Diffusion mechanism of non-interacting Brownian particles through a deformed substrate

NASA Astrophysics Data System (ADS)

Arfa, Lahcen; Ouahmane, Mehdi; El Arroum, Lahcen

2018-02-01

We study the diffusion mechanism of non-interacting Brownian particles through a deformed substrate. The study is done at low temperature for different values of the friction. The deformed substrate is represented by a periodic Remoissenet-Peyrard potential with deformability parameter s. In this potential, the particles (impurity, adatoms…) can diffuse. We ignore the interactions between these mobile particles consider them merely as non-interacting Brownian particles and this system is described by a Fokker-Planck equation. We solve this equation numerically using the matrix continued fraction method to calculate the dynamic structure factor S(q , ω) . From S(q , ω) some relevant correlation functions are also calculated. In particular, we determine the half-width line λ(q) of the peak of the quasi-elastic dynamic structure factor S(q , ω) and the diffusion coefficient D. Our numerical results show that the diffusion mechanism is described, depending on the structure of the potential, either by a simple jump diffusion process with jump length close to the lattice constant a or by a combination of a jump diffusion model with jump length close to lattice constant a and a liquid-like motion inside the unit cell. It shows also that, for different friction regimes and various potential shapes, the friction attenuates the diffusion mechanism. It is found that, in the high friction regime, the diffusion process is more important through a deformed substrate than through a non-deformed one.

Birth-jump processes and application to forest fire spotting.

PubMed

Hillen, T; Greese, B; Martin, J; de Vries, G

2015-01-01

Birth-jump models are designed to describe population models for which growth and spatial spread cannot be decoupled. A birth-jump model is a nonlinear integro-differential equation. We present two different derivations of this equation, one based on a random walk approach and the other based on a two-compartmental reaction-diffusion model. In the case that the redistribution kernels are highly concentrated, we show that the integro-differential equation can be approximated by a reaction-diffusion equation, in which the proliferation rate contributes to both the diffusion term and the reaction term. We completely solve the corresponding critical domain size problem and the minimal wave speed problem. Birth-jump models can be applied in many areas in mathematical biology. We highlight an application of our results in the context of forest fire spread through spotting. We show that spotting increases the invasion speed of a forest fire front.

Molecular Dynamics Simulation of Salt Diffusion in Polyelectrolyte Assemblies.

PubMed

Zhang, Ran; Duan, Xiaozheng; Ding, Mingming; Shi, Tongfei

2018-06-05

The diffusion of salt ions and charged probe molecules in polyelectrolyte assemblies is often assumed to follow a theoretical hopping model, in which the diffusing ion is hopping between charged sites of chains based on electroneutrality. However, experimental verification of diffusing pathway at such microscales is difficult, and the corresponding molecular mechanisms remain elusive. In this study, we perform all-atom molecular dynamics (MD) simulations of salt diffusion in polyelectrolyte (PE) assembly of poly (sodium 4-styrenesulfonate) (PSS) and poly (diallyldimethylammonium chloride) (PDAC). Besides the ion hopping mode, the diffusing trajectories are found presenting common features of a jump process, i.e., subjecting to PE relaxation, water pockets in the structure open and close, thus the ion can move from one pocket to another. Anomalous subdiffusion of ions and water is observed due to the trapping scenarios in these water pockets. The jump events are much rarer compared with ion hopping but significantly increases salt diffusion with increasing temperature. Our result strongly indicates that salt diffusion in hydrated PDAC/PSS is a combined process of ion hopping and jump motion. This provides new molecular explanation for the coupling of salt motion with chain motion and the nonlinear increase of salt diffusion at glass transition temperature.

Valuing options in shot noise market

NASA Astrophysics Data System (ADS)

Laskin, Nick

2018-07-01

A new exactly solvable option pricing model has been introduced and elaborated. It is assumed that a stock price follows a Geometric shot noise process. An arbitrage-free integro-differential option pricing equation has been obtained and solved. The new Greeks have been analytically calculated. It has been shown that in diffusion approximation the developed option pricing model incorporates the well-known Black-Scholes equation and its solution. The stochastic dynamic origin of the Black-Scholes volatility has been uncovered. To model the observed market stock price patterns consisting of high frequency small magnitude and low frequency large magnitude jumps, the superposition of two Geometric shot noises has been implemented. A new generalized option pricing equation has been obtained and its exact solution was found. Merton's jump-diffusion formula for option price was recovered in diffusion approximation. Despite the non-Gaussian nature of probability distributions involved, the new option pricing model has the same degree of analytical tractability as the Black-Scholes model and the Merton jump-diffusion model. This attractive feature allows one to derive exact formulas to value options and option related instruments in the market with jump-like price patterns.

Post-processing interstitialcy diffusion from molecular dynamics simulations

NASA Astrophysics Data System (ADS)

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.

Post-processing interstitialcy diffusion from molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhardwaj, U., E-mail: haptork@gmail.com; Bukkuru, S.; Warrier, M.

2016-01-15

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 ismore » 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. -- Graphical abstract:.« less

From quantum mechanics to finance: Microfoundations for jumps, spikes and high volatility phases in diffusion price processes

NASA Astrophysics Data System (ADS)

Henkel, Christof

2017-03-01

We present an agent behavior based microscopic model that induces jumps, spikes and high volatility phases in the price process of a traded asset. We transfer dynamics of thermally activated jumps of an unexcited/excited two state system discussed in the context of quantum mechanics to agent socio-economic behavior and provide microfoundations. After we link the endogenous agent behavior to price dynamics we establish the circumstances under which the dynamics converge to an Itô-diffusion price processes in the large market limit.

Understanding and controlling regime switching in molecular diffusion

NASA Astrophysics Data System (ADS)

Hallerberg, S.; de Wijn, A. S.

2014-12-01

Diffusion can be strongly affected by ballistic flights (long jumps) as well as long-lived sticking trajectories (long sticks). Using statistical inference techniques in the spirit of Granger causality, we investigate the appearance of long jumps and sticks in molecular-dynamics simulations of diffusion in a prototype system, a benzene molecule on a graphite substrate. We find that specific fluctuations in certain, but not all, internal degrees of freedom of the molecule can be linked to either long jumps or sticks. Furthermore, by changing the prevalence of these predictors with an outside influence, the diffusion of the molecule can be controlled. The approach presented in this proof of concept study is very generic and can be applied to larger and more complex molecules. Additionally, the predictor variables can be chosen in a general way so as to be accessible in experiments, making the method feasible for control of diffusion in applications. Our results also demonstrate that data-mining techniques can be used to investigate the phase-space structure of high-dimensional nonlinear dynamical systems.

Approximation of epidemic models by diffusion processes and their statistical inference.

PubMed

Guy, Romain; Larédo, Catherine; Vergu, Elisabeta

2015-02-01

Multidimensional continuous-time Markov jump processes [Formula: see text] on [Formula: see text] form a usual set-up for modeling [Formula: see text]-like epidemics. However, when facing incomplete epidemic data, inference based on [Formula: see text] is not easy to be achieved. Here, we start building a new framework for the estimation of key parameters of epidemic models based on statistics of diffusion processes approximating [Formula: see text]. First, previous results on the approximation of density-dependent [Formula: see text]-like models by diffusion processes with small diffusion coefficient [Formula: see text], where [Formula: see text] is the population size, are generalized to non-autonomous systems. Second, our previous inference results on discretely observed diffusion processes with small diffusion coefficient are extended to time-dependent diffusions. Consistent and asymptotically Gaussian estimates are obtained for a fixed number [Formula: see text] of observations, which corresponds to the epidemic context, and for [Formula: see text]. A correction term, which yields better estimates non asymptotically, is also included. Finally, performances and robustness of our estimators with respect to various parameters such as [Formula: see text] (the basic reproduction number), [Formula: see text], [Formula: see text] are investigated on simulations. Two models, [Formula: see text] and [Formula: see text], corresponding to single and recurrent outbreaks, respectively, are used to simulate data. The findings indicate that our estimators have good asymptotic properties and behave noticeably well for realistic numbers of observations and population sizes. This study lays the foundations of a generic inference method currently under extension to incompletely observed epidemic data. Indeed, contrary to the majority of current inference techniques for partially observed processes, which necessitates computer intensive simulations, our method being mostly an analytical approach requires only the classical optimization steps.

Hydrogen diffusion in liquid aluminum from ab initio molecular dynamics

NASA Astrophysics Data System (ADS)

Jakse, N.; Pasturel, A.

2014-05-01

Ab initio molecular dynamics simulations are used to describe the diffusion of hydrogen in liquid aluminum at different temperatures. Quasi-instantaneous jumps separating periods of localized vibrations around a mean position are found to characterize the hydrogen motion at the microscopic scale. The hydrogen motion is furthermore analyzed using the van Hove function. We highlight a non-Fickian behavior for the hydrogen diffusion due to a large spatial distribution of hydrogen jumps. We show that a generalized continuous time random walk (CTRW) model describes the experimental diffusion coefficients in a satisfactory manner. Finally, the impact of impurities and alloying elements on hydrogen diffusion in aluminum is discussed.

Density functional calculation of activation energies for lattice and grain boundary diffusion in alumina

NASA Astrophysics Data System (ADS)

Lei, Yinkai; Gong, Yu; Duan, Zhiyao; Wang, Guofeng

2013-06-01

To acquire knowledge on the lattice and grain boundary diffusion processes in alumina, we have determined the activation energies of elementary O and Al diffusive jumps in the bulk crystal, Σ3(0001) grain boundaries, and Σ3(101¯0) grain boundaries of α-Al2O3 using the first-principles density functional theory method. Specifically, we calculated the activation energies for four elementary jumps of both O and Al lattice diffusion in alumina. It was predicted that the activation energy of O lattice diffusion varied from 3.58 to 5.03 eV, while the activation energy of Al lattice diffusion ranged from 1.80 to 3.17 eV. As compared with experimental measurements, the theoretical predictions of the activation energy for lattice diffusion were lower and thus implied that there might be other high-energy diffusive jumps in the experimental alumina samples. Moreover, our results suggested that the Al lattice diffusion was faster than the O lattice diffusion in alumina, in agreement with experiment observations. Furthermore, it was found from our calculations for α-Al2O3 that the activation energies of O and Al grain boundary diffusion in the high-energy Σ3(0001) grain boundaries were significantly lower than those of the lattice diffusion. In contrast, the activation energies of O and Al grain boundary diffusion in the low-energy Σ3(101¯0) grain boundaries could be even higher than those of the lattice diffusion.

Continuous-time safety-first portfolio selection with jump-diffusion processes

NASA Astrophysics Data System (ADS)

Yan, Wei

2012-04-01

This article is concerned with continuous-time portfolio selection based on a safety-first criterion under discontinuous price processes (jump-diffusion processes). The solution of the corresponding Hamilton-Jacobi-Bellman equation of the problem is demonstrated. The analytical solutions are presented when there does not exist any riskless asset. Moreover, the problem is also discussed while there exists one riskless asset.

A two-dimensional Riemann solver with self-similar sub-structure - Alternative formulation based on least squares projection

NASA Astrophysics Data System (ADS)

Balsara, Dinshaw S.; Vides, Jeaniffer; Gurski, Katharine; Nkonga, Boniface; Dumbser, Michael; Garain, Sudip; Audit, Edouard

2016-01-01

Just as the quality of a one-dimensional approximate Riemann solver is improved by the inclusion of internal sub-structure, the quality of a multidimensional Riemann solver is also similarly improved. Such multidimensional Riemann problems arise when multiple states come together at the vertex of a mesh. The interaction of the resulting one-dimensional Riemann problems gives rise to a strongly-interacting state. We wish to endow this strongly-interacting state with physically-motivated sub-structure. The self-similar formulation of Balsara [16] proves especially useful for this purpose. While that work is based on a Galerkin projection, in this paper we present an analogous self-similar formulation that is based on a different interpretation. In the present formulation, we interpret the shock jumps at the boundary of the strongly-interacting state quite literally. The enforcement of the shock jump conditions is done with a least squares projection (Vides, Nkonga and Audit [67]). With that interpretation, we again show that the multidimensional Riemann solver can be endowed with sub-structure. However, we find that the most efficient implementation arises when we use a flux vector splitting and a least squares projection. An alternative formulation that is based on the full characteristic matrices is also presented. The multidimensional Riemann solvers that are demonstrated here use one-dimensional HLLC Riemann solvers as building blocks. Several stringent test problems drawn from hydrodynamics and MHD are presented to show that the method works. Results from structured and unstructured meshes demonstrate the versatility of our method. The reader is also invited to watch a video introduction to multidimensional Riemann solvers on http://www.nd.edu/ dbalsara/Numerical-PDE-Course.

Approximate series solution of multi-dimensional, time fractional-order (heat-like) diffusion equations using FRDTM.

PubMed

Singh, Brajesh K; Srivastava, Vineet K

2015-04-01

The main goal of this paper is to present a new approximate series solution of the multi-dimensional (heat-like) diffusion equation with time-fractional derivative in Caputo form using a semi-analytical approach: fractional-order reduced differential transform method (FRDTM). The efficiency of FRDTM is confirmed by considering four test problems of the multi-dimensional time fractional-order diffusion equation. FRDTM is a very efficient, effective and powerful mathematical tool which provides exact or very close approximate solutions for a wide range of real-world problems arising in engineering and natural sciences, modelled in terms of differential equations.

Approximate series solution of multi-dimensional, time fractional-order (heat-like) diffusion equations using FRDTM

PubMed Central

Singh, Brajesh K.; Srivastava, Vineet K.

2015-01-01

The main goal of this paper is to present a new approximate series solution of the multi-dimensional (heat-like) diffusion equation with time-fractional derivative in Caputo form using a semi-analytical approach: fractional-order reduced differential transform method (FRDTM). The efficiency of FRDTM is confirmed by considering four test problems of the multi-dimensional time fractional-order diffusion equation. FRDTM is a very efficient, effective and powerful mathematical tool which provides exact or very close approximate solutions for a wide range of real-world problems arising in engineering and natural sciences, modelled in terms of differential equations. PMID:26064639

Detection of multiple airborne targets from multisensor data

NASA Astrophysics Data System (ADS)

Foltz, Mark A.; Srivastava, Anuj; Miller, Michael I.; Grenander, Ulf

1995-08-01

Previously we presented a jump-diffusion based random sampling algorithm for generating conditional mean estimates of scene representations for the tracking and recongition of maneuvering airborne targets. These representations include target positions and orientations along their trajectories and the target type associated with each trajectory. Taking a Bayesian approach, a posterior measure is defined on the parameter space by combining sensor models with a sophisticated prior based on nonlinear airplane dynamics. The jump-diffusion algorithm constructs a Markov process which visits the elements of the parameter space with frequencies proportional to the posterior probability. It consititutes both the infinitesimal, local search via a sample path continuous diffusion transform and the larger, global steps through discrete jump moves. The jump moves involve the addition and deletion of elements from the scene configuration or changes in the target type assoviated with each target trajectory. One such move results in target detection by the addition of a track seed to the inference set. This provides initial track data for the tracking/recognition algorithm to estimate linear graph structures representing tracks using the other jump moves and the diffusion process, as described in our earlier work. Target detection ideally involves a continuous research over a continuum of the observation space. In this work we conclude that for practical implemenations the search space must be discretized with lattice granularity comparable to sensor resolution, and discuss how fast Fourier transforms are utilized for efficient calcuation of sufficient statistics given our array models. Some results are also presented from our implementation on a networked system including a massively parallel machine architecture and a silicon graphics onyx workstation.

Molecular dynamics simulations of substitutional diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Xiaowang; Jones, Reese E.; Gruber, Jacob

2016-12-18

In atomistic simulations, diffusion energy barriers are usually calculated for each atomic jump path using a nudged elastic band method. Practical materials often involve thousands of distinct atomic jump paths that are not known a priori. Hence, it is often preferred to determine an overall diffusion energy barrier and an overall pre-exponential factor from the Arrhenius equation constructed through molecular dynamics simulations of mean square displacement of the diffusion species at different temperatures. This approach has been well established for interstitial diffusion, but not for substitutional diffusion at the same confidence. Using In 0.1 Ga 0.9 N as an example,more » we have identified conditions where molecular dynamics simulations can be used to calculate highly converged Arrhenius plots for substitutional alloys. As a result, this may enable many complex diffusion problems to be easily and reliably studied in the future using molecular dynamics, provided that moderate computing resources are available.« less

First-principles investigation of point defect and atomic diffusion in Al2Ca

NASA Astrophysics Data System (ADS)

Tian, Xiao; Wang, Jia-Ning; Wang, Ya-Ping; Shi, Xue-Feng; Tang, Bi-Yu

2017-04-01

Point defects and atomic diffusion in Al2Ca have been studied from first-principles calculations within density functional framework. After formation energy and relative stability of point defects are investigated, several predominant diffusion processes in Al2Ca are studied, including sublattice one-step mechanism, 3-jump vacancy cycles and antistructure sublattice mechanism. The associated energy profiles are calculated with climbing image nudged elastic band (CI-NEB) method, then the saddle points and activation barriers during atomic diffusion are further determined. The resulted activation barriers show that both Al and Ca can diffuse mainly mediated by neighbor vacancy on their own sublattice. 3-jump cycle mechanism mediated by VCa may make some contribution to the overall Al diffusion. And antistructure (AS) sublattice mechanism can also play an important role in Ca atomic diffusion owing to the moderate activation barrier.

Monte Carlo simulation of the mixed alkali effect with cooperative jumps

NASA Astrophysics Data System (ADS)

Habasaki, Junko; Hiwatari, Yasuaki

2000-12-01

In our previous works on molecular dynamics (MD) simulations of lithium metasilicate (Li2SiO3), it has been shown that the long time behavior of the lithium ions in Li2SiO3 has been characterized by the component showing the enhanced diffusion (Lévy flight) due to cooperative jumps. It has also been confirmed that the contribution of such component decreases by interception of the paths in the mixed alkali silicate (LiKSiO3). Namely, cooperative jumps of like ions are much decreased in number owing to the interception of the path for unlike alkali-metal ions. In the present work, we have performed a Monte Carlo simulation using a cubic lattice in order to establish the role of the cooperative jumps in the transport properties in a mixed alkali glass. Fixed particles (blockage) were introduced instead of the interception of the jump paths for unlike alkali-metal ions. Two types of cooperative motions (a pull type and a push type) were taken into account. Low-dimensionality of the jump path caused by blockage resulted in a decrease of a diffusion coefficient of the particles. The effect of blockage is enhanced when the cooperative motions were introduced.

Bayesian reconstruction of projection reconstruction NMR (PR-NMR).

PubMed

Yoon, Ji Won

2014-11-01

Projection reconstruction nuclear magnetic resonance (PR-NMR) is a technique for generating multidimensional NMR spectra. A small number of projections from lower-dimensional NMR spectra are used to reconstruct the multidimensional NMR spectra. In our previous work, it was shown that multidimensional NMR spectra are efficiently reconstructed using peak-by-peak based reversible jump Markov chain Monte Carlo (RJMCMC) algorithm. We propose an extended and generalized RJMCMC algorithm replacing a simple linear model with a linear mixed model to reconstruct close NMR spectra into true spectra. This statistical method generates samples in a Bayesian scheme. Our proposed algorithm is tested on a set of six projections derived from the three-dimensional 700 MHz HNCO spectrum of a protein HasA. Copyright © 2014 Elsevier Ltd. All rights reserved.

Diffusion in Ordered Alloys, Symposium Held in Chicago, Illinois on November 3 - 4, 1992

DTIC Science & Technology

1992-11-04

calculation of transport proneres The essence of an atomistic theory of diffusion within the linear approximation of the Onsager formalism is to derive...the pair model may be extended to the low temperature range and that this linear behavior exists nearly over the whole temperature range where SRO...being the concentration of the component X. The successive jumps of vacancies are considered to be the elementary process of orde- ring. The jump

Disentangling the stochastic behavior of complex time series

NASA Astrophysics Data System (ADS)

Anvari, Mehrnaz; Tabar, M. Reza Rahimi; Peinke, Joachim; Lehnertz, Klaus

2016-10-01

Complex systems involving a large number of degrees of freedom, generally exhibit non-stationary dynamics, which can result in either continuous or discontinuous sample paths of the corresponding time series. The latter sample paths may be caused by discontinuous events - or jumps - with some distributed amplitudes, and disentangling effects caused by such jumps from effects caused by normal diffusion processes is a main problem for a detailed understanding of stochastic dynamics of complex systems. Here we introduce a non-parametric method to address this general problem. By means of a stochastic dynamical jump-diffusion modelling, we separate deterministic drift terms from different stochastic behaviors, namely diffusive and jumpy ones, and show that all of the unknown functions and coefficients of this modelling can be derived directly from measured time series. We demonstrate appli- cability of our method to empirical observations by a data-driven inference of the deterministic drift term and of the diffusive and jumpy behavior in brain dynamics from ten epilepsy patients. Particularly these different stochastic behaviors provide extra information that can be regarded valuable for diagnostic purposes.

Fast oxygen diffusion in bismuth oxide probed by quasielastic neutron scattering

DOE PAGES

Mamontov, Eugene

2016-09-24

In this paper, we present the first, to our knowledge, study of solid state oxygen translational diffusion by quasielastic neutron scattering. Such studies in the past might have been precluded by relatively low diffusivities of oxygen anions in the temperature range amenable to neutron scattering experiments. To explore the potential of the quasielastic scattering technique, which can deduce atomic diffusion jump length of oxygen anions through the momentum transfer dependence of the scattering signal, we have selected the fastest known oxygen conductor, bismuth oxide. Finally, we have found the oxygen anion jump length in excellent agreement with the nearest oxygen-vacancymore » distance in the anion sublattice of the fluorite-related structure of bismuth oxide.« less

Jump-Diffusion models and structural changes for asset forecasting in hydrology

NASA Astrophysics Data System (ADS)

Tranquille Temgoua, André Guy; Martel, Richard; Chang, Philippe J. J.; Rivera, Alfonso

2017-04-01

Impacts of climate change on surface water and groundwater are of concern in many regions of the world since water is an essential natural resource. Jump-Diffusion models are generally used in economics and other related fields but not in hydrology. The potential application could be made for hydrologic data series analysis and forecast. The present study uses Jump-Diffusion models by adding structural changes to detect fluctuations in hydrologic processes in relationship with climate change. The model implicitly assumes that modifications in rivers' flowrates can be divided into three categories: (a) normal changes due to irregular precipitation events especially in tropical regions causing major disturbance in hydrologic processes (this component is modelled by a discrete Brownian motion); (b) abnormal, sudden and non-persistent modifications in hydrologic proceedings are handled by Poisson processes; (c) the persistence of hydrologic fluctuations characterized by structural changes in hydrological data related to climate variability. The objective of this paper is to add structural changes in diffusion models with jumps, in order to capture the persistence of hydrologic fluctuations. Indirectly, the idea is to observe if there are structural changes of discharge/recharge over the study area, and to find an efficient and flexible model able of capturing a wide variety of hydrologic processes. Structural changes in hydrological data are estimated using the method of nonlinear discrete filters via Method of Simulated Moments (MSM). An application is given using sensitive parameters such as baseflow index and recession coefficient to capture discharge/recharge. Historical dataset are examined by the Volume Spread Analysis (VSA) to detect real time and random perturbations in hydrologic processes. The application of the method allows establishing more accurate hydrologic parameters. The impact of this study is perceptible in forecasting floods and groundwater recession. Keywords: hydrologic processes, Jump-Diffusion models, structural changes, forecast, climate change

Transition from single-jump type to highly cooperative diffusion during structural relaxation of a metallic glass

NASA Astrophysics Data System (ADS)

Rätzke, K.; Hüppe, P. W.; Faupel, F.

1992-04-01

The isotope effect E=(Dα/Dβ-1)/[(mβ/mα)1/2-1] of cobalt diffusion has been measured in melt-spun amorphous Co76.7Fe2Nb14.3B7 ribbon at different stages of structural relaxation. A drastic drop of the isotope effect from E>0.5 in the as-quenched glass to E=0.1 in the relaxed state wass observed. While the latter value relflects highly cooperative diffusion, the large isotope effect in the as-quenched ribbon points to the prevalence of single-atom jumps and vacancylike holes of excess volume.

Radiation- and pair-loaded shocks

NASA Astrophysics Data System (ADS)

Lyutikov, Maxim

2018-06-01

We consider the structure of mildly relativistic shocks in dense media, taking into account the radiation and pair loading, and diffusive radiation energy transfer within the flow. For increasing shock velocity (increasing post-shock temperature), the first important effect is the efficient energy redistribution by radiation within the shock that leads to the appearance of an isothermal jump, whereby the flow reaches the final state through a discontinuous isothermal transition. The isothermal jump, on scales much smaller than the photon diffusion length, consists of a weak shock and a quick relaxation to the isothermal conditions. Highly radiation-dominated shocks do not form isothermal jump. Pair production can mildly increase the overall shock compression ratio to ≈10 (4 for matter-dominated shocks and 7 of the radiation-dominated shocks).

Hetero-diffusion of Au epitaxy on stepped Ag(110) surface: Study of the jump rate and diffusion coefficient

NASA Astrophysics Data System (ADS)

Benlattar, M.; El koraychy, E.; Kotri, A.; Mazroui, M.

2017-12-01

We have used molecular dynamics simulations combined with an interatomic potential derived from the embedded atom method, to investigate the hetero-diffusion of Au adatom near a stepped Ag(110) surface with the height of one monoatomic layer. The activation energies for different diffusion processes, which occur on the terrace and near the step edge, are calculated both by molecular statics and molecular dynamics simulations. Static energies are found by the drag method, whereas the dynamic barriers are computed at high temperature from the Arrhenius plots. Our numerical results reveal that the jump process requires very high activation energy compared to the exchange process either on the terrace or near the step edge. In this work, other processes, such as upward and downward diffusion at step edges, have also been discussed.

Evidence of infinite and finite jump processes in commodity futures prices: Crude oil and natural gas

NASA Astrophysics Data System (ADS)

Cao, Wenbin; Guernsey, Scott B.; Linn, Scott C.

2018-07-01

We examine the frequency and character of price jumps in front month oil and natural gas futures prices. Prices are sampled every five seconds over the period 2006-2014. Our test results indicate that jumps in crude oil and natural gas futures prices can be decomposed into an infinite activity jump diffusion process and a less frequent but larger jump process. We also find that we cannot reject the hypothesis that Brownian motion is also present in both return series. The results are based on a battery of tests that are "model free". We further find that jumps account for respectively 36 and 41 percent of the realized variances of the crude oil and the natural gas returns.

Real-space analysis of diffusion behavior and activation energy of individual monatomic ions in a liquid.

PubMed

Miyata, Tomohiro; Uesugi, Fumihiko; Mizoguchi, Teruyasu

2017-12-01

Investigation of the local dynamic behavior of atoms and molecules in liquids is crucial for revealing the origin of macroscopic liquid properties. Therefore, direct imaging of single atoms to understand their motions in liquids is desirable. Ionic liquids have been studied for various applications, in which they are used as electrolytes or solvents. However, atomic-scale diffusion and relaxation processes in ionic liquids have never been observed experimentally. We directly observe the motion of individual monatomic ions in an ionic liquid using scanning transmission electron microscopy (STEM) and reveal that the ions diffuse by a cage-jump mechanism. Moreover, we estimate the diffusion coefficient and activation energy for the diffusive jumps from the STEM images, which connect the atomic-scale dynamics to macroscopic liquid properties. Our method is the only available means to observe the motion, reactions, and energy barriers of atoms/molecules in liquids.

A cross-diffusion system derived from a Fokker-Planck equation with partial averaging

NASA Astrophysics Data System (ADS)

Jüngel, Ansgar; Zamponi, Nicola

2017-02-01

A cross-diffusion system for two components with a Laplacian structure is analyzed on the multi-dimensional torus. This system, which was recently suggested by P.-L. Lions, is formally derived from a Fokker-Planck equation for the probability density associated with a multi-dimensional Itō process, assuming that the diffusion coefficients depend on partial averages of the probability density with exponential weights. A main feature is that the diffusion matrix of the limiting cross-diffusion system is generally neither symmetric nor positive definite, but its structure allows for the use of entropy methods. The global-in-time existence of positive weak solutions is proved and, under a simplifying assumption, the large-time asymptotics is investigated.

On the source of stochastic volatility: Evidence from CAC40 index options during the subprime crisis

NASA Astrophysics Data System (ADS)

Slim, Skander

2016-12-01

This paper investigates the performance of time-changed Lévy processes with distinct sources of return volatility variation for modeling cross-sectional option prices on the CAC40 index during the subprime crisis. Specifically, we propose a multi-factor stochastic volatility model: one factor captures the diffusion component dynamics and two factors capture positive and negative jump variations. In-sample and out-of-sample tests show that our full-fledged model significantly outperforms nested lower-dimensional specifications. We find that all three sources of return volatility variation, with different persistence, are needed to properly account for market pricing dynamics across moneyness, maturity and volatility level. Besides, the model estimation reveals negative risk premium for both diffusive volatility and downward jump intensity whereas a positive risk premium is found to be attributed to upward jump intensity.

Master equation for She-Leveque scaling and its classification in terms of other Markov models of developed turbulence

NASA Astrophysics Data System (ADS)

Nickelsen, Daniel

2017-07-01

The statistics of velocity increments in homogeneous and isotropic turbulence exhibit universal features in the limit of infinite Reynolds numbers. After Kolmogorov’s scaling law from 1941, many turbulence models aim for capturing these universal features, some are known to have an equivalent formulation in terms of Markov processes. We derive the Markov process equivalent to the particularly successful scaling law postulated by She and Leveque. The Markov process is a jump process for velocity increments u(r) in scale r in which the jumps occur randomly but with deterministic width in u. From its master equation we establish a prescription to simulate the She-Leveque process and compare it with Kolmogorov scaling. To put the She-Leveque process into the context of other established turbulence models on the Markov level, we derive a diffusion process for u(r) using two properties of the Navier-Stokes equation. This diffusion process already includes Kolmogorov scaling, extended self-similarity and a class of random cascade models. The fluctuation theorem of this Markov process implies a ‘second law’ that puts a loose bound on the multipliers of the random cascade models. This bound explicitly allows for instances of inverse cascades, which are necessary to satisfy the fluctuation theorem. By adding a jump process to the diffusion process, we go beyond Kolmogorov scaling and formulate the most general scaling law for the class of Markov processes having both diffusion and jump parts. This Markov scaling law includes She-Leveque scaling and a scaling law derived by Yakhot.

Relation of short-range and long-range lithium ion dynamics in glass-ceramics: Insights from 7Li NMR field-cycling and field-gradient studies

NASA Astrophysics Data System (ADS)

Haaks, Michael; Martin, Steve W.; Vogel, Michael

2017-09-01

We use various 7Li NMR methods to investigate lithium ion dynamics in 70Li 2S-30 P 2S5 glass and glass-ceramic obtained from this glass after heat treatment. We employ 7Li spin-lattice relaxometry, including field-cycling measurements, and line-shape analysis to investigate short-range ion jumps as well as 7Li field-gradient approaches to characterize long-range ion diffusion. The results show that ceramization substantially enhances the lithium ion mobility on all length scales. For the 70Li 2S-30 P 2S5 glass-ceramic, no evidence is found that bimodal dynamics result from different ion mobilities in glassy and crystalline regions of this sample. Rather, 7Li field-cycling relaxometry shows that dynamic susceptibilities in broad frequency and temperature ranges can be described by thermally activated jumps governed by a Gaussian distribution of activation energies g (Ea) with temperature-independent mean value Em=0.43 eV and standard deviation σ =0.07 eV . Moreover, use of this distribution allows us to rationalize 7Li line-shape results for the local ion jumps. In addition, this information about short-range ion dynamics further explains 7Li field-gradient results for long-range ion diffusion. In particular, we quantitatively show that, consistent with our experimental results, the temperature dependence of the self-diffusion coefficient D is not described by the mean activation energy Em of the local ion jumps, but by a significantly smaller apparent value whenever the distribution of correlation times G (logτ ) of the jump motion derives from an invariant distribution of activation energies and, hence, continuously broadens upon cooling. This effect occurs because the harmonic mean, which determines the results of diffusivity or also conductivity studies, continuously separates from the peak position of G (logτ ) when the width of this distribution increases.

Leapfrog Diffusion Mechanism for One-Dimensional Chains on Missing-Row Reconstructed Surfaces

NASA Astrophysics Data System (ADS)

Montalenti, F.; Ferrando, R.

1999-02-01

We analyze the in-channel diffusion of dimers and longer n-adatom chains on Au and Pt (110) \\(1×2\\) surfaces by molecular dynamics simulations. From our calculations it arises that, on the missing-row reconstructed surface, a novel diffusion process, called leapfrog, dominates over concerted jumps, thus becoming the most frequent diffusion mechanism.

A 3D finite element ALE method using an approximate Riemann solution

DOE PAGES

Chiravalle, V. P.; Morgan, N. R.

2016-08-09

Arbitrary Lagrangian–Eulerian finite volume methods that solve a multidimensional Riemann-like problem at the cell center in a staggered grid hydrodynamic (SGH) arrangement have been proposed. This research proposes a new 3D finite element arbitrary Lagrangian–Eulerian SGH method that incorporates a multidimensional Riemann-like problem. Here, two different Riemann jump relations are investigated. A new limiting method that greatly improves the accuracy of the SGH method on isentropic flows is investigated. A remap method that improves upon a well-known mesh relaxation and remapping technique in order to ensure total energy conservation during the remap is also presented. Numerical details and test problemmore » results are presented.« less

A 3D finite element ALE method using an approximate Riemann solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiravalle, V. P.; Morgan, N. R.

Arbitrary Lagrangian–Eulerian finite volume methods that solve a multidimensional Riemann-like problem at the cell center in a staggered grid hydrodynamic (SGH) arrangement have been proposed. This research proposes a new 3D finite element arbitrary Lagrangian–Eulerian SGH method that incorporates a multidimensional Riemann-like problem. Here, two different Riemann jump relations are investigated. A new limiting method that greatly improves the accuracy of the SGH method on isentropic flows is investigated. A remap method that improves upon a well-known mesh relaxation and remapping technique in order to ensure total energy conservation during the remap is also presented. Numerical details and test problemmore » results are presented.« less

General Metropolis-Hastings jump diffusions for automatic target recognition in infrared scenes

NASA Astrophysics Data System (ADS)

Lanterman, Aaron D.; Miller, Michael I.; Snyder, Donald L.

1997-04-01

To locate and recognize ground-based targets in forward- looking IR (FLIR) images, 3D faceted models with associated pose parameters are formulated to accommodate the variability found in FLIR imagery. Taking a Bayesian approach, scenes are simulated from the emissive characteristics of the CAD models and compared with the collected data by a likelihood function based on sensor statistics. This likelihood is combined with a prior distribution defined over the set of possible scenes to form a posterior distribution. To accommodate scenes with variable numbers of targets, the posterior distribution is defined over parameter vectors of varying dimension. An inference algorithm based on Metropolis-Hastings jump- diffusion processes empirically samples from the posterior distribution, generating configurations of templates and transformations that match the collected sensor data with high probability. The jumps accommodate the addition and deletion of targets and the estimation of target identities; diffusions refine the hypotheses by drifting along the gradient of the posterior distribution with respect to the orientation and position parameters. Previous results on jumps strategies analogous to the Metropolis acceptance/rejection algorithm, with proposals drawn from the prior and accepted based on the likelihood, are extended to encompass general Metropolis-Hastings proposal densities. In particular, the algorithm proposes moves by drawing from the posterior distribution over computationally tractible subsets of the parameter space. The algorithm is illustrated by an implementation on a Silicon Graphics Onyx/Reality Engine.

Helix formation via conformation diffusion search

PubMed Central

Huang, Cheng-Yen; Getahun, Zelleka; Zhu, Yongjin; Klemke, Jason W.; DeGrado, William F.; Gai, Feng

2002-01-01

The helix-coil transition kinetics of an α-helical peptide were investigated by time-resolved infrared spectroscopy coupled with laser-induced temperature-jump initiation method. Specific isotope labeling of the amide carbonyl groups with 13C at selected residues was used to obtain site-specific information. The relaxation kinetics following a temperature jump, obtained by probing the amide I′ band of the peptide backbone, exhibit nonexponential behavior and are sensitive to both initial and final temperatures. These data are consistent with a conformation diffusion process on the folding energy landscape, in accord with a recent molecular dynamics simulation study. PMID:11867741

Carbon diffusion in bulk hcp zirconium: A multi-scale approach

NASA Astrophysics Data System (ADS)

Xu, Y.; Roques, J.; Domain, C.; Simoni, E.

2016-05-01

In the framework of the geological repository of the used fuel claddings of pressurized water reactor, carbon behavior in bulk zirconium is studied by periodic Density Functional Theory calculations. The C interstitial sites were investigated and it was found that there are two possible carbon interstitial sites: a distorted basal tetragonal site and an octahedral site. There are four types of possible atomic jumps between them. After calculating the migration energies, the attempt frequencies and the jump probabilities for each possible migration path, kinetic Monte Carlo (KMC) simulations were performed to simulate carbon diffusion at the macroscopic scale. The results show that carbon diffusion in pure Zr bulk is extremely limited at the storage temperature (50 °C). Since there are defects in Zr bulk, in a second step, the effect of atomic vacancy was studied and it was proved that vacancies cannot increase carbon diffusion.

Effect of sharp maximum in ion diffusivity for liquid xenon

NASA Astrophysics Data System (ADS)

Lankin, A. V.; Orekhov, M. A.

2016-11-01

Ion diffusion in a liquid usually could be treated as a movement of an ion cluster in a viscous media. For small ions this leads to a special feature: diffusion coefficient is either independent of the ion size or increases with it. We find a different behavior for small ions in liquid xenon. Calculation of the dependence of an ion diffusion coefficient in liquid xenon on the ion size is carried out. Classical molecular dynamics method is applied. Calculated dependence of the ion diffusion coefficient on its radius has sharp maximums at the ion radiuses 1.75 and 2 Å. Every maximum is placed between two regions with different stable ion cluster configurations. This leads to the instability of these configurations in a small region between them. Consequently ion with radius near 1.75 or 2 Å could jump from one configuration to another. This increases the speed of the diffusion. A simple qualitative model for this effect is suggested. The decomposition of the ion movement into continuous and jump diffusion shows that continuous part of the diffusion is the same as for the ion cluster in the stable region.

Diffusivity of the interstitial hydrogen shallow donor in In2O3

NASA Astrophysics Data System (ADS)

Qin, Ying; Weiser, Philip; Villalta, Karla; Stavola, Michael; Fowler, W. Beall; Biaggio, Ivan; Boatner, Lynn

2018-04-01

Hydrogen has been found to be an n-type dopant in In2O3 that gives rise to unintentional conductivity. An infrared (IR) absorption line observed at 3306 cm-1 has been assigned to the Hi+ center. Two types of experiments have been performed to determine the diffusivity of Hi+ in In2O3 from its IR absorption spectra. (i) At temperatures near 700 K, the O-H line at 3306 cm-1 has been used to determine the diffusivity of Hi+ from its in-diffusion and out-diffusion behaviors. (ii) At temperatures near 160 K, stress has been used to produce a preferential alignment of the Hi+ center that has been detected in IR absorption experiments made with polarized light. With the help of theory, the kinetics with which a stress-induced alignment can be produced yield the time constant for a single jump of the Hi+ center and also the diffusivity of Hi+ near 160 K. The combination of the diffusivity of Hi+ found near 700 K by mass-transport measurements and that found near 160 K from the time constant for a single Hi+ jump determines the diffusivity for Hi+ over eleven decades!

Interpretation of gypsy moth frontal advance using meteorology in a conditional algorithm

Treesearch

K.L. Frank; P.C. Tobin; Jr. Thistle; Laurence S. Kalkstein

2013-01-01

The gypsy moth, Lymantria dispar, is a nonnative species that continues to invade areas in North America. It spreads generally through stratified dispersal where local growth and diffusive spread are coupled with long-distance jumps ahead of the leading edge. Long distance jumps due to anthropogenic movement of life stages is a well-documented...

Diffusivity of the interstitial hydrogen shallow donor in In 2 O 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qin, Ying; Weiser, Philip; Villalta, Karla

Hydrogen has been found to be an n-type dopant in In2O3 that gives rise to unintentional conductivity. An infrared (IR) absorption line observed at 3306 cm-1 has been assigned to the Hi+ center. Two types of experiments have been performed to determine the diffusivity of Hi+ in In2O3 from its IR absorption spectra. (i) At temperatures near 700 K, the O-H line at 3306 cm-1 has been used to determine the diffusivity of Hi+ from its in-diffusion and out-diffusion behavior. (ii) At temperatures near 160 K, stress has been used to produce a preferential alignment of the Hi+ center thatmore » has been detected in IR absorption experiments made with polarized light. With the help of theory, the kinetics with which a stress-induced alignment can be produced yield the time constant for a single jump of the Hi+ center and also the diffusivity of Hi+ near 160 K. The combination of the diffusivity of Hi+ found near 700 K by mass-transport measurements along with the diffusivity found near 160 K from the time constant for a single Hi+ jump determines the diffusivity for Hi+ over eleven decades!« less

An exact and efficient first passage time algorithm for reaction-diffusion processes on a 2D-lattice

NASA Astrophysics Data System (ADS)

Bezzola, Andri; Bales, Benjamin B.; Alkire, Richard C.; Petzold, Linda R.

2014-01-01

We present an exact and efficient algorithm for reaction-diffusion-nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for large ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.

A renewal jump-diffusion process with threshold dividend strategy

NASA Astrophysics Data System (ADS)

Li, Bo; Wu, Rong; Song, Min

2009-06-01

In this paper, we consider a jump-diffusion risk process with the threshold dividend strategy. Both the distributions of the inter-arrival times and the claims are assumed to be in the class of phase-type distributions. The expected discounted dividend function and the Laplace transform of the ruin time are discussed. Motivated by Asmussen [S. Asmussen, Stationary distributions for fluid flow models with or without Brownian noise, Stochastic Models 11 (1) (1995) 21-49], instead of studying the original process, we study the constructed fluid flow process and their closed-form formulas are obtained in terms of matrix expression. Finally, numerical results are provided to illustrate the computation.

Multi-Dimensional Asymptotically Stable 4th Order Accurate Schemes for the Diffusion Equation

NASA Technical Reports Server (NTRS)

Abarbanel, Saul; Ditkowski, Adi

1996-01-01

An algorithm is presented which solves the multi-dimensional diffusion equation on co mplex shapes to 4th-order accuracy and is asymptotically stable in time. This bounded-error result is achieved by constructing, on a rectangular grid, a differentiation matrix whose symmetric part is negative definite. The differentiation matrix accounts for the Dirichlet boundary condition by imposing penalty like terms. Numerical examples in 2-D show that the method is effective even where standard schemes, stable by traditional definitions fail.

Multi-Dimensional, Mesoscopic Monte Carlo Simulations of Inhomogeneous Reaction-Drift-Diffusion Systems on Graphics-Processing Units

PubMed Central

Vigelius, Matthias; Meyer, Bernd

2012-01-01

For many biological applications, a macroscopic (deterministic) treatment of reaction-drift-diffusion systems is insufficient. Instead, one has to properly handle the stochastic nature of the problem and generate true sample paths of the underlying probability distribution. Unfortunately, stochastic algorithms are computationally expensive and, in most cases, the large number of participating particles renders the relevant parameter regimes inaccessible. In an attempt to address this problem we present a genuine stochastic, multi-dimensional algorithm that solves the inhomogeneous, non-linear, drift-diffusion problem on a mesoscopic level. Our method improves on existing implementations in being multi-dimensional and handling inhomogeneous drift and diffusion. The algorithm is well suited for an implementation on data-parallel hardware architectures such as general-purpose graphics processing units (GPUs). We integrate the method into an operator-splitting approach that decouples chemical reactions from the spatial evolution. We demonstrate the validity and applicability of our algorithm with a comprehensive suite of standard test problems that also serve to quantify the numerical accuracy of the method. We provide a freely available, fully functional GPU implementation. Integration into Inchman, a user-friendly web service, that allows researchers to perform parallel simulations of reaction-drift-diffusion systems on GPU clusters is underway. PMID:22506001

Modeling persistence of motion in a crowded environment: The diffusive limit of excluding velocity-jump processes

NASA Astrophysics Data System (ADS)

Gavagnin, Enrico; Yates, Christian A.

2018-03-01

Persistence of motion is the tendency of an object to maintain motion in a direction for short time scales without necessarily being biased in any direction in the long term. One of the most appropriate mathematical tools to study this behavior is an agent-based velocity-jump process. In the absence of agent-agent interaction, the mean-field continuum limit of the agent-based model (ABM) gives rise to the well known hyperbolic telegraph equation. When agent-agent interaction is included in the ABM, a strictly advective system of partial differential equations (PDEs) can be derived at the population level. However, no diffusive limit of the ABM has been obtained from such a model. Connecting the microscopic behavior of the ABM to a diffusive macroscopic description is desirable, since it allows the exploration of a wider range of scenarios and establishes a direct connection with commonly used statistical tools of movement analysis. In order to connect the ABM at the population level to a diffusive PDE at the population level, we consider a generalization of the agent-based velocity-jump process on a two-dimensional lattice with three forms of agent interaction. This generalization allows us to take a diffusive limit and obtain a faithful population-level description. We investigate the properties of the model at both the individual and population levels and we elucidate some of the models' key characteristic features. In particular, we show an intrinsic anisotropy inherent to the models and we find evidence of a spontaneous form of aggregation at both the micro- and macroscales.

An exact and efficient first passage time algorithm for reaction–diffusion processes on a 2D-lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bezzola, Andri, E-mail: andri.bezzola@gmail.com; Bales, Benjamin B., E-mail: bbbales2@gmail.com; Alkire, Richard C., E-mail: r-alkire@uiuc.edu

2014-01-01

We present an exact and efficient algorithm for reaction–diffusion–nucleation processes on a 2D-lattice. The algorithm makes use of first passage time (FPT) to replace the computationally intensive simulation of diffusion hops in KMC by larger jumps when particles are far away from step-edges or other particles. Our approach computes exact probability distributions of jump times and target locations in a closed-form formula, based on the eigenvectors and eigenvalues of the corresponding 1D transition matrix, maintaining atomic-scale resolution of resulting shapes of deposit islands. We have applied our method to three different test cases of electrodeposition: pure diffusional aggregation for largemore » ranges of diffusivity rates and for simulation domain sizes of up to 4096×4096 sites, the effect of diffusivity on island shapes and sizes in combination with a KMC edge diffusion, and the calculation of an exclusion zone in front of a step-edge, confirming statistical equivalence to standard KMC simulations. The algorithm achieves significant speedup compared to standard KMC for cases where particles diffuse over long distances before nucleating with other particles or being captured by larger islands.« less

Signal Processing for Radar Target Tracking and Identification

DTIC Science & Technology

1996-12-01

Computes the likelihood for various potential jump moves. 12. matrix_mult.m: Parallel implementation of linear algebra ... Elementary Lineary Algebra with Applications, John Wiley k Sons, Inc., New York, 1987. [9] A. K. Bhattacharyya, and D. L. Sengupta, Radar Cross...Miller, ’Target Tracking and Recognition Using Jump-Diffusion Processes," ARO’s 11th Army Conf. on Applied Mathemat- ics and Computing, June 8-11

Molecular dynamics of acetamide based ionic deep eutectic solvents

NASA Astrophysics Data System (ADS)

Srinivasan, H.; Dubey, P. S.; Sharma, V. K.; Biswas, R.; Mitra, S.; Mukhopadhyay, R.

2018-04-01

Deep eutectic solvents are multi-component mixtures that have freezing point lower than their individual components. Mixture of acetamide+ lithium nitrate in the molar ratio 78:22 and acetamide+ lithium perchlorate in the molar ratio 81:19 are found to form deep eutectic solvents with melting point lower than the room temperature. It is known that the depression in freezing point is due to the hydrogen bond breaking ability of anions in the system. Quasielastic neutron scattering experiments on these systems were carried out to study the dynamics of acetamide molecules which may be influenced by this hydrogen bond breaking phenomena. The motion of acetamide molecules is modeled using jump diffusion mechanism to demonstrate continuous breaking and reforming hydrogen bonds in the solvent. Using the jump diffusion model, it is inferred that the jump lengths of acetamide molecules are better approximated by a Gaussian distribution. The shorter residence time of acetamide in presence of perchlorate ions suggest that the perchlorate ions have a higher hydrogen bond breaking ability compared to nitrate ions.

A one-dimensional free energy surface does not account for two-probe folding kinetics of protein alpha(3)D.

PubMed

Liu, Feng; Dumont, Charles; Zhu, Yongjin; DeGrado, William F; Gai, Feng; Gruebele, Martin

2009-02-14

We present fluorescence-detected measurements of the temperature-jump relaxation kinetics of the designed three-helix bundle protein alpha(3)D taken under solvent conditions identical to previous infrared-detected kinetics. The fluorescence-detected rate is similar to the IR-detected rate only at the lowest temperature where we could measure it (326 K). The fluorescence-detected rate decreases by a factor of 3 over the 326-344 K temperature range, whereas the IR-detected rate remains nearly constant over the same range. To investigate this probe dependence, we tested an extensive set of physically reasonable one-dimensional (1D) free energy surfaces by Langevin dynamics simulation. The simulations included coordinate- and temperature-dependent roughness, diffusion coefficients, and IR/fluorescence spectroscopic signatures. None of these can reproduce the IR and fluorescence data simultaneously, forcing us to the conclusion that a 1D free energy surface cannot accurately describe the folding of alpha(3)D. This supports the hypothesis that alpha(3)D has a multidimensional free energy surface conducive to downhill folding at 326 K, and that it is already an incipient downhill folder with probe-dependent kinetics near its melting point.

Existence and uniqueness, attraction for stochastic age-structured population systems with diffusion and Poisson jump

NASA Astrophysics Data System (ADS)

Chen, Huabin

2013-08-01

In this paper, the problems about the existence and uniqueness, attraction for strong solution of stochastic age-structured population systems with diffusion and Poisson jump are considered. Under the non-Lipschitz condition with the Lipschitz condition being considered as a special case, the existence and uniqueness for such systems is firstly proved by using the Burkholder-Davis-Gundy inequality (B-D-G inequality) and Itô's formula. And then by using a novel inequality technique, some sufficient conditions ensuring the existence for the domain of attraction are established. As another by-product, the exponential stability in mean square moment of strong solution for such systems can be also discussed.

An ion displacement membrame model.

PubMed

Hladky, S B; Harris, J D

1967-09-01

The usual assumption in treating the diffusion of ions in an electric field has been that the movement of each ion is independent of the movement of the others. The resulting equation for diffusion by a succession of spontaneous jumps has been well stated by Parlin and Eyring. This paper will consider one simple case in which a different assumption is reasonable. Diffusion of monovalent positive ions is considered as a series of jumps from one fixed negative site to another. The sites are assumed to be full (electrical neutrality). Interaction occurs by the displacement of one ion by another. An ion leaves a site if and only if another ion, not necessarily of the same species, attempts to occupy the same site. Flux ratios and net fluxes are given as functions of the electrical potential, concentration ratios, and number of sites encountered in crossing the membrane. Quantitative comparisons with observations of Hodgkin and Keynes are presented.

Protons migrate along interfacial water without significant contributions from jumps between ionizable groups on the membrane surface

PubMed Central

Springer, Andreas; Hagen, Volker; Cherepanov, Dmitry A.; Antonenko, Yuri N.; Pohl, Peter

2011-01-01

Proton diffusion along membrane surfaces is thought to be essential for many cellular processes such as energy transduction. Commonly, it is treated as a succession of jumps between membrane-anchored proton-binding sites. Our experiments provide evidence for an alternative model. We released membrane-bound caged protons by UV flashes and monitored their arrival at distant sites by fluorescence measurements. The kinetics of the arrival is probed as a function of distance for different membranes and for different water isotopes. We found that proton diffusion along the membrane is fast even in the absence of ionizable groups in the membrane, and it decreases strongly in D2O as compared to H2O. We conclude that the fast proton transport along the membrane is dominated by diffusion via interfacial water, and not via ionizable lipid moieties. PMID:21859952

The application of a multi-dimensional assessment approach to talent identification in Australian football.

PubMed

Woods, Carl T; Raynor, Annette J; Bruce, Lyndell; McDonald, Zane; Robertson, Sam

2016-07-01

This study investigated whether a multi-dimensional assessment could assist with talent identification in junior Australian football (AF). Participants were recruited from an elite under 18 (U18) AF competition and classified into two groups; talent identified (State U18 Academy representatives; n = 42; 17.6 ± 0.4 y) and non-talent identified (non-State U18 Academy representatives; n = 42; 17.4 ± 0.5 y). Both groups completed a multi-dimensional assessment, which consisted of physical (standing height, dynamic vertical jump height and 20 m multistage fitness test), technical (kicking and handballing tests) and perceptual-cognitive (video decision-making task) performance outcome tests. A multivariate analysis of variance tested the main effect of status on the test criterions, whilst a receiver operating characteristic curve assessed the discrimination provided from the full assessment. The talent identified players outperformed their non-talent identified peers in each test (P < 0.05). The receiver operating characteristic curve reflected near perfect discrimination (AUC = 95.4%), correctly classifying 95% and 86% of the talent identified and non-talent identified participants, respectively. When compared to single assessment approaches, this multi-dimensional assessment reflects a more comprehensive means of talent identification in AF. This study further highlights the importance of assessing multi-dimensional performance qualities when identifying talented team sports.

Molecular dynamics simulation of framework flexibility effects on noble gas diffusion in HKUST-1 and ZIF-8

DOE PAGES

Parkes, Marie V.; Demir, Hakan; Teich-McGoldrick, Stephanie L.; ...

2014-03-28

Molecular dynamics simulations were used to investigate trends in noble gas (Ar, Kr, Xe) diffusion in the metal-organic frameworks HKUST-1 and ZIF-8. Diffusion occurs primarily through inter-cage jump events, with much greater diffusion of guest atoms in HKUST-1 compared to ZIF-8 due to the larger cage and window sizes in the former. We compare diffusion coefficients calculated for both rigid and flexible frameworks. For rigid framework simulations, in which the framework atoms were held at their crystallographic or geometry optimized coordinates, sometimes dramatic differences in guest diffusion were seen depending on the initial framework structure or the choice of frameworkmore » force field parameters. When framework flexibility effects were included, argon and krypton diffusion increased significantly compared to rigid-framework simulations using general force field parameters. Additionally, for argon and krypton in ZIF-8, guest diffusion increased with loading, demonstrating that guest-guest interactions between cages enhance inter-cage diffusion. No inter-cage jump events were seen for xenon atoms in ZIF-8 regardless of force field or initial structure, and the loading dependence of xenon diffusion in HKUST-1 is different for rigid and flexible frameworks. Diffusion of krypton and xenon in HKUST-1 depends on two competing effects: the steric effect that decreases diffusion as loading increases, and the “small cage effect” that increases diffusion as loading increases. Finally, a detailed analysis of the window size in ZIF-8 reveals that the window increases beyond its normal size to permit passage of a (nominally) larger krypton atom.« less

Time series analysis of particle tracking data for molecular motion on the cell membrane.

PubMed

Ying, Wenxia; Huerta, Gabriel; Steinberg, Stanly; Zúñiga, Martha

2009-11-01

Biophysicists use single particle tracking (SPT) methods to probe the dynamic behavior of individual proteins and lipids in cell membranes. The mean squared displacement (MSD) has proven to be a powerful tool for analyzing the data and drawing conclusions about membrane organization, including features like lipid rafts, protein islands, and confinement zones defined by cytoskeletal barriers. Here, we implement time series analysis as a new analytic tool to analyze further the motion of membrane proteins. The experimental data track the motion of 40 nm gold particles bound to Class I major histocompatibility complex (MHCI) molecules on the membranes of mouse hepatoma cells. Our first novel result is that the tracks are significantly autocorrelated. Because of this, we developed linear autoregressive models to elucidate the autocorrelations. Estimates of the signal to noise ratio for the models show that the autocorrelated part of the motion is significant. Next, we fit the probability distributions of jump sizes with four different models. The first model is a general Weibull distribution that shows that the motion is characterized by an excess of short jumps as compared to a normal random walk. We also fit the data with a chi distribution which provides a natural estimate of the dimension d of the space in which a random walk is occurring. For the biological data, the estimates satisfy 1 < d < 2, implying that particle motion is not confined to a line, but also does not occur freely in the plane. The dimension gives a quantitative estimate of the amount of nanometer scale obstruction met by a diffusing molecule. We introduce a new distribution and use the generalized extreme value distribution to show that the biological data also have an excess of long jumps as compared to normal diffusion. These fits provide novel estimates of the microscopic diffusion constant. Previous MSD analyses of SPT data have provided evidence for nanometer-scale confinement zones that restrict lateral diffusion, supporting the notion that plasma membrane organization is highly structured. Our demonstration that membrane protein motion is autocorrelated and is characterized by an excess of both short and long jumps reinforces the concept that the membrane environment is heterogeneous and dynamic. Autocorrelation analysis and modeling of the jump distributions are powerful new techniques for the analysis of SPT data and the development of more refined models of membrane organization. The time series analysis also provides several methods of estimating the diffusion constant in addition to the constant provided by the mean squared displacement. The mean squared displacement for most of the biological data shows a power law behavior rather the linear behavior of Brownian motion. In this case, we introduce the notion of an instantaneous diffusion constant. All of the diffusion constants show a strong consistency for most of the biological data.

Modeling and estimating the jump risk of exchange rates: Applications to RMB

NASA Astrophysics Data System (ADS)

Wang, Yiming; Tong, Hanfei

2008-11-01

In this paper we propose a new type of continuous-time stochastic volatility model, SVDJ, for the spot exchange rate of RMB, and other foreign currencies. In the model, we assume that the change of exchange rate can be decomposed into two components. One is the normally small-cope innovation driven by the diffusion motion; the other is a large drop or rise engendered by the Poisson counting process. Furthermore, we develop a MCMC method to estimate our model. Empirical results indicate the significant existence of jumps in the exchange rate. Jump components explain a large proportion of the exchange rate change.

Water diffusion in silicate glasses: the effect of glass structure

NASA Astrophysics Data System (ADS)

Kuroda, M.; Tachibana, S.

2016-12-01

Water diffusion in silicate melts (glasses) is one of the main controlling factors of magmatism in a volcanic system. Water diffusivity in silicate glasses depends on its own concentration. However, the mechanism causing those dependences has not been fully understood yet. In order to construct a general model for water diffusion in various silicate glasses, we performed water diffusion experiments in silica glass and proposed a new water diffusion model [Kuroda et al., 2015]. In the model, water diffusivity is controlled by the concentration of both main diffusion species (i.e. molecular water) and diffusion pathways, which are determined by the concentrations of hydroxyl groups and network modifier cations. The model well explains the water diffusivity in various silicate glasses from silica glass to basalt glass. However, pre-exponential factors of water diffusivity in various glasses show five orders of magnitude variations although the pre-exponential factor should ideally represent the jump frequency and the jump distance of molecular water and show a much smaller variation. Here, we attribute the large variation of pre-exponential factors to a glass structure dependence of activation energy for molecular water diffusion. It has been known that the activation energy depends on the water concentration [Nowak and Behrens, 1997]. The concentration of hydroxyls, which cut Si-O-Si network in the glass structure, increases with water concentration, resulting in lowering the activation energy for water diffusion probably due to more fragmented structure. Network modifier cations are likely to play the same role as water. With taking the effect of glass structure into account, we found that the variation of pre-exponential factors of water diffusivity in silicate glasses can be much smaller than the five orders of magnitude, implying that the diffusion of molecular water in silicate glasses is controlled by the same atomic process.

Onset of anomalous diffusion from local motion rules

NASA Astrophysics Data System (ADS)

de Nigris, Sarah; Carletti, Timoteo; Lambiotte, Renaud

2017-02-01

Anomalous diffusion processes, in particular superdiffusive ones, are known to be efficient strategies for searching and navigation in animals and also in human mobility. One way to create such regimes are Lévy 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 one-dimensional lattice, "cascades" of n unitary steps instead of one jump of a randomly generated length, as in the Lévy case, where n is drawn from a cascade distribution pn. We show that this local mechanism may give rise to superdiffusion or normal diffusion when pn is distributed as a power law. We also introduce waiting times that are power-law distributed as well and therefore the probability distribution scaling is steered by the two local distributions power-law exponents. As a perspective, our approach may engender a possible generalization of anomalous diffusion in context where distances are difficult to define, as in the case of complex networks, and also provide an interesting model for diffusion in temporal networks.

Statistical theory of diffusion in concentrated bcc and fcc alloys and concentration dependencies of diffusion coefficients in bcc alloys FeCu, FeMn, FeNi, and FeCr

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vaks, V. G.; Khromov, K. Yu., E-mail: khromov-ky@nrcki.ru; Pankratov, I. R.

2016-07-15

The statistical theory of diffusion in concentrated bcc and fcc alloys with arbitrary pairwise interatomic interactions based on the master equation approach is developed. Vacancy–atom correlations are described using both the second-shell-jump and the nearest-neighbor-jump approximations which are shown to be usually sufficiently accurate. General expressions for Onsager coefficients in terms of microscopic interatomic interactions and some statistical averages are given. Both the analytical kinetic mean-field and the Monte Carlo methods for finding these averages are described. The theory developed is used to describe sharp concentration dependencies of diffusion coefficients in several iron-based alloy systems. For the bcc alloys FeCu,more » FeMn, and FeNi, we predict the notable increase of the iron self-diffusion coefficient with solute concentration c, up to several times, even though values of c possible for these alloys do not exceed some percent. For the bcc alloys FeCr at high temperatures T ≳ 1400 K, we show that the very strong and peculiar concentration dependencies of both tracer and chemical diffusion coefficients observed in these alloys can be naturally explained by the theory, without invoking exotic models discussed earlier.« less

Effect of Static Strains on Diffusion

NASA Technical Reports Server (NTRS)

Girifalco, L. A.; Grimes, H. H.

1961-01-01

A theory is developed that gives the diffusion coefficient in strained systems as an exponential function of the strain. This theory starts with the statistical theory of the atomic jump frequency as developed by Vineyard. The parameter determining the effect of strain on diffusion is related to the changes in the inter-atomic forces with strain. Comparison of the theory with published experimental results for the effect of pressure on diffusion shows that the experiments agree with the form of the theoretical equation in all cases within experimental error.

On the chaotic diffusion in multidimensional Hamiltonian systems

NASA Astrophysics Data System (ADS)

Cincotta, P. M.; Giordano, C. M.; Martí, J. G.; Beaugé, C.

2018-01-01

We present numerical evidence that diffusion in the herein studied multidimensional near-integrable Hamiltonian systems departs from a normal process, at least for realistic timescales. Therefore, the derivation of a diffusion coefficient from a linear fit on the variance evolution of the unperturbed integrals fails. We review some topics on diffusion in the Arnold Hamiltonian and yield numerical and theoretical arguments to show that in the examples we considered, a standard coefficient would not provide a good estimation of the speed of diffusion. However, numerical experiments concerning diffusion would provide reliable information about the stability of the motion within chaotic regions of the phase space. In this direction, we present an extension of previous results concerning the dynamical structure of the Laplace resonance in Gliese-876 planetary system considering variations of the orbital parameters accordingly to the error introduced by the radial velocity determination. We found that a slight variation of the eccentricity of planet c would destabilize the inner region of the resonance that, though chaotic, shows stable when adopting the best fit values for the parameters.

The theory of n-scales

NASA Astrophysics Data System (ADS)

Dündar, Furkan Semih

2018-01-01

We provide a theory of n-scales previously called as n dimensional time scales. In previous approaches to the theory of time scales, multi-dimensional scales were taken as product space of two time scales [1, 2]. n-scales make the mathematical structure more flexible and appropriate to real world applications in physics and related fields. Here we define an n-scale as an arbitrary closed subset of ℝn. Modified forward and backward jump operators, Δ-derivatives and Δ-integrals on n-scales are defined.

The nonconvex multi-dimensional Riemann problem for Hamilton-Jacobi equations

NASA Technical Reports Server (NTRS)

Osher, Stanley

1989-01-01

Simple inequalities for the Riemann problem for a Hamilton-Jacobi equation in N space dimension when neither the initial data nor the Hamiltonian need be convex (or concave) are presented. The initial data is globally continuous, affine in each orthant, with a possible jump in normal derivative across each coordinate plane, x sub i = 0. The inequalities become equalities wherever a maxmin equals a minmax and thus an exact closed form solution to this problem is then obtained.

A single-sweep, nanosecond time resolution laser temperature-jump apparatus

NASA Astrophysics Data System (ADS)

Ballew, R. M.; Sabelko, J.; Reiner, C.; Gruebele, M.

1996-10-01

We describe a fast temperature-jump (T-jump) apparatus capable of acquiring kinetic relaxation transients via real-time fluorescence detection over a time interval from nanoseconds to milliseconds in a single sweep. The method is suitable for aqueous solutions, relying upon the direct absorption of laser light by the bulk water. This obviates the need for additives (serving as optical or conductive heaters) that may interact with the sample under investigation. The longitudinal temperature profile is made uniform by counterpropagating heating pulses. Dead time is limited to one period of the probe laser (16 ns). The apparatus response is tested with aqueous tryptophan and the diffusion-controlled dimerization of proflavine.

