WorldWideScience

Sample records for macro-molecular force dynamics

  1. Nonlinear Dynamic Force Spectroscopy

    CERN Document Server

    Björnham, Oscar

    2016-01-01

    Dynamic force spectroscopy (DFS) is an experimental technique that is commonly used to assess information of the strength, energy landscape, and lifetime of noncovalent bio-molecular interactions. DFS traditionally requires an applied force that increases linearly with time so that the bio-complex under investigation is exposed to a constant loading rate. However, tethers or polymers can modulate the applied force in a nonlinear regime. For example, bacterial adhesion pili and polymers with worm-like chain properties are examples of structures that show nonlinear force responses. In these situations, the theory for traditional DFS cannot be readily applied. In this work we expand the theory for DFS to also include nonlinear external forces while still maintaining compatibility with the linear DFS theory. To validate the theory we modeled a bio-complex expressed on a stiff, an elastic and a worm-like chain polymer, using Monte Carlo methods, and assessed the corresponding rupture force spectra. It was found th...

  2. Force Dynamics of Verb Complementation

    Directory of Open Access Journals (Sweden)

    Jacek Woźny

    2015-12-01

    Full Text Available Force Dynamics of Verb Complementation The concepts of motion and force are both extensively discussed in cognitive linguistics literature. But they are discussed separately. The first usually in the context of ‘motion situations’ (Talmy, Slobin, Zlatev, the other as part of the Force Dynamics framework, which was developed by Talmy. The aim of this paper is twofold: first, to argue that the concepts of force and motion should not be isolated but considered as two inseparable parts of force-motion events. The second goal is to prove that the modified Force Dynamics (force-motion framework can be used for precise characterization of the verb complementation patterns. To this end, a random sample of 50 sentences containing the verb ‘went’ is analyzed, demonstrating the differences between the categories of intensive and intransitive complementation with respect to the linguistically coded parameters of force and motion.

  3. Dynamics of forced biopolymer translocation

    CERN Document Server

    Lehtola, V V; Kaski, K; 10.1209/0295-5075/85/58006

    2009-01-01

    We present results from our simulations of biopolymer translocation in a solvent which explain the main experimental findings. The forced translocation can be described by simple force balance arguments for the relevant range of pore potentials in experiments and biological systems. Scaling of translocation time with polymer length varies with pore force and friction. Hydrodynamics affects this scaling and significantly reduces translocation times.

  4. Undulator with dynamic compensation of magnetic forces

    Energy Technology Data Exchange (ETDEWEB)

    Gluskin, Efim; Trakhtenberg, Emil; Xu, Joseph Z.

    2016-05-31

    A method and apparatus for implementing dynamic compensation of magnetic forces for undulators are provided. An undulator includes a respective set of magnet arrays, each attached to a strongback, and placed on horizontal slides and positioned parallel relative to each other with a predetermined gap. Magnetic forces are compensated by a set of compensation springs placed along the strongback. The compensation springs are conical springs having exponential-force characteristics that substantially match undulator magnetic forces independently of the predetermined gap. The conical springs are positioned along the length of the magnets.

  5. Undulator with dynamic compensation of magnetic forces

    Science.gov (United States)

    Gluskin, Efim; Trakhtenberg, Emil; Xu, Joseph Z.

    2016-05-31

    A method and apparatus for implementing dynamic compensation of magnetic forces for undulators are provided. An undulator includes a respective set of magnet arrays, each attached to a strongback, and placed on horizontal slides and positioned parallel relative to each other with a predetermined gap. Magnetic forces are compensated by a set of compensation springs placed along the strongback. The compensation springs are conical springs having exponential-force characteristics that substantially match undulator magnetic forces independently of the predetermined gap. The conical springs are positioned along the length of the magnets.

  6. Force dynamics in fixed-ratio schedules.

    Science.gov (United States)

    Pinkston, Jonathan W; McBee, Lindsey N

    2014-03-01

    Fixed-ratio schedules are widely used in behavioral research. Although fixed-ratio schedules often conjure up relationships to work and effort, little is known about effort-related measures in these schedules. Early research had shown that force and effort of operant behavior vary systematically during the execution of ratio schedules, and the goal of the present study was to revisit early research on force dynamics in fixed-ratio schedules. Four rats earned sucrose by pressing an isometric force transducer. Presses produced sucrose after ten or twenty responses. In general, the force of responses increased then decreased systematically across the ratio. The possibility that decreases in force during ratio execution was due to a trade-off with the differential reinforcement of short inter-response times (IRT) was investigated in an additional condition where sucrose was made available according to a tandem fixed-ratio 19 inter-response (IRT)> t schedule. The tandem IRT requirement did not eliminate decreasing trends in force across the ratio; unexpectedly, the tandem requirement did eliminate increases in force early in the ratio, which may reflect sequence-level organization operating in the control of force dynamics.

  7. Handling of impact forces in inverse dynamics

    NARCIS (Netherlands)

    Bisseling, Rob W.; Hof, At L.

    2006-01-01

    In the standard inverse dynamic method, joint moments are assessed from ground reaction force data and position data, where segmental accelerations are calculated by numerical differentiation of position data after low-pass filtering. This method falls short in analyzing the impact phase, e.g.

  8. Contact force models for multibody dynamics

    CERN Document Server

    Flores, Paulo

    2016-01-01

    This book analyzes several compliant contact force models within the context of multibody dynamics, while also revisiting the main issues associated with fundamental contact mechanics. In particular, it presents various contact force models, from linear to nonlinear, from purely elastic to dissipative, and describes their parameters. Addressing the different numerical methods and algorithms for contact problems in multibody systems, the book describes the gross motion of multibody systems by using a two-dimensional formulation based on the absolute coordinates and employs different contact models to represent contact-impact events. Results for selected planar multibody mechanical systems are presented and utilized to discuss the main assumptions and procedures adopted throughout this work. The material provided here indicates that the prediction of the dynamic behavior of mechanical systems involving contact-impact strongly depends on the choice of contact force model. In short, the book provides a comprehens...

  9. Forced synchronization of autonomous dynamical Boolean networks

    Energy Technology Data Exchange (ETDEWEB)

    Rivera-Durón, R. R., E-mail: roberto.rivera@ipicyt.edu.mx; Campos-Cantón, E., E-mail: eric.campos@ipicyt.edu.mx [División de Matemáticas Aplicadas, Instituto Potosino de Investigación Científica y Tecnológica A. C., Camino a la Presa San José 2055, Col. Lomas 4 Sección, C.P. 78216, San Luis Potosí, S.L.P. (Mexico); Campos-Cantón, I. [Facultad de Ciencias, Universidad Autónoma de San Luis Potosí, Álvaro Obregón 64, C.P. 78000, San Luis Potosí, S.L.P. (Mexico); Gauthier, Daniel J. [Department of Physics and Center for Nonlinear and Complex Systems, Duke University, Box 90305, Durham, North Carolina 27708 (United States)

    2015-08-15

    We present the design of an autonomous time-delay Boolean network realized with readily available electronic components. Through simulations and experiments that account for the detailed nonlinear response of each circuit element, we demonstrate that a network with five Boolean nodes displays complex behavior. Furthermore, we show that the dynamics of two identical networks display near-instantaneous synchronization to a periodic state when forced by a common periodic Boolean signal. A theoretical analysis of the network reveals the conditions under which complex behavior is expected in an individual network and the occurrence of synchronization in the forced networks. This research will enable future experiments on autonomous time-delay networks using readily available electronic components with dynamics on a slow enough time-scale so that inexpensive data collection systems can faithfully record the dynamics.

  10. Forced synchronization of autonomous dynamical Boolean networks.

    Science.gov (United States)

    Rivera-Durón, R R; Campos-Cantón, E; Campos-Cantón, I; Gauthier, Daniel J

    2015-08-01

    We present the design of an autonomous time-delay Boolean network realized with readily available electronic components. Through simulations and experiments that account for the detailed nonlinear response of each circuit element, we demonstrate that a network with five Boolean nodes displays complex behavior. Furthermore, we show that the dynamics of two identical networks display near-instantaneous synchronization to a periodic state when forced by a common periodic Boolean signal. A theoretical analysis of the network reveals the conditions under which complex behavior is expected in an individual network and the occurrence of synchronization in the forced networks. This research will enable future experiments on autonomous time-delay networks using readily available electronic components with dynamics on a slow enough time-scale so that inexpensive data collection systems can faithfully record the dynamics.

  11. Adaptive control of force microscope cantilever dynamics

    Science.gov (United States)

    Jensen, S. E.; Dougherty, W. M.; Garbini, J. L.; Sidles, J. A.

    2007-09-01

    Magnetic resonance force microscopy (MRFM) and other emerging scanning probe microscopies entail the detection of attonewton-scale forces. Requisite force sensitivities are achieved through the use of soft force microscope cantilevers as high resonant-Q micromechanical oscillators. In practice, the dynamics of these oscillators are greatly improved by the application of force feedback control computed in real time by a digital signal processor (DSP). Improvements include increased sensitive bandwidth, reduced oscillator ring up/down time, and reduced cantilever thermal vibration amplitude. However, when the cantilever tip and the sample are in close proximity, electrostatic and Casimir tip-sample force gradients can significantly alter the cantilever resonance frequency, foiling fixed-gain narrow-band control schemes. We report an improved, adaptive control algorithm that uses a Hilbert transform technique to continuously measure the vibration frequency of the thermally-excited cantilever and seamlessly adjust the DSP program coefficients. The closed-loop vibration amplitude is typically 0.05 nm. This adaptive algorithm enables narrow-band formally-optimal control over a wide range of resonance frequencies, and preserves the thermally-limited signal to noise ratio (SNR).

  12. Force field dependence of riboswitch dynamics.

    Science.gov (United States)

    Hanke, Christian A; Gohlke, Holger

    2015-01-01

    Riboswitches are noncoding regulatory elements that control gene expression in response to the presence of metabolites, which bind to the aptamer domain. Metabolite binding appears to occur through a combination of conformational selection and induced fit mechanism. This demands to characterize the structural dynamics of the apo state of aptamer domains. In principle, molecular dynamics (MD) simulations can give insights at the atomistic level into the dynamics of the aptamer domain. However, it is unclear to what extent contemporary force fields can bias such insights. Here, we show that the Amber force field ff99 yields the best agreement with detailed experimental observations on differences in the structural dynamics of wild type and mutant aptamer domains of the guanine-sensing riboswitch (Gsw), including a pronounced influence of Mg2+. In contrast, applying ff99 with parmbsc0 and parmχOL modifications (denoted ff10) results in strongly damped motions and overly stable tertiary loop-loop interactions. These results are based on 58 MD simulations with an aggregate simulation time>11 μs, careful modeling of Mg2+ ions, and thorough statistical testing. Our results suggest that the moderate stabilization of the χ-anti region in ff10 can have an unwanted damping effect on functionally relevant structural dynamics of marginally stable RNA systems. This suggestion is supported by crystal structure analyses of Gsw aptamer domains that reveal χ torsions with high-anti values in the most mobile regions. We expect that future RNA force field development will benefit from considering marginally stable RNA systems and optimization toward good representations of dynamics in addition to structural characteristics.

  13. Dynamical friction force exerted on spherical bodies

    CERN Document Server

    Esquivel, O

    2007-01-01

    We present a rigorous calculation of the dynamical friction force exerted on a spherical massive perturber moving through an infinite homogenous system of field stars. By calculating the shape and mass of the polarization cloud induced by the perturber in the background system, which decelerates the motion of the perturber, we recover Chandrasekhar's drag force law with a modified Coulomb logarithm. As concrete examples we calculate the drag force exerted on a Plummer sphere or a sphere with the density distribution of a Hernquist profile. It is shown that the shape of the perturber affects only the exact form of the Coulomb logarithm. The latter converges on small scales, because encounters of the test and field stars with impact parameters less than the size of the massive perturber become inefficient. We confirm this way earlier results based on the impulse approximation of small angle scatterings.

  14. Debye Entropic Force and Modified Newtonian Dynamics*

    Institute of Scientific and Technical Information of China (English)

    LI Xin; CHANG Zhe

    2011-01-01

    Verlinde has suggested that the gravity has an entropic origin, and a gravitational system could be regarded as a thermodynamical system.It is well-known that the equipartition law of energy is invalid at very low temperature.Therefore, entropic force should be modified while the temperature of the holographic screen is very low.It is shown that the modified entropic force is proportional to the square of the acceleration, while the temperature of the holographic screen is much lower than the Debye temperature TD.The modified entropic force returns to the Newton's law of gravitation while the temperature of the holographic screen is much higher than the Debye temperature.The modified entropic force is connected with modified Newtonian dynamics (MOND).The constant ao involved in MOND is linear in the Debye frequency ωD, which can be regarded as the largest frequency of the bits in screen.We find that there do have a strong connection between MOND and cosmology in the framework of Verlinde's entropic force, if the holographic screen is taken to be bound of the Universe.The Debye frequency is linear in the Hubble constant Ho.

  15. Eulerian Dynamics with a Commutator Forcing

    Science.gov (United States)

    2017-01-09

    not. The results below are stated over the torus, Ω = T1, for the purely technical reason of securing a uniform lower bound of the density away from...2.1. L∞-bound of the velocity. We assume that L satisfies the following monotonicity condition. Let x+ = arg max x g(x) and x− = arg min x g(x). Then...special case of the monotonicity condition (2.1) with (f, g) = (1, ρ) implies L(ρ)(x−) > L(1(x−))ρ− = 0. EULERIAN DYNAMICS WITH A COMMUTATOR FORCING 9 Here

  16. Relativistic Newtonian Dynamics under a central force

    Science.gov (United States)

    Friedman, Yaakov

    2016-10-01

    Planck's formula and General Relativity indicate that potential energy influences spacetime. Using Einstein's Equivalence Principle and an extension of his Clock Hypothesis, an explicit description of this influence is derived. We present a new relativity model by incorporating the influence of the potential energy on spacetime in Newton's dynamics for motion under a central force. This model extends the model used by Friedman and Steiner (EPL, 113 (2016) 39001) to obtain the exact precession of Mercury without curving spacetime. We also present a solution of this model for a hydrogen-like atom, which explains the reason for a probabilistic description.

  17. Irreversible energy flow in forced Vlasov dynamics

    KAUST Repository

    Plunk, Gabriel G.

    2014-10-01

    © EDP Sciences, Società Italiana di Fisica, Springer-Verlag. The recent paper of Plunk [G.G. Plunk, Phys. Plasmas 20, 032304 (2013)] considered the forced linear Vlasov equation as a model for the quasi-steady state of a single stable plasma wavenumber interacting with a bath of turbulent fluctuations. This approach gives some insight into possible energy flows without solving for nonlinear dynamics. The central result of the present work is that the forced linear Vlasov equation exhibits asymptotically zero (irreversible) dissipation to all orders under a detuning of the forcing frequency and the characteristic frequency associated with particle streaming. We first prove this by direct calculation, tracking energy flow in terms of certain exact conservation laws of the linear (collisionless) Vlasov equation. Then we analyze the steady-state solutions in detail using a weakly collisional Hermite-moment formulation, and compare with numerical solution. This leads to a detailed description of the Hermite energy spectrum, and a proof of no dissipation at all orders, complementing the collisionless Vlasov result.

  18. Influence of surfactants in forced dynamic dewetting.

    Science.gov (United States)

    Henrich, Franziska; Fell, Daniela; Truszkowska, Dorota; Weirich, Marcel; Anyfantakis, Manos; Nguyen, Thi-Huong; Wagner, Manfred; Auernhammer, Günter K; Butt, Hans-Jürgen

    2016-09-20

    In this work we show that the forced dynamic dewetting of surfactant solutions depends sensitively on the surfactant concentration. To measure this effect, a hydrophobic rotating cylinder was horizontally half immersed in aqueous surfactant solutions. Dynamic contact angles were measured optically by extrapolating the contour of the meniscus to the contact line. Anionic (sodium 1-decanesulfonate, S-1DeS), cationic (cetyl trimethylammonium bromide, CTAB) and nonionic surfactants (C4E1, C8E3 and C12E5) with critical micelle concentrations (CMCs) spanning four orders of magnitude were used. The receding contact angle in water decreased with increasing velocity. This decrease was strongly enhanced when adding surfactant, even at surfactant concentrations of 10% of the critical micelle concentration. Plots of the receding contact angle-versus-velocity almost superimpose when being plotted at the same relative concentration (concentration/CMC). Thus the rescaled concentration is the dominating property for dynamic dewetting. The charge of the surfactants did not play a role, thus excluding electrostatic effects. The change in contact angle can be interpreted by local surface tension gradients, i.e. Marangoni stresses, close to the three-phase contact line. The decrease of dynamic contact angles with velocity follows two regimes. Despite the existence of Marangoni stresses close to the contact line, for a dewetting velocity above 1-10 mm s(-1) the hydrodynamic theory is able to describe the experimental results for all surfactant concentrations. At slower velocities an additional steep decrease of the contact angle with velocity was observed. Particle tracking velocimetry showed that the flow profiles do not differ with and without surfactant on a scales >100 μm.

  19. Dynamic force microscopy imaging of native membranes

    Energy Technology Data Exchange (ETDEWEB)

    Kienberger, Ferry; Stroh, Cordula; Kada, Gerald; Moser, Rosita; Baumgartner, Werner; Pastushenko, Vassili; Rankl, Christian; Schmidt, Ute; Mueller, Harald; Orlova, Elena; LeGrimellec, Christian; Drenckhahn, Detlev; Blaas, Dieter; Hinterdorfer, Peter

    2003-10-15

    We employed magnetic ACmode atomic force microscopy (MACmode AFM) as a novel dynamic force microscopy method to image surfaces of biological membranes in their native environments. The lateral resolution achieved under optimized imaging conditions was in the nanometer range, even when the sample was only weakly attached to the support. Purple membranes (PM) from Halobacterium salinarum were used as a test standard for topographical imaging. The hexagonal arrangement of the bacteriorhodopsin trimers on the cytoplasmic side of PM was resolved with 1.5 nm lateral accuracy, a resolution similar to images obtained in contact and tapping-mode AFM. Human rhinovirus 2 (HRV2) particles were attached to mica surfaces via nonspecific interactions. The capsid structure and 2 nm sized protein loops of HRV2 were routinely obtained without any displacement of the virus. Globular and filamentous structures on living and fixed endothelial cells were observed with a resolution of 5-20 nm. These examples show that MACmode AFM is a favorable method in studying the topography of soft and weakly attached biological samples with high resolution under physiological conditions.

  20. Hydrodynamic Boundary Conditions and Dynamic Forces between Bubbles and Surfaces

    Science.gov (United States)

    Manor, Ofer; Vakarelski, Ivan U.; Tang, Xiaosong; O'Shea, Sean J.; Stevens, Geoffrey W.; Grieser, Franz; Dagastine, Raymond R.; Chan, Derek Y. C.

    2008-07-01

    Dynamic forces between a 50μm radius bubble driven towards and from a mica plate using an atomic force microscope in electrolyte and in surfactant exhibit different hydrodynamic boundary conditions at the bubble surface. In added surfactant, the forces are consistent with the no-slip boundary condition at the mica and bubble surfaces. With no surfactant, a new boundary condition that accounts for the transport of trace surface impurities explains variations of dynamic forces at different speeds and provides a direct connection between dynamic forces and surface transport effects at the air-water interface.

  1. Dynamic balancing with rotating radial electromagnetic force

    Institute of Scientific and Technical Information of China (English)

    李勇; 陆永平

    2004-01-01

    A method of producing rotating radial electromagnetic force with a separable structure is proposed,and an experimental model was designed on which open loop vibration control experiments were carried out. Experimental results prove that the electromagnetic force designed has a constant magnitude and an uniform speed,and the idea of using an electromagnetic force as an active control in automatic balancing is correct in principle,and practicable in engineering.

  2. Dynamic force patterns of an undulatory microswimmer.

    Science.gov (United States)

    Schulman, Rafael D; Backholm, Matilda; Ryu, William S; Dalnoki-Veress, Kari

    2014-05-01

    We probe the viscous forces involved in the undulatory swimming of the model organism C. elegans. Using micropipette deflection, we attain direct measurements of lateral and propulsive forces produced in response to the motion of the worm. We observe excellent agreement of the results with resistive force theory, through which we determine the drag coefficients of this organism. The drag coefficients are in accordance with theoretical predictions. Using a simple scaling argument, we obtain a relationship between the size of the worm and the forces that we measure, which well describes our data.

  3. Dynamic force spectroscopy on multiple bonds: experiments and model

    CERN Document Server

    Erdmann, T; Nassoy, P; Schwarz, U S

    2007-01-01

    We probe the dynamic strength of multiple biotin-streptavidin adhesion bonds under linear loading using the biomembrane force probe setup for dynamic force spectroscopy. Measured rupture force histograms are compared to results from a master equation model for the stochastic dynamics of bond rupture under load. This allows us to extract the distribution of the number of initially closed bonds. We also extract the molecular parameters of the adhesion bonds, in good agreement with earlier results from single bond experiments. Our analysis shows that the peaks in the measured histograms are not simple multiples of the single bond values, but follow from a superposition procedure which generates different peak positions.

  4. Wavelet transforms to probe long- and short-range forces by thermally excited dynamic force spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Malegori, Giovanna; Ferrini, Gabriele, E-mail: gabriele@dmf.unicatt.it [Dipartimento di Matematica e Fisica, Universita Cattolica, I-25121 Brescia (Italy)

    2011-05-13

    The use of wavelet transforms in thermally excited dynamic force spectroscopy allows us to gain insight into the fundamental thermodynamical properties of a cantilever's Brownian motion as well as giving a meaningful and intuitive representation of the cantilever dynamics in time and frequency caused by the interaction with long- and short-range forces. The possibility of carrying out measurements across the jump-to-contact transition without interruption, providing information on both van der Waals forces and short-range adhesion surface forces, is remarkable.

  5. Force Factor Modulation in Electro Dynamic Loudspeakers

    DEFF Research Database (Denmark)

    Risbo, Lars; Agerkvist, Finn T.; Tinggaard, Carsten

    2016-01-01

    The relationship between the non-linear phenomenon of ’reluctance force’ and the position dependency of the voice coil inductance was established in 1949 by Cunningham, who called it ’magnetic attraction force’. This paper revisits Cunningham’s analysis and expands it into a generalised form...... that includes the frequency dependency and applies to coils with non-inductive (lossy) blocked impedance. The paper also demonstrates that Cunningham’s force can be explained physically as a modulation of the force factor which again is directly linked to modulation of the flux of the coil. A verification based...... on both experiments and simulations is presented along discussions of the impact of force factor modulation for various motor topologies. Finally, it is shown that the popular L2R2 coil impedance model does not correctly predict the force unless the new analysis is applied....

  6. Force Factor Modulation in Electro Dynamic Loudspeakers

    DEFF Research Database (Denmark)

    Risbo, Lars; Agerkvist, Finn T.; Tinggaard, Carsten

    2016-01-01

    The relationship between the non-linear phenomenon of ’reluctance force’ and the position dependency of the voice coil inductance was established in 1949 by Cunningham, who called it ’magnetic attraction force’. This paper revisits Cunningham’s analysis and expands it into a generalised form that...... on both experiments and simulations is presented along discussions of the impact of force factor modulation for various motor topologies. Finally, it is shown that the popular L2R2 coil impedance model does not correctly predict the force unless the new analysis is applied....... that includes the frequency dependency and applies to coils with non-inductive (lossy) blocked impedance. The paper also demonstrates that Cunningham’s force can be explained physically as a modulation of the force factor which again is directly linked to modulation of the flux of the coil. A verification based...

  7. Bifurcation, chaos, and scan instability in dynamic atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Cantrell, John H., E-mail: john.h.cantrell@nasa.gov [Research Directorate, NASA Langley Research Center, Hampton, Virginia 23681 (United States); Cantrell, Sean A., E-mail: scantrell@nlsanalytics.com [NLS Analytics, LLC, 375 Dundee Road, Glencoe, Illinois 60022 (United States)

    2016-03-28

    The dynamical motion at any point on the cantilever of an atomic force microscope can be expressed quite generally as a superposition of simple harmonic oscillators corresponding to the vibrational modes allowed by the cantilever shape. Central to the dynamical equations is the representation of the cantilever-sample interaction force as a polynomial expansion with coefficients that account for the interaction force “stiffness,” the cantilever-to-sample energy transfer, and the displacement amplitude of cantilever oscillation. Renormalization of the cantilever beam model shows that for a given cantilever drive frequency cantilever dynamics can be accurately represented by a single nonlinear mass-spring model with frequency-dependent stiffness and damping coefficients [S. A. Cantrell and J. H. Cantrell, J. Appl. Phys. 110, 094314 (2011)]. Application of the Melnikov method to the renormalized dynamical equation is shown to predict a cascade of period doubling bifurcations with increasing cantilever drive force that terminates in chaos. The threshold value of the drive force necessary to initiate bifurcation is shown to depend strongly on the cantilever setpoint and drive frequency, effective damping coefficient, nonlinearity of the cantilever-sample interaction force, and the displacement amplitude of cantilever oscillation. The model predicts the experimentally observed interruptions of the bifurcation cascade for cantilevers of sufficiently large stiffness. Operational factors leading to the loss of image quality in dynamic atomic force microscopy are addressed, and guidelines for optimizing scan stability are proposed using a quantitative analysis based on system dynamical parameters and choice of feedback loop parameter.

  8. Corticomuscular synchronization with small and large dynamic force output

    Directory of Open Access Journals (Sweden)

    Witte Matthias

    2007-11-01

    Full Text Available Abstract Background Over the last few years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study 1 that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic generated by a manipulandum. The CMC, the cortical EEG spectral power (SP, the EMG SP and the errors in motor performance (as the difference between target and exerted force were analyzed. Results For the static force condition we found the well-documented, significant beta-range CMC (15–30 Hz over the contralateral sensorimotor cortex. Gamma-band CMC (30–45 Hz occurred in both small and large dynamic force conditions without any significant difference between both conditions. Although in some subjects beta-range CMC was observed during both dynamic force conditions no significant difference between conditions could be detected. With respect to the motor performance, the lowest errors were obtained in the static force condition and the highest ones in the dynamic condition with large amplitude. However, when we normalized the magnitude of the errors to the amplitude of the applied force (relative errors no significant difference between both dynamic conditions was observed. Conclusion These findings confirm that during dynamic force output the corticomuscular network oscillates at gamma frequencies. Moreover, we show that amplitude modulation of dynamic force has no

  9. Corticomuscular synchronization with small and large dynamic force output.

    Science.gov (United States)

    Andrykiewicz, Agnieszka; Patino, Luis; Naranjo, Jose Raul; Witte, Matthias; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

    2007-11-27

    Over the last few years much research has been devoted to investigating the synchronization between cortical motor and muscular activity as measured by EEG/MEG-EMG coherence. The main focus so far has been on corticomuscular coherence (CMC) during static force condition, for which coherence in beta-range has been described. In contrast, we showed in a recent study 1 that dynamic force condition is accompanied by gamma-range CMC. The modulation of the CMC by various dynamic force amplitudes, however, remained uninvestigated. The present study addresses this question. We examined eight healthy human subjects. EEG and surface EMG were recorded simultaneously. The visuomotor task consisted in isometric compensation for 3 forces (static, small and large dynamic) generated by a manipulandum. The CMC, the cortical EEG spectral power (SP), the EMG SP and the errors in motor performance (as the difference between target and exerted force) were analyzed. For the static force condition we found the well-documented, significant beta-range CMC (15-30 Hz) over the contralateral sensorimotor cortex. Gamma-band CMC (30-45 Hz) occurred in both small and large dynamic force conditions without any significant difference between both conditions. Although in some subjects beta-range CMC was observed during both dynamic force conditions no significant difference between conditions could be detected. With respect to the motor performance, the lowest errors were obtained in the static force condition and the highest ones in the dynamic condition with large amplitude. However, when we normalized the magnitude of the errors to the amplitude of the applied force (relative errors) no significant difference between both dynamic conditions was observed. These findings confirm that during dynamic force output the corticomuscular network oscillates at gamma frequencies. Moreover, we show that amplitude modulation of dynamic force has no effect on the gamma CMC in the low force range investigated

  10. Traceable dynamic calibration of force transducers by primary means

    Science.gov (United States)

    Vlajic, Nicholas; Chijioke, Ako

    2016-08-01

    We describe an apparatus for traceable, dynamic calibration of force transducers using harmonic excitation, and report calibration measurements of force transducers using this apparatus. In this system, the force applied to the transducer is produced by the acceleration of an attached mass, and is determined according to Newton’s second law, F  =  ma. The acceleration is measured by primary means, using laser interferometry. The capabilities of this system are demonstrated by performing dynamic calibrations of two shear-web-type force transducers up to a frequency of 2 kHz, with an expanded uncertainty below 1.2%. We give an account of all significant sources of uncertainty, including a detailed consideration of the effects of dynamic tilting (rocking), which is a leading source of uncertainty in such harmonic force calibration systems.

  11. EMG-force relation in dynamically contracting cat plantaris muscle.

    Science.gov (United States)

    Herzog, W; Sokolosky, J; Zhang, Y T; Guimarães, A C

    1998-06-01

    The purpose of this study was to revisit the electromyographical (EMG)-force relationship of dynamically contracting muscles using direct measurements of EMG and force in cat hindlimb muscles during locomotion. EMG signals were recorded from the plantaris muscle using bipolar indwelling wire electrodes, and the corresponding forces were measured using a tendon force transducer. Force-time histories of cat plantaris muscle were predicted by estimating selected force parameters from EMG and timing parameters, and then constructing two smoothly fitting quintic spline functions from the estimated force parameters. The force predictions did not contain information on force-length or force-velocity properties of the cat plantaris and did not use instantaneous contractile conditions as input. It was found that two smoothly fitting quintic spline functions provided the required properties to approximate plantaris force-time histories accurately, and approximations of the force-time histories using EMG and timing parameters as input for the quintic splines were good. The root mean square errors (RMS) of the predicted compared to the actual plantaris forces were smaller than corresponding results reported in the literature, even though the prediction model did not require the force-length-velocity properties or the instantaneous contractile conditions of the target muscles as input. From the results obtained in this study, it appears that force-time histories of the cat plantaris muscle during locomotion can be predicted adequately from information obtained using EMG and video records, without information on either the force-length and force-velocity properties, or the instantaneous contractile conditions of the muscle.

  12. Dynamic Correction Algorithm of Rolling Force in Plate Rolling

    Institute of Scientific and Technical Information of China (English)

    QIU Hong-lei; WANG Jun; HU Xian-lei; WANG Zhao-dong; WANG Guo-dong

    2005-01-01

    Based on the Shougang plat mill project, an on-line dynamic correction algorithm was analyzed. This algorithm can adjust model coefficients better because the reasonable correction is based on the measured and calculated rolling force. The results of application on site show that this on-line dynamic correction algorithm is effective.

  13. Effects of nonlinear forces on dynamic mode atomic force microscopy and spectroscopy.

    Science.gov (United States)

    Das, Soma; Sreeram, P A; Raychaudhuri, A K

    2007-06-01

    In this paper, we describe the effects of nonlinear tip-sample forces on dynamic mode atomic force microscopy and spectroscopy. The jumps and hysteresis observed in the vibration amplitude (A) versus tip-sample distance (h) curves have been traced to bistability in the resonance curve. A numerical analysis of the basic dynamic equation was used to explain the hysteresis in the experimental curve. It has been found that the location of the hysteresis in the A-h curve depends on the frequency of the forced oscillation relative to the natural frequency of the cantilever.

  14. MD1405: Demonstration of forced dynamic aperture measurements at injection

    CERN Document Server

    Carlier, Felix Simon; Persson, Tobias Hakan Bjorn; Tomas Garcia, Rogelio; CERN. Geneva. ATS Department

    2017-01-01

    Accurate measurements of dynamic aperture become more important for the LHC as it advances into increasingly nonlinear regimes of operations, as well as for the High Luminosity LHC where machine nonlinearities will have a significantly larger impact. Direct dynamic aperture measurements at top energy in the LHC are challenging, and conventional single kick methods are not viable. Dynamic aperture measurements under forced oscillation of AC dipoles have been proposed as s possible alternative observable. A first demonstration of forced DA measurements at injections energy is presented.

  15. Dynamic Analysis of Axial Magnetic Forces for DVD Spindle Motors

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The axial magnetic force, induced by the complicated flux linkage distribution from rotor magnet and stator slotted, is constructed by different relative heights and calculated by 3D finite element method (FEM) to analyze the dynamic characteristics for a DVD spindle motor. The axial magnetic force is designed to provide an axial stiffness and govern the natural frequency of the dynamic performance. According to the simulation results and experimental measurements, the dynamic behaviors are significantly improved with a variation of relative height of rotor magnet and stator slotted on a DVD spindle motor.

  16. Simplistic Coulomb Forces in Molecular Dynamics

    DEFF Research Database (Denmark)

    Hansen, Jesper Schmidt; Schrøder, Thomas; Dyre, J. C.

    2012-01-01

    salt model the SF approximation overall reproduces the structural and dynamical properties as accurately as does the Wolf method. It is shown that the optimal Wolf damping parameter depends on the property in focus and that neither the potential energy nor the radial distribution function are useful...

  17. NONLINEAR DYNAMICS OF CARBON NANOTUBES UNDER LARGE ELECTROSTATIC FORCE

    KAUST Repository

    Xu, Tiantian

    2015-06-01

    Because of the inherent nonlinearities involving the behavior of CNTs when excited by electrostatic forces, modeling and simulating their behavior is challenging. The complicated form of the electrostatic force describing the interaction of their cylindrical shape, forming upper electrodes, to lower electrodes poises serious computational challenges. This presents an obstacle against applying and using several nonlinear dynamics tools typically used to analyze the behavior of complicated nonlinear systems undergoing large motion, such as shooting, continuation, and integrity analysis techniques. This works presents an attempt to resolve this issue. We present an investigation of the nonlinear dynamics of carbon nanotubes when actuated by large electrostatic forces. We study expanding the complicated form of the electrostatic force into enough number of terms of the Taylor series. Then, we utilize this form along with an Euler-Bernoulli beam model to study for the first time the dynamic behavior of CNTs when excited by large electrostatic force. The geometric nonlinearity and the nonlinear electrostatic force are considered. An efficient reduced-order model (ROM) based on the Galerkin method is developed and utilized to simulate the static and dynamic responses of the CNTs. Several results are generated demonstrating softening and hardening behavior of the CNTs near their primary and secondary resonances. The effects of the DC and AC voltage loads on the behavior have been studied. The impacts of the initial slack level and CNT diameter are also demonstrated.

  18. Software for Correcting the Dynamic Error of Force Transducers

    Directory of Open Access Journals (Sweden)

    Naoki Miyashita

    2014-07-01

    Full Text Available Software which corrects the dynamic error of force transducers in impact force measurements using their own output signal has been developed. The software corrects the output waveform of the transducers using the output waveform itself, estimates its uncertainty and displays the results. In the experiment, the dynamic error of three transducers of the same model are evaluated using the Levitation Mass Method (LMM, in which the impact forces applied to the transducers are accurately determined as the inertial force of the moving part of the aerostatic linear bearing. The parameters for correcting the dynamic error are determined from the results of one set of impact measurements of one transducer. Then, the validity of the obtained parameters is evaluated using the results of the other sets of measurements of all the three transducers. The uncertainties in the uncorrected force and those in the corrected force are also estimated. If manufacturers determine the correction parameters for each model using the proposed method, and provide the software with the parameters corresponding to each model, then users can obtain the waveform corrected against dynamic error and its uncertainty. The present status and the future prospects of the developed software are discussed in this paper.

  19. Dynamics of gecko locomotion: a force-measuring array to measure 3D reaction forces.

    Science.gov (United States)

    Dai, Zhendong; Wang, Zhouyi; Ji, Aihong

    2011-03-01

    Measuring the interaction between each foot of an animal and the substrate is one of the most effective ways to understand the dynamics of legged locomotion. Here, a new facility - the force-measuring array (FMA) - was developed and applied to measure 3D reaction forces of geckos on different slope surfaces. The FMA consists of 16 3D sensors with resolution to the mN level. At the same time the locomotion behaviour of geckos freely moving on the FMA was recorded by high speed camera. The reaction forces acting on the gecko's individual feet measured by the FMA and correlated with locomotion behaviour provided enough information to reveal the mechanical and dynamic secrets of gecko locomotion. Moreover, dynamic forces were also measured by a force platform and correlated with locomotion behaviour. The difference between the forces measured by the two methods is discussed. From the results we conclude that FMA is the best way to obtain true reaction forces acting on the gecko's individual feet.

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

    Science.gov (United States)

    Shimada, Yuhki; Ohe, Jun-ichiro

    2015-05-01

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

  1. Jamming transitions in force-based models for pedestrian dynamics

    CERN Document Server

    Chraibi, Mohcine; Tordeux, Antoine; Nishinari, Katsuhiro; Schadschneider, Andreas; Seyfried, Armin

    2015-01-01

    Force-based models describe pedestrian dynamics in analogy to classical mechanics by a system of second order ordinary differential equations. By investigating the linear stability of two main classes of forces, parameter regions with unstable homogeneous states are identified. In this unstable regime it is then checked whether phase transitions or stop-and-go waves occur. Results based on numerical simulations show, however, that the investigated models lead to unrealistic behavior in form of backwards moving pedestrians and overlapping. This is one reason why stop-and-go waves have not been observed in these models. The unrealistic behavior is not related to the numerical treatment of the dynamic equations but rather indicates an intrinsic problem of this model class. Identifying the underlying generic problems gives indications how to define models that do not show such unrealistic behavior. As an example we introduce a new force-based model which produces realistic jam dynamics without the appearance of u...

  2. Identifying the Stern-Gerlach force of classical electron dynamics

    Science.gov (United States)

    Wen, Meng; Bauke, Heiko; Keitel, Christoph H.

    2016-08-01

    Different classical theories are commonly applied in various branches of physics to describe the relativistic dynamics of electrons by coupled equations for the orbital motion and spin precession. Exemplarily, we benchmark the Frenkel model and the classical Foldy-Wouthuysen model with spin-dependent forces (Stern-Gerlach forces) to the quantum dynamics as predicted by the Dirac equation. Both classical theories can lead to different or even contradicting predictions how the Stern-Gerlach forces modify the electron’s orbital motion, when the electron moves in strong electromagnetic field configurations of emerging high-intensity laser facilities. In this way, one may evaluate the validity and identify the limits of these classical theories via a comparison with possible experiments to provide a proper description of spin-induced dynamics. Our results indicate that the Foldy-Wouthuysen model is qualitatively in better agreement with the Dirac theory than the widely used Frenkel model.

  3. Dynamic forces between bubbles and surfaces and hydrodynamic boundary conditions.

    Science.gov (United States)

    Manor, Ofer; Vakarelski, Ivan U; Stevens, Geoffrey W; Grieser, Franz; Dagastine, Raymond R; Chan, Derek Y C

    2008-10-21

    A bubble attached to the end of an atomic force microscope cantilever and driven toward or away from a flat mica surface across an aqueous film is used to characterize the dynamic force that arises from hydrodynamic drainage and electrical double layer interactions across the nanometer thick intervening aqueous film. The hydrodynamic response of the air/water interface can range from a classical fully immobile, no-slip surface in the presence of added surfactants to a partially mobile interface in an electrolyte solution without added surfactants. A model that includes the convection and diffusion of trace surface contaminants can account for the observed behavior presented. This model predicts quantitatively different interfacial dynamics to the Navier slip model that can also be used to fit dynamic force data with a post hoc choice of a slip length.

  4. [The Northeast: fertility and recent dynamics of the labor force].

    Science.gov (United States)

    De Oliveira, L A

    1985-01-01

    Data from the 1970 and 1980 censuses of Brazil are analyzed to examine the economic growth of the Notheast, changes in the region's population dynamics, and changes in fertility. Consideration is given to the segmentation of the urban labor market, the income of the economically active population, children in the labor force, female education versus fertility, and family income versus female participation in the work force.

  5. Dynamics of a Parametrically Excited System with Two Forcing Terms

    Directory of Open Access Journals (Sweden)

    Anastasia Sofroniou

    2014-09-01

    Full Text Available Motivated by the dynamics of a trimaran, an investigation of the dynamic behaviour of a double forcing parametrically excited system is carried out. Initially, we provide an outline of the stability regions, both numerically and analytically, for the undamped linear, extended version of the Mathieu equation. This paper then examines the anticipated form of response of our proposed nonlinear damped double forcing system, where periodic and quasiperiodic routes to chaos are graphically demonstrated and compared with the case of the single vertically-driven pendulum.

  6. Approximate photochemical dynamics of azobenzene with reactive force fields

    Science.gov (United States)

    Li, Yan; Hartke, Bernd

    2013-12-01

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).

  7. Approximate photochemical dynamics of azobenzene with reactive force fields.

    Science.gov (United States)

    Li, Yan; Hartke, Bernd

    2013-12-14

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).

  8. Gamma-range corticomuscular coherence during dynamic force output.

    Science.gov (United States)

    Omlor, Wolfgang; Patino, Luis; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

    2007-02-01

    The beta-range synchronization between cortical motor and muscular activity as revealed by EEG/MEG-EMG coherence has been extensively investigated for steady-state motor output. However, there is a lack of information on the modulation of the corticomuscular coherence in conjunction with dynamic force output. We addressed this question comparing the EEG-EMG coherence and the cortical motor spectral power in eight healthy subjects in a visuomotor task, in which the subjects exerted a steady-state or periodically modulated dynamic isometric force output with their right-index finger to keep a visual cursor within a target zone. In the static condition, significant coherence was confined to the beta-range. In the dynamic condition, the most distinct coherence occurred in the gamma-range and the significant beta-range coherence was strikingly reduced. The cortical motor power in the beta-range during dynamic force output was decreased, whereas the power in the gamma-range remained without significant change. We conclude that during dynamic force the corticospinal oscillation mode of the sensorimotor system shifts towards higher (principally gamma) frequencies for the rapid integration of the visual and somatosensory information required to produce the appropriate motor command.

  9. Dynamic steering beams for efficient force measurement in optical manipulation

    Institute of Scientific and Technical Information of China (English)

    Xiaocong Yuan; Yuquan Zhang; Rui Cao; Xing Zhao; Jing Bu; Siwei Zhu

    2011-01-01

    @@ An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported.Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions, respectively, in a viscous medium.The trapped bead will be rotated following the beam's motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force.The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead.The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications.%An efficient and inexpensive method that uses a glass plate mounted onto a motorized rotating stage as a beam-steering device for the generation of dynamic optical traps is reported. Force analysis reveals that there are drag and trapping forces imposed on the bead in the opposite directions, respectively, in a viscous medium. The trapped bead will be rotated following the beam's motion before it reaches the critical escape velocity when the drag force is equal to the optical trapping force. The equilibrium condition facilitates the experimental measurement of the drag force with potential extensions to the determination of the viscosity of the medium or the refractive index of the bead. The proposed technique can easily be integrated into conventional optical microscopic systems with minimum modifications.

  10. Switched Dynamical Latent Force Models for Modelling Transcriptional Regulation

    CERN Document Server

    López-Lopera, Andrés F

    2015-01-01

    In order to develop statistical approaches for transcription networks, statistical community has proposed several methods to infer activity levels of proteins, from time-series measurements of targets' expression levels. A few number of approaches have been proposed in order to outperform the representation of fast switching time instants, but computational overheads are significant due to complex inference algorithms. Using the theory related to latent force models (LFM), the development of this project provide a switched dynamical hybrid model based on Gaussian processes (GPs). To deal with discontinuities in dynamical systems (or latent driving force), an extension of the single input motif approach is introduced, that switches between different protein concentrations, and different dynamical systems. This creates a versatile representation for transcription networks that can capture discrete changes and non-linearities in the dynamics. The proposed method is evaluated on both simulated data and real data,...

  11. Nonergodic dynamics of force-free granular gases

    OpenAIRE

    Bodrova, Anna; Chechkin, Aleksei V.; Cherstvy, Andrey G.; Metzler, Ralf

    2015-01-01

    We study analytically and by event-driven molecular dynamics simulations the nonergodic and aging properties of force-free cooling granular gases with both constant and velocity-dependent (viscoelastic) restitution coefficient $\\varepsilon$ for particle pair collisions. We compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behavior of the ensembl...

  12. Model based control of dynamic atomic force microscope

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chibum [Department of Mechanical System Design Engineering, Seoul National University of Science and Technology, Seoul 139-743 (Korea, Republic of); Salapaka, Srinivasa M., E-mail: salapaka@illinois.edu [Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    2015-04-15

    A model-based robust control approach is proposed that significantly improves imaging bandwidth for the dynamic mode atomic force microscopy. A model for cantilever oscillation amplitude and phase dynamics is derived and used for the control design. In particular, the control design is based on a linearized model and robust H{sub ∞} control theory. This design yields a significant improvement when compared to the conventional proportional-integral designs and verified by experiments.

  13. Model based control of dynamic atomic force microscope.

    Science.gov (United States)

    Lee, Chibum; Salapaka, Srinivasa M

    2015-04-01

    A model-based robust control approach is proposed that significantly improves imaging bandwidth for the dynamic mode atomic force microscopy. A model for cantilever oscillation amplitude and phase dynamics is derived and used for the control design. In particular, the control design is based on a linearized model and robust H(∞) control theory. This design yields a significant improvement when compared to the conventional proportional-integral designs and verified by experiments.

  14. Monitoring dynamic loads on wind tunnel force balances

    Science.gov (United States)

    Ferris, Alice T.; White, William C.

    1989-01-01

    Two devices have been developed at NASA Langley to monitor the dynamic loads incurred during wind-tunnel testing. The Balance Dynamic Display Unit (BDDU), displays and monitors the combined static and dynamic forces and moments in the orthogonal axes. The Balance Critical Point Analyzer scales and sums each normalized signal from the BDDU to obtain combined dynamic and static signals that represent the dynamic loads at predefined high-stress points. The display of each instrument is a multiplex of six analog signals in a way that each channel is displayed sequentially as one-sixth of the horizontal axis on a single oscilloscope trace. Thus this display format permits the operator to quickly and easily monitor the combined static and dynamic level of up to six channels at the same time.

  15. Dynamic Stability of Euler Beams under Axial Unsteady Wind Force

    Directory of Open Access Journals (Sweden)

    You-Qin Huang

    2014-01-01

    Full Text Available Dynamic instability of beams in complex structures caused by unsteady wind load has occurred more frequently. However, studies on the parametric resonance of beams are generally limited to harmonic loads, while arbitrary dynamic load is rarely involved. The critical frequency equation for simply supported Euler beams with uniform section under arbitrary axial dynamic forces is firstly derived in this paper based on the Mathieu-Hill equation. Dynamic instability regions with high precision are then calculated by a presented eigenvalue method. Further, the dynamically unstable state of beams under the wind force with any mean or fluctuating component is determined by load normalization, and the wind-induced parametric resonant response is computed by the Runge-Kutta approach. Finally, a measured wind load time-history is input into the dynamic system to indicate that the proposed methods are effective. This study presents a new method to determine the wind-induced dynamic stability of Euler beams. The beam would become dynamically unstable provided that the parametric point, denoting the relation between load properties and structural frequency, is located in the instability region, no matter whether the wind load component is large or not.

  16. Relationships between Isometric Force-Time Characteristics and Dynamic Performance

    Directory of Open Access Journals (Sweden)

    Thomas Dos’Santos

    2017-09-01

    Full Text Available The purpose of this study was to explore the relationships between isometric mid-thigh pull (IMTP force-time characteristics (peak force and time-specific force vales (100–250 ms and dynamic performance and compare dynamic performance between stronger and weaker athletes. Forty-three athletes from different sports (rowing, soccer, bicycle motocross, and hockey performed three trials of the squat jump (SJ, countermovement jump (CMJ, and IMTP, and performed a one repetition maximum power clean (PC. Reactive strength index modified (RSImod was also calculated from the CMJ. Statistically significant large correlations between IMTP force-time characteristics and PC (ρ = 0.569–0.674, p < 0.001, and moderate correlations between IMTP force-time characteristics (excluding force at 100 ms and RSImod (ρ = 0.389–0.449, p = 0.013–0.050 were observed. Only force at 250 ms demonstrated a statistically significant moderate correlation with CMJ height (ρ = 0.346, p = 0.016 and no statistically significant associations were observed between IMTP force-time characteristics and SJ height. Stronger athletes (top 10 demonstrated statistically significantly greater CMJ heights, RSImods, and PCs (p ≤ 0.004, g = 1.32–1.89 compared to weaker (bottom 10 athletes, but no differences in SJ height were observed (p = 0.871, g = 0.06. These findings highlight that the ability to apply rapidly high levels of force in short time intervals is integral for PC, CMJ height, and reactive strength.

  17. Force-dynamic cultural models in a scalar adjectival construction

    DEFF Research Database (Denmark)

    Jensen, Kim Ebensgaard

    'm in a certain group that's almost too old to hire. (COCA 2011 NEWS Denver) (6) Mr. Turman insisted he was too busy to meet at any other time. (COCA 2011 NEWS NYTimes) In all instances, semantic relations of force-dynamics are set up between the adjective and verb positions, such that the adjective describes...

  18. Vertically polarizing undulator with dynamic compensation of magnetic forces

    National Research Council Canada - National Science Library

    Strelnikov, N; Vasserman, I; Xu, J; Jensen, D; Schmidt, O; Trakhtenberg, E; Suthar, K; Moog, E. R; Pile, G; Gluskin, E

    2017-01-01

    As part of the R&D program of the LCLS-II project, a novel 3.4-meter-long undulator prototype with horizontal magnetic field and dynamic force compensation has recently been developed at the Advanced Photon Source (APS...

  19. Forced Fluid Dynamics from Blackfolds in General Supergravity Backgrounds

    CERN Document Server

    Armas, Jay; Niarchos, Vasilis; Obers, Niels A; Pedersen, Andreas Vigand

    2016-01-01

    We present a general treatment of the leading order dynamics of the collective modes of charged dilatonic $p$-brane solutions of (super)gravity theories in arbitrary backgrounds. To this end we employ the general strategy of the blackfold approach which is based on a long-wavelength derivative expansion around an exact or approximate solution of the (super)gravity equations of motion. The resulting collective mode equations are formulated as forced hydrodynamic equations on dynamically embedded hypersurfaces. We derive them in full generality (including all possible asymptotic fluxes and dilaton profiles) in a far-zone analysis of the (super)gravity equations and in representative examples in a near-zone analysis. An independent treatment based on the study of external couplings in hydrostatic partition functions is also presented. Special emphasis is given to the forced collective mode equations that arise in type IIA/B and eleven-dimensional supergravities, where besides the standard Lorentz force couplings...

  20. Estimation of the shear force in transverse dynamic force microscopy using a sliding mode observer

    Directory of Open Access Journals (Sweden)

    Thang Nguyen

    2015-09-01

    Full Text Available In this paper, the problem of estimating the shear force affecting the tip of the cantilever in a Transverse Dynamic Force Microscope (TDFM using a real-time implementable sliding mode observer is addressed. The behaviour of a vertically oriented oscillated cantilever, in close proximity to a specimen surface, facilitates the imaging of the specimen at nano-metre scale. Distance changes between the cantilever tip and the specimen can be inferred from the oscillation amplitudes, but also from the shear force acting at the tip. Thus, the problem of accurately estimating the shear force is of significance when specimen images and mechanical properties need to be obtained at submolecular precision. A low order dynamic model of the cantilever is derived using the method of lines, for the purpose of estimating the shear force. Based on this model, an estimator using sliding mode techniques is presented to reconstruct the unknown shear force, from only tip position measurements and knowledge of the excitation signal applied to the top of the cantilever. Comparisons to methods assuming a quasi-static harmonic balance are made.

  1. Modeling of Dynamic Fluid Forces in Fast Switching Valves

    DEFF Research Database (Denmark)

    Roemer, Daniel Beck; Johansen, Per; Pedersen, Henrik Clemmensen;

    2015-01-01

    Switching valves experience opposing fluid forces due to movement of the moving member itself, as the surrounding fluid volume must move to accommodate the movement. This movement-induced fluid force may be divided into three main components; the added mass term, the viscous term and the socalled...... history term. For general valve geometries there are no simple solution to either of these terms. During development and design of such switching valves, it is therefore, common practice to use simple models to describe the opposing fluid forces, neglecting all but the viscous term which is determined...... based on shearing areas and venting channels. For fast acting valves the opposing fluid force may retard the valve performance significantly, if appropriate measures are not taken during the valve design. Unsteady Computational Fluid Dynamics (CFD) simulations are available to simulate the total fluid...

  2. High-Resolution Force Balance Analyses of Tidewater Glacier Dynamics

    Science.gov (United States)

    Enderlin, E. M.; Hamilton, G. S.; O'Neel, S.

    2015-12-01

    Changes in glacier velocity, thickness, and terminus position have been used to infer the dynamic response of tidewater glaciers to environmental perturbations, yet few analyses have attempted to quantify the associated variations in the glacier force balance. Where repeat high-resolution ice thickness and velocity estimates are available, force balance time series can be constructed to investigate the redistribution of driving and resistive forces associated with changes in terminus position. Comparative force balance analyses may, therefore, help us understand the variable dynamic response observed for glaciers in close proximity to each other. Here we construct force balance time series for Helheim Glacier, SE Greenland, and Columbia Glacier, SE Alaska, to investigate differences in dynamic sensitivity to terminus position change. The analysis relies on in situ and remotely sensed observations of ice thickness, velocity, and terminus position. Ice thickness time series are obtained from stereo satellite image-derived surface elevation and continuity-derived bed elevations that are constrained by airborne radar observations. Surface velocity time series are obtained from interferometric synthetic aperture radar (InSAR) observations. Approximately daily terminus positions are from a combination of satellite images and terrestrial time-lapse photographs. Helheim and Columbia glaciers are two of the best-studied Arctic tidewater glaciers with comprehensive high-resolution observational time series, yet we find that bed elevation uncertainties and poorly-constrained stress-coupling length estimates still hinder the analysis of spatial and temporal force balance variations. Here we use a new observationally-based method to estimate the stress-coupling length which successfully reduces noise in the derived force balance but preserves spatial variations that can be over-smoothed when estimating the stress-coupling length as a scalar function of the ice thickness

  3. Sequential reconstruction of driving-forces from nonlinear nonstationary dynamics

    Science.gov (United States)

    Güntürkün, Ulaş

    2010-07-01

    This paper describes a functional analysis-based method for the estimation of driving-forces from nonlinear dynamic systems. The driving-forces account for the perturbation inputs induced by the external environment or the secular variations in the internal variables of the system. The proposed algorithm is applicable to the problems for which there is too little or no prior knowledge to build a rigorous mathematical model of the unknown dynamics. We derive the estimator conditioned on the differentiability of the unknown system’s mapping, and smoothness of the driving-force. The proposed algorithm is an adaptive sequential realization of the blind prediction error method, where the basic idea is to predict the observables, and retrieve the driving-force from the prediction error. Our realization of this idea is embodied by predicting the observables one-step into the future using a bank of echo state networks (ESN) in an online fashion, and then extracting the raw estimates from the prediction error and smoothing these estimates in two adaptive filtering stages. The adaptive nature of the algorithm enables to retrieve both slowly and rapidly varying driving-forces accurately, which are illustrated by simulations. Logistic and Moran-Ricker maps are studied in controlled experiments, exemplifying chaotic state and stochastic measurement models. The algorithm is also applied to the estimation of a driving-force from another nonlinear dynamic system that is stochastic in both state and measurement equations. The results are judged by the posterior Cramer-Rao lower bounds. The method is finally put into test on a real-world application; extracting sun’s magnetic flux from the sunspot time series.

  4. Dynamic stability of repulsive-force maglev suspension systems

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Y.; Rote, D.M.; Mulcahy, T.M.; Wang, Z. [and others

    1996-11-01

    This report summarizes the research performed on maglev vehicle dynamic stability at Argonne National Laboratory during the past few years. It also documents both measured and calculated magnetic-force data. Because dynamic instability is not acceptable for any commercial maglev system, it is important to consider this phenomenon in the development of all maglev systems. This report presents dynamic stability experiments on maglev systems and compares the results with predictions calculated by a nonlinear-dynamics computer code. Instabilities of an electrodynamic-suspension system type vehicle model were obtained by experimental observation and computer simulation of a five-degree-of-freedom maglev vehicle moving on a guideway that consists of a pair of L-shaped aluminum conductors attached to a rotating wheel. The experimental and theoretical analyses developed in this study identify basic stability characteristics and future research needs of maglev systems.

  5. [Tension force in dynamic splints made of neoprene].

    Science.gov (United States)

    Punsola-Izard, V; Rouzaud, J C; Thomas, D; Lluch; Garcia-Elias

    2001-06-01

    Dynamic splints are the most difficult ortheses to make. Unrestricted finger joint mobility is usually prevented by the size of their components. Ortheses made out of neoprene material have the advantage of being pliable and at the same time can be constructed as dynamic splints. Neoprene material elasticity allows conforming it into a tube that can be fitted over a finger, spreading uniform pressure. A traction slip can be cemented to the neoprene finger tube. With neoprene splints, lever arms are more efficient. Their tubular design applies and spreads traction and countertraction forces in all directions. Neoprene material's elasticity contributes in reducing edema formation as well as distributes forces applied to the finger over a large area. The risk of excessive pressure is the only drawback of an elastic tubular design, it may cause pain and tissue ischemia. A meticulous tailoring prevents this potential risk.

  6. Forced dynamic position control of PMSM with DTC utilization

    Science.gov (United States)

    Malek, Michal

    2012-11-01

    Almost one and a half century after the publication of Maxwell’s On Governors, feedback theory with PID controllers in cascade structure is still an essential part of control structures of most controlled electric drives. There are a few control strategies which are “ready” to replace it but they usually miss one of the essential fundamentals of every successful approach - simplicity hand in hand with lucidity. But there is one close relative which is simple and powerful at the same time, is not excessively abstract and without complicated mathematics. The name of this technique is Forced Dynamic Control. In this paper forced dynamic control is presented together with direct torque controlled PMSM drive as unique combination of simple algorithms for inner and outer loop of cascade structure.

  7. Monitoring RNA release from human rhinovirus by dynamic force microscopy.

    Science.gov (United States)

    Kienberger, Ferry; Zhu, Rong; Moser, Rosita; Blaas, Dieter; Hinterdorfer, Peter

    2004-04-01

    Human rhinoviruses were imaged under physiological conditions by dynamic force microscopy. Topographical images revealed various polygonal areas on the surfaces of the 30-nm viral particles. RNA release was initiated by exposure to a low-pH buffer. The lengths of the RNAs that were released but still connected to the virus capsid varied between 40 and 330 nm, whereas RNA molecules that were completely released from the virus were observed with lengths up to 1 micro m. Fork-like structure elements with 30-nm extensions were sometimes resolved at one end of the RNA molecules. They possibly correspond to the characteristic multi-stem-loop conformation, the internal ribosomal entry site, located at the 5' region of the genome. This study demonstrates that dynamic force microscopy can be used to study viral RNA release in situ under physiological conditions.

  8. Evaluation of the sensing block method for dynamic force measurement

    Science.gov (United States)

    Zhang, Qinghui; Chen, Hao; Li, Wenzhao; Song, Li

    2017-01-01

    Sensing block method was proposed for the dynamic force measurement by Tanimura et al. in 1994. Comparing with the Split Hopkinson pressure bar (SHPB) technique, it can provide a much longer measuring time for the dynamic properties test of materials. However, the signals recorded by sensing block are always accompanied with additional oscillations. Tanimura et al. discussed the effect of force rising edge on the test results, whereas more research is still needed. In this paper, some more dominant factors have been extracted through dimensional analysis. The finite element simulation has been performed to assess these factors. Base on the analysis and simulation, some valuable results are obtained and some criterions proposed in this paper can be applied in design or selection of the sensing block.

  9. Dynamic force microscopy for imaging of viruses under physiological conditions

    Directory of Open Access Journals (Sweden)

    Kienberger Ferry

    2004-01-01

    Full Text Available Dynamic force microscopy (DFM allows imaging of the structure and the assessment of the function of biological specimens in their physiological environment. In DFM, the cantilever is oscillated at a given frequency and touches the sample only at the end of its downward movement. Accordingly, the problem of lateral forces displacing or even destroying bio-molecules is virtually inexistent as the contact time and friction forces are reduced. Here, we describe the use of DFM in studies of human rhinovirus serotype 2 (HRV2 weakly adhering to mica surfaces. The capsid of HRV2 was reproducibly imaged without any displacement of the virus. Release of the genomic RNA from the virions was initiated by exposure to low pH buffer and snapshots of the extrusion process were obtained. In the following, the technical details of previous DFM investigations of HRV2 are summarized.

  10. Subharmonic Oscillations and Chaos in Dynamic Atomic Force Microscopy

    Science.gov (United States)

    Cantrell, John H.; Cantrell, Sean A.

    2015-01-01

    The increasing use of dynamic atomic force microscopy (d-AFM) for nanoscale materials characterization calls for a deeper understanding of the cantilever dynamics influencing scan stability, predictability, and image quality. Model development is critical to such understanding. Renormalization of the equations governing d- AFM provides a simple interpretation of cantilever dynamics as a single spring and mass system with frequency dependent cantilever stiffness and damping parameters. The renormalized model is sufficiently robust to predict the experimentally observed splitting of the free-space cantilever resonance into multiple resonances upon cantilever-sample contact. Central to the model is the representation of the cantilever sample interaction force as a polynomial expansion with coefficients F(sub ij) (i,j = 0, 1, 2) that account for the effective interaction stiffness parameter, the cantilever-to-sample energy transfer, and the amplitude of cantilever oscillation. Application of the Melnikov method to the model equation is shown to predict a homoclinic bifurcation of the Smale horseshoe type leading to a cascade of period doublings with increasing drive displacement amplitude culminating in chaos and loss of image quality. The threshold value of the drive displacement amplitude necessary to initiate subharmonic generation depends on the acoustic drive frequency, the effective damping coefficient, and the nonlinearity of the cantilever-sample interaction force. For parameter values leading to displacement amplitudes below threshold for homoclinic bifurcation other bifurcation scenarios can occur, some of which lead to chaos.

