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
Fermi-surface collapse and dynamical scaling near a quantum-critical point
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
Fermi-surface collapse and dynamical scaling near a quantum-critical point.
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.
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.
Critical insight into the influence of the potential energy surface on fission dynamics
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.
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.
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.
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.
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
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.
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.
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.
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.
Symmetry in critical random Boolean network dynamics.
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.
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.
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.
Quantum chaos on a critical Fermi surface.
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.
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.
Dynamics and Thermodynamics beyond the critical point
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
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.
Animal population dynamics: Identification of critical components
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.
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.
Static and Dynamic Criticality: Are They Different?
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.
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.
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.
Critical heat flux maxima during boiling crisis on textured surfaces
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
Critical heat flux maxima during boiling crisis on textured surfaces.
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.
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.
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.
Surface structure determines dynamic wetting
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
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.
Critical surface for explosions of rotational core-collapse supernovae
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.
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.
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_c1
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) .
Conserved nonlocal dynamics and critical behavior of uranium ferromagnetic superconductors.
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}).
Protein hydration dynamics in solution: a critical survey.
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
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
Partial dynamical symmetry at critical points of quantum phase transitions.
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.
Generalized dynamic scaling for quantum critical relaxation in imaginary time.
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.
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.
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.
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.
Critical Casimir forces in colloidal suspensions on chemically patterned surfaces.
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.
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.
Criticality in dynamic arrest: correspondence between glasses and traffic.
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.
Toward Control of Universal Scaling in Critical Dynamics
2016-01-27
magnetism and surface growth, to ecology , epidemiology, synthetic biology, and social system dynamics. Our in-depth discussions and analysis...thresholds or active-to-absorbing phase transitions. He is also investigating noise-induced pattern formation and evolutionary dynamics in ecological models...from materials science, e.g., magnetism and surface growth, to ecology , epidemiology, synthetic biology, and social system dynamics. Our in-depth
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.
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.
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.
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.
Gene expression dynamics in the macrophage exhibit criticality.
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.
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.
Criticality in conserved dynamical systems: experimental observation vs. exact properties.
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.
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.
Critical domain-wall dynamics of model B.
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) .
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.
The Dynamic Surface Tension of Water.
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.
The Dynamic Surface Tension of Water
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.
Critical Casimir forces between homogeneous and chemically striped surfaces.
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.
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.
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.
Critical dynamics on a large human Open Connectome network.
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.
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.
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.
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.
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.
Dynamics of nanoscale droplets on moving surfaces.
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.
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.
Critical dynamics of a nonlocal model and critical behavior of perovskite manganites.
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.
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.
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.
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.
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.
Measurement of dynamic surface tension by mechanically vibrated sessile droplets.
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.
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.
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.
Hydration dynamics at fluorinated protein surfaces.
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.
Hydration dynamics at fluorinated protein surfaces
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
SATELLITE DYNAMICS ON THE LAPLACE SURFACE
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.
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.
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.
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.
Chemical Dynamics at Surfaces of Metal Nanomaterials
2014-07-23
AFRL-OSR-VA-TR-2014-0168 Chemical Dynamics at Surfaces of Metal Nanomaterials Junrong Zheng WILLIAM MARSH RICE UNIV HOUSTON TX Final Report 07/23...Junrong Zheng Department of Chemistry, Rice University 1. Proposed summary The project was designed to develop novel spectroscopic tools for
Modeling surface water critical loads with PROFILE: possibilities and challenges.
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.
Dynamic air layer on textured superhydrophobic surfaces.
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.
Molecular dynamics description of grafted monolayers: effect of the surface coverage.
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.
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.
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
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.
Network Randomization and Dynamic Defense for Critical Infrastructure Systems
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.
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
Surface Wave Dynamics in the Coastal Zone
2014-09-30
heights, rip currents etc), coastal management, and help mitigate pollution hazards for humans (recreation) and coastal ecosystems . TRANSITIONS...1 Surface Wave Dynamics in the Coastal Zone Gerbrant Ph. van Vledder Department of Civil engineering and Geosciences, Delft University of...will be applicable in the coastal zone from deep water up to and including the surf zone. Our efforts will focus on analyzing high quality datasets to
Dynamic loads in surface dragline ropes. [ADINA
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.
Unstable dynamics, nonequilibrium phases, and criticality in networked excitable media
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.
Unstable dynamics, nonequilibrium phases, and criticality in networked excitable media.
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.
General Critical Properties of the Dynamics of Scientific Discovery
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.
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
Dynamic contact angle cycling homogenizes heterogeneous surfaces.
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.
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.
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.
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.
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.
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
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.
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.
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.
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
NASA Astrophysics Data System (ADS)
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.
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.
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.
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.
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.
Dynamic wormholes, antitrapped surfaces, and energy conditions
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}
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.
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
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.
Static and dynamic friction of hierarchical surfaces.
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.
Aqueous solvation dynamics at metal oxide surfaces.
Portuondo-Campa, Erwin; Tortschanoff, Andreas; van Mourik, Frank; Moser, Jacques-Edouard; Kornherr, Andreas; Chergui, Majed
2006-04-20
Broadband transient absorption (TA) spectroscopy, three-pulse photon echo peak shift (3PEPS), and anisotropy decay measurements were used to study the solvation dynamics in bulk water and interfacial water at ZrO(2) surfaces, using Eosin Y as a probe. The 3PEPS results show a multiexponential behavior with two subpicosecond components that are similar in bulk and interfacial water, while a third component of several picoseconds is significantly lengthened at the interface. The bandwidth correlation function from TA spectra exhibits the same behavior, and the TA spectra are well reproduced using the doorway-window picture with the time constants from PEPS. Our results suggest that interfacial water is restricted to a thickness of less than 5 A. Also the high-frequency collective dynamics of water does not seem to be affected by the interface. On the other hand, the increase of the third component may point to a slowing down of diffusional motion at the interface, although other effects, may play a role, which are discussed.
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.
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.
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.
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.
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
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.
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.
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.
Cell-surface translational dynamics of nicotinic acetylcholine receptors
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
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…
Critical Appraisal and Hazards of Surface Electromyography Data Acquisition in Sport and Exercise
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
Critical appraisal and hazards of surface electromyography data acquisition in sport and exercise.
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.
Hydration dynamics near a model protein surface
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.
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.
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
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.
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…
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.
Reactor Dynamics Experiments with a Sub-Critical Assembly
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.
Hydrodynamic boundary conditions and dynamic forces between bubbles and surfaces.
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.
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.
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.
Dynamic recrystallization in friction surfaced austenitic stainless steel coatings
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.
Dynamics of inelastic and reactive gas-surface collisions
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.
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.
DSTR/501-M62B Dynamic Interface Critical Speed Problem
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
Critical dynamics of vesicle stretching transition in elongational flow.
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 epsilon
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
Does the Sverdrup critical depth model explain bloom dynamics in estuaries?
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
Temperature dependent droplet impact dynamics on flat and textured surfaces
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.
Nanoparticle-Based Antimicrobials: Surface Functionality is Critical
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
Electrostatic cloaking of surface structure for dynamic wetting
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
Electrostatic cloaking of surface structure for dynamic wetting.
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.
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
Surface Characterization of Nanoparticles: critical needs and significant challenges
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
Critical appraisal of the fewest switches algorithm for surface hopping.
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.
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.
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…
Evolution as a critical component of plankton dynamics.
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.
Dynamics of inhomogeneous condensates in contact with a surface
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.
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
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.
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.
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
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.
Vortex-Surface Interactions: Vortex Dynamics and Instabilities
2015-10-16
from the surface, in a 3D version of the "vortex rebound" in 2D vortex dynamics. Many of the discoveries of phenomena in this work are seen for the... 3D vortex-wall interactions. The key to the significant reorganization of vortex structure, is the rapid circulation decay at regions along the vortex...development of vortex configurations interacting with a surface. In further studies, the dynamics of secondary vorticity and the development of 3D
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.
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 .
Fast track surface mine installation on the critical path
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.
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.
Separate effects of surface roughness, wettability, and porosity on the boiling critical heat flux
NASA Astrophysics Data System (ADS)
O'Hanley, Harry; Coyle, Carolyn; Buongiorno, Jacopo; McKrell, Tom; Hu, Lin-Wen; Rubner, Michael; Cohen, Robert
2013-07-01
The separate effects of surface wettability, porosity, and roughness on the critical heat flux (CHF) of water were examined using engineered surfaces. Values explored were 0, 5, 10, and 15 μm for Rz (roughness), <5°, ˜75°, and >110° for static contact angle (wettability), and 0 and 50% for pore volume fraction. The porous hydrophilic surface enhanced CHF by 50%-60%, while the porous hydrophobic surface resulted in a reduction of CHF by 97%. Wettability had little effect on the smooth non-porous surface CHF. Surface roughness (Ra, Rq, Rz) had no effect on CHF within the limit of this database.
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
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.
Critical design aspects of dynamic titanium alloy risers
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.
Using surface deformation to image reservoir dynamics
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.
SYSTEM IDENTIFICATION OF SURFACE SHIP DYNAMICS.
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
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.
Simulation of Gas-Surface Dynamical Interactions
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
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.
Dynamic sensitivity of photon-dressed atomic ensemble with quantum criticality
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.
Improved Criteria for Acceptable Yield Point Elongation in Surface Critical Steels
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.
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.
Sticky surface: sphere-sphere adhesion dynamics
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
Hyperelasticity governs dynamic fracture at a critical length scale.
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.
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.
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.
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.
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
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.
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.
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.
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
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.
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.
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.
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.
Using what you get: dynamic physiologic signatures of critical illness
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
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.
Fading signatures of critical brain dynamics during sustained wakefulness in humans.
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.
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.
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.
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.
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.
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.
Molecular dynamics simulation of annealed ZnO surfaces
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.
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.
Dynamic forces between bubbles and surfaces and hydrodynamic boundary conditions.
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.
Molecular dynamics studies of interfacial water at the alumina surface.
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.
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
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.
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.
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.
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.
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.
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.
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
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.
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.
Molecular dynamics simulation of a binary mixture near the lower critical point.
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.
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.
[Determination of critical surface tension--a comparison of 2 methods].
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.
Sub-nanometer glass surface dynamics induced by illumination
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.
Static and Dynamic Wetting Behavior of Triglycerides on Solid Surfaces.
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.
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
Constraining quantum critical dynamics: (2+1)D Ising model and beyond.
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.
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.
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…
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.
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.
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
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…
Decay of surface nanostructures via long-time-scale dynamics
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.
Wetting dynamics of alkyl ketene dimer on cellulosic model surfaces
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.
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.
Spinodals and critical point using short-time dynamics for a simple model of liquid.
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.
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.
Anomalously Rapid Hydration Water Diffusion Dynamics Near DNA Surfaces.
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.
Simultaneous droplet impingement dynamics and heat transfer on nano-structured surfaces
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)
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.
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.
Optimal system size for complex dynamics in random neural networks near criticality
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.
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.
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.
Oxidation-driven surface dynamics on NiAl(100)
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
Oxidation-driven surface dynamics on NiAl(100)
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
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.
Oxidation-driven surface dynamics on NiAl(100)
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.
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.
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
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.
Decoupling of surface diffusion and relaxation dynamics of molecular glasses.
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.
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.
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.
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.
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.
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.
Critical heat flux (CHF) phenomenon on a downward facing curved surface
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.
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.
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.
Investigating the dynamics of surface-immobilized DNA nanomachines
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
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.
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.
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.
Efficient modelling of droplet dynamics on complex surfaces.
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.
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.
Dynamic surface tension analysis of dodecyl sulfate association complexes.
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
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.
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.
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.
Dynamic Imaging of Surface Motion with a Stereo Borescope
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.
Critical behavior of gelation probed by the dynamics of latex spheres
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.
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.
Cryogenic design of the liquid helium experiment ``critical dynamics in microgravity``
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.
Adsorption dynamics of molecular nitrogen at an Fe(111) surface.
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.
Modeling apple surface temperature dynamics based on weather data.
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.
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.
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.
Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops.
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.
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.
Sodium diffusion through amorphous silica surfaces: a molecular dynamics study.
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.
Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements
2015-03-31
2. REPORT DATE 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 6. AUTHOR(S) 7. PERFORMING ORGANIZATION NAME(S) AND...WORK UNIT NUMBER 1. REPORT DATE (DD-MM-YYYY) 16. SECURITY CLASSIFICATION OF: PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 31-03-2015...Final March 2013 -- February 2015 Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements N00014-13-1-0352 Yue, Dick K.P
Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurements
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
Quantifying the Dynamic Ocean Surface Using Underwater Radiometric Measurement
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
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.
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.
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.
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.
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.
Dynamic Melting of Freezing Droplets on Ultraslippery Superhydrophobic Surfaces.
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.
Behavior of the critical temperature of Ising thin films with variable surface magnetic moments.
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.
An efficient threshold dynamics method for wetting on rough surfaces
NASA Astrophysics Data System (ADS)
Xu, Xianmin; Wang, Dong; Wang, Xiao-Ping
2017-02-01
The threshold dynamics method developed by Merriman, Bence and Osher (MBO) is an efficient method for simulating the motion by mean curvature flow when the interface is away from the solid boundary. Direct generalization of MBO-type methods to the wetting problem with interfaces intersecting the solid boundary is not easy because solving the heat equation in a general domain with a wetting boundary condition is not as efficient as it is with the original MBO method. The dynamics of the contact point also follows a different law compared with the dynamics of the interface away from the boundary. In this paper, we develop an efficient volume preserving threshold dynamics method for simulating wetting on rough surfaces. This method is based on minimization of the weighted surface area functional over an extended domain that includes the solid phase. The method is simple, stable with O (Nlog N) complexity per time step and is not sensitive to the inhomogeneity or roughness of the solid boundary.
A Method for Molecular Dynamics on Curved Surfaces
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
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
Observation of dynamic water microadsorption on Au surface
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.
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.
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.
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.
Dynamics of adsorbed polymers on attractive homogeneous surfaces
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
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)
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.
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
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.
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.
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.
Critical dynamics of self-gravitating Langevin particles and bacterial populations.
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 M
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.
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
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
Criticality in large-scale brain FMRI dynamics unveiled by a novel point process analysis.
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.
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.
Critical CuI buffer layer surface density for organic molecular crystal orientation change
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.
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.
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.
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
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.
Neuronal avalanches imply maximum dynamic range in cortical networks at criticality.
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.
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.
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
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.
Study of SRM critical surfaces using near infrared optical fiber spectrometry
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.
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.
Dynamic effects induced transition of droplets on biomimetic superhydrophobic surfaces.
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.
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.
Noncontact friction and relaxational dynamics of surface defects.
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.
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.
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.
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.
Dynamical Signatures of Structural Connectivity Damage to a Model of the Brain Posed at Criticality.
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.
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.
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).
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.
A unique Critical State two-surface hyperplasticity model for fine-grained particulate media
NASA Astrophysics Data System (ADS)
Coombs, W. M.; Crouch, R. S.; Augarde, C. E.
2013-01-01
Even mild compression can cause re-arrangement of the internal structure of clay-like geomaterials, whereby clusters of particles rotate and collapse as face-to-face contacts between the constituent mineral platelets increase at the expense of edge-to-face (or edge-to-edge) contacts. The collective action of local particle re-orientation ultimately leads to path-independent isochoric macroscopic deformation under continuous shearing. This asymptotic condition is the governing feature of Critical State elasto-plasticity models. Unlike earlier formulations, the two-surface anisotropic model proposed herein is able to reproduce a unique isotropic Critical State stress envelope which agrees well with test data. Material point predictions are compared against triaxial experimental results and five other existing constitutive models. The hyperplastic formulation is seen to offer a significantly improved descriptor of the anisotropic behaviour of fine-grained particulate materials.
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.
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.
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).
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).
Novel dynamic flux chamber for measuring air-surface exchange of Hg(o) from soils.
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.
Surface dating of dynamic landforms: young boulders on aging moraines.
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.
Dynamics of water droplet on a heated nanotubes surface
NASA Astrophysics Data System (ADS)
Kim, Seol Ha; Seon Ahn, Ho; Kim, Joonwon; Kaviany, Massoud; Hwan Kim, Moo
2013-06-01
This study investigated an effect of nanotubes on a heated surface onto Leidenfrost droplet through high speed visualization and momentum balance analysis. Delayed cutback phenomena and Leidenfrost Point (LFP) by dramatically high heating level were observed, and it is elucidated through wettable and spreadable features induced by nanotubes. As much delayed LFP, transient boiling regime with explosion-like dynamics of a water droplet on the nanotubes was observed. Furthermore, nanotubes required higher wall temperature to maintain non wetting cushion, due to the induced slip condition by porous features.
Structure and Dynamics of Octamethylcyclotetrasiloxane Confined between Mica Surfaces.
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
The dynamics of marginality and self-organized criticality as a paradigm for turbulent transport
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.
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.
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.
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.
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.
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.
NASA Astrophysics Data System (ADS)
Bunker, Alex; Landau, D. P.; Chen, Kun
1996-03-01
Using 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 that we may directly compare our results to experiment we have set the single site anisotropy term to match the degree of anisotropy found^2 in MnF_2. Through the determination and analysis of the form of the neutron scattering function S(q,ω) at and below T_c, we have found the dispersion curves for different temperatures and studied the critical dynamics. We have compared our results to simulations^1 for the isotropic case and experiment^2 on MnF_2. Research supported in part by the NSF ^**current address: Solid State Division, Oak Ridge National Laboratory ^1 K. Chen, D. P. Landau, Phys. Rev. B \\underline49, 3266, (1994) ^2 J. Als-Nielsen in Phase Transitions and Critical Phenomena, ed. C. Domb, M. S. Green, (Academic Press, 1976)
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.
Dynamic growth of slip surfaces in catastrophic landslides
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
Pseudospectral Gaussian quantum dynamics: Efficient sampling of potential energy surfaces.
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.
Dynamic growth of slip surfaces in catastrophic landslides.
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.
Surface dynamics of voltage-gated ion channels
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
Scaled Correlations of Critical Points of Random Sections on Riemann Surfaces
NASA Astrophysics Data System (ADS)
Baber, John
2012-08-01
In this paper we prove that as N goes to infinity, the scaling limit of the correlation between critical points z 1 and z 2 of random holomorphic sections of the N-th power of a positive line bundle over a compact Riemann surface tends to 2/(3 π 2) for small sqrt{N}|z1-nobreak z2|. The scaling limit is directly calculated using a general form of the Kac-Rice formula and formulas and theorems of Pavel Bleher, Bernard Shiffman, and Steve Zelditch.
Dynamic surface tension of surfactant TA: experiments and theory.
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.
Dynamic and reversible surface topography influences cell morphology.
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.
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.
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.
