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Sample records for critical surface dynamics

  1. Universality classes for the dynamic surface critical behavior of systems with relaxational dynamics

    NASA Astrophysics Data System (ADS)

    Diehl, H. W.

    1994-01-01

    We investigate the problem of which universality classes of dynamic surface critical behavior exist for semi-infinite systems whose dynamic bulk critical behavior and static surface critical behavior are representative of a given dynamic bulk universality class and a given static surface universality class. To this end systems whose bulk dynamics are described by either model B or model A of Halperin, Hohenberg, and Ma are considered, where the dynamics are allowed to be modified near the surface as follows: In the case of model B, surface terms that locally break the conservation law for the order-parameter density φ are allowed; in the case of model A, φ is assumed to be locally conserved near the surface. Semi-infinite field-theory models are constructed that are (i) compatible with the requested bulk dynamics and the requirements of causality, detailed balance, and relaxation to thermal equilibrium and (ii) minimal in the sense that no redundant or irrelevant surface terms are included. The boundary conditions to which the surface terms of the action correspond are worked out. For model B it is shown that nonconservative surface terms are relevant. Their strength can be parametrized by a coupling constant c~0>=0 whose inverse plays the role of an extrapolation length for the auxiliary (Martin-Siggia-Rose) field φ~. Thus two distinct semi-infinite extensions of model B exist-one with c~0>0 called model BA, and one with c~0=0 called model BB-and each static surface universality class splits up into two dynamic surface universality classes. The static and dynamic surface critical exponents of these dynamic surface universality classes as well as the crossover exponent associated with the nonconservative surface term are shown to be expressible in terms of static bulk and surface exponents. Model BA and its results should apply, e.g., to uniaxial ferromagnets whose rotational spin symmetry is broken in the vicinity of a surface plane. For model A the considered

  2. Fermi-surface collapse and dynamical scaling near a quantum-critical point

    PubMed Central

    Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

    2010-01-01

    Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh2Si2, a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems. PMID:20668246

  3. Fermi-surface collapse and dynamical scaling near a quantum-critical point.

    PubMed

    Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

    2010-08-17

    Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh(2)Si(2), a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.

  4. Optical feather and foil for shape and dynamic load sensing of critical flight surfaces

    NASA Astrophysics Data System (ADS)

    Black, Richard J.; Costa, Joannes M.; Faridian, Fereydoun; Moslehi, Behzad; Pakmehr, Mehrdad; Schlavin, Jon; Sotoudeh, Vahid; Zagrai, Andrei

    2014-04-01

    Future flight vehicles may comprise complex flight surfaces requiring coordinated in-situ sensing and actuation. Inspired by the complexity of the flight surfaces on the wings and tail of a bird, it is argued that increasing the number of interdependent flight surfaces from just a few, as is normal in an airplane, to many, as in the feathers of a bird, can significantly enlarge the flight envelope. To enable elements of an eco-inspired Dynamic Servo-Elastic (DSE) flight control system, IFOS is developing a multiple functionality-sensing element analogous to a feather, consisting of a very thin tube with optical fiber based strain sensors and algorithms for deducing the shape of the "feather" by measuring strain at multiple points. It is envisaged that the "feather" will act as a unit of sensing and/or actuation for establishing shape, position, static and dynamic loads on flight surfaces and in critical parts. Advanced sensing hardware and software control algorithms will enable the proposed DSE flight control concept. The hardware development involves an array of optical fiber based sensorized needle tubes for attachment to key parts for dynamic flight surface measurement. Once installed the optical fiber sensors, which can be interrogated over a wide frequency range, also allow damage detection and structural health monitoring.

  5. Critical speed for the dynamics of truck events on bridges with a smooth road surface

    NASA Astrophysics Data System (ADS)

    González, Arturo; OBrien, Eugene J.; Cantero, Daniel; Li, Yingyan; Dowling, Jason; Žnidarič, Ales

    2010-05-01

    Simple numerical models of point loads are used to represent single and multiple vehicle events on two-lane bridges with a good road profile. While such models are insufficiently complex to calculate dynamic amplification accurately, they are presented here to provide an understanding of the influence of speed and distance between vehicles on the bridge dynamic response. Critical combinations of speed as a function of main bridge natural frequency and meeting point of two vehicles travelling in opposite directions are identified. It is proposed that such simple models can be used to estimate the pattern of critical speeds versus dynamic amplification of the bridge response for trucks on a relatively smooth surface. The crossing of a three-dimensional spring-dashpot truck is simulated over a bridge plate model to test this hypothesis for a range of road roughness. Further validation is carried out using the site-specific mean pattern associated to field measurements of bridge strains when traversed by a truck population. The latter is found to be closely resembled by the theoretical pattern derived from simple point load models.

  6. Critical insight into the influence of the potential energy surface on fission dynamics

    NASA Astrophysics Data System (ADS)

    Mazurek, K.; Schmitt, C.; Wieleczko, J. P.; Nadtochy, P. N.; Ademard, G.

    2011-07-01

    The present work is dedicated to a careful investigation of the influence of the potential energy surface on the fission process. The time evolution of nuclei at high excitation energy and angular momentum is studied by means of three-dimensional Langevin calculations performed for two different parametrizations of the macroscopic potential: the Finite Range Liquid Drop Model (FRLDM) and the Lublin-Strasbourg Drop (LSD) prescription. Depending on the mass of the system, the topology of the potential throughout the deformation space of interest in fission is observed to noticeably differ within these two approaches, due to the treatment of curvature effects. When utilized in the dynamical calculation as the driving potential, the FRLDM and LSD models yield similar results in the heavy-mass region, whereas the predictions can be strongly dependent on the Potential Energy Surface (PES) for medium-mass nuclei. In particular, the mass, charge, and total kinetic energy distributions of the fission fragments are found to be narrower with the LSD prescription. The influence of critical model parameters on our findings is carefully investigated. The present study sheds light on the experimental conditions and signatures well suited for constraining the parametrization of the macroscopic potential. Its implication regarding the interpretation of available experimental data is briefly discussed.

  7. Critical insight into the influence of the potential energy surface on fission dynamics

    SciTech Connect

    Mazurek, K.

    2011-07-15

    The present work is dedicated to a careful investigation of the influence of the potential energy surface on the fission process. The time evolution of nuclei at high excitation energy and angular momentum is studied by means of three-dimensional Langevin calculations performed for two different parametrizations of the macroscopic potential: the Finite Range Liquid Drop Model (FRLDM) and the Lublin-Strasbourg Drop (LSD) prescription. Depending on the mass of the system, the topology of the potential throughout the deformation space of interest in fission is observed to noticeably differ within these two approaches, due to the treatment of curvature effects. When utilized in the dynamical calculation as the driving potential, the FRLDM and LSD models yield similar results in the heavy-mass region, whereas the predictions can be strongly dependent on the Potential Energy Surface (PES) for medium-mass nuclei. In particular, the mass, charge, and total kinetic energy distributions of the fission fragments are found to be narrower with the LSD prescription. The influence of critical model parameters on our findings is carefully investigated. The present study sheds light on the experimental conditions and signatures well suited for constraining the parametrization of the macroscopic potential. Its implication regarding the interpretation of available experimental data is briefly discussed.

  8. Critical dynamics in mixtures

    NASA Astrophysics Data System (ADS)

    Folk, R.; Moser, G.

    1998-11-01

    We derive the nonasymptotic expressions for the frequency- and temperature-dependent sound velocity and sound absorption near a critical point in a mixture within renormalization group theory in one-loop order. The dynamic model considered is an extension of the corresponding model for pure fluids including concentration fluctuations. The theoretical result for the complex sound velocity is the same as at consolute points and gas-liquid critical points reflecting universality. Differences observed in the experiments at the two critical points mentioned are due to the different behavior of the sound velocity at Tc, which is finite in mixtures and zero in pure fluids, as well as due to nonasymptotic effects. Near the consolute point we compare our result with the phenomenological theory of Ferrell and Bhattacharjee [Phys. Rev. B 24, 4095 (1981); Phys. Rev. A 31, 1788 (1985)] and near the gas-liquid critical point with experiments in the 3He-4He mixture. A genuine dynamic parameter not considered so far and related to the critical enhancement of the thermal conductivity appears in the nonasymptotic expressions of the transport coefficients and the complex sound velocity. All nonuniversal background parameters of the complex sound velocity are fixed by a comparison of the corresponding theoretical expressions for the transport coefficients with experiments.

  9. Critical dynamics and decoherence

    SciTech Connect

    Damski, Bogdan; Quan, Haitao T; Zurek, Wojciech H

    2009-01-01

    We study dynamics of decoherence in a generic model where the environment is driven and undergoes a quantum phase transition. We model the environment by the Ising chain in the transverse field, and assume that the decohering system is a central spin-1/2. We found that when the environment is quenched slowly through the critical point, the decoherence factor of the central spin undergoes rapid decay that encodes the critical exponents of the environment. We also found that decoherence in a non-equilibrated, kink-contaminated, environment can be stronger than in a vacuum one. We derived a remarkably simple analytical expression that describes post-transition decoherence and predicts periodicities involving all system parameters. This research connects the fields of decoherence, quantum phase transitions, and Kibble-Zurek non-equilibrium dynamics.

  10. Spin-liquid Mott quantum criticality in two dimensions: Destabilization of a spinon Fermi surface and emergence of one-dimensional spin dynamics

    NASA Astrophysics Data System (ADS)

    Han, Jae-Ho; Cho, Yong-Heum; Kim, Ki-Seok

    2017-06-01

    Resorting to a recently developed theoretical device called dimensional regularization for quantum criticality with a Fermi surface, we examine a metal-insulator quantum phase transition from a Landau's Fermi-liquid state to a U(1) spin-liquid phase with a spinon Fermi surface in two dimensions. Unfortunately, we fail to approach the spin-liquid Mott quantum critical point from the U(1) spin-liquid state within the dimensional regularization technique. Self-interactions between charge fluctuations called holons are not screened, which shows a run-away renormalization group flow, interpreted as holons remain gapped. This leads us to consider another fixed point, where the spinon Fermi surface can be destabilized across the Mott transition. Based on this conjecture, we reveal the nature of the spin-liquid Mott quantum critical point: Dimensional reduction to one dimension occurs for spin dynamics described by spinons. As a result, Landau damping for both spin and charge dynamics disappear in the vicinity of the Mott quantum critical point. When the flavor number of holons is over its critical value, an interacting fixed point appears to be identified with an inverted X Y universality class, controlled within the dimensional regularization technique. On the other hand, a fluctuation-driven first order metal-insulator transition results when it is below the critical number. We propose that the destabilization of a spinon Fermi surface and the emergence of one-dimensional spin dynamics near the spin-liquid Mott quantum critical point can be checked out by spin susceptibility with a 2 kF transfer momentum, where kF is a Fermi momentum in the U(1) spin-liquid state: The absence of Landau damping in U(1) gauge fluctuations gives rise to a divergent behavior at zero temperature while it vanishes in the presence of a spinon Fermi surface.

  11. Critical Behaviors in Contagion Dynamics

    NASA Astrophysics Data System (ADS)

    Böttcher, L.; Nagler, J.; Herrmann, H. J.

    2017-02-01

    We study the critical behavior of a general contagion model where nodes are either active (e.g., with opinion A , or functioning) or inactive (e.g., with opinion B , or damaged). The transitions between these two states are determined by (i) spontaneous transitions independent of the neighborhood, (ii) transitions induced by neighboring nodes, and (iii) spontaneous reverse transitions. The resulting dynamics is extremely rich including limit cycles and random phase switching. We derive a unifying mean-field theory. Specifically, we analytically show that the critical behavior of systems whose dynamics is governed by processes (i)-(iii) can only exhibit three distinct regimes: (a) uncorrelated spontaneous transition dynamics, (b) contact process dynamics, and (c) cusp catastrophes. This ends a long-standing debate on the universality classes of complex contagion dynamics in mean field and substantially deepens its mathematical understanding.

  12. Critical Behaviors in Contagion Dynamics.

    PubMed

    Böttcher, L; Nagler, J; Herrmann, H J

    2017-02-24

    We study the critical behavior of a general contagion model where nodes are either active (e.g., with opinion A, or functioning) or inactive (e.g., with opinion B, or damaged). The transitions between these two states are determined by (i) spontaneous transitions independent of the neighborhood, (ii) transitions induced by neighboring nodes, and (iii) spontaneous reverse transitions. The resulting dynamics is extremely rich including limit cycles and random phase switching. We derive a unifying mean-field theory. Specifically, we analytically show that the critical behavior of systems whose dynamics is governed by processes (i)-(iii) can only exhibit three distinct regimes: (a) uncorrelated spontaneous transition dynamics, (b) contact process dynamics, and (c) cusp catastrophes. This ends a long-standing debate on the universality classes of complex contagion dynamics in mean field and substantially deepens its mathematical understanding.

  13. Dynamics at Surfaces

    SciTech Connect

    Sylvia Ceyer, Nancy Ryan Gray

    2010-05-04

    The 2009 Gordon Conference on Dynamics at Surfaces is the 30th anniversary of a meeting held every two years that is attended by leading researchers in the area of experimental and theoretical dynamics at liquid and solid surfaces. The conference focuses on the dynamics of the interaction of molecules with either liquid or solid surfaces, the dynamics of the outermost layer of liquid and solid surfaces and the dynamics at the liquid-solid interface. Specific topics that are featured include state-to-state dynamics, non-adiabatic interactions in molecule-metal systems, photon induced desorption from semiconductor and metal surfaces, ultrafast x-ray and electron diffraction as probes of the dynamics of ablation, ultrafast vibrational spectroscopy of water surface dynamics, dynamics of a single adsorbate, growth at nano-scale mineral surfaces, dynamics of atom recombination on interstellar dust grains and the dynamics of the interaction of water with lipid bilayers. The conference brings together investigators from a variety of scientific disciplines including chemistry, physics, materials science, geology and biophysics.

  14. Criticality in finite dynamical networks

    NASA Astrophysics Data System (ADS)

    Rohlf, Thimo; Gulbahce, Natali; Teuscher, Christof

    2007-03-01

    It has been shown analytically and experimentally that both random boolean and random threshold networks show a transition from ordered to chaotic dynamics at a critical average connectivity Kc in the thermodynamical limit [1]. By looking at the statistical distributions of damage spreading (damage sizes), we go beyond this extensively studied mean-field approximation. We study the scaling properties of damage size distributions as a function of system size N and initial perturbation size d(t=0). We present numerical evidence that another characteristic point, Kd exists for finite system sizes, where the expectation value of damage spreading in the network is independent of the system size N. Further, the probability to obtain critical networks is investigated for a given system size and average connectivity k. Our results suggest that, for finite size dynamical networks, phase space structure is very complex and may not exhibit a sharp order-disorder transition. Finally, we discuss the implications of our findings for evolutionary processes and learning applied to networks which solve specific computational tasks. [1] Derrida, B. and Pomeau, Y. (1986), Europhys. Lett., 1, 45-49

  15. Scale criticality in estimating ecosystem carbon dynamics

    USGS Publications Warehouse

    Zhao, Shuqing; Liu, Shuguang

    2014-01-01

    Scaling is central to ecology and Earth system sciences. However, the importance of scale (i.e. resolution and extent) for understanding carbon dynamics across scales is poorly understood and quantified. We simulated carbon dynamics under a wide range of combinations of resolution (nine spatial resolutions of 250 m, 500 m, 1 km, 2 km, 5 km, 10 km, 20 km, 50 km, and 100 km) and extent (57 geospatial extents ranging from 108 to 1 247 034 km2) in the southeastern United States to explore the existence of scale dependence of the simulated regional carbon balance. Results clearly show the existence of a critical threshold resolution for estimating carbon sequestration within a given extent and an error limit. Furthermore, an invariant power law scaling relationship was found between the critical resolution and the spatial extent as the critical resolution is proportional to An (n is a constant, and A is the extent). Scale criticality and the power law relationship might be driven by the power law probability distributions of land surface and ecological quantities including disturbances at landscape to regional scales. The current overwhelming practices without considering scale criticality might have largely contributed to difficulties in balancing carbon budgets at regional and global scales.

  16. An investigation of dynamic surface tension, critical micelle concentration, and aggregation number of three nonionic surfactants using NMR, time-resolved fluorescence quenching, and maximum bubble pressure tensiometry.

    PubMed

    Kjellin, U R Mikael; Reimer, Johan; Hansson, Per

    2003-06-15

    Several physicochemical properties have been determined for N-dodecyllactobionamide (LABA), maltose 6'-O-dodecanoate (C12-maltose ester), and tetra(ethylene oxide) dodecyl amide (TEDAd). The increase in the flexibility of the sugar headgroup, enabling more possible molecular conformations, reduces the minimum area/molecule at the liquid-vapor interface obtained at the critical micelle concentration (cmc). The obtained cmc's were 0.35 mM (LABA), 0.3 mM (C12-maltose ester), and 0.5 mM (TEDAd). The monomer diffusion coefficient decreased with the molecular weight and increasing headgroup flexibility of the sugar headgroup, and values were in the range from 3.1 x 10(-10) to 3.6 x 10(-10) m2/s. The micelle diffusion coefficients (0.46 x 10(-10) to 0.68 x 10(-10) m2/s) indicated that the TEDAd micelles deviated most from spherical shape. The micelle aggregation numbers determined by time-resolved fluorescence quenching (TRFQ) were estimated to be 120+/-10 (LABA), 90+/-10 (C12-maltose ester), and 130+/-10 (TEDAd). The dynamic surface tension measurements show that the adsorption of TEDAd onto the liquid-vapor interface at short surface lifetimes is diffusion-limited, whereas an adsorption barrier is present for the sugar surfactants. The analysis of the dynamic surface tension data above the cmc shows that the rate of demicellization is faster for TEDAd than for the two sugar-based surfactants.

  17. Surface Hold Advisor Using Critical Sections

    NASA Technical Reports Server (NTRS)

    Law, Caleb Hoi Kei (Inventor); Hsiao, Thomas Kun-Lung (Inventor); Mittler, Nathan C. (Inventor); Couluris, George J. (Inventor)

    2013-01-01

    The Surface Hold Advisor Using Critical Sections is a system and method for providing hold advisories to surface controllers to prevent gridlock and resolve crossing and merging conflicts among vehicles traversing a vertex-edge graph representing a surface traffic network on an airport surface. The Advisor performs pair-wise comparisons of current position and projected path of each vehicle with other surface vehicles to detect conflicts, determine critical sections, and provide hold advisories to traffic controllers recommending vehicles stop at entry points to protected zones around identified critical sections. A critical section defines a segment of the vertex-edge graph where vehicles are in crossing or merging or opposite direction gridlock contention. The Advisor detects critical sections without reference to scheduled, projected or required times along assigned vehicle paths, and generates hold advisories to prevent conflicts without requiring network path direction-of-movement rules and without requiring rerouting, rescheduling or other network optimization solutions.

  18. Critical dynamics in associative memory networks

    PubMed Central

    Uhlig, Maximilian; Levina, Anna; Geisel, Theo; Herrmann, J. Michael

    2013-01-01

    Critical behavior in neural networks is characterized by scale-free avalanche size distributions and can be explained by self-regulatory mechanisms. Theoretical and experimental evidence indicates that information storage capacity reaches its maximum in the critical regime. We study the effect of structural connectivity formed by Hebbian learning on the criticality of network dynamics. The network only endowed with Hebbian learning does not allow for simultaneous information storage and criticality. However, the critical regime can be stabilized by short-term synaptic dynamics in the form of synaptic depression and facilitation or, alternatively, by homeostatic adaptation of the synaptic weights. We show that a heterogeneous distribution of maximal synaptic strengths does not preclude criticality if the Hebbian learning is alternated with periods of critical dynamics recovery. We discuss the relevance of these findings for the flexibility of memory in aging and with respect to the recent theory of synaptic plasticity. PMID:23898261

  19. Nonuniversal surface behavior of dynamic phase transitions

    NASA Astrophysics Data System (ADS)

    Riego, Patricia; Berger, Andreas

    2015-06-01

    We have studied the dynamic phase transition (DPT) of the kinetic Ising model in systems with surfaces within the mean-field approximation. Varying the surface exchange coupling strength Js, the amplitude of the externally applied oscillating field h0, and its period P , we explore the dynamic behavior of the layer-dependent magnetization and the associated DPTs. The surface phase diagram shows several features that resemble those of the equilibrium case, with an extraordinary bulk transition and a surface transition for high Js values, independent from the value of h0. For low Js, however, h0 is found to be a crucial parameter that leads to nonuniversal surface behavior at the ordinary bulk transition point. Specifically, we observed here a bulk-supported surface DPT for high field amplitudes h0 and correspondingly short critical periods Pc, whereas this surface transition simultaneous to the bulk one is suppressed for slow critical dynamics occurring for low values of h0. The suppression of the DPT for low h0 not only occurs for the topmost surface layer, but also affects a significant number of subsurface layers. We find that the key physical quantity that explains this nonuniversal behavior is the time correlation between the dynamic surface and bulk magnetizations at the bulk critical point. This time correlation has to pass a threshold value to trigger a bulk-induced DPT in the surface layers. Otherwise, dynamic phase transitions are absent at the surface in stark contrast to the equilibrium behavior of the corresponding thermodynamic Ising model. Also, we have analyzed the penetration depth of the dynamically ordered phase for the surface DPT that occurs for large Js values. Here we find that the penetration depth depends strongly on Js and behaves identically to the corresponding equilibrium Ising model.

  20. Critical slowing down in a dynamic duopoly

    NASA Astrophysics Data System (ADS)

    Escobido, M. G. O.; Hatano, N.

    2015-01-01

    Anticipating critical transitions is very important in economic systems as it can mean survival or demise of firms under stressful competition. As such identifying indicators that can provide early warning to these transitions are very crucial. In other complex systems, critical slowing down has been shown to anticipate critical transitions. In this paper, we investigate the applicability of the concept in the heterogeneous quantity competition between two firms. We develop a dynamic model where the duopoly can adjust their production in a logistic process. We show that the resulting dynamics is formally equivalent to a competitive Lotka-Volterra system. We investigate the behavior of the dominant eigenvalues and identify conditions that critical slowing down can provide early warning to the critical transitions in the dynamic duopoly.

  1. Dynamical selection of critical exponents.

    PubMed

    Wiese, Kay Jörg

    2016-04-01

    In renormalized field theories there are in general one or few fixed points that are accessible by the renormalization-group flow. They can be identified from the fixed-point equations. Exceptionally, an infinite family of fixed points exists, parameterized by a scaling exponent ζ, itself a function of a nonrenormalizing parameter. Here we report a different scenario with an infinite family of fixed points of which seemingly only one is chosen by the renormalization-group flow. This dynamical selection takes place in systems with an attractive interaction V(ϕ), as in standard ϕ^{4} theory, but where the potential V at large ϕ goes to zero, as, e.g., the attraction by a defect.

  2. Symmetry in Critical Random Boolean Networks Dynamics

    NASA Astrophysics Data System (ADS)

    Bassler, Kevin E.; Hossein, Shabnam

    2014-03-01

    Using Boolean networks as prototypical examples, the role of symmetry in the dynamics of heterogeneous complex systems is explored. We show that symmetry of the dynamics, especially in critical states, is a controlling feature that can be used to both greatly simplify analysis and to characterize different types of dynamics. Symmetry in Boolean networks is found by determining the frequency at which the various Boolean output functions occur. Classes of functions occur at the same frequency. These classes are orbits of the controlling symmetry group. We find the nature of the symmetry that controls the dynamics of critical random Boolean networks by determining the frequency of output functions utilized by nodes that remain active on dynamical attractors. This symmetry preserves canalization, a form of network robustness. We compare it to a different symmetry known to control the dynamics of an evolutionary process that allows Boolean networks to organize into a critical state. Our results demonstrate the usefulness and power of using symmetry to characterize complex network dynamics, and introduce a novel approach to the analysis of heterogeneous complex systems. This work was supported by the NSF through grants DMR-0908286 and DMR-1206839, and by the AFSOR and DARPA through grant FA9550-12-1-0405.

  3. Surface Critical Phenomena in Smoothly Inhomogeneous Systems.

    NASA Astrophysics Data System (ADS)

    Guim, Ihnsouk

    We consider the surface critical behavior of semi -infinite magnetic systems with short-range couplings that depend smoothly on the distance from the surface. We study how the inhomogeneity of the couplings modifies the surface critical behavior at the bulk critical temperature. According to renormalization-group or scaling arguments, the modifications depend on how fast the inhomogeneity decays into the bulk. In the case of couplings that vary as K(m) = K(,B)+A/m('y), where K(,B) is the bulk coupling and m is the distance from the surface, the scaling theory predicts that for y > (nu)('-1), the surface critical behavior is the same as in the homogeneous case A = 0. Here is the critical exponent of the bulk correlation length. For y < (nu)(' -1), the scaling theory predicts an anomalous exponential decay of the boundary pair correlation function. In this thesis we calculate exact results for inhomogeneous two-dimensional Gaussian and Ising models. The results are in complete agreement with the scaling predictions. For y < (nu)('-1), the pair correlation function of surface spins separated by r decays as g(,(PARLL))(r)(TURN)exp {-(r/(')(xi))('1-(nu)y)}, (')(xi)(TURN)A('-(nu)/(1 -(nu)y)), with (nu) = 1/2 and 1 for the Gaussian and Ising models, respectively. In the Ising model with A > 0 and y < (nu)('-1), there is a spontaneous boundary magnetization m(,1) at the bulk critical temperature. In the limit A (--->) 0, m(,1) vanishes as A('1/{2(1-y)}). At y = (nu)('-1), we find nonuniversal surface critical behavior in both the Gaussian and Ising models. The exponent (eta)(,(PARLL)) which characterizes the correlation function in the large -r limit depends on A. In the Ising model with A > A(,c) > 0, y = (nu)('-1), we also find a non-zero spontaneous boundary magnetization at the bulk critical temperature, which vanishes as (A-A(,c))(' 1/2) as A (--->) A(,c). At A(,c) the correlation function exhibits an unusual logarithmic decay. The method we use for obtaining these

  4. Dynamic electrowetting on microstructured surfaces

    NASA Astrophysics Data System (ADS)

    Nita, Satoshi; Wang, Jiayu; Do-Quang, Minh; Chen, Yu-Chung; Suzuki, Yuji; Amberg, Gustav; Shiomi, Junichiro

    2015-11-01

    Surface modification such as surface charging or microstructuring has been shown as an effective method to control static wetting, but its influence on dynamic wetting is still unclear. Previously, we found that the initial stage of droplet spreading can be significantly hindered by surface microstructures, while previous experiments showed that the effect of surface charge on dynamic wetting on a flat surface is minor. Here, we combine microstructuring and electrowetting to further enhance the controllability of the dynamic wetting. Microstructures are fabricated on silicon wafers and the spontaneous spreading of a droplet is imaged with a high-speed camera. We reveal that the spreading rate sensitivity to surface charge increases in the presence of microstructures. Furthermore, numerical simulations solving Cahn-Hilliard/Navier-Stokes equations are performed and the effect of surface modification is quantified in terms of the contact-line friction. This work was financially supported in part by the Japan Science and Technology Agency through CREST.

  5. Inspection tools for aerospace critical surfaces

    NASA Astrophysics Data System (ADS)

    Workman, Gary L.; Thompson, G. W.; Nerren, Billy H.; Burns, H. Dewitt, Jr.

    1998-03-01

    The measurement and control of cleanliness for critical surfaces during manufacturing and in service operations provides unique challenges in aerospace. For re-usable propulsion systems, such as the solid rocket motors, the current thrust for environmentally benign processes has had a major impact on programs designed for maintaining quality in the production of bondline surfaces. The major goal is to improve upon our ability to detect and identify possible contaminants which are detrimental to the integrity of the bondline. This effort requires an in-depth study of the possible sources of contamination, methodologies to detect and identify contaminants, discriminate between contaminants and chemical species caused by environmental conditions, and the effect of particular contaminants on the bondline integrity of the critical surfaces. This presentation will provide an overview of several optical methods used to detect and identify contamination on critical surfaces, currently being performed by the Surface Contamination and Analysis Team at Marshall Space Flight Center. The methods under development for contamination monitoring include FTIR and Near-IR SPectrometry, UV Fluorescence, and Variable Angle Spectroscopic Ellipsometry. Comparisons between these methods and the current primary tool, optical stimulation of electron emission for on-line inspection will be presented. Experiments include quantitative measurement of silicone and Conoco HD2 greases, metal hydroxides, tape residues, etc. on solid rocket motor surfaces.

  6. Symmetry in critical random Boolean network dynamics.

    PubMed

    Hossein, Shabnam; Reichl, Matthew D; Bassler, Kevin E

    2014-04-01

    Using Boolean networks as prototypical examples, the role of symmetry in the dynamics of heterogeneous complex systems is explored. We show that symmetry of the dynamics, especially in critical states, is a controlling feature that can be used both to greatly simplify analysis and to characterize different types of dynamics. Symmetry in Boolean networks is found by determining the frequency at which the various Boolean output functions occur. There are classes of functions that consist of Boolean functions that behave similarly. These classes are orbits of the controlling symmetry group. We find that the symmetry that controls the critical random Boolean networks is expressed through the frequency by which output functions are utilized by nodes that remain active on dynamical attractors. This symmetry preserves canalization, a form of network robustness. We compare it to a different symmetry known to control the dynamics of an evolutionary process that allows Boolean networks to organize into a critical state. Our results demonstrate the usefulness and power of using the symmetry of the behavior of the nodes to characterize complex network dynamics, and introduce an alternative approach to the analysis of heterogeneous complex systems.

  7. Symmetry in critical random Boolean network dynamics

    NASA Astrophysics Data System (ADS)

    Hossein, Shabnam; Reichl, Matthew D.; Bassler, Kevin E.

    2014-04-01

    Using Boolean networks as prototypical examples, the role of symmetry in the dynamics of heterogeneous complex systems is explored. We show that symmetry of the dynamics, especially in critical states, is a controlling feature that can be used both to greatly simplify analysis and to characterize different types of dynamics. Symmetry in Boolean networks is found by determining the frequency at which the various Boolean output functions occur. There are classes of functions that consist of Boolean functions that behave similarly. These classes are orbits of the controlling symmetry group. We find that the symmetry that controls the critical random Boolean networks is expressed through the frequency by which output functions are utilized by nodes that remain active on dynamical attractors. This symmetry preserves canalization, a form of network robustness. We compare it to a different symmetry known to control the dynamics of an evolutionary process that allows Boolean networks to organize into a critical state. Our results demonstrate the usefulness and power of using the symmetry of the behavior of the nodes to characterize complex network dynamics, and introduce an alternative approach to the analysis of heterogeneous complex systems.

  8. Functional dynamics of cell surface membrane proteins

    NASA Astrophysics Data System (ADS)

    Nishida, Noritaka; Osawa, Masanori; Takeuchi, Koh; Imai, Shunsuke; Stampoulis, Pavlos; Kofuku, Yutaka; Ueda, Takumi; Shimada, Ichio

    2014-04-01

    Cell surface receptors are integral membrane proteins that receive external stimuli, and transmit signals across plasma membranes. In the conventional view of receptor activation, ligand binding to the extracellular side of the receptor induces conformational changes, which convert the structure of the receptor into an active conformation. However, recent NMR studies of cell surface membrane proteins have revealed that their structures are more dynamic than previously envisioned, and they fluctuate between multiple conformations in an equilibrium on various timescales. In addition, NMR analyses, along with biochemical and cell biological experiments indicated that such dynamical properties are critical for the proper functions of the receptors. In this review, we will describe several NMR studies that revealed direct linkage between the structural dynamics and the functions of the cell surface membrane proteins, such as G-protein coupled receptors (GPCRs), ion channels, membrane transporters, and cell adhesion molecules.

  9. Quantum chaos on a critical Fermi surface.

    PubMed

    Patel, Aavishkar A; Sachdev, Subir

    2017-02-21

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  10. Quantum chaos on a critical Fermi surface

    PubMed Central

    Patel, Aavishkar A.

    2017-01-01

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of N species of fermions at nonzero density coupled to a U(1) gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of N, the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details. PMID:28174270

  11. Dynamic Land Surface Classifcations using Microwave Frequencies

    NASA Astrophysics Data System (ADS)

    Jackson, H.; Tian, Y.; Peters-Lidard, C. D.; Harrison, K. W.

    2014-12-01

    Land surface emissivity in microwave frequencies is critical to the remote sensing of soil moisture, precipitation, and vegetation. Different land surfaces have different spectral signatures in the microwave portions of the electromagnetic spectrum. Their spatial and temporal behaviors are also highly variable. These properties are yet not well understood in microwave frequencies, despite their capability in detecting water-related variables in the atmosphere and land surface. A classification scheme was developed to stratify the Earth's land surfaces based on their seasonally dynamic microwave signatures. An unsupervised clustering approach was used identify and distinguish data groupings along two microwave based indicies. Land surface data clusters were mapped to determine their spatial relationships to known land cover groupings. Differences in land surface clusters were analyzed in their spatial consistency and their direction and magnitude of land surface change. It was found that vegetation and topography were the predominant contributors to change between seasons. Land surface extremes of sandy desert and closed canopy tropical forest displayed minimal intra-annual variability while transitional zones, such as the Sahel and North American temperate forests, exhibited the most variability. Distinct microwave signatures varied between seasons along a latittudinal gradient. Overall variability in land surface types increased at high lattitudes. This classification will help inform research studies maniputlating the microwave frequencies of the electromagnetic spectrum to better characterize land surface dynamics, and will be very useful in the validation of radiative transfer models and quantification of uncertainty in global precipitation monitoring.

  12. Dynamics and Thermodynamics beyond the critical point

    PubMed Central

    Gorelli, F. A.; Bryk, T.; Krisch, M.; Ruocco, G.; Santoro, M.; Scopigno, T.

    2013-01-01

    Sudden changes in the dynamical properties of a supercritical fluid model have been found as a function of pressure and temperature (T/Tc = 2–5 and P/Pc = 10–103), striving with the notion of a single phase beyond the critical point established by thermodynamics. The sound propagation in the Terahertz frequency region reveals a sharp dynamic crossover between the gas like and the liquid like regimes along several isotherms, which involves, at sufficiently low densities, the interplay between purely acoustic waves and heat waves. Such a crossover allows one to determine a dynamic line in the phase diagram which exhibits a very tight correlation with a number of thermodynamic observables, showing that the supercritical state is remarkably more complex than thought so far. PMID:23383373

  13. The ising model on the dynamical triangulated random surface

    SciTech Connect

    Aleinov, I.D.; Migelal, A.A.; Zmushkow, U.V. )

    1990-04-20

    The critical properties of Ising model on the dynamical triangulated random surface embedded in D-dimensional Euclidean space are investigated. The strong coupling expansion method is used. The transition to thermodynamical limit is performed by means of continuous fractions.

  14. Surface and Near Surface Dynamics on Phobos

    NASA Astrophysics Data System (ADS)

    Hamelin, M.

    2008-12-01

    Phobos as a few small satellites in the solar system is orbiting around its primary inside the Roche limit. Therefore the surface material is loosely bounded and easily ejected by impactors. Whereas dynamics in the close vicinity of Phobos has been studied for both geophysical and navigation reasons, the dynamics on the surface itself has not been studied to the same extent. The gravitational field used here is the ellipsoidal model of Davis, 1981, that describes as well the past and future Phobos as it gets closer to Mars. We look at the trajectory of a test mass for any initial position and velocity. It can exhibit an unusual shape: for some initial positions a gliding test mass released with zero velocity can take off over some distance! Generally the trajectories are not 'down hill' as the motion is strongly dependent on the velocity. We discuss the consequences for material transport on or close to the surface, with in particular the possibility that some of the Phobos groves could have been dug out by rolling blocks.

  15. Quantum chaos on a critical Fermi surface

    NASA Astrophysics Data System (ADS)

    Patel, Aavishkar A.; Sachdev, Subir

    2017-02-01

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of NN species of fermions at nonzero density coupled to a U(1)U(1) gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of NN, the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  16. Dynamical Response near Quantum Critical Points

    NASA Astrophysics Data System (ADS)

    Lucas, Andrew; Gazit, Snir; Podolsky, Daniel; Witczak-Krempa, William

    2017-02-01

    We study high-frequency response functions, notably the optical conductivity, in the vicinity of quantum critical points (QCPs) by allowing for both detuning from the critical coupling and finite temperature. We consider general dimensions and dynamical exponents. This leads to a unified understanding of sum rules. In systems with emergent Lorentz invariance, powerful methods from quantum field theory allow us to fix the high-frequency response in terms of universal coefficients. We test our predictions analytically in the large-N O (N ) model and using the gauge-gravity duality and numerically via quantum Monte Carlo simulations on a lattice model hosting the interacting superfluid-insulator QCP. In superfluid phases, interacting Goldstone bosons qualitatively change the high-frequency optical conductivity and the corresponding sum rule.

  17. Surface structure determines dynamic wetting

    PubMed Central

    Wang, Jiayu; Do-Quang, Minh; Cannon, James J.; Yue, Feng; Suzuki, Yuji; Amberg, Gustav; Shiomi, Junichiro

    2015-01-01

    Liquid wetting of a surface is omnipresent in nature and the advance of micro-fabrication and assembly techniques in recent years offers increasing ability to control this phenomenon. Here, we identify how surface roughness influences the initial dynamic spreading of a partially wetting droplet by studying the spreading on a solid substrate patterned with microstructures just a few micrometers in size. We reveal that the roughness influence can be quantified in terms of a line friction coefficient for the energy dissipation rate at the contact line, and that this can be described in a simple formula in terms of the geometrical parameters of the roughness and the line-friction coefficient of the planar surface. We further identify a criterion to predict if the spreading will be controlled by this surface roughness or by liquid inertia. Our results point to the possibility of selectively controlling the wetting behavior by engineering the surface structure. PMID:25683872

  18. Animal population dynamics: Identification of critical components

    USGS Publications Warehouse

    Emlen, J.M.; Pikitch, E.K.

    1989-01-01

    There is a growing interest in the use of population dynamics models in environmental risk assessment and the promulgation of environmental regulatory policies. Unfortunately, because of species and areal differences in the physical and biotic influences on population dynamics, such models must almost inevitably be both complex and species- or site-specific. Given the emormous variety of species and sites of potential concern, this fact presents a problem; it simply is not possible to construct models for all species and circumstances. Therefore, it is useful, before building predictive population models, to discover what input parameters are of critical importance to the desired output. This information should enable the construction of simpler and more generalizable models. As a first step, it is useful to consider population models as composed to two, partly separable classes, one comprising the purely mechanical descriptors of dynamics from given demographic parameter values, and the other describing the modulation of the demographic parameters by environmental factors (changes in physical environment, species interactions, pathogens, xenobiotic chemicals). This division permits sensitivity analyses to be run on the first of these classes, providing guidance for subsequent model simplification. We here apply such a sensitivity analysis to network models of mammalian and avian population dynamics.

  19. Dynamics and conductivity near quantum criticality

    NASA Astrophysics Data System (ADS)

    Gazit, Snir; Podolsky, Daniel; Auerbach, Assa; Arovas, Daniel P.

    2013-12-01

    Relativistic O(N) field theories are studied near the quantum-critical point in two space dimensions. We compute dynamical correlations by large-scale Monte Carlo simulations and numerical analytic continuation. In the ordered side, the scalar spectral function exhibits a universal peak at the Higgs mass. For N=3 and 4, we confirm its ω3 rise at low frequency. On the disordered side, the spectral function exhibits a sharp gap. For N=2, the dynamical conductivity rises above a threshold at the Higgs mass (density gap), in the superfluid (Mott insulator) phase. For charged bosons (Josephson arrays), the power-law rise above the Higgs mass increases from two to four. Approximate charge-vortex duality is reflected in the ratio of imaginary conductivities on either side of the transition. We determine the critical conductivity to be σc*=0.3(±0.1)×4e2/h and describe a generalization of the worm algorithm to N>2. We use a singular value decomposition error analysis for the numerical analytic continuation.

  20. Static and Dynamic Criticality: Are They Different?

    SciTech Connect

    Cullen, D E; Clouse, C J; Procassini, R; Little, R C

    2003-12-12

    Let us start by stating that this paper does not contain anything new. It only contains material that has been known for decades, but which is periodically forgotten. As such this paper is intended merely to refresh people's memories. We will also mention that this paper is an example of the occasional discrepancy between textbook methodologies and real world applications, in the sense that the conclusions reached here contradict what it says in most textbooks, i.e., most textbooks incorrectly interpret the methods presented here, particularly with respect to the use of importance sampling to maintain population control. This paper is not intended as a general tutorial on criticality calculations. It is intended only to clarify the accuracy of various methods for solving criticality problems, such as a true time dependent dynamic calculation, versus an alpha or K static calculation. In particular, we address the long standing controversy between users of the TART code [1] with the dynamic method, and users of the MCNP code [2] with the alpha static method. In this paper we will prove which methods are accurate and inaccurate.

  1. Critical Surface Cleaning and Verification Alternatives

    NASA Technical Reports Server (NTRS)

    Melton, Donald M.; McCool, A. (Technical Monitor)

    2000-01-01

    As a result of federal and state requirements, historical critical cleaning and verification solvents such as Freon 113, Freon TMC, and Trichloroethylene (TCE) are either highly regulated or no longer 0 C available. Interim replacements such as HCFC 225 have been qualified, however toxicity and future phase-out regulations necessitate long term solutions. The scope of this project was to qualify a safe and environmentally compliant LOX surface verification alternative to Freon 113, TCE and HCFC 225. The main effort was focused on initiating the evaluation and qualification of HCFC 225G as an alternate LOX verification solvent. The project was scoped in FY 99/00 to perform LOX compatibility, cleaning efficiency and qualification on flight hardware.

  2. Critical heat flux maxima during boiling crisis on textured surfaces

    NASA Astrophysics Data System (ADS)

    Dhillon, Navdeep Singh; Buongiorno, Jacopo; Varanasi, Kripa K.

    2015-09-01

    Enhancing the critical heat flux (CHF) of industrial boilers by surface texturing can lead to substantial energy savings and global reduction in greenhouse gas emissions, but fundamentally this phenomenon is not well understood. Prior studies on boiling crisis indicate that CHF monotonically increases with increasing texture density. Here we report on the existence of maxima in CHF enhancement at intermediate texture density using measurements on parametrically designed plain and nano-textured micropillar surfaces. Using high-speed optical and infrared imaging, we study the dynamics of dry spot heating and rewetting phenomena and reveal that the dry spot heating timescale is of the same order as that of the gravity and liquid imbibition-induced dry spot rewetting timescale. Based on these insights, we develop a coupled thermal-hydraulic model that relates CHF enhancement to rewetting of a hot dry spot on the boiling surface, thereby revealing the mechanism governing the hitherto unknown CHF enhancement maxima.

  3. Critical heat flux maxima during boiling crisis on textured surfaces.

    PubMed

    Dhillon, Navdeep Singh; Buongiorno, Jacopo; Varanasi, Kripa K

    2015-09-08

    Enhancing the critical heat flux (CHF) of industrial boilers by surface texturing can lead to substantial energy savings and global reduction in greenhouse gas emissions, but fundamentally this phenomenon is not well understood. Prior studies on boiling crisis indicate that CHF monotonically increases with increasing texture density. Here we report on the existence of maxima in CHF enhancement at intermediate texture density using measurements on parametrically designed plain and nano-textured micropillar surfaces. Using high-speed optical and infrared imaging, we study the dynamics of dry spot heating and rewetting phenomena and reveal that the dry spot heating timescale is of the same order as that of the gravity and liquid imbibition-induced dry spot rewetting timescale. Based on these insights, we develop a coupled thermal-hydraulic model that relates CHF enhancement to rewetting of a hot dry spot on the boiling surface, thereby revealing the mechanism governing the hitherto unknown CHF enhancement maxima.

  4. Critical heat flux maxima during boiling crisis on textured surfaces

    PubMed Central

    Dhillon, Navdeep Singh; Buongiorno, Jacopo; Varanasi, Kripa K.

    2015-01-01

    Enhancing the critical heat flux (CHF) of industrial boilers by surface texturing can lead to substantial energy savings and global reduction in greenhouse gas emissions, but fundamentally this phenomenon is not well understood. Prior studies on boiling crisis indicate that CHF monotonically increases with increasing texture density. Here we report on the existence of maxima in CHF enhancement at intermediate texture density using measurements on parametrically designed plain and nano-textured micropillar surfaces. Using high-speed optical and infrared imaging, we study the dynamics of dry spot heating and rewetting phenomena and reveal that the dry spot heating timescale is of the same order as that of the gravity and liquid imbibition-induced dry spot rewetting timescale. Based on these insights, we develop a coupled thermal-hydraulic model that relates CHF enhancement to rewetting of a hot dry spot on the boiling surface, thereby revealing the mechanism governing the hitherto unknown CHF enhancement maxima. PMID:26346098

  5. Criticality in a dynamic mixed system.

    PubMed

    Shnirman, M G; Blanter, E M

    2001-11-01

    We suggest a dynamic generalization of the simplest static hierarchical mixed model introduced by Shnirman and Blanter [Phys. Rev. Lett. 81, 5445 (1998); Phys. Rev. E. 60, 5111 (1998). We show that the stationary solution of the dynamic mixed model (DMM) demonstrates, in general, a linear form of the magnitude-frequency relation and may be considered a self-organized critical system. The dynamic mixed model demonstrates three principal kinds of system behavior: stability, catastrophe, and scale invariance. We show that the catastrophic area exists for all parameters of the mixture, and obtain three analytical expressions for boundary conditions of the stability and the scale invariance domains. As in the static model scale invariance appears as a result of a strong heterogeneity of the mixture. We describe how the magnitude-frequency relation reflects parameters of the heterogeneity and healing conditions for different domains of system behavior. Deviation of the DMM from the static mixed model and possible applications to earthquake prediction are discussed.

  6. Critical Surface Tension, Critical Surface Energy and Parachor of MnSO3 Thin Film

    NASA Astrophysics Data System (ADS)

    Kariper, I. A.

    2016-02-01

    This study examines the critical surface energy of manganese sulfite (MnSO3) crystalline thin film, produced via chemical bath deposition (CBD) on substrates. In addition, parachor, which is an important parameter of chemical physics, and its relationship with grain size, film thickness, etc., has been investigated for thin films. For this purpose, MnSO3 thin films were deposited at room temperature using different deposition times. Structural properties of the films, such as film thickness and average grain size, were examined using X-ray diffraction; film thickness and surface properties were measured by and atomic force microscope; and critical surface tension of MnSO3 thin films was measured with Optical Tensiometer and calculated using Zisman method. The results showed that critical surface tension and parachor of the films have varied with average grain size and film thickness. Critical surface tension was calculated as 32.97, 24.55, 21.03 and 12.76mN/m for 14.66, 30.84, 37.07 and 44.56nm grain sizes, respectively. Film thickness and average grain size have been increased with the deposition time and they were found to be negatively correlated with surface tension and parachor. The relationship between film thickness and parachor was found as P=-0.1856t+183.45; whereas the relationship between average grain size and parachor was found as P=-0.8911D+150.52. We also showed the relationships between parachor and some thin films parameters.

  7. Critical dynamic viscosities in a binary mixture

    NASA Astrophysics Data System (ADS)

    Izumi, Y.; Sawano, H.; Sato, H.; Miyake, Y.; Kono, R.; Yoshizaki, H.

    1989-03-01

    Ultrasonic shear measurements were conducted on polystyrene-cyclohexane solutions at 3, 51, and 252 kHz using the crystal fork and torsion methods. The real and imaginary parts of the complex shear modulus above the critical point are compared with modified theoretical expressions derived within the framework of the decoupled-mode theory. For this comparison, a background part was assumed to be described by a scaling form proposed by de Gennes. Numerical analysis of the data shows a satisfactory agreement between the theory and the experiments for ultrasonic shear data over a wide range of reduced frequency ω ... In addition, it is shown that the description of the simple viscosity dynamical scaling function is broken at a high-frequency limit.

  8. Dynamical Modeling of Surface Tension

    NASA Technical Reports Server (NTRS)

    Brackbill, Jeremiah U.; Kothe, Douglas B.

    1996-01-01

    In a recent review it is said that free-surface flows 'represent some of the difficult remaining challenges in computational fluid dynamics'. There has been progress with the development of new approaches to treating interfaces, such as the level-set method and the improvement of older methods such as the VOF method. A common theme of many of the new developments has been the regularization of discontinuities at the interface. One example of this approach is the continuum surface force (CSF) formulation for surface tension, which replaces the surface stress given by Laplace's equation by an equivalent volume force. Here, we describe how CSF formulation might be made more useful. Specifically, we consider a derivation of the CSF equations from a minimization of surface energy as outlined by Jacqmin (1996). This reformulation suggests that if one eliminates the computation of curvature in terms of a unit normal vector, parasitic currents may be eliminated. For this reformulation to work, it is necessary that transition region thickness be controlled. Various means for this, in addition to the one discussed by Jacqmin (1996), are discussed.

  9. Well-defined critical association concentration and rapid adsorption at the air/water interface of a short amphiphilic polymer, amphipol A8-35: a study by Förster resonance energy transfer and dynamic surface tension measurements.

    PubMed

    Giusti, Fabrice; Popot, Jean-Luc; Tribet, Christophe

    2012-07-17

    Amphipols (APols) are short amphiphilic polymers designed to handle membrane proteins (MPs) in aqueous solutions as an alternative to small surfactants (detergents). APols adsorb onto the transmembrane, hydrophobic surface of MPs, forming small, water-soluble complexes, in which the protein is biochemically stabilized. At variance with MP/detergent complexes, MP/APol ones remain stable even at extreme dilutions. Pure APol solutions self-associate into well-defined micelle-like globules comprising a few APol molecules, a rather unusual behavior for amphiphilic polymers, which typically form ill-defined assemblies. The best characterized APol to date, A8-35, is a random copolymer of acrylic acid, isopropylacrylamide, and octylacrylamide. In the present work, the concentration threshold for self-association of A8-35 in salty buffer (NaCl 100 mM, Tris/HCl 20 mM, pH 8.0) has been studied by Förster resonance energy transfer (FRET) measurements and tensiometry. In a 1:1 mol/mol mixture of APols grafted with either rhodamine or 7-nitro-1,2,3-benzoxadiazole, the FRET signal as a function of A8-35 concentration is essentially zero below a threshold concentration of 0.002 g·L(-1) and increases linearly with concentration above this threshold. This indicates that assembly takes place in a narrow concentration interval around 0.002 g·L(-1). Surface tension measurements decreases regularly with concentration until a threshold of ca. 0.004 g·L(-1), beyond which it reaches a plateau at ca. 30 mN·m(-1). Within experimental uncertainties, the two techniques thus yield a comparable estimate of the critical self-assembly concentration. The kinetics of variation of the surface tension was analyzed by dynamic surface tension measurements in the time window 10 ms-100 s. The rate of surface tension decrease was similar in solutions of A8-35 and of the anionic surfactant sodium dodecylsulfate when both compounds were at a similar molar concentration of n-alkyl moieties. Overall, the

  10. Surface Dynamics and Roughening in Metal Nanowires

    NASA Astrophysics Data System (ADS)

    Zhang, C. H.; Stafford, C. A.; Goldstein, R. E.; Kassubek, F.

    2002-03-01

    Surface phonons and surface self-diffusion of atoms in metal nanowires are investigated in a continuum approach (jellium model). Electron-shell effects in such a system lead to islands of stability: regions in the (R_0,T) plane where arbitrarily long wires are stable with respect to small perturbations, R0 being the mean radius of the wire and T the temperature. We find that inertial dynamics always dominate over diffusion as one approaches the stability boundary. On the stability boundary, the surface of the nanowire becomes rough at any finite temperature, but remains smooth at T=0. The critical exponents describing this roughening transition are different than those for two-dimensional surfaces, due to the different dispersion relation for surface waves. We also find a novel reentrant roughening transition: for certain ranges of R_0, nanowires are stable within a temperature interval T_c1surfaces roughen exponentially, dominated by the maximum instability mode q_m, and finally will be trapped into a state with a permanent deformation if qm R_0>1. Research supported in part by NSF grant DMR0072703 and by an award from Research Corporation.

  11. Dynamics of Nanostructures at Surfaces

    SciTech Connect

    Schmid, Andreas K.

    2001-02-28

    Currently, much effort is being devoted to the goal of achieving useful nanotechnologies, which depend on the ability to control and manipulate things on a very small scale. One promising approach to the construction of nanostructures is 'self-assembly', which means that under suitable conditions desired nanostructures might form automatically due to physical and chemical forces. Remarkably, the forces controlling such self-assembly mechanisms are only poorly understood, even though highly successful examples of self-assembly are known in nature (e.g., complex biochemical machinery regularly self-assembles in the conditions inside living cells). This talk will highlight basic measurements of fundamental forces governing the dynamics of nanostructures at prototypical metal surfaces. We use advanced surface microscopy techniques to track the motions of very small structures in real time and up to atomic resolution. One classic example of self-organized nanostructures are networks of surface dislocations (linear crystal defects). The direct observation of thermally activated atomic motions of dislocations in a reconstructed gold surface allows us to measure the forces stabilizing the remarkable long-range order of this nanostructure. In another example, the rapid migration of nano-scale tin crystals deposited on a pure copper surface was traced to an atomic repulsion between tin atoms absorbed on the crystal surface and bronze alloy formed in the footprint of the tin crystals. It is intriguing to consider the clusters as simple chemo-mechanical energy transducers, essentially tiny linear motors built of 100,000 Sn atoms. We can support this view by providing estimates of the power and energy-efficiency of these nano-motors.

  12. Critical surface for explosions of rotational core-collapse supernovae

    SciTech Connect

    Iwakami, Wakana; Nagakura, Hiroki; Yamada, Shoichi

    2014-09-20

    The effect of rotation on the explosion of core-collapse supernovae is investigated systematically in three-dimensional simulations. In order to obtain the critical conditions for explosion as a function of mass accretion rate, neutrino luminosity, and specific angular momentum, rigidly rotating matter was injected from the outer boundary with an angular momentum, which is increased every 500 ms. It is found that there is a critical value of the specific angular momentum, above which the standing shock wave revives, for a given combination of mass accretion rate and neutrino luminosity, i.e., an explosion can occur by rotation even if the neutrino luminosity is lower than the critical value for a given mass accretion rate in non-rotational models. The coupling of rotation and hydrodynamical instabilities plays an important role in characterizing the dynamics of shock revival for the range of specific angular momentum that are supposed to be realistic. Contrary to expectations from past studies, the most rapidly expanding direction of the shock wave is not aligned with the rotation axis. Being perpendicular to the rotation axis on average, it can be oriented in various directions. Its dispersion is small when the spiral mode of the standing accretion shock instability (SASI) governs the dynamics, while it is large when neutrino-driven convection is dominant. As a result of the comparison between two-dimensional and three-dimensional rotational models, it is found that m ≠ 0 modes of neutrino-driven convection or SASI are important for shock revival around the critical surface.

  13. Bioinspired, dynamic, structured surfaces for biofilm prevention

    NASA Astrophysics Data System (ADS)

    Epstein, Alexander K.

    Bacteria primarily exist in robust, surface-associated communities known as biofilms, ubiquitous in both natural and anthropogenic environments. Mature biofilms resist a wide range of biocidal treatments and pose persistent pathogenic threats. Treatment of adherent biofilm is difficult, costly, and, in medical systems such as catheters, frequently impossible. Adding to the challenge, we have discovered that biofilm can be both impenetrable to vapors and extremely nonwetting, repelling even low surface tension commercial antimicrobials. Our study shows multiple contributing factors, including biochemical components and multiscale reentrant topography. Reliant on surface chemistry, conventional strategies for preventing biofilm only transiently affect attachment and/or are environmentally toxic. In this work, we look to Nature's antifouling solutions, such as the dynamic spiny skin of the echinoderm, and we develop a versatile surface nanofabrication platform. Our benchtop approach unites soft lithography, electrodeposition, mold deformation, and material selection to enable many degrees of freedom—material, geometric, mechanical, dynamic—that can be programmed starting from a single master structure. The mechanical properties of the bio-inspired nanostructures, verified by AFM, are precisely and rationally tunable. We examine how synthetic dynamic nanostructured surfaces control the attachment of pathogenic biofilms. The parameters governing long-range patterning of bacteria on high-aspect-ratio (HAR) nanoarrays are combinatorially elucidated, and we discover that sufficiently low effective stiffness of these HAR arrays mechanoselectively inhibits ˜40% of Pseudomonas aeruginosa biofilm attachment. Inspired by the active echinoderm skin, we design and fabricate externally actuated dynamic elastomer surfaces with active surface microtopography. We extract from a large parameter space the critical topographic length scales and actuation time scales for achieving

  14. Protein hydration dynamics in solution: a critical survey.

    PubMed Central

    Halle, Bertil

    2004-01-01

    The properties of water in biological systems have been studied for well over a century by a wide range of physical techniques, but progress has been slow and erratic. Protein hydration--the perturbation of water structure and dynamics by the protein surface--has been a particularly rich source of controversy and confusion. Our aim here is to critically examine central concepts in the description of protein hydration, and to assess the experimental basis for the current view of protein hydration, with the focus on dynamic aspects. Recent oxygen-17 magnetic relaxation dispersion (MRD) experiments have shown that the vast majority of water molecules in the protein hydration layer suffer a mere twofold dynamic retardation compared with bulk water. The high mobility of hydration water ensures that all thermally activated processes at the protein-water interface, such as binding, recognition and catalysis, can proceed at high rates. The MRD-derived picture of a highly mobile hydration layer is consistent with recent molecular dynamics simulations, but is incompatible with results deduced from intermolecular nuclear Overhauser effect spectroscopy, dielectric relaxation and fluorescence spectroscopy. It is also inconsistent with the common view of hydration effects on protein hydrodynamics. Here, we show how these discrepancies can be resolved. PMID:15306377

  15. Conserved nonlocal dynamics and critical behavior of uranium ferromagnetic superconductors.

    PubMed

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K

    2017-01-01

    A recent theoretical study [Phys. Rev. Lett. 112, 037202 (2014)10.1103/PhysRevLett.112.037202] has revealed that systems such as uranium ferromagnetic superconductors obey conserved dynamics. To capture the critical behavior near the paramagnetic to ferromagnetic phase transition of these compounds, we study the conserved critical dynamics of a nonlocal Ginzburg-Landau model. A dynamic renormalization-group calculation at one-loop order yields the critical indices in the leading order of ε=d_{c}-d, where d_{c}=4-2ρ is the upper critical dimension, with ρ an exponent in the nonlocal interaction. The predicted static critical exponents are found to be comparable with the available experimentally observed critical exponents for strongly uniaxial uranium ferromagnetic superconductors. The corresponding dynamic exponent z and linewidth exponent w are found to be z=4-ρε/4+O(ε^{2}) and w=1+ρ+3ε/4+O(ε^{2}).

  16. Conserved nonlocal dynamics and critical behavior of uranium ferromagnetic superconductors

    NASA Astrophysics Data System (ADS)

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K.

    2017-01-01

    A recent theoretical study [Phys. Rev. Lett. 112, 037202 (2014), 10.1103/PhysRevLett.112.037202] has revealed that systems such as uranium ferromagnetic superconductors obey conserved dynamics. To capture the critical behavior near the paramagnetic to ferromagnetic phase transition of these compounds, we study the conserved critical dynamics of a nonlocal Ginzburg-Landau model. A dynamic renormalization-group calculation at one-loop order yields the critical indices in the leading order of ɛ =dc-d , where dc=4 -2 ρ is the upper critical dimension, with ρ an exponent in the nonlocal interaction. The predicted static critical exponents are found to be comparable with the available experimentally observed critical exponents for strongly uniaxial uranium ferromagnetic superconductors. The corresponding dynamic exponent z and linewidth exponent w are found to be z =4 -ρ ɛ /4 +O (ɛ2) and w =1 +ρ +3 ɛ /4 +O (ɛ2) .

  17. Dynamic contact angle measurements on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Hyun; Kavehpour, H. Pirouz; Rothstein, Jonathan P.

    2015-03-01

    In this paper, the dynamic advancing and receding contact angles of a series of aqueous solutions were measured on a number of hydrophobic and superhydrophobic surfaces using a modified Wilhelmy plate technique. Superhydrophobic surfaces are hydrophobic surfaces with micron or nanometer sized surface roughness. These surfaces have very large static advancing contact angles and little static contact angle hysteresis. In this study, the dynamic advancing and dynamic receding contact angles on superhydrophobic surfaces were measured as a function of plate velocity and capillary number. The dynamic contact angles measured on a smooth hydrophobic Teflon surface were found to obey the scaling with capillary number predicted by the Cox-Voinov-Tanner law, θD3 ∝ Ca. The response of the dynamic contact angle on the superhydrophobic surfaces, however, did not follow the same scaling law. The advancing contact angle was found to remain constant at θA = 160∘, independent of capillary number. The dynamic receding contact angle measurements on superhydrophobic surfaces were found to decrease with increasing capillary number; however, the presence of slip on the superhydrophobic surface was found to result in a shift in the onset of dynamic contact angle variation to larger capillary numbers. In addition, a much weaker dependence of the dynamic contact angle on capillary number was observed for some of the superhydrophobic surfaces tested.

  18. Partial dynamical symmetry at critical points of quantum phase transitions.

    PubMed

    Leviatan, A

    2007-06-15

    We show that partial dynamical symmetries can occur at critical points of quantum phase transitions, in which case underlying competing symmetries are conserved exactly by a subset of states, and mix strongly in other states. Several types of partial dynamical symmetries are demonstrated with the example of critical-point Hamiltonians for first- and second-order transitions in the framework of the interacting boson model, whose dynamical symmetries correspond to different shape phases in nuclei.

  19. Generalized dynamic scaling for quantum critical relaxation in imaginary time.

    PubMed

    Zhang, Shuyi; Yin, Shuai; Zhong, Fan

    2014-10-01

    We study the imaginary-time relaxation critical dynamics of a quantum system with a vanishing initial correlation length and an arbitrary initial order parameter M0. We find that in quantum critical dynamics, the behavior of M0 under scale transformations deviates from a simple power law, which was proposed for very small M0 previously. A universal characteristic function is then suggested to describe the rescaled initial magnetization, similar to classical critical dynamics. This characteristic function is shown to be able to describe the quantum critical dynamics in both short- and long-time stages of the evolution. The one-dimensional transverse-field Ising model is employed to numerically determine the specific form of the characteristic function. We demonstrate that it is applicable as long as the system is in the vicinity of the quantum critical point. The universality of the characteristic function is confirmed by numerical simulations of models belonging to the same universality class.

  20. Stochastic Dynamics and Critical Phenomena in Permafrost Models

    NASA Astrophysics Data System (ADS)

    Sudakov, I.

    2016-12-01

    There is an estimated 400 PgC of CH4 stored as frozen gas hydrates under boreal permafrost, and it is thought that permafrost melting could release a considerable amount of CH4 to the atmosphere. Methane emissions from tundra permafrost lakes are a significant positive feedback to the atmosphere in a changing climate. The evolution of tundra lakes on the surface of boreal permafrost is a complex stochastic process that is important in climate modeling. We propose a model (based on the Fokker-Planck equation) describing the stochastic dynamics of tundra lakes. We use this model to compute the methane emission generated by tundra permafrost lakes. This model facilitates investigation of critical phenomena in Earth's cryosphere, and methane emission from permafrost in particular.

  1. Dynamic Defrosting on Nanostructured Superhydrophobic Surfaces

    SciTech Connect

    Boreyko, Jonathan B.; Srijanto, Bernadeta R.; Nguyen, Trung Dac; Vega, Carlos; Fuentes-Cabrera, Miguel; Collier, C. Patrick

    2013-07-03

    Water suspended on chilled superhydrophobic surfaces exhibits delayed freezing; however, the interdrop growth of frost through subcooled condensate forming on the surface seems unavoidable in humid environments. It is therefore of great practical importance to determine whether facile defrosting is possible on superhydrophobic surfaces. Here in this paper, we report that nanostructured superhydrophobic surfaces promote the growth of frost in a suspended Cassie state, enabling its dynamic removal upon partial melting at low tilt angles (<15°). The dynamic removal of the melting frost occurred in two stages: spontaneous dewetting followed by gravitational mobilization. This dynamic defrosting phenomenon is driven by the low contact angle hysteresis of the defrosted meltwater relative to frost on microstructured superhydrophobic surfaces, which forms in the impaled Wenzel state. Dynamic defrosting on nanostructured superhydrophobic surfaces minimizes the time, heat, and gravitational energy required to remove frost from the surface, and is of interest for a variety of systems in cold and humid environments.

  2. Dynamic critical phenomena from spectral functions on the lattice

    NASA Astrophysics Data System (ADS)

    Berges, Jürgen; Schlichting, Sören; Sexty, Dénes

    2010-06-01

    We investigate spectral functions in the vicinity of the critical temperature of a second-order phase transition. Since critical phenomena in quantum field theories are governed by classical dynamics, universal properties can be computed using real-time lattice simulations. For the example of a relativistic single-component scalar field theory in 2+1 dimensions, we compute the spectral function described by universal scaling functions and extract the dynamic critical exponent z. Together with exactly known static properties of this theory, we obtain a verification from first principles that the relativistic theory is well described by the dynamic universality class of relaxational models with conserved density (Model C).

  3. Superconducting quantum criticality of topological surface states at three loops

    NASA Astrophysics Data System (ADS)

    Zerf, Nikolai; Lin, Chien-Hung; Maciejko, Joseph

    2016-11-01

    The semimetal-superconductor quantum phase transition on the two-dimensional (2D) surface of a 3D topological insulator is conjectured to exhibit an emergent N =2 supersymmetry, based on a one-loop renormalization group (RG) analysis in the ɛ expansion. We provide additional support for this conjecture by performing a three-loop RG analysis and showing that the supersymmetric fixed point found at this order survives the extrapolation to 2D. We compute critical exponents to order ɛ3, obtaining the more accurate value ν ≈0.985 for the correlation length exponent and confirming that the fermion and boson anomalous dimensions remain unchanged beyond one loop, as expected from non-renormalization theorems in supersymmetric theories. We further couple the system to a dynamical U(1) gauge field, and argue that the transition becomes fluctuation-induced first order in an appropriate type-I regime. We discuss implications of this result for quantum phase transitions between certain symmetry-preserving correlated surface states of 3D topological insulators.

