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Sample records for fluctuation induced forces

  1. Physical origin of nonequilibrium fluctuation-induced forces in fluids.

    PubMed

    Kirkpatrick, T R; Ortiz de Zárate, J M; Sengers, J V

    2016-01-01

    Long-range thermal fluctuations appear in fluids in nonequilibrium states leading to fluctuation-induced Casimir-like forces. Two distinct mechanisms have been identified for the origin of the long-range nonequilibrium fluctuations in fluids subjected to a temperature or concentration gradient. One is a coupling between the heat or mass-diffusion mode with a viscous mode in fluids subjected to a temperature or concentration gradient. Another one is the spatial inhomogeneity of thermal noise in the presence of a gradient. We show that in fluids fluctuation-induced forces arising from mode coupling are several orders of magnitude larger than those from inhomogeneous noise.

  2. Constraints on stable equilibria with fluctuation-induced (Casimir) forces.

    PubMed

    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. PMID:20868024

  3. 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.

  4. Mechanical temporal fluctuation induced distance and force systematic errors in Casimir force experiments

    NASA Astrophysics Data System (ADS)

    Lamoreaux, Steve; Wong, Douglas

    2015-06-01

    The basic theory of temporal mechanical fluctuation induced systematic errors in Casimir force experiments is developed and applications of this theory to several experiments is reviewed. This class of systematic error enters in a manner similar to the usual surface roughness correction, but unlike the treatment of surface roughness for which an exact result requires an electromagnetic mode analysis, time dependent fluctuations can be treated exactly, assuming the fluctuation times are much longer than the zero point and thermal fluctuation correlation times of the electromagnetic field between the plates. An experimental method for measuring absolute distance with high bandwidth is also described and measurement data presented.

  5. Fluctuation-induced forces in a fluid membrane under tension

    NASA Astrophysics Data System (ADS)

    Zandi, Roya

    2012-02-01

    We develop an exact method to calculate thermal Casimir forces between inclusions of arbitrary shapes and separation, embedded in a fluid membrane whose fluctuations are governed by the combined action of surface tension, bending modulus, and Gaussian rigidity. Each object's shape and mechanical properties enter only through a characteristic matrix, a static analog of the scattering matrix. We calculate the Casimir interaction between two elastic disks embedded in a membrane. In particular, we find that at short separations the interaction is strong and independent of surface tension.

  6. 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.

  7. 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.

  8. 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.

  9. Force Fluctuations and Correlations

    NASA Astrophysics Data System (ADS)

    Behringer, Robert

    1998-03-01

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

  10. 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.

  11. Fluctuation-Induced Forces Between Inclusions in a Fluid Membrane Under Tension

    NASA Astrophysics Data System (ADS)

    Lin, Hsiang-Ku; Zandi, Roya; Mohideen, Umar; Pryadko, Leonid P.

    2011-11-01

    We develop an exact method to calculate thermal Casimir forces between inclusions of arbitrary shapes and separation, embedded in a fluid membrane whose fluctuations are governed by the combined action of surface tension, bending modulus, and Gaussian rigidity. Each object’s shape and mechanical properties enter only through a characteristic matrix, a static analog of the scattering matrix. We calculate the Casimir interaction between two elastic disks embedded in a membrane. In particular, we find that at short separations the interaction is strong and independent of surface tension.

  12. Fluctuation-induced forces between inclusions in a fluid membrane under tension.

    PubMed

    Lin, Hsiang-Ku; Zandi, Roya; Mohideen, Umar; Pryadko, Leonid P

    2011-11-25

    We develop an exact method to calculate thermal Casimir forces between inclusions of arbitrary shapes and separation, embedded in a fluid membrane whose fluctuations are governed by the combined action of surface tension, bending modulus, and Gaussian rigidity. Each object's shape and mechanical properties enter only through a characteristic matrix, a static analog of the scattering matrix. We calculate the Casimir interaction between two elastic disks embedded in a membrane. In particular, we find that at short separations the interaction is strong and independent of surface tension.

  13. Shear-induced force fluctuations and acoustic emissions in granular material

    NASA Astrophysics Data System (ADS)

    Michlmayr, Gernot; Cohen, Denis; Or, Dani

    2013-12-01

    We conducted a series of strain-controlled experiments to study the characteristics of a shear zone forming in dense flow of confined dry granular media. The primary objective was to link force fluctuations due to jamming and force network reformation with episodic release of elastic energy as passively monitored by acoustic emission sensors. Under constant deformation rate, the shear stress exhibits a characteristic sawtooth behavior reflecting the strong influence of micromechanical processes on the macroscopic stress-strain behavior. Measured shear stress jumps were highly correlated with low-frequency (< 20 kHz) acoustic emission events. High-frequency (30 kHz-80 kHz) acoustic signals that were measured with different sensors appear to be directly linked to continual grain-scale interactions (e.g., friction, rolling). A conceptual mechanical fiber bundle model (FBM) was used to represent dynamics at the shear zone of large granular assemblies. The model was capable of reproducing the dynamics of stress jumps and associated elastic energy release events. The combination of acoustic emission (AE) measurements and FBM framework offers new insights into the behavior of shear failure and enhances capabilities for resolving grain-scale mechanical processes and for predicting rapid mass movement such as shallow landslides and debris flows.

  14. 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.

  15. Force fluctuations assist nanopore unzipping of DNA

    NASA Astrophysics Data System (ADS)

    Viasnoff, V.; Chiaruttini, N.; Muzard, J.; Bockelmann, U.

    2010-11-01

    We experimentally study the statistical distributions and the voltage dependence of the unzipping time of 45 base-pair-long double-stranded DNA through a nanopore. We then propose a quantitative theoretical description considering the nanopore unzipping process as a random walk of the opening fork through the DNA sequence energy landscape biased by a time-fluctuating force. To achieve quantitative agreement fluctuations need to be correlated over the millisecond range and have an amplitude of order kBT/bp. Significantly slower or faster fluctuations are not appropriate, suggesting that the unzipping process is efficiently enhanced by noise in the kHz range. We further show that the unzipping time of short 15 base-pair hairpins does not always increase with the global stability of the double helix and we theoretically study the role of DNA elasticity on the conversion of the electrical bias into a mechanical unzipping force.

  16. 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.

  17. Force fluctuation in a semiflexible loop

    NASA Astrophysics Data System (ADS)

    Waters, James; Kim, Harold; Harold Kim Team

    DNA-binding proteins can regulate genetic expression by holding two sites in close proximity, forming a closed loop. Such complexes may require strong bending of DNA segments on the order of one persistence length or less. Both this elastic bending and the thermal fluctuations of the DNA molecule are necessary to describe the resulting behavior. To explore this problem, we consider a discrete model of a wormlike chain, kept in the fixed extension ensemble. By using a novel method to sample conformations in both position and momentum space, we can obtain a distribution of constraint forces as a function of chain length, extension, and flexibility. Our coarse-grained model allows us to explore the space of these parameters more efficiently than a detailed molecular dynamics approach. We find that increasing contour length decreases average force by relieving bending stress, but that the additional freedom allows fluctuations in the constraint force to increase. This implies that the probability of large forces may go up even as the mean goes down, impacting the lifetime of such bound states in a way unforeseen by purely equilibrium methods.

  18. Entropic Force and its Fluctuation in Euclidean Quantum Gravity

    NASA Astrophysics Data System (ADS)

    Zhao, Yue

    In this paper, we study the idea about gravity as entropic force proposed by Verlinde. By interpreting Euclidean gravity in the language of thermodynamic quantities on holographic screen, we find the gravitational force can be calculated from the change of entropy on the screen. We show that normal gravity calculation can be reinterpreted in the language of thermodynamic variables. We also study the fluctuation of the force and find the fluctuation acting on the point-like particle can never be larger than the expectation value of the force. For a black hole in AdS space, by gauge/gravity duality, the fluctuation may be interpreted as arising from thermal fluctuation in the boundary description. And for a black hole in flat space, the ratio between fluctuation and force goes to a constant (T)/(m) at infinity.

  19. Dynamics of intermittent force fluctuations in vesicular nanotubulation

    NASA Astrophysics Data System (ADS)

    Ashok, B.; Ananthakrishna, G.

    2014-11-01

    Irregular force fluctuations are seen in most nanotubulation experiments. The dynamics behind their presence has, however, been neither commented upon nor modeled. A simple estimate of the mean energy dissipated in force drops turns out to be several times the thermal energy. This coupled with the rate dependent nature of the deformation reported in several experiments point to a dynamical origin of the serrations. We simplify the whole process of tether formation through a three-stage model of successive deformations of sphere to ellipsoid, neck-formation, and tubule birth and extension. Based on this, we envisage a rate-softening frictional force at the neck that must be overcome before a nanotube can be pulled out. Our minimal model includes elastic and visco-elastic deformation of the vesicle, and has built-in dependence on pull velocity, vesicle radius, and other material parameters, enabling us to capture various kinds of serrated force-extension curves for different parameter choices. Serrations are predicted in the nanotubulation region. Other features of force-extension plots reported in the literature such as a plateauing serrated region beyond a force drop, serrated flow region with a small positive slope, an increase in the elastic threshold with pull velocity, force-extension curves for vesicles with larger radius lying lower than those for smaller radius, are all also predicted by the model. A toy model is introduced to demonstrate that the role of the friction law is limited to inducing stick-slip oscillations in the force, and all other qualitative and quantitative features emerging from the model can only be attributed to other physical mechanisms included in the deformation dynamics of the vesicle.

  20. 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. PMID:18554042

  1. Calculation of a fluctuating entropic force by phase space sampling.

    PubMed

    Waters, James T; Kim, Harold D

    2015-07-01

    A polymer chain pinned in space exerts a fluctuating force on the pin point in thermal equilibrium. The average of such fluctuating force is well understood from statistical mechanics as an entropic force, but little is known about the underlying force distribution. Here, we introduce two phase space sampling methods that can produce the equilibrium distribution of instantaneous forces exerted by a terminally pinned polymer. In these methods, both the positions and momenta of mass points representing a freely jointed chain are perturbed in accordance with the spatial constraints and the Boltzmann distribution of total energy. The constraint force for each conformation and momentum is calculated using Lagrangian dynamics. Using terminally pinned chains in space and on a surface, we show that the force distribution is highly asymmetric with both tensile and compressive forces. Most importantly, the mean of the distribution, which is equal to the entropic force, is not the most probable force even for long chains. Our work provides insights into the mechanistic origin of entropic forces, and an efficient computational tool for unbiased sampling of the phase space of a constrained system. PMID:26274308

  2. On the fluctuation induced mass enhancement

    NASA Astrophysics Data System (ADS)

    Van Hoa, Nguyen; Tuan, Vu Ngoc; Van Xuan, Le; Lan, Nguyen Tri; Viet, Nguyen Ai

    2016-06-01

    The effective mass induced by the background fluctuation on particles is considered. The analytical results show that the effective mass depends only on the properties of fluctuation, and takes non-zero value when and only when fluctuation mean value is non-zero. The possible applications of the obtained results to complex systems such as biology and ecology where environmental factors lead to the changes of the information exchange ranges from long to short one are discussed, i.e. the possibility of using physical modeling techniques to investigate macroscopic behaviors of some complex systems under consideration.

  3. Dislocation dynamical approach to force fluctuations in nanoindentation experiments

    NASA Astrophysics Data System (ADS)

    Ananthakrishna, G.; Katti, Rohit; K, Srikanth

    2014-09-01

    We develop an approach that combines the power of nonlinear dynamics with the evolution equations for the mobile and immobile dislocation densities and force to explain force fluctuations in nanoindentation experiments. The model includes nucleation, multiplication, and propagation thresholds for mobile dislocations, and other well known dislocation transformation mechanisms. The model predicts all the generic features of nanoindentation such as the Hertzian elastic branch followed by several force drops of decreasing magnitudes, and residual plasticity after unloading. The stress corresponding to the elastic force maximum is close to the yield stress of an ideal solid. The predicted values for all the quantities are close to those reported by experiments. Our model allows us to address the indentation-size effect including the ambiguity in defining the hardness in the force drop dominated regime. At large indentation depths, the hardness remains nearly constant with a marginal decreasing trend.

  4. 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

  5. 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.

  6. 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. PMID:26651796

  7. 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.

  8. 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.

  9. 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

  10. Traction force and tension fluctuations in growing axons

    PubMed Central

    Polackwich, Robert J.; Koch, Daniel; McAllister, Ryan; Geller, Herbert M.; Urbach, Jeffrey S.

    2015-01-01

    Actively generated mechanical forces play a central role in axon growth and guidance, but the mechanisms that underly force generation and regulation in growing axons remain poorly understood. We report measurements of 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 stress field from a reference frame that moves with it, we are able to show that there is a clear and consistent average stress field that underlies 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. Using high time-resolution measurements of the growth cone traction stresses, we show that the stress field is composed of fluctuating local stress peaks, with a large number peaks that live for a short time, a population of peaks whose lifetime distribution follows an exponential decay, and a small number of very long-lived peaks. We show that the high time-resolution data also reveal 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. PMID:26578882

  11. 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.

  12. Fluctuation-induced interactions in nematics with disordered anchoring energy.

    PubMed

    Haddadan, Fahimeh Karimi Pour; Naji, Ali; Shirzadiani, Nafiseh; Podgornik, Rudolf

    2014-12-17

    We examine fluctuation-induced (pseudo-Casimir) interactions in nematic liquid-crystalline films confined between two surfaces, where one of the surfaces imposes a strong homeotropic anchoring (ensuring a uniform mean director profile), while the other one is assumed to be a chemically disordered substrate exhibiting an annealed distribution of anchoring energies. We employ a saddle-point approximation to evaluate the free energy of interaction mediated between the two surfaces and investigate how the interaction force is influenced by the presence of disordered surface anchoring energy. It is shown that the disorder results in a renormalization of the effective surface anchoring parameter in a way that it leads to quantitative and qualitative changes (including a change of sign at intermediate inter-surface separations) in the pseudo-Casimir interaction force when compared with the interaction force in the absence of disorder.

  13. Quantum fluctuations of the optical forces on atoms in a squeezed vacuum

    NASA Astrophysics Data System (ADS)

    Shevy, Y.; Crosignani, B.; Yariv, A.

    1992-08-01

    Squeezing the vacuum fluctuations of the electromagnetic field modifies the quantum fluctuations of the optical forces exerted on laser-cooled two-level atoms. Under certain conditions, this modification when combined with the enhanced average forces can lead to equilibrium temperatures below those attained under normal-vacuum fluctuations.

  14. Forces and fluctuations in planar, spherical and tubular membranes

    NASA Astrophysics Data System (ADS)

    Barbetta, Camilla

    2010-11-01

    Lipid membranes constitute very particular materials: on the one hand, they break very easily under microscopical stretching; on the other hand, they are extremely flexible, presenting deformations even at small scales. Consequently, a piece of membrane has an area excess relative to its optically resolvable area, also called projected area. From a mechanical point of view, we can thus identify three tensions associated to lipid membranes: the mechanical effective tension τ, associated to an increase in the projected area and to the flattening of the fluctuations; the tension sigma, associated to the microscopical area of the membrane and thus non measurable, but commonly used in theoretical predictions; and its macroscopical counterpart measured through the fluctuation spectrum, r. Up to now, the equality between these quantities was taken for granted when analyzing experimental data. In this dissertation, we have studied, using the projected stress tensor, whether and under which conditions it is justified to assume τ = sigma. We studied three geometries (planar, spherical and cylindrical) and obtained the relation τ approx sigma - sigma_0, where sigma_0 is a constant depending only on the membrane's high frequency cutoff and on the temperature. Accordingly, we conclude that neglecting the difference between τ and sigma is justifiable only to membranes under large tensions: in the case of small tensions, corrections must be taken into account. We have studied the implications of this result to the interpretation of experiments involving membrane nanotubes. Regarding r, we have questioned a former demonstration concerning its equality with τ. Finally, the force fluctuation for planar membranes and membrane nanotubes was quantified for the first time.

  15. 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.

  16. 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.

  17. 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. PMID:24320286

  18. 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.

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

    NASA Astrophysics Data System (ADS)

    Rekker, A.; Mankin, R.

    2015-10-01

    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.

  20. 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.

  1. 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

  2. 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.

  3. Trapped Electron Precession Shear Induced Fluctuation Decorrelation

    SciTech Connect

    T.S. Hahm; P.H. Diamond; E.-J. Kim

    2002-07-29

    We consider the effects of trapped electron precession shear on the microturbulence. In a similar way the strong E x B shear reduces the radial correlation length of ambient fluctuations, the radial variation of the trapped electron precession frequency can reduce the radial correlation length of fluctuations associated with trapped electrons. In reversed shear plasmas, with the explicit dependence of the trapped electron precession shearing rate on B(subscript)theta, the sharp radial gradient of T(subscript)e due to local electron heating inside qmin can make the precession shearing mechanism more effective, and reduce the electron thermal transport constructing a positive feedback loop for the T(subscript)e barrier formation.

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

    PubMed

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

    2016-02-23

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

  5. 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.

  6. 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.

  7. Fluctuation-induced linewidth in oscillator FEL

    NASA Astrophysics Data System (ADS)

    Shevchenko, Oleg A.; Vinokurov, Nikolay A.

    2004-08-01

    Due to relatively small number of microscopic radiators, the noise (spontaneous emission contribution to the radiation field) level in free electron lasers (FELs) is much more than in other types of lasers. The influence of this noise on the FEL linewidth is considered. A low gain optical klystron model is used. It is shown that in the most of practically interesting cases the noise-induced linewidth is negligible.

  8. Temporal step fluctuations on a conductor surface: electromigration force, surface resistivity and low-frequency noise

    NASA Astrophysics Data System (ADS)

    Williams, E. D.; Bondarchuk, O.; Tao, C. G.; Yan, W.; Cullen, W. G.; Rous, P. J.; Bole, T.

    2007-10-01

    Scattering of charge carriers from surface structures will become an increasing factor in the resistivity as the structure decreases in size to the nanoscale. The effects of scattering at the most basic surface defect, a kink in a step edge, are here analyzed using the continuum step model. Using a Langevin analysis, it has been shown that the electromigration force on the atoms at the step edge causes changes in the temporal evolution of the step-edge. For an electromigration force acting perpendicular to the average step edge and mass-transport dominated by step-edge diffusion, significant deviations from the usual t1/4 scaling of the displacement correlation function occur dependent on a critical time τ and the direction of the force relative to the step edge (i.e. uphill or downhill). Experimental observations of step fluctuations on Ag(111) show the predicted changes among step fluctuations without current, and with current in the up- and down-hill directions for a current density of order 105 A cm-2. The results yield the magnitude of the electromigration force acting on kinked sites at the step-edge. This in turn yields the contribution of the fluctuating steps to the surface resistivity, which exceeds 1% of the bulk resistivity as wire diameters decrease below 10s of nanometres. The temporal fluctuations of kink density can thus also be related to resistivity noise. Relating the known fluctuation spectrum of the step displacements to fluctuations in their lengths, the corresponding resistivity noise is predicted to show spectral signatures of ~f-1/2 for step fluctuations governed by random attachment/detachment, and ~f-3/4 for step fluctuations governed by step-edge diffusion.

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

    PubMed

    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.

  10. 'Elastic' fluctuation-induced effects in smectic wetting films

    SciTech Connect

    Pikina, E. S.

    2009-11-15

    The Li-Kardar field theory approach is generalized to wetting smectic films and the 'elastic' fluctuation-induced interaction is obtained between the external flat bounding surface and distorted IA (isotropic liquid-smectic A) interface acting as an 'internal' (bulk) boundary of the wetting smectic film under the assumption that the IA interface is essentially 'softer' than the surface smectic layer. This field theory approach allows calculating the fluctuation-induced corrections in Hamiltonians of the so-called 'correlated' liquids confined by two surfaces, in the case where one of the bounding surfaces is 'rough' and with different types of surface smectic layer anchoring. We obtain that in practice, the account of thermal displacements of the smectic layers in a wetting smectic film reduces to the addition of two contributions to the IA interface Hamiltonian. The first, so-called local contribution describes the long-range thermal 'elastic' repulsion of the fluctuating IA interface from the flat bounding surface. The second, so-called nonlocal contribution is connected with the occurrence of an 'elastic' fluctuation-induced correction to the stiffness of the IA interface. An analytic expression for this correction is obtained.

  11. Endpoint force fluctuations reveal flexible rather than synergistic patterns of muscle cooperation.

    PubMed

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

    2008-11-01

    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.

  12. Characterization of speed fluctuation and drag force in young swimmers: a gender comparison.

    PubMed

    Barbosa, Tiago M; Costa, Mário J; Morais, Jorge E; Morouço, Pedro; Moreira, Marc; Garrido, Nuno D; Marinho, Daniel A; Silva, António J

    2013-12-01

    The aim of this study was to compare the speed fluctuation and the drag force in young swimmers between genders. Twenty-three young pubertal swimmers (12 boys and 11 girls) volunteered as subjects. Speed fluctuation was measured using a kinematical mechanical method (i.e., speedo-meter) during a maximal 25-m front crawl bout. Active drag, active drag coefficient and power needed to overcome drag were measured with the velocity perturbation method for another two maximal 25m front crawl bouts with and without the perturbation device. Passive drag and the passive drag coefficient were estimated using the gliding decay velocity method after a maximal push-off from the wall while being fully immersed. The technique drag index was also assessed as a ratio between active and passive drag. Boys presented meaningfully higher speed fluctuation, active drag, power needed to overcome drag and technique drag index than the girls. There were no significant gender differences for active drag coefficient, passive drag and passive drag coefficient. There were positive and moderate-strong associations between active drag and speed fluctuation when controlling the effects of swim velocity. So, increasing speed fluctuation leads to higher drag force values and those are even higher for boys than for girls.

  13. Measurement of magnetic fluctuation-induced particle flux (invited)

    SciTech Connect

    Ding, W. X.; Brower, D. L.; Yates, T. Y.

    2008-10-15

    Magnetic field fluctuation-induced particle transport has been directly measured in the high-temperature core of the MST reversed field pinch plasma. Measurement of radial particle transport is achieved by combining various interferometry techniques, including Faraday rotation, conventional interferometry, and differential interferometry. It is observed that electron convective particle flux and its divergence exhibit a significant increase during a sawtooth crash. In this paper, we describe the basic techniques employed to determine the particle flux.

  14. 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.

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

    PubMed

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

    2015-11-01

    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. PMID:26437575

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Large-eddy simulation - prediction of fluctuating lift and drag forces and comparison with experiment

    SciTech Connect

    Pruitt, J.M.; Hassan, Y.A. ); Steininger, D.A.

    1990-01-01

    Excessive tube vibration caused by turbulent flow buffeting and fluid-elastic excitation is one of the main problems associated with steam generators. Vibration can lead to rupture of tubes within the steam generator, necessitating plugging, and perhaps even replacement of the component. Turbulence buffeting, and resulting excitation, is believed to be one of the mechanisms leading to tube vibration. The large-eddy simulation (LES) technique is being considered as a possible design analysis tool for defining the temporally fluctuating forces on steam generator tube banks. The present investigation uses LES to calculate the flow field for an array of tubes subject to turbulent flow and to compare the fluctuating lift and drag forces on a central tube with experimental findings. Predictions to date using LES methodology compare quite favorably with experimental data.

  1. Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    We use atomic force microscopy to measure the distance-dependent solvation forces and the dissipation across liquid films of octamethylcyclotetrasiloxane (OMCTS) confined between a silicon tip and a highly oriented pyrolytic graphite substrate without active excitation of the cantilever. By analyzing the thermal bending fluctuations, we minimize possible nonlinearities of the tip-substrate interaction due to finite excitation amplitudes because these fluctuations are smaller than the typical 1 Å, which is much smaller than the characteristic interaction length. Moreover, we avoid the need to determine the phase lag between cantilever excitation and response, which suffers from complications due to hydrodynamic coupling between cantilever and fluid. Consistent results, and especially high-quality dissipation data, are obtained by analyzing the power spectrum and the time autocorrelation of the force fluctuations. We validate our approach by determining the bulk viscosity of OMCTS using tips with a radius of approximately 1 μm at tip-substrate separations >5 nm. For sharp tips we consistently find an exponentially decaying oscillatory tip-substrate interaction stiffness as well as a clearly nonmonotonic variation of the dissipation for tip-substrate distances up to 8 and 6 nm, respectively. Both observations are in line with the results of recent simulations which relate them to distance-dependent transitions of the molecular structure in the liquid.

  2. Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever.

    PubMed

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

    2013-06-01

    We use atomic force microscopy to measure the distance-dependent solvation forces and the dissipation across liquid films of octamethylcyclotetrasiloxane (OMCTS) confined between a silicon tip and a highly oriented pyrolytic graphite substrate without active excitation of the cantilever. By analyzing the thermal bending fluctuations, we minimize possible nonlinearities of the tip-substrate interaction due to finite excitation amplitudes because these fluctuations are smaller than the typical 1 Å, which is much smaller than the characteristic interaction length. Moreover, we avoid the need to determine the phase lag between cantilever excitation and response, which suffers from complications due to hydrodynamic coupling between cantilever and fluid. Consistent results, and especially high-quality dissipation data, are obtained by analyzing the power spectrum and the time autocorrelation of the force fluctuations. We validate our approach by determining the bulk viscosity of OMCTS using tips with a radius of approximately 1 μm at tip-substrate separations >5 nm. For sharp tips we consistently find an exponentially decaying oscillatory tip-substrate interaction stiffness as well as a clearly nonmonotonic variation of the dissipation for tip-substrate distances up to 8 and 6 nm, respectively. Both observations are in line with the results of recent simulations which relate them to distance-dependent transitions of the molecular structure in the liquid. PMID:23848696

  3. Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever.

    PubMed

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

    2013-06-01

    We use atomic force microscopy to measure the distance-dependent solvation forces and the dissipation across liquid films of octamethylcyclotetrasiloxane (OMCTS) confined between a silicon tip and a highly oriented pyrolytic graphite substrate without active excitation of the cantilever. By analyzing the thermal bending fluctuations, we minimize possible nonlinearities of the tip-substrate interaction due to finite excitation amplitudes because these fluctuations are smaller than the typical 1 Å, which is much smaller than the characteristic interaction length. Moreover, we avoid the need to determine the phase lag between cantilever excitation and response, which suffers from complications due to hydrodynamic coupling between cantilever and fluid. Consistent results, and especially high-quality dissipation data, are obtained by analyzing the power spectrum and the time autocorrelation of the force fluctuations. We validate our approach by determining the bulk viscosity of OMCTS using tips with a radius of approximately 1 μm at tip-substrate separations >5 nm. For sharp tips we consistently find an exponentially decaying oscillatory tip-substrate interaction stiffness as well as a clearly nonmonotonic variation of the dissipation for tip-substrate distances up to 8 and 6 nm, respectively. Both observations are in line with the results of recent simulations which relate them to distance-dependent transitions of the molecular structure in the liquid.

  4. 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.

  5. 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.

  6. Vibrational spectra from atomic fluctuations in dynamics simulations. II. Solvent-induced frequency fluctuations at femtosecond time resolution

    NASA Astrophysics Data System (ADS)

    Schmitz, Matthias; Tavan, Paul

    2004-12-01

    The midinfrared (MIR) spectra of molecules in polar solvents exhibit inhomogeneously broadened bands whose spectral positions are shifted as compared to the gas phase. The shifts are caused by interactions with structured solvation shells and the broadenings by fluctuations of these interactions. The MIR spectra can be calculated from hybrid molecular dynamics (MD) simulations, which treat the solute molecule by density functional theory and the solvent by molecular mechanics by the so-called instantaneous normal mode analysis (INMA) or by Fourier transforming the time correlation function (FTTCF) of the molecular dipole moment. In Paper I of this work [M. Schmitz and P. Tavan, J. Chem. Phys. 121, 12233 (2004)] we explored an alternative method based on generalized virial (GV) frequencies noting, however, that GV systematically underestimates frequencies. As shown by us these artifacts are caused by solvent-induced fluctuations of the (i) equilibrium geometry, (ii) force constants, and (iii) normal mode directions as well as by (iv) diagonal and (v) off-diagonal anharmonicities. Here we now show, by analyzing the time scales of fluctuations and sample MD trajectories of formaldehyde in the gas phase and in water, that all these sources of computational artifacts can be made visible by a Fourier analysis of the normal coordinates. Correspondingly, the error sources (i) and (iii)-(v) can be removed by bandpass filtering, as long as the spectral signatures of the respective effects are well separated from the fundamental band. Furthermore, the artifacts arising from effect (ii) can be strongly diminished by a time-resolved version of the GV approach (TF-GV). The TF-GV method then yields for each mode j a trajectory of the vibrational frequency ωj(t|τ) at a time resolution τ>τj, which is only limited by the corresponding oscillation time τj=2π/ωj and, thus, is in the femtosecond range. A correlation analysis of these trajectories clearly separates the

  7. 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.

  8. Force generation and step-size fluctuations in a dynein motor

    NASA Astrophysics Data System (ADS)

    Bameta, Tripti; Padinhateeri, Ranjith; Inamdar, Mandar M.

    2013-02-01

    Molecular motors such as dynein are known to move by taking steps of different sizes, depending on the load. Here, we develop a simple, discrete, minimal ratchet model for a motor that can take steps of sizes δ∘ and 2δ∘ in order to provide a bare-bones description of dynein. We obtain the force-velocity curves and diffusivity for this motor for different concentrations of ATP. We also study the mechano-chemical energy transduction and thermodynamic efficiency of the motor. Further, by investigating the statistics of step sizes for the motor, we show that the average step size and fluctuation in step sizes have a non-monotonic force dependence. We develop closed-form analytical expressions for all our results, which despite the simplicity of the model give a reasonable match with the known experiments and simulations on dynein.

  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. 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.

  11. Turbulence-induced pressure fluctuations in snow and their effect on heat and moisture transport

    NASA Astrophysics Data System (ADS)

    Huwald, H.; Higgins, C. W.; Drake, S.; Nolin, A. W.; Parlange, M. B.

    2010-12-01

    Accurate measurement of the heat and moisture flux components of the energy budget of a snow pack is difficult, and to date no generally satisfying solutions exist. In particular, little quantitative knowledge exists on heat and water vapor exchange associated to dynamically driven air movement in the snow pack as a consequence of atmospheric turbulence. This so-called wind-pumping constitutes a mechanism for forced release of saturated air form the snow pack and thus determines evaporation or sublimation rates from the snow and consequently affects the turbulent latent heat flux. A unique experiment and measurement system has been developed and deployed in the field to investigate and quantify the influence of atmospheric turbulence on heat and moisture transport across the snow-air interface. To this end, high-frequency measurements of 3-dimensional wind components, air temperature, and water vapor fluctuations above the snow surface were taken simultaneously together with differential air pressure fluctuations at several depths in the snow pack. The analysis addresses changes in frequency, amplitude, and penetration depth of the pressure fluctuations with depth, and the relationship of turbulence intensity to attenuation characteristics of the pressure within the snow pack. Finally, the study aims at understanding how turbulence-induced air pressure dynamics within the snow pack impacts on the heat budget of the snow pack and the turbulent sensible and latent heat flux above the snow surface.

  12. Entropy production for velocity-dependent macroscopic forces: The problem of dissipation without fluctuations

    NASA Astrophysics Data System (ADS)

    Cerino, L.; Puglisi, A.

    2015-08-01

    In macroscopic systems, velocity-dependent phenomenological forces F(v) are used to model friction, feedback devices or self-propulsion. Such forces usually include a dissipative component which conceals the fast energy exchanges with a thermostat at the environment temperature T, ruled by a microscopic Hamiltonian H. The mapping (H,T) \\to F(v) —even if effective for many purposes— may lead to applications of stochastic thermodynamics where an incomplete fluctuating entropy production (FEP) is derived. An enlighting example is offered by recent macroscopic experiments where dissipation is dominated by solid-on-solid friction, typically modelled through a deterministic Coulomb force F(v). Through an adaptation of the microscopic Prandtl-Tomlinson model for friction, we show how the FEP is dominated by the heat released to the T-thermostat, ignored by the macroscopic Coulomb model. This problem, which haunts several studies in the literature, cannot be cured by weighing the time-reversed trajectories with a different auxiliary dynamics: it is only solved by a more accurate stochastic modelling of the thermostat underlying dissipation.

  13. A fluctuation-induced plasma transport diagnostic based upon fast-Fourier transform spectral analysis

    NASA Technical Reports Server (NTRS)

    Powers, E. J.; Kim, Y. C.; Hong, J. Y.; Roth, J. R.; Krawczonek, W. M.

    1978-01-01

    A diagnostic, based on fast Fourier-transform spectral analysis techniques, that provides experimental insight into the relationship between the experimentally observable spectral characteristics of the fluctuations and the fluctuation-induced plasma transport is described. The model upon which the diagnostic technique is based and its experimental implementation is discussed. Some characteristic results obtained during the course of an experimental study of fluctuation-induced transport in the electric field dominated NASA Lewis bumpy torus plasma are presented.

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

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Yang, D.

    2014-12-01

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

  15. Competing-fluctuation-induced anomalous magnetocaloric effects in perovskite manganites

    NASA Astrophysics Data System (ADS)

    Sakai, Hideaki; Taguchi, Yasujiro; Tokura, Yoshinori

    2010-03-01

    A magnetocaloric (MC) effect refers to the isothermal entropy change induced by applying (or removing) a magnetic field to the materials, which is a performance index of the magnetic refrigeration technology. In this study, the variation of MC effects has been systematically investigated for colossal magnetoresistive manganites R0.6Sr0.4MnO3 (R=La-Gd) by controlling the R-dependent one-electron bandwidth. With decreasing the bandwidth, the temperature profile of entropy change exhibits a larger peak at the ferromagnetic transition temperature and a steeper drop below it, due to the first-order nature of the transition promoted by a competing charge-orbital ordering instability. For the smallest-bandwidth systems adjacent to the metal- insulator phase boundary, a rectangular-shaped profile for the entropy change emerges with an anomalously wide temperature range. Model calculations have indicated that the bicritical fluctuation enhanced in the phase-competing region has a strong impact on such MC features [1]. [1] H. Sakai et al., J. Phys. Soc. Jpn. 78, 113708 (2009).

  16. 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

  17. 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.

  18. Star polymers rupture induced by constant forces

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  19. 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. PMID:25362341

  20. Mean and fluctuating basal forces generated by granular flows: Laboratory observations in a large vertically rotating drum

    NASA Astrophysics Data System (ADS)

    Hsu, L.; Dietrich, W. E.; Sklar, L. S.