Lee, Ming-Tsung; Vishnyakov, Aleksey; Neimark, Alexander V
2013-09-05
Micelle formation in surfactant solutions is a self-assembly process governed by complex interplay of solvent-mediated interactions between hydrophilic and hydrophobic groups, which are commonly called heads and tails. However, the head-tail repulsion is not the only factor affecting the micelle formation. For the first time, we present a systematic study of the effect of chain rigidity on critical micelle concentration and micelle size, which is performed with the dissipative particle dynamics simulation method. Rigidity of the coarse-grained surfactant molecule was controlled by the harmonic bonds set between the second-neighbor beads. Compared to flexible molecules with the nearest-neighbor bonds being the only type of bonded interactions, rigid molecules exhibited a lower critical micelle concentration and formed larger and better-defined micelles. By varying the strength of head-tail repulsion and the chain rigidity, we constructed two-dimensional diagrams presenting how the critical micelle concentration and aggregation number depend on these parameters. We found that the solutions of flexible and rigid molecules that exhibited approximately the same critical micelle concentration could differ substantially in the micelle size and shape depending on the chain rigidity. With the increase of surfactant concentration, primary micelles of more rigid molecules were found less keen to agglomeration and formation of nonspherical aggregates characteristic of flexible molecules.
de Andrade, M F; Figueiredo, W
2011-03-01
We determine the critical behavior of a reactive model with many absorbing configurations. Monomers A and B land on the sites of a linear lattice and can react depending on the state of their nearest-neighbor sites. The probability of a reaction depends on temperature of the catalyst as well as on the energy coupling between pairs of nearest-neighbor monomers. We employ Monte Carlo simulations to calculate the moments of the order parameter of the model as a function of temperature. Some ratios between pairs of moments are independent of temperature and are in the same universality class of the contact process. We also find the dynamical critical exponents of the model and we show that they are in the directed percolation universality class whatever the values of temperature.
Critical heat flux and dynamics of boiling in nanofluids at stepwise heat release
NASA Astrophysics Data System (ADS)
Moiseev, M. I.; Kuznetsov, D. V.
2016-10-01
In this paper results of an experimental study on critical heat flux and dynamics of boiling crisis onset in nanofluids at stepwise heat generation are presented. Freon R21 with three types of nanoparticles - SiO2, Cu and Al2O3 was used as test fluid. Critical heat fluxes and temperatures of boiling initiation were obtained. It was shown that the addition of nanoparticles increased CHF at stepwise heat generation by up to 21%. Under conditions of the experiment transition to film boiling occurred via evaporation fronts. Data on propagation velocity and structure of evaporation fronts were obtained; the spectral analysis of fluctuations of the evaporation front interface was carried out. The characteristic frequencies and amplitudes of interface fluctuations were determined depending on the velocity of evaporation front propagation. It was shown that the addition of nano-sized particles significantly affects development of interface instability and increases the front velocity.
Quantum critical dynamics of a magnetic impurity in a semiconducting host
NASA Astrophysics Data System (ADS)
Dasari, Nagamalleswararao; Acharya, Swagata; Taraphder, A.; Moreno, Juana; Jarrell, Mark; Vidhyadhiraja, N. S.; N. S. Vidhyadhiraja Collaboration, Prof.; Mark Jarrell Collaboration, Prof.; A. Taraphder Collaboration, Prof.
We have investigated the finite temperature dynamics of the singlet to doublet continuous quantum phase transition in the gapped Anderson impurity model using hybridization expansion continuous time quantum Monte Carlo. Using the self-energy and the longitudinal static susceptibility, we obtain a phase diagram in the temperature-gap plane. The separatrix between the low-temperature local moment phase and the high temperature generalized Fermi liquid phase is shown to be the lower bound of the critical scaling region of the zero gap interacting quantum critical point. We have computed the nuclear magnetic spin-lattice relaxation rate, the Knight shift, and the Korringa ratio, which show strong deviations for any non-zero gap from the corresponding quantities in the gapless Kondo screened impurity case. This work is supported by NSF DMR-1237565 and NSF EPSCoR Cooperative Agreement EPS-1003897 with additional support from the Louisiana Board of Regents, and by CSIR and DST, India.
Universal time fluctuations in near-critical out-of-equilibrium quantum dynamics.
Campos Venuti, Lorenzo; Zanardi, Paolo
2014-02-01
Out-of-equilibrium quantum systems display complex temporal patterns. Such time fluctuations are generically exponentially small in the system volume and therefore can be safely ignored in most of the cases. However, if one consider small quench experiments, time fluctuations can be greatly enhanced. We show that time fluctuations may become stronger than other forms of equilibrium quantum fluctuations if the quench is performed close to a critical point. For sufficiently relevant operators the full distribution function of dynamically evolving observable expectation values becomes a universal function uniquely characterized by the critical exponents and the boundary conditions. At regular points of the phase diagram and for nonsufficiently relevant operators the distribution becomes Gaussian. Our predictions are confirmed by an explicit calculation on the quantum Ising model.
Using Surface Science to Probe Critical Interfaces in Organic and Hybrid Systems (PReSS Talk)
Brumback, Michael T.
2010-03-25
This talk will address several uses of surface science for understanding critical interfaces in energy-related devices and for materials characterization. Primary emphasis will be on photoelectron spectroscopy applied to understanding interfaces in organic photovoltaics (OPV). In organic photovoltaics, where solar-to-electric conversion efficiencies are typically low, interfacial phenomena dictate the performance of the solar cell. It is therefore important to understand the interfacial chemistry and energy level alignment at these interfaces to better optimize them for increased PV performance. UV-photoelectron spectroscopy and X-ray photoelectron spectroscopy (UPS/XPS) are ideally suited to examine these interfaces. Several examples of interfacial energy level alignments will be discussed. More general applications of surface science will also be discussed including work from a collaborative effort at the National Synchrotron Light Source where NEXAFS, imaging NEXAFS, and variable energy XPS have been used for a variety of applications.
Surface Plasmon States in Inhomogeneous Media at Critical and Subcritical Metal Concentrations
Seal, Katyayani; Genov, Dentcho A.
2012-01-01
Semicontinuous metal-dielectric films are composed of a wide range of metal clusters of various geometries—sizes as well as structures. This ensures that at any given wavelength of incident radiation, clusters exist in the film that will respond resonantly, akin to resonating nanoantennas, resulting in the broad optical response (absorption) that is a characteristic of semicontinuous films. The physics of the surface plasmon states that are supported by such systems is complex and can involve both localized and propagating plasmons. This chapter describes near-field experimental and numerical studies of the surface plasmon states in semicontinuous films at critical and subcritical metalmore » concentrations and evaluates the local field intensity statistics to discuss the interplay between various eigenmodes.« less
Modeling the Self-organized Critical Behavior of Earth's Plasma Sheet Reconnection Dynamics
NASA Technical Reports Server (NTRS)
Klimas, Alexander J.
2006-01-01
Analyses of Polar UVI auroral image data show that bright night-side high-latitude W emissions exhibit so many of the key properties of systems in self-organized criticality that an alternate interpretation has become virtually impossible. These analyses will be reviewed. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the magnetotail plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques (and more) that have been applied to the auroral image data have also been applied to this Poynting flux. New results will be presented showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. A strong correlation between these key properties of the model and those of the auroral UV emissions will be demonstrated. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.
Modeling the Self-organized Critical Behavior of the Plasma Sheet Reconnection Dynamics
NASA Technical Reports Server (NTRS)
Klimas, Alex; Uritsky, Vadim; Baker, Daniel
2006-01-01
Analyses of Polar UVI auroral image data reviewed in our other presentation at this meeting (V. Uritsky, A. Klimas) show that bright night-side high-latitude UV emissions exhibit so many of the key properties of systems in self-organized criticality (SOC) that an alternate interpretation has become virtually impossible. It is now necessary to find and model the source of this behavior. We note that the most common models of self-organized criticality are numerical sandpiles. These are, at root, models that govern the transport of some quantity from a region where it is loaded to another where it is unloaded. Transport is enabled by the excitation of a local threshold instability; it is intermittent and bursty, and it exhibits a number of scale-free statistical properties. Searching for a system in the magnetosphere that is analogous and that, in addition, is known to produce auroral signatures, we focus on the reconnection dynamics of the plasma sheet. In our previous work, a driven reconnection model has been constructed and has been under study. The transport of electromagnetic (primarily magnetic) energy carried by the Poynting flux into the reconnection region of the model has been examined. All of the analysis techniques, and more, that have been applied to the auroral image data have also been applied to this Poynting flux. Here, we report new results showing that this model also exhibits so many of the key properties of systems in self-organized criticality that an alternate interpretation is implausible. Further, we find a strong correlation between these key properties of the model and those of the auroral UV emissions. We suggest that, in general, the driven reconnection model is an important step toward a realistic plasma physical model of self-organized criticality and we conclude, more specifically, that it is also a step in the right direction toward modeling the multiscale reconnection dynamics of the magnetotail.
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.
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.
Critical Dynamics of the Dirty Boson Problem: Revisiting the Equality z=d
Weichman, Peter B.; Mukhopadhyay, Ranjan
2007-06-15
It is shown that previous arguments, leading to the equality z=d for the dynamical exponent describing the Bose glass to superfluid transition in d dimensions, may break down, as apparently seen in recent simulations. The key observation is that the major contribution to the compressibility, which remains finite through the transition and was predicted to scale as {kappa}{approx} vertical bar {delta} vertical bar{sup (d-z){nu}} (where {delta} is the deviation from criticality and {nu} is the correlation length exponent) comes from the analytic, not the singular part of the free energy, and is not restricted by any conventional scaling hypothesis.
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.
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.
NASA Astrophysics Data System (ADS)
Dubail, J.; Santachiara, R.; Emig, T.
2017-03-01
Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szegö formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.
Critical Heat Flux in Pool Boiling on Metal-Graphite Composite Surfaces
NASA Technical Reports Server (NTRS)
Zhang, Nengli; Yang, Wen-Jei; Chao, David F.; Chao, David F. (Technical Monitor)
2000-01-01
A study is conducted on high heat-flux pool boiling of pentane on micro-configured composite surfaces. The boiling surfaces are copper-graphite (Cu-Gr) and aluminum-graphite (Al-Gr) composites with a fiber volume concentration of 50%. The micro-graphite fibers embedded in the matrix contribute to a substantial enhancement in boiling heat-transfer performance. Correlation equations are obtained for both the isolated and coalesced bubble regimes, utilizing a mathematical model based on a metal-graphite, two-tier configuration with the aid of experimental data. A new model to predict the critical heat flux (CHF) on the composites is proposed to explain the fundamental aspects of the boiling phenomena. Three different factors affecting the CHF are considered in the model. Two of them are expected to become the main agents driving vapor volume detachment under microgravity conditions, using the metal-graphite composite surfaces as the heating surface and using liquids with an unusual Marangoni effect as the working fluid.
Contamination of Critical Surfaces from NVR Glove Residues Via Dry Handling and Solvent Cleaning
NASA Technical Reports Server (NTRS)
Sovinski, Marjorie F.
2004-01-01
Gloves are often used to prevent the contamination of critical surfaces during handling. The type of glove chosen for use should be the glove that produces the least amount of non-volatile residue (NVR). This paper covers the analysis of polyethylene, nitrile, latex, vinyl, and polyurethane gloves using the contact transfer and gravimetric determination methods covered in the NASA GSFC work instruction Gravimetric Determination and Contact Transfer of Non-volatile Residue (NVR) in Cleanroom Glove Samples, 541-WI-5330.1.21 and in the ASTM Standard E-1731M-95, Standard Test Method for Gravimetric Determination of Non-Volatile Residue from Cleanroom Gloves. The tests performed focus on contamination of critical surfaces at the molecular level. The study found that for the most part, all of the gloves performed equally well in the contact transfer testing. However, the polyethylene gloves performed the best in the gravimetric determination testing, and therefore should be used whenever solvent contact is a possibility. The nitrile gloves may be used as a substitute for latex gloves when latex sensitivity is an issue. The use of vinyl gloves should be avoided, especially if solvent contact is a possibility. A glove database will be established by Goddard Space Flight Center (GSFC) Code 541 to compile the results from future testing of new gloves and different glove lots.
NASA Astrophysics Data System (ADS)
Murase, Yohsuke; Ito, Nobuyasu
2008-01-01
Values of dynamic critical exponents are numerically estimated for various models with the nonequilibrium relaxation method to test the dynamic universality hypothesis. The dynamics used here are single-spin update with Metropolis-type transition probabities. The estimated values of nonequilibrium relaxation exponent of magnetization λm (=β/zν) of Ising models on bcc and fcc lattices are estimated to be 0.251(3) and 0.252(3), respectively, which are consistent with the value of the model on simple-cubic lattice, 0.250(2). The dynamic critical exponents of three-states Potts models on square, honeycomb and triangular lattices are also estimated to be 2.193(5), 2.198(4), and 2.199(3), respectively. They are consistent within the error bars. It is also confirmed that Ising models with regularly modulated coupling constants on square lattice have the same dynamic critical exponents with the uniformly ferromagnetic Ising model.
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
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.
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.
Dynamics of fibronectin adsorption on TiO2 surfaces.
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
Dynamic control over cell adhesive properties using molecular-based surface engineering strategies.
Robertus, Jort; Browne, Wesley R; Feringa, Ben L
2010-01-01
In complex organisms, cells are often dependent on their extracellular matrix (ECM) for structural integrity, the mechanical properties of tissues, and for signaled regulation of cellular processes including adhesion, migration, growth, secretion, gene expression and apoptosis. Achieving dynamic control, i.e. by using an external stimulus, over the interactions between cells and artificial interfaces holds considerable promise in tissue engineering, medicine, cell biology and immunology. For example, improved spatial control over cell-surface interaction is potentially useful in the design of cell-based screening devices. Dynamic control over SAMs for cell adhesion provides an additional handle to direct and study the attachment of cells to surfaces, e.g., in studying cell spreading from a predetermined pattern in order to screen the cytotoxicity of drug candidates. However, 'reversible' control of cell adhesion onto substrates is an area that is still in its infancy. In this critical review recent developments in cell adhesion of mammalian cells to SAM-modified surfaces, the physical properties of which can be controlled by an external stimulus, e.g. by light, electrochemistry, etc., are discussed (118 references).
Karvounis, George; Nerukh, Dmitry; Glen, Robert C
2004-09-08
All-atom molecular dynamics simulations for a single molecule of Leu-Enkephalin in aqueous solution have been used to study the role of the water network during the formation of beta-turns. We give a detailed account of the intramolecular hydrogen bonding, the water-peptide hydrogen bonding, and the orientation and residence times of water molecules focusing on the short critical periods of transition to the stable beta-turns. These studies suggest that, when intramolecular hydrogen bonding between the first and fourth residue of the beta-turn is not present, the disruption of the water network and the establishment of water bridges constitute decisive factors in the formation and stability of the beta-turn. Finally, we provide possible explanations and mechanisms for the formations of different kinds of beta-turns.
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.
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.
Critical role of surface roughness on colloid retention and release in porous media.
Torkzaban, Saeed; Bradford, Scott A
2016-01-01
This paper examines the critical role of surface roughness (both nano- and micro-scale) on the processes of colloid retention and release in porous media under steady-state and transient chemical conditions. Nanoscale surface roughness (NSR) in the order of a few nanometers, which is common on natural solid surfaces, was incorporated into extended-DLVO calculations to quantify the magnitudes of interaction energy parameters (e.g. the energy barrier to attachment, ΔΦa , and detachment, ΔΦd , from a primary minimum). This information was subsequently used to explain the behavior of colloid retention and release in column and batch experiments under different ionic strength (IS) and pH conditions. Results demonstrated that the density and height of NSR significantly influenced the interaction energy parameters and consequently the extent and kinetics of colloid retention and release. In particular, values of ΔΦa and ΔΦd significantly decreased in the presence of NSR. Therefore, consistent with findings of column experiments, colloid retention in the primary minimum was predicted to occur at some specific locations on the sand surface, even at low IS conditions. However, NSR yielded a much weaker primary minimum interaction compared with that of smooth surfaces. Colloid release from primary minima upon decreasing IS and increasing pH was attributed to the impact of NSR on the values of ΔΦd . Pronounced differences in the amount of colloid retention in batch and column experiments indicated that primary minimum interactions were weak even at high IS conditions. Negligible colloid retention in batch experiments was attributed to hydrodynamic torques overcoming adhesive torques, whereas significant colloid retention in column experiments was attributed to nano- and micro-scale roughness which would dramatically alter the lever arms associated with hydrodynamic and adhesive torques.
Molecular dynamics studies of water deposition on hematite surfaces
NASA Astrophysics Data System (ADS)
Kvamme, Bjørn; Kuznetsova, Tatiana; Haynes, Martin
2012-12-01
The interest in carbon dioxide for enhanced oil recovery is increasing proportional to the decrease in naturally driven oil production and also due to the increasing demand for reduced emission of carbon dioxide to the atmosphere. Transport of carbon dioxide in offshore pipelines involves high pressure and low temperatures which may lead to the formation of hydrate between residual water dissolved in carbon dioxide. The critical question is whether the water at some condition of temperature and pressure will drop out as liquid droplets or as water adsorbed on the surfaces of the pipeline and then subsequently form hydrates heterogeneously. In this work we have used the 6-311G basis set with B3LYP to estimate the charge distribution of different sizes of hematite crystals. The obtained surface charge distribution were kept unchanged while the inner charge distribution where scaled so as to result in an overall neutral crystal. These rust particles were embedded in water and chemical potential for adsorbed water molecules were estimated through thermodynamic integration and compared to similar estimates for same size water cluster. Estimated values of water chemical potentials indicate that it is thermodynamically favorable for water to adsorb on hematite, and that evaluation of potential carbon dioxide hydrate formation conditions and kinetics should be based this sequence of processes.
Dynamics of the Si(111) surface phase transition
HANNON,J.B.; HIBINO,H.; BARTELT,N.C.; SWARTZENTRUBER,BRIAN S.; OGINO,T.; KELLOGG,G.L.
1999-01-27
The authors have used low-energy electron microscopy to investigate the dynamics of the Si(111) 7 x 7 {r_arrow} 1 x 1 phase transition. Because the densities of the two phases differ, the phase transformation is analogous to precipitation in bulk systems: additional material must diffuse to the phase boundaries in order for the transformation to occur. By measuring the size evolution of an ensemble of domains, and comparing the results to simulations, they have identified a new mechanism of precipitate growth. The source of material necessary for the transformation is the random creation of atom/vacancy pairs at the surface. This mechanism contrasts sharply with classical theories of precipitation, in which mass transport kinetics determine the rate of transformation.
Exploring the free energy surface using ab initio molecular dynamics
Samanta, Amit; Morales, Miguel A.; Schwegler, Eric
2016-04-22
Efficient exploration of the configuration space and identification of metastable structures are challenging from both computational as well as algorithmic perspectives. Here, we extend the recently proposed orderparameter aided temperature accelerated sampling schemes to efficiently and systematically explore free energy surfaces, and search for metastable states and reaction pathways within the framework of density functional theory based molecular dynamics. The sampling method is applied to explore the relevant parts of the configuration space in prototypical materials SiO_{2} and Ti to identify the different metastable structures corresponding to different phases in these materials. In addition, we use the string method in collective variables to study the melting pathways in the high pressure cotunnite phase of SiO_{2} and the hcp to fcc phase transition in Ti.