  11. Satellite Dynamic Damping via Active Force Control Augmentation

    Science.gov (United States)

    Varatharajoo, Renuganth

    2012-07-01

    An approach that incorporates the Active Force Control (AFC) technique into a conventional Proportional-Derivative (PD) controller is proposed for a satellite active dynamic damping towards a full attitude control. The AFC method has been established to facilitate a robust motion control of dynamical systems in the presence of disturbances, parametric uncertainties and changes that are commonly prevalent in the real-world environment. The usefulness of the method can be extended by introducing intelligent mechanisms to approximate the mass or inertia matrix of the dynamic system to trigger the compensation effect of the controller. AFC is a technique that relies on the appropriate estimation of the inertial or mass parameters of the dynamic system and the measurements of the acceleration and force signals induced by the system if practical implementation is ever considered. In AFC, it is shown that the system subjected to a number of disturbances remains stable and robust via the compensating action of the control strategy. We demonstrate that it is possible to design a spacecraft attitude feedback controller that will ensure the system dynamics set point remains unchanged even in the presence of the disturbances provided that the actual disturbances can be modeled effectively. In order to further facilitate this analysis, a combined energy and attitude control system (CEACS) is proposed as a model satellite attitude control actuator. All the governing equations are established and the proposed satellite attitude control architecture is made amenable to numerical treatments. The results show that the PD-AFC attitude damping performances are superiorly better than that of the solely PD type. It is also shown that the tunings of the AFC system gains are crucial to ensure a better attitude damping performance and this process is mandatory for AFC systems. Finally, the results demonstrate an important satellite dynamic damping enhancement capability using the AFC

  12. Minimizing tip-sample forces and enhancing sensitivity in atomic force microscopy with dynamically compliant cantilevers

    Science.gov (United States)

    Keyvani, Aliasghar; Sadeghian, Hamed; Tamer, Mehmet Selman; Goosen, Johannes Frans Loodewijk; van Keulen, Fred

    2017-06-01

    Due to the harmonic motion of the cantilever in Tapping Mode Atomic Force Microscopy, it is seemingly impossible to estimate the tip-sample interactions from the motion of the cantilever. Not directly observing the interaction force, it is possible to damage the surface or the tip by applying an excessive mechanical load. The tip-sample interactions scale with the effective stiffness of the probe. Thus, the reduction of the mechanical load is usually limited by the manufacturability of low stiffness probes. However, the one-to-one relationship between spring constant and applied force only holds when higher modes of the cantilever are not excited. In this paper, it is shown that, by passively tuning higher modes of the cantilever, it is possible to reduce the peak repulsive force. These tuned probes can be dynamically more compliant than conventional probes with the same static spring constant. Both theoretical and experimental results show that a proper tuning of dynamic modes of cantilevers reduces the contact load and increases the sensitivity considerably. Moreover, due to the contribution of higher modes, the tuned cantilevers provide more information on the tip-sample interaction. This extra information from the higher harmonics can be used for mapping and possibly identification of material properties of samples.

  13. Dynamic force spectroscopy of parallel individual mucin1-antibody bonds

    Energy Technology Data Exchange (ETDEWEB)

    Sulchek, T A; Friddle, R W; Langry, K; Lau, E; Albrecht, H; Ratto, T; DeNardo, S; Colvin, M E; Noy, A

    2005-05-02

    We used atomic force microscopy (AFM) to measure the binding forces between Mucin1 (MUC1) peptide and a single chain antibody fragment (scFv) selected from a scFv library screened against MUC1. This binding interaction is central to the design of the molecules for targeted delivery of radioimmunotherapeutic agents for prostate and breast cancer treatment. Our experiments separated the specific binding interaction from non-specific interactions by tethering the antibody and MUC1 molecules to the AFM tip and sample surface with flexible polymer spacers. Rupture force magnitude and elastic characteristics of the spacers allowed identification of the bond rupture events corresponding to different number of interacting proteins. We used dynamic force spectroscopy to estimate the intermolecular potential widths and equivalent thermodynamic off rates for mono-, bi-, and tri-valent interactions. Measured interaction potential parameters agree with the results of molecular docking simulation. Our results demonstrate that an increase of the interaction valency leads to a precipitous decline in the dissociation rate. Binding forces measured for mono and multivalent interactions match the predictions of a Markovian model for the strength of multiple uncorrelated bonds in parallel configuration. Our approach is promising for comparison of the specific effects of molecular modifications as well as for determination of the best configuration of antibody-based multivalent targeting agents.

  14. Frequency adaptation for enhanced radiation force amplitude in dynamic elastography.

    Science.gov (United States)

    Ouared, Abderrahmane; Montagnon, Emmanuel; Kazemirad, Siavash; Gaboury, Louis; Robidoux, André; Cloutier, Guy

    2015-08-01

    In remote dynamic elastography, the amplitude of the generated displacement field is directly related to the amplitude of the radiation force. Therefore, displacement improvement for better tissue characterization requires the optimization of the radiation force amplitude by increasing the push duration and/or the excitation amplitude applied on the transducer. The main problem of these approaches is that the Food and Drug Administration (FDA) thresholds for medical applications and transducer limitations may be easily exceeded. In the present study, the effect of the frequency used for the generation of the radiation force on the amplitude of the displacement field was investigated. We found that amplitudes of displacements generated by adapted radiation force sequences were greater than those generated by standard nonadapted ones (i.e., single push acoustic radiation force impulse and supersonic shear imaging). Gains in magnitude were between 20 to 158% for in vitro measurements on agar-gelatin phantoms, and 170 to 336% for ex vivo measurements on a human breast sample, depending on focus depths and attenuations of tested samples. The signal-to-noise ratio was also improved more than 4-fold with adapted sequences. We conclude that frequency adaptation is a complementary technique that is efficient for the optimization of displacement amplitudes. This technique can be used safely to optimize the deposited local acoustic energy without increasing the risk of damaging tissues and transducer elements.

  15. Forced versus coupled dynamics in Earth system modelling and prediction

    Directory of Open Access Journals (Sweden)

    B. Knopf

    2005-01-01

    Full Text Available We compare coupled nonlinear climate models and their simplified forced counterparts with respect to predictability and phase space topology. Various types of uncertainty plague climate change simulation, which is, in turn, a crucial element of Earth System modelling. Since the currently preferred strategy for simulating the climate system, or the Earth System at large, is the coupling of sub-system modules (representing, e.g. atmosphere, oceans, global vegetation, this paper explicitly addresses the errors and indeterminacies generated by the coupling procedure. The focus is on a comparison of forced dynamics as opposed to fully, i.e. intrinsically, coupled dynamics. The former represents a particular type of simulation, where the time behaviour of one complex systems component is prescribed by data or some other external information source. Such a simplifying technique is often employed in Earth System models in order to save computing resources, in particular when massive model inter-comparisons need to be carried out. Our contribution to the debate is based on the investigation of two representative model examples, namely (i a low-dimensional coupled atmosphere-ocean simulator, and (ii a replica-like simulator embracing corresponding components.Whereas in general the forced version (ii is able to mimic its fully coupled counterpart (i, we show in this paper that for a considerable fraction of parameter- and state-space, the two approaches qualitatively differ. Here we take up a phenomenon concerning the predictability of coupled versus forced models that was reported earlier in this journal: the observation that the time series of the forced version display artificial predictive skill. We present an explanation in terms of nonlinear dynamical theory. In particular we observe an intermittent version of artificial predictive skill, which we call on-off synchronization, and trace it back to the appearance of unstable periodic orbits. We also

  16. Guided crowd dynamics via modified social force model

    Science.gov (United States)

    Yang, Xiaoxia; Dong, Hairong; Wang, Qianling; Chen, Yao; Hu, Xiaoming

    2014-10-01

    Pedestrian dynamics is of great theoretical significance for strategy design of emergency evacuation. Modification of pedestrian dynamics based on the social force model is presented to better reflect pedestrians' behavioral characteristics in emergency. Specifically, the modified model can be used for guided crowd dynamics in large-scale public places such as subway stations and stadiums. This guided crowd model is validated by explicitly comparing its density-speed and density-flow diagrams with fundamental diagrams. Some social phenomena such as gathering, balance and conflicts are clearly observed in simulation, which further illustrate the effectiveness of the proposed modeling method. Also, time delay for pedestrians with time-dependent desired velocities is observed and explained using the established model in this paper. Furthermore, this guided crowd model is applied to the simulation system of Beijing South Railway Station for predictive evacuation experiments.

  17. Dynamic force matching: Construction of dynamic coarse-grained models with realistic short time dynamics and accurate long time dynamics

    Science.gov (United States)

    Davtyan, Aram; Voth, Gregory A.; Andersen, Hans C.

    2016-12-01

    We recently developed a dynamic force matching technique for converting a coarse-grained (CG) model of a molecular system, with a CG potential energy function, into a dynamic CG model with realistic dynamics [A. Davtyan et al., J. Chem. Phys. 142, 154104 (2015)]. This is done by supplementing the model with additional degrees of freedom, called "fictitious particles." In that paper, we tested the method on CG models in which each molecule is coarse-grained into one CG point particle, with very satisfactory results. When the method was applied to a CG model of methanol that has two CG point particles per molecule, the results were encouraging but clearly required improvement. In this paper, we introduce a new type (called type-3) of fictitious particle that exerts forces on the center of mass of two CG sites. A CG model constructed using type-3 fictitious particles (as well as type-2 particles previously used) gives a much more satisfactory dynamic model for liquid methanol. In particular, we were able to construct a CG model that has the same self-diffusion coefficient and the same rotational relaxation time as an all-atom model of liquid methanol. Type-3 particles and generalizations of it are likely to be useful in converting more complicated CG models into dynamic CG models.

  18. Forced fluid dynamics from blackfolds in general supergravity backgrounds

    Science.gov (United States)

    Armas, Jay; Gath, Jakob; Niarchos, Vasilis; Obers, Niels A.; Pedersen, Andreas Vigand

    2016-10-01

    We present a general treatment of the leading order dynamics of the collective modes of charged dilatonic p-brane solutions of (super) gravity theories in arbitrary backgrounds. To this end we employ the general strategy of the blackfold approach which is based on a long-wavelength derivative expansion around an exact or approximate solution of the (super)gravity equations of motion. The resulting collective mode equations are formulated as forced hydrodynamic equations on dynamically embedded hypersurfaces. We derive them in full generality (including all possible asymptotic fluxes and dilaton profiles) in a far-zone analysis of the (super)gravity equations and in representative examples in a near-zone analysis. An independent treatment based on the study of external couplings in hydrostatic partition functions is also presented. Special emphasis is given to the forced collective mode equations that arise in type IIA/B and eleven-dimensional supergravities, where besides the standard Lorentz force couplings our analysis reveals additional couplings to the background, including terms that arise from Chern-Simons interactions. We also present a general overview of the blackfold approach and some of the key conceptual issues that arise when applied to arbitrary backgrounds.

  19. Forced fluid dynamics from blackfolds in general supergravity backgrounds

    Energy Technology Data Exchange (ETDEWEB)

    Armas, Jay [Physique Théorique et Mathématique,Université Libre de Bruxelles and International Solvay Institutes,ULB-Campus Plaine CP231, B-1050 Brussels (Belgium); Gath, Jakob [Centre de Physique Théorique, École Polytechnique,CNRS UMR 7644, Université Paris-Saclay,F-91128 Palaiseau (France); Niarchos, Vasilis [Crete Center for Theoretical Physics, Institute of Theoretical and Computational Physics,Crete Center for Quantum Complexity and Nanotechnology,Department of Physics, University of Crete,Heraklion, 71303 (Greece); Obers, Niels A.; Pedersen, Andreas Vigand [The Niels Bohr Institute, Copenhagen University,Blegdamsvej 17, DK-2100 Copenhagen Ø (Denmark)

    2016-10-27

    We present a general treatment of the leading order dynamics of the collective modes of charged dilatonic p-brane solutions of (super)gravity theories in arbitrary backgrounds. To this end we employ the general strategy of the blackfold approach which is based on a long-wavelength derivative expansion around an exact or approximate solution of the (super)gravity equations of motion. The resulting collective mode equations are formulated as forced hydrodynamic equations on dynamically embedded hypersurfaces. We derive them in full generality (including all possible asymptotic fluxes and dilaton profiles) in a far-zone analysis of the (super)gravity equations and in representative examples in a near-zone analysis. An independent treatment based on the study of external couplings in hydrostatic partition functions is also presented. Special emphasis is given to the forced collective mode equations that arise in type IIA/B and eleven-dimensional supergravities, where besides the standard Lorentz force couplings our analysis reveals additional couplings to the background, including terms that arise from Chern-Simons interactions. We also present a general overview of the blackfold approach and some of the key conceptual issues that arise when applied to arbitrary backgrounds.

  20. A modified social force model for crowd dynamics

    Science.gov (United States)

    Hassan, Ummi Nurmasyitah; Zainuddin, Zarita; Abu-Sulyman, Ibtesam M.

    2017-08-01

    The Social Force Model (SFM) is one of the most successful models in microscopic pedestrian studies that is used to study the movement of pedestrians. Many modifications have been done to improvise the SFM by earlier researchers such as the incorporation of a constant respect factor into the self-stopping mechanism. Before the new mechanism is introduced, the researchers found out that a pedestrian will immediately come to a halt if other pedestrians are near to him, which seems to be an unrealistic behavior. Therefore, researchers introduce a self-slowing mechanism to gradually stop a pedestrian when he is approaching other pedestrians. Subsequently, the dynamic respect factor is introduced into the self-slowing mechanism based on the density of the pedestrians to make the model even more realistic. In real life situations, the respect factor of the pedestrians should be dynamic values instead of a constant value. However, when we reproduce the simulation of the dynamic respect factor, we found that the movement of the pedestrians are unrealistic because the pedestrians are lacking perception of the pedestrians in front of him. In this paper, we adopted both dynamic respect factor and dynamic angular parameter, called modified dynamic respect factor, which is dependent on the density of the pedestrians. Simulations are performed in a normal unidirectional walkway to compare the simulated pedestrians' movements produced by both models. The results obtained showed that the modified dynamic respect factor produces more realistic movement of the pedestrians which conform to the real situation. Moreover, we also found that the simulations endow the pedestrian with a self-slowing mechanism and a perception of other pedestrians in front of him.

  1. A stochastic boundary forcing for dissipative particle dynamics

    Science.gov (United States)

    Altenhoff, Adrian M.; Walther, Jens H.; Koumoutsakos, Petros

    2007-07-01

    The method of dissipative particle dynamics (DPD) is an effective, coarse grained model of the hydrodynamics of complex fluids. DPD simulations of wall-bounded flows are however often associated with spurious fluctuations of the fluid properties near the wall. We present a novel stochastic boundary forcing for DPD simulations of wall-bounded flows, based on the identification of fluctuations in simulations of the corresponding homogeneous system at equilibrium. The present method is shown to enforce accurately the no-slip boundary condition, while minimizing spurious fluctuations of material properties, in a number of benchmark problems.

  2. The Dynamics and Driving Force of Farmland Ecosystem Productivity

    Institute of Scientific and Technical Information of China (English)

    ZHONG Liang-ping; SHAO Ming-an; LI Yu-shan

    2005-01-01

    Based on the experimental data of crop yield, soil water and fertility of a dryland farming ecosystem in northwest China, a systematic analysis is carried out to study the dynamics of dryland farming ecosystem productivity and its limiting factors. This paper also discusses which of the two limiting factors, i.e., soil water or fertility, is the primary factor and their dynamics. The result shows that fertility is the primary limiting factor when the productivity is rather low. As chemical fertilizer input increases and the productivity promotes, water gradually becomes the primary limiting factor. Chemical fertilizers and plastic film mulching are the two major driving forces that determine the crop productivity and its stability in these areas.

  3. Design and testing of magnetorheological valve with fast force response time and great dynamic force range

    Science.gov (United States)

    Kubík, M.; Macháček, O.; Strecker, Z.; Roupec, J.; Mazůrek, I.

    2017-04-01

    The paper deals with design, simulation and experimental testing of a magnetorheological (MR) valve with short response time. The short response time is achieved by a suitable design of an active zone in combination with use of a ferrite material for magnetic circuit. The magneto-static model and the simplified hydraulic model of the MR valve are examined and experimentally verified. The development the MR valve achieves an average response time 4.1 ms and the maximum dynamic force range of eight.

  4. Research on the Earth system multi-body force system dynamical model

    Institute of Scientific and Technical Information of China (English)

    CHEN; Xiaofei; BI; Siwen; WU; Fei; DONG; Qianlin

    2006-01-01

    This paper presents an overview of the binding force and freedom force of Earth system, and describes force moment to point and line and force system in the Earth system. It introduces the force theory of the Earth system multi-body force system from special or equivalent force system of Earth system mechanics, general force and no-power force of Earth system. Finally it describes the force and moment of nodes of Earth system and provides basic model for the research of the Earth system multi-body dynamics.

  5. Vertically polarizing undulator with dynamic compensation of magnetic forces

    Science.gov (United States)

    Strelnikov, N.; Vasserman, I.; Xu, J.; Jensen, D.; Schmidt, O.; Trakhtenberg, E.; Suthar, K.; Moog, E. R.; Pile, G.; Gluskin, E.

    2017-01-01

    As part of the R&D program of the LCLS-II project, a novel 3.4-meter-long undulator prototype with horizontal magnetic field and dynamic force compensation has recently been developed at the Advanced Photon Source (APS). Previous steps in this development were the shorter 0.8-meter-long and 2.8-meter-long prototypes. Extensive mechanical and magnetic testing were carried out for each prototype, and each prototype was magnetically tuned using magnetic shims. The resulting performance of the 3.4-meter-long undulator prototype meets all requirements for the LCLS-II insertion device, including limits on the field integrals, phase errors, higher-order magnetic moments, and electron-beam trajectory for all operational gaps, as well as the reproducibility and accuracy of the gap settings.

  6. Molecular dynamics simulation of amplitude modulation atomic force microscopy.

    Science.gov (United States)

    Hu, Xiaoli; Egberts, Philip; Dong, Yalin; Martini, Ashlie

    2015-06-12

    Molecular dynamics (MD) simulations were used to model amplitude modulation atomic force microscopy (AM-AFM). In this novel simulation, the model AFM tip responds to both tip-substrate interactions and to a sinusoidal excitation signal. The amplitude and phase shift of the tip oscillation observed in the simulation and their variation with tip-sample distance were found to be consistent with previously reported trends from experiments and theory. These simulation results were also fit to an expression enabling estimation of the energy dissipation, which was found to be smaller than that in a corresponding experiment. The difference was analyzed in terms of the effects of tip size and substrate thickness. Development of this model is the first step toward using MD to gain insight into the atomic-scale phenomena that occur during an AM-AFM measurement.

  7. Vertically Polarizing Undulator with Dynamic Compensation of Magnetic Forces

    Energy Technology Data Exchange (ETDEWEB)

    Strelnikov, N.; Vasserman, I.; Xu, J.; Jensen, D.; Schmidt, O.; Trakhtenberg, E.; Suthar, K.; Moog, E. R.; Pile, G.; Gluskin, E.

    2017-01-20

    As part of the R&D program of the LCLS-II project, a novel 3.4-meter-long undulator prototype with horizontal magnetic field and dynamic force compensation has recently been developed at the Advanced Photon Source (APS). Previous steps in this development were the shorter 0.8-meter-long and 2.8-meter-long prototypes. Extensive mechanical and magnetic testing was carried out for each prototype, and each prototype was magnetically tuned using magnetic shims. The resulting performance of the 3.4-meter-long undulator prototype meets all requirements for the LCLS-II insertion device, including limits on the field integrals, phase errors, higher-order magnetic moments, and electron-beam trajectory for all operational gaps, as well as the reproducibility and accuracy of the gap settings.

  8. Dynamic Force Identification for Beamlike Structures Using an Improved Dynamic Stiffness Method

    Directory of Open Access Journals (Sweden)

    S.L. Chen

    1996-01-01

    Full Text Available In this study a procedure of dynamic force identification for beamlike structures is developed based on an improved dynamic stiffness method. In this procedure, the entire structure is first divided into substructures according to the excitation locations and the measured response sites. Each substructure is then represented by an equivalent element. The resulting model only retains the degree of freedom (DOF associated with the excitations and the measured responses and the DOF corresponding to the boundaries of the structures. Because the technique partly bypasses the processes of modal parameter extraction, global matrix inversion, and model reduction, it can eliminate many of the approximations and errors that may be introduced during these processes. The principle of the method is described in detail and its efficiency is demonstrated via numerical simulations of three different structures. The sensitivity of the estimated force to random noise is discussed and the limitation of the technique is pointed out.

  9. Dynamic force matching: A method for constructing dynamical coarse-grained models with realistic time dependence

    Energy Technology Data Exchange (ETDEWEB)

    Davtyan, Aram; Dama, James F.; Voth, Gregory A. [Department of Chemistry, The James Franck Institute, Institute for Biophysical Dynamics, and Computation Institute, The University of Chicago, Chicago, Illinois 60637 (United States); Andersen, Hans C., E-mail: hca@stanford.edu [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)

    2015-04-21

    Coarse-grained (CG) models of molecular systems, with fewer mechanical degrees of freedom than an all-atom model, are used extensively in chemical physics. It is generally accepted that a coarse-grained model that accurately describes equilibrium structural properties (as a result of having a well constructed CG potential energy function) does not necessarily exhibit appropriate dynamical behavior when simulated using conservative Hamiltonian dynamics for the CG degrees of freedom on the CG potential energy surface. Attempts to develop accurate CG dynamic models usually focus on replacing Hamiltonian motion by stochastic but Markovian dynamics on that surface, such as Langevin or Brownian dynamics. However, depending on the nature of the system and the extent of the coarse-graining, a Markovian dynamics for the CG degrees of freedom may not be appropriate. In this paper, we consider the problem of constructing dynamic CG models within the context of the Multi-Scale Coarse-graining (MS-CG) method of Voth and coworkers. We propose a method of converting a MS-CG model into a dynamic CG model by adding degrees of freedom to it in the form of a small number of fictitious particles that interact with the CG degrees of freedom in simple ways and that are subject to Langevin forces. The dynamic models are members of a class of nonlinear systems interacting with special heat baths that were studied by Zwanzig [J. Stat. Phys. 9, 215 (1973)]. The properties of the fictitious particles can be inferred from analysis of the dynamics of all-atom simulations of the system of interest. This is analogous to the fact that the MS-CG method generates the CG potential from analysis of equilibrium structures observed in all-atom simulation data. The dynamic models generate a non-Markovian dynamics for the CG degrees of freedom, but they can be easily simulated using standard molecular dynamics programs. We present tests of this method on a series of simple examples that demonstrate that

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

    Science.gov (United States)

    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. Copyright © 2016 Elsevier Inc. All rights reserved.

  11. Implementation of force distribution analysis for molecular dynamics simulations

    Directory of Open Access Journals (Sweden)

    Seifert Christian

    2011-04-01

    Full Text Available Abstract Background The way mechanical stress is distributed inside and propagated by proteins and other biopolymers largely defines their function. Yet, determining the network of interactions propagating internal strain remains a challenge for both, experiment and theory. Based on molecular dynamics simulations, we developed force distribution analysis (FDA, a method that allows visualizing strain propagation in macromolecules. Results To be immediately applicable to a wide range of systems, FDA was implemented as an extension to Gromacs, a commonly used package for molecular simulations. The FDA code comes with an easy-to-use command line interface and can directly be applied to every system built using Gromacs. We provide an additional R-package providing functions for advanced statistical analysis and presentation of the FDA data. Conclusions Using FDA, we were able to explain the origin of mechanical robustness in immunoglobulin domains and silk fibers. By elucidating propagation of internal strain upon ligand binding, we previously also successfully revealed the functionality of a stiff allosteric protein. FDA thus has the potential to be a valuable tool in the investigation and rational design of mechanical properties in proteins and nano-materials.

  12. Modeling of Dynamic Fluid Forces in Fast Switching Valves

    DEFF Research Database (Denmark)

    Roemer, Daniel Beck; Johansen, Per; Pedersen, Henrik Clemmensen;

    2015-01-01

    force, but these models are computationally expensive and are not suitable for evaluating large numbers of different operation conditions or even design optimization. In the present paper, an effort is done to describe these fluid forces and their origin. An example of the total opposing fluid force...

  13. INVESTIGATION OF THE DYNAMIC BUCKLING OF DOUBLEWALLED CARBON NANOTUBE SUBJECTED TO AXIAL PERIODIC DISTURBING FORCES

    Institute of Scientific and Technical Information of China (English)

    SHA Feng-huan; ZHAO Long-mao; YANG Gui-tong

    2005-01-01

    The dynamic response of a double-walled carbon nanotube embedded in elastic medium subjected to periodic disturbing forces is investigated. Investigation of the dynamic buckling of a double-walled carbon nanotube develops continuum model. The effect of the van der Waals forces between two tubes and the surrounding elastic medium for axial dynamic buckling are considered. The buckling model subjected to periodic disturbing forces and the critical axial strain and the critical frequencies are given. It is found that the critical axial strain of the embedded multi-walled carbon nanotube due to the intertube van der Waals forces is lower than that of an embedded single-walled carbon nanotube. The van der Waals forces and the surrounding elastic medium affect region of dynamic instability. The van der Waals forces increase the critical frequencies of a double-walled carbon nanotube. The effect of the surrounding elastic medium for the critical frequencies is small.

  14. Dynamic force microscopy simulator (dForce: A tool for planning and understanding tapping and bimodal AFM experiments

    Directory of Open Access Journals (Sweden)

    Horacio V. Guzman

    2015-02-01

    Full Text Available We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever–tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip–surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of non-experts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years.

  15. Dynamic force microscopy simulator (dForce): A tool for planning and understanding tapping and bimodal AFM experiments.

    Science.gov (United States)

    Guzman, Horacio V; Garcia, Pablo D; Garcia, Ricardo

    2015-01-01

    We present a simulation environment, dForce, which can be used for a better understanding of dynamic force microscopy experiments. The simulator presents the cantilever-tip dynamics for two dynamic AFM methods, tapping mode AFM and bimodal AFM. It can be applied for a wide variety of experimental situations in air or liquid. The code provides all the variables and parameters relevant in those modes, for example, the instantaneous deflection and tip-surface force, velocity, virial, dissipated energy, sample deformation and peak force as a function of time or distance. The simulator includes a variety of interactions and contact mechanics models to describe AFM experiments including: van der Waals, Hertz, DMT, JKR, bottom effect cone correction, linear viscoelastic forces or the standard linear solid viscoelastic model. We have compared two numerical integration methods to select the one that offers optimal accuracy and speed. The graphical user interface has been designed to facilitate the navigation of non-experts in simulations. Finally, the accuracy of dForce has been tested against numerical simulations performed during the last 18 years.

  16. Modeling Robot Dynamic Performance for Endpoint Force Control

    Science.gov (United States)

    1988-08-01

    Task Dynamics 55 2.5.1 The Dynamic Workpiece Model 55 2.5.2 Adding Robot Dynamics 56 2.5.3 Adding Actuator Dynamics 56 Tabie I o iiau 6 2.6 Grip...motion control system. Robot dynamics couple with the task dynamics in a very complex way. When the robot makes contact with the environment, the impact...robot flexibility or actuator dynamics. 2.5.2 Adding Robot Dynamics Figure 2.29 shows the robot now represented by two lumped masses, as in the robot

  17. Accelerating Steered Molecular Dynamics: Toward Smaller Velocities in Forced Unfolding Simulations.

    Science.gov (United States)

    Mücksch, Christian; Urbassek, Herbert M

    2016-03-08

    The simulation of forced unfolding experiments, in which proteins are pulled apart, is conventionally done using steered molecular dynamics. We present here a hybrid scheme in which accelerated molecular dynamics is used together with steered molecular dynamics. We show that the new scheme changes the force-distance curves mainly in the region around the force maximum and thus demonstrate that the improved equilibration of the protein-solvent system brought about by using accelerated molecular dynamics makes the simulation more comparable to experimental data.

  18. Forcing of stratospheric chemistry and dynamics during the Dalton Minimum

    Directory of Open Access Journals (Sweden)

    J. G. Anet

    2013-06-01

    Full Text Available The response of atmospheric chemistry and climate to volcanic eruptions and a decrease in solar activity during the Dalton Minimum is investigated with the fully coupled atmosphere-ocean-chemistry general circulation model SOCOL-MPIOM covering the time period 1780 to 1840 AD. We carried out several sensitivity ensemble experiments to separate the effects of (i reduced solar ultra-violet (UV irradiance, (ii reduced solar visible and near infrared irradiance, (iii enhanced galactic cosmic ray intensity as well as less intensive solar energetic proton events and auroral electron precipitation, and (iv volcanic aerosols. The introduced changes of UV irradiance and volcanic aerosols significantly influence stratospheric climate in the early 19th century, whereas changes in the visible part of the spectrum and energetic particles have smaller effects. A reduction of UV irradiance by 15% causes global ozone decrease below the stratopause reaching 8% in the midlatitudes at 5 hPa and a significant stratospheric cooling of up to 2 °C in the midstratosphere and to 6 °C in the lower mesosphere. Changes in energetic particle precipitation lead only to minor changes in the yearly averaged temperature fields in the stratosphere. Volcanic aerosols heat the tropical lower stratosphere allowing more water vapor to enter the tropical stratosphere, which, via HOx reactions, decreases upper stratospheric and mesospheric ozone by roughly 4%. Conversely, heterogeneous chemistry on aerosols reduces stratospheric NOx leading to a 12% ozone increase in the tropics, whereas a decrease in ozone of up to 5% is found over Antarctica in boreal winter. The linear superposition of the different contributions is not equivalent to the response obtained in a simulation when all forcing factors are applied during the DM – this effect is especially well visible for NOx/NOy. Thus, this study highlights the non-linear behavior of the coupled chemistry-climate system. Finally, we

  19. Force feedback coupling with dynamics for physical simulation of product assembly and operation performance

    Science.gov (United States)

    Liu, Zhenyu; Tan, Jianrong; Duan, Guifang; Fu, Yun

    2015-01-01

    Most existing force feedback methods are still difficult to meet the requirements of real-time force calculation in virtual assembly and operation with complex objects. In addition, there is often an assumption that the controlled objects are completely free and the target object is only completely fixed or free, thus, the dynamics of the kinematic chain where the controlled objects are located are neglected during the physical simulation of the product manipulation with force feedback interaction. This paper proposes a physical simulation method of product assembly and operation manipulation based on statistically learned contact force prediction model and the coupling of force feedback and dynamics. In the proposed method, based on hidden Markov model (HMM) and local weighting learning (LWL), contact force prediction model is constructed, which can estimate the contact force in real time during interaction. Based on computational load balance model, the computing resources are dynamically assigned and the dynamics integral step is optimized. In addition, smoothing process is performed to the force feedback on the synchronization points. Consequently, we can solve the coupling and synchronization problems of high-frequency feedback force servo, low-frequency dynamics solver servo and scene rendering servo, and realize highly stable and accurate force feedback in the physical simulation of product assembly and operation manipulation. This research proposes a physical simulation method of product assembly and operation manipulation.

  20. Molecular Dynamics Simulation of Atomic Force Microscopy at the Water-Muscovite Interface: Hydration Layer Structure and Force Analysis.

    Science.gov (United States)

    Kobayashi, Kazuya; Liang, Yunfeng; Amano, Ken-ichi; Murata, Sumihiko; Matsuoka, Toshifumi; Takahashi, Satoru; Nishi, Naoya; Sakka, Tetsuo

    2016-04-19

    With the development of atomic force microscopy (AFM), it is now possible to detect the buried liquid-solid interfacial structure in three dimensions at the atomic scale. One of the model surfaces used for AFM is the muscovite surface because it is atomically flat after cleavage along the basal plane. Although it is considered that force profiles obtained by AFM reflect the interfacial structures (e.g., muscovite surface and water structure), the force profiles are not straightforward because of the lack of a quantitative relationship between the force and the interfacial structure. In the present study, molecular dynamics simulations were performed to investigate the relationship between the muscovite-water interfacial structure and the measured AFM force using a capped carbon nanotube (CNT) AFM tip. We provide divided force profiles, where the force contributions from each water layer at the interface are shown. They reveal that the first hydration layer is dominant in the total force from water even after destruction of the layer. Moreover, the lateral structure of the first hydration layer transcribes the muscovite surface structure. It resembles the experimentally resolved surface structure of muscovite in previous AFM studies. The local density profile of water between the tip and the surface provides further insight into the relationship between the water structure and the detected force structure. The detected force structure reflects the basic features of the atomic structure for the local hydration layers. However, details including the peak-peak distance in the force profile (force-distance curve) differ from those in the density profile (density-distance curve) because of disturbance by the tip.

  1. Cell Adhesion on Dynamic Supramolecular Surfaces Probed by Fluid Force Microscopy-Based Single-Cell Force Spectroscopy.

    Science.gov (United States)

    Sankaran, Shrikrishnan; Jaatinen, Leena; Brinkmann, Jenny; Zambelli, Tomaso; Vörös, Janos; Jonkheijm, Pascal

    2017-04-25

    Biomimetic and stimuli-responsive cell-material interfaces are actively being developed to study and control various cell-dynamics phenomena. Since cells naturally reside in the highly dynamic and complex environment of the extracellular matrix, attempts are being made to replicate these conditions in synthetic biomaterials. Supramolecular chemistry, dealing with noncovalent interactions, has recently provided possibilities to incorporate such dynamicity and responsiveness in various types of architectures. Using a cucurbit[8]uril-based host-guest system, we have successfully established a dynamic and electrochemically responsive interface for the display of the integrin-specific ligand, Arg-Gly-Asp (RGD), to promote cell adhesion. Due to the weak nature of the noncovalent forces by which the components at the interface are held together, we expected that cell adhesion would also be weaker in comparison to traditional interfaces where ligands are usually immobilized by covalent linkages. To assess the stability and limitations of our noncovalent interfaces, we performed single-cell force spectroscopy studies using fluid force microscopy. This technique enabled us to measure rupture forces of multiple cells that were allowed to adhere for several hours on individual substrates. We found that the rupture forces of cells adhered to both the noncovalent and covalent interfaces were nearly identical for up to several hours. We have analyzed and elucidated the reasons behind this result as a combination of factors including the weak rupture force between linear Arg-Gly-Asp and integrin, high surface density of the ligand, and increase in effective concentration of the supramolecular components under spread cells. These characteristics enable the construction of highly dynamic biointerfaces without compromising cell-adhesive properties.

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

    Directory of Open Access Journals (Sweden)

    Li-Chieh Kuo

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

  3. Force modulating dynamic disorder: A physical model of catch-slip bond transitions in receptor-ligand forced dissociation experiments

    Science.gov (United States)

    Liu, Fei; Ou-Yang, Zhong-Can

    2006-11-01

    Recent experiments found that some adhesive receptor-ligand complexes have counterintuitive catch-slip transition behaviors: the mean lifetimes of these complexes first increase (catch) with initial application of a small external force, and then decrease (slip) when the force is beyond some threshold. In this work we suggest that the forced dissociation of these complexes might be a typical rate process with dynamic disorder. The one-dimensional force modulating Agmon-Hopfield model is used to describe the transitions in the single-bond P-selectin glycoprotein ligand 1-P-selectin forced dissociation experiments, which were respectively performed in the constant force [Marshall , Nature (Landon) 423, 190 (2003)] and the ramping force [Evans , Proc. Natl. Acad. Sci. U.S.A 98, 11281 (2004)] modes. We find that, an external force can not only accelerate the bond dissociation, but also modulate the complex from the lower-energy barrier to the higher one; the catch-slip bond transition can arise from a particular energy barrier shape. The agreement between our calculation and the experimental data is satisfactory.

  4. Membrane tube formation by motor proteins : forces and dynamics

    NARCIS (Netherlands)

    Koster, Gerbrand

    2005-01-01

    Membrane tubes are ubiquitous within cells. They have a diameter of approximately 50 nanometers, and are formed when a sufficiently large localized force is exerted on a membrane. Important generators of this force are the motor proteins that can move along cytoskeletal filaments. We studied

  5. Synchronous monitoring of muscle dynamics and muscle force for maximum isometric tetanus

    Science.gov (United States)

    Zakir Hossain, M.; Grill, Wolfgang

    2010-03-01

    Skeletal muscle is a classic example of a biological soft matter . At both macro and microscopic levels, skeletal muscle is exquisitely oriented for force generation and movement. In addition to the dynamics of contracting and relaxing muscle which can be monitored with ultrasound, variations in the muscle force are also expected to be monitored. To observe such force and sideways expansion variations synchronously for the skeletal muscle a novel detection scheme has been developed. As already introduced for the detection of sideways expansion variations of the muscle, ultrasonic transducers are mounted sideways on opposing positions of the monitored muscle. To detect variations of the muscle force, angle of pull of the monitored muscle has been restricted by the mechanical pull of the sonic force sensor. Under this condition, any variation in the time-of-flight (TOF) of the transmitted ultrasonic signals can be introduced by the variation of the path length between the transducers. The observed variations of the TOF are compared to the signals obtained by ultrasound monitoring for the muscle dynamics. The general behavior of the muscle dynamics and muscle force shows almost an identical concept. Since muscle force also relates the psychological boosting-up effects, the influence of boosting-up on muscle force and muscle dynamics can also be quantified form this study. Length-tension or force-length and force-velocity relationship can also be derived quantitatively with such monitoring.

  6. Role of attractive forces in determining the equilibrium structure and dynamics of simple liquids

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2015-01-01

    condensed fluids, even the attractive forces outside the FCS play a role. The changes in the distribution caused by neglecting the attractive forces, lead to a too high pressure. The weak long-range attractions damp the dynamics and the diffusion of the particles in gas-, super critical fluid- and in liquid......Molecular Dynamics simulations of a Lennard-Jones system with different range of attraction show that the attractive forces modify the radial distribution of the particles. For condensed liquids only, the forces within the the first coordination shell (FCS) are important, but for gases and moderate...

  7. Role of attractive forces in determining the equilibrium structure and dynamics of simple liquids

    DEFF Research Database (Denmark)

    Toxværd, Søren

    2015-01-01

    Molecular Dynamics simulations of a Lennard-Jones system with different range of attraction show that the attractive forces modify the radial distribution of the particles. For condensed liquids only, the forces within the the first coordination shell (FCS) are important, but for gases and moderate...... condensed fluids, even the attractive forces outside the FCS play a role. The changes in the distribution caused by neglecting the attractive forces, lead to a too high pressure. The weak long-range attractions damp the dynamics and the diffusion of the particles in gas-, super critical fluid- and in liquid...

  8. Analysis of dynamic foot pressure distribution and ground reaction forces

    Science.gov (United States)

    Ong, F. R.; Wong, T. S.

    2005-04-01

    The purpose of this study was to assess the relationship between forces derived from in-shoe pressure distribution and GRFs during normal gait. The relationship served to demonstrate the accuracy and reliability of the in-shoe pressure sensor. The in-shoe pressure distribution from Tekscan F-Scan system outputs vertical forces and Centre of Force (COF), while the Kistler force plate gives ground reaction forces (GRFs) in terms of Fz, Fx and Fy, as well as vertical torque, Tz. The two systems were synchronized for pressure and GRFs measurements. Data was collected from four volunteers through three trials for both left and right foot under barefoot condition with the in-shoe sensor. The forces derived from pressure distribution correlated well with the vertical GRFs, and the correlation coefficient (r2) was in the range of 0.93 to 0.99. This is a result of extended calibration, which improves pressure measurement to give better accuracy and reliability. The COF from in-shoe sensor generally matched well with the force plate COP. As for the maximum vertical torque at the forefoot during toe-off, there was no relationship with the pressure distribution. However, the maximum torque was shown to give an indication of the rotational angle of the foot.

  9. Modeling of Dynamic Fluid Forces in Fast Switching Valves

    DEFF Research Database (Denmark)

    Roemer, Daniel Beck; Johansen, Per; Pedersen, Henrik Clemmensen

    2015-01-01

    Switching valves experience opposing fluid forces due to movement of the moving member itself, as the surrounding fluid volume must move to accommodate the movement. This movement-induced fluid force may be divided into three main components; the added mass term, the viscous term and the socalled...... is given using an analytically solvable example, showing the explicit form of the force terms and highlighting the significance of the added mass and history term in certain fast switching valve applications. A general approximate model for arbitrary valve geometries is then proposed with offset...

  10. Unified Model of Dynamic Forced Barrier Crossing in Single Molecules

    Energy Technology Data Exchange (ETDEWEB)

    Friddle, R W

    2007-06-21

    Thermally activated barrier crossing in the presence of an increasing load can reveal kinetic rate constants and energy barrier parameters when repeated over a range of loading rates. Here we derive a model of the mean escape force for all relevant loading rates--the complete force spectrum. Two well-known approximations emerge as limiting cases; one of which confirms predictions that single-barrier spectra should converge to a phenomenological description in the slow loading limit.

  11. Conservative and dissipative force field for simulation of coarse-grained alkane molecules: A bottom-up approach

    Energy Technology Data Exchange (ETDEWEB)

    Trément, Sébastien; Rousseau, Bernard, E-mail: bernard.rousseau@u-psud.fr [Laboratoire de Chimie-Physique, UMR 8000 CNRS, Université Paris-Sud, Orsay (France); Schnell, Benoît; Petitjean, Laurent; Couty, Marc [Manufacture Française des Pneumatiques MICHELIN, Centre de Ladoux, 23 place des Carmes, 63000 Clermont-Ferrand (France)

    2014-04-07

    We apply operational procedures available in the literature to the construction of coarse-grained conservative and friction forces for use in dissipative particle dynamics (DPD) simulations. The full procedure rely on a bottom-up approach: large molecular dynamics trajectories of n-pentane and n-decane modeled with an anisotropic united atom model serve as input for the force field generation. As a consequence, the coarse-grained model is expected to reproduce at least semi-quantitatively structural and dynamical properties of the underlying atomistic model. Two different coarse-graining levels are studied, corresponding to five and ten carbon atoms per DPD bead. The influence of the coarse-graining level on the generated force fields contributions, namely, the conservative and the friction part, is discussed. It is shown that the coarse-grained model of n-pentane correctly reproduces self-diffusion and viscosity coefficients of real n-pentane, while the fully coarse-grained model for n-decane at ambient temperature over-predicts diffusion by a factor of 2. However, when the n-pentane coarse-grained model is used as a building block for larger molecule (e.g., n-decane as a two blobs model), a much better agreement with experimental data is obtained, suggesting that the force field constructed is transferable to large macro-molecular systems.

  12. Flight Dynamics of Flexible Aircraft with Aeroelastic and Inertial Force Interactions

    Science.gov (United States)

    Nguyen, Nhan T.; Tuzcu, Ilhan

    2009-01-01

    This paper presents an integrated flight dynamic modeling method for flexible aircraft that captures coupled physics effects due to inertial forces, aeroelasticity, and propulsive forces that are normally present in flight. The present approach formulates the coupled flight dynamics using a structural dynamic modeling method that describes the elasticity of a flexible, twisted, swept wing using an equivalent beam-rod model. The structural dynamic model allows for three types of wing elastic motion: flapwise bending, chordwise bending, and torsion. Inertial force coupling with the wing elasticity is formulated to account for aircraft acceleration. The structural deflections create an effective aeroelastic angle of attack that affects the rigid-body motion of flexible aircraft. The aeroelastic effect contributes to aerodynamic damping forces that can influence aerodynamic stability. For wing-mounted engines, wing flexibility can cause the propulsive forces and moments to couple with the wing elastic motion. The integrated flight dynamics for a flexible aircraft are formulated by including generalized coordinate variables associated with the aeroelastic-propulsive forces and moments in the standard state-space form for six degree-of-freedom flight dynamics. A computational structural model for a generic transport aircraft has been created. The eigenvalue analysis is performed to compute aeroelastic frequencies and aerodynamic damping. The results will be used to construct an integrated flight dynamic model of a flexible generic transport aircraft.

  13. Muscle force estimation with surface EMG during dynamic muscle contractions: a wavelet and ANN based approach.

    Science.gov (United States)

    Bai, Fengjun; Chew, Chee-Meng

    2013-01-01

    Human muscle force estimation is important in biomechanics studies, sports and assistive devices fields. Therefore, it is essential to develop an efficient algorithm to estimate force exerted by muscles. The purpose of this study is to predict force/torque exerted by muscles under dynamic muscle contractions based on continuous wavelet transform (CWT) and artificial neural networks (ANN) approaches. Mean frequency (MF) of the surface electromyography (EMG) signals power spectrum was calculated from CWT. ANN models were trained to derive the MF-force relationships from the subset of EMG signals and the measured forces. Then we use the networks to predict the individual muscle forces for different muscle groups. Fourteen healthy subjects (10 males and 4 females) were voluntarily recruited in this study. EMG signals were collected from the biceps brachii, triceps, hamstring and quadriceps femoris muscles to evaluate the proposed method. Root mean square errors (RMSE) and correlation coefficients between the predicted forces and measured actual forces were calculated.

  14. Theory of dynamic force spectroscopy for kinetochore-microtubule attachments: rupture force distribution

    CERN Document Server

    Ghanti, Dipanwita

    2016-01-01

    Application of pulling force, under force-clamp conditions, to kinetochore-microtubule attachments {\\it in-vitro} revealed a catch-bond-like behavior. In an earlier paper ({\\it Sharma et al. Phys. Biol. (2014)} the physical origin of this apparently counter-intuitive phenomenon was traced to the nature of the force-dependence of the (de-)polymerization kinetics of the microtubules. In this brief communication that work is extended to situations where the external forced is ramped up till the attachment gets ruptured. In spite of the fundamental differences in the underlying mechanisms, the trend of variation of the rupture force distribution observed in our model kinetochore-microtubule attachment with the increasing loading rate is qualitatively similar to that displayed by the catch bonds formed in some other ligand-receptor systems. Our theoretical predictions can be tested experimentally by a straightforward modification of the protocol for controlling the force in the optical trap set up that was used in...

  15. Analysis of limit forces on the vehicle wheels using an algorithm of Dynamic Square Method

    Science.gov (United States)

    Brukalski, M.

    2016-09-01

    This article presents a method named as Dynamic Square Method (DSM) used for dynamic analysis of a vehicle equipped with a four wheel drive system. This method allows determination of maximum (limit) forces acting on the wheels. Here, the maximum longitudinal forces acting on the wheels are assumed and then used to predict whether they can be achieved by a specific dynamic motion or whether the actual friction forces under a given wheel is large enough to transfer lateral forces. For the analysis of DSM a four wheel vehicle model is used. On the basis of this characteristic it is possible to determine the maximum longitudinal force acting on the wheels of the given axle depending on the lateral acceleration of the vehicle. The results of this analysis may be useful in the development of a control algorithm used for example in active differentials.

  16. Dynamics of bow-tie shaped bursting: Forced pendulum with dynamic feedback

    Science.gov (United States)

    Hongray, Thotreithem; Balakrishnan, Janaki

    2016-12-01

    A detailed study is performed on the parameter space of the mechanical system of a driven pendulum with damping and constant torque under feedback control. We report an interesting bow-tie shaped bursting oscillatory behaviour, which is exhibited for small driving frequencies, in a certain parameter regime, which has not been reported earlier in this forced system with dynamic feedback. We show that the bursting oscillations are caused because of a transition of the quiescent state to the spiking state by a saddle-focus bifurcation, and because of another saddle-focus bifurcation, which leads to cessation of spiking, bringing the system back to the quiescent state. The resting period between two successive bursts (Trest) is estimated analytically.

  17. WearDY: Wearable dynamics. A prototype for human whole-body force and motion estimation

    Science.gov (United States)

    Latella, Claudia; Kuppuswamy, Naveen; Nori, Francesco

    2016-06-01

    Motion capture is a powerful tool used in a large range of applications towards human movement analysis. Although it is a well-established technique, its main limitation is the lack of dynamic information such as forces and torques during the motion capture. In this paper, we present a novel approach for human wearable dynamic (WearDY) motion capture for the simultaneous estimation of whole-body forces along with the motion. Our conceptual framework encompasses traditional passive markers based methods, inertial and contact force sensor modalities and harnesses a probabilistic computational framework for estimating dynamic quantities originally proposed in the domain of humanoid robot control. We present preliminary experimental analysis of our framework on subjects performing a two Degrees-of-Freedom bowing task and we estimate the motion and dynamic quantities. We discuss the implication of our proposal towards the design of a novel wearable force and motion capture suit and its applications.

  18. Refolding dynamics of stretched biopolymers upon force quench

    CERN Document Server

    Hyeon, Changbong; Pincus, David L; Thirumalai, D

    2009-01-01

    Single molecule force spectroscopy methods can be used to generate folding trajectories of biopolymers from arbitrary regions of the folding landscape. We illustrate the complexity of the folding kinetics and generic aspects of the collapse of RNA and proteins upon force quench, using simulations of an RNA hairpin and theory based on the de Gennes model for homopolymer collapse. The folding time, $\\tau_F$, depends asymmetrically on $\\delta f_S = f_S - f_m$ and $\\delta f_Q = f_m - f_Q$ where $f_S$ ($f_Q$) is the stretch (quench) force, and $f_m$ is the transition mid-force of the RNA hairpin. In accord with experiments, the relaxation kinetics of the molecular extension, $R(t)$, occurs in three stages: a rapid initial decrease in the extension is followed by a plateau, and finally an abrupt reduction in $R(t)$ that occurs as the native state is approached. The duration of the plateau increases as $\\lambda =\\tau_Q/\\tau_F$ decreases (where $\\tau_Q$ is the time in which the force is reduced from $f_S$ to $f_Q$). ...

  19. Forcing-dependent dynamics and emergence of helicity in rotating turbulence

    CERN Document Server

    Dallas, Vassilios

    2016-01-01

    The effects of large scale mechanical forcing on the dynamics of rotating turbulent flows are studied by means of numerical simulations, varying systematically the nature of the mechanical force in time. We demonstrate that the statistically stationary solutions of these flows depend on the nature of the forcing mechanism. Rapidly enough rotating flows with a forcing that has a persistent direction relatively to the axis of rotation bifurcate from a non-helical state to a helical state despite the fact that the forcing is non-helical. We find that the nature of the mechanical force in time and the emergence of helicity have direct implications on the cascade dynamics of these flows, determining the anisotropy in the flow, the energy condensation at large scales and the power-law energy spectra that are consistent with previous findings and phenomenologies under strong and weak-wave turbulent conditions.

  20. Force

    CERN Document Server

    Graybill, George

    2007-01-01

    Forces are at work all around us. Discover what a force is, and different kinds of forces that work on contact and at a distance. We use simple language and vocabulary to make this invisible world easy for students to ""see"" and understand. Examine how forces ""add up"" to create the total force on an object, and reinforce concepts and extend learning with sample problems.

  1. Attitude dynamics and control of spacecraft using geomagnetic Lorentz force

    CERN Document Server

    Abdel-Aziz, Yehia A

    2014-01-01

    The attitude stabilization of a charged rigid spacecraft in Low Earth Orbit (LEO) using torques due to Lorentz force in pitch and roll directions is considered. A spacecraft that generates an electrostatic charge on its surface in the Earth magnetic field will be subject to perturbations from Lorentz force. The Lorentz force acting on an electrostatically charged spacecraft may provide a useful thrust for controlling a spacecraft's orientation. We assume that the spacecraft is moving in the Earth's magnetic field in an elliptical orbit under the effects of the gravitational, geomagnetic and Lorentz torques. The magnetic field of the Earth is modeled as a non-tilted dipole. A model incorporating all Lorentz torques as a function of orbital elements has been developed on the basis of electric and magnetic fields. The stability of the spacecraft orientation is investigated both analytically and numerically. The existence and stability of equilibrium positions is investigated for different values of the charge to...

  2. Earth's Inner Core dynamics induced by the Lorentz force

    CERN Document Server

    Lasbleis, M; Cardin, P; Labrosse, S

    2015-01-01

    Seismic studies indicate that the Earth's inner core has a complex structure and exhibits a strong elastic anisotropy with a cylindrical symmetry. Among the various models which have been proposed to explain this anisotropy, one class of models considers the effect of the Lorentz force associated with the magnetic field diffused within the inner core. In this paper we extend previous studies and use analytical calculations and numerical simulations to predict the geometry and strength of the flow induced by the poloidal component of the Lorentz force in a neutrally or stably stratified growing inner core, exploring also the effect of different types of boundary conditions at the inner core boundary (ICB). Unlike previous studies, we show that the boundary condition that is most likely to produce a significant deformation and seismic anisotropy is impermeable, with negligible radial flow through the boundary. Exact analytical solutions are found in the case of a negligible effect of buoyancy forces in the inne...

  3. A Bimorph Moment/Force Actuator for Dynamic Testing

    Directory of Open Access Journals (Sweden)

    Hou Xiaoyan

    2009-09-01

    Full Text Available This paper focuses on a novel bimorph actuator which can produce pure moment or pure force to structures under testing. Due to its unique construction, this actuator is only sensitive to one translational and one rotational degree of freedom (DOF, which can be further decoupled from each other through controlling the phase of the excitation voltage supplied to the actuator. To correlate the input electrical voltage with the output moment (or force, angular velocity, linear velocity, rotational (or translational conversion functions are defined and then numerically determined. Compared with conventional twin-shaker setup to generate moment, the bimorph actuator is simple, compact, light-weight, effective and cheap. When generating moment, the usually-existing unwanted force excitation is avoided. The working frequency range of the actuator is much wider and the loading effect is greatly reduced.

  4. A COMPARISON OF STATIC AND DYNAMIC OPTIMIZATION MUSCLE FORCE PREDICTIONS DURING WHEELCHAIR PROPULSION

    OpenAIRE

    Morrow, Melissa M.; Rankin, Jeffery W.; Neptune, Richard R.; Kaufman, Kenton R.

    2014-01-01

    The primary purpose of this study was to compare static and dynamic optimization muscle force and work predictions during the push phase of wheelchair propulsion. A secondary purpose was to compare the differences in predicted shoulder and elbow kinetics and kinematics and handrim forces. The forward dynamics simulation minimized differences between simulated and experimental data (obtained from 10 manual wheelchair users) and muscle co-contraction. For direct comparison between models, the s...

  5. Refolding dynamics of stretched biopolymers upon force quench

    Science.gov (United States)

    Hyeon, Changbong; Morrison, Greg; Pincus, David L.; Thirumalai, D.

    2009-01-01

    Single-molecule force spectroscopy methods can be used to generate folding trajectories of biopolymers from arbitrary regions of the folding landscape. We illustrate the complexity of the folding kinetics and generic aspects of the collapse of RNA and proteins upon force quench by using simulations of an RNA hairpin and theory based on the de Gennes model for homopolymer collapse. The folding time, τF, depends asymmetrically on δfS = f S − f m and δf Q = f m − f Q where f S (f Q) is the stretch (quench) force and f m is the transition midforce of the RNA hairpin. In accord with experiments, the relaxation kinetics of the molecular extension, R(t), occurs in three stages: A rapid initial decrease in the extension is followed by a plateau and finally, an abrupt reduction in R(t) occurs as the native state is approached. The duration of the plateau increases as λ = τ Q/τ F decreases (where τ Q is the time in which the force is reduced from f S to f Q). Variations in the mechanisms of force-quench relaxation as λ is altered are reflected in the experimentally measurable time-dependent entropy, which is computed directly from the folding trajectories. An analytical solution of the de Gennes model under tension reproduces the multistage stage kinetics in R(t). The prediction that the initial stages of collapse should also be a generic feature of polymers is validated by simulation of the kinetics of toroid (globule) formation in semiflexible (flexible) homopolymers in poor solvents upon quenching the force from a fully stretched state. Our findings give a unified explanation for multiple disparate experimental observations of protein folding. PMID:19915145

  6. Analytical and Numerical Studies for Chaotic Dynamics of a Duffing Oscillator with a Parametric Force

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The chaotic dynamics of a Duffing oscillator with a parametric force is investigated. By using the direct perturbation technique, we analytically obtain the general solution of the 1st-order equation. Through the boundedness condition of the general solution we get the famous Melnikov function predicting the onset of chaos. When the parametric and external forces are strong, numerical simulations show that increasing the amplitude of the parametric or external force can lead the system into chaos via period doubling.

  7. How sensitive are nanosecond molecular dynamics simulations of proteins to changes in the force field?

    NARCIS (Netherlands)

    Villa, Alessandra; Fan, Hao; Wassenaar, Tsjerk; Mark, Alan E.

    2007-01-01

    The sensitivity of molecular dynamics simulations to variations in the force field has been examined in relation to a set of 36 structures corresponding to 31 proteins simulated by using different versions of the GROMOS force field. The three parameter sets used (43a1, 53a5, and 53a6) differ signifi

  8. WRIST FORCE SENSOR'S DYNAMIC PERFORMANCE CALIBRATION BASED ON NEGATIVE STEP RESPONSE

    Institute of Scientific and Technical Information of China (English)

    ZHENG Hongmei

    2008-01-01

    Negative step response experimental method is used in wrist force sensor's dynamic performance calibration. The exciting manner of negative step response method is the same as wrist force sensor's load in working. This experimental method needn't special experiment equipments. Experiment's dynamic repeatability is good. So wrist force sensor's dynamic performance is suitable to be calibrated by negative step response method. A new correlation wavelet transfer method is studied. By wavelet transfer method, the signal is decomposed into two dimensional spaces of time-frequency. So the problem of negative step exciting energy concentrating in the low frequency band is solved. Correlation wavelet transfer doesn't require that wavelet primary function be orthogonal and needn't wavelet reconstruction. So analyzing efficiency is high. An experimental bench is designed and manufactured to load the wrist force sensor orthogonal excitation force/moment. A piezoelectric force sensor is used to setup soft trigger and calculate the value of negative step excitation. A wrist force sensor is calibrated. The pulse response function is calculated after negative step excitation and step response have been transformed to positive step excitation and step response. The pulse response function is transferred to frequency response function. The wrist force sensor's dynamic characteristics are identified by the frequency response function.

  9. Influence of materials' optical response on actuation dynamics by Casimir forces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.

    2015-01-01

    The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the f

  10. Dynamic Image Forces Near a Metal Surface and the Point-Charge Motion

    Science.gov (United States)

    Gabovich, A. M.; Voitenko, A. I.

    2012-01-01

    The problem of charge motion governed by image force attraction near a plane metal surface is considered and solved self-consistently. The temporal dispersion of metal dielectric permittivity makes the image forces dynamic and, hence, finite, contrary to the results of the conventional approach. Therefore, the maximal attainable velocity turns out…

  11. Quantification of in-contact probe-sample electrostatic forces with dynamic atomic force microscopy

    Science.gov (United States)

    Balke, Nina; Jesse, Stephen; Carmichael, Ben; Baris Okatan, M.; Kravchenko, Ivan I.; Kalinin, Sergei V.; Tselev, Alexander

    2017-02-01

    Atomic force microscopy (AFM) methods utilizing resonant mechanical vibrations of cantilevers in contact with a sample surface have shown sensitivities as high as few picometers for detecting surface displacements. Such a high sensitivity is harnessed in several AFM imaging modes. Here, we demonstrate a cantilever-resonance-based method to quantify electrostatic forces on a probe in the probe-sample junction in the presence of a surface potential or when a bias voltage is applied to the AFM probe. We find that the electrostatic forces acting on the probe tip apex can produce signals equivalent to a few pm of surface displacement. In combination with modeling, the measurements of the force were used to access the strength of the electrical field at the probe tip apex in contact with a sample. We find an evidence that the electric field strength in the junction can reach ca. 1 V nm-1 at a bias voltage of a few volts and is limited by non-ideality of the tip-sample contact. This field is sufficiently strong to significantly influence material states and kinetic processes through charge injection, Maxwell stress, shifts of phase equilibria, and reduction of energy barriers for activated processes. Besides, the results provide a baseline for accounting for the effects of local electrostatic forces in electromechanical AFM measurements as well as offer additional means to probe ionic mobility and field-induced phenomena in solids.

  12. Stochastic model for aerodynamic force dynamics on wind turbine blades in unsteady wind inflow

    CERN Document Server

    Luhur, Muhammad Ramzan; Kühn, Martin; Wächter, Matthias

    2015-01-01

    The paper presents a stochastic approach to estimate the aerodynamic forces with local dynamics on wind turbine blades in unsteady wind inflow. This is done by integrating a stochastic model of lift and drag dynamics for an airfoil into the aerodynamic simulation software AeroDyn. The model is added as an alternative to the static table lookup approach in blade element momentum (BEM) wake model used by AeroDyn. The stochastic forces are obtained for a rotor blade element using full field turbulence simulated wind data input and compared with the classical BEM and dynamic stall models for identical conditions. The comparison shows that the stochastic model generates additional extended dynamic response in terms of local force fluctuations. Further, the comparison of statistics between the classical BEM, dynamic stall and stochastic models' results in terms of their increment probability density functions gives consistent results.

  13. Atomic Force Microscopy of dynamic protein DNA interactions

    NARCIS (Netherlands)

    Noort, van Simon Johannes Theodorus

    1999-01-01

    In this thesis a dedicated Atomic Force Microscopy (AFM) setup is used for imaging biochemical reactions with molecular resolution. The basis for the high resolution of AFM is the combination of a small probe, close proximity to the sample and a short-range interaction between the probe and the samp

  14. Application of dynamic impedance spectroscopy to atomic force microscopy

    Directory of Open Access Journals (Sweden)

    Kazimierz Darowicki, Artur Zieliński and Krzysztof J Kurzydłowski

    2008-01-01

    Full Text Available Atomic force microscopy (AFM is a universal imaging technique, while impedance spectroscopy is a fundamental method of determining the electrical properties of materials. It is useful to combine those techniques to obtain the spatial distribution of an impedance vector. This paper proposes a new combining approach utilizing multifrequency scanning and simultaneous AFM scanning of an investigated surface.

  15. Soliton ratchetlike dynamics by ac forces with harmonic mixing

    DEFF Research Database (Denmark)

    Salerno, Mario; Zolotaryuk, Yaroslav

    2002-01-01

    The possibility of unidirectional motion of a kink (topological soliton) of a dissipative sine-Gordon equation in the presence of ac forces with harmonic mixing (at least biharmonic) and of zero mean, is presented. The dependence of the kink mean velocity on system parameters is investigated...

  16. Estimation of changes in dynamic hydraulic force in a magnetically suspended centrifugal blood pump with transient computational fluid dynamics analysis.

    Science.gov (United States)

    Masuzawa, Toru; Ohta, Akiko; Tanaka, Nobuatu; Qian, Yi; Tsukiya, Tomonori

    2009-01-01

    The effect of the hydraulic force on magnetically levitated (maglev) pumps should be studied carefully to improve the suspension performance and the reliability of the pumps. A maglev centrifugal pump, developed at Ibaraki University, was modeled with 926 376 hexahedral elements for computational fluid dynamics (CFD) analyses. The pump has a fully open six-vane impeller with a diameter of 72.5 mm. A self-bearing motor suspends the impeller in the radial direction. The maximum pressure head and flow rate were 250 mmHg and 14 l/min, respectively. First, a steady-state analysis was performed using commercial code STAR-CD to confirm the model's suitability by comparing the results with the real pump performance. Second, transient analysis was performed to estimate the hydraulic force on the levitated impeller. The impeller was rotated in steps of 1 degrees using a sliding mesh. The force around the impeller was integrated at every step. The transient analysis revealed that the direction of the radial force changed dynamically as the vane's position changed relative to the outlet port during one circulation, and the magnitude of this force was about 1 N. The current maglev pump has sufficient performance to counteract this hydraulic force. Transient CFD analysis is not only useful for observing dynamic flow conditions in a centrifugal pump but is also effective for obtaining information about the levitation dynamics of a maglev pump.

  17. Structure and Dynamics of Dinucleosomes Assessed by Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Nina A. Filenko

    2012-01-01

    Full Text Available Dynamics of nucleosomes and their interactions are important for understanding the mechanism of chromatin assembly. Internucleosomal interaction is required for the formation of higher-order chromatin structures. Although H1 histone is critically involved in the process of chromatin assembly, direct internucleosomal interactions contribute to this process as well. To characterize the interactions of nucleosomes within the nucleosome array, we designed a dinucleosome and performed direct AFM imaging. The analysis of the AFM data showed dinucleosomes are very dynamic systems, enabling the nucleosomes to move in a broad range along the DNA template. Di-nucleosomes in close proximity were observed, but their population was low. The use of the zwitterionic detergent, CHAPS, increased the dynamic range of the di-nucleosome, facilitating the formation of tight di-nucleosomes. The role of CHAPS and similar natural products in chromatin structure and dynamics is also discussed.

