radiative heating rate (CRH) of the single-layered cloud (SLC) and the multi-layered cloud (MLC), and their differences is presented, based on the 2B-CLDCLASS-LIDAR and 2B-FLXHR-LIDAR products on the global scale. The CRH at a given atmospheric level is defined as the cloudy minus clear-sky radiative heating rate. The statistical results show that the globally averaged cloud fraction of the MLC (24.9%), which is primarily prevalent in equatorial regions, is smaller than that of the SLC (46.6%). The globally averaged net radiative forcings (NET CRFs) induced by the SLC (MLC) at the top and bottom of the atmosphere (TOA and BOA) and in the atmosphere (ATM) are-60.8 (-40.9),-67.5 (-49.6), and 6.6 (8.7) W m-2, respectively, where the MLC contributes approximately 40.2%, 42.4%, and 57% to the NET CRF at the TOA, BOA, and in the ATM, respectively. The MLC exhibits distinct differences to the SLC in terms of CRH. The shortwave CRH of the SLC (MLC) reaches a heating peak at 9.75 (7.5) km, with a value of 0.35 (0.60) K day-1, and the differences between SLC and MLC transform from positive to negative with increasing altitude. However, the longwave CRH of the SLC (MLC) reaches a cooling peak at 2 (8) km, with a value of-0.45 (-0.42) K day-1, and the differences transform from negative to positive with increasing altitude. In general, the NET CRH differences between SLC and MLC are negative below 7.5 km. These results provide an observational basis for the assessment and improvement of the cloud parameterization schemes in global models.

  14. Effect of Elastase-induced Emphysema on the Force-generating Ability of the Diaphragm

    PubMed Central

    Supinski, Gerald S.; Kelsen, Steven G.

    1982-01-01

    The effect of emphysema on the ability of the diaphragm to generate force was examined in costal diaphragm muscle strips from 10 Golden hamsters killed 18 mo after intratracheal injection of pancreatic elastase in a dose producing hyperinflation (mean total lung capacity [TLC] = 163% of control) and generalized panacinar emphysema. 13 saline-injected normal animals served as controls. The time course of isometric tension and the effect of alterations in muscle fiber and sarcomere length on the isometric tension (T) generated in response to tetanizing electrical stimuli (length-tension [L-T] relationship) were examined. Elastase administration caused an increase in diaphragm muscle thickness and reduction in the length of costal diaphragm muscle fibers measured in situ. Emphysema significantly increased the maximum tetanic tension as a result of hypertrophy. Maximal tension corrected for increases in muscle cross-sectional area (T/cm2), however, was the same in emphysematous (E) and control (C) animals. Emphysema also shifted the muscle fiber L-T curve of the diaphragm but not of a control muscle, the soleus, toward shorter lengths. In contrast to the effects of E on the diaphragm muscle fiber L-T curve, the sarcomere L-T curve was the same in E and C. Since the length at which tension was maximal correlated closely with sarcomere number (r = 0.94; P < 0.001) reduction in the number of sarcomeres in series in muscles from emphysematous animals appeared to explain the shift in the muscle fiber L-T curve. We conclude that in elastase-induced emphysema adaptive changes both in diaphragm cross-sectional area and sarcomere number augment the force-generating ability of the diaphragm. We speculate that changes in sarcomere number compensate for alterations in muscle fiber length resulting from chronic hyperinflation of the thorax, while diaphragmatic muscle hypertrophy represents a response to changes in respiratory load and/or diaphragm configuration (La

  15. Effects of temporal fluctuations on mixing

    NASA Astrophysics Data System (ADS)

    Pool, Maria; Dentz, Marco; Post, Vincent E. A.; Simmons, Craig T.

    2016-04-01

    Mixing and dispersion in coastal aquifers are strongly influenced by periodic temporal flow fluctuations on multiple time-scales ranging from days (tides), seasons (pumping and recharge) to glacial cycles (regression and transgressions). Transient forcing effects lead to a complex space- ant time-dependent flow response which induces enhanced spreading and mixing of a dissolved substance. We study effective mixing and solute transport in temporally fluctuating one-dimensional flow for a stable stratification of two fluids of different density. We derive explicit expressions for the concentration distribution and variance to identify the controls and obtain realistic predictions of the coupling between mixing and oscillatory transient flow. We find that the magnitude of transient-driven mixing is mainly controlled by the hydraulic diffusivity, the period and the initial interface location. We also find a spatial dependence of the effective dispersion coefficient which at long times causes the concentration profile to become asymmetric. Sand column experiments under well-controlled laboratory conditions are presented to validate the theoretical effective model defined. The proposed formulation is found to provide very good predictions and correctly reproduces the experimental mixing dynamics.

  16. Concerning gauge field fluctuations around classical configurations

    SciTech Connect

    Dietrich, Dennis D.

    2009-05-15

    We treat the fluctuations of non-Abelian gauge fields around a classical configuration by means of a transformation from the Yang-Mills gauge field to a homogeneously transforming field variable. We use the formalism to compute the effective action induced by these fluctuations in a static background without Wu-Yang ambiguity.

  17. Mapping near-field environments of plasmonic and 2D materials with photo-induced force imaging (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Tumkur, Thejaswi U.; Doiron, Chloe; Yang, Xiao; Li, Bo; Swearer, Dayne F.; Cerjan, Benjamin W.; Nordlander, Peter; Halas, Naomi J.; Ajayan, Pulickel M.; Ringe, Emilie; Thomann, Isabell

    2016-09-01

    We demonstrate the ability to map photo-induced gradient forces in materials, using a setup akin to atomic force microscopy. This technique allows for the simultaneous characterization of topographical features and optical near-fields in materials, with a high spatio-temporal resolution. We show that the near-field gradient forces can be translated onto electric fields, enabling the mapping of plasmonic hot-spots in gold nanostructures, and the resolution of sub-10 nm features in photocatalytic materials. We further show that the dispersion-sensitive nature of near-field gradient forces can be used to image and distinguish atomically thin layers of 2-D materials, with high contrast.

  18. Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David

    2005-01-01

    We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

  19. INTERMOLECULAR FORCES IN ASSOCIATION OF PURINES WITH POLYBENZENOID HYDROCARBONS.

    PubMed

    PULLMAN, B; CLAVERIE, P; CAILLET, J

    1965-03-12

    The interactions in solution between purine or pyrimidine bases and polybenzenoid aromatic hydrocarbons probably consist in a vertical, stacking-type physical association. By molecular orbital calculations the role of the Van der Waals-London intermolecular forces in these interactions is determined. The electrostatic dipole-dipole forces are negligible, the polarization (or induction) dipole-induced dipole forces are contributory, but most important are the dispersion (or fluctuation) forces. This loose, physical type of interaction should not show any specificity with respect to the carcinogenic activity of the hydrocarbons.

  20. Evaluating the forced oscillation technique in the detection of early smoking-induced respiratory changes

    PubMed Central

    Faria, Alvaro CD; Lopes, Agnaldo J; Jansen, José M; Melo, Pedro L

    2009-01-01

    Background Early detection of the effects of smoking is of the utmost importance in the prevention of chronic obstructive pulmonary disease (COPD). The forced oscillation technique (FOT) is easy to perform since it requires only tidal breathing and offers a detailed approach to investigate the mechanical properties of the respiratory system. The FOT was recently suggested as an attractive alternative for diagnosing initial obstruction in COPD, which may be helpful in detecting COPD in its initial phases. Thus, the purpose of this study was twofold: (1) to evaluate the ability of FOT to detect early smoking-induced respiratory alterations; and (2) to compare the sensitivity of FOT with spirometry in a sample of low tobacco-dose subjects. Methods Results from a group of 28 smokers with a tobacco consumption of 11.2 ± 7.3 pack-years were compared with a control group formed by 28 healthy subjects using receiver operating characteristic (ROC) curves and a questionnaire as a gold standard. The early adverse effects of smoking were adequately detected by the absolute value of the respiratory impedance (Z4Hz), the intercept resistance (R0), and the respiratory system dynamic compliance (Crs, dyn). Z4Hz was the most accurate parameter (Se = 75%, Sp = 75%), followed by R0 and Crs, dyn. The performances of the FOT parameters in the detection of the early effects of smoking were higher than that of spirometry (p < 0.05). Conclusion This study shows that FOT can be used to detect early smoking-induced respiratory changes while these pathologic changes are still potentially reversible. These findings support the use of FOT as a versatile clinical diagnostic tool in aiding COPD prevention and treatment. PMID:19781078

  1. The effect of temperature dependent tissue parameters on acoustic radiation force induced displacements.

    PubMed

    Suomi, Visa; Han, Yang; Konofagou, Elisa; Cleveland, Robin O

    2016-10-21

    Multiple ultrasound elastography techniques rely on acoustic radiation force (ARF) in monitoring high-intensity focused ultrasound (HIFU) therapy. However, ARF is dependent on tissue attenuation and sound speed, both of which are also known to change with temperature making the therapy monitoring more challenging. Furthermore, the viscoelastic properties of tissue are also temperature dependent, which affects the displacements induced by ARF. The aim of this study is to quantify the temperature dependent changes in the acoustic and viscoelastic properties of liver and investigate their effect on ARF induced displacements by using both experimental methods and simulations. Furthermore, the temperature dependent viscoelastic properties of liver are experimentally measured over a frequency range of 0.1-200 Hz at temperatures reaching 80 °C, and both conventional and fractional Zener models are used to fit the data. The fractional Zener model was found to fit better with the experimental viscoelasticity data with respect to the conventional model with up to two orders of magnitude lower sum of squared errors (SSE). The characteristics of experimental displacement data were also seen in the simulations due to the changes in attenuation coefficient and lesion development. At low temperatures before thermal ablation, attenuation was found to affect the displacement amplitude. At higher temperature, the decrease in displacement amplitude occurs approximately at 60-70 °C due to the combined effect of viscoelasticity changes and lesion growth overpowering the effect of attenuation. The results suggest that it is necessary to monitor displacement continuously during HIFU therapy in order to ascertain when ablation occurs.

  2. The effect of temperature dependent tissue parameters on acoustic radiation force induced displacements

    NASA Astrophysics Data System (ADS)

    Suomi, Visa; Han, Yang; Konofagou, Elisa; Cleveland, Robin O.

    2016-10-01

    Multiple ultrasound elastography techniques rely on acoustic radiation force (ARF) in monitoring high-intensity focused ultrasound (HIFU) therapy. However, ARF is dependent on tissue attenuation and sound speed, both of which are also known to change with temperature making the therapy monitoring more challenging. Furthermore, the viscoelastic properties of tissue are also temperature dependent, which affects the displacements induced by ARF. The aim of this study is to quantify the temperature dependent changes in the acoustic and viscoelastic properties of liver and investigate their effect on ARF induced displacements by using both experimental methods and simulations. Furthermore, the temperature dependent viscoelastic properties of liver are experimentally measured over a frequency range of 0.1-200 Hz at temperatures reaching 80 °C, and both conventional and fractional Zener models are used to fit the data. The fractional Zener model was found to fit better with the experimental viscoelasticity data with respect to the conventional model with up to two orders of magnitude lower sum of squared errors (SSE). The characteristics of experimental displacement data were also seen in the simulations due to the changes in attenuation coefficient and lesion development. At low temperatures before thermal ablation, attenuation was found to affect the displacement amplitude. At higher temperature, the decrease in displacement amplitude occurs approximately at 60-70 °C due to the combined effect of viscoelasticity changes and lesion growth overpowering the effect of attenuation. The results suggest that it is necessary to monitor displacement continuously during HIFU therapy in order to ascertain when ablation occurs.