Exploring the free energy surface using ab initio molecular dynamics
Samanta, Amit; Morales, Miguel A.; Schwegler, Eric
2016-04-22
Efficient exploration of the configuration space and identification of metastable structures are challenging from both computational as well as algorithmic perspectives. Here, we extend the recently proposed orderparameter aided temperature accelerated sampling schemes to efficiently and systematically explore free energy surfaces, and search for metastable states and reaction pathways within the framework of density functional theory based molecular dynamics. The sampling method is applied to explore the relevant parts of the configuration space in prototypical materials SiO2 and Ti to identify the different metastable structures corresponding to different phases in these materials. In addition, we use the string method inmore » collective variables to study the melting pathways in the high pressure cotunnite phase of SiO2 and the hcp to fcc phase transition in Ti.« less
Marine biofilms on artificial surfaces: structure and dynamics.
Salta, Maria; Wharton, Julian A; Blache, Yves; Stokes, Keith R; Briand, Jean-Francois
2013-11-01
The search for new antifouling (AF) coatings that are environmentally benign has led to renewed interest in the ways that micro-organisms colonize substrates in the marine environment. This review covers recently published research on the global species composition and dynamics of marine biofilms, consisting mainly of bacteria and diatoms found on man-made surfaces including AF coatings. Marine biofilms directly interact with larger organisms (macrofoulers) during colonization processes; hence, recent literature on understanding the basis of the biofilm/macrofouling interactions is essential and will also be reviewed here. Overall, differences have been identified in species composition between biofilm and planktonic forms for both diatoms and bacteria at various exposure sites. In most studies, the underlying biofilm was found to induce larval and spore settlement of macrofoulers; however, issues such as reproducibility, differences in exposure sites and biofilm composition (natural multispecies vs. monospecific species) may influence the outcomes.
A molecular dynamics investigation of surface reconstruction on magnetite (001)
NASA Astrophysics Data System (ADS)
Rustad, J. R.; Wasserman, E.; Felmy, A. R.
1999-07-01
Molecular dynamics calculations using analytical potential functions with polarizable oxygen ions have been used to identify a novel mode of reconstruction on the half-occupied tetrahedral layer termination of the magnetite (Fe 3O 4) (001) surface. In the proposed reconstruction, the twofold coordinated iron ion in the top monolayer rotates downward to occupy a vacant half-octahedral site in the plane of the second-layer iron ions. At the same time, half of the tetrahedral iron ions in the third iron layer are pushed upward to occupy an adjacent octahedral vacancy at the level of the second-layer iron ions. The other half of the third-layer iron ions remain roughly in their original positions. The proposed reconstruction is consistent with recent low-energy electron diffraction and X-ray photoelectron spectroscopy results. It also provides a compelling interpretation for the arrangement of atoms suggested by high-resolution scanning-tunneling microscopy studies.
NASA Astrophysics Data System (ADS)
Nakagawa, K.; Nakayama, S.; Saito, A.; Ono, S.; Kai, H.; Mukaida, M.; Honma, T.; Ohshima, S.
2010-11-01
We investigated the relationship between the intrinsic surface resistance (Rsint) and critical current density (Jc) of YBa2Cu3Oy (YBCO) film thinner than the penetration depth (λL). The measured YBCO films were deposited on CeO2-buffered r-cut Al2O3 substrates by the pulsed laser deposition method. The thicknesses of these films were 300, 200, and 100 nm, respectively. The Rsint means the surface resistance of YBCO film removing the loss by the impedance of the substrates. The effective surface resistance (Rseff) including the impedance of the substrate and the Jc of each YBCO film were measured using the dielectric resonator method at 21.8 GHz and the inductive method. We calculated Rsint by using phenomenological expressions and the Rseff value. The Rsint values of each YBCO film were almost the same in the measured temperature region. As a result, we found that Rsint was in inverse proportion to the Jc of YBCO film thinner than λL.
Hot electron dynamics and impurity scattering on gold nanoshell surfaces
NASA Astrophysics Data System (ADS)
Wolfgang, John Adam
2000-10-01
Recent ultrafast pump-probe experiments studying the relaxation rate of an optically excited hot electron distribution on Au/Au2S gold nanoshells indicate that this relaxation rate can be modified by the chemical environment surrounding the shell. This work will begin a theoretical investigation of the effect of chemical adsorbates---solvents and impurities---upon nanoshell hot electron dynamics. The effects of water, polyvinyl alcohol (PVA), sulfur, p-aminobenzoic acid, p-mercaptobenzoic acid and propylamine adsorbates are examined for their electronic interaction with a noble metal surface. p-Aminobenzoic acid is found to have a very large dipole moment when adsorbed to the metal surface, in contrast to p-mercaptobenzoic acid, propylamine and water. This correlates well to the experimentally observed results where nanoshells dispersed in an aqueous soulution with p-aminobenzoic acid display a faster relaxation rate compared to nanoshells dispersed in a pure water, aqueous propylamine or aqueous p-mercaptobenzoic acid environments. This thesis will also introduce a non-equilibrium Green's function approach, based on the formalism developed by Baym and Kadanoff, to model the dynamics of a hot electron distribution. The model will be discussed in terms of a simple potential scattering mechanism, which may in later work be expanded to include more complex electron-electron and electron-phonon interactions. Lastly acoustic oscillation modes are calculated for solid gold spheres and gold-silicon nanoshells. These modes describe an effect of electron-phonon coupling between the hot electron distribution and the nanoshell lattice, whereby the electronic energy is converted into mechanical energy.
He atom surface scattering: Surface dynamics of insulators, overlayers and crystal growth
Safron, S. A.; Skofronick, J. G.
1992-01-01
Investigations have focused primarily on surface structure and dynamics of ionic insulators, epitaxial growth onto alkali halide crystals and multiphoton studies. The surface dynamics of RbCl has been re-examined. We have developed a simple force constant model which provides insight into the dynamics of KBr overlayers on NaCl(001), a system with a large lattice mismatch. The KBr/NaCl(001) results are compared to Na/Cu(001) and NaCl/Ge(001). We have completed epitaxial growth experiments for KBr onto RbCl(001). Slab dynamics calculations using a shell model for this system with very small lattice mismatch are being carried out in collaboration with Professor Manson of Clemson University and with Professor Schroeder in Regensburg, Germany. Extensive experiments on multiphoton scattering of helium atoms onto NaCl and, particularly, LiF have been carried out and the theory has been developed to a rather advanced stage by Professor Manson. This work will permit the extraction of more information from time-of-flight spectra. It is shown that the theoretical model provides a very good description of the multiphoton scattering from organic films. Work has started on self-assembling organic films on gold (alkyl thiols/Au(111)). We have begun to prepare and characterize the gold crystal; one of the group members has spent two weeks at the Oak Ridge National Laboratory learning the proper Au(111) preparation techniques. One of our students has carried out neutron scattering experiments on NiO, measuring both bulk phonon and magnon dispersion curves.
NASA Astrophysics Data System (ADS)
Moosavi, S. Amin; Montakhab, Afshin
2014-05-01
Motivated by recent experiments in neuroscience which indicate that neuronal avalanches exhibit scale invariant behavior similar to self-organized critical systems, we study the role of noisy (nonconservative) local dynamics on the critical behavior of a sandpile model which can be taken to mimic the dynamics of neuronal avalanches. We find that despite the fact that noise breaks the strict local conservation required to attain criticality, our system exhibits true criticality for a wide range of noise in various dimensions, given that conservation is respected on the average. Although the system remains critical, exhibiting finite-size scaling, the value of critical exponents change depending on the intensity of local noise. Interestingly, for a sufficiently strong noise level, the critical exponents approach and saturate at their mean-field values, consistent with empirical measurements of neuronal avalanches. This is confirmed for both two and three dimensional models. However, the addition of noise does not affect the exponents at the upper critical dimension (D =4). In addition to an extensive finite-size scaling analysis of our systems, we also employ a useful time-series analysis method to establish true criticality of noisy systems. Finally, we discuss the implications of our work in neuroscience as well as some implications for the general phenomena of criticality in nonequilibrium systems.
NASA Astrophysics Data System (ADS)
Pathak, Anand; Sinha, Sitabhra
2015-09-01
Many complex systems can be represented as networks of dynamical elements whose states evolve in response to interactions with neighboring elements, noise and external stimuli. The collective behavior of such systems can exhibit remarkable ordering phenomena such as chimera order corresponding to coexistence of ordered and disordered regions. Often, the interactions in such systems can also evolve over time responding to changes in the dynamical states of the elements. Link adaptation inspired by Hebbian learning, the dominant paradigm for neuronal plasticity, has been earlier shown to result in structural balance by removing any initial frustration in a system that arises through conflicting interactions. Here we show that the rate of the adaptive dynamics for the interactions is crucial in deciding the emergence of different ordering behavior (including chimera) and frustration in networks of Ising spins. In particular, we observe that small changes in the link adaptation rate about a critical value result in the system exhibiting radically different energy landscapes, viz., smooth landscape corresponding to balanced systems seen for fast learning, and rugged landscapes corresponding to frustrated systems seen for slow learning.
The Ramifications of Meddling with Systems Governed by Self-organized Critical Dynamics
NASA Astrophysics Data System (ADS)
Carreras, B. A.; Newman, D. E.; Dobson, I.
2002-12-01
Complex natural, well as man-made, systems often exhibit characteristics similar to those seen in self-organized critical (SOC) systems. The concept of self-organized criticality brings together ideas of self-organization of nonlinear dynamical systems with the often-observed near critical behavior of many natural phenomena. These phenomena exhibit self-similarities over extended ranges of spatial and temporal scales. In those systems, scale lengths may be described by fractal geometry and time scales that lead to 1/f-like power spectra. Natural applications include modeling the motion of tectonics plates, forest fires, magnetospheric dynamics, spin glass systems, and turbulent transport. In man-made systems, applications have included traffic dynamics, power and communications networks, and financial markets among many others. Simple cellular automata models such as the running sandpile model have been very useful in reproducing the complexity and characteristics of these systems. One characteristic property of the SOC systems is that they relax through what we call events. These events can happen over all scales of the system. Examples of these events are: earthquakes in the case of plate tectonic; fires in forest evolution extinction in the co evolution of biological species; and blackouts in power transmission systems. In a time-averaged sense, these systems are subcritical (that is, they lie in an average state that should not trigger any events) and the relaxation events happen intermittently. The time spent in a subcritical state relative to the time of the events varies from one system to another. For instance, the chance of finding a forest on fire is very low with the frequency of fires being on the order of one fire every few years and with many of these fires small and inconsequential. Very large fires happen over time periods of decades or even centuries. However, because of their consequences, these large but infrequent events are the important ones
Ocean surface winds drive dynamics of transoceanic aerial movements.
Felicísimo, Angel M; Muñoz, Jesús; González-Solis, Jacob
2008-08-13
Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through "wind highways" that do not match the shortest great circle routes. Bird routes closely followed the low-cost "wind-highways" linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns.
Jaworska, Aleksandra; Fornasaro, Stefano; Sergo, Valter; Bonifacio, Alois
2016-09-19
Surface-Enhanced Raman Spectroscopy (SERS) is a label-free technique that enables quick monitoring of substances at low concentrations in biological matrices. These advantages make it an attractive tool for the development of point-of-care tests suitable for Therapeutic Drug Monitoring (TDM) of drugs with a narrow therapeutic window, such as chemotherapeutic drugs, immunosuppressants, and various anticonvulsants. In this article, the current applications of SERS in the field of TDM for cancer therapy are discussed in detail and illustrated according to the different strategies and substrates. In particular, future perspectives are provided and special concerns regarding the standardization of self-assembly methods and nanofabrication procedures, quality assurance, and technology readiness are critically evaluated.
Jaworska, Aleksandra; Fornasaro, Stefano; Sergo, Valter; Bonifacio, Alois
2016-01-01
Surface-Enhanced Raman Spectroscopy (SERS) is a label-free technique that enables quick monitoring of substances at low concentrations in biological matrices. These advantages make it an attractive tool for the development of point-of-care tests suitable for Therapeutic Drug Monitoring (TDM) of drugs with a narrow therapeutic window, such as chemotherapeutic drugs, immunosuppressants, and various anticonvulsants. In this article, the current applications of SERS in the field of TDM for cancer therapy are discussed in detail and illustrated according to the different strategies and substrates. In particular, future perspectives are provided and special concerns regarding the standardization of self-assembly methods and nanofabrication procedures, quality assurance, and technology readiness are critically evaluated. PMID:27657146
Surface and Shear Wave Analysis of the Critical Zone in Betasso Catchment, Colorado
NASA Astrophysics Data System (ADS)
Andrus, A. B.; Befus, K. M.; Sheehan, A. F.
2009-12-01
Seismic surface waves, once considered an inhibitor to the interpretation of active source seismic data, have become useful in determining shear wave velocity (Vs) structure of the shallow subsurface. We employed three seismic methods to characterize the shallow subsurface of the Betasso catchment, west of Boulder, Colorado. As part of a multidisciplinary study of the weathered and weathering hydrologically active near surface environment, shallow geophysical data provide an essential, noninvasive subsurface image of the critical zone. In general, weathered rock (saprolite) overlies granitic bedrock with soils and transported material above. Shear wave-derived velocity structure offer an independent confirmation of compressional wave (Vp) profiles and allow us to calculate Poisson's ratio and Vp/Vs as indicators of material properties, porosity, and water content. We obtained Vs structure using three seismic collection methods: (1) S-refraction with horizontal component geophones, (2) Multichannel Analysis of Surface Waves (MASW), and (3) Refraction Microtremor (ReMi) surface wave analysis. Based upon this field test, the S-refraction method is preferred based on data quality. The MASW technique produces Vs images with lower resolution than S-refraction, but has the distinct advantage that MASW data can be collected simultaneously with our standard P-refraction data acquisition. The Vs techniques all result in similar velocity structures to the Vp profile with roughly half the velocity for corresponding layers. Bedrock Vp values appear in the 2400-4400 m/s range while Vs values are 1200-2000 m/s. S-refraction yields bedrock Vs values 0-40% higher than MASW. Additionally, the depth to layer interfaces remains generally within 1 m (approx. 2-5%) between results from each survey method. Profiles showing Poisson's ratio and Vp/Vs across each survey line show reasonable values for the expected subsurface materials. In general, for the three-layer structure of soil
NASA Astrophysics Data System (ADS)
Vishwanath, Ashvin; Senthil, T.
2013-01-01
We discuss physical properties of “integer” topological phases of bosons in D=3+1 dimensions, protected by internal symmetries like time reversal and/or charge conservation. These phases invoke interactions in a fundamental way but do not possess topological order; they are bosonic analogs of free-fermion topological insulators and superconductors. While a formal cohomology-based classification of such states was recently discovered, their physical properties remain mysterious. Here, we develop a field-theoretic description of several of these states and show that they possess unusual surface states, which, if gapped, must either break the underlying symmetry or develop topological order. In the latter case, symmetries are implemented in a way that is forbidden in a strictly two-dimensional theory. While these phases are the usual fate of the surface states, exotic gapless states can also be realized. For example, tuning parameters can naturally lead to a deconfined quantum critical point or, in other situations, to a fully symmetric vortex metal phase. We discuss cases where the topological phases are characterized by a quantized magnetoelectric response θ, which, somewhat surprisingly, is an odd multiple of 2π. Two different surface theories are shown to capture these phenomena: The first is a nonlinear sigma model with a topological term. The second invokes vortices on the surface that transform under a projective representation of the symmetry group. We identify a bulk-field theory consistent with these properties, which is a multicomponent background-field theory supplemented, crucially, with a topological term. We also provide bulk sigma-model field theories of these phases and discuss a possible topological phase characterized by the thermal analog of the magnetoelectric effect.
NASA Astrophysics Data System (ADS)
Bourque, Alexander; Rutledge, Gregory
2015-03-01
Crystal growth from the melt of n-pentacontane (C50) was studied by molecular dynamics simulation using a validated united atom model. By quenching below the melting temperature of C50 (370 K), propagation of the crystal growth front into the C50 melt from a crystalline polyethylene surface was observed. By tracking the location of the midpoint in the orientational order parameter profile between the crystal and melt, crystal growth rates between 0.015-0.040 m/s were observed, for quench depths of 10 to 70 K below the melting point. In this work, surface nucleation is identified with the formation of 2D clusters of crystalline sites within layers parallel to the propagating growth front, by analogy to the formation of 3D clusters in primary, homogeneous nucleation. These surface nucleation events were tracked over several layers and numerous simulations, and a mean first passage time analysis was employed to estimate critical nucleus sizes, induction times and rates for surface nucleation. Based on new insights provided by the detailed molecular trajectories obtained from simulation, the classical theory proposed by Lauritzen and Hoffman is re-examined.
On trajectory-based nonadiabatic dynamics: Bohmian dynamics versus trajectory surface hopping
NASA Astrophysics Data System (ADS)
Curchod, Basile F. E.; Tavernelli, Ivano
2013-05-01
In this work, we present a complete derivation of the NonAdiabatic Bohmian DYnamics (NABDY) equations of motion. This approach naturally emerges from a transformation of the molecular time-dependent Schrödinger equation in the adiabatic representation of the electronic states. The numerical implementation of the method is discussed while simple nonadiabatic models are employed to address the accuracy of NABDY and to reveal its ability to capture nuclear quantum effects that are missed in trajectory surface hopping (TSH) due to the independent trajectory approximation. A careful comparison of the correlated, NABDY, and the uncorrelated, TSH, propagation is also given together with a description of the main approximations and assumptions underlying the "derivation" of a nonadiabatic molecular dynamics scheme based on classical trajectories.
On trajectory-based nonadiabatic dynamics: Bohmian dynamics versus trajectory surface hopping.
Curchod, Basile F E; Tavernelli, Ivano
2013-05-14
In this work, we present a complete derivation of the NonAdiabatic Bohmian DYnamics (NABDY) equations of motion. This approach naturally emerges from a transformation of the molecular time-dependent Schrödinger equation in the adiabatic representation of the electronic states. The numerical implementation of the method is discussed while simple nonadiabatic models are employed to address the accuracy of NABDY and to reveal its ability to capture nuclear quantum effects that are missed in trajectory surface hopping (TSH) due to the independent trajectory approximation. A careful comparison of the correlated, NABDY, and the uncorrelated, TSH, propagation is also given together with a description of the main approximations and assumptions underlying the "derivation" of a nonadiabatic molecular dynamics scheme based on classical trajectories.
He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth
Not Available
1992-01-01
Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices.
NASA Astrophysics Data System (ADS)
Anokhina, E. V.
2010-05-01
Data on critical heat loads q cr for the saturated and unsaturated pool boiling of water and ethanol under atmospheric pressure are reported. It is found experimentally that the critical heat load does not necessarily coincide with the heat load causing burnout of the heater, which should be taken into account. The absolute values of q cr for the boiling of water and ethanol on copper surfaces 65, 80, 100, 120, and 200 μm in diameter; tungsten surface 100 μm in diameter; and nichrome surface 100 μm in diameter are obtained experimentally.