  18. Exploring the Contribution of Collective Motions to the Dynamics of Forced-Unfolding in Tubulin

    Science.gov (United States)

    Joshi, Harshad; Momin, Farhana; Haines, Kelly E.; Dima, Ruxandra I.

    2010-01-01

    Abstract Decomposition of the intrinsic dynamics of proteins into collective motions among distant regions of the protein structure provides a physically appealing approach that couples the dynamics of the system with its functional role. The cellular functions of microtubules (an essential component of the cytoskeleton in all eukaryotic cells) depend on their dynamic instability, which is altered by various factors among which applied forces are central. To shed light on the coupling between forces and the dynamic instability of microtubules, we focus on the investigation of the response of the microtubule subunits (tubulin) to applied forces. We address this point by adapting an approach designed to survey correlations for the equilibrium dynamics of proteins to the case of correlations for proteins forced-dynamics. The resulting collective motions in tubulin have a number of functional implications, such as the identification of long-range couplings with a role in blocking the dynamic instability of microtubules. A fundamental implication of our study for the life of a cell is that, to increase the likelihood of unraveling of large cytoskeletal filaments under physiological forces, molecular motors must use a combination of pulling and torsion rather than just pulling. PMID:20159162

  19. Force on Force Modeling with Formal Task Structures and Dynamic Geometry

    Science.gov (United States)

    2017-03-24

    shared metrics and an executable integration architecture. • Generate a formal top-down mission specification for sample operating force organizations...in a simulation environment. The mission specification team applied best military judgement to specify required capability for collective tasks by

  20. Absence of gamma-range corticomuscular coherence during dynamic force in a deafferented patient.

    Science.gov (United States)

    Patino, Luis; Omlor, Wolfgang; Chakarov, Vihren; Hepp-Reymond, Marie-Claude; Kristeva, Rumyana

    2008-04-01

    Recently, we studied corticomuscular coherence (CMC) in a visuomotor task and showed for the first time gamma-range (30-45 Hz) CMC during isometric compensation of a periodically modulated dynamic force. We speculated that for the control of such forces, the sensorimotor system resonates at gamma-range frequencies to rapidly integrate the visual and proprioceptive information and produce the appropriate motor command. In this study, we tested the role of the proprioceptive afferent feedback on gamma-range CMC by comparing the deafferented patient GL to six age- and sex-matched subjects during the performance of a visuomotor force task consisting of isometric compensation of static and dynamic forces applied on the finger. Patient GL presented no significant gamma-band CMC during dynamic force. Instead, she had only beta-range CMC as in the static force condition; concurrently, her performance was significantly worse than that of the controls in both conditions. This gives support to the conclusions of our previous paper and suggests that proprioceptive information is mandatory in the genesis of gamma-band CMC during the generation and control of dynamic forces.

  1. Attitude dynamics and control of spacecraft using geomagnetic Lorentz force

    Science.gov (United States)

    Abdel-Aziz, Yehia A.; Shoaib, Muhammad

    2015-01-01

    Attitude stabilization of a charged rigid spacecraft in Low Earth Orbit using torques due to Lorentz force in pitch and roll directions is considered. A spacecraft that generates an electrostatic charge on its surface in the Earth's magnetic field will be subject to perturbations from the Lorentz force. The Lorentz force acting on an electrostatically charged spacecraft may provide a useful thrust for controlling a spacecraft's orientation. We assume that the spacecraft is moving in the Earth's magnetic field in an elliptical orbit under the effects of gravitational, geomagnetic and Lorentz torques. The magnetic field of the Earth is modeled as a non-tilted dipole. A model incorporating all Lorentz torques as a function of orbital elements has been developed on the basis of electric and magnetic fields. The stability of the spacecraft orientation is investigated both analytically and numerically. The existence and stability of equilibrium positions is investigated for different values of the charge to mass ratio (α*). Stable orbits are identified for various values of α*. The main parameters for stabilization of the spacecraft are α* and the difference between the components of the moment of inertia for the spacecraft.

  2. Static and Dynamic Performance Simulation of Direct-Acting Force Motor Valve

    Science.gov (United States)

    Ye, Xinghai; Ding, Jianjun; Zheng, Gang; Jiang, Kunpeng; Chen, Dongdong

    2017-07-01

    This work focuses on static and dynamic characteristics of direct-acting force motor valve. First, we analyzed the structure features and operating principle of the Mitsubishi-Hitachi force motor valve (FMV) and the operating principle of its internal permanent-magnet moving-coil force motor magnetic circuit, determined the transfer function of the FMV force motor system, and established a mathematical model for the system. Secondly, we established a static performance analysis model using the AMESIM software and utilized the model in combination with experimental results to analyze the effects of electro-hydraulic servo valve structural parameters on static characteristics. Lastly, we deduced the trajectory equation of the system, established the relationship between dynamic characteristic indexes and structural parameters, and analyzed the effects of different parameter values on the dynamic characteristics of the system. This research can provide a theoretical guidance for designing and manufacturing the FMV body.

  3. Interacting trophic forcing and the population dynamics of herring

    DEFF Research Database (Denmark)

    Lindegren, Martin; Ostman, Orjan; Gardmark, Anna

    2011-01-01

    Small pelagic fish occupy a central position in marine ecosystems worldwide, largely by determining the energy transfer from lower trophic levels to predators at the top of the food web, including humans. Population dynamics of small pelagic fish may therefore be regulated neither strictly bottom......-up nor top-down, but rather through multiple external and internal drivers. While in many studies single drivers have been identified, potential synergies of multiple factors, as well as their relative importance in regulating population dynamics of small pelagic fish, is a largely unresolved issue....... Using a statistical, age-structured modeling approach, we demonstrate the relative importance and influence of bottom-up (e.g., climate, zooplankton availability) and top-down (i.e., fishing and predation) factors on the population dynamics of Bothnian Sea herring (Clupea harengus) throughout its life...

  4. Investigation of Multiscale Non-equilibrium Flow Dynamics Under External Force Field

    CERN Document Server

    Xiao, Tianbai

    2016-01-01

    The multiple scale non-equilibrium gaseous flow behavior under external force field is investigated. Both theoretical analysis based on the kinetic model equation and numerical study are presented to demonstrate the dynamic effect of external force on the flow evolution, especially on the non-equilibrium heat flux. The current numerical experiment is based on the well-balanced unified gas-kinetic scheme (UGKS), which presents accurate solutions in the whole flow regime from the continuum Navier-Stokes solution to the transition and free molecular ones. The heat conduction in the non-equilibrium regime due to the external forcing term is quantitatively investigated. In the lid-driven cavity flow study, due to the external force field the density distribution inside cavity gets stratified and a multiscale non-equilibrium flow transport appears in a single gas dynamic system. With the increment of external forcing term, the flow topological structure changes dramatically, and the temperature gradient, shearing s...

  5. Identification of dynamic forces using group-sparsity in frequency domain

    Science.gov (United States)

    Rezayat, A.; Nassiri, V.; De Pauw, B.; Ertveldt, J.; Vanlanduit, S.; Guillaume, P.

    2016-03-01

    The knowledge of acting dynamic forces is required for the design of structures. Given the structural model, inverse techniques offer the possibility to reconstruct the system's input forces from vibration data. The inverse problem is highly sensitive to measurement noise, and the classical pseudo-inverse method generally fails to find the correct loads. In this paper we propose a new penalty function that combines the advantages of the ℓp-norm properties, together with a modified iterative optimization technique. The new algorithm (G-FISTA) is used to localize and reconstruct dynamic point-forces on a beam structure, with no prior knowledge on the force locations. The algorithm is validated by means of several simulations and experiments. The strain data is measured using Fiber Bragg Gratings (FBG) attached to the beam. The obtained results show that the location and time history of point forces are better estimated using the proposed technique.

  6. A discrete force allocation algorithm for modelling wind turbines in computational fluid dynamics

    DEFF Research Database (Denmark)

    Réthoré, Pierre-Elouan; Sørensen, Niels N.

    2012-01-01

    This paper describes an algorithm for allocating discrete forces in computational fluid dynamics (CFD). Discrete forces are useful in wind energy CFD. They are used as an approximation of the wind turbine blades’ action on the wind (actuator disc/line), to model forests and to model turbulent......, this algorithm does not address the specific cases where discrete forces are present. The velocities and pressure exhibit some significant numerical fluctuations at the position where the body forces are applied. While this issue is limited in space, it is usually critical to accurately estimate the velocity...

  7. BIFURCATION AND DYNAMICS OF THIN SLIPPING FILMS UNDER THE INFLUENCE OF INTERMOLECULAR FORCES

    Institute of Scientific and Technical Information of China (English)

    HU Guo-hui

    2006-01-01

    The effects of the Born repulsive force on the stability and dynamics of ultra-thin slipping films under the influences of intermolecular forces are investigated with bifurcation theory and numerical simulation. Results show that the repulsive force has a stabilizing effect on the development of perturbations, and can suppress the rupture process induced by the van der Waals attractive force. Although slippage will enhance the growth of disturbances, it does not have influence on the linear cutoff wave number and the final shape of the film thickness as time approaches to infinity.

  8. A comparison of static and dynamic optimization muscle force predictions during wheelchair propulsion.

    Science.gov (United States)

    Morrow, Melissa M; Rankin, Jeffery W; Neptune, Richard R; Kaufman, Kenton R

    2014-11-07

    The primary purpose of this study was to compare static and dynamic optimization muscle force and work predictions during the push phase of wheelchair propulsion. A secondary purpose was to compare the differences in predicted shoulder and elbow kinetics and kinematics and handrim forces. The forward dynamics simulation minimized differences between simulated and experimental data (obtained from 10 manual wheelchair users) and muscle co-contraction. For direct comparison between models, the shoulder and elbow muscle moment arms and net joint moments from the dynamic optimization were used as inputs into the static optimization routine. RMS errors between model predictions were calculated to quantify model agreement. There was a wide range of individual muscle force agreement that spanned from poor (26.4% Fmax error in the middle deltoid) to good (6.4% Fmax error in the anterior deltoid) in the prime movers of the shoulder. The predicted muscle forces from the static optimization were sufficient to create the appropriate motion and joint moments at the shoulder for the push phase of wheelchair propulsion, but showed deviations in the elbow moment, pronation-supination motion and hand rim forces. These results suggest the static approach does not produce results similar enough to be a replacement for forward dynamics simulations, and care should be taken in choosing the appropriate method for a specific task and set of constraints. Dynamic optimization modeling approaches may be required for motions that are greatly influenced by muscle activation dynamics or that require significant co-contraction.

  9. A COMPARISON OF STATIC AND DYNAMIC OPTIMIZATION MUSCLE FORCE PREDICTIONS DURING WHEELCHAIR PROPULSION

    Science.gov (United States)

    Morrow, Melissa M.; Rankin, Jeffery W.; Neptune, Richard R.; Kaufman, Kenton R.

    2014-01-01

    The primary purpose of this study was to compare static and dynamic optimization muscle force and work predictions during the push phase of wheelchair propulsion. A secondary purpose was to compare the differences in predicted shoulder and elbow kinetics and kinematics and handrim forces. The forward dynamics simulation minimized differences between simulated and experimental data (obtained from 10 manual wheelchair users) and muscle co-contraction. For direct comparison between models, the shoulder and elbow muscle moment arms and net joint moments from the dynamic optimization were used as inputs into the static optimization routine. RMS errors between model predictions were calculated to quantify model agreement. There was a wide range of individual muscle force agreement that spanned from poor (26.4 % Fmax error in the middle deltoid) to good (6.4 % Fmax error in the anterior deltoid) in the prime movers of the shoulder. The predicted muscle forces from the static optimization were sufficient to create the appropriate motion and joint moments at the shoulder for the push phase of wheelchair propulsion, but showed deviations in the elbow moment, pronation-supination motion and hand rim forces. These results suggest the static approach does not produce results similar enough to be a replacement for forward dynamics simulations, and care should be taken in choosing the appropriate method for a specific task and set of constraints. Dynamic optimization modeling approaches may be required for motions that are greatly influenced by muscle activation dynamics or that require significant co-contraction. PMID:25282075

  10. Dynamical Fluctuating Charge Force Fields Application to Liquid Water

    CERN Document Server

    Rick, S W; Berne, B J; Rick, Steven W.; Stuart, Steven J.

    1994-01-01

    A new molecular dynamics model in which the point charges on atomic sites are allowed to fluctuate in response to the environment is developed and applied to water. The idea for treating charges as variables is based on the concept of electronegativity equalization according to which: (a) The electronegativity of an atomic site is dependent on the atom's type and charge and is perturbed by the electrostatic potential it experiences from its neighbors and (b) Charge is transferred between atomic sites in such a way that electronegativities are equalized. The charges are treated as dynamical variables using an extended Lagrangian method in which the charges are given a fictitious mass, velocities and kinetic energy and then propagated according to Newtonian mechanics along with the atomic degrees of freedom. Models for water with fluctuating charges are developed using the geometries of two common fixed-charge water potentials: the simple point charge (SPC) and the 4-point transferable intermolecular potential ...

  11. Integrated dynamic and static tactile sensor: focus on static force sensing

    Science.gov (United States)

    Wettels, Nicholas; Pletner, Baruch

    2012-04-01

    Object grasping by robotic hands in unstructured environments demands a sensor that is durable, compliant, and responsive to static and dynamic force conditions. In order for a tactile sensor to be useful for grasp control in these, it should have the following properties: tri-axial force sensing (two shear plus normal component), dynamic event sensing across slip frequencies, compliant surface for grip, wide dynamic range (depending on application), insensitivity to environmental conditions, ability to withstand abuse and good sensing behavior (e.g. low hysteresis, high repeatability). These features can be combined in a novel multimodal tactile sensor. This sensor combines commercial-off-the-shelf MEMS technology with two proprietary force sensors: a high bandwidth device based on PZT technology and low bandwidth device based on elastomers and optics. In this study, we focus on the latter transduction mechanism and the proposed architecture of the completed device. In this study, an embedded LED was utilized to produce a constant light source throughout a layer of silicon rubber which covered a plastic mandrel containing a set of sensitive phototransistors. Features about the contacted object such as center of pressure and force vectors can be extracted from the information in the changing patterns of light. The voltage versus force relationship obtained with this molded humanlike finger had a wide dynamic range that coincided with forces relevant for most human grip tasks.

  12. The acute effects of dynamic and ballistic stretching on vertical jump height, force, and power.

    Science.gov (United States)

    Jaggers, Jason R; Swank, Ann M; Frost, Karen L; Lee, Chong D

    2008-11-01

    Stretching before performance is a common practice among athletes in hopes of increasing performance and reducing the risk of injury. However, cumulative results indicate a negative impact of static stretching and proprioceptive neuromuscular facilitation (PNF) on performance; thus, there is a need for evaluating other stretching strategies for effective warm-up. The purpose of this study was to compare the differences between two sets of ballistic stretching and two sets of a dynamic stretching routine on vertical jump performance. Twenty healthy male and female college students between the ages of 22 and 34 (24.8 +/- 3 years) volunteered to participate in this study. All subjects completed three individual testing sessions on three nonconsecutive days. On each day, the subjects completed one of three treatments (no stretch, ballistic stretch, and dynamic stretch). Intraclass reliability was determined using the data obtained from each subject. A paired samples t-test revealed no significant difference in jump height, force, or power when comparing no stretch with ballistic stretch. A significant difference was found on jump power when comparing no stretch with dynamic stretch, but no significant difference was found for jump height or force. Statistics showed a very high reliability when measuring jump height, force, and power using the Kistler Quattro Jump force plate. It seems that neither dynamic stretching nor ballistic stretching will result in an increase in vertical jump height or force. However, dynamic stretching elicited gains in jump power poststretch.

  13. Dynamics of sessile drops. Part 3. Theory of forced oscillations

    CERN Document Server

    Bostwick, Joshua B

    2016-01-01

    A partially-wetting sessile drop is driven by a sinusoidal pressure field that produces capillary waves on the liquid/gas interface. The analysis presented in Part 1 of this series (Bostwick & Steen 2014) is extended by computing response diagrams and phase shifts for the viscous droplet, whose three phase contact-line moves with contact-angle that is a smooth function of the contact line speed. Viscous dissipation is incorporated through the viscous potential flow approximation and the critical Ohnesorge number bounding regions beyond which a given mode becomes over-damped is computed. Davis dissipation originating from the contact-line speed condition leads to damped oscillations for drops with finite contact-line mobility, even for inviscid fluids. The critical mobility and associated driving frequency to generate the largest Davis dissipation is computed. Lastly, regions of modal coexistence where two modes can be simultaneously excited by a single forcing frequency are identified. Predictions compare...

  14. Foot force models of crowd dynamics on a wobbly bridge

    CERN Document Server

    Belykh, Igor; Belykh, Vladamir

    2016-01-01

    Modern pedestrian and suspension bridges are designed using industry-standard packages, yet disastrous resonant vibrations are observed, necessitating multi-million dollar repairs. Recent examples include pedestrian induced vibrations during the openings of the Solf\\'erino Bridge in Paris in 1999 and the increased bouncing of the Squibb Park Bridge in Brooklyn in 2014. The most prominent example of an unstable lively bridge is the London Millennium Bridge which started wobbling as a result of pedestrian-bridge interactions. Pedestrian phase-locking due to footstep phase adjustment, is suspected to be the main cause of its large lateral vibrations; however, its role in the initiation of wobbling was debated. In this paper, we develop foot force models of pedestrians' response to bridge motion and detailed, yet analytically tractable models of crowd phase-locking. We use bio-mechanically inspired models of crowd lateral movement to investigate to what degree pedestrian synchrony must be present for a bridge to ...

  15. Recording the dynamic endocytosis of single gold nanoparticles by AFM-based force tracing

    Science.gov (United States)

    Ding, Bohua; Tian, Yongmei; Pan, Yangang; Shan, Yuping; Cai, Mingjun; Xu, Haijiao; Sun, Yingchun; Wang, Hongda

    2015-04-01

    We utilized force tracing to directly record the endocytosis of single gold nanoparticles (Au NPs) with different sizes, revealing the size-dependent endocytosis dynamics and the crucial role of membrane cholesterol. The force, duration and velocity of Au NP invagination are accurately determined at the single-particle and microsecond level unprecedentedly.We utilized force tracing to directly record the endocytosis of single gold nanoparticles (Au NPs) with different sizes, revealing the size-dependent endocytosis dynamics and the crucial role of membrane cholesterol. The force, duration and velocity of Au NP invagination are accurately determined at the single-particle and microsecond level unprecedentedly. Electronic supplementary information (ESI) available: Details of the experimental procedures and the results of the control experiments. See DOI: 10.1039/c5nr01020a

  16. An ab initio approach to free-energy reconstruction using logarithmic mean force dynamics.

    Science.gov (United States)

    Nakamura, Makoto; Obata, Masao; Morishita, Tetsuya; Oda, Tatsuki

    2014-05-14

    We present an ab initio approach for evaluating a free energy profile along a reaction coordinate by combining logarithmic mean force dynamics (LogMFD) and first-principles molecular dynamics. The mean force, which is the derivative of the free energy with respect to the reaction coordinate, is estimated using density functional theory (DFT) in the present approach, which is expected to provide an accurate free energy profile along the reaction coordinate. We apply this new method, first-principles LogMFD (FP-LogMFD), to a glycine dipeptide molecule and reconstruct one- and two-dimensional free energy profiles in the framework of DFT. The resultant free energy profile is compared with that obtained by the thermodynamic integration method and by the previous LogMFD calculation using an empirical force-field, showing that FP-LogMFD is a promising method to calculate free energy without empirical force-fields.

  17. Dynamical forcing of sub-seasonal variability in the tropical Brewer-Dobson circulation

    Science.gov (United States)

    Abalos, Marta; Randel, William; Serrano, Encarna

    2014-05-01

    Upwelling across the tropical tropopause exhibits strong sub-seasonal variability superimposed on the well-known annual cycle, and these variations directly affect temperature and tracers in the tropical lower stratosphere. The dynamical forcing of tropical upwelling on sub-seasonal timescales is investigated using the ERA-Interim reanalysis for 1979-2011. Momentum balance diagnostics reveal that transience is linked to the effects of extratropical wave forcing, with centers of action in the extratropical winter stratosphere and in the subtropical upper troposphere of both hemispheres. From a diagnostic point of view, the zonal-mean wind transient response is important for communicating the remote wave forcing to the tropical stratosphere. Dynamical patterns reflect distinctive forcing of the shallow versus deep branches of the Brewer-Dobson circulation.

  18. Research on Dynamic Tension for Belt Conveyor with Constant Force Automatic Take-Up Assembly

    Institute of Scientific and Technical Information of China (English)

    MENG Guo-ying; CHEN Jing-li; LI Yu-jin

    2003-01-01

    The article Provides a dynamic model for belt conveyor. Based on the drive-force of conveyor, take-up tension of take-up assembly, gravity of conveyor belt and material, and friction between belt and idlers, it gives a viscoelastic dynamic equation for conveyor belt. It presents a calculation method of analytic solution to both viscoelastic dynamic equation and geometric dynamic equation when automatic take-up assembly is applied to belt conveyor. The article also makes a study of design method of limiting and eliminating the conveyor belt's elastic vibration.

  19. Accelerated molecular dynamics force evaluation on graphics processing units for thermal conductivity calculations

    OpenAIRE

    Fan, Zheyong; Siro, Topi; Harju, Ari

    2012-01-01

    In this paper, we develop a highly efficient molecular dynamics code fully implemented on graphics processing units for thermal conductivity calculations using the Green-Kubo formula. We compare two different schemes for force evaluation, a previously used thread-scheme where a single thread is used for one particle and each thread calculates the total force for the corresponding particle, and a new block-scheme where a whole block is used for one particle and each thread in the block calcula...

  20. Dynamics of the Dermatologic Microbiome in U.S. Air Force Basic Training

    Science.gov (United States)

    2017-04-05

    DEPARTMENT OF THE AIR FORCE 59TH MEDICAL WING (AETC) JOINT BASE SAN ANTONIO - LACKLAND TEXAS MEMORANDUMFORSGTf ATfN: CAPT ANDREW PATfERSON FROM...59 MDW/SGVU SUBJECT: Professional Presentation Approval 7 APR 20 17 1. Your paper, entitled Dvnamics of the Dermatologic Microbiome in U.S. Air ...PUBLISHED OR PRESENTED: Dynamics of the dennatologic microbiome in U.S. Air Force Basic Training 7. FUNDING RECEIVED FOR THIS STUDY? r8J YES 0 NO

  1. Instrumented Footwear Inserts: A New Tool for Measuring Forces and Biomechanical State Changes During Dynamic Movements

    Science.gov (United States)

    2017-03-03

    1 Instrumented Footwear Inserts: A New Tool For Measuring Forces and Biomechanical State Changes During Dynamic Movements Joe Lacirignola1...bones and joints are repeatedly subjected to aggressive movements and high forces. The ability to measure these elements during training would be a...critical enabler for prevention of injury and development of more quantitative training procedures that focus on ambulatory mobility and agility. It

  2. DYNAMIC COMPACTION OF PURE COPPER POWDER USING PULSED MAGNETIC FORCE

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The compaction of pure Cu powder was carried out through a series of experiments using dynamic magnetic pulse compaction, and the effects of process parameters, such as discharge energy and compacting direction, on the homogeneity and the compaction density of compacted specimens were presented and discussed. The results indicated that the compaction density of specimens increased with the augment of discharge voltage and time. During unidirectional compaction, there was a density gradient along the loading direction in the compacted specimen, and the minimum compaction density was localized to the center of the bottom of the specimen. The larger the aspect ratio of a powder body, the higher the compaction density of the compacted specimen. And high conductivity drivers were beneficial to the increase of the compaction density. The iterative and the double direction compaction were efficient means to manufacture the homogeneous and high-density powder parts.

  3. Galactic Dynamics Using 1/r Force Without Dark Matter

    CERN Document Server

    Lo, Martin Wen-Yu

    2013-01-01

    Dark matter, a conjectured substance not directly observable but which has tremendous mass, was proposed to explain why galaxies hold together and rotate faster at their edges than predicted by Newton's Inverse Square (1/r2) Law of Gravity. Here we propose an alternative, an Inverse Law (1/r), which explains galactic morphology and rotation without dark matter. By varying initial conditions, the Inverse Law can systematically and easily generate realistic galactic formations including spirals, cartwheels (extremely difficult under Newtonian gravity), bars, rings, and spokes. This model can also produce filaments and void structures reminiscent of the large-scale structure of the universe. Newtonian gravity cannot do all this without dark matter. Occam's Razor suggests that at galactic scales, gravity should be 1/r and dark matter is unnecessary. This simple model with its self-organizing emergent properties, combined with dynamical systems theory, has broader implications. It may help us understand more compl...

  4. Haptic perception of force magnitude and its relation to postural arm dynamics in 3D.

    Science.gov (United States)

    van Beek, Femke E; Bergmann Tiest, Wouter M; Mugge, Winfred; Kappers, Astrid M L

    2015-12-08

    In a previous study, we found the perception of force magnitude to be anisotropic in the horizontal plane. In the current study, we investigated this anisotropy in three dimensional space. In addition, we tested our previous hypothesis that the perceptual anisotropy was directly related to anisotropies in arm dynamics. In experiment 1, static force magnitude perception was studied using a free magnitude estimation paradigm. This experiment revealed a significant and consistent anisotropy in force magnitude perception, with forces exerted perpendicular to the line between hand and shoulder being perceived as 50% larger than forces exerted along this line. In experiment 2, postural arm dynamics were measured using stochastic position perturbations exerted by a haptic device and quantified through system identification. By fitting a mass-damper-spring model to the data, the stiffness, damping and inertia parameters could be characterized in all the directions in which perception was also measured. These results show that none of the arm dynamics parameters were oriented either exactly perpendicular or parallel to the perceptual anisotropy. This means that endpoint stiffness, damping or inertia alone cannot explain the consistent anisotropy in force magnitude perception.

  5. Traceable calibration and demonstration of a portable dynamic force transfer standard

    Science.gov (United States)

    Vlajic, Nicholas; Chijioke, Ako

    2017-08-01

    In general, the dynamic sensitivity of a force transducer depends upon the mechanical system in which it is used. This dependence serves as motivation to develop a dynamic force transfer standard, which can be used to calibrate an application transducer in situ. In this work, we SI-traceably calibrate a hand-held force transducer, namely an impact hammer, by using a mass suspended from a thin line which is cut to produce a known dynamic force in the form of a step function. We show that this instrument is a promising candidate as a transfer standard, since its dynamic response has small variance between different users. This calibrated transfer standard is then used to calibrate a secondary force transducer in an example application setting. The combined standard uncertainty (k  =  2) in the calibration of the transfer standard was determined to be 2.1% or less, up to a bandwidth of 5 kHz. The combined standard uncertainty (k  =  2) in the performed transfer calibration was less than 4%, up to 3 kHz. An advantage of the transfer calibration framework presented here, is that the transfer standard can be used to transfer SI-traceable calibrations without the use of any SI-traceable voltage metrology instrumentation.

  6. Effect of three-body forces on the lattice dynamics of noble metals

    Indian Academy of Sciences (India)

    P R Vyas; C V Pandya; T C Pandya; V B Gohel

    2001-04-01

    A simple method to generate an effective electron–ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.

  7. Precision Measurement of the Casimir Force for Au Using a Dynamic Afm

    Science.gov (United States)

    Chang, C.-C.; Banishev, A. A.; Castillo-Garza, R.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.

    2012-07-01

    The gradient of the Casimir force between carefully cleaned Au surfaces of a sphere and a plate is measured using a dynamic atomic force microscope in the frequency modulation regime in high vacuum. The electrostatic calibration of the setup did not reveal any effect of patches or surface contaminants. The experimental data for the force gradient are found to be consistent with theory using the plasma model approach over the entire measurement range. The Drude model approach is excluded by the data at separations from 235 to 400 nm at a 67% confidence level.

  8. Influence of materials' optical response on actuation dynamics by Casimir forces

    Science.gov (United States)

    Sedighi, M.; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.

    2015-06-01

    The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the far-infrared range. For less conductive systems, such as phase change materials or conductive silicon carbide, the reduced force offers the advantage of increased stable operation of MEMS devices against pull-in instabilities that lead to unwanted stiction. Bifurcation analysis with phase portraits has been used to compare the sensitivity of a model actuator when the optical properties are altered.

  9. Dynamics of drag and force distributions for projectile impact in a granular medium

    CERN Document Server

    Ciamarra, M P; Lee, A T; Goldman, D I; Swinney, H L; Ciamarra, Massimo Pica; Lara, Antonio H.; Lee, Andrew T.; Goldman, Daniel I.; Swinney, Harry L.

    2003-01-01

    Our experiments and molecular dynamics simulations on a projectile penetrating a two-dimensional granular medium reveal that the mean deceleration of the projectile is constant and proportional to the impact velocity. Thus, the time taken for a projectile to decelerate to a stop is independent of its impact velocity. The simulations show that the probability distribution function of forces on grains is time-independent during a projectile's penetration of the medium. At all times the force distribution function decreases exponentially for large forces.

  10. Cross talk between matrix elasticity and mechanical force regulates myoblast traction dynamics

    Science.gov (United States)

    Al-Rekabi, Zeinab; Pelling, Andrew E.

    2013-12-01

    Growing evidence suggests that critical cellular processes are profoundly influenced by the cross talk between extracellular nanomechanical forces and the material properties of the cellular microenvironment. Although many studies have examined either the effect of nanomechanical forces or the material properties of the microenvironment on biological processes, few have investigated the influence of both. Here, we performed simultaneous atomic force microscopy and traction force microscopy to demonstrate that muscle precursor cells (myoblasts) rapidly generate a significant increase in traction when stimulated with a local 10 nN force. Cells were cultured and nanomechanically stimulated on hydrogel substrates with controllable local elastic moduli varying from ˜16-89 kPa, as confirmed with atomic force microscopy. Importantly, cellular traction dynamics in response to nanomechanical stimulation only occurred on substrates that were similar to the elasticity of working muscle tissue (˜64-89 kPa) as opposed to substrates mimicking resting tissue (˜16-51 kPa). The traction response was also transient, occurring within 30 s, and dissipating by 60 s, during constant nanomechanical stimulation. The observed biophysical dynamics are very much dependent on rho-kinase and myosin-II activity and likely contribute to the physiology of these cells. Our results demonstrate the fundamental ability of cells to integrate nanoscale information in the cellular microenvironment, such as nanomechanical forces and substrate mechanics, during the process of mechanotransduction.

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

    Science.gov (United States)

    Stehle, Robert

    2017-01-24

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

  12. Quantifying non-ergodic dynamics of force-free granular gases

    OpenAIRE

    Bodrova, Anna; Chechkin, Aleksei V.; Cherstvy, Andrey G.; Metzler, Ralf

    2015-01-01

    Brownianmotion is ergodic in the Boltzmann–Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a...

  13. An attempt to bridge muscle architecture dynamics and its instantaneous rate of force development using ultrasonography.

    Science.gov (United States)

    Li, Jizhou; Zhou, Yongjin; Zheng, Yong-Ping; Li, Guanglin

    2015-08-01

    Muscle force output is an essential index in rehabilitation assessment or physical exams, and could provide considerable insights for various applications such as load monitoring and muscle assessment in sports science or rehabilitation therapy. Besides direct measurement of force output using a dynamometer, electromyography has earlier been used in several studies to quantify muscle force as an indirect means. However, its spatial resolution is easily compromised as a summation of the action potentials from neighboring motor units of electrode site. To explore an alternative method to indirectly estimate the muscle force output, and with better muscle specificity, we started with an investigation on the relationship between architecture dynamics and force output of triceps surae. The muscular architecture dynamics is captured in ultrasonography sequences and estimated using a previously reported motion estimation method. Then an indicator named as the dorsoventrally averaged motion profile (DAMP) is employed. The performance of force output is represented by an instantaneous version of the rate of force development (RFD), namely I-RFD. From experimental results on ten normal subjects, there were significant correlations between the I-RFD and DAMP for triceps surae, both normalized between 0 and 1, with the sum of squares error at 0.0516±0.0224, R-square at 0.7929±0.0931 and root mean squared error at 0.0159±0.0033. The statistical significance results were less than 0.01. The present study suggested that muscle architecture dynamics extracted from ultrasonography during contraction is well correlated to the I-RFD and it can be a promising option for indirect estimation of muscle force output.

  14. Dynamical role of phosphorylation on serine/threonine-proline Pin1 substrates from constant force molecular dynamics simulations.

    Science.gov (United States)

    Velazquez, Hector A; Hamelberg, Donald

    2015-02-21

    Cis-trans isomerization of peptidyl-prolyl bonds of the protein backbone plays an important role in numerous biological processes. Cis-trans isomerization can be the rate-limiting step due its extremely slow dynamics, compared to the millisecond time scale of many processes, and is catalyzed by a widely studied family of peptidyl-prolyl cis-trans isomerase enzymes. Also, mechanical forces along the peptide chain can speed up the rate of isomerization, resulting in "mechanical catalysis," and have been used to study peptidyl-prolyl cis-trans isomerization and other mechanical properties of proteins. Here, we use constant force molecular dynamics simulations to study the dynamical effects of phosphorylation on serine/threonine-proline protein motifs that are involved in the function of many proteins and have been implicated in many aberrant biological processes. We show that the rate of cis-trans isomerization is slowed down by phosphorylation, in excellent agreement with experiments. We use a well-grounded theory to describe the force dependent rate of isomerization. The calculated rates at zero force are also in excellent agreement with experimentally measured rates, providing additional validation of the models and force field parameters. Our results suggest that the slowdown in the rate upon phosphorylation is mainly due to an increase in the friction along the peptidyl-prolyl bond angle during isomerization. Our results provide a microscopic description of the dynamical effects of post-translational phosphorylation on cis-trans isomerization and insights into the properties of proteins under tension.

  15. Relationship between jaw opening force and hyoid bone dynamics in healthy elderly subjects.

    Science.gov (United States)

    Shinozaki, Hiromichi; Tohara, Haruka; Matsubara, Mariko; Inokuchi, Nobuhiro; Yamazaki, Yasuhiro; Nakane, Ayako; Wakasugi, Yoko; Minakuchi, Shunsuke

    2017-01-01

    This study aimed to examine the relationship between jaw opening force and hyoid bone dynamics and resting position in elderly individuals based on gender. Subjects were 36 healthy elderly individuals aged ≥65 years without dysphagia (16 men and 20 women; mean age 75.5 years, range 65-88 years). Videofluorographic images during the swallowing of 10 mL of 40% (w/v) barium sulfate were obtained and the degrees of anterior, superior, and hypotenuse displacements of the hyoid bone and maximum/resting hyoid position were evaluated. Jaw opening force was measured three times using a jaw opening force sthenometer; the mean of these three measurements was used for analysis. In men, there was a positive correlation between jaw opening force and resting hyoid position and negative correlations among all the degrees of anterior, superior, and hypotenuse displacements of the hyoid bone. In women, there was no statistically significant correlation between jaw opening force and any of the measurement items. There was no statistically significant correlation between jaw opening force and maximum hyoid position in either men or women. Our findings suggest that low jaw opening force leads to low resting hyoid position only in elderly men, and a lower hyoid position in healthy elderly men results in a larger total amount of hyoid displacement during swallowing. Moreover, a maximum hyoid position in healthy individuals of either gender does not differ depending on their jaw opening force.

  16. Nonlinear Dynamics of Cantilever-Sample Interactions in Atomic Force Microscopy

    Science.gov (United States)

    Cantrell, John H.; Cantrell, Sean A.

    2010-01-01

    The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation.

  17. Dynamical systems analysis of electrostatic and aerodynamic forced vibrations of a thin flexible electrode

    Science.gov (United States)

    Madanu, Sushma Bala

    Transverse vibrations of an electrostatically actuated thin flexible cantilever perturbed by low-speed air flow is studied using both experiments and numerical modeling. In the experiments the dynamic characteristics of the cantilever are studied by supplying a DC voltage with an AC component for electrostatic forcing and a constant uniform air flow around the cantilever system for aerodynamic forcing. The maximum voltage applied varies from 1 - 9 kV and air flow speeds range from 0.224 - 3.58 m/s (0.5 - 8 mile/hr). The Reynolds numbers for these speeds lie in the range of 1000 - 20000. A range of control parameters leading to stable vibrations are established using the Strouhal number as the operating parameter whose inverse values change from 100 - 2500. The Numerical results are validated with experimental results. Assuming the amplitude of vibrations are small, then a non-linear dynamic Euler-Bernoulli beam equation with viscous damping and gravitational effects is used to model the vibrations of the dynamical system. Aerodynamic forcing is modeled as a temporally sinusoidal and uniform force acting perpendicular to the beam length. The forcing amplitude is found to be proportional to square of air flow velocity by obtaining relationship between the experimental amplitude of vibrations and air flow velocity. Numerical results strongly agree with those of experiments predicting accurate vibration amplitudes, displacement frequency and quasi-periodic displacements of the cantilever tip.

  18. Standard practice for verification of constant amplitude dynamic forces in an axial fatigue testing system

    CERN Document Server

    American Society for Testing and Materials. Philadelphia

    2008-01-01

    1.1 This practice covers procedures for the dynamic verification of cyclic force amplitude control or measurement accuracy during constant amplitude testing in an axial fatigue testing system. It is based on the premise that force verification can be done with the use of a strain gaged elastic element. Use of this practice gives assurance that the accuracies of forces applied by the machine or dynamic force readings from the test machine, at the time of the test, after any user applied correction factors, fall within the limits recommended in Section 9. It does not address static accuracy which must first be addressed using Practices E 4 or equivalent. 1.2 Verification is specific to a particular test machine configuration and specimen. This standard is recommended to be used for each configuration of testing machine and specimen. Where dynamic correction factors are to be applied to test machine force readings in order to meet the accuracy recommended in Section 9, the verification is also specific to the c...

  19. Modeling the desired direction in a force-based model for pedestrian dynamics

    CERN Document Server

    Chraibi, Mohcine; Schadschneider, Andreas; Seyfried, Armin

    2012-01-01

    We introduce an enhanced model based on the generalized centrifugal force model. Furthermore, the desired direction of pedestrians is investigated. A new approach leaning on the well-known concept of static and dynamic floor-fields in cellular automata is presented. Numerical results of the model are presented and compared with empirical data.

  20. Dynamics of a Disturbed Sessile Drop Measured by Atomic Force Microscopy (AFM)

    NARCIS (Netherlands)

    McGuiggan, Patricia M.; Grave, Daniel A.; Wallace, Jay S.; Cheng, Shengfeng; Prosperetti, Andrea; Robbins, Mark O.

    2011-01-01

    A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r 20–30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liq

  1. Dynamical ordering of non-Birkhoff periodic orbits in a forced pendulum

    Energy Technology Data Exchange (ETDEWEB)

    Yamaguchi, Yoshihiro [Teikyo Heisei Univ., Ichihara, Chiba (Japan); Tanikawa, Kiyotaka [National Astronomical Observatory, Mitaka, Tokyo (Japan)

    2001-12-01

    Forced pendulums induce reversible non-monotone twist mappings. Non-Birkhoff periodic orbits (NBO) are found in these mappings, and hence in the pendulums. The existence of an NBO is equivalent to the non-integrability of the system. Two types of dynamical ordering for NBOs are obtained. (author)

  2. Dynamical Ordering of Non-Birkhoff Periodic Orbits in a Forced Pendulum

    Science.gov (United States)

    Yamaguchi, Y.; Tanikawa, K.

    2001-12-01

    Forced pendulums induce reversible non-monotone twist mappings. Non-Birkhoff periodic orbits (NBO) are found in these mappings, and hence in the pendulums. The existence of an NBO is equivalent to the non-integrability of the system. Two types of dynamical ordering for NBOs are obtained.

  3. Boundedness and vanishing of solutions for a forced delay dynamic equation

    Directory of Open Access Journals (Sweden)

    Anderson Douglas R

    2006-01-01

    Full Text Available We give conditions under which all solutions of a time-scale first-order nonlinear variable-delay dynamic equation with forcing term are bounded and vanish at infinity, for arbitrary time scales that are unbounded above. A nontrivial example illustrating an application of the results is provided.

  4. Molecular dynamics simulation study of friction force and torque on a rough spherical particle.

    Science.gov (United States)

    Kohale, Swapnil C; Khare, Rajesh

    2010-06-21

    Recent developments in techniques of micro- and nanofluidics have led to an increased interest in nanoscale hydrodynamics in confined geometries. In our previous study [S. C. Kohale and R. Khare, J. Chem. Phys. 129, 164706 (2008)], we analyzed the friction force experienced by a smooth spherical particle that is translating in a fluid confined between parallel plates. The magnitude of three effects--velocity slip at particle surface, the presence of confining surfaces, and the cooperative hydrodynamic interactions between periodic images of the moving particle--that determine the friction force was quantified in that work using molecular dynamics simulations. In this work, we have studied the motion of a rough spherical particle in a confined geometry. Specifically, the friction force experienced by a translating particle and the torque experienced by a rotating particle are studied using molecular dynamics simulations. Our results demonstrate that the surface roughness of the particle significantly reduces the slip at the particle surface, thus leading to higher values of the friction force and hence a better agreement with the continuum predictions. The particle size dependence of the friction force and the torque values is shown to be consistent with the expectations from the continuum theory. As was observed for the smooth sphere, the cooperative hydrodynamic interactions between the images of the sphere have a significant effect on the value of the friction force experienced by the translating sphere. On the other hand, the torque experienced by a spherical particle that is rotating at the channel center is insensitive to this effect.

  5. Spatial and Temporal Dynamics in the Ionic Driving Force for GABAA Receptors

    Directory of Open Access Journals (Sweden)

    R. Wright

    2011-01-01

    Full Text Available It is becoming increasingly apparent that the strength of GABAergic synaptic transmission is dynamic. One parameter that can establish differences in the actions of GABAergic synapses is the ionic driving force for the chloride-permeable GABAA receptor (GABAAR. Here we review some of the sophisticated ways in which this ionic driving force can vary within neuronal circuits. This driving force for GABAARs is subject to tight spatial control, with the distribution of Cl− transporter proteins and channels generating regional variation in the strength of GABAAR signalling across a single neuron. GABAAR dynamics can result from short-term changes in their driving force, which involve the temporary accumulation or depletion of intracellular Cl−. In addition, activity-dependent changes in the expression and function of Cl− regulating proteins can result in long-term shifts in the driving force for GABAARs. The multifaceted regulation of the ionic driving force for GABAARs has wide ranging implications for mature brain function, neural circuit development, and disease.

  6. Hydrophobic, electrostatic, and dynamic polymer forces at silicone surfaces modified with long-chain bolaform surfactants.

    Science.gov (United States)

    Rapp, Michael V; Donaldson, Stephen H; Gebbie, Matthew A; Das, Saurabh; Kaufman, Yair; Gizaw, Yonas; Koenig, Peter; Roiter, Yuri; Israelachvili, Jacob N

    2015-05-06

    Surfactant self-assembly on surfaces is an effective way to tailor the complex forces at and between hydrophobic-water interfaces. Here, the range of structures and forces that are possible at surfactant-adsorbed hydrophobic surfaces are demonstrated: certain long-chain bolaform surfactants-containing a polydimethylsiloxane (PDMS) mid-block domain and two cationic α, ω-quarternary ammonium end-groups-readily adsorb onto thin PDMS films and form dynamically fluctuating nanostructures. Through measurements with the surface forces apparatus (SFA), it is found that these soft protruding nanostructures display polymer-like exploration behavior at the PDMS surface and give rise to a long-ranged, temperature- and rate-dependent attractive bridging force (not due to viscous forces) on approach to a hydrophilic bare mica surface. Coulombic interactions between the cationic surfactant end-groups and negatively-charged mica result in a rate-dependent polymer bridging force during separation as the hydrophobic surfactant mid-blocks are pulled out from the PDMS interface, yielding strong adhesion energies. Thus, (i) the versatile array of surfactant structures that may form at hydrophobic surfaces is highlighted, (ii) the need to consider the interaction dynamics of such self-assembled polymer layers is emphasized, and (iii) it is shown that long-chain surfactants can promote robust adhesion in aqueous solutions.

  7. Dynamics of the Bogie of Maglev Train with Distributed Magnetic Forces

    Directory of Open Access Journals (Sweden)

    Yaozong Liu

    2015-01-01

    Full Text Available A dynamic model of the bogie of maglev train with distributed magnetic forces and four identical levitating controllers is formulated. The vertical, pitching, and rolling degree of freedom of the electromagnet modules and their coupling are considered. The frequency responses of the bogie to track irregularity are investigated with numerical simulation. The results tell us that there are resonances related to the first electromagnetic suspension whose frequencies are determined by the control parameters. A comparative analysis has been carried out between the models with distributed or concentrated magnetic forces. The comparison indicates that simplifying the distributed magnetic force to concentrated one degenerates the dynamic behavior of the maglev bogie, especially resulting in overestimated resonances of the first electromagnetic suspension of maglev trains. The results also indicate that those resonances only occur on specific wavelengths of irregularity that relate to the length of the electromagnets.

  8. Dynamic tunneling force microscopy for characterizing electronic trap states in non-conductive surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Wang, R.; Williams, C. C., E-mail: clayton@physics.utah.edu [Department of Physics and Astronomy, University of Utah, Salt Lake City, Utah 84112 (United States)

    2015-09-15

    Dynamic tunneling force microscopy (DTFM) is a scanning probe technique for real space mapping and characterization of individual electronic trap states in non-conductive films with atomic scale spatial resolution. The method is based upon the quantum mechanical tunneling of a single electron back and forth between a metallic atomic force microscopy tip and individual trap states in completely non-conducting surface. This single electron shuttling is measured by detecting the electrostatic force induced on the probe tip at the shuttling frequency. In this paper, the physical basis for the DTFM method is unfolded through a physical model and a derivation of the dynamic tunneling signal as a function of several experimental parameters is shown. Experimental data are compared with the theoretical simulations, showing quantitative consistency and verifying the physical model used. The experimental system is described and representative imaging results are shown.

  9. Determination of Quantum Chemistry Based Force Fields for Molecular Dynamics Simulations of Aromatic Polymers

    Science.gov (United States)

    Jaffe, Richard; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Ab initio quantum chemistry calculations for model molecules can be used to parameterize force fields for molecular dynamics simulations of polymers. Emphasis in our research group is on using quantum chemistry-based force fields for molecular dynamics simulations of organic polymers in the melt and glassy states, but the methodology is applicable to simulations of small molecules, multicomponent systems and solutions. Special attention is paid to deriving reliable descriptions of the non-bonded and electrostatic interactions. Several procedures have been developed for deriving and calibrating these parameters. Our force fields for aromatic polyimide simulations will be described. In this application, the intermolecular interactions are the critical factor in determining many properties of the polymer (including its color).

  10. Dynamics and Optimal Feet Force Distributions of a Realistic Four-legged Robot

    Directory of Open Access Journals (Sweden)

    Saurav Agarwal

    2012-08-01

    Full Text Available This paper presents a detailed dynamic modeling of realistic four-legged robot. The direct and inverse kinematic analysis for each leg has been considered in order to develop an overall kinematic model of the robot, when it follows a straight path. This study also aims to estimate optimal feet force distributions of the said robot, which is necessary for its real-time control. Three different approaches namely, minimization of norm of feet forces (approach 1, minimization of norm of joint torques (approach 2 and minimization of norm of joint power (approach 3 have been developed. Simulation result shows that approach 3 is more energy efficient foot force formulation than other two approaches. Lagrange-Euler formulation has been utilized to determine the joint torques. The developed dynamic models have been examined through computer simulation of continuous gait of the four-legged robot.

  11. Modification of 56ACARBO force field for molecular dynamic calculations of chitosan and its derivatives.

    Science.gov (United States)

    Naumov, Vladimir S; Ignatov, Stanislav K

    2017-08-01

    The GROMOS 56ACARBO force field for the description of carbohydrates was modified for calculations of chitosan (poly-1,4-(N-acetyl)-β-D-glucopyranosamine-2) with protonated and non-protonated amino groups and its derivatives. Additional parameterization was developed on the basis of quantum chemical calculations. The modified force field (56ACARBO_CHT) allows performing the molecular dynamic calculations of chitosans with different degrees of protonation corresponding to various acidity of medium. Test calculations of the conformational transitions in the chitosan rings and polymeric chains as well as the chitosan nanocrystal dissolution demonstrate good agreement with experimental data. Graphical abstract The GROMOS 56ACARBO_CHT force field allows performing the molecular dynamic calculations of chitosans with different types of amio-group: free, protonated, substituted.

  12. Complexity of the tensegrity structure for dynamic energy and force distribution of cytoskeleton during cell spreading.

    Directory of Open Access Journals (Sweden)

    Ting-Jung Chen

    Full Text Available Cytoskeleton plays important roles in intracellular force equilibrium and extracellular force transmission from/to attaching substrate through focal adhesions (FAs. Numerical simulations of intracellular force distribution to describe dynamic cell behaviors are still limited. The tensegrity structure comprises tension-supporting cables and compression-supporting struts that represent the actin filament and microtubule respectively, and has many features consistent with living cells. To simulate the dynamics of intracellular force distribution and total stored energy during cell spreading, the present study employed different complexities of the tensegrity structures by using octahedron tensegrity (OT and cuboctahedron tensegrity (COT. The spreading was simulated by assigning specific connection nodes for radial displacement and attachment to substrate to form FAs. The traction force on each FA was estimated by summarizing the force carried in sounding cytoskeletal elements. The OT structure consisted of 24 cables and 6 struts and had limitations soon after the beginning of spreading by declining energy stored in struts indicating the abolishment of compression in microtubules. The COT structure, double the amount of cables and struts than the OT structure, provided sufficient spreading area and expressed similar features with documented cell behaviors. The traction force pointed inward on peripheral FAs in the spread out COT structure. The complex structure in COT provided further investigation of various FA number during different spreading stages. Before the middle phase of spreading (half of maximum spreading area, cell attachment with 8 FAs obtained minimized cytoskeletal energy. The maximum number of 12 FAs in the COT structure was required to achieve further spreading. The stored energy in actin filaments increased as cells spread out, while the energy stored in microtubules increased at initial spreading, peaked in middle phase, and then

  13. Flexible Piezoelectric Tactile Sensor Array for Dynamic Three-Axis Force Measurement.

    Science.gov (United States)

    Yu, Ping; Liu, Weiting; Gu, Chunxin; Cheng, Xiaoying; Fu, Xin

    2016-06-03

    A new flexible piezoelectric tactile sensor array based on polyvinylidene fluoride (PVDF) film is proposed for measuring three-axis dynamic contact force distribution. The array consists of six tactile units arranged as a 3 × 2 matrix with spacing 8 mm between neighbor units. In each unit, a PVDF film is sandwiched between four square-shaped upper electrodes and one square-shaped lower electrode, forming four piezoelectric capacitors. A truncated pyramid bump is located above the four piezoelectric capacitors to improve force transmission. A three-axis contact force transmitted from the top of the bump will lead to the four piezoelectric capacitors underneath undergoing different charge changes, from which the normal and shear components of the force can be calculated. A series of dynamic tests have been carried out by exerting sinusoidal forces with amplitudes ranging from 0 to 0.5 N in the x-axis, 0 to 0.5 N in the y-axis, and 0 to 1.5 N in the z-axis, separately. The tactile units show good sensitivities with 14.93, 14.92, and 6.62 pC/N in the x-, y-, and z-axes, respectively. They can work with good linearity, relatively low coupling effect, high repeatability, and acceptable frequency response in the range of 5-400 Hz to both normal and shear load. In addition, dynamic three-axis force measurement has been conducted for all of the tactile units. The average errors between the applied and calculated forces are 10.68% ± 6.84%. Furthermore, the sensor array can be easily integrated onto a curved surface, such as robotic and prosthetic hands, due to its excellent flexibility.

  14. Mori-Zwanzig theory for dissipative forces in coarse-grained dynamics in the Markov limit

    Science.gov (United States)

    Izvekov, Sergei

    2017-01-01

    We derive alternative Markov approximations for the projected (stochastic) force and memory function in the coarse-grained (CG) generalized Langevin equation, which describes the time evolution of the center-of-mass coordinates of clusters of particles in the microscopic ensemble. This is done with the aid of the Mori-Zwanzig projection operator method based on the recently introduced projection operator [S. Izvekov, J. Chem. Phys. 138, 134106 (2013), 10.1063/1.4795091]. The derivation exploits the "generalized additive fluctuating force" representation to which the projected force reduces in the adopted projection operator formalism. For the projected force, we present a first-order time expansion which correctly extends the static fluctuating force ansatz with the terms necessary to maintain the required orthogonality of the projected dynamics in the Markov limit to the space of CG phase variables. The approximant of the memory function correctly accounts for the momentum dependence in the lowest (second) order and indicates that such a dependence may be important in the CG dynamics approaching the Markov limit. In the case of CG dynamics with a weak dependence of the memory effects on the particle momenta, the expression for the memory function presented in this work is applicable to non-Markov systems. The approximations are formulated in a propagator-free form allowing their efficient evaluation from the microscopic data sampled by standard molecular dynamics simulations. A numerical application is presented for a molecular liquid (nitromethane). With our formalism we do not observe the "plateau-value problem" if the friction tensors for dissipative particle dynamics (DPD) are computed using the Green-Kubo relation. Our formalism provides a consistent bottom-up route for hierarchical parametrization of DPD models from atomistic simulations.

  15. Influence of the 3D inverse dynamic method on the joint forces and moments during gait.

    Science.gov (United States)

    Dumas, R; Nicol, E; Chèze, L

    2007-10-01

    The joint forces and moments are commonly used in gait analysis. They can be computed by four different 3D inverse dynamic methods proposed in the literature, either based on vectors and Euler angles, wrenches and quaternions, homogeneous matrices, or generalized coordinates and forces. In order to analyze the influence of the inverse dynamic method, the joint forces and moments were computed during gait on nine healthy subjects. A ratio was computed between the relative dispersions (due to the method) and the absolute amplitudes of the gait curves. The influence of the inverse dynamic method was negligible at the ankle (2%) but major at the knee and the hip joints (40%). This influence seems to be due to the dynamic computation rather than the kinematic computation. Compared to the influence of the joint center location, the body segment inertial parameter estimation, and more, the influence of the inverse dynamic method is at least of equivalent importance. This point should be confirmed with other subjects, possibly pathologic, and other movements.

  16. Relationship between maximum dynamic force of inferior members and body balance in strength training apprentices

    Directory of Open Access Journals (Sweden)

    Ariane Martins

    2010-08-01

    Full Text Available The relationship between force and balance show controversy results and has directimplications in exercise prescription practice. The objective was to investigate the relationshipbetween maximum dynamic force (MDF of inferior limbs and the static and dynamic balances.Participated in the study 60 individuals, with 18 to 24 years old, strength training apprentices.The MDF was available by mean the One Maximum Repetition (1MR in “leg press” and “kneeextension” and motor testes to available of static and dynamic balances. The correlation testsand multiple linear regression were applied. The force and balance variables showed correlationin females (p=0.038. The corporal mass and static balance showed correlation for the males(p=0.045. The explication capacity at MDF and practices time were small: 13% for staticbalance in males, 18% and 17%, respectively, for static and dynamic balance in females. Inconclusion: the MDF of inferior limbs showed low predictive capacity for performance in staticand dynamic balances, especially for males.

  17. Dynamic tensile forces drive collective cell migration through three-dimensional extracellular matrices

    Science.gov (United States)

    Gjorevski, Nikolce; S. Piotrowski, Alexandra; Varner, Victor D.; Nelson, Celeste M.

    2015-01-01

    Collective cell migration drives tissue remodeling during development, wound repair, and metastatic invasion. The physical mechanisms by which cells move cohesively through dense three-dimensional (3D) extracellular matrix (ECM) remain incompletely understood. Here, we show directly that migration of multicellular cohorts through collagenous matrices occurs via a dynamic pulling mechanism, the nature of which had only been inferred previously in 3D. Tensile forces increase at the invasive front of cohorts, serving a physical, propelling role as well as a regulatory one by conditioning the cells and matrix for further extension. These forces elicit mechanosensitive signaling within the leading edge and align the ECM, creating microtracks conducive to further migration. Moreover, cell movements are highly correlated and in phase with ECM deformations. Migrating cohorts use spatially localized, long-range forces and consequent matrix alignment to navigate through the ECM. These results suggest biophysical forces are critical for 3D collective migration. PMID:26165921

  18. Wheel-rail dynamic forces induced by random vertical track irregularities

    Science.gov (United States)

    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.

  19. An Improved Force-Angle Stability Margin for Radial Symmetrical Hexapod Robot Subject to Dynamic Effects

    Directory of Open Access Journals (Sweden)

    Shidong Long

    2015-05-01

    Full Text Available This paper presents a study on stability monitoring for a radial symmetrical hexapod robot under dynamic conditions. The force-angle stability margin (FASM measure method has been chosen as the stability criterion. This is because it is suitable for the stability analysis, in terms of external forces or manipulator loads acting on the body. Considering that a radial symmetrical hexapod robot can tumble along the contact point besides tip-over axis, this paper proposes an improved FASM measure method. Furthermore, it provides the method for calculating the stability angle of contact point and simplifies the algorithm of FASM. To verify the improved FASM measure method, three potential dynamic situations have been simulated. The simulation results confirm that, under dynamic conditions, the improved FASM is efficient, simple in terms of calculation cost and sensitive to manipulator loads and external disturbances. This means it has practical value in on-line controllers.

  20. The Dynamics of Voluntary Force Production in Afferented Muscle Influence Involuntary Tremor

    Directory of Open Access Journals (Sweden)

    Christopher M Laine

    2016-08-01

    Full Text Available Voluntary control of force is always marked by some degree of error and unsteadiness. Both neural and mechanical factors contribute to these fluctuations, but how they interact to produce them is poorly understood. In this study, we identify and characterize a previously undescribed neuromechanical interaction where the dynamics of voluntary force production suffice to generate involuntary tremor. Specifically, participants were asked to produce isometric force with the index finger and use visual feedback to track a sinusoidal target spanning 5 to 9 % of each individual’s maximal voluntary force level. Force fluctuations and EMG activity over the flexor digitorum superficialis (FDS muscle were recorded and their frequency content was analyzed as a function target phase. Force variability in either the 1 to 5 or 6 to 15 Hz frequency ranges tended to be largest at the peaks and valleys of the target sinusoid. In those same periods, FDS EMG activity was synchronized with force fluctuations. We then constructed a physiologically-realistic computer simulation in which a muscle-tendon complex was set inside of a feedback-driven control loop. Surprisingly, the model sufficed to produce phase-dependent modulation of tremor similar to that observed in humans. Further, the gain of afferent feedback from muscle spindles was critical for appropriately amplifying and shaping this tremor. We suggest that the experimentally-induced tremor may represent the response of a viscoelastic muscle-tendon system to dynamic drive, and therefore does not fall into known categories of tremor generation, such as tremorogenic descending drive, stretch-reflex loop oscillations, motor unit behavior, or mechanical resonance. Our findings motivate future efforts to understand tremor from a perspective that considers neuromechanical coupling within the context of closed-loop control. The strategy of combining experimental recordings with physiologically-sound simulations will

  1. Forced extension of P-selectin construct using steered molecular dynamics

    Institute of Scientific and Technical Information of China (English)

    L(U) Shouqin; LONG Mian

    2004-01-01

    P-selectin, a 70-nm-long cellular adhesive molecule, possesses elastic and extensible properties when neutrophils roll over the activated endotheliam of blood vessel in inflammatory reaction. Transient formation and dissociation of P-selectin/ligand bond on applied force of blood flow induces the extension of P-selectin and relevant ligands. Steered molecular dynamics simulations were performed to stretch a single P-selectin construct consisting of a lectin (Lec) domain and an epithelial growth factor (EGF)-like domain, where P-selectin construct was forced to extend in water with pulling velocities of 0.005-0.05 nm/ps and with constant forces of 1000-2500 pN respectively. Resulting force-extension profiles exhibited a dual-peak pattern on vari- ous velocities, while both plateaus and shoulders appeared in the extension-time profiles on various forces. The force or extension profiles along stretching pathways were correlated to the conformational changes, suggesting that the structural collapses of P-selectin Lec/EGF domains were mainly attributed to the burst of hydrogen bonds within the major βsheet of EGF domain and the disruptions of two hydrophobic cores of Lec domain. This work furthers the understanding of forced dissociation of P-selectin/ligand bond.

  2. Dynamic peripheral traction forces balance stable neurite tension in regenerating Aplysia bag cell neurons.

    Science.gov (United States)

    Hyland, Callen; Mertz, Aaron F; Forscher, Paul; Dufresne, Eric

    2014-05-14

    Growth cones of elongating neurites exert force against the external environment, but little is known about the role of force in outgrowth or its relationship to the mechanical organization of neurons. We used traction force microscopy to examine patterns of force in growth cones of regenerating Aplysia bag cell neurons. We find that traction is highest in the peripheral actin-rich domain and internal stress reaches a plateau near the transition between peripheral and central microtubule-rich domains. Integrating stress over the area of the growth cone reveals that total scalar force increases with area but net tension on the neurite does not. Tensions fall within a limited range while a substantial fraction of the total force can be balanced locally within the growth cone. Although traction continuously redistributes during extension and retraction of the peripheral domain, tension is stable over time, suggesting that tension is a tightly regulated property of the neurite independent of growth cone dynamics. We observe that redistribution of traction in the peripheral domain can reorient the end of the neurite shaft. This suggests a role for off-axis force in growth cone turning and neuronal guidance.

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

    Science.gov (United States)

    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.

  4. Computational Intelligence Based Data Fusion Algorithm for Dynamic sEMG and Skeletal Muscle Force Modelling

    Energy Technology Data Exchange (ETDEWEB)

    Chandrasekhar Potluri,; Madhavi Anugolu; Marco P. Schoen; D. Subbaram Naidu

    2013-08-01

    In this work, an array of three surface Electrography (sEMG) sensors are used to acquired muscle extension and contraction signals for 18 healthy test subjects. The skeletal muscle force is estimated using the acquired sEMG signals and a Non-linear Wiener Hammerstein model, relating the two signals in a dynamic fashion. The model is obtained from using System Identification (SI) algorithm. The obtained force models for each sensor are fused using a proposed fuzzy logic concept with the intent to improve the force estimation accuracy and resilience to sensor failure or misalignment. For the fuzzy logic inference system, the sEMG entropy, the relative error, and the correlation of the force signals are considered for defining the membership functions. The proposed fusion algorithm yields an average of 92.49% correlation between the actual force and the overall estimated force output. In addition, the proposed fusionbased approach is implemented on a test platform. Experiments indicate an improvement in finger/hand force estimation.

  5. Vehicle Sliding Mode Control with Adaptive Upper Bounds: Static versus Dynamic Allocation to Saturated Tire Forces

    Directory of Open Access Journals (Sweden)

    Ali Tavasoli

    2012-01-01

    Full Text Available Nonlinear vehicle control allocation is achieved through distributing the task of vehicle control among individual tire forces, which are constrained to nonlinear saturation conditions. A high-level sliding mode control with adaptive upper bounds is considered to assess the body yaw moment and lateral force for the vehicle motion. The proposed controller only requires the online adaptation of control gains without acquiring the knowledge of upper bounds on system uncertainties. Static and dynamic control allocation approaches have been formulated to distribute high-level control objectives among the system inputs. For static control allocation, the interior-point method is applied to solve the formulated nonlinear optimization problem. Based on the dynamic control allocation method, a dynamic update law is derived to allocate vehicle control to tire forces. The allocated tire forces are fed into a low-level control module, where the applied torque and active steering angle at each wheel are determined through a slip-ratio controller and an inverse tire model. Computer simulations are used to prove the significant effects of the proposed control allocation methods on improving the stability and handling performance. The advantages and limitations of each method have been discussed, and conclusions have been derived.