  3. Fluctuation Induced Almost Invariant Sets

    DTIC Science & Technology

    2006-12-28

    the methods are used to illustrate the technique. 28-12-2006 Interim Report Office of Naval Research One Liberty Center 875 North Randolph Street...Markov processes. Two examples of the methods are used to illustrate the technique. I. INTRODUCTION Transport in dynamical systems is an important topic...chaotic saddle present. As an alternative to the above analysis methods , set theoretic methods have been used to quantify the stochastic attractors

  4. Atomic Force Microscopy of Vertically Stacked Focused-Ion-Beam Induced Quantum Dots

    NASA Astrophysics Data System (ADS)

    Luengo-Kovac, Marta; Saucer, Timothy; Martin, Andrew; Millunchick, Joanna; Sih, Vanessa

    2013-03-01

    Control over the positioning of semiconductor quantum dots (QDs) could facilitate the coupling of QDs to photonic crystal cavities and has applications in the development of high-efficiency solar cells. QDs grown through self-assembly nucleate at random spatial locations. However, a focused ion beam (FIB) can be used to create preferential sites for QD nucleation, and this pattern can be transferred to subsequent layers of QDs, either due to strain or residual effects of the templating. Multilayer QD stacks can therefore maintain the lateral pattern of the initial layer while separating QDs from material damage induced by the patterning. Multilayer QD structures were grown on FIB-patterned GaAs(001) substrates with 10 nm thick GaAs spacers between the layers. The substrates were patterned with sixteen square arrays of holes with spacings of 0.25, 0.5, 1.0, and 2.0 μm each at FIB dwell times of 1.0, 3.0, 6.0, and 9.0 ms. We report on the effects of multilayer QD growth on the initial layers through atomic force microscope (AFM) imaging of single, two-, and three-layer FIB-templated QD samples.

  5. Depletion forces induce visco-elasto-capillary thinning of non-Brownian suspensions

    NASA Astrophysics Data System (ADS)

    Harich, R.; Deblais, A.; Colin, A.; Kellay, H.

    2016-06-01

    Droplet pinch-off, which occurs when a drop of liquid detaches from a capillary, can be strongly modified in the presence of complex fluids such as polymer solutions and suspensions giving rise to long and slender filaments that thin slowly in time. While for polymers, the molecular conformations of the molecules in the filament are responsible for such a behavior, in suspensions the mechanisms at play remain to be deciphered. Here we show, experimentally, that while liquid bridges of non-Brownian suspensions of moderate concentrations have a thinning behavior very close to that of the solvent, the addition of short-chain polymers inducing depletion attractions between the particles in the suspension changes the thinning dynamics and gives rise to exponential thinning in time. The characteristic time of this dynamics increases with polymer concentration and therefore the intensity of the depletion forces at play. The tunability of this dynamics may be important for injket and 3D printing applications where short rupture times are sought for or in other situations where drop formation has to be minimized or inhibited.

  6. +GZ-induced neck injuries in Royal Australian Air Force fighter pilots.

    PubMed

    Newman, D G

    1997-06-01

    +GZ-induced neck injuries are a relatively common occurrence in pilots of high performance fighter aircraft. We surveyed 52 fighter pilots from the Royal Australian Air Force Base at Williamtown via an anonymous questionnaire in order to determine the prevalence and operational significance of these injuries. The pilots flew either the F/A-18 Hornet or the MB326H Macchi. Of the respondents, 44 reported having had a neck injury under +GZ. A higher rate was reported in pilots of the F/A-18. Most of these injuries were simple muscle sprains. There were 20 pilots who reported their neck injury as having interfered with mission completion. Only 12 pilots reported doing any regular neck strengthening exercises, while 33 pilots reported doing preflight neck stretches immediately prior to high +GZ exposure. There were 14 pilots who sought medical attention for their injury, with 9 being taken off flight status for an average of 2 weeks. Air combat maneuvering sorties and the "check six" head position were identified as causal factors by most pilots. This study demonstrates the operational significance of these injuries, and highlights the need for more research into this important aerospace medicine issue.

  7. Features of vestibuloocular reflex modulations induced by altered gravitational forces in tadpoles ( Xenopus laevis)

    NASA Astrophysics Data System (ADS)

    Sebastian, C.; Horn, E.

    2001-01-01

    In Xenopus laevis tadpoles, we studied the static vestibuloocular reflex (rVOR) in relation to modifications of the gravitational environment to find basic mechanisms of how altered gravitational forces (AGF) affect this reflex. Animals were exposed to microgravity during space flight or hypergravity (3g) for 4 to 12 days. Basic observations were that (1) the development of the rVOR is significantly affected by altered gravitational conditions, (2) the duration of 1g-readaptation depends on the strength of the test stimulus, (3) μg induces malformations of the body which are related to the rVOR depression. Future studies are based on the hypotheses (1) that the vestibular nuclei play a key roll in the adaptation to AGF conditions, (2) that the stimulus transducing systems in the sense organ are affected by AGF conditions, and (3) that fertilized eggs will be converted to normal adults guided by physiological and morphological set points representing the genetic programs. Developmental retardation or acceleration, or otherwise occurring deviations from standard development during embryonic and postembryonic life will activate genes that direct the developmental processes towards normality.

  8. Study of laser uncaging induced morphological alteration of rat cortical neurites using atomic force microscopy.

    PubMed

    Tian, Jian; Tu, Chunlong; Liang, Yitao; Zhou, Jian; Ye, Xuesong

    2015-09-30

    Activity-dependent structural remodeling is an important aspect of neuronal plasticity. In the previous researches, neuronal structure variations resulting from external interventions were detected by the imaging instruments such as the fluorescence microscopy, the scanning/transmission electron microscopy (SEM/TEM) and the laser confocal microscopy. In this article, a new platform which combined the photochemical stimulation with atomic force microscopy (AFM) was set up to detect the activity-dependent structural remodeling. In the experiments, the cortical neurites on the glass coverslips were stimulated by locally uncaged glutamate under the ultraviolet (UV) laser pulses, and a calcium-related structural collapse of neurites (about 250 nm height decrease) was observed by an AFM. This was the first attempt to combine the laser uncaging with AFM in living cell researches. With the advantages of highly localized stimulation (<5 μm), super resolution imaging (<3.8 nm), and convenient platform building, this system was suitable for the quantitative observation of the neuron mechanical property variations and morphological alterations modified by neural activities under different photochemical stimulations, which would be helpful for studying physiological and pathological mechanisms of structural and functional changes induced by the biomolecule acting.

  9. An atomic force microscopy statistical analysis of laser-induced azo-polyimide periodic tridimensional nanogrooves.

    PubMed

    Stoica, Iuliana; Epure, Luiza; Sava, Ion; Damian, Victor; Hurduc, Nicolae

    2013-09-01

    The surface morphology of azo-polyimide films was investigated after 355 nm Nd: YAG laser irradiation with two different incident fluencies. Atomic force microscopy (AFM) was employed to correlate the laser-induced tridimensional nanogrooved surface relief with the incident fluence and the number of irradiation pulses. The height images revealed that the grooves depth increased even tens of times by increasing the incident fluence, using the same numbers of irradiation pulses. For low incident fluence, the films were uniformly patterned till 100 pulses of irradiation. Instead, when using higher fluence, after 15 pulses of irradiation the accuracy of the surface relief definition was reduced. This behavior could be explained by means of two different mechanisms, one that suppose the film photo-fluidization due to the cis-trans isomerization processes of the azo-groups and the second one responsible for the directional mass displacement. The dominant surface direction and parameters like isotropy, periodicity, and period were evaluated from the polar representation for texture analysis, revealing the appearance of ordered and directionated nanostructures for most of the experimental conditions. Also, the graphical studies of the functional volume parameters have evidenced the improvement of the relief structuration during surface nanostructuration. The correlation of these statistical texture parameters with the irradiation characteristics is important in controlling the alignment of either the liquid crystals or the cells/tissues on patterned azo-polyimide surfaces for optoelectronic devices and implantable biomaterials, respectively.

  10. Resonant tunneling of fluctuation Cooper pairs

    SciTech Connect

    Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.

    2015-02-09

    Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.

  11. Resonant tunneling of fluctuation Cooper pairs

    DOE PAGES

    Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.

    2015-02-09

    Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool formore » direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.« less

  12. The influence of higher harmonic flow forces on the response of a curved circular cylinder undergoing vortex-induced vibration

    NASA Astrophysics Data System (ADS)

    Seyed-Aghazadeh, Banafsheh; Budz, Collin; Modarres-Sadeghi, Yahya

    2015-09-01

    Vortex-induced vibration (VIV) of a curved circular cylinder (a quarter of a ring, with no extension added to either end) free to oscillate in the crossflow direction was studied experimentally. Both the concave and the convex orientations (with respect to the oncoming flow direction) were considered. As expected, the amplitude of oscillations in both configurations was decreased compared to a vertical cylinder with the same mass ratio. Flow visualizations showed that the vortices were shed in parallel to the curved cylinder, when the cylinder was free to oscillate. The sudden jump in the phase difference between the flow forces and the cylinder displacement observed in the VIV of vertical cylinders was not observed in the curved cylinders. Higher harmonic force components at frequencies twice and three times the frequency of oscillations were observed in flow forces acting on the vertical cylinder, as well as the curved cylinder. Asymmetry in the wake was responsible for the 2nd harmonic force component and the relative velocity of the structure with respect to the oncoming flow was responsible for the 3rd harmonic force component. The lock-in occurred over the same range of reduced velocities for the curved cylinder in the convex orientation as for a vertical cylinder, but it was extended to higher reduced velocities for a curved cylinder in the concave orientation. Higher harmonic force components were found to be responsible for the extended lock-in range in the concave orientation. Within this range, the higher harmonic forces were even larger than the first harmonic force and the structure was being excited mainly by these higher harmonic forces.

  13. Theoretical modeling of the Casimir force-induced instability in freestanding nanowires with circular cross-section

    NASA Astrophysics Data System (ADS)

    Farrokhabadi, Amin; Abadian, Naeime; Rach, Randolph; Abadyan, Mohamadreza

    2014-09-01

    The Casimir force can induce instability and adhesion in freestanding nanostructures. Previous research efforts in this area have exclusively focused on modeling the instability in structures with planar or rectangular cross-section, while, to the best knowledge of the authors, no attention has been paid to investigate this phenomenon for nanowires with circular cross-section. In this study, effects of the Casimir force on the instability and adhesion of freestanding Cylinder-Plate and Cylinder-Cylinder geometries are investigated, which are commonly encountered in real nanodevices. To compute the Casimir force, two approaches, i.e. the proximity force approximation (PFA) for small separations and Dirichlet asymptotic approximation (scattering theory) for large separations, are considered. A continuum mechanics theory is employed, in conjunction with the Euler-beam model, to obtain constitutive equations of the systems. The governing nonlinear constitutive equations of the nanostructures are solved using two different approaches, i.e. the analytical modified Adomian decomposition (MAD) and the numerical finite difference method (FDM). The detachment length and minimum gap, both of which prevent the Casimir force-induced adhesion, are computed for both configurations.