Simulation of adsorbed hydrogen on tungsten surface

NASA Astrophysics Data System (ADS)

Degtyarenko, N. N.; Pisarev, A. A.

2017-12-01

Calculations of the energy of the H-W system were performed using DFT method based on plane waves. Adsorption energies, equilibrium states, vibration spectra, saddle points, activation energies of jumps, and diffusion paths have been analyzed for H atom on W(100) and W(110). Diffusion coefficient for H on W(110) agrees very well with experimental data.

Electrostatic Estimation of Intercalant Jump-Diffusion Barriers Using Finite-Size Ion Models.

PubMed

Zimmermann, Nils E R; Hannah, Daniel C; Rong, Ziqin; Liu, Miao; Ceder, Gerbrand; Haranczyk, Maciej; Persson, Kristin A

2018-02-01

We report on a scheme for estimating intercalant jump-diffusion barriers that are typically obtained from demanding density functional theory-nudged elastic band calculations. The key idea is to relax a chain of states in the field of the electrostatic potential that is averaged over a spherical volume using different finite-size ion models. For magnesium migrating in typical intercalation materials such as transition-metal oxides, we find that the optimal model is a relatively large shell. This data-driven result parallels typical assumptions made in models based on Onsager's reaction field theory to quantitatively estimate electrostatic solvent effects. Because of its efficiency, our potential of electrostatics-finite ion size (PfEFIS) barrier estimation scheme will enable rapid identification of materials with good ionic mobility.

The hydrogen diffusion in liquid aluminum alloys from ab initio molecular dynamics

NASA Astrophysics Data System (ADS)

Jakse, N.; Pasturel, A.

2014-09-01

We study the hydrogen diffusion in liquid aluminum alloys through extensive ab initio molecular dynamics simulations. At the microscopic scale, we show that the hydrogen motion is characterized by a broad distribution of spatial jumps that does not correspond to a Brownian motion. To determine the self-diffusion coefficient of hydrogen in liquid aluminum alloys, we use a generalized continuous time random walk model recently developed to describe the hydrogen diffusion in pure aluminum. In particular, we show that the model successfully accounts the effects of alloying elements on the hydrogen diffusion in agreement with experimental features.

Electrochemical force microscopy

DOEpatents

Kalinin, Sergei V.; Jesse, Stephen; Collins, Liam F.; Rodriguez, Brian J.

2017-01-10

A system and method for electrochemical force microscopy are provided. The system and method are based on a multidimensional detection scheme that is sensitive to forces experienced by a biased electrode in a solution. The multidimensional approach allows separation of fast processes, such as double layer charging, and charge relaxation, and slow processes, such as diffusion and faradaic reactions, as well as capturing the bias dependence of the response. The time-resolved and bias measurements can also allow probing both linear (small bias range) and non-linear (large bias range) electrochemical regimes and potentially the de-convolution of charge dynamics and diffusion processes from steric effects and electrochemical reactivity.

Continuous time anomalous diffusion in a composite medium.

PubMed

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.

Structural properties and diffusion processes of the Cu 3Au (0 0 1) surface

NASA Astrophysics Data System (ADS)

Wang, Fang; Zhang, Jian-Min; Zhang, Yan; Ji, Vincent

2010-09-01

The surface relaxation and surface energy of both the mixed AuCu and pure Cu terminated Cu 3Au (0 0 1) surfaces are simulated and calculated by using the modified analytical embedded-atom method. We find that the mixed AuCu termination is energetically preferred over the pure Cu termination thereby the mono-vacancy diffusion is also investigated in the topmost few layers of the mixed AuCu terminated Cu 3Au (0 0 1) surface. In the mixed AuCu terminated surface the relaxed Au atoms are raised above Cu atoms for 0.13 Å in the topmost layer. All the surface atoms displace outwards, this effect occurs in the first three layers and changes the first two inter-layer spacing. For mono-vacancy migration in the first layer, the migration energies of Au and Cu mono-vacancy via two-type in-plane displace: the nearest neighbor jump (NNJ) and the second nearest neighbor jump (2NNJ), are calculated and the results show that the NNJ requires a much lower energy than 2NNJ. For the evolution of the energy requirements for successive nearest neighbor jumps (SNNJ) along three different paths: circularity, zigzag and beeline, we find that the circularity path is preferred over the other two paths due to its minimum energy barriers and final energies. In the second layer, the NN jumps in intra- and inter-layer of the Cu mono-vacancy are investigated. The calculated energy barriers and final energies show that the vacancy prefer jump up to a proximate Cu site. This replacement between the Cu vacancy in the second layer and Cu atom in the first layer is remunerative for the Au atoms enrichment in the topmost layer.

The Influence of Turbulent Coherent Structure on Suspended Sediment Transport

NASA Astrophysics Data System (ADS)

Huang, S. H.; Tsai, C.

2017-12-01

The anomalous diffusion of turbulent sedimentation has received more and more attention in recent years. With the advent of new instruments and technologies, researchers have found that sediment behavior may deviate from Fickian assumptions when particles are heavier. In particle-laden flow, bursting phenomena affects instantaneous local concentrations, and seems to carry suspended particles for a longer distance. Instead of the pure diffusion process in an analogy to Brownian motion, Levy flight which allows particles to move in response to bursting phenomena is suspected to be more suitable for describing particle movement in turbulence. And the fractional differential equation is a potential candidate to improve the concentration profile. However, stochastic modeling (the Differential Chapmen-Kolmogorov Equation) also provides an alternative mathematical framework to describe system transits between different states through diffusion/the jump processes. Within this framework, the stochastic particle tracking model linked with advection diffusion equation is a powerful tool to simulate particle locations in the flow field. By including the jump process to this model, a more comprehensive description for suspended sediment transport can be provided with a better physical insight. This study also shows the adaptability and expandability of the stochastic particle tracking model for suspended sediment transport modeling.

Hybrid finite element and Brownian dynamics method for diffusion-controlled reactions.

PubMed

Bauler, Patricia; Huber, Gary A; McCammon, J Andrew

2012-04-28

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 symmetric diffusion systems.

Random walk in nonhomogeneous environments: A possible approach to human and animal mobility

NASA Astrophysics Data System (ADS)

Srokowski, Tomasz

2017-03-01

The random walk process in a nonhomogeneous medium, characterized by a Lévy stable distribution of jump length, is discussed. The width depends on a position: either before the jump or after that. In the latter case, the density slope is affected by the variable width and the variance may be finite; then all kinds of the anomalous diffusion are predicted. In the former case, only the time characteristics are sensitive to the variable width. The corresponding Langevin equation with different interpretations of the multiplicative noise is discussed. The dependence of the distribution width on position after jump is interpreted in terms of cognitive abilities and related to such problems as migration in a human population and foraging habits of animals.

Orientational dynamics in a room temperature ionic liquid: Are angular jumps predominant?

NASA Astrophysics Data System (ADS)

Das, Suman; Mukherjee, Biswaroop; Biswas, Ranjit

2018-05-01

Reorientational dynamics of the constituent ions in a room temperature ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), are explored via molecular dynamics simulations, and several features of orientation dynamics are summarized. The anion, [PF6]-, not only exhibits a higher propensity to orientation jumps than the cation, [BMIM]+ but also accesses a wider jump angle distribution and larger peak-angle. Jump and waiting time distributions for both the ions depict power-law dependences, suggesting temporally heterogeneous dynamics for the medium. This heterogeneity feature is further highlighted by the finding that the simulated first rank (ℓ = 1) and second rank (ℓ = 2) average reorientational correlation times reflect a severe break-down of Debye's ℓ(ℓ + 1) law for orientational diffusion in an isotropic homogeneous medium. Simulated average H-bond lifetime resides between the mean orientation jump and waiting times, while the structural H-bond relaxation suggests, as in normal liquids, a pronounced presence of translational motion of the partnering ions. Average simulated jump trajectories reveal a strong rotation-translation coupling and indicate relatively larger changes in spatial and angular arrangements for the anion during an orientation jump. In fact, a closer inspection of all these results points toward more heterogeneous dynamics for [PF6]- than [BMIM]+. This is a new observation and may simply be linked to the ion-size. However, such a generalization warrants further study.

Diffusion equations and the time evolution of foreign exchange rates

NASA Astrophysics Data System (ADS)

Figueiredo, Annibal; de Castro, Marcio T.; da Fonseca, Regina C. B.; Gleria, Iram

2013-10-01

We investigate which type of diffusion equation is most appropriate to describe the time evolution of foreign exchange rates. We modify the geometric diffusion model assuming a non-exponential time evolution and the stochastic term is the sum of a Wiener noise and a jump process. We find the resulting diffusion equation to obey the Kramers-Moyal equation. Analytical solutions are obtained using the characteristic function formalism and compared with empirical data. The analysis focus on the first four central moments considering the returns of foreign exchange rate. It is shown that the proposed model offers a good improvement over the classical geometric diffusion model.

From analytical solutions of solute transport equations to multidimensional time-domain random walk (TDRW) algorithms

NASA Astrophysics Data System (ADS)

Bodin, Jacques

2015-03-01

In this study, new multi-dimensional time-domain random walk (TDRW) algorithms are derived from approximate one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) analytical solutions of the advection-dispersion equation and from exact 1-D, 2-D, and 3-D analytical solutions of the pure-diffusion equation. These algorithms enable the calculation of both the time required for a particle to travel a specified distance in a homogeneous medium and the mass recovery at the observation point, which may be incomplete due to 2-D or 3-D transverse dispersion or diffusion. The method is extended to heterogeneous media, represented as a piecewise collection of homogeneous media. The particle motion is then decomposed along a series of intermediate checkpoints located on the medium interface boundaries. The accuracy of the multi-dimensional TDRW method is verified against (i) exact analytical solutions of solute transport in homogeneous media and (ii) finite-difference simulations in a synthetic 2-D heterogeneous medium of simple geometry. The results demonstrate that the method is ideally suited to purely diffusive transport and to advection-dispersion transport problems dominated by advection. Conversely, the method is not recommended for highly dispersive transport problems because the accuracy of the advection-dispersion TDRW algorithms degrades rapidly for a low Péclet number, consistent with the accuracy limit of the approximate analytical solutions. The proposed approach provides a unified methodology for deriving multi-dimensional time-domain particle equations and may be applicable to other mathematical transport models, provided that appropriate analytical solutions are available.

Surface hydration amplifies single-well protein atom diffusion propagating into the macromolecular core

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Liang; Cheng, Xiaolin; Glass, Dennis C.

2012-06-05

The effect of surface hydration water on internal protein motion is of fundamental interest in molecular biophysics. Here, by decomposing the picosecond to nanosecond atomic motion in molecular dynamics simulations of lysozyme at different hydration levels into three components localized single-well diffusion, methyl group rotation, and nonmethyl jumps we show that the effect of surface hydration is mainly to increase the volume of the localized single-well diffusion. As a result, these diffusive motions are coupled in such a way that the hydration effect propagates from the protein surface into the dry core.

Detection of confinement and jumps in single-molecule membrane trajectories

NASA Astrophysics Data System (ADS)

Meilhac, N.; Le Guyader, L.; Salomé, L.; Destainville, N.

2006-01-01

We propose a variant of the algorithm by [R. Simson, E. D. Sheets, and K. Jacobson, Biophys. 69, 989 (1995)]. Their algorithm was developed to detect transient confinement zones in experimental single-particle tracking trajectories of diffusing membrane proteins or lipids. We show that our algorithm is able to detect confinement in a wider class of confining potential shapes than that of Simson Furthermore, it enables to detect not only temporary confinement but also jumps between confinement zones. Jumps are predicted by membrane skeleton fence and picket models. In the case of experimental trajectories of μ -opioid receptors, which belong to the family of G-protein-coupled receptors involved in a signal transduction pathway, this algorithm confirms that confinement cannot be explained solely by rigid fences.

FAST TRACK COMMUNICATION: Suppressing anomalous diffusion by cooperation

NASA Astrophysics Data System (ADS)

Dybiec, Bartłomiej

2010-08-01

Within a continuous time random walk scenario we consider a motion of a complex of particles which moves coherently. The motion of every particle is characterized by the waiting time and jump length distributions which are of the power-law type. Due to the interactions between particles it is assumed that the waiting time is adjusted to the shortest or to the longest waiting time. Analogously, the jump length is adjusted to the shortest or to the longest jump length. We show that adjustment to the shortest waiting time can suppress the subdiffusive behavior even in situations when the exponent characterizing the waiting time distribution assures subdiffusive motion of a single particle. Finally, we demonstrate that the characteristic of the motion depends on the number of particles building a complex.

Microscopic models for uphill diffusion

NASA Astrophysics Data System (ADS)

Colangeli, Matteo; De Masi, Anna; Presutti, Errico

2017-10-01

We study a system of particles which jump on the sites of the interval [1, L] of { Z} . The density at the boundaries is kept fixed to simulate the action of mass reservoirs. The evolution depends on two parameters \

Single Molecule Spectral Diffusion in a Solid Detected Via Fluorescence Spectroscopy

DTIC Science & Technology

1991-10-15

other local fields) at the position of the molecule, the spectral jumps may occur because the class II pentacene molecules are coupled to an...and identify by block number) FIELD jGROUP SUB-GROUP_ Single molecule spectroscopy Precision detection Spectral diffusion, Pentacene in p-terphenyl 19...significant increases in detection sensitivity for single pentacene molecules in crystals of p-terphenyl at low temperatures. With the increased signal to

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiser, Philip; Qin, Ying; Yin, Weikai

Uniaxial stress experiments performed for the 3306 cm -1 vibrational line assigned to the interstitial-hydrogen, shallow-donor center in In 2O 3 reveal its symmetry and transition- moment direction. The defect alignment that can be produced by a [001] stress applied at 165 K is due to a process that is also a hydrogen- diffusion jump, providing a microscopic determination of the diffusion constant for H in In 2O 3 and its mechanism. Lastly, our experimental results strongly complement theoretical predictions for the structure and diffusion of the interstitial hydrogen donor center in In 2O 3.

Zooplankton can actively adjust their motility to turbulent flow

PubMed Central

Michalec, François-Gaël; Fouxon, Itzhak

2017-01-01

Calanoid copepods are among the most abundant metazoans in the ocean and constitute a vital trophic link within marine food webs. They possess relatively narrow swimming capabilities, yet are capable of significant self-locomotion under strong hydrodynamic conditions. Here we provide evidence for an active adaptation that allows these small organisms to adjust their motility in response to background flow. We track simultaneously and in three dimensions the motion of flow tracers and planktonic copepods swimming freely at several intensities of quasi-homogeneous, isotropic turbulence. We show that copepods synchronize the frequency of their relocation jumps with the frequency of small-scale turbulence by performing frequent relocation jumps of low amplitude that seem unrelated to localized hydrodynamic signals. We develop a model of plankton motion in turbulence that shows excellent quantitative agreement with our measurements when turbulence is significant. We find that, compared with passive tracers, active motion enhances the diffusion of organisms at low turbulence intensity whereas it dampens diffusion at higher turbulence levels. The existence of frequent jumps in a motion that is otherwise dominated by turbulent transport allows for the possibility of active locomotion and hence to transition from being passively advected to being capable of controlling diffusion. This behavioral response provides zooplankton with the capability to retain the benefits of self-locomotion despite turbulence advection and may help these organisms to actively control their distribution in dynamic environments. Our study reveals an active adaptation that carries strong fitness advantages and provides a realistic model of plankton motion in turbulence. PMID:29229858

Large-scale Instability during Gravitational Collapse with Neutrino Transport and a Core-Collapse Supernova

NASA Astrophysics Data System (ADS)

Aksenov, A. G.; Chechetkin, V. M.

2018-04-01

Most of the energy released in the gravitational collapse of the cores of massive stars is carried away by neutrinos. Neutrinos play a pivotal role in explaining core-collape supernovae. Currently, mathematical models of the gravitational collapse are based on multi-dimensional gas dynamics and thermonuclear reactions, while neutrino transport is considered in a simplified way. Multidimensional gas dynamics is used with neutrino transport in the flux-limited diffusion approximation to study the role of multi-dimensional effects. The possibility of large-scale convection is discussed, which is interesting both for explaining SN II and for setting up observations to register possible high-energy (≳10MeV) neutrinos from the supernova. A new multi-dimensional, multi-temperature gas dynamics method with neutrino transport is presented.

A New Ghost Cell/Level Set Method for Moving Boundary Problems: Application to Tumor Growth

PubMed Central

Macklin, Paul

2011-01-01

In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth. PMID:21331304

Addendum to foundations of multidimensional wave field signal theory: Gaussian source function

NASA Astrophysics Data System (ADS)

Baddour, Natalie

2018-02-01

Many important physical phenomena are described by wave or diffusion-wave type equations. Recent work has shown that a transform domain signal description from linear system theory can give meaningful insight to multi-dimensional wave fields. In N. Baddour [AIP Adv. 1, 022120 (2011)], certain results were derived that are mathematically useful for the inversion of multi-dimensional Fourier transforms, but more importantly provide useful insight into how source functions are related to the resulting wave field. In this short addendum to that work, it is shown that these results can be applied with a Gaussian source function, which is often useful for modelling various physical phenomena.

Symmetry and diffusivity of the interstitial hydrogen shallow-donor center in In 2O 3

DOE PAGES

Weiser, Philip; Qin, Ying; Yin, Weikai; ...

2016-11-16

Uniaxial stress experiments performed for the 3306 cm -1 vibrational line assigned to the interstitial-hydrogen, shallow-donor center in In 2O 3 reveal its symmetry and transition- moment direction. The defect alignment that can be produced by a [001] stress applied at 165 K is due to a process that is also a hydrogen- diffusion jump, providing a microscopic determination of the diffusion constant for H in In 2O 3 and its mechanism. Lastly, our experimental results strongly complement theoretical predictions for the structure and diffusion of the interstitial hydrogen donor center in In 2O 3.

Disrupted white matter connectivity underlying developmental dyslexia: A machine learning approach.

PubMed

Cui, Zaixu; Xia, Zhichao; Su, Mengmeng; Shu, Hua; Gong, Gaolang

2016-04-01

Developmental dyslexia has been hypothesized to result from multiple causes and exhibit multiple manifestations, implying a distributed multidimensional effect on human brain. The disruption of specific white-matter (WM) tracts/regions has been observed in dyslexic children. However, it remains unknown if developmental dyslexia affects the human brain WM in a multidimensional manner. Being a natural tool for evaluating this hypothesis, the multivariate machine learning approach was applied in this study to compare 28 school-aged dyslexic children with 33 age-matched controls. Structural magnetic resonance imaging (MRI) and diffusion tensor imaging were acquired to extract five multitype WM features at a regional level: white matter volume, fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. A linear support vector machine (LSVM) classifier achieved an accuracy of 83.61% using these MRI features to distinguish dyslexic children from controls. Notably, the most discriminative features that contributed to the classification were primarily associated with WM regions within the putative reading network/system (e.g., the superior longitudinal fasciculus, inferior fronto-occipital fasciculus, thalamocortical projections, and corpus callosum), the limbic system (e.g., the cingulum and fornix), and the motor system (e.g., the cerebellar peduncle, corona radiata, and corticospinal tract). These results were well replicated using a logistic regression classifier. These findings provided direct evidence supporting a multidimensional effect of developmental dyslexia on WM connectivity of human brain, and highlighted the involvement of WM tracts/regions beyond the well-recognized reading system in dyslexia. Finally, the discriminating results demonstrated a potential of WM neuroimaging features as imaging markers for identifying dyslexic individuals. © 2016 Wiley Periodicals, Inc.

Diffusion of small Cu islands on the Ni(111) surface: A self-learning kinetic Monte Carlo study

NASA Astrophysics Data System (ADS)

Acharya, Shree Ram; Shah, Syed Islamuddin; Rahman, Talat S.

2017-08-01

We elucidate the diffusion kinetics of a heteroepitaxial system consisting of two-dimensional small (1-8 atoms) Cu islands on the Ni(111) surface at (100-600) K using the Self-Learning Kinetic Monte Carlo (SLKMC-II) method. Study of the statics of the system shows that compact CuN (3≤N≤8) clusters made up of triangular units on fcc occupancy sites are the energetically most stable structures of those clusters. Interestingly, we find a correlation between the height of the activation energy barrier (Ea) and the location of the transition state (TS). The Ea of processes for Cu islands on the Ni(111) surface are in general smaller than those of their counterpart Ni islands on the same surface. We find this difference to correlate with the relative strength of the lateral interaction of the island atoms in the two systems. While our database consists of hundreds of possible processes, we identify and discuss the energetics of those that are the most dominant, or are rate-limiting, or most contributory to the diffusion of the islands. Since the Ea of single- and multi-atom processes that convert compact island shapes into non-compact ones are larger (with a significantly smaller Ea for their reverse processes) than that for the collective (concerted) motion of the island, the later dominate in the system kinetics - except for the cases of the dimer, pentamer and octamer. Short-jump involving one atom, long jump dimer-shearing, and long-jump corner shearing (via a single-atom) are, respectively, the dominating processes in the diffusion of the dimer, pentamer and octamer. Furthermore single-atom corner-rounding are the rate-limiting processes for the pentamer and octamer islands. Comparison of the energetics of selected processes and lateral interactions obtained from semi-empirical interatomic potentials with those from density functional theory show minor quantitative differences and overall qualitative agreement.

Front fingering and complex dynamics driven by the interaction of buoyancy and diffusive instabilities.

PubMed

D'Hernoncourt, J; Merkin, J H; De Wit, A

2007-09-01

Traveling fronts can become transversally unstable either because of a diffusive instability arising when the key variables diffuse at sufficiently different rates or because of a buoyancy-driven Rayleigh-Taylor mechanism when the density jump across the front is statically unfavorable. The interaction between such diffusive and buoyancy instabilities of fronts is analyzed theoretically for a simple model system. Linear stability analysis and nonlinear simulations show that their interplay changes considerably the stability properties with regard to the pure Rayleigh-Taylor or diffusive instabilities of fronts. In particular, an instability scenario can arise which triggers convection around statically stable fronts as a result of differential diffusion. Moreover, spatiotemporal chaos can be observed when both buoyancy and diffusive effects cooperate to destabilize the front. Experimental conditions to test our predictions are suggested.

Electrostatic control of DNA intersegmental translocation by the ETS transcription factor ETV6.

PubMed

Vo, Tam; Wang, Shuo; Poon, Gregory M K; Wilson, W David

2017-08-11

To find their DNA target sites in complex solution environments containing excess heterogeneous DNA, sequence-specific DNA-binding proteins execute various translocation mechanisms known collectively as facilitated diffusion. For proteins harboring a single DNA contact surface, long-range translocation occurs by jumping between widely spaced DNA segments. We have configured biosensor-based surface plasmon resonance to directly measure the affinity and kinetics of this intersegmental jumping by the ETS-family transcription factor ETS variant 6 (ETV6). To isolate intersegmental target binding in a functionally defined manner, we pre-equilibrated ETV6 with excess salmon sperm DNA, a heterogeneous polymer, before exposing the nonspecifically bound protein to immobilized oligomeric DNA harboring a high-affinity ETV6 site. In this way, the mechanism of ETV6-target association could be toggled electrostatically through varying NaCl concentration in the bulk solution. Direct measurements of association and dissociation kinetics of the site-specific complex indicated that 1) freely diffusive binding by ETV6 proceeds through a nonspecific-like intermediate, 2) intersegmental jumping is rate-limited by dissociation from the nonspecific polymer, and 3) dissociation of the specific complex is independent of the history of complex formation. These results show that target searches by proteins with an ETS domain, such as ETV6, whose single DNA-binding domain cannot contact both source and destination sites simultaneously, are nonetheless strongly modulated by intersegmental jumping in heterogeneous site environments. Our findings establish biosensors as a general technique for directly and specifically measuring target site search by DNA-binding proteins via intersegmental translocation. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

A Fractional PDE Approach to Turbulent Mixing; Part II: Numerical Simulation

NASA Astrophysics Data System (ADS)

Samiee, Mehdi; Zayernouri, Mohsen

2016-11-01

We propose a generalizing fractional order transport model of advection-diffusion kind with fractional time- and space-derivatives, governing the evolution of passive scalar turbulence. This approach allows one to incorporate the nonlocal and memory effects in the underlying anomalous diffusion i.e., sub-to-standard diffusion to model the trapping of particles inside the eddied, and super-diffusion associated with the sudden jumps of particles from one coherent region to another. For this nonlocal model, we develop a high order numerical (spectral) method in addition to a fast solver, examined in the context of some canonical problems. PhD student, Department of Mechanical Engineering, & Department Computational Mathematics, Science, and Engineering.

The Shannon entropy as a measure of diffusion in multidimensional dynamical systems

NASA Astrophysics Data System (ADS)

Giordano, C. M.; Cincotta, P. M.

2018-05-01

In the present work, we introduce two new estimators of chaotic diffusion based on the Shannon entropy. Using theoretical, heuristic and numerical arguments, we show that the entropy, S, provides a measure of the diffusion extent of a given small initial ensemble of orbits, while an indicator related with the time derivative of the entropy, S', estimates the diffusion rate. We show that in the limiting case of near ergodicity, after an appropriate normalization, S' coincides with the standard homogeneous diffusion coefficient. The very first application of this formulation to a 4D symplectic map and to the Arnold Hamiltonian reveals very successful and encouraging results.

XMM-Newton Observations of the Southeastern Radio Relic in Abell 3667

NASA Astrophysics Data System (ADS)

Storm, Emma; Vink, Jacco; Zandanel, Fabio; Akamatsu, Hiroki

2018-06-01

Radio relics, elongated, non-thermal, structures located at the edges of galaxy clusters, are the result of synchrotron radiation from cosmic-ray electrons accelerated by merger-driven shocks at the cluster outskirts. However, X-ray observations of such shocks in some clusters suggest that they are too weak to efficiently accelerate electrons via diffusive shock acceleration to energies required to produce the observed radio power. We examine this issue in the merging galaxy cluster Abell 3667 (A3667), which hosts a pair of radio relics. While the Northwest relic in A3667 has been well studied in the radio and X-ray by multiple instruments, the Southeast relic region has only been observed so far by Suzaku, which detected a temperature jump across the relic, suggesting the presence of a weak shock. We present observations of the Southeastern region of A3667 with XMM-Newton centered on the radio relic. We confirm the existence of an X-ray shock with Mach number of about 1.8 from a clear detection of temperature jump and a tentative detection of a density jump, consistent with previous measurements by Suzaku. We discuss the implications of this measurement for diffusive shock acceleration as the main mechanism for explaining the origin of radio relics. We then speculate on the plausibility of alternative scenarios, including re-acceleration and variations in the Mach number along shock fronts.

Spectral diffusion in poly(para-phenylene)-type polymers with different energetic disorder

NASA Astrophysics Data System (ADS)

Hoffmann, Sebastian T.; Bässler, Heinz; Koenen, Jan-Moritz; Forster, Michael; Scherf, Ullrich; Scheler, Esther; Strohriegl, Peter; Köhler, Anna

2010-03-01

We have employed quasicontinuous fluorescence and phosphorescence spectroscopy within a temperature range between 10 and 500 K to monitor the spectral diffusion of singlet and triplet excitons in a series of π -conjugated polymers. We investigated (i) how spectral diffusion is controlled by the degree of energetic disorder present in the amorphous film (that is reflected by the inhomogeneous broadening of the photoluminescence spectra) and (ii) how this process depends on the range of the electronic coupling (by comparing singlet exciton diffusion via long-range Förster transfer against triplet exciton diffusion by short-range Dexter transfer). For singlets, we find that the fluorescence spectra bear out a bathochromic shift upon cooling the sample down to a critical temperature below which the shift saturates. This bathochromic shift is a signature of spectral relaxation. Random-walk theory applied to excitation transport within a Gaussian density-of-states distribution is both necessary and sufficient to rationalize the experimental results in a quantitative fashion. The same behavior is observed for triplets in weakly disordered systems, such as in a polymer containing platinum in the main chain and a ladder-type polyphenylene. In contrast we observe a hypsochromic shift of the phosphorescence spectra below a characteristic temperature for triplets in systems with at least moderate energetic disorder. The hypsochromic shift proves that triplet exciton relaxation becomes frustrated because thermally activated exciton jumps that otherwise promote spectral diffusion become progressively frozen out. The frustration effect is controlled by the jump distance and thus it is specific for triplet excitations that migrate via short-range coupling among strongly localized states as compared to singlet excitons.

Phase transition in conservative diffusive contact processes

NASA Astrophysics Data System (ADS)

Fiore, Carlos E.; de Oliveira, Mário J.

2004-10-01

We determine the phase diagrams of conservative diffusive contact processes by means of numerical simulations. These models are versions of the ordinary diffusive single-creation, pair-creation, and triplet-creation contact processes in which the particle number is conserved. The transition between the frozen and active states was determined by studying the system in the subcritical regime, and the nature of the transition, whether continuous or first order, was determined by looking at the fractal dimension of the critical cluster. For the single-creation model the transition remains continuous for any diffusion rate. For pair- and triplet-creation models, however, the transition becomes first order for high enough diffusion rate. Our results indicate that in the limit of infinite diffusion rate the jump in density equals 2/3 for the pair-creation model and 5/6 for the triplet-creation model.

Cauchy flights in confining potentials

NASA Astrophysics Data System (ADS)

Garbaczewski, Piotr

2010-03-01

We analyze confining mechanisms for Lévy flights evolving under an influence of external potentials. Given a stationary probability density function (pdf), we address the reverse engineering problem: design a jump-type stochastic process whose target pdf (eventually asymptotic) equals the preselected one. To this end, dynamically distinct jump-type processes can be employed. We demonstrate that one “targeted stochasticity” scenario involves Langevin systems with a symmetric stable noise. Another derives from the Lévy-Schrödinger semigroup dynamics (closely linked with topologically induced super-diffusions), which has no standard Langevin representation. For computational and visualization purposes, the Cauchy driver is employed to exemplify our considerations.

A stability analysis of the power-law steady state of marine size spectra.

PubMed

Datta, Samik; Delius, Gustav W; Law, Richard; Plank, Michael J

2011-10-01

This paper investigates the stability of the power-law steady state often observed in marine ecosystems. Three dynamical systems are considered, describing the abundance of organisms as a function of body mass and time: a "jump-growth" equation, a first order approximation which is the widely used McKendrick-von Foerster equation, and a second order approximation which is the McKendrick-von Foerster equation with a diffusion term. All of these yield a power-law steady state. We derive, for the first time, the eigenvalue spectrum for the linearised evolution operator, under certain constraints on the parameters. This provides new knowledge of the stability properties of the power-law steady state. It is shown analytically that the steady state of the McKendrick-von Foerster equation without the diffusion term is always unstable. Furthermore, numerical plots show that eigenvalue spectra of the McKendrick-von Foerster equation with diffusion give a good approximation to those of the jump-growth equation. The steady state is more likely to be stable with a low preferred predator:prey mass ratio, a large diet breadth and a high feeding efficiency. The effects of demographic stochasticity are also investigated and it is concluded that these are likely to be small in real systems.

Numerical investigations on the characteristics of thermomagnetic instability in MgB2 bulks

NASA Astrophysics Data System (ADS)

Xia, Jing; Li, Maosheng; Zhou, Youhe

2017-07-01

This paper presents the characteristics of thermomagnetic instability in MgB2 bulks by numerically solving the macroscopic dynamics of thermomagnetic interaction governed by the coupled magnetic and heat diffusion equations in association with a modified E-J power-law relationship. The finite element method is used to discretize the system of partial differential equations. The calculated magnetization loops with flux jumps are consistent with the experimental results for MgB2 slabs bathed in a wide range of ambient temperatures. We reveal the evolution process of the thermomagnetic instability and present the distributions of the magnetic field, temperature, and current density before and after flux jumps. A 2D axisymmetric model is used to study the thermomagnetic instability in cylindrical MgB2 bulks. It is found that the number of flux jumps monotonously reduces as the ambient temperature rises and no flux jump appears when the ambient temperature exceeds a certain value. Moreover, the flux-jump phenomenon exists in a wide range of the ramp rate of the applied external field, i.e. 10-2-102 T s-1. Furthermore, the dependences of the first flux-jump field on the ambient temperature, ramp rate, and bulk thickness are investigated. The critical bulk thicknesses for stability are obtained for different ambient temperatures and sample radii. In addition, the influence of the capability of the interfacial heat transfer on the temporal response of the bulk temperature is discussed. We also find that the prediction of thermomagnetic instability is sensitive to the employment of the flux creep exponent in the simulations.

Jump Rope Training: Balance and Motor Coordination in Preadolescent Soccer Players

PubMed Central

Trecroci, Athos; Cavaggioni, Luca; Caccia, Riccardo; Alberti, Giampietro

2015-01-01

General physical practice and multidimensional exercises are essential elements that allow young athletes to enhance their coordinative traits, balance, and strength and power levels, which are linked to the learning soccer-specific skills. Jumping rope is a widely-used and non-specific practical method for the development of athletic conditioning, balance and coordination in several disciplines. Thus, the aim of this study was to investigate the effects of a short-term training protocol including jumping rope (JR) exercises on motor abilities and body balance in young soccer players. Twenty-four preadolescent soccer players were recruited and placed in two different groups. In the Experimental group (EG), children performed JR training at the beginning of the training session. The control group (CG), executed soccer specific drills. Harre circuit test (HCT) and Lower Quarter Y balance test (YBT-LQ) were selected to evaluate participant’s motor ability (e.g. ability to perform rapidly a course with different physical tasks such as somersault and passages above/below obstacles ) and to assess unilateral dynamic lower limb balance after 8 weeks of training. Statistical analysis consisted of paired t-test and mixed analysis of variance scores to determine any significant interactions. Children who performed jumping rope exercises showed a significant decrease of 9% (p < 0.01, ES = 0.50-0.80) in the performance time of HCT. With regard to the CG, no differences were highlighted (p > 0.05, ES = 0.05-0.2) from pre- to post-training. A training-by-group interaction was found for the composite score in both legs (p < 0.05, Part η2 > 0.14). Our findings demonstrated that JR practice within regular soccer training enhanced general motor coordination and balance in preadolescent soccer players. Therefore, the inclusion of JR practice within regular soccer training session should encouraged to improve children’s motor skills. Key points Performing jumping rope exercises within a regular soccer program can be an additional method to improve balance and motor coordination. The performance improvement in the Harre Circuit Test associated with jump rope training can potentially be attributed to an enhancement of the inter-limb coordination and SSC ability. Results from the present study indicate that young soccer players should be encouraged to practice general physical activities together with sport-specific exercise during their training sessions. PMID:26664276

Jump Rope Training: Balance and Motor Coordination in Preadolescent Soccer Players.

PubMed

Trecroci, Athos; Cavaggioni, Luca; Caccia, Riccardo; Alberti, Giampietro

2015-12-01

General physical practice and multidimensional exercises are essential elements that allow young athletes to enhance their coordinative traits, balance, and strength and power levels, which are linked to the learning soccer-specific skills. Jumping rope is a widely-used and non-specific practical method for the development of athletic conditioning, balance and coordination in several disciplines. Thus, the aim of this study was to investigate the effects of a short-term training protocol including jumping rope (JR) exercises on motor abilities and body balance in young soccer players. Twenty-four preadolescent soccer players were recruited and placed in two different groups. In the Experimental group (EG), children performed JR training at the beginning of the training session. The control group (CG), executed soccer specific drills. Harre circuit test (HCT) and Lower Quarter Y balance test (YBT-LQ) were selected to evaluate participant's motor ability (e.g. ability to perform rapidly a course with different physical tasks such as somersault and passages above/below obstacles ) and to assess unilateral dynamic lower limb balance after 8 weeks of training. Statistical analysis consisted of paired t-test and mixed analysis of variance scores to determine any significant interactions. Children who performed jumping rope exercises showed a significant decrease of 9% (p < 0.01, ES = 0.50-0.80) in the performance time of HCT. With regard to the CG, no differences were highlighted (p > 0.05, ES = 0.05-0.2) from pre- to post-training. A training-by-group interaction was found for the composite score in both legs (p < 0.05, Part η(2) > 0.14). Our findings demonstrated that JR practice within regular soccer training enhanced general motor coordination and balance in preadolescent soccer players. Therefore, the inclusion of JR practice within regular soccer training session should encouraged to improve children's motor skills. Key pointsPerforming jumping rope exercises within a regular soccer program can be an additional method to improve balance and motor coordination.The performance improvement in the Harre Circuit Test associated with jump rope training can potentially be attributed to an enhancement of the inter-limb coordination and SSC ability.Results from the present study indicate that young soccer players should be encouraged to practice general physical activities together with sport-specific exercise during their training sessions.

An inverse finance problem for estimation of the volatility

NASA Astrophysics Data System (ADS)

Neisy, A.; Salmani, K.

2013-01-01

Black-Scholes model, as a base model for pricing in derivatives markets has some deficiencies, such as ignoring market jumps, and considering market volatility as a constant factor. In this article, we introduce a pricing model for European-Options under jump-diffusion underlying asset. Then, using some appropriate numerical methods we try to solve this model with integral term, and terms including derivative. Finally, considering volatility as an unknown parameter, we try to estimate it by using our proposed model. For the purpose of estimating volatility, in this article, we utilize inverse problem, in which inverse problem model is first defined, and then volatility is estimated using minimization function with Tikhonov regularization.

Long-range Li+ dynamics in the lithium argyrodite Li7PSe6 as probed by rotating-frame spin-lattice relaxation NMR.

PubMed

Epp, V; Gün, O; Deiseroth, H-J; Wilkening, M

2013-05-21

Lithium-rich argyrodites belong to a relatively new group of fast ion conducting solids. They might serve as powerful electrolytes in all-solid-state lithium-ion batteries being, from a medium-term point of view, the key technology when safe energy storage systems have to be developed. Spin-lattice relaxation (SLR) nuclear magnetic resonance (NMR) measurements carried out in the rotating frame of reference turned out to be the method of choice to study Li dynamics in argyrodites. When plotted as a function of the inverse temperature, the SLR rates log10(R1ρ) reveal an asymmetric diffusion-induced rate peak. The rate peak contains information on the Li jump rate, the activation energy of the hopping process as well as correlation effects. In particular, considering the high-temperature flank of the SLR NMR rate peak recorded in the rotating frame of reference, an activation energy of approximately 0.49 eV is found. This value represents long-range lithium jump diffusion in crystalline Li7PSe6. As an example, at 325 K the Li jump rate determined from SLR NMR is in the order of 1.4 × 10(5) s(-1). The pronounced asymmetry of the rate peak R1ρ(1/T) points to correlated Li motion. It is comparable to that which is typically found for structurally disordered materials showing a broad range of correlation times.

A comment on Baker et al. 'The time dependence of an atom-vacancy encounter due to the vacancy mechanism of diffusion'

NASA Astrophysics Data System (ADS)

Dasenbrock-Gammon, Nathan; Zacate, Matthew O.

2017-05-01

Baker et al. derived time-dependent expressions for calculating average number of jumps per encounter and displacement probabilities for vacancy diffusion in crystal lattice systems with infinitesimal vacancy concentrations. As shown in this work, their formulation is readily expanded to include finite vacancy concentration, which allows calculation of concentration-dependent, time-averaged quantities. This is useful because it provides a computationally efficient method to express lineshapes of nuclear spectroscopic techniques through the use of stochastic fluctuation models.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dubey, P., E-mail: purushd@barc.gov.in; Sharma, V. K.; Mitra, S.

Synthetic hydroxyapatite (HAp) is an important material in biomedical engineering due to its excellent biocompatibility and bioactivity. Here we report dynamics of cetyltrimethylammonium bromide (CTAB) in HAp composite, prepared by co-precipitation method, as studied by quasielastic neutron scattering (QENS) technique. It is found that the observed dynamics involved two time scales associated with fast torsional motion and segmental motion of the CTAB monomers. In addition to segmental motion of the hydrogen atoms, few undergo torsional motion as well. Torsional dynamics was described by a 2-fold jump diffusion model. The segmental dynamics of CTAB has been described assumimg the hydrogen atomsmore » undergoing diffusion inside a sphere of confined volume. While the diffusivity is found to increase with temperature, the spherical volumes within which the hydrogen atoms are undergoing diffusion remain almost unchanged.« less

Edge Diffusion Flame Propagation and Stabilization Studied

NASA Technical Reports Server (NTRS)

Takahashi, Fumiaki; Katta, Viswanath R.

2004-01-01

In most practical combustion systems or fires, fuel and air are initially unmixed, thus forming diffusion flames. As a result of flame-surface interactions, the diffusion flame often forms an edge, which may attach to burner walls, spread over condensed fuel surfaces, jump to another location through the fuel-air mixture formed, or extinguish by destabilization (blowoff). Flame holding in combustors is necessary to achieve design performance and safe operation of the system. Fires aboard spacecraft behave differently from those on Earth because of the absence of buoyancy in microgravity. This ongoing in-house flame-stability research at the NASA Glenn Research Center is important in spacecraft fire safety and Earth-bound combustion systems.

Differential Microscopic Mobility of Components within a Deep Eutectic Solvent

DOE PAGES

Wagle, Durgesh V.; Baker, Gary A.; Mamontov, Eugene

2015-07-13

From macroscopic measurements of deep eutectic solvents such as glyceline (1:2 molar ratio of choline chloride to glycerol), the long-range translational diffusion of the larger cation (choline) is known to be slower compared to that of the smaller hydrogen bond donor (glycerol). However, when the diffusion dynamics are analyzed on the subnanometer length scale, we discover that the displacements associated with the localized diffusive motions are actually larger for choline. This counterintuitive diffusive behavior can be understood as follows. The localized diffusive motions confined in the transient cage of neighbor particles, which precede the cage-breaking long-range diffusion jumps, are moremore » spatially constrained for glycerol than for choline because of the stronger hydrogen bonds the former makes with chloride anions. The implications of differential localized mobility of the constituents should be especially important for applications where deep eutectic solvents are confined on the nanometer length scale and their long-range translational diffusion is strongly inhibited (e.g., within microporous media).« less

Multidimensional flamelet-generated manifolds for partially premixed combustion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Phuc-Danh; Vervisch, Luc; Subramanian, Vallinayagam

2010-01-15

Flamelet-generated manifolds have been restricted so far to premixed or diffusion flame archetypes, even though the resulting tables have been applied to nonpremixed and partially premixed flame simulations. By using a projection of the full set of mass conservation species balance equations into a restricted subset of the composition space, unsteady multidimensional flamelet governing equations are derived from first principles, under given hypotheses. During the projection, as in usual one-dimensional flamelets, the tangential strain rate of scalar isosurfaces is expressed in the form of the scalar dissipation rates of the control parameters of the multidimensional flamelet-generated manifold (MFM), which ismore » tested in its five-dimensional form for partially premixed combustion, with two composition space directions and three scalar dissipation rates. It is shown that strain-rate-induced effects can hardly be fully neglected in chemistry tabulation of partially premixed combustion, because of fluxes across iso-equivalence-ratio and iso-progress-of-reaction surfaces. This is illustrated by comparing the 5D flamelet-generated manifold with one-dimensional premixed flame and unsteady strained diffusion flame composition space trajectories. The formal links between the asymptotic behavior of MFM and stratified flame, weakly varying partially premixed front, triple-flame, premixed and nonpremixed edge flames are also evidenced. (author)« less

Parsimony and goodness-of-fit in multi-dimensional NMR inversion

NASA Astrophysics Data System (ADS)

Babak, Petro; Kryuchkov, Sergey; Kantzas, Apostolos

2017-01-01

Multi-dimensional nuclear magnetic resonance (NMR) experiments are often used for study of molecular structure and dynamics of matter in core analysis and reservoir evaluation. Industrial applications of multi-dimensional NMR involve a high-dimensional measurement dataset with complicated correlation structure and require rapid and stable inversion algorithms from the time domain to the relaxation rate and/or diffusion domains. In practice, applying existing inverse algorithms with a large number of parameter values leads to an infinite number of solutions with a reasonable fit to the NMR data. The interpretation of such variability of multiple solutions and selection of the most appropriate solution could be a very complex problem. In most cases the characteristics of materials have sparse signatures, and investigators would like to distinguish the most significant relaxation and diffusion values of the materials. To produce an easy to interpret and unique NMR distribution with the finite number of the principal parameter values, we introduce a new method for NMR inversion. The method is constructed based on the trade-off between the conventional goodness-of-fit approach to multivariate data and the principle of parsimony guaranteeing inversion with the least number of parameter values. We suggest performing the inversion of NMR data using the forward stepwise regression selection algorithm. To account for the trade-off between goodness-of-fit and parsimony, the objective function is selected based on Akaike Information Criterion (AIC). The performance of the developed multi-dimensional NMR inversion method and its comparison with conventional methods are illustrated using real data for samples with bitumen, water and clay.

Na Diffusion in Quasi One-Dimensional Ion Conductor NaMn2O4 Observed by μ+SR

NASA Astrophysics Data System (ADS)

Umegaki, Izumi; Nozaki, Hiroshi; Harada, Masashi; Månsson, Martin; Sakurai, Hiroya; Kawasaki, Ikuto; Watanabe, Isao; Sugiyama, Jun

A quasi one-dimensional (1D) compound, NaMn2O4, in which Mn2O4 zigzag chains form a 1D channel along the b-axis and Na ions locate at the center of the channel, is thought to be a good Na ionic conductor. In order to study Na-ion diffusion, we have measured μ+SR spectra using a powder sample in the temperature range between 100 and 500 K. A diffusive behavior was clearly observed above 325 K. Assuming a thermal activate process for jump diffusion of Na-ion between two nearest neighboring sites, a self diffusion coefficient of Na ion (DNa) and its activation energy (Ea) were estimated as DNa = (3.1 ± 0.2) × 10 - 11 cm2/s at 350 K and Ea = 180(9) meV.

Analysis and design of numerical schemes for gas dynamics 1: Artificial diffusion, upwind biasing, limiters and their effect on accuracy and multigrid convergence

NASA Technical Reports Server (NTRS)

Jameson, Antony

1994-01-01

The theory of non-oscillatory scalar schemes is developed in this paper in terms of the local extremum diminishing (LED) principle that maxima should not increase and minima should not decrease. This principle can be used for multi-dimensional problems on both structured and unstructured meshes, while it is equivalent to the total variation diminishing (TVD) principle for one-dimensional problems. A new formulation of symmetric limited positive (SLIP) schemes is presented, which can be generalized to produce schemes with arbitrary high order of accuracy in regions where the solution contains no extrema, and which can also be implemented on multi-dimensional unstructured meshes. Systems of equations lead to waves traveling with distinct speeds and possibly in opposite directions. Alternative treatments using characteristic splitting and scalar diffusive fluxes are examined, together with modification of the scalar diffusion through the addition of pressure differences to the momentum equations to produce full upwinding in supersonic flow. This convective upwind and split pressure (CUSP) scheme exhibits very rapid convergence in multigrid calculations of transonic flow, and provides excellent shock resolution at very high Mach numbers.

Instability-driven interfacial dynamo in protoneutron stars

NASA Astrophysics Data System (ADS)

Mastrano, A.; Melatos, A.

2011-10-01

The existence of a tachocline in the Sun has been proven by helioseismology. It is unknown whether a similar shear layer, widely regarded as the seat of magnetic dynamo action, also exists in a protoneutron star. Sudden jumps in magnetic diffusivity η and turbulent vorticity α, for example at the interface between the neutron-finger and convective zones, are known to be capable of enhancing mean-field dynamo effects in a protoneutron star. Here, we apply the well-known, plane-parallel, MacGregor-Charbonneau analysis of the solar interfacial dynamo to the protoneutron star problem and analytically calculate the growth rate under a range of conditions. It is shown that, like the solar dynamo, it is impossible to achieve self-sustained growth if the discontinuities in α, η and shear are coincident and the magnetic diffusivity is isotropic. In contrast, when the jumps in η and α are situated away from the shear layer, self-sustained growth is possible for P≲ 49.8 ms (if the velocity shear is located at 0.3R) or P≲ 83.6 ms (if the velocity shear is located at 0.6R). This translates into stronger shear and/or α-effect than in the Sun. Self-sustained growth is also possible if the magnetic diffusivity is anisotropic, through the Ω×J effect, even when the α, η and shear discontinuities are coincident.

Effects of configurational changes on molecular dynamics in polyvinylidene fluoride and poly(vinylidene fluoride-trifluoroethylene) ferroelectric polymers

DOE PAGES

Jalarvo, N.; Pramanick, A.; Do, C.; ...

2015-08-28

Here, we present a comparative study of proton dynamics in unpoled non-ferroelectric polymer polyvinylidene fluoride (PVDF) and in its trifluoroethylene containing ferroelectric copolymer (with 70/30 molar proportion), using quasi-elastic neutron scattering. The neutron data reveal the existence of two distinct types of molecular motions in the temperature range investigated. Moreover, the slower motion, which is characterized in details here, is ascribed to protons jump diffusion along the polymeric carbon chains, while the faster motion could be attributed to localized rotational motion of methylene groups. At temperatures below the Curie point (T-c similar to 385 K) of the composite polymer, themore » slower diffusive mode experiences longer relaxation times in the ferroelectric blend than in the bare PVDF, although the net corresponding diffusion coefficient remains comparatively the same in both polymers with characteristic activation energy of E-A approximate to 27-33 kJ/mol. This arises because of a temperature dependent jump length r(0), which we observe to be effectively longer in the copolymer, possibly due to the formation of ordered ferroelectric domains below Tc. Above Tc, there is no appreciable difference in r(0) between the two systems. Our observation directly relates the known dependence of Tc on molar ratio to changes in r(0), providing fundamental insight into the ferroelectric properties of PVDF-based copolymers.« less

Motoneuron membrane potentials follow a time inhomogeneous jump diffusion process.

PubMed

Jahn, Patrick; Berg, Rune W; Hounsgaard, Jørn; Ditlevsen, Susanne

2011-11-01

Stochastic leaky integrate-and-fire models are popular due to their simplicity and statistical tractability. They have been widely applied to gain understanding of the underlying mechanisms for spike timing in neurons, and have served as building blocks for more elaborate models. Especially the Ornstein-Uhlenbeck process is popular to describe the stochastic fluctuations in the membrane potential of a neuron, but also other models like the square-root model or models with a non-linear drift are sometimes applied. Data that can be described by such models have to be stationary and thus, the simple models can only be applied over short time windows. However, experimental data show varying time constants, state dependent noise, a graded firing threshold and time-inhomogeneous input. In the present study we build a jump diffusion model that incorporates these features, and introduce a firing mechanism with a state dependent intensity. In addition, we suggest statistical methods to estimate all unknown quantities and apply these to analyze turtle motoneuron membrane potentials. Finally, simulated and real data are compared and discussed. We find that a square-root diffusion describes the data much better than an Ornstein-Uhlenbeck process with constant diffusion coefficient. Further, the membrane time constant decreases with increasing depolarization, as expected from the increase in synaptic conductance. The network activity, which the neuron is exposed to, can be reasonably estimated to be a threshold version of the nerve output from the network. Moreover, the spiking characteristics are well described by a Poisson spike train with an intensity depending exponentially on the membrane potential.

A stochastic maximum principle for backward control systems with random default time

NASA Astrophysics Data System (ADS)

Shen, Yang; Kuen Siu, Tak

2013-05-01

This paper establishes a necessary and sufficient stochastic maximum principle for backward systems, where the state processes are governed by jump-diffusion backward stochastic differential equations with random default time. An application of the sufficient stochastic maximum principle to an optimal investment and capital injection problem in the presence of default risk is discussed.

Surface diffusion of cyclic hydrocarbons on nickel

NASA Astrophysics Data System (ADS)

Silverwood, I. P.; Armstrong, J.

2018-08-01

Surface diffusion of adsorbates is difficult to measure on realistic systems, yet it is of fundamental interest in catalysis and coating reactions. quasielastic neutron scattering (QENS) was used to investigate the diffusion of cyclohexane and benzene adsorbed on a nickel metal sponge catalyst. Molecular dynamics simulations of benzene on a model (111) nickel surface showed localised motion with diffusion by intermittent jumps. The experimental data was therefore fitted to the Singwi-Sjölander model and activation energies for diffusion of 4.0 kJ mol-1 for benzene and 4.3 kJ mol-1 for cyclohexane were calculated for the two dimensional model. Limited motion out-of plane was seen in the dynamics simulations and is discussed, although the resolution of the scattering experiment is insufficient to quantify this. Good agreement is seen between the use of a perfect crystal as a model for a disordered system over short time scales, suggesting that simple models are adequate to describe diffusion over polycrystalline metal surfaces on the timescale of QENS measurement.

Numerical simulation of multi-dimensional NMR response in tight sandstone

NASA Astrophysics Data System (ADS)

Guo, Jiangfeng; Xie, Ranhong; Zou, Youlong; Ding, Yejiao

2016-06-01

Conventional logging methods have limitations in the evaluation of tight sandstone reservoirs. The multi-dimensional nuclear magnetic resonance (NMR) logging method has the advantage that it can simultaneously measure transverse relaxation time (T 2), longitudinal relaxation time (T 1) and diffusion coefficient (D). In this paper, we simulate NMR measurements of tight sandstone with different wettability and saturations by the random walk method and obtain the magnetization decays of Carr-Purcell-Meiboom-Gill pulse sequences with different wait times (TW) and echo spacings (TE) under a magnetic field gradient, resulting in D-T 2-T 1 maps by the multiple echo trains joint inversion method. We also study the effects of wettability, saturation, signal-to-noise ratio (SNR) of data and restricted diffusion on the D-T 2-T 1 maps in tight sandstone. The results show that with decreasing wetting fluid saturation, the surface relaxation rate of the wetting fluid gradually increases and the restricted diffusion phenomenon becomes more and more obvious, which leads to the wetting fluid signal moving along the direction of short relaxation and the direction of the diffusion coefficient decreasing in D-T 2-T 1 maps. Meanwhile, the non-wetting fluid position in D-T 2-T 1 maps does not change with saturation variation. With decreasing SNR, the ability to identify water and oil signals based on NMR maps gradually decreases. The wetting fluid D-T 1 and D-T 2 correlations in NMR diffusion-relaxation maps of tight sandstone are obtained through expanding the wetting fluid restricted diffusion models, and are further applied to recognize the wetting fluid in simulated D-T 2 maps and D-T 1 maps.

A slow atomic diffusion process in high-entropy glass-forming metallic melts

NASA Astrophysics Data System (ADS)

Chen, Changjiu; Wong, Kaikin; Krishnan, Rithin P.; Embs, Jan P.; Chathoth, Suresh M.

2018-04-01

Quasi-elastic neutron scattering has been used to study atomic relaxation processes in high-entropy glass-forming metallic melts with different glass-forming ability (GFA). The momentum transfer dependence of mean relaxation time shows a highly collective atomic transport process in the alloy melts with the highest and lowest GFA. However, a jump diffusion process is the long-range atomic transport process in the intermediate GFA alloy melt. Nevertheless, atomic mobility close to the melting temperature of these alloy melts is quite similar, and the temperature dependence of the diffusion coefficient exhibits a non-Arrhenius behavior. The atomic mobility in these high-entropy melts is much slower than that of the best glass-forming melts at their respective melting temperatures.

Abundance stratification in the atmospheres of blue horizontal-branch stars

NASA Astrophysics Data System (ADS)

LeBlanc, F.

2013-12-01

Horizontal-branch stars with effective temperatures larger than approximately 11 500 K show abundance anomalies as well as other peculiar observational properties believed to be due to atomic diffusion in their atmosphere. These stars possess low rotational velocities that makes it possible for atomic diffusion to come into play and are therefore of great interest with respect to diffusion theory. Observational anomalies of blue horizontal-branch stars found in globular clusters such as photometric jumps and gaps are reviewed. Recent detections of vertical stratification of elements are also discussed. These results are compared to predictions of atmospheric modeling while including vertical stratification of the elements. The atmospheric structure of these models is calculated self-consistently while taking into account vertical stratification of the elements.

Gradual Crossover from Subdiffusion to Normal Diffusion: A Many-Body Effect in Protein Surface Water

NASA Astrophysics Data System (ADS)

Tan, Pan; Liang, Yihao; Xu, Qin; Mamontov, Eugene; Li, Jinglai; Xing, Xiangjun; Hong, Liang

2018-06-01

Dynamics of hydration water is essential for the function of biomacromolecules. Previous studies have demonstrated that water molecules exhibit subdiffusion on the surface of biomacromolecules; yet the microscopic mechanism remains vague. Here, by performing neutron scattering, molecular dynamics simulations, and analytic modeling on hydrated perdeuterated protein powders, we found water molecules jump randomly between trapping sites on protein surfaces, whose waiting times obey a broad distribution, resulting in subdiffusion. Moreover, the subdiffusive exponent gradually increases with observation time towards normal diffusion due to a many-body volume-exclusion effect.

Strength, Multijoint Coordination, and Sensorimotor Processing Are Independent Contributors to Overall Balance Ability

PubMed Central

Lawrence, Emily L.; Cesar, Guilherme M.; Bromfield, Martha R.; Peterson, Richard; Valero-Cuevas, Francisco J.; Sigward, Susan M.

2015-01-01

For young adults, balance is essential for participation in physical activities but is often disrupted following lower extremity injury. Clinical outcome measures such as single limb balance (SLB), Y-balance (YBT), and the single limb hop and balance (SLHB) tests are commonly used to quantify balance ability following injury. Given the varying demands across tasks, it is likely that such outcome measures provide useful, although task-specific, information. But the extent to which they are independent and contribute to understanding the multiple contributors to balance is not clear. Therefore, the purpose of this study was to investigate the associations among these measures as they relate to the different contributors to balance. Thirty-seven recreationally active young adults completed measures including Vertical Jump, YBT, SLB, SLHB, and the new Lower Extremity Dexterity test. Principal components analysis revealed that these outcome measures could be thought of as quantifying the strength, multijoint coordination, and sensorimotor processing contributors to balance. Our results challenge the practice of using a single outcome measure to quantify the naturally multidimensional mechanisms for everyday functions such as balance. This multidimensional approach to, and interpretation of, multiple contributors to balance may lead to more effective, specialized training and rehabilitation regimens. PMID:26665007

Reconstruction of multidimensional carbon hosts with combined 0D, 1D and 2D networks for enhanced lithium-sulfur batteries

NASA Astrophysics Data System (ADS)

Li, S. H.; Xia, X. H.; Wang, Y. D.; Wang, X. L.; Tu, J. P.

2017-02-01

It is a core task to find solutions to suppress the "shuttle effect" of polysulfides and improve high rate capability at the sulfur cathode of lithium sulfur batteries. Herein we first time propose a concept of multileveled blocking "dams" to suppress the diffusion of polysulfides. We report a facile and effective strategy to construct multidimensional conductive carbon hosts for accommodation of active sulfur. Multidimensional ternary carbon networks (MTCNs) with 0D nanospheres, 1D nanotubes and 2D nanoflakes are organically combined together to provide multileveled conductive channels to reserve active sulfur and promote stable sustained reactions. In the light of enhanced conductivity and multileveled blocking "dams" for polysulfides, the designed MTCNs/S cathode has been demonstrated with noticeable improvement in discharge capacity (1472 mAh g-1 at 0.l C) and long-term cycling stability (65% retention at 5.0 C after 500 cycles). Our research may provide a new insight in the gradient blocking of polysulfides with the help of multidimensional carbon networks.

Site occupation of indium and jump frequencies of cadmium in FeGa 3

NASA Astrophysics Data System (ADS)

Newhouse, Randal; Collins, Gary S.; Zacate, Matthew O.

2016-12-01

Perturbed angular correlation (PAC) measurements using the In-111 probe were carried out on FeGa3 as part of a broader investigation of indium site occupation and cadmium diffusion in intermetallic compounds. One PAC signal was observed with hyperfine parameters ω 1= 513.8(1) Mrad/s and η= 0.939(2) at room temperature. By comparison with quadrupole frequencies observed in PAC measurements on isostructural RuIn3, it was determined that indium occupies only the 8j site in the FeGa3 structure, denoted Ga(2) below because two out of the three Ga sites have this point symmetry. PAC spectra at elevated temperature exhibited damping characteristic of electric field gradients (EFGs) that fluctuate as Cd probes jump among Ga(2) sites within the lifetime of the excited PAC level. A stochastic model for the EFG fluctuations based on four conceivable, single-step jump-pathways connecting one Ga(2) site to neighboring Ga(2) sites was developed and used to fit PAC spectra. The four pathways lead to two observable EFG reorientation rates, and these reorientation rates were found to be strongly dependent on EFG orientation. Calculations using density functional theory were used to reduce the number of unknowns in the model with respect to EFG orientation. This made it possible to determine with reasonable precision the total jump rate of Cd among Ga(2) sites that correspond to a change in mirror plane orientation of site-symmetry. This total jump rate was found to be thermally activated with an activation enthalpy of 1.8 ±0.1 eV.

A multidimensional unified gas-kinetic scheme for radiative transfer equations on unstructured mesh

NASA Astrophysics Data System (ADS)

Sun, Wenjun; Jiang, Song; Xu, Kun

2017-12-01

In order to extend the unified gas kinetic scheme (UGKS) to solve radiative transfer equations in a complex geometry, a multidimensional asymptotic preserving implicit method on unstructured mesh is constructed in this paper. With an implicit formulation, the CFL condition for the determination of the time step in UGKS can be much relaxed, and a large time step is used in simulations. Differently from previous direction-by-direction UGKS on orthogonal structured mesh, on unstructured mesh the interface flux transport takes into account multi-dimensional effect, where gradients of radiation intensity and material temperature in both normal and tangential directions of a cell interface are included in the flux evaluation. The multiple scale nature makes the UGKS be able to capture the solutions in both optically thin and thick regions seamlessly. In the optically thick region the condition of cell size being less than photon's mean free path is fully removed, and the UGKS recovers a solver for diffusion equation in such a limit on unstructured mesh. For a distorted quadrilateral mesh, the UGKS goes to a nine-point scheme for the diffusion equation, and it naturally reduces to the standard five-point scheme for a orthogonal quadrilateral mesh. Numerical computations covering a wide range of transport regimes on unstructured and distorted quadrilateral meshes will be presented to validate the current approach.

Variational calculation of macrostate transition rates

NASA Astrophysics Data System (ADS)

Ulitsky, Alex; Shalloway, David

1998-08-01

We develop the macrostate variational method (MVM) for computing reaction rates of diffusive conformational transitions in multidimensional systems by a variational coarse-grained "macrostate" decomposition of the Smoluchowski equation. MVM uses multidimensional Gaussian packets to identify and focus computational effort on the "transition region," a localized, self-consistently determined region in conformational space positioned roughly between the macrostates. It also determines the "transition direction" which optimally specifies the projected potential of mean force for mean first-passage time calculations. MVM is complementary to variational transition state theory in that it can efficiently solve multidimensional problems but does not accommodate memory-friction effects. It has been tested on model 1- and 2-dimensional potentials and on the 12-dimensional conformational transition between the isoforms of a microcluster of six-atoms having only van der Waals interactions. Comparison with Brownian dynamics calculations shows that MVM obtains equivalent results at a fraction of the computational cost.

Estimating the Diffusion Coefficients of Sugars Using Diffusion Experiments in Agar-Gel and Computer Simulations.

PubMed

Miyamoto, Shuichi; Atsuyama, Kenji; Ekino, Keisuke; Shin, Takashi

2018-01-01

The isolation of useful microbes is one of the traditional approaches for the lead generation in drug discovery. As an effective technique for microbe isolation, we recently developed a multidimensional diffusion-based gradient culture system of microbes. In order to enhance the utility of the system, it is favorable to have diffusion coefficients of nutrients such as sugars in the culture medium beforehand. We have, therefore, built a simple and convenient experimental system that uses agar-gel to observe diffusion. Next, we performed computer simulations-based on random-walk concepts-of the experimental diffusion system and derived correlation formulas that relate observable diffusion data to diffusion coefficients. Finally, we applied these correlation formulas to our experimentally-determined diffusion data to estimate the diffusion coefficients of sugars. Our values for these coefficients agree reasonably well with values published in the literature. The effectiveness of our simple technique, which has elucidated the diffusion coefficients of some molecules which are rarely reported (e.g., galactose, trehalose, and glycerol) is demonstrated by the strong correspondence between the literature values and those obtained in our experiments.

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Zhang, Yongfeng; Jiang, Chao; Bai, Xianming

2017-01-01

This report presents an accelerated kinetic Monte Carlo (KMC) method to compute the diffusivity of hydrogen in hcp metals and alloys, considering both thermally activated hopping and quantum tunneling. The acceleration is achieved by replacing regular KMC jumps in trapping energy basins formed by neighboring tetrahedral interstitial sites, with analytical solutions for basin exiting time and probability. Parameterized by density functional theory (DFT) calculations, the accelerated KMC method is shown to be capable of efficiently calculating hydrogen diffusivity in α-Zr and Zircaloy, without altering the kinetics of long-range diffusion. Above room temperature, hydrogen diffusion in α-Zr and Zircaloy is dominated by thermal hopping, with negligible contribution from quantum tunneling. The diffusivity predicted by this DFT + KMC approach agrees well with that from previous independent experiments and theories, without using any data fitting. The diffusivity along is found to be slightly higher than that along , with the anisotropy saturated at about 1.20 at high temperatures, resolving contradictory results in previous experiments. Demonstrated using hydrogen diffusion in α-Zr, the same method can be extended for on-lattice diffusion in hcp metals, or systems with similar trapping basins.