    2014-06-01

    A flowing granular mass generates forces on the boundary that drive near-bed grain dynamics, bed surface erosion, and energy dissipation. Few quantitative analyses exist of the controls on the dynamically fluctuating force caused by granular flows with wide-grain-size distributions and a liquid phase in the pores. To study the mechanisms controlling the boundary forces, we used a 225 cm2 load plate to measure the bed-normal force from a suite of granular flows in a 4 m diameter, 80 cm wide vertically rotating drum. We analyzed the time series of bed forces generated in flows composed of granular material for both narrow (gravel-water) and wide (muddy, sand-gravel-cobble) grain-size distributions. The tail of the force distribution was captured more closely by a generalized Pareto distribution than an exponential distribution, suggesting a way to predict empirically the force distribution. We show that the impulse on the bed, related to kinetic energy transferred to the bed from the granular collisions, is quantified by the standard deviation of the force. The mean bulk force equaled the static weight of the flow, whereas the force fluctuations, represented by the standard deviation and the averaged top 1% of force, were a near-linear function of effective grain diameter and flow velocity, and a ˜0.5 power function of an inertial stress scaling term. The force fluctuations depend on both Savage and Bagnold numbers. The correlations revealed in this study suggest that it may be possible to estimate dynamic forces on the bed from gross properties of the flows.

  1. Field Theoretical Investigation of Fluctuation-Induced Phenomena

    NASA Astrophysics Data System (ADS)

    Langsjoen, Luke Schell

    This thesis presents a field-theoretical investigation of the emergent properties of random fluctuations. We resolve a long-standing dilemma involving the ultraviolet divergences that often occur in Casimir calculations. We show that all formally divergent terms in the Casimir energy orgininate from geometrical properties of the boundary in question. Any material boundary will become transparent to sufficiently high-energy modes, and the formally divergent component of the energy is derived as an expansion in powers of this cutoff frequency. We demonstrate that the Casimir self-energy of a smooth boundary in two dimensions is a sum of two Weyl terms (exhibiting quadratic and logarithmic cutoff dependence), a geometrical term that is independent of the cutoff, and a non-geometrical intrinsic term. As by-products we resolve the puzzle of the divergent Casimir force on a ring and correct the sign of the coefficient of linear tension of a Dirichlet line predicted in earlier treatments. Next, we compute the generic mode sum that quantifies the effect on the spectrum of a harmonic field when a spherical shell is inserted into vacuum. We demonstrate that in the case of a scalar field obeying Dirichlet or Neumann boundary conditions on the shell surface the Casimir self-energy is cutoff-dependent while in the case of the electromagnetic field perturbed by a conductive shell the Casimir self-energy is universal. We also discuss generalized Casimir effects, for example an analog of the non-relativistic Casimir effect which can be realized in ferromagnets due to zero-point excitation of spin waves. We introduce a unique model for the Casimir effect of a boundary of finite thickness, with preliminary results. We present a calculation of the energy of N spinless non-interacting fermions confined to a one-dimensional interval. These results are shown to reinforce those obtained in the previous work of Kolomeisky et.al., [89]. Finally, we examine the classical Euler buckling

  2. Influence of dust charge fluctuation and polarization force on radiative condensation instability of magnetized gravitating dusty plasma

    NASA Astrophysics Data System (ADS)

    Prajapati, R. P.; Bhakta, S.

    2015-10-01

    The influence of dust charge fluctuation, thermal speed and polarization force due to massive charged dust grains is studied on the radiative condensation instability (RCI) of magnetized self-gravitating astrophysical dusty (complex) plasma. The dynamics of the charged dust and inertialess electrons are considered while the Boltzmann distributed ions are assumed to be thermal. The dusty fluid model is formulated and the general dispersion relations are derived analytically using the plane wave solutions under the long wavelength limits in both the presence and the absence of dust charge fluctuations. The combined effects of polarization force, dust thermal speed, dust charge fluctuation and dust cyclotron frequency are observed on the low frequency wave modes and radiative modified Jeans Instability. The classical criterion of RCI is also derived which remains unaffected due to the presence of these parameters. Numerical calculations have been performed to calculate the growth rate of the system and plotted graphically. We find that dust charge fluctuation, radiative cooling and polarization force have destabilizing while dust thermal speed and dust cyclotron frequency have stabilizing influence on the growth rate of Jeans instability. The results have been applied to understand the radiative cooling process in dusty molecular cloud when both the dust charging and polarization force are dominant.

  3. Direction reversal of fluctuation-induced biased Brownian motion on distorted ratchets.

    PubMed

    Yan, B; Miura, R M; Chen, Y D

    2001-05-21

    The biased movement of Brownian particles on a fluctuating two-state periodic potential made of identical distorted ratchets is studied. The purpose is to investigate how the direction of the particle movement is related to the asymmetry of the potential. In general, distorting one of the two linear arms of a regular symmetric ratchet (with equal arm lengths) can create a driving force for the Brownian particle to execute biased movement. The direction of the induced biased movement depends on the type of the distortion. It has been found that if one linear arm is kinked into two linear sub-arms, the direction of the movement can be either positive or negative depending on the frequency of the fluctuation and the location and the degree of the kink. In contrast, if one arm of the symmetric ratchet is replaced by a continuous nonlinear sinusoidal function, the movement is always unidirectional. Thus, for the latter case to generate the direction reversal phenomenon, the ratchets have to have an additional asymmetry. We also have found that two potentials with different distorted ratchets can generate identical fluxes if the distortions are polar symmetric about the mid-point of the arm(s) of the basic linear two-arm ratchet. The results are useful for designing experimental apparatuses for the separation of protein particles based on their sizes and charges and the viscosity of the medium.

  4. 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.

  5. Limits on cloud-induced fluctuation in photovoltaic generation

    SciTech Connect

    Jewell, W.T. ); Unruh, T.D. )

    1990-03-01

    When cloud shadows move across a photovoltaic (PV) array, the array's power output is reduced. It resumes full production when the shadow moves away. The utility must follow these changes with other types of generations. Under certain cloud conditions, the changes can be large and fast. A methodology is presented to assess the cost of such fluctuations and their effect on a utility's ability to serve its load. A case study is also presented.

  6. 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.

  7. Rotation shear induced fluctuation decorrelation in a toroidal plasma

    SciTech Connect

    Hahm, T.S.

    1994-06-01

    The enhanced decorrelation of fluctuations by the combined effects of the E {times} B flow (V{sub E}) shear, the parallel flow (V{sub {parallel}}) shear, and the magnetic shear is studied in toroidal geometry. A two-point nonlinear analysis previously utilized in a cylindrical model shows that the reduction of the radial correlation length below its ambient turbulence value ({Delta}r{sub 0}) is characterized by the ratio between the shearing rate {omega}{sub s} and the ambient turbulence scattering rate {Delta}{omega}{sub T}. The derived shearing rate is given by {omega}{sub s}{sup 2} = ({Delta}r{sub 0}){sup 2}[1/{Delta}{phi}{sup 2}{l_brace}{partial_derivative}/{partial_derivative}r(qV{sub E}/r){r_brace}{sup 2} + 1/{Delta}{eta}{sup 2}{l_brace}{partial_derivative}/{partial_derivative}r(V{parallel}/qR){r_brace}{sup 2}], where {Delta}{phi} and {Delta}{eta} are the correlation angles of the ambient turbulence along the toroidal and parallel directions. This result deviates significantly from the cylindrical result for high magnetic shear or for ballooning-like fluctuations. For suppression of flute-like fluctuations, only the radial shear of qV{sub E}/r contributes, and the radial shear of V{parallel}/qR is irrelevant regardless of the plasma rotation direction.

  8. 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

  9. 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.

  10. Measurements of ICRF wave-induced density fluctuations in LHD by a microwave reflectometer

    NASA Astrophysics Data System (ADS)

    Ejiri, A.; Tokuzawa, T.; Tsujii, N.; Saito, K.; Seki, T.; Kasahara, H.; Kamio, S.; Seki, R.; Mutoh, T.; Yamada, I.; Takase, Y.

    2015-12-01

    An O-mode microwave reflectometer has been developed to measure ICRF wave induced electron density fluctuations in LHD plasmas. The system has two probing frequencies (28.8 and 30.1 GHz) to measure two spatial points simultaneously. The rms density fluctuation levels are typically 0.01%. The linearity between the measured density fluctuation amplitude and the square root of the RF power is discussed. The decay length of the RF field was estimated to be 1 to 7 m under the operational condition investigated. A typical spatial distance between the two measurement points corresponding to the two probing frequencies is a few centimeters, and the fluctuation amplitudes at the two points are similar in amplitude. The phase difference between the two fluctuations show in-phase relationship on average. Out-of phase relationships, which implies a standing wave structure, are often observed when the wave absorption is expected to be poor.

  11. 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.

  12. Vibration-induced field fluctuations in a superconducting magnet

    NASA Astrophysics Data System (ADS)

    Britton, J. W.; Bohnet, J. G.; Sawyer, B. C.; Uys, H.; Biercuk, M. J.; Bollinger, J. J.

    2016-06-01

    Superconducting magnets enable precise control of nuclear and electron spins, and are used in experiments that explore biological and condensed-matter systems, and fundamental atomic particles. In high-precision applications, a common view is that slow (<1 Hz ) drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10-200 Hz) that limits the coherence time of Be+9 electron-spin qubits in the 4.46 -T field of a superconducting magnet. We measure a spin-echo T2 coherence time of ˜6 ms for the Be+9 electron-spin resonance at 124 GHz , limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved T2 to ˜50 ms.

  13. 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

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

    PubMed

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

    2015-06-01

    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 eight 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 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. 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).

  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. Drift- or fluctuation-induced ordering and self-organization in driven many-particle systems

    NASA Astrophysics Data System (ADS)

    Helbing, D.; Platkowski, T.

    2002-10-01

    According to empirical observations, some pattern formation phenomena in driven many-particle systems are more pronounced in the presence of a certain noise level. We investigate this phenomenon of fluctuation-driven ordering with a cellular-automaton model of interactive motion in space and find an optimal noise strength, while order breaks down at high(er) fluctuation levels. Additionally, we discuss the phenomenon of noise- and drift-induced self-organization in systems that would show disorder in the absence of fluctuations. In the future, related studies may have applications to the control of many-particle systems such as the efficient separation of particles. The rather general formulation of our model in the spirit of game theory may allow to shed some light on several different kinds of noise-induced ordering phenomena observed in physical, chemical, biological, and socio-economic systems (e.g., attractive and repulsive agglomeration, or segregation).

  19. Thermal fluctuations and stability of a particle levitated by a repulsive Casimir force in a liquid.

    PubMed

    Inui, Norio; Goto, Kosuke

    2013-11-01

    We study the vertical Brownian motion of a gold particle levitated by a repulsive Casimir force to a silica plate immersed in bromobenzene. The time evolution of the particle distribution starting from an equilibrium position, where the Casimir force and gravitational force are balanced, is considered by solving the Langevin equation using the Monte Carlo method. When the gold particle is very close to the silica plate, the Casimir force changes from repulsive to attractive, and the particle eventually sticks to the surface. The escape rate from a metastable position is calculated by solving the Fokker-Plank equation; it agrees with the value obtained by Kramers' escape theory. The duration of levitation increases as the particle radius increases up to around 2.3 μm. As an example, we show that a 1-μm-diameter gold particle can be levitated for a significantly long time by the repulsive Casimir force at room temperature.

  20. 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. PMID:26898313

  1. 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.

  2. 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

  3. 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. PMID:27626630

  4. Activation-induced force enhancement in human adductor pollicis.

    PubMed

    Oskouei, Ali E; Herzog, Walter

    2009-10-01

    It has been known for a long time that the steady-state isometric force after muscle stretch is bigger than the corresponding force obtained in a purely isometric contraction for electrically stimulated and maximal voluntary contractions (MVC). Recent studies using sub-maximal voluntary contractions showed that force enhancement only occurred in a sub-group of subjects suggesting that force enhancement for sub-maximal voluntary contractions has properties different from those of electrically-induced and maximal voluntary contractions. Specifically, force enhancement for sub-maximal voluntary contractions may contain an activation-dependent component that is independent of muscle stretching. To address this hypothesis, we tested for force enhancement using (i) sub-maximal electrically-induced contractions and stretch and (ii) using various activation levels preceding an isometric reference contraction at 30% of MVC (no stretch). All tests were performed on human adductor pollicis muscles. Force enhancement following stretching was found for all subjects (n=10) and all activation levels (10%, 30%, and 60% of MVC) for electrically-induced contractions. In contrast, force enhancement at 30% of MVC, preceded by 6s of 10%, 60%, and 100% of MVC was only found in a sub-set of the subjects and only for the 60% and 100% conditions. This result suggests that there is an activation-dependent force enhancement for some subjects for sub-maximal voluntary contractions. This activation-dependent force enhancement was always smaller than the stretch-induced force enhancement obtained at the corresponding activation levels. Active muscle stretching increased the force enhancement in all subjects, independent whether they showed activation dependence or not. It appears that post-activation potentiation, and the associated phosphorylation of the myosin light chains, might account for the stretch-independent force enhancement observed here.

  5. Fluctuation-induced noise in out-of-equilibrium disordered superconducting films

    NASA Astrophysics Data System (ADS)

    Petković, Aleksandra; Vinokur, Valerii M.

    2013-12-01

    We study out-of-equilibrium transport in disordered superconductors close to the superconducting transition. We consider a thin film connected by resistive tunnel interfaces to thermal reservoirs having different chemical potentials and temperatures. The nonequilibrium longitudinal current-current correlation function is calculated within the nonlinear sigma model description and nonlinear dependence on temperatures and chemical potentials is obtained. Different contributions are calculated, originating from the fluctuation-induced suppression of the quasiparticle density of states, Maki-Thompson and Aslamazov-Larkin processes. As a special case of our results, close-to-equilibrium we obtain the longitudinal ac conductivity using the fluctuation-dissipation theorem.

  6. Nonlinear fluctuations-induced rate equations for linear birth-death processes

    NASA Astrophysics Data System (ADS)

    Honkonen, J.

    2008-05-01

    The Fock-space approach to the solution of master equations for one-step Markov processes is reconsidered. It is shown that in birth-death processes with an absorbing state at the bottom of the occupation-number spectrum and occupation-number independent annihilation probability of occupation-number fluctuations give rise to rate equations drastically different from the polynomial form typical of birth-death processes. The fluctuation-induced rate equations with the characteristic exponential terms are derived for Mikhailov’s ecological model and Lanchester’s model of modern warfare.

  7. 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.

  8. Fluctuation Induced Structure in Chemical Reaction with Small Number of Molecules

    NASA Astrophysics Data System (ADS)

    Suzuki, Yasuhiro

    We investigate the behaviors of chemical reactions of the Lotka-Volterra model with small number of molecules; hence the occurrence of random fluctuations modifies the deterministic behavior and the law of mass action is replaced by a stochastic model. We model it by using Abstract Rewriting System on Multisets, ARMS; ARMS is a stochastic method of simulating chemical reactions and it is based on the reaction rate equation. We confirmed that the magnitude of fluctuations on periodicity of oscillations becomes large, as the number of involved molecules is getting smaller; and these fluctuations induce another structure, which have not observed in the reactions with large number of molecules. We show that the underling mechanism through investigating the coarse grained phase space of ARMS.

  9. 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.

  10. Detection of discrete surface charge dynamics in GaAs-based nanowire through metal-tip-induced current fluctuation

    NASA Astrophysics Data System (ADS)

    Sato, Masaki; Yin, Xiang; Kuroda, Ryota; Kasai, Seiya

    2016-02-01

    We investigated the detection of discrete charge dynamics of an electron trap in a GaAs-based nanowire surface through current fluctuation induced by a metallic scanning probe tip. An equivalent circuit model indicated that the charge state in the surface strongly reflects the channel potential when the local surface potential is fixed by the metal tip, which suggests that random charging and discharging dynamics of the trap appears as random telegraph signal (RTS) noise in the nanowire current. Experimental demonstration of the concept was carried out using a GaAs-based nanowire and an atomic force microscope (AFM) system with a conductive tip. We observed the RTS noise in the drain current and superposition of the Lorentzian component in the noise spectrum when the metal tip was in contact with the nanowire surface at specific positions. The obtained results indicate the possibility of detecting charge dynamics of the individual surface trap in semiconductor devices.

  11. Cardiac-induced physiologic noise in tissue is a direct observation of cardiac-induced fluctuations.

    PubMed

    Bhattacharyya, Pallab K; Lowe, Mark J

    2004-01-01

    Recent studies have shown that in certain cases, cardiac and respiratory rate fluctuations in BOLD-weighted MRI time courses may be an artifact unique to rapid sampled acquisitions and may not be present in longer repetition-time acquisitions. The implication of this is that, in these cases, cardiac and respiratory rate fluctuations are not aliased into data that undersample these effects and do not affect the resulting time course measurements. In this study, we show that these cases are specific to regions of large cerebrospinal fluid content and are not generally true for gray matter regions of the brain. We demonstrate that in many brain regions of interest, these fluctuations are directly observed as BOLD fluctuations and thus will affect measurements that undersample these effects.

  12. 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.

  13. 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.

  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 noise in out-of-equilibrium disordered superconducting films

    SciTech Connect

    Petković, Aleksandra; Vinokur, Valerii M.

    2013-12-15

    We study out-of-equilibrium transport in disordered superconductors close to the superconducting transition. We consider a thin film connected by resistive tunnel interfaces to thermal reservoirs having different chemical potentials and temperatures. The nonequilibrium longitudinal current–current correlation function is calculated within the nonlinear sigma model description and nonlinear dependence on temperatures and chemical potentials is obtained. Different contributions are calculated, originating from the fluctuation-induced suppression of the quasiparticle density of states, Maki–Thompson and Aslamazov–Larkin processes. As a special case of our results, close-to-equilibrium we obtain the longitudinal ac conductivity using the fluctuation–dissipation theorem. -- Highlights: •Contributions to the current noise induced by superconducting fluctuations are calculated. •Nonequilibrium physics is studied. •Nonlinear dependence of the noise on temperatures and chemical potentials of the reservoirs is found.

  16. 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.

  17. Valence state parameters of all transition metal atoms in metalloproteins--development of ABEEMσπ fluctuating charge force field.

    PubMed

    Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia

    2014-09-01

    To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy.

  18. 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

  19. 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

  20. 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.

  1. Analytical Solution for Subsurface Gas Flow to a Well Induced by Surface Pressure Fluctuations

    SciTech Connect

    Rossabi, J.

    2001-06-20

    A simple analytical model is presented for predicting subsurface gas flow to a vadose zone well in response to atmospheric pressure fluctuations (barometric pumping). The effective radial permeability (kr) in the vicinity of the well is determined during model calibration using less than two weeks of data. By combining the flow solution with a solution for the vertical gas pressure, only atmospheric pressure data are required to predict the induced flow through a well. The ability to quantitatively predict naturally induced flow in vadose zone wells by simple and inexpensive measurements is invaluable for systems using barometric pumping for remediation.

  2. Analytical solution for subsurface gas flow to a well induced by surface pressure fluctuations.

    PubMed

    Rossabi, Joseph; Falta, Ronald W

    2002-01-01

    A simple analytical model is presented for predicting subsurface gas flow to a vadose-zone well in response to atmospheric pressure fluctuations (barometric pumping). The effective radial permeability (kr) in the vicinity of the well is determined during model calibration using less than two weeks worth of data. By combining the flow solution with a solution for the vertical gas pressure, only atmospheric pressure data are required to predict the induced flow through a well. The ability to quantitatively predict naturally induced flow in vadose-zone wells by simple and inexpensive measurements is invaluable for systems using barometric pumping for remediation. PMID:11798048

  3. Force-induced tautomerization in a single molecule.

    PubMed

    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.

  4. 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. PMID:21797399

  5. Force-induced tautomerization in a single molecule.

    PubMed

    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. PMID:27657869

  6. 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.

  7. Photo-induced force for spectroscopic imaging at the nanoscale

    NASA Astrophysics Data System (ADS)

    Jahng, Junghoon; Tork Ladani, Faezeh; Khan, Ryan M.; Potma, Eric O.

    2016-03-01

    Photo-induced force microscopy (PiFM) is a new scan probe method that enables imaging with spectroscopic contrast at the nanoscale. The operating principle of PiFM is based on the coupling between a sharp atomic tip and a polarizable object, as mediated by the electromagnetic field in the vicinity of the tip-sample junction. In this contribution, we develop a description of the photo-induced force in the limit where the tip and object can be approximated as dipoles. This description provides an insightful picture of the forces at play in the tip-sample junction in terms of the gradient and scattering forces. We consider various approximations that are relevant to experimental conditions. The theoretical approach described here successfully explains the previous spectroscopic PiFM measurements in the visible and in the near-IR range, and the anticipated spectral information that can be retrieved under mid infrared illumination.

  8. Nonconservative current-induced forces: A physical interpretation.

    PubMed

    Todorov, Tchavdar N; Dundas, Daniel; Paxton, Anthony T; Horsfield, Andrew P

    2011-01-01

    We give a physical interpretation of the recently demonstrated nonconservative nature of interatomic forces in current-carrying nanostructures. We start from the analytical expression for the curl of these forces, and evaluate it for a point defect in a current-carrying system. We obtain a general definition of the capacity of electrical current flow to exert a nonconservative force, and thus do net work around closed paths, by a formal noninvasive test procedure. Second, we show that the gain in atomic kinetic energy over time, generated by nonconservative current-induced forces, is equivalent to the uncompensated stimulated emission of directional phonons. This connection with electron-phonon interactions quantifies explicitly the intuitive notion that nonconservative forces work by angular momentum transfer.

  9. Pressure induced by thermal fluctuation of an elastic filament confined within a narrow channel

    NASA Astrophysics Data System (ADS)

    Freund, L. B.

    2016-08-01

    Consider a flexible macro-molecule that is immersed in water at or above room temperature. As a result of thermal motion within the water, the filament is driven to undergo random fluctuations in shape. These fluctuations are a consequence of uncoordinated motion of water molecules. If the range of filament motion is restricted by nearby surfaces, the phenomenon becomes more complex. In this study, it is presumed that the filament is restricted to lie within a plane so that the motion is two dimensional. Furthermore, the range of the planar motion of the filament is confined to the region between inflexible straight boundaries lying in the plane of motion. A result of thermal fluctuation of the filament is that, when in close proximity to a boundary, a normal pressure is induced between the filament and that confining boundary. In the present development, frictional interaction of the filament with either confining boundary is presumed to be negligible. The goal is to determine the dependence of the induced pressure on the separation distance between the confining boundaries in terms of prevailing thermal conditions and physical characteristics of the system.

  10. Changes in Relative Thylakoid Protein Abundance Induced by Fluctuating Light in the Diatom Thalassiosira pseudonana.

    PubMed

    Grouneva, Irina; Muth-Pawlak, Dorota; Battchikova, Natalia; Aro, Eva-Mari

    2016-05-01

    One of the hallmarks of marine diatom biology is their ability to cope with rapid changes in light availability due to mixing of the water column and the lens effect. We investigated how irradiance fluctuations influence the relative abundance of key photosynthetic proteins in the centric diatom Thalassiosira pseudonana by means of mass-spectrometry-based approaches for relative protein quantitation. Most notably, fluctuating-light conditions lead to a substantial overall up-regulation of light-harvesting complex proteins as well as several subunits of photosystems II and I. Despite an initial delay in growth under FL, there were no indications of FL-induced photosynthesis limitation, in contrast to other photosynthetic organisms. Our findings further strengthen the notion that diatoms use a qualitatively different mechanism of photosynthetic regulation in which chloroplast-mitochondria interaction has overtaken crucial regulatory processes of photosynthetic light reactions that are typical for the survival of land plants, green algae, and cyanobacteria. PMID:27025989

  11. 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.

  12. 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.

  13. Flow-induced agitations create a granular fluid: Effective viscosity and fluctuations

    NASA Astrophysics Data System (ADS)

    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.

  14. 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.

  15. Interrelation between ball lightning and optically induced forces

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    Optically induced forces are considered as a key factor for explaining the phenomenon of ball lightning. They can provide not only the existence of ball lightning in the form of self-confined intense white light circulating in a spherical shell of air strongly compressed by the light but also the anomalous motion of ball lightning in the terrestrial atmosphere.

  16. Optical-force-induced artifacts in scanning probe microscopy.

    PubMed

    Kohlgraf-Owens, Dana C; Sukhov, Sergey; Dogariu, Aristide

    2011-12-15

    In the practice of near-field scanning probe microscopy, it is typically assumed that the distance regulation is independent of the optical signal. However, we demonstrate that these two signals are entangled due to the inherent action of optically induced force. This coupling leads to artifacts in both estimating the magnitude of optical fields and recording topographic maps.

  17. 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.

  18. 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.

  19. Force-Induced Rupture of a DNA Duplex: From Fundamentals to Force Sensors.

    PubMed

    Mosayebi, Majid; Louis, Ard A; Doye, Jonathan P K; Ouldridge, Thomas E

    2015-12-22

    The rupture of double-stranded DNA under stress is a key process in biophysics and nanotechnology. In this article, we consider the shear-induced rupture of short DNA duplexes, a system that has been given new importance by recently designed force sensors and nanotechnological devices. We argue that rupture must be understood as an activated process, where the duplex state is metastable and the strands will separate in a finite time that depends on the duplex length and the force applied. Thus, the critical shearing force required to rupture a duplex depends strongly on the time scale of observation. We use simple models of DNA to show that this approach naturally captures the observed dependence of the force required to rupture a duplex within a given time on duplex length. In particular, this critical force is zero for the shortest duplexes, before rising sharply and then plateauing in the long length limit. The prevailing approach, based on identifying when the presence of each additional base pair within the duplex is thermodynamically unfavorable rather than allowing for metastability, does not predict a time-scale-dependent critical force and does not naturally incorporate a critical force of zero for the shortest duplexes. We demonstrate that our findings have important consequences for the behavior of a new force-sensing nanodevice, which operates in a mixed mode that interpolates between shearing and unzipping. At a fixed time scale and duplex length, the critical force exhibits a sigmoidal dependence on the fraction of the duplex that is subject to shearing.

  20. 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.

  1. Evaluating effects of wind-induced pressure fluctuations on soil-atmosphere gas exchange at a landfill using stochastic modelling.

    PubMed

    Poulsen, Tjalfe G; Møldrup, Per

    2006-10-01

    The impact of wind turbulence-induced pressure fluctuations at the soil surface on landfill gas transport and emissions to the atmosphere at an old Danish landfill site was investigated using stochastic modelling combined with soil property and gas transport data measured at the site. The impacts of soil physical properties (including air permeability and volumetric water content) and wind-induced pressure fluctuation properties (amplitude and temporal correlation) on landfill gas emissions to the atmosphere were evaluated. Soil-air permeability and pressure fluctuation amplitude were found to be the most important parameters. Wind-induced gas emissions were further compared with gas emissions caused by diffusion and by long-term pressure variations (due to passing weather systems). Here diffusion and wind-induced gas transport were found to be equally important with wind-induced gas transport becoming the most important at lower soil-air contents.

  2. 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

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

    PubMed

    Ali, Olivier; Traas, Jan

    2016-05-01

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

  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. 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.

  6. 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.

  7. Fluctuations in central and peripheral temperatures induced by intravenous nicotine: central and peripheral contributions.

    PubMed

    Tang, Jeremy S; Kiyatkin, Eugene A

    2011-04-01

    Nicotine (NIC) is a highly addictive substance that interacts with different subtypes of nicotinic acetylcholine receptors widely distributed in the central and peripheral nervous systems. While the direct action of NIC on central neurons appears to be essential for its reinforcing properties, the role of peripheral actions of this drug remains a matter of controversy. In this study, we examined changes in locomotor activity and temperature fluctuations in the brain (nucleus accumbens and ventral tegmental area), temporal muscle, and skin induced by intravenous (iv) NIC at low human-relevant doses (10 and 30μg/kg) in freely moving rats. These effects were compared to those induced by social interaction, an arousing procedure that induces behavioral activation and temperature responses via pure neural mechanisms, and iv injections of a peripherally acting NIC analog, NIC pyrrolidine methiodide (NIC-PM) used at equimolar doses. We found that NIC at 30μg/kg induces a modest locomotor activation, rapid and strong decrease in skin temperature, and weak increases in brain and muscle temperature. While these effects were qualitatively similar to those induced by social interaction, they were much weaker and showed a tendency to increase with repeated drug administrations. In contrast, NIC-PM did not affect locomotion and induced much weaker than NIC increases in brain and muscle temperatures and decreases in skin temperature; these effects showed a tendency to be weaker with repeated drug administrations. Our data indicate that NIC's actions in the brain are essential to induce locomotor activation and brain and body hyperthermic responses. However, rapid peripheral action of NIC on sensory afferents could be an important factor in triggering its central effects, contributing to neural and physiological activation following repeated drug use. PMID:21295014

  8. Local force induced conical protrusions of phagocytic cells.

    PubMed

    Vonna, Laurent; Wiedemann, Agnès; Aepfelbacher, Martin; Sackmann, Erich

    2003-03-01

    Magnetic tweezers were used to study the passive and active response of macrophages to local centripetal nanonewton forces on beta1 integrins. Superparamagnetic beads coated with the beta1-integrin-binding protein invasin were attached to J774 murine macrophages to mimic phagocytosis of bacterial pathogens. Forces exceeding approximately 0.5 nN induce the active formation of trumpet-like protrusions resembling pseudopodia after an initial elastic deflection and a response time of approximately 30 seconds. The speed of advancement of the protrusion is =0.065+/-0.020 micro m second(-1) and is force independent. After saturation (after about 100 seconds) the protrusion stops abruptly and is completely retracted again against forces exceeding 5 nN with an effective relaxation time of approximately 30 seconds. The active protrusion is tentatively attributed to the growth of the actin cortex in the direction of the force, and evidence for the involvement of actin is provided by the finding that Latrunculin A abolishes the activated cone growth. The growth is assumed to be activated by cell signaling mediated by the invasin-specific integrins (exhibiting beta1 chains) and could play a role in phagocytic and protrusive events during immune response by macrophages. PMID:12571276

  9. Alluvial deposition and lake-level fluctuations forced by Late Quaternary climate change: the Dead Sea case example

    NASA Astrophysics Data System (ADS)

    Klinger, Y.; Avouac, J. P.; Bourles, D.; Tisnerat, N.

    2003-11-01

    Based on geomorphic observations, we discuss lake-level fluctuations, alluvial deposition and river entrenchment in the Dead Sea-Wadi Araba area. The bulk of alluvium in the northern Wadi Araba was probably deposited before the Lisan period of lake transgression that started at about 70 kyears B.P. The lake reached a maximum elevation about 150 m below sea level (b.s.l.), possibly around 15 cal. kyears B.P. as indicated by the highest preserved beach ridges. Cosmogenic exposure dates show that the ridge material consists mainly of remobilized Pleistocene gravel indicating little sediment supply during most of the Lisan period. During this period, a reduced sediment flux fed subaquatic fan deltas along the margin of the Dead Sea. Wetter conditions settled at the end of this period, the water level rose to about 280 m b.s.l. around 15 kyears B.P. and prevailed in the early Holocene (10.5-7 cal. kyears B.P.). Following that humid period, the lake level dropped and two major episodes of fluvial aggradation occurred during periods of relative low lake level. The first aggradational episode took place between about 7.0 and 6.2 cal. kyears B.P. Beach bars indicate a subsequent lake transgression between 6.2 and 4.4 kyears B.P. up to 350 m b.s.l. The second aggradational episode happened between 4.4 and 2.0 cal. kyears B.P., and was also followed by a late transgression up to 375 m b.s.l., dated to 1960-1715 cal. years B.P. The correlation between low lake level and fluvial aggradation is taken to reflect the synchronous change of the fluvial regime and of the lake hydrologic balance, forced by climate changes, rather than a base-level control. We also exclude large tectonic forcing on fan emplacement and river entrenchment. Alluviation appears in this setting as a very irregular process, characterized by long periods of quiescence alternating with periods of fan build-up, reflecting the transient response of the water drainage system to climate change.

  10. Ion-Specific Induced Fluctuations and Free Energetics of Aqueous Protein Hydrophobic Interfaces: Toward Connecting to Specific-Ion Behaviors at Aqueous Liquid–Vapor Interfaces

    PubMed Central

    2015-01-01

    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. B2010, 114, 1954−195820055377). 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. PMID:24701961

  11. Investigation of the static and dynamic fragmentation of metallic liquid sheets induced by random surface fluctuations

    NASA Astrophysics Data System (ADS)

    Durand, O.; Soulard, L.; Bourasseau, E.; Filippini, G.

    2016-07-01

    We perform molecular dynamics simulations to investigate the static and dynamic fragmentation of metallic liquid sheets of tin induced by random surface fluctuations. The static regime is analyzed by simulating sheets of different thicknesses, and the dynamic fragmentation is ensured by applying along the longitudinal direction of a sheet an instantaneous expansion velocity per initial unit length (expansion rate) with values ranging from 1 × 109 to 3 × 1010 s-1. The simulations show that the static/dynamic fragmentation becomes possible when the fluctuations of the upper and lower surfaces of the sheets can either overlap or make the local volume density of the system go down below a critical value. These two mechanisms cause locally in the sheet the random nucleation of pores of void, on a timescale that exponentially increases with the sheet thickness. Afterwards, the pores develop following distinct stages of growth, coalescence, and percolation, and later in time aggregates of liquid metal are formed. The simulations also show that the fragmentation of static sheets is characterized by relatively mono-dispersed surface and volume distributions of the pores and aggregates, respectively, whereas in extreme conditions of dynamic fragmentation (expansion rate typically in the range of 1 × 1010 s-1), the distributions are rather poly-dispersed and obey a power law decay with surface (volume). A model derived from the simulations suggests that both dynamic and static regimes of fragmentation are similar for expansion rates below typically 1 × 107 s-1.

  12. 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.

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

    SciTech Connect

    Hickey, M.P. )

    1988-05-01

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

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

    PubMed Central

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

    2014-01-01

    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. PMID:24686398

  15. Observation of fluctuation-induced tunneling conduction in micrometer-sized tunnel junctions

    NASA Astrophysics Data System (ADS)

    Lai, Yu-Ren; Yu, Kai-Fu; Lin, Yong-Han; Wu, Jong-Ching; Lin, Juhn-Jong

    2012-09-01

    Micrometer-sized Al/AlOx/Y tunnel junctions were fabricated by the electron-beam lithography technique. The thin (≈ 1.5-2 nm thickness) insulating AlOx layer was grown on top of the Al base electrode by O2 glow discharge. The zero-bias conductances G(T) and the current-voltage characteristics of the junctions were measured in a wide temperature range 1.5-300 K. In addition to the direct tunneling conduction mechanism observed in low-G junctions, high-G junctions reveal a distinct charge transport process which manifests the thermally fluctuation-induced tunneling conduction (FITC) through short nanoconstrictions. We ascribe the experimental realization of the FITC mechanism to originating from the formations of "hot spots" (incomplete pinholes) in the AlOx layer owing to large junction-barrier interfacial roughness.

  16. Two experimental tests of a fluctuation-induced first-order phase transition: intensity fluctuation microscopy at the nematic-smectic-A transition.