Critical appraisal of excited state nonadiabatic dynamics simulations of 9H-adenine.
Barbatti, Mario; Lan, Zhenggang; Crespo-Otero, Rachel; Szymczak, Jaroslaw J; Lischka, Hans; Thiel, Walter
2012-12-14
In spite of the importance of nonadiabatic dynamics simulations for the understanding of ultrafast photo-induced phenomena, simulations based on different methodologies have often led to contradictory results. In this work, we proceed through a comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods). Simulations that employ ab initio and semi-empirical multireference configuration interaction methods predict the experimentally observed ultrafast deactivation of 9H-adenine with similar time scales, however, through different internal conversion channels. Simulations based on time-dependent density functional theory with six different hybrid and range-corrected functionals fail to predict the ultrafast deactivation. The origin of these differences is analyzed by systematic calculations of the relevant reaction pathways, which show that these discrepancies can always be traced back to topographical features of the underlying potential energy surfaces.
Critical appraisal of excited state nonadiabatic dynamics simulations of 9H-adeninea)
NASA Astrophysics Data System (ADS)
Barbatti, Mario; Lan, Zhenggang; Crespo-Otero, Rachel; Szymczak, Jaroslaw J.; Lischka, Hans; Thiel, Walter
2012-12-01
In spite of the importance of nonadiabatic dynamics simulations for the understanding of ultrafast photo-induced phenomena, simulations based on different methodologies have often led to contradictory results. In this work, we proceed through a comprehensive investigation of on-the-fly surface-hopping simulations of 9H-adenine in the gas phase using different electronic structure theories (ab initio, semi-empirical, and density functional methods). Simulations that employ ab initio and semi-empirical multireference configuration interaction methods predict the experimentally observed ultrafast deactivation of 9H-adenine with similar time scales, however, through different internal conversion channels. Simulations based on time-dependent density functional theory with six different hybrid and range-corrected functionals fail to predict the ultrafast deactivation. The origin of these differences is analyzed by systematic calculations of the relevant reaction pathways, which show that these discrepancies can always be traced back to topographical features of the underlying potential energy surfaces.
NASA Astrophysics Data System (ADS)
Lazo, M. J.; Ferreira, A. A.; Alcaraz, F. C.
2015-11-01
We obtained the exact solution of a probabilistic cellular automaton related to the diagonal-to-diagonal transfer matrix of the six-vertex model on a square lattice. The model describes the flow of ants (or particles), traveling on a one-dimensional lattice whose sites are small craters containing sleeping or awake ants (two kinds of particles). We found the Bethe ansatz equations and the spectral gap for the time-evolution operator of the cellular automaton. From the spectral gap we show that in the asymmetric case it belongs to the Kardar-Parisi-Zhang (KPZ) universality class, exhibiting a dynamical critical exponent value z = 3/2. This result is also obtained from a direct Monte Carlo simulation, by evaluating the lattice-size dependence of the decay time to the stationary state.
Karki, Pragalv; Loh, Yen Lee
2016-11-02
We simulate three types of random inductor-capacitor (LC) networks on [Formula: see text] square lattices. We calculate the dynamical conductivity using an equation-of-motion method in which timestep error is eliminated and windowing error is minimized. We extract the critical exponent a such that [Formula: see text] at low frequencies. The results suggest that there are three different universality classes. The [Formula: see text] model, with capacitances from each site to ground, has a = 0.314(4). The [Formula: see text] model, with capacitances along bonds, has a = 0. The [Formula: see text] model, with both types of capacitances, has a = 0.304(1). This implies that classical percolative 2D superconductor-insulator transitions (SITs) generically have [Formula: see text] as [Formula: see text]. Therefore, any experiments that give a constant conductivity as [Formula: see text] must be explained in terms of quantum effects.
NASA Astrophysics Data System (ADS)
Karki, Pragalv; Loh, Yen Lee
We simulate three types of random inductor-capacitor (LC) networks on 4000x4000 lattices. We calculate the dynamical conductivity using an equation-of-motion method in which timestep error is eliminated and windowing error is minimized. We extract the critical exponent a such that σ (ω) ~ω-a at low frequencies. The results suggest that there are three different universality classes. The LijCi model, with capacitances from each site to ground, has a = 0 . 32 . The LijCij model, with capacitances along bonds, has a = 0 . The LijCiCij model, with both types of capacitances, has a = 0 . 30 . This implies that classical percolative 2D superconductor-insulator transitions (SITs) generically have σ (ω) --> ∞ as ω --> 0 . Therefore, experiments that give a constant conductivity as ω --> 0 must be explained in terms of quantum effects.
Inhomogeneous quasi-adiabatic driving of quantum critical dynamics in weakly disordered spin chains
NASA Astrophysics Data System (ADS)
Rams, Marek M.; Mohseni, Masoud; del Campo, Adolfo
2016-12-01
We introduce an inhomogeneous protocol to drive a weakly disordered quantum spin chain quasi-adiabatically across a quantum phase transition and minimize the residual energy of the final state. The number of spins that simultaneously reach the critical point is controlled by the length scale in which the magnetic field is modulated, introducing an effective size that favors adiabatic dynamics. The dependence of the residual energy on this length scale and the velocity at which the magnetic field sweeps out the chain is shown to be nonmonotonic. We determine the conditions for an optimal suppression of the residual energy of the final state and show that inhomogeneous driving can outperform conventional adiabatic schemes based on homogeneous control fields by several orders of magnitude.
LDEF (Postflight), S1002 : Investigation of Critical Surface Degradation Effects on Coating and Sola
NASA Technical Reports Server (NTRS)
1990-01-01
LDEF (Postflight), S1002 : Investigation of Critical Surface Degradation Effects on Coating and Solar Cells Developed in Germany, Tray E03 The postflight photograph was taken in the SAEF II at KSC after the experiment was removed from the LDEF. The capture cells of experiment A0187-02 are in the left two thirdsThe Experiment Exposure Control Canister containing experiment S1002 is the item located in the right one third section of the tray. Details of the EECC containing the experiment cannot be defined due to the glare of the lights on the aluminum surfaces. The brown stain is clearly visible on the left end of the bottom tray flange. Note the spring collar near the lower end of the lead screw. The collar, pushed along the lead screw as the door opens, is an indication that the EECC did open and close while in orbit. The green tint on the two (2) debris panels is a by-product of the chromic anodize coating process and not attributed to contamination and/or exposure to the space environment. A light colored irregular shaped vertical streak is seen on the right debris panel. The light band across the top and bottom edges of the panels is caused by light reflecting from the tray sidewalls.
NASA Astrophysics Data System (ADS)
Xi, Yakun; Zhang, Cheng
2017-03-01
We show that one can obtain improved L 4 geodesic restriction estimates for eigenfunctions on compact Riemannian surfaces with nonpositive curvature. We achieve this by adapting Sogge's strategy in (Improved critical eigenfunction estimates on manifolds of nonpositive curvature, Preprint). We first combine the improved L 2 restriction estimate of Blair and Sogge (Concerning Toponogov's Theorem and logarithmic improvement of estimates of eigenfunctions, Preprint) and the classical improved {L^∞} estimate of Bérard to obtain an improved weak-type L 4 restriction estimate. We then upgrade this weak estimate to a strong one by using the improved Lorentz space estimate of Bak and Seeger (Math Res Lett 18(4):767-781, 2011). This estimate improves the L 4 restriction estimate of Burq et al. (Duke Math J 138:445-486, 2007) and Hu (Forum Math 6:1021-1052, 2009) by a power of {(log logλ)^{-1}}. Moreover, in the case of compact hyperbolic surfaces, we obtain further improvements in terms of {(logλ)^{-1}} by applying the ideas from (Chen and Sogge, Commun Math Phys 329(3):435-459, 2014) and (Blair and Sogge, Concerning Toponogov's Theorem and logarithmic improvement of estimates of eigenfunctions, Preprint). We are able to compute various constants that appeared in (Chen and Sogge, Commun Math Phys 329(3):435-459, 2014) explicitly, by proving detailed oscillatory integral estimates and lifting calculations to the universal cover H^2.
NASA Astrophysics Data System (ADS)
Ukkola, A.; Pitman, A.; Decker, M. R.; De Kauwe, M. G.; Abramowitz, G.; Wang, Y.; Kala, J.
2015-12-01
Surface fluxes from land surface models (LSM) have traditionally been evaluated against monthly, seasonal or annual mean states. Previous studies have noted the limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions but very few studies have systematically evaluated LSMs during rainfall deficits. We investigate the performance of the Community Atmosphere Biosphere Land Exchange (CABLE) LSM in simulating latent heat fluxes in offline mode. CABLE is evaluated against eddy covariance measurements of latent heat flux across 20 flux tower sites at sub-annual to inter-annual time scales, with a focus on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux is explored by employing alternative representations of hydrology, soil properties, leaf area index and stomatal conductance. We demonstrate the critical role of hydrological processes for capturing observed declines in latent heat. The effects of soil, LAI and stomatal conductance are shown to be highly site-specific. The default CABLE performs reasonably well at annual scales despite grossly underestimating latent heat during rainfall deficits, highlighting the importance for evaluating models explicitly under water-stressed conditions across multiple vegetation and climate regimes. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions but remaining deficiencies point to future research needs.
NASA Astrophysics Data System (ADS)
Ukkola, Anna M.; Pitman, Andy J.; Decker, Mark; De Kauwe, Martin G.; Abramowitz, Gab; Kala, Jatin; Wang, Ying-Ping
2016-06-01
Surface fluxes from land surface models (LSMs) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual timescales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux was explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance were highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions, but remaining biases point to future research needs. Our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.
NASA Astrophysics Data System (ADS)
Ukkola, A. M.; Pitman, A. J.; Decker, M.; De Kauwe, M. G.; Abramowitz, G.; Kala, J.; Wang, Y.-P.
2015-10-01
Surface fluxes from land surface models (LSM) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat flux simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual time scales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux are explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance are shown to be highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions but remaining biases point to future research needs. Our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.
Rapid filamentation of high power lasers at the quarter critical surface
Brady, C. S.; Lawrence-Douglas, A.; Arber, T. D.
2012-06-15
A novel mechanism for initiating laser filamentation for intensities above 5 Multiplication-Sign 10{sup 17} W/cm{sup 2} is presented, seeded by the transient interference of an incident laser and its Raman backscattered daughter wave. For lasers propagating up short scale-length density gradients, the Raman reflectivity is peaked near the relativistically corrected quarter critical surface (RCQCS) and thus filamentation is observed to start on this surface. The filamentation at the RCQCS occurs on timescales comparable to the laser period. A series of 2D particle-in-cell (PIC) simulations confirm this physical model. Growth rates are obtained from simulations for a variety of simulation parameters and a simplified model in which the RCQCS behaves as a partially reflecting mirror, with the reflected light at double the wavelength of the incident light, is shown to reproduce the number and approximate location of filaments from PIC simulations. It was also proposed that field ionisation may alter RCQCS formation and the method of inclusion for this into the PIC simulation is presented. Additional simulations demonstrate field ionisation to have a negligible effect on the formation of the RCQCS. The implications of this filamentation mechanism for plasma experiments which require focused light of intensities above 5 Multiplication-Sign 10{sup 17} W/cm{sup 2} to propagate beyond the RCQCS are discussed.
Ukkola, Anna M.; Pitman, Andy J.; Decker, Mark; De Kauwe, Martin G.; Abramowitz, Gab; Kala, Jatin; Wang, Ying -Ping
2016-06-21
Surface fluxes from land surface models (LSMs) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual timescales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux was explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance were highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions, but remaining biases point to future research needs. Lastly, our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.
Ukkola, Anna M.; Pitman, Andy J.; Decker, Mark; ...
2016-06-21
Surface fluxes from land surface models (LSMs) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual timescales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux was explored by employing alternative representations of hydrology, leafmore » area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance were highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions, but remaining biases point to future research needs. Lastly, our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.« less
Knoeri, Christof; Wäger, Patrick A; Stamp, Anna; Althaus, Hans-Joerg; Weil, Marcel
2013-09-01
Emerging technologies such as information and communication-, photovoltaic- or battery technologies are expected to increase significantly the demand for scarce metals in the near future. The recently developed methods to evaluate the criticality of mineral raw materials typically provide a 'snapshot' of the criticality of a certain material at one point in time by using static indicators both for supply risk and for the impacts of supply restrictions. While allowing for insights into the mechanisms behind the criticality of raw materials, these methods cannot account for dynamic changes in products and/or activities over time. In this paper we propose a conceptual framework intended to overcome these limitations by including the dynamic interactions between different possible demand and supply configurations. The framework integrates an agent-based behaviour model, where demand emerges from individual agent decisions and interaction, into a dynamic material flow model, representing the materials' stocks and flows. Within the framework, the environmental implications of substitution decisions are evaluated by applying life-cycle assessment methodology. The approach makes a first step towards a dynamic criticality assessment and will enhance the understanding of industrial substitution decisions and environmental implications related to critical metals. We discuss the potential and limitation of such an approach in contrast to state-of-the-art methods and how it might lead to criticality assessments tailored to the specific circumstances of single industrial sectors or individual companies.
Moosavi, S Amin; Montakhab, Afshin
2015-01-01
Critical dynamics of cortical neurons have been intensively studied over the past decade. Neuronal avalanches provide the main experimental as well as theoretical tools to consider criticality in such systems. Experimental studies show that critical neuronal avalanches show mean-field behavior. There are structural as well as recently proposed [Phys. Rev. E 89, 052139 (2014)] dynamical mechanisms that can lead to mean-field behavior. In this work we consider a simple model of neuronal dynamics based on threshold self-organized critical models with synaptic noise. We investigate the role of high-average connectivity, random long-range connections, as well as synaptic noise in achieving mean-field behavior. We employ finite-size scaling in order to extract critical exponents with good accuracy. We conclude that relevant structural mechanisms responsible for mean-field behavior cannot be justified in realistic models of the cortex. However, strong dynamical noise, which can have realistic justifications, always leads to mean-field behavior regardless of the underlying structure. Our work provides a different (dynamical) origin than the conventionally accepted (structural) mechanisms for mean-field behavior in neuronal avalanches.
Wennberg, Christian L; Murtola, Teemu; Hess, Berk; Lindahl, Erik
2013-08-13
The accuracy of electrostatic interactions in molecular dynamics advanced tremendously with the introduction of particle-mesh Ewald (PME) summation almost 20 years ago. Lattice summation electrostatics is now the de facto standard for most types of biomolecular simulations, and in particular, for lipid bilayers, it has been a critical improvement due to the large charges typically present in zwitterionic lipid headgroups. In contrast, Lennard-Jones interactions have continued to be handled with increasingly longer cutoffs, partly because few alternatives have been available despite significant difficulties in tuning cutoffs and parameters to reproduce lipid properties. Here, we present a new Lennard-Jones PME implementation applied to lipid bilayers. We confirm that long-range contributions are well approximated by dispersion corrections in simple systems such as pentadecane (which makes parameters transferable), but for inhomogeneous and anisotropic systems such as lipid bilayers there are large effects on surface tension, resulting in up to 5.5% deviations in area per lipid and order parameters-far larger than many differences for which reparameterization has been attempted. We further propose an approximation for combination rules in reciprocal space that significantly reduces the computational cost of Lennard-Jones PME and makes accurate treatment of all nonbonded interactions competitive with simulations employing long cutoffs. These results could potentially have broad impact on important applications such as membrane proteins and free energy calculations.
Ocean Surface Winds Drive Dynamics of Transoceanic Aerial Movements
Felicísimo, Ángel M.; Muñoz, Jesús; González-Solis, Jacob
2008-01-01
Global wind patterns influence dispersal and migration processes of aerial organisms, propagules and particles, which ultimately could determine the dynamics of colonizations, invasions or spread of pathogens. However, studying how wind-mediated movements actually happen has been hampered so far by the lack of high resolution global wind data as well as the impossibility to track aerial movements. Using concurrent data on winds and actual pathways of a tracked seabird, here we show that oceanic winds define spatiotemporal pathways and barriers for large-scale aerial movements. We obtained wind data from NASA SeaWinds scatterometer to calculate wind cost (impedance) models reflecting the resistance to the aerial movement near the ocean surface. We also tracked the movements of a model organism, the Cory's shearwater (Calonectris diomedea), a pelagic bird known to perform long distance migrations. Cost models revealed that distant areas can be connected through “wind highways” that do not match the shortest great circle routes. Bird routes closely followed the low-cost “wind-highways” linking breeding and wintering areas. In addition, we found that a potential barrier, the near surface westerlies in the Atlantic sector of the Intertropical Convergence Zone (ITCZ), temporally hindered meridional trans-equatorial movements. Once the westerlies vanished, birds crossed the ITCZ to their winter quarters. This study provides a novel approach to investigate wind-mediated movements in oceanic environments and shows that large-scale migration and dispersal processes over the oceans can be largely driven by spatiotemporal wind patterns. PMID:18698354
Trajectory surface-hopping study of methane photodissociation dynamics
Lodriguito, Maricris D.; Schatz, George C.; Lendvay, Gyoergy
2009-12-14
We use the fewest switches nonadiabatic trajectory surface hopping approach to study the photodissociation of methane on its lowest singlet excited state potential surface (1 {sup 1}T{sub 2}) at 122 nm, with emphasis on product state branching and energy partitioning. The trajectories and couplings are based on CASSCF(8,9) calculations with an aug-cc-pvdz basis set. We demonstrate that nonadiabatic dynamics is important to describe the dissociation processes. We find that CH{sub 3}(X-tilde{sup 2}A{sub 2}{sup ''})+H and CH{sub 2}(a-tilde{sup 1}A{sub 1})+H{sub 2} are the major dissociation channels, as have been observed experimentally. CH{sub 3}+H is mostly formed by direct dissociation that is accompanied by hopping to the ground state. CH{sub 2}+H{sub 2} can either be formed by hopping to the ground state to give CH{sub 2}(a-tilde{sup 1}A{sub 1})+H{sub 2} or by adiabatic dissociation to CH{sub 2}(b-tilde{sup 1}B{sub 1})+H{sub 2}. In the latter case, the CH{sub 2}(b-tilde{sup 1}B{sub 1}) can then undergo internal conversion to the ground singlet state by Renner-Teller induced hopping. Less important dissociation mechanisms lead to CH{sub 2}+H+H and to CH+H{sub 2}+H. Intersystem crossing effects, which are not included, do not seem essential to describe the experimentally observed branching behavior. About 5% of trajectories involve a roaming atom mechanism which can eventually lead to formation of products in any of the dissociation channels. Branching fractions to give H and H{sub 2} are in good agreement with experiment, and the H atom translational energy distribution shows bimodal character which also matches observations.
