Computational analysis of the roles of biochemical reactions in anomalous diffusion dynamics
Naruemon, Rueangkham; Charin, Modchang
2016-04-01
Most biochemical processes in cells are usually modeled by reaction–diffusion (RD) equations. In these RD models, the diffusive process is assumed to be Gaussian. However, a growing number of studies have noted that intracellular diffusion is anomalous at some or all times, which may result from a crowded environment and chemical kinetics. This work aims to computationally study the effects of chemical reactions on the diffusive dynamics of RD systems by using both stochastic and deterministic algorithms. Numerical method to estimate the mean-square displacement (MSD) from a deterministic algorithm is also investigated. Our computational results show that anomalous diffusion can be solely due to chemical reactions. The chemical reactions alone can cause anomalous sub-diffusion in the RD system at some or all times. The time-dependent anomalous diffusion exponent is found to depend on many parameters, including chemical reaction rates, reaction orders, and chemical concentrations. Project supported by the Thailand Research Fund and Mahidol University (Grant No. TRG5880157), the Thailand Center of Excellence in Physics (ThEP), CHE, Thailand, and the Development Promotion of Science and Technology.
Fractal Location and Anomalous Diffusion Dynamics for Oil Wells from the KY Geological Survey
Andrew, Keith; Andrew, Kevin A
2009-01-01
Utilizing data available from the Kentucky Geonet (KYGeonet.ky.gov) the fossil fuel mining locations created by the Kentucky Geological Survey geo-locating oil and gas wells are mapped using ESRI ArcGIS in Kentucky single plain 1602 ft projection. This data was then exported into a spreadsheet showing latitude and longitude for each point to be used for modeling at different scales to determine the fractal dimension of the set. Following the porosity and diffusivity studies of Tarafdar and Roy1 we extract fractal dimensions of the fossil fuel mining locations and search for evidence of scaling laws for the set of deposits. The Levy index is used to determine a match to a statistical mechanically motivated generalized probability function for the wells. This probability distribution corresponds to a solution of a dynamical anomalous diffusion equation of fractional order that describes the Levy paths which can be solved in the diffusion limit by the Fox H function ansatz.
Martelloni, Gianluca; Bagnoli, Franco
2016-04-01
Richardson's treatise on turbulent diffusion in 1926 [24] and today, the list of system displaying anomalous dynamical behavior is quite extensive. We only report some examples: charge carrier transport in amorphous semiconductors [25], porous systems [26], reptation dynamics in polymeric systems [27, 28], transport on fractal geometries [29], the long-time dynamics of DNA sequences [30]. In this scenario, the fractional calculus is used to generalized the Fokker-Planck linear equation -∂P (x,t)=D ∇2P (x,t), ∂t (3) where P (x,t) is the density of probability in the space x=[x1, x2, x3] and time t, while D >0 is the diffusion coefficient. Such processes are characterized by Eq. (1). An example of Eq. (3) generalization is ∂∂tP (x,t)=D∇ αP β(x,t) ‑ ∞ ‑ 1 , (4) where the fractional based-derivatives Laplacian Σ(∂α/∂xα)i, (i = 1, 2, 3), of non-linear term Pβ(x,t) is taken into account [31]. Another generalized form is represented by equation ∂∂tδδP(x,t)=D ∇ αP(x,t) δ > 0 α ≤ 2 , (5) that considers also the fractional time-derivative [32]. These fractional-described processes exhibit a power law patters as expressed by Eq. (2). This general introduction introduces the presented work, whose aim is to develop a theoretical model in order to forecast the triggering and propagation of landslides, using the techniques of fractional calculus. The latter is suitable for modeling the water infiltration (i.e., the pore water pressure diffusion in the soil) and the dynamical processes in the fractal media [33]. Alternatively the fractal representation of temporal and spatial derivative (the fractal order only appears in the denominator of the derivative) is considered and the results are compared to the fractional one. The prediction of landslides and the discovering of the triggering mechanism, is one of the challenging problems in earth science. Landslides can be triggered by different factors but in most cases the trigger is an intense or long
Martelloni, Gianluca; Bagnoli, Franco
2016-04-01
Richardson's treatise on turbulent diffusion in 1926 [24] and today, the list of system displaying anomalous dynamical behavior is quite extensive. We only report some examples: charge carrier transport in amorphous semiconductors [25], porous systems [26], reptation dynamics in polymeric systems [27, 28], transport on fractal geometries [29], the long-time dynamics of DNA sequences [30]. In this scenario, the fractional calculus is used to generalized the Fokker-Planck linear equation -∂P (x,t)=D ∇2P (x,t), ∂t (3) where P (x,t) is the density of probability in the space x=[x1, x2, x3] and time t, while D >0 is the diffusion coefficient. Such processes are characterized by Eq. (1). An example of Eq. (3) generalization is ∂∂tP (x,t)=D∇ αP β(x,t) ‑ ∞ ‑ 1 , (4) where the fractional based-derivatives Laplacian Σ(∂α/∂xα)i, (i = 1, 2, 3), of non-linear term Pβ(x,t) is taken into account [31]. Another generalized form is represented by equation ∂∂tδδP(x,t)=D ∇ αP(x,t) δ > 0 α ≤ 2 , (5) that considers also the fractional time-derivative [32]. These fractional-described processes exhibit a power law patters as expressed by Eq. (2). This general introduction introduces the presented work, whose aim is to develop a theoretical model in order to forecast the triggering and propagation of landslides, using the techniques of fractional calculus. The latter is suitable for modeling the water infiltration (i.e., the pore water pressure diffusion in the soil) and the dynamical processes in the fractal media [33]. Alternatively the fractal representation of temporal and spatial derivative (the fractal order only appears in the denominator of the derivative) is considered and the results are compared to the fractional one. The prediction of landslides and the discovering of the triggering mechanism, is one of the challenging problems in earth science. Landslides can be triggered by different factors but in most cases the trigger is an intense or long
Propagators and Time-Dependent Diffusion Coefficients for Anomalous Diffusion
Wu, Jianrong; Berland, Keith M.
2008-01-01
Complex diffusive dynamics are often observed when one is investigating the mobility of macromolecules in living cells and other complex environments, yet the underlying physical or chemical causes of anomalous diffusion are often not fully understood and are thus a topic of ongoing research interest. Theoretical models capturing anomalous dynamics are widely used to analyze mobility data from fluorescence correlation spectroscopy and other experimental measurements, yet there is significant ...
Yuste, S B; Abad, E; Baumgaertner, A
2016-07-01
We address the problem of diffusion on a comb whose teeth display varying lengths. Specifically, the length ℓ of each tooth is drawn from a probability distribution displaying power law behavior at large ℓ,P(ℓ)∼ℓ^{-(1+α)} (α>0). To start with, we focus on the computation of the anomalous diffusion coefficient for the subdiffusive motion along the backbone. This quantity is subsequently used as an input to compute concentration recovery curves mimicking fluorescence recovery after photobleaching experiments in comblike geometries such as spiny dendrites. Our method is based on the mean-field description provided by the well-tested continuous time random-walk approach for the random-comb model, and the obtained analytical result for the diffusion coefficient is confirmed by numerical simulations of a random walk with finite steps in time and space along the backbone and the teeth. We subsequently incorporate retardation effects arising from binding-unbinding kinetics into our model and obtain a scaling law characterizing the corresponding change in the diffusion coefficient. Finally, we show that recovery curves obtained with the help of the analytical expression for the anomalous diffusion coefficient cannot be fitted perfectly by a model based on scaled Brownian motion, i.e., a standard diffusion equation with a time-dependent diffusion coefficient. However, differences between the exact curves and such fits are small, thereby providing justification for the practical use of models relying on scaled Brownian motion as a fitting procedure for recovery curves arising from particle diffusion in comblike systems. PMID:27575088
Anomalous Diffusion in Velocity Space
Trigger, S. A.
2009-01-01
The problem of anomalous diffusion in the momentum space is considered on the basis of the appropriate probability transition function (PTF). New general equation for description of the diffusion of heavy particles in the gas of the light particles is formulated on basis of the new approach similar to one in coordinate space (S. Trigger et al.). The obtained results permit to describe the various situations when the probability transition function (PTF) has a long tail in the momentum space. ...
Communication: Probing anomalous diffusion in frequency space
International Nuclear Information System (INIS)
Anomalous diffusion processes are usually detected by analyzing the time-dependent mean square displacement of the diffusing particles. The latter evolves asymptotically as W(t) ∼ 2Dαtα, where Dα is the fractional diffusion constant and 0 < α < 2. In this article we show that both Dα and α can also be extracted from the low-frequency Fourier spectrum of the corresponding velocity autocorrelation function. This offers a simple method for the interpretation of quasielastic neutron scattering spectra from complex (bio)molecular systems, in which subdiffusive transport is frequently encountered. The approach is illustrated and validated by analyzing molecular dynamics simulations of molecular diffusion in a lipid POPC bilayer
Anomalous extracellular diffusion in rat cerebellum.
Xiao, Fanrong; Hrabe, Jan; Hrabetova, Sabina
2015-05-01
Extracellular space (ECS) is a major channel transporting biologically active molecules and drugs in the brain. Diffusion-mediated transport of these substances is hindered by the ECS structure but the microscopic basis of this hindrance is not fully understood. One hypothesis proposes that the hindrance originates in large part from the presence of dead-space (DS) microdomains that can transiently retain diffusing molecules. Because previous theoretical and modeling work reported an initial period of anomalous diffusion in similar environments, we expected that brain regions densely populated by DS microdomains would exhibit anomalous extracellular diffusion. Specifically, we targeted granular layers (GL) of rat and turtle cerebella that are populated with large and geometrically complex glomeruli. The integrative optical imaging (IOI) method was employed to evaluate diffusion of fluorophore-labeled dextran (MW 3000) in GL, and the IOI data analysis was adapted to quantify the anomalous diffusion exponent dw from the IOI records. Diffusion was significantly anomalous in rat GL, where dw reached 4.8. In the geometrically simpler turtle GL, dw was elevated but not robustly anomalous (dw = 2.6). The experimental work was complemented by numerical Monte Carlo simulations of anomalous ECS diffusion in several three-dimensional tissue models containing glomeruli-like structures. It demonstrated that both the duration of transiently anomalous diffusion and the anomalous exponent depend on the size of model glomeruli and the degree of their wrapping. In conclusion, we have found anomalous extracellular diffusion in the GL of rat cerebellum. This finding lends support to the DS microdomain hypothesis. Transiently anomalous diffusion also has a profound effect on the spatiotemporal distribution of molecules released into the ECS, especially at diffusion distances on the order of a few cell diameters, speeding up short-range diffusion-mediated signals in less permeable
Current distribution in systems with anomalous diffusion: renormalization group approach
International Nuclear Information System (INIS)
We investigate the asymptotic properties of the large deviation function of the integrated particle current in systems, in or out of thermal equilibrium, whose dynamics exhibits anomalous diffusion. The physical systems covered by our study include mutually repelling particles with a drift, a driven lattice gas displaying a continuous nonequilibrium phase transition and particles diffusing in an anisotropic random advective field. It is exemplified how renormalization group techniques allow for a systematic determination of power laws in the corresponding current large deviation functions. We show that the latter are governed by known universal scaling exponents, specifically the anomalous dimension of the noise correlators
Anomalous Diffusion with Absorbing Boundary
Kantor, Yacov; Kardar, Mehran
2007-01-01
In a very long Gaussian polymer on time scales shorter that the maximal relaxation time, the mean squared distance travelled by a tagged monomer grows as ~t^{1/2}. We analyze such sub-diffusive behavior in the presence of one or two absorbing boundaries and demonstrate the differences between this process and the sub-diffusion described by the fractional Fokker-Planck equation. In particular, we show that the mean absorption time of diffuser between two absorbing boundaries is finite. Our res...
Li, Baowen; Wang, Jiao; Wang, Lei; Zhang, Gang
2004-01-01
We study anomalous heat conduction and anomalous diffusion in low dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is $\\sigma^2(t)\\equiv =2Dt^{\\alpha} (01$) implies an anomalous heat conduction with a divergent thermal conductivity ($\\beta>0$), and more interestingly, a subdiffusion ($\\a...
Modeling anomalous diffusion of dense fluids in carbon nanotubes
Wang, Gerald; Hadjiconstantinou, Nicolas
2015-11-01
Molecular diffusive mechanisms exhibited under nanoconfinement can differ considerably from the Fickian self-diffusion expected in a bulk fluid. We propose a theoretical description of this phenomenon in a nanofluidic system of considerable interest - namely, a dense fluid confined within a carbon nanotube (CNT). We show that the anomalous diffusion reported in the literature is closely related to the fluid layering widely observed in this system and recently theoretically described [Wang and Hadjiconstantinou, Physics of Fluids, 052006, 2015]. In particular, we find that the key to describing the anomalous molecular diffusion (within sufficiently large CNTs) lies in recognizing that the diffusion mechanism is spatially dependent: while fluid in the center of the nanotube (at least three molecular diameters away from the wall) exhibits Fickian diffusion, fluid near the CNT wall can demonstrate non-Fickian diffusive behavior. The previously reported anomalous diffusive behavior can be reproduced, to a good approximation level, by appropriately combining the bulk and near-wall behavior to form a model for the overall diffusion rate within the nanotube. Such models produce results in quantitative agreement with molecular dynamics simulations.
Anomalous copper diffusion through samarium
International Nuclear Information System (INIS)
We report the observation of enhanced diffusion of Cu through thick films of Sm at temperatures of 250--300 K. The rate of diffusion of Cu to the surface is found to be independent of temperature. The time dependence of the intensities of the Sm divalent and trivalent features indicate the Cu occupies interstitial sites below the divalent Sm surface layer and above the trivalent Sm bulk. The measured binding energies of the divalent and trivalent Sm show no shift with respect to pure Sm, indicating the Cu does not react with the Sm. The spectral features associated with Cu indicate it is in an atomic-like configuration. An examination of these intensities also provide evidence for heterogeneous mixed valence in Sm
Anomalous diffusion spreads its wings
Energy Technology Data Exchange (ETDEWEB)
Klafter, J. [School of Chemistry, Tel Aviv University, Tel-Aviv (Israel)]. E-mail: klafter@post.tau.ac.il; Sokolov, I.M. [Institute of Physics, Humboldt University, Berlin (Germany)]. E-mail: igor.sokolov@physik.hu-berlin.de
2005-08-01
An increasing number of natural phenomena do not fit into the relatively simple description of diffusion developed by Einstein a century ago. As all of us are no doubt aware, this year has been declared 'world year of physics' to celebrate the three remarkable breakthroughs made by Albert Einstein in 1905. However, it is not so well known that Einstein's work on Brownian motion - the random motion of tiny particles first observed and investigated by the botanist Robert Brown in 1827 - has been cited more times in the scientific literature than his more famous papers on special relativity and the quantum nature of light. In a series of publications that included his doctoral thesis, Einstein derived an equation for Brownian motion from microscopic principles - a feat that ultimately enabled Jean Perrin and others to prove the existence of atoms (see 'Einstein's random walk' Physics World January pp19-22). Einstein was not the only person thinking about this type of problem. The 27 July 1905 issue of Nature contained a letter with the title 'The problem of the random walk' by the British statistician Karl Pearson, who was interested in the way that mosquitoes spread malaria, which he showed was described by the well-known diffusion equation. As such, the displacement of a mosquito from its initial position is proportional to the square root of time, and the distribution of the positions of many such 'random walkers' starting from the same origin is Gaussian in form. The random walk has since turned out to be intimately linked to Einstein's work on Brownian motion, and has become a major tool for understanding diffusive processes in nature. (U.K.)
Anomalous Diffusion in Fractal Globules
Tamm, M. V.; Nazarov, L. I.; Gavrilov, A. A.; Chertovich, A. V.
2015-05-01
The fractal globule state is a popular model for describing chromatin packing in eukaryotic nuclei. Here we provide a scaling theory and dissipative particle dynamics computer simulation for the thermal motion of monomers in the fractal globule state. Simulations starting from different entanglement-free initial states show good convergence which provides evidence supporting the existence of a unique metastable fractal globule state. We show monomer motion in this state to be subdiffusive described by ⟨X2(t )⟩˜tαF with αF close to 0.4. This result is in good agreement with existing experimental data on the chromatin dynamics, which makes an additional argument in support of the fractal globule model of chromatin packing.
Anomalous diffusions induced by enhancement of memory
Kim, Hyun-Joo
2014-01-01
We introduced simple microscopic non-Markovian walk models which describe underlying mechanism of anomalous diffusions. In the models, we considered the competitions between randomness and memory effects of previous history by introducing the probability parameters. The memory effects were considered in two aspects, one is the perfect memory of whole history and the other is the latest memory improved with time. In the perfect memory model superdiffusion was induced with the relation the Hurs...
Anomalous diffusion induced by enhancement of memory
Kim, Hyun-Joo
2014-07-01
We introduced simple microscopic non-Markovian walk models which describe the underlying mechanism of anomalous diffusions. In the models, we considered the competitions between randomness and memory effects of previous history by introducing the probability parameters. The memory effects were considered in two aspects: one is the perfect memory of whole history and the other is the latest memory enhanced with time. In the perfect memory model superdiffusion was induced with the relation of the Hurst exponent H to the controlling parameter p as H =p for p >1/2, while in the latest memory enhancement models, anomalous diffusions involving both superdiffusion and subdiffusion were induced with the relations H =(1+α)/2 and H =(1-α)/2 for 0≤α≤1, where α is the parameter controlling the degree of the latest memory enhancement. Also we found that, although the latest memory was only considered, the memory improved with time results in the long-range correlations between steps and the correlations increase as time goes on. Thus we suggest the memory enhancement as a key origin describing anomalous diffusions.
Anomalous Diffusion on the Hanoi Networks
Boettcher, S.; B. Goncalves
2008-01-01
Diffusion is modeled on the recently proposed Hanoi networks by studying the mean- square displacement of random walks with time, ~t^{2/d_w}. It is found that diffusion - the quintessential mode of transport throughout Nature - proceeds faster than ordinary, in one case with an exact, anomalous exponent dw = 2-log_2(\\phi) = 1.30576 . . .. It is an instance of a physical exponent containing the "golden ratio" \\phi=(1+\\sqrt{5})/2 that is intimately related to Fibonacci sequences and since Eucli...
Anomalous Dynamical Responses in a Driven System
Dutta, Suman
2016-01-01
The interplay between structure and dynamics in non-equilibrium steady-state is far from understood. We address this interplay by tracking Brownian Dynamics trajectories of particles in a binary colloid of opposite charges in an external electric field, undergoing cross-over from homogeneous to lane state, a prototype of heterogeneous structure formation in non-equilibrium systems. We show that the length scale of structural correlations controls heterogeneity in diffusion and consequent anomalous dynamic responses, like the exponential tail in probability distributions of particle displacements and stretched exponential structural relaxation. We generalise our observations using equations for steady state density which may aid to understand microscopic basis of heterogeneous diffusion in condensed matter systems.
Violation of Fourier's Law and Anomalous Heat Diffusion in Silicon
Yang, Nuo; Zhang, Gang; Li, Baowen
2010-01-01
We study heat conduction and diffusion in silicon nanowires (SiNWs) systematically by using non-equilibrium molecular dynamics. It is found that the thermal conductivity of SiNWs diverges with the length, even when the length is up to 1,100 nm which is much longer than the phonon mean free path. Moreover, an anomalous heat diffusion is observed which is believed to be responsible for the length dependent thermal conductivity. Our results provide strong evidence that Fourier's law of heat cond...
Anomalous diffusion and scaling in coupled stochastic processes
Energy Technology Data Exchange (ETDEWEB)
Bel, Golan [Los Alamos National Laboratory; Nemenman, Ilya [Los Alamos National Laboratory
2009-01-01
Inspired by problems in biochemical kinetics, we study statistical properties of an overdamped Langevin processes with the friction coefficient depending on the state of a similar, unobserved, process. Integrating out the latter, we derive the Pocker-Planck the friction coefficient of the first depends on the state of the second. Integrating out the latter, we derive the Focker-Planck equation for the probability distribution of the former. This has the fonn of diffusion equation with time-dependent diffusion coefficient, resulting in an anomalous diffusion. The diffusion exponent can not be predicted using a simple scaling argument, and anomalous scaling appears as well. The diffusion exponent of the Weiss-Havlin comb model is derived as a special case, and the same exponent holds even for weakly coupled processes. We compare our theoretical predictions with numerical simulations and find an excellent agreement. The findings caution against treating biochemical systems with unobserved dynamical degrees of freedom by means of standandard, diffusive Langevin descritpion.
Anomalous diffusion in geophysical and laboratory turbulence
Directory of Open Access Journals (Sweden)
A. Tsinober
1994-01-01
Full Text Available We present an overview and some new results on anomalous diffusion of passive scalar in turbulent flows (including those used by Richardson in his famous paper in 1926. The obtained results are based on the analysis of the properties of invariant quantities (energy, enstrophy, dissipation, enstrophy generation, helicity density, etc. - i.e. independent of the choice of the system of reference as the most appropriate to describe physical processes - in three different turbulent laboratory flows (grid-flow, jet and boundary layer, see Tsinober et al. (1992 and Kit et al. (1993. The emphasis is made on the relations between the asymptotic properties of the intermittency exponents of higher order moments of different turbulent fields (energy, dissipation, helicity, spontaneous breaking of isotropy and reflexional symmetry and the variability of turbulent diffusion in the atmospheric boundary layer, in the troposphere and in the stratosphere. It is argued that local spontaneous breaking of isotropy of turbulent flow results in anomalous scaling laws for turbulent diffusion (as compared to the scaling law of Richardson which are observed, as a rule, in different atmospheric layers from the atmospheric boundary layer (ABL to the stratosphere. Breaking of rotational symmetry is important in the ABL, whereas reflexional symmetry breaking is dominating in the troposphere locally and in the stratosphere globally. The results are of speculative nature and further analysis is necessary to validate or disprove the claims made, since the correspondence with the experimental results may occur for the wrong reasons as happens from time to time in the field of turbulence.
Anomalous Diffusion of Mo Implanted into Aluminium
Institute of Scientific and Technical Information of China (English)
张通和; 吴瑜光; 邓志威; 钱卫东
2001-01-01
Mo ions are implanted into aluminium with a high ion flux and high dose at elevated temperatures of 300℃, 400℃ and 500℃ . X-ray diffraction spectra show that the Al12Mo phases are formed. Rutherford backscattering spectroscopy indicates that a profile of Mo appears in Al around the depth of 550nm and with an atomic concentration of ～7%, when Mo is implanted to the dose of 3 × 1017/cm2 with an ion flux of 45μA/cm2 (400℃).If the dose increases to 1 × 1018/cm2 at the same ion flux, the penetration of Mo ions in Al can reach a depth of 2μm, which is greater than the ion project range Rp (52.5nm). The results show that anomalous diffusion takes place. Owing to the intense atom collision cascades, the diffusion coefficient increases greatly with the increase of the ion flux and dose. The Mo diffusion coefficients in Al are calculated. The Mo retained dose in A1 increases obviously with the increase of the ion flux.
Heterogeneous anomalous diffusion in view of superstatistics
Energy Technology Data Exchange (ETDEWEB)
Itto, Yuichi
2014-08-22
Highlights: • A theory is developed for a generalized fractional kinetics in view of superstatistics. • The present theory explicitly takes into account the existence of a large time-scale separation in the infection pathway. • The present theory implies a scaling nature of the motion of the virus. - Abstract: It is experimentally known that virus exhibits stochastic motion in cytoplasm of a living cell in the free form as well as the form being contained in the endosome and the exponent of anomalous diffusion of the virus fluctuates depending on localized areas of the cytoplasm. Here, a theory is developed for establishing a generalized fractional kinetics for the infection pathway of the virus in the cytoplasm in view of superstatistics, which offers a general framework for describing nonequilibrium complex systems with two largely separated time scales. In the present theory, the existence of a large time-scale separation in the infection pathway is explicitly taken into account. A comment is also made on scaling nature of the motion of the virus that is suggested by the theory.
Heterogeneous anomalous diffusion in view of superstatistics
International Nuclear Information System (INIS)
Highlights: • A theory is developed for a generalized fractional kinetics in view of superstatistics. • The present theory explicitly takes into account the existence of a large time-scale separation in the infection pathway. • The present theory implies a scaling nature of the motion of the virus. - Abstract: It is experimentally known that virus exhibits stochastic motion in cytoplasm of a living cell in the free form as well as the form being contained in the endosome and the exponent of anomalous diffusion of the virus fluctuates depending on localized areas of the cytoplasm. Here, a theory is developed for establishing a generalized fractional kinetics for the infection pathway of the virus in the cytoplasm in view of superstatistics, which offers a general framework for describing nonequilibrium complex systems with two largely separated time scales. In the present theory, the existence of a large time-scale separation in the infection pathway is explicitly taken into account. A comment is also made on scaling nature of the motion of the virus that is suggested by the theory
Normal and anomalous diffusion in a deterministic area-preserving map
International Nuclear Information System (INIS)
Chaotic deterministic dynamics of a particle can give rise to diffusive Brownian motion. The diffusion coefficient for a particular two-dimensional stochastic layer induced by the kicked Harper map is computed analytically. The variations of the transport coefficient as a parameter is varied are analyzed in terms of the underlying classical trajectories with particular emphasis in the appearance and bifurcations of periodic orbits. When accelerator modes are present, anomalous diffusion of the Levy type can occur. The exponent characterizing the anomalous diffusion is computed numerically and analyzed as a function of the parameter. (author)
Mesoscopic description of reactions under anomalous diffusion: A case study
Schmidt, M. G. W.; Sagues, F.; I. M. Sokolov
2006-01-01
Reaction-diffusion equations deliver a versatile tool for the description of reactions in inhomogeneous systems under the assumption that the characteristic reaction scales and the scales of the inhomogeneities in the reactant concentrations separate. In the present work we discuss the possibilities of a generalization of reaction-diffusion equations to the case of anomalous diffusion described by continuous-time random walks with decoupled step length and waiting time probability densities, ...
What Matters When and Where for Anomalous Dispersion/Diffusion
O'Malley, D.; Vesselinov, V. V.
2013-12-01
The classical Lagrangian model of Fickian dispersion/diffusion is given by Brownian motion of fluid particles representing contaminant migration. Brownian motion is defined via three conceptual assumptions about the distribution of (spatial) displacements: 1. The displacements are independent. 2. The displacements are stationary. 3. The displacements are normally distributed. Anomalous dispersion/diffusion occurs when one or more of these assumptions fails. Two of the hallmarks of anomalous dispersion/diffusion are nonlinear mean square displacement (often modeled as a power-law) and heavy tails. While these calling cards are important indicators of anomalous behavior, its origin is in the violation of any of the three assumptions. Anomalous behavior associated with such as violation has been observed in a variety of application areas including surface and subsurface hydrology. Anomalous dispersion/diffusion can create significant problems in efforts to characterize contaminant transport and design remediation strategies that protect groundwater resources. The impact at varied spatial and temporal scales of relaxing these assumptions in concert is not well understood. In order to gain a better understanding, a global sensitivity analysis (based on Sobol's method) of predicted contaminant concentrations at a number of spatial and temporal scales is performed with respect to the relaxation of these three assumptions. That is, the sensitivity of contaminant concentration (particle density) to variations in the degree to which the displacements are correlated, nonstationary, and non-normal is computed. The analyses are performed using the code MADS (Model Analyses for Decision Support; http://mads.lanl.gov).
Normal and anomalous diffusion of Brownian particles on disordered potentials
Salgado-García, R.
2016-07-01
In this work we study the transition from normal to anomalous diffusion of Brownian particles on disordered potentials. The potential model consists of a series of "potential hills" (defined on a unit cell of constant length) whose heights are chosen randomly from a given distribution. We calculate the exact expression for the diffusion coefficient in the case of uncorrelated potentials for arbitrary distributions. We show that when the potential heights have a Gaussian distribution (with zero mean and a finite variance) the diffusion of the particles is always normal. In contrast, when the distribution of the potential heights is exponentially distributed the diffusion coefficient vanishes when the system is placed below a critical temperature. We calculate analytically the diffusion exponent for the anomalous (subdiffusive) phase by using the so-called "random trap model". Our predictions are tested by means of Langevin simulations obtaining good agreement within the accuracy of our numerical calculations.
On anomalous diffusion in a plasma in velocity space
Trigger, SA; Ebeling, W.; Heijst, van, A.F.; Schram, PPJM Piet; Sokolov, M
2010-01-01
The problem of anomalous diffusion in momentum space is considered for plasma-like systems on the basis of a new collision integral, which is appropriate for consideration of the probability transition function (PTF) with long tails in momentum space. The generalized Fokker-Planck equation for description of diffusion (in momentum space) of particles (ions, grains etc.) in a stochastic system of light particles (electrons, or electrons and ions, respectively) is applied to the evolution of th...
Fractional phenomenology of cosmic ray anomalous diffusion
International Nuclear Information System (INIS)
We review the evolution of the cosmic ray diffusion concept from the ordinary (Einstein) model of Brownian motion to the fractional models that appeared in the last decade. The mathematical and physical foundations of these models are discussed, as are their consequences, related problems, and prospects for further development. (reviews of topical problems)
Continuous time anomalous diffusion in a composite medium.
Stickler, B A; Schachinger, E
2011-08-01
The one-dimensional continuous time anomalous diffusion in composite media consisting of a finite number of layers in immediate contact is investigated. The diffusion process itself is described with the help of two probability density functions (PDFs), one of which is an arbitrary jump-length PDF, and the other is a long-tailed waiting-time PDF characterized by the waiting-time index β∈(0,1). The former is assumed to be a function of the space coordinate x and the time coordinate t while the latter is a function of x and the time interval. For such an environment a very general form of the diffusion equation is derived which describes the continuous time anomalous diffusion in a composite medium. This result is then specialized to two particular forms of the jump-length PDF, namely the continuous time Lévy flight PDF and the continuous time truncated Lévy flight PDF. In both cases the PDFs are characterized by the Lévy index α∈(0,2) which is regarded to be a function of x and t. It is possible to demonstrate that for particular choices of the indices α and β other equations for anomalous diffusion, well known from the literature, follow immediately. This demonstrates the very general applicability of the derivation and of the resulting fractional differential equation discussed here. PMID:21928958
Anomalous diffusion and transport beta limits in dense tokamak plasmas
International Nuclear Information System (INIS)
For tokamak plasmas which are sufficiently large and/or dense that the ionization source on axis may be neglected, particle balance is achieved by the inward diffusion due to the Ware pinch compensating the outward flow due to both neoclassical and anomalous diffusion. Insertion of measured data into the particle flux balance relation determines the anomalous particle diffusion coefficient Dsub(A); comparison of the results from a variety of tokamaks implies that the dominant dependence on machine and/or plasma parameters is Dsub(A) proportional to 1/n. Particle flux balance also implies an upper bound on the central value of βsub(e), the limiting value being obtained when the plasma parameters are chosen such that Dsub(A)<< Dsub(NEO). This limit has been computed for circular-cross-section tokamaks, and the results so obtained are of the same order as magnetohydrodynamic beta limits. (author)
Characterization of diffusion processes: Normal and anomalous regimes
Alves, Samuel B.; de Oliveira, Gilson F.; de Oliveira, Luimar C.; Passerat de Silans, Thierry; Chevrollier, Martine; Oriá, Marcos; de S. Cavalcante, Hugo L. D.
2016-04-01
Many man-made and natural processes involve the diffusion of microscopic particles subject to random or chaotic, random-like movements. Besides the normal diffusion characterized by a Gaussian probability density function, whose variance increases linearly in time, so-called anomalous-diffusion regimes can also take place. They are characterized by a variance growing slower (subdiffusive) or faster (superdiffusive) than normal. In fact, many different underlying processes can lead to anomalous diffusion, with qualitative differences between mechanisms producing subdiffusion and mechanisms resulting in superdiffusion. Thus, a general description, encompassing all three regimes and where the specific mechanisms of each system are not explicit, is desirable. Here, our goal is to present a simple method of data analysis that enables one to characterize a model-less diffusion process from data observation, by observing the temporal evolution of the particle spread. To generate diffusive processes in different regimes, we use a Monte-Carlo routine in which both the step-size and the time-delay of the diffusing particles follow Pareto (inverse-power law) distributions, with either finite or diverging statistical momenta. We discuss on the application of this method to real systems.
Oscillatory variation of anomalous diffusion in pendulum systems
Indian Academy of Sciences (India)
G Sakthivel; S Rajasekar
2011-03-01
Numerical studies of anomalous diffusion in undamped but periodically-driven and parametrically-driven pendulum systems are presented. When the frequency of the periodic driving force is varied, the exponent , which is the rate of divergence of the mean square displacement with time, is found to vary in an oscillatory manner. We show the presence of such a variation in other statistical measures such as variance of position, kurtosis, and exponents in the power-exponential law of probability distribution of position.
Advances in the studies of anomalous diffusion in velocity space
Dubinova, A. A.; Trigger, S. A.
2011-01-01
A generalized Fokker-Planck equation is derived to describe particle kinetics in specific situations when the probability transition function (PTF) has a long tail in momentum space. The equation is valid for an arbitrary value of the transferred in a collision act momentum and for the arbitrary mass ratio of the interacting particles. On the basis of the generalized Fokker-Planck equation anomalous diffusion in velocity space is considered for hard sphere model of particle interactions, Coul...
A Fractional Fokker-Planck Model for Anomalous Diffusion
Anderson, Johan; Kim, Eun-Jin; Moradi, Sara
2014-01-01
In this paper we present a study of anomalous diffusion using a Fokker-Planck description with fractional velocity derivatives. The distribution functions are found using numerical means for varying degree of fractionality observing the transition from a Gaussian distribution to a L\\'evy distribution. The statistical properties of the distribution functions are assessed by a generalized expectation measure and entropy in terms of Tsallis statistical mechanics. We find that the ratio of the ge...
Asymptotic neutron scattering laws for anomalously diffusing quantum particles.
Kneller, Gerald R
2016-07-28
The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ∝t(α), with 0 ≤ α diffusion (α = 0) is here explicitly included. We discuss in particular the intermediate scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers. PMID:27475344
Anomalous Diffusion and Long-range Correlations in the Score Evolution of the Game of Cricket
Ribeiro, H V; Zeng, Xiao Han T
2012-01-01
We investigate the time evolution of the scores of the second most popular sport in world: the game of cricket. By analyzing the scores event-by-event of more than two thousand matches, we point out that the score dynamics is an anomalous diffusive process. Our analysis reveals that the variance of the process is described by a power-law dependence with a super-diffusive exponent, that the scores are statistically self-similar following a universal Gaussian distribution, and that there are long-range correlations in the score evolution. We employ a generalized Langevin equation with a power-law correlated noise that describe all the empirical findings very well. These observations suggest that competition among agents may be a mechanism leading to anomalous diffusion and long-range correlation.
Magin, Richard L.; Akpa, Belinda S.; Neuberger, Thomas; Webb, Andrew G.
2011-12-01
We report the appearance of anomalous water diffusion in hydrophilic Sephadex gels observed using pulse field gradient (PFG) nuclear magnetic resonance (NMR). The NMR diffusion data was collected using a Varian 14.1 Tesla imaging system with a home-built RF saddle coil. A fractional order analysis of the data was used to characterize heterogeneity in the gels for the dynamics of water diffusion in this restricted environment. Several recent studies of anomalous diffusion have used the stretched exponential function to model the decay of the NMR signal, i.e., exp[-( bD) α], where D is the apparent diffusion constant, b is determined the experimental conditions (gradient pulse separation, durations and strength), and α is a measure of structural complexity. In this work, we consider a different case where the spatial Laplacian in the Bloch-Torrey equation is generalized to a fractional order model of diffusivity via a complexity parameter, β, a space constant, μ, and a diffusion coefficient, D. This treatment reverts to the classical result for the integer order case. The fractional order decay model was fit to the diffusion-weighted signal attenuation for a range of b-values (0 < b < 4000 s mm -2). Throughout this range of b values, the parameters β, μ and D, were found to correlate with the porosity and tortuosity of the gel structure.
Weak Disorder: Anomalous Transport and Diffusion Are Normal Yet Again
Khoury, M.; Lacasta, A. M.; Sancho, J. M.; Lindenberg, Katja
2011-03-01
We carry out a detailed study of the motion of particles driven by a constant external force over a landscape consisting of a periodic potential corrugated by a small amount of spatial disorder. We observe anomalous behavior in the form of subdiffusion and superdiffusion and even subtransport over very long time scales. Recent studies of transport over slightly random landscapes have focused only on parameters leading to normal behavior, and while enhanced diffusion has been identified when the external force approaches the critical value associated with the transition from locked to running solutions, the regime of anomalous behavior had not been recognized. We provide a qualitative explanation for the origin of these anomalies, and make connections with a continuous time random walk approach.
Stochastic Loewner evolution relates anomalous diffusion and anisotropic percolation
Credidio, Heitor F.; Moreira, André A.; Herrmann, Hans J.; Andrade, José S.
2016-04-01
We disclose the origin of anisotropic percolation perimeters in terms of the stochastic Loewner evolution (SLE) process. Precisely, our results from extensive numerical simulations indicate that the perimeters of multilayered and directed percolation clusters at criticality are the scaling limits of the Loewner evolution of an anomalous Brownian motion, being superdiffusive and subdiffusive, respectively. The connection between anomalous diffusion and fractal anisotropy is further tested by using long-range power-law correlated time series (fractional Brownian motion) as the driving functions in the evolution process. The fact that the resulting traces are distinctively anisotropic corroborates our hypothesis. Under the conceptual framework of SLE, our study therefore reveals different perspectives for mathematical and physical interpretations of non-Markovian processes in terms of anisotropic paths at criticality and vice versa.
Anomalous and anisotropic nanoscale diffusion of hydration water molecules in fluid lipid membranes.
Toppozini, Laura; Roosen-Runge, Felix; Bewley, Robert I; Dalgliesh, Robert M; Perring, Toby; Seydel, Tilo; Glyde, Henry R; García Sakai, Victoria; Rheinstädter, Maikel C
2015-11-14
We have studied nanoscale diffusion of membrane hydration water in fluid-phase lipid bilayers made of 1,2-dimyristoyl-3-phosphocholine (DMPC) using incoherent quasi-elastic neutron scattering. Dynamics were fit directly in the energy domain using the Fourier transform of a stretched exponential. By using large, 2-dimensional detectors, lateral motions of water molecules and motions perpendicular to the membranes could be studied simultaneously, resulting in 2-dimensional maps of relaxation time, τ, and stretching exponent, β. We present experimental evidence for anomalous (sub-diffusive) and anisotropic diffusion of membrane hydration water molecules over nanometer distances. By combining molecular dynamics and Brownian dynamics simulations, the potential microscopic origins for the anomaly and anisotropy of hydration water were investigated. Bulk water was found to show intrinsic sub-diffusive motion at time scales of several picoseconds, likely related to caging effects. In membrane hydration water, however, the anisotropy of confinement and local dynamical environments leads to an anisotropy of relaxation times and stretched exponents, indicative of anomalous dynamics. PMID:26338138
Asymptotic neutron scattering laws for anomalously diffusing quantum particles
Kneller, Gerald R.
2016-07-01
The paper deals with a model-free approach to the analysis of quasielastic neutron scattering intensities from anomalously diffusing quantum particles. All quantities are inferred from the asymptotic form of their time-dependent mean square displacements which grow ∝tα, with 0 ≤ α scattering function for long times and the Fourier spectrum of the velocity autocorrelation function for small frequencies. Quantum effects enter in both cases through the general symmetry properties of quantum time correlation functions. It is shown that the fractional diffusion constant can be expressed by a Green-Kubo type relation involving the real part of the velocity autocorrelation function. The theory is exact in the diffusive regime and at moderate momentum transfers.
Deviation of the statistical fluctuation in heterogeneous anomalous diffusion
Itto, Yuichi
2016-01-01
The exponent of anomalous diffusion of virus in cytoplasm of a living cell is experimentally known to fluctuate depending on localized areas of the cytoplasm, indicating heterogeneity of diffusion. In a recent paper (Itto, 2012), a maximum-entropy-principle approach has been developed in order to propose an Ansatz for the statistical distribution of such exponent fluctuations. Based on this approach, here the deviation of the statistical distribution of the fluctuations from the proposed one is studied from the viewpoint of Einstein's theory of fluctuations (of the thermodynamic quantities). This may present a step toward understanding the statistical property of the deviation. It is shown in a certain class of small deviations that the deviation obeys the multivariate Gaussian distribution.
Lattice Monte Carlo simulation of Galilei variant anomalous diffusion
International Nuclear Information System (INIS)
The observation of an increasing number of anomalous diffusion phenomena motivates the study to reveal the actual reason for such stochastic processes. When it is difficult to get analytical solutions or necessary to track the trajectory of particles, lattice Monte Carlo (LMC) simulation has been shown to be particularly useful. To develop such an LMC simulation algorithm for the Galilei variant anomalous diffusion, we derive explicit solutions for the conditional and unconditional first passage time (FPT) distributions with double absorbing barriers. According to the theory of random walks on lattices and the FPT distributions, we propose an LMC simulation algorithm and prove that such LMC simulation can reproduce both the mean and the mean square displacement exactly in the long-time limit. However, the error introduced in the second moment of the displacement diverges according to a power law as the simulation time progresses. We give an explicit criterion for choosing a small enough lattice step to limit the error within the specified tolerance. We further validate the LMC simulation algorithm and confirm the theoretical error analysis through numerical simulations. The numerical results agree with our theoretical predictions very well
Lattice Monte Carlo simulation of Galilei variant anomalous diffusion
Energy Technology Data Exchange (ETDEWEB)
Guo, Gang, E-mail: hndzgg@aliyun.com [School of Information System and Management, National University of Defense Technology, Changsha, 410073 (China); Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany); Bittig, Arne, E-mail: arne.bittig@uni-rostock.de [Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany); Uhrmacher, Adelinde, E-mail: lin@informatik.uni-rostock.de [Institute of Computer Science, University of Rostock, Albert Einstein Str. 22, Rostock, 18059 (Germany)
2015-05-01
The observation of an increasing number of anomalous diffusion phenomena motivates the study to reveal the actual reason for such stochastic processes. When it is difficult to get analytical solutions or necessary to track the trajectory of particles, lattice Monte Carlo (LMC) simulation has been shown to be particularly useful. To develop such an LMC simulation algorithm for the Galilei variant anomalous diffusion, we derive explicit solutions for the conditional and unconditional first passage time (FPT) distributions with double absorbing barriers. According to the theory of random walks on lattices and the FPT distributions, we propose an LMC simulation algorithm and prove that such LMC simulation can reproduce both the mean and the mean square displacement exactly in the long-time limit. However, the error introduced in the second moment of the displacement diverges according to a power law as the simulation time progresses. We give an explicit criterion for choosing a small enough lattice step to limit the error within the specified tolerance. We further validate the LMC simulation algorithm and confirm the theoretical error analysis through numerical simulations. The numerical results agree with our theoretical predictions very well.
Tierno, Pietro; Shaebani, M Reza
2016-04-14
We combine experiments and theory to investigate the diffusive and the subdiffusive dynamics of paramagnetic colloids driven above a two-state flashing potential. The magnetic potential was realized by periodically modulating the stray field of a magnetic bubble lattice in a uniaxial ferrite garnet film. At large amplitudes H0 of the driving field, the dynamics of the particle resemble an ordinary random walk with a frequency-dependent diffusion coefficient. However, subdiffusive and oscillatory dynamics at short time scales are observed when decreasing H0. We present a persistent random walk model to elucidate the underlying mechanism of motion, and perform numerical simulations to demonstrate that the anomalous motion originates from the dynamic disorder in the structure of the magnetic lattice, induced by the slightly irregular shape of bubbles. PMID:26936328
Anomalous Diffusion of Water in Lamellar Membranes Formed by Pluronic Polymers
Zhang, Zhe; Ohl, Michael; Han, Youngkyu; Smith, Gregory; Do, Changwoo; Biology; Soft-Matter Division, Oak Ridge National Laboratory Team; Julich Center for Neutron Science Team
Water diffusion is playing an important role in polymer systems. We calculated the water diffusion coefficient at different layers along z-direction which is perpendicular to the lamellar membrane formed by Pluronic block copolymers (L62: (EO6-PO34-EO6)) with the molecular dynamics simulation trajectories. Water molecules at bulk layers are following the normal diffusion, while that at hydration layers formed by polyethylene oxide (PEO) and hydrophobic layers formed by polypropylene oxide (PPO) are following anomalous diffusion. We find that although the subdiffusive regimes at PEO layers and PPO layers are the same, which is the fractional Brownian motion, however, the dynamics are different, i.e. diffusion at the PEO layers is much faster than that at the PPO layers, and meanwhile it exhibits a normal diffusive approximation within a short time period which is governed by the localized free self-diffusion, but becomes subdiffusive after t >8 ps, which is governed by the viscoelastic medium. The Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy; and Zhe Zhang gratefully acknowledges financial support from Julich Center for Neutron Science.
Lagrangian stochastic modeling of anomalous diffusion in two-dimensional turbulence
Reynolds, A. M.
2002-04-01
It is shown that at intermediate times, the Langevin equation corresponding to the nonlinear Fokker-Planck equation with exponents μ=1 and ν>1 produces trajectories with multifractal scaling and anomalous power-law dispersion, in common with observations of drifters in the ocean and numerical simulations of tracer particles in two-dimensional turbulence. The extent of this regime and the occurrence of anomalously large normal diffusion at much later times are shown to be in close agreement with dispersion data from numerical simulations of two-dimensional turbulence. In analogy with the dynamics of point vortices in two-dimensional turbulence, the modeled dynamics are nonergodic and effectively comprise of a background Ornstein-Uhlenbeck process punctuated by occasional fast long flights. It is shown that these dynamics optimize the nonextensive (Tsallis) entropy. It is tentatively suggested that the anomalous dispersion in two-dimensional turbulence is a consequence of smaller than average Lagrangian accelerations in regions of the flow with faster than average velocities.
Cisternas, Jaime; Descalzi, Orazio; Albers, Tony; Radons, Günter
2016-05-20
We demonstrate the occurrence of anomalous diffusion of dissipative solitons in a "simple" and deterministic prototype model: the cubic-quintic complex Ginzburg-Landau equation in two spatial dimensions. The main features of their dynamics, induced by symmetric-asymmetric explosions, can be modeled by a subdiffusive continuous-time random walk, while in the case dominated by only asymmetric explosions, it becomes characterized by normal diffusion. PMID:27258868
Cisternas, Jaime; Descalzi, Orazio; Albers, Tony; Radons, Günter
2016-05-01
We demonstrate the occurrence of anomalous diffusion of dissipative solitons in a "simple" and deterministic prototype model: the cubic-quintic complex Ginzburg-Landau equation in two spatial dimensions. The main features of their dynamics, induced by symmetric-asymmetric explosions, can be modeled by a subdiffusive continuous-time random walk, while in the case dominated by only asymmetric explosions, it becomes characterized by normal diffusion.
Onset of anomalous diffusion from local motion rules
de Nigris, Sarah; Lambiotte, Renaud
2016-01-01
Anomalous diffusion processes, in particular superdiffusive ones, are known to be efficient strategies for searching and navigation by animals and also in human mobility. One way to create such regimes are L\\'evy flights, where the walkers are allowed to perform jumps, the "flights", that can eventually be very long as their length distribution is asymptotically power-law distributed. In our work, we present a model in which walkers are allowed to perform, on a 1D lattice, "cascades" of $n$ unitary steps instead of one jump of a randomly generated length, as in the L\\'evy case. Instead of imposing a length distribution, we thus define our process by its cascade distribution $p_n$. We first derive the connections between the two distributions and show that this local mechanism may give rise to superdiffusion or normal diffusion when $p_n$ is distributed as a power law. We also investigate the interplay of this process with the possibility to be stuck on a node, introducing waiting times that are power-law dist...
Anomalous diffusion and multiple-periodic accelerator modes in the standard map
International Nuclear Information System (INIS)
Analysis of the structure of magnetic fields, and of long time behavior of plasma particles in toroidal magnetic devices is the central problem for magnetic control fusion. Extensive research has been developed on these problems in terms of non-linear dynamical approach. Thus the mapping analysis attracts active interests in co-operation with full advantage of computational methods. Since almost of all non-linear dynamical mappings are reduced to the standard map in local approximation, the standard map have been the central focus in the field of nonlinear dynamics of the Hamiltonian system. In spite of the extensive studies of the systems continuing over three decades, there remains still unsolved critical problems. Here, we examine interplay of the anomalous stochastic diffusion phenomena and multiple-periodic accelerator modes in the standard map. Detailed analysis has been carried out to identify the observed anomalous enhancement of stochastic diffusion in the small nonlinear parameter region as due to contribution of the period-2, period-3 and period-5 accelerator modes. (author)
A generalized Fokker–Planck equation for anomalous diffusion in velocity space
International Nuclear Information System (INIS)
A more general quasi-Fokker–Planck equation is derived to describe particle kinetics in situations when the usual Fokker–Planck equation is not applicable. The equation is valid for an arbitrary value of the transferred in a collision act momentum and for the arbitrary mass ratio of the interacting particles. The only assumption is smallness of the typical velocity of the particles, undergoing diffusion. The developed approach is another tool to study anomalous diffusion, avoiding conventional in such problems fractional differentiation. In this Letter anomalous diffusion in velocity space is considered for hard-sphere, Coulomb and dusty plasma collision models. -- Highlights: ► We expand the Master equation into a series. ► We derive a generalized equation for description of anomalous diffusion. ► We consider special cases of anomalous diffusion for hard-sphere interactions, Coulomb systems and dusty plasmas.
Anomalous diffusion and multiple-periodic accelerator modes in the standard map
International Nuclear Information System (INIS)
Multiple-periodic accelerator modes give rise to anomalous enhancement of the stochastic diffusion process in the standard map in the domain of the nonlinear stochastic parameter A < 1. The quantitative analysis of the multiple-periodic accelerator modes has been undertaken to explore contribution of the accelerator modes for the anomalous diffusion. In particular, detailed information of the period-3 and the period-5 accelerator modes such as their existence domain and their stability have been presented in connection with the anomalous enhancement of the diffusion process. (author)
Méndez, Vicenç; Bartumeus, Frederic
2014-01-01
This book presents the fundamental theory for non-standard diffusion problems in movement ecology. Lévy processes and anomalous diffusion have shown to be both powerful and useful tools for qualitatively and quantitatively describing a wide variety of spatial population ecological phenomena and dynamics, such as invasion fronts and search strategies. Adopting a self-contained, textbook-style approach, the authors provide the elements of statistical physics and stochastic processes on which the modeling of movement ecology is based and systematically introduce the physical characterization of ecological processes at the microscopic, mesoscopic and macroscopic levels. The explicit definition of these levels and their interrelations is particularly suitable to coping with the broad spectrum of space and time scales involved in bio-ecological problems. Including numerous exercises (with solutions), this text is aimed at graduate students and newcomers in this field at the interface of theoretical ecology, mat...
Jeon, Jae-Hyung; Javanainen, Matti; Martinez-Seara, Hector; Metzler, Ralf; Vattulainen, Ilpo
2016-04-01
Biomembranes are exceptionally crowded with proteins with typical protein-to-lipid ratios being around 1 ∶50 -1 ∶100 . Protein crowding has a decisive role in lateral membrane dynamics as shown by recent experimental and computational studies that have reported anomalous lateral diffusion of phospholipids and membrane proteins in crowded lipid membranes. Based on extensive simulations and stochastic modeling of the simulated trajectories, we here investigate in detail how increasing crowding by membrane proteins reshapes the stochastic characteristics of the anomalous lateral diffusion in lipid membranes. We observe that correlated Gaussian processes of the fractional Langevin equation type, identified as the stochastic mechanism behind lipid motion in noncrowded bilayer, no longer adequately describe the lipid and protein motion in crowded but otherwise identical membranes. It turns out that protein crowding gives rise to a multifractal, non-Gaussian, and spatiotemporally heterogeneous anomalous lateral diffusion on time scales from nanoseconds to, at least, tens of microseconds. Our investigation strongly suggests that the macromolecular complexity and spatiotemporal membrane heterogeneity in cellular membranes play critical roles in determining the stochastic nature of the lateral diffusion and, consequently, the associated dynamic phenomena within membranes. Clarifying the exact stochastic mechanism for various kinds of biological membranes is an important step towards a quantitative understanding of numerous intramembrane dynamic phenomena.
Cages and Anomalous Diffusion in Vibrated Dense Granular Media
Scalliet, Camille; Gnoli, Andrea; Puglisi, Andrea; Vulpiani, Angelo
2015-05-01
A vertically shaken granular medium hosts a blade rotating around a fixed vertical axis, which acts as a mesorheological probe. At high densities, independently of the shaking intensity, the blade's dynamics shows strong caging effects, marked by transient subdiffusion and a maximum in the velocity power density spectrum, at a resonant frequency ˜10 Hz . Interpreting the data through a diffusing harmonic cage model allows us to retrieve the elastic constant of the granular medium and its collective diffusion coefficient. For high frequencies f , a tail ˜1 /f in the velocity power density spectrum reveals nontrivial correlations in the intracage microdynamics. At very long times (larger than 10 s), a superdiffusive behavior emerges, ballistic in the most extreme cases. Consistently, the distribution of slow velocity inversion times τ displays a power-law decay, likely due to persistent collective fluctuations of the host medium.
Cages and anomalous diffusion in vibrated dense granular media.
Scalliet, Camille; Gnoli, Andrea; Puglisi, Andrea; Vulpiani, Angelo
2015-05-15
A vertically shaken granular medium hosts a blade rotating around a fixed vertical axis, which acts as a mesorheological probe. At high densities, independently of the shaking intensity, the blade's dynamics shows strong caging effects, marked by transient subdiffusion and a maximum in the velocity power density spectrum, at a resonant frequency ~10 Hz. Interpreting the data through a diffusing harmonic cage model allows us to retrieve the elastic constant of the granular medium and its collective diffusion coefficient. For high frequencies f, a tail ~1/f in the velocity power density spectrum reveals nontrivial correlations in the intracage microdynamics. At very long times (larger than 10 s), a superdiffusive behavior emerges, ballistic in the most extreme cases. Consistently, the distribution of slow velocity inversion times τ displays a power-law decay, likely due to persistent collective fluctuations of the host medium. PMID:26024199
Anomalous chain diffusion in polymer nanocomposites for varying polymer-filler interaction strengths
Goswami, Monojoy; Sumpter, Bobby G.
2010-04-01
Anomalous diffusion of polymer chains in a polymer nanocomposite melt is investigated for different polymer-nanoparticle interaction strengths using stochastic molecular dynamics simulations. For spherical nanoparticles dispersed in a polymer matrix the results indicate that the chain motion exhibits three distinct regions of diffusion, the Rouse-like motion, an intermediate subdiffusive regime followed by a normal Fickian diffusion. The motion of the chain end monomers shows a scaling that can be attributed to the formation of strong “networklike” structures, which have been seen in a variety of polymer nanocomposite systems. Irrespective of the polymer-particle interaction strengths, these three regimes seem to be present with small deviations. Further investigation on dynamic structure factor shows that the deviations simply exist due to the presence of strong enthalpic interactions between the monomers with the nanoparticles, albeit preserving the anomaly in the chain diffusion. The time-temperature superposition principle is also tested for this system and shows a striking resemblance with systems near glass transition and biological systems with molecular crowding. The universality class of the problem can be enormously important in understanding materials with strong affinity to form either a glass, a gel or networklike structures.
Effect of anomalous resistivity on the dynamics of plasma switching
International Nuclear Information System (INIS)
Some of the conditions for electron MHD are recollected, and it is shown how this leads to anomalous resistivity which may play an important role in the dynamics of POS. It has been shown that not only the order of value of the resistance of the plasma-filled diode but rather basic scalings have to be changed in the regime of essential anomalous resistivity. (author). 11 refs
Cowie, L.; Kusznir, N. J.