  6. Anharmonic force constants extracted from first-principles molecular dynamics: applications to heat transfer simulations.

    Science.gov (United States)

    Tadano, T; Gohda, Y; Tsuneyuki, S

    2014-06-04

    A systematic method to calculate anharmonic force constants of crystals is presented. The method employs the direct-method approach, where anharmonic force constants are extracted from the trajectory of first-principles molecular dynamics simulations at high temperature. The method is applied to Si where accurate cubic and quartic force constants are obtained. We observe that higher-order correction is crucial to obtain accurate force constants from the trajectory with large atomic displacements. The calculated harmonic and anharmonic force constants are, then, combined with the Boltzmann transport equation (BTE) and non-equilibrium molecular dynamics (NEMD) methods in calculating the thermal conductivity. The BTE approach successfully predicts the lattice thermal conductivity of bulk Si, whereas NEMD shows considerable underestimates. To evaluate the linear extrapolation method employed in NEMD to estimate bulk values, we analyze the size dependence in NEMD based on BTE calculations. We observe strong nonlinearity in the size dependence of NEMD in Si, which can be ascribed to acoustic phonons having long mean-free-paths and carrying considerable heat. Subsequently, we also apply the whole method to a thermoelectric material Mg2Si and demonstrate the reliability of the NEMD method for systems with low thermal conductivities.

  7. On the Effectiveness of the Dynamic Force Adjustment for Reducing the Scatter of Instrumented Charpy Results

    Energy Technology Data Exchange (ETDEWEB)

    Lucon, E.

    2008-09-15

    One of the key factors for obtaining reliable instrumented Charpy results is the calibration of the instrumented striker. An interesting alternative to the conventional static calibration recommended by the standards is the Dynamic Force Adjustment (DFA), in which forces and displacements are iteratively adjusted until equality is achieved between absorbed energies calculated under the test record (Wt) and measured by the machine encoder (KV). In this study, this procedure has been applied to the instrumented data obtained by 10 international laboratories using notched and precracked Charpy specimens, in the framework of a Coordinated Research Project (CRP8) of IAEA. DFA is extremely effective in reducing the between-laboratory scatter for both general yield and maximum forces. The effect is less significant for dynamic reference temperatures measured from precracked Charpy specimens using the Master Curve procedure, but a moderate reduction of the standard deviation is anyway observed. It is shown that striker calibration is a prominent contribution to the interlaboratory variability of instrumented impact forces, particularly in the case of maximum forces.

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

    Science.gov (United States)

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

    2012-01-17

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

  9. Lateral shear forces applied to cells with single elastic micropillars to influence focal adhesion dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Heil, Patrick; Spatz, Joachim P, E-mail: spatz@mf.mpg.d [Department of New Materials and Biosystems, Max Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart (Germany); Department of Biophysical Chemistry, University of Heidelberg, Heisenbergstrasse 3, D-70569 Stuttgart (Germany)

    2010-05-19

    Focal adhesions (FAs) are important adhesion sites between eukaryotic cells and the extracellular matrix, their size depending on the locally applied force. To quantitatively study the mechanosensitivity of FAs, we induce their growth and disassembly by varying the distribution of intracellular stress. We present a novel method for micromanipulation of living cells to explore the dynamics of focal adhesion (FA) assembly under force. Fibroblasts are sheared laterally to their adhesion surface with single PDMS micropillars in order to apply laterally stretch or compression to focal adhesions. This allows for measuring the shear force exerted by the micropillar and correlates it with FA length and growth velocity. Furthermore, we analyze the resulting dynamics of FA molecules (paxillin) and compare intensity profiles along FAs before and after the application of external force. The responses of stretched and relaxed FAs differ fundamentally: relaxed and compressed FAs disassemble isotropically and show no length variation while stretched FAs grow unisotropically in the direction of the applied force and show protein influx only at their front.

  10. A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants

    Directory of Open Access Journals (Sweden)

    James P. Ewen

    2016-08-01

    Full Text Available For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, the accuracy of the results depend on the chosen force-field. In this study, we demonstrate that the use of an accurate, all-atom force-field is critical in order to; (i accurately predict important properties of long-chain, linear molecules; and (ii reproduce experimental friction behavior of multi-component tribological systems. In particular, we focus on n-hexadecane, an important model lubricant with a wide range of industrial applications. Moreover, simulating conditions common in tribological systems, i.e., high temperatures and pressures (HTHP, allows the limits of the selected force-fields to be tested. In the first section, a large number of united-atom and all-atom force-fields are benchmarked in terms of their density and viscosity prediction accuracy of n-hexadecane using equilibrium molecular dynamics (EMD simulations at ambient and HTHP conditions. Whilst united-atom force-fields accurately reproduce experimental density, the viscosity is significantly under-predicted compared to all-atom force-fields and experiments. Moreover, some all-tom force-fields yield elevated melting points, leading to significant overestimation of both the density and viscosity. In the second section, the most accurate united-atom and all-atom force-field are compared in confined NEMD simulations which probe the structure and friction of stearic acid adsorbed on iron oxide and separated by a thin layer of n-hexadecane. The united-atom force-field provides an accurate representation of the structure of the confined stearic acid film; however, friction coefficients are

  11. A Database of Force-Field Parameters, Dynamics, and Properties of Antimicrobial Compounds

    Directory of Open Access Journals (Sweden)

    Giuliano Malloci

    2015-08-01

    Full Text Available We present an on-line database of all-atom force-field parameters and molecular properties of compounds with antimicrobial activity (mostly antibiotics and some beta-lactamase inhibitors. For each compound, we provide the General Amber Force Field parameters for the major species at physiological pH, together with an analysis of properties of interest as extracted from µs-long molecular dynamics simulations in explicit water solution. The properties include number and population of structural clusters, molecular flexibility, hydrophobic and hydrophilic molecular surfaces, the statistics of intraand inter-molecular H-bonds, as well as structural and dynamical properties of solvent molecules within first and second solvation shells. In addition, the database contains several key molecular parameters, such as energy of the frontier molecular orbitals, vibrational properties, rotational constants, atomic partial charges and electric dipole moment, computed by Density Functional Theory. The present database (to our knowledge the first extensive one including dynamical properties is part of a wider project aiming to build-up a database containing structural, physico-chemical and dynamical properties of medicinal compounds using different force-field parameters with increasing level of complexity and reliability. The database is freely accessible at http://www.dsf.unica.it/translocation/db/.

  12. Studying Climate Response to Forcing by the Nonlinear Dynamical Mode Decomposition

    Science.gov (United States)

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

    2017-04-01

    An analysis of global climate response to external forcing, both anthropogenic (mainly, CO2 and aerosol) and natural (solar and volcanic), is needed for adequate predictions of global climate change. Being complex dynamical system, the climate reacts to external perturbations exciting feedbacks (both positive and negative) making the response non-trivial and poorly predictable. Thus an extraction of internal modes of climate system, investigation of their interaction with external forcings and further modeling and forecast of their dynamics, are all the problems providing the success of climate modeling. In the report the new method for principal mode extraction from climate data is presented. The method is based on the Nonlinear Dynamical Mode (NDM) expansion [1,2], but takes into account a number of external forcings applied to the system. Each NDM is represented by hidden time series governing the observed variability, which, together with external forcing time series, are mapped onto data space. While forcing time series are considered to be known, the hidden unknown signals underlying the internal climate dynamics are extracted from observed data by the suggested method. In particular, it gives us an opportunity to study the evolution of principal system's mode structure in changing external conditions and separate the internal climate variability from trends forced by external perturbations. Furthermore, the modes so obtained can be extrapolated beyond the observational time series, and long-term prognosis of modes' structure including characteristics of interconnections and responses to external perturbations, can be carried out. In this work the method is used for reconstructing and studying the principal modes of climate variability on inter-annual and decadal time scales accounting the external forcings such as anthropogenic emissions, variations of the solar activity and volcanic activity. The structure of the obtained modes as well as their response to

  13. A novel proof of the DFT formula for the interatomic force field of Molecular Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Morante, S., E-mail: morante@roma2.infn.it [Dipartimento di Fisica, Università di Roma, “ Tor Vergata ”, INFN, Sezione di Roma 2, Via della Ricerca Scientifica - 00133 Roma (Italy); Rossi, G.C., E-mail: rossig@roma2.infn.it [Dipartimento di Fisica, Università di Roma, “ Tor Vergata ”, INFN, Sezione di Roma 2, Via della Ricerca Scientifica - 00133 Roma (Italy); Centro Fermi-Museo Storico della Fisica e Centro Studi e Ricerche E. Fermi, Compendio del Viminale, Piazza del Viminale 1, I-00184 Rome (Italy)

    2017-02-15

    We give a novel and simple proof of the DFT expression for the interatomic force field that drives the motion of atoms in classical Molecular Dynamics, based on the observation that the ground state electronic energy, seen as a functional of the external potential, is the Legendre transform of the Hohenberg–Kohn functional, which in turn is a functional of the electronic density. We show in this way that the so-called Hellmann–Feynman analytical formula, currently used in numerical simulations, actually provides the exact expression of the interatomic force.

  14. A novel proof of the DFT formula for the interatomic force field of Molecular Dynamics

    Science.gov (United States)

    Morante, S.; Rossi, G. C.

    2017-02-01

    We give a novel and simple proof of the DFT expression for the interatomic force field that drives the motion of atoms in classical Molecular Dynamics, based on the observation that the ground state electronic energy, seen as a functional of the external potential, is the Legendre transform of the Hohenberg-Kohn functional, which in turn is a functional of the electronic density. We show in this way that the so-called Hellmann-Feynman analytical formula, currently used in numerical simulations, actually provides the exact expression of the interatomic force.

  15. Parametrization of a Reactive Force Field (ReaxFF) for Molecular Dynamics Simulations of Si Nanoparticles.

    Science.gov (United States)

    Barcaro, Giovanni; Monti, Susanna; Sementa, Luca; Carravetta, Vincenzo

    2017-08-08

    A novel computational approach, based on classical reactive molecular dynamics simulations (RMD) and quantum chemistry (QC) global energy optimizations, is proposed for modeling large Si nanoparticles. The force field parameters, which can describe bond breaking and formation, are derived by reproducing energetic and structural properties of a set of Si clusters increasing in size. These reference models are obtained through a new protocol based on a joint high temperature RMD/low temperature Basin Hopping QC search. The different procedures of estimating optimal force field parameters and their performance are discussed in detail.

  16. Static and dynamic stability of the guidance force in a side-suspended HTS maglev system

    Science.gov (United States)

    Zhou, Dajin; Cui, Chenyu; Zhao, Lifeng; Zhang, Yong; Wang, Xiqing; Zhao, Yong

    2017-02-01

    The static and dynamic stability of the guidance force in a side-suspended HTS-PMG (permanent magnetic guideway) system were studied theoretically and experimentally. It is found that there are two types of guidance force that exist in the HTS-PMG system, which are sensitive to the levitation gap and the arrangement of YBCO bulks around the central axis of the PMG. An optimized YBCO array was used to stabilize the system, which enabled a side-suspended HTS-PMG maglev vehicle to run stably at 102 km h-1 on a circular test track with 6.5 m in diameter.

  17. Prioritized motion-force control of constrained fully-actuated robots: "Task Space Inverse Dynamics"

    OpenAIRE

    Del Prete, Andrea; Nori, Francesco; Metta, Giorgio; Natale, Lorenzo

    2014-01-01

    We present a new framework for prioritized multi-task motion-force control of fully-actuated robots. This work is established on a careful review and comparison of the state of the art. Some control frameworks are not optimal, that is they do not find the optimal solution for the secondary tasks. Other frameworks are optimal, but they tackle the control problem at kinematic level, hence they neglect the robot dynamics and they do not allow for force control. Still other frameworks are optimal...

  18. Dynamic force response of spherical hydrostatic journal bearing for cryogenic applications

    Science.gov (United States)

    Sanandres, Luis

    1994-01-01

    Hydrostatic Journal Bearings (HJB's) are reliable and resilient fluid film rotor support elements ideal to replace roller bearings in cryogenic turbomachinery. HJB' will be used for primary space-power applications due to their long lifetime, low friction and wear, large load capacity, large direct stiffness, and damping force coefficients. An analysis for the performance characteristics of turbulent flow, orifice compensated, spherical hydrostatic journal bearings (HJB's) is presented. Spherical bearings allow tolerance for shaft misalignment without force performance degradation and have also the ability to support axial loads. The spherical HJB combines these advantages to provide a bearing design which could be used efficiently on high performance turbomachinery. The motion of a barotropic liquid on the thin film bearing lands is described by bulk-flow mass and momentum equations. These equations are solved numerically using an efficient CFD method. Numerical predictions of load capacity and force coefficients for a 6 recess, spherical HJB in a LO2 environment are presented. Fluid film axial forces and force coefficients of a magnitude about 20% of the radial load capacity are predicted for the case analyzed. Fluid inertia effects, advective and centrifugal, are found to affect greatly the static and dynamic force performance of the bearing studied.

  19. Relative dynamics and control of spacecraft formations subject to lorentz force perturbations

    Science.gov (United States)

    Abdel-Aziz, Yehia; Shoaib, Muhammad

    A spacecraft that generates an electrostatic charge on its surface in the Earth magnetic field will be subject to a perturbative Lorentz force. The Lorentz force acting on an electrostatically charged spacecraft may provide a useful thrust for controlling a spacecraft’s orbit. We develop Lorentz force as a function of the orbital elements. The orbital perturbations of a charged spacecraft by Lorentz force in the Earth’s magnetic field are investigated using the Gauss variation of the Lagrange planetary Equations. The Earth’s magnetic field is modeled as a tilted dipole. The perturbations in the orbital elements depend on the value of the charge to mass ratio (q/m). The dynamical model of relative motion developed leads to approximate analytical solutions for the motion of a charged spacecraft subject to Lorentz force. The chief spacecraft’s reference orbit is taken to be either circular or elliptical. The deputy spacecraft is capable of accumulating electrostatic charge. The numerical results show that Lorentz force can be used to change the in-track position and plane orbit of the spacecraft. The numerical analysis shows that the target trajectory of the Lorentz spacecraft can be reached by varying the ratio (q/m) in different Low Earth Orbits.

  20. Nonlinear Dynamical Analysis for the Cable Excited with Parametric and Forced Excitation

    Directory of Open Access Journals (Sweden)

    C. Z. Qian

    2014-01-01

    Full Text Available Considering the deck vibration effect on the cable in cable-stayed bridge, using nonlinear structure dynamics theory, the nonlinear dynamical equation for the stayed cable excited with deck vibration is proposed. Research shows that the vertical vibration of the deck has a combined parametric and forced excitation effect on the cable when the angle of the cable is taken into consideration. Using multiscale method, the 1/2 principle parametric resonance is studied and the bifurcation equation is obtained. Despite the parameters analysis, the bifurcation characters of the dynamical system are studied. At last, by means of numerical method and software MATHMATIC, the effect rules of system parameters to the dynamical behavior of the system are studied, and some useful conclusions are obtained.

  1. Multipolar Force Fields and Their Effects on Solvent Dynamics around Simple Solutes

    DEFF Research Database (Denmark)

    Jakobsen, Sofie; Bereau, Tristan; Meuwly, Markus

    2015-01-01

    The performance of multipole (MTP) and point charge (PC) force fields in classical molecular dynamics (MD) simulations of condensed-phase systems for both equilibrium and dynamical quantities is compared. MTP electrostatics provides an improved description of the anisotropic electrostatic potential......, which is especially important to describe key, challenging interactions, such as lone pairs, π-interactions, and hydrogen bonds. These chemical environments are probed by focusing on the hydration properties of two molecules: N-methylacetamide and phenyl bromide. Both, equilibrium and dynamical......, quantities are affected by the quality of the electrostatic model. The alteration of the first solvation shell in MTP simulations is validated by comparing with lifetimes and correlation times of solute–solvent interactions from experiment. The improved dynamical behavior found in the MTP simulations...

  2. A review of dynamic stability of repulsive-force maglev suspension systems

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Y.; Rote, D.M.

    1998-07-01

    Vehicle dynamics and the need to satisfy ride quality requirements have long been recognized as crucial to the commercial success of passenger-carrying transportation systems. Design concepts for maglev systems are no exception. Early maglev investigators and designers were well aware of the importance of ride quality and took care to ensure that their designs would meet acceptable ride quality standards. In contrast, the dynamic stability of electrodynamic suspension (EDS) systems, which has obvious implications for system safety and cost as well as for ride quality, has not received nearly as much attention. Because of the well-known under-damped nature of EDS suspension systems and the observation of instabilities in laboratory-scale model systems, it is prudent to develop a better understanding of vehicle stability characteristics. The work reported in this was undertaken with the intention of summarizing information that has been accumulated worldwide and that is relevant to dynamic stability of repulsive-force maglev suspension systems, assimilating that information, and gaining an understanding of the factors that influence that stability. Included in the paper is a discussion and comparison of results acquired from some representative tests of large-scale vehicles on linear test tracks, together with analytical and laboratory-scale investigations of stability and dynamics of EDS systems. This paper will also summarize the R and D activities at Argonne National Laboratory (ANL) since 1991 to study the nature of the forces that are operative in an EDS system and the dynamic stability of such systems.

  3. Position Control of Linear Synchronous Motor Drives with Exploitation of Forced Dynamics Control Principles

    Directory of Open Access Journals (Sweden)

    Jan Vittek

    2004-01-01

    Full Text Available Closed-loop position control of mechanisms directly driven by linear synchronous motors with permanent magnets is presented. The control strategy is based on forced dynamic control, which is a form of feedback linearisation, yielding a non-liner multivariable control law to obtain a prescribed linear speed dynamics together with the vector control condition of mutal orthogonality between the stator current and magnetic flux vectors (assuming perfect estimates of the plant parameters. Outer position control loop is closed via simple feedback with proportional gain. Simulations of the design control sysstem, including the drive with power electronic switching, predict the intended drive performance.

  4. Preliminary Experimental Results for Indirect Vector-Control of Induction Motor Drives with Forced Dynamics

    Directory of Open Access Journals (Sweden)

    Jan Vittek

    2003-01-01

    Full Text Available The contribution presents an extension of indirect vector control of electric drives employing induction motors to 'Forced Dynamic Control'. This method of control offers an accurate realisation of dynamic response profiles, which can be selected by the user. The developed system can be integrated into a drive with a shaft position encoder or a shaft sensoriess drive, in which only the stator currents are measured. The applied stator voltages are determined by a computed inverter switching algorithm. Simulation results and preliminary experimental results for indirect vector control of an idle running induction motor indicate good agreement with the theoretical predictions.

  5. Parameter estimation of social forces in pedestrian dynamics models via a probabilistic method.

    Science.gov (United States)

    Corbetta, Alessandro; Muntean, Adrian; Vafayi, Kiamars

    2015-04-01

    Focusing on a specific crowd dynamics situation, including real life experiments and measurements, our paper targets a twofold aim: (1) we present a Bayesian probabilistic method to estimate the value and the uncertainty (in the form of a probability density function) of parameters in crowd dynamic models from the experimental data; and (2) we introduce a fitness measure for the models to classify a couple of model structures (forces) according to their fitness to the experimental data, preparing the stage for a more general model-selection and validation strategy inspired by probabilistic data analysis. Finally, we review the essential aspects of our experimental setup and measurement technique.

  6. State Feedback Control for Adjusting the Dynamic Behavior of a Piezoactuated Bimorph Atomic Force Microscopy Probe

    CERN Document Server

    Orun, Bilal; Basdogan, Cagatay; Guvenc, Levent

    2012-01-01

    We adjust the transient dynamics of a piezo-actuated bimorph Atomic Force Microscopy (AFM) probe using a state feedback controller. This approach enables us to adjust the quality factor and the resonance frequency of the probe simultaneously. First, we first investigate the effect of feedback gains on dynamic response of the probe and then show that the time constant of the probe can be reduced by reducing its quality factor and/or increasing its resonance frequency to reduce the scan error in tapping mode AFM.

  7. Dissolution study of active pharmaceutical ingredients using molecular dynamics simulations with classical force fields

    Science.gov (United States)

    Greiner, Maximilian; Elts, Ekaterina; Schneider, Julian; Reuter, Karsten; Briesen, Heiko

    2014-11-01

    The CHARMM, general Amber and OPLS force fields are evaluated for their suitability in simulating the molecular dynamics of the dissolution of the hydrophobic, small-molecule active pharmaceutical ingredients aspirin, ibuprofen, and paracetamol in aqueous media. The force fields are evaluated by comparison with quantum chemical simulations or experimental references on the basis of the following capabilities: accurately representing intra- and intermolecular interactions, appropriately reproducing crystal lattice parameters, adequately describing thermodynamic properties, and the qualitative description of the dissolution behavior. To make this approach easily accessible for evaluating the dissolution properties of novel drug candidates in the early stage of drug development, the force field parameter files are generated using online resources such as the SWISS PARAM servers, and the software packages ACPYPE and Maestro. All force fields are found to reproduce the intermolecular interactions with a reasonable degree of accuracy, with the general Amber and CHARMM force fields showing the best agreement with quantum mechanical calculations. A stable crystal bulk structure is obtained for all model substances, except for ibuprofen, where the reproductions of the lattice parameters and observed crystal stability are considerably poor for all force fields. The heat of solution used to evaluate the solid-to-solution phase transitions is found to be in qualitative agreement with the experimental data for all combinations tested, with the results being quantitatively optimum for the general Amber and CHARMM force fields. For aspirin and paracetamol, stable crystal-water interfaces were obtained. The (100), (110), (011) and (001) interfaces of aspirin or paracetamol and water were simulated for each force field for 30 ns. Although generally expected as a rare event, in some of the simulations, dissolution is observed at 310 K and ambient pressure conditions.

  8. Relationship between jaw opening force and hyoid bone dynamics in healthy elderly subjects

    Directory of Open Access Journals (Sweden)

    Shinozaki H

    2017-04-01

    Full Text Available Hiromichi Shinozaki, Haruka Tohara, Mariko Matsubara, Nobuhiro Inokuchi, Yasuhiro Yamazaki, Ayako Nakane, Yoko Wakasugi, Shunsuke Minakuchi Department of Gerodontology, Tokyo Medical and Dental University, Tokyo, Japan Purpose: This study aimed to examine the relationship between jaw opening force and hyoid bone dynamics and resting position in elderly individuals based on gender. Subjects and methods: Subjects were 36 healthy elderly individuals aged ≥65 years without dysphagia (16 men and 20 women; mean age 75.5 years, range 65–88 years. Videofluorographic images during the swallowing of 10 mL of 40% (w/v barium sulfate were obtained and the degrees of anterior, superior, and hypotenuse displacements of the hyoid bone and maximum/resting hyoid position were evaluated. Jaw opening force was measured three times using a jaw opening force sthenometer; the mean of these three measurements was used for analysis. Results: In men, there was a positive correlation between jaw opening force and resting hyoid position and negative correlations among all the degrees of anterior, superior, and hypotenuse displacements of the hyoid bone. In women, there was no statistically significant correlation between jaw opening force and any of the measurement items. There was no statistically significant correlation between jaw opening force and maximum hyoid position in either men or women. Conclusion: Our findings suggest that low jaw opening force leads to low resting hyoid position only in elderly men, and a lower hyoid position in healthy elderly men results in a larger total amount of hyoid displacement during swallowing. Moreover, a maximum hyoid position in healthy individuals of either gender does not differ depending on their jaw opening force. Keywords: aging, deglutition disorders, dysphasia, gender differences

  9. Capillary climb dynamics in the limits of prevailing capillary and gravity force.

    Science.gov (United States)

    Bijeljic, B; Markicevic, B; Navaz, H K

    2011-05-01

    The dynamics of capillary climb of a wetting liquid into a porous medium that is opposed by gravity force is studied numerically. We use the capillary network model, in which an actual porous medium is represented as a network of pores and throats, each following a predefined size distribution function. The liquid potential in the pores along the liquid interface within the network is calculated as a result of capillary and gravity forces. The solution is general, and accounts for changes in the climbing height and climbing velocity. The numerical results for the capillary climb reveal that there are at least two distinct flow mechanisms. Initially, the flow is characterized by high climbing velocity, in which the capillary force is higher than the gravity force, and the flow is the viscous force dominated. For this single-phase flow, the Washburn equation can be used to predict the changes of climbing height over time. Later, for longer times and larger climbing height, the capillary and gravity forces become comparable, and one observes a slower increase in the climbing height as a function of time. Due to the two forces being comparable, the gas-liquid sharp interface transforms into flow front, where the multiphase flow develops. The numerical results from this study, expressed as the climbing height as a power law function of time, indicate that the two powers, which correspond to the two distinct mechanisms, differ significantly. The comparison of the powers with experimental data indicates good agreement. Furthermore, the power value from the Washburn solution is also analyzed, where it should be equal to 1/2 for purely viscous force driven flow. This is in contrast to the power value of ∼0.43 that is found experimentally. We show from the numerical solution that this discrepancy is due to the momentum dissipation on the liquid interface.

  10. Force Relations and Dynamics of Cutting Knife in a Vertical Disc Mobile Wood Chipper

    Directory of Open Access Journals (Sweden)

    Segun R. BELLO

    2011-06-01

    Full Text Available The force relations and dynamics of cutting knife in a vertical disc wood chipper were investigated. The tool geometry determined include: rake angle (20 deg C; Shear angle, (fi= 52.15 deg C; the mean frictional angle, (t = 5.71 deg C. The analysis and comparison of the cutting forces has shown that the chips separated from the wood are being formed by off cutting, since normal applied force N is compressive in nature, the magnitude of the forces used by the knife on the wood is expected to increase as the cutting edge of the knife goes deeper into the wood until the value of the resisting force acting against the cut wood Ff is reached and exceeded. The evaluated forces acting on the knife and the chip are: F = 3.63Nmm^-1; N = 34.7 Nmm^-1; Fs= 27.45Nmm^-1; Fn =31.92 Nmm^-1; Ft = -8.46Nmm^-1; Fc = 33.85Nmm^-1. The resultant force acting on the tool face, Pr = 34.89Nmm^-1. The specific cutting pressure, Pc and cutting force needed to cut the timber, Fc, are 1.79 × 10^6 N/m2 and 644.84N respectively. The energy consumed in removing a unit volume of material is 69.96kJ/mm^-3 and the maximum power developed in cutting the chip is 3591.77W (4.82hp. The chipper efficiency (86.6% was evaluated by the highest percentage of accepted chip sizes.

  11. A force-based model to reproduce stop-and-go waves in pedestrian dynamics

    CERN Document Server

    Chraibi, Mohcine; Schadschneider, Andreas

    2015-01-01

    Stop-and-go waves in single-file movement are a phenomenon that is ob- served empirically in pedestrian dynamics. It manifests itself by the co-existence of two phases: moving and stopping pedestrians. We show analytically based on a simplified one-dimensional scenario that under some conditions the system can have instable homogeneous solutions. Hence, oscillations in the trajectories and in- stabilities emerge during simulations. To our knowledge there exists no force-based model which is collision- and oscillation-free and meanwhile can reproduce phase separation. We develop a new force-based model for pedestrian dynamics able to reproduce qualitatively the phenomenon of phase separation. We investigate analytically the stability condition of the model and define regimes of parameter values where phase separation can be observed. We show by means of simulations that the predefined conditions lead in fact to the expected behavior and validate our model with respect to empirical findings.

  12. Influence of forced respiration on nonlinear dynamics in heart rate variability

    DEFF Research Database (Denmark)

    Kanters, J K; Højgaard, M V; Agner, E;

    1997-01-01

    of this study was to test whether the known nonlinear input from spontaneous respiration is a source for the nonlinearities in heart rate variability. Twelve healthy subjects were examined in supine position with 3-h electrocardiogram recordings during both spontaneous and forced respiration in accordance...... expressed as the nonlinear prediction error did not differ between spontaneous respiration, 32.3 +/- 3.4 ms, and forced respiration, 31.9 +/- 5.7. It is concluded that the origin of the nonlinear dynamics in heart rate variability is not a nonlinear input from the respiration into the cardiovascular...... oscillator. Additional studies are needed to elucidate the mechanisms behind the nonlinear dynamics in heart rate variability....

  13. Empirical tight-binding force model for molecular-dynamics simulation of Si

    Science.gov (United States)

    Wang, C. Z.; Chan, C. T.; Ho, K. M.

    1989-04-01

    A scheme of molecular-dynamics simulation using the empirical tight-binding force model is proposed. The scheme allows the interatomic interactions involved in the molecular dynamics to be determined by first-principles total-energy and electronic-structure calculations without resorting to fitting experimental data. For a first application of the scheme we show that a very simple nearest-neighbor two-center empirical tight-binding force model is able to stabilize the diamond structure of Si within a reasonable temperature range. We also show that the scheme makes possible the quantitative calculation of the temperature dependence of various anharmonic effects such as lattice thermal expansion, temperature-dependent phonon linewidths, and phonon frequency shifts.

  14. Variability and trends in dynamical forcing of tropical lower stratospheric temperatures

    Directory of Open Access Journals (Sweden)

    S. Fueglistaler

    2014-05-01

    Full Text Available We analyse the relation between tropical lower stratospheric temperatures and dynamical forcing over the period 1980–2011 using NCEP, MERRA and ERA-Interim reanalyses. The tropical mean thermodynamic energy equation with Newtonian cooling for radiation is forced with two dynamical predictors: (i the average eddy heat flux of both hemispheres; and (ii tropical upwelling estimated from momentum balance following Randel et al. (2002. The correlation (1995–2011 for deseasonalised tropical average temperatures at 70 hPa with the eddy heat flux based predictor is 0.84 for ERA-Interim (0.77 for the momentum balance calculation, and 0.87 for MERRA. The eddy heat flux based predictor indicates a dynamically forced cooling of the tropics of ∼−0.1 K decade−1 (∼−0.2 K decade−1 excluding volcanic periods for the period 1980–2011 in MERRA and ERA-Interim. ERA-Interim eddy heat fluxes drift slightly relative to MERRA in the 2000's, possibly due to onset of GPS temperature data assimilation. While NCEP gives a small warming trend, all 3 reanalyses show a similar seasonality, with strongest cooling in January/February (∼−0.4 K decade−1, from northern hemispheric forcing and October (∼−0.3 K decade−1, from southern hemispheric forcing. Months preceding and following the peaks in cooling trends show pronounced smaller, or even warming, trends. Consequently, the seasonality in the trends arises in part due to a temporal shift in eddy activity. Over all months, the Southern Hemisphere contributes more to the tropical cooling in both MERRA and ERA-Interim. The residual time series (observed minus estimate of dynamically forced temperature are well correlated between ERA-Interim and MERRA, with differences largely due to temperature differences. The residual time series is dominated by the modification of the radiative balance by volcanic aerosol following the eruption of El Chichon (maximum warming of ∼3 K at 70 hPa and Pinatubo

  15. Nonlinear dynamics of plasma oscillations modeled by a forced modified Van der Pol-Duffing oscillator

    CERN Document Server

    Miwadinou, C H; Monwanou, A V; Orou, J B Chabi

    2013-01-01

    This paper considers nonlinear dynamics of plasma oscillations modeled by a forced modified Van der Pol-Duffing oscillator. These plasma oscillations are described by a nonlinear differential equation of the form $ \\ddot{x}+ \\epsilon (1 +{x}^{2}){\\dot{x}} + x+ \\alpha \\epsilon{x}{\\dot{x}} + {\\beta}x^{2}+\\gamma x^{3}= F\\cos{\\Omega t}.$ The amplitudes of the forced harmonic, superharmonic and subharmonic oscillatory states are obtained using the harmonic balance technique and the multiple time scales methods. Bifurcation sequences displayed by the model for each type of oscillatory states are performed numerically through the fourth order Runge- Kutta scheme. The influences of the differents parameters and of amplitude of external forced have been found.

  16. Fusing heterogeneous data for the calibration of molecular dynamics force fields using hierarchical Bayesian models.

    Science.gov (United States)

    Wu, Stephen; Angelikopoulos, Panagiotis; Tauriello, Gerardo; Papadimitriou, Costas; Koumoutsakos, Petros

    2016-12-28

    We propose a hierarchical Bayesian framework to systematically integrate heterogeneous data for the calibration of force fields in Molecular Dynamics (MD) simulations. Our approach enables the fusion of diverse experimental data sets of the physico-chemical properties of a system at different thermodynamic conditions. We demonstrate the value of this framework for the robust calibration of MD force-fields for water using experimental data of its diffusivity, radial distribution function, and density. In order to address the high computational cost associated with the hierarchical Bayesian models, we develop a novel surrogate model based on the empirical interpolation method. Further computational savings are achieved by implementing a highly parallel transitional Markov chain Monte Carlo technique. The present method bypasses possible subjective weightings of the experimental data in identifying MD force-field parameters.

  17. Molecular Dynamics Simulations of a Linear Nanomotor Driven by Thermophoretic Forces

    DEFF Research Database (Denmark)

    Zambrano, Harvey A; Walther, Jens Honore; Jaffe, Richard L.

    ,7,8,9 Nanomotors are an attractive goal for nanotechnology.9-13 Such nano-scale structures capable of converting thermal energy into work will be needed in many types of nanodevices, including nanoconveyors14, memory devices15 and nano-encapsulated material delivery systems16,17. Moreover to design and manufacture...... future molecular machines a complete understanding of the friction forces involved on the transport process at the molecular level have to be addressed.18 In this work we perform Molecular Dynamics (MD) simulations using the MD package FASTTUBE19 to study a molecular linear motor consisting of coaxial...... of the capsule is driven by thermophoresis we perform additional simulations in order to study the friction and thermophoretic forces acting on the inner CNT. In these simulations, we constrain the velocity of center of mass of the inner CNT and extract from the simulations the external forces required to drive...

  18. Pairwise Force Smoothed Particle Hydrodynamics model for multiphase flow: Surface tension and contact line dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Tartakovsky, Alexandre M.; Panchenko, Alexander

    2016-01-01

    We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics Model (PF-SPH) and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the accuracy of the model under static and dynamic conditions. Finally, to demonstrate the capabilities and robustness of the model we use it to simulate flow of three fluids in a porous material.

  19. Pairwise Force Smoothed Particle Hydrodynamics model for multiphase flow: Surface tension and contact line dynamics

    Science.gov (United States)

    Tartakovsky, Alexandre M.; Panchenko, Alexander

    2016-01-01

    We present a novel formulation of the Pairwise Force Smoothed Particle Hydrodynamics (PF-SPH) model and use it to simulate two- and three-phase flows in bounded domains. In the PF-SPH model, the Navier-Stokes equations are discretized with the Smoothed Particle Hydrodynamics (SPH) method, and the Young-Laplace boundary condition at the fluid-fluid interface and the Young boundary condition at the fluid-fluid-solid interface are replaced with pairwise forces added into the Navier-Stokes equations. We derive a relationship between the parameters in the pairwise forces and the surface tension and static contact angle. Next, we demonstrate the model's accuracy under static and dynamic conditions. Finally, we use the Pf-SPH model to simulate three phase flow in a porous medium.

  20. Quantitative Verification of a Force-based Model for Pedestrian Dynamics

    CERN Document Server

    Chraibi, Mohcine; Schadschneider, Andreas; Mackens, Wolfgang

    2009-01-01

    This paper introduces a spatially continuous force-based model for simulating pedestrian dynamics. The main intention of this work is the quantitative description of pedestrian movement through bottlenecks and in corridors. Measurements of flow and density at bottlenecks will be presented and compared with empirical data. Furthermore the fundamental diagram for the movement in a corridor is reproduced. The results of the proposed model show a good agreement with empirical data.

  1. Solvation structure and dynamics of Ni{sup 2+}(aq) from a polarizable force field

    Energy Technology Data Exchange (ETDEWEB)

    Mareš, Jiří, E-mail: jiri.mares@oulu.fi; Vaara, Juha

    2014-10-31

    Highlights: • We parameterize the Ni{sup 2+} ion within the AMOEBA polarizable forcefield. • Besides vdW parameters, we fit also polarizability, Thole damping and charge. • We use an empirical adjustment to account for the transition into condensed phase. • Very good structural and dynamical properties of Ni{sup 2+}(aq) are demonstrated. - Abstract: An aqueous solution of Ni{sup 2+} has often been used as a prototypic transition-metal system for experimental and theoretical studies in nuclear and electron-spin magnetic resonance (NMR and ESR). Molecular dynamics (MD) simulation of Ni{sup 2+}(aq) has been a part of many of these studies. As a transition metal complex, its MD simulation is particularly difficult using common force fields. In this work, we parameterize the Ni{sup 2+} ion for a simulation of the aqueous solution within the modern polarizable force field AMOEBA. We show that a successful parameterization is possible for this specific case when releasing the physical interpretation of the electrostatic and polarization parameters of the force field. In doing so, particularly the Thole damping parameter and also the ion charge and polarizability were used as fitting parameters. The resulting parameterizations give in a MD simulation good structural and dynamical properties of the [Ni(H{sub 2}O){sub 6}]{sup 2+} complex, along with the expected excellent performance of AMOEBA for the water solvent. The presented parameterization is appropriate for high-accuracy simulations of both structural and dynamic properties of Ni{sup 2+}(aq). This work documents possible approaches of parameterization of a transition metal within the AMOEBA force field.

  2. Enhancing the accuracy of virtual screening: molecular dynamics with quantum-refined force fields.

    Science.gov (United States)

    Curioni, Alessandro; Mordasini, Tiziana; Andreoni, Wanda

    2004-12-01

    A methodology aimed at improving the accuracy of current docking-scoring procedures is proposed, and validated through detailed tests of its performance in predicting the activity of HIV-1 protease inhibitors. This methodology is based on molecular dynamics simulations using a force field whose effective charges are refined by means of a novel procedure that relies on quantum-mechanical calculations and preserves the internal consistency of the parameterization scheme.

  3. Dynamics of the Bogie of Maglev Train with Distributed Magnetic Forces

    OpenAIRE

    2015-01-01

    A dynamic model of the bogie of maglev train with distributed magnetic forces and four identical levitating controllers is formulated. The vertical, pitching, and rolling degree of freedom of the electromagnet modules and their coupling are considered. The frequency responses of the bogie to track irregularity are investigated with numerical simulation. The results tell us that there are resonances related to the first electromagnetic suspension whose frequencies are determined by the control...

  4. Air Force Dynamic Mechanical Analysis of NATO Round Robin Propellant Testing for Development of AOP-4717

    Science.gov (United States)

    2015-09-23

    Round Robin Propellant Testing for Development of AOP-4717 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S...area code) N/A Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18 0 Air Force Dynamic Mechanical Analysis of NATO Round Robin ...the clamps are tight at the coldest temperature. • Long tests such as the frequency sweep sequences prescribed in this round robin may be

  5. Investigations of the intermolecular forces between RDX and polyethylene by force-distance spectroscopy and molecular dynamics simulations.

    Science.gov (United States)

    Taylor, D E; Strawhecker, K E; Shanholtz, E R; Sorescu, D C; Sausa, R C

    2014-07-10

    The development of novel nanoenergetic materials with enhanced bulk properties requires an understanding of the intermolecular interactions occurring between molecular components. We investigate the surface interactions between 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and polyethylene (PE) crystals on the basis of combined use of molecular dynamics (MD) simulations and force-distance spectroscopy, in conjunction with Lifshitz macroscopic theory of van der Waals forces between continuous materials. The binding energy in the RDX-PE system depends both on the degree of PE crystallinity and on the RDX crystal face. Our MD simulations yield binding energies of approximately 132 and 120 mJ/m(2) for 100% amorphous and 100% crystalline PE on RDX (210), respectively. The average value is about 36% greater than our experimental value of 81 ± 15 mJ/m(2) for PE (∼48% amorphous) on RDX (210). By comparison, Liftshitz theory predicts a value of about 79 mJ/m(2) for PE interacting with RDX. Our MD simulations also predict larger binding energies for both amorphous and crystalline PE on RDX (210) compared to the RDX (001) surface. Analysis of the interaction potential indicates that about 60% of the binding energy in the PE-RDX system is due to attractive interactions between HPE-ORDX and CPE-NRDX pairs of atoms. Further, amorphous PE shows a much longer interaction distance than crystalline PE with the (210) and (001) RDX surfaces due to the possibility of larger polymer elongations in the case of amorphous PE as strain is applied. Also, we report estimates of the binding energies of energetic materials RDX and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with PE, propylene, polystyrene, and several fluorine-containing polymers using Lifshitz theory and compare these with reported MD calculations.

  6. A Piezoelectric PZT Ceramic Mulitlayer Stack for Energy Harvesting Under Dynamic Forces

    Science.gov (United States)

    Xu, Tian-Bing; Siochi, Emilie J.; Kang, Jin Ho; Zuo, Lei; Zhou, Wanlu; Tang, Xiudong; Jiang, Xiaoning

    2011-01-01

    Piezoelectric energy harvesting transducers (PEHTs) are commonly used in motion/vibration energy scavenging devices. To date, most researchers have focused on energy harvesting at narrow bandwidths around the mechanical resonance frequency, and most piezoelectric harvesting devices reported in the literature have very low effective piezoelectric coefficient (d(sub eff)) (piezoelectric coefficients of about 100 pC/N. The level of harvested electrical power for CBPEHTs is on the order of microW even at resonance mode. In order to harvest more electrical energy across broader bandwidth, high effective piezoelectric coefficient structures are needed. In this study, we investigate a "33" longitudinal mode, piezoelectric PZT ceramic multilayer stack (PZT-Stack) with high effective piezoelectric coefficient for high-performance PEHTs. The PZT-Stack is composed of 300 layers of 0.1 mm thick PZT plates, with overall dimensions of 32.4 mm X 7.0 mm X 7.0 mm. Experiments were carried out with dynamic forces in a broad bandwidth ranging from 0.5 Hz to 25 kHz. The measured results show that the effective piezoelectric coefficient of the PZT-stack is about 1 X 10(exp 5) pC/N at off-resonance frequencies and 1.39 X 10(exp 6) pC/N at resonance, which is order of magnitude larger than that of traditional PEHTs. The effective piezoelectric coefficients (d(sub eff)) do not change significantly with applied dynamic forces having root mean square (RMS) values ranging from 1 N to 40 N. In resonance mode, 231 mW of electrical power was harvested at 2479 Hz with a dynamic force of 11.6 N(sub rms), and 7.6 mW of electrical power was generated at a frequency of 2114 Hz with 1 N(sub rms) dynamic force. In off-resonance mode, an electrical power of 18.7 mW was obtained at 680 Hz with a 40 N(sub rms) dynamic force. A theoretical model of energy harvesting for the PZT-Stack is established. The modeled results matched well with experimental measurements. This study demonstrated that high

  7. A Piezoelectric PZT Ceramic Mulitlayer Stack for Energy Harvesting Under Dynamic Forces

    Science.gov (United States)

    Xu, Tian-Bing; Siochi, Emilie J.; Kang, Jin Ho; Zuo, Lei; Zhou, Wanlu; Tang, Xiudong; Jiang, Xiaoning

    2011-01-01

    Piezoelectric energy harvesting transducers (PEHTs) are commonly used in motion/vibration energy scavenging devices. To date, most researchers have focused on energy harvesting at narrow bandwidths around the mechanical resonance frequency, and most piezoelectric harvesting devices reported in the literature have very low effective piezoelectric coefficient (d(sub eff)) (harvested electrical power for CBPEHTs is on the order of microW even at resonance mode. In order to harvest more electrical energy across broader bandwidth, high effective piezoelectric coefficient structures are needed. In this study, we investigate a "33" longitudinal mode, piezoelectric PZT ceramic multilayer stack (PZT-Stack) with high effective piezoelectric coefficient for high-performance PEHTs. The PZT-Stack is composed of 300 layers of 0.1 mm thick PZT plates, with overall dimensions of 32.4 mm X 7.0 mm X 7.0 mm. Experiments were carried out with dynamic forces in a broad bandwidth ranging from 0.5 Hz to 25 kHz. The measured results show that the effective piezoelectric coefficient of the PZT-stack is about 1 X 10(exp 5) pC/N at off-resonance frequencies and 1.39 X 10(exp 6) pC/N at resonance, which is order of magnitude larger than that of traditional PEHTs. The effective piezoelectric coefficients (d(sub eff)) do not change significantly with applied dynamic forces having root mean square (RMS) values ranging from 1 N to 40 N. In resonance mode, 231 mW of electrical power was harvested at 2479 Hz with a dynamic force of 11.6 N(sub rms), and 7.6 mW of electrical power was generated at a frequency of 2114 Hz with 1 N(sub rms) dynamic force. In off-resonance mode, an electrical power of 18.7 mW was obtained at 680 Hz with a 40 N(sub rms) dynamic force. A theoretical model of energy harvesting for the PZT-Stack is established. The modeled results matched well with experimental measurements. This study demonstrated that high effective piezoelectric coefficient structures enable PEHTs to

  8. A Piezoelectric PZT Ceramic Mulitlayer Stack for Energy Harvesting Under Dynamic Forces

    Science.gov (United States)

    Xu, Tian-Bing; Siochi, Emilie J.; Kang, Jin Ho; Zuo, Lei; Zhou, Wanlu; Tang, Xiudong; Jiang, Xiaoning

    2011-01-01

    Piezoelectric energy harvesting transducers (PEHTs) are commonly used in motion/vibration energy scavenging devices. To date, most researchers have focused on energy harvesting at narrow bandwidths around the mechanical resonance frequency, and most piezoelectric harvesting devices reported in the literature have very low effective piezoelectric coefficient (d(sub eff)) (ceramic multilayer stack (PZT-Stack) with high effective piezoelectric coefficient for high-performance PEHTs. The PZT-Stack is composed of 300 layers of 0.1 mm thick PZT plates, with overall dimensions of 32.4 mm X 7.0 mm X 7.0 mm. Experiments were carried out with dynamic forces in a broad bandwidth ranging from 0.5 Hz to 25 kHz. The measured results show that the effective piezoelectric coefficient of the PZT-stack is about 1 X 10(exp 5) pC/N at off-resonance frequencies and 1.39 X 10(exp 6) pC/N at resonance, which is order of magnitude larger than that of traditional PEHTs. The effective piezoelectric coefficients (d(sub eff)) do not change significantly with applied dynamic forces having root mean square (RMS) values ranging from 1 N to 40 N. In resonance mode, 231 mW of electrical power was harvested at 2479 Hz with a dynamic force of 11.6 N(sub rms), and 7.6 mW of electrical power was generated at a frequency of 2114 Hz with 1 N(sub rms) dynamic force. In off-resonance mode, an electrical power of 18.7 mW was obtained at 680 Hz with a 40 N(sub rms) dynamic force. A theoretical model of energy harvesting for the PZT-Stack is established. The modeled results matched well with experimental measurements. This study demonstrated that high effective piezoelectric coefficient structures enable PEHTs to harvest more electrical energy from mechanical vibrations or motions, suggesting an effective design for high-performance low-footprint PEHTs with potential applications in military, aerospace, and portable electronics. In addition, this study provides a route for using piezoelectric multilayer

  9. Accelerated Molecular Dynamics Simulations with the AMOEBA Polarizable Force Field on Graphics Processing Units.

    Science.gov (United States)

    Lindert, Steffen; Bucher, Denis; Eastman, Peter; Pande, Vijay; McCammon, J Andrew

    2013-11-12

    The accelerated molecular dynamics (aMD) method has recently been shown to enhance the sampling of biomolecules in molecular dynamics (MD) simulations, often by several orders of magnitude. Here, we describe an implementation of the aMD method for the OpenMM application layer that takes full advantage of graphics processing units (GPUs) computing. The aMD method is shown to work in combination with the AMOEBA polarizable force field (AMOEBA-aMD), allowing the simulation of long time-scale events with a polarizable force field. Benchmarks are provided to show that the AMOEBA-aMD method is efficiently implemented and produces accurate results in its standard parametrization. For the BPTI protein, we demonstrate that the protein structure described with AMOEBA remains stable even on the extended time scales accessed at high levels of accelerations. For the DNA repair metalloenzyme endonuclease IV, we show that the use of the AMOEBA force field is a significant improvement over fixed charged models for describing the enzyme active-site. The new AMOEBA-aMD method is publicly available (http://wiki.simtk.org/openmm/VirtualRepository) and promises to be interesting for studying complex systems that can benefit from both the use of a polarizable force field and enhanced sampling.

  10. Force and torque on spherical particles in micro-channel flows using computational fluid dynamics

    Science.gov (United States)

    Suo, Jin; Edwards, Erin E.; Anilkumar, Ananyaveena; Sulchek, Todd; Giddens, Don P.

    2016-01-01

    To delineate the influence of hemodynamic force on cell adhesion processes, model in vitro fluidic assays that mimic physiological conditions are commonly employed. Herein, we offer a framework for solution of the three-dimensional Navier–Stokes equations using computational fluid dynamics (CFD) to estimate the forces resulting from fluid flow near a plane acting on a sphere that is either stationary or in free flow, and we compare these results to a widely used theoretical model that assumes Stokes flow with a constant shear rate. We find that while the full three-dimensional solutions using a parabolic velocity profile in CFD simulations yield similar translational velocities to those predicted by the theoretical method, the CFD approach results in approximately 50% larger rotational velocities over the wall shear stress range of 0.1–5.0 dynes cm−2. This leads to an approximately 25% difference in force and torque calculations between the two methods. When compared with experimental measurements of translational and rotational velocities of microspheres or cells perfused in microfluidic channels, the CFD simulations yield significantly less error. We propose that CFD modelling can provide better estimations of hemodynamic force levels acting on perfused microspheres and cells in flow fields through microfluidic devices used for cell adhesion dynamics analysis. PMID:27493783

  11. Force and torque on spherical particles in micro-channel flows using computational fluid dynamics.

    Science.gov (United States)

    Suo, Jin; Edwards, Erin E; Anilkumar, Ananyaveena; Sulchek, Todd; Giddens, Don P; Thomas, Susan N

    2016-07-01

    To delineate the influence of hemodynamic force on cell adhesion processes, model in vitro fluidic assays that mimic physiological conditions are commonly employed. Herein, we offer a framework for solution of the three-dimensional Navier-Stokes equations using computational fluid dynamics (CFD) to estimate the forces resulting from fluid flow near a plane acting on a sphere that is either stationary or in free flow, and we compare these results to a widely used theoretical model that assumes Stokes flow with a constant shear rate. We find that while the full three-dimensional solutions using a parabolic velocity profile in CFD simulations yield similar translational velocities to those predicted by the theoretical method, the CFD approach results in approximately 50% larger rotational velocities over the wall shear stress range of 0.1-5.0 dynes cm(-2). This leads to an approximately 25% difference in force and torque calculations between the two methods. When compared with experimental measurements of translational and rotational velocities of microspheres or cells perfused in microfluidic channels, the CFD simulations yield significantly less error. We propose that CFD modelling can provide better estimations of hemodynamic force levels acting on perfused microspheres and cells in flow fields through microfluidic devices used for cell adhesion dynamics analysis.

  12. Dynamics of cell shape and forces on micropatterned substrates predicted by a cellular Potts model.

    Science.gov (United States)

    Albert, Philipp J; Schwarz, Ulrich S

    2014-06-03

    Micropatterned substrates are often used to standardize cell experiments and to quantitatively study the relation between cell shape and function. Moreover, they are increasingly used in combination with traction force microscopy on soft elastic substrates. To predict the dynamics and steady states of cell shape and forces without any a priori knowledge of how the cell will spread on a given micropattern, here we extend earlier formulations of the two-dimensional cellular Potts model. The third dimension is treated as an area reservoir for spreading. To account for local contour reinforcement by peripheral bundles, we augment the cellular Potts model by elements of the tension-elasticity model. We first parameterize our model and show that it accounts for momentum conservation. We then demonstrate that it is in good agreement with experimental data for shape, spreading dynamics, and traction force patterns of cells on micropatterned substrates. We finally predict shapes and forces for micropatterns that have not yet been experimentally studied. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  13. Energetic dynamics of a rotating horizontal convection model of an ocean basin with wind forcing

    Science.gov (United States)

    Zemskova, Varvara; White, Brian; Scotti, Alberto

    2016-11-01

    We analyze the energetic dynamics in a rotating horizontal convection model, where flow is driven by a differential buoyancy forcing along a horizontal surface. This model is used to quantify the influence of surface heating and cooling and surface wind stress on the Meridional Overturning Circulation. We study a model of the Southern Ocean in a rectangular basin with surface cooling on one end (the South pole) and surface warming on the other end (mid-latitudes). Free-slip boundary conditions are imposed in the closed box, while zonally periodic boundary conditions are enforced in the reentrant channel. Wind stress and differential buoyancy forcing are applied at the top boundary. The problem is solved numerically using a 3D DNS model based on a finite-volume AMR solver for the Boussinesq Navier-Stokes equations with rotation. The overall dynamics, including large-scale overturning, baroclinic eddying, turbulent mixing, and resulting energy cascades are investigated using the local Available Potential Energy framework introduced in. We study the relative contributions of surface buoyancy and wind forcing along with the effects of bottom topography to the energetic balance of this dynamic model. This research is part of the Blue Waters sustained-petascale computing project, supported by the NSF (awards OCI-0725070, ACI-1238993 and ACI-14-44747) and the state of Illinois.

  14. Assessment of dynamic finger forces in pianists: effects of training and expertise.

    Science.gov (United States)

    Parlitz, D; Peschel, T; Altenmüller, E

    1998-11-01

    Playing a musical instrument requires complex sensorimotor programming of hand and finger movements. During musical training motor programs are optimized to achieve highest accuracy with a minimum of effort. In the lack of handy measurement tools these rational assumptions of piano theorists did not undergo an experimental evaluation up to now. In the present pilot study we used a dynamic pressure measurement system with the pianoforte. Three finger exercises with increasing degrees of difficulty had to be performed by a group of musical amateurs and a group of expert players. From the dynamic force measurements we calculated (a) the mean pulse per touch and (b) the mean touch-duration for each exercise and each subject. To achieve the same tempo and the same loudness, amateurs applied significantly more and longer force to the keys, leading to higher mean pulses per touch. Pulse and duration values increased with higher demands on finger coordination in both, expert pianists and amateurs. The results show that dynamic force measurement systems can support music learners and teachers in training a relaxed piano technique and preventing musicians from overuse injuries.

  15. Binaries traveling through a gaseous medium: Dynamical drag forces and internal torques

    CERN Document Server

    Sanchez-Salcedo, F J

    2014-01-01

    Using time-dependent linear theory, we investigate the morphology of the gravitational wake induced by a binary, whose center of mass moves at velocity Vcm against a uniform background of gas. For simplicity, we assume that the binary's components are on circular orbits about their common center of mass. The consequences of dynamical friction is twofold. First, gas dynamical friction may drag the binary's center of mass and cause the binary to migrate. Second, drag forces also induce a braking torque, which causes the orbits of the binary components to shrink. We compute the drag forces acting on one component of the binary due to the gravitational interaction with its own wake. We show that the dynamical friction force responsible to decelerate the binary's center of mass is smaller than it is in the point-mass case because of the loss of gravitational focusing. We show that the braking internal torque depends on the Mach numbers of each binary component about their center of mass, and also on the Mach numbe...

  16. Dynamic allostery in the methionine repressor revealed by force distribution analysis.

    Directory of Open Access Journals (Sweden)

    Wolfram Stacklies

    2009-11-01

    Full Text Available Many fundamental cellular processes such as gene expression are tightly regulated by protein allostery. Allosteric signal propagation from the regulatory to the active site requires long-range communication, the molecular mechanism of which remains a matter of debate. A classical example for long-range allostery is the activation of the methionine repressor MetJ, a transcription factor. Binding of its co-repressor SAM increases its affinity for DNA several-fold, but has no visible conformational effect on its DNA binding interface. Our molecular dynamics simulations indicate correlated domain motions within MetJ, and quenching of these dynamics upon SAM binding entropically favors DNA binding. From monitoring conformational fluctuations alone, it is not obvious how the presence of SAM is communicated through the largely rigid core of MetJ and how SAM thereby is able to regulate MetJ dynamics. We here directly monitored the propagation of internal forces through the MetJ structure, instead of relying on conformational changes as conventionally done. Our force distribution analysis successfully revealed the molecular network for strain propagation, which connects collective domain motions through the protein core. Parts of the network are directly affected by SAM binding, giving rise to the observed quenching of fluctuations. Our results are in good agreement with experimental data. The force distribution analysis suggests itself as a valuable tool to gain insight into the molecular function of a whole class of allosteric proteins.

  17. Force generation by a dynamic Z-ring in Escherichia coli cell division.

    Science.gov (United States)

    Allard, Jun F; Cytrynbaum, Eric N

    2009-01-06

    FtsZ, a bacterial homologue of tubulin, plays a central role in bacterial cell division. It is the first of many proteins recruited to the division site to form the Z-ring, a dynamic structure that recycles on the time scale of seconds and is required for division to proceed. FtsZ has been recently shown to form rings inside tubular liposomes and to constrict the liposome membrane without the presence of other proteins, particularly molecular motors that appear to be absent from the bacterial proteome. Here, we propose a mathematical model for the dynamic turnover of the Z-ring and for its ability to generate a constriction force. Force generation is assumed to derive from GTP hydrolysis, which is known to induce curvature in FtsZ filaments. We find that this transition to a curved state is capable of generating a sufficient force to drive cell-wall invagination in vivo and can also explain the constriction seen in the in vitro liposome experiments. Our observations resolve the question of how FtsZ might accomplish cell division despite the highly dynamic nature of the Z-ring and the lack of molecular motors.

  18. Selecting a Dynamic Simulation Modeling Method for Health Care Delivery Research—Part 2: Report of the ISPOR Dynamic Simulation Modeling Emerging Good Practices Task Force

    NARCIS (Netherlands)

    Marshall, Deborah A.; Burgos-Liz, Lina; IJzerman, Maarten Joost; Crown, William; Padula, William V.; Wong, Peter K.; Pasupathy, Kalyan S.; Higashi, Mitchell K.; Osgood, Nathaniel D.

    2015-01-01

    In a previous report, the ISPOR Task Force on Dynamic Simulation Modeling Applications in Health Care Delivery Research Emerging Good Practices introduced the fundamentals of dynamic simulation modeling and identified the types of health care delivery problems for which dynamic simulation modeling

  19. Selecting a Dynamic Simulation Modeling Method for Health Care Delivery Research—Part 2: Report of the ISPOR Dynamic Simulation Modeling Emerging Good Practices Task Force

    NARCIS (Netherlands)

    Marshall, Deborah A.; Burgos-Liz, Lina; IJzerman, Maarten Joost; Crown, William; Padula, William V.; Wong, Peter K.; Pasupathy, Kalyan S.; Higashi, Mitchell K.; Osgood, Nathaniel D.

    2015-01-01

    In a previous report, the ISPOR Task Force on Dynamic Simulation Modeling Applications in Health Care Delivery Research Emerging Good Practices introduced the fundamentals of dynamic simulation modeling and identified the types of health care delivery problems for which dynamic simulation modeling c

  20. Paramfit: automated optimization of force field parameters for molecular dynamics simulations.

    Science.gov (United States)

    Betz, Robin M; Walker, Ross C

    2015-01-15

    The generation of bond, angle, and torsion parameters for classical molecular dynamics force fields typically requires fitting parameters such that classical properties such as energies and gradients match precalculated quantum data for structures that scan the value of interest. We present a program, Paramfit, distributed as part of the AmberTools software package that automates and extends this fitting process, allowing for simplified parameter generation for applications ranging from single molecules to entire force fields. Paramfit implements a novel combination of a genetic and simplex algorithm to find the optimal set of parameters that replicate either quantum energy or force data. The program allows for the derivation of multiple parameters simultaneously using significantly fewer quantum calculations than previous methods, and can also fit parameters across multiple molecules with applications to force field development. Paramfit has been applied successfully to systems with a sparse number of structures, and has already proven crucial in the development of the Assisted Model Building with Energy Refinement Lipid14 force field.

  1. Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

    Science.gov (United States)

    Balke, Nina; Jesse, Stephen; Yu, Pu; Carmichael, Ben; Kalinin, Sergei V.; Tselev, Alexander

    2016-10-01

    Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ˜1-3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip-sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

  2. Whole-Body Human Inverse Dynamics with Distributed Micro-Accelerometers, Gyros and Force Sensing †

    Science.gov (United States)

    Latella, Claudia; Kuppuswamy, Naveen; Romano, Francesco; Traversaro, Silvio; Nori, Francesco

    2016-01-01

    Human motion tracking is a powerful tool used in a large range of applications that require human movement analysis. Although it is a well-established technique, its main limitation is the lack of estimation of real-time kinetics information such as forces and torques during the motion capture. In this paper, we present a novel approach for a human soft wearable force tracking for the simultaneous estimation of whole-body forces along with the motion. The early stage of our framework encompasses traditional passive marker based methods, inertial and contact force sensor modalities and harnesses a probabilistic computational technique for estimating dynamic quantities, originally proposed in the domain of humanoid robot control. We present experimental analysis on subjects performing a two degrees-of-freedom bowing task, and we estimate the motion and kinetics quantities. The results demonstrate the validity of the proposed method. We discuss the possible use of this technique in the design of a novel soft wearable force tracking device and its potential applications. PMID:27213394

  3. Dynamics of cross-bridge cycling, ATP hydrolysis, force generation, and deformation in cardiac muscle.

    Science.gov (United States)

    Tewari, Shivendra G; Bugenhagen, Scott M; Palmer, Bradley M; Beard, Daniel A

    2016-07-01

    Despite extensive study over the past six decades the coupling of chemical reaction and mechanical processes in muscle dynamics is not well understood. We lack a theoretical description of how chemical processes (metabolite binding, ATP hydrolysis) influence and are influenced by mechanical processes (deformation and force generation). To address this need, a mathematical model of the muscle cross-bridge (XB) cycle based on Huxley's sliding filament theory is developed that explicitly accounts for the chemical transformation events and the influence of strain on state transitions. The model is identified based on elastic and viscous moduli data from mouse and rat myocardial strips over a range of perturbation frequencies, and MgATP and inorganic phosphate (Pi) concentrations. Simulations of the identified model reproduce the observed effects of MgATP and MgADP on the rate of force development. Furthermore, simulations reveal that the rate of force re-development measured in slack-restretch experiments is not directly proportional to the rate of XB cycling. For these experiments, the model predicts that the observed increase in the rate of force generation with increased Pi concentration is due to inhibition of cycle turnover by Pi. Finally, the model captures the observed phenomena of force yielding suggesting that it is a result of rapid detachment of stretched attached myosin heads.