  4. Critical dynamics of classical systems under slow quench

    NASA Astrophysics Data System (ADS)

    Priyanka; Jain, Kavita

    2016-10-01

    We study the slow quench dynamics of a one-dimensional nonequilibrium lattice gas model which exhibits a phase transition in the stationary state between a fluid phase with homogeneously distributed particles and a jammed phase with a macroscopic hole cluster. Our main result is that in the critical region (i.e., at the critical point and in its vicinity) where the dynamics are assumed to be frozen in the standard Kibble-Zurek argument, the defect density exhibits an algebraic decay in the inverse annealing rate with an exponent that can be understood using critical coarsening dynamics. However, in a part of the critical region in the fluid phase, the standard Kibble-Zurek scaling holds. We also find that when the slow quench occurs deep into the jammed phase, the defect density behavior is explained by the rapid quench dynamics in this phase.

  5. Crossover of critical Casimir forces between different surface universality classes.

    PubMed

    Mohry, T F; Maciołek, A; Dietrich, S

    2010-06-01

    In confined systems near a continuous phase transition the long-ranged fluctuations of the corresponding order parameter are subject to boundary conditions. These constraints result in so-called critical Casimir forces acting as effective forces on the confining surfaces. For systems belonging to the Ising bulk universality class corresponding to a scalar order parameter the critical Casimir force is studied for the film geometry in the crossover regime characterized by different surface fields at the two surfaces. The scaling function of the critical Casimir force is calculated within mean-field theory. Within our approach, the scaling functions of the critical Casimir force and of the order parameter profile for finite surface fields can be mapped by rescaling, except for a narrow crossover regime, onto the corresponding scaling function of the so-called normal fixed point of strong surface fields. In the crossover regime, the critical Casimir force as function of temperature exhibits more than one extremum and for certain ranges of surface field strengths it changes sign twice upon varying temperature. Monte Carlo simulation data obtained for a three-dimensional Ising film show similar trends. The sign of the critical Casimir force can be inferred from the comparison of the order parameter profiles in the film and in the semi-infinite geometry.

  6. Critical Casimir forces in colloidal suspensions on chemically patterned surfaces.

    PubMed

    Soyka, Florian; Zvyagolskaya, Olga; Hertlein, Christopher; Helden, Laurent; Bechinger, Clemens

    2008-11-14

    We investigate the behavior of colloidal particles immersed in a binary liquid mixture of water and 2,6-lutidine in the presence of a chemically patterned substrate. Close to the critical point of the mixture, the particles are subjected to critical Casimir interactions with force components normal and parallel to the surface. Because the strength and sign of these interactions can be tuned by variations in the surface properties and the mixtures temperature, critical Casimir forces allow the formation of highly ordered monolayers but also extend the use of colloids as model systems.

  7. Critical Casimir Forces in Colloidal Suspensions on Chemically Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Soyka, Florian; Zvyagolskaya, Olga; Hertlein, Christopher; Helden, Laurent; Bechinger, Clemens

    2008-11-01

    We investigate the behavior of colloidal particles immersed in a binary liquid mixture of water and 2,6-lutidine in the presence of a chemically patterned substrate. Close to the critical point of the mixture, the particles are subjected to critical Casimir interactions with force components normal and parallel to the surface. Because the strength and sign of these interactions can be tuned by variations in the surface properties and the mixtures temperature, critical Casimir forces allow the formation of highly ordered monolayers but also extend the use of colloids as model systems.

  8. Criticality in Dynamic Arrest: Correspondence between Glasses and Traffic

    NASA Astrophysics Data System (ADS)

    de Wijn, A. S.; Miedema, D. M.; Nienhuis, B.; Schall, P.

    2012-11-01

    Dynamic arrest is a general phenomenon across a wide range of dynamic systems including glasses, traffic flow, and dynamics in cells, but the universality of dynamic arrest phenomena remains unclear. We connect the emergence of traffic jams in a simple traffic flow model directly to the dynamic slowing down in kinetically constrained models for glasses. In kinetically constrained models, the formation of glass becomes a true (singular) phase transition in the limit T→0. Similarly, using the Nagel-Schreckenberg model to simulate traffic flow, we show that the emergence of jammed traffic acquires the signature of a sharp transition in the deterministic limit p→1, corresponding to overcautious driving. We identify a true dynamic critical point marking the onset of coexistence between free flowing and jammed traffic, and demonstrate its analogy to the kinetically constrained glass models. We find diverging correlations analogous to those at a critical point of thermodynamic phase transitions.

  9. Criticality in dynamic arrest: correspondence between glasses and traffic.

    PubMed

    de Wijn, A S; Miedema, D M; Nienhuis, B; Schall, P

    2012-11-30

    Dynamic arrest is a general phenomenon across a wide range of dynamic systems including glasses, traffic flow, and dynamics in cells, but the universality of dynamic arrest phenomena remains unclear. We connect the emergence of traffic jams in a simple traffic flow model directly to the dynamic slowing down in kinetically constrained models for glasses. In kinetically constrained models, the formation of glass becomes a true (singular) phase transition in the limit T→0. Similarly, using the Nagel-Schreckenberg model to simulate traffic flow, we show that the emergence of jammed traffic acquires the signature of a sharp transition in the deterministic limit p→1, corresponding to overcautious driving. We identify a true dynamic critical point marking the onset of coexistence between free flowing and jammed traffic, and demonstrate its analogy to the kinetically constrained glass models. We find diverging correlations analogous to those at a critical point of thermodynamic phase transitions.

  10. Critical Casimir forces between planar and crenellated surfaces.

    PubMed

    Tröndle, M; Harnau, L; Dietrich, S

    2015-06-03

    We study critical Casimir forces between planar walls and geometrically structured substrates within mean-field theory. As substrate structures, crenellated surfaces consisting of periodic arrays of rectangular crenels and merlons are considered. Within the widely used proximity force approximation, both the top surfaces of the merlons and the bottom surfaces of the crenels contribute to the critical Casimir force. However, for such systems the full, numerically determined critical Casimir forces deviate significantly from the pairwise addition formalism underlying the proximity force approximation. A first-order correction to the proximity force approximation is presented in terms of a step contribution arising from the critical Casimir interaction between a planar substrate and the right-angled steps of the merlons consisting of their upper and lower edges as well as their sidewalls.

  11. Can dynamical synapses produce true self-organized criticality?

    NASA Astrophysics Data System (ADS)

    Costa, Ariadne de Andrade; Copelli, Mauro; Kinouchi, Osame

    2015-06-01

    Neuronal networks can present activity described by power-law distributed avalanches presumed to be a signature of a critical state. Here we study a random-neighbor network of excitable cellular automata coupled by dynamical synapses. The model exhibits a very similar to conservative self-organized criticality (SOC) models behavior even with dissipative bulk dynamics. This occurs because in the stationary regime the model is conservative on average, and, in the thermodynamic limit, the probability distribution for the global branching ratio converges to a delta-function centered at its critical value. So, this non-conservative model pertain to the same universality class of conservative SOC models and contrasts with other dynamical synapses models that present only self-organized quasi-criticality (SOqC). Analytical results show very good agreement with simulations of the model and enable us to study the emergence of SOC as a function of the parametric derivatives of the stationary branching ratio.

  12. Experimental Observations of Dynamic Critical Phenomena in a Lipid Membrane

    NASA Astrophysics Data System (ADS)

    Honerkamp-Smith, Aurelia R.; Machta, Benjamin B.; Keller, Sarah L.

    2012-06-01

    Near a critical point, the time scale of thermally induced fluctuations diverges in a manner determined by the dynamic universality class. Experiments have verified predicted three-dimensional dynamic critical exponents in many systems, but similar experiments in two dimensions have been lacking for the case of conserved order parameter. Here we analyze the time-dependent correlation functions of a quasi-two-dimensional lipid bilayer in water to show that its critical dynamics agree with a recently predicted universality class. In particular, the effective dynamic exponent zeff crosses over from ˜2 to ˜3 as the correlation length of fluctuations exceeds a hydrodynamic length set by the membrane and bulk viscosities.

  13. CRITICAL SURFACE TENSION FOR SPREADING ON A LIQUID SUBSTRATE

    DTIC Science & Technology

    A plot of the initial spreading pressures (F sub ba) or initial spreading coefficients (S sub ba) against the surface tensions of a homologous series...of organic liquids b can be used to determine the critical surface tension for spreading on a second substrate liquid phase a. Straight-line...floating on liquid a, it can be applied to any liquid substrate, and it is applicable even when spreading does not lie within the range of surface tensions

  14. Criticality Characteristics of Current Oil Price Dynamics

    NASA Astrophysics Data System (ADS)

    Drożdż, S.; Kwapień, J.; Oświęcimka, P.

    2008-10-01

    Methodology that recently leads us to predict to an amazing accuracy the date (July 11, 2008) of reverse of the oil price up trend is briefly summarized and some further aspects of the related oil price dynamics elaborated. This methodology is based on the concept of discrete scale invariance whose finance-prediction-oriented variant involves such elements as log-periodic self-similarity, the universal preferred scaling factor λ≈2, and allows a phenomenon of the "super-bubble". From this perspective the present (as of August 22, 2008) violent - but still log-periodically decelerating - decrease of the oil prices is associated with the decay of such a "super-bubble" that has started developing about one year ago on top of the longer-term oil price increasing phase (normal bubble) whose ultimate termination is evaluated to occur in around mid 2010.

  15. Uncertainty and Sensitivity in Surface Dynamics Modeling

    NASA Astrophysics Data System (ADS)

    Kettner, Albert J.; Syvitski, James P. M.

    2016-05-01

    Papers for this special issue on 'Uncertainty and Sensitivity in Surface Dynamics Modeling' heralds from papers submitted after the 2014 annual meeting of the Community Surface Dynamics Modeling System or CSDMS. CSDMS facilitates a diverse community of experts (now in 68 countries) that collectively investigate the Earth's surface-the dynamic interface between lithosphere, hydrosphere, cryosphere, and atmosphere, by promoting, developing, supporting and disseminating integrated open source software modules. By organizing more than 1500 researchers, CSDMS has the privilege of identifying community strengths and weaknesses in the practice of software development. We recognize, for example, that progress has been slow on identifying and quantifying uncertainty and sensitivity in numerical modeling of earth's surface dynamics. This special issue is meant to raise awareness for these important subjects and highlight state-of-the-art progress.

  16. The Dynamic Surface Tension of Water

    PubMed Central

    2017-01-01

    The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m–1) than under equilibrium conditions (∼72 mN m–1) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments. PMID:28301160

  17. The Dynamic Surface Tension of Water.

    PubMed

    Hauner, Ines M; Deblais, Antoine; Beattie, James K; Kellay, Hamid; Bonn, Daniel

    2017-03-23

    The surface tension of water is an important parameter for many biological or industrial processes, and roughly a factor of 3 higher than that of nonpolar liquids such as oils, which is usually attributed to hydrogen bonding and dipolar interactions. Here we show by studying the formation of water drops that the surface tension of a freshly created water surface is even higher (∼90 mN m(-1)) than under equilibrium conditions (∼72 mN m(-1)) with a relaxation process occurring on a long time scale (∼1 ms). Dynamic adsorption effects of protons or hydroxides may be at the origin of this dynamic surface tension. However, changing the pH does not significantly change the dynamic surface tension. It also seems unlikely that hydrogen bonding or dipole orientation effects play any role at the relatively long time scale probed in the experiments.

  18. Dynamic contact interactions of fractal surfaces

    NASA Astrophysics Data System (ADS)

    Jana, Tamonash; Mitra, Anirban; Sahoo, Prasanta

    2017-01-01

    Roughness parameters and material properties have significant influence on the static and dynamic properties of a rough surface. In the present paper, fractal surface is generated using the modified two-variable Weierstrass-Mandelbrot function in MATLAB and the same is imported to ANSYS to construct the finite element model of the rough surface. The force-deflection relationship between the deformable rough fractal surface and a contacting rigid flat is studied by finite element analysis. For the dynamic analysis, the contacting system is represented by a single degree of freedom spring mass-damper-system. The static force-normal displacement relationship obtained from FE analysis is used to determine the dynamic characteristics of the rough surface for free, as well as for forced damped vibration using numerical methods. The influence of fractal surface parameters and the material properties on the dynamics of the rough surface is also analyzed. The system exhibits softening property for linear elastic surface and the softening nature increases with rougher topography. The softening nature of the system increases with increase in tangent modulus value. Above a certain value of yield strength the nature of the frequency response curve is observed to change its nature from softening to hardening.

  19. Antimicrobial activity of a formulation for the low temperature disinfection of critical and semi-critical medical equipment and surfaces.

    PubMed

    Raffo, Paolo; Salliez, A C; Collignon, Christian; Clementi, Massimo

    2007-10-01

    The antimicrobial activity of the disinfectant formulation UMONIUM38 (Isopropyl-tridecyl-dimethyl-ammonium; Huckert's International, Nivelles, Belgium) planned for the low temperature disinfection of critical and semi-critical medical equipment and surfaces was evaluated under clean and dirty experimental conditions (high and low concentrations of organic material). The formulation was obtained by a synergic combination of three different active compounds, two alcohols and a quaternary ammonium. The anti-mycobacterial (Mycobacterium avium and Mycobacterium terrae), and antiviral (Poliovirus type 1, Adenovirus type 5, hepatitis B virus, and human immunodeficiency virus type 1) activities of this formulation were addressed using suspension assays. In addition, surface assays were also used to test the antibacterial (Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Enterococcus hirae) and antimycotic (Candida albicans and Aspergillus niger) activities. The data document the dynamics of the antimicrobial activity under in vitro controlled conditions and highlight the relatively low influence of organic material on its activity.

  20. Surface critical behavior of the smoothly inhomogeneous Ising model

    NASA Astrophysics Data System (ADS)

    Burkhardt, Theodore W.; Guim, Ihnsouk

    1984-01-01

    We consider a semi-infinite two-dimensional Ising model with nearest-neighbor coupling constants that deviate from the bulk coupling by Am-y for large m, m being the distance from the edge. The case A<0 of couplings which are weaker near the surface has been discussed by Hilhorst and van Leeuwen. We report exact results for the boundary magnetization and boundary pair-correlation function when A>0. At the bulk critical temperature there is a rich variety of critical behavior in the A -y plane with both paramagnetic and ferromagnetic surface phases. Some of our results can be derived and generalized with simple scaling arguments.

  1. Universal short-time quantum critical dynamics in imaginary time

    NASA Astrophysics Data System (ADS)

    Yin, Shuai; Mai, Peizhi; Zhong, Fan

    2014-04-01

    We propose a scaling theory for the universal imaginary-time quantum critical dynamics for both short and long times. We discover that there exists a universal critical initial slip related to a small initial order parameter M0. In this stage, the order parameter M increases with the imaginary time τ as M ∝M0τθ with a universal initial-slip exponent θ. For the one-dimensional transverse-field Ising model, we estimate θ to be 0.373, which is markedly distinct from its classical counterpart. Apart from the local order parameter, we also show that the entanglement entropy exhibits universal behavior in the short-time region. As the critical exponents in the early stage and in equilibrium are identical, we apply the short-time dynamics method to determine quantum critical properties. The method is generally applicable in both the Landau-Ginzburg-Wilson paradigm and topological phase transitions.

  2. Gene expression dynamics in the macrophage exhibit criticality.

    PubMed

    Nykter, Matti; Price, Nathan D; Aldana, Maximino; Ramsey, Stephen A; Kauffman, Stuart A; Hood, Leroy E; Yli-Harja, Olli; Shmulevich, Ilya

    2008-02-12

    Cells are dynamical systems of biomolecular interactions that process information from their environment to mount diverse yet specific responses. A key property of many self-organized systems is that of criticality: a state of a system in which, on average, perturbations are neither dampened nor amplified, but are propagated over long temporal or spatial scales. Criticality enables the coordination of complex macroscopic behaviors that strike an optimal balance between stability and adaptability. It has long been hypothesized that biological systems are critical. Here, we address this hypothesis experimentally for system-wide gene expression dynamics in the macrophage. To this end, we have developed a method, based on algorithmic information theory, to assess macrophage criticality, and we have validated the method on networks with known properties. Using global gene expression data from macrophages stimulated with a variety of Toll-like receptor agonists, we found that macrophage dynamics are indeed critical, providing the most compelling evidence to date for this general principle of dynamics in biological systems.

  3. Dynamic Wetting on Graphene-Coated Surface: Molecular Dynamics Investigation

    NASA Astrophysics Data System (ADS)

    Hung, Shih-Wei; Shiomi, Junichiro

    2015-11-01

    Wettability of graphene-coated surface gained significant attention recently due to discussion on the ``transparency'' (whether the wetting characteristics follow that of graphene or the underlying surface) and practical applications of graphene. In terms of static contact angle, the wettability of graphene-coated surfaces have been widely studied by experiments, simulations, and theory in recent years. However, the studies of dynamic wetting on graphene-coated surfaces are limited. In the present study, molecular dynamics simulation was performed to study the dynamic wetting of water droplet on graphene-coated surfaces from a microscopic point of view. The results show that the degree of similarity between the spreading behavior on graphene-coated surface and that on pure graphene (or that on the underlying surface) depends on time, i.e. how nonequilibrium the interface dynamics is. We also found that this feature can be altered by introducing defects into graphene. The work is partially supported by Grant-in-Aid for JSPS Fellows 26-04364 and JST CREST.

  4. Critical Dynamics of Sound in KMnF3

    NASA Astrophysics Data System (ADS)

    Fossheim, K.; Holt, R. M.

    1980-09-01

    The critical dynamics of KMnF3 above the cubic-tetragonal transition were studied by ultrasonics, including a novel phonon-echo technique. Well above Tc, the results confirm predictions obtained from the three-dimensional Heisenberg model, including the value of the crossover exponent φ=1.26. Analysis of deviations from quasistatic behavior near Tc yields for the first time a dynamic scaling function G(ωτ) for the critical attenuation of ultrasound. τ may be interpreted as the relaxation time of ordered clusters. We find that τ~9×10-13t-1.41 s.

  5. Dynamics of nanoscale droplets on moving surfaces.

    PubMed

    Ritos, Konstantinos; Dongari, Nishanth; Borg, Matthew K; Zhang, Yonghao; Reese, Jason M

    2013-06-11

    We use molecular dynamics (MD) simulations to investigate the dynamic wetting of nanoscale water droplets on moving surfaces. The density and hydrogen bonding profiles along the direction normal to the surface are reported, and the width of the water depletion layer is evaluated first for droplets on three different static surfaces: silicon, graphite, and a fictitious superhydrophobic surface. The advancing and receding contact angles, and contact angle hysteresis, are then measured as a function of capillary number on smooth moving silicon and graphite surfaces. Our results for the silicon surface show that molecular displacements at the contact line are influenced greatly by interactions with the solid surface and partly by viscous dissipation effects induced through the movement of the surface. For the graphite surface, however, both the advancing and receding contact angles values are close to the static contact angle value and are independent of the capillary number; i.e., viscous dissipation effects are negligible. This finding is in contrast with the wetting dynamics of macroscale water droplets, which show significant dependence on the capillary number.

  6. Criticality in conserved dynamical systems: experimental observation vs. exact properties.

    PubMed

    Marković, Dimitrije; Gros, Claudius; Schuelein, André

    2013-03-01

    Conserved dynamical systems are generally considered to be critical. We study a class of critical routing models, equivalent to random maps, which can be solved rigorously in the thermodynamic limit. The information flow is conserved for these routing models and governed by cyclic attractors. We consider two classes of information flow, Markovian routing without memory and vertex routing involving a one-step routing memory. Investigating the respective cycle length distributions for complete graphs, we find log corrections to power-law scaling for the mean cycle length, as a function of the number of vertices, and a sub-polynomial growth for the overall number of cycles. When observing experimentally a real-world dynamical system one normally samples stochastically its phase space. The number and the length of the attractors are then weighted by the size of their respective basins of attraction. This situation is equivalent, for theory studies, to "on the fly" generation of the dynamical transition probabilities. For the case of vertex routing models, we find in this case power law scaling for the weighted average length of attractors, for both conserved routing models. These results show that the critical dynamical systems are generically not scale-invariant but may show power-law scaling when sampled stochastically. It is hence important to distinguish between intrinsic properties of a critical dynamical system and its behavior that one would observe when randomly probing its phase space.

  7. Criticality in dynamic arrest: Correspondence between glasses and traffic

    NASA Astrophysics Data System (ADS)

    Miedema, Daniel; de Wijn, Astrid; Nienhuis, Bernard; Schall, Peter

    2013-03-01

    Dynamic arrest is a general phenomenon across a wide range of dynamic systems including glasses, traffic flow, and dynamics in cells, but the universality of dynamic arrest phenomena remains unclear. We connect the emergence of traffic jams in traffic flow to the dynamic slow down in glasses. A direct correspondence is established by identifying a simple traffic model as a kinetically constrained model. In kinetically constrained models, the formation of glass becomes a (singular) phase transition in the zero temperature limit. Similarly, using the Nagel-Schreckenberg model to simulate traffic flow, we show that the emergence of jammed traffic acquires the signature of a sharp transition in the deterministic limit, corresponding to overcautious driving. We identify a true dynamical critical point marking the onset of coexistence between free flowing and jammed traffic, and demonstrate its analogy to the kinetically constrained glass models.

  8. Correlation between surface tension and critical temperatures of liquid metals.

    PubMed

    Blairs, Sidney; Abbasi, Mohammad Hassan

    2006-12-15

    The inter-relationship of surface tension sigma, molar volume V, and critical temperature Tc has been examined using experimental values for eighteen liquid metals. Hard-sphere diameters a correlate with the equation a(5/2) = 8.9733 x 10(-19) V (sigma/Tc)(1/4) - 1.0459 x 10(-25). Unknown Tc may be estimated using surface tension and liquid density values.

  9. Critical clusters and efficient dynamics for frustrated spin models

    NASA Astrophysics Data System (ADS)

    Cataudella, V.; Franzese, G.; Nicodemi, M.; Scala, A.; Coniglio, A.

    1994-03-01

    A general method to find, in a systematic way, efficient Monte Carlo cluster dynamics among the vast class of dynamics introduced by Kandel et al. [Phys. Rev. Lett. 65, 941 (1990)] is proposed. The method is successfully applied to a class of frustrated two-dimensional Ising systems. In the case of the fully frustrated model, we also find the intriguing result that critical clusters consist of self-avoiding walk at the θ point.

  10. Critical domain-wall dynamics of model B.

    PubMed

    Dong, R H; Zheng, B; Zhou, N J

    2009-05-01

    With Monte Carlo methods, we simulate the critical domain-wall dynamics of model B, taking the two-dimensional Ising model as an example. In the macroscopic short-time regime, a dynamic scaling form is revealed. Due to the existence of the quasirandom walkers, the magnetization shows intrinsic dependence on the lattice size L . An exponent which governs the L dependence of the magnetization is measured to be sigma=0.243(8) .

  11. Modelling Martian surface channel dynamics

    NASA Astrophysics Data System (ADS)

    Coulthard, T. J.; Skinner, C.; Kim, J.; Schumann, G.; Neal, J. C.; Bates, P. D.

    2014-12-01

    Extensive and large surface channel features found at Athabasca and Kasei have previously been attributed to the erosional power of flowing water with palaeoflood discharges being estimated from the surface channel dimensions. However, in order for these channels to be alluvial there are several basic questions to be answered. Are water flows under Martian conditions capable of eroding the amounts of sediment required to leave these channels? Are our present estimates of palaeoflood discharge of correct magnitude to carry out this erosion? And are the channels a product of one or many flood events? Here, we use a numerical model (CAESAR-Lisflood) that links a two-dimensional hydrodynamic flow scheme to a sediment transport model to simulate fluvial morphodynamics in the Athabasca and Kasei regions. CAESAR-Lisflood has been successfully applied to simulating flooding, erosion and deposition on Earth in a number of locations, and allows the development of channels, bars, braids and other fluvial features to be modelled. The numerical scheme of the model was adapted to Martian conditions by adjusting gravity, drag co-efficient, roughness and grainsize terms. Preliminary findings indicate that fluvial erosion and deposition is capable of creating mega channel features found at these sites and that existing palaeflood estimates are commensurate with channel forming discharges for these features.

  12. Critical Casimir forces between homogeneous and chemically striped surfaces.

    PubMed

    Parisen Toldin, Francesco; Tröndle, Matthias; Dietrich, S

    2013-11-01

    Recent experiments have measured the critical Casimir force acting on a colloid immersed in a binary liquid mixture near its continuous demixing phase transition and exposed to a chemically structured substrate. Motivated by these experiments, we study the critical behavior of a system, which belongs to the Ising universality class, for the film geometry with one planar wall chemically striped, such that there is a laterally alternating adsorption preference for the two species of the binary liquid mixture, which is implemented by surface fields. For the opposite wall we employ alternatively a homogeneous adsorption preference or homogeneous Dirichlet boundary conditions, which within a lattice model are realized by open boundary conditions. By means of mean-field theory, Monte Carlo simulations, and finite-size scaling analysis we determine the critical Casimir force acting on the two parallel walls and its corresponding universal scaling function. We show that in the limit of stripe widths small compared with the film thickness, on the striped surface the system effectively realizes Dirichlet boundary conditions, which generically do not hold for actual fluids. Moreover, the critical Casimir force is found to be attractive or repulsive, depending on the width of the stripes of the chemically patterned surface and on the boundary condition applied to the opposing surface.

  13. Nonadiabatic dynamics at metal surfaces: Independent-electron surface hopping

    NASA Astrophysics Data System (ADS)

    Shenvi, Neil; Roy, Sharani; Tully, John C.

    2009-05-01

    Recent experiments have shown convincing evidence for nonadiabatic energy transfer from adsorbate degrees of freedom to surface electrons during the interaction of molecules with metal surfaces. In this paper, we propose an independent-electron surface hopping algorithm for the simulation of nonadiabatic gas-surface dynamics. The transfer of energy to electron-hole pair excitations of the metal is successfully captured by hops between electronic adiabats. The algorithm is able to account for the creation of multiple electron-hole pairs in the metal due to nonadiabatic transitions. Detailed simulations of the vibrational relaxation of nitric oxide on a gold surface, employing a multistate potential energy surface fit to density functional theory calculations, confirm that our algorithm can capture the underlying physics of the inelastic scattering process.

  14. Entanglement dynamics in critical random quantum Ising chain with perturbations

    NASA Astrophysics Data System (ADS)

    Huang, Yichen

    2017-05-01

    We simulate the entanglement dynamics in a critical random quantum Ising chain with generic perturbations using the time-evolving block decimation algorithm. Starting from a product state, we observe super-logarithmic growth of entanglement entropy with time. The numerical result is consistent with the analytical prediction of Vosk and Altman using a real-space renormalization group technique.

  15. Measurement of dynamic surface tension by mechanically vibrated sessile droplets.

    PubMed

    Iwata, Shuichi; Yamauchi, Satoko; Yoshitake, Yumiko; Nagumo, Ryo; Mori, Hideki; Kajiya, Tadashi

    2016-04-01

    We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplet's height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

  16. Measurement of dynamic surface tension by mechanically vibrated sessile droplets

    NASA Astrophysics Data System (ADS)

    Iwata, Shuichi; Yamauchi, Satoko; Yoshitake, Yumiko; Nagumo, Ryo; Mori, Hideki; Kajiya, Tadashi

    2016-04-01

    We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplet's height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

  17. Glassy Dynamics Altered by a Free Surface

    NASA Astrophysics Data System (ADS)

    Tsui, Ophelia

    Studies of polymer dynamics in thin films showed that a highly mobile region exists at the free surface of most if not all polymers. In this talk, I shall review some of these observations, with highlights given to the recent findings that chain flexibility and connectivity may on occasions be necessary for the free surface to exercise its influence. Afterward, I shall ponder on how the influence of the free surface may penetrate as far as several polymer radii of gyration into the inner region, as found both in experiments and simulations. Near the glass transition temperature, our MD simulations showed that the dynamics consist mainly of string-like particle hopping motions, as found by others. Importantly, as the temperature decreases, the hopping motions become increasingly repetitive and back-and-forth, contributing no structural relaxations. We propose that structural relaxations are then brought about by pair-interactions between strings. Near the free surface, however, similar repetitive hopping motions are only observed sufficiently far removed from the free surface. We propose that the free surface induces a penetrating surface mobile region by breaking the memory in the particle dynamics. A possible mechanism based on string interactions will be discussed. We are grateful to the support of NSF through Project DMR-1310536 and Hong Kong GRF Grant 15301014.

  18. Critical dynamics on a large human Open Connectome network

    NASA Astrophysics Data System (ADS)

    Ódor, Géza

    2016-12-01

    Extended numerical simulations of threshold models have been performed on a human brain network with N =836 733 connected nodes available from the Open Connectome Project. While in the case of simple threshold models a sharp discontinuous phase transition without any critical dynamics arises, variable threshold models exhibit extended power-law scaling regions. This is attributed to fact that Griffiths effects, stemming from the topological or interaction heterogeneity of the network, can become relevant if the input sensitivity of nodes is equalized. I have studied the effects of link directness, as well as the consequence of inhibitory connections. Nonuniversal power-law avalanche size and time distributions have been found with exponents agreeing with the values obtained in electrode experiments of the human brain. The dynamical critical region occurs in an extended control parameter space without the assumption of self-organized criticality.

  19. Critical dynamics on a large human Open Connectome network.

    PubMed

    Ódor, Géza

    2016-12-01

    Extended numerical simulations of threshold models have been performed on a human brain network with N=836733 connected nodes available from the Open Connectome Project. While in the case of simple threshold models a sharp discontinuous phase transition without any critical dynamics arises, variable threshold models exhibit extended power-law scaling regions. This is attributed to fact that Griffiths effects, stemming from the topological or interaction heterogeneity of the network, can become relevant if the input sensitivity of nodes is equalized. I have studied the effects of link directness, as well as the consequence of inhibitory connections. Nonuniversal power-law avalanche size and time distributions have been found with exponents agreeing with the values obtained in electrode experiments of the human brain. The dynamical critical region occurs in an extended control parameter space without the assumption of self-organized criticality.

  20. Sleep dynamics: A self-organized critical system

    NASA Astrophysics Data System (ADS)

    Comte, J. C.; Ravassard, P.; Salin, P. A.

    2006-05-01

    In psychiatric and neurological diseases, sleep is often perturbed. Moreover, recent works on humans and animals tend to show that sleep plays a strong role in memory processes. Reciprocally, sleep dynamics following a learning task is modified [Hubert , Nature (London) 02663, 1 (2004), Peigneux , Neuron 44, 535 (2004)]. However, sleep analysis in humans and animals is often limited to the total sleep and wake duration quantification. These two parameters are not fully able to characterize the sleep dynamics. In mammals sleep presents a complex organization with an alternation of slow wave sleep (SWS) and paradoxical sleep (PS) episodes. Moreover, it has been shown recently that these sleep episodes are frequently interrupted by micro-arousal (without awakening). We present here a detailed analysis of the basal sleep properties emerging from the mechanisms underlying the vigilance states alternation in an animal model. These properties present a self-organized critical system signature and reveal the existence of two W, two SWS, and a PS structure exhibiting a criticality as met in sand piles. We propose a theoretical model of the sleep dynamics based on several interacting neuronal populations. This new model of sleep dynamics presents the same properties as experimentally observed, and explains the variability of the collected data. This experimental and theoretical study suggests that sleep dynamics shares several common features with critical systems.

  1. Hydration dynamics at fluorinated protein surfaces.

    PubMed

    Kwon, Oh-Hoon; Yoo, Tae Hyeon; Othon, Christina M; Van Deventer, James A; Tirrell, David A; Zewail, Ahmed H

    2010-10-05

    Water-protein interactions dictate many processes crucial to protein function including folding, dynamics, interactions with other biomolecules, and enzymatic catalysis. Here we examine the effect of surface fluorination on water-protein interactions. Modification of designed coiled-coil proteins by incorporation of 5,5,5-trifluoroleucine or (4S)-2-amino-4-methylhexanoic acid enables systematic examination of the effects of side-chain volume and fluorination on solvation dynamics. Using ultrafast fluorescence spectroscopy, we find that fluorinated side chains exert electrostatic drag on neighboring water molecules, slowing water motion at the protein surface.

  2. Hydration dynamics at fluorinated protein surfaces

    PubMed Central

    Kwon, Oh-Hoon; Yoo, Tae Hyeon; Othon, Christina M.; Van Deventer, James A.; Tirrell, David A.; Zewail, Ahmed H.

    2010-01-01

    Water-protein interactions dictate many processes crucial to protein function including folding, dynamics, interactions with other biomolecules, and enzymatic catalysis. Here we examine the effect of surface fluorination on water-protein interactions. Modification of designed coiled-coil proteins by incorporation of 5,5,5-trifluoroleucine or (4S)-2-amino-4-methylhexanoic acid enables systematic examination of the effects of side-chain volume and fluorination on solvation dynamics. Using ultrafast fluorescence spectroscopy, we find that fluorinated side chains exert electrostatic drag on neighboring water molecules, slowing water motion at the protein surface. PMID:20855583

  3. Dynamic scaling of the critical binary mixture methanol-hexane.

    PubMed

    Iwanowski, I; Sattarow, A; Behrends, R; Mirzaev, S Z; Kaatze, U

    2006-04-14

    Acoustical attenuation spectrometry, dynamic light scattering, shear viscosity, density, and heat capacity measurements of the methanol/n-hexane mixture of critical composition have been performed. The critical part in the sonic attenuation coefficients nicely fits to the empirical scaling function of the Bhattacharjee-Ferrell [Phys. Rev. A 24, 1643 (1981)] dynamic scaling model if the theoretically predicted scaled half-attenuation frequency Omega(12) (BF)=2.1 is used. The relaxation rates of order parameter fluctuations, as resulting from the acoustical spectra, within the limits of experimental error agree with those from a combined evaluation of the light scattering and shear viscosity measurements. Both series of data display power law with amplitude Gamma(0)=44x10(9) s(-1). The amplitude of the fluctuation correlation length follows as xi(0)=0.33 nm from the light scattering data and as xi(0)=0.32 nm from the amplitude of the singular part of the heat capacity if the two-scale factor universality relation is used. The adiabatic coupling constant g=0.11 results from the amplitude of the critical contribution to the acoustical spectrum near the critical point, in conformity with g=0.12 as following from the variation of the critical temperature with pressure along the critical line and the thermal expansion coefficient.

  4. Adaptation tunes cortical dynamics to a critical regime during vision

    NASA Astrophysics Data System (ADS)

    Shew, Woodrow; Clawson, Wesley; Pobst, Jeff; Karimipanah, Yahya; Wright, Nathaniel; Wessel, Ralf; Shew Lab Team; Wessel Lab Team

    2015-03-01

    A long-standing hypothesis at the interface of physics and neuroscience is that neural networks self-organize to the critical point of a phase transition, thereby optimizing aspects of sensory information processing. This idea is partially supported by strong evidence for critical dynamics observed in the cerebral cortex, but has not been tested in systems with significant sensory input. Thus, the foundations of this hypothesis - the self-organization process and how it manifests during strong sensory input - remain unstudied experimentally. Here we report microelectrode array measurements from visual cortex of turtles during visual stimulation of the retina. We show experimentally and in a computational model that strong sensory input initially elicits cortical network dynamics that are not critical, but adaptive changes in the network rapidly tune the system to criticality. This conclusion is based on observations of multifaceted scaling laws predicted to occur at criticality. Our findings establish sensory adaptation as a self-organizing mechanism which maintains criticality in visual cortex during sensory information processing. Supported by NSF CRCNS Grant 1308174.

  5. Forecasting critical transitions using data-driven nonstationary dynamical modeling

    NASA Astrophysics Data System (ADS)

    Kwasniok, Frank

    2015-12-01

    An approach to predicting critical transitions from time series is introduced. A nonstationary low-order stochastic dynamical model of appropriate complexity to capture the transition mechanism under consideration is estimated from data. In the simplest case, the model is a one-dimensional effective Langevin equation, but also higher-dimensional dynamical reconstructions based on time-delay embedding and local modeling are considered. Integrations with the nonstationary models are performed beyond the learning data window to predict the nature and timing of critical transitions. The technique is generic, not requiring detailed a priori knowledge about the underlying dynamics of the system. The method is demonstrated to successfully predict a fold and a Hopf bifurcation well beyond the learning data window.

  6. Criticality of environmental information obtainable by dynamically controlled quantum probes

    NASA Astrophysics Data System (ADS)

    Zwick, Analia; Álvarez, Gonzalo A.; Kurizki, Gershon

    2016-10-01

    A universal approach to decoherence control combined with quantum estimation theory reveals a critical behavior, akin to a phase transition, of the information obtainable by a qubit probe concerning the memory time of environmental fluctuations of generalized Ornstein-Uhlenbeck processes. The criticality is intrinsic to the environmental fluctuations but emerges only when the probe is subject to suitable dynamical control aimed at inferring the memory time. A sharp transition is anticipated between two dynamical phases characterized by either a short or long memory time compared to the probing time. This phase transition of the environmental information is a fundamental feature that characterizes open quantum-system dynamics and is important for attaining the highest estimation precision of the environment memory time under experimental limitations.

  7. Dynamic critical temperature in MnIIFeIII bimetallic oxalates

    NASA Astrophysics Data System (ADS)

    Huang, Jinhua; Shi, Xiaoling; Song, Zhaoyuan; Shi, Yingguo

    2017-08-01

    MnIIFeIII bimetallic oxalates are described by a spin-5/2 Blume-Capel (BC) model on a layered honeycomb structure. The effects of the interlayer coupling, the single-ion anisotropy and the oscillating magnetic field on the dynamic critical temperature of the compounds are studied by a effective-field method based on Glauber-type stochastic dynamic. Dynamic phase diagrams are presented in the DA /|J1 |- T /|J1 | and T /|J1 |-h0 /|J1 | planes, and the first-order phase transition lines and the critical end point are found. Compensated magnetization regions have also been plotted and the compounds exhibit an uncompensated magnetization in the antiferromagnetic phase. In particular, a two-compensation-temperature phenomenon has also been observed in MnIIFeIII bimetallic oxalates.

  8. SATELLITE DYNAMICS ON THE LAPLACE SURFACE

    SciTech Connect

    Tremaine, Scott; Touma, Jihad; Namouni, Fathi E-mail: jihad.touma@gmail.com

    2009-03-15

    The orbital dynamics of most planetary satellites is governed by the quadrupole moment from the equatorial bulge of the host planet and the tidal field from the Sun. On the Laplace surface, the long-term orbital evolution driven by the combined effects of these forces is zero, so that orbits have a fixed orientation and shape. The 'classical' Laplace surface is defined for circular orbits, and coincides with the planet's equator at small planetocentric distances and with its orbital plane at large distances. A dissipative circumplanetary disk should settle to this surface, and hence satellites formed from such a disk are likely to orbit in or near the classical Laplace surface. This paper studies the properties of Laplace surfaces. Our principal results are: (1) if the planetary obliquity exceeds 68.{sup 0}875, there is a range of semimajor axes in which the classical Laplace surface is unstable; (2) at some obliquities and planetocentric distances, there is a distinct Laplace surface consisting of nested eccentric orbits, which bifurcates from the classical Laplace surface at the point where instability sets in; (3) there is also a 'polar' Laplace surface perpendicular to the line of nodes of the planetary equator on the planetary orbit; (4) for circular orbits, the polar Laplace surface is stable at small planetocentric distances and unstable at large distances; (5) at the onset of instability, this polar Laplace surface bifurcates into two polar Laplace surfaces composed of nested eccentric orbits.

  9. Geostrophic dynamics at surfaces in the atmosphere and ocean

    NASA Astrophysics Data System (ADS)

    Tulloch, Ross

    Observed dynamics near bounding upper surfaces in the atmosphere and ocean are interpreted in terms of quasi-geostrophic theory. The quasi-geostrophic equations consist of advection of linearized potential vorticity coupled with advection of temperature at the upper and lower bounding surfaces. We show that the standard vertical finite difference formulation of 3D quasi-geostrophic flow accurately represents the flow only down to a critical horizontal scale that decreases with vertical grid spacing. To overcome this constraint, we derive a surface-modal formulation which accurately and efficiently captures both the surface dynamics due to temperature anomalies on the upper and lower boundaries, and the interior dynamics due to potential vorticity anomalies, without the need for high vertical resolution. In the atmosphere, the horizontal wavenumber spectra of wind and temperature near the tropopause have a steep -3 slope at synoptic scales and a shallow -5/3 slope at mesoscales, with a smooth transition between the two regimes from 800km to 200km. We demonstrate that when the surface temperature anomalies are resolved, quasi-geostrophic flow driven by baroclinic instability exhibits such a transition near the tropopause. The horizontal scale of transition between -3 and -5/3 slopes depends on the relative magnitudes of the mean surface temperature gradient and the mean potential vorticity gradient. In the ocean, sea surface height anomalies measured by satellite altimetry exhibit shallower spectral slopes than quasi-geostrophic theory predicts, and faster than expected westward phase propagation of sea surface height in the midlatitudes. We argue that, in some regions, the shallow spectral slopes are due to surface quasi-geostrophic dynamics, and that the westward phase propagation in the midlatitudes is indicative of a transition from a linear Rossby wave regime in the tropics to a nonlinear turbulent regime in the midlatitudes.

  10. Critical dynamics of a nonlocal model and critical behavior of perovskite manganites

    NASA Astrophysics Data System (ADS)

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K.

    2016-05-01

    We investigate the nonconserved critical dynamics of a nonlocal model Hamiltonian incorporating screened long-range interactions in the quartic term. Employing dynamic renormalization group analysis at one-loop order, we calculate the dynamic critical exponent z =2 +ɛ f1(σ ,κ ,n ) +O (ɛ2) and the linewidth exponent w =-σ +ɛ f2(σ ,κ ,n ) +O (ɛ2) in the leading order of ɛ , where ɛ =4 -d +2 σ , with d the space dimension, n the number of components in the order parameter, and σ and κ the parameters coming from the nonlocal interaction term. The resulting values of linewidth exponent w for a wide range of σ is found to be in good agreement with the existing experimental estimates from spin relaxation measurements in perovskite manganite samples.

  11. Critical dynamics of a nonlocal model and critical behavior of perovskite manganites.

    PubMed

    Singh, Rohit; Dutta, Kishore; Nandy, Malay K

    2016-05-01

    We investigate the nonconserved critical dynamics of a nonlocal model Hamiltonian incorporating screened long-range interactions in the quartic term. Employing dynamic renormalization group analysis at one-loop order, we calculate the dynamic critical exponent z=2+εf_{1}(σ,κ,n)+O(ε^{2}) and the linewidth exponent w=-σ+εf_{2}(σ,κ,n)+O(ε^{2}) in the leading order of ε, where ε=4-d+2σ, with d the space dimension, n the number of components in the order parameter, and σ and κ the parameters coming from the nonlocal interaction term. The resulting values of linewidth exponent w for a wide range of σ is found to be in good agreement with the existing experimental estimates from spin relaxation measurements in perovskite manganite samples.

  12. Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

    NASA Astrophysics Data System (ADS)

    Aburas, Muhamad; Pautrat, Alain; Bellido, Natalia

    2017-01-01

    A systematic study of irreversible magnetization was performed in bulk niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up to an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic fields perpendicular to large facets in terms of nucleation of superconductivity along bumps of a corrugated surface.

  13. Balanced excitation and inhibition lead to statistical and dynamical criticality

    NASA Astrophysics Data System (ADS)

    Cecchi, Guillermo

    2010-03-01

    We present a simple abstract model, an anti-Hebbian network which spontaneously poises itself, by balancing excitation and inhibition, at a dynamically critical state: an extensive number of degrees of freedom approach Hopf bifurcations, becoming arbitrarily sensitive to external perturbations (PRL 102, 258102 - 2009). As the dynamics controlling this state has itself a marginal fixed point, the eigenvalues fluctuate close to the imaginary axis; when they become slightly unstable, the corresponding mode ``breaks out'' and becomes more prominent, and as they become slightly stable the mode slowly damps out. This breakout dynamics displays avalanche-like activity bursts whose sizes may be power-law distributed, i.e. statistically critical. Within these epochs the neurons of our model are slightly correlated; yet, as the number of small but significant correlations is high, the model has strongly correlated network states. This system is, on the short time-scale, sensitive in bulk to any outside input, even if applied only to a small subset of the neurons. We also present preliminary results showing that human brain electro-physiological recordings display both statistical and dynamical criticality.

  14. Static and dynamic properties of critical fluctuations in lipid bilayers

    NASA Astrophysics Data System (ADS)

    Honerkamp-Smith, Aurelia Rose

    A current popular view in cell biology is that sub-micron, dynamic heterogeneity in lipid and protein composition arises within the plasma membranes of resting cells. Local changes in membrane composition may affect protein activity, which is sensitive to the lipid environment. We have observed dynamic heterogeneity in lipid membranes in the form of composition fluctuations near a miscibility critical point. In this thesis we quantitatively describe the dynamic and static properties of these fluctuations. We evaluate the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes in order to extract a critical exponent, nu. We obtain nu = 1.2 +/- 0.2, consistent with the Ising model prediction nu = 1. From probability distributions of pixel intensities in fluorescence images of membranes, we also extract an independent critical exponent of beta = 0.124 +/- 0.03, which is consistent with the Ising prediction of beta = 1/8. We have systematically measured the effective dynamic critical exponent z eff in a lipid membrane while cooling the system toward a critical point. We observe that zeff slightly increases from a value of roughly 2.6 as xi → 0, to zeff = 3.0 +/- 0.15 at xi = 13 sm. Our measurements are consistent with the prediction that zeff → 3.00 as T → Tc for a 2-D system with conserved order parameter in contact with a bulk 3-D liquid. To our knowledge, no other systematic measurement of zeff with increasing xi exists for a 2-D system with conserved order parameter. We also report the solubility limit of several biologically relevant sterols in electroformed giant unilamellar vesicle membranes containing phosphatidylcholine (PC) lipids in ratios of 1:1:X DPPC:DOPC:sterol. We find solubility limits of cholesterol, lanosterol, ergosterol, stigmasterol, and beta-sitosterol using nuclear magnetic resonance.

  15. Dynamic Defrosting on Scalable Superhydrophobic Surfaces

    DOE PAGES

    Murphy, Kevin R.; McClintic, William T.; Lester, Kevin C.; ...

    2017-06-27

    Recent studies have shown that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces. During defrosting, the melting sheet of Cassie frost spontaneously dewets into quasi-spherical slush droplets that are highly mobile. Promoting Cassie frost would therefore seem advantageous from a defrosting standpoint; however, nobody has systematically compared the efficiency of defrosting Cassie ice versus defrosting conventional surfaces. Here, we characterize the defrosting of an aluminum plate, one-half of which exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. For thick frost sheets (>1 mm), the superhydrophobic surface was able to dynamically shed themore » meltwater, even at very low tilt angles. In contrast, the hydrophobic surface was unable to shed any appreciable meltwater even at a 90° tilt angle. For thin frost layers (≲1 mm), not even the superhydrophobic surface could mobilize the meltwater. We attribute this to the large apparent contact angle of the meltwater, which for small amounts of frost serves to minimize coalescence events and prevent droplets from approaching the capillary length. Finally, we demonstrate a new mode of dynamic defrosting using an upside-down surface orientation, where the melting frost was able to uniformly detach from the superhydrophobic side and subsequently pull the frost from the hydrophobic side in a chain reaction. Treating surfaces to enable Cassie frost is therefore very desirable for enabling rapid and low-energy thermal defrosting, but only for frost sheets that are sufficiently thick.« less

  16. Dynamic Defrosting on Scalable Superhydrophobic Surfaces.

    PubMed

    Murphy, Kevin R; McClintic, William T; Lester, Kevin C; Collier, C Patrick; Boreyko, Jonathan B

    2017-07-19

    Recent studies have shown that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces. During defrosting, the melting sheet of Cassie frost spontaneously dewets into quasi-spherical slush droplets that are highly mobile. Promoting Cassie frost would therefore seem advantageous from a defrosting standpoint; however, nobody has systematically compared the efficiency of defrosting Cassie ice versus defrosting conventional surfaces. Here, we characterize the defrosting of an aluminum plate, one-half of which exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. For thick frost sheets (>1 mm), the superhydrophobic surface was able to dynamically shed the meltwater, even at very low tilt angles. In contrast, the hydrophobic surface was unable to shed any appreciable meltwater even at a 90° tilt angle. For thin frost layers (≲1 mm), not even the superhydrophobic surface could mobilize the meltwater. We attribute this to the large apparent contact angle of the meltwater, which for small amounts of frost serves to minimize coalescence events and prevent droplets from approaching the capillary length. Finally, we demonstrate a new mode of dynamic defrosting using an upside-down surface orientation, where the melting frost was able to uniformly detach from the superhydrophobic side and subsequently pull the frost from the hydrophobic side in a chain reaction. Treating surfaces to enable Cassie frost is therefore very desirable for enabling rapid and low-energy thermal defrosting, but only for frost sheets that are sufficiently thick.

  17. Dynamic air layer on textured superhydrophobic surfaces.

    PubMed

    Vakarelski, Ivan U; Chan, Derek Y C; Marston, Jeremy O; Thoroddsen, Sigurdur T

    2013-09-03

    We provide an experimental demonstration that a novel macroscopic, dynamic continuous air layer or plastron can be sustained indefinitely on textured superhydrophobic surfaces in air-supersaturated water by a natural gas influx mechanism. This type of plastron is an intermediate state between Leidenfrost vapor layers on superheated surfaces and the equilibrium Cassie-Baxter wetting state on textured superhydrophobic surfaces. We show that such a plastron can be sustained on the surface of a centimeter-sized superhydrophobic sphere immersed in heated water and variations of its dynamic behavior with air saturation of the water can be regulated by rapid changes of the water temperature. The simple experimental setup allows for quantification of the air flux into the plastron and identification of the air transport model of the plastron growth. Both the observed growth dynamics of such plastrons and millimeter-sized air bubbles seeded on the hydrophilic surface under identical air-supersaturated solution conditions are consistent with the predictions of a well-mixed gas transport model.

  18. Quantum critical point revisited by dynamical mean-field theory

    DOE PAGES

    Xu, Wenhu; Kotliar, Gabriel; Tsvelik, Alexei M.

    2017-03-31

    Dynamical mean-field theory is used to study the quantum critical point (QCP) in the doped Hubbard model on a square lattice. We characterize the QCP by a universal scaling form of the self-energy and a spin density wave instability at an incommensurate wave vector. The scaling form unifies the low-energy kink and the high-energy waterfall feature in the spectral function, while the spin dynamics includes both the critical incommensurate and high-energy antiferromagnetic paramagnons. Here, we use the frequency-dependent four-point correlation function of spin operators to calculate the momentum-dependent correction to the electron self-energy. Furthermore, by comparing with the calculations basedmore » on the spin-fermion model, our results indicate the frequency dependence of the quasiparticle-paramagnon vertices is an important factor to capture the momentum dependence in quasiparticle scattering.« less

  19. Molecular dynamics description of grafted monolayers: effect of the surface coverage.

    PubMed

    Goujon, F; Bonal, C; Limoges, B; Malfreyt, P

    2008-11-13

    Molecular dynamics simulations of monolayers of metal-chelating ligands grafted onto a graphite surface in water are carried out to calculate structural (density profiles, radius of gyration, and asphericity coefficients), dynamical (diffusion coefficients), and energetical properties as a function of the surface coverage. The purpose is to provide a better understanding of the dependence of various properties of these monolayers on the surface coverage. A critical value of the surface coverage from which all structural properties derive a limiting value has been established. It also appears that the chains rather adopt an elongated conformation along the direction normal to the surface from this critical surface coverage. The hydrogen-bonding structure and dynamics of water molecules are reported. An ordered structure of water in the region close to the terminal groups of the grafted molecules is shown at a relatively high surface coverage. This ordering is similar to that observed in the case of water in interaction with a solid surface.

  20. Vortex dynamics in nonlinear free surface flows

    NASA Astrophysics Data System (ADS)

    Curtis, Christopher W.; Kalisch, Henrik

    2017-03-01

    The two-dimensional motion of point vortices in an inviscid fluid with a free surface and an impenetrable bed is investigated. The work is based on forming a closed system of equations for surface variables and vortex positions using a variant of the Ablowitz, Fokas, and Musslimani formulation [M. J. Ablowitz, A. S. Fokas, and Z. H. Musslimani, J. Fluid Mech. 562, 313-343 (2006)] of the water-wave free-surface problem. The equations are approximated with a dealiased spectral method making use of a high-order approximation of the Dirichlet-Neumann operator and a high-order time-stepping scheme. Numerical simulations reveal that the combination of vortex motion and solid bottom boundary yields interesting dynamics not seen in the case of vortex motion in an infinitely deep fluid. In particular, strong deformations of the free surface, including non-symmetric surface profiles and regions of large energy concentration, are observed. Our simulations also uncover a rich variety of vortex trajectories including orbiting and nearly parallel patterns of motion. The dynamics of the free surface and of the point vortices are strongly influenced by the initial placement and polarity of the vortices. The method put forward here is flexible enough to handle a large number of vortices and may easily be extended to include the effects of varying bathymetry, stratification, and background shear currents.

  1. Communicating by Doppler: Detecting Spacecraft Dynamics During Critical Maneuvers

    NASA Technical Reports Server (NTRS)

    Asmar, Sami W.

    2012-01-01

    Communicating information from spacecraft in deep space utilizes sophisticated techniques of modulations onto a microwave signal carrier. Under most conditions, there is a high success rate of sending commands to the spacecraft and receiving science data acquired by on-board instruments along with health and status information. There are conditions, however, where the signal dynamics are too high and/or the received signal-to-noise ratio is below the receiver threshold. Under these conditions, often by design and sometimes as a result of planned or unplanned critical maneuvers, events (e.g., orbit insertion or descent and landing), safe mode, etc., it becomes highly critical but exceedingly challenging to receive information about the health and dynamical behavior of the spacecraft. The Deep Space Network, being a world-class instrument for Radio Science research, developed openloop receivers, called the Radio Science Receiver, designed to capture the raw incoming electromagnetic signals and associated noise for Radio Science experiments; post data capture digital signal processing extracts the signal carrier for scientific analysis. This receiver provides a high level of configuration flexibility and can be optimized for the various types of experiments. In addition to its scientific utility, it proved to be useful, and in some cases critical, for the support of missions during specific scenarios were the link budget is below the threshold of the tracking receiver to maintain lock or the frequency dynamics are faster than the limits of the tracking receiver. In these cases, the signal carrier is often detected only in the open-loop receiver to provide information on the specific behavior of the spacecraft from the carrier dynamics. This paper describes the utility of the system to support mission-critical events for the three cases of Cassini's Saturn orbit insertion, Huygens Titan landing, and Mars rovers landing.

  2. Communicating by Doppler: Detecting Spacecraft Dynamics During Critical Maneuvers

    NASA Technical Reports Server (NTRS)

    Asmar, Sami W.

    2012-01-01

    Communicating information from spacecraft in deep space utilizes sophisticated techniques of modulations onto a microwave signal carrier. Under most conditions, there is a high success rate of sending commands to the spacecraft and receiving science data acquired by on-board instruments along with health and status information. There are conditions, however, where the signal dynamics are too high and/or the received signal-to-noise ratio is below the receiver threshold. Under these conditions, often by design and sometimes as a result of planned or unplanned critical maneuvers, events (e.g., orbit insertion or descent and landing), safe mode, etc., it becomes highly critical but exceedingly challenging to receive information about the health and dynamical behavior of the spacecraft. The Deep Space Network, being a world-class instrument for Radio Science research, developed openloop receivers, called the Radio Science Receiver, designed to capture the raw incoming electromagnetic signals and associated noise for Radio Science experiments; post data capture digital signal processing extracts the signal carrier for scientific analysis. This receiver provides a high level of configuration flexibility and can be optimized for the various types of experiments. In addition to its scientific utility, it proved to be useful, and in some cases critical, for the support of missions during specific scenarios were the link budget is below the threshold of the tracking receiver to maintain lock or the frequency dynamics are faster than the limits of the tracking receiver. In these cases, the signal carrier is often detected only in the open-loop receiver to provide information on the specific behavior of the spacecraft from the carrier dynamics. This paper describes the utility of the system to support mission-critical events for the three cases of Cassini's Saturn orbit insertion, Huygens Titan landing, and Mars rovers landing.

  3. Study on contaminants on flight and other critical surfaces

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Hughes, Charles; Arendale, William F.

    1994-01-01

    The control of surface contamination in the manufacture of space hardware can become a critical step in the production process. Bonded surfaces have been shown to be affected markedly by contamination. It is important to insure surface cleanliness by preventing contamination prior to bonding. In this vein techniques are needed in which the contamination which may affect bonding are easily found and removed. Likewise, if materials which are detrimental to bonding are not easily removed, then they should not be used in the manufacturing process. This study will address the development of techniques to locate and quantify contamination levels of particular contaminants. With other data becoming available from MSFC and its contractors, this study will also quantify how certain contaminants affect bondlines and how easily they are removed in manufacturing.

  4. Structure, biomimetics, and fluid dynamics of fish skin surfaces*

    NASA Astrophysics Data System (ADS)

    Lauder, George V.; Wainwright, Dylan K.; Domel, August G.; Weaver, James C.; Wen, Li; Bertoldi, Katia

    2016-10-01

    The interface between the fluid environment and the surface of the body in swimming fishes is critical for both physiological and hydrodynamic functions. The skin surface in most species of fishes is covered with bony scales or toothlike denticles (in sharks). Despite the apparent importance of fish surfaces for understanding aquatic locomotion and near-surface boundary layer flows, relatively little attention has been paid to either the nature of surface textures in fishes or possible hydrodynamic effects of variation in roughness around the body surface within an individual and among species. Fish surfaces are remarkably diverse and in many bony fishes scales can have an intricate surface texture with projections, ridges, and comblike extensions. Shark denticles (or scales) are toothlike and project out of the skin to form a complexly textured surface that interacts with free-stream flow. Manufacturing biomimetic foils with fishlike surfaces allows hydrodynamic testing and we emphasize here the importance of dynamic test conditions where the effect of surface textures is assessed under conditions of self-propulsion. We show that simple two-dimensional foils with patterned cuts do not perform as well as a smooth control surface, but that biomimetic shark skin foils can swim at higher self-propelled speeds than smooth controls. When the arrangement of denticles on the foil surface is altered, we find that a staggered-overlapped pattern outperforms other arrangements. Flexible foils made of real shark skin outperform sanded controls when foils are moved with a biologically realistic motion program. We suggest that focus on the mechanisms of drag reduction by fish surfaces has been too limiting and an additional role of fish surface textures may be to alter leading edge vortices and flow patterns on moving surfaces in a way that enhances thrust. Analysis of water flow over an artificial shark skin foil under both static and dynamic conditions shows that a shear layer

  5. Floquet Dynamics of Boundary-Driven Systems at Criticality

    NASA Astrophysics Data System (ADS)

    Berdanier, William; Kolodrubetz, Michael; Vasseur, Romain; Moore, Joel E.

    2017-06-01

    A quantum critical system described at low energy by a conformal field theory (CFT) and subjected to a time-periodic boundary drive displays multiple dynamical regimes, depending on the drive frequency. We compute the behavior of quantities including the entanglement entropy and Loschmidt echo, confirming analytic predictions from field theory by exact numerics on the transverse field Ising model and demonstrate universality by adding nonintegrable perturbations. The dynamics naturally separate into three regimes: a slow-driving limit, which has an interpretation as multiple quantum quenches with amplitude corrections from CFT; a fast-driving limit, in which the system behaves as though subject to a single quantum quench; and a crossover regime displaying heating. The universal Floquet dynamics in all regimes can be understood using a combination of boundary CFT and Kibble-Zurek scaling arguments.

  6. Modeling surface water critical loads with PROFILE: possibilities and challenges.

    PubMed

    Rapp, L; Bishop, K

    2003-01-01

    The critical load concept has become a valuable tool for policymakers in the European negotiations on emission reductions. Despite the international acceptance, ongoing validation of critical load methodology is of the utmost importance to avoid a situation where the calculation results are difficult to defend. In this paper we explore the potential of using the steady state soil chemistry model PROFILE as an alternative to the Steady State Water Chemistry (SSWC) method for calculating critical loads of acidity. The hypothesis is that the uncertainty in prediction of preindustrial leaching of base cations is reduced when soil properties instead of lake chemistry are used as input data. Paleolimnological reconstructions of preindustrial lake chemistry are used to test PROFILE. As PROFILE requires soil data that are not generally available on a catchment level, we used distributions of crucial parameters from soil survey data within the vicinity of five lakes for which paleoecological pH reconstructions were available. An important concern is the characterization of catchment hydrology. A calibration of the "effective" soil depth, needed to give PROFILE predictions that coincided with paleolimnology, suggested that approximately 0.6 m of the total soil depth was hydrologically active in supplying acid neutralizing capacity (ANC) to runoff through weathering. At present, there is insufficient evidence to either recommend or reject the PROFILE model for surface water critical loads. Before such a judgement can be made, the approach presented here has to be tested for other regions, and the definition of catchment hydrology needs to be investigated further.

  7. Geometrical critical phenomena on a random surface of arbitrary genus

    NASA Astrophysics Data System (ADS)

    Duplantier, Bertrand; Kostov, Ivan K.

    1990-08-01

    The statistical mechanics of self-avoiding walks (SAW) or of the O( n)-loop model on a two-dimensional random surface are shown to be exactly solvable. The partition functions of SAW and surface configurations (possibly in the presence of vacuum loops) are calculated by planar diagram enumeration techniques. Two critical regimes are found: a dense phase where the infinite walks and loops fill the infinite surface, the non-filled part staying finite, and a dilute phase where the infinite surface singularity on the one hand, and walk and loop singularities on the other, merge together. The configuration critical exponents of self-avoiding networks of any fixed topology G, on a surface with arbitrary genus H, are calculated as universal functions of G and H. For self-avoiding walks, the exponents are built from an infinite set of basic conformal dimensions associated with central charges c = -2 (dense phase) and c = 0 (dilute phase). The conformal spectrum ΔL, L ⩾ 1 associated with L-leg star polymers is calculated exactly, for c = -2 and c = 0. This is generalized to the set of L-line "watermelon" exponents ΔL of the O( n) model on a random surface. The results are in perfect agreement with the conformal theory of Knizhnik, Polyakov and Zamolodchikov describing matter fields coupled to 2D quantum gravity. The infinite series of dimensions ΔL dressed by gravity calculated here, together with the corresponding SAW conformal dimensions ΔL(0) in the plane, known independently from Coulomb-gas techniques, match the KPZ relation Δ - Δ (0) = {Δ(1 - Δ)}/{κ}, where c = {1 - 6(1 - κ) 2}/{k}. This provides a cross check of Coulomb-gas techniques, the KPZ conformal theory of matter fields with 2D quantum gravity and the universality of random lattices. The divergences of the partition functions of self-avoiding networks on the random surface, possibly in the presence of vacuum loops, are shown to satisfy a factorization theorem over the vertices of the network. This

  8. Dynamic loads in surface dragline ropes. [ADINA

    SciTech Connect

    Alzheimer, J.M.; Bampton, M.C.C.; Griffiths, J.A.

    1980-03-01

    In order to analyze the failure of the large diameter wire ropes used in large surface mining draglines, the stresses in the ropes due to operational loadings must be known. To be meaningful, the calculation of these loads must take into account the dynamic behavior of the ropes and the dragline. Since there is a lack of data concerning the actual loads in ropes of surface draglines, an investigation was undertaken to characterize these loads. An existing finite element computer code, ADINA, capable of modeling large displacement, dynamic behavior of cable-like structures was selected to perform the analyses. However, because ADINA is a general purpose nonlinear finite element program, not specifically written for cable type problems, it was necessary to investigate its capabilities along these lines. Therefore, a series of benchmark problems was selected to establish its capabilities. These benchmark problems are discussed. This computer analysis resulted in two conclusions: first, the ability of ADINA truss elements with large displacement capabilities to model static and dynamic behavior of wire ropes has been clearly shown. The nonlinear static stiffness of catenary cables was modeled precisely. Significant dynamic phenomena such as mode shapes and frequencies, pulse propagation, and freely falling cables were also well represented by ADINA models. Second, care must be taken to ensure that sufficiently small load increments (i.e., time steps) are used to obtain convergence. The nonlinear truss element behavior is quite sensitive to load increment size.

  9. Dynamic bioactive stimuli-responsive polymeric surfaces

    NASA Astrophysics Data System (ADS)

    Pearson, Heather Marie

    This dissertation focuses on the design, synthesis, and development of antimicrobial and anticoagulant surfaces of polyethylene (PE), polypropylene (PP), and poly(tetrafluoroethylene) (PTFE) polymers. Aliphatic polymeric surfaces of PE and PP polymers functionalized using click chemistry reactions by the attachment of --COOH groups via microwave plasma reactions followed by functionalization with alkyne moieties. Azide containing ampicillin (AMP) was synthesized and subsequently clicked into the alkyne prepared PE and PP surfaces. Compared to non-functionalized PP and PE surfaces, the AMP clicked surfaces exhibited substantially enhanced antimicrobial activity against Staphylococcus aureus bacteria. To expand the biocompatibility of polymeric surface anticoagulant attributes, PE and PTFE surfaces were functionalized with pH-responsive poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) polyelectrolyte tethers terminated with NH2 and COOH groups. The goal of these studies was to develop switchable stimuli-responsive polymeric surfaces that interact with biological environments and display simultaneous antimicrobial and anticoagulant properties. Antimicrobial AMP was covalently attached to --COOH terminal ends of protected PAA, while anticoagulant heparin (HEP) was attached to terminal --NH2 groups of P2VP. When pH < 2.3, the P2VP segments are protonated and extend, but for pH > 5.5, they collapse while the PAA segments extend. Such surfaces, when exposed to Staphylococcus aureus, inhibit bacterial growth due to the presence of AMP, as well as are effective anticoagulants due to the presence of covalently attached HEP. Comparison of these "dynamic" pH responsive surfaces with "static" surfaces terminated with AMP entities show significant enhancement of longevity and surface activity against microbial film formation. The last portion of this dissertation focuses on the covalent attachment of living T1 and Φ11 bacteriophages (phages) on PE and PTFE surface

  10. Dynamic contact angle cycling homogenizes heterogeneous surfaces.

    PubMed

    Belibel, R; Barbaud, C; Mora, L

    2016-12-01

    In order to reduce restenosis, the necessity to develop the appropriate coating material of metallic stent is a challenge for biomedicine and scientific research over the past decade. Therefore, biodegradable copolymers of poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) were prepared in order to develop a new coating exhibiting different custom groups in its side chain and being able to carry a drug. This material will be in direct contact with cells and blood. It consists of carboxylic acid and hexylic groups used for hydrophilic and hydrophobic character, respectively. The study of this material wettability and dynamic surface properties is of importance due to the influence of the chemistry and the potential motility of these chemical groups on cell adhesion and polymer kinetic hydrolysis. Cassie theory was used for the theoretical correction of contact angles of these chemical heterogeneous surfaces coatings. Dynamic Surface Analysis was used as practical homogenizer of chemical heterogeneous surfaces by cycling during many cycles in water. In this work, we confirmed that, unlike receding contact angle, advancing contact angle is influenced by the difference of only 10% of acidic groups (%A) in side-chain of polymers. It linearly decreases with increasing acidity percentage. Hysteresis (H) is also a sensitive parameter which is discussed in this paper. Finally, we conclude that cycling provides real information, thus avoiding theoretical Cassie correction. H(10)is the most sensible parameter to %A.