2012-12-01
It has been proposed that some continental rifted margins have anomalous subsidence histories and that at breakup they were elevated at shallower bathymetries than the isostatic response of classical rift models (McKenzie 1978) would predict. The existence of anomalous syn or post breakup subsidence of this form would have important implications for our understanding of the geodynamics of continental breakup and rifted continental margin formation, margin subsidence history and the evolution of syn and post breakup depositional systems. We have investigated three rifted continental margins; the Gulf of Aden, Galicia Bank and the Gulf of Lions, to determine whether the oceanic crust in the ocean-continent transition of these margins has present day anomalous subsidence and if so, whether it is caused by mantle dynamic topography or anomalous oceanic crustal thickness. Residual depth anomalies (RDA) corrected for sediment loading, using flexural backstripping and decompaction, have been calculated by comparing observed and age predicted oceanic bathymetries in order to identify anomalous oceanic bathymetry and subsidence at these margins. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions from Crosby & McKenzie (2009). Non-zero sediment corrected RDAs may result from anomalous oceanic crustal thickness with respect to the global average, or from mantle dynamic uplift. Positive RDAs may result from thicker than average oceanic crust or mantle dynamic uplift; negative RDAs may result from thinner than average oceanic crust or mantle dynamic subsidence. Gravity inversion incorporating a lithosphere thermal gravity anomaly correction and sediment thickness from 2D seismic data has been used to determine Moho depth and oceanic crustal basement thickness. The reference Moho depths used in the gravity inversion have been calibrated against seismic refraction Moho depths. The gravity inversion crustal basement thicknesses
Anomalous structural dynamics in liquid Al80Cu20: An ab initio molecular dynamics study
International Nuclear Information System (INIS)
In this work, the structural dynamics of liquid Al80Cu20 is systematically investigated in terms of the evolution of its atomic structure, diffusivity, viscosity and fragility through ab initio molecular dynamics simulations. In addition to using pair correlation functions and coordination numbers, the various local ordered clusters are characterized comprehensively by Honeycutt-Anderson bond pairs and Voronoi polyhedra. Compared to the self diffusivity of pure liquid Cu, the tracer diffusion coefficients of Cu in liquid Al80Cu20 are increased, in agreement with the results measured by quasielastic neutron-scattering (QENS). Although the interdiffusion coefficients predicted by Darken’s equation match well to those obtained from the viscosity measurements via the Stokes-Einstein relation, they are smaller than those measured by QENS or X-ray radiography, indicative of an anomalous nature of the structural dynamics, dominated by the local ordered clusters in liquid Al80Cu20. Furthermore, Vogel–Fulcher–Tammann fitting results indicate that the liquid Al80Cu20 can be classified into a strong liquid. The deformation electron density shows that the intrinsic tetrahedral-type bonds in FCC Al and Cu are transformed into an amorphous type in liquid Al80Cu20. The present work provides insights into the understanding of structural dynamics and the kinetic properties of such metallic melts
International Nuclear Information System (INIS)
Any first course on polymer physics teaches that the dynamics of a tagged monomer of a polymer is anomalously subdiffusive, i.e., the mean-square displacement of a tagged monomer increases as tα for some α < 1 until the terminal relaxation time τ of the polymer. Beyond time τ the motion of the tagged monomer becomes diffusive. Classical examples of anomalous dynamics in polymer physics are single polymeric systems, such as phantom Rouse, self-avoiding Rouse, self-avoiding Zimm, reptation, translocation through a narrow pore in a membrane, and many-polymeric systems such as polymer melts. In this pedagogical paper I report that all these instances of anomalous dynamics in polymeric systems are robustly characterized by power-law memory kernels within a unified generalized Langevin equation (GLE) scheme, and therefore are non-Markovian. The exponents of the power-law memory kernels are related to the relaxation response of the polymers to local strains, and are derived from the equilibrium statistical physics of polymers. The anomalous dynamics of a tagged monomer of a polymer in these systems is then reproduced from the power-law memory kernels of the GLE via the fluctuation-dissipation theorem (FDT). Using this GLE formulation I further show that the characteristics of the drifts caused by a (weak) applied field on these polymeric systems are also obtained from the corresponding memory kernels
Anomalous structure and dynamics of the Gaussian-core fluid
Krekelberg, William P.; Kumar, Tanuj; Mittal, Jeetain; Errington, Jeffrey R.; Truskett, Thomas M.
2009-01-01
It is known that there are thermodynamic states for which the Gaussian-core (GC) fluid displays anomalous properties such as expansion upon isobaric cooling (density anomaly) and increased single-particle mobility upon isothermal compression (self-diffusivity anomaly). We investigate how temperature and density affect its short-range translational structural order, as characterized by the two-body excess entropy. We find that there is a wide range of conditions for which the short-range trans...
Molecular dynamics simulation of diffusivity
Institute of Scientific and Technical Information of China (English)
Juanfang LIU; Danling ZENG; Qin LI; Hong GAO
2008-01-01
Equilibrium molecular dynamics simulation was performed on water to calculate its diffusivity by adopting different potential models. The results show that the potential models have great influence on the simulated results. In addition, the diffusivities obtained by the SPCE model conform well to the experimental values.
Directory of Open Access Journals (Sweden)
Lund Frederik W
2012-10-01
Full Text Available Abstract Background Cholesterol is an important membrane component, but our knowledge about its transport in cells is sparse. Previous imaging studies using dehydroergosterol (DHE, an intrinsically fluorescent sterol from yeast, have established that vesicular and non-vesicular transport modes contribute to sterol trafficking from the plasma membrane. Significant photobleaching, however, limits the possibilities for in-depth analysis of sterol dynamics using DHE. Co-trafficking studies with DHE and the recently introduced fluorescent cholesterol analog BODIPY-cholesterol (BChol suggested that the latter probe has utility for prolonged live-cell imaging of sterol transport. Results We found that BChol is very photostable under two-photon (2P-excitation allowing the acquisition of several hundred frames without significant photobleaching. Therefore, long-term tracking and diffusion measurements are possible. Two-photon temporal image correlation spectroscopy (2P-TICS provided evidence for spatially heterogeneous diffusion constants of BChol varying over two orders of magnitude from the cell interior towards the plasma membrane, where D ~ 1.3 μm2/s. Number and brightness (N&B analysis together with stochastic simulations suggest that transient partitioning of BChol into convoluted membranes slows local sterol diffusion. We observed sterol endocytosis as well as fusion and fission of sterol-containing endocytic vesicles. The mobility of endocytic vesicles, as studied by particle tracking, is well described by a model for anomalous subdiffusion on short time scales with an anomalous exponent α ~ 0.63 and an anomalous diffusion constant of Dα = 1.95 x 10-3 μm2/sα. On a longer time scale (t > ~5 s, a transition to superdiffusion consistent with slow directed transport with an average velocity of v ~ 6 x 10-3 μm/s was observed. We present an analytical model that bridges the two regimes and fit this model to vesicle
Fringe field NMR diffusometry of anomalous self-diffusion in molecular sieves
Ylihautala, Mika; Jokisaari, Jukka; Fischer, Elmar; Kimmich, Rainer
1998-06-01
Superconducting magnet fringe field NMR diffusometry is applied to an adsorbate-molecular sieve system in order to obtain intracrystalline self-diffusion of adsorbed molecules. Effects of self-diffusion, exchange, relaxation, and dipolar correlation are discussed. The proper equations for one- and two-dimensional anomalous self-diffusion with and without macroscopic order are derived. The method is applied to investigate methane self-diffusion in the molecular sieve silicoaluminophosphate, type 11 (SAPO-11). It is concluded that the nature of the methane displacements in the sieve channels is single-file self-diffusion.
Anomalous diffusion of a tracer advected by wave turbulence
Balk, Alexander M.
2001-02-01
We consider the advection of a passive tracer when the velocity field is a superposition of random waves. Green's function for the turbulent transport (turbulent diffusion and turbulent drift) is derived. This Green's function is shown to imply sub-diffusive or super-diffusive behavior of the tracer. For the analysis we introduce the statistical near-identity transformation. The results are confirmed by numerical simulations.
Superfast front propagation in reactive systems with anomalous diffusion
Mancinelli, Rosaria; Vergni, Davide; Vulpiani, Angelo
2002-01-01
We study a reaction diffusion system where we consider a non-gaussian process instead of a standard diffusion. If the process increments follow a probability distribution with tails approaching to zero faster than a power law, the usual qualitative behaviours of the standard reaction diffusion system, i.e., exponential tails for the reacting field and a constant front speed, are recovered. On the contrary if the process has power law tails, also the reacting field shows power law tail and the...
Anisotropic Anomalous Diffusion assessed in the human brain by scalar invariant indices
De Santis, S; Bozzali, M; Maraviglia, B; Macaluso, E; Capuani, S
2010-01-01
A new method to investigate anomalous diffusion in human brain is proposed. The method has been inspired by both the stretched-exponential model proposed by Hall and Barrick (HB) and DTI. Quantities extracted using HB method were able to discriminate different cerebral tissues on the basis of their complexity, expressed by the stretching exponent gamma and of the anisotropy of gamma across different directions. Nevertheless, these quantities were not defined as scalar invariants like mean diffusivity and fractional anisotropy, which are eigenvalues of the diffusion tensor. We hypotesize instead that the signal may be espressed as a simple stretched-exponential only along the principal axes of diffusion, while in a generic direction the signal is modeled as a combination of three different stretched-exponentials. In this way, we derived indices to quantify both the tissue anomalous diffusion and its anisotropy, independently of the reference frame of the experiment. We tested and compare our new method with DT...
Anomalous diffusion and Tsallis statistics in an optical lattice
International Nuclear Information System (INIS)
We point out a connection between anomalous transport in an optical lattice and Tsallis' generalized statistics. Specifically, we show that the momentum equation for the semiclassical Wigner function which describes atomic motion in the optical potential, belongs to a class of transport equations recently studied by Borland [Phys. Lett. A 245, 67 (1998)]. The important property of these ordinary linear Fokker-Planck equations is that their stationary solutions are exactly given by Tsallis distributions. An analytical expression of the Tsallis index q in terms of the microscopic parameters of the quantum-optical problem is given and the spatial coherence of the atomic wave packets is discussed
Anomalous diffusion in polymers: long-time behaviour
Vorotnikov, Dmitry A.
2009-01-01
We study the Dirichlet boundary value problem for viscoelastic diffusion in polymers. We show that its weak solutions generate a dissipative semiflow. We construct the minimal trajectory attractor and the global attractor for this problem.
Analysis of Reaction-Diffusion Systems with Anomalous Subdiffusion
Haugh, Jason M
2009-01-01
Reaction-diffusion equations are the cornerstone of modeling biochemical systems with spatial gradients, which are relevant to biological processes such as signal transduction. Implicit in the formulation of these equations is the assumption of Fick's law, which states that the local diffusive flux of species i is proportional to its concentration gradient; however, in the context of complex fluids such as cytoplasm and cell membranes, the use of Fick's law is based on empiricism, whereas evi...
Oxygen atom diffusion-driven anomalous Hall behavior in Co/Pt multilayers
International Nuclear Information System (INIS)
Anomalous Hall effect (AHE) studies have been carried out in Co/Pt multilayers prepared by magnetron sputtering under annealing. The AHE behavior can be deteriorated by annealing in Pt/[Co/Pt]3/Pt thin films, while saturation anomalous Hall resistivity in MgO/[Co/Pt]3/MgO multilayers after annealing at 623 K for 30 min is 124% larger than that in the as-deposited films. The X-ray photoelectron spectroscopy analysis exhibits that the increased AHE is primarily ascribed to annealing dependent oxygen atom diffusion at the Co/MgO interface. - Highlights: • The electronic transport properties in Co/Pt multilayers were studied. • The chemical states were investigated by X-ray photoelectron spectroscopy. • Oxygen atom diffusion has an effect on anomalous Hall effect in Co/Pt multilayers
Modeling double slit interference via anomalous diffusion: independently variable slit widths
Pascasio, Johannes Mesa; Fussy, Siegfried; Schwabl, Herbert; Groessing, Gerhard
2013-01-01
Based on a re-formulation of the classical explanation of quantum mechanical Gaussian dispersion (Groessing et al. 2010) as well as interference of two Gaussians (Groessing et al. 2012), we present a new and more practical way of their simulation. The quantum mechanical "decay of the wave packet" can be described by anomalous sub-quantum diffusion with a specific diffusivity varying in time due to a particle's changing thermal environment. In a simulation of the double-slit experiment with di...
International Nuclear Information System (INIS)
We introduce an approximation of the risk processes by anomalous diffusion. In the paper we consider the case, where the waiting times between successive occurrences of the claims belong to the domain of attraction of α -stable distribution. The relationship between the obtained approximation and the celebrated fractional diffusion equation is emphasised. We also establish upper bounds for the ruin probability in the considered model and give some numerical examples. (author)
Crouseilles, Nicolas; Hivert, Hélène; Lemou, Mohammed
2015-01-01
In this work, we propose some numerical schemes for linear kinetic equations in the diffusion and anomalous diffusion limit. When the equilibrium distribution function is a Maxwellian distribution, it is well known that for an appropriate time scale, the small mean free path limit gives rise to a diffusion type equation. However, when a heavy-tailed distribution is considered, another time scale is required and the small mean free path limit leads to a fractional anomalous diffusion equation....
Czech Academy of Sciences Publication Activity Database
Čermák, Jiří; Král, Lubomír
Ostrava : Tanger Ltd, 2014. ISBN 978-80-87294-52-9. [Metal 2014. International Conference on Metallurgy and Materials /23./. Brno (CZ), 21.05.2014-23.05.2014] R&D Projects: GA ČR(CZ) GAP108/11/0148; GA MŠk(CZ) ED1.1.00/02.0068 Institutional support: RVO:68081723 Keywords : Diffusion * Carbon * phase decomposition * Carbon-supersaturation * Cr-Mo steels Subject RIV: BJ - Thermodynamics http://www.metal2014.com/cz/zobrazit-seznam-prispevku/2498-carbon-diffusion-in-carbon-supersaturated-9cr-1mo-steel-anomalous-temperature-dependence-of-carbon-diffusivity/
Marshall, Wallace F.; Fung, Jennifer C.
2016-04-01
The recognition and pairing of homologous chromosomes during meiosis is a complex physical and molecular process involving a combination of polymer dynamics and molecular recognition events. Two highly conserved features of meiotic chromosome behavior are the attachment of telomeres to the nuclear envelope and the active random motion of telomeres driven by their interaction with cytoskeletal motor proteins. Both of these features have been proposed to facilitate the process of homolog pairing, but exactly what role these features play in meiosis remains poorly understood. Here we investigate the roles of active motion and nuclear envelope tethering using a Brownian dynamics simulation in which meiotic chromosomes are represented by a Rouse polymer model subjected to tethering and active forces at the telomeres. We find that tethering telomeres to the nuclear envelope slows down pairing relative to the rates achieved by unattached chromosomes, but that randomly directed active forces applied to the telomeres speed up pairing dramatically in a manner that depends on the statistical properties of the telomere force fluctuations. The increased rate of initial pairing cannot be explained by stretching out of the chromosome conformation but instead seems to correlate with anomalous diffusion of sub-telomeric regions.
Lin, Guoxing
2016-01-01
Pulsed field gradient (PFG) has been increasingly employed to study anomalous diffusions in Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI). However, the analysis of PFG anomalous diffusion is complicated. In this paper, a fractal derivative model based modified Gaussian phase distribution method is proposed to describe PFG anomalous diffusion. By using the phase distribution obtained from the effective phase shift diffusion method based on fractal derivatives, and employing some of the traditional Gaussian phase distribution approximation techniques, a general signal attenuation expression for free fractional diffusion is derived. This expression describes a stretched exponential function based attenuation, which is distinct from both the exponential attenuation for normal diffusion obtained from conventional Gaussian phase distribution approximation, and the Mittag-Leffler function based attenuation for anomalous diffusion obtained from fractional derivative. The obtained signal attenu...
Zonal flow dynamics and anomalous transport
International Nuclear Information System (INIS)
Nonlinear equations for the slow space-time evolution of the radial drift wave-ion-temperature gradient (DW-ITG) envelope and zonal flow (ZF) amplitude have been derived within a coherent four-wave drift wave-zonal flow model. In the local limit this model demonstrates spontaneous generation of zonal flow and nonlinear drift wave-zonal flow dynamics in toroidal plasmas. The model allows slow temporal and spatial variations of the DW-ITG radial envelope, incorporating the effects of equilibrium variations, i.e., turbulence spreading and size dependence of the saturated wave intensities and transport coefficients. The competition between linear drive/damping and drift wave spreading due to linear and nonlinear group velocities and nonlinear energy transfer between DW and ZF determines the saturation levels of the fluctuating fields. The turbulence intensity level exhibits a transition from Bohm scaling at small system size (Lp/ρi) to gyro-Bohm for large system size. This system exhibits chaotic behavior and intermittency, depending on system size and proximity to marginal stability
Anomalous diffusion and electron distribution function in a tokamak
International Nuclear Information System (INIS)
Degree of distortion of high-energy part of electron distribution function, conditioned by direct diffusion of subthermal particles transverse to magnetic field in tokamak plasma with nonuniform profile of electron temperature is analyzed. Estimations of electron energy range, where the distortion is more pronounced and is not 'slurred over' by other effects, are presented
Subdiffusion, Anomalous Diffusion and Propagation of a Particle Moving in Random and Periodic Media
Mishra, Shradha; Bhattacharya, Sanchari; Webb, Benjamin; Cohen, E. G. D.
2016-02-01
We investigate the motion of a single particle moving on a two-dimensional square lattice whose sites are occupied by right and left rotators. These left and right rotators deterministically rotate the particle's velocity to the right or left, respectively and flip orientation from right to left or from left to right after scattering the particle. We study three types of configurations of left and right rotators, which we think of as types of media, through with the particle moves. These are completely random (CR), random periodic (RP), and completely periodic (CP) configurations. For CR configurations the particle's dynamics depends on the ratio r of right to left scatterers in the following way. For small r˜eq 0, when the configuration is nearly homogeneous, the particle subdiffuses with an exponent of 2/3, similar to the diffusion of a macromolecule in a crowded environment. Also, the particle's trajectory has a fractal dimension of d_f˜eq 4/3, comparable to that of a self-avoiding walk. As the ratio increases to r˜eq 1, the particle's dynamics transitions from subdiffusion to anomalous diffusion with a fractal dimension of d_f˜eq 7/4, similar to that of a percolating cluster in 2-d. In RP configurations, which are more structured than CR configurations but also randomly generated, we find that the particle has the same statistic as in the CR case. In contrast, CP configurations, which are highly structured, typically will cause the particle to go through a transient stage of subdiffusion, which then abruptly changes to propagation. Interestingly, the subdiffusive stage has an exponent of approximately 2/3 and a fractal dimension of d_f˜eq 4/3, similar to the case of CR and RP configurations for small r.
Density approach to ballistic anomalous diffusion: An exact analytical treatment
Bologna, Mauro; Ascolani, Gianluca; Grigolini, Paolo
2010-04-01
This paper addresses the problem of deriving the probability distribution density of a diffusion process generated by a nonergodic dichotomous fluctuation using the Liouville equation (density method). The velocity of the diffusing particles fluctuates from the value of 1 to the value of -1, and back, with the distribution density of time durations τ of the two states proportional to 1/τμ in the asymptotic time limit. The adopted density method allows us to establish an exact analytical expression for the probability distribution density of the diffusion process generated by these fluctuations. Contrary to intuitive expectations, the central part of the diffusion distribution density is not left empty when moving from μ >2 (ergodic condition) to μ μcr, the monomodal distribution density with a minimum at the origin is turned into a bimodal one, with a central bump whose intensity increases for μ →2. The exact theoretical treatment applies to the asymptotic time limit, which establishes for the diffusion process the ballistic scaling value δ =1. To assess the time evolution toward this asymptotic time condition, we use a numerical approach which relates the emergence of the central bump at μ =μcr with the generation of the ordinary scaling δ =0.5, which lasts for larger and larger times for μ coming closer and closer to the critical value μ =2. We assign to the waiting time distribution density two different analytical forms: one derived from the Manneville intermittence (MI) theory and one from the Mittag-Leffler (ML) survival probability. The adoption of the ML waiting time distribution density generates an exact analytical prediction, whereas the MI method allows us to get the same asymptotic time limit as the ML one for μ adoption of these two waiting time distribution densities sheds light into the critical nature of the condition μ =2 and into why this is the critical point for the MI process, representing the phase transition from the
Nonlinear dynamics induced anomalous Hall effect in topological insulators
Wang, Guanglei; Xu, Hongya; Lai, Ying-Cheng
2016-01-01
We uncover an alternative mechanism for anomalous Hall effect. In particular, we investigate the magnetisation dynamics of an insulating ferromagnet (FM) deposited on the surface of a three-dimensional topological insulator (TI), subject to an external voltage. The spin-polarised current on the TI surface induces a spin-transfer torque on the magnetisation of the top FM while its dynamics can change the transmission probability of the surface electrons through the exchange coupling and hence the current. We find a host of nonlinear dynamical behaviors including multistability, chaos, and phase synchronisation. Strikingly, a dynamics mediated Hall-like current can arise, which exhibits a nontrivial dependence on the channel conductance. We develop a physical understanding of the mechanism that leads to the anomalous Hall effect. The nonlinear dynamical origin of the effect stipulates that a rich variety of final states exist, implying that the associated Hall current can be controlled to yield desirable behaviors. The phenomenon can find applications in Dirac-material based spintronics.
Anomalous structure and dynamics of the Gaussian-core fluid.
Krekelberg, William P; Kumar, Tanuj; Mittal, Jeetain; Errington, Jeffrey R; Truskett, Thomas M
2009-03-01
It is known that there are thermodynamic states for which the Gaussian-core fluid displays anomalous properties such as expansion upon isobaric cooling (density anomaly) and increased single-particle mobility upon isothermal compression (self-diffusivity anomaly). Here, we investigate how temperature and density affect its short-range translational structural order, as characterized by the two-body excess entropy. We find that there is a wide range of conditions for which the short-range translational order of the Gaussian-core fluid decreases upon isothermal compression (structural order anomaly). As we show, the origin of the structural anomaly is qualitatively similar to that of other anomalous fluids (e.g., water or colloids with short-range attractions) and is connected to how compression affects static correlations at different length scales. Interestingly, we find that the self-diffusivity of the Gaussian-core fluid obeys a scaling relationship with the two-body excess entropy that is very similar to the one observed for a variety of simple liquids. One consequence of this relationship is that the state points for which structural, self-diffusivity, and density anomalies of the Gaussian-core fluid occur appear as cascading regions on the temperature-density plane; a phenomenon observed earlier for models of waterlike fluids. There are, however, key differences between the anomalies of Gaussian-core and waterlike fluids, and we discuss how those can be qualitatively understood by considering the respective interparticle potentials of these models. Finally, we note that the self-diffusivity of the Gaussian-core fluid obeys different scaling laws depending on whether the two-body or total excess entropy is considered. This finding, which deserves more comprehensive future study, appears to underscore the significance of higher-body correlations for the behavior of fluids with bounded interactions. PMID:19391927
Lin, Guoxing
2016-01-01
Anomalous diffusion exists widely in polymer and biological systems. Pulsed field gradient (PFG) techniques have been increasingly used to study anomalous diffusion in NMR and MRI. However, the interpretation of PFG anomalous diffusion is complicated. Moreover, there is not an exact signal attenuation expression based on fractional derivatives for PFG anomalous diffusion, which includes the finite gradient pulse width effect. In this paper, a new method, a Mainardi-Luchko-Pagnini (MLP) phase distribution approximation, is proposed to describe PFG fractional diffusion. MLP phase distribution is a non-Gaussian phase distribution. From the fractional diffusion equation based on fractional derivatives in both real space and phase space, the obtained probability distribution function is a MLP distribution. The MLP distribution leads to a Mittag-Leffler function based PFG signal attenuation rather than the exponential or stretched exponential attenuation that is obtained from a Gaussian phase distribution (GPD) und...
Serva, Maurizio; Vergni, Davide; Vulpiani, Angelo
2016-07-01
We investigate front propagation in systems with diffusive and subdiffusive behavior. The scaling behavior of moments of the diffusive problem, both in the standard and in the anomalous cases, is not enough to determine the features of the reactive front. In fact, the shape of the bulk of the probability distribution of the transport process, which determines the diffusive properties, is important just for preasymptotic behavior of front propagation, while the precise shape of the tails of the probability distribution determines asymptotic behavior of front propagation. PMID:27575110
Anomalous diffusion and distribution function of electrons in a tokamak
International Nuclear Information System (INIS)
Experimentally determining the electron thermal diffusivity ψe across the magnetic field is important for reaching an understanding of the physics of the processes which occur in tokamaks. Unfortunately, the possibilities for such an experimental determination are severely limited. The most direct way to measured ψe is to study the propagation of a heat pulse. It has been suggested in several pulses (e.g., Ref. 2) that the behavior of the superthermal particles which appear when a current is driven by lower hybrid waves be studied in order to determine ψe. In the present paper the authors analyze the extent to which the high-energy part of the electron distribution function which is due directly to the diffusion of superthermal particles across the magnetic field is distorted in a plasma with a nonuniform electron temperature profile. They also derive estimates of the range of electron energies in which this distortion is seen most clearly and is not painted over by other effects
Anomalous shift of magnetic diffuse scattering studied by neutron diffraction
Energy Technology Data Exchange (ETDEWEB)
Prokes, K [Helmholtz Centre Berlin for Materials and Energy, SF-2, Glienicker Strasse 100, 14109 Berlin (Germany); Lander, G H [European Commission, JRC, Institute for Transuranium Elements, Postfach 2340, 76125 Karlsruhe (Germany); Bernhoeft, N [CEA Grenoble, DRFMC/SPSMS, F-38054 Grenoble (France)], E-mail: prokes@helmholtz-berlin.de
2009-07-15
Neutron diffraction results, in the vicinity of the magnetic phase transition of USb and MnF{sub 2}, are reported. The thermal evolution of the magnetic diffuse signal and nuclear Bragg reflections demonstrate that the centre of gravity of the magnetic signals does not lie at the predicted position as calculated from nuclear reflections. This phenomenon, called the q-shift, was first found using resonance x-ray scattering (RXS). The present results show that, (i) the effect is not an artefact of RXS and is also found with neutrons (ii) that the effect arises from the bulk of the sample and is not restricted to the near surface layer ({approx}2000 A) associated with the RXS probe in actinide systems, (iii) the effect is not restricted to actinide compounds.
Nonlinear Theory of Anomalous Diffusion and Application to Fluorescence Correlation Spectroscopy
Boon, Jean Pierre; Lutsko, James F.
2015-12-01
The nonlinear theory of anomalous diffusion is based on particle interactions giving an explicit microscopic description of diffusive processes leading to sub-, normal, or super-diffusion as a result of competitive effects between attractive and repulsive interactions. We present the explicit analytical solution to the nonlinear diffusion equation which we then use to compute the correlation function which is experimentally measured by correlation spectroscopy. The theoretical results are applicable in particular to the analysis of fluorescence correlation spectroscopy of marked molecules in biological systems. More specifically we consider the cases of fluorescently labeled lipids in the plasma membrane and of fluorescent apoferritin (a spherically shaped oligomer) in a crowded dextran solution and we find that the nonlinear correlation spectra reproduce very well the experimental data indicating sub-diffusive molecular motion.
Improved estimation of anomalous diffusion exponents in single particle tracking experiments
Bronshtein, Eldad Kepten Irena
2013-01-01
The Mean Square Displacement is a central tool in the analysis of Single Particle Tracking experiments, shedding light on various biophysical phenomena. Frequently, parameters are extracted by performing time-averages on single particle trajectories followed by ensemble averaging. This procedure however, suffers from two systematic errors when applied to particles that perform anomalous diffusion. The first is significant at short time lags and is induced by measurement errors. The second arises from the natural heterogeneity in biophysical systems. We show how to estimate and correct these two errors and improve the estimation of the anomalous parameters for the whole particle distribution. As a consequence we manage to characterize ensembles of heterogeneous particles even for rather short and noisy measurements where regular time averaged mean square displacement analysis fails. We apply this method to both simulations and in vivo measurements of telomere diffusion in 3T3 mouse embryonic fibroblast cells. ...
Anomalous Viscosity, Resistivity, and Thermal Diffusivity of the Solar Wind Plasma
Verma, Mahendra K.
1995-01-01
In this paper we have estimated typical anomalous viscosity, resistivity, and thermal difffusivity of the solar wind plasma. Since the solar wind is collsionless plasma, we have assumed that the dissipation in the solar wind occurs at proton gyro radius through wave-particle interactions. Using this dissipation length-scale and the dissipation rates calculated using MHD turbulence phenomenology [{\\it Verma et al.}, 1995a], we estimate the viscosity and proton thermal diffusivity. The resistiv...
Convective cell formation and anomalous diffusion due to electromagnetic drift wave turbulence
International Nuclear Information System (INIS)
Convective cell formation and spectral cascade processes due to gravitational drift Alfven waves are studied using a new type of model equation. Conservation relations are derived and explosive instability is found for systems near marginal finite β stability. This instability also remains when the effects of poor as well as favorable curvature regions are included, i.e., for ballooning modes. The anomalous diffusion due to convective cells and quasi-linear effects are compared
Improved estimation of anomalous diffusion exponents in single particle tracking experiments
Bronshtein, Eldad Kepten Irena; Garini, Yuval
2012-01-01
The Mean Square Displacement is a central tool in the analysis of Single Particle Tracking experiments, shedding light on various biophysical phenomena. Frequently, parameters are extracted by performing time-averages on single particle trajectories followed by ensemble averaging. This procedure however, suffers from two systematic errors when applied to particles that perform anomalous diffusion. The first is significant at short time lags and is induced by measurement errors. The second ari...
Burov, Stas; Jeon, Jae-Hyung; Metzler, Ralf; Barkai, Eli
2011-02-01
Anomalous diffusion has been widely observed by single particle tracking microscopy in complex systems such as biological cells. The resulting time series are usually evaluated in terms of time averages. Often anomalous diffusion is connected with non-ergodic behaviour. In such cases the time averages remain random variables and hence irreproducible. Here we present a detailed analysis of the time averaged mean squared displacement for systems governed by anomalous diffusion, considering both unconfined and restricted (corralled) motion. We discuss the behaviour of the time averaged mean squared displacement for two prominent stochastic processes, namely, continuous time random walks and fractional Brownian motion. We also study the distribution of the time averaged mean squared displacement around its ensemble mean, and show that this distribution preserves typical process characteristics even for short time series. Recently, velocity correlation functions were suggested to distinguish between these processes. We here present analytical expressions for the velocity correlation functions. The knowledge of the results presented here is expected to be relevant for the correct interpretation of single particle trajectory data in complex systems. PMID:21203639
Self-similar motion for modeling anomalous diffusion and nonextensive statistical distributions
Huang, Zhifu; Su, Guozhen; Wang, Qiuping A.; Chen, Jincan
2010-01-01
We introduce a new universality class of one-dimensional iteration model giving rise to self-similar motion, in which the Feigenbaum constants are generalized as self-similar rates and can be predetermined. The curves of the mean-square displacement versus time generated here show that the motion is a kind of anomalous diffusion with the diffusion coefficient depending on the self-similar rates. In addition, it is found that the distribution of displacement agrees to a reliable precision with...
Long-lived anomalous thermal diffusion induced by elastic cell membranes on nearby particles
Daddi-Moussa-Ider, Abdallah; Guckenberger, Achim; Gekle, Stephan
2016-01-01
The physical approach of a small particle (virus, medical drug) to the cell membrane represents the crucial first step before active internalization and is governed by thermal diffusion. Using a fully analytical theory we show that the stretching and bending of the elastic membrane by the approaching particle induces a memory in the system, which leads to anomalous diffusion, even though the particle is immersed in a purely Newtonian liquid. For typical cell membranes the transient subdiffusive regime extends beyond 10 ms and can enhance residence times and possibly binding rates up to 50%. Our analytical predictions are validated by numerical simulations.
Elastic cell membranes induce long-lived anomalous thermal diffusion on nearby particles
Daddi-Moussa-Ider, Abdallah; Gekle, Stephan
2016-01-01
The physical approach of a small particle (virus, medical drug) to the cell membrane represents the crucial first step before active internalization and is governed by thermal diffusion. Using a fully analytical theory we show that the stretching and bending of the elastic membrane by the approaching particle induces a memory in the system which leads to anomalous diffusion, even though the particle is immersed in a purely Newtonian liquid. For typical cell membranes the transient subdiffusive regime extends beyond 10ms and can enhance residence times and binding rates up to 50\\%. Our analytical predictions are validated by numerical simulations.
Regime Interpretation of Anomalous Vortex Dynamics in 2D Superconductors
International Nuclear Information System (INIS)
Low-frequency dynamic impedance [σ-1(ω,T)≡(σ1+iσ2)-1] measurements on Josephson junction arrays found that σ1∼|lnω|, σ2∼const. This implies anomalously sluggish vortex mobilities μV(ω)∼σ-11, and is in conflict with general dynamical scaling expressions. We calculate (a) σ(ω,T) by real-space vortex scaling and (b) μV(ω) using Mori close-quote s formalism for a screened Coulomb gas. We find, in addition to the usual critical (large-ω) and hydrodynamic (low-ω) regimes, a new intermediate-frequency scaling regime into which the experimental data fall. This resolves the above mentioned conflict and makes explicit predictions for the scaling form of σ(ω,T). copyright 1997 The American Physical Society
Anomalous dynamics of capillary rise in porous media
Shikhmurzaev, Yulii D.
2012-07-09
The anomalous dynamics of capillary rise in a porous medium discovered experimentally more than a decade ago is described. The developed theory is based on considering the principal modes of motion of the menisci that collectively form the wetting front on the Darcy scale. These modes, which include (i) dynamic wetting mode, (ii) threshold mode, and (iii) interface depinning process, are incorporated into the boundary conditions for the bulk equations formulated in the regular framework of continuum mechanics of porous media, thus allowing one to consider a general case of three-dimensional flows. The developed theory makes it possible to describe all regimes observed in the experiment, with the time spanning more than four orders of magnitude, and highlights the dominant physical mechanisms at different stages of the process. © 2012 American Physical Society.
A gedankenexperiment for anomalous diffusion in a charge-fluctuating dusty plasma
International Nuclear Information System (INIS)
Brownian motion with Gaussian-distributed step-sizes is the prototype of diffusive processes with the typical scaling of the mean-square displacement linear with time. There are, however, processes scaling slower or faster in time due to differently (e.g., power-law) distributed step-sizes, commonly referred to as sub- and superdiffusion, respectively. We address the question whether there is actually a physical reason for a discrimination between normal and anomalous diffusion or whether such processes can be regarded as a special case of normal diffusion with a complicated space- and time-dependent diffusion coefficient. In order to get to the bottom of this question, we construct a numerical gedankenexperiment, which is designed to be as simple as possible and consists of dust particles embedded as test particles into a homogeneous magnetic field that randomly changes their charge. The only parameter governing the system is the ratio of the time-scales for gyration and for recharging. By performing full-orbit simulations of such particles, we are for the first time able to (i) describe a system exhibiting sub-, normal, or superdiffusion as an asymptotic behavior, i.e., not merely as an intermediate state during the evolution of the system. We (ii) observe superdiffusion for low values of the controlling parameter, normal diffusion over a wide plateau of intermediate values, and subdiffusion for high values, i.e., we found (iii) a simple system with one single and illustrative parameter controlling whether the system exhibits super-, normal, or subdiffusion. The crucial point is (iv) a competition between ballistic (particles uncharged, extreme superdiffusion) and confined (charged, extreme subdiffusion) motions. Our system is homogeneous in space and time, so that its (v) behavior cannot be described by normal diffusion with a special diffusion coefficient, and the competition is (vi) fundamentally different from a Gaussian random walk and may be regarded as one
Directory of Open Access Journals (Sweden)
Eldad Kepten
Full Text Available Single particle tracking is an essential tool in the study of complex systems and biophysics and it is commonly analyzed by the time-averaged mean square displacement (MSD of the diffusive trajectories. However, past work has shown that MSDs are susceptible to significant errors and biases, preventing the comparison and assessment of experimental studies. Here, we attempt to extract practical guidelines for the estimation of anomalous time averaged MSDs through the simulation of multiple scenarios with fractional Brownian motion as a representative of a large class of fractional ergodic processes. We extract the precision and accuracy of the fitted MSD for various anomalous exponents and measurement errors with respect to measurement length and maximum time lags. Based on the calculated precision maps, we present guidelines to improve accuracy in single particle studies. Importantly, we find that in some experimental conditions, the time averaged MSD should not be used as an estimator.
Modeling anomalous diffusion by a subordinated fractional Lévy-stable process
International Nuclear Information System (INIS)
Two phenomena that can be discovered in systems with anomalous diffusion are long-range dependence and trapping events. The first effect concerns events that are arbitrarily distant but still influence each other exceptionally strongly, which is characteristic for anomalous regimes. The second corresponds to the presence of constant values of the underlying process. Motivated by the relatively poor class of models that can cover these two phenomena, we introduce subordinated fractional Lévy-stable motion with tempered stable waiting times. We present in detail its main properties, propose a simulation scheme and give an estimation procedure for its parameters. The last part of the paper is a presentation, via the Monte Carlo approach, of the effectiveness of the estimation of the parameters. (paper)
York, D. G.; Dahlstrom, J.; Welty, D. E.; Oka, T.; Hobbs, L. M.; Johnson, S.; Friedman, S. D.; Jiang, Z.; Rachford, B. L.; Snow, T. P.; Sherman, R.; Sonnentrucker, P.
2014-02-01
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.
Anomalous reaction-transport processes: the dynamics beyond the Mass Action Law
Campos Moreno, Daniel; Fedotov, Sergei; Méndez López, Vicenç
2008-01-01
In this paper we reconsider the Mass Action Law (MAL) for the anomalous reversible reaction $A\\rightleftarrows B$ with diffusion. We provide a mesoscopic description of this reaction when the transitions between two states $A$ and $B$ are governed by anomalous (heavy-tailed) waiting-time distributions. We derive the set of mesoscopic integro-differential equations for the mean densities of reacting and diffusing particles in both states. We show that the effective reaction rate memory kernels...
Anomalous diffusion of Ibuprofen in cyclodextrin nanosponge hydrogels: an HRMAS NMR study
Directory of Open Access Journals (Sweden)
Monica Ferro
2014-11-01
Full Text Available Ibuprofen sodium salt (IP was encapsulated in cyclodextrin nanosponges (CDNS obtained by cross-linking of β-cyclodextrin with ethylenediaminetetraacetic acid dianhydride (EDTAn in two different preparations: CDNSEDTA 1:4 and 1:8, where the 1:n notation indicates the CD to EDTAn molar ratio. The entrapment of IP was achieved by swelling the two polymers with a 0.27 M solution of IP in D2O, leading to colourless, homogeneous hydrogels loaded with IP. The molecular environment and the transport properties of IP in the hydrogels were studied by high resolution magic angle spinning (HRMAS NMR spectroscopy. The mean square displacement (MSD of IP in the gels was obtained by a pulsed field gradient spin echo (PGSE NMR pulse sequence at different observation times td. The MSD is proportional to the observation time elevated to a scaling factor α. The α values define the normal Gaussian random motion (α = 1, or the anomalous diffusion (α 1 superdiffusion. The experimental data here reported point out that IP undergoes subdiffusive regime in CDNSEDTA 1:4, while a slightly superdiffusive behaviour is observed in CDNSEDTA 1:8. The transition between the two dynamic regimes is triggered by the polymer structure. CDNSEDTA 1:4 is characterized by a nanoporous structure able to induce confinement effects on IP, thus causing subdiffusive random motion. CDNSEDTA 1:8 is characterized not only by nanopores, but also by dangling EDTA groups ending with ionized COO− groups. The negative potential provided by such groups to the polymer backbone is responsible for the acceleration effects on the IP anion thus leading to the superdiffusive behaviour observed. These results point out that HRMAS NMR spectroscopy is a powerful direct method for the assessment of the transport properties of a drug encapsulated in polymeric scaffolds. The diffusion properties of IP in CDNS can be modulated by suitable polymer synthesis; this finding opens the possibility to design
Anomalous diffusion for bed load transport with a physically-based model
Fan, N.; Singh, A.; Foufoula-Georgiou, E.; Wu, B.
2013-12-01
Diffusion of bed load particles shows both normal and anomalous behavior for different spatial-temporal scales. Understanding and quantifying these different types of diffusion is important not only for the development of theoretical models of particle transport but also for practical purposes, e.g., river management. Here we extend a recently proposed physically-based model of particle transport by Fan et al. [2013] to further develop an Episodic Langevin equation (ELE) for individual particle motion which reproduces the episodic movement (start and stop) of sediment particles. Using the proposed ELE we simulate particle movements for a large number of uniform size particles, incorporating different probability distribution functions (PDFs) of particle waiting time. For exponential PDFs of waiting times, particles reveal ballistic motion in short time scales and turn to normal diffusion at long time scales. The PDF of simulated particle travel distances also shows a change in its shape from exponential to Gamma to Gaussian with a change in timescale implying different diffusion scaling regimes. For power-law PDF (with power - μ) of waiting times, the asymptotic behavior of particles at long time scales reveals both super-diffusion and sub-diffusion, however, only very heavy tailed waiting times (i.e. 1.0 < μ < 1.5) could result in sub-diffusion. We suggest that the contrast between our results and previous studies (for e.g., studies based on fractional advection-diffusion models of thin/heavy tailed particle hops and waiting times) results could be due the assumption in those studies that the hops are achieved instantaneously, but in reality, particles achieve their hops within finite times (as we simulate here) instead of instantaneously, even if the hop times are much shorter than waiting times. In summary, this study stresses on the need to rethink the alternative models to the previous models, such as, fractional advection-diffusion equations, for studying
On The Anomalous Fast Ion Energy Diffusion in Toroidal Plasmas Due to Cavity Modes
Energy Technology Data Exchange (ETDEWEB)
N.N. Gorelenkov, N.J. Fisch and E. Fredrickson
2010-03-09
An enormous wave-particle diffusion coefficient along paths suitable for alpha channeling had been deduced in mode converted ion Bernstein wave experiments on Tokamak Fusion Test Reactor (TFTR) the only plausible explanation advanced for such a large diffusion coefficient was the excitation of internal cavity modes which induce particle diffusion along identical diffusion paths, but at much higher rates. Although such a mode was conjectured, it was never observed. However, recent detailed observations of high frequency compressional Alfven eigenmodes (CAEs) on the National Spherical torus Experiment (NSTX) indirectly support the existence of the related conjectured modes on TFTR. The eigenmodes responsible for the high frequency magnetic activity can be identified as CAEs through the polarization of the observed magnetic field oscillations in NSTX and through a comparison with the theoretically derived freuency dispersion relation. Here, we show how these recent observations of high frequency CAEs lend support to this explanation of the long-standing puzzle of anomalous fast ion energy diffusion on TFTR. The support of the conjecure that these internal modes could have caused the remarkable ion energy diffusion on TFTR carries significant and favorable implications for the possibilities in achieving the alpha channeling effect with small injected power in a tokamak reactor.
On The Anomalous Fast Ion Energy Diffusion in Toroidal Plasmas Due to Cavity Modes
International Nuclear Information System (INIS)
An enormous wave-particle diffusion coefficient along paths suitable for alpha channeling had been deduced in mode converted ion Bernstein wave experiments on Tokamak Fusion Test Reactor (TFTR) the only plausible explanation advanced for such a large diffusion coefficient was the excitation of internal cavity modes which induce particle diffusion along identical diffusion paths, but at much higher rates. Although such a mode was conjectured, it was never observed. However, recent detailed observations of high frequency compressional Alfven eigenmodes (CAEs) on the National Spherical torus Experiment (NSTX) indirectly support the existence of the related conjectured modes on TFTR. The eigenmodes responsible for the high frequency magnetic activity can be identified as CAEs through the polarization of the observed magnetic field oscillations in NSTX and through a comparison with the theoretically derived freuency dispersion relation. Here, we show how these recent observations of high frequency CAEs lend support to this explanation of the long-standing puzzle of anomalous fast ion energy diffusion on TFTR. The support of the conjecure that these internal modes could have caused the remarkable ion energy diffusion on TFTR carries significant and favorable implications for the possibilities in achieving the alpha channeling effect with small injected power in a tokamak reactor.
Zhao, Yi; Cao, Xiangyu; Gao, Jun; Liu, Xiao; Li, Sijia
2016-05-16
We demonstrate a simple reconfigurable metasurface with multiple functions. Anisotropic tiles are investigated and manufactured as fundamental elements. Then, the tiles are combined in a certain sequence to construct a metasurface. Each of the tiles can be adjusted independently which is like a jigsaw puzzle and the whole metasurface can achieve diverse functions by different layouts. For demonstration purposes, we realize polarization conversion, anomalous reflection and diffusion by a jigsaw puzzle metasurface with 6 × 6 pieces of anisotropic tile. Simulated and measured results prove that our method offers a simple and effective strategy for metasurface design. PMID:27409942
In vivo anomalous diffusion and weak ergodicity breaking of lipid granules.
Jeon, Jae-Hyung; Tejedor, Vincent; Burov, Stas; Barkai, Eli; Selhuber-Unkel, Christine; Berg-Sørensen, Kirstine; Oddershede, Lene; Metzler, Ralf
2011-01-28
Combining extensive single particle tracking microscopy data of endogenous lipid granules in living fission yeast cells with analytical results we show evidence for anomalous diffusion and weak ergodicity breaking. Namely we demonstrate that at short times the granules perform subdiffusion according to the laws of continuous time random walk theory. The associated violation of ergodicity leads to a characteristic turnover between two scaling regimes of the time averaged mean squared displacement. At longer times the granule motion is consistent with fractional Brownian motion. PMID:21405366
From moving averages to anomalous diffusion: a Rényi-entropy approach
International Nuclear Information System (INIS)
Moving averages, also termed convolution filters, are widely applied in science and engineering at large. As moving averages transform inputs to outputs by convolution, they induce correlation. In effect, moving averages are perhaps the most fundamental and ubiquitous mechanism of transforming uncorrelated inputs to correlated outputs. In this paper we study the correlation structure of general moving averages, unveil the Rényi-entropy meaning of a moving-average's overall correlation, address the maximization of this overall correlation, and apply this overall correlation to the dispersion-measurement and to the classification of regular and anomalous diffusion transport processes. (fast track communication)
Anomalous diffusion and radial electric field generation due to edge plasma turbulence
Czech Academy of Sciences Publication Activity Database
Pánek, Radomír; Krlín, Ladislav; Taskhakaya, D.; Kuhn, S.; Stöckel, Jan; Pavlo, Pavol; Tender, M.; Svoboda, Vojtěch; Petržílka, Václav
2004-01-01
Roč. 44, 1-3 (2004), s. 203-204. ISSN 0863-1042. [International Workshop on Plasma Edge Theory in Fusion Devices/9th./. San Diego, 03.09.2003-05.09.2003] R&D Projects: GA AV ČR(CZ) IAA1043201; GA ČR GP202/03/P062; GA ČR(CZ) GA202/03/0786 Institutional research plan: CEZ:AV0Z2043910 Keywords : anomalous diffusion * transport * radial electric field Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 0.701, year: 2004
Dynamics and diffusion mechanism in network forming liquid under high pressure: A new approach
International Nuclear Information System (INIS)
The static and dynamic properties of liquid silica (SiO2) are investigated by molecular dynamics simulation at temperature of 3200 K and in the 0–25 GPa pressure range. To clarify diffusion mechanism and the anomalous diffusivity under compression, we have traced the time evolution of breakage and formation of the Si–O bond in the basic structural units SiOx (x = 4, 5, 6). The investigation reveals that atomic diffusion is realized through the transition Si[n] ↔ Si[n+1] (Si[n] means that Si atom has n coordinated oxygens) and the instability of units SiO5 is the cause of the anomalous diffusivity. Moreover, the transitions Si[n] ↔ Si[n+1] are not uniformly distributed but strongly localized in the space. The distribution of coordination units SiOx in network structure is not uniform but tends to form clusters of SiO4, SiO5 and SiO6 and this is the origin of localization of transitions resulted in the spatially heterogeneous dynamics in liquid SiO2. - Highlights: ► The microstructure under high pressure. ► The structural dynamics under high pressure. ► Apply a new approach to clarify the diffusion mechanism and anomalous diffusivity. ► The spatially heterogeneous dynamics, the relation between microstructure and spatially heterogeneous dynamics
Spatio-temporal anomalous diffusion in heterogeneous media by nuclear magnetic resonance
Palombo, M.; Gabrielli, A.; De Santis, S.; Cametti, C.; Ruocco, G.; Capuani, S.
2011-07-01
In this paper, we describe nuclear magnetic resonance measurements of water diffusion in highly confined and heterogeneous colloidal systems using an anomalous diffusion model. For the first time, temporal and spatial fractional exponents, α and μ, introduced within the framework of continuous time random walk, are simultaneously measured by pulsed gradient spin-echo NMR technique in samples of micro-beads dispersed in aqueous solution. In order to mimic media with low and high level of disorder, mono-dispersed and poly-dispersed samples are used. We find that the exponent α depends on the disorder degree of the system. Conversely, the exponent μ depends on both bead sizes and magnetic susceptibility differences within samples. The new procedure proposed here may be a useful tool to probe porous materials and microstructural features of biological tissue.
Volpe, Giorgio; Volpe, Giovanni; Gigan, Sylvain
2014-01-01
The motion of particles in random potentials occurs in several natural phenomena ranging from the mobility of organelles within a biological cell to the diffusion of stars within a galaxy. A Brownian particle moving in the random optical potential associated to a speckle pattern, i.e., a complex interference pattern generated by the scattering of coherent light by a random medium, provides an ideal model system to study such phenomena. Here, we derive a theory for the motion of a Brownian particle in a speckle field and, in particular, we identify its universal characteristic timescale. Based on this theoretical insight, we show how speckle light fields can be used to control the anomalous diffusion of a Brownian particle and to perform some basic optical manipulation tasks such as guiding and sorting. Our results might broaden the perspectives of optical manipulation for real-life applications. PMID:24496461
Improved estimation of anomalous diffusion exponents in single-particle tracking experiments
Kepten, Eldad; Bronshtein, Irena; Garini, Yuval
2013-05-01
The mean square displacement is a central tool in the analysis of single-particle tracking experiments, shedding light on various biophysical phenomena. Frequently, parameters are extracted by performing time averages on single-particle trajectories followed by ensemble averaging. This procedure, however, suffers from two systematic errors when applied to particles that perform anomalous diffusion. The first is significant at short-time lags and is induced by measurement errors. The second arises from the natural heterogeneity in biophysical systems. We show how to estimate and correct these two errors and improve the estimation of the anomalous parameters for the whole particle distribution. As a consequence, we manage to characterize ensembles of heterogeneous particles even for rather short and noisy measurements where regular time-averaged mean square displacement analysis fails. We apply this method to both simulations and in vivo measurements of telomere diffusion in 3T3 mouse embryonic fibroblast cells. The motion of telomeres is found to be subdiffusive with an average exponent constant in time. Individual telomere exponents are normally distributed around the average exponent. The proposed methodology has the potential to improve experimental accuracy while maintaining lower experimental costs and complexity.
Anomalous Kinetics of Hard Charged Particles Dynamical Renormalization Group Resummation
Boyanovsky, D
1999-01-01
We study the kinetics of the distribution function for charged particles of hard momentum in scalar QED. The goal is to understand the effects of infrared divergences associated with the exchange of quasistatic magnetic photons in the relaxation of the distribution function. We begin by obtaining a kinetic transport equation for the distribution function for hard charged scalars in a perturbative expansion that includes hard thermal loop resummation. Solving this transport equation, the infrared divergences arising from absorption and emission of soft quasi-static magnetic photons are manifest in logarithmic secular terms. We then implement the dynamical renormalization group resummation of these secular terms in the relaxation time approximation. The distribution function (in the linearized regime) is found to approach equilibrium as $\\delta n_k(t) =\\delta n_k(t_o) e^{-2\\alpha T (t-t_o) and $\\alpha =e^2/4\\pi$. This anomalous relaxation is recognized to be the square of the relaxation of the single particle p...
International Nuclear Information System (INIS)
We present a classical molecular dynamics simulation of uranium dioxide in the temperature range of 300-3000 K. Temperature dependences of thermal conductivity, heat capacity and ionic conductivity are investigated. Our study shows the rise of thermal conductivity of uranium dioxide at very high temperatures (above 2500 K), which is not predicted by the former anharmonic theories. Several pair potentials are used in the simulation, and they depict similar effects. Long range forces are accounted by Ewald sums. Static thermal properties are evaluated in NPT ensemble. It is shown that a high-temperature peak on heat capacity is present and is more legible in large systems. To ensure the best reliability, transport properties are evaluated using the theory of autocorrelation functions in NVE ensemble. In order to properly define thermal conductivity in ionic systems with charge fluxes, an expression which accounts the thermoelectric effect is derived from Onsager reciprocal relations. The rise on temperature dependence of thermal conductivity is accompanied by the peak on heat capacity and an anomalous rise of ionic conductivity. However, it is shown that there is no partial melting of the oxygen sublattice, which suggests that the system does not necessarily exhibit a superionic transition. Instead, kick-out diffusion in oxygen sublattice is proposed to be the origin of such anomalous behavior of thermophysical properties. (author)
International Nuclear Information System (INIS)
The understanding of the thermodynamic properties of solids has important applications in diverse areas like condensed matter physics, materials science, mineralogy, geophysics, etc. We have been extensively investigating anomalous thermodynamic properties of compounds using the techniques of lattice dynamics, inelastic neutron scattering, inelastic x-ray scattering and synchrotron x-ray diffraction. Here we present some of the results from our recent studies. Studies of materials exhibiting anomalous thermal expansion are of interest due to their fundamental scientific importance and potential applications in ceramic, optical and electronic industry etc. We have studied the thermodynamic properties of negative thermal expansion (NTE) compounds ZrWO8, HfW2O8, ZrMO2O8, Zn(CN)2, Cu2O, Ag2O; Ag3Co(CN)6 and Ag3Fe(CN)6. Our calculations predicted that large softening of the phonon spectrum involving librational and translational modes below 10 MeV would be responsible for anomalous thermal expansion behaviour. High pressure inelastic neutron scattering experiments carried by us on cubic ZrW2O8, ZrMo2O8 and Zn(CN)2 confirmed the phonon softening. The thermal expansion as derived from the phonon measurements is in good agreement with that obtained from diffraction data. This indicates that unusual phonon softening of low energy modes is able to account for the thermal expansion behaviour in these compounds. Superionic conduction in fluorite-structured (anti-fluorite, Li2O) oxides and LiMPO4 (M=Fe, Mn) have applications in energy storage, conversion and nuclear industry. Fast ion conductors exhibit high ionic conductivity, which allow macroscopic movement of ions through their structure. The possible role of phonon in initiation of diffusion has been studied in Li2O and LiMPO4 (M=Fe, Mn). The simulations play a pivotal role in understanding the conduction processes at high temperatures in these compounds. (author)
Quantum diffusion dynamics in nonlinear systems: A modified kicked-rotor model
International Nuclear Information System (INIS)
Using a simple method analogous to a quantum rephasing technique, a simple modification to a paradigm of classical and quantum chaos is proposed. The interesting quantum maps thus obtained display remarkably rich quantum dynamics. Emphasis is placed on the destruction of dynamical localization without breaking periodicity, unbounded quantum anomalous diffusion in integrable systems, and transient dynamical localization. Experimental realizations of this work are also discussed
Boyer, D.; Romo-Cruz, J. C. R.
2014-10-01
Motivated by studies on the recurrent properties of animal and human mobility, we introduce a path-dependent random-walk model with long-range memory for which not only the mean-square displacement (MSD) but also the propagator can be obtained exactly in the asymptotic limit. The model consists of a random walker on a lattice, which, at a constant rate, stochastically relocates at a site occupied at some earlier time. This time in the past is chosen randomly according to a memory kernel, whose temporal decay can be varied via an exponent parameter. In the weakly non-Markovian regime, memory reduces the diffusion coefficient from the bare value. When the mean backward jump in time diverges, the diffusion coefficient vanishes and a transition to an anomalous subdiffusive regime occurs. Paradoxically, at the transition, the process is an anticorrelated Lévy flight. Although in the subdiffusive regime the model exhibits some features of the continuous time random walk with infinite mean waiting time, it belongs to another universality class. If memory is very long-ranged, a second transition takes place to a regime characterized by a logarithmic growth of the MSD with time. In this case the process is asymptotically Gaussian and effectively described as a scaled Brownian motion with a diffusion coefficient decaying as 1 /t .