    PubMed

    Yethiraj, Anand; Mukhopadhyay, Ranjan; Bechhoefer, John

    2002-02-01

    We have developed a new, extremely sensitive real-space technique (intensity fluctuation microscopy) to probe the order of the nematic-smectic-A (NA) transition. Using this technique, we show that the NA transition in 4'-n-octyl-4-cyanobiphenyl (8CB) is clearly first order, contrary to calorimetric studies but in agreement with conclusions drawn from front-velocity measurements. We characterize the strength of the discontinuity at the first-order transition by the dimensionless quantity t(0)=(T(NA)-T*)/T(*). By precisely measuring t(0), we have made the first detailed tests of predictions based on the Halperin-Lubensky-Ma (HLM) theory of fluctuation-induced, first-order phase transitions. First, we explore the effect of an external magnetic field on the NA transition. Although modest fields (of order 10 T) are predicted to drive the weakly first-order transition in pure 8CB second order, we observe no such effect; we establish instead that the lower bound on this critical field is approximately 30 T. Likewise, we observe no effect in mixtures of 8CB with its longer chemical homolog 4'-n-decyl-4-cyanobiphenyl (10CB). Second, we examine the dependence of t(0) as a function of 8CB-10CB mixture concentration and find that the data in mixtures with small nematic temperature range are well-fit by the parameters derived by Anisimov et al. based on calorimetric measurements. As we increase the nematic range (by using concentrations closer to pure 8CB), the measured t(0) deviates more and more from the HLM predictions. Smectic fluctuations, which are neglected in the HLM calculation, are an obvious candidate to explain such a discrepancy, but one's naive expectation is that they would reduce t(0) below the HLM levels, whereas the observed values are too large. However, a recent renormalization-group calculation concludes that smectic fluctuations, surprisingly, should indeed increase t(0), explaining the observations presented here.

  17. Experimental investigation of impulsive magnetic reconnection induced by large amplitude electromagnetic fluctuations in the presence of a guide field

    NASA Astrophysics Data System (ADS)

    Kuwahata, Akihiro; Inomoto, Michiaki; Yanai, Ryoma; Ono, Yasushi

    2015-11-01

    Impulsive enhancement of magnetic reconnection is one of the potential candidates to invoke various explosive events observed in nature and laboratory plasmas. In TS-3 laboratory experiment with a guide field of Bguide /Brec = 1-2.5, impulsive growth of the reconnection electric field was observed just behind the onset of large-amplitude electromagnetic fluctuations (f = 1.5-2 fci and the amplitude was 0.1Brec). It was found that both the fluctuation amplitude and the enhanced reconnection electric field during the fluctuation period showed positive correlation with the guide field. The normalized reconnection rate of about 0.03 before the onset of fluctuations was reasonably comparable with the classical reconnection rate of Sweet-Parker model. However, the reconnection rate rose up to 0.11 after the fluctuations onset, suggesting that the transition from slow steady reconnection to fast impulsive reconnection took place. Since the fluctuation amplitude was so large that the nonlinear terms of the induced electric field was not negligible. The electric field enhancement due to the nonlinear contribution from the observed fluctuation was 650 V/m, which showed good agreement with the experimentally observed electric field increment of about 800 V/m.

  18. Polarizable force fields.

    PubMed

    Antila, Hanne S; Salonen, Emppu

    2013-01-01

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

  19. DNA fragmentation induced by ionizing radiation - Atomic Force Microscopy study .

    NASA Astrophysics Data System (ADS)

    Gudowska-Nowak, E.; Psonka, K.; Elsaesser, Th.; Brons, S.; Taucher-Scholz, G.

    DNA as a carrier of genetic information is considered to be the critical target for radiation induced damage Especially severe are DNA double-strand breaks DSBs formed when breaks occur in both strands of the molecule The DSBs production is determined by the spatial distribution of ionization events dependent on the physical properties of the energy deposition and the chemical environment of the DNA According to theoretical predictions high LET charged particle radiation induces lesions in close proximity forming so called clustered damage in the DNA Atomic Force Microscopy AFM was newly established as a technique allowing the direct visualization of DNA fragments resulting from DSBs induced in small DNA molecules plasmids by ionizing radiation We have used AFM to visualize the DNA fragmentation induced by heavy ions high LET radiation and to compare it to the fragmentation pattern obtained after X-rays low LET radiation Plasmid supercoiled DNA was irradiated in vitro with X-rays and 3 9 MeV u Ni ions within a dose range 0 -- 3000 Gy Afterwards the samples were analyzed using AFM which allowed the detection and length measurement of individual fragments with a nanometer resolution Recording of the length of the induced fragments allowed to distinguish between molecules broken by a single DSB or by multiple DSBs The fragment length distributions were derived for different doses and different radiation qualities The first results of the measurement of radiation-induced DNA fragmentation show an influence of radiation quality on

  20. 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.

  1. Deformation field of the soft substrate induced by capillary force

    NASA Astrophysics Data System (ADS)

    Liu, J. L.; Nie, Z. X.; Jiang, W. G.

    2009-05-01

    Prediction on the deformation of a soft substrate induced by capillary force has been widely paid attention in the broad range of applications, such as metallurgy, material science, astronavigation, micro/nano-technology, etc., which is also a supplementary result to the classical Young's equation. We quantitatively analyzed the deformation of an elastic substrate under capillary force by means of the energy principle and the continuum mechanics method. The actual drop's morphology was investigated and was compared with that calculated based on the classical spherical shape assumption of the droplet. The displacement field of the substrate was obtained, especially, its singularity at the droplet edge was also discussed. The results are beneficial to engineering application and micro/nano-measurement.

  2. 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.

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

    PubMed

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

    2015-03-01

    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. PMID:25793838

  4. 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

  5. Fluctuations in induced charge introduced by Te inclusions within CdZnTe radiation detectors

    SciTech Connect

    Bale, Derek S.

    2010-07-15

    Recently, homogenization theory based on a multiple-scale perturbation of the electron transport equation has been used to derive a mathematical framework for modeling the excess charge lost to Te inclusions within radiation detectors based on semi-insulating cadmium zinc telluride (CdZnTe). In that theory, the heterogeneous material is mathematically replaced by a homogenized CdZnTe crystal whose effective electron attenuation length incorporates the additional uniform electron trapping caused by the inclusions. In this paper, the homogenization theory is extended to incorporate fluctuations in the induced charge (i.e., charge collection nonuniformities) introduced by the random position and size distributions of a noncorrelated population of small (i.e, <20 {mu}m) Te inclusions. Analysis of the effective parameters derived within the homogenized framework is used to develop a probability distribution of effective electron attenuation lengths, and therefore effective mobility-lifetime products, as a function of both the position and size distribution of Te inclusions. Example distributions are detailed for the case of an exponential size distribution at various number densities. Further, it is demonstrated that the inclusion-induced material nonuniformities derived in this paper can be numerically sampled efficiently, making them applicable to Monte Carlo device simulation of realistic CdZnTe detectors. Simulated charge induction maps and pulse-height spectra are presented and compared to recently published measurements.

  6. 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.

  7. Experimental identification of pedestrian-induced lateral forces on footbridges

    NASA Astrophysics Data System (ADS)

    Ingólfsson, E. T.; Georgakis, C. T.; Ricciardelli, F.; Jönsson, J.

    2011-03-01

    This paper presents a comprehensive experimental analysis of lateral forces generated by single pedestrians during continuous walking on a treadmill. Two different conditions are investigated; initially the treadmill is fixed and then it is laterally driven in a sinusoidal motion at varying combinations of frequencies (0.33-1.07 Hz) and amplitudes (4.5-48 mm). The experimental campaign involved 71 male and female human adults and covered approximately 55 km of walking distributed between 4954 individual tests. When walking on a laterally moving surface, motion-induced forces develop at the frequency of the movement and are herewith quantified through equivalent velocity and acceleration proportional coefficients. Their dependency on the vibration frequency and amplitude is presented, both in terms of mean values and probabilistically to illustrate the randomness associated with intra- and inter-subject variability. It is shown that the motion-induced portion of the pedestrian load (on average) inputs energy into the structure in the frequency range (normalised by the mean walking frequency) between approximately 0.6 and 1.2. Furthermore, it is shown that the load component in phase with the acceleration of the treadmill depends on the frequency of the movement, such that pedestrians (on average) subtract from the overall modal mass for low frequency motion and add to the overall modal mass at higher frequencies.

  8. Dust Eruptions on Mars by Temperature Gradient Induced Forces

    NASA Astrophysics Data System (ADS)

    Kelling, Thorben; Wurm, G.; Reiss, D.; Kocifaj, M.; Klacka, J.; Teiser, J.

    2009-09-01

    Dust lifting processes on Mars are an active field of investigation. Explanations for dust phenomena even on high elevations on Mars have to be found. In general, wind stress is supposed to be the main lifting process but on average wind velocities are too low. We found, that temperature induced forces are capable of procuring dust ejections and even massive dust eruptions from a dust bed. A Mars soil simulant (JSC Mars 1A) was placed within a vacuum chamber which was evacuated to typical martian pressures of some mbar and particle ejections and eruptions were observed. Several different temperature gradient dependend lifting processes are at work. While e.g. photophoretic and thermophoretic forces only result in minor particle ejections, Knudsen Compressor effects cause continuous and major eruptions. These eruptions are even enhanced if a transition from illumination to no illumination occurs. We argue that the massive transition eruptions may be the dominant dust lifting process for e.g. dust devils. Moving dust devils, which are optically thick, induce a fast transition from light to shadow for the underlying dust bed. Even for lower initial radiation intensities, this will result in particle eruptions. As long as the wind eddy exists, dust devils on Mars may be self sustained even at low pressures or high altitudes. This work recieved support by the DFG and DAAD.

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  11. Fluctuations of visual awareness: Combining motion-induced blindness with binocular rivalry

    PubMed Central

    Jaworska, Katarzyna; Lages, Martin

    2014-01-01

    Binocular rivalry (BR) and motion-induced blindness (MIB) are two phenomena of visual awareness where perception alternates between multiple states despite constant retinal input. Both phenomena have been extensively studied, but the underlying processing remains unclear. It has been suggested that BR and MIB involve the same neural mechanism, but how the two phenomena compete for visual awareness in the same stimulus has not been systematically investigated. Here we introduce BR in a dichoptic stimulus display that can also elicit MIB and examine fluctuations of visual awareness over the course of each trial. Exploiting this paradigm we manipulated stimulus characteristics that are known to influence MIB and BR. In two experiments we found that effects on multistable percepts were incompatible with the idea of a common oscillator. The results suggest instead that local and global stimulus attributes can affect the dynamics of each percept differently. We conclude that the two phenomena of visual awareness share basic temporal characteristics but are most likely influenced by processing at different stages within the visual system. PMID:25240063

  12. Fluctuations of visual awareness: combining motion-induced blindness with binocular rivalry.

    PubMed

    Jaworska, Katarzyna; Lages, Martin

    2014-09-19

    Binocular rivalry (BR) and motion-induced blindness (MIB) are two phenomena of visual awareness where perception alternates between multiple states despite constant retinal input. Both phenomena have been extensively studied, but the underlying processing remains unclear. It has been suggested that BR and MIB involve the same neural mechanism, but how the two phenomena compete for visual awareness in the same stimulus has not been systematically investigated. Here we introduce BR in a dichoptic stimulus display that can also elicit MIB and examine fluctuations of visual awareness over the course of each trial. Exploiting this paradigm we manipulated stimulus characteristics that are known to influence MIB and BR. In two experiments we found that effects on multistable percepts were incompatible with the idea of a common oscillator. The results suggest instead that local and global stimulus attributes can affect the dynamics of each percept differently. We conclude that the two phenomena of visual awareness share basic temporal characteristics but are most likely influenced by processing at different stages within the visual system.

  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

    2015-01-01

    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

  14. 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.

  15. 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

  16. 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.

  17. Underwater sediment analyses by laser induced breakdown spectroscopy and calibration procedure for fluctuating plasma parameters

    NASA Astrophysics Data System (ADS)

    Lazic, V.; Colao, F.; Fantoni, R.; Spizzichino, V.; Jovićević, S.

    2007-01-01

    Laser Induced Breakdown Spectroscopy (LIBS) was applied on sediments directly under water. The aim of the research was to develop a method for measuring the sediment elemental composition, including minor elements, which could be implemented in-situ. The plasma was generated by a double-pulse, Q-Switched Nd:YAG laser operated at 1064 nm. For signal detection, both ICCD and non-gated, compact detectors were used. The major difficulties in underwater sediment analyses are related to the natural and laser induced surface roughness, and to the sample softness. The latter is responsible for the formation of particle clouds above the surface, which scatter both the laser and plasma radiation, and often results in breakdown formation above the analyzed surface. In such cases, a broad sonoluminescence emission from water, formed during the gas bubble collapse was sometimes registered. Under optimized experimental conditions, even by using a non-gated detector and single shot acquisition, it was possible to detect several minor sediment constituents, such as titanium, barium, manganese and others. A crude estimation of the Limit of Detection (LODs) for these elements was performed by underwater measurements on certified soils/sediments. Due to strong shot-to-shot fluctuations in the plasma temperature, well correlated calibration curves, aimed for quantitative analyses, could only be obtained after applying an appropriate data processing procedure. The latter selects automatically only the spectra characterized by similar plasma parameters, which are related to their continuum spectral distribution. Application of such a procedure improves the measurement accuracy also in other surroundings and on samples different from the ones analyzed here.

  18. 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.

  19. 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)

  20. 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.

  1. 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.

  2. 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

  3. Heterogeneity in (2-butoxyethanol + water) mixtures: Hydrophobicity-induced aggregation or criticality-driven concentration fluctuations?

    NASA Astrophysics Data System (ADS)

    Indra, Sandipa; Biswas, Ranjit

    2015-05-01

    Micro-heterogeneity in aqueous solutions of 2-butoxyethanol (BE), a system with closed loop miscibility gap, has been explored via absorption and time-resolved fluorescence measurements of a dissolved dipolar solute, coumarin 153 (C153), in the water-rich region at various BE mole fractions (0 ≤ XBE ≤ 0.25) in the temperature range, 278 ≤ T/K ≤ 320. Evidences for both alcohol-induced H-bond strengthening and subsequent structural transition of H-bond network have been observed. Analyses of steady state and time-resolved spectroscopic data for these aqueous mixtures and comparisons with the results for aqueous solutions of ethanol and tertiary butanol indicate that alcohol aggregation in BE/water mixtures is driven by hydrophobic interaction with no or insignificant role for criticality-driven concentration fluctuations preceding phase separation. Excitation energy dependence of fluorescence emission of C153 confirms formation of aggregated structures at very low BE mole fractions. No asymptotic critical power law dependence for relaxation rates of the type, k ∝ (|T - Tc|/Tc)γ, with γ denoting universal critical constant, has been observed for both solute's rotational relaxation and population relaxation rates in these mixtures upon either approaching to critical concentration or critical temperature. Estimated activation energies for rotational relaxation rate of C153 and solution viscosity have been found to follow each other with no abrupt changes in either of them at any mixture composition. In addition, measured C153 rotation times at various compositions and temperatures reflect near-hydrodynamic viscosity coupling through the dependence, <τr> ∝ (η/T)p, with p = 0.8-1.0, suggesting solute's orientational relaxation dynamics being, on an average, temporally homogeneous.

  4. 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.

  5. 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.

  6. Effect of self-induced magnetic force in a coronal loop transient

    NASA Technical Reports Server (NTRS)

    Yeh, T.; Dryer, M.

    1981-01-01

    The distribution of the self-induced magnetic force in a section of a model coronal loop is examined and it is found that an axial current produces a pointwise magnetic force in the direction toward the axis of the loop. The direction of the pointwise magnetic force indicates that the effect of this force, acting alone, is to cause a contraction of the cross section of the magnetic loop toward the axis, but not the translation motion of the loop as a whole. It is concluded that forces other than the self-induced magnetic force, such as thermal force of pressure gradient or extra-induced magnetic force of magnetic buoyancy, must be involved in the acceleration mechanisms for the heliocentrifugal motion of coronal transients.

  7. 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.

  8. An observational study of MHD wave-induced density fluctuations upstream of the earth's bow shock

    NASA Technical Reports Server (NTRS)

    Spangler, Steven; Fey, Alan; Anderson, Gregory; Fuselier, Stephen

    1988-01-01

    An investigation of plasma density fluctations upstream of the earth's bow shock and their association with MHD waves is reported. The normalized density fluctuation was 14 percent on a day when the plasma beta was less than unity and the waves were circularly polarized and of relatively low amplitude, and 17 percent on a day when the plasma beta was in excess of unity and the waves were elliptically polarized and of large fractional amplitude. On both days there was a feature of the density power spectrum at the MHD carrier wave frequency attributable to oblique propagation of the waves with propagation angles of a few degrees with respect to the mean field. Ponderomotive effects due to spatial gradient in the MHD wave energy density are proposed as responsible for a correlation betweeen density and transverse wave intensity on both days. Generation of density fluctuations by linear polarized MHD waves is not an important contributor to the observed density fluctuations.

  9. Thermally relativistic flows induced by gravitational-force-free particle motion in curved spacetime

    SciTech Connect

    Yano, Ryosuke; Suzuki, Kojiro; Kuroda, Hisayasu

    2009-12-15

    Thermally relativistic flows in the early Universe can be characterized by the emergence of flows induced by gravitational-force-free particle motion in curved spacetime as well as induced by the gravitational force. In this paper, thermally relativistic flows induced by gravitational-force-free particle motion in curved spacetime are discussed on the basis of the general relativistic Boltzmann equation. As an object of analysis, we consider the flow from the static state inside the Schwarzschild radius of a thermally relativistic stuffed black hole induced by such motion. Analytical results obtained using the collisionless, nongravitational general relativistic Boltzmann equation reveal that the initial cluster is induced by gravitational-force-free particle motion. Numerical results obtained using the nongravitational general relativistic Anderson-Witting model confirm the presence of an initial cluster inside the thermally relativistic stuffed black hole, which is induced by gravitational-force-free particle motion.

  10. 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. PMID:21668607

  11. 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

  12. 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

  13. Noise-Induced Hearing Loss in the Police Force

    PubMed Central

    Win, Kyaw N.; Balalla, Nayake B.P.; Lwin, Min Z.; Lai, Alice

    2015-01-01

    Background Noise-induced hearing loss (NIHL) is a major preventable occupational health problem with 250 million people worldwide known to have disabling impairment of moderate to greater severity. The aims of the study are to estimate the prevalence of NIHL in the police force; and study its association with age, sex, duration of service (years), smoking and alcohol habits, use of hearing protective devices, as well as preexisting chronic diseases. Methods A cross-sectional study was conducted on 543 police personnel who had undergone periodic medical examination over a 12-month period. The diagnostic criteria for NIHL were (1) history of occupational noise exposure, (2) bilateral hearing loss, (3) hearing loss of ≥ 25 dBA at 4,000 Hz in two consecutive audiograms, and (4) no significant medical history affecting hearing. Severity of NIHL was based on the World Health Organization grading. Results Males (74.8%) made up the majority of the police force. The mean age for police personnel was 35.55 ± 9.57 years, and the mean duration of service was 14.75 ± 9.39 years. Compliance with the usage of hearing protective devices was seen in 64.4%. The prevalence of NIHL in this study population was 34.2%, with a higher prevalence in males (37.7%) than in females (23.9%). The study also showed strong associations between NIHL and male sex (odds ratio, 1.9; P < 0.05), and hypertension (odds ratio, 3.3; P < 0.001). Overall, 93% were found to have mild NIHL, 3.5% had moderate NIHL, and 3.5% had severe NIHL. No police personnel were found to have profound hearing loss. Conclusion The prevalence of NIHL in this study is high compared to other similar studies among police personnel. This study shows that increasing age, male, presence of hypertension, diabetes, and longer duration of service are significant associated factors for NIHL. Preventative strategies include health surveillance, implementation of a hearing conservation program, and legislation. PMID

  14. 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.

  15. Fluctuation-induced dielectric permittivity in the isotropic phase of cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Mukherjee, Prabir K.; Das, Asok K.

    2016-03-01

    The temperature and pressure dependence of the static dielectric permittivity in the isotropic phase of the isotropic to cholesteric phase transition is calculated using Landau-de Gennes’s fluctuation theory, allowing spatial variation of the orientational order parameter. A comparison is made with experimental data available in the isotropic phase of the isotropic to cholesteric phase transition.

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

    PubMed Central

    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. PMID:25678749

  17. Discussion on sea level fluctuations along the Adriatic coasts coupling to climate indices forced by solar activity: Insights into the future of Venice

    NASA Astrophysics Data System (ADS)

    Zanchettin, Davide; Traverso, Pietro; Tomasino, Mario

    2006-04-01

    The North Atlantic Oscillation (NAO), which is a dominant circulation pattern in Northern Hemisphere winter, is known to affect sea-level variability in the Mediterranean Sea mainly through the hydrostatic response of water masses to pressure anomalies and changes in evaporation/precipitation budgets. In this study the influence of the NAO on sea levels along the Adriatic coasts is re-assessed in the attempt to uncover the potential causes of the observed high sensitivity of the northern basin to NAO fluctuations. The investigation is focused on the role of the NAO as forcing factor of the winds blowing in the area and of the freshwaters input from the Po River, both of which influence the hydrodynamics of the Northern Adriatic. In addition, some insights into the future of Venice are discussed on the basis of the hypothesis that NAO phases are modulated by the varying solar activity through the intensity of the Earth's geomagnetic activity.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  20. Rapid fluctuations in extracellular brain glucose levels induced by natural arousing stimuli and intravenous cocaine: fueling the brain during neural activation

    PubMed Central

    Lenoir, Magalie

    2012-01-01

    Glucose, a primary energetic substrate for neural activity, is continuously influenced by two opposing forces that tend to either decrease its extracellular levels due to enhanced utilization in neural cells or increase its levels due to entry from peripheral circulation via enhanced cerebral blood flow. How this balance is maintained under physiological conditions and changed during neural activation remains unclear. To clarify this issue, enzyme-based glucose sensors coupled with high-speed amperometry were used in freely moving rats to evaluate fluctuations in extracellular glucose levels induced by brief audio stimulus, tail pinch (TP), social interaction with another rat (SI), and intravenous cocaine (1 mg/kg). Measurements were performed in nucleus accumbens (NAcc) and substantia nigra pars reticulata (SNr), which drastically differ in neuronal activity. In NAcc, where most cells are powerfully excited after salient stimulation, glucose levels rapidly (latency 2–6 s) increased (30–70 μM or 6–14% over baseline) by all stimuli; the increase differed in magnitude and duration for each stimulus. In SNr, where most cells are transiently inhibited by salient stimuli, TP, SI, and cocaine induced a biphasic glucose response, with the initial decrease (−20–40 μM or 5–10% below baseline) followed by a reboundlike increase. The critical role of neuronal activity in mediating the initial glucose response was confirmed by monitoring glucose currents after local microinjections of glutamate (GLU) or procaine (PRO). While intra-NAcc injection of GLU transiently increased glucose levels in this structure, intra-SNr PRO injection resulted in rapid, transient decreases in SNr glucose. Therefore, extracellular glucose levels in the brain change very rapidly after physiological and pharmacological stimulation, the response is structure specific, and the pattern of neuronal activity appears to be a critical factor determining direction and magnitude of physiological

  1. 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.

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

    DOE PAGES

    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 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

  3. 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.

  4. 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.

  5. Precipitation-Induced Voltage-Dependent Ion Current Fluctuations in Conical Nanopores

    SciTech Connect

    Vlassiouk, Ivan V

    2010-01-01

    Single conically shaped nanopores produce stable ion current fluctuations when in contact with weakly soluble salts, such as calcium hydrogen phosphate (CaHPO{sub 4}) and cobalt hydrogen phosphate (CoHPO{sub 4}). The pore spontaneously switches between high and low conductance states, called open and closed states, respectively. Pore opening and closing are linked to the dynamic formation of the calcium and cobalt precipitates at the small opening of the pore. The probabilities of pore opening and closing are voltage-dependent, and this characteristic of ion current signal is known for biological voltage-gated channels. We show that new types of ion current fluctuations are obtained in conditions at which precipitates of CaHPO{sub 4} and CoHPO{sub 4} can form in the pore at the same time.

  6. Model for fluctuating inflaton coupling: sneutrino induced adiabatic perturbations and nonthermal leptogenesis.

    PubMed

    Mazumdar, Anupam

    2004-06-18

    We discuss a unique possibility of generating adiabatic density perturbations and leptogenesis from the spatial fluctuations of the inflaton decay rate. The key assumption is that the initial isocurvature perturbations are created in the right-handed sneutrino sector during inflation which is then converted into adiabatic perturbations when the inflaton decays. We discuss distinct imprints on the cosmic microwave background radiation, which can distinguish nonthermal versus thermal leptogenesis.

  7. 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.

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

    PubMed

    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.

  9. 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.

  10. 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.

  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. 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.

  13. Fluctuations and randomness of movement of the bead powered by a single kinesin molecule in a force-clamped motility assay: Monte Carlo simulations.

    PubMed

    Chen, Yi-der; Yan, Bo; Rubin, Robert J

    2002-11-01

    The motility assay of K. Visscher, M. J. Schnitzer, and S. M. Block (Nature, 400:184-189, 1999) in which the movement of a bead powered by a single kinesin motor can be measured is a very useful tool in characterizing the force-dependent steps of the mechanochemical cycle of kinesin motors, because in this assay the external force applied to the bead can be controlled (clamped) arbitrarily. However, because the bead is elastically attached to the motor and the response of the clamp is not fast enough to compensate the Brownian motion of the bead, interpretation or analysis of the data obtained from the assay is not trivial. In a recent paper (Y. Chen and B. Yan, Biophys. Chem. 91:79-91, 2001), we showed how to evaluate the mean velocity of the bead and the motor in the motility assay for a given mechanochemical cycle. In this paper we extend the study to the evaluation of the fluctuation or the randomness of the velocity using a Monte Carlo simulation method. Similar to the mean, we found that the randomness of the velocity of the motor is also influenced by the parameters that affect the dynamic behavior of the bead, such as the viscosity of the medium, the size of the bead, the stiffness of the elastic element connecting the bead and the motor, etc. The method presented in this paper should be useful in modeling the kinetic mechanism of any processive motor (such as conventional kinesin and myosin V) based on measured force-clamp motility data.

  14. Grip force adjustments induced by predictable load perturbations during a manipulative task.

    PubMed

    Serrien, D J; Kaluzny, P; Wicki, U; Wiesendanger, M

    1999-01-01

    The experiment examined the anticipatory modulation of grip force with respect to load force during a drawer opening task. An impact force was introduced by a mechanical stop that arrested movement of the pulling hand. The results showed a typical grip force profile which consisted of two evolving phases, one to control drawer movement onset, and the other to secure grip force at the expected impact. Initially, grip force increased with the load force that was developed to overcome the inertia of the drawer. After the first peak, a small decline was observed, followed by a proactive grip force increase prior to the time of impact. During this ramp-like increase of grip force, load force remained unchanged. In addition, a reactive response was triggered by the impact. That anticipatory control with respect to an impact force is not innate but, rather, is learned by experience was evidenced by a comparison of adults and children. Whereas adults made the characteristic grip force adjustments to anticipate the impact, children used a probing strategy with irregular build-up of force until impact. Furthermore, adults calibrated the second phase of the grip force profile in the initial trials of the task, indicating that grip force was rapidly updated with information related to the impact force. The present results demonstrate that grip-load force coordination during manipulation is a necessity for dealing with destabilizing load perturbations produced by self-induced movement and impact forces. It is concluded that grip force is adjusted automatically, but in a flexible manner, to secure grip in accordance with the characteristics of the pulling synergy. PMID:9928794

  15. 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.

  16. Impact of random discrete dopant in extension induced fluctuation in gate-source/drain underlap FinFET

    NASA Astrophysics Data System (ADS)

    Wang, Yijiao; Huang, Peng; Xin, Zheng; Zeng, Lang; Liu, Xiaoyan; Du, Gang; Kang, Jinfeng

    2014-01-01

    In this work, three dimensional technology computer-aided design (TCAD) simulations are performed to investigate the impact of random discrete dopant (RDD) including extension induced fluctuation in 14 nm silicon-on-insulator (SOI) gate-source/drain (G-S/D) underlap fin field effect transistor (FinFET). To fully understand the RDD impact in extension, RDD effect is evaluated in channel and extension separately and together. The statistical variability of FinFET performance parameters including threshold voltage (Vth), subthreshold slope (SS), drain induced barrier lowering (DIBL), drive current (Ion), and leakage current (Ioff) are analyzed. The results indicate that RDD in extension can lead to substantial variability, especially for SS, DIBL, and Ion and should be taken into account together with that in channel to get an accurate estimation on RDF. Meanwhile, higher doping concentration of extension region is suggested from the perspective of overall variability control.

  17. Barometric and tidal-induced aquifer water level fluctuation near the Ariake Sea.

    PubMed

    Dong, Linyao; Shimada, Jun; Kagabu, Makoto; Yang, Heejun

    2015-01-01

    Observations of water levels in coastal aquifers and corresponding tides coupled with meteorological variances near the Ariake Sea show that groundwater in this area mainly fluctuates with atmospheric and tidal variations. Tidal effects occur with semi-monthly, diurnal, or semi-diurnal periodicity, whereas the barometric influences commonly act in the low-frequency domain. Tidal and barometric effects in water levels are separable using wavelet techniques and can be evaluated statistically. Results show the following. (1) The tidal coefficients are 0.002-0.154, attenuating roughly exponentially from the seashore. The time lags in water levels increase linearly approximately with increasing inshore distance. Relations between tidal coefficients and time lags and the inshore distance indicate higher hydraulic diffusivity in the south aquifer, which was confirmed by the hydraulic property calibrations in analytical simulations. (2) Water levels related to meteorological phenomena fluctuate inversely according to barometric loading variation with time lags of 2-3 h. The effective barometric efficiencies are 0.022-0.12. Lower barometric influences were found in the south aquifer.

  18. Barometric and tidal-induced aquifer water level fluctuation near the Ariake Sea.

    PubMed

    Dong, Linyao; Shimada, Jun; Kagabu, Makoto; Yang, Heejun

    2015-01-01

    Observations of water levels in coastal aquifers and corresponding tides coupled with meteorological variances near the Ariake Sea show that groundwater in this area mainly fluctuates with atmospheric and tidal variations. Tidal effects occur with semi-monthly, diurnal, or semi-diurnal periodicity, whereas the barometric influences commonly act in the low-frequency domain. Tidal and barometric effects in water levels are separable using wavelet techniques and can be evaluated statistically. Results show the following. (1) The tidal coefficients are 0.002-0.154, attenuating roughly exponentially from the seashore. The time lags in water levels increase linearly approximately with increasing inshore distance. Relations between tidal coefficients and time lags and the inshore distance indicate higher hydraulic diffusivity in the south aquifer, which was confirmed by the hydraulic property calibrations in analytical simulations. (2) Water levels related to meteorological phenomena fluctuate inversely according to barometric loading variation with time lags of 2-3 h. The effective barometric efficiencies are 0.022-0.12. Lower barometric influences were found in the south aquifer. PMID:25467417

  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. 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.

  1. 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.

  2. 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. PMID:27154600

  3. Fluctuation theorem for a small engine and magnetization switching by spin torque.

    PubMed

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.

  4. Fluctuation Theorem for a Small Engine and Magnetization Switching by Spin Torque

    NASA Astrophysics Data System (ADS)

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.

  5. Fluctuation theorem for a small engine and magnetization switching by spin torque.

    PubMed

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem. PMID:26001013

  6. Radiation Force induced Liquid Flow within a Homogeneous Medium

    NASA Astrophysics Data System (ADS)

    Choi, Honggu; Joo, Boram; Jisung, Jeong; Oh, Kyunghwan; Yonsei Univ Collaboration

    2015-05-01

    The visualization of optical force required refractive index inhomogeneous boundary, or absorption to generate radiation pressure. However, the dilute liquid medium with low attenuation coefficient is affected by light carrying momentum, and generated flow. The optical force density within a dielectric medium oscillates, and their time averaged value was regarded as a vanishing parameter, however the existence of light carrying momentum within a dielectric media generates material momentum density and it results localized liquid flow. We used 980 nm fiber laser source guided along HI1060 single mode fiber which guides localized single mode Poynting vector, in order to generate effectively measureable radiation pressure during light propagation within deionized water. The micro beads with 2 micrometer diameter were deployed to visualize the flow and their location was out of beam to reject the effect of radiation pressure at the refractive index inhomogeneity between water and polymer beads.

  7. 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.

  8. 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

  9. 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. PMID:25669286

  10. 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.

  11. Transport reversals of chiral active particles induced by a perpendicular constant force

    NASA Astrophysics Data System (ADS)

    Wu, Jian-chun; Zhou, Jia-ning; Ai, Bao-quan

    2016-11-01

    Transport of chiral active particles in a symmetric periodic potential is investigated in the presence of a constant force. It is found that due to chirality of active particles the transversal constant force can break the symmetry of the system and induce a longitudinal net current. There exists an optimal constant force at which the rectification is maximal. Remarkably, longitudinal current reversals can occur by suitably tailoring the transversal constant force. Therefore, particles with different chiralities move to different directions and can be effectively separated.

  12. Chronic exposure to environmental stressors induces fluctuating asymmetry in shrews inhabiting protected Mediterranean sites.

    PubMed

    Sánchez-Chardi, Alejandro; García-Pando, Marián; López-Fuster, María José

    2013-10-01

    Many ecotoxicological studies have addressed the effects of contaminant exposure at various levels of biological organization. However, little information exists on the effects of toxicants on wildlife populations. Here we examined exposure of populations of the greater white-toothed shrew Crocidura russula (Soricomorpha, Soricidae) occupying two protected Mediterranean sites (a polluted area, the Ebro Delta, and a control site, Garraf Massif). Bioaccumulation of selected elements (Pb, Hg, Cd, Zn, Cu, Fe, Mn, Cr, Mo, Sr, Ba, and B), a body condition index (BCI) and fluctuating asymmetry (FA) were used to assess the chronic exposure to environmental pollution. BCI was correlated neither to metal concentrations nor to FA, suggesting that this fitness measure only reflects environmental disturbances at a local level. However, shrews from the polluted area showed higher concentrations of metals and metalloids (Pb, Hg, B, and Sr) and greater shape FA than specimens from the reference area. A correlation between FA was found for both first and second principal component vectors suggesting that developmental instability increases as a result of exposure to multiple pollutants. Our results corroborate the suitability of C. russula as a bioindicator of environmental quality and show that FA is an appropriate index to examine impact of developmental stressors in populations inhabiting disturbed areas.

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

    PubMed

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

    1998-07-01

    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

  14. 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.

  15. 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.

  16. 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.

  17. 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

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

    PubMed

    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

  19. Force-Induced Dynamical Properties of Multiple Cytoskeletal Filaments Are Distinct from that of Single Filaments

    PubMed Central

    Das, Dipjyoti; Das, Dibyendu; Padinhateeri, Ranjith

    2014-01-01

    How cytoskeletal filaments collectively undergo growth and shrinkage is an intriguing question. Collective properties of multiple bio-filaments (actin or microtubules) undergoing hydrolysis have not been studied extensively earlier within simple theoretical frameworks. In this paper, we study the collective dynamical properties of multiple filaments under force, and demonstrate the distinct properties of a multi-filament system in comparison to a single filament. Comparing stochastic simulation results with recent experimental data, we show that multi-filament collective catastrophes are slower than catastrophes of single filaments. Our study also shows further distinctions as follows: (i) force-dependence of the cap-size distribution of multiple filaments are quantitatively different from that of single filaments, (ii) the diffusion constant associated with the system length fluctuations is distinct for multiple filaments, and (iii) switching dynamics of multiple filaments between capped and uncapped states and the fluctuations therein are also distinct. We build a unified picture by establishing interconnections among all these collective phenomena. Additionally, we show that the collapse times during catastrophes can be sharp indicators of collective stall forces exceeding the additive contributions of single filaments. PMID:25531397

  20. 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.