  11. Percolation transition in dynamical traffic network with evolving critical bottlenecks

    NASA Astrophysics Data System (ADS)

    Li, Daqing

    A critical phenomenon is an intrinsic feature of traffic dynamics, during which transition between isolated local flows and global flows occurs. However, very little attention has been given to the question of how the local flows in the roads are organized collectively into a global city flow. Here we characterize this organization process of traffic as ``traffic percolation,'' where the giant cluster of local flows disintegrates when the second largest cluster reaches its maximum. We find in real-time data of city road traffic that global traffic is dynamically composed of clusters of local flows, which are connected by bottleneck links. This organization evolves during a day with different bottleneck links appearing in different hours, but similar in the same hours in different days. A small improvement of critical bottleneck roads is found to benefit significantly the global traffic, providing a method to improve city traffic with low cost. Our results may provide insights on the relation between traffic dynamics and percolation, which can be useful for efficient transportation, epidemic control, and emergency evacuation.

  12. Surface Dynamics at Low Weber Numbers

    NASA Astrophysics Data System (ADS)

    Bacon, John Bartlett

    A quantitative surface-slope measurement tool is developed for liquids, using the schlieren optical testing technique. Clean free-surface deformations are studied in low Weber number interactions with isolated, symmetric, ellipsoidal vortices impinging vertically from below. Four linearly independent dynamic equations are deduced from the data, to completely characterize the time-dependent parameters of the problem. The surface deformations are modelled at all stages of the interaction as being symmetric Gaussian curves, with good agreement of the first moment of such curves with the observed slope profile data. The derived equations show strong evidence of the existence of a trapped volume of fluid, between the vortex and the surface, which mechanically couples the two entities. The same equipment is used to observe surface slope profiles of grid-generated turbulence in an open channel. The qualitative results are compared to general tendencies predicted by the isolated vortex equations, with good general agreement. A special case of liquid lithium at power-reactor temperatures is examined. It is determined that the random angular fluctuations of the surface due to turbulence are so large that channel-like liquid metal mirrors cannot be used for laser-fusion reactor applications.

  13. Network Randomization and Dynamic Defense for Critical Infrastructure Systems

    SciTech Connect

    Chavez, Adrian R.; Martin, Mitchell Tyler; Hamlet, Jason; Stout, William M.S.; Lee, Erik

    2015-04-01

    Critical Infrastructure control systems continue to foster predictable communication paths, static configurations, and unpatched systems that allow easy access to our nation's most critical assets. This makes them attractive targets for cyber intrusion. We seek to address these attack vectors by automatically randomizing network settings, randomizing applications on the end devices themselves, and dynamically defending these systems against active attacks. Applying these protective measures will convert control systems into moving targets that proactively defend themselves against attack. Sandia National Laboratories has led this effort by gathering operational and technical requirements from Tennessee Valley Authority (TVA) and performing research and development to create a proof-of-concept solution. Our proof-of-concept has been tested in a laboratory environment with over 300 nodes. The vision of this project is to enhance control system security by converting existing control systems into moving targets and building these security measures into future systems while meeting the unique constraints that control systems face.

  14. Critical dynamics in systems controlled by fractional kinetic equations

    NASA Astrophysics Data System (ADS)

    Batalov, Lev; Batalova, Anastasia

    2013-02-01

    The field theory renormalization group is used for analyzing the fractional Langevin equation with the order of the temporal derivative 0<α<1, fractional Laplacian of the order σ, and Gaussian noise correlator. The case of non-linearity φm with odd m≥3 is considered. It is proved that the model is multiplicatively renormalizable. Propagators were found in the momentum and coordinate representation, expressed in terms of Fox’s H functions. Existence of the dissipative scaling regime in the framework of the ε expansion for σ=2, α=1/l, l=1,2,… is proved. Requirement of the continuous dependence of the critical exponents on α imposes the condition m=3. The main quantitative result is the calculation of the dynamical critical exponent z for α=1/2 up to ε2. We have obtained for it the expression z=4+0.1555ε2+O(ε3).

  15. Quantum Theory as a Critical Regime of Language Dynamics

    NASA Astrophysics Data System (ADS)

    Grinbaum, Alexei

    2015-10-01

    Some mathematical theories in physics justify their explanatory superiority over earlier formalisms by the clarity of their postulates. In particular, axiomatic reconstructions drive home the importance of the composition rule and the continuity assumption as two pillars of quantum theory. Our approach sits on these pillars and combines new mathematics with a testable prediction. If the observer is defined by a limit on string complexity, information dynamics leads to an emergent continuous model in the critical regime. Restricting it to a family of binary codes describing `bipartite systems,' we find strong evidence of an upper bound on bipartite correlations equal to 2.82537. This is measurably different from the Tsirelson bound. The Hilbert space formalism emerges from this mathematical investigation as an effective description of a fundamental discrete theory in the critical regime.

  16. Dynamical Conductivity near the Superconductor to Insulator Critical Point

    NASA Astrophysics Data System (ADS)

    Auerbach, Assa

    2015-03-01

    I review our results for the dynamical complex conductivity near the two dimensional superconductor to insulator transition. The relativistic field theory is relevant to ordered Jospehson junction arrays and bosons trapped in an optical lattice. In the superconducting phase, the real conductivity reveals the Higgs mode mass as a threshold, with a weak ω5 sub-gap tail. The imaginary conductivity measures the critically vanishing superfluid density. In the insulator phase, the real conductivity has a sharp threshold at the Mott (charge) gap, and the imaginary conductivity goes as - Cω , where the capacitance C measures the inverse of the vortex superfluid density, which vanishes at the critical point. For layered, short coherence length (bosonic), superconductors, the Higgs threshold is raised by the inter-plane plasmon energy. Support of US-Israel Binational Science Foundation is gratefully acknowledged.

  17. Criticality and Universality in Healthy Heart Rate Dynamics

    NASA Astrophysics Data System (ADS)

    Struzik, Zbigniew R.; Kiyono, Ken; Hayano, Junichiro; Sakata, Seiichiro; Kwak, Shin; Yamamoto, Yoshiharu

    2005-08-01

    Methodologies originally developed in the field of statistical physics of complex phenomena have been proven to provide new insights into the modeling, description and understanding of the human heart rate regulatory system. Recent studies have shown the heart rate control system to maintain universality properties characteristic of physical systems exhibiting far-from-equilibrium, critical state-like dynamics. Simultaneously, heart rate regulation has been shown to display correlation properties of antagonist dynamics involving antagonist actors, pertinent to some far-from-equilibrium systems. We discuss the range of validity and breakdown scenarios of the universal properties in heart rate regulation leading to the diagnostic capability and also to new challenges for both analysis methods and up-to-date simulation models.

  18. Water at DNA surfaces: Ultrafast dynamics in minor groove recognition

    PubMed Central

    Pal, Samir Kumar; Zhao, Liang; Zewail, Ahmed H.

    2003-01-01

    Water molecules at the surface of DNA are critical to its equilibrium structure, DNA–protein function, and DNA–ligand recognition. Here we report direct probing of the dynamics of hydration, with femtosecond resolution, at the surface of a DNA dodecamer duplex whose native structure remains unperturbed on recognition in minor groove binding with the bisbenzimide drug (Hoechst 33258). By following the temporal evolution of fluorescence, we observed two well separated hydration times, 1.4 and 19 ps, whereas in bulk water the same drug is hydrated with time constants of 0.2 and 1.2 ps. For comparison, we also studied calf thymus DNA for which the hydration exhibits similar time scales to that of dodecamer DNA. However, the time-resolved polarization anisotropy is very different for the two types of DNA and clearly elucidates the rigidity in drug binding and difference in DNA rotational motions. These results demonstrate that hydration at the surface of the groove is a dynamical process with two general types of trajectories; the slowest of them (≈20 ps) are those describing dynamically ordered water. Because of their ultrafast time scale, the “ordered” water molecules are the most weakly bound and are accordingly involved in the entropic (hydration/dehydration) process of recognition. PMID:12815094

  19. Communicability angles reveal critical edges for network consensus dynamics

    NASA Astrophysics Data System (ADS)

    Estrada, Ernesto; Vargas-Estrada, Eusebio; Ando, Hiroyasu

    2015-11-01

    We consider the question of determining how the topological structure influences a consensus dynamical processes taking place on a network. By considering a large data set of real-world networks we first determine that the removal of edges according to their communicability angle, an angle between position vectors of the nodes in an Euclidean communicability space, increases the average time of consensus by a factor of 5.68 in real-world networks. The edge betweenness centrality also identifies, in a smaller proportion, those critical edges for the consensus dynamics; i.e., its removal increases the time of consensus by a factor of 3.70 . We justify theoretically these findings on the basis of the role played by the algebraic connectivity and the isoperimetric number of networks on the dynamical process studied and their connections with the properties mentioned before. Finally, we study the role played by global topological parameters of networks on the consensus dynamics. We determine that the network density and the average distance-sum, which is analogous of the node degree for shortest-path distances, account for more than 80% of the variance of the average time of consensus in the real-world networks studied.

  20. Stochastic Approximation of Dynamical Exponent at Quantum Critical Point

    NASA Astrophysics Data System (ADS)

    Suwa, Hidemaro; Yasuda, Shinya; Todo, Synge

    We have developed a unified finite-size scaling method for quantum phase transitions that requires no prior knowledge of the dynamical exponent z. During a quantum Monte Carlo simulation, the temperature is automatically tuned by the Robbins-Monro stochastic approximation method, being proportional to the lowest gap of the finite-size system. The dynamical exponent is estimated in a straightforward way from the system-size dependence of the temperature. As a demonstration of our novel method, the two-dimensional S = 1 / 2 quantum XY model, or equivalently the hard-core boson system, in uniform and staggered magnetic fields is investigated in the combination of the world-line quantum Monte Carlo worm algorithm. In the absence of a uniform magnetic field, we obtain the fully consistent result with the Lorentz invariance at the quantum critical point, z = 1 . Under a finite uniform magnetic field, on the other hand, the dynamical exponent becomes two, and the mean-field universality with effective dimension (2+2) governs the quantum phase transition. We will discuss also the system with random magnetic fields, or the dirty boson system, bearing a non-trivial dynamical exponent.Reference: S. Yasuda, H. Suwa, and S. Todo Phys. Rev. B 92, 104411 (2015); arXiv:1506.04837

  1. Surface profile acquisition using dynamic speckles

    NASA Astrophysics Data System (ADS)

    Semenov, Dmitry V.; Nippolainen, Ervin; Raita, Erik; Kamshilin, Alexei A.

    2006-01-01

    In this work we present the novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. The complete optical-electronic system was designed and fabricated for fast measurement of the speckles velocity, its recalculation into the distance, and further data acquisition into computer. The measured surface profile is displayed in a PC monitor in real time. Main advantage of the proposed technique is high scanning speed providing an extremely short response time below 1 μs. Important parameters of the system such as accuracy, range of measurements, and spatial resolution are analyzed. Limits of the spatial filtering technique used for continuous tracking of the speckle-pattern velocity are shown. Possible ways of further improvement of the measurements accuracy are demonstrated. Due to its extremely fast operation the proposed technique could find applications in such areas as online quality control of materials (paper thickness, rolled metal roughness, etc.) moving on production lines with high velocities (up to 20 m/s) or online control of the 3D-shape of complex objects (e.g., electronic circuits) during their assembling.

  2. Frictional dynamics of viscoelastic solids driven on a rough surface.

    PubMed

    Landes, François P; Rosso, Alberto; Jagla, E A

    2015-07-01

    We study the effect of viscoelastic dynamics on the frictional properties of a (mean-field) spring-block system pulled on a rough surface by an external drive. When the drive moves at constant velocity V, two dynamical regimes are observed: at fast driving, above a critical threshold V(c), the system slides at the drive velocity and displays a friction force with velocity weakening. Below V(c) the steady sliding becomes unstable and a stick-slip regime sets in. In the slide-hold-slide driving protocol, a peak of the friction force appears after the hold time and its amplitude increases with the hold duration. These observations are consistent with the frictional force encoded phenomenologically in the rate-and-state equations. Our model gives a microscopical basis for such macroscopic description.

  3. Unstable dynamics, nonequilibrium phases, and criticality in networked excitable media.

    PubMed

    de Franciscis, S; Torres, J J; Marro, J

    2010-10-01

    Excitable systems are of great theoretical and practical interest in mathematics, physics, chemistry, and biology. Here, we numerically study models of excitable media, namely, networks whose nodes may occasionally be dormant and the connection weights are allowed to vary with the system activity on a short-time scale, which is a convenient and realistic representation. The resulting global activity is quite sensitive to stimuli and eventually becomes unstable also in the absence of any stimuli. Outstanding consequences of such unstable dynamics are the spontaneous occurrence of various nonequilibrium phases--including associative-memory phases and one in which the global activity wanders irregularly, e.g., chaotically among all or part of the dynamic attractors--and 1/f noise as the system is driven into the phase region corresponding to the most irregular behavior. A net result is resilience which results in an efficient search in the model attractor space that can explain the origin of some observed behavior in neural, genetic, and ill-condensed matter systems. By extensive computer simulation we also address a previously conjectured relation between observed power-law distributions and the possible occurrence of a "critical state" during functionality of, e.g., cortical networks, and describe the precise nature of such criticality in the model which may serve to guide future experiments.

  4. Unstable dynamics, nonequilibrium phases, and criticality in networked excitable media

    SciTech Connect

    Franciscis, S. de; Torres, J. J.; Marro, J.

    2010-10-15

    Excitable systems are of great theoretical and practical interest in mathematics, physics, chemistry, and biology. Here, we numerically study models of excitable media, namely, networks whose nodes may occasionally be dormant and the connection weights are allowed to vary with the system activity on a short-time scale, which is a convenient and realistic representation. The resulting global activity is quite sensitive to stimuli and eventually becomes unstable also in the absence of any stimuli. Outstanding consequences of such unstable dynamics are the spontaneous occurrence of various nonequilibrium phases--including associative-memory phases and one in which the global activity wanders irregularly, e.g., chaotically among all or part of the dynamic attractors--and 1/f noise as the system is driven into the phase region corresponding to the most irregular behavior. A net result is resilience which results in an efficient search in the model attractor space that can explain the origin of some observed behavior in neural, genetic, and ill-condensed matter systems. By extensive computer simulation we also address a previously conjectured relation between observed power-law distributions and the possible occurrence of a ''critical state'' during functionality of, e.g., cortical networks, and describe the precise nature of such criticality in the model which may serve to guide future experiments.

  5. General Critical Properties of the Dynamics of Scientific Discovery

    SciTech Connect

    Bettencourt, L. M. A.; Kaiser, D. I.

    2011-05-31

    Scientific fields are difficult to define and compare, yet there is a general sense that they undergo similar stages of development. From this point of view it becomes important to determine if these superficial similarities can be translated into a general framework that would quantify the general advent and subsequent dynamics of scientific ideas. Such a framework would have important practical applications of allowing us to compare fields that superficially may appear different, in terms of their subject matter, research techniques, typical collaboration size, etc. Particularh' important in a field's history is the moment at which conceptual and technical unification allows widespread exchange of ideas and collaboration, at which point networks of collaboration show the analog of a percolation phenomenon, developing a giant connected component containing most authors. Here we investigate the generality of this topological transition in the collaboration structure of scientific fields as they grow and become denser. We develop a general theoretical framework in which each scientific field is an instantiation of the same large-scale topological critical phenomenon. We consider whether the evidence from a variety of specific fields is consistent with this picture, and estimate critical exponents associated with the transition. We then discuss the generality of the phenomenon and to what extent we may expect other scientific fields — including very large ones — to follow the same dynamics.

  6. Interactions between nonlinear spur gear dynamics and surface wear

    NASA Astrophysics Data System (ADS)

    Ding, Huali; Kahraman, Ahmet

    2007-11-01

    In this study, two different dynamic models, a finite elements-based deformable-body model and a simplified discrete model, and a surface wear model are combined to study the interaction between gear surface wear and gear dynamic response. The proposed dynamic gear wear model includes the influence of worn surface profiles on dynamic tooth forces and transmission error as well as the influence of dynamic tooth forces on wear profiles. This paper first introduces the nonlinear dynamic models that include gear backlash and time-varying gear mesh stiffness, and a wear model separately. It presents a comparison to experiments for validation of the dynamic models. The dynamic models are combined with the wear model to study the interaction of surface wear and dynamic behavior in both linear and nonlinear response regimes. At the end, several sets of simulation results are used to demonstrate the two-way relationship between nonlinear gear dynamics and surface wear.

  7. Critical behavior of epidemic spreading in dynamic small world networks

    NASA Astrophysics Data System (ADS)

    Stone, Thomas; McKay, Susan

    2010-03-01

    Dynamic small-world (DSW) contact networks model populations that have fixed short range links but time varying stochastic long range links between individuals, such as in mobile populations. The measure of mobility is given by a parameter p that is directly analogous to the rewiring parameter in standard small-world networks. This study investigates the relative effects of vaccinations and avoidance of infected individuals in a susceptible-infected-recovered (SIR) epidemic model on a DSW network. We derive (1) the critical mobility required for an outbreak to occur as a function of the disease's infectivity, recovery rate, avoidance rate, and vaccination rate and (2) an expression to calculate the amount of vaccination and/or avoidance necessary to prevent the disease-free to endemic transition. Agreement between these calculated points and numerical simulation is excellent. We then show via finite size scaling that the transition is indeed a continuous phase transition and find the associated critical exponent. From this and other scaling relations at the critical point we can comment on the model's potential universality.

  8. Stochastic approximation of dynamical exponent at quantum critical point

    NASA Astrophysics Data System (ADS)

    Yasuda, Shinya; Suwa, Hidemaro; Todo, Synge

    2015-09-01

    We have developed a unified finite-size scaling method for quantum phase transitions that requires no prior knowledge of the dynamical exponent z . During a quantum Monte Carlo simulation, the temperature is automatically tuned by the Robbins-Monro stochastic approximation method, being proportional to the lowest gap of the finite-size system. The dynamical exponent is estimated in a straightforward way from the system-size dependence of the temperature. As a demonstration of our novel method, the two-dimensional S =1 /2 quantum X Y model in uniform and staggered magnetic fields is investigated in the combination of the world-line quantum Monte Carlo worm algorithm. In the absence of a uniform magnetic field, we obtain the fully consistent result with the Lorentz invariance at the quantum critical point, z =1 , i.e., the three-dimensional classical X Y universality class. Under a finite uniform magnetic field, on the other hand, the dynamical exponent becomes two, and the mean-field universality with effective dimension (2 +2 ) governs the quantum phase transition.

  9. Phase dynamics of low critical current density YBCO Josephson junctions

    NASA Astrophysics Data System (ADS)

    Massarotti, D.; Stornaiuolo, D.; Rotoli, G.; Carillo, F.; Galletti, L.; Longobardi, L.; Beltram, F.; Tafuri, F.

    2014-08-01

    High critical temperature superconductors (HTS) based devices can have impact in the study of the phase dynamics of Josephson junctions (JJs) thanks to the wide range of junction parameters they offer and to their unconventional properties. Measurements of current-voltage characteristics and of switching current distributions constitute a direct way to classify different regimes of the phase dynamics and of the transport, also in nontrivial case of the moderately damped regime (MDR). MDR is going to be more and more common in JJs with advances in nanopatterning superconductors and synthesizing novel hybrid systems. Distinctive signatures of macroscopic quantum tunneling and of thermal activation in presence of different tunable levels of dissipation have been detected in YBCO grain boundary JJs. Experimental data are supported by Monte Carlo simulations of the phase dynamics, in a wide range of temperatures and dissipation levels. This allows us to quantify dissipation in the MDR and partially reconstruct a phase diagram as guideline for a wide range of moderately damped systems.

  10. Critical dynamics of the classical anisotropic BCC Heisenberg antiferromagnet.

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Ho; Bunker, Alex; Landau, D. P.

    2001-03-01

    Large-scale spin-dynamics simulations have been used to investigate the dynamic behavior of the classical Heisenberg antiferromagnet with single-site uniaxial anisotropy, in bcc lattices. Time evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using an algorithm implemented by Krech et al [1], which is based on fourth-order Suzuki-Trotter decompositions of exponential operators. The dynamic structure factor S(q,ω) was calculated from the space- and time-displaced spin-spin correlation function. Preliminary results for the transverse and the longitudinal components of S(q,ω) show that while the former is propagative, with a relatively short time scale, the latter is diffusive and its computation requires very long time integrations. Because of difficulties for experiments to probe the critical region, experimental data have not yet been able to distinguish between competing theories. While limited by finite lattice size and finite integration time, simulations offer the hope of shedding light on the differences between theories and experiment. [1] M. Krech, A. Bunker, D.P. Landau, Comput. Phys. Commun. 111, 1 (1998). Supported by NSF and SDSC

  11. Criticality and surface tension in rotating horizon thermodynamics

    NASA Astrophysics Data System (ADS)

    Hansen, Devin; Kubizňák, David; Mann, Robert B.

    2016-08-01

    We study a modified horizon thermodynamics and the associated criticality for rotating black hole spacetimes. Namely, we show that under a virtual displacement of the black hole horizon accompanied by an independent variation of the rotation parameter, the radial Einstein equation takes a form of a ‘cohomogeneity two’ horizon first law, δ E=Tδ S+{{Ω }}δ J-σ δ A, where E and J are the horizon energy (an analogue of the Misner-Sharp mass) and the horizon angular momentum, Ω is the horizon angular velocity, A is the horizon area, and σ is the surface tension induced by the matter fields. For fixed angular momentum, the above equation simplifies and the more familiar (cohomogeneity one) horizon first law δ E=Tδ S-Pδ V is obtained, where P is the pressure of matter fields and V is the horizon volume. A universal equation of state is obtained in each case and the corresponding critical behavior is studied.

  12. Critical adsorption of copolymer tethered on selective surfaces

    NASA Astrophysics Data System (ADS)

    Li, Hong; Qian, Chang-Ji; Luo, Meng-Bo

    2016-04-01

    Critical adsorption behaviors of flexible copolymer chains tethered to a flat homogeneous surface are studied by using Monte Carlo simulations. We have compared the critical adsorption temperature Tc, estimated by a finite-size scaling method, for different AB copolymer sequences with A the attractive monomer and B the inert monomer. We find that Tc increases with an increase in the fraction of monomers A, fA, in copolymers, and it increases with an increase in the length of block A for the same fA. In particular, Tc of copolymer (AnBn)r can be expressed as a function of the block length, n, and Tc of copolymer (AnB)r and (ABm)r can be expressed as a linear function of fA. Tc of random copolymer chains also can be expressed as a linear function of fA and it can be estimated by using weight-average of Tc of different diblocks in the random copolymer. However, the crossover exponent is roughly independent of AB sequence distributions either for block copolymers or for random copolymers.

  13. Dynamical critical behavior of the Ziff-Gulari-Barshad model with quenched impurities

    NASA Astrophysics Data System (ADS)

    de Andrade, M. F.; Figueiredo, W.

    2016-08-01

    The simplest model to explain the CO oxidation in some catalytic processes is the Ziff-Gulari-Barshad (ZGB) model. It predicts a continuous phase transition between an active phase and an absorbing phase composed of O atoms. By employing Monte Carlo simulations we investigate the dynamical critical behavior of the model as a function of the concentration of fixed impurities over the catalytic surface. By means of an epidemic analysis we calculate the critical exponents related to the survival probability Ps (t), the number of empty sites nv (t), and the mean square displacement R2 (t). We show that the critical exponents depend on the concentration of impurities over the lattice, even for small values of this quantity. We also show that the exponents do not belong to the Directed Percolation universality class and are in agreement with the Harris criterion since the quenched impurities behave as a weak disorder in the system.

  14. Dynamic wormholes, antitrapped surfaces, and energy conditions

    SciTech Connect

    Hochberg, D.; Visser, M.

    1998-08-01

    It is by now apparent that topology is too crude a tool to accurately characterize a generic traversable wormhole. In two earlier papers we developed a complete characterization of generic but static traversable wormholes, and in the present paper extend the discussion to arbitrary time-dependent (dynamical) wormholes. A local definition of a wormhole throat, free from assumptions about asymptotic flatness, symmetries, future and past null infinities, embedding diagrams, topology, and even time dependence is developed that accurately captures the essence of what a wormhole throat is, and where it is located. Adapting and extending a suggestion due to Page, we define a wormhole throat to be a marginally anti-trapped surface, that is, a closed two-dimensional spatial hypersurface such that one of the two future-directed null geodesic congruences orthogonal to it is just beginning to diverge. Typically a dynamic wormhole will possess {ital two} such throats, corresponding to the two orthogonal null geodesic congruences, and these two throats will not coincide (though they do coalesce into a single throat in the static limit). The divergence property of the null geodesics at the marginally anti-trapped surface generalizes the {open_quotes}flare-out{close_quotes} condition for an arbitrary wormhole. We derive theorems regarding violations of the null energy condition (NEC) at and near these throats and find that, even for wormholes with arbitrary time dependence, the violation of the NEC is a generic property of wormhole throats. We also discuss wormhole throats in the presence of fully antisymmetric torsion and find that the energy condition violations {ital cannot} be dumped into the torsion degrees of freedom. Finally by means of a concrete example we demonstrate that even temporary suspension of energy-condition violations is incompatible with the flare-out property of dynamic throats. {copyright} {ital 1998} {ital The American Physical Society}

  15. Dynamic wormholes, antitrapped surfaces, and energy conditions

    NASA Astrophysics Data System (ADS)

    Hochberg, David; Visser, Matt

    1998-08-01

    It is by now apparent that topology is too crude a tool to accurately characterize a generic traversable wormhole. In two earlier papers we developed a complete characterization of generic but static traversable wormholes, and in the present paper extend the discussion to arbitrary time-dependent (dynamical) wormholes. A local definition of a wormhole throat, free from assumptions about asymptotic flatness, symmetries, future and past null infinities, embedding diagrams, topology, and even time dependence is developed that accurately captures the essence of what a wormhole throat is, and where it is located. Adapting and extending a suggestion due to Page, we define a wormhole throat to be a marginally anti-trapped surface, that is, a closed two-dimensional spatial hypersurface such that one of the two future-directed null geodesic congruences orthogonal to it is just beginning to diverge. Typically a dynamic wormhole will possess two such throats, corresponding to the two orthogonal null geodesic congruences, and these two throats will not coincide (though they do coalesce into a single throat in the static limit). The divergence property of the null geodesics at the marginally anti-trapped surface generalizes the ``flare-out'' condition for an arbitrary wormhole. We derive theorems regarding violations of the null energy condition (NEC) at and near these throats and find that, even for wormholes with arbitrary time dependence, the violation of the NEC is a generic property of wormhole throats. We also discuss wormhole throats in the presence of fully antisymmetric torsion and find that the energy condition violations cannot be dumped into the torsion degrees of freedom. Finally by means of a concrete example we demonstrate that even temporary suspension of energy-condition violations is incompatible with the flare-out property of dynamic throats.

  16. Collective motion of macroscopic spheres floating on capillary ripples: dynamic heterogeneity and dynamic criticality.

    PubMed

    Sanlı, Ceyda; Saitoh, Kuniyasu; Luding, Stefan; van der Meer, Devaraj

    2014-09-01

    When a densely packed monolayer of macroscopic spheres floats on chaotic capillary Faraday waves, a coexistence of large scale convective motion and caging dynamics typical for glassy systems is observed. We subtract the convective mean flow using a coarse graining (homogenization) method and reveal subdiffusion for the caging time scales followed by a diffusive regime at later times. We apply the methods developed to study dynamic heterogeneity and show that the typical time and length scales of the fluctuations due to rearrangements of observed particle groups significantly increase when the system approaches its largest experimentally accessible packing concentration. To connect the system to the dynamic criticality literature, we fit power laws to our results. The resultant critical exponents are consistent with those found in densely packed suspensions of colloids.

  17. Static and Dynamic Verification of Critical Software for Space Applications

    NASA Astrophysics Data System (ADS)

    Moreira, F.; Maia, R.; Costa, D.; Duro, N.; Rodríguez-Dapena, P.; Hjortnaes, K.

    Space technology is no longer used only for much specialised research activities or for sophisticated manned space missions. Modern society relies more and more on space technology and applications for every day activities. Worldwide telecommunications, Earth observation, navigation and remote sensing are only a few examples of space applications on which we rely daily. The European driven global navigation system Galileo and its associated applications, e.g. air traffic management, vessel and car navigation, will significantly expand the already stringent safety requirements for space based applications Apart from their usefulness and practical applications, every single piece of onboard software deployed into the space represents an enormous investment. With a long lifetime operation and being extremely difficult to maintain and upgrade, at least when comparing with "mainstream" software development, the importance of ensuring their correctness before deployment is immense. Verification &Validation techniques and technologies have a key role in ensuring that the onboard software is correct and error free, or at least free from errors that can potentially lead to catastrophic failures. Many RAMS techniques including both static criticality analysis and dynamic verification techniques have been used as a means to verify and validate critical software and to ensure its correctness. But, traditionally, these have been isolated applied. One of the main reasons is the immaturity of this field in what concerns to its application to the increasing software product(s) within space systems. This paper presents an innovative way of combining both static and dynamic techniques exploiting their synergy and complementarity for software fault removal. The methodology proposed is based on the combination of Software FMEA and FTA with Fault-injection techniques. The case study herein described is implemented with support from two tools: The SoftCare tool for the SFMEA and SFTA

  18. Free surface dynamics of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Cummings, Linda; Kondic, Lou; Lam, Michael; Lin, Te-Sheng

    2014-11-01

    Spreading thin films of nematic liquid crystal (NLC) are known to behave very differently to those of isotropic fluids. The polar interactions of the rod-like molecules with each other, and the interactions with the underlying substrate, can lead to intricate patterns and instabilities that are not yet fully understood. The physics of a system even as simple as a film of NLC spreading slowly over a surface (inclined or horizontal) are remarkably complex: the outcome depends strongly on the details of the NLC's behavior at both the substrate and the free surface (so-called ``anchoring'' effects). We will present a dynamic flow model that takes careful account of such nematic-substrate and nematic-free surface interactions. We will present model simulations for several different flow scenarios that indicate the variety of behavior that can emerge. Spreading over a horizontal substrate may exhibit a range of unstable behavior. Flow down an incline also exhibits intriguing instabilities: in addition to the usual transverse fingering, instabilities can be manifested behind the flowing front in a manner reminiscent of Newtonian flow down an inverted substrate. NSF DMS-1211713.

  19. Water dynamics near solutes and surfaces

    NASA Astrophysics Data System (ADS)

    Moilanen, David Emil

    The hydrogen bonding structure and dynamics of water are fundamentally important in a wide range of chemical, biological, geological, and industrial systems. Infrared spectroscopy of the OD stretch of dilute HOD in H2 O provides a sensitive probe of the hydrogen bonding network of water. Water forms a nominally tetrahedral hydrogen bonding network as a liquid but rapid hydrogen bond switching events lead to fast water reorientation. A mechanism for water reorientation that involves large amplitude angular jumps has recently been proposed to describe the long time orientational dynamics. At short times, water molecules quickly sample a restricted range of angular space within an intact hydrogen bonding configuration. The amplitude of this inertial reorientation depends on the strength of the local hydrogen bonding network. When hydrogen bonds are stronger, the water is restricted to a smaller angular range about the hydrogen bond axis. Weaker hydrogen bonds allow larger angular excursions. A simple model for the angular hydrogen bond potential energy surface is presented based on the experimental data. Water is rarely found as a pure liquid in real systems. Often it is in contact with a surface and its dynamics are modified near the surface. Reverse micelles formed using the surfactant Aerosol-OT (AOT), water, and isooctane, as well as AOT lamellar structures provide well-defined, tunable model systems to study the dynamics of water interacting with an interface. Reverse micelles are spherical water pools with radii that can be varied from less than one nanometer up to tens of nanometers. Lamellar structures are surfactant bilayers separated by thin sheets of water ranging in thickness from approximately one nanometer up to four nanometers. In large reverse micelles and lamellar structures, the confined water can be separated into two components, a core of bulk-like water and a shell of interfacial water. Polarization selective pump-probe spectroscopy of the OD

  20. Critical dynamics of cluster algorithms in the dilute Ising model

    NASA Astrophysics Data System (ADS)

    Hennecke, M.; Heyken, U.

    1993-08-01

    Autocorrelation times for thermodynamic quantities at T C are calculated from Monte Carlo simulations of the site-diluted simple cubic Ising model, using the Swendsen-Wang and Wolff cluster algorithms. Our results show that for these algorithms the autocorrelation times decrease when reducing the concentration of magnetic sites from 100% down to 40%. This is of crucial importance when estimating static properties of the model, since the variances of these estimators increase with autocorrelation time. The dynamical critical exponents are calculated for both algorithms, observing pronounced finite-size effects in the energy autocorrelation data for the algorithm of Wolff. We conclude that, when applied to the dilute Ising model, cluster algorithms become even more effective than local algorithms, for which increasing autocorrelation times are expected.

  1. Dynamical criticality in the collective activity of a neural population

    NASA Astrophysics Data System (ADS)

    Mora, Thierry

    The past decade has seen a wealth of physiological data suggesting that neural networks may behave like critical branching processes. Concurrently, the collective activity of neurons has been studied using explicit mappings to classic statistical mechanics models such as disordered Ising models, allowing for the study of their thermodynamics, but these efforts have ignored the dynamical nature of neural activity. I will show how to reconcile these two approaches by learning effective statistical mechanics models of the full history of the collective activity of a neuron population directly from physiological data, treating time as an additional dimension. Applying this technique to multi-electrode recordings from retinal ganglion cells, and studying the thermodynamics of the inferred model, reveals a peak in specific heat reminiscent of a second-order phase transition.

  2. Dynamic neuroendocrine changes in critically ill patients with polytrauma.

    PubMed

    Galusova, Andrea; Pauliny, Matus; Majek, Milan; Mackova, Jaroslava; Meskova, Milada; Vlcek, Miroslav; Imrich, Richard; Penesova, Adela

    2015-01-01

    Acute multiple-trauma induces activation of neuroendocrine system. Nonthyroidal illness syndrome (NTIS) is considered to be associated with adverse outcome in intensive care unit (ICU) patients. This study was aimed to assess dynamic changes of neuroendocrine hormones in patients with polytrauma and their association with the polytrauma score (PTS). Blood samples from 24 critically ill patients with polytrauma were obtained on 1st, 2nd, 3rd and 7th day after admission to ICU for analysis of thyroid-stimulating hormone (TSH), total triiodothyronine (T3); free triiodothyronine (fT3), total thyroxine (T4), free thyroxine (fT4), growth hormone (GH), prolactin (PRL) and procalcitonin levels. Acute Physiology and Chronic Health Evaluation (APACHE) II score was 16±5 points on average at the admission to ICU. All patients had normal baseline TSH, T4, fT4, but low T3, and fT3 levels were found in 20% and 33% ICU patients, respectively. On the 7th day after admission to ICU TSH had tendency to increase (p=0.07) and fT4 significantly decreased (p=0.03). The PRL level significantly increased on the 3rd day after admission as compared to 1st day (p=0.04). PTS positively correlated with fT3 (r=0.582, p=0.004) and negatively with fT4 (r=-0.422, p=0.04) at the 1st day in ICU. Critical illness in patients with polytrauma leaded to trauma severity-dependent alterations of the thyroid axis response early after injury. Our findings suggest that detection of dynamic hormonal response is more appropriate than single measurement. However supplemental therapy for NTIS should be used after more detailed studies are completed.

  3. Static and dynamic friction of hierarchical surfaces

    NASA Astrophysics Data System (ADS)

    Costagliola, Gianluca; Bosia, Federico; Pugno, Nicola M.

    2016-12-01

    Hierarchical structures are very common in nature, but only recently have they been systematically studied in materials science, in order to understand the specific effects they can have on the mechanical properties of various systems. Structural hierarchy provides a way to tune and optimize macroscopic mechanical properties starting from simple base constituents and new materials are nowadays designed exploiting this possibility. This can be true also in the field of tribology. In this paper we study the effect of hierarchical patterned surfaces on the static and dynamic friction coefficients of an elastic material. Our results are obtained by means of numerical simulations using a one-dimensional spring-block model, which has previously been used to investigate various aspects of friction. Despite the simplicity of the model, we highlight some possible mechanisms that explain how hierarchical structures can significantly modify the friction coefficients of a material, providing a means to achieve tunability.

  4. Static and dynamic friction of hierarchical surfaces.

    PubMed

    Costagliola, Gianluca; Bosia, Federico; Pugno, Nicola M

    2016-12-01

    Hierarchical structures are very common in nature, but only recently have they been systematically studied in materials science, in order to understand the specific effects they can have on the mechanical properties of various systems. Structural hierarchy provides a way to tune and optimize macroscopic mechanical properties starting from simple base constituents and new materials are nowadays designed exploiting this possibility. This can be true also in the field of tribology. In this paper we study the effect of hierarchical patterned surfaces on the static and dynamic friction coefficients of an elastic material. Our results are obtained by means of numerical simulations using a one-dimensional spring-block model, which has previously been used to investigate various aspects of friction. Despite the simplicity of the model, we highlight some possible mechanisms that explain how hierarchical structures can significantly modify the friction coefficients of a material, providing a means to achieve tunability.

  5. Quantum surface and intertwiner dynamics in loop quantum gravity

    NASA Astrophysics Data System (ADS)

    Feller, Alexandre; Livine, Etera R.

    2017-06-01

    We introduce simple generic models of surface dynamics in loop quantum gravity (LQG). A quantum surface is defined as a set of elementary patches of area glued together. We provide it with an extra structure of locality (nearest neighbors), thought of as induced by the whole spin network state defining the 3d bulk geometry around the quantum surface. Here, we focus on classical surface dynamics, using a spinorial description of surface degrees of freedom. We introduce two classes of dynamics, to be thought as templates for future investigation of LQG dynamics with the dynamics of quantum black holes in mind. The first defines global dynamics of the closure defect of the surface, with two basic toy models, either a dissipative dynamics relaxing towards the closure constraint or a Hamiltonian dynamics precessing the closure defect. The second class of dynamics describes the isolated regime, when both area and closure defect are conserved throughout the evolution. The surface dynamics is implemented through U (N ) transformations and generalizes to a Bose-Hubbard Hamiltonian with a local quadratic potential interaction. We briefly discuss the implications of modeling the quantum black hole dynamics by a surface Bose-Hubbard model.

  6. Dynamics of Gas-Surface Interactions.

    DTIC Science & Technology

    1993-01-26

    inelastic scattering, metallic alloys, surface oxidation, S...surface phonon spectroscopy, gas-surface energy transfer. 19. ABSTRACT (Continue on...surface oxidation, the technological need to characterize the physical properties of thin films and surfaces, and the desire to understand how energy ... energy and momentum are exchanged at the surface of a material when it is subjected to gas- surface collisions, electron-surface collisions, optical

  7. Condensation and Wetting Dynamics on Micro/Nano-Structured Surfaces

    NASA Astrophysics Data System (ADS)

    Olceroglu, Emre

    Because of their adjustable wetting characteristics, micro/nanostructured surfaces are attractive for the enhancement of phase-change heat transfer where liquid-solid-vapor interactions are important. Condensation, evaporation, and boiling processes are traditionally used in a variety of applications including water harvesting, desalination, industrial power generation, HVAC, and thermal management systems. Although they have been studied by numerous researchers, there is currently a lack of understanding of the underlying mechanisms by which structured surfaces improve heat transfer during phase-change. This PhD dissertation focuses on condensation onto engineered surfaces including fabrication aspect, the physics of phase-change, and the operational limitations of engineered surfaces. While superhydrophobic condensation has been shown to produce high heat transfer rates, several critical issues remain in the field. These include surface manufacturability, heat transfer coefficient measurement limitations at low heat fluxes, failure due to surface flooding at high supersaturations, insufficient modeling of droplet growth rates, and the inherent issues associated with maintenance of non-wetted surface structures. Each of these issues is investigated in this thesis, leading to several contributions to the field of condensation on engineered surfaces. A variety of engineered surfaces have been fabricated and characterized, including nanostructured and hierarchically-structured superhydrophobic surfaces. The Tobacco mosaic virus (TMV) is used here as a biological template for the fabrication of nickel nanostructures, which are subsequently functionalized to achieve superhydrophobicity. This technique is simple and sustainable, and requires no applied heat or external power, thus making it easily extendable to a variety of common heat transfer materials and complex geometries. To measure heat transfer rates during superhydrophobic condensation in the presence of non

  8. Statistical characteristics of topographic surfaces and dynamic smoothing of landscapes

    NASA Astrophysics Data System (ADS)

    Bartlett, M. S.; Laio, F.; Ridolfi, L.; Vico, G.; Porporato, A. M.

    2011-12-01

    We analyze the local statistics of topographic surfaces, including slope and aspect, as a function of scale, and explore their relations with landscape features, such as age, vegetation, and geology. These results build upon the previous work of Vico and Porporato (JGR 114, F01011, 2009), which characterized slope using generalized t-Student distributions. We find that the number of degrees of freedom of such distributions, which determines the heaviness of their tails, is linked to the age of the topographic relief of the considered regions, tending to normal distributions for very old mountain ranges. Based on these findings, and inspired by models of critical phenomena, we develop physically-based, space-time stochastic differential equations that reproduce this dynamic smoothing of rough landscapes.

  9. Liquid dynamics and surface wettability in splashing

    NASA Astrophysics Data System (ADS)

    Latka, Andrzej; Boelens, Arnout; de Pablo, Juan; Nagel, Sidney

    2016-11-01

    The impact of a drop results in a beautiful splash that depends on the properties of the liquid, the substrate, and the surrounding air. The interactions of the three phases, particularly those of the ambient gas, have proven difficult to understand. Here, we focus on two aspects of splashing that make it exceptionally challenging: the surprising role of substrate wetting and the complicated hydrodynamics of drop impact. Splashing theories, by analogy to forced wetting, have predicted a strong dependence on wetting properties. By using high-speed interference imaging and simulations, we find that the dynamics of the air-liquid interface at the contact line are independent of substrate wetting properties. We also investigate the effect of the drop's evolving shape. When the drop first contacts the surface, it initially exhibits a region of high negative curvature that later disappears after the drop has spread sufficiently. We find that the effect of air on splashing is significantly stronger in the initial regime and demonstrate that this difference leads to a high and low impact velocity regime.

  10. Interfacial wicking dynamics and its impact on critical heat flux of boiling heat transfer

    NASA Astrophysics Data System (ADS)

    Kim, Beom Seok; Lee, Hwanseong; Shin, Sangwoo; Choi, Geehong; Cho, Hyung Hee

    2014-11-01

    Morphologically driven dynamic wickability is essential for determining the hydrodynamic status of solid-liquid interface. We demonstrate that the dynamic wicking can play an integral role in supplying and propagating liquid through the interface, and govern the critical heat flux (CHF) against surface dry-out during boiling heat transfer. For the quantitative control of wicking, we manipulate the characteristic lengths of hexagonally arranged nanopillars within sub-micron range through nanosphere lithography combined with top-down metal-assisted chemical etching. Strong hemi-wicking over the manipulated interface (i.e., wicking coefficients) of 1.28 mm/s0.5 leads to 164% improvement of CHF compared to no wicking. As a theoretical guideline, our wickability-CHF model can make a perfect agreement with improved CHF, which cannot be predicted by the classic models pertaining to just wettability and roughness effects, independently.

  11. Surface water acidification and critical loads: exploring the F-factor

    NASA Astrophysics Data System (ADS)

    Rapp, L.; Bishop, K.

    2009-05-01

    As acid deposition decreases, uncertainties in methods for calculating critical loads become more important when judgements have to be made about whether or not further emission reductions are needed. An important aspect of one type of model that has been used to calculate surface water critical loads is the empirical F-factor which estimates the degree to which acid deposition is neutralised before it reaches a lake at any particular point in time relative to the pre-industrial, steady-state water chemistry conditions. In this paper we will examine how well the empirical F-functions are able to estimate pre-industrial lake chemistry as lake chemistry changes during different phases of acidification and recovery. To accomplish this, we use the dynamic, process-oriented biogeochemical model SAFE to generate a plausible time series of annual runoff chemistry for ca 140 Swedish catchments between 1800 and 2100. These annual hydrochemistry data are then used to generate empirical F-factors that are compared to the "actual" F-factor seen in the SAFE data for each lake and year in the time series. The dynamics of the F-factor as catchments acidify, and then recover are not widely recognised. Our results suggest that the F-factor approach worked best during the acidification phase when soil processes buffer incoming acidity. However, the empirical functions for estimating F from contemporary lake chemistry are not well suited to the recovery phase when the F-factor turns negative due to recovery processes in the soil. Therefore, the empirical estimates of the F-factor are a significant source of uncertainty in the estimate of surface water critical loads and related calculations for quantifying lake acidification status, especially now that acid deposition has declined across large areas of Europe and North America.

  12. Dynamic Perturbation of a Turbulent Boundary Layer and Experimental Identification of Critical-Layer-Type Behavior

    NASA Astrophysics Data System (ADS)

    Jacobi, Ian; McKeon, Beverley J.

    2010-11-01

    A zero-pressure gradient turbulent boundary layer is perturbed by a spatially impulsive patch of two-dimensional roughness elements, which are actuated dynamically to alternate between smooth and rough surface conditions, and the downstream response is measured by hot-wire anemometry and particle image velocimetry. The dynamic perturbation is observed to contribute a periodic signature to the downstream flow-field, which manifests itself in critical-layer type behavior. The downstream flow field is reconstructed in a phase-locked sense in order to compare the observed behavior with asymptotic representations of the expected behavior at matched flow conditions. Perturbation using a periodic disturbance is shown to reveal underlying features of the turbulent boundary layer which are intimately connected to the critical layer framework for turbulent pipe flow proposed by McKeon & Sharma (see the DFD-2010 presentation on `Structure from the critical layer framework in turbulent flow' by Sharma & McKeon), while simultaneously providing practical insight on the manipulation of the structure of boundary layers.

  13. Critical Steady Surface Waves of Idea Fluid over a Bump with Surface Tension

    NASA Astrophysics Data System (ADS)

    Choi, Jeongwhan; Lee, Sangwon; Kim, Joonkyoung; Whang, Sungim

    2016-11-01

    The paper deals with steady forced surface waves propagating on a two-dimensional incompressible and inviscid fluid with a small bump placed on a rigid flat bottom. If the surface tension coefficient T on the free surface is not zero and the wave is moving with a constant speed C, the wave motion is determined by two non-dimensional constants, F = √ gh and I = T / (ρgh 2) , where g is the gravity constant and h is the height of the fluid at infinity. It has been known that F = 1 and t = 1/3 are the critical values of F and t, respectively. In the critical case F = 1 + λ 1 ɛ 2 and t = 1/3 + t1 ɛ with ɛ > 0 a small parameter, a time-dependent forced Kawahara (F-Kawahara)equation is derived to model the wave propagation on the free surface and the steady F-Kawahara equation is studied both theoretically and merically. It is shown that the steady F-Kawahara equation has many different kinds of one and multi-hump solutions when t1 and λ 1 vary. In particular, for a fixed t 1, there is a λ 0 < 0 such that if λ 1 < λ 0 , two one-hump steady solutions can be obtained, one with small amplitude and the other with large amplitude. By using the unsteady F-Kawahara equation, it appears that the small one-hump solution is stable while the large one is nstable. In addition, two-hump solutions are unstable.

  14. Cell-surface translational dynamics of nicotinic acetylcholine receptors

    PubMed Central

    Barrantes, Francisco J.

    2014-01-01

    Synapse efficacy heavily relies on the number of neurotransmitter receptors available at a given time. In addition to the equilibrium between the biosynthetic production, exocytic delivery and recycling of receptors on the one hand, and the endocytic internalization on the other, lateral diffusion and clustering of receptors at the cell membrane play key roles in determining the amount of active receptors at the synapse. Mobile receptors traffic between reservoir compartments and the synapse by thermally driven Brownian motion, and become immobilized at the peri-synaptic region or the synapse by: (a) clustering mediated by homotropic inter-molecular receptor–receptor associations; (b) heterotropic associations with non-receptor scaffolding proteins or the subjacent cytoskeletal meshwork, leading to diffusional “trapping,” and (c) protein-lipid interactions, particularly with the neutral lipid cholesterol. This review assesses the contribution of some of these mechanisms to the supramolecular organization and dynamics of the paradigm neurotransmitter receptor of muscle and neuronal cells -the nicotinic acetylcholine receptor (nAChR). Currently available information stemming from various complementary biophysical techniques commonly used to interrogate the dynamics of cell-surface components is critically discussed. The translational mobility of nAChRs at the cell surface differs between muscle and neuronal receptors in terms of diffusion coefficients and residence intervals at the synapse, which cover an ample range of time regimes. A peculiar feature of brain α7 nAChR is its ability to spend much of its time confined peri-synaptically, vicinal to glutamatergic (excitatory) and GABAergic (inhibitory) synapses. An important function of the α7 nAChR may thus be visiting the territories of other neurotransmitter receptors, differentially regulating the dynamic equilibrium between excitation and inhibition, depending on its residence time in each domain. PMID

  15. Hydration dynamics near a model protein surface

    SciTech Connect

    Russo, Daniela; Hura, Greg; Head-Gordon, Teresa

    2003-09-01

    The evolution of water dynamics from dilute to very high concentration solutions of a prototypical hydrophobic amino acid with its polar backbone, N-acetyl-leucine-methylamide (NALMA), is studied by quasi-elastic neutron scattering and molecular dynamics simulation for both the completely deuterated and completely hydrogenated leucine monomer. We observe several unexpected features in the dynamics of these biological solutions under ambient conditions. The NALMA dynamics shows evidence of de Gennes narrowing, an indication of coherent long timescale structural relaxation dynamics. The translational water dynamics are analyzed in a first approximation with a jump diffusion model. At the highest solute concentrations, the hydration water dynamics is significantly suppressed and characterized by a long residential time and a slow diffusion coefficient. The analysis of the more dilute concentration solutions takes into account the results of the 2.0M solution as a model of the first hydration shell. Subtracting the first hydration layer based on the 2.0M spectra, the translational diffusion dynamics is still suppressed, although the rotational relaxation time and residential time are converged to bulk-water values. Molecular dynamics analysis shows spatially heterogeneous dynamics at high concentration that becomes homogeneous at more dilute concentrations. We discuss the hydration dynamics results of this model protein system in the context of glassy systems, protein function, and protein-protein interfaces.

  16. Europan Ocean Dynamics Inferred from Surface Geology

    NASA Astrophysics Data System (ADS)

    Schmidt, B. E.; Soderlund, K. M.; Blankenship, D. D.; Wicht, J.

    2012-12-01

    Europa possesses a global liquid water ocean that mediates heat exchange from the silicate interior to the outer icy shell. Since no direct observations of ocean dynamics are presently available, possible oceanographic processes must be inferred remotely through their implications for surface geology. For example, regions of disrupted ice known as chaos terrain are thought to represent locations of high heat flow from the ocean into the ice shell and tend to be concentrated at low latitudes. Since ocean currents can reorganize the flow of heat from the interior and potentially deliver regionally-varying basal heat to the ice shell, we hypothesize that oceanic heat transfer may peak near the equator. We also suggest that Europan ocean convection may be strongly turbulent with three-dimensional plumes, behavior that is fundamentally different from the prevailing assumption in the literature that Europa's ocean is organized into coherent, columnar structures that are aligned with the rotation axis. Towards testing these hypotheses, we simulate turbulent thermal convection in a thin, rotating spherical shell with Europa-relevant conditions. The small-scale, poorly-organized convective motions in our simulation homogenize the system's absolute angular momentum at low latitudes. Zonal flows develop with retrograde (westward) flow near the equator and prograde (eastward) flow near the rotation axis in order to conserve angular momentum. This angular momentum transport is achieved through Hadley-like cells with upwelling flow near the equator, poleward flow near the outer boundary, downwelling at mid-latitudes, and equatorward return flow near the inner boundary. These circulation cells, which control the mean ocean temperature and the mean flux of heat from the ocean into the ice shell, cause heat to be preferentially emitted in a low latitude. Mean ocean temperatures also have implications for vertical gradients in salinity since seawater is able to maintain more

  17. Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements

    DTIC Science & Technology

    2015-03-31

    Final March 2013 -- February 2015 Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements N00014-13-1-0352 Yue, Dick K.P... Dick K.P. and Yuming Liu 617-253-6823; 617-252-1647 1 Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements Dick K.P

  18. Maximum drop radius and critical Weber number for splashing in the dynamical Leidenfrost regime

    NASA Astrophysics Data System (ADS)

    Riboux, Guillaume; Gordillo, Jose Manuel

    2015-11-01

    At room temperature, when a drop impacts against a smooth solid surface at a velocity above the so called critical velocity for splashing, the drop loses its integrity and fragments into tiny droplets violently ejected radially outwards. Below this critical velocity, the drop simply spreads over the substrate. Splashing is also reported to occur for solid substrate temperatures above the Leidenfrost temperature, T, for which a vapor layer prevents the drop from touching the substrate. In this case, the splashing morphology largely differs from the one reported at room temperature because, thanks to the presence of the gas layer, the shear stresses on the liquid do not decelerate the ejected lamella. Our purpose here is to predict, for wall temperatures above T, the dependence of the critical impact velocity on the temperature of the substrate as well as the maximum spreading radius for impacting velocities below the critical velocity for splashing. This is done making use of boundary integral simulations, where the velocity and the height of the liquid layer at the root of the ejected lamella are calculated numerically. This information constitutes the initial conditions for the one dimensional mass and momentum equations governing the dynamics of the toroidal rim limiting the edge of the lamella.

  19. Surface water acidification and critical loads: exploring the F-factor

    NASA Astrophysics Data System (ADS)

    Rapp, L.; Bishop, K.

    2009-11-01

    As acid deposition decreases, uncertainties in methods for calculating critical loads become more important when judgements have to be made about whether or not further emission reductions are needed. An important aspect of one type of model that has been used to calculate surface water critical loads is the empirical F-factor which estimates the degree to which acid deposition is neutralised before it reaches a lake at any particular point in time relative to the pre-industrial, steady-state water chemistry conditions. In this paper we will examine how well the empirical F-functions are able to estimate pre-industrial lake chemistry as lake chemistry changes during different phases of acidification and recovery. To accomplish this, we use the dynamic, process-oriented biogeochemical model SAFE to generate a plausible time series of annual runoff chemistry for ca. 140 Swedish catchments between 1800 and 2100. These annual hydrochemistry data are then used to generate empirical F-factors that are compared to the "actual" F-factor seen in the SAFE data for each lake and year in the time series. The dynamics of the F-factor as catchments acidify, and then recover are not widely recognised. Our results suggest that the F-factor approach worked best during the acidification phase when soil processes buffer incoming acidity. However, the empirical functions for estimating F from contemporary lake chemistry are not well suited to the recovery phase when the F-factor turns negative due to recovery processes in the soil. This happens when acid deposition has depleted the soil store of BC, and then acid deposition declines, reducing the leaching of base cations to levels below those in the pre-industrial era. An estimate of critical load from water chemistry during recovery and empirical F functions would therefore result in critical loads that are too low. Therefore, the empirical estimates of the F-factor are a significant source of uncertainty in the estimate of surface

  20. Hydrodynamic boundary conditions and dynamic forces between bubbles and surfaces.

    PubMed

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

    2008-07-11

    Dynamic forces between a 50 microm 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. Hydrodynamic Boundary Conditions and Dynamic Forces between Bubbles and Surfaces

    NASA Astrophysics Data System (ADS)

    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.

  2. Critical Dynamics Behavior of the Wolff Algorithm in the Site-Bond-Correlated Ising Model

    NASA Astrophysics Data System (ADS)

    Campos, P. R. A.; Onody, R. N.

    Here we apply the Wolff single-cluster algorithm to the site-bond-correlated Ising model and study its critical dynamical behavior. We have verified that the autocorrelation time diminishes in the presence of dilution and correlation, showing that the Wolff algorithm performs even better in such situations. The critical dynamical exponents are also estimated.

  3. Dynamic recrystallization in friction surfaced austenitic stainless steel coatings

    SciTech Connect

    Puli, Ramesh Janaki Ram, G.D.

    2012-12-15

    Friction surfacing involves complex thermo-mechanical phenomena. In this study, the nature of dynamic recrystallization in friction surfaced austenitic stainless steel AISI 316L coatings was investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the alloy 316L undergoes discontinuous dynamic recrystallization under conditions of moderate Zener-Hollomon parameter during friction surfacing. - Highlights: Black-Right-Pointing-Pointer Dynamic recrystallization in alloy 316L friction surfaced coatings is examined. Black-Right-Pointing-Pointer Friction surfacing leads to discontinuous dynamic recrystallization in alloy 316L. Black-Right-Pointing-Pointer Strain rates in friction surfacing exceed 400 s{sup -1}. Black-Right-Pointing-Pointer Estimated grain size matches well with experimental observations in 316L coatings.

  4. Dynamics of inelastic and reactive gas-surface collisions

    SciTech Connect

    Smoliar, Laura Ann

    1995-04-01

    The dynamics of inelastic and reactive collisions in atomic beam-surface scattering are presented. The inelastic scattering of hyperthermal rare gaseous atoms from three alkali halide surfaces (LiF, NaCl, GI)was studied to understand mechanical energy transfer in unreactive systems. The dynamics of the chemical reaction in the scattering of H(D) atoms from the surfaces of LIF(001) and the basal plane of graphite were also studied.

  5. Critical appraisal and hazards of surface electromyography data acquisition in sport and exercise.

    PubMed

    Pieter Clarys, Jan; Scafoglieri, Aldo; Tresignie, Jonathan; Reilly, Thomas; Van Roy, Peter

    2010-06-01

    The aim of this critical appraisal and hazards of surface electromyography (SEMG) is to enhance the data acquisition quality in voluntary but complex movements, sport and exercise in particular. The methodological and technical registration strategies deal with telemetry and online data acquisition, the placement of the detection electrodes and the choice of the most adequate normalization mode.Findings compared with the literature suggest detection quality differences between registration methods and between water and air data acquisition allowing for output differences up to 30% between registration methods and up to 25% decrease in water, considering identical measures in air and in water. Various hazards deal with erroneous choices of muscles or electrode placement and the continuous confusion created by static normalization for dynamic motion. Peak dynamic intensities ranged from 111% (in archery) to 283% (in giant slalom) of a static 100% reference. In addition, the linear relationship between integrated EMG (IEMG) as a reference for muscle intensity and muscle force is not likely to exist in dynamic conditions since it is muscle - joint angle - and fatigue dependent. Contrary to expectations, the literature shows 30% of non linear relations in isometric conditions also.SEMG in sport and exercise is highly variable and different from clinical (e.g. neurological) EMG. Choices of electrodes, registration methods, muscles, joint angles and normalization techniques may lead to confusing and erroneous or incomparable results.

  6. Critical Appraisal and Hazards of Surface Electromyography Data Acquisition in Sport and Exercise

    PubMed Central

    Pieter Clarys, Jan; Scafoglieri, Aldo; Tresignie, Jonathan; Reilly, Thomas; Van Roy, Peter

    2010-01-01

    The aim of this critical appraisal and hazards of surface electromyography (SEMG) is to enhance the data acquisition quality in voluntary but complex movements, sport and exercise in particular. The methodological and technical registration strategies deal with telemetry and online data acquisition, the placement of the detection electrodes and the choice of the most adequate normalization mode. Findings compared with the literature suggest detection quality differences between registration methods and between water and air data acquisition allowing for output differences up to 30% between registration methods and up to 25% decrease in water, considering identical measures in air and in water. Various hazards deal with erroneous choices of muscles or electrode placement and the continuous confusion created by static normalization for dynamic motion. Peak dynamic intensities ranged from 111% (in archery) to 283% (in giant slalom) of a static 100% reference. In addition, the linear relationship between integrated EMG (IEMG) as a reference for muscle intensity and muscle force is not likely to exist in dynamic conditions since it is muscle – joint angle – and fatigue dependent. Contrary to expectations, the literature shows 30% of non linear relations in isometric conditions also. SEMG in sport and exercise is highly variable and different from clinical (e.g. neurological) EMG. Choices of electrodes, registration methods, muscles, joint angles and normalization techniques may lead to confusing and erroneous or incomparable results. PMID:22375194

  7. Probing critical surfaces in momentum space using real-space entanglement entropy: Bose versus Fermi

    NASA Astrophysics Data System (ADS)

    Lai, Hsin-Hua; Yang, Kun

    2016-03-01

    A codimension-one critical surface in momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the noninteracting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. The presence of such surfaces gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real-space entanglement entropy. The fundamental difference between a Fermi surface and a Bose surface is revealed by the fact that the logarithmic terms in entanglement entropies differ by a factor of 2: SlogBose=2 SlogFermi , even when they have identical geometry. Our method has remarkable similarity with determining Fermi surface shape using quantum oscillation. We also discuss possible probes of concave critical surfaces in momentum space.

  8. Critical contaminant/critical pathway analysis - surface water transport for nonradioactive contaminants

    SciTech Connect

    Chen, Kuo-Fu

    1996-11-01

    The health risks for an individual exposed to contaminants released from SRS outfalls from 1989 to 1995 were estimated. The exposure pathways studied are ingestion of drinking water, ingestion of contaminated fish and dermal contact with contaminants in water while swimming. The estimated incremental risks for an individual developing cancer vary from 3.E-06 to 1.0E-05. The estimated total exposure chronic noncancer hazard indices vary from 6.E-02 to 1.E-01. The critical contaminants were ranked based on their cancer risks and chronic noncarcinogenic hazard quotients. For cancer risks, the critical contaminants released from SRS outfalls are arsenic, tetrachloroethylene, and benzene. For chronic noncarcinogenic risks, the critical contaminants released from srs outfalls are cadmium, arsenic, silver, chromium, mercury, selenium, nitrate, manganese, zinc, nickel, uranium, barium, copper, tetrachloroethylene, cyanide, and phenol. The critical pathways in decreasing risk order are ingestion of contaminated fish, ingestion of drinking water and dermal contact with contaminants in water while swimming.

  9. Flow Dynamics and Breakdown of Falling Liquid Films on the Heated Smooth and Structured Surface

    NASA Astrophysics Data System (ADS)

    Pecherkin, N. I.; Pavlenko, A. N.; Volodin, O. A.

    2011-09-01

    This paper presents the experimental results on heat transfer and hydrodynamics of the falling films of binary Freon mixtures on the tubes with smooth and textured surfaces. The range of Re number alteration at the working section inlet was Re = 10-155. The wave surface of the falling liquid film and the process of dry spot formation were recorded by the high-speed digital video camera. Results of investigation of the wave surface structure, measurements of heat transfer coefficients and dynamics of dry spot formation on the heated surface with corresponding critical heat fluxes are shown in this paper.

  10. Dynamic Diversity: Toward a Contextual Understanding of Critical Mass

    ERIC Educational Resources Information Center

    Garces, Liliana M.; Jayakumar, Uma M.

    2014-01-01

    Through an analysis of relevant social science evidence, this article provides a deeper understanding of critical mass, a concept that has become central in litigation efforts related to affirmative action admissions policies that seek to further the educational benefits of diversity. We demonstrate that the concept of critical mass requires an…

  11. Dynamic Diversity: Toward a Contextual Understanding of Critical Mass

    ERIC Educational Resources Information Center

    Garces, Liliana M.; Jayakumar, Uma M.

    2014-01-01

    Through an analysis of relevant social science evidence, this article provides a deeper understanding of critical mass, a concept that has become central in litigation efforts related to affirmative action admissions policies that seek to further the educational benefits of diversity. We demonstrate that the concept of critical mass requires an…

  12. Dynamics of free surface perturbations along an annular viscous film.

    PubMed

    Smolka, Linda B; North, Justin; Guerra, Bree K

    2008-03-01

    It is known that the free surface of an axisymmetric viscous film flowing down the outside of a thin vertical fiber under the influence of gravity becomes unstable to interfacial perturbations. We present an experimental study using fluids with different densities, surface tensions, and viscosities to investigate the growth and dynamics of these interfacial perturbations and to test the assumptions made by previous authors. We find that the initial perturbation growth is exponential, followed by a slower phase as the amplitude and wavelength saturate in size. Measurements of the perturbation growth for experiments conducted at low and moderate Reynolds numbers are compared to theoretical predictions developed from linear stability theory. Excellent agreement is found between predictions from a long-wave Stokes flow model [Craster and Matar, J. Fluid Mech. 553, 85 (2006)] and data, while fair to excellent agreement (depending on fiber size) is found between predictions from a moderate-Reynolds-number model [Sisoev, Chem. Eng. Sci. 61, 7279 (2006)] and data. Furthermore, we find that a known transition in the longer-time perturbation dynamics from unsteady to steady behavior at a critical flow rate Q(c) is correlated with a transition in the rate at which perturbations naturally form along the fiber. For QQ(c) (unsteady case), the rate of perturbation formation is modulated. As a result, the position along the fiber where perturbations form oscillates irregularly, and the initial speed and spacing between perturbations varies, resulting in the coalescence of neighboring perturbations further down the fiber.