Characterizations and simulations of a class of stochastic processes to model anomalous diffusion
International Nuclear Information System (INIS)
In this paper, we study a parametric class of stochastic processes to model both fast and slow anomalous diffusions. This class, called generalized grey Brownian motion (ggBm), is made up of self-similar with stationary increments processes (H-sssi) and depends on two real parameters α element of (0, 2) and β element of (0, 1]. It includes fractional Brownian motion when α element of (0, 2) and β = 1, and time-fractional diffusion stochastic processes when α = β element of (0, 1). The latter have a marginal probability density function governed by time-fractional diffusion equations of order β. The ggBm is defined through the explicit construction of the underlying probability space. However, in this paper we show that it is possible to define it in an unspecified probability space. For this purpose, we write down explicitly all the finite-dimensional probability density functions. Moreover, we provide different ggBm characterizations. The role of the M-Wright function, which is related to the fundamental solution of the time-fractional diffusion equation, emerges as a natural generalization of the Gaussian distribution. Furthermore, we show that the ggBm can be represented in terms of the product of a random variable, which is related to the M-Wright function, and an independent fractional Brownian motion. This representation highlights the H-sssi nature of the ggBm and provides a way to study and simulate the trajectories. For this purpose, we developed a random walk model based on a finite difference approximation of a partial integro-differential equation of a fractional type
International Nuclear Information System (INIS)
The diffusion coefficient D⊥ for electron diffusion across a magnetic field of strength B is calculated in terms of the spectral function of the electric-field fluctuations. For a Maxwellian plasma, we find that an effective electron-ion collision frequency defined by v = ω2e(me/Te)D⊥, where ωe = -eB/mec and Te is the electron temperature in energy units, contains an anomalous term v* in addition to the usual classical term; the diffusion coefficient arising from v* is proportional to B-1 if k 2D (Te/me) >> ωe2, and to B-2 In B when k2D (Te/me) 2e, where kD is the Debye wave-number. The electron fluctuations in the lowfrequency domain with ω e| give rise to the anomalous term. When such fluctuations are enhanced above a thermal level owing to the onset of an instability, the anomalous term will grow accordingly, resulting in an enhanced diffusion; a microscopic account of the Bohm diffusion is thereby obtained in terms of a theory of strong turbulence. The factor of enhancement of the low-frequency fluctuations necessary to produce a Bohm-diffusion rate is estimated numerically for a C-Stellarator and for a Tokamak; the comparison may offer an, at least, partial account of the difference in containment times between the two cases. (author)
Universality in edge-source diffusion dynamics
DEFF Research Database (Denmark)
Mortensen, Asger; Okkels, Fridolin; Bruus, Henrik
2006-01-01
We show that in edge-source diffusion dynamics the integrated concentration N(t) has a universal dependence with a characteristic time scale tau=(A/P)(2)pi/(4D), where D is the diffusion constant while A and P are the cross-sectional area and perimeter of the domain, respectively. For the short...
Diffusion dynamics on multiplex networks
Gomez, S; Gomez-Gardeñes, J; Perez-Vicente, C J; Moreno, Y; Arenas, A
2012-01-01
We study the time scales associated to diffusion processes that take place on multiplex networks (a set of networks structured in interconnected layers). To this end we propose the construction of a supra-Laplacian matrix, which consists of a dimensional lifting of the Laplacian matrix of each layer of the multiplex network. We use perturbative analysis to reveal analytically the structure of eigenvectors and eigenvalues of the complete network in terms of the spectral properties of the individual layers. The spectrum of the supra-Laplacian allows us to understand the physics of diffusion-like processes on top of multiplex networks.
Protein Dynamical Transition: Role of Methyl Dynamics and Local Diffusion
Krishnan, M.; Schulz, R.; Smith, Jeremy C.
2009-03-01
The temperature-dependent protein dynamical transition is investigated using the Instanteous Normal mode analysis (INM) and molecular dynamics (MD) simulation of crystalline myoglobin and Toxin II. The onset of anharmonic dynamics in myoglobin is observed at 150 K, far below the much-studied solvent-activated dynamical transition at 220 K. A significant fraction of methyl groups exhibit nanosecond anharmonic rotational jump diffusion at 150 K indicating the essential role of methyl dynamics in the low-temperature onset of anharmonic protein dynamics. The methyl groups that exhibit many rotational excitations are located near xenon cavities, suggesting that cavities in proteins act as activation centers of anharmonic dynamics. INM analysis of Toxin II indicates the presence of non-zero barrier-crossing, diffusive degrees of freedom accessible to the protein below the dynamical transition. The number of these diffusive degrees of freedom increases abruptly at the dynamical transition. In summary, the present investigation suggests that local diffusive processes (for example, methyl dynamics) are activated at low temperatures (much below 220 K) leading to global diffusive protein dynamics (this involves excitation of many protein atoms) at the dynamical transition.
International Nuclear Information System (INIS)
The understanding of the thermodynamic properties of solids has important applications in diverse areas like condensed matter physics, materials science, mineralogy, geophysics, etc. We have been extensively investigating anomalous thermodynamic properties of compounds using the techniques of inelastic neutron scattering and lattice dynamics. We would present some of the results from our recent studies. Studies of materials exhibiting anomalous thermal expansion are of interest due to their fundamental scientific importance and potential applications in ceramic, optical and electronic industry etc. We have studied the thermodynamic properties of negative thermal expansion (NTE) compounds ZrW2O8, HfW2O8, ZrMo2O8, ZrV2O7, HfV2O7, Zn(CN)2, Cu2O, Ag2O, Ag3Co(CN)6 and Ag3Fe(CN)6. Our calculations predicted that large softening of the phonon spectrum involving librational and translational modes below 10 MeV would be responsible for anomalous thermal expansion behaviour. High pressure inelastic neutron scattering experiments carried by us on cubic ZrW2O8, ZrMo2O8 and Zn(CN)2 confirmed the phonon softening. Our studies indicate that unusual phonon softening of low energy modes is able to account for the thermal expansion behaviour in these compounds. Superionic conduction in fluorite-structured (anti-fluorite, Li2O) oxides (MO2, M= U, Th) have applications in energy storage, conversion and nuclear industry. The possible role of phonon in initiation of diffusion has been studied in Li2O. We found that in the superionic regime lithium atoms may exhibit macroscopic movement along (100) direction. The microscopic modeling or simulation is found to play a pivotal role in understanding the conduction processes at high temperatures in Li2O. We have also studied zircon structured compounds MSiO4 (M=Zr, Hf, Th, U), RPO4, (R=rare earth atom). The compounds are known to transform to the scheelite (body centered tetragonal, I41/a) or monoclinic phase (P21/n) at high pressure and
Anomalous diffusion as modeled by a nonstationary extension of Brownian motion
Cushman, John H.; O'Malley, Daniel; Park, Moongyu
2009-03-01
If the mean-square displacement of a stochastic process is proportional to tβ , β≠1 , then it is said to be anomalous. We construct a family of Markovian stochastic processes with independent nonstationary increments and arbitrary but a priori specified mean-square displacement. We label the family as an extended Brownian motion and show that they satisfy a Langevin equation with time-dependent diffusion coefficient. If the time derivative of the variance of the process is homogeneous, then by computing the fractal dimension it can be shown that the complexity of the family is the same as that of the Brownian motion. For two particles initially separated by a distance x , the finite-size Lyapunov exponent (FSLE) measures the average rate of exponential separation to a distance ax . An analytical expression is developed for the FSLEs of the extended Brownian processes and numerical examples presented. The explicit construction of these processes illustrates that contrary to what has been stated in the literature, a power-law mean-square displacement is not necessarily related to a breakdown in the classical central limit theorem (CLT) caused by, for example, correlation (fractional Brownian motion or correlated continuous-time random-walk schemes) or infinite variance (Levy motion). The classical CLT, coupled with nonstationary increments, can and often does give rise to power-law moments such as the mean-square displacement.
Diffusion in randomly perturbed dissipative dynamics
Rodrigues, Christian S; de Moura, Alessandro P S; Grebogi, Celso; Klages, Rainer
2014-01-01
Dynamical systems having many coexisting attractors present interesting properties from both fundamental theoretical and modelling points of view. When such dynamics is under bounded random perturbations, the basins of attraction are no longer invariant and there is the possibility of transport among them. Here we introduce a basic theoretical setting which enables us to study this hopping process from the perspective of anomalous transport using the concept of a random dynamical system with holes. We apply it to a simple model by investigating the role of hyperbolicity for the transport among basins. We show numerically that our system exhibits non-Gaussian position distributions, power-law escape times, and subdiffusion. Our simulation results are reproduced consistently from stochastic Continuous Time Random Walk theory.
Diffusion Dynamics with Changing Network Composition
Baños, Raquel A; Wang, Ning; Moreno, Yamir; González-Bailón, Sandra
2013-01-01
We analyze information diffusion using empirical data that tracks online communication around two instances of mass political mobilization, including the year that lapsed in-between the protests. We compare the global properties of the topological and dynamic networks through which communication took place as well as local changes in network composition. We show that changes in network structure underlie aggregated differences on how information diffused: an increase in network hierarchy is accompanied by a reduction in the average size of cascades. The increasing hierarchy affects not only the underlying communication topology but also the more dynamic structure of information exchange; the increase is especially noticeable amongst certain categories of nodes (or users). This suggests that the relationship between the structure of networks and their function in diffusing information is not as straightforward as some theoretical models of diffusion in networks imply.
Diffusion Dynamics with Changing Network Composition
Directory of Open Access Journals (Sweden)
Sandra González-Bailón
2013-10-01
Full Text Available We analyze information diffusion using empirical data that tracks online communication around two instances of mass political mobilization that took place in Spain in 2011 and 2012. We also analyze protest-related communications during the year that elapsed between those protests. We compare the global properties of the topological and dynamic networks through which communication took place, as well as local changes in network composition. We show that changes in network structure underlie aggregated differences on how information diffused: an increase in network hierarchy is accompanied by a reduction in the average size of cascades. The increasing hierarchy affects not only the underlying communication topology but also the more dynamic structure of information exchange; the increase is especially noticeable amongst certain categories of nodes (or users. Our findings suggest that the relationship between the structure of networks and their function in diffusing information is not as straightforward as some theoretical models of diffusion in networks imply.
A simple non-chaotic map generating subdiffusive, diffusive, and superdiffusive dynamics
International Nuclear Information System (INIS)
Analytically tractable dynamical systems exhibiting a whole range of normal and anomalous deterministic diffusion are rare. Here, we introduce a simple non-chaotic model in terms of an interval exchange transformation suitably lifted onto the whole real line which preserves distances except at a countable set of points. This property, which leads to vanishing Lyapunov exponents, is designed to mimic diffusion in non-chaotic polygonal billiards that give rise to normal and anomalous diffusion in a fully deterministic setting. As these billiards are typically too complicated to be analyzed from first principles, simplified models are needed to identify the minimal ingredients generating the different transport regimes. For our model, which we call the slicer map, we calculate all its moments in position analytically under variation of a single control parameter. We show that the slicer map exhibits a transition from subdiffusion over normal diffusion to superdiffusion under parameter variation. Our results may help to understand the delicate parameter dependence of the type of diffusion generated by polygonal billiards. We argue that in different parameter regions the transport properties of our simple model match to different classes of known stochastic processes. This may shed light on difficulties to match diffusion in polygonal billiards to a single anomalous stochastic process
A simple non-chaotic map generating subdiffusive, diffusive, and superdiffusive dynamics.
Salari, Lucia; Rondoni, Lamberto; Giberti, Claudio; Klages, Rainer
2015-07-01
Analytically tractable dynamical systems exhibiting a whole range of normal and anomalous deterministic diffusion are rare. Here, we introduce a simple non-chaotic model in terms of an interval exchange transformation suitably lifted onto the whole real line which preserves distances except at a countable set of points. This property, which leads to vanishing Lyapunov exponents, is designed to mimic diffusion in non-chaotic polygonal billiards that give rise to normal and anomalous diffusion in a fully deterministic setting. As these billiards are typically too complicated to be analyzed from first principles, simplified models are needed to identify the minimal ingredients generating the different transport regimes. For our model, which we call the slicer map, we calculate all its moments in position analytically under variation of a single control parameter. We show that the slicer map exhibits a transition from subdiffusion over normal diffusion to superdiffusion under parameter variation. Our results may help to understand the delicate parameter dependence of the type of diffusion generated by polygonal billiards. We argue that in different parameter regions the transport properties of our simple model match to different classes of known stochastic processes. This may shed light on difficulties to match diffusion in polygonal billiards to a single anomalous stochastic process. PMID:26232964
Dynamical corrections to the anomalous holographic softwall model: the pomeron and the odderon
Capossoli, Eduardo Folco; Boschi-Filho, Henrique
2016-01-01
In this work we use the holographic softwall AdS/QCD model with anomalous dimension contributions coming from two different QCD beta functions to calculate the masses of higher spin glueball states for both even and odd spins and its respective Regge trajectories, related to the pomeron and the odderon, respectively. We further investigate this model taking into account dynamical corrections due to a dilaton potential consistent with Einstein equations in 5 dimensions. The results found in this work for the Regge trajectories within the anomalous softwall model with dynamical corrections are consistent with those presented in the literature.
International Nuclear Information System (INIS)
It is proposed to apply the fractional spatial derivatives for describing the effect of the fast electrons anomalous diffusion in the stochastic magnetic field on the distribution function form/ The self-simulating form of the kinetic equation is considered. Application of the self-simulating variables makes it possible to determine the velocities range, wherein the distribution function distortion becomes extremely strong. The accomplished calculations make it possible to evaluate the values, connected with the stochasticity of the magnetic power lines
Energy Technology Data Exchange (ETDEWEB)
Ram, Abhay K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Dasgupta, Brahmananda [Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, Alabama 35805 (United States); Krishnamurthy, V. [Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, Virginia 22030 (United States); Mitra, Dhrubaditya [Nordita, KTH Royal Institute of Technology and Stockholm University, 10691 Stockholm (Sweden)
2014-07-15
The cosmic magnetic fields in regions of low plasma pressure and large currents, such as in interstellar space and gaseous nebulae, are force-free in the sense that the Lorentz force vanishes. The three-dimensional Arnold-Beltrami-Childress (ABC) field is an example of a force-free, helical magnetic field. In fluid dynamics, ABC flows are steady state solutions of the Euler equation. The ABC magnetic field lines exhibit a complex and varied structure that is a mix of regular and chaotic trajectories in phase space. The characteristic features of field line trajectories are illustrated through the phase space distribution of finite-distance and asymptotic-distance Lyapunov exponents. In regions of chaotic trajectories, an ensemble-averaged variance of the distance between field lines reveals anomalous diffusion—in fact, superdiffusion—of the field lines. The motion of charged particles in the force-free ABC magnetic fields is different from the flow of passive scalars in ABC flows. The particles do not necessarily follow the field lines and display a variety of dynamical behavior depending on their energy, and their initial pitch-angle. There is an overlap, in space, of the regions in which the field lines and the particle orbits are chaotic. The time evolution of an ensemble of particles, in such regions, can be divided into three categories. For short times, the motion of the particles is essentially ballistic; the ensemble-averaged, mean square displacement is approximately proportional to t{sup 2}, where t is the time of evolution. The intermediate time region is defined by a decay of the velocity autocorrelation function—this being a measure of the time after which the collective dynamics is independent of the initial conditions. For longer times, the particles undergo superdiffusion—the mean square displacement is proportional to t{sup α}, where α > 1, and is weakly dependent on the energy of the particles. These super-diffusive characteristics
Anomalous scaling of Cu-island dynamics on Ag(100)
Energy Technology Data Exchange (ETDEWEB)
Zaum, Christopher; Morgenstern, Karina [Institut fuer Festkoerperphysik, Gottfried Wilhelm Leibniz Universitaet, Appelstr. 2, D-30167 Hannover (Germany)
2008-07-01
We deposited Cu-islands containing 10 to 500 atoms on a clean Ag(100) surface at room temperature and investigated diffusion and decay of these islands with a fast scanning tunneling microscope. Islands at sizes above 80 atoms per island are adsorbed in hollow-sites. Islands at sizes below 80 atoms per island are adsorbed in bridge-sites. Diffusion and decay behavior of the hollow-site islands is similar to the behavior of both Ag-islands on Ag(100) and Cu-islands on Cu(100). In contrast, the diffusivity and the decay time of the bridge-site islands are significantly higher than any previously measured values. This indicates a novel mechanism of diffusion.
Michas, Georgios; Vallianatos, Filippos; Karakostas, Vassilios; Papadimitriou, Eleftheria; Sammonds, Peter
2014-05-01
result that is in accordance to earthquake triggering in global scale (Huc and Main, 2003) and aftershocks diffusion in California (Helmstetter et al., 2003). While other mechanisms may be plausible, the results indicate that anomalous stress transfer due to the occurrence of the two major events control the migration of the aftershock activity, activating different fault segments and having strong implications for the seismic hazard of the area. Acknowledgments. G. Michas wishes to acknowledge the partial financial support from the Greek State Scholarships Foundation (IKY). This work has been accomplished in the framework of the postgraduate program and co-funded through the action "Program for scholarships provision I.K.Y. through the procedure of personal evaluation for the 2011-2012 academic year" from resources of the educational program "Education and Life Learning" of the European Social Register and NSRF 2007- 2013. References Ganas, A., Chousianitis, K., Batsi, E., Kolligri, M., Agalos, A., Chouliaras, G., Makropoulos, K. (2013). The January 2010 Efpalion earthquakes (Gulf of Corinth, central Greece): Earthquake interactions and blind normal faulting. J. of Seism., 17(2), 465-484. Helmstetter, A., Ouillon, G., Sornette, D. (2003). Are aftershocks of large California earthquakes diffusing? J. of Geophys. Res. B, 108(10), 2483. Huc, M., Main, I. G. (2003). Anomalous stress diffusion in earthquake triggering: Correlation length, time dependence, and directionality. J. of Geophys. Res. B, 108(7), 2324. Karakostas, V., Karagianni, E., Paradisopoulou, P. (2012). Space-time analysis, faulting and triggering of the 2010 earthquake doublet in western Corinth gulf. Nat.Haz., 63(2), 1181-1202. Metzler, R., Klafter, J. (2000). The random walk's guide to anomalous diffusion: a fractional dynamics approach. Physics Reports, 339, 1-77. Michas, G., Vallianatos, F., Sammonds, P. (2013). Non-extensivity and long-range correlations in the earthquake activity at the West Corinth
D. Panja
2010-01-01
Any first course on polymer physics teaches that the dynamics of a tagged monomer of a polymer is anomalously subdiffusive, i.e., the mean-square displacement of a tagged monomer increases as tα for some α < 1 until the terminal relaxation time τ of the polymer. Beyond time τ the motion of the tagge
Institute of Scientific and Technical Information of China (English)
徐明瑜; 谭文长
2001-01-01
The velocity field of generalized second order fluid with fractional anomalous diffusion caused by a plate moving impulsively in its own plane is investigated and the anomalous diffusion problems of the stress field and vortex sheet caused by this process are studied. Many previous and classical results can be considered as particular cases of this paper, such as the solutions of the fractional diffusion equations obtained by Wyss; the classical Rayleigh' s time-space similarity solution; the relationship between stress field and velocity field obtained by Bagley and co-worker and Podlubny' s results on the fractional motion equation of a plate. In addition, a lot of significant results also are obtained. For example, the necessary condition for causing the vortex sheet is that the time fractional diffusion index β must be greater than that of generalized second order fluid α; the establishment of the vorticity distribution function depends on the time history of the velocity profile at a given point, and the time history can be described by the fractional calculus.
Diffusive dynamics of nanoparticles in aqueous dispersions
He, Kai
2012-01-01
The diffusive dynamics of 100 nm to 400 nm diameter polystyrene nanoparticles dispersed in water were studied using brightfield and fluorescence based differential dynamic microscopy (DDM) and compared to those obtained from dynamic light scattering. The relaxation times measured with brightfield and fluorescence DDM over a broad range of concentration of nanoparticles (10 -6 ≤ φ ≤ 10-3) and scattering vectors (0.5 μm-1 < q < 10 μm-1) are in excellent agreement with each other and extrapolate quantitatively to those obtained from DLS measurements. The diffusion coefficients extracted from the q-dependent relaxation times using all three methods are independent of the nanoparticle concentration. © 2012 The Royal Society of Chemistry.
A Diffusive Strategic Dynamics for Social Systems
Agliari, Elena; Burioni, Raffaella; Contucci, Pierluigi
2010-05-01
We propose a model for the dynamics of a social system, which includes diffusive effects and a biased rule for spin-flips, reproducing the effect of strategic choices. This model is able to mimic some phenomena taking place during marketing or political campaigns. Using a cost function based on the Ising model defined on the typical quenched interaction environments for social systems (Erdös-Renyi graph, small-world and scale-free networks), we find, by numerical simulations, that a stable stationary state is reached, and we compare the final state to the one obtained with standard dynamics, by means of total magnetization and magnetic susceptibility. Our results show that the diffusive strategic dynamics features a critical interaction parameter strictly lower than the standard one. We discuss the relevance of our findings in social systems.
Diffusion dynamics in microfluidic dye lasers
DEFF Research Database (Denmark)
Gersborg-Hansen, Morten; Balslev, Søren; Mortensen, Niels Asger;
2007-01-01
We have investigated the bleaching dynamics that occur in opto-fluidic dye lasers, where the liquid laser dye in a channel is locally bleached due to optical pumping. Our studies suggest that for micro-fluidic devices, the dye bleaching may be compensated through diffusion of dye molecules alone....... By relying on diffusion rather than convection to generate the necessary dye replenishment, our observation potentially allows for a significant simplification of opto-fluidic dye laser device layouts, omitting the need for cumbersome and costly external fluidic handling or on-chip micro-fluidic...
Anomalous dynamics of intruders in a crowded environment of mobile obstacles
Sentjabrskaja, Tatjana; Zaccarelli, Emanuela; De Michele, Cristiano; Sciortino, Francesco; Tartaglia, Piero; Voigtmann, Thomas; Egelhaaf, Stefan U.; Laurati, Marco
2016-01-01
Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials or gels, individuals in highly dense collectives and vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some glass-like dynamics. Here we investigate constrained transport in a colloidal model system, in which dilute small spheres move in a slowly rearranging, glassy matrix of large spheres. Using confocal differential dynamic microscopy and simulations, here we discover a critical size asymmetry, at which anomalous collective transport of the small particles appears, manifested as a logarithmic decay of the density autocorrelation functions. We demonstrate that the matrix mobility is central for the observed anomalous behaviour. These results, crucially depending on size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology. PMID:27041068
Anomalous dynamics of intruders in a crowded environment of mobile obstacles
Sentjabrskaja, Tatjana; Zaccarelli, Emanuela; de Michele, Cristiano; Sciortino, Francesco; Tartaglia, Piero; Voigtmann, Thomas; Egelhaaf, Stefan U.; Laurati, Marco
2016-04-01
Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials or gels, individuals in highly dense collectives and vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some glass-like dynamics. Here we investigate constrained transport in a colloidal model system, in which dilute small spheres move in a slowly rearranging, glassy matrix of large spheres. Using confocal differential dynamic microscopy and simulations, here we discover a critical size asymmetry, at which anomalous collective transport of the small particles appears, manifested as a logarithmic decay of the density autocorrelation functions. We demonstrate that the matrix mobility is central for the observed anomalous behaviour. These results, crucially depending on size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology.
Anomalous Contagion and Renormalization in Dynamical Networks with Nodal Mobility
Manrique, Pedro D; Zheng, Minzhang; Xu, Chen; Hui, Pak Ming; Johnson, Neil F
2015-01-01
The common real-world feature of individuals migrating through a network -- either in real space or online -- significantly complicates understanding of network processes. Here we show that even though a network may appear static on average, underlying nodal mobility can dramatically distort outbreak profiles. Highly nonlinear dynamical regimes emerge in which increasing mobility either amplifies or suppresses outbreak severity. Predicted profiles mimic recent outbreaks of real-space contagion (social unrest) and online contagion (pro-ISIS support). We show that this nodal mobility can be renormalized in a precise way for a particular class of dynamical networks.
Diffuse-dynamic multiparameter diffractometry: A review
Molodkin, V. B.; Shpak, A. P.; Kovalchuk, M. V.; Nosik, V. L.; Machulin, V. F.
2010-12-01
The results reported at the Conference on Application of X-Rays, Synchrotron Radiation, Neutrons, and Electrons in Nano-, Bio-, Information-, and Cognitive Technologies (RSNE-NBIC 2009) are briefly reviewed. This review is based on a cycle of studies [1-6] where a new method for studying the structure of real crystals—diffuse-dynamic multiparameter diffractometry (DDMD)—was proposed and substantiated.
Diffusion Dynamics with Changing Network Composition
Sandra González-Bailón; Yamir Moreno; Javier Borge-Holthoefer; Ning Wang; Baños, Raquel A.
2013-01-01
We analyze information diffusion using empirical data that tracks online communication around two instances of mass political mobilization that took place in Spain in 2011 and 2012. We also analyze protest-related communications during the year that elapsed between those protests. We compare the global properties of the topological and dynamic networks through which communication took place, as well as local changes in network composition. We show that changes in network structure underlie ag...
Anomalous partially hyperbolic diffeomorphisms I: dynamically coherent examples
Bonatti, Christian; Parwani, Kamlesh; Potrie, Rafael
2014-01-01
We build an example of a non-transitive, dynamically coherent partially hyperbolic diffeomorphism $f$ on a closed $3$-manifold with exponential growth in its fundamental group such that $f^n$ is not isotopic to the identity for all $n\
International Nuclear Information System (INIS)
It is proposed to use fractional spatial derivatives to describe the effect of anomalous diffusion of fast electrons in a stochastic magnetic field on the shape of the distribution function. A self-similar kinetic equation is considered. The use of self-similar variables makes it possible to determine the velocity range in which the distribution function is distorted to the greatest extent. Calculations show that the quantities associated with the stochasticity of the magnetic field lines can be estimated from the experimentally measured characteristic energies of suprathermal electrons in the energy range in which the behavior of the distribution function changes substantially
Panja, Debabrata
2010-06-01
Any first course on polymer physics teaches that the dynamics of a tagged monomer of a polymer is anomalously subdiffusive, i.e., the mean-square displacement of a tagged monomer increases as tα for some α kernels within a unified generalized Langevin equation (GLE) scheme, and therefore are non-Markovian. The exponents of the power-law memory kernels are related to the relaxation response of the polymers to local strains, and are derived from the equilibrium statistical physics of polymers. The anomalous dynamics of a tagged monomer of a polymer in these systems is then reproduced from the power-law memory kernels of the GLE via the fluctuation-dissipation theorem (FDT). Using this GLE formulation I further show that the characteristics of the drifts caused by a (weak) applied field on these polymeric systems are also obtained from the corresponding memory kernels.
A Diffusive Strategic Dynamics for Social Systems
Agliari, Elena; Burioni, Raffaella; Contucci, Pierluigi
2008-01-01
We propose a model for the dynamics of a social system, which includes diffusive effects and a biased rule for spin-flips, reproducing the effect of strategic choices. This model is able to mimic some phenomena taking place during marketing or political campaigns. Using a cost function based on the Ising model defined on the typical quenched interaction environments for social systems (Erdos-Renyi graph, small-world and scale-free networks), we find, by numerical simulations, that a stable st...
Anomalous behavior of the coherent light diffusion by a tilted translucent rough surface: part I
Rebollo, M. A.; Perez Quintian, F.; Hogert, Elsa N.; Landau, Monica R.; Gaggioli, Nestor G.
1996-02-01
When a translucent rough surface is illuminated, light is diffused in different directions. The envelope the intensity distribution is called diffusion curve. As the diffuser is rotated with respect to the incident beam, the diffuser curve changes its appearance: the maximum suffers a displacement and changes its shape. Some authors have studied this phenomenon, but none of them explained it properly. In this work we make an additional contribution to address the problem, showing experimentally that the maximum displacement depends on the incident angle and the diffuser ratio T/(sigma) . We compare our experimental results with those that can be calculated with the reformulated Beckmann's theory. We could observe important agreements and differences. For example, Beckmann's theory predicts that the diffusion results are asymmetric, while our measured results are indefectibly symmetric.
Lattice dynamical investigations on Zn diffusion in zinc oxide
Indian Academy of Sciences (India)
P Vinotha Boorana Lakshmi; K Ramachandran
2011-04-01
Zinc self diffusion in bulk zinc oxide is studied by lattice dynamical approach here to get more insight into the diffusion in nano ZnO. The results reveal that only cationic self diffusion is dominant over anionic self diffusion and that too by single vacancy mechanism. The results are compared with the available experiments and discussed.
Galactic civilizations - Population dynamics and interstellar diffusion
Newman, W. I.; Sagan, C.
1981-01-01
A model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds.
Ribeiro, H V; Alves, L G A; Zola, R S; Lenzi, E L
2014-01-01
The comb model is a simplified description for anomalous diffusion under geometric constraints. It represents particles spreading out in a two-dimensional space where the motions in the x-direction are allowed only when the y coordinate of the particle is zero. Here, we propose an extension for the comb model via Langevin-like equations driven by fractional Gaussian noises (long-range correlated). By carrying out computer simulations, we show that the correlations in the y-direction affect the diffusive behavior in the x-direction in a non-trivial fashion, resulting in a quite rich diffusive scenario characterized by usual, superdiffusive or subdiffusive scaling of second moment in the x-direction. We further show that the long-range correlations affect the probability distribution of the particle positions in the x-direction, making their tails longer when noise in the y-direction is persistent and shorter for anti-persistent noise. Our model thus combines and allows the study/analysis of the interplay betwe...
Seki, Kazuhiko; Bagchi, Kaushik; Bagchi, Biman
2016-05-21
Diffusion in one dimensional rugged energy landscape (REL) is predicted to be pathologically different (from any higher dimension) with a much larger chance of encountering broken ergodicity [D. L. Stein and C. M. Newman, AIP Conf. Proc. 1479, 620 (2012)]. However, no quantitative study of this difference has been reported, despite the prevalence of multidimensional physical models in the literature (like a high dimensional funnel guiding protein folding/unfolding). Paradoxically, some theoretical studies of these phenomena still employ a one dimensional diffusion description for analytical tractability. We explore the dimensionality dependent diffusion on REL by carrying out an effective medium approximation based analytical calculations and compare them with the available computer simulation results. We find that at an intermediate level of ruggedness (assumed to have a Gaussian distribution), where diffusion is well-defined, the value of the effective diffusion coefficient depends on dimensionality and changes (increases) by several factors (∼5-10) in going from 1d to 2d. In contrast, the changes in subsequent transitions (like 2d to 3d and 3d to 4d and so on) are far more modest, of the order of 10-20% only. When ruggedness is given by random traps with an exponential distribution of barrier heights, the mean square displacement (MSD) is sub-diffusive (a well-known result), but the growth of MSD is described by different exponents in one and higher dimensions. The reason for such strong ruggedness induced retardation in the case of one dimensional REL is discussed. We also discuss the special limiting case of infinite dimension (d = ∞) where the effective medium approximation becomes exact and where theoretical results become simple. We discuss, for the first time, the role of spatial correlation in the landscape on diffusion of a random walker. PMID:27208935
Anomalous scaling of structure functions and dynamic constraints on turbulence simulations
International Nuclear Information System (INIS)
The connection between anomalous scaling of structure functions (intermittency) and numerical methods for turbulence simulations is discussed. It is argued that the computational work for direct numerical simulations (DNS) of fully developed turbulence increases as Re4, and not as Re3 expected from Kolmogorov's theory, where Re is a large-scale Reynolds number. Various relations for the moments of acceleration and velocity derivatives are derived. An infinite set of exact constraints on dynamically consistent subgrid models for Large Eddy Simulations (LES) is derived from the Navier-Stokes equations, and some problems of principle associated with existing LES models are highlighted. (author)
Energy Technology Data Exchange (ETDEWEB)
Migliori, A.; Maxton, P.M.; Clogston, A.M.; Zirngiebl, E.; Lowe, M.
1988-12-15
We measured the temperature dependence of the intensity of the two lowest Raman modes in single crystals of l-alanine. The sum of the intensities obeys Maxwell-Boltzman statistics accurately from 20 to 340 K but the intensities of the individual lines are anomalous. This behavior is explained by assuming that both lines share the same degrees of freedom but that a mode instability is triggered abruptly at an occupation of seven quanta. This instability, which has an activation energy of 500 K, is observed at temperatures as low as 20 K, possibly indicating the existence of dynamic localization of vibrational energy.
Dynamic correlation of photo-excited electrons: Anomalous levels induced by light–matter coupling
International Nuclear Information System (INIS)
Nonlinear light–matter coupling plays an important role in many aspects of modern physics, such as spectroscopy, photo-induced phase transition, light-based devices, light-harvesting systems, light-directed reactions and bio-detection. However, excited states of electrons are still unclear for nano-structures and molecules in a light field. Our studies unexpectedly present that light can induce anomalous levels in the electronic structure of a donor–acceptor nanostructure with the help of the photo-excited electrons transferring dynamically between the donor and the acceptor. Furthermore, the physics underlying is revealed to be the photo-induced dynamical spin–flip correlation among electrons. These anomalous levels can significantly enhance the electron current through the nanostructure. These findings are expected to contribute greatly to the understanding of the photo-excited electrons with dynamic correlations, which provides a push to the development and application of techniques based on photosensitive molecules and nanostructures, such as light-triggered molecular devices, spectroscopic analysis, bio-molecule detection, and systems for solar energy conversion.
Raudino, Antonio; Raciti, Domenica; Grassi, Antonio; Pannuzzo, Martina; Corti, Mario
2016-08-30
We investigate, both theoretically and experimentally, the role played by the oscillations of the cell membrane on the capture rate of substances freely diffusing around the cell. To obtain quantitative results, we propose and build up a reproducible and tunable biomimetic experimental model system to simulate the phenomenon of an oscillation-enhanced (or depressed) capture rate (chemoreception) of a diffusant. The main advantage compared to real biological systems is that the different oscillation parameters (type of deformation, frequencies, and amplitudes) can be finely tuned. The model system that we use is an anchored gas drop submitted to a diffusive flow of charged surfactants. When the surfactant meets the surface of the bubble, it is reversibly adsorbed. Bubble oscillations of the order of a few nanometers are selectively excited, and surfactant transport is accurately measured. The surfactant concentration past the oscillating bubbles was detected by conductivity measurements. The results highlight the role of surface oscillations on the diffusant capture rate. Particularly unexpected is the onset of intense overshoots during the adsorption process. The phenomenon is particularly relevant when the bubbles are exposed to intense forced oscillations near resonance. PMID:27509197
Diffusion of Particle in Hyaluronan Solution, a Brownian Dynamics Simulation
Takasu, Masako; Tomita, Jungo
2004-04-01
Diffusion of a particle in hyaluronan solution is investigated using Brownian dynamics simulation. The slowing down of diffusion is observed, in accordance with the experimental results. The temperature dependence of the diffusion is calculated, and a turnover is obtained when the temperature is increased.
Balankin, Alexander S.; Valdivia, Juan-Carlos; Marquez, Jesús; Susarrey, Orlando; Solorio-Avila, Marco A.
2016-08-01
In this Letter, we report experimental and theoretical studies of Newtonian fluid flow through permeable media with fractal porosity. Darcy flow experiments were performed on samples with a deterministic pre-fractal pore network. We found that the seepage velocity is linearly proportional to the pressure drop, but the apparent absolute permeability increases with the increase of sample length in the flow direction L. We claim that a violation of the Hagen-Poiseuille law is due to an anomalous diffusion of the fluid momentum. In this regard we argue that the momentum diffusion is governed by the flow metric induced by the fractal topology of the pore network. The Darcy-like equation for laminar flow in a fractal pore network is derived. This equation reveals that the apparent absolute permeability is independent of L, only if the number of effective spatial degrees of freedom in the pore-network ν is equal to the network fractal (self-similarity) dimension D, e.g. it is in the case of fractal tree-like networks. Otherwise, the apparent absolute permeability either decreases with L, if ν D, as this is in the case of the inverse Menger sponge.
Volpe, Giorgio; Volpe, Giovanni; Gigan, Sylvain
2014-01-01
The motion of particles in random potentials occurs in several natural phenomena ranging from the mobility of organelles within a biological cell to the diffusion of stars within a galaxy. A Brownian particle moving in the random optical potential associated to a speckle, i.e., a complex interference pattern generated by the scattering of coherent light by a random medium, provides an ideal mesoscopic model system to study such phenomena. Here, we derive a theory for the motion of a Brownian ...
Fan, Niannian; Singh, Arvind; Guala, Michele; Foufoula-Georgiou, Efi; Wu, Baosheng
2016-04-01
Bed load transport is a highly stochastic, multiscale process, where particle advection and diffusion regimes are governed by the dynamics of each sediment grain during its motion and resting states. Having a quantitative understanding of the macroscale behavior emerging from the microscale interactions is important for proper model selection in the absence of individual grain-scale observations. Here we develop a semimechanistic sediment transport model based on individual particle dynamics, which incorporates the episodic movement (steps separated by rests) of sediment particles and study their macroscale behavior. By incorporating different types of probability distribution functions (PDFs) of particle resting times Tr, under the assumption of thin-tailed PDF of particle velocities, we study the emergent behavior of particle advection and diffusion regimes across a wide range of spatial and temporal scales. For exponential PDFs of resting times Tr, we observe normal advection and diffusion at long time scales. For a power-law PDF of resting times (i.e., f>(Tr>)˜Tr-ν), the tail thickness parameter ν is observed to affect the advection regimes (both sub and normal advective), and the diffusion regimes (both subdiffusive and superdiffusive). By comparing our semimechanistic model with two random walk models in the literature, we further suggest that in order to reproduce accurately the emerging diffusive regimes, the resting time model has to be coupled with a particle motion model able to produce finite particle velocities during steps, as the episodic model discussed here.
Rumor Diffusion in an Interests-Based Dynamic Social Network
Mingsheng Tang; Xinjun Mao; Zahia Guessoum; Huiping Zhou
2013-01-01
To research rumor diffusion in social friend network, based on interests, a dynamic friend network is proposed, which has the characteristics of clustering and community, and a diffusion model is also proposed. With this friend network and rumor diffusion model, based on the zombie-city model, some simulation experiments to analyze the characteristics of rumor diffusion in social friend networks have been conducted. The results show some interesting observations: (1) positive information may ...
Anomalous dynamical scaling in anharmonic chains and plasma models with multiparticle collisions
Di Cintio, Pierfrancesco; Livi, Roberto; Bufferand, Hugo; Ciraolo, Guido; Lepri, Stefano; Straka, Mika J.
2015-12-01
We study the anomalous dynamical scaling of equilibrium correlations in one-dimensional systems. Two different models are compared: the Fermi-Pasta-Ulam chain with cubic and quartic nonlinearity and a gas of point particles interacting stochastically through multiparticle collision dynamics. For both models—that admit three conservation laws—by means of detailed numerical simulations we verify the predictions of nonlinear fluctuating hydrodynamics for the structure factors of density and energy fluctuations at equilibrium. Despite this, violations of the expected scaling in the currents correlation are found in some regimes, hindering the observation of the asymptotic scaling predicted by the theory. In the case of the gas model this crossover is clearly demonstrated upon changing the coupling constant.
Anomalous dynamical scaling in anharmonic chains and plasma models with multi-particle collisions
Di Cintio, Pierfrancesco; Bufferand, Hugo; Ciraolo, Guido; Lepri, Stefano; Straka, Mika J
2015-01-01
We study the anomalous dynamical scaling of equilibrium correlations in one dimensional systems. Two different models are compared: the Fermi-Pasta-Ulam chain with cubic and quartic nonlinearity and a gas of point particles interacting stochastically through the Multi-Particle Collision dynamics. For both models -that admit three conservation laws- by means of detailed numerical simulations we verify the predictions of Nonlinear Fluctuating Hydrodynamics for the structure factors of density and energy fluctuations at equilibrium. Despite of this, violations of the expected scaling in the currents correlation are found in some regimes, hindering the observation of the asymptotic scaling predicted by the theory. In the case of the gas model this crossover is clearly demonstrated upon changing the coupling constant.
Dynamic Nuclear Polarization as Kinetically Constrained Diffusion
Karabanov, A.; Wiśniewski, D.; Lesanovsky, I.; Köckenberger, W.
2015-07-01
Dynamic nuclear polarization (DNP) is a promising strategy for generating a significantly increased nonthermal spin polarization in nuclear magnetic resonance (NMR) and its applications that range from medicine diagnostics to material science. Being a genuine nonequilibrium effect, DNP circumvents the need for strong magnetic fields. However, despite intense research, a detailed theoretical understanding of the precise mechanism behind DNP is currently lacking. We address this issue by focusing on a simple instance of DNP—so-called solid effect DNP—which is formulated in terms of a quantum central spin model where a single electron is coupled to an ensemble of interacting nuclei. We show analytically that the nonequilibrium buildup of polarization heavily relies on a mechanism which can be interpreted as kinetically constrained diffusion. Beyond revealing this insight, our approach furthermore permits numerical studies of ensembles containing thousands of spins that are typically intractable when formulated in terms of a quantum master equation. We believe that this represents an important step forward in the quest of harnessing nonequilibrium many-body quantum physics for technological applications.
Universal Earthquake-Occurrence Jumps, Correlations with Time, and Anomalous Diffusion
International Nuclear Information System (INIS)
Spatiotemporal properties of seismicity are investigated for a worldwide (WW) catalog and for southern California in the stationary case (SC), showing a nearly universal scaling behavior. Distributions of distances between consecutive earthquakes (jumps) are magnitude independent and show two power-law regimes, separated by jump values about 200 (WW) and 15 km (SC). Distributions of waiting times conditioned to the value of jumps show that both variables are correlated, in general, but turn out to be independent when only short or long jumps are considered. Finally, diffusion profiles are found to be independent on the magnitude, contrary to what the waiting-time distributions suggest
Universal earthquake-occurrence jumps, correlations with time, and anomalous diffusion.
Corral, Alvaro
2006-10-27
Spatiotemporal properties of seismicity are investigated for a worldwide (WW) catalog and for southern California in the stationary case (SC), showing a nearly universal scaling behavior. Distributions of distances between consecutive earthquakes (jumps) are magnitude independent and show two power-law regimes, separated by jump values about 200 (WW) and 15 km (SC). Distributions of waiting times conditioned to the value of jumps show that both variables are correlated, in general, but turn out to be independent when only short or long jumps are considered. Finally, diffusion profiles are found to be independent on the magnitude, contrary to what the waiting-time distributions suggest. PMID:17155513
Anomalous diffusion, clustering, and pinch of impurities in plasma edge turbulence
DEFF Research Database (Denmark)
Priego, M.; Garcia, O.E.; Naulin, V.; Juul Rasmussen, J.
2005-01-01
The turbulent transport of impurity particles in plasma edge turbulence is investigated. The impurities are modeled as a passive fluid advected by the electric and polarization drifts, while the ambient plasma turbulence is modeled using the two-dimensional Hasegawa-Wakatani paradigm for resistive......-diffusion analysis of the evolution of impurity puffs. Additional effects appear for inertial impurities as a consequence of compressibility. First, the density of inertial impurities is found to correlate with the vorticity of the electric drift velocity, that is, impurities cluster in vortices of a precise...
A dynamic Monte Carlo study of anomalous current voltage behaviour in organic solar cells
International Nuclear Information System (INIS)
We present a dynamic Monte Carlo (DMC) study of s-shaped current-voltage (I-V) behaviour in organic solar cells. This anomalous behaviour causes a substantial decrease in fill factor and thus power conversion efficiency. We show that this s-shaped behaviour is induced by charge traps that are located at the electrode interface rather than in the bulk of the active layer, and that the anomaly becomes more pronounced with increasing trap depth or density. Furthermore, the s-shape anomaly is correlated with interface recombination, but not bulk recombination, thus highlighting the importance of controlling the electrode interface. While thermal annealing is known to remove the s-shape anomaly, the reason has been not clear, since these treatments induce multiple simultaneous changes to the organic solar cell structure. The DMC modelling indicates that it is the removal of aluminium clusters at the electrode, which act as charge traps, that removes the anomalous I-V behaviour. Finally, this work shows that the s-shape becomes less pronounced with increasing electron-hole recombination rate; suggesting that efficient organic photovoltaic material systems are more susceptible to these electrode interface effects
Dynamic problem of generalized thermoelastic diffusive medium
International Nuclear Information System (INIS)
The equations of generalized thermoelastic diffusion, based on the theory of Lord and Shulman with one relaxation time, are derived for anisotropic media with rotation. The variational principle and reciprocity theorem for the governing equations are derived. The propagation of leaky Rayleigh waves in a viscous fluid layer overlying a homogeneous isotropic, generalized thermoelastic diffusive half space with rotating frame of reference is studied
International Nuclear Information System (INIS)
An anomalous behavior of Gear's predictor-corrector algorithm is observed during a microcanonical molecular dynamics simulation of amorphous silicon. While the amorphous silicon network generated by quenching was being annealed, an anomaly is started: both the total energy and the temperature of the system spontaneously and indefinitely increased, in violation of energy conservation. No such phenomenon was observed when the integrator was switched to the Verlet algorithm. To remove this anomaly with the Gear's algorithm, it was necessary to reduce the size of the time step to 1/32 of the 'usual value (∼ 1/100 of the fastest vibration period in the system)' at least. Our results show that Gear's algorithm may become very unstable in a realistic simulation when the time step is not small enough, that is, orders of magnitude smaller than conventional value.
Thermodynamic and dynamic controls on changes in the zonally anomalous hydrological cycle
Wills, Robert C.; Byrne, Michael P.; Schneider, Tapio
2016-05-01
The wet gets wetter, dry gets drier paradigm explains the expected moistening of the extratropics and drying of the subtropics as the atmospheric moisture content increases with global warming. Here we show, using precipitation minus evaporation (P - E) data from climate models, that it cannot be extended to apply regionally to deviations from the zonal mean. Wet and dry zones shift substantially in response to shifts in the stationary-eddy circulations that cause them. Additionally, atmospheric circulation changes lead to a smaller increase in the zonal variance of P - E than would be expected from atmospheric moistening alone. The P - E variance change can be split into dynamic and thermodynamic components through an analysis of the atmospheric moisture budget. This reveals that a weakening of stationary-eddy circulations and changes in the zonal variation of transient-eddy moisture fluxes moderate the strengthening of the zonally anomalous hydrological cycle with global warming.
Crossover of two power laws in the anomalous diffusion of a two lipid membrane
Energy Technology Data Exchange (ETDEWEB)
Bakalis, Evangelos, E-mail: ebakalis@gmail.com, E-mail: francesco.zerbetto@unibo.it; Höfinger, Siegfried; Zerbetto, Francesco, E-mail: ebakalis@gmail.com, E-mail: francesco.zerbetto@unibo.it [Dipartimento di Chimica “G. Ciamician”, Universita’ di Bologna, Via F. Selmi 2, 40126 Bologna (Italy); Venturini, Alessandro [Institute for the Organic Synthesis and Photoreactivity, National Research Council of Italy, Via Gobetti 101, 40129 Bologna (Italy)
2015-06-07
Molecular dynamics simulations of a bi-layer membrane made by the same number of 1-palmitoyl-2-oleoyl-glycero-3-phospho-ethanolamine and palmitoyl-oleoyl phosphatidylserine lipids reveal sub-diffusional motion, which presents a crossover between two different power laws. Fractional Brownian motion is the stochastic mechanism that governs the motion in both regimes. The location of the crossover point is justified with simple geometrical arguments and is due to the activation of the mechanism of circumrotation of lipids about each other.
Czech Academy of Sciences Publication Activity Database
Pánek, Radomír; Krlín, Ladislav; Tender, M.; Tskhakaya, D.; Kuhn, S.; Svoboda, Vojtěch; Klíma, Richard; Pavlo, Pavol; Stöckel, Jan; Petržílka, Václav
2005-01-01
Roč. 72, - (2005), s. 327-332. ISSN 0031-8949 R&D Projects: GA ČR(CZ) GP202/03/P062; GA AV ČR(CZ) IAA100430502 Institutional research plan: CEZ:AV0Z20430508 Keywords : anomalous diffusion * plasma turbulence Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 0.661, year: 2004
Suppression and Enhancement of Diffusion in Disordered Dynamical Systems
Klages, R.
2001-01-01
The impact of quenched disorder on deterministic diffusion in chaotic dynamical systems is studied. As a simple example, we consider piecewise linear maps on the line. In computer simulations we find a complicated scenario of multiple suppression and enhancement of normal diffusion under variation of the perturbation strength. These results are explained by a theoretical argument showing that the oscillations emerge as a direct consequence of the unperturbed diffusion coefficient, which is kn...
Restoration of rhythmicity in diffusively coupled dynamical networks
Zou, W.; Senthilkumar, D. V.; Nagao, R.; Kiss, I Z; Tang, Y; KOSESKA, A.; Duan, J.; Kurths, J.
2015-01-01
Oscillatory behaviour is essential for proper functioning of various physical and biological processes. However, diffusive coupling is capable of suppressing intrinsic oscillations due to the manifestation of the phenomena of amplitude and oscillation deaths. Here we present a scheme to revoke these quenching states in diffusively coupled dynamical networks, and demonstrate the approach in experiments with an oscillatory chemical reaction. By introducing a simple feedback factor in the diffus...
Diffusive Dynamics of Nanoparticles in Arrays of Nanoposts
He, Kai
2013-06-25
The diffusive dynamics of dilute dispersions of nanoparticles of diameter 200-400 nm were studied in microfabricated arrays of nanoposts using differential dynamic microscopy and single particle tracking. Posts of diameter 500 nm and height 10 μm were spaced by 1.2-10 μm on a square lattice. As the spacing between posts was decreased, the dynamics of the nanoparticles slowed. Moreover, the dynamics at all length scales were best represented by a stretched exponential rather than a simple exponential. Both the relative diffusivity and the stretching exponent decreased linearly with increased confinement and, equivalently, with decreased void volume. The slowing of the overall diffusive dynamics and the broadening distribution of nanoparticle displacements with increased confinement are consistent with the onset of dynamic heterogeneity and the approach to vitrification. © 2013 American Chemical Society.
Fluid dynamics of double diffusive systems
Energy Technology Data Exchange (ETDEWEB)
Koseff, J.R.
1988-05-01
A study of mixing processes in doubly diffusive systems is being conducted. Continuous gradients of two diffusing components (heat and salinity) are being used as initial conditions, and forcing is introduced by lateral heating, surface shear and sloping boundaries. The goals of the proposed work include: quantification of the effects of finite amplitude disturbances on stable, double diffusive systems, particularly with respect to lateral heating, development of an improved understanding of the physical phenomena present in wind-driven shear flows in double diffusive stratified environments, increasing our knowledge-base on turbulent flow in stratified environments and how to represent it, and formulation of numerical code for such flows. The work is being carried out in a new experimental facility at Stanford and on laboratory minicomputers and CRAY computers. In particular we are focusing on the following key issues. The formation and propagation of double diffusive intrusions away from a heated wall and the effects of lateral heating on the double diffusive system; The interaction between the double diffusively influenced fluxes and the turbulence induced fluxes; The formation of gravitational intrusions; and The influence of double diffusive gradients on mixed layer deepening. The goals of the project were as follows. Physical experiments: Construct experimental facility; Modify and fabricate instrument rakes; Develop sampling and calibration software; Develop stratification techniques; Conduct flow visualization studies; Qualify wind tunnel over a range of wind speeds. Numerical experiments: Adapt REMIXCS to handle turbulent flows; Investigate approaches for specifying wind field; Perform calculations for low wind speeds. With the exception of the wind tunnel qualification, all the tasks have already been completed and we are now conducting quantitative experiments. 2 figs.
The diffusive dynamics of water confined in ganglioside micelles
Cantù, L.; Cavatorta, F.; Corti, M.; Del Favero, E.; Deriu, A.
1997-02-01
We have investigated by QENS the dynamics of water associated to gangliosides. The dependence of the QENS line-broadening versus Q indicates that proton diffusion is restricted when investigated over scale lengths of about 6-8 Å; at smaller distances the diffusivity parameters are similar to those of pure water at a lower temperature.
Dynamic structure factor study of diffusion in strongly sheared suspensions
Leshansky, Alexander M.; Brady, John F.
2005-01-01
Diffusion of neutrally buoyant spherical particles in concentrated monodisperse suspensions under simple shear flow is investigated. We consider the case of non-Brownian particles in Stokes flow, which corresponds to the limits of infinite Péclet number and zero Reynolds number. Using an approach based upon ideas of dynamic light scattering we compute self- and gradient diffusion coefficients in the principal directions normal to the flow numerically from Accelerated Stokesian Dynamics simula...
Kuentz, M
2003-01-01
A two-dimensional lattice gas automaton (LGA) is used for simulating concentration-dependent diffusion in a microscopically random heterogeneous structure. The heterogeneous medium is initialized at a low density rho sub 0 and then submitted to a steep concentration gradient by continuous injection of particles at a concentration rho sub 1 >rho sub 0 from a one-dimensional source to model spreading of a density front. Whereas the nonlinear diffusion equation generally used to describe concentration-dependent diffusion processes predicts a scaling law of the type phi = xt sup - sup 1 sup / sup 2 in one dimension, the spreading process is shown to deviate from the expected t sup 1 sup / sup 2 scaling. The time exponent is found to be larger than 1/2, i.e. diffusion of the density front is enhanced with respect to standard Fickian diffusion. It is also established that the anomalous time exponent decreases as time elapses: anomalous spreading is thus not a timescaling process. We demonstrate that occurrence of a...
Galactic civilizations: Population dynamics and interstellar diffusion
Newman, W. I.; Sagan, C.
1978-01-01
The interstellar diffusion of galactic civilizations is reexamined by potential theory; both numerical and analytical solutions are derived for the nonlinear partial differential equations which specify a range of relevant models, drawn from blast wave physics, soil science, and, especially, population biology. An essential feature of these models is that, for all civilizations, population growth must be limited by the carrying capacity of the environment. Dispersal is fundamentally a diffusion process; a density-dependent diffusivity describes interstellar emigration. Two models are considered: the first describing zero population growth (ZPG), and the second which also includes local growth and saturation of a planetary population, and for which an asymptotic traveling wave solution is found.
Interestingness-Driven Diffusion Process Summarization in Dynamic Networks
DEFF Research Database (Denmark)
Qu, Qiang; Liu, Siyuan; Jensen, Christian Søndergaard;
2014-01-01
The widespread use of social networks enables the rapid diffusion of information, e.g., news, among users in very large communities. It is a substantial challenge to be able to observe and understand such diffusion processes, which may be modeled as networks that are both large and dynamic. A key...... tool in this regard is data summarization. However, few existing studies aim to summarize graphs/networks for dynamics. Dynamic networks raise new challenges not found in static settings, including time sensitivity and the needs for online interestingness evaluation and summary traceability, which...... render existing techniques inapplicable. We study the topic of dynamic network summarization: how to summarize dynamic networks with millions of nodes by only capturing the few most interesting nodes or edges over time, and we address the problem by finding interestingness-driven diffusion processes...
Dynamics and pattern formation in a cancer network with diffusion
Zheng, Qianqian; Shen, Jianwei
2015-10-01
Diffusion is ubiquitous inside cells, and it is capable of inducing spontaneous pattern formation in reaction-diffusion systems on a spatially homogeneous domain. In this paper, we investigate the dynamics of a diffusive cancer network regulated by microRNA and obtain the condition that the network undergoes a Hopf bifurcation and a Turing pattern bifurcation. In addition, we also develop the amplitude equation of the network model by using Taylor series expansion, multi-scaling and further expansion in powers of a small parameter. As a result of these analyses, we obtain the explicit condition on how the dynamics of the diffusive cancer network evolve. These results reveal that this system has rich dynamics, such as spotted stripe and hexagon patterns. The bifurcation diagram helps us understand the biological mechanism in the cancer network. Finally, numerical simulations confirm our analytical results.
Dynamics Studies on Molecular Diffusion in Zeolites
Institute of Scientific and Technical Information of China (English)
王秋霞; 樊建芬; 肖鹤鸣
2003-01-01
A review about the applications of molecular dynamics（MD）simulation in zeolites is presented. MD simulation has been proved to be a useful tool due to its applications in this field for the recent two decades. The fundamental theory of MD is introduced and the hydrocarbon diffusion in zeolites is mainly focused on in this paper.
Arrese-Igor, Silvia; Alegría, Ángel; Moreno Segurado, Ángel J.; Colmenero de León, Juan
2011-01-01
We address the general question of how the molecular weight dependence of chain dynamics in unentangled polymers is modified by blending. By dielectric spectroscopy we measure the normal mode relaxation of polyisoprene in blends with a slower component of poly(ter-butylstyrene). Unentangled polyisoprene in the blend exhibits strong deviations from Rouse scaling, approaching 'entangled-like' behavior at low temperatures in concomitance with the increase of the dynamic asymmetry in the blend. T...