  1. Destabilization induced by electropermeabilization analyzed by atomic force microscopy.

    PubMed

    Chopinet, Louise; Roduit, Charles; Rols, Marie-Pierre; Dague, Etienne

    2013-09-01

    Electropermeabilization is a physical method that uses electric field pulses to deliver molecules into cells and tissues. Despite its increasing interest in clinics, little is known about plasma membrane destabilization process occurring during electropermeabilization. In this work, we took advantage of atomic force microscopy to directly visualize the consequences of electropermeabilization in terms of membrane reorganization and to locally measure the membrane elasticity. We visualized transient rippling of membrane surface and measured a decrease in membrane elasticity by 40%. Our results obtained both on fixed and living CHO cells give evidence of an inner effect affecting the entire cell surface that may be related to cytoskeleton destabilization. Thus, AFM appears as a useful tool to investigate basic process of electroporation on living cells in absence of any staining or cell preparation.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

  3. 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.

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

    PubMed

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

    2015-11-21

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

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

    DOEpatents

    Bernitsas, Michael M.; Raghavan, Kamaldev

    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).

  6. Fluctuations in Brain Temperature Induced by Lypopolysaccharides: Central and Peripheral Contributions

    PubMed Central

    Tang, Jeremy S.; Kiyatkin, Eugene A.

    2010-01-01

    In this study, we examined changes in central (anterior-preoptic hypothalamus) and peripheral (temporal muscle and facial skin) temperatures in freely moving rats following intravenous administration of bacterial lipopolysaccharides (LPS) at low doses (1 and 10 μg/kg) at thermoneutral conditions (28°C). Recordings were made with high temporal resolution (5-s bin) and the effects of LPS were compared with those induced by a tail-pinch, a standard arousing somato-sensory stimulus. At each dose, LPS moderately elevated brain, muscle and skin temperatures. In contrast to rapid, monophasic and relatively short hyperthermic responses induced by a tail-pinch, LPS-induced increases in brain and muscle temperatures occurred with ~40 min onset latencies, showed three not clearly defined phases, were slightly larger with the 10 μm/kg dose and maintained for the entire 4-hour post-injection recording duration. Based on dynamics of brain-muscle and skin-muscle temperature differentials, it appears that the hyperthermic response induced by LPS at the lowest dose originates from enhanced peripheral heat production, with no evidence of brain metabolic activation and skin vasoconstriction. While peripheral heat production also appears to determine the first phase of brain and body temperature elevation with LPS at 10 μg/kg, a further prolonged increase in brain-muscle differentials (onset at ~100 min) suggests metabolic brain activation as a factor contributing to brain and body hyperthermia. At this dose, skin temperature increase was weaker than in temporal muscle, suggesting vasoconstriction as another contributor to brain/ body hyperthermia. Therefore, although both LPS at low doses and salient sensory stimuli moderately increase brain and body temperatures, these hyperthermic responses have important qualitative differences, reflecting unique underlying mechanisms. PMID:21150339

  7. Surface-induced weak orientational order and role of isotropic-nematic interface fluctuations in the appearance of an induced nematic film.

    PubMed

    Pikina, E; Rosenblatt, C

    2012-09-01

    Recently the nontrivial spatial and temperature dependence of the surface-induced weak planar orientational order parameter Q(z, T) was determined just above the isotropic-nematic (IN) phase transition point (Ji-H. Lee et al., Phys. Rev. Lett. 102, 167801 (2009)). In this paper we present a theoretical explanation of the observed behaviour. We obtain expressions for the short-range and long-range contributions to the interface potential of the induced nematic film and specify the repulsive character of the interaction between the soft IN interface and the external bounding substrate. It is shown that the small value of the IN interfacial tension results in the renormalization of the repulsive interaction potential due to the thermal fluctuations of the soft IN interface. This leads to an increase of the equilibrium thickness of the induced nematic film and the appearance of a step-like orientational order parameter profile. We find that only renormalized short-range and thermal pseudo-Casimir interactions are essential for the appearance of the induced nematic film, which provide the observed thickness, h ~ 30 nm, of this film. The long-range van der Waals interaction is shown to be negligibly small and the dominant role is played by the renormalized short-range repulsion. Fitting of the experimental order parameter profiles (Ji-H. Lee et al. (2009)) with the expressions based on these interactions makes it possible to determine the material parameters of the system, including the amplitudes of the surface interaction, the IN interfacial tension and the interfacial coherence length. The agreement between theory and experiment confirms the importance of the interface fluctuation renormalization of the interface potentials for soft interfaces.

  8. Centrifugal force induces human ligamentum flavum fibroblasts inflammation through activation of JNK and p38 pathways.

    PubMed

    Chao, Yuan-Hung; Tsuang, Yang-Hwei; Sun, Jui-Sheng; Sun, Man-Ger; Chen, Ming-Hong

    2012-01-01

    Inflammation has been proposed to be an important causative factor in ligamentum flavum hypertrophy. However, the mechanisms of mechanical load on inflammation of ligamentum flavum remain unclear. In this study, we used an in vitro model of human ligamentum flavum fibroblasts subjected to centrifugal force to elucidate the effects of mechanical load on cultured human ligamentum flavum fibroblasts; we further studied its molecular and biochemical mechanisms. Human ligamentum flavum fibroblasts were obtained from six patients undergoing lumbar spine surgery. Monolayer cultures of human ligamentum flavum fibroblasts were subjected to different magnitudes of centrifugal forces. Cell viability, cell death, biochemical response, and molecular response to centrifugal forces were analyzed. It was found that centrifugal stress significantly suppressed cell viability without inducing cell death. Centrifugal force at 67.1 g/cm(2) for 60 min significantly increases the production of prostaglandin E2 and nitric oxide as well as gene expression of proinflammatory cytokines, including interleukin (IL)-1α, IL-1β and IL-6, showed that centrifugal force-dependent induction of cyclooxygense-2 and inducible NO synthase required JNK and p38 mitogen-activated protein kinase, but not ERK 1/2 activities. This study suggested that centrifugal force does induce inflammatory responses in human ligamentum flavum fibroblasts. The activation of both JNK and p38 mitogen-activated protein kinase mechanotransduction cascades is a crucial intracellular mechanism that mediates cyclooxygense-2/prostaglandin E2 and inducible NO synthase/nitric oxide production.

  9. 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

  10. Centrifugal force induced by relativistically rotating spheroids and cylinders

    NASA Astrophysics Data System (ADS)

    Katz, Joseph; Lynden Bell, Donald; Bičák, Jiří

    2011-03-01

    Starting from the gravitational potential of a Newtonian spheroidal shell we discuss electrically charged rotating prolate spheroidal shells in the Maxwell theory. In particular we consider two confocal charged shells which rotate oppositely in such a way that there is no magnetic field outside the outer shell. In the Einstein theory we solve the Ernst equations in the region where the long prolate spheroids are almost cylindrical; in equatorial regions the exact Lewis 'rotating cylindrical' solution is so derived by a limiting procedure from a spatially bound system. In the second part we analyze two cylindrical shells rotating in opposite directions in such a way that the static Levi-Civita metric is produced outside and no angular momentum flux escapes to infinity. The rotation of the local inertial frames in flat space inside the inner cylinder is thus exhibited without any approximation or interpretational difficulties within this model. A test particle within the inner cylinder kept at rest with respect to axes that do not rotate as seen from infinity experiences a centrifugal force. Although in suitably chosen axes the spacetime there is exactly Minkowskian out to the inner cylinder, nevertheless, those inertial frame axes rotate with respect to infinity, so relative to the inertial frame inside the inner cylinder a test particle is traversing a circular orbit.

  11. Fluctuating pulse propagation in resonant nonlinear media: self-induced transparency random phase soliton formation.

    PubMed

    Mokhtarpour, Laleh; Ponomarenko, Sergey A

    2015-11-16

    We numerically investigate partially coherent short pulse propagation in nonlinear media near optical resonance. We examine how the pulse state of coherence at the source affects the evolution of the ensemble averaged intensity, mutual coherence function, and temporal degree of coherence of the pulse ensemble. We report evidence of self-induced transparency random phase soliton formation for the relatively coherent incident pulses with sufficiently large average areas. We also show that random pulses lose their coherence on propagation in resonant media and we explain this phenomenon in qualitative terms.

  12. Beat-induced fluctuations in auditory cortical beta-band activity: using EEG to measure age-related changes

    PubMed Central

    Cirelli, Laura K.; Bosnyak, Dan; Manning, Fiona C.; Spinelli, Christina; Marie, Céline; Fujioka, Takako; Ghahremani, Ayda; Trainor, Laurel J.

    2014-01-01

    People readily extract regularity in rhythmic auditory patterns, enabling prediction of the onset of the next beat. Recent magnetoencephalography (MEG) research suggests that such prediction is reflected by the entrainment of oscillatory networks in the brain to the tempo of the sequence. In particular, induced beta-band oscillatory activity from auditory cortex decreases after each beat onset and rebounds prior to the onset of the next beat across tempi in a predictive manner. The objective of the present study was to examine the development of such oscillatory activity by comparing electroencephalography (EEG) measures of beta-band fluctuations in 7-year-old children to adults. EEG was recorded while participants listened passively to isochronous tone sequences at three tempi (390, 585, and 780 ms for onset-to-onset interval). In adults, induced power in the high beta-band (20–25 Hz) decreased after each tone onset and rebounded prior to the onset of the next tone across tempo conditions, consistent with MEG findings. In children, a similar pattern was measured in the two slower tempo conditions, but was weaker in the fastest condition. The results indicate that the beta-band timing network works similarly in children, although there are age-related changes in consistency and the tempo range over which it operates. PMID:25071691

  13. Fluctuation-induced patterns and rapid evolution in predator-prey ecosystems

    NASA Astrophysics Data System (ADS)

    Goldenfeld, Nigel

    2014-03-01

    Predator-prey ecosystems exhibit noisy, persistent cycles that cannot be described by intuitive population-level differential equations such as the Lotka-Volterra equations. Traditionally this paradox has been met by including additional nonlinearities such as predator satiation to force limit cycle behavior. Over the last few years, it has been realized that individual-level descriptions, combined with systematic perturbation techniques can reproduce the key features of such systems in a minimal way, without requiring many additional assumptions or fine tunings. Here I review work in this area that uses these techniques to treat spatial patterns and the phenomenon of rapidly evolving prey sub-populations. In the latter case, I show how stochastic individual-level models reproduce the key features observed in chemostats and in the wild, including anomalous phase shifts between predator and prey species, evolutionary cycles and cryptic cycles. This work shows that stochastic individual-level models naturally describe systems where evolutionary time scales surprisingly match ecosystem time scales.

  14. 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.

  15. 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

  16. Imaging of shear waves induced by Lorentz force in soft tissues.

    PubMed

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

    2014-07-18

    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.

  17. Inducing forced and auto oscillations in one-dimensional photonic crystals with light

    NASA Astrophysics Data System (ADS)

    Lugo, J. E.; Doti, Rafael; Sanchez, Noemi; Faubert, Jocelyn

    2014-09-01

    We induced forced and auto oscillations in one-dimensional photonic crystals with localized defects when light impinges transversally to the defect layer. The photonic structure consists of a microcavity like structure formed of two onedimensional photonic crystals made of free-standing porous silicon, separated by variable air gap and the working wavelength is 633 nm. The force generation is made evident by driving a laser light by means of a chopper; the light hits the photonic structure and induces a vibration and the vibration is characterized by using a very sensitive vibrometer. Moreover we measured peak displacements and velocities ranging from 2 up to 35 microns and 0.4 up to 2.1 mm/s with a power of 13 mW. Recent evidence showed that giant resonant light forces could induce average velocity values of 0.45 mm/s in microspheres embedded in water with 43 mW light power.

  18. 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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27213399

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

    SciTech Connect

    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.

  1. Calculation of motion induced eddy current forces in null flux coils

    SciTech Connect

    Davey, K.; Morris, T.; Shaaf, J.; Rote, D.

    1995-11-01

    Time dependent motion induced eddy current forces can be quite difficult to compute. The movement of null flux coils between magnets is approached using a coupled boundary element-circuit approach to compute the forces on the structure. The technique involves treating the magnets as a separate circuit whose current is dictated by the product of the magnet thickness and the working coercivity. The mutual inductance between the windows of the moving null flux coil and the stationary equivalent magnet coil hold the key for predicting lift, guidance, and drag forces on the coil. The rate of change of these inductances with respect to position determines the forces and currents. A steady state approximation to these forces is derived in addition to a numerical simulation when the steady state assumption is invalid. The results compare favorably to laboratory results from a 4 ft. diameter experimental test wheel.

  2. Excited and enhanced twinborn acoustic-induced mutual forces in oblique grating structures

    NASA Astrophysics Data System (ADS)

    Lu, Shuifang; Zhang, Xin; Wu, Fugen; Yao, Yuanwei; Chen, Zongwang

    2016-07-01

    We propose a water-immersed geometrically oblique grating structure patterned with a 1D periodic array of oblique rhombuses. Twin acoustic-induced mutual forces (both repulsive and attractive) between coupled steel plates were realized in this system when the external plane wave normally impacted the plates. Calculations showed that the emerging forces are more than an order of magnitude larger than the corresponding induced force of a conventional grating structure. We also found that the strong acoustic-induced mutual forces stem from the resonant excitation of nonleaky flexural Lamb modes in the coupled plates, and that these forces couple more strongly with the external incident acoustic waves. Furthermore, the amplitudes and resonant wavelengths of these forces can be coarsely controlled by changing the symmetry of the system and finely adjusted by varying the slant angle and the edge-length of the oblique rhombus. The proposed acoustic system could potentially be applied in sensors and in the ultrasonic detection of weak signals in water.

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

    NASA Astrophysics Data System (ADS)

    Valentine, Megan; Yang, Yali; Bai, Mo; Klug, William; Levine, Alex

    2013-03-01

    We determine the viscoelastic responses of reconstituted networks of microtubules that have been strongly bonded by labile crosslinkers using 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, for rigidly crosslinked networks, the material 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 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.

  4. Experimental study on unsteady cloud cavity behaviour and induced pressure fluctuation in a convergent-divergent channel using simultaneous measurement technique

    NASA Astrophysics Data System (ADS)

    Chen, G. H.; Y Wang, G.; Huang, B.; Huang, X.; Gao, Y.

    2013-12-01

    To address the unsteady cavity behaviour and induced pressure fluctuation in cloud cavitating flow, cavitation images and pressure fluctuation signals are simultaneously acquired by high speed visualization system and 4 piezo-electric transducers in a convergent-divergent channel. The cavitation images are processed by using a home-developed software to obtain the time evolutions of global cavity area. Frequency analysis is conducted for both global cavity area and pressure signal. Bubble dynamics is introduced to analyze the correlation between pressure fluctuation in the downstream and global cavity behaviour. Two conclusions are achieved: First, in cloud cavitating flow, the time evolution of both the cavity behaviour and pressure fluctuation are quasi-periodic, one quasi-period can be divided into three main stages: growth of attached cavity, shedding of attached cavity, coalescence and collapse of detached cavity. Second, the dominant frequency of global cavity area and pressure fluctuation on 4 transducers are the same, it's 20Hz in this study. Third, it's found that during the stage of growth of attached cavity and growth, collapse of detached cavity, the correlation between global cavity area and induced pressure in the downstream is similar with that of a single bubble; while, such correlation is not clear when several travelling cavities exist at the same time.

  5. 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.

  6. Interplay between Solo and keratin filaments is crucial for mechanical force-induced stress fiber reinforcement.

    PubMed

    Fujiwara, Sachiko; Ohashi, Kazumasa; Mashiko, Toshiya; Kondo, Hiroshi; Mizuno, Kensaku

    2016-03-15

    Mechanical force-induced cytoskeletal reorganization is essential for cell and tissue remodeling and homeostasis; however, the underlying cellular mechanisms remain elusive. Solo (ARHGEF40) is a RhoA-targeting guanine nucleotide exchange factor (GEF) involved in cyclical stretch-induced human endothelial cell reorientation and convergent extension cell movement in zebrafish gastrula. In this study, we show that Solo binds to keratin-8/keratin-18 (K8/K18) intermediate filaments through multiple sites. Solo overexpression promotes the formation of thick actin stress fibers and keratin bundles, whereas knockdown of Solo, expression of a GEF-inactive mutant of Solo, or inhibition of ROCK suppresses stress fiber formation and leads to disorganized keratin networks, indicating that the Solo-RhoA-ROCK pathway serves to precisely organize keratin networks, as well as to promote stress fibers. Of importance, knockdown of Solo or K18 or overexpression of GEF-inactive or deletion mutants of Solo suppresses tensile force-induced stress fiber reinforcement. Furthermore, knockdown of Solo or K18 suppresses tensile force-induced RhoA activation. These results strongly suggest that the interplay between Solo and K8/K18 filaments plays a crucial role in tensile force-induced RhoA activation and consequent actin cytoskeletal reinforcement.

  7. 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.

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

    PubMed

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

    2014-11-01

    Distance measurements using double electron-electron resonance (DEER) and Gd(3+) chelates for spin labels (GdSL) have been shown to be an attractive alternative to nitroxide spin labels at W-band (95GHz). The maximal distance that can be accessed by DEER measurements and the sensitivity of such measurements strongly depends on the phase relaxation of Gd(3+) chelates in frozen, glassy solutions. In this work, we explore the phase relaxation of Gd(3+)-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

  9. 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

  10. 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.

  11. 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

  12. 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.

  13. 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.

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

    DOE PAGES

    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 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

  15. 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.

  16. 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

  17. Correction of the viscous drag induced errors in macromolecular manipulation experiments using atomic force microscope.

    PubMed

    Liu, Runcong; Roman, Marisa; Yang, Guoliang

    2010-06-01

    We describe a method to correct the errors induced by viscous drag on the cantilever in macromolecular manipulation experiments using the atomic force microscope. The cantilever experiences a viscous drag force in these experiments because of its motion relative to the surrounding liquid. This viscous force superimposes onto the force generated by the macromolecule under study, causing ambiguity in the experimental data. To remove this artifact, we analyzed the motions of the cantilever and the liquid in macromolecular manipulation experiments, and developed a novel model to treat the viscous drag on the cantilever as the superposition of the viscous force on a static cantilever in a moving liquid and that on a bending cantilever in a static liquid. The viscous force was measured under both conditions and the results were used to correct the viscous drag induced errors from the experimental data. The method will be useful for many other cantilever based techniques, especially when high viscosity and high cantilever speed are involved. PMID:20590242

  18. 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.

  19. Intrinsic spontaneous emission-induced fluctuations of the output optical beam power and phase in a diode amplifier

    NASA Astrophysics Data System (ADS)

    Bogatov, A. P.; Drakin, A. E.; D'yachkov, N. V.; Gushchik, T. I.

    2016-08-01

    Output optical beam intensity and phase fluctuations are analysed in a classical approach to describing the propagation and amplification of spontaneous emission in the active region of a laser diode with a gain saturated by input monochromatic light. We find their spectral densities and dispersion and the correlation coefficient of the two-dimensional probability distribution function of the fluctuations.

  20. Analysis of dynamic characteristics of fluid force induced by labyrinth seal

    NASA Technical Reports Server (NTRS)

    Iwatsubo, T.; Kawai, R.; Kagawa, N.; Kakiuchi, T.; Takahara, K.

    1984-01-01

    Flow patterns of the labyrinth seal are experimentally investigated for making a mathematical model of labyrinth seal and to obtain the flow induced force of the seal. First, the flow patterns in the labyrinth chamber are studied on the circumferential flow using bubble and on the cross section of the seal chamber using aluminum powder as tracers. And next, the fluid force and its phase angle are obtained from the measured pressure distribution in the chamber and the fluid force coefficients are derived from the fluid force and the phase angle. Those are similar to the expression of oil film coefficients. As a result, it is found that the vortices exist in the labyrinth chambers and its center moves up and down periodically. The pressure drop is biggest in the first stage of chambers and next in the last stage of chambers.

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

    PubMed Central

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

    2015-01-01

    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 Ca2+- and MgADP-activating solutions. Shortening in Ca2+-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. PMID:26037312

  2. 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.

  3. Measurements of laser phase fluctuations induced by atmospheric turbulence over 2 km and 17.5 km distances.

    PubMed

    Ridley, Kevin D

    2011-09-10

    A laser heterodyne system was used to measure the phase fluctuations imposed on a 1.5 μm wavelength laser beam when double-passed over long atmospheric paths. Two distances were used: 2 and 17.5 km. Results are given for intensity scintillation, phase fluctuation time series and spectra, and phase structure function. The results are found to agree well with theory: the spectrum of phase fluctuations follows the 8/3 power law predicted for Kolmogorov turbulence over 3 orders of magnitude in frequency. The methods reported here could be used to investigate large-scale temperature variations in the atmosphere. PMID:21946989

  4. Resonant-pattern formation induced by additive noise in periodically forced reaction-diffusion systems

    NASA Astrophysics Data System (ADS)

    Wang, Hongli; Zhang, Ke; Ouyang, Qi

    2006-09-01

    We report frequency-locked resonant patterns induced by additive noise in periodically forced reaction-diffusion Brusselator model. In the regime of 2:1 frequency-locking and homogeneous oscillation, the introduction of additive noise, which is colored in time and white in space, generates and sustains resonant patterns of hexagons, stripes, and labyrinths which oscillate at half of the forcing frequency. Both the noise strength and the correlation time control the pattern formation. The system transits from homogeneous to hexagons, stripes, and to labyrinths successively as the noise strength is adjusted. Good frequency-locked patterns are only sustained by the colored noise and a finite time correlation is necessary. At the limit of white noise with zero temporal correlation, irregular patterns which are only nearly resonant come out as the noise strength is adjusted. The phenomenon induced by colored noise in the forced reaction-diffusion system is demonstrated to correspond to noise-induced Turing instability in the corresponding forced complex Ginzburg-Landau equation.

  5. Resonant-pattern formation induced by additive noise in periodically forced reaction-diffusion systems.

    PubMed

    Wang, Hongli; Zhang, Ke; Ouyang, Qi

    2006-09-01

    We report frequency-locked resonant patterns induced by additive noise in periodically forced reaction-diffusion Brusselator model. In the regime of 2:1 frequency-locking and homogeneous oscillation, the introduction of additive noise, which is colored in time and white in space, generates and sustains resonant patterns of hexagons, stripes, and labyrinths which oscillate at half of the forcing frequency. Both the noise strength and the correlation time control the pattern formation. The system transits from homogeneous to hexagons, stripes, and to labyrinths successively as the noise strength is adjusted. Good frequency-locked patterns are only sustained by the colored noise and a finite time correlation is necessary. At the limit of white noise with zero temporal correlation, irregular patterns which are only nearly resonant come out as the noise strength is adjusted. The phenomenon induced by colored noise in the forced reaction-diffusion system is demonstrated to correspond to noise-induced Turing instability in the corresponding forced complex Ginzburg-Landau equation. PMID:17025732

  6. Phenotypic plasticity in growth and fecundity induced by strong population fluctuations affects reproductive traits of female fish.

    PubMed

    Karjalainen, Juha; Urpanen, Olli; Keskinen, Tapio; Huuskonen, Hannu; Sarvala, Jouko; Valkeajärvi, Pentti; Marjomäki, Timo J

    2016-02-01

    Fish are known for their high phenotypic plasticity in life-history traits in relation to environmental variability, and this is particularly pronounced among salmonids in the Northern Hemisphere. Resource limitation leads to trade-offs in phenotypic plasticity between life-history traits related to the reproduction, growth, and survival of individual fish, which have consequences for the age and size distributions of populations, as well as their dynamics and productivity. We studied the effect of plasticity in growth and fecundity of vendace females on their reproductive traits using a series of long-term incubation experiments. The wild parental fish originated from four separate populations with markedly different densities, and hence naturally induced differences in their growth and fecundity. The energy allocation to somatic tissues and eggs prior to spawning served as a proxy for total resource availability to individual females, and its effects on offspring survival and growth were analyzed. Vendace females allocated a rather constant proportion of available energy to eggs (per body mass) despite different growth patterns depending on the total resources in the different lakes; investment into eggs thus dictated the share remaining for growth. The energy allocation to eggs per mass was higher in young than in old spawners and the egg size and the relative fecundity differed between them: Young females produced more and smaller eggs and larvae than old spawners. In contrast to earlier observations of salmonids, a shortage of maternal food resources did not increase offspring size and survival. Vendace females in sparse populations with ample resources and high growth produced larger eggs and larvae. Vendace accommodate strong population fluctuations by their high plasticity in growth and fecundity, which affect their offspring size and consequently their recruitment and productivity, and account for their persistence and resilience in the face of high

  7. 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.

  8. Sensitivity of Granular Force Chain Orientation to Disorder-Induced Metastable Relaxation.

    PubMed

    Iikawa, N; Bandi, M M; Katsuragi, H

    2016-03-25

    A two-dimensional system of photoelastic disks subject to vertical tapping against gravity was experimentally monitored from ordered to disordered configurations by varying bidispersity. The packing fraction ϕ, coordination number Z, and an appropriately defined force-chain orientational order parameter S all exhibit as similar sharp transition with a small increase in disorder. A measurable change in S, but not ϕ and Z, was detected under tapping. We find disorder-induced metastability does not show configurational relaxation, but can be detected via force-chain reorientations.

  9. Quantitatively Resolving Ligand–Receptor Bonds on Cell Surfaces Using Force-Induced Remnant Magnetization Spectroscopy

    PubMed Central

    2016-01-01

    Molecule-specific noncovalent bonding on cell surfaces is the foundation for cellular recognition and functioning. A major challenge in probing these bonds is to resolve the specific bonds quantitatively and efficiently from the nonspecific interactions in a complex environment. Using force-induced remnant magnetization spectroscopy (FIRMS), we were able to resolve quantitatively three different interactions for magnetic beads bearing anti-CD4 antibodies with CD4+ T cell surfaces based upon their binding forces. The binding force of the CD4 antibody–antigen bonds was determined to be 75 ± 3 pN. For comparison, the same bonds were also studied on a functionalized substrate surface, and the binding force was determined to be 90 ± 6 pN. The 15 pN difference revealed by high-resolution FIRMS illustrates the significant impact of the bonding environment. Because the force difference was unaffected by the cell number or the receptor density on the substrate, we attributed it to the possible conformational or local environmental differences of the CD4 antigens between the cell surface and substrate surface. Our results show that the high force resolution and detection efficiency afforded by FIRMS are valuable for studying protein–protein interactions on cell surfaces. PMID:27163031

  10. Optomechanically induced transparency in the presence of an external time-harmonic-driving force

    NASA Astrophysics Data System (ADS)

    Ma, Jinyong; You, Cai; Si, Liu-Gang; Xiong, Hao; Li, Jiahua; Yang, Xiaoxue; Wu, Ying

    2015-06-01

    We propose a potentially valuable scheme to measure the properties of an external time-harmonic-driving force with frequency ω via investigating its interaction with the combination of a pump field and a probe field in a generic optomechanical system. We show that the spectra of both the cavity field and output field in the configuration of optomechanically induced transparency are greatly modified by such an external force, leading to many interesting linear and non-linear effects, such as the asymmetric structure of absorption in the frequency domain and the antisymmetry breaking of dispersion near ω = ωm. Furthermore, we find that our scheme can be used to measure the initial phase of the external force. More importantly, this setup may eliminate the negative impact of thermal noise on the measurement of the weak external force in virtue of the process of interference between the probe field and the external force. Finally, we show that our configuration can be employed to improve the measurement resolution of the radiation force produced by a weak ultrasonic wave.

  11. Optomechanically induced transparency in the presence of an external time-harmonic-driving force

    PubMed Central

    Ma, Jinyong; You, Cai; Si, Liu-Gang; Xiong, Hao; Li, Jiahua; Yang, Xiaoxue; Wu, Ying

    2015-01-01

    We propose a potentially valuable scheme to measure the properties of an external time-harmonic-driving force with frequency ω via investigating its interaction with the combination of a pump field and a probe field in a generic optomechanical system. We show that the spectra of both the cavity field and output field in the configuration of optomechanically induced transparency are greatly modified by such an external force, leading to many interesting linear and non-linear effects, such as the asymmetric structure of absorption in the frequency domain and the antisymmetry breaking of dispersion near ω = ωm. Furthermore, we find that our scheme can be used to measure the initial phase of the external force. More importantly, this setup may eliminate the negative impact of thermal noise on the measurement of the weak external force in virtue of the process of interference between the probe field and the external force. Finally, we show that our configuration can be employed to improve the measurement resolution of the radiation force produced by a weak ultrasonic wave. PMID:26062029

  12. 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.

  13. Dielectrophoretic forces and potentials induced on pairs of cells in an electric field.

    PubMed

    Foster, K R; Sowers, A E

    1995-09-01

    A combined numerical/experimental study is reported of the membrane potentials and dielectrophoretically induced forces between cells, membrane pressures, and velocity of attraction of cells under the influence of an electric field. This study was designed to explore electrical and mechanical effects produced by a field on cells in close proximity or undergoing electrically induced fusion. Laplace's equation for pairs of membrane-covered spheres in close proximity was solved numerically by the boundary element method, and the electrically induced forces on the cells and between cells were obtained by evaluating the Maxwell stress tensor. The velocity of approach of erythrocyte ghosts or fused ghosts in a 60-Hz field of 6 V/mm was measured experimentally, and the data were interpreted by using Batchelor's theory for hydrodynamic interaction of hard spheres. The numerical results show clearly the origin of the dielectrophoretic pressures and forces in fused and unfused cells and the effects of a nearby cell on the induced membrane potentials. The experimental results agree well with predictions based on the simple electrical model of the cell. The analysis shows the strong effect of hydrodynamic interactions between the cells in determining their velocity of approach. PMID:8519978

  14. Dielectrophoretic forces and potentials induced on pairs of cells in an electric field.

    PubMed Central

    Foster, K R; Sowers, A E

    1995-01-01

    A combined numerical/experimental study is reported of the membrane potentials and dielectrophoretically induced forces between cells, membrane pressures, and velocity of attraction of cells under the influence of an electric field. This study was designed to explore electrical and mechanical effects produced by a field on cells in close proximity or undergoing electrically induced fusion. Laplace's equation for pairs of membrane-covered spheres in close proximity was solved numerically by the boundary element method, and the electrically induced forces on the cells and between cells were obtained by evaluating the Maxwell stress tensor. The velocity of approach of erythrocyte ghosts or fused ghosts in a 60-Hz field of 6 V/mm was measured experimentally, and the data were interpreted by using Batchelor's theory for hydrodynamic interaction of hard spheres. The numerical results show clearly the origin of the dielectrophoretic pressures and forces in fused and unfused cells and the effects of a nearby cell on the induced membrane potentials. The experimental results agree well with predictions based on the simple electrical model of the cell. The analysis shows the strong effect of hydrodynamic interactions between the cells in determining their velocity of approach. PMID:8519978

  15. 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

  16. Fluctuations in granular media

    NASA Astrophysics Data System (ADS)

    Howell, Daniel W.; Behringer, R. P.; Veje, C. T.

    1999-09-01

    Dense slowly evolving or static granular materials exhibit strong force fluctuations even though the spatial disorder of the grains is relatively weak. Typically, forces are carried preferentially along a network of "force chains." These consist of linearly aligned grains with larger-than-average force. A growing body of work has explored the nature of these fluctuations. We first briefly review recent work concerning stress fluctuations. We then focus on a series of experiments in both two- and three-dimension [(2D) and (3D)] to characterize force fluctuations in slowly sheared systems. Both sets of experiments show strong temporal fluctuations in the local stress/force; the length scales of these fluctuations extend up to 102 grains. In 2D, we use photoelastic disks that permit visualization of the internal force structure. From this we can make comparisons to recent models and calculations that predict the distributions of forces. Typically, these models indicate that the distributions should fall off exponentially at large force. We find in the experiments that the force distributions change systematically as we change the mean packing fraction, γ. For γ's typical of dense packings of nondeformable grains, we see distributions that are consistent with an exponential decrease at large forces. For both lower and higher γ, the observed force distributions appear to differ from this prediction, with a more Gaussian distribution at larger γ and perhaps a power law at lower γ. For high γ, the distributions differ from this prediction because the grains begin to deform, allowing more grains to carry the applied force, and causing the distributions to have a local maximum at nonzero force. It is less clear why the distributions differ from the models at lower γ. An exploration in γ has led to the discovery of an interesting continuous or "critical" transition (the strengthening/softening transition) in which the mean stress is the order parameter, and the mean

  17. Theoretical and experimental study of electromagnetic forces induced in one-dimensional photonic crystals

    NASA Astrophysics Data System (ADS)

    Lugo, J. E.; Doti, Rafael; Faubert, Jocelyn; Sanchez, Noemi; Sanchez, Javier; Palomino, Martha A.; de la Mora, M. Beatriz; del Rio, J. Antonio

    2013-10-01

    We studied theoretically and experimentally the induction of electromagnetic forces in one-dimensional photonic crystals with localized defects when light impinges transversally to the defect layer. The theoretical calculations indicate that the electromagnetic forces increases at a certain frequency that coincide with a defect photonic state. The photonic structure consists of a microcavity like structure formed of two one-dimensional photonic crystals made of free-standing porous silicon, separated by variable air gap and the working wavelength is 633 nm. The force generation is made evident by driving a laser light by means of a chopper; the light hits the photonic structure and induces a vibration and the vibration is characterized by using a very sensitive vibrometer.

  18. An experimental investigation of vortex-induced vibration with nonlinear restoring forces

    NASA Astrophysics Data System (ADS)

    Mackowski, A. W.; Williamson, C. H. K.

    2013-08-01

    We experimentally examine the amplitude of a bluff body undergoing vortex-induced vibration (VIV) supported by linear and various nonlinear structural forces. This investigation is made possible by our Cyber-Physical Fluid Dynamics force-feedback technique; using it, we can impose arbitrary nonlinear restoring forces on a circular cylinder in our water channel. For the range of nonlinearities examined, detailed analysis allows one to understand and predict the response of the nonlinear structural system using knowledge of a standard, linear VIV system. We also present a case study examining the potential of nonlinear springs to aid in a VIV-based energy harvesting device. Appropriate choices of the spring's nonlinearity allow the hypothetical energy harvester to operate at high performance over a much larger range of Reynolds number than a standard system.

  19. Universal laws in the force-induced unraveling of biological bonds

    NASA Astrophysics Data System (ADS)

    Pereverzev, Yuriy V.; Prezhdo, Oleg V.