  14. Coupled Quantum Fluctuations and Quantum Annealing

    NASA Astrophysics Data System (ADS)

    Hormozi, Layla; Kerman, Jamie

    We study the relative effectiveness of coupled quantum fluctuations, compared to single spin fluctuations, in the performance of quantum annealing. We focus on problem Hamiltonians resembling the the Sherrington-Kirkpatrick model of Ising spin glass and compare the effectiveness of different types of fluctuations by numerically calculating the relative success probabilities and residual energies in fully-connected spin systems. We find that for a small class of instances coupled fluctuations can provide improvement over single spin fluctuations and analyze the properties of the corresponding class. Disclaimer: This research was funded by ODNI, IARPA via MIT Lincoln Laboratory under Air Force Contract No. FA8721-05-C-0002. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of ODNI, IARPA, or the US Government.

  15. Accelerated greenhouse gases versus slow insolation forcing induced climate changes in southern South America since the Mid-Holocene

    NASA Astrophysics Data System (ADS)

    Berman, Ana Laura; Silvestri, Gabriel E.; Rojas, Maisa; Tonello, Marcela S.

    2017-01-01

    This paper is a pioneering analysis of past climates in southern South America combining multiproxy reconstructions and the state-of-the-art CMIP5/PMIP3 paleoclimatic models to investigate the time evolution of regional climatic conditions from the Mid-Holocene (MH) to the present. This analysis allows a comparison between the impact of the long term climate variations associated with insolation changes and the more recent effects of anthropogenic forcing on the region. The PMIP3 multimodel experiments suggest that changes in precipitation over almost all southern South America between MH and pre-industrial (PI) times due to insolation variations are significantly larger than those between PI and the present, which are due to changes in greenhouse gas concentrations. Anthropogenic forcing has been particularly intense over western Patagonia inducing reduction of precipitation in summer, autumn and winter as a consequence of progressively weaker westerly winds over the region, which have moved further poleward, between ca. 35-55°S and have become stronger south of about 50°S. Orbital variations between the MH to the PI period increased insolation over southern South America during summer and autumn inducing warmer conditions in the PI, accentuated by the effect of anthropogenic forcing during the last century. On the other hand, changes in orbital parameters from the MH to the PI period reduced insolation during winter and spring inducing colder conditions, which have been reversed by the anthropogenic forcing.

  16. Fluctuation relations for a driven Brownian particle.

    PubMed

    Imparato, A; Peliti, L

    2006-08-01

    We consider a driven Brownian particle, subject to both conservative and nonconservative applied forces, whose probability evolves according to the Kramers equation. We derive a general fluctuation relation, expressing the ratio of the probability of a given Brownian path in phase space with that of the time-reversed path, in terms of the entropy flux to the heat reservoir. This fluctuation relation implies those of Seifert, Jarzynski, and Gallavotti-Cohen in different special cases.

  17. Fluctuation relations for a driven Brownian particle

    NASA Astrophysics Data System (ADS)

    Imparato, A.; Peliti, L.

    2006-08-01

    We consider a driven Brownian particle, subject to both conservative and nonconservative applied forces, whose probability evolves according to the Kramers equation. We derive a general fluctuation relation, expressing the ratio of the probability of a given Brownian path in phase space with that of the time-reversed path, in terms of the entropy flux to the heat reservoir. This fluctuation relation implies those of Seifert, Jarzynski, and Gallavotti-Cohen in different special cases.

  18. Optically Induced Forces Imposed in an Optical Funnel on a Stream of Particles in Air or Vacuum

    NASA Astrophysics Data System (ADS)

    Eckerskorn, Niko; Bowman, Richard; Kirian, Richard A.; Awel, Salah; Wiedorn, Max; Küpper, Jochen; Padgett, Miles J.; Chapman, Henry N.; Rode, Andrei V.

    2015-12-01

    Optical trapping of light-absorbing particles in a gaseous environment is governed by a laser-induced photophoretic force, which can be orders of magnitude stronger than the force of radiation pressure induced by the same light intensity. In spite of many experimental studies, the exact theoretical background underlying the photophoretic force and the prediction of its influence on the particle motion is still in its infancy. Here, we report the results of a quantitative analysis of the photophoretic force and the stiffness of trapping achieved by levitating graphite and graphite-coated glass shells of calibrated sizes in an upright diverging hollow-core vortex beam, which we refer to as an "optical funnel". The measurements of forces are conducted in air at various gas pressures in the range from 5 mbar to 2 bar. The results of these measurements lay the foundation for mapping the optically induced force to the intensity distribution in the trap. The mapping, in turn, provides the necessary information to model flight trajectories of particles of various sizes entering the beam at given initial speed and position relative to the beam axis. Finally, we determine the limits of the parameter space for the particle speed, size, and radial offset to the beam axis, all linked to the laser power and the particular laser-beam structure. These results establish the grounds for developing a touch-free optical system for precisely positioning submicrometer bioparticles at the focal spot of an x-ray free-electron laser, which will significantly enhance the efficiency of studying nanoscale morphology of proteins and biomolecules in femtosecond coherent diffractive imaging experiments.

  19. Nanoscale patterning of chemical order induced by displacement cascades in irradiated L1{sub 0} alloys: Scaling analysis of the fluctuations of order

    SciTech Connect

    Ye Jia; Bellon, Pascal

    2006-06-01

    Atomistic kinetic Monte Carlo simulations are employed to analyze the dynamical stabilization of nanoscale patterning of L1{sub 0} chemical order in a model binary alloy subjected to sustained irradiation. The effect of irradiation-induced displacement cascades on the chemical order is modeled by the introduction at a controlled rate of nearly fully disordered spherical zones, which compete with the reordering promoted by the thermally activated migration of vacancies. When the size of the disordered zones is small, the alloy reaches a steady state that is either long-range ordered at low irradiation-induced ballistic jump frequency, {gamma}{sub b}, or disordered at high {gamma}{sub b}, with a first-order dynamical transition between these two steady states at {gamma}{sub b}={gamma}{sub b}{sup c}. Furthermore, in the disordered steady state, the intensity of order fluctuations scales with the reduced variable {gamma}{sub b}/{gamma}{sub b}{sup c}, a scaling that is consistent with an effective temperature approach. For larger cascade sizes, however, an additional steady state is stabilized at intermediate ballistic jump frequency, with a microstructure comprised of well-ordered nanoscale domains. In this patterning-of-order steady state, the above rescaling breaks down but we show that, after deconvolution of the structure factor into Gaussian and Lorentzian components, scaling of the Gaussian component is recovered by introducing a new reduced variable, {gamma}{sub b}/{gamma}{sub b}{sup p}, where 1/{gamma}{sub b}{sup p} is interpreted as the characteristic time for new domains to form in a disordered zone. This new scaling relationship provides a rigorous definition of the regime of patterning of order. This regime corresponds to the steady states stabilized by cascade sizes and ballistic jump frequencies satisfying {gamma}{sub b}{sup c}{<=}{gamma}{sub b}{<=}{gamma}{sub b}{sup p}. A dynamical phase diagram based on this new criterion is constructed and it agrees

  20. Distinguishing cells by their first-order transient motion response under an optically induced dielectrophoretic force field

    NASA Astrophysics Data System (ADS)

    Zhao, Yuliang; Liang, Wenfeng; Zhang, Guanglie; Mai, John D.; Liu, Lianqing; Lee, Gwo-Bin; Li, Wen J.

    2013-10-01

    This letter reports our characterization of the transient motion of cells under an optically induced dielectrophoresis (ODEP) force field. Different types of human cells repeatably undergo a first-order transient motion response when subjected to a specific ODEP force field. A kernel function is derived to describe this transient motion. This function can be generally matched to experimental data for Raji cells and red blood cells by measuring two parameters: the initial velocity and the transient time-constant. They are uniquely different for Raji cells and RBCs. Support vector machine is used to distinguish between them based on their transient response characteristics.

  1. The jet impact force of laser-induced bubble under the water-film with different thickness

    NASA Astrophysics Data System (ADS)

    Li, Beibei; Wang, Bingyang; Liu, Xiumei; He, Jie; Lu, Jian

    2015-05-01

    The effect of water-film on the laser-induced bubble was investigated by a piezoelectric ceramic transducer (PZT) sensor. Both of the collapse time and liquid-jet impact force of the bubble under the water-film were obtained, and the experiments were also completed in different laser energy. The collapse time increase with the thickness of the waterfilm, but the liquid-jet impact force decrease. We consider that the collapse time was affected by both of the rigid boundary and surface, and the increasing of the collapse time is the reason the decreasing of the liquid-jet impact force. The velocity of bubble wall is lower with the longer collapse time for the uniform bubbles energy, so the liquid-jet impact force is lower. For the other reasons, more laser energy would be absorbed by the thicker water-film, but the water was also splashed for the thinner water-film. So, for the thinner water-film, the bubble energy is higher, the liquidjet impact force is higher, but the maximal radius is smaller because of the splash process. In the other hand, both of the collapse time and the liquid-jet impact force are increase with the laser energy. These researches are useful for the laser processing under water.

  2. Intermolecular forces.

    PubMed

    Buckingham, A D

    1975-11-06

    The nature of molecular interactions is examined. Intermolecular forces are divided into long-range and short-range components; the former operate at distances where the effects of electron exchange are negligible and decrease as an inverse power of the separation. The long-range interactions may be subdividied into electrostatic, induction and dispersion contributions, where the electrostatic component is the interaction of the permanent charge distributions and the others originate in the fluctuations in the distributions. Typical magnitudes of the various contributions are given. The forces between macroscopic bodies are briefly considered, as are the effects of a medium. Some of the manifestations of molecular interactions are discussed.

  3. Asian Summer Monsoon Anomalies Induced by Aerosol Direct Forcing: The Role of the Tibetan Plateau

    NASA Technical Reports Server (NTRS)

    Lau, K. M.; Kim, M. K.; Kim, K. M.

    2006-01-01

    In this paper we present results of a numerical study using the NASA finite-volume GCM to elucidate a plausible mechanism for aerosol impact on the Asian summer monsoon involving interaction with physical processes over the Tibetan Plateau (TP). During the premonsoon season of March April, dusts from the deserts of western China, Afghanistan/Pakistan, and the Middle East are transported into and stacked up against the northern and southern slopes of the TP. The absorption of solar radiation by dust heats up the elevated surface air over the slopes. On the southern slopes, the atmospheric heating is reinforced by black carbon from local emission. The heated air rises via dry convection, creating a positive temperature anomaly in the mid-to-upper troposphere over the TP relative to the region to the south. In May through early June in a manner akin to an elevated heat pump , the rising hot air forced by the increasing heating in the upper troposphere, draws in warm and moist air over the Indian subcontinent, setting the stage for the onset of the South Asia summer monsoon. Our results suggest that increased dust loading coupled with black carbon emission from local sources in northern India during late spring may lead to an advance of the rainy periods and subsequently an intensification of the Indian summer monsoon. The enhanced rainfall over India is associated with the development of an aerosol-induced large-scale sea level pressure anomaly pattern, which causes the East Asia (Mei-yu) rain belt to shift northwestward, suppressing rainfall over East Asia and the adjacent oceanic regions.

  4. Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows

    NASA Astrophysics Data System (ADS)

    Chuang, Yao-Li; Chou, Tom; D'Orsogna, Maria R.