Anomalous Raman scattering and lattice dynamics in mono- and few-layer WTe2
Kim, Younghee; Jhon, Young In; Park, June; Kim, Jae Hun; Lee, Seok; Jhon, Young Min
2016-01-01
Tungsten ditelluride (WTe2) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics of this material. Here, we report comprehensive characterization of Raman spectra of WTe2 from bulk to monolayer using experimental and computational methods. We find that mono and bi-layer WTe2 are easily identified by Raman spectroscopy since two or one Raman modes that are observed in higher-layer WTe2 are greatly suppressed below the noise level in the mono- and bi-layer WTe2, respectively. In addition, the frequency of in-plane A17 mode of WTe2 remains almost constant as the layer number decreases, while all the other Raman modes consistently blueshift, which is completely different from the vibrational behavior of hexagonal metal dichalcogenides. First-principles calculation validates experimental results and reveals that anomalous lattice vibrations in WTe2 are attributed to the formation of tungsten chains that make WTe2 structurally one-dimensional.Tungsten ditelluride (WTe2) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics of this material. Here, we report comprehensive characterization of Raman spectra of WTe2 from bulk to monolayer using experimental and computational methods. We find that mono and bi-layer WTe2 are easily identified by Raman spectroscopy since two or one Raman modes that are observed in higher-layer WTe2 are greatly suppressed below the noise level in the mono- and bi-layer WTe2, respectively. In addition, the frequency of in-plane A17 mode of WTe2 remains almost constant as the layer number decreases, while all the other Raman modes consistently blueshift, which is completely different from the vibrational behavior of hexagonal metal dichalcogenides
Hydrodynamic theory of convective transport across a dynamically stabilized diffuse boundary layer
International Nuclear Information System (INIS)
The diffuse boundary layer between miscible liquids is subject to Rayleigh-Taylor instabilities if the heavy fluid is supported by the light one. The resulting rapid interchange of the liquids can be suppressed by enforcing vertical oscillations on the whole system. This dynamic stabilization is incomplete and produces some peculiar novel transport phenomena such as decay off the density profile into several steps, periodic peeling of density sheets of the boundary layer and the appearance of steady vortex flow. The theory presented in this paper identifies the basic mechanism as formation of convective cells leading to enhanced diffusion, and explains previous experimental results with water and ZnJ2-solutions. A nonlinear treatment of the stationary convective flow problem gives the saturation amplitude of the ground mode and provides an upper bound for the maximum convective transport. The hydrodynamic model can be used for visualizing similar transport processes in the plasma of toroidal confinement devices such as sawtooth oscillations in soft disruptions of tokamak discharges and anomalous diffusion by excitation of convective cells. The latter process is investigated here in some detail, leading to the result that the maximum possible transport is of the order of Bohm diffusion. (orig.)
Dynamic Diffusion Estimation in Exponential Family Models
Czech Academy of Sciences Publication Activity Database
Dedecius, Kamil; Sečkárová, Vladimíra
2013-01-01
Roč. 20, č. 11 (2013), s. 1114-1117. ISSN 1070-9908 R&D Projects: GA MŠk 7D12004; GA ČR GA13-13502S Keywords : diffusion estimation * distributed estimation * paremeter estimation Subject RIV: BB - Applied Statistics, Operational Research Impact factor: 1.639, year: 2013 http://library.utia.cas.cz/separaty/2013/AS/dedecius-0396518.pdf
Energy Technology Data Exchange (ETDEWEB)
Vermeersch, B; Mey, G de [Department of Electronics and Information Systems, Ghent University, Sint Pietersnieuwstraat 41, Gent 9000 (Belgium)
2007-04-21
This paper presents a theoretical investigation of the temperature distributions generated by a small heat source mounted on or embedded in semiconductor material. The dynamic thermal behaviour of the structures is studied in the frequency domain using phasor notation for the temperature and heat flux fields. Both classical and hyperbolic thermal conductions are considered. The latter accounts for the finite heat propagation speed, which is necessary for accurately describing very fast transitions. Although a uniform power density is applied, the temperature distribution inside the source is spatially non-uniform. As is already well known, this even holds for steady state conditions. For high frequencies, however, the maximum magnitude (i.e. largest oscillations) of the temperature occurs near the edges and corners of the heat source, rather than in the centre where it could intuitively be expected. This anomalous behaviour is observed for a wide variety of configurations, ranging from a simple 1D analytical slab model to numerical results for a 3D multi-layered electronic package. The classical theory clearly underestimates the edge effect, particularly for submicrometre structures. The substantial deviation from the distributions obtained by non-Fourier theory illustrates that special care should be taken when analysing fast heat transfer in small electronic devices.
Anomalous dynamic back-action in interferometers: beyond the scaling law
Tarabrin, Sergey P; Kaufer, Henning; Schnabel, Roman; Hammerer, Klemens
2013-01-01
We analyze dynamic optomechanical back-action effects in signal-recycled Michelson and Michelson-Sagnac interferometers that are operated off dark port. Up to now, their optomechanics has been studied under dark port condition only. For the dark port case and in the context of gravitational wave detectors, the `scaling law' assured that all back-action effects can be understood on the basis of the much simpler topology of a Fabry-Perot interferometer. Off dark port, our theoretical and experimental analysis reveals certain `anomalous' features as compared to the ones of `canonical' back-action, obtained within the scope of scaling law. In particular, optical damping as a function of detuning acquires a non-zero value on cavity resonance, and several stability/instability regions on either side of the cavity resonance appear. We report on the experimental observation of these instabilities on both sides of the cavity resonance in a Michelson-Sagnac interferometer with a micromechanical membrane. For a certain ...
International Nuclear Information System (INIS)
This paper presents a theoretical investigation of the temperature distributions generated by a small heat source mounted on or embedded in semiconductor material. The dynamic thermal behaviour of the structures is studied in the frequency domain using phasor notation for the temperature and heat flux fields. Both classical and hyperbolic thermal conductions are considered. The latter accounts for the finite heat propagation speed, which is necessary for accurately describing very fast transitions. Although a uniform power density is applied, the temperature distribution inside the source is spatially non-uniform. As is already well known, this even holds for steady state conditions. For high frequencies, however, the maximum magnitude (i.e. largest oscillations) of the temperature occurs near the edges and corners of the heat source, rather than in the centre where it could intuitively be expected. This anomalous behaviour is observed for a wide variety of configurations, ranging from a simple 1D analytical slab model to numerical results for a 3D multi-layered electronic package. The classical theory clearly underestimates the edge effect, particularly for submicrometre structures. The substantial deviation from the distributions obtained by non-Fourier theory illustrates that special care should be taken when analysing fast heat transfer in small electronic devices
Weak diffusion limits of dynamic conditional correlation models
DEFF Research Database (Denmark)
Hafner, Christian M.; Laurent, Sebastien; Violante, Francesco
diffusion matrix of reduced rank. The degeneracy is due to perfect collinearity between the innovations of the volatility and correlation dynamics. For the special case of constant conditional correlations, a non-degenerate diffusion limit can be obtained. Alternative sets of conditions are considered for......The properties of dynamic conditional correlation (DCC) models are still not entirely understood. This paper fills one of the gaps by deriving weak diffusion limits of a modified version of the classical DCC model. The limiting system of stochastic differential equations is characterized by a...... the rate of convergence of the parameters, obtaining time-varying but deterministic variances and/or correlations. A Monte Carlo experiment confirms that the quasi approximate maximum likelihood (QAML) method to estimate the diffusion parameters is inconsistent for any fixed frequency, but that it may...
Diffusion-Oscillatory Dynamics in Liquid Water on Data of Dielectric Spectroscopy
Volkov, A A; Volkov, A A; Sysoev, N N
2016-01-01
When analyzing the broadband absorption spectrum of liquid water (10^10 - 10^13 Hz), we find its relaxation-resonance features to be an indication of Frenkel's translation-oscillation motion of particles, which is fundamentally inherent to liquids. We have developed a model of water structure, of which the dynamics is due to diffusion of particles, neutral H2O molecules and H3O+ and OH- ions - with their periodic localizations and mutual transformations. This model establishes for the first time a link between the dc conductivity, the Debye and the high frequency sub-Debye relaxations and the infrared absorption peak at 180 cm-1. The model reveals the characteristic times of the relaxations, 50 ps and 3 ps, as the lifetimes of water molecules and water ions, respectively. The model sheds light on the anomalous mobility of a proton and casts doubt on the long lifetime of a water molecule, 10 hours, commonly associated with autoionization.
Jourdan, Fred; Benedix, Gretchen; Eroglu, Ela.; Bland, Phil. A.; Bouvier, Audrey.
2014-09-01
The Bunburra Rockhole meteorite is a brecciated anomalous basaltic achondrite containing coarse-, medium- and fine-grained lithologies. Petrographic observations constrain the limited shock pressure to between ca. 10 GPa and 20 GPa. In this study, we carried out nine 40Ar/39Ar step-heating experiments on distinct single-grain fragments extracted from the coarse and fine lithologies. We obtained six plateau ages and three mini-plateau ages. These ages fall into two internally concordant populations with mean ages of 3640 ± 21 Ma (n = 7; P = 0.53) and 3544 ± 26 Ma (n = 2; P = 0.54), respectively. Based on these results, additional 40Ar/39Ar data of fusion crust fragments, argon diffusion modelling, and petrographic observations, we conclude that the principal components of the Bunburra Rockhole basaltic achondrite are from a melt rock formed at ∼3.64 Ga by a medium to large impact event. The data imply that this impact generated high enough energy to completely melt the basaltic target rock and reset the Ar systematics, but only partially reset the Pb-Pb age. We also conclude that a complete 40Ar∗ resetting of pyroxene and plagioclase at this time could not have been achieved at solid-state conditions. Comparison with a terrestrial analog (Lonar crater) shows that the time-temperature conditions required to melt basaltic target rocks upon impact are relatively easy to achieve. Ar data also suggest that a second medium-size impact event occurred on a neighbouring part of the same target rock at ∼3.54 Ga. Concordant low-temperature step ages of the nine aliquots suggest that, at ∼3.42 Ga, a third smaller impact excavated parts of the ∼3.64 Ga and ∼3.54 Ga melt rocks and brought the fragments together. The lack of significant impact activity after 3.5 Ga, as recorded by the Bunburra Rockhole suggests that (1) either the meteorite was ejected in a small secondary parent body where it resided untouched by large impacts, or (2) it was covered by a porous heat
Effects of Lateral Diffusion on the Dynamics of Desorption
Juwono, Tjipto; Hamad, Ibrahim Abou; Rikvold, Per Arne
2012-01-01
The adsorbate dynamics during simultaneous action of desorption and lateral adsorbate diffusion is studied in a simple lattice-gas model by kinetic Monte Carlo simulations. It is found that the action of the coverage-conserving diffusion process during the course of the desorption has two distinct, competing effects: a general acceleration of the desorption process, and a coarsening of the adsorbate configuration through Ostwald ripening. The balance between these two effects is governed by t...
Dynamics Of Innovation Diffusion With Two Step Decision Process
Szymczyk Michał; Kamiński Bogumił
2014-01-01
The paper discusses the dynamics of innovation diffusion among heterogeneous consumers. We assume that customers’ decision making process is divided into two steps: testing the innovation and later potential adopting. Such a model setup is designed to imitate the mobile applications market. An innovation provider, to some extent, can control the innovation diffusion by two parameters: product quality and marketing activity. Using the multi-agent approach we identify factors influencing the sa...
Crossover from superdiffusive to diffusive dynamics in fluctuating light fields
Marqués, Manuel I.
2016-06-01
The expressions for the optical drag force, the equilibrium kinetic energy, and the diffusion constant of an electric dipole in a light field consisting of electromagnetic plane waves with polarizations randomly distributed and fluctuating phases are obtained. The drag force is proportional to the extinction cross section of the dipole and to the intensity. The diffusion constant does not depend on the amplitude of the electromagnetic field and is proportional to the time interval between fluctuations. Numerical simulations for the dynamics of a resonant dipole, initially at rest, show the crossover between the superdiffusive and the diffusive regimes theoretically predicted.
Dynamic aperture and transverse proton diffusion in HERA
International Nuclear Information System (INIS)
The dynamic aperture caused by persistent-current nonlinear field errors is an important concern in the design of superconducting hadron storage rings. The HERA proton ring is the second superconducting accelerator in operation. In this lecture note, its measured dynamic aperture is compared with that inferred from comprehensive trackig studies. To understand the difference between prediction and measurement, a semi-analytical method is developed for evaluating transverse diffusion rates due to various processes, such as modulational diffusion or sweeping diffusion this analysis makes use of parameters for high-order resonances in the transverse phase space, which are obtained by normal-form algorithms using differential-algebra software. This semi-analytical results are consistent wit the measurements, and suggest that the actual dynamic aperture is caused by an interplay of tune modulation and nonlinear magnetic fields
The interstitialcy diffusion in FCC copper: A molecular dynamics study
Energy Technology Data Exchange (ETDEWEB)
Bukkuru, S., E-mail: srinivasaraobukkuru@gmail.com; Rao, A. D. P. [Nucl. Phys Dept., Andhra University, Visakhapatnam– 530003 (India); Warrier, M. [Computational Analysis Division, Bhabha Atomic Research Centre, Visakhapatnam – 530012 (India)
2015-06-24
Damage of materials due to neutron irradiation occurs via energetic cascades caused by energetic primary knock-on atoms (PKA) created by the energetic neutron as it passes through the material. These cascades result in creation of Frenkel Pairs (interstitials and vacancies). The interstitials and vacancies diffuse and recombine to (I) nullify the damage when an interstitial recombines with a vacancy, (II) form interstitial clusters when two or more interstitials recombine, and (III) form vacancy clusters when several vacancies come together. The latter two processes result in change of material properties. Interstitial diffusion has reported time-scales of microseconds and vacancy diffusion has diffusion time-scales of the order of seconds. We have carried out molecular dynamics (MD) simulations of interstitial diffusion in crystal Cu to study the mechanism of diffusion. It is found that interstitialcy diffusion – wherein an interstitial displaces a lattice atom thereby making the lattice atom an interstitial – has time-scales of a few tens of pico-seconds. Therefore we propose that the “interstitialcy diffusion” mechanism could play a major part in the diffusive-recombinations of the Frenkel Pairs created during the cascade.
The interstitialcy diffusion in FCC copper: A molecular dynamics study
International Nuclear Information System (INIS)
Damage of materials due to neutron irradiation occurs via energetic cascades caused by energetic primary knock-on atoms (PKA) created by the energetic neutron as it passes through the material. These cascades result in creation of Frenkel Pairs (interstitials and vacancies). The interstitials and vacancies diffuse and recombine to (I) nullify the damage when an interstitial recombines with a vacancy, (II) form interstitial clusters when two or more interstitials recombine, and (III) form vacancy clusters when several vacancies come together. The latter two processes result in change of material properties. Interstitial diffusion has reported time-scales of microseconds and vacancy diffusion has diffusion time-scales of the order of seconds. We have carried out molecular dynamics (MD) simulations of interstitial diffusion in crystal Cu to study the mechanism of diffusion. It is found that interstitialcy diffusion – wherein an interstitial displaces a lattice atom thereby making the lattice atom an interstitial – has time-scales of a few tens of pico-seconds. Therefore we propose that the “interstitialcy diffusion” mechanism could play a major part in the diffusive-recombinations of the Frenkel Pairs created during the cascade
Institute of Scientific and Technical Information of China (English)
XU; Mingyu(
2001-01-01
［1］Nonnemacher, T. F., Metzler, R., On the Riemann-Liouville fractional calculus and some recent applications, Fractals,1995, 3(3): 557－566.［2］Mainardi, F., Fractional calculus: some basic problems in continuum and statistical mechanics, in Fractals and Fractional Calculus in Continuum Mechanics (eds. Cappinteri, A., Mainardi, F.), New York: Springer Wien, 1997, 291－348.［3］Rossikhin, Y. A., Shitikova, M. V. , Applications of fractional calculus to dynamic problems of linear and nonlinear hereditary mechanics of solids, Appl. Mech. Rev., 1997, 50(1): 15－67.［4］Podlubny, I., Fractional Differential Equations, San Diego: Academic Press, 1999, 86－231.［5］Henry, B. I. , Wearne, S. L. , Fractional reaction-diffusion, Physica A, 2000, 276(3): 448－455.［6］Wyss, W., The fractional diffusion equation, J. Math. Phys., 1986, 27(11): 2782－2785.［7］Bagley, R. L. , Torvik, P. J., On the appearance of the fractional derivative in the behavior of real materials, J. Appl.Mech., 1984, 51(2): 294－298.［8］Mathai, A. M., Saxena, R. K., The H-function with Applications in Statistics and Other Disciplines, New Delhi-BangaloreBombay: Wiley Eastern Limited, 1978, 1－12.［9］Gorentlo, R. , Luchko, Y., Mainardi, F., Wright function as scale-invariant solutions of the diffusion-wave equation, J.Comput. Appl. Math., 2000, 118(1): 175－191.［10］Yih, C. S. , Fluid Mechanics: A Concise Introduction to the Theory, New York: MeGraw-Hill, Inc. , 1969, 321－324.［11］Wu Wangyi, Fluid Mechanics (in Chinese), Beijing: Peking Univ. Press, 1983, 226－230.［12］Mainardi, F., Gorenflo, R., On Mittag-Leffler-Type function in fractional evolution processes, J. Comput. Appl. Math.2000, 118(2): 283－299.［13］Anhand, V. V., Leonenko, N. N., Scaling law for fractional diffusion-wave equations with singular data, Statistics and Probability Letters, 2000, 48(3): 239－252.［14］Kivyakova, V., Multiple (multiindex) Mittag-Leffler functions and relations to
Mohebbi, Akbar; Abbaszadeh, Mostafa; Dehghan, Mehdi
2013-05-01
The aim of this paper is to study the high order difference scheme for the solution of modified anomalous fractional sub-diffusion equation. The time fractional derivative is described in the Riemann-Liouville sense. In the proposed scheme we discretize the space derivative with a fourth-order compact scheme and use the Grünwald-Letnikov discretization of the Riemann-Liouville derivative to obtain a fully discrete implicit scheme. We analyze the solvability, stability and convergence of the proposed scheme using the Fourier method. The convergence order of method is O(τ+h4). Numerical examples demonstrate the theoretical results and high accuracy of the proposed scheme.
Rumor Diffusion in an Interests-Based Dynamic Social Network
Directory of Open Access Journals (Sweden)
Mingsheng Tang
2013-01-01
Full Text Available To research rumor diffusion in social friend network, based on interests, a dynamic friend network is proposed, which has the characteristics of clustering and community, and a diffusion model is also proposed. With this friend network and rumor diffusion model, based on the zombie-city model, some simulation experiments to analyze the characteristics of rumor diffusion in social friend networks have been conducted. The results show some interesting observations: (1 positive information may evolve to become a rumor through the diffusion process that people may modify the information by word of mouth; (2 with the same average degree, a random social network has a smaller clustering coefficient and is more beneficial for rumor diffusion than the dynamic friend network; (3 a rumor is spread more widely in a social network with a smaller global clustering coefficient than in a social network with a larger global clustering coefficient; and (4 a network with a smaller clustering coefficient has a larger efficiency.
Classical diffusive dynamics for the quasiperiodic kicked rotor
Lemarié, Gabriel; Delande, Dominique; Garreau, Jean Claude; Szriftgiser, Pascal
2010-01-01
We study the classical dynamics of a quasiperiodic kicked rotor, whose quantum counterpart is known to be an equivalent of the 3D Anderson model. Using this correspondence allowed for a recent experimental observation of the Anderson transition with atomic matter waves. In such a context, it is particularly important to assert the chaotic character of the classical dynamics of this system. We show here that it is a 3D anisotropic diffusion. Our simple analytical predictions for the associated...
On the origin of the anomalous ultraslow solvation dynamics in heterogeneous environments
Indian Academy of Sciences (India)
Kankan Bhattacharyya; Biman Bagchi
2007-03-01
Many recent experimental studies have reported a surprising ultraslow component (even >10 ns) in the solvation dynamics of a polar probe in an organized assembly, the origin of which is not understood at present. Here we propose two molecular mechanisms in explanation. The first one involves the motion of the `buried water’ molecules (both translation and rotation), accompanied by cooperative relaxation (‘local melting’) of several surfactant chains. An estimate of the time is obtained by using an effective Rouse chain model of chain dynamics, coupled with a mean first passage time calculation. The second explanation invokes self-diffusion of the (di)polar probe itself from a less polar to a more polar region. This may also involve cooperative motion of the surfactant chains in the hydrophobic core, if the probe has a sizeable distribution inside the core prior to excitation, or escape of the probe to the bulk from the surface of the self-assembly. The second mechanism should result in the narrowing of the full width of the emission spectrum with time, which has indeed been observed in recent experiments. It is argued that both the mechanisms may give rise to an ultraslow time constant and may be applicable to different experimental situations. The effectiveness of solvation as a dynamical probe in such complex systems has been discussed.
Measurement of the dynamic characteristics of atmospheric diffusion
International Nuclear Information System (INIS)
A new method is proposed for studying the diffusion of atmospheric pollutants above real sites which considers the actual magnitudes encountered. The dynamic application of this method yields original information. In view of justifying the method, fundamental theories concerning diffusion are presented together with different models for the atmosphere. The atmosphere is then considered as a linear filter to which the process identification method is applied. The pulse response of the filter is examined in the pollutant - time plane. The limits of the method and its field of application are discussed. The concept of ergodism and stationariness are introduced. Various diffusion experiments carried out under different conditions are reviewed. Information on the effect of obstacles, and the roughness of the ground is given together with calculations of the longitudinal diffusion and the transport velocity. A brief description is then given of the apparatus used to measure the concentrations and the meteorological conditions. The correlation calculation is also briefly presented. (author)
Extracting the diffusion tensor from molecular dynamics simulation with Milestoning.
Mugnai, Mauro L; Elber, Ron
2015-01-01
We propose an algorithm to extract the diffusion tensor from Molecular Dynamics simulations with Milestoning. A Kramers-Moyal expansion of a discrete master equation, which is the Markovian limit of the Milestoning theory, determines the diffusion tensor. To test the algorithm, we analyze overdamped Langevin trajectories and recover a multidimensional Fokker-Planck equation. The recovery process determines the flux through a mesh and estimates local kinetic parameters. Rate coefficients are converted to the derivatives of the potential of mean force and to coordinate dependent diffusion tensor. We illustrate the computation on simple models and on an atomically detailed system-the diffusion along the backbone torsions of a solvated alanine dipeptide. PMID:25573551
Bleaching and diffusion dynamics in optofluidic dye lasers
DEFF Research Database (Denmark)
Gersborg-Hansen, Morten; Balslev, Søren; Mortensen, Asger;
2007-01-01
The authors have investigated the bleaching dynamics that occur in optofluidic dye lasers where the liquid laser dye in a microfluidic channel is locally bleached due to optical pumping. They find that for microfluidic devices, the dye bleaching may be compensated through diffusion of dye molecules...... pumping devices. ©2007 American Institute of Physics....
International Nuclear Information System (INIS)
In order to discuss the finite-size effect and the anomalous dynamic scaling behaviour of Das Sarma–Tamborenea growth model, the (1+1)-dimensional Das Sarma–Tamborenea model is simulated on a large length scale by using the kinetic Monte–Carlo method. In the simulation, noise reduction technique is used in order to eliminate the crossover effect. Our results show that due to the existence of the finite-size effect, the effective global roughness exponent of the (1+1)-dimensional Das Sarma–Tamborenea model systematically decreases with system size L increasing when L > 256. This finding proves the conjecture by Aarao Reis[Aarao Reis F D A 2004 Phys. Rev. E 70 031607]. In addition, our simulation results also show that the Das Sarma–Tamborenea model in 1+1 dimensions indeed exhibits intrinsic anomalous scaling behaviour. (general)
Diffusion and internal dynamics of proteins in crowded solutions
Roosen-Runge, Felix; Hennig, Marcus; Seydel, Tilo; Zhang, Fajun; Schreiber, Frank
2013-03-01
Protein function is determined through the interplay of structure, dynamics and the aqueous, but crowded cellular environment. We present a comprehensive study accessing the full hierarchy of protein dynamics in solutions, e.g. vibrations, interdomain motions and diffusion of the entire protein. Quasi-elastic neutron and dynamic light scattering experiments are performed and compared to theoretical predictions. In crowded solutions, both self diffusion Ds and collective diffusion Dc of protein solutions are well described by colloidal concepts, with Ds reduced to 20 % at ~ 20 % volume fraction. Separating the motion of the entire protein molecule, the internal motions are accessed under native conditions. We studied the dynamics before, during and after thermal denaturation, supporting the notion of protein unfolding with subsequent chain entanglement. While long-range motions are reduced in the denatured state, the local flexibility of side chains is found to be enhanced. The frameworks enable further experimental access to the relation of protein function and dynamics at fast time scales.
Post-processing interstitialcy diffusion from molecular dynamics simulations
Bhardwaj, U.; Bukkuru, S.; Warrier, M.
2016-01-01
An algorithm to rigorously trace the interstitialcy diffusion trajectory in crystals is developed. The algorithm incorporates unsupervised learning and graph optimization which obviate the need to input extra domain specific information depending on crystal or temperature of the simulation. The algorithm is implemented in a flexible framework as a post-processor to molecular dynamics (MD) simulations. We describe in detail the reduction of interstitialcy diffusion into known computational problems of unsupervised clustering and graph optimization. We also discuss the steps, computational efficiency and key components of the algorithm. Using the algorithm, thermal interstitialcy diffusion from low to near-melting point temperatures is studied. We encapsulate the algorithms in a modular framework with functionality to calculate diffusion coefficients, migration energies and other trajectory properties. The study validates the algorithm by establishing the conformity of output parameters with experimental values and provides detailed insights for the interstitialcy diffusion mechanism. The algorithm along with the help of supporting visualizations and analysis gives convincing details and a new approach to quantifying diffusion jumps, jump-lengths, time between jumps and to identify interstitials from lattice atoms.
Effects of Lateral Diffusion on the Dynamics of Desorption
Juwono, Tjipto; Rikvold, Per Arne
2012-01-01
The adsorbate dynamics during simultaneous action of desorption and lateral adsorbate diffusion is studied in a simple lattice-gas model by kinetic Monte Carlo simulations. It is found that the action of the coverage-conserving diffusion process during the course of the desorption has two distinct, competing effects: a general acceleration of the desorption process, and a coarsening of the adsorbate configuration through Ostwald ripening. The balance between these two effects is governed by the structure of the adsorbate layer at the beginning of the desorption process.
Bleaching and diffusion dynamics in optofluidic dye lasers
Gersborg-Hansen, M; Kristensen, A; Mortensen, N A
2007-01-01
We have investigated the bleaching dynamics that occur in optofluidic dye lasers where the liquid laser dye in a microfluidic channel is locally bleached due to optical pumping. We find that for microfluidic devices, the dye bleaching may be compensated through diffusion of dye molecules alone. By relying on diffusion rather than convection to generate the necessary dye replenishment, our observation potentially allows for a significant simplification of optofluidic dye laser device layouts, omitting the need for cumbersome and costly external fluidic handling or on-chip microfluidic pumping devices.
Intercrystalline diffusion, dynamical and magnetic properties of grain boundaries
International Nuclear Information System (INIS)
Using the method, developed by the authors, which, combines diffusion over grain boundaries and nuclear gamma-resonance spectroscopy, electron, dynamic, magnetic, diffusion properties of impurity states of atomic probes (57Fe) in the nucleus of grain boundary (GB) of metallic polycrystals and in the regions of neighbour crystallite adjacent to GB, have been investigated. It is shown that for a wide number of metals the atomic probes in the nucleus of wide-angle GB polycrystals occupy the only state, which differs significantly as to its properties from the states in the interstitials of the metal regular lattice
Dynamics Of Innovation Diffusion With Two Step Decision Process
Directory of Open Access Journals (Sweden)
Szymczyk Michał
2014-02-01
Full Text Available The paper discusses the dynamics of innovation diffusion among heterogeneous consumers. We assume that customers’ decision making process is divided into two steps: testing the innovation and later potential adopting. Such a model setup is designed to imitate the mobile applications market. An innovation provider, to some extent, can control the innovation diffusion by two parameters: product quality and marketing activity. Using the multi-agent approach we identify factors influencing the saturation level and the speed of innovation adaptation in the artificial population. The results show that the expected level of innovation adoption among customer’s friends and relative product quality and marketing campaign intensity are crucial factors explaining them. It has to be stressed that the product quality is more important for innovation saturation level and marketing campaign has bigger influence on the speed of diffusion. The topology of social network between customers is found important, but within investigated parameter range it has lover impact on innovation diffusion dynamics than the above mentioned factors
Untangling knots via reaction-diffusion dynamics of vortex strings
Maucher, Fabian
2016-01-01
We introduce and illustrate a new approach to the unknotting problem via the dynamics of vortex strings in a nonlinear partial differential equation of reaction-diffusion type. To untangle a given knot, a Biot-Savart construction is used to initialize the knot as a vortex string in the FitzHugh-Nagumo equation. Remarkably, we find that the subsequent evolution preserves the topology of the knot and can untangle an unknot into a circle. Illustrative test case examples are presented, including the untangling of a hard unknot known as the culprit. Our approach to the unknotting problem has two novel features, in that it applies field theory rather than particle mechanics and uses reaction-diffusion dynamics in place of energy minimization.
Untangling Knots Via Reaction-Diffusion Dynamics of Vortex Strings.
Maucher, Fabian; Sutcliffe, Paul
2016-04-29
We introduce and illustrate a new approach to the unknotting problem via the dynamics of vortex strings in a nonlinear partial differential equation of reaction-diffusion type. To untangle a given knot, a Biot-Savart construction is used to initialize the knot as a vortex string in the FitzHugh-Nagumo equation. Remarkably, we find that the subsequent evolution preserves the topology of the knot and can untangle an unknot into a circle. Illustrative test case examples are presented, including the untangling of a hard unknot known as the culprit. Our approach to the unknotting problem has two novel features, in that it applies field theory rather than particle mechanics and uses reaction-diffusion dynamics in place of energy minimization. PMID:27176541
Untangling Knots Via Reaction-Diffusion Dynamics of Vortex Strings
Maucher, Fabian; Sutcliffe, Paul
2016-04-01
We introduce and illustrate a new approach to the unknotting problem via the dynamics of vortex strings in a nonlinear partial differential equation of reaction-diffusion type. To untangle a given knot, a Biot-Savart construction is used to initialize the knot as a vortex string in the FitzHugh-Nagumo equation. Remarkably, we find that the subsequent evolution preserves the topology of the knot and can untangle an unknot into a circle. Illustrative test case examples are presented, including the untangling of a hard unknot known as the culprit. Our approach to the unknotting problem has two novel features, in that it applies field theory rather than particle mechanics and uses reaction-diffusion dynamics in place of energy minimization.
Spatiotemporal mapping of diffusion dynamics and organization in plasma membranes
Bag, Nirmalya; Ng, Xue Wen; Sankaran, Jagadish; Wohland, Thorsten
2016-09-01
Imaging fluorescence correlation spectroscopy (FCS) and the related FCS diffusion law have been applied in recent years to investigate the diffusion modes of lipids and proteins in membranes. These efforts have provided new insights into the membrane structure below the optical diffraction limit, new information on the existence of lipid domains, and on the influence of the cytoskeleton on membrane dynamics. However, there has been no systematic study to evaluate how domain size, domain density, and the probe partition coefficient affect the resulting imaging FCS diffusion law parameters. Here, we characterize the effects of these factors on the FCS diffusion law through simulations and experiments on lipid bilayers and live cells. By segmenting images into smaller 7 × 7 pixel areas, we can evaluate the FCS diffusion law on areas smaller than 2 µm and thus provide detailed maps of information on the membrane structure and heterogeneity at this length scale. We support and extend this analysis by deriving a mathematical expression to calculate the mean squared displacement (MSDACF) from the autocorrelation function of imaging FCS, and demonstrate that the MSDACF plots depend on the existence of nanoscopic domains. Based on the results, we derive limits for the detection of domains depending on their size, density, and relative viscosity in comparison to the surroundings. Finally, we apply these measurements to bilayers and live cells using imaging total internal reflection FCS and single plane illumination microscopy FCS.
Dynamic diffuse optical tomography imaging of peripheral arterial disease
Khalil, Michael A.; Kim, Hyun K.; Kim, In-Kyong; Flexman, Molly; Dayal, Rajeev; Shrikhande, Gautam; Hielscher, Andreas H.
2012-01-01
Peripheral arterial disease (PAD) is the narrowing of arteries due to plaque accumulation in the vascular walls. This leads to insufficient blood supply to the extremities and can ultimately cause cell death. Currently available methods are ineffective in diagnosing PAD in patients with calcified arteries, such as those with diabetes. In this paper we investigate the potential of dynamic diffuse optical tomography (DDOT) as an alternative way to assess PAD in the lower extremities. DDOT is a ...
Dynamics of diffusive bubble growth in magmas: Isothermal case
Prousevitch, A. A.; Sahagian, D. L.; Anderson, A. T.
1993-12-01
We have conducted a parametric study and developed a new cell model describing diffusion-induced growth of closely spaced bubbles in magmatic sytems. The model accounts for (1) the effects of advection of melt resulting from bubble growth, and its affect on the local concentration profile; (2) dynamic resistence of the viscous melt during diffusive growth; (3) diffusion of volatiles in response to evolving concentration gradients; (4) mass balance between dissolved volatiles and gas inside the bubble; (5) changes in the equilibrium saturation concentration at the bubble-melt interface; (6) total pressure within the bubble consisting of ambient, surface tension, and dynamic pressures. The results of this study reveal that bubble growth depends strongly on ambient pressure, volatile oversaturation in the melt, and diffusivity coefficients, but only weakly on bubble separation and inital bubble radius. Increased volatile oversaturation increases growth rate to the point at which it actually reduces time for complete bubble growth. This counterintuitive result is due to significant advective volatile flux toward the bubble interface during growth. Viscosity controls growth dynamics only for cases of high viscosity (greater than 10(exp 4) Pa s). The documentation of the evolution of gas fraction in the melt and bubble wall thickness as a function of time makes it possible to estimate bubble disruption thresholds which bear on volcanic eruption mechanisms. Model results can be applied to the larger-scale problem of magmatic degassing in terms of bubble coalescence, flotation and the development of foams in magma chambers and vent systems, and ultimately to the dynamics of eruption mechanisms.
Estimation of water diffusivity parameters on grape dynamic drying
Ramos, Inês N.; Miranda, João M.R.; Brandão, Teresa R. S.; Cristina L.M. Silva
2010-01-01
A computer program was developed, aiming at estimating water diffusivity parameters in a dynamic drying process with grapes, assessing the predictability of corresponding non-isothermal drying curves. It numerically solves Fick’s second law for a sphere, by explicit finite differences, in a shrinking system, with anisotropic properties and changing boundary conditions. Experiments were performed in a pilot convective dryer, with simulated air conditions observed in a solar dryer, for modellin...
Diffusion measurements in fluids by dynamic light scattering
Fröba, Andreas P.; Leipertz, Alfred
2016-01-01
In the course of the last thirty years, light scattering techniques have been used with increasing effort and attention for the measurement of the thermophysical properties of pure fluids and fluid mixtures. Here, an introduction is given to dynamic light scattering (DLS) as a valuable tool for the measurement of diffusion processes. First, the basic principles of the method and its experimental realization are presented in some detail. A survey on various applications is given, which espe...
Anomalous bootstrap current due to drift waves
International Nuclear Information System (INIS)
An anomalous parallel current driven by radial flux in tokamak is discussed. Drift waves, which cause an anomalous cross field diffusion, can generate a parallel current in a sheared magnetic field, if the fluctuation level has radial dependence. (author)
Dynamics of Robertson–Walker spacetimes with diffusion
Energy Technology Data Exchange (ETDEWEB)
Alho, A., E-mail: aalho@math.ist.utl.pt [Centro de Análise Matemática, Geometria e Sistemas Dinâmicos, Instituto Superior Técnico, Lisboa (Portugal); Calogero, S., E-mail: calogero@chalmers.se [Department of Mathematical Sciences, Chalmers University of Technology, University of Gothenburg, Gothenburg (Sweden); Machado Ramos, M.P., E-mail: mpr@mct.uminho.pt [Departamento de Matemática e Aplicações, Universidade do Minho, Guimarães (Portugal); Soares, A.J., E-mail: ajsoares@math.uminho.pt [Centro de Matemática, Universidade do Minho, Braga (Portugal)
2015-03-15
We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time directions and which undergo accelerated expansion at all times.
Convection-diffusion effects in marathon race dynamics
Rodriguez, E.; Espinosa-Paredes, G.; Alvarez-Ramirez, J.
2014-01-01
In the face of the recent terrorist attack event on the 2013 Boston Marathon, the increasing participation of recreational runners in large marathon races has imposed important logistical and safety issues for organizers and city authorities. An accurate understanding of the dynamics of the marathon pack along the race course can provide important insights for improving safety and performance of these events. On the other hand, marathon races can be seen as a model of pedestrian movement under confined conditions. This work used data of the 2011 Chicago Marathon event for modeling the dynamics of the marathon pack from the corral zone to the finish line. By considering the marathon pack as a set of particles moving along the race course, the dynamics are modeled as a convection-diffusion partial differential equation with position-dependent mean velocity and diffusion coefficient. A least-squares problem is posed and solved with optimization techniques for fitting field data from the 2011 Chicago Marathon. It was obtained that the mean pack velocity decreases while the diffusion coefficient increases with distance. This means that the dispersion rate of the initially compact marathon pack increases as the marathon race evolves along the race course.
Zhigao Liao; Jiuping Xu; Liming Yao
2013-01-01
This paper studies the innovation diffusion problem with the affection of urbanization, proposing a dynamical innovation diffusion model with fuzzy coefficient, and uses the shifting rate of people from rural areas stepping into urban areas to show the process of urbanization. The numerical simulation shows the diffusion process for telephones in China with Genetic Algorithms and this model is effective to show the process of innovation diffusion with the condition of urbanization process.
Modeling Dynamics of Diffusion Across Heterogeneous Social Networks: News Diffusion in Social Media
Directory of Open Access Journals (Sweden)
Peter Christen
2013-10-01
Full Text Available Diverse online social networks are becoming increasingly interconnected by sharing information. Accordingly, emergent macro-level phenomena have been observed, such as the synchronous spread of information across different types of social media. Attempting to analyze the emergent global behavior is impossible from the examination of a single social platform, and dynamic influences between different social networks are not negligible. Furthermore, the underlying structural property of networks is important, as it drives the diffusion process in a stochastic way. In this paper, we propose a macro-level diffusion model with a probabilistic approach by combining both the heterogeneity and structural connectivity of social networks. As real-world phenomena, we explore instances of news diffusion across different social media platforms from a dataset that contains over 386 million web documents covering a one-month period in early 2011. We find that influence between different media types is varied by the context of information. News media are the most influential in the arts and economy categories, while social networking sites (SNS and blog media are in the politics and culture categories, respectively. Furthermore, controversial topics, such as political protests and multiculturalism failure, tend to spread concurrently across social media, while entertainment topics, such as film releases and celebrities, are more likely driven by interactions within single social platforms. We expect that the proposed model applies to a wider class of diffusion phenomena in diverse fields and that it provides a way of interpreting the dynamics of diffusion in terms of the strength and directionality of influences among populations.
Origins of Anomalous Transport in Disordered Media: Structural and Dynamic Controls
Edery, Yaniv; Guadagnini, Alberto; Berkowitz, Brian
2013-01-01
We quantitatively identify the origin of anomalous transport in a representative model of a heterogeneous system---tracer migration in the complex flow patterns of a lognormally distributed hydraulic conductivity ($K$) field. The transport, determined by a particle tracking technique, is characterized by breakthrough curves; the ensemble averaged curves document anomalous transport in this system, which is entirely accounted for by a truncated power-law distribution of local transition times $\\psi(t)$ within the framework of a continuous time random walk. Unique to this study is the linking of $\\psi(t)$ directly to the system heterogeneity. We assess the statistics of the dominant preferred pathways by forming a particle-visitation weighted histogram $\\{wK\\}$. Converting the ln($K$) dependence of $\\{wK\\}$ into time yields the equivalence of $\\{wK\\}$ and $\\psi(t)$, and shows the part of $\\{wK\\}$ that forms the power-law of $\\psi(t)$, which is the origin of anomalous transport. We also derive an expression defi...
Origins of Anomalous Transport in Disordered Media: Structural and Dynamic Controls
Edery, Y.; Scher, H.; Guadagnini, A.; Berkowitz, B.
2013-12-01
We quantitatively identify the origin of anomalous transport in a representative model of a heterogeneous system-tracer migration in the complex flow patterns of a lognormally distributed hydraulic conductivity (K) field. The transport, determined by a particle tracking technique, is characterized by breakthrough curves; the ensemble averaged curves document anomalous transport in this system, which is entirely accounted for by a truncated power-law distribution of local transition times ψ(t) within the framework of a continuous time random walk. Unique to this study is the linking of ψ(t) directly to the system heterogeneity. We assess the statistics of the dominant preferred pathways by forming a particle-visitation weighted histogram {wK}. Converting the ln(K) dependence of {wK} into time yields the equivalence of {wK} and ψ(t), and shows the part of {wK} that forms the power-law of ψ(t), which is the origin of anomalous transport. We also derive an expression defining the power law exponent in terms of the {wK} parameters. This equivalence is a remarkable result, particularly given the correlated K-field, the complexity of the flow field and the statistics of the particle transitions.
Dynamics of the diffusive DM-DE interaction – Dynamical system approach
Haba, Zbigniew; Stachowski, Aleksander; Szydłowski, Marek
2016-07-01
We discuss dynamics of a model of an energy transfer between dark energy (DE) and dark matter (DM) . The energy transfer is determined by a non-conservation law resulting from a diffusion of dark matter in an environment of dark energy. The relativistic invariance defines the diffusion in a unique way. The system can contain baryonic matter and radiation which do not interact with the dark sector. We treat the Friedman equation and the conservation laws as a closed dynamical system. The dynamics of the model is examined using the dynamical systems methods for demonstration how solutions depend on initial conditions. We also fit the model parameters using astronomical observation: SNIa, H(z), BAO and Alcock-Paczynski test. We show that the model with diffuse DM-DE is consistent with the data.
Dynamics of the diffusive DM-DE interaction--dynamical system approach
Haba, Zbigniew; Szydlowski, Marek
2016-01-01
We discuss dynamics of a model of an energy transfer between dark energy (DE) and dark matter (DM). The energy transfer is determined by a non-conservation law resulting from a diffusion of dark matter in an environment of dark energy. The relativistic invariance defines the diffusion in a unique way. The system can contain baryonic matter and radiation which do not interact with the dark sector. We treat the Friedman equation and the conservation laws as a closed dynamical system. The dynamics of the model is examined using the dynamical systems methods for demonstration how solutions depend on initial conditions. We also fit the model parameters using astronomical observation: SNIa, $H(z)$, BAO and Alcock-Paczynski test. We show that the model with diffuse DM-DE is consistent with the data.
Basu, Tania; Tarafdar, Sujata
2016-08-01
Solid polymer electrolytes with gelatin as host polymer are subjected to gamma irradiation with dose varying from 0 to 100 kGy. Two sets of samples are studied, one with and one without addition of lithium perchlorate as ionic salt. The effect of varying plasticizer content, salt fraction and radiation dose on the impedance is measured. The dc (direct current) ion-conductivity is determined from impedance spectroscopy results. It is shown that relative to the unirradiated sample, the room temperature dc ion-conductivity decreases in general on irradiation, by an order of magnitude. However on comparing results for the irradiated samples, a dose of 60 kGy is seen to produce the highest ion-conductivity. Considering the variation of all parameters, the highest dc-conductivity of 6.06x10-2 S/m is obtained for the un-irradiated sample at room temperature, with 12.5 wt% LiClO4 and 35.71 wt% of glycerol as plasticizer. The samples are characterized in addition by XRD, SEM and FTIR respectively. Cyclic voltametry is performed for the confirmation of the electrolytic performance for pristine and gamma irradiated samples. To understand the experimental results, a model incorporating normal, as well as anomalous diffusion has been applied. Generalized calculus is used to model the anomalous diffusion. It is shown that this model successfully reproduces the experimental frequency dependence of the complex impedance for samples subjected to varying gamma dose. The physical interpretation of the model parameters and their variation with sample composition and irradiation dose is discussed.
Diffusion dynamics in liquid and undercooled Al-Ni alloys
International Nuclear Information System (INIS)
This work presents data on Ni self-diffusion in binary Al-Ni alloys with high precision. For this, we combined two techniques: containerless electromagnetic levitation to position the samples, and neutron time-of-flight spectroscopy to measure the decay of the self-correlation. This combination offers new measurement ranges, especially at low temperatures, several hundreds of Kelvin below the liquidus temperature. Because without container, the primary cristallization seeds for the metallic melt are avoided. But it is also possible to measure reactive samples, and at very high temperatures at and above 2000K, as problematic reactions with the containing cask won't occur. Furthermore this technique also enables measurements at higher momentum transfer q, as one does not have to limit the q-range of the measurement to avoid Bragg peaks of the solid container material. By this time-of-flight spectroscopy on levitated metallic melts, it is possible to determine the Ni self-diffusion in these alloys directly and on an absolute scale. The dependence of the Ni self-diffusion coefficient on temperature and concentration was studied in pure Ni and binary Al-Ni alloys. In a temperature range of several hundred degrees, we always found Arrhenius-like temperature dependence of the diffusion, irrespective of possible undercooling. In the context of these measurements, we also studied the interdependence between diffusivity in the metallic melt and its quasielastic structure factor. Time-of-flight spectroscopy made it also possible to derive the dynamic partial structure factors of the binary alloy Al80Ni20. All this to enable a better understanding of the atomic processes in the metallic melt, especially of the undercooled melt, as an alloy is always formed out of the (undercooled) melt of its stoichiometric compounds. For this, material transport and diffusion are immensely important. The final goal would be materials design from the melt, i.e. the prediction of alloy
Diffusion dynamics in liquid and undercooled Al-Ni alloys
Energy Technology Data Exchange (ETDEWEB)
Stueber, Sebastian
2009-10-05
This work presents data on Ni self-diffusion in binary Al-Ni alloys with high precision. For this, we combined two techniques: containerless electromagnetic levitation to position the samples, and neutron time-of-flight spectroscopy to measure the decay of the self-correlation. This combination offers new measurement ranges, especially at low temperatures, several hundreds of Kelvin below the liquidus temperature. Because without container, the primary cristallization seeds for the metallic melt are avoided. But it is also possible to measure reactive samples, and at very high temperatures at and above 2000K, as problematic reactions with the containing cask won't occur. Furthermore this technique also enables measurements at higher momentum transfer q, as one does not have to limit the q-range of the measurement to avoid Bragg peaks of the solid container material. By this time-of-flight spectroscopy on levitated metallic melts, it is possible to determine the Ni self-diffusion in these alloys directly and on an absolute scale. The dependence of the Ni self-diffusion coefficient on temperature and concentration was studied in pure Ni and binary Al-Ni alloys. In a temperature range of several hundred degrees, we always found Arrhenius-like temperature dependence of the diffusion, irrespective of possible undercooling. In the context of these measurements, we also studied the interdependence between diffusivity in the metallic melt and its quasielastic structure factor. Time-of-flight spectroscopy made it also possible to derive the dynamic partial structure factors of the binary alloy Al{sub 80}Ni{sub 20}. All this to enable a better understanding of the atomic processes in the metallic melt, especially of the undercooled melt, as an alloy is always formed out of the (undercooled) melt of its stoichiometric compounds. For this, material transport and diffusion are immensely important. The final goal would be materials design from the melt, i.e. the prediction
Molecular dynamics investigation of tracer diffusion in a simple liquid
International Nuclear Information System (INIS)
Extensive Molecular-Dynamics (MD) simulations have been carried out for a model trace-solvent system made up of 100 solvent molecules and 8 tracer molecules interacting through truncated Lennard-Jones potentials. The influence of the size ratio between solute and solvent, of their mass ratio and of the solvent viscosity on the diffusivity of a small tracer were investigated. Positive deviations from a Stokes-Einstein behaviour are observed, in qualitative agreement with experimental observations. It was also observed that as tracer and solvent become increasingly dissimilar, their respective dynamics becomes decoupled. We suggest that such decouplings can be interpreted by writing their mobility of the tracer as the sum of two terms, the first one arising from a coupling between tracer dynamics and hydrodynamics modes of the solvent, and the second one describing jump motion in a locally nearly frozen environment. (author). 17 refs, 4 figs, 6 tabs
Modeling Earth's Outer Radiation Belt Electron Dynamics---Radial Diffusion, Heating, and Loss
Tu, Weichao
Earth's outer radiation belt is a relativistic electron environment that is hazardous to space systems. It is characterized by large variations in the electron flux, which are controlled by the competition between source, transport, and loss processes. One of the central questions in outer radiation belt research is to resolve the relative contribution of radial diffusion, wave heating, and loss to the enhancement and decay of the radiation belt electrons. This thesis studies them together and separately. Firstly, we develop an empirical Fokker-Planck model that includes radial diffusion, an internal source, and finite electron lifetimes parameterized as functions of geomagnetic indices. By simulating the observed electron variations, the model suggests that the required magnitudes of radial diffusion and internal heating for the enhancement of energetic electrons in the outer radiation belt vary from storm to storm, and generally internal heating contributes more to the enhancements of MeV energy electrons at L=4 (L is approximately the radial distance in Earth radii at the equator). However, since the source, transport, and loss terms in the model are empirical, the model results have uncertainties. To eliminate the uncertainty in the loss rate, both the precipitation and the adiabatic loss of radiation belt electrons are quantitatively studied. Based on the observations from Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX), a Drift-Diffusion model is applied to quantify electron precipitation loss, which is the dominant non-adiabatic loss mechanism for electrons in the heart of the outer radiation belt. Model results for a small storm, a moderate storm, and an intense storm indicate that fast precipitation losses of relativistic electrons, on the time scale of hours, persistently occur in the storm main phases and with more efficient losses at higher energies over wide range of L regions. Additionally, calculations of adiabatic effects on radiation
Reaction-Diffusion Modeling ERK- and STAT-Interaction Dynamics
Directory of Open Access Journals (Sweden)
Georgiev Nikola
2006-01-01
Full Text Available The modeling of the dynamics of interaction between ERK and STAT signaling pathways in the cell needs to establish the biochemical diagram of the corresponding proteins interactions as well as the corresponding reaction-diffusion scheme. Starting from the verbal description available in the literature of the cross talk between the two pathways, a simple diagram of interaction between ERK and STAT5a proteins is chosen to write corresponding kinetic equations. The dynamics of interaction is modeled in a form of two-dimensional nonlinear dynamical system for ERK—and STAT5a —protein concentrations. Then the spatial modeling of the interaction is accomplished by introducing an appropriate diffusion-reaction scheme. The obtained system of partial differential equations is analyzed and it is argued that the possibility of Turing bifurcation is presented by loss of stability of the homogeneous steady state and forms dissipative structures in the ERK and STAT interaction process. In these terms, a possible scaffolding effect in the protein interaction is related to the process of stabilization and destabilization of the dissipative structures (pattern formation inherent to the model of ERK and STAT cross talk.
Colmenero, J.
2013-05-01
In a recent paper by Ngai and Capaccioli ["Unified explanation of the anomalous dynamic properties of highly asymmetric polymer blends," J. Chem. Phys. 138, 054903 (2013), 10.1063/1.4789585] the authors claimed that the so-called coupling model (CM) provides a unified explanation of all dynamical anomalies that have been reported for dynamically asymmetric blends over last ten years. Approximately half of the paper is devoted to chain-dynamic properties involving un-entangled polymers. According to the authors, the application of the CM to these results is based on the existence of a crossover at a time tc ≈ 1-2 ns of the magnitudes describing chain-dynamics. Ngai and Capaccioli claimed that the existence of such a crossover is supported by the neutron scattering and MD-simulation results, corresponding to the blend poly(methyl methacrylate)/poly(ethylene oxide), by Niedzwiedz et al. [Phys. Rev. Lett. 98, 168301 (2007), 10.1103/PhysRevLett.98.168301] and Brodeck et al. [Macromolecules 43, 3036 (2010), 10.1021/ma902820a], respectively. Being one of the authors of these two papers, I will demonstrate here that there is no evidence supporting such a crossover in the data reported in these papers.
MO-G-BRF-07: Anomalously Fast Diffusion of Carbon Nanotubes Carriers in 3D Tissue Model
International Nuclear Information System (INIS)
Purpose: We aim to investigate and understand diffusion process of carbon nanotubes (CNTs) and other nanoscale particles in tissue and organs. Methods: In this research, we utilized a 3D model tissue of hepatocellular carcinoma (HCC)cultured in inverted colloidal crystal (ICC) scaffolds to compare the diffusivity of CNTs with small molecules such as Rhodamine and FITC in vitro, and further investigated the transportation of CNTs with and without targeting ligand, TGFβ1. The real-time permeation profiles of CNTs in HCC tissue model with high temporal and spatial resolution was demonstrated by using standard confocal microscopy. Quantitative analysis of the diffusion process in 3D was carried out using luminescence intensity in a series of Z-stack images obtained for different time points of the diffusion process after initial addition of CNTs or small molecules to the cell culture and the image data was analyzed by software ImageJ and Mathematica. Results: CNTs display diffusion rate in model tissues substantially faster than small molecules of the similar charge such as FITC, and the diffusion rate of CNTs are significantly enhanced with targeting ligand, TGFβ1. Conclusion: In terms of the advantages of in-vitro model, we were able to have access to measuring the rate of CNT penetration at designed conditions with variable parameters. And the findings by using this model, changed our understanding about advantages of CNTs as nanoscale drug carriers and provides design principles for making new drug carriers for both treatment and diagnostics. Additionally the fast diffusion opens the discussion of the best possible drug carriers to reach deep parts of cancerous tissues, which is often a prerequisite for successful cancer treatment. This work was supported by the Center for Photonic and Multiscale Nanomaterials funded by National Science Foundation Materials Research Science and Engineering Center program DMR 1120923. The work was also partially supported by NSF
Diffusion dynamics of an electron gas confined between two plates
Degond, Pierre; Latocha, Vladimir; Mancini, Simona; Mellet, Antoine
2002-01-01
We consider electrons constrained to move in the gap between two plane parallel plates, confined by a magnetic field perpendicular to the plates and accelerated by an electric field parallel to them. The electrons are subject to elastic collisions against the solid plates on the one hand and against atoms or ions in the gap between the plates on the other hand. Under the assumption that the dynamics is dominated by the collisions, we derive a diffusion type model for the energy distribution f...
Dynamic hysteresis modeling including skin effect using diffusion equation model
Hamada, Souad; Louai, Fatima Zohra; Nait-Said, Nasreddine; Benabou, Abdelkader
2016-07-01
An improved dynamic hysteresis model is proposed for the prediction of hysteresis loop of electrical steel up to mean frequencies, taking into account the skin effect. In previous works, the analytical solution of the diffusion equation for low frequency (DELF) was coupled with the inverse static Jiles-Atherton (JA) model in order to represent the hysteresis behavior for a lamination. In the present paper, this approach is improved to ensure the reproducibility of measured hysteresis loops at mean frequency. The results of simulation are compared with the experimental ones. The selected results for frequencies 50 Hz, 100 Hz, 200 Hz and 400 Hz are presented and discussed.
Dynamics of the diffusive DM-DE interaction--dynamical system approach
Haba, Zbigniew; Stachowski, Aleksander; Szydlowski, Marek
2016-01-01
We discuss dynamics of a model of an energy transfer between dark energy (DE) and dark matter (DM). The energy transfer is determined by a non-conservation law resulting from a diffusion of dark matter in an environment of dark energy. The relativistic invariance defines the diffusion in a unique way. The system can contain baryonic matter and radiation which do not interact with the dark sector. We treat the Friedman equation and the conservation laws as a closed dynamical system. The dynami...
Parallel Algorithm and Dynamic Exponent for Diffusion-limited Aggregation
Moriarty, K J M; Greenlaw, R
1997-01-01
A parallel algorithm for ``diffusion-limited aggregation'' (DLA) is described and analyzed from the perspective of computational complexity. The dynamic exponent z of the algorithm is defined with respect to the probabilistic parallel random-access machine (PRAM) model of parallel computation according to $T \\sim L^{z}$, where L is the cluster size, T is the running time, and the algorithm uses a number of processors polynomial in D_2 is the second generalized dimension. Simulations of DLA are carried out to measure D_2 and to test scaling assumptions employed in the complexity analysis of the parallel algorithm. It is plausible that the parallel algorithm attains the minimum possible value of the dynamic exponent in which case z characterizes the intrinsic history dependence of DLA.