  4. A feasibility study for experimentally determining dynamic force distribution in a lap joint

    Energy Technology Data Exchange (ETDEWEB)

    Mayes, Randall Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2013-11-01

    Developing constitutive models of the physics in mechanical joints is currently stymied by inability to measure forces and displacements within the joint. The current state of the art estimates whole joint stiffness and energy loss per cycle from external measured force input and one or two acceleration responses. To validate constitutive models beyond this state requires a measurement of the distributed forces and displacements at the joint interface. Unfortunately, introducing measurement devices at the interface completely disrupts the desired physics. A feasibility study is presented for a non-intrusive method of solving for the interface dynamic forces from an inverse problem using full field measured responses. The responses come from the viewable surface of a beam. The noise levels associated with digital image correlation and continuous scanning laser Doppler velocimetry are evaluated from typical beam experiments. Two inverse problems are simulated. One utilizes the extended Sum of Weighted Accelerations Technique (SWAT). The second is a new approach dubbed the method of truncated orthogonal forces. These methods are much more robust if the contact patch geometry is well identified. Various approaches to identifying the contact patch are investigated, including ion marker tracking, Prussian blue and ultrasonic measurements. A typical experiment is conceived for a beam which has a lap joint at one end with a single bolt connecting it to another identical beam. In a virtual test using the beam finite element analysis, it appears that the SWAT inverse method requires evaluation of too many coefficients to adequately identify the force distribution to be viable. However, the method of truncated orthogonal forces appears viable with current digital image correlation (and probably other) imaging techniques.

  5. Molecular dynamics study of the potential of mean force of SDS aggregates

    Science.gov (United States)

    Kawada, Shinji; Fujimoto, Kazushi; Yoshii, Noriyuki; Okazaki, Susumu

    2017-08-01

    In our previous study, all-atomistic molecular dynamics (MD) calculations have been carried out for the aggregation of ionic sodium dodecyl sulfate in water [S. Kawada et al., Chem. Phys. Lett. 646, 36 (2016)]. Aggregates of 20-30 dodecyl sulfate ions were formed within a short MD run for 10 ns. However, further aggregation did not occur despite a long MD calculation for more than 100 ns. This suggests that strong electrostatic repulsive interactions between the aggregates prevent the fusion of the aggregates. In the present study, mean force and potential of mean force acting between two aggregates with aggregation number N = 30 were evaluated as a function of their separation by MD calculations. The repulsive force becomes strong with decreasing distance between the two aggregates before they merge into one. An origin of the repulsive force is an electric double layer formed by the sulfate group and counter sodium ions. Strength of the repulsive force is in good agreement with the theoretical value given by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Once the aggregates establish contact, the force between them turns to be a large attractive force that can be explained by the interfacial tension. In order to form a single micelle from the two aggregates, it is necessary for them to climb over a free energy barrier of 23 kJ/mol. Once, the barrier is overcome, the micelle is stabilized by ˜200 kJ/mol. The time constant of aggregation evaluated from the calculated free energy barrier was about 28 μs at the concentration in our previous study.

  6. Atomic force microscope adhesion measurements and atomistic molecular dynamics simulations at different humidities

    Science.gov (United States)

    Seppä, Jeremias; Reischl, Bernhard; Sairanen, Hannu; Korpelainen, Virpi; Husu, Hannu; Heinonen, Martti; Raiteri, Paolo; Rohl, Andrew L.; Nordlund, Kai; Lassila, Antti

    2017-03-01

    Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected—both in experiments and simulations—factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20-60 %rh. Force-distance adhesion studies at humidity levels between 25 %rh and 53 %rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.

  7. Dynamic Force Reduction and Heat Transfer Improvement for Horizontal Tubes in Large-Particle Gas-Fluidized Beds

    Institute of Scientific and Technical Information of China (English)

    Yusumi Nagahashi; John R.Grace; Kok-Seng Lim; Yutaka Asako

    2008-01-01

    The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces ate smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces.

  8. Embedded atom approach for gold–silicon system from ab initio molecular dynamics simulations using the force matching method

    Indian Academy of Sciences (India)

    A NASSOUR

    2016-09-01

    In the present paper, an empirical embedded atom method (EAM) potential for gold–silicon (Au–Si) is developed by fitting to ab initio force (the ‘force matching’ method) and experimental data. The force database is generated within ab initio molecular dynamics (AIMD). The database includes liquid phase at various temperatures. Classical molecular dynamics simulations are performed to examine structural, coordination numbers, structure factors and dynamic properties of Au$_{81}$Si$_{19}$ alloy, with the interaction described via EAM model. The results are in good agreement with AIMD simulations and experimental data.

  9. Experimental investigation of the link between static and dynamic wetting by forced wetting of nylon filament.

    Science.gov (United States)

    Vega, M J; Gouttière, C; Seveno, D; Blake, T D; Voué, M; De Coninck, J; Clarke, A

    2007-10-09

    Forced wetting experiments with various liquids were conducted to study the dynamic wetting properties of nylon filament. The molecular-kinetic theory of wetting (MKT) was used to interpret the dynamic contact angle data and evaluate the contact-line friction zeta0 at the microscopic scale. By taking account of the viscosity of the liquid, zeta0 could be related exponentially to the reversible work of adhesion. This clearly establishes an experimental link between the static and dynamic wetting properties of the material. Moreover, statistical analysis of the equilibrium molecular displacement frequency K0 and the length of the displacements lambda reveals that these two fundamental parameters of the MKT are strongly correlated, not only in the linearized form of the theory (valid close to equilibrium) but also when the nonlinear form of the equations has to be considered at higher wetting speeds.

  10. Molecular dynamics simulations of lipid membranes with lateral force: rupture and dynamic properties.

    Science.gov (United States)

    Xie, Jun Yu; Ding, Guang Hong; Karttunen, Mikko

    2014-03-01

    Membranes' response to lateral tension, and eventual rupture, remains poorly understood. In this study, pure dipalmitoylphosphatidylcholine (DPPC) lipid bilayers, under tension/pressure, were studied using molecular dynamics (MD) simulations. The irreversible membrane breakdown is demonstrated to depend on the amplitude of lateral tension, loading rate, and the size of the bilayer. In all of our simulations, -200bar lateral pressure was found to be enough to rupture lipid membrane regardless of the loading rate or the membrane size. Loading rate and membrane size had a significant impact on rupture. A variety of dynamic properties of lipid molecules, probability distribution of area per lipid particularly, have been determined, and found to be fundamental for describing membrane behavior in detail, thus providing the quantitative description for the requirement of membrane rupture.

  11. Molecular dynamics simulation of free and forced BSA adsorption on a hydrophobic graphite surface.

    Science.gov (United States)

    Mücksch, Christian; Urbassek, Herbert M

    2011-11-01

    The adsorption of bovine serum albumin (BSA) onto a hydrophobic graphite surface is studied using molecular-dynamics simulation. In addition to the free, that is, unsteered, adsorption, we also investigate forced adsorption, in which the action of an AFM tip pushing the protein with constant force to the surface is modeled. Using an implicit inviscid water model, the adsorption dynamics and energetics are monitored for two different initial protein orientations toward the surface. In all cases, we find that the protein partially unfolds and spreads on the surface. The spreading is in agreement with the well-known high biocompatibility of graphite-based implants. The denaturation is, however, greatly enhanced in the case of forced adsorption. We follow the position of the so-called lipid-binding pocket found in subdomain IIIA (Sudlow site II) during adsorption and find that it is tilted and moved toward the graphite surface in all cases, in agreement with its hydrophobic character. The relevance of our findings for the common measurement procedure of studying protein adhesion using AFM experiments is discussed.

  12. Both contractile axial and lateral traction force dynamics drive amoeboid cell motility.

    Science.gov (United States)

    Bastounis, Effie; Meili, Ruedi; Álvarez-González, Begoña; Francois, Joshua; del Álamo, Juan C; Firtel, Richard A; Lasheras, Juan C

    2014-03-17

    Chemotaxing Dictyostelium discoideum cells adapt their morphology and migration speed in response to intrinsic and extrinsic cues. Using Fourier traction force microscopy, we measured the spatiotemporal evolution of shape and traction stresses and constructed traction tension kymographs to analyze cell motility as a function of the dynamics of the cell's mechanically active traction adhesions. We show that wild-type cells migrate in a step-wise fashion, mainly forming stationary traction adhesions along their anterior-posterior axes and exerting strong contractile axial forces. We demonstrate that lateral forces are also important for motility, especially for migration on highly adhesive substrates. Analysis of two mutant strains lacking distinct actin cross-linkers (mhcA(-) and abp120(-) cells) on normal and highly adhesive substrates supports a key role for lateral contractions in amoeboid cell motility, whereas the differences in their traction adhesion dynamics suggest that these two strains use distinct mechanisms to achieve migration. Finally, we provide evidence that the above patterns of migration may be conserved in mammalian amoeboid cells.

  13. Effects of a multichannel dynamic functional electrical stimulation system on hemiplegic gait and muscle forces.

    Science.gov (United States)

    Qian, Jing-Guang; Rong, Ke; Qian, Zhenyun; Wen, Chen; Zhang, Songning

    2015-11-01

    [Purpose] The purpose of the study was to design and implement a multichannel dynamic functional electrical stimulation system and investigate acute effects of functional electrical stimulation of the tibialis anterior and rectus femoris on ankle and knee sagittal-plane kinematics and related muscle forces of hemiplegic gait. [Subjects and Methods] A multichannel dynamic electrical stimulation system was developed with 8-channel low frequency current generators. Eight male hemiplegic patients were trained for 4 weeks with electric stimulation of the tibia anterior and rectus femoris muscles during walking, which was coupled with active contraction. Kinematic data were collected, and muscle forces of the tibialis anterior and rectus femoris of the affected limbs were analyzed using a musculoskelatal modeling approach before and after training. A paired sample t-test was used to detect the differences between before and after training. [Results] The step length of the affected limb significantly increased after the stimulation was applied. The maximum dorsiflexion angle and maximum knee flexion angle of the affected limb were both increased significantly during stimulation. The maximum muscle forces of both the tibia anterior and rectus femoris increased significantly during stimulation compared with before functional electrical stimulation was applied. [Conclusion] This study established a functional electrical stimulation strategy based on hemiplegic gait analysis and musculoskeletal modeling. The multichannel functional electrical stimulation system successfully corrected foot drop and altered circumduction hemiplegic gait pattern.

  14. Hamiltonian formulation of the conservative self-force dynamics in the Kerr geometry

    Science.gov (United States)

    Fujita, Ryuichi; Isoyama, Soichiro; Le Tiec, Alexandre; Nakano, Hiroyuki; Sago, Norichika; Tanaka, Takahiro

    2017-07-01

    We formulate a Hamiltonian description of the orbital motion of a point particle in Kerr spacetime for generic (eccentric, inclined) orbits, which accounts for the effects of the conservative part of the gravitational self-force. This formulation relies on a description of the particle’s motion as geodesic in a certain smooth effective spacetime, in terms of (generalized) action-angle variables. Clarifying the role played by the gauge freedom in the Hamiltonian dynamics, we extract the gauge-invariant information contained in the conservative self-force. We also propose a possible gauge choice for which the orbital dynamics can be described by an effective Hamiltonian, written solely in terms of the action variables. As an application of our Hamiltonian formulation in this gauge, we derive the conservative self-force correction to the orbital frequencies of Kerr innermost stable spherical (inclined or circular) orbits. This gauge choice also allows us to establish a ‘first law of mechanics’ for black-hole-particle binary systems, at leading order beyond the test-mass approximation.

  15. The development of a two-component force dynamometer and tool control system for dynamic machine tool research

    Science.gov (United States)

    Sutherland, I. A.

    1973-01-01

    The development is presented of a tooling system that makes a controlled sinusoidal oscillation simulating a dynamic chip removal condition. It also measures the machining forces in two mutually perpendicular directions without any cross sensitivity.

  16. Dynamic retentive force of a mandibular unilateral removable partial denture framework with a back-action clasp

    National Research Council Canada - National Science Library

    Park, Innim; Eto, Miho; Wakabayashi, Noriyuki; Hideshima, Masayuki; Ohyama, Takashi

    2001-01-01

    Purpose: The purpose of this study was to investigate the dynamic retentive force of a mandibular unilateral distal-extension partial denture framework with a back-action clasp that was designed in a buccally...

  17. Hydration free energies of cyanide and hydroxide ions from molecular dynamics simulations with accurate force fields

    Science.gov (United States)

    Lee, M.W.; Meuwly, M.

    2013-01-01

    The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.

  18. Modeling of stochastic dynamics of time-dependent flows under high-dimensional random forcing

    Science.gov (United States)

    Babaee, Hessam; Karniadakis, George

    2016-11-01

    In this numerical study the effect of high-dimensional stochastic forcing in time-dependent flows is investigated. To efficiently quantify the evolution of stochasticity in such a system, the dynamically orthogonal method is used. In this methodology, the solution is approximated by a generalized Karhunen-Loeve (KL) expansion in the form of u (x , t ω) = u ̲ (x , t) + ∑ i = 1 N yi (t ω)ui (x , t) , in which u ̲ (x , t) is the stochastic mean, the set of ui (x , t) 's is a deterministic orthogonal basis and yi (t ω) 's are the stochastic coefficients. Explicit evolution equations for u ̲ , ui and yi are formulated. The elements of the basis ui (x , t) 's remain orthogonal for all times and they evolve according to the system dynamics to capture the energetically dominant stochastic subspace. We consider two classical fluid dynamics problems: (1) flow over a cylinder, and (2) flow over an airfoil under up to one-hundred dimensional random forcing. We explore the interaction of intrinsic with extrinsic stochasticity in these flows. DARPA N66001-15-2-4055, Office of Naval Research N00014-14-1-0166.

  19. Molecular dynamics simulations of forced unbending of integrin α(vβ₃.

    Directory of Open Access Journals (Sweden)

    Wei Chen

    2011-02-01

    Full Text Available Integrins may undergo large conformational changes during activation, but the dynamic processes and pathways remain poorly understood. We used molecular dynamics to simulate forced unbending of a complete integrin α(vβ₃ ectodomain in both unliganded and liganded forms. Pulling the head of the integrin readily induced changes in the integrin from a bent to an extended conformation. Pulling at a cyclic RGD ligand bound to the integrin head also extended the integrin, suggesting that force can activate integrins. Interactions at the interfaces between the hybrid and β tail domains and between the hybrid and epidermal growth factor 4 domains formed the major energy barrier along the unbending pathway, which could be overcome spontaneously in ~1 µs to yield a partially-extended conformation that tended to rebend. By comparison, a fully-extended conformation was stable. A newly-formed coordination between the α(v Asp457 and the α-genu metal ion might contribute to the stability of the fully-extended conformation. These results reveal the dynamic processes and pathways of integrin conformational changes with atomic details and provide new insights into the structural mechanisms of integrin activation.

  20. Dynamical Inference from a Kinematic Snapshot: The Force Law in the Solar System

    Science.gov (United States)

    Bovy, Jo; Murray, Iain; Hogg, David W.

    2010-03-01

    If a dynamical system is long-lived and non-resonant (that is, if there is a set of tracers that have evolved independently through many orbital times), and if the system is observed at any non-special time, it is possible to infer the dynamical properties of the system (such as the gravitational force or acceleration law) from a snapshot of the positions and velocities of the tracer population at a single moment in time. In this paper, we describe a general inference technique that solves this problem while allowing (1) the unknown distribution function of the tracer population to be simultaneously inferred and marginalized over, and (2) prior information about the gravitational field and distribution function to be taken into account. As an example, we consider the simplest problem of this kind: we infer the force law in the solar system using only an instantaneous kinematic snapshot (valid at 2009 April 1.0) for the eight major planets. We consider purely radial acceleration laws of the form ar = -A [r/r 0]-α, where r is the distance from the Sun. Using a probabilistic inference technique, we infer 1.989 things, inference of Milky Way dynamics from Gaia-like observations.

  1. Polymer Droplet Dynamic Wetting Measurement at the Nanometer Scale on Smooth Surfaces Using Atomic Force Microscopy

    Science.gov (United States)

    Soleymaniha, Mohammadreza; Felts, Jonathan Robert; Anml Team

    2016-11-01

    Fluid spreading is a complex phenomenon driven strongly by intermolecular forces that requires nanometer scale microscopy to observe and understand. We present a technique for measuring molten polymer spreading dynamics with nanometer scale spatial resolution at elevated temperatures on sapphire, silicon oxide and mica using tapping-mode atomic force microscopy (AFM). The experimental setup is used to measure the spreading dynamics of polystyrene droplets with 2 μ m diameters at 115-175 C. Custom image processing algorithms realize the droplet height, radius, volume and contact angle of the droplet over time. The contact angle evolution followed a power law with time with experimental exponent values of -0.26, -0.08, and -0.2 for sapphire, silicon oxide, and mica, respectively at 115 C. The non-zero steady state contact angles result in a slower evolution of contact angle with time compared to Tanner's Law, as expected. We observe local crystallinity on the molten droplet surface, where crystalline structures appear to nucleate at the contact line and migrate toward the top of the droplet. Increasing the temperature from 115 C to 175 C reduced surface crystallinity from 35% to 12%, consistent with increasingly energetically favorable amorphous phase as the temperature approaches the melting temperature. This platform provides a way to measure spreading dynamics of extremely small volumes of heterogeneously complex fluids not possible through other means. Dr.Jonathan Felts is the principal investigator of the ANML research group in Mechanical Engineering Department of Texas A&M University.

  2. Climate–Glacier Dynamics and Topographic Forcing in the Karakoram Himalaya: Concepts, Issues and Research Directions

    Directory of Open Access Journals (Sweden)

    Iliyana D. Dobreva

    2017-06-01

    Full Text Available Understanding climate-glacier dynamics in High Mountain Asia is of critical importance to address issues including water resources, sea-level rise, mountain geodynamics, natural hazards and ecosystem sustainability. The Karakoram Himalaya is arguably the least understood region, given its extreme topography, climate-system coupling, and advancing and surge-type glaciers that exhibit complex flow patterns. Glacier fluctuations in the Karakoram Himalaya are highly variable in space and time because of numerous controlling factors, including the westerlies, the Indian summer monsoon, various teleconnections, topographic effects, glacier debris-cover characteristics, glacier dynamics, and geological conditions. The influence of the integrative coupling of forcing factors, however, has not been adequately assessed for characterizing the glaciers in the Karakoram Himalaya. Given the scarcity of in-situ data and the difficulty of conducting fieldwork on these glaciers, recent research has focused on utilizing remote sensing, geospatial technologies, and scientific modeling to obtain baseline information about the state of glaciers in the region. This review summarizes our current knowledge of glaciers, climate-glacier interaction, and topographic forcing in the Karakoram Himalaya, and demonstrates the complexities in mountain geodynamics that influence climate-glacier dynamics. Innovative analysis is also presented in support of our review and discussion.

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

    Science.gov (United States)

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

    2013-02-07

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

  4. Dynamics of dissipative self-assembly of particles interacting through oscillatory forces

    Energy Technology Data Exchange (ETDEWEB)

    Tagliazucchi, M. [Department of Biomedical Engineering; Department of Chemistry and Chemistry of Life Processes Institute; Northwestern University; Evanston, USA; INQUIMAE-CONICET; Szleifer, I. [Department of Biomedical Engineering; Department of Chemistry and Chemistry of Life Processes Institute; Northwestern University; Evanston, USA

    2016-01-01

    Dissipative self-assembly is the formation of ordered structures far from equilibrium, which continuously uptake energy and dissipate it into the environment. Due to its dynamical nature, dissipative self-assembly can lead to new phenomena and possibilities of self-organization that are unavailable to equilibrium systems. Understanding the dynamics of dissipative self-assembly is required in order to direct the assembly to structures of interest. In the present work, Brownian dynamics simulations and analytical theory were used to study the dynamics of self-assembly of a mixture of particles coated with weak acids and bases under continuous oscillations of the pH. The pH of the system modulates the charge of the particles and, therefore, the interparticle forces oscillate in time. This system produces a variety of self-assembled structures, including colloidal molecules, fibers and different types of crystalline lattices. The most important conclusions of our study are: (i) in the limit of fast oscillations, the whole dynamics (and not only those at the non-equilibrium steady state) of a system of particles interacting through time-oscillating interparticle forces can be described by an effective potential that is the time average of the time-dependent potential over one oscillation period; (ii) the oscillation period is critical to determine the order of the system. In some cases the order is favored by very fast oscillations while in others small oscillation frequencies increase the order. In the latter case, it is shown that slow oscillations remove kinetic traps and, thus, allow the system to evolve towards the most stable non-equilibrium steady state.

  5. Cantilever tilt causing amplitude related convolution in dynamic mode atomic force microscopy.

    Science.gov (United States)

    Wang, Chunmei; Sun, Jielin; Itoh, Hiroshi; Shen, Dianhong; Hu, Jun

    2011-01-01

    It is well known that the topography in atomic force microscopy (AFM) is a convolution of the tip's shape and the sample's geometry. The classical convolution model was established in contact mode assuming a static probe, but it is no longer valid in dynamic mode AFM. It is still not well understood whether or how the vibration of the probe in dynamic mode affects the convolution. Such ignorance complicates the interpretation of the topography. Here we propose a convolution model for dynamic mode by taking into account the typical design of the cantilever tilt in AFMs, which leads to a different convolution from that in contact mode. Our model indicates that the cantilever tilt results in a dynamic convolution affected by the absolute value of the amplitude, especially in the case that corresponding contact convolution has sharp edges beyond certain angle. The effect was experimentally demonstrated by a perpendicular SiO(2)/Si super-lattice structure. Our model is useful for quantitative characterizations in dynamic mode, especially in probe characterization and critical dimension measurements.

  6. Droplet spreading driven by van der Waals force: a molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Wu Congmin [Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Qian Tiezheng [Department of Mathematics and Joint KAUST-HKUST Micro/Nanofluidics Laboratory, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Sheng Ping, E-mail: maqian@ust.h [Department of Physics and William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2010-08-18

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t){approx}{radical}t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid.

  7. Droplet spreading driven by van der Waals force: a molecular dynamics study

    KAUST Repository

    Wu, Congmin

    2010-07-07

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t) ∼ √t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid. © 2010 IOP Publishing Ltd.

  8. Vegetation Dynamics and Associated Driving Forces in Eastern China during 1999–2008

    Directory of Open Access Journals (Sweden)

    Jian Peng

    2015-10-01

    Full Text Available Vegetation is one of the most important components of the terrestrial ecosystem and, thus, monitoring the spatial and temporal dynamics of vegetation has become the key to exploring the basic process of the terrestrial ecosystem. Vegetation change studies have focused on the relationship between climatic factors and vegetation dynamics. However, correlations among the climatic factors always disturb the results. In addition, the impact of anthropogenic activities on vegetation dynamics was indeterminate. Here, vegetation dynamics in 14 provinces in Eastern China over a 10-year period was quantified to determine the driving mechanisms relating to climate and anthropogenic factors using partial correlation analysis. The results showed that from 1999 to 2008, the vegetation density increased in the whole, with spatial variations. The vegetation improvement was concentrated in the Yangtze River Delta, with the vegetation degradation concentrated in the other developed areas, such as Beijing-Tianjin-Hebei Region and the Pearl River Delta. The annual NDVI changes were mainly driven by temperature in Northeast China and the Pearl River Delta, and by precipitation in the Bohai Rim; while in the Yangtze River Delta, the driving forces of temperature and precipitation almost equaled each other.  Furthermore, the impact of anthropogenic activities on vegetation dynamics had accumulative effects in the time series, and had a phase effect on the vegetation change trend.

  9. Dynamics of a disturbed sessile drop measured by atomic force microscopy (AFM).

    Science.gov (United States)

    McGuiggan, Patricia M; Grave, Daniel A; Wallace, Jay S; Cheng, Shengfeng; Prosperetti, Andrea; Robbins, Mark O

    2011-10-04

    A new method for studying the dynamics of a sessile drop by atomic force microscopy (AFM) is demonstrated. A hydrophobic microsphere (radius, r ∼ 20-30 μm) is brought into contact with a small sessile water drop resting on a polytetrafluoroethylene (PTFE) surface. When the microsphere touches the liquid surface, the meniscus rises onto it because of capillary forces. Although the microsphere volume is 6 orders of magnitude smaller than the drop, it excites the normal resonance modes of the liquid interface. The sphere is pinned at the interface, whose small (drop volumes between 5 and 200 μL. The results for the two lowest normal modes are quantitatively consistent with continuum calculations for the natural frequency of hemispherical drops with no adjustable parameters. The method may enable sensitive measurements of volume, surface tension, and viscosity of small drops.

  10. Self-Sterilized Flexible Single-Electrode Triboelectric Nanogenerator for Energy Harvesting and Dynamic Force Sensing.

    Science.gov (United States)

    Guo, Huijuan; Li, Tao; Cao, Xiaotao; Xiong, Jin; Jie, Yang; Willander, Magnus; Cao, Xia; Wang, Ning; Wang, Zhong Lin

    2017-01-24

    Triboelectric nanogenerators (TENGs) offer great opportunities to deploy advanced wearable electronics that integrate a power generator and smart sensor, which eliminates the associated cost and sustainability concerns. Here, an embodiment of such integrated platforms has been presented in a graphene oxide (GO) based single-electrode TENG (S-TENG). The as-designed multifunctional device could not only harvest tiny bits of mechanical energy from ambient movements with a high power density of 3.13 W·m(-2) but also enable detecting dynamic force with an excellent sensitivity of about 388 μA·MPa(-1). Because of the two-dimensional nanostructure and excellent surface properties, the GO-based S-TENG shows sensitive force detection and sound antimicrobial activity in comparison with conventional poly(tetrafluoroethylene) (PTFE) electrodes. This technology offers great applicability prospects in portable/wearable electronics, micro/nanoelectromechanical devices, and self-powered sensors.

  11. Force-induced dynamical properties of multiple cytoskeletal filaments are distinct from that of single filaments

    CERN Document Server

    Das, Dipjyoti; 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 show that collective properties of multiple filaments under force are very distinct from the properties of a single filament under similar conditions -- these distinctions manifest as follows: (i) the collapse time during collective catastrophe for a multifilament system is much larger than that of a single filament with the same average length, (ii) force-dependence of the cap-size distribution of multiple filaments are quantitatively different from that of single filament, (iii) the diffusion constant associated with the system length fluctuations is distinct for multiple filaments, (iv) switching dynamics of multiple filaments between capped and uncapped states and the fluctuations therein are also distinct. We build a un...

  12. A Fluid Dynamics Approach for the Computation of Non-linear Force-Free Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    Jing-Qun Li; Jing-Xiu Wang; Feng-Si Wei

    2003-01-01

    Inspired by the analogy between the magnetic field and velocity fieldof incompressible fluid flow, we propose a fluid dynamics approach for comput-ing nonlinear force-free magnetic fields. This method has the advantage that thedivergence-free condition is automatically satisfied, which is a sticky issue for manyother algorithms, and we can take advantage of modern high resolution algorithmsto process the force-free magnetic field. Several tests have been made based on thewell-known analytic solution proposed by Low & Lou. The numerical results arein satisfactory agreement with the analytic ones. It is suggested that the newlyproposed method is promising in extrapolating the active region or the whole sunmagnetic fields in the solar atmosphere based on the observed vector magnetic fieldon the photosphere.

  13. Dynamics and Complexity in a Time Delay Model of RNA Silencing with Periodic Forcing

    Directory of Open Access Journals (Sweden)

    Svetoslav Nikolov

    2008-10-01

    Full Text Available Simple periodic behavior and occurrence of complex oscillatory phenomena underlie of a large number of biochemical system models. In many cases the transition from stable to simple/complex oscillatory behavior can be connected with the appearance of abnormal process likes as cancer. In this paper we propose a time delay model of RNA silencing (also known as RNA interference with periodic forcing. In organisms with RNA silencing, each cell has a miniature "immune system" able to generate and amplify specific responses to a variety of gene transcripts. The consequences of a time delay on the dynamics of this model are analysed using Hopf's theorem. Our analytical calculations predict that time delay acts as a key bifurcation parameter. From the accomplished numerical results, it becomes clear that model has complexity oscillatory behavior when the amplitude of periodic force (i.e. the confusion in the target mRNA synthesis is large.

  14. Spiral Wave Dynamics in a Response System Subjected to a Spiral Wave Forcing

    Institute of Scientific and Technical Information of China (English)

    LI Guang-Zhao; CHEN Yong-Qi; TANG Guo-Ning; LIU Jun-Xian

    2011-01-01

    @@ Unidirectional linear error feedback coupling of two excitable medium systems displaying spiral waves is considered.The spiral wave in the response system is thus subjected to a spiral wave forcing.We find that the unidirectional feedback coupling can lead to richer behaviour than the mutual coupling.The spiral wave dynamics in the response system depends on the coupling strength and frequency mismatch.When the coupling strength is small, the feedback coupling induces the drift or meander of the forced spiral wave.When the coupling strength is large enough, the feedback coupling may lead to the transition from spiral wave to anti-target or target-like wave.The generation of anti-target wave in coupled excitable media is observed for the first time.Furthermore, when the coupling strength is strong, the synchronization between two subsystems can be established.%Unidirectional linear error feedback coupling of two excitable medium systems displaying spiral waves is considered. The spiral wave in the response system is thus subjected to a spiral wave forcing. We find that the unidirectional feedback coupling can lead to richer behaviour than the mutual coupling. The spiral wave dynamics in the response system depends on the coupling strength and frequency mismatch. When the coupling strength is small, the feedback coupling induces the drift or meander of the forced spiral wave. When the coupling strength is large enough, the feedback coupling may lead to the transition from spiral wave to anti-target or target-like wave. The generation of anti-target wave in coupled excitable media is observed for the first time. Furthermore,when the coupling strength is strong, the synchronization between two subsystems can be established.

  15. Inverse Force Determination on a Small Scale Launch Vehicle Model Using a Dynamic Balance

    Science.gov (United States)

    Ngo, Christina L.; Powell, Jessica M.; Ross, James C.

    2017-01-01

    A launch vehicle can experience large unsteady aerodynamic forces in the transonic regime that, while usually only lasting for tens of seconds during launch, could be devastating if structural components and electronic hardware are not designed to account for them. These aerodynamic loads are difficult to experimentally measure and even harder to computationally estimate. The current method for estimating buffet loads is through the use of a few hundred unsteady pressure transducers and wind tunnel test. Even with a large number of point measurements, the computed integrated load is not an accurate enough representation of the total load caused by buffeting. This paper discusses an attempt at using a dynamic balance to experimentally determine buffet loads on a generic scale hammer head launch vehicle model tested at NASA Ames Research Center's 11' x 11' transonic wind tunnel. To use a dynamic balance, the structural characteristics of the model needed to be identified so that the natural modal response could be and removed from the aerodynamic forces. A finite element model was created on a simplified version of the model to evaluate the natural modes of the balance flexures, assist in model design, and to compare to experimental data. Several modal tests were conducted on the model in two different configurations to check for non-linearity, and to estimate the dynamic characteristics of the model. The experimental results were used in an inverse force determination technique with a psuedo inverse frequency response function. Due to the non linearity, the model not being axisymmetric, and inconsistent data between the two shake tests from different mounting configuration, it was difficult to create a frequency response matrix that satisfied all input and output conditions for wind tunnel configuration to accurately predict unsteady aerodynamic loads.

  16. Measurement and analysis of traction force dynamics in response to vasoactive agonists.

    Science.gov (United States)

    Yang, Michael T; Reich, Daniel H; Chen, Christopher S

    2011-06-01

    Mechanical traction forces exerted by adherent cells on their surroundings serve an important role in a multitude of cellular and physiological processes including cell motility and multicellular rearrangements. For endothelial cells, contraction also provides a means to disrupt cell-cell junctions during inflammation to increase permeability between blood and interstitial tissue compartments. The degree of contractility exhibited by endothelial cells is influenced by numerous soluble factors, such as thrombin, histamine, lysophosphatidic acid, sphingosine-1-phosphate, and vascular endothelial growth factor (VEGF). Upon binding to cell surface receptors, these agents trigger changes in cytoskeletal organization, adhesion and myosin II activity to varying degrees. While conventional antibody-based biochemical assays are suitable for detecting relatively large changes in biomarkers of contractility in an end-point format, they cannot resolve subtle or rapid changes in contractility and cannot do so noninvasively. To overcome these limitations, we developed an approach to measure the contractile response of single cells exposed to contractility agonists with high spatiotemporal resolution. A previously developed traction force sensor, comprised of dense arrays of elastomeric microposts on which cells are cultured, was combined with custom, semi-automated software developed here to extract strain energy measurements from thousands of time-lapse images of micropost arrays deformed by adherent cells. Using this approach we corroborated the differential effects of known agonists of contractility and characterized the dynamics of their effects. All of these agonists produced a characteristic first-order rise and plateau in forces, except VEGF, which stimulated an early transient spike in strain energy followed by a sustained increase. This novel, two-phase contractile response was present in a subpopulation of cells, was mediated through both VEGFR2 and ROCK activation

  17. Influence of coupling on thermal forces and dynamic friction in plasmas with multiple ion species

    CERN Document Server

    Kagan, Grigory; Daligault, Jerome

    2016-01-01

    The recently proposed effective potential theory [Phys. Rev. Lett. 110, 235001 (2013)] is used to investigate the influence of coupling on inter-ion-species diffusion and momentum exchange in multi-component plasmas. Thermo-diffusion and the thermal force are found to diminish rapidly as strong coupling onsets. For the same coupling parameters, the dynamic friction coefficient is found to tend to unity. These results provide an impetus for addressing the role of coupling on diffusive processes in inertial confinement fusion experiments.

  18. Dynamics of ions in a water drop using the AMOEBA polarizable force field

    Science.gov (United States)

    Thaunay, Florian; Ohanessian, Gilles; Clavaguéra, Carine

    2017-03-01

    Various ions carrying a charge from -2 to +3 were confined in a drop of 100 water molecules as a way to model coordination properties inside the cluster and at the interface. The behavior of the ions has been followed by molecular dynamics with the AMOEBA polarizable force field. Multiply charged ions and small singly charged ions are found to lie inside the droplet, while bigger monovalent ions sit near the surface. The results provide a coherent picture of average structural properties as well as residence times for which a general trend is proposed, especially for the anions.

  19. Is transcription the dominant force during dynamic changes in gene expression?

    Science.gov (United States)

    Turner, Martin

    2011-01-01

    Dynamic changes in gene expression punctuate lymphocyte development and are a characteristic of lymphocyte activation. A prevailing view has been that these changes are driven by DNA transcription factors, which are the dominant force in gene expression. Accumulating evidence is challenging this DNA centric view and has highlighted the prevalence and dynamic nature of RNA handling mechanisms. Alternative splicing and differential polyadenylation appear to be more widespread than first thought. Changes in mRNA decay rates also affect the abundance of transcripts and this mechanism may contribute significantly to gene expression. Additional RNA handling mechanisms that control the intracellular localization of mRNA and association with translating ribosomes are also important. Thus, gene expression is regulated through the coordination of transcriptional and post-transcriptional mechanisms. Developing a more "RNA centric" view of gene expression will allow a more systematic understanding of how gene expression and cell function are integrated.

  20. Impact of External Forcing on Glacier Dynamics at Jakobshavn Isbræ during 1840-2012

    DEFF Research Database (Denmark)

    Muresan, Ioana Stefania; Khan, Shfaqat Abbas; Aschwanden, Andy

    thickness or retreat of the floating tongue of a glacier) caused by enhanced calving or a longer-term thinning due to a mass deficit of the ice sheet. Recent findings indicate the reduced buttressing at the marine terminus is responsible for the recent dynamic changes observed in Greenland......-term trends of several decade time scales. Here, we study the mechanisms controlling dynamic changes at the terminus of Jakobshavn Isbræ over a period of 172 years. The recent glacier acceleration began in late 1990s but there is evidence for glacier retreat of comparable magnitude in 1930s, when a similarly...... warm period occurred. To control the acceleration and retreat based on observed front positions during 1840-2012, we use an ocean model modifier that implements forcing at the ocean boundary using melange back pressure offsets. The mean temperature anomaly in west Greenland, the North Atlantic...

  1. Invited Review Nanoscale devices fabricated by dynamic ploughing with an atomic force microscope

    Science.gov (United States)

    Kunze, Ulrich

    2002-01-01

    A review is given on the dynamic ploughing technique and its application on the fabrication of nanoscale semiconductor structures. The vibrating tip of an atomic force microscope is used to dynamically plough furrows into a polymer layer of a few nm thickness on top of the semiconductor surface. Wet-chemical etching transfers the desired line pattern. The resulting grooves of 50-100 nm width form an arrangement of barriers in the electron layer of a conventional modulation-doped GaAs/AlGaAs heterostructure. A new type of heterostructure with a compensating p-type doped cap layer shows an electron enhancement if the cap layer is selectively removed. Etching a groove in these structures enables one to induce a one-dimensional electron system. Both types of structures are used to fabricate various ballistic quantum devices and Coulomb-blockade structures.

  2. BAL: A library for the brute-force analysis of dynamical systems

    Science.gov (United States)

    Linaro, Daniele; Storace, Marco

    2016-04-01

    This paper describes the functionality and usage of BAL, a C/C++ library with a Python front-end for the brute-force analysis of continuous-time dynamical systems described by ordinary differential equations (ODEs). BAL provides an easy-to-use wrapper for the efficient numerical integration of ODEs and, by detecting intersections of the trajectory with appropriate Poincaré sections, allows to classify the asymptotic trajectory of a dynamical system for bifurcation analysis. Some examples of application are discussed, concerning two-dimensional bifurcation diagrams, Lyapunov exponents and finite-time Lyapunov exponents, basins of attraction, simulation of switching ODE systems, and integration with AUTO, a software package for continuation analysis.

  3. Correlation networks from flows. The case of forced and time-dependent advection-diffusion dynamics

    CERN Document Server

    Tupikina, Liubov; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen

    2016-01-01

    Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our r...

  4. Boundary slip study on hydrophilic, hydrophobic, and superhydrophobic surfaces with dynamic atomic force microscopy.

    Science.gov (United States)

    Bhushan, Bharat; Wang, Yuliang; Maali, Abdelhamid

    2009-07-21

    Slip length has been measured using the dynamic atomic force microscopy (AFM) method. Unlike the contact AFM method, the sample surface approaches an oscillating sphere with a very low velocity in the dynamic AFM method. During this process, the amplitude and phase shift data are recorded to calculate the hydrodynamic damping coefficient, which is then used to obtain slip length. In this study, a glass sphere with a large radius was glued to the end of an AFM cantilever to measure the slip length on rough surfaces. Experimental results for hydrophilic, hydrophobic, and superhydrophobic surfaces show that the hydrodynamic damping coefficient decreases from the hydrophilic surface to the hydrophobic surface and from the hydrophobic one to the superhydrophobic one. The slip lengths obtained on the hydrophobic and superhydrophobic surfaces are 43 and 236 nm, respectively, which indicates increasing boundary slip from the hydrophobic surface to the superhydrophobic one.

  5. Inertial forces affect fluid front displacement dynamics in a pore-throat network model.

    Science.gov (United States)

    Moebius, Franziska; Or, Dani

    2014-08-01

    The seemingly regular and continuous motion of fluid displacement fronts in porous media at the macroscopic scale is propelled by numerous (largely invisible) pore-scale abrupt interfacial jumps and pressure bursts. Fluid fronts in porous media are characterized by sharp phase discontinuities and by rapid pore-scale dynamics that underlie their motion; both attributes challenge standard continuum theories of these flow processes. Moreover, details of pore-scale dynamics affect front morphology and subsequent phase entrapment behind a front and thereby shape key macroscopic transport properties of the unsaturated zone. The study presents a pore-throat network model that focuses on quantifying interfacial dynamics and interactions along fluid displacement fronts. The porous medium is represented by a lattice of connected pore throats capable of detaining menisci and giving rise to fluid-fluid interfacial jumps (the study focuses on flow rate controlled drainage). For each meniscus along the displacement front we formulate a local inertial, capillary, viscous, and hydrostatic force balance that is then solved simultaneously for the entire front. The model enables systematic evaluation of the role of inertia and boundary conditions. Results show that while displacement patterns are affected by inertial forces mainly by invasion of throats with higher capillary resistance, phase entrapment (residual saturation) is largely unaffected by inertia, limiting inertial effects on hydrological properties behind a front. Interfacial jump velocities are often an order of magnitude larger than mean front velocity, are strongly dependent on geometrical throat dimensions, and become less predictable (more scattered) when inertia is considered. Model simulations of the distributions of capillary pressure fluctuations and waiting times between invasion events follow an exponential distribution and are in good agreement with experimental results. The modeling approach provides insights

  6. Nonlinear dynamics of tapping mode atomic force microscopy in the bistable phase

    Science.gov (United States)

    Bahrami, Arash; Nayfeh, Ali H.

    2013-03-01

    Nonlinear dynamics of amplitude modulation atomic force microscopy (AFM) is studied employing a reduced-order model based on a differential quadrature method (DQM). The AFM microcantilever is assumed to be operating in the dynamic contact or tapping mode while the microcantilever tip being initially located in the bistable region. We have found that the DQM is capable of precise prediction of the static bifurcation diagram and natural frequencies of the microcantilever. We have used the DQM to discretize the partial-differential equation governing the microcantilever motion and a finite difference method (FDM) to calculate limit-cycle responses of the AFM tip. It is shown that a combination of the DQM and FDM applied, respectively, to discretize the spatial and temporal derivatives provides an efficient, accurate procedure to address the complicated dynamic behavior exhibited by the AFM probe. The procedure was, therefore, utilized to study the response of the microcantilever to a base harmonic excitation through several numerical examples. We found that the dynamics of the AFM probe in the bistable region is totally different from those in the monostable region.

  7. Communication: Contrasting effects of glycerol and DMSO on lipid membrane surface hydration dynamics and forces

    Science.gov (United States)

    Schrader, Alex M.; Cheng, Chi-Yuan; Israelachvili, Jacob N.; Han, Songi

    2016-07-01

    Glycerol and dimethyl sulfoxide (DMSO) are commonly used cryoprotectants in cellular systems, but due to the challenges of measuring the properties of surface-bound solvent, fundamental questions remain regarding the concentration, interactions, and conformation of these solutes at lipid membrane surfaces. We measured the surface water diffusivity at gel-phase dipalmitoylphosphatidylcholine (DPPC) bilayer surfaces in aqueous solutions containing ≤7.5 mol. % of DMSO or glycerol using Overhauser dynamic nuclear polarization. We found that glycerol similarly affects the diffusivity of water near the bilayer surface and that in the bulk solution (within 20%), while DMSO substantially increases the diffusivity of surface water relative to bulk water. We compare these measurements of water dynamics with those of equilibrium forces between DPPC bilayers in the same solvent mixtures. DMSO greatly decreases the range and magnitude of the repulsive forces between the bilayers, whereas glycerol increases it. We propose that the differences in hydrogen bonding capability of the two solutes leads DMSO to dehydrate the lipid head groups, while glycerol affects surface hydration only as much as it affects the bulk water properties. The results suggest that the mechanism of the two most common cryoprotectants must be fundamentally different: in the case of DMSO by decoupling the solvent from the lipid surface, and in the case of glycerol by altering the hydrogen bond structure and intermolecular cohesion of the global solvent, as manifested by increased solvent viscosity.

  8. Precipitation rate spectra as dependent on dynamic forcing: application to probabilistic forecasting

    Directory of Open Access Journals (Sweden)

    A. R. Ivanova

    2007-04-01

    Full Text Available Occurrence frequencies, OF, of 12-h precipitation amounts, P, at stations in the former European USSR are displayed as dependent on dynamic forcing of vertical motions. The dynamic forcing is described by a "frontal parameter", F (calculated in the points of objective analysis grid, which depends on the surface pressure field curvature and on the baroclinicity in the lower half of the troposphere. The precipitation rate spectra for 4 seasons, calculated from a large sample of data (7 years, about 650 000 values of P for one season, show a monotonous OF growth of all ranges of P>1 mm/12 h with F increase. The growth is especially significant for heavy precipitation. As a result, F is shown to be an informative predictor of P spectrum or of probability of any given range of P. As a next step, two-dimensional spectra of precipitation occurrence frequency, as a function of F and LNB, that is, OF (F, LNB, are calculated, LNB being the level of neutral buoyancy at the gridpoint, an estimate of grid-scale convective instability. On this basis, an approach to probabilistic forecasting is suggested.

  9. Dynamic light scattering and atomic force microscopy techniques for size determination of polyurethane nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Giehl Zanetti-Ramos, Betina [Laboratorio de Bioenergetica e Bioquimica de Macromoleculas, Departamento de Ciencias Farmaceuticas (Brazil)], E-mail: betinagzramos@pq.cnpq.br; Beddin Fritzen-Garcia, Mauricia [Laboratorio de Bioenergetica e Bioquimica de Macromoleculas, Departamento de Ciencias Farmaceuticas (Brazil); Schweitzer de Oliveira, Cristian; Avelino Pasa, Andre [Laboratorio de Filmes Finos e Superficie, Departamento de Fisica (Brazil); Soldi, Valdir [Grupo de Estudos em Materiais Polimericos, Departamento de Quimica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, SC (Brazil); Borsali, Redouane [Centre de Recherche sur les Macromolecules Vegetales CERMAV/CNRS, 38041 - Grenoble (France); Creczynski-Pasa, Tania Beatriz [Laboratorio de Bioenergetica e Bioquimica de Macromoleculas, Departamento de Ciencias Farmaceuticas (Brazil)

    2009-03-01

    Nanoparticles have applications in various industrial fields principally in drug delivery. Nowadays, there are several processes for manufacturing colloidal polymeric systems and methods of preparation as well as of characterization. In this work, Dynamic Light Scattering and Atomic Force Microscopy techniques were used to characterize polyurethane nanoparticles. The nanoparticles were prepared by miniemulsion technique. The lipophilic monomers, isophorone diisocyanate (IPDI) and natural triol, were emulsified in water containing surfactant. In some formulations the poly(ethylene glycol) was used as co-monomer to obtain the hydrophilic and pegylated nanoparticles. Polyurethane nanoparticles observed by atomic force microscopy (AFM) were spherical with diameter around 209 nm for nanoparticles prepared without PEG. From AFM imaging two populations of nanoparticles were observed in the formulation prepared with PEG (218 and 127 nm) while dynamic light scattering (DLS) measurements showed a monodisperse size distribution around 250 nm of diameters for both formulations. The polydispersity index of the formulations and the experimental procedures could influence the particle size determination with these techniques.

  10. Development of reactive force fields using ab initio molecular dynamics simulation minimally biased to experimental data

    Science.gov (United States)

    Chen, Chen; Arntsen, Christopher; Voth, Gregory A.

    2017-10-01

    Incorporation of quantum mechanical electronic structure data is necessary to properly capture the physics of many chemical processes. Proton hopping in water, which involves rearrangement of chemical and hydrogen bonds, is one such example of an inherently quantum mechanical process. Standard ab initio molecular dynamics (AIMD) methods, however, do not yet accurately predict the structure of water and are therefore less than optimal for developing force fields. We have instead utilized a recently developed method which minimally biases AIMD simulations to match limited experimental data to develop novel multiscale reactive molecular dynamics (MS-RMD) force fields by using relative entropy minimization. In this paper, we present two new MS-RMD models using such a parameterization: one which employs water with harmonic internal vibrations and another which uses anharmonic water. We show that the newly developed MS-RMD models very closely reproduce the solvation structure of the hydrated excess proton in the target AIMD data. We also find that the use of anharmonic water increases proton hopping, thereby increasing the proton diffusion constant.

  11. Molecular recognition imaging using tuning fork-based transverse dynamic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Hofer, Manuel; Adamsmaier, Stefan [University of Linz, Institute for Biophysics, Altenbergerstr. 69, 4040 Linz (Austria); Zanten, Thomas S. van [IBEC-Institute for Bioengineering of Catalonia and CIBER-Bbn, Baldiri i Reixac 15-21, Barcelona 08028 (Spain); Chtcheglova, Lilia A. [University of Linz, Institute for Biophysics, Altenbergerstr. 69, 4040 Linz (Austria); Manzo, Carlo [IBEC-Institute for Bioengineering of Catalonia and CIBER-Bbn, Baldiri i Reixac 15-21, Barcelona 08028 (Spain); Duman, Memed [University of Linz, Institute for Biophysics, Altenbergerstr. 69, 4040 Linz (Austria); Mayer, Barbara [Christian Doppler Laboratory for Nanoscopic Methods in Biophysics, Institute for Biophysics, University of Linz, Altenbergerstr. 69, 4040 Linz (Austria); Ebner, Andreas [University of Linz, Institute for Biophysics, Altenbergerstr. 69, 4040 Linz (Austria); Christian Doppler Laboratory for Nanoscopic Methods in Biophysics, Institute for Biophysics, University of Linz, Altenbergerstr. 69, 4040 Linz (Austria); Moertelmaier, Manuel; Kada, Gerald [Agilent Technologies Austria GmbH, Aubrunnerweg 11, 4040 Linz (Austria); Garcia-Parajo, Maria F. [IBEC-Institute for Bioengineering of Catalonia and CIBER-Bbn, Baldiri i Reixac 15-21, Barcelona 08028 (Spain); ICREA-Institucio Catalana de Recerca i Estudis Avancats, 08010 Barcelona (Spain); Hinterdorfer, Peter, E-mail: peter.hinterdorfer@jku.at [University of Linz, Institute for Biophysics, Altenbergerstr. 69, 4040 Linz (Austria); Christian Doppler Laboratory for Nanoscopic Methods in Biophysics, Institute for Biophysics, University of Linz, Altenbergerstr. 69, 4040 Linz (Austria); Kienberger, Ferry [Agilent Technologies Austria GmbH, Aubrunnerweg 11, 4040 Linz (Austria)

    2010-05-15

    We demonstrate simultaneous transverse dynamic force microscopy and molecular recognition imaging using tuning forks as piezoelectric sensors. Tapered aluminum-coated glass fibers were chemically functionalized with biotin and anti-lysozyme molecules and attached to one of the prongs of a 32 kHz tuning fork. The lateral oscillation amplitude of the tuning fork was used as feedback signal for topographical imaging of avidin aggregates and lysozyme molecules on mica substrate. The phase difference between the excitation and detection signals of the tuning fork provided molecular recognition between avidin/biotin or lysozyme/anti-lysozyme. Aggregates of avidin and lysozyme molecules appeared as features with heights of 1-4 nm in the topographic images, consistent with single molecule atomic force microscopy imaging. Recognition events between avidin/biotin or lysozyme/anti-lysozyme were detected in the phase image at high signal-to-noise ratio with phase shifts of 1-2{sup o}. Because tapered glass fibers and shear-force microscopy based on tuning forks are commonly used for near-field scanning optical microscopy (NSOM), these results open the door to the exciting possibility of combining optical, topographic and biochemical recognition at the nanometer scale in a single measurement and in liquid conditions.

  12. Forced Desorption of Bovine Serum Albumin and Lysozyme from Graphite: Insights from Molecular Dynamics Simulation.

    Science.gov (United States)

    Mücksch, Christian; Urbassek, Herbert M

    2016-08-18

    We use molecular dynamics (MD) simulation to study the adsorption and desorption of two widely different proteins, bovine serum albumin (BSA) and lysozyme, on a graphite surface. The adsorption is modeled using accelerated MD to allow the proteins to find optimum conformations on the surface. Our results demonstrate that the "hard protein" lysozyme retains much of its secondary structure during adsorption, whereas BSA loses it almost completely. BSA has a considerably larger adsorption energy compared to that of lysozyme, which does not scale with chain length. Desorption simulations are carried out using classical steered MD. The BSA molecule becomes fully unzipped during pull-off, whereas several helices survive this process in lysozyme. The unzipping process shows up in the force-distance curve of BSA as a series of peaks, whereas only a single or few, depending on protein orientation, force peaks occur for lysozyme. The maximum desorption force is larger for BSA than for lysozyme, but only by a factor of about 2.3.

  13. Dynamic control of aerodynamic forces on a moving platform using active flow control

    Science.gov (United States)

    Brzozowski, Daniel P.

    The unsteady interaction between trailing edge aerodynamic flow control and airfoil motion in pitch and plunge is investigated in wind tunnel experiments using a two degree-of-freedom traverse which enables application of time-dependent external torque and forces by servo motors. The global aerodynamic forces and moments are regulated by controlling vorticity generation and accumulation near the trailing edge of the airfoil using hybrid synthetic jet actuators. The dynamic coupling between the actuation and the time-dependent flow field is characterized using simultaneous force and particle image velocimetry (PIV) measurements that are taken phase-locked to the commanded actuation waveform. The effect of the unsteady motion on the model-embedded flow control is assessed in both trajectory tracking and disturbance rejection maneuvers. The time-varying aerodynamic lift and pitching moment are estimated from a PIV wake survey using a reduced order model based on classical unsteady aerodynamic theory. These measurements suggest that the entire flow over the airfoil readjusts within 2--3 convective time scales, which is about two orders of magnitude shorter than the characteristic time associated with the controlled maneuver of the wind tunnel model. This illustrates that flow-control actuation can be typically effected on time scales that are commensurate with the flow's convective time scale, and that the maneuver response is primarily limited by the inertia of the platform.

  14. High-resolution dynamic atomic force microscopy in liquids with different feedback architectures

    Directory of Open Access Journals (Sweden)

    John Melcher

    2013-02-01

    Full Text Available The recent achievement of atomic resolution with dynamic atomic force microscopy (dAFM [Fukuma et al., Appl. Phys. Lett. 2005, 87, 034101], where quality factors of the oscillating probe are inherently low, challenges some accepted beliefs concerning sensitivity and resolution in dAFM imaging modes. Through analysis and experiment we study the performance metrics for high-resolution imaging with dAFM in liquid media with amplitude modulation (AM, frequency modulation (FM and drive-amplitude modulation (DAM imaging modes. We find that while the quality factors of dAFM probes may deviate by several orders of magnitude between vacuum and liquid media, their sensitivity to tip–sample forces can be remarkable similar. Furthermore, the reduction in noncontact forces and quality factors in liquids diminishes the role of feedback control in achieving high-resolution images. The theoretical findings are supported by atomic-resolution images of mica in water acquired with AM, FM and DAM under similar operating conditions.

  15. Structures and orientation-dependent interaction forces of titania nanowires using molecular dynamics simulations

    Science.gov (United States)

    Okeke, George; Antony, S. Joseph; Hammond, Robert B.; Ahmed, Kamran

    2017-07-01

    Engineering nanowires to develop new products and processes is highly topical due to their ability to provide highly enhanced physical, chemical, mechanical, thermal and electrical properties. In this work, using molecular dynamics simulations, we report fundamental information, about the structural and thermodynamic properties of individual anatase titania (TiO2) nanowires with cross-sectional diameters between 2 and 6 nm, and aspect ratio (length to diameter) of 6:1 at temperatures ranging from 300 to 3000 K. Estimates of the melting transition temperature of the nanowires are between 2000 and 2500 K. The melting transition temperature predicted from the radial distribution functions (RDFs) shows strong agreement with those predicted from the total energy profiles. Overall, the transition temperature is in reasonable agreement with melting points predicted from experiments and simulations reported in the literature for spherical nanoparticles of similar sizes. Hence, the melting transition temperature of TiO2 nanowires modelled here can be considered as shape independent. Furthermore, for the first time based on MD simulations, interaction forces between two nanowires are reported at ambient temperature (300 K) for different orientations: parallel, perpendicular and end-to-end. It is observed that end-to-end orientations manifested the strongest attraction forces, while the parallel and perpendicular orientations displayed weaker attractions. The results reported here could form a foundation in future multiscale modelling studies of the structured titania nanowire assemblies, depending on the inter-wire interaction forces.

  16. Velocity, temperature and normal force dependence on friction: An analytical and molecular dynamic study

    CERN Document Server

    Dias, R A; Rapini, M; Costa, B V

    2007-01-01

    In this work we propose an extension to the analytical one-dimensional model proposed by E. Gnecco (Phys. Rev. Lett. 84:1172) to describe friction. Our model includes normal forces and the dependence with the angular direction of movement in which the object is dragged over a surface. The presence of the normal force in the model allow us to define judiciously the friction coefficient, instead of introducing it as an {\\sl a posteriori} concept. We compare the analytical results with molecular dynamics simulations. The simulated model corresponds to a tip sliding over a surface. The tip is simulated as a single particle interacting with a surface through a Lennard-Jones $(6-12)$ potential. The surface is considered as consisting of a regular BCC(001) arrangement of particles interacting with each other through a Lennard-Jones $(6-12)$ potential. We investigate the system under several conditions of velocity, temperature and normal forces. Our analytical results are in very good agreement with those obtained by...

  17. Dynamics and mass balance of Taylor Glacier, Antarctica: 2. Force balance and longitudinal coupling

    Science.gov (United States)

    Kavanaugh, J. L.; Cuffey, K. M.

    2009-11-01

    Taylor Glacier, Antarctica, exemplifies an ice sheet outlet that flows through a region of rugged topography and dry climate. In contrast to other well-studied outlets, Taylor Glacier moves very slowly, despite a thickness of order 1 km and driving stresses averaging 1.5 bars. Here we analyze new measurements of glacier geometry and surface velocity to elucidate flow dynamics of Taylor Glacier. Force balance and basal temperatures are calculated at six locations along the glacier's length using an algorithm developed for this study. The effects of stress-gradient coupling on longitudinal flow variations are also examined; we ask whether Kamb and Echelmeyer's (1986) linearized theory adequately describes the observed response of flow to large-amplitude variations in driving stress. The force balance calculations indicate that no basal motion is needed to explain the observed flow of Taylor Glacier. Inferred basal temperatures are within a few degrees of the melting point in regions of kilometer-thick ice and well below the melting point elsewhere; deformation of subfreezing ice largely controls the flow of Taylor Glacier. Basal drags are mostly in the range 0.9 to 1.2 bars, and lateral drags are in the range 0.2 to 0.5 bar. Stress-gradient coupling strongly reduces the variability of velocities along the glacier. The velocity variations can be described as the convolution of a forcing function with a spatial filter, as Kamb and Echelmeyer suggested, but the form of the forcing function differs from the theoretical relation derived for small-amplitude perturbations (the power on driving stress is one, not three).

  18. Dynamic calibration and validation of an accelerometer force balance for hypersonic lifting models.

    Science.gov (United States)

    Singh, Prakash; Trivedi, Sharad; Menezes, Viren; Hosseini, Hamid

    2014-01-01

    An accelerometer-based force balance was designed and developed for the measurement of drag, lift, and rolling moment on a blunt-nosed, flapped delta wing in a short-duration hypersonic shock tunnel. Calibration and validation of the balance were carried out by a convolution technique using hammer pulse test and surface pressure measurements. In the hammer pulse test, a known impulse was applied to the model in the appropriate direction using an impulse hammer, and the corresponding output of the balance (acceleration) was recorded. Fast Fourier Transform (FFT) was operated on the output of the balance to generate a system response function, relating the signal output to the corresponding load input. Impulse response functions for three components of the balance, namely, axial, normal, and angular, were obtained for a range of input load. The angular system response function was corresponding to rolling of the model. The impulse response functions thus obtained, through dynamic calibration, were operated on the output (signals) of the balance under hypersonic aerodynamic loading conditions in the tunnel to get the time history of the unknown aerodynamic forces and moments acting on the model. Surface pressure measurements were carried out on the model using high frequency pressure transducers, and forces and moments were deduced thereon. Tests were carried out at model angles of incidence of 0, 5, 10, and 15 degrees. A good agreement was observed among the results of different experimental methods. The balance developed is a comprehensive force/moment measurement device that can be used on complex, lifting, aerodynamic geometries in ground-based hypersonic test facilities.

  19. Modeling of time-dependent force response of fingertip to dynamic loading.

    Science.gov (United States)

    Wu, J Z; Dong, R G; Smutz, W P; Schopper, A W

    2003-03-01

    An extended exposure to repeated loading on fingertip has been associated to many vascular, sensorineural, and musculoskeletal disorders in the fingers, such as carpal tunnel syndrome, hand-arm vibration syndrome, and flexor tenosynovitis. A better understanding of the pathomechanics of these sensorineural and vascular diseases in fingers requires a formulation of a biomechanical model of the fingertips and analyses to predict the mechanical responses of the soft tissues to dynamic loading. In the present study, a model based on finite element techniques has been developed to simulate the mechanical responses of the fingertips to dynamic loading. The proposed model is two-dimensional and incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue was considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an invicid fluid, while its hydraulic permeability was considered to be deformation dependent. Two series of numerical tests were performed using the proposed finger tip model to: (a) simulate the responses of the fingertip to repeated loading, where the contact plate was assumed to be fixed, and the bone within the fingertip was subjected to a prescribed sinusoidal displacement in vertical direction; (b) simulate the force response of the fingertip in a single keystroke, where the keyboard was composed of a hard plastic keycap, a rigid support block, and a nonlinear spring. The time-dependent behavior of the fingertip under dynamic loading was derived. The model predictions of the time-histories of force response of the fingertip and the phenomenon of fingertip separation from the contacting plate during cyclic loading agree well with the reported experimental observations.

  20. Effects of Non-phosphate Macro-molecular Water-retention Agents on Meat Quality%大分子无磷持水剂对肉类品质的影响

    Institute of Scientific and Technical Information of China (English)

    王黎明; 李晶; 龙志芳; 彭恒

    2016-01-01

    It was investigated in this paper that the effects of non-phosphate macro-molecular water-retention agents on the water-retention ability, sensory quality and oxidation resistance of fish meat, shrimp meat and pork. The results showed that sodium alginate can improve obviously the water-retention ability, sensory quality and oxidation resistance of fish meat, shrimp meat and pork. While pectin, xanthan gum, water soluble chitosan can increase obviously the water-retention ability and oxidation resistance of fish meat, shrimp meat and pork. Glucan can improve obviously the water-retention ability and sensory quality of fish meat, shrimp meat and pork.%主要研究常用大分子无磷持水剂对鱼肉、猪肉、虾仁的持水能力、感官品质以及抗氧化能力的影响,以便配制出效果更好的肉类无磷保水剂。研究结果表明,海藻酸钠对鱼肉、虾仁、猪肉的持水能力、感官品质以及抗氧化能力都提高较多,而果胶、黄原胶、水溶性壳聚糖则对鱼肉、虾仁、猪肉的持水能力和抗氧化能力的改善效果较好,聚葡萄糖对鱼肉、虾仁、猪肉的持水能力、感官品质的提高效果较好。

  1. Velocity Potential in Engineering Hydraulics versus Force Potential in Groundwater Dynamics

    Science.gov (United States)

    Weyer, K.

    2013-12-01

    required to overcome the resistance to downward flow in penetrated rocks. As one of the consequences, the engineering hydraulics concept of buoyancy forces does not comply with physics. In general the vectorial forces within gravitationally-driven flow systems are ignored when using engineering hydraulics. Scheidegger (1974, p. 79) states, however, verbatim and unequivocally: 'It is thus a force potential and not a velocity potential which governs flow through porous media' (emphasis added). This presentation will outline the proper forces for groundwater flow and their calculations based on Hubbert's force potential and additional physical insights by Weyer (1978). REFERENCES Bear, J. 1972. Dynamics of Fluids in Porous Media. American Elsevier Publishing Company, Inc., New York, NY, USA. de Marsily, G. 1986. Quantitative Hydrogeology: Groundwater Hydrology for Engineers. Academic Press, San Diego, California, USA. Hubbert, M.K. 1940. The theory of groundwater motion. Journal of Geology 48(8): 785-944. Muskat, Morris, 1937. The flow of homogeneous fluids through porous media. McGraw-Hill Book Company Inc., New York, NY, USA Scheidegger. A.E., 1974. The physics of flow through permeable media. Third Edition. University of Toronto Press, Toronto, Ontario, Canada Weyer, K.U., 1978. Hydraulic forces in permeable media. Bulletin du B.R.G.M., Vol. 91, pp. 286-297, Orléans, France.