    2016-04-01

    We derive a three-dimensional theory of self-propelled particle swarming in a viscous fluid environment. Our model predicts emergent collective behavior that depends critically on fluid opacity, mechanism of self-propulsion, and type of particle-particle interaction. In "clear fluids" swimmers have full knowledge of their surroundings and can adjust their velocities with respect to the lab frame, while in "opaque fluids" they control their velocities only in relation to the local fluid flow. We also show that "social" interactions that affect only a particle's propensity to swim towards or away from neighbors induces a flow field that is qualitatively different from the long-ranged flow fields generated by direct "physical" interactions. The latter can be short-ranged but lead to much longer-ranged fluid-mediated hydrodynamic forces, effectively amplifying the range over which particles interact. These different fluid flows conspire to profoundly affect swarm morphology, kinetically stabilizing or destabilizing swarm configurations that would arise in the absence of fluid. Depending upon the overall interaction potential, the mechanism of swimming ( e.g., pushers or pullers), and the degree of fluid opaqueness, we discover a number of new collective three-dimensional patterns including flocks with prolate or oblate shapes, recirculating pelotonlike structures, and jetlike fluid flows that entrain particles mediating their escape from the center of mill-like structures. Our results reveal how the interplay among general physical elements influence fluid-mediated interactions and the self-organization, mobility, and stability of new three-dimensional swarms and suggest how they might be used to kinetically control their collective behavior.

  5. Fluctuation-induced magnetoconductivity in pristine and proton-irradiated Ca8.5La1.5(Pt3As8)(Fe2As2)5 single crystals

    NASA Astrophysics Data System (ADS)

    Ahmad, D.; Seo, Y. I.; Choi, W. J.; Kwon, Yong Seung

    2017-02-01

    The influence of the proton irradiation on the fluctuation-induced conductivity in Ca8.5La1.5(Pt3As8)(Fe2As2)5 single crystal was investigated. The in-plane magnetoconductivity was measured up to μ 0 H = 13 T. It is observed that the T c was suppressed up to 30.3 K from 32.5 K as a result of proton irradiation whereas the amplitude of the superconducting fluctuations is almost the same in both pristine and irradiated samples. The magnetoconductivity results analyzed by the Ullah and Dorsey scaling approaches showed that in the pristine sample, the 3D-2D crossover is situated near the T c. Furthermore, once the 3D-2D crossover occurs, it is found that there is a regime simultaneously described by 2D and 3D fluctuation behaviors in our Ca8.5La1.5(Pt3As8)(Fe2As2)5 sample. Meanwhile, the proton-irradiated sample showed the 3D fluctuation behavior.

  6. Use of a Laser-Induced Optical Force Trap to Study Chromosome Movement on the Mitotic Spindle

    NASA Astrophysics Data System (ADS)

    Berns, Michael W.; Wright, William H.; Tromberg, Bruce J.; Profeta, Glen A.; Andrews, Jeffrey J.; Walter, Robert J.

    1989-06-01

    A laser-induced optical force trap was used to alter the movement of chromosomes in mitotic cells in vitro. The trap was produced by using a 1.06-μ m neodymium YAG (yttrium/aluminum garnet) laser focused through a phase-contrast microscope. The trap was applied to one side of centrophilic chromosomes off the mitotic spindle and to latemoving chromosomes on the mitotic spindle. In both situations, chromosome movement was initiated in the direction opposite to that of the applied force. When the force was applied, chromosomes moved at velocities 10-20 times normal. These studies verify and extend the feasibility of using this new technique to study factors that influence organelle motility.

  7. Theoretical development of a magnetic force and an induced motion in elastic media for a magneto-motive technique

    NASA Astrophysics Data System (ADS)

    Lim, In Gweon; Park, Suhyun; Oh, Junghwan

    2016-08-01

    The theoretical development of a magnetic force and an induced motion while applying a magnetic field to magnetic nanoparticles in elastic media is described. An analytical expression for tissue-surface displacement derived from Mindlin's theory of elasticity in semi-infinite media was used to analyze the magneto-motive technique. The initial motion of the magnetic nanoparticles is driven by a constant magnetic force that displays a dampened transient motion before steady-state movement at twice the modulation frequency of the applied sinusoidal magnetic field. The motion of the nanoparticles at double the modulation frequency originated from the magnetic force being proportional to the product of the magnetic flux density and its gradient. Finally, we demonstrate the detection of iron-oxide nanoparticles taken up by liver parenchymal Kupffer cells and macrophages in atherosclerotic plaques by using a differential-phase optical coherence tomography (DP-OCT) system to compare simulation results with experimental data.

  8. Molecular mechanism of force induced stabilization of collagen against enzymatic breakdown.

    PubMed

    Chang, Shu-Wei; Flynn, Brendan P; Ruberti, Jeffrey W; Buehler, Markus J

    2012-05-01

    Collagen cleavage, facilitated by collagenases of the matrix metalloproteinase (MMP) family, is crucial for many physiological and pathological processes such as wound healing, tissue remodeling, cancer invasion and organ morphogenesis. Earlier work has shown that mechanical force alters the cleavage rate of collagen. However, experimental results yielded conflicting data on whether applying force accelerates or slows down the degradation rate. Here we explain these discrepancies and propose a molecular mechanism by which mechanical force might change the rate of collagen cleavage. We find that a type I collagen heterotrimer is unfolded in its equilibrium state and loses its triple helical structure at the cleavage site without applied force, possibly enhancing enzymatic breakdown as each chain is exposed and can directly undergo hydrolysis. Under application of force, the naturally unfolded region refolds into a triple helical structure, potentially protecting the molecule against enzymatic breakdown. In contrast, a type I collagen homotrimer retains a triple helical structure even without applied force, making it more resistant to enzyme cleavage. In the case of the homotrimer, the application of force may directly lead to molecular unwinding, resulting in a destabilization of the molecule under increased mechanical loading. Our study explains the molecular mechanism by which force may regulate the formation and breakdown of collagenous tissue.

  9. Hybrid electro-optical stimulation of the rat sciatic nerve induces force generation in the plantarflexor muscles

    NASA Astrophysics Data System (ADS)

    Duke, Austin R.; Peterson, Erik; Mackanos, Mark A.; Atkinson, James; Tyler, Dustin; Jansen, E. Duco

    2012-12-01

    Objective. Optical methods of neural activation are becoming important tools for the study and treatment of neurological disorders. Infrared nerve stimulation (INS) is an optical technique exhibiting spatially precise activation in the native neural system. While this technique shows great promise, the risk of thermal damage may limit some applications. Combining INS with traditional electrical stimulation, a method known as hybrid electro-optical stimulation, reduces the laser power requirements and mitigates the risk of thermal damage while maintaining spatial selectivity. Here we investigate the capability of inducing force generation in the rat hind limb through hybrid stimulation of the sciatic nerve. Approach. Hybrid stimulation was achieved by combining an optically transparent nerve cuff for electrical stimulation and a diode laser coupled to an optical fiber for infrared stimulation. Force generation in the rat plantarflexor muscles was measured in response to hybrid stimulation with 1 s bursts of pulses at 15 and 20 Hz and with a burst frequency of 0.5 Hz. Main results. Forces were found to increase with successive stimulus trains, ultimately reaching a plateau by the 20th train. Hybrid evoked forces decayed at a rate similar to the rate of thermal diffusion in tissue. Preconditioning the nerve with an optical stimulus resulted in an increase in the force response to both electrical and hybrid stimulation. Histological evaluation showed no signs of thermally induced morphological changes following hybrid stimulation. Our results indicate that an increase in baseline temperature is a likely contributor to hybrid force generation. Significance. Extraneural INS of peripheral nerves at physiologically relevant repetition rates is possible using hybrid electro-optical stimulation.

  10. Lab-on-a disc platform for particle focusing induced by inertial forces

    NASA Astrophysics Data System (ADS)

    Kitsara, Maria; Aguirre, Gerson R.; Efremov, Vitaly; Ducree, Jens

    2013-05-01

    Dean forces have been consistently used in microfluidic mixing units and recently also have been utilized to separate particles in inertial force driven systems by secondary flows. Microfluidic separation systems using inertial forces created by curved asymmetric channels have already been established in the literature. In the present work, we propose a centrifugal lab-on-a-disc platform, which can provide focusing of particles of 21μm diameter size and high separation of two different density types of particles (polystyrene and silica) using of both the inertial focusing forces and sedimentation forces. This comprises the primary advantage of the proposed platform compared to a pump-driven system. This platform can be utilized for the separation of different types of cells bound to specifically-functionalized particles of different densities.

  11. Analysis of radiation pressure force exerted on a biological cell induced by high-order Bessel beams using Debye series

    NASA Astrophysics Data System (ADS)

    Li, Renxian; Ren, Kuan Fang; Han, Xiang'e.; Wu, Zhensen; Guo, Lixin; Gong, Shuxi

    2013-09-01

    Debye series expansion (DSE) is employed to the analysis of radiation pressure force (RPF) exerted on biological cells induced by high-order Bessel beams (BB). The beam shape coefficients (BSCs) for high-order Bessel beams are calculated using analytical expressions obtained by the integral localized approximation (ILA). Different types of cells, including a real Chinese Hamster Ovary (CHO) cell and a lymphocyte which are respectively modeled by a coated and five-layered sphere, are considered. The RPF induced by high-order Bessel beams is compared with that by Gaussian beams and zeroth-order Bessel beams, and the effect of different scattering processes on RPF is studied. Numerical calculations show that high-order Bessel beams with zero central intensity can also transversely trap particle in the beam center, and some scattering processes can provide longitudinal pulling force.

  12. Single Molecule Study of Force-Induced Rotation of Carbon-Carbon Double Bonds in Polymers.

    PubMed

    Huang, Wenmao; Zhu, Zhenshu; Wen, Jing; Wang, Xin; Qin, Meng; Cao, Yi; Ma, Haibo; Wang, Wei

    2017-01-24

    Carbon-carbon double bonds (C═C) are ubiquitous in natural and synthetic polymers. In bulk studies, due to limited ways to control applied force, they are thought to be mechanically inert and not to contribute to the extensibility of polymers. Here, we report a single molecule force spectroscopy study on a polymer containing C═C bonds using atomic force microscope. Surprisingly, we found that it is possible to directly observe the cis-to-trans isomerization of C═C bonds at the time scale of ∼1 ms at room temperature by applying a tensile force ∼1.7 nN. The reaction proceeds through a diradical intermediate state, as confirmed by both a free radical quenching experiment and quantum chemical modeling. The force-free activation length to convert the cis C═C bonds to the transition state is ∼0.5 Å, indicating that the reaction rate is accelerated by ∼10(9) times at the transition force. On the basis of the density functional theory optimized structure, we propose that because the pulling direction is not parallel to C═C double bonds in the polymer, stretching the polymer not only provides tension to lower the transition barrier but also provides torsion to facilitate the rotation of cis C═C bonds. This explains the apparently low transition force for such thermally "forbidden" reactions and offers an additional explanation of the "lever-arm effect" of polymer backbones on the activation force for many mechanophores. This work demonstrates the importance of precisely controlling the force direction at the nanoscale to the force-activated reactions and may have many implications on the design of stress-responsive materials.