  13. Dynamics of free surface perturbations along an annular viscous film

    NASA Astrophysics Data System (ADS)

    Smolka, Linda B.; North, Justin; Guerra, Bree K.

    2008-03-01

    It is known that the free surface of an axisymmetric viscous film flowing down the outside of a thin vertical fiber under the influence of gravity becomes unstable to interfacial perturbations. We present an experimental study using fluids with different densities, surface tensions, and viscosities to investigate the growth and dynamics of these interfacial perturbations and to test the assumptions made by previous authors. We find that the initial perturbation growth is exponential, followed by a slower phase as the amplitude and wavelength saturate in size. Measurements of the perturbation growth for experiments conducted at low and moderate Reynolds numbers are compared to theoretical predictions developed from linear stability theory. Excellent agreement is found between predictions from a long-wave Stokes flow model [Craster and Matar, J. Fluid Mech. 553, 85 (2006)] and data, while fair to excellent agreement (depending on fiber size) is found between predictions from a moderate-Reynolds-number model [Sisoev , Chem. Eng. Sci. 61, 7279 (2006)] and data. Furthermore, we find that a known transition in the longer-time perturbation dynamics from unsteady to steady behavior at a critical flow rate Qc is correlated with a transition in the rate at which perturbations naturally form along the fiber. For QQc (unsteady case), the rate of perturbation formation is modulated. As a result, the position along the fiber where perturbations form oscillates irregularly, and the initial speed and spacing between perturbations varies, resulting in the coalescence of neighboring perturbations further down the fiber.

  14. Critical-point analysis of the liquid-vapor interfacial surface tension

    NASA Technical Reports Server (NTRS)

    Salvino, R. E.

    1990-01-01

    The interfacial surface tension of the liquid-vapor system is analyzed near the critical point in a manner similar to bulk thermodynamic critical-point analyses. This is accomplished by a critical-point analysis of the single-phase hard-wall surface tension. Both a Landau expansion and a scaling theory equation of state are investigated. Some general exponent relations are derived and, in addition, some thermodynamically defined correlation lengths are discussed.

  15. Surface critical behavior of thin Ising films at the ‘special point’

    NASA Astrophysics Data System (ADS)

    Moussa, Najem; Bekhechi, Smaine

    2003-03-01

    The critical surface phenomena of a magnetic thin Ising film is studied using numerical Monte-Carlo method based on Wolff cluster algorithm. With varying the surface coupling, js= Js/ J, the phase diagram exhibits a special surface coupling jsp at which all the films have a unique critical temperature Tc for an arbitrary thickness n. In spite of this, the critical exponent of the surface magnetization at the special point is found to increase with n. Moreover, non-universal features as well as dimensionality crossover from two- to three-dimensional behavior are found at this point.

  16. Another View of Dynamic Criteria: A Critical Reanalysis of Barrett, Caldwell, and Alexander.

    ERIC Educational Resources Information Center

    Austin, James T.; And Others

    1989-01-01

    A critical reanalysis of Barrett, Caldwell, and Alexander's (1985) critique of dynamic criteria. Summarizes and questions Barrett, et al.'s three definitions of dynamic criteria and their conclusion that reported temporal changes in criteria could be explained by methodological artifacts. A greater focus on dynamic criteria as constructs is…

  17. A Critical Summary of Sea Surface Heat Exchange Equations.

    DTIC Science & Technology

    SOLAR RADIATION, SEA WATER), (*SEA WATER, HEAT TRANSFER), (* HEAT TRANSFER, MATHEMATICAL ANALYSIS), SURFACE PROPERTIES, THERMAL PROPERTIES, ALBEDO... HEAT FLUX, EVAPORATION, CONVECTION(ATMOSPHERIC), BOUNDARY LAYER, CLOUD COVER, WIND, VELOCITY.

  18. MR measurement of critical phase transition dynamics and supercritical fluid dynamics in capillary and porous media flow.

    PubMed

    Rassi, Erik M; Codd, Sarah L; Seymour, Joseph D

    2012-01-01

    Supercritical fluids (SCF) are useful solvents in green chemistry and oil recovery and are of great current interest in the context of carbon sequestration. Magnetic resonance techniques were applied to study near critical and supercritical dynamics for pump driven flow through a capillary and a packed bed porous media. Velocity maps and displacement propagators measure the dynamics of C(2)F(6) at pressures below, at, and above the critical pressure and at temperatures below and above the critical temperature. Displacement propagators were measured at various displacement observation times to quantify the time evolution of dynamics. In capillary flow, the critical phase transition fluid C(2)F(6) showed increased compressibility compared to the near critical gas and supercritical fluid. These flows exhibit large variations in buoyancy arising from large changes in density due to very small changes in temperature.

  19. Temperature dependent droplet impact dynamics on flat and textured surfaces

    SciTech Connect

    Azar Alizadeh; Vaibhav Bahadur; Sheng Zhong; Wen Shang; Ri Li; James Ruud; Masako Yamada; Liehi Ge; Ali Dhinojwala; Manohar S Sohal

    2012-03-01

    Droplet impact dynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling and heat transfer. We study impact dynamics of water droplets on surfaces with chemistry/texture ranging from hydrophilic to superhydrophobic and across a temperature range spanning below freezing to near boiling conditions. Droplet retraction shows very strong temperature dependence especially for hydrophilic surfaces; it is seen that lower substrate temperatures lead to lesser retraction. Physics-based analyses show that the increased viscosity associated with lower temperatures can explain the decreased retraction. The present findings serve to guide further studies of dynamic fluid-structure interaction at various temperatures.

  20. A critical assessment of finite element modeling approach for protein dynamics

    NASA Astrophysics Data System (ADS)

    Yun, Giseok; Kim, Jaehoon; Kim, Do-Nyun

    2017-07-01

    Finite element (FE) modeling approach has emerged as an efficient way of calculating the dynamic properties of supramolecular protein structures and their complexes. Its efficiency mainly stems from the fact that the complexity of three-dimensional shape of a molecular surface dominates the computational cost rather than the molecular size or the number of atoms. However, no critical evaluation of the method has been made yet particularly for its sensitivity to the parameters used in model construction. Here, we make a close investigation on the effect of FE model parameters by analyzing 135 representative protein structures whose normal modes calculated using all-atom normal mode analysis are publicly accessible online. Results demonstrate that it is more beneficial to use a contour surface of electron densities as the molecular surface, in general, rather than to employ a solvent excluded surface, and that the solution accuracy is almost insensitive to the model parameters unless we avoid extreme values leading to an inaccurate depiction of the characteristic shapes.

  1. Electrostatic cloaking of surface structure for dynamic wetting

    PubMed Central

    Nita, Satoshi; Do-Quang, Minh; Wang, Jiayu; Chen, Yu-Chung; Suzuki, Yuji; Amberg, Gustav; Shiomi, Junichiro

    2017-01-01

    Dynamic wetting problems are fundamental to understanding the interaction between liquids and solids. Even in a superficially simple experimental situation, such as a droplet spreading over a dry surface, the result may depend not only on the liquid properties but also strongly on the substrate-surface properties; even for macroscopically smooth surfaces, the microscopic geometrical roughness can be important. In addition, because surfaces may often be naturally charged or electric fields are used to manipulate fluids, electric effects are crucial components that influence wetting phenomena. We investigate the interplay between electric forces and surface structures in dynamic wetting. Although surface microstructures can significantly hinder spreading, we find that electrostatics can “cloak” the microstructures, that is, deactivate the hindering. We identify the physics in terms of reduction in contact-line friction, which makes the dynamic wetting inertial force dominant and insensitive to the substrate properties. PMID:28275725

  2. Electrostatic cloaking of surface structure for dynamic wetting.

    PubMed

    Nita, Satoshi; Do-Quang, Minh; Wang, Jiayu; Chen, Yu-Chung; Suzuki, Yuji; Amberg, Gustav; Shiomi, Junichiro

    2017-02-01

    Dynamic wetting problems are fundamental to understanding the interaction between liquids and solids. Even in a superficially simple experimental situation, such as a droplet spreading over a dry surface, the result may depend not only on the liquid properties but also strongly on the substrate-surface properties; even for macroscopically smooth surfaces, the microscopic geometrical roughness can be important. In addition, because surfaces may often be naturally charged or electric fields are used to manipulate fluids, electric effects are crucial components that influence wetting phenomena. We investigate the interplay between electric forces and surface structures in dynamic wetting. Although surface microstructures can significantly hinder spreading, we find that electrostatics can "cloak" the microstructures, that is, deactivate the hindering. We identify the physics in terms of reduction in contact-line friction, which makes the dynamic wetting inertial force dominant and insensitive to the substrate properties.

  3. Reactor Dynamics Experiments with a Sub-Critical Assembly

    SciTech Connect

    Miley, G.H.; Yang, Y.; Wu, L.; Momota, H.

    2004-10-06

    A resurgence in use of nuclear power is now underway worldwide. However due to the shutdown of many university research reactors , student laboratories must rely more heavily on use of sub-critical assemblies. Here a driven sub-critical is described that uses a cylindrical Inertial Electrostatic Confinement (IEC) device to provide a fusion neutron source. The small IEC neutron source would be inserted in a fuel element position, with its power input controlled externally at a control panel. This feature opens the way to use of the critical assembly for a number of transient experiments such as sub-critical pulsing and neutron wave propagation. That in turn adds important new insights and excitement for the student teaching laboratory.

  4. Dynamics of surface catalyzed reactions; the roles of surface defects, surface diffusion, and hot electrons.

    PubMed

    Somorjai, Gabor A; Bratlie, Kaitlin M; Montano, Max O; Park, Jeong Y

    2006-10-12

    The mechanism that controls bond breaking at transition metal surfaces has been studied with sum frequency generation (SFG), scanning tunneling microscopy (STM), and catalytic nanodiodes operating under the high-pressure conditions. The combination of these techniques permits us to understand the role of surface defects, surface diffusion, and hot electrons in dynamics of surface catalyzed reactions. Sum frequency generation vibrational spectroscopy and kinetic measurements were performed under 1.5 Torr of cyclohexene hydrogenation/dehydrogenation in the presence and absence of H(2) and over the temperature range 300-500 K on the Pt(100) and Pt(111) surfaces. The structure specificity of the Pt(100) and Pt(111) surfaces is exhibited by the surface species present during reaction. On Pt(100), pi-allyl c-C6H9, cyclohexyl (C6H11), and 1,4-cyclohexadiene are identified adsorbates, while on the Pt(111) surface, pi-allyl c-C6H9, 1,4-cyclohexadiene, and 1,3-cyclohexadiene are present. A scanning tunneling microscope that can be operated at high pressures and temperatures was used to study the Pt(111) surface during the catalytic hydrogenation/dehydrogenation of cyclohexene and its poisoning with CO. It was found that catalytically active surfaces were always disordered, while ordered surface were always catalytically deactivated. Only in the case of the CO poisoning at 350 K was a surface with a mobile adsorbed monolayer not catalytically active. From these results, a CO-dominated mobile overlayer that prevents reactant adsorption was proposed. By using the catalytic nanodiode, we detected the continuous flow of hot electron currents that is induced by the exothermic catalytic reaction. During the platinum-catalyzed oxidation of carbon monoxide, we monitored the flow of hot electrons over several hours using a metal-semiconductor Schottky diode composed of Pt and TiO2. The thickness of the Pt film used as the catalyst was 5 nm, less than the electron mean free path

  5. Nonlinear Dynamics and Nucleation Kinetics in Near-Critical Liquids

    NASA Technical Reports Server (NTRS)

    Patashinski, Alexander Z.; Ratner, Mark A.; Pines, Vladimir

    1996-01-01

    The objective of our study is to model the nonlinear behavior of a near-critical liquid following a rapid change of the temperature and/or other thermodynamic parameters (pressure, external electric or gravitational field). The thermodynamic critical point is manifested by large, strongly correlated fluctuations of the order parameter (particle density in liquid-gas systems, concentration in binary solutions) in the critical range of scales. The largest critical length scale is the correlation radius r(sub c). According to the scaling theory, r(sub c) increases as r(sub c) = r(sub 0)epsilon(exp -alpha) when the nondimensional distance epsilon = (T - T(sub c))/T(sub c) to the critical point decreases. The normal gravity alters the nature of correlated long-range fluctuations when one reaches epsilon approximately equal to 10(exp -5), and correspondingly the relaxation time, tau(r(sub c)), is approximately equal to 10(exp -3) seconds; this time is short when compared to the typical experimental time. Close to the critical point, a rapid, relatively small temperature change may perturb the thermodynamic equilibrium on many scales. The critical fluctuations have a hierarchical structure, and the relaxation involves many length and time scales. Above the critical point, in the one-phase region, we consider the relaxation of the liquid following a sudden temperature change that simultaneously violates the equilibrium on many scales. Below T(sub c), a non-equilibrium state may include a distribution of small scale phase droplets; we consider the relaxation of such a droplet following a temperature change that has made the phase of the matrix stable.

  6. Dynamics of inhomogeneous condensates in contact with a surface

    SciTech Connect

    Bludov, Yu. V.; Yan Zhenya; Konotop, V. V.

    2010-06-15

    We show that interplay of linear attractive (repulsive) boundary with inhomogeneous repulsive (attractive) interatomic interactions results in nonlinear localized surface modes (surface solitons), some of which are stable. We consider several example systems describing interaction of inhomogeneous Bose-Einstein condensates with rigid surfaces and allowing for exact solutions. The stability of the obtained modes is analyzed analytically and numerically. Stable localized surface modes are found and dynamics of the unstable modes is described.

  7. Fast Surface Dynamics of Metallic Glass Enable Superlatticelike Nanostructure Growth.

    PubMed

    Chen, L; Cao, C R; Shi, J A; Lu, Z; Sun, Y T; Luo, P; Gu, L; Bai, H Y; Pan, M X; Wang, W H

    2017-01-06

    Contrary to the formation of complicated polycrystals induced by general crystallization, a modulated superlatticelike nanostructure, which grows layer by layer from the surface to the interior of a Pd_{40}Ni_{10}Cu_{30}P_{20} metallic glass, is observed via isothermal annealing below the glass transition temperature. The generation of the modulated nanostructure can be solely controlled by the annealing temperature, and it can be understood based on the fast dynamic and liquidlike behavior of the glass surface. The observations have implications for understanding the glassy surface dynamics and pave a way for the controllable fabrication of a unique and sophisticated nanostructure on a glass surface to realize the properties' modification.

  8. Fast Surface Dynamics of Metallic Glass Enable Superlatticelike Nanostructure Growth

    NASA Astrophysics Data System (ADS)

    Chen, L.; Cao, C. R.; Shi, J. A.; Lu, Z.; Sun, Y. T.; Luo, P.; Gu, L.; Bai, H. Y.; Pan, M. X.; Wang, W. H.

    2017-01-01

    Contrary to the formation of complicated polycrystals induced by general crystallization, a modulated superlatticelike nanostructure, which grows layer by layer from the surface to the interior of a Pd40Ni10Cu30P20 metallic glass, is observed via isothermal annealing below the glass transition temperature. The generation of the modulated nanostructure can be solely controlled by the annealing temperature, and it can be understood based on the fast dynamic and liquidlike behavior of the glass surface. The observations have implications for understanding the glassy surface dynamics and pave a way for the controllable fabrication of a unique and sophisticated nanostructure on a glass surface to realize the properties' modification.

  9. Hydrology: The dynamics of Earth's surface water

    NASA Astrophysics Data System (ADS)

    Yamazaki, Dai; Trigg, Mark A.

    2016-12-01

    High-resolution satellite mapping of Earth's surface water during the past 32 years reveals changes in the planet's water systems, including the influence of natural cycles and human activities. See Letter p.418

  10. Critical dynamics of burst instabilities in the Portevin-Le Ch atelier effect.

    PubMed

    D'Anna, G; Nori, F

    2000-11-06

    We investigate the Portevin-Le Châtelier effect (PLC), by compressing Al-Mg alloys in a very large deformation range, and interpret the results from the viewpoint of phase transitions and critical phenomena. The system undergoes two dynamical phase transitions between intermittent (or "jerky") and "laminar" plastic dynamic phases. Near these two dynamic critical points, the order parameter 1/tau of the PLC effect exhibits large fluctuations, and "critical slowing down" (i.e., the number tau of bursts, or plastic instabilities, per unit time slows down considerably).

  11. Truncatable bootstrap equations in algebraic form and critical surface exponents

    NASA Astrophysics Data System (ADS)

    Gliozzi, Ferdinando

    2016-10-01

    We describe examples of drastic truncations of conformal bootstrap equations encoding much more information than that obtained by a direct numerical approach. A three-term truncation of the four point function of a free scalar in any space dimensions provides algebraic identities among conformal block derivatives which generate the exact spectrum of the infinitely many primary operators contributing to it. In boundary conformal field theories, we point out that the appearance of free parameters in the solutions of bootstrap equations is not an artifact of truncations, rather it reflects a physical property of permeable conformal interfaces which are described by the same equations. Surface transitions correspond to isolated points in the parameter space. We are able to locate them in the case of 3d Ising model, thanks to a useful algebraic form of 3d boundary bootstrap equations. It turns out that the low-lying spectra of the surface operators in the ordinary and the special transitions of 3d Ising model form two different solutions of the same polynomial equation. Their interplay yields an estimate of the surface renormalization group exponents, y h = 0 .72558(18) for the ordinary universality class and y h = 1 .646(2) for the special universality class, which compare well with the most recent Monte Carlo calculations. Estimates of other surface exponents as well as OPE coefficients are also obtained.

  12. Localization and Dynamics Determinations Over Spherical Surfaces

    DTIC Science & Technology

    1975-06-01

    where the variable SIs equal to unity, equations (4-1) and (4-2) become simply, ds .D/ r -2 (4-6) d" and, oYU - Y/12 (4-7) Thus, at the particular...miles was cho ,,n and source ranges in the near to intermediate tield are prvriumed rhe resulting -. indard deviation for the dynamic variables 84

  13. Cinematic Operation of the Cerebral Cortex Interpreted via Critical Transitions in Self-Organized Dynamic Systems

    PubMed Central

    Kozma, Robert; Freeman, Walter J.

    2017-01-01

    Measurements of local field potentials over the cortical surface and the scalp of animals and human subjects reveal intermittent bursts of beta and gamma oscillations. During the bursts, narrow-band metastable amplitude modulation (AM) patters emerge for a fraction of a second and ultimately dissolve to the broad-band random background activity. The burst process depends on previously learnt conditioned stimuli (CS), thus different AM patterns may emerge in response to different CS. This observation leads to our cinematic theory of cognition when perception happens in discrete steps manifested in the sequence of AM patterns. Our article summarizes findings in the past decades on experimental evidence of cinematic theory of cognition and relevant mathematical models. We treat cortices as dissipative systems that self-organize themselves near a critical level of activity that is a non-equilibrium metastable state. Criticality is arguably a key aspect of brains in their rapid adaptation, reconfiguration, high storage capacity, and sensitive response to external stimuli. Self-organized criticality (SOC) became an important concept to describe neural systems. We argue that transitions from one AM pattern to the other require the concept of phase transitions, extending beyond the dynamics described by SOC. We employ random graph theory (RGT) and percolation dynamics as fundamental mathematical approaches to model fluctuations in the cortical tissue. Our results indicate that perceptions are formed through a phase transition from a disorganized (high entropy) to a well-organized (low entropy) state, which explains the swiftness of the emergence of the perceptual experience in response to learned stimuli. PMID:28352218

  14. Does the Sverdrup critical depth model explain bloom dynamics in estuaries?

    USGS Publications Warehouse

    Lucas, L.V.; Cloern, J.E.; Koseff, Jeffrey R.; Monismith, Stephen G.; Thompson, J.K.

    1998-01-01

    In this paper we use numerical models of coupled biological-hydrodynamic processes to search for general principles of bloom regulation in estuarine waters. We address three questions: what are the dynamics of stratification in coastal systems as influenced by variable freshwater input and tidal stirring? How does phytoplankton growth respond to these dynamics? Can the classical Sverdrup Critical Depth Model (SCDM) be used to predict the timing of bloom events in shallow coastal domains such as estuaries? We present results of simulation experiments which assume that vertical transport and net phytoplankton growth rates are horizontally homogeneous. In the present approach the temporally and spatially varying turbulent diffusivities for various stratification scenarios are calculated using a hydrodynamic code that includes the Mellor-Yamada 2.5 turbulence closure model. These diffusivities are then used in a time- and depth-dependent advection-diffusion equation, incorporating sources and sinks, for the phytoplankton biomass. Our modeling results show that, whereas persistent stratification greatly increases the probability of a bloom, semidiurnal periodic stratification does not increase the likelihood of a phytoplankton bloom over that of a constantly unstratified water column. Thus, for phytoplankton blooms, the physical regime of periodic stratification is closer to complete mixing than to persistent stratification. Furthermore, the details of persistent stratification are important: surface layer depth, thickness of the pycnocline, vertical density difference, and tidal current speed all weigh heavily in producing conditions which promote the onset of phytoplankton blooms. Our model results for shallow tidal systems do not conform to the classical concepts of stratification and blooms in deep pelagic systems. First, earlier studies (Riley, 1942, for example) suggest a monotonic increase in surface layer production as the surface layer shallows. Our model

  15. Critical dynamics of randomly assembled and diluted threshold networks

    NASA Astrophysics Data System (ADS)

    Kürten, Karl E.; Clark, John W.

    2008-04-01

    The dynamical behavior of a class of randomly assembled networks of binary threshold units subject to random deletion of connections is studied based on the annealed approximation suitable in the thermodynamic limit. The dynamical phase diagram is constructed for several forms of the probability density distribution of nonvanishing connection strengths. The family of power-law distribution functions ρ0(x)=(1-α)/(2|x|α) is found to play a special role in expanding the domain of stable, ordered dynamics at the expense of the disordered, “chaotic” phase. Relationships with other recent studies of the dynamics of complex networks allowing for variable in-degree of the units are explored. The relevance of the pruning of network connections to neural modeling and developmental neurobiology is discussed.

  16. DSTR/501-M62B Dynamic Interface Critical Speed Problem

    DTIC Science & Technology

    1977-05-01

    The speed reduction for the helicopter rotors is accomplished in the heli- copter transmission. Such a concept results in smaller diameter (lighter...coupling of the engine and drive shafting in the Dynamic System Test Rig (DSTR). This rig is an integrated rotor and drive shafting test vehicle for...showed that each major component of the drive train had acceptable rotor dynamic characteristics when analyzed separately. A more detailed coupled shafting

  17. Molecular dynamics simulation of wetting on modified amorphous silica surface

    NASA Astrophysics Data System (ADS)

    Chai, Jingchun; Liu, Shuyan; Yang, Xiaoning

    2009-08-01

    The microscopic wetting of water on amorphous silica surfaces has been investigated by molecular dynamics simulation. Different degrees of surface hydroxylation/silanization were considered. It was observed that the hydrophobicity becomes enhanced with an increase in the degree of surface silanization. A continuous transformation from hydrophilicity to hydrophobicity can be attained for the amorphous silica surfaces through surface modification. From the simulation result, the contact angle can exceed 90° when surface silanization percentage is above 50%, showing a hydrophobic character. It is also found that when the percentage of surface silanization is above 70% on the amorphous silica surface, the water contact angle almost remains unchanged (110-120°). This phenomenon is a little different from the wetting behavior on smooth quartz plates in previous experimental report. This change in the wettability on modified amorphous silica surfaces can be interpreted in terms of the interaction between water molecules and the silica surfaces.

  18. Critical dynamics of vesicle stretching transition in elongational flow.

    PubMed

    Kantsler, Vasiliy; Segre, Enrico; Steinberg, Victor

    2008-07-25

    We present results on the stretching of single tubular vesicles in an elongation flow toward dumbbell shapes, and on their relaxation. A critical strain rate epsilonc exists; for strain rates epsiloncritical point is a slowdown of the vesicle relaxation to the final extended state in the vesicle stretching. Such feature is similar to that found in continuous phase transitions and to the critical effects recently observed for polymer molecules near the coil-stretch transition in elongation flow.

  19. Dynamic rearrangement of surface proteins is essential for cytokinesis.

    PubMed

    Bauer, Tobias; Motosugi, Nami; Miura, Koichi; Sabe, Hisataka; Hiiragi, Takashi

    2008-03-01

    Cytokinesis is a complex process that involves dynamic cortical rearrangement. Our recent time-lapse recordings of the mouse egg unexpectedly revealed a high motility of the second polar body (2pb). Experiments to address its underlying mechanism show that neither mechanical compression by the zona pellucida nor the connection via the mid-body is required for the 2pb movement. Time-lapse recordings establish that the 2pb moves together with the cell membrane. These recordings, in which cell surface proteins are labeled with fluorescent latex-microbeads or monovalent antibodies against whole mouse proteins, indicate that the majority of the surface proteins dynamically accumulate in the cleavage furrow at every cell division. Comparable dynamics of the cell surface proteins, and specifically of E-cadherin, are also observed in cultured epithelial cells. The surface protein dynamics are closely correlated with, and dependent on, those of the underlying cortical actin. The cortical actin network may form a scaffold for membrane proteins and thereby transfer them during contractile ring formation toward the cleavage furrow. Immobilization of surface proteins by tetravalent lectin-mediated crosslinking results in the failure of cleavage, demonstrating that the observed protein dynamics are essential for cytokinesis. We propose that dynamic rearrangement of the cell surface proteins is a common feature of cytokinesis, playing a key role in modifying the mechanical properties of the cell membrane during cortical ingression. (c) 2008 Wiley-Liss, Inc.

  20. Monitoring Earth Surface Dynamics With Optical Imagery

    NASA Astrophysics Data System (ADS)

    Leprince, Sébastien; Berthier, Etienne; Ayoub, François; Delacourt, Christophe; Avouac, Jean-Philippe

    2008-01-01

    The increasing availability of high-quality optical satellite images should allow, in principle, continuous monitoring of Earth's surface changes due to geologic processes, climate change, or anthropic activity. For instance, sequential optical images have been used to measure displacements at Earth's surface due to coseismic ground deformation [e.g., Van Puymbroeck et al., 2000], ice flow [Scambos et al., 1992; Berthier et al., 2005], sand dune migration [Crippen, 1992], and landslides [Kääb, 2002; Delacourt et al., 2004]. Surface changes related to agriculture, deforestation, urbanization, and erosion-which do not involve ground displacement-might also be monitored, provided that the images can be registered with sufficient accuracy. Although the approach is simple in principle, its use is still limited, mainly because of geometric distortion of the images induced by the imaging system, biased correlation techniques, and implementation difficulties.

  1. Bulk water freezing dynamics on superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Chavan, S.; Carpenter, J.; Nallapaneni, M.; Chen, J. Y.; Miljkovic, N.

    2017-01-01

    In this study, we elucidate the mechanisms governing the heat-transfer mediated, non-thermodynamic limited, freezing delay on non-wetting surfaces for a variety of characteristic length scales, Lc (volume/surface area, 3 mm < Lc < 6 mm) using carefully designed freezing experiments in a temperature-controlled, zero-humidity environment on thin water slabs. To probe the effect of surface wettability, we investigated the total time for room temperature water to completely freeze into ice on superhydrophilic ( θaapp→ 0°), hydrophilic (0° < θa < 90°), hydrophobic (90° < θa < 125°), and superhydrophobic ( θaapp→ 180°) surfaces. Our results show that at macroscopic length scales, heat conduction through the bulk water/ice layer dominates the freezing process when compared to heat conduction through the functional coatings or nanoscale gaps at the superhydrophobic substrate-water/ice interface. In order to verify our findings, and to determine when the surface structure thermal resistance approaches the water/ice resistance, we fabricated and tested the additional substrates coated with commercial superhydrophobic spray coatings, showing a monotonic increase in freezing time with coating thickness. The added thermal resistance of thicker coatings was much larger than that of the nanoscale superhydrophobic features, which reduced the droplet heat transfer and increased the total freezing time. Transient finite element method heat transfer simulations of the water slab freezing process were performed to calculate the overall heat transfer coefficient at the substrate-water/ice interface during freezing, and shown to be in the range of 1-2.5 kW/m2K for these experiments. The results shown here suggest that in order to exploit the heat-transfer mediated freezing delay, thicker superhydrophobic coatings must be deposited on the surface, where the coating resistance is comparable to the bulk water/ice conduction resistance.

  2. Dynamics of photoinduced reactions at oxide surfaces

    NASA Astrophysics Data System (ADS)

    Al-Shamery, K.

    1996-11-01

    This report summarizes our work on UV-laser induced desorption of small molecules and atoms from transition metal oxides. The systems presented serve as examples for a simple photochemical reaction, the fission of the molecule surface bond. State resolved detection methods were used to record the final state distributions of the desorbing neutral molecules. Detailed results on the systems NO/NiO(1 1 1) and CO/Cr2O3(0 0 0 1) are presented. The experiments include investigations on stereodynamic aspects like the angular distributions of the desorbing molecules and, in the case of CO desorption, the rotational alignment with respect to the surface normal. Large desorption cross sections of (6±1) ṡ 10-17 cm2 for NO and (3.5±1) ṡ 10-17 cm2 for CO have been found for the desorption at 6.4 eV. The wavelength dependence indicates that the primary excitation step is substrate induced. The final state distributions show a high degree of translational, rotational and vibrational excitation and are clearly nonthermal of origin. The results are consistent with the formation of a negative ion intermediate state of the adsorbate. This observation is supported from a comparison to former results on NO/NiO(1 0 0) for which extensive ab initio calculations including electronically excited states exist. A spin state dependence of the vibrational excitation of NO could only be observed for NO/NiO(1 1 1) and is absent for NO/NiO(1 0 0). We attribute this observation to a spin state dependent coupling of the desorbing molecule to the surface in case the spin lattice orientation of the surface shows a preferential orientation. In the (1 1 1) plane the spin orientation is parallel within neighbour nickel ions while it is alternating in the (1 0 0) plane. For both systems studied the velocity component parallel to the surface is constant leading to a strong peaking along the surface normal for the fast molecules. The change from a preferred helicopter rotation (angular momentum

  3. Assessment of dynamic surface leaching of monolithic surface road materials.

    PubMed

    Paulus, Hélène; Schick, Joachim; Poirier, Jean-Eric

    2016-07-01

    Construction materials have to satisfy, among others, health and environment requirements. To check the environmental compatibility of road construction materials, release of hazardous substances into water must be assessed. Literature mostly describes the leaching behaviour of recycled aggregates for potential use in base or sub-base layers of roads. But little is known about the release of soluble substances by materials mixed with binders and compacted for intended use on road surface. In the present study, we thus performed a diffusion test with sequential renewal of water during a 64 day period according to CEN/TS 16637-2 specifications, on asphalt concretes and hydraulically bound monoliths, two common surface road materials. It is shown that release of dangerous substances is limited in these hydrodynamic conditions. It was particularly true for asphalt concrete leachates where no metallic trace element, sulphate, chloride or fluoride ion could be quantified. This is because of the low hydraulic conductivity and the low polarity of the petroleum hydrocarbon binder of these specimens. For hydraulically bound materials around 20,000 mg/m(2) of sulphate diffused from the monoliths. It is one order of magnitude higher than chloride diffusion and two orders of magnitude higher than fluoride release. No metallic trace element, except small quantities of copper in the last eluate could be quantified. No adverse effect is to be expected for human and environmental health from the leachates of these compacted surface road construction materials, because all the measured parameters were below EU (Council Directive 98/83/EC) or WHO guidelines for drinking water standards. Copyright © 2016 Elsevier Ltd. All rights reserved.

  4. Simulation of Gas-Surface Dynamical Interactions

    DTIC Science & Technology

    2007-07-01

    the interacting particle on the surface. Trapping probabilities often scale as Ei cosn θi with n < 2. An exponent of n = 0 corresponds to total energy...1996). [85] A. E. Wiskerke, F. H. Geuzebroek, A. W. Kleyn, and B. E. Hayden, Surf. Sci. 272, 256 (1992). [86] J. E. Hurst , L. Wharton, K. C. Janda

  5. Using surface deformation to image reservoir dynamics

    SciTech Connect

    Vasco, D.W.; Karasaki, K.; Doughty, C.

    2000-02-01

    The inversion of surface deformation data such as tilt, displacement, or strain provides a noninvasive method for monitoring subsurface volume change. Reservoir volume change is related directly to processes such as pressure variations induced by injection and withdrawal. The inversion procedure is illustrated by an application to tiltmeter data from the Hijiori test site in Japan. An inversion of surface tilt data allows one to image flow processes in a fractured granodiorite. Approximately 650 barrels of water, injected 2 km below the surface, produces a peak surface tilt of the order of 0.8 microradians. The authors find that the pattern of volume change in the granodiorite is very asymmetrical, elongated in a north-northwesterly direction, and the maximum volume change is offset by more than 0.7 km to the east of the pumping well. The inversion of a suite of leveling data from the Wilmington oil field in Long Beach, California, images large-scale reservoir volume changes in 12 one- to two-year increments from 1976 to 1996. The influence of various production strategies is seen in the reservoir volume changes. In particular, a steam flood in fault block 2 in the northwest portion of the field produced a sudden decrease in reservoir volume.

  6. Bubble Dynamics on a Heated Surface

    NASA Technical Reports Server (NTRS)

    Kassemi, Mohammad; Rashidnia, Nasser

    1996-01-01

    In this work, we study the combined thermocapillary and natural convective flow generated by a bubble on a heated solid surface. The interaction between gas and vapor bubbles with the surrounding fluid is of interest for both space and ground-based processing. On earth, the volumetric forces are dominant, especially, in apparatuses with large volume to surface ratio. But in the reduced gravity environment of orbiting spacecraft, surface forces become more important and the effects of Marangoni convection are easily unmasked. In order to delineate the roles of the various interacting phenomena, a combined numerical-experimental approach is adopted. The temperature field is visualized using Mach-Zehnder interferometry and the flow field is observed by a laser sheet flow visualization technique. A finite element numerical model is developed which solves the two-dimensional momentum and energy equations and includes the effects of bubble surface deformation. Steady state temperature and velocity fields predicted by the finite element model are in excellent qualitative agreement with the experimental results. A parametric study of the interaction between Marangoni and natural convective flows including conditions pertinent to microgravity space experiments is presented. Numerical simulations clearly indicate that there is a considerable difference between 1-g and low-g temperature and flow fields induced by the bubble.

  7. SYSTEM IDENTIFICATION OF SURFACE SHIP DYNAMICS.

    DTIC Science & Technology

    The feasibility of applying a Newtonian system identification technique to a nonlinear three degree of freedom system of equations describing the...steering and maneuvering of a surface ship is investigated. The input to the system identification program is provided by both analog and digital

  8. Nanoparticle-Based Antimicrobials: Surface Functionality is Critical

    PubMed Central

    Gupta, Akash; Landis, Ryan F.; Rotello, Vincent M.

    2016-01-01

    Bacterial infections cause 300 million cases of severe illness each year worldwide. Rapidly accelerating drug resistance further exacerbates this threat to human health. While dispersed (planktonic) bacteria represent a therapeutic challenge, bacterial biofilms present major hurdles for both diagnosis and treatment. Nanoparticles have emerged recently as tools for fighting drug-resistant planktonic bacteria and biofilms. In this review, we present the use of nanoparticles as active antimicrobial agents and drug delivery vehicles for antibacterial therapeutics. We further focus on how surface functionality of nanomaterials can be used to target both planktonic bacteria and biofilms. PMID:27006760

  9. Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping

    PubMed Central

    van der Krogt, Marjolein M.; de Graaf, Wendy W.; Farley, Claire T.; Moritz, Chet T.; Richard Casius, L. J.; Bobbert, Maarten F.

    2009-01-01

    When human hoppers are surprised by a change in surface stiffness, they adapt almost instantly by changing leg stiffness, implying that neural feedback is not necessary. The goal of this simulation study was first to investigate whether leg stiffness can change without neural control adjustment when landing on an unexpected hard or unexpected compliant (soft) surface, and second to determine what underlying mechanisms are responsible for this change in leg stiffness. The muscle stimulation pattern of a forward dynamic musculoskeletal model was optimized to make the model match experimental hopping kinematics on hard and soft surfaces. Next, only surface stiffness was changed to determine how the mechanical interaction of the musculoskeletal model with the unexpected surface affected leg stiffness. It was found that leg stiffness adapted passively to both unexpected surfaces. On the unexpected hard surface, leg stiffness was lower than on the soft surface, resulting in close-to-normal center of mass displacement. This reduction in leg stiffness was a result of reduced joint stiffness caused by lower effective muscle stiffness. Faster flexion of the joints due to the interaction with the hard surface led to larger changes in muscle length, while the prescribed increase in active state and resulting muscle force remained nearly constant in time. Opposite effects were found on the unexpected soft surface, demonstrating the bidirectional stabilizing properties of passive dynamics. These passive adaptations to unexpected surfaces may be critical when negotiating disturbances during locomotion across variable terrain. PMID:19589956

  10. Robust passive dynamics of the musculoskeletal system compensate for unexpected surface changes during human hopping.

    PubMed

    van der Krogt, Marjolein M; de Graaf, Wendy W; Farley, Claire T; Moritz, Chet T; Richard Casius, L J; Bobbert, Maarten F

    2009-09-01

    When human hoppers are surprised by a change in surface stiffness, they adapt almost instantly by changing leg stiffness, implying that neural feedback is not necessary. The goal of this simulation study was first to investigate whether leg stiffness can change without neural control adjustment when landing on an unexpected hard or unexpected compliant (soft) surface, and second to determine what underlying mechanisms are responsible for this change in leg stiffness. The muscle stimulation pattern of a forward dynamic musculoskeletal model was optimized to make the model match experimental hopping kinematics on hard and soft surfaces. Next, only surface stiffness was changed to determine how the mechanical interaction of the musculoskeletal model with the unexpected surface affected leg stiffness. It was found that leg stiffness adapted passively to both unexpected surfaces. On the unexpected hard surface, leg stiffness was lower than on the soft surface, resulting in close-to-normal center of mass displacement. This reduction in leg stiffness was a result of reduced joint stiffness caused by lower effective muscle stiffness. Faster flexion of the joints due to the interaction with the hard surface led to larger changes in muscle length, while the prescribed increase in active state and resulting muscle force remained nearly constant in time. Opposite effects were found on the unexpected soft surface, demonstrating the bidirectional stabilizing properties of passive dynamics. These passive adaptations to unexpected surfaces may be critical when negotiating disturbances during locomotion across variable terrain.

  11. Surface Characterization of Nanoparticles: critical needs and significant challenges

    PubMed Central

    Baer, D. R.

    2013-01-01

    There is a growing recognition that nanoparticles and other nanostructured materials are sometimes inadequately characterized and that this may limit or even invalidate some of the conclusions regarding particle properties and behavior. A number of international organizations are working to establish the essential measurement requirements that enable adequate understanding of nanoparticle properties for both technological applications and for environmental health issues. Our research on the interaction of iron metal-core oxide-shell nanoparticles with environmental contaminants and studies of the behaviors of ceria nanoparticles, with a variety of medical, catalysis and energy applications, have highlighted a number of common nanoparticle characterization challenges that have not been fully recognized by parts of the research community. This short review outlines some of these characterization challenges based on our research observations and using other results reported in the literature. Issues highlighted include: 1) the importance of surfaces and surface characterization, 2) nanoparticles are often not created equal – subtle differences in synthesis and processing can have large impacts; 3) nanoparticles frequently change with time having lifetime implications for products and complicating understanding of health and safety impacts; 4) the high sensitivity of nanoparticles to their environment complicates characterization and applications in many ways; 5) nanoparticles are highly unstable and easily altered (damaged) during analysis. PMID:25342927

  12. Critical appraisal of the fewest switches algorithm for surface hopping.

    PubMed

    Granucci, Giovanni; Persico, Maurizio

    2007-04-07

    In this paper the authors address the problem of internal consistency in trajectory surface hopping methods, i.e., the requirement that the fraction of trajectories running on each electronic state equals the probabilities computed by the electronic time-dependent Schrodinger equation, after averaging over all trajectories. They derive a formula for the hopping probability in Tully's "fewest switches" spirit that would yield a rigorously consistent treatment. They show the relationship of Tully's widely used surface hopping algorithm with the "exact" prescription that cannot be applied when running each trajectory independently. They also bring out the connection of the consistency problem with the coherent propagation of the electronic wave function and the artifacts caused by coherent Rabi-type oscillations of the state probabilities in weak coupling regimes. A real molecule (azobenzene) and two ad hoc models serve as examples to illustrate the above theoretical arguments. Following a proposal by Truhlar's group [Zhu et al., J. Chem. Phys. 121, 7658 (2004) Zhu et al., J. Chem. Theory Comput. 1, 527 (2005)], they apply a decoherence correction to the state probabilities, in conjunction with Tully's algorithm, and they obtain satisfactory results in terms of internal consistency and of agreement with the outcomes of quantum wave packet calculations.

  13. Critical appraisal of the fewest switches algorithm for surface hopping

    NASA Astrophysics Data System (ADS)

    Granucci, Giovanni; Persico, Maurizio

    2007-04-01

    In this paper the authors address the problem of internal consistency in trajectory surface hopping methods, i.e., the requirement that the fraction of trajectories running on each electronic state equals the probabilities computed by the electronic time-dependent Schrödinger equation, after averaging over all trajectories. They derive a formula for the hopping probability in Tully's "fewest switches" spirit that would yield a rigorously consistent treatment. They show the relationship of Tully's widely used surface hopping algorithm with the "exact" prescription that cannot be applied when running each trajectory independently. They also bring out the connection of the consistency problem with the coherent propagation of the electronic wave function and the artifacts caused by coherent Rabi-type oscillations of the state probabilities in weak coupling regimes. A real molecule (azobenzene) and two ad hoc models serve as examples to illustrate the above theoretical arguments. Following a proposal by Truhlar's group [Zhu et al., J. Chem. Phys. 121, 7658 (2004) Zhu et al., J. Chem. Theory Comput. 1, 527 (2005)], they apply a decoherence correction to the state probabilities, in conjunction with Tully's algorithm, and they obtain satisfactory results in terms of internal consistency and of agreement with the outcomes of quantum wave packet calculations.

  14. Dynamics of Critical Dedicated Cores for Minor Actinide Transmutation

    SciTech Connect

    Massara, S.; Tommasi, J.; Vanier, M.; Koeberl, O.

    2005-02-15

    Fast spectrum minor actinide (MA) burner designs, with high minor actinide loads and consumptions, have been assessed. As reactivity and kinetic coefficients are poor in such cores (low delayed neutron fraction and Doppler feedback, high coolant void coefficient), special attention has been paid to their dynamic behavior during transient conditions. A dynamics code, MAT4 DYN, has been expressly developed to study loss-of-flow, reactivity insertion, and loss-of-coolant accidents. It takes into account two fuel geometries (cylindrical and spherical) and two thermal-hydraulics models for the coolant (incompressible for liquid metals and compressible for helium).Three nitride-fuel configurations are analyzed according to their coolant: sodium and lead (both with pin fuel) and helium (with particle fuel). Dynamics calculations show that if the fuel nature is appropriately chosen, with sufficient margins during transients, then this can counterbalance the poor reactivity coefficients for liquid-metal-cooled cores, thus proving the interest of this kind of concept. On the other hand, the gas-cooled core dynamics is very badly affected by the high value of the helium void coefficient in a hard spectrum, this effect being amplified by the very low thermal inertia of the fuel particles. Hence, concepts other than a particle-bed fuel should be investigated for a helium-cooled fast-spectrum MA burner.

  15. Evolution as a critical component of plankton dynamics.

    PubMed

    Fussmann, Gregor F; Ellner, Stephen P; Hairston, Nelson G

    2003-05-22

    Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.

  16. Classroom Dynamic Assessment: A Critical Examination of Constructs and Practices

    ERIC Educational Resources Information Center

    Davin, Kristin J.

    2016-01-01

    This article explores the implementation of dynamic assessment (DA) in an elementary school foreign language classroom by considering its theoretical basis and its applicability to second language (L2) teaching, learning, and development. In existing applications of L2 classroom DA, errors serve as a window into learners' instructional needs and…

  17. Classroom Dynamic Assessment: A Critical Examination of Constructs and Practices

    ERIC Educational Resources Information Center

    Davin, Kristin J.

    2016-01-01

    This article explores the implementation of dynamic assessment (DA) in an elementary school foreign language classroom by considering its theoretical basis and its applicability to second language (L2) teaching, learning, and development. In existing applications of L2 classroom DA, errors serve as a window into learners' instructional needs and…

  18. Sticky surface: sphere-sphere adhesion dynamics

    PubMed Central

    Sircar, Sarthok; Younger, John G.; Bortz, David M.

    2014-01-01

    We present a multi-scale model to study the attachment of spherical particles with a rigid core, coated with binding ligands and suspended in the surrounding, quiescent fluid medium. This class of fluid-immersed adhesion is widespread in many natural and engineering settings, particularly in microbial surface adhesion. Our theory highlights how the micro-scale binding kinetics of these ligands, as well as the attractive / repulsive surface potential in an ionic medium affects the eventual macro-scale size distribution of the particle aggregates (flocs). The bridge between the micro-macro model is made via an aggregation kernel. Results suggest that the presence of elastic ligands on the particle surface lead to the formation of larger floc aggregates via efficient inter-floc collisions (i.e., non-zero sticking probability, g). Strong electrolytic composition of the surrounding fluid favors large floc formation as well. The kernel for the Brownian diffusion for hard spheres is recovered in the limit of perfect binding effectiveness (g → 1) and in a neutral solution with no dissolved salts. PMID:25159830

  19. Dynamic interactions of Leidenfrost droplets on liquid metal surface

    NASA Astrophysics Data System (ADS)

    Ding, Yujie; Liu, Jing

    2016-09-01

    Leidenfrost dynamic interaction effects of the isopentane droplets on the surface of heated liquid metal were disclosed. Unlike conventional rigid metal, such conductive and deformable liquid metal surface enables the levitating droplets to demonstrate rather abundant and complex dynamics. The Leidenfrost droplets at different diameters present diverse morphologies and behaviors like rotation and oscillation. Depending on the distance between the evaporating droplets, they attract and repulse each other through the curved surfaces beneath them and their vapor flows. With high boiling point up to 2000 °C, liquid metal offers a unique platform for testing the evaporating properties of a wide variety of liquid even solid.

  20. 3D vesicle dynamics simulations with a linearly triangulated surface

    NASA Astrophysics Data System (ADS)

    Boedec, G.; Leonetti, M.; Jaeger, M.

    2011-02-01

    Simulations of biomembranes have gained an increasing interest in the past years. Specificities of these membranes propose new challenges for the numerics. In particular, vesicle dynamics are governed by bending forces as well as a surface incompressibility constraint. A method to compute the bending force density resultant onto piecewise linearly triangulated surface meshes is described. This method is coupled with a boundary element method solver for inner and outer fluids, to compute vesicle dynamics under external flows. The surface incompressibility constraint is satisfied by the construction of a projection operator.

  1. Global observations and modeling of atmosphere-surface exchange of elemental mercury: a critical review

    NASA Astrophysics Data System (ADS)

    Zhu, Wei; Lin, Che-Jen; Wang, Xun; Sommar, Jonas; Fu, Xuewu; Feng, Xinbin

    2016-04-01

    Reliable quantification of air-surface fluxes of elemental Hg vapor (Hg0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoted to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in the past three decades. However, large uncertainties remain due to the complexity of Hg0 bidirectional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a critical review on the state of science in the atmosphere-surface exchange of Hg0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air-surface Hg exchange and modeling efforts are presented. Due to the semi-volatile nature of Hg0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence and the presence of reactants (e.g., O3, radicals, etc.). However, the effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling. We compile an up-to-date global observational flux database and discuss the implication of flux data on the global Hg budget. Mean Hg0 fluxes obtained by micrometeorological measurements do not appear to be significantly greater than the fluxes measured by dynamic flux chamber methods over unpolluted surfaces (p = 0.16, one-tailed, Mann-Whitney U test). The spatiotemporal coverage of existing Hg0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of the evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg0 flux observations in East

  2. Local and cluster critical dynamics of the 3d random-site Ising model

    NASA Astrophysics Data System (ADS)

    Ivaneyko, D.; Ilnytskyi, J.; Berche, B.; Holovatch, Yu.

    2006-10-01

    We present the results of Monte Carlo simulations for the critical dynamics of the three-dimensional site-diluted quenched Ising model. Three different dynamics are considered, these correspond to the local update Metropolis scheme as well as to the Swendsen-Wang and Wolff cluster algorithms. The lattice sizes of L=10-96 are analysed by a finite-size-scaling technique. The site dilution concentration p=0.85 was chosen to minimize the correction-to-scaling effects. We calculate numerical values of the dynamical critical exponents for the integrated and exponential autocorrelation times for energy and magnetization. As expected, cluster algorithms are characterized by lower values of dynamical critical exponent than the local one: also in the case of dilution critical slowing down is more pronounced for the Metropolis algorithm. However, the striking feature of our estimates is that they suggest that dilution leads to decrease of the dynamical critical exponent for the cluster algorithms. This phenomenon is quite opposite to the local dynamics, where dilution enhances critical slowing down.

  3. Critical behavior at dynamical phase transition in the generalized Bose-Anderson model

    NASA Astrophysics Data System (ADS)

    Chichinadze, Dmitry V.; Rubtsov, Alexey N.

    2017-05-01

    Critical properties of the dynamical phase transition in the quenched generalized Bose-Anderson impurity model are studied in the mean-field limit of an infinite number of channels. The transition separates the evolution toward ground state and toward the branch of stable excited states. We perform numerically exact simulations of a close vicinity of the critical quench amplitude. The relaxation constant describing the asymptotic evolution toward ground state, as well as asymptotic frequency of persistent phase rotation and number of cloud particles at stable excited state are power functions of the detuning from the critical quench amplitude. The critical evolution (separatrix between the two regimes) shows a non-Lyapunov power-law instability arising after a certain critical time. The observed critical behavior is attributed to the irreversibility of the dynamics of particles leaving the cloud and to memory effects related to the low-energy behavior of the lattice density of states.

  4. Molecular Dynamics Simulations of Uranyl and Uranyl Carbonate Adsorption at Alumino-silicate Surfaces

    SciTech Connect

    Kerisit, Sebastien N.; Liu, Chongxuan

    2014-03-03

    Adsorption at mineral surfaces is a critical factor controlling the mobility of uranium(VI) in aqueous environments. Therefore, molecular dynamics (MD) simulations were performed to investigate uranyl(VI) adsorption onto two neutral alumino-silicate surfaces, namely the orthoclase (001) surface and the octahedral aluminum sheet of the kaolinite (001) surface. Although uranyl preferentially adsorbed as a bi-dentate innersphere complex on both surfaces, the free energy of adsorption at the orthoclase surface (-15 kcal mol-1) was significantly more favorable than that at the kaolinite surface (-3 kcal mol-1), which was attributed to differences in surface functional groups and to the ability of the orthoclase surface to dissolve a surface potassium ion upon uranyl adsorption. The structures of the adsorbed complexes compared favorably with X-ray absorption spectroscopy results. Simulations of the adsorption of uranyl complexes with up to three carbonate ligands revealed that uranyl complexes coordinated to up to 2 carbonate ions are stable on the orthoclase surface whereas uranyl carbonate surface complexes are unfavored at the kaolinite surface. Combining the MD-derived equilibrium adsorption constants for orthoclase with aqueous equilibrium constants for uranyl carbonate species indicates the presence of adsorbed uranium complexes with one or two carbonates in alkaline conditions, in support of current uranium(VI) surface complexation models.

  5. Molecular dynamics simulations of uranyl and uranyl carbonate adsorption at aluminosilicate surfaces.

    PubMed

    Kerisit, Sebastien; Liu, Chongxuan

    2014-04-01

    Adsorption at mineral surfaces is a critical factor controlling the mobility of uranium(VI) in aqueous environments. Therefore, molecular dynamics (MD) simulations were performed to investigate uranyl(VI) adsorption onto two neutral aluminosilicate surfaces, namely, the orthoclase (001) surface and the octahedral aluminum sheet of the kaolinite (001) surface. Although uranyl preferentially adsorbs as a bidentate inner-sphere complex on both surfaces, the free energy of adsorption on the orthoclase surface (-15 kcal mol(-1)) is significantly more favorable than that at the kaolinite surface (-3 kcal mol(-1)), which is attributed to differences in surface functional groups and the ability of the orthoclase surface to release a surface potassium ion upon uranyl adsorption. The structures of the adsorbed complexes compare favorably with X-ray absorption spectroscopy results. Simulations of the adsorption of uranyl complexes with up to three carbonate ligands revealed that uranyl complexes coordinated to up to two carbonate ions are stable on the orthoclase surface whereas uranyl carbonate surface complexes are unfavored at the kaolinite surface. Combining the MD-derived equilibrium adsorption constants for orthoclase with aqueous equilibrium constants for uranyl carbonate species indicates the presence of adsorbed uranium complexes with one or two carbonates under alkaline conditions, in support of current uranium(VI) surface complexation models.

  6. Dynamic friction of self-affine surfaces

    NASA Astrophysics Data System (ADS)

    Schmittbuhl, Jean; Vilotte, Jean-Pierre; Roux, Stéphane

    1994-02-01

    We investigate the velocity dependence of the friction between two rigid blocks limited by a self-affine surface such as the one generated by a crack. The upper solid is subjected either to gravity or to an external elastic stiffness, and is driven horizontally at constant velocity, V, while the lower solid is fixed. For low velocities, the apparent friction coefficient is constant. For high velocities, the apparent friction is shown to display a velocity weakening. The weakening can be related to the variation of the mean contact time due to the occurrence of jumps during the motions. The cross-over between these two regimes corresponds to a characteristic velocity which depends on the geometry of the surfaces and on the mean normal force. In the case of simple gravity loading, the velocity dependence of the apparent friction at high velocities is proportional to 1/V^2 where V is the imposed tangential velocity. In the case of external elastic stiffness, two velocity weakening regimes can be identified, the first is identical to the gravity case with a 1/V^2 dependence, the second appears at higher velocities and is characterized by a 1/V variation. The characteristic velocity of this second cross-over depends on the roughness and the elastic stiffness. The statistical distribution of ballistic flight distances is analysed, and is shown to reveal in all cases the self-affinity of the contacting surfaces. Nous analysons la dépendence en vitesse du frottement entre deux solides limités par une surface rugueuse auto-affine comme celle d'une surface de fracture. Le solide supérieur est soumis soit à la gravité, soit à une raideur élastique externe, et est entraîné à vitesse horizontale constante V sur le solide inférieur fixe. A faible vitesse, le coefficient de friction apparent, est constant. A forte vitesse, le coefficient de friction apparent devient inversement proportionnel à la vitesse. Cette dépendance peut être reliée à la variation du temps

  7. Temperature dependent droplet impact dynamics on flat and textured surfaces

    NASA Astrophysics Data System (ADS)

    Alizadeh, Azar; Bahadur, Vaibhav; Zhong, Sheng; Shang, Wen; Li, Ri; Ruud, James; Yamada, Masako; Ge, Liehui; Dhinojwala, Ali; Sohal, Manohar

    2012-03-01

    Droplet impact dynamics determines the performance of surfaces used in many applications such as anti-icing, condensation, boiling, and heat transfer. We study impact dynamics of water droplets on surfaces with chemistry/texture ranging from hydrophilic to superhydrophobic and across a temperature range spanning below freezing to near boiling conditions. Droplet retraction shows very strong temperature dependence especially on hydrophilic surfaces; it is seen that lower substrate temperatures lead to lesser retraction. Physics-based analyses show that the increased viscosity associated with lower temperatures combined with an increased work of adhesion can explain the decreased retraction. The present findings serve as a starting point to guide further studies of dynamic fluid-surface interaction at various temperatures.

  8. Modeling changes in rill erodibility and critical shear stress on native surface roads

    Treesearch

    Randy B. Foltz; Hakjun Rhee; William J. Elliot

    2008-01-01

    This study investigated the effect of cumulative overland flow on rill erodibility and critical shear stress on native surface roads in central Idaho. Rill erodibility decreased exponentially with increasing cumulative overland flow depth; however, critical shear stress did not change. The study demonstrated that road erodibility on the studied road changes over the...

  9. Dynamics of Spreading on Micro-Textured Surfaces

    NASA Astrophysics Data System (ADS)

    Mohammad Karim, Alireza; Rothstein, Jonathan; Kavehpour, Pirouz

    2015-11-01

    Ultrahydrophobic surfaces, due to their large water-repellency characteristic, have a vast variety of applications in technology and nature, such as de-icing of airplane wings, efficiency increase of power plants, and efficiency of pesticides on plants, etc. The significance of ultrahydrophobic surfaces requires enhancing the knowledge on the spreading dynamics on such surfaces. The best way to produce an ultrahydrophobic surface is by patterning of smooth hydrophobic surfaces with micron sized posts. In this research, the micro-textured surfaces have been fabricated by patterning several different sizes of micro-textured posts on Teflon plates. The experimental study has been performed using forced spreading with Tensiometer to obtain the dependencw of dynamic contact angle to the contact line velocity to describe the spreading dynamics of Newtonian liquids on the micro-textured surfaces. The effect of the geometrical descriptions of the micro-posts along with the physical properties of liquids on the spreading dynamics on micro-textured Teflon plates have been also studied.

  10. The Surface Wave Dynamics Experiment (SWADE)

    NASA Technical Reports Server (NTRS)

    Long, S. R.; Oberholtzer, J. D.; Wright, C. W.; Shirk, H. G.

    1988-01-01

    SWADE was developed to study the dynamics of the wave field development in the open ocean with the following specific objectives: (1) to understand the development of the wave directional spectrum under various conditions; (2) to determine the effect of waves on the air/sea transfers of momentum, heat, and mass; (3) to determine breaking distributions as a function of sea state, wind, and boundary stability; and (4) to provide data and analyses for ERS-1 validation. The experiment is designed for the winter of 1990 to 1991. Four buoys will be deployed for 6 months starting October 1990 and ending March 1991. During that time period, three intensive periods of 2 weeks duration each will be selected for frequent aircraft flights for wave data collection to satisfy scientific studies, as well as ERS-1 validation needs.

  11. Chemical Dynamics at Surfaces of Metal Nanomaterials

    DTIC Science & Technology

    2014-07-23

    and to use the new tools to investigate whether a fundamental physical principle, the Born-Oppenheimer Approximation ( BOA ), is valid on the surfaces...systems largely depend on whether BOA is valid12-14. In the following, the accomplishments will be briefly described. 2.1 The vibrational cross angle...nct vibrati ite boxes in (marked w with a simil oretical calc f 4nm Au p rface of 4n angstrom m ation ( BOA d to be much BOA is wh vibrationa very

  12. Dynamical quantum filtering in hydrogen surface reactions

    NASA Astrophysics Data System (ADS)

    Diño, Wilson Agerico; Kasai, Hideaki; Okiji, Ayao

    1998-11-01

    We report on how surfaces that adsorb hydrogen could act as rotational quantum state filters and cause, for example, D 2 molecules desorbing in the vibrational ground state from Cu(111) to exhibit strong rotational alignment. For low final translational energies, we found that desorbing D 2 molecules have rotational alignment factor values corresponding to cartwheel-type rotational preference. As the final translational energy increases, the corresponding alignment factor increases initially to values corresponding to helicopter-type rotational preference and then, eventually, decreases to values almost compatible with a spatially isotropic distribution, as the translational energy increases further.

  13. Ultrasonic investigation of critical dynamics in KMnF3

    NASA Astrophysics Data System (ADS)

    Holt, R. M.; Fossheim, K.

    1981-09-01

    An extensive ultrasonic investigation of the cubic-tetragonal phase transition in KMnF3 with respect to temperature, frequency, mode, and sample dependence has been carried out by means of wave-vector-reversed echo technique as well as conventional pulse reflections. All measurements of the attenuation α obey a dynamic scaling law α~ω2t-ρG(ωτ). We have measured ρ=1.87+/-0.05, in accord with the predictions of the three-dimensional Heisenberg model, a result which is consistent with the expected value φ~1.26 for the anisotropy cross-over exponent. The relaxation time τ, governing the dynamics of ordered clusters, is found to be ~(9×10-13)t-1.41 s. The form of the scaling function G is experimentally determined, and its expected limiting forms at low and high ωτ values discussed.

  14. Applications of granular-dynamics numerical simulations to asteroid surfaces

    NASA Astrophysics Data System (ADS)

    Richardson, D. C.; Michel, P.; Schwartz, S. R.; Yu, Y.; Ballouz, R.-L.; Matsumura, S.

    2014-07-01

    Spacecraft images and indirect observations including thermal inertia measurements indicate most small bodies have surface regolith. Evidence of granular flow is also apparent in the images. This material motion occurs in very low gravity, therefore in a totally different gravitational environment than on the Earth. Upcoming sample-return missions to small bodies, and possible future manned missions, will involve interaction with the surface regolith, so it is important to develop tools to predict the surface response. We have added new capabilities to the N-body gravity tree code pkdgrav [1,2] that permit the simulation of granular dynamics, including multi-contact physics and friction forces, using the soft-sphere discrete-element method [3]. The numerical approach has been validated through comparison with laboratory experiments (e.g., [3,4]). (1) We carried out impacts into granular materials using different projectile shapes under Earth's gravity [5] and compared the results to laboratory experiments [6] in support of JAXA's Hayabusa 2 asteroid sample-return mission. We tested different projectile shapes and confirmed that the 90-degree cone was the most efficient at excavating mass when impacting 5-mm-diameter glass beads. Results are sensitive to the normal coefficient of restitution and the coefficient of static friction. Preliminary experiments in micro-gravity for similar impact conditions show both the amount of ejected mass and the timescale of the impact process increase, as expected. (2) It has been found (e.g., [7,8]) that ''fresh'' (unreddened) Q-class asteroids have a high probability of recent planetary encounters (˜1 Myr; also see [9]), suggesting that surface refreshening may have occurred due to tidal effects. As an application of the potential effect of tidal interactions, we carried out simulations of Apophis' predicted 2029 encounter with the Earth to see whether regolith motion might occur, using a range of plausible material parameters

  15. Fast track surface mine installation on the critical path

    SciTech Connect

    Willison, L.R.

    1986-07-01

    A deep mining area, located in the rugged woodland hills of central West Virginia, was transformed into a beehive of activity as a major new mine and preparation plant was constructed on a very tight deadline. By the time the mine was on line, BethEnergy Mines had spent $40 million to develop the two million tpy (ton per year) surface coal mining complex. In early 1984 not a stick of timber had been cut. But within a very short time (coal-wise) there was a mining area; a 600-tph heavy media cyclone preparation plant, with 36,000 and 24,000 tons of raw and clean coal storage respectively; three miles of haul roads and access roads; a 64,000-ton clean coal stocking facility with a 4000-tph reclaim system that feeds a batch-weighing, floodloading, unit-train loadout facility; a 3.5-mile railroad spur and loop; and all incidental infrastructure. This feat entailed moving more than four million cu-yd of earth, building the preparation plant and loadout facility from ground to operating in six moths, and constructing a railroad spur bridging a major highway.

  16. AWARE: Adaptive Software Monitoring and Dynamic Reconfiguration for Critical Infrastructure Protection

    DTIC Science & Technology

    2015-04-29

    SECURITY CLASSIFICATION OF: The ARO-supported AWARE project addressed the design and performance of adaptive software technologies for highly trusted... software systems. A dynamically adaptive system (DAS) monitors itself and its execution environment at run time. This monitoring enables a DAS not only...Approved for Public Release; Distribution Unlimited Final Report: AWARE: Adaptive Software Monitoring and Dynamic Reconfiguration for Critical

  17. Static and dynamic contact angles of water droplet on a solid surface using molecular dynamics simulation.

    PubMed

    Hong, Seung Do; Ha, Man Yeong; Balachandar, S

    2009-11-01

    The present study investigates the variation of static contact angle of a water droplet in equilibrium with a solid surface in the absence of a body force and the dynamic contact angles of water droplet moving on a solid surface for different characteristic energies using the molecular dynamics simulation. With increasing characteristic energy, the static contact angle in equilibrium with a solid surface in the absence of a body force decreases because the hydrophobic surface changes its characteristics to the hydrophilic surface. In order to consider the effect of moving water droplet on the dynamic contact angles, we apply the constant acceleration to an individual oxygen and hydrogen atom. In the presence of a body force, the water droplet changes its shape with larger advancing contact angle than the receding angle. The dynamic contact angles are compared with the static contact angle in order to see the effect of the presence of a body force.

  18. Dynamics of parabolic problems with memory. Subcritical and critical nonlinearities

    NASA Astrophysics Data System (ADS)

    Li, Xiaojun

    2016-08-01

    In this paper, we study the long-time behavior of the solutions of non-autonomous parabolic equations with memory in cases when the nonlinear term satisfies subcritical and critical growth conditions. In order to do this, we show that the family of processes associated to original systems with heat source f(x, t) being translation bounded in Lloc 2 ( R ; L 2 ( Ω ) ) is dissipative in higher energy space M α , 0 < α ≤ 1, and possesses a compact uniform attractor in M 0 .

  19. Critical transitions of stratocumulus dynamical systems due to perturbation in free-atmosphere moisture

    NASA Astrophysics Data System (ADS)

    Tsai, Jia-Ying; Wu, Chien-Ming

    2016-12-01

    The bi-stable behavior of stratocumulus systems is here investigated in a 3D cloud-resolving model based on vector vorticity equations (VVM). This study demonstrates the response of the stratocumulus system to small perturbations of free atmospheric moisture under specified forcings of warm sea surface temperature (SST) and weak subsidence. A critical transition, indicated by the strong decoupling and large variation of cloud properties, separates fast dynamics from slow dynamics. During the fast process governed by the thermodynamic adjustment, the liquid water path (LWP) decreases with a decreasing cloud-top entrainment rate; on the other hand, during the slow process determined by the cloud-top inversion adjustment, LWP increases. The model exhibits two coexisting (cloudy and non-cloudy) quasi-stationary states through the fast process. A key process for the bifurcation is that the non-cloudy state shows the presence of active cumulus convection that allows the destruction of stratocumulus. The results suggest that the direct entrainment drying is enhanced due to an increased moisture gradient across the inversion layer. This tends to develop more broken clouds, which is an important signal for the stratocumulus to cumulus transition. This conceptual model provides a simple framework for developing a timely switch of regime transition in the cloud parameterization in large-scale models.