He atom surface spectroscopy: Surface lattice dynamics of insulators, metals and metal overlayers
Not Available
1990-01-01
During the first three years of this grant (1985--1988) the effort was devoted to the construction of a state-of-the-art He atom scattering (HAS) instrument which would be capable of determining the structure and dynamics of metallic, semiconductor or insulator crystal surfaces. The second three year grant period (1988--1991) has been dedicated to measurements. The construction of the instrument went better than proposed; it was within budget, finished in the proposed time and of better sensitivity and resolution than originally planned. The same success has been carried over to the measurement phase where the concentration has been on studies of insulator surfaces, as discussed in this paper. The experiments of the past three years have focused primarily on the alkali halides with a more recent shift to metal oxide crystal surfaces. Both elastic and inelastic scattering experiments were carried out on LiF, NaI, NaCl, RbCl, KBr, RbBr, RbI, CsF, CsI and with some preliminary work on NiO and MgO.
Toward an improved understanding of the role of transpiration in critical zone dynamics
NASA Astrophysics Data System (ADS)
Mitra, B.; Papuga, S. A.
2012-12-01
Evapotranspiration (ET) is an important component of the total water balance across any ecosystem. In subalpine mixed-conifer ecosystems, transpiration (T) often dominates the total water flux and therefore improved understanding of T is critical for accurate assessment of catchment water balance and for understanding of the processes that governs the complex dynamics across critical zone (CZ). The interaction between T and plant vegetation not only modulates soil water balance but also influences water transit time and hydrochemical flux - key factors in our understanding of how the CZ evolves and responds. Unlike an eddy covariance system which provides only an integrated ET flux from an ecosystem, a sap flow system can provide an estimate of the T flux from the ecosystem. By isolating T, the ecohydrological drivers of this major water loss from the CZ can be identified. Still, the species composition of mixed-conifer ecosystems vary and the drivers of T associated with each species are expected to be different. Therefore, accurate quantification of T from a mixed-conifer requires knowledge of the unique transpiration dynamics of each of the tree species. Here, we installed a sap flow system within two mixed-conifer study sites of the Jemez River Basin - Santa Catalina Mountains Critical Zone Observatory (JRB - SCM CZO). At both sites, we identified the dominant tree species and installed sap flow sensors on healthy representatives for each of those species. At the JRB CZO site, sap sensors were installed in fir (4) and spruce (4) trees; at the SCM CZO site, sap sensors were installed at white fir (4) and maple (4) and one dead tree. Meteorological data as well as soil temperature (Ts) and soil moisture (θ) at multiple depths were also collected from each of the two sites. Preliminary analysis of two years of sap flux rate at JRB - SCM CZO shows that the environmental drivers of fir, spruce, and maple are different and also vary throughout the year. For JRB fir
U{sub A}(1) anomaly in hot and dense QCD and the critical surface
Chen, J.-W.; Fukushima, Kenji; Kohyama, Hiroaki; Ohnishi, Kazuaki; Raha, Udit
2009-09-01
We discuss the chiral phase transition in hot and dense QCD with three light flavors. Inspired by the well-known fact that the U{sub A}(1) anomaly could induce first order phase transitions, we study the effect of the possible restoration of the U{sub A}(1) symmetry at finite density. In particular, we explore the link between the U{sub A}(1) restoration and the recent lattice QCD results of de Forcrand and Philipsen, in which the first order phase transition region near zero chemical potential ({mu}) shrinks in the quark mass and {mu} space when {mu} is increased. Starting from the Ginzburg-Landau theory for general discussions, we then use the Nambu-Jona-Lasinio model for quantitative studies. With the partial U{sub A}(1) restoration modeled by the density dependent 't Hooft interaction, we fit the shrinking of the first order region found in de Forcrand and Philipsen's lattice calculation at low {mu}. At higher {mu}, the first order region might shrink or expand, depending on the scenarios. This raises the possibility that despite the shrinking of the first order region at lower {mu}, the QCD critical end point might still exist due to the expansion at higher {mu}. In this case, very high precision lattice data will be needed to detect the recently observed backbending of the critical surface with the currently available analytic continuation or Taylor expansion approaches. Lattice computations could, however, test whether the U{sub A}(1) restoration is responsible for the shrinking of the first order region by computing the {eta}{sup '} mass or the topological susceptibility at small {mu}.
Catchment organisation, free energy dynamics and network control on critical zone water flows
NASA Astrophysics Data System (ADS)
Zehe, E.; Ehret, U.; Kleidon, A.; Jackisch, C.; Scherer, U.; Blume, T.
2012-04-01
as that these flow structures organize and dominate flows of water, dissolved matter and sediments during rainfall driven conditions at various scales: - Surface connected vertical flow structures of anecic worm burrows or soil cracks organize and dominated vertical flows at the plot scale - this is usually referred to as preferential flow; - Rill networks at the soil surface organise and dominate hillslope scale overland flow response and sediment yields; - Subsurface pipe networks at the bedrock interface organize and dominate hillslope scale lateral subsurface water and tracer flows; - The river net organizes and dominates flows of water, dissolved matter and sediments to the catchment outlet and finally across continental gradients to the sea. Fundamental progress with respect to the parameterization of hydrological models, subscale flow networks and to understand the adaptation of hydro-geo ecosystems to change could be achieved by discovering principles that govern the organization of catchments flow networks in particular at least during steady state conditions. This insight has inspired various scientists to suggest principles for organization of ecosystems, landscapes and flow networks; as Bejans constructural law, Minimum Energy Expenditure , Maximum Entropy Production. In line with these studies we suggest that a thermodynamic/energetic treatment of the catchment is might be a key for understanding the underlying principles that govern organisation of flow and transport. Our approach is to employ a) physically based hydrological model that address at least all the relevant hydrological processes in the critical zone in a coupled way, behavioural representations of the observed organisation of flow structures and textural elements, that are consistent with observations in two well investigated research catchments and have been tested against distributed observations of soil moisture and catchment scale discharge; to simulate the full concert of hydrological
Exploring the free energy surface using ab initio molecular dynamics
NASA Astrophysics Data System (ADS)
Samanta, Amit; Morales, Miguel A.; Schwegler, Eric
2016-04-01
Efficient exploration of configuration space and identification of metastable structures in condensed phase systems are challenging from both computational and algorithmic perspectives. In this regard, schemes that utilize a set of pre-defined order parameters to sample the relevant parts of the configuration space [L. Maragliano and E. Vanden-Eijnden, Chem. Phys. Lett. 426, 168 (2006); J. B. Abrams and M. E. Tuckerman, J. Phys. Chem. B 112, 15742 (2008)] have proved useful. Here, we demonstrate how these order-parameter aided temperature accelerated sampling schemes can be used within the Born-Oppenheimer and the Car-Parrinello frameworks of ab initio molecular dynamics to efficiently and systematically explore free energy surfaces, and search for metastable states and reaction pathways. We have used these methods to identify the metastable structures and reaction pathways in SiO2 and Ti. In addition, we have used the string method [W. E, W. Ren, and E. Vanden-Eijnden, Phys. Rev. B 66, 052301 (2002); L. Maragliano et al., J. Chem. Phys. 125, 024106 (2006)] within the density functional theory to study the melting pathways in the high pressure cotunnite phase of SiO2 and the hexagonal closed packed to face centered cubic phase transition in Ti.
Bullock, James H.; Youchison, Dennis Lee; Ulrickson, Michael Andrew
2010-11-01
Several commercial computational fluid dynamics (CFD) codes now have the capability to analyze Eulerian two-phase flow using the Rohsenow nucleate boiling model. Analysis of boiling due to one-sided heating in plasma facing components (pfcs) is now receiving attention during the design of water-cooled first wall panels for ITER that may encounter heat fluxes as high as 5 MW/m2. Empirical thermalhydraulic design correlations developed for long fission reactor channels are not reliable when applied to pfcs because fully developed flow conditions seldom exist. Star-CCM+ is one of the commercial CFD codes that can model two-phase flows. Like others, it implements the RPI model for nucleate boiling, but it also seamlessly transitions to a volume-of-fluid model for film boiling. By benchmarking the results of our 3d models against recent experiments on critical heat flux for both smooth rectangular channels and hypervapotrons, we determined the six unique input parameters that accurately characterize the boiling physics for ITER flow conditions under a wide range of absorbed heat flux. We can now exploit this capability to predict the onset of critical heat flux in these components. In addition, the results clearly illustrate the production and transport of vapor and its effect on heat transfer in pfcs from nucleate boiling through transition to film boiling. This article describes the boiling physics implemented in CCM+ and compares the computational results to the benchmark experiments carried out independently in the United States and Russia. Temperature distributions agreed to within 10 C for a wide range of heat fluxes from 3 MW/m2 to 10 MW/m2 and flow velocities from 1 m/s to 10 m/s in these devices. Although the analysis is incapable of capturing the stochastic nature of critical heat flux (i.e., time and location may depend on a local materials defect or turbulence phenomenon), it is highly reliable in determining the heat flux where boiling instabilities begin
Setterbo, Jacob J.; Chau, Anh; Fyhrie, Patricia B.; Hubbard, Mont; Upadhyaya, Shrini K.; Symons, Jennifer E.; Stover, Susan M.
2012-01-01
Background Racetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior. Objective To develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties. Methods Track-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression. Results Most dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces. Conclusions Laboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD
STRUCTURAL DYNAMICS OF METAL PARTITIONING TO MINERAL SURFACES
The conceptual understanding of surface complexation reactions that control trace element partitioning to mineral surfaces is limited by the assumption that the solid reactant possesses a finite, time-invariant population of surface functional groups. This assumption has limited...
LDEF (Prelaunch), S1002 : Investigation of Critical Surface Degradation Effects on Coating and Solar
NASA Technical Reports Server (NTRS)
1984-01-01
LDEF (Prelaunch), S1002 : Investigation of Critical Surface Degradation Effects on Coating and Solar Cells Developed in Germany, Tray E03 The prelaunch photograph provides a view of the two (2) experiments located in a six (6) inch LDEF experiment tray. The A0187-02 is located in the right two thirds (2/3rd) of the tray and the EECC containing the S1002 experiment occupies the remaining section. The tan colored strips on the tray flanges are protective coatings that are removed prior to tray testing. S1002 - The Effects on Coatings and Solar Cells experiment is contained within the Experiment Exposure Control Canister (EECC) that is located in the left one third (1/3rd) of the experiment tray. The EECC hardware consists of the housing, the drawer that contains the experiment samples, the drawer opening and closing mechanism (a screw drive system) and chromic anodized aluminum thermal covers that are seen in the photograph. The hardware is fabricated from aluminum or non-magnetic steels and is assembled with non-magnetic stainless steel fasteners. The canister will be opened in orbit after the LDEF has been deployed, the Orbiter has departed and initial outgassing of materials on the LDEF has occurred. The canister is programmed to close approximately nine (9) months after opening and prior to the scheduled LDEF retrieval. Experiment samples located in the EECC consist of Second Surface Mirrors (SSM), SSM with Interference Filters (SSM/IF), SSM/IF with a Conductive Layer (SSM/IF/LS, Optical Solar Reflectors (OSR), Quartz Crystal Microbalance (QCM), Coatings and Solar Cell Modules of the types flown on the GEOS and OTS satellites.
NASA Astrophysics Data System (ADS)
Tao, Yu; Muller, Jan-Peter
2016-10-01
Higher spatial resolution imaging data is always desirable to the international community of planetary scientists interested in improving understanding of surface formation processes. We have previously developed a novel Super-resolution restoration (SRR) technique using Gotcha sub-pixel matching [Shin & Muller, PR, 2012], orthorectification, segmentation, and 4th order PDE-TV, called GPT SRR [Tao & Muller, PSS, 2016]. This technique is able to restore 5cm-12.5cm near rover scale images (Navcam at a range of ≥5m) from multi-angle repeat-pass 25cm resolution MRO HiRISE images [Tao & Muller, ISPRS, 2016].We have successfully applied the GPT-SRR to the MER and MSL missions (http://www.progisweb.eu), as well as the alleged site of the Beagle-2 spacecraft (https://www.flickr.com/photos/uclnews/albums/72157667609698345). In this work, we further apply GPT-SRR on areas with known dynamic changes, including Recurring Slope Lineae (RSL), Gullies, and Polar Dune Flows. We restore static surface and meanwhile track the dynamic features to characterise the "change", including directions and speed of the changes. We also demonstrate that such repeat images can be used to image the MER-A rover stuck in the sands.AcknowledgementsThe research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under iMars grant agreement no. 607379 as well as partial funding from the STFC "MSSL Consolidated Grant" ST/K000977/1.
Slovin, Mitchell R; Shirts, Michael R
2015-07-28
We quantify some of the effects of patterned nanoscale surface texture on static contact angles, dynamic contact angles, and dynamic contact angle hysteresis using molecular dynamics simulations of a moving Lennard-Jones droplet in contact with a solid surface. We observe static contact angles that change with the introduction of surface texture in a manner consistent with theoretical and experimental expectations. However, we find that the introduction of nanoscale surface texture at the length scale of 5-10 times the fluid particle size does not affect dynamic contact angle hysteresis even though it changes both the advancing and receding contact angles significantly. This result differs significantly from microscale experimental results where dynamic contact angle hysteresis decreases with the addition of surface texture due to an increase in the receding contact angle. Instead, we find that molecular-kinetic theory, previously applied only to nonpatterned surfaces, accurately describes dynamic contact angle and dynamic contact angle hysteresis behavior as a function of terminal fluid velocity. Therefore, at length scales of tens of nanometers, the kinetic phenomena such as contact line pinning observed at larger scales become insignificant in comparison to the effects of molecular fluctuations for moving droplets, even though the static properties are essentially scale-invariant. These findings may have implications for the design of highly hierarchical structures with particular wetting properties. We also find that quantitatively determining the trends observed in this article requires the careful selection of system and analysis parameters in order to achieve sufficient accuracy and precision in calculated contact angles. Therefore, we provide a detailed description of our two-surface, circular-fit approach to calculating static and dynamic contact angles on surfaces with nanoscale texturing.
Dynamics of groundwater-surface water interactions in urban streams
NASA Astrophysics Data System (ADS)
Musolff, A.; Schmidt, C.; Fleckenstein, J. H.
2010-12-01
In industrialized countries the majority of streams and rivers have been subject to changes in the hydrological regime and alteration of the channel morphology. Urban streams are typically characterized by “flashier” hydrographs as a result of more direct runoff from impervious surfaces. Channel structure and complexity are often impaired compared to pristine streams. As a consequence the potential for bedform-driven water flow in the streambed is reduced. The downward transport of oxygen by advective flow in the streambed is known to be of great ecological importance for the hyporheic macro and micro fauna and facilitates nutrient cycling and the degradation of organic pollutants. We studied the dynamics of groundwater-surface water exchange of two anthropogenically impacted streams in urban areas to examine the effects of variable hydrologic boundary conditions on water flux and redox conditions in the streambed. The first stream is fed by groundwater as well as storm-water from a large industrial area. Here, we monitored the variability of vertical hydraulic gradients, streambed temperature and redox conditions in the streambed over the course of 5 months. The second stream is frequently polluted by combined sewer overflows (CSO) from an urban watershed. Here, we measured the vertical hydraulic gradients, streambed temperature and electrical conductivity (EC) in the stream, the streambed and in the adjacent aquifer. Both streams are characterized by strong variations in hydraulic gradients due to the dynamic hydrographs as well as the variations in total head in the shallow aquifer. Therefore, magnitude and direction of water flux through the streambed changed significantly over time. At the first site long-term variations of redox conditions in the shallow streambed (0.1 m) were related to the direction of water fluxes. Downward water flow resulted in increased redox potentials. However, the high short-term variability of redox conditions could not be
Microscopic Receding Contact Line Dynamics on Pillar and Irregular Superhydrophobic Surfaces
Yeong, Yong Han; Milionis, Athanasios; Loth, Eric; Bayer, Ilker S.
2015-01-01
Receding angles have been shown to have great significance when designing a superhydrophobic surface for applications involving self-cleaning. Although apparent receding angles under dynamic conditions have been well studied, the microscopic receding contact line dynamics are not well understood. Therefore, experiments were performed to measure these dynamics on textured square pillar and irregular superhydrophobic surfaces at micron length scales and at micro-second temporal scales. Results revealed a consistent “slide-snap” motion of the microscopic receding line as compared to the “stick-slip” dynamics reported in previous studies. Interface angles between 40–60° were measured for the pre-snap receding lines on all pillar surfaces. Similar “slide-snap” dynamics were also observed on an irregular nanocomposite surface. However, the sharper features of the surface asperities resulted in a higher pre-snap receding line interface angle (~90°). PMID:25670630
Lu, Gui; Wang, Xiao-Dong; Duan, Yuan-Yuan
2016-10-01
Dynamic wetting is an important interfacial phenomenon in many industrial applications. There have been many excellent reviews of dynamic wetting, especially on super-hydrophobic surfaces with physical or chemical coatings, porous layers, hybrid micro/nano structures and biomimetic structures. This review summarizes recent research on dynamic wetting from the viewpoint of the fluids rather than the solid surfaces. The reviewed fluids range from simple Newtonian fluids to non-Newtonian fluids and complex nanofluids. The fundamental physical concepts and principles involved in dynamic wetting phenomena are also reviewed. This review focus on recent investigations of dynamic wetting by non-Newtonian fluids, including the latest experimental studies with a thorough review of the best dynamic wetting models for non-Newtonian fluids, to illustrate their successes and limitations. This paper also reports on new results on the still fledgling field of nanofluid wetting kinetics. The challenges of research on nanofluid dynamic wetting is not only due to the lack of nanoscale experimental techniques to probe the complex nanoparticle random motion, but also the lack of multiscale experimental techniques or theories to describe the effects of nanoparticle motion at the nanometer scale (10(-9) m) on the dynamic wetting taking place at the macroscopic scale (10(-3) m). This paper describes the various types of nanofluid dynamic wetting behaviors. Two nanoparticle dissipation modes, the bulk dissipation mode and the local dissipation mode, are proposed to resolve the uncertainties related to the various types of dynamic wetting mechanisms reported in the literature.
Greg Sitz
2011-08-12
The 2011 Gordon Conference on Dynamics at Surfaces is the 32nd 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 scattering dynamics, chemical reaction dynamics, non-adiabatic effects in reactive and inelastic scattering of molecules from surfaces, single molecule dynamics at surfaces, surface photochemistry, ultrafast dynamics at surfaces, and dynamics at water interfaces. The conference brings together investigators from a variety of scientific disciplines including chemistry, physics, materials science, geology, biophysics, and astronomy.
Study of cell-matrix adhesion dynamics using surface plasmon resonance imaging ellipsometry.