    2007-01-01

    Universal laws in the force-induced unbinding of receptor-ligand complexes are established for a general functional dependence of the dissociation rate constant on the applied force and are detailed with the two-pathway model that describes the recently discovered biological catch bond. The relationships link the data obtained with constant and time-dependent forces in different regimes, provide common representation for the previously unrelated data sets, and, thereby, greatly facilitate analysis and interpretation of experiments. The universal laws are demonstrated with the monomeric and dimeric catch-slip bonds between P-selectins and P-selectin glycoprotein ligands-1, and the slip bond between E-selectin and sialyl Lewisx antigen.

  20. 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

  1. Native topology determines force-induced unfolding pathways in globular proteins

    NASA Astrophysics Data System (ADS)

    Klimov, D. K.; Thirumalai, D.

    2000-06-01

    Single-molecule manipulation techniques reveal that stretching unravels individually folded domains in the muscle protein titin and the extracellular matrix protein tenascin. These elastic proteins contain tandem repeats of folded domains with -sandwich architecture. Herein, we propose by stretching two model sequences (S1 and S2) with four-stranded -barrel topology that unfolding forces and pathways in folded domains can be predicted by using only the structure of the native state. Thermal refolding of S1 and S2 in the absence of force proceeds in an all-or-none fashion. In contrast, phase diagrams in the force-temperature (f,T) plane and steered Langevin dynamics studies of these sequences, which differ in the native registry of the strands, show that S1 unfolds in an allor-none fashion, whereas unfolding of S2 occurs via an obligatory intermediate. Force-induced unfolding is determined by the native topology. After proving that the simulation results for S1 and S2 can be calculated by using native topology alone, we predict the order of unfolding events in Ig domain (Ig27) and two fibronectin III type domains (9FnIII and 10FnIII). The calculated unfolding pathways for these proteins, the location of the transition states, and the pulling speed dependence of the unfolding forces reflect the differences in the way the strands are arranged in the native states. We also predict the mechanisms of force-induced unfolding of the coiled-coil spectrin (a three-helix bundle protein) for all 20 structures deposited in the Protein Data Bank. Our approach suggests a natural way to measure the phase diagram in the (f,C) plane, where C is the concentration of denaturants.

  2. 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.

  3. 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.

  4. Orthodontic Forces Induce the Cytoprotective Enzyme Heme Oxygenase-1 in Rats.

    PubMed

    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

  5. Orthodontic Forces Induce the Cytoprotective Enzyme Heme Oxygenase-1 in Rats.

    PubMed

    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.

  6. 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

  7. Inducing forced and auto-oscillations in one-dimensional photonic crystals with light

    NASA Astrophysics Data System (ADS)

    Lugo, J. Eduardo; Doti, Rafael; Sanchez, Noemi; Faubert, Jocelyn

    2014-01-01

    We induced forced and auto-oscillations in one-dimensional photonic crystals (1-D-PCs) with localized defects when light impinges transversally to the defect layer. The photonic structure used consists of a microcavity-like structure formed of two 1-D-PCs made of free-standing porous silicon, separated by a variable air gap (the defect) and the working wavelength is 633 nm. The force generation was made evident by driving a laser light by means of a chopper; the light hit the photonic structure and induced a vibration and the vibration was characterized by using a very sensitive vibrometer. For example, we measured peak displacements and velocities ranging from 2 to 167 μm and 0.4 to 2.1 mm/s with a power light level from 2.6 to 13 mW. In comparison, recent evidence showed that giant resonant light forces could induce average velocity values of 0.45 mm/s in microspheres embedded in water with a 43-mW light power.

  8. 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.

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

    PubMed

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

    2016-03-21

    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.

  10. 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

  11. 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

  12. 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.

  13. Spin-fluctuation induced non-Fermi-liquid behaviour with suppressed superconductivity in LiFe1-xCoxAs

    NASA Astrophysics Data System (ADS)

    Miao, Hu; Dai, Yaomin; Xing, Lingyi; Wang, Xiancheng; Wang, Pengshuai; Xiao, Hong; Qian, Tian; Richard, Pierre; Qiu, Xianggang; Yu, Weiqiang; Jin, Changqing; Wang, Ziqiang; Johnson, P. D.; Homes, C. C.; Ding, Hong

    We study a series of LiFe1-xCoxAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behaviour in LiFe1-xCoxAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1-xCoxAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

  14. Spin-Fluctuation-Induced Non-Fermi-Liquid Behavior with Suppressed Superconductivity in LiFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Dai, Y. M.; Miao, H.; Xing, L. Y.; Wang, X. C.; Wang, P. S.; Xiao, H.; Qian, T.; Richard, P.; Qiu, X. G.; Yu, W.; Jin, C. Q.; Wang, Z.; Johnson, P. D.; Homes, C. C.; Ding, H.

    2015-07-01

    We study a series of LiFe1 -xCox As compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe1 -xCox As is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1 -xCox As where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

  15. Noise-induced resonance-like phenomena in InP crystals embedded in fluctuating electric fields

    NASA Astrophysics Data System (ADS)

    Persano Adorno, D.; Pizzolato, N.; Spagnolo, B.

    2016-05-01

    We explore and discuss the complex electron dynamics inside a low-doped n-type InP bulk embedded in a sub-THz electric field, fluctuating for the superimposition of an external source of Gaussian correlated noise. The results presented in this study derive from numerical simulations obtained by means of a multi-valley Monte Carlo approach to simulate the nonlinear transport of electrons inside the semiconductor crystal. The electronic noise characteristics are statistically investigated by calculating the correlation function of the velocity fluctuations, its spectral density and the integrated spectral density, i.e. the total noise power, for different values of both amplitude and frequency of the driving oscillating electric field and for different correlation times of the field fluctuations. Our results show that the nonlinear response of electrons is strongly affected by the field fluctuations. In particular, crucially depending on the relationship between the correlation times of the external Gaussian noise and the timescales of complex phenomena involved in the electron dynamical behavior: (i) electrons self-organize among different valleys, giving rise to intrinsic noise suppression; (ii) this cooperative behavior causes the appearance of a resonance-like phenomenon in the noise spectra.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

    Roy, Susmita; Jana, Biman; Bagchi, Biman

    2012-03-01

    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. Strain, stress and energy in lipid bilayer induced by electrostatic/electrokinetic forces.

    PubMed

    Tajparast, M; Glavinović, M I

    2012-03-01

    Lipid bilayer was deformed by the electrostatic/electrokinetic forces induced by the fixed charges on the top monolayer-solution interface. The strains, stresses and energy were simulated using finite element method. The elastic moduli of the heads were four times greater than those of tails sections, but were individually isotropic. The physics of the situation was evaluated using a coupled system of linear elastic equations and electrostatic-electrokinetic (Poisson-Nernst-Planck) equations. The Coulomb force (due to fixed charges in the electric field), and the dielectric force (due to uneven electric field and the solution-membrane permittivity mismatch) bend the membrane, but unevenly. Whereas the bottom monolayer extends vertically (towards charged surface), the top monolayer compresses. In contrast the top monolayer extends horizontally, but the bottom monolayer compresses. The horizontal normal stress is higher in the heads than in the tails sections, but is similar in two monolayers, whereas the vertical normal stress is small. The horizontal normal stress is associated with horizontal normal strain, and vertical with both vertical and horizontal strain. Surprisingly, the shear stress (an indicator where the membrane will deform), is greater in the tails sections. Finally, the elastic energy (which is clearly greater in the heads sections) is dominated by its horizontal component and peaks in the middle of the membrane. The shear component dominates in the tails sections, and is minimal in the membrane center. Even spatially uniform external force thus leads to complex membrane deformation and generates complex profiles of stress and elastic energy.

  19. Convective initiation by topographically induced convergence forcing over the Dabie Mountains on 24 June 2010

    NASA Astrophysics Data System (ADS)

    Wang, Qiwei; Xue, Ming; Tan, Zhemin

    2016-10-01

    The initiation of convective cells in the late morning of 24 June 2010 along the eastward extending ridge of the Dabie Mountains in the Anhui region, China, is studied through numerical simulations that include local data assimilation. A primary convergence line is found over the ridge of the Dabie Mountains, and along the ridge line several locally enhanced convergence centers preferentially initiate convection. Three processes responsible for creating the overall convergence pattern are identified. First, thermally-driven upslope winds induce convergence zones over the main mountain peaks along the ridge, which are shifted slightly downwind in location by the moderate low-level easterly flow found on the north side of a Mei-yu front. Second, flows around the main mountain peaks along the ridge create further convergence on the lee side of the peaks. Third, upslope winds develop along the roughly north-south oriented valleys on both sides of the ridge due to thermal and dynamic channeling effects, and create additional convergence between the peaks along the ridge. The superposition of the above convergence features creates the primary convergence line along the ridge line of the Dabie Mountains. Locally enhanced convergence centers on the primary line cause the initiation of the first convection cells along the ridge. These conclusions are supported by two sensitivity experiments in which the environmental wind (dynamic forcing) or radiative and land surface thermal forcing are removed, respectively. Overall, the thermal forcing effects are stronger than dynamic forcing given the relatively weak environmental flow.

  20. 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.

  1. On combining Thole's induced point dipole model with fixed charge distributions in molecular mechanics force fields.

    PubMed

    Antila, Hanne S; Salonen, Emppu

    2015-04-15

    The Thole induced point dipole model is combined with three different point charge fitting methods, Merz-Kollman (MK), charges from electrostatic potentials using a grid (CHELPG), and restrained electrostatic potential (RESP), and two multipole algorithms, distributed multipole analysis (DMA) and Gaussian multipole model (GMM), which can be used to describe the electrostatic potential (ESP) around molecules in molecular mechanics force fields. This is done to study how the different methods perform when intramolecular polarizability contributions are self-consistently removed from the fitting done in the force field parametrization. It is demonstrated that the polarizable versions of the partial charge models provide a good compromise between accuracy and computational efficiency in describing the ESP of small organic molecules undergoing conformational changes. For the point charge models, the inclusion of polarizability reduced the the average root mean square error of ESP over the test set by 4-10%.

  2. a Simple Model to Estimate the Impact Force Induced by Piston Slap

    NASA Astrophysics Data System (ADS)

    CHO, S.-H.; AHN, S.-T.; KIM, Y.-H.

    2002-08-01

    The dynamics of piston's secondary motion (lateral and rotational motion) across the clearance between piston and cylinder inner wall of reciprocating machines are analyzed. This paper presents an analytical model, which can predict the impact forces and vibratory response of engine block surface induced by the piston slap of an internal combustion engine. A piston is modelled on a three-degree-of-freedom system to represent its planar motion. When slap occurs, the impact point between piston skirt and cylinder inner wall is modelled on a two-degree-of-freedom vibratory system. The equivalent parameters such as mass, spring constant, and damping constant of piston and cylinder inner wall are estimated by using measured (driving) point mobility. Those parameters are used to calculate the impact force and for estimating the vibration level of engine block surfaces. The predicted results are compared with experimental results to verify the model.

  3. Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy

    NASA Astrophysics Data System (ADS)

    Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

    2014-07-01

    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.

  4. 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

    2014-08-01

    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. PMID:24953042

  5. The influence of ice slushy on voluntary contraction force following exercise-induced hyperthermia.

    PubMed

    Burdon, Catriona A; Easthope, Christopher S; Johnson, Nathan A; Chapman, Phillip G; O'Connor, Helen

    2014-07-01

    This study aimed to investigate the effect of exercise-induced hyperthermia on central fatigue and force decline in exercised and nonexercised muscles and whether ingestion of ice slushy (ICE) ameliorates fatigue. Eight participants (5 males, 3 females) completed 45 s maximal voluntary isometric contractions (MVIC) with elbow flexors and knee extensors at baseline and following an exercise-induced rectal temperature (Trec) of 39.3 ± 0.2 °C. Percutaneous electrical muscle stimulation was superimposed at 15, 30 and 44 s during MVICs to assess muscle activation. To increase Trec to 39.3 °C, participants cycled at 60% maximum power output for 42 ± 11 min in 40 °C and 50% relative humidity. Immediately prior to each MVIC, participants consumed 50 g of ICE (-1 °C) or thermoneutral drink (38 °C, CON) made from 7.4% carbohydrate beverage. Participants consumed water (19 °C) during exercise to prevent hypohydration. Voluntary muscle force production and activation in both muscle groups were unchanged at Trec 39.3 °C with ICE (knee extensors: 209 ± 152 N) versus CON (knee extensors: 255 ± 157 N, p = 0.19). At Trec 39.3 °C, quadriceps mean force (232 ± 151 N) decreased versus baseline (302 ± 180 N, p < 0.001) and mean voluntary activation was also decreased (by 15% ± 11%, p < 0.001). Elbow flexor mean force decreased from 179 ± 67 N to 148 ± 65 N when Trec was increased to 39.3 °C (p < 0.001) but mean voluntary activation was not reduced at 39.3 °C (5% ± 25%, p = 0.79). After exercise-induced hyperthermia, ICE had no effect on voluntary activation or force production; however, both were reduced from baseline in the exercised muscle group. Peripheral fatigue was greater than the central component and limited the ability of an intervention designed to alter central fatigue.

  6. The influence of ice slushy on voluntary contraction force following exercise-induced hyperthermia.

    PubMed

    Burdon, Catriona A; Easthope, Christopher S; Johnson, Nathan A; Chapman, Phillip G; O'Connor, Helen

    2014-07-01

    This study aimed to investigate the effect of exercise-induced hyperthermia on central fatigue and force decline in exercised and nonexercised muscles and whether ingestion of ice slushy (ICE) ameliorates fatigue. Eight participants (5 males, 3 females) completed 45 s maximal voluntary isometric contractions (MVIC) with elbow flexors and knee extensors at baseline and following an exercise-induced rectal temperature (Trec) of 39.3 ± 0.2 °C. Percutaneous electrical muscle stimulation was superimposed at 15, 30 and 44 s during MVICs to assess muscle activation. To increase Trec to 39.3 °C, participants cycled at 60% maximum power output for 42 ± 11 min in 40 °C and 50% relative humidity. Immediately prior to each MVIC, participants consumed 50 g of ICE (-1 °C) or thermoneutral drink (38 °C, CON) made from 7.4% carbohydrate beverage. Participants consumed water (19 °C) during exercise to prevent hypohydration. Voluntary muscle force production and activation in both muscle groups were unchanged at Trec 39.3 °C with ICE (knee extensors: 209 ± 152 N) versus CON (knee extensors: 255 ± 157 N, p = 0.19). At Trec 39.3 °C, quadriceps mean force (232 ± 151 N) decreased versus baseline (302 ± 180 N, p < 0.001) and mean voluntary activation was also decreased (by 15% ± 11%, p < 0.001). Elbow flexor mean force decreased from 179 ± 67 N to 148 ± 65 N when Trec was increased to 39.3 °C (p < 0.001) but mean voluntary activation was not reduced at 39.3 °C (5% ± 25%, p = 0.79). After exercise-induced hyperthermia, ICE had no effect on voluntary activation or force production; however, both were reduced from baseline in the exercised muscle group. Peripheral fatigue was greater than the central component and limited the ability of an intervention designed to alter central fatigue. PMID:24971678

  7. Parallel magnetic field-induced conductance fluctuations in GaAs/AlGaAs ballistic quantum dots.

    NASA Astrophysics Data System (ADS)

    Faniel, S.; Gustin, C.; Melinte, S.; Hackens, B.; Bayot, V.; Shayegan, M.

    2004-03-01

    We present magnetotransport measurements in ballistic quantum dots under a parallel magnetic field. The dots were fabricated on two different GaAs/AlGaAs quantum wells with thicknesses of 15 and and 45 nm and with one and two subbands occupied, respectively. The samples were patterned using e-beam lithography and wet etching. A Cr/Au electrostatic top gate was used in order to tune the width of the dot openings. The measurements were performed down to 300 mK with the magnetic field applied strictly parallel to the plane of the two-dimensional electron gas. For both dots, we observe universal conductance fluctuations and, in the case of the wide quantum well, a reduction of their amplitude at large magnetic field. We discuss these conductance fluctuations in terms of orbital effect(V.I. Fal'ko and T. Jungwirth, Phys Rev B 65), 081306 (2002) and magnetic subband depopulation.

  8. Cold-Atom Physics Using Ultrathin Optical Fibers: Light-Induced Dipole Forces and Surface Interactions

    SciTech Connect

    Sague, G.; Vetsch, E.; Alt, W.; Meschede, D.; Rauschenbeutel, A.

    2007-10-19

    The strong evanescent field around ultrathin unclad optical fibers bears a high potential for detecting, trapping, and manipulating cold atoms. Introducing such a fiber into a cold-atom cloud, we investigate the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface. Using high resolution spectroscopy, we observe and analyze light-induced dipole forces, van der Waals interaction, and a significant enhancement of the spontaneous emission rate of the atoms. The latter can be assigned to the modification of the vacuum modes by the fiber.

  9. Modeling of wave-induced irradiance fluctuations at near-surface depths in the ocean: a comparison with measurements.

    PubMed

    You, Yu; Stramski, Dariusz; Darecki, Miroslaw; Kattawar, George W

    2010-02-20

    We develop a computationally fast radiative transfer model for simulating the fluctuations of the underwater downwelling irradiance E(d) at near-surface depths, which occur due to focusing of sunlight by wind-driven surface waves. The model is based on the hybrid matrix operator-Monte Carlo method, which was specifically designed for simulating radiative transfer in a coupled atmosphere-surface-ocean system involving a dynamic ocean surface. In the current version of the model, we use a simplified description of surface waves, which accounts for surface slope statistics, but not surface wave elevation, as a direct source of underwater light fluctuations. We compare the model results with measurements made in the Santa Barbara Channel. The model-simulated and measured time series of E(d)(t) show remarkable similarity. Major features of the probability distribution of instantaneous irradiance, the frequency content of irradiance fluctuations, and the statistical properties of light flashes produced by wave focusing are also generally consistent between the model simulations and measurements for a few near-surface depths and light wavelengths examined. Despite the simplification in the representation of surface waves, this model provides a reasonable first-order approximation to modeling the wave focusing effects at near-surface depths, which require high temporal and spatial resolution (of the order of 1 ms and 1 mm, respectively) to be adequately resolved.

  10. 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

  11. Experimental study of radiation induced electromotive force effects on mineral insulated cables

    NASA Astrophysics Data System (ADS)

    Van Nieuwenhove, R.; Vermeeren, L.

    2003-11-01

    Measurements of radiation induced electromotive force (RIEMF) effects on mineral insulated cables in a pure gamma field and in a combined neutron and gamma field are presented and compared to model calculations. The effect of materials in the immediate surroundings of the cable, as predicted by the model calculations, is clearly demonstrated. In a fission reactor environment, delayed current contributions due to the neutron activation and subsequent beta emission in base materials as well as in impurities such as Mn are clearly observed and are well reproduced by model calculations. The prediction of the gamma induced current component was severely complicated by its strong sensitivity to the detailed geometry and the spectrum and the directivity of the gamma field. Although the RIEMF effect on MI cables can therefore in general not be completely eliminated, some guidelines are provided to minimize them.

  12. A Microfluidic Approach for Inducing Cell Rotation by Means of Hydrodynamic Forces.

    PubMed

    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

  13. Chemical activity induces dynamical force with global structure in a reaction-diffusion-convection system.

    PubMed

    Mahara, Hitoshi; Okada, Koichi; Nomura, Atsushi; Miike, Hidetoshi; Sakurai, Tatsunari

    2009-07-01

    We found a rotating global structure induced by the dynamical force of local chemical activity in a thin solution layer of excitable Belousov-Zhabotinsky reaction coupled with diffusion. The surface flow and deformation associated with chemical spiral waves (wavelength about 1 mm) represents a global unidirectional structure and a global tilt in the entire Petri dish (100 mm in diameter), respectively. For these observations, we scanned the condition of hierarchal pattern selection. From this result, the bromomalonic acid has an important role to induce the rotating global structure. An interaction between a reaction-diffusion process and a surface-tension-driven effect leads to such hierarchal pattern with different scales. PMID:19658764

  14. 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

  15. 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

  16. 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.

  17. The CB1 cannabinoid receptor agonist reduces L-DOPA-induced motor fluctuation and ERK1/2 phosphorylation in 6-OHDA-lesioned rats

    PubMed Central

    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. PMID:25395834

  18. Particle-induced indentation of the alveolar epithelium caused by surface tension forces

    PubMed Central

    Kojic, M.; Tsuda, A.

    2010-01-01

    Physical contact between an inhaled particle and alveolar epithelium at the moment of particle deposition must have substantial effects on subsequent cellular functions of neighboring cells, such as alveolar type-I, type-II pneumocytes, alveolar macrophage, as well as afferent sensory nerve cells, extending their dendrites toward the alveolar septal surface. The forces driving this physical insult are born at the surface of the alveolar air-liquid layer. The role of alveolar surfactant submerging a hydrophilic particle has been suggested by Gehr and Schürch's group (e.g., Respir Physiol 80: 17–32, 1990). In this paper, we extended their studies by developing a further comprehensive and mechanistic analysis. The analysis reveals that the mechanics operating in the particle-tissue interaction phenomena can be explained on the basis of a balance between surface tension force and tissue resistance force; the former tend to move a particle toward alveolar epithelial cell surface, the latter to resist the cell deformation. As a result, the submerged particle deforms the tissue and makes a noticeable indentation, which creates unphysiological stress and strain fields in tissue around the particle. This particle-induced microdeformation could likely trigger adverse mechanotransduction and mechanosensing pathways, as well as potentially enhancing particle uptake by the cells. PMID:20634359

  19. Are neutron stars crushed? Gravitomagnetic tidal forces as a mechanism for binary-induced collapse

    NASA Astrophysics Data System (ADS)

    Favata, Marc; Thorne, Kip S.

    2002-04-01

    Numerical simulations of coalescing binary neutron stars performed by Wilson, Mathews, and Marronetti indicated that a binary companion could cause a stable neutron star to undergo gravitational collapse prior to merger if the neutron star is close to its maximum allowed mass. Subsequent studies by several authors failed to explain this surprising effect. Although Flanagan’s correction accounted for most of the effect, a small residual compression remained. This has prompted us to ask: what physical mechanism, if any, could cause binary-induced compression of a neutron star? We have found that a compressive force can exist when gravitomagnetic tidal fields, generated by the companion's orbital motion, couple to certain velocity patterns (or modes of stellar oscillation) in the neutron star. Specifically, we find that if one decomposes the star's fluid velocity into a sum over vector spherical harmonics, a radial compression force exists for certain vector harmonic indices. However, this force can only affect stability if the star is already very close to its maximum mass. We derive expressions for the evolution of the star's fundamental radial mode (along which compression and expansion occur) and the change in the central density. We also estimate how close a neutron star needs to be to its maximum mass in order for this compression to initiate gravitational collapse. Our analysis demonstrates techniques that can be applied to the study of relativistic tidal fields on various modes of stellar oscillation.

  20. Running induces nausea in rats: Kaolin intake generated by voluntary and forced wheel running.

    PubMed

    Nakajima, Sadahiko

    2016-10-01

    Three experiments were conducted showing rats' pica behavior (kaolin clay intake) due to running in activity wheels. The amount of kaolin consumed was a positive function of the available time of voluntary running (20, 40, or 60 min), although this relationship was blunted by a descending (i.e., 60 → 40 → 20 min) test series of execution (Experiment 1). Pica was also generated by forced running in a motorized wheel for 60 min as a positive function of the speed of wheel rotations at 98, 185, or 365 m/h, independent of the order of execution (Experiment 2). Voluntary running generated more pica than did forced running at 80 m/h, although the distance travelled in the former condition was 27% lesser than that in the latter condition (Experiment 3). Because kaolin intake is regarded as a reliable measure of nausea in rats, these results show that wheel running, either voluntary or forced, induces nausea in rats.

  1. Buoyancy and Pressure Induced Flow of Hot Gases in Vertical Shafts with Natural and Forced Ventilation

    NASA Astrophysics Data System (ADS)

    Jaluria, Yogesh; Tamm, Gunnar Olavi

    2014-11-01

    An experimental investigation was conducted to study buoyancy and pressure induced flow of hot gases in vertical shafts to model smoke propagation in elevator and ventilation shafts of high rise building fires. Various configurations were tested with regard to natural and forced ventilation imposed at the upper and lower surfaces of the vertical shaft. The aspect ratio was taken at a typical value of 6. From a lower vent, the inlet conditions for smoke and hot gases were varied in terms of the Reynolds and Grashof numbers. The forced ventilation at the upper or lower boundary was of the same order as the bulk shaft flow. Measurements were taken within the shaft to allow a detailed study of the steady state flow and thermal fields established for various shaft configurations and inlet conditions, from which optimal means for smoke alleviation in high rise building fires may be developed. Results indicated a wall plume as the primary transport mechanism for smoke propagating from the inlet towards the exhaust region. Recirculation and entrainment dominated at high inlet Grashof number flows, while increased inlet Reynolds numbers allowed greater mixing in the shaft. The development and stability of these flow patterns and their effects on the smoke behavior were assessed for several shaft configurations with different inlet conditions. The comparisons indicated that the fastest smoke removal and lowest overall shaft temperatures occur for a configuration with natural ventilation at the top surface and forced ventilation up from the shaft bottom.

  2. Chirp excitation technique to enhance microbubble displacement induced by ultrasound radiation force.

    PubMed

    Hu, Yi; Zhang, Dong; Zheng, Hairong; Gong, Xiufen

    2009-03-01

    Ultrasound radiation force has been proposed to increase the targeting efficiency in ultrasonic molecular imaging and drug delivery. A chirp excitation technique is proposed to increase the radiation force induced microbubble displacement and might potentially be used for enhancing the targeting efficiency of microbubble clouds. In this study, a modified Rayleigh-Plesset equation is used to estimate the radius-time behavior of insonified microbubbles, and the translation of insonified microbubbles is calculated by using the particle trajectory equation. Simulations demonstrate that the chirp excitation is superior to the sinusoidal one in displacing microbubbles with a wide-size distribution, and that the performance is dependent on the parameters of the chirp signal such as the center frequency and frequency range. For Gaussian size distributed microbubble clouds with mean diameter of 3.5 microm and variance of 1, a 2.25 MHz chirp with frequency range of 1.5 MHz induces about 59.59% more microbubbles over a distance of 10 microm during 200 micros insonification, compared to a 2.25 MHz sinusoidal excitation with equal acoustic pressure.

  3. Chirp excitation technique to enhance microbubble displacement induced by ultrasound radiation force.

    PubMed

    Hu, Yi; Zhang, Dong; Zheng, Hairong; Gong, Xiufen

    2009-03-01

    Ultrasound radiation force has been proposed to increase the targeting efficiency in ultrasonic molecular imaging and drug delivery. A chirp excitation technique is proposed to increase the radiation force induced microbubble displacement and might potentially be used for enhancing the targeting efficiency of microbubble clouds. In this study, a modified Rayleigh-Plesset equation is used to estimate the radius-time behavior of insonified microbubbles, and the translation of insonified microbubbles is calculated by using the particle trajectory equation. Simulations demonstrate that the chirp excitation is superior to the sinusoidal one in displacing microbubbles with a wide-size distribution, and that the performance is dependent on the parameters of the chirp signal such as the center frequency and frequency range. For Gaussian size distributed microbubble clouds with mean diameter of 3.5 microm and variance of 1, a 2.25 MHz chirp with frequency range of 1.5 MHz induces about 59.59% more microbubbles over a distance of 10 microm during 200 micros insonification, compared to a 2.25 MHz sinusoidal excitation with equal acoustic pressure. PMID:19275298

  4. Optical tracking of acoustic radiation force impulse-induced dynamics in a tissue-mimicking phantom

    PubMed Central

    Bouchard, Richard R.; Palmeri, Mark L.; Pinton, Gianmarco F.; Trahey, Gregg E.; Streeter, Jason E.; Dayton, Paul A.

    2009-01-01

    Optical tracking was utilized to investigate the acoustic radiation force impulse (ARFI)-induced response, generated by a 5-MHz piston transducer, in a translucent tissue-mimicking phantom. Suspended 10-μm microspheres were tracked axially and laterally at multiple locations throughout the field of view of an optical microscope with 0.5-μm displacement resolution, in both dimensions, and at frame rates of up to 36 kHz. Induced dynamics were successfully captured before, during, and after the ARFI excitation at depths of up to 4.8 mm from the phantom’s proximal boundary. Results are presented for tracked axial and lateral displacements resulting from on-axis and off-axis (i.e., shear wave) acquisitions; these results are compared to matched finite element method modeling and independent ultrasonically based empirical results and yielded reasonable agreement in most cases. A shear wave reflection, generated by the proximal boundary, consistently produced an artifact in tracked displacement data later in time (i.e., after the initial ARFI-induced displacement peak). This tracking method provides high-frame-rate, two-dimensional tracking data and thus could prove useful in the investigation of complex ARFI-induced dynamics in controlled experimental settings. PMID:19894849

  5. 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.

  6. Stimulated Raman spectroscopy and nanoscopy of molecules using near field photon induced forces without resonant electronic enhancement gain

    NASA Astrophysics Data System (ADS)

    Tamma, Venkata Ananth; Huang, Fei; Nowak, Derek; Kumar Wickramasinghe, H.

    2016-06-01

    We report on stimulated Raman spectroscopy and nanoscopy of molecules, excited without resonant electronic enhancement gain, and recorded using near field photon induced forces. Photon-induced interaction forces between the sharp metal coated silicon tip of an Atomic Force Microscope (AFM) and a sample resulting from stimulated Raman excitation were detected. We controlled the tip to sample spacing using the higher order flexural eigenmodes of the AFM cantilever, enabling the tip to come very close to the sample. As a result, the detection sensitivity was increased compared with previous work on Raman force microscopy. Raman vibrational spectra of azobenzene thiol and l-phenylalanine were measured and found to agree well with published results. Near-field force detection eliminates the need for far-field optical spectrometer detection. Recorded images show spatial resolution far below the optical diffraction limit. Further optimization and use of ultrafast pulsed lasers could push the detection sensitivity towards the single molecule limit.

  7. Phase speed saturation of Farley-Buneman waves due to stochastic, self-induced fluctuations in the background flow

    NASA Astrophysics Data System (ADS)

    Rojas, E. L.; Young, M. A.; Hysell, D. L.

    2016-06-01

    The phase speed saturation of Farley-Buneman waves is studied as an interaction with the random turbulent fluctuations in the background. We used the formalism of stochastic differential equations to model the complex interactions with a linearized system plus a stochastic term. Applying an averaging technique, we can obtain an augmented linear system that depends on the random behavior of the waves. The results show that following this approach we can obtain phase velocities that saturate close to the ion acoustic speed (Cs). This approach seems promising for the study of the influence of plasma turbulence generated by different kinds of instabilities on the mean state of the ionosphere.

  8. A Critical Review of Constraint-Induced Movement Therapy and Forced Use in Children With Hemiplegia

    PubMed Central

    Charles, Jeanne; Gordon, Andrew M.

    2005-01-01

    Hemiplegia is a physical impairment that can occur in childhood following head trauma, cerebral vascular accident or transient ischemic attack (stroke), brain tumor, or congenital or perinatal injury. One of the most disabling symptoms of hemiplegia is unilaterally impaired hand and arm function. Sensory and motor impairments in children with hemiplegia compromise movement efficiency. Such children often tend not to use the affected extremity, which may further exacerbate the impairments, resulting in a developmentally learned non-use of the involved upper extremity, termed ‘developmental disuse’. Recent studies suggest that children with hemiplegia benefit from intensive practice. Forced use and Constraint-lnduced Movement Therapy (CI therapy) are recent therapeutic interventions involving the restraint of the non-involved upper extremity and intensive practice with the involved upper extremity. These approaches were designed for adults with hemiplegia, and increasing evidence suggests that they are efficacious in this population. Recently, forced use and constraint-induced therapy have been applied to children with hemiplegia. In this review, we provide a brief description of forced use and CI therapy and their historical basis, provide a summary of studies of these interventions in children, and discuss a number of important theoretical considerations, as well as implications for postural control. We will show that whereas the studies to date suggest that both forced use and CI therapy appear to be promising for improving hand function in children with hemiplegia, the data are limited. Substantially more work must be performed before this approach can be advocated for general clinical use. PMID:16097492

  9. Factors of force potentiation induced by stretch-shortening cycle in plantarflexors.

    PubMed

    Fukutani, Atsuki; Kurihara, Toshiyuki; Isaka, Tadao

    2015-01-01

    Muscle force is potentiated by countermovement; this phenomenon is called stretch-shortening cycle (SSC) effect. In this study, we examined the factors strongly related to SSC effect in vivo, focusing on tendon elongation, preactivation, and residual force enhancement. Twelve healthy men participated in this study. Ankle joint angle was passively moved by a dynamometer, with a range of motion from 15° dorsiflexion (DF) to 15° plantarflexion (PF). Muscle contraction was evoked by electrical stimulation, with stimulation timing adjusted to elicit three types of contraction: (1) concentric contraction without preliminary contraction (CON), (2) concentric contraction after preliminary eccentric contraction (ECC), and (3) concentric contraction after preliminary isometric contraction (ISO). Joint torque was recorded at DF5°, PF0°, and PF5°, respectively. SSC effect was calculated as the ratio of joint torque obtained in ECC or ISO with respect to that obtained in CON at the aforementioned three joint angles. SSC effect was prominent in the first half of movement in both ECC (DF5°, 329.3 ± 101.2%; PF0°, 159.2 ± 29.4%; PF5°, 125.5 ± 20.8%) and ISO (DF5°, 276.4 ± 87.0%; PF0°, 134.5 ± 24.5%; PF5°, 106.8 ± 18.0%) conditions. SSC effect was significantly larger in ECC than in ISO at all joint angles (P < 0.001). Even without preliminary eccentric contraction (i.e., ISO condition), SSC effect was clearly large, indicating that a significant part of SSC effect is derived from preactivation. However, the active lengthening-induced force potentiation mechanism (residual force enhancement) also contributes to SSC effect.

  10. 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.

  11. Effect of thioperamide on modified forced swimming test-induced oxidative stress in mice.

    PubMed

    Akhtar, Mohd; Pillai, K K; Vohora, Divya

    2005-10-01

    This study was designed i) to investigate the role of histamine H3-receptor ligands on mouse modified forced swimming test, a method that distinguishes the catecholaminergic behaviour with that of serotonergic compounds and ii) to evaluate the role of free radicals in mediation of such effects. Swiss strain albino mice were treated with different doses of histamine H3-receptor antagonist thioperamide (3.75, 7.5 and 15 mg/kg intraperitoneally) and agonist (R)-alpha-methylhistamine (5 microg intracerebroventricularly). The climbing, swimming and immobility times were recorded for 6 min. Immediately after modified forced swimming test, the animals were sacrificed and parameters of oxidative stress were assessed in the brain by measuring the thiobarbituric acid reactive substance (TBARS), glutathione (GSH) and catalase levels. Thioperamide (7.5 and 15 mg/kg intraperitoneally) dose-dependently decreased immobility time and increased swimming time but not climbing time. The behaviour of mice treated with (R)-alpha-methylhistamine was similar to that of control mice. A significant reduction in GSH and an increase in catalase levels were observed in brains of mice exposed to modified forced swimming test. Thioperamide pretreatment dose-dependently reversed such an alteration in oxidative stress parameters. (R)-alpha-methylhistamine caused a reversal of altered catalase but not GSH levels. Thioperamide shows antidepressant effects in the modified forced swimming test and causes a reversal of the test-induced oxidative stress indicating its antioxidant potential. The antidepressant effect of thioperamide appears to be mediated via serotonergic and/or antioxidant mechanisms.