  2. Quantifying non-ergodic dynamics of force-free granular gases.

    Science.gov (United States)

    Bodrova, Anna; Chechkin, Aleksei V; Cherstvy, Andrey G; Metzler, Ralf

    2015-09-14

    Brownian motion is ergodic in the Boltzmann-Khinchin sense that long time averages of physical observables such as the mean squared displacement provide the same information as the corresponding ensemble average, even at out-of-equilibrium conditions. This property is the fundamental prerequisite for single particle tracking and its analysis in simple liquids. We study analytically and by event-driven molecular dynamics simulations the dynamics of force-free cooling granular gases and reveal a violation of ergodicity in this Boltzmann-Khinchin sense as well as distinct ageing of the system. Such granular gases comprise materials such as dilute gases of stones, sand, various types of powders, or large molecules, and their mixtures are ubiquitous in Nature and technology, in particular in Space. We treat-depending on the physical-chemical properties of the inter-particle interaction upon their pair collisions-both a constant and a velocity-dependent (viscoelastic) restitution coefficient ε. Moreover we compare the granular gas dynamics with an effective single particle stochastic model based on an underdamped Langevin equation with time dependent diffusivity. We find that both models share the same behaviour of the ensemble mean squared displacement (MSD) and the velocity correlations in the limit of weak dissipation. Qualitatively, the reported non-ergodic behaviour is generic for granular gases with any realistic dependence of ε on the impact velocity of particles.

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

    Science.gov (United States)

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

    2016-11-01

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

  4. Effect of cell and microvillus mechanics on the transmission of applied loads to single bonds in dynamic force spectroscopy.

    Science.gov (United States)

    Gupta, V K; Eggleton, C D

    2011-07-01

    Receptor-ligand interactions that mediate cellular adhesion are often subjected to forces that regulate their detachment via modulating off-rates. Although the dynamics of detachment is primarily controlled by the physical chemistry of adhesion molecules, cellular features such as cell deformability and microvillus viscoelasticity have been shown to affect the rolling velocity of leukocytes in vitro through experiments and simulation. In this work, we demonstrate via various micromechanical models of two cells adhered by a single (intramolecular) bond that cell deformability and microvillus viscoelasticity modulate transmission of an applied external load to an intramolecular bond, and thus the dynamics of detachment. Specifically, it is demonstrated that the intermolecular bond force is not equivalent to the instantaneous applied force and that the instantaneous bond force decreases with cellular and microvillus compliance. As cellular compliance increases, not only does the time lag between the applied load and the bond force increase, an initial response time is observed during which cell deformation is observed without transfer of force to the bond. It is further demonstrated that following tether formation the instantaneous intramoleular bond force increases linearly at a rate dependent on microvillus viscosity. Monte Carlo simulations with fixed kinetic parameters predict that both cell and microvillus compliance increase the average rupture time, although the average rupture force based on bond length remains nearly unchanged.

  5. Numerical integration of dynamical systems with Lie series: Relativistic acceleration and non-gravitational forces

    CERN Document Server

    Bancelin, D; Thuillot, W

    2016-01-01

    The integration of the equations of motion in gravitational dynamical systems -- either in our Solar System or for extra-solar planetary system -- being non integrable in the global case, is usually performed by means of numerical integration. Among the different numerical techniques available for solving ordinary differential equations, the numerical integration using Lie series has shown some advantages. In its original form (Hanslmeier 1984), it was limited to the N-body problem where only gravitational interactions are taken into account. We present in this paper a generalisation of the method by deriving an expression of the Lie-terms when other major forces are considered. As a matter of fact, previous studies had been made but only for objects moving under gravitational attraction. If other perturbations are added, the Lie integrator has to be re-built. In the present work we consider two cases involving position and position-velocity dependent perturbations: relativistic acceleration in the framework ...

  6. Fatigue evaluation of the JT-60 vacuum vessel under the dynamic electromagnetic forces

    Energy Technology Data Exchange (ETDEWEB)

    Takatsu, H.; Shimizu, M.; Ohta, M. (Japan Atomic Energy Research Inst., Tokai, Ibaraki); Nakamura, Y.; Sakai, K.; Uchino, K. (Ishikawajima-Harima Heavy Industries Co. Ltd., Tokyo (Japan))

    1983-03-01

    Fatigue evaluation of the JT-60 vacuum vessel was carried out under the dynamic electromagnetic forces. In the present method, fatigue strength of the vacuum vessel is evaluated not only during the transient response but during the free vibration following the transient response. Stress amplitudes during the transient response are counted using the range-pair count method faithful to the stress strain hysteresis loop. And fatigue damage during the transient response and the free vibration following the transient response is evaluated based on Miner's law. The fatigue evaluation results showed that the JT-60 vacuum vessel has the sufficient fatigue strength and the free vibration has much larger contribution to the fatigue damage than the transient response.

  7. Dynamics of quartz tuning fork force sensors used in standoff photoacoustic detection

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhouqiang; Jia, Shuhai; Ma, Binshan; Chen, Hualing [Xi' an Jiao tong University, Xi' an (China); Wei, Yuan [Harbin Institute of Technology, Harbin (Korea, Republic of)

    2015-08-15

    In this paper, a two-degrees-of-freedom model with two coupled oscillators is established to study the dynamics of quartz tuning fork force sensors. Air squeeze-film damping is considered in this model. When the laser power is 40 mW and the distance between the tuning fork and detected objects is approximately 0.5 m, the resonance amplitude of the tuning fork under the electromagnetic radiation pressure of the laser can reach 0.22 pm. Electromagnetic radiation pressure and resonance amplitude have the tendency to exponentially decay along with the distance between the tuning fork and detected objects. The influence of laser power and distance between the tuning fork and detected objects on electromagnetic radiation pressure is also considered. Lastly, an experimental device is set up to verify the calculation result of the model. Analysis shows that the experimental data are in good agreement with the theoretical calculation results.

  8. Mechanical Properties of Boehmite Evaluated by Atomic Force Microscopy Experiments and Molecular Dynamic Finite Element Simulations

    Directory of Open Access Journals (Sweden)

    J. Fankhänel

    2016-01-01

    Full Text Available Boehmite nanoparticles show great potential in improving mechanical properties of fiber reinforced polymers. In order to predict the properties of nanocomposites, knowledge about the material parameters of the constituent phases, including the boehmite particles, is crucial. In this study, the mechanical behavior of boehmite is investigated using Atomic Force Microscopy (AFM experiments and Molecular Dynamic Finite Element Method (MDFEM simulations. Young’s modulus of the perfect crystalline boehmite nanoparticles is derived from numerical AFM simulations. Results of AFM experiments on boehmite nanoparticles deviate significantly. Possible causes are identified by experiments on complementary types of boehmite, that is, geological and hydrothermally synthesized samples, and further simulations of imperfect crystals and combined boehmite/epoxy models. Under certain circumstances, the mechanical behavior of boehmite was found to be dominated by inelastic effects that are discussed in detail in the present work. The studies are substantiated with accompanying X-ray diffraction and Raman experiments.

  9. The importance of cantilever dynamics in the interpretation of Kelvin probe force microscopy.

    Science.gov (United States)

    Satzinger, Kevin J; Brown, Keith A; Westervelt, Robert M

    2012-09-15

    A realistic interpretation of the measured contact potential difference (CPD) in Kelvin probe force microscopy (KPFM) is crucial in order to extract meaningful information about the sample. Central to this interpretation is a method to include contributions from the macroscopic cantilever arm, as well as the cone and sharp tip of a KPFM probe. Here, three models of the electrostatic interaction between a KPFM probe and a sample are tested through an electrostatic simulation and compared with experiment. In contrast with previous studies that treat the KPFM cantilever as a rigid object, we allow the cantilever to bend and rotate; accounting for cantilever bending provides the closest agreement between theory and experiment. We demonstrate that cantilever dynamics play a major role in CPD measurements and provide a simulation technique to explore this phenomenon.

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

    Energy Technology Data Exchange (ETDEWEB)

    Boubekri, R.; Cambril, E.; Couraud, L.; Bernardi, L.; Madouri, A. [LPN, CNRS-UPR20, route de Nozay, 91460 Marcoussis (France); Portail, M. [Centre de Recherche sur l' Hetero-Epitaxie et ses Applications CNRS, Rue Bernard Gregory, 06560 Valhonne (France); Chassagne, T.; Moisson, C.; Zielinski, M. [NOVASiC, Savoie Technolac, Arche bât 4, BP 267, 73375 Le Bourget du Lac Cedex (France); Jiao, S.; Michaud, J.-F.; Alquier, D. [Université François Rabelais, Tours, GREMAN, CNRS-UMR7347, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours Cedex 2 (France); Bouloc, J.; Nony, L.; Bocquet, F.; Loppacher, C. [IM2NP-CNRS/Aix-Marseille University, 38 rue Frédéric Joliot-Curie, 13451 Marseille (France); Martrou, D.; Gauthier, S., E-mail: gauthier@cemes.fr [CEMES, CNRS UPR 8011 et Université de Toulouse, 29 rue Jeanne Marvig, 31055 Toulouse (France)

    2014-08-07

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

  11. Acoustic Imaging Frequency Dynamics of Ferroelectric Domains by Atomic Force Microscopy

    Institute of Scientific and Technical Information of China (English)

    ZHAO Kun-Yu; Shunji Takekawa; Kenji Kitamura; ZENG Hua-Rong; SONG Hong-Zhang; HUI Sen-Xing; LI Guo-Rong; YIN Qing-Rui; Kiyoshi Shimamura; Chinna Venkadasamy Kannan; Encarnacion Antonia Garcia Villora

    2008-01-01

    We report the acoustic imaging frequency dynamics of ferroelectric domains by low-frequency acoustic probe microscopy based on the commercial atomic force microscopy. It is found that ferroelectric domain could be firstly visualized at lower frequency down to 0.h kHz by AFM-based acoustic microscopy. The frequency-dependent acoustic signal revealed a strong acoustic response in the frequency range from 7 kHz to lO kHz, and reached maximum at 8.1 kHz. The acoustic contrast mechanism can be ascribed to the different elastic response of ferroelectric microstructures to local elastic stress fields, which is induced by the acoustic wave transmitting in the sample when the piezoelectric transducer is vibrating and exciting acoustic wave under ac electric fields due to normal piezoelectric effects.

  12. Effects of the van der Waals Force on the Dynamics Performance for a Micro Resonant Pressure Sensor

    Directory of Open Access Journals (Sweden)

    Lizhong Xu

    2016-01-01

    Full Text Available The micro resonant pressure sensor outputs the frequency signals where the distortion does not take place in a long distance transmission. As the dimensions of the sensor decrease, the effects of the van der Waals forces should be considered. Here, a coupled dynamic model of the micro resonant pressure sensor is proposed and its coupled dynamic equation is given in which the van der Waals force is considered. By the equation, the effects of the van der Waals force on the natural frequencies and vibration amplitudes of the micro resonant pressure sensor are investigated. Results show that the natural frequency and the vibrating amplitudes of the micro resonant pressure sensor are affected significantly by van der Waals force for a small clearance between the film and the base plate, a small initial tension stress of the film, and some other conditions.

  13. Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation

    Science.gov (United States)

    Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Montague, Gerald; Duffy, Kirsten; Mehmed, Oral; Johnson, Dexter; Jansen, Ralph

    2004-01-01

    The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig, a significant advancement in the Dynamic Spin Rig (DSR), is used to perform vibration tests of turbomachinery blades and components under rotating and nonrotating conditions in a vacuum. The rig has as its critical components three magnetic bearings: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feed-forward control feature, which will enable the excitation of various natural blade modes in bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and nonrotating, unbladed rotor and a fully levitated, rotating and nonrotating, bladed rotor in which a pair of blades was arranged 180 degrees apart from each other. These tests include the bounce mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For nonrotating blades, a blade-tip excitation amplitude of approximately 100 g/A was achieved at the first-bending critical (approximately 144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 70 mils was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 908 relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

  14. Morphology and Dynamics of Lithospheric Body Force Instabilities: Sheets, Drips and In-Between

    Science.gov (United States)

    Beall, A.; Moresi, L. N.

    2014-12-01

    Foundering of the Earth's lithosphere, and consequent energy and mass flux across the upper boundary layer and mantle interface, is driven locally by gravitational body forces. The related instabilities are usually classified as having sheet-like or drip-like morphologies. The former is associated with whole lithosphere (subduction) or delamination type foundering such as suggested for beneath the southern Sierra-Nevada and the Colorado Plateau, the latter to classic Rayleigh-Taylor instability below an upper layer, suggested to have occurred beneath the Tibetan Plateau and North Island, New Zealand. This dichotomy is non-trivial; classification of phenomena into one or the other is often debated and is difficult to infer from observables. The two morphologies are most likely end-members. Here I refine the dynamics driving morphology selection as a function of rheological lamination and boundary layer Rayleigh number in 2D and 3D, using the finite-element particle-in-cell code Underworld. I explore the influence of morphology on mass flux, topography and crustal deformation as well as deviation from classic 2D scalings. Additionally, tectonic displacement interference with instability development is discussed using basic 3D shear-box style models. By quantifying and describing the theoretical instability dynamics which could result in a plausible range of morphological expressions, I aim to build a general framework which can be paired to the discussion involving firstly, the recognition of varied styles of body force instabilities in the modern Earth and rock record and secondly, to what degree pattern selection impacts boundary layer mass and energy flux.

  15. Quantitative attribution of major driving forces on soil organic carbon dynamics

    Science.gov (United States)

    Wu, Yiping; Liu, Shuguang; Tan, Zhengxi

    2015-03-01

    Soil organic carbon (SOC) storage plays a major role in the global carbon cycle and is affected by many factors including land use/management changes (e.g., biofuel production-oriented changes). However, the contributions of various factors to SOC changes are not well understood and quantified. This study was designed to investigate the impacts of changing farming practices, initial SOC levels, and biological enhancement of grain production on SOC dynamics and to attribute the relative contributions of major driving forces (CO2 enrichment and farming practices) using a fractional factorial modeling design. The case study at a crop site in Iowa in the United States demonstrated that the traditional corn-soybean (CS) rotation could still accumulate SOC over this century (from 4.2 to 6.8 kg C/m2) under the current condition; whereas the continuous-corn (CC) system might have a higher SOC sequestration potential than CS. In either case, however, residue removal could reduce the sink potential substantially. Long-term simulation results also suggested that the equilibrium SOC level may vary greatly (˜5.7 to ˜11 kg C/m2) depending on cropping systems and management practices, and projected growth enhancement could make the magnitudes higher (˜7.8 to ˜13 kg C/m2). Importantly, the factorial design analysis indicated that residue management had the most significant impact (contributing 49.4%) on SOC changes, followed by CO2 Enrichment (37%), Tillage (6.2%), the combination of CO2 Enrichment-Residue removal (5.8%), and Fertilization (1.6%). In brief, this study is valuable for understanding the major forces driving SOC dynamics of agroecosystems and informative for decision-makers when seeking the enhancement of SOC sequestration potential and sustainability of biofuel production, especially in the Corn Belt region of the United States.

  16. Dynamics and control of spacecraft hovering using the geomagnetic Lorentz force

    Science.gov (United States)

    Huang, Xu; Yan, Ye; Zhou, Yang

    2014-02-01

    To achieve hovering, a spacecraft thrusts continuously to induce an equilibrium state at a desired position. Due to the constraints on the quantity of propellant onboard, long-time hovering around low-Earth orbits (LEO) is hardly achievable using traditional chemical propulsion. The Lorentz force, acting on an electrostatically charged spacecraft as it moves through a planetary magnetic field, provides a new propellantless method for orbital maneuvers. This paper investigates the feasibility of using the induced Lorentz force as an auxiliary means of propulsion for spacecraft hovering. Assuming that the Earth's magnetic field is a dipole that rotates with the Earth, a dynamical model that characterizes the relative motion of Lorentz spacecraft is derived to analyze the required open-loop control acceleration for hovering. Based on this dynamical model, we first present the hovering configurations that could achieve propellantless hovering and the corresponding required specific charge of a Lorentz spacecraft. For other configurations, optimal open-loop control laws that minimize the control energy consumption are designed. Likewise, the optimal trajectories of required specific charge and control acceleration are both presented. The effect of orbital inclination on the expenditure of control energy is also analyzed. Further, we also develop a closed-loop control approach for propellantless hovering. Numerical results prove the validity of proposed control methods for hovering and show that hovering around low-Earth orbits would be achievable if the required specific charge of a Lorentz spacecraft becomes feasible in the future. Typically, hovering radially several kilometers above a target in LEO requires specific charges on the order of 0.1 C/kg.

  17. Analysis of Adhesive Characteristics of Asphalt Based on Atomic Force Microscopy and Molecular Dynamics Simulation.

    Science.gov (United States)

    Xu, Meng; Yi, Junyan; Feng, Decheng; Huang, Yudong; Wang, Dongsheng

    2016-05-18

    Asphalt binder is a very important building material in infrastructure construction; it is commonly mixed with mineral aggregate and used to produce asphalt concrete. Owing to the large differences in physical and chemical properties between asphalt and aggregate, adhesive bonds play an important role in determining the performance of asphalt concrete. Although many types of adhesive bonding mechanisms have been proposed to explain the interaction forces between asphalt binder and mineral aggregate, few have been confirmed and characterized. In comparison with chemical interactions, physical adsorption has been considered to play a more important role in adhesive bonding between asphalt and mineral aggregate. In this study, the silicon tip of an atomic force microscope was used to represent silicate minerals in aggregate, and a nanoscale analysis of the characteristics of adhesive bonding between asphalt binder and the silicon tip was conducted via an atomic force microscopy (AFM) test and molecular dynamics (MD) simulations. The results of the measurements and simulations could help in better understanding of the bonding and debonding procedures in asphalt-aggregate mixtures during hot mixing and under traffic loading. MD simulations on a single molecule of a component of asphalt and monocrystalline silicon demonstrate that molecules with a higher atomic density and planar structure, such as three types of asphaltene molecules, can provide greater adhesive strength. However, regarding the real components of asphalt binder, both the MD simulations and AFM test indicate that the colloidal structural behavior of asphalt also has a large influence on the adhesion behavior between asphalt and silicon. A schematic model of the interaction between asphalt and silicon is presented, which can explain the effect of aging on the adhesion behavior of asphalt.

  18. Effect of intermolecular force on the static/dynamic behaviour of M/NEM devices.

    Science.gov (United States)

    Kim, Namjung; Aluru, N R

    2014-12-01

    Advances made in the fabrication of micro/nano-electromechanical (M/NEM) devices over the last ten years necessitate the understanding of the attractive force that arises from quantum fluctuations (generally referred to as Casimir effects) [Casimir H B G 1948 Proc. K. Ned. Akad. Wet. 51 793]. The fundamental mechanisms underlying quantum fluctuations have been actively investigated through various theoretical and experimental approaches. However, the effect of the force on M/NEM devices has not been fully understood yet, especially in the transition region involving gaps ranging from 10 nm to 1 μm, due to the complexity of the force. Here, we numerically calculate the Casimir effects in M/NEM devices by using the Lifshitz formula, the general expression for the Casimir effects [Lifshitz E 1956 Sov. Phys. JETP 2 73]. Since the Casimir effects are highly dependent on the permittivity of the materials, the Kramer-Kronig relation [Landau L D, Lifshitz E M and Pitaevskii L P 1984 Electrodynamics of Continuous Media (New York: Pergamon Press)] and the optical data for metals and dielectrics are used in order to obtain the permittivity. Several simplified models for the permittivity of the materials, such as the Drude and Lorentz models [Jackson J D 1975 Classical Electrodynamics (New York: Wiley)], are also used to extrapolate the optical data. Important characteristic values of M/NEM devices, such as the pull-in voltage, pull-in gap, detachment length, etc, are calculated for devices operating in the transition region. Our results show that accurate predictions for the pull-in behaviour are possible when the Lifshitz formula is used instead of the idealized expressions for Casimir effects. We expand this study into the dynamics of M/NEM devices, so that the time and frequency response of M/NEM devices with Casimir effects can be explored.

  19. Dynamics of highly-flexible solar sail subjected to various forces

    Science.gov (United States)

    Liu, Jiafu; Cui, Naigang; Shen, Fan; Rong, Siyuan

    2014-10-01

    Solar sail is a novel spacecraft and has the potential applications in the near future. The large amplitude vibration should be considered because it is characterized by its huge and lightweight structure. In this paper, the supporting beam of solar sail is regarded as the most important structure and used to model the sailcraft as it accounts for most of the mechanical energies when it is in deformed configuration, also as the Euler beam can model the bending motion dominant sailcraft when it experiences attitude motions. The structural dynamics of solar sail supporting beam with geometric nonlinearity undergoing the forces generated by solar radiation pressure, sliding masses and control vanes are presented. The axial and transverse vibration equations with the properties of strong coupling, nonlinearity and time-varying coefficient matrices are obtained by using Lagrange equation method after calculating the related energies and works. The vibration equations are transformed into nonlinear algebraic equations utilizing implicit unconditionally stable Newmark-β algorithm for each time step. The nonlinear algebraic equations are solved by Newton-iterative algorithm. We compute and analyze the linear and nonlinear vibration responses affected by the mass and velocity of the sliding mass, the angular velocity of the force generated by control vane in detail. The computational results indicate that the mass and velocity of sliding mass affect the vibration responses (including the vibration frequency), but the angular velocity of the force generated by control vane hardly affects the vibration responses. Moreover, the linear and nonlinear vibrations are distinct obviously by comparing the linear and nonlinear responses. It is demonstrated that the geometric nonlinearity of the highly-flexible structure should be considered for performing vibration analysis exactly, and the vibration responses excited by the prescribed motion of the attitude control actuators should

  20. Coupling density functional theory to polarizable force fields for efficient and accurate Hamiltonian molecular dynamics simulations.

    Science.gov (United States)

    Schwörer, Magnus; Breitenfeld, Benedikt; Tröster, Philipp; Bauer, Sebastian; Lorenzen, Konstantin; Tavan, Paul; Mathias, Gerald

    2013-06-28

    Hybrid molecular dynamics (MD) simulations, in which the forces acting on the atoms are calculated by grid-based density functional theory (DFT) for a solute molecule and by a polarizable molecular mechanics (PMM) force field for a large solvent environment composed of several 10(3)-10(5) molecules, pose a challenge. A corresponding computational approach should guarantee energy conservation, exclude artificial distortions of the electron density at the interface between the DFT and PMM fragments, and should treat the long-range electrostatic interactions within the hybrid simulation system in a linearly scaling fashion. Here we describe a corresponding Hamiltonian DFT/(P)MM implementation, which accounts for inducible atomic dipoles of a PMM environment in a joint DFT/PMM self-consistency iteration. The long-range parts of the electrostatics are treated by hierarchically nested fast multipole expansions up to a maximum distance dictated by the minimum image convention of toroidal boundary conditions and, beyond that distance, by a reaction field approach such that the computation scales linearly with the number of PMM atoms. Short-range over-polarization artifacts are excluded by using Gaussian inducible dipoles throughout the system and Gaussian partial charges in the PMM region close to the DFT fragment. The Hamiltonian character, the stability, and efficiency of the implementation are investigated by hybrid DFT/PMM-MD simulations treating one molecule of the water dimer and of bulk water by DFT and the respective remainder by PMM.

  1. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    Science.gov (United States)

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen

    2016-08-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

  2. Measurement and characterization of force dynamics in high T(sub c) superconductors

    Science.gov (United States)

    Higuchi, Toshiro; Kelley, Allan J.; Tsutsui, Yukio

    1994-01-01

    Magnetic bearing implementations using more exotic superconducting phenomena have been proliferating in recent years because they have important advantages over conventional implementations. For example, the stable suspension of a six degrees-of-freedom object by superconducting means can be achieved without a control system and with the use of only a single superconductor. It follows that the construction becomes much simpler with decreased need for position sensors and stabilizers. However, it is recognized that the design of superconducting systems can be difficult because important characteristics relating to the 6 degree-of-freedom dynamics of an object suspended magnetically are not readily available and the underlying principles of superconducting phenomena are not yet completely understood. To eliminate some of the guesswork in the design process, this paper proposes a system which can resolve the mechanical properties of suspension by superconductivity and provide position and orientation dependent data about the system's damping, stiffness, and frequency response characteristics. This system employs an actively-controlled magnetically-suspended fine-motion device that can also be used as a six degree-of-freedom force sensor. By attaching the force sensor to a permanent magnet that is being levitated above a superconducting magnet, mechanical characteristics of the superconductor levitation can be extracted. Such information would prove useful for checking the validity of theoretical models and may even give insights into superconducting phenomena.

  3. A hierarchical Bayesian framework for force field selection in molecular dynamics simulations.

    Science.gov (United States)

    Wu, S; Angelikopoulos, P; Papadimitriou, C; Moser, R; Koumoutsakos, P

    2016-02-13

    We present a hierarchical Bayesian framework for the selection of force fields in molecular dynamics (MD) simulations. The framework associates the variability of the optimal parameters of the MD potentials under different environmental conditions with the corresponding variability in experimental data. The high computational cost associated with the hierarchical Bayesian framework is reduced by orders of magnitude through a parallelized Transitional Markov Chain Monte Carlo method combined with the Laplace Asymptotic Approximation. The suitability of the hierarchical approach is demonstrated by performing MD simulations with prescribed parameters to obtain data for transport coefficients under different conditions, which are then used to infer and evaluate the parameters of the MD model. We demonstrate the selection of MD models based on experimental data and verify that the hierarchical model can accurately quantify the uncertainty across experiments; improve the posterior probability density function estimation of the parameters, thus, improve predictions on future experiments; identify the most plausible force field to describe the underlying structure of a given dataset. The framework and associated software are applicable to a wide range of nanoscale simulations associated with experimental data with a hierarchical structure.

  4. Forced oscillations dynamic tribometer with real-time insights of lubricated interfaces

    Science.gov (United States)

    Yahiaoui, M.; Rigaud, E.; Mazuyer, D.; Cayer-Barrioz, J.

    2017-03-01

    This paper presents an innovative forced oscillations dynamic tribometer, the CHRONOS tribometer, with a lubricated ball-on-flat contact configuration fitted out with an in situ optical visualization system and a triggered high-speed camera. The CHRONOS tribometer generates controlled oscillating kinematics by means of a shaker with a range of strokes from 5 μm to 2.5 mm and an oscillation frequency which can be adjusted from 5 Hz to 250 Hz. Displacement and velocity are measured using a vibrometer. The ball-on-flat mean contact pressure is set between 200 MPa and 600 MPa. During motion, the instantaneous normal and friction forces and the interfacial film thickness distribution (in the nanometer scale) are simultaneously measured. In addition to this instantaneous approach, a more macroscopic approach is developed in terms of moving averages of friction and velocity. Another parameter, the friction-velocity tilt angle, is also introduced. This last parameter may give information on the friction-velocity dependence. Eventually, the experiments performed on the CHRONOS device lead to the representation of synchronized temporal signals of displacement/velocity, friction, and lubricant central film thickness. This superimposition of key parameters reveals time effects introduced by the periodical fluid squeeze and flow in the contact.

  5. DYNAMIC CHANGES OF THE WETLAND AND ITS DRIVING FORCES IN FUJIN REGION IN SANJIANG PLAIN, CHINA

    Institute of Scientific and Technical Information of China (English)

    WANG Zhi-Qiang; CHEN Ming; WANG Dan-Dan; ZHANG Bai; ZHANG Shu-Qing

    2005-01-01

    Wetland is a kind of key natural resources. However, the wetlands have been shrinking rapidly in Sangjiang Plain and its functions have been degrading. These all hold back the sustainable development of human communities, and lead to great change in the land use /cover (LUCC), consequently caused global changes in climate, water cycling, etc.. Taken Fujin region as a case study, spatial and temporal dynamic processes of wetland and its driving forces were analyzed from 1954 to 2000 in this paper. It showed that the wetlands had been reduced from 52×104 ha to 11×104 ha in areas during the nearly 50 years . The percentage of wetland areas reduced from 61.27% to 12.39%. On the other hand, cultivated land increased from 22×104 ha to 60×104 ha in areas. The percentage of the areas increased from 25.31% to 70.45%. Further quantitative analysis of the wetland landscape conversion characteristics and the correlation analysis between the change of wetland areas and population increase were made. The results showed that 40×104 ha wetlands had been converted to cultivated land within half of a century; the correlation between the rate of wetland loss and that of population increased is nearly -0.922. So it was concluded that the main driving force of wetland shrinkage in Fujin region was the colonization of human being.

  6. Static and dynamic mechanics of the temporomandibular joint: plowing forces, joint load and tissue stress.

    Science.gov (United States)

    Nickel, J; Spilker, R; Iwasaki, L; Gonzalez, Y; McCall, W D; Ohrbach, R; Beatty, M W; Marx, D

    2009-08-01

    OBJECTIVES - To determine the combined effects 1) of stress-field aspect ratio and velocity and compressive strain and 2) joint load, on temporomandibular joint (TMJ) disc mechanics. SETTING AND SAMPLE POPULATION - Fifty-two subjects (30 female; 22 male) participated in the TMJ load experiments. MATERIAL AND METHODS - In the absence of human tissue, pig TMJ discs were used to determine the effects of variables 1) on surface plowing forces, and to build a biphasic finite element model (bFEM) to test the effect of human joint loads and 2) on tissue stresses. In the laboratory, discs received a 7.6 N static load via an acrylic indenter before cyclic movement. Data were recorded and analysed using anova. To determine human joint loads, Research Diagnostic Criteria calibrated investigators classified subjects based on signs of disc displacement (DD) and pain (+DD/+pain, n = 18; +DD/-pain, n = 17; -DD/-pain, n = 17). Three-dimensional geometries were produced for each subject and used in a computer model to calculate joint loads. RESULTS - The combined effects of compressive strain, and aspect ratio and velocity of stress-field translation correlated with plowing forces (R(2) = 0.85). +DD/-pain subjects produced 60% higher joint loads (ANOVA, p dynamic variables of the stress-field and subject-dependent joint load significantly affect disc mechanics.

  7. The Role of Rac1 in the Growth Cone Dynamics and Force Generation of DRG Neurons.

    Directory of Open Access Journals (Sweden)

    Wasim A Sayyad

    Full Text Available We used optical tweezers, video imaging, immunocytochemistry and a variety of inhibitors to analyze the role of Rac1 in the motility and force generation of lamellipodia and filopodia from developing growth cones of isolated Dorsal Root Ganglia neurons. When the activity of Rac1 was inhibited by the drug EHop-016, the period of lamellipodia protrusion/retraction cycles increased and the lamellipodia retrograde flow rate decreased; moreover, the axial force exerted by lamellipodia was reduced dramatically. Inhibition of Arp2/3 by a moderate amount of the drug CK-548 caused a transient retraction of lamellipodia followed by a complete recovery of their usual motility. This recovery was abolished by the concomitant inhibition of Rac1. The filopodia length increased upon inhibition of both Rac1 and Arp2/3, but the speed of filopodia protrusion increased when Rac1 was inhibited and decreased instead when Arp2/3 was inhibited. These results suggest that Rac1 acts as a switch that activates upon inhibition of Arp2/3. Rac1 also controls the filopodia dynamics necessary to explore the environment.

  8. An individual and dynamic Body Segment Inertial Parameter validation method using ground reaction forces.

    Science.gov (United States)

    Hansen, Clint; Venture, Gentiane; Rezzoug, Nasser; Gorce, Philippe; Isableu, Brice

    2014-05-01

    Over the last decades a variety of research has been conducted with the goal to improve the Body Segment Inertial Parameters (BSIP) estimations but to our knowledge a real validation has never been completely successful, because no ground truth is available. The aim of this paper is to propose a validation method for a BSIP identification method (IM) and to confirm the results by comparing them with recalculated contact forces using inverse dynamics to those obtained by a force plate. Furthermore, the results are compared with the recently proposed estimation method by Dumas et al. (2007). Additionally, the results are cross validated with a high velocity overarm throwing movement. Throughout conditions higher correlations, smaller metrics and smaller RMSE can be found for the proposed BSIP estimation (IM) which shows its advantage compared to recently proposed methods as of Dumas et al. (2007). The purpose of the paper is to validate an already proposed method and to show that this method can be of significant advantage compared to conventional methods.

  9. Dynamics of the east India coastal current. 1. Analytic solutions forced by interior Ekman pumping and local alongshore winds

    Digital Repository Service at National Institute of Oceanography (India)

    Shankar, D.; McCreary, J.P.; Han, W.; Shetye, S.R.

    OF GEOPHYSICAL RESEARCH, VOL. 101, NO. C6, PAGES 13,975-13,991, JUNE 15, 1996 Dynamics of the East India Coastal Current 1. Analytic solutions forced by interior Ekman pumping and local alongshore winds D. Snankar Centre for Mathematical Modelling... linear, continuously stratified model is used to investigate how forcing by interior Ekman pumping and local alongshore winds affects the East India Coastal Current (EICC). Solutions are found analytically to an approximate version of the equations...

  10. Using Maximal Isometric Force to Determine the Optimal Load for Measuring Dynamic Muscle Power

    Science.gov (United States)

    Spiering, Barry A.; Lee, Stuart M. C.; Mulavara, Ajitkumar P.; Bentley, Jason R.; Nash, Roxanne E.; Sinka, Joseph; Bloomberg, Jacob J.

    2009-01-01

    Maximal power output occurs when subjects perform ballistic exercises using loads of 30-50% of one-repetition maximum (1-RM). However, performing 1-RM testing prior to power measurement requires considerable time, especially when testing involves multiple exercises. Maximal isometric force (MIF), which requires substantially less time to measure than 1-RM, might be an acceptable alternative for determining the optimal load for power testing. PURPOSE: To determine the optimal load based on MIF for maximizing dynamic power output during leg press and bench press exercises. METHODS: Twenty healthy volunteers (12 men and 8 women; mean +/- SD age: 31+/-6 y; body mass: 72 +/- 15 kg) performed isometric leg press and bench press movements, during which MIF was measured using force plates. Subsequently, subjects performed ballistic leg press and bench press exercises using loads corresponding to 20%, 30%, 40%, 50%, and 60% of MIF presented in randomized order. Maximal instantaneous power was calculated during the ballistic exercise tests using force plates and position transducers. Repeated-measures ANOVA and Fisher LSD post hoc tests were used to determine the load(s) that elicited maximal power output. RESULTS: For the leg press power test, six subjects were unable to be tested at 20% and 30% MIF because these loads were less than the lightest possible load (i.e., the weight of the unloaded leg press sled assembly [31.4 kg]). For the bench press power test, five subjects were unable to be tested at 20% MIF because these loads were less than the weight of the unloaded aluminum bar (i.e., 11.4 kg). Therefore, these loads were excluded from analysis. A trend (p = 0.07) for a main effect of load existed for the leg press exercise, indicating that the 40% MIF load tended to elicit greater power output than the 60% MIF load (effect size = 0.38). A significant (p . 0.05) main effect of load existed for the bench press exercise; post hoc analysis indicated that the effect of

  11. Molecular Dynamics Simulation of Cross-Linked Epoxy Polymers: the Effect of Force Field on the Estimation of Properties

    Directory of Open Access Journals (Sweden)

    B. Arab

    2013-03-01

    Full Text Available In this paper, the molecular dynamics method was used to calculate the physical and mechanical properties of the cross-linked epoxy polymer composed of diglycidyl ether of bisphenol-A (DGEBA as resin and diethylenetriamine (DETA as curing agent. Calculation of the properties was performed using the constant-strain (static approach. A series of independent simulations were carried out based on four widely used force fields; COMPASS, PCFF, UFF and Dreiding. Proper comparisons between the results and also with experimental observations were made to find the most suitable force field for molecular dynamics simulation of polymer materials.

  12. The Dynamic Change in the Total Arable Land and its Driving Forces in Tongling City of Anhui Province

    Institute of Scientific and Technical Information of China (English)

    Yan; LI; Zhongxiang; YU

    2014-01-01

    According to Anhui Statistical Yearbook( 2003-2012) and the second national land survey data,this article analyzes the current situation of land use and the dynamic change in the total arable land in Tongling City. On the basis of this,using grey relational analysis,this article analyzes the driving forces for arable land changes in Tongling City. Studies show that population growth,the improvement of level of urbanization and the rapid development of the economy are the main driving forces for arable land changes. Based on the findings,the strategies are put forth in order to ensure the dynamic balance of total arable land.

  13. Dynamic myosin activation promotes collective morphology and migration by locally balancing oppositional forces from surrounding tissue.

    Science.gov (United States)

    Aranjuez, George; Burtscher, Ashley; Sawant, Ketki; Majumder, Pralay; McDonald, Jocelyn A

    2016-06-15

    Migrating cells need to overcome physical constraints from the local microenvironment to navigate their way through tissues. Cells that move collectively have the additional challenge of negotiating complex environments in vivo while maintaining cohesion of the group as a whole. The mechanisms by which collectives maintain a migratory morphology while resisting physical constraints from the surrounding tissue are poorly understood. Drosophila border cells represent a genetic model of collective migration within a cell-dense tissue. Border cells move as a cohesive group of 6-10 cells, traversing a network of large germ line-derived nurse cells within the ovary. Here we show that the border cell cluster is compact and round throughout their entire migration, a shape that is maintained despite the mechanical pressure imposed by the surrounding nurse cells. Nonmuscle myosin II (Myo-II) activity at the cluster periphery becomes elevated in response to increased constriction by nurse cells. Furthermore, the distinctive border cell collective morphology requires highly dynamic and localized enrichment of Myo-II. Thus, activated Myo-II promotes cortical tension at the outer edge of the migrating border cell cluster to resist compressive forces from nurse cells. We propose that dynamic actomyosin tension at the periphery of collectives facilitates their movement through restrictive tissues.

  14. Holocene dynamics of vegetation change in southern and southeastern Brazil is consistent with climate forcing

    Science.gov (United States)

    Rodrigues, Jackson Martins; Behling, Hermann; Giesecke, Thomas

    2016-08-01

    At mid to high northern latitudes postglacial vegetation change has often occurred synchronously over large regions triggered mainly by abrupt climate change. Based on 19 pollen diagrams from southern and southeastern Brazil we explore if similar synchronicities in vegetation change were also characteristic for the vegetation dynamics in low latitudes. We used sequence splitting to detect past vegetation change in the pollen diagrams and computed principal curves and rates of change to visually evaluate the changes in composition and dynamics. The results show that vegetation change occurred mostly during the second half of the Holocene with distinct episodes of change. The character of vegetation change is generally consistent with shifts to wetter conditions and agrees with inferred shifts of the South American Monsoon. Speleothems as well as the titanium record from the Cariaco Basin indicate several episodes of rapid shifts in the precipitation regime, which are within the dating uncertainty of the here detected periods of vegetation change (8900, 5900, 2800, 1200 and 550 cal yrs BP). Our results indicate that low latitude vegetation composition follows precession forcing of the hydrology, while change is often triggered and synchronized by rapid climate change much like in high and mid latitudes. Pollen diagrams document changes in the abundance of individual taxa and changes in the amount of woodland cover, while small compositional changes indicate a regional stability of vegetation types during the Holocene.

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

    Science.gov (United States)

    Nikolov, Alex; Zhang, Hua

    2015-07-01

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

  16. Contact forces between a particle and a wet wall at both quasi-static and dynamic state

    Directory of Open Access Journals (Sweden)

    Zhang Huang

    2017-01-01

    Full Text Available The contact regime of particle-wall is investigated by the atomic force microscope (AFM and theoretical models. First, AFM is used to measure the cohesive force between a micron-sized grain and a glass plate at quasi-static state under various humidity. It is found out that the cohesive force starts to grow slowly and suddenly increase rapidly beyond a critical Relative Humidity (RH. Second, mathematical models of contacting forces are presented to depict the dynamic process that a particle impacts on a wet wall. Then the energy loss of a falling grain is calculated in comparison with the models and the experimental data from the previous references. The simulation results show that the force models presented here are adaptive for both low and high viscosity fluid films with different thickness.

  17. STUDY OF STATIC AND DYNAMIC STABILITY OF THIN-WALLED BARS EXCITED BY PERIODICAL AXIAL EXTERNAL FORCES.

    Directory of Open Access Journals (Sweden)

    Minodora Maria PASĂRE

    2010-10-01

    Full Text Available In these paper, starting from the relations for the displacements and spinning the transversal section of a bar with thin walls of sections opened expressed by the corresponding influence functions and introducing the components of the exterior forces distributed and the moments of the exterior forces distributed due to the inertia forces, the exciting axial forces together with the following effect of these and of the reaction forces of the elastic environment for leaning it may reach to the system of the equations of parametric vibrations under the form of three integral equation These equations may serve for the study of vibrations of the bars, to study the static stability and to study the dynamic stability

  18. Investigation of protein folding by coarse-grained molecular dynamics with the UNRES force field.

    Science.gov (United States)

    Maisuradze, Gia G; Senet, Patrick; Czaplewski, Cezary; Liwo, Adam; Scheraga, Harold A

    2010-04-08

    Coarse-grained molecular dynamics simulations offer a dramatic extension of the time-scale of simulations compared to all-atom approaches. In this article, we describe the use of the physics-based united-residue (UNRES) force field, developed in our laboratory, in protein-structure simulations. We demonstrate that this force field offers about a 4000-times extension of the simulation time scale; this feature arises both from averaging out the fast-moving degrees of freedom and reduction of the cost of energy and force calculations compared to all-atom approaches with explicit solvent. With massively parallel computers, microsecond folding simulation times of proteins containing about 1000 residues can be obtained in days. A straightforward application of canonical UNRES/MD simulations, demonstrated with the example of the N-terminal part of the B-domain of staphylococcal protein A (PDB code: 1BDD, a three-alpha-helix bundle), discerns the folding mechanism and determines kinetic parameters by parallel simulations of several hundred or more trajectories. Use of generalized-ensemble techniques, of which the multiplexed replica exchange method proved to be the most effective, enables us to compute thermodynamics of folding and carry out fully physics-based prediction of protein structure, in which the predicted structure is determined as a mean over the most populated ensemble below the folding-transition temperature. By using principal component analysis of the UNRES folding trajectories of the formin-binding protein WW domain (PDB code: 1E0L; a three-stranded antiparallel beta-sheet) and 1BDD, we identified representative structures along the folding pathways and demonstrated that only a few (low-indexed) principal components can capture the main structural features of a protein-folding trajectory; the potentials of mean force calculated along these essential modes exhibit multiple minima, as opposed to those along the remaining modes that are unimodal. In addition

  19. Dynamic stability of nearly cylindrical orthotropic shells of revolution subjected to meridional forces

    Science.gov (United States)

    Kukudzhanov, S. N.

    2008-10-01

    We study the natural vibrations and the dynamic stability of nearly cylindrical orthotropic shells of revolution subjected to meridional forces uniformly distributed over the shell ends. We consider shells of medium length for which the shape of the midsurface generatrix is described by a parabolic function. Using the theory of shallow shells, we obtain the resolving equation for the vibrations of the corresponding prestressed shell. In the isotropic case, this equation differs from the well-known equation [1] by an additional term, which can be of the same order as the other terms taken into account. We consider shells of both positive and negative Gaussian curvature. We assumed that the shell ends are freely supported. The formulas and universal curves describing the dependence of the minimum frequency, the wave generation shape, and the dynamic instability domain boundaries on the orthotropy parameters, the preliminary stress, the Gaussian curvature, and the amplitude of the shell deviation from the cylinder are given in dimensionless form. We find that in the case of prestresses the orthotropy parameters and the shell deviation from the cylinder (of the order of thickness) can significantly change the least frequencies, the wave generation shape, and the dynamic instability domain boundaries of the corresponding prestressed orthotropic cylindrical shell. In this case, we note that for convex shells under preliminary compression the influence of the elastic parameter in the axial direction is stronger than the influence of the elastic parameter in the circular direction, while the situation is opposite in the case of concave shells. In the case of preliminary extension, the leading role of any orthotropy parameter can vary depending on the value of the preliminary stress and the Gaussian curvature.

  20. Grand canonical Molecular Dynamics Simulations

    CERN Document Server

    Fritsch, S; Junghans, C; Ciccotti, G; Site, L Delle; Kremer, K

    2011-01-01

    For simulation studies of (macro-) molecular liquids it would be of significant interest to be able to adjust/increase the level of resolution within one region of space, while allowing for the free exchange of molecules between (open) regions of different resolution/representation. In the present work we generalize the adaptive resolution idea in terms of a generalized Grand Canonical approach. This provides a robust framework for truly open Molecular Dynamics systems. We apply the method to liquid water at ambient conditions.

  1. Biopolymers under large external forces and mean-field RNA virus evolutionary dynamics

    Science.gov (United States)

    Ahsan, Syed Amir

    The modeling of the mechanical response of single-molecules of DNA and RNA under large external forces through statistical mechanical methods is central to this thesis with a small portion devoted to modeling the evolutionary dynamics of positive-sense single-stranded RNA viruses. In order to develop and test models of biopolymer mechanics and illuminate the mechanisms underlying biological processes where biopolymers undergo changes in energy on the order of the thermal energy, , entails measuring forces and lengths on the scale of piconewtons (pN) and nanometers (nm), respectively. A capacity achieved in the past two decades at the single-molecule level through the development of micromanipulation techniques such as magnetic and optical tweezers, atomic force microscopy, coupled with advances in micro- and nanofabrication. The statistical mechanical models of biopolymers developed in this dissertation are dependent upon and the outcome of these advancements and resulting experiments. The dissertation begins in chapter 1 with an introduction to the structure and thermodynamics of DNA and RNA, highlighting the importance and effectiveness of simple, two-state models in their description as a prelude to the emergence of two-state models in the research manuscripts. In chapter 2 the standard models of the elasticity of polymers and of a polymer gel are reviewed, characterizing the continuum and mean-field models, including the scaling behavior of DNA in confined spaces. The research manuscript presented in the last section of chapter 2 (section 2.5), subsequent to a review of a Flory gel and in contrast to it, is a model of the elasticity of RNA as a gel, with viral RNA illustrating an instance of such a network, and shown to exhibit anomalous elastic behavior, a negative Poisson ratio, and capable of facilitating viral RNA encapsidation with further context provided in section 5.1. In chapter 3 the experimental methods and behavior of DNA and RNA under mechanical

  2. Cellular adhesome screen identifies critical modulators of focal adhesion dynamics, cellular traction forces and cell migration behaviour.

    Science.gov (United States)

    Fokkelman, Michiel; Balcıoğlu, Hayri E; Klip, Janna E; Yan, Kuan; Verbeek, Fons J; Danen, Erik H J; van de Water, Bob

    2016-08-17

    Cancer cells migrate from the primary tumour into surrounding tissue in order to form metastasis. Cell migration is a highly complex process, which requires continuous remodelling and re-organization of the cytoskeleton and cell-matrix adhesions. Here, we aimed to identify genes controlling aspects of tumour cell migration, including the dynamic organization of cell-matrix adhesions and cellular traction forces. In a siRNA screen targeting most cell adhesion-related genes we identified 200+ genes that regulate size and/or dynamics of cell-matrix adhesions in MCF7 breast cancer cells. In a subsequent secondary screen, the 64 most effective genes were evaluated for growth factor-induced cell migration and validated by tertiary RNAi pool deconvolution experiments. Four validated hits showed significantly enlarged adhesions accompanied by reduced cell migration upon siRNA-mediated knockdown. Furthermore, loss of PPP1R12B, HIPK3 or RAC2 caused cells to exert higher traction forces, as determined by traction force microscopy with elastomeric micropillar post arrays, and led to considerably reduced force turnover. Altogether, we identified genes that co-regulate cell-matrix adhesion dynamics and traction force turnover, thereby modulating overall motility behaviour.

  3. An Agent-Based Discrete Collagen Fiber Network Model of Dynamic Traction Force-Induced Remodeling.

    Science.gov (United States)

    Reinhardt, James W; Gooch, Keith

    2017-09-21

    We developed an agent-based model that incorporates repetitively applied traction force within a discrete fiber network to understand how microstructural properties of the network influence mechanical properties and traction force-induced remodeling. An important difference between our model and similar finite-element models is that by implementing more biologically-realistic dynamic traction, we can explore a greater range of matrix remodeling. Here, we validated our model by reproducing qualitative trends observed in three sets of experimental data reported by others: tensile and shear testing of cell-free collagen gels, collagen remodeling around a single isolated cell, and collagen remodeling between pairs of cells. In response to tensile and shear strain, simulated acellular networks exhibited biphasic stress-strain curves indicative of strain-stiffening. Our data support the notion that strain-stiffening might occur as individual fibrils successively align along the axis of strain and become engaged in tension. In simulations with a single, contractile cell, peak collagen displacement occurred closest to the cell and decreased with increasing distance. In simulations with two cells, compaction of collagen between cells appeared inversely related to the initial distance between cells. Further analysis revealed strain energy was relatively uniform around the outer surface of cells separated by 250 microns, but became increasingly non-uniform as the distance between cells decreased. This pattern was partly attributable to the pattern of collagen compaction. These findings are of interest because fibril alignment, density, and strain energy may each contribute to contact guidance during tissue morphogenesis.

  4. Dynamic behaviour of dagger-shaped cantilevers for atomic force microscopy

    Science.gov (United States)

    Shen, Kangzhi; Hurley, Donna C.; Turner, Joseph A.

    2004-11-01

    Experimental techniques based on the atomic force microscope (AFM) have been developed for characterizing mechanical properties at the nanoscale and applied to a variety of materials and structures. Atomic force acoustic microscopy (AFAM) is one such technique that uses spectral information of the AFM cantilever as it vibrates in contact with a sample. In this paper, the dynamic behaviour of AFM cantilevers that have a dagger shape is investigated using a power-series method. Dagger-shaped cantilevers have plan-view geometry consisting of a rectangular section at the clamped end and a triangular section at the tip. Their geometry precludes modelling using closed-form expressions. The convergence of the series is demonstrated and the convergence radius is shown to be related to the given geometry. The accuracy and efficiency of the method are investigated by comparison with finite element results for several different cases. AFAM experiments are modelled by including a linear spring at the tip that represents the contact stiffness. The technique developed is shown to be very effective for inversion of experimental frequency information into contact stiffness results for AFAM. In addition, the sensitivities of the frequencies to the contact stiffness are discussed in terms of the various geometric parameters of the problem including the slope, the ratio of the rectangular to triangular lengths and the tip location. Calculations of contact stiffness from experimental data using this model are shown to be very good in comparison with other models. It is anticipated that this approach may be useful for other cantilever geometries as well, such that AFAM accuracy may be improved.

  5. The entropic forces and dynamic integrity of single file water in hydrophobic nanotube confinements

    Energy Technology Data Exchange (ETDEWEB)

    Sahu, Pooja; Ali, Sk. M., E-mail: musharaf@barc.gov.in [Chemical Engineering Division, Bhabha Atomic Research Center, Mumbai 400085 (India)

    2015-11-14

    Water in nanotube exhibits remarkably different properties from the bulk phase, which can be exploited in various nanoconfinement based technologies. The properties of water within nanotube can be further tuned by varying the nanotube electrostatics and functionalization of nanotube ends. Here, therefore, we investigate the effect of quantum partial charges and carbon nanotube (CNT) termination in terms of associated entropic forces. An attempt has been made to correlate the entropic forces with various dynamical and structural properties. The simulated structural features are consistent with general theoretical aspects, in which the interfacial water molecules at H terminated CNT are found to be distributed in a different way as compared to other CNTs. The rotational entropy components for different cases of CNTs are well corroborated by the decay time of hydrogen bond (HB) correlation functions. A part of this event has been explained in terms of orientation of water molecules in the chain, i.e., the change in direction of dipole moment of water molecules in the chain and it has been revealed that the HBs of CNT confined water molecules show long preserving correlation if their rotations inside CNT are restricted. Furthermore, the translational entropy components are rationally integrated with the differing degree of translational constraints, added by the CNTs. To the best of our information, perhaps this is the first study where the thermodynamic effects introduced by H-termination and induced dipole of CNT have been investigated. Additionally, we present a bridge relation between “translational diffusivity and configurational entropy” for water transport from bulk phase to inside CNTs.

  6. Long-term dynamics in land resource use and the driving forces in the Beressa watershed, highlands of Ethiopia

    NARCIS (Netherlands)

    Amsalu Taye, A.; Stroosnijder, L.; Graaff, de J.

    2007-01-01

    Land degradation in the Ethiopian highlands is considered to be one of the major problems threatening agricultural development and food security in the country. However, knowledge about the forces driving the long-term dynamics in land resources use is limited. This research integrates biophysical i

  7. Molecular Dynamics Simulation of a Membrane/Water Interface : The Ordering of Water and Its Relation to the Hydration Force

    NARCIS (Netherlands)

    Marrink, Siewert-Jan; Berkowitz, Max; Berendsen, Herman J.C.

    1993-01-01

    In order to obtain a better understanding of the origin of the hydration force, three molecular dynamic simulations of phospholipid/water multilamellar systems were performed. The simulated systems only differed in the amount of interbilayer water, ranging from the minimum to the maximum amount of

  8. An accurate and efficient spectral method for studies of the dynamical properties of forced, circular shear layers

    DEFF Research Database (Denmark)

    Lynov, Jens-Peter; Bergeron, K.; Coutsias, E.A.;

    2000-01-01

    We present an efficient spectral method for studies of fundamental vortex dynamics in forced, circular shear flows. The numerical results are compared with results from experiments carried out in rotating flows with both planar and parabolic geometries, Due to the high accuracy of the code, it can...

  9. Measurement of dynamic cell-induced 3D displacement fields in vitro for traction force optical coherence microscopy.

    Science.gov (United States)

    Mulligan, Jeffrey A; Bordeleau, François; Reinhart-King, Cynthia A; Adie, Steven G

    2017-02-01

    Traction force microscopy (TFM) is a method used to study the forces exerted by cells as they sense and interact with their environment. Cell forces play a role in processes that take place over a wide range of spatiotemporal scales, and so it is desirable that TFM makes use of imaging modalities that can effectively capture the dynamics associated with these processes. To date, confocal microscopy has been the imaging modality of choice to perform TFM in 3D settings, although multiple factors limit its spatiotemporal coverage. We propose traction force optical coherence microscopy (TF-OCM) as a novel technique that may offer enhanced spatial coverage and temporal sampling compared to current methods used for volumetric TFM studies. Reconstructed volumetric OCM data sets were used to compute time-lapse extracellular matrix deformations resulting from cell forces in 3D culture. These matrix deformations revealed clear differences that can be attributed to the dynamic forces exerted by normal versus contractility-inhibited NIH-3T3 fibroblasts embedded within 3D Matrigel matrices. Our results are the first step toward the realization of 3D TF-OCM, and they highlight the potential use of OCM as a platform for advancing cell mechanics research.

  10. Numerical analysis of dynamic response of jacket structures subject to slamming forces by breaking waves

    Directory of Open Access Journals (Sweden)

    Chanjo Woo

    2017-07-01

    Full Text Available The present study numerically analyzed the dynamic behavior of 3D framed structures subject to impulsive slamming forces by violent breaking waves. The structures were modeled using multiple lumped masses for the vertical projections of each member, and the slamming forces from the breaking waves were concentrated on these lumped masses. A numerical algorithm was developed to properly incorporate the slamming forces into a dynamic analysis to numerically determine the structural responses. Then, the validity of the numerical analysis was verified using the results of an existing hydraulic experiment. The numerical and experimental results for various model structures were generally in good agreement. The uncertainties concerning the properties of the breaking waves used in the verification are also discussed here.

  11. Upper limb dynamic responses to impulsive forces for selected assembly workers.

    Science.gov (United States)

    Sesto, Mary E; Radwin, Robert G; Block, Walter F; Best, Thomas M

    2006-02-01

    This study evaluated the upper limb, dynamic, mechanical response parameters for 14 male assembly workers recruited from selected jobs based on power tool use. It was hypothesized that the type of power tool operation would affect stiffness, effective mass, and damping of the upper extremity; and workers with symptoms and positive physical examination findings would have different mechanical responses than asymptomatic workers without physical examination findings. Participants included operators who regularly used torque reaction power hand tools, such as nutrunners and screwdrivers, and nontorque reaction power hand tools, such as riveters. The mechanical parameters of the upper limb were characterized from the loading response of an apparatus having known dynamic properties while worker grasps an oscillating handle in free vibration. In addition, all workers underwent a physical examination, magnetic resonance imaging, and completed a symptom survey. Workers were categorized as controls or cases based on reported forearm symptoms and physical exam findings. A total of seven workers were categorized as cases and had less average mechanical stiffness (46%, p > 0.01), damping (74%, p > 0.01), and effective mass (59%, p > 0.05) than the seven workers categorized as controls. Magnetic resonance imaging (MRI) findings suggestive of muscle edema were observed for two workers classified as cases and who regularly used torque reaction power tools. No MRI enhancement was observed in the seven subjects who did not regularly use torque reaction power tools. The ergonomic consequences of less stiffness, effective mass, and damping in symptomatic workers may include reduced capacity to react against rapidly building torque reaction forces encountered when operating power hand tools.

  12. Sensitivity of oxygen dynamics in the water column of the Baltic Sea to external forcing

    Directory of Open Access Journals (Sweden)

    S. Miladinova

    2010-04-01

    Full Text Available A 1-D biogeochemical/physical model of marine systems has been applied to study the oxygen cycle in four stations of different sub-basins of the Baltic Sea, namely, in the Gotland Deep, Bornholm, Arkona and Fladen. The model consists of the biogeochemical model of Neumann et al. (2002 coupled with the 1-D General Ocean Turbulence Model (GOTM. The model has been forced with meteorological data from the ECMWF reanalysis project for the period 1998–2003, producing a six year hindcast which is validated with datasets from the Baltic Environmental Database (BED for the same period. The vertical profiles of temperature and salinity are relaxed towards both profiles provided by 3-D simulations of General Estuarine Transport Model (GETM and observed profiles from BED. Modifications in the parameterisation of the air-sea oxygen fluxes have led to a significant improvement of the model results in the surface and intermediate water layers. The largest mismatch with observations is found in simulating the oxygen dynamics in the Baltic Sea bottom waters. The model results demonstrate the good capability of the model to predict the time-evolution of the physical and biogeochemical variables at all different stations. Comparative analysis of the modelled oxygen concentrations with respect to observation data is performed to distinguish the relative importance of several factors on the seasonal, interannual and long-term variations of oxygen. It is found that natural physical factors, like the magnitude of the vertical turbulent mixing, wind speed and the variation of temperature and salinity fields are the major factors controlling the oxygen dynamics in the Baltic Sea. The influence of limiting nutrients is less pronounced, at least under the nutrient flux parameterisation assumed in the model.

  13. The dynamical evolution and the force model for asteroid (196256) 2003 EH1

    Science.gov (United States)

    Galushina, T. Yu.; Sambarov, G. E.

    2017-08-01

    This paper is devoted to the dynamics of asteroid (196256) 2003 EH1 which belongs to the Amor group. It is known that asteroid 2003 EH1 is associated with one of the main annual meteor showers - the Quadrantids. In this work we analyze the influence of various perturbing factors on the asteroid motion. The perturbations' estimation was done by five different methods based on the nominal orbit evolution and the size of the initial confidence region. The most significant influences on the dynamical evolution of 2003 EH1 are gravitational forces from the Sun, major planets and the Moon, and the relativistic effects (RE) of the Sun. The Earth, the Sun and Jupiter oblateness; gravitational perturbations from Pallas, Ceres, Vesta and Pluto; and the RE of planets, the Moon, and Pluto are of less importance. The researches of chaoticity and evolution of asteroid 2003 EH1 were examined by integrating its motion equations along with 500 clones. The time interval (1000-4000 years) has been determined by integration precision estimation. We estimated the mean exponential growth factor of nearby orbits (MEGNO) and found that MEGNO < 2 only in the interval from 1700 year to 2300 year. After 2300 year the MEGNO parameter increases that indicates motion instability. It shows that the orbit may be considered as regular on the time interval of ±300 years from now, and as chaotic outside this interval. We suppose that the reasons are the frequent close approaches of the asteroid with Jupiter and the overlap of apsidal-nodal resonances.

  14. Forcing mechanisms and hydrodynamics in Loch Linnhe, a dynamically wide Scottish estuary

    Science.gov (United States)

    Rabe, Berit; Hindson, Jennifer

    2017-09-01

    Hydrodynamic conditions in Loch Linnhe, a dynamifcally wide estuary on the west coast of Scotland, are primarily influenced by wind forcing, freshwater input, and tides. Winds in the region are orographically steered along the axis of the estuary due to surrounding mountains. A large rainfall catchment area results in a large freshwater inflow into Loch Linnhe which in turn produces low salinity waters at the head of the estuary. This, combined with a connection to the open sea with coastal salinities, leads to salinity gradients in the horizontal and vertical. Even though a range of observational programmes have focussed on Loch Linnhe, the literature still lacks an evaluation of its physical dynamics. Here we present a first description of the hydrodynamics in Loch Linnhe based on observations. Wind stress predominantly influences the surface layer, especially at low frequencies and with a stronger influence than tides during neap tides. The buoyancy-driven flow due to the large river runoff influences the circulation independent of wind stress. Seasonal (spring, autumn) and interannual (2011, 2012) variability of water masses occur especially in the surface layer. Tides are dominated by the semi-diurnal constituent M2 with tidal ellipses aligned in the along-estuary direction and a stronger influence during spring tides compared to wind. An evaluation of dimensionless numbers reveal laterally and vertically sheared exchange flows. Compared to other Scottish estuaries Loch Linnhe is wide enough to be influenced by the Earth's rotation and demonstrates an enhanced freshwater outflow along its north-western coast as the freshwater is diverted to the right in the direction of the flow. These observed patterns are important for the sustainable environmental management of this socio-economically valuable region, e.g. through their relevance to aquaculture pathogen transmission patterns. A thorough understanding of the dynamics of the system is essential for a

  15. Micropillar displacements by cell traction forces are mechanically correlated with nuclear dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Li, Qingsen; Makhija, Ekta; Hameed, F.M. [Mechanobiology Institute, National University of Singapore (Singapore); Shivashankar, G.V., E-mail: shiva.gvs@gmail.com [Mechanobiology Institute, National University of Singapore (Singapore); Department of Biological Sciences, National University of Singapore (Singapore)

    2015-05-29

    Cells sense physical cues at the level of focal adhesions and transduce them to the nucleus by biochemical and mechanical pathways. While the molecular intermediates in the mechanical links have been well studied, their dynamic coupling is poorly understood. In this study, fibroblast cells were adhered to micropillar arrays to probe correlations in the physical coupling between focal adhesions and nucleus. For this, we used novel imaging setup to simultaneously visualize micropillar deflections and EGFP labeled chromatin structure at high spatial and temporal resolution. We observed that micropillar deflections, depending on their relative positions, were positively or negatively correlated to nuclear and heterochromatin movements. Our results measuring the time scales between micropillar deflections and nucleus centroid displacement are suggestive of a strong elastic coupling that mediates differential force transmission to the nucleus. - Highlights: • Correlation between focal adhesions and nucleus studied using novel imaging setup. • Micropillar and nuclear displacements were measured at high resolution. • Correlation timescales show strong elastic coupling between cell edge and nucleus.