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

PubMed Central

Zhang, Yongfeng; Jiang, Chao; Bai, Xianming

2017-01-01

This report presents an accelerated kinetic Monte Carlo (KMC) method to compute the diffusivity of hydrogen in hcp metals and alloys, considering both thermally activated hopping and quantum tunneling. The acceleration is achieved by replacing regular KMC jumps in trapping energy basins formed by neighboring tetrahedral interstitial sites, with analytical solutions for basin exiting time and probability. Parameterized by density functional theory (DFT) calculations, the accelerated KMC method is shown to be capable of efficiently calculating hydrogen diffusivity in α-Zr and Zircaloy, without altering the kinetics of long-range diffusion. Above room temperature, hydrogen diffusion in α-Zr and Zircaloy is dominated by thermal hopping, with negligible contribution from quantum tunneling. The diffusivity predicted by this DFT + KMC approach agrees well with that from previous independent experiments and theories, without using any data fitting. The diffusivity along is found to be slightly higher than that along , with the anisotropy saturated at about 1.20 at high temperatures, resolving contradictory results in previous experiments. Demonstrated using hydrogen diffusion in α-Zr, the same method can be extended for on-lattice diffusion in hcp metals, or systems with similar trapping basins. PMID:28106154

Anisotropic hydrogen diffusion in α-Zr and Zircaloy predicted by accelerated kinetic Monte Carlo simulations

DOE PAGES

Zhang, Yongfeng; Jiang, Chao; Bai, Xianming

2017-01-20

Here, this report presents an accelerated kinetic Monte Carlo (KMC) method to compute the diffusivity of hydrogen in hcp metals and alloys, considering both thermally activated hopping and quantum tunneling. The acceleration is achieved by replacing regular KMC jumps in trapping energy basins formed by neighboring tetrahedral interstitial sites, with analytical solutions for basin exiting time and probability. Parameterized by density functional theory (DFT) calculations, the accelerated KMC method is shown to be capable of efficiently calculating hydrogen diffusivity in α-Zr and Zircaloy, without altering the kinetics of long-range diffusion. Above room temperature, hydrogen diffusion in α-Zr and Zircaloy ismore » dominated by thermal hopping, with negligible contribution from quantum tunneling. The diffusivity predicted by this DFT + KMC approach agrees well with that from previous independent experiments and theories, without using any data fitting. The diffusivity along < c > is found to be slightly higher than that along < a >, with the anisotropy saturated at about 1.20 at high temperatures, resolving contradictory results in previous experiments. Demonstrated using hydrogen diffusion in α-Zr, the same method can be extended for on-lattice diffusion in hcp metals, or systems with similar trapping basins.« less

Nanoscopic dynamics in hybrid hydroxyapatite-CTAB composite

NASA Astrophysics Data System (ADS)

Dubey, P. S.; Sharma, V. K.; Mitra, S.; Verma, G.; Hassan, P. A.; Dutta, B.; Johnson, M.; Mukhopadhyay, R.

2017-06-01

Synthetic hydroxyapatite (HAp) is an important material in biomedical engineering due to its excellent biocompatibility and bioactivity. HAp nanoparticles were synthesized by the co-precipitation method using cetyltrimethylammonium bromide (CTAB) micelles as a template and are characterized using x-ray diffraction, electron microscopy, and thermal gravimetric measurements. Transmission electron microscope (TEM) demonstrates the formation of rod-shaped HAp. Dynamics of CTAB in HAp-CTAB composite as studied by using quasielastic neutron scattering (QENS) technique is reported here. HAp-CTAB composite provides an ideal system for studying the dynamics of CTAB micelles without any aqueous media. QENS data indicate that the observed dynamics are reminiscent of localized motions in ionic micellar systems, consisting of segmental and fast torsional motions. Segmental dynamics has been described with a model, in which hydrogen atoms in the alkyl chain undergoes localized translation diffusion and the CH3 unit associated with the head group undergo 3-fold jump rotation. Within this model, the hydrogen atoms in the alkyl chain undergo diffusion within spherical domains having different radii and diffusivities. A simple linear distribution of the radius and diffusivity has been assumed, in which the CH2 unit nearest to the head group has the least value and the ones furthest from the head group, that is, at the end of the alkyl chain has the largest value. The fast torsional motion is described by a 2-fold jump rotation model. Quantitative estimate of the different parameters characterizing various dynamical motions active within the time scale of the instrument is also presented. We have provided a detailed description of the observed dynamical features in hybrid HAp-CTAB composite, a potential candidate for biomedical applications.

Continuous-time random-walk model for anomalous diffusion in expanding media

NASA Astrophysics Data System (ADS)

Le Vot, F.; Abad, E.; Yuste, S. B.

2017-09-01

Expanding media are typical in many different fields, e.g., in biology and cosmology. In general, a medium expansion (contraction) brings about dramatic changes in the behavior of diffusive transport properties such as the set of positional moments and the Green's function. Here, we focus on the characterization of such effects when the diffusion process is described by the continuous-time random-walk (CTRW) model. As is well known, when the medium is static this model yields anomalous diffusion for a proper choice of the probability density function (pdf) for the jump length and the waiting time, but the behavior may change drastically if a medium expansion is superimposed on the intrinsic random motion of the diffusing particle. For the case where the jump length and the waiting time pdfs are long-tailed, we derive a general bifractional diffusion equation which reduces to a normal diffusion equation in the appropriate limit. We then study some particular cases of interest, including Lévy flights and subdiffusive CTRWs. In the former case, we find an analytical exact solution for the Green's function (propagator). When the expansion is sufficiently fast, the contribution of the diffusive transport becomes irrelevant at long times and the propagator tends to a stationary profile in the comoving reference frame. In contrast, for a contracting medium a competition between the spreading effect of diffusion and the concentrating effect of contraction arises. In the specific case of a subdiffusive CTRW in an exponentially contracting medium, the latter effect prevails for sufficiently long times, and all the particles are eventually localized at a single point in physical space. This "big crunch" effect, totally absent in the case of normal diffusion, stems from inefficient particle spreading due to subdiffusion. We also derive a hierarchy of differential equations for the moments of the transport process described by the subdiffusive CTRW model in an expanding medium. From this hierarchy, the full time evolution of the second-order moment is obtained for some specific types of expansion. In the case of an exponential expansion, exact recurrence relations for the Laplace-transformed moments are obtained, whence the long-time behavior of moments of arbitrary order is subsequently inferred. Our analytical and numerical results for both Lévy flights and subdiffusive CTRWs confirm the intuitive expectation that the medium expansion hinders the mixing of diffusive particles occupying separate regions. In the case of Lévy flights, we quantify this effect by means of the so-called "Lévy horizon."

Continuous-time random-walk model for anomalous diffusion in expanding media.

PubMed

Le Vot, F; Abad, E; Yuste, S B

2017-09-01

Expanding media are typical in many different fields, e.g., in biology and cosmology. In general, a medium expansion (contraction) brings about dramatic changes in the behavior of diffusive transport properties such as the set of positional moments and the Green's function. Here, we focus on the characterization of such effects when the diffusion process is described by the continuous-time random-walk (CTRW) model. As is well known, when the medium is static this model yields anomalous diffusion for a proper choice of the probability density function (pdf) for the jump length and the waiting time, but the behavior may change drastically if a medium expansion is superimposed on the intrinsic random motion of the diffusing particle. For the case where the jump length and the waiting time pdfs are long-tailed, we derive a general bifractional diffusion equation which reduces to a normal diffusion equation in the appropriate limit. We then study some particular cases of interest, including Lévy flights and subdiffusive CTRWs. In the former case, we find an analytical exact solution for the Green's function (propagator). When the expansion is sufficiently fast, the contribution of the diffusive transport becomes irrelevant at long times and the propagator tends to a stationary profile in the comoving reference frame. In contrast, for a contracting medium a competition between the spreading effect of diffusion and the concentrating effect of contraction arises. In the specific case of a subdiffusive CTRW in an exponentially contracting medium, the latter effect prevails for sufficiently long times, and all the particles are eventually localized at a single point in physical space. This "big crunch" effect, totally absent in the case of normal diffusion, stems from inefficient particle spreading due to subdiffusion. We also derive a hierarchy of differential equations for the moments of the transport process described by the subdiffusive CTRW model in an expanding medium. From this hierarchy, the full time evolution of the second-order moment is obtained for some specific types of expansion. In the case of an exponential expansion, exact recurrence relations for the Laplace-transformed moments are obtained, whence the long-time behavior of moments of arbitrary order is subsequently inferred. Our analytical and numerical results for both Lévy flights and subdiffusive CTRWs confirm the intuitive expectation that the medium expansion hinders the mixing of diffusive particles occupying separate regions. In the case of Lévy flights, we quantify this effect by means of the so-called "Lévy horizon."

Dynamics of oxygen species on reduced TiO2 (110) rutile

NASA Astrophysics Data System (ADS)

Wang, Yun; Pillay, Devina; Hwang, Gyeong S.

2004-11-01

Using density functional theory calculations, we have investigated the adsorption and diffusion of oxygen species on the reduced TiO2(110) surface. We have found that molecular O2 strongly binds not only to O vacancies, but also to Ti(5c) neighbors, due to delocalization of unpaired electrons arising from removal of neutral bridging oxygen. Our results show that molecular O2 can jump across an oxygen vacancy and diffuse along a Ti(5c) row with moderate barriers. On the other hand, atomic O diffusion along a Ti(5c) row is rather unlikely at low temperatures (<300K) , because of the relatively higher probability of O-O formation from interaction with an adjacent bridging O(2c) atom. Based on our calculation results, we discuss the diffusion and healing of O vacancies associated with O2 adsorption.

Light-induced spatial control of pH-jump reaction at smart gel interface.

PubMed

Techawanitchai, Prapatsorn; Ebara, Mitsuhiro; Idota, Naokazu; Aoyagi, Takao

2012-11-01

We proposed here a 'smart' control of an interface movement of proton diffusion in temperature- and pH-responsive hydrogels using a light-induced spatial pH-jump reaction. A photoinitiated proton-releasing reaction of o-nitrobenzaldehyde (NBA) was integrated into poly(N-isopropylacrylamide-o-2-carboxyisopropylacrylamide) (P(NIPAAm-co-CIPAAm)) hydrogels. NBA-integrated hydrogels demonstrated quick release of proton upon UV irradiation, allowing the pH inside the gel to decrease below the pK(a) of P(NIPAAm-co-CIPAAm) within a minute. The NBA-integrated gel was shown to shrink rapidly upon UV irradiation without polymer "skin layer" formation due to a uniform decrease of pH inside the gel. Spatial control of gel shrinking was also created by irradiating UV light to a limited region of the gel through a photomask. The interface of proton diffusion ("active interface") gradually moved toward non-illuminated area. The apparent position of "active interface", however, did not change remarkably above the LCST, while protons continuously diffused outward direction. This is because the "active interface" also moved inward direction as gel shrank above the LCST. As a result, slow movement of the apparent interface was observed. The NBA-integrated gel was also successfully employed for the controlled release of an entrapped dextran in a light controlled manner. This system is highly promising as smart platforms for triggered and programmed transportation of drugs. Copyright © 2011 Elsevier B.V. All rights reserved.

Calorimetric and Neutron Scattering Studies on Glass Transitions and Ionic Diffusions in Imidazolium-based Ionic Liquids

NASA Astrophysics Data System (ADS)

Yamamuro, O.; Kofu, M.

2017-05-01

Glass transition is one of the central research issues of ionic liquids (ILs). In particular, the most typical ILs, imidazolium-basedones (ImILs) are readily supercooled and exhibit glass transitions below room temperature. We have measured the heat capacities of several ImILs, encoded as CnmimX (n: alkyl carbon number, n = 2-8, X: anion, X = Cl, I, FeCl4, TFSI) using an adiabatic calorimeter. We found that most of ImILs exhibit glass transitions with large Cp jumps in a temperature range between 170 K and 230 K. The large Cp jumps reflect that these ILs are fragile liquids that exhibit large structural change depending on temperature near the glass transition temperature T g. It is also revealed that T g does not depend much on n but on the anion radius. We have investigated the dynamics of CnmimX (n = 2-8, X = Cl, NO3, PF6, TF, FSI, TFSI) by means of a quasielastic neutron scattering (QENS) technique. It was clarified that the ionic diffusion is directly associated with the viscosity and glass transition. The activation energy ΔE a of the ionic diffusion increases with decreasing anion size but remains almost unchanged with n as found for T g. These systematic change of T g and ΔE a can be explained well by taking account the nano-domain structure which is the most characteristic feature of ImILs.

Effects of configurational changes on molecular dynamics in polyvinylidene fluoride and poly(vinylidene fluoride-trifluoroethylene) ferroelectric polymers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jalarvo, N., E-mail: jalarvonh@ornl.gov, E-mail: abhijit.pramanick@gmail.com, E-mail: omardiallos@ornl.gov; Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831; Pramanick, A., E-mail: jalarvonh@ornl.gov, E-mail: abhijit.pramanick@gmail.com, E-mail: omardiallos@ornl.gov

2015-08-24

We present a comparative study of proton dynamics in unpoled non-ferroelectric polymer polyvinylidene fluoride (PVDF) and in its trifluoroethylene containing ferroelectric copolymer (with 70/30 molar proportion), using quasi-elastic neutron scattering. The neutron data reveal the existence of two distinct types of molecular motions in the temperature range investigated. The slower motion, which is characterized in details here, is ascribed to protons jump diffusion along the polymeric carbon chains, while the faster motion could be attributed to localized rotational motion of methylene groups. At temperatures below the Curie point (T{sub c} ∼ 385 K) of the composite polymer, the slower diffusive mode experiences longermore » relaxation times in the ferroelectric blend than in the bare PVDF, although the net corresponding diffusion coefficient remains comparatively the same in both polymers with characteristic activation energy of E{sub A} ≈ 27–33 kJ/mol. This arises because of a temperature dependent jump length r{sub 0}, which we observe to be effectively longer in the copolymer, possibly due to the formation of ordered ferroelectric domains below T{sub c}. Above T{sub c}, there is no appreciable difference in r{sub 0} between the two systems. This observation directly relates the known dependence of T{sub c} on molar ratio to changes in r{sub 0}, providing fundamental insight into the ferroelectric properties of PVDF-based copolymers.« less

The Stability and Structure of Lean Hydrogen-Air Flames: Effects of Gravity

DTIC Science & Technology

1990-05-17

INTRODUCTION ................................................................................................. 1 MULTIDIMENSIONAL FLAME MODEL ...combustion, molecular diffusion between the reactants, intermediates, and products, thermal conduction, convection, and gravity. Such a detailed model allows...instabil- ity, generally called the Rayleigh-Taylor instability5 . A numerical model of the premixed hydrogen flame that includes all the physical

Kinetics of phloretin binding to phosphatidylcholine vesicle membranes

PubMed Central

1980-01-01

The submillisecond kinetics for phloretin binding to unilamellar phosphatidylcholine (PC) vesicles was investigated using the temperature-jump technique. Spectrophotometric studies of the equilibrium binding performed at 328 nm demonstrated that phloretin binds to a single set of independent, equivalent sites on the vesicle with a dissociation constant of 8.0 microM and a lipid/site ratio of 4.0. The temperature of the phloretin-vesicle solution was jumped by 4 degrees C within 4 microseconds producing a monoexponential, concentration-dependent relaxation process with time constants in the 30--200-microseconds time range. An analysis of the concentration dependence of relaxation time constants at pH 7.30 and 24 degrees C yielded a binding rate constant of 2.7 X 10(8) M-1 s-1 and an unbinding constant of 2,900 s-1; approximately 66 percent of total binding sites are exposed at the outer vesicle surface. The value of the binding rate constant and three additional observations suggest that the binding kinetics are diffusion limited. The phloretin analogue, naringenin, which has a diffusion coefficient similar to phloretin yet a dissociation constant equal to 24 microM, bound to PC vesicle with the same rate constant as phloretin did. In addition, the phloretin-PC system was studied in buffers made one to six times more viscous than water by addition of sucrose or glycerol to the differ. The equilibrium affinity for phloretin binding to PC vesicles is independent of viscosity, yet the binding rate constant decreases with the expected dependence (kappa binding alpha 1/viscosity) for diffusion-limited processes. Thus, the binding rate constant is not altered by differences in binding affinity, yet depends upon the diffusion coefficient in buffer. Finally, studies of the pH dependence of the binding rate constant showed a dependence (kappa binding alpha [1 + 10pH-pK]) consistent with the diffusion-limited binding of a weak acid. PMID:7391812

The Hot Horizontal-Branch Stars in NGC288 - Effects of Diffusion and Stratification on Their Atmospheric Parameters*

NASA Technical Reports Server (NTRS)

Moehler, S.; Dreizler, S.; LeBlanc, F.; Khalack, V.; Michaud, G.; Richer, J.; Sweigart, Allen V.; Grundahl, F.

2014-01-01

Context. NGC288 is a globular cluster with a well developed blue horizontal branch covering the so-called u-jump which indicates the onset of diffusion. It is therefore well suited to study the effects of diffusion in blue horizontal branch (HB) stars. Aims. We compare observed abundances to predictions from stellar evolution models calculated with diffusion and from stratified atmospheric models. We verify the effect of using stratified model spectra to derive atmospheric parameters. In addition we investigate the nature of the overluminous blue HB stars around the u-jump. Methods. We define a new photometric index sz from uvby measurements that is gravity sensitive between 8 000K and 12 000 K. Using medium-resolution spectra and Stroemgren photometry we determine atmospheric parameters (Teff, logg) and abundances for the blue HB stars. We use both homogeneous and stratified model spectra for our spectroscopic analyses. Results. The atmospheric parameters and masses of the hot HB stars in NGC288 show a behaviour seen also in other clusters for temperatures between 9 000K and 14 000 K. Outside this temperature range, however, they follow rather the results found for such stars in (omega)Cen. The abundances derived from our observations are for most elements (except He and P) within the abundance range expected from evolutionary models that include the effects of atomic diffusion and assume a surface mixed mass of 10(exp -7) M. The abundances predicted by stratified model atmospheres are generally significantly more extreme than observed, except for Mg. The use of stratified model spectra to determine effective temperatures, surface gravities and masses moves the hotter stars to a closer agreement with canonical evolutionary predictions. Conclusions. Our results show definite promise towards solving the long-standing issue of surface gravity and mass discrepancies for hot HB stars, but there is still much work needed to arrive at a self-consistent solution.

Wave reflection in a reaction-diffusion system: breathing patterns and attenuation of the echo.

PubMed

Tsyganov, M A; Ivanitsky, G R; Zemskov, E P

2014-05-01

Formation and interaction of the one-dimensional excitation waves in a reaction-diffusion system with the piecewise linear reaction functions of the Tonnelier-Gerstner type are studied. We show that there exists a parameter region where the established regime of wave propagation depends on initial conditions. Wave phenomena with a complex behavior are found: (i) the reflection of waves at a growing distance (the remote reflection) upon their collision with each other or with no-flux boundaries and (ii) the periodic transformation of waves with the jumping from one regime of wave propagation to another (the periodic trigger wave).

Wave reflection in a reaction-diffusion system: Breathing patterns and attenuation of the echo

NASA Astrophysics Data System (ADS)

Tsyganov, M. A.; Ivanitsky, G. R.; Zemskov, E. P.

2014-05-01

Formation and interaction of the one-dimensional excitation waves in a reaction-diffusion system with the piecewise linear reaction functions of the Tonnelier-Gerstner type are studied. We show that there exists a parameter region where the established regime of wave propagation depends on initial conditions. Wave phenomena with a complex behavior are found: (i) the reflection of waves at a growing distance (the remote reflection) upon their collision with each other or with no-flux boundaries and (ii) the periodic transformation of waves with the jumping from one regime of wave propagation to another (the periodic trigger wave).

American option pricing in Gauss-Markov interest rate models

NASA Astrophysics Data System (ADS)

Galluccio, Stefano

1999-07-01

In the context of Gaussian non-homogeneous interest-rate models, we study the problem of American bond option pricing. In particular, we show how to efficiently compute the exercise boundary in these models in order to decompose the price as a sum of a European option and an American premium. Generalizations to coupon-bearing bonds and jump-diffusion processes for the interest rates are also discussed.

Cusping, transport and variance of solutions to generalized Fokker-Planck equations

NASA Astrophysics Data System (ADS)

Carnaffan, Sean; Kawai, Reiichiro

2017-06-01

We study properties of solutions to generalized Fokker-Planck equations through the lens of the probability density functions of anomalous diffusion processes. In particular, we examine solutions in terms of their cusping, travelling wave behaviours, and variance, within the framework of stochastic representations of generalized Fokker-Planck equations. We give our analysis in the cases of anomalous diffusion driven by the inverses of the stable, tempered stable and gamma subordinators, demonstrating the impact of changing the distribution of waiting times in the underlying anomalous diffusion model. We also analyse the cases where the underlying anomalous diffusion contains a Lévy jump component in the parent process, and when a diffusion process is time changed by an uninverted Lévy subordinator. On the whole, we present a combination of four criteria which serve as a theoretical basis for model selection, statistical inference and predictions for physical experiments on anomalously diffusing systems. We discuss possible applications in physical experiments, including, with reference to specific examples, the potential for model misclassification and how combinations of our four criteria may be used to overcome this issue.

Fractional Diffusion Processes: Probability Distributions and Continuous Time Random Walk

NASA Astrophysics Data System (ADS)

Gorenflo, R.; Mainardi, F.

A physical-mathematical approach to anomalous diffusion may be based on generalized diffusion equations (containing derivatives of fractional order in space or/and time) and related random walk models. By the space-time fractional diffusion equation we mean an evolution equation obtained from the standard linear diffusion equation by replacing the second-order space derivative with a Riesz-Feller derivative of order alpha in (0,2] and skewness theta (\\verttheta\\vertlemin \\{alpha ,2-alpha \\}), and the first-order time derivative with a Caputo derivative of order beta in (0,1] . The fundamental solution (for the Cauchy problem) of the fractional diffusion equation can be interpreted as a probability density evolving in time of a peculiar self-similar stochastic process. We view it as a generalized diffusion process that we call fractional diffusion process, and present an integral representation of the fundamental solution. A more general approach to anomalous diffusion is however known to be provided by the master equation for a continuous time random walk (CTRW). We show how this equation reduces to our fractional diffusion equation by a properly scaled passage to the limit of compressed waiting times and jump widths. Finally, we describe a method of simulation and display (via graphics) results of a few numerical case studies.

Large-amplitude jumps and non-Gaussian dynamics in highly concentrated hard sphere fluids.

PubMed

Saltzman, Erica J; Schweizer, Kenneth S

2008-05-01

Our microscopic stochastic nonlinear Langevin equation theory of activated dynamics has been employed to study the real-space van Hove function of dense hard sphere fluids and suspensions. At very short times, the van Hove function is a narrow Gaussian. At sufficiently high volume fractions, such that the entropic barrier to relaxation is greater than the thermal energy, its functional form evolves with time to include a rapidly decaying component at small displacements and a long-range exponential tail. The "jump" or decay length scale associated with the tail increases with time (or particle root-mean-square displacement) at fixed volume fraction, and with volume fraction at the mean alpha relaxation time. The jump length at the alpha relaxation time is predicted to be proportional to a measure of the decoupling of self-diffusion and structural relaxation. At long times corresponding to mean displacements of order a particle diameter, the volume fraction dependence of the decay length disappears. A good superposition of the exponential tail feature based on the jump length as a scaling variable is predicted at high volume fractions. Overall, the theoretical results are in good accord with recent simulations and experiments. The basic aspects of the theory are also compared with a classic jump model and a dynamically facilitated continuous time random-walk model. Decoupling of the time scales of different parts of the relaxation process predicted by the theory is qualitatively similar to facilitated dynamics models based on the concept of persistence and exchange times if the elementary event is assumed to be associated with transport on a length scale significantly smaller than the particle size.

Asymptotic analysis of dissipative waves with applications to their numerical simulation

NASA Technical Reports Server (NTRS)

Hagstrom, Thomas

1990-01-01

Various problems involving the interplay of asymptotics and numerics in the analysis of wave propagation in dissipative systems are studied. A general approach to the asymptotic analysis of linear, dissipative waves is developed. It was applied to the derivation of asymptotic boundary conditions for numerical solutions on unbounded domains. Applications include the Navier-Stokes equations. Multidimensional traveling wave solutions to reaction-diffusion equations are also considered. A preliminary numerical investigation of a thermo-diffusive model of flame propagation in a channel with heat loss at the walls is presented.

On Multi-Dimensional Unstructured Mesh Adaption

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1999-01-01

Anisotropic unstructured mesh adaption is developed for a truly multi-dimensional upwind fluctuation splitting scheme, as applied to scalar advection-diffusion. The adaption is performed locally using edge swapping, point insertion/deletion, and nodal displacements. Comparisons are made versus the current state of the art for aggressive anisotropic unstructured adaption, which is based on a posteriori error estimates. Demonstration of both schemes to model problems, with features representative of compressible gas dynamics, show the present method to be superior to the a posteriori adaption for linear advection. The performance of the two methods is more similar when applied to nonlinear advection, with a difference in the treatment of shocks. The a posteriori adaption can excessively cluster points to a shock, while the present multi-dimensional scheme tends to merely align with a shock, using fewer nodes. As a consequence of this alignment tendency, an implementation of eigenvalue limiting for the suppression of expansion shocks is developed for the multi-dimensional distribution scheme. The differences in the treatment of shocks by the adaption schemes, along with the inherently low levels of artificial dissipation in the fluctuation splitting solver, suggest the present method is a strong candidate for applications to compressible gas dynamics.

Detailed Multidimensional Simulations of the Structure and Dynamics of Flames

NASA Technical Reports Server (NTRS)

Patnaik, G.; Kailasanath, K.

1999-01-01

Numerical simulations in which the various physical and chemical processes can be independently controlled can significantly advance our understanding of the structure, stability, dynamics and extinction of flames. Therefore, our approach has been to use detailed time-dependent, multidimensional, multispecies numerical models to perform carefully designed computational experiments of flames on Earth and in microgravity environments. Some of these computational experiments are complementary to physical experiments performed under the Microgravity Program while others provide a fundamental understanding that cannot be obtained from physical experiments alone. In this report, we provide a brief summary of our recent research highlighting the contributions since the previous microgravity combustion workshop. There are a number of mechanisms that can cause flame instabilities and result in the formation of dynamic multidimensional structures. In the past, we have used numerical simulations to show that it is the thermo-diffusive instability rather than an instability due to preferential diffusion that is the dominant mechanism for the formation of cellular flames in lean hydrogen-air mixtures. Other studies have explored the role of gravity on flame dynamics and extinguishment, multi-step kinetics and radiative losses on flame instabilities in rich hydrogen-air flames, and heat losses on burner-stabilized flames in microgravity. The recent emphasis of our work has been on exploring flame-vortex interactions and further investigating the structure and dynamics of lean hydrogen-air flames in microgravity. These topics are briefly discussed after a brief discussion of our computational approach for solving these problems.

Hot Horizontal-Branch Stars: The Ubiquitous Nature of the ``Jump'' in Strömgren u, Low Gravities, and the Role of Radiative Levitation of Metals

NASA Astrophysics Data System (ADS)

Grundahl, F.; Catelan, M.; Landsman, W. B.; Stetson, P. B.; Andersen, M. I.

1999-10-01

A ``jump'' in the blue horizontal-branch (HB) distribution in the (V, u-y) color-magnitude diagram has recently been detected in the globular cluster (GC) M13 (NGC 6205) by Grundahl and coworkers. Such an effect is morphologically best characterized as a discontinuity in the (u, u-y) locus, with stars in the range 11,500 K<~Teff<~20,000 K deviating systematically from (in the sense of appearing brighter and/or hotter than) canonical zero-age HB models. In this article, we present Strömgren u, y photometry of 14 GCs obtained with three different telescopes (ESO Danish, Nordic Optical Telescope, and the Hubble Space Telescope) and demonstrate that the jump in Strömgren u is present in every GC whose HB extends beyond Teff>~11,500 K, irrespective of metallicity, mixing history on the red giant branch (RGB), or any known parameter characterizing our sample of GCs. We thus suggest that the u jump is a ubiquitous feature, intrinsic to all HB stars hotter than Teff~=11,500 K. We draw a parallel between the ubiquitous nature of the u jump and the well-known problem of low measured gravities among blue HB stars in GCs and in the field. We note that the ``gravity jump'' occurs over the same temperature range as the u jump and also that it occurs in every metal-poor cluster for which gravities have been determined--again irrespective of metallicity, mixing history on the RGB, or any known parameter characterizing the surveyed GCs. Furthermore, we demonstrate that the u jump and the gravity jump are connected on a star-by-star basis. We thus suggest that the two most likely are different manifestations of one and the same physical phenomenon. We present an interpretative framework which may be capable of simultaneously accounting for both the u jump and the gravity jump. Reviewing spectroscopic data for several field blue HB stars, as well as two blue HB stars in NGC 6752, we find evidence that radiative levitation of elements heavier than carbon and nitrogen takes place at Teff>~11,500 K, dramatically enhancing the abundances of such heavy elements in the atmospheres of blue HB stars in the ``critical'' temperature region. We argue that model atmospheres which take diffusion effects into account are badly needed and will likely lead to better overall agreement between canonical evolutionary theory and the observations for these stars. Based on observations made with the NOT, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations obtained with the Danish 1.5 m telescope at the European Southern Observatory, La Silla, Chile.

Accelerating population balance-Monte Carlo simulation for coagulation dynamics from the Markov jump model, stochastic algorithm and GPU parallel computing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Zuwei; Zhao, Haibo, E-mail: klinsmannzhb@163.com; Zheng, Chuguang

2015-01-15

This paper proposes a comprehensive framework for accelerating population balance-Monte Carlo (PBMC) simulation of particle coagulation dynamics. By combining Markov jump model, weighted majorant kernel and GPU (graphics processing unit) parallel computing, a significant gain in computational efficiency is achieved. The Markov jump model constructs a coagulation-rule matrix of differentially-weighted simulation particles, so as to capture the time evolution of particle size distribution with low statistical noise over the full size range and as far as possible to reduce the number of time loopings. Here three coagulation rules are highlighted and it is found that constructing appropriate coagulation rule providesmore » a route to attain the compromise between accuracy and cost of PBMC methods. Further, in order to avoid double looping over all simulation particles when considering the two-particle events (typically, particle coagulation), the weighted majorant kernel is introduced to estimate the maximum coagulation rates being used for acceptance–rejection processes by single-looping over all particles, and meanwhile the mean time-step of coagulation event is estimated by summing the coagulation kernels of rejected and accepted particle pairs. The computational load of these fast differentially-weighted PBMC simulations (based on the Markov jump model) is reduced greatly to be proportional to the number of simulation particles in a zero-dimensional system (single cell). Finally, for a spatially inhomogeneous multi-dimensional (multi-cell) simulation, the proposed fast PBMC is performed in each cell, and multiple cells are parallel processed by multi-cores on a GPU that can implement the massively threaded data-parallel tasks to obtain remarkable speedup ratio (comparing with CPU computation, the speedup ratio of GPU parallel computing is as high as 200 in a case of 100 cells with 10 000 simulation particles per cell). These accelerating approaches of PBMC are demonstrated in a physically realistic Brownian coagulation case. The computational accuracy is validated with benchmark solution of discrete-sectional method. The simulation results show that the comprehensive approach can attain very favorable improvement in cost without sacrificing computational accuracy.« less

A fast semi-discrete Kansa method to solve the two-dimensional spatiotemporal fractional diffusion equation

NASA Astrophysics Data System (ADS)

Sun, HongGuang; Liu, Xiaoting; Zhang, Yong; Pang, Guofei; Garrard, Rhiannon

2017-09-01

Fractional-order diffusion equations (FDEs) extend classical diffusion equations by quantifying anomalous diffusion frequently observed in heterogeneous media. Real-world diffusion can be multi-dimensional, requiring efficient numerical solvers that can handle long-term memory embedded in mass transport. To address this challenge, a semi-discrete Kansa method is developed to approximate the two-dimensional spatiotemporal FDE, where the Kansa approach first discretizes the FDE, then the Gauss-Jacobi quadrature rule solves the corresponding matrix, and finally the Mittag-Leffler function provides an analytical solution for the resultant time-fractional ordinary differential equation. Numerical experiments are then conducted to check how the accuracy and convergence rate of the numerical solution are affected by the distribution mode and number of spatial discretization nodes. Applications further show that the numerical method can efficiently solve two-dimensional spatiotemporal FDE models with either a continuous or discrete mixing measure. Hence this study provides an efficient and fast computational method for modeling super-diffusive, sub-diffusive, and mixed diffusive processes in large, two-dimensional domains with irregular shapes.

A first-principles study of elastic and diffusion properties of magnesium based alloys

NASA Astrophysics Data System (ADS)

Ganeshan, Swetha

2011-12-01

In this thesis, the influence of alloying elements on the elastic and diffusion properties of Magnesium (Mg) has been studied based on first-principles density functional theory. The stress-strain method has been used to predict the elastic constants of the Mg based alloys studied herein. This method involves calculating the resultant change in stress due to application of strain. The validity of this method has been successfully tested for both 0K as well as at finite temperatures. The elastic constants predicted in this work have been correlated to ductility, fracture toughness, stiffness, elastic anisotropy and bond directionality, thus providing a better understanding of the influence of alloying elements on the mechanical and physical properties of Mg. Elastic constants, as a function of temperature have been predicted using first-principles quasi-static approximation. In this approach elastic stiffness coefficients calculated with respect to volume (cij( V)) have been correlated to the equilibrium volume as a function of temperature V(T) from phonon calculations to obtain temperature dependence of elastic stiffness coefficients cij(T). To compare our calculated temperature dependent elastic constants with that of experiments an isentropic correction term has been introduced. It is seen that the influence of this isentropic correction term on the elastic constants becomes significant at high temperatures. The quasi-static approximation has been primarily applied to calculate temperature dependent elastic constants of Mg2Ge, Mg2Si, Mg 2Sn and Mg2Pb. In the case of dilute Mg alloys, a 36 atom supercell with 35 atoms of Mg and one atom of the alloying impurity has been used for calculating the corresponding elastic constants. It is seen that there is a direct correspondence between the trends in the elastic constants and the lattice parameters of all the Mg based alloys studied herein. Elements that cause a decrease (increase) in the lattice constants result in an increase (decrease) in the bulk modulus. Self-diffusion calculations of Mg have been performed within both LDA and GGA. It is seen that, in the absence of surface corrections, while results of the two approximations (i.e. LDA and GGA) bound experimental data, better agreement is seen with respect to results from LDA, in comparison with experimental measurements. The effect of thermal expansion on the diffusivity of Mg has been studied using both HA and QHA. It is seen that the influence of anharmonicity on the diffusivity of Mg is negligible. Self-diffusion of Mg is faster in the basal plane than between adjacent basal planes. Partial correlation factors corresponding to the diffusion of a Mg atom from one basal plane to the adjacent basal plane, i.e. fBx and fBz, decrease with temperature whereas the partial correlation factor corresponding to the diffusion of Mg atom within the basal plane, i.e. fAx , increases with temperature. The ratio of jump frequencies w⊥/w∥ for self-diffusion of Mg increase with increase in temperature. The method used to calculate self-diffusion coefficients has been extended to compute impurity diffusion coefficients of Al, Ca, Sn and Zn in Mg. For these calculations, a 36 atom supercell with 1 vacant site and 1 impurity has been used. The 8-frequencey model has been implemented to obtain the different atom jump frequencies in order to calculate impurity diffusion coefficients in Mg. The trend in the impurity diffusion coefficients, with the exception of DZn-Mg is as follows: D Mg-Ca>DMg>DMg-Sn> DMg-Al. For impurity diffusion of Zn in Mg, at high temperatures DMg-Zn overlaps with that of DMg-Al , while at low temperatures it overlaps with that of D Mg-Sn. The different atom jump frequencies computed during the diffusion calculations are seen to be temperature dependent, increasing with increase in temperature. The correlation factors for all the alloy systems considered herein, is close to 1. This is expected to be due to the close packing of Mg lattice. (Abstract shortened by UMI.)

Measuring internal friction of an ultrafast-folding protein.

PubMed

Cellmer, Troy; Henry, Eric R; Hofrichter, James; Eaton, William A

2008-11-25

Nanosecond laser T-jump was used to measure the viscosity dependence of the folding kinetics of the villin subdomain under conditions where the viscogen has no effect on its equilibrium properties. The dependence of the unfolding/refolding relaxation time on solvent viscosity indicates a major contribution to the dynamics from internal friction. The internal friction increases with increasing temperature, suggesting a shift in the transition state along the reaction coordinate toward the native state with more compact structures, and therefore, a smaller diffusion coefficient due to increased landscape roughness. Fitting the data with an Ising-like model yields a relatively small position dependence for the diffusion coefficient. This finding is consistent with the excellent correlation found between experimental and calculated folding rates based on free energy barrier heights using the same diffusion coefficient for every protein.

Composite Ceramic Superconducting Wires for Electric Motor Applications

DTIC Science & Technology

1989-07-07

generators that have been built using NbTi superconducting wire at liquid 3 helium temperature (4.2*K). Most of these magnets , motors, and generators have...temperature superconductors. A magnetic diffusivity value cannot be rigorously determined for the superconductor in the superconducting state when flux jump...cv, FIRST ANNUAL REPORT FOR THE PROJECT "COMPOSITE CERAMIC SUPERCONDUCTING WIRES FOR ELECTRIC MOTOR APPLICATIONS" 2 PRIME CONTRACTOR CERAMICS PROCESS

Dynamic Decision Making under Uncertainty and Partial Information

DTIC Science & Technology

2013-11-14

integral under the natural filtration generated by the Brownian motions . This compact expression potentially enables us to design sub- optimal penalties...bounds on bermudan option price under jump diffusion processes. Quantitative Finance , 2013. Under review, available at http://arxiv.org/abs/1305.4321... Finance , 19:53 – 71, 2009. [3] D.P. Bertsekas. Dynamic Programming and Optimal Control. Athena Scientific, 4th edition, 2012. [4] D.B. Brown and J.E

Lévy processes on a generalized fractal comb

NASA Astrophysics Data System (ADS)

Sandev, Trifce; Iomin, Alexander; Méndez, Vicenç

2016-09-01

Comb geometry, constituted of a backbone and fingers, is one of the most simple paradigm of a two-dimensional structure, where anomalous diffusion can be realized in the framework of Markov processes. However, the intrinsic properties of the structure can destroy this Markovian transport. These effects can be described by the memory and spatial kernels. In particular, the fractal structure of the fingers, which is controlled by the spatial kernel in both the real and the Fourier spaces, leads to the Lévy processes (Lévy flights) and superdiffusion. This generalization of the fractional diffusion is described by the Riesz space fractional derivative. In the framework of this generalized fractal comb model, Lévy processes are considered, and exact solutions for the probability distribution functions are obtained in terms of the Fox H-function for a variety of the memory kernels, and the rate of the superdiffusive spreading is studied by calculating the fractional moments. For a special form of the memory kernels, we also observed a competition between long rests and long jumps. Finally, we considered the fractal structure of the fingers controlled by a Weierstrass function, which leads to the power-law kernel in the Fourier space. This is a special case, when the second moment exists for superdiffusion in this competition between long rests and long jumps.

Persistent random walk of cells involving anomalous effects and random death

NASA Astrophysics Data System (ADS)

Fedotov, Sergei; Tan, Abby; Zubarev, Andrey

2015-04-01

The purpose of this paper is to implement a random death process into a persistent random walk model which produces sub-ballistic superdiffusion (Lévy walk). We develop a stochastic two-velocity jump model of cell motility for which the switching rate depends upon the time which the cell has spent moving in one direction. It is assumed that the switching rate is a decreasing function of residence (running) time. This assumption leads to the power law for the velocity switching time distribution. This describes the anomalous persistence of cell motility: the longer the cell moves in one direction, the smaller the switching probability to another direction becomes. We derive master equations for the cell densities with the generalized switching terms involving the tempered fractional material derivatives. We show that the random death of cells has an important implication for the transport process through tempering of the superdiffusive process. In the long-time limit we write stationary master equations in terms of exponentially truncated fractional derivatives in which the rate of death plays the role of tempering of a Lévy jump distribution. We find the upper and lower bounds for the stationary profiles corresponding to the ballistic transport and diffusion with the death-rate-dependent diffusion coefficient. Monte Carlo simulations confirm these bounds.

Stochastic thermodynamics across scales: Emergent inter-attractoral discrete Markov jump process and its underlying continuous diffusion

NASA Astrophysics Data System (ADS)

Santillán, Moisés; Qian, Hong

2013-01-01

We investigate the internal consistency of a recently developed mathematical thermodynamic structure across scales, between a continuous stochastic nonlinear dynamical system, i.e., a diffusion process with Langevin and Fokker-Planck equations, and its emergent discrete, inter-attractoral Markov jump process. We analyze how the system’s thermodynamic state functions, e.g. free energy F, entropy S, entropy production ep, free energy dissipation Ḟ, etc., are related when the continuous system is described with coarse-grained discrete variables. It is shown that the thermodynamics derived from the underlying, detailed continuous dynamics gives rise to exactly the free-energy representation of Gibbs and Helmholtz. That is, the system’s thermodynamic structure is the same as if one only takes a middle road and starts with the natural discrete description, with the corresponding transition rates empirically determined. By natural we mean in the thermodynamic limit of a large system, with an inherent separation of time scales between inter- and intra-attractoral dynamics. This result generalizes a fundamental idea from chemistry, and the theory of Kramers, by incorporating thermodynamics: while a mechanical description of a molecule is in terms of continuous bond lengths and angles, chemical reactions are phenomenologically described by a discrete representation, in terms of exponential rate laws and a stochastic thermodynamics.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duncan, Andrew, E-mail: a.duncan@imperial.ac.uk; Erban, Radek, E-mail: erban@maths.ox.ac.uk; Zygalakis, Konstantinos, E-mail: k.zygalakis@ed.ac.uk

Stochasticity plays a fundamental role in various biochemical processes, such as cell regulatory networks and enzyme cascades. Isothermal, well-mixed systems can be modelled as Markov processes, typically simulated using the Gillespie Stochastic Simulation Algorithm (SSA) [25]. While easy to implement and exact, the computational cost of using the Gillespie SSA to simulate such systems can become prohibitive as the frequency of reaction events increases. This has motivated numerous coarse-grained schemes, where the “fast” reactions are approximated either using Langevin dynamics or deterministically. While such approaches provide a good approximation when all reactants are abundant, the approximation breaks down when onemore » or more species exist only in small concentrations and the fluctuations arising from the discrete nature of the reactions become significant. This is particularly problematic when using such methods to compute statistics of extinction times for chemical species, as well as simulating non-equilibrium systems such as cell-cycle models in which a single species can cycle between abundance and scarcity. In this paper, a hybrid jump-diffusion model for simulating well-mixed stochastic kinetics is derived. It acts as a bridge between the Gillespie SSA and the chemical Langevin equation. For low reactant reactions the underlying behaviour is purely discrete, while purely diffusive when the concentrations of all species are large, with the two different behaviours coexisting in the intermediate region. A bound on the weak error in the classical large volume scaling limit is obtained, and three different numerical discretisations of the jump-diffusion model are described. The benefits of such a formalism are illustrated using computational examples.« less

Effect of temperature and pressure on the dynamics of nanoconfined propane

NASA Astrophysics Data System (ADS)

Gautam, Siddharth; Liu, Tingting; Rother, Gernot; Jalarvo, Niina; Mamontov, Eugene; Welch, Susan; Cole, David

2014-04-01

We report the effect of temperature and pressure on the dynamical properties of propane confined in nanoporous silica aerogel studied using quasielastic neutron scattering (QENS). Our results demonstrate that the effect of a change in the pressure dominates over the effect of temperature variation on the dynamics of propane nano-confined in silica aerogel. At low pressures, most of the propane molecules are strongly bound to the pore walls, only a small fraction is mobile. As the pressure is increased, the fraction of mobile molecules increases. A change in the mechanism of motion, from continuous diffusion at low pressures to jump diffusion at higher pressures has also been observed.

Pore-scale modeling of phase change in porous media

NASA Astrophysics Data System (ADS)

Juanes, Ruben; Cueto-Felgueroso, Luis; Fu, Xiaojing

2017-11-01

One of the main open challenges in pore-scale modeling is the direct simulation of flows involving multicomponent mixtures with complex phase behavior. Reservoir fluid mixtures are often described through cubic equations of state, which makes diffuse interface, or phase field theories, particularly appealing as a modeling framework. What is still unclear is whether equation-of-state-driven diffuse-interface models can adequately describe processes where surface tension and wetting phenomena play an important role. Here we present a diffuse interface model of single-component, two-phase flow (a van der Waals fluid) in a porous medium under different wetting conditions. We propose a simplified Darcy-Korteweg model that is appropriate to describe flow in a Hele-Shaw cell or a micromodel, with a gap-averaged velocity. We study the ability of the diffuse-interface model to capture capillary pressure and the dynamics of vaporization/condensation fronts, and show that the model reproduces pressure fluctuations that emerge from abrupt interface displacements (Haines jumps) and from the break-up of wetting films.

BCA-kMC Hybrid Simulation for Hydrogen and Helium Implantation in Material under Plasma Irradiation

NASA Astrophysics Data System (ADS)

Kato, Shuichi; Ito, Atsushi; Sasao, Mamiko; Nakamura, Hiroaki; Wada, Motoi

2015-09-01

Ion implantation by plasma irradiation into materials achieves the very high concentration of impurity. The high concentration of impurity causes the deformation and the destruction of the material. This is the peculiar phenomena in the plasma-material interaction (PMI). The injection process of plasma particles are generally simulated by using the binary collision approximation (BCA) and the molecular dynamics (MD), while the diffusion of implanted atoms have been traditionally solved by the diffusion equation, in which the implanted atoms is replaced by the continuous concentration field. However, the diffusion equation has insufficient accuracy in the case of low concentration, and in the case of local high concentration such as the hydrogen blistering and the helium bubble. The above problem is overcome by kinetic Monte Carlo (kMC) which represents the diffusion of the implanted atoms as jumps on interstitial sites in a material. In this paper, we propose the new approach ``BCA-kMC hybrid simulation'' for the hydrogen and helium implantation under the plasma irradiation.

Random walk numerical simulation for hopping transport at finite carrier concentrations: diffusion coefficient and transport energy concept.

PubMed

Gonzalez-Vazquez, J P; Anta, Juan A; Bisquert, Juan

2009-11-28

The random walk numerical simulation (RWNS) method is used to compute diffusion coefficients for hopping transport in a fully disordered medium at finite carrier concentrations. We use Miller-Abrahams jumping rates and an exponential distribution of energies to compute the hopping times in the random walk simulation. The computed diffusion coefficient shows an exponential dependence with respect to Fermi-level and Arrhenius behavior with respect to temperature. This result indicates that there is a well-defined transport level implicit to the system dynamics. To establish the origin of this transport level we construct histograms to monitor the energies of the most visited sites. In addition, we construct "corrected" histograms where backward moves are removed. Since these moves do not contribute to transport, these histograms provide a better estimation of the effective transport level energy. The analysis of this concept in connection with the Fermi-level dependence of the diffusion coefficient and the regime of interest for the functioning of dye-sensitised solar cells is thoroughly discussed.

Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP)

NASA Astrophysics Data System (ADS)

Snyder, David A.; Chantova, Mihaela; Chaudhry, Saadia

2015-06-01

NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase.

Dynamics of ligand substitution in labile cobalt complexes resolved by ultrafast T-jump

PubMed Central

Ma, Hairong; Wan, Chaozhi; Zewail, Ahmed H.

2008-01-01

Ligand exchange of hydrated metal complexes is common in chemical and biological systems. Using the ultrafast T-jump, we examined this process, specifically the transformation of aqua cobalt (II) complexes to their fully halogenated species. The results reveal a stepwise mechanism with time scales varying from hundreds of picoseconds to nanoseconds. The dynamics are significantly faster when the structure is retained but becomes rate-limited when the octahedral-to-tetrahedral structural change bottlenecks the transformation. Evidence is presented, from bimolecular kinetics and energetics (enthalpic and entropic), for a reaction in which the ligand assists the displacement of water molecules, with the retention of the entering ligand in the activated state. The reaction time scale deviates by one to two orders of magnitude from that of ionic diffusion, suggesting the involvement of a collisional barrier between the ion and the much larger complex. PMID:18725628

Numerical modeling of time-dependent bio-convective stagnation flow of a nanofluid in slip regime

NASA Astrophysics Data System (ADS)

Kumar, Rakesh; Sood, Shilpa; Shehzad, Sabir Ali; Sheikholeslami, Mohsen

A numerical investigation of unsteady stagnation point flow of bioconvective nanofluid due to an exponential deforming surface is made in this research. The effects of Brownian diffusion, thermophoresis, slip velocity and thermal jump are incorporated in the nanofluid model. By utilizing similarity transformations, the highly nonlinear partial differential equations governing present nano-bioconvective boundary layer phenomenon are reduced into ordinary differential system. The resultant expressions are solved for numerical solution by employing a well-known implicit finite difference approach termed as Keller-box method (KBM). The influence of involved parameters (unsteadiness, bioconvection Schmidt number, velocity slip, thermal jump, thermophoresis, Schmidt number, Brownian motion, bioconvection Peclet number) on the distributions of velocity, temperature, nanoparticle and motile microorganisms concentrations, the coefficient of local skin-friction, rate of heat transport, Sherwood number and local density motile microorganisms are exhibited through graphs and tables.

Numerical methods of solving a system of multi-dimensional nonlinear equations of the diffusion type

NASA Technical Reports Server (NTRS)

Agapov, A. V.; Kolosov, B. I.

1979-01-01

The principles of conservation and stability of difference schemes achieved using the iteration control method were examined. For the schemes obtained of the predictor-corrector type, the conversion was proved for the control sequences of approximate solutions to the precise solutions in the Sobolev metrics. Algorithms were developed for reducing the differential problem to integral relationships, whose solution methods are known, were designed. The algorithms for the problem solution are classified depending on the non-linearity of the diffusion coefficients, and practical recommendations for their effective use are given.

Gas Sorption and Storage Properties of Calixarenes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patil, Rahul S.; Banerjee, Debasis; Atwood, Jerry L.

2016-12-01

Calixarenes, a class of organic macrocyclic molecules have shown interesting gas sorption properties towards industrially important gases such as carbon di-oxide, hydrogen, methane and acetylene. These macrocycles are involved in weak van der Waals interaction to form multidimensional supramolecular frameworks. The gas-diffusion and subsequent sorption occurs due to a cooperative behavior between neighboring macrocycles. Furthermore, the flexibility at the upper rim functional group also plays a key role in the overall gas uptake of calixarene. In this book chapter, we give a brief account of interaction and diffusion of gases in calixarene and selected derivatives.

Comments on the Diffusive Behavior of Two Upwind Schemes

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1998-01-01

The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and locally one-dimensional finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2.5 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a speedup of 29 over finite volume.

Diffusion Characteristics of Upwind Schemes on Unstructured Triangulations

NASA Technical Reports Server (NTRS)

Wood, William A.; Kleb, William L.

1998-01-01

The diffusive characteristics of two upwind schemes, multi-dimensional fluctuation splitting and dimensionally-split finite volume, are compared for scalar advection-diffusion problems. Algorithms for the two schemes are developed for node-based data representation on median-dual meshes associated with unstructured triangulations in two spatial dimensions. Four model equations are considered: linear advection, non-linear advection, diffusion, and advection-diffusion. Modular coding is employed to isolate the effects of the two approaches for upwind flux evaluation, allowing for head-to-head accuracy and efficiency comparisons. Both the stability of compressive limiters and the amount of artificial diffusion generated by the schemes is found to be grid-orientation dependent, with the fluctuation splitting scheme producing less artificial diffusion than the dimensionally-split finite volume scheme. Convergence rates are compared for the combined advection-diffusion problem, with a speedup of 2-3 seen for fluctuation splitting versus finite volume when solved on the same mesh. However, accurate solutions to problems with small diffusion coefficients can be achieved on coarser meshes using fluctuation splitting rather than finite volume, so that when comparing convergence rates to reach a given accuracy, fluctuation splitting shows a 20-25 speedup over finite volume.

Density Large Deviations for Multidimensional Stochastic Hyperbolic Conservation Laws

NASA Astrophysics Data System (ADS)

Barré, J.; Bernardin, C.; Chetrite, R.

2018-02-01

We investigate the density large deviation function for a multidimensional conservation law in the vanishing viscosity limit, when the probability concentrates on weak solutions of a hyperbolic conservation law. When the mobility and diffusivity matrices are proportional, i.e. an Einstein-like relation is satisfied, the problem has been solved in Bellettini and Mariani (Bull Greek Math Soc 57:31-45, 2010). When this proportionality does not hold, we compute explicitly the large deviation function for a step-like density profile, and we show that the associated optimal current has a non trivial structure. We also derive a lower bound for the large deviation function, valid for a more general weak solution, and leave the general large deviation function upper bound as a conjecture.

Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

NASA Astrophysics Data System (ADS)

Baraffe, I.; Pratt, J.; Goffrey, T.; Constantino, T.; Folini, D.; Popov, M. V.; Walder, R.; Viallet, M.

2017-08-01

We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a young low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ˜50 Myr to ˜4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.

Lithium Depletion in Solar-like Stars: Effect of Overshooting Based on Realistic Multi-dimensional Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baraffe, I.; Pratt, J.; Goffrey, T.

We study lithium depletion in low-mass and solar-like stars as a function of time, using a new diffusion coefficient describing extra-mixing taking place at the bottom of a convective envelope. This new form is motivated by multi-dimensional fully compressible, time-implicit hydrodynamic simulations performed with the MUSIC code. Intermittent convective mixing at the convective boundary in a star can be modeled using extreme value theory, a statistical analysis frequently used for finance, meteorology, and environmental science. In this Letter, we implement this statistical diffusion coefficient in a one-dimensional stellar evolution code, using parameters calibrated from multi-dimensional hydrodynamic simulations of a youngmore » low-mass star. We propose a new scenario that can explain observations of the surface abundance of lithium in the Sun and in clusters covering a wide range of ages, from ∼50 Myr to ∼4 Gyr. Because it relies on our physical model of convective penetration, this scenario has a limited number of assumptions. It can explain the observed trend between rotation and depletion, based on a single additional assumption, namely, that rotation affects the mixing efficiency at the convective boundary. We suggest the existence of a threshold in stellar rotation rate above which rotation strongly prevents the vertical penetration of plumes and below which rotation has small effects. In addition to providing a possible explanation for the long-standing problem of lithium depletion in pre-main-sequence and main-sequence stars, the strength of our scenario is that its basic assumptions can be tested by future hydrodynamic simulations.« less

Logarithmic Superdiffusion in Two Dimensional Driven Lattice Gases

NASA Astrophysics Data System (ADS)

Krug, J.; Neiss, R. A.; Schadschneider, A.; Schmidt, J.

2018-03-01

The spreading of density fluctuations in two-dimensional driven diffusive systems is marginally anomalous. Mode coupling theory predicts that the diffusivity in the direction of the drive diverges with time as (ln t)^{2/3} with a prefactor depending on the macroscopic current-density relation and the diffusion tensor of the fluctuating hydrodynamic field equation. Here we present the first numerical verification of this behavior for a particular version of the two-dimensional asymmetric exclusion process. Particles jump strictly asymmetrically along one of the lattice directions and symmetrically along the other, and an anisotropy parameter p governs the ratio between the two rates. Using a novel massively parallel coupling algorithm that strongly reduces the fluctuations in the numerical estimate of the two-point correlation function, we are able to accurately determine the exponent of the logarithmic correction. In addition, the variation of the prefactor with p provides a stringent test of mode coupling theory.

New mechanisms of cluster diffusion on metal fcc(100) surfaces

NASA Astrophysics Data System (ADS)

Trushin, Oleg; Salo, Petri; Alatalo, Matti; Ala-Nissila, Tapio

2001-03-01

We have studied atomic mechanisms of the diffusion of small clusters on the fcc(100) metal surfaces using semi-empirical and ab-initio molecular static calculations. Primary goal of these studies was to investigate possible many-body mechanisms of cluster motion which can contribute to low temperature crystal growth. We used embedded atom and Glue potentials in semi-empirical simulations of Cu and Al. Combination of the Nudged Elastic Band and Eigenvector Following methods allowed us to find all the possible transition paths for cluster movements on flat terrace. In case of Cu(001) we have found several new mechanisms for diffusion of clusters, including mechanisms called row-shearing and dimer-rotating in which a whole row inside an island moves according to a concerted jump and a dimer rotates at the periphery of an island, respectively. In some cases these mechanisms yield a lower energy barrier than the standard mechanisms.

Best dispersal strategies in spatially heterogeneous environments: optimization of the principal eigenvalue for indefinite fractional Neumann problems.

PubMed

Pellacci, Benedetta; Verzini, Gianmaria

2018-05-01

We study the positive principal eigenvalue of a weighted problem associated with the Neumann spectral fractional Laplacian. This analysis is related to the investigation of the survival threshold in population dynamics. Our main result concerns the optimization of such threshold with respect to the fractional order [Formula: see text], the case [Formula: see text] corresponding to the standard Neumann Laplacian: when the habitat is not too fragmented, the principal positive eigenvalue can not have local minima for [Formula: see text]. As a consequence, the best strategy for survival is either following the diffusion with [Formula: see text] (i.e. Brownian diffusion), or with the lowest possible s (i.e. diffusion allowing long jumps), depending on the size of the domain. In addition, we show that analogous results hold for the standard fractional Laplacian in [Formula: see text], in periodic environments.

Nuclear quadrupole resonance lineshape analysis for different motional models: Stochastic Liouville approach

NASA Astrophysics Data System (ADS)

Kruk, D.; Earle, K. A.; Mielczarek, A.; Kubica, A.; Milewska, A.; Moscicki, J.

2011-12-01

A general theory of lineshapes in nuclear quadrupole resonance (NQR), based on the stochastic Liouville equation, is presented. The description is valid for arbitrary motional conditions (particularly beyond the valid range of perturbation approaches) and interaction strengths. It can be applied to the computation of NQR spectra for any spin quantum number and for any applied magnetic field. The treatment presented here is an adaptation of the "Swedish slow motion theory," [T. Nilsson and J. Kowalewski, J. Magn. Reson. 146, 345 (2000), 10.1006/jmre.2000.2125] originally formulated for paramagnetic systems, to NQR spectral analysis. The description is formulated for simple (Brownian) diffusion, free diffusion, and jump diffusion models. The two latter models account for molecular cooperativity effects in dense systems (such as liquids of high viscosity or molecular glasses). The sensitivity of NQR slow motion spectra to the mechanism of the motional processes modulating the nuclear quadrupole interaction is discussed.

Data mining of molecular dynamics data reveals Li diffusion characteristics in garnet Li7La3Zr2O12

PubMed Central

Chen, Chi; Lu, Ziheng; Ciucci, Francesco

2017-01-01

Understanding Li diffusion in solid conductors is essential for the next generation Li batteries. Here we show that density-based clustering of the trajectories computed using molecular dynamics simulations helps elucidate the Li diffusion mechanism within the Li7La3Zr2O12 (LLZO) crystal lattice. This unsupervised learning method recognizes lattice sites, is able to give the site type, and can identify Li hopping events. Results show that, while the cubic LLZO has a much higher hopping rate compared to its tetragonal counterpart, most of the Li hops in the cubic LLZO do not contribute to the diffusivity due to the dominance of back-and-forth type jumps. The hopping analysis and local Li configuration statistics give evidence that Li diffusivity in cubic LLZO is limited by the low vacancy concentration. The hopping statistics also shows uncorrelated Poisson-like diffusion for Li in the cubic LLZO, and correlated diffusion for Li in the tetragonal LLZO in the temporal scale. Further analysis of the spatio-temporal correlation using site-to-site mutual information confirms the weak site dependence of Li diffusion in the cubic LLZO as the origin for the uncorrelated diffusion. This work puts forward a perspective on combining machine learning and information theory to interpret results of molecular dynamics simulations. PMID:28094317

Data mining of molecular dynamics data reveals Li diffusion characteristics in garnet Li7La3Zr2O12

NASA Astrophysics Data System (ADS)

Chen, Chi; Lu, Ziheng; Ciucci, Francesco

2017-01-01

Understanding Li diffusion in solid conductors is essential for the next generation Li batteries. Here we show that density-based clustering of the trajectories computed using molecular dynamics simulations helps elucidate the Li diffusion mechanism within the Li7La3Zr2O12 (LLZO) crystal lattice. This unsupervised learning method recognizes lattice sites, is able to give the site type, and can identify Li hopping events. Results show that, while the cubic LLZO has a much higher hopping rate compared to its tetragonal counterpart, most of the Li hops in the cubic LLZO do not contribute to the diffusivity due to the dominance of back-and-forth type jumps. The hopping analysis and local Li configuration statistics give evidence that Li diffusivity in cubic LLZO is limited by the low vacancy concentration. The hopping statistics also shows uncorrelated Poisson-like diffusion for Li in the cubic LLZO, and correlated diffusion for Li in the tetragonal LLZO in the temporal scale. Further analysis of the spatio-temporal correlation using site-to-site mutual information confirms the weak site dependence of Li diffusion in the cubic LLZO as the origin for the uncorrelated diffusion. This work puts forward a perspective on combining machine learning and information theory to interpret results of molecular dynamics simulations.

Simultaneous Multi-Scale Diffusion Estimation and Tractography Guided by Entropy Spectrum Pathways

PubMed Central

Galinsky, Vitaly L.; Frank, Lawrence R.

2015-01-01

We have developed a method for the simultaneous estimation of local diffusion and the global fiber tracts based upon the information entropy flow that computes the maximum entropy trajectories between locations and depends upon the global structure of the multi-dimensional and multi-modal diffusion field. Computation of the entropy spectrum pathways requires only solving a simple eigenvector problem for the probability distribution for which efficient numerical routines exist, and a straight forward integration of the probability conservation through ray tracing of the convective modes guided by a global structure of the entropy spectrum coupled with a small scale local diffusion. The intervoxel diffusion is sampled by multi b-shell multi q-angle DWI data expanded in spherical waves. This novel approach to fiber tracking incorporates global information about multiple fiber crossings in every individual voxel and ranks it in the most scientifically rigorous way. This method has potential significance for a wide range of applications, including studies of brain connectivity. PMID:25532167

Imaging energy landscapes with concentrated diffusing colloidal probes

NASA Astrophysics Data System (ADS)

Bahukudumbi, Pradipkumar; Bevan, Michael A.

2007-06-01

The ability to locally interrogate interactions between particles and energetically patterned surfaces provides essential information to design, control, and optimize template directed self-assembly processes. Although numerous techniques are capable of characterizing local physicochemical surface properties, no current method resolves interactions between colloids and patterned surfaces on the order of the thermal energy kT, which is the inherent energy scale of equilibrium self-assembly processes. Here, the authors describe video microscopy measurements and an inverse Monte Carlo analysis of diffusing colloidal probes as a means to image three dimensional free energy and potential energy landscapes due to physically patterned surfaces. In addition, they also develop a consistent analysis of self-diffusion in inhomogeneous fluids of concentrated diffusing probes on energy landscapes, which is important to the temporal imaging process and to self-assembly kinetics. Extension of the concepts developed in this work suggests a general strategy to image multidimensional and multiscale physical, chemical, and biological surfaces using a variety of diffusing probes (i.e., molecules, macromolecules, nanoparticles, and colloids).

Homogenization of Large-Scale Movement Models in Ecology

USGS Publications Warehouse

Garlick, M.J.; Powell, J.A.; Hooten, M.B.; McFarlane, L.R.

2011-01-01

A difficulty in using diffusion models to predict large scale animal population dispersal is that individuals move differently based on local information (as opposed to gradients) in differing habitat types. This can be accommodated by using ecological diffusion. However, real environments are often spatially complex, limiting application of a direct approach. Homogenization for partial differential equations has long been applied to Fickian diffusion (in which average individual movement is organized along gradients of habitat and population density). We derive a homogenization procedure for ecological diffusion and apply it to a simple model for chronic wasting disease in mule deer. Homogenization allows us to determine the impact of small scale (10-100 m) habitat variability on large scale (10-100 km) movement. The procedure generates asymptotic equations for solutions on the large scale with parameters defined by small-scale variation. The simplicity of this homogenization procedure is striking when compared to the multi-dimensional homogenization procedure for Fickian diffusion,and the method will be equally straightforward for more complex models. ?? 2010 Society for Mathematical Biology.

A Physical Mechanism for the Asymmetry in Top-Down and Bottom-Up Diffusion.

NASA Astrophysics Data System (ADS)

Wyngaard, J. C.