Dynamics of diffuse oceanic plate boundaries: insensitivity to rheology
Zatman, Stephen; Gordon, Richard G.; Mutnuri, Kartik
2005-07-01
Diffuse plate boundaries, which are zones of deformation hundreds to thousands of kilometres wide, occur in both continental and oceanic lithosphere. Here, we build on our prior work in which we described analytic approximations to simple dynamical models that assume that the vertically averaged viscous force resisting deformation in diffuse oceanic plate boundaries (DOPBs) is described by either a linear Newtonian viscous rheology or a yield-stress (high-exponent power-law) rheology. An important observation is that the poles of relative rotation of adjacent component plates tend to lie in the diffuse plate boundary that separates them. A key cause of this tendency is that a faster spin is needed to balance a component of torque through the middle of a diffuse plate boundary than to balance an equal component of torque lying 90° from the middle of the diffuse boundary. The strength of that tendency depends on rheology, however, with the tendency being stronger for a yield-stress rheology than for a Newtonian viscous rheology. For the special case of the pole of rotation lying outside of and along the strike of the boundary, these large differences can be simply explained in terms of the distribution of boundary-perpendicular normal forces acting across the boundary. In the Newtonian case, the distribution of forces has an along-strike gradient that can balance a component of torque about the middle of the boundary, while in the yield-stress case, the distribution of forces has zero along-strike gradient and cannot balance a component of torque about the middle of the diffuse plate boundary. To expand our analysis to intermediate power laws of geophysical interest (i.e. power-law exponents of 3 to 30), as well as to investigate more thoroughly the behaviour for a high-exponent power law, we numerically integrate the force distribution to obtain the torques. Results for intermediate power laws resemble the yield-stress rheology much more than they resemble the
DEFF Research Database (Denmark)
Lund, F. W.; Lomholt, M. A.; Solanko, L. M.;
2012-01-01
latter probe has utility for prolonged live-cell imaging of sterol transport. Results: We found that BChol is very photostable under two-photon (2P)-excitation allowing the acquisition of several hundred frames without significant photobleaching. Therefore, long-term tracking and diffusion measurements...... are possible. Two-photon temporal image correlation spectroscopy (2P-TICS) provided evidence for spatially heterogeneous diffusion constants of BChol varying over two orders of magnitude from the cell interior towards the plasma membrane, where D similar to 1.3 mu m(2)/s. Number and brightness (N...... slow directed transport with an average velocity of v similar to 6 x 10(-3) mu m/s was observed. We present an analytical model that bridges the two regimes and fit this model to vesicle trajectories from control cells and cells with disrupted microtubule or actin filaments. Both treatments reduced the...
Al-Shakran, Mohammad; Kibler, Ludwig A.; Jacob, Timo; Ibach, Harald; Beltramo, Guillermo L.; Giesen, Margret
2016-09-01
This is Part I of two closely related papers, where we show that the specific adsorption of anions leads to a failure of the nearest-neighbor Ising model to describe island perimeter curvatures on Au(100) electrodes in dilute KBr, HCl and H2SO4 electrolytes and the therewith derived step diffusivity vs. step orientation. This result has major consequences for theoretical studies aiming at the understanding of growth, diffusion and degradation phenomena. Part I focuses on the experimental data. As shown theoretically in detail in Part II (doi:10.1016/j.susc.2016.03.022), a set of nearest-neighbor and next-nearest-neighbor interaction energies (ɛNN, ɛNNN) can uniquely be derived from the diffusivity of steps along and . We find strong repulsive next-nearest neighbor (NNN) interaction in KBr and HCl, whereas NNN interaction is negligibly for H2SO4. The NNN repulsive interaction energy ɛNNN therefore correlates positively with the Gibbs adsorption energy of the anions. We find furthermore that ɛNNN increases with increasing Br- and Cl- coverage. The results for ɛNN and ɛNNN are quantitatively consistent with the coverage dependence of the step line tension. We thereby establish a sound experimental base for theoretical studies on the energetics of steps in the presence of specific adsorption.
Diffusion dynamics in the disordered Bose Hubbard model
Wadleigh, Laura; Russ, Philip; Demarco, Brian
2016-05-01
We explore the dynamics of diffusion for out-of-equilibrium superfluid, Mott insulator, and Bose glass states using an atomic realization of the disordered Bose Hubbard (DBH) model. Dynamics in strongly correlated systems, especially far from equilibrium, are not well understood. The introduction of disorder further complicates these systems. We realize the DBH model--which has been central to our understanding of quantum phase transitions in disordered systems--using ultracold Rubidium-87 atoms trapped in a cubic disordered optical lattice. By tightly focusing a beam into the center of the gas, we create a hole in the atomic density profile. We achieve Mott insulator, superfluid, or Bose glass states by varying the interaction and disorder strength, and measure the time evolution of the density profile after removing the central barrier. This allows us to infer diffusion rates from the velocities at the edge of the hole and to look for signatures of superfluid puddles in the Bose glass state. We acknowledge funding from NSF Grant PHY 15-05468, NSF Grant DGE-1144245, and ARO Grant W911NF-12-1-0462.
Chaotic dynamics and diffusion in a piecewise linear equation
Energy Technology Data Exchange (ETDEWEB)
Shahrear, Pabel, E-mail: pabelshahrear@yahoo.com [Department of Mathematics, Shah Jalal University of Science and Technology, Sylhet–3114 (Bangladesh); Glass, Leon, E-mail: glass@cnd.mcgill.ca [Department of Physiology, 3655 Promenade Sir William Osler, McGill University, Montreal, Quebec H3G 1Y6 (Canada); Edwards, Rod, E-mail: edwards@uvic.ca [Department of Mathematics and Statistics, University of Victoria, P.O. Box 1700 STN CSC, Victoria, British Columbia V8W 2Y2 (Canada)
2015-03-15
Genetic interactions are often modeled by logical networks in which time is discrete and all gene activity states update simultaneously. However, there is no synchronizing clock in organisms. An alternative model assumes that the logical network is preserved and plays a key role in driving the dynamics in piecewise nonlinear differential equations. We examine dynamics in a particular 4-dimensional equation of this class. In the equation, two of the variables form a negative feedback loop that drives a second negative feedback loop. By modifying the original equations by eliminating exponential decay, we generate a modified system that is amenable to detailed analysis. In the modified system, we can determine in detail the Poincaré (return) map on a cross section to the flow. By analyzing the eigenvalues of the map for the different trajectories, we are able to show that except for a set of measure 0, the flow must necessarily have an eigenvalue greater than 1 and hence there is sensitive dependence on initial conditions. Further, there is an irregular oscillation whose amplitude is described by a diffusive process that is well-modeled by the Irwin-Hall distribution. There is a large class of other piecewise-linear networks that might be analyzed using similar methods. The analysis gives insight into possible origins of chaotic dynamics in periodically forced dynamical systems.
Chaotic dynamics and diffusion in a piecewise linear equation
Shahrear, Pabel; Glass, Leon; Edwards, Rod
2015-03-01
Genetic interactions are often modeled by logical networks in which time is discrete and all gene activity states update simultaneously. However, there is no synchronizing clock in organisms. An alternative model assumes that the logical network is preserved and plays a key role in driving the dynamics in piecewise nonlinear differential equations. We examine dynamics in a particular 4-dimensional equation of this class. In the equation, two of the variables form a negative feedback loop that drives a second negative feedback loop. By modifying the original equations by eliminating exponential decay, we generate a modified system that is amenable to detailed analysis. In the modified system, we can determine in detail the Poincaré (return) map on a cross section to the flow. By analyzing the eigenvalues of the map for the different trajectories, we are able to show that except for a set of measure 0, the flow must necessarily have an eigenvalue greater than 1 and hence there is sensitive dependence on initial conditions. Further, there is an irregular oscillation whose amplitude is described by a diffusive process that is well-modeled by the Irwin-Hall distribution. There is a large class of other piecewise-linear networks that might be analyzed using similar methods. The analysis gives insight into possible origins of chaotic dynamics in periodically forced dynamical systems.
Dynamic Simulation of Backward Diffusion Based on Random Walk Theory
Dung, Vu Ba; Nguyen, Bui Huu
2016-06-01
Results of diffusion study in silicon showed that diffusion of the selfinterstitial and vacancy could be backward diffusion and their diffusivity could be negative [1]. The backward diffusion process and negative diffusivity is contrary to the fundamental laws of diffusion such as the law of Fick law, namely the diffusive flux of backward diffusion goes from regions of low concentration to regions of high concentration. The backward diffusion process have been explained [2]. In this paper, the backward diffusion process is simulated. Results is corresponding to theory and show that when thermal velocity of the low concentration area is greater than thermal velocity of the high concentration area, the backward diffusion can be occurred.
Dynamical Properties of Diffusion Process on Complex Networks with Arbitrary Degree Distribution
International Nuclear Information System (INIS)
Dynamical properties of diffusion process on complex networks with arbitrary degree distribution are investigated. The rule of the diffusion process encompasses both the structural characteristics and the information processing dynamics. Considering the influence of a node on the global dynamical behavior, the dynamical generating function of the process, which is deeply reflecting the basic characteristic of the process and mutually decided with the dynamical process, is proposed. Based on the analysis of the dynamical generating function we introduce dynamical centrality for each node, which determines the relative importance of nodes and the capability of the given node to collect and communicate information with its neighbouring environment in the network via the diffusion process. Furthermore, a new parameter, dynamical entropy, is proposed to measure the interplay between dynamical centrality and diffusion dynamics. The experimental results on large-scale complex networks with Poisson distribution confirm our analytical prediction. (authors)
Scherer, Christoph
2015-01-01
Molecular dynamics simulations of silicate and borate glasses and melts: Structure, diffusion dynamics and vibrational properties. In this work computer simulations of the model glass formers SiO2 and B2O3 are presented, using the techniques of classical molecular dynamics (MD) simulations and quantum mechanical calculations, based on density functional theory (DFT). The latter limits the system size to about 100−200 atoms. SiO2 and B2O3 are the two most important network formers for industri...
Panda, Manas K; Centore, Roberto; Causà, Mauro; Tuzi, Angela; Borbone, Fabio; Naumov, Panče
2016-01-01
The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with αa = 225.9 × 10(-6) K(-1), αb = 238.8 × 10(-6) K(-1) and αc = -290.0 × 10(-6) K(-1), the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously. PMID:27403616
Panda, Manas K.; Centore, Roberto; Causà, Mauro; Tuzi, Angela; Borbone, Fabio; Naumov, Panče
2016-01-01
The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with αa = 225.9 × 10−6 K−1, αb = 238.8 × 10−6 K−1 and αc = −290.0 × 10−6 K−1, the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously. PMID:27403616
International Nuclear Information System (INIS)
We study the energetics and dispersion of anomalous dimers that are induced by the Pauli blocking effect in a quantum Fermi gas of majority atoms near interspecies resonances. Unlike in vacuum, we find that both the sign and magnitude of the dimer masses are tunable via Feshbach resonances. We also investigate the effects of particle-hole fluctuations on the dispersion of dimers and demonstrate that the particle-hole fluctuations near a Fermi surface (with Fermi momentum (ℎ/2π)kF) generally reduce the effective two-body interactions and the binding energy of dimers. Furthermore, in the limit of light minority atoms the particle-hole fluctuations disfavor the formation of dimers with a total momentum (ℎ/2π)kF, because near (ℎ/2π)kF the modes where the dominating particle-hole fluctuations appear are the softest. Our calculation suggests that near broad interspecies resonances when the minority-majority mass ratio mB/mF is smaller than a critical value (estimated to be 0.136), dimers in a finite-momentum channel are energetically favored over dimers in the zero-momentum channel. We apply our theory to quantum gases of 6Li40K, 6Li87Rb, 40K87Rb, and 6Li23Na near broad interspecies resonances, and discuss the limitations of our calculations and implications.
Energy Technology Data Exchange (ETDEWEB)
Lapas, Luciano C., E-mail: luciano.lapas@unila.edu.br [Universidade Federal da Integração Latino-Americana, Caixa Postal 2067, 85867-970 Foz do Iguaçu, Paraná (Brazil); Ferreira, Rogelma M. S., E-mail: rogelma.maria@gmail.com [Centro de Ciências Exatas e Tecnológicas, Universidade Federal do Recôncavo da Bahia, 44380-000 Cruz das Almas, Bahia (Brazil); Rubí, J. Miguel, E-mail: mrubi@ub.edu [Departament de Física Fonamental, Facultat de Física, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona (Spain); Oliveira, Fernando A., E-mail: fernando.oliveira@pq.cnpq.br [Instituto de Física and Centro Internacional de Física da Matéria Condensada, Universidade de Brasília, Caixa Postal 04513, 70919-970 Brasília, Distrito Federal (Brazil)
2015-03-14
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton’s law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.
International Nuclear Information System (INIS)
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton’s law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics
Lapas, Luciano C.; Ferreira, Rogelma M. S.; Rubí, J. Miguel; Oliveira, Fernando A.
2015-03-01
We analyze the temperature relaxation phenomena of systems in contact with a thermal reservoir that undergoes a non-Markovian diffusion process. From a generalized Langevin equation, we show that the temperature is governed by a law of cooling of the Newton's law type in which the relaxation time depends on the velocity autocorrelation and is then characterized by the memory function. The analysis of the temperature decay reveals the existence of an anomalous cooling in which the temperature may oscillate. Despite this anomalous behavior, we show that the variation of entropy remains always positive in accordance with the second law of thermodynamics.
Study of superionic conductors dynamics by continued diffusion model
International Nuclear Information System (INIS)
The superionic conductors form a special category of solids characterized by their remarkable transport properties and are in general, Simplified as being constituted by the superposition of two inter penetrable crystal lattices. The ions of the first one form a rigid structure through which the other ions of opposite charge diffuse in quasi-liquid way. Basing on experimental and theoretical arguments, it was proved necessary to adopt a model of N-body continued diffusion which the basic theory is that of brownian movement. This thesis deals with the study of the dynamic structure factor S (q,w) and its line half width by the method of development in continued fractions issued from the Mori theory. With regard to the analytical difficulty met at the time of the static correlations functions calculation, the homogeneous approximation was applied and the notion of effective strength was introduced. So, it was obtained general relationships which give the static correlation functions, only in term of the static structure factor of liquids and effective potential. 98 refs.; 22 figs. (F.M.)
Multiscale Reaction-Diffusion Algorithms: PDE-Assisted Brownian Dynamics
Franz, Benjamin
2013-06-19
Two algorithms that combine Brownian dynami cs (BD) simulations with mean-field partial differential equations (PDEs) are presented. This PDE-assisted Brownian dynamics (PBD) methodology provides exact particle tracking data in parts of the domain, whilst making use of a mean-field reaction-diffusion PDE description elsewhere. The first PBD algorithm couples BD simulations with PDEs by randomly creating new particles close to the interface, which partitions the domain, and by reincorporating particles into the continuum PDE-description when they cross the interface. The second PBD algorithm introduces an overlap region, where both descriptions exist in parallel. It is shown that the overlap region is required to accurately compute variances using PBD simulations. Advantages of both PBD approaches are discussed and illustrative numerical examples are presented. © 2013 Society for Industrial and Applied Mathematics.
Dahlstrom, Julie; Welty, Daniel E; Oka, Takeshi; Hobbs, L M; Johnson, Sean; Friedman, Scott D; Jiang, Zihao; Rachford, Brian L; Sherman, Reid; Snow, Theodore P; Sonnentrucker, Paule
2013-01-01
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 A are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH+ in the J=1 level and from excited CH in the J=3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH+ and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is cor...
Anomalous thermal dynamics of Bragg gratings inscribed in germanosilicate optical fiber
Rahman, A.; Madhav, Venu K; B. Srinivasan; S. Asokan
2009-01-01
An interesting, periodic appearance of a new peak has been observed in the reflected spectrum of a Fiber Bragg Grating (FBG) inscribed in a germanosilicate fiber during thermal treatment. The new peak occurs on the longer wavelength side of the spectrum during heating and on the shorter wavelength side during cooling, following an identical reverse dynamics. Comparison with a commercial grating with 99.9% reflectivity shows a similar decay dynamics. It is proposed that the distortion due to s...
Wobbe, Florian; Lindeque, Ansa; Gohl, Karsten
2014-12-01
Paleotopographic models of the West Antarctic margin, which are essential for robust simulations of paleoclimate scenarios, lack information on sediment thickness and geodynamic conditions, resulting in large uncertainties. A new total sediment thickness grid spanning the Ross Sea-Amundsen Sea-Bellingshausen Sea basins is presented and is based on all the available seismic reflection, borehole, and gravity modeling data offshore West Antarctica. This grid was combined with NGDC's global 5 arc minute grid of ocean sediment thickness (Whittaker et al., 2013) and extends the NGDC grid further to the south. Sediment thickness along the West Antarctic margin tends to be 3-4 km larger than previously assumed. The sediment volume in the Bellingshausen, Amundsen, and Ross Sea basins amounts to 3.61, 3.58, and 2.78 million km3, respectively. The residual basement topography of the South Pacific has been revised and the new data show an asymmetric trend over the Pacific-Antarctic Ridge. Values are anomalously high south of the spreading ridge and in the Ross Sea area, where the topography seems to be affected by persistent mantle processes. In contrast, the basement topography offshore Marie Byrd Land cannot be attributed to dynamic topography, but rather to crustal thickening due to intraplate volcanism. Present-day dynamic topography models disagree with the presented revised basement topography of the South Pacific, rendering paleotopographic reconstructions with such a limited dataset still fairly uncertain.
Schiffer, Christian; Nielsen, Søren Bom
2016-08-01
With convergent plate boundaries at some distance, the sources of the lithospheric stress field of the North Atlantic Realm are mainly mantle tractions at the base of the lithosphere, lithospheric density structure and topography. Given this, we estimate horizontal deviatoric stresses using a well-established thin sheet model in a global finite element representation. We adjust the lithospheric thickness and the sub-lithospheric pressure iteratively, comparing modelled in plane stress with the observations of the World Stress Map. We find that an anomalous mantle pressure associated with the Iceland and Azores melt anomalies, as well as topography are able to explain the general pattern of the principle horizontal stress directions. The Iceland melt anomaly overprints the classic ridge push perpendicular to the Mid Atlantic ridge and affects the conjugate passive margins in East Greenland more than in western Scandinavia. The dynamic support of topography shows a distinct maximum of c. 1000 m in Iceland and amounts North Atlantic Realm have been estimated to be sub-aerial during the time of break-up, two components of dynamic topography seem to have affected the area: a short-lived, which affected a wider area along the rift system and quickly dissipated after break-up, and a more durable in the close vicinity of Iceland. This is consistent with the appearance of a buoyancy anomaly at the base of the North Atlantic lithosphere at or slightly before continental breakup, relatively fast dissipation of the fringes of this, and continued melt generation below Iceland.
Test of the diffusing-diffusivity mechanism using near-wall colloidal dynamics
Matse, Mpumelelo
2016-01-01
The diffusing-diffusivity mechanism proposed by Chubynsky and Slater [PRL 113, 098302, 2014] predicts that, in environments where the diffusivity changes gradually, the displacement distribution becomes non-Gaussian, even though the mean-squared displacement (MSD) grows linearly with time. Here, we report single-particle tracking measurements of the diffusion of colloidal spheres near a planar wall. Because the local effective diffusivity is known, we have been able to carry out the first direct test of this mechanism for diffusion in inhomogeneous media.
Network Structure and Innovation Ambiguity Effects on Diffusion in Dynamic Organizational Fields
Gibbons, Deborah E.
2004-01-01
Computational modeling simulated innovation diffusion through six prototypical interregional network structures and two distributions of partnering tendencies in dynamic organizational fields. Compared to regional constraints, connections among all geographic regions decreased clearly beneficial innovation diffusion (a low-threshold adoption model) but increased ambiguous innovation diffusion (a social influence model). Compared with uniform partnering tendencies, normally dist...
Swenson, Jan; Elamin, Khalid; Chen, Guo; Lohstroh, Wiebke; Sakai, Victoria Garcia
2014-12-01
The molecular dynamics of solutions of di-propylene glycol methylether (2PGME) and H2O (or D2O) confined in 28 Å pores of MCM-41 have been studied by quasielastic neutron scattering and differential scanning calorimetry over the concentration range 0-90 wt.% water. This system is of particular interest due to its pronounced non-monotonic concentration dependent dynamics of 2PGME in the corresponding bulk system, showing the important role of hydrogen bonding for the dynamics. In this study we have elucidated how this non-monotonic concentration dependence is affected by the confined geometry. The results show that this behaviour is maintained in the confinement, but the slowest diffusive dynamics of 2PGME is now observed at a considerably higher water concentration; at 75 wt.% water in MCM-41 compared to 30 wt.% water in the corresponding bulk system. This difference can be explained by an improper mixing of the two confined liquids. The results suggest that water up to a concentration of about 20 wt.% is used to hydrate the hydrophilic hydroxyl surface groups of the silica pores, and that it is only at higher water contents the water becomes partly mixed with 2PGME. Hence, due to this partial micro-phase separation of the two liquids larger, and thereby slower relaxing, structural entities of hydrogen bonded water and 2PGME molecules can only be formed at higher water contents than in the bulk system. However, the Q-dependence is unchanged with confinement, showing that the nature of the molecular motions is preserved. Thus, there is no indication of localization of the dynamics at length scales of less than 20 Å. The dynamics of both water and 2PGME is strongly dominated by translational diffusion at a temperature of 280 K.
Energy Technology Data Exchange (ETDEWEB)
Swenson, Jan, E-mail: jan.swenson@chalmers.se; Elamin, Khalid; Chen, Guo [Department of Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg (Sweden); Lohstroh, Wiebke [Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München, Lichtenbergstr. 1, 85748 Garching (Germany); Sakai, Victoria Garcia [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX Oxfordshire (United Kingdom)
2014-12-07
The molecular dynamics of solutions of di-propylene glycol methylether (2PGME) and H{sub 2}O (or D{sub 2}O) confined in 28 Å pores of MCM-41 have been studied by quasielastic neutron scattering and differential scanning calorimetry over the concentration range 0–90 wt.% water. This system is of particular interest due to its pronounced non-monotonic concentration dependent dynamics of 2PGME in the corresponding bulk system, showing the important role of hydrogen bonding for the dynamics. In this study we have elucidated how this non-monotonic concentration dependence is affected by the confined geometry. The results show that this behaviour is maintained in the confinement, but the slowest diffusive dynamics of 2PGME is now observed at a considerably higher water concentration; at 75 wt.% water in MCM-41 compared to 30 wt.% water in the corresponding bulk system. This difference can be explained by an improper mixing of the two confined liquids. The results suggest that water up to a concentration of about 20 wt.% is used to hydrate the hydrophilic hydroxyl surface groups of the silica pores, and that it is only at higher water contents the water becomes partly mixed with 2PGME. Hence, due to this partial micro-phase separation of the two liquids larger, and thereby slower relaxing, structural entities of hydrogen bonded water and 2PGME molecules can only be formed at higher water contents than in the bulk system. However, the Q-dependence is unchanged with confinement, showing that the nature of the molecular motions is preserved. Thus, there is no indication of localization of the dynamics at length scales of less than 20 Å. The dynamics of both water and 2PGME is strongly dominated by translational diffusion at a temperature of 280 K.
International Nuclear Information System (INIS)
Applying Green–Kubo formalism and equilibrium molecular dynamics (MD) simulations, we have studied the dynamic correlation, Onsager coeeficients and Maxwell–Stefan (MS) Diffusivities of molten salt LiF-BeF2, which is used as coolant in high temperature reactor. All the diffusive flux correlations show back-scattering or cage dynamics which becomes pronouced at higher temperature. Although the MS diffusivities are expected to depend very lightly on the composition due to decoupling of thermodynamic factor, the diffusivity ĐLi-F and ĐBe-F decreases sharply for higher concentration of LiF and BeF2 respectively. Interestingly, all three MS diffusivities have highest magnitude for eutectic mixture at 1000K (except ĐBe-F at lower LiF mole fraction) which is desirable from coolant point of view. Although the diffusivity for positive-positive ion pair is negative it is not in violation of the second law of thermodynamics as it satisfies the non-negative entropic constraints
Oka, Takeshi; Welty, Daniel E.; Johnson, Sean; York, Donald G.; Dahlstrom, Julie; Hobbs, L. M.
2013-08-01
Absorption spectra toward Herschel 36 (Her 36) for the \\tilde{A}^1\\Pi \\leftarrow \\tilde{X}^1\\Sigma transitions of CH+ in the J = 1 excited rotational level and for the \\tilde{A}^2\\Delta \\leftarrow \\tilde{X}^2\\Pi transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and ~25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, β ≡ (B' - B)/B, is sufficiently high (3%-5%) and the radiative temperature is high (T r > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs λ5780.5, λ5797.1, and λ6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high β favors relatively small molecules with three to six heavy atoms. DIBs λ5849.8, λ6196.0, and λ6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small β.
International Nuclear Information System (INIS)
Absorption spectra toward Herschel 36 (Her 36) for the A-bar1Π ⇽ X-tilde1Σ transitions of CH+ in the J = 1 excited rotational level and for the A-bar2Δ ⇽ X-tilde2Π transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and ∼25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, β ≡ (B' – B)/B, is sufficiently high (3%-5%) and the radiative temperature is high (Tr > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs λ5780.5, λ5797.1, and λ6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high β favors relatively small molecules with three to six heavy atoms. DIBs λ5849.8, λ6196.0, and λ6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small β
Energy Technology Data Exchange (ETDEWEB)
Oka, Takeshi; Welty, Daniel E.; Johnson, Sean; York, Donald G.; Hobbs, L. M. [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Dahlstrom, Julie, E-mail: t-oka@uchicago.edu [Department of Physics and Astronomy, Carthage College, 2001 Alford Park Drive, Kenosha, WI 53140 (United States)
2013-08-10
Absorption spectra toward Herschel 36 (Her 36) for the A-bar{sup 1}{Pi} Leftwards-Open-Headed-Arrow X-tilde{sup 1}{Sigma} transitions of CH{sup +} in the J = 1 excited rotational level and for the A-bar{sup 2}{Delta} Leftwards-Open-Headed-Arrow X-tilde{sup 2}{Pi} transitions of CH in the J = 3/2 excited fine structure level have been analyzed. These excited levels are above their ground levels by 40.1 K and {approx}25.7 K and indicate high radiative temperatures of the environment of 14.6 K and 6.7 K, respectively. The effect of the high radiative temperature is more spectacular in some diffuse interstellar bands (DIBs) observed toward Her 36; remarkable extended tails toward red (ETRs) were observed. We interpret these ETRs as being due to a small decrease of the rotational constants upon excitation of the excited electronic states. Along with radiative pumping of a great many high-J rotational levels, this causes the ETRs. In order to study this effect quantitatively, we have developed a model calculation in which the effects of collisions and radiation are treated simultaneously. The simplest case of linear molecules is considered. It has been found that the ETR is reproduced if the fraction of the variation of the rotational constant, {beta} {identical_to} (B' - B)/B, is sufficiently high (3%-5%) and the radiative temperature is high (T{sub r} > 50 K). Although modeling for general molecules is beyond the scope of this paper, the results indicate that the prototypical DIBs {lambda}5780.5, {lambda}5797.1, and {lambda}6613.6 which show the pronounced ETRs are due to polar molecules that are sensitive to the radiative excitation. The requirement of high {beta} favors relatively small molecules with three to six heavy atoms. DIBs {lambda}5849.8, {lambda}6196.0, and {lambda}6379.3 that do not show the pronounced ETRs are likely due to non-polar molecules or large polar molecules with small {beta}.
Anomalous Lattice Dynamics of Mono-, Bi-, and Tri-layer WTe2
Kim, YoungHee; Jhon, Young In; Park, June; Kim, Jae Hun; Lee, Seok; Jhon, Young Min
2015-01-01
Tungsten ditelluride (WTe2) is a layered material that exhibits excellent magnetoresistance and thermoelectric behaviors, which are deeply related with its distorted orthorhombic phase that may critically affect the lattice dynamics. Here, for the first time, we present comprehensive characterization of the Raman spectroscopic behavior of WTe2 from bulk to monolayer using experimental and computational methods. We discover that mono and bi-layer WTe2 can be easily identified by Raman spectros...
Anomalous Magnetohydrodynamics
Giovannini, Massimo
2013-01-01
Anomalous symmetries induce currents which can be parallel rather than orthogonal to the hypermagnetic field. Building on the analogy with charged liquids at high magnetic Reynolds numbers, the persistence of anomalous currents is scrutinized for parametrically large conductivities when the plasma approximation is accurate. Different examples in globally neutral systems suggest that the magnetic configurations minimizing the energy density with the constraint that the helicity be conserved co...
Institute of Scientific and Technical Information of China (English)
肖吉; 陆九芳; 陈健; 李以圭
2001-01-01
Molecular dynamics simulation has been performed to determine the infinite-dilution diffusion coefficients of oxygen and nitrogen, and the diffusion coefficients of NaCl in supercritical water from 703.2- 763.2 K and 30-45 MPa.The results obtained show that the diffusion coefficients in supercritical water increase with temperature, while decreasing with pressure. Nevertheless, the diffusion coefficients in supercritical water are much larger than those in normal water.
Lithium diffusion in silicon and induced structure disorder: A molecular dynamics study
Huanyu Wang; Xiao Ji; Chi Chen; Kui Xu; Ling Miao
2013-01-01
Using molecular dynamics method, we investigate the diffusion property of lithium in different silicon structures and silicon structure's disorder extent during lithium's diffusion process. We find that the pathway and the incident angle between the direction of barrier and diffusion of lithium are also the essential factors to the lithium's diffusion property in silicon anode besides the barrier. Smaller incident angle could decrease the scattering of lithium in silicon structure effectively...
Diffusion of dynamic innovations : A case study of residential solar PV systems
Karakaya, Emrah
2015-01-01
In the literature on diffusion of innovations, it is widely known that the characteristics and socio-environmental settings of adopters do evolve in space and time. What about innovations themselves? During the diffusion process, don’t some innovations continuously alter in space and time? If so, how does the dynamic character of an innovation influence the diffusion process? In previous research, it has been often assumed that innovations do not continuously alter or get modified when diffus...
Contributions of microtubule dynamic instability and rotational diffusion to kinetochore capture
Blackwell, Robert; Edelmaier, Christopher; Gergely, Zachary R; Flynn, Patrick J; Montes, Salvador; Crapo, Ammon; Doostan, Alireza; McIntosh, J Richard; Glaser, Matthew A; Betterton, Meredith D
2016-01-01
Microtubule dynamic instability allows search and capture of kinetochores during spindle formation, an important process for accurate chromosome segregation during cell division. Recent work has found that microtubule rotational diffusion about minus-end attachment points contributes to kinetochore capture in fission yeast, but the relative contributions of dynamic instability and rotational diffusion are not well understood. We have developed a biophysical model of kinetochore capture in small fission-yeast nuclei using hybrid Brownian dynamics/kinetic Monte Carlo simulation techniques. With this model, we have studied the importance of dynamic instability and microtubule rotational diffusion for kinetochore capture, both to the lateral surface of a microtubule and at or near its end. Over a range of biologically relevant parameters, microtubule rotational diffusion decreased capture time, but made a relatively small contribution compared to dynamic instability. At most, rotational diffusion reduced capture ...
Dahlstrom, Julie; York, Donald G.; Welty, Daniel E.; Oka, Takeshi; Hobbs, L. M.; Johnson, Sean; Friedman, Scott D.; Jiang, Zihao; Rachford, Brian L.; Sherman, Reid; Snow, Theodore P.; Sonnentrucker, Paule
2013-08-01
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH+ in the J = 1 level and from excited CH in the J = 3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH+ and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is correct and applicable to most DIBs, the 2.7 K cosmic microwave background may set the minimum widths (about 0.35 Å) of known DIBs, with molecular processes and/or local radiation fields producing the larger widths found for the broader DIBs. Despite the intense local UV radiation field within the cluster NGC 6530, no previously undetected DIBs stronger than 10 mÅ in equivalent width are found in the optical spectrum of Herschel 36, suggesting that neither dissociation nor ionization of the carriers of the known DIBs by this intense field creates new carriers with easily detectable DIB-like features. Possibly related profile anomalies for several other DIBs are noted. Based in part on data obtained from the ESO Science Archive Facility by user DWELTY.
International Nuclear Information System (INIS)
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH+ in the J = 1 level and from excited CH in the J = 3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH+ and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is correct and applicable to most DIBs, the 2.7 K cosmic microwave background may set the minimum widths (about 0.35 Å) of known DIBs, with molecular processes and/or local radiation fields producing the larger widths found for the broader DIBs. Despite the intense local UV radiation field within the cluster NGC 6530, no previously undetected DIBs stronger than 10 mÅ in equivalent width are found in the optical spectrum of Herschel 36, suggesting that neither dissociation nor ionization of the carriers of the known DIBs by this intense field creates new carriers with easily detectable DIB-like features. Possibly related profile anomalies for several other DIBs are noted
Anomalous effect of turning off long-range mobility interactions in Stokesian Dynamics
Wilson, Adam K Townsend Helen J
2016-01-01
In Stokesian Dynamics, particles are assumed to interact in two ways: through long-range mobility interactions and through short-range lubrication interactions. To speed up computations, in concentrated suspensions it is common to consider only lubrication. We show that, although this approximation provides acceptable results in monodisperse suspensions, in bidisperse suspensions it produces physically unreasonable results - "bunching" - whenever external forces are applied. We suggest that this problem could be mitigated by a careful choice of pairs of particles on which lubrication interactions should be included.
Diffusive Boltzmann equation, its fluid dynamics, Couette flow and Knudsen layers
Abramov, Rafail V
2016-01-01
In the current work we propose a diffusive modification of the Boltzmann equation. This naturally leads to the corresponding diffusive fluid dynamics equations, which we numerically investigate in a simple Couette flow setting. This diffusive modification is based on the assumption of the "imperfect" model collision term, which is unable to track all collisions in the corresponding real gas particle system. The effect of missed collisions is then modeled by an appropriately scaled long-term homogenization process of the particle dynamics. The corresponding diffusive fluid dynamics equations are produced in a standard way by closing the hierarchy of the moment equations using either the Euler or the Grad closure. In the numerical experiments with the Couette flow, we discover that the diffusive Euler equations behave similarly to the conventional Navier-Stokes equations, while the diffusive Grad equations additionally exhibit Knudsen-like velocity boundary layers. We compare the simulations with the correspond...
Moderately nonlinear diffuse-charge dynamics under an ac voltage.
Stout, Robert F; Khair, Aditya S
2015-09-01
The response of a symmetric binary electrolyte between two parallel, blocking electrodes to a moderate amplitude ac voltage is quantified. The diffuse charge dynamics are modeled via the Poisson-Nernst-Planck equations for a dilute solution of point-like ions. The solution to these equations is expressed as a Fourier series with a voltage perturbation expansion for arbitrary Debye layer thickness and ac frequency. Here, the perturbation expansion in voltage proceeds in powers of V_{o}/(k_{B}T/e), where V_{o} is the amplitude of the driving voltage and k_{B}T/e is the thermal voltage with k_{B} as Boltzmann's constant, T as the temperature, and e as the fundamental charge. We show that the response of the electrolyte remains essentially linear in voltage amplitude at frequencies greater than the RC frequency of Debye layer charging, D/λ_{D}L, where D is the ion diffusivity, λ_{D} is the Debye layer thickness, and L is half the cell width. In contrast, nonlinear response is predicted at frequencies below the RC frequency. We find that the ion densities exhibit symmetric deviations from the (uniform) equilibrium density at even orders of the voltage amplitude. This leads to the voltage dependence of the current in the external circuit arising from the odd orders of voltage. For instance, the first nonlinear contribution to the current is O(V_{o}^{3}) which contains the expected third harmonic but also a component oscillating at the applied frequency. We use this to compute a generalized impedance for moderate voltages, the first nonlinear contribution to which is quadratic in V_{o}. This contribution predicts a decrease in the imaginary part of the impedance at low frequency, which is due to the increase in Debye layer capacitance with increasing V_{o}. In contrast, the real part of the impedance increases at low frequency, due to adsorption of neutral salt from the bulk to the Debye layer. PMID:26465471
The spring 2011 final stratospheric warming above Eureka: anomalous dynamics and chemistry
Directory of Open Access Journals (Sweden)
C. Adams
2012-08-01
Full Text Available In spring 2011, the Arctic polar vortex was stronger than in any other year on record. As the polar vortex started to break up in April, ozone and NO_{2} columns were measured with UV-visible spectrometers above the Polar Environment Atmospheric Research Laboratory (PEARL in Eureka, Canada (80.05° N, 86.42° W using the differential optical absorption spectroscopy (DOAS technique. These ground-based column measurements were complemented by Ozone Monitoring Instrument (OMI and Optical Spectrograph and Infra-Red Imager System (OSIRIS satellite measurements, Global Modeling Initiative (GMI simulations, and dynamical parameters. On 8 April 2011, NO_{2} columns above PEARL from the DOAS, OMI, and GMI datasets were approximately twice as large as in previous years. On this day, temperatures and ozone volume mixing ratios above Eureka were high, suggesting enhanced chemical production of NO_{2} from NO. Additionally, GMI NO_{x} and N_{2}O fields suggest that downward transport along the vortex edge and horizontal transport from lower latitudes also contributed to the enhanced NO_{2}. The anticyclone that transported lower-latitude NO_{x} above PEARL became frozen-in and persisted in dynamical and GMI N_{2}O fields until the end of the measurement period on 31 May 2011. Ozone isolated within this frozen-in anticyclone (FrIAC in the middle stratosphere was depleted due to reactions with the enhanced NO_{x}. Ozone loss was calculated using the passive tracer technique, with passive ozone profiles from the Lagrangian Chemistry and Transport Model, ATLAS. At 600 K, ozone losses between 1 December 2010 and 20 May 2011 reached 4.2 parts per million by volume (ppmv (58% and 4.4 ppmv (61%, when calculated using GMI and OSIRIS ozone profiles, respectively. This middle-stratosphere gas-phase ozone loss led to a more rapid decrease in ozone column amounts in April/May 2011 compared with
Adsorption and diffusion of argon confined in ordered and disordered microporous carbons
International Nuclear Information System (INIS)
We use a combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations to study the adsorption and diffusion of argon at 77 K and 120 K confined in previously generated models of a disordered bituminous coal-based carbon, BPL, and an ordered carbon replica of Faujasite zeolite (C-FAU). Both materials exhibit a maximum in the diffusion coefficient as well as anomalous (sub-diffusive) behavior in the mean-squared displacements at short times at some relative pressures. In BPL, the anomalous diffusion occurs at low relative pressures, due to the trapping of argon atoms in small pores. In C-FAU, the anomalous diffusion occurs at high relative pressures, due to competitive diffusion of atoms traveling through windows and constrictions which interconnect the pores. All diffusion eventually tends to Fickian diffusion at longer times.
Role of ice dynamics in anomalous ice conditions in the Beaufort Sea during 2006 and 2007
Hutchings, J. K.; Rigor, I. G.
2012-05-01
A new record minimum in summer sea ice extent was set in 2007 and an unusual polynya formed in the Beaufort Sea ice cover during the summer of 2006. Using a combination of visual observations from cruises, ice drift, and satellite passive microwave sea ice concentration, we show that ice dynamics during preceding years included events that preconditioned the Beaufort ice pack for the unusual patterns of opening observed in both summers. Intrusions of first year ice from the Chukchi Sea to the Northern Beaufort, and increased pole-ward ice transport from the western Arctic during summer has led to reduced replenishment of multiyear ice, older than five years, in the western Beaufort, resulting in a younger, thinner ice pack in most of the Beaufort. We find ice younger than five years melts out completely by the end of summer, south of 76N. The 2006 unusual polynya was bounded to the south by an ice tongue composed of sea ice older than 5 years, and formed when first year and second year ice melted between 76N and the older ice to the south. In this paper we demonstrate that a recent shift in ice circulation patterns in the western Arctic preconditions the Beaufort ice pack for increased seasonal ice zone extent.
Investigating Diffusion Coefficient Using Dynamic Light Scattering Technique
Sun, Yong
2006-01-01
In this work, the Z-average, effective, apparent diffusion coefficients and their poly-dispersity indexes were investigated for dilute poly-disperse homogeneous spherical particles in dispersion where the Rayleigh-Gans-Debye approximation is valid. The results reveal that the values of the apparent and effective diffusion coefficients at a scattering angle investigated are consistent and the difference between the effective and Z-average diffusion coefficients is a function of the mean partic...
Dynamic polarization of the LiH molecule in strong light field in anomalous-dispersion domain
Shtoff, A V; Gusarov, S I; Dmitriev, Yu
1995-01-01
A new method is proposed to calculate the polarization vector of a molecule in a monochromatic external field in the anomalous-despersion domain. The method takes into account the instantaneous switching of the field. A simple modification of the method allows one to consider a more general switching procedure. As an illustration of the method Fourier components of the polarization vector of the LiH molecule in the anomalous -dispersion domain is calculated.
Disentangling sources of anomalous diffusion
Thiel, Felix; Sokolov, Igor M
2013-01-01
We show that some important properties of subbdiffusion of unknown origin (including those of mixed origin) can be easily assessed when findeng the "fundamental moment" of the corresponding process, i.e., the one which is additive in time. In subordinated processes, the index of the fundamental moment is inherited from the parent process and its time-dependence from the leading one. In models of particle's motion in disordered potentials, the index is governed by the structural part of the disorder while the time dependence is given by its energetic part.
Anomalous diffusion of volcanic earthquakes
Abe, Sumiyoshi
2015-01-01
Volcanic seismicity at Mt. Etna is studied. It is found that the associated stochastic process exhibits a subdiffusive phenomenon. The jump probability distribution well obeys an exponential law, whereas the waiting-time distribution follows a power law in a wide range. Although these results would seem to suggest that the phenomenon could be described by temporally-fractional kinetic theory based on the viewpoint of continuous-time random walks, the exponent of the power-law waiting-time distribution actually lies outside of the range allowed in the theory. In addition, there exists the aging phenomenon in the event-time averaged mean squared displacement, in contrast to the picture of fractional Brownian motion. Comments are also made on possible relevances of random walks on fractals as well as nonlinear kinetics. Thus, problems of volcanic seismicity are highly challenging for science of complex systems.
TRAWA, LWR Dynamic by Coupled Neutron Diffusion and Thermohydraulics Calculation
International Nuclear Information System (INIS)
1 - Description of problem or function: The purpose of the program is to study reactor dynamics in thermal water-cooled reactors. It treats the core as one or a few axially one-dimensional subregions. The two group neutron diffusion equations are solved simultaneously with the heat conduction equations and the two-phase hydraulic equations for one or more channels. Neither thermal nor hydraulic mixing appear between channels. Doppler, coolant density, coolant temperature, and soluble poison density feedbacks due to the thermo- hydraulics of the channels are described by using polynomial expansions for the group constants. The hydraulic circuit outside the reactor core consists of by-pass channels and risers with two- phase flow and of pump lines with incompressible flow. Various transients can be calculated by applying external disturbances. They can affect e.g. on movements of control rods, core inlet hydraulic conditions, system pressure or coefficients of neutronic shape function expansion between subregions. 2 - Method of solution: Nontrivial implicit methods are employed in the discretization of the equations to allow for sparse spatial mesh and flexible choice of time steps. The same spatial and temporal discretization is used for neutronics and thermohydraulics. 3 - Restrictions on the complexity of the problem: The dimensions of the program variable tables can easily be extended. Now the main dimensions are: 52 axial mesh points in core; 3 subregions; 10 axial regions with different fuel compositions; 7 radial mesh points in fuel rod; 6 delayed neutron groups; 6 coupled legs in pressure balance calculation; No flow reversals are allowed
The spring 2011 final stratospheric warming above Eureka: anomalous dynamics and chemistry
Adams, C.; Strong, K.; Zhao, X.; Bourassa, A. E.; Daffer, W. H.; Degenstein, D.; Drummond, J. R.; Farahani, E. E.; Fraser, A.; Lloyd, N. D.; Manney, G. L.; McLinden, C. A.; Rex, M.; Roth, C.; Strahan, S. E.; Walker, K. A.; Wohltmann, I.
2013-01-01
In spring 2011, the Arctic polar vortex was stronger than in any other year on record. As the polar vortex started to break up in April, ozone and NO2 columns were measured with UV-visible spectrometers above the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Canada (80.05° N, 86.42° W) using the differential optical absorption spectroscopy (DOAS) technique. These ground-based column measurements were complemented by Ozone Monitoring Instrument (OMI) and Optical Spectrograph and Infra-Red Imager System (OSIRIS) satellite measurements, Global Modeling Initiative (GMI) simulations, and meteorological quantities. On 8 April 2011, NO2 columns above PEARL from the DOAS, OMI, and GMI datasets were approximately twice as large as in previous years. On this day, temperatures and ozone volume mixing ratios above Eureka were high, suggesting enhanced chemical production of NO2 from NO. Additionally, GMI NOx (NO + NO2) and N2O fields suggest that downward transport along the vortex edge and horizontal transport from lower latitudes also contributed to the enhanced NO2. The anticyclone that transported lower-latitude NOx above PEARL became frozen-in and persisted in dynamical and GMI N2O fields until the end of the measurement period on 31 May 2011. Ozone isolated within this frozen-in anticyclone (FrIAC) in the middle stratosphere was lost due to reactions with the enhanced NOx. Below the FrIAC (from the tropopause to 700 K), NOx driven ozone loss above Eureka was larger than in previous years, according to GMI monthly average ozone loss rates. Using the passive tracer technique, with passive ozone profiles from the Lagrangian Chemistry and Transport Model, ATLAS, ozone losses since 1 December 2010 were calculated at 600 K. In the air mass that was above Eureka on 20 May 2011, ozone losses reached 4.2 parts per million by volume (ppmv) (58%) and 4.4 ppmv (61%), when calculated using GMI and OSIRIS ozone profiles, respectively. This gas-phase ozone loss
Diffusion of gold nanoparticles in toluene and water as seen by dynamic light scattering
International Nuclear Information System (INIS)
Although the range of applications for gold nanoparticles (Au NPs) is growing rapidly, the study of the diffusion in different solvents is rare. This paper describes the translational diffusion coefficient of Au NPs inside toluene and water measured by dynamic light scattering. The size of the nanoparticles is examined by transmission electron microscopy and compared with the hydrodynamic radius. The diffusion of the nanoparticles is measured in different angles and temperatures in the two solvents. It is shown that the diffusion measured in both systems obeys Arrhenius relation with the temperature. Although the viscosity of toluene is higher than that of water, the Au NPs are found to diffuse faster in toluene
The spring 2011 final stratospheric warming above Eureka: anomalous dynamics and chemistry
Directory of Open Access Journals (Sweden)
C. Adams
2013-01-01
Full Text Available In spring 2011, the Arctic polar vortex was stronger than in any other year on record. As the polar vortex started to break up in April, ozone and NO_{2} columns were measured with UV-visible spectrometers above the Polar Environment Atmospheric Research Laboratory (PEARL in Eureka, Canada (80.05° N, 86.42° W using the differential optical absorption spectroscopy (DOAS technique. These ground-based column measurements were complemented by Ozone Monitoring Instrument (OMI and Optical Spectrograph and Infra-Red Imager System (OSIRIS satellite measurements, Global Modeling Initiative (GMI simulations, and meteorological quantities. On 8 April 2011, NO_{2} columns above PEARL from the DOAS, OMI, and GMI datasets were approximately twice as large as in previous years. On this day, temperatures and ozone volume mixing ratios above Eureka were high, suggesting enhanced chemical production of NO_{2} from NO. Additionally, GMI NO_{x} (NO + NO_{2} and N_{2}O fields suggest that downward transport along the vortex edge and horizontal transport from lower latitudes also contributed to the enhanced NO_{2}. The anticyclone that transported lower-latitude NO_{x} above PEARL became frozen-in and persisted in dynamical and GMI N_{2}O fields until the end of the measurement period on 31 May 2011. Ozone isolated within this frozen-in anticyclone (FrIAC in the middle stratosphere was lost due to reactions with the enhanced NO_{x}. Below the FrIAC (from the tropopause to 700 K, NO_{x} driven ozone loss above Eureka was larger than in previous years, according to GMI monthly average ozone loss rates. Using the passive tracer technique, with passive ozone profiles from the Lagrangian Chemistry and Transport Model, ATLAS, ozone losses since 1 December 2010 were calculated at 600 K. In the air mass that was above Eureka on 20 May 2011, ozone losses reached 4.2 parts per million by
Molecular Dynamics Simulation of Solvent-Polymer Interdiffusion. I. Fickian diffusion
Tsige, Mesfin; Grest, Gary S.
2003-01-01
The interdiffusion of a solvent into a polymer melt has been studied using large scale molecular dynamics and Monte Carlo simulation techniques. The solvent concentration profile and weight gain by the polymer have been measured as a function of time. The weight gain is found to scale as t^{1/2}, which is expected for Fickian type of diffusion. The concentration profiles are fit very well assuming Fick's second law with a constant diffusivity. The diffusivity found from fitting Fick's second ...
A Dynamic Flexible Partial-Adjustment Model of International Diffusion of the Internet
Lee, Minkyu; Heshmati, Almas
2006-01-01
The paper introduces a dynamic, flexible partial-adjustment model and uses it to analyze the diffusion of Internet connectivity. It specifies and estimates desired levels of Internet diffusion and the speed at which countries achieve the target levels. The target levels and speed of adjustment are both country and time specific. Factors affecting Internet diffusion across countries are identified, and, using nonlinear least squares, the Gompertz growth model is generalized and estimated using...
Hybrid finite element and Brownian dynamics method for diffusion-controlled reactions
Bauler, Patricia; Huber, Gary A.; McCammon, J. Andrew
2012-01-01
Diffusion is often the rate determining step in many biological processes. Currently, the two main computational methods for studying diffusion are stochastic methods, such as Brownian dynamics, and continuum methods, such as the finite element method. This paper proposes a new hybrid diffusion method that couples the strengths of each of these two methods. The method is derived for a general multidimensional system, and is presented using a basic test case for 1D linear and radially symmetri...
Diffusing-wave spectroscopy: dynamic light scattering in the multiple scattering limit
Pine, D. J.; Weitz, D. A.; Zhu, J.X.; Herbolzheimer, E.
1990-01-01
Dynamic light scattering is extended to optically thick (opaque) media which exhibit a very high degree of multiple scattering. This new technique, called diffusing-wave spectroscopy (DWS), exploits the diffusive nature of the transport of light in strongly scattering media to relate the temporal fluctuations of the multiply scattered light to the motion of the scatterers. A simple theory of DWS, based on the diffusion approximation for the transport of light, is developed to calculate the te...
Diffusive Dynamics of Contact Formation in Disordered Polypeptides.
Zerze, Gül H; Mittal, Jeetain; Best, Robert B
2016-02-12
Experiments measuring contact formation between probes in disordered chains provide information on the fundamental time scales relevant to protein folding. However, their interpretation usually relies on one-dimensional (1D) diffusion models, as do many experiments probing a single distance. Here, we use all-atom molecular simulations to capture both the time scales of contact formation, as well as the scaling with peptide length for tryptophan triplet quenching experiments, revealing the sensitivity of the experimental quenching times to the configurational space explored by the chain. We find a remarkable consistency between the results of the full calculation and from Szabo-Schulten-Schulten theory applied to a 1D diffusion model, supporting the validity of such models. The significant reduction in diffusion coefficient at the small probe separations which most influence quenching rate, suggests that contact formation and Förster resonance energy transfer correlation experiments provide complementary information on diffusivity. PMID:26919016
Diffusive Dynamics of Contact Formation in Disordered Polypeptides
Zerze, Gül H.; Mittal, Jeetain; Best, Robert B.
2016-02-01
Experiments measuring contact formation between probes in disordered chains provide information on the fundamental time scales relevant to protein folding. However, their interpretation usually relies on one-dimensional (1D) diffusion models, as do many experiments probing a single distance. Here, we use all-atom molecular simulations to capture both the time scales of contact formation, as well as the scaling with peptide length for tryptophan triplet quenching experiments, revealing the sensitivity of the experimental quenching times to the configurational space explored by the chain. We find a remarkable consistency between the results of the full calculation and from Szabo-Schulten-Schulten theory applied to a 1D diffusion model, supporting the validity of such models. The significant reduction in diffusion coefficient at the small probe separations which most influence quenching rate, suggests that contact formation and Förster resonance energy transfer correlation experiments provide complementary information on diffusivity.
Quantum graphs with mixed dynamics: the transport/diffusion case
International Nuclear Information System (INIS)
We introduce a class of partial differential equations on metric graphs associated with mixed evolution: on some edges we consider diffusion processes, and on others transport phenomena. This yields a system of equations with possibly nonlocal couplings at the boundary. We provide sufficient conditions for these to be governed by a contractive semigroup on a Hilbert space naturally associated with the system. We show that our setting is also adequate to discuss specific systems of diffusion equations with boundary delays. (paper)
Molecular Dynamics Simulation of Gas Diffusion in B2O3 and SiC
Institute of Scientific and Technical Information of China (English)
Yajing YE; Litong ZHANG; Laifei CHENG; Yongdong XU
2003-01-01
Molecular dynamics simulation using a universal force field has been employed to determine the diffusion coefficients of O2 and Na2SO4 vapor into B2O3 and SiC from 700 K to 1273 K, respectively. Einstein diffusion was observed in a 250～300 ps simulation.
Lithium diffusion in silicon and induced structure disorder: A molecular dynamics study
Directory of Open Access Journals (Sweden)
Huanyu Wang
2013-11-01
Full Text Available Using molecular dynamics method, we investigate the diffusion property of lithium in different silicon structures and silicon structure's disorder extent during lithium's diffusion process. We find that the pathway and the incident angle between the direction of barrier and diffusion of lithium are also the essential factors to the lithium's diffusion property in silicon anode besides the barrier. Smaller incident angle could decrease the scattering of lithium in silicon structure effectively. Moreover, lithium diffuses easier in the Li-Si alloy structure of higher lithium concentration with deeper injection depth. The silicon's structure will be damaged gradually during the charge and discharge process. However, it will also recover to initial state to a great extent after relaxation. Therefore, the damage of lithium diffusion to silicon anode in the structure of low lithium concentration is reversible to a great degree. In addition, the silicon structure of crystal orientation perform better properties in both lithium's diffusivity and structural stability.
Molecular dynamics simulation of diffusion bonding of Al–Cu interface
International Nuclear Information System (INIS)
The effects of temperature on diffusion bonding of Al–Cu interface have been investigated by using molecular dynamics (MD) technique with the embedded atomic method (EAM) potentials. The simulated results indicate that the Cu atoms predominantly diffuse into the Al side in the process of diffusion bonding, and the thickness of the interfacial region depends on temperature, with higher temperatures resulting in larger thickness. In the course of diffusion bonding, the interfacial region became disordered. In addition, the Cu atoms diffuse at low ratios but can deeply diffuse into the interior of Al, and the Al atoms diffuse at high ratios but hardly diffuse into the interior of Cu. The results show that the appropriate temperature range for diffusion bonding of Al–Cu interface is 750–800 K, and the diffusion activation energies of Al and Cu are 0.77 eV and 0.50 eV, respectively. Finally, in this work, three diffusion mechanisms of Cu atoms in Al lattice have been found and the main diffusion mechanism is the nearest neighbor hopping mechanism. (paper)
C. Sousa; Bento, N.; Fontes, M.
2014-01-01
The objective of this paper is to contribute to a better understanding of the relation between the dynamics of knowledge production and technology diffusion along the process of emergence of a new technology, as it unfolds in diverse spatial locations. For this purpose, the paper traces the process of knowledge production over time – expressed in the number of scientific publications - and assesses how its dynamics relate with those of technology up-scaling and diffusion, for the case of a ne...
Anomalous transport in the crowded world of biological cells
Höfling, Felix; Franosch, Thomas
2013-04-01
A ubiquitous observation in cell biology is that the diffusive motion of macromolecules and organelles is anomalous, and a description simply based on the conventional diffusion equation with diffusion constants measured in dilute solution fails. This is commonly attributed to macromolecular crowding in the interior of cells and in cellular membranes, summarizing their densely packed and heterogeneous structures. The most familiar phenomenon is a sublinear, power-law increase of the mean-square displacement (MSD) as a function of the lag time, but there are other manifestations like strongly reduced and time-dependent diffusion coefficients, persistent correlations in time, non-Gaussian distributions of spatial displacements, heterogeneous diffusion and a fraction of immobile particles. After a general introduction to the statistical description of slow, anomalous transport, we summarize some widely used theoretical models: Gaussian models like fractional Brownian motion and Langevin equations for visco-elastic media, the continuous-time random walk model, and the Lorentz model describing obstructed transport in a heterogeneous environment. Particular emphasis is put on the spatio-temporal properties of the transport in terms of two-point correlation functions, dynamic scaling behaviour, and how the models are distinguished by their propagators even if the MSDs are identical. Then, we review the theory underlying commonly applied experimental techniques in the presence of anomalous transport like single-particle tracking, fluorescence correlation spectroscopy (FCS) and fluorescence recovery after photobleaching (FRAP). We report on the large body of recent experimental evidence for anomalous transport in crowded biological media: in cyto- and nucleoplasm as well as in cellular membranes, complemented by in vitro experiments where a variety of model systems mimic physiological crowding conditions. Finally, computer simulations are discussed which play an important
Numerical Diffusion Effect in Dynamic Simulation of Thermohydraulic Systems
International Nuclear Information System (INIS)
In this work, the behavior of the explicit - up-wind method is studied in two phase natural convection circuit, near the instabilities boundaries.The effect of the numerical diffusion of the scheme upon the system stability is evaluated by means of linearization by small perturbations.The results are compared with a non-diffusive method, in the frequency domain, that solves analytically the linearized equations around a steady state condition.Moreover, a conservation equation transport model using the method of characteristics is implemented and studied.This method is compared with the explicit - up-wind scheme and it is found that it significantly reduces numerical diffusion in the equations solution. Several advantages are visualized for particular cases
New dynamic model for non-Fickian diffusion of calcium spark in cardiac myocytes
Institute of Scientific and Technical Information of China (English)
TAN Wenchang; LIU Shiqiang; GUO Jingjing; WANG Shiqiang; CHENG Heping; T. Masuoka
2003-01-01
A new dynamic model for non-Fickian diffusion of calcium spark in cardiac myocytes was developed by introducing time lags on the basis of the microscale mass transport theory. Numerical simulation showed that the size of the calcium spark produced by the new dynamic model was larger than that of Fick diffusion and was in more agreement with experimental results. In addition, the time lags of the calcium spark in cardiac myocytes were about 0.1-0.8 ms. These results can be used to understand the mechanism of calcium spark diffusion in cardiac myocytes.