  16. Dynamics of the force of infection: insights from Echinococcus multilocularis infection in foxes.

    Directory of Open Access Journals (Sweden)

    Fraser I Lewis

    2014-03-01

    Full Text Available Characterizing the force of infection (FOI is an essential part of planning cost effective control strategies for zoonotic diseases. Echinococcus multilocularis is the causative agent of alveolar echinococcosis in humans, a serious disease with a high fatality rate and an increasing global spread. Red foxes are high prevalence hosts of E. multilocularis. Through a mathematical modelling approach, using field data collected from in and around the city of Zurich, Switzerland, we find compelling evidence that the FOI is periodic with highly variable amplitude, and, while this amplitude is similar across habitat types, the mean FOI differs markedly between urban and periurban habitats suggesting a considerable risk differential. The FOI, during an annual cycle, ranges from (0.1,0.8 insults (95% CI in urban habitat in the summer to (9.4, 9.7 (95% CI in periurban (rural habitat in winter. Such large temporal and spatial variations in FOI suggest that control strategies are optimal when tailored to local FOI dynamics.

  17. Deciphering the energy landscape of the interaction uranyl-DCP with antibodies using dynamic force spectroscopy.

    Science.gov (United States)

    Teulon, Jean-Marie; Parot, Pierre; Odorico, Michael; Pellequer, Jean-Luc

    2008-11-15

    Previous studies on molecular recognition of uranyl-DCP (dicarboxy-phenanthroline chelator) compound by two distinct monoclonal antibodies (Mabs U04S and U08S) clearly showed the presence of a biphasic shape in Bell-Evans' plots and an accentuated difference in slopes at the high loading rates. To further explore the basis in the slope difference, we have performed complementary experiments using antibody PHE03S, raised against uranyl-DCP but, presenting a strong cross-reactivity toward the DCP chelator. This work allowed us to obtain a reallocation of the respective contributions of the metal ion itself and that of the chelator. Results led us to propose a 2D schematic model representing two energy barriers observed in the systems Mabs U04S- and U08S-[UO(2)-DCP] where the outer barrier characterizes the interaction between UO(2) and Mab whereas the inner barrier characterizes the interaction between DCP and Mab. Using dynamic force spectroscopy, it is thus possible to dissect molecular interactions during the unbinding between proteins and ligands.

  18. Viewing dynamic interactions of proteins and a model lipid membrane with atomic force microscopy.

    Science.gov (United States)

    Quinn, Anthony S; Rand, Jacob H; Wu, Xiao-Xuan; Taatjes, Douglas J

    2013-01-01

    The information covered in this chapter will present a model homogenous membrane preparation technique and dynamic imaging procedure that can be successfully applied to more than one type of lipid study and atomic force microscope (AFM) instrument setup. The basic procedural steps have been used with an Asylum Research MFP-3D BIO and the Bruker (formerly, Veeco) BioScope. The AFM imaging protocol has been supplemented by procedures (not to be presented in this chapter) of ellipsometry, standardized western blotting, and dot-blots to verify appropriate purity and activity of all experimental molecular components; excellent purity and activity level of the lipids, proteins, and drug(s) greatly influence the success of imaging experiments in the scanning probe microscopy field. The major goal of the chapter is to provide detailed procedures for sample preparation and operation of the Asylum Research MFP-3D BIO AFM. In addition, one should be cognizant that our comprehensive description in the use of the MFP-3D BIO's functions for successful image acquisitions and analyses is greatly enhanced by Asylum Research's (AR's) accompanying extensive manual(s), technical notes, and AR's users forum. Ultimately, the stepwise protocol and information will allow novice personnel to begin acquiring quality images for processing and analysis with minimal supervision.

  19. Spindle pole mechanics studied in mitotic asters: dynamic distribution of spindle forces through compliant linkages.

    Science.gov (United States)

    Charlebois, Blake D; Kollu, Swapna; Schek, Henry T; Compton, Duane A; Hunt, Alan J

    2011-04-06

    During cell division, chromosomes must faithfully segregate to maintain genome integrity, and this dynamic mechanical process is driven by the macromolecular machinery of the mitotic spindle. However, little is known about spindle mechanics. For example, spindle microtubules are organized by numerous cross-linking proteins yet the mechanical properties of those cross-links remain unexplored. To examine the mechanical properties of microtubule cross-links we applied optical trapping to mitotic asters that form in mammalian mitotic extracts. These asters are foci of microtubules, motors, and microtubule-associated proteins that reflect many of the functional properties of spindle poles and represent centrosome-independent spindle-pole analogs. We observed bidirectional motor-driven microtubule movements, showing that microtubule linkages within asters are remarkably compliant (mean stiffness 0.025 pN/nm) and mediated by only a handful of cross-links. Depleting the motor Eg5 reduced this stiffness, indicating that Eg5 contributes to the mechanical properties of microtubule asters in a manner consistent with its localization to spindle poles in cells. We propose that compliant linkages among microtubules provide a mechanical architecture capable of accommodating microtubule movements and distributing force among microtubules without loss of pole integrity-a mechanical paradigm that may be important throughout the spindle.

  20. Dynamic simulation of viscoelastic soft tissue in acoustic radiation force creep imaging.

    Science.gov (United States)

    Zhao, Xiaodong; Pelegri, Assimina A

    2014-09-01

    Acoustic radiation force (ARF) creep imaging applies step ARF excitation to induce creep displacement of soft tissue, and the corresponding time-dependent responses are used to estimate soft tissue viscoelasticity or its contrast. Single degree of freedom (SDF) and homogeneous analytical models have been used to characterize soft tissue viscoelasticity in ARF creep imaging. The purpose of this study is to investigate the fundamental limitations of the commonly used SDF and homogeneous assumptions in ARF creep imaging. In this paper, finite element (FE) models are developed to simulate the dynamic behavior of viscoelastic soft tissue subjected to step ARF. Both homogeneous and heterogeneous models are studied with different soft tissue viscoelasticity and ARF configurations. The results indicate that the SDF model can provide good estimations for homogeneous soft tissue with high viscosity, but exhibits poor performance for low viscosity soft tissue. In addition, a smaller focal region of the ARF is desirable to reduce the estimation error with the SDF models. For heterogeneous media, the responses of the focal region are highly affected by the local heterogeneity, which results in deterioration of the effectiveness of the SDF and homogeneous simplifications.

  1. Experimental evidence of dynamic re-organization of evolving landscapes under changing climatic forcing

    Science.gov (United States)

    Singh, Arvind; Tejedor, Alejandro; Zaliapin, Ilya; Reinhardt, Liam; Foufoula-Georgiou, Efi

    2015-04-01

    The aim of this study is to better understand the dynamic re-organization of an evolving landscape under a scenario of changing climatic forcing for improving our knowledge of geomorphic transport laws under transient conditions and developing predictive models of landscape response to external perturbations. Real landscape observations for long-term analysis are limited and to this end a high resolution controlled laboratory experiment was conducted at the St. Anthony Falls laboratory at the University of Minnesota. Elevation data were collected at temporal resolution of 5 mins and spatial resolution of 0.5 mm as the landscape approached steady state (constant uplift and precipitation rate) and in the transient state (under the same uplift and 5x precipitation). The results reveal rapid topographic re-organization under a five-fold precipitation increase with the fluvial regime expanding into the previously debris dominated regime, accelerated erosion happening at hillslope scales, and rivers shifting from an erosion-limited to a transport-limited regime. From a connectivity and clustering analysis of the erosional and depositional events, we demonstrate the strikingly different spatial patterns of landscape evolution under steady-state (SS) and transient-state (TS), even when the time under SS is "stretched" compared to that under TS such as to match the total volume and PDF of erosional and depositional amounts. We quantify the spatial coupling of hillslopes and channels and demonstrate that hillslopes lead and channels follow in re-organizing the whole landscape under such an amplified precipitation regime.

  2. Chaotic dynamics and thermodynamics of periodic systems with long-range forces

    Science.gov (United States)

    Kumar, Pankaj

    Gravitational and electromagnetic interactions form the backbone of our theoretical understanding of the universe. While, in general, such interactions are analytically inexpressible for three-dimensional infinite systems, one-dimensional modeling allows one to treat the long-range forces exactly. Not only are one-dimensional systems of profound intrinsic interest, physicists often rely on one-dimensional models as a starting point in the analysis of their more complicated higher-dimensional counterparts. In the analysis of large systems considered in cosmology and plasma physics, periodic boundary conditions are a natural choice and have been utilized in the study of one dimensional Coulombic and gravitational systems. Such studies often employ numerical simulations to validate the theoretical predictions, and in cases where theoretical relations have not been mathematically formulated, numerical simulations serve as a powerful method in characterizing the system's physical properties. In this dissertation, analytic techniques are formulated to express the exact phase-space dynamics of spatially-periodic one-dimensional Coulombic and gravitational systems. Closed-form versions of the Hamiltonian and the electric field are derived for single-component and two-component Coulombic systems, placing the two on the same footing as the gravitational counterpart. Furthermore, it is demonstrated that a three-body variant of the spatially-periodic Coulombic or gravitational system may be reduced isomorphically to a periodic system of a single particle in a two-dimensional rhombic potential. The analytic results are utilized for developing and implementing efficient computational tools to study the dynamical and the thermodynamic properties of the systems without resorting to numerical approximations. Event-driven algorithms are devised to obtain Lyapunov spectra, radial distribution function, pressure, caloric curve, and Poincare surface of section through an N

  3. Vortical flows in strongly coupled Yukawa liquids under external forcing - A molecular dynamics approach

    Science.gov (United States)

    Ganesh, Rajaraman; Charan, Harish

    2016-07-01

    Understanding vortical flows under external forcing in two dimensional (2D) fluids is a fundamental paradigm for structure formation in driven, dissipative systems. Considering Yukawa liquid as a prototype for strongly correlated or strongly coupled plasmas characterized by coupling strength (Γ, the ratio of average potential to kinetic energy per particle) and screening parameter (κ, ratio of mean inter-particle distance to shielding length), we address two important problems: 1. Onset of Rayleigh Benard convection cell (RBCC) in 2D Yukawa liquids subject to gravity and external temperature gradient 2. Onset of von Karman vortices in 2D Yukawa liquid under external pressure head, using large scale, first principles molecular dynamics simulations. For typical values of (Γ,κ), existence of a critical external temperature difference is demonstrated, beyond which RBCC are seen to set in. Beyond this critical external temperature difference, the strength of the maximum convective flow velocity is shown to exhibit a new, hitherto unsuspected linear relationship with external temperature difference and with a slope independent of (Γ,κ). The time taken for the transients to settle down to a steady state RBCC τ_s, is found to be maximum close to the above said critical external temperature difference and is seen to reduce with increasing external temperature difference. For the range of values of (Γ, κ) considered here, τ_s ≃ 10 000-20 000;ω^{-1}_{pd}, where ω_{pd} is dust plasma frequency. As Γ is increased to very high values, due to strong coupling effects, RBC cells are seen to be in a transient state without attaining a steady state for as long as 100 000;ω^{-1}_{pd}, even for a very high external temperature difference. In the second part, we address the existence of universal relation between Strouhal (St) and Rayleigh (Ry) numbers for Yukawa liquid using first principles based classical molecular dynamics. The flow past an obstacle is seen to indeed

  4. Identification of the nonlinear excitation force acting on a bowed string using the dynamical responses at remote locations

    Energy Technology Data Exchange (ETDEWEB)

    Debut, V.; Antunes, J. [ITN, ADL, P-2686 Sacavem Codex (Portugal); Delaune, X. [CEA Saclay, DEN, DM2S, SEMT, Lab Etud Dynam, F-01101 Gif Sur Yvette (France)

    2010-07-01

    For achieving realistic numerical simulations of bowed string instruments, based on physical modeling, a good understanding of the actual friction interaction phenomena is of great importance. Most work published in the field including our own has assumed that bow/string frictional forces behave according to the classical Coulomb stick-slip model, with an empirical velocity-dependent sliding friction coefficient. Indeed, the basic self-excited string motions (such as the Helmholtz regime) are well captured using such friction model. However, recent work has shown that the tribological behavior of the bow/string rosin interface is rather complex, therefore the basic velocity-dependent Coulomb model may be an over-simplistic representation of the friction force. More specifically, it was suggested that a more accurate model of the interaction force can be achieved by coupling the system dynamical equations with a thermal model which encapsulates the complex interface phenomena. In spite of the interesting work performed by Askenfelt, a direct measurement of the actual dynamical friction forces without disturbing the string motion is quite difficult. Therefore, in this work we develop a modal-based identification technique making use of inverse methods and optimization techniques, which enables the identification of the interface force, as well as the string self-excited motion, from the dynamical reactions measured at the string end supports. The method gives convincing results using simulated data originated from nonlinear computations of a bowed string. Furthermore, in cases where the force identifications are very sensitive to errors in the transfer function modal parameters, we suggest a method to improve the modal frequencies used for the identifications. Preliminary experimental results obtained using a basic bowing device, by which the string is excited with the stick of the bow, are then presented. Our identifications, from the two dynamical string reactions

  5. Two barriers or not? Dynamic force spectroscopy on the integrin α7β1 invasin complex

    DEFF Research Database (Denmark)

    Boye, Kristian; Ligezowska, Agnieszka; Eble, Johannes A.

    2013-01-01

    Dynamic force spectroscopy was used to test force-induced dissociation of the complex between the integrin α7β1 and the bacterial protein invasin. Both proteins were used in truncated forms comprising the respective binding sites. Using the biomembrane force-probe, the bond system was exposed to ...

  6. Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator.

    Science.gov (United States)

    Kiracofe, Daniel; Melcher, John; Raman, Arvind

    2012-01-01

    Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

  7. Dynamically forced cantilever system: A piezo-polymer characterization tool with possible application for micromechanical HF resonator devices

    Science.gov (United States)

    Schwödiauer, Reinhard

    2005-04-01

    A cantilever system, driven to a dynamically forced oscillation by a small piezoelectric specimen is presented as a simple and accurate tool to determine the converse dynamic piezocoefficient up to several kHz. The piezoelectric sample is mounted on top of a reflective cantilever where it is free to oscillate without any mechanical constraint. A Nomarsky-interferometer detects the induced cantilever displacement. The presented technique is especially suited for a precise characterization of small and soft piezoelectric polymer-samples with rough surfaces. The capability of the dynamically forced cantilever principle is demonstrated with a LiNbO3 crystal and with a porous ferroelectretic polypropylene foam. Results from measurements between 400 Hz and 5 kHz were found to be in excellent agreement with published values. Additionally, the dynamically forced cantilever principle may possibly improve the sensitivity of some micromechanical cantilever-sensors and it could also be interesting for the design of enhanced micromechanical high frequency mixer filters. Some ideas about are briefly presented.

  8. Solar forcing and atmospheric control of paleoflood dynamics in the Bernese Alps, Switzerland

    Science.gov (United States)

    Schulte, Lothar; Peña, Juan Carlos; Burjachs, Francesc; Carvalho, Filipe; Llorca, Jaime; Julià, Ramon; Lomax, Johanna; Schmidt, Thomas; Rubio, Patricio; Losada, Justino; Veit, Heinz

    2014-05-01

    A multidisciplinary approach provides data from natural, historical, and instrumental time series, for the study of potential effects of climatic changes on alpine floods outside the known range of extreme events. The research focuses on the densely populated Bernese Alps, which are a true "hot spot" of hydrological risk. For the reconstruction of climate variability and floods, interdecadal-resolution alluvial delta plain records were examined. The multi-proxy approach affords insight into alpine flood dynamics of mid-scale catchments during the last three millennia. Spectral analysis of the geochemical and pollen time series records and climate proxies (δ14C, δ18O isotopes from the Greenland ice, NAO) evidence similar periodicities of 60, 85, 105 and 200 yrs. Thus, the mechanisms of the flood processes are strongly influenced by the North Atlantic dynamics and solar activity. The proxies indicate that cooler climate pulses and transitions from cool to warm climate pulses were an important external driving force of floods. This hypothesis is supported by the reconstructed floods of the Aare and Lütschine rivers from local documentary sources during the last 500 yrs. Flood periods inferred from sedimentary archives (flood layers, geochemical proxies and shifts of river channel) were calibrated by local documentary flood records and compared with the pattern of settlement on flood prone landforms. The generated data series shows also a good correlation with climate proxies, such as the annual temperatures of Europe (Luterbacher et al., 2004), tree ring based summer temperatures of Central Europe (Büntgen et al., 2011) and total solar irradiance according to the model of Steinhilber et al. (2009). With regard to the last two centuries flood magnitude and frequencies (exact dating) as well as driving mechanisms were reconstructed with more precision. Furthermore, a summer flood index of Switzerland (INU) based on damages recorded from 1800 to 2008 AD was performed

  9. Impact of External Forcing on Glacier Dynamics at Jakobshavn Isbræ during 1840-2012

    Science.gov (United States)

    Muresan, I. S.; Khan, S. A.; Aschwanden, A.; Khroulev, C.; Bjork, A. A.; Box, J. E.

    2014-12-01

    Greenland's main outlet glaciers have more than doubled their contribution to global sea-level rise over the past decade through acceleration of ice discharge. One of the triggering mechanisms is a reduction in resistance (buttressing) at the marine based glacier front (i.e. through reduced thickness or retreat of the floating tongue of a glacier) caused by enhanced calving or a longer-term thinning due to a mass deficit of the ice sheet. Recent findings indicate the reduced buttressing at the marine terminus is responsible for the recent dynamic changes observed in Greenland, but the controlling processes and triggering mechanisms are still unclear. Furthermore, our current understanding is almost entirely based on observations from a short-term record spanning only from a year to a decade, and is characterized by short-term fluctuations and therefore not representative for longer-term trends of several decade time scales. Here, we study the mechanisms controlling dynamic changes at the terminus of Jakobshavn Isbræ over a period of 172 years. The recent glacier acceleration began in late 1990s but there is evidence for glacier retreat of comparable magnitude in 1930s, when a similarly warm period occurred. To control the acceleration and retreat based on observed front positions during 1840-2012, we use an ocean model modifier that implements forcing at the ocean boundary using melange back pressure offsets. The mean temperature anomaly in west Greenland, the North Atlantic oscillation (NAO) winter index and the Atlantic multidecadal oscillation (AMO) index anomalies for the period 1900-2012 sustain our modelling results. The modelled surface elevation changes near the front are considered and compared with observed surface elevation changes for the period 1880-2012. Furthermore, the modelled mass loss signal between 1997-2012 is validated based on ice mass change observations which we estimate using altimeter surveys from NASA's ATM flights during 1997

  10. A new fluid dynamics model to evaluate the contractile force of a biological spring, Vorticella convallaria

    Science.gov (United States)

    Ryu, Sangjin; Matsudaira, Paul

    2008-11-01

    Vorticella convallaria, a sessile peritrich having a body and spring-like stalk, is a model for a bioinspired actuator because of its remarkably fast (msec) and powerful contractions (nN). An example of a biological spring, the stalk converts biochemical energy to physical motion, but the mechanics of contraction are poorly understood. To evaluate contraction force, past models have assumed the body to be a sphere moving in quiescent water and have equated contraction force to drag force on the body described by Stokes' law. However, flow induced by contracting Vorticella does not satisfy conditions of Stokes' law because the flow is unsteady (Womersley number > 1) and bound with a solid substrate to which the cell is tethered. We develop a more rigorous model for contraction force evaluation by assuming the body to be a sphere unsteadily moving perpendicularly toward a solid surface. The model comprises quasi-steady drag force, added mass force and history force with wall effect correction terms for each force. Vorticella not only generates a maximum contraction force greater than Stokes' drag, but it also experiences drag force in the direction of contraction in the later stage of contraction due to the memory effect of water.

  11. Coupling the nongravitational forces and modified Newton dynamics for cometary orbits

    Science.gov (United States)

    Maquet, Lucie; Pierret, Frédéric

    2015-04-01

    In recent work [L. Blanchet and J. Novak, Mon. Not. R. Astron. Soc. 412, 2530 (2011); L. Blanchet and J. Novak, Testing MOND in the Solar System (2011); and M. Milgrom, Mon. Not. R. Astron. Soc. 399, 474 (2009)], the authors showed that modified Newton dynamics (MOND) has a non-negligible secular perturbation effect on planets with large semimajor axes (gaseous planets) in the Solar System. Some comets also have a very eccentric orbit with a large semimajor axis (Halley family comets) going far away from the Sun (more than 15 AU) in a low acceleration regime where they would be subject to MOND perturbation. They also approach the Sun very closely (less than 3 AU) and are affected by the sublimation of ices from their nucleus, triggering so-called nongravitational forces. The main goal of this paper is to investigate the effect of MOND perturbation on three comets with various orbital elements (2 P /Encke , 1 P /Halley and 153 P /Ikeya-Zhang ) and then compare it to the nongravitational perturbations. It is motivated by the fact that when fitting an outgassing model for a comet, we have to take into account all of the small perturbing effects to avoid absorbing these effects into the nongravitational parameters. Otherwise, we could derive a completely wrong estimation of the outgassing. For this work, we use six different forms of MOND functions and compute the secular variations of the orbital elements due to MOND and nongravitational perturbations. We show that, for comets with large semimajor axis, the MONDian effects are not negligible compared to the nongravitational perturbations.

  12. Effect of capillary-condensed water on the dynamic friction force at nanoasperity contacts

    Science.gov (United States)

    Sirghi, L.

    2003-05-01

    A single nanoasperity contact in ambient air is usually wetted by capillary condensation of water vapor and is surrounded by a water meniscus. This phenomenon strongly affects the contact friction, not only by the effect of meniscus loading force (superficial tension and capillary forces), but also by a friction force that accounts for the energy loss in the meniscus movement along with the sliding contact. Occurrence of the water-meniscus-generated friction is experimentally proved by atomic force microscopy measurements of the tip-sample friction force at minimum possible external load (before pull-off). A qualitative explanation for the observed dependence of the friction force on air humidity and solid surface wettability is proposed.

  13. Stochastic Modeling of Lift and Drag Dynamics to Obtain Aerodynamic Forces with Local Dynamics on Rotor Blade under Unsteady Wind Inflow

    Directory of Open Access Journals (Sweden)

    Muhammad Ramzan Luhur

    2014-01-01

    Full Text Available This contribution provides the development of a stochastic lift and drag model for an airfoil FX 79-W-151A under unsteady wind inflow based on wind tunnel measurements. Here we present the integration of the stochastic model into a well-known standard BEM (Blade Element Momentum model to obtain the corresponding aerodynamic forces on a rotating blade element. The stochastic model is integrated as an alternative to static tabulated data used by classical BEM. The results show that in comparison to classical BEM, the BEM with stochastic approach additionally reflects the local force dynamics and therefore provides more information on aerodynamic forces that can be used by wind turbine simulation codes

  14. Dynamics of completely unfolded and native proteins through solid-state nanopores as a function of electric driving force.

    Science.gov (United States)

    Oukhaled, Abdelghani; Cressiot, Benjamin; Bacri, Laurent; Pastoriza-Gallego, Manuela; Betton, Jean-Michel; Bourhis, Eric; Jede, Ralf; Gierak, Jacques; Auvray, Loïc; Pelta, Juan

    2011-05-24

    We report experimentally the dynamic properties of the entry and transport of unfolded and native proteins through a solid-state nanopore as a function of applied voltage, and we discuss the experimental data obtained as compared to theory. We show an exponential increase in the event frequency of current blockades and an exponential decrease in transport times as a function of the electric driving force. The normalized current blockage ratio remains constant or decreases for folded or unfolded proteins, respectively, as a function of the transmembrane potential. The unfolded protein is stretched under the electric driving force. The dwell time of native compact proteins in the pore is almost 1 order of magnitude longer than that of unfolded proteins, and the event frequency for both protein conformations is low. We discuss the possible phenomena hindering the transport of proteins through the pores, which could explain these anomalous dynamics, in particular, electro-osmotic counterflow and protein adsorption on the nanopore wall.

  15. Combined dynamic stiffness matrix and precise time integration method for transient forced vibration response analysis of beams

    Science.gov (United States)

    Tang, Bin

    2008-01-01

    A method has been developed for determining the transient response of a beam. The beam is divided into several continuous Timoshenko beam elements. The overall dynamic stiffness matrix is assembled in turn. Using Leung's equation, we derive the overall mass and stiffness matrices which are more suitable for response analysis than the overall dynamic stiffness matrix. The forced vibration of the beam is computed by the precise time integration method. Three illustrative beams are discussed to evaluate the performance of the current method. Solutions calculated by the finite element method and theoretical analysis are also enumerated for comparison. In these examples, we have found that the current method can solve the forced vibration of structures with a higher precision.

  16. Impact of sea-level rise and coral mortality on the wave dynamics and wave forces on barrier reefs.

    Science.gov (United States)

    Baldock, T E; Golshani, A; Callaghan, D P; Saunders, M I; Mumby, P J

    2014-06-15

    A one-dimensional wave model was used to investigate the reef top wave dynamics across a large suite of idealized reef-lagoon profiles, representing barrier coral reef systems under different sea-level rise (SLR) scenarios. The modeling shows that the impacts of SLR vary spatially and are strongly influenced by the bathymetry of the reef and coral type. A complex response occurs for the wave orbital velocity and forces on corals, such that the changes in the wave dynamics vary reef by reef. Different wave loading regimes on massive and branching corals also leads to contrasting impacts from SLR. For many reef bathymetries, wave orbital velocities increase with SLR and cyclonic wave forces are reduced for certain coral species. These changes may be beneficial to coral health and colony resilience and imply that predicting SLR impacts on coral reefs requires careful consideration of the reef bathymetry and the mix of coral species.

  17. Interval Oscillation Criteria for Forced Second-Order Nonlinear Delay Dynamic Equations with Damping and Oscillatory Potential on Time Scales

    Directory of Open Access Journals (Sweden)

    Hassan A. Agwa

    2016-01-01

    Full Text Available We are concerned with the interval oscillation of general type of forced second-order nonlinear dynamic equation with oscillatory potential of the form rtg1xt,xΔtΔ+p(tg2(x(t,xΔ(txΔ(t+q(tf(x(τ(t=e(t, on a time scale T. We will use a unified approach on time scales and employ the Riccati technique to establish some oscillation criteria for this type of equations. Our results are more general and extend the oscillation criteria of Erbe et al. (2010. Also our results unify the oscillation of the forced second-order nonlinear delay differential equation and the forced second-order nonlinear delay difference equation. Finally, we give some examples to illustrate our results.

  18. Dynamic Elbow Flexion Force Estimation Through a Muscle Twitch Model and sEMG in a Fatigue Condition.

    Science.gov (United States)

    Na, Youngjin; Kim, Jung

    2016-11-14

    We propose a joint force estimation method to compute elbow flexion force using surface electromyogram (sEMG) considering time-varying effects in a fatigue condition. Muscle fatigue is a major cause inducing sEMG changes with respect to time over long periods and repetitive contractions. The proposed method composed the muscle-twitch model representing the force generated by a single spike and the spikes extracted from sEMG. In this study, isometric contractions at six different joint angles (ten subjects) and dynamic contractions with constant velocity (six subjects) were performed under non-fatigue and fatigue conditions. Performance of the proposed method was evaluated and compared with that of previous methods using mean absolute value (MAV). The proposed method achieved average 6.7±2.8 %RMSE for isometric contraction and 15.6±24.7 %RMSE for isokinetic contraction under fatigue condition with more accurate results than the previous methods.

  19. CME Dynamics Using STEREO and LASCO Observations: The Relative Importance of Lorentz Forces and Solar Wind Drag

    Science.gov (United States)

    Sachdeva, Nishtha; Subramanian, Prasad; Vourlidas, Angelos; Bothmer, Volker

    2017-09-01

    We seek to quantify the relative contributions of Lorentz forces and aerodynamic drag on the propagation of solar coronal mass ejections (CMEs). We use Graduated Cylindrical Shell (GCS) model fits to a representative set of 38 CMEs observed with the Solar and Heliospheric Observatory (SOHO) and the Solar and Terrestrial Relations Observatory (STEREO) spacecraft. We find that the Lorentz forces generally peak between 1.65 and 2.45 R⊙ for all CMEs. For fast CMEs, Lorentz forces become negligible in comparison to aerodynamic drag as early as 3.5 - 4 R⊙. For slow CMEs, however, they become negligible only by 12 - 50 R⊙. For these slow events, our results suggest that some of the magnetic flux might be expended in CME expansion or heating. In other words, not all of it contributes to the propagation. Our results are expected to be important in building a physical model for understanding the Sun-Earth dynamics of CMEs.

  20. Driving forces behind the increasing cardiovascular treatment intensity.A dynamic epidemiologic model of trends in Danish cardiovascular drug utilization.

    DEFF Research Database (Denmark)

    Kildemoes, Helle Wallach; Andersen, Morten

    to 619 DDD/TID from 1996 to 2005 (117%). Population ageing accounted for 22 percentage points. Treatment intensity with statins increased from 5 to 121 DDD/TID. Population ageing accounted for one eighth of this increase. Increasing incidence rates was the main driving force behind the growing statin......Background: In many Western countries cardiovascular treatment intensity (DDD/1000 inhabitants/day, DDD/TID) has grown substantially during the last decades. Changed drug utilization pattern - rather than population ageing - was hypothesized to be the main driving force behind the growth....... Objectives: To investigate the driving forces behind the increasing treatment prevalence of cardiovascular drugs, in particular statins, by means of a dynamic epidemiologic drug utilization model. Methods: Material: All Danish residents older than 20 years by January 1, 1996 (4.0 million inhabitants), were...

  1. A review of a method for dynamic load distribution, dynamical modeling, and explicit internal force control when two manipulators mutually lift and transport a rigid body object

    Energy Technology Data Exchange (ETDEWEB)

    Unseren, M.A.

    1997-04-20

    The paper reviews a method for modeling and controlling two serial link manipulators which mutually lift and transport a rigid body object in a three dimensional workspace. A new vector variable is introduced which parameterizes the internal contact force controlled degrees of freedom. A technique for dynamically distributing the payload between the manipulators is suggested which yields a family of solutions for the contact forces and torques the manipulators impart to the object. A set of rigid body kinematic constraints which restrict the values of the joint velocities of both manipulators is derived. A rigid body dynamical model for the closed chain system is first developed in the joint space. The model is obtained by generalizing the previous methods for deriving the model. The joint velocity and acceleration variables in the model are expressed in terms of independent pseudovariables. The pseudospace model is transformed to obtain reduced order equations of motion and a separate set of equations governing the internal components of the contact forces and torques. A theoretic control architecture is suggested which explicitly decouples the two sets of equations comprising the model. The controller enables the designer to develop independent, non-interacting control laws for the position control and internal force control of the system.

  2. Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator

    OpenAIRE

    Kiracofe, Daniel; Melcher, John; Raman, Arvind

    2012-01-01

    Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often ...

  3. Numerical Analysis of Dynamic Force Acting Perpendicularly on a Wall Made of Concrete Blocks with Rubber Inserts

    Directory of Open Access Journals (Sweden)

    Major Maciej

    2016-12-01

    Full Text Available In this paper numerical analysis considering the influence of dynamical force acting on wall made of concrete blocks with rubber inserts is presented. By examining the stress values on front and back surface of the analysed wall structure model, the effectiveness of proposed solution can be measured comparing to the wall made of concrete blocks without rubber inserts. Complete numerical analysis was performed in ADINA program.

  4. Dynamic Patterns of Forces and Loading Rate in Runners with Unilateral Plantar Fasciitis: A Cross-Sectional Study.

    Directory of Open Access Journals (Sweden)

    Ana Paula Ribeiro

    Full Text Available The etiology of plantar fasciitis (PF has been related to several risk factors, but the magnitude of the plantar load is the most commonly described factor. Although PF is the third most-common injury in runners, only two studies have investigated this factor in runners, and their results are still inconclusive regarding the injury stage.Analyze and compare the plantar loads and vertical loading rate during running of runners in the acute stage of PF to those in the chronic stage of the injury in relation to healthy runners.Forty-five runners with unilateral PF (30 acute and 15 chronic and 30 healthy control runners were evaluated while running at 12 km/h for 40 meters wearing standardized running shoes and Pedar-X insoles. The contact area and time, maximum force, and force-time integral over the rearfoot, midfoot, and forefoot were recorded and the loading rate (20-80% of the first vertical peak was calculated. Groups were compared by ANOVAs (p<0.05.Maximum force and force-time integral over the rearfoot and the loading rate was higher in runners with PF (acute and chronic compared with controls (p<0.01. Runners with PF in the acute stage showed lower loading rate and maximum force over the rearfoot compared to runners in the chronic stage (p<0.01.Runners with PF showed different dynamic patterns of plantar loads during running over the rearfoot area depending on the injury stage (acute or chronic. In the acute stage of PF, runners presented lower loading rate and forces over the rearfoot, possibly due to dynamic mechanisms related to pain protection of the calcaneal area.

  5. Control of dynamical self-assembly of strongly Brownian nanoparticles through convective forces induced by ultrafast laser

    Science.gov (United States)

    Ilday, Serim; Akguc, Gursoy B.; Tokel, Onur; Makey, Ghaith; Yavuz, Ozgun; Yavuz, Koray; Pavlov, Ihor; Ilday, F. Omer; Gulseren, Oguz

    We report a new dynamical self-assembly mechanism, where judicious use of convective and strong Brownian forces enables effective patterning of colloidal nanoparticles that are almost two orders of magnitude smaller than the laser beam. Optical trapping or tweezing effects are not involved, but the laser is used to create steep thermal gradients through multi-photon absorption, and thereby guide the colloids through convective forces. Convective forces can be thought as a positive feedback mechanism that helps to form and reinforce pattern, while Brownian motion act as a competing negative feedback mechanism to limit the growth of the pattern, as well as to increase the possibilities of bifurcation into different patterns, analogous to the competition observed in reaction-diffusion systems. By steering stochastic processes through these forces, we are able to gain control over the emergent pattern such as to form-deform-reform of a pattern, to change its shape and transport it spatially within seconds. This enables us to dynamically initiate and control large patterns comprised of hundreds of colloids. Further, by not relying on any specific chemical, optical or magnetic interaction, this new method is, in principle, completely independent of the material type being assembled.

  6. A Study of Dynamic Lorentz Force Detuning of 650 MHz {\\beta}g= 0.9 Superconducting Radiofrequency Cavity

    CERN Document Server

    Kumar, Abhay

    2013-01-01

    The small bandwidth of superconducting cavities makes the study of dynamic Lorentz force detuning and its compensation indispensable in case of pulsed mode operation of high gradient accelerators. In this paper, we present the study of this detuning and also propose an optimized design for five cell 650 MHz {\\beta}g= 0.9 elliptic superconducting cavities, which will be used in the high energy section of the 1 GeV H-LINAC for the proposed Indian Spallation Neutron Source project, by suitably inserting the inter-cell stiffeners. The paper presents a sequential design methodology which starts with study of static Lorentz force detuning and tunability; and progresses to find out the structural modes and related dynamic detuning values by performing transient calculations. The developed methodology is general in nature and can be used for a three dimensional model of any geometry. The work will be useful for optimizing the design against dynamic Lorentz force detuning of SRF cavities of any shape.

  7. Using Molecular Dynamics Simulation to Reinforce Student Understanding of Intermolecular Forces

    Science.gov (United States)

    Burkholder, Phillip R.; Purser, Gordon H.; Cole, Renee S.

    2008-01-01

    Intermolecular forces play an important role in many aspects of chemistry ranging from inorganic to biological chemistry. These forces dictate molecular conformation, species aggregation (including self-assembly), trends in solubility and boiling points, adsorption characteristics, viscosity, phase changes, surface tension, capillary action, vapor…

  8. Using Molecular Dynamics Simulation to Reinforce Student Understanding of Intermolecular Forces

    Science.gov (United States)

    Burkholder, Phillip R.; Purser, Gordon H.; Cole, Renee S.

    2008-01-01

    Intermolecular forces play an important role in many aspects of chemistry ranging from inorganic to biological chemistry. These forces dictate molecular conformation, species aggregation (including self-assembly), trends in solubility and boiling points, adsorption characteristics, viscosity, phase changes, surface tension, capillary action, vapor…

  9. INTER-CONTACT FORCE ANALYSIS OF IMPACTED DISK ASSEMBLY BY DYNAMIC CAUSTICS

    Institute of Scientific and Technical Information of China (English)

    LI Ming(李明); ZHANG Jue; FANG Jing(方竞)

    2003-01-01

    The caustic method was utilized to study the contact force transmission in disk assemblies under impact load. The mapping equations were obtained based on the first invariant of the stress components in the disk subject to a normal concentrated force, and a characteristic dimension of the maximum size in the caustic curve was proposed to evaluate the contact force between the disks.Transient patterns of the caustic shadows were recorded by means of a high-speed camera of off-focus imaging, then the histories of the inter-contact forces among the disks were obtained with respect to the conditions of different masses and heights of the falling hammers. The influence of the impact loading and impulsive velocity was analyzed with respect to the force responses of the disk assembly,the double-peak phenomenon with comparison to the initial masses, and the energy dissipation of the systems under impact of different momentums.

  10. Structural and dynamic properties of liquid tin from a new modified embedded-atom method force field

    Science.gov (United States)

    Vella, Joseph R.; Chen, Mohan; Stillinger, Frank H.; Carter, Emily A.; Debenedetti, Pablo G.; Panagiotopoulos, Athanassios Z.

    2017-02-01

    A new modified embedded-atom method (MEAM) force field is developed for liquid tin. Starting from the Ravelo and Baskes force field [Phys. Rev. Lett. 79, 2482 (1997), 10.1103/PhysRevLett.79.2482], the parameters are adjusted using a simulated annealing optimization procedure in order to obtain better agreement with liquid-phase data. The predictive capabilities of the new model and the Ravelo and Baskes force field are evaluated using molecular dynamics by comparing to a wide range of first-principles and experimental data. The quantities studied include crystal properties (cohesive energy, bulk modulus, equilibrium density, and lattice constant of various crystal structures), melting temperature, liquid structure, liquid density, self-diffusivity, viscosity, and vapor-liquid surface tension. It is shown that although the Ravelo and Baskes force field generally gives better agreement with the properties related to the solid phases of tin, the new MEAM force field gives better agreement with liquid tin properties.

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

    Science.gov (United States)

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

    2016-01-01

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

  12. Control of a Thrust Alignment Table for Modeling the Coning Dynamics of a Spinning Spacecraft with a Follower Force

    Science.gov (United States)

    Halsmer, Dominic; Bennett, J. Damon; DeHaven, Max; Ligard, Vidar

    1999-01-01

    This document presents a system controlling the motion of a spherical air bearing used in the modeling of spacecraft dynamics and controls in a laboratory environment. The system is part of the Spinning Rocket Simulator (SRS), used to simulate the coning of spacecraft during a thrusting stage. The reaction force at the spherical air bearing supporting the spacecraft model must coincide with the thrust axis of the model for proper simulation. Therefore, the bearing is translated in a circular path to introduce a centrifugal force. This horizontal force along with the gravitational reaction force at the bearing combines to simulate the direction of the spacecraft's thrust force. The control system receives attitude information from the spacecraft model via a laser beam embedded in the model that impinges on a photosensitive array. The non-linear system is controlled using high-speed lookup tables and digital techniques. A vector-controlled motor and a stepper motor are given the necessary signals to accurately control the turntable and platform supporting the air bearing. Preliminary performance data is presented. Mechanical elements of the table and platform are described in detail. A wireless (RF) data path for all devices on the spacecraft model to an off-table command computer is also described.

  13. Resolving the phasing and forcing dynamics between North Atlantic climate and deep ocean circulation changes

    Science.gov (United States)

    Irvali, Nil; Ninnemann, Ulysses S.; Kleiven, Helga (Kikki) F.; Haflidason, Haflidi; Mjell, Tor L.

    2017-04-01

    Multidecadal changes in North Atlantic climate (e.g., AMO/AMV) have been attributed to changes in the Atlantic Meridional Overturning Circulation (AMOC) and suggested as a driver of overturning changes. While simulations find an in-phase relationship when AMOC modulates basin-wide climate, AMOC lags when basin scale climate is forced externally (e.g., volcanoes and solar). Unfortunately the observational records are too short to assess these multi-decadal scale dynamics. The surface climate reconstructions, based on annually resolved archives, have excellent time control raising the possibility for precise determination of phasing with other well dated records. Yet, all currently available reconstructions of deep ocean circulation have radiometric based age models; with inherent errors (±30-50 years minimum) preventing the determination of the absolute phasing between deep ocean circulation changes and AMO/AMV. In order to reduce these uncertainties we use stratigraphical appearance, abundance and geochemical composition of tephra grains from a high sedimentation rate site off the Gardar Drift, south of Iceland (GS06-144-09MC-D; 60˚ 19'N, 23˚ 58'W, 2081 m water depth). Identifying tephra layers (and their association) in the core and fingerprinting with known volcanic eruptions on Iceland provides absolute age markers. Combining these age markers with 210Pb and 14C AMS dates within the same core, we have built a new chronology for the core GS06-144-09MC-D. Changes in surface ocean hydrography and climate are further portrayed using planktonic foraminiferal δ18O, assemblage counts, modern analog technique derived sea surface temperatures and Mg/Ca paleothermometry. Records of Iceland Scotland Overflow Water (ISOW) vigor (Sortable Silt mean grain size; Mjell et al., 2016) and benthic carbon isotopes from the same core allow us to determine the absolute phasing between changes in basin-wide climate, deep ocean circulation, and deep water carbon chemistry spanning

  14. Steered molecular dynamics simulations of a type IV pilus probe initial stages of a force-induced conformational transition.

    Directory of Open Access Journals (Sweden)

    Joseph L Baker

    2013-04-01

    Full Text Available 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

  15. Correlating steric hydration forces with water dynamics through surface force and diffusion NMR measurements in a lipid–DMSO–H2O system

    Science.gov (United States)

    Schrader, Alex M.; Donaldson, Stephen H.; Song, Jinsuk; Cheng, Chi-Yuan; Lee, Dong Woog; Han, Songi; Israelachvili, Jacob N.

    2015-01-01

    Dimethyl sulfoxide (DMSO) is a common solvent and biological additive possessing well-known utility in cellular cryoprotection and lipid membrane permeabilization, but the governing mechanisms at membrane interfaces remain poorly understood. Many studies have focused on DMSO–lipid interactions and the subsequent effects on membrane-phase behavior, but explanations often rely on qualitative notions of DMSO-induced dehydration of lipid head groups. In this work, surface forces measurements between gel-phase dipalmitoylphosphatidylcholine membranes in DMSO–water mixtures quantify the hydration- and solvation-length scales with angstrom resolution as a function of DMSO concentration from 0 mol% to 20 mol%. DMSO causes a drastic decrease in the range of the steric hydration repulsion, leading to an increase in adhesion at a much-reduced intermembrane distance. Pulsed field gradient NMR of the phosphatidylcholine (PC) head group analogs, dimethyl phosphate and tetramethylammonium ions, shows that the ion hydrodynamic radius decreases with increasing DMSO concentration up to 10 mol% DMSO. The complementary measurements indicate that, at concentrations below 10 mol%, the primary effect of DMSO is to decrease the solvated volume of the PC head group and that, from 10 mol% to 20 mol%, DMSO acts to gradually collapse head groups down onto the surface and suppress their thermal motion. This work shows a connection between surface forces, head group conformation and dynamics, and surface water diffusion, with important implications for soft matter and colloidal systems. PMID:26261313

  16. Consideration of nonlinear wheel-rail contact forces for dynamic vehicle-bridge interaction in high-speed railways

    Science.gov (United States)

    Antolín, Pablo; Zhang, Nan; Goicolea, José M.; Xia, He; Astiz, Miguel Á.; Oliva, Javier

    2013-03-01

    In this work models with nonlinear wheel-rail contact forces are considered for analysing the dynamic interaction between high speed trains and bridges, in order to study dynamic effects both in the bridge and in the vehicles resulting from the coupling. Nonlinear contact models may be necessary for evaluating the stability and the safety of running traffic in situations such as vehicle overturn when the train is crossing a bridge under strong lateral winds or when an earthquake occurs. For studying the coupled dynamic response of trains and bridges, models of multibody dynamics are used for vehicles and the finite element method for structures. Special relevance is given here to the consideration of contact interaction forces between railway vehicles and the track. Four different interaction models are compared in this work: (1) a model where the vehicle wheelset is considered to be rigidly coupled to the track; (2) a staggered uncoupled method in which vehicle and structure are analysed separately; (3) a linear contact model in which lateral relative displacements between rails and train wheels are allowed, assuming biconic wheel and rail profiles and linear Kalker theory for tangential contact; (4) a nonlinear model in which realistic wheel and rail profiles, Hertz's nonlinear theory for normal contact and Kalker's nonlinear theory for tangential contact are used. The different models are applied and compared to experimental measurements for a test case of a high-speed train in China.

  17. Using Data Mining Approaches for Force Prediction of a Dynamically Loaded Flexible Structure

    DEFF Research Database (Denmark)

    Schlechtingen, Meik; Achiche, Sofiane; Lourenco Costa, Tiago

    2014-01-01

    -deterministic excitation forces with different excitation frequencies and amplitudes. Additionally, the influence of the sampling frequency and sensor location on the model performance is investigated. The results obtained in this paper show that most data mining approaches can be used, when a certain degree of inaccuracy...... of freedom and a force transducer for validation and training. The models are trained using data obtained from applying a random excitation force on the flexible structure. The performance of the developed models is evaluated by analyzing the prediction capabilities based on a normalized prediction error...

  18. Finite Element Analysis of the Misalignment Effects on the Dynamic Force Coefficients of Spiral Groove Gas Face Seals

    Science.gov (United States)

    Faria, Marco Tulio C.

    This paper presents a finite element procedure specially devised to analyze the misalignment effects on the behavior of spiral groove gas face seals operating at high speeds. In this study, the seal stationary face is slightly misaligned and the flexibly mounted face is perfectly aligned. Predictions of some steady-state and dynamic performance characteristics versus misalignment angle are presented for spirally grooved gas seals operating under stringent conditions. Curves of dynamic force coefficients versus the static misalignment angle of the seal face indicate that the seal misalignment affects considerably the dynamic response of gas lubricated face seals. At high speeds, the static seal misalignment not only results in increased stiffness coefficients but also leads to negative damping coefficients, which may be a sign of the seal susceptibility to excessive angular motions.

  19. Analysis of Seismic Damage of Underground Powerhouse Structure of Hydropower Plants Based on Dynamic Contact Force Method

    Directory of Open Access Journals (Sweden)

    Yang Yang

    2014-01-01

    Full Text Available Based on the characteristics of the dynamic interaction between an underground powerhouse concrete structure and its surrounding rock in a hydropower plant, an algorithm of dynamic contact force was proposed. This algorithm enables the simulation of three states of contact surface under dynamic loads, namely, cohesive contact, sliding contact, and separation. It is suitable for the numerical analysis of the dynamic response of the large and complex contact system consisting of underground powerhouse concrete structure and the surrounding rock. This algorithm and a 3D plastic-damage model were implemented in a dynamic computing platform, SUCED, to analyze the dynamic characteristics of the underground powerhouse structure of Yingxiuwan Hydropower Plant. By comparing the numerical results and postearthquake investigations, it was concluded that the amplitude and duration of seismic waves were the external factors causing seismic damage of the underground powerhouse structure, and the spatial variations in structural properties were the internal factors. The existence of rock mass surrounding the underground powerhouse was vital to the seismic stability of the structure. This work provides the theoretical basis for the anti-seismic design of underground powerhouse structures.

  20. Large-scale molecular dynamics simulation of DNA: implementation and validation of the AMBER98 force field in LAMMPS.

    Science.gov (United States)

    Grindon, Christina; Harris, Sarah; Evans, Tom; Novik, Keir; Coveney, Peter; Laughton, Charles

    2004-07-15

    Molecular modelling played a central role in the discovery of the structure of DNA by Watson and Crick. Today, such modelling is done on computers: the more powerful these computers are, the more detailed and extensive can be the study of the dynamics of such biological macromolecules. To fully harness the power of modern massively parallel computers, however, we need to develop and deploy algorithms which can exploit the structure of such hardware. The Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is a scalable molecular dynamics code including long-range Coulomb interactions, which has been specifically designed to function efficiently on parallel platforms. Here we describe the implementation of the AMBER98 force field in LAMMPS and its validation for molecular dynamics investigations of DNA structure and flexibility against the benchmark of results obtained with the long-established code AMBER6 (Assisted Model Building with Energy Refinement, version 6). Extended molecular dynamics simulations on the hydrated DNA dodecamer d(CTTTTGCAAAAG)(2), which has previously been the subject of extensive dynamical analysis using AMBER6, show that it is possible to obtain excellent agreement in terms of static, dynamic and thermodynamic parameters between AMBER6 and LAMMPS. In comparison with AMBER6, LAMMPS shows greatly improved scalability in massively parallel environments, opening up the possibility of efficient simulations of order-of-magnitude larger systems and/or for order-of-magnitude greater simulation times.

  1. Temperature of electro dynamic tether for space debris removal and its effect on Lorentz force

    OpenAIRE

    2014-01-01

    Electrodynamics tether (EDT) systems is expected as an effective system for deorbiting space debris. EDT systems is a high efficiency propulsion system using the Lorentz force generated by the interference with the earth's magnetic field and the current through the tether. The conductivity of the tether varies with temperacture of tether in orbit, and it affects the Lorentz force that EDT systems can generate. Tether temperature in orbit depends on the thermal optical property. However, the s...

  2. Graphene on SiC(0001 inspected by dynamic atomic force microscopy at room temperature

    Directory of Open Access Journals (Sweden)

    Mykola Telychko

    2015-04-01

    Full Text Available We investigated single-layer graphene on SiC(0001 by atomic force and tunneling current microscopy, to separate the topographic and electronic contributions from the overall landscape. The analysis revealed that the roughness evaluated from the atomic force maps is very low, in accord with theoretical simulations. We also observed that characteristic electron scattering effects on graphene edges and defects are not accompanied by any out-of-plane relaxations of carbon atoms.

  3. Parameterization and optimization of the menthol force field for molecular dynamics simulations.

    Science.gov (United States)

    Jasik, Mateusz; Szefczyk, Borys

    2016-10-01

    Menthol's various biological properties render it a useful component for medical and cosmetological applications, while its three centers of asymmetry mean that it can be used in a range of organic reactions. Menthol-substituted ionic liquids (ILs) have been found to exhibit promising antimicrobial and antielectrostatic properties, as well as being useful in organic catalysis and biochemical studies. However, so far, a force field designed and validated specifically for the menthol molecule has not been constructed. In the present work, the validation and optimization of force field parameters with regard to the ability to reproduce the macroscopic properties of menthol is presented. The set of optimized potentials for liquid simulations all atom (OPLS-AA) compatible parameters was tested and carefully tuned. The refinement of parameters included fitting of partial atomic charges, optimization of Lennard-Jones parameters, and recalculation of the dihedral angle parameters needed to reproduce quantum energy profiles. To validate the force field, a variety of physicochemical properties were calculated for liquid menthol. Both thermodynamic and kinetic properties were taken into account, including density, surface tension, enthalpy of vaporization, and shear viscosity. The obtained force field was proven to accurately reproduce the properties of the investigated compound while being fully compatible with the OPLS-AA force field.

  4. Molecular dynamic study of Shock wave response of bulk amorphous polyvinyl chloride: effect of chain length and force field

    Science.gov (United States)

    Neogi, Anupam; Mitra, Nilanjan

    2015-06-01

    Atomistic molecular dynamics in conjunction with multi-scale shock technique is utilized to investigate shock wave response of bulk amorphous polyvinyl chloride. Dependence of chain length on physical and mechanical behaviour of polymeric material at ambient condition of temperature and pressure are well known but unknown for extreme conditions. Non-reactive force fields PCFF, COMPASS and PCFF+ were used to determine applicability of the force field for the study of the material subjected to shock loads. Several samples of PVC with various chain lengths were subjected to a range of shock compression from 1.5-10.0 km/s. Even though dependence of chain length was observed for lower shock strengths but was not for intense shock loads. The principle Hugoniot points, calculated by applying hydrostatic Rankine-Hugoniot equations and as well as multi-scale shock technique, were compared against LASL experimental shock data, demonstrating superior performance of PCFF+ force-field over PCFF and COMPASS. Shock induced melting characteristic and vibrational spectroscopic study were conducted and compared with experimental data to observe differences in response with relation to different force fields, chain length of the material for different shock intensities.

  5. Exact dynamic stiffness matrix of non-symmetric thin-walled curved beams subjected to initial axial force

    Science.gov (United States)

    Nam-Il, Kim; Moon-Young, Kim

    2005-06-01

    An improved numerical method to exactly evaluate the dynamic element stiffness matrix is proposed for the spatially coupled free vibration analysis of non-symmetric thin-walled curved beams subjected to uniform axial force. For this purpose, firstly equations of motion, boundary conditions and force-deformation relations are rigorously derived from the total potential energy for a curved beam element. Next systems of linear algebraic equations with non-symmetric matrices are constructed by introducing 14 displacement parameters and transforming the fourth-order simultaneous differential equations into the first-order simultaneous equations. And then explicit expressions for displacement parameters are numerically evaluated via eigensolutions and the exact 14×14 element stiffness matrix is determined using force-deformation relations. In order to demonstrate the validity and the accuracy of this study, the spatially coupled natural frequencies of non-symmetric thin-walled curved beams subjected to uniform compressive and tensile forces are evaluated and compared with analytical and finite element solutions using Hermitian curved beam elements or ABAQUS's shell element. In addition, some results by the parametric study are reported.

  6. Ab initio molecular dynamics with noisy forces: Validating the quantum Monte Carlo approach with benchmark calculations of molecular vibrational properties

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Ye, E-mail: xw111luoye@gmail.com; Sorella, Sandro, E-mail: sorella@sissa.it [International School for Advanced Studies (SISSA), and CRS Democritos, CNR-INFM, Via Bonomea 265, I-34136 Trieste (Italy); Zen, Andrea, E-mail: zen.andrea.x@gmail.com [Dipartimento di Fisica, Università di Roma “La Sapienza,” Piazzale Aldo Moro 2, I-00185 Rome (Italy)

    2014-11-21

    We present a systematic study of a recently developed ab initio simulation scheme based on molecular dynamics and quantum Monte Carlo. In this approach, a damped Langevin molecular dynamics is employed by using a statistical evaluation of the forces acting on each atom by means of quantum Monte Carlo. This allows the use of an highly correlated wave function parametrized by several variational parameters and describing quite accurately the Born-Oppenheimer energy surface, as long as these parameters are determined at the minimum energy condition. However, in a statistical method both the minimization method and the evaluation of the atomic forces are affected by the statistical noise. In this work, we study systematically the accuracy and reliability of this scheme by targeting the vibrational frequencies of simple molecules such as the water monomer, hydrogen sulfide, sulfur dioxide, ammonia, and phosphine. We show that all sources of systematic errors can be controlled and reliable frequencies can be obtained with a reasonable computational effort. This work provides convincing evidence that this molecular dynamics scheme can be safely applied also to realistic systems containing several atoms.

  7. Numerical analysis of dynamic force spectroscopy using the torsional harmonic cantilever

    Energy Technology Data Exchange (ETDEWEB)

    Solares, Santiago D [Department of Mechanical Engineering, University of Maryland, 2181 Glenn L. Martin Hall, College Park, MD 20742 (United States); Hoelscher, Hendrik, E-mail: ssolares@umd.edu [Karlsruhe Institute for Technology (KIT), Institute for Microstructure Technology (IMT), Hermann-von Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen (Germany)

    2010-02-19

    A spectral analysis method has been recently introduced by Stark et al (2002 Proc. Natl Acad. Sci. USA 99 8473-8) and implemented by Sahin et al (2007 Nat. Nanotechnol. 2 507-14) using a T-shaped cantilever design, the torsional harmonic cantilever (THC), which is capable of performing simultaneous tapping-mode atomic force microscopy imaging and force spectroscopy. Here we report on numerical simulations of the THC system using a simple dual-mass flexural-torsional model, which is applied in combination with Fourier data processing software to illustrate the spectroscopy process for quality factors corresponding to liquid, air and vacuum environments. We also illustrate the acquisition of enhanced topographical images and deformed surface contours under the application of uniform forces, and compare the results to those obtained with a previously reported linear dual-spring-mass model.

  8. New method for oblique impact dynamics research of a flexible beam with large overall motion considering impact friction force

    Institute of Scientific and Technical Information of China (English)

    W Yuan; L Li; D G Zhang; J Z Hong

    2016-01-01

    A flexible beam with large overall rotating motion impacting with a rigid slope is studied in this paper. The tangential friction force caused by the oblique impact is analyzed. The tangential motion of the system is divided into a stick state and a slip state. The contact constraint model and Coulomb friction model are used respectively to deal with the two states. Based on this hybrid mod-eling method, dynamic equations of the system, which include all states (before, during, and after the collision) are obtained. Simulation results of a concrete example are compared with the results obtained from two other models: a nontangential friction model and a modified Coulomb model. Differences in the results from the three models are discussed. The tangential friction force cannot be ignored when an oblique impact occurs. In addition, the results obtained from the model proposed in this paper are more consistent with real movement.

  9. Dynamical and statistical phenomena of circulation and heat transfer in periodically forced rotating turbulent Rayleigh-Benard convection

    CERN Document Server

    Sterl, Sebastian; Zhong, Jin-Qiang

    2016-01-01

    In this paper, we present results from an experimental study into turbulent Rayleigh-Benard convection forced externally by periodically modulated unidirectional rotation rates. We find that the azimuthal rotation velocity $\\dot{\\theta}$(t) and thermal amplitude $\\delta$(t) of the large-scale circulation (LSC) are modulated by the forcing, exhibiting a variety of dynamics including increasing phase delays and a resonant peak in the amplitude of $\\dot{\\theta}$(t). We also focus on the influence of modulated rotation rates on the frequency of occurrence $\\eta$ of stochastic cessation/reorientation events, and on the interplay between such events and the periodically modulated response of $\\dot{\\theta}$(t). Here we identify a mechanism by which $\\eta$ can be amplfied by the modulated response and these normally stochastic events can occur with high regularity. We provide a modeling framework that explains the observed amplitude and phase responses, and extend this approach to make predictions for the occurrence ...

  10. Dynamics of the chain of forced oscillators with long-range interaction: From synchronization to chaos

    Science.gov (United States)

    Zaslavsky, G. M.; Edelman, M.; Tarasov, V. E.

    2007-12-01

    We consider a chain of nonlinear oscillators with long-range interaction of the type 1/l1+α, where l is a distance between oscillators and 0continuous limit, the system's dynamics is described by a fractional generalization of the Ginzburg-Landau equation with complex coefficients. Such a system has a new parameter α that is responsible for the complexity of the medium and that strongly influences possible regimes of the dynamics, especially near α =2 and α =1. We study different spatiotemporal patterns of the dynamics depending on α and show transitions from synchronization of the motion to broad-spectrum oscillations and to chaos.

  11. Influence of Damping on the Dynamical Behavior of the Electrostatic Parallel-plate and Torsional Actuators with Intermolecular Forces

    OpenAIRE

    Ya-Pu Zhao; Wen-Hui Lin

    2007-01-01

    The influence of damping on the dynamical behavior of the electrostatic parallel-plate and torsional actuators with the van der Waals (vdW) or Casimir force (torque) is presented. The values of the pull-in parameters and the number of the equilibrium points do not change whether there is damping or not. The ability of equilibrium points is varied with the appearance of damping. One equilibrium point is an unstable saddle with a different damping coefficient, the other equilibrium point is a s...

  12. Structural Characterization of Self-Assembled Monolayers of Organosilanes Chemically Bonded on Silica Wafers by Dynamical Force Microscopy

    CERN Document Server

    Navarre, S; Bousbaa, J; Bennetau, B; Nony, L; Aimé, J P; Choplin, Franck; Bennetau, Bernard; Nony, Laurent; Aim\\'{e}, Jean-Pierre

    2001-01-01

    In this article, a dynamical force microscopy study of self-assembled monolayers of organosilanes, grafted on a silica support, is reported. Organosilanes, terminated either with a functional group (ethylene glycol) or with a methyl group, were used. The influence of the reaction time and the solvent composition on the grafting was investigated to improve the homogeneity of the self-assembled monolayers. Numerical simulations of approach-retract curves, obtained in the tapping mode, were performed and compared to experimental ones. Informations, such as mechanical response and height of the grafted organic layers, have been obtained.

  13. Dynamics of a forced 2 dof piece-wise linear system by consideration of the weight

    Directory of Open Access Journals (Sweden)

    Dimitrijevic Z.

    2012-07-01

    Full Text Available Energy pumping phenomenon between a linear system and a non-smooth system by taking into account the weight of the system is studied. The system faces bifurcation when it reaches to its unstable border and then according to external forcing term it can follow lower stable branch or to face strongly modulated response by hysteresis jumps between its stable branches.

  14. Estimation of Cable Forces of a Guyed Mast from Dynamic Measurements

    DEFF Research Database (Denmark)

    Kirkegaard, Poul Henning; Hansen, Lars Pilegaard

    This paper presents how the tension forces in the cables of a 200 m. high guyed mast have been estimated from natural frequencies obtained from acceleration measurements.The mast is guyed at five levels with three guys at 120 degree intervals at each level. The accelerations in three directions...

  15. AN EFFICIENT, BOX SHAPE INDEPENDENT NONBONDED FORCE AND VIRIAL ALGORITHM FOR MOLECULAR-DYNAMICS

    NARCIS (Netherlands)

    Bekker, H.; Dijkstra, E.J; Renardus, M.K.R.; Berendsen, H.J.C.

    1995-01-01

    A notation is introduced and used to transform a conventional specification of the non-bonded force and virial algorithm in the case of periodic boundary conditions into an alternative specification. The implementation of the transformed specification is simpler and typically a factor of 1.5 faster

  16. Rich dynamics in a predator–prey model with both noise and periodic force

    NARCIS (Netherlands)

    Sun, G.Q.; Jin, Z.; Liu, Q.X.; Li, B.L.

    2010-01-01

    A spatial version of the predator–prey model with Holling III functional response, which includes some important factors such as external periodic forces, noise, and diffusion processes is investigated. For the model only with diffusion, it exhibits spiral waves in the two-dimensional space. However

  17. Influence of low optical frequencies on actuation dynamics of microelectromechanical systems via Casimir forces

    NARCIS (Netherlands)

    Sedighi Ghozotkhar, Mehdi; Palasantzas, Georgios

    2015-01-01

    The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled usi

  18. Active dynamic balancing unit for controlled shaking force and shaking moment balancing

    NARCIS (Netherlands)

    van der Wijk, V.; Herder, Justus Laurens

    2010-01-01

    For a mechanism with many elements that needs to be shaking-force and shaking-moment balanced with a low addition of mass, a low addition of inertia, and a low addition of complexity, the use of actively computer-controlled balancing elements is promising. With these actively controlled elements the

  19. Perfect position/force tracking of robots with dynamical terminal sliding mode control

    NARCIS (Netherlands)

    Parra-Vega, V.; Rodriguez-Angeles, A.; Hirzinger, G.