  13. Evidence for non-conservative current-induced forces in the breaking of Au and Pt atomic chains.

    PubMed

    Sabater, Carlos; Untiedt, Carlos; van Ruitenbeek, Jan M

    2015-01-01

    This experimental work aims at probing current-induced forces at the atomic scale. Specifically it addresses predictions in recent work regarding the appearance of run-away modes as a result of a combined effect of the non-conservative wind force and a 'Berry force'. The systems we consider here are atomic chains of Au and Pt atoms, for which we investigate the distribution of break down voltage values. We observe two distinct modes of breaking for Au atomic chains. The breaking at high voltage appears to behave as expected for regular break down by thermal excitation due to Joule heating. However, there is a low-voltage breaking mode that has characteristics expected for the mechanism of current-induced forces. Although a full comparison would require more detailed information on the individual atomic configurations, the systems we consider are very similar to those considered in recent model calculations and the comparison between experiment and theory is very encouraging for the interpretation we propose.

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

    NASA Technical Reports Server (NTRS)

    Kuhn, Richard E.

    1997-01-01

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

  15. Pressure-Induced Antiferromagnetic Fluctuations in the Pnictide Superconductor FeSe0.5Te0.5: 125Te NMR Study

    NASA Astrophysics Data System (ADS)

    Shimizu, Yasuhiro; Yamada, Takato; Takami, Tsuyoshi; Niitaka, Seiji; Takagi, Hidenori; Itoh, Masayuki

    2009-12-01

    To investigate the relationship between superconductivity and low-energy spin fluctuations in the iron-based superconductor FeSe0.5Te0.5, we have conducted 125Te NMR measurements at ambient pressure and 2 GPa. As the superconducting transition temperature Tc is increased by applying pressure, the nuclear spin-lattice relaxation rate divided by temperature, 1/T1T, shows the development of antiferromagnetic fluctuations upon lowering temperature toward Tc. This supports the scenario that spin fluctuations promote superconducting pairing. The depressed Knight shift 125K and the absence of a coherence peak in 1/T1 below Tc are consistent with spin-singlet superconducting pairing with an anisotropic order parameter. In the normal metallic state, the comparison between the uniform and dynamic spin susceptibilities suggests the existence of a Fermi level located near the singularity of the band structure.

  16. Low force contractions induce fatigue consistent with muscle mRNA expression in people with spinal cord injury

    PubMed Central

    Petrie, Michael A.; Suneja, Manish; Faidley, Elizabeth; Shields, Richard K.

    2014-01-01

    Abstract Spinal cord injury (SCI) is associated with muscle atrophy, transformation of muscle fibers to a fast fatigable phenotype, metabolic inflexibility (diabetes), and neurogenic osteoporosis. Electrical stimulation of paralyzed muscle may mitigate muscle metabolic abnormalities after SCI, but there is a risk for a fracture to the osteoporotic skeletal system. The goal of this study was to determine if low force stimulation (3 Hz) causes fatigue of chronically paralyzed muscle consistent with selected muscle gene expression profiles. We tested 29 subjects, nine with a SCI and 20 without and SCI, during low force fatigue protocol. Three SCI and three non‐SCI subjects were muscle biopsied for gene and protein expression analysis. The fatigue index (FI) was 0.21 ± 0.27 and 0.91 ± 0.01 for the SCI and non‐SCI groups, respectively, supporting that the low force protocol physiologically fatigued the chronically paralyzed muscle. The post fatigue potentiation index (PI) for the SCI group was increased to 1.60 ± 0.06 (P <0.001), while the non‐SCI group was 1.26 ± 0.02 supporting that calcium handling was compromised with the low force stimulation. The mRNA expression from genes that regulate atrophy and fast properties (MSTN, ANKRD1, MYH8, and MYCBP2) was up regulated, while genes that regulate oxidative and slow muscle properties (MYL3, SDHB, PDK2, and RyR1) were repressed in the chronic SCI muscle. MSTN, ANKRD1, MYH8, MYCBP2 gene expression was also repressed 3 h after the low force stimulation protocol. Taken together, these findings support that a low force single twitch activation protocol induces paralyzed muscle fatigue and subsequent gene regulation. These findings suggest that training with a low force protocol may elicit skeletal muscle adaptations in people with SCI. PMID:24744911

  17. Effect of oblique force source induced by laser ablation on ultrasonic generation.

    PubMed

    Guo, Yuning; Yang, Dexing; Chang, Ying; Gao, Wei

    2014-01-13

    The effect of asymmetry caused by oblique line-shaped laser ablation on the generation of ultrasonic waves in metal, especially the effect of transverse component of the ablation force source on the ultrasonic waves is analyzed. Due to the oblique force source, the displacements of shear wave increase obviously by the enhanced shear force, the energy concentration area of longitudinal wave deflects to the small range centered on the incident direction while that of shear wave is approximately perpendicular to incident direction. In addition, surface wave enhances in the direction of transverse power flow. Furthermore, some ultrasonic characteristics under vortex laser ablation condition are inferred.

  18. Proteins, fluctuations and complexity

    SciTech Connect

    Frauenfelder, Hans; Chen, Guo; Fenimore, Paul W

    2008-01-01

    Glasses, supercooled liquids, and proteins share common properties, in particular the existence of two different types of fluctuations, {alpha} and {beta}. While the effect of the {alpha} fluctuations on proteins has been known for a few years, the effect of {beta} fluctuations has not been understood. By comparing neutron scattering data on the protein myoglobin with the {beta} fluctuations in the hydration shell measured by dielectric spectroscopy we show that the internal protein motions are slaved to these fluctuations. We also show that there is no 'dynamic transition' in proteins near 200 K. The rapid increase in the mean square displacement with temperature in many neutron scattering experiments is quantitatively predicted by the {beta} fluctuations in the hydration shell.

  19. Heterogeneous Force Chains in Cellularized Biopolymer Network

    NASA Astrophysics Data System (ADS)

    Liang, Long; Jones, Christopher Allen Rucksack; Sun, Bo; Jiao, Yang

    Biopolymer Networks play an important role in coordinating and regulating collective cellular dynamics via a number of signaling pathways. Here, we investigate the mechanical response of a model biopolymer network due to the active contraction of embedded cells. Specifically, a graph (bond-node) model derived from confocal microscopy data is used to represent the network microstructure, and cell contraction is modeled by applying correlated displacements at specific nodes, representing the focal adhesion sites. A force-based stochastic relaxation method is employed to obtain force-balanced network under cell contraction. We find that the majority of the forces are carried by a small number of heterogeneous force chains emerged from the contracting cells. The force chains consist of fiber segments that either possess a high degree of alignment before cell contraction or are aligned due to the reorientation induced by cell contraction. Large fluctuations of the forces along different force chains are observed. Importantly, the decay of the forces along the force chains is significantly slower than the decay of radially averaged forces in the system, suggesting that the fibreous nature of biopolymer network structure could support long-range mechanical signaling between cells.

  20. Fluctuations in Cerebral Hemodynamics

    DTIC Science & Technology

    2007-11-02

    Determination of scaling properties Detrended Fluctuations Analysis (see (28) and references therein) is commonly used to determine scaling...pressure (averaged over a cardiac beat) of a healthy subject. First 1000 values of the time series are shown. (b) Detrended fluctuation analysis (DFA...1000 values of the time series are shown. (b) Detrended fluctuation analysis of the time series shown in (a). Fig . 3 Side-by-side boxplot for the

  1. Label-Free Sensing of Adenosine Based on Force Variations Induced by Molecular Recognition

    PubMed Central

    Li, Jingfeng; Li, Qing; Colombi Ciacchi, Lucio; Wei, Gang

    2015-01-01

    We demonstrate a simple force-based label-free strategy for the highly sensitive sensing of adenosine. An adenosine ssDNA aptamer was bound onto an atomic force microscopy (AFM) probe by covalent modification, and the molecular-interface adsorption force between the aptamer and a flat graphite surface was measured by single-molecule force spectroscopy (SMFS). In the presence of adenosine, the molecular recognition between adenosine and the aptamer resulted in the formation of a folded, hairpin-like DNA structure and hence caused a variation of the adsorption force at the graphite/water interface. The sensitive force response to molecular recognition provided an adenosine detection limit in the range of 0.1 to 1 nM. The addition of guanosine, cytidine, and uridine had no significant interference with the sensing of adenosine, indicating a strong selectivity of this sensor architecture. In addition, operational parameters that may affect the sensor, such as loading rate and solution ionic strength, were investigated. PMID:25808841

  2. Fluctuation relations for spintronics.

    PubMed

    López, Rosa; Lim, Jong Soo; Sánchez, David

    2012-06-15

    Fluctuation relations are derived in systems where the spin degree of freedom and magnetic interactions play a crucial role. The form of the nonequilibrium fluctuation theorems relies on the assumption of a local balance condition. We demonstrate that in some cases the presence of magnetic interactions violates this condition. Nevertheless, fluctuation relations can be obtained from the microreversibility principle sustained only at equilibrium as a symmetry of the cumulant generating function for spin currents. We illustrate the spintronic fluctuation relations for a quantum dot coupled to partially polarized helical edge states.

  3. Controlling dispersion forces between small particles with artificially created random light fields.

    PubMed

    Brügger, Georges; Froufe-Pérez, Luis S; Scheffold, Frank; José Sáenz, Juan

    2015-06-22

    Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systems.

  4. Controlling dispersion forces between small particles with artificially created random light fields

    PubMed Central

    Brügger, Georges; Froufe-Pérez, Luis S.; Scheffold, Frank; José Sáenz, Juan

    2015-01-01

    Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir–Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systems. PMID:26096622

  5. Effect of force-induced mechanical stress at the coronary artery bifurcation stenting: Relation to in-stent restenosis

    SciTech Connect

    Lee, Cheng-Hung; Jhong, Guan-Heng; Hsu, Ming-Yi; Wang, Chao-Jan; Liu, Shih-Jung; Hung, Kuo-Chun

    2014-05-28

    The deployment of metallic stents during percutaneous coronary intervention has become common in the treatment of coronary bifurcation lesions. However, restenosis occurs mostly at the bifurcation area even in present era of drug-eluting stents. To achieve adequate deployment, physicians may unintentionally apply force to the strut of the stents through balloon, guiding catheters, or other devices. This force may deform the struts and impose excessive mechanical stresses on the arterial vessels, resulting in detrimental outcomes. This study investigated the relationship between the distribution of stress in a stent and bifurcation angle using finite element analysis. The unintentionally applied force following stent implantation was measured using a force sensor that was made in the laboratory. Geometrical information on the coronary arteries of 11 subjects was extracted from contrast-enhanced computed tomography scan data. The numerical results reveal that the application of force by physicians generated significantly higher mechanical stresses in the arterial bifurcation than in the proximal and distal parts of the stent (post hoc P < 0.01). The maximal stress on the vessels was significantly higher at bifurcation angle <70° than at angle ≧70° (P < 0.05). The maximal stress on the vessels was negatively correlated with bifurcation angle (P < 0.01). Stresses at the bifurcation ostium may cause arterial wall injury and restenosis, especially at small bifurcation angles. These finding highlight the effect of force-induced mechanical stress at coronary artery bifurcation stenting, and potential mechanisms of in-stent restenosis, along with their relationship with bifurcation angle.

  6. Force sensitivity of multilayer graphene optomechanical devices

    PubMed Central

    Weber, P.; Güttinger, J.; Noury, A.; Vergara-Cruz, J.; Bachtold, A.