Kim, Se-Hwa; Chegal, Won; Doh, Junsang; Cho, Hyun Mo; Moon, Dae Won
2011-04-06
The interaction of cells with extracellular matrix, termed cell-matrix adhesions, importantly governs multiple cellular phenomena. Knowledge of the functional dynamics of cell-matrix adhesion could provide critical clues for understanding biological phenomena. We developed surface plasmon resonance imaging ellipsometry (SPRIE) to provide high contrast images of the cell-matrix interface in unlabeled living cells. To improve the contrast and sensitivity, the null-type imaging ellipsometry technique was integrated with an attenuated total reflection coupler. We verified that the imaged area of SPRIE was indeed a cell-matrix adhesion area by confocal microscopy imaging. Using SPRIE, we demonstrated that three different cell types exhibit distinct features of adhesion. SPRIE was applied to diverse biological systems, including during cell division, cell migration, and cell-cell communication. We imaged the cell-matrix anchorage of mitotic cells, providing the first label-free imaging of this interaction to our knowledge. We found that cell-cell communication can alter cell-matrix adhesion, possibly providing direct experimental evidence for cell-cell communication-mediated changes in cell adhesion. We also investigated shear-stress-induced adhesion dynamics in real time. Based on these data, we expect that SPRIE will be a useful methodology for studying the role of cell-matrix adhesion in important biological phenomena.
Universal critical-like scaling of dynamic properties in symmetry-selected glass formers
NASA Astrophysics Data System (ADS)
Drozd-Rzoska, Aleksandra; Rzoska, Sylwester J.; Paluch, Marian
2008-11-01
Evidence for a possible general validity of the critical-like behavior of dielectric relaxation time or viscosity τ,η∝(T-TC)-ϕ with ϕ →9 and TC
Study of spatio-temporal dynamics of laser-hole boring in near critical plasma
NASA Astrophysics Data System (ADS)
Tochitsky, Sergei; Gong, Chao; Fiuza, Frederico; Pigeon, Jeremy; Joshi, Chan
2015-11-01
At high-intensities of light, radiation pressure becomes one of the dominant mechanisms in laser-plasma interaction. The radiation pressure of an intense laser pulse can steepen and push the critical density region of an overdense plasma creating a cavity or a hole. This hole boring phenomenon is of importance in fast-ignition fusion, high-gradient laser-plasma ion acceleration, and formation of collisionless shocks. Here multi-frame picosecond optical interferometry is used for the first direct measurements of space and time dynamics of the density cavity as it is pushed forward by a train of CO2 laser pulses in a helium plasma. The measured values of the hole boring velocity into an overdense plasma as a function of laser intensity are consistent with a theory based on energy and momentum balance between the heated plasma and the laser and with two-dimensional numerical simulations. We show possibility to extract a relative plasma electron temperature within the laser pulse by applying an analytical theory to the measured hole boring velocities. This work was supported by DOE grant DE-SC0010064.
Poverty alleviation strategies in eastern China lead to critical ecological dynamics.
Zhang, Ke; Dearing, John A; Dawson, Terence P; Dong, Xuhui; Yang, Xiangdong; Zhang, Weiguo
2015-02-15
Poverty alleviation linked to agricultural intensification has been achieved in many regions but there is often only limited understanding of the impacts on ecological dynamics. A central need is to observe long term changes in regulating and supporting services as the basis for assessing the likelihood of sustainable agriculture or ecological collapse. We show how the analyses of 55 time-series of social, economic and ecological conditions can provide an evolutionary perspective for the modern Lower Yangtze River Basin region since the 1950s with powerful insights about the sustainability of modern ecosystem services. Increasing trends in provisioning ecosystem services within the region over the past 60 years reflect economic growth and successful poverty alleviation but are paralleled by steep losses in a range of regulating ecosystem services mainly since the 1980s. Increasing connectedness across the social and ecological domains after 1985 points to a greater uniformity in the drivers of the rural economy. Regime shifts and heightened levels of variability since the 1970s in local ecosystem services indicate progressive loss of resilience across the region. Of special concern are water quality services that have already passed critical transitions in several areas. Viewed collectively, our results suggest that the regional social-ecological system passed a tipping point in the late 1970s and is now in a transient phase heading towards a new steady state. However, the long-term relationship between economic growth and ecological degradation shows no sign of decoupling as demanded by the need to reverse an unsustainable trajectory.
NASA Technical Reports Server (NTRS)
Hui, W. H.
1985-01-01
Bifurcation theory is used to analyze the nonlinear dynamic stability characteristics of an aircraft subject to single-degree-of-freedom. The requisite moment of the aerodynamic forces in the equations of motion is shown to be representable in a form equivalent to the response to finite amplitude oscillations. It is shown how this information can be deduced from the case of infinitesimal-amplitude oscillations. The bifurcation theory analysis reveals that when the bifurcation parameter is increased beyond a critical value at which the aerodynamic damping vanishes, new solutions representing finite amplitude periodic motions bifurcate from the previously stable steady motion. The sign of a simple criterion, cast in terms of aerodynamic properties, determines whether the bifurcating solutions are stable or unstable. For the pitching motion of flat-plate airfoils flying at supersonic/hypersonic speed and for oscillation of flaps at transonic speed, the bifurcation is subcritical, implying either the exchanges of stability between steady and periodic motion are accompanied by hysteresis phenomena, or that potentially large aperiodic departures from steady motion may develop.
Critical dynamics of gravito-convective mixing in geological carbon sequestration
Soltanian, Mohamad Reza; Amooie, Mohammad Amin; Dai, Zhenxue; ...
2016-11-03
When CO2 is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO2 throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees. Zones with low effective vertical permeability may suppress fingering and reduce vertical spreading, while potentially increasing transverse mixing. In more complex heterogeneity, arising from the spatial organization of sedimentary facies, finger propagation is reduced in low permeability facies, but may be enhanced through more permeable facies. The connectivity of faciesmore » is critical in determining the large-scale transport of CO2-rich brine. We perform high-resolution finite element simulations of advection-diffusion transport of CO2 with a focus on facies-based bimodal heterogeneity. Permeability fields are generated by a Markov Chain approach, which represent facies architecture by commonly observed characteristics such as volume fractions. CO2 dissolution and phase behavior are modeled with the cubic-plus-association equation-of-state. Our results show that the organization of high-permeability facies and their connectivity control the dynamics of gravitationally unstable flow. Lastly, we discover new flow regimes in both homogeneous and heterogeneous media and present quantitative scaling relations for their temporal evolution.« less
NASA Astrophysics Data System (ADS)
Karki, Pragalv; Loh, Yen Lee
2016-11-01
We simulate three types of random inductor-capacitor (LC) networks on 6000× 6000 square lattices. We calculate the dynamical conductivity using an equation-of-motion method in which timestep error is eliminated and windowing error is minimized. We extract the critical exponent a such that σ ≤ft(ω \\right)\\propto {ω-a} at low frequencies. The results suggest that there are three different universality classes. The {{L}ij}{{C}i} model, with capacitances from each site to ground, has a = 0.314(4). The {{L}ij}{{C}ij} model, with capacitances along bonds, has a = 0. The {{L}ij}{{C}i}{{C}ij} model, with both types of capacitances, has a = 0.304(1). This implies that classical percolative 2D superconductor-insulator transitions (SITs) generically have σ ≤ft(ω \\right)\\to ∞ as ω \\to 0 . Therefore, any experiments that give a constant conductivity as ω \\to 0 must be explained in terms of quantum effects.
Critical Dynamics of Gravito-Convective Mixing in Geological Carbon Sequestration
Soltanian, Mohamad Reza; Amooie, Mohammad Amin; Dai, Zhenxue; Cole, David; Moortgat, Joachim
2016-01-01
When CO2 is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO2 throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees. Zones with low effective vertical permeability may suppress fingering and reduce vertical spreading, while potentially increasing transverse mixing. In more complex heterogeneity, arising from the spatial organization of sedimentary facies, finger propagation is reduced in low permeability facies, but may be enhanced through more permeable facies. The connectivity of facies is critical in determining the large-scale transport of CO2-rich brine. We perform high-resolution finite element simulations of advection-diffusion transport of CO2 with a focus on facies-based bimodal heterogeneity. Permeability fields are generated by a Markov Chain approach, which represent facies architecture by commonly observed characteristics such as volume fractions. CO2 dissolution and phase behavior are modeled with the cubic-plus-association equation-of-state. Our results show that the organization of high-permeability facies and their connectivity control the dynamics of gravitationally unstable flow. We discover new flow regimes in both homogeneous and heterogeneous media and present quantitative scaling relations for their temporal evolution. PMID:27808178
Critical Dynamics of Gravito-Convective Mixing in Geological Carbon Sequestration
NASA Astrophysics Data System (ADS)
Soltanian, Mohamad Reza; Amooie, Mohammad Amin; Dai, Zhenxue; Cole, David; Moortgat, Joachim
2016-11-01
When CO2 is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO2 throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees. Zones with low effective vertical permeability may suppress fingering and reduce vertical spreading, while potentially increasing transverse mixing. In more complex heterogeneity, arising from the spatial organization of sedimentary facies, finger propagation is reduced in low permeability facies, but may be enhanced through more permeable facies. The connectivity of facies is critical in determining the large-scale transport of CO2-rich brine. We perform high-resolution finite element simulations of advection-diffusion transport of CO2 with a focus on facies-based bimodal heterogeneity. Permeability fields are generated by a Markov Chain approach, which represent facies architecture by commonly observed characteristics such as volume fractions. CO2 dissolution and phase behavior are modeled with the cubic-plus-association equation-of-state. Our results show that the organization of high-permeability facies and their connectivity control the dynamics of gravitationally unstable flow. We discover new flow regimes in both homogeneous and heterogeneous media and present quantitative scaling relations for their temporal evolution.
Dynamic Critical Rainfall-Based Flash Flood Early Warning and Forecasting for Medium-Small Rivers
NASA Astrophysics Data System (ADS)
Liu, Z.; Yang, D.; Hu, J.
2012-04-01
China is extremely frequent food disasters hit countries, annual flood season flash floods triggered by rainfall, mudslides, landslides have caused heavy casualties and property losses, not only serious threaten the lives of the masses, but the majority of seriously restricting the mountain hill areas of economic and social development and the people become rich, of building a moderately prosperous society goals. In the next few years, China will focus on prevention and control area in the flash flood disasters initially built "for the surveillance, communications, forecasting, early warning and other non-engineering measure based, non-engineering measures and the combinations of engineering measures," the mitigation system. The latest progresses on global torrential flood early warning and forecasting techniques are reviewed in this paper, and then an early warning and forecasting approach is proposed on the basis of a distributed hydrological model according to dynamic critical rainfall index. This approach has been applied in Suichuanjiang River basin in Jiangxi province, which is expected to provide valuable reference for building a national flash flood early warning and forecasting system as well as control of such flooding.
Critical dynamics of gravito-convective mixing in geological carbon sequestration
Soltanian, Mohamad Reza; Amooie, Mohammad Amin; Dai, Zhenxue; Cole, David; Moortgat, Joachim
2016-11-03
When CO_{2} is injected in saline aquifers, dissolution causes a local increase in brine density that can cause Rayleigh-Taylor-type gravitational instabilities. Depending on the Rayleigh number, density-driven flow may mix dissolved CO_{2} throughout the aquifer at fast advective time-scales through convective mixing. Heterogeneity can impact density-driven flow to different degrees. Zones with low effective vertical permeability may suppress fingering and reduce vertical spreading, while potentially increasing transverse mixing. In more complex heterogeneity, arising from the spatial organization of sedimentary facies, finger propagation is reduced in low permeability facies, but may be enhanced through more permeable facies. The connectivity of facies is critical in determining the large-scale transport of CO_{2}-rich brine. We perform high-resolution finite element simulations of advection-diffusion transport of CO_{2} with a focus on facies-based bimodal heterogeneity. Permeability fields are generated by a Markov Chain approach, which represent facies architecture by commonly observed characteristics such as volume fractions. CO_{2} dissolution and phase behavior are modeled with the cubic-plus-association equation-of-state. Our results show that the organization of high-permeability facies and their connectivity control the dynamics of gravitationally unstable flow. Lastly, we discover new flow regimes in both homogeneous and heterogeneous media and present quantitative scaling relations for their temporal evolution.
NASA Technical Reports Server (NTRS)
deGroh, Kim K.; Smith, Daniela C.
1999-01-01
Solar-dynamic space power systems require durable, high-emittance surfaces on a number of critical components, such as heat receiver interior surfaces and parasitic load radiator (PLR) elements. An alumina-titania coating, which has been evaluated for solar-dynamic heat receiver canister applications, has been chosen for a PLR application (an electrical sink for excess power from the turboalternator/compressor) because of its demonstrated high emittance and high-temperature durability in vacuum. Under high vacuum conditions (+/- 10(exp -6) torr), the alumina-titania coating was found to be durable at temperatures of 1520 F (827 C) for approx. 2700 hours with no degradation in optical properties. This coating has been successfully applied to the 2-kW solar-dynamic ground test demonstrator at the NASA Lewis Research Center, to the 500 thermal-energy-storage containment canisters inside the heat receiver and to the PLR radiator. The solar-dynamic demonstrator has successfully operated for over 800 hours in Lewis large thermal/vacuum space environment facility, demonstrating the feasibility of solar-dynamic power generation for space applications.
NASA Astrophysics Data System (ADS)
Shevyrnogov, Anatoly; Vysotskaya, Galina
Continuous monitoring of phytopigment concentrations and sea surface temperature in the ocean by space-borne methods makes possible to estimate ecological condition of biocenoses in critical areas. Unlike land vegetation, hydrological processes largely determine phytoplank-ton dynamics, which may be either recurrent or random. The types of chlorophyll concentration dynamics and sea surface temperature can manifest as zones quasistationary by seasonal dynamics, quasistationary areas (QSA). In the papers of the authors (A. Shevyrnogov, G. Vysotskaya, E. Shevyrnogov, A study of the stationary and the anomalous in the ocean surface chlorophyll distribution by satellite data. International Journal of Remote Sensing, Vol. 25, №7-8, pp. 1383-1387, April 2004 & A. P. Shevyrnogov, G. S. Vysotskaya, J. I. Gitelson, Quasistationary areas of chlorophyll concentra-tion in the world ocean as observed satellite data Advances in Space Research, Volume 18, Issue 7, Pages 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 processing of time series of satellite images SeaWiFS. It was shown that fronts and frontal zones coincide with dividing lines between quasi-stationary are-as, especially in areas of large oceanic streams. To study the dynamics of the ocean for the period from 1985 through 2012 we used data on the temperature of the surface layer of the ocean and chlorophyll concentration (AVHRR, SeaWiFS and MODIS). Biota of surface oceanic layer is more stable in comparison with quickly changing surface tem-perature. It gives a possibility to circumvent influence of high-frequency component (for exam-ple, a diurnal cycle) in investigation of dynamics of spatial distribution of surface streams. In addition, an analyses of nonstable ocean productivity phenomena, stood out time series of satellite images, showed existence of areas with
A critical review on the survival and elimination of norovirus in food and on food contact surfaces
Technology Transfer Automated Retrieval System (TEKTRAN)
This critical review covers the survival of human norovirus (NoV) in foods and on food contact surfaces as well as the state-of-the-art on the effectiveness of methods to eliminate these viruses. Virus survival studies are reviewed for water, soils and organic wastes, on fomites, hands, fruits and v...
Assessment of Zero Power Critical Experiments and Needs for a Fission Surface Power System
Jim R Parry; John Darrell bess; Brad T. Rearden; Gary A. Harms
2009-06-01
The National Aeronautics and Space Administration (NASA) is providing funding to the Department of Energy (DOE) to assess, develop, and test nuclear technologies that could provide surface power to a lunar outpost. Sufficient testing of this fission surface power (FSP) system will need to be completed to enable a decision by NASA for flight development. The near-term goal for the FSP work is to conduct the minimum amount of testing needed to validate the system performance within an acceptable risk. This report attempts to assess the current modeling capabilities and quantify any bias associated with the modeling methods for designing the nuclear reactor. The baseline FSP system is a sodium-potassium (NaK) cooled, fast spectrum reactor with 93% 235U enriched HEU-O2 fuel, SS316 cladding, and beryllium reflectors with B4C control drums. The FSP is to produce approximately 40 kWe net power with a lifetime of at least 8 years at full power. A flight-ready FSP is to be ready for launch and deployment by 2020. Existing benchmarks from the International Criticality Safety Benchmark Evaluation Program (ICSBEP) were reviewed and modeled in MCNP. An average bias of less than 0.6% was determined using the ENDF/B-VII cross-section libraries except in the case of subcritical experiments, which exhibited an average bias of approximately 1.5%. The bias increases with increasing reflector worth of the beryllium. The uncertainties and sensitivities in cross section data for the FSP model and ZPPR-20 configurations were assessed using TSUNAMI-3D. The cross-section covariance uncertainty in the FSP model was calculated as 2.09%, which was dominated by the uncertainty in the 235U(n,?) reactions. Global integral indices were generated in TSUNAMI-IP using pre-release SCALE 6 cross-section covariance data. The ZPPR-20 benchmark models exhibit strong similarity with the FSP model. A penalty assessment was performed to determine the degree of which the FSP model could not be characterized
NASA Astrophysics Data System (ADS)
Hamano, K.; Fukuhara, K.; Kuwahara, N.; Ducros, E.; Benseddik, M.; Rouch, J.; Tartaglia, P.
1995-07-01
Extensive sets of measurements of the shear viscosity, the scattered light intensity, and the relaxation rate of the order-parameter fluctuations lead us to reexamine the static and dynamic critical behaviors of binary solutions of pentaethylene glycol n-dodecylether (C12E5) and water. The scattered intensity, the scattered field correlation function, and the relaxation rate of the order parameter show systematic deviations from the behavior usually observed for simple or molecular binary fluids. A modified version of the Sorensen et al. [Phys. Rev. A 13, 1593 (1976)] dynamical droplet model that assumes that close to the critical point the critical clusters can be treated much like percolating aggregates having a fractal dimension df=2.49 and an associated polydispersity exponent τ=2.21 and which includes the finite size of the micelles, very well accounts for all our experimental results.
Poil, Simon-Shlomo; Hardstone, Richard; Mansvelder, Huibert D; Linkenkaer-Hansen, Klaus
2012-07-18
Criticality has gained widespread interest in neuroscience as an attractive framework for understanding the character and functional implications of variability in brain activity. The metastability of critical systems maximizes their dynamic range, storage capacity, and computational power. Power-law scaling-a hallmark of criticality-has been observed on different levels, e.g., in the distribution of neuronal avalanches in vitro and in vivo, but also in the decay of temporal correlations in behavioral performance and ongoing oscillations in humans. An unresolved issue is whether power-law scaling on different organizational levels in the brain-and possibly in other hierarchically organized systems-can be related. Here, we show that critical-state dynamics of avalanches and oscillations jointly emerge in a neuronal network model when excitation and inhibition is balanced. The oscillatory activity of the model was qualitatively similar to what is typically observed in recordings of human resting-state MEG. We propose that homeostatic plasticity mechanisms tune this balance in healthy brain networks, and that it is essential for critical behavior on multiple levels of neuronal organization with ensuing functional benefits. Based on our network model, we introduce a concept of multi-level criticality in which power-law scaling can emerge on multiple time scales in oscillating networks.