1987-04-01

Recent large-eddy simulations of the vertical diffusion of a passive, conservative scalar through the convective boundary layer (CBL) show strikingly different eddy diffusivity profiles in the `top-down' and `bottom-up' cases. These results indicate that for a given turbulent velocity field and associated scalar flux, the mean change in scalar mixing ratio across the CBL is several times larger if the flux originates at the top of the boundary layer (i.e., in top-down diffusion) rather than at the bottom. The large-eddy simulation (LES) data show that this asymmetry is due to a breakdown of the eddy-diffusion concept.A simple updraft-downdraft model of the CBL reveals a physical mechanism that could cause this unexpected behavior. The large, positive skewness of the convectively driven vertical velocity gives an appreciably higher probability of downdrafts than updrafts; this excess probability of downdrafts, interacting with the time changes of the mean mixing ratio caused by the nonstationarity of the bottom-up and top-down diffusion processes, decreases the equilibrium value of mean mixing-ratio jump across the mixed layer in the bottom-up case and increases it in the top-down case. The resulting diffusion asymmetry agrees qualitatively with that found through LES.

VENTURE/PC manual: A multidimensional multigroup neutron diffusion code system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shapiro, A.; Huria, H.C.; Cho, K.W.

1991-12-01

VENTURE/PC is a recompilation of part of the Oak Ridge BOLD VENTURE code system, which will operate on an IBM PC or compatible computer. Neutron diffusion theory solutions are obtained for multidimensional, multigroup problems. This manual contains information associated with operating the code system. The purpose of the various modules used in the code system, and the input for these modules are discussed. The PC code structure is also given. Version 2 included several enhancements not given in the original version of the code. In particular, flux iterations can be done in core rather than by reading and writing tomore » disk, for problems which allow sufficient memory for such in-core iterations. This speeds up the iteration process. Version 3 does not include any of the special processors used in the previous versions. These special processors utilized formatted input for various elements of the code system. All such input data is now entered through the Input Processor, which produces standard interface files for the various modules in the code system. In addition, a Standard Interface File Handbook is included in the documentation which is distributed with the code, to assist in developing the input for the Input Processor.« less

VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics

NASA Astrophysics Data System (ADS)

Pearce, C. J. J.; van Weeren, R. J.; Andrade-Santos, F.; Jones, C.; Forman, W. R.; Brüggen, M.; Bulbul, E.; Clarke, T. E.; Kraft, R. P.; Medezinski, E.; Mroczkowski, T.; Nonino, M.; Nulsen, P. E. J.; Randall, S. W.; Umetsu, K.

2017-08-01

Cluster mergers leave distinct signatures in the intracluster medium (ICM) in the form of shocks and diffuse cluster radio sources that provide evidence for the acceleration of relativistic particles. However, the physics of particle acceleration in the ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very Large Array (VLA) and archival Chandra observations of the HST Frontier Fields Cluster Abell 2744. In our new VLA images, we detect the previously known ˜2.1 Mpc radio halo and ˜1.5 Mpc radio relic. We carry out a radio spectral analysis from which we determine the relic’s injection spectral index to be {α }{inj}=-1.12+/- 0.19. This corresponds to a shock Mach number of { M }={2.05}-0.19+0.31 under the assumption of diffusive shock acceleration. We also find evidence for spectral steepening in the post-shock region. We do not find evidence for a significant correlation between the radio halo’s spectral index and ICM temperature. In addition, we observe three new polarized diffuse sources and determine two of these to be newly discovered giant radio relics. These two relics are located in the southeastern and northwestern outskirts of the cluster. The corresponding integrated spectral indices measure -1.81 ± 0.26 and -0.63 ± 0.21 for the SE and NW relics, respectively. From an X-ray surface brightness profile we also detect a possible density jump of R={1.39}-0.22+0.34 co-located with the newly discovered SE relic. This density jump would correspond to a shock front Mach number of { M }={1.26}-0.15+0.25.

Hybrid finite element and Brownian dynamics method for charged particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huber, Gary A., E-mail: ghuber@ucsd.edu; Miao, Yinglong; Zhou, Shenggao

2016-04-28

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. A previous study introduced a new hybrid diffusion method that couples the strengths of each of these two methods, but was limited by the lack of interactions among the particles; the force on each particle had to be from an external field. This study further develops the method to allow charged particles. The method is derived for a general multidimensional system and is presented usingmore » a basic test case for a one-dimensional linear system with one charged species and a radially symmetric system with three charged species.« less

Detecting chaos, determining the dimensions of tori and predicting slow diffusion in Fermi-Pasta-Ulam lattices by the Generalized Alignment Index method

NASA Astrophysics Data System (ADS)

Skokos, C.; Bountis, T.; Antonopoulos, C.

2008-12-01

The recently introduced GALI method is used for rapidly detecting chaos, determining the dimensionality of regular motion and predicting slow diffusion in multi-dimensional Hamiltonian systems. We propose an efficient computation of the GALIk indices, which represent volume elements of k randomly chosen deviation vectors from a given orbit, based on the Singular Value Decomposition (SVD) algorithm. We obtain theoretically and verify numerically asymptotic estimates of GALIs long-time behavior in the case of regular orbits lying on low-dimensional tori. The GALIk indices are applied to rapidly detect chaotic oscillations, identify low-dimensional tori of Fermi-Pasta-Ulam (FPU) lattices at low energies and predict weak diffusion away from quasiperiodic motion, long before it is actually observed in the oscillations.

Balance in Astronauts Performing Jumps, Walking and Quiet Stance Following Spaceflight

NASA Technical Reports Server (NTRS)

Reschke, Millard F.; Bloomberg, J. J.; Wood, S. J.; Harm, D. L.

2011-01-01

Introduction: Both balance and locomotor ataxia is severe in astronauts returning from spaceflight with serious implications for unassisted landings. As a part of an ongoing effort to demonstrate the functional significance of the postflight ataxia problem our laboratory has evaluated jumping, walking heel-to-toe and quite stance balance immediately following spaceflight. Methods: Six astronauts from 12-16 day flights and three from 6-month flights were asked to perform three self-initiated two-footed jumps from a 30-cm-high platform, walking for 10 steps (three trials) placing the feet heel to toe in tandem, arms folded across the chest and the eyes closed, and lastly, recover from a simulated fall by standing from a prone position on the floor and with eyes open maintain a quiet stance for 3 min with arms relaxed along the side of the body and feet comfortably positioned on a force plate. Crewmembers were tested twice before flight, on landing day (short-duration), and days 1, 6, and 30 following all flight durations. Results/Conclusions: Many of astronauts tested fell on their first postflight jump but recovered by the third jump showing a rapid learning progression. Changes in take-off strategy were clearly evident in duration of time in the air between the platform and the ground (significant reduction in time to land), and also in increased asymmetry in foot latencies on take-off postflight. During the tandem heel-to-toe walking task there was a significant decrease in percentage of correct steps on landing day (short-duration crew) and on first day following landing (long-duration) with only partial recovery the following day. Astronauts for both short and long duration flight times appeared to be unaware of foot position relative to their bodies or the floor. During quite stance most of crewmembers tested exhibited increased stochastic activity (larger short-term COP diffusion coefficients postflight in all planes and increases in mean sway speed).

Nonlinear subdiffusive fractional equations and the aggregation phenomenon.

PubMed

Fedotov, Sergei

2013-09-01

In this article we address the problem of the nonlinear interaction of subdiffusive particles. We introduce the random walk model in which statistical characteristics of a random walker such as escape rate and jump distribution depend on the mean density of particles. We derive a set of nonlinear subdiffusive fractional master equations and consider their diffusion approximations. We show that these equations describe the transition from an intermediate subdiffusive regime to asymptotically normal advection-diffusion transport regime. This transition is governed by nonlinear tempering parameter that generalizes the standard linear tempering. We illustrate the general results through the use of the examples from cell and population biology. We find that a nonuniform anomalous exponent has a strong influence on the aggregation phenomenon.

NMR Observation of Mobile Protons in Proton-Implanted ZnO Nanorods

PubMed Central

Park, Jun Kue; Kwon, Hyeok-Jung; Lee, Cheol Eui

2016-01-01

The diffusion properties of H+ in ZnO nanorods are investigated before and after 20 MeV proton beam irradiation by using 1H nuclear magnetic resonance (NMR) spectroscopy. Herein, we unambiguously observe that the implanted protons occupy thermally unstable site of ZnO, giving rise to a narrow NMR line at 4.1 ppm. The activation barrier of the implanted protons was found to be 0.46 eV by means of the rotating-frame spin-lattice relaxation measurements, apparently being interstitial hydrogens. High-energy beam irradiation also leads to correlated jump diffusion of the surface hydroxyl group of multiple lines at ~1 ppm, implying the presence of structural disorder at the ZnO surface. PMID:26988733

Quasi elastic and inelastic neutron scattering study of vitamin C aqueous solutions

NASA Astrophysics Data System (ADS)

Migliardo, F.; Branca, C.; Magazù, S.; Migliardo, P.; Coppolino, S.; Villari, A.; Micali, N.

2002-02-01

In this paper, new results obtained by quasi elastic and inelastic neutron scattering experiments performed on vitamin C ( L-ascorbic acid)/H 2O mixtures are reported. The data analysis of the QENS measurements, by a separation of the diffusive dynamics of hydrated L-ascorbic acid from that of water, furnishes quantitative evidences of a random jump diffusion motion of vitamin C and shows that the water dynamics is strongly affected by the presence of L-ascorbic acid. Concerning the INS experiment, we are able, through the behaviour of neutron spectra across the glass transition temperature ( T g≈233 K for the vitamin C/water system), to collocate the investigated system in the Angell “strong-fragile” scheme.

Modelling on optimal portfolio with exchange rate based on discontinuous stochastic process

NASA Astrophysics Data System (ADS)

Yan, Wei; Chang, Yuwen

2016-12-01

Considering the stochastic exchange rate, this paper is concerned with the dynamic portfolio selection in financial market. The optimal investment problem is formulated as a continuous-time mathematical model under mean-variance criterion. These processes follow jump-diffusion processes (Weiner process and Poisson process). Then the corresponding Hamilton-Jacobi-Bellman(HJB) equation of the problem is presented and its efferent frontier is obtained. Moreover, the optimal strategy is also derived under safety-first criterion.

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

NASA Astrophysics Data System (ADS)

Cassar, Daniel R.; Lancelotti, Ricardo F.; Nuernberg, Rafael; Nascimento, Marcio L. F.; Rodrigues, Alisson M.; Diz, Luiza T.; Zanotto, Edgar D.

2017-07-01

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO3 liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range Td (1.2Tg-1.3Tg), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, Td marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below Td is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.

Automatic deformable diffusion tensor registration for fiber population analysis.

PubMed

Irfanoglu, M O; Machiraju, R; Sammet, S; Pierpaoli, C; Knopp, M V

2008-01-01

In this work, we propose a novel method for deformable tensor-to-tensor registration of Diffusion Tensor Images. Our registration method models the distances in between the tensors with Geode-sic-Loxodromes and employs a version of Multi-Dimensional Scaling (MDS) algorithm to unfold the manifold described with this metric. Defining the same shape properties as tensors, the vector images obtained through MDS are fed into a multi-step vector-image registration scheme and the resulting deformation fields are used to reorient the tensor fields. Results on brain DTI indicate that the proposed method is very suitable for deformable fiber-to-fiber correspondence and DTI-atlas construction.

The Space-Time Conservation Element and Solution Element Method: A New High-Resolution and Genuinely Multidimensional Paradigm for Solving Conservation Laws. 1; The Two Dimensional Time Marching Schemes

NASA Technical Reports Server (NTRS)

Chang, Sin-Chung; Wang, Xiao-Yen; Chow, Chuen-Yen

1998-01-01

A new high resolution and genuinely multidimensional numerical method for solving conservation laws is being, developed. It was designed to avoid the limitations of the traditional methods. and was built from round zero with extensive physics considerations. Nevertheless, its foundation is mathmatically simple enough that one can build from it a coherent, robust. efficient and accurate numerical framework. Two basic beliefs that set the new method apart from the established methods are at the core of its development. The first belief is that, in order to capture physics more efficiently and realistically, the modeling, focus should be placed on the original integral form of the physical conservation laws, rather than the differential form. The latter form follows from the integral form under the additional assumption that the physical solution is smooth, an assumption that is difficult to realize numerically in a region of rapid chance. such as a boundary layer or a shock. The second belief is that, with proper modeling of the integral and differential forms themselves, the resulting, numerical solution should automatically be consistent with the properties derived front the integral and differential forms, e.g., the jump conditions across a shock and the properties of characteristics. Therefore a much simpler and more robust method can be developed by not using the above derived properties explicitly.

Multidimensional FEM-FCT schemes for arbitrary time stepping

NASA Astrophysics Data System (ADS)

Kuzmin, D.; Möller, M.; Turek, S.

2003-05-01

The flux-corrected-transport paradigm is generalized to finite-element schemes based on arbitrary time stepping. A conservative flux decomposition procedure is proposed for both convective and diffusive terms. Mathematical properties of positivity-preserving schemes are reviewed. A nonoscillatory low-order method is constructed by elimination of negative off-diagonal entries of the discrete transport operator. The linearization of source terms and extension to hyperbolic systems are discussed. Zalesak's multidimensional limiter is employed to switch between linear discretizations of high and low order. A rigorous proof of positivity is provided. The treatment of non-linearities and iterative solution of linear systems are addressed. The performance of the new algorithm is illustrated by numerical examples for the shock tube problem in one dimension and scalar transport equations in two dimensions.

Analysis of ligand-protein exchange by Clustering of Ligand Diffusion Coefficient Pairs (CoLD-CoP).

PubMed

Snyder, David A; Chantova, Mihaela; Chaudhry, Saadia

2015-06-01

NMR spectroscopy is a powerful tool in describing protein structures and protein activity for pharmaceutical and biochemical development. This study describes a method to determine weak binding ligands in biological systems by using hierarchic diffusion coefficient clustering of multidimensional data obtained with a 400 MHz Bruker NMR. Comparison of DOSY spectrums of ligands of the chemical library in the presence and absence of target proteins show translational diffusion rates for small molecules upon interaction with macromolecules. For weak binders such as compounds found in fragment libraries, changes in diffusion rates upon macromolecular binding are on the order of the precision of DOSY diffusion measurements, and identifying such subtle shifts in diffusion requires careful statistical analysis. The "CoLD-CoP" (Clustering of Ligand Diffusion Coefficient Pairs) method presented here uses SAHN clustering to identify protein-binders in a chemical library or even a not fully characterized metabolite mixture. We will show how DOSY NMR and the "CoLD-CoP" method complement each other in identifying the most suitable candidates for lysozyme and wheat germ acid phosphatase. Copyright © 2015 Elsevier Inc. All rights reserved.

A finite elements method to solve the Bloch-Torrey equation applied to diffusion magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Nguyen, Dang Van; Li, Jing-Rebecca; Grebenkov, Denis; Le Bihan, Denis

2014-04-01

The complex transverse water proton magnetization subject to diffusion-encoding magnetic field gradient pulses in a heterogeneous medium can be modeled by the multiple compartment Bloch-Torrey partial differential equation (PDE). In addition, steady-state Laplace PDEs can be formulated to produce the homogenized diffusion tensor that describes the diffusion characteristics of the medium in the long time limit. In spatial domains that model biological tissues at the cellular level, these two types of PDEs have to be completed with permeability conditions on the cellular interfaces. To solve these PDEs, we implemented a finite elements method that allows jumps in the solution at the cell interfaces by using double nodes. Using a transformation of the Bloch-Torrey PDE we reduced oscillations in the searched-for solution and simplified the implementation of the boundary conditions. The spatial discretization was then coupled to the adaptive explicit Runge-Kutta-Chebyshev time-stepping method. Our proposed method is second order accurate in space and second order accurate in time. We implemented this method on the FEniCS C++ platform and show time and spatial convergence results. Finally, this method is applied to study some relevant questions in diffusion MRI.

A Multi-Level Investigation into the Antecedents of Enterprise Architecture (EA) Assimilation in the U.S. Federal Government: A Longitudinal Mixed Methods Research Study

ERIC Educational Resources Information Center

Makiya, George K.

2012-01-01

This dissertation reports on a multi-dimensional longitudinal investigation of the factors that influence Enterprise Architecture (EA) diffusion and assimilation within the U.S. federal government. The study uses publicly available datasets of 123 U.S. federal departments and agencies, as well as interview data among CIOs and EA managers within…

Exact representation of the asymptotic drift speed and diffusion matrix for a class of velocity-jump processes

NASA Astrophysics Data System (ADS)

Mascia, Corrado

2016-01-01

This paper examines a class of linear hyperbolic systems which generalizes the Goldstein-Kac model to an arbitrary finite number of speeds vi with transition rates μij. Under the basic assumptions that the transition matrix is symmetric and irreducible, and the differences vi -vj generate all the space, the system exhibits a large-time behavior described by a parabolic advection-diffusion equation. The main contribution is to determine explicit formulas for the asymptotic drift speed and diffusion matrix in term of the kinetic parameters vi and μij, establishing a complete connection between microscopic and macroscopic coefficients. It is shown that the drift speed is the arithmetic mean of the velocities vi. The diffusion matrix has a more complicate representation, based on the graph with vertices the velocities vi and arcs weighted by the transition rates μij. The approach is based on an exhaustive analysis of the dispersion relation and on the application of a variant of the Kirchoff's matrix tree Theorem from graph theory.

From elemental tellurium to Ge2Sb2Te5 melts: High temperature dynamic and relaxation properties in relationship with the possible fragile to strong transition

NASA Astrophysics Data System (ADS)

Flores-Ruiz, H.; Micoulaut, M.

2018-01-01

We investigate the dynamic properties of Ge-Sb-Te phase change melts using first principles molecular dynamics with a special emphasis on the effect of tellurium composition on melt dynamics. From structural models and trajectories established previously [H. Flores-Ruiz et al., Phys. Rev. B 92, 134205 (2015)], we calculate the diffusion coefficients for the different species, the activation energies for diffusion, the Van Hove correlation, and the intermediate scattering functions able to substantiate the dynamics and relaxation behavior of the liquids as a function of temperature and composition that is also compared to experiment whenever possible. We find that the diffusion is mostly Arrhenius-like and that the addition of Ge/Sb atoms leads to a global decrease of the jump probability and to an increase in activated dynamics for diffusion. Relaxation behavior is analyzed and used in order to evaluate the possibility of a fragile to strong transition that is evidenced from the calculated high fragility (M = 129) of Ge2Sb2Te5 at high temperatures.

Cross-diffusion-driven hydrodynamic instabilities in a double-layer system: General classification and nonlinear simulations

NASA Astrophysics Data System (ADS)

Budroni, M. A.

2015-12-01

Cross diffusion, whereby a flux of a given species entrains the diffusive transport of another species, can trigger buoyancy-driven hydrodynamic instabilities at the interface of initially stable stratifications. Starting from a simple three-component case, we introduce a theoretical framework to classify cross-diffusion-induced hydrodynamic phenomena in two-layer stratifications under the action of the gravitational field. A cross-diffusion-convection (CDC) model is derived by coupling the fickian diffusion formalism to Stokes equations. In order to isolate the effect of cross-diffusion in the convective destabilization of a double-layer system, we impose a starting concentration jump of one species in the bottom layer while the other one is homogeneously distributed over the spatial domain. This initial configuration avoids the concurrence of classic Rayleigh-Taylor or differential-diffusion convective instabilities, and it also allows us to activate selectively the cross-diffusion feedback by which the heterogeneously distributed species influences the diffusive transport of the other species. We identify two types of hydrodynamic modes [the negative cross-diffusion-driven convection (NCC) and the positive cross-diffusion-driven convection (PCC)], corresponding to the sign of this operational cross-diffusion term. By studying the space-time density profiles along the gravitational axis we obtain analytical conditions for the onset of convection in terms of two important parameters only: the operational cross-diffusivity and the buoyancy ratio, giving the relative contribution of the two species to the global density. The general classification of the NCC and PCC scenarios in such parameter space is supported by numerical simulations of the fully nonlinear CDC problem. The resulting convective patterns compare favorably with recent experimental results found in microemulsion systems.

Diffusion of interacting particles in discrete geometries: Equilibrium and dynamical properties

NASA Astrophysics Data System (ADS)

Becker, T.; Nelissen, K.; Cleuren, B.; Partoens, B.; Van den Broeck, C.

2014-11-01

We expand on a recent study of a lattice model of interacting particles [Phys. Rev. Lett. 111, 110601 (2013), 10.1103/PhysRevLett.111.110601]. The adsorption isotherm and equilibrium fluctuations in particle number are discussed as a function of the interaction. Their behavior is similar to that of interacting particles in porous materials. Different expressions for the particle jump rates are derived from transition-state theory. Which expression should be used depends on the strength of the interparticle interactions. Analytical expressions for the self- and transport diffusion are derived when correlations, caused by memory effects in the environment, are neglected. The diffusive behavior is studied numerically with kinetic Monte Carlo (kMC) simulations, which reproduces the diffusion including correlations. The effect of correlations is studied by comparing the analytical expressions with the kMC simulations. It is found that the Maxwell-Stefan diffusion can exceed the self-diffusion. To our knowledge, this is the first time this is observed. The diffusive behavior in one-dimensional and higher-dimensional systems is qualitatively the same, with the effect of correlations decreasing for increasing dimension. The length dependence of both the self- and transport diffusion is studied for one-dimensional systems. For long lengths the self-diffusion shows a 1 /L dependence. Finally, we discuss when agreement with experiments and simulations can be expected. The assumption that particles in different cavities do not interact is expected to hold quantitatively at low and medium particle concentrations if the particles are not strongly interacting.

Li diffusion and the effect of local structure on Li mobility in Li2O-SiO2 glasses.

PubMed

Bauer, Ute; Welsch, Anna-Maria; Behrens, Harald; Rahn, Johanna; Schmidt, Harald; Horn, Ingo

2013-12-05

Aimed to improve the understanding of lithium migration mechanisms in ion conductors, this study focuses on Li dynamics in binary Li silicate glasses. Isotope exchange experiments and conductivity measurements were carried out to determine self-diffusion coefficients and activation energies for Li migration in Li2Si3O7 and Li2Si6O13 glasses. Samples of identical composition but different isotope content were combined for diffusion experiments in couples or triples. Diffusion profiles developed between 511 and 664 K were analyzed by femtosecond laser ablation combined with multiple collector inductively coupled plasma mass spectrometry (fs LA-MC-ICP-MS) and secondary ion mass spectrometry (SIMS). Analyses of diffusion profiles and comparison of diffusion data reveal that the isotope effect of lithium diffusion in silicate glasses is rather small, consistent with classical diffusion behavior. Ionic conductivity of glasses was measured between 312 and 675 K. The experimentally obtained self-diffusion coefficient, D(IE), and ionic diffusion coefficient, D(σ), derived from specific DC conductivity provided information about correlation effects during Li diffusion. The D(IE)/D(σ) is higher for the trisilicate (0.27 ± 0.05) than that for the hexasilicate (0.17 ± 0.02), implying that increasing silica content reduces the efficiency of Li jumps in terms of long-range movement. This trend can be rationalized by structural concepts based on nuclear magnetic resonance (NMR) and Raman spectroscopy as well as molecular dynamic simulations, that is, lithium is percolating in low-dimensional, alkali-rich regions separated by a silica-rich matrix.

Dynamics and control of coherent structures in the turbulent wall layer: An overview

NASA Technical Reports Server (NTRS)

Berkooz, Gal; Holmes, Philip; Lumley, John

1993-01-01

We expand the velocity field in the vicinity of the wall in empirical eigenfunctions obtained from experiment. Truncating our system and using Galerkin projection, we obtain a closed set of non-linear ordinary differential equations with ten degrees of freedom. We find a rich dynamical behavior, including in particular a heteroclinic attracting orbit giving rise to intermittency. The intermittent jump from one attracting point to the other resembles in many respects the bursts observed in experiments. Specifically, the time between jumps and the duration of the jumps, is approximately that observed in a burst; the jump begins with the formation of a narrowed and intensified updraft, like the ejection phase of a burst, and is followed by a gentle, diffuse downdraft like the sweep phase of a burst. The magnitude of the Reynolds stress spike produced during a burst is limited by our truncation. The behavior is quite robust, much of it being due to the symmetries present (Aubry's group has examined dimensions up to 128 with persistence of the global behavior). We have examined eigenvalues and coefficients obtained from experiment, and from exact simulation, which differ in magnitude. Similar behavior is obtained in both cases; in the latter case, the heteroclinic orbits connect limit cycles instead of fixed points, corresponding to cross-stream waving of the streamwise rolls. The bifurcation diagram remains structurally similar, but somewhat distorted. The role of the pressure term is made clear - it triggers the intermittent jumps, which otherwise would occur at longer and longer intervals, as the system trajectory is attracted closer and closer to the heteroclinic cycle. The pressure term results in the jumps occurring at essentially random times, and the magnitude of the signal determines the average timing. Stretching of the wall region shows that the model is consistent with observations of polymer drag reduction. Change of the third order coefficients, corresponding to acceleration or deceleration of the mean flow, changes the heteroclinic cycles from attracting to repelling, increasing or decreasing the stability, in agreement with observations. The existence of fixed points is an artifact introduced by the projection; however, a decoupled model still displays the rich dynamics. Numerous assumptions made in Aubry et al. (1988) can now be proved exactly. Feeding back eigenfuncitons with the proper phase can delay the bursting, (the heteroclinic jump to the other fixed point), decreasing the drag. It is also possible to speed up the bursting, increasing mixing to control separation. Our approach is optimal for short time tracking in control.

Strange kinetics of bulk-mediated diffusion on lipid bilayers

PubMed Central

Campagnola, Grace; Nepal, Kanti; Peersen, Olve B.

2016-01-01

Diffusion at solid-liquid interfaces is crucial in many technological and biophysical processes. Although its behavior seems deceivingly simple, recent studies showing passive superdiffusive transport suggest diffusion on surfaces may hide rich complexities. In particular, bulk-mediated diffusion occurs when molecules are transiently released from the surface to perform three-dimensional excursions into the liquid bulk. This phenomenon bears the dichotomy where a molecule always return to the surface but the mean jump length is infinite. Such behavior is associated with a breakdown of the central limit theorem and weak ergodicity breaking. Here, we use single-particle tracking to study the statistics of bulk-mediated diffusion on a supported lipid bilayer. We find that the time-averaged mean square displacement (MSD) of individual trajectories, the archetypal measure in diffusion processes, does not converge to the ensemble MSD but it remains a random variable, even in the long observation-time limit. The distribution of time averages is shown to agree with a Lévy flight model. Our results also unravel intriguing anomalies in the statistics of displacements. The time averaged MSD is shown to depend on experimental time and investigations of fractional moments show a scaling 〈|r(t)|q〉 ∼ tqv(q) with non-linear exponents, i.e. v(q) ≠ const. This type of behavior is termed strong anomalous diffusion and is rare among experimental observations. PMID:27095275

Jumping, Rotating, and Flapping: The Atomic-Scale Motion of Thiophene on Cu(111).

PubMed

Lechner, Barbara A J; Sacchi, Marco; Jardine, Andrew P; Hedgeland, Holly; Allison, William; Ellis, John; Jenkins, Stephen J; Dastoor, Paul C; Hinch, B J

2013-06-06

Self-assembled monolayers of sulfur-containing heterocycles and linear oligomers containing thiophene groups have been widely employed in organic electronic applications. Here, we investigate the dynamics of isolated thiophene molecules on Cu(111) by combining helium spin-echo (HeSE) spectroscopy with density functional theory calculations. We show that the thiophene/Cu(111) system displays a rich array of aperiodic dynamical phenomena that include jump diffusion between adjacent atop sites over a 59-62 meV barrier and activated rotation around a sulfur-copper anchor, two processes that have been observed previously for related systems. In addition, we present experimental evidence for a new, weakly activated process, the flapping of the molecular ring. Repulsive inter-adsorbate interactions and an exceptionally high friction coefficient of 5 ± 2 ps(-1) are also observed. These experiments demonstrate the versatility of the HeSE technique, and the quantitative information extracted in a detailed analysis provides an ideal benchmark for state-of-the-art theoretical techniques including nonlocal adsorbate-substrate interactions.

Bootstrapping Least Squares Estimates in Biochemical Reaction Networks

PubMed Central

Linder, Daniel F.

2015-01-01

The paper proposes new computational methods of computing confidence bounds for the least squares estimates (LSEs) of rate constants in mass-action biochemical reaction network and stochastic epidemic models. Such LSEs are obtained by fitting the set of deterministic ordinary differential equations (ODEs), corresponding to the large volume limit of a reaction network, to network’s partially observed trajectory treated as a continuous-time, pure jump Markov process. In the large volume limit the LSEs are asymptotically Gaussian, but their limiting covariance structure is complicated since it is described by a set of nonlinear ODEs which are often ill-conditioned and numerically unstable. The current paper considers two bootstrap Monte-Carlo procedures, based on the diffusion and linear noise approximations for pure jump processes, which allow one to avoid solving the limiting covariance ODEs. The results are illustrated with both in-silico and real data examples from the LINE 1 gene retrotranscription model and compared with those obtained using other methods. PMID:25898769

Compact vacuum tubes with GaAs(Cs,O) photocathodes for studying spin-dependent phenomena

NASA Astrophysics Data System (ADS)

Alperovich, V. L.; Orlov, D. A.; Grishaev, V. G.; Kosolobov, S. N.; Jaroshevich, A. S.; Scheibler, H. E.; Terekhov, A. S.

2009-08-01

Compact proximity focused vacuum tubes with GaAs(Cs,O) photocathodes are used for experimental studying spindependent phenomena. Firstly, spin-dependent emission of optically oriented electrons from p-GaAs(Cs,O) into vacuum in a magnetic field normal to the surface was observed in a nonmagnetic vacuum diode. This phenomenon is explained by the jump in the electron g-factor at the semiconductor-vacuum interface. Due to this jump, the effective electron affinity on the semiconductor surface depends on the mutual direction of optically oriented electron spins and the magnetic field, resulting in the spin-dependent photoemission. It is demonstrated that the observed effect can be used for the determination of spin diffusion length in semiconductors. Secondly, we developed a prototype of a new spin filter, which consists of a vacuum tube with GaAs(Cs,O) photocathode and a nickel-covered venetian blind dynode. Preliminary results on spin-dependent reflection of electrons from the oxidized polycrystal nickel layer are presented.

Nonequilibrium ab initio molecular dynamics determination of Ti monovacancy migration rates in B 1 TiN

NASA Astrophysics Data System (ADS)

Gambino, D.; Sangiovanni, D. G.; Alling, B.; Abrikosov, I. A.

2017-09-01

We use the color diffusion (CD) algorithm in nonequilibrium (accelerated) ab initio molecular dynamics simulations to determine Ti monovacancy jump frequencies in NaCl-structure titanium nitride (TiN), at temperatures ranging from 2200 to 3000 K. Our results show that the CD method extended beyond the linear-fitting rate-versus-force regime [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016), 10.1103/PhysRevB.93.094305] can efficiently determine metal vacancy migration rates in TiN, despite the low mobilities of lattice defects in this type of ceramic compound. We propose a computational method based on gamma-distribution statistics, which provides unambiguous definition of nonequilibrium and equilibrium (extrapolated) vacancy jump rates with corresponding statistical uncertainties. The acceleration-factor achieved in our implementation of nonequilibrium molecular dynamics increases dramatically for decreasing temperatures from 500 for T close to the melting point Tm, up to 33 000 for T ≈0.7 Tm .

Unifying models of dialect spread and extinction using surface tension dynamics

PubMed Central

2018-01-01

We provide a unified mathematical explanation of two classical forms of spatial linguistic spread. The wave model describes the radiation of linguistic change outwards from a central focus. Changes can also jump between population centres in a process known as hierarchical diffusion. It has recently been proposed that the spatial evolution of dialects can be understood using surface tension at linguistic boundaries. Here we show that the inclusion of long-range interactions in the surface tension model generates both wave-like spread, and hierarchical diffusion, and that it is surface tension that is the dominant effect in deciding the stable distribution of dialect patterns. We generalize the model to allow population mixing which can induce shrinkage of linguistic domains, or destroy dialect regions from within. PMID:29410847

A Nonequilibrium Rate Formula for Collective Motions of Complex Molecular Systems

NASA Astrophysics Data System (ADS)

Yanao, Tomohiro; Koon, Wang Sang; Marsden, Jerrold E.

2010-09-01

We propose a compact reaction rate formula that accounts for a non-equilibrium distribution of residence times of complex molecules, based on a detailed study of the coarse-grained phase space of a reaction coordinate. We take the structural transition dynamics of a six-atom Morse cluster between two isomers as a prototype of multi-dimensional molecular reactions. Residence time distribution of one of the isomers shows an exponential decay, while that of the other isomer deviates largely from the exponential form and has multiple peaks. Our rate formula explains such equilibrium and non-equilibrium distributions of residence times in terms of the rates of diffusions of energy and the phase of the oscillations of the reaction coordinate. Rapid diffusions of energy and the phase generally give rise to the exponential decay of residence time distribution, while slow diffusions give rise to a non-exponential decay with multiple peaks. We finally make a conjecture about a general relationship between the rates of the diffusions and the symmetry of molecular mass distributions.

Analytical and numerical solutions for mass diffusion in a composite cylindrical body

NASA Astrophysics Data System (ADS)

Kumar, A.

1980-12-01

The analytical and numerical solution techniques were investigated to study moisture diffusion problems in cylindrical bodies that are assumed to be composed of a finite number of layers of different materials. A generalized diffusion model for an n-layer cylindrical body with discontinuous moisture content at the interfaces was developed and the formal solutions were obtained. The model is to be used for describing mass transfer rates of any composite body, such as an ear of corn which could be assumed of consisting two different layers: the inner core represents the woody cob and the outer cylinder represents the kernel layer. Data describing the fully exposed drying characteristics of ear corn at high air velocity were obtained under different drying conditions. Ear corns were modeled as homogeneous bodies since composite model did not improve the fit substantially. A computer program using multidimensional optimization technique showed that diffusivity was an exponential function of moisture content and an arrhenius function of temperature of drying air.

Li-Diffusion in Spinel Li[Ni1/2Mn3/2]O4 Powder and Film Studied with μ+SR

NASA Astrophysics Data System (ADS)

Sugiyama, Jun; Nozaki, Hiroshi; Umegaki, Izumi; Mukai, Kazuhiko; Cottrell, Stephen P.; Shiraki, Susumu; Hitosugi, Taro; Sassa, Yasmine; Suter, Andreas; Salman, Zaher; Prokscha, Thomas; Månsson, Martin

A dynamic behavior in spinel Li[Ni1/2Mn3/2]O4 has been studied with μ+SR measurements in film and powder samples in the temperature range between 5 and 500 K. Both samples exhibited a broad ferromagnetic transition below 120 K, indicating the random distribution of Ni and Mn ions at the octahedral 16d site. Above 150 K, the ZF-μ+SR spectrum showed a dynamic behavior well explained by a dynamic Kubo-Toyabe function. Assuming a jump diffusion of Li+ at the tetrahedral 8a site to the vacant octahedral 16c site, a diffusion coefficient of Li+ is estimated as ˜5 × 10-11 cm2/s at 300 K and ˜8 × 10-11 cm2/s at 350 K and ˜14 × 10-11 cm2/s at 400 K, with thermal activation energy Ea ˜ 0.1 eV.

QENS study of methane diffusion in Mo/H-ZSM-5 used for the methane dehydroaromatisation reaction

NASA Astrophysics Data System (ADS)

Silverwood, Ian P.; Arán, Miren Agote; González, Ines Lezcano; Kroner, Anna; Beale, Andrew M.

2018-05-01

There is commercial interest in understanding the deactivation of Mo loaded H-ZSM-5 catalyst by coke fouling during the methane dehydroaromatization reaction (MDA). The effect of coke on methane diffusion inside the zeolite pores was studied by quasielastic neutron scattering (QENS) measurements on Mo/H-ZSM-5 samples reacted with methane for 0, 7, 25 and 60 min. Catalytic activity of the samples followed by mass spectrometry indicate that the induction period in which Mo species are carburized lasts for ˜9 min; after this period the material shows selectivity to aromatics. Characterization by TGA and N2 physisorption suggest that practically no carbon is deposited during the induction period. The ˜2 wt % of coke formed after one hour of reaction has a negligible effect in the zeolite crystal structurebut a small effect on the micropore volume. The QENS studies show that the methane transport by jump diffusion is however not measurably affected by the accumulated coke in the samples.

Numerical Methods for 2-Dimensional Modeling

DTIC Science & Technology

1980-12-01

high-order finite element methods, and a multidimensional version of the method of lines, both utilizing an optimized stiff integrator for the time...integration. The finite element methods have proved disappointing, but the method of lines has provided an unexpectedly large gain in speed. Two...diffusion problems with the same number of unknowns (a 21 x 41 grid), solved by second-order finite element methods, took over seven minutes on the Cray-i

VENTURE/PC manual: A multidimensional multigroup neutron diffusion code system. Version 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shapiro, A.; Huria, H.C.; Cho, K.W.

1991-12-01

VENTURE/PC is a recompilation of part of the Oak Ridge BOLD VENTURE code system, which will operate on an IBM PC or compatible computer. Neutron diffusion theory solutions are obtained for multidimensional, multigroup problems. This manual contains information associated with operating the code system. The purpose of the various modules used in the code system, and the input for these modules are discussed. The PC code structure is also given. Version 2 included several enhancements not given in the original version of the code. In particular, flux iterations can be done in core rather than by reading and writing tomore » disk, for problems which allow sufficient memory for such in-core iterations. This speeds up the iteration process. Version 3 does not include any of the special processors used in the previous versions. These special processors utilized formatted input for various elements of the code system. All such input data is now entered through the Input Processor, which produces standard interface files for the various modules in the code system. In addition, a Standard Interface File Handbook is included in the documentation which is distributed with the code, to assist in developing the input for the Input Processor.« less

Two-dimensional numerical simulation of boron diffusion for pyramidally textured silicon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ma, Fa-Jun, E-mail: Fajun.Ma@nus.edu.sg; Duttagupta, Shubham; Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, 117576

2014-11-14

Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime samples. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured samples. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boronmore » diffusion recipes on planar samples. The established parameters are subsequently used to simulate the boron diffusion process on textured samples. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured samples is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured samples to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured samples. The differences between planar and textured samples are discussed.« less

Multidimensional infrared spectroscopy reveals the vibrational and solvation dynamics of isoniazid

NASA Astrophysics Data System (ADS)

Shaw, Daniel J.; Adamczyk, Katrin; Frederix, Pim W. J. M.; Simpson, Niall; Robb, Kirsty; Greetham, Gregory M.; Towrie, Michael; Parker, Anthony W.; Hoskisson, Paul A.; Hunt, Neil T.

2015-06-01

The results of infrared spectroscopic investigations into the band assignments, vibrational relaxation, and solvation dynamics of the common anti-tuberculosis treatment Isoniazid (INH) are reported. INH is known to inhibit InhA, a 2-trans-enoyl-acyl carrier protein reductase enzyme responsible for the maintenance of cell walls in Mycobacterium tuberculosis but as new drug-resistant strains of the bacterium appear, next-generation therapeutics will be essential to combat the rise of the disease. Small molecules such as INH offer the potential for use as a biomolecular marker through which ultrafast multidimensional spectroscopies can probe drug binding and so inform design strategies but a complete characterization of the spectroscopy and dynamics of INH in solution is required to inform such activity. Infrared absorption spectroscopy, in combination with density functional theory calculations, is used to assign the vibrational modes of INH in the 1400-1700 cm-1 region of the infrared spectrum while ultrafast multidimensional spectroscopy measurements determine the vibrational relaxation dynamics and the effects of solvation via spectral diffusion of the carbonyl stretching vibrational mode. These results are discussed in the context of previous linear spectroscopy studies on solid-phase INH and its usefulness as a biomolecular probe.

Molecular dynamics simulation of three plastic additives' diffusion in polyethylene terephthalate.

PubMed

Li, Bo; Wang, Zhi-Wei; Lin, Qin-Bao; Hu, Chang-Ying

2017-06-01

Accurate diffusion coefficient data of additives in a polymer are of paramount importance for estimating the migration of the additives over time. This paper shows how this diffusion coefficient can be estimated for three plastic additives [2-(2'-hydroxy-5'-methylphenyl) (UV-P), 2,6-di-tert-butyl-4-methylphenol (BHT) and di-(2-ethylhexyl) phthalate (DEHP)] in polyethylene terephthalate (PET) using the molecular dynamics (MD) simulation method. MD simulations were performed at temperatures of 293-433 K. The diffusion coefficient was calculated through the Einstein relationship connecting the data of mean-square displacement at different times. Comparison of the diffusion coefficients simulated by the MD simulation technique, predicted by the Piringer model and experiments, showed that, except for a few samples, the MD-simulated values were in agreement with the experimental values within one order of magnitude. Furthermore, the diffusion process for additives is discussed in detail, and four factors - the interaction energy between additive molecules and PET, fractional free volume, molecular shape and size, and self-diffusion of the polymer - are proposed to illustrate the microscopic diffusion mechanism. The movement trajectories of additives in PET cell models suggested that the additive molecules oscillate slowly rather than hopping for a long time. Occasionally, when a sufficiently large hole was created adjacently, the molecule could undergo spatial motion by jumping into the free-volume hole and consequently start a continuous oscillation and hop. The results indicate that MD simulation is a useful approach for predicting the microstructure and diffusion coefficient of plastic additives, and help to estimate the migration level of additives from PET packaging.

Accurate reaction-diffusion operator splitting on tetrahedral meshes for parallel stochastic molecular simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hepburn, I.; De Schutter, E., E-mail: erik@oist.jp; Theoretical Neurobiology & Neuroengineering, University of Antwerp, Antwerp 2610

Spatial stochastic molecular simulations in biology are limited by the intense computation required to track molecules in space either in a discrete time or discrete space framework, which has led to the development of parallel methods that can take advantage of the power of modern supercomputers in recent years. We systematically test suggested components of stochastic reaction-diffusion operator splitting in the literature and discuss their effects on accuracy. We introduce an operator splitting implementation for irregular meshes that enhances accuracy with minimal performance cost. We test a range of models in small-scale MPI simulations from simple diffusion models to realisticmore » biological models and find that multi-dimensional geometry partitioning is an important consideration for optimum performance. We demonstrate performance gains of 1-3 orders of magnitude in the parallel implementation, with peak performance strongly dependent on model specification.« less

A finite elements method to solve the Bloch–Torrey equation applied to diffusion magnetic resonance imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Dang Van; NeuroSpin, Bat145, Point Courrier 156, CEA Saclay Center, 91191 Gif-sur-Yvette Cedex; Li, Jing-Rebecca, E-mail: jingrebecca.li@inria.fr

2014-04-15

The complex transverse water proton magnetization subject to diffusion-encoding magnetic field gradient pulses in a heterogeneous medium can be modeled by the multiple compartment Bloch–Torrey partial differential equation (PDE). In addition, steady-state Laplace PDEs can be formulated to produce the homogenized diffusion tensor that describes the diffusion characteristics of the medium in the long time limit. In spatial domains that model biological tissues at the cellular level, these two types of PDEs have to be completed with permeability conditions on the cellular interfaces. To solve these PDEs, we implemented a finite elements method that allows jumps in the solution atmore » the cell interfaces by using double nodes. Using a transformation of the Bloch–Torrey PDE we reduced oscillations in the searched-for solution and simplified the implementation of the boundary conditions. The spatial discretization was then coupled to the adaptive explicit Runge–Kutta–Chebyshev time-stepping method. Our proposed method is second order accurate in space and second order accurate in time. We implemented this method on the FEniCS C++ platform and show time and spatial convergence results. Finally, this method is applied to study some relevant questions in diffusion MRI.« less

Interpretation of diffusion coefficients in nanostructured materials from random walk numerical simulation.

PubMed

Anta, Juan A; Mora-Seró, Iván; Dittrich, Thomas; Bisquert, Juan

2008-08-14

We make use of the numerical simulation random walk (RWNS) method to compute the "jump" diffusion coefficient of electrons in nanostructured materials via mean-square displacement. First, a summary of analytical results is given that relates the diffusion coefficient obtained from RWNS to those in the multiple-trapping (MT) and hopping models. Simulations are performed in a three-dimensional lattice of trap sites with energies distributed according to an exponential distribution and with a step-function distribution centered at the Fermi level. It is observed that once the stationary state is reached, the ensemble of particles follow Fermi-Dirac statistics with a well-defined Fermi level. In this stationary situation the diffusion coefficient obeys the theoretical predictions so that RWNS effectively reproduces the MT model. Mobilities can be also computed when an electrical bias is applied and they are observed to comply with the Einstein relation when compared with steady-state diffusion coefficients. The evolution of the system towards the stationary situation is also studied. When the diffusion coefficients are monitored along simulation time a transition from anomalous to trap-limited transport is observed. The nature of this transition is discussed in terms of the evolution of electron distribution and the Fermi level. All these results will facilitate the use of RW simulation and related methods to interpret steady-state as well as transient experimental techniques.

Conditioning exercises in ski jumping: biomechanical relationship of squat jumps, imitation jumps, and hill jumps.

PubMed

Lorenzetti, Silvio; Ammann, Fabian; Windmüller, Sabrina; Häberle, Ramona; Müller, Sören; Gross, Micah; Plüss, Michael; Plüss, Stefan; Schödler, Berni; Hübner, Klaus

2017-11-22

As hill jumps are very time-consuming, ski jumping athletes often perform various imitation jumps during training. The performed jumps should be similar to hill jumps, but a direct comparison of the kinetic and kinematic parameters has not been performed yet. Therefore, this study aimed to correlate 11 common parameters during hill jumps (Oberstdorf Germany), squat jumps (wearing indoor shoes), and various imitation jumps (rolling 4°, rolling flat, static; jumping equipment or indoor shoes) on a custom-built instrumented vehicle with a catch by the coach. During the performed jumps, force and video data of the take-off of 10 athletes were measured. The imitation and squat jumps were then ranked. The main difference between the hill jumps and the imitation and squat jumps is the higher maximal force loading rate during the hill jumps. Imitation jumps performed on a rolling platform, on flat ground were the most similar to hill jumps in terms of the force-time, and leg joint kinematic properties. Thus, non-hill jumps with a technical focus should be performed from a rolling platform with a flat inrun with normal indoor shoes or jumping equipment, and high normal force loading rates should be the main focus of imitation training.

Itô and Stratonovich integrals on compound renewal processes: the normal/Poisson case

NASA Astrophysics Data System (ADS)

Germano, Guido; Politi, Mauro; Scalas, Enrico; Schilling, René L.

2010-06-01

Continuous-time random walks, or compound renewal processes, are pure-jump stochastic processes with several applications in insurance, finance, economics and physics. Based on heuristic considerations, a definition is given for stochastic integrals driven by continuous-time random walks, which includes the Itô and Stratonovich cases. It is then shown how the definition can be used to compute these two stochastic integrals by means of Monte Carlo simulations. Our example is based on the normal compound Poisson process, which in the diffusive limit converges to the Wiener process.

Loss aversion, large deviation preferences and optimal portfolio weights for some classes of return processes

NASA Astrophysics Data System (ADS)

Duffy, Ken; Lobunets, Olena; Suhov, Yuri

2007-05-01

We propose a model of a loss averse investor who aims to maximize his expected wealth under certain constraints. The constraints are that he avoids, with high probability, incurring an (suitably defined) unacceptable loss. The methodology employed comes from the theory of large deviations. We explore a number of fundamental properties of the model and illustrate its desirable features. We demonstrate its utility by analyzing assets that follow some commonly used financial return processes: Fractional Brownian Motion, Jump Diffusion, Variance Gamma and Truncated Lévy.

Wealth and price distribution by diffusive approximation in a repeated prediction market

NASA Astrophysics Data System (ADS)

Bottazzi, Giulio; Giachini, Daniele

2017-04-01

The approximate agents' wealth and price invariant densities of a repeated prediction market model is derived using the Fokker-Planck equation of the associated continuous-time jump process. We show that the approximation obtained from the evolution of log-wealth difference can be reliably exploited to compute all the quantities of interest in all the acceptable parameter space. When the risk aversion of the trader is high enough, we are able to derive an explicit closed-form solution for the price distribution which is asymptotically correct.

Compact stochastic models for multidimensional quasiballistic thermal transport

NASA Astrophysics Data System (ADS)

Vermeersch, Bjorn

2016-11-01

The Boltzmann transport equation (BTE) has proven indispensable in elucidating quasiballistic heat dynamics. The experimental observations of nondiffusive thermal transients, however, are interpreted almost exclusively through purely diffusive formalisms that merely extract "effective" Fourier conductivities. Here, we build upon stochastic transport theory to provide a characterisation framework that blends the rich physics contained within the BTE solutions with the convenience of conventional analyses. The multidimensional phonon dynamics are described in terms of an isotropic Poissonian flight process with a rigorous Fourier-Laplace single pulse response P (ξ → ,s )=1 /[s +ψ(∥ ξ → ∥ )] . The spatial propagator ψ(∥ ξ → ∥ ) , unlike commonly reconstructed mean free path spectra κΣ(Λ) , serves as a genuine thermal blueprint of the medium that can be identified in a compact form directly from the raw measurement signals. Practical illustrations for transient thermal grating and time domain thermoreflectance experiments on respectively GaAs and InGaAs are provided.

Similarity from multi-dimensional scaling: solving the accuracy and diversity dilemma in information filtering.

PubMed

Zeng, Wei; Zeng, An; Liu, Hao; Shang, Ming-Sheng; Zhang, Yi-Cheng

2014-01-01

Recommender systems are designed to assist individual users to navigate through the rapidly growing amount of information. One of the most successful recommendation techniques is the collaborative filtering, which has been extensively investigated and has already found wide applications in e-commerce. One of challenges in this algorithm is how to accurately quantify the similarities of user pairs and item pairs. In this paper, we employ the multidimensional scaling (MDS) method to measure the similarities between nodes in user-item bipartite networks. The MDS method can extract the essential similarity information from the networks by smoothing out noise, which provides a graphical display of the structure of the networks. With the similarity measured from MDS, we find that the item-based collaborative filtering algorithm can outperform the diffusion-based recommendation algorithms. Moreover, we show that this method tends to recommend unpopular items and increase the global diversification of the networks in long term.

Influence of lumbar spine extension on vertical jump height during maximal squat jumping.

PubMed

Blache, Yoann; Monteil, Karine

2014-01-01

The purpose of this study was to determine the influence of lumbar spine extension and erector spinae muscle activation on vertical jump height during maximal squat jumping. Eight male athletes performed maximal squat jumps. Electromyograms of the erector spinae were recorded during these jumps. A simulation model of the musculoskeletal system was used to simulate maximal squat jumping with and without spine extension. The effect on vertical jump height of changing erector spinae strength was also tested through the simulated jumps. Concerning the participant jumps, the kinematics indicated a spine extension and erector spinae activation. Concerning the simulated jumps, vertical jump height was about 5.4 cm lower during squat jump without trunk extension compared to squat jump. These results were explained by greater total muscle work during squat jump, more especially by the erector spinae work (+119.5 J). The erector spinae may contribute to spine extension during maximal squat jumping. The simulated jumps confirmed this hypothesis showing that vertical jumping was decreased if this muscle was not taken into consideration in the model. Therefore it is concluded that the erector spinae should be considered as a trunk extensor, which enables to enhance total muscle work and consequently vertical jump height.

Drop jumping. I. The influence of jumping technique on the biomechanics of jumping.

PubMed

Bobbert, M F; Huijing, P A; van Ingen Schenau, G J

1987-08-01

In the literature, drop jumping is advocated as an effective exercise for athletes who prepare themselves for explosive activities. When executing drop jumps, different jumping techniques can be used. In this study, the influence of jumping technique on the biomechanics of jumping is investigated. Ten subjects executed drop jumps from a height of 20 cm and counter-movement jumps. For the execution of the drop jumps, two different techniques were adopted. The first technique, referred to as bounce drop jump, required the subjects to reverse the downward velocity into an upward one as soon as possible after landing. The second technique, referred to as counter-movement drop jump, required them to do this more gradually by making a larger downward movement. During jumping, the subjects were filmed, ground reaction forces were registered, and electromyograms were recorded. The results of a biomechanical analysis show that moments and power output about knee and ankle joints reach larger values during the drop jumps than during counter-movement jumps. The largest values were attained during bounce drop jumps. Based on this finding, it was hypothesized that bounce drop jump is better suited than counter-movement drop jump for athletes who seek to improve the mechanical output of knee extensors and plantar flexors. Researchers are, therefore, advised to control jumping technique when investigating training effects of executing drop jumps.

Modeling of molecular diffusion and thermal conduction with multi-particle interaction in compressible turbulence

NASA Astrophysics Data System (ADS)

Tai, Y.; Watanabe, T.; Nagata, K.

2018-03-01

A mixing volume model (MVM) originally proposed for molecular diffusion in incompressible flows is extended as a model for molecular diffusion and thermal conduction in compressible turbulence. The model, established for implementation in Lagrangian simulations, is based on the interactions among spatially distributed notional particles within a finite volume. The MVM is tested with the direct numerical simulation of compressible planar jets with the jet Mach number ranging from 0.6 to 2.6. The MVM well predicts molecular diffusion and thermal conduction for a wide range of the size of mixing volume and the number of mixing particles. In the transitional region of the jet, where the scalar field exhibits a sharp jump at the edge of the shear layer, a smaller mixing volume is required for an accurate prediction of mean effects of molecular diffusion. The mixing time scale in the model is defined as the time scale of diffusive effects at a length scale of the mixing volume. The mixing time scale is well correlated for passive scalar and temperature. Probability density functions of the mixing time scale are similar for molecular diffusion and thermal conduction when the mixing volume is larger than a dissipative scale because the mixing time scale at small scales is easily affected by different distributions of intermittent small-scale structures between passive scalar and temperature. The MVM with an assumption of equal mixing time scales for molecular diffusion and thermal conduction is useful in the modeling of the thermal conduction when the modeling of the dissipation rate of temperature fluctuations is difficult.

Asymmetric skew Bessel processes and their applications to finance

NASA Astrophysics Data System (ADS)

Decamps, Marc; Goovaerts, Marc; Schoutens, Wim

2006-02-01

In this paper, we extend the Harrison and Shepp's construction of the skew Brownian motion (1981) and we obtain a diffusion similar to the two-dimensional Bessel process with speed and scale densities discontinuous at one point. Natural generalizations to multi-dimensional and fractional order Bessel processes are then discussed as well as invariance properties. We call this family of diffusions asymmetric skew Bessel processes in opposition to skew Bessel processes as defined in Barlow et al. [On Walsh's Brownian motions, Seminaire de Probabilities XXIII, Lecture Notes in Mathematics, vol. 1372, Springer, Berlin, New York, 1989, pp. 275-293]. We present factorizations involving (asymmetric skew) Bessel processes with random time. Finally, applications to the valuation of perpetuities and Asian options are proposed.

Exact calculations of survival probability for diffusion on growing lines, disks, and spheres: The role of dimension.

PubMed

Simpson, Matthew J; Baker, Ruth E

2015-09-07

Unlike standard applications of transport theory, the transport of molecules and cells during embryonic development often takes place within growing multidimensional tissues. In this work, we consider a model of diffusion on uniformly growing lines, disks, and spheres. An exact solution of the partial differential equation governing the diffusion of a population of individuals on the growing domain is derived. Using this solution, we study the survival probability, S(t). For the standard non-growing case with an absorbing boundary, we observe that S(t) decays to zero in the long time limit. In contrast, when the domain grows linearly or exponentially with time, we show that S(t) decays to a constant, positive value, indicating that a proportion of the diffusing substance remains on the growing domain indefinitely. Comparing S(t) for diffusion on lines, disks, and spheres indicates that there are minimal differences in S(t) in the limit of zero growth and minimal differences in S(t) in the limit of fast growth. In contrast, for intermediate growth rates, we observe modest differences in S(t) between different geometries. These differences can be quantified by evaluating the exact expressions derived and presented here.

Assessing the multiscale architecture of muscular tissue with Q-space magnetic resonance imaging: Review.

PubMed

Hoffman, Matthew P; Taylor, Erik N; Aninwene, George E; Sadayappan, Sakthivel; Gilbert, Richard J

2018-02-01

Contraction of muscular tissue requires the synchronized shortening of myofibers arrayed in complex geometrical patterns. Imaging such myofiber patterns with diffusion-weighted MRI reveals architectural ensembles that underlie force generation at the organ scale. Restricted proton diffusion is a stochastic process resulting from random translational motion that may be used to probe the directionality of myofibers in whole tissue. During diffusion-weighted MRI, magnetic field gradients are applied to determine the directional dependence of proton diffusion through the analysis of a diffusional probability distribution function (PDF). The directions of principal (maximal) diffusion within the PDF are associated with similarly aligned diffusion maxima in adjacent voxels to derive multivoxel tracts. Diffusion-weighted MRI with tractography thus constitutes a multiscale method for depicting patterns of cellular organization within biological tissues. We provide in this review, details of the method by which generalized Q-space imaging is used to interrogate multidimensional diffusion space, and thereby to infer the organization of muscular tissue. Q-space imaging derives the lowest possible angular separation of diffusion maxima by optimizing the conditions by which magnetic field gradients are applied to a given tissue. To illustrate, we present the methods and applications associated with Q-space imaging of the multiscale myoarchitecture associated with the human and rodent tongues. These representations emphasize the intricate and continuous nature of muscle fiber organization and suggest a method to depict structural "blueprints" for skeletal and cardiac muscle tissue. © 2016 Wiley Periodicals, Inc.

Numerical simulation of double‐diffusive finger convection

USGS Publications Warehouse

Hughes, Joseph D.; Sanford, Ward E.; Vacher, H. Leonard

2005-01-01

A hybrid finite element, integrated finite difference numerical model is developed for the simulation of double‐diffusive and multicomponent flow in two and three dimensions. The model is based on a multidimensional, density‐dependent, saturated‐unsaturated transport model (SUTRA), which uses one governing equation for fluid flow and another for solute transport. The solute‐transport equation is applied sequentially to each simulated species. Density coupling of the flow and solute‐transport equations is accounted for and handled using a sequential implicit Picard iterative scheme. High‐resolution data from a double‐diffusive Hele‐Shaw experiment, initially in a density‐stable configuration, is used to verify the numerical model. The temporal and spatial evolution of simulated double‐diffusive convection is in good agreement with experimental results. Numerical results are very sensitive to discretization and correspond closest to experimental results when element sizes adequately define the spatial resolution of observed fingering. Numerical results also indicate that differences in the molecular diffusivity of sodium chloride and the dye used to visualize experimental sodium chloride concentrations are significant and cause inaccurate mapping of sodium chloride concentrations by the dye, especially at late times. As a result of reduced diffusion, simulated dye fingers are better defined than simulated sodium chloride fingers and exhibit more vertical mass transfer.

Position-Dependent Diffusion Tensors in Anisotropic Media from Simulation: Oxygen Transport in and through Membranes.

PubMed

Ghysels, An; Venable, Richard M; Pastor, Richard W; Hummer, Gerhard

2017-06-13

A Bayesian-based methodology is developed to estimate diffusion tensors from molecular dynamics simulations of permeants in anisotropic media, and is applied to oxygen in lipid bilayers. By a separation of variables in the Smoluchowski diffusion equation, the multidimensional diffusion is reduced to coupled one-dimensional diffusion problems that are treated by discretization. The resulting diffusivity profiles characterize the membrane transport dynamics as a function of the position across the membrane, discriminating between diffusion normal and parallel to the membrane. The methodology is first validated with neat water, neat hexadecane, and a hexadecane slab surrounded by water, the latter being a simple model for a lipid membrane. Next, a bilayer consisting of pure 1-palmitoyl 2-oleoylphosphatidylcholine (POPC), and a bilayer mimicking the lipid composition of the inner mitochondrial membrane, including cardiolipin, are investigated. We analyze the detailed time evolution of oxygen molecules, in terms of both normal diffusion through and radial diffusion inside the membrane. Diffusion is fast in the more loosely packed interleaflet region, and anisotropic, with oxygen spreading more rapidly in the membrane plane than normal to it. Visualization of the propagator shows that oxygen enters the membrane rapidly, reaching its thermodynamically favored center in about 1 ns, despite the free energy barrier at the headgroup region. Oxygen transport is quantified by computing the oxygen permeability of the membranes and the average radial diffusivity, which confirm the anisotropy of the diffusion. The position-dependent diffusion constants and free energies are used to construct compartmental models and test assumptions used in estimating permeability, including Overton's rule. In particular, a hexadecane slab surrounded by water is found to be a poor model of oxygen transport in membranes because the relevant energy barriers differ substantially.

Chasing maximal performance: a cautionary tale from the celebrated jumping frogs of Calaveras County.

PubMed

Astley, H C; Abbott, E M; Azizi, E; Marsh, R L; Roberts, T J

2013-11-01

Maximal performance is an essential metric for understanding many aspects of an organism's biology, but it can be difficult to determine because a measured maximum may reflect only a peak level of effort, not a physiological limit. We used a unique opportunity provided by a frog jumping contest to evaluate the validity of existing laboratory estimates of maximum jumping performance in bullfrogs (Rana catesbeiana). We recorded video of 3124 bullfrog jumps over the course of the 4-day contest at the Calaveras County Jumping Frog Jubilee, and determined jump distance from these images and a calibration of the jump arena. Frogs were divided into two groups: 'rental' frogs collected by fair organizers and jumped by the general public, and frogs collected and jumped by experienced, 'professional' teams. A total of 58% of recorded jumps surpassed the maximum jump distance in the literature (1.295 m), and the longest jump was 2.2 m. Compared with rental frogs, professionally jumped frogs jumped farther, and the distribution of jump distances for this group was skewed towards long jumps. Calculated muscular work, historical records and the skewed distribution of jump distances all suggest that the longest jumps represent the true performance limit for this species. Using resampling, we estimated the probability of observing a given jump distance for various sample sizes, showing that large sample sizes are required to detect rare maximal jumps. These results show the importance of sample size, animal motivation and physiological conditions for accurate maximal performance estimates.

A third-order computational method for numerical fluxes to guarantee nonnegative difference coefficients for advection-diffusion equations in a semi-conservative form

NASA Astrophysics Data System (ADS)

Sakai, K.; Watabe, D.; Minamidani, T.; Zhang, G. S.

2012-10-01

According to Godunov theorem for numerical calculations of advection equations, there exist no higher-order schemes with constant positive difference coefficients in a family of polynomial schemes with an accuracy exceeding the first-order. We propose a third-order computational scheme for numerical fluxes to guarantee the non-negative difference coefficients of resulting finite difference equations for advection-diffusion equations in a semi-conservative form, in which there exist two kinds of numerical fluxes at a cell surface and these two fluxes are not always coincident in non-uniform velocity fields. The present scheme is optimized so as to minimize truncation errors for the numerical fluxes while fulfilling the positivity condition of the difference coefficients which are variable depending on the local Courant number and diffusion number. The feature of the present optimized scheme consists in keeping the third-order accuracy anywhere without any numerical flux limiter. We extend the present method into multi-dimensional equations. Numerical experiments for advection-diffusion equations showed nonoscillatory solutions.

Relationships Between Countermovement Jump Ground Reaction Forces and Jump Height, Reactive Strength Index, and Jump Time.

PubMed

Barker, Leland A; Harry, John R; Mercer, John A

2018-01-01

Barker, LA, Harry, JR, and Mercer, JA. Relationships between countermovement jump ground reaction forces and jump height, reactive strength index, and jump time. J Strength Cond Res 32(1): 248-254, 2018-The purpose of this study was to determine the relationship between ground reaction force (GRF) variables to jump height, jump time, and the reactive strength index (RSI). Twenty-six, Division-I, male, soccer players performed 3 maximum effort countermovement jumps (CMJs) on a dual-force platform system that measured 3-dimensional kinetic data. The trial producing peak jump height was used for analysis. Vertical GRF (Fz) variables were divided into unloading, eccentric, amortization, and concentric phases and correlated with jump height, RSI (RSI = jump height/jump time), and jump time (from start to takeoff). Significant correlations were observed between jump height and RSI, concentric kinetic energy, peak power, concentric work, and concentric displacement. Significant correlations were observed between RSI and jump time, peak power, unload Fz, eccentric work, eccentric rate of force development (RFD), amortization Fz, amortization time, second Fz peak, average concentric Fz, and concentric displacement. Significant correlations were observed between jump time and unload Fz, eccentric work, eccentric RFD, amortization Fz, amortization time, average concentric Fz, and concentric work. In conclusion, jump height correlated with variables derived from the concentric phase only (work, power, and displacement), whereas Fz variables from the unloading, eccentric, amortization, and concentric phases correlated highly with RSI and jump time. These observations demonstrate the importance of countermovement Fz characteristics for time-sensitive CMJ performance measures. Researchers and practitioners should include RSI and jump time with jump height to improve their assessment of jump performance.

A valid and reliable method to measure jump-specific training and competition load in elite volleyball players.