  12. Patterns and intrinsic fluctuations in semi-dilute motor-filament systems.

    SciTech Connect

    Swaminathan, S.; Ziebert, F.; Aranson, I. S.; Karpeev, D.; Northwestern Univ.; UMR CNRS Gulliver

    2010-04-01

    We perform Brownian dynamics simulations of molecular motor-induced ordering and structure formations in semi-dilute cytoskeletal filament solutions. In contrast to the previously studied dilute case where binary filament interactions prevail, the semi-dilute regime is characterized by multiple motor-mediated interactions. Moreover, the forces and torques exerted by motors on filaments are intrinsically fluctuating quantities. We incorporate the influences of thermal and motor fluctuations into our model as additive and multiplicative noises, respectively. Numerical simulations reveal that filament bundles and vortices emerge from a disordered initial state. Subsequent analysis of motor noise effects reveals: (i) Pattern formation is very robust against fluctuations in motor force; (ii) bundle formation is associated with a significant reduction of the motor fluctuation contributions; (iii) the time scale of vortex formation and coalescence decreases with increases in motor noise amplitude.

  13. Current-induced forces: a new mechanism to induce negative differential resistance and current-switching effect in molecular junctions

    NASA Astrophysics Data System (ADS)

    Gu, Lei; Fu, Hua-Hua

    2015-12-01

    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.

  14. Energy change of a heavy quark in a viscous quark-gluon plasma with fluctuations

    NASA Astrophysics Data System (ADS)

    Jiang, Bing-feng; Hou, De-fu; Li, Jia-rong

    2016-09-01

    When a heavy quark travels through the quark-gluon plasma, the polarization and fluctuating chromoelectric fields will be produced simultaneously in the plasma. The drag force due to those fields exerting in return on the moving heavy quark will cause energy change to it. Based on the dielectric functions derived from the viscous chromohydrodynamics, we have studied the collisional energy change of a heavy quark traversing the viscous quark-gluon plasma including fluctuations of chromoelectric field. Numerical results indicate that the chromoelectric field fluctuations lead to an energy gain of the moving heavy quark. Shear viscosity suppresses the fluctuation-induced energy gain and the viscous suppression effect for the charm quark is much more remarkable than that for the bottom quark. While, the fluctuation energy gain is much smaller than the polarization energy loss in magnitude and the net energy change for the heavy quark is at loss.

  15. Wind-tunnel investigation of surface-pressure fluctuations associated with aircraft buffet

    NASA Technical Reports Server (NTRS)

    Riddle, D. W.

    1975-01-01

    Fluctuating pressures and forces that cause aircraft buffeting have been measured on a semispan rigid-wing model of a typical variable-sweep fighter-type aircraft at transonic speeds. The rms spectral and spatial correlation characteristics of wing fluctuating pressures, fluctuating pressure summations, and structural responses are presented and discussed for a Mach number of 0.85, wing sweep angles of 26 and 72 deg, and angles of attack up to 12 deg. The fluctuating pressure characteristics beneath wing shock waves and leading-edge vortices and in regions of attached and separated flows are presented. Results indicate that: (1) the mean and fluctuating static pressure characteristics are related; (2) a circulation oscillation exists for attached flow conditions below buffet onset; and (3) a significant coupling exists between the wing shock-wave oscillation and the wing first torsional mode when shock-induced separation is present.

  16. 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

    2013-10-01

    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. PMID:23925640

  17. Fluctuation-induced first-order phase transitions in type-1.5 superconductors in zero external field

    NASA Astrophysics Data System (ADS)

    Meier, Hannes; Babaev, Egor; Wallin, Mats

    2015-03-01

    In a single-component Ginzburg-Landau model which possesses thermodynamically stable vortex excitations, the zero-field superconducting phase transition is second order even when fluctuations are included. Beyond the mean-field approximation the transition is described in terms of proliferation of vortex loops. Here we determine the order of the superconducting transition in an effective 3D vortex-loop model for the recently proposed multiband type-1.5 superconductors. The vortex interaction is nonmonotonic, i.e., exponentially screened and attractive at large separations, and short-range repulsive. We show that the details of the vortex interaction, despite its short-range nature, can lead to very different properties of the superconducting transition than found in type-1 and type-2 systems. Namely, the type-1.5 regime with nonmonotonic intervortex interaction can have a first-order vortex-driven phase transition not found in the single-band case.

  18. Shear-induced concentration fluctuations and form factor changes in polymer solution in the good-solvent regime.

    PubMed

    Morfin, I; Lindner, P; Boué, F

    2004-09-01

    Small-Angle Scattering from sheared semidilute polymer solution is reported in the good-solvent regime, at variance with former light and neutron measurements in the theta regime. First, concentration fluctuations are observed: the scattering increases noticeably along the flow at low q, but at variance with former results for the theta-solvent regime, no demixing is observed at higher shear. Here, instead, the effects follow a time-temperature superposition and saturate above a Weissenberg number around 5, like the stress which is known to present a plateau for these systems. Using the Zero Average Contrast technique, we have also measured the form factor, which displays the same saturation effect reaching a deformation ratio of the order of 2. These results agree with the Convective Constraint Release models (CCR) elaborated in order to predict the stress effects in the non-Newtonian regime (Marrucci-Ianniruberto) and their extension predicting also the scattering (Likhtman-Milner-McLeish).

  19. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane

    NASA Astrophysics Data System (ADS)

    Rajapaksha, Suneth P.; Pal, Nibedita; Zheng, Desheng; Lu, H. Peter

    2015-11-01

    We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ˜15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a

  20. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane.

    PubMed

    Rajapaksha, Suneth P; Pal, Nibedita; Zheng, Desheng; Lu, H Peter

    2015-01-01

    We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ∼15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a

  1. Protein-fluctuation-induced water-pore formation in ion channel voltage-sensor translocation across a lipid bilayer membrane.

    PubMed

    Rajapaksha, Suneth P; Pal, Nibedita; Zheng, Desheng; Lu, H Peter

    2015-01-01

    We have applied a combined fluorescence microscopy and single-ion-channel electric current recording approach, correlating with molecular dynamics (MD) simulations, to study the mechanism of voltage-sensor domain translocation across a lipid bilayer. We use the colicin Ia ion channel as a model system, and our experimental and simulation results show the following: (1) The open-close activity of an activated colicin Ia is not necessarily sensitive to the amplitude of the applied cross-membrane voltage when the cross-membrane voltage is around the resting potential of excitable membranes; and (2) there is a significant probability that the activation of colicin Ia occurs by forming a transient and fluctuating water pore of ∼15 Å diameter in the lipid bilayer membrane. The location of the water-pore formation is nonrandom and highly specific, right at the insertion site of colicin Ia charged residues in the lipid bilayer membrane, and the formation is intrinsically associated with the polypeptide conformational fluctuations and solvation dynamics. Our results suggest an interesting mechanistic pathway for voltage-sensitive ion channel activation, and specifically for translocation of charged polypeptide chains across the lipid membrane under a transmembrane electric field: the charged polypeptide domain facilitates the formation of hydrophilic water pore in the membrane and diffuses through the hydrophilic pathway across the membrane; i.e., the charged polypeptide chain can cross a lipid membrane without entering into the hydrophobic core of the lipid membrane but entirely through the aqueous and hydrophilic environment to achieve a cross-membrane translocation. This mechanism sheds light on the intensive and fundamental debate on how a hydrophilic and charged peptide domain diffuses across the biologically inaccessible high-energy barrier of the hydrophobic core of a lipid bilayer: The peptide domain does not need to cross the hydrophobic core to move across a

  2. Anomalous cyclic voltammetric response from pores smaller than ion size by voltage-induced force.

    PubMed

    Yang, Cheol-Min; Jung, Hwan Jung; Kim, Yong Jung

    2015-05-15

    Nanoporous carbons, with different micropore size distributions, were prepared based on waste coffee grounds by a chemical activation process in order to elucidate the correlation between desolvated ions and pores smaller than the sizes of ions using an organic electrolyte. The pore structure of the coffee-based nanoporous carbon was strongly dependent on the heat-treatment temperature prior to the activation process. Cyclic voltammograms of the nanoporous carbons mainly dominated by the smaller pore relative to that of the bare ion size clearly showed deviation from an ideal feature of the current response. It was clearly envisaged that even a bare ion of a size larger than the pore size can penetrate into the pore by voltage-induced force. PMID:25668782

  3. 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.

  4. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    NASA Astrophysics Data System (ADS)

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-06-01

    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.

  5. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    PubMed Central

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-01-01

    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. PMID:26108369

  6. Evidence that bacteriophage λ lysogens may induce in response to the proton motive force uncoupler CCCP.

    PubMed

    Thomason, Lynn C; Court, Donald L

    2016-02-01

    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

  7. High-speed rotary microvalves in water using hydrodynamic force due to induced-charge electrophoresis.

    PubMed

    Sugioka, Hideyuki

    2010-03-01

    The development of a high-speed microactuator in water is difficult because of electrostatic problems and hydrodynamic resistance. To overcome these problems, we consider using induced-charge electrophoresis (ICEP) to move actuators. We propose rotary microvalves in water using hydrodynamic force due to ICEP and numerically examine the performance of valves. By the multiphysics coupled simulation technique between fluidics and electrostatics based on the boundary element method along with the thin-double-layer approximation, we find rotary valves using ICEP function effectively at high frequency. In the calculations, the electric and flow field problems in a bounded domain are solved, and the proper boundary conditions are discussed. By employing similar actuators using ICEP, we can dramatically improve the performance of promising microfluidic systems such as lab-on-a-chip.

  8. Cell Volume Fluctuations in MDCK Monolayers

    PubMed Central

    Zehnder, Steven M.; Suaris, Melanie; Bellaire, Madisonclaire M.; Angelini, Thomas E.

    2015-01-01

    Cells moving collectively in tissues constitute a form of active matter, in which collective motion depends strongly on driven fluctuations at the single-cell scale. Fluctuations in cell area and number density are often seen in monolayers, yet their role in collective migration is not known. Here we study density fluctuations at the single- and multicell level, finding that single-cell volumes oscillate with a timescale of 4 h and an amplitude of 20%; the timescale and amplitude are found to depend on cytoskeletal activity. At the multicellular scale, density fluctuations violate the central limit theorem, highlighting the role of nonequilibrium driving forces in multicellular density fluctuations. PMID:25606673

  9. 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.

  10. Cholesterol favors the emergence of a long-range autocorrelated fluctuation pattern in voltage-induced ionic currents through lipid bilayers.

    PubMed

    Corvalán, Natalia A; Kembro, Jackelyn M; Clop, Pedro D; Perillo, María A

    2013-08-01

    The present paper was aimed at evaluating the effect of cholesterol (CHO) on the voltage-induced lipid pore formation in bilayer membranes through a global characterization of the temporal dynamics of the fluctuation pattern of ion currents. The bilayer model used was black lipid membranes (BLMs) of palmitoyloleoylphosphatidylethanolamine and palmitoyloleoylphosphatidylcholine (POPE:POPC) at a 7:3 molar ratio in the absence (BLM0) or in the presence of 30 (BLM30), 40 (BLM40) or 50(BLM50)mol% of cholesterol with respect to total phospholipids. Electrical current intensities (I) were measured in voltage (ΔV) clamped conditions at ΔV ranging between 0 and ±200mV. The autocorrelation parameter α derived from detrended fluctuation analysis (DFA) on temporal fluctuation patterns of electrical currents allowed discriminating between non-correlated (α=0.5, white noise) and long-range correlated (0.5<α<1) behaviors. The increase in |ΔV| as well as in cholesterol content increased the number of conductance states, the magnitude of conductance level, the capacitance of the bilayers and increased the tendency towards the development of long-range autocorrelated (fractal) processes (0.5<α<1) in lipid channel generation. Experiments were performed above the phase transition temperature of the lipid mixtures, but compositions used predicted a superlattice-like organization. This leads to the conclusion that structural defects other than phase coexistence may promote lipid channel formation under voltage clamped conditions. Furthermore, cholesterol controls the voltage threshold that allows the percolation of channel behavior where isolated channels become an interconnected network.

  11. Three-dimensional morphogenesis of MDCK cells induced by cellular contractile forces on a viscous substrate

    PubMed Central

    Imai, Misako; Furusawa, Kazuya; Mizutani, Takeomi; Kawabata, Kazushige; Haga, Hisashi

    2015-01-01

    Substrate physical properties are essential for many physiological events such as embryonic development and 3D tissue formation. Physical properties of the extracellular matrix such as viscoelasticity and geometrical constraints are understood as factors that affect cell behaviour. In this study, we focused on the relationship between epithelial cell 3D morphogenesis and the substrate viscosity. We observed that Madin-Darby Canine Kidney (MDCK) cells formed 3D structures on a viscous substrate (Matrigel). The structures appear as a tulip hat. We then changed the substrate viscosity by genipin (GP) treatment. GP is a cross-linker of amino groups. Cells cultured on GP-treated-matrigel changed their 3D morphology in a substrate viscosity-dependent manner. Furthermore, to elucidate the spatial distribution of the cellular contractile force, localization of mono-phosphorylated and di-phosphorylated myosin regulatory light chain (P-MRLCs) was visualized by immunofluorescence. P-MRLCs localized along the periphery of epithelial sheets. Treatment with Y-27632, a Rho-kinase inhibitor, blocked the P-MRLCs localization at the edge of epithelial sheets and halted 3D morphogenesis. Our results indicate that the substrate viscosity, the substrate deformation, and the cellular contractile forces induced by P-MRLCs play crucial roles in 3D morphogenesis. PMID:26374384

  12. Three-dimensional morphogenesis of MDCK cells induced by cellular contractile forces on a viscous substrate.

    PubMed

    Imai, Misako; Furusawa, Kazuya; Mizutani, Takeomi; Kawabata, Kazushige; Haga, Hisashi

    2015-01-01

    Substrate physical properties are essential for many physiological events such as embryonic development and 3D tissue formation. Physical properties of the extracellular matrix such as viscoelasticity and geometrical constraints are understood as factors that affect cell behaviour. In this study, we focused on the relationship between epithelial cell 3D morphogenesis and the substrate viscosity. We observed that Madin-Darby Canine Kidney (MDCK) cells formed 3D structures on a viscous substrate (Matrigel). The structures appear as a tulip hat. We then changed the substrate viscosity by genipin (GP) treatment. GP is a cross-linker of amino groups. Cells cultured on GP-treated-matrigel changed their 3D morphology in a substrate viscosity-dependent manner. Furthermore, to elucidate the spatial distribution of the cellular contractile force, localization of mono-phosphorylated and di-phosphorylated myosin regulatory light chain (P-MRLCs) was visualized by immunofluorescence. P-MRLCs localized along the periphery of epithelial sheets. Treatment with Y-27632, a Rho-kinase inhibitor, blocked the P-MRLCs localization at the edge of epithelial sheets and halted 3D morphogenesis. Our results indicate that the substrate viscosity, the substrate deformation, and the cellular contractile forces induced by P-MRLCs play crucial roles in 3D morphogenesis. PMID:26374384

  13. Mechanism of vibration-induced repulsion force on a particle in a viscous fluid cell.

    PubMed

    Saadatmand, Mehrrad; Kawaji, Masahiro

    2013-08-01

    Space platforms such as the Space Shuttle and International Space Station have been considered an ideal environment for production of protein and semiconductor crystals of superior quality due to the negligible gravity-induced convection. Although it was believed that under microgravity environment diffusive mass transport would dominate the growth of the crystals, some related experiments have not shown satisfactory results possibly due to the movement of the growing crystals in fluid cells caused by small vibrations present in the space platforms called g-jitter. In ground-based experiments, there have been clear observations of attraction and repulsion of a solid particle with respect to a nearby wall of the fluid cell due to small vibrations. The present work is a numerical investigation on the physical mechanisms responsible for the repulsion force, which has been predicted to increase with the cell vibration frequency and amplitude, as well as the fluid viscosity. Moreover, the simulations have revealed that the repulsion force occurs mostly due to the increased pressure in the narrow gap between the particle and the nearest wall. PMID:24032936

  14. 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.

  15. Kank2 activates talin, reduces force transduction across integrins and induces central adhesion formation.

    PubMed

    Sun, Zhiqi; Tseng, Hui-Yuan; Tan, Steven; Senger, Fabrice; Kurzawa, Laetitia; Dedden, Dirk; Mizuno, Naoko; Wasik, Anita A; Thery, Manuel; Dunn, Alexander R; Fässler, Reinhard

    2016-09-01

    Integrin-based adhesions play critical roles in cell migration. Talin activates integrins and flexibly connects integrins to the actomyosin cytoskeleton, thereby serving as a 'molecular clutch' that transmits forces to the extracellular matrix to drive cell migration. Here we identify the evolutionarily conserved Kank protein family as novel components of focal adhesions (FAs). Kank proteins accumulate at the lateral border of FAs, which we term the FA belt, and in central sliding adhesions, where they directly bind the talin rod domain through the Kank amino-terminal (KN) motif and induce talin and integrin activation. In addition, Kank proteins diminish the talin-actomyosin linkage, which curbs force transmission across integrins, leading to reduced integrin-ligand bond strength, slippage between integrin and ligand, central adhesion formation and sliding, and reduced cell migration speed. Our data identify Kank proteins as talin activators that decrease the grip between the integrin-talin complex and actomyosin to regulate cell migration velocity. PMID:27548916

  16. Mechanism of vibration-induced repulsion force on a particle in a viscous fluid cell

    NASA Astrophysics Data System (ADS)

    Saadatmand, Mehrrad; Kawaji, Masahiro

    2013-08-01

    Space platforms such as the Space Shuttle and International Space Station have been considered an ideal environment for production of protein and semiconductor crystals of superior quality due to the negligible gravity-induced convection. Although it was believed that under microgravity environment diffusive mass transport would dominate the growth of the crystals, some related experiments have not shown satisfactory results possibly due to the movement of the growing crystals in fluid cells caused by small vibrations present in the space platforms called g-jitter. In ground-based experiments, there have been clear observations of attraction and repulsion of a solid particle with respect to a nearby wall of the fluid cell due to small vibrations. The present work is a numerical investigation on the physical mechanisms responsible for the repulsion force, which has been predicted to increase with the cell vibration frequency and amplitude, as well as the fluid viscosity. Moreover, the simulations have revealed that the repulsion force occurs mostly due to the increased pressure in the narrow gap between the particle and the nearest wall.

  17. Non-equilibrium Casimir force between vibrating plates.

    PubMed

    Hanke, Andreas

    2013-01-01

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

  18. 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. PMID:27167473

  19. 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.

  20. Expectations induced by natural-like temporal fluctuations are independent of attention decrement: evidence from behavior and early visual evoked potentials.

    PubMed

    Derosiere, Gerard; Farrugia, Nicolas; Perrey, Stéphane; Ward, Tomas; Torre, Kjerstin

    2015-01-01

    Temporal expectations and attention decrement affect human behavior in opposing ways: the former positively, the latter negatively yet both exhibit similar neural signatures - i.e., reduction in the early event-related potential components' amplitude - despite different underlying mechanisms. Furthermore, there is a significant and growing debate in the literature regarding the putative role of attention in the encoding of expectations in perception. The question then arises as to what are the behavioral and neural consequences, if any, of attention decrement on temporal expectations and related enhancement of sensory information processing. Here, we investigated behavioral performance and visual N1a, N1p and P1 components during a sustained attention reaction time task inducing attention decrement under two conditions. In one condition, the inter-stimulus intervals (ISIs) were randomly distributed to impede expectation effects while for the other, the ISI exhibited natural-like long-term correlations supposed to induce temporal expectations. Behavioral results show that natural-like fluctuations in ISI indeed induced faster RT due to temporal expectations. These temporal expectations were beneficial even under attention decrement circumstances. Further, temporal expectations were associated with reduced N1a amplitude while attention decrement was associated with reduced N1p amplitude. Our findings provide evidence that the effects of temporal expectations and attention decrement induced in a single task can be independent at the behavioral level, and are supported at separate information processing stages at the neural level in vision. PMID:25224996

  1. 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

  2. Frequency fluctuations in silicon nanoresonators

    NASA Astrophysics Data System (ADS)

    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

    2016-06-01

    Frequency stability is key to the 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 that 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.

  3. 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.

  4. Long lasting increase in nociceptive threshold induced in mice by forced swimming: involvement of an endorphinergic mechanism.

    PubMed

    Suaudeau, C; Costentin, J

    2000-05-01

    Mice submitted to forced swimming session(s) displayed a long lasting modification in their nociceptive threshold, assessed through their jump latency from a hot plate (55 degrees C). Thus two forced swimming sessions (6 min each, 8h apart), in water at 33 degrees C, increased by about 50% the jump latency when the hot plate test was performed 14 hours, 3 days or 6 days thereafter. The water temperature (16 degrees C vs 33 degrees C) had no critical influence in this respect. To be clearly effective (at 33 degrees C) the swimming session had to be performed twice (when performed only once it was irregularly effective); it apparently culminated for a 6 min duration, since its effectiveness was not significantly increased by extending the swimming time to 12 min or 18 min. Performing 2 forced swimming sessions (6 min each, 8h apart), 5 consecutive days, resulted in a suppression of the increase in jump latency in the hot plate test. The two forced swimming episodes-induced analgesia was prevented by the s.c. administration of diazepam (from 0.125 mg/kg) or morphine (from 5 mg/kg) or scopolamine (1 mg/kg) before each forced swimming episode. Morphine (7.5 mg/kg) was uneffective to prevent the induction of two forced swimming episodes-induced analgesia when it was administered immediately after each forced swimming session. Finally this analgesia was dose dependently reversed by naloxone (ID(50) = 0.14 mg/kg, s.c., 30 min before the hot plate test). It is hypothesized that the handling of mice immediately before the hot plate test induces the remembrance of the stress induced by previous forced swimming episodes, triggering a fear reaction which increases the nociceptive threshold. PMID:10938583

  5. 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.

  6. Forced expression of Hnf4a induces hepatic gene activation through directed differentiation.

    PubMed

    Yahoo, Neda; Pournasr, Behshad; Rostamzadeh, Jalal; Fathi, Fardin

    2016-08-01

    Embryonic stem (ES) cells are capable of unlimited self-renewal and have a diverse differentiation potential. These unique features make ES cells as an attractive source for developmental biology studies. Having the mature hepatocyte in the lab with functional activities is valuable in drug discovery studies. Overexpression of hepatocyte lineage-specific transcription factors (TFs) becomes a promising approach in pluripotent cell differentiation toward liver cells. Many studies generate transgenic ES cell lines to examine the effects of specific TFs overexpression in cell differentiation. In the present report, we have addressed whether a suspension or adherent model of differentiation is an appropriate way to study the role of Hnf4a overexpression. We generated ES cells that carried a doxycycline (Dox)-inducible Hnf4a using lentiviral vectors. The transduced cells were subjected to induced Hnf4a overexpression through both spontaneous and directed differentiation methods. Gene expression analysis showed substantially increased expression of hepatic gene markers, particularly Ttr and endogenous Hnf4a, in transduced cells differentiated by the directed approach. These results demonstrated that forced expression of TFs during directed differentiation would be an appropriate way to study relevant gene activation and the effects of overexpression in the context of hepatic differentiation. PMID:27233607

  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. Mechanical Force-induced TGFB1 Increases Expression of SOST/POSTN by hPDL Cells.

    PubMed

    Manokawinchoke, J; Limjeerajarus, N; Limjeerajarus, C; Sastravaha, P; Everts, V; Pavasant, P

    2015-07-01

    The aim of this study was to investigate the response of human periodontal ligament (hPDL) fibroblasts to an intermittent compressive force and its effect on the expression of SOST, POSTN, and TGFB1. A computerized cell compressive force loading apparatus was introduced, and hPDL cells were subjected to intermittent compressive force. The changes in messenger RNA (mRNA) and protein expression were monitored by real-time polymerase chain reaction and Western blot analysis, respectively. An increased expression of SOST, POSTN, and TGFB1 was observed in a time-dependent fashion. Addition of cycloheximide, a transforming growth factor (TGF)-β inhibitor (SB431542), or a neutralizing antibody against TGF-β1 attenuated the force-induced expression of SOST and POSTN as well as sclerostin and periostin, indicating a role of TGF-β1 in the pressure-induced expression of these proteins. Enzyme-linked immunosorbent assay analysis revealed an increased level of TGF-β1 in the cell extracts but not in the medium, suggesting that intermittent compressive force promoted the accumulation of TGF-β1 in the cells or their surrounding matrix. In conclusion, an intermittent compressive force regulates SOST/POSTN expression by hPDL cells via the TGF-β1 signaling pathway. Since these proteins play important roles in the homeostasis of the periodontal tissue, our results indicate the importance of masticatory forces in this process.

  9. 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.

  10. Density-of-states Fluctuation-induced Negative Out-of-plane Magnetoresistance in Overdoped Bi-2212

    NASA Astrophysics Data System (ADS)

    Usui, Tomohiro; Adachi, Shintaro; Watanabe, Takao; Nishizaki, Terukazu

    We analyzed the in-plane and out -of-plane m agnetoresistance (MR) f or o verdoped B i1.6Pb0.4Sr2CaCu2O8+δ (Bi-2212) s ingle crystals us ing s uperconductive f luctuation t heory, which considers the d ensity-of-states (DOS) contribution i n l ayered superconductors with the conventional s-wave pairing state. The out-of-plane results are well reproduced by the theory, implying that the large, negative out-of-plane MR as well as the sharp increase in the zero-field out-of-plane resistivityρc near the superconducting transition temperature Tc originate from the superconductive DOS fluctuation effect. On the other hand, the in-plane results are better reproduced without the D OS c ontribution (i.e., using only th e Aslamazov-Larkin (AL) contribution), which may be e xplained in terms of the d-wave superconductivity of the layered superconductors.

  11. 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

  12. 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

  13. Steered Molecular Dynamics Simulations of a Type IV Pilus Probe Initial Stages of a Force-Induced Conformational Transition

    PubMed Central

    Baker, Joseph L.; Biais, Nicolas; Tama, Florence

    2013-01-01

    Type IV pili are long, protein filaments built from a repeating subunit that protrudes from the surface of a wide variety of infectious bacteria. They are implicated in a vast array of functions, ranging from bacterial motility to microcolony formation to infection. One of the most well-studied type IV filaments is the gonococcal type IV pilus (GC-T4P) from Neisseria gonorrhoeae, the causative agent of gonorrhea. Cryo-electron microscopy has been used to construct a model of this filament, offering insights into the structure of type IV pili. In addition, experiments have demonstrated that GC-T4P can withstand very large tension forces, and transition to a force-induced conformation. However, the details of force-generation, and the atomic-level characteristics of the force-induced conformation, are unknown. Here, steered molecular dynamics (SMD) simulation was used to exert a force in silico on an 18 subunit segment of GC-T4P to address questions regarding the nature of the interactions that lead to the extraordinary strength of bacterial pili. SMD simulations revealed that the buried pilin α1 domains maintain hydrophobic contacts with one another within the core of the filament, leading to GC-T4P's structural stability. At the filament surface, gaps between pilin globular head domains in both the native and pulled states provide water accessible routes between the external environment and the interior of the filament, allowing water to access the pilin α1 domains as reported for VC-T4P in deuterium exchange experiments. Results were also compared to the experimentally observed force-induced conformation. In particular, an exposed amino acid sequence in the experimentally stretched filament was also found to become exposed during the SMD simulations, suggesting that initial stages of the force induced transition are well captured. Furthermore, a second sequence was shown to be initially hidden in the native filament and became exposed upon stretching. PMID

  14. 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.

  15. Forced bars induced by variations of channel width: Implications for incipient bifurcation

    NASA Astrophysics Data System (ADS)

    Wu, Fu-Chun; Yeh, Tzu-Hao

    2005-06-01

    In this study we investigate forced bars that form in a channel with periodic width variations. A depth-averaged two-dimensional (2-D) model incorporating a simplified correction for the helical flows induced by streamline curvature is used to obtain analytical solution of bed deformation. Flume experiments are conducted to verify the model results. With the correction included, the 2-D model will be comparable to the 3-D model. Because the no-slip condition is relaxed at the sidewalls, the model gives distorted results in the near-bank region, particularly at narrow sections, but the bed topography is satisfactory for the major part of the channel. The forced bars are classified into four types according to the locations of peak deformations. Transition from one type to another is controlled mainly by the aspect ratio β. Increasing the value of β exhibits sequentially the purely central bars (mode 1), transverse bars (central mode 1), side bars, and transverse bars (central mode 2). The analytical solution is used to derive a criterion for central bar formation, which implies a condition required for incipient bifurcation. Given the bank profile, flow, and sediment conditions, the central bars of mode 1 would develop for β < βc1 (a lower critical value), the central bars of mode 2 would develop for β > βc2 (an upper critical value), whereas side bars would form for βc1 < β < βc2. Such criteria for formation of different bar patterns are necessary but not sufficient conditions for establishing stable regimes.

  16. 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

  17. Expression of myosin heavy-chain mRNA in cultured myoblasts induced by centrifugal force.

    PubMed

    Kurokawa, Katsuhide; Sakiyama, Koji; Abe, Shinichi; Hiroki, Emi; Naito, Kaoru; Nakajima, Kazunori; Takeda, Tomotaka; Inoue, Takashi; Ide, Yoshinobu; Ishigami, Keiichi

    2008-11-01

    Ballistic muscle training leads to hypertrophy of fast type fibers and training for endurance induces that of slow type fibers. Numerous studies have been conducted on electrical, extending and magnetic stimulation of cells, but the effect of centrifugal force on cells remains to be investigated. In this study, we investigated the effect of stimulating cultured myoblasts with centrifugal force at different speeds on cell proliferation and myosin heavy-chain (MyHC) mRNA expression in muscle fiber. Stimulation of myoblasts was carried out at 2 different speeds for 20 min using the Himac CT6D, a desk centrifuge, and cells were observed at 1, 3 and 5 days later. Number of cells 1 and 5 days after centrifugal stimulation was significantly larger in the 62.5 x g and 4,170 x g stimulation groups than in the control group. Expression of MyHC-2b mRNA 1 day after centrifugal stimulation was significantly higher in the 2 stimulation groups than in the control group. Almost no expression of MyHC-2a was observed in any group at 1 and 3 days after centrifugal stimulation. However, 5 days after stimulation, MyHC-2a was strongly expressed in the 2 stimulation groups in comparison to the control group. Three days after centrifugal stimulation, expression of MyHC-1 was significantly higher in the 2 stimulation groups than in the control group. The results of this study clarified the effect of different centrifugal stimulation speeds on muscle fiber characteristics, and suggest that centrifugal stimulation of myoblasts enhances cell proliferation.

  18. Shear-induced force transmission in a multicomponent, multicell model of the endothelium

    PubMed Central

    Dabagh, Mahsa; Jalali, Payman; Butler, Peter J.; Tarbell, John M.

    2014-01-01

    Haemodynamic forces applied at the apical surface of vascular endothelial cells (ECs) provide the mechanical signals at intracellular organelles and through the inter-connected cellular network. The objective of this study is to quantify the intracellular and intercellular stresses in a confluent vascular EC monolayer. A novel three-dimensional, multiscale and multicomponent model of focally adhered ECs is developed to account for the role of potential mechanosensors (glycocalyx layer, actin cortical layer, nucleus, cytoskeleton, focal adhesions (FAs) and adherens junctions (ADJs)) in mechanotransmission and EC deformation. The overriding issue addressed is the stress amplification in these regions, which may play a role in subcellular localization of mechanotransmission. The model predicts that the stresses are amplified 250–600-fold over apical values at ADJs and 175–200-fold at FAs for ECs exposed to a mean shear stress of 10 dyne cm−2. Estimates of forces per molecule in the cell attachment points to the external cellular matrix and cell–cell adhesion points are of the order of 8 pN at FAs and as high as 3 pN at ADJs, suggesting that direct force-induced mechanotransmission by single molecules is possible in both. The maximum deformation of an EC in the monolayer is calculated as 400 nm in response to a mean shear stress of 1 Pa applied over the EC surface which is in accord with measurements. The model also predicts that the magnitude of the cell–cell junction inclination angle is independent of the cytoskeleton and glycocalyx. The inclination angle of the cell–cell junction is calculated to be 6.6° in an EC monolayer, which is somewhat below the measured value (9.9°) reported previously for ECs subjected to 1.6 Pa shear stress for 30 min. The present model is able, for the first time, to cross the boundaries between different length scales in order to provide a global view of potential locations of mechanotransmission. PMID:24966239

  19. Improved Ligand Discrimination by Force-Induced Unbinding of the T Cell Receptor from Peptide-MHC

    PubMed Central

    Klotzsch, Enrico; Schütz, Gerhard J.

    2013-01-01

    T cell activation is mediated via the recognition of peptides by the T cell receptor (TCR). This receptor ligand interaction is highly specific, and the TCR has to discriminate between a huge number of peptides presented by the products of the major histocompatibility complexes (MHCs). Recent studies indicate that cells probe the TCR-pMHC interaction by imposing force on the interaction. Here we investigated in a theoretical analysis the consequences of such force-induced unbinding for T cell recognition. Our findings are as follows. First, the bond rupture under force is much faster, improving the time resolution of the discrimination process. Second, cells can access additional parameters characterizing the shape of the binding energy surface. Third, load-induced unbinding yields a reduced coefficient of variation of the bond lifetimes, which improves the discriminative power even between peptide/MHCs (pMHCs) with similar off-rates. PMID:23601314

  20. The forced walking test: a novel test for pinpointing the anesthetic-induced transition in consciousness in mouse.

    PubMed

    Hwang, Eunjin; Kim, Seunghwan; Shin, Hee-Sup; Choi, Jee Hyun

    2010-04-30

    In consciousness or anesthesia studies, pinpointing the precise moment of consciousness or anesthetic transition has been challenging because of the variable lag time between a treatment and its induced response. Here, we describe a novel behavioral method, a forced walking test, which pinpoints the moment of the anesthetic-induced loss of motion (LOM) without handling the animals manually. The mouse is forced to walk on a treadmill, and an anesthetic drug is administered into the peritoneum via a previously secured injection route. The physical activity and the angle of head posture are tracked using a motion sensor preinstalled on the animal's head. The moments of LOM and recovery of motion (ROM) are identified from the physical activity parameters obtained by the sensor. Comparison of our method with the conventional loss-of-righting-reflex assay showed that the time point of LOM was not significantly different between the two methods when examined with two different types of anesthetic agents, propofol and ketamine/xylazine cocktail. In addition, the electrophysiological signals simultaneously acquired in the cortex and the thalamus of the mouse during the forced walking test showed that the brain rhythms induced by ketamine/xylazine anesthesia were generated and terminated in a time-locked manner with respect to LOM and ROM, respectively. In conclusion, the forced walking test allows an objective and precise detection of anesthetic-induced LOM, as well as ROM during awakening from anesthesia, in test animals.