Calculation of the coefficient and dynamics of water diffusion in graphite joints
Institute of Scientific and Technical Information of China (English)
WANG Jun; LIU Wen-bin
2006-01-01
The coefficient and dynamics of water diffusion in adhesive-graphite joints were calculated insitu with energy dispersive X-ray (EDX) analysis, a method that is significantly simpler than elemental analysis. Water diffusion coefficient and dynamics of adhesive-graphite joints treated by different surface treatment methods were also investigated. Calculation results indicated that the water diffusion rate in adhesive-graphite joints treated by sandpaper was higher than that treated by chemical oxidation or by silane couple agent. Also the durability of graphite joints treated by coupling agent is superior to that treated by chemical oxidation or sandpaper burnishing.
Coexistence and efficiency of normal and anomalous transport by molecular motors in living cells
Goychuk, Igor; Metzler, R
2013-01-01
Recent experiments reveal both passive subdiffusion of various nanoparticles and anomalous active transport of such particles by molecular motors in the molecularly crowded environment of living biological cells. Passive and active microrheology reveals that the origin of this anomalous dynamics is due to the viscoelasticity of the intracellular fluid. How do molecular motors perform in such a highly viscous, dissipative environment? Can we explain the observed co-existence of the anomalous transport of relatively large particles of 100 to 500 nm in size by kinesin motors with the normal transport of smaller particles by the same molecular motors? What is the efficiency of molecular motors in the anomalous transport regime? Here we answer these seemingly conflicting questions and consistently explain experimental findings in a generalization of the well-known continuous diffusion model for molecular motors with two conformational states in which viscoelastic effects are included.
Anomalous transport effects in magnetically-confined plasma columns
International Nuclear Information System (INIS)
The evolution of density structure in a magnetized plasma column is analyzed accounting for anomalous diffusion due to the lower hybrid drift instability. The plasma column is found to be divided into regions of classical, anomalous, and intermediate diffusivity. The bulk behavior, described in terms of radial confinement time, depends most sensitively upon the particle line density (ion/cm). For broad plasmas (large line density), the transport is characteristic of classical diffusion, and for slender plasmas (small line density) the transport is characteristic of anomalous diffusion. For intermediate line densities, the transport undertakes a rapid transition from classical to anomalous. Correlations between the theoretical results and past experiments are described
Molecular dynamics simulation on diffusion properties of Pb-Mg alloy
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
A new method to calculate mutual-diffusion coefficients of the binary alloy has been proposed in this report.At first self-diffusion coefficient of the constituent element was calculated using molecular dynamics method,thermodynamic factor of the alloy was got with the NRTL (non-random-two-liquid) equation,then mutual-diffusion coefficient was obtained with Darken formula.Using this method the mutual-diffusion coefficient of Pb-Mg alloy with different Pb content was calculated.The calculated values were compared with the available experimental ones and the reason of the maximal mutual-diffusion coefficient appearing at 33.3 at.%Pb was discussed.Partial pair correlation function and partial coordination number were calculated to analyze the effect of the melt structure on mutual-diffusion coefficient.
Energy Technology Data Exchange (ETDEWEB)
Mares, Jeremy W.; Weiss, Sharon M.
2011-09-20
Time-dependent laser reflectometry measurements are presented as a means to rigorously characterize analyte diffusion dynamics of small molecules from mesoporous silicon (PSi) films for drug delivery and membrane physics applications. Calculations based on inclusion of a spatially and temporally dependent solute concentration profile in a one-dimensional Fickian diffusion flow model are performed to determine the diffusion coefficients for the selected prototypical polar species, sucrose (340 Da), exiting from PSi films. The diffusion properties of the molecules depend on both PSi pore size and film thickness. For films with average pore diameters between 10-30 nm and film thicknesses between 300-900 nm, the sucrose diffusion coefficient can be tuned between approximately 100 and 550 {mu}m{sup 2}/s. Extensions of the real-time measurement and modeling approach for determining the diffusivity of small molecules that strongly interact with and corrode the internal surfaces of PSi films are also discussed.
Experimental investigation of the starting process of short diffusers for gas dynamic lasers
Energy Technology Data Exchange (ETDEWEB)
Oudekerk, M.M.
1975-06-01
The diffuser section of a Gas Dynamic Laser (GDL) is one of the largest components in the system. The purpose of this investigation was to examine the problem of starting supersonic flow in short diffusers with fixed walls, incorporating various bleed arrangements for boundary layer control (BLC). A Mach number of 4, ramp angle of 19 degrees diffuser length of 4.5 in. and a diffuser width of 1.0 in. were used throughout this investigation. Intrusion by the atmosphere into the diffuser causes a separation region or bubble to form. The presence of this 'bubble' could be made to improve the diffuser performance by making a variable area diffuser out of a fixed wall diffuser without the use of any external apparatus. BLC was helpful in increasing the over all pressure recovery of the diffuser. BLC also affects the unsteady flow, which was present in the diffuser, but only when it is applied at a point prior to the converging section of the GDL.
First invader dynamics in diffusion-controlled absorption
International Nuclear Information System (INIS)
We investigate the average time for the earliest particle to hit a spherical absorber when a homogeneous gas of freely diffusing particles with density ρ and diffusivity D is prepared in a deterministic state and is initially separated by a minimum distance ℓ from this absorber. In the high-density limit, this first absorption time scales as ((ℓ2)/D)(1/(ln ρℓ)) in one dimension; a similar scaling behavior occurs in greater than one dimension. In one dimension, we also determine the probability that the kth-closest particle is the first one to hit the absorber. At large k, this probability decays as k1/3exp(−Ak2/3), with A = 1.932 99… analytically calculable. As a corollary, the characteristic hitting time Tk for the kth-closest particle scales as k4/3; this corresponds to superdiffusive but still subballistic motion. (paper)
Diffusion dynamics of socially learned foraging techniques in squirrel monkeys.
Claidière, Nicolas; Messer, Emily J E; Hoppitt, William; Whiten, Andrew
2013-07-01
Social network analyses and experimental studies of social learning have each become important domains of animal behavior research in recent years yet have remained largely separate. Here we bring them together, providing the first demonstration of how social networks may shape the diffusion of socially learned foraging techniques. One technique for opening an artificial fruit was seeded in the dominant male of a group of squirrel monkeys and an alternative technique in the dominant male of a second group. We show that the two techniques spread preferentially in the groups in which they were initially seeded and that this process was influenced by monkeys' association patterns. Eigenvector centrality predicted both the speed with which an individual would first succeed in opening the artificial fruit and the probability that they would acquire the cultural variant seeded in their group. These findings demonstrate a positive role of social networks in determining how a new foraging technique diffuses through a population. PMID:23810529
Global Dynamics Analysis of Homogeneous New Products Diffusion Model
Shuping Li; Zhen Jin
2013-01-01
A mathematical model with stage structures is presented that incorporates the awareness stage and the decision-making stage; individuals exchange product information by two channels: mass media and interpersonal communication. When the persuasive advertisement is neglected in the decision-making stage, we find a threshold value about whether new products diffusion is successful or not. When the persuasive advertisement is considered, there must exist a positive equilibrium unde...
Dynamic analysis of house price diffusion across Asian financial centres
Nanda, Anupam; Yeh, Jia-Huey
2012-01-01
The aim of the paper is to explore both of the effects of macroeconomic variables on house prices and the lead-lag relationships of real estate markets to examine house price diffusion across Asian financial centres. The analysis is based on the Global Vector Auto-Regression (GVAR) model estimated using quarterly data for six Asian financial centres (Hong Kong, Tokyo, Seoul, Singapore, Taipei and Bangkok) over the period from 1991 to 2009. The empirical results indicate that the global econom...
Dynamic response of a pulsed Burke-Schumann diffusion flame
Sheu, Jyh-Cherng; Stocker, Dennis P.; Chen, Lea-Der
1995-01-01
Turbulent flames are often envisioned as an ensemble of random vortices interacting with the combustion process. A better understanding of the vortex-flame interactions therefore would be useful in improving the modeling of turbulent diffusion flames. Substantial simplification may be made by investigating controlled interactions in a laminar flame, as opposed to random interactions in a turbulent flame. The general goals of the research project are to improve our understanding of (1) the influence of buoyancy on co-flow diffusion flames and (2) the effects of buoyancy on vortex-flame interactions in co-flow diffusion flames. As a first step toward objective (2), we conducted a joint experimental and numerical investigation of the vortex-flame interaction. Vortices were produced by mechanically pulsing the fuel flow at a low frequency, e.g., 10 Hz. Experiments were conducted using a nonflickering Burke-Schumann flame in both microgravity (mu-g) and normal gravity (1g) as a means of varying the buoyant force without modification of the pressure (i.e., density). The effects of buoyant convection may then be determined by a comparison of the mu-g and 1g results. The mu-g results may also reveal the important mechanisms which are masked or overwhelmed by buoyant convection in 1g. A numerical investigation was conducted using a validated, time-accurate numerical code to study the underlying physics during the flame interaction and to assist the interpretation of the experimental results.
International Nuclear Information System (INIS)
In order to quantify effect of temperature on diffusivity of deuterated water (HDO) in compacted sodium-bentonite, through-diffusion experiments were conducted at elevated temperature from 298 to 333 K. Kunipia F (Na-montmorillonite content > 98 wt. %; Kunimine Industry Co.) was compacted to a dry density of 0.9 and 1.35 Mg/m3. Since smectite flakes were perpendicularly oriented to a direction of compaction, anisotropy of diffusivity was investigated parallel and normal to the preferred orientation of smectite. Effective diffusion coefficient De of HDO was larger for a diffusional direction parallel to the preferred orientation than normal to that for both dry densities. These results well agreed to the previously reported ones for tritiated water. Activation energies of De in compacted bentonite increased with increasing dry density in the range of 19-25 kJ/mol which was slightly larger than that in bulk water (18 kJ/mol). This relationship can be considered to be due to both the pore structure development and high activation energy of water (18-23 kJ/mol) in the vicinity of smectite surface (within 2 nm) on the basis of molecular dynamics simulations. (author)
Dipole diffusion in a random electrical potential
Energy Technology Data Exchange (ETDEWEB)
Touya, Clement; Dean, David S; Sire, Clement [Laboratoire de Physique Theorique, IRSAMC, Universite de Toulouse, CNRS, 31062 Toulouse (France)
2009-09-18
We study the Langevin dynamics of a dipole diffusing in a random electrical field E derived from a quenched Gaussian potential. We show that in a suitable adiabatic limit (where the dynamics of the dipole moment is much faster than the dynamics of its position), one can reduce the coupled stochastic equations to an effective Langevin equation for a particle diffusing in an effective potential with a spatially varying and anisotropic local diffusivity {kappa}{sub ij}. Analytic results, close to the adiabatic limit, for the diffusion constant {kappa}{sub e} are found in one dimension and a finite temperature dynamical transition is found. The system is also studied numerically. In particular, we study the anomalous diffusion exponent in the low-temperature regime. Our findings strongly support the conclusion that the location of the dynamical transition and the anomalous diffusion exponents are determined by purely static considerations, i.e. they are independent of the relative values of the diffusion constants of the particle position and its dipole moment.
Space-dependent self-diffusion processes in molten copper halides: a molecular dynamics study
Alcaraz Sendra, Olga; Trullàs Simó, Joaquim
2001-01-01
This work is concerned with single ion dynamics in molten copper halides (CuI and CuCl) which exhibit fast ionic conduction before melting. The self-dynamic structure factor of the two ionic species in each melt have been calculated by molecular dynamics simulations and the corresponding effective wavelength-dependent self-diffusion coefficients have been studied. The results have been compared with those obtained for molten alkali halides (KCl and RbCl).
Two competing species in super-diffusive dynamical regimes
La Cognata, A.; Valenti, D.; Spagnolo, B.; Dubkov, A. A.
2010-09-01
The dynamics of two competing species within the framework of the generalized Lotka-Volterra equations, in the presence of multiplicative α-stable Lévy noise sources and a random time dependent interaction parameter, is studied. The species dynamics is characterized by two different dynamical regimes, exclusion of one species and coexistence of both, depending on the values of the interaction parameter, which obeys a Langevin equation with a periodically fluctuating bistable potential and an additive α-stable Lévy noise. The stochastic resonance phenomenon is analyzed for noise sources asymmetrically distributed. Finally, the effects of statistical dependence between multiplicative noise and additive noise on the dynamics of the two species are studied.
Global dynamics of a reaction-diffusion system
Directory of Open Access Journals (Sweden)
Yuncheng You
2011-02-01
Full Text Available In this work the existence of a global attractor for the semiflow of weak solutions of a two-cell Brusselator system is proved. The method of grouping estimation is exploited to deal with the challenge in proving the absorbing property and the asymptotic compactness of this type of coupled reaction-diffusion systems with cubic autocatalytic nonlinearity and linear coupling. It is proved that the Hausdorff dimension and the fractal dimension of the global attractor are finite. Moreover, the existence of an exponential attractor for this solution semiflow is shown.
Market Dynamics and Indirect Network Effects in Electric Vehicle Diffusion
Zhe Yu; Shanjun Li; Lang Tong
2015-01-01
The diffusion of electric vehicles (EVs) is studied in a two-sided market framework consisting of EVs on the one side and EV charging stations (EVCSs) on the other. A sequential game is introduced as a model for the interactions between an EVCS investor and EV consumers. A consumer chooses to purchase an EV or a conventional gasoline alternative based on the upfront costs of purchase, the future operating costs and the availability of charging stations. The investor, on the other hand, maximi...
Long-time diffusivity of DNA chains in nanochannels: A Brownian dynamics study
Jain, Aashish; Dorfman, Kevin
2015-03-01
The simplest approach to calculate the diffusivity of any polymer chain is to use the double sum Kirkwood formula, which is based on preaveraging approximation of diffusion tensor. The error due to the preaveraging approximation has been reported by a number of researchers in the context of free solution by computing both Kirkwood diffusivity D (K) (also known as short-time diffusivity) and long-time diffusivity DL. In nanochannels, the main approach to compute the diffusivity is the Kirkwood formula. However, the error due to the preaveraging approximation is not known in a confined system. We use Brownian dynamics simulation algorithm with excluded volume and hydrodynamic interactions to calculate both short-time and long-time diffusivities of DNA chains in nanochannels, and compare them for a range of channel sizes and DNA chain sizes. Our results indicate that the long-time diffusivity is always smaller than the short-time diffusivity, which is consistent with the result obtained in free solution using linear response theory DL
Identification of the dynamics of a lead acid battery by a diffusive model
Energy Technology Data Exchange (ETDEWEB)
Garcia, G.; Bernussou, J.
1998-11-01
In this paper, some preliminary results on identification of diffusive models using input/output measurements are proposed. The idea consists in considering a finite dimensional approximation of the diffusive model and formulating an optimisation problem of a least square error type. To identify such a model, it is necessary to estimate a distribution {mu} which fully characterises the system dynamics. This distribution constitutes the unknown of the problem. These results are applied to the model identification of a lead acid battery. (author)
Self-diffusion and structural properties of confined fluids in dynamic coexistence
International Nuclear Information System (INIS)
Self-diffusion and radial distribution functions are studied in a strongly confined Lennard-Jones fluid. Surprisingly, in the solid–liquid phase transition region, where the system exhibits dynamic coexistence, the self-diffusion constants are shown to present up to three-fold variations from solid to liquid phases at fixed temperature, while the radial distribution function corresponding to both the liquid and the solid phases are essentially indistinguishable. (paper)
Application of the Clustering Method in Molecular Dynamics Simulation of the Diffusion Coefficient
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
Using molecular dynamics (MD) simulation, the diffusion of oxygen, methane, ammonia and carbon dioxide in water was simulated in the canonical NVT ensemble, and the diffusion coefficient was analyzed by the clustering method. By comparing to the conventional method (using the Einstein model) and the differentiation-interval variation method, we found that the results obtained by the clustering method used in this study are more close to the experimental values. This method proved to be more reasonable than the other two methods.
Ab-initio molecular dynamics simulation of hydrogen diffusion in $\\alpha$-iron
Sanchez, J; Fullea García, José; Andrade Perdrix, Maria del Carmen; de Andres, P. L.
2011-01-01
First-principles atomistic molecular dynamics simulation in the micro-canonical and canonical ensembles has been used to study the diffusion of interstitial hydrogen in $\\alpha$-iron. Hydrogen to Iron ratios between $\\theta=1/16 and 1/2 have been considered by locating interstitial hydrogen atoms at random positions in a $2 \\times 2 \\times 2$ supercell. We find that the average optimum absorption site and the barrier for diffusion depend on the concentration of interestitials. Iron Debye temp...
Turing pattern dynamics and adaptive discretization for a super-diffusive Lotka-Volterra model.
Bendahmane, Mostafa; Ruiz-Baier, Ricardo; Tian, Canrong
2016-05-01
In this paper we analyze the effects of introducing the fractional-in-space operator into a Lotka-Volterra competitive model describing population super-diffusion. First, we study how cross super-diffusion influences the formation of spatial patterns: a linear stability analysis is carried out, showing that cross super-diffusion triggers Turing instabilities, whereas classical (self) super-diffusion does not. In addition we perform a weakly nonlinear analysis yielding a system of amplitude equations, whose study shows the stability of Turing steady states. A second goal of this contribution is to propose a fully adaptive multiresolution finite volume method that employs shifted Grünwald gradient approximations, and which is tailored for a larger class of systems involving fractional diffusion operators. The scheme is aimed at efficient dynamic mesh adaptation and substantial savings in computational burden. A numerical simulation of the model was performed near the instability boundaries, confirming the behavior predicted by our analysis. PMID:26219250
Dissipative particle dynamics of diffusion-NMR requires high Schmidt-numbers
Azhar, Mueed; Greiner, Andreas; Korvink, Jan G.; Kauzlarić, David
2016-06-01
We present an efficient mesoscale model to simulate the diffusion measurement with nuclear magnetic resonance (NMR). On the level of mesoscopic thermal motion of fluid particles, we couple the Bloch equations with dissipative particle dynamics (DPD). Thereby we establish a physically consistent scaling relation between the diffusion constant measured for DPD-particles and the diffusion constant of a real fluid. The latter is based on a splitting into a centre-of-mass contribution represented by DPD, and an internal contribution which is not resolved in the DPD-level of description. As a consequence, simulating the centre-of-mass contribution with DPD requires high Schmidt numbers. After a verification for fundamental pulse sequences, we apply the NMR-DPD method to NMR diffusion measurements of anisotropic fluids, and of fluids restricted by walls of microfluidic channels. For the latter, the free diffusion and the localisation regime are considered.
Molecular Dynamics Study on the Diffusion Properties of Hydrogen Atoms in Bulk Tungsten
International Nuclear Information System (INIS)
Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen atoms in body-centered cubic(bcc) tungsten(W). The energy distribution of a single hydrogen atom in the (001) plane of tungsten lattice was computed. The values of diffusion barriers agree well with other theoretical and experimental results. The interaction between an H atom and a vacancy was simulated, which shows evidence of strong binding effect. The temperature effect on the diffusion behavior of hydrogen atoms was investigated. The critical temperature for an H atom to diffuse in bulk W with and without vacancies were calculated to be 950 K and 450 K, respectively, which is supported by several experimental results. In addition, the diffusion coefficient of hydrogen atoms in tungsten was evaluated and analyzed
Indian Academy of Sciences (India)
Bhabani S Mallik; Amalendu Chandra
2012-01-01
We present an ab initio molecular dynamics study of vibrational spectral diffusion and hydrogen bond dynamics in aqueous solution of acetone at room temperature. It is found that the frequencies of OD bonds in the acetone hydration shell have a higher stretch frequency than those in the bulk water. Also, on average, the frequencies of hydration shell OD modes are found to increase with increase in the acetone-water hydrogen bond distance. The vibrational spectral diffusion of the hydration shell water molecules reveals three time scales: A short-time relaxation (∼80 fs) corresponding to the dynamics of intact acetone-water hydrogen bonds, a slower relaxation (∼1.3 ps) corresponding to the lifetime of acetone-water hydrogen bonds and another longer time constant (∼12 ps) corresponding to the escape dynamics of water from the solute hydration shell. The present first principles results are compared with those of available experiments and classical simulations.
Wu, Xiaobin; Qiu, Jian; Luo, Kaiqing; Han, Peng
2015-08-01
Dynamic Light Scattering is used for measuring particle size distribution of nano-particle under Brownian motion. Signal is detected through a photomultiplier and processed by correlation analysis, and results are inverted at last. Method by using CCD camera can record the procedure of motion. However, there are several weaknesses such as low refresh speed and noise from CCD camera, and this method depends on particle size and detecting angle. A simulation of nano-particle under Brownian motion is proposed to record dynamic images, studies contrast of dynamic images which can represent speed of diffusion, and its characteristic under different conditions. The results show that through contrast of dynamic images diffusion coefficient can be obtained, which is independent on density of scattering volume.
Molecular-dynamics analysis of the diffusion of molecular hydrogen in all-silica sodalite
Van den Berg, A.W.C.; Bromley, S.T.; Flikkema, E.; Wojdel, J.; Maschmeyer, T; Jansen, J C
2004-01-01
In order to investigate the technical feasibility of crystalline porous silicates as hydrogen storage materials, the self-diffusion of molecular hydrogen in all-silica sodalite is modeled using large-scale classical molecular-dynamics simulations employing full lattice flexibility. In the temperature range of 700–1200 K, the diffusion coefficient is found to range from 1.6⋅10−10 to 1.8⋅10−9 m2/s. The energy barrier for hydrogen diffusion is determined from the simulations allowing the applica...
Copper diffusivity in boron-doped silicon wafer measured by dynamic secondary ion mass spectrometry
International Nuclear Information System (INIS)
Highlights: ► Effective copper diffusivity in boron-doped silicon wafer was measured. ► Dynamic secondary ion mass spectrometry was used. ► Interstitial copper ions were first drifted to surface region and allowed to back-diffuse. ► Boron concentration largely influenced the effect copper diffusivity. -- Abstract: The effective copper diffusivity (Deff) in boron-doped silicon wafer was measured using a Dynamic Secondary Ion Mass Spectrometry (D-SIMS) that was incorporated with an out-drift technique. By this technique, positive interstitial copper ions (CuI+) migrated to the surface region when a continuous charge of electrons showered on the oxidized silicon wafer, which was also bombarded by primary O2+ ions. The CuI+ ions at the surface region diffused back to the bulk when the electron showering stopped. The D-SIMS recorded the real-time distribution of CuI+ ions, generating depth profiles for in-diffusion of copper for silicon-wafer samples with different boron concentrations. These were curve-fitted using the standard diffusion expressions to obtain different Deff values, and compared with other measurement techniques
Copper diffusivity in boron-doped silicon wafer measured by dynamic secondary ion mass spectrometry
Energy Technology Data Exchange (ETDEWEB)
Koh, Songfoo [S.E.H (M) Sdn. Bhd., Lot 2, Lorong Enggang 35, Ulu Klang FTZ, 54200 Selangor (Malaysia); You, Ahheng [Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, Bukit Beruang, 75450 Melaka (Malaysia); Tou, Teckyong, E-mail: tytou@mmu.edu.my [Faculty of Engineering, Multimedia Univesity, Jalan Multimedia, 63100 Cyberjaya (Malaysia)
2013-03-20
Highlights: ► Effective copper diffusivity in boron-doped silicon wafer was measured. ► Dynamic secondary ion mass spectrometry was used. ► Interstitial copper ions were first drifted to surface region and allowed to back-diffuse. ► Boron concentration largely influenced the effect copper diffusivity. -- Abstract: The effective copper diffusivity (D{sub eff}) in boron-doped silicon wafer was measured using a Dynamic Secondary Ion Mass Spectrometry (D-SIMS) that was incorporated with an out-drift technique. By this technique, positive interstitial copper ions (Cu{sub I}{sup +}) migrated to the surface region when a continuous charge of electrons showered on the oxidized silicon wafer, which was also bombarded by primary O{sub 2}{sup +} ions. The Cu{sub I}{sup +} ions at the surface region diffused back to the bulk when the electron showering stopped. The D-SIMS recorded the real-time distribution of Cu{sub I}{sup +} ions, generating depth profiles for in-diffusion of copper for silicon-wafer samples with different boron concentrations. These were curve-fitted using the standard diffusion expressions to obtain different D{sub eff} values, and compared with other measurement techniques.
Modeling Dynamics of Diffusion Across Heterogeneous Social Networks: News Diffusion in Social Media
Peter Christen; David Newth; Minkyoung Kim
2013-01-01
Diverse online social networks are becoming increasingly interconnected by sharing information. Accordingly, emergent macro-level phenomena have been observed, such as the synchronous spread of information across different types of social media. Attempting to analyze the emergent global behavior is impossible from the examination of a single social platform, and dynamic influences between different social networks are not negligible. Furthermore, the underlying structural property of networks...
Cultural fragmentation and innovation diffusion in a dynamic scenario
Apolloni, Andrea; Gargiulo, Floriana
2009-01-01
Axelrod model describes the dissemination of a set of cultural traits in a society constituted by individual agents. In a social context, nevertheless, individual choices toward a specific attitude are also at the basis of the formation of communities, groups, parties. The membership in a group changes completely the behavior of single agents who start acting according to a social identity. Groups act and interact among them as single entities, but still conserve an internal dynamics. We show...
Effects of social networks on innovation diffusion and marketing dynamics
Delre, Sebastiano Alessio
2007-01-01
The main goal of this thesis is to incorporate part of the flourishing literature on network structures in a marketing context. Most of the results we have obtained and presented generate several implications. First of all we hope that the reader, after going through these chapters is convinced that often networks do play a role, that they can explain different market dynamics and that studying networks can be used to develop marketing strategies. Most of the theoretical implications derive f...
Large-scale dynamics of sandy coastlines: diffusivity and instability
Falqués Serra, Albert; Calvete Manrique, Daniel
2005-01-01
The dynamics of small-amplitude perturbations of an otherwise rectilinear coastline due to the wave-driven alongshore sediment transport is examined at large time and length scales (years and kilometers). A linear stability analysis is performed by using an extended one-line shoreline model with two main improvements: (1) the curvature of the coastline features is accounted for and (2) the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance....
Diffusive dynamics and stochastic models of turbulent axisymmetric wakes
Rigas, G; Brackston, R D; Morrison, J F
2015-01-01
A modelling methodology to reproduce the experimental measurements of a turbulent flow under the presence of symmetry is presented. The flow is a three-dimensional wake generated by an axisymmetric body. We show that the dynamics of the turbulent wake- flow can be assimilated by a nonlinear two-dimensional Langevin equation, the deterministic part of which accounts for the broken symmetries which occur at the laminar and transitional regimes at low Reynolds numbers and the stochastic part of which accounts for the turbulent fluctuations. Comparison between theoretical and experimental results allows the extraction of the model parameters.
Enhanced Lipid Diffusion and Mixing in Accelerated Molecular Dynamics
Wang, Yi; Markwick, Phineus R.L.; de Oliveira, César Augusto F.; McCammon, J. Andrew
2011-01-01
Accelerated molecular dynamics (aMD) is an enhanced sampling technique that expedites conformational space sampling by reducing the barriers separating various low-energy states of a system. Here, we present the first application of the aMD method on lipid membranes. Altogether, ∼1.5 μs simulations were performed on three systems: a pure POPC bilayer, a pure DMPC bilayer, and a mixed POPC:DMPC bilayer. Overall, the aMD simulations are found to produce significant speedup in trans–gauche isome...
Chen, Wei; Huang, Dayu; Kulkarni, Ankur A.; Unnikrishnan, Jayakrishnan; Zhu, Quanyan; Mehta, Prashant; Meyn, Sean; Wierman, Adam
2013-01-01
Neuro-dynamic programming is a class of powerful techniques for approximating the solution to dynamic programming equations. In their most computationally attractive formulations, these techniques provide the approximate solution only within a prescribed finite-dimensional function class. Thus, the question that always arises is how should the function class be chosen? The goal of this paper is to propose an approach using the solutions to associated fluid and diffusion approximations. In ord...
International Nuclear Information System (INIS)
Dislocation climb mobilities, assuming vacancy bulk diffusion, are derived and implemented in dislocation dynamics simulations to study the coarsening of vacancy prismatic loops in fcc metals. When loops cannot glide, comparison of the simulations with a coarsening model based on the line tension approximation shows good agreement. Dislocation dynamics simulations with both glide and climb are then performed. Allowing for glide of the loops along their prismatic cylinders leads to faster coarsening kinetics, as direct coalescence of the loops is now possible. (authors)
Specific Ions Modulate Diffusion Dynamics of Hydration Water on Lipid Membrane Surfaces
Song, Jinsuk; Franck, John; Pincus, Philip; Kim, Mahn Won; Han, Songi
2014-01-01
Effects of specific ions on the local translational diffusion of water near large hydrophilic lipid vesicle surfaces were measured by Overhauser dynamic nuclear polarization (ODNP). ODNP relies on an unpaired electron spin-containing probe located at molecular or surface sites to report on the dynamics of water protons within ∼10 Å from the spin probe, which give rise to spectral densities for electron–proton cross-relaxation processes in the 10 GHz regime. This pushes nuclear magnetic resona...
How Local and Average Particle Diffusivities of Inhomogeneous Fluids Depend on Microscopic Dynamics.
Bollinger, Jonathan A; Jain, Avni; Truskett, Thomas M
2015-07-23
Computer simulations and a stochastic Fokker-Planck equation based approach are used to compare the single-particle diffusion coefficients of equilibrium hard-sphere fluids exhibiting identical inhomogeneous static structure and governed by either Brownian (i.e., overdamped Langevin) or Newtonian microscopic dynamics. The physics of inhomogeneity is explored via the imposition of one-dimensional sinusoidal density profiles of different wavelengths and amplitudes. When imposed density variations are small in magnitude for distances on the scale of a particle diameter, bulk-like average correlations between local structure and mobility are observed. In contrast, when density variations are significant on that length scale, qualitatively different structure-mobility correlations emerge that are sensitive to the governing microscopic dynamics. Correspondingly, a previously proposed scaling between long-time diffusivities for bulk isotropic fluids of particles exhibiting Brownian versus Newtonian dynamics [Pond et al. Soft Matter 2011, 7, 9859-9862] cannot be generalized to describe the position-dependent behaviors of strongly inhomogeneous fluids. While average diffusivities in the inhomogeneous and homogeneous directions are coupled, their qualitative dependencies on inhomogeneity wavelength are sensitive to the details of the microscopic dynamics. Nonetheless, average diffusivities of the inhomogeneous fluids can be approximately predicted for either type of dynamics based on knowledge of bulk isotropic fluid behavior and how inhomogeneity modifies the distribution of available volume. Analogous predictions for average diffusivities of experimental, inhomogeneous colloidal dispersions (based on known bulk behavior) suggest that they will exhibit qualitatively different trends than those predicted by models governed by overdamped Langevin dynamics that do not account for hydrodynamic interactions. PMID:25350488
Ziemys, A.; Kojic, M.; Milosevic, M.; Kojic, N.; Hussain, F.; Ferrari, M.; Grattoni, A.
2011-06-01
We present a successful hierarchical modeling approach which accounts for interface effects on diffusivity, ignored in classical continuum theories. A molecular dynamics derived diffusivity scaling scheme is incorporated into a finite element method to model transport through a nanochannel. In a 5 nm nanochannel, the approach predicts 2.2 times slower mass release than predicted by Fick's law by comparing time spent to release 90% of mass. The scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. We show robustness of our discrete continuum model in addressing complex diffusion phenomena in biomedical and engineering applications by providing flexible hierarchical coupling of molecular scale effects and preserving computational finite element method speed.
Energy Technology Data Exchange (ETDEWEB)
Fontaine, J.R.; Rapp, R. [French National Research and Safety Institute, Vandoeuvre (France). Process Engineering Dept.; Koskela, H. [Finnish Institute for Occupational Health, Turku (Finland); Niemela, R. [Finnish Institute for Occupational Health, Vantaa (Finland)
2005-03-01
The application of computational fluid dynamics to the study of room ventilation presupposes precise specification of the boundary conditions associated with air diffusers. The geometric complexity of these devices requires the use of special techniques such as jet-type approximation, relocation of the velocity-fixing surface downstream of the device, or even simulation of the flow within the diffuser. This paper presents a quantitative evaluation of these techniques based on experimental and numerical analysis of the flow of a circular induction diffuser. All the comparisons are performed by linear regression on the three velocity components obtained at over 900 points. A general methodology for characterising complex diffusers is deduced from the results. (author)
Institute of Scientific and Technical Information of China (English)
Wang Chun-Yang
2013-01-01
The diffusion process in an extemal noise-activated non-equilibrium open system-reservoir coupling environment is studied by analytically solving the generalized Langevin equation.The dynamical property of the system near the barrier top is investigated in detail by numerically calculating the quantities such as mean diffusion path,invariance,barrier passing probability,and so on.It is found that,comparing with the unfavorable effect of internal fluctuations,the external noise activation is sometimes beneficial to the diffusion process.An optimal strength of external activation or correlation time of the internal fluctuation is expected for the diffusing particle to have a maximal probability to escape from the potential well.
Dense fluid self-diffusion coefficient calculations using perturbation theory and molecular dynamics
Directory of Open Access Journals (Sweden)
COELHO L. A. F.
1999-01-01
Full Text Available A procedure to correlate self-diffusion coefficients in dense fluids by using the perturbation theory (WCA coupled with the smooth-hard-sphere theory is presented and tested against molecular simulations and experimental data. This simple algebraic expression correlates well the self-diffusion coefficients of carbon dioxide, ethane, propane, ethylene, and sulfur hexafluoride. We have also performed canonical ensemble molecular dynamics simulations by using the Hoover-Nosé thermostat and the mean-square displacement formula to compute self-diffusion coefficients for the reference WCA intermolecular potential. The good agreement obtained from both methods, when compared with experimental data, suggests that the smooth-effective-sphere theory is a useful procedure to correlate diffusivity of pure substances.
Shape optimization of the diffuser blade of an axial blood pump by computational fluid dynamics.
Zhu, Lailai; Zhang, Xiwen; Yao, Zhaohui
2010-03-01
Computational fluid dynamics (CFD) has been a viable and effective way to predict hydraulic performance, flow field, and shear stress distribution within a blood pump. We developed an axial blood pump with CFD and carried out a CFD-based shape optimization of the diffuser blade to enhance pressure output and diminish backflow in the impeller-diffuser connecting region at a fixed design point. Our optimization combined a computer-aided design package, a mesh generator, and a CFD solver in an automation environment with process integration and optimization software. A genetic optimization algorithm was employed to find the pareto-optimal designs from which we could make trade-off decisions. Finally, a set of representative designs was analyzed and compared on the basis of the energy equation. The role of the inlet angle of the diffuser blade was analyzed, accompanied by its relationship with pressure output and backflow in the impeller-diffuser connecting region. PMID:20447042
Dynamical Behavior of Core 3 He Nuclear Reaction-Diffusion Systems and Sun's Gravitational Field
Institute of Scientific and Technical Information of China (English)
DU Jiulin; SHEN Hong
2005-01-01
The coupling of the sun's gravitational field with processes of diffusion and convection exerts a significant influence on the dynamical behavior of the core 3He nuclear reaction-diffusion system. Stability analyses of the system are made in this paper by using the theory of nonequilibrium dynamics. It is showed that, in the nuclear reaction regions extending from the center to about 0.38 times of the radius of the sun, the gravitational field enables the core 3He nuclear reaction-diffusion system to become unstable and, after the instability, new states to appear in the system have characteristic of time oscillation. This may change the production rates of both 7Be and 8B neutrinos.
Accelerated molecular dynamics and equation-free methods for simulating diffusion in solids.
Energy Technology Data Exchange (ETDEWEB)
Deng, Jie; Zimmerman, Jonathan A.; Thompson, Aidan Patrick; Brown, William Michael (Oak Ridge National Laboratories, Oak Ridge, TN); Plimpton, Steven James; Zhou, Xiao Wang; Wagner, Gregory John; Erickson, Lindsay Crowl
2011-09-01
Many of the most important and hardest-to-solve problems related to the synthesis, performance, and aging of materials involve diffusion through the material or along surfaces and interfaces. These diffusion processes are driven by motions at the atomic scale, but traditional atomistic simulation methods such as molecular dynamics are limited to very short timescales on the order of the atomic vibration period (less than a picosecond), while macroscale diffusion takes place over timescales many orders of magnitude larger. We have completed an LDRD project with the goal of developing and implementing new simulation tools to overcome this timescale problem. In particular, we have focused on two main classes of methods: accelerated molecular dynamics methods that seek to extend the timescale attainable in atomistic simulations, and so-called 'equation-free' methods that combine a fine scale atomistic description of a system with a slower, coarse scale description in order to project the system forward over long times.
Institute of Scientific and Technical Information of China (English)
XIAO Fu-Liang; HE Zhao-Guo; ZHANG Sai; SU Zhen-Peng; CHEN Liang-Xu
2011-01-01
Temporal evolution of outer radiation belt electron dynamics resulting from superluminous L-O mode waves is simulated at L＝6.5. Diffusion rates are evaluated and then used as inputs to solve a 2D momentum-pitch-angle diffusion equation, particularly with and without cross diffusion terms. Simulated results demonstrate that phase space density(PSD) of energetic electrons due to L-O mode waves can enhance significantly within 24 h, covering a broader pitch-angle range in the absence of cross terms than that in the presence of cross terms. PSD evolution is also determined by the peak wave frequency, particularly at high kinetic energies. This result indicates that superluminous waves can be a potential candidate responsible for outer radiation belt electron dynamics.
Molecular dynamics simulation of hydrogen dissolution and diffusion in a tungsten grain boundary
International Nuclear Information System (INIS)
We employ a classic molecular dynamics method to investigate the dissolution and diffusion properties of hydrogen (H) in a Σ5(3 1 0) tilt grain boundary (GB). A maximum binding energy of 2.5 eV and a diffusion barrier of 1.65 eV indicate that GB plays an important role in H trapping. Dynamic simulations with temperature ranging from 600 K to 1200 K verify the diffusion and the aggregation of H in the GB are closely associated with the temperature. Pair radius distribution function analysis suggests a high local GB concentration of H such as 30% at 900 K can lead to a disordered GB structure
A model of riots dynamics: shocks, diffusion and thresholds
Berestycki, Henri; Rodriguez, Nancy
2015-01-01
We introduce and analyze several variants of a system of differential equations which model the dynamics of social outbursts, such as riots. The systems involve the coupling of an explicit variable representing the intensity of rioting activity and an underlying (implicit) field of social tension. Our models include the effects of exogenous and endogenous factors as well as various propagation mechanisms. From numerical and mathematical analysis of these models we show that the assumptions made on how different locations influence one another and how the tension in the system disperses play a major role on the qualitative behavior of bursts of social unrest. Furthermore, we analyze here various properties of these systems, such as the existence of traveling wave solutions, and formulate some new open mathematical problems which arise from our work.
Directory of Open Access Journals (Sweden)
Amninder S Virk
2015-02-01
Full Text Available Molecular crowding occurs when the total concentration of macromolecular species in a solution is so high that a considerable proportion of the volume is physically occupied and therefore not accessible to other molecules. This results in significant changes in the solution properties of the molecules in such systems. Macromolecular crowding is ubiquitous in biological systems due to the generally high intracellular protein concentrations. The major hindrance to understanding crowding is the lack of direct comparison of experimental data with theoretical or simulated data. Self-diffusion is sensitive to changes in the molecular weight and shape of the diffusing species, and the available diffusion space (i.e., diffusive obstruction. Consequently, diffusion measurements are a direct means for probing crowded systems including the self-association of molecules. In this work, nuclear magnetic resonance measurements of the self-diffusion of four amino acids (glycine, alanine, valine and phenylalanine up to their solubility limit in water were compared directly with molecular dynamics simulations. The experimental data were then analyzed using various models of aggregation and obstruction. Both experimental and simulated data revealed that the diffusion of both water and the amino acids were sensitive to the amino acid concentration. The direct comparison of the simulated and experimental data afforded greater insights into the aggregation and obstruction properties of each amino acid.
Energy Technology Data Exchange (ETDEWEB)
Barbante, Paolo [Dipartimento di Matematica, Politecnico di Milano - Piazza Leonardo da Vinci 32 - 20133 Milano (Italy); Frezzotti, Aldo; Gibelli, Livio [Dipartimento di Scienze e Tecnologie Aerospaziali, Politecnico di Milano - Via La Masa 34 - 20156 Milano (Italy)
2014-12-09
The unsteady evaporation of a thin planar liquid film is studied by molecular dynamics simulations of Lennard-Jones fluid. The obtained results are compared with the predictions of a diffuse interface model in which capillary Korteweg contributions are added to hydrodynamic equations, in order to obtain a unified description of the liquid bulk, liquid-vapor interface and vapor region. Particular care has been taken in constructing a diffuse interface model matching the thermodynamic and transport properties of the Lennard-Jones fluid. The comparison of diffuse interface model and molecular dynamics results shows that, although good agreement is obtained in equilibrium conditions, remarkable deviations of diffuse interface model predictions from the reference molecular dynamics results are observed in the simulation of liquid film evaporation. It is also observed that molecular dynamics results are in good agreement with preliminary results obtained from a composite model which describes the liquid film by a standard hydrodynamic model and the vapor by the Boltzmann equation. The two mathematical model models are connected by kinetic boundary conditions assuming unit evaporation coefficient.
Dynamics and waves near multiple magnetic null points in reconnection diffusion region
Czech Academy of Sciences Publication Activity Database
Deng, X. H.; Zhou, M.; Li, S. Y.; Baumjohann, W.; Andre, M.; Cornilleau, N.; Santolík, Ondřej; Pontin, D. I.; Reme, H.; Lucek, E.; Fazakerley, A. N.; Decreau, P.; Daly, P.; Nakamura, R.; Tang, R. X.; Hu, Y. H.; Pang, Y.; Büchner, J.; Zhao, H.; Vaivads, A.; Pickett, J. S.; Ng, C. S.; Lin, X.; Fu, S.; Yuan, Z. G.; Su, Z. W.; Wang, J. F.
2009-01-01
Roč. 114, - (2009), A07216/1-A07216/7. ISSN 0148-0227 Institutional research plan: CEZ:AV0Z30420517 Keywords : waves * dynamics * reconnection * diffusion Subject RIV: BL - Plasma and Gas Discharge Physics Impact factor: 3.082, year: 2009
Sharma, Manju; Yashonath, S.
2009-01-01
We report results of molecular dynamics investigations into neutral impurity diffusing within an amorphous solid as a function of the size of the diffusant and density of the host amorphous matrix. We find that self diffusivity exhibits an anomalous maximum as a function of the size of the impurity species. An analysis of properties of the impurity atom with maximum diffusivity shows that it is associated with lower mean square force, reduced backscattering of velocity autocorrelation functio...
Effects of Heterogeneous Diffuse Fibrosis on Arrhythmia Dynamics and Mechanism.
Kazbanov, Ivan V; ten Tusscher, Kirsten H W J; Panfilov, Alexander V
2016-01-01
Myocardial fibrosis is an important risk factor for cardiac arrhythmias. Previous experimental and numerical studies have shown that the texture and spatial distribution of fibrosis may play an important role in arrhythmia onset. Here, we investigate how spatial heterogeneity of fibrosis affects arrhythmia onset using numerical methods. We generate various tissue textures that differ by the mean amount of fibrosis, the degree of heterogeneity and the characteristic size of heterogeneity. We study the onset of arrhythmias using a burst pacing protocol. We confirm that spatial heterogeneity of fibrosis increases the probability of arrhythmia induction. This effect is more pronounced with the increase of both the spatial size and the degree of heterogeneity. The induced arrhythmias have a regular structure with the period being mostly determined by the maximal local fibrosis level. We perform ablations of the induced fibrillatory patterns to classify their type. We show that in fibrotic tissue fibrillation is usually of the mother rotor type but becomes of the multiple wavelet type with increase in tissue size. Overall, we conclude that the most important factor determining the formation and dynamics of arrhythmia in heterogeneous fibrotic tissue is the value of maximal local fibrosis. PMID:26861111
International Nuclear Information System (INIS)
Based on ballistic-diffusive approximation, a method is presented to model heat transfer in nanocomposites containing metal nanoparticles. This method provides analytical expression for the temperature dynamics of metallic nanoparticles embedded in a dielectric medium. In this study, nanoparticles are considered as spherical shells, so that Boltzmann equation is solved using ballistic-diffusive approximation to calculate the electron and lattice thermal dynamics in gold nanoparticles, while thermal exchange between the particles is taken into account. The model was used to investigate the influence of particle size and metal concentration of the medium on the electron and lattice thermal dynamics. It is shown that these two parameters are crucial in determining the nanocomposite thermal behavior. Our results showed that the heat transfer rate from nanoparticles to the matrix decreases as the nanoparticle size increases. On the other hand, increasing the metal concentration of the medium can also decrease the heat transfer rate
Specific ions modulate diffusion dynamics of hydration water on lipid membrane surfaces.
Song, Jinsuk; Franck, John; Pincus, Philip; Kim, Mahn Won; Han, Songi
2014-02-12
Effects of specific ions on the local translational diffusion of water near large hydrophilic lipid vesicle surfaces were measured by Overhauser dynamic nuclear polarization (ODNP). ODNP relies on an unpaired electron spin-containing probe located at molecular or surface sites to report on the dynamics of water protons within ~10 Å from the spin probe, which give rise to spectral densities for electron-proton cross-relaxation processes in the 10 GHz regime. This pushes nuclear magnetic resonance relaxometry to more than an order of magnitude higher frequencies than conventionally feasible, permitting the measurement of water moving with picosecond to subnanosecond correlation times. Diffusion of water within ~10 Å of, i.e., up to ~3 water layers around the spin probes located on hydrophilic lipid vesicle surfaces is ~5 times retarded compared to the bulk water translational diffusion. This directly reflects on the activation barrier for surface water diffusion, i.e., how tightly water is bound to the hydrophilic surface and surrounding waters. We find this value to be modulated by the presence of specific ions in solution, with its order following the known Hofmeister series. While a molecular description of how ions affect the hydration structure at the hydrophilic surface remains to be answered, the finding that Hofmeister ions directly modulate the surface water diffusivity implies that the strength of the hydrogen bond network of surface hydration water is directly modulated on hydrophilic surfaces. PMID:24456096
Kim, Changho; Borodin, Oleg; Karniadakis, George Em
2015-12-01
We analyze two standard methods to compute the diffusion coefficient of a tracer particle in a medium from molecular dynamics (MD) simulation, the velocity autocorrelation function (VACF) method, and the mean-squared displacement (MSD) method. We show that they are equivalent in the sense that they provide the same mean values with the same level of statistical errors. We obtain analytic expressions for the level of the statistical errors present in the time-dependent diffusion coefficient as well as the VACF and the MSD. Under the assumption that the velocity of the tracer particle is a Gaussian process, all results are expressed in terms of the VACF. Hence, the standard errors of all relevant quantities are computable once the VACF is obtained from MD simulation. By using analytic models described by the Langevin equations driven by Gaussian white noise and Poissonian white shot noise, we verify our theoretical error estimates and discuss the non-Gaussianity effect in the error estimates when the Gaussian process approximation does not hold exactly. For validation, we perform MD simulations for the self-diffusion of a Lennard-Jones fluid and the diffusion of a large and massive colloid particle suspended in the fluid. Our theoretical framework is also applicable to mesoscopic simulations, e.g., Langevin dynamics and dissipative particle dynamics.
Molecular dynamics simulation of nanoscale surface diffusion of heterogeneous adatoms clusters
Muhammad, Imran; Fayyaz, Hussain; Muhammad, Rashid; Muhammad, Ismail; Hafeez, Ullah; Yongqing, Cai; M Arshad, Javid; Ejaz, Ahmad; S, A. Ahmad
2016-07-01
Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface diffusion of heterogeneous adatoms clusters can be vital for the binary island growth on the surface and can be useful for the formation of alloy-based thin film surface through atomic exchange process. The results of the diffusion process show that at 300 K, the diffusion of small adatoms clusters shows hopping, sliding, and shear motion; whereas for large adatoms clusters (hexamer and above), the diffusion is negligible. At 500 K, small adatoms clusters, i.e., dimer, show almost all possible diffusion mechanisms including the atomic exchange process; however no such exchange is observed for adatoms clusters greater than dimer. At 700 K, the exchange mechanism dominates for all types of clusters, where Zr adatoms show maximum tendency and Ag adatoms show minimum or no tendency toward the exchange process. Separation and recombination of one or more adatoms are also observed at 500 K and 700 K. The Ag adatoms also occupy pop-up positions over the adatoms clusters for short intervals. At 700 K, the vacancies are also generated in the vicinity of the adatoms cluster, vacancy formation, filling, and shifting can be observed from the results.
Chen, J. -Y.; Echekki, T.
1999-01-01
Triple flames arise in a number of practical configurations where fuel and oxidizer are partially premixed, such as in the base of a lifted jet flame. Past experimental studies, theoretical analyses, and numerical modeling of triple flames suggested the potential role of triple flames in stabilizing turbulent flames and in promoting flame propagation. From recent numerical simulations of laminar triple flames, a strong influence of differential diffusion among species and heat on the triple flame structure has been gradually appreciated. This paper reports preliminary numerical results on the influence of gravity and differential diffusion effects on the structure and dynamics of triple flames with a one-step global irreversible chemistry model.
International Nuclear Information System (INIS)
Using a numerical library for arbitrary precision arithmetic I study the irregular dependence of the diffusion coefficient on the slope of a piecewise linear map defining a dynamical system. I find that the graph of the diffusion coefficient as a function of the slope has the fractal dimension 1, but the convergence to this limit is slowed down by logarithmic corrections. The exponent controlling this correction depends on the slope and is either 1 or 2 depending on existence and properties of a Markov partition. (author)
Room temperature compressibility and the diffusivity anomaly of liquid water from first principles
Corsetti, Fabiano; Soler, José M; Alexandre, S S; Fernández-Serra, M -V
2013-01-01
The isothermal compressibility of water is essential to understand its anomalous properties. We compute it by ab initio molecular dynamics simulations of 200 molecules at five densities, using two different van der Waals density functionals. While both functionals predict compressibilities within ~30% of experiment, only one of them reproduces the density dependence of the self-diffusion constant and its anomalous behavior. Their discrepancies are explained in terms of the low- and high-density structures of the liquid.
International Nuclear Information System (INIS)
We have developed an N-body interatomic potential, based on the second moment approximation of the tight-binding scheme, by fitting its four adjustable parameters to the cohesive energy, atomic volume, and elastic constants of hcp-Zr. We then showed that various properties of this potential compare favorably with those of zirconium in both the low temperatures hcp phase and the high temperature bcc phase. Such is the case in particular for the elastic constants, the phonon dispersion curves, the thermal expansion, and the melting temperature. We reproduced by molecular dynamics (MD) simulations on this potential the hcp/bcc phase transformation in both ways. It indeed occurs following the mechanism predicted by Burgers. We find a vibrational entropy of transformation equal to 0.13 kB. Our calculations suggest that in real zirconium the electronic contribution to the transformation entropy is important. We show that some interatomic potential lead to a higher value of the vibrational entropy in the hcp phase than in the bcc phase. We specified the dynamics of the vacancy migration in the bcc phase. The atomic jumps are almost exclusively nearest neighbour ones. The walk of the vacancy becomes strongly correlated at high temperatures. The vacancy jump frequency is very large and has a perfectly arrhenian behaviour. There is no evicence of a dynamical lowering of the vacancy migration barrier: the static and dynamic values of the vacancy migration energy are almost equal, both being unusually small (0.3 eV). The self diffusion coefficent of our model for the vacancy mechanism reproduces an anomalous fast diffusion close to that measured experimentally in bcc-Zr. In our model at high temperatures the time interval between successive jumps is almost equal to the time of flight. The migration events will therefore influence the formation of the vacancies
On an explicit finite difference method for fractional diffusion equations
S. B. Yuste; Acedo, L.
2003-01-01
A numerical method to solve the fractional diffusion equation, which could also be easily extended to many other fractional dynamics equations, is considered. These fractional equations have been proposed in order to describe anomalous transport characterized by non-Markovian kinetics and the breakdown of Fick's law. In this paper we combine the forward time centered space (FTCS) method, well known for the numerical integration of ordinary diffusion equations, with the Grunwald-Letnikov defin...
Dynamical invariants in a non-Markovian quantum-state-diffusion equation
Luo, Da-Wei; Pyshkin, P. V.; Lam, Chi-Hang; Yu, Ting; Lin, Hai-Qing; You, J. Q.; Wu, Lian-Ao
2015-12-01
We find dynamical invariants for open quantum systems described by the non-Markovian quantum-state-diffusion (QSD) equation. In stark contrast to closed systems where the dynamical invariant can be identical to the system density operator, these dynamical invariants no longer share the equation of motion for the density operator. Moreover, the invariants obtained with a biorthonormal basis can be used to render an exact solution to the QSD equation and the corresponding non-Markovian dynamics without using master equations or numerical simulations. Significantly we show that we can apply these dynamical invariants to reverse engineering a Hamiltonian that is capable of driving the system to the target state, providing a different way to design control strategy for open quantum systems.
Sub-diffusion and population dynamics of water confined in soft environments
Hanot, Samuel; Lyonnard, Sandrine; Mossa, Stefano
2016-02-01
We have studied by using molecular dynamics computer simulations the dynamics of water confined in ionic surfactant phases, ranging from well ordered lamellar structures to micelles at low and high water loading, respectively. We have analysed in depth the main dynamical features in terms of mean-squared displacements and intermediate scattering functions, and found clear evidence of sub-diffusive behaviour. We have identified water molecules lying at the charged interface with the hydrophobic confining matrix as the main factor responsible for this unusual feature, and given a comprehensive picture of dynamics based on a very precise analysis of lifetimes at the interface. We conclude by providing, for the first time to our knowledge, a unique framework for rationalizing the existence of important dynamical heterogeneities in fluids adsorbed in soft confining environments.We have studied by using molecular dynamics computer simulations the dynamics of water confined in ionic surfactant phases, ranging from well ordered lamellar structures to micelles at low and high water loading, respectively. We have analysed in depth the main dynamical features in terms of mean-squared displacements and intermediate scattering functions, and found clear evidence of sub-diffusive behaviour. We have identified water molecules lying at the charged interface with the hydrophobic confining matrix as the main factor responsible for this unusual feature, and given a comprehensive picture of dynamics based on a very precise analysis of lifetimes at the interface. We conclude by providing, for the first time to our knowledge, a unique framework for rationalizing the existence of important dynamical heterogeneities in fluids adsorbed in soft confining environments. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR05853H
INTRODUCTION: Surface Dynamics, Phonons, Adsorbate Vibrations and Diffusion
Bruch, L. W.