PubMed

Skazalski, C; Whiteley, R; Hansen, C; Bahr, R

2018-05-01

Use of a commercially available wearable device to monitor jump load with elite volleyball players has become common practice. The purpose of this study was to evaluate the validity and reliability of this device, the Vert, to count jumps and measure jump height with professional volleyball players. Jump count accuracy was determined by comparing jumps recorded by the device to jumps observed through systematic video analysis of three practice sessions and two league matches performed by a men's professional volleyball team. Jumps performed by 14 players were each coded for time and jump type and individually matched to device recorded jumps. Jump height validity of the device was examined against reference standards as participants performed countermovement jumps on a force plate and volleyball-specific jumps with a Vertec. The Vert device accurately counted 99.3% of the 3637 jumps performed during practice and match play. The device showed excellent jump height interdevice reliability for two devices placed in the same pouch during volleyball jumps (r = .99, 95% CI 0.98-0.99). The device had a minimum detectable change (MDC) of 9.7 cm and overestimated jump height by an average of 5.5 cm (95% CI 4.5-6.5) across all volleyball jumps. The Vert device demonstrates excellent accuracy counting volleyball-specific jumps during training and competition. While the device is not recommended to measure maximal jumping ability when precision is needed, it provides an acceptable measure of on-court jump height that can be used to monitor athlete jump load. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Relative net vertical impulse determines jumping performance.

PubMed

Kirby, Tyler J; McBride, Jeffrey M; Haines, Tracie L; Dayne, Andrea M

2011-08-01

The purpose of this investigation was to determine the relationship between relative net vertical impulse and jump height in a countermovement jump and static jump performed to varying squat depths. Ten college-aged males with 2 years of jumping experience participated in this investigation (age: 23.3 ± 1.5 years; height: 176.7 ± 4.5 cm; body mass: 84.4 ± 10.1 kg). Subjects performed a series of static jumps and countermovement jumps in a randomized fashion to a depth of 0.15, 0.30, 0.45, 0.60, and 0.75 m and a self-selected depth (static jump depth = 0.38 ± 0.08 m, countermovement jump depth = 0.49 ± 0.06 m). During the concentric phase of each jump, peak force, peak velocity, peak power, jump height, and net vertical impulse were recorded and analyzed. Net vertical impulse was divided by body mass to produce relative net vertical impulse. Increasing squat depth corresponded to a decrease in peak force and an increase in jump height and relative net vertical impulse for both static jump and countermovement jump. Across all depths, relative net vertical impulse was statistically significantly correlated to jump height in the static jump (r = .9337, p < .0001, power = 1.000) and countermovement jump (r = .925, p < .0001, power = 1.000). Across all depths, peak force was negatively correlated to jump height in the static jump (r = -0.3947, p = .0018, power = 0.8831) and countermovement jump (r = -0.4080, p = .0012, power = 0.9050). These results indicate that relative net vertical impulse can be used to assess vertical jump performance, regardless of initial squat depth, and that peak force may not be the best measure to assess vertical jump performance.

Structural dynamics of supercooled water from quasielastic neutron scattering and molecular simulations.

PubMed

Qvist, Johan; Schober, Helmut; Halle, Bertil

2011-04-14

One of the outstanding challenges presented by liquid water is to understand how molecules can move on a picosecond time scale despite being incorporated in a three-dimensional network of relatively strong H-bonds. This challenge is exacerbated in the supercooled state, where the dramatic slowing down of structural dynamics is reminiscent of the, equally poorly understood, generic behavior of liquids near the glass transition temperature. By probing single-molecule dynamics on a wide range of time and length scales, quasielastic neutron scattering (QENS) can potentially reveal the mechanistic details of water's structural dynamics, but because of interpretational ambiguities this potential has not been fully realized. To resolve these issues, we present here an extensive set of high-quality QENS data from water in the range 253-293 K and a corresponding set of molecular dynamics (MD) simulations to facilitate and validate the interpretation. Using a model-free approach, we analyze the QENS data in terms of two motional components. Based on the dynamical clustering observed in MD trajectories, we identify these components with two distinct types of structural dynamics: picosecond local (L) structural fluctuations within dynamical basins and slower interbasin jumps (J). The Q-dependence of the dominant QENS component, associated with J dynamics, can be quantitatively rationalized with a continuous-time random walk (CTRW) model with an apparent jump length that depends on low-order moments of the jump length and waiting time distributions. Using a simple coarse-graining algorithm to quantitatively identify dynamical basins, we map the newtonian MD trajectory on a CTRW trajectory, from which the jump length and waiting time distributions are computed. The jump length distribution is gaussian and the rms jump length increases from 1.5 to 1.9 Å as the temperature increases from 253 to 293 K. The rms basin radius increases from 0.71 to 0.75 Å over the same range. The waiting time distribution is exponential at all investigated temperatures, ruling out significant dynamical heterogeneity. However, a simulation at 238 K reveals a small but significant dynamical heterogeneity. The macroscopic diffusion coefficient deduced from the QENS data agrees quantitatively with NMR and tracer results. We compare our QENS analysis with existing approaches, arguing that the apparent dynamical heterogeneity implied by stretched exponential fitting functions results from the failure to distinguish intrabasin (L) from interbasin (J) structural dynamics. We propose that the apparent dynamical singularity at ∼220 K corresponds to freezing out of J dynamics, while the calorimetric glass transition corresponds to freezing out of L dynamics.

Structural dynamics of supercooled water from quasielastic neutron scattering and molecular simulations

NASA Astrophysics Data System (ADS)

Qvist, Johan; Schober, Helmut; Halle, Bertil

2011-04-01

One of the outstanding challenges presented by liquid water is to understand how molecules can move on a picosecond time scale despite being incorporated in a three-dimensional network of relatively strong H-bonds. This challenge is exacerbated in the supercooled state, where the dramatic slowing down of structural dynamics is reminiscent of the, equally poorly understood, generic behavior of liquids near the glass transition temperature. By probing single-molecule dynamics on a wide range of time and length scales, quasielastic neutron scattering (QENS) can potentially reveal the mechanistic details of water's structural dynamics, but because of interpretational ambiguities this potential has not been fully realized. To resolve these issues, we present here an extensive set of high-quality QENS data from water in the range 253-293 K and a corresponding set of molecular dynamics (MD) simulations to facilitate and validate the interpretation. Using a model-free approach, we analyze the QENS data in terms of two motional components. Based on the dynamical clustering observed in MD trajectories, we identify these components with two distinct types of structural dynamics: picosecond local (L) structural fluctuations within dynamical basins and slower interbasin jumps (J). The Q-dependence of the dominant QENS component, associated with J dynamics, can be quantitatively rationalized with a continuous-time random walk (CTRW) model with an apparent jump length that depends on low-order moments of the jump length and waiting time distributions. Using a simple coarse-graining algorithm to quantitatively identify dynamical basins, we map the Newtonian MD trajectory on a CTRW trajectory, from which the jump length and waiting time distributions are computed. The jump length distribution is Gaussian and the rms jump length increases from 1.5 to 1.9 Å as the temperature increases from 253 to 293 K. The rms basin radius increases from 0.71 to 0.75 Å over the same range. The waiting time distribution is exponential at all investigated temperatures, ruling out significant dynamical heterogeneity. However, a simulation at 238 K reveals a small but significant dynamical heterogeneity. The macroscopic diffusion coefficient deduced from the QENS data agrees quantitatively with NMR and tracer results. We compare our QENS analysis with existing approaches, arguing that the apparent dynamical heterogeneity implied by stretched exponential fitting functions results from the failure to distinguish intrabasin (L) from interbasin (J) structural dynamics. We propose that the apparent dynamical singularity at ˜220 K corresponds to freezing out of J dynamics, while the calorimetric glass transition corresponds to freezing out of L dynamics.

Quasiballistic heat removal from small sources studied from first principles

NASA Astrophysics Data System (ADS)

Vermeersch, Bjorn; Mingo, Natalio

2018-01-01

Heat sources whose characteristic dimension R is comparable to phonon mean free paths display thermal resistances that exceed conventional diffusive predictions. This has direct implications to (opto)electronics thermal management and phonon spectroscopy. Theoretical analyses have so far limited themselves to particular experimental configurations. Here, we build upon the multidimensional Boltzmann transport equation (BTE) to derive universal expressions for the apparent conductivity suppression S (R ) =κeff(R ) /κbulk experienced by radially symmetric 2D and 3D sources. In striking analogy to cross-plane heat conduction in thin films, a distinct quasiballistic regime emerges between ballistic (κeff˜R ) and diffusive (κeff≃κbulk ) asymptotes that displays a logarithmic dependence κeff˜ln(R ) in single crystals and fractional power dependence κeff˜R2 -α in alloys (with α the Lévy superdiffusion exponent). Analytical solutions and Monte Carlo simulations for spherical and circular heat sources in Si, GaAs, Si0.99Ge0.01 , and Si0.82Ge0.18 , all carried out from first principles, confirm the predicted generic tendencies. Contrary to the thin film case, common approximations like kinetic theory estimates κeff≃∑Sωgreyκω and modified Fourier temperature curves perform relatively poorly. Up to threefold deviations from the BTE solutions for sub-100 nm sources underline the need for rigorous treatment of multidimensional nondiffusive transport.

Escape driven by alpha-stable white noises.

PubMed

Dybiec, B; Gudowska-Nowak, E; Hänggi, P

2007-02-01

We explore the archetype problem of an escape dynamics occurring in a symmetric double well potential when the Brownian particle is driven by white Lévy noise in a dynamical regime where inertial effects can safely be neglected. The behavior of escaping trajectories from one well to another is investigated by pointing to the special character that underpins the noise-induced discontinuity which is caused by the generalized Brownian paths that jump beyond the barrier location without actually hitting it. This fact implies that the boundary conditions for the mean first passage time (MFPT) are no longer determined by the well-known local boundary conditions that characterize the case with normal diffusion. By numerically implementing properly the set up boundary conditions, we investigate the survival probability and the average escape time as a function of the corresponding Lévy white noise parameters. Depending on the value of the skewness beta of the Lévy noise, the escape can either become enhanced or suppressed: a negative asymmetry parameter beta typically yields a decrease for the escape rate while the rate itself depicts a non-monotonic behavior as a function of the stability index alpha that characterizes the jump length distribution of Lévy noise, exhibiting a marked discontinuity at alpha=1. We find that the typical factor of 2 that characterizes for normal diffusion the ratio between the MFPT for well-bottom-to-well-bottom and well-bottom-to-barrier-top no longer holds true. For sufficiently high barriers the survival probabilities assume an exponential behavior versus time. Distinct non-exponential deviations occur, however, for low barrier heights.

The Gini coefficient: a methodological pilot study to assess fetal brain development employing postmortem diffusion MRI.

PubMed

Viehweger, Adrian; Riffert, Till; Dhital, Bibek; Knösche, Thomas R; Anwander, Alfred; Stepan, Holger; Sorge, Ina; Hirsch, Wolfgang

2014-10-01

Diffusion-weighted imaging (DWI) is important in the assessment of fetal brain development. However, it is clinically challenging and time-consuming to prepare neuromorphological examinations to assess real brain age and to detect abnormalities. To demonstrate that the Gini coefficient can be a simple, intuitive parameter for modelling fetal brain development. Postmortem fetal specimens(n = 28) were evaluated by diffusion-weighted imaging (DWI) on a 3-T MRI scanner using 60 directions, 0.7-mm isotropic voxels and b-values of 0, 150, 1,600 s/mm(2). Constrained spherical deconvolution (CSD) was used as the local diffusion model. Fractional anisotropy (FA), apparent diffusion coefficient (ADC) and complexity (CX) maps were generated. CX was defined as a novel diffusion metric. On the basis of those three parameters, the Gini coefficient was calculated. Study of fetal brain development in postmortem specimens was feasible using DWI. The Gini coefficient could be calculated for the combination of the three diffusion parameters. This multidimensional Gini coefficient correlated well with age (Adjusted R(2) = 0.59) between the ages of 17 and 26 gestational weeks. We propose a new method that uses an economics concept, the Gini coefficient, to describe the whole brain with one simple and intuitive measure, which can be used to assess the brain's developmental state.

Performance analysis of jump-gliding locomotion for miniature robotics.

PubMed

Vidyasagar, A; Zufferey, Jean-Christohphe; Floreano, Dario; Kovač, M

2015-03-26

Recent work suggests that jumping locomotion in combination with a gliding phase can be used as an effective mobility principle in robotics. Compared to pure jumping without a gliding phase, the potential benefits of hybrid jump-gliding locomotion includes the ability to extend the distance travelled and reduce the potentially damaging impact forces upon landing. This publication evaluates the performance of jump-gliding locomotion and provides models for the analysis of the relevant dynamics of flight. It also defines a jump-gliding envelope that encompasses the range that can be achieved with jump-gliding robots and that can be used to evaluate the performance and improvement potential of jump-gliding robots. We present first a planar dynamic model and then a simplified closed form model, which allow for quantification of the distance travelled and the impact energy on landing. In order to validate the prediction of these models, we validate the model with experiments using a novel jump-gliding robot, named the 'EPFL jump-glider'. It has a mass of 16.5 g and is able to perform jumps from elevated positions, perform steered gliding flight, land safely and traverse on the ground by repetitive jumping. The experiments indicate that the developed jump-gliding model fits very well with the measured flight data using the EPFL jump-glider, confirming the benefits of jump-gliding locomotion to mobile robotics. The jump-glide envelope considerations indicate that the EPFL jump-glider, when traversing from a 2 m height, reaches 74.3% of optimal jump-gliding distance compared to pure jumping without a gliding phase which only reaches 33.4% of the optimal jump-gliding distance. Methods of further improving flight performance based on the models and inspiration from biological systems are presented providing mechanical design pathways to future jump-gliding robot designs.

Entrainment dominates the interaction of microalgae with micron-sized objects

NASA Astrophysics Data System (ADS)

Jeanneret, Raphaël; Kantsler, Vasily; Polin, Marco

Swimming microorganisms usually navigate through fluids containing a variety of microparticles, with which they inevitably interact with important biological and ecological implications. Regarding the prokaryotic realm, it has been shown that the colloidal dynamics within bacterial suspensions is well described by a persistent random walk. As to the other major class of microorganisms, the eukaryotes, much less is known. By directly tracking polystyrene colloids in baths of the model puller-type alga Chlamydomonas reinhardtii, a pioneering work has shown that they still behave diffusively asymptotically with diffusivities linearly increasing with the concentration. The values reported as well as the distribution of displacements having exponential tails are well explained theoretically when considering the hydrodynamic far-field contribution of the algae. However nothing has yet been described regarding the short range interactions that inevitably exist. In this work we show, by means of 3 different experiments, that the coarse-grained dynamics of the colloids is in fact dominated by very rare but large jumps due to entrainment by the algae leading to a total effective diffusion an order of magnitude higher than previously reported.

ULTRA-SHARP nonoscillatory convection schemes for high-speed steady multidimensional flow

NASA Technical Reports Server (NTRS)

Leonard, B. P.; Mokhtari, Simin

1990-01-01

For convection-dominated flows, classical second-order methods are notoriously oscillatory and often unstable. For this reason, many computational fluid dynamicists have adopted various forms of (inherently stable) first-order upwinding over the past few decades. Although it is now well known that first-order convection schemes suffer from serious inaccuracies attributable to artificial viscosity or numerical diffusion under high convection conditions, these methods continue to enjoy widespread popularity for numerical heat transfer calculations, apparently due to a perceived lack of viable high accuracy alternatives. But alternatives are available. For example, nonoscillatory methods used in gasdynamics, including currently popular TVD schemes, can be easily adapted to multidimensional incompressible flow and convective transport. This, in itself, would be a major advance for numerical convective heat transfer, for example. But, as is shown, second-order TVD schemes form only a small, overly restrictive, subclass of a much more universal, and extremely simple, nonoscillatory flux-limiting strategy which can be applied to convection schemes of arbitrarily high order accuracy, while requiring only a simple tridiagonal ADI line-solver, as used in the majority of general purpose iterative codes for incompressible flow and numerical heat transfer. The new universal limiter and associated solution procedures form the so-called ULTRA-SHARP alternative for high resolution nonoscillatory multidimensional steady state high speed convective modelling.

Tempered fractional calculus

NASA Astrophysics Data System (ADS)

Sabzikar, Farzad; Meerschaert, Mark M.; Chen, Jinghua

2015-07-01

Fractional derivatives and integrals are convolutions with a power law. Multiplying by an exponential factor leads to tempered fractional derivatives and integrals. Tempered fractional diffusion equations, where the usual second derivative in space is replaced by a tempered fractional derivative, govern the limits of random walk models with an exponentially tempered power law jump distribution. The limiting tempered stable probability densities exhibit semi-heavy tails, which are commonly observed in finance. Tempered power law waiting times lead to tempered fractional time derivatives, which have proven useful in geophysics. The tempered fractional derivative or integral of a Brownian motion, called a tempered fractional Brownian motion, can exhibit semi-long range dependence. The increments of this process, called tempered fractional Gaussian noise, provide a useful new stochastic model for wind speed data. A tempered fractional difference forms the basis for numerical methods to solve tempered fractional diffusion equations, and it also provides a useful new correlation model in time series.

TEMPERED FRACTIONAL CALCULUS.

PubMed

Meerschaert, Mark M; Sabzikar, Farzad; Chen, Jinghua

2015-07-15

Fractional derivatives and integrals are convolutions with a power law. Multiplying by an exponential factor leads to tempered fractional derivatives and integrals. Tempered fractional diffusion equations, where the usual second derivative in space is replaced by a tempered fractional derivative, govern the limits of random walk models with an exponentially tempered power law jump distribution. The limiting tempered stable probability densities exhibit semi-heavy tails, which are commonly observed in finance. Tempered power law waiting times lead to tempered fractional time derivatives, which have proven useful in geophysics. The tempered fractional derivative or integral of a Brownian motion, called a tempered fractional Brownian motion, can exhibit semi-long range dependence. The increments of this process, called tempered fractional Gaussian noise, provide a useful new stochastic model for wind speed data. A tempered difference forms the basis for numerical methods to solve tempered fractional diffusion equations, and it also provides a useful new correlation model in time series.

TEMPERED FRACTIONAL CALCULUS

PubMed Central

MEERSCHAERT, MARK M.; SABZIKAR, FARZAD; CHEN, JINGHUA

2014-01-01

Fractional derivatives and integrals are convolutions with a power law. Multiplying by an exponential factor leads to tempered fractional derivatives and integrals. Tempered fractional diffusion equations, where the usual second derivative in space is replaced by a tempered fractional derivative, govern the limits of random walk models with an exponentially tempered power law jump distribution. The limiting tempered stable probability densities exhibit semi-heavy tails, which are commonly observed in finance. Tempered power law waiting times lead to tempered fractional time derivatives, which have proven useful in geophysics. The tempered fractional derivative or integral of a Brownian motion, called a tempered fractional Brownian motion, can exhibit semi-long range dependence. The increments of this process, called tempered fractional Gaussian noise, provide a useful new stochastic model for wind speed data. A tempered difference forms the basis for numerical methods to solve tempered fractional diffusion equations, and it also provides a useful new correlation model in time series. PMID:26085690

Tempered fractional calculus

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabzikar, Farzad, E-mail: sabzika2@stt.msu.edu; Meerschaert, Mark M., E-mail: mcubed@stt.msu.edu; Chen, Jinghua, E-mail: cjhdzdz@163.com

2015-07-15

Fractional derivatives and integrals are convolutions with a power law. Multiplying by an exponential factor leads to tempered fractional derivatives and integrals. Tempered fractional diffusion equations, where the usual second derivative in space is replaced by a tempered fractional derivative, govern the limits of random walk models with an exponentially tempered power law jump distribution. The limiting tempered stable probability densities exhibit semi-heavy tails, which are commonly observed in finance. Tempered power law waiting times lead to tempered fractional time derivatives, which have proven useful in geophysics. The tempered fractional derivative or integral of a Brownian motion, called a temperedmore » fractional Brownian motion, can exhibit semi-long range dependence. The increments of this process, called tempered fractional Gaussian noise, provide a useful new stochastic model for wind speed data. A tempered fractional difference forms the basis for numerical methods to solve tempered fractional diffusion equations, and it also provides a useful new correlation model in time series.« less

Superdiffusive motion of membrane-targeting C2 domains

NASA Astrophysics Data System (ADS)

Campagnola, Grace; Nepal, Kanti; Schroder, Bryce W.; Peersen, Olve B.; Krapf, Diego

2015-12-01

Membrane-targeting domains play crucial roles in the recruitment of signalling molecules to the plasma membrane. For most peripheral proteins, the protein-to-membrane interaction is transient. After proteins dissociate from the membrane they have been observed to rebind following brief excursions in the bulk solution. Such membrane hops can have broad implications for the efficiency of reactions on membranes. We study the diffusion of membrane-targeting C2 domains using single-molecule tracking in supported lipid bilayers. The ensemble-averaged mean square displacement (MSD) exhibits superdiffusive behaviour. However, traditional time-averaged MSD analysis of individual trajectories remains linear and does not reveal superdiffusion. Our observations are explained in terms of bulk excursions that introduce jumps with a heavy-tail distribution. These hopping events allow proteins to explore large areas in a short time. The experimental results are shown to be consistent with analytical models of bulk-mediated diffusion and numerical simulations.

Laterality and Plantar Pressure Distribution During Gait in Healthy Children: Comment on Mayolas Pi, Arrese, Aparicio, and Masià (2015).

PubMed

Zverev, Yury

2016-08-01

In a recent paper, Mayolas Pi, Arrese, Aparicio, and Masià reported the absence of significant bilateral differences between legs in the average plantar pressure during walking in six- to seven-year-old children. However, the authors demonstrated bilateral differences in the distribution of plantar pressure during walking independent of foot preference in three tests: kicking a ball with precision, balancing on one foot, and jumping on one foot. From the results, Mayolas Pi et al. proposed that this asymmetric pattern of plantar pressure distribution is not caused by laterality. This paper suggests that the selected age range of participants and methods of diagnosing of laterality and data analysis could have significant effects on the results. Indeed, according to the literature, laterality in humans is a multidimensional trait with poor stabilization and conformity between different dimensions in preschool and younger school children. © The Author(s) 2016.

Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

NASA Astrophysics Data System (ADS)

Zhang, Rui; Schweizer, Kenneth S.

2015-10-01

We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratio for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.

Theory of activated penetrant diffusion in viscous fluids and colloidal suspensions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Rui; Schweizer, Kenneth S., E-mail: kschweiz@illinois.edu

2015-10-14

We heuristically formulate a microscopic, force level, self-consistent nonlinear Langevin equation theory for activated barrier hopping and non-hydrodynamic diffusion of a hard sphere penetrant in very dense hard sphere fluid matrices. Penetrant dynamics is controlled by a rich competition between force relaxation due to penetrant self-motion and collective matrix structural (alpha) relaxation. In the absence of penetrant-matrix attraction, three activated dynamical regimes are predicted as a function of penetrant-matrix size ratio which are physically distinguished by penetrant jump distance and the nature of matrix motion required to facilitate its hopping. The penetrant diffusion constant decreases the fastest with size ratiomore » for relatively small penetrants where the matrix effectively acts as a vibrating amorphous solid. Increasing penetrant-matrix attraction strength reduces penetrant diffusivity due to physical bonding. For size ratios approaching unity, a distinct dynamical regime emerges associated with strong slaving of penetrant hopping to matrix structural relaxation. A crossover regime at intermediate penetrant-matrix size ratio connects the two limiting behaviors for hard penetrants, but essentially disappears if there are strong attractions with the matrix. Activated penetrant diffusivity decreases strongly with matrix volume fraction in a manner that intensifies as the size ratio increases. We propose and implement a quasi-universal approach for activated diffusion of a rigid atomic/molecular penetrant in a supercooled liquid based on a mapping between the hard sphere system and thermal liquids. Calculations for specific systems agree reasonably well with experiments over a wide range of temperature, covering more than 10 orders of magnitude of variation of the penetrant diffusion constant.« less

The effect of dropping height on jumping performance in trained and untrained prepubertal boys and girls.

PubMed

Bassa, Eleni I; Patikas, Dimitrios A; Panagiotidou, Aikaterini I; Papadopoulou, Sophia D; Pylianidis, Theofilos C; Kotzamanidis, Christos M

2012-08-01

Plyometric training in children, including different types of jumps, has become common practice during the last few years in different sports, although there is limited information about the adaptability of children with respect to different loads and the differences in performance between various jump types. The purpose of this study was to examine the effect of gender and training background on the optimal drop jump height of 9- to 11-year-old children. Sixty prepubertal (untrained and track and field athletes, boys and girls, equally distributed in each group [n = 15]), performed the following in random order: 3 squat jumps, 3 countermovement jumps (CMJs) and 3 drop jumps from heights of 10, 20, 30, 40, and 50 cm. The trial with the best performance in jump height of each test was used for further analysis. The jump type significantly affected the jump height. The jump height during the CMJ was the highest among all other jump types, resulting in advanced performance for both trained and untrained prepubertal boys and girls. However, increasing the dropping height did not change the jumping height or contact time during the drop jump. This possibly indicates an inability of prepubertal children to use their stored elastic energy to increase jumping height during drop jumps, irrespective of their gender or training status. This indicates that children, independent of gender and training status, have no performance gain during drop jumps from heights up to 50 cm, and therefore, it is recommended that only low drop jump heights be included in plyometric training to limit the probability of sustaining injuries.

Fluctuation theorem: A critical review

NASA Astrophysics Data System (ADS)

Malek Mansour, M.; Baras, F.

2017-10-01

Fluctuation theorem for entropy production is revisited in the framework of stochastic processes. The applicability of the fluctuation theorem to physico-chemical systems and the resulting stochastic thermodynamics were analyzed. Some unexpected limitations are highlighted in the context of jump Markov processes. We have shown that these limitations handicap the ability of the resulting stochastic thermodynamics to correctly describe the state of non-equilibrium systems in terms of the thermodynamic properties of individual processes therein. Finally, we considered the case of diffusion processes and proved that the fluctuation theorem for entropy production becomes irrelevant at the stationary state in the case of one variable systems.

Systematic derivation of reaction-diffusion equations with distributed delays and relations to fractional reaction-diffusion equations and hyperbolic transport equations: application to the theory of Neolithic transition.

PubMed

Vlad, Marcel Ovidiu; Ross, John

2002-12-01

We introduce a general method for the systematic derivation of nonlinear reaction-diffusion equations with distributed delays. We study the interactions among different types of moving individuals (atoms, molecules, quasiparticles, biological organisms, etc). The motion of each species is described by the continuous time random walk theory, analyzed in the literature for transport problems, whereas the interactions among the species are described by a set of transformation rates, which are nonlinear functions of the local concentrations of the different types of individuals. We use the time interval between two jumps (the transition time) as an additional state variable and obtain a set of evolution equations, which are local in time. In order to make a connection with the transport models used in the literature, we make transformations which eliminate the transition time and derive a set of nonlocal equations which are nonlinear generalizations of the so-called generalized master equations. The method leads under different specified conditions to various types of nonlocal transport equations including a nonlinear generalization of fractional diffusion equations, hyperbolic reaction-diffusion equations, and delay-differential reaction-diffusion equations. Thus in the analysis of a given problem we can fit to the data the type of reaction-diffusion equation and the corresponding physical and kinetic parameters. The method is illustrated, as a test case, by the study of the neolithic transition. We introduce a set of assumptions which makes it possible to describe the transition from hunting and gathering to agriculture economics by a differential delay reaction-diffusion equation for the population density. We derive a delay evolution equation for the rate of advance of agriculture, which illustrates an application of our analysis.

Sign Crossover in All Maxwell-Stefan Diffusivities for Molten Salt LiF-BeF2: A Molecular Dynamics Study.

PubMed

Chakraborty, Brahmananda

2015-08-20

Applying Green-Kubo formalism and equilibrium molecular dynamics (MD) simulations, we have studied for the first time the dynamic correlation, Onsager coefficients, and Maxwell-Stefan (MS) diffusivities of molten salt LiF-BeF2, which is a potential candidate for a coolant in a high temperature reactor. We observe an unusual composition dependence and strikingly a crossover in sign for all the MS diffusivities at a composition of around 7% of LiF where the MS diffusivity between cation-anion pair (Đ(BeF) and Đ(LiF)) jumps from positive to negative value while the MS diffusivity between cation-cation pair (Đ(LiBe)) becomes positive from a negative value. Even though the negative MS diffusivities have been observed for electrolyte solutions between cation-cation pair, here we report negative MS diffusivity between cation-anion pair where Đ(BeF) shows a sharp rise around 66% of BeF2, reaches maximum value at 70% of BeF2, and then decreases almost exponentially with a sign change for BeF2 around 93%. For low mole fraction of LiF, Đ(BeF) follows the Debye-Huckel theory and rises with the square root of LiF mole fraction similar to the MS diffusivity between cation-anion pair in aqueous solution of electrolyte salt. Negative MS diffusivities while unusual are, however, shown to satisfy the non-negative entropy constraints at all thermodynamic states as required by the second law of thermodynamics. We have established a strong correlation between the structure and dynamics and predict that the formation of flouride polyanion network between Be and F ions and coulomb interaction is responsible for sharp variation of the MS diffusivities which controls the multicomponent diffusion phenomenon in LiF-BeF2 which has a strong impact on the performance of the reactor.

A Basin-Wide Examination of the Arctic Ocean's Double-Diffusive Staircase

NASA Astrophysics Data System (ADS)

Shibley, N.; Timmermans, M. L.; Carpenter, J. R.; Toole, J. M.

2016-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure above the Atlantic Water Layer consisting of multiple mixed layers of order 1-m in height separated by sharp interfaces. This double-diffusive staircase structure is characterized across the entire Arctic Ocean through a detailed analysis of Ice-Tethered Profiler measurements acquired between 2004 and 2013. Staircase properties (mixed layer thicknesses and temperature-salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio for 50-m spanning the staircase stratification. It is shown that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (on the Eurasian side) and higher density ratio (on the Canadian side). We find that the diffusive staircase in the Eurasian Basin is characterized by fewer, thinner mixed layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin staircase mixed layers. Using a double-diffusive 4/3 flux law parameterization, the distribution of vertical heat fluxes through the staircase is estimated across the Arctic; it is found that heat fluxes in the Eurasian Basin [O(1) W/m^2] are generally an order of magnitude larger than those in the Canadian Basin [O(0.1) W/m^2].

Nitrogen vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in B 1 TiN studied by ab initio and classical molecular dynamics with optimized potentials

NASA Astrophysics Data System (ADS)

Sangiovanni, D. G.; Alling, B.; Steneteg, P.; Hultman, L.; Abrikosov, I. A.

2015-02-01

We use ab initio and classical molecular dynamics (AIMD and CMD) based on the modified embedded-atom method (MEAM) potential to simulate diffusion of N vacancy and N self-interstitial point defects in B 1 TiN. TiN MEAM parameters are optimized to obtain CMD nitrogen point-defect jump rates in agreement with AIMD predictions, as well as an excellent description of Ti Nx(˜0.7

Li dynamics in carbon-rich polymer-derived SiCN ceramics probed by NMR

NASA Astrophysics Data System (ADS)

Baek, Seung-Ho; Reinold, Lukas; Graczyk-Zajac, Magdalena; Riedel, Ralf; Hammerath, Franziska; Buechner, Bernd; Grafe, Hajo

2014-03-01

We report 7Li, 29Si, and 13C NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei at room temperature, we find that only the 13C spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature and Larmor frequency (ωL) dependences of the 7Li linewidth and spin-lattice relaxation rates T1-1 are described by an activated law with the activation energy EA of 0.31 eV and the correlation time τ0 in the high temperature limit of 1.3 ps. The 3 / 2 power law dependence of T1-1 on ωL which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the μs timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T1ρ-1 results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes.

Lithium dynamics in carbon-rich polymer-derived SiCN ceramics probed by nuclear magnetic resonance

NASA Astrophysics Data System (ADS)

Baek, Seung-Ho; Reinold, Lukas Mirko; Graczyk-Zajac, Magdalena; Riedel, Ralf; Hammerath, Franziska; Büchner, Bernd; Grafe, Hans-Joachim

2014-05-01

We report 7Li, 29Si, and 13C NMR studies of two different carbon-rich SiCN ceramics SiCN-1 and SiCN-3 derived from the preceramic polymers polyphenylvinylsilylcarbodiimide and polyphenylvinylsilazane, respectively. From the spectral analysis of the three nuclei, we find that only the 13C spectrum is strongly influenced by Li insertion/extraction, suggesting that carbon phases are the major electrochemically active sites for Li storage. Temperature (T) and Larmor frequency (ωL) dependences of the 7Li linewidth and spin-lattice relaxation rates T1-1 are described by an activated law with the activation energy EA of 0.31 eV and the correlation time τ0 in the high temperature limit of 1.3 ps. The 3 / 2 power law dependence of T1-1 on ωL which deviates from the standard Bloembergen, Purcell, and Pound (BPP) model implies that the Li motion on the μs timescale is governed by continuum diffusion mechanism rather than jump diffusion. On the other hand, the rotating frame relaxation rate T1ρ-1 results suggest that the slow motion of Li on the ms timescale may be affected by complex diffusion and/or non-diffusion processes.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-12-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations.

Does trampoline or hard surface jumping influence lower extremity alignment?

PubMed Central

Akasaka, Kiyokazu; Tamura, Akihiro; Katsuta, Aoi; Sagawa, Ayako; Otsudo, Takahiro; Okubo, Yu; Sawada, Yutaka; Hall, Toby

2017-01-01

[Purpose] To determine whether repetitive trampoline or hard surface jumping affects lower extremity alignment on jump landing. [Subjects and Methods] Twenty healthy females participated in this study. All subjects performed a drop vertical jump before and after repeated maximum effort trampoline or hard surface jumping. A three-dimensional motion analysis system and two force plates were used to record lower extremity angles, moments, and vertical ground reaction force during drop vertical jumps. [Results] Knee extensor moment after trampoline jumping was greater than that after hard surface jumping. There were no significant differences between trials in vertical ground reaction force and lower extremity joint angles following each form of exercise. Repeated jumping on a trampoline increased peak vertical ground reaction force, hip extensor, knee extensor moments, and hip adduction angle, while decreasing hip flexion angle during drop vertical jumps. In contrast, repeated jumping on a hard surface increased peak vertical ground reaction force, ankle dorsiflexion angle, and hip extensor moment during drop vertical jumps. [Conclusion] Repeated jumping on the trampoline compared to jumping on a hard surface has different effects on lower limb kinetics and kinematics. Knowledge of these effects may be useful in designing exercise programs for different clinical presentations. PMID:29643592

Mobile Jump Assessment (mJump): A Descriptive and Inferential Study.

PubMed

Mateos-Angulo, Alvaro; Galán-Mercant, Alejandro; Cuesta-Vargas, Antonio

2015-08-26

Vertical jump tests are used in athletics and rehabilitation to measure physical performance in people of different age ranges and fitness. Jumping ability can be analyzed through different variables, and the most commonly used are fly time and jump height. They can be obtained by a variety of measuring devices, but most are limited to laboratory use only. The current generation of smartphones contains inertial sensors that are able to record kinematic variables for human motion analysis, since they are tools for easy access and portability for clinical use. The aim of this study was to describe and analyze the kinematics characteristics using the inertial sensor incorporated in the iPhone 4S, the lower limbs strength through a manual dynamometer, and the jump variables obtained with a contact mat in the squat jump and countermovement jump tests (fly time and jump height) from a cohort of healthy people. A cross sectional study was conducted on a population of healthy young adults. Twenty-seven participants performed three trials (n=81 jumps) of squat jump and countermovement jump tests. Acceleration variables were measured through a smartphone's inertial sensor. Additionally, jump variables from a contact mat and lower limbs dynamometry were collected. In the present study, the kinematic variables derived from acceleration through the inertial sensor of a smartphone iPhone 4S, dynamometry of lower limbs with a handheld dynamometer, and the height and flight time with a contact mat have been described in vertical jump tests from a cohort of young healthy subjects. The development of the execution has been described, examined and identified in a squat jump test and countermovement jump test under acceleration variables that were obtained with the smartphone. The built-in iPhone 4S inertial sensor is able to measure acceleration variables while performing vertical jump tests for the squat jump and countermovement jump in healthy young adults. The acceleration kinematics variables derived from the smartphone's inertial sensor are higher in the countermovement jump test than the squat jump test. ©Alvaro Mateos-Angulo, Alejandro Galán-Mercant, Antonio Cuesta-Vargas. Originally published in JMIR Rehabilitation and Assistive Technology (http://rehab.jmir.org), 26.08.2015.

Long-term aging behaviors in a model soft colloidal system.

PubMed

Li, Qi; Peng, Xiaoguang; McKenna, Gregory B

2017-02-15

Colloidal and molecular systems share similar behaviors near to the glass transition volume fraction or temperature. Here, aging behaviors after volume fraction up-jump (induced by performing temperature down-jumps) conditions for a PS-PNIPAM/AA soft colloidal system were investigated using light scattering (diffusing wave spectroscopy, DWS). Both aging responses and equilibrium dynamics were investigated. For the aging responses, long-term experiments (100 000 s) were performed, and both equilibrium and non-equilibrium behaviors of the system were obtained. In the equilibrium state, as effective volume fraction increases (or temperature decreases), the colloidal dispersion displays a transition from the liquid to a glassy state. The equilibrium α-relaxation dynamics strongly depend on both the effective volume fraction and the initial mass concentration for the studied colloidal systems. Compared with prior results from our lab [X. Di, X. Peng and G. B. McKenna, J. Chem. Phys., 2014, 140, 054903], the effective volume fractions investigated spanned a wider range, to deeper into the glassy domain. The results show that the α-relaxation time τ α of the samples aged into equilibrium deviate from the classical Vogel-Fulcher-Tammann (VFT)-type expectations and the super-Arrhenius signature disappears above the glass transition volume fraction. The non-equilibrium aging response shows that the time for the structural evolution into equilibrium and the α-relaxation time are decoupled. The DWS investigation of the aging behavior after different volume fraction jumps reveals a different non-equilibrium or aging behavior for the considered colloidal systems compared with either molecular glasses or the macroscopic rheology of a similar colloidal dispersions.

Evaluation of Potential Climate Change Impacts on Particle Movement in Open Channel Flow

NASA Astrophysics Data System (ADS)

Lin, E.; Tsai, C.

2014-12-01

It is important to develop a forecast model to predict the trajectory of sediment particles when extreme flow events occur. In extreme flow environments, the stochastic jump diffusion particle tracking model (SJD-PTM) can be used to model the movement of sediment particles in response to extreme events. This proposed SJD-PTM can be separated into three main parts — a drift motion, a turbulence term and a jump term due to random occurrences of extreme flow events. The study is intended to modify the jump term, which models the abrupt changes of particle position in the extreme flow environments. The frequency of extreme flow occurrences might change due to many uncertain factors such as climate change. The study attempts to use the concept of the logistic regression and the parameter of odds ratio, namely the trend magnitude to investigate the frequency change of extreme flow event occurrences and its impact on sediment particle movement. With the SJD-PTM, the ensemble mean and variance of particle trajectory can be quantified via simulations. The results show that by taking the effect of the trend magnitude into consideration, the particle position and its uncertainty may undergo a significant increase. Such findings will have many important implications to the environmental and hydraulic engineering design and planning. For instance, when the frequency of the occurrence of flow events with higher extremity increases, particles can travel further and faster downstream. It is observed that flow events with higher extremity can induce a higher degree of entrainment and particle resuspension, and consequently more significant bed and bank erosion.

Vertical jumping tests in volleyball: reliability, validity, and playing-position specifics.

PubMed

Sattler, Tine; Sekulic, Damir; Hadzic, Vedran; Uljevic, Ognjen; Dervisevic, Edvin

2012-06-01

Vertical jumping is known to be important in volleyball, and jumping performance tests are frequently studied for their reliability and validity. However, most studies concerning jumping in volleyball have dealt with standard rather than sport-specific jumping procedures and tests. The aims of this study, therefore, were (a) to determine the reliability and factorial validity of 2 volleyball-specific jumping tests, the block jump (BJ) test and the attack jump (AJ) test, relative to 2 frequently used and systematically validated jumping tests, the countermovement jump test and the squat jump test and (b) to establish volleyball position-specific differences in the jumping tests and simple anthropometric indices (body height [BH], body weight, and body mass index [BMI]). The BJ was performed from a defensive volleyball position, with the hands positioned in front of the chest. During an AJ, the players used a 2- to 3-step approach and performed a drop jump with an arm swing followed by a quick vertical jump. A total of 95 high-level volleyball players (all men) participated in this study. The reliability of the jumping tests ranged from 0.97 to 0.99 for Cronbach's alpha coefficients, from 0.93 to 0.97 for interitem correlation coefficients and from 2.1 to 2.8 for coefficients of variation. The highest reliability was found for the specific jumping tests. The factor analysis extracted one significant component, and all of the tests were highly intercorrelated. The analysis of variance with post hoc analysis showed significant differences between 5 playing positions in some of the jumping tests. In general, receivers had a greater jumping capacity, followed by libero players. The differences in jumping capacities should be emphasized vis-a-vis differences in the anthropometric measures of players, where middle hitters had higher BH and body weight, followed by opposite hitters and receivers, with no differences in the BMI between positions.

Effects of timing of signal indicating jump directions on knee biomechanics in jump-landing-jump tasks.

PubMed

Stephenson, Mitchell L; Hinshaw, Taylour J; Wadley, Haley A; Zhu, Qin; Wilson, Margaret A; Byra, Mark; Dai, Boyi

2018-03-01

A variety of the available time to react (ATR) has been utilised to study knee biomechanics during reactive jump-landing tasks. The purpose was to quantify knee kinematics and kinetics during a jump-land-jump task of three possible directions as the ATR was reduced. Thirty-four recreational athletes performed 45 trials of a jump-land-jump task, during which the direction of the second jump (lateral, medial or vertical) was indicated before they initiated the first jump, the instant they initiated the first jump, 300 ms before landing, 150 ms before landing or at the instant of landing. Knee joint angles and moments close to the instant of landing were significantly different when the ATR was equal to or more than 300 ms before landing, but became similar when the ATR was 150 ms or 0 ms before landing. As the ATR was decreased, knee moments decreased for the medial jump direction, but increased for the lateral jump direction. When the ATR is shorter than an individual's reaction time, the movement pattern cannot be pre-planned before landing. Knee biomechanics are dependent on the timing of the signal and the subsequent jump direction. Precise control of timing and screening athletes with low ATR are suggested.

Validation of an inertial measurement unit for the measurement of jump count and height.

PubMed

MacDonald, Kerry; Bahr, Roald; Baltich, Jennifer; Whittaker, Jackie L; Meeuwisse, Willem H

2017-05-01

To validate the use of an inertial measurement unit (IMU) for the collection of total jump count and assess the validity of an IMU for the measurement of jump height against 3-D motion analysis. Cross sectional validation study. 3D motion-capture laboratory and field based settings. Thirteen elite adolescent volleyball players. Participants performed structured drills, played a 4 set volleyball match and performed twelve counter movement jumps. Jump counts from structured drills and match play were validated against visual count from recorded video. Jump height during the counter movement jumps was validated against concurrent 3-D motion-capture data. The IMU device captured more total jumps (1032) than visual inspection (977) during match play. During structured practice, device jump count sensitivity was strong (96.8%) while specificity was perfect (100%). The IMU underestimated jump height compared to 3D motion-capture with mean differences for maximal and submaximal jumps of 2.5 cm (95%CI: 1.3 to 3.8) and 4.1 cm (3.1-5.1), respectively. The IMU offers a valid measuring tool for jump count. Although the IMU underestimates maximal and submaximal jump height, our findings demonstrate its practical utility for field-based measurement of jump load. Copyright © 2016 Elsevier Ltd. All rights reserved.

Kinematics and Kinetics of Squats, Drop Jumps and Imitation Jumps of Ski Jumpers.

PubMed

Pauli, Carole A; Keller, Melanie; Ammann, Fabian; Hübner, Klaus; Lindorfer, Julia; Taylor, William R; Lorenzetti, Silvio

2016-03-01

Squats, drop jumps, and imitation jumps are commonly used training exercises in ski jumping to enhance maximum force, explosive force, and sport-specific skills. The purpose of this study was to evaluate the kinetics and kinematics of training exercises in ski jumping and to find objective parameters in training exercises that most correlate with the competition performance of ski jumpers. To this end, barbell squats, drop jumps, and imitation jumps were measured in a laboratory environment for 10 elite ski jumpers. Force and motion data were captured, and the influence of maximum vertical force, force difference, vertical take-off velocity, knee moments, knee joint power, and a knee valgus/varus index was evaluated and correlated with their season jump performance. The results indicate that, especially for the imitation jumps, a good correlation exists between the vertical take-off velocity and the personal jump performance on the hill (R = 0.718). Importantly, however, the more the athletes tended toward a valgus knee alignment during the measured movements, the worse their performance (R = 0.729 imitation jumps; R = 0.685 squats). Although an evaluation of the athletes' lower limb alignment during competitive jumping on the hill is still required, these preliminary data suggest that performance training should additionally concentrate on improving knee alignment to increase ski jumping performance.

Validity of Hip-worn Inertial Measurement Unit Compared to Jump Mat for Jump Height Measurement in Adolescents.

PubMed

Rantalainen, T; Hesketh, K D; Rodda, C; Duckham, R L

2018-06-16

Jump tests assess lower body power production capacity, and can be used to evaluate athletic ability and development during growth. Wearable inertial measurement units (IMU) seem to offer a feasible alternative to laboratory-based equipment for jump height assessments. Concurrent validity of these devices for jump height assessments has only been established in adults. Therefore, the purpose of this study was to evaluate the concurrent validity of IMU-based jump height estimate compared to contact mat-based jump height estimate in adolescents. Ninety-five adolescents (10-13 years-of-age; girls N=41, height = 154 (SD 9) cm, weight = 44 (11) kg; boys N=54, height=156 (10) cm, weight = 46 (13) kg) completed three counter-movement jumps for maximal jump height on a contact mat. Inertial recordings (accelerations, rotations) were concurrently recorded with a hip-worn IMU (sampling at 256 Hz). Jump height was evaluated based on flight time. The mean IMU-derived jump height was 27.1 (SD 3.8) cm, and the corresponding mean jump-mat-derived value was 21.5 (3.4) cm. While a significant 26% mean difference was observed between the methods (5.5 [95% limits of agreement 2.2 to 8.9] cm, p = 0.006), the correspondence between methods was excellent (ICC = 0.89). The difference between methods was weakly positively associated with jump height (r = 0.28, P = 0.007). Take-off velocity derived jump height was also explored but produced only fair congruence. In conclusion, IMU-derived jump height exhibited excellent congruence to contact mat-based jump height and therefore presents a feasible alternative for jump height assessments in adolescents. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Potential for Non-Contact ACL Injury Between Step-Close-Jump and Hop-Jump Tasks.

PubMed

Wang, Li-I; Gu, Chin-Yi; Chen, Wei-Ling; Chang, Mu-San

2010-01-01

This study aimed to compare the kinematics and kinetics during the landing of hop-jump and step-close-jump movements in order to provide further inferring that the potential risk of ACL injuries. Eleven elite male volleyball players were recruited to perform hop-jump and step-close-jump tasks. Lower extremity kinematics and ground reaction forces during landing in stop-jump tasks were recorded. Lower extremity kinetics was calculated by using an inverse dynamic process. Step-close-jump tasks demonstrated smaller peak proximal tibia anterior shear forces during the landing phase. In step-close-jump tasks, increasing hip joint angular velocity during initial foot-ground contact decreased peak posterior ground reaction force during the landing phase, which theoretically could reduce the risk of ACL injury. Key pointsThe different landing techniques required for these two stop-jump tasks do not necessarily affect the jump height.Hop-jump decreased the hip joint angular velocity at initial foot contact with ground, which could lead to an increasing peak posterior GRF during the landing phase.Hop-jump decreased hip and knee joint angular flexion displacement during the landing, which could increase the peak vertical loading rate during the landing phase.

Multi-dimensional Core-Collapse Supernova Simulations with Neutrino Transport

NASA Astrophysics Data System (ADS)

Pan, Kuo-Chuan; Liebendörfer, Matthias; Hempel, Matthias; Thielemann, Friedrich-Karl

We present multi-dimensional core-collapse supernova simulations using the Isotropic Diffusion Source Approximation (IDSA) for the neutrino transport and a modified potential for general relativity in two different supernova codes: FLASH and ELEPHANT. Due to the complexity of the core-collapse supernova explosion mechanism, simulations require not only high-performance computers and the exploitation of GPUs, but also sophisticated approximations to capture the essential microphysics. We demonstrate that the IDSA is an elegant and efficient neutrino radiation transfer scheme, which is portable to multiple hydrodynamics codes and fast enough to investigate long-term evolutions in two and three dimensions. Simulations with a 40 solar mass progenitor are presented in both FLASH (1D and 2D) and ELEPHANT (3D) as an extreme test condition. It is found that the black hole formation time is delayed in multiple dimensions and we argue that the strong standing accretion shock instability before black hole formation will lead to strong gravitational waves.

Bridging the gap between supernovae and their remnants through multi-dimensional hydrodynamic modeling

NASA Astrophysics Data System (ADS)

Orlando, S.; Miceli, M.; Petruk, O.

2017-02-01

Supernova remnants (SNRs) are diffuse extended sources characterized by a complex morphology and a non-uniform distribution of ejecta. Such a morphology reflects pristine structures and features of the progenitor supernova (SN) and the early interaction of the SN blast wave with the inhomogeneous circumstellar medium (CSM). Deciphering the observations of SNRs might open the possibility to investigate the physical properties of both the interacting ejecta and the shocked CSM. This requires accurate numerical models which describe the evolution from the SN explosion to the remnant development and which connect the emission properties of the remnants to the progenitor SNe. Here we show how multi-dimensional SN-SNR hydrodynamic models have been very effective in deciphering observations of SNR Cassiopeia A and SN 1987A, thus unveiling the structure of ejecta in the immediate aftermath of the SN explosion and constraining the 3D pre-supernova structure and geometry of the environment surrounding the progenitor SN.

Similarity from Multi-Dimensional Scaling: Solving the Accuracy and Diversity Dilemma in Information Filtering

PubMed Central

Zeng, Wei; Zeng, An; Liu, Hao; Shang, Ming-Sheng; Zhang, Yi-Cheng

2014-01-01

Recommender systems are designed to assist individual users to navigate through the rapidly growing amount of information. One of the most successful recommendation techniques is the collaborative filtering, which has been extensively investigated and has already found wide applications in e-commerce. One of challenges in this algorithm is how to accurately quantify the similarities of user pairs and item pairs. In this paper, we employ the multidimensional scaling (MDS) method to measure the similarities between nodes in user-item bipartite networks. The MDS method can extract the essential similarity information from the networks by smoothing out noise, which provides a graphical display of the structure of the networks. With the similarity measured from MDS, we find that the item-based collaborative filtering algorithm can outperform the diffusion-based recommendation algorithms. Moreover, we show that this method tends to recommend unpopular items and increase the global diversification of the networks in long term. PMID:25343243

Development of Numerical Tools for the Investigation of Plasma Detachment from Magnetic Nozzles

NASA Technical Reports Server (NTRS)

Sankaran, Kamesh; Polzin, Kurt A.

2007-01-01

A multidimensional numerical simulation framework aimed at investigating the process of plasma detachment from a magnetic nozzle is introduced. An existing numerical code based on a magnetohydrodynamic formulation of the plasma flow equations that accounts for various dispersive and dissipative processes in plasmas was significantly enhanced to allow for the modeling of axisymmetric domains containing three.dimensiunai momentum and magnetic flux vectors. A separate magnetostatic solver was used to simulate the applied magnetic field topologies found in various nozzle experiments. Numerical results from a magnetic diffusion test problem in which all three components of the magnetic field were present exhibit excellent quantitative agreement with the analytical solution, and the lack of numerical instabilities due to fluctuations in the value of del(raised dot)B indicate that the conservative MHD framework with dissipative effects is well-suited for multi-dimensional analysis of magnetic nozzles. Further studies will focus on modeling literature experiments both for the purpose of code validation and to extract physical insight regarding the mechanisms driving detachment.

Numerical simulation of two-dimensional flow over a heated carbon surface with coupled heterogeneous and homogeneous reactions

NASA Astrophysics Data System (ADS)

Johnson, Ryan Federick; Chelliah, Harsha Kumar

2017-01-01

For a range of flow and chemical timescales, numerical simulations of two-dimensional laminar flow over a reacting carbon surface were performed to understand further the complex coupling between heterogeneous and homogeneous reactions. An open-source computational package (OpenFOAM®) was used with previously developed lumped heterogeneous reaction models for carbon surfaces and a detailed homogeneous reaction model for CO oxidation. The influence of finite-rate chemical kinetics was explored by varying the surface temperatures from 1800 to 2600 K, while flow residence time effects were explored by varying the free-stream velocity up to 50 m/s. The reacting boundary layer structure dependence on the residence time was analysed by extracting the ratio of chemical source and species diffusion terms. The important contributions of radical species reactions on overall carbon removal rate, which is often neglected in multi-dimensional simulations, are highlighted. The results provide a framework for future development and validation of lumped heterogeneous reaction models based on multi-dimensional reacting flow configurations.

Kinematic and Microphysical Significance of Lightning Jumps versus Non-Jump Increases in Total Flash Rate

PubMed Central

Schultz, Christopher J.; Carey, Lawrence D.; Schultz, Elise V.; Blakeslee, Richard J.

2017-01-01

Thirty-nine thunderstorms are examined using multiple-Doppler, polarimetric and total lightning observations to understand the role of mixed phase kinematics and microphysics in the development of lightning jumps. This sample size is larger than those of previous studies on this topic. The principal result of this study is that lightning jumps are a result of mixed phase updraft intensification. Larger increases in intense updraft volume (≥ 10 m s−1) and larger changes in peak updraft speed are observed prior to lightning jump occurrence when compared to other non-jump increases in total flash rate. Wilcoxon-Mann-Whitney Rank Sum testing yields p-values ≤0.05, indicating statistical independence between lightning jump and non-jump distributions for these two parameters. Similar changes in mixed phase graupel mass magnitude are observed prior to lightning jumps and non-jump increases in total flash rate. The p-value for graupel mass change is p=0.096, so jump and non-jump distributions for graupel mass change are not found statistically independent using the p=0.05 significance level. Timing of updraft volume, speed and graupel mass increases are found to be 4 to 13 minutes in advance of lightning jump occurrence. Also, severe storms without lightning jumps lack robust mixed phase updrafts, demonstrating that mixed phase updrafts are not always a requirement for severe weather occurrence. Therefore, the results of this study show that lightning jump occurrences are coincident with larger increases in intense mixed phase updraft volume and peak updraft speed than smaller non-jump increases in total flash rate. PMID:29158622

Kinematic and Microphysical Significance of Lightning Jumps versus Non-Jump Increases in Total Flash Rate.

PubMed

Schultz, Christopher J; Carey, Lawrence D; Schultz, Elise V; Blakeslee, Richard J

2017-02-01

Thirty-nine thunderstorms are examined using multiple-Doppler, polarimetric and total lightning observations to understand the role of mixed phase kinematics and microphysics in the development of lightning jumps. This sample size is larger than those of previous studies on this topic. The principal result of this study is that lightning jumps are a result of mixed phase updraft intensification. Larger increases in intense updraft volume (≥ 10 m s -1 ) and larger changes in peak updraft speed are observed prior to lightning jump occurrence when compared to other non-jump increases in total flash rate. Wilcoxon-Mann-Whitney Rank Sum testing yields p-values ≤0.05, indicating statistical independence between lightning jump and non-jump distributions for these two parameters. Similar changes in mixed phase graupel mass magnitude are observed prior to lightning jumps and non-jump increases in total flash rate. The p-value for graupel mass change is p=0.096, so jump and non-jump distributions for graupel mass change are not found statistically independent using the p=0.05 significance level. Timing of updraft volume, speed and graupel mass increases are found to be 4 to 13 minutes in advance of lightning jump occurrence. Also, severe storms without lightning jumps lack robust mixed phase updrafts, demonstrating that mixed phase updrafts are not always a requirement for severe weather occurrence. Therefore, the results of this study show that lightning jump occurrences are coincident with larger increases in intense mixed phase updraft volume and peak updraft speed than smaller non-jump increases in total flash rate.

Kinematic and Microphysical Significance of Lightning Jumps Versus Non-Jump Increases in Total Flash Rate

NASA Technical Reports Server (NTRS)

Schultz, Christopher J.; Carey, Lawrence D.; Schultz, Elise V.; Blakeslee, Richard J.

2017-01-01

Thirty-nine thunderstorms are examined using multiple-Doppler, polarimetric and total lightning observations to understand the role of mixed phase kinematics and microphysics in the development of lightning jumps. This sample size is larger than those of previous studies on this topic. The principal result of this study is that lightning jumps are a result of mixed phase updraft intensification. Larger increases in intense updraft volume greater than or equal to 10 m(sup -1) and larger changes in peak updraft speed are observed prior to lightning jump occurrence when compared to other non-jump increases in total ash rate. Wilcoxon-Mann-Whitney Rank Sum testing yields p-values 0.05, indicating statistical independence between lightning jump and non-jump distributions for these two parameters. Similar changes in mixed phase graupel mass magnitude are observed prior to lightning jumps and non-jump increases in total ash rate. The p-value for graupel mass change is p=0.096, so jump and non-jump distributions for graupel mass change are not found statistically independent using the p=0.05 significance level. Timing of updraft volume, speed and graupel mass increases are found to be 4 to 13 minutes in advance of lightning jump occurrence. Also, severe storms without lightning jumps lack robust mixed phase updrafts, demonstrating that mixed phase updrafts are not always a requirement for severe weather occurrence. Therefore, the results of this study show that lightning jump occurrences are coincident with larger increases in intense mixed phase updraft volume and peak updraft speed than smaller non-jump increases in total ash rate.

Do Bilateral Vertical Jumps With Reactive Jump Landings Achieve Osteogenic Thresholds With and Without Instruction in Premenopausal Women?

PubMed

Clissold, Tracey L; Winwood, Paul W; Cronin, John B; De Souza, Mary Jane

2018-04-01

Jumps have been investigated as a stimulus for bone development; however, effects of instruction, jump type, and jump-landing techniques need investigation. This study sought to identify whether ground reaction forces (GRFs) for bilateral vertical jumps (countermovement jumps and drop jumps) with reactive jump-landings (ie, jumping immediately after initial jump-landing), with instruction and with instruction withdrawn, achieve magnitudes and rates of strain previously shown to improve bone mass among premenopausal women. Twenty-one women (Mean ± SD: 43.3 ± 5.9 y; 69.4 ± 9.6 kg; 167 ± 5.5 cm; 27.5 ± 8.7% body fat) performed a testing session 'with instruction' followed by a testing session performed 1 week later with 'instruction withdrawn.' The magnitudes (4.59 to 5.49 body weight [BW]) and rates of strain (263 to 359 BW·s -1 ) for the jump-landings, performed on an AMTI force plate, exceeded previously determined thresholds (>3 BWs and >43 BW·s -1 ). Interestingly, significantly larger peak resultant forces, (↑10%; P = .002) and peak rates of force development (↑20%; P < .001) values (in relation to BW and BW·s -1 , respectively) were observed for the second jump-landing (postreactive jump). Small increases (ES = 0.22-0.42) in all landing forces were observed in the second jump-landing with 'instruction withdrawn.' These jumps represent a unique training stimulus for premenopausal women and achieve osteogenic thresholds thought prerequisite for bone growth.

Kinematics and Kinetics of Squats, Drop Jumps and Imitation Jumps of Ski Jumpers

PubMed Central

Pauli, Carole A.; Keller, Melanie; Ammann, Fabian; Hübner, Klaus; Lindorfer, Julia; Taylor, William R.

2016-01-01

Abstract Pauli, CA, Keller, M, Ammann, F, Hübner, K, Lindorfer, J, Taylor, WR, and Lorenzetti, S. Kinematics and kinetics of squats, drop jumps and imitation jumps of ski jumpers. J Strength Cond Res 30(3): 643–652, 2016—Squats, drop jumps, and imitation jumps are commonly used training exercises in ski jumping to enhance maximum force, explosive force, and sport-specific skills. The purpose of this study was to evaluate the kinetics and kinematics of training exercises in ski jumping and to find objective parameters in training exercises that most correlate with the competition performance of ski jumpers. To this end, barbell squats, drop jumps, and imitation jumps were measured in a laboratory environment for 10 elite ski jumpers. Force and motion data were captured, and the influence of maximum vertical force, force difference, vertical take-off velocity, knee moments, knee joint power, and a knee valgus/varus index was evaluated and correlated with their season jump performance. The results indicate that, especially for the imitation jumps, a good correlation exists between the vertical take-off velocity and the personal jump performance on the hill (R = 0.718). Importantly, however, the more the athletes tended toward a valgus knee alignment during the measured movements, the worse their performance (R = 0.729 imitation jumps; R = 0.685 squats). Although an evaluation of the athletes' lower limb alignment during competitive jumping on the hill is still required, these preliminary data suggest that performance training should additionally concentrate on improving knee alignment to increase ski jumping performance. PMID:26418370

Lagrangian statistics across the turbulent-nonturbulent interface in a turbulent plane jet.

PubMed

Taveira, Rodrigo R; Diogo, José S; Lopes, Diogo C; da Silva, Carlos B

2013-10-01

Lagrangian statistics from millions of particles are used to study the turbulent entrainment mechanism in a direct numerical simulation of a turbulent plane jet at Re(λ) ≈ 110. The particles (tracers) are initially seeded at the irrotational region of the jet near the turbulent shear layer and are followed as they are drawn into the turbulent region across the turbulent-nonturbulent interface (TNTI), allowing the study of the enstrophy buildup and thereby characterizing the turbulent entrainment mechanism in the jet. The use of Lagrangian statistics following fluid particles gives a more correct description of the entrainment mechanism than in previous works since the statistics in relation to the TNTI position involve data from the trajectories of the entraining fluid particles. The Lagrangian statistics for the particles show the existence of a velocity jump and a characteristic vorticity jump (with a thickness which is one order of magnitude greater than the Kolmogorov microscale), in agreement with previous results using Eulerian statistics. The particles initially acquire enstrophy by viscous diffusion and later by enstrophy production, which becomes "active" only deep inside the turbulent region. Both enstrophy diffusion and production near the TNTI differ substantially from inside the turbulent region. Only about 1% of all particles find their way into pockets of irrotational flow engulfed into the turbulent shear layer region, indicating that "engulfment" is not significant for the present flow, indirectly suggesting that the entrainment is largely due to "nibbling" small-scale mechanisms acting along the entire TNTI surface. Probability density functions of particle positions suggests that the particles spend more time crossing the region near the TNTI than traveling inside the turbulent region, consistent with the particles moving tangent to the interface around the time they cross it.

A data-driven wavelet-based approach for generating jumping loads

NASA Astrophysics Data System (ADS)

Chen, Jun; Li, Guo; Racic, Vitomir

2018-06-01

This paper suggests an approach to generate human jumping loads using wavelet transform and a database of individual jumping force records. A total of 970 individual jumping force records of various frequencies were first collected by three experiments from 147 test subjects. For each record, every jumping pulse was extracted and decomposed into seven levels by wavelet transform. All the decomposition coefficients were stored in an information database. Probability distributions of jumping cycle period, contact ratio and energy of the jumping pulse were statistically analyzed. Inspired by the theory of DNA recombination, an approach was developed by interchanging the wavelet coefficients between different jumping pulses. To generate a jumping force time history with N pulses, wavelet coefficients were first selected randomly from the database at each level. They were then used to reconstruct N pulses by the inverse wavelet transform. Jumping cycle periods and contract ratios were then generated randomly based on their probabilistic functions. These parameters were assigned to each of the N pulses which were in turn scaled by the amplitude factors βi to account for energy relationship between successive pulses. The final jumping force time history was obtained by linking all the N cycles end to end. This simulation approach can preserve the non-stationary features of the jumping load force in time-frequency domain. Application indicates that this approach can be used to generate jumping force time history due to single people jumping and also can be extended further to stochastic jumping loads due to groups and crowds.

Analysis of the association between isokinetic knee strength with offensive and defensive jumping capacity in high-level female volleyball athletes.

PubMed

Sattler, Tine; Sekulic, Damir; Esco, Michael R; Mahmutovic, Ifet; Hadzic, Vedran

2015-09-01

Isokinetic-knee-strength was hypothesized to be an important factor related to jumping performance. However, studies examining this relation among elite female athletes and sport-specific jumps are lacking. This investigation determined the influence of isokinetic-knee flexor/extensor strength measures on spike-jump (offensive) and block-jump (defensive) performance among high-level female volleyball players. Cross-sectional laboratory study. Eighty-two female volleyball athletes (age = 21.3 ± 3.8 years, height = 175.4 ± 6.76 cm, and weight = 68.29 ± 8.53 kg) volunteered to participate in this study. The studied variables included spike-jump and block-jump performance and a set of isokinetic tests to evaluate the eccentric and concentric strength capacities of the knee extensors (quadriceps - Q), and flexors (hamstring - H) for both legs. Both jumping tests showed high intra-session reliability (ICC of 0.87 and 0.95 for spike-jump and block-jump, respectively). The athletes were clustered into three achievement-groups based on their spike-jump and block-jump performances. For the block-jump, ANOVA identified significant differences between achievement-groups for all isokinetic variables except the Right-Q-Eccentric-Strength. When observed for spike-jump, achievement-groups differed significantly in all tests but Right-H-Concentric-Strength. Discriminant canonical analysis showed that the isokinetic-strength variables were more associated with block-jump then spike-jump-performance. The eccentric isokinetic measures were relatively less important determinants of block-jump than for the spike-jump performance. Data support the hypothesis of the importance of isokinetic strength measures for the expression of rapid muscular performance in volleyball. The results point to the necessity of the differential approach in sport training for defensive and offensive duties. Copyright © 2014 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Determination of K-shell absorption jump factors and jump ratios for La2O3, Ce and Gd using two different methods

NASA Astrophysics Data System (ADS)

Akman, Ferdi; Durak, Rıdvan; Kaçal, Mustafa Recep; Turhan, Mehmet Fatih; Akdemir, Fatma

2015-02-01

The K shell absorption jump factors and jump ratios for La2O3, Ce and Gd samples have been determined using the gamma or X-ray attenuation and EDXRF methods. It is the first time that the K shell absorption jump factor and jump ratio have been discussed for present elements using two different methods. To detect K X-rays, a high resolution Si(Li) detector was used. The experimental results of K shell absorption jump factors and jump ratios were compared with the theoretically calculated ones.