  20. Fluid dynamics of liquids on Titans surface

    NASA Astrophysics Data System (ADS)

    Ori, Gian Gabriele; Marinangeli, Lucia; Baliva, Antonio; Bressan, Mario; Strom, Robert G.

    1998-10-01

    On the surface of Titan liquids can be present in three types of environments : (i) oceans, (ii) seas and lakes, and (iii) fluvial channels. The liquid in these environments will be affected by several types of motion: progressive (tidal) waves, wind-generated waves and unidirectional currents. The physical parameters of the liquid on Titans surface can be reconstructed using the Peng-Robinson equation of state. The total energy of the waves, both tidal and wind, depends on the gravity and liquid density ; both values are lower on Titan than on Earth. Thus, the same total energy will produce larger waves on Titan. This is also valid also for the progressive waves, as it is confirmed by the physical relationship between horizontal velocity, wave amplitude, and depth of the liquid. Wind-driven waves also will tend to be larger, because the viscosity of the liquid (which is lower on Titan) controls the deformation of the liquid under shear stress. Wind-generated waves would be rather large, but the dimension of the liquid basin limits the size of the waves ; in small lakes or seas the wave power cannot reach large values. Unidirectional currents are also affected by the liquid properties. Both the relations from driving and resting forces and the Reynolds number suggests that the flows exhibit a large erosional capacity and that, theoretically, a true fluvial network could be formed. However, caution should be exercised, because the cohesion of the sedimentary interface can armour bottom and induce laterally extensive, unchanelled sheet flows with small erosional capacity.

  1. Land Surface Microwave Emissivity Dynamics: Observations, Analysis and Modeling

    NASA Technical Reports Server (NTRS)

    Tian, Yudong; Peters-Lidard, Christa D.; Harrison, Kenneth W.; Kumar, Sujay; Ringerud, Sarah

    2014-01-01

    Land surface microwave emissivity affects remote sensing of both the atmosphere and the land surface. The dynamical behavior of microwave emissivity over a very diverse sample of land surface types is studied. With seven years of satellite measurements from AMSR-E, we identified various dynamical regimes of the land surface emission. In addition, we used two radiative transfer models (RTMs), the Community Radiative Transfer Model (CRTM) and the Community Microwave Emission Modeling Platform (CMEM), to simulate land surface emissivity dynamics. With both CRTM and CMEM coupled to NASA's Land Information System, global-scale land surface microwave emissivities were simulated for five years, and evaluated against AMSR-E observations. It is found that both models have successes and failures over various types of land surfaces. Among them, the desert shows the most consistent underestimates (by approx. 70-80%), due to limitations of the physical models used, and requires a revision in both systems. Other snow-free surface types exhibit various degrees of success and it is expected that parameter tuning can improve their performances.

  2. Land Surface Microwave Emissivity Dynamics: Observations, Analysis and Modeling

    NASA Technical Reports Server (NTRS)

    Tian, Yudong; Peters-Lidard, Christa D.; Harrison, Kenneth W.; Kumar, Sujay; Ringerud, Sarah

    2014-01-01

    Land surface microwave emissivity affects remote sensing of both the atmosphere and the land surface. The dynamical behavior of microwave emissivity over a very diverse sample of land surface types is studied. With seven years of satellite measurements from AMSR-E, we identified various dynamical regimes of the land surface emission. In addition, we used two radiative transfer models (RTMs), the Community Radiative Transfer Model (CRTM) and the Community Microwave Emission Modeling Platform (CMEM), to simulate land surface emissivity dynamics. With both CRTM and CMEM coupled to NASA's Land Information System, global-scale land surface microwave emissivities were simulated for five years, and evaluated against AMSR-E observations. It is found that both models have successes and failures over various types of land surfaces. Among them, the desert shows the most consistent underestimates (by approx. 70-80%), due to limitations of the physical models used, and requires a revision in both systems. Other snow-free surface types exhibit various degrees of success and it is expected that parameter tuning can improve their performances.

  3. Critical design aspects of dynamic titanium alloy risers

    SciTech Connect

    Baxter, C.F.; Schutz, R.W.

    1996-12-01

    Titanium alloys offer a unique, attractive combination of physical, mechanical, and corrosion properties for design of dynamic, compliant offshore risers. The Ti-6Al-4V ELI alloy, in a beta-transformed condition and with minor ruthenium or palladium additions for chloride resistance above 80 C, represent logical base-case metallic materials for compliant risers. All of the technology and components needed to produce a complete, viable titanium alloy compliant riser system, including pipe, termination designs, joining methods, and coatings are available, and are reviewed in this paper.

  4. Dynamic sensitivity of photon-dressed atomic ensemble with quantum criticality

    SciTech Connect

    Huang Jinfeng; Kuang Leman; Li Yong; Liao Jieqiao; Sun, C. P.

    2009-12-15

    We study the dynamic sensitivity of an atomic ensemble dressed by a single-mode cavity field (called a photon-dressed atomic ensemble), which is described by the Dicke model near the quantum critical point. It is shown that when an extra atom in a pure initial state passes through the cavity, the photon-dressed atomic ensemble will experience a quantum phase transition showing an explicit sudden change in its dynamics characterized by the Loschmidt echo of this quantum critical system. With such dynamic sensitivity, the Dicke model can resemble the cloud chamber for detecting a flying particle by the enhanced trajectory due to the classical phase transition.

  5. Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition

    NASA Astrophysics Data System (ADS)

    Midya, Jiarul; Das, Subir K.

    2017-01-01

    Via a combination of molecular dynamics (MD) simulations and finite-size scaling (FSS) analysis, we study dynamic critical phenomena for the vapor-liquid transition in a three dimensional Lennard-Jones system. The phase behavior of the model has been obtained via the Monte Carlo simulations. The transport properties, viz., the bulk viscosity and the thermal conductivity, are calculated via the Green-Kubo relations, by taking inputs from the MD simulations in the microcanonical ensemble. The critical singularities of these quantities are estimated via the FSS method. The results thus obtained are in nice agreement with the predictions of the dynamic renormalization group and mode-coupling theories.

  6. Finite-size scaling study of dynamic critical phenomena in a vapor-liquid transition.

    PubMed

    Midya, Jiarul; Das, Subir K

    2017-01-28

    Via a combination of molecular dynamics (MD) simulations and finite-size scaling (FSS) analysis, we study dynamic critical phenomena for the vapor-liquid transition in a three dimensional Lennard-Jones system. The phase behavior of the model has been obtained via the Monte Carlo simulations. The transport properties, viz., the bulk viscosity and the thermal conductivity, are calculated via the Green-Kubo relations, by taking inputs from the MD simulations in the microcanonical ensemble. The critical singularities of these quantities are estimated via the FSS method. The results thus obtained are in nice agreement with the predictions of the dynamic renormalization group and mode-coupling theories.

  7. Controlling surfaces in plasma processing: role of ions via molecular dynamics simulations of surface chemistry

    NASA Astrophysics Data System (ADS)

    Humbird, David; Graves, David B.

    2002-08-01

    A study of the interactions of energetic ions with various surfaces using molecular dynamics simulations is reported. Silicon atoms in the amorphous region are readily mixed by argon ions. Limited mixing in the crystalline layer is observed. Fluorine adsorbed on the silicon surface does not mix into the layer with argon ion impact. When an energetic F+ impacts a silicon surface, the uptake and apparent sub-surface mixing of F is much greater than Ar+-induced mixing. However, a closer examination shows that the F impacts have primarily increased the Si surface area by creating crevices and cracks, and that the F remains mainly on the surface of this layer.

  8. Improved Criteria for Acceptable Yield Point Elongation in Surface Critical Steels

    SciTech Connect

    Dr. David Matlock; Dr. John Speer

    2007-05-30

    Yield point elongation (YPE) is considered undesirable in surface critical applications where steel is formed since "strain lines" or Luders bands are created during forming. This project will examine in detail the formation of luders bands in industrially relevant strain states including the influence of substrate properties and coatings on Luders appearance. Mechanical testing and surface profilometry were the primary methods of investigation.

  9. Molecular dynamics simulation of annealed ZnO surfaces

    SciTech Connect

    Min, Tjun Kit; Yoon, Tiem Leong; Lim, Thong Leng

    2015-04-24

    The effect of thermally annealing a slab of wurtzite ZnO, terminated by two surfaces, (0001) (which is oxygen-terminated) and (0001{sup ¯}) (which is Zn-terminated), is investigated via molecular dynamics simulation by using reactive force field (ReaxFF). We found that upon heating beyond a threshold temperature of ∼700 K, surface oxygen atoms begin to sublimate from the (0001) surface. The ratio of oxygen leaving the surface at a given temperature increases as the heating temperature increases. A range of phenomena occurring at the atomic level on the (0001) surface has also been explored, such as formation of oxygen dimers on the surface and evolution of partial charge distribution in the slab during the annealing process. It was found that the partial charge distribution as a function of the depth from the surface undergoes a qualitative change when the annealing temperature is above the threshold temperature.

  10. Dynamics of small mobile helium clusters near tungsten surfaces

    NASA Astrophysics Data System (ADS)

    Hu, Lin; Hammond, Karl D.; Wirth, Brian D.; Maroudas, Dimitrios

    2014-08-01

    We report the results of a systematic atomic-scale analysis of the dynamics of small mobile helium clusters in tungsten, near tungsten surfaces. These helium clusters are attracted to tungsten surfaces due to an elastic interaction force that drives surface segregation. As the clusters migrate toward the surface, trap mutation and cluster dissociation are activated at rates higher than in the bulk. These kinetic processes are responsible for important structural, morphological, and compositional features in plasma-exposed tungsten, including surface adatoms, near-surface immobile helium-vacancy complexes, and retained helium content. Detailed results are presented for di-helium and tri-helium clusters near low-Miller-index tungsten surfaces.

  11. Surface dielectric relaxation: probing technique and its application to thermal activation dynamics of polymer surface.

    PubMed

    Ishii, Masashi

    2010-09-01

    For dynamic analyses of a polymer surface, a dielectric relaxation measurement technique with parallel electrodes placed away from the surface was developed. In this technique, a liquid heating medium was filled in the space between the polymer surface and the electrodes. The construction that maintains the surface can clarify the physical interactions between the liquid and the bare surface and controlling the temperature of the liquid reveals the thermal activation property of the surface. The dielectric relaxation spectrum of the surface convoluted into the bulk and liquid spectra can be obtained by a reactance analysis and the surface spectrum is expressed with an equivalent resistance-capacitance parallel circuit. On the basis of the electromechanical analogy, the electric elements can be converted into mechanical elements that indicate the viscoelasticity of the polymer surface. Using these measurement and analysis techniques, the electric and mechanical properties of the surface of a gelatinized chloroprene rubber sample were analyzed.

  12. Structure and dynamics of fluorinated alkanes on silicon dioxide surfaces

    NASA Astrophysics Data System (ADS)

    Tsige, Mesfin

    2007-03-01

    Despite their great promise in various applications, the structure and dynamics of fluorinated alkanes at interfaces is still an open question. In particular, the knowledge from both theoretical and experimental perspectives is very limited when it comes to understanding the interface between these systems and a solid substrate. Molecular dynamics simulations based on the All Atom OPLS model are used to predict the equilibrium structure and dynamics of short fluorinated alkanes on both amorphous and crystalline silicon dioxide surfaces. In order to understand the effect of layer-layer interaction on the ordering of chains in a given layer, the thickness of the liquid film is increased layer-by-layer from monolayer to multilayers. Results for structural and dynamics of the liquid films near the silicon dioxide surfaces will be presented.

  13. A mathematical framework for critical transitions: Bifurcations, fast-slow systems and stochastic dynamics

    NASA Astrophysics Data System (ADS)

    Kuehn, Christian

    2011-06-01

    Bifurcations can cause dynamical systems with slowly varying parameters to transition to far-away attractors. The terms “critical transition” or “tipping point” have been used to describe this situation. Critical transitions have been observed in an astonishingly diverse set of applications from ecosystems and climate change to medicine and finance. The main goal of this paper is to give an overview which standard mathematical theories can be applied to critical transitions. We shall focus on early-warning signs that have been suggested to predict critical transitions and point out what mathematical theory can provide in this context. Starting from classical bifurcation theory and incorporating multiple time scale dynamics one can give a detailed analysis of local bifurcations that induce critical transitions. We suggest that the mathematical theory of fast-slow systems provides a natural definition of critical transitions. Since noise often plays a crucial role near critical transitions the next step is to consider stochastic fast-slow systems. The interplay between sample path techniques, partial differential equations and random dynamical systems is highlighted. Each viewpoint provides potential early-warning signs for critical transitions. Since increasing variance has been suggested as an early-warning sign we examine it in the context of normal forms analytically, numerically and geometrically; we also consider autocorrelation numerically. Hence we demonstrate the applicability of early-warning signs for generic models. We end with suggestions for future directions of the theory.

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

    PubMed

    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.

  15. Molecular dynamics studies of interfacial water at the alumina surface.

    SciTech Connect

    Argyris, Dr. Dimitrios; Ho, Thomas; Cole, David

    2011-01-01

    Interfacial water properties at the alumina surface were investigated via all-atom equilibrium molecular dynamics simulations at ambient temperature. Al-terminated and OH-terminated alumina surfaces were considered to assess the structural and dynamic behavior of the first few hydration layers in contact with the substrates. Density profiles suggest water layering up to {approx}10 {angstrom} from the solid substrate. Planar density distribution data indicate that water molecules in the first interfacial layer are organized in well-defined patterns dictated by the atomic terminations of the alumina surface. Interfacial water exhibits preferential orientation and delayed dynamics compared to bulk water. Water exhibits bulk-like behavior at distances greater than {approx}10 {angstrom} from the substrate. The formation of an extended hydrogen bond network within the first few hydration layers illustrates the significance of water?water interactions on the structural properties at the interface.

  16. Dynamical Criticality in the Collective Activity of a Population of Retinal Neurons

    NASA Astrophysics Data System (ADS)

    Mora, Thierry; Deny, Stéphane; Marre, Olivier

    2015-02-01

    Recent experimental results based on multielectrode and imaging techniques have reinvigorated the idea that large neural networks operate near a critical point, between order and disorder. However, evidence for criticality has relied on the definition of arbitrary order parameters, or on models that do not address the dynamical nature of network activity. Here we introduce a novel approach to assess criticality that overcomes these limitations, while encompassing and generalizing previous criteria. We find a simple model to describe the global activity of large populations of ganglion cells in the rat retina, and show that their statistics are poised near a critical point. Taking into account the temporal dynamics of the activity greatly enhances the evidence for criticality, revealing it where previous methods would not. The approach is general and could be used in other biological networks.

  17. Structural and dynamical properties of water on chemically modified surfaces: The role of the instantaneous surface

    NASA Astrophysics Data System (ADS)

    Bekele, Selemon; Tsige, Mesfin

    Surfaces of polymers such as atactic polystyrene (aPS) represent very good model systems for amorphous material surfaces. Such polymer surfaces are usually modified either chemically or physically for a wide range of applications that include friction, lubrication and adhesion. It is thus quite important to understand the structural and dynamical properties of liquids that come in contact with them to achieve the desired functional properties. Using molecular dynamics (MD) simulations, we investigate the structural and dynamical properties of water molecules in a slab of water in contact with atactic polystyrene surfaces of varying polarity. We find that the density of water molecules and the number distribution of hydrogen bonds as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering of water molecules near the water/PS interface. For the dynamics, we use time correlation functions of hydrogen bonds and the incoherent structure function for the water molecules. Our results indicate that the polarity of the surface dramatically affects the dynamics of the interfacial water molecules with the dynamics slowing down with increasing polarity. This work was supported by NSF Grant DMR1410290.

  18. Ultrafast exciton dynamics at molecular surfaces

    NASA Astrophysics Data System (ADS)

    Monahan, Nicholas R.

    Further improvements to device performance are necessary to make solar energy conversion a compelling alternative to fossil fuels. Singlet exciton fission and charge separation are two processes that can heavily influence the power conversion efficiency of a solar cell. During exciton fission one singlet excitation converts into two triplet excitons, potentially doubling the photocurrent generated by higher energy photons. There is significant discord over the singlet fission mechanism and of particular interest is whether the process involves a multiexciton intermediate state. I used time-resolved two-photon photoemission to investigate singlet fission in hexacene thin films, a model system with strong electronic coupling. My results indicate that a multiexciton state forms within 40 fs of photoexcitation and loses singlet character on a 280 fs timescale, creating two triplet excitons. This is concordant with the transient absorption spectra of hexacene single crystals and definitively proves that exciton fission in hexacene proceeds through a multiexciton state. This state is likely common to all strongly-coupled systems and my results suggest that a reassessment of the generally-accepted singlet fission mechanism is required. Charge separation is the process of splitting neutral excitons into carriers that occurs at donor-acceptor heterojunctions in organic solar cells. Although this process is essential for device functionality, there are few compelling explanations for why it is highly efficient in certain organic photovoltaic systems. To investigate the charge separation process, I used the model system of charge transfer excitons at hexacene surfaces and time-resolved two-photon photoemission. Charge transfer excitons with sufficient energy spontaneously delocalize, growing from about 14 nm to over 50 nm within 200 fs. Entropy drives this delocalization, as the density of states within the Coulomb potential increases significantly with energy. This charge

  19. Hyperelasticity governs dynamic fracture at a critical length scale.

    PubMed

    Buehler, Markus J; Abraham, Farid F; Gao, Huajian

    2003-11-13

    The elasticity of a solid can vary depending on its state of deformation. For example, metals will soften and polymers may stiffen as they are deformed to levels approaching failure. It is only when the deformation is infinitesimally small that elastic moduli can be considered constant, and hence the elasticity linear. Yet, many existing theories model fracture using linear elasticity, despite the fact that materials will experience extreme deformations at crack tips. Here we show by large-scale atomistic simulations that the elastic behaviour observed at large strains--hyperelasticity--can play a governing role in the dynamics of fracture, and that linear theory is incapable of fully capturing all fracture phenomena. We introduce the concept of a characteristic length scale for the energy flux near the crack tip, and demonstrate that the local hyperelastic wave speed governs the crack speed when the hyperelastic zone approaches this energy length scale.

  20. Ionization dynamics of water dimer on ice surface

    NASA Astrophysics Data System (ADS)

    Tachikawa, Hiroto

    2016-05-01

    The solid surface provides an effective two-dimensional reaction field because the surface increases the encounter probability of bi-molecular collision reactions. Also, the solid surface stabilizes a reaction intermediate because the excess energy generated by the reaction dissipates into the bath modes of surface. The ice surface in the universe is one of the two dimensional reaction fields. However, it is still unknown how the ice surface affects to the reaction mechanism. In the present study, to elucidate the specific property of the ice surface reaction, ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated by means of direct ab-initio molecular dynamics (AIMD) method combined with ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) technique, and the result was compared with that of gas phase reaction. It was found that a proton is transferred from H2O+ to H2O within the dimer and the intermediate complex H3O+(OH) is formed in both cases. However, the dynamic features were different from each other. The reaction rate of the proton transfer on the ice surface was three times faster than that in the gas phase. The intermediate complex H3O+(OH) was easily dissociated to H3O+ and OH radical on the ice surface, and the lifetime of the complex was significantly shorter than that of gas phase (100 fs vs. infinite). The reason why the ice surface accelerates the reaction was discussed in the present study.

  1. Bayesian inversion analysis of nonlinear dynamics in surface heterogeneous reactions

    NASA Astrophysics Data System (ADS)

    Omori, Toshiaki; Kuwatani, Tatsu; Okamoto, Atsushi; Hukushima, Koji

    2016-09-01

    It is essential to extract nonlinear dynamics from time-series data as an inverse problem in natural sciences. We propose a Bayesian statistical framework for extracting nonlinear dynamics of surface heterogeneous reactions from sparse and noisy observable data. Surface heterogeneous reactions are chemical reactions with conjugation of multiple phases, and they have the intrinsic nonlinearity of their dynamics caused by the effect of surface-area between different phases. We adapt a belief propagation method and an expectation-maximization (EM) algorithm to partial observation problem, in order to simultaneously estimate the time course of hidden variables and the kinetic parameters underlying dynamics. The proposed belief propagation method is performed by using sequential Monte Carlo algorithm in order to estimate nonlinear dynamical system. Using our proposed method, we show that the rate constants of dissolution and precipitation reactions, which are typical examples of surface heterogeneous reactions, as well as the temporal changes of solid reactants and products, were successfully estimated only from the observable temporal changes in the concentration of the dissolved intermediate product.

  2. Quantum wavepacket ab initio molecular dynamics: an approach for computing dynamically averaged vibrational spectra including critical nuclear quantum effects.

    PubMed

    Sumner, Isaiah; Iyengar, Srinivasan S

    2007-10-18

    We have introduced a computational methodology to study vibrational spectroscopy in clusters inclusive of critical nuclear quantum effects. This approach is based on the recently developed quantum wavepacket ab initio molecular dynamics method that combines quantum wavepacket dynamics with ab initio molecular dynamics. The computational efficiency of the dynamical procedure is drastically improved (by several orders of magnitude) through the utilization of wavelet-based techniques combined with the previously introduced time-dependent deterministic sampling procedure measure to achieve stable, picosecond length, quantum-classical dynamics of electrons and nuclei in clusters. The dynamical information is employed to construct a novel cumulative flux/velocity correlation function, where the wavepacket flux from the quantized particle is combined with classical nuclear velocities to obtain the vibrational density of states. The approach is demonstrated by computing the vibrational density of states of [Cl-H-Cl]-, inclusive of critical quantum nuclear effects, and our results are in good agreement with experiment. A general hierarchical procedure is also provided, based on electronic structure harmonic frequencies, classical ab initio molecular dynamics, computation of nuclear quantum-mechanical eigenstates, and employing quantum wavepacket ab initio dynamics to understand vibrational spectroscopy in hydrogen-bonded clusters that display large degrees of anharmonicities.

  3. Dynamic Topography at Earth's Surface: Fact or Fiction? (Invited)

    NASA Astrophysics Data System (ADS)

    Lithgow-Bertelloni, C. R.; Silver, P. G.

    2009-12-01

    Contributions to Earth’s surface topography range from short-wavelength uncompensated features due to tectonic activity, to variations in crustal structure and long-wavelength deflections of the lithosphere caused by mantle dynamics. The latter we call dynamic topography. Dynamic topography elevates or depresses the surface even if the density anomaly giving rise to flow is deep in the mantle. Dynamic topography is also a major contributor to Earth’s gravitational potential and to surface deformation. However, direct observations of dynamic topography are elusive, because signals are obscured by the isostatic contribution due to crustal and lithospheric structure. The only seemingly unequivocal signals of dynamically supported topography have been found over mantle upwellings on both continents (Africa [Lithgow-Bertelloni and Silver, 1998] and Arabia [Daradich et al., 2004]) and oceanic basins (North-Atlantic [Conrad et al., 2004]). Recent work on Africa’s geomorphic history [Moore et al., 2009] and North Atlantic gravity and topography have called even these results into questions. In downwelling regions (near slabs) no clear signals have been found. I will explore why this dichotomy may exist and relate it to the need for dynamic topography in mantle flow models, with an eye towards the effects of phase transitions, lateral variations in viscosity and layered convection. I will also present recent results on dynamic topography over flat slab segments that overturn the conventional wisdom and explain basin topography in the Andean foreland. Along with the new models I will discuss a recent global lithospheric structure model with which to compute the residual topography, i.e. the “observed” dynamic topography.

  4. Investigation of drop dynamic contact angle on copper surface

    NASA Astrophysics Data System (ADS)

    Orlova, Evgenija; Feoktistov, Dmitriy; Kuznetsov, Geniy

    2015-01-01

    This paper presents experimental results of the studying the effect of surface roughness, microstructure and flow rate on the dynamic contact angle at spreading of distilled non deaerate water drop on a solid horizontal substrates. Copper substrates with different roughness have been investigated. For each substrate static contact angles depending on volume flow rate have been obtained using shadow system. Increasing the volume flow rate resulted in an increase of the static contact angle. It was found that with increasing surface roughness dynamic contact angle arises. Also difference in formation of the equilibrium contact angle at low and high rates of drop growth has been detected.

  5. Monitoring Earth Surface Dynamics With Optical Imagery

    NASA Astrophysics Data System (ADS)

    Leprince, S.; Berthier, E.; Ayoub, F.; Delacourt, C.; Avouac, J.

    2007-12-01

    Optical images can be used to measure accurately a variety of Earth surface processes such as co-seismic ground deformation, ice-flow, landsliding and sand-dunes migration. Although the technique of correlating multi- temporal images is not new, it is not widely used yet due to technical limitations - mainly geometric distortion of the images induced by the imaging system, biased correlation techniques, and implementation difficulties. Most of these obstacles were overcome by recent methodological advances implemented in a user-friendly software package, COSI-Corr, which allows for automatic and precise ortho-rectification, co-registration, and subpixel correlation of pushbroom satellite and aerial images. The procedure does not require external information such as GPS measurements of ground control points, and is solely based on the knowledge of the topography and on the ancillary data provided with the observing platform. In particular, we take advantage of the availability of accurate digital elevation models with global coverage (SRTM). Sub-pixel change detection, i.e. correlation, is then applied on the set of ortho-images produced. COSI-Corr makes it possible to measure local displacements between temporal series of images, possibly acquired by different instruments and at different resolutions, with accuracy of the measurements on the order of a small fraction of the nominal images' resolution. We apply this methodology to the measurement of the horizontal coseismic displacement field induced by the Mw 7.1 1999 Hector Mine earthquake, California, using a 10-m SPOT 4 pre-earthquake image and a 15-m ASTER post-earthquake image. We illustrate the potential of this approach to measure glacier flow, and present the horizontal displacements in the Mer de Glace area (Alps), over 26 days derived from SPOT 5 images. Landsliding is also investigated on the La Valette landslide (southern French Alps), and we present a dense measurement of the cumulative horizontal

  6. Minding the gap: Thinking through spatiotemporal scaling challenges in Earth surface dynamics research

    NASA Astrophysics Data System (ADS)

    Viles, Heather

    2017-04-01

    Research into the dynamics of Earth's surface is diverse, interdisciplinary and challenging, but also an important geoscience contribution to understanding human-landscape interactions in the Anthropocene. Scale issues often thwart our ability to provide answers to important questions of how the Earth's surface has changed in the past and may change in the future. This paper reflects on four major common components of Earth surface dynamics research projects (i.e. how to identify and frame a research question, how to design a study to answer that question, difficulties with data, how to use data to answer the question) and identifies the most important spatiotemporal scale challenges. A case study of an experimental study of rock breakdown in arid environments is used to illustrate these challenges, and to demonstrate the importance of clear conceptualisation and critical thinking in overcoming them.

  7. Surface Segregation in Bimetallic Nanoparticles: A Critical Issue in Electrocatalyst Engineering.

    PubMed

    Liao, Hanbin; Fisher, Adrian; Xu, Zhichuan J

    2015-07-15

    Bimetallic nanoparticles are a class of important electrocatalyst. They exhibit a synergistic effect that critically depends on the surface composition, which determines the surface properties and the adsorption/desorption behavior of the reactants and intermediates during catalysis. The surface composition can be varied, as nanoparticles are exposed to certain environments through surface segregation. Thermodynamically, this is caused by a difference in surface energy between the two metals. It may lead to the enrichment of one metal on the surface and the other in the core. The external conditions that influence the surface energy may lead to the variation of the thermodynamic steady state of the particle surface and, thus, offer a chance to vary the surface composition. In this review, the most recent and important progress in surface segregation of bimetallic nanoparticles and its impact in electrocatalysis are introduced. Typical segregation inducements and surface characterization techniques are discussed in detail. It is concluded that surface segregation is a critical issue when designing bimetallic catalysts. It is necessary to explore methods to control it and utilize it as a way towards producing robust, bimetallic electrocatalysts. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Analysis of insulin receptor substrate signaling dynamics on microstructured surfaces.

    PubMed

    Lanzerstorfer, Peter; Yoneyama, Yosuke; Hakuno, Fumihiko; Müller, Ulrike; Höglinger, Otmar; Takahashi, Shin-Ichiro; Weghuber, Julian

    2015-03-01

    Insulin receptor substrates (IRS) are phosphorylated by activated insulin/insulin-like growth factor I receptor tyrosine kinases, with this comprising an initial key event for downstream signaling and bioactivities. Despite the structural similarities, increasing evidence shows that IRS family proteins have nonredundant functions. Although the specificity of insulin/insulin-like growth factor signaling and biological responses partly reflects which IRS proteins are dominantly phosphorylated by the receptors, the precise properties of the respective IRS interaction with the receptors remain elusive. In the present study, we utilized a technique that combines micropatterned surfaces and total internal reflection fluorescence microscopy for the quantitative analysis of the interaction between IRS proteins and insulin/insulin-like growth factor in living cells. Our experimental set-up enabled the measurement of equilibrium associations and interaction dynamics of these molecules with high specificity. We revealed that several domains of IRS including pleckstrin homology and phosphotyrosine binding domains critically determine the turnover rate of the receptors. Furthermore, we found significant differences among IRS proteins in the strength and kinetic stability of the interaction with the receptors, suggesting that these interaction properties could account for the diverse functions of IRS. In addition, our analyses using fluorescent recovery after photobleaching revealed that kinases such as c-Jun N-terminal kinase and IκB kinase β, which phosphorylate serine/threonine residues of IRS and contribute to insulin resistance, altered the interaction kinetics of IRS with insulin receptor. Collectively, our experimental set-up is a valuable system for quantitifying the physiological interaction of IRS with the receptors in insulin/insulin-like growth factor signaling. © 2015 FEBS.

  9. New measurement technology for 'Critical Dynamics in Microgravity'

    NASA Astrophysics Data System (ADS)

    Duncan, Robert

    2000-03-01

    When driven away from equilibrium by a heat flux Q, the superfluid transition in ^4He evolves from a simple critical point into a fascinating and complex nonlinear region, where the onset of macroscopic quantum order is masked by Earth's gravity. Prior measurements of heat transport within this nonlinear region on Earth (and scheduled measurements on the International Space Station) require temperature resolution to 0.1 nK at 2.2 K in an exceptionally stable thermometer, with all heat flow stable to 3 fW/s. These measurements of the liquid helium temperature must be localized along the side of the experimental cell with a spatial resolution of 5 microns, and systematic offsets of the measured temperature from the true helium temperature must be controlled to within 0.3 nK. Such measurement technology has recently been developed, out-performing these demanding requirements by a comfortable margin. A new class of fundamental physics experiments may be facilitated by these recent advances in metrology. This work has been supported by the Microgravity Science Division of NASA, conducted in cooperation with JPL, and in collaboration with Mary Jayne Adriaans, Alex Babkin, S.T.P. Boyd, Peter Day, David Elliott, Beverly Klemme, T.D. McCarson, Ray Nelson, and Dmitri Sergatskov.

  10. Quantum-Critical Dynamics of the Skyrmion Lattice.

    NASA Astrophysics Data System (ADS)

    Green, Andrew G.

    2002-03-01

    Slightly away from exact filling of the lowest Landau level, the quantum Hall ferromagnet contains a finite density of magnetic vortices or Skyrmions[1,2]. These Skyrmions are expected to form a square lattice[3], the low energy excitations of which (translation/phonon modes and rotation/breathing modes) lead to dramatically enhanced nuclear relaxation[4,5]. Upon changing the filling fraction, the rotational modes undergo a quantum phase transition where zero-point fluctuations destroy the orientational order of the Skyrmions[4,6]. I will discuss the effect of this quantum critical point upon nuclear spin relaxation[7]. [1]S. L. Sondhi et al., Phys. Rev. B47, 16419 (1993). [2]S. E. Barrett et al., Phys. Rev. Lett. 74, 5112 (1995), A. Schmeller et al., Phys. Rev. Lett. 75, 4290 (1995). [3]L. Brey et al, Phys. Rev. Lett. 75, 2562 (1995). [4]R. Côté et al., Phys. Rev. Lett. 78, 4825 (1997). [5]R. Tycko et al., Science 268, 1460 (1995). [6]Yu V. Nazarov and A. V. Khaetskii, Phys. Rev. Lett. 80, 576 (1998). [7]A. G. Green, Phys. Rev. B61, R16 299 (2000).

  11. Potential energy surfaces and reaction dynamics of polyatomic molecules

    SciTech Connect

    Chang, Yan-Tyng

    1991-11-01

    A simple empirical valence bond (EVB) model approach is suggested for constructing global potential energy surfaces for reactions of polyatomic molecular systems. This approach produces smooth and continuous potential surfaces which can be directly utilized in a dynamical study. Two types of reactions are of special interest, the unimolecular dissociation and the unimolecular isomerization. For the first type, the molecular dissociation dynamics of formaldehyde on the ground electronic surface is investigated through classical trajectory calculations on EVB surfaces. The product state distributions and vector correlations obtained from this study suggest very similar behaviors seen in the experiments. The intramolecular hydrogen atom transfer in the formic acid dimer is an example of the isomerization reaction. High level ab initio quantum chemistry calculations are performed to obtain optimized equilibrium and transition state dimer geometries and also the harmonic frequencies.

  12. The role of dynamic surface tension in cloud droplet activation

    NASA Astrophysics Data System (ADS)

    Petters, Markus D.; Suda, Sarah R.; Christensen, Sara I.

    2013-05-01

    We present new data on the cloud droplet forming abilities of two-component particles that contain the surfactant sodium dodecyl sulfate and sodium chloride or ammonium sulfate. The experiments were designed to test specific predictions made by Kohler theory that accounts for the reduction of surface tension and the partitioning of the surfactant between the interior and the surface of the droplet. We also introduced a pre-humidification step followed by a six minute time delay to test whether dynamic surface tension may lead to kinetic limitations on the partitioning process. Our results confirm previous studies that show that surfactants do not enhance cloud droplet activation relative to what would be predicted from water activity alone. The data obtained with and without time delay were indistinguishable within measurement uncertainty, suggesting that dynamic surface tension does not need to be considered in Kohler theory.

  13. Self-organized criticality in sandpiles - Nature of the critical phenomenon. [dynamic models in phase transition

    NASA Technical Reports Server (NTRS)

    Carlson, J. M.; Chayes, J. T.; Swindle, G. H.; Grannan, E. R.

    1990-01-01

    The scaling behavior of sandpile models is investigated analytically. First, it is shown that sandpile models contain a set of domain walls, referred to as troughs, which bound regions that can experience avalanches. It is further shown that the dynamics of the troughs is governed by a simple set of rules involving birth, death, and coalescence events. A simple trough model is then introduced, and it is proved that the model has a phase transition with the density of the troughs as an order parameter and that, in the thermodynamic limit, the trough density goes to zero at the transition point. Finally, it is shown that the observed scaling behavior is a consequence of finite-size effects.

  14. Self-organized criticality in sandpiles - Nature of the critical phenomenon. [dynamic models in phase transition

    NASA Technical Reports Server (NTRS)

    Carlson, J. M.; Chayes, J. T.; Swindle, G. H.; Grannan, E. R.

    1990-01-01

    The scaling behavior of sandpile models is investigated analytically. First, it is shown that sandpile models contain a set of domain walls, referred to as troughs, which bound regions that can experience avalanches. It is further shown that the dynamics of the troughs is governed by a simple set of rules involving birth, death, and coalescence events. A simple trough model is then introduced, and it is proved that the model has a phase transition with the density of the troughs as an order parameter and that, in the thermodynamic limit, the trough density goes to zero at the transition point. Finally, it is shown that the observed scaling behavior is a consequence of finite-size effects.

  15. Surface water connectivity dynamics of a large scale extreme flood

    NASA Astrophysics Data System (ADS)

    Trigg, Mark A.; Michaelides, Katerina; Neal, Jeffrey C.; Bates, Paul D.

    2013-11-01

    Uses the MODIS surface water product observations of the 2011 Bangkok flood.A data gap filling method is developed to better preserve the dynamics of the event.We quantify surface water connectivity geostatistically to give new flood insights.There is a clear structure to the connectivity of the event through time and space.Changes and thresholds in the connectivity are linked to major flood mechanisms.

  16. Laser scanning dynamic measurement of the curved surface

    NASA Astrophysics Data System (ADS)

    Hong, Xin; Zheng, Wenxue

    1996-10-01

    A new measurement of the curved surface has been developed. The paper provides an effective, real time and dynamic optical measurement which is suitable for the measurement of airfoil, turbine blade, car and tank's curved surface. The system consists of a laser probe, a charge couple device (CCD), a computer, three servomotors. Consideration is also given to the design of the laser probe and CCD driving circuit.

  17. Using what you get: dynamic physiologic signatures of critical illness

    PubMed Central

    Holder, Andre L.; Clermont, Gilles

    2015-01-01

    A physiologic signature can be defined as a consistent and robust collection of physiologic measurements characterizing a disease process and its temporal evolution. If a library of physiologic signatures of impending cardiopulmonary instability were available to clinicians caring for inpatients, many episodes of clinical decompensation and their downstream effects could potentially be averted. The development and resolution of cardiopulmonary instability are processes that take time to become clinically apparent, and the treatments provided take time to have an impact. The characterization of dynamic changes in hemodynamic and metabolic variables is implicit in the concept of physiologic signatures. Changes in vital signs such as blood pressure and heart rate, as well as measures of flow such as cardiac output are some of the standard variables used by clinicians to determine cardiopulmonary instability. When these primary variables are collected with high enough frequency to derive new variables, this data hierarchy can be used to development physiologic signatures. The construction of new variables from primary variables, and therefore the creation of physiologic signatures requires no new information; additional knowledge is extracted from data that already exists. It is possible to create physiologic signatures for each stage in the process of clinical decompensation and recovery to improve patient outcomes. PMID:25435482

  18. Sub-nanometer glass surface dynamics induced by illumination.

    PubMed

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T; Lyding, Joseph; Gruebele, Martin

    2015-06-21

    Illumination is known to induce stress and morphology changes in opaque glasses. Amorphous silicon carbide (a-SiC) has a smaller bandgap than the crystal. Thus, we were able to excite with 532 nm light a 1 μm amorphous surface layer on a SiC crystal while recording time-lapse movies of glass surface dynamics by scanning tunneling microscopy (STM). Photoexcitation of the a-SiC surface layer through the transparent crystal avoids heating the STM tip. Up to 6 × 10(4) s, long movies of surface dynamics with 40 s time resolution and sub-nanometer spatial resolution were obtained. Clusters of ca. 3-5 glass forming units diameter are seen to cooperatively hop between two states at the surface. Photoexcitation with green laser light recruits immobile clusters to hop, rather than increasing the rate at which already mobile clusters hop. No significant laser heating was observed. Thus, we favor an athermal mechanism whereby electronic excitation of a-SiC directly controls glassy surface dynamics. This mechanism is supported by an exciton migration-relaxation-thermal diffusion model. Individual clusters take ∼1 h to populate states differently after the light intensity has changed. We believe the surrounding matrix rearranges slowly when it is stressed by a change in laser intensity, and clusters serve as a diagnostic. Such cluster hopping and matrix rearrangement could underlie the microscopic mechanism of photoinduced aging of opaque glasses.

  19. Sub-nanometer glass surface dynamics induced by illumination

    SciTech Connect

    Nguyen, Duc; Nienhaus, Lea; Haasch, Richard T.; Lyding, Joseph; Gruebele, Martin

    2015-06-21

    Illumination is known to induce stress and morphology changes in opaque glasses. Amorphous silicon carbide (a-SiC) has a smaller bandgap than the crystal. Thus, we were able to excite with 532 nm light a 1 μm amorphous surface layer on a SiC crystal while recording time-lapse movies of glass surface dynamics by scanning tunneling microscopy (STM). Photoexcitation of the a-SiC surface layer through the transparent crystal avoids heating the STM tip. Up to 6 × 10{sup 4} s, long movies of surface dynamics with 40 s time resolution and sub-nanometer spatial resolution were obtained. Clusters of ca. 3-5 glass forming units diameter are seen to cooperatively hop between two states at the surface. Photoexcitation with green laser light recruits immobile clusters to hop, rather than increasing the rate at which already mobile clusters hop. No significant laser heating was observed. Thus, we favor an athermal mechanism whereby electronic excitation of a-SiC directly controls glassy surface dynamics. This mechanism is supported by an exciton migration-relaxation-thermal diffusion model. Individual clusters take ∼1 h to populate states differently after the light intensity has changed. We believe the surrounding matrix rearranges slowly when it is stressed by a change in laser intensity, and clusters serve as a diagnostic. Such cluster hopping and matrix rearrangement could underlie the microscopic mechanism of photoinduced aging of opaque glasses.

  20. Fading Signatures of Critical Brain Dynamics during Sustained Wakefulness in Humans

    PubMed Central

    Olbrich, Eckehard; Shriki, Oren; Achermann, Peter

    2013-01-01

    Sleep encompasses approximately a third of our lifetime, yet its purpose and biological function are not well understood. Without sleep optimal brain functioning such as responsiveness to stimuli, information processing, or learning may be impaired. Such observations suggest that sleep plays a crucial role in organizing or reorganizing neuronal networks of the brain toward states where information processing is optimized. Increasing evidence suggests that cortical neuronal networks operate near a critical state characterized by balanced activity patterns, which supports optimal information processing. However, it remains unknown whether critical dynamics is affected in the course of wake and sleep, which would also impact information processing. Here, we show that signatures of criticality are progressively disturbed during wake and restored by sleep. We demonstrate that the precise power-laws governing the cascading activity of neuronal avalanches and the distribution of phase-lock intervals in human electroencephalographic recordings are increasingly disarranged during sustained wakefulness. These changes are accompanied by a decrease in variability of synchronization. Interpreted in the context of a critical branching process, these seemingly different findings indicate a decline of balanced activity and progressive distance from criticality toward states characterized by an imbalance toward excitation where larger events prevail dynamics. Conversely, sleep restores the critical state resulting in recovered power-law characteristics in activity and variability of synchronization. These findings support the intriguing hypothesis that sleep may be important to reorganize cortical network dynamics to a critical state thereby assuring optimal computational capabilities for the following time awake. PMID:24174669

  1. Fading signatures of critical brain dynamics during sustained wakefulness in humans.

    PubMed

    Meisel, Christian; Olbrich, Eckehard; Shriki, Oren; Achermann, Peter

    2013-10-30

    Sleep encompasses approximately a third of our lifetime, yet its purpose and biological function are not well understood. Without sleep optimal brain functioning such as responsiveness to stimuli, information processing, or learning may be impaired. Such observations suggest that sleep plays a crucial role in organizing or reorganizing neuronal networks of the brain toward states where information processing is optimized. Increasing evidence suggests that cortical neuronal networks operate near a critical state characterized by balanced activity patterns, which supports optimal information processing. However, it remains unknown whether critical dynamics is affected in the course of wake and sleep, which would also impact information processing. Here, we show that signatures of criticality are progressively disturbed during wake and restored by sleep. We demonstrate that the precise power-laws governing the cascading activity of neuronal avalanches and the distribution of phase-lock intervals in human electroencephalographic recordings are increasingly disarranged during sustained wakefulness. These changes are accompanied by a decrease in variability of synchronization. Interpreted in the context of a critical branching process, these seemingly different findings indicate a decline of balanced activity and progressive distance from criticality toward states characterized by an imbalance toward excitation where larger events prevail dynamics. Conversely, sleep restores the critical state resulting in recovered power-law characteristics in activity and variability of synchronization. These findings support the intriguing hypothesis that sleep may be important to reorganize cortical network dynamics to a critical state thereby assuring optimal computational capabilities for the following time awake.

  2. Static and Dynamic Wetting Behavior of Triglycerides on Solid Surfaces.

    PubMed

    Michalski; Saramago

    2000-07-15

    Triglyceride wetting properties on solid surfaces of different hydro-phobicities were investigated using three different methods, namely, the sessile drop method for static contact angle measurements, the Wilhelmy method for dynamic contact angle measurements, and the captive bubble method to investigate thin triglyceride film stability. For solid surfaces having a surface free energy higher than the surface tension of triglycerides (tributyrin, tricaprylin, and triolein), a qualitative correlation was observed between wetting and solid/triglyceride relative hydrophobicities. On surfaces presenting extreme hydrophobic or hydrophilic properties, medium-chain triglycerides had a behavior similar to that of long-chain unsaturated ones. On a high-energy surface (glass), tricaprylin showed an autophobic effect subsequent to molecular adsorption in trident conformation on the solid, observed with the three methods. Thin triglyceride films between an air bubble and a solid surface were stable for a short time, for solids with a surface free energy larger than the triglyceride surface tension. If the solid surface had a lower surface free energy, the thin film collapsed after a time interval which increased with triglyceride viscosity. Copyright 2000 Academic Press.

  3. Molecular Dynamics Simulations of Surface Processes: Oxygen Recombination on Silica Surfaces at High Temperature

    DTIC Science & Technology

    2007-07-01

    size-scalable cluster approach with SixOy clusters of increasing size cleaved from the β- cristobalite unit cell. In this study the hybrid Hartree...values of the β- cristobalite cell and extending the Molecular Dynamics Simulations of Surface Processes: Oxygen Recombination on Silica Surfaces at... cristobalite surface is reported as a function of the distance of the N atom from the Si active atom. The dashed line shows the interaction

  4. Probing Critical Surfaces in Momentum Space Using Real-Space Entanglement Entropy: Bose versus Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Kun; Lai, Hsin-Hua

    A co-dimension one critical surface in the momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the non-interacting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. Their presence gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real space entanglement entropy. The fundamental difference between a Fermi surface and a Bose surface is revealed by the fact that the logarithmic terms in entanglement entropies differ by a factor of two: SlogBose = 2SlogFermi , even when they have identical geometry. Our method has remarkable similarity with determining Fermi surface shape using quantum oscillation. We also discuss possible probes of concave critical surfaces in momentum space. HHL and KY acknowledge the National Science Foundation through Grants No. DMR-1004545, DMR-1157490, No. DMR-1442366, and State of Florida. HHL is also partially supported by NSF Grant No. DMR-1309531, and the Smalley Postdoctoral Fellowship in Quantum Ma.

  5. Universal short-time quantum critical dynamics of finite-size systems

    NASA Astrophysics Data System (ADS)

    Shu, Yu-Rong; Yin, Shuai; Yao, Dao-Xin

    2017-09-01

    We investigate the short-time quantum critical dynamics in the imaginary-time relaxation processes of finite-size systems. Universal scaling behaviors exist in the imaginary-time evolution. In particular, the system undergoes a critical initial slip stage characterized by an exponent θ , in which an initial power-law increase emerges in the imaginary-time correlation function when the initial state has a zero order parameter and a vanishing correlation length. Under different initial conditions, the quantum critical point and critical exponents can be determined from the universal scaling behaviors. We apply the method to the one- and two-dimensional transverse field Ising models using quantum Monte Carlo (QMC) simulations. In the one-dimensional case, we locate the quantum critical point at (h/J ) c=1.000 03 (8 ) in the thermodynamic limit, and we estimate the critical initial slip exponent θ =0.3734 (2 ) and the static exponent β /ν =0.1251 (2 ) by analyzing data on chains of length L =32 -256 and 48-256, respectively. For the two-dimensional square-lattice system, the critical coupling ratio is given by 3.044 51 (7 ) in the thermodynamic limit, while the critical exponents are θ =0.209 (4 ) and β /ν =0.518 (1 ) estimated by data on systems of size L =24 -64 and 32-64, respectively. Remarkably, the critical initial slip exponents obtained in both models are notably distinct from their classical counterparts due to the essential differences between classical and quantum dynamics. The short-time critical dynamics and the imaginary-time relaxation QMC approach can be readily adapted to various models.

  6. Using Dynamic Geometry Software for the Intersection Surfaces

    ERIC Educational Resources Information Center

    Koparan, Timur; Yilmaz, Gül Kaleli

    2015-01-01

    The purpose of this study is to define prospective teacher views about using dynamic geometry software for intersection surfaces. The study was conducted as a case study. For this purpose, data collection tool was developed based on the opinion of two experts. The data collection tool consists of 4 open-ended questions related to the intersection…

  7. Determination of dynamic surface forces using piezoelectric arrays

    NASA Astrophysics Data System (ADS)

    Nitsche, W.; Mirow, P.

    The experimental determination of static and dynamic surface forces on flow bodies using piezoelectric arrays is outlined. The fundamentals of the piezo-array sensor technique (sensor construction, signal separation, and signal transmission) are presented. Practical applications of piezo-arrays in the fields of airfoil aerodynamics and general flow investigations are explained. The obtained measuring results are purely qualitative.

  8. Dynamics of Wetting and Wicking on Rough Surfaces

    NASA Astrophysics Data System (ADS)

    Antao, Dion; Preston, Daniel; Adera, Solomon; Zhu, Yangying; Wang, Evelyn

    Micro/nano engineering of surfaces to enhance the performance of phase-change heat transfer processes has recently gained wide interest. Interfacial phenomena at the micro/nanoscale play an important role in defining the dynamic wetting and wicking characteristics of the surfaces. Here we report experiments that characterize the dynamic wetting and wicking processes on microstructured silicon surfaces. We investigated cylindrical micropillar arrays in a square pattern with various diameter, pitch, and height to characterize key interfacial behavior over a wide range of surface roughness. The experiments were performed by dipping the microstructured sample vertically into a reservoir of de-ionized water and the spreading dynamics were captured with a high speed camera. We observed that both wetting and wicking exhibit a power law dependence on time, however they occur at different time scales. The instantaneous (~10-100 ms) wetting behavior occurs due to the interfacial tensions, and the resultant force acting at the three-phase contact line. The longer time scale (>100 ms) wicking behavior results from the balance of the capillary pressure generated within the microstructure and the viscous pressure loss from flow through the micropillar array. We develop analytical models to predict these different time scale behavior and compare them to experimental results. This work provides insight into key dynamic processes affecting micro/nanostructure enhanced phase-change heat transfer devices.

  9. Investigation on critical strain of dynamic recrystallization for SiCp/Al-Cu composite

    NASA Astrophysics Data System (ADS)

    Sun, Yali; Xie, Jingpei; Hao, Shiming; Wang, Aiqin; Liu, Pei; Li, Min

    2015-07-01

    Using Gleeble-1500D simulator, the critical strain of dynamic recrystallization of SiCp/Al-Cu composite were investigated at 623-773 K with strain rate of 0.01-10 s-1. The results show that the main softening mechanism is the dynamic recrystallization through the stress-strain curves of SiCp/Al-Cu composite, the activation energy is 272.831 KJ/mol. lnθ-ε and (-∂(lnθ)/∂ε)-ε) curves were plotted based on the experimental data to further obtain the critical strain and steady strain of DRX. Then the critical strain model and the steady-state strain model of DRX were set up. Furthermore, the dynamic recrystallization volume fraction of SiCp/Al-Cu composite was investigated.

  10. Early stage of critical clusters growth in phenomenological and molecular dynamics simulation models

    NASA Astrophysics Data System (ADS)

    Puzyrewski, Romuald; Rybicki, Jarosław; Białoskórski, Michał

    2006-12-01

    The growth of critical clusters is discussed in the paper according to the classical and molecular dynamics (MD) approaches. A new formula for molecule numbers in critical clusters has been derived within the framework of the classical approach. A set of equations controlling the early stage of growth in a neighborhood of a critical size is presented. As far as molecular dynamics simulation is concerned, a computational technique based on the DL_POLY code is described in brief. Computation results are presented concerning cluster formation of H 2O vapor, distribution of clusters versus time, cluster growth and radial density distribution of isolated clusters. A comparison with the classical results is made for a case of dense vapor, where the mechanism of strong condensation is predominant. The Hertz-Knudsen formula seems to be verified by the molecular dynamics results.

  11. Relaxational dynamics of water molecules at protein surface

    NASA Astrophysics Data System (ADS)

    Dellerue, S.; Bellissent-Funel, M.-C.

    2000-08-01

    Relaxational dynamics of water molecules at the surface of a C-phycocyanin protein is studied by high resolution quasi-elastic neutron scattering. The neutron quasi-elastic spectra are well described by the α-relaxation process of mode coupling theory of supercooled liquids. The relaxation times of interfacial water exhibit a power law dependence on the wave vector Q. The average diffusion coefficient is 10 times lower than that of bulk water. This confirms that there is a retardation of water molecules at the protein surface which is in good agreement with the results of water at the surface of hydrophilic model systems.

  12. Low-Frequency Surface Backscattering Strengths Measured in the Critical Sea Test Experiments

    DTIC Science & Technology

    2017-01-19

    Test Experiments January 19, 2017 Approved for public release; distribution is unlimited. RogeR C. gauss Joseph M. Fialkowski Acoustic Signal...LIMITATION OF ABSTRACT Low-Frequency Surface Backscattering Strengths Measured in the Critical Sea Test Experiments Roger C. Gauss1 and Joseph M...significantly- updated results from 55 broadband SUS SSS measurements in 6 Critical Sea Test (CST) experiments. Since the time of the previously

  13. Decay of surface nanostructures via long-time-scale dynamics

    SciTech Connect

    Voter, A.F.; Stanciu, N.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have developed a new approach for extending the time scale of molecular dynamics simulations. For infrequent-event systems, the category that includes most diffusive events in the solid phase, this hyperdynamics method can extend the simulation time by a few orders of magnitude compared to direct molecular dynamics. The trajectory is run on a potential surface that has been biased to raise the energy in the potential basins without affecting the transition state region. The method is described and applied to surface and bulk diffusion processes, achieving microsecond and millisecond simulation times. The authors have also developed a new parallel computing method that is efficient for small system sizes. The combination of the hyperdynamics with this parallel replica dynamics looks promising as a general materials simulation tool.

  14. Critical short-time dynamics in a system with interacting static and diffusive populations

    NASA Astrophysics Data System (ADS)

    Argolo, C.; Quintino, Yan; Gleria, Iram; Lyra, M. L.

    2012-01-01

    We study the critical short-time dynamical behavior of a one-dimensional model where diffusive individuals can infect a static population upon contact. The model presents an absorbing phase transition from an active to an inactive state. Previous calculations of the critical exponents based on quasistationary quantities have indicated an unusual crossover from the directed percolation to the diffusive contact process universality classes. Here we show that the critical exponents governing the slow short-time dynamic evolution of several relevant quantities, including the order parameter, its relative fluctuations, and correlation function, reinforce the lack of universality in this model. Accurate estimates show that the critical exponents are distinct in the regimes of low and high recovery rates.

  15. Critical behavior and out-of-equilibrium dynamics of a two-dimensional Ising model with dynamic couplings

    NASA Astrophysics Data System (ADS)

    Pinto, Oscar A.; Romá, Federico; Bustingorry, Sebastian

    2014-12-01

    We study the critical behavior and the out-of-equilibrium dynamics of a two-dimensional Ising model with non-static interactions. In our model, bonds are dynamically changing according to a majority rule depending on the set of closest neighbors of each spin pair, which prevents the system from ordering in a full ferromagnetic or antiferromagnetic state. Using a parallel-tempering Monte Carlo algorithm, we find that the model undergoes a continuous phase transition at finite temperature, which belongs to the Ising universality class. The properties of the bond structure and the ground-state entropy are also studied. Finally, we analyze the out-of-equilibrium dynamics which displays typical glassy characteristics at a temperature well below the critical one.

  16. Wetting dynamics of alkyl ketene dimer on cellulosic model surfaces

    SciTech Connect

    Garnier, G.; Bertin, M.; Smrckova, M.

    1999-10-26

    The dynamic wetting of a commercial alkyl ketene dimer (AKD) wax was measured on model cellulosic surfaces. The variables investigated were temperature and the surface composition. The model surfaces consisted of cellulose and cellulose acetate films as well as glass. These surfaces are smooth by industrial standards but not on a molecular level. The objective of the study was to predict the extent of AKD wetting during the time frame of papermaking. For smooth surfaces, AKD particles wet but do not spread on the hydrophilic surfaces investigated. AKD wetting proceeds from the balance of the interfacial forces with the viscous dissipation. The effect of gravity can be neglected for papermaking conditions. The Hoffman-Tanner equation modified for partial wetting provided a very good fit of the dynamic wetting. The slope of the graph is a function of temperature but not of the solid surface composition. Maslyiah's model also fits the experimental results well, but with a physically unrealistic value of the fitting parameter. For partial wetting, the complex but rigorous Cox equation is recommended to estimate the slip length over macroscopic wetting dimensions.

  17. Line contribution to the critical Casimir force between a homogeneous and a chemically stepped surface.

    PubMed

    Toldin, Francesco Parisen; Tröndle, Matthias; Dietrich, S

    2015-06-03

    Recent experimental realizations of the critical Casimir effect have been implemented by monitoring colloidal particles immersed in a binary liquid mixture near demixing and exposed to a chemically structured substrate. In particular, critical Casimir forces have been measured for surfaces consisting of stripes with periodically alternating adsorption preferences, forming chemical steps between them. Motivated by these experiments, we analyze the contribution of such chemical steps to the critical Casimir force for the film geometry and within the Ising universality class. By means of Monte Carlo simulations, mean-field theory and finite-size scaling analysis we determine the universal scaling function associated with the contribution to the critical Casimir force due to individual, isolated chemical steps facing a surface with homogeneous adsorption preference or with Dirichlet boundary condition. In line with previous findings, these results allow one to compute the critical Casimir force for the film geometry and in the presence of arbitrarily shaped, but wide stripes. In this latter limit the force decomposes into a sum of the contributions due to the two homogeneous parts of the surface and due to the chemical steps between the stripes. We assess this decomposition by comparing the resulting sum with actual simulation data for the critical Casimir force in the presence of a chemically striped substrate.

  18. Surface and bulk hot electron dynamics in silicon

    NASA Astrophysics Data System (ADS)

    Jeong, Seongtae; Bokor, Jeffrey

    1997-03-01

    The direct time domain study of hot electron dynamics on the silicon surface has been an active area of research. Dynamics in Si(100) surface states was observed(M.W. Rowe, H. Liu, G. P. Williams, Jr., and R. T. Williams, Phys. Rev. B 47, 2048 (1993)) as well as cooling of a hot but thermal distribution of carriers in bulk silicon(J. R. Goldman, and J. A. Prybyla, Phys. Rev. Lett. 72, 1364 (1994)). In this work, a time-resolved photoemission study on the Si(100)2x1 surface with 1.55 eV pump and 4.66 eV probe with 0.2 psec time resolution is reported. It is observed that two-photon absorption is responsible for high kinetic energy electrons above the conduction band minimum (CBM) but direct single-photon excitation into surface states and conduction band states followed by the surface recombination dominates the dynamics. Also observed are an early nonthermal electronic distribution in silicon and its transition into a thermal one followed by a rapid cooling.

  19. Drop impact dynamics on oil-infused nanostructured surfaces.

    PubMed

    Lee, Choongyeop; Kim, Hyunsik; Nam, Youngsuk

    2014-07-22

    We experimentally investigated the impact dynamics of a water drop on oil-infused nanostructured surfaces using high-speed microscopy and scalable metal oxide nano surfaces. The effects of physical properties of the oil and impact velocity on complex fluid dynamics during drop impact were investigated. We show that the oil viscosity does not have significant effects on the maximal spreading radius of the water drop, while it moderately affects the retraction dynamics. The oil viscosity also determines the stability of the infused lubricant oil during the drop impact; i.e., the low viscosity oil layer is easily displaced by the impacting drop, which is manifested by a residual mark on the impact region and earlier initiation of prompt splashing. Also, because of the liquid (water)-liquid (oil) interaction on oil-infused surfaces, various instabilities are developed at the rim during impact under certain conditions, resulting in the flower-like pattern during retraction or elongated filaments during spreading. We believe that our findings will contribute to the rational design of oil-infused surfaces under drop impact conditions by illuminating the complex fluid phenomena on oil-infused surfaces during drop impact.

  20. Scaling in driven dynamics starting in the vicinity of a quantum critical point

    NASA Astrophysics Data System (ADS)

    Yin, Shuai; Lo, Chung-Yu; Chen, Pochung

    2016-08-01

    Driven dynamics across a quantum critical point is usually described by the Kibble-Zurek scaling. Although the original Kibble-Zurek scaling requires an adiabatic initial state, it has been shown that scaling behaviors exist even when the driven dynamics is triggered from a thermal equilibrium state exactly at the critical point, in spite of the breakdown of the initial adiabaticity. In this paper, we show that the existence of the scaling behavior can be generalized to the case of the initial state being a thermal equilibrium state near the critical point. We propose a scaling theory in which the initial parameters are included as additional scaling variables due to the breakdown of the initial adiabaticity. In particular, we demonstrate that for the driven critical dynamics in a closed system, the nontrivial thermal effects are closely related to the initial distance to the critical point. We numerically confirm the scaling theory by simulating the real-time dynamics of the one-dimensional quantum Ising model at both zero and finite temperatures.

  1. Anomalously Rapid Hydration Water Diffusion Dynamics Near DNA Surfaces.

    PubMed

    Franck, John M; Ding, Yuan; Stone, Katherine; Qin, Peter Z; Han, Songi

    2015-09-23

    The emerging Overhauser effect dynamic nuclear polarization (ODNP) technique measures the translational mobility of water within the vicinity (5-15 Å) of preselected sites. The work presented here expands the capabilities of the ODNP technique and illuminates an important, previously unseen, property of the translational diffusion dynamics of water at the surface of DNA duplexes. We attach nitroxide radicals (i.e., spin labels) to multiple phosphate backbone positions of DNA duplexes, allowing ODNP to measure the hydration dynamics at select positions along the DNA surface. With a novel approach to ODNP analysis, we isolate the contributions of water molecules at these sites that undergo free translational diffusion from water molecules that either loosely bind to or exchange protons with the DNA. The results reveal that a significant population of water in a localized volume adjacent to the DNA surface exhibits fast, bulk-like characteristics and moves unusually rapidly compared to water found in similar probe volumes near protein and membrane surfaces. Control studies show that the observation of these characteristics are upheld even when the DNA duplex is tethered to streptavidin or the mobility of the nitroxides is altered. This implies that, as compared to protein or lipid surfaces, it is an intrinsic feature of the DNA duplex surface that it interacts only weakly with a significant fraction of the surface hydration water network. The displacement of this translationally mobile water is energetically less costly than that of more strongly bound water by up to several kBT and thus can lower the activation barrier for interactions involving the DNA surface.

  2. Quantum simulation of molecular interaction and dynamics at surfaces

    NASA Astrophysics Data System (ADS)

    Ding, Zi-Jing; Jiao, Yang; Meng, Sheng

    2011-09-01

    The interaction between molecules and solid surfaces plays important roles in various applications, including catalysis, sensors, nanoelectronics, and solar cells. Surprisingly, a full understanding of molecule-surface interaction at the quantum mechanical level has not been achieved even for very simple molecules, such as water. In this mini-review, we report recent progresses and current status of studies on interaction between representative molecules and surfaces. Taking water/metal, DNA bases/carbon nanotube, and organic dye molecule/oxide as examples, we focus on the understanding on the microstructure, electronic property, and electron-ion dynamics involved in these systems obtained from first-principles quantum mechanical calculations. We find that a quantum mechanical description of molecule-surface interaction is essential for understanding interface phenomenon at the microscopic level, such as wetting. New theoretical developments, including van der Waals density functional and quantum nuclei treatment, improve further our understanding of surface interactions.

  3. Modeling the effect of dynamic surfaces on membrane penetration

    NASA Astrophysics Data System (ADS)

    van Lehn, Reid; Alexander-Katz, Alfredo

    2011-03-01

    The development of nanoscale materials for targeted drug delivery is an important current pursuit in materials science. One task of drug carriers is to release therapeutic agents within cells by bypassing the cell membrane to maximize the effectiveness of their payload and minimize bodily exposure. In this work, we use coarse-grained simulations to study nanoparticles (NPs) grafted with hydrophobic and hydrophilic ligands that rearrange in response to the amphiphilic lipid bilayer. We demonstrate that this dynamic surface permits the NP to spontaneously penetrate to the bilayer midplane when the surface ligands are near an order-disorder transition. We believe that this work will lead to the design of new drug carriers capable of non-specifically accessing cell interiors based solely on their dynamic surface properties. Our work is motivated by existing nanoscale systems such as micelles, or NPs grafted with highly mobile ligands or polymer brushes.

  4. Mean-field dynamic criticality and geometric transition in the Gaussian core model

    NASA Astrophysics Data System (ADS)

    Coslovich, Daniele; Ikeda, Atsushi; Miyazaki, Kunimasa

    2016-04-01

    We use molecular dynamics simulations to investigate dynamic heterogeneities and the potential energy landscape of the Gaussian core model (GCM). Despite the nearly Gaussian statistics of particles' displacements, the GCM exhibits giant dynamic heterogeneities close to the dynamic transition temperature. The divergence of the four-point susceptibility is quantitatively well described by the inhomogeneous version of the mode-coupling theory. Furthermore, the potential energy landscape of the GCM is characterized by large energy barriers, as expected from the lack of activated, hopping dynamics, and display features compatible with a geometric transition. These observations demonstrate that all major features of mean-field dynamic criticality can be observed in a physically sound, three-dimensional model.