2004-07-01
well infrared photodetectors (QWIPs) and resonant cavity-enhanced photodiodes (RCEPDs) based on dilute nitrides need to be investigated extensively. To date, most theoretical attention has been focused on understanding the band structure of the GaInAsN/GaAs system and on evaluating gain spectra and threshold conditions for 1.3 µm lasers. However, as our understanding of band structure and the effects of strain, defects, etc in dilute nitrides improves we can calculate the electrical and optical properties, including radiative and non-radiative recombination for the materials and structures of interest. The spontaneous and stimulated emission rates have already been calculated for GaInNAs at 1.3 µm by many authors, but extension to other dilute nitrides and other wavelength ranges still represents a major challenge. Many-body effects, including exchange-correlation effects, are essential for accurate models of gain spectra in lasers and optical amplifiers. The differential gain is a key parameter for laser modulation and remains an important subject of study as new materials and structures are explored. Similarly the differential refractive index and linewidth enhancement factor have strong influences on laser spectrum (chirp, linewidth), dynamics and noise, and these must also be studied theoretically. As regards to non-radiative recombination, in addition to recombination through defects, the Auger effect is of especial significance for wavelengths beyond 1 µm and is a worthy subject for theoretical study. The converse effect, impact ionization, is of key importance for avalanche photodiodes (APDs) and has yet to be evaluated for the dilute nitride materials. Inter-valence band absorption (IVBA) is of significance, as a possible cause of temperature sensitivity in lasers and this must be investigated theoretically in the dilute nitrides. Third-order non-linear optical coefficients should be calculated in order to assess the scope for all-optical signal processing
Sub-diffusion and trapped dynamics of neutral and charged probes in DNA-protein coacervates
International Nuclear Information System (INIS)
The physical mechanism leading to the formation of large intermolecular DNA-protein complexes has been studied. Our study aims to explain the occurrence of fast coacervation dynamics at the charge neutralization point, followed by the appearance of smaller complexes and slower coacervation dynamics as the complex experiences overcharging. Furthermore, the electrostatic potential and probe mobility was investigated to mimic the transport of DNA / DNA-protein complex in a DNA-protein complex coacervate medium [N. Arfin and H. B. Bohidar, J. Phys. Chem. B 116, 13192 (2012)] by assigning neutral, negative, or positive charge to the probe particle. The mobility of the neutral probe was maximal at low matrix concentrations and showed random walk behavior, while its mobility ceased at the jamming concentration of c = 0.6, showing sub-diffusion and trapped dynamics. The positively charged probe showed sub-diffusive random walk followed by trapped dynamics, while the negatively charged probe showed trapping with occasional hopping dynamics at much lower concentrations. Sub-diffusion of the probe was observed in all cases under consideration, where the electrostatic interaction was used exclusively as the dominant force involved in the dynamics. For neutral and positive probes, the mean square displacement 〈R2〉 exhibits a scaling with time as 〈R2〉 ∼ tα, distinguishing random walk and trapped dynamics at α = 0.64 ± 0.04 at c = 0.12 and c = 0.6, respectively. In addition, the same scaling factors with the exponent β = 0.64 ± 0.04 can be used to distinguish random walk and trapped dynamics for the neutral and positive probes using the relation between the number of distinct sites visited by the probe, S(t), which follows the scaling, S(t) ∼ tβ/ln (t). Our results established the occurrence of a hierarchy of diffusion dynamics experienced by a probe in a dense medium that is either charged or neutral
Sub-diffusion and trapped dynamics of neutral and charged probes in DNA-protein coacervates
Directory of Open Access Journals (Sweden)
Najmul Arfin
2013-11-01
Full Text Available The physical mechanism leading to the formation of large intermolecular DNA-protein complexes has been studied. Our study aims to explain the occurrence of fast coacervation dynamics at the charge neutralization point, followed by the appearance of smaller complexes and slower coacervation dynamics as the complex experiences overcharging. Furthermore, the electrostatic potential and probe mobility was investigated to mimic the transport of DNA / DNA-protein complex in a DNA-protein complex coacervate medium [N. Arfin and H. B. Bohidar, J. Phys. Chem. B 116, 13192 (2012] by assigning neutral, negative, or positive charge to the probe particle. The mobility of the neutral probe was maximal at low matrix concentrations and showed random walk behavior, while its mobility ceased at the jamming concentration of c = 0.6, showing sub-diffusion and trapped dynamics. The positively charged probe showed sub-diffusive random walk followed by trapped dynamics, while the negatively charged probe showed trapping with occasional hopping dynamics at much lower concentrations. Sub-diffusion of the probe was observed in all cases under consideration, where the electrostatic interaction was used exclusively as the dominant force involved in the dynamics. For neutral and positive probes, the mean square displacement ⟨R2⟩ exhibits a scaling with time as ⟨R2⟩ ∼ tα, distinguishing random walk and trapped dynamics at α = 0.64 ± 0.04 at c = 0.12 and c = 0.6, respectively. In addition, the same scaling factors with the exponent β = 0.64 ± 0.04 can be used to distinguish random walk and trapped dynamics for the neutral and positive probes using the relation between the number of distinct sites visited by the probe, S(t, which follows the scaling, S(t ∼ tβ/ln (t. Our results established the occurrence of a hierarchy of diffusion dynamics experienced by a probe in a dense medium that is either charged or neutral.
Sub-diffusion and trapped dynamics of neutral and charged probes in DNA-protein coacervates
Arfin, Najmul; Yadav, Avinash Chand; Bohidar, H. B.
2013-11-01
The physical mechanism leading to the formation of large intermolecular DNA-protein complexes has been studied. Our study aims to explain the occurrence of fast coacervation dynamics at the charge neutralization point, followed by the appearance of smaller complexes and slower coacervation dynamics as the complex experiences overcharging. Furthermore, the electrostatic potential and probe mobility was investigated to mimic the transport of DNA / DNA-protein complex in a DNA-protein complex coacervate medium [N. Arfin and H. B. Bohidar, J. Phys. Chem. B 116, 13192 (2012)] by assigning neutral, negative, or positive charge to the probe particle. The mobility of the neutral probe was maximal at low matrix concentrations and showed random walk behavior, while its mobility ceased at the jamming concentration of c = 0.6, showing sub-diffusion and trapped dynamics. The positively charged probe showed sub-diffusive random walk followed by trapped dynamics, while the negatively charged probe showed trapping with occasional hopping dynamics at much lower concentrations. Sub-diffusion of the probe was observed in all cases under consideration, where the electrostatic interaction was used exclusively as the dominant force involved in the dynamics. For neutral and positive probes, the mean square displacement ⟨R2⟩ exhibits a scaling with time as ⟨R2⟩ ˜ tα, distinguishing random walk and trapped dynamics at α = 0.64 ± 0.04 at c = 0.12 and c = 0.6, respectively. In addition, the same scaling factors with the exponent β = 0.64 ± 0.04 can be used to distinguish random walk and trapped dynamics for the neutral and positive probes using the relation between the number of distinct sites visited by the probe, S(t), which follows the scaling, S(t) ˜ tβ/ln (t). Our results established the occurrence of a hierarchy of diffusion dynamics experienced by a probe in a dense medium that is either charged or neutral.
International Nuclear Information System (INIS)
Dynamical decoupling, a generalization of the original NMR spin-echo sequence, is becoming increasingly relevant as a tool for reducing decoherence in quantum systems. Such sequences apply non-equidistant refocusing pulses for optimizing the coupling between systems, and environmental fluctuations characterized by a given noise spectrum. One such sequence, dubbed Selective Dynamical Recoupling (SDR) [P. E. S. Smith, G. Bensky, G. A. Álvarez, G. Kurizki, and L. Frydman, Proc. Natl. Acad. Sci. 109, 5958 (2012)], allows one to coherently reintroduce diffusion decoherence effects driven by fluctuations arising from restricted molecular diffusion [G. A. Álvarez, N. Shemesh, and L. Frydman, Phys. Rev. Lett. 111, 080404 (2013)]. The fully-refocused, constant-time, and constant-number-of-pulses nature of SDR also allows one to filter out “intrinsic” T1 and T2 weightings, as well as pulse errors acting as additional sources of decoherence. This article explores such features when the fluctuations are now driven by unrestricted molecular diffusion. In particular, we show that diffusion-driven SDR can be exploited to investigate the decoherence arising from the frequency fluctuations imposed by internal gradients. As a result, SDR presents a unique way of probing and characterizing these internal magnetic fields, given an a priori known free diffusion coefficient. This has important implications in studies of structured systems, including porous media and live tissues, where the internal gradients may serve as fingerprints for the system's composition or structure. The principles of this method, along with full analytical solutions for the unrestricted diffusion-driven modulation of the SDR signal, are presented. The potential of this approach is demonstrated with the generation of a novel source of MRI contrast, based on the background gradients active in an ex vivo mouse brain. Additional features and limitations of this new method are discussed
A network of discrete events for the representation and analysis of diffusion dynamics
Pintus, Alberto M.; Pazzona, Federico G.; Demontis, Pierfranco; Suffritti, Giuseppe B.
2015-11-01
We developed a coarse-grained description of the phenomenology of diffusive processes, in terms of a space of discrete events and its representation as a network. Once a proper classification of the discrete events underlying the diffusive process is carried out, their transition matrix is calculated on the basis of molecular dynamics data. This matrix can be represented as a directed, weighted network where nodes represent discrete events, and the weight of edges is given by the probability that one follows the other. The structure of this network reflects dynamical properties of the process of interest in such features as its modularity and the entropy rate of nodes. As an example of the applicability of this conceptual framework, we discuss here the physics of diffusion of small non-polar molecules in a microporous material, in terms of the structure of the corresponding network of events, and explain on this basis the diffusivity trends observed. A quantitative account of these trends is obtained by considering the contribution of the various events to the displacement autocorrelation function.
Self-diffusion dynamic behavior of atomic clusters on Re(0 0 0 1) surface
International Nuclear Information System (INIS)
Using molecular dynamics simulations and a modified analytic embedded atom potential, the self-diffusion dynamics of rhenium atomic clusters up to seven atoms on Re(0 0 0 1) surface have been studied in the temperature ranges from 600 K to 1900 K. The simulation time varies from 20 ns to 200 ns according to the cluster sizes and the temperature. The heptamer and trimer are more stable comparing to other neighboring non-compact clusters. The diffusion coefficients of clusters are derived from the mean square displacement of cluster's mass-center, and diffusion prefactors D0 and activation energies Ea are derived from the Arrhenius relation. It is found that the Arrhenius relation of the adatom can be divided into two parts at different temperature range. The activation energy of clusters increases with the increasing of the atom number in clusters. The prefactor of the heptamer is 2-3 orders of magnitude higher than a usual prefactor because of a large number of nonequivalent diffusion processes. The trimer and heptamer are the nuclei at different temperature range according to the nucleation theory.
Critical short-time dynamics in a system with interacting static and diffusive populations.
Argolo, C; Quintino, Yan; Gleria, Iram; Lyra, M L
2012-01-01
We study the critical short-time dynamical behavior of a one-dimensional model where diffusive individuals can infect a static population upon contact. The model presents an absorbing phase transition from an active to an inactive state. Previous calculations of the critical exponents based on quasistationary quantities have indicated an unusual crossover from the directed percolation to the diffusive contact process universality classes. Here we show that the critical exponents governing the slow short-time dynamic evolution of several relevant quantities, including the order parameter, its relative fluctuations, and correlation function, reinforce the lack of universality in this model. Accurate estimates show that the critical exponents are distinct in the regimes of low and high recovery rates. PMID:22400516
Dynamic Medical Material Distribution Model Based on Epidemic Diffusion Rule and Clustering Approach
Directory of Open Access Journals (Sweden)
Wu Guangmin
2015-01-01
Full Text Available Due to the fact that the dynamic medical material distribution is vital to the quick response to urgent demand when the Ebola virus occurs, the optimal distribution approach is explored according to the Ebola virus diffusion rule and different severity of the epidemic. First, we choose the more serious epidemic state of Sierra Leone in West Africa as the research object and the SIQR (susceptible, infected, quarantined, required epidemic model with pulse vaccination is introduced to describe the Ebola diffusion rule and obtain the demanded vaccine and drug in each pulse. Based on the SIQR model, thirteen areas in Sierra Leone are classified into three emergency levels by clustering analysis. Then a dynamic medical material distribution model is formulated, with goals of both reducing the transportation cost and shortages. The results indicate that the proposed approach can make an outstanding contribution to fight against the Ebola virus.
A comparative molecular dynamics study of diffusion of -decane and 3-methyl pentane in Y zeolite
Indian Academy of Sciences (India)
F G Pazzona; B J Borah; P Demontis; G B Suffritti; S Yashonath
2009-09-01
Molecular dynamics simulations are reported on the structure and dynamics of -decane and 3-methylpentane in zeolite NaY. We have calculated several properties such as the center of mass-center of mass rdf, the end-end distance distribution, bond angle distribution and dihedral angle distribution. We have also analysed trajectory to obtain diffusivity and velocity autocorrelation function (VACF). Surprisingly, the diffusivity of 3-methylpentane which is having larger cross-section perpendicular to the long molecular axis is higher than -decane at 300 K. Activation energies have been obtained from simulations performed at 200 K, 300 K, 350 K, 400 K and 450 K in the NVE ensemble. These results can be understood in terms of the previously known levitation effect. Arrhenious plot has higher value of slope for -decane (5.9 kJ/mol) than 3-methylpentane (3.7 kJ/mol) in agreement with the prediction of levitation effect.
Ionization dynamics in ionic liquids probed via self-diffusion coefficient measurements
International Nuclear Information System (INIS)
Graphical abstract: - Highlights: • Exploiting non-Arrhenius nature of physiochemical properties of ionic liquids to understand ion dynamics. • Estimation of ion concentration in ionic liquids via self-diffusion coefficient measurements. • Thermodynamics of the ionization process in ionic liquids. • Thermodynamics of the self-diffusion of cations and anions through Arrhenius and Eyring equations. - Abstract: Ionic liquids contain ions and ion pairs with fast exchange between them. We propose a novel process to deduce the fraction of ions present in an ionic liquid and the equilibrium constants of ionization processes from measured ion self-diffusion coefficients using Pulsed Field Gradient (PFG) NMR. The enthalpy and entropy changes of ionization and ion self-diffusion processes are obtained for a series of ionic liquids using this method. These data were used to explain the interactions between cations and anions of ionic liquids. The interactions are also interpreted by the delocalization of the ion’s charge densities. The self-diffusion coefficients of cations and anions for measured ionic liquids are discussed
Ionization dynamics in ionic liquids probed via self-diffusion coefficient measurements
Energy Technology Data Exchange (ETDEWEB)
Mao, Yougang; Damodaran, Krishnan, E-mail: damodak@pitt.edu
2014-08-31
Graphical abstract: - Highlights: • Exploiting non-Arrhenius nature of physiochemical properties of ionic liquids to understand ion dynamics. • Estimation of ion concentration in ionic liquids via self-diffusion coefficient measurements. • Thermodynamics of the ionization process in ionic liquids. • Thermodynamics of the self-diffusion of cations and anions through Arrhenius and Eyring equations. - Abstract: Ionic liquids contain ions and ion pairs with fast exchange between them. We propose a novel process to deduce the fraction of ions present in an ionic liquid and the equilibrium constants of ionization processes from measured ion self-diffusion coefficients using Pulsed Field Gradient (PFG) NMR. The enthalpy and entropy changes of ionization and ion self-diffusion processes are obtained for a series of ionic liquids using this method. These data were used to explain the interactions between cations and anions of ionic liquids. The interactions are also interpreted by the delocalization of the ion’s charge densities. The self-diffusion coefficients of cations and anions for measured ionic liquids are discussed.
A molecular dynamics simulation of self-diffusion on Fe surfaces
Energy Technology Data Exchange (ETDEWEB)
Wang Changqing, E-mail: cqw@lit.edu.cn [School of Physics and Engineering, Center for Clean Energy and Quantum Structures, Zhengzhou University, Zhengzhou 450052 (China); Department of Mathematics and Physics, Luoyang Institute of Science and Technology, Luoyang 471023 (China); Qin Zhen [School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); Zhang Yongsheng [Department of Mathematics and Physics, Luoyang Institute of Science and Technology, Luoyang 471023 (China); Sun Qiang; Jia Yu [School of Physics and Engineering, Center for Clean Energy and Quantum Structures, Zhengzhou University, Zhengzhou 450052 (China)
2012-03-01
Using embedded-atom-method (EAM) potential, an adatom and a vacancy diffusion processes have been simulated in detail by molecular dynamics on three Fe surfaces, Fe (1 1 0), Fe (1 0 0), and Fe (1 1 1). Our results reveal that adatom adsorption energies and diffusion migration energies on these surfaces have similar monotonic trend to the relative layer spacing relaxation, R{sub (110)} < R{sub (100)} < R{sub (111)}, adsorption energy, E{sub a(110)}{sup a}
Investigation of the performance of a variable area diffuser for gas dynamic lasers
Energy Technology Data Exchange (ETDEWEB)
Nuttbrock, D.L.
1974-06-01
An experimental study was performed to determine the performance of a variable area diffuser downstrem of an array of supersonic nozzles, and to determine the Mach number profile between the nozzle exit and the diffuser entrance. The study was conducted on a blowdown wind tunnel and the test section was designed to model a gas dynamic laser with an array of five nozzle blades, a constant area section, and a converging-diverging diffuser. Air at a temperature of 70/sup 0/F and at total pressures ranging from 100 to 210 psig was expanded through an area ratio of approximately 66. Using various pressure measurements the Mach number was found to decrease from M = 6.4 at the nozzle exit to approximately M = 4.0 at the diffuser entrance. The rapid decrease was attributed to the irreversible effects of friction, the nozzle blade wakes, and the nozzle throat shocks. The minimum starting area ratio of the diffuser was 0.59, which agrees well with one dimensional theory.
On the dynamic programming principle for controlled diffusion processes in a cylindrical region
Dmitry B. Rokhlin
2012-01-01
We prove the dynamic programming principle for a class of diffusion processes controlled up to the time of exit from a cylindrical region $[0,T)\\times G$. It is assumed that the functional to be maximized is in the Lagrange form with nonnegative integrand. Besides this we only adopt the standard assumptions, ensuring the existence of a unique strong solution of a stochastic differential equation for the state process.
Dynamics for a diffusive prey-predator model with different free boundaries
Wang, Mingxin
2015-01-01
To understand the spreading and interaction of prey and predator, in this paper we study the dynamics of the diffusive Lotka-Volterra type prey-predator model with different free boundaries. These two free boundaries, which may intersect each other as time evolves, are used to describe the spreading of prey and predator. We investigate the existence and uniqueness, regularity and uniform estimates, and long time behaviors of global solution. Some sufficient conditions for spreading and vanish...
Dynamic Medical Material Distribution Model Based on Epidemic Diffusion Rule and Clustering Approach
Wu Guangmin; Peng Jiarun; Xi Bowen
2015-01-01
Due to the fact that the dynamic medical material distribution is vital to the quick response to urgent demand when the Ebola virus occurs, the optimal distribution approach is explored according to the Ebola virus diffusion rule and different severity of the epidemic. First, we choose the more serious epidemic state of Sierra Leone in West Africa as the research object and the SIQR (susceptible, infected, quarantined, required) epidemic model with pulse vaccination is introduced to describe ...
Data Diffusion: Dynamic Resource Provision and Data-Aware Scheduling for Data Intensive Applications
Raicu, Ioan; Zhao, Yong; Foster, Ian; Szalay, Alex
2008-01-01
Data intensive applications often involve the analysis of large datasets that require large amounts of compute and storage resources. While dedicated compute and/or storage farms offer good task/data throughput, they suffer low resource utilization problem under varying workloads conditions. If we instead move such data to distributed computing resources, then we incur expensive data transfer cost. In this paper, we propose a data diffusion approach that combines dynamic resource provisioning...
Relaxation time in a non-conserving driven-diffusive system with parallel dynamics
International Nuclear Information System (INIS)
We introduce a two-state non-conserving driven-diffusive system in one dimension under a discrete-time updating scheme. We show that the steady state of the system can be obtained using a matrix product approach. On the other hand, the steady state of the system can be expressed in terms of a linear superposition of Bernoulli shock measures with random walk dynamics. The dynamics of a shock position is studied in detail. The spectrum of the transfer matrix and the relaxation times to the steady state have also been studied in the limit of large system size. (paper)
Spatio-temporal patterns with hyperchaotic dynamics in diffusively coupled biochemical oscillators
Directory of Open Access Journals (Sweden)
Gerold Baier
1997-01-01
Full Text Available We present three examples how complex spatio-temporal patterns can be linked to hyperchaotic attractors in dynamical systems consisting of nonlinear biochemical oscillators coupled linearly with diffusion terms. The systems involved are: (a a two-variable oscillator with two consecutive autocatalytic reactions derived from the Lotka–Volterra scheme; (b a minimal two-variable oscillator with one first-order autocatalytic reaction; (c a three-variable oscillator with first-order feedback lacking autocatalysis. The dynamics of a finite number of coupled biochemical oscillators may account for complex patterns in compartmentalized living systems like cells or tissue, and may be tested experimentally in coupled microreactors.
The Dynamics of a Diffusive Nutrient-Algae Model Based upon the Sanyang Wetland
Directory of Open Access Journals (Sweden)
Yi Wang
2015-01-01
Full Text Available The stability and spatiotemporal dynamics of a diffusive nutrient-algae model are investigated mathematically and numerically. Mathematical theoretical studies have considered the positivity and boundedness of the solution and the existence, local stability, and global stability of equilibria. Turing instability has also been studied. Furthermore, a series of numerical simulations was performed and a complex Turing pattern found. These results indicate that the nutrient input rate has an important influence on the density and spatial distribution of algae populations. This may help us to obtain a better understanding of the interactions of nutrient and algae and to investigate plankton dynamics in aquatic ecosystems.
Institute of Scientific and Technical Information of China (English)
WANG Chao; WANG Zhi; WANG Jing; SU Tao
2007-01-01
To determinate the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis(EDX) is used to establish the content change of oxygen in the adhesive in adhesive/carbon fiber reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carbon fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analysis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of both energy dispersive X-ray spectroscopy and elemental analysis. The determined results with EDX analysis are almost the same as those determined with elemental analysis and the results also show that the durability of the adhesive/carbon fiber reinforced epoxy resin composite joints subjected to silane coupling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treatment.
Transport dissipative particle dynamics model for mesoscopic advection- diffusion-reaction problems
Energy Technology Data Exchange (ETDEWEB)
Zhen, Li; Yazdani, Alireza; Tartakovsky, Alexandre M.; Karniadakis, George E.
2015-07-07
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic DPD framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between particles, and an analytical formula is proposed to relate the mesoscopic concentration friction to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Active-Site Hydration and Water Diffusion in Cytochrome P450cam: A Highly Dynamic Process
Energy Technology Data Exchange (ETDEWEB)
Miao, Yinglong [ORNL; Baudry, Jerome Y [ORNL
2011-01-01
Long-timescale molecular dynamics simulations (300 ns) are performed on both the apo- (i.e., camphor-free) and camphor-bound cytochrome P450cam (CYP101). Water diffusion into and out of the protein active site is observed without biased sampling methods. During the course of the molecular dynamics simulation, an average of 6.4 water molecules is observed in the camphor-binding site of the apo form, compared to zero water molecules in the binding site of the substrate-bound form, in agreement with the number of water molecules observed in crystal structures of the same species. However, as many as 12 water molecules can be present at a given time in the camphor-binding region of the active site in the case of apo-P450cam, revealing a highly dynamic process for hydration of the protein active site, with water molecules exchanging rapidly with the bulk solvent. Water molecules are also found to exchange locations frequently inside the active site, preferentially clustering in regions surrounding the water molecules observed in the crystal structure. Potential-of-mean-force calculations identify thermodynamically favored trans-protein pathways for the diffusion of water molecules between the protein active site and the bulk solvent. Binding of camphor in the active site modifies the free-energy landscape of P450cam channels toward favoring the diffusion of water molecules out of the protein active site.
Frank, Stefan; Roberts, Daniel E.; Rikvold, Per Arne
2004-01-01
The influence of nearest-neighbor diffusion on the decay of a metastable low-coverage phase (monolayer adsorption) in a square lattice-gas model of electrochemical metal deposition is investigated by kinetic Monte Carlo simulations. The phase-transformation dynamics are compared to the well-established Kolmogorov-Johnson-Mehl-Avrami theory. The phase transformation is accelerated by diffusion, but remains in accord with the theory for continuous nucleation up to moderate diffusion rates. At v...
Rotational diffusion affects the dynamical self-assembly pathways of patchy particles.
Newton, Arthur C; Groenewold, Jan; Kegel, Willem K; Bolhuis, Peter G
2015-12-15
Predicting the self-assembly kinetics of particles with anisotropic interactions, such as colloidal patchy particles or proteins with multiple binding sites, is important for the design of novel high-tech materials, as well as for understanding biological systems, e.g., viruses or regulatory networks. Often stochastic in nature, such self-assembly processes are fundamentally governed by rotational and translational diffusion. Whereas the rotational diffusion constant of particles is usually considered to be coupled to the translational diffusion via the Stokes-Einstein relation, in the past decade it has become clear that they can be independently altered by molecular crowding agents or via external fields. Because virus capsids naturally assemble in crowded environments such as the cell cytoplasm but also in aqueous solution in vitro, it is important to investigate how varying the rotational diffusion with respect to transitional diffusion alters the kinetic pathways of self-assembly. Kinetic trapping in malformed or intermediate structures often impedes a direct simulation approach of a kinetic network by dramatically slowing down the relaxation to the designed ground state. However, using recently developed path-sampling techniques, we can sample and analyze the entire self-assembly kinetic network of simple patchy particle systems. For assembly of a designed cluster of patchy particles we find that changing the rotational diffusion does not change the equilibrium constants, but significantly affects the dynamical pathways, and enhances (suppresses) the overall relaxation process and the yield of the target structure, by avoiding (encountering) frustrated states. Besides insight, this finding provides a design principle for improved control of nanoparticle self-assembly. PMID:26621742
Spectrum of anomalous magnetohydrodynamics
Giovannini, Massimo
2016-05-01
The equations of anomalous magnetohydrodynamics describe an Abelian plasma where conduction and chiral currents are simultaneously present and constrained by the second law of thermodynamics. At high frequencies the magnetic currents play the leading role, and the spectrum is dominated by two-fluid effects. The system behaves instead as a single fluid in the low-frequency regime where the vortical currents induce potentially large hypermagnetic fields. After deriving the physical solutions of the generalized Appleton-Hartree equation, the corresponding dispersion relations are scrutinized and compared with the results valid for cold plasmas. Hypermagnetic knots and fluid vortices can be concurrently present at very low frequencies and suggest a qualitatively different dynamics of the hydromagnetic nonlinearities.
An Asymptotic Analysis of a 2-D Model of Dynamically Active Compartments Coupled by Bulk Diffusion
Gou, J.; Ward, M. J.
2016-04-01
A class of coupled cell-bulk ODE-PDE models is formulated and analyzed in a two-dimensional domain, which is relevant to studying quorum-sensing behavior on thin substrates. In this model, spatially segregated dynamically active signaling cells of a common small radius ɛ ≪ 1 are coupled through a passive bulk diffusion field. For this coupled system, the method of matched asymptotic expansions is used to construct steady-state solutions and to formulate a spectral problem that characterizes the linear stability properties of the steady-state solutions, with the aim of predicting whether temporal oscillations can be triggered by the cell-bulk coupling. Phase diagrams in parameter space where such collective oscillations can occur, as obtained from our linear stability analysis, are illustrated for two specific choices of the intracellular kinetics. In the limit of very large bulk diffusion, it is shown that solutions to the ODE-PDE cell-bulk system can be approximated by a finite-dimensional dynamical system. This limiting system is studied both analytically, using a linear stability analysis and, globally, using numerical bifurcation software. For one illustrative example of the theory, it is shown that when the number of cells exceeds some critical number, i.e., when a quorum is attained, the passive bulk diffusion field can trigger oscillations through a Hopf bifurcation that would otherwise not occur without the coupling. Moreover, for two specific models for the intracellular dynamics, we show that there are rather wide regions in parameter space where these triggered oscillations are synchronous in nature. Unless the bulk diffusivity is asymptotically large, it is shown that a diffusion-sensing behavior is possible whereby more clustered spatial configurations of cells inside the domain lead to larger regions in parameter space where synchronous collective oscillations between the small cells can occur. Finally, the linear stability analysis for these cell
An Asymptotic Analysis of a 2-D Model of Dynamically Active Compartments Coupled by Bulk Diffusion
Gou, J.; Ward, M. J.
2016-08-01
A class of coupled cell-bulk ODE-PDE models is formulated and analyzed in a two-dimensional domain, which is relevant to studying quorum-sensing behavior on thin substrates. In this model, spatially segregated dynamically active signaling cells of a common small radius ɛ ≪ 1 are coupled through a passive bulk diffusion field. For this coupled system, the method of matched asymptotic expansions is used to construct steady-state solutions and to formulate a spectral problem that characterizes the linear stability properties of the steady-state solutions, with the aim of predicting whether temporal oscillations can be triggered by the cell-bulk coupling. Phase diagrams in parameter space where such collective oscillations can occur, as obtained from our linear stability analysis, are illustrated for two specific choices of the intracellular kinetics. In the limit of very large bulk diffusion, it is shown that solutions to the ODE-PDE cell-bulk system can be approximated by a finite-dimensional dynamical system. This limiting system is studied both analytically, using a linear stability analysis and, globally, using numerical bifurcation software. For one illustrative example of the theory, it is shown that when the number of cells exceeds some critical number, i.e., when a quorum is attained, the passive bulk diffusion field can trigger oscillations through a Hopf bifurcation that would otherwise not occur without the coupling. Moreover, for two specific models for the intracellular dynamics, we show that there are rather wide regions in parameter space where these triggered oscillations are synchronous in nature. Unless the bulk diffusivity is asymptotically large, it is shown that a diffusion-sensing behavior is possible whereby more clustered spatial configurations of cells inside the domain lead to larger regions in parameter space where synchronous collective oscillations between the small cells can occur. Finally, the linear stability analysis for these cell
Molecular dynamics calculation of rotational diffusion coefficient of a carbon nanotube in fluid
Cao, Bing-Yang; Dong, Ruo-Yu
2014-01-01
Rotational diffusion processes are correlated with nanoparticle visualization and manipulation techniques, widely used in nanocomposites, nanofluids, bioscience, and so on. However, a systematical methodology of deriving this diffusivity is still lacking. In the current work, three molecular dynamics (MD) schemes, including equilibrium (Green-Kubo formula and Einstein relation) and nonequilibrium (Einstein-Smoluchowski relation) methods, are developed to calculate the rotational diffusion coefficient, taking a single rigid carbon nanotube in fluid argon as a case. We can conclude that the three methods produce same results on the basis of plenty of data with variation of the calculation parameters (tube length, diameter, fluid temperature, density, and viscosity), indicative of the validity and accuracy of the MD simulations. However, these results have a non-negligible deviation from the theoretical predictions of Tirado et al. [J. Chem. Phys. 81, 2047 (1984)], which may come from several unrevealed factors of the theory. The three MD methods proposed in this paper can also be applied to other situations of calculating rotational diffusion coefficient.
International Nuclear Information System (INIS)
The measurement of volatile organic compound (VOC) concentration changes, in the range of 10 ppt–1ppb, is essential in several applications. The World Meteorological Organization has identified a set of VOCs that are critical because of their long-term instability. The measurement of such changes demands generation of reference mixtures at a high accuracy and stability level. The dynamic preparation of gas mixtures based on diffusion is a suitable way of generating accurate reference mixtures, particularly of unstable VOCs. Diffusion rate and dilution gas flow rate uncertainties are the main contributors to the overall VOC concentration uncertainty. This paper presents a comprehensive overview of the uncertainty of the diffusion rate. Stress is laid on the advantages offered by a modified measurand equation. The validity of this analysis and the modified equation has been confirmed experimentally. Temperature variability and mass difference uncertainty make the main contributions to the uncertainty: a 0.01 °C variability results in a 0.2% uncertainty. The new measurand equation provides both a better indication of the systematic effects at a narrow temperature variability and a more realistic calculation of the uncertainty. The modified equation enhances calculation of uncertainty at the low diffusion rates needed to generate very low VOC concentration mixtures
Molecular-Dynamics Simulation of Self-Diffusion of Molecular Hydrogen in X-Type Zeolite
Directory of Open Access Journals (Sweden)
Xiaoming Du
2013-01-01
Full Text Available The self-diffusion of hydrogen in NaX zeolite has been studied by molecular-dynamics simulations for various temperatures and pressures. The results indicate that in the temperature range of 77–293 K and the pressure range of 10–2700 kPa, the self-diffusion coefficients are found to range from 1.61 × 10−9 m2·s−1 to 3.66 × 10−8 m2·s−1 which are in good agreement with the experimental values from the quasielastic neutron scattering (QENS and pulse field gradients nuclear magnetic resonance (PFG NMR measurements. The self-diffusion coefficients decrease with increasing pressure due to packing of sorbate-sorbate molecules which causes frequent collusion among hydrogen molecules in pores and increase with increasing temperature because increasing the kinetic energy of the gas molecules enlarges the mean free path of gas molecule. The activated energy for hydrogen diffusion determined from the simulation is pressure-dependent.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-07-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of these Lagrangian particles. An analytical formula is proposed to relate the tDPD parameters to the effective diffusion coefficient. To validate the present tDPD model and the boundary conditions, we perform three tDPD simulations of one-dimensional diffusion with different boundary conditions, and the results show excellent agreement with the theoretical solutions. We also performed two-dimensional simulations of ADR systems and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, we present an application of the tDPD model to the dynamic process of blood coagulation involving 25 reacting species in order to demonstrate the potential of tDPD in simulating biological dynamics at the mesoscale. We find that the tDPD solution of this comprehensive 25-species coagulation model is only twice as computationally expensive as the conventional DPD simulation of the hydrodynamics only, which is a significant advantage over available continuum solvers.
Simulation of micro-CHP diffusion by means of System Dynamics
International Nuclear Information System (INIS)
This paper presents a simulation analysis with System Dynamics of the possible diffusion of micro-systems for combined heat-power generation (μ-CHP) as a substitute for centralised electricity generation and local boilers in the residential sector. Decentralised energy production is an important challenge in the 21st century to respond to the threats of exhaustion of non-renewable resources, and of global pollution. The purpose of the System Dynamics modelling is to show the difficulties μ-CHP faces, like most innovative technologies, mainly due to its high investment costs. Feedbacks are important in modelling the diffusion process of this technology and the fundamental aspect of learning effects on the cost decrease. The consumer model is based on the replacement of traditional boilers by μ-CHP installations using the Bass diffusion model. It is shown that natural economic forces are probably not sufficient to achieve a sustained growth. Several incentive schemes to be implemented by the regulatory authorities are investigated to promote this technology
Zha, Yunfei; Li, Maojin; YANG, JIANYONG
2010-01-01
Objective To investigate the significance of the dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) parameters of diffuse spinal bone marrow infiltration in patients with hematological malignancies. Materials and Methods Dynamic gadolinium-enhanced MR imaging of the lumbar spine was performed in 26 patients with histologically proven diffuse bone marrow infiltration, including multiple myeloma (n = 6), acute lymphoblastic leukemia (n = 6), acute myeloid leukemia (n = 5), chronic m...
Indian Academy of Sciences (India)
Srinivasa R Varanasi; S Yashonath
2012-01-01
A molecular dynamics study of the dependence of diffusivity of the cation on ionic radii in molten AgI is reported.We have employed modified Parinello-Rahman-Vashistha interionic pair potential proposed by Shimojo and Kobayashi. Our results suggest that the diffusivity of the cation exhibits an increase followed by a decrease as the ionic radius is increased. Several structural and dynamical properties are reported.
Institute of Scientific and Technical Information of China (English)
Pin Lv; Zhenan Tang; Jun Yu; Yanbing Xue
2006-01-01
For gas sensor application, adsorption and diffusion of formaldehyde gas in single-wall carbon nanotube were investigated by using molecular dynamics simulation. The conformations of formaldehyde molecule adsorbed in carbon nanotube were optimized according to principle of minimum energy. The axis of conformatiot is parallel to the axis of carbon nanotube and about 0.3 nm～0.4 nm away from carbon nanotube wall. The conformation, which is different from that of the formaldehyde molecule in the gas-phase, rotates around carbon nanotube axis. The adsorption energy and diffusivity of formaldehyde molecule in single-wall carbon nanotube is of-56.2 kJ/mol and of 0.2× 10-4 cm2/s, respectively.
DEFF Research Database (Denmark)
Galliero, Guillaume; Medvedev, Oleg; Shapiro, Alexander
2005-01-01
different binary liquid mixtures of non-polar components that computed penetration lengths, for various temperatures and compositions, are consistent with those deduced from experiments in the framework of the formalism of the fluctuation theory. Moreover, the mutual diffusion coefficients obtained from a......Mutual diffusion in condensed phases is a theoretically and practically important subject of active research. One of the most rigorous and theoretically advanced approaches to the problem is a recently developed approach based on the concept of penetration lengths (Physica A 320 (2003) 211; Physica...... coupled fluctuation theory and molecular dynamics scheme exhibit consistent trends and average deviations from experimental data around 10-20%. (c) 2004 Elsevier B.V. All rights reserved....
Critical Role of Dynamic Flexibility in Ge-Containing Zeolites: Impact on Diffusion.
Gutiérrez-Sevillano, Juan José; Calero, Sofía; Hamad, Said; Grau-Crespo, Ricardo; Rey, Fernando; Valencia, Susana; Palomino, Miguel; Balestra, Salvador R G; Ruiz-Salvador, A Rabdel
2016-07-11
Incorporation of germanium in zeolites is well known to confer static flexibility to their framework, by stabilizing the formation of small rings. In this work, we show that the flexibility associated to Ge atoms in zeolites goes beyond this static effect, manifesting also a clear dynamic nature, in the sense that it leads to enhanced molecular diffusion. Our study combines experimental and theoretical methods providing evidence for this effect, which has not been described previously, as well as a rationalization for it, based on atomistic grounds. We have used both pure-silica and silico-germanate ITQ-29 (LTA topology) zeolites as a case study. Based on our simulations, we identify the flexibility associated to the pore breathing-like behavior induced by the Ge atoms, as the key factor leading to the enhanced diffusion observed experimentally in Ge-containing zeolites. PMID:27305363
Dynamical diffusion and renormalization group equation for the Fermi velocity in doped graphene
Ardenghi, J. S.; Bechthold, P.; Jasen, P.; Gonzalez, E.; Juan, A.
2014-11-01
The aim of this work is to study the electron transport in graphene with impurities by introducing a generalization of linear response theory for linear dispersion relations and spinor wave functions. Current response and density response functions are derived and computed in the Boltzmann limit showing that in the former case a minimum conductivity appears in the no-disorder limit. In turn, from the generalization of both functions, an exact relation can be obtained that relates both. Combining this result with the relation given by the continuity equation it is possible to obtain general functional behavior of the diffusion pole. Finally, a dynamical diffusion is computed in the quasistatic limit using the definition of relaxation function. A lower cutoff must be introduced to regularize infrared divergences which allow us to obtain a full renormalization group equation for the Fermi velocity, which is solved up to order O(ℏ2).
Michailidou, V. N.; Swan, J. W.; Brady, J. F.; Petekidis, G.
2013-01-01
Evanescent wave dynamic light scattering and Stokesian dynamics simulations were employed to study the dynamics of hard-sphere colloidal particles near a hard wall in concentrated suspensions. The evanescent wave averaged short-time diffusion coefficients were determined from experimental correlation functions over a range of scattering wave vectors and penetration depths. Stokesian dynamics simulations performed for similar conditions allow a direct comparison of both the short-time self- an...
Directory of Open Access Journals (Sweden)
Stamatakis Michail
2010-04-01
Full Text Available Abstract Background An adaptive coarse-grained (kinetic Monte Carlo (ACGMC simulation framework is applied to reaction and diffusion dynamics in inhomogeneous domains. The presented model is relevant to the diffusion and dimerization dynamics of epidermal growth factor receptor (EGFR in the presence of plasma membrane heterogeneity and specifically receptor clustering. We perform simulations representing EGFR cluster dissipation in heterogeneous plasma membranes consisting of higher density clusters of receptors surrounded by low population areas using the ACGMC method. We further investigate the effect of key parameters on the cluster lifetime. Results Coarse-graining of dimerization, rather than of diffusion, may lead to computational error. It is shown that the ACGMC method is an effective technique to minimize error in diffusion-reaction processes and is superior to the microscopic kinetic Monte Carlo simulation in terms of computational cost while retaining accuracy. The low computational cost enables sensitivity analysis calculations. Sensitivity analysis indicates that it may be possible to retain clusters of receptors over the time scale of minutes under suitable conditions and the cluster lifetime may depend on both receptor density and cluster size. Conclusions The ACGMC method is an ideal platform to resolve large length and time scales in heterogeneous biological systems well beyond the plasma membrane and the EGFR system studied here. Our results demonstrate that cluster size must be considered in conjunction with receptor density, as they synergistically affect EGFR cluster lifetime. Further, the cluster lifetime being of the order of several seconds suggests that any mechanisms responsible for EGFR aggregation must operate on shorter timescales (at most a fraction of a second, to overcome dissipation and produce stable clusters observed experimentally.
Lateral diffusivity coefficients from the dynamics of a SF6 patch in a coastal environment
Kersalé, M.; Petrenko, A. A.; Doglioli, A. M.; Nencioli, F.; Bouffard, J.; Blain, S.; Diaz, F.; Labasque, T.; Quéguiner, B.; Dekeyser, I.
2016-01-01
The dispersion of a patch of the tracer sulfur hexafluoride (SF6) is used to assess the lateral diffusivity in the coastal waters of the western part of the Gulf of Lion (GoL), northwestern Mediterranean Sea, during the Latex10 experiment (September 2010). Immediately after the release, the spreading of the patch is associated with a strong decrease of the SF6 concentrations due to the gas exchange from the ocean to the atmosphere. This has been accurately quantified, evidencing the impact of the strong wind conditions during the first days of this campaign. Few days after the release, as the atmospheric loss of SF6 decreased, lateral diffusivity coefficient at spatial scales of 10 km has been computed using two approaches. First, the evolution of the patch with time was combined with a diffusion-strain model to obtain estimates of the strain rate (γ = 2.5 10- 6 s- 1) and of the lateral diffusivity coefficient (Kh = 23.2 m2 s- 1). Second, a steady state model was applied, showing Kh values similar to the previous method after a period of adjustment between 2 and 4.5 days. This implies that after such period, our computation of Kh becomes insensitive to the inclusion of further straining of the patch. Analysis of sea surface temperature satellite imagery shows the presence of a strong front in the study area. The front clearly affected the dynamics within the region and thus the temporal evolution of the patch. Our results are consistent with previous studies in open ocean and demonstrate the success and feasibility of those methods also under small-scale, rapidly-evolving dynamics typical of coastal environments.
Nemoto, Yuya; Ohno, Fumitaka; Maeshima, Nobuya; Hino, Ken-ichi
2016-09-01
We examine a resonance structure of Floquet state in dynamic fractional Stark ladder (DFSL) realized in biased semiconductor superlattices driven by a terahertz cw laser on the basis of the R-matrix Floquet theory. To do this, we calculate an excess density of state ρ (ex)(E) corresponding to lifetime of the Floquet state with a fractional matching ratio η, where η is the ratio of a Bloch frequency ΩB to a laser frequency ω, namely, η =ΩB / ω. The results for η = 3 / 2 demonstrate the appearance of discernibly large peaks associated with Floquet states with longevity in a region of relatively high laser-intensity. The underlying physics is discussed in terms of an analytical expression of ρ (ex)(E) and the associated Green function in which ponderomotive couplings are included in a non-perturbative way.
Inference of protein diffusion probed via fluorescence correlation spectroscopy
Tsekouras, Konstantinos
2015-03-01
Fluctuations are an inherent part of single molecule or few particle biophysical data sets. Traditionally, ``noise'' fluctuations have been viewed as a nuisance, to be eliminated or minimized. Here we look on how statistical inference methods - that take explicit advantage of fluctuations - have allowed us to draw an unexpected picture of single molecule diffusional dynamics. Our focus is on the diffusion of proteins probed using fluorescence correlation spectroscopy (FCS). First, we discuss how - in collaboration with the Bustamante and Marqusee labs at UC Berkeley - we determined using FCS data that individual enzymes are perturbed by self-generated catalytic heat (Riedel et al, Nature, 2014). Using the tools of inference, we found how distributions of enzyme diffusion coefficients shift in the presence of substrate revealing that enzymes performing highly exothermic reactions dissipate heat by transiently accelerating their center of mass following a catalytic reaction. Next, when molecules diffuse in the cell nucleus they often appear to diffuse anomalously. We analyze FCS data - in collaboration with Rich Day at the IU Med School - to propose a simple model for transcription factor binding-unbinding in the nucleus to show that it may give rise to apparent anomalous diffusion. Here inference methods extract entire binding affinity distributions for the diffusing transcription factors, allowing us to precisely characterize their interactions with different components of the nuclear environment. From this analysis, we draw key mechanistic insight that goes beyond what is possible by simply fitting data to ``anomalous diffusion'' models.
Energy Technology Data Exchange (ETDEWEB)
Tringe, J.W., E-mail: tringe2@llnl.gov [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Ileri, N. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Department of Chemical Engineering & Materials Science, University of California, Davis, CA (United States); Levie, H.W. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA (United States); Stroeve, P.; Ustach, V.; Faller, R. [Department of Chemical Engineering & Materials Science, University of California, Davis, CA (United States); Renaud, P. [Swiss Federal Institute of Technology, Lausanne, (EPFL) (Switzerland)
2015-08-18
Highlights: • WGA proteins in nanochannels modeled by Molecular Dynamics and Monte Carlo. • Protein surface coverage characterized by atomic force microscopy. • Models indicate transport characteristics depend strongly on surface coverage. • Results resolve of a four orders of magnitude difference in diffusion coefficient values. - Abstract: We use Molecular Dynamics and Monte Carlo simulations to examine molecular transport phenomena in nanochannels, explaining four orders of magnitude difference in wheat germ agglutinin (WGA) protein diffusion rates observed by fluorescence correlation spectroscopy (FCS) and by direct imaging of fluorescently-labeled proteins. We first use the ESPResSo Molecular Dynamics code to estimate the surface transport distance for neutral and charged proteins. We then employ a Monte Carlo model to calculate the paths of protein molecules on surfaces and in the bulk liquid transport medium. Our results show that the transport characteristics depend strongly on the degree of molecular surface coverage. Atomic force microscope characterization of surfaces exposed to WGA proteins for 1000 s show large protein aggregates consistent with the predicted coverage. These calculations and experiments provide useful insight into the details of molecular motion in confined geometries.
International Nuclear Information System (INIS)
Highlights: • WGA proteins in nanochannels modeled by Molecular Dynamics and Monte Carlo. • Protein surface coverage characterized by atomic force microscopy. • Models indicate transport characteristics depend strongly on surface coverage. • Results resolve of a four orders of magnitude difference in diffusion coefficient values. - Abstract: We use Molecular Dynamics and Monte Carlo simulations to examine molecular transport phenomena in nanochannels, explaining four orders of magnitude difference in wheat germ agglutinin (WGA) protein diffusion rates observed by fluorescence correlation spectroscopy (FCS) and by direct imaging of fluorescently-labeled proteins. We first use the ESPResSo Molecular Dynamics code to estimate the surface transport distance for neutral and charged proteins. We then employ a Monte Carlo model to calculate the paths of protein molecules on surfaces and in the bulk liquid transport medium. Our results show that the transport characteristics depend strongly on the degree of molecular surface coverage. Atomic force microscope characterization of surfaces exposed to WGA proteins for 1000 s show large protein aggregates consistent with the predicted coverage. These calculations and experiments provide useful insight into the details of molecular motion in confined geometries
Anomalous magnetohydrodynamics in the extreme relativistic domain
Giovannini, Massimo
2016-01-01
The evolution equations of anomalous magnetohydrodynamics are derived in the extreme relativistic regime and contrasted with the treatment of hydromagnetic nonlinearities pioneered by Lichnerowicz in the absence of anomalous currents. In particular we explore the situation where the conventional vector currents are complemented by the axial-vector currents arising either from the pseudo Nambu-Goldstone bosons of a spontaneously broken symmetry or because of finite fermionic density effects. After expanding the generally covariant equations in inverse powers of the conductivity, the relativistic analog of the magnetic diffusivity equation is derived in the presence of vortical and magnetic currents. While the anomalous contributions are generally suppressed by the diffusivity, they are shown to disappear in the perfectly conducting limit. When the flow is irrotational, boost-invariant and with vanishing four-acceleration the corresponding evolution equations are explicitly integrated so that the various physic...
Havlin, Shlomo; Ben-Avraham, Daniel
2002-01-01
Diffusion in disordered systems does not follow the classical laws which describe transport in ordered crystalline media, and this leads to many anomalous physical properties. Since the application of percolation theory, the main advances in the understanding of these processes have come from fractal theory. Scaling theories and numerical simulations are important tools to describe diffusion processes (random walks: the 'ant in the labyrinth') on percolation systems and fractals. Different types of disordered systems exhibiting anomalous diffusion are presented (the incipient infinite percolation cluster, diffusion-limited aggregation clusters, lattice animals, and random combs), and scaling theories as well as numerical simulations of greater sophistication are described. Also, diffusion in the presence of singular distributions of transition rates is discussed and related to anomalous diffusion on disordered structures.
Zhao, Tongyang; Wang, Xiaogong
2013-09-01
In this study, dissipative particle dynamics (DPD) method was employed to investigate the translational diffusion of rodlike polymer in its nematic phase. The polymer chain was modeled by a rigid rod composed of consecutive DPD particles and solvent was represented by independent DPD particles. To fully understand the translational motion of the rods in the anisotropic phase, four diffusion coefficients, D_{||}u, D_ bot u, D_{||}n, D_ bot n were obtained from the DPD simulation. By definition, D_{||}n and D_ bot n denote the diffusion coefficients parallel and perpendicular to the nematic director, while D_{||}u and D_ bot u denote the diffusion coefficients parallel and perpendicular to the long axis of a rigid rod u. In the simulation, the velocity auto-correlation functions were used to calculate the corresponding diffusion coefficients from the simulated velocity of the rods. Simulation results show that the variation of orientational order caused by concentration and temperature changes has substantial influences on D_{||}u and D_ bot u. In the nematic phase, the changes of concentration and temperature will result in a change of local environment of rods, which directly influence D_{||}u and D_ bot u. Both D_{||}n and D_ bot n can be represented as averages of D_{||}u and D_ bot u, and the weighted factors are functions of the orientational order parameter S2. The effect of concentration and temperature on D_{||}n and D_ bot n demonstrated by the DPD simulation can be rationally interpreted by considering their influences on D_{||}u, D_ bot u and the order parameter S2.
Investigation of cation self-diffusion mechanisms in UO2±x using molecular dynamics
International Nuclear Information System (INIS)
This article is devoted to investigation of cation self-diffusion mechanisms, taking place in UO2, UO2+x, and UO2−x crystals simulated under periodic (PBC) and isolated (IBC) boundary conditions using the method of molecular dynamics in the approximation of rigid ions and pair interactions. It is shown that under PBC the cations diffuse via an exchange mechanism (with the formation of Frenkel defects) with activation energy of 15–22 eV, while under IBC there is competition between the exchange and vacancy (via Schottky defects) diffusion mechanisms, which give the effective activation energy of 11–13 eV near the melting temperature of the simulated UO2.00 nanocrystals. Vacancy diffusion with lower activation energy of 6–7 eV was dominant in the non-stoichiometric crystals UO2.10, UO2.15 and UO1.85. Observations showed that a cation vacancy is accompanied by different number of anion vacancies depending on the deviation from stoichiometry: no vacancies in UO2.15, single vacancy in UO2.00 and four vacancies in UO1.85. The corresponding law of mass action formulas derived within the Lidiard–Matzke model allowed explaining the obtained activation energies and predicting a change in the activation energy within the temperature range of the superionic phase transition. The diffusion of cations on the surface of nanocrystals had activation energy of 3.1–3.6 eV
Aldrin-Denny, R
1998-01-01
The methodology of formulating spatio-temporal diffusion-migration equations in an applied electric field for two competing diffusion processes is outlined using kinetic Ising model versions with the help of spin-exchange dynamics due to Kawasaki. The two transport processes considered here correspond to bounded displacement of species attached to supramolecular structures and electron hopping between spatially separated electron transfer active centres. The dependence of the diffusion coefficient on number density as well as the microscopic basis underlying phenomenological diffusion-migration equations are pointed out. (author)
International Nuclear Information System (INIS)
By using polarizable molecular dynamics (MD) simulations of lanthanoid(III) and actinoid(III) ions in water, we obtained ionic diffusion coefficients and hydration enthalpies for both series. These values are in good agreement with experiments. Simulations thus allow us to relate them to microscopic structure. In particular, across the series the diffusion coefficients decrease, reflecting the increase of ion-water interaction. Hydration enthalpies also show that interactions increase from light to heavy ions in agreement with experiment. The apparent contradictory result of the decrease of the diffusion coefficient with decreasing ionic radius is tentatively explained in terms of dielectric friction predominance on Stokes' diffusive regime. (authors)
International Nuclear Information System (INIS)
Highlights: ► Calculation of human brain multifractal spectra. ► Calculations are based on Diffusion Tensor MRI Images. ► Spectra are modelled by coupled Ikeda map dynamics. ► Coupled lattice Ikeda maps model well only positive multifractal spectra. ► Appropriately modified coupled lattice Ikeda maps give correct spectra. - Abstract: The multifractal spectra of 3d Diffusion Tensor Images (DTI) obtained by magnetic resonance imaging of the human brain are studied. They are shown to deviate substantially from artificial brain images with the same white matter intensity. All spectra, obtained from 12 healthy subjects, show common characteristics indicating non-trivial moments of the intensity. To model the spectra the dynamics of the chaotic Ikeda map are used. The DTI multifractal spectra for positive q are best approximated by 3d coupled Ikeda maps in the fully developed chaotic regime. The coupling constants are as small as α = 0.01. These results reflect not only the white tissue non-trivial architectural complexity in the human brain, but also demonstrate the presence and importance of coupling between neuron axons. The architectural complexity is also mirrored by the deviations in the negative q-spectra, where the rare events dominate. To obtain a good agreement in the DTI negative q-spectrum of the brain with the Ikeda dynamics, it is enough to slightly modify the most rare events of the coupled Ikeda distributions. The representation of Diffusion Tensor Images with coupled Ikeda maps is not unique: similar conclusions are drawn when other chaotic maps (Tent, Logistic or Henon maps) are employed in the modelling of the neuron axons network.
Dynamical Analysis of a Delayed Reaction-Diffusion Predator-Prey System
Directory of Open Access Journals (Sweden)
Yanuo Zhu
2012-01-01
Full Text Available This work deals with the analysis of a delayed diffusive predator-prey system under Neumann boundary conditions. The dynamics are investigated in terms of the stability of the nonnegative equilibria and the existence of Hopf bifurcation by analyzing the characteristic equations. The direction of Hopf bifurcation and the stability of bifurcating periodic solution are also discussed by employing the normal form theory and the center manifold reduction. Furthermore, we prove that the positive equilibrium is asymptotically stable when the delay is less than a certain critical value and unstable when the delay is greater than the critical value.
Energy Technology Data Exchange (ETDEWEB)
Hebden, Jeremy C; Brunker, Joanna; Correia, Teresa; Price, Ben D; Gibson, Adam P; Everdell, N L [Department of Medical Physics and Bioengineering, University College London, Gower Street, London WC1E 6BT (United Kingdom)
2008-01-21
A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system.
Hebden, Jeremy C.; Brunker, Joanna; Correia, Teresa; Price, Ben D.; Gibson, Adam P.; Everdell, N. L.
2008-01-01
A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system.
International Nuclear Information System (INIS)
A novel design of solid dynamic phantom with tissue-like optical properties is presented, which contains variable regions of contrast which are activated electrically. Reversible changes in absorption are produced by localized heating of targets impregnated with thermochromic pigment. A portable, battery-operated prototype has been constructed, and its optical and temporal characteristics have been investigated. The phantom has been developed as a means of assessing the performance of diffuse optical imaging systems, such as those used to monitor haemodynamic changes in the brain and other tissues. Images of the phantom have been reconstructed using data acquired with a continuous wave optical topography system
Gunther, Jacqueline E.; Lim, Emerson; Kim, Hyun Keol; Brown, Mindy; Refice, Susan; Kalinsky, Kevin; Hershman, Dawn; Hielscher, Andreas H.
2015-03-01
We have developed a dynamic diffuse optical tomography imaging system that is capable of 3D imaging of both breasts simultaneously. In an ongoing study subjects receiving neoadjuvant chemotherapy are imaged at 6 time points throughout their 5-month treatment. At each time point the subjects preform a breath hold to observe the hemodynamic effects in the breasts. For each session the percent change of various hemodynamic parameters during the breath hold is determined. Preliminary results from show statistically significant differences in washout rates and deoxyhemoglobin changes at the 2-week imaging point between subjects that respond and do not respond to treatment.
Carrier diffusion and higher order transversal modes in spectral dynamics of the semiconductor laser
DEFF Research Database (Denmark)
Buus, Jens; Danielsen, Magnus
1977-01-01
The dynamic and spectral behavior of the semiconductor stripe laser has been investigated. For this purpose the rate equations have been generalized to include several longitudinal and transversal modes, spontaneous emission into the active modes, and position dependence of the electron density...... through a term describing the charge-carrier diffusion in the plane of the active layer. The parameters used for solving these equations are found by theoretical and experimental considerations. The results show a broadening of the spectrum together with a significant content of higher order transversal...