Recent advances in computational-analytical integral transforms for convection-diffusion problems

NASA Astrophysics Data System (ADS)

Cotta, R. M.; Naveira-Cotta, C. P.; Knupp, D. C.; Zotin, J. L. Z.; Pontes, P. C.; Almeida, A. P.

2017-10-01

An unifying overview of the Generalized Integral Transform Technique (GITT) as a computational-analytical approach for solving convection-diffusion problems is presented. This work is aimed at bringing together some of the most recent developments on both accuracy and convergence improvements on this well-established hybrid numerical-analytical methodology for partial differential equations. Special emphasis is given to novel algorithm implementations, all directly connected to enhancing the eigenfunction expansion basis, such as a single domain reformulation strategy for handling complex geometries, an integral balance scheme in dealing with multiscale problems, the adoption of convective eigenvalue problems in formulations with significant convection effects, and the direct integral transformation of nonlinear convection-diffusion problems based on nonlinear eigenvalue problems. Then, selected examples are presented that illustrate the improvement achieved in each class of extension, in terms of convergence acceleration and accuracy gain, which are related to conjugated heat transfer in complex or multiscale microchannel-substrate geometries, multidimensional Burgers equation model, and diffusive metal extraction through polymeric hollow fiber membranes. Numerical results are reported for each application and, where appropriate, critically compared against the traditional GITT scheme without convergence enhancement schemes and commercial or dedicated purely numerical approaches.

Jump events in a 3D Edwards-Anderson spin glass

NASA Astrophysics Data System (ADS)

Mártin, Daniel A.; Iguain, José Luis

2017-11-01

The statistical properties of infrequent particle displacements, greater than a certain distance, are known as jump dynamics in the context of structural glass formers. We generalize the concept of a jump to the case of a spin glass, by dividing the system into small boxes, and considering the infrequent cooperative spin flips in each box. Jumps defined this way share similarities with jumps in structural glasses. We perform numerical simulations for the 3D Edwards-Anderson model, and study how the properties of these jumps depend on the waiting time after a quench. Similar to the results for structural glasses, we find that while jump frequency depends strongly on time, the jump duration and jump length are roughly stationary. At odds with some results reported on studies of structural glass formers, at long enough times, the rest time between jumps varies as the inverse of jump frequency. We give a possible explanation for this discrepancy. We also find that our results are qualitatively reproduced by a fully-connected trap model.

Does gymnastics practice improve vertical jump reliability from the age of 8 to 10 years?

PubMed

Marina, Michel; Torrado, Priscila

2013-01-01

The objective of this study was to confirm whether gymnastics practice from a young age can induce greater vertical jump reliability. Fifty young female gymnasts (8.84 ± 0.62 years) and 42 females in the control group (8.58 ± 0.92 years) performed the following jump tests on a contact mat: squat jump, countermovement jump, countermovement jump with arm swing and drop jump from heights of 40 and 60 cm. The two testing sessions had three trials each and were separated by one week. A 2 (groups) × 2 (sessions) × 3 (trials) repeated measures analysis of variance (ANOVA) and a test-retest correlation analysis were used to study the reliability. There was no systematic source of error in either group for non-plyometric jumps such as squat jump, countermovement jump, and countermovement jump with arm swing. A significant group per trial interaction revealed a learning effect in gymnasts' drop jumps from 40 cm height. Additionally, the test-retest correlation analysis and the higher minimum detectable error suggest that the quick drop jump technique was not fully consolidated in either group. At an introductory level of gymnastics and between the ages of 8-10 years, the condition of being a gymnast did not lead to conclusively higher reliability, aside from better overall vertical jump performance.

On the diffusion of ferrocenemethanol in room-temperature ionic liquids: an electrochemical study.

PubMed

Lovelock, Kevin R J; Ejigu, Andinet; Loh, Sook Fun; Men, Shuang; Licence, Peter; Walsh, Darren A

2011-06-07

The electrochemical behaviour of ferrocenemethanol (FcMeOH) has been studied in a range of room-temperature ionic liquids (RTILs) using cyclic voltammetry, chronoamperomery and scanning electrochemical microscopy (SECM). The diffusion coefficient of FcMeOH, measured using chronoamperometry, decreased with increasing RTIL viscosity. Analysis of the mass transport properties of the RTILs revealed that the Stokes-Einstein equation did not apply to our data. The "correlation length" was estimated from diffusion coefficient data and corresponded well to the average size of holes (voids) in the liquid, suggesting that a model in which the diffusing species jumps between holes in the liquid is appropriate in these liquids. Cyclic voltammetry at ultramicroelectrodes demonstrated that the ability to record steady-state voltammograms during ferrocenemethanol oxidation depended on the voltammetric scan rate, the electrode dimensions and the RTIL viscosity. Similarly, the ability to record steady-state SECM feedback approach curves depended on the RTIL viscosity, the SECM tip radius and the tip approach speed. Using 1.3 μm Pt SECM tips, steady-state SECM feedback approach curves were obtained in RTILs, provided that the tip approach speed was low enough to maintain steady-state diffusion at the SECM tip. In the case where tip-induced convection contributed significantly to the SECM tip current, this effect could be accounted for theoretically using mass transport equations that include diffusive and convective terms. Finally, the rate of heterogeneous electron transfer across the electrode/RTIL interface during ferrocenemethanol oxidation was estimated using SECM, and k(0) was at least 0.1 cm s(-1) in one of the least viscous RTILs studied.

Molecular dynamics simulations of propane in slit shaped silica nano-pores: direct comparison with quasielastic neutron scattering experiments.

PubMed

Gautam, Siddharth; Le, Thu; Striolo, Alberto; Cole, David

2017-12-13

Molecular motion under confinement has important implications for a variety of applications including gas recovery and catalysis. Propane confined in mesoporous silica aerogel as studied using quasielastic neutron scattering (QENS) showed anomalous pressure dependence in its diffusion coefficient (J. Phys. Chem. C, 2015, 119, 18188). Molecular dynamics (MD) simulations are often employed to complement the information obtained from QENS experiments. Here, we report an MD simulation study to probe the anomalous pressure dependence of propane diffusion in silica aerogel. Comparison is attempted based on the self-diffusion coefficients and on the time scales of the decay of the simulated intermediate scattering functions. While the self-diffusion coefficients obtained from the simulated mean squared displacement profiles do not exhibit the anomalous pressure dependence observed in the experiments, the time scales of the decay of the intermediate scattering functions calculated from the simulation data match the corresponding quantities obtained in the QENS experiment and thus confirm the anomalous pressure dependence of the diffusion coefficient. The origin of the anomaly in pressure dependence lies in the presence of an adsorbed layer of propane molecules that seems to dominate the confined propane dynamics at low pressure, thereby lowering the diffusion coefficient. Further, time scales for rotational motion obtained from the simulations explain the absence of rotational contribution to the QENS spectra in the experiments. In particular, the rotational motion of the simulated propane molecules is found to exhibit large angular jumps at lower pressure. The present MD simulation work thus reveals important new insights into the origin of anomalous pressure dependence of propane diffusivity in silica mesopores and supplements the information obtained experimentally by QENS data.

Neuromuscular function during drop jumps in young and elderly males.

PubMed

Piirainen, Jarmo M; Linnamo, Vesa; Sippola, Niina; Avela, Janne

2012-12-01

The Hoffman reflex (H-reflex), indicating alpha-motoneuron pool activity, has been shown to be task - and in resting conditions - age dependent. How aging affects H-reflex activity during explosive movements is not clear at present. The purpose of this study was to examine the effects of aging on H-reflexes during drop jumps, and its possible role in drop jump performance. Ten young (26.8 ± 2.7 years) and twenty elderly (64.2 ± 2.7 years) subjects participated in the study. Maximal drop jump performance and soleus H-reflex response (H/M jump) 20 ms after ground contact were measured in a sledge ergometer. Maximal H-reflex, maximal M-wave, Hmax/Mmax-ratio and H-reflex excitability curves were measured during standing rest. Although in young the H-reflex response (Hmax/Mmax) was 6.5% higher during relaxed standing and 19.7% higher during drop jumps (H jump/M jump) than in the elderly group, these differences were not statistically significant. In drop jumps, the elderly subjects had lower jumping height (30.4%, p < 0.001), longer braking time (32.4%, p < 0.01), lower push-off force (18.0%, p < 0.05) and longer push-off time (31.0% p < 0.01). H jump/M jump correlated with the average push-off force (r = 0.833, p < 0.05) and with push-off time (r = -0.857, p < 0.01) in young but not in the elderly. Correlations between H-reflex response and jumping parameters in young may indicate different jumping and activation strategies in drop jumps. However, it does not fully explain age related differences in jumping performance, since age related differences in H-reflex activity were non-significant. Copyright © 2012 Elsevier Ltd. All rights reserved.

Accuracy of Jump-Mat Systems for Measuring Jump Height.

PubMed

Pueo, Basilio; Lipinska, Patrycja; Jiménez-Olmedo, José M; Zmijewski, Piotr; Hopkins, Will G

2017-08-01

Vertical-jump tests are commonly used to evaluate lower-limb power of athletes and nonathletes. Several types of equipment are available for this purpose. To compare the error of measurement of 2 jump-mat systems (Chronojump-Boscosystem and Globus Ergo Tester) with that of a motion-capture system as a criterion and to determine the modifying effect of foot length on jump height. Thirty-one young adult men alternated 4 countermovement jumps with 4 squat jumps. Mean jump height and standard deviations representing technical error of measurement arising from each device and variability arising from the subjects themselves were estimated with a novel mixed model and evaluated via standardization and magnitude-based inference. The jump-mat systems produced nearly identical measures of jump height (differences in means and in technical errors of measurement ≤1 mm). Countermovement and squat-jump height were both 13.6 cm higher with motion capture (90% confidence limits ±0.3 cm), but this very large difference was reduced to small unclear differences when adjusted to a foot length of zero. Variability in countermovement and squat-jump height arising from the subjects was small (1.1 and 1.5 cm, respectively, 90% confidence limits ±0.3 cm); technical error of motion capture was similar in magnitude (1.7 and 1.6 cm, ±0.3 and ±0.4 cm), and that of the jump mats was similar or smaller (1.2 and 0.3 cm, ±0.5 and ±0.9 cm). The jump-mat systems provide trustworthy measurements for monitoring changes in jump height. Foot length can explain the substantially higher jump height observed with motion capture.

Costs and benefits of larval jumping behaviour of Bathyplectes anurus.

PubMed

Saeki, Yoriko; Tani, Soichiro; Fukuda, Katsuto; Iwase, Shun-ichiro; Sugawara, Yuma; Tuda, Midori; Takagi, Masami

2016-02-01

Bathyplectes anurus, a parasitoid of the alfalfa weevils, forms a cocoon in the late larval stage and exhibits jumping behaviour. Adaptive significance and costs of the cocoon jumping have not been thoroughly studied. We hypothesised that jumping has the fitness benefits of enabling habitat selection by avoiding unfavourable environments. We conducted laboratory experiments, which demonstrated that jumping frequencies increased in the presence of light, with greater magnitudes of temperature increase and at lower relative humidity. In addition, when B. anurus individuals were allowed to freely jump in an arena with a light gradient, more cocoons were found in the shady area, suggesting microhabitat selection. In a field experiment, mortality of cocoons placed in the sun was significantly higher than for cocoons placed in the shade. B. anurus cocoons respond to environmental stress by jumping, resulting in habitat selection. In the presence of potential predators (ants), jumping frequencies were higher than in the control (no ant) arenas, though jumping frequencies decreased after direct contact with the predators. Body mass of B. anurus cocoons induced to jump significantly decreased over time than cocoons that did not jump, suggesting a cost to jumping. We discuss the benefits and costs of jumping behaviour and potential evolutionary advantages of this peculiar trait, which is present in a limited number of species.

Validity Study of a Jump Mat Compared to the Reference Standard Force Plate.

PubMed

Rogan, Slavko; Radlinger, Lorenz; Imhasly, Caroline; Kneubuehler, Andrea; Hilfiker, Roger

2015-12-01

In the field of vertical jump diagnostics, force plates (FP) are the reference standard. Recently, despite a lack of evidence, jump mats have been used increasingly. Important factors in favor of jumping mats are their low cost and portability. This validity study compared the Haynl-Elektronik jump mat (HE jump mat) with the reference standard force plate. Ten healthy volunteers participated and each participant completed three series of five drop jumps (DJ). The parameters ground contact time (GCT) and vertical jump height (VJH) from the HE jump mat and the FP were used to evaluate the concurrent validity. The following statistical calculations were performed: Pearson's correlation (r), Bland-Altman plots (standard and for adjusted trend), and regression equations. The Bland-Altman plots suggest that the HE jump mat measures shorter contact times and higher jump heights than the FP. The trend-adjusted Bland-Altman plot shows higher mean differences and wider wing-spreads of confidence limits during longer GCT. During the VJH the mean differences and the wing-spreads of the confidence limits throughout the range present as relatively constant. The following regression equations were created, as close as possible to the true value: GCT = 5.920385 + 1.072293 × [value HE jump mat] and VJH = -1.73777 + 1.011156 × [value HE jump mat]. The HE jump mat can be recommended in relation to the validity of constraints. In this study, only a part of the quality criteria were examined. For the final recommendation it is advised to examine the HE jump mat on the other quality criteria (test-retest reliability, sensitivity change).

Lévy targeting and the principle of detailed balance.

PubMed

Garbaczewski, Piotr; Stephanovich, Vladimir

2011-07-01

We investigate confining mechanisms for Lévy flights under premises of the principle of detailed balance. In this case, the master equation of the jump-type process admits a transformation to the Lévy-Schrödinger semigroup dynamics akin to a mapping of the Fokker-Planck equation into the generalized diffusion equation. This sets a correspondence between above two stochastic dynamical systems, within which we address a (stochastic) targeting problem for an arbitrary stability index μ ε (0,2) of symmetric Lévy drivers. Namely, given a probability density function, specify the semigroup potential, and thence the jump-type dynamics for which this PDF is actually a long-time asymptotic (target) solution of the master equation. Here, an asymptotic behavior of different μ-motion scenarios ceases to depend on μ. That is exemplified by considering Gaussian and Cauchy family target PDFs. A complementary problem of the reverse engineering is analyzed: given a priori a semigroup potential, quantify how sensitive upon the choice of the μ driver is an asymptotic behavior of solutions of the associated master equation and thus an invariant PDF itself. This task is accomplished for so-called μ family of Lévy oscillators.

Steady-state heat transport: Ballistic-to-diffusive with Fourier's law

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maassen, Jesse, E-mail: jmaassen@purdue.edu; Lundstrom, Mark

2015-01-21

It is generally understood that Fourier's law does not describe ballistic phonon transport, which is important when the length of a material is similar to the phonon mean-free-path. Using an approach adapted from electron transport, we demonstrate that Fourier's law and the heat equation do capture ballistic effects, including temperature jumps at ideal contacts, and are thus applicable on all length scales. Local thermal equilibrium is not assumed, because allowing the phonon distribution to be out-of-equilibrium is important for ballistic and quasi-ballistic transport. The key to including the non-equilibrium nature of the phonon population is to apply the proper boundarymore » conditions to the heat equation. Simple analytical solutions are derived, showing that (i) the magnitude of the temperature jumps is simply related to the material properties and (ii) the observation of reduced apparent thermal conductivity physically stems from a reduction in the temperature gradient and not from a reduction in actual thermal conductivity. We demonstrate how our approach, equivalent to Fourier's law, easily reproduces results of the Boltzmann transport equation, in all transport regimes, even when using a full phonon dispersion and mean-free-path distribution.« less

Level set immersed boundary method for gas-liquid-solid interactions with phase-change

NASA Astrophysics Data System (ADS)

Dhruv, Akash; Balaras, Elias; Riaz, Amir; Kim, Jungho

2017-11-01

We will discuss an approach to simulate the interaction between two-phase flows with phase changes and stationary/moving structures. In our formulation, the Navier-Stokes and heat advection-diffusion equations are solved on a block-structured grid using adaptive mesh refinement (AMR) along with sharp jump in pressure, velocity and temperature across the interface separating the different phases. The jumps are implemented using a modified Ghost Fluid Method (Lee et al., J. Comput. Physics, 344:381-418, 2017), and the interface is tracked with a level set approach. Phase transition is achieved by calculating mass flux near the interface and extrapolating it to the rest of the domain using a Hamilton-Jacobi equation. Stationary/moving structures are simulated with an immersed boundary formulation based on moving least squares (Vanella & Balaras, J. Comput. Physics, 228:6617-6628, 2009). A variety of canonical problems involving vaporization, film boiling and nucleate boiling is presented to validate the method and demonstrate the its formal accuracy. The robustness of the solver in complex problems, which are crucial in efficient design of heat transfer mechanisms for various applications, will also be demonstrated. Work supported by NASA, Grant NNX16AQ77G.

Jump spillover between oil prices and exchange rates

NASA Astrophysics Data System (ADS)

Li, Xiao-Ping; Zhou, Chun-Yang; Wu, Chong-Feng

2017-11-01

In this paper, we investigate the jump spillover effects between oil prices and exchange rates. To identify the latent historical jumps for exchange rates and oil prices, we use a Bayesian MCMC approach to estimate the stochastic volatility model with correlated jumps in both returns and volatilities for each. We examine the simultaneous jump intensities and the conditional jump spillover probabilities between oil prices and exchange rates, finding strong evidence of jump spillover effects. Further analysis shows that the jump spillovers are mainly due to exogenous events such as financial crises and geopolitical events. Thus, the findings have important implications for financial risk management.

Jump frequency may contribute to risk of jumper's knee: a study of interindividual and sex differences in a total of 11,943 jumps video recorded during training and matches in young elite volleyball players.

PubMed

Bahr, Martin A; Bahr, Roald

2014-09-01

Male sex, total training volume (number of hours per week) and match exposure (number of sets played per week) are risk factors for jumper's knee among young elite volleyball players. However, it is not known whether jump frequency differs among players on the same squad. To examine interindividual and sex differences in jump frequency during training and matches in young elite volleyball players. Observational study. Norwegian elite volleyball boarding school training programme. Student-athletes (26 boys and 18 girls, 16-18 years). Individual jump counts were recorded based on visual analysis of video recordings obtained from 1 week of volleyball training (9 training sessions for boys and 10 for girls, 14.1 h and 17.8 h of training, respectively) and 10 matches (5.9 h for boys (16 sets) and 7.7 h for girls (21 sets). A total of 11,943 jumps were recorded, 4138 during matches and 7805 during training. As training attendance and jump frequency varied substantially between players, the total exposure in training ranged from 50 to 666 jumps/week among boys and from 11 to 251 jumps/week among girls. On average, this corresponded to 35.7 jumps/h for boys and 13.7 jumps/h for girls (Student t test, p=0.002). Total jump exposure during matches ranged between 1 and 339 jumps among boys and between 0 and 379 jumps among girls, corresponding to an average jump frequency of 62.2 jumps/h for boys and 41.9 jumps/h for girls (Student t test, p<0.039). The interindividual differences in jump frequency were substantially greater than any differences observed among player functions. Jump frequency has substantial interindividual and sex differences during training and matches in young elite volleyball players. Total jump volume may represent a more important risk factor for jumper's knee than total training volume, warranting further research attention. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Modeling and simulation of Cu diffusion and drift in porous CMOS backend dielectrics

NASA Astrophysics Data System (ADS)

Ali, R.; Fan, Y.; King, S.; Orlowski, M.

2018-06-01

With the advent of porous dielectrics, Cu drift-diffusion reliability issues in CMOS backend have only been exacerbated. In this regard, a modeling and simulation study of Cu atom/ion drift-diffusion in porous dielectrics is presented to assess the backend reliability and to explore conditions for a reliable Resistive Random Access Memory (RRAM) operation. The numerical computation, using elementary jump frequencies for a random walk in 2D and 3D, is based on an extended adjacency tensor concept. It is shown that Cu diffusion and drift transport are affected as much by the level of porosity as by the pore morphology. Allowance is made for different rates of Cu dissolution into the dielectric and for Cu absorption and transport at and on the inner walls of the pores. Most of the complex phenomena of the drift-diffusion transport in porous media can be understood in terms of local lateral and vertical gradients and the degree of their perturbation caused by the presence of pores in the transport domain. The impact of pore morphology, related to the concept of tortuosity, is discussed in terms of "channeling" and "trapping" effects. The simulations are calibrated to experimental results of porous SiCOH layers of 25 nm thickness, sandwiched between Cu and Pt(W) electrodes with experimental porosity levels of 0%, 8%, 12%, and 25%. We find that porous SICOH is more immune to Cu+ drift at 300 K than non-porous SICOH.

Structural and functional neuroplasticity in human learning of spatial routes.

PubMed

Keller, Timothy A; Just, Marcel Adam

2016-01-15

Recent findings with both animals and humans suggest that decreases in microscopic movements of water in the hippocampus reflect short-term neuroplasticity resulting from learning. Here we examine whether such neuroplastic structural changes concurrently alter the functional connectivity between hippocampus and other regions involved in learning. We collected both diffusion-weighted images and fMRI data before and after humans performed a 45min spatial route-learning task. Relative to a control group with equal practice time, there was decreased diffusivity in the posterior-dorsal dentate gyrus of the left hippocampus in the route-learning group accompanied by increased synchronization of fMRI-measured BOLD signal between this region and cortical areas, and by changes in behavioral performance. These concurrent changes characterize the multidimensionality of neuroplasticity as it enables human spatial learning. Copyright © 2015 Elsevier Inc. All rights reserved.

RELATIONSHIP BETWEEN ISOKINETIC KNEE STRENGTH AND JUMP CHARACTERISTICS FOLLOWING ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION.

PubMed

Laudner, Kevin; Evans, Daniel; Wong, Regan; Allen, Aaron; Kirsch, Tom; Long, Brian; Meister, Keith

2015-06-01

Clinicians are often challenged when making return-to-play decisions following anterior cruciate ligament reconstruction (ACL-R). Isokinetic strength and jump performance testing are common tools used to make this decision. Unfortunately, vertical jump performance standards have not been clearly established and many clinicians do not have access to isokinetic testing equipment. To establish normative jump and strength characteristics in ACL-R patients cleared by an orthopedic physician to return-to-play and to determine if relationships exist between knee isokinetic strength measurements and jump characteristics described using an electronic jump map system. Descriptive laboratory study. Thirty-three ACL-R patients who had been cleared to return to athletic competition participated in this study. Twenty-six of these ACL-R participants were also matched to 26 asymptomatic athletes based on sex, limb, height, and mass to determine isokinetic strength and jump characteristic differences between groups. Jump tests consisted of single leg vertical, double leg vertical, and a 4-jump single leg vertical jump assessed using an electronic jump mat system. Independent t-tests were used to determine differences between groups and multiple regression analyses were used to identify any relationships between jump performance and knee strength (p<0.05). The ACL-R group had lower vertical jump capabilities and some bilateral knee strength deficiencies compared to the matched control group. The ACL-R group also showed several moderate-to-strong positive relationships for both knee extension and flexion strength with several jump performance characteristics, such as single and double leg vertical jump height. The current results indicate that ACL-R patients present with several knee strength and vertical jump differences compared to a matched control group at the time of return-to-play. Also, ACL-R patient's performance on an electronic jump mat system is strongly related to isokinetic knee strength measures. 2b.

Aminopolymer Mobility and Support Interactions in Silica-PEI Composites for CO 2 Capture Applications: A Quasielastic Neutron Scattering Study

DOE PAGES

Holewinski, Adam; Sakwa-Novak, Miles A.; Carrillo, Jan-Michael Y.; ...

2017-05-30

Composite gas sorbents, formed from an active polymer phase and a porous support, are promising materials for the separation of acid gases from a variety of gas streams. Significant changes in sorption performance (capacity, rate, stability etc.) can be achieved by tuning the properties of the polymer and the nature of interactions between polymer and support. We utilize quasielastic neutron scattering (QENS) and coarse-grained molecular dynamics (MD) simulations to characterize the dynamic behavior of the most commonly reported polymer in such materials, poly(ethylenimine) (PEI), both in bulk form and when supported in a mesoporous silica framework. The polymer chain dynamicsmore » (rotational and translational diffusion) are characterized using two neutron backscattering spectrometers that have overlapping time scales, ranging from picoseconds to a few nanoseconds. Two modes of motion are detected for the PEI molecule in QENS. At low energy transfers, a “slow process” on the time scale of ~200 ps is found and attributed to jump-mediated, center-of-mass diffusion. Second, a “fast process” at ~20 ps scale is also found and is attributed to a locally confined, jump-diffusion. Characteristic data (time scale and spectral weight) of these processes are compared to those characterized by MD, and reasonable agreement is found. For the nanopore-confined PEI, we observe a significant reduction in the time scale of polymer motion as compared to the bulk. The impacts of silica surface functionalization and of polymer fill fraction in the silica pores (controlling the portion of polymer molecules in contact with the pore walls), are both studied in detail. Hydrophobic functionalization of the silica leads to an increase of the PEI mobility above that in native silanol-terminated silica, but the dynamics are still slower than those in bulk PEI. Sorbents with faster PEI dynamics are also found to be more efficient for CO 2 capture, possibly because sorption sites are more accessible than those in systems with slower PEI dynamics. Therefore, this work supports the existence of a link between the affinity of the support for PEI and the accessibility of active sorbent functional groups.« less

Froghopper-inspired direction-changing concept for miniature jumping robots.

PubMed

Jung, Gwang-Pil; Cho, Kyu-Jin

2016-09-14

To improve the maneuverability and agility of jumping robots, several researchers have studied steerable jumping mechanisms. This steering ability enables robots to reach a particular target by controlling their jumping direction. To this end, we propose a novel direction-changing concept for miniature jumping robots. The proposed concept allows robots to be steerable while exerting minimal effects on jumping performance. The key design principles were adopted from the froghopper's power-producing hind legs and the moment cancellation accomplished by synchronized leg operation. These principles were applied via a pair of symmetrically positioned legs and conventional gears, which were modeled on the froghopper's anatomy. Each leg has its own thrusting energy, which improves jumping performance by allowing the mechanism to thrust itself with both power-producing legs. Conventional gears were utilized to simultaneously operate the legs and cancel out the moments that they induce, which minimizes body spin. A prototype to verify the concept was built and tested by varying the initial jumping posture. Three jumping postures (synchronous, asynchronous, and single-legged) were tested to investigate how synchronization and moment cancelling affect jumping performance. The results show that synchronous jumping allows the mechanism to change direction from -40° to 40°, with an improved take-off speed. The proposed concept can only be steered in a limited range of directions, but it has potential for use in miniature jumping robots that can change jumping direction with a minimal drop in jumping performance.

Fast Xe-129 relaxation in solid xenon near its melting point: Cross-over from Raman scattering of phonons to vacancy diffusion.

NASA Astrophysics Data System (ADS)

Kuzma, N. N.; Patton, B.; Raman, K.; Happer, W.

2002-03-01

NMR measurements of longitudinal relaxation times T1 in pure solid xenon were carried out using both natural-abundance and isotopically-enriched samples of hyperpolarized ^129Xe. At temperatures below 120 K and fields above 500 Gauss, the relaxation rate 1/T1 is field- and abundance-independent, consistent with the model of ^129Xe spin-flip Raman scattering of phonons(R. J. Fitzgerald et al.), Phys. Rev. B 59, 8795 (1999).. Above 120 K, vacancies invade the xenon lattice(P. R. Granfors et al.) Phys. Rev. B 24, 4753 (1981)., and a dramatic cross-over to the nuclear dipole-dipole relaxation due to the diffusion of vacancies is observed. As a result, the measured relaxation times of xenon near its melting point strongly depend on field and somewhat on ^129Xe abundance, and can be as short as several seconds, leading to potential difficulties in cryogenic applications of hyperpolarized ^129Xe. The data are analyzed using the theory of nuclear relaxation due to spin diffusion in cubic crystals(C. A. Sholl, J. Phys. C 21), 319 (1988)., and some estimates of the vacancy density and jump rates are discussed.

Coupling volume-excluding compartment-based models of diffusion at different scales: Voronoi and pseudo-compartment approaches

PubMed Central

Taylor, P. R.; Baker, R. E.; Simpson, M. J.; Yates, C. A.

2016-01-01

Numerous processes across both the physical and biological sciences are driven by diffusion. Partial differential equations are a popular tool for modelling such phenomena deterministically, but it is often necessary to use stochastic models to accurately capture the behaviour of a system, especially when the number of diffusing particles is low. The stochastic models we consider in this paper are ‘compartment-based’: the domain is discretized into compartments, and particles can jump between these compartments. Volume-excluding effects (crowding) can be incorporated by blocking movement with some probability. Recent work has established the connection between fine- and coarse-grained models incorporating volume exclusion, but only for uniform lattices. In this paper, we consider non-uniform, hybrid lattices that incorporate both fine- and coarse-grained regions, and present two different approaches to describe the interface of the regions. We test both techniques in a range of scenarios to establish their accuracy, benchmarking against fine-grained models, and show that the hybrid models developed in this paper can be significantly faster to simulate than the fine-grained models in certain situations and are at least as fast otherwise. PMID:27383421

A Comparison of Mechanical Parameters Between the Counter Movement Jump and Drop Jump in Biathletes

PubMed Central

Król, Henryk; Mynarski, Władysław

2012-01-01

The main objective of the study was to determine to what degree higher muscular activity, achieved by increased load in the extension phase (eccentric muscle action) of the vertical jump, affects the efficiency of the vertical jump. Sixteen elite biathletes participated in this investigation. The biathletes performed tests that consisted of five, single “maximal” vertical jumps (counter movement jump – CMJ) and five, single vertical jumps, in which the task was to touch a bar placed over the jumping biathletes (specific task counter movement jump – SCMJ). Then, they performed five, single drop jumps from an elevation of 0.4m (DJ). Ground reaction forces were registered using the KISTLER 9182C force platform. MVJ software was used for signal processing (Król, 1999) and enabling calculations for kinematic and kinetic parameters of the subject’s jump movements (on-line system). The results indicate that only height of the jump (h) and mean power (Pmean) during the takeoff are statistically significant. Both h and Pmean are higher in the DJ. The results of this study may indicate that elite biathletes are well adapted to eccentric work of the lower limbs, thus reaching greater values of power during the drop jump. These neuromuscular adaptive changes may allow for a more dynamic and efficient running technique. PMID:23487157

Time-resolved methods in biophysics. 9. Laser temperature-jump methods for investigating biomolecular dynamics.

PubMed

Kubelka, Jan

2009-04-01

Many important biochemical processes occur on the time-scales of nanoseconds and microseconds. The introduction of the laser temperature-jump (T-jump) to biophysics more than a decade ago opened these previously inaccessible time regimes up to direct experimental observation. Since then, laser T-jump methodology has evolved into one of the most versatile and generally applicable methods for studying fast biomolecular kinetics. This perspective is a review of the principles and applications of the laser T-jump technique in biophysics. A brief overview of the T-jump relaxation kinetics and the historical development of laser T-jump methodology is presented. The physical principles and practical experimental considerations that are important for the design of the laser T-jump experiments are summarized. These include the Raman conversion for generating heating pulses, considerations of size, duration and uniformity of the temperature jump, as well as potential adverse effects due to photo-acoustic waves, cavitation and thermal lensing, and their elimination. The laser T-jump apparatus developed at the NIH Laboratory of Chemical Physics is described in detail along with a brief survey of other laser T-jump designs in use today. Finally, applications of the laser T-jump in biophysics are reviewed, with an emphasis on the broad range of problems where the laser T-jump methodology has provided important new results and insights into the dynamics of the biomolecular processes.

Inter-segmental moment analysis characterises the partial correspondence of jumping and jerking

PubMed Central

Cleather, Daniel J; Goodwin, Jon E; Bull, Anthony MJ

2014-01-01

The aim of this study was to quantify internal joint moments of the lower limb during vertical jumping and the weightlifting jerk in order to improve awareness of the control strategies and correspondence between these activities, and to facilitate understanding of the likely transfer of training effects. Athletic males completed maximal unloaded vertical jumps (n=12) and explosive push jerks at 40 kg (n=9). Kinematic data were collected using optical motion tracking and kinetic data via a force plate, both at 200 Hz. Joint moments were calculated using a previously described biomechanical model of the right lower limb. Peak moment results highlighted that sagittal plane control strategies differed between jumping and jerking (p<0.05) with jerking being a knee dominant task in terms of peak moments as opposed to a more balanced knee and hip strategy in jumping and landing. Jumping and jerking exhibited proximal to distal joint involvement and landing was typically reversed. High variability was seen in non-sagittal moments at the hip and knee. Significant correlations were seen between jump height and hip and knee moments in jumping (p<0.05). Whilst hip and knee moments were correlated between jumping and jerking (p<0.05), joint moments in the jerk were not significantly correlated to jump height (p>0.05) possibly indicating a limit to the direct transferability of jerk performance to jumping. Ankle joint moments were poorly related to jump performance (p>0.05). Peak knee and hip moment generating capacity are important to vertical jump performance. The jerk appears to offer an effective strategy to overload joint moment generation in the knee relative to jumping. However, an absence of hip involvement would appear to make it a general, rather than specific, training modality in relation to jumping. PMID:22362089

Validity and intra-rater reliability of MyJump app on iPhone 6s in jump performance.

PubMed

Stanton, Robert; Wintour, Sally-Anne; Kean, Crystal O

2017-05-01

Smartphone applications are increasingly used by researchers, coaches, athletes and clinicians. The aim of this study was to examine the concurrent validity and intra-rater reliability of the smartphone-based application, MyJump, against laboratory-based force plate measurements. Cross sectional study. Participants completed counter-movement jumps (CMJ) (n=29) and 30cm drop jumps (DJ) (n=27) on a force plate which were simultaneously recorded using MyJump. To assess concurrent validity, jump height, derived from flight time acquired from each device, was compared for each jump type. Intra-rater reliability was determined by replicating data analysis of MyJump recordings on two occasions separated by seven days. CMJ and DJ heights derived from MyJump showed excellent agreement with the force plate (ICC values range from 0.991 for CMJ to 0.993) However mean DJ height from the force plate was significantly higher than MyJump (mean difference: 0.87cm, 95% CI: 0.69-1.04cm). Intra-rater reliability of MyJump for both CMJ and DJ was almost perfect (ICC values range from 0.997 for CMJ to 0.998 for DJ); however, mean CMJ and DJ jump height for Day 1 was significantly higher than Day 2 (CMJ: 0.43cm, 95% CI: 0.23-0.62cm); (DJ: 0.38cm, 95% CI: 0.23-0.53cm). The present study finds MyJump to be a valid and highly reliable tool for researchers, coaches, athletes and clinicians; however, systematic bias should be considered when comparing MyJump outputs to other testing devices. Copyright © 2016 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Test-retest reliability of jump execution variables using mechanography: A comparison of jump protocols

USDA-ARS?s Scientific Manuscript database

Mechanography during the vertical jump test allows for evaluation of force-time variables reflecting jump execution, which may enhance screening for functional deficits that reduce physical performance and determining mechanistic causes underlying performance changes. However, utility of jump mechan...

Psychophysiological response in parachute jumps, the effect of experience and type of jump.

PubMed

Clemente-Suárez, Vicente Javier; Robles-Pérez, José Juan; Fernández-Lucas, Jesús

2017-10-01

We aimed to analyse the effect of experience and type of parachute jump on the psychophysiological responses of jumpers. We analysed blood oxygen saturation, heart rate, blood glucose, lactate and creatinkinase, leg strength, isometric hand strength, cortical arousal, specific fine motor skills, self-confidence and cognition, and somatic and state anxiety, before and after four different parachute jumps: a sport parachute jump, a manual tactical parachute jump, tandem pilots, and tandem passengers. Independently of the parachute jump, the psychophysiological responses of experienced paratroopers were not affected by the jumps, except for an increase in anaerobic metabolism. Novice parachute jumpers presented a higher psychophysiological stress response than the experienced jumpers, together with a large anticipatory anxiety response before the jump; however, this decreased after the jump, although the high physiological activation was maintained. This information could be used by civil and military paratroopers' instructors to improve their training programmes. Copyright © 2017 Elsevier Inc. All rights reserved.

The reliability of vertical jump tests between the Vertec and My Jump phone application.

PubMed

Yingling, Vanessa R; Castro, Dimitri A; Duong, Justin T; Malpartida, Fiorella J; Usher, Justin R; O, Jenny

2018-01-01

The vertical jump is used to estimate sports performance capabilities and physical fitness in children, elderly, non-athletic and injured individuals. Different jump techniques and measurement tools are available to assess vertical jump height and peak power; however, their use is limited by access to laboratory settings, excessive cost and/or time constraints thus making these tools oftentimes unsuitable for field assessment. A popular field test uses the Vertec and the Sargent vertical jump with countermovement; however, new low cost, easy to use tools are becoming available, including the My Jump iOS mobile application (app). The purpose of this study was to assess the reliability of the My Jump relative to values obtained by the Vertec for the Sargent stand and reach vertical jump (VJ) test. One hundred and thirty-five healthy participants aged 18-39 years (94 males, 41 females) completed three maximal Sargent VJ with countermovement that were simultaneously measured using the Vertec and the My Jump . Jump heights were quantified for each jump and peak power was calculated using the Sayers equation. Four separate ICC estimates and their 95% confidence intervals were used to assess reliability. Two analyses (with jump height and calculated peak power as the dependent variables, respectively) were based on a single rater, consistency, two-way mixed-effects model, while two others (with jump height and calculated peak power as the dependent variables, respectively) were based on a single rater, absolute agreement, two-way mixed-effects model. Moderate to excellent reliability relative to the degree of consistency between the Vertec and My Jump values was found for jump height (ICC = 0.813; 95% CI [0.747-0.863]) and calculated peak power (ICC = 0.926; 95% CI [0.897-0.947]). However, poor to good reliability relative to absolute agreement for VJ height (ICC = 0.665; 95% CI [0.050-0.859]) and poor to excellent reliability relative to absolute agreement for peak power (ICC = 0.851; 95% CI [0.272-0.946]) between the Vertec and My Jump values were found; Vertec VJ height, and thus, Vertec calculated peak power values, were significantly higher than those calculated from My Jump values ( p < 0.0001). The My Jump app may provide a reliable measure of vertical jump height and calculated peak power in multiple field and laboratory settings without the need of costly equipment such as force plates or Vertec. The reliability relative to degree of consistency between the Vertec and My Jump app was moderate to excellent. However, the reliability relative to absolute agreement between Vertec and My Jump values contained significant variation (based on CI values), thus, it is recommended that either the My Jump or the Vertec be used to assess VJ height in repeated measures within subjects' designs; these measurement tools should not be considered interchangeable within subjects or in group measurement designs.

The reliability of vertical jump tests between the Vertec and My Jump phone application

PubMed Central

Castro, Dimitri A.; Duong, Justin T.; Malpartida, Fiorella J.; Usher, Justin R.; O, Jenny

2018-01-01

Background The vertical jump is used to estimate sports performance capabilities and physical fitness in children, elderly, non-athletic and injured individuals. Different jump techniques and measurement tools are available to assess vertical jump height and peak power; however, their use is limited by access to laboratory settings, excessive cost and/or time constraints thus making these tools oftentimes unsuitable for field assessment. A popular field test uses the Vertec and the Sargent vertical jump with countermovement; however, new low cost, easy to use tools are becoming available, including the My Jump iOS mobile application (app). The purpose of this study was to assess the reliability of the My Jump relative to values obtained by the Vertec for the Sargent stand and reach vertical jump (VJ) test. Methods One hundred and thirty-five healthy participants aged 18–39 years (94 males, 41 females) completed three maximal Sargent VJ with countermovement that were simultaneously measured using the Vertec and the My Jump. Jump heights were quantified for each jump and peak power was calculated using the Sayers equation. Four separate ICC estimates and their 95% confidence intervals were used to assess reliability. Two analyses (with jump height and calculated peak power as the dependent variables, respectively) were based on a single rater, consistency, two-way mixed-effects model, while two others (with jump height and calculated peak power as the dependent variables, respectively) were based on a single rater, absolute agreement, two-way mixed-effects model. Results Moderate to excellent reliability relative to the degree of consistency between the Vertec and My Jump values was found for jump height (ICC = 0.813; 95% CI [0.747–0.863]) and calculated peak power (ICC = 0.926; 95% CI [0.897–0.947]). However, poor to good reliability relative to absolute agreement for VJ height (ICC = 0.665; 95% CI [0.050–0.859]) and poor to excellent reliability relative to absolute agreement for peak power (ICC = 0.851; 95% CI [0.272–0.946]) between the Vertec and My Jump values were found; Vertec VJ height, and thus, Vertec calculated peak power values, were significantly higher than those calculated from My Jump values (p < 0.0001). Discussion The My Jump app may provide a reliable measure of vertical jump height and calculated peak power in multiple field and laboratory settings without the need of costly equipment such as force plates or Vertec. The reliability relative to degree of consistency between the Vertec and My Jump app was moderate to excellent. However, the reliability relative to absolute agreement between Vertec and My Jump values contained significant variation (based on CI values), thus, it is recommended that either the My Jump or the Vertec be used to assess VJ height in repeated measures within subjects’ designs; these measurement tools should not be considered interchangeable within subjects or in group measurement designs. PMID:29692955

Comparison of the Hang High-Pull and Loaded Jump Squat for the Development of Vertical Jump and Isometric Force-Time Characteristics.

PubMed

Oranchuk, Dustin J; Robinson, Tracey L; Switaj, Zachary J; Drinkwater, Eric J

2017-04-15

Weightlifting movements have high skill demands and require expert coaching. Loaded jumps have a comparably lower skill demand, but may be similarly effective for improving explosive performance. The purpose of this study was to compare vertical jump performance, isometric force, and rate of force development (RFD) following a ten-week intervention employing the hang high-pull (hang-pull) or trap-bar jump squat (jump-squat). Eighteen NCAA Division II swimmers (8 males, 10 females) with at least one year of resistance training experience volunteered to participate. Testing included the squat jump (SJ), countermovement jump (CMJ) and the isometric mid-thigh pull (IMTP). Vertical ground reaction forces were analyzed to obtain jump height and relative peak power. Relative peak force, peak RFD and relative force at five time bands were obtained from the IMTP. Subjects were randomly assigned to either a hang-pull (n = 9) or jump-squat (n = 9) training group and completed a ten-week, volume-equated, periodized training program. While there was a significant main effect of training for both groups, no statistically significant between-group differences were found (p ≥ 0.17) for any of the dependent variables. However, medium effect sizes in favor of the jump-squat training group were seen in SJ height (d = 0.56) and SJ peak power (d = 0.69). Loaded jumps seem equally effective as weightlifting derivatives for improving lower-body power in experienced athletes. Since loaded jumps require less skill and less coaching expertise than weightlifting, loaded jumps should be considered where coaching complex movements is difficult.

Keeping Your Eye on the Rail: Gaze Behaviour of Horse Riders Approaching a Jump

PubMed Central

Hall, Carol; Varley, Ian; Kay, Rachel; Crundall, David

2014-01-01

The gaze behaviour of riders during their approach to a jump was investigated using a mobile eye tracking device (ASL Mobile Eye). The timing, frequency and duration of fixations on the jump and the percentage of time when their point of gaze (POG) was located elsewhere were assessed. Fixations were identified when the POG remained on the jump for 100 ms or longer. The jumping skill of experienced but non-elite riders (n = 10) was assessed by means of a questionnaire. Their gaze behaviour was recorded as they completed a course of three identical jumps five times. The speed and timing of the approach was calculated. Gaze behaviour throughout the overall approach and during the last five strides before take-off was assessed following frame-by-frame analyses. Differences in relation to both round and jump number were found. Significantly longer was spent fixated on the jump during round 2, both during the overall approach and during the last five strides (p<0.05). Jump 1 was fixated on significantly earlier and more frequently than jump 2 or 3 (p<0.05). Significantly more errors were made with jump 3 than with jump 1 (p = 0.01) but there was no difference in errors made between rounds. Although no significant correlations between gaze behaviour and skill scores were found, the riders who scored higher for jumping skill tended to fixate on the jump earlier (p = 0.07), when the horse was further from the jump (p = 0.09) and their first fixation on the jump was of a longer duration (p = 0.06). Trials with elite riders are now needed to further identify sport-specific visual skills and their relationship with performance. Visual training should be included in preparation for equestrian sports participation, the positive impact of which has been clearly demonstrated in other sports. PMID:24846055

Validity of two alternative systems for measuring vertical jump height.

PubMed

Leard, John S; Cirillo, Melissa A; Katsnelson, Eugene; Kimiatek, Deena A; Miller, Tim W; Trebincevic, Kenan; Garbalosa, Juan C

2007-11-01

Vertical jump height is frequently used by coaches, health care professionals, and strength and conditioning professionals to objectively measure function. The purpose of this study is to determine the concurrent validity of the jump and reach method (Vertec) and the contact mat method (Just Jump) in assessing vertical jump height when compared with the criterion reference 3-camera motion analysis system. Thirty-nine college students, 25 females and 14 males between the ages of 18 and 25 (mean age 20.65 years), were instructed to perform the countermovement jump. Reflective markers were placed at the base of the individual's sacrum for the 3-camera motion analysis system to measure vertical jump height. The subject was then instructed to stand on the Just Jump mat beneath the Vertec and perform the jump. Measurements were recorded from each of the 3 systems simultaneously for each jump. The Pearson r statistic between the video and the jump and reach (Vertec) was 0.906. The Pearson r between the video and contact mat (Just Jump) was 0.967. Both correlations were significant at the 0.01 level. Analysis of variance showed a significant difference among the 3 means F(2,235) = 5.51, p < 0.05. The post hoc analysis showed a significant difference between the criterion reference (M = 0.4369 m) and the Vertec (M = 0.3937 m, p = 0.005) but not between the criterion reference and the Just Jump system (M = 0.4420 m, p = 0.972). The Just Jump method of measuring vertical jump height is a valid measure when compared with the 3-camera system. The Vertec was found to have a high correlation with the criterion reference, but the mean differed significantly. This study indicates that a higher degree of confidence is warranted when comparing Just Jump results with a 3-camera system study.

Nature of the Diffuse Source and Its Central Point-like Source in SNR 0509–67.5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Litke, Katrina C.; Chu, You-Hua; Holmes, Abigail

We examine a diffuse emission region near the center of SNR 0509−67.5 to determine its nature. Within this diffuse region we observe a point-like source that is bright in the near-IR, but is not visible in the B and V bands. We consider an emission line observed at 6766 Å and the possibilities that it is Ly α , H α , and [O ii] λ 3727. We examine the spectral energy distribution (SED) of the source, comprised of Hubble Space Telescope B , V , I , J , and H bands in addition to Spitzer /IRAC 3.6, 4.5,more » 5.8, and 8 μ m bands. The peak of the SED is consistent with a background galaxy at z ≈ 0.8 ± 0.2 and a possible Balmer jump places the galaxy at z ≈ 0.9 ± 0.3. These SED considerations support the emission line’s identification as [O ii] λ 3727. We conclude that the diffuse source in SNR 0509−67.5 is a background galaxy at z ≈ 0.82. Furthermore, we identify the point-like source superposed near the center of the galaxy as its central bulge. Finally, we find no evidence for a surviving companion star, indicating a double-degenerate origin for SNR 0509−67.5.« less

Numerical study of laminar, standing hydraulic jumps in a planar geometry.

PubMed

Dasgupta, Ratul; Tomar, Gaurav; Govindarajan, Rama

2015-05-01

We solve the two-dimensional, planar Navier-Stokes equations to simulate a laminar, standing hydraulic jump using a Volume-of-Fluid method. The geometry downstream of the jump has been designed to be similar to experimental conditions by including a pit at the edge of the platform over which liquid film flows. We obtain jumps with and without separation. Increasing the inlet Froude number pushes the jump downstream and makes the slope of the jump weaker, consistent with experimental observations of circular jumps, and decreasing the Reynolds number brings the jump upstream while making it steeper. We study the effect of the length of the domain and that of a downstream obstacle on the structure and location of the jump. The transient flow which leads to a final steady jump is described for the first time to our knowledge. In the moderate Reynolds number regime, we obtain steady undular jumps with a separated bubble underneath the first few undulations. Interestingly, surface tension leads to shortening of wavelength of these undulations. We show that the undulations can be explained using the inviscid theory of Benjamin and Lighthill (Proc. R. Soc. London, Ser. A, 1954). We hope this new finding will motivate experimental verification.

Dynamics and stability of directional jumps in the desert locust.

PubMed

Gvirsman, Omer; Kosa, Gabor; Ayali, Amir

2016-01-01

Locusts are known for their ability to jump large distances to avoid predation. The jump also serves to launch the adult locust into the air in order to initiate flight. Various aspects of this important behavior have been studied extensively, from muscle physiology and biomechanics, to the energy storage systems involved in powering the jump, and more. Less well understood are the mechanisms participating in control of the jump trajectory. Here we utilise video monitoring and careful analysis of experimental directional jumps by adult desert locusts, together with dynamic computer simulation, in order to understand how the locusts control the direction and elevation of the jump, the residual angular velocities resulting from the jump and the timing of flapping-flight initiation. Our study confirms and expands early findings regarding the instrumental role of the initial body position and orientation. Both real-jump video analysis and simulations based on our expanded dynamical model demonstrate that the initial body coordinates of position (relative to the hind-legs ground-contact points) are dominant in predicting the jumps' azimuth and elevation angles. We also report a strong linear correlation between the jumps' pitch-angular-velocity and flight initiation timing, such that head downwards rotations lead to earlier wing opening. In addition to offering important insights into the bio-mechanical principles of locust jumping and flight initiation, the findings from this study will be used in designing future prototypes of a bio-inspired miniature jumping robot that will be employed in animal behaviour studies and environmental monitoring applications.

Maximum height and minimum time vertical jumping.

PubMed

Domire, Zachary J; Challis, John H

2015-08-20

The performance criterion in maximum vertical jumping has typically been assumed to simply raise the center of mass as high as possible. In many sporting activities minimizing movement time during the jump is likely also critical to successful performance. The purpose of this study was to examine maximum height jumps performed while minimizing jump time. A direct dynamics model was used to examine squat jump performance, with dual performance criteria: maximize jump height and minimize jump time. The muscle model had activation dynamics, force-length, force-velocity properties, and a series of elastic component representing the tendon. The simulations were run in two modes. In Mode 1 the model was placed in a fixed initial position. In Mode 2 the simulation model selected the initial squat configuration as well as the sequence of muscle activations. The inclusion of time as a factor in Mode 1 simulations resulted in a small decrease in jump height and moderate time savings. The improvement in time was mostly accomplished by taking off from a less extended position. In Mode 2 simulations, more substantial time savings could be achieved by beginning the jump in a more upright posture. However, when time was weighted more heavily in these simulations, there was a more substantial reduction in jump height. Future work is needed to examine the implications for countermovement jumping and to examine the possibility of minimizing movement time as part of the control scheme even when the task is to jump maximally. Copyright © 2015 Elsevier Ltd. All rights reserved.

Evaluation of different jumping tests in defining position-specific and performance-level differences in high level basketball players

PubMed Central

Pehar, Miran; Sekulic, Damir; Sisic, Nedim; Spasic, Miodrag; Uljevic, Ognjen; Krolo, Ante; Sattler, Tine

2017-01-01

The importance of jumping ability in basketball is well known, but there is an evident lack of studies that have examined different jumping testing protocols in basketball players at advanced levels. The aim of this study was to assess the applicability of different tests of jumping capacity in identifying differences between (i) playing position and (ii) competitive levels of professional players. Participants were 110 male professional basketball players (height: 194.92±8.09 cm; body mass: 89.33±10.91 kg; 21.58±3.92 years of age; Guards, 49; Forwards, 22; Centres, 39) who competed in the first (n = 58) and second division (n = 52). The variables included anthropometrics and jumping test performance. Jumping performances were evaluated by the standing broad jump (SBJ), countermovement jump (CMJ), reactive strength index (RSI), repeated reactive strength ability (RRSA) and four running vertical jumps: maximal jump with (i) take-off from the dominant leg and (ii) non-dominant leg, lay-up shot jump with take-off from the (iii) dominant leg and (iv) non-dominant leg. First-division players were taller (ES: 0.76, 95%CI: 0.35-1.16, moderate differences), heavier (0.69, 0.29-1.10), had higher maximal reach height (0.67, 0.26-1.07, moderate differences), and had lower body fat % (-0.87, -1.27-0.45, moderate differences) than second-division players. The playing positions differed significantly in three of four running jump achievements, RSI and RRSA, with Centres being least successful. The first-division players were superior to second-division players in SBJ (0.63, 0.23-1.03; 0.87, 0.26-1.43; 0.76, 0.11-1.63, all moderate differences, for total sample, Guards, and Forwards, respectively). Running vertical jumps and repeated jumping capacity can be used as valid measures of position-specific jumping ability in basketball. The differences between playing levels in vertical jumping achievement can be observed by assessing vertical jump scores together with differences in anthropometric indices between levels. PMID:29158620

The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

PubMed Central

Snelling, Edward P.; Becker, Christie L.; Seymour, Roger S.

2013-01-01

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M 0.17±0.08 (95% CI), jump take-off angle (A; degrees) scales as A = 52.5M 0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M 1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q10 of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L f+t; mm) of the femur and tibia of the hind leg, L f+t = 34.9M 0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur's cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur's cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight. PMID:23967304

A comparison of men's and women's strength to body mass ratio and varus/valgus knee angle during jump landings.

PubMed

Haines, Tracie L; McBride, Jeffrey M; Triplett, N Travis; Skinner, Jared W; Fairbrother, Kimberly R; Kirby, Tyler J

2011-10-01

The purpose of this investigation was to compare valgus/varus knee angles during various jumps and lower body strength between males and females relative to body mass. Seventeen recreationally active females (age: 21.94 ± 2.59 years; height: 1.67 ± 0.05 m; mass: 64.42 ± 8.39 kg; percent body fat: 26.89 ± 6.26%; squat one-repetition maximum: 66.18 ± 19.47 kg; squat to body mass ratio: 1.03 ± 0.28) and 13 recreationally active males (age: 21.69 ± 1.65 years; height: 1.77 ± 0.07 m; mass: 72.39 ± 9.23 kg; percent body fat: 13.15 ± 5.18%; squat one-repetition maximum: 115.77 ± 30.40 kg; squat to body mass ratio: 1.59 ± 0.31) performed a one-repetition maximum in the squat and three of each of the following jumps: countermovement jump, 30 cm drop jump, 45 cm drop jump, and 60 cm drop jump. Knee angles were analysed using videography and body composition was analysed by dual-energy X-ray absorptiometry to allow for squat to body mass ratio and squat to fat free mass ratio to be calculated. Significant differences (P ≤ 0.05) were found between male and female one-repetition maximum, male and female squat to body mass ratio, and male and female squat to fat free mass ratio. Significant differences were found between male and female varus/valgus knee positions during maximum flexion of the right and left leg in the countermovement jump, drop jump from 30 cm, drop jump from 45 cm, and drop jump from 60 cm. Correlations between varus/valgus knee angles and squat to body mass ratio for all jumps displayed moderate, non-significant relationships (countermovement jump: r = 0.445; drop jump from 30 cm: r = 0.448; drop jump from 45 cm: r = 0.449; drop jump from 60 cm: r = 0.439). In conclusion, males and females have significantly different lower body strength and varus/valgus knee position when landing from jumps.

Diffusion of benzene confined in the oriented nanochannels of chrysotile asbestos fibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mamontov, E.; Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742-2115; Kumzerov, Yu.A.

We used quasielastic neutron scattering to study the dynamics of benzene that completely fills the nanochannels of chrysotile asbestos fibers with a characteristic diameter of about 5 nm. The macroscopical alignment of the nanochannels in fibers provided an interesting opportunity to study anisotropy of the dynamics of confined benzene by means of collecting the data with the scattering vector either parallel or perpendicular to the fibers axes. The translational diffusive motion of benzene molecules was found to be isotropic. While bulk benzene freezes at 278.5 K, we observed the translational dynamics of the supercooled confined benzene on the time scalemore » of hundreds of picoseconds even below 200 K, until at about 160 K its dynamics becomes too slow for the {mu}eV resolution of the neutron backscattering spectrometer. The residence time between jumps for the benzene molecules measured in the temperature range of 260 K to 320 K demonstrated low activation energy of 2.8 kJ/mol.« less

Enhancement and degradation of the R2* relaxation rate resulting from the encapsulation of magnetic particles with hydrophilic coatings.

PubMed

de Haan, Hendrick W; Paquet, Chantal

2011-12-01

The effects of including a hydrophilic coating around the particles are studied across a wide range of particle sizes by performing Monte Carlo simulations of protons diffusing through a system of magnetic particles. A physically realistic methodology of implementing the coating by cross boundary jump scaling and transition probabilities at the coating surface is developed. Using this formulation, the coating has three distinct impacts on the relaxation rate: an enhancement at small particle sizes, a degradation at intermediate particle sizes, and no effect at large particles sizes. These varied effects are reconciled with the underlying dephasing mechanisms by using the concept of a full dephasing zone to present a physical picture of the dephasing process with and without the coating for all sizes. The enhancement at small particle sizes is studied systemically to demonstrate the existence of an optimal ratio of diffusion coefficients inside/outside the coating to achieve maximal increase in the relaxation rate. Copyright © 2011 Wiley Periodicals, Inc.

The fractional diffusion limit of a kinetic model with biochemical pathway

NASA Astrophysics Data System (ADS)

Perthame, Benoît; Sun, Weiran; Tang, Min

2018-06-01

Kinetic-transport equations that take into account the intracellular pathways are now considered as the correct description of bacterial chemotaxis by run and tumble. Recent mathematical studies have shown their interest and their relations to more standard models. Macroscopic equations of Keller-Segel type have been derived using parabolic scaling. Due to the randomness of receptor methylation or intracellular chemical reactions, noise occurs in the signaling pathways and affects the tumbling rate. Then comes the question to understand the role of an internal noise on the behavior of the full population. In this paper we consider a kinetic model for chemotaxis which includes biochemical pathway with noises. We show that under proper scaling and conditions on the tumbling frequency as well as the form of noise, fractional diffusion can arise in the macroscopic limits of the kinetic equation. This gives a new mathematical theory about how long jumps can be due to the internal noise of the bacteria.

Geometrically nonlinear continuum thermomechanics with surface energies coupled to diffusion

NASA Astrophysics Data System (ADS)

McBride, A. T.; Javili, A.; Steinmann, P.; Bargmann, S.

2011-10-01

Surfaces can have a significant influence on the overall response of a continuum body but are often neglected or accounted for in an ad hoc manner. This work is concerned with a nonlinear continuum thermomechanics formulation which accounts for surface structures and includes the effects of diffusion and viscoelasticity. The formulation is presented within a thermodynamically consistent framework and elucidates the nature of the coupling between the various fields, and the surface and the bulk. Conservation principles are used to determine the form of the constitutive relations and the evolution equations. Restrictions on the jump in the temperature and the chemical potential between the surface and the bulk are not a priori assumptions, rather they arise from the reduced dissipation inequality on the surface and are shown to be satisfiable without imposing the standard assumptions of thermal and chemical slavery. The nature of the constitutive relations is made clear via an example wherein the form of the Helmholtz energy is explicitly given.

Numerical simulation of the hydrodynamical combustion to strange quark matter

NASA Astrophysics Data System (ADS)

Niebergal, Brian; Ouyed, Rachid; Jaikumar, Prashanth

2010-12-01

We present results from a numerical solution to the burning of neutron matter inside a cold neutron star into stable u,d,s quark matter. Our method solves hydrodynamical flow equations in one dimension with neutrino emission from weak equilibrating reactions, and strange quark diffusion across the burning front. We also include entropy change from heat released in forming the stable quark phase. Our numerical results suggest burning front laminar speeds of 0.002-0.04 times the speed of light, much faster than previous estimates derived using only a reactive-diffusive description. Analytic solutions to hydrodynamical jump conditions with a temperature-dependent equation of state agree very well with our numerical findings for fluid velocities. The most important effect of neutrino cooling is that the conversion front stalls at lower density (below ≈2 times saturation density). In a two-dimensional setting, such rapid speeds and neutrino cooling may allow for a flame wrinkle instability to develop, possibly leading to detonation.

Strong diffusion formulation of Markov chain ensembles and its optimal weaker reductions

NASA Astrophysics Data System (ADS)

Güler, Marifi

2017-10-01

Two self-contained diffusion formulations, in the form of coupled stochastic differential equations, are developed for the temporal evolution of state densities over an ensemble of Markov chains evolving independently under a common transition rate matrix. Our first formulation derives from Kurtz's strong approximation theorem of density-dependent Markov jump processes [Stoch. Process. Their Appl. 6, 223 (1978), 10.1016/0304-4149(78)90020-0] and, therefore, strongly converges with an error bound of the order of lnN /N for ensemble size N . The second formulation eliminates some fluctuation variables, and correspondingly some noise terms, within the governing equations of the strong formulation, with the objective of achieving a simpler analytic formulation and a faster computation algorithm when the transition rates are constant or slowly varying. There, the reduction of the structural complexity is optimal in the sense that the elimination of any given set of variables takes place with the lowest attainable increase in the error bound. The resultant formulations are supported by numerical simulations.

A theory of growing crystalline nanorods - Mode I

NASA Astrophysics Data System (ADS)

Du, Feng; Huang, Hanchen

2018-08-01

Nanorods grow in two possible modes during physical vapor deposition (PVD). In mode I, monolayer surface steps dictate the diameter of nanorods. In mode II, multiple-layer surface steps dictate the diameter, which is the smallest possible under physical vapor deposition [5,10]. This paper reports closed-form theories of terrace lengths and nanorod diameter during the growth in mode I, as a function of deposition conditions. The accompanying lattice kinetic Monte Carlo simulations verify these theories. This study reveals that (1) quasi-steady growth exists for each set of nanorod growth conditions, and (2) the characteristic length scales, including terrace lengths and nanorod diameter at the quasi-steady state, depend on the deposition conditions - deposition rate F, substrate temperature T, and incidence angle θ - only as a function of l2D/tan θ, with l2 D = 2(v2 D/Fcosθ) 1/3 as a diffusion-limited length scale and v2D as the atomic diffusion jump rate over monolayer surface steps.

The Lower Extremity Biomechanics of Single- and Double-Leg Stop-Jump Tasks

PubMed Central

2011-01-01

The anterior cruciate ligament (ACL) injury is a common occurrence in sports requiring stop-jump tasks. Single- and double-leg stop-jump techniques are frequently executed in sports. The higher risk of ACL injury in single-leg drop landing task compared to a double-leg drop landing task has been identified. However the injury bias between single- and double-leg landing techniques has not been investigated for stop-jump tasks. The purpose of this study was to determine the differences between single- and double-leg stop-jump tasks in knee kinetics that were influenced by the lower extremity kinematics during the landing phase. Ground reaction force, lower extremity kinematics, and knee kinetics data during the landing phase were obtained from 10 subjects performing single- and double-leg stop-jump tasks, using motion-capture system and force palates. Greater peak posterior and vertical ground reaction forces, and peak proximal tibia anterior and lateral shear forces (p < 0.05) during landing phase were observed of single-leg stop-jump. Single-leg stop-jump exhibited smaller hip and knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground (p < 0.05). We found smaller peak hip and knee flexion angles (p < 0.05) during the landing phase of single-leg stop-jump. These results indicate that single-leg landing may have higher ACL injury risk than double-leg landing in stop-jump tasks that may be influenced by the lower extremity kinematics during the landing phase. Key points Non-contact ACL injuries are more likely to occur during the single-leg stop-jump task than during the double-leg stop-jump task. Single-leg stop-jump exhibited greater peak proximal tibia anterior and lateral shear forces, and peak posterior and vertical ground reaction forces during the landing phase than the double-leg stop-jump task. Single-leg stop-jump exhibited smaller hip flexion angle, knee flexion angle, and knee flexion angular velocity at initial foot contact with the ground. Single-leg stop-jump exhibited greater peak knee extension and valgus moment during the landing phase than the double-leg stop-jump task. Single-leg stop-jump extended the hip joint at initial foot contact with the ground. PMID:24149308

Development of morphogen gradient: The role of dimension and discreteness

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teimouri, Hamid; Kolomeisky, Anatoly B.