  1. 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.

  2. Dissociable effects of antipsychotics on ketamine-induced changes in regional oxygenation and inter-regional coherence of low frequency oxygen fluctuations in the rat.

    PubMed

    Li, Jennifer; Ishiwari, Keita; Conway, Michael W; Francois, Jennifer; Huxter, John; Lowry, John P; Schwarz, Adam J; Tricklebank, Mark; Gilmour, Gary

    2014-06-01

    Typical and atypical antipsychotics have been shown to alleviate N-methyl-D-aspartate (NMDA) receptor antagonist-induced BOLD signals in healthy humans and animals to differing degrees; factors that might relate to their different molecular mechanisms and clinical profiles. Recent studies have also extended these investigations to the analysis of resting state functional connectivity measures of BOLD signals in different brain regions. Using constant potential amperometry, we examined the effects of the NMDA receptor antagonist S-(+)-ketamine on tissue oxygen levels in medial prefrontal cortex (mPFC) and medial ventral striatum (mVS), and temporal coherence of low-frequency oxygen fluctuations between these regions in freely moving rats. Furthermore, we assessed the extent to which the atypical antipsychotic clozapine and the typical antipsychotic haloperidol could modulate the effects of S-(+)-ketamine on these measures. Acute S-(+)-ketamine (5-25 mg/kg) produced dose-dependent increases in both tissue O2 levels and coherence. Although effects of clozapine and haloperidol alone were relatively minor, their effects on ketamine-induced signals were markedly more distinct. Clozapine dose-dependently attenuated the absolute S-(+)-ketamine (25 mg/kg) O2 signal in both regions, and also attenuated ketamine-induced increases in regional coherence. Haloperidol had no effect on the absolute ketamine O2 signal yet potentiated increases in regional coherence. The dissociable effects of haloperidol and clozapine on ketamine-induced hyperoxygenation and mPFC-mVS coherence elucidate potentially important mechanistic differences between these classes of pharmacology. This study demonstrates for the first time that in vivo amperometry can measure both regional brain tissue O2 levels and inter-regional coherence, advancing BOLD-like measurements of functional connectivity into awake, unconstrained animals.

  3. 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.

  4. 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.

  5. Atomic force microscopy study of laser induced phase transitions in Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Weidenhof, V.; Friedrich, I.; Ziegler, S.; Wuttig, M.

    1999-11-01

    Micron- and submicron-size changes induced by local laser heating in thin films of Ge2Sb2Te5 are studied by atomic force microscopy (AFM). This material is presently used for rewritable data storage that employs phase change recording. Reversible switching between the amorphous and crystalline states, which is accompanied by a considerable change in optical properties and film density, is exploited to store bits of information. The density change can be detected by AFM, which we use here to study the amorphization (writing) and recrystallization (erasure) of single bits. Both processes have been measured as a function of modification pulse power and duration. Morphology changes can be detected even if the phase change film is covered by a thin protective layer. AFM allows a precise determination of the bit size and bit depth, which characterizes the progress of the phase change in the direction of the surface normal. The present setup allows the correlation of the change in optical reflectance ΔR caused by a specific laser pulse to the bit topography. This enables a detailed study of the mechanisms of bit writing and erasure.

  6. Understanding the influence of solvent field and fluctuations on the stability of photo-induced charge-separated state in molecular triad

    NASA Astrophysics Data System (ADS)

    Balamurugan, D.; Aquino, Adelia; Lischka, Hans; Dios, Francis; Flores, Lionel; Cheung, Margaret

    2013-03-01

    Molecular triad composed of fullerene, porphyrin, and carotene is an artificial analogue of natural photosynthetic system and is considered for applications in solar energy conversion because of its ability to produce long-lived photo-induced charge separated state. The goal of the present multiscale simulation is to understand how the stability of photo-induced charge-separated state in molecular triad is influenced by a polar organic solvent, namely tetrahydrofuran (THF). The multiscale approach is based on combined quantum, classical molecular dynamics, and statistical physics calculations. The quantum chemical calculations were performed on the triad using the second order algebraic diagrammatic perturbation and time-dependent density functional theory. Molecular dynamics simulations were performed on triad in a box of THF solvent with the replica exchange method. The two methods on different length and time scales are bridged through an important sampling technique. We have analyzed the free energy landscape, structural fluctuations, and the long- range electrostatic interactions between triad and solvent molecules. The results suggest that the polarity and re-organization of the solvent is critical in stabilization of charge-separated state in triad. Supported by DOE (DE-FG02-10ER16175)

  7. 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.

    2016-03-01

    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.

  8. Heat Shock–Induced Fluctuations in Clock and Light Signaling Enhance Phytochrome B–Mediated Arabidopsis Deetiolation[C][W

    PubMed Central

    Karayekov, Elizabeth; Sellaro, Romina; Legris, Martina; Yanovsky, Marcelo J.; Casal, Jorge J.

    2013-01-01

    Moderately warm constant ambient temperatures tend to oppose light signals in the control of plant architecture. By contrast, here we show that brief heat shocks enhance the inhibition of hypocotyl growth induced by light perceived by phytochrome B in deetiolating Arabidopsis thaliana seedlings. In darkness, daily heat shocks transiently increased the expression of PSEUDO-RESPONSE REGULATOR7 (PRR7) and PRR9 and markedly enhanced the amplitude of the rhythms of LATE ELONGATED HYPOCOTYL (LHY) and CIRCADIAN CLOCK ASSOCIATED1 (CCA1) expression. In turn, these rhythms gated the hypocotyl response to red light, in part by changing the expression of PHYTOCHROME INTERACTING FACTOR4 (PIF4) and PIF5. After light exposure, heat shocks also reduced the nuclear abundance of CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) and increased the abundance of its target ELONGATED HYPOCOTYL5 (HY5). The synergism between light and heat shocks was deficient in the prr7 prr9, lhy cca1, pif4 pif5, cop1, and hy5 mutants. The evening element (binding site of LHY and CCA1) and G-box promoter motifs (binding site of PIFs and HY5) were overrepresented among genes with expression controlled by both heat shock and red light. The heat shocks experienced by buried seedlings approaching the surface of the soil prepare the seedlings for the impending exposure to light by rhythmically lowering LHY, CCA1, PIF4, and PIF5 expression and by enhancing HY5 stability. PMID:23933882

  9. Preventive Effects of Forced Exercise against Alcohol-induced Physical Dependency and Reduction of Pain Perception Threshold

    PubMed Central

    Motaghinejad, Majid; Ghaleni, Majid Asadi; Motaghinejad, Ozra

    2014-01-01

    Background: Treatment of postabstinence syndrome of alcohol is one of the major strategies of alcoholism treatment. Exercise can be modulated major brain pathways such as a reward system and pain perception centers. The aim of this study was to evaluation the effects of forced exercise in the management of alcohol dependence and pain perception alteration which induced by alcoholism. Methods: 72 adult male rats were divided into 2 major groups: (1) 40 of them was divided into groups of positive control (alcohol dependent) negative control and alcohol dependent groups under treatment by forced exercise, diazepam (0.4 mg/kg) and forced exercise in combination with diazepam and alcohol withdrawal signs, and blood cortisols, were measured in this groups. (2) 32 rats were divided into control, alcohol dependent (without treatment), and alcohol-dependent groups under treatment by forced exercise or indometacin (5 mg/kg) and then pain perception was assessed by using writhing test, tail-flick and hot plate test. Results: Forced exercise, diazepam, and their combinations significantly attenuates withdrawal syndrome to 20 ± 2, 22 ± 1.3 and 16 ± 2 and blood cortisol level to 6.8 ± 1.3,7.9 ± 1.2 and 5.8 ± 1.1, respectively, in comparison with the positive control group (P < 0.05 and P < 0.001). In alcohol dependent animal under treatment by forced exercise, pain response significantly inhibited with 37%, 57% and 38% decreases in writhing test, hot plate, and tail-flick test, respectively, in comparison with alcohol dependent (without treatment) group (P < 0.05). Conclusions: This study suggested that forced exercise can be useful as adjunct therapy in alcoholism patient and also can be effective in modulation of pain threshold reduction that was induced by alcohol dependency. PMID:25400889

  10. 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.

  11. 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

  12. 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.

  13. Swarming in viscous fluids: Three-dimensional patterns in swimmer- and force-induced flows.

    PubMed

    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. PMID:27176395

  14. 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.

  15. Traction force dynamics predict gap formation in activated endothelium.

    PubMed

    Valent, Erik T; van Nieuw Amerongen, Geerten P; van Hinsbergh, Victor W M; Hordijk, Peter L

    2016-09-10

    In many pathological conditions the endothelium becomes activated and dysfunctional, resulting in hyperpermeability and plasma leakage. No specific therapies are available yet to control endothelial barrier function, which is regulated by inter-endothelial junctions and the generation of acto-myosin-based contractile forces in the context of cell-cell and cell-matrix interactions. However, the spatiotemporal distribution and stimulus-induced reorganization of these integral forces remain largely unknown. Traction force microscopy of human endothelial monolayers was used to visualize contractile forces in resting cells and during thrombin-induced hyperpermeability. Simultaneously, information about endothelial monolayer integrity, adherens junctions and cytoskeletal proteins (F-actin) were captured. This revealed a heterogeneous distribution of traction forces, with nuclear areas showing lower and cell-cell junctions higher traction forces than the whole-monolayer average. Moreover, junctional forces were asymmetrically distributed among neighboring cells. Force vector orientation analysis showed a good correlation with the alignment of F-actin and revealed contractile forces in newly formed filopodia and lamellipodia-like protrusions within the monolayer. Finally, unstable areas, showing high force fluctuations within the monolayer were prone to form inter-endothelial gaps upon stimulation with thrombin. To conclude, contractile traction forces are heterogeneously distributed within endothelial monolayers and force instability, rather than force magnitude, predicts the stimulus-induced formation of intercellular gaps. PMID:27498166

  16. A stochastic model and Monte Carlo algorithm for fluctuation-induced H{sub 2} formation on the surface of interstellar dust grains

    SciTech Connect

    Sabelfeld, K.K.

    2015-09-01

    A stochastic algorithm for simulation of fluctuation-induced kinetics of H{sub 2} 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 H{sub 2} 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.

  17. 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.

  18. Molecular characterization of the cold- and heat-induced Arabidopsis PXL1 gene and its potential role in transduction pathways under temperature fluctuations.

    PubMed

    Jung, Chang Gyo; Hwang, Sun-Goo; Park, Yong Chan; Park, Hyeon Mi; Kim, Dong Sub; Park, Duck Hwan; Jang, Cheol Seong

    2015-03-15

    LRR-RLK (Leucine-Rich Repeat Receptor-Like Kinase) proteins are believed to play essential roles in cell-to-cell communication during various cellular processes including development, hormone perception, and abiotic stress responses. We isolated an LRR-RLK gene previously named Arabidopsis PHLOEM INTERCALATED WITH XYLEM-LIKE 1 (AtPXL1) and examined its expression patterns. AtPXL1 was highly induced by cold and heat stress, but not by drought. The fluorescence signal of 35S::AtPXL1-EGFP was closely localized to the plasma membrane. A yeast two-hybrid and bimolecular fluorescence complementation assay exhibited that AtPXL1 interacts with both proteins, A. thaliana histidine-rich dehydrin1 (AtHIRD1) and A. thaliana light-harvesting protein complex I (AtLHCA1). We found that AtPXL1 possesses autophosphorylation activity and phosphorylates AtHIRD1 and AtLHCA1 in an in vitro assay. Subsequently, we found that the knockout line (atpxl1) showed hypersensitive phenotypes when subjected to cold and heat during the germination stage, while the AtPXL1 overexpressing line as well as wild type plants showed high germination rates compared to the knockout plants. These results provide an insight into the molecular function of AtPXL1 in the regulation of signal transduction pathways under temperature fluctuations.

  19. Molecular characterization of the cold- and heat-induced Arabidopsis PXL1 gene and its potential role in transduction pathways under temperature fluctuations.

    PubMed

    Jung, Chang Gyo; Hwang, Sun-Goo; Park, Yong Chan; Park, Hyeon Mi; Kim, Dong Sub; Park, Duck Hwan; Jang, Cheol Seong

    2015-03-15

    LRR-RLK (Leucine-Rich Repeat Receptor-Like Kinase) proteins are believed to play essential roles in cell-to-cell communication during various cellular processes including development, hormone perception, and abiotic stress responses. We isolated an LRR-RLK gene previously named Arabidopsis PHLOEM INTERCALATED WITH XYLEM-LIKE 1 (AtPXL1) and examined its expression patterns. AtPXL1 was highly induced by cold and heat stress, but not by drought. The fluorescence signal of 35S::AtPXL1-EGFP was closely localized to the plasma membrane. A yeast two-hybrid and bimolecular fluorescence complementation assay exhibited that AtPXL1 interacts with both proteins, A. thaliana histidine-rich dehydrin1 (AtHIRD1) and A. thaliana light-harvesting protein complex I (AtLHCA1). We found that AtPXL1 possesses autophosphorylation activity and phosphorylates AtHIRD1 and AtLHCA1 in an in vitro assay. Subsequently, we found that the knockout line (atpxl1) showed hypersensitive phenotypes when subjected to cold and heat during the germination stage, while the AtPXL1 overexpressing line as well as wild type plants showed high germination rates compared to the knockout plants. These results provide an insight into the molecular function of AtPXL1 in the regulation of signal transduction pathways under temperature fluctuations. PMID:25602612

  20. 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.

  1. 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.

  2. Veratrine blocks the lamotrigine-induced swimming increase and immobility decrease in the modified forced swimming test.

    PubMed

    Codagnone, F T; Consoni, F T; Rodrigues, A L S; Vital, M A B F; Andreatini, R

    2007-08-15

    Lamotrigine exhibits an anti-immobility effect in the modified forced swimming test, increasing swimming and climbing, behaviors that are related to serotonergic and noradrenergic effects, respectively. However, these effects could be secondary to lamotrigine blockade of Na(+) sensitive channel. Thus, this study investigated the influence of veratrine (0.1 mg/kg, ip, 10 min before each lamotrigine administration), an Na(+) channel activator, in the effect of lamotrigine (20 mg/kg, ip, 24, 5, 1 h before the test session) in the modified forced swimming test. Veratrine pre-treatment blocked lamotrigine-induced immobility decrease and swimming increase but it did not change the effect of lamotrigine on climbing. These results suggest that the serotonergic effect of lamotrigine in the modified forced swimming test is dependent on Na(+) voltage sensitive channel blockade, whereas its noradrenergic effect is not.

  3. 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.

  4. 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. PMID:26734525

  5. 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.

  6. 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.

  7. Scanning-force-microscopy study of MeV-atomic-ion-induced surface tracks in organic crystals

    SciTech Connect

    Kopniczky, J.; Reimann, C.T.; Hallen, A.; Sundqvist, B.U.R. ); Tengvall, P.; Erlandsson, R. )

    1994-01-01

    We present scanning force microscope images of craterlike defects induced by individual 78.2-MeV [sup 127]I ions incident on organic single-crystal [ital L]-valine surfaces. For grazing incidence ions, the craters are elongated along the ion azimuth of incidence and display a raised tail in the surface above the ion track. This permanent plastic deformation of the surface indicates that a hydrodynamic pressure-pulse phenomenon occurs in response to the electronically deposited energy.

  8. Measurement of velocity fluctuations in microfluidics with simultaneously ultrahigh spatial and temporal resolution

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Yang, Fang; Khan, Jamil; Reifsnider, Ken; Wang, Guiren

    2016-01-01

    Although unsteady and electrokinetic flows are widely used in microfluidics, there is unfortunately no velocimeter today that can measure the random velocity fluctuation at high temporal and spatial resolution simultaneously in microfluidics. Here we, for the first time, theoretically study the temporal resolution of laser induced fluorescence photobleaching anemometer (LIFPA) and experimentally verify that LIFPA can have simultaneously ultrahigh temporal ({˜ } 4 \\upmu s) and spatial ({˜ }203 nm) resolution and can measure velocity fluctuation up to at least 2 kHz, whose corresponding wave number is about 6× 10^6 {/}m in an electrokinetically forced unsteady flow in microfluidics.

  9. Attosecond and femtosecond forces exerted on gold nanoparticles induced by swift electrons

    NASA Astrophysics Data System (ADS)

    Lagos, Maureen J.; Reyes-Coronado, Alejandro; Konečná, Andrea; Echenique, Pedro M.; Aizpurua, Javier; Batson, Philip E.

    2016-05-01

    We report time-dependent calculations of attosecond and femtosecond forces imposed by a kilovolt swift electron during passage near a nanometer-sized metal particle. Contrary to expectations based on dielectric theory, which suggest that the forces should always be attractive, we find that for very close approaches, attosecond forces are repulsive, and are caused by interaction of the magnetic field of the relativistic electron with currents within even nominally nonmagnetic nanoparticles. These results suggest an explanation for the observation of both attractive and repulsive nanoparticle movement during the first use of Ångstrom-sized electron beams in electron microscopy.

  10. Force-induced on-rate switching and modulation by mutations in gain-of-function von Willebrand diseases

    PubMed Central

    Kim, Jongseong; Hudson, Nathan E.; Springer, Timothy A.

    2015-01-01

    Mutations in the ultralong vascular protein von Willebrand factor (VWF) cause the common human bleeding disorder, von Willebrand disease (VWD). The A1 domain in VWF binds to glycoprotein Ibα (GPIbα) on platelets, in a reaction triggered, in part, by alterations in flow during bleeding. Gain-of-function mutations in A1 and GPIbα in VWD suggest conformational regulation. We report that force application switches A1 and/or GPIbα to a second state with faster on-rate, providing a mechanism for activating VWF binding to platelets. Switching occurs near 10 pN, a force that also induces a state of the receptor−ligand complex with slower off-rate. Force greatly increases the effects of VWD mutations, explaining pathophysiology. Conversion of single molecule kon (s−1) to bulk phase kon (s−1M−1) and the kon and koff values extrapolated to zero force for the low-force pathways show remarkably good agreement with bulk-phase measurements. PMID:25810255

  11. Force-induced on-rate switching and modulation by mutations in gain-of-function von Willebrand diseases.

    PubMed

    Kim, Jongseong; Hudson, Nathan E; Springer, Timothy A

    2015-04-14

    Mutations in the ultralong vascular protein von Willebrand factor (VWF) cause the common human bleeding disorder, von Willebrand disease (VWD). The A1 domain in VWF binds to glycoprotein Ibα (GPIbα) on platelets, in a reaction triggered, in part, by alterations in flow during bleeding. Gain-of-function mutations in A1 and GPIbα in VWD suggest conformational regulation. We report that force application switches A1 and/or GPIbα to a second state with faster on-rate, providing a mechanism for activating VWF binding to platelets. Switching occurs near 10 pN, a force that also induces a state of the receptor-ligand complex with slower off-rate. Force greatly increases the effects of VWD mutations, explaining pathophysiology. Conversion of single molecule kon (s(-1)) to bulk phase kon (s(-1)M(-1)) and the kon and koff values extrapolated to zero force for the low-force pathways show remarkably good agreement with bulk-phase measurements.

  12. Ultrasound stimulation attenuates resorption of tooth root induced by experimental force application.

    PubMed

    Inubushi, Toshihiro; Tanaka, Eiji; Rego, Emanuel B; Ohtani, Junji; Kawazoe, Aki; Tanne, Kazuo; Miyauchi, Mutsumi; Takata, Takashi

    2013-04-01

    at 12h (p<0.01). Moreover, LIPUS application suppressed the up-regulation of RANKL mRNA induced by compression force in OCCM-30, but no similar effect could be observed in MC3T3-E1. In conclusion, it is suggested that LIPUS exposure significantly reduces root resorption by the suppression of cementoclastogenesis by altering OPG/RANKL ratio during orthodontic tooth movement without interfering tooth movement. LIPUS may be an effective tool to prevent root resorption during tooth movement and is applicable to clinical use in near future.

  13. Low force contractions induce fatigue consistent with muscle mRNA expression in people with spinal cord injury.

    PubMed

    Petrie, Michael A; Suneja, Manish; Faidley, Elizabeth; Shields, Richard K

    2014-02-01

    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

  14. Probing Nanoscale Surface Enhanced Raman Scattering Fluctuation Dynamics using Correlated AFM and Confocal Ultramicroscopy

    SciTech Connect

    Suh, Yung D.; Schenter, Gregory K.; Zhu, Leyun; Lu, H PETER.

    2003-10-01

    We have studied the laser-excitation-intensity-dependent and Ag-nanocluster interstitial-site-dependent SERS intensity fluctuations under low molecule surface coverage of rhodamine 6G and cytochrome c. a new two-channel photon time-stamping system coupled with atomic force microscopic (AFM), Raman spectroscopic, and imaging microscopy was developed and applied to record Raman intensity fluctuation trajectories at sub-microsecond resolution correlated with in-situ characterization of the nanoparticle clusters. Our experimental results suggest that the nanoconfinement of the local electromagnetic-field enhancement and the interaction of the local field with the molecules, presumably under rotational motions, result in nano-Raman fluctuations. The SERS spectral fluctuation was pertinent to the nanoscale local enhancement and local interaction of the molecules with the surface when the number of molecules to contribute the microscopic Raman signal collected from a diffraction-limited focus spot. The SERS fluctuation dynamics were both photo-induced and spontaneous for rhodamine 6G, but only the photo-induced interstitial sites with heterogeneous geometries. To interpret the observed nano-SERS fluctuation dynamics, we used computer simulation of optical multiple scattering, based on multi-sphere scattering Mie theory, and rotational diffusion of molecules at an interstitial site, based on a random walk in orientation space.

  15. Effect of genome sequence on the force-induced unzipping of a DNA molecule

    NASA Astrophysics Data System (ADS)

    Singh, N.; Singh, Y.

    2006-02-01

    We considered a dsDNA polymer in which distribution of bases are random at the base pair level but ordered at a length of 18 base pairs and calculated its force elongation behaviour in the constant extension ensemble. The unzipping force F(y) vs. extension y is found to have a series of maxima and minima. By changing base pairs at selected places in the molecule we calculated the change in F(y) curve and found that the change in the value of force is of the order of few pN and the range of the effect depending on the temperature, can spread over several base pairs. We have also discussed briefly how to calculate in the constant force ensemble a pause or a jump in the extension-time curve from the knowledge of F(y).

  16. 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.

  17. 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

  18. A review of terms for regulated vs. forced, neurochemical-induced changes in body temperature.

    PubMed

    Gordon, C J

    1983-03-21

    Deviations of the body temperature of homeothermic animals may be regulated or forced. A regulated change in core temperature is caused by a natural or synthetic compound that displaces the set-point temperature. A forced shift occurs when an excessive environmental or endogenous heat load, or heat sink, exceeds the body's capacity to thermoregulate but does not affect set-point. A fever is the paradigm of a regulated increase in body temperature, but the term fever has acquired a strict pathological definition over the past two decades. Consequently, other forms of nonpathological, regulated elevations in body temperature have generally been classified as hyperthermia; and decreases in core temperature--either forced or regulated--have generally been classified as hypothermia. Since the terms hyperthermia and hypothermia fail to distinguish a regulated vs. a forced temperature change, a confusion of terms has been created in the literature. It would appear that "resisted or unregulated hyperthermia" and "hypothermia," respectively, are appropriate terms for describing a forced increase and decrease in core temperature. A nonpathological but regulated elevation in temperature may be defined as unresisted or regulated hyperthermia, whereas a regulated decrease in temperature may be termed unresisted or regulated hypothermia. This simple scheme appears to be the most practical means for distinguishing between forced and regulated changes in core temperature. PMID:6339853

  19. Label-free sensing of adenosine based on force variations induced by molecular recognition.

    PubMed

    Li, Jingfeng; Li, Qing; Ciacchi, Lucio Colombi; Wei, Gang

    2015-03-01

    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.

  20. Depression of tetanic force induced by loaded shortening of frog muscle fibres.

    PubMed

    Edman, K A; Caputo, C; Lou, F

    1993-07-01

    1. Single fibres isolated from the anterior tibialis muscle of Rana temporaria were allowed to shorten against a high load during a 2.5-4.0 s fused tetanus (1-3 degrees C) and the maximum force produced at the short length was compared with that recorded during a fixed-end tetanus at the same overall fibre length. Changes in length of marked, consecutive segments (ca 0.5 mm in length) along the fibre were measured throughout the tetanus using a photoelectric recording system. 2. Loaded shortening (load ca 3/4 of maximum tetanic force) starting from approximately 2.55 microns sarcomere length and ending near slack fibre length depressed the tetanic force by 13 +/- 2% (mean +/- S.E.M., n = 10) and caused a marked redistribution of sarcomere length along the fibre. Unloaded shortening over the same range caused no force deficit and did not lead to increased dispersion of sarcomere length. 3. Loaded shortening below slack length produced less force depression and less non-uniformity of sarcomere length than did a corresponding intervention above slack length. 4. The force deficit after loaded shortening, both above and below slack fibre length, was positively correlated (P < 0.005) to the coefficient of variation of the sarcomere length along the fibre. 5. The decrease in active force after loaded shortening, and its relation to increased dispersion of sarcomere length along the fibre, could be simulated closely by a computer model in which the muscle fibre was assumed to consist of eleven discrete segments acting in series with a passive elastic element. 6. Experiments were performed in which the length of an individual segment of the intact muscle fibre was strictly controlled throughout a tetanus. Loaded shortening of such a 'length-clamped' segment caused no force depression during the subsequent isometric phase either above or below slack fibre length. 7. The results suggest strongly that force depression after loaded shortening of a single muscle fibre is

  1. Effects of water-misting spray combined with forced ventilation on heat induced meat gelation in broiler after summer transport.

    PubMed

    Wang, Peng; Zhao, Yingying; Jiang, Nannan; Li, Ke; Xing, Tong; Chen, Lin; Wang, Xiaoming; Tang, Yong; Xu, Xinglian

    2016-10-01

    This study aims to explore the use of non-chemical addition in improving the functions of meat proteins in broilers transported during summer. The effects of a water-misting spray with forced ventilation on heat induced ground meat gelation in broilers were investigated through rheology, texture, and nuclear magnetic resonance analyses. The facilities of water-misting sprays with forced ventilation characterized with an extremely thin droplet (diameter: approximately 0.05 mm) and supplying updraughting air ventilation in an enclosed space were examined. For comparison, typical processing treatments using sodium bicarbonate or sodium tripolyphosphate were performed to grind the broiler meat which had not undergone water-misting and forced ventilation. Results showed that transport for 45-min followed by application of water-misting spray with forced ventilation for 15-min and resting for 45-min (TWFR) increased water holding capacity (WHC) by 2.51%; this finding was not significantly different from the effect of transport for 45 min followed by 1 h rest and sodium tripolyphosphate treatment (TRT) on meat batter (P > 0.05). TWFR treatment exhibited the highest storage modulus increase among four samples well as significant higher hardness and chewiness values on than those of sample treated with 45-min transport and 1-h rest (TR) (P < 0.05). TWFR, 45 min of transport, 1 h rest, and addition of sodium bicarbonate (TRB) and TRT induced T22 (relaxation time of water trapped within myofibrils) shift to shorter relaxation time and narrower relaxation distribution compared with TR. Overall, TWFR treatment can be a potential non-chemical addition method for improving the heat induced gelation protein function after broiler undergoing summer transport. PMID:27418661

  2. GCM simulations of volcanic aerosol forcing. Part I: Climate changes induced by stead-state perturbations

    SciTech Connect

    Pollack, J.B. ); Rind, D.; Lacis, A.; Hansen, J.E.; Sato, M.; Ruedy, R. )

    1993-09-01

    The Goddard Institute for Space Studies Climate Model II was used to simulate the response of the climate system to a spatially and temporally constant forcing by volcanic aerosols. The climatic changes produced by differencing this simulation and one made for the present climate with no volcanic aerosol forcing. These climatic changes are also compared with those obtained when CO[sub 2] in the atmosphere was doubled and when the boundary conditions associated with the peak of the last ice age. In all three cases, the absolute magnitude of the change in the globally averaged air temperature at the surface is approximately 5K. The simulations imply 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, such as occurred at the end of the nineteenth and beginning of the twentieth centuries. The steady-state climate response to volcanic forcing includes a expansion of sea ice, especially Southern Hemisphere; a large increase in surface and planetary albedo at high latitudes; and sizable changes in the annually and zonally averaged air temperature. The climate response to three different forcings is similar in 3 ways: direct radiative forcing accounts for 30% and 25% of the total [delta]T[sub s]; Changes in atmospheric water vapor are the most important positive feedback; Albedo feedback is significant, positive at high latitudes. The climate response to the three forcings also differs. The latitudinal profiles of [delta]T[sub s] differ, reflecting significant variations in the latitudinal profiles of the primary radiative forcing. Changes in eddy kinetic energy, heat transport by atmospheric eddies, and total atmospheric heat transport are quite different. These results raise questions about the ease with which atmospheric heat transport can be parameterized in a simple way in energy climate models. 44 refs., 32 figs.

  3. Bone remodelling in the natural acetabulum is influenced by muscle force-induced bone stress.

    PubMed

    Fernandez, Justin; Sartori, Massimo; Lloyd, David; Munro, Jacob; Shim, Vickie

    2014-01-01

    A modelling framework using the international Physiome Project is presented for evaluating the role of muscles on acetabular stress patterns in the natural hip. The novel developments include the following: (i) an efficient method for model generation with validation; (ii) the inclusion of electromyography-estimated muscle forces from gait; and (iii) the role that muscles play in the hip stress pattern. The 3D finite element hip model includes anatomically based muscle area attachments, material properties derived from Hounsfield units and validation against an Instron compression test. The primary outcome from this study is that hip loading applied as anatomically accurate muscle forces redistributes the stress pattern and reduces peak stress throughout the pelvis and within the acetabulum compared with applying the same net hip force without muscles through the femur. Muscle forces also increased stress where large muscles have small insertion sites. This has implications for the hip where bone stress and strain are key excitation variables used to initiate bone remodelling based on the strain-based bone remodelling theory. Inclusion of muscle forces reduces the predicted sites and degree of remodelling. The secondary outcome is that the key muscles that influenced remodelling in the acetabulum were the rectus femoris, adductor magnus and iliacus.

  4. Effect of force-induced mechanical stress at the coronary artery bifurcation stenting: Relation to in-stent restenosis

    NASA Astrophysics Data System (ADS)

    Lee, Cheng-Hung; Jhong, Guan-Heng; Hsu, Ming-Yi; Liu, Shih-Jung; Wang, Chao-Jan; Hung, Kuo-Chun

    2014-05-01

    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.

  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. Laser-induced force on a microfluidic drop: origin and magnitude.

    PubMed

    Verneuil, Emilie; Cordero, Maríaluisa; Gallaire, François; Baroud, Charles N

    2009-05-01

    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.

  7. Theory of light scattering at nanoparticles and optical forces between small particles

    NASA Astrophysics Data System (ADS)

    Saenz, Juan Jose

    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. Here we review some basic concepts related to the optical forces on small (subwavelength) particles, focusing on the interplay between scattering asymmetry and momentum transfer. These forces are, in general, non-conservative (curl forces) which lead to a number of intriguing predictions regarding the dynamics of nanoparticles. Optical forces between small particles are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. As we will see, artificially created random fluctuating light fields can be used to induce and control dispersion forces between small colloidal particles. Interestingly, for relatively high refractive index semiconductor nanoparticles, the interactions can be tuned from attractive to strongly repulsive when the frequency of the external fluctuating field is tuned near the first magnetic Mie-resonance. Interactions induced by randomly fluctuating light fields open a path towards the control of translational invariant interactions with tuneable strength and range in colloidal systems.

  8. Water spray-induced grooming is negatively correlated with depressive behavior in the forced swimming test in rats.

    PubMed

    Shiota, Noboru; Narikiyo, Kimiya; Masuda, Akira; Aou, Shuji

    2016-05-01

    Rodents show grooming, a typical self-care behavior, under stress and non-stress conditions. Previous studies revealed that grooming under stress conditions such as the open-field test (OFT) or the elevated plus-maze test (EPM) is associated with anxiety, but the roles of grooming under non-stress conditions are not well understood. Here, we examined spray-induced grooming as a model of grooming under a non-stress condition to investigate the relationship between this grooming and depression-like behavior in the forced swim test (FST) and tail suspension test, and we compared spray-induced grooming with OFT- and EPM-induced grooming. The main finding was that the duration of spray-induced grooming, but not that of OFT/EPM-induced grooming, was negatively correlated with the duration of immobility in the FST, an index of depression-like behavior. The results suggest that spray-induced grooming is functionally different from the grooming in the OFT and EPM and is related to reduction of depressive behavior.

  9. 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

  10. Theoretical calculation of light-induced forces and torques on complex microrotors

    NASA Astrophysics Data System (ADS)

    Liu, Yuxiang; Zhu, Anding; Huang, Wenhao

    2004-12-01

    In this letter, we propose the new theoretical investigation on the optical forces and torques on complex microrotors. On the basis of R. C. Gauthier"s hybrid ray-wave model, the optical forces and toques on two complex asymmetric micro-objects, the conical microrotor and the helical microrotor, are analyzed. The viscous drag torque is estimated by Stokes flow to obtain the rotational speed. The results of our computation agree well with the previously published experimental results, which indicates that our approach of the optical torque calculation is suitable for other complex microrotors and that the theoretical calculation is very helpful to optimum design of light-driven microrotors.

  11. Surface deformation effects induced by radiation pressure and electrostriction forces in dielectric solids

    NASA Astrophysics Data System (ADS)

    Astrath, N. G. C.; Lukasievicz, G. V. B.; Malacarne, L. C.; Bialkowski, S. E.

    2013-06-01

    The surface displacement produced by radiation pressure and electrostriction forces is investigated considering the commonly accepted theories proposed by Minkowski and Abraham for the energy-momentum tensor. The contributions are modeled considering each effect separately assuming non-absorbing and absorbing solids and the thermoelastic deformation equations are solved numerically. We show that the surface deformation profiles as calculated by the Minkowski or Abraham momenta give different surface curvature, which could in principle be detected by measuring the surface displacement. Finally, an all-optical pump-probe photothermal method to detect the radiation pressure and electrostriction forces in transparent dielectric solids is proposed.

  12. 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

  13. 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.

  14. The force generated by biological membranes on a polymer rod and its response: Statics and dynamics

    NASA Astrophysics Data System (ADS)

    Daniels, D. R.; Turner, M. S.

    2004-10-01

    We propose a theory for the force exerted by a fluctuating membrane on a polymer rod tip. Using statistical mechanical methods, the expression for the generated force is written in terms of the distance of the rod tip from the membrane "frame." We apply the theory in calculating the stall force and membrane displacement required to cease the growth of a growing fiber induced by membrane fluctuations, as well as the membrane force and membrane displacement required for rod/fiber buckling. We also consider the dynamics of a growing fiber tip under the influence of a fluctuation-induced membrane force. We discuss the importance of our results in various biological contexts. Finally, we present a method to simultaneously extract both the rigidity of the semiflexible rod and the force applied by, e.g., the membrane from the measurements of the bending fluctuations of the rod. Such a measurement of the force would give information about the thermodynamics of the rod polymerization that involves the usual Brownian ratchet mechanism.