    2016-01-01

    Mechanical resonators based on low-dimensional materials are promising for force and mass sensing experiments. The force sensitivity in these ultra-light resonators is often limited by the imprecision in the measurement of the vibrations, the fluctuations of the mechanical resonant frequency and the heating induced by the measurement. Here, we strongly couple multilayer graphene resonators to superconducting cavities in order to achieve a displacement sensitivity of 1.3 fm Hz−1/2. This coupling also allows us to damp the resonator to an average phonon occupation of 7.2. Our best force sensitivity, 390 zN Hz−1/2 with a bandwidth of 200 Hz, is achieved by balancing measurement imprecision, optomechanical damping, and measurement-induced heating. Our results hold promise for studying the quantum capacitance of graphene, its magnetization, and the electron and nuclear spins of molecules adsorbed on its surface. PMID:27502017

  7. Force sensitivity of multilayer graphene optomechanical devices

    NASA Astrophysics Data System (ADS)

    Weber, P.; Güttinger, J.; Noury, A.; Vergara-Cruz, J.; Bachtold, A.

    2016-08-01

    Mechanical resonators based on low-dimensional materials are promising for force and mass sensing experiments. The force sensitivity in these ultra-light resonators is often limited by the imprecision in the measurement of the vibrations, the fluctuations of the mechanical resonant frequency and the heating induced by the measurement. Here, we strongly couple multilayer graphene resonators to superconducting cavities in order to achieve a displacement sensitivity of 1.3 fm Hz-1/2. This coupling also allows us to damp the resonator to an average phonon occupation of 7.2. Our best force sensitivity, 390 zN Hz-1/2 with a bandwidth of 200 Hz, is achieved by balancing measurement imprecision, optomechanical damping, and measurement-induced heating. Our results hold promise for studying the quantum capacitance of graphene, its magnetization, and the electron and nuclear spins of molecules adsorbed on its surface.

  8. Facing rim cavities fluctuation modes

    NASA Astrophysics Data System (ADS)

    Casalino, Damiano; Ribeiro, André F. P.; Fares, Ehab

    2014-06-01

    Cavity modes taking place in the rims of two opposite wheels are investigated through Lattice-Boltzmann CFD simulations. Based on previous observations carried out by the authors during the BANC-II/LAGOON landing gear aeroacoustic study, a resonance mode can take place in the volume between the wheels of a two-wheel landing gear, involving a coupling between shear-layer vortical fluctuations and acoustic modes resulting from the combination of round cavity modes and wheel-to-wheel transversal acoustic modes. As a result, side force fluctuations and tonal noise side radiation take place. A parametric study of the cavity mode properties is carried out in the present work by varying the distance between the wheels. Moreover, the effects due to the presence of the axle are investigated by removing the axle from the two-wheel assembly. The azimuthal properties of the modes are scrutinized by filtering the unsteady flow in narrow bands around the tonal frequencies and investigating the azimuthal structure of the filtered fluctuation modes. Estimation of the tone frequencies with an ad hoc proposed analytical formula confirms the observed modal properties of the filtered unsteady flow solutions. The present study constitutes a primary step in the description of facing rim cavity modes as a possible source of landing gear tonal noise.

  9. Evidence for non-conservative current-induced forces in the breaking of Au and Pt atomic chains

    PubMed Central

    Sabater, Carlos; Untiedt, Carlos

    2015-01-01

    Summary This experimental work aims at probing current-induced forces at the atomic scale. Specifically it addresses predictions in recent work regarding the appearance of run-away modes as a result of a combined effect of the non-conservative wind force and a ‘Berry force’. The systems we consider here are atomic chains of Au and Pt atoms, for which we investigate the distribution of break down voltage values. We observe two distinct modes of breaking for Au atomic chains. The breaking at high voltage appears to behave as expected for regular break down by thermal excitation due to Joule heating. However, there is a low-voltage breaking mode that has characteristics expected for the mechanism of current-induced forces. Although a full comparison would require more detailed information on the individual atomic configurations, the systems we consider are very similar to those considered in recent model calculations and the comparison between experiment and theory is very encouraging for the interpretation we propose. PMID:26734525

  10. Structure and agency in development-induced forced migration: the case of Brazil’s Belo Monte Dam

    PubMed Central

    2017-01-01

    This paper examines how structure and agency interact to shape forced migration outcomes. Specifically, I ask how structural factors such as compensation policies as well as social, financial, and human capital may either foster or constrain migration aspirations and capabilities. I use longitudinal, semi-structured interview data to study forced migration among farmers displaced by the Belo Monte Dam in the Brazilian Amazon. Results from baseline interviews indicate that nearly all community members aspired to purchase rural land in the region and maintain livelihoods as cacao farmers or cattle ranchers. Constraints limiting the ability to attain aspirations included strict requirements on land titles for properties, delays in receiving compensation, rising land prices, and the lack of power to negotiate for better compensation. Despite these constraints, most migrants succeeded in attaining aspirations, as they were able to mobilize resources such as social networks, financial capital, skills, and knowledge. These findings highlight the importance of considering the relationship between structure and agency within forced migration research. I conclude by discussing how the findings may inform resettlement policies for future cases of development- or environment-induced forced migration. PMID:28298745

  11. Population Genetics with Fluctuating Population Sizes

    NASA Astrophysics Data System (ADS)

    Chotibut, Thiparat; Nelson, David R.

    2017-02-01

    Standard neutral population genetics theory with a strictly fixed population size has important limitations. An alternative model that allows independently fluctuating population sizes and reproduces the standard neutral evolution is reviewed. We then study a situation such that the competing species are neutral at the equilibrium population size but population size fluctuations nevertheless favor fixation of one species over the other. In this case, a separation of timescales emerges naturally and allows adiabatic elimination of a fast population size variable to deduce the fluctuation-induced selection dynamics near the equilibrium population size. The results highlight the incompleteness of the standard population genetics with a strictly fixed population size.

  12. Delta(9)-tetrahydrocannabinol enhances an increase of plasma corticosterone levels induced by forced swim-stress.

    PubMed

    Sano, Kazunori; Koushi, Emi; Irie, Keiichi; Higuchi, Sei; Tsuchihashi, Ryota; Kinjo, Junei; Egashira, Nobuaki; Oishi, Ryozo; Uchida, Naoki; Nagai, Hiroshi; Nishimura, Ryoji; Tanaka, Hiroyuki; Morimoto, Satoshi; Mishima, Kenichi; Iwasaki, Katsunori; Fujiwara, Michihiro

    2009-12-01

    The present study was designed to determine the effect of delta(9)-tetrahydrocannabinol (THC) on susceptibility to stress. We reported that THC significantly prolonged the immobility time during the forced swim-stress. The selective cannabinoid CB(1) receptor antagonist O-2050 significantly reduced the enhancement of immobility by THC. We investigated the effect of THC on levels of stress hormone corticosterone under non-stress and forced swim-stress conditions. THC did not affect plasma corticosterone levels under non-stress conditions. However, THC, together with forced swim-stress, significantly increased plasma corticosterone levels. This effect was inhibited by O-2050. This evidence suggests that THC, under stressful conditions, enhances the susceptibility of the hypothalamus-pituitary-adrenal-axis to stress via the CB(1) receptor, thereby increasing the risk of depression.

  13. Laser-induced force on a microfluidic drop: origin and magnitude.

    PubMed

    Verneuil, Emilie; Cordero, Maríaluisa; Gallaire, François; Baroud, Charles N

    2009-05-05

    The localized heating produced by a tightly focused infrared laser leads to surface tension gradients at the interface of microfluidic drops covered with surfactants, resulting in a net force on the drop whose origin and magnitude are the focus of this paper. First, by colocalization of the surfactant micelles with a fluorescent dye, we demonstrate that the heating alters their spatial distribution, driving the interface out of equilibrium. This soluto-capillary effect opposes and overcomes the purely thermal dependence of the surface tension, leading to reversed interfacial flows. As the surface of the drop is set into motion, recirculation rolls are created outside and inside the drop, which we measure using time-resolved micro-Particle Image Velocimetry. Second, the net force produced on the drop is measured using an original microfluidic design. For a drop 300 microm-long and 100 microm-wide, we obtain a force of 180 nN for a laser power of 100 mW. This micro-dynanometer further shows that the magnitude of the heating, which is determined by the laser power and its absorption in the water, sets the magnitude of the net force on the drop. On the other hand, the dynamics of the force generation is limited by the time scale for heating, which has independently been measured to be tau(Theta) = 4 ms. This time scale sets the maximum velocity that the drops can have and still be blocked, by requiring that the interface passes the laser spot in a time longer than tau(Theta). The maximum velocity is measured at U(max) = 0.7 mm/s for our geometric conditions. Finally, a scaling model is derived that describes the blocking force in a confined geometry as the result of the viscous stresses produced by the shear between the drop and the lateral walls.

  14. Theory of stress fluctuations

    PubMed

    Wallace

    2000-09-01

    The current status of the theory of stress fluctuations is marked by two circumstances: no currently available formulas are valid for a metallic system, and a series of contradictory formulas remains unresolved. Here we derive formulas for shear- and isotropic-stress energy fluctuations, in the primary statistical mechanics ensembles. These formulas are valid for a classical monatomic system representing a metal or nonmetal, in cubic crystal, amorphous solid, or liquid phases. Current contradictions in fluctuation formulas are resolved through the following observations. First, the expansion of a dynamical variable A in terms of the fluctuations explicit in a given ensemble distribution, for example deltaA=adeltaN+bdeltaH in the grand canonical ensemble, is correct if and only if deltaA is a function only of deltaN and deltaH. The common use of this expansion has produced incorrect fluctuation formulas. Second, the thermodynamic fluctuations of Landau and Lifshitz do not correspond to statistical mechanics fluctuations, and the two types of fluctuations have essentially different values.

  15. Characterisation of stochastically-induced climate jumps to other histories paced by the astronomical forcing.

    NASA Astrophysics Data System (ADS)

    De Saedeleer, B.

    2012-04-01

    The mystery of ice ages induced by a varying incoming solar radiation has drawn ceaseless attention for several decades. A pleiad of paleoclimatic models has been developed in order to have a try at catching the underlying climate dynamics, and their validity is challenged by comparison with typical milestones in paleoclimatic records. In several published works, the astronomical forcing synchronises the climate to a unique climatic attracting trajectory representing the ice volume evolution. Other studies, though, reported multistability, i.e. the fact that several climatic attracting trajectories could coexist for some given set of parameters, in a deterministic framework. More importantly, it has been illustrated that additional disturbances may cause some 'jumps' from one trajectory to other ones in the climatic history over the last millions years of the Pleistocene. These stochastic effects hence indirectly affect the timing of the glacial inceptions and terminations. The jumping mechanism is closely linked to the widely spread hypothesis that the glacial-interglacial cycles could be primarily triggered by random internal climate variability. A conjecture has recently been made that these externally triggered jumps are the most likely when the temporary desynchronisation (positive largest local Lyapunov exponent) due to the loss of local stability coalesces with the weakening of the global stability due to the proximity to the basin boundary. No proof of this conjecture has however been provided sofar; it is precisely the aim of the present research to assess the conditions for such a jump to occur. We uncover the details of the underlying mechanisms by providing a systematic numerical study of the conditions under which these jumps are likely to occur. Extensive Monte Carlo experiments are performed in order to show that the jumps occur preferentially at specific times or locations in the phase space, for a given level of noise. We show how the most critical

  16. ENSO Modulations by Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating feedbacks in the Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, R. H.

    2015-12-01

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Niño-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other.

  17. ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, Rong-Hua; Gao, Chuan; Kang, Xianbiao; Zhi, Hai; Wang, Zhanggui; Feng, Licheng

    2015-12-01

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Niño-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other.