Interface Dynamics of a Metastable Mass-Conserving Spatially Extended Diffusion
Berglund, Nils; Dutercq, Sébastien
2016-01-01
We study the metastable dynamics of a discretised version of the mass-conserving stochastic Allen-Cahn equation. Consider a periodic one-dimensional lattice with N sites, and attach to each site a real-valued variable, which can be interpreted as a spin, as the concentration of one type of metal in an alloy, or as a particle density. Each of these variables is subjected to a local force deriving from a symmetric double-well potential, to a weak ferromagnetic coupling with its nearest neighbours, and to independent white noise. In addition, the dynamics is constrained to have constant total magnetisation or mass. Using tools from the theory of metastable diffusion processes, we show that the long-term dynamics of this system is similar to a Kawasaki-type exchange dynamics, and determine explicit expressions for its transition probabilities. This allows us to describe the system in terms of the dynamics of its interfaces, and to compute an Eyring-Kramers formula for its spectral gap. In particular, we obtain that the spectral gap scales like the inverse system size squared.
Interface dynamics of a metastable mass-conserving spatially extended diffusion
Berglund, Nils
2015-01-01
We study the metastable dynamics of a discretised version of the mass-conserving stochastic Allen-Cahn equation. Consider a periodic one-dimensional lattice with $N$ sites, and attach to each site a real-valued variable, which can be interpreted as a spin, as the concentration of one type of metal in an alloy, or as a particle density. Each of these variables is subjected to a local force deriving from a symmetric double-well potential, to a weak ferromagnetic coupling with its nearest neighbours, and to independent white noise. In addition, the dynamics is constrained to have constant total magnetisation or mass. Using tools from the theory of metastable diffusion processes, we show that the long-term dynamics of this system is similar to a Kawasaki-type exchange dynamics, and determine explicit expressions for its transition probabilities. This allows us to describe the system in terms of the dynamics of its interfaces, and to compute an Eyring-Kramers formula for its spectral gap. In particular, we obtain ...
International Nuclear Information System (INIS)
Elastic fixed window scans of incoherent neutron scattering are an established and frequently employed method to study dynamical changes, usually over a broad temperature range or during a process such as a conformational change in the sample. In particular, the apparent mean-squared displacement can be extracted via a model-free analysis based on a solid physical interpretation as an effective amplitude of molecular motions. Here, we provide a new account of elastic and inelastic fixed window scans, defining a generalized mean-squared displacement for all fixed energy transfers. We show that this generalized mean-squared displacement in principle contains all information on the real mean-square displacement accessible in the instrumental time window. The derived formula provides a clear understanding of the effects of instrumental resolution on the apparent mean-squared displacement. Finally, we show that the generalized mean-square displacement can be used as a model-free indicator on confinement effects within the instrumental time window. (authors)
Correlation networks from flows. The case of forced and time-dependent advection-diffusion dynamics
Tupikina, Liubov; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our r...
The dynamics of nonlinear reaction-diffusion equations with small Lévy noise
Debussche, Arnaud; Imkeller, Peter
2013-01-01
This work considers a small random perturbation of alpha-stable jump type nonlinear reaction-diffusion equations with Dirichlet boundary conditions over an interval. It has two stable points whose domains of attraction meet in a separating manifold with several saddle points. Extending a method developed by Imkeller and Pavlyukevich it proves that in contrast to a Gaussian perturbation, the expected exit and transition times between the domains of attraction depend polynomially on the noise intensity in the small intensity limit. Moreover the solution exhibits metastable behavior: there is a polynomial time scale along which the solution dynamics correspond asymptotically to the dynamic behavior of a finite-state Markov chain switching between the stable states.
Quantum phase communication channels in the presence of static and dynamical phase diffusion
Trapani, Jacopo; Teklu, Berihu; Olivares, Stefano; Paris, Matteo G. A.
2015-07-01
We address quantum communication channels based on phase modulation of coherent states and analyze in detail the effects of static and dynamical (stochastic) phase diffusion. We evaluate mutual information for an ideal phase receiver and for a covariant phase-space-based receiver, and compare their performances by varying the number of symbols in the alphabet and/or the overall energy of the channel. Our results show that phase communication channels are generally robust against phase noise, especially for large alphabets in the low-energy regime. In the presence of dynamical (non-Markovian) noise the mutual information is preserved by the time correlation of the environment, and when the noise spectra are detuned with respect to the information carrier, revivals of mutual information appear.
Christien, F.; Barbu, A.
2005-11-01
A model based on the cluster dynamics approach was proposed in [A. Hardouin Duparc, C. Moingeon, N. Smetniansky-de-Grande, A. Barbu, J. Nucl. Mater. 302 (2002) 143] to describe point defect agglomeration in metals under irradiation. This model is restricted to materials where point defect diffusion is isotropic and is thus not applicable to anisotropic metals such as zirconium. Following the approach proposed by Woo [C.H. Woo, J. Nucl. Mater. 159 (1988) 237], we extended in this work the model to the case where self-interstitial atoms (SIA) diffusion is anisotropic. The model was then applied to the loop microstructure evolution of a zirconium thin foil irradiated with electrons in a high-voltage microscope. First, the inputs were validated by comparing the numerical results with Hellio et al. experimental results [C. Hellio, C.H. de Novion, L. Boulanger, J. Nucl. Mater. 159 (1988) 368]. Further calculations were made to evidence the effect of the thin foil orientation on the dislocation loop microstructure under irradiation. The result is that it is possible to reproduce for certain orientations the 'unexpected' vacancy loop growth experimentally observed in electron-irradiated zirconium [M. Griffiths, M.H. Loretto, R.E. Sallmann, J. Nucl. Mater. 115 (1983) 313; J. Nucl. Mater. 115 (1983) 323; Philos. Mag. A 49 (1984) 613]. This effect is directly linked to SIA diffusion anisotropy.
Energy Technology Data Exchange (ETDEWEB)
Christien, F. [Service de Recherches de Metallurgie Physique, CEA Saclay, 91191 Gif-sur-Yvette cedex (France)]. E-mail: frederic.christien@polytech.univ-nantes.fr; Barbu, A. [Service de Recherches de Metallurgie Physique, CEA Saclay, 91191 Gif-sur-Yvette cedex (France)
2005-11-15
A model based on the cluster dynamics approach was proposed in [A. Hardouin Duparc, C. Moingeon, N. Smetniansky-de-Grande, A. Barbu, J. Nucl. Mater. 302 (2002) 143] to describe point defect agglomeration in metals under irradiation. This model is restricted to materials where point defect diffusion is isotropic and is thus not applicable to anisotropic metals such as zirconium. Following the approach proposed by Woo [C.H. Woo, J. Nucl. Mater. 159 (1988) 237], we extended in this work the model to the case where self-interstitial atoms (SIA) diffusion is anisotropic. The model was then applied to the loop microstructure evolution of a zirconium thin foil irradiated with electrons in a high-voltage microscope. First, the inputs were validated by comparing the numerical results with Hellio et al. experimental results [C. Hellio, C.H. de Novion, L. Boulanger, J. Nucl. Mater. 159 (1988) 368]. Further calculations were made to evidence the effect of the thin foil orientation on the dislocation loop microstructure under irradiation. The result is that it is possible to reproduce for certain orientations the 'unexpected' vacancy loop growth experimentally observed in electron-irradiated zirconium [M. Griffiths, M.H. Loretto, R.E. Sallmann, J. Nucl. Mater. 115 (1983) 313; J. Nucl. Mater. 115 (1983) 323; Philos. Mag. A 49 (1984) 613]. This effect is directly linked to SIA diffusion anisotropy.
Diffusive Heat Transport in Budyko's Energy Balance Climate Model with a Dynamic Ice Line
Walsh, James
2016-01-01
M. Budyko and W. Sellers independently introduced seminal energy balance climate models in 1969, each with a goal of investigating the role played by positive ice albedo feedback in climate dynamics. In this paper we replace the relaxation to the mean horizontal heat transport mechanism used in the models of Budyko and Sellers with diffusive heat transport. We couple the resulting surface temperature equation with an equation for movement of the edge of the ice sheet (called the ice line), recently introduced by E. Widiasih. We apply the spectral method to the temperature-ice line system and consider finite approximations. We prove there exists a stable equilibrium solution with a small ice cap, and an unstable equilibrium solution with a large ice cap, for a range of parameter values. If the diffusive transport is too efficient, however, the small ice cap disappears and an ice free Earth becomes a limiting state. In addition, we analyze a variant of the coupled diffusion equations appropriate as a model for ...
Computing the blood brain barrier (BBB) diffusion coefficient: A molecular dynamics approach
Shamloo, Amir; Pedram, Maysam Z.; Heidari, Hossein; Alasty, Aria
2016-07-01
Various physical and biological aspects of the Blood Brain Barrier (BBB) structure still remain unfolded. Therefore, among the several mechanisms of drug delivery, only a few have succeeded in breaching this barrier, one of which is the use of Magnetic Nanoparticles (MNPs). However, a quantitative characterization of the BBB permeability is desirable to find an optimal magnetic force-field. In the present study, a molecular model of the BBB is introduced that precisely represents the interactions between MNPs and the membranes of Endothelial Cells (ECs) that form the BBB. Steered Molecular Dynamics (SMD) simulations of the BBB crossing phenomenon have been carried out. Mathematical modeling of the BBB as an input-output system has been considered from a system dynamics modeling viewpoint, enabling us to analyze the BBB behavior based on a robust model. From this model, the force profile required to overcome the barrier has been extracted for a single NP from the SMD simulations at a range of velocities. Using this data a transfer function model has been obtained and the diffusion coefficient is evaluated. This study is a novel approach to bridge the gap between nanoscale models and microscale models of the BBB. The characteristic diffusion coefficient has the nano-scale molecular effects inherent, furthermore reducing the computational costs of a nano-scale simulation model and enabling much more complex studies to be conducted.
Modeling of advection-diffusion-reaction processes using transport dissipative particle dynamics
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-11-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. In particular, the transport of concentration is modeled by a Fickian flux and a random flux between tDPD particles, and the advection is implicitly considered by the movements of Lagrangian particles. To validate the proposed tDPD model and the boundary conditions, three benchmark simulations of one-dimensional diffusion with different boundary conditions are performed, and the results show excellent agreement with the theoretical solutions. Also, two-dimensional simulations of ADR systems are performed and the tDPD simulations agree well with the results obtained by the spectral element method. Finally, an application of tDPD to the spatio-temporal dynamics of blood coagulation involving twenty-five reacting species is performed to demonstrate the promising biological applications of the tDPD model. Supported by the DOE Center on Mathematics for Mesoscopic Modeling of Materials (CM4) and an INCITE grant.
Duality of diffusion dynamics in particle motion in soft-mode turbulence
Suzuki, Masaru; Sueto, Hiroshi; Hosokawa, Yusaku; Muramoto, Naoyuki; Narumi, Takayuki; Hidaka, Yoshiki; Kai, Shoichi
2013-10-01
Nonthermal Brownian motion is investigated experimentally by injecting a particle into soft-mode turbulence (SMT), in the electroconvection of a nematic liquid crystal. It is clarified that the particle motion can be classified into two phases: fast motion, where particles move with the local convective flow, and slow motion, where they are carried by global slow pattern dynamics. We propose a simplified model to clarify the mechanism of the short-time and asymptotic behavior of diffusion. In our model, the correlation time is estimated as a function of a control parameter ɛ. The scaling of the SMT pattern correlation time, τd˜ɛ-1, is estimated from the particle dynamics, which is consistent with a previous report observed from the Eulerian viewpoint. The origin of the non-Gaussian distribution of the displacement in the short-time regime is also discussed and an analytical curve is introduced that quantitatively agrees with the experimental data. Our results clearly illustrate the characteristics of diffusive motion in SMT, which are considerably different from the conventional Brownian motion.
Molecular dynamics simulation of diffusion of gases in a carbon-nanotube-polymer composite
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Extensive molecular dynamics (MD) simulations were carried out to compute the solubilities and self-diffusivities of CO2 and CH4 in amorphous polyetherimide (PEI) and mixed-matrix PEI generated by inserting single-walled carbon nanotubes into the polymer. Atomistic models of PEI and its composites were generated using energy minimizations, MD simulations, and the polymer-consistent force field. Two types of polymer composite were generated by inserting (7,0) and (12,0) zigzag carbon nanotubes into the PEI structure. The morphologies of PEI and its composites were characterized by their densities, radial distribution functions, and the accessible free volumes, which were computed with probe molecules of different sizes. The distributions of the cavity volumes were computed using the Voronoi tessellation method. The computed self-diffusivities of the gases in the polymer composites are much larger than those in pure PEI. We find, however, that the increase is not due to diffusion of the gases through the nanotubes which have smooth energy surfaces and, therefore, provide fast transport paths. Instead, the MD simulations indicate a squeezing effect of the nanotubes on the polymer matrix that changes the composite polymers' free-volume distributions and makes them more sharply peaked. The presence of nanotubes also creates several cavities with large volumes that give rise to larger diffusivities in the polymer composites. This effect is due to the repulsive interactions between the polymer and the nanotubes. The solubilities of the gases in the polymer composites are also larger than those in pure PEI, hence indicating larger gas permeabilities for mixed-matrix PEI than PEI itself
Diffusion within α-CuI studied using ab initio molecular dynamics simulations
Mohn, Chris E.; Stølen, Svein; Hull, Stephen
2009-08-01
The structure and dynamics of superionic α-CuI are studied in detail by means of ab initio Born-Oppenheimer molecular dynamics simulations. The extreme cation disorder and a soft immobile face centred cubic sublattice are evident from the highly diffuse atomic density profiles. The Cu-Cu pair distribution function and distribution of Cu-I-Cu bond angles possess distinct peaks at 2.6 Å and 60° respectively, which are markedly lower than the values expected from the average cationic density, pointing to the presence of pronounced short-range copper-copper correlations. Comparison with lattice static calculations shows that these correlations and the marked shift in the cationic density profile in the lang111rang directions are associated with a locally distorted cation sublattice, and that the movements within the tetrahedral cavities involve rapid jumps into and out of shallow basins on the system potential energy surface. On average, the iodines are surrounded by three coppers within their first coordination shell, with the fourth copper being located in a transition zone between two neighbouring iodine cavities. However, time-resolved analysis reveals that the local structure actually involves a mixture of threefold-, fourfold- and fivefold-coordinated iodines. Examination of the ionic trajectories shows that the copper ions jump rapidly to nearest neighbouring tetrahedral cavities (aligned in the lang100rang directions) following a markedly curved trajectory and often involving short-lived (~1 ps) interstitial positions. The nature of the correlated diffusion underlying the unusually high fraction of coppers with short residence time can be attributed to the presence of a large number of 'unsuccessful' jumps and the likelihood of cooperative motion of pairs of coppers. The calculated diffusion coefficient at 750 K, DCu = 2.8 × 10-5 cm2 s-1, is in excellent agreement with that found experimentally.
Diffusion within α-CuI studied using ab initio molecular dynamics simulations
International Nuclear Information System (INIS)
The structure and dynamics of superionic α-CuI are studied in detail by means of ab initio Born-Oppenheimer molecular dynamics simulations. The extreme cation disorder and a soft immobile face centred cubic sublattice are evident from the highly diffuse atomic density profiles. The Cu-Cu pair distribution function and distribution of Cu-I-Cu bond angles possess distinct peaks at 2.6 A and 60 deg. respectively, which are markedly lower than the values expected from the average cationic density, pointing to the presence of pronounced short-range copper-copper correlations. Comparison with lattice static calculations shows that these correlations and the marked shift in the cationic density profile in the (111) directions are associated with a locally distorted cation sublattice, and that the movements within the tetrahedral cavities involve rapid jumps into and out of shallow basins on the system potential energy surface. On average, the iodines are surrounded by three coppers within their first coordination shell, with the fourth copper being located in a transition zone between two neighbouring iodine cavities. However, time-resolved analysis reveals that the local structure actually involves a mixture of threefold-, fourfold- and fivefold-coordinated iodines. Examination of the ionic trajectories shows that the copper ions jump rapidly to nearest neighbouring tetrahedral cavities (aligned in the (100) directions) following a markedly curved trajectory and often involving short-lived (∼1 ps) interstitial positions. The nature of the correlated diffusion underlying the unusually high fraction of coppers with short residence time can be attributed to the presence of a large number of 'unsuccessful' jumps and the likelihood of cooperative motion of pairs of coppers. The calculated diffusion coefficient at 750 K, DCu = 2.8 x 10-5 cm2 s-1, is in excellent agreement with that found experimentally.
Energy Technology Data Exchange (ETDEWEB)
Dahlstrom, Julie [Carthage College, 2001 Alford Park Dr., Kenosha, WI 53140 (United States); York, Donald G.; Welty, Daniel E.; Oka, Takeshi; Johnson, Sean; Jiang Zihao; Sherman, Reid [University of Chicago, Astronomy and Astrophysics Center, 5640 S. Ellis Avenue, Chicago, IL 60637 (United States); Hobbs, L. M. [University of Chicago, Yerkes Observatory, Williams Bay, WI 53191 (United States); Friedman, Scott D.; Sonnentrucker, Paule [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Rachford, Brian L. [Department of Physics, Embry-Riddle Aeronautical University, 3700 Willow Creek Road, Prescott, AZ 86301 (United States); Snow, Theodore P., E-mail: jdahlstrom1@carthage.edu [University of Colorado, CASA-Campus Box 389, Boulder, CO 80309 (United States)
2013-08-10
Anomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 A are found in absorption along the line of sight to Herschel 36, the star illuminating the bright Hourglass region of the H II region Messier 8. Interstellar absorption from excited CH{sup +} in the J = 1 level and from excited CH in the J = 3/2 level is also seen. To our knowledge, neither those excited molecular lines nor such strongly extended DIBs have previously been seen in absorption from interstellar gas. These unusual features appear to arise in a small region near Herschel 36 which contains most of the neutral interstellar material in the sight line. The CH{sup +} and CH in that region are radiatively excited by strong far-IR radiation from the adjacent infrared source Her 36 SE. Similarly, the broadening of the DIBs toward Herschel 36 may be due to radiative pumping of closely spaced high-J rotational levels of relatively small, polar carrier molecules. If this picture of excited rotational states for the DIB carriers is correct and applicable to most DIBs, the 2.7 K cosmic microwave background may set the minimum widths (about 0.35 A) of known DIBs, with molecular processes and/or local radiation fields producing the larger widths found for the broader DIBs. Despite the intense local UV radiation field within the cluster NGC 6530, no previously undetected DIBs stronger than 10 mA in equivalent width are found in the optical spectrum of Herschel 36, suggesting that neither dissociation nor ionization of the carriers of the known DIBs by this intense field creates new carriers with easily detectable DIB-like features. Possibly related profile anomalies for several other DIBs are noted.
Koller, Thomas M; Heller, Andreas; Rausch, Michael H; Wasserscheid, Peter; Economou, Ioannis G; Fröba, Andreas P
2015-07-01
Ionic liquids (ILs) are possible working fluids for the separation of carbon dioxide (CO2) from flue gases. For evaluating their performance in such processes, reliable mutual-diffusivity data are required for mixtures of ILs with relevant flue gas components. In the present study, dynamic light scattering (DLS) and molecular dynamics (MD) simulations were used for the investigation of the molecular diffusion in binary mixtures of the IL 1-ethyl-3-methylimidazolium tetracyanoborate ([EMIM][B(CN)4]) with the dissolved gases carbon dioxide, nitrogen, carbon monoxide, hydrogen, methane, oxygen, and hydrogen sulfide at temperatures from 298.15 to 363.15 K and pressures up to 63 bar. At conditions approaching infinite dilution of a gas, the Fick mutual diffusivity of the mixture measured by DLS and the self-diffusivity of the corresponding gas calculated by MD simulations match, which could be generally found within combined uncertainties. The obtained diffusivities are in agreement with literature data for the same or comparable systems as well as with the general trend of increasing diffusivities for decreasing IL viscosities. The DLS and MD results reveal distinctly larger molecular diffusivities for [EMIM][B(CN)4]-hydrogen mixtures compared to mixtures with all other gases. This behavior results in the failure of an empirical correlation with the molar volumes of the gases at their normal boiling points. The DLS experiments also showed that there is no noticeable influence of the dissolved gas and temperature on the thermal diffusivity of the studied systems. PMID:26075680
Anomalous cross field flux in CHS
International Nuclear Information System (INIS)
Anomalous quasi-linear fluxes induced by the curvature drift resonance and transit resonance are evaluated in a rotating helical plasma. The radial electric field makes the Doppler shift, but does not contribute to the anomalous fluxes. The curvature drift resonance induces the new curvature term in the quasi-linear fluxes. The effect of helical magnetic field is through this curvature of magnetic field lines, and contributes to the inward transport. The ion heat diffusivity due to the curvature drift resonance is obtained in the form modified gyro-Bohm coefficient, and is compared with experimentally observed one in CHS Heliotron. (author)
Anomalous transport equations in toroidal plasmas
International Nuclear Information System (INIS)
Reduced transport equations for a toroidal plasma with fluctuations are derived. These equations include the effects of both anomalous and standard neoclassical transport, and allow clarification of the structure of convective fluxes caused by electrostatic and magnetic fluctuations. Special attention is paid to the combined effects of fluctuations and toroidicity on the transport. The formulation retains the effects of a magnetic field inhomogeneity on the anomalous transport. It is shown that phase space diffusion caused by the gradient in the equilibrium magnetic field appears as a pinch flux in the real space
Sanjay Bhushan
2013-01-01
This paper shows the utility of systems approach by extending the traditional innovation models and incorporating and integrating into them selective critical structural variables to map their interaction and explain the inherent dynamism. Conventionally, the approaches in explaining the innovation diffusion process assume that the process takes place in a stable and homogeneous system in which the innovation diffuses or spreads without being affected by the systemâ€™s structural variables ev...
Farid Chighoub; Brahim Mezerdi
2014-01-01
The main objective of this paper is to explore the relationship between the stochastic maximum principle (SMP in short) and dynamic programming principle (DPP in short), for singular control problems of jump diffusions. First, we establish necessary as well as sufficient conditions for optimality by using the stochastic calculus of jump diffusions and some properties of singular controls. Then, we give, under smoothness conditions, a useful verification theorem and we show that the solution o...
Wave diffusion and mesoscopic dynamics, towards a universal time-dependent random scattering matrix
Weaver, Richard L.
2007-01-01
We concern ourselves with the prediction of mesoscopic wave phenomena from statistical knowledge of classical trajectories. A diffusing particle picture for the flow of mean probability in chaotic systems is used to estimate dynamical features of mean square time-domain S matrices for waves coupled in and out through one perfectly open channel. A random process with that mean square, and with the additional constraint of unitarity, is then shown to lead to plausible S matrices with familiar mesoscopic wave dynamics. Features that are generated by this procedure include enhanced backscatter, quantum echo, power law tails, level repulsion and spectral rigidity. It is remarkable that such rich behaviours arise from such simple constraints. We conjecture that a generalization to n × n S matrices would exhibit behaviour identical to that of a Hamiltonian taken from the Gaussian Orthogonal or Unitary Ensembles (GOE or GUE) depending on its symmetries. Further constraining the S matrices to reproduce non universal aspects of classical dynamics, (known short time behaviours, periodic orbits, stable islands...) may generate mesoscopic wave features of such systems.
DEFF Research Database (Denmark)
Boned, C.; Allal, A.; Baylaucq, A.;
2004-01-01
In this work, a simultaneous modeling of the self-diffusion coefficient and the dynamic viscosity is presented. In the microstructural theory these two quantities are governed by the same friction coefficient related to the mobility of the molecule. A recent free-volume model, already successfully...... applied to dynamic viscosity, has been considered and generalized. In this generalized model the compound is characterized by only four parameters. But if the quadratic length is known, the number of adjustable parameters is three. The compounds considered in this work are benzene, carbon tetrachloride......, chlorotrifluoromethane, cyclohexane, methylcyclohexane, and tetramethylsilane. For these pure compounds we have found in the literature several data for both the self-diffusion and the dynamic viscosity in large viscosity, diffusion, temperature, and pressure intervals (up to around 500 MPa for methylcyclohexane and...
Non-Brownian diffusion in lipid membranes: Experiments and simulations.
Metzler, R; Jeon, J-H; Cherstvy, A G
2016-10-01
The dynamics of constituents and the surface response of cellular membranes-also in connection to the binding of various particles and macromolecules to the membrane-are still a matter of controversy in the membrane biophysics community, particularly with respect to crowded membranes of living biological cells. We here put into perspective recent single particle tracking experiments in the plasma membranes of living cells and supercomputing studies of lipid bilayer model membranes with and without protein crowding. Special emphasis is put on the observation of anomalous, non-Brownian diffusion of both lipid molecules and proteins embedded in the lipid bilayer. While single component, pure lipid bilayers in simulations exhibit only transient anomalous diffusion of lipid molecules on nanosecond time scales, the persistence of anomalous diffusion becomes significantly longer ranged on the addition of disorder-through the addition of cholesterol or proteins-and on passing of the membrane lipids to the gel phase. Concurrently, experiments demonstrate the anomalous diffusion of membrane embedded proteins up to macroscopic time scales in the minute time range. Particular emphasis will be put on the physical character of the anomalous diffusion, in particular, the occurrence of ageing observed in the experiments-the effective diffusivity of the measured particles is a decreasing function of time. Moreover, we present results for the time dependent local scaling exponent of the mean squared displacement of the monitored particles. Recent results finding deviations from the commonly assumed Gaussian diffusion patterns in protein crowded membranes are reported. The properties of the displacement autocorrelation function of the lipid molecules are discussed in the light of their appropriate physical anomalous diffusion models, both for non-crowded and crowded membranes. In the last part of this review we address the upcoming field of membrane distortion by elongated membrane
International Nuclear Information System (INIS)
The variation of the core structure of an easy glide dislocation with temperature and its influence on the stacking fault energy (γ) have been investigated for the first time by molecular-dynamics simulation in copper. The calculations have been performed at various temperatures, using an ab-initio pseudo-potential. Our results show that the core of the Shockley partials, into which the perfect edge dislocation dissociates, becomes increasingly extended as temperature increases. However their separation remains constant. The calculated energy values of the infinite extension stacking fault and the ribbon fault between the partials are quite different, but the evolution of the core structure does not affect the temperature dependence of the latter. We have found that a high disorder appears in the core region when temperature increases due to important anharmonicity effects of the atomic vibrations. The core structure remains solid-like for T m (Tm: melting point of bulk) in spite of the high disorder. Above Tm, the liquid nucleus germinates in the core region, and then propagates into the bulk. In addition we studied the mobility of vacancies and interstitials trapped on the partials. Although fast diffusion is thought to occur exclusively in a pipe surrounding the dislocation core, in the present study a quasi two-dimensional diffusion is observed for both defects not only in the cores but also in the stacking fault ribbon. On the opposite of current assumptions, the activation energy for diffusion is found to be identical for both defects, which may therefore comparably contribute to mass transport along the dislocations. (author)
Dynamic free energy surfaces for sodium diffusion in type II silicon clathrates.
Slingsby, J G; Rorrer, N A; Krishna, L; Toberer, E S; Koh, C A; Maupin, C M
2016-02-21
Earth abundant semiconducting type II Si clathrates have attracted attention as photovoltaic materials due to their wide band gaps. To realize the semiconducting properties of these materials, guest species that arise during the synthesis process must be completely evacuated from the host cage structure post synthesis. A common guest species utilized in the synthesis of Si clathrates is Na (metal), which templates the clathrate cage formation. Previous experimental investigations have identified that it is possible to evacuate Na from type II clathrates to an occupancy of less than 1 Na per unit cell. This work investigates the energetics, kinetics, and resulting mechanism of Na diffusion through type II Si clathrates by means of biased molecular dynamics and kinetic Monte Carlo simulations. Well-tempered metadynamics has been used to determine the potential of mean force for Na moving between clathrate cages, from which the thermodynamic preferences and transition barrier heights have been obtained. Kinetic Monte Carlo simulations based on the metadynamics results have identified the mechanism of Na diffusion in type II Si clathrates. The overall mechanism consists of a coupled diffusive process linked via electrostatic guest-guest interactions. The large occupied hexakaidechedral cages initially empty their Na guests to adjacent empty large cages, thereby changing the local electrostatic environment around the occupied small pentagonal dodecahedral cages and increasing the probability of Na guests to leave the small cages. This coupled process continues through the cross-over point that is identified as the point where large and small cages are equally occupied by Na guests. Further Na removal results in the majority of guests residing in the large cages as opposed to the small cages, in agreement with experiments, and ultimately a Na free structure. PMID:26658349
Non-Markovian Dynamics and Self-Diffusion in Strongly Coupled Plasmas
Strickler, Trevor; Langin, Thomas; McQuillen, Patrick; Daligault, Jerome; Maksimovich, Nikola; Killian, Thomas
2015-11-01
In weakly coupled plasmas, collisions are dominated by long range, small angle scattering, and each collision is an uncorrelated binary event. In contrast, collisions in strongly coupled plasmas (coupling parameter Γ > 1) are dominated by short range, large angle scattering in which the collisions may be correlated and non-independent in time, i.e., non-Markovian. In this work, we present experimental results indicative of non-Markovian processes in a strongly coupled ultracold neutral plasma (UCNP) created by photoionizing strontium atoms in a magneto-optical trap. We use optical pumping to create spin ``tagged'' subpopulations of ions having non-zero average velocity , and use laser induced fluorescence (LIF) imaging to measure the relaxation of back to equilibrium. We observe clear non-exponential decay in , which indicates non-Markovian dynamics. We further demonstrate there is a theoretical basis to consider as an approximation to the ion velocity autocorrelation function (VAF). We then calculate diffusion coefficients from our data, demonstrating experimental measurement of self-diffusion coefficients for 0 . 3 Air Force Office of Scientific Research (FA9550- 12-1-0267).
On the dynamics of flame edges in diffusion-flame/vortex interactions
Energy Technology Data Exchange (ETDEWEB)
Hermanns, Miguel; Linan, Amable [Departamento de Motopropulsion y Termofluidodinamica, Universidad Politecnica de Madrid, Pza. Cardenal Cisneros 3, 28040 Madrid (Spain); Vera, Marcos [Area de Mecanica de Fluidos, Universidad Carlos III de Madrid, 28911 Leganes (Spain)
2007-04-15
We analyze the local flame extinction and reignition of a counterflow diffusion flame perturbed by a laminar vortex ring. Local flame extinction leads to the appearance of flame edges separating the burning and extinguished regions of the distorted mixing layer. The dynamics of these edges is modeled based on previous numerical results, with heat release effects fully taken into account, which provide the propagation velocity of triple and edge flames in terms of the upstream unperturbed value of the scalar dissipation. The temporal evolution of the mixing layer is determined using the classical mixture fraction approach, with both unsteady and curvature effects taken into account. Although variable density effects play an important role in exothermic reacting mixing layers, in this paper the description of the mixing layer is carried out using the constant density approximation, leading to a simplified analytical description of the flow field. The mathematical model reveals the relevant nondimensional parameters governing diffusion-flame/vortex interactions and provides the parameter range for the more relevant regime of local flame extinction followed by reignition via flame edges. Despite the simplicity of the model, the results show very good agreement with previously published experimental results. (author)
The dynamics of localized spot patterns for reaction-diffusion systems on the sphere
Trinh, Philippe H.; Ward, Michael J.
2016-03-01
In the singularly perturbed limit corresponding to a large diffusivity ratio between two components in a reaction-diffusion (RD) system, quasi-equilibrium spot patterns are often admitted, producing a solution that concentrates at a discrete set of points in the domain. In this paper, we derive and study the differential algebraic equation (DAE) that characterizes the slow dynamics for such spot patterns for the Brusselator RD model on the surface of a sphere. Asymptotic and numerical solutions are presented for the system governing the spot strengths, and we describe the complex bifurcation structure and demonstrate the occurrence of imperfection sensitivity due to higher order effects. Localized spot patterns can undergo a fast time instability and we derive the conditions for this phenomena, which depend on the spatial configuration of the spots and the parameters in the system. In the absence of these instabilities, our numerical solutions of the DAE system for N = 2 to N = 8 spots suggest a large basin of attraction to a small set of possible steady-state configurations. We discuss the connections between our results and the study of point vortices on the sphere, as well as the problem of determining a set of elliptic Fekete points, which correspond to globally minimizing the discrete logarithmic energy for N points on the sphere.
Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow
Devanathan, Ram; Chase-Woods, Dylan; Shin, Yongsoon; Gotthold, David W.
2016-01-01
Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step. PMID:27388562
Diffusive and rotational dynamics of condensed n-H2 confined in MCM-41
Energy Technology Data Exchange (ETDEWEB)
Prisk, Timothy R [ORNL; Bryan, Matthew [Indiana University; Sokol, Paul E [ORNL
2014-01-01
In this paper, we report an inelastic neutron scattering study of liquid and solid n-H2 confined within MCM-41. This is a high surface area, mesoporous silica glass with a narrow pore size distribution centered at 3.5 nm. The scattering data provides information about the diffusive and rotational dynamics of the adsorbed n-H2 at low temperatures. In the liquid state, the neutron scattering data demonstrates that only a fraction of the adsorbed o-H2 is mobile on the picosecond time scale. This mobile fraction undergoes liquid-like jump diffusion, and values for the residence time t and effective mean-squared displacement hu2i are reported as a function of pore filling. In the solid state, the rotational energy levels of adsorbed H2 are strongly perturbed from their free quantum rotor behavior in the bulk solid. The underlying orientational potential of the hindered rotors is due to the surface roughness and heterogeneity of the MCM-41 pore walls. This potential is compared to the hindering potential of other porous silicas, such as Vycor. Strong selective adsorption makes the interfacial layer rich in o-H2, leaving the inner core volume consisting of a depleted mixture of o-H2 and p-H2.
Wang, Sibo; Xu, Junbo; Wen, Hao
2014-12-01
The heavy crude oil consists of thousands of compounds and much of them have large molecular weights and complex structures. Studying the aggregation and diffusion behavior of asphaltenes can facilitate the understanding of the heavy crude oil. In previous studies, the fused aromatic rings were treated as rigid bodies so that dissipative particle dynamics (DPD) integrated with the quaternion method can be used to study asphaltene systems. In this work, DPD integrated with the quaternion method is implemented on graphics processing units (GPUs). Compared with the serial program, tens of times speedup can be achieved when simulations performed on a single GPU. Using multiple GPUs can provide faster computation speed and more storage space for simulations of significant large systems. By using large systems, simulations of the asphaltene-toluene system at extremely dilute concentrations can be performed. The determined diffusion coefficients of asphaltenes are similar to that in experimental studies. At last, the aggregation behavior of asphaltenes in heptane was investigated, and the simulation results agreed with the modified Yen model. Monomers, nanoaggregates and clusters were observed from the simulations at different concentrations.
Molecular Dynamics Simulations Reveal that Water Diffusion between Graphene Oxide Layers is Slow
Energy Technology Data Exchange (ETDEWEB)
Devanathan, Ram; Chase-Woods, Dylan G.; Shin, Yongsoon; Gotthold, David W.
2016-07-08
Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of a molecular dynamics simulation study of water intercalated between GO layers that have a C/O ratio of 4. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 14% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.
McDonnell, Marshall T; Greeley, Duncan A; Kit, Kevin M; Keffer, David J
2016-09-01
The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in sustainable, biodegradable chitosan/chitin food packaging films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane has a more homogeneous water distribution with the polymer chains being fully solvated. The diffusivity increased by a factor of 4 for oxygen molecules and by an order of magnitude for water with increasing the humidity. To calculate the Henry's constant and solubility of oxygen in the membranes with changing hydration, the excess chemical potential was calculated via free energy perturbation, thermodynamic integration and direct particle deletion methods. The simulations predicted a higher solubility and permeability for the lower humidity, in contradiction to experimental results. All three methods for calculating the solubility were in good agreement. It was found that the Coulombic interactions in the potential caused the oxygen to bind too strongly to the protonated amine group. Insight from this work will help guide molecular modeling of chitosan/chitin membranes, specifically permeability measurements for small solute molecules. Efforts to chemically tailor chitosan/chitin membranes to favor discrete as opposed to continuous aqueous domains could reduce oxygen permeability. PMID:27487964
Molecular Dynamics Study of Stability and Diffusion of Graphene-Based Drug Delivery Systems
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Xiunan Wang
2015-01-01
Full Text Available Graphene, a two-dimensional nanomaterial with unique biomedical properties, has attracted great attention due to its potential applications in graphene-based drug delivery systems (DDS. In this work graphene sheets with various sizes and graphene oxide functionalized with polyethylene glycol (GO-PEG are utilized as nanocarriers to load anticancer drug molecules including CE6, DOX, MTX, and SN38. We carried out molecular dynamics calculations to explore the energetic stabilities and diffusion behaviors of the complex systems with focuses on the effects of the sizes and functionalization of graphene sheets as well as the number and types of drug molecules. Our study shows that the binding of graphene-drug complex is favorable when the drug molecules and finite graphene sheets become comparable in sizes. The boundaries of finite sized graphene sheets restrict the movement of drug molecules. The double-side loading often slows down the diffusion of drug molecules compared with the single-side loading. The drug molecules bind more strongly with GO-PEG than with pristine graphene sheets, demonstrating the advantages of functionalization in improving the stability and biocompatibility of graphene-based DDS.
Faster is More Different: Mean-Field Dynamics of Innovation Diffusion
Baek, Seung Ki; Kim, Mina
2013-01-01
Based on a recent model of paradigm shifts by Bornholdt et al., we studied mean-field opinion dynamics in an infinite population where an infinite number of ideas compete simultaneously with their values publicly known. We found that a highly innovative society is not characterized by heavy concentration in highly valued ideas: Rather, ideas are more broadly distributed in a more innovative society with faster progress, provided that the rate of adoption is constant, which suggests a positive correlation between innovation and technological disparity. Furthermore, the distribution is generally skewed in such a way that the fraction of innovators is substantially smaller than has been believed in conventional innovation-diffusion theory based on normality. Thus, the typical adoption pattern is predicted to be asymmetric with slow saturation in the ideal situation, which is compared with empirical data sets.
Experimental measurement of non-Markovian dynamics and self-diffusion in a strongly coupled plasma
Strickler, T S; McQuillen, P; Daligault, J; Killian, T C
2015-01-01
We present a study of the collisional relaxation of ion velocities in a strongly coupled, ultracold neutral plasma on short timescales compared to the inverse collision rate. Non-exponential decay towards equilibrium for the average velocity of a tagged population of ions heralds non-Markovian dynamics and a breakdown of assumptions underlying standard kinetic theory. We prove the equivalence of the average-velocity curve to the velocity autocorrelation function, a fundamental statistical quantity that provides access to equilibrium transport coefficients and aspects of individual particle trajectories in a regime where experimental measurements have been lacking. From our data, we calculate the ion self-diffusion constant. This demonstrates the utility of ultracold neutral plasmas for isolating the effects of strong coupling on collisional processes, which is of interest for dense laboratory and astrophysical plasmas.
Chalub, Fabio A C C
2008-01-01
We study the large population limit of the Moran process, assuming weak-selection, and for different scalings. Depending on the particular choice of scalings, we obtain a continuous model that may highlight the genetic-drift (neutral evolution) or natural selection; for one precise scaling, both effects are present. For the scalings that take the genetic-drift into account, the continuous model is given by a singular diffusion equation, together with two conservation laws that are already present at the discrete level. For scalings that take into account only natural selection, we obtain a hyperbolic singular equation that embeds the Replicator Dynamics and satisfies only one conservation law. The derivation is made in two steps: a formal one, where the candidate limit model is obtained, and a rigorous one, where convergence of the probability density is proved. Additional results on the fixation probabilities are also presented.
International Nuclear Information System (INIS)
Highlights: • Functional MRI in the characterization of testicular germ cell tumors was assessed. • ADC values proved useful in the characterization of testicular germ cell tumors. • Testicular germ cell tumors had similar enhancement patterns of dynamic MRI. - Abstract: Introduction: The aim of this study is to investigate the role of apparent diffusion coefficient (ADC) values and dynamic contrast enhancement (DCE) patterns in differentiating seminomas from nonseminomatous germ cell tumors (NSGCTs). Materials and methods: The MRI examinations of the scrotum of 26 men with histologically proven testicular GCTs were reviewed. DWI was performed in all patients, using a single shot, multi-slice spin-echo planar diffusion pulse sequence and b-values of 0 and 900 s/mm2. Subtraction DCE-MRI was performed in 20 cases using a 3D fast-field echo sequence after gadolinium administration. Time-signal intensity curves were created and semi-quantitative parameters (peak enhancement, time to peak, wash-in and wash-out rate) were calculated. The Student's t-test was used to compare the mean values of ADC, peak enhancement, time to peak, wash-in and wash-out rate between seminomas and NSGCTs. ROC analysis was also performed. Results: Histopathology disclosed the presence of 15 seminomas and 11 NSGCTs. The mean ± s.d. of ADC values (× 10−3 mm2/s) of seminomas (0.59 ± 0.009) were significantly lower than those of NSGCTs (0.90 ± 0.33) (P = 0.01). The optimal ADC cut-off value was 0.68 × 10−3 mm2/s. No differences between the two groups were observed for peak enhancement (P = 0.18), time to peak (P = 0.63) wash-in rate (P = 0.32) and wash-out rate (P = 0.18). Conclusions: ADC values may be used to preoperatively differentiate seminomas from NSGCTs
The role of diffusion coefficients in the dynamics of nuclear processes
International Nuclear Information System (INIS)
The dissipation process in open quantum systems at initial time before the setting of the equilibrium state plays a key role in such physical processes, as quantum-optical processes, nuclear fission and fusion and deep inelastic collisions of heavy ions. The goal of a given work is to demonstrate the advanced method for the calculation of non-stationary diffusion coefficients of the collective system, in case when the collective subsystem and thermostat are linearly coupled in the coordinate and momentum. As a result of the interaction between the degrees of freedom of collective and intrinsic subsystems, the transport and diffusion coefficients on coordinate, momentum and coordinate-momentum appear in the system. The Langevin formalism which is effective in description of fluctuation and dissipative processes in macroscopic systems has been introduced in derivation of equations of motion. In the kinetic theory the Leaving's method significantly simplifies a procedure of calculation of non-stationary quantum and thermal fluctuations and provides a clear picture of the dynamics of the process. The microscopic Hamiltonian of the system (thermostat plus collective system) is given. For example, while describing the interaction of nuclei at low energies, the coupling in the coordinate responses for the influence of the mean field of each nucleus on the single-particle motion in other nucleus whereas the last term describes the relation between the currents of intrinsic and collective motion. In the procedure of solving the second order Heisenberg equations, the integro-differential quantum stochastic Langevin Equations are obtained directly. Knowing its solution we may write the equations for the first and second moments which provide us the expressions for the transport and diffusion coefficients. In the figure the time dependencies of diffusion coefficients at the temperature T=0.1 MeV are given. In our calculations we consider the case of a large mass μ=448m0 (m0
Reduced Lorenz models for anomalous transport and profile resilience
International Nuclear Information System (INIS)
The physical basis for the Lorenz equations for convective cells in stratified fluids, and for magnetized plasmas imbedded in curved magnetic fields, are reexamined with emphasis on anomalous transport. It is shown that the Galerkin truncation leading to the Lorenz equations for the closed boundary problem is incompatible with finite fluxes through the system in the limit of vanishing diffusion. An alternative formulation leading to the Lorenz equations is proposed, invoking open boundaries and the notion of convective streamers and their back-reaction on the profile gradient, giving rise to resilience of the profile. Particular emphasis is put on the diffusionless limit, where these equations reduce to a simple dynamical system depending only on one single forcing parameter. This model is studied numerically, stressing experimentally observable signatures, and some of the perils of dimension-reducing approximations are discussed
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Directory of Open Access Journals (Sweden)
Liubov Tupikina
Full Text Available Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet.
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics.
Tupikina, Liubov; Molkenthin, Nora; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network's structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet. PMID:27128846
Correlation Networks from Flows. The Case of Forced and Time-Dependent Advection-Diffusion Dynamics
Tupikina, Liubov; Molkenthin, Nora; López, Cristóbal; Hernández-García, Emilio; Marwan, Norbert; Kurths, Jürgen
2016-01-01
Complex network theory provides an elegant and powerful framework to statistically investigate different types of systems such as society, brain or the structure of local and long-range dynamical interrelationships in the climate system. Network links in climate networks typically imply information, mass or energy exchange. However, the specific connection between oceanic or atmospheric flows and the climate network’s structure is still unclear. We propose a theoretical approach for verifying relations between the correlation matrix and the climate network measures, generalizing previous studies and overcoming the restriction to stationary flows. Our methods are developed for correlations of a scalar quantity (temperature, for example) which satisfies an advection-diffusion dynamics in the presence of forcing and dissipation. Our approach reveals that correlation networks are not sensitive to steady sources and sinks and the profound impact of the signal decay rate on the network topology. We illustrate our results with calculations of degree and clustering for a meandering flow resembling a geophysical ocean jet. PMID:27128846
Turbulent structure and dynamics of swirled, strongly pulsed jet diffusion flames
Liao, Ying-Hao
2013-11-02
The structure and dynamics of swirled, strongly pulsed, turbulent jet diffusion flames were examined experimentally in a co-flow swirl combustor. The dynamics of the large-scale flame structures, including variations in flame dimensions, the degree of turbulent flame puff interaction, and the turbulent flame puff celerity were determined from high-speed imaging of the luminous flame. All of the tests presented here were conducted with a fixed fuel injection velocity at a Reynolds number of 5000. The flame dimensions were generally found to be more impacted by swirl for the cases of longer injection time and faster co-flow flow rate. Flames with swirl exhibited a flame length up to 34% shorter compared to nonswirled flames. Both the turbulent flame puff separation and the flame puff celerity generally decreased when swirl was imposed. The decreased flame length, flame puff separation, and flame puff celerity are consistent with a greater momentum exchange between the flame and the surrounding co-flow, resulting from an increased rate of air entrainment due to swirl. Three scaling relations were developed to account for the impact of the injection time, the volumetric fuel-to-air flow rate ratio, and the jet-on fraction on the visible flame length. © 2013 Copyright Taylor and Francis Group, LLC.
A molecular dynamics simulation study of diffuse x-ray scattering from C10H16
International Nuclear Information System (INIS)
Adamantane C10H16 is an interesting archetypal plastic crystal which has been extensively studied. It undergoes transition from a low temperature ordered phase to a high temperature disordered phase at T=208.6K. The C10H16 molecule has tetrahedral symmetry and the orientational disorder in the plastic phase has been interpreted in terms of the distribution of the molecules between two equally preferred orientations. A molecular dynamics simulation of C10H16 has been carried out using the CCP5 Library program moliq-dynamo, written by Dr. D. Fincham of Keele University. The simulation model consists of rigid molecules interacting with an atom-atom pairwise additive potential. The dynamics of the adamantane molecules in the plastic phase have been investigated and results have been compared with previous work. The molecular trajectories generated by the simulation have been used to evaluate the intensity of diffuse x-ray scattering from the crystal. Results have been compared with experimental data obtained from energy-dispersive x-ray scattering measurements made at the Daresbury SRS. Using a series of simplified models of the crystal, the relative contributions to the scattered intensity from translational and orientational disorder have been investigated. (author)
Forecasting Latin America’s Country Risk Scores by Means of a Dynamic Diffusion Model
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R. Cervelló-Royo
2013-01-01
Full Text Available Over the last years, worldwide financial market instability has shaken confidence in global economies. Global financial crisis and changes in sovereign debts ratings have affected the Latin American financial markets and their economies. However, Latin American’s relative resilience to the more acute rise in risk seen in other regions like Europe during last years is offering investors new options for improving risk-return trade-offs. Therefore, forecasting the future of economic situation involves high levels of uncertainty. The Country Risk Score (CRS represents a broadly used indicator to measure the current situation of a country regarding measures of economic, political, and financial risk in order to determine country risk ratings. In this contribution, we present a diffusion model to study the dynamics of the CRS in 18 Latin American countries which considers both the endogenous effect of each country policies and the contagion effect among them. The model predicts quite well the evolution of the CRS in the short term despite the economic and political instability. Furthermore, the model reproduces and forecasts a slight increasing trend, on average, in the CRS dynamics for almost all Latin American countries over the next months.
Wu, Jie; Huang, Jun-Jie
2015-07-01
Water management is one of the key issues in proton exchange membrane fuel cells. Fundamentally, it is related to dynamic behaviors of droplets on a gas diffusion layer (GDL) surface, and consequently they are investigated in this work. A two-dimensional hybrid method is employed to implement numerical simulations, in which the flow field is solved by using the lattice Boltzmann method and the interface between droplet and gas is captured by solving the Cahn-Hilliard equation directly. One or two liquid droplets are initially placed on the GDL surface of a gas channel, which is driven by the fully developed Poiseuille flow. At a fixed channel size, the effects of viscosity ratio of droplet to gas ( μ ∗ ), Capillary number (Ca, ratio of gas viscosity to surface tension), and droplet interaction on the dynamic behaviors of droplets are systematically studied. By decreasing viscosity ratio or increasing Capillary number, the single droplet can detach from the GDL surface easily. On the other hand, when two identical droplets stay close to each other or a larger droplet is placed in front of a smaller droplet, the removal of two droplets is promoted.
Uhrig dynamical control of a three-level system via non-Markovian quantum state diffusion
Shu, Wenchong; Zhao, Xinyu; Jing, Jun; Wu, Lian-Ao; Yu, Ting
2013-09-01
In this paper, we use the quantum state diffusion (QSD) equation to implement the Uhrig dynamical decoupling to a three-level quantum system coupled to a non-Markovian reservoir comprising of infinite numbers of degrees of freedom. For this purpose, we first reformulate the non-Markovian QSD to incorporate the effect of the external control fields. With this stochastic QSD approach, we demonstrate that an unknown state of the three-level quantum system can be universally protected against both coloured phase and amplitude noises when the control-pulse sequences and control operators are properly designed. The advantage of using non-Markovian QSD equations is that the control dynamics of open quantum systems can be treated exactly without using Trotter product formula and be efficiently simulated even when the environment is comprised of infinite numbers of degrees of freedom. We also show how the control efficacy depends on the environment memory time and the designed time points of applied control pulses.
Chun, Myung-Suk; Kim, Chongyoup; Lee, Duck E.
2009-05-01
In our recent Brownian dynamics (BD) simulation study, the structure and dynamics of anionic polyelectrolyte xanthan in bulk solution as well as confined spaces of slitlike channel were examined by applying a coarse-grained model with nonlinear bead-spring discretization of a whole chain [J. Jeon and M.-S. Chun, J. Chem. Phys. 126, 154904 (2007)]. This model goes beyond other simulations as they did not consider both long-range electrostatic and hydrodynamic interactions between pairs of beads. Simulation parameters are obtained from the viscometric method of rheology data on the native and sonicated xanthan polysaccharides, which have a contour length less than 1μm . The size of the semiflexible polyelectrolyte can be well described by the wormlike chain model once the electrostatic effects are taken into account by the persistence length measured at a long length scale. For experimental verifications, single molecule visualization was performed on fluorescein-labeled xanthan using an inverted fluorescence microscope, and the motion of an individual molecule was quantified. Experimental results on the conformational changes in xanthan chain in the electrolyte solution have a reasonable trend to agree with the prediction by BD simulations. In the translational diffusion induced by the Debye screening effect, the simulation prediction reveals slightly higher values compared to those of our measurements, although it agrees with the literature data. Considering the experimental restrictions, our BD simulations are verified to model the single polyelectrolyte well.
Analytical solutions for anomalous dispersion transport
O'Malley, D.; Vesselinov, V. V.
2014-06-01
Groundwater flow and transport often occur in a highly heterogeneous environment (potentially heterogeneous at multiple spatial scales) and is impacted by geochemical reactions, advection, diffusion, and other pore scale processes. All these factors can give rise to large-scale anomalous dispersive behavior that can make complex model representation and prediction of plume concentrations challenging due to difficulties unraveling all the complexities associated with the governing processes, flow medium, and their parameters. An alternative is to use upscaled stochastic models of anomalous dispersion, and this is the approach used here. Within a probabilistic framework, we derive a number of analytical solutions for several anomalous dispersion models. The anomalous dispersion models are allowed to be either non-Gaussian (α-stable Lévy), correlated, or nonstationary from the Lagrangian perspective. A global sensitivity analysis is performed to gain a greater understanding of the extent to which uncertainty in the parameters associated with the anomalous behavior can be narrowed by examining concentration measurements from a network of monitoring wells and to demonstrate the computational speed of the solutions. The developed analytical solutions are encoded and available for use in the open source computational framework MADS (http://mads.lanl.gov).
Anomalous transport in high-temperature plasmas with applications to solenoidal fusion systems
International Nuclear Information System (INIS)
The linear, non-linear, and anomalous transport properties associated with various micro-instabilities driven by cross-field currents in high-temperature plasmas are reviewed. Particular emphasis is placed on instabilities pertinent to the implosion and post-implosion phases of theta-pinch plasmas, e.g. Buneman (electron-ion two-stream), ion acoustic, lower-hybrid-drift, electromagnetic ion cyclotron, and ion-ion cross-field instabilities. Analytic studies of the non-linear and quasi-linear evolution of these instabilities are presented, together with a detailed comparison with computer simulation experiments to test the validity of the various theoretical models and non-linear saturation mechanisms. A general theoretical formalism is presented which describes, in a self-consistent manner, the macroscopic transport produced by the (short-wave-length) turbulence associated with the microinstabilities enumerated above. The experimental evidence that such a self-consistent anomalous transport model is required for describing the implosion behaviour (characterized by diffuse current sheaths) in rapidly pulsed theta pinches is reviewed, together with the early attempts at modelling these implosions numerically with a one-fluid (MHD) model including artificial viscosity. It is shown that fluid-numerical simulations that include (at each space and time step) the effects of anomalous transport in a fully self-consistent manner, explain several features of the experimental observations. The relevance of reflected ions to sheath structure and implosion dynamics is also discussed, and state-of-the-art hybrid-numerical studies (Vlasov ions and fluid electrons) of pinch implosions are presented, which include reflected ion dynamics as well as the anomalous transport associated with cross-field instabilities. Finally, instability mechanisms for producing long-time interpenetration of plasma and magnetic field in post-implosion theta pinches are discussed, together with estimates
Mukherjee, Arnab; Bagchi, Biman
2002-01-01
Diffusion of a tagged particle near a constraining biological surface is examined numerically by modeling the surface-water interaction by an effective potential. The effective potential is assumed to be given by an asymmetric double well constrained by a repulsive surface towards $r=0$ and unbound at large distances. The time and space dependent probability distribution $P(r,t)$ of the underlying Smoluchowski equation is solved by using Crank-Nicholson method. The mean square displacement sh...
Michailidou, V. N.; Swan, J. W.; Brady, J. F.; Petekidis, G.
2013-10-01
Evanescent wave dynamic light scattering and Stokesian dynamics simulations were employed to study the dynamics of hard-sphere colloidal particles near a hard wall in concentrated suspensions. The evanescent wave averaged short-time diffusion coefficients were determined from experimental correlation functions over a range of scattering wave vectors and penetration depths. Stokesian dynamics simulations performed for similar conditions allow a direct comparison of both the short-time self- and collective diffusivity. As seen earlier [V. N. Michailidou, G. Petekidis, J. W. Swan, and J. F. Brady, Phys. Rev. Lett. 102, 068302 (2009)] while the near wall dynamics in the dilute regime slow down compared to the free bulk diffusion, the reduction is negligible at higher volume fractions due to an interplay between the particle-wall and particle-particle hydrodynamic interactions. Here, we provide a comprehensive comparison between experiments and simulations and discuss the interplay of particle-wall and particle-particle hydrodynamics in the self- and cooperative dynamics determined at different scattering wave vectors and penetration depths.
Mercure, J -F; Foley, A M; Chewpreecha, U; Pollitt, H
2013-01-01
This paper presents an analysis of possible uses of climate policy instruments for the decarbonisation of the global electricity sector in a non-equilibrium economic and technology innovation-diffusion perspective. Emissions reductions occur through changes in technology and energy consumption; in this context, investment decision-making opportunities occur periodically, which energy policy can incentivise in order to transform energy systems and meet reductions targets. Energy markets are driven by innovation, dynamic costs and technology diffusion; yet, the incumbent systems optimisation methodology in energy modelling does not address these aspects nor the effectiveness of policy onto decision-making since the dynamics modelled take their source from the top-down `social-planner' assumption. This leads to an underestimation of strong technology lock-ins in cost-optimal scenarios of technology. Our approach explores the global diffusion of low carbon technology in connection to a highly disaggregated sector...