Segmental dynamics simulation of the deformation for polymer adhesive between surfaces
Lee, K.; Adams, J.B.
1996-12-31
The deformation of polymer adhesives between surfaces is investigated using the authors Segmental Dynamics Model. A simple tensile test is simulated by placing an equilibrated polymer adhesive film between two surfaces. The equilibrium structure and dynamics of the adhesive deformation are investigated. The density of anchor segments ({rho}) and the bond strength of the anchor segment to the surface ({phi}) were varied to determine the effects on deformation.
On Equivalence between Critical Probabilities of Dynamic Gossip Protocol and Static Site Percolation
NASA Astrophysics Data System (ADS)
Ishikawa, Tetsuya; Hayakawa, Tomohisa
The relationship between the critical probability of gossip protocol on the square lattice and the critical probability of site percolation on the square lattice is discussed. Specifically, these two critical probabilities are analytically shown to be equal to each other. Furthermore, we present a way of evaluating the critical probability of site percolation by approximating the saturation of gossip protocol. Finally, we provide numerical results which support the theoretical analysis.
Klihm, K.D.
1993-09-01
Experiments were conducted to measure dynamic surface tension of various coal-water slurry (CWS) fuel samples containing different surfactants and coal loadings. A maximum air bubble pressure technique was used to measure dynamic surface tension. The coal used for the CWS had 50 {mu}m volume mean diameter (VMD) mined from the Upper Elkhom Seam in Virginia. Five surfactants were selected for the study: Witconol NP-100, Ammonium DDBS (bard), Ammonium DDBS (soft), Witconate 1223H and Witconate 1840X. To detemfine critical micelle concentration (CMC), static surface tension was also measured using a Du-Nouy ring tensiometer. Detailed and comprehensive data for dynamic surface tension for a 50% CWS mixture are documented and presented.
Davalos, Rafael V; McGraw, Gregory J; Wallow, Thomas I; Morales, Alfredo M; Krafcik, Karen L; Fintschenko, Yolanda; Cummings, Eric B; Simmons, Blake A
2008-02-01
Efficient and robust particle separation and enrichment techniques are critical for a diverse range of lab-on-a-chip analytical devices including pathogen detection, sample preparation, high-throughput particle sorting, and biomedical diagnostics. Previously, using insulator-based dielectrophoresis (iDEP) in microfluidic glass devices, we demonstrated simultaneous particle separation and concentration of various biological organisms, polymer microbeads, and viruses. As an alternative to glass, we evaluate the performance of similar iDEP structures produced in polymer-based microfluidic devices. There are numerous processing and operational advantages that motivate our transition to polymers such as the availability of numerous innate chemical compositions for tailoring performance, mechanical robustness, economy of scale, and ease of thermoforming and mass manufacturing. The polymer chips we have evaluated are fabricated through an injection molding process of the commercially available cyclic olefin copolymer Zeonor 1060R. This publication is the first to demonstrate insulator-based dielectrophoretic biological particle differentiation in a polymeric device injection molded from a silicon master. The results demonstrate that the polymer devices achieve the same performance metrics as glass devices. We also demonstrate an effective means of enhancing performance of these microsystems in terms of system power demand through the use of a dynamic surface coating. We demonstrate that the commercially available nonionic block copolymer surfactant, Pluronic F127, has a strong interaction with the cyclic olefin copolymer at very low concentrations, positively impacting performance by decreasing the electric field necessary to achieve particle trapping by an order of magnitude. The presence of this dynamic surface coating, therefore, lowers the power required to operate such devices and minimizes Joule heating. The results of this study demonstrate that iDEP polymeric
The shape, stability and dynamics of elastic surfaces
NASA Astrophysics Data System (ADS)
Mahadevan, L.
2008-03-01
Bending a thin sheet is easier than stretching it, an observation which has its roots in geometry. We will use this fact to explain some unusual problems in biology, physics and geology. At the everyday scale, I will discuss the morphology of avascular algal blades, the dynamics of defects in an elastic ribbon, and the dynamics of prey capture by certain carnivorous plants. At the geological scale, I will try to explain the shape of island arcs on our planet. Finally, time permitting, I will discuss how we might extend these ideas to the macromolecular scale, to derive a mechanical model for the dynamic instability of a growing microtubule.
Yang, Yang; Yu, Ye; Cheng, Jin; Liu, Yan; Liu, Di-Shi; Wang, Jin; Zhu, Michael X.; Wang, Rui; Xu, Tian-Le
2012-01-01
Acid-sensing ion channels (ASICs) are non-selective cation channels activated by extracellular acidosis associated with many physiological and pathological conditions. A detailed understanding of the mechanisms that govern cell surface expression of ASICs, therefore, is critical for better understanding of the cell signaling under acidosis conditions. In this study, we examined the role of a highly conserved salt bridge residing at the extracellular loop of rat ASIC3 (Asp107-Arg153) and human ASIC1a (Asp107-Arg160) channels. Comprehensive mutagenesis and electrophysiological recordings revealed that the salt bridge is essential for functional expression of ASICs in a pH sensing-independent manner. Surface biotinylation and immunolabeling of an extracellular epitope indicated that mutations, including even minor alterations, at the salt bridge impaired cell surface expression of ASICs. Molecular dynamics simulations, normal mode analysis, and further mutagenesis studies suggested a high stability and structural constrain of the salt bridge, which serves to separate an adjacent structurally rigid signal patch, important for surface expression, from a flexible gating domain. Thus, we provide the first evidence of structural requirement that involves a stabilizing salt bridge and an exposed rigid signal patch at the destined extracellular loop for normal surface expression of ASICs. These findings will allow evaluation of new strategies aimed at preventing excessive excitability and neuronal injury associated with tissue acidosis and ASIC activation. PMID:22399291
Dynamics of Hydrated tRNA on Nanodiamond Surface Studied by Quasi-elastic Neutron Scattering
NASA Astrophysics Data System (ADS)
Dhindsa, Gurpreet; Mochalin, Vadym N.; O'Neill, Hugh; Gogotsi, Yury; Chu, Xiang Qiang
2014-03-01
Diamond is an outstanding material in many aspects, and nanodiamond (ND) inherits most of the superior properties of bulk diamond and delivers them at the nanoscale. ND has excellent properties that can be applied in biomedical field such as a good platform for drug delivery. In this study, we show that hydrated tRNA can be adsorbed on the surfaces of nanodiamonds and further demonstrate specific properties in its dynamics. We investigate the dynamics of the system by Quasielastic neutron scattering (QENS) technique. The dynamics of hydrated tRNA on ND surfaces exhibits a logarithmic-like decay within the time range of 10 ps to 1 ns, which has also been observed in the freestanding proteins and other biopolymers. We further compare the dynamics of tRNA hydrated with D2O on ND surface with that of freestanding hydrated tRNA molecules. Our results show that the relaxational dynamics of tRNA on ND surface is much faster than that of the freestanding tRNA molecules. This gives the hint that the folded states of tRNA is modified by ND surfaces to engage faster dynamics. The difference in the dynamics of the hydration water modified by ND is another possible reason which causes the faster dynamics in tRNA on ND surface.
Li, Cai; Lowe, Robert; Ziemke, Tom
2014-01-01
In this article, we propose an architecture of a bio-inspired controller that addresses the problem of learning different locomotion gaits for different robot morphologies. The modeling objective is split into two: baseline motion modeling and dynamics adaptation. Baseline motion modeling aims to achieve fundamental functions of a certain type of locomotion and dynamics adaptation provides a "reshaping" function for adapting the baseline motion to desired motion. Based on this assumption, a three-layer architecture is developed using central pattern generators (CPGs, a bio-inspired locomotor center for the baseline motion) and dynamic motor primitives (DMPs, a model with universal "reshaping" functions). In this article, we use this architecture with the actor-critic algorithms for finding a good "reshaping" function. In order to demonstrate the learning power of the actor-critic based architecture, we tested it on two experiments: (1) learning to crawl on a humanoid and, (2) learning to gallop on a puppy robot. Two types of actor-critic algorithms (policy search and policy gradient) are compared in order to evaluate the advantages and disadvantages of different actor-critic based learning algorithms for different morphologies. Finally, based on the analysis of the experimental results, a generic view/architecture for locomotion learning is discussed in the conclusion.
Applying Parallel Adaptive Methods with GeoFEST/PYRAMID to Simulate Earth Surface Crustal Dynamics
NASA Technical Reports Server (NTRS)
Norton, Charles D.; Lyzenga, Greg; Parker, Jay; Glasscoe, Margaret; Donnellan, Andrea; Li, Peggy
2006-01-01
This viewgraph presentation reviews the use Adaptive Mesh Refinement (AMR) in simulating the Crustal Dynamics of Earth's Surface. AMR simultaneously improves solution quality, time to solution, and computer memory requirements when compared to generating/running on a globally fine mesh. The use of AMR in simulating the dynamics of the Earth's Surface is spurred by future proposed NASA missions, such as InSAR for Earth surface deformation and other measurements. These missions will require support for large-scale adaptive numerical methods using AMR to model observations. AMR was chosen because it has been successful in computation fluid dynamics for predictive simulation of complex flows around complex structures.
Dynamic, Hot Surface Ignition of Aircraft Fuels and Hydraulic Fluids
1980-10-01
alloys involved the formation of surface catalysts in the form of oxides of the parent metal, iron, nickel, and chromium , on the heated surfaces. Some...stainless steels and inconel X, the formed oxides or spinels (e.g. (FeO) 0 . 2 5 (Cr 2 03 ) 1 . 7 5 ) were quite stable and while protecting the heated
Ab initio dynamics of field emission from diamond surfaces
NASA Astrophysics Data System (ADS)
Miyamoto, Yoshiyuki; Miyazaki, Takehide; Takeuchi, Daisuke; Okushi, Hideyo; Yamasaki, Satoshi
2013-09-01
We propose a new interpretation of the efficiency of field emission, which is understood based on the concept of electron affinity. We use time-dependent density functional theory to simulate field emission from clean and chemically modified diamond (001) surfaces under applied electric fields. We find that the emission efficiency is governed by the self-consistent electrostatic potential (VSCF) at the surface rather than by the sign of the electron affinity, which is determined by VSCF in the vacuum region far from the surface. We resolve the paradox that the emission efficiency of a clean (001) surface with positive electron affinity is even higher than that of a H/OH-co-terminated (001) surface with negative electron affinity.
Anjos, Daniela M; Mamontov, Eugene; Brown, Gilbert M; Overbury, Steven {Steve} H; Mavila Chathoth, Suresh
2012-01-01
We used quasielastic neutron scattering (QENS) to study the dynamics of phenanthrenequinone (PQ) on the surface of onion-like carbon (OLC), or so called carbon onions, as a function of surface coverage and temperature. For both the high- and low-coverage samples, we observed two diffusion processes; a faster process and nearly an order of magnitude slower process. On the high-coverage surface, the slow diffusion process is of long-range translational character, whereas the fast diffusion process is spatially localized on the length scale of ~ 4.7 . On the low-coverage surface, both diffusion processes are spatially localized; on the same length scale of ~ 4.7 for the fast diffusion and a somewhat larger length scale for the slow diffusion. Arrhenius temperature dependence is observed except for the long-range diffusion on the high-coverage surface. We attribute the fast diffusion process to the generic localized in-cage dynamics of PQ molecules, and the slow diffusion process to the long-range translational dynamics of PQ molecules, which, depending on the coverage, may be either spatially restricted, or long-range. On the low-coverage surface, uniform surface coverage is not attained, and the PQ molecules experience the effect of spatial constraints on their long-range translational dynamics. Unexpectedly, the dynamics of PQ molecules on OLC as a function of temperature and surface coverage bears qualitative resemblance to the dynamics of water molecules on oxide surfaces, including practically temperature-independent residence times for the low-coverage surface. The dynamics features that we observed may be universal across different classes of surface adsorbates.
Dyatkin, Boris; Zhang, Yu; Mamontov, Eugene; ...
2016-04-07
Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces andmore » enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.« less
Dyatkin, Boris; Zhang, Yu; Mamontov, Eugene; Kolesnikov, Alexander I.; Cheng, Yongqiang; Meyer, III, Harry M.; Cummings, Peter T.; Gogotsi, Yury G.
2016-04-07
Here, we investigate the influence of surface chemistry and ion confinement on capacitance and electrosorption dynamics of room-temperature ionic liquids (RTILs) in supercapacitors. Using air oxidation and vacuum annealing, we produced defunctionalized and oxygen-rich surfaces of carbide-derived carbons (CDCs) and graphene nanoplatelets (GNPs). While oxidized surfaces of porous CDCs improve capacitance and rate handling abilities of ions, defunctionalized nonporous GNPs improve charge storage densities on planar electrodes. Quasi-elastic neutron scattering (QENS) and inelastic neutron scattering (INS) probed the structure, dynamics, and orientation of RTIL ions confined in divergently functionalized pores. Oxidized, ionophilic surfaces draw ions closer to pore surfaces and enhance potential-driven ion transport during electrosorption. Molecular dynamics (MD) simulations corroborated experimental data and demonstrated the significance of surface functional groups on ion orientations, accumulation densities, and capacitance.
Self-organized criticality and coevolution of network structure and dynamics.
Fronczak, Piotr; Fronczak, Agata; Hołyst, Janusz A
2006-04-01
We investigate, by numerical simulations, how the avalanche dynamics of the Bak-Tang-Wiesenfeld sandpile model can induce emergence of scale-free networks and how this emerging structure affects dynamics of the system.
Relaxation and dynamics of the (001) surfaces of crystals with perovskite structure
NASA Astrophysics Data System (ADS)
Schröder, U.; Prade, J.; de Wette, F. W.; Kulkarni, A. D.; Kress, W.
Surface relaxation is the result of the imbalance of the forces acting on particles at or near a crystal surface, when they occupy their unrelaxed bulk positions. While in most alkali halides the relaxation has practically no influence on the surface dynamics, the situation is totally different for crystals with perovskite structure. These compounds undergo various structural phase transitions which are associated with a softening of bulk lattice modes. Correspondingly, there exist soft surface modes which are strongly dependent on relaxation. In this paper we investigate the relaxation pattern and the surface dynamics of KMnF 3 and SrTiO 3. The temperature dependence of the surface modes and the surface reconstruction associated with the soft surface mode in KMnF 3 will be discussed.
Droplet-surface Impingement Dynamics for Intelligent Spray Design
NASA Technical Reports Server (NTRS)
VanderWal, Randy L.; Kizito, John P.; Tryggvason, Gretar; Berger, Gordon M.; Mozes, Steven D.
2004-01-01
Spray cooling has high potential in thermal management and life support systems by overcoming the deleterious effect of microgravity upon two-phase heat transfer. In particular spray cooling offers several advantages in heat flux removal that include the following: 1. By maintaining a wetted surface, spray droplets impinge upon a thin fluid film rather than a dry solid surface 2. Most heat transfer surfaces will not be smooth but rough. Roughness can enhance conductive cooling, aid liquid removal by flow channeling. 3. Spray momentum can be used to a) substitute for gravity delivering fluid to the surface, b) prevent local dryout and potential thermal runaway and c) facilitate liquid and vapor removal. Yet high momentum results in high We and Re numbers characterizing the individual spray droplets. Beyond an impingement threshold, droplets splash rather than spread. Heat flux declines and spray cooling efficiency can markedly decrease. Accordingly we are investigating droplet impingement upon a) dry solid surfaces, b) fluid films, c) rough surfaces and determining splashing thresholds and relationships for both dry surfaces and those covered by fluid films. We are presently developing engineering correlations delineating the boundary between splashing and non-splashing regions.
Dynamics of Defrosting on Hydrophobic and Superhydrophobic Surfaces
NASA Astrophysics Data System (ADS)
Murphy, Kevin; McClintic, William; Lester, Kevin; Collier, Patrick; Boreyko, Jonathan
2016-11-01
It has recently been demonstrated that frost can grow in a suspended Cassie state on nanostructured superhydrophobic surfaces, which has implications for enhanced defrosting rates. However, to date there have been no direct comparisons of the defrosting kinetics of Cassie frost versus frost on conventional surfaces. Here, we fabricate a hybrid aluminum plate where half of the top face exhibits a superhydrophobic nanostructure while the other half is smooth and hydrophobic. By growing frost to varying thicknesses and melting at several tilt angles, we reveal the advantages and disadvantages of each surface with regards to the extent and speed of the shedding of melt water. For sufficiently thick frost layers, the Cassie state of frost on the superhydrophobic surface uniquely enabled the rapid and effective shedding of melt water even at low tilt angles. On the other hand, the hydrophobic surface was more effective at removing very thin frost sheets, as the reduced contact angle of water on the surface facilitated the coalescence of droplets to grow the melt water beyond the capillary length for gravitational removal. Therefore, the utilization of superhydrophobic versus hydrophobic surfaces for defrosting applications depends upon the context of the system conditions.
Evaporation dynamics of water droplets on inclined surfaces
NASA Astrophysics Data System (ADS)
Kim, Jin Young; Hwang, In Gyu; Weon, Byung Mook
2016-11-01
When a water droplet is gently placed on a flat substrate, particularly which is tilted at an inclined angle, usually there are advancing and receding angles inside the droplet formed by inclination under gravitational force. Evaporation dynamics of an nonspherical inclined droplet at inclinations would deviate from that of a spherical droplet. Here we study on evaporation dynamics rates of inclined droplets by measuring mass changes with time and their lifetimes. We find that the lifetime of an evaporating inclined droplets becomes longer as the gravitational influence becomes stronger. The lifetime depends on the pinning-depinning transitions and the depinning onset times, which are changed by the gravitational influence. This The dependence inclination-induced evaporation behavior would be useful important in understanding evaporation dynamics of inclined droplets. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1D1A1B01007133).
Conditions for the critical phenomena in a dynamic model of an electrocatalytic reaction
NASA Astrophysics Data System (ADS)
Firstova, Natalia; Shchepakina, Elena
2017-02-01
In the paper, a detailed study of the critical phenomena mechanism in a model of an electrocatalytic reaction is carried out. The use of the geometric theory of integral manifolds allows us to show the relationship between the critical regime and the stability loss delay of the slow integral manifold of the corresponding differential system. The asymptotic formula for the critical value of the control parameter is obtained.
Relaxation and dynamics of (001) surfaces of KZnF 3 and KMnF 3
NASA Astrophysics Data System (ADS)
Reiger, R.; Prade, J.; Schröder, U.; Kress, W.; De Wette, F. W.
1987-10-01
Calculations of the static and dynamical properties of (001) surfaces are reported for KZnF 3 and KMnF 3. Several surface-localized modes have been identified in both relaxed and unrelaxed geometries. In particular a soft surface mode atwas obtained for KMnF 3. The surface reconstruction associated with this soft mode is discussed; it can be considered as a precursor of the bulk transition.