  18. ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific.

    PubMed

    Zhang, Rong-Hua; Gao, Chuan; Kang, Xianbiao; Zhi, Hai; Wang, Zhanggui; Feng, Licheng

    2015-12-18

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Niño-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other.

  19. Monoamine depletion attenuates the REM sleep deprivation-induced increase in clonidine response in the forced swimming test.

    PubMed

    Asakura, W; Matsumoto, K; Ohta, H; Watanabe, H

    1994-09-01

    Effect of monoamine depletion on the REM sleep (REMs) deprivation-induced increase in clonidine response in the forced swimming test was investigated. Mice were deprived of REMs by the small pedestal method. Clonidine HCl (10-1000 micrograms/kg, IP), an alpha 2-adrenoceptor agonist, dose dependently increased swimming activities in group-housed and socially isolated mice used as the control groups. The dose-response relationship shifted to the left following REMs deprivation (ED50 values in the group-housed, isolated, and REMs-deprived mice were 250, 200, and 27 micrograms/kg, respectively). Monoamine depletion, induced by reserpine (5 mg/kg, IP) plus alpha-methyl-p-tyrosine (250 mg/kg, IP), did not produce any changes in the effects of clonidine in the control groups. However, in REMs-deprived mice, monoamine depletion significantly decreased the effect of 100 micrograms/kg clonidine, but not that of 300 micrograms/kg clonidine on swimming activity. These results indicate that clonidine-induced increase in swimming activity in the forced swimming test is mainly mediated by postsynaptic alpha 2-adrenoceptor, and that endogenous noradrenaline in the brain plays an important role in the increase of clonidine response following REMs deprivation treatment. The neuronal mechanism of the increase in clonidine response is discussed.

  20. Resonance energy transfer (RET)-Induced intermolecular pairing force: a tunable weak interaction and its application in SWNT separation.

    PubMed

    Pan, Xiaoyong; Chen, Hui; Wang, Wei Zhi; Ng, Siu Choon; Chan-Park, Mary B

    2011-07-21

    This paper explores evidence of an optically mediated interaction that is active in the separation mechanism of certain selective agents through consideration of the contrasting selective behaviors of two conjugated polymers with distinct optical properties. The involvement of a RET-induced intermolecular pairing force is implied by the different illumination response behaviors. The magnitude of this interaction scales with the external stimulus parameter, the illumination irradiance (I), and thus is tunable. This suggests a facile technique to modify the selectivity of polymers toward specific SWNT species by altering the polymer structure to adjust the corresponding intermolecular interaction. This is the first experimental verification and application of a RET-induced intermolecular pairing force to SWNT separation. With this kind of interaction taken into account, reasonable interpretation of some conflicting data, especially PLE maps, can be easily made. The above conclusion can be applied to other substances as long as they are electrically neutral and there is photon-induced RET between them. The significant magnitude of this interaction makes direct manipulation of molecules/particles possible and is expected to have applications in molecular engineering.

  1. Alterations in task-induced activity and resting-state fluctuations in visual and DMN areas revealed in long-term meditators.

    PubMed

    Berkovich-Ohana, Aviva; Harel, Michal; Hahamy, Avital; Arieli, Amos; Malach, Rafael

    2016-07-15

    Recently we proposed that the information contained in spontaneously emerging (resting-state) fluctuations may reflect individually unique neuro-cognitive traits. One prediction of this conjecture, termed the "spontaneous trait reactivation" (STR) hypothesis, is that resting-state activity patterns could be diagnostic of unique personalities, talents and life-styles of individuals. Long-term meditators could provide a unique experimental group to test this hypothesis. Using fMRI we found that, during resting-state, the amplitude of spontaneous fluctuations in long-term mindfulness meditation (MM) practitioners was enhanced in the visual cortex and significantly reduced in the DMN compared to naïve controls. Importantly, during a visual recognition memory task, the MM group showed heightened visual cortex responsivity, concomitant with weaker negative responses in Default Mode Network (DMN) areas. This effect was also reflected in the behavioral performance, where MM practitioners performed significantly faster than the control group. Thus, our results uncover opposite changes in the visual and default mode systems in long-term meditators which are revealed during both rest and task. The results support the STR hypothesis and extend it to the domain of local changes in the magnitude of the spontaneous fluctuations.

  2. GCM simulations of volcanic aerosol forcing. I - Climate changes induced by steady-state perturbations

    NASA Technical Reports Server (NTRS)

    Pollack, James B.; Rind, David; Lacis, Andrew; Hansen, James E.; Sato, Makiko; Ruedy, Reto

    1993-01-01

    The response of the climate system to a temporally and spatially constant amount of volcanic particles is simulated using a general circulation model (GCM). The optical depth of the aerosols is chosen so as to produce approximately the same amount of forcing as results from doubling the present CO2 content of the atmosphere and from the boundary conditions associated with the peak of the last ice age. The climate changes produced by long-term volcanic aerosol forcing are obtained by differencing this simulation and one made for the present climate with no volcanic aerosol forcing. The simulations indicate that a significant cooling of the troposphere and surface can occur at times of closely spaced multiple sulfur-rich volcanic explosions that span time scales of decades to centuries. The steady-state climate response to volcanic forcing includes a large expansion of sea ice, especially in the Southern Hemisphere; a resultant large increase in surface and planetary albedo at high latitudes; and sizable changes in the annually and zonally averaged air temperature.

  3. Aviation-induced radiative forcing and surface temperature change in dependency of the emission altitude

    NASA Astrophysics Data System (ADS)

    FröMming, C.; Ponater, M.; Dahlmann, K.; Grewe, V.; Lee, D. S.; Sausen, R.

    2012-10-01

    The present study provides a detailed assessment of the net impact of global flight altitude changes on radiative forcing and temperature response. Changes in contrail coverage, chemical perturbations (H2O, O3, CH4) and associated radiative forcings were determined from simulations with a quasi CTM. Future development of global mean radiative forcing and temperature response was calculated by means of a linear response model. The range of possible effects arising from various future scenarios is analyzed, and tradeoffs between partially counteracting short- and long term effects are studied. Present-day global mean radiative forcing of short-lived species and CH4 is reduced when flying lower, whereas that of CO2increases. The opposite effect is found for higher flight altitudes. For increasing and sustained emissions, the climate impact changes are dominated by the effect of short-lived species, yielding a reduction for lower flight altitudes and an increase for higher flight altitudes. For future scenarios involving a reduction or termination of emissions, radiative forcing of short-lived species decreases immediately, that of longer lived species decreases gradually, and respective temperature responses start to decay slowly. After disappearance of the shorter lived effects, only the counteracting CO2 effect remains, resulting in an increased climate effect for lower flight altitudes and a decrease for higher flight altitudes. Incorporating knowledge about the altitude sensitivity of aviation climate impact in the route planning process offers substantial mitigation potential. Scenarios and time horizons for the evaluation of future effects of mitigation instruments must be chosen carefully depending on the mitigation aim.

  4. Interaction of free and forced convection in horizontal tubes in the transition regime.

    NASA Technical Reports Server (NTRS)

    Nagendra, H. R.

    1973-01-01

    Experimental investigation of some new aspects of the combined free and forced convection interacting in the transition regime of a horizontal tube under uniform heat flux conditions. The results obtained include indications that thermally induced secondary flows attenuate the fluctuations in low inlet turbulence flows, while they restabilize the flow as the inlet turbulence is increased.

  5. Dissipation of proton motive force is not sufficient to induce the phage shock protein response in Escherichia coli.

    PubMed

    Engl, Christoph; Beek, Alex Ter; Bekker, Martijn; de Mattos, Joost Teixeira; Jovanovic, Goran; Buck, Martin

    2011-05-01

    Phage shock proteins (Psp) and their homologues are found in species from the three domains of life: Bacteria, Archaea and Eukarya (e.g. higher plants). In enterobacteria, the Psp response helps to maintain the proton motive force (PMF) of the cell when the inner membrane integrity is impaired. The presumed ability of ArcB to sense redox changes in the cellular quinone pool and the strong decrease of psp induction in ΔubiG or ΔarcAB backgrounds suggest a link between the Psp response and the quinone pool. The authors now provide evidence indicating that the physiological signal for inducing psp by secretin-induced stress is neither the quinone redox state nor a drop in PMF. Neither the loss of the H(+)-gradient nor the dissipation of the electrical potential alone is sufficient to induce the Psp response. A set of electron transport mutants differing in their redox states due to the lack of a NADH dehydrogenase and a quinol oxidase, but retaining a normal PMF displayed low levels of psp induction inversely related to oxidised ubiquinone levels under microaerobic growth and independent of PMF. In contrast, cells displaying higher secretin induced psp expression showed increased levels of ubiquinone. Taken together, this study suggests that not a single but likely multiple signals are needed to be integrated to induce the Psp response.

  6. Use of induced acceleration to quantify the (de)stabilization effect of external and internal forces on postural responses.

    PubMed

    van Asseldonk, Edwin H F; Carpenter, Mark G; van der Helm, Frans C T; van der Kooij, Herman

    2007-12-01

    Due to the mechanical coupling between the body segments, it is impossible to see with the naked eye the causes of body movements and understand the interaction between movements of different body parts. The goal of this paper is to investigate the use of induced acceleration analysis to reveal the causes of body movements. We derive the analytical equations to calculate induced accelerations and evaluate its potential to study human postural responses to support-surface translations. We measured the kinematic and kinetic responses of a subject to sudden forward and backward translations of a moving platform. The kinematic and kinetics served as input to the induced acceleration analyses. The induced accelerations showed explicitly that the platform acceleration and deceleration contributed to the destabilization and restabilization of standing balance, respectively. Furthermore, the joint torques, coriolis and centrifugal forces caused by swinging of the arms, contributed positively to stabilization of the Center of Mass. It is concluded that induced acceleration analyses is a valuable tool in understanding balance responses to different kinds of perturbations and may help to identify the causes of movement in different pathologies.

  7. Ongoing characterization of the forced electron beam induced arc discharge ion source for the selective production of exotic species facility

    SciTech Connect

    Manzolaro, M. Andrighetto, A.; Monetti, A.; Scarpa, D.; Rossignoli, M.; Vasquez, J.; Corradetti, S.; Calderolla, M.; Prete, G.; Meneghetti, G.

    2014-02-15

    An intense research and development activity to finalize the design of the target ion source system for the selective production of exotic species (SPES) facility (operating according to the isotope separation on line technique) is at present ongoing at Legnaro National Laboratories. In particular, the characterization of ion sources in terms of ionization efficiency and transversal emittance is currently in progress, and a preliminary set of data is already available. In this work, the off-line ionization efficiency and emittance measurements for the SPES forced electron beam induced arc discharge ion source in the case of a stable Ar beam are presented in detail.

  8. Wheel-rail dynamic forces induced by random vertical track irregularities

    NASA Astrophysics Data System (ADS)

    Spiroiu, M. A.

    2016-08-01

    The present paper investigates the wheel-rail dynamic forces produced by railway vehicles in motion, which are an important issue especially for the high-speed rail transport from the point of view of traffic safety, ride quality and undesirable effects on vehicles, on track and on the land in the vicinity of railways. The research is carried out on a model which includes track system, vehicle unsprung mass, vehicle primary suspension and the bogie sprung mass. The wheel-rail dynamic overloads are evaluated assuming random vertical irregularities of the track. The estimation of wheel-rail dynamic forces is made for a range of vehicle speeds up to 300 km/h and the influence of track and vehicle various parameters is investigated.