  5. Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces

    SciTech Connect

    Shen, Jian; Graber, Christof; Liburdy, James; Pence, Deborah; Narayanan, Vinod

    2010-05-15

    This study examines the hydrodynamics and temperature characteristics of distilled deionized water droplets impinging on smooth and nano-structured surfaces using high speed (HS) and infrared (IR) imaging at We = 23.6 and Re = 1593, both based on initial drop impingement parameters. Results for a smooth and nano-structured surface for a range of surface temperatures are compared. Droplet impact velocity, transient spreading diameter and dynamic contact angle are measured. The near surface average droplet fluid temperatures are evaluated for conditions of evaporative cooling and boiling. Also included are surface temperature results using a gold layered IR opaque surface on silicon. Four stages of the impingement process are identified: impact, boiling, near constant surface diameter evaporation, and final dry-out. For the boiling conditions there is initial nucleation followed by severe boiling, then near constant diameter evaporation resulting in shrinking of the droplet height. When a critical contact angle is reached during evaporation the droplet rapidly retracts to a smaller diameter reducing the contact area with the surface. This continues as a sequence of retractions until final dry out. The basic trends are the same for all surfaces, but the nano-structured surface has a lower dissipated energy during impact and enhances the heat transfer for evaporative cooling with a 20% shorter time to achieve final dry out. (author)

  6. Firm Size, a Self-Organized Critical Phenomenon: Evidence from the Dynamical Systems Theory

    NASA Astrophysics Data System (ADS)

    Chandra, Akhilesh

    This research draws upon a recent innovation in the dynamical systems literature called the theory of self -organized criticality (SOC) (Bak, Tang, and Wiesenfeld 1988) to develop a computational model of a firm's size by relating its internal and the external sub-systems. As a holistic paradigm, the theory of SOC implies that a firm as a composite system of many degrees of freedom naturally evolves to a critical state in which a minor event starts a chain reaction that can affect either a part or the system as a whole. Thus, the global features of a firm cannot be understood by analyzing its individual parts separately. The causal framework builds upon a constant capital resource to support a volume of production at the existing level of efficiency. The critical size is defined as the production level at which the average product of a firm's factors of production attains its maximum value. The non -linearity is inferred by a change in the nature of relations at the border of criticality, between size and the two performance variables, viz., the operating efficiency and the financial efficiency. The effect of breaching the critical size is examined on the stock price reactions. Consistent with the theory of SOC, it is hypothesized that the temporal response of a firm breaching the level of critical size should behave as a flicker noise (1/f) process. The flicker noise is characterized by correlations extended over a wide range of time scales, indicating some sort of cooperative effect among a firm's degrees of freedom. It is further hypothesized that a firm's size evolves to a spatial structure with scale-invariant, self-similar (fractal) properties. The system is said to be self-organized inasmuch as it naturally evolves to the state of criticality without any detailed specifications of the initial conditions. In this respect, the critical state is an attractor of the firm's dynamics. Another set of hypotheses examines the relations between the size and the

  7. Oxidation-driven surface dynamics on NiAl(100)

    PubMed Central

    Qin, Hailang; Chen, Xidong; Li, Liang; Sutter, Peter W.; Zhou, Guangwen

    2015-01-01

    Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). By comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps. PMID:25548155

  8. Oxidation-driven surface dynamics on NiAl(100)

    DOE PAGES

    Qin, Hailang; Chen, Xidong; Li, Liang; ...

    2014-12-29

    Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling upmore » of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). As a result, by comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps, we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.« less

  9. Oxidation-driven surface dynamics on NiAl(100)

    SciTech Connect

    Qin, Hailang; Chen, Xidong; Li, Liang; Sutter, Peter W.; Zhou, Guangwen

    2014-12-29

    Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). As a result, by comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps, we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.

  10. Oxidation-driven surface dynamics on NiAl(100)

    NASA Astrophysics Data System (ADS)

    Qin, Hailang; Chen, Xidong; Li, Liang; Sutter, Peter W.; Zhou, Guangwen

    2015-01-01

    Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). By comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.

  11. Molecular dynamics simulation of a binary mixture near the lower critical point.

    PubMed

    Pousaneh, Faezeh; Edholm, Olle; Maciołek, Anna

    2016-07-07

    2,6-lutidine molecules mix with water at high and low temperatures but in a wide intermediate temperature range a 2,6-lutidine/water mixture exhibits a miscibility gap. We constructed and validated an atomistic model for 2,6-lutidine and performed molecular dynamics simulations of 2,6-lutidine/water mixture at different temperatures. We determined the part of demixing curve with the lower critical point. The lower critical point extracted from our data is located close to the experimental one. The estimates for critical exponents obtained from our simulations are in a good agreement with the values corresponding to the 3D Ising universality class.

  12. [Determination of critical surface tension--a comparison of 2 methods].

    PubMed

    Lippold, B C; Ohm, A

    1988-03-01

    Two methods for the determination of the critical surface tension (gamma c) of pharmaceutical powders are compared: the so called "sinking-technique", which works by measuring the complete sinking of powders in liquids of varying surface tension and the determination of the critical surface tension by measuring the contact angle in dependence on the surface tension of wetting solvent/water-mixtures by means of the sessile drop-technique. The simple sinking-technique gives gamma c-values which only show a moderate degree of agreement with those determined by the sessile drop-technique. Thus the values determined by the sinking-technique are usually 1-3 mN/m higher than those determined by the sessile drop-technique.

  13. Molecular dynamics simulation of water at mineral surfaces: Structure, dynamics, energetics and hydrogen bonding

    NASA Astrophysics Data System (ADS)

    Kalinichev, A. G.; Wang, J.; Kirkpatrick, R.

    2006-05-01

    Fundamental molecular-level understanding of the properties of aqueous mineral interfaces is of great importance for many geochemical and environmental systems. Interaction between water and mineral surfaces substantially affects the properties of both phases, including the reactivity and functionality of the substrate surface, and the structure, dynamics, and energetics of the near surface aqueous phase. Experimental studies of interfacial water structure and dynamics using surface-sensitive techniques such as sum-frequency vibrational spectroscopy or X-ray and neutron reflectivity are not always possible for many practically important substrates, and their results often require interpretation concerning the atomistic mechanisms responsible for the observed behavior. Molecular computer simulations can provide new insight into the underlying molecular- level relationships between the inorganic substrate structure and composition and the structure, ordering, and dynamics of interfacial water. We have performed a series of molecular dynamics (MD) computer simulations of aqueous interfaces with several silicates (quartz, muscovite, and talc) and hydroxides (brucite, portlandite, gibbsite, Ca/Al and Mg/Al double hydroxides) to quantify the effects of the substrate mineral structure and composition on the structural, transport, and thermodynamic properties of water on these mineral surfaces. Due to the prevalent effects of the development of well-interconnected H-bonding networks across the mineral- water interfaces, all the hydroxide surfaces (including a fully hydroxylated quartz surface) show very similar H2O density profiles perpendicular to the interface. However, the predominant orientations of the interfacial H2O molecules and their detailed 2-dimensional near-surface structure and dynamics parallel to the interface are quite different reflecting the differences in the substrate structural charge distribution and the density and orientations of the surface OH

  14. First Principles Studies of Surface Vibrational Dynamics: Li(100)

    NASA Astrophysics Data System (ADS)

    Staikov, Pavlin; Kara, Abdelkader; Rahman, Talat. S.

    1996-03-01

    We present studies of the structure and the dynamics of Li(100) using ab initio, norm-conserving, non-local and soft pseudopotentials with partial core correction, and a plane wave basis. A preconditioned steepest descent method (N. Chetty, M. Weinert, T. S. Rahman, and J. W. Davenport, Phys. Rev. B 52) (1995) 6313. is used to solve iteratively Kohn-Sham equations for a given set of atomic positions. Forces and thereby force constants matrix for ion-cores at the surface and in the bulk are calculated using Hellman-Feynman theorem. We relate the large outward relaxation (K. Kokko, P. T. Salo, R. Laihia, and K. Mansikka, Phys. Rev. B 52) (1995) 7868. of the surface layer to the changes in the surface force constants. Vibrational dynamics at and near the surface are calculated. The polarizations and the frequencies of the surface modes are contrasted with the more usual case of inward top-layer relaxation. The local vibrational density of states are also evaluated and surface thermodynamical properties are explored.

  15. Decoupling of surface diffusion and relaxation dynamics of molecular glasses.

    PubMed

    Zhang, Yue; Fakhraai, Zahra

    2017-04-03

    Tobacco mosaic virus is used as a probe to measure surface diffusion of ultrathin films of N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) (12 nm [Formula: see text] 53 nm, where [Formula: see text] is the film thickness) at various temperatures below the glass transition temperature, [Formula: see text], of all films. As the film thickness is decreased, [Formula: see text] decreases rapidly and the average film dynamics are enhanced by 6-14 orders of magnitude. We show that the surface diffusion is invariant of the film thickness decrease and the resulting enhanced overall mobility. The values of the surface diffusion coefficient and its temperature dependence are invariant of film thickness and are the same as the corresponding bulk values ([Formula: see text]400 nm). For the thinnest films ([Formula: see text]20 nm), the effective activation energy for rearrangement (temperature dependence of relaxation times) becomes smaller than the activation energy for surface diffusion. These results suggest that the fast surface diffusion is decoupled from film relaxation dynamics and is a solely free surface property.

  16. Drop impact dynamics on liquid-infused superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Hyun; Rothstein, Jonathan

    2015-11-01

    In this talk, we present a series of experiments investigating the drop impact dynamics on hydrophobic, air-infused and lubricant-infused superhydrophobic surfaces. To create the superhydrophobic surfaces, smooth Teflon (PTFE) surfaces were roughened by a 240-grit sandpaper. The immiscible and incompressible silicone oils with different viscosities were infused into features of the superhydrophobic surfaces by a skim coating technique. The spreading and retraction dynamics on a series of the tested surfaces will be presented. We will show that the maximal deformation of the drops on lubricant-infused surfaces grows with increasing viscosity ratio between a water drop and the infused oil. We will show that this increase in the maximal deformation with the viscosity ratio is consistent with increasing the velocity and the viscosity of the drops but the rims of the drops destabilize with increasing the drop velocity. Finally, we will demonstrate that increasing the viscosity of the infused oil induces higher viscous force at the contact line, resulting in reduction in the movement of the drops during retraction and corresponding increase in the final drop size.

  17. Drop impact and rebound dynamics on an inclined superhydrophobic surface.

    PubMed

    Yeong, Yong Han; Burton, James; Loth, Eric; Bayer, Ilker S

    2014-10-14

    Due to its potential in water-repelling applications, the impact and rebound dynamics of a water drop impinging perpendicular to a horizontal superhydrophobic surface have undergone extensive study. However, drops tend to strike a surface at an angle in applications. In such cases, the physics governing the effects of oblique impact are not well studied or understood. Therefore, the objective of this study was to conduct an experiment to investigate the impact and rebound dynamics of a drop at various liquid viscosities, in an isothermal environment, and on a nanocomposite superhydrophobic surface at normal and oblique impact conditions (tilted at 15°, 30°, 45°, and 60°). This study considered drops falling from various heights to create normal impact Weber numbers ranging from 6 to 110. In addition, drop viscosity was varied by decreasing the temperature for water drops and by utilizing water-glycerol mixtures, which have similar surface tension to water but higher viscosities. Results revealed that oblique and normal drop impact behaved similarly (in terms of maximum drop spread as well as rebound dynamics) at low normal Weber numbers. However, at higher Weber numbers, normal and oblique impact results diverged in terms of maximum spread, which could be related to asymmetry and more complex outcomes. These asymmetry effects became more pronounced as the inclination angle increased, to the point where they dominated the drop impact and rebound characteristics when the surface was inclined at 60°. The drop rebound characteristics on inclined surfaces could be classified into eight different outcomes driven primarily by normal Weber number and drop Ohnesorge numbers. However, it was found that these outcomes were also a function of the receding contact angle, whereby reduced receding angles yielded tail-like structures. Nevertheless, the contact times of the drops with the coating were found to be generally independent of surface inclination.

  18. Molecular Dynamics of a Protein Surface: Ion-Residues Interactions

    PubMed Central

    Friedman, Ran; Nachliel, Esther; Gutman, Menachem

    2005-01-01

    Time-resolved measurements indicated that protons could propagate on the surface of a protein or a membrane by a special mechanism that enhanced the shuttle of the proton toward a specific site. It was proposed that a suitable location of residues on the surface contributes to the proton shuttling function. In this study, this notion was further investigated by the use of molecular dynamics simulations, where Na+ and Cl− are the ions under study, thus avoiding the necessity for quantum mechanical calculations. Molecular dynamics simulations were carried out using as a model a few Na+ and Cl− ions enclosed in a fully hydrated simulation box with a small globular protein (the S6 of the bacterial ribosome). Three independent 10-ns-long simulations indicated that the ions and the protein's surface were in equilibrium, with rapid passage of the ions between the protein's surface and the bulk. However, it was noted that close to some domains the ions extended their duration near the surface, thus suggesting that the local electrostatic potential hindered their diffusion to the bulk. During the time frame in which the ions were detained next to the surface, they could rapidly shuttle between various attractor sites located under the electrostatic umbrella. Statistical analysis of the molecular dynamics and electrostatic potential/entropy consideration indicated that the detainment state is an energetic compromise between attractive forces and entropy of dilution. The similarity between the motion of free ions next to a protein and the proton transfer on the protein's surface are discussed. PMID:15894639

  19. Investigating the dynamics of surface-immobilized DNA nanomachines

    PubMed Central

    Dunn, Katherine E.; Trefzer, Martin A.; Johnson, Steven; Tyrrell, Andy M.

    2016-01-01

    Surface-immobilization of molecules can have a profound influence on their structure, function and dynamics. Toehold-mediated strand displacement is often used in solution to drive synthetic nanomachines made from DNA, but the effects of surface-immobilization on the mechanism and kinetics of this reaction have not yet been fully elucidated. Here we show that the kinetics of strand displacement in surface-immobilized nanomachines are significantly different to those of the solution phase reaction, and we attribute this to the effects of intermolecular interactions within the DNA layer. We demonstrate that the dynamics of strand displacement can be manipulated by changing strand length, concentration and G/C content. By inserting mismatched bases it is also possible to tune the rates of the constituent displacement processes (toehold-binding and branch migration) independently, and information can be encoded in the time-dependence of the overall reaction. Our findings will facilitate the rational design of surface-immobilized dynamic DNA nanomachines, including computing devices and track-based motors. PMID:27387252

  20. Investigating the dynamics of surface-immobilized DNA nanomachines

    NASA Astrophysics Data System (ADS)

    Dunn, Katherine E.; Trefzer, Martin A.; Johnson, Steven; Tyrrell, Andy M.

    2016-07-01

    Surface-immobilization of molecules can have a profound influence on their structure, function and dynamics. Toehold-mediated strand displacement is often used in solution to drive synthetic nanomachines made from DNA, but the effects of surface-immobilization on the mechanism and kinetics of this reaction have not yet been fully elucidated. Here we show that the kinetics of strand displacement in surface-immobilized nanomachines are significantly different to those of the solution phase reaction, and we attribute this to the effects of intermolecular interactions within the DNA layer. We demonstrate that the dynamics of strand displacement can be manipulated by changing strand length, concentration and G/C content. By inserting mismatched bases it is also possible to tune the rates of the constituent displacement processes (toehold-binding and branch migration) independently, and information can be encoded in the time-dependence of the overall reaction. Our findings will facilitate the rational design of surface-immobilized dynamic DNA nanomachines, including computing devices and track-based motors.

  1. Fast and Slow Wetting Dynamics on nanostructured surfaces

    NASA Astrophysics Data System (ADS)

    Nandyala, Dhiraj; Rahmani, Amir; Cubaud, Thomas; Colosqui, Carlos

    2015-11-01

    This talk will present force-displacement and spontaneous drop spreading measurements on diverse nanostructured surfaces (e.g., mesoporous titania thin films, nanoscale pillared structures, on silica or glass substrates). Experimental measurements are performed for water-air and water-oil systems. The dynamics of wetting observed in these experiments can present remarkable crossovers from fast to slow or arrested dynamics. The emergence of a slow wetting regime is attributed to a multiplicity of metastable equilibrium states induced by nanoscale surface features. The crossover point can be dramatically advanced or delayed by adjusting specific physical parameters (e.g., viscosity of the wetting phases) and geometric properties of the surface nanostructure (e.g., nanopore/pillar radius and separation). Controlling the crossover point to arrested dynamics can effectively modify the degree of contact angle hysteresis and magnitude of liquid adhesion forces observed on surfaces of different materials. This work is supported by a SEED Award from The Office of Brookhaven National Laboratory Affairs at Stony Brook University.

  2. Efficient modelling of droplet dynamics on complex surfaces.

    PubMed

    Karapetsas, George; Chamakos, Nikolaos T; Papathanasiou, Athanasios G

    2016-03-02

    This work investigates the dynamics of droplet interaction with smooth or structured solid surfaces using a novel sharp-interface scheme which allows the efficient modelling of multiple dynamic contact lines. The liquid-gas and liquid-solid interfaces are treated in a unified context and the dynamic contact angle emerges simply due to the combined action of the disjoining and capillary pressure, and viscous stresses without the need of an explicit boundary condition or any requirement for the predefinition of the number and position of the contact lines. The latter, as it is shown, renders the model able to handle interfacial flows with topological changes, e.g. in the case of an impinging droplet on a structured surface. Then it is possible to predict, depending on the impact velocity, whether the droplet will fully or partially impregnate the structures of the solid, or will result in a 'fakir', i.e. suspended, state. In the case of a droplet sliding on an inclined substrate, we also demonstrate the built-in capability of our model to provide a prediction for either static or dynamic contact angle hysteresis. We focus our study on hydrophobic surfaces and examine the effect of the geometrical characteristics of the solid surface. It is shown that the presence of air inclusions trapped in the micro-structure of a hydrophobic substrate (Cassie-Baxter state) result in the decrease of contact angle hysteresis and in the increase of the droplet migration velocity in agreement with experimental observations for super-hydrophobic surfaces. Moreover, we perform 3D simulations which are in line with the 2D ones regarding the droplet mobility and also indicate that the contact angle hysteresis may be significantly affected by the directionality of the structures with respect to the droplet motion.

  3. Efficient modelling of droplet dynamics on complex surfaces

    NASA Astrophysics Data System (ADS)

    Karapetsas, George; Chamakos, Nikolaos T.; Papathanasiou, Athanasios G.

    2016-03-01

    This work investigates the dynamics of droplet interaction with smooth or structured solid surfaces using a novel sharp-interface scheme which allows the efficient modelling of multiple dynamic contact lines. The liquid-gas and liquid-solid interfaces are treated in a unified context and the dynamic contact angle emerges simply due to the combined action of the disjoining and capillary pressure, and viscous stresses without the need of an explicit boundary condition or any requirement for the predefinition of the number and position of the contact lines. The latter, as it is shown, renders the model able to handle interfacial flows with topological changes, e.g. in the case of an impinging droplet on a structured surface. Then it is possible to predict, depending on the impact velocity, whether the droplet will fully or partially impregnate the structures of the solid, or will result in a ‘fakir’, i.e. suspended, state. In the case of a droplet sliding on an inclined substrate, we also demonstrate the built-in capability of our model to provide a prediction for either static or dynamic contact angle hysteresis. We focus our study on hydrophobic surfaces and examine the effect of the geometrical characteristics of the solid surface. It is shown that the presence of air inclusions trapped in the micro-structure of a hydrophobic substrate (Cassie-Baxter state) result in the decrease of contact angle hysteresis and in the increase of the droplet migration velocity in agreement with experimental observations for super-hydrophobic surfaces. Moreover, we perform 3D simulations which are in line with the 2D ones regarding the droplet mobility and also indicate that the contact angle hysteresis may be significantly affected by the directionality of the structures with respect to the droplet motion.

  4. Dynamics of tungsten and cobalt carbonyls on silica surfaces

    NASA Astrophysics Data System (ADS)

    Muthukumar, Kaliappan; Valenti, Roser; Jeschke, Harald O.

    2013-03-01

    Metal carbonyl species adsorbed on a substrate are the starting point for the electron beam induced deposition of metallic nanostructures. We employ first principles molecular dynamics simulations to investigate the dynamics of tungsten hexa- and pentacarbonyl as well as cobalt octacarbonyl precursor molecules on fully and partially hydroxylated silica substrates. We find that physisorbed carbonyls are quite mobile on a silica surface saturated with hydroxy groups, moving around half an Angstrom per picosecond. In contrast, chemisorbed ions like [W(CO)5]- or [Co(CO)4]- are more stable at room temperature. We determine the vibrational spectra which can provide signatures for experimentally distinguishing the form in which precursors cover a substrate.

  5. Dynamic surface tension analysis of dodecyl sulfate association complexes.

    PubMed

    Quigley, W W; Nabi, A; Prazen, B J; Lenghor, N; Grudpan, K; Synovec, R E

    2001-09-13

    First, a novel calibration method is used to expand the current understanding of spherical drop growth and elongation that occurs during on-line measurements of surface pressure using the dynamic surface tension detector (DSTD). Using a novel surface tension calibration method, the drop radius is calculated as a function of time from experimental drop pressure data and compared to the theoretical drop radius calculated from volumetric flow rate. From this comparison, the drop volume at which the drop shape starts to deviate ( approximately 4 mul) from a spherical shape is readily observed and deviates more significantly by approximately 6 mul drop volume (5% deviation in the ideal spherical drop radius) for the capillary sensing tip employed in the DSTD. From this assessment of drop shape, an experimental method for precise drop detachment referred to as pneumatic drop detachment is employed at a drop volume of 2 mul (two second drops at 60 mul/min) in order to provide rapid dynamic surface tension measurements via the novel on-line calibration methodology. Second, the DSTD is used to observe and study kinetic information for surface-active molecules and association complexes adsorbing to an air-liquid drop interface. Dynamic surface tension measurements are made for sodium dodecyl sulfate (SDS) in the absence and presence of either tetra butyl ammonium (TBA) or chromium (III). Sensitive, indirect detection of chromium and other multiply charged metals at low concentrations is also investigated. The DSTD is utilized in examining the dynamic nature of SDS: cation association at the air-liquid interface of a growing drop. Either TBA or Cr(III) were found to substantially enhance the surface tension lowering of dodecyl sulfate (DS), but the surface tension lowering is accompanied by a considerable kinetic dependence. Essentially, the surface tension lowering of these DS: cation complexes is found to be a fairly slow process in the context of the two second DSTD

  6. Molecular-dynamics analysis of mobile helium cluster reactions near surfaces of plasma-exposed tungsten

    NASA Astrophysics Data System (ADS)

    Hu, Lin; Hammond, Karl D.; Wirth, Brian D.; Maroudas, Dimitrios

    2015-10-01

    We report the results of a systematic atomic-scale analysis of the reactions of small mobile helium clusters (Hen, 4 ≤ n ≤ 7) near low-Miller-index tungsten (W) surfaces, aiming at a fundamental understanding of the near-surface dynamics of helium-carrying species in plasma-exposed tungsten. These small mobile helium clusters are attracted to the surface and migrate to the surface by Fickian diffusion and drift due to the thermodynamic driving force for surface segregation. As the clusters migrate toward the surface, trap mutation (TM) and cluster dissociation reactions are activated at rates higher than in the bulk. TM produces W adatoms and immobile complexes of helium clusters surrounding W vacancies located within the lattice planes at a short distance from the surface. These reactions are identified and characterized in detail based on the analysis of a large number of molecular-dynamics trajectories for each such mobile cluster near W(100), W(110), and W(111) surfaces. TM is found to be the dominant cluster reaction for all cluster and surface combinations, except for the He4 and He5 clusters near W(100) where cluster partial dissociation following TM dominates. We find that there exists a critical cluster size, n = 4 near W(100) and W(111) and n = 5 near W(110), beyond which the formation of multiple W adatoms and vacancies in the TM reactions is observed. The identified cluster reactions are responsible for important structural, morphological, and compositional features in the plasma-exposed tungsten, including surface adatom populations, near-surface immobile helium-vacancy complexes, and retained helium content, which are expected to influence the amount of hydrogen re-cycling and tritium retention in fusion tokamaks.

  7. Molecular-dynamics analysis of mobile helium cluster reactions near surfaces of plasma-exposed tungsten

    SciTech Connect

    Hu, Lin; Maroudas, Dimitrios; Hammond, Karl D.; Wirth, Brian D.

    2015-10-28

    We report the results of a systematic atomic-scale analysis of the reactions of small mobile helium clusters (He{sub n}, 4 ≤ n ≤ 7) near low-Miller-index tungsten (W) surfaces, aiming at a fundamental understanding of the near-surface dynamics of helium-carrying species in plasma-exposed tungsten. These small mobile helium clusters are attracted to the surface and migrate to the surface by Fickian diffusion and drift due to the thermodynamic driving force for surface segregation. As the clusters migrate toward the surface, trap mutation (TM) and cluster dissociation reactions are activated at rates higher than in the bulk. TM produces W adatoms and immobile complexes of helium clusters surrounding W vacancies located within the lattice planes at a short distance from the surface. These reactions are identified and characterized in detail based on the analysis of a large number of molecular-dynamics trajectories for each such mobile cluster near W(100), W(110), and W(111) surfaces. TM is found to be the dominant cluster reaction for all cluster and surface combinations, except for the He{sub 4} and He{sub 5} clusters near W(100) where cluster partial dissociation following TM dominates. We find that there exists a critical cluster size, n = 4 near W(100) and W(111) and n = 5 near W(110), beyond which the formation of multiple W adatoms and vacancies in the TM reactions is observed. The identified cluster reactions are responsible for important structural, morphological, and compositional features in the plasma-exposed tungsten, including surface adatom populations, near-surface immobile helium-vacancy complexes, and retained helium content, which are expected to influence the amount of hydrogen re-cycling and tritium retention in fusion tokamaks.

  8. Constraining quantum critical dynamics: (2+1)D Ising model and beyond.

    PubMed

    Witczak-Krempa, William

    2015-05-01

    Quantum critical (QC) phase transitions generally lead to the absence of quasiparticles. The resulting correlated quantum fluid, when thermally excited, displays rich universal dynamics. We establish nonperturbative constraints on the linear-response dynamics of conformal QC systems at finite temperature, in spatial dimensions above 1. Specifically, we analyze the large frequency or momentum asymptotics of observables, which we use to derive powerful sum rules and inequalities. The general results are applied to the O(N) Wilson-Fisher fixed point, describing the QC Ising model when N=1. We focus on the order parameter and scalar susceptibilities, and the dynamical shear viscosity. Connections to simulations, experiments, and gauge theories are made.

  9. Molecular dynamics study of screening at ionic surfaces

    NASA Astrophysics Data System (ADS)

    Desai, T. G.

    2007-10-01

    Molecular dynamics simulations of NaCl fluid are used to understand the behavior of ionic fluid to screen the field generated by charges on the ionic crystal surfaces in absence of any external electric field. The NaCl fluid in the strongly coupled regime (corresponding to the melt) in contact with the charged octopolar (111) NaCl surface shows that the spatial correlations decay in an oscillatory manner, with a screening length λQ given by the envelope of the damped oscillations. By contrast to the Debye-Huckel theory, in the strongly coupled regime, λQ increases with increasing coupling strength (also seen in bulk ionic simulations). The NaCl fluid confined between neutral (100) NaCl surfaces also shows weak oscillatory charge decay near the surface. Similar oscillatory exponential decay was seen when the NaCl fluid was confined between two analytically smooth neutral walls. The origin of these oscillations was due to the difference in ion sizes. NaCl fluid confined between neutral octopolar (110) and dipolar (110) surface show stronger density oscillations than (100) surface but comparatively very weak charge oscillations. This paper shows that the strength of the charges on the crystal surfaces is enough to induce a characteristic spatial distribution of charges in the contacting fluid and the extent of distribution depends on the type of surface.

  10. Molecular Dynamics Study of Screening at Ionic Surfaces

    SciTech Connect

    T.G. Desai

    2007-10-01

    Molecular-dynamics simulations of NaCl fluid are used to understand the behavior of ionic fluid to screen the field generated by charges on the ionic crystal surfaces in absence of any external electric field. The NaCl fluid in the strongly-coupled regime (corresponding to the melt) in contact with the charged octopolar (111) NaCl surface shows that the spatial correlations decay in an oscillatory manner, with a screening length, ?Q, given by the envelope of the damped oscillations. By contrast to the Debye-Huckel theory, in the strongly-coupled regime, ?Q increases with increasing coupling strength (also seen in bulk ionic simulations). The NaCl fluid confined between neutral (100) NaCl surfaces also shows weak oscillatory charge decay near the surface. Similar oscillatory exponential decay was seen when the NaCl fluid was confined between two analytically smooth neutral walls. The origin of these oscillations was due to the difference in ion sizes. NaCl fluid confined between neutral octopolar (110) and dipolar (110) surface show stronger density oscillations than (100) surface but omparatively very weak charge oscillations. This paper shows that the strength of the charges on the crystal surfaces is enough to induce a characteristic spatial distribution of charges in the contacting fluid and the extent of distribution depends on the type of surface.

  11. The global distribution and dynamics of surface soil moisture

    NASA Astrophysics Data System (ADS)

    McColl, Kaighin A.; Alemohammad, Seyed Hamed; Akbar, Ruzbeh; Konings, Alexandra G.; Yueh, Simon; Entekhabi, Dara

    2017-01-01

    Surface soil moisture has a direct impact on food security, human health and ecosystem function. It also plays a key role in the climate system, and the development and persistence of extreme weather events such as droughts, floods and heatwaves. However, sparse and uneven observations have made it difficult to quantify the global distribution and dynamics of surface soil moisture. Here we introduce a metric of soil moisture memory and use a full year of global observations from NASA's Soil Moisture Active Passive mission to show that surface soil moisture--a storage believed to make up less than 0.001% of the global freshwater budget by volume, and equivalent to an, on average, 8-mm thin layer of water covering all land surfaces--plays a significant role in the water cycle. Specifically, we find that surface soil moisture retains a median 14% of precipitation falling on land after three days. Furthermore, the retained fraction of the surface soil moisture storage after three days is highest over arid regions, and in regions where drainage to groundwater storage is lowest. We conclude that lower groundwater storage in these regions is due not only to lower precipitation, but also to the complex partitioning of the water cycle by the surface soil moisture storage layer at the land surface.

  12. Dynamics of ice nucleation on water repellent surfaces.

    PubMed

    Alizadeh, Azar; Yamada, Masako; Li, Ri; Shang, Wen; Otta, Shourya; Zhong, Sheng; Ge, Liehui; Dhinojwala, Ali; Conway, Ken R; Bahadur, Vaibhav; Vinciquerra, A Joseph; Stephens, Brian; Blohm, Margaret L

    2012-02-14

    Prevention of ice accretion and adhesion on surfaces is relevant to many applications, leading to improved operation safety, increased energy efficiency, and cost reduction. Development of passive nonicing coatings is highly desirable, since current antiicing strategies are energy and cost intensive. Superhydrophobicity has been proposed as a lead passive nonicing strategy, yet the exact mechanism of delayed icing on these surfaces is not clearly understood. In this work, we present an in-depth analysis of ice formation dynamics upon water droplet impact on surfaces with different wettabilities. We experimentally demonstrate that ice nucleation under low-humidity conditions can be delayed through control of surface chemistry and texture. Combining infrared (IR) thermometry and high-speed photography, we observe that the reduction of water-surface contact area on superhydrophobic surfaces plays a dual role in delaying nucleation: first by reducing heat transfer and second by reducing the probability of heterogeneous nucleation at the water-substrate interface. This work also includes an analysis (based on classical nucleation theory) to estimate various homogeneous and heterogeneous nucleation rates in icing situations. The key finding is that ice nucleation delay on superhydrophobic surfaces is more prominent at moderate degrees of supercooling, while closer to the homogeneous nucleation temperature, bulk and air-water interface nucleation effects become equally important. The study presented here offers a comprehensive perspective on the efficacy of textured surfaces for nonicing applications.

  13. Bouncing dynamics of impact droplets on the convex superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Shen, Yizhou; Liu, Senyun; Zhu, Chunling; Tao, Jie; Chen, Zhong; Tao, Haijun; Pan, Lei; Wang, Guanyu; Wang, Tao

    2017-05-01

    Bouncing dynamics of impact droplets on solid surfaces intensively appeal to researchers due to the importance in many industrial fields. Here, we found that droplets impacting onto dome convex superhydrophobic surfaces could rapidly bounce off with a 28.5% reduction in the contact time, compared with that on flat superhydrophobic surfaces. This is mainly determined by the retracting process of impact droplets. Under the action of dome convexity, the impact droplet gradually evolves into an annulus shape with a special hydrodynamic distribution. As a consequence, both the inner and external rims of the annulus shape droplet possess a higher retracting velocity under the actions of the inertia force and the surface energy change, respectively. Also, the numerical simulation provides a quantitative evidence to further verify the interpretation on the regimes behind the rapidly detached phenomenon of impact droplets.

  14. Molecular Dynamic Simulations on Surface Tension of Methanol

    NASA Astrophysics Data System (ADS)

    Obeidat, Abdalla

    2015-04-01

    Molecular dynamic simulations have been performed to study the surface tension of methanol at low temperatures. Six different models of methanol have been studied to compute the surface tension of different models. The models have been used to predict the surface tensions are: OPLS, Gromos 96, H1, J1, J2, and van Leeuwen model. Our results show that the most accurate model compared to true methanol was van Leeuwen model. The results were fitted to a straight line to predict other data of surface tension at specific temperature. The simulation were performed using the Gromacs package at temperatures: 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, and 300 K. This work is supported by JUST.

  15. Influence of chemistry on wetting dynamics of nanotextured hydrophobic surfaces.

    PubMed

    Di Mundo, Rosa; Palumbo, Fabio; d'Agostino, Riccardo

    2010-04-06

    In this work, the role of a chemical parameter, such as the degree of fluorination, on the wetting behavior of nanotextured hydrophobic surfaces is investigated. Texture and chemistry tuning of the surfaces has been accomplished with single batch radiofrequency low-pressure plasma processes. Polystyrene substrates have been textured by CF(4) plasma etching and subsequently covered by thin films with a tunable F-to-C ratio, obtained in discharges fed with C(4)F(8)-C(2)H(4). Measurements of wetting dynamics reveal a regime transition from adhesive-hydrophobic to slippery-superhydrophobic, i.e., from wet to non wet states, as the F-to-C rises at constant topography. Such achievements are strengthened by calculation of the solid fraction of surface water contact area applying Cassie-Baxter advancing and receding equations to water contact angle data of textured and flat reference surfaces.

  16. Persistence and elimination of human norovirus in food and on food contact surfaces: a critical review

    USDA-ARS?s Scientific Manuscript database

    This critical review addresses the persistence of human norovirus (NoV) in water, shellfish, processed meats, soils and organic wastes; on berries, herbs, vegetables, fruits and salads; and on food contact surfaces. The review focuses on studies using NoV; information from studies involving only su...

  17. Controlling and prevention of surface wrinkling via size-dependent critical wrinkling strain.

    PubMed

    Han, Xue; Zhao, Yan; Cao, Yanping; Lu, Conghua

    2015-06-14

    Surface wrinkling may occur in a film-substrate system when the applied strain exceeds the critical value. However, the practically required strain for the onset of surface wrinkling can be different from the theoretically predicted value. Here we investigate the film size effect-dependent critical strain for the mechanical strain-induced surface wrinkling via a combination of experiments and theoretical analysis. In the poly(dimethylsiloxane)-based system fabricated by the smart combination of mechanical straining and selective O2 plasma (OP) exposure through Cu grids, the film size effect on the critical wrinkling strain is systematically studied by considering OP exposure duration, the mesh number and geometry of Cu grids. Meanwhile, a simple analytical solution revealing the film size effect is well established, which shows good consistency with the experimental results. This study provides an experimental and theoretical basis for finely tuning the critical wrinkling strain in a simple and quantitative manner, which can find a wide range of applications in such fields as microelectronic circuits and optical devices, where controlling and/or prevention of surface wrinkling are of great importance.

  18. Beneath the Surface: Teacher Subjectivities and the Appropriation of Critical Pedagogies

    ERIC Educational Resources Information Center

    Niesz, Tricia

    2006-01-01

    Little has been written about the complexity of educators' appropriation of critical pedagogies in the context of everyday life in schools. In this article, based on analyses of two teachers' practice drawn from a larger ethnographic study of an urban public middle school, I explore the emergence of classroom practice that on the surface seemed to…

  19. Euler Strut: A Mechanical Analogy for Dynamics in the Vicinity of a Critical Point

    ERIC Educational Resources Information Center

    Bobnar, Jaka; Susman, Katarina; Parsegian, V. Adrian; Rand, Peter R.; Cepic, Mojca; Podgornik, Rudolf

    2011-01-01

    An anchored elastic filament (Euler strut) under an external point load applied to its free end is a simple model for a second-order phase transition. In the static case, a load greater than the critical load causes a Euler buckling instability, leading to a change in the filament's shape. The analysis of filament dynamics with an external point…

  20. Euler Strut: A Mechanical Analogy for Dynamics in the Vicinity of a Critical Point

    ERIC Educational Resources Information Center

    Bobnar, Jaka; Susman, Katarina; Parsegian, V. Adrian; Rand, Peter R.; Cepic, Mojca; Podgornik, Rudolf

    2011-01-01

    An anchored elastic filament (Euler strut) under an external point load applied to its free end is a simple model for a second-order phase transition. In the static case, a load greater than the critical load causes a Euler buckling instability, leading to a change in the filament's shape. The analysis of filament dynamics with an external point…

  1. Dynamic Imaging of Surface Motion with a Stereo Borescope

    SciTech Connect

    Michael Berninger, Stuart Baker

    2008-12-11

    A new stereo borescope has been investigated that would provide a time-resolved calibrated method of recording the motion and deformation of a three-dimensional (3-D) surface during explosively driven dynamic shock experiments at the Nevada Test Site. In these experiments, geometries would likely prove to be incompatible with conventional direct optical systems. Single line-of-sight borescopes lack adequate depth-of-field for quantitative imaging of the 3-D surface. To improve depth-of-field and provide time resolution, a stereo borescope has been fabricated for use with a nine-frame framing camera. At one end, stereo optics couple light from the dynamic surface into a pair of flexible 1-mm-diameter correlated fiber-optic bundles. At the other end, small-format lenses (~3 mm) interface with the framing camera, which is set up to simultaneously record the separate-perspective views. All nine frames could be recorded in a period as short as 1.8 μs, and spatial resolution is optimized to 11 line-pairs per mm. To achieve pseudo 3-D depth perception, photogrammetric analysis has been demonstrated with commercial software from ADAM technology (Australia). This paper presents the results from time-resolved stereo images of dynamic surfaces collected in a series of high-explosives experiments at the National Security Technologies, LLC, “Boom Box” in Santa Barbara, CA. Experience with the stereo borescope has suggested other potentially useful stereoscopic applications, such as stereo viewing of moving surfaces on the interiors of engines and the heating of moving components, and the viewing material deposition on interior surfaces during machine operations and fabrication processes.

  2. Comparative surface dynamics of amorphous and semicrystalline polymer films

    PubMed Central

    Becker, James S.; Brown, Ryan D.; Killelea, Daniel R.; Yuan, Hanqiu; Sibener, S. J.

    2011-01-01

    The surface dynamics of amorphous and semicrystalline polymer films have been measured using helium atom scattering. Time-of-flight data were collected to resolve the elastic and inelastic scattering components in the diffuse scattering of neutral helium atoms from the surface of a thin poly(ethylene terephthalate) film. Debye–Waller attenuation was observed for both the amorphous and semicrystalline phases of the polymer by recording the decay of elastically scattered helium atoms with increasing surface temperature. Thermal attenuation measurements in the specular scattering geometry yielded perpendicular mean-square displacements of 2.7•10-4 Å2 K-1 and 3.1•10-4 Å2 K-1 for the amorphous and semicrystalline surfaces, respectively. The semicrystalline surface was consistently ∼15% softer than the amorphous across a variety of perpendicular momentum transfers. The Debye–Waller factors were also measured at off-specular angles to characterize the parallel mean-square displacements, which were found to increase by an order of magnitude over the perpendicular mean-square displacements for both surfaces. In contrast to the perpendicular motion, the semicrystalline state was ∼25% stiffer than the amorphous phase in the surface plane. These results were uniquely accessed through low-energy neutral helium atom scattering due to the highly surface-sensitive and nonperturbative nature of these interactions. The goal of tailoring the chemical and physical properties of complex advanced materials requires an improved understanding of interfacial dynamics, information that is obtainable through atomic beam scattering methods. PMID:20713734

  3. Sub-surface imaging of carbon nanotube-polymer composites using dynamic AFM methods.

    PubMed

    Cadena, Maria J; Misiego, Rocio; Smith, Kyle C; Avila, Alba; Pipes, Byron; Reifenberger, Ron; Raman, Arvind

    2013-04-05

    High-resolution sub-surface imaging of carbon nanotube (CNT) networks within polymer nanocomposites is demonstrated through electrical characterization techniques based on dynamic atomic force microscopy (AFM). We compare three techniques implemented in the single-pass configuration: DC-biased amplitude modulated AFM (AM-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) in terms of the physics of sub-surface image formation and experimental robustness. The methods were applied to study the dispersion of sub-surface networks of single-walled nanotubes (SWNTs) in a polyimide (PI) matrix. We conclude that among these methods, the KPFM channel, which measures the capacitance gradient (∂C/∂d) at the second harmonic of electrical excitation, is the best channel to obtain high-contrast images of the CNT network embedded in the polymer matrix, without the influence of surface conditions. Additionally, we propose an analysis of the ∂C/∂d images as a tool to characterize the dispersion and connectivity of the CNTs. Through the analysis we demonstrate that these AFM-based sub-surface methods probe sufficiently deep within the SWNT composites, to resolve clustered networks that likely play a role in conductivity percolation. This opens up the possibility of dynamic AFM-based characterization of sub-surface dispersion and connectivity in nanostructured composites, two critical parameters for nanocomposite applications in sensors and energy storage devices.

  4. Modeling apple surface temperature dynamics based on weather data.

    PubMed

    Li, Lei; Peters, Troy; Zhang, Qin; Zhang, Jingjin; Huang, Danfeng

    2014-10-27

    The exposure of fruit surfaces to direct sunlight during the summer months can result in sunburn damage. Losses due to sunburn damage are a major economic problem when marketing fresh apples. The objective of this study was to develop and validate a model for simulating fruit surface temperature (FST) dynamics based on energy balance and measured weather data. A series of weather data (air temperature, humidity, solar radiation, and wind speed) was recorded for seven hours between 11:00-18:00 for two months at fifteen minute intervals. To validate the model, the FSTs of "Fuji" apples were monitored using an infrared camera in a natural orchard environment. The FST dynamics were measured using a series of thermal images. For the apples that were completely exposed to the sun, the RMSE of the model for estimating FST was less than 2.0 °C. A sensitivity analysis of the emissivity of the apple surface and the conductance of the fruit surface to water vapour showed that accurate estimations of the apple surface emissivity were important for the model. The validation results showed that the model was capable of accurately describing the thermal performances of apples under different solar radiation intensities. Thus, this model could be used to more accurately estimate the FST relative to estimates that only consider the air temperature. In addition, this model provides useful information for sunburn protection management.

  5. Adsorption dynamics of molecular nitrogen at an Fe(111) surface.

    PubMed

    Nosir, M A; Martin-Gondre, L; Bocan, G A; Díez Muiño, R

    2017-03-08

    We present an extensive theoretical study of N2 adsorption mechanisms on an Fe(111) surface. We combine the static analysis of a six-dimensional potential energy surface (6D-PES), based on ab initio density functional theory (DFT) calculations for the system, with quasi-classical trajectory (QCT) calculations to simulate the adsorption dynamics. There are four molecular adsorption states, usually called γ, δ, α, and ε, arising from our DFT calculations. We find that N2 adsorption in the γ-state is non-activated, while the threshold energy is associated with the entrance channel for the other three adsorption states. Our QCT calculations confirm that there are activated and nonactivated paths for the adsorption of N2 on the Fe(111) surface, which is in agreement with previous experimental investigations. Molecular dynamics at a surface temperature Ts = 300 K and impact energies Ei in the 0-5 eV range show the relative occupancy of the γ, δ, α, and ε states. The δ-state, however, is only marginally populated despite its adsorption energy being very similar to that of the γ-state. Our QCT calculations trace the dependence of molecular trapping on the surface temperature Ts and initial impact energy Ei and quantify the rates of the different competitive channels that eventually lead to molecular adsorption.

  6. Dissociative adsorption dynamics of nitrogen on a Fe(111) surface.

    PubMed

    Nosir, M A; Martin-Gondre, L; Bocan, G A; Díez Muiño, R

    2017-09-20

    We study the dissociative adsorption dynamics of N2 on clean bcc Fe(111) surfaces. We base our theoretical analysis on a multidimensional potential energy surface built from density functional theory. The dissociative sticking probability is computed by means of quasi-classical trajectory calculations. For normal incidence and impact energies of the order of a few eV, our theoretical results agree well with existing experimental values. For these energies, the dynamics of the dissociated molecules shows that dissociation is a direct process that follows narrow paths in the multidimensional space. For lower energies of the beam, this direct process is not enough to explain the measured values. A better agreement with the experiment is obtained if we increase the surface temperature to promote the transfer to dissociation of molecules previously trapped. Most of the molecules dissociate very close to the Fe(111) third layer atoms and with an orientation parallel to the surface. A comparison between the dissociation of N2 on Fe(111) and Fe(110) highlights the role of the different energy barriers in both surfaces.

  7. Modeling Apple Surface Temperature Dynamics Based on Weather Data

    PubMed Central

    Li, Lei; Peters, Troy; Zhang, Qin; Zhang, Jingjin; Huang, Danfeng

    2014-01-01

    The exposure of fruit surfaces to direct sunlight during the summer months can result in sunburn damage. Losses due to sunburn damage are a major economic problem when marketing fresh apples. The objective of this study was to develop and validate a model for simulating fruit surface temperature (FST) dynamics based on energy balance and measured weather data. A series of weather data (air temperature, humidity, solar radiation, and wind speed) was recorded for seven hours between 11:00–18:00 for two months at fifteen minute intervals. To validate the model, the FSTs of “Fuji” apples were monitored using an infrared camera in a natural orchard environment. The FST dynamics were measured using a series of thermal images. For the apples that were completely exposed to the sun, the RMSE of the model for estimating FST was less than 2.0 °C. A sensitivity analysis of the emissivity of the apple surface and the conductance of the fruit surface to water vapour showed that accurate estimations of the apple surface emissivity were important for the model. The validation results showed that the model was capable of accurately describing the thermal performances of apples under different solar radiation intensities. Thus, this model could be used to more accurately estimate the FST relative to estimates that only consider the air temperature. In addition, this model provides useful information for sunburn protection management. PMID:25350507

  8. Fractal and Small-World Networks Formed by Self-Organized Critical Dynamics

    NASA Astrophysics Data System (ADS)

    Watanabe, Akitomo; Mizutaka, Shogo; Yakubo, Kousuke

    2015-11-01

    We propose a dynamical model in which a network structure evolves in a self-organized critical (SOC) manner and explain a possible origin of the emergence of fractal and small-world networks. Our model combines a network growth and its decay by failures of nodes. The decay mechanism reflects the instability of large functional networks against cascading overload failures. It is demonstrated that the dynamical system surely exhibits SOC characteristics, such as power-law forms of the avalanche size distribution, the cluster size distribution, and the distribution of the time interval between intermittent avalanches. During the network evolution, fractal networks are spontaneously generated when networks experience critical cascades of failures that lead to a percolation transition. In contrast, networks far from criticality have small-world structures. We also observe the crossover behavior from fractal to small-world structure in the network evolution.

  9. Spinodals and critical point using short-time dynamics for a simple model of liquid.

    PubMed

    Loscar, Ernesto S; Ferrara, C Gastón; Grigera, Tomás S

    2016-04-07

    We have applied the short-time dynamics method to the gas-liquid transition to detect the supercooled gas instability (gas spinodal) and the superheated liquid instability (liquid spinodal). Using Monte Carlo simulation, we have obtained the two spinodals for a wide range of pressure in sub-critical and critical conditions and estimated the critical temperature and pressure. Our method is faster than previous approaches and allows studying spinodals without needing equilibration of the system in the metastable region. It is thus free of the extrapolation problems present in other methods, and in principle could be applied to systems such as glass-forming liquids, where equilibration is very difficult even far from the spinodal. We have also done molecular dynamics simulations, where we find the method again able to detect the both spinodals. Our results are compared with different previous results in the literature and show a good agreement.

  10. Helium atom surface scattering apparatus for studies of crystalline surface dynamics

    NASA Astrophysics Data System (ADS)

    Safron, S. A.; Skofronick, J. G.

    The primary goal of this grant was the construction of a state-of-the-art He atom-surface spectroscopy (HASS) scattering instrument capable of determining both structure and dynamics of metal, insulator and semiconductor surfaces. The method measures the elastic and inelastic scattering of He atoms from the crystal surface as a function of angle and energy gains or losses. The project was begun on May 1, 1985, and this report covers the progress from inception to present. The nozzle beam has been characterized, both before and after scattering from a LiF crystal surface, and angular distributions from this surface have also been taken. In addition to the specular and Bragg peaks, fine structure between the peaks is shown to be due to various inelastic collision processes reported previously. Current efforts are to measure the inelastic processes by time-of-flight methods so as to repeat the previous surface dispersion measurements.

  11. Differential renormalization-group generators for static and dynamic critical phenomena

    NASA Astrophysics Data System (ADS)

    Chang, T. S.; Vvedensky, D. D.; Nicoll, J. F.

    1992-09-01

    The derivation of differential renormalization-group (DRG) equations for applications to static and dynamic critical phenomena is reviewed. The DRG approach provides a self-contained closed-form representation of the Wilson renormalization group (RG) and should be viewed as complementary to the Callan-Symanzik equations used in field-theoretic approaches to the RG. The various forms of DRG equations are derived to illustrate the general mathematical structure of each approach and to point out the advantages and disadvantages for performing practical calculations. Otherwise, the review focuses upon the one-particle-irreducible DRG equations derived by Nicoll and Chang and by Chang, Nicoll, and Young; no attempt is made to provide a general treatise of critical phenomena. A few specific examples are included to illustrate the utility of the DRG approach: the large- n limit of the classical n-vector model (the spherical model), multi- or higher-order critical phenomena, and crit ical dynamics far from equilibrium. The large- n limit of the n-vector model is used to introduce the application of DRG equations to a well-known example, with exact solution obtained for the nonlinear trajectories, generating functions for nonlinear scaling fields, and the equation of state. Trajectory integrals and nonlinear scaling fields within the framework of ɛ-expansions are then discussed for tricritical crossover, and briefly for certain aspects of multi- or higher-order critical points, including the derivation of the Helmholtz free energy and the equation of state. The discussion then turns to critical dynamics with a development of the path integral formulation for general dynamic processes. This is followed by an application to a model far-from-equilibrium system that undergoes a phase transformation analogous to a second-order critical point, the Schlögl model for a chemical instability.

  12. Optimal system size for complex dynamics in random neural networks near criticality

    SciTech Connect

    Wainrib, Gilles; García del Molino, Luis Carlos

    2013-12-15

    In this article, we consider a model of dynamical agents coupled through a random connectivity matrix, as introduced by Sompolinsky et al. [Phys. Rev. Lett. 61(3), 259–262 (1988)] in the context of random neural networks. When system size is infinite, it is known that increasing the disorder parameter induces a phase transition leading to chaotic dynamics. We observe and investigate here a novel phenomenon in the sub-critical regime for finite size systems: the probability of observing complex dynamics is maximal for an intermediate system size when the disorder is close enough to criticality. We give a more general explanation of this type of system size resonance in the framework of extreme values theory for eigenvalues of random matrices.

  13. Optimal system size for complex dynamics in random neural networks near criticality

    SciTech Connect

    Wainrib, Gilles; García del Molino, Luis Carlos

    2013-12-15

    In this article, we consider a model of dynamical agents coupled through a random connectivity matrix, as introduced by Sompolinsky et al. [Phys. Rev. Lett. 61(3), 259–262 (1988)] in the context of random neural networks. When system size is infinite, it is known that increasing the disorder parameter induces a phase transition leading to chaotic dynamics. We observe and investigate here a novel phenomenon in the sub-critical regime for finite size systems: the probability of observing complex dynamics is maximal for an intermediate system size when the disorder is close enough to criticality. We give a more general explanation of this type of system size resonance in the framework of extreme values theory for eigenvalues of random matrices.

  14. Surface hopping investigation of the relaxation dynamics in radical cations

    NASA Astrophysics Data System (ADS)

    Assmann, Mariana; Weinacht, Thomas; Matsika, Spiridoula

    2016-01-01

    Ionization processes can lead to the formation of radical cations with population in several ionic states. In this study, we examine the dynamics of three radical cations starting from an excited ionic state using trajectory surface hopping dynamics in combination with multiconfigurational electronic structure methods. The efficiency of relaxation to the ground state is examined in an effort to understand better whether fragmentation of cations is likely to occur directly on excited states or after relaxation to the ground state. The results on cyclohexadiene, hexatriene, and uracil indicate that relaxation to the ground ionic state is very fast in these systems, while fragmentation before relaxation is rare. Ultrafast relaxation is facilitated by the close proximity of electronic states and the presence of two- and three-state conical intersections. Examining the properties of the systems in the Franck-Condon region can give some insight into the subsequent dynamics.

  15. Surface hopping investigation of the relaxation dynamics in radical cations

    SciTech Connect

    Assmann, Mariana; Matsika, Spiridoula; Weinacht, Thomas

    2016-01-21

    Ionization processes can lead to the formation of radical cations with population in several ionic states. In this study, we examine the dynamics of three radical cations starting from an excited ionic state using trajectory surface hopping dynamics in combination with multiconfigurational electronic structure methods. The efficiency of relaxation to the ground state is examined in an effort to understand better whether fragmentation of cations is likely to occur directly on excited states or after relaxation to the ground state. The results on cyclohexadiene, hexatriene, and uracil indicate that relaxation to the ground ionic state is very fast in these systems, while fragmentation before relaxation is rare. Ultrafast relaxation is facilitated by the close proximity of electronic states and the presence of two- and three-state conical intersections. Examining the properties of the systems in the Franck-Condon region can give some insight into the subsequent dynamics.

  16. Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements

    DTIC Science & Technology

    2013-09-30

    Radiometric Measurements Dick K.P. Yue Center for Ocean Engineering Massachusetts Institute of Technology Room 5-321 77 Massachusetts Ave...comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 30 SEP 2013 2. REPORT TYPE 3. DATES ...COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements 5a

  17. Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurement

    DTIC Science & Technology

    2013-09-30

    Radiometric Measurement Lian Shen Department of Mechanical Engineering & St. Anthony Falls Laboratory University of Minnesota Minneapolis, MN...information if it does not display a currently valid OMB control number. 1. REPORT DATE 30 SEP 2013 2. REPORT TYPE 3. DATES COVERED 00-00-2013 to 00-00...2013 4. TITLE AND SUBTITLE Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurement 5a. CONTRACT NUMBER 5b. GRANT NUMBER

  18. Sodium diffusion through amorphous silica surfaces: a molecular dynamics study.

    PubMed

    Rarivomanantsoa, Michaël; Jund, Philippe; Jullien, Rémi

    2004-03-08

    We have studied the diffusion inside the silica network of sodium atoms initially located outside the surfaces of an amorphous silica film. We have focused our attention on structural and dynamical quantities, and we have found that the local environment of the sodium atoms is close to the local environment of the sodium atoms inside bulk sodo-silicate glasses obtained by quench. This is in agreement with recent experimental results.

  19. Dynamic optometer. [for electronic recording of human lens anterior surface

    NASA Technical Reports Server (NTRS)

    Wilson, D. C.

    1974-01-01

    A dynamic optometer that electronically records the position of the anterior surface of the human lens is described. The geometrical optics of the eye and optometer, and the scattering of light from the lens, are closely examined to determine the optimum conditions for adjustment of the instrument. The light detector and associated electronics are also considered, and the operating conditions for obtaining the best signal-to-noise ratio are determined.

  20. Study of SRM Critical Surfaces Using Near Infrared Optical Fiber Spectrometry

    NASA Technical Reports Server (NTRS)

    Workman, G. L.; Hughes, C.; Arendale, W. A.

    1997-01-01

    The measurement and control of cleanliness for critical surfaces during manufacturing and in service operations provides a unique challenge in the current thrust for environmentally benign processes. Of particular interest has been work performed in maintaining quality in the production of bondline surfaces in propulsion systems and the identification of possible contaminants which are detrimental to the integrity of the bondline. This work requires an in-depth study of the possible sources of contamination, methodologies to identify contaminants, discrimination between contaminants and chemical species caused by environment, and the effect of particular contaminants on the bondline integrity of the critical surfaces. This paper will provide an introduction to the use of Near Infrared (NIR) optical fiber spectrometry in a nondestructive measurement system for process monitoring and how it can be used to help clarify issues concerning surface chemistry. In a previous conference, experimental results for quantitative measurement of silicone and Conoco HD2 greases, and tape residues on solid rocket motor surfaces were presented. This paper will present data for metal hydroxides and discuss the use of the integrating sphere to minimize the effects of physical properties of the surfaces (such as surface roughness) on the results obtained from the chemometric methods used for quantitative analysis.

  1. Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops.

    PubMed

    Chen, Longquan; Bonaccurso, Elmar

    2014-08-01

    In this paper, we experimentally investigated the dynamic spreading of liquid drops on solid surfaces. Drop of glycerol water mixtures and pure water that have comparable surface tensions (62.3-72.8 mN/m) but different viscosities (1.0-60.1 cP) were used. The size of the drops was 0.5-1.2 mm. Solid surfaces with different lyophilic and lyophobic coatings (equilibrium contact angle θ(eq) of 0°-112°) were used to study the effect of surface wettability. We show that surface wettability and liquid viscosity influence wetting dynamics and affect either the coefficient or the exponent of the power law that describes the growth of the wetting radius. In the early inertial wetting regime, the coefficient of the wetting power law increases with surface wettability but decreases with liquid viscosity. In contrast, the exponent of the power law does only depend on surface wettability as also reported in literature. It was further found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does. For low viscosity liquids, the duration of inertial wetting corresponds to the time of capillary wave propagation, which can be determined by Lamb's drop oscillation model for inviscid liquids. For relatively high viscosity liquids, the inertial wetting time increases with liquid viscosity, which may due to the viscous damping of the surface capillary waves. Furthermore, we observed a viscous wetting regime only on surfaces with an equilibrium contact angle θ(eq) smaller than a critical angle θ(c) depending on viscosity. A scaling analysis based on Navier-Stokes equations is presented at the end, and the predicted θ(c) matches with experimental observations without any additional fitting parameters.

  2. Dynamic Melting of Freezing Droplets on Ultraslippery Superhydrophobic Surfaces.

    PubMed

    Chu, Fuqiang; Wu, Xiaomin; Wang, Lingli

    2017-03-08

    Condensed droplet freezing and freezing droplet melting phenomena on the prepared ultraslippery superhydrophobic surface were observed and discussed in this study. Although the freezing delay performance of the surface is common, the melting of the freezing droplets on the surface is quite interesting. Three self-propelled movements of the melting droplets (ice- water mixture) were found including the droplet rotating, the droplet jumping, and the droplet sliding. The melting droplet rotating, which means that the melting droplet rotates spontaneously on the superhydrophobic surface like a spinning top, is first reported in this study and may have some potential applications in various engineering fields. The melting droplet jumping and sliding are similar to those occurring during condensation but have larger size scale and motion scale, as the melting droplets have extra-large specific surface area with much more surface energy available. These self-propelled movements make all the melting droplets on the superhydrophobic surface dynamic, easily removed, which may be promising for the anti-icing/frosting applications.

  3. On the dynamics of homogeneous turbulence near a surface

    NASA Astrophysics Data System (ADS)

    Flores, Oscar; Riley, James J.

    2011-11-01

    It is becoming increasing clear that stably-stratified flows can support a stratified turbulence k - 5 / 3 inertial range, different from Kolmogorov's. Stratification inhibits vertical motions, but the large-scale quasi-horizontal motions produce strong vertical shearing and small-scale instabilities. The result is a k - 5 / 3 horizontal spectrum for the horizontal velocities at scales larger than the Ozmidov scale, the largest scale that can overturn. For smaller scales, the classical Kolmogorov k - 5 / 3 applies. Inspired by data taken near the water surface in a tidal river, we here explore to what extent the dynamics of the nonlinear spectral energy transfer of near-surface turbulence with no mean shear (i.e., horizontally isotropic turbulence bounded by free-slip and no-slip surfaces) is analogous to stably stratified turbulence. To that end, we perform DNS of decaying isotropic turbulence with Reλ ~ 100 , but bounded by a non-slip surface and a free slip surface. The behavior of the flow near the free-slip surface is similar to stratified turbulence, with a tentative k - 5 / 3 range, but the same is not true for the no-slip surface at the present Reynolds numbers. This research was supported by ARO and NSF. Chickadel et al. (2011) to appear in IEEE Geosci. Remote Sens. Lett.

  4. Highly collimated monoenergetic target-surface electron acceleration in near-critical-density plasmas

    SciTech Connect

    Mao, J. Y.; Chen, L. M.; Huang, K.; Ma, Y.; Zhao, J. R.; Yan, W. C.; Ma, J. L.; Wei, Z. Y.; Li, D. Z.; Aeschlimann, M.; Zhang, J.

    2015-03-30

    Optimized-quality monoenergetic target surface electron beams at MeV level with low normalized emittance (0.03π mm mrad) and high charge (30 pC) per shot have been obtained from 3 TW laser-solid interactions at a grazing incidence. The 2-Dimension particle-in-cell simulations suggest that electrons are wake-field accelerated in a large-scale, near-critical-density preplasma. It reveals that a bubble-like structure as an accelerating cavity appears in the near-critical-density plasma region and travels along the target surface. A bunch of electrons are pinched transversely and accelerated longitudinally by the wake field in the bubble. The outstanding normalized emittance and monochromaticity of such highly collimated surface electron beams could make it an ideal beam for fast ignition or may serve as an injector in traditional accelerators.

  5. Wetting layers caused by surface ionization in a near-critical binary liquid mixture

    NASA Astrophysics Data System (ADS)

    Ripple, Dean; Wu, Xiao-Lun; Franck, Carl

    1988-11-01

    Kayser [Phys. Rev. Lett. 56, 1831 (1986)] has proposed that surface ionization provides the long-range force responsible for the wetting layers seen in the binary liquid mixture CS2+CH3NO2 on borosilicate glass substrates. We use scaling theory to find the equation of state for the near-critical mixtures, and then derive a free-energy functional for the wetting layer that incorporates surface ionization forces. This model includes critical adsorption effects and is well suited for calculations of wetting layers in the single-phase region. Within the uncertainties of the material properties, reflectivities of the glass-liquid interface derived from the theoretical concentration profiles do agree with experimental reflectivity values for wetting layers in the one-phase region. We confirm that surface ionization produces the dominant long-range force in CS2+CH3NO2 on glass.

  6. Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone

    SciTech Connect

    Mauguière, Frédéric A. L. Collins, Peter Wiggins, Stephen; Kramer, Zeb C. Ezra, Gregory S.; Carpenter, Barry K.; Farantos, Stavros C.

    2016-02-07

    We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariant manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.

  7. Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone.

    PubMed

    Mauguière, Frédéric A L; Collins, Peter; Kramer, Zeb C; Carpenter, Barry K; Ezra, Gregory S; Farantos, Stavros C; Wiggins, Stephen

    2016-02-07

    We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariant manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.

  8. Phase space barriers and dividing surfaces in the absence of critical points of the potential energy: Application to roaming in ozone

    NASA Astrophysics Data System (ADS)

    Mauguière, Frédéric A. L.; Collins, Peter; Kramer, Zeb C.; Carpenter, Barry K.; Ezra, Gregory S.; Farantos, Stavros C.; Wiggins, Stephen

    2016-02-01

    We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariant manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models with zero total angular momentum. We have located the normally hyperbolic invariant manifold from which the orbiting (outer) transition state is constructed. This forms the basis for our analysis of trajectories for ozone in general, but with particular emphasis on the roaming trajectories.

  9. A Method for Molecular Dynamics on Curved Surfaces

    PubMed Central

    Paquay, Stefan; Kusters, Remy

    2016-01-01

    Dynamics simulations of constrained particles can greatly aid in understanding the temporal and spatial evolution of biological processes such as lateral transport along membranes and self-assembly of viruses. Most theoretical efforts in the field of diffusive transport have focused on solving the diffusion equation on curved surfaces, for which it is not tractable to incorporate particle interactions even though these play a crucial role in crowded systems. We show here that it is possible to take such interactions into account by combining standard constraint algorithms with the classical velocity Verlet scheme to perform molecular dynamics simulations of particles constrained to an arbitrarily curved surface. Furthermore, unlike Brownian dynamics schemes in local coordinates, our method is based on Cartesian coordinates, allowing for the reuse of many other standard tools without modifications, including parallelization through domain decomposition. We show that by applying the schemes to the Langevin equation for various surfaces, we obtain confined Brownian motion, which has direct applications to many biological and physical problems. Finally we present two practical examples that highlight the applicability of the method: 1) the influence of crowding and shape on the lateral diffusion of proteins in curved membranes; and 2) the self-assembly of a coarse-grained virus capsid protein model. PMID:27028633

  10. The European Continent : Surface Expression of Upper Mantle Dynamics

    NASA Astrophysics Data System (ADS)

    Tondi, M. R.; Schivardi, R.; Molinari, I.; Morelli, A.

    2012-12-01

    The surface topography of Europe shows important variations, most of which are relatively well explained by isostatic compensation of density contrasts within the crust and lithosphere. However, not all of the density contrasts leading to topography reside within the lithosphere. The crucial problem is how to detect the extra topography signal, in addition to that associated with both crustal and lithospheric anomalies. Forte and Perry, 2000 estimate the amplitude of the dynamic topography by removal of the crustal isostatic topography signal from the surface of the Earth. Faccenna and Becker, 2010 infer the equivalent dynamic topography from the normal stress generated at the surface by mantle viscous flow driven by thermal anomalies. Here we consider the correlation between residual topography and mantle residual gravity anomalies. As shown by Pekeris, 1935 and Hager et al., 1985, the viscous mantle flow that is driven by the thermal density contrasts is responsible for the long-wavelength gravity anomalies observed at the surface. They have demonstrated that the gravitational effects of surface deformation caused by the flow is opposite in sign and comparable in magnitude to that of the driving density contrast. The 1°x1° recently assembled European crustal model, EPCrust (Molinari and Morelli, 2011) is used to estimate the effects of the isostatic crust and the mantle residual gravity anomalies. We calculate the correlation matrix between the residual topography and the mantle residual gravity anomalies and we define the regions where the sublithospheric mantle density, below the European continent, contributes to surface topography. To recover the residual topography, the effects of the isostatic crust is estimated with the Panasyuk and Hager (2000) algorithm and subtracted from the observed elevation (ETOPO-1). The mantle residual gravity anomalies are estimated as the differences between the produced gravity field of EPCrust and the observations. 3-D

  11. Ab initio molecular dynamics simulations of the adsorption of H2 on palladium surfaces.

    PubMed

    Gross, Axel

    2010-05-17

    The interaction of hydrogen with palladium surfaces represents a model system for the study of the adsorption and absorption at metal surfaces. Theoretical gas-surface dynamics studies have usually concentrated on the adsorption dynamics on clean surfaces. Only recently has it become possible, based on advances in electronic structure codes and improvements in computer power, to address the much more complex problem of the adsorption dynamics on precovered surfaces. Herein, recent ab initio molecular dynamics studies are discussed that address the adsorption dynamics of hydrogen molecules on hydrogen- and sulfur-precovered Pd surfaces. In addition, the relaxation dynamics of the hydrogen atoms after the dissociation on clean Pd(100) are presented.