2014-02-28

The fundamental processes of biological development are governed by multiple signaling molecules that create non-uniform concentration profiles known as morphogen gradients. It is widely believed that the establishment of morphogen gradients is a result of complex processes that involve diffusion and degradation of locally produced signaling molecules. We developed a multi-dimensional discrete-state stochastic approach for investigating the corresponding reaction-diffusion models. It provided a full analytical description for stationary profiles and for important dynamic properties such as local accumulation times, variances, and mean first-passage times. The role of discreteness in developing of morphogen gradients is analyzed by comparing with available continuummore » descriptions. It is found that the continuum models prediction about multiple time scales near the source region in two-dimensional and three-dimensional systems is not supported in our analysis. Using ideas that view the degradation process as an effective potential, the effect of dimensionality on establishment of morphogen gradients is also discussed. In addition, we investigated how these reaction-diffusion processes are modified with changing the size of the source region.« less

Vectorization of transport and diffusion computations on the CDC Cyber 205

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abu-Shumays, I.K.

1986-01-01

The development and testing of alternative numerical methods and computational algorithms specifically designed for the vectorization of transport and diffusion computations on a Control Data Corporation (CDC) Cyber 205 vector computer are described. Two solution methods for the discrete ordinates approximation to the transport equation are summarized and compared. Factors of 4 to 7 reduction in run times for certain large transport problems were achieved on a Cyber 205 as compared with run times on a CDC-7600. The solution of tridiagonal systems of linear equations, central to several efficient numerical methods for multidimensional diffusion computations and essential for fluid flowmore » and other physics and engineering problems, is also dealt with. Among the methods tested, a combined odd-even cyclic reduction and modified Cholesky factorization algorithm for solving linear symmetric positive definite tridiagonal systems is found to be the most effective for these systems on a Cyber 205. For large tridiagonal systems, computation with this algorithm is an order of magnitude faster on a Cyber 205 than computation with the best algorithm for tridiagonal systems on a CDC-7600.« less

Biomechanical analysis of the jump shot in basketball.

PubMed

Struzik, Artur; Pietraszewski, Bogdan; Zawadzki, Jerzy

2014-09-29

Basketball players usually score points during the game using the jump shot. For this reason, the jump shot is considered to be the most important element of technique in basketball and requires a high level of performance. The aim of this study was to compare the biomechanical characteristics of the lower limbs during a jump shot without the ball and a countermovement jump without an arm swing. The differences between variables provide information about the potential that an athlete can utilise during a game when performing a jump shot. The study was conducted among 20 second-league basketball players by means of a Kistler force plate and the BTS SMART system for motion analysis. The variables measured included the take-off time, mean power, peak power, relative mean power, jump height, maximum landing force and calculated impact ratio. Surprisingly, more advantageous variables were found for the jump shot. This finding suggests a very high performance level in the jump shot in the studied group and a maximum utilisation of their motor abilities. Both types of jumps were characterised by high mean and peak power values and average heights. The high forces at landing, which result in considerable impact ratios, may have prompted the studied group to land softly. Use of the countermovement jump without an arm swing is recommended to assess and predict the progression of player's jumping ability.

Measurements of K shell absorption jump factors and jump ratios using EDXRF technique

NASA Astrophysics Data System (ADS)

Kacal, Mustafa Recep; Han, İbrahim; Akman, Ferdi

2015-04-01

In the present work, the K-shell absorption jump factors and jump ratios for 30 elements between Ti ( Z = 22) and Er ( Z = 68) were measured by energy dispersive X-ray fluorescence (EDXRF) technique. The jump factors and jump ratios for these elements were determined by measuring the K shell fluorescence parameters such as the Kα X-ray production cross-sections, K shell fluorescence yields, Kβ-to- Kα X-rays intensity ratios, total atomic absorption cross sections and mass attenuation coefficients. The measurements were performed using an Am-241 radioactive point source and a Si (Li) detector in direct excitation and transmission experimental geometry. The results for jump factors and jump ratios were compared with theoretically calculated and the ones available in the literature.

Strength Determinants of Jump Height in the Jump Throw Movement in Women Handball Players.

PubMed

McGhie, David; Østerås, Sindre; Ettema, Gertjan; Paulsen, Gøran; Sandbakk, Øyvind

2018-06-08

McGhie, D, Østerås, S, Ettema, G, Paulsen, G, and Sandbakk, Ø. Strength determinants of jump height in the jump throw movement in women handball players. J Strength Cond Res XX(X): 000-000, 2018-The purpose of the study was to improve the understanding of the strength demands of a handball-specific jump through examining the associations between jump height in a jump throw jump (JTJ) and measures of lower-body maximum strength and impulse in handball players. For comparison, whether the associations between jump height and strength differed between the JTJ and the customarily used countermovement jump (CMJ) was also examined. Twenty women handball players from a Norwegian top division club participated in the study. Jump height was measured in the JTJ and in unilateral and bilateral CMJ. Lower-body strength (maximum isometric force, one-repetition maximum [1RM], impulse at ∼60% and ∼35% 1RM) was measured in seated leg press. The associations between jump height and strength were assessed with correlation analyses and t-tests of dependent r's were performed to determine if correlations differed between jump tests. Only impulse at ∼35% 1RM correlated significantly with JTJ height (p < 0.05), whereas all strength measures correlated significantly with CMJ heights (p < 0.001). The associations between jump height and strength were significantly weaker in the JTJ than in both CMJ tests for all strength measures (p = 0.001-0.044) except one. Maximum strength and impulse at ∼60% 1RM did not seem to sufficiently capture the capabilities associated with JTJ height, highlighting the importance of employing tests targeting performance-relevant neuromuscular characteristics when assessing jump-related strength in handball players. Further, CMJ height seemed to represent a wider range of strength capabilities and care should be taken when using it as a proxy for handball-specific movements.

Influence of sports flooring and shoes on impact forces and performance during jump tasks.

PubMed

Malisoux, Laurent; Gette, Paul; Urhausen, Axel; Bomfim, Joao; Theisen, Daniel

2017-01-01

We aim to determine the influence of sports floorings and sports shoes on impact mechanics and performance during standardised jump tasks. Twenty-one male volunteers performed ankle jumps (four consecutive maximal bounds with very dynamic ankle movements) and multi-jumps (two consecutive maximal counter-movement jumps) on force plates using minimalist and cushioned shoes under 5 sports flooring (SF) conditions. The shock absorption properties of the SF, defined as the proportion of peak impact force absorbed by the tested flooring when compared with a concrete hard surface, were: SF0 = 0% (no flooring), SF1 = 19%, SF2 = 26%, SF3 = 37% and SF4 = 45%. Shoe and flooring effects were compared using 2x5 repeated-measures ANOVA with post-hoc Bonferroni-corrected comparisons. A significant interaction between SF and shoe conditions was found for VILR only (p = 0.003). In minimalist shoes, SF influenced Vertical Instantaneous Loading Rate (VILR) during ankle jumps (p = 0.006) and multi-jumps (p<0.001), in accordance with shock absorption properties. However, in cushioned shoes, SF influenced VILR during ankle jumps only (p<0.001). Contact Time was the only additional variable affected by SF, but only during multi-jumps in minimalist shoes (p = 0.037). Cushioned shoes induced lower VILR (p<0.001) and lower Contact Time (p≤0.002) during ankle jumps and multi-jumps compared to minimalist shoes. During ankle jumps, cushioned shoes induced greater Peak Vertical Ground Reaction Force (PVGRF, p = 0.002), greater Vertical Average Loading Rate (p<0.001), and lower eccentric (p = 0.008) and concentric (p = 0.004) work. During multi-jumps, PVGRF was lower (p<0.001) and jump height was higher (p<0.001) in cushioned compared to minimalist shoes. In conclusion, cushioning influenced impact forces during standardised jump tasks, whether it was provided by the shoes or the sports flooring. VILR is the variable that was the most affected.

Influence of sports flooring and shoes on impact forces and performance during jump tasks

PubMed Central

Urhausen, Axel; Bomfim, Joao

2017-01-01

We aim to determine the influence of sports floorings and sports shoes on impact mechanics and performance during standardised jump tasks. Twenty-one male volunteers performed ankle jumps (four consecutive maximal bounds with very dynamic ankle movements) and multi-jumps (two consecutive maximal counter-movement jumps) on force plates using minimalist and cushioned shoes under 5 sports flooring (SF) conditions. The shock absorption properties of the SF, defined as the proportion of peak impact force absorbed by the tested flooring when compared with a concrete hard surface, were: SF0 = 0% (no flooring), SF1 = 19%, SF2 = 26%, SF3 = 37% and SF4 = 45%. Shoe and flooring effects were compared using 2x5 repeated-measures ANOVA with post-hoc Bonferroni-corrected comparisons. A significant interaction between SF and shoe conditions was found for VILR only (p = 0.003). In minimalist shoes, SF influenced Vertical Instantaneous Loading Rate (VILR) during ankle jumps (p = 0.006) and multi-jumps (p<0.001), in accordance with shock absorption properties. However, in cushioned shoes, SF influenced VILR during ankle jumps only (p<0.001). Contact Time was the only additional variable affected by SF, but only during multi-jumps in minimalist shoes (p = 0.037). Cushioned shoes induced lower VILR (p<0.001) and lower Contact Time (p≤0.002) during ankle jumps and multi-jumps compared to minimalist shoes. During ankle jumps, cushioned shoes induced greater Peak Vertical Ground Reaction Force (PVGRF, p = 0.002), greater Vertical Average Loading Rate (p<0.001), and lower eccentric (p = 0.008) and concentric (p = 0.004) work. During multi-jumps, PVGRF was lower (p<0.001) and jump height was higher (p<0.001) in cushioned compared to minimalist shoes. In conclusion, cushioning influenced impact forces during standardised jump tasks, whether it was provided by the shoes or the sports flooring. VILR is the variable that was the most affected. PMID:29020108

Anomalous dimensionality dependence of diffusion in a rugged energy landscape: How pathological is one dimension?

NASA Astrophysics Data System (ADS)

Seki, Kazuhiko; Bagchi, Kaushik; Bagchi, Biman

2016-05-01

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.

Anomalous dimensionality dependence of diffusion in a rugged energy landscape: How pathological is one dimension?

PubMed

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.

Countermovement depth - a variable which clarifies the relationship between the maximum power output and height of a vertical jump.

PubMed

Gajewski, Jan; Michalski, Radosław; Buśko, Krzysztof; Mazur-Różycka, Joanna; Staniak, Zbigniew

2018-01-01

The aim of this study was to identify the determinants of peak power achieved during vertical jumps in order to clarify relationship between the height of jump and the ability to exert maximum power. One hundred young (16.8±1.8 years) sportsmen participated in the study (body height 1.861 ± 0.109 m, body weight 80.3 ± 9.2 kg). Each participant performed three jump tests: countermovement jump (CMJ), akimbo countermovement jump (ACMJ), and spike jump (SPJ). A force plate was used to measure ground reaction force and to determine peak power output. The following explanatory variables were included in the model: jump height, body mass, and the lowering of the centre of mass before launch (countermovement depth). A model was created using multiple regression analysis and allometric scaling. The model was used to calculate the expected power value for each participant, which correlated strongly with real values. The value of the coefficient of determination R2 equalled 0.89, 0.90 and 0.98, respectively, for the CMJ, ACMJ, and SPJ jumps. The countermovement depth proved to be a variable strongly affecting the maximum power of jump. If the countermovement depth remains constant, the relative peak power is a simple function of jump height. The results suggest that the jump height of an individual is an exact indicator of their ability to produce maximum power. The presented model has a potential to be utilized under field condition for estimating the maximum power output of vertical jumps.

The validity and reliability of the my jump 2 app for measuring the reactive strength index and drop jump performance.

PubMed

Haynes, Tom; Bishop, Chris; Antrobus, Mark; Brazier, Jon

2018-03-27

This is the first study to independently assess the concurrent validity and reliability of the My Jump 2 app for measuring drop jump performance. It is also the first to evaluate the app's ability to measure the reactive strength index (RSI). Fourteen male sport science students (age: 29.5 ± 9.9 years) performed three drop jumps from 20 cm and 40 cm (totalling 84 jumps), assessed via a force platform and the My Jump 2 app. Reported metrics included reactive strength index, jump height, ground contact time, and mean power. Measurements from both devices were compared using the intraclass correlation coefficient (ICC), Pearson product moment correlation coefficient (r), Cronbach's alpha (α), coefficient of variation (CV) and BlandAltman plots. Near perfect agreement was seen between devices at 20 cm for RSI (ICC = 0.95) and contact time (ICC = 0.99) and at 40 cm for RSI (ICC = 0.98), jump height (ICC = 0.96) and contact time (ICC = 0.92); with very strong agreement seen at 20 cm for jump height (ICC = 0.80). In comparison with the force plate the app showed good validity for RSI (20 cm: r = 0.94; 40 cm; r = 0.97), jump height (20 cm: r = 0.80; 40 cm; r = 0.96) and contact time (20 cm = 0.96; 40 cm; r = 0.98). The results of the present study show that the My Jump 2 app is a valid and reliable tool for assessing drop jump performance.

Control strategy of maximum vertical jumps: The preferred countermovement depth may not be fully optimized for jump height.

PubMed

Mandic, Radivoj; Knezevic, Olivera M; Mirkov, Dragan M; Jaric, Slobodan

2016-09-01

The aim of the present study was to explore the control strategy of maximum countermovement jumps regarding the preferred countermovement depth preceding the concentric jump phase. Elite basketball players and physically active non-athletes were tested on the jumps performed with and without an arm swing, while the countermovement depth was varied within the interval of almost 30 cm around its preferred value. The results consistently revealed 5.1-11.2 cm smaller countermovement depth than the optimum one, but the same difference was more prominent in non-athletes. In addition, although the same differences revealed a marked effect on the recorded force and power output, they reduced jump height for only 0.1-1.2 cm. Therefore, the studied control strategy may not be based solely on the countermovement depth that maximizes jump height. In addition, the comparison of the two groups does not support the concept of a dual-task strategy based on the trade-off between maximizing jump height and minimizing the jumping quickness that should be more prominent in the athletes that routinely need to jump quickly. Further research could explore whether the observed phenomenon is based on other optimization principles, such as the minimization of effort and energy expenditure. Nevertheless, future routine testing procedures should take into account that the control strategy of maximum countermovement jumps is not fully based on maximizing the jump height, while the countermovement depth markedly confound the relationship between the jump height and the assessed force and power output of leg muscles.

Intra-Personal and Inter-Personal Kinetic Synergies During Jumping.

PubMed

Slomka, Kajetan; Juras, Grzegorz; Sobota, Grzegorz; Furmanek, Mariusz; Rzepko, Marian; Latash, Mark L

2015-12-22

We explored synergies between two legs and two subjects during preparation for a long jump into a target. Synergies were expected during one-person jumping. No such synergies were expected between two persons jumping in parallel without additional contact, while synergies were expected to emerge with haptic contact and become stronger with strong mechanical contact. Subjects performed jumps either alone (each foot standing on a separate force platform) or in dyads (parallel to each other, each person standing on a separate force platform) without any contact, with haptic contact, and with strong coupling. Strong negative correlations between pairs of force variables (strong synergies) were seen in the vertical force in one-person jumps and weaker synergies in two-person jumps with the strong contact. For other force variables, only weak synergies were present in one-person jumps and no negative correlations between pairs of force variable for two-person jumps. Pairs of moment variables from the two force platforms at steady state showed positive correlations, which were strong in one-person jumps and weaker, but still significant, in two-person jumps with the haptic and strong contact. Anticipatory synergy adjustments prior to action initiation were observed in one-person trials only. We interpret the different results for the force and moment variables at steady state as reflections of postural sway.

Intra-Personal and Inter-Personal Kinetic Synergies During Jumping

PubMed Central

Slomka, Kajetan; Juras, Grzegorz; Sobota, Grzegorz; Furmanek, Mariusz; Rzepko, Marian; Latash, Mark L.

2015-01-01

We explored synergies between two legs and two subjects during preparation for a long jump into a target. Synergies were expected during one-person jumping. No such synergies were expected between two persons jumping in parallel without additional contact, while synergies were expected to emerge with haptic contact and become stronger with strong mechanical contact. Subjects performed jumps either alone (each foot standing on a separate force platform) or in dyads (parallel to each other, each person standing on a separate force platform) without any contact, with haptic contact, and with strong coupling. Strong negative correlations between pairs of force variables (strong synergies) were seen in the vertical force in one-person jumps and weaker synergies in two-person jumps with the strong contact. For other force variables, only weak synergies were present in one-person jumps and no negative correlations between pairs of force variable for two-person jumps. Pairs of moment variables from the two force platforms at steady state showed positive correlations, which were strong in one-person jumps and weaker, but still significant, in two-person jumps with the haptic and strong contact. Anticipatory synergy adjustments prior to action initiation were observed in one-person trials only. We interpret the different results for the force and moment variables at steady state as reflections of postural sway. PMID:26839608

Application of a tri-axial accelerometer to estimate jump frequency in volleyball.

PubMed

Jarning, Jon M; Mok, Kam-Ming; Hansen, Bjørge H; Bahr, Roald

2015-03-01

Patellar tendinopathy is prevalent among athletes, and most likely associated with a high jumping load. If methods for estimating jump frequency were available, this could potentially assist in understanding and preventing this condition. The objective of this study was to explore the possibility of using peak vertical acceleration (PVA) or peak resultant acceleration (PRA) measured by an accelerometer to estimate jump frequency. Twelve male elite volleyball players (22.5 ± 1.6 yrs) performed a training protocol consisting of seven typical motion patterns, including jumping and non-jumping movements. Accelerometer data from the trial were obtained using a tri-axial accelerometer. In addition, we collected video data from the trial. Jump-float serving and spike jumping could not be distinguished from non-jumping movements using differences in PVA or PRA. Furthermore, there were substantial inter-participant differences in both the PVA and the PRA within and across movement types (p < 0.05). These findings suggest that neither PVA nor PRA measured by a tri-axial accelerometer is an applicable method for estimating jump frequency in volleyball. A method for acquiring real-time estimates of jump frequency remains to be verified. However, there are several alternative approaches, and further investigations are needed.

Lower Extremity Kinematics Differed Between a Controlled Drop-Jump and Volleyball-Takeoffs.

PubMed

Beardt, Bradley S; McCollum, Myranda R; Hinshaw, Taylour J; Layer, Jacob S; Wilson, Margaret A; Zhu, Qin; Dai, Boyi

2018-04-03

Previous studies utilizing jump-landing biomechanics to predict anterior cruciate ligament injuries have shown inconsistent findings. The purpose of this study was to quantify the differences and correlations in jump-landing kinematics between a drop-jump, a controlled volleyball-takeoff, and a simulated-game volleyball-takeoff. Seventeen female volleyball players performed these three tasks on a volleyball court while three-dimensional kinematic data were collected by three calibrated camcorders. Participants demonstrated significantly increased jump height, shorter stance time, increased time differences in initial contact between two feet, increased knee and hip flexion at initial contact and decreased peak knee and hip flexion for both left and right legs, and decreased knee-ankle distance ratio at the lowest height of mid-hip for the two volleyball-takeoffs compared with the drop-jump (p < 0.05, Cohen's dz ≥ 0.8). Significant correlations were observed for all variables between the two volleyball-takeoffs (p < 0.05, ρ ≥ 0.6), but were not for most variables between the drop-jump and two volleyball-takeoffs. Controlled drop-jump kinematics may not represent jump-landing kinematics exhibited during volleyball competition. Jump-landing mechanics during sports-specific tasks may better represent those exhibited during sports competition and their associated risk of ACL injury compared with the drop-jump.

Salticid predation as one potential driving force of ant mimicry in jumping spiders

PubMed Central

Huang, Jin-Nan; Cheng, Ren-Chung; Li, Daiqin; Tso, I-Min

2011-01-01

Many spiders possess myrmecomorphy, and species of the jumping spider genus Myrmarachne exhibit nearly perfect ant mimicry. Most salticids are diurnal predators with unusually high visual acuity that prey on various arthropods, including conspecifics. In this study, we tested whether predation pressure from large jumping spiders is one possible driving force of perfect ant mimicry in jumping spiders. The results showed that small non-ant-mimicking jumping spiders were readily treated as prey by large ones (no matter whether heterospecific or conspecific) and suffered high attack and mortality rates. The size difference between small and large jumping spiders significantly affected the outcomes of predatory interactions between them: the smaller the juvenile jumping spiders, the higher the predation risk from large ones. The attack and mortality rates of ant-mimicking jumping spiders were significantly lower than those of non-ant-mimicking jumping spiders, indicating that a resemblance to ants could provide protection against salticid predation. However, results of multivariate behavioural analyses showed that the responses of large jumping spiders to ants and ant-mimicking salticids differed significantly. Results of this study indicate that predation pressure from large jumping spiders might be one selection force driving the evolution of nearly perfect myrmecomorphy in spiders and other arthropods. PMID:20961898

The validity and reliability of an iPhone app for measuring vertical jump performance.

PubMed

Balsalobre-Fernández, Carlos; Glaister, Mark; Lockey, Richard Anthony

2015-01-01

The purpose of this investigation was to analyse the concurrent validity and reliability of an iPhone app (called: My Jump) for measuring vertical jump performance. Twenty recreationally active healthy men (age: 22.1 ± 3.6 years) completed five maximal countermovement jumps, which were evaluated using a force platform (time in the air method) and a specially designed iPhone app. My jump was developed to calculate the jump height from flight time using the high-speed video recording facility on the iPhone 5 s. Jump heights of the 100 jumps measured, for both devices, were compared using the intraclass correlation coefficient, Pearson product moment correlation coefficient (r), Cronbach's alpha (α), coefficient of variation and Bland-Altman plots. There was almost perfect agreement between the force platform and My Jump for the countermovement jump height (intraclass correlation coefficient = 0.997, P < 0.001; Bland-Altman bias = 1.1 ± 0.5 cm, P < 0.001). In comparison with the force platform, My Jump showed good validity for the CMJ height (r = 0.995, P < 0.001). The results of the present study showed that CMJ height can be easily, accurately and reliably evaluated using a specially developed iPhone 5 s app.

Intersession and Intrasession Reliability and Validity of the My Jump App for Measuring Different Jump Actions in Trained Male and Female Athletes.

PubMed

Gallardo-Fuentes, Francisco; Gallardo-Fuentes, Jorge; Ramírez-Campillo, Rodrigo; Balsalobre-Fernández, Carlos; Martínez, Cristian; Caniuqueo, Alexis; Cañas, Rodrigo; Banzer, Winfried; Loturco, Irineu; Nakamura, Fabio Y; Izquierdo, Mikel

2016-07-01

Gallardo-Fuentes, F, Gallardo-Fuentes, J, Ramírez-Campillo, R, Balsalobre-Fernández, C, Martínez, C, Caniuqueo, A, Cañas, R, Banzer, W, Loturco, I, Nakamura, FY, and Izquierdo, M. Intersession and intrasession reliability and validity of the My Jump app for measuring different jump actions in trained male and female athletes. J Strength Cond Res 30(7): 2049-2056, 2016-The purpose of this study was to analyze the concurrent validity and reliability of the iPhone app named My Jump for measuring jump height in 40-cm drop jumps (DJs), countermovement jumps (CMJs), and squat jumps (SJs). To do this, 21 male and female athletes (age, 22.1 ± 3.6 years) completed 5 maximal DJs, CMJs, and SJs on 2 separate days, which were evaluated using a contact platform and the app My Jump, developed to calculate jump height from flight time using the high-speed video recording facility on the iPhone. A total of 630 jumps were compared using the intraclass correlation coefficient (ICC), Bland-Altman plots, Pearson's product moment correlation coefficient (r), Cronbach's alpha (α), and coefficient of variation (CV). There was almost perfect agreement between the measurement instruments for all jump height values (ICC = 0.97-0.99), with no differences between the instruments (p > 0.05; mean difference of 0.2 cm). Almost perfect correlation was observed between the measurement instruments for SJs, CMJs, and DJs (r = 0.96-0.99). My Jump showed very good within-subject reliability (α = 0.94-0.99; CV = 3.8-7.6) and interday reliability (r = 0.86-0.95) for SJs, CMJs, and DJs in all subjects. Therefore, the iPhone app named My Jump provides reliable intersession and intrasession data, as well as valid measurements for maximal jump height during fast (i.e., DJs) and slow (i.e., CMJs) stretch-shortening cycle muscle actions, and during concentric-only explosive muscle actions (i.e., SJs), in both male and female athletes in comparison with a professional contact platform.

Biomechanical Analysis of Locust Jumping in a Physically Realistic Virtual Environment

NASA Astrophysics Data System (ADS)

Cofer, David; Cymbalyuk, Gennady; Heitler, William; Edwards, Donald

2008-03-01

The biomechanical and neural components that underlie locust jumping have been extensively studied. Previous research suggested that jump energy is stored primarily in the extensor apodeme, and in a band of cuticle called the semi-lunar process (SLP). As it has thus far proven impossible to experimentally alter the SLP without rendering a locust unable to jump, it has not been possible to test whether the energy stored in the SLP has a significant impact on the jump. To address problems such as this we have developed a software toolkit, AnimatLab, which allows researchers to build and test virtual organisms. We used this software to build a virtual locust, and then asked how the SLP is utilized during jumping. The results show that without the SLP the jump distance was reduced by almost half. Further, the simulations were also able to show that loss of the SLP had a significant impact on the final phase of the jump. We are currently working on postural control mechanisms for targeted jumping in locust.

Numerical solutions of Navier-Stokes equations for compressible turbulent two/three dimensional flows in terminal shock region of an inlet/diffuser

NASA Technical Reports Server (NTRS)

Liu, N. S.; Shamroth, S. J.; Mcdonald, H.

1983-01-01

The multidimensional ensemble averaged compressible time dependent Navier Stokes equations in conjunction with mixing length turbulence model and shock capturing technique were used to study the terminal shock type of flows in various flight regimes occurring in a diffuser/inlet model. The numerical scheme for solving the governing equations is based on a linearized block implicit approach and the following high Reynolds number calculations were carried out: (1) 2 D, steady, subsonic; (2) 2 D, steady, transonic with normal shock; (3) 2 D, steady, supersonic with terminal shock; (4) 2 D, transient process of shock development and (5) 3 D, steady, transonic with normal shock. The numerical results obtained for the 2 D and 3 D transonic shocked flows were compared with corresponding experimental data; the calculated wall static pressure distributions agree well with the measured data.

Computations of spray, fuel-air mixing, and combustion in a lean-premixed-prevaporized combustor

NASA Technical Reports Server (NTRS)

Dasgupta, A.; Li, Z.; Shih, T. I.-P.; Kundu, K.; Deur, J. M.

1993-01-01

A code was developed for computing the multidimensional flow, spray, combustion, and pollutant formation inside gas turbine combustors. The code developed is based on a Lagrangian-Eulerian formulation and utilizes an implicit finite-volume method. The focus of this paper is on the spray part of the code (both formulation and algorithm), and a number of issues related to the computation of sprays and fuel-air mixing in a lean-premixed-prevaporized combustor. The issues addressed include: (1) how grid spacings affect the diffusion of evaporated fuel, and (2) how spurious modes can arise through modelling of the spray in the Lagrangian computations. An upwind interpolation scheme is proposed to account for some effects of grid spacing on the artificial diffusion of the evaporated fuel. Also, some guidelines are presented to minimize errors associated with the spurious modes.

NOR-USA Scientific Traverse of East Antarctica: Science and Logistics on a Three-Month Expedition Across Antarctica's Farthest Frontier

NASA Technical Reports Server (NTRS)

Albert, Mary R.

2012-01-01

Dr. Albert's current research is centered on transfer processes in porous media, including air-snow exchange in the Polar Regions and in soils in temperate areas. Her research includes field measurements, laboratory experiments, and theoretical modeling. Mary conducts field and laboratory measurements of the physical properties of natural terrain surfaces, including permeability, microstructure, and thermal conductivity. Mary uses the measurements to examine the processes of diffusion and advection of heat, mass, and chemical transport through snow and other porous media. She has developed numerical models for investigation of a variety of problems, from interstitial transport to freezing of flowing liquids. These models include a two-dimensional finite element code for air flow with heat, water vapor, and chemical transport in porous media, several multidimensional codes for diffusive transfer, as well as a computational fluid dynamics code for analysis of turbulent water flow in moving-boundary phase change problems.

Goniochromatic and sparkle properties of effect pigmented samples in multidimensional configuration

NASA Astrophysics Data System (ADS)

Höpe, Andreas; Hauer, Kai-Olaf; Teichert, Sven; Hünerhoff, Dirk; Strothkämper, Christian

2015-03-01

The effects of goniochromatism and sparkle are gaining more and more interest for surface refinement applications driven by demanding requirements from such different branches as automotive, cosmetics, printing and packaging industry. The common background and intention in all of these implementations is improvement of the visual appearance of the related commercial products. Goniochromatic materials show strong angular-dependent reflection characteristics and hence a color impression depending on the effective spatial arrangement of illumination and observation relative to the surface of the artifact. Sparkle is a texture related effect giving a surface which is irradiated directionally, like direct sun light, a bright glittering effect, similar to twinkling stars at the night sky. The prototype for this new effect is the Xirallic® pigment of MERCK KGaA, Germany. The same pigment shows in diffuse irradiation, like on a cloudy day, a different visual effect called graininess (coarseness) which appears as a granular structure of the surface. Both effects were studied on especially manufactured samples of a dilution series in pigment concentration and a tonality series with carbon black. The experiments were carried out with the robot-based gonioreflectometer and integrating sphere facilities at Physikalisch-Technische Bundesanstalt (PTB) in multidimensional configurations of directional and diffuse irradiation. The research is part of the European Metrology Research Program (EMRP), which is a metrology-focused program of coordinated Research & Development (R&D) funded by the European Commission and participating countries within the European Association of National Metrology Institutes (EURAMET). More information and updated news concerning the project can be found on the xD-Reflect website http://www.xdreflect.eu/.

Determination of K shell absorption jump factors and jump ratios of 3d transition metals by measuring K shell fluorescence parameters.

PubMed

Kaçal, Mustafa Recep; Han, İbrahim; Akman, Ferdi

2015-01-01

Energy dispersive X-ray fluorescence technique (EDXRF) has been employed for measuring K-shell absorption jump factors and jump ratios for Ti, Cr, Fe, Co, Ni and Cu elements. The jump factors and jump ratios for these elements were determined by measuring K shell fluorescence parameters such as the Kα X-ray production cross-sections, K shell fluorescence yields, Kβ-to-Kα X-rays intensity ratios, total atomic absorption cross sections and mass attenuation coefficients. The measurements were performed using a Cd-109 radioactive point source and an Si(Li) detector in direct excitation and transmission experimental geometry. The measured values for jump factors and jump ratios were compared with theoretically calculated and the ones available in the literature. Copyright © 2014 Elsevier Ltd. All rights reserved.

Concurrent validity and reliability of torso-worn inertial measurement unit for jump power and height estimation.

PubMed

Rantalainen, Timo; Gastin, Paul B; Spangler, Rhys; Wundersitz, Daniel

2018-09-01

The purpose of the present study was to evaluate the concurrent validity and test-retest repeatability of torso-worn IMU-derived power and jump height in a counter-movement jump test. Twenty-seven healthy recreationally active males (age, 21.9 [SD 2.0] y, height, 1.76 [0.7] m, mass, 73.7 [10.3] kg) wore an IMU and completed three counter-movement jumps a week apart. A force platform and a 3D motion analysis system were used to concurrently measure the jumps and subsequently derive power and jump height (based on take-off velocity and flight time). The IMU significantly overestimated power (mean difference = 7.3 W/kg; P < 0.001) compared to force-platform-derived power but good correspondence between methods was observed (Intra-class correlation coefficient [ICC] = 0.69). IMU-derived power exhibited good reliability (ICC = 0.67). Velocity-derived jump heights exhibited poorer concurrent validity (ICC = 0.72 to 0.78) and repeatability (ICC = 0.68) than flight-time-derived jump heights, which exhibited excellent validity (ICC = 0.93 to 0.96) and reliability (ICC = 0.91). Since jump height and power are closely related, and flight-time-derived jump height exhibits excellent concurrent validity and reliability, flight-time-derived jump height could provide a more desirable measure compared to power when assessing athletic performance in a counter-movement jump with IMUs.

The relationship between vertical jump power estimates and weightlifting ability: a field-test approach.

PubMed

Carlock, Jon M; Smith, Sarah L; Hartman, Michael J; Morris, Robert T; Ciroslan, Dragomir A; Pierce, Kyle C; Newton, Robert U; Harman, Everett A; Sands, William A; Stone, Michael H

2004-08-01

The purpose of this study was to assess the usefulness of the vertical jump and estimated vertical-jump power as a field test for weightlifting. Estimated PP output from the vertical jump was correlated with lifting ability among 64 USA national-level weightlifters (junior and senior men and women). Vertical jump was measured using the Kinematic Measurement System, consisting of a switch mat interfaced with a laptop computer. Vertical jumps were measured using a hands-on-hips method. A counter-movement vertical jump (CMJ) and a static vertical jump (SJ, 90 degrees knee angle) were measured. Two trials were given for each condition. Test-retest reliability for jump height was intra-class correlation (ICC) = 0.98 (CMJ) and ICC = 0.96 (SJ). Athletes warmed up on their own for 2-3 minutes, followed by 2 practice jumps at each condition. Peak power (PP) was estimated using the equations developed by Sayers et al. (24). The athletes' current lifting capabilities were assessed by a questionnaire, and USA national coaches checked the listed values. Differences between groups (i.e., men versus women, juniors versus resident lifters) were determined using t-tests (p < or = 0.05). Correlations were determined using Pearson's r. Results indicate that vertical jumping PP is strongly associated with weightlifting ability. Thus, these results indicate that PP derived from the vertical jump (CMJ or SJ) can be a valuable tool in assessing weightlifting performance.

Comparison of stretch reflex responses evoked during drop jumping in highly skilled atheles versus untrained subjects.

PubMed

Judge, L W; Burke, J R

2015-06-01

The purpose of the study was to describe changes in the excitability of the stretch reflex response (SRR) during different drop jumps as a function of training background and as an adaptation to a preseason sport-specific resistance training program. Twelve collegiate field event athletes (discus, hammer, javelin, shot put, and weight; 9 males and 3 females) and 12 college-aged control subjects performed the following three jumps: (1) countermovement jump (CMJ); (2) countermovement drop jump; and (3) bounce-drop jump (BDJ). Neuromechanical changes in the performance of drop jumps by athletes were measured during the sport-specific resistance training program. Pre-post testing of drop jump performance by control subjects was included for comparison. For each jump trial, ground reaction forces (GRF), electromyograms (EMG) and cinematographic data were collected. There were no training adaptations. However, jump heights were greater for the athletes than the controls among the different jumps with the jump heights for all subjects being less during the BDJ than CMJ and CDJ. In athletes only, there was a differential modulation of the SRR from the gastrocnemius muscle with different levels of background muscle activity for the CDJ and BDJ. There were changes in excitability of SRR from the gastrocnemius muscle as a function of training background. Interrelated neuromechanical mechanisms to include landing biomechanics, intrinsic musculotendinous tissue properties of the ankle, and centrally regulated motor commands may underlie the facilitation of the SRR from the gastrocnemius muscle in athletes as compared to controls.

Combined Effects of Fatigue and Surface Instability on Jump Biomechanics in Elite Athletes.

PubMed

Prieske, Olaf; Demps, Marie; Lesinski, Melanie; Granacher, Urs

2017-09-01

The present study aimed to examine the effects of fatigue and surface instability on kinetic and kinematic jump performance measures. Ten female and 10 male elite volleyball players (18±2 years) performed repetitive vertical double-leg box jumps until failure. Pre and post fatigue, jump height/performance index, ground reaction force and knee flexion/valgus angles were assessed during drop and countermovement jumps on stable and unstable surfaces. Fatigue, surface condition, and sex resulted in significantly lower drop jump performance and ground reaction force (p≤0.031, 1.1≤d≤3.5). Additionally, drop jump knee flexion angles were significantly lower following fatigue (p=0.006, d=1.5). A significant fatigue×surface×sex interaction (p=0.020, d=1.2) revealed fatigue-related decrements in drop jump peak knee flexion angles under unstable conditions and in men only. Knee valgus angles were higher on unstable compared to stable surfaces during drop jumps and in females compared to males during drop and countermovement jumps (p≤0.054, 1.0≤d≤1.1). Significant surface×sex interactions during countermovement jumps (p=0.002, d=1.9) indicated that knee valgus angles at onset of ground contact were significantly lower on unstable compared to stable surfaces in males but higher in females. Our findings revealed that fatigue and surface instability resulted in sex-specific knee motion strategies during jumping in elite volleyball players. © Georg Thieme Verlag KG Stuttgart · New York.

Sign realized jump risk and the cross-section of stock returns: Evidence from China's stock market.

PubMed

Chao, Youcong; Liu, Xiaoqun; Guo, Shijun

2017-01-01

Using 5-minute high frequency data from the Chinese stock market, we employ a non-parametric method to estimate Fama-French portfolio realized jumps and investigate whether the estimated positive, negative and sign realized jumps could forecast or explain the cross-sectional stock returns. The Fama-MacBeth regression results show that not only have the realized jump components and the continuous volatility been compensated with risk premium, but also that the negative jump risk, the positive jump risk and the sign jump risk, to some extent, could explain the return of the stock portfolios. Therefore, we should pay high attention to the downside tail risk and the upside tail risk.

Biomechanics research in ski jumping, 1991-2006.

PubMed

Schwameder, Hermann

2008-01-01

In this paper, I review biomechanics research in ski jumping with a specific focus on publications presented between 1991 and 2006 on performance enhancement, limiting factors of the take-off, specific training and conditioning, aerodynamics, and safety. The first section presents a brief description of ski jumping phases (in-run, take-off, early flight, stable flight, and landing) regarding the biomechanical and functional fundamentals. The most important and frequently used biomechanical methods in ski jumping (kinematics, ground reaction force analyses, muscle activation patterns, aerodynamics) are summarized in the second section. The third section focuses on ski jumping articles and research findings published after the establishment of the V-technique in 1991, as the introduction of this technique has had a major influence on performance enhancement, ski jumping regulations, and the construction of hill profiles. The final section proposes topics for future research in the biomechanics of ski jumping, including: take-off and early flight and the relative roles of vertical velocity and forward somersaulting angular momentum; optimal jumping patterns utilizing the capabilities of individual athletes; development of kinematic and kinetic feedback systems for hill jumps; comparisons of simulated and hill jumps; effect of equipment modifications on performance and safety enhancement.

Determination of the best pre-jump height for improvement of two-legged vertical jump.

PubMed

Jafari, Mahsa; Zolaktaf, Vahid; Marandi, Sayyed M

2013-04-01

Athletic performance in many sports depends on two-legged vertical jump. The objective of this study was to examine the effect of different pre-jump height exercises on two-legged vertical jump and to determine the best pre-jump height(s). Subjects included 35 females and 42 males. By matched randomized sampling, subjects of each sex were assigned into four groups, namely, control, 10-cm hurdle, 20-cm hurdle, and 30-cm hurdle. They participated in the same training program for 6 weeks. Statistical analyses were based on one-way and repeated-measure analysis of variance (ANOVA). Analysis of the data showed that practice over hurdles of 10 cm was better than no hurdle and hurdles of >10 cm. Also, jump attempts over hurdles were efficient for trained athletes, but not for untrained athletes. For both sexes, the rate of spike improvement was much better in the experimental groups than in the control groups; it was independent from the rate of progress in jump, which was relatively less evident. It is likely that rather than increasing jump height, training over hurdle enabled the players to use a higher percent of their jump potentials.

Aerial Rotation Effects on Vertical Jump Performance Among Highly Skilled Collegiate Soccer Players.

PubMed

Barker, Leland A; Harry, John R; Dufek, Janet S; Mercer, John A

2017-04-01

Barker, LA, Harry, JR, Dufek, JS, and Mercer, JA. Aerial rotation effects on vertical jump performance among highly skilled collegiate soccer players. J Strength Cond Res 31(4): 932-938, 2017-In soccer matches, jumps involving rotations occur when attempting to head the ball for a shot or pass from set pieces, such as corner kicks, goal kicks, and lob passes. However, the 3-dimensional ground reaction forces used to perform rotational jumping tasks are currently unknown. Therefore, the purpose of this study was to compare bilateral, 3-dimensional, and ground reaction forces of a standard countermovement jump (CMJ0) with those of a countermovement jump with a 180° rotation (CMJ180) among Division-1 soccer players. Twenty-four participants from the soccer team of the University of Nevada performed 3 trials of CMJ0 and CMJ180. Dependent variables included jump height, downward and upward phase times, vertical (Fz) peak force and net impulse relative to mass, and medial-lateral and anterior-posterior force couple values. Statistical significance was set a priori at α = 0.05. CMJ180 reduced jump height, increased the anterior-posterior force couple in the downward and upward phases, and increased upward peak Fz (p ≤ 0.05). All other variables were not significantly different between groups (p > 0.05). However, we did recognize that downward peak Fz trended lower in the CMJ0 condition (p = 0.059), and upward net impulse trended higher in the CMJ0 condition (p = 0.071). It was concluded that jump height was reduced during the rotational jumping task, and rotation occurred primarily via AP ground reaction forces through the entire countermovement jump. Coaches and athletes may consider additional rotational jumping in their training programs to mediate performance decrements during rotational jump tasks.

Validity and reliability of Optojump photoelectric cells for estimating vertical jump height.

PubMed

Glatthorn, Julia F; Gouge, Sylvain; Nussbaumer, Silvio; Stauffacher, Simone; Impellizzeri, Franco M; Maffiuletti, Nicola A

2011-02-01

Vertical jump is one of the most prevalent acts performed in several sport activities. It is therefore important to ensure that the measurements of vertical jump height made as a part of research or athlete support work have adequate validity and reliability. The aim of this study was to evaluate concurrent validity and reliability of the Optojump photocell system (Microgate, Bolzano, Italy) with force plate measurements for estimating vertical jump height. Twenty subjects were asked to perform maximal squat jumps and countermovement jumps, and flight time-derived jump heights obtained by the force plate were compared with those provided by Optojump, to examine its concurrent (criterion-related) validity (study 1). Twenty other subjects completed the same jump series on 2 different occasions (separated by 1 week), and jump heights of session 1 were compared with session 2, to investigate test-retest reliability of the Optojump system (study 2). Intraclass correlation coefficients (ICCs) for validity were very high (0.997-0.998), even if a systematic difference was consistently observed between force plate and Optojump (-1.06 cm; p < 0.001). Test-retest reliability of the Optojump system was excellent, with ICCs ranging from 0.982 to 0.989, low coefficients of variation (2.7%), and low random errors (±2.81 cm). The Optojump photocell system demonstrated strong concurrent validity and excellent test-retest reliability for the estimation of vertical jump height. We propose the following equation that allows force plate and Optojump results to be used interchangeably: force plate jump height (cm) = 1.02 × Optojump jump height + 0.29. In conclusion, the use of Optojump photoelectric cells is legitimate for field-based assessments of vertical jump height.

Spatial variability of the Arctic Ocean's double-diffusive staircase

NASA Astrophysics Data System (ADS)

Shibley, N. C.; Timmermans, M.-L.; Carpenter, J. R.; Toole, J. M.

2017-02-01

The Arctic Ocean thermohaline stratification frequently exhibits a staircase structure overlying the Atlantic Water Layer that can be attributed to the diffusive form of double-diffusive convection. The staircase consists of multiple layers of O(1) m in thickness separated by sharp interfaces, across which temperature and salinity change abruptly. Through a detailed analysis of Ice-Tethered Profiler measurements from 2004 to 2013, the double-diffusive staircase structure is characterized across the entire Arctic Ocean. We demonstrate how the large-scale Arctic Ocean circulation influences the small-scale staircase properties. These staircase properties (layer thicknesses and temperature and salinity jumps across interfaces) are examined in relation to a bulk vertical density ratio spanning the staircase stratification. We show that the Lomonosov Ridge serves as an approximate boundary between regions of low density ratio (approximately 3-4) on the Eurasian side and higher density ratio (approximately 6-7) on the Canadian side. We find that the Eurasian Basin staircase is characterized by fewer, thinner layers than that in the Canadian Basin, although the margins of all basins are characterized by relatively thin layers and the absence of a well-defined staircase. A double-diffusive 4/3 flux law parametrization is used to estimate vertical heat fluxes in the Canadian Basin to be O(0.1) W m-2. It is shown that the 4/3 flux law may not be an appropriate representation of heat fluxes through the Eurasian Basin staircase. Here molecular heat fluxes are estimated to be between O(0.01) and O(0.1) W m-2. However, many uncertainties remain about the exact nature of these fluxes.

Influence of Knee-to-Feet Jump Training on Vertical Jump and Hang Clean Performance.

PubMed

Stark, Laura; Pickett, Karla; Bird, Michael; King, Adam C

2016-11-01

Stark, L, Pickett, K, Bird, M, and King, AC. Influence of knee-to-feet jump training on vertical jump and hang clean performance. J Strength Cond Res 30(11): 3084-3089, 2016-From a motor learning perspective, the practice/training environment can result in positive, negative, or neutral transfer to the testing conditions. The purpose of this study was to examine the training effect of a novel movement (knee-to-feet [K2F] jumps) and whether a 6-week training program induced a positive transfer effect to other power-related movements (vertical jump and hang clean [HC]). Twenty-six intercollegiate athletes from power-emphasized sports were paired and counter-balanced into a control (i.e., maintained their respective sport-specific lifting regimen) or an experimental group (i.e., completed a 6-week progressive training program of K2F jumps in addition to respective lifting regimen). A pre- and posttest design was used to investigate the effect of training on K2F jump height and transfer effect to vertical jump height (VJH) and 2-repetition maximum (RM) HC performance. A significant increase in K2F jump height was found for the experimental group. Vertical jump height significantly increased from pre- to posttest but no group or interaction (group × time) effect was found, and there were nonsignificant differences for HC. Posttest data showed significant correlations between all pairs of the selected exercises with the highest correlation between K2F jump height and VJ H (R = 0.40) followed by VJH and 2RM HC (R = 0.38) and 2RM HC and K2F jump height (R = 0.23). The results suggest that K2F jump training induced the desired learning effect but was specific to the movement in that no effect of transfer occurred to the other power-related movements. This finding is value for strength and condition professionals who design training programs to enhance athletic performance.

Long memory behavior of returns after intraday financial jumps

NASA Astrophysics Data System (ADS)

Behfar, Stefan Kambiz

2016-11-01

In this paper, characterization of intraday financial jumps and time dynamics of returns after jumps is investigated, and will be analytically and empirically shown that intraday jumps are power-law distributed with the exponent 1 < μ < 2; in addition, returns after jumps show long-memory behavior. In the theory of finance, it is important to be able to distinguish between jumps and continuous sample path price movements, and this can be achieved by introducing a statistical test via calculating sums of products of returns over small period of time. In the case of having jump, the null hypothesis for normality test is rejected; this is based on the idea that returns are composed of mixture of normally-distributed and power-law distributed data (∼ 1 /r 1 + μ). Probability of rejection of null hypothesis is a function of μ, which is equal to one for 1 < μ < 2 within large intraday sample size M. To test this idea empirically, we downloaded S&P500 index data for both periods of 1997-1998 and 2014-2015, and showed that the Complementary Cumulative Distribution Function of jump return is power-law distributed with the exponent 1 < μ < 2. There are far more jumps in 1997-1998 as compared to 2015-2016; and it represents a power law exponent in 2015-2016 greater than one in 1997-1998. Assuming that i.i.d returns generally follow Poisson distribution, if the jump is a causal factor, high returns after jumps are the effect; we show that returns caused by jump decay as power-law distribution. To test this idea empirically, we average over the time dynamics of all days; therefore the superposed time dynamics after jump represent a power-law, which indicates that there is a long memory with a power-law distribution of return after jump.

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices

NASA Technical Reports Server (NTRS)

Biegel, Bryan A.; Rafferty, Conor S.; Ancona, Mario G.; Yu, Zhi-Ping

2000-01-01

We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction to the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion or quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.

Scaled Jump in Gravity-Reduced Virtual Environments.

PubMed

Kim, MyoungGon; Cho, Sunglk; Tran, Tanh Quang; Kim, Seong-Pil; Kwon, Ohung; Han, JungHyun

2017-04-01

The reduced gravity experienced in lunar or Martian surfaces can be simulated on the earth using a cable-driven system, where the cable lifts a person to reduce his or her weight. This paper presents a novel cable-driven system designed for the purpose. It is integrated with a head-mounted display and a motion capture system. Focusing on jump motion within the system, this paper proposes to scale the jump and reports the experiments made for quantifying the extent to which a jump can be scaled without the discrepancy between physical and virtual jumps being noticed by the user. With the tolerable range of scaling computed from these experiments, an application named retargeted jump is developed, where a user can jump up onto virtual objects while physically jumping in the real-world flat floor. The core techniques presented in this paper can be extended to develop extreme-sport simulators such as parasailing and skydiving.

Energy and time optimal trajectories in exploratory jumps of the spider Phidippus regius.

PubMed

Nabawy, Mostafa R A; Sivalingam, Girupakaran; Garwood, Russell J; Crowther, William J; Sellers, William I

2018-05-08

Jumping spiders are proficient jumpers that use jumps in a variety of behavioural contexts. We use high speed, high resolution video to measure the kinematics of a single regal jumping spider for a total of 15 different tasks based on a horizontal gap of 2-5 body lengths and vertical gap of +/-2 body lengths. For short range jumps, we show that low angled trajectories are used that minimise flight time. For longer jumps, take-off angles are steeper and closer to the optimum for minimum energy cost of transport. Comparison of jump performance against other arthropods shows that Phidippus regius is firmly in the group of animals that use dynamic muscle contraction for actuation as opposed to a stored energy catapult system. We find that the jump power requirements can be met from the estimated mass of leg muscle; hydraulic augmentation may be present but appears not to be energetically essential.

Laterality versus jumping performance in men and women.

PubMed

Trzaskoma, Zbigniew; Ilnicka, Lidia; Wiszomirska, Ida; Wit, Andrzej; Wychowański, Michał

2015-01-01

The aim of this study was to investigate relationships between functional asymmetry of lower limbs, taking into account morphological features of the feet, and jumping ability in men and women. The study population consisted of 56 subjects, 30 women (age: 20.29 ± 0.59 years; body mass: 58.13 ± 4.58 kg, body height: 165.60 ± 5.03 cm) and 26 men (age: 20.41 ± 0.78 years, body mass: 78.39 ± 8.42 kg, body height: 181.15 ± 6.52 cm). The measurements of longitudinal arches were performed with the plan- tographic method on the basis of Clarke's angle mapped on a computer foot print. The measurements of jumping performance during bilateral (two legs) and unilateral (single-leg) counter movement jump (CMJ) were done on force plate. All subjects jumped three times each type of jump (total 9 jumps): three right leg, three left leg and three two legs. We put the test results through a detailed statistical analysis with the Statistica 8.0. The t-test for dependent variables and the Wilcoxon signed-rank test for divergent variances of the fea- tures compared. The analysis of relationships between the chosen podometric and plantographic features and jumping performance was conducted on the basis of the Pearson product-moment correlation coefficient (for the features which presented normal distribution, according to the Shapiro-Wilk test). The correlations between values of height of single-leg jumps (right and left) and bilateral jumps, and foot indices were found in few cases only in men who had greater values of jump height with the non-dominant limb. We did not find a significant difference in jumping ability between the dominant limb and the non-dominant limb in women. We found bilateral deficits in jumping ability in the study groups, though we did not find significant differences (P ≤ 0.05) between the values for women (a mean of 6.5%) and for men (a mean of 8.4%). We found significant gender differences of the correlations between the values of height of jumps (single-leg and bilateral jumps) and foot indices.

The Advanced Tactical Parachute System (T-11): injuries during basic military parachute training.

PubMed

Knapik, Joseph J; Graham, Bria; Steelman, Ryan; Colliver, Keith; Jones, Bruce H

2011-10-01

Since the 1950s, the standard U.S. military troop parachute system has been the T-10. TheT-10 is currently being replaced by the newer T-11 system. This investigation compared injury incidence between the T-10 and T-11 military parachute systems. Participants were students in basic parachute training at the U.S. Army Airborne School (USAAS). Students performed their first parachute jumps with the T-11 and subsequent jumps with the T-10. Injury data were collected from routine reports produced by the USAAS. Combat loaded jumps and night jumps were excluded from the analysis since these were only conducted with the T-10. There were a total of 76 injuries in 30,755 jumps for an overall cumulative injury incidence of 2.5/1000 jumps. With the T-10 parachute, there were 61 injuries in 21,404 jumps for a cumulative injury incidence of 2.9/1000 jumps; with the T-11 parachute there were 15 injuries in 9351 jumps for a cumulative injury incidence of 1.6/1000 jumps [risk ratio (T10/T11) = 1.78, 95% confidence interval = 1.01-3.12, P = 0.04]. Limitations to this analysis included the fact that the T-11 was only used on the first jumps among students who had likely never previously performed a parachute jump and that aircraft exit procedures differed very slightly for the two parachutes. Nonetheless, the data suggest that injury incidence is lower with the T-11 parachute than with the T-10 parachute when airborne training operations are conducted during the day without combat loads.

Take-off analysis of the Olympic ski jumping competition (HS-106m).

PubMed

Virmavirta, Mikko; Isolehto, Juha; Komi, Paavo; Schwameder, Hermann; Pigozzi, Fabio; Massazza, Giuseppe

2009-05-29

The take-off phase (approximately 6m) of the jumps of all athletes participating in the individual HS-106m hill ski jumping competition at the Torino Olympics was filmed with two high-speed cameras. The high altitude of the Pragelato ski jumping venue (1600m) and slight tail wind in the final jumping round were expected to affect the results of this competition. The most significant correlation with the length of the jump was found in the in-run velocity (r=0.628, p<0.001, n=50). This was a surprise in Olympic level ski jumping, and suggests that good jumpers simply had smaller friction between their skis and the in-run tracks and/or the aerodynamic quality of their in-run position was better. Angular velocity of the hip joint of the best jumpers was also correlated with jumping distance (r=0.651, p<0.05, n=10). The best jumpers in this competition exhibited very different take-off techniques, but still they jumped approximately the same distance. This certainly improves the interests in ski jumping among athletes and spectators. The comparison between the take-off techniques of the best jumpers showed that even though the more marked upper body movement creates higher air resistance, it does not necessarily result in shorter jumping distance if the exposure time to high air resistance is not too long. A comparison between the first and second round jumps of the same jumpers showed that the final results in this competition were at least partly affected by the wind conditions.

Computer simulation of the last support phase of the long jump.

PubMed

Chow, John W; Hay, James G

2005-01-01

The purpose was to examine the interacting roles played by the approach velocity, the explosive strength (represented by vertical ground reaction force [VGRF]), and the change in angular momentum about a transverse axis through the jumper's center of mass (deltaHzz) during the last support phase of the long jump, using a computer simulation technique. A two-dimensional inverted-pendulum-plus-foot segment model was developed to simulate the last support phase. Using a reference jump derived from a jump performance reported in the literature, the effects of varying individual parameters were studied using sensitivity analyses. In each sensitivity analysis, the kinematic characteristics of the longest jumps with the deltaHzz considered and not considered when the parameter of interest was altered were noted. A sensitivity analysis examining the influence of altering both approach velocity and VGRF at the same time was also conducted. The major findings were that 1) the jump distance was more sensitive to changes in approach velocity (e.g., a 10% increase yielded a 10.0% increase in jump distance) than to changes in the VGRF (e.g., a 10% increase yielded a 7.2% increase in jump distance); 2) the relatively large change in jump distance when both the approach velocity and VGRF were altered (e.g., a 10% increase in both parameters yielded a 20.4% increase in jump distance), suggesting that these two parameters are not independent factors in determining the jump distance; and 3) the jump distance was overestimated if the deltaHzz was not considered in the analysis.

Effects of fatigue and surface instability on neuromuscular performance during jumping.

PubMed

Lesinski, M; Prieske, O; Demps, M; Granacher, U

2016-10-01

It has previously been shown that fatigue and unstable surfaces affect jump performance. However, the combination thereof is unresolved. Thus, the purpose of this study was to examine the effects of fatigue and surface instability on jump performance and leg muscle activity. Twenty elite volleyball players (18 ± 2 years) performed repetitive vertical double-leg box jumps until failure. Before and after a fatigue protocol, jump performance (i.e., jump height) and electromyographic activity of selected lower limb muscles were recorded during drop jumps (DJs) and countermovement jumps (CMJs) on a force plate on stable and unstable surfaces (i.e., balance pad on top of force plate). Jump performance (3-7%; P < 0.05; 1.14 ≤ d ≤ 2.82), and muscle activity (2-27%; P < 0.05; 0.59 ≤ d ≤ 3.13) were lower following fatigue during DJs and CMJs, and on unstable compared with stable surfaces during DJs only (jump performance: 8%; P < 0.01; d = 1.90; muscle activity: 9-25%; P < 0.05; 1.08 ≤ d ≤ 2.54). No statistically significant interactions of fatigue by surface condition were observed. Our findings revealed that fatigue impairs neuromuscular performance during DJs and CMJs in elite volleyball players, whereas surface instability affects neuromuscular DJ performance only. Absent fatigue × surface interactions indicate that fatigue-induced changes in jump performance are similar on stable and unstable surfaces in jump-trained athletes. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Leg stiffness and expertise in men jumping.

PubMed

Laffaye, Guillaume; Bardy, Benoît G; Durey, Alain

2005-04-01

The aim of the present study is to investigate: a) the leg spring behavior in the one-leg vertical jump, b) the contribution of impulse parameters to this behavior, and c) the effect of jumping expertise on leg stiffness. Four categories of experts (handball, basketball, volleyball players, and Fosbury athletes), as well as novice subjects performed a run-and-jump test to touch a ball with the head. Five experimental conditions were tested from 55 to 95% of the maximum jump height. Kinematic and kinetic data were collected using six cameras and a force plate. The mechanical behavior of the musculoskeleton component of the human body can be modeled as a simple mass-spring system, from which leg stiffness values can be extracted to better understand energy transfer during running or jumping. The results indicate that leg stiffness (mean value of 11.5 kN.m) decreased with jumping height. Leg shortening at takeoff also increased with jumping height, whereas contact time decreased (-18%). No difference was found between experts and novices for leg stiffness. However, a principal components analysis (PCA) indicated the contribution of two main factors to the performance. The first factor emerged out of vertical force, stiffness, and duration of impulse. The second factor included leg shortening and jumping height. Differences between experts and novices were observed in terms of the contribution of leg stiffness to jump height, and more importantly, clear differences existed between experts in jumping parameters. The analysis performed on the sport categories indeed revealed different jumping profiles, characterized by specific, sport-related impulse parameters.

The trampoline aftereffect: the motor and sensory modulations associated with jumping on an elastic surface.

PubMed

Márquez, Gonzalo; Aguado, Xavier; Alegre, Luis M; Lago, Angel; Acero, Rafael M; Fernández-del-Olmo, Miguel

2010-08-01

After repeated jumps over an elastic surface (e.g. a trampoline), subjects usually report a strange sensation when they jump again overground (e.g. they feel unable to jump because their body feels heavy). However, the motor and sensory effects of exposure to an elastic surface are unknown. In the present study, we examined the motor and perceptual effects of repeated jumps over two different surfaces (stiff and elastic), measuring how this affected maximal countermovement vertical jump (CMJ). Fourteen subjects participated in two counterbalanced sessions, 1 week apart. Each experimental session consisted of a series of maximal CMJs over a force plate before and after 1 min of light jumping on an elastic or stiff surface. We measured actual motor performance (height jump and leg stiffness during CMJ) and how that related to perceptual experience (jump height estimation and subjective sensation). After repeated jumps on an elastic surface, the first CMJ showed a significant increase in leg stiffness (P < or = 0.01), decrease in jump height (P < or = 0.01) increase in perceptual misestimation (P < or = 0.05) and abnormal subjective sensation (P < or = 0.001). These changes were not observed after repeated jumps on a rigid surface. In a complementary experiment, continuous surface transitions show that the effects persist across cycles, and the effects over the leg stiffness and subjective experience are minimized (P < or = 0.05). We propose that these aftereffects could be the consequence of an erroneous internal model resulting from the high vertical forces produced by the elastic surface.

Sign realized jump risk and the cross-section of stock returns: Evidence from China's stock market

PubMed Central

Chao, Youcong; Liu, Xiaoqun; Guo, Shijun

2017-01-01

Using 5-minute high frequency data from the Chinese stock market, we employ a non-parametric method to estimate Fama-French portfolio realized jumps and investigate whether the estimated positive, negative and sign realized jumps could forecast or explain the cross-sectional stock returns. The Fama-MacBeth regression results show that not only have the realized jump components and the continuous volatility been compensated with risk premium, but also that the negative jump risk, the positive jump risk and the sign jump risk, to some extent, could explain the return of the stock portfolios. Therefore, we should pay high attention to the downside tail risk and the upside tail risk. PMID:28771514

Effect of liquid surface tension on circular and linear hydraulic jumps; theory and experiments

NASA Astrophysics Data System (ADS)

Bhagat, Rajesh Kumar; Jha, Narsing Kumar; Linden, Paul F.; Wilson, David Ian

2017-11-01

The hydraulic jump has attracted considerable attention since Rayleigh published his account in 1914. Watson (1964) proposed the first satisfactory explanation of the circular hydraulic jump by balancing the momentum and hydrostatic pressure across the jump, but this solution did not explain what actually causes the jump to form. Bohr et al. (1992) showed that the hydraulic jump happens close to the point where the local Froude number equals to one, suggesting a balance between inertial and hydrostatic contributions. Bush & Aristoff (2003) subsequently incorporated the effect of surface tension and showed that this is important when the jump radius is small. In this study, we propose a new account to explain the formation and evolution of hydraulic jumps under conditions where the jump radius is strongly influenced by the liquid surface tension. The theory is compared with experiments employing liquids of different surface tension and different viscosity, in circular and linear configurations. The model predictions and the experimental results show excellent agreement. Commonwealth Scholarship Commission, St. John's college, University of Cambridge.

Playing with inclined circular hydraulic jumps

NASA Astrophysics Data System (ADS)

Lebon, Luc; Saget, Beryl; Durand, Marc; Limat, Laurent; Couder, Yves; Receveur, Mathieu

2008-11-01

We have investigated the structure of the circular hydraulic jump, when the jet impacts an inclined plate. At low plate slope, quasi-circular shapes, evolving towards elliptic shapes are observed. At moderate inclinations, the upper and lower jumps become markedly different, and the lower jump is even rejected to infinity when a critical inclination is reached. Above this critical inclination, the jump is coupled to an outer dewetting contact line to give a specific object (expanding impact sheet feeding a curved rim in which the liquid is flowing tangentially). In this regime, both the position and curvature of the upper jump follows unusual scalings with the flow rate that completely differ from those observed on horizontal plates. Finally we have looked to metastable drops trapped in the circular jump at very small inclinations. As reported in a previous APS, the lowest position in the jump can become unstable and the drops oscillate around the jump perimeter. We show that this behavior requires very specific conditions of surface tension and viscosity and propose simple interpretations for the instability mechanism.

Valuation of exotic options in the framework of Levy processes

NASA Astrophysics Data System (ADS)

Milev, Mariyan; Georgieva, Svetla; Markovska, Veneta

2013-12-01

In this paper we explore a straightforward procedure to price derivatives by using the Monte Carlo approach when the underlying process is a jump-diffusion. We have compared the Black-Scholes model with one of its extensions that is the Merton model. The latter model is better in capturing the market's phenomena and is comparative to stochastic volatility models in terms of pricing accuracy. We have presented simulations of asset paths and pricing of barrier options for both Geometric Brownian motion and exponential Levy processes as it is the concrete case of the Merton model. A desired level of accuracy is obtained with simple computer operations in MATLAB for efficient computational time.

Jump Training in Youth Soccer Players: Effects of Haltere Type Handheld Loading.

PubMed

Rosas, F; Ramirez-Campillo, R; Diaz, D; Abad-Colil, F; Martinez-Salazar, C; Caniuqueo, A; Cañas-Jamet, R; Loturco, I; Nakamura, F Y; McKenzie, C; Gonzalez-Rivera, J; Sanchez-Sanchez, J; Izquierdo, M

2016-12-01

The aim of this study was to compare the effects of a jump training program, with or without haltere type handheld loading, on maximal intensity exercise performance. Youth soccer players (12.1±2.2 y) were assigned to either a jump training group (JG, n=21), a jump training group plus haltere type handheld loading (LJG, n=21), or a control group following only soccer training (CG, n=21). Athletes were evaluated for maximal-intensity performance measures before and after 6 weeks of training, during an in-season training period. The CG achieved a significant change in maximal kicking velocity only (ES=0.11-0.20). Both jump training groups improved in right leg (ES=0.28-0.45) and left leg horizontal countermovement jump with arms (ES=0.32-0.47), horizontal countermovement jump with arms (ES=0.28-0.37), vertical countermovement jump with arms (ES=0.26), 20-cm drop jump reactive strength index (ES=0.20-0.37), and maximal kicking velocity (ES=0.27-0.34). Nevertheless, compared to the CG, only the LJG exhibited greater improvements in all performance tests. Therefore, haltere type handheld loading further enhances performance adaptations during jump training in youth soccer players. © Georg Thieme Verlag KG Stuttgart · New York.