  9. Laser-induced rocket force on a microparticle in a complex (dusty) plasma

    SciTech Connect

    Nosenko, V.; Ivlev, A. V.; Morfill, G. E.

    2010-12-15

    The interaction of a focused powerful laser beam with micron-sized melamine formaldehyde (MF) particles was studied experimentally. The microspheres had a thin palladium coating on their surface and were suspended in a radio frequency argon plasma as a single layer (plasma crystal). A particle hit by the laser beam usually accelerated in the direction of the laser beam, consistent with the radiation pressure force mechanism. However, random-direction acceleration up to the speeds on the order 1 m/s was sometimes observed. Rocket-force mechanism is proposed to account for the random-direction acceleration. Similar, but much less pronounced, effect was also observed for MF particles without palladium coating.

  10. Mirror force induced wave dispersion in Alfvén waves

    SciTech Connect

    Damiano, P. A.; Johnson, J. R.

    2013-06-15

    Recent hybrid MHD-kinetic electron simulations of global scale standing shear Alfvén waves along the Earth's closed dipolar magnetic field lines show that the upward parallel current region within these waves saturates and broadens perpendicular to the ambient magnetic field and that this broadening increases with the electron temperature. Using resistive MHD simulations, with a parallel Ohm's law derived from the linear Knight relation (which expresses the current-voltage relationship along an auroral field line), we explore the nature of this broadening in the context of the increased perpendicular Poynting flux resulting from the increased parallel electric field associated with mirror force effects. This increased Poynting flux facilitates wave energy dispersion across field lines which in-turn allows for electron acceleration to carry the field aligned current on adjacent field lines. This mirror force driven dispersion can dominate over that associated with electron inertial effects for global scale waves.

  11. Spatial fluctuation theorem

    NASA Astrophysics Data System (ADS)

    Pérez-Espigares, Carlos; Redig, Frank; Giardinà, Cristian

    2015-08-01

    For non-equilibrium systems of interacting particles and for interacting diffusions in d-dimensions, a novel fluctuation relation is derived. The theorem establishes a quantitative relation between the probabilities of observing two current values in different spatial directions. The result is a consequence of spatial symmetries of the microscopic dynamics, generalizing in this way the Gallavotti-Cohen fluctuation theorem related to the time-reversal symmetry. This new perspective opens up the possibility of direct experimental measurements of fluctuation relations of vectorial observables.

  12. Hadronic Correlations and Fluctuations

    SciTech Connect

    Koch, Volker

    2008-10-09

    We will provide a review of some of the physics which can be addressed by studying fluctuations and correlations in heavy ion collisions. We will discuss Lattice QCD results on fluctuations and correlations and will put them into context with observables which have been measured in heavy-ion collisions. Special attention will be given to the QCD critical point and the first order co-existence region, and we will discuss how the measurement of fluctuations and correlations can help in an experimental search for non-trivial structures in the QCD phase diagram.

  13. Continuous information flow fluctuations

    NASA Astrophysics Data System (ADS)

    Rosinberg, Martin Luc; Horowitz, Jordan M.

    2016-10-01

    Information plays a pivotal role in the thermodynamics of nonequilibrium processes with feedback. However, much remains to be learned about the nature of information fluctuations in small-scale devices and their relation with fluctuations in other thermodynamics quantities, like heat and work. Here we derive a series of fluctuation theorems for information flow and partial entropy production in a Brownian particle model of feedback cooling and extend them to arbitrary driven diffusion processes. We then analyze the long-time behavior of the feedback-cooling model in detail. Our results provide insights into the structure and origin of large deviations of information and thermodynamic quantities in autonomous Maxwell's demons.

  14. Forced engagement of a RNA/protein complex by a chemical inducer of dimerization to modulate gene expression

    NASA Astrophysics Data System (ADS)

    Harvey, Isabelle; Garneau, Philippe; Pelletier, Jerry

    2002-02-01

    A general strategy is described for forcing the engagement of an RNA/protein complex by using small-molecule ligands. A bivalent molecule was created by linking a protein-binding ligand to an RNA-binding ligand. On presentation of the chemical inducer of dimerization to the RNA by the protein, cooperative binding ensued, resulting in higher-affinity complexes. When the chemical inducer of dimerization was used to target the protein to an mRNA template, the resulting RNA/protein complex was sufficiently stable to inhibit mRNA translation. This approach provides a logic to modulate gene expression by using small-molecule ligands to recruit protein surfaces to mRNAs.

  15. Cofilin-induced unidirectional cooperative conformational changes in actin filaments revealed by high-speed atomic force microscopy

    PubMed Central

    Ngo, Kien Xuan; Kodera, Noriyuki; Katayama, Eisaku; Ando, Toshio; Uyeda, Taro QP

    2015-01-01

    High-speed atomic force microscopy was employed to observe structural changes in actin filaments induced by cofilin binding. Consistent with previous electron and fluorescence microscopic studies, cofilin formed clusters along actin filaments, where the filaments were 2-nm thicker and the helical pitch was ∼25% shorter, compared to control filaments. Interestingly, the shortened helical pitch was propagated to the neighboring bare zone on the pointed-end side of the cluster, while the pitch on the barbed-end side was similar to the control. Thus, cofilin clusters induce distinctively asymmetric conformational changes in filaments. Consistent with the idea that cofilin favors actin structures with a shorter helical pitch, cofilin clusters grew unidirectionally toward the pointed-end of the filament. Severing was often observed near the boundaries between bare zones and clusters, but not necessarily at the boundaries. DOI: http://dx.doi.org/10.7554/eLife.04806.001 PMID:25642645

  16. Current imaging and electromigration-induced splitting of GaN nanowires as revealed by conductive atomic force microscopy.

    PubMed

    Li, Chun; Bando, Yoshio; Golberg, Dmitri

    2010-04-27

    Current images of electromigration-induced common vapor-liquid-solid-grown GaN nanowires were obtained using a conductive atomic force microscope. Structural characterization indicated that these wurtzite (ZW) [0110] nanowires contained longitudinal zinc blende (ZB) defects as stacking faults. The current was attributed to tunneling current through the Schottky barrier between the AFM tip and a nanowire, which was dominated by the local nanowire surface work function. Due to the electromigration induced by large current densities around the defects, the axial splitting process of the nanowires was directly observed under continuous current scanning. The electromigration was likely enhanced by non-uniformly distributed electrostatic pressure around the axial ZW/ZB domain interfaces.

  17. Atomic vacancy-induced friction on the graphite surface: observation by lateral force microscopy.

    PubMed

    Paredes, J I; Martínez-Alonso, A; Tascón, J M D

    2003-05-01

    Lateral force microscopy has been employed to investigate the frictional behaviour of atomic vacancies on the graphite surface. Such a study was only made possible by the controlled expansion of originally single-atom vacancies into multiatom vacancies, employing oxygen plasma etching for this purpose. Enhanced friction was observed on the vacancy regions compared with pristine areas of graphite, the origin of which is examined and discussed.

  18. Steady dynein forces induce flutter instability and propagating waves in mathematical models of flagella.

    PubMed

    Bayly, P V; Dutcher, S K

    2016-10-01

    Cilia and flagella are highly conserved organelles that beat rhythmically with propulsive, oscillatory waveforms. The mechanism that produces these autonomous oscillations remains a mystery. It is widely believed that dynein activity must be dynamically regulated (switched on and off, or modulated) on opposite sides of the axoneme to produce oscillations. A variety of regulation mechanisms have been proposed based on feedback from mechanical deformation to dynein force. In this paper, we show that a much simpler interaction between dynein and the passive components of the axoneme can produce coordinated, propulsive oscillations. Steady, distributed axial forces, acting in opposite directions on coupled beams in viscous fluid, lead to dynamic structural instability and oscillatory, wave-like motion. This 'flutter' instability is a dynamic analogue to the well-known static instability, buckling. Flutter also occurs in slender beams subjected to tangential axial loads, in aircraft wings exposed to steady air flow and in flexible pipes conveying fluid. By analysis of the flagellar equations of motion and simulation of structural models of flagella, we demonstrate that dynein does not need to switch direction or inactivate to produce autonomous, propulsive oscillations, but must simply pull steadily above a critical threshold force.

  19. Temperature jump induced force generation in rabbit muscle fibres gets faster with shortening and shows a biphasic dependence on velocity.

    PubMed

    Ranatunga, K W; Roots, H; Offer, G W

    2010-02-01

    We examined the tension responses to ramp shortening and rapid temperature jump (<0.2 ms, 3-4 degrees C T-jump) in maximally Ca(2+)-activated rabbit psoas muscle fibres at 8-9 degrees C (the fibre length (L(0)) was approximately 1.5 mm and sarcomere length 2.5 microm). The aim was to investigate the strain sensitivity of crossbridge force generation in muscle. The T-jump induced tension rise was examined during steady shortening over a wide range of velocities (V) approaching the V(max) (V range approximately 0.01 to approximately 1.5 L(0) s(1)). In the isometric state, a T-jump induced a biphasic tension rise consisting of a fast (approximately 50 s(1), phase 2b) and a slow (approximately 10 s(1), phase 3) component, but if treated as monophasic the rate was approximately 20 s(1). During steady shortening the T-jump tension rise was monophasic; the rate of tension rise increased linearly with shortening velocity, and near V(max) it was approximately 200 s(1), approximately 10x faster than in the isometric state. Relative to the tension reached after the T-jump, the amplitude increased with shortening velocity, and near V(max) it was 4x larger than in the isometric state. Thus, the temperature sensitivity of muscle force is markedly increased with velocity during steady shortening, as found in steady state experiments. The rate of tension decline during ramp shortening also increased markedly with increase of velocity. The absolute amplitude of T-jump tension rise was larger than that in the isometric state at the low velocities (<0.5 L(0) s(1)) but decreased to below that of the isometric state at the higher velocities. Such a biphasic velocity dependence of the absolute amplitude of T-jump tension rise implies interplay between, at least, two processes that have opposing effects on the tension output as the shortening velocity is increased, probably enhancement of crossbridge force generation and faster (post-stroke) crossbridge detachment by negative strain

  20. Hydrodynamic fluctuations in thermostatted multiparticle collision dynamics.

    PubMed

    Híjar, Humberto; Sutmann, Godehard

    2011-04-01

    In this work we study the behavior of mesoscopic fluctuations of a fluid simulated by Multiparticle Collision Dynamics when this is applied together with a local thermostatting procedure that constrains the strength of temperature fluctuations. We consider procedures in which the thermostat interacts with the fluid at every simulation step as well as cases in which the thermostat is applied only at regular time intervals. Due to the application of the thermostat temperature fluctuations are forced to relax to equilibrium faster than they do in the nonthermostatted, constant-energy case. Depending on the interval of application of the thermostat, it is demonstrated that the thermodynamic state changes gradually from isothermal to adiabatic conditions. In order to exhibit this effect we compute from simulations diverse correlation functions of the hydrodynamic fluctuating fields. These correlation functions are compared with those predicted by a linearized hydrodynamic theory of a simple fluid in which a thermostat is applied locally. We find a good agreement between the model and the numerical results, which confirms that hydrodynamic fluctuations in Multiparticle Collision Dynamics in the presence of the thermostat have the properties expected for spontaneous fluctuations in fluids in contact with a heat reservoir.