  12. Observation of dynamic water microadsorption on Au surface

    SciTech Connect

    Huang, Xiaokang Gupta, Gaurav; Gao, Weixiang; Tran, Van; Nguyen, Bang; McCormick, Eric; Cui, Yongjie; Yang, Yinbao; Hall, Craig; Isom, Harold

    2014-05-15

    Experimental and theoretical research on water wettability, adsorption, and condensation on solid surfaces has been ongoing for many decades because of the availability of new materials, new detection and measurement techniques, novel applications, and different scales of dimensions. Au is a metal of special interest because it is chemically inert, has a high surface energy, is highly conductive, and has a relatively high melting point. It has wide applications in semiconductor integrated circuitry, microelectromechanical systems, microfluidics, biochips, jewelry, coinage, and even dental restoration. Therefore, its surface condition, wettability, wear resistance, lubrication, and friction attract a lot of attention from both scientists and engineers. In this paper, the authors experimentally investigated Au{sub 2}O{sub 3} growth, wettability, roughness, and adsorption utilizing atomic force microscopy, scanning electron microscopy, reflectance spectrometry, and contact angle measurement. Samples were made using a GaAs substrate. Utilizing a super-hydrophilic Au surface and the proper surface conditions of the surrounding GaAs, dynamic microadsorption of water on the Au surface was observed in a clean room environment. The Au surface area can be as small as 12 μm{sup 2}. The adsorbed water was collected by the GaAs groove structure and then redistributed around the structure. A model was developed to qualitatively describe the dynamic microadsorption process. The effective adsorption rate was estimated by modeling and experimental data. Devices for moisture collection and a liquid channel can be made by properly arranging the wettabilities or contact angles of different materials. These novel devices will be very useful in microfluid applications or biochips.

  13. Biofilm attachment reduction on bioinspired, dynamic, micro-wrinkling surfaces

    NASA Astrophysics Data System (ADS)

    Epstein, Alexander K.; Hong, Donggyoon; Kim, Philseok; Aizenberg, Joanna

    2013-09-01

    Most bacteria live in multicellular communities known as biofilms that are adherent to surfaces in our environment, from sea beds to plumbing systems. Biofilms are often associated with clinical infections, nosocomial deaths and industrial damage such as bio-corrosion and clogging of pipes. As mature biofilms are extremely challenging to eradicate once formed, prevention is advantageous over treatment. However, conventional surface chemistry strategies are either generally transient, due to chemical masking, or toxic, as in the case of leaching marine antifouling paints. Inspired by the nonfouling skins of echinoderms and other marine organisms, which possess highly dynamic surface structures that mechanically frustrate bio-attachment, we have developed and tested a synthetic platform based on both uniaxial mechanical strain and buckling-induced elastomer microtopography. Bacterial biofilm attachment to the dynamic substrates was studied under an array of parameters, including strain amplitude and timescale (1-100 mm s-1), surface wrinkle length scale, bacterial species and cell geometry, and growth time. The optimal conditions for achieving up to ˜ 80% Pseudomonas aeruginosa biofilm reduction after 24 h growth and ˜ 60% reduction after 48 h were combinatorially elucidated to occur at 20% strain amplitude, a timescale of less than ˜ 5 min between strain cycles and a topography length scale corresponding to the cell dimension of ˜ 1 μm. Divergent effects on the attachment of P. aeruginosa, Staphylococcus aureus and Escherichia coli biofilms showed that the dynamic substrate also provides a new means of species-specific biofilm inhibition, or inversely, selection for a desired type of bacteria, without reliance on any toxic or transient surface chemical treatments.

  14. Oxide formation and alloying elements enrichment on TRIP steel surface during inter-critical annealing.

    PubMed

    Gong, Y F; Birosca, S; Kim, H S; De Cooman, B C

    2008-06-01

    The gas atmosphere in continuous annealing and galvanizing lines alters both composition and microstructure of the surface and sub-surface of sheet steels. The alloying element enrichments and the oxide morphology on transformation-induced plasticity steel surfaces are strongly influenced by the dew point of the furnace atmosphere and annealing temperature. The formation of a thin oxide film and enrichment of the alloying elements during annealing may result in surface defects on galvanized sheet products. The present contribution reports on the use of microanalysis techniques such as electron backscatter diffraction, glow discharge optical emission spectroscopy and electron probe micro-analysis for the detailed surface analysis of inter-critically annealed transformation-induced plasticity steel such as oxide phase determination, microstructure and microtexture evolutions.

  15. Imbibition dynamics on surfaces of legs of a small animal and on artificial surfaces mimicking them

    NASA Astrophysics Data System (ADS)

    Tani, Marie; Ishii, Daisuke; Ito, Shuto; Hariyama, Takahiko; Shimomura, Masatsugu; Okumura, Ko

    2014-03-01

    Recently, imbibition of textured surfaces covered with homogeneous micro-pillar arrays has been actively studied partly because of the potential for transport of a small amount of liquids. In most cases, the dynamics is described by the Washburn law, in which the imbibition distance scales with the square root of elapsed time, while a different scaling law has been recently found. In this study, we studied imbibition on legs of a small animal that absorbs water via its legs to find yet another scaling law. Furthermore, imbibition of artificial surfaces mimicking the leg surface was found to be described well by a composite theory.

  16. Qualitative Analysis of Critical Transitions in Complex Disease Propagation from a Dynamical Systems Perspective

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Zou, Xiufen

    2016-12-01

    Considerable evidence suggests that in complex diseases the deteriorations are often abrupt, and can be viewed as a bifurcation or a critical transition from one asymptotically stable equilibrium to another one at a tipping point. Here, we propose some new ideas to detect early-warning signals of such critical transitions from the perspective of qualitative theory of ordinary differential equations. Specifically, we theoretically derive three indicators that serve as a general early-warning signal indicating an imminent bifurcation or sudden deterioration before the critical transition occurs. Then, we verify our theoretical results by numerical simulations for three examples. Our work forms a starting point to motivate new mathematical insights into predictability for critical transitions of dynamical systems from a new perspective.

  17. Critical heat flux (CHF) phenomenon on a downward facing curved surface

    SciTech Connect

    Cheung, F.B.; Haddad, K.H.; Liu, Y.C.

    1997-06-01

    This report describes a theoretical and experimental study of the boundary layer boiling and critical heat flux phenomena on a downward facing curved heating surface, including both hemispherical and toroidal surfaces. A subscale boundary layer boiling (SBLB) test facility was developed to measure the spatial variation of the critical heat flux and observe the underlying mechanisms. Transient quenching and steady-state boiling experiments were performed in the SBLB facility under both saturated and subcooled conditions to obtain a complete database on the critical heat flux. To complement the experimental effort, an advanced hydrodynamic CHF model was developed from the conservation laws along with sound physical arguments. The model provides a clear physical explanation for the spatial variation of the CHF observed in the SBLB experiments and for the weak dependence of the CHF data on the physical size of the vessel. Based upon the CHF model, a scaling law was established for estimating the local critical heat flux on the outer surface of a heated hemispherical vessel that is fully submerged in water. The scaling law, which compares favorably with all the available local CHF data obtained for various vessel sizes, can be used to predict the local CHF limits on large commercial-size vessels. This technical information represents one of the essential elements that is needed in assessing the efficacy of external cooling of core melt by cavity flooding as a severe accident management strategy. 83 figs., 3 tabs.

  18. Analysis of the relation between exposure parameters and critical dimension by response surface model

    NASA Astrophysics Data System (ADS)

    Sohn, Dong-Soo; Sohn, Young-Soo; Bak, Heungin; Oh, Hye-Keun

    2001-08-01

    It is important to know the relationship between the soft bake conditions and the Dill exposure parameters in order to control the lithographic process well. It has been reported that exposure parameter A can be significantly affected by the soft bake conditions, while the exposure parameters B and C show no dependency on the soft bake conditions. The exposure parameters have been considered less important in 193 nm chemically amplified resist (CAR) simulation. Since the critical dimension variation depends on the exposure parameters, if we know the relationship between them it would be helpful in developing resist and resist process. In this paper the profiles of a 193nm CAR were simulated with the various Dill exposure parameters and the results were analyzed by response surface model. The response surface methodology (RSM) approach was used to analyze the influence of independent factors on a dependent response, and to optimize each process. A method of steepest ascent was utilized to produce first-order models, which were verified by lack of fit testing. As optimum operation points were approached, a second-order model was fitted and analyzed. The Dill exposure parameter C affects critical dimension greatly whereas A and B have much less effect. Among parameters other than exposure parameters, PEB time and PEB temperature are great factors to affect critical dimension. Even small change of them can make great critical dimension changes. Process optimization for the target response value as well as process latitude was possible through the use of the response surface.

  19. Dynamics of adsorbed polymers on attractive homogeneous surfaces

    PubMed Central

    Yang, Qing-Hui; Luo, Meng-Bo

    2016-01-01

    Dynamic behaviors of polymer chains adsorbed on an attractive, homogeneous surface are studied by using dynamic Monte Carlo simulations. The translational diffusion coefficient Dxy parallel to the surface decreases as the intra-polymer attraction strength EPP or the polymer-surface attraction strength EPS increases. The rotational relaxation time τR increases with EPS, but the dependence of τR on EPP is dependent on the adsorption state of the polymer. We find that τR decreases with increasing EPP for a partially adsorbed polymer but it increases with EPP for a fully adsorbed polymer. Scaling relations Dxy ~ N−α and τR ~ Nβ are found for long polymers. The scaling exponent α is independent of EPS for long polymers but increases with EPP from α = 1.06 at EPP = 0. While β ≈ 2.7 is also roughly independent of EPS for the adsorbed polymer at EPP = 0, but β increases with EPS at EPP > 0. Moreover, we find that β always decreases with increasing EPP. Our results reveal different effects of the attractive surface on the diffusion and rotation of adsorbed polymers. PMID:27849002

  20. Viscoplasticity with dynamic yield surface coupled to damage

    NASA Astrophysics Data System (ADS)

    Johansson, M.; Runesson, K.

    1997-07-01

    A formulation of viscoplasticity theory, with kinetic coupling to damage, is presented. The main purpose is to describe rate-dependent material behavior and failure processes, including creep-rupture (for constant load) and creep-fatigue (for cyclic load). The Duvaut-Lions' formulation of viscoplasticity is adopted with quite general hardening of the quasistatic yield surface. The formulation is thermodynamically consistent, i.e. the dissipation inequality is satisfied. Like in the classical viscoplasticity formulations, the rate-independent response is activated at a very small loading rate. In addition, an (unconventional) dynamic yield surface is introduced, and this is approached asymptotically at infinite loading rate. Explicit constitutive relations are established for a quasistatic yield surface of von Mises type with nonlinear hardening. The resulting model is assessed for a variety of loading situations.

  1. Application of the dynamical droplet model to critical nonionic amphiphile-water micellar solutions

    NASA Astrophysics Data System (ADS)

    Ducros, E.; Haouache, S.; Rouch, J.; Hamano, K.; Fukuhara, K.; Tartaglia, P.

    1994-08-01

    A modified version of the dynamical droplet model, originally derived by Sorensen et al. [Phys. Rev. A 13, 1593 (1976)], is used to explain experimental results on alkyl-oxyethylene-glycol monoether (CiEj)-water critical micellar solutions. The model assumes that the physical clusters formed close to the critical point can be treated much like percolating clusters with a fractal dimension df=2.49 and a polydispersity exponent τ=2.21. For C6E3-H2O and C10E4-H2O critical mixtures, the modified version of the dynamical droplet model provides results in very good agreement with the experimental determinations of the scattered intensity, the turbidity, and the order parameter relaxation rate, when using as input parameters the three-dimensionsal universal Ising values of the critical exponents and the proper sizes of the individual scattering micelles. Static and dynamical background effects can be explained by the finite size of the monomers, which is explicitly taken into account by the model.

  2. Correlations induced by depressing synapses in critically self-organized networks with quenched dynamics

    NASA Astrophysics Data System (ADS)

    Campos, João Guilherme Ferreira; Costa, Ariadne de Andrade; Copelli, Mauro; Kinouchi, Osame

    2017-04-01

    In a recent work, mean-field analysis and computer simulations were employed to analyze critical self-organization in networks of excitable cellular automata where randomly chosen synapses in the network were depressed after each spike (the so-called annealed dynamics). Calculations agree with simulations of the annealed version, showing that the nominal branching ratio σ converges to unity in the thermodynamic limit, as expected of a self-organized critical system. However, the question remains whether the same results apply to the biological case where only the synapses of firing neurons are depressed (the so-called quenched dynamics). We show that simulations of the quenched model yield significant deviations from σ =1 due to spatial correlations. However, the model is shown to be critical, as the largest eigenvalue of the synaptic matrix approaches unity in the thermodynamic limit, that is, λc=1 . We also study the finite size effects near the critical state as a function of the parameters of the synaptic dynamics.

  3. Critical Velocity in the Presence of Surface Bound States in Superfluid 3He -B

    NASA Astrophysics Data System (ADS)

    Zheng, P.; Jiang, W. G.; Barquist, C. S.; Lee, Y.; Chan, H. B.

    2017-02-01

    A microelectromechanical oscillator with a gap of 1.25 μ m was immersed in superfluid 3He -B and cooled below 250 μ K at various pressures. Mechanical resonances of its shear motion were measured at various levels of driving force. The oscillator enters into a nonlinear regime above a certain threshold velocity. The damping increases rapidly in the nonlinear region and eventually prevents the velocity of the oscillator from increasing beyond the critical velocity which is much lower than the Landau critical velocity. We propose that this peculiar nonlinear behavior stems from the escape of quasiparticles from the surface bound states into the bulk fluid.

  4. Spreading dynamics of droplet on an inclined surface

    NASA Astrophysics Data System (ADS)

    Shen, Chaoqun; Yu, Cheng; Chen, Yongping

    2016-06-01

    A three-dimensional unsteady theoretical model of droplet spreading process on an inclined surface is developed and numerically analyzed to investigate the droplet spreading dynamics via the lattice Boltzmann simulation. The contact line motion and morphology evolution for the droplet spreading on an inclined surface, which are, respectively, represented by the advancing/receding spreading factor and droplet wetted length, are evaluated and analyzed. The effects of surface wettability and inclination on the droplet spreading behaviors are examined. The results indicate that, dominated by gravity and capillarity, the droplet experiences a complex asymmetric deformation and sliding motion after the droplet comes into contact with the inclined surfaces. The droplet firstly deforms near the solid surface and mainly exhibits a radial expansion flow in the start-up stage. An evident sliding-down motion along the inclination is observed in the middle stage. And the surface-tension-driven retraction occurs during the retract stage. Increases in inclination angle and equilibrium contact angle lead to a faster droplet motion and a smaller wetted area. In addition, increases in equilibrium contact angle lead to a shorter duration time of the middle stage and an earlier entry into the retract stage.

  5. Population dynamics of sinking phytoplankton in light-limited environments: simulation techniques and critical parameters

    NASA Astrophysics Data System (ADS)

    Huisman, Jef; Sommeijer, Ben

    2002-10-01

    Phytoplankton use light for photosynthesis, and the light flux decreases with depth. As a result of this simple light dependence, reaction-advection-diffusion models describing the dynamics of phytoplankton species contain an integral over depth. That is, models that simulate phytoplankton dynamics in relation to mixing processes generally have the form of an integro-partial differential equation (integro-PDE). Integro-PDEs are computationally more demanding than standard PDEs. Here, we outline a reliable and efficient technique for numerical simulation of integro-PDEs. The simulation technique is illustrated by several examples on the population dynamics of sinking phytoplankton, using both single-species models and competition models with several phytoplankton species. Our results confirm recent findings that Sverdrup's critical-depth theory breaks down if turbulent mixing is reduced below a critical turbulence. In fact, our results show that suitable conditions for bloom development of sinking phytoplankton depend on a number of critical parameters, including a minimal depth of the thermocline, a maximal depth of the thermocline, a minimal turbulence, and a maximal turbulence. We therefore conclude that models that do not carefully consider the population dynamics of phytoplankton in relation to the turbulence structure of the water column may easily lead to erroneous predictions.

  6. System Dynamics Approach for Critical Infrastructure and Decision Support. A Model for a Potable Water System.

    NASA Astrophysics Data System (ADS)

    Pasqualini, D.; Witkowski, M.

    2005-12-01

    The Critical Infrastructure Protection / Decision Support System (CIP/DSS) project, supported by the Science and Technology Office, has been developing a risk-informed Decision Support System that provides insights for making critical infrastructure protection decisions. The system considers seventeen different Department of Homeland Security defined Critical Infrastructures (potable water system, telecommunications, public health, economics, etc.) and their primary interdependencies. These infrastructures have been modeling in one model called CIP/DSS Metropolitan Model. The modeling approach used is a system dynamics modeling approach. System dynamics modeling combines control theory and the nonlinear dynamics theory, which is defined by a set of coupled differential equations, which seeks to explain how the structure of a given system determines its behavior. In this poster we present a system dynamics model for one of the seventeen critical infrastructures, a generic metropolitan potable water system (MPWS). Three are the goals: 1) to gain a better understanding of the MPWS infrastructure; 2) to identify improvements that would help protect MPWS; and 3) to understand the consequences, interdependencies, and impacts, when perturbations occur to the system. The model represents raw water sources, the metropolitan water treatment process, storage of treated water, damage and repair to the MPWS, distribution of water, and end user demand, but does not explicitly represent the detailed network topology of an actual MPWS. The MPWS model is dependent upon inputs from the metropolitan population, energy, telecommunication, public health, and transportation models as well as the national water and transportation models. We present modeling results and sensitivity analysis indicating critical choke points, negative and positive feedback loops in the system. A general scenario is also analyzed where the potable water system responds to a generic disruption.

  7. Nonlinear Dynamics of Biofilm Growth on Sediment Surfaces

    NASA Astrophysics Data System (ADS)

    Molz, F. J.; Murdoch, L. C.; Faybishenko, B.

    2013-12-01

    Bioclogging often begins with the establishment of small colonies (microcolonies), which then form biofilms on the surfaces of a porous medium. These biofilm-porous media surfaces are not simple coatings of single microbes, but complex assemblages of cooperative and competing microbes, interacting with their chemical environment. This leads one to ask: what are the underlying dynamics involved with biofilm growth? To begin answering this question, we have extended the work of Kot et al. (1992, Bull. Mathematical Bio.) from a fully mixed chemostat to an idealized, one-dimensional, biofilm environment, taking into account a simple predator-prey microbial competition, with the prey feeding on a specified food source. With a variable (periodic) food source, Kot et al. (1992) were able to demonstrate chaotic dynamics in the coupled substrate-prey-predator system. Initially, deterministic chaos was thought by many to be mainly a mathematical phenomenon. However, several recent publications (e.g., Becks et al, 2005, Nature Letters; Graham et al. 2007, Int. Soc Microb. Eco. J.; Beninca et al., 2008, Nature Letters; Saleh, 2011, IJBAS) have brought together, using experimental studies and relevant mathematics, a breakthrough discovery that deterministic chaos is present in relatively simple biochemical systems. Two of us (Faybishenko and Molz, 2013, Procedia Environ. Sci)) have numerically analyzed a mathematical model of rhizosphere dynamics (Kravchenko et al., 2004, Microbiology) and detected patterns of nonlinear dynamical interactions supporting evidence of synchronized synergetic oscillations of microbial populations, carbon and oxygen concentrations driven by root exudation into a fully mixed system. In this study, we have extended the application of the Kot et al. model to investigate a spatially-dependent biofilm system. We will present the results of numerical simulations obtained using COMSOL Multi-Physics software, which we used to determine the nature of the

  8. Critical behavior at a dynamic vortex insulator-to-metal transition

    SciTech Connect

    Poccia, Nicola; Baturina, Tatyana I.; Coneri, Francesco; Molenaar, Cor G.; Wang, X. Renshaw; Bianconi, Ginestra; Brinkman, Alexander; Hilgenkamp, Hans; Golubov, Alexander A.; Vinokur, Valerii M.

    2015-09-10

    An array of superconducting islands placed on a normal metal film offers a tunable realization of nanopatterned superconductivity. This system enables elucidating open questions concerning the nature of competing vortex states and phase transitions between them. A square array creates the egg crate potential in which magnetic field-induced vortices are frozen into a vortex insulator. We observe a vortex insulator-to-vortex metal transition driven by the applied electric current and determine critical exponents strikingly coinciding with those for thermodynamic liquid-gas transition. Lastly, our findings offer a comprehensive description of dynamic critical behavior and establish a deep connection between equilibrium and nonequilibrium phase transitions.

  9. Critical behavior of gelation probed by the dynamics of latex spheres

    SciTech Connect

    Fadda, G. C.; Lairez, D.; Pelta, J.

    2001-06-01

    We report a quasielastic light scattering study of the dynamics of large latex probe particles (R=225nm) in gelatin solution undergoing gelation. We show that by focusing on the short-time and long-time behavior of the autocorrelation function, it is possible to simply interpret out data in terms of the divergence of the viscosity and emergence of the shear elastic modulus near the gel point. Our crude analysis allows us to grasp the critical behavior of gelation and to obtain the two critical exponents of the transport properties.

  10. Nonequilibrium critical dynamics of the two-dimensional Ising model quenched from a correlated initial state.

    PubMed

    Környei, László; Pleimling, Michel; Iglói, Ferenc

    2008-01-01

    The universality class, even the order of the transition, of the two-dimensional Ising model depends on the range and the symmetry of the interactions (Onsager model, Baxter-Wu model, Turban model, etc.), but the critical temperature is generally the same due to self-duality. Here we consider a sudden change in the form of the interaction and study the nonequilibrium critical dynamical properties of the nearest-neighbor model. The relaxation of the magnetization and the decay of the autocorrelation function are found to display a power law behavior with characteristic exponents that depend on the universality class of the initial state.

  11. Cryogenic design of the liquid helium experiment ``critical dynamics in microgravity``

    SciTech Connect

    Moeur, W.A.; Adriaans, M.J.; Boyd, S.T.; Strayer, D.M.; Duncan, R.V. |

    1995-10-01

    Although many well controlled experiments have been conducted to measure the static properties of systems near criticality, few experiments have explored the transport properties in systems driven far away from equilibrium as a phase transition occurs. The cryogenic design of an experiment to study the dynamic aspect of critical phenomena is reported here. Measurements of the thermal gradient across the superfluid (He II) -- normal fluid (He I) interface in helium under microgravity conditions will be performed as a heat flux holds the system away from equilibrium. New technologies are under development for this experiment, which is in the definition phase for a space shuttle flight.

  12. The critical indices of the quark gluon bags with surface tension model with tricritical endpoint

    NASA Astrophysics Data System (ADS)

    Ivanytskyi, A. I.

    2012-04-01

    The critical indices α', β, γ' and δ of the quark gluon bags with surface tension model with the tricritical endpoint are calculated as functions of the usual parameters of this model and two newly introduces parameters (indices) in order to perform a thorough comparison with the critical exponents of other models. It is shown that for the newly introduced indices χ=0 and ξT⩽1 there is a branch of solutions for which the critical exponents of the present model and the statistical multifragmentation model coincide, otherwise these models have different critical exponents. The critical exponents α', β, γ' and δ of ordinary liquids and 3-dimensional Ising model are reproduced by several sets of the model parameters, but the resulting range of the Fisher exponent τ is rather narrow and lies between 20/11 and 2. The scaling relations for the found critical exponents are verified and it is demonstrated that for the standard definition of the index α' the Fisher and Griffiths scaling inequalities are not fulfilled for some values of the model parameters, whereas the Liberman scaling inequality is always obeyed. It is also shown that the specially defined index αs' recovers the scaling relations. A thorough analysis of the critical exponents obeying the scaling relations along with the condition αs'>-β is performed. The found solutions enable us to reproduce the critical exponents of the 3-dimensional O(4) spin model and to show that for this case the exponent τ falls almost in the same range of values as for the ordinary liquids.

  13. Critical Role of Surface Energy in Guiding Crystallization of Solution Coated Conjugated Polymer Thin Films.

    PubMed

    Zhang, Fengjiao; Mohammadi, Erfan; Luo, Xuyi; Strzalka, Joseph; Mei, Jianguo; Diao, Ying

    2017-10-02

    It is well-known that substrate surface properties have a profound impact on morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution coated semiconducting polymers, as the substrate-directed thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We perform in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing a donor-accepter (D-A) conjugated polymer. We find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate lead to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step towards establishing design rules and understanding the critical role of substrates in determining morphology of solution coated thin films.

  14. Method and apparatus for monitoring dynamic cardiovascular function using n-dimensional representatives of critical functions

    NASA Technical Reports Server (NTRS)

    Westinskow, Dwayne (Inventor); Agutter, James (Inventor); Syroid, Noah (Inventor); Strayer, David (Inventor); Albert, Robert (Inventor); Wachter, S. Blake (Inventor); Drews, Frank (Inventor)

    2010-01-01

    A method, system, apparatus and device for the monitoring, diagnosis and evaluation of the state of a dynamic pulmonary system is disclosed. This method and system provides the processing means for receiving sensed and/or simulated data, converting such data into a displayable object format and displaying such objects in a manner such that the interrelationships between the respective variables can be correlated and identified by a user. This invention provides for the rapid cognitive grasp of the overall state of a pulmonary critical function with respect to a dynamic system.

  15. Predicting critical transitions in dynamical systems from time series using nonstationary probability density modeling.

    PubMed

    Kwasniok, Frank

    2013-11-01

    A time series analysis method for predicting the probability density of a dynamical system is proposed. A nonstationary parametric model of the probability density is estimated from data within a maximum likelihood framework and then extrapolated to forecast the future probability density and explore the system for critical transitions or tipping points. A full systematic account of parameter uncertainty is taken. The technique is generic, independent of the underlying dynamics of the system. The method is verified on simulated data and then applied to prediction of Arctic sea-ice extent.

  16. Predicting critical transitions in dynamical systems from time series using nonstationary probability density modeling

    NASA Astrophysics Data System (ADS)

    Kwasniok, Frank

    2013-11-01

    A time series analysis method for predicting the probability density of a dynamical system is proposed. A nonstationary parametric model of the probability density is estimated from data within a maximum likelihood framework and then extrapolated to forecast the future probability density and explore the system for critical transitions or tipping points. A full systematic account of parameter uncertainty is taken. The technique is generic, independent of the underlying dynamics of the system. The method is verified on simulated data and then applied to prediction of Arctic sea-ice extent.

  17. Behavior of the critical temperature of Ising thin films with variable surface magnetic moments.

    PubMed

    Monroe, James L

    2005-01-01

    Properties of magnetic thin films are of considerable interest both for applied as well as theoretical reasons. I study the behavior of Ising thin films through the use of layered Bethe lattices and Husimi trees. In particular the behavior of the critical temperature both as a function of the number of layers and as a function of variable magnetic moments of surface spins is presented. The later is motivated by that fact that such variation has been found to occur in physical systems such as Ni and Fe free surfaces and Ni/Co interfaces. The approach used is more accurate than many previously used and most importantly shows a different qualitative behavior of the critical temperature from previous studies.

  18. Dynamic Corneal Surface Mapping with Electronic Speckle Pattern Interferometry

    NASA Astrophysics Data System (ADS)

    Iqbal, S.; Gualini, M. M. S.

    2013-06-01

    In view of the fast advancement in ophthalmic technology and corneal surgery, there is a strong need for the comprehensive mapping and characterization techniques for corneal surface. Optical methods with precision non-contact approaches have been found to be very useful for such bio measurements. Along with the normal mapping approaches, elasticity of corneal surface has an important role in its characterization and needs to be appropriately measured or estimated for broader diagnostics and better prospective surgical results, as it has important role in the post-op corneal surface reconstruction process. Use of normal corneal topographic devices is insufficient for any intricate analysis since these devices operate at relatively moderate resolution. In the given experiment, Pulsed Electronic Speckle Pattern Interferometry has been utilized along with an excitation mechanism to measure the dynamic response of the sample cornea. A Pulsed ESPI device has been chosen for the study because of its micron-level resolution and other advantages in real-time deformation analysis. A bovine cornea has been used as a sample in the subject experiment. The dynamic response has been taken on a chart recorder and it is observed that it does show a marked deformation at a specific excitation frequency, which may be taken as a characteristic elasticity parameter for the surface of that corneal sample. It was seen that outside resonance conditions the bovine cornea was not that much deformed. Through this study, the resonance frequency and the corresponding corneal deformations are mapped and plotted in real time. In these experiments, data was acquired and processed by FRAMES plus computer analysis system. With some analysis of the results, this technique can help us to refine a more detailed corneal surface mathematical model and some preliminary work was done on this. Such modelling enhancements may be useful for finer ablative surgery planning. After further experimentation

  19. Thermal dynamics of silver clusters grown on rippled silica surfaces

    NASA Astrophysics Data System (ADS)

    Bhatnagar, Mukul; Ranjan, Mukesh; Jolley, Kenny; Lloyd, Adam; Smith, Roger; Mukherjee, Subroto

    2017-02-01

    Silver nanoparticles have been deposited on silicon rippled patterned templates at an angle of incidence of 70° to the surface normal. The templates are produced by oblique incidence argon ion bombardment and as the fluence increases, the periods and heights of the structures increase. Structures with periods of 20 nm, 35 nm and 45 nm have been produced. Moderate temperature vacuum annealing shows the phenomenon of cluster coalescence following the contour of the more exposed faces of the ripple for the case of 35 nm and 45 nm but not at 20 nm where the silver aggregates into larger randomly distributed clusters. In order to understand this effect, the morphological changes of silver nanoparticles deposited on an asymmetric rippled silica surface are investigated through the use of molecular dynamics simulations for different deposition angles of incidence between 0° and 70° and annealing temperatures between 500 K and 900 K. Near to normal incidence, clusters are observed to migrate over the entire surface but for deposition at 70°, a similar patterning is observed as in the experiment. The random distribution of clusters for the periodicity ≈ of 20 nm is linked to the geometry of the silica surface which has a lower ripple height than the longer wavelength structures. Calculations carried out on a surface with such a lower ripple height also demonstrate a similar effect.

  20. Tracer surface diffusion at high pressures: Molecular-dynamics study

    NASA Astrophysics Data System (ADS)

    Zeiri, Yehuda

    2000-09-01

    Molecular-dynamics simulations were employed to investigate the influence of high pressure on tracer surface diffusion. A model potential was used to describe the interaction among the various species in the system. The different binding energy values and masses used in this model simulation correspond to surface diffusion of N2 on Ru(001) surface under pressure of Ar. A pronounced enhancement in the magnitude of the diffusion coefficients was observed when pressure increased from P=0 to P=200 atm. The relationship between diffusion coefficient and three parameters that characterize the system was explored. It was found that the gas temperature and the nature of gas-adsorbate interaction (i.e., attractive or repulsive) have only a negligible influence on the diffusion coefficient. However, a marked variation in the diffusion coefficient was observed when the magnitude of gas-substrate binding energy was altered. The temperature dependence of the surface diffusion coefficient exhibits an Arrhenius behavior for all cases investigated. The relationship between the pressure and both pre-exponential factor and activation energy for surface diffusion was discussed based on a detailed analysis of the diffusion mechanism. The diffusion mechanism was deduced by careful examination of large number of individual trajectories.

  1. Noncontact friction and relaxational dynamics of surface defects.

    PubMed

    She, Jian-Huang; Balatsky, Alexander V

    2012-03-30

    The motion of a cantilever near sample surfaces exhibits additional friction even before two bodies come into mechanical contact. Called noncontact friction (NCF), this friction is of great practical importance to the ultrasensitive force detection measurements. The observed large NCF of a micron-scale cantilever found an anomalously large damping that exceeds theoretical predictions by 8-11 orders of magnitude. This finding points to a contribution beyond fluctuating electromagnetic fields within the van der Waals approach. Recent experiments reported by Saitoh et al. [Phys. Rev. Lett. 105, 236103 (2010)] also found a nontrivial distance dependence of NCF. Motivated by these observations, we propose a mechanism based on the coupling of a cantilever to the relaxation dynamics of surface defects. We assume that the surface defects couple to the cantilever tip via spin-spin coupling and their spin relaxation dynamics gives rise to the backaction terms and modifies both the friction coefficient and the spring constant. We explain the magnitude, as well as the distance dependence of the friction due to these backaction terms. Reasonable agreement is found with the experiments.

  2. Dynamic effects induced transition of droplets on biomimetic superhydrophobic surfaces.

    PubMed

    Jung, Yong Chae; Bhushan, Bharat

    2009-08-18

    Superhydrophobic surfaces have considerable technological potential for various applications because of their extreme water-repellent properties. Dynamic effects, such as the bouncing and vibration of a droplet, can destroy the composite solid-air-liquid interface. The impact pressure of a bouncing droplet and the inertia force of a vibrating droplet affect the transition from a solid-air-liquid interface to a solid-liquid interface. Therefore, it is necessary to study the dynamic effect of droplets under various system parameters (impact velocity and frequency and amplitude of vibration). A new model for the prediction of the wetting and dewetting process during droplet vibration based on the relationship between the adhesion force and the inertia force of a droplet is proposed. To investigate whether micro-, nano-, and hierarchical structures can resist the destabilizing factors responsible for the transition, a study of bouncing and vibration of a water droplet is systematically conducted on various surfaces. The physics of wetting phenomena for water droplet studies is of fundamental importance in the geometrical design of superhydrophobic surfaces.

  3. Droplets impact on textured surfaces: Mesoscopic simulation of spreading dynamics

    NASA Astrophysics Data System (ADS)

    Wang, Yuxiang; Chen, Shuo

    2015-02-01

    Superhydrophobic surfaces have attracted much attention due to their excellent water-repellent property. In the present study, droplets in the ideal Cassie state were focused on, and a particle-based numerical method, many-body dissipative particle dynamics, was employed to explore the mechanism of droplets impact on textured surfaces. A solid-fluid interaction with three linear weight functions was used to generate different wettability and a simple but efficient method was introduced to compute the contact angle. The simulated results show that the static contact angle is in good agreement with the Cassie-Baxter formula for smaller ∅S and Fa, but more deviation will be produced for larger ∅S and Fa, and it is related to the fact that the Cassie-Baxter theory does not consider the contact angle hysteresis effect in their formula. Furthermore, high impact velocity can induce large contact angle hysteresis on textured surfaces with larger ∅S and Fa. The typical time-based evolutions of the spreading diameter were simulated, and they were analyzed from an energy transformation viewpoint. These results also show that the dynamical properties of droplet, such as rebounding or pinning, contact time and maximum spreading diameters, largely depend on the comprehensive effects of the material wettability, fraction of the pillars and impact velocities of the droplets.

  4. Quantum critical point in the superconducting transition on the surface of a topological insulator

    NASA Astrophysics Data System (ADS)

    Li, Dingping; Rosenstein, Baruch; Shapiro, B. Ya.; Shapiro, I.

    2014-08-01

    Pairing in the Weyl semimetal appearing on the surface of a topological insulator is considered. It is shown that due to an "ultrarelativistic" dispersion relation there is a quantum critical point governing the zero-temperature transition to a superconducting state. Starting from the microscopic Hamiltonian with local attraction, we calculated using the Gor'kov equations, the phase diagram of the superconducting transition at arbitrary chemical potential, and its magnetic properties and critical exponents close to the quantum critical point. The Ginzburg-Landau (GL) effective theory is derived for small chemical potential, allowing us to consider effects of spatial dependence of order parameters in a magnetic field. The GL equations are very different from the conventional ones reflecting the chiral universality class of the quantum phase transition. The order-parameter distribution of a single vortex is found to be different as well. The magnetization near the upper critical field is found to be quadratic, not linear as usual. We discuss the application of these results to recent experiments in which surface superconductivity was found for some three-dimensional topological insulators, and we estimate feasibility of the phonon pairing.

  5. Analytical description of critical dynamics for two-dimensional dissipative nonlinear maps

    NASA Astrophysics Data System (ADS)

    Méndez-Bermúdez, J. A.; de Oliveira, Juliano A.; Leonel, Edson D.

    2016-05-01

    The critical dynamics near the transition from unlimited to limited action diffusion for two families of well known dissipative nonlinear maps, namely the dissipative standard and dissipative discontinuous maps, is characterized by the use of an analytical approach. The approach is applied to explicitly obtain the average squared action as a function of the (discrete) time and the parameters controlling nonlinearity and dissipation. This allows to obtain a set of critical exponents so far obtained numerically in the literature. The theoretical predictions are verified by extensive numerical simulations. We conclude that all possible dynamical cases, independently on the map parameter values and initial conditions, collapse into the universal exponential decay of the properly normalized average squared action as a function of a normalized time. The formalism developed here can be extended to many other different types of mappings therefore making the methodology generic and robust.

  6. Dynamics and transport properties of three surface quasigeostrophic point vortices

    NASA Astrophysics Data System (ADS)

    Taylor, C. K.; Llewellyn Smith, Stefan G.

    2016-11-01

    The surface quasi-geostrophic (SQG) equations are a model for low-Rossby number geophysical flows in which the dynamics are governed by potential temperature dynamics on the boundary. We examine point vortex solutions to this model as well as the chaotic flows induced by three point vortices. The chaotic transport induced by these flows is investigated using techniques of Poincaré maps and the Finite Time Braiding Exponent (FTBE). This chaotic transport is representative of the mixing in the flow, and these terms are used interchangeably in this work. Compared with point vortices in two-dimensional flow, the SQG vortices are found to produce flows with higher FTBE, indicating more mixing. Select results are presented for analyzing mixing for arbitrary vortex strengths.

  7. Dynamics and transport properties of three surface quasigeostrophic point vortices.

    PubMed

    Taylor, C K; Llewellyn Smith, Stefan G

    2016-11-01

    The surface quasi-geostrophic (SQG) equations are a model for low-Rossby number geophysical flows in which the dynamics are governed by potential temperature dynamics on the boundary. We examine point vortex solutions to this model as well as the chaotic flows induced by three point vortices. The chaotic transport induced by these flows is investigated using techniques of Poincaré maps and the Finite Time Braiding Exponent (FTBE). This chaotic transport is representative of the mixing in the flow, and these terms are used interchangeably in this work. Compared with point vortices in two-dimensional flow, the SQG vortices are found to produce flows with higher FTBE, indicating more mixing. Select results are presented for analyzing mixing for arbitrary vortex strengths.

  8. Adaptive integral dynamic surface control of a hypersonic flight vehicle

    NASA Astrophysics Data System (ADS)

    Aslam Butt, Waseem; Yan, Lin; Amezquita S., Kendrick

    2015-07-01

    In this article, non-linear adaptive dynamic surface air speed and flight path angle control designs are presented for the longitudinal dynamics of a flexible hypersonic flight vehicle. The tracking performance of the control design is enhanced by introducing a novel integral term that caters to avoiding a large initial control signal. To ensure feasibility, the design scheme incorporates magnitude and rate constraints on the actuator commands. The uncertain non-linear functions are approximated by an efficient use of the neural networks to reduce the computational load. A detailed stability analysis shows that all closed-loop signals are uniformly ultimately bounded and the ? tracking performance is guaranteed. The robustness of the design scheme is verified through numerical simulations of the flexible flight vehicle model.

  9. Dynamic Scaling of Island-size Distribution on Anisotropic Surfaces

    NASA Astrophysics Data System (ADS)

    Li, Maozhi; Wang, E. G.; Liu, Banggui; Zhang, Zhenyu

    2002-03-01

    Dynamic scaling of island-size distribution on isotropic and anisotropic surfaces in submonolayer growth is systematically studied using kinetic Monte Carlo simulations. It is found that the island-size distribution in anisotropic submonolayer growth exhibits a general dynamic scaling behavior. An analytic expression is proposed for the scaling function, and is compared with the simulation results. This scaling function not only improves previous results for the isotropic growth (1), but also describes the scaling behavior of the island-size distribution in anisotropic submonolayer growth very well (2). 1. J. G. Amar and F. Family, Phys. Rev. Lett. 74, 2066 (1995). 2. M. Z. Li, E. G. Wang, B. G. Liu, and Z. Y. Zhang, Phys. Rev. Lett. (submitted).

  10. Ocean Processes Revealing by Seasonal Dynamics of Surface Chlorophyll Concentration (by Satellite Data)

    NASA Astrophysics Data System (ADS)

    Shevyrnogov, Anatoly; Vysotskaya, Galina

    Continuous monitoring of phytopigment concentrations in the ocean by space-borne methods makes possible to estimate ecological condition of biocenoses in critical areas. Unlike land vege-tation, hydrological processes largely determine phytoplankton dynamics, which may be either recurrent or random. The types of chlorophyll concentration dynamics can manifest as zones quasistationary by seasonal chlorophyll dynamics, perennial variations of phytopigment con-centrations, anomalous variations, etc., that makes possible revealing of hydrological structure of the ocean. While large-scale and frequently occurring phenomena have been much studied, the seldom-occurring changes of small size may be of interest for analysis of long-term processes and rare natural variations. Along with this, the ability to reflect consequences of anthropoge-nous impact or natural ecological disasters on the ocean biota makes the anomalous variations ecologically essential. Civilization aspiring for steady development and preservation of the bio-sphere, must have the knowledge of spatial distribution, seasonal dynamics and anomalies of the primary production process on the planet. In the papers of the authors (Shevyrnogov A.P., Vysotskaya G.S., Gitelzon J.I. Quasistationary areas of chlorophyll concentration in the world ocean as observed satellite data. Adv. Space Res. Vol. 18, No. 7, pp. 129-132, 1996) existence of zones, which are quasi-stationary with similar seasonal dynamics of chlorophyll concentration at surface layer of ocean, was shown. Results were obtained on the base of pro-cessing of time series of satellite images SeaWiFS. It was shown that fronts and frontal zones coincide with dividing lines between quasi-stationary areas, especially in areas of large oceanic streams. Biota of surface oceanic layer is more stable in comparison with quickly changing sur-face temperature. It gives a possibility to circumvent influence of high-frequency component (for example, a diurnal cycle

  11. Surface dating of dynamic landforms: young boulders on aging moraines.

    PubMed

    Hallet, B; Putkonen, J

    1994-08-12

    The dating of landforms is crucial to understanding the evolution, history, and stability of landscapes. Cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces. A pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data. Consideration of the dynamic nature of landforms and of the ever-present processes of erosion, deposition, and weathering leads to a resolution of this inconsistency and, more generally, offers guidance for realistic interpretation of exposure ages.

  12. Structure and Dynamics of Octamethylcyclotetrasiloxane Confined between Mica Surfaces.

    PubMed

    Vadhana, V; Ayappa, K G

    2016-03-24

    Using a molecular model for octamethylcyclotetrasiloxane (OMCTS), molecular dynamics simulations are carried out to probe the phase state of OMCTS confined between two mica surfaces in equilibrium with a reservoir. Molecular dynamics simulations are carried out for elevations ranging from 5 to 35 K above the melting point for the OMCTS model used in this study. The Helmholtz free energy is computed for a specific confinement using the two-phase thermodynamic (2PT) method. Analysis of the in-plane pair correlation functions did not reveal signatures of freezing even under an extreme confinement of two layers. OMCTS is found to orient with a wide distribution of orientations with respect to the mica surface, with a distinct preference for the surface parallel configuration in the contact layers. The self-intermediate scattering function is found to decay with increasing relaxation times as the surface separation is decreased, and the two-step relaxation in the scattering function, a signature of glassy dynamics, distinctly evolves as the temperature is lowered. However, even at 5 K above the melting point, we did not observe a freezing transition and the self-intermediate scattering functions relax within 200 ps for the seven-layered confined system. The self-diffusivity and relaxation times obtained from the Kohlrausch-Williams-Watts stretched exponential fits to the late α-relaxation exhibit power law scalings with the packing fraction as predicted by mode coupling theory. A distinct discontinuity in the Helmholtz free energy, potential energy, and a sharp change in the local bond order parameter, Q4, was observed at 230 K for a five-layered system upon cooling, indicative of a first-order transition. A freezing point depression of about 30 K was observed for this five-layered confined system, and at the lower temperatures, contact layers were found to be disordered with long-range order present only in the inner layers. These dynamical signatures indicate that

  13. Identifying early-warning signals of critical transitions with strong noise by dynamical network markers

    NASA Astrophysics Data System (ADS)

    Liu, Rui; Chen, Pei; Aihara, Kazuyuki; Chen, Luonan

    2015-12-01

    Identifying early-warning signals of a critical transition for a complex system is difficult, especially when the target system is constantly perturbed by big noise, which makes the traditional methods fail due to the strong fluctuations of the observed data. In this work, we show that the critical transition is not traditional state-transition but probability distribution-transition when the noise is not sufficiently small, which, however, is a ubiquitous case in real systems. We present a model-free computational method to detect the warning signals before such transitions. The key idea behind is a strategy: “making big noise smaller” by a distribution-embedding scheme, which transforms the data from the observed state-variables with big noise to their distribution-variables with small noise, and thus makes the traditional criteria effective because of the significantly reduced fluctuations. Specifically, increasing the dimension of the observed data by moment expansion that changes the system from state-dynamics to probability distribution-dynamics, we derive new data in a higher-dimensional space but with much smaller noise. Then, we develop a criterion based on the dynamical network marker (DNM) to signal the impending critical transition using the transformed higher-dimensional data. We also demonstrate the effectiveness of our method in biological, ecological and financial systems.

  14. Dynamics of turbulent transport dominated by the geodesic acoustic mode near the critical gradient regime

    SciTech Connect

    Miki, Kazuhiro; Kishimoto, Yasuaki; Li, Jiquan; Miyato, Naoaki

    2008-05-15

    The effects of geodesic acoustic modes (GAMs) on the toroidal ion temperature gradient turbulence and associated transport near the critical gradient regime in tokamak plasma are investigated based on global Landau-fluid simulations and extended predator-prey modeling analyses. A new type of intermittent dynamics of transport accompanied with the emission and propagation of the GAMs, i.e., GAM intermittency [K. Miki et al., Phys. Rev. Lett. 99, 145003 (2007)], has been found. The intermittent bursts are triggered by the onset of spatially propagating GAMs when the turbulent energy exceeds a critical value. The GAMs suffer collisionless damping during the propagation and nonlocally transfer local turbulence energy to wide radial region. The stationary zonal flows gradually increase due to the accumulation of non-damped residual part over many periods of quasi-periodic intermittent bursts and eventually quench the turbulence, leading to a nonlinear upshift of the linear critical gradient; namely, the Dimits shift. This process is categorized as a new class of transient dynamics, referred to as growing intermittency. The Dimits shift is found to be established through this dynamical process. An extended minimal predator-prey model with collisionless damping of the GAMs is proposed, which qualitatively reproduce the main features of the growing intermittency and approximately predict its various time scales observed in the simulations.

  15. Critical Dynamics of The Classical 3-D Heisenberg Antiferromagnet with Anisotropy

    NASA Astrophysics Data System (ADS)

    Bunker, Alex; Chen, Kun; Landau, D. P.

    1997-03-01

    Using large scale Monte Carlo and spin-dynamics techniques^1 we studied the dynamic behavior of the body-centered cubic classical Heisenberg antiferromagnet with single site anisotropy. In order to directly compare our results to experiment, we set the anisotropy to match that found^2 in FeF2 (strong anisotropy) and MnF2 (weak anisotropy). We determined the form of the dynamic structure factor, S(q,ω), at Tc and found agreement with experiment^3 and theory^4 which indicate a strong diffusive longitudinal component that is critical and a weak, non-critical propagative transverse component. Supported in part by the NSF ^**current address: Solid State Division, ORNL ^1 K. Chen, D. P. Landau, Phys. Rev. B \\underline49, 3266, (1994) ^2 J. Als-Nielsen in Phase Transitions and Critical Phenomena, \\underline5A, C. Domb, M. S. Green, (Academic Press, 1976) ^3 M. P. Schulhof et. al., Phys. Rev. B \\underline1, 2304, (1970) ^4 S. W. Lovesey, E. Balcar, J. Phys. Cond. Matt. \\underline7, 2147, (1995)

  16. Identifying early-warning signals of critical transitions with strong noise by dynamical network markers.

    PubMed

    Liu, Rui; Chen, Pei; Aihara, Kazuyuki; Chen, Luonan

    2015-12-09

    Identifying early-warning signals of a critical transition for a complex system is difficult, especially when the target system is constantly perturbed by big noise, which makes the traditional methods fail due to the strong fluctuations of the observed data. In this work, we show that the critical transition is not traditional state-transition but probability distribution-transition when the noise is not sufficiently small, which, however, is a ubiquitous case in real systems. We present a model-free computational method to detect the warning signals before such transitions. The key idea behind is a strategy: "making big noise smaller" by a distribution-embedding scheme, which transforms the data from the observed state-variables with big noise to their distribution-variables with small noise, and thus makes the traditional criteria effective because of the significantly reduced fluctuations. Specifically, increasing the dimension of the observed data by moment expansion that changes the system from state-dynamics to probability distribution-dynamics, we derive new data in a higher-dimensional space but with much smaller noise. Then, we develop a criterion based on the dynamical network marker (DNM) to signal the impending critical transition using the transformed higher-dimensional data. We also demonstrate the effectiveness of our method in biological, ecological and financial systems.

  17. Identifying early-warning signals of critical transitions with strong noise by dynamical network markers

    PubMed Central

    Liu, Rui; Chen, Pei; Aihara, Kazuyuki; Chen, Luonan

    2015-01-01

    Identifying early-warning signals of a critical transition for a complex system is difficult, especially when the target system is constantly perturbed by big noise, which makes the traditional methods fail due to the strong fluctuations of the observed data. In this work, we show that the critical transition is not traditional state-transition but probability distribution-transition when the noise is not sufficiently small, which, however, is a ubiquitous case in real systems. We present a model-free computational method to detect the warning signals before such transitions. The key idea behind is a strategy: “making big noise smaller” by a distribution-embedding scheme, which transforms the data from the observed state-variables with big noise to their distribution-variables with small noise, and thus makes the traditional criteria effective because of the significantly reduced fluctuations. Specifically, increasing the dimension of the observed data by moment expansion that changes the system from state-dynamics to probability distribution-dynamics, we derive new data in a higher-dimensional space but with much smaller noise. Then, we develop a criterion based on the dynamical network marker (DNM) to signal the impending critical transition using the transformed higher-dimensional data. We also demonstrate the effectiveness of our method in biological, ecological and financial systems. PMID:26647650

  18. Surface conductivity dependent dynamic behaviour of an ultrafine atmospheric pressure plasma jet for microscale surface processing

    NASA Astrophysics Data System (ADS)

    Abuzairi, Tomy; Okada, Mitsuru; Bhattacharjee, Sudeep; Nagatsu, Masaaki

    2016-12-01

    An experimental study on the dynamic behaviour of microcapillary atmospheric pressure plasma jets (APPJs) with 5 μm tip size for surfaces of different conductivity is reported. Electrical and spatio-temporal characteristics of the APPJs are monitored using high voltage probe, current monitor and high speed intensified charge couple device camera. From these experimental results, we presented a simple model to understand the electrical discharge characteristics of the capillary APPJs with double electrodes, and estimated the velocity of the ionization fronts in the jet and the electron density to be 3.5-4.2 km/s and 2-7 × 1017 m-3. By analyzing the dynamics of the microcapillary APPJs for different substrate materials, it was found that the surface irradiation area strongly depended on the substrate conductivity and permittivity, especially in the case of polymer-like substrate, surface irradiation area was significantly broadened probably due to the repelling behaviour of the plasma jets from the accumulated electrical charges on the polymer surface. The effect of applying a substrate bias in the range from -900 V to +900 V on the plasma irradiation onto the substrates was also investigated. From the knowledge of the present results, it is helpful for choosing the substrate materials for microscale surface modification.

  19. Nonequilibrium critical dynamics of the two-dimensional Ashkin-Teller model at the Baxter line

    NASA Astrophysics Data System (ADS)

    Fernandes, H. A.; da Silva, R.; Caparica, A. A.; de Felício, J. R. Drugowich

    2017-04-01

    We investigate the short-time universal behavior of the two-dimensional Ashkin-Teller model at the Baxter line by performing time-dependent Monte Carlo simulations. First, as preparatory results, we obtain the critical parameters by searching the optimal power-law decay of the magnetization. Thus, the dynamic critical exponents θm and θp, related to the magnetic and electric order parameters, as well as the persistence exponent θg, are estimated using heat-bath Monte Carlo simulations. In addition, we estimate the dynamic exponent z and the static critical exponents β and ν for both order parameters. We propose a refined method to estimate the static exponents that considers two different averages: one that combines an internal average using several seeds with another, which is taken over temporal variations in the power laws. Moreover, we also performed the bootstrapping method for a complementary analysis. Our results show that the ratio β /ν exhibits universal behavior along the critical line corroborating the conjecture for both magnetization and polarization.

  20. Novel dynamic flux chamber for measuring air-surface exchange of Hg(o) from soils.

    PubMed

    Lin, Che-Jen; Zhu, Wei; Li, Xianchang; Feng, Xinbin; Sommar, Jonas; Shang, Lihai

    2012-08-21

    Quantifying the air-surface exchange of Hg(o) from soils is critical to understanding the cycling of mercury in different environmental compartments. Dynamic flux chambers (DFCs) have been widely employed for Hg(o) flux measurement over soils. However, DFCs of different sizes, shapes, and sampling flow rates yield distinct measured fluxes for a soil substrate under identical environmental conditions. In this study, we performed an integrated modeling, laboratory and field study to design a DFC capable of producing a steady and uniform air flow over a flat surface. The new DFC was fabricated using polycarbonate sheets. The internal velocity field was experimentally verified against model predictions using both theoretical and computational fluid dynamics techniques, suggesting fully developed flow with velocity profiles in excellent agreement with model results. Laboratory flux measurements demonstrated that the new design improves data reproducibility as compared to a conventional DFC, and reproduces the model-predicted flux trend with increasing sampling flow. A mathematical relationship between the sampling flow rate and surface friction velocity, a variable commonly parametrized in atmospheric models, was developed for field application. For the first time, the internal shear property of a DFC can be precisely controlled using the sampling flow rate, and the flux under atmospheric condition can be inferred from the measured flux and surface shear property. The demonstrated methodology potentially bridges the gap in measured fluxes obtained by the DFC method and the micrometeorological methods.

  1. Wetting dynamics of colloidal dispersions on agar gel surfaces.

    PubMed

    Seino, Eri; Chida, Shigeki; Mayama, Hiroyuki; Hotta, Jun-ichi; Nonomura, Yoshimune

    2014-10-01

    The effects of silica particle addition on the wetting velocity on flat and fractal agar gel surfaces were analyzed along with the applicability of such particles for controlling the wetting dynamics of water. The contact angles (θD) of the colloidal dispersions obeyed the power law, i.e., θD∝t(-x), where t is time and x is a constant. Wetting was inhibited by the addition of a suitable amount of 20-nm-diameter silica particles. Specifically, the exponent x reached a minimum value for a silica composition of 0.1wt%. However, such inhibition effects were not observed upon the addition of silica particles with diameters of 100, 550, and, 1000nm. The mechanism of the inhibition of the liquid wetting on gel surfaces may be attributed to a slight increase in local viscosity around the contact line during wetting. Copyright © 2014 Elsevier B.V. All rights reserved.

  2. Drops subjected to surface acoustic waves: flow dynamics

    NASA Astrophysics Data System (ADS)

    Brunet, Philippe; Baudoin, Michael; Bou Matar, Olivier; Dynamique Des Systèmes Hors Equilibre Team; Aiman-Films Team

    2012-11-01

    Ultrasonic acoustic waves of frequency beyond the MHz are known to induce streaming flow in fluids that can be suitable to perform elementary operations in microfluidics systems. One of the currently appealing geometry is that of a sessile drop subjected to surface acoustic waves (SAW). Such Rayleigh waves produce non-trival actuation in the drop leading to internal flow, drop displacement, free-surface oscillations and atomization. We recently carried out experiments and numerical simulations that allowed to better understand the underlying physical mechanisms that couple acoustic propagation and fluid actuation. We varied the frequency and amplitude of actuation, as well as the properties of the fluid, and we measured the effects of these parameters on the dynamics of the flow. We compared these results to finite-elements numerical simulations.

  3. Critical dynamics of self-gravitating Langevin particles and bacterial populations.

    PubMed

    Sire, Clément; Chavanis, Pierre-Henri

    2008-12-01

    We study the critical dynamics of the generalized Smoluchowski-Poisson system (for self-gravitating Langevin particles) or generalized Keller-Segel model (for the chemotaxis of bacterial populations). These models [P. H. Chavanis and C. Sire, Phys. Rev. E 69, 016116 (2004)] are based on generalized stochastic processes leading to the Tsallis statistics. The equilibrium states correspond to polytropic configurations with index n similar to polytropic stars in astrophysics. At the critical index n_{3}=d(d-2) (where d>or=2 is the dimension of space), there exists a critical temperature Theta_{c} (for a given mass) or a critical mass M_{c} (for a given temperature). For Theta>Theta_{c} or MM_{c} the system collapses and forms, in a finite time, a Dirac peak containing a finite fraction M_{c} of the total mass surrounded by a halo. We study these regimes numerically and, when possible, analytically by looking for self-similar or pseudo-self-similar solutions. This study extends the critical dynamics of the ordinary Smoluchowski-Poisson system and Keller-Segel model in d=2 corresponding to isothermal configurations with n_{3}-->+infinity . We also stress the analogy between the limiting mass of white dwarf stars (Chandrasekhar's limit) and the critical mass of bacterial populations in the generalized Keller-Segel model of chemotaxis.

  4. Dynamic growth of slip surfaces in catastrophic landslides

    PubMed Central

    Germanovich, Leonid N.; Kim, Sihyun; Puzrin, Alexander M.

    2016-01-01

    This work considers a landslide caused by the shear band that emerges along the potential slip (rupture) surface. The material above the band slides downwards, causing the band to grow along the slope. This growth may first be stable (progressive), but eventually becomes dynamic (catastrophic). The landslide body acquires a finite velocity before it separates from the substrata. The corresponding initial-boundary value problem for a dynamic shear band is formulated within the framework of Palmer & Rice's (Proc. R. Soc. Lond. A 332, 527–548. (doi:10.1098/rspa.1973.0040)) approach, which is generalized to the dynamic case. We obtain the exact, closed-form solution for the band velocity and slip rate. This solution assesses when the slope fails owing to a limiting condition near the propagating tip of the shear band. Our results are applicable to both submarine and subaerial landslides of this type. It appears that neglecting dynamic (inertia) effects can lead to a significant underestimation of the slide size, and that the volumes of catastrophic slides can exceed the volumes of progressive slides by nearly a factor of 2. As examples, we consider the Gaviota and Humboldt slides offshore of California, and discuss landslides in normally consolidated sediments and sensitive clays. In particular, it is conceivable that Humboldt slide is unfinished and may still displace a large volume of sediments, which could generate a considerable tsunami. We show that in the case of submarine slides, the effect of water resistance on the shear band dynamics may frequently be limited during the slope failure stage. For a varying slope angle, we formulate a condition of slide cessation. PMID:26997904

  5. Dynamic growth of slip surfaces in catastrophic landslides.

    PubMed

    Germanovich, Leonid N; Kim, Sihyun; Puzrin, Alexander M

    2016-01-01

    This work considers a landslide caused by the shear band that emerges along the potential slip (rupture) surface. The material above the band slides downwards, causing the band to grow along the slope. This growth may first be stable (progressive), but eventually becomes dynamic (catastrophic). The landslide body acquires a finite velocity before it separates from the substrata. The corresponding initial-boundary value problem for a dynamic shear band is formulated within the framework of Palmer & Rice's (Proc. R. Soc. Lond. A332, 527-548. (doi:10.1098/rspa.1973.0040)) approach, which is generalized to the dynamic case. We obtain the exact, closed-form solution for the band velocity and slip rate. This solution assesses when the slope fails owing to a limiting condition near the propagating tip of the shear band. Our results are applicable to both submarine and subaerial landslides of this type. It appears that neglecting dynamic (inertia) effects can lead to a significant underestimation of the slide size, and that the volumes of catastrophic slides can exceed the volumes of progressive slides by nearly a factor of 2. As examples, we consider the Gaviota and Humboldt slides offshore of California, and discuss landslides in normally consolidated sediments and sensitive clays. In particular, it is conceivable that Humboldt slide is unfinished and may still displace a large volume of sediments, which could generate a considerable tsunami. We show that in the case of submarine slides, the effect of water resistance on the shear band dynamics may frequently be limited during the slope failure stage. For a varying slope angle, we formulate a condition of slide cessation.

  6. Pseudospectral Gaussian quantum dynamics: Efficient sampling of potential energy surfaces.

    PubMed

    Heaps, Charles W; Mazziotti, David A

    2016-04-28

    Trajectory-based Gaussian basis sets have been tremendously successful in describing high-dimensional quantum molecular dynamics. In this paper, we introduce a pseudospectral Gaussian-based method that achieves accurate quantum dynamics using efficient, real-space sampling of the time-dependent basis set. As in other Gaussian basis methods, we begin with a basis set expansion using time-dependent Gaussian basis functions guided by classical mechanics. Unlike other Gaussian methods but characteristic of the pseudospectral and collocation methods, the basis set is tested with N Dirac delta functions, where N is the number of basis functions, rather than using the basis function as test functions. As a result, the integration for matrix elements is reduced to function evaluation. Pseudospectral Gaussian dynamics only requires O(N) potential energy calculations, in contrast to O(N(2)) evaluations in a variational calculation. The classical trajectories allow small basis sets to sample high-dimensional potentials. Applications are made to diatomic oscillations in a Morse potential and a generalized version of the Henon-Heiles potential in two, four, and six dimensions. Comparisons are drawn to full analytical evaluation of potential energy integrals (variational) and the bra-ket averaged Taylor (BAT) expansion, an O(N) approximation used in Gaussian-based dynamics. In all cases, the pseudospectral Gaussian method is competitive with full variational calculations that require a global, analytical, and integrable potential energy surface. Additionally, the BAT breaks down when quantum mechanical coherence is particularly strong (i.e., barrier reflection in the Morse oscillator). The ability to obtain variational accuracy using only the potential energy at discrete points makes the pseudospectral Gaussian method a promising avenue for on-the-fly dynamics, where electronic structure calculations become computationally significant.

  7. Collective non-equilibrium dynamics at surfaces and the spatio-temporal edge

    NASA Astrophysics Data System (ADS)

    Marcuzzi, M.; Gambassi, A.; Pleimling, M.

    2012-11-01

    Symmetries represent a fundamental constraint for physical systems and relevant new phenomena often emerge as a consequence of their breaking. An important example is provided by space- and time-translational invariance in statistical systems, which hold at a coarse-grained scale in equilibrium and are broken by spatial and temporal boundaries, the former being implemented by surfaces —unavoidable in real samples— the latter by some initial condition for the dynamics which causes a non-equilibrium evolution. While the separate effects of these two boundaries are well understood, we demonstrate here that additional, unexpected features arise upon approaching the effective edge formed by their intersection. For this purpose, we focus on the classical semi-infinite Ising model with spin-flip dynamics evolving out of equilibrium at its critical point. Considering both subcritical and critical values of the coupling among surface spins, we present numerical evidence of a scaling regime with universal features which emerges upon approaching the spatio-temporal edge and we rationalise these findings within a field-theoretical approach.

  8. A highly accurate dynamic contact angle algorithm for drops on inclined surface based on ellipse-fitting.

    PubMed

    Xu, Z N; Wang, S Y

    2015-02-01

    To improve the accuracy in the calculation of dynamic contact angle for drops on the inclined surface, a significant number of numerical drop profiles on the inclined surface with different inclination angles, drop volumes, and contact angles are generated based on the finite difference method, a least-squares ellipse-fitting algorithm is used to calculate the dynamic contact angle. The influences of the above three factors are systematically investigated. The results reveal that the dynamic contact angle errors, including the errors of the left and right contact angles, evaluated by the ellipse-fitting algorithm tend to increase with inclination angle/drop volume/contact angle. If the drop volume and the solid substrate are fixed, the errors of the left and right contact angles increase with inclination angle. After performing a tremendous amount of computation, the critical dimensionless drop volumes corresponding to the critical contact angle error are obtained. Based on the values of the critical volumes, a highly accurate dynamic contact angle algorithm is proposed and fully validated. Within nearly the whole hydrophobicity range, it can decrease the dynamic contact angle error in the inclined plane method to less than a certain value even for different types of liquids.

  9. Molecular dynamics simulation of UO 2 nanocrystals surface

    NASA Astrophysics Data System (ADS)

    Boyarchenkov, A. S.; Potashnikov, S. I.; Nekrasov, K. A.; Kupryazhkin, A. Ya.

    2012-02-01

    In this article we investigated surface of nanocrystals (NCs) of uranium dioxide (UO 2) using molecular dynamics (MD) under isolated (non-periodic) boundary conditions in the approximation of rigid ions and pair potentials (RIPI). It is shown that a cubic shape of NCs is metastable and equilibrium is reached in the process of structural relaxation to the octahedral shape during long simulations of 1000 ns (200 million MD steps), which increase with the size of NC. We measured the size dependences of the lattice parameter and the surface energy density of cubic and octahedral NCs with volumes up to 1000 nm 3 (50 000 particles) at temperatures of 2200 K and 2300 K. For the surfaces {1 0 0} and {1 1 1} we obtained the energy densities σ100 = 1.60 ± 0.02 J/m 2, σ111 = 1.14 ± 0.03 J/m 2 and surface tension constant γ111 = 0.841 ± 0.008 J/m 2. The resulting ratio of σ100/ σ111 = 1.41 ± 0.04 within the error coincides with the experimental value of 1.42 ± 0.05 measured for microscopic cavities in UO 2 monocrystals.