    2001-01-01

    According to a given performance criteria, perfect tracking is defined as the performance of zero tracking error in finite time. It is evident that robotic systems, in particular those that carry out compliant task, can benefit from this performance since perfect tracking of contact forces endows

  20. Transcription dependent dynamic supercoiling is a short-range genomic force

    Science.gov (United States)

    Kouzine, Fedor; Gupta, Ashutosh; Baranello, Laura; Wojtowicz, Damian; Benaissa, Khadija; Liu, Juhong; Przytycka, Teresa M.; Levens, David

    2013-01-01

    Transcription has the capacity to modify mechanically DNA topology, DNA structure, and nucleosome arrangement. Resulting from ongoing transcription, these modifications in turn, may provide instant feedback to the transcription machinery. To substantiate the connection between transcription and DNA dynamics, we charted an ENCODE map of transcription-dependent dynamic supercoiling in human Burkitt lymphoma cells using psoralen photobinding to probe DNA topology in vivo. Dynamic supercoils spread ~1.5 kb upstream of the start sites of active genes. Low and high output promoters handle this torsional stress differently as shown using inhibitors of transcription and topoisomerases, and by chromatin immunoprecipation of RNA polymerase and topoisomerases I and II. Whereas lower outputs are managed adequately by topoisomerase I, high output promoters additionally require topoisomerase II. The genome-wide coupling between transcription and DNA topology emphasizes the importance of dynamic supercoiling for gene regulation. PMID:23416947

  1. Morphological analysis of force/velocity relationship in dynamic exercise at varying loads.

    Science.gov (United States)

    Limonta, Eloisa; Sacchi, Massimiliano

    2010-08-01

    This study examined the force/velocity (F/V) curve morphology among the entire concentric phase of the countermovement squat (CMS). The hypothesis is that F/V curve shape of the lower limb muscles complex is different from F/V isolated muscle curve and that these analyses could be useful in characterizing athletes' muscular capacity and training programs. Squat exercise was performed by 29 subjects (15 men and 14 women, divided into resistance and endurance athletes). The protocol was 6 x 1 CMS at maximal speed with increasing loads: 20, 35, 50, 65, 80, 90% of 1 repetition maximum (1RM). Displacement, speed, and acceleration of the weight bar, joint knee angles, knee angular speed, and total and normalized forces were collected. F/V relation was obtained by force and velocity values of each 10 degrees angular interval of the concentric phase for any load. Results show that the F/V relationship does not follow a linear shape and an equivalent criterion for all loads. We observed a "second peak force" statistically higher (p men showed a "second peak" higher and larger than that shown by endurance trained men. This indicated a higher ability to produce and maintain greater force at higher relative speed. These results may be helpful to identify the muscle characteristics of the athletes at various speeds and joint positions. With a phase division of the specific move, it will be possible to determine an individualized program to monitor the specific phases of technical moves and to evaluate the training effect in long run.

  2. Numerical Simulation of a Grinding Process for the Spatial Work-pieces: Modeling of Grinding Forces and System Dynamics

    Directory of Open Access Journals (Sweden)

    I. A. Kiselev

    2015-01-01

    Full Text Available The paper describes a computation-experimental technique to determine model coefficients of grinding forces using a Nelder-Mead algorithm. As an error function, the paper offers a deviation measure of calculating and experimental grinding forces averaged for a single-pass of the grinding wheel. As an example of cutting forces model coefficients calculation for linear model, in which the grinding forces depend on uncut chip thickness is analyzed. The coefficients vary on abrasive grain geometric parameters and are determined applying the authors-developed method based on Nelder-Mead technique. The measured forces while plane grinding of test work-piece are used to determine the coefficients. Model coefficients are identified if compare the measured data with the results of modeling for grinding by tool with the uniformly distributed abrasive grains with the triangular shape of cutting edge.Grinding dynamics simulation applying the determined coefficients was carried out for the processing of cantilever plane work-piece as a test example. The work-piece was processed by grinding wheel transverse passages made at different distances from the fixation. A selfoscillating process accompanied by vibration of high level was observed for some selected technological parameters of grinding. The simulation has shown qualitative and quantitative compliance with the experiment. It was shown that the intensity of the self-oscillating process arising during the processing depends on the work-piece rigidity and cutting conditions. The results of modeling can be applied in practice in developing the technology process of grinding the spatial work-pieces.

  3. Urban DNA for cities evolutions. Cities as physical expression of dynamic equilibriums between competitive and cooperative forces

    CERN Document Server

    D'Acci, Luca

    2014-01-01

    Cities are physical manifestations of our competitive and cooperative behaviours. The tension between these two forces generates dynamic equilibriums whose material expressions are cities and their evolutions. In a Darwinian cooperative view, as Darwinism does not involve only competition, the public benefit obtained by cooperation, return in terms of private benefit too. An urban genetic code is proposed, according to which cities emerge connecting nature and urbanity, and as sum of multiuse, independent micro-areas, each one with its centrality, job locations, parks and daily shops-services and amenities. This mechanism, called Isobenefit Urbanism, is not static and pre-designed, but allows infinitely dynamic changes and expansions. Rather than describing The ideal city, which doesn't exist outside our own minds, Isobenefit Urbanism describes what a city should avoid to be in order to not become an unideal city. Its six principles are the urban DNA which does not give predetermined forms but indications to ...

  4. Coil Springs Layer Used to Support a Car Vertical Dynamics Simulator and to Reduce the Maximum Actuation Force

    Directory of Open Access Journals (Sweden)

    Dan N. Dumitriu

    2015-09-01

    Full Text Available A Danaher Thomson linear actuator with ball screw drive and a realtime control system are used here to induce vertical displacements under the driver/user seat of an in-house dynamic car simulator. In order to better support the car simulator and to dynamically protect the actuator’s ball screw drive, a layer of coil springs is used to support the whole simulator chassis. More precisely, one coil spring is placed vertically under each corner of the rectangular chassis. The paper presents the choice of the appropriate coil springs, so that to minimize as much as possible the ball screw drive task of generating linear motions, corresponding to the vertical displacements and accelerations encountered by a driver during a real ride. For this application, coil springs with lower spring constant are more suited to reduce the forces in the ball screw drive and thus to increase the ball screw drive life expectancy.

  5. On the nonlinear on-off dynamics of a butterfly valve actuated by an induced electromotive force

    Science.gov (United States)

    Kwuimy, C. A. Kitio; Ramakrishnan, S.; Nataraj, C.

    2013-11-01

    In this paper, we study the nonlinear dynamics of a butterfly valve actuated by the induced electromotive force (emf) of a permanent magnet, with a focus on the on-off dynamics of the valve and its nonlinear response under ambient perturbation. The complex interplay between the electromagnetic, hydrodynamic and mechanical forces leads to a fundamentally multiphysical, nonlinear dynamical model for the problem. First, we analyze the stability of the on-off conditions in terms of three critical dynamical parameters - the actuating DC voltage, inlet velocity and the opening angle. Next, the response of the system to perturbations around the equilibrium points is studied in terms of the frequency response using the method of multiple scales. Finally, evidence of fractality is established using Melnikov analysis and a plot of the basins of attraction. The results reported in the article, in addition to being of fundamental theoretical interest, are expected to impact practical design considerations of electromechanical butterfly valves. For a voltage ve>vc, theoretically, the system may undergo bifurcations into the physically infeasible domain α>αm (beyond the physical boundary). Practically however, this jump cannot be realized due to the stopper in the plunger. In other words, the valve will completely close the pipe under this condition, leading to catastrophic behavior. For a voltage vevalve) using small rotational angles at the valve. In Fig. 2c, the critical inlet velocity and the critical angle of the valve are both plotted as a function of the setting coefficient. Note that the domain of stability of the valve corresponds to the region indicated in the graph. The lowest value of the inlet velocity is obtained for the full open valve and η=0. As can be observed in the figure, the seating torque η tends to reduce the upper bound for stability. In practice, it is possible to adjust the value of η by using lubrication.

  6. A miniaturized, high frequency mechanical scanner for high speed atomic force microscope using suspension on dynamically determined points

    Energy Technology Data Exchange (ETDEWEB)

    Herfst, Rodolf; Dekker, Bert; Witvoet, Gert; Crowcombe, Will; Lange, Dorus de [Department of Optomechatronics, Netherlands Organization for Applied Scientific Research, TNO, Delft (Netherlands); Sadeghian, Hamed, E-mail: hamed.sadeghianmarnani@tno.nl, E-mail: h.sadeghianmarnani@tudelft.nl [Department of Optomechatronics, Netherlands Organization for Applied Scientific Research, TNO, Delft (Netherlands); Department of Precision and Microsystems Engineering, Delft University of Technology, Delft (Netherlands)

    2015-11-15

    One of the major limitations in the speed of the atomic force microscope (AFM) is the bandwidth of the mechanical scanning stage, especially in the vertical (z) direction. According to the design principles of “light and stiff” and “static determinacy,” the bandwidth of the mechanical scanner is limited by the first eigenfrequency of the AFM head in case of tip scanning and by the sample stage in terms of sample scanning. Due to stringent requirements of the system, simply pushing the first eigenfrequency to an ever higher value has reached its limitation. We have developed a miniaturized, high speed AFM scanner in which the dynamics of the z-scanning stage are made insensitive to its surrounding dynamics via suspension of it on specific dynamically determined points. This resulted in a mechanical bandwidth as high as that of the z-actuator (50 kHz) while remaining insensitive to the dynamics of its base and surroundings. The scanner allows a practical z scan range of 2.1 μm. We have demonstrated the applicability of the scanner to the high speed scanning of nanostructures.

  7. A miniaturized, high frequency mechanical scanner for high speed atomic force microscope using suspension on dynamically determined points.

    Science.gov (United States)

    Herfst, Rodolf; Dekker, Bert; Witvoet, Gert; Crowcombe, Will; de Lange, Dorus; Sadeghian, Hamed

    2015-11-01

    One of the major limitations in the speed of the atomic force microscope (AFM) is the bandwidth of the mechanical scanning stage, especially in the vertical (z) direction. According to the design principles of "light and stiff" and "static determinacy," the bandwidth of the mechanical scanner is limited by the first eigenfrequency of the AFM head in case of tip scanning and by the sample stage in terms of sample scanning. Due to stringent requirements of the system, simply pushing the first eigenfrequency to an ever higher value has reached its limitation. We have developed a miniaturized, high speed AFM scanner in which the dynamics of the z-scanning stage are made insensitive to its surrounding dynamics via suspension of it on specific dynamically determined points. This resulted in a mechanical bandwidth as high as that of the z-actuator (50 kHz) while remaining insensitive to the dynamics of its base and surroundings. The scanner allows a practical z scan range of 2.1 μm. We have demonstrated the applicability of the scanner to the high speed scanning of nanostructures.

  8. The Role of Forcing and Internal Dynamics in explaining the 'Medieval Climate Anomaly'

    Science.gov (United States)

    Goossee, Hugues; Crespin, Elisabeth; Dubinkina, Svetlana; Loutre, Marie-France; Mann, Michael E.; Renssen, Hans; Shindell, Drew

    2012-01-01

    Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950-1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.

  9. Dynamics of excited instantons in the system of forced Gursey nonlinear differential equations

    Energy Technology Data Exchange (ETDEWEB)

    Aydogmus, F., E-mail: fatma.aydogmus@gmail.com [Istanbul University, Department of Physics, Faculty of Science (Turkey)

    2015-02-15

    The Gursey model is a 4D conformally invariant pure fermionic model with a nonlinear spinor self-coupled term. Gursey proposed his model as a possible basis for a unitary description of elementary particles following the “Heisenberg dream.” In this paper, we consider the system of Gursey nonlinear differential equations (GNDEs) formed by using the Heisenberg ansatz. We use it to understand how the behavior of spinor-type Gursey instantons can be affected by excitations. For this, the regular and chaotic numerical solutions of forced GNDEs are investigated by constructing their Poincaré sections in phase space. A hierarchical cluster analysis method for investigating the forced GNDEs is also presented.

  10. DYNAMICS OF SANDY DESERTIFICATION AND ITS DRIVING FORCES IN WESTERN JILIN PROVINCE

    Institute of Scientific and Technical Information of China (English)

    LI Fang; HE Yan-fen; LIU Zhi-ming; ZHANG Bai

    2004-01-01

    By establishing the interpreting elements, and applying supervised classification, the sandy desertification was interpreted and the desertified land areas of the counties in the western Jilin Province in 1986 and in 2000 were obtained. Taking Tongyu and Qian'an as examples, the natural driving forces and man-made driving forces were analyzed. The paper comes the conclusions that the material sources and the warming and dry climate are the internal causes of potential land desertification; the irrational human activities, such as destroying forest and reclaiming the grassland, are the external causes of potential land desertification; while more rational human activities, such as planting trees and restoring grassland can reverse the land desertification. Furthermore, the countermeasures and suggestions for the development of agriculture and animal husbandry in the western Jilin Province are put forward.

  11. Retail structural dynamics and the forces behind big-box retailing

    OpenAIRE

    Scott Munroe

    2001-01-01

    Recent change on the American retail landscape warrants a revisit to the catastrophe framework originated by Harris and Wilson (1978). A retail revolution, centered around the growth of big-box retailing, is recreating metropolitan retail structure. Alterations to both the sizes and spatial distributions of retailers in nearly every sector have resulted. This research presents a theoretical inquiry into the forces behind this change through an adoption and extension of the catastrophe theory ...

  12. Study of the interactions between endolysin and bacterial peptidoglycan on S. aureus by dynamic force spectroscopy

    Science.gov (United States)

    Liu, Jianli; Zhang, Xuejie; Yang, Hang; Yuan, Jinghe; Wei, Hongping; Yu, Junping; Fang, Xiaohong

    2015-09-01

    The cell wall binding domain (CBD) of bacteriophage lysins can recognize target bacteria with extraordinary specificity through binding to bacterial peptidoglycan, thus it is a promising new probe to identify the corresponding bacterial pathogen. In this work, we used atomic force microscopy (AFM) based single-molecule force spectroscopy to investigate the interaction between the CBD of lysin PlyV12 (PlyV12C) and pathogenic bacterium Staphylococcus aureus (S. aureus). The binding forces of PlyV12C with S. aureus have been measured, and the dissociation process of their binding complex has been characterized. Furthermore, we compared the interactions of PlyV12C-S. aureus and antibody-S. aureus. It is revealed that PlyV12C has a comparable affinity to bacterial peptidoglycans as that of the S. aureus antibody. The results provide new information on the binding properties of lysin CBD with bacterium, and the application of lysin CBD in bacterium detection.

  13. Study of the interactions between endolysin and bacterial peptidoglycan on S. aureus by dynamic force spectroscopy.

    Science.gov (United States)

    Liu, Jianli; Zhang, Xuejie; Yang, Hang; Yuan, Jinghe; Wei, Hongping; Yu, Junping; Fang, Xiaohong

    2015-10-07

    The cell wall binding domain (CBD) of bacteriophage lysins can recognize target bacteria with extraordinary specificity through binding to bacterial peptidoglycan, thus it is a promising new probe to identify the corresponding bacterial pathogen. In this work, we used atomic force microscopy (AFM) based single-molecule force spectroscopy to investigate the interaction between the CBD of lysin PlyV12 (PlyV12C) and pathogenic bacterium Staphylococcus aureus (S. aureus). The binding forces of PlyV12C with S. aureus have been measured, and the dissociation process of their binding complex has been characterized. Furthermore, we compared the interactions of PlyV12C-S. aureus and antibody-S. aureus. It is revealed that PlyV12C has a comparable affinity to bacterial peptidoglycans as that of the S. aureus antibody. The results provide new information on the binding properties of lysin CBD with bacterium, and the application of lysin CBD in bacterium detection.

  14. Role of tip chemical reactivity on atom manipulation process in dynamic force microscopy.

    Science.gov (United States)

    Sugimoto, Yoshiaki; Yurtsever, Ayhan; Abe, Masayuki; Morita, Seizo; Ondráček, Martin; Pou, Pablo; Pérez, Ruben; Jelínek, Pavel

    2013-08-27

    The effect of tip chemical reactivity on the lateral manipulation of intrinsic Si adatoms toward a vacancy site on a Si(111)-(7 × 7) surface has been investigated by noncontact atomic force microscopy at room temperature. Here we measure the atom-hopping probabilities associated with different manipulation processes as a function of the tip-surface distance by means of constant height scans with chemically different types of tips. The interactions between different tips and Si atoms are evaluated by force spectroscopic measurements. Our results demonstrate that the ability to manipulate Si adatoms depends extremely on the chemical nature of the tip apex and is correlated with the maximal attractive force measured over Si adatoms. We rationalize the observed dependence of the atom manipulation process on tip-apex chemical reactivity by means of density functional theory calculations. The results of these calculations suggest that the ability to reduce the energy barrier associated with the Si adatom movement depends profoundly on tip chemical reactivity and that the level of energy barrier reduction is higher with tips that exhibit high chemical reactivity with Si adatoms. The results of this study provide a better way to control the efficiency of the atomic manipulation process for chemisorption systems.

  15. Influence of typical faults over the dynamic behavior of pantograph-catenary contact force in electric rail transport

    Science.gov (United States)

    Rusu-Anghel, S.; Ene, A.

    2017-05-01

    The quality of electric energy capture and also the equipment operational safety depend essentially of the technical state of the contact line (CL). The present method for determining the technical state of CL based on advance programming is no longer efficient, due to the faults which can occur into the not programmed areas. Therefore, they cannot be remediated. It is expected another management method for the repairing and maintenance of CL based on its real state which must be very well known. In this paper a new method for determining the faults in CL is described. It is based on the analysis of the variation of pantograph-CL contact force in dynamical regime. Using mathematical modelling and also experimental tests, it was established that each type of fault is able to generate ‘signatures’ into the contact force diagram. The identification of these signatures can be accomplished by an informatics system which will provide the fault location, its type and also in the future, the probable evolution of the CL technical state. The measuring of the contact force is realized in optical manner using a railway inspection trolley which has appropriate equipment. The analysis of the desired parameters can be accomplished in real time by a data acquisition system, based on dedicated software.

  16. Vertically polarizing undulator with the dynamic compensation of magnetic forces for the next generation of light sources.

    Science.gov (United States)

    Strelnikov, N; Trakhtenberg, E; Vasserman, I; Xu, J; Gluskin, E

    2014-11-01

    A short prototype (847-mm-long) of an Insertion Device (ID) with the dynamic compensation of ID magnetic forces has been designed, built, and tested at the Advanced Photon Source (APS) of the Argonne National Laboratory. The ID magnetic forces were compensated by the set of conical springs placed along the ID strongback. Well-controlled exponential characteristics of conical springs permitted a very close fit to the ID magnetic forces. Several effects related to the imperfections of actual springs, their mounting and tuning, and how these factors affect the prototype performance has been studied. Finally, series of tests to determine the accuracy and reproducibility of the ID magnetic gap settings have been carried out. Based on the magnetic measurements of the ID Beff, it has been demonstrated that the magnetic gaps within an operating range were controlled accurately and reproducibly within ±1 μm. Successful tests of this ID prototype led to the design of a 3-m long device based on the same concept. The 3-m long prototype is currently under construction. It represents R&D efforts by the APS toward APS Upgrade Project goals as well as the future generation of IDs for the Linac Coherent Light Source (LCLS).

  17. Dispersion Forces

    CERN Document Server

    Buhmann, Stefan Yoshi

    2012-01-01

    In this book, a modern unified theory of dispersion forces on atoms and bodies is presented which covers a broad range of advanced aspects and scenarios. Macroscopic quantum electrodynamics is shown to provide a powerful framework for dispersion forces which allows for discussing general properties like their non-additivity and the relation between microscopic and macroscopic interactions. It is demonstrated how the general results can be used to obtain dispersion forces on atoms in the presence of bodies of various shapes and materials. Starting with a brief recapitulation of volume I, this volume II deals especially with bodies of irregular shapes, universal scaling laws, dynamical forces on excited atoms, enhanced forces in cavity quantum electrodynamics, non-equilibrium forces in thermal environments and quantum friction. The book gives both the specialist and those new to the field a thorough overview over recent results in the field. It provides a toolbox for studying dispersion forces in various contex...

  18. The generalized Langevin equation revisited: Analytical expressions for the persistence dynamics of a viscous fluid under a time dependent external force

    Science.gov (United States)

    Olivares-Rivas, Wilmer; Colmenares, Pedro J.

    2016-09-01

    The non-static generalized Langevin equation and its corresponding Fokker-Planck equation for the position of a viscous fluid particle were solved in closed form for a time dependent external force. Its solution for a constant external force was obtained analytically. The non-Markovian stochastic differential equation, associated to the dynamics of the position under a colored noise, was then applied to the description of the dynamics and persistence time of particles constrained within absorbing barriers. Comparisons with molecular dynamics were very satisfactory.

  19. Forces affecting employment dynamics in Groningen; Case study in a lagging rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Groningen since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Groningen increased by 36,000 jobs or with one quarter in

  20. A High Performance Piezoelectric Sensor for Dynamic Force Monitoring of Landslide

    Directory of Open Access Journals (Sweden)

    Ming Li

    2017-02-01

    Full Text Available Due to the increasing influence of human engineering activities, it is important to monitor the transient disturbance during the evolution process of landslide. For this purpose, a high-performance piezoelectric sensor is presented in this paper. To adapt the high static and dynamic stress environment in slope engineering, two key techniques, namely, the self-structure pressure distribution method (SSPDM and the capacitive circuit voltage distribution method (CCVDM are employed in the design of the sensor. The SSPDM can greatly improve the compressive capacity and the CCVDM can quantitatively decrease the high direct response voltage. Then, the calibration experiments are conducted via the independently invented static and transient mechanism since the conventional testing machines cannot match the calibration requirements. The sensitivity coefficient is obtained and the results reveal that the sensor has the characteristics of high compressive capacity, stable sensitivities under different static preload levels and wide-range dynamic measuring linearity. Finally, to reduce the measuring error caused by charge leakage of the piezoelectric element, a low-frequency correction method is proposed and experimental verified. Therefore, with the satisfactory static and dynamic properties and the improving low-frequency measuring reliability, the sensor can complement dynamic monitoring capability of the existing landslide monitoring and forecasting system.

  1. Forces affecting employment dynamics in Drenthe; Case study in a leading rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Drenthe since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Drenthe increased by 24,500 jobs or with over 20% in the

  2. A High Performance Piezoelectric Sensor for Dynamic Force Monitoring of Landslide.

    Science.gov (United States)

    Li, Ming; Cheng, Wei; Chen, Jiangpan; Xie, Ruili; Li, Xiongfei

    2017-02-17

    Due to the increasing influence of human engineering activities, it is important to monitor the transient disturbance during the evolution process of landslide. For this purpose, a high-performance piezoelectric sensor is presented in this paper. To adapt the high static and dynamic stress environment in slope engineering, two key techniques, namely, the self-structure pressure distribution method (SSPDM) and the capacitive circuit voltage distribution method (CCVDM) are employed in the design of the sensor. The SSPDM can greatly improve the compressive capacity and the CCVDM can quantitatively decrease the high direct response voltage. Then, the calibration experiments are conducted via the independently invented static and transient mechanism since the conventional testing machines cannot match the calibration requirements. The sensitivity coefficient is obtained and the results reveal that the sensor has the characteristics of high compressive capacity, stable sensitivities under different static preload levels and wide-range dynamic measuring linearity. Finally, to reduce the measuring error caused by charge leakage of the piezoelectric element, a low-frequency correction method is proposed and experimental verified. Therefore, with the satisfactory static and dynamic properties and the improving low-frequency measuring reliability, the sensor can complement dynamic monitoring capability of the existing landslide monitoring and forecasting system.

  3. Forces affecting employment dynamics in Drenthe; Case study in a leading rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Drenthe since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Drenthe increased by 24,500 jobs or with over 20% in the per

  4. Forces affecting employment dynamics in Groningen; Case study in a lagging rural region in the Netherlands

    NARCIS (Netherlands)

    Terluin, I.J.; Post, J.H.; Wisselink, A.J.; Overbeek, M.M.M.

    1999-01-01

    In this report the focus is on employment dynamics in Groningen since the beginning of the 1980s. This study is part of an EU wide research project on employment development in leading and lagging rural regions of the EU. Total employment in Groningen increased by 36,000 jobs or with one quarter in

  5. Multipolar Force Fields and Their Effects on Solvent Dynamics around Simple Solutes

    DEFF Research Database (Denmark)

    Jakobsen, Sofie; Bereau, Tristan; Meuwly, Markus

    2015-01-01

    , quantities are affected by the quality of the electrostatic model. The alteration of the first solvation shell in MTP simulations is validated by comparing with lifetimes and correlation times of solute–solvent interactions from experiment. The improved dynamical behavior found in the MTP simulations...

  6. Evolving Responsibilities in Work Force Development: Incorporating the Dynamics of Change.

    Science.gov (United States)

    Flynn, Patricia M.

    Changes in skill requirements, training needs, the industrial and occupational mix of employment, and the spatial location of jobs are 'natural' consequences of a dynamic economy. These changes, in turn, influence employers' hiring and staffing patterns, workers' career paths, and economic growth and development. However, the evolving nature of…

  7. Nonlinear dynamic analysis of atomic force microscopy under deterministic and random excitation

    Energy Technology Data Exchange (ETDEWEB)

    Pishkenari, Hossein Nejat [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Behzad, Mehdi [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)], E-mail: m_behzad@sharif.edu; Meghdari, Ali [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2008-08-15

    The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. This paper is devoted to the analysis of nonlinear behavior of amplitude modulation (AM) and frequency modulation (FM) modes of atomic force microscopy. For this, the microcantilever (which forms the basis for the operation of AFM) is modeled as a single mode approximation and the interaction between the sample and cantilever is derived from a van der Waals potential. Using perturbation methods such as averaging, and Fourier transform nonlinear equations of motion are analytically solved and the advantageous results are extracted from this nonlinear analysis. The results of the proposed techniques for AM-AFM, clearly depict the existence of two stable and one unstable (saddle) solutions for some of exciting parameters under deterministic vibration. The basin of attraction of two stable solutions is different and dependent on the exciting frequency. From this analysis the range of the frequency which will result in a unique periodic response can be obtained and used in practical experiments. Furthermore the analytical responses determined by perturbation techniques can be used to detect the parameter region where the chaotic motion is avoided. On the other hand for FM-AFM, the relation between frequency shift and the system parameters can be extracted and used for investigation of the system nonlinear behavior. The nonlinear behavior of the oscillating tip can easily explain the observed shift of frequency as a function of tip sample distance. Also in this paper we have investigated the AM-AFM system response under a random excitation. Using two different methods we have obtained the statistical properties of the tip motion. The results show that we can use the mean square value of tip motion to image the sample when the excitation signal is random.

  8. Sea ice dynamics and the role of wind forcing over the Beaufort Sea

    Science.gov (United States)

    Petty, A.; Hutchings, J. K.; Farrell, S. L.; Richter-Menge, J.; Tschudi, M. A.

    2014-12-01

    Both the ocean circulation and overlying sea ice cover of the Beaufort and Chukchi seas have experienced significant change in recent decades. We use sea ice drift estimates from satellite feature tracking (NSIDC/CERSAT), wind forcing from atmospheric reanalysis products (NCEP-R2/ERA-I/JRA-55), and ice type information from satellite and direct ship-based observations (obtained during the Beaufort Gyre Exploration Project), to investigate the role of wind forcing and ice mechanics in driving these changes. An assessment of ice drift shows reasonable agreement across the different products, revealing interannual variability in the ice flux around the Beaufort Sea. However, clear uncertainties remain in determining the magnitude of these fluxes, especially in regions of low ice concentration. We find an increase in ice export out of the southern Beaufort Sea (into the Chukchi Sea) across all seasons. We find slight differences in the strength of the decadal (1980-2013) trends in the mean seasonal wind curl over the Beaufort Sea, although all reanalysis products indicate a strong and significant increase in anti-cyclonic winds in summer. Analysis of ice drift curl suggests increasing anti-cyclonic drift across all seasons, despite the wind curl showing a similar trend in summer only. The strongest trend in ice drift curl appears to be in autumn, however recent years have seen a strong reduction in this anti-cyclonic drift, likely due to a combination of changes in the wind forcing and sea ice state. The implication of this finding is an enhanced response of the ocean circulation to shifts in atmospheric circulation compared to that experienced prior to 2000.

  9. Dynamic Analysis for Two Kinds of Jacket Platforms under Wave Force

    Institute of Scientific and Technical Information of China (English)

    Meng Xun(孟珣); Huang Weiping; Li Huajun

    2004-01-01

    A detailed finite element analysis is presented in this paper in order to obtain the different vibration properties of two kinds of fixed jacket platforms under wave force. More attention is paid to the platform with prism shape jacket because of its more possibly excessive vibration in service than that of the jacket platform with slant piles. Numerical simulations are compared with the results from actual platform test and an effective strengthening technique is proposed. The conclusion of the paper may be taken as the basis of following control work.It also gives some guidance to the future design of the fixed platform with prism shape jacket.

  10. Loadcell supports for a dynamic force plate. [using piezoelectric tranducers and electromyography to study human gait

    Science.gov (United States)

    Keller, C. W.; Musil, L. M.; Hagy, J. L.

    1975-01-01

    An apparatus was developed to accurately measure components of force along three mutually perpendicular axes, torque, and the center of pressure imposed by the foot of a subject walking over its surface. The data obtained were used to supplement high-speed motion picture and electromyographic (EMG) data for in-depth studies of normal or abnormal human gait. Significant features of the design (in particular, the mechanisms used to support the loadcell transducers) are described. Results of the development program and typical data obtained with the device are presented and discussed.

  11. Influence of low optical frequencies on actuation dynamics of microelectromechanical systems via Casimir forces

    Science.gov (United States)

    Sedighi, Mehdi; Palasantzas, George

    2015-04-01

    The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled using the Drude and Plasma models. Indeed, for metallic systems, which have strong Casimir attraction, the details of the modeling of the low optical frequency regime can be dramatic, leading to predictions of either stable motion or stiction instability. However, this difference is strongly minimized for weakly conductive systems as are the doped insulators making actuation modeling more certain to predict.

  12. Ice flow dynamics forced by rapid water pressure variations in subglacial granular beds

    DEFF Research Database (Denmark)

    Damsgaard, Anders; Egholm, David Lundbek; Beem, Lucas H.;

    2016-01-01

    mechanical processes driving transitions from stability to slip. We performed computational experiments that show how rearrangements of load-bearing force chains within the granular sediments drive the mechanical transitions. Cyclic variations in pore water pressure give rise to rate-dependent creeping......Glaciers and ice streams can move by deforming underlying water-saturated sediments, and the nonlinear mechanics of these materials are often invoked as the main reason for initiation, persistence, and shutdown of fast-flowing ice streams. Existing models have failed to fully explain the internal...

  13. Approximate Dynamic Programming Algorithms for United States Air Force Officer Sustainment

    Science.gov (United States)

    2015-03-26

    21 The action selected is defined by: Xt = ( Xd ,t)d∈D. (19) Additionally, there are upper bounds, βd, and lower bounds, ζd, for each decision, as...the force. βd ≤ Xd ,t ≤ ζd ∀d ∈ D. (20) A deterministic transition is made from pre-decision to post-decision state, Sxt , with each non-promotion...binomial distribution. The probability of any eligible individual transitioning to the next highest grade is determined by the promotion decisions Xd

  14. Advances in RNA molecular dynamics: a simulator's guide to RNA force fields.

    Science.gov (United States)

    Vangaveti, Sweta; Ranganathan, Srivathsan V; Chen, Alan A

    2017-03-01

    Molecular simulations have become an essential tool for biochemical research. When they work properly, they are able to provide invaluable interpretations of experimental results and ultimately provide novel, experimentally testable predictions. Unfortunately, not all simulation models are created equal, and with inaccurate models it becomes unclear what is a bona fide prediction versus a simulation artifact. RNA models are still in their infancy compared to the many robust protein models that are widely in use, and for that reason the number of RNA force field revisions in recent years has been rapidly increasing. As there is no universally accepted 'best' RNA force field at the current time, RNA simulators must decide which one is most suited to their purposes, cognizant of its essential assumptions and their inherent strengths and weaknesses. Hopefully, armed with a better understanding of what goes inside the simulation 'black box,' RNA biochemists can devise novel experiments and provide crucial thermodynamic and structural data that will guide the development and testing of improved RNA models. WIREs RNA 2017, 8:e1396. doi: 10.1002/wrna.1396 For further resources related to this article, please visit the WIREs website. © 2016 Wiley Periodicals, Inc.

  15. An estimation of the influence of force decrease on the mean power spectral frequency shift of the EMG during repetitive maximum dynamic knee extensions.

    Science.gov (United States)

    Karlsson, J S; Ostlund, N; Larsson, B; Gerdle, B

    2003-10-01

    Frequency analysis of myoelectric (ME) signals, using the mean power spectral frequency (MNF), has been widely used to characterize peripheral muscle fatigue during isometric contractions assuming constant force. However, during repetitive isokinetic contractions performed with maximum effort, output (force or torque) will decrease markedly during the initial 40-60 contractions, followed by a phase with little or no change. MNF shows a similar pattern. In situations where there exist a significant relationship between MNF and output, part of the decrease in MNF may per se be related to the decrease in force during dynamic contractions. This study estimated force effects on the MNF shifts during repetitive dynamic knee extensions. Twenty healthy volunteers participated in the study and both surface ME signals (from the right vastus lateralis, vastus medialis, and rectus femoris muscles) and the biomechanical signals (force, position, and velocity) of an isokinetic dynamometer were measured. Two tests were performed: (i) 100 repetitive maximum isokinetic contractions of the right knee extensors, and (ii) five gradually increasing static knee extensions before and after (i). The corresponding ME signal time-frequency representations were calculated using the continuous wavelet transform. Compensation of the MNF variables of the repetitive contractions was performed with respect to the individual MNF-force relation based on an average of five gradually increasing contractions. Whether or not compensation was necessary was based on the shape of the MNF-force relationship. A significant compensation of the MNF was found for the repetitive isokinetic contractions. In conclusion, when investigating maximum dynamic contractions, decreases in MNF can be due to mechanisms similar to those found during sustained static contractions (force-independent component of fatigue) and in some subjects due to a direct effect of the change in force (force-dependent component of fatigue

  16. Modelling of Nonlinear Dynamic of Mechanic Systems with the Force Tribological Interaction

    Directory of Open Access Journals (Sweden)

    K.A. Nuzhdin

    2015-09-01

    Full Text Available This paper considers the mechanisms with different structure: tribometric device and a mechanism for handling of optical glasses. In the first device, the movement of the upper platform is due to a reciprocating friction interaction. In the second device, the processing of the optical element or group of elements occurs due to the rotational motion. Modelling of the dynamic of these systems with Matlab/Simmechanic allowed carrying out the analysis of dynamic of mechanisms, considering nonlinearity tribological interactions for these systems. The article shows that using of the computer models can effectively carry out the selection of the control parameters to create the desired mode of operation, as well as to investigate the behaviour of systems with nonlinear parameters and processes of self-oscillations. The organization of the managed self-oscillation process is realized to create the relevant high-performance manufacturing, for example, for the processing of optical glasses.

  17. "Could Charm (\\& $\\tau$) Transitions be the `Poor Princesses' of Deeper Understanding of Fundamental Dynamics?" -- or -- "Finding Novel Forces?"

    CERN Document Server

    Bigi, Ikaros I

    2015-01-01

    We know that `our' Universe consists of `known' matter only $\\sim$ 4.5\\%: our understanding is incomplete seeing directly in neutrino oscillations (never mind about `other' Universes). Charm quarks had great impact on our understanding of known matter. QCD is the only local quantum field theory to describe strong forces. We can learn novel lessons about strong dynamics by measuring rates around the thresholds of $[\\bar Q Q]$ states with $Q = b, c$. Furthermore they give us gateways for New Dynamics (ND), where we have to go from `accuracy' to `precision' eras. Finally we can connect with $\\tau$ transitions and -- maybe -- with dark matter. Charm dynamics acts as a bridge between the worlds of light flavor hadrons with the heavy one, namely beauty hadrons. Finding {\\em regional asymmetries} in many-body final states could be a `game changer'. There are several different `roads' to get closer to our goals: experiments act as gatekeepers like Super-tau-charm-factories, Super-beauty-factories and/or Super-$Z^0$-f...

  18. Spatiotemporal dynamics of the nuclear pore complex transport barrier resolved by high-speed atomic force microscopy

    Science.gov (United States)

    Sakiyama, Yusuke; Mazur, Adam; Kapinos, Larisa E.; Lim, Roderick Y. H.

    2016-08-01

    Nuclear pore complexes (NPCs) are biological nanomachines that mediate the bidirectional traffic of macromolecules between the cytoplasm and nucleus in eukaryotic cells. This process involves numerous intrinsically disordered, barrier-forming proteins known as phenylalanine-glycine nucleoporins (FG Nups) that are tethered inside each pore. The selective barrier mechanism has so far remained unresolved because the FG Nups have eluded direct structural analysis within NPCs. Here, high-speed atomic force microscopy is used to visualize the nanoscopic spatiotemporal dynamics of FG Nups inside Xenopus laevis oocyte NPCs at timescales of ∼100 ms. Our results show that the cytoplasmic orifice is circumscribed by highly flexible, dynamically fluctuating FG Nups that rapidly elongate and retract, consistent with the diffusive motion of tethered polypeptide chains. On this basis, intermingling FG Nups exhibit transient entanglements in the central channel, but do not cohere into a tightly crosslinked meshwork. Therefore, the basic functional form of the NPC barrier is comprised of highly dynamic FG Nups that manifest as a central plug or transporter when averaged in space and time.

  19. An Assessment of Team Development at the Air Force Flight Dynamics Laboratory.

    Science.gov (United States)

    1980-09-01

    Burke , W. Warner and Warren H. Schmidt. "Management and Organizational Development: What is the Target of Change?," Personnel Administration (Mar-Apr...1970. Lippit, Ronald, Jeanne Watson and Bruce Westley. The Dynamics of Planned Change. New York: Harcourt, Brace, and World,~Inc., 1958. Litwin , G...H. "Achievement Motivation and Industrial Climates," in R. Taiuri and G. H. Litwin (eds.) Organizational Climate: Explorations of a Concept. Boston

  20. The Dependence of Amyloid‐β Dynamics on Protein Force Fields and Water Models

    DEFF Research Database (Denmark)

    Somavarapu, Arun Kumar; Kepp, Kasper Planeta

    2015-01-01

    We studied the dynamics of Aβ40, involved in Alzheimer's disease, by using 21 methods combined from Amber03, Amber99sb‐ILDN, Charmm27, Charmm22*, OPLS‐2001, OPLS‐2006, OPLS‐2008, Gromos96‐43a1, Gromos96‐53a6, Gromos96‐54a7, and the water models SPC, TIP3P, TIP4P. Major differences in the structural...

  1. Computationally exact methods for stochastic periodic dynamics: Spatiotemporal dispersal and temporally forced transmission.

    Science.gov (United States)

    Ross, J V

    2010-01-07

    The dynamics of many diseases and populations possess distinct recurring phases. For example, many species breed only during a subset of the year and the infection dynamics of many pathogens have transmission rates that vary with season. Here I investigate computational methods for studying transient and long-term behaviour of stochastic models which have periodic phases-several different potential techniques for studying long-term behaviour will be contrasted. I illustrate the results with two studies: The first is of a spatially realistic metapopulation model of malleefowl (Leipoa ocellata), a species which disperses only during a quarter of the year; this model is used to highlight the advantages and disadvantages of the particular methods presented. The second study is of a model for disease dynamics which incorporates seasonality in both the rate of within-population transmission and also in the rate of transmission effected via aerosol importation. This model has applications to studying disease invasion and persistence in captive-breeding populations. We demonstrate, via comparison to appropriately matched models with constant transmission rates and also no aerosol transmission, that seasonality and aerosol importation may alter control choices, with possibly an increase in the threshold population size for local control surveillance, transfer of importance to limiting aerosol transmission, and the use of temporally targetted surveillance. The methodology presented is the gold-standard for dealing with many phased processes in ecology and epidemiology, but its application is limited to systems of small size.

  2. Molecular dynamics study of DNA binding by INT-DBD under a polarized force field.

    Science.gov (United States)

    Yao, Xue X; Ji, Chang G; Xie, Dai Q; Zhang, John Z H

    2013-05-15

    The DNA binding domain of transposon Tn916 integrase (INT-DBD) binds to DNA target site by positioning the face of a three-stranded antiparallel β-sheet within the major groove. As the negatively charged DNA directly interacts with the positively charged residues (such as Arg and Lys) of INT-DBD, the electrostatic interaction is expected to play an important role in the dynamical stability of the protein-DNA binding complex. In the current work, the combined use of quantum-based polarized protein-specific charge (PPC) for protein and polarized nucleic acid-specific charge (PNC) for DNA were employed in molecular dynamics simulation to study the interaction dynamics between INT-DBD and DNA. Our study shows that the protein-DNA structure is stabilized by polarization and the calculated protein-DNA binding free energy is in good agreement with the experimental data. Furthermore, our study revealed a positive correlation between the measured binding energy difference in alanine mutation and the occupancy of the corresponding residue's hydrogen bond. This correlation relation directly relates the contribution of a specific residue to protein-DNA binding energy to the strength of the hydrogen bond formed between the specific residue and DNA.

  3. Cholera and shigellosis in Bangladesh: similarities and differences in population dynamics under climate forcing

    Science.gov (United States)

    Pascual, M.; Cash, B.; Reiner, R.; King, A.; Emch, M.; Yunus, M.; Faruque, A. S.

    2012-12-01

    The influence of climate variability on the population dynamics of infectious diseases is considered a large scale, regional, phenomenon, and as such, has been previously addressed for cholera with temporal models that do not incorporate fine-scale spatial structure. In our previous work, evidence for a role of ENSO (El Niño Southern Oscillation) on cholera in Bangladesh was elucidated, and shown to influence the regional climate through precipitation. With a probabilistic spatial model for cholera dynamics in the megacity of Dhaka, we found that the action of climate variability (ENSO and flooding) is localized: there is a climate-sensitive urban core that acts to propagate risk to the rest of the city. Here, we consider long-term surveillance data for shigellosis, another diarrheal disease that coexists with cholera in Bangladesh. We compare the patterns of association with climate variables for these two diseases in a rural setting, as well as the spatial structure in their spatio-temporal dynamics in an urban one. Evidence for similar patterns is presented, and discussed in the context of the differences in the routes of transmission of the two diseases and the proposed role of an environmental reservoir in cholera. The similarities provide evidence for a more general influence of hydrology and of socio-economic factors underlying human susceptibility and sanitary conditions.

  4. Force-Based Incremental Algorithm for Mining Community Structure in Dynamic Network

    Institute of Scientific and Technical Information of China (English)

    Bo Yang; Da-You Liu

    2006-01-01

    Community structure is an important property of network. Being able to identify communities can provide invaluable help in exploiting and understanding both social and non-social networks. Several algorithms have been developed up till now. However, all these algorithms can work well only with small or moderate networks with vertexes of order 104.Besides, all the existing algorithms are off-line and cannot work well with highly dynamic networks such as web, in which web pages are updated frequently. When an already clustered network is updated, the entire network including original and incremental parts has to be recalculated, even though only slight changes are involved. To address this problem, an incremental algorithm is proposed, which allows for mining community structure in large-scale and dynamic networks. Based on the community structure detected previously, the algorithm takes little time to reclassify the entire network including both the original and incremental parts. Furthermore, the algorithm is faster than most of the existing algorithms such as Girvan and Newman's algorithm and its improved versions. Also, the algorithm can help to visualize these community structures in network and provide a new approach to research on the evolving process of dynamic networks.

  5. Coupling the non-gravitational forces and Modified Newton Dynamics for cometary orbits

    CERN Document Server

    Maquet, Lucie

    2014-01-01

    The sublimation of ices of a cometary nucleus affects its gravitational orbit. This sublimation triggers a so-called non-gravitational forces. Moreover, some comets with large orbit ($a>15$ AU) are in low-acceleration regime at their aphelion. We investigate the effect of MOND and non-gravitational perturbations for three comets with various orbital elements (2P/Encke, 1P/Halley and 153P/Ikeya-Zhang). We used six different forms of MOND functions and compute the secular variations of the orbital elements due to both perturbations. We show that the MONDian effects are not negligible for comets with high semi-major axis compared to the non-gravitational perturbations and this effect are currently close to the detection threshold.

  6. Modeling ocean and sea ice dynamics of the Canadian Arctic Archipelago: Aspects of forcing

    Science.gov (United States)

    Wekerle, Claudia; Wang, Qiang; Danilov, Sergey; Myers, Paul G.; Jung, Thomas; Schröter, Jens

    2013-04-01

    The Canadian Arctic Archipelago (CAA) is one of the main pathways for freshwater exiting the Arctic Ocean. Freshwater exported to the North Atlantic may influence the deep water formation in the Labrador Sea, and thus the meridional overturning circulation. Modeling ocean and sea ice conditions of the CAA is difficult because of narrow straits and complex coastlines. The Finite-Element Sea-ice Ocean circulation Model (FESOM) configured on a global mesh is applied to assess the volume, freshwater and sea ice transports through the CAA. With a mesh resolution of 5 km in the CAA we are able to accurately resolve complex coastlines. Outside the CAA the mesh is refined to 24 km north of 55°N with a global background resolution of 1.5°. In this study, first, it is shown that the transports modeled with FESOM correlate well with the available observational data. Second, the model is used to learn about the impact of different atmospheric forcing datasets differing in spatial and temporal resolution (CORE 2 and the Reforecast dataset from Environment Canada). The CORE 2 dataset is on the T62 grid, which is coarse compared to the Reforecast dataset with grid resolution of 0.45° longitude and 0.3° latitude. The temporal resolution of the Reforecast dataset is higher than the CORE 2 dataset (one hourly and 6-hourly data, respectively, for wind, surface temperature and specific humidity fields). The representation of sea ice in the CAA can be improved by using the high resolution atmospheric forcing.

  7. Atmospheric forcing controlling inter-annual nutrient dynamics in the open Gulf of Finland

    Science.gov (United States)

    Lehtoranta, Jouni; Savchuk, Oleg P.; Elken, Jüri; Dahlbo, Kim; Kuosa, Harri; Raateoja, Mika; Kauppila, Pirkko; Räike, Antti; Pitkänen, Heikki

    2017-07-01

    The loading of P into the Gulf of Finland has decreased markedly, but no overall trend in the concentration of P has been observed in the open Gulf, where the concentrations of both inorganic N and P still have a pronounced inter-annual variability. Our main aim was to study whether the internal processes driven by atmospheric forcing can explain the variation in the nutrient conditions in the Gulf during the period 1992-2014. We observed that the long-term salinity variation of the bottom water in the northern Baltic Proper controls that in the Gulf, and that the deep-water concentrations of oxygen and nutrients are significantly correlated between the basins. This imposes preconditions regarding how atmospheric forcing may influence deep water flows and stratification in the Gulf on a long-term scale. We found that over short timescales, winter winds in particular can control the in- and outflows of water and the vertical stratification and mixing, which to a large extent explained the inter-annual variation in the DIN and TP pools in the Gulf. We conclude that the inter-annual variation in the amounts, ratios, and spatial distribution of nutrients sets variable preconditions for the spring and potential blue-green algae blooms, and that internal processes were able to mask the effects of the P load reductions implemented across the whole Gulf. The transportation of P along the bottom from the northern Baltic Proper and its evident uplift in the Gulf highlights the fact that the nutrient reductions are also needed in the entire catchment of the Baltic Sea to improve the trophic status of the open Gulf.

  8. Sensitivity of simulated circulation dynamics to the choice of surface wind forcing in the Japan/East Sea

    Science.gov (United States)

    Hogan, Patrick J.; Hurlburt, Harley E.

    2005-06-01

    The circulation sensitivity to the choice of wind-forcing product is investigated with the NRL Layered Ocean Model (NLOM) configured for the Japan/East Sea. Monthly climatologies from seven different wind-stress data sets (and wind-stress curl) are formed from observed and model-derived atmospheric data sets. The resulting maps of wind-stress curl reveal significantly different spatial patterns and magnitudes, even two with largely opposite large-scale patterns of wind-stress curl. These wind sets were used in forcing three sets of simulations, 1/8° linear and 1/8° and 1/32° nonlinear. In addition, seasonally varying straits forcing (inflow through Tsushima balanced by outflow through Tsugaru and Soya) was included in all the simulations, and simulations with straits forcing only were performed. The 1.5-layer linear reduced-gravity simulations include only the lowest order dynamics, mainly Munk β 1/3 western boundary layers (due to both wind and straits forcing) and a Sverdrup interior. The nonlinear simulations add bottom topography, multiple internal modes, diapycnal mixing, and ventilation of layer interfaces. At 1/8° resolution, only weak barotropic/baroclinic instabilities occur, but at 1/32° resolution these are much stronger, allowing vigorous transfer of energy from the upper ocean to the abyssal layer via baroclinic instability. This drives much stronger mean abyssal currents that more strongly steer upper-ocean current pathways than at 1/8°, i.e. there is much stronger upper ocean-topographical coupling. The linear model simulates most of the basic features, e.g., the subpolar gyre with all but the straits forcing only, the East Korean Warm Current (EKWC) and its connection to the subpolar front with all but one wind-forcing set, but the remaining wind set gives a continuous Nearshore Branch (NB) of the Tsushima Warm Current along the coast of Honshu. In all of the linear simulations with an EKWC, the separation latitude from the coast of Korea is

  9. The Dynamics of a Periodically Forced Cortical Microcircuit, With an Application to Schizophrenia

    Science.gov (United States)

    Vierling-Claassen, Dorea; Kopell, Nancy

    2009-01-01

    Synchronous neural activity in the brain in the gamma and beta frequency bands (50-70 Hz)is thought to be important for sensory processing and is altered in schizophrenia. In a previous study, gamma/beta click-train auditory stimuli were used to probe cortical oscillatory activity in control and schizophrenic subjects. We found that control subjects exhibited preferential 40 Hz responses to both 20 and 40 Hz stimulations, while schizophrenic subjects had enhanced 20 Hz responses to the same stimuli [D. Vierling-Claassen, P. Siekmeier, S. Stufflebeam, and N. Kopell, J. Neurophysiol., 99 (2008), p. 2656]. High-dimensional computational network models constructed previously, which were based on evidence of altered inhibition in schizophrenia, numerically generated the entrainment behaviors observed experimentally. However, questions regarding the dynamic origin of model behaviors remained. It was not clear that the 20 Hz response to 40 Hz drive in the schizophrenic network was robust to parameter changes, which would be necessary for the predicted mechanism to explain data from a heterogeneous subject population. In the schizophrenic network we observed 30 Hz drive responses with a frequency component below 30 Hz, for which no analogue appeared in experimental data, and wondered if these were dynamically distinct from the modeled 20 Hz response to 40 Hz drive. We also wished to explore the role of background noise in model behavior. To address these questions, we consider a system of two mutually coupled oscillators representative of neural cells, driven periodically in the gamma/beta frequency band. We show that there is a one-parameter family of discontinuous discrete maps, whose dynamics clarifies issues of robustness, classifies entrainment patterns, and provides insight into the role of excitatory noise.

  10. Experimental investigation of the dynamics of a hybrid morphing wing: time resolved particle image velocimetry and force measures

    Science.gov (United States)

    Jodin, Gurvan; Scheller, Johannes; Rouchon, Jean-François; Braza, Marianna; Mit Collaboration; Imft Collaboration; Laplace Collaboration

    2016-11-01

    A quantitative characterization of the effects obtained by high frequency-low amplitude trailing edge actuation is performed. Particle image velocimetry, as well as pressure and aerodynamic force measurements, are carried out on an airfoil model. This hybrid morphing wing model is equipped with both trailing edge piezoelectric-actuators and camber control shape memory alloy actuators. It will be shown that this actuation allows for an effective manipulation of the wake turbulent structures. Frequency domain analysis and proper orthogonal decomposition show that proper actuating reduces the energy dissipation by favoring more coherent vortical structures. This modification in the airflow dynamics eventually allows for a tapering of the wake thickness compared to the baseline configuration. Hence, drag reductions relative to the non-actuated trailing edge configuration are observed. Massachusetts Institute of Technology.

  11. Systematic study of the dolomite (104) surface by bimodal dynamic force microscopy in ultra-high vacuum.

    Science.gov (United States)

    Kawai, Shigeki; Pina, Carlos M; Bubendorf, Alexander; Fessler, Gregor; Glatzel, Thilo; Gnecco, Enrico; Meyer, Ernst

    2013-02-08

    We have investigated the morphology and structure of dolomite MgCa(CO(3))(2)(104) surfaces by bimodal dynamic force microscopy with flexural and torsional resonance modes in ultra-high vacuum at room temperature. We found that the surface slowly decomposes by degassing CO(2) in a vacuum and becomes covered by amorphous clusters, presumably MgO and CaO. By choosing an optimal sample preparation procedure (i.e. cleaving in a vacuum and mild annealing for stabilizing clusters for a short time), atomically clean surfaces were obtained. The complex tip-sample interaction, arising from carbonate groups and Mg and Ca atoms of the surface, induces a large variety of atomic-scale imaging features.

  12. Influence of Damping on the Dynamical Behavior of the Electrostatic Parallel-plate and Torsional Actuators with Intermolecular Forces

    Science.gov (United States)

    Lin, Wen-Hui; Zhao, Ya-Pu

    2007-01-01

    The influence of damping on the dynamical behavior of the electrostatic parallel-plate and torsional actuators with the van der Waals (vdW) or Casimir force (torque) is presented. The values of the pull-in parameters and the number of the equilibrium points do not change whether there is damping or not. The ability of equilibrium points is varied with the appearance of damping. One equilibrium point is an unstable saddle with a different damping coefficient, the other equilibrium point is a stable node when the damping coefficient is greater than some critical value, and otherwise it is a stable focus. Then there are two heteroclinic orbits passing from the unstable saddle point to the stable node or focus.

  13. Influence of Damping on the Dynamical Behavior of the Electrostatic Parallel-plate and Torsional Actuators with Intermolecular Forces

    Directory of Open Access Journals (Sweden)

    Ya-Pu Zhao

    2007-11-01

    Full Text Available The influence of damping on the dynamical behavior of the electrostaticparallel-plate and torsional actuators with the van der Waals (vdW or Casimir force(torque is presented. The values of the pull-in parameters and the number of theequilibrium points do not change whether there is damping or not. The ability ofequilibrium points is varied with the appearance of damping. One equilibrium point is anunstable saddle with a different damping coefficient, the other equilibrium point is astable node when the damping coefficient is greater than some critical value, andotherwise it is a stable focus. Then there are two heteroclinic orbits passing from theunstable saddle point to the stable node or focus.

  14. Development of Constraint Force Equation Methodology for Application to Multi-Body Dynamics Including Launch Vehicle Stage Seperation

    Science.gov (United States)

    Pamadi, Bandu N.; Toniolo, Matthew D.; Tartabini, Paul V.; Roithmayr, Carlos M.; Albertson, Cindy W.; Karlgaard, Christopher D.

    2016-01-01

    The objective of this report is to develop and implement a physics based method for analysis and simulation of multi-body dynamics including launch vehicle stage separation. The constraint force equation (CFE) methodology discussed in this report provides such a framework for modeling constraint forces and moments acting at joints when the vehicles are still connected. Several stand-alone test cases involving various types of joints were developed to validate the CFE methodology. The results were compared with ADAMS(Registered Trademark) and Autolev, two different industry standard benchmark codes for multi-body dynamic analysis and simulations. However, these two codes are not designed for aerospace flight trajectory simulations. After this validation exercise, the CFE algorithm was implemented in Program to Optimize Simulated Trajectories II (POST2) to provide a capability to simulate end-to-end trajectories of launch vehicles including stage separation. The POST2/CFE methodology was applied to the STS-1 Space Shuttle solid rocket booster (SRB) separation and Hyper-X Research Vehicle (HXRV) separation from the Pegasus booster as a further test and validation for its application to launch vehicle stage separation problems. Finally, to demonstrate end-to-end simulation capability, POST2/CFE was applied to the ascent, orbit insertion, and booster return of a reusable two-stage-to-orbit (TSTO) vehicle concept. With these validation exercises, POST2/CFE software can be used for performing conceptual level end-to-end simulations, including launch vehicle stage separation, for problems similar to those discussed in this report.

  15. Transient Dynamics of Elastic Hele-Shaw Cell Due to External Forces with Application to Impulse Mitigation

    CERN Document Server

    Tulchinsky, Arie

    2015-01-01

    We study the transient dynamics of a viscous liquid contained in a narrow gap between a rigid surface and a parallel elastic plate. The elastic plate is deformed due to an externally applied time-varying pressure-field. We model the flow-field via the lubrication approximation, and the plate deformation by the Kirchhoff-Love plate theory. We obtain a self-similarity solution for the case of an external point force acting on the elastic plate. The pressure and deformation field during and after the application of the external force are derived and presented by closed form expressions. We examine a uniform external pressure acting on the elastic plate over a finite region and during a finite time period, similar to the viscous-elastic interaction time-scale. The interaction between elasticity and viscosity is shown to reduce by order of magnitude the pressure within the Hele-Shaw cell compared with the externally applied pressure, thus suggesting such configurations may be used for impact mitigation.

  16. Evaluation on the analogy between the dynamic magnetosphere and a forced and/or self-organized critical system

    Directory of Open Access Journals (Sweden)

    A. T. Y. Lui

    2002-01-01

    Full Text Available The dissipation power and size of auroral blobs are investigated in detail to examine the possible analogy between the dynamic magnetosphere and a forced and/or self-organized critical system. The distributions of these auroral parameters are sorted in terms of different levels of activity, namely substorms, pseudo-breakups, and quiet conditions. A power law (scale-free component is seen in all these distributions. In addition, a peak distribution is found for substorm intervals and a hump for pseudo-breakup intervals. The peak distribution is present prominently during magnetic storms, i.e. when the magnetosphere is strongly driven by the solar wind. It is interpreted that the scale-free component is associated with the activity of the diffuse aurora, corresponding to disturbances at all permissible scales within the plasma sheet. Ionospheric feedback appears to be essential for the presence of two components in the distribution for auroral dissipation power. These results are consistent with the concept that the magnetosphere is in a forced and/or self-organized critical state, although they do not constitute conclusive evidence for the analogy.

  17. Molecular dynamics simulations and Kelvin probe force microscopy to study of cholesterol-induced electrostatic nanodomains in complex lipid mixtures

    Science.gov (United States)

    Drolle, E.; Bennett, W. F. D.; Hammond, K.; Lyman, E.; Karttunen, M.; Leonenko, Z.

    The molecular arrangement of lipids and proteins within biomembranes and monolayers gives rise to complex film morphologies as well as regions of distinct electrical surface potential, topographical and electrostatic nanoscale domains. To probe these nanodomains in soft matter is a challenging task both experimentally and theoretically. This work addresses the effects of cholesterol, lipid composition, lipid charge, and lipid phase on the monolayer structure and the electrical surface potential distribution. Atomic Force Microscopy (AFM) was used to resolve topographical nanodomains and Kelvin Probe Force Microscopy (KPFM) to resolve electrical surface potential of these nanodomains in lipid monolayers. Model monolayers composed of dipalmitoylphosphatidylcholine (DPPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(3-lysyl(1-glycerol))] (DOPG), sphingomyelin, and cholesterol were studied. It is shown that cholesterol changes nanoscale domain formation, affecting both topography and electrical surface potential. The molecular basis for differences in electrical surface potential was addressed with atomistic molecular dynamics (MD). MD simulations qualitatively match the experimental results, with 100s of mV difference in electrostatic potential between liquid-disordered bilayer (Ld, less cholesterol and lower chain order) and a liquid-ordered bilayer (Lo, more cholesterol and higher chain order). Importantly, the difference in electrostatic properties between Lo and Ld phases suggests a new mechanism by which membrane composition couples to membrane function.

  18. Unified description of $^6$Li structure and deuterium-$^4$He dynamics with chiral two- and three-nucleon forces

    CERN Document Server

    Hupin, Guillaume; Navrátil, Petr

    2014-01-01

    Prototype for the study of weakly bound projectiles colliding on stable targets, the scattering of deuterium ($d$) on $^4$He ($\\alpha$) is an important milestone in the search for a fundamental understanding of low-energy reactions. At the same time, it is also important for its role in the Big-bang nucleosynthesis of $^6$Li and applications in the characterization of deuterium impurities in materials. We present the first unified {\\em ab initio} study of the $^6$Li ground state and $d$-$^4$He elastic scattering using two- and three-nucleon forces derived within the framework of chiral effective field theory. The six-nucleon bound-state and scattering observables are calculated by means of the no-core shell model with continuum. %and are compared to available experimental data. We analyze the influence of the dynamic polarization of the deuterium and of the chiral three-nucleon force, and examine the role of the continuum degrees of freedom in shaping the low-lying spectrum of $^6$Li. We find that the adopted...

  19. Corticomuscular coherence reflects interindividual differences in the state of the corticomuscular network during low-level static and dynamic forces.

    Science.gov (United States)

    Mendez-Balbuena, Ignacio; Huethe, Frank; Schulte-Mönting, Jürgen; Leonhart, Rainer; Manjarrez, Elias; Kristeva, Rumyana

    2012-03-01

    In the investigation of corticomuscular coherence (CMC), it remained unclear why some subjects do not present significant CMC. We predicted that such subjects will develop CMC as a result of learning as indexed by improved performance during a visuomotor task. We investigated CMC, cortical motor spectral power (SP), and performance in 14 subjects during isometric compensation of a static force or dynamic force (DF) with their right index finger. We compared data from the beginning of the experiment (Time-Period 1) and after learning (Time-Period 2). Eight subjects (Group CMC++) presented CMC during Period 1 which increased during Period 2. Six subjects (Group CMC-+) presented CMC only during Period 2. Group CMC-+ was "more desynchronized" (lower SP, and stronger task-related desynchronization) than Group CMC++. The performance was better in Group CMC++ than in Group CMC-+. Learning was associated with higher SP, higher CMC, and better performance in both groups. However, in the more complicated DF condition, Group CMC++ learned better than Group CMC-+. The present study demonstrates the presence of CMC in all subjects tested and evidence that this is due to the fact that individuals may fall into 2 different groups in terms of oscillatory motor control: Group CMC-+ presents CMC only after learning.

  20. Selecting a dynamic simulation modeling method for health care delivery research-part 2: report of the ISPOR Dynamic Simulation Modeling Emerging Good Practices Task Force.

    Science.gov (United States)

    Marshall, Deborah A; Burgos-Liz, Lina; IJzerman, Maarten J; Crown, William; Padula, William V; Wong, Peter K; Pasupathy, Kalyan S; Higashi, Mitchell K; Osgood, Nathaniel D

    2015-03-01

    In a previous report, the ISPOR Task Force on Dynamic Simulation Modeling Applications in Health Care Delivery Research Emerging Good Practices introduced the fundamentals of dynamic simulation modeling and identified the types of health care delivery problems for which dynamic simulation modeling can be used more effectively than other modeling methods. The hierarchical relationship between the health care delivery system, providers, patients, and other stakeholders exhibits a level of complexity that ought to be captured using dynamic simulation modeling methods. As a tool to help researchers decide whether dynamic simulation modeling is an appropriate method for modeling the effects of an intervention on a health care system, we presented the System, Interactions, Multilevel, Understanding, Loops, Agents, Time, Emergence (SIMULATE) checklist consisting of eight elements. This report builds on the previous work, systematically comparing each of the three most commonly used dynamic simulation modeling methods-system dynamics, discrete-event simulation, and agent-based modeling. We review criteria for selecting the most suitable method depending on 1) the purpose-type of problem and research questions being investigated, 2) the object-scope of the model, and 3) the method to model the object to achieve the purpose. Finally, we provide guidance for emerging good practices for dynamic simulation modeling in the health sector, covering all aspects, from the engagement of decision makers in the model design through model maintenance and upkeep. We conclude by providing some recommendations about the application of these methods to add value to informed decision making, with an emphasis on stakeholder engagement, starting with the problem definition. Finally, we identify areas in which further methodological development will likely occur given the growing "volume, velocity and variety" and availability of "big data" to provide empirical evidence and techniques