Droplet-Surface Impingement Dynamics for Intelligent Spray Design
NASA Technical Reports Server (NTRS)
Wal, Randy L. Vander; Kizito, John P.; Tryggvason, Gretar
2004-01-01
Spray cooling has high potential in thermal management and life support systems by overcoming the deleterious effect of microgravity upon two-phase heat transfer. In particular spray cooling offers several advantages in heat flux removal that include the following: 1) By maintaining a wetted surface, spray droplets impinge upon a thin fluid film rather than a dry solid surface; 2. Most heat transfer surfaces will not be smooth but rough. Roughness can enhance conductive cooling, aid liquid removal by flow channeling; and 3. Spray momentum can be used to a) substitute for gravity delivering fluid to the surface, b) prevent local dryout and potential thermal runaway and c) facilitate liquid and vapor removal. Yet high momentum results in high We and Re numbers characterizing the individual spray droplets. Beyond an impingement threshold, droplets splash rather than spread. Heat flux declines and spray cooling efficiency can markedly decrease. Accordingly we are investigating droplet impingement upon a) dry solid surfaces, b) fluid films, c) rough surfaces and determining splashing thresholds and relationships for both dry surfaces and those covered by fluid films. We are presently developing engineering correlations delineating the boundary between splashing and non-splashing regions. Determining the splash/non-splash boundary is important for many practical applications. Coating and cooling processes would each benefit from near-term empirical relations and subsequent models. Such demonstrations can guide theoretical development by providing definitive testing of its predictive capabilities. Thus, empirical relations describing the boundary between splash and non-splash are given for drops impinging upon a dry solid surface and upon a thin fluid film covering a similar surface. Analytical simplification of the power laws describing the boundary between the splash and non-splash regions yields insight into the engineering parameters governing the splash and non
Dynamic Moon: New Impacts and Contemporary Surface Changes
NASA Astrophysics Data System (ADS)
Speyerer, E. J.; Povilaitis, R. Z.; Robinson, M. S.; Thomas, P. C.; Wagner, R. V.
2016-05-01
Before and after image pairs acquired by the Lunar Reconnaissance Orbiter Camera enable the identification of new impact craters and secondary surface changes revealing new insight into the cratering process and regolith gardening.
Oscillon dynamics and rogue wave generation in Faraday surface ripples.
Xia, H; Maimbourg, T; Punzmann, H; Shats, M
2012-09-14
We report new experimental results which suggest that the generation of extreme wave events in the Faraday surface ripples is related to the increase in the horizontal mobility of oscillating solitons (oscillons). The analysis of the oscillon trajectories in a horizontal plane shows that at higher vertical acceleration, oscillons move chaotically, merge and form enclosed areas on the water surface. The probability of the formation of such craters, which precede large wave events, increases with the increase in horizontal mobility.
Employing a cylindrical single crystal in gas-surface dynamics.
Hahn, Christine; Shan, Junjun; Liu, Ying; Berg, Otto; Kleijn, Aart W; Juurlink, Ludo B F
2012-03-21
We describe the use of a polished, hollow cylindrical nickel single crystal to study effects of step edges on adsorption and desorption of gas phase molecules. The crystal is held in an ultra-high vacuum apparatus by a crystal holder that provides axial rotation about a [100] direction, and a crystal temperature range of 89 to 1100 K. A microchannel plate-based low energy electron diffraction/retarding field Auger electron spectrometer (AES) apparatus identifies surface structures present on the outer surface of the cylinder, while a separate double pass cylindrical mirror analyzer AES verifies surface cleanliness. A supersonic molecular beam, skimmed by a rectangular slot, impinges molecules on a narrow longitudinal strip of the surface. Here, we use the King and Wells technique to demonstrate how surface structure influences the dissociation probability of deuterium at various kinetic energies. Finally, we introduce spatially-resolved temperature programmed desorption from areas exposed to the supersonic molecular beam to show how surface structures influence desorption features.
Surface dynamics and mechanics in liquid crystal polymer coatings
NASA Astrophysics Data System (ADS)
Liu, Danqing; Broer, Dirk J.
2015-03-01
Based on liquid crystal networks we developed `smart' coatings with responsive surface topographies. Either by prepatterning or by the formation of self-organized structures they can be switched on and off in a pre-designed manner. Here we provide an overview of our methods to generate coatings that form surface structures upon the actuation by light. The coating oscillates between a flat surface and a surface with pre-designed 3D micro-patterns by modulating a light source. With recent developments in solid state lighting, light is an attractive trigger medium as it can be integrated in a device for local control or can be used remotely for flood or localized exposure. The basic principle of formation of surface topographies is based on the change of molecular organization in ordered liquid crystal polymer networks. The change in order leads to anisotropic dimensional changes with contraction along the director and expansion to the two perpendicular directions and an increase in volume by the formation of free volume. These two effects work in concert to provide local expansion and contraction in the coating steered by the local direction of molecular orientation. The surface deformation, expressed as the height difference between the activated regions and the non-activated regions divided by the initial film thickness, is of the order of 20%. Switching occurs immediately when the light is switched `on' and `off' and takes several tens of seconds.
Electrically modulated dynamic spreading of drops on soft surfaces
NASA Astrophysics Data System (ADS)
Dey, Ranabir; Daga, Ashish; DasGupta, Sunando; Chakraborty, Suman
2015-07-01
The intricate interaction between the deformability of a substrate and the dynamic spreading of a liquid drop on the same, under the application of an electrical voltage, has remained far from being well understood. Here, we demonstrate that electrospreading dynamics on soft substrates is dictated by the combined interplay of electrocapillarity, the wetting line friction, and the viscoelastic energy dissipation at the contact line. Our results reveal that during such electro-elastocapillarity mediated spreading of a sessile drop, the contact radius evolution exhibits a universal power-law in a substrate elasticity based non-dimensional time, with an electrical voltage dependent spreading exponent. Simultaneously, the macroscopic dynamic contact angle variation follows a general power-law in the contact line velocity, normalized by elasticity dependent characteristic velocity scale. These findings will be beneficial for comprehending droplet spreading dynamics stemming from the combination of electrically modulated spreading and "soft wetting." Hence, our results are likely to provide the foundation for the development of a plethora of applications involving droplet manipulations by exploiting the interplay between electrically triggered spreading and substrate-compliance over interfacial scales.
Dabsie, Firas; Grégoire, Geneviève; Sharrock, Patrick
2012-01-01
Self-adhesive composite cements are increasingly used for cementing inlays/onlays, intraradicular posts, crowns and laminate veneers. Wider clinical acceptance is driven by simpler and faster handling procedures, much like observed for self-etching adhesives. 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) is a bi-functional monomer incorporated as the reactive ingredient in a contemporary self-adhesive cement. We have examined the surface free energy parameters of this cement and studied the mode of action of the cement on dentine substrate by contact angle measurements to determine the critical surface energy of the cement. Retention of the infrared absorption bands characteristic of the acrylate moieties on the surface of hydroxyapatite particles suggests that MDP contributes to the overall bonding to dentine by forming ionic chemical bonds with surface calcium ions in dentine crystalites.
INTRODUCTION: Surface Dynamics, Phonons, Adsorbate Vibrations and Diffusion
NASA Astrophysics Data System (ADS)
Bruch, L. W.
2004-07-01
understanding of the underlying factors determining the optical quality of GaInNAs, such as composition, growth and annealing conditions. We are still far from establishing an understanding of the band structure and its dependence on composition. Fundamental electronic interactions such as electron-electron and electron-phonon scattering, dependence of effective mass on composition, strain and orientation, quantum confinement effects, effects of localized nitrogen states on high field transport and on galvanometric properties, and mechanisms for light emission in these materials, are yet to be fully understood. Nature and formation mechanisms of grown-in and processing-induced defects that are important for material quality and device performance are still unknown. Such knowledge is required in order to design strategies to efficiently control and eliminate harmful defects. For many potential applications (such as solar cells, HBTs) it is essential to get more information on the transport properties of dilute nitride materials. The mobility of minority carriers is known to be low in GaInNAs and related material. The experimental values are far from reaching the theoretical ones, due to defects and impurities introduced in the material during the growth. The role of the material inhomogeneities on the lateral carrier transport also needs further investigation. From the device's point of view most attention to date has been focused on the GaInNAs/GaAs system, mainly because of its potential for optoelectronic devices covering the 1.3-1.55 µm data and telecommunications wavelength bands. As is now widely appreciated, these GaAs-compatible structures allow monolithic integration of AlGaAs-based distributed Bragg reflector mirrors (DBRs) for vertical cavity surface-emitting lasers with low temperature sensitivity and compatibility with AlOx-based confinement techniques. In terms of conventional edge-emitting lasers (EELs), the next step is to extend the wavelength range for cw room
Nitrogen dynamics at the groundwater-surface water interface of a degraded urban stream (journal)
Urbanization degrades stream ecosystems by altering hydrology and nutrient dynamics, yet relatively little effort has been devoted to understanding biogeochemistry of urban streams at the ground water-surface water interface. This zone may be especially important for nitrogen re...
NASA Astrophysics Data System (ADS)
Heyl, Markus
2017-02-01
Quantum critical states exhibit strong quantum fluctuations and are therefore highly susceptible to perturbations. In this Rapid Communication we study the dynamical stability against a sudden coupling to these strong fluctuations by quenching the order parameter of the underlying transition. Such a quench can generate superextensive energy fluctuations. This leads to a dynamical quantum phase transition (DQPT) with nonanalytic real-time behavior in the resulting decay of the initial state. By establishing a general connection between DQPTs and quantum speed limits, this allows us to obtain a quantum speed limit with unconventional system-size dependence. These findings are illustrated for the one-dimensional and the infinitely connected transverse-field Ising model. The main concepts, however, are general and can be applied also to other critical states. An outlook is given on the implications of superextensive energy fluctuations on potential restricted thermalization despite nonintegrability.
CSDMS2.0: Computational Infrastructure for Community Surface Dynamics Modeling
NASA Astrophysics Data System (ADS)
Syvitski, J. P.; Hutton, E.; Peckham, S. D.; Overeem, I.; Kettner, A.
2012-12-01
The Community Surface Dynamic Modeling System (CSDMS) is an NSF-supported, international and community-driven program that seeks to transform the science and practice of earth-surface dynamics modeling. CSDMS integrates a diverse community of more than 850 geoscientists representing 360 international institutions (academic, government, industry) from 60 countries and is supported by a CSDMS Interagency Committee (22 Federal agencies), and a CSDMS Industrial Consortia (18 companies). CSDMS presently distributes more 200 Open Source models and modeling tools, access to high performance computing clusters in support of developing and running models, and a suite of products for education and knowledge transfer. CSDMS software architecture employs frameworks and services that convert stand-alone models into flexible "plug-and-play" components to be assembled into larger applications. CSDMS2.0 will support model applications within a web browser, on a wider variety of computational platforms, and on other high performance computing clusters to ensure robustness and sustainability of the framework. Conversion of stand-alone models into "plug-and-play" components will employ automated wrapping tools. Methods for quantifying model uncertainty are being adapted as part of the modeling framework. Benchmarking data is being incorporated into the CSDMS modeling framework to support model inter-comparison. Finally, a robust mechanism for ingesting and utilizing semantic mediation databases is being developed within the Modeling Framework. Six new community initiatives are being pursued: 1) an earth - ecosystem modeling initiative to capture ecosystem dynamics and ensuing interactions with landscapes, 2) a geodynamics initiative to investigate the interplay among climate, geomorphology, and tectonic processes, 3) an Anthropocene modeling initiative, to incorporate mechanistic models of human influences, 4) a coastal vulnerability modeling initiative, with emphasis on deltas and
Near soliton dynamics and singularity formation for L^2 critical problems
NASA Astrophysics Data System (ADS)
Martel, Y.; Merle, F.; Raphaël, P.; Szeftel, J.
2014-04-01
This survey reviews the state of the art concerning singularity formation for two canonical dispersive problems: the L^2 critical non-linear Schrödinger equation and the L^2 critical generalized KdV equation. In particular, the currently very topical question of classifying flows with initial data near a soliton is addressed. Bibliography: 72 titles.
Photoluminescence properties of AgInS2-ZnS nanocrystals: the critical role of the surface
NASA Astrophysics Data System (ADS)
Chevallier, Théo; Le Blevennec, Gilles; Chandezon, Frédéric
2016-03-01
AgInS2-ZnS (ZAIS) nanocrystals are very good candidates for easily synthesized, highly efficient cadmium-free nano-phosphors. They can be employed for the development of next generation white-LED technologies, taking advantage of their nanometric size. This paper describes the combined use of time-resolved emission spectroscopy and photoluminescence quantum yield measurements to quantitatively compare the efficiency of each recombination pathway involved in the photoluminescence of ZAIS nanocrystals. This approach, applied to nanocrystals of different sizes, compositions and surface chemistry revealed the critical role of surface effects. Moreover, we developed a new type of surface passivation that increases the photoluminescence quantum yield of all nanocrystal compositions by 15 to 20%. This molecular surface passivation can be applied as a replacement or in addition to the already established ZnS shell passivation method.AgInS2-ZnS (ZAIS) nanocrystals are very good candidates for easily synthesized, highly efficient cadmium-free nano-phosphors. They can be employed for the development of next generation white-LED technologies, taking advantage of their nanometric size. This paper describes the combined use of time-resolved emission spectroscopy and photoluminescence quantum yield measurements to quantitatively compare the efficiency of each recombination pathway involved in the photoluminescence of ZAIS nanocrystals. This approach, applied to nanocrystals of different sizes, compositions and surface chemistry revealed the critical role of surface effects. Moreover, we developed a new type of surface passivation that increases the photoluminescence quantum yield of all nanocrystal compositions by 15 to 20%. This molecular surface passivation can be applied as a replacement or in addition to the already established ZnS shell passivation method. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR07082A
Molecular Dynamics Studies of Surface Difference Effect on Gas Separation by Zeolite Membranes
NASA Astrophysics Data System (ADS)
Mizukami, Koichi; Kobayashi, Yasunori; Morito, Hideaki; Takami, Seiichi; Kubo, Momoji; Belosludov, Rodion; Miyamoto, Akira
2000-07-01
The permeation of CO2/N2 gas mixture through zeolite membranes was investigated by molecular dynamics (MD) study. MD calculation successfully reproduced the experimental results of CO2/N2 separation by NaY membrane. Furthermore, the surface difference effect on gas separation was examined using the NaA zeolite (100) surface and its (111) surface. The CO2/N2 separation factor of the (111) surface was much lower than that of the (100) surface. This was caused by the difference in surface structure, since the pore structures of both models were the same.
McDowell, J J; Calvin, Olivia L; Hackett, Ryan; Klapes, Bryan
2017-03-31
Two competing predictions of matching theory and an evolutionary theory of behavior dynamics, and one additional prediction of the evolutionary theory, were tested in a critical experiment in which human participants worked on concurrent schedules for money (Dallery, Soto, and McDowell, 2005). The three predictions concerned the descriptive adequacy of matching theory equations, and of equations describing emergent equilibria of the evolutionary theory. Tests of the predictions falsified matching theory and supported the evolutionary theory.
Dynamics and Interactions in Room Temperature Ionic Liquids, Surfaces and Interfaces
2016-01-13
AFRL-AFOSR-VA-TR-2016-0067 Dynamics and Interactions in Room Temperature Ionic Liquids, Surfaces and Interfaces Michael Fayer LELAND STANFORD JUNIOR...2016 4. TITLE AND SUBTITLE Dynamics and Interactions in Room Temperature Ionic Liquids, Surfaces and Interfaces 5a. CONTRACT NUMBER 5b. GRANT...were performed. Room temperature ionic liquids were also investigated. Room temperature ionic liquids (RTIL) are intrinsically interesting because
NASA Astrophysics Data System (ADS)
Lu, Jianfeng; Zhou, Zhennan
2016-09-01
In the spirit of the fewest switches surface hopping, the frozen Gaussian approximation with surface hopping (FGA-SH) method samples a path integral representation of the non-adiabatic dynamics in the semiclassical regime. An improved sampling scheme is developed in this work for FGA-SH based on birth and death branching processes. The algorithm is validated for the standard test examples of non-adiabatic dynamics.
Near-Surface Dynamics of a Separated Jet in the Coastal Transition Zone off Oregon
2009-08-08
Near-surface dynamics of a separated jet in the Coastal Transition Zone off Oregon A. O. Koch, A. L. Kurapov, J. S. Allen College of Oceanic and...2009 Abstract Three-dimensional circulation in the coastal transition zone (CTZ) off Oregon is studied using a 3-km resolution model based on the...00-00-2009 4. TITLE AND SUBTITLE Near-surface dynamics of a separated jet in the Coastal Transition Zone off Oregon 5a. CONTRACT NUMBER 5b. GRANT
Direct measurement of the surface dynamics of supercooled liquid-glycerol by optical scanning a film
NASA Astrophysics Data System (ADS)
Zhang, Fang; Zhang, Guo-Feng; Dong, Shuang-Li; Sun, Jian-Hu; Chen, Rui-Yun; Xiao, Lian-Tuan; Jia, Suo-Tang
2009-09-01
The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glycerol's glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel-Fulcher-Tammann-Hesse (VFTH) law is also presented experimentally.
Bhushan, Bharat; Wang, Yuliang; Maali, Abdelhamid
2009-07-21
Slip length has been measured using the dynamic atomic force microscopy (AFM) method. Unlike the contact AFM method, the sample surface approaches an oscillating sphere with a very low velocity in the dynamic AFM method. During this process, the amplitude and phase shift data are recorded to calculate the hydrodynamic damping coefficient, which is then used to obtain slip length. In this study, a glass sphere with a large radius was glued to the end of an AFM cantilever to measure the slip length on rough surfaces. Experimental results for hydrophilic, hydrophobic, and superhydrophobic surfaces show that the hydrodynamic damping coefficient decreases from the hydrophilic surface to the hydrophobic surface and from the hydrophobic one to the superhydrophobic one. The slip lengths obtained on the hydrophobic and superhydrophobic surfaces are 43 and 236 nm, respectively, which indicates increasing boundary slip from the hydrophobic surface to the superhydrophobic one.
A stochastic, local mode study of neon-liquid surface collision dynamics.
Packwood, Daniel M; Phillips, Leon F
2011-01-14
Equations of motion for a fast, light rare gas atom passing over a liquid surface are derived and used to infer the dynamics of neon collisions with squalane and perfluorinated polyether surfaces from experimental data. The equations incorporate the local mode model of a liquid surface via a stochastic process and explicitly account for impulsive collisional energy loss to the surface. The equations predict angular distributions for scattering of neon that are in good quantitative agreement with experimental data. Our key dynamical conclusions are that experimental angular distributions derive mainly from local mode surface topography rather than from structural features of individual surface molecules, and that the available data for these systems can be accounted for almost exclusively by single collisions between neon atoms and the liquid surface.
Nguyen, Duc; Zhu, Zhi-Guang; Pringle, Brian; Lyding, Joseph; Wang, Wei-Hua; Gruebele, Martin
2016-06-22
Glassy metallic alloys are richly tunable model systems for surface glassy dynamics. Here we study the correlation between atomic mobility, and the hopping rate of surface regions (clusters) that rearrange collectively on a minute to hour time scale. Increasing the proportion o