  10. Can foot anthropometric measurements predict dynamic plantar surface contact area?

    PubMed

    McPoil, Thomas G; Vicenzino, Bill; Cornwall, Mark W; Collins, Natalie

    2009-10-28

    Previous studies have suggested that increased plantar surface area, associated with pes planus, is a risk factor for the development of lower extremity overuse injuries. The intent of this study was to determine if a single or combination of foot anthropometric measures could be used to predict plantar surface area. Six foot measurements were collected on 155 subjects (97 females, 58 males, mean age 24.5 +/- 3.5 years). The measurements as well as one ratio were entered into a stepwise regression analysis to determine the optimal set of measurements associated with total plantar contact area either including or excluding the toe region. The predicted values were used to calculate plantar surface area and were compared to the actual values obtained dynamically using a pressure sensor platform. A three variable model was found to describe the relationship between the foot measures/ratio and total plantar contact area (R2 = 0.77, p < 0.0001)). A three variable model was also found to describe the relationship between the foot measures/ratio and plantar contact area minus the toe region (R2 = 0.76, p < 0.0001). The results of this study indicate that the clinician can use a combination of simple, reliable, and time efficient foot anthropometric measurements to explain over 75% of the plantar surface contact area, either including or excluding the toe region.

  11. Dynamic surface tension of surfactant TA: experiments and theory.

    PubMed

    Otis, D R; Ingenito, E P; Kamm, R D; Johnson, M

    1994-12-01

    A bubble surfactometer was used to measure the surface tension of an aqueous suspension of surfactant TA as a function of bubble area over a range of cycling rates and surfactant bulk concentrations. Results of the surface tension-interfacial area loops exhibited a rich variety of phenomena, the character of which varied systematically with frequency and bulk concentration. A model was developed to interpret and explain these data and for use in describing the dynamics of surface layers under more general circumstances. Surfactant was modeled as a single component with surface tension taken to depend on only the interfacial surfactant concentration. Two distinct mechanisms were considered for the exchange of surfactant between the bulk phase and interface. The first is described by a simple kinetic relationship for adsorption and desorption that pertains only when the interfacial concentration is below its maximum equilibrium value. The second mechanism is "squeeze-out" by which surfactant molecules are expelled from an interface compressed past a maximum packing state. The model provided good agreement with experimental measurements for cycling rates from 1 to 100 cycles/min and for bulk concentrations between 0.0073 and 7.3 mg/ml.

  12. Dynamic and reversible surface topography influences cell morphology.

    PubMed

    Kiang, Jennifer D; Wen, Jessica H; del Álamo, Juan C; Engler, Adam J

    2013-08-01

    Microscale and nanoscale surface topography changes can influence cell functions, including morphology. Although in vitro responses to static topography are novel, cells in vivo constantly remodel topography. To better understand how cells respond to changes in topography over time, we developed a soft polyacrylamide hydrogel with magnetic nickel microwires randomly oriented in the surface of the material. Varying the magnetic field around the microwires reversibly induced their alignment with the direction of the field, causing the smooth hydrogel surface to develop small wrinkles; changes in surface roughness, ΔRRMS , ranged from 0.05 to 0.70 μm and could be oscillated without hydrogel creep. Vascular smooth muscle cell morphology was assessed when exposed to acute and dynamic topography changes. Area and shape changes occurred when an acute topographical change was imposed for substrates exceeding roughness of 0.2 μm, but longer-term oscillating topography did not produce significant changes in morphology irrespective of wire stiffness. These data imply that cells may be able to use topography changes to transmit signals as they respond immediately to changes in roughness. Copyright © 2013 Wiley Periodicals, Inc.

  13. Criticality in large-scale brain FMRI dynamics unveiled by a novel point process analysis.

    PubMed

    Tagliazucchi, Enzo; Balenzuela, Pablo; Fraiman, Daniel; Chialvo, Dante R

    2012-01-01

    Functional magnetic resonance imaging (fMRI) techniques have contributed significantly to our understanding of brain function. Current methods are based on the analysis of gradual and continuous changes in the brain blood oxygenated level dependent (BOLD) signal. Departing from that approach, recent work has shown that equivalent results can be obtained by inspecting only the relatively large amplitude BOLD signal peaks, suggesting that relevant information can be condensed in discrete events. This idea is further explored here to demonstrate how brain dynamics at resting state can be captured just by the timing and location of such events, i.e., in terms of a spatiotemporal point process. The method allows, for the first time, to define a theoretical framework in terms of an order and control parameter derived from fMRI data, where the dynamical regime can be interpreted as one corresponding to a system close to the critical point of a second order phase transition. The analysis demonstrates that the resting brain spends most of the time near the critical point of such transition and exhibits avalanches of activity ruled by the same dynamical and statistical properties described previously for neuronal events at smaller scales. Given the demonstrated functional relevance of the resting state brain dynamics, its representation as a discrete process might facilitate large-scale analysis of brain function both in health and disease.

  14. Effect of Molecular Architecture on Polymer Melt Surface Dynamics

    NASA Astrophysics Data System (ADS)

    Foster, Mark

    The dynamics of the thermally stimulated surface height fluctuations in a polymer melt dictate wetting, adhesion, and tribology at that surface. These surface fluctuations can be profoundly altered by tethering of the chains. One type of tethering is the tethering of one part of a molecule to another part of the same molecule. This tethering is found in both long chain branched polymers and in macrocycles. We have studied the surface fluctuations with X-ray Photon Correlation Spectroscopy for melts of well-defined, anionically polymerized polystyrenes of various architectures, including linear, 6 arm star, pom-pom, comb and cyclic architectures. For linear chains, the variation of surface relaxation time with in-plane scattering vector can be fit using a hydrodynamic continuum theory (HCT) of thermally stimulated capillary waves that knows nothing of the chain architecture. Assuming the theory is applicable, apparent viscosities of the films may then be inferred from the XPCS data. For unentangled linear chains, the viscosity inferred from XPCS data in this manner is the same as that measured by conventional bulk rheometry. The HCT does a reasonable job of describing the variation of relaxation time with scattering vector for long branched chains also, but only if a viscosity much larger than that of the bulk is assumed. The discrepancy between the viscosity inferred from surface relaxation times using the HCT and that derived from conventional rheometry grows larger as the bulk Tg is approached and is different for each long chain branched architecture. However, for densely branched combs and cyclic chains different behaviors are found. Acknowledgement: Thanks to NSF (CBET 0730692) and the Advanced Photon Source, supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Science, under Contract No. W-31-109-ENG-38.

  15. Molecular dynamics simulation of silicate glasses and their surfaces

    NASA Astrophysics Data System (ADS)

    Yuan, Xianglong

    1999-12-01

    The bulk and surface structures of vitreous silica and silicate glasses have been modeled using the molecular dynamics technique. An extensive preliminary study, on the influences of different potential models and of different simulation approaches on the final bulk and surface structures, concludes that good result can be obtained using the constant volume simulation with a modified pair-wise potential from van Beest and coworkers, together with alkali-oxygen potential models developed in this study. Glass structures with the reliability factors, Rchi of 7.2% for vitreous silica and 5.6% for sodium silicate have been achieved. The environments of O, Si and Na in silicate glasses have been thoroughly examined. Considerable similarities in local structures exist between crystalline and the simulated glass structures. It is found that our simulated glasses more resemble high-pressured experimental glasses, which is implied by the existence of fivefold silicon species. Based on bulk structures studied, glass surfaces were created by a fracture process. It is speculated that surface defect concentrations depend on the topological characteristics of the network structure, and are essential for the viability of surfaces. Analysis of local structures for difference species implies that the sodium silicate surfaces resemble more the Na-rich regions in the bulk structures. An efficient algorithm for finding primitive rings in a topological network has been developed. Analysis using this algorithm shows that reconstruction of Na-rich regions occurs on extending simulation size, demonstrating simulation size influence on modeled glass structures. Finally, our detailed analysis of Si-O-Si bond angle distributions demonstrates that vitreous silica glass has a broader Si-O-Si BAD, whilst sodium silicate glasses favor narrower distributions.

  16. Surface dynamics of voltage-gated ion channels

    PubMed Central

    Heine, Martin; Ciuraszkiewicz, Anna; Voigt, Andreas; Heck, Jennifer; Bikbaev, Arthur

    2016-01-01

    ABSTRACT Neurons encode information in fast changes of the membrane potential, and thus electrical membrane properties are critically important for the integration and processing of synaptic inputs by a neuron. These electrical properties are largely determined by ion channels embedded in the membrane. The distribution of most ion channels in the membrane is not spatially uniform: they undergo activity-driven changes in the range of minutes to days. Even in the range of milliseconds, the composition and topology of ion channels are not static but engage in highly dynamic processes including stochastic or activity-dependent transient association of the pore-forming and auxiliary subunits, lateral diffusion, as well as clustering of different channels. In this review we briefly discuss the potential impact of mobile sodium, calcium and potassium ion channels and the functional significance of this for individual neurons and neuronal networks. PMID:26891382

  17. Dual characterization of critical fluctuations: Density functional theory & nonlinear dynamics close to a tangent bifurcation

    NASA Astrophysics Data System (ADS)

    Riquelme-Galván, Mauricio; Robledo, Alberto

    2017-02-01

    We improve on the description of the relationship that exists between critical clusters in thermal systems and intermittency near the onset of chaos in low-dimensional systems. We make use of the statistical-mechanical language of inhomogeneous systems and of the renormalization group (RG) method in nonlinear dynamics to provide a more accurate, formal, approach to the subject. The description of this remarkable correspondence encompasses, on the one hand, the density functional formalism, where classical and quantum mechanical analogues match the procedure for one-dimensional clusters, and, on the other, the RG fixed-point map of functional compositions that captures the essential dynamical behavior. We provide details of how the above-referred theoretical approaches interrelate and discuss the implications of the correspondence between the high-dimensional (degrees of freedom) phenomenon and low-dimensional dynamics.

  18. Linking Weathering, Rock Moisture Dynamics, Geochemistry, Runoff, Vegetation and Atmospheric Processes through the Critical Zone: Graduate Student led Research at the Eel River Critical Zone Observatory

    NASA Astrophysics Data System (ADS)

    Dietrich, W. E.

    2014-12-01

    In the Eel River Critical Zone Observatory lies Rivendell, a heavily-instrumented steep forested hillslope underlain by nearly vertically dipping argillite interbedded with sandstone. Under this convex hillslope lies "Zb", the transition to fresh bedrock, which varies from less than 6 m below the surface near the channel to 20 m at the divide. Rempe and Dietrich (2014, PNAS) show that the Zb profile can be predicted from the assumption that weathering occurs when drainage is induced in the uplifting fresh bedrock under hillslopes by lateral head gradients driven by channel incision at the hillslope boundary. Infiltrating winter precipitation is impeded at the lower conductivity boundary at Zb, generating perched groundwater that dynamically pulses water laterally to the channel, controlling stream runoff. Below the soil and above the water table lies an unsaturated zone through which all recharge to the perched groundwater (and thus all runoff to channels) occurs. It is this zone and the waters in them that profoundly affect critical zone processes. In our seasonally dry environment, the first rains penetrate past the soil and moisten the underlying weathered bedrock (Salve et al., 2012, WRR). It takes about 200 to 400 mm of cumulative rain, however, before the underlying groundwater rises significantly. Oshun et al (in review) show that by this cumulative rainfall the average of the wide-ranging isotopic signature of rain reaches a nearly constant average annual value. Consequently, the recharging perched groundwater shows only minor temporal isotopic variation. Kim et al, (2014, GCA) find that the winter high-flow groundwater chemistry is controlled by relatively fast-reacting cation exchange processes, likely occurring in transit in the unsaturated zone. Oshun also demonstrates that the Douglas fir rely on this rock moisture as a water source, while the broadleaf trees (oaks and madrone) use mostly soil moisture. Link et al (2014 WRR) show that Doug fir declines

  19. Critical CuI buffer layer surface density for organic molecular crystal orientation change

    SciTech Connect

    Ahn, Kwangseok; Kim, Jong Beom; Lee, Dong Ryeol; Kim, Hyo Jung; Lee, Hyun Hwi

    2015-01-21

    We have determined the critical surface density of the CuI buffer layer inserted to change the preferred orientation of copper phthalocyanine (CuPc) crystals grown on the buffer layer. X-ray reflectivity measurements were performed to obtain the density profiles of the buffer layers and out-of-plane and 2D grazing-incidence X-ray diffraction measurements were performed to determine the preferred orientations of the molecular crystals. Remarkably, it was found that the preferred orientation of the CuPc film is completely changed from edge-on (1 0 0) to face-on (1 1 −2) by a CuI buffer layer with a very low surface density, so low that a large proportion of the substrate surface is bare.

  20. Movement, demographics, and occupancy dynamics of a federally-threatened salamander: evaluating the adequacy of critical habitat.

    PubMed

    Bendik, Nathan F; McEntire, Kira D; Sissel, Blake N

    2016-01-01

    Critical habitat for many species is often limited to occupied localities. For rare and cryptic species, or those lacking sufficient data, occupied habitats may go unrecognized, potentially hindering species recovery. Proposed critical habitat for the aquatic Jollyville Plateau salamander (Eurycea tonkawae) and two sister species were delineated based on the assumption that surface habitat is restricted to springs and excludes intervening stream reaches. To test this assumption, we performed two studies to understand aspects of individual, population, and metapopulation ecology of E. tonkawae. First, we examined movement and population demographics using capture-recapture along a spring-influenced stream reach. We then extended our investigation of stream habitat use with a study of occupancy and habitat dynamics in multiple headwater streams. Indications of extensive stream channel use based on capture-recapture results included frequent movements of >15 m, and high juvenile abundance downstream of the spring. Initial occupancy of E. tonkawae was associated with shallow depths, maidenhair fern presence and low temperature variation (indicative of groundwater influence), although many occupied sites were far from known springs. Additionally, previously dry sites were three times more likely to be colonized than wet sites. Our results indicate extensive use of stream habitats, including intermittent ones, by E. tonkawae. These areas may be important for maintaining population connectivity or even as primary habitat patches. Restricting critical habitat to occupied sites will result in a mismatch with actual habitat use, particularly when assumptions of habitat use are untested, thus limiting the potential for recovery.

  1. Movement, demographics, and occupancy dynamics of a federally-threatened salamander: evaluating the adequacy of critical habitat

    PubMed Central

    McEntire, Kira D.; Sissel, Blake N.

    2016-01-01

    Critical habitat for many species is often limited to occupied localities. For rare and cryptic species, or those lacking sufficient data, occupied habitats may go unrecognized, potentially hindering species recovery. Proposed critical habitat for the aquatic Jollyville Plateau salamander (Eurycea tonkawae) and two sister species were delineated based on the assumption that surface habitat is restricted to springs and excludes intervening stream reaches. To test this assumption, we performed two studies to understand aspects of individual, population, and metapopulation ecology of E. tonkawae. First, we examined movement and population demographics using capture-recapture along a spring-influenced stream reach. We then extended our investigation of stream habitat use with a study of occupancy and habitat dynamics in multiple headwater streams. Indications of extensive stream channel use based on capture-recapture results included frequent movements of >15 m, and high juvenile abundance downstream of the spring. Initial occupancy of E. tonkawae was associated with shallow depths, maidenhair fern presence and low temperature variation (indicative of groundwater influence), although many occupied sites were far from known springs. Additionally, previously dry sites were three times more likely to be colonized than wet sites. Our results indicate extensive use of stream habitats, including intermittent ones, by E. tonkawae. These areas may be important for maintaining population connectivity or even as primary habitat patches. Restricting critical habitat to occupied sites will result in a mismatch with actual habitat use, particularly when assumptions of habitat use are untested, thus limiting the potential for recovery. PMID:26998413

  2. The emergence of topographic steady state in a perpetually dynamic self-organized critical landscape

    NASA Astrophysics Data System (ADS)

    Reinhardt, Liam; Ellis, Michael A.

    2015-07-01

    We conducted a series of four physical modeling experiments of mountain growth at differing rates of uplift and three distinct climates ranging from relatively wet to relatively dry. The spatial and temporal pattern of landscape behavior is characterized by ˜f-1 scaling in sediment discharge and power law scaling in the magnitude and frequency of ridge movement in all four experiments. We find that internally generated self-organized critical (SOC) processes generate dynamically stable catchment geometries after ˜1 relief depths of erosion: these regularly spaced catchments have an average outlet-spacing ratio of 2.16, well within the range of values reported in field studies. Once formed, large catchment bounding ridges oscillate about a critically balanced mean location, with occasional large-scale changes in catchment size. Ridge movement appears to be driven by the competition for discharge as landslides push ridges back and forth. These dynamics lead to the emergence of a complex twofold scaling in catchment dynamics that is fully established by 1.8 relief depths of erosion; at this stage, a clear threshold has emerged separating two distinct scaling regimes, where large ridge mobility is insensitive to relief and small ridge mobility is relief dependent. Overall, we demonstrate that the development of dynamically stable large-scale landforms is related to the emergence of a complex-system hierarchy in topographic dynamics. Once formed, these landscapes do not evolve; statistical properties such as average topography and discharge become stationary while topography remains highly dynamic at smaller length scales.

  3. Flexible star polymer chain adsorption by a flat surface: a molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zenak, Siham; Guenachi, Aicha; Sabeur, Sid Ahmed

    2016-08-01

    In this work, we have studied the adsorption of a single flexible star polymer chain by a flat surface. The molecular dynamics simulation has been validated for the case of a free star polymer chain using the diffusion experiment. The scaling laws found are in agreement with the Flory theory predictions and the Rouse model. For the adsorption, preliminary results were obtained for chains of different sizes N=31 to N=199 and different functionalities (f=3,4,6,8,10). For the case of semi-flexible star polymer chains, further investigation is needed to locate the critical point of adsorption when varying the potential interaction strength between the chain and the surface.

  4. Body surface adaptations to boundary-layer dynamics.

    PubMed

    Videler, J J

    1995-01-01

    Evolutionary processes have adapted nektonic animals to interact efficiently with the water that surrounds them. Not all these adaptations serve the same purpose. This paper concentrates on reduction of drag due to friction in the boundary layer close to the body surface. Mucus, compliant skins, scales, riblets and roughness may influence the flow velocity gradient, the type of flow and the thickness of the boundary layer around animals, and may seriously affect their drag in a positive or negative way. The long-chain polymers found in mucus decrease the pressure gradient and considerably reduced drag due to friction. The effect is probably due to channelling of the flow particles in the direction of the main flow, resulting in a reduction of turbulence. Compliant surfaces could probably reduce drag by equalising and distributing pressure pulses. However, the existing evidence that drag reduction actually occurs is not convincing. There is no indication that instantaneous heating, reducing the viscosity in the boundary layer, is used by animals as a drag-reducing technique. Small longitudinal ridges on rows of scales on fish can reduce shear stress in the boundary by a maximum of 10% compared with the shear stress of a smooth surface. The mechanism is based on the impedance of cross flow under well-defined conditions. The effect has been visualized with the use of particle image velocimetry techniques. The function of the swords and spears of several fast, pelagic, predatory fish species is still enigmatic. The surface structure of the sword of a swordfish is shown to be both rough and porous. The height of the roughness elements on the tip of the sword is close to the critical value for the induction of a laminar-to-turbulent flow transition at moderate cruising speeds. A flow tank is described that is designed to visualize the effects of surface imperfections on flow in the boundary layer in direct comparison with a smooth flat wall. The flow in a 1 m long, 10 cm

  5. Coffee-stain growth dynamics on dry and wet surfaces

    NASA Astrophysics Data System (ADS)

    Boulogne, François; Ingremeau, François; Stone, Howard A.

    2017-02-01

    The drying of a drop containing particles often results in the accumulation of the particles at the contact line. In this work, we investigate the drying of an aqueous colloidal drop surrounded by a hydrogel that is also evaporating. We combine theoretical and experimental studies to understand how the surrounding vapor concentration affects the particle deposit during the constant radius evaporation mode. In addition to the common case of evaporation on an otherwise dry surface, we show that in a configuration where liquid is evaporating from a flat surface around the drop, the singularity of the evaporative flux at the contact line is suppressed and the drop evaporation is homogeneous. For both conditions, we derive the velocity field and we establish the temporal evolution of the number of particles accumulated at the contact line. We predict the growth dynamics of the stain and the drying timescales. Thus, dry and wet conditions are compared with experimental results and we highlight that only the dynamics is modified by the evaporation conditions, not the final accumulation at the contact line.

  6. Dynamical Properties of Surface-mounted Dipolar Molecular Rotators

    NASA Astrophysics Data System (ADS)

    Underwood, Jason; Price, John; Caskey, Douglas; Michl, Josef

    2007-03-01

    We use dielectric relaxation spectroscopy (DRS) to study the rotational dynamics of dipolar molecules mounted on fused SiO2 surfaces. Each ``molecular rotor'' consists of three parts: 1) a mounting group for attachment to the substrate, 2) a rotating group having a permanent dipole moment, and 3) an axis connecting the rotor to the attachment group. Attachment is facilitated either by covalent bonding through reaction of silane groups with surface hydroxyls or by van der Waals interactions. Fused SiO2 substrates are patterned with interdigitated electrode Au capacitors (C ˜ 1 pF), and rotor molecule dynamics are characterized by measurement of the capacitance C and loss tangent δ≡ReZ/ImZ. We employ a ratio-transformer bridge technique to measure these quantities, with sensitivities in C and δ of 1 aF and 1 ppm, respectively. A unique aspect of this work is the experimental apparatus, which allows us to prepare sub-monolayer films, determine coverage via two independent methods (DRS and XPS), and study molecule rotational motion, in-situ in ultra-high vacuum. Results will be presented on the kinetics of rotor adsorption/desorption, barrier height and asymmetry of the rotational potential of the molecules, and the effects of varying rotor coverages and adventitious H2O.

  7. Nuclear spin dynamics in double quantum dots: Multistability, dynamical polarization, criticality, and entanglement

    NASA Astrophysics Data System (ADS)

    Schuetz, M. J. A.; Kessler, E. M.; Vandersypen, L. M. K.; Cirac, J. I.; Giedke, G.

    2014-05-01

    We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically defined double quantum dot in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.

  8. Neuronal avalanches imply maximum dynamic range in cortical networks at criticality.

    PubMed

    Shew, Woodrow L; Yang, Hongdian; Petermann, Thomas; Roy, Rajarshi; Plenz, Dietmar

    2009-12-09

    Spontaneous neuronal activity is a ubiquitous feature of cortex. Its spatiotemporal organization reflects past input and modulates future network output. Here we study whether a particular type of spontaneous activity is generated by a network that is optimized for input processing. Neuronal avalanches are a type of spontaneous activity observed in superficial cortical layers in vitro and in vivo with statistical properties expected from a network operating at "criticality." Theory predicts that criticality and, therefore, neuronal avalanches are optimal for input processing, but until now, this has not been tested in experiments. Here, we use cortex slice cultures grown on planar microelectrode arrays to demonstrate that cortical networks that generate neuronal avalanches benefit from a maximized dynamic range, i.e., the ability to respond to the greatest range of stimuli. By changing the ratio of excitation and inhibition in the cultures, we derive a network tuning curve for stimulus processing as a function of distance from criticality in agreement with predictions from our simulations. Our findings suggest that in the cortex, (1) balanced excitation and inhibition establishes criticality, which maximizes the range of inputs that can be processed, and (2) spontaneous activity and input processing are unified in the context of critical phenomena.

  9. Effects of Hydrogen on the Critical Conditions for Dynamic Recrystallization of Titanium Alloy During Hot Deformation

    NASA Astrophysics Data System (ADS)

    Zhao, Jingwei; Ding, Hua; Jiang, Zhengyi; Wei, Dongbin; Linghu, Kezhi

    2014-10-01

    Hot deformation tests were performed to study the flow behavior and microstructural evolution of a Ti600 titanium alloy with different hydrogen contents. The effects of hydrogen on the critical conditions for the initiation of dynamic recrystallization (DRX) were investigated. The DRX kinetics models of hydrogenated Ti600 alloy were developed, and the DRX volume fractions were quantified under different deformation conditions. The results indicate that the addition of proper hydrogen (no greater than 0.3 pct) benefits the decrease of both the critical stress and critical strain for the initiation of DRX. The critical stress and critical strain are dependent linearly on the peak stress and the strain to peak stress, respectively. The strain range from the initiation to the completion of DRX increases gradually with hydrogen in the hydrogen range of 0 to 0.3 pct, and a slightly decreased strain range is observed at the hydrogen content of 0.5 pct relative to that of 0.3 pct. The addition of large amounts of hydrogen (0.3 pct or greater) in Ti600 alloy induces incomplete DRX during hot deformation.

  10. Nanostructures and dynamics of macromolecules bound to attractive filler surfaces

    NASA Astrophysics Data System (ADS)

    Koga, Tad; Barkley, Deborah; Jiang, Naisheng; Endoh, Maya; Masui, Tomomi; Kishimoto, Hiroyuki; Nagao, Michihiro; Satija, Sushil; Taniguchi, Takashi

    We report in-situ nanostructures and dynamics of polybutadiene (PB) chains bound to carbon black (CB) fillers (the so-called ``bound polymer layer (BPL)'') in a good solvent. The BPL on the CB fillers were extracted by solvent leaching of a CB-filled PB compound and subsequently dispersed in deuterated toluene to label the BPL for small-angle neutron scattering and neutron spin echo techniques. Intriguingly, the results demonstrate that the BPL is composed of two regions regardless of molecular weights of PB: the inner unswollen region of ~ 0.5 nm thick and outer swollen region where the polymer chains display a parabolic profile with a diffuse tail. This two-layer formation on the filler surface is similar to that reported for polymer chains adsorbed on planar substrates from melts. In addition, the results show that the dynamics of the swollen bound chains can be explained by the so-called ``breathing mode'' and is generalized with the thickness of the swollen BPL. Furthermore, we will discuss how the breathing collective dynamics is affected by the presence of polymer chains in a matrix solution. We acknowledge the financial support from NSF Grant No. CMMI-1332499.

  11. Muscular endurance and surface electromyogram in isometric and dynamic exercise.

    PubMed

    Hagberg, M

    1981-07-01

    In nine male volunteers, the endurance time for sustained isometric exercise (right-angle elbow flexion) and dynamic exercise (continuous concentric and eccentric elbow flexions) was measured at different contraction levels. Intermittent isometric exercises were also performed by four of the subjects in whom surface electromyographic elbow flexor recordings were obtained during the three types of exercise. A rapid decrease of the endurance time was seen at contraction levels above 15-20% of the maximum voluntary contraction for both the sustained isometric and dynamic exercise. There were no significant difference between the regression of the endurance time vs. the contraction level for the sustained isometric exercise and that of the dynamic exercise. However, the endurance time was enhanced in the intermittent isometric exercise compared with the sustained isometric exercise. The development of muscle fatigue was well correlated to change of the myoelectric rootmean-square amplitude and the mean power frequency. Differences in exercise did not significantly affect the relation between the time constant of the mean power frequency decrease and the endurance time.

  12. Deterministic nature of the underlying dynamics of surface wind fluctuations

    NASA Astrophysics Data System (ADS)

    Sreelekshmi, R. C.; Asokan, K.; Satheesh Kumar, K.

    2012-10-01

    Modelling the fluctuations of the Earth's surface wind has a significant role in understanding the dynamics of atmosphere besides its impact on various fields ranging from agriculture to structural engineering. Most of the studies on the modelling and prediction of wind speed and power reported in the literature are based on statistical methods or the probabilistic distribution of the wind speed data. In this paper we investigate the suitability of a deterministic model to represent the wind speed fluctuations by employing tools of nonlinear dynamics. We have carried out a detailed nonlinear time series analysis of the daily mean wind speed data measured at Thiruvananthapuram (8.483° N,76.950° E) from 2000 to 2010. The results of the analysis strongly suggest that the underlying dynamics is deterministic, low-dimensional and chaotic suggesting the possibility of accurate short-term prediction. As most of the chaotic systems are confined to laboratories, this is another example of a naturally occurring time series showing chaotic behaviour.

  13. A shallow landslide analysis method consisting of contour line based method and slope stability model with critical slip surface

    NASA Astrophysics Data System (ADS)

    Tsutsumi, D.

    2015-12-01

    To mitigate sediment related disaster triggered by rainfall event, it is necessary to predict a landslide occurrence and subsequent debris flow behavior. Many landslide analysis method have been developed and proposed by numerous researchers for several decades. Among them, distributed slope stability models simulating temporal and spatial instability of local slopes are more essential for early warning or evacuation in area of lower part of hill-slopes. In the present study, a distributed, physically based landslide analysis method consisting of contour line-based method that subdivide a watershed area into stream tubes, and a slope stability analysis in which critical slip surface is searched to identify location and shape of the most instable slip surface in each stream tube, is developed. A target watershed area is divided into stream tubes using GIS technique, grand water flow for each stream tubes during a rainfall event is analyzed by a kinematic wave model, and slope stability for each stream tube is calculated by a simplified Janbu method searching for a critical slip surface using a dynamic programming method. Comparing to previous methods that assume infinite slope for slope stability analysis, the proposed method has advantage simulating landslides more accurately in spatially and temporally, and estimating amount of collapsed slope mass, that can be delivered to a debris flow simulation model as a input data. We applied this method to a small watershed in the Izu Oshima, Tokyo, Japan, where shallow and wide landslides triggered by heavy rainfall and subsequent debris flows attacked Oshima Town, in 2013. Figure shows the temporal and spatial change of simulated grand water level and landslides distribution. The simulated landslides are correspond to the uppermost part of actual landslide area, and the timing of the occurrence of landslides agree well with the actual landslides.

  14. Study of SRM critical surfaces using near infrared optical fiber spectrometry

    NASA Astrophysics Data System (ADS)

    Workman, G. L.; Thompson, G. W.; Arendale, W. A.

    1999-12-01

    The measurement and control of cleanliness for critical bonding surfaces during manufacturing provides a unique challenge in the current thrust for the use of environmentally benign processes. Of particular interest has been work performed in maintaining quality in the production of bonds in aerospace propulsion systems and the identification of possible contaminants which are detrimental to the integrity of the bondline. This work requires an in-depth study of the possible sources of contamination, methodologies to identify contaminants, discrimination between contaminants and chemical species caused by environment, and the effect of particular contaminants on the bondline integrity of the critical bonds. Current research explores the use of near infrared (NIR) optical fiber spectrometry for process monitoring of materials used in aerospace systems. Characterization of contaminants on critical bondlines for aerospace materials such as D6AC steel, aluminum alloys and graphite epoxy composites will be presented. Experiments include quantitative measurement of silicone and Conoco HD2 grease, metal hydroxides, and tape residues on solid rocket motor surfaces.

  15. Study of SRM critical surfaces using near infrared optical fiber spectrometry

    SciTech Connect

    Workman, G. L.; Thompson, G. W.; Arendale, W. A.

    1999-12-02

    The measurement and control of cleanliness for critical bonding surfaces during manufacturing provides a unique challenge in the current thrust for the use of environmentally benign processes. Of particular interest has been work performed in maintaining quality in the production of bonds in aerospace propulsion systems and the identification of possible contaminants which are detrimental to the integrity of the bondline. This work requires an in-depth study of the possible sources of contamination, methodologies to identify contaminants, discrimination between contaminants and chemical species caused by environment, and the effect of particular contaminants on the bondline integrity of the critical bonds. Current research explores the use of near infrared (NIR) optical fiber spectrometry for process monitoring of materials used in aerospace systems. Characterization of contaminants on critical bondlines for aerospace materials such as D6AC steel, aluminum alloys and graphite epoxy composites will be presented. Experiments include quantitative measurement of silicone and Conoco HD2 grease, metal hydroxides, and tape residues on solid rocket motor surfaces.

  16. Field-theoretical Renormalization-Group approach to critical dynamics of crosslinked polymer blends

    NASA Astrophysics Data System (ADS)

    Benhamou, M.; Chahid, M.

    2008-09-01

    We consider a crosslinked polymer blend that may undergo a microphase separation. When the temperature is changed from an initial value towards a final one very close to the spinodal point, the mixture is out equilibrium. The aim is the study of dynamics at a given time t , before the system reaches its final equilibrium state. The dynamics is investigated through the structure factor, S(q, t) , which is a function of the wave vector q , temperature T , time t , and reticulation dose D . To determine the phase behavior of this dynamic structure factor, we start from a generalized Langevin equation (model C) solved by the time composition fluctuation. Beside the standard de Gennes Hamiltonian, this equation incorporates a Gaussian local noise, ζ . First, by averaging over ζ , we get an effective Hamiltonian. Second, we renormalize this dynamic field theory and write a Renormalization-Group equation for the dynamic structure factor. Third, solving this equation yields the behavior of S(q, t) , in space of relevant parameters. As result, S(q, t) depends on three kinds of lengths, which are the wavelength q-1, a time length scale R(t) thicksim t1/z , and the mesh size ξ* . The scale R(t) is interpreted as the size of growing microdomains at time t . When R(t) becomes of the order of ξ* , the dynamics is stopped. The final time, t * , then scales as t * thicksim ξ{ast z} , with the dynamic exponent z = 6 - η . Here, η is the usual Ising critical exponent. Since the final size of microdomains ξ* is very small (few nanometers), the dynamics is of short time. Finally, all these results we obtained from renormalization theory are compared to those we stated in some recent work using a scaling argument.

  17. Field theory of bicritical and tetracritical points. IV. Critical dynamics including reversible terms

    NASA Astrophysics Data System (ADS)

    Folk, R.; Holovatch, Yu.; Moser, G.

    2012-02-01

    This article concludes a series of papers [Folk, Holovatch, and Moser, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.78.04112478, 041124 (2008); Folk, Holovatch, and Moser, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.78.04112578, 041125 (2008); Folk, Holovatch, and Moser, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.79.03110979, 031109 (2009)] where the tools of the field theoretical renormalization group were employed to explain and quantitatively describe different types of static and dynamic behavior in the vicinity of multicritical points. Here we give the complete two-loop calculation and analysis of the dynamic renormalization-group flow equations at the multicritical point in anisotropic antiferromagnets in an external magnetic field. We find that the time scales of the order parameters characterizing the parallel and perpendicular ordering with respect to the external field scale in the same way. This holds independent whether the Heisenberg fixed point or the biconical fixed point in statics is the stable one. The nonasymptotic analysis of the dynamic flow equations shows that due to cancellation effects the critical behavior is described, in distances from the critical point accessible to experiments, by the critical behavior qualitatively found in one-loop order. Although one may conclude from the effective dynamic exponents (taking almost their one-loop values) that weak scaling for the order parameter components is valid, the flow of the time-scale ratios is quite different, and they do not reach their asymptotic values.

  18. Land surface dynamics monitoring using microwave passive satellite sensors

    NASA Astrophysics Data System (ADS)

    Guijarro, Lizbeth Noemi

    Soil moisture, surface temperature and vegetation are variables that play an important role in our environment. There is growing demand for accurate estimation of these geophysical parameters for the research of global climate models (GCMs), weather, hydrological and flooding models, and for the application to agricultural assessment, land cover change, and a wide variety of other uses that meet the needs for the study of our environment. The different studies covered in this dissertation evaluate the capabilities and limitations of microwave passive sensors to monitor land surface dynamics. The first study evaluates the 19 GHz channel of the SSM/I instrument with a radiative transfer model and in situ datasets from the Illinois stations and the Oklahoma Mesonet to retrieve land surface temperature and surface soil moisture. The surface temperatures were retrieved with an average error of 5 K and the soil moisture with an average error of 6%. The results show that the 19 GHz channel can be used to qualitatively predict the spatial and temporal variability of surface soil moisture and surface temperature at regional scales. In the second study, in situ observations were compared with sensor observations to evaluate aspects of low and high spatial resolution at multiple frequencies with data collected from the Southern Great Plains Experiment (SGP99). The results showed that the sensitivity to soil moisture at each frequency is a function of wavelength and amount of vegetation. The results confirmed that L-band is more optimal for soil moisture, but each sensor can provide soil moisture information if the vegetation water content is low. The spatial variability of the emissivities reveals that resolution suffers considerably at higher frequencies. The third study evaluates C- and X-bands of the AMSR-E instrument. In situ datasets from the Soil Moisture Experiments (SMEX03) in South Central Georgia were utilized to validate the AMSR-E soil moisture product and to

  19. Study of the critical behavior of the driven lattice gas model with limited nonequilibrium dynamics

    NASA Astrophysics Data System (ADS)

    Saracco, Gustavo P.; Rubio Puzzo, M. Leticia; Bab, Marisa A.

    2017-02-01

    In this paper the nonequilibrium critical behavior is investigated using a variant of the well-known two-dimensional driven lattice gas (DLG) model, called modified driven lattice gas (MDLG). In this model, the application of the external field is regulated by a parameter p ɛ [ 0 , 1 ] in such a way that if p = 0, the field is not applied, and it becomes the Ising model, while if p = 1, the DLG model is recovered. The behavior of the model is investigated for several values of p by studying the dynamic evolution of the system within the short-time regime in the neighborhood of a phase transition. It is found that the system experiences second-order phase transitions in all the interval of p for the density of particles ρ = 0.5. The determined critical temperatures Tc(p) are greater than the critical temperature of the Ising model TcI, and increase with p up to the critical temperature of the DLG model in the limit of infinite driving fields. The dependence of Tc(p) on p is compatible with a power-law behavior whose exponent is ψ = 0.27(3) . Furthermore, the complete set of the critical and the anisotropic exponents is estimated. For the smallest value of p, the ​dynamics and β exponents are close to that calculated for the Ising model, and the anisotropic exponent Δ is near zero. As p is increased, the exponents and Δ change, meaning that the anisotropy effects increase. For the largest value investigated, the set of exponents approaches to that reported by the most recent theoretical framework developed for the DLG model.

  20. Dynamical Signatures of Structural Connectivity Damage to a Model of the Brain Posed at Criticality.

    PubMed

    Haimovici, Ariel; Balenzuela, Pablo; Tagliazucchi, Enzo

    2016-12-01

    Synchronization of brain activity fluctuations is believed to represent communication between spatially distant neural processes. These interareal functional interactions develop in the background of a complex network of axonal connections linking cortical and subcortical neurons, termed the human "structural connectome." Theoretical considerations and experimental evidence support the view that the human brain can be modeled as a system operating at a critical point between ordered (subcritical) and disordered (supercritical) phases. Here, we explore the hypothesis that pathologies resulting from brain injury of different etiologies are related to this model of a critical brain. For this purpose, we investigate how damage to the integrity of the structural connectome impacts on the signatures of critical dynamics. Adopting a hybrid modeling approach combining an empirical weighted network of human structural connections with a conceptual model of critical dynamics, we show that lesions located at highly transited connections progressively displace the model toward the subcritical regime. The topological properties of the nodes and links are of less importance when considered independently of their weight in the network. We observe that damage to midline hubs such as the middle and posterior cingulate cortex is most crucial for the disruption of criticality in the model. However, a similar effect can be achieved by targeting less transited nodes and links whose connection weights add up to an equivalent amount. This implies that brain pathology does not necessarily arise due to insult targeted at well-connected areas and that intersubject variability could obscure lesions located at nonhub regions. Finally, we discuss the predictions of our model in the context of clinical studies of traumatic brain injury and neurodegenerative disorders.

  1. Crowded surfaces change annealing dynamics of actin filaments.

    PubMed

    Popp, David; Yamamoto, Akihiro; Maéda, Yuichiro

    2007-04-27

    Changes in cell shape that occur in many cellular processes are thought to arise from polymerization of actin filaments near the cell membrane. End-to-end annealing of actin filaments is believed to play only a minor role in this process, as annealing in solution was shown to be a slow process, which is not typical for a bimolecular reaction, its rate constant decreasing over time, being inversely proportional to the filament length. Furthermore, in vitro studies on f-actin solutions were found to display an exponential steady-state length distribution. In the cell, many physiologically important parameters, such as mechanical strength or viscoelastic response are a direct function of the physical properties of the underlying actin cytoskeleton, such as actin filament length distribution and dynamics. How the underlying physical parameters of the actin cytoskeleton may be influenced by the cell surface or molecular crowding remains poorly understood. Using total internal reflection fluorescence (TIRF) microscopy we reinvestigated actin end-to-end annealing in vitro in a more realistic environment. We studied the process near a hydrophilic surface together with crowding agents, in order to mimic the physiological media near the cell membrane, which has substantial amounts of macromolecules present. We find that actin end-to-end annealing changes in three ways near a crowded hydrophilic surface as compared to solution. First the annealing rate becomes a factor of 20 faster than in solution. Second the rate of annealing becomes typical of a bimolecular reaction, shows no length dependence and is basically just a function of the square of the concentration of ends. Lastly the length distribution is Gaussian throughout the entire annealing process. This implicates that dynamic rearrangement of actin filaments by annealing near the leading edge of the cell, could change physical parameters like the mechanical response and contribute significantly to cell motility.

  2. A study of dynamic finite size scaling behavior of the scaling functions—calculation of dynamic critical index of Wolff algorithm

    NASA Astrophysics Data System (ADS)

    Gündüç, Semra; Dilaver, Mehmet; Aydın, Meral; Gündüç, Yiğit

    2005-02-01

    In this work we have studied the dynamic scaling behavior of two scaling functions and we have shown that scaling functions obey the dynamic finite size scaling rules. Dynamic finite size scaling of scaling functions opens possibilities for a wide range of applications. As an application we have calculated the dynamic critical exponent (z) of Wolff's cluster algorithm for 2-, 3- and 4-dimensional Ising models. Configurations with vanishing initial magnetization are chosen in order to avoid complications due to initial magnetization. The observed dynamic finite size scaling behavior during early stages of the Monte Carlo simulation yields z for Wolff's cluster algorithm for 2-, 3- and 4-dimensional Ising models with vanishing values which are consistent with the values obtained from the autocorrelations. Especially, the vanishing dynamic critical exponent we obtained for d=3 implies that the Wolff algorithm is more efficient in eliminating critical slowing down in Monte Carlo simulations than previously reported.

  3. Magnetic field-induced Fermi surface reconstruction and quantum criticality in CeRhIn5

    DOE PAGES

    Jiao, Lin; Weng, Z. F.; Smidman, Michael; ...

    2017-02-06

    Here, we present detailed results of the field evolution of the de Haas–van Alphen (dHvA) effect in CeRhIn5. A magnetic field-induced reconstruction of the Fermi surface is clearly shown to occur inside the antiferromagnetic state, in an applied field of around B* ≃ 30 T, which is evidenced by the appearance of several new dHvA branches. The angular dependence of the dHvA frequencies reveals that the Fermi surfaces of CeRhIn5 at B > B* and CeCoIn5 are similar. The results suggest that the Ce-4f electrons in become itinerant at B > B* due to the Kondo effect, prior to themore » field-induced quantum critical point (QCP) at Bc0 ≃ 50 T. The electronic states at the field-induced QCP are therefore different from that of the pressure-induced QCP where a dramatic Fermi surface reconstruction occurs exactly at the critical pressure, indicating that multiple types of QCP may exist in CeRhIn5.« less

  4. Surface reconstruction in reactive dynamics: A kinetic Monte Carlo approach

    NASA Astrophysics Data System (ADS)

    Noussiou, V. K.; Provata, A.

    2007-07-01

    The oscillatory CO oxidation reaction on the restructuring surface of Pt(1 0 0) is studied through a mesoscopic kinetic Monte Carlo (KMC) approach. The present model is an extension of the standard ZGB model with specific attention to the emergence of oscillations in surface reactions. A square and a purely hexagonal lattice are used as substrates on which the CO oxidation reaction steps take place. The dynamics of the reaction on the two substrates exhibit the ZGB kinetic phase transitions, at different kinetic parameter values for each substrate. Surface reconstruction is modelled through switching between the two lattice types. Oscillations are produced in those parametric areas where the steady state concentrations on the two substrates are considerably different. The parametric area where notable oscillations are observed is narrow, but is greatly enhanced when different sticking coefficients of oxygen are taken into account. CO diffusion introduced microscopically to the model on the hexagonal lattice shifts the kinetic transition points and increases considerably the time needed to reach the steady state.

  5. Evaporation dynamics from wetted porous surfaces affected by internal drainage

    NASA Astrophysics Data System (ADS)

    Lehmann, Peter; Fuchs, Josefa; Dehaspe, Joni; Breitenstein, Daniel; Wunderli, Hans; Or, Dani

    2017-04-01

    Land surface evaporation dynamics following periodic rainfall events is complicated by liquid phase redistribution and concurrent internal drainage. The maintenance of constant and high evaporation rates (stage 1 evaporation) is predicated on water supply to the surface via continuous capillary pathways up to a characteristic depth defined by porous media properties. The objective is to extend the description to realistic conditions where evaporation and internal drainage occur concurrently. Column experiments have shown that evaporative losses were drastically reduced when drainage takes place. For initially high water content (and hydraulic conductivity) drainage dominates and shortens opportunity for stage 1 evaporation. A range of intermediate results emerges in which transition to stage 2 evaporation depends on initial conditions and soil properties. We derived a new definition of evaporative characteristic length that links soil hydraulic properties and initial conditions with predicted evaporative losses from wetted land surface. Experiments and theoretical considerations confirm the existence of an optimal water content defining conditions for maximal evaporative losses during stage 1.

  6. Plankton dynamics in thermally-stratified free-surface turbulence

    NASA Astrophysics Data System (ADS)

    Lovecchio, Salvatore; Soldati, Alfredo

    2015-11-01

    Thermal stratification induced by solar heating near the ocean-atmosphere interface influences the transfer fluxes of heat, momentum and chemical species across the interface. Due to thermal stratification, a region of large temperature gradients (thermocline) may form with strong consequences for the marine ecosystem. In particular, the thermocline is believed to prevent phytoplankton from reaching the well-lit surface layer, where they can grow through the process of photosynthesis. In this paper, we use a DNS-based Eulerian-Lagrangian approach to examine the role of stratification on phytoplankton dynamics in thermally-stratified free-surface turbulence. We focus on gyrotactic self-propelled phytoplankton cells, considering different stratification levels (quantified by the Richardson number) and different gyro tactic re-orientation times. We show that the modulation of turbulent fluctuations induced by stable stratification has a strong effect on the orientation and distribution of phytoplankton, possibly leading to trapping of some species within the thermocline. Specifically, we observe the appearance of a depletion layer just below the free-surface as stratification increases, accompanied by a reduction in the vertical stability of phytoplankton cells.

  7. The dynamics of marginality and self-organized criticality as a paradigm for turbulent transport

    SciTech Connect

    Newman, D.E.; Carreras, B.A.; Diamond, P.H.; Hahm, T.S.

    1995-12-31

    A general paradigm, based on the concept of self-organized criticality (SOC), for turbulent transport in magnetically confined plasmas has been recently suggested as an explanation for some of the apparent discrepancies between most theoretical models of turbulent transport and experimental observations of the transport in magnetically confined plasmas. This model describes the dynamics of the transport without relying on the underlying local fluctuation mechanisms. Computations based on a cellular automata realization of such a model have found that noise driven SOC systems can maintain average profiles that are linearly stable (submarginal) and yet are able to sustain active transport dynamics. It is also found that the dominant scales in the transport dynamics in the absence of sheared flow are system scales rather than the underlying local fluctuation scales. The addition of sheared flow into the dynamics leads to a large reduction of the system-scale transport events and a commensurate increase in the fluctuation-scale transport events needed to maintain the constant flux. The dynamics of these models and the potential ramifications for transport studies are discussed.

  8. Soil Moisture/ Tree Water Status Dynamics in a Mid-Latitude Montane Forest, Southern Sierra Critical Zone Observatory, CA

    NASA Astrophysics Data System (ADS)

    Hartsough, P. C.; Malazian, A.; Kamai, T.; Roudneva, E.; Hopmans, J. W.

    2009-12-01

    In the Mediterranean climate of the Sierra Nevada, snow pack persists well into the spring after precipitation has effectively stopped. With the onset of summer and continued dry conditions, snow quickly melts, and soil profiles dry out as shrubs and trees deplete the available soil moisture. A better understanding of surface and subsurface water budgets in remote landscapes warrants closer monitoring of moisture and temperature variability in near surfaces soils. As part of the Southern Sierra Critical Zone Observatory (CZO), investigators from University of California deployed approximately 150 soil moisture, water potential and temperature sensors within the root structure of an individual white fir tree (Abies concolor) located in the Kings River Experimental Watershed (KREW). These sensors complement sap flow measurements in the trunk, stem water potential measurements in the canopy, and snow depth measurements, to enable the Southern Sierra CZO researchers to investigate how soil environmental stresses (water, temperature, and nutrients) impact forest ecosystems across the rain-to-snow-dominated transition zone. We captured the dynamics of the soil profile desiccation at various depths beneath the snow pack as soils went from wet to very dry conditions. Monitoring of sap flow and periodic leaf water potential measurements, we tracked the activity of the tree as it responded to changing available moisture in the root zone. All sensors were reactive to moisture and temperature variations and showed dynamic responses to precipitation, snow melt and changes in vegetative demand. We demonstrate here the initial phase of a multi-year deployment of soil moisture sensors as a critical integrator of hydrologic/ biotic interaction in a forested catchment as part of a wider effort to document changing ecosystem response to changing environmental inputs.

  9. Critical dynamics of the binary system nitroethane/3-methylpentane: relaxation rate and scaling function.

    PubMed

    Iwanowski, I; Leluk, K; Rudowski, M; Kaatze, U

    2006-04-06

    Shear viscosity and dynamic light scattering measurements as well as ultrasonic spectrometry studies of the nitroethane/3-methylpentane mixture of critical composition have been performed at various temperatures near the critical temperature, T(c). A combined evaluation of the shear viscosity and mutual diffusion coefficient data yielded the amplitude, xi(0), of the fluctuation correlation length, xi, assumed to follow power law, and the relaxation rate, Gamma, or order parameter fluctuations. The latter was found to follow power law with the theoretical universal exponent. The amplitudes xi(0) = 0.23 +/- 0.02 nm and Gamma(0) = (125 +/- 5) x 10(9) s(-1) nicely agree with literature values. Using the relaxation rates resulting from the viscosity and diffusion coefficient data, the scaling function has been calculated assuming the ultrasonic spectra to be composed of a critical part and a noncritical background contribution. The experimental scaling function fits well to the predictions of the Bhattacharjee-Ferrell dynamic scaling model with scaled half-attenuation frequency, Omega(BF)1/2= 2.1. The amplitude of the sonic spectra yields the amount |g| = 0.26 of the adiabatic coupling constant, g, in fair agreement with -0.29 from another thermodynamic relation.

  10. Inhibitory neurons promote robust critical firing dynamics in networks of integrate-and-fire neurons

    NASA Astrophysics Data System (ADS)

    Lu, Zhixin; Squires, Shane; Ott, Edward; Girvan, Michelle

    2016-12-01

    We study the firing dynamics of a discrete-state and discrete-time version of an integrate-and-fire neuronal network model with both excitatory and inhibitory neurons. When the integer-valued state of a neuron exceeds a threshold value, the neuron fires, sends out state-changing signals to its connected neurons, and returns to the resting state. In this model, a continuous phase transition from non-ceaseless firing to ceaseless firing is observed. At criticality, power-law distributions of avalanche size and duration with the previously derived exponents, -3 /2 and -2 , respectively, are observed. Using a mean-field approach, we show analytically how the critical point depends on model parameters. Our main result is that the combined presence of both inhibitory neurons and integrate-and-fire dynamics greatly enhances the robustness of critical power-law behavior (i.e., there is an increased range of parameters, including both sub- and supercritical values, for which several decades of power-law behavior occurs).

  11. A Comparison of Critical Regimes in Collapsible Tube, Pipe, Open Channel and Gas-Dynamic Flows

    NASA Astrophysics Data System (ADS)

    Arun, C. P.

    2003-11-01

    Though of considerable interest to clinical scientists, collapsible tubes are only recently receiving due interest by fluid physicists. The subject of critical phenomena in collapsible tube flow appears not to have been examined critically. For example, it has been proposed in the past that shock waves in physiological tubes are abnormal. We propose a classification of flow through collapsible tubes recognising that compressibility in gas-dynamic and pipe flow (cf.waterhammer) corresponds to distensibility in collapsible tube flow. Thus, opening and closing waves of collapsible tube flow (predistension regime) is subcritical flow and the post-distension regime, supercritical. Physiological tubes are often hyperelastic and contractile and often, when distension is very significant, a hypercritical regime corresponding to hypersonic gas-dynamic flow is admissible. Such a hypercritical regime would allow storage of energy and muscle contraction in the wall of the tube and hence continuance of propulsion in the essentially intermittent flow that is seen in collapsible tubes. Such a mechanism appears to be in operation in the human aorta, bowel and urethra. The present work offers a comparison of critical regimes in various fluid flow situations including collapsible tubes, that is in harmony with known phenomena seen in nature.

  12. Inhibitory neurons promote robust critical firing dynamics in networks of integrate-and-fire neurons.

    PubMed

    Lu, Zhixin; Squires, Shane; Ott, Edward; Girvan, Michelle

    2016-12-01

    We study the firing dynamics of a discrete-state and discrete-time version of an integrate-and-fire neuronal network model with both excitatory and inhibitory neurons. When the integer-valued state of a neuron exceeds a threshold value, the neuron fires, sends out state-changing signals to its connected neurons, and returns to the resting state. In this model, a continuous phase transition from non-ceaseless firing to ceaseless firing is observed. At criticality, power-law distributions of avalanche size and duration with the previously derived exponents, -3/2 and -2, respectively, are observed. Using a mean-field approach, we show analytically how the critical point depends on model parameters. Our main result is that the combined presence of both inhibitory neurons and integrate-and-fire dynamics greatly enhances the robustness of critical power-law behavior (i.e., there is an increased range of parameters, including both sub- and supercritical values, for which several decades of power-law behavior occurs).

  13. A tool for exploring the dynamics of innovative interventions for public health: the critical event card.

    PubMed

    Figueiro, Ana Claudia; de Araújo Oliveira, Sydia Rosana; Hartz, Zulmira; Couturier, Yves; Bernier, Jocelyne; do Socorro Machado Freire, Maria; Samico, Isabella; Medina, Maria Guadalupe; de Sa, Ronice Franco; Potvin, Louise

    2017-03-01

    Public health interventions are increasingly represented as complex systems. Research tools for capturing the dynamic of interventions processes, however, are practically non-existent. This paper describes the development and proof of concept process of an analytical tool, the critical event card (CEC), which supports the representation and analysis of complex interventions' evolution, based on critical events. Drawing on the actor-network theory (ANT), we developed and field-tested the tool using three innovative health interventions in northeastern Brazil. Interventions were aimed to promote health equity through intersectoral approaches; were engaged in participatory evaluation and linked to professional training programs. The CEC developing involve practitioners and researchers from projects. Proof of concept was based on document analysis, face-to-face interviews and focus groups. Analytical categories from CEC allow identifying and describing critical events as milestones in the evolution of complex interventions. Categories are (1) event description; (2) actants (human and non-human) involved; (3) interactions between actants; (4) mediations performed; (5) actions performed; (6) inscriptions produced; and (7) consequences for interventions. The CEC provides a tool to analyze and represent intersectoral internvetions' complex and dynamic evolution.

  14. Dynamics of fibronectin adsorption on TiO2 surfaces.

    PubMed

    Sousa, S R; Brás, M Manuela; Moradas-Ferreira, P; Barbosa, M A

    2007-06-19

    In the present work we analyze the dynamics of fibronectin (FN) adsorption on two different stable titanium oxides, with varied surface roughness, and chemically similar to those used in clinical practice. The two types of titanium oxide surfaces used were TiO2 sputtered on Si (TiO2 sp) and TiO2 formed on commercially pure titanium after immersion in H2O2 (TiO2 cp). Surface characterization was previously carried out using different techniques (Sousa, S. R.; Moradas-Ferreira, P.; Melo, L. V.; Saramago, B.; Barbosa, M. A. Langmuir 2004, 20 (22), 9745-9754). Imaging and roughness analysis before and after FN adsorption used atomic force microscopy (AFM) in tapping mode, in air, and in magnetic alternating current mode, in liquid (water). FN adsorption as a function of time was followed by X-ray photoelectron spectroscopy (XPS), by radiolabeling of FN with 125I (125I-FN), and by ellipsometry. Exchangeability studies were performed using FN and HSA. AFM roughness analysis revealed that, before FN adsorption, both TiO2 surfaces exhibited a lower root-mean-square (Rq) and maximum peak with the depth of the maximum valley (Rmax) roughness in air than in water, due to TiO2 hydration. After protein adsorption, the same behavior was observed for the TiO2 sp substrate, while Rq and Rmax roughness values in air and in water were similar in the case of the TiO2 cp substrate, for the higher FN concentration used. Surface roughness was always significantly higher on the TiO2 cp surfaces. AFM led to direct visualization of adsorbed FN on both surfaces tested, indicating that after 10 min of FN incubation the TiO2 sp surface was partially covered by FN. The adsorbed protein seems to form globular aggregates or ellipsoids, and FN aggregates coalesce, forming clusters as the time of adsorption and the concentration increase. Radiolabeling of FN revealed that a rapid adsorption occurs on both surfaces and the amount adsorbed increased with time, reaching a maximum after 60 min of

  15. Tissue-type plasminogen activator controls neuronal death by raising surface dynamics of extrasynaptic NMDA receptors

    PubMed Central

    Lesept, Flavie; Chevilley, Arnaud; Jezequel, Julie; Ladépêche, Laurent; Macrez, Richard; Aimable, Margaux; Lenoir, Sophie; Bertrand, Thomas; Rubrecht, Laëtitia; Galea, Pascale; Lebouvier, Laurent; Petersen, Karl-Uwe; Hommet, Yannick; Maubert, Eric; Ali, Carine; Groc, Laurent; Vivien, Denis

    2016-01-01

    N-methyl-d-aspartate receptors (NMDARs) are ion channels whose synaptic versus extrasynaptic localization critically influences their functions. This distribution of NMDARs is highly dependent on their lateral diffusion at the cell membrane. Each obligatory subunit of NMDARs (GluN1 and GluN2) contains two extracellular clamshell-like domains with an agonist-binding domain and a distal N-terminal domain (NTD). To date, the roles and dynamics of the NTD of the GluN1 subunit in NMDAR allosteric signaling remain poorly understood. Using single nanoparticle tracking in mouse neurons, we demonstrate that the extracellular neuronal protease tissue-type plasminogen activator (tPA), well known to have a role in the synaptic plasticity and neuronal survival, leads to a selective increase of the surface dynamics and subsequent diffusion of extrasynaptic NMDARs. This process explains the previously reported ability of tPA to promote NMDAR-mediated calcium influx. In parallel, we developed a monoclonal antibody capable of specifically blocking the interaction of tPA with the NTD of the GluN1 subunit of NMDAR. Using this original approach, we demonstrate that the tPA binds the NTD of the GluN1 subunit at a lysine in position 178. Accordingly, when applied to mouse neurons, our selected antibody (named Glunomab) leads to a selective reduction of the tPA-mediated surface dynamics of extrasynaptic NMDARs, subsequent signaling and neurotoxicity, both in vitro and in vivo. Altogether, we demonstrate that the tPA is a ligand of the NTD of the obligatory GluN1 subunit of NMDAR acting as a modulator of their dynamic distribution at the neuronal surface and subsequent signaling. PMID:27831563

  16. Analysis of critical dynamics for shock-induced adiabatic explosions by means of the Cauchy problem for the shock transformation

    NASA Astrophysics Data System (ADS)

    Vidal, P.; Khasainov, B. A.

    We present a theoretical and numerical study on the induction of adiabatic explosions by accelerated curved shocks in homogeneous explosives, and pay a special attention to critical conditions for initiation. We characterize the first stage of the decomposition process, or induction, as an initial-value problem. During induction, the reaction progress-variable remains small; the induction time is given by the runaway of the dependent variables and corresponds to a logarithmic singularity in theirs material distributions. We express these distributions as first-order expansions in the progress variable about the shock. Then, the framework of our procedure is the formal Cauchy problem for quasi-linear hyperbolic sets of first-order differential equations, such as the balance laws for adiabatic flows of inviscid fluids considered in this study. When a shock front is used as data surface, the solution to the Cauchy problem yields the flow derivatives at the shock, then the induction time, as functions of the shock normal velocity and acceleration, Dn and δ Dn/δ t, and the shock total curvature C. We next derive a necessary condition for explosion as a constraint among Dn, δ Dn/δ t and C that ensures bounded values of the induction time. This criterion is akin to Semenov's, in the sense that the critical condition for explosion is that the heat-production rate must just exceed the heat-loss rate, here given by the volumetric expansion rate at the shock. The violation of the criterion defines a critical shock dynamics as a relationship among Dn, δ Dn/δ t and C that generates infinite induction times. Depending on the rear-boundary conditions, which determine the shock dynamics, this event can be interpreted as either a non-initiation, or the decoupling of the shock and of the flame front induced by the shock. We illustrate our approach by a simple solution to the problem of the initiation by impact of a noncompressible piston. From the continuity constraint in the

  17. Critical heat flux maxima resulting from the controlled morphology of nanoporous hydrophilic surface layers

    NASA Astrophysics Data System (ADS)

    Tetreault-Friend, Melanie; Azizian, Reza; Bucci, Matteo; McKrell, Thomas; Buongiorno, Jacopo; Rubner, Michael; Cohen, Robert

    2016-06-01

    Porous hydrophilic surfaces have been shown to enhance the critical heat flux (CHF) in boiling heat transfer. In this work, the separate effects of pore size and porous layer thickness on the CHF of saturated water at atmospheric pressure were experimentally investigated using carefully engineered surfaces. It was shown that, for a fixed pore diameter (˜20 nm), there is an optimum layer thickness (˜2 μm), for which the CHF value is maximum, corresponding to ˜115% enhancement over the value for uncoated surfaces. Similarly, a maximum CHF value (˜100% above the uncoated surface CHF) was observed while changing the pore size at a constant layer thickness (˜1 μm). To explain these CHF maxima, we propose a mechanistic model that can capture the effect of pore size and pore thickness on CHF. The good agreement found between the model and experimental data supports the hypothesis that CHF is governed by the competition between capillary wicking, viscous pressure drop and evaporation, as well as conduction heat transfer within the porous layer. The model can be used to guide the development of engineered surfaces with superior boiling performance.

  18. Universal Modified Newtonian Dynamics Relation between the Baryonic and "Dynamical" Central Surface Densities of Disc Galaxies

    NASA Astrophysics Data System (ADS)

    Milgrom, Mordehai

    2016-09-01

    I derive a new modified Newtonian dynamics (MOND) relation for pure-disc galaxies: The "dynamical" central surface density, ΣD0 , deduced from the measured velocities, is a universal function of only the true, "baryonic'' central surface density, ΣB0 : ΣD0=ΣMS (ΣB0/ΣM) , where ΣM≡a0/2 π G is the MOND surface density constant. This surprising result is shown to hold in both existing, nonrelativistic MOND theories. S (y ) is derived: S (y )=∫0yν (y')d y' , with ν (y ) being the interpolating function of the theory. The relation aymptotes to ΣD0=ΣB0 for ΣB0≫ΣM , and to ΣD0=(4 ΣMΣB0)1 /2 for ΣB0≪ΣM . This study was prompted by the recent finding of a correlation between related attributes of disc galaxies by Lelli et al.. The MOND central-surface-densities relation agrees very well with these results.

  19. Universal Modified Newtonian Dynamics Relation between the Baryonic and "Dynamical" Central Surface Densities of Disc Galaxies.

    PubMed

    Milgrom, Mordehai

    2016-09-30

    I derive a new modified Newtonian dynamics (MOND) relation for pure-disc galaxies: The "dynamical" central surface density, Σ_{D}^{0}, deduced from the measured velocities, is a universal function of only the true, "baryonic'' central surface density, Σ_{B}^{0}: Σ_{D}^{0}=Σ_{M}S(Σ_{B}^{0}/Σ_{M}), where Σ_{M}≡a_{0}/2πG is the MOND surface density constant. This surprising result is shown to hold in both existing, nonrelativistic MOND theories. S(y) is derived: S(y)=∫_{0}^{y}ν(y^{'})dy^{'}, with ν(y) being the interpolating function of the theory. The relation aymptotes to Σ_{D}^{0}=Σ_{B}^{0} for Σ_{B}^{0}≫Σ_{M}, and to Σ_{D}^{0}=(4Σ_{M}Σ_{B}^{0})^{1/2} for Σ_{B}^{0}≪Σ_{M}. This study was prompted by the recent finding of a correlation between related attributes of disc galaxies by Lelli et al.. The MOND central-surface-densities relation agrees very well with these results.

  20. Combined Molecular Dynamics Simulation-Molecular-Thermodynamic Theory Framework for Predicting Surface Tensions.

    PubMed

    Sresht, Vishnu; Lewandowski, Eric P; Blankschtein, Daniel; Jusufi, Arben

    2017-08-22

    A molecular modeling approach is presented with a focus on quantitative predictions of the surface tension of aqueous surfactant solutions. The approach combines classical Molecular Dynamics (MD) simulations with a molecular-thermodynamic theory (MTT) [ Y. J. Nikas, S. Puvvada, D. Blankschtein, Langmuir 1992 , 8 , 2680 ]. The MD component is used to calculate thermodynamic and molecular parameters that are needed in the MTT model to determine the surface tension isotherm. The MD/MTT approach provides the important link between the surfactant bulk concentration, the experimental control parameter, and the surfactant surface concentration, the MD control parameter. We demonstrate the capability of the MD/MTT modeling approach on nonionic alkyl polyethylene glycol surfactants at the air-water interface and observe reasonable agreement of the predicted surface tensions and the experimental surface tension data over a wide range of surfactant concentrations below the critical micelle concentration. Our modeling approach can be extended to ionic surfactants and their mixtures with both ionic and nonionic surfactants at liquid-liquid interfaces.