  15. 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.

  16. Cooperative dynamics of microtubule ensembles: Polymerization forces and rescue-induced oscillations

    NASA Astrophysics Data System (ADS)

    Zelinski, Björn; Kierfeld, Jan

    2013-01-01

    We investigate the cooperative dynamics of an ensemble of N microtubules growing against an elastic barrier. Microtubules undergo so-called catastrophes, which are abrupt stochastic transitions from a growing to a shrinking state, and rescues, which are transitions back to the growing state. Microtubules can exert pushing or polymerization forces on an obstacle, such as an elastic barrier, if the growing end is in contact with the obstacle. We use dynamical mean-field theory and stochastic simulations to analyze a model where each microtubule undergoes catastrophes and rescues and where microtubules interact by force sharing. For zero rescue rate, cooperative growth terminates in a collective catastrophe. The maximal polymerization force before catastrophes grows linearly with N for small N or a stiff elastic barrier, in agreement with available experimental results, whereas it crosses over to a logarithmic dependence for larger N or a soft elastic barrier. For a nonzero rescue rate and a soft elastic barrier, the dynamics becomes oscillatory with both collective catastrophe and rescue events, which are part of a robust limit cycle. Both the average and maximal polymerization forces then grow linearly with N, and we investigate their dependence on tubulin on-rates and rescue rates, which can be involved in cellular regulation mechanisms. We further investigate the robustness of the collective catastrophe and rescue oscillations with respect to different catastrophe models.

  17. 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

    2015-01-01

    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. 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

  19. 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.

  20. 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

  1. 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.

  2. Viability evaluation of culture cells patterned by femtosecond laser-induced impulsive force

    NASA Astrophysics Data System (ADS)

    Takizawa, Noriko; Okano, Kazunori; Uwada, Takayuki; Hosokawa, Yoichiroh; Masuhara, Hiroshi

    2008-02-01

    PC12 cells, which are derived from a rat pheochromocytoma, were independently patterned utilizing an impulsive force resulting in impulsive shockwave and cavitation bubble generation by focused femtosecond laser irradiation. Since the PC12 cells respond reversibly to nerve growth factor by induction of the neuronal phenotype, we can assess an influence that the impulsive force gives to the bioactivity in term of the cell differentiation. The patterned cells were accumulated on an intact dish and cultured for 3 days. The behavior of appearance and cell differentiation was observed by multipoint time-lapse system. On bases of these results, it was proved that the biological activity of the cell is unaffected by the femtosecond laser patterning.

  3. 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.

  4. Capillary-force-induced formation of luminescent polystyrene/(rare-earth-doped nanoparticle) hybrid hollow spheres.

    PubMed

    Chen, Min; Xie, Lin; Li, Fuyou; Zhou, Shuxue; Wu, Limin

    2010-10-01

    This paper presents a "one-pot" procedure to synthesize polystyrene/(rare-earth-doped nanoparticles) (PS/REDNPs) hybrid hollow spheres via the in situ diffusion of organic core into inorganic shell under strong capillary force. In this approach, when carboxyl-capped PS colloids were deposited by different REDNPs in aqueous medium, such as LaF3:Eu3+, LaF3:Ce3+-Tb3+, and YVO4:Dy3+, PS/REDNPs inorganic-organic hybrid hollow spheres could be directly obtained via the in situ diffusion of core PS chains into the voids between rare-earth-doped nanoparticles through the strong capillary force. Not only is the synthetic procedure versatile and very simple, but also the obtained hybrid hollow spheres are hydrophilic and luminescent and could be directly used in chemical and biological fields.

  5. 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.

  6. Laser-induced rocket force on a microparticle in a complex (dusty) plasma

    NASA Astrophysics Data System (ADS)

    Nosenko, V.; Ivlev, A. V.; Morfill, G. E.

    2010-12-01

    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.

  7. GCM Simulations of Volcanic Aerosol Forcing. Part I: Climate Changes Induced by Steady-State Perturbations.

    NASA Astrophysics Data System (ADS)

    Pollack, James B.; Rind, David; Lacis, Andrew; Hansen, James E.; Sato, Makiko; Ruedy, Reto

    1993-09-01

    The authors have used the Goddard Institute for Space Studies Climate Model II to simulate the response of the climate system to a spatially and temporally constant forcing by volcanic aerosols having an optical depth of 0.15. The climatic 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. These climatic changes are compared with those obtained with the same climate model when the C02 content of the atmosphere was doubled (2×C02) and when the boundary conditions associated with the peak of the last ice age were used (18 K). In all three cases, the absolute magnitude of the change in the globally averaged air temperature at the surface is approximately the same, 5 K.The simulations imply 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, such as occurred at the end of the nineteenth and beginning of the twentieth 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, T; T at the surface (Ts) does not sharply increase with increasing latitude, while T in the lower stratosphere is positive at low latitudes and negative at high latitudes.In certain ways, the climate response to the three different forcings is similar. Direct radiative forcing accounts for 30% and 25% of the total Ts in the volcano and 2×C02 runs, respectively. Changes in atmospheric water vapor act as the most important feedback, and are positive in all three cases. Albedo feedback is a significant, positive feedback at high latitudes in all three simulations, although the land ice feedback is prominent only in the

  8. 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.

  9. Capillary force induced assembly of high aspect-ratio polymeric micropillar arrays

    NASA Astrophysics Data System (ADS)

    Chandra, Dinesh; Yang, Shu

    2010-03-01

    We present experimental evidence and theoretical calculations to show that when a liquid is evaporated off the surface of 2D arrays of micropillars, the micropillars cluster together due to lateral capillary meniscus interaction force rather than due to often reported Laplace pressure difference resulting from isolated capillary bridges. Experiments show that the pillars assemble while still completely surrounded by wetting liquid except at the tips and calculations reveal that the lateral capillary meniscus interaction forces are much smaller than those estimated from Laplace pressure approach. The cluster sizes of the collapsed micropillars as a function of their elastic modulus and the critical modulus for stability as estimated from capillary meniscus interaction approach agree well with the experimental observation. We also discuss the utility of such clustered micropillars as ultrathin whitening layers.

  10. Spin-motive forces and current-induced torques in ferromagnets

    NASA Astrophysics Data System (ADS)

    Hals, Kjetil M. D.; Brataas, Arne

    2015-06-01

    In metallic ferromagnets, the spin-transfer torque and spin-motive force are known to exhibit a reciprocal relationship. Recent experiments on ferromagnets with strong spin-orbit coupling have revealed a rich complexity in the interaction between itinerant charge carriers and magnetization, but a full understanding of this coupled dynamics is lacking. Here, we develop a general phenomenology of the two reciprocal processes of charge pumping by spin-motive forces and current-driven magnetization dynamics. The formalism is valid for spin-orbit coupling of any strength and presents a systematic scheme for deriving all possible torque and charge-pumping terms that obey the symmetry requirements imposed by the point group of the system. We demonstrate how the different charge pumping and torque contributions are connected via the Onsager reciprocal relations. The formalism is applied to two important classes of systems: isotropic ferromagnets with nonuniform magnetization and homogeneous ferromagnets described by the point group C2 v.

  11. Experimental validation of acoustic radiation force induced shear wave interference patterns.

    PubMed

    Hoyt, Kenneth; Hah, Zaegyoo; Hazard, Chris; Parker, Kevin J

    2012-01-01

    A novel elasticity imaging system founded on the use of acoustic radiation forces from a dual beam arrangement to generate shear wave interference patterns is described. Acquired pulse-echo data and correlation-based techniques were used to estimate the resultant deformation and to visualize tissue viscoelastic response. The use of normal versus axicon focal configurations was investigated for effects on shear wave generation. Theoretical models were introduced and shown in simulation to accurately predict shear wave propagation and interference pattern properties. In a tissue-mimicking phantom, experimental results are in congruence with theoretical predictions. Using dynamic acoustic radiation force excitation, results confirm that shear wave interference patterns can be produced remotely in a particular tissue region of interest (ROI). Overall, preliminary results are encouraging and the system described may prove feasible for interrogating the viscoelastic properties of normal and diseased tissue types.

  12. Biomechanically inspired modelling of pedestrian-induced forces on laterally oscillating structures

    NASA Astrophysics Data System (ADS)

    Bocian, M.; Macdonald, J. H. G.; Burn, J. F.

    2012-07-01

    Despite considerable interest among engineers and scientists, bi-directional interaction between walking pedestrians and lively bridges has still not been well understood. In an attempt to bridge this gap a biomechanically inspired model of the human response to lateral bridge motion is presented and explored. The simple inverted pendulum model captures the key features of pedestrian lateral balance and the resulting forces on the structure. The forces include self-excited components that can be effectively modelled as frequency-dependent added damping and mass to the structure. The results of numerical simulations are in reasonable agreement with recent experimental measurements of humans walking on a laterally oscillating treadmill, and in very good agreement with measurements on full-scale bridges. In contrast to many other models of lateral pedestrian loading, synchronisation with the bridge motion is not involved. A parametric study of the model is conducted, revealing that as pedestrians slow down as a crowd becomes more dense, their resulting lower pacing rates generate larger self-excited forces. For typical pedestrian parameters, the potential to generate negative damping arises for any lateral bridge vibration frequency above 0.43 Hz, depending on the walking frequency. Stability boundaries of the combined pedestrian-structure system are presented in terms of the structural damping ratio and pedestrian-to-bridge mass ratio, revealing complex relations between damping demand and bridge and pedestrian frequencies, due to the added mass effect. Finally it is demonstrated that the model can produce simultaneous self-excited forces on multiple structural modes, and a realistic full simulation of a large number of pedestrians, walking randomly and interacting with a bridge, produces structural behaviour in very good agreement with site observations.

  13. A multi-structural single cell model of force-induced interactions of cytoskeletal components.

    PubMed

    Barreto, Sara; Clausen, Casper H; Perrault, Cecile M; Fletcher, Daniel A; Lacroix, Damien

    2013-08-01

    Several computational models based on experimental techniques and theories have been proposed to describe cytoskeleton (CSK) mechanics. Tensegrity is a prominent model for force generation, but it cannot predict mechanics of individual CSK components, nor explain the discrepancies from the different single cell stimulating techniques studies combined with cytoskeleton-disruptors. A new numerical concept that defines a multi-structural 3D finite element (FE) model of a single-adherent cell is proposed to investigate the biophysical and biochemical differences of the mechanical role of each cytoskeleton component under loading. The model includes prestressed actin bundles and microtubule within cytoplasm and nucleus surrounded by the actin cortex. We performed numerical simulations of atomic force microscopy (AFM) experiments by subjecting the cell model to compressive loads. The numerical role of the CSK components was corroborated with AFM force measurements on U2OS-osteosarcoma cells and NIH-3T3 fibroblasts exposed to different cytoskeleton-disrupting drugs. Computational simulation showed that actin cortex and microtubules are the major components targeted in resisting compression. This is a new numerical tool that explains the specific role of the cortex and overcomes the difficulty of isolating this component from other networks in vitro. This illustrates that a combination of cytoskeletal structures with their own properties is necessary for a complete description of cellular mechanics. PMID:23702149

  14. Relationship between sound radiation from sound-induced and force-excited vibration: Analysis using an infinite elastic plate model.

    PubMed

    Yairi, Motoki; Sakagami, Kimihiro; Nishibara, Kosuke; Okuzono, Takeshi

    2016-07-01

    Although sound radiation from sound-induced vibration and from force-excited vibration of solid structures are similar phenomena in terms of radiating from vibrating structures, the general relationship between them has not been explicitly studied to date. In particular, airborne sound transmission through walls and sound radiation from structurally vibrating surfaces in buildings are treated as different issues in architectural acoustics. In this paper, a fundamental relationship is elucidated through the use of a simple model. The transmission coefficient for random-incidence sound and the radiated sound power under point force excitation of an infinite elastic plate are both analyzed. Exact and approximate solutions are derived for the two problems, and the relationship between them is theoretically discussed. A conversion function that relates the transmission coefficient and radiated sound power is obtained in a simple closed form through the approximate solutions. The exact solutions are also related by the same conversion function. It is composed of the specific impedance and the wavenumber, and is independent of any elastic plate parameters. The sound radiation due to random-incidence sound and point force excitation are similar phenomena, and the only difference is the gradient of those characteristics with respect to the frequency.

  15. Relationship between sound radiation from sound-induced and force-excited vibration: Analysis using an infinite elastic plate model.

    PubMed

    Yairi, Motoki; Sakagami, Kimihiro; Nishibara, Kosuke; Okuzono, Takeshi

    2016-07-01

    Although sound radiation from sound-induced vibration and from force-excited vibration of solid structures are similar phenomena in terms of radiating from vibrating structures, the general relationship between them has not been explicitly studied to date. In particular, airborne sound transmission through walls and sound radiation from structurally vibrating surfaces in buildings are treated as different issues in architectural acoustics. In this paper, a fundamental relationship is elucidated through the use of a simple model. The transmission coefficient for random-incidence sound and the radiated sound power under point force excitation of an infinite elastic plate are both analyzed. Exact and approximate solutions are derived for the two problems, and the relationship between them is theoretically discussed. A conversion function that relates the transmission coefficient and radiated sound power is obtained in a simple closed form through the approximate solutions. The exact solutions are also related by the same conversion function. It is composed of the specific impedance and the wavenumber, and is independent of any elastic plate parameters. The sound radiation due to random-incidence sound and point force excitation are similar phenomena, and the only difference is the gradient of those characteristics with respect to the frequency. PMID:27475169

  16. 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

  17. 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

  18. Reynolds-number dependence of turbulent skin-friction drag reduction induced by spanwise forcing

    NASA Astrophysics Data System (ADS)

    Gatti, Davide; Quadrio, Maurizio

    2016-09-01

    This paper examines how increasing the value of the Reynolds number $Re$ affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The considered forcing is based on the streamwise-travelling waves of spanwise wall velocity (Quadrio {\\em et al. J. Fluid Mech.}, vol. 627, 2009, pp. 161--178). The study builds upon an extensive drag-reduction database created with Direct Numerical Simulation of a turbulent channel flow for two, 5-fold separated values of $Re$, namely $Re_\\tau=200$ and $Re_\\tau=1000$. The sheer size of the database, which for the first time systematically addresses the amplitude of the forcing, allows a comprehensive view of the drag-reducing characteristics of the travelling waves, and enables a detailed description of the changes occurring when $Re$ increases. The effect of using a viscous scaling based on the friction velocity of either the non-controlled flow or the drag-reduced flow is described. In analogy with other wall-based drag reduction techniques, like for example riblets, the performance of the travelling waves is well described by a vertical shift of the logarithmic portion of the mean streamwise velocity profile. Except when $Re$ is very low, this shift remains constant with $Re$, at odds with the percentage reduction of the friction coefficient, which is known to present a mild, logarithmic decline. Our new data agree with the available literature, which is however mostly based on low-$Re$ information and hence predicts a quick drop of maximum drag reduction with $Re$. The present study supports a more optimistic scenario, where for an airplane at flight Reynolds numbers a drag reduction of nearly 30\\% would still be possible thanks to the travelling waves.

  19. Amyloid beta oligomers induce neuronal elasticity changes in age-dependent manner: a force spectroscopy study on living hippocampal neurons.

    PubMed

    Ungureanu, Andreea-Alexandra; Benilova, Iryna; Krylychkina, Olga; Braeken, Dries; De Strooper, Bart; Van Haesendonck, Chris; Dotti, Carlos G; Bartic, Carmen

    2016-01-01

    Small soluble species of amyloid-beta (Aβ) formed during early peptide aggregation stages are responsible for several neurotoxic mechanisms relevant to the pathology of Alzheimer's disease (AD), although their interaction with the neuronal membrane is not completely understood. This study quantifies the changes in the neuronal membrane elasticity induced by treatment with the two most common Aβ isoforms found in AD brains: Aβ40 and Aβ42. Using quantitative atomic force microscopy (AFM), we measured for the first time the static elastic modulus of living primary hippocampal neurons treated with pre-aggregated Aβ40 and Aβ42 soluble species. Our AFM results demonstrate changes in the elasticity of young, mature and aged neurons treated for a short time with the two Aβ species pre-aggregated for 2 hours. Neurons aging under stress conditions, showing aging hallmarks, are the most susceptible to amyloid binding and show the largest decrease in membrane stiffness upon Aβ treatment. Membrane stiffness defines the way in which cells respond to mechanical forces in their environment and has been shown to be important for processes such as gene expression, ion-channel gating and neurotransmitter vesicle transport. Thus, one can expect that changes in neuronal membrane elasticity might directly induce functional changes related to neurodegeneration.

  20. Amyloid beta oligomers induce neuronal elasticity changes in age-dependent manner: a force spectroscopy study on living hippocampal neurons

    PubMed Central

    Ungureanu, Andreea-Alexandra; Benilova, Iryna; Krylychkina, Olga; Braeken, Dries; De Strooper, Bart; Van Haesendonck, Chris; Dotti, Carlos G.; Bartic, Carmen

    2016-01-01

    Small soluble species of amyloid-beta (Aβ) formed during early peptide aggregation stages are responsible for several neurotoxic mechanisms relevant to the pathology of Alzheimer’s disease (AD), although their interaction with the neuronal membrane is not completely understood. This study quantifies the changes in the neuronal membrane elasticity induced by treatment with the two most common Aβ isoforms found in AD brains: Aβ40 and Aβ42. Using quantitative atomic force microscopy (AFM), we measured for the first time the static elastic modulus of living primary hippocampal neurons treated with pre-aggregated Aβ40 and Aβ42 soluble species. Our AFM results demonstrate changes in the elasticity of young, mature and aged neurons treated for a short time with the two Aβ species pre-aggregated for 2 hours. Neurons aging under stress conditions, showing aging hallmarks, are the most susceptible to amyloid binding and show the largest decrease in membrane stiffness upon Aβ treatment. Membrane stiffness defines the way in which cells respond to mechanical forces in their environment and has been shown to be important for processes such as gene expression, ion-channel gating and neurotransmitter vesicle transport. Thus, one can expect that changes in neuronal membrane elasticity might directly induce functional changes related to neurodegeneration. PMID:27173984

  1. Local Muscle Metabolic Demand Induced by Neuromuscular Electrical Stimulation and Voluntary Contractions at Different Force Levels: A NIRS Study

    PubMed Central

    Muthalib, Makii; Kerr, Graham; Nosaka, Kazunori; Perrey, Stephane

    2016-01-01

    Functional Muscle metabolic demand during contractions evoked by neuromuscular electrical stimulation (NMES) has been consistently documented to be greater than voluntary contractions (VOL) at the same force level (10-50% maximal voluntary contraction-MVC). However, we have shown using a near-infrared spectroscopy (NIRS) technique that local muscle metabolic demand is similar between NMES and VOL performed at MVC levels, thus controversy exists. This study therefore compared biceps brachii muscle metabolic demand (tissue oxygenation index-TOI and total hemoglobin volume-tHb) during a 10s isometric contraction of the elbow flexors between NMES (stimulation frequency of 30Hz and current level to evoke 30% MVC) and VOL at 30% MVC (VOL-30%MVC) and MVC (VOL-MVC) level in 8 healthy men (23-33-y). Greater changes in TOI and tHb induced by NMES than VOL-30%MVC confirm previous studies of a greater local metabolic demand for NMES than VOL at the same force level. The same TOI and tHb changes for NMES and VOL-MVC suggest that local muscle metabolic demand and intramuscular pressure were similar between conditions. In conclusion, these findings indicate that NMES induce a similar local muscle metabolic demand as that of maximal VOL. PMID:27478574

  2. Atomic Force Microscopy Studies on DNA Structural Changes Induced by Vincristine Sulfate and Aspirin

    NASA Astrophysics Data System (ADS)

    Zhu, Yi; Zeng, Hu; Xie, Jianming; Ba, Long; Gao, Xiang; Lu, Zuhong

    2004-04-01

    We report that atomic force microscopy (AFM) studies on structural variations of a linear plasmid DNA interact with various concentrations of vincristine sulfate and aspirin. The different binding images show that vincrinstine sulfate binding DNA chains caused some loops and cleavages of the DNA fragments, whereas aspirin interaction caused the width changes and conformational transition of the DNA fragments. Two different DNA structural alternations could be explained by the different mechanisms of the interactions with these two components. Our work indicates that the AFM is a powerful tool in studying the interaction between DNA and small molecules.

  3. Ferromagnetic-resonance induced electromotive forces in Ni81Fe19 | p-type diamond

    NASA Astrophysics Data System (ADS)

    Fukui, Naoki; Morishita, Hiroki; Kobayashi, Satoshi; Miwa, Shinji; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-10-01

    We report on direct-current (DC) electromotive forces (emfs) in a nickel-iron alloy (Ni81 Fe19) | p-type diamond under the ferromagnetic resonance of the Ni81Fe19 layer at room temperature. The observed DC emfs take its maximum around the ferromagnetic resonant frequency of the Ni81Fe19, and their signs are reversed by reversing the direction of an externally-applied magnetic field; it shows that the observed DC emfs are spin-related emfs.

  4. Size determination of field-induced water menisci in noncontact atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Calleja, Montserrat; Tello, Marta; Garcia, Ricardo

    2002-11-01

    We have studied the dimensions of water capillaries formed by an applied electrical field between an atomic force microscope tip and a flat silicon surface. The lateral and vertical dimensions of the liquid meniscus are in the 5-30 nm range. The size depends on the duration and strength of the voltage pulse. It increases by increasing the voltage strength or the pulse duration. The meniscus size is deduced from the experimental measurement of the snap-off separation. These results are of special relevance to optimize local oxidation nanolithography.

  5. Defining a longitudinal survival model to examine forced treadmill running as a countermeasure for diet-induced weight gain.

    PubMed

    Esposito, Lisa M; Simpson, Richard J; Strohacker, Kelley; Carpenter, Katie C; McFarlin, Brian K

    2010-10-01

    Diet-induced weight gain increases disease risk via disruption of the innate immune system. Flow cytometry is commonly used to assess the immune system; however, in mice such measurements traditionally require terminal procedures and tissue collection to generate sufficient sample. The present study refined an existing flow cytometry method to reduce the number of mice needed to longitudinally measure monocytes. CD-1 male mice were randomly assigned to one of the three groups: DS (diet-induced weight gain + sedentary), DE (diet-induced weight gain + forced treadmill running [total distance 35,755 ± 1832 m]) or NS (normal weight gain + sedentary). DS and DE consumed a 60% fat diet and NS consumed a 10% fat diet ad libitum. Saphenous vein blood samples were collected weekly for a period of six weeks and three-colour flow cytometry was used to measure changes in monocyte (CD11b(+)/14(+)) concentration and cell-surface toll-like receptor 4 (TLR4) expression. DS (18%) and DE (17%) gained more weight than NS (P < 0.001). On a group basis, DS expressed 17% more TLR4 than DE and NS (P = 0.005). The present study demonstrates that a longitudinal survival model can be used to reduce the number of animals needed to complete flow cytometry experiments. Exercise during diet-induced weight prevented some (decreased monocyte TLR4 expression) but not all aspects of innate immune system function.

  6. Equilibrium & Nonequilibrium Fluctuation Effects in Biopolymer Networks

    NASA Astrophysics Data System (ADS)

    Kachan, Devin Michael

    Fluctuation-induced interactions are an important organizing principle in a variety of soft matter systems. In this dissertation, I explore the role of both thermal and active fluctuations within cross-linked polymer networks. The systems I study are in large part inspired by the amazing physics found within the cytoskeleton of eukaryotic cells. I first predict and verify the existence of a thermal Casimir force between cross-linkers bound to a semi-flexible polymer. The calculation is complicated by the appearance of second order derivatives in the bending Hamiltonian for such polymers, which requires a careful evaluation of the the path integral formulation of the partition function in order to arrive at the physically correct continuum limit and properly address ultraviolet divergences. I find that cross linkers interact along a filament with an attractive logarithmic potential proportional to thermal energy. The proportionality constant depends on whether and how the cross linkers constrain the relative angle between the two filaments to which they are bound. The interaction has important implications for the synthesis of biopolymer bundles within cells. I model the cross-linkers as existing in two phases: bound to the bundle and free in solution. When the cross-linkers are bound, they behave as a one-dimensional gas of particles interacting with the Casimir force, while the free phase is a simple ideal gas. Demanding equilibrium between the two phases, I find a discontinuous transition between a sparsely and a densely bound bundle. This discontinuous condensation transition induced by the long-ranged nature of the Casimir interaction allows for a similarly abrupt structural transition in semiflexible filament networks between a low cross linker density isotropic phase and a higher cross link density bundle network. This work is supported by the results of finite element Brownian dynamics simulations of semiflexible filaments and transient cross-linkers. I

  7. Diffusive mass transfer by nonequilibrium fluctuations: Fick's law revisited.

    PubMed

    Brogioli, D; Vailati, A

    2001-01-01

    Recent experimental and theoretical works have shown that giant fluctuations are present during diffusion in liquid systems. We use linearized fluctuating hydrodynamics to calculate the net mass transfer due to these nonequilibrium fluctuations. Remarkably, the mass flow turns out to coincide with the usual Fick's one. The renormalization of the hydrodynamic equations allows us to quantify the gravitational modifications of the diffusion coefficient induced by the gravitational stabilization of long wavelength fluctuations.

  8. 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.

  9. van der Waals force-induced loading of proangiogenic nanoparticles on microbubbles for enhanced neovascularization

    NASA Astrophysics Data System (ADS)

    Chen, Jinrong; Lee, Min Kyung; Qin, Ellen; Misra, Sanjay; Kong, Hyunjoon

    2015-10-01

    Nanoparticles emerged as carriers of promising diagnostic and therapeutic molecules due to their unique size, injectability, and potential to sustainably release molecular cargos. However, with local injection of particles into target tissue, the significant particle loss caused by external biomechanical forces is a great challenge yet to be resolved to date. We hypothesized that nanoparticles associated with tissue-adherent microbubbles in the form of core-shell particles due to van der Waals attractive forces would stably remain on an implanted site and significantly increase therapeutic efficacy of drug cargos. To examine this hypothesis, we used 100 nm diameter nanoparticles made of poly(lactide-co-glycolic acid) (PLGA) as a model nanoparticle and 50 μm diameter microbubbles made of poly(2-hydroxyethyl aspartamide) (PHEA) grafted with octadecyl chains, PHEA-g-C18, as a model microbubble. Simple mixing of PLGA nanoparticles and PHEA-g-C18 microbubbles resulted in the core-shell particles. Following implantation, the PHEA-g-C18 microbubbles acted as glue to minimize the displacement of PLGA nanoparticles, because of the association between the octadecyl chains on PHEA-g-C18 and the epithelium of the tissue. As a consequence, the core-shell particles prepared with Angiopoietin-1 (Ang1)-encapsulated PLGA nanoparticles significantly promoted vascularization in the implanted tissue. Overall, the results of this study provide a simple but advanced strategy for improving therapeutic efficacy of drug-carrying nanoparticles without altering their surface chemistry and potential.Nanoparticles emerged as carriers of promising diagnostic and therapeutic molecules due to their unique size, injectability, and potential to sustainably release molecular cargos. However, with local injection of particles into target tissue, the significant particle loss caused by external biomechanical forces is a great challenge yet to be resolved to date. We hypothesized that nanoparticles

  10. Elasticity-induced force reversal between active spinning particles in dense passive media

    PubMed Central

    Aragones, J. L.; Steimel, J. P.; Alexander-Katz, A.

    2016-01-01

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium. PMID:27112961

  11. Elasticity-induced force reversal between active spinning particles in dense passive media.

    PubMed

    Aragones, J L; Steimel, J P; Alexander-Katz, A

    2016-04-26

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

  12. Surface-force-induced deformations of monodisperse polystyrene spheres on planar silicon substrates

    NASA Astrophysics Data System (ADS)

    Rimai, D. S.; DeMejo, L. P.; Bowen, R. C.

    1990-12-01

    The contact radii between polystyrene spheres, having diameters between approximately 1.5 and 12 μm, and polished silicon wafers, arising from adhesion forces, were determined using scanning electron microscopy. It was found that the contact radius varied approximately as the square root of the particle radius. This dependence is consistent with nonelastic response models of adhesion, such as those proposed by Krupp [H. Krupp, Adv. Colloid Interface Sci. 1, 111 (1967)] and by Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984)], but is inconsistent with various elastic response models which assume Hertzian deformations. The experimentally determined contact radii are also compared to those obtained for polystyrene spheres on a polyurethane substrate [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. Appl. Phys. 66, 3574 (1989)].

  13. Modeling of the Deformation of Living Cells Induced by Atomic Force Microscopy

    SciTech Connect

    Rudd, R E; McElfresh, M; Baesu, E; Balhorn, R; Allen, M J; Belak, J

    2001-12-21

    We describe finite element modeling of the deformation of living cells by atomic force microscopy (AFM). Cells are soft systems, susceptible to large deformations in the course of an AFM measurement. Often the local properties, the subject of the measurement, are obscured by the response of the cell as a whole. The Lagrangian finite deformation model we have developed and implemented in finite elements analysis offers a solution to this problem. The effect of the gross deformation of the cell can be subtracted from the experimentally measured data in order to give a reproducible value for local properties. This facilitates concurrent experimental efforts to measure the mechanical properties at specific receptor sites on the membrane of a living cell.

  14. Elasticity-induced force reversal between active spinning particles in dense passive media

    NASA Astrophysics Data System (ADS)

    Aragones, J. L.; Steimel, J. P.; Alexander-Katz, A.

    2016-04-01

    The self-organization of active particles is governed by their dynamic effective interactions. Such interactions are controlled by the medium in which such active agents reside. Here we study the interactions between active agents in a dense non-active medium. Our system consists of actuated, spinning, active particles embedded in a dense monolayer of passive, or non-active, particles. We demonstrate that the presence of the passive monolayer alters markedly the properties of the system and results in a reversal of the forces between active spinning particles from repulsive to attractive. The origin of such reversal is due to the coupling between the active stresses and elasticity of the system. This discovery provides a mechanism for the interaction between active agents in complex and structured media, opening up opportunities to tune the interaction range and directionality via the mechanical properties of the medium.

  15. Computing solvent-induced forces in the solvation approach called Semi Explicit Assembly

    NASA Astrophysics Data System (ADS)

    Brini, Emiliano; Hummel, Michelle H.; Coutsias, Evangelos A.; Fennell, Christopher J.; Dill, Ken A.

    2014-03-01

    Many biologically relevant processes (e.g. protein folding) are often too big and slow to be simulated by computer methods that model atomically detailed water. Faster physical models of water are needed. We have developed an approach called Semi Explicit Assembly (SEA) [C.J. Fennell, C.W. Kehoe, K.A. Dill, PNAS, 108, 3234 (2011)]. It is physical because it uses pre-simulations of explicit-solvent models, and it is fast because at runtime, we just combine the pre-simulated results in rapid computations. SEA has also now been proven physically accurate in two blind tests called SAMPL. Here, we describe the computation of solvation forces in SEA, so that this solvation procedure can be incorporated into standard molecular dynamics codes. We describe experimental tests.

  16. Experimental studies in magnetically induced transverse force-frequency effect in thin quartz microresonators

    SciTech Connect

    Hatipoglu, Gokhan; Tadigadapa, Srinivas

    2015-07-21

    In this work, the transverse force-frequency sensitivity of magnetostrictive Metglas{sup ®} (Fe{sub 85}B{sub 5}Si{sub 10}) thin film coated AT-cut thickness shear mode quartz thin plate microresonator (500 μm × 500 μm × 19 μm) is experimentally measured and modeled in Lagrangian formulation by coupling magnetostrictive deformation equations with the basic plate equations from the theory of small deformation. The quartz plate resonator is fabricated by micromachining techniques and released into fixed-free structure using focused ion beam milling. Application of a magnetic field results in the out-of-plane bending of the structure due to elastic coupling between the magnetostrictive Metglas{sup ®} and quartz resonator layers. As a result of the transverse loading and out-of-plane bending, the admittance characteristics of the resonator shifts, and these shifts are recorded in real time utilizing a network analyzer. The sensitivity is experimentally measured to be 162.3 mdeg/Oe for phase, corresponding to a frequency sensitivity of Δf/H = 11 Hz/Oe. The equivalent force-frequency sensitivity can then be calculated as 2.36 μN/Hz using the developed model. The coupled domain analysis fits well with the experimental data. Further reduction of quartz thickness and optimization of the thickness ratio of the magnetostrictive to quartz layers offers the possibility of exploiting the stress sensitivity of plate microresonators as sensitive magnetic field sensors capable of low nanoTesla to picoTesla level magnetic flux densities.

  17. Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

    USGS Publications Warehouse

    Huang, Shengli; Dahal, Devendra; Liu, Heping; Jin, Suming; Young, Claudia J.; Liu, Shuang; Liu, Shu-Guang

    2015-01-01

    The albedo change caused by both fires and subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming fires had not occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of around 10 years. Our results showed that while postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 Wm-2. The integrated annual SSF map showed significant spatial variation with a mean of -3.15 Wm-2 and a standard deviation of 3.26 Wm-2, 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and non-radiative forcings to determine the effect of boreal fires on climate.

  18. Forced diffusion via electrically induced crystallization for fabricating ZnO–Ti–Si structures

    SciTech Connect

    Chen, Yen-Ting; Hung, Fei-Yi

    2014-11-15

    Highlights: • ZnO–Ti–Si system is very important for the structural design. • The electrically induced crystallization method is useful to diffusion process. • Intermetallic compound characteristics have been presented using electrically induced crystallization. • Interface mechanism about diffusion of TZO–TiSi{sub x}–Si structure is presented. - Abstract: Electrically induced crystallization (EIC) is a recently developed process for material modification. This study is applied to EIC to fabricate ZnO–Ti–Si multi-layer structures of various thicknesses to dope Ti into ZnO thin film and to form TiSi{sub x} intermetallic compound (IMC) in a single step. The IMC layer was confirmed using transmission electron microscopy images. The Ti layer thickness was more than 40 nm, which enhanced electron transmission and decreased the total electrical resistance in the structure. Finally, the diffusion mechanisms of EIC and the annealing process were investigated. This study shows that the EIC process has potential for industrial applications.

  19. 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.

  20. Strange fluctuations at RHIC

    NASA Astrophysics Data System (ADS)

    Abdel Aziz, Mohamed; Gavin, Sean

    2004-01-01

    Net charge fluctuations measured by the STAR experiment at RHIC agree with hadronic event generators, suggesting that more sensitive fluctuation observables are needed to extract information on collision dynamics. Important information on isospin fluctuations can be extracted from K0SK± measurements. Gavin and Kapusta proposed that disoriented chiral condensate can produce extraordinary isospin fluctuations in both strange and non-strange mesons. However, even in the absence of such a contribution, we argue that this observable is very sensitive to the collision dynamics.