Tuning Superhydrophobic Nanostructures To Enhance Jumping-Droplet Condensation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulroe, Megan D.; Srijanto, Bernadeta R.; Ahmadi, S. Farzad

It was recently discovered that condensation growing on a nanostructured superhydrophobic surface can spontaneously jump off the surface, triggered by naturally occurring coalescence events. Many reports have observed that droplets must grow to a size of order 10 μm before jumping is enabled upon coalescence; however, it remains unknown how the critical jumping size relates to the topography of the underlying nanostructure. Here, we characterize the dynamic behavior of condensation growing on six different superhydrophobic nanostructures, where the topography of the nanopillars was systematically varied. The critical jumping diameter was observed to be highly dependent upon the height, diameter, andmore » pitch of the nanopillars: tall and slender nanopillars promoted 2 μm jumping droplets while short and stout nanopillars increased the critical size to over 20 μm. The topology of each surface is successfully correlated to the critical jumping diameter by constructing an energetic model that predicts how large a nucleating embryo needs to grow before it can inflate into the air with an apparent contact angle large enough for jumping. Furthermore, by extending our model to consider any possible surface, it is revealed that properly designed nanostructures should enable nanometric jumping droplets, which would further enhance jumping droplet condensers for heat transfer, anti-fogging, and anti-frosting applications.« less

Tuning Superhydrophobic Nanostructures To Enhance Jumping-Droplet Condensation

DOE PAGES

Mulroe, Megan D.; Srijanto, Bernadeta R.; Ahmadi, S. Farzad; ...

2017-07-18

It was recently discovered that condensation growing on a nanostructured superhydrophobic surface can spontaneously jump off the surface, triggered by naturally occurring coalescence events. Many reports have observed that droplets must grow to a size of order 10 μm before jumping is enabled upon coalescence; however, it remains unknown how the critical jumping size relates to the topography of the underlying nanostructure. Here, we characterize the dynamic behavior of condensation growing on six different superhydrophobic nanostructures, where the topography of the nanopillars was systematically varied. The critical jumping diameter was observed to be highly dependent upon the height, diameter, andmore » pitch of the nanopillars: tall and slender nanopillars promoted 2 μm jumping droplets while short and stout nanopillars increased the critical size to over 20 μm. The topology of each surface is successfully correlated to the critical jumping diameter by constructing an energetic model that predicts how large a nucleating embryo needs to grow before it can inflate into the air with an apparent contact angle large enough for jumping. Furthermore, by extending our model to consider any possible surface, it is revealed that properly designed nanostructures should enable nanometric jumping droplets, which would further enhance jumping droplet condensers for heat transfer, anti-fogging, and anti-frosting applications.« less

Yeast hexokinase. A fluorescence temperature-jump study of the kinetics of the binding of glucose to the monomer forms of hexokinases P-I and P-II.

PubMed

Hoggett, J G; Kellett, G L

1976-09-15

The binding of glucose to the monomeric forms of hexokinases P-I and P-II in Tris and phosphate buffers at pH 8.0 in the presence of 1 mol l-1 KCl has been studied using the fluorescence temperature-jump technique. For both isozymes only one relaxation time was observed; values of tau-1 increased linearly with increasing concentration of free reacting partners. The apparent second-order rate constant for association was about 2 X 10(6) 1 mol-1 s-1 for both isozymes; the differences in the stabilities of the complexes with P-I and P-II are entirely attributable to the fact that glucose dissociates more slowly from its complex with P-I than P-II (approximately 300 s-1 and 1100 s-1 respectively). Although the kinetic data are compatible with a single-step mechanism for glucose binding the association rate constant was much lower than that expected for a diffusion-limited rate of encounter. Other mechanisms for describing an induced-fit are discussed. It is shown that the data are incompatible with a slow 'prior-isomerization' pathway of substrate binding, but are consistent with a 'substrate-guided' pathway involving isomerization of the enzyme-substrate complex.

Lithium ion dynamics in Li2S+GeS2+GeO2 glasses studied using (7)Li NMR field-cycling relaxometry and line-shape analysis.

PubMed

Gabriel, Jan; Petrov, Oleg V; Kim, Youngsik; Martin, Steve W; Vogel, Michael

2015-09-01

We use (7)Li NMR to study the ionic jump motion in ternary 0.5Li2S+0.5[(1-x)GeS2+xGeO2] glassy lithium ion conductors. Exploring the "mixed glass former effect" in this system led to the assumption of a homogeneous and random variation of diffusion barriers in this system. We exploit that combining traditional line-shape analysis with novel field-cycling relaxometry, it is possible to measure the spectral density of the ionic jump motion in broad frequency and temperature ranges and, thus, to determine the distribution of activation energies. Two models are employed to parameterize the (7)Li NMR data, namely, the multi-exponential autocorrelation function model and the power-law waiting times model. Careful evaluation of both of these models indicates a broadly inhomogeneous energy landscape for both the single (x=0.0) and the mixed (x=0.1) network former glasses. The multi-exponential autocorrelation function model can be well described by a Gaussian distribution of activation barriers. Applicability of the methods used and their sensitivity to microscopic details of ionic motion are discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

Artificial Neural Networks: an overview and their use in the analysis of the AMPHORA-3 dataset.

PubMed

Buscema, Paolo Massimo; Massini, Giulia; Maurelli, Guido

2014-10-01

The Artificial Adaptive Systems (AAS) are theories with which generative algebras are able to create artificial models simulating natural phenomenon. Artificial Neural Networks (ANNs) are the more diffused and best-known learning system models in the AAS. This article describes an overview of ANNs, noting its advantages and limitations for analyzing dynamic, complex, non-linear, multidimensional processes. An example of a specific ANN application to alcohol consumption in Spain, as part of the EU AMPHORA-3 project, during 1961-2006 is presented. Study's limitations are noted and future needed research using ANN methodologies are suggested.

Neural pulse frequency modulation of an exponentially correlated Gaussian process

NASA Technical Reports Server (NTRS)

Hutchinson, C. E.; Chon, Y.-T.

1976-01-01

The effect of NPFM (Neural Pulse Frequency Modulation) on a stationary Gaussian input, namely an exponentially correlated Gaussian input, is investigated with special emphasis on the determination of the average number of pulses in unit time, known also as the average frequency of pulse occurrence. For some classes of stationary input processes where the formulation of the appropriate multidimensional Markov diffusion model of the input-plus-NPFM system is possible, the average impulse frequency may be obtained by a generalization of the approach adopted. The results are approximate and numerical, but are in close agreement with Monte Carlo computer simulation results.

Jump Horse Safety: Reconciling Public Debate and Australian Thoroughbred Jump Racing Data, 2012-2014.

PubMed

Ruse, Karen; Davison, Aidan; Bridle, Kerry

2015-10-22

Thoroughbred jump racing sits in the spotlight of contemporary welfare and ethical debates about horse racing. In Australia, jump racing comprises hurdle and steeplechase races and has ceased in all but two states, Victoria and South Australia. This paper documents the size, geography, composition, and dynamics of Australian jump racing for the 2012, 2013, and 2014 seasons with a focus on debate about risks to horses. We found that the majority of Australian jump racing is regional, based in Victoria, and involves a small group of experienced trainers and jockeys. Australian jump horses are on average 6.4 years of age. The jump career of the majority of horses involves participating in three or less hurdle races and over one season. Almost one quarter of Australian jump horses race only once. There were ten horse fatalities in races over the study period, with an overall fatality rate of 5.1 fatalities per 1000 horses starting in a jump race (0.51%). There was significant disparity between the fatality rate for hurdles, 0.75 fatalities per 1000 starts (0.075%) and steeplechases, 14 fatalities per 1000 starts (1.4%). Safety initiatives introduced by regulators in 2010 appear to have significantly decreased risks to horses in hurdles but have had little or no effect in steeplechases. Our discussion considers these Animals 2015, 5 1073 data in light of public controversy, political debate, and industry regulation related to jump horse safety.

A Correction Equation for Jump Height Measured Using the Just Jump System.

PubMed

McMahon, John J; Jones, Paul A; Comfort, Paul

2016-05-01

To determine the concurrent validity and reliability of the popular Just Jump system (JJS) for determining jump height and, if necessary, provide a correction equation for future reference. Eighteen male college athletes performed 3 bilateral countermovement jumps (CMJs) on 2 JJSs (alternative method) that were placed on top of a force platform (criterion method). Two JJSs were used to establish consistency between systems. Jump height was calculated from flight time obtained from the JJS and force platform. Intraclass correlation coefficients (ICCs) demonstrated excellent within-session reliability of the CMJ height measurement derived from both the JJS (ICC = .96, P < .001) and the force platform (ICC = .96, P < .001). Dependent t tests revealed that the JJS yielded a significantly greater CMJ jump height (0.46 ± 0.09 m vs 0.33 ± 0.08 m) than the force platform (P < .001, Cohen d = 1.39, power = 1.00). There was, however, an excellent relationship between CMJ heights derived from the JJS and force platform (r = .998, P < .001, power = 1.00), with a coefficient of determination (R2) of .995. Therefore, the following correction equation was produced: Criterion jump height = (0.8747 × alternative jump height) - 0.0666. The JJS provides a reliable but overestimated measure of jump height. It is suggested, therefore, that practitioners who use the JJS as part of future work apply the correction equation presented in this study to resultant jump-height values.

Improvement of Long-Jump Performance During Competition Using a Plyometric Exercise.

PubMed

Bogdanis, Gregory C; Tsoukos, Athanasios; Veligekas, Panagiotis

2017-02-01

To examine the acute effects of a conditioning plyometric exercise on long-jump performance during a simulated long-jump competition. Eight national-level track and field decathletes performed 6 long-jump attempts with a full approach run separated by 10-min recoveries. In the experimental condition subjects performed 3 rebound vertical jumps with maximal effort 3 min before the last 5 attempts, while the 1st attempt served as baseline. In the control condition the participants performed 6 long jumps without executing the conditioning exercise. Compared with baseline, long-jump performance progressively increased only in the experimental condition, from 3.0%, or 17.5 cm, in the 3rd attempt (P = .046, d = 0.56), to 4.8%, or 28.2 cm, in the 6th attempt (P = .0001, d = 0.84). The improvement in long-jump performance was due to a gradual increase in vertical takeoff velocity from the 3rd (by 8.7%, P = .0001, d = 1.82) to the 6th jump (by 17.7%, P = .0001, d = 4.38). Horizontal-approach velocity, takeoff duration, and horizontal velocity at takeoff were similar at all long-jump attempts in both conditions (P = .80, P = .36, and P = .15, respectively). Long-jump performance progressively improved during a simulated competition when a plyometric conditioning exercise was executed 3 min before each attempt. This improvement was due to a progressive increase in vertical velocity of takeoff, while there was no effect on the horizontal velocity.

Validation of the iPhone app using the force platform to estimate vertical jump height.

PubMed

Carlos-Vivas, Jorge; Martin-Martinez, Juan P; Hernandez-Mocholi, Miguel A; Perez-Gomez, Jorge

2018-03-01

Vertical jump performance has been evaluated with several devices: force platforms, contact mats, Vertec, accelerometers, infrared cameras and high-velocity cameras; however, the force platform is considered the gold standard for measuring vertical jump height. The purpose of this study was to validate an iPhone app called My Jump, that measures vertical jump height by comparing it with other methods that use the force platform to estimate vertical jump height, namely, vertical velocity at take-off and time in the air. A total of 40 sport sciences students (age 21.4±1.9 years) completed five countermovement jumps (CMJs) over a force platform. Thus, 200 CMJ heights were evaluated from the vertical velocity at take-off and the time in the air using the force platform, and from the time in the air with the My Jump mobile application. The height obtained was compared using the intraclass correlation coefficient (ICC). Correlation between APP and force platform using the time in the air was perfect (ICC=1.000, P<0.001). Correlation between APP and force platform using the vertical velocity at take-off was also very high (ICC=0.996, P<0.001), with an error margin of 0.78%. Therefore, these results showed that application, My Jump, is an appropriate method to evaluate the vertical jump performance; however, vertical jump height is slightly overestimated compared with that of the force platform.

Jump Shrug Height and Landing Forces Across Various Loads.

PubMed

Suchomel, Timothy J; Taber, Christopher B; Wright, Glenn A

2016-01-01

The purpose of this study was to examine the effect that load has on the mechanics of the jump shrug. Fifteen track and field and club/intramural athletes (age 21.7 ± 1.3 y, height 180.9 ± 6.6 cm, body mass 84.7 ± 13.2 kg, 1-repetition-maximum (1RM) hang power clean 109.1 ± 17.2 kg) performed repetitions of the jump shrug at 30%, 45%, 65%, and 80% of their 1RM hang power clean. Jump height, peak landing force, and potential energy of the system at jump-shrug apex were compared between loads using a series of 1-way repeated-measures ANOVAs. Statistical differences in jump height (P < .001), peak landing force (P = .012), and potential energy of the system (P < .001) existed; however, there were no statistically significant pairwise comparisons in peak landing force between loads (P > .05). The greatest magnitudes of jump height, peak landing force, and potential energy of the system at the apex of the jump shrug occurred at 30% 1RM hang power clean and decreased as the external load increased from 45% to 80% 1RM hang power clean. Relationships between peak landing force and potential energy of the system at jump-shrug apex indicate that the landing forces produced during the jump shrug may be due to the landing strategy used by the athletes, especially at lighter loads. Practitioners may prescribe heavier loads during the jump-shrug exercise without viewing landing force as a potential limitation.

Jumping robots: a biomimetic solution to locomotion across rough terrain.

PubMed

Armour, Rhodri; Paskins, Keith; Bowyer, Adrian; Vincent, Julian; Megill, William; Bomphrey, Richard

2007-09-01

This paper introduces jumping robots as a means to traverse rough terrain; such terrain can pose problems for traditional wheeled, tracked and legged designs. The diversity of jumping mechanisms found in nature is explored to support the theory that jumping is a desirable ability for a robot locomotion system to incorporate, and then the size-related constraints are determined from first principles. A series of existing jumping robots are presented and their performance summarized. The authors present two new biologically inspired jumping robots, Jollbot and Glumper, both of which incorporate additional locomotion techniques of rolling and gliding respectively. Jollbot consists of metal hoop springs forming a 300 mm diameter sphere, and when jumping it raises its centre of gravity by 0.22 m and clears a height of 0.18 m. Glumper is of octahedral shape, with four 'legs' that each comprise two 500 mm lengths of CFRP tube articulating around torsion spring 'knees'. It is able to raise its centre of gravity by 1.60 m and clears a height of 1.17 m. The jumping performance of the jumping robot designs presented is discussed and compared against some specialized jumping animals. Specific power output is thought to be the performance-limiting factor for a jumping robot, which requires the maximization of the amount of energy that can be stored together with a minimization of mass. It is demonstrated that this can be achieved through optimization and careful materials selection.

Investigation of water droplet dynamics in PEM fuel cell gas channels

NASA Astrophysics Data System (ADS)

Gopalan, Preethi

Water management in Proton Exchange Membrane Fuel Cell (PEMFC) has remained one of the most important issues that need to be addressed before its commercialization in automotive applications. Accumulation of water on the gas diffusion layer (GDL) surface in a PEMFC introduces a barrier for transport of reactant gases through the GDL to the catalyst layer. Despite the fact that the channel geometry is one of the key design parameters of a fluidic system, very limited research is available to study the effect of microchannel geometry on the two-phase flow structure. In this study, the droplet-wall dynamics and two-phase pressure drop across the water droplet present in a typical PEMFC channel, were examined in auto-competitive gas channel designs (0.4 x 0.7 mm channel cross section). The liquid water flow pattern inside the gas channel was analyzed for different air velocities. Experimental data was analyzed using the Concus-Finn condition to determine the wettability characteristics in the corner region. It was confirmed that the channel angle along with the air velocity and the channel material influences the water distribution and holdup within the channel. Dynamic contact angle emerged as an important parameter in controlling the droplet-wall interaction. Experiments were also performed to understand how the inlet location of the liquid droplet on the GDL surface affects the droplet dynamic behavior in the system. It was found that droplets emerging near the channel wall or under the land lead to corner filling of the channel. Improvements in the channel design has been proposed based on the artificial channel roughness created to act as capillary grooves to transport the liquid water away from the land area. For droplets emerging near the center of the channel, beside the filling and no-filling behavior reported in the literature, a new droplet jumping behavior was observed. As droplets grew and touched the sidewalls, they jumped off to the sidewall leaving the whole GDL exposed for gases to diffuse to the catalyst layer. A theoretical model was developed and a criterion was proposed to predict the droplet jumping behavior in the gas channel. A theoretical force balance model was proposed to predict the pressure force and air velocity required to remove the droplet from the channel to avoid complete channel blockage. The overall goal of this work was to identify the gas channel configuration that provides efficient water removal with a lower pressure drop in the system efficiency while meeting the US Department of Energy's specifications for a PEMFC for automotive application.

A Quantitative Comparison of Single-Dye Tracking Analysis Tools Using Monte Carlo Simulations

PubMed Central

McColl, James; Irvine, Kate L.; Davis, Simon J.; Gay, Nicholas J.; Bryant, Clare E.; Klenerman, David

2013-01-01

Single-particle tracking (SPT) is widely used to study processes from membrane receptor organization to the dynamics of RNAs in living cells. While single-dye labeling strategies have the benefit of being minimally invasive, this comes at the expense of data quality; typically a data set of short trajectories is obtained and analyzed by means of the mean square displacements (MSD) or the distribution of the particles’ displacements in a set time interval (jump distance, JD). To evaluate the applicability of both approaches, a quantitative comparison of both methods under typically encountered experimental conditions is necessary. Here we use Monte Carlo simulations to systematically compare the accuracy of diffusion coefficients (D-values) obtained for three cases: one population of diffusing species, two populations with different D-values, and a population switching between two D-values. For the first case we find that the MSD gives more or equally accurate results than the JD analysis (relative errors of D-values <6%). If two diffusing species are present or a particle undergoes a motion change, the JD analysis successfully distinguishes both species (relative error <5%). Finally we apply the JD analysis to investigate the motion of endogenous LPS receptors in live macrophages before and after treatment with methyl-β-cyclodextrin and latrunculin B. PMID:23737978

A quantitative comparison of single-dye tracking analysis tools using Monte Carlo simulations.

PubMed

Weimann, Laura; Ganzinger, Kristina A; McColl, James; Irvine, Kate L; Davis, Simon J; Gay, Nicholas J; Bryant, Clare E; Klenerman, David

2013-01-01

Single-particle tracking (SPT) is widely used to study processes from membrane receptor organization to the dynamics of RNAs in living cells. While single-dye labeling strategies have the benefit of being minimally invasive, this comes at the expense of data quality; typically a data set of short trajectories is obtained and analyzed by means of the mean square displacements (MSD) or the distribution of the particles' displacements in a set time interval (jump distance, JD). To evaluate the applicability of both approaches, a quantitative comparison of both methods under typically encountered experimental conditions is necessary. Here we use Monte Carlo simulations to systematically compare the accuracy of diffusion coefficients (D-values) obtained for three cases: one population of diffusing species, two populations with different D-values, and a population switching between two D-values. For the first case we find that the MSD gives more or equally accurate results than the JD analysis (relative errors of D-values <6%). If two diffusing species are present or a particle undergoes a motion change, the JD analysis successfully distinguishes both species (relative error <5%). Finally we apply the JD analysis to investigate the motion of endogenous LPS receptors in live macrophages before and after treatment with methyl-β-cyclodextrin and latrunculin B.

Transmembrane protein CD93 diffuses by a continuous time random walk.

NASA Astrophysics Data System (ADS)

Goiko, Maria; de Bruyn, John; Heit, Bryan

Molecular motion within the cell membrane is a poorly-defined process. In this study, we characterized the diffusion of the transmembrane protein CD93. By careful analysis of the dependence of the ensemble-averaged mean squared displacement (EA-MSD, r2) on time t and the ensemble-averaged, time-averaged MSD (EA-TAMSD, δ2) on lag time τ and total measurement time T, we showed that the motion of CD93 is well-described by a continuous-time random walk (CTRW). CD93 tracks were acquired using single particle tracking. The tracks were classified as confined or free, and the behavior of the MSD analyzed. EA-MSDs of both populations grew non-linearly with t, indicative of anomalous diffusion. Their EA-TAMSDs were found to depend on both τ and T, indicating non-ergodicity. Free molecules had r2 tα and δ2 (τ /T 1 - α) , with α 0 . 5 , consistent with a CTRW. Mean maximal excursion analysis supported this result. Confined CD93 had r2 t0 and δ2 (τ / T) α , with α 0 . 3 , consistent with a confined CTRW. CTRWs are described by a series of random jumps interspersed with power-law distributed waiting times, and may arise due to the interactions of CD93 with the endocytic machinery. NSERC.

Diffusive Cosmic-Ray Acceleration at Shock Waves of Arbitrary Speed with Magnetostatic Turbulence. I. General Theory and Correct Nonrelativistic Speed Limit

NASA Astrophysics Data System (ADS)

Schlickeiser, R.; Oppotsch, J.

2017-12-01

The analytical theory of diffusive acceleration of cosmic rays at parallel stationary shock waves of arbitrary speed with magnetostatic turbulence is developed from first principles. The theory is based on the diffusion approximation to the gyrotropic cosmic-ray particle phase-space distribution functions in the respective rest frames of the up- and downstream medium. We derive the correct cosmic-ray jump conditions for the cosmic-ray current and density, and match the up- and downstream distribution functions at the position of the shock. It is essential to account for the different particle momentum coordinates in the up- and downstream media. Analytical expressions for the momentum spectra of shock-accelerated cosmic rays are calculated. These are valid for arbitrary shock speeds including relativistic shocks. The correctly taken limit for nonrelativistic shock speeds leads to a universal broken power-law momentum spectrum of accelerated particles with velocities well above the injection velocity threshold, where the universal power-law spectral index q≃ 2-{γ }1-4 is independent of the flow compression ratio r. For nonrelativistic shock speeds, we calculate for the first time the injection velocity threshold, settling the long-standing injection problem for nonrelativistic shock acceleration.

Diffusive and rotational dynamics of condensed n-H2 confined in MCM-41

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prisk, Timothy R; Bryan, Matthew; Sokol, Paul E

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 reportedmore » 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.« less

Promoting balance and jumping skills in children with Down syndrome.

PubMed

Wang, Wai-Yi; Ju, Yun-Huei

2002-04-01

The purpose of this study was to investigate the changes in balance and qualitative and quantitative jumping performances by 20 children with Down syndrome (3 to 6 years) on jumping lessons. 30 typical children ages 3 to 6 years were recruited as a comparison group. Before the jumping lesson, a pretest was given subjects for balance and jumping skill measures based on the Motor Proficiency and Motor Skill Inventory, respectively. Subjects with Down syndrome received 3 sessions on jumping per week for 6 weeks but not the typical children. Then, a posttest was administered to all subjects. Analysis of covariance showed the pre- and posttest differences on scores for floor walk, beam walk, and horizontal and vertical jumping by subjects with Down syndrome were significantly greater than those for the typical children.

Neuromuscular adaptations to 4 weeks of intensive drop jump training in well-trained athletes

PubMed Central

Alkjaer, Tine; Meyland, Jacob; Raffalt, Peter C; Lundbye-Jensen, Jesper; Simonsen, Erik B

2013-01-01

This study examined the effects of 4 weeks of intensive drop jump training in well-trained athletes on jumping performance and underlying changes in biomechanics and neuromuscular adaptations. Nine well-trained athletes at high national competition level within sprinting and jumping disciplines participated in the study. The training was supervised and augmented feedback on performance was used to ensure maximal training intensity. The drop jumps were performed with minimal contact time and maximal jumping height. Assessment of performance during training showed effects of motor learning. Before and after the training intervention maximal isometric muscle strength, the biomechanics, muscle activity pattern of the lower extremities and the soleus H-reflex and V-wave during drop jumping were measured. Maximal jump height and performance index (PI) defined as jumping height divided by contact time improved significantly by 11.9% (P = 0.024) and 16.2% (P = 0.009), respectively. Combined ankle and knee joint peak power was significantly increased by 7% after training (P = 0.047). The preactivity in the soleus muscle decreased 16% (P = 0.015). The soleus H-reflex was unchanged after training, while the soleus V-wave increased significantly at 45 msec after touchdown. This may indicate an increased drive to the α-motor neuron pool following training. Muscle strength parameters were unaffected by the training. The results demonstrate that 4 weeks of intensive drop jump training can improve jumping performance also in well-trained athletes without concomitant changes in muscle strength. It is suggested that the behavioral improvement is primarily due to neural factors regulating the activation pattern controlling the drop jump movement. PMID:24303171

Effects of a Low-Load Gluteal Warm-Up on Explosive Jump Performance

PubMed Central

Comyns, Thomas; Kenny, Ian; Scales, Gerard

2015-01-01

The purpose of this study was to investigate the effects of a low-load gluteal warm-up protocol on countermovement and squat jump performance. Research by Crow et al. (2012) found that a low-load gluteal warm-up could be effective in enhancing peak power output during a countermovement jump. Eleven subjects performed countermovement and squat jumps before and after the gluteal warm-up protocol. Both jumps were examined in separate testing sessions and performed 30 seconds, and 2, 4, 6 & 8 minutes post warm-up. Height jumped and peak ground reaction force were the dependent variables examined in both jumps, with 6 additional variables related to fast force production being examined in the squat jump only. All jumps were performed on a force platform (AMTI OR6-5). Repeated measures analysis of variance found a number of significant differences (p ≤ 0.05) between baseline and post warm-up scores. Height jumped decreased significantly in both jumps at all rest intervals excluding 8 minutes. Improvement was seen in 7 of the 8 recorded SJ variables at the 8 minute interval. Five of these improvements were deemed statistically significant, namely time to peak GRF (43.0%), and time to the maximum rate of force development (65.7%) significantly decreased, while starting strength (63.4%), change of force in first 100 ms of contraction (49.1%) and speed strength (43.6%) significantly increased. The results indicate that a gluteal warm-up can enhance force production in squat jumps performed after 8 minutes recovery. Future research in this area should include additional warm-up intervention groups for comparative reasons. PMID:26240661

Immediate effects of different types of stretching exercises on badminton jump smash.

PubMed

Jang, Hwi S; Kim, Daeho; Park, Jihong

2018-01-01

Since different types of stretching exercises may alter athletic performance, we compared the effects of three types of stretching exercises on badminton jump smash. Sixteen male collegiate badminton players performed one of three different stretching exercises in a counterbalanced order on different days. Static stretching had seven typical stretches, while dynamic stretching involved nine dynamic movements, and resistance dynamic stretching was performed with weighted vests and dumbbells. Before and after each stretching exercise, subjects performed 20 trials of jump smashes. Dependent measurements were the jump heights during jump smashes, velocities of jump-smashed shuttlecocks, and drop point of jump-smashed shuttlecocks. To test the effects of each stretching exercise, we performed mixed model ANOVAs and calculated between-time effect sizes (ES). Each stretching exercise improved the jump heights during jump smashes (type main effect: F(2,75)=1.19, P=0.31; static stretching: 22.1%, P<0.01, ES=0.98; dynamic stretching: 30.1%, P<0.01, ES=1.49; resistance dynamic stretching: 17.7%, P=0.03, ES=0.98) and velocities of jump-smashed shuttlecocks (type main effect: F(2,75)=2.18, P=0.12; static stretching: 5.7%, P=0.61, ES=0.39; dynamic stretching: 3.4%, P=0.94, ES=0.28; resistance dynamic stretching: 6%, P=0.50, ES=0.66). However, there were no differences among the stretching exercises for any measurement. The drop point of jump-smashed shuttlecocks did not change (interaction: F(2,75)=0.88, P=0.42). All stretching exercises improved badminton jump smash performance, but we could not determine the best protocol. Since badminton requires high-speed movement and explosive force, we suggest performing dynamic stretching or resistance dynamic stretching.

Variability of Plyometric and Ballistic Exercise Technique Maintains Jump Performance.

PubMed

Chandler, Phillip T; Greig, Matthew; Comfort, Paul; McMahon, John J

2018-06-01

Chandler, PT, Greig, M, Comfort, P, and McMahon, JJ. Variability of plyometric and ballistic exercise technique maintains jump performance. J Strength Cond Res 32(6): 1571-1582, 2018-The aim of this study was to investigate changes in vertical jump technique over the course of a training session. Twelve plyometric and ballistic exercise-trained male athletes (age = 23.4 ± 4.6 years, body mass = 78.7 ± 18.8 kg, height = 177.1 ± 9.0 cm) performed 3 sets of 10 repetitions of drop jump (DJ), rebound jump (RJ) and squat jump (SJ). Each exercise was analyzed from touchdown to peak joint flexion and peak joint flexion to take-off. Squat jump was analyzed from peak joint flexion to take-off only. Jump height, flexion and extension time and range of motion, and instantaneous angles of the ankle, knee, and hip joints were measured. Separate 1-way repeated analyses of variance compared vertical jump technique across exercise sets and repetitions. Exercise set analysis found that SJ had lower results than DJ and RJ for the angle at peak joint flexion for the hip, knee, and ankle joints and take-off angle of the hip joint. Exercise repetition analysis found that the ankle joint had variable differences for the angle at take-off, flexion, and extension time for RJ. The knee joint had variable differences for flexion time for DJ and angle at take-off and touchdown for RJ. There was no difference in jump height. Variation in measured parameters across repetitions highlights variable technique across plyometric and ballistic exercises. This did not affect jump performance, but likely maintained jump performance by overcoming constraints (e.g., level of rate coding).

Short-Term Effects of Kinesio Taping on Muscle Recruitment Order During a Vertical Jump: A Pilot Study.

PubMed

Mendez-Rebolledo, Guillermo; Ramirez-Campillo, Rodrigo; Guzman-Muñoz, Eduardo; Gatica-Rojas, Valeska; Dabanch-Santis, Alexis; Diaz-Valenzuela, Francisco

2018-06-22

Kinesio taping is commonly used in sports and rehabilitation settings with the aim of prevention and treatment of musculoskeletal injuries. However, limited evidence exists regarding the effects of 24 and 72 hours of kinesio taping on trunk and lower limb neuromuscular and kinetic performance during a vertical jump. The purpose of this study was to analyze the short-term effects of kinesio taping on height and ground reaction force during a vertical jump, in addition to trunk and lower limb muscle latency and recruitment order. Single-group pretest-posttest. University laboratory. Twelve male athletes from different sports (track and field, basketball, and soccer). They completed a single squat and countermovement jump at basal time (no kinesio taping), 24, and 72 hours of kinesio taping application on the gluteus maximus, biceps femoris, rectus femoris, gastrocnemius medialis, and longissimus. Muscle onset latencies were assessed by electromyography during a squat and countermovement jump, in addition to measurements of the jump height and normalized ground reaction force. The kinesio taping had no effect after 24 hours on either the countermovement or squat jump. However, at 72 hours, the kinesio taping increased the jump height (P = .02; d = 0.36) and normalized ground reaction force (P = .001; d = 0.45) during the countermovement jump. In addition, 72-hour kinesio taping reduced longissimus onset latency (P = .03; d = 1.34) and improved muscle recruitment order during a countermovement jump. These findings suggest that kinesio taping may improve neuromuscular and kinetic performance during a countermovement jump only after 72 hours of application on healthy and uninjured male athletes. However, no changes were observed on a squat jump. Future studies should incorporate a control group to verify kinesio taping's effects and its influence on injured athletes.

Bilateral asymmetries in max effort single-leg vertical jumps.

PubMed

Stephens, Thomas M; Lawson, Brooke R; Reiser, Raoul F

2005-01-01

While asymmetries in the lower extremity during jumping may have implications during rehabilitation, it is not clear if healthy subjects should be expected to jump equivalently on each leg. Therefore, the goal of this study was to determine if asymmetries exist in maximal effort single-leg vertical jumps. After obtaining university-approved informed consent, 13 men and 12 women with competitive volleyball playing experience and no injuries of the lower-extremity that would predispose them to asymmetries participated. After thorough warm-up, five maximal effort vertical jumps with countermovement were performed on each leg (random order) with ground reaction forces and lower extremity kinematics recorded. The best three jumps from each leg were analyzed, assigning the leg with the highest jump height average as the dominant side. Asymmetry was assessed by determining statistical significance in the dominant versus non-dominant sides (p < 0.05). A significant interaction existed between side and gender for thigh length and peak vertical ground reaction force. Women had a significantly shorter thigh and men a greater peak vertical ground reaction force on their dominant side. All other parameters were assessed as whole group. Jumps were significantly greater off the dominant leg (2.8 cm on average). No other differences between sides were observed. Significant differences in magnitude (p < 0.05) existed between the men and women in jump height, several anthropometric parameters, minimum ankle and hip angles, and vertical ground reaction forces (peak and average). In conclusion, though a person may jump slightly higher on one leg relative to the other, and women may jump slightly differently than men, the magnitude of the difference should be relatively small and due to the multi-factorial nature of jump performance, individual parameters related to performance may not be consistently different.

The type of mat (Contact vs. Photocell) affects vertical jump height estimated from flight time.

PubMed

García-López, Juan; Morante, Juan C; Ogueta-Alday, Ana; Rodríguez-Marroyo, Jose A

2013-04-01

The purposes of this study were to analyze the validity and reliability of 2 photocell mats and to probe the possible influence of the type of mat (contact vs. photocell) on vertical jump height estimated from flight time. In 2 separate studies, 89 and 92 physical students performed 3 countermovement jumps that were simultaneously registered by a Force Plate (gold standard method), 2 photocell mats (SportJump System Pro and ErgoJump Plus), and a contact mat (SportJump-v1.0). The first study showed that the 2 photocell mats underestimated the vertical jump height (1.3 ± 0.2 cm and 5.9 ± 5.2 cm, respectively), but only SportJump System Pro showed a high correlation with the Force Plate (r = 0.999 and 0.676, respectively) and good intraday reliability (coefficient of variation = 2.98 and 15.94%, intraclass correlation coefficients = 0.95-0.97 and 0.45-0.57, respectively). The second study demonstrated a strong correlation (r = 0.994) between the 2 technologies (contact vs. photocell mats) with differences in vertical jump height of 2.0 ± 0.8 cm (95% confidence interval = 1.9-2.1 cm), which depended on both flight time and subjects' body mass. In conclusion, SportJump System Pro was a valid and reliable device. The new devices to measure vertical jump height from flight time should be validated. The type of mat (contact vs. photocell) affected approximately 6% the vertical jump height (approximately 2 cm in this study), which should be considered in further studies. The use of validated photocell mats instead of the contact mats was recommended.

Ballistic stretching increases flexibility and acute vertical jump height when combined with basketball activity.

PubMed

Woolstenhulme, Mandy T; Griffiths, Christine M; Woolstenhulme, Emily M; Parcell, Allen C

2006-11-01

Stretching is often included as part of a warm-up procedure for basketball activity. However, the efficacy of stretching with respect to sport performance has come into question. We determined the effects of 4 different warm-up protocols followed by 20 minutes of basketball activity on flexibility and vertical jump height. Subjects participated in 6 weeks (2 times per week) of warm-up and basketball activity. The warm-up groups participated in ballistic stretching, static stretching, sprinting, or basketball shooting (control group). We asked 3 questions. First, what effect does 6 weeks of warm-up exercise and basketball play have on both flexibility and vertical jump height? We measured sit and reach and vertical jump height before (week -1) and after (week 7) the 6 weeks. Flexibility increased for the ballistic, static, and sprint groups compared to the control group (p < 0.0001), while vertical jump height did not change for any of the groups. Our second question was what is the acute effect of each warm-up on vertical jump height? We measured vertical jump immediately after the warm-up on 4 separate occasions during the 6 weeks (at weeks 0, 2, 4, and 6). Vertical jump height was not different for any group. Finally, our third question was what is the acute effect of each warm-up on vertical jump height following 20 minutes of basketball play? We measured vertical jump height immediately following 20 minutes of basketball play at weeks 0, 2, 4, and 6. Only the ballistic stretching group demonstrated an acute increase in vertical jump 20 minutes after basketball play (p < 0.05). Coaches should consider using ballistic stretching as a warm-up for basketball play, as it is beneficial to vertical jump performance.

Jumping and Landing Techniques in Elite Women’s Volleyball

PubMed Central

Tillman, Mark D.; Hass, Chris J.; Brunt, Denis; Bennett, Gregg R.

2004-01-01

Volleyball has become one of the most widely played participant sports in the world. Participation requires expertise in many physical skills and performance is often dependent on an individual’s ability to jump and land. The incidence of injury in volleyball is similar to the rates reported for sports that are considered more physical contact sports. Though the most common source of injury in volleyball is the jump landing sequence, little research exists regarding the prevalence of jumping and landing techniques. The purpose of this study was to quantify the number of jumps performed by female volleyball players in competitive matches and to determine the relative frequency of different jump-landing techniques. Videotape recordings of two matches among four volleyball teams were analyzed for this study. Each activity was categorized by jump type (offensive spike or defensive block) and phase (jump or landing). Phase was subcategorized by foot use patterns (right, left, or both). Each of the players averaged nearly 22 jump-landings per game. Foot use patterns occurred in unequal amounts (p < 0.001) with over 50% of defensive landings occurring on one foot. Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to help prevent injuries in volleyball. Key Points The incidence of injury in volleyball is nearly equivalent to injury rates reported for ice hockey and soccer. Most injuries in volleyball occur during the jump landing sequence, but few data exist regarding jump landing techniques for elite female players. Our data indicate that the vast majority of jumps utilize two feet, but approximately half of landings occur with only one foot. Coaches, physical educators, and recreation providers may utilize the findings of this inquiry to prevent possible injuries in athletes, students, or those who participate in volleyball for recreational purposes. PMID:24497818

Jump Horse Safety: Reconciling Public Debate and Australian Thoroughbred Jump Racing Data, 2012–2014

PubMed Central

Ruse, Karen; Davison, Aidan; Bridle, Kerry

2015-01-01

Simple Summary This paper documents the dynamics of Australian thoroughbred jump racing in the 2012, 2013, and 2014 seasons with the aim of informing debate about risks to horses and the future of this activity. We conclude that the safety of Australian jump racing has improved in recent years but that steeplechases are considerably riskier for horses than hurdle races. Abstract Thoroughbred jump racing sits in the spotlight of contemporary welfare and ethical debates about horse racing. In Australia, jump racing comprises hurdle and steeplechase races and has ceased in all but two states, Victoria and South Australia. This paper documents the size, geography, composition, and dynamics of Australian jump racing for the 2012, 2013, and 2014 seasons with a focus on debate about risks to horses. We found that the majority of Australian jump racing is regional, based in Victoria, and involves a small group of experienced trainers and jockeys. Australian jump horses are on average 6.4 years of age. The jump career of the majority of horses involves participating in three or less hurdle races and over one season. Almost one quarter of Australian jump horses race only once. There were ten horse fatalities in races over the study period, with an overall fatality rate of 5.1 fatalities per 1000 horses starting in a jump race (0.51%). There was significant disparity between the fatality rate for hurdles, 0.75 fatalities per 1000 starts (0.075%) and steeplechases, 14 fatalities per 1000 starts (1.4%). Safety initiatives introduced by regulators in 2010 appear to have significantly decreased risks to horses in hurdles but have had little or no effect in steeplechases. Our discussion considers these data in light of public controversy, political debate, and industry regulation related to jump horse safety. PMID:26506396

Predicting vertical jump height from bar velocity.

PubMed

García-Ramos, Amador; Štirn, Igor; Padial, Paulino; Argüelles-Cienfuegos, Javier; De la Fuente, Blanca; Strojnik, Vojko; Feriche, Belén

2015-06-01

The objective of the study was to assess the use of maximum (Vmax) and final propulsive phase (FPV) bar velocity to predict jump height in the weighted jump squat. FPV was defined as the velocity reached just before bar acceleration was lower than gravity (-9.81 m·s(-2)). Vertical jump height was calculated from the take-off velocity (Vtake-off) provided by a force platform. Thirty swimmers belonging to the National Slovenian swimming team performed a jump squat incremental loading test, lifting 25%, 50%, 75% and 100% of body weight in a Smith machine. Jump performance was simultaneously monitored using an AMTI portable force platform and a linear velocity transducer attached to the barbell. Simple linear regression was used to estimate jump height from the Vmax and FPV recorded by the linear velocity transducer. Vmax (y = 16.577x - 16.384) was able to explain 93% of jump height variance with a standard error of the estimate of 1.47 cm. FPV (y = 12.828x - 6.504) was able to explain 91% of jump height variance with a standard error of the estimate of 1.66 cm. Despite that both variables resulted to be good predictors, heteroscedasticity in the differences between FPV and Vtake-off was observed (r(2) = 0.307), while the differences between Vmax and Vtake-off were homogenously distributed (r(2) = 0.071). These results suggest that Vmax is a valid tool for estimating vertical jump height in a loaded jump squat test performed in a Smith machine. Key pointsVertical jump height in the loaded jump squat can be estimated with acceptable precision from the maximum bar velocity recorded by a linear velocity transducer.The relationship between the point at which bar acceleration is less than -9.81 m·s(-2) and the real take-off is affected by the velocity of movement.Mean propulsive velocity recorded by a linear velocity transducer does not appear to be optimal to monitor ballistic exercise performance.

Traditional vs. Sport-Specific Vertical Jump Tests: Reliability, Validity, and Relationship With the Legs Strength and Sprint Performance in Adult and Teen Soccer and Basketball Players.

PubMed

Rodríguez-Rosell, David; Mora-Custodio, Ricardo; Franco-Márquez, Felipe; Yáñez-García, Juan M; González-Badillo, Juan J

2017-01-01

Rodríguez-Rosell, D, Mora-Custodio, R, Franco-Márquez, F, Yáñez-García, JM, González-Badillo, JJ. Traditional vs. sport-specific vertical jump tests: reliability, validity, and relationship with the legs strength and sprint performance in adult and teen soccer and basketball players. J Strength Cond Res 31(1): 196-206, 2017-The vertical jump is considered an essential motor skill in many team sports. Many protocols have been used to assess vertical jump ability. However, controversy regarding test selection still exists based on the reliability and specificity of the tests. The main aim of this study was to analyze the reliability and validity of 2 standardized (countermovement jump [CMJ] and Abalakov jump [AJ]) and 2 sport-specific (run-up with 2 [2-LEGS] or 1 leg [1-LEG] take-off jump) vertical jump tests, and their usefulness as predictors of sprint and strength performance for soccer (n = 127) and basketball (n = 59) players in 3 different categories (Under-15, Under-18, and Adults). Three attempts for each of the 4 jump tests were recorded. Twenty-meter sprint time and estimated 1 repetition maximum in full squat were also evaluated. All jump tests showed high intraclass correlation coefficients (0.969-0.995) and low coefficients of variation (1.54-4.82%), although 1-LEG was the jump test with the lowest absolute and relative reliability. All selected jump tests were significantly correlated (r = 0.580-0.983). Factor analysis resulted in the extraction of one principal component, which explained 82.90-95.79% of the variance of all jump tests. The 1-LEG test showed the lowest associations with sprint and strength performance. The results of this study suggest that CMJ and AJ are the most reliable tests for the estimation of explosive force in soccer and basketball players in different age categories.

Predicting Vertical Jump Height from Bar Velocity

PubMed Central

García-Ramos, Amador; Štirn, Igor; Padial, Paulino; Argüelles-Cienfuegos, Javier; De la Fuente, Blanca; Strojnik, Vojko; Feriche, Belén

2015-01-01

The objective of the study was to assess the use of maximum (Vmax) and final propulsive phase (FPV) bar velocity to predict jump height in the weighted jump squat. FPV was defined as the velocity reached just before bar acceleration was lower than gravity (-9.81 m·s-2). Vertical jump height was calculated from the take-off velocity (Vtake-off) provided by a force platform. Thirty swimmers belonging to the National Slovenian swimming team performed a jump squat incremental loading test, lifting 25%, 50%, 75% and 100% of body weight in a Smith machine. Jump performance was simultaneously monitored using an AMTI portable force platform and a linear velocity transducer attached to the barbell. Simple linear regression was used to estimate jump height from the Vmax and FPV recorded by the linear velocity transducer. Vmax (y = 16.577x - 16.384) was able to explain 93% of jump height variance with a standard error of the estimate of 1.47 cm. FPV (y = 12.828x - 6.504) was able to explain 91% of jump height variance with a standard error of the estimate of 1.66 cm. Despite that both variables resulted to be good predictors, heteroscedasticity in the differences between FPV and Vtake-off was observed (r2 = 0.307), while the differences between Vmax and Vtake-off were homogenously distributed (r2 = 0.071). These results suggest that Vmax is a valid tool for estimating vertical jump height in a loaded jump squat test performed in a Smith machine. Key points Vertical jump height in the loaded jump squat can be estimated with acceptable precision from the maximum bar velocity recorded by a linear velocity transducer. The relationship between the point at which bar acceleration is less than -9.81 m·s-2 and the real take-off is affected by the velocity of movement. Mean propulsive velocity recorded by a linear velocity transducer does not appear to be optimal to monitor ballistic exercise performance. PMID:25983572

Does plyometric training improve vertical jump height? A meta-analytical review.

PubMed

Markovic, Goran

2007-06-01

The aim of this study was to determine the precise effect of plyometric training (PT) on vertical jump height in healthy individuals. Meta-analyses of randomised and non-randomised controlled trials that evaluated the effect of PT on four typical vertical jump height tests were carried out: squat jump (SJ); countermovement jump (CMJ); countermovement jump with the arm swing (CMJA); and drop jump (DJ). Studies were identified by computerised and manual searches of the literature. Data on changes in jump height for the plyometric and control groups were extracted and statistically pooled in a meta-analysis, separately for each type of jump. A total of 26 studies yielding 13 data points for SJ, 19 data points for CMJ, 14 data points for CMJA and 7 data points for DJ met the initial inclusion criteria. The pooled estimate of the effect of PT on vertical jump height was 4.7% (95% CI 1.8 to 7.6%), 8.7% (95% CI 7.0 to 10.4%), 7.5% (95% CI 4.2 to 10.8%) and 4.7% (95% CI 0.8 to 8.6%) for the SJ, CMJ, CMJA and DJ, respectively. When expressed in standardised units (ie, effect sizes), the effect of PT on vertical jump height was 0.44 (95% CI 0.15 to 0.72), 0.88 (95% CI 0.64 to 1.11), 0.74 (95% CI 0.47 to 1.02) and 0.62 (95% CI 0.18 to 1.05) for the SJ, CMJ, CMJA and DJ, respectively. PT provides a statistically significant and practically relevant improvement in vertical jump height with the mean effect ranging from 4.7% (SJ and DJ), over 7.5% (CMJA) to 8.7% (CMJ). These results justify the application of PT for the purpose of development of vertical jump performance in healthy individuals.

Manifestations of Proprioception During Vertical Jumps to Specific Heights

PubMed Central

Struzik, Artur; Pietraszewski, Bogdan; Winiarski, Sławomir; Juras, Grzegorz; Rokita, Andrzej

2017-01-01

Abstract Artur, S, Bogdan, P, Kawczyński, A, Winiarski, S, Grzegorz, J, and Andrzej, R. Manifestations of proprioception during vertical jumps to specific heights. J Strength Cond Res 31(6): 1694–1701, 2017—Jumping and proprioception are important abilities in many sports. The efficiency of the proprioceptive system is indirectly related to jumps performed at specified heights. Therefore, this study recorded the ability of young athletes who play team sports to jump to a specific height compared with their maximum ability. A total of 154 male (age: 14.8 ± 0.9 years, body height: 181.8 ± 8.9 cm, body weight: 69.8 ± 11.8 kg, training experience: 3.8 ± 1.7 years) and 151 female (age: 14.1 ± 0.8 years, body height: 170.5 ± 6.5 cm, body weight: 60.3 ± 9.4 kg, training experience: 3.7 ± 1.4 years) team games players were recruited for this study. Each participant performed 2 countermovement jumps with arm swing to 25, 50, 75, and 100% of the maximum height. Measurements were performed using a force plate. Jump height and its accuracy with respect to a specified height were calculated. The results revealed no significant differences in jump height and its accuracy to the specified heights between the groups (stratified by age, sex, and sport). Individuals with a higher jumping accuracy also exhibited greater maximum jump heights. Jumps to 25% of the maximum height were approximately 2 times higher than the target height. The decreased jump accuracy to a specific height when attempting to jump to lower heights should be reduced with training, particularly among athletes who play team sports. These findings provide useful information regarding the proprioceptive system for team sport coaches and may shape guidelines for training routines by working with submaximal loads. PMID:28538322

Movement Analysis Applied to the Basketball Jump Shot--Part II.

ERIC Educational Resources Information Center

Martin, Thomas P.

1981-01-01

The jump shot is one of the most important shots in the game of basketball. The movement analysis of the jump shot designates four phases: (1) preparatory position; (2) movement phase I (crouch); (3) movement phase II (jump); and (4) follow-through. (JN)

A Survey of Bioinspired Jumping Robot: Takeoff, Air Posture Adjustment, and Landing Buffer

PubMed Central

2017-01-01

A bioinspired jumping robot has a strong ability to overcome obstacles. It can be applied to the occasion with complex and changeable environment, such as detection of planet surface, postdisaster relief, and military reconnaissance. So the bioinspired jumping robot has broad application prospect. The jumping process of the robot can be divided into three stages: takeoff, air posture adjustment, and landing buffer. The motivation of this review is to investigate the research results of the most published bioinspired jumping robots for these three stages. Then, the movement performance of the bioinspired jumping robots is analyzed and compared quantitatively. Then, the limitation of the research on bioinspired jumping robots is discussed, such as the research on the mechanism of biological motion is not thorough enough, the research method about structural design, material applications, and control are still traditional, and energy utilization is low, which make the robots far from practical applications. Finally, the development trend is summarized. This review provides a reference for further research of bioinspired jumping robots. PMID:29311756

Low peak jump power is associated with elevated odds of dysmobility syndrome in community-dwelling elderly individuals: the Korean Urban Rural Elderly (KURE) study.

PubMed

Hong, Namki; Kim, Chang Oh; Youm, Yoosik; Kim, Hyeon Chang; Rhee, Yumie

2018-06-01

In a community-dwelling elderly cohort (Korean Urban Rural Elderly), low peak jump power was associated with elevated odds of dysmobility syndrome and its components, independent of age and comorbidities. Jump power measurement improved discrimination of individuals with dysmobility syndrome when added to conventional risk factors. Dysmobility syndrome was proposed to encompass the risks affecting musculoskeletal outcomes. Jump power measurement is a safe, reproducible high-intensity test for physical function in elderly. However, the relationship between jump power and dysmobility syndrome remains unknown. A total of 1369 subjects (mean 71.6 years; women, 66%) were analyzed from a community-based cohort. Dysmobility syndrome was defined as the presence of ≥ 3 factors among falls in the preceding year, low lean mass, high fat mass, osteoporosis, low grip strength, and low timed get-up-and-go (TUG) performance. Subjects were grouped into tertiles of jump power relative to weight based on sex-stratified cutoffs (32.4 and 27.6 W/kg in men; 23.9 and 19.9 W/kg in women) or into the failed-to-jump group. The prevalence of dysmobility syndrome was 20% overall, increasing from the highest (T1) to lowest (T3) jump power tertile (1, 11, 15% in men; 11, 16, 39% in women) and the failed-to-jump group (39% in men; 48% in women). Low jump power or failed-to-jump was associated with elevated odds of dysmobility syndrome (T3 vs. T1, adjusted odds ratio [aOR] 4.35, p < 0.001; failed-to-jump vs. T1, aOR 7.60, p < 0.001) and its components including falls, low lean mass, high fat mass, and poor TUG performance but not osteoporosis after adjustment for covariates. Jump power modestly discriminated dysmobility syndrome (area under the curve [AUC], 0.71, p < 0.001), which improved discriminatory performance when added to conventional risk factors (AUC, from 0.75 to 0.79, p < 0.001). Low peak jump power was associated with elevated odds of dysmobility syndrome and its components, independent of age and comorbidities.

Acceleration and Orientation Jumping Performance Differences Among Elite Professional Male Handball Players With or Without Previous ACL Reconstruction: An Inertial Sensor Unit-Based Study.

PubMed

Setuain, Igor; González-Izal, Miriam; Alfaro, Jesús; Gorostiaga, Esteban; Izquierdo, Mikel

2015-12-01

Handball is one of the most challenging sports for the knee joint. Persistent biomechanical and jumping capacity alterations can be observed in athletes with an anterior cruciate ligament (ACL) injury. Commonly identified jumping biomechanical alterations have been described by the use of laboratory technologies. However, portable and easy-to-handle technologies that enable an evaluation of jumping biomechanics at the training field are lacking. To analyze unilateral/bilateral acceleration and orientation jumping performance differences among elite male handball athletes with or without previous ACL reconstruction via a single inertial sensor unit device. Case control descriptive study. At the athletes' usual training court. Twenty-two elite male (6 ACL-reconstructed and 16 uninjured control players) handball players were evaluated. The participants performed a vertical jump test battery that included a 50-cm vertical bilateral drop jump, a 20-cm vertical unilateral drop jump, and vertical unilateral countermovement jump maneuvers. Peak 3-dimensional (X, Y, Z) acceleration (m·s(-2)), jump phase duration and 3-dimensional orientation values (°) were obtained from the inertial sensor unit device. Two-tailed t-tests and a one-way analysis of variance were performed to compare means. The P value cut-off for significance was set at P < .05. The ACL-reconstructed male athletes did not show any significant (P < .05) residual jumping biomechanical deficits regarding the measured variables compared with players who had not suffered this knee injury. A dominance effect was observed among non-ACL reconstructed controls but not among their ACL-reconstructed counterparts (P < .05). Elite male handball athletes with previous ACL reconstruction demonstrated a jumping biomechanical profile similar to control players, including similar jumping performance values in both bilateral and unilateral jumping maneuvers, several years after ACL reconstruction. These findings are in agreement with previous research showing full functional restoration of abilities in top-level male athletes after ACL reconstruction, rehabilitation and subsequent return to sports at the previous level. Copyright © 2015 American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved.

Non-Local Diffusion of Energetic Electrons during Solar Flares

NASA Astrophysics Data System (ADS)

Bian, N. H.; Emslie, G.; Kontar, E.

2017-12-01

The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.

Aeromechanics of the Spider Cricket Jump: How to Jump 60+ Times Your Body Length and Still Land on Your Feet

NASA Astrophysics Data System (ADS)

Palmer, Emily; Deshler, Nicolas; Gorman, David; Neves, Catarina; Mittal, Rajat

2015-11-01

Flapping, gliding, running, crawling and swimming have all been studied extensively in the past and have served as a source of inspiration for engineering designs. In the current project, we explore a mode of locomotion that straddles ground and air: jumping. The subject of our study is among the most proficient of long-jumpers in Nature: the spider cricket of the family Rhaphidophoridae, which can jump more than 60 times its body length. Despite jumping this immense distance, these crickets usually land on their feet, indicating an ability to control their posture during ``flight.'' We employ high-speed videogrammetry, to examine the jumps and to track the crickets' posture and appendage orientation throughout their jumps. Simple aerodynamic models are developed to predict the aerodynamic forces and moment on the crickets during `flight`. The analysis shows that these wingless insects employ carefully controlled and coordinated positioning of the limbs during flight so as to increase jump distance and to stabilize body posture during flight. The principles distilled from this study could serve as an inspiration for small jumping robots that can traverse complex terrains.

Immediate Effects of Different Trunk Exercise Programs on Jump Performance.

PubMed

Imai, A; Kaneoka, K; Okubo, Y; Shiraki, H

2016-03-01

The aim of this study was to investigate the immediate effects of trunk stabilization exercise (SE) and conventional trunk exercise (CE) programs on jump performance. 13 adolescent male soccer players performed 2 kinds of jump testing before and immediate after 3 experimental conditions: SE, CE, and non-exercise (NE). The SE program consisted of the elbow-toe, hand-knee, and back bridge, and the CE program consisted of the sit-up, sit-up with trunk rotation and back extension. Testing of a countermovement jump (CMJ) and rebound jump (RJ) were performed to assess jump performance. Jump height of the CMJ and RJ-index, contact time, and jump height of the RJ were analyzed. The RJ index was improved significantly only after SE (p=0.017). However, contact time and jump height did not improve significantly in the SE condition. Moreover, no significant interaction or main effects of time or group were observed in the CMJ. Consequently, this study showed the different immediate effect on the RJ between the SE and CE, and suggested the possibility that the SE used in this study is useful as a warm-up program to improve the explosive movements. © Georg Thieme Verlag KG Stuttgart · New York.

Ultrafast NMR diffusion measurements exploiting chirp spin echoes.

PubMed

Ahola, Susanna; Mankinen, Otto; Telkki, Ville-Veikko

2017-04-01

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Stress, social support, emotional regulation, and exacerbation of diffuse plaque psoriasis.

PubMed

Picardi, A; Mazzotti, E; Gaetano, P; Cattaruzza, M S; Baliva, G; Melchi, C F; Biondi, M; Pasquini, P

2005-01-01

The authors' aim was to investigate the role of stressful events, perceived social support, attachment security, and alexithymia in triggering exacerbations of diffuse plaque psoriasis. Inpatients experiencing a recent exacerbation of diffuse plaque psoriasis (N=33) were compared with inpatients with skin conditions believed to have a negligible psychosomatic component (N=73). Stressful events during the last year were assessed with Paykel's Interview for Recent Life Events. Attachment style, alexithymia, and perceived social support were assessed with the Experiences in Close Relationships questionnaire, the Toronto Alexithymia Scale, and the Multidimensional Scale of Perceived Social Support, respectively. Multiple logistic regression analysis was used to control for age, gender, education, marital status, and alcohol consumption. In relation to comparison subjects, the patients with psoriasis had lower perceived social support and higher attachment-related avoidance. Also, they were more likely to have high alexithymic characteristics. There were no differences between the patients with psoriasis and the comparison subjects in scores on the Experiences in Close Relationships anxiety scale, the total number of stressful events, and the number of undesirable, uncontrollable, or major events. Although caution should be applied in generalizing these findings to outpatients, this study suggests that alexithymia, attachment-related avoidance, and poor social support might increase susceptibility to exacerbations of diffuse plaque psoriasis, possibly through impaired emotional regulation. Several physiological mechanisms involving the neuroendocrine and the immune system might mediate the interplay between stress, personality, and diffuse plaque psoriasis.

Neuromechanical simulation of the locust jump

PubMed Central

Cofer, D.; Cymbalyuk, G.; Heitler, W. J.; Edwards, D. H.

2010-01-01

The neural circuitry and biomechanics of kicking in locusts have been studied to understand their roles in the control of both kicking and jumping. It has been hypothesized that the same neural circuit and biomechanics governed both behaviors but this hypothesis was not testable with current technology. We built a neuromechanical model to test this and to gain a better understanding of the role of the semi-lunar process (SLP) in jump dynamics. The jumping and kicking behaviors of the model were tested by comparing them with a variety of published data, and were found to reproduce the results from live animals. This confirmed that the kick neural circuitry can produce the jump behavior. The SLP is a set of highly sclerotized bands of cuticle that can be bent to store energy for use during kicking and jumping. It has not been possible to directly test the effects of the SLP on jump performance because it is an integral part of the joint, and attempts to remove its influence prevent the locust from being able to jump. Simulations demonstrated that the SLP can significantly increase jump distance, power, total energy and duration of the jump impulse. In addition, the geometry of the joint enables the SLP force to assist leg flexion when the leg is flexed, and to assist extension once the leg has begun to extend. PMID:20228342

Loaded and unloaded jump performance of top-level volleyball players from different age categories

PubMed Central

Kitamura, Katia; Pereira, Lucas Adriano; Kobal, Ronaldo; Cal Abad, Cesar Cavinato; Finotti, Ronaldo; Nakamura, Fábio Yuzo

2017-01-01

The aim of this study was to investigate the differences in loaded and unloaded jump performances between different age categories of top-level volleyball players from the same club. Forty-three volleyball players were divided into four age groups: under-17, under-19, under-21 and professional. Vertical jumping height for squat jump (SJ), countermovement jump (CMJ) and CMJ with arm swing (CMJa) and mean propulsive velocity (MPV) in the loaded jump squat exercise with 40% of the athlete’s body mass were compared among the different age categories, considering body mass as a covariate. SJ and CMJ jump height values were higher for professional and under-21 players than under-17 players (p<0.05). CMJa height was higher for under-21 players than under-19 and under-17 players (p<0.05). MPV in the loaded jump squat was higher for under-21 players than under-17 players (p<0.05). From a general perspective, these results suggest that aging per se is not capable of substantially improving loaded and unloaded vertical jump performances across different age categories of top-level volleyball players. Therefore, to increase the vertical jumping ability of these team sport athletes throughout their long-term development, coaches and strength and conditioning professionals are encouraged to implement consistent neuromuscular training strategies, in accordance with the specific needs and physiological characteristics of each age group. PMID:29158621

Validation of the VERT wearable jump monitor device in elite youth volleyball players

PubMed Central

Borges, Thiago O.; Moreira, Alexandre; Bacchi, Renato; Finotti1, Ronaldo L.; Ramos, Mayara; Lopes, Charles R.

2017-01-01

This technical report aims to determine the validity and the accuracy of the VERT Wearable Jump Monitor. The participants of this study were all experienced volleyball players from the U18 category from the Brazilian National team. To assess jump performance, the VERT scores were compared to the VERTEC (jump and reach device). Each athlete performed 3 attack and 3 block jumps in a random, counterbalanced order, and the average score was registered. In the attack jumps, the VERTEC and VERT mean ± SD scores were 70.9±8.2 and 76.3±7.5 cm, respectively, and the typical error of the estimate (TEE) as a coefficient of variation (CV) was 7.8% (90% CL 7.0 to 8.9%). VERTEC and VERT devices presented a very large Pearson’s correlation for attack jumps (r=0.75; 90% CL 0.68 to 0.81). In addition, the mean±SD block jumps were 53.7±6.1 and 58.5±5.7 cm for the VERTEC and VERT, respectively and the TEE as a CV was 7.9% (90% CL 7.1 to 8.9%). Pearson’s correlation coefficient was very large for block jumps (r=0.75; 90% CL 0.67 to 0.81). The VERT device was found to be a very practical tool to quantify jump performance in volleyball players. PMID:29158616

Validity of a Jump Mat for assessing Countermovement Jump Performance in Elite Rugby Players.

PubMed

Dobbin, Nick; Hunwicks, Richard; Highton, Jamie; Twist, Craig

2017-02-01

This study determined the validity of the Just Jump System ® (JJS) for measuring flight time, jump height and peak power output (PPO) in elite rugby league players. 37 elite rugby league players performed 6 countermovement jumps (CMJ; 3 with and 3 without arms) on a jump mat and force platform. A sub-sample (n=28) was used to cross-validate the equations for flight time, jump height and PPO. The JJS systematically overestimated flight time and jump height compared to the force platform (P<0.05), but demonstrated strong associations for flight time ( with R 2 =0.938; without R 2 =0.972) and jump height ( with R 2 =0.945; without R 2 =0.987). Our equations revealed no systematic difference between corrected and force platform scores and an improved the agreement for flight time (Ratio limits of agreement: with 1.00 vs. 1.36; without 1.00 vs. 1.16) and jump height ( with 1.01 vs. 1.34; without 1.01 vs. 1.15), meaning that our equations can be used to correct JJS scores for elite rugby players. While our equation improved the estimation of PPO ( with 1.02; without 1.01) compared to existing equations (Harman: 1.20; Sayers: 1.04), this only accounted for 64 and 69% of PPO. © Georg Thieme Verlag KG Stuttgart · New York.

Loaded and unloaded jump performance of top-level volleyball players from different age categories.

PubMed

Kitamura, Katia; Pereira, Lucas Adriano; Kobal, Ronaldo; Cal Abad, Cesar Cavinato; Finotti, Ronaldo; Nakamura, Fábio Yuzo; Loturco, Irineu

2017-09-01

The aim of this study was to investigate the differences in loaded and unloaded jump performances between different age categories of top-level volleyball players from the same club. Forty-three volleyball players were divided into four age groups: under-17, under-19, under-21 and professional. Vertical jumping height for squat jump (SJ), countermovement jump (CMJ) and CMJ with arm swing (CMJa) and mean propulsive velocity (MPV) in the loaded jump squat exercise with 40% of the athlete's body mass were compared among the different age categories, considering body mass as a covariate. SJ and CMJ jump height values were higher for professional and under-21 players than under-17 players (p<0.05). CMJa height was higher for under-21 players than under-19 and under-17 players (p<0.05). MPV in the loaded jump squat was higher for under-21 players than under-17 players (p<0.05). From a general perspective, these results suggest that aging per se is not capable of substantially improving loaded and unloaded vertical jump performances across different age categories of top-level volleyball players. Therefore, to increase the vertical jumping ability of these team sport athletes throughout their long-term development, coaches and strength and conditioning professionals are encouraged to implement consistent neuromuscular training strategies, in accordance with the specific needs and physiological characteristics of each age group.

Characteristics of Air Entrainment in Hydraulic Jump

NASA Astrophysics Data System (ADS)

Albarkani, M. S. S.; Tan, L. W.; Al-Gheethi, A.

2018-04-01

The characteristics of hydraulic jump, especially the air entrainment within jump is still not properly understood. Therefore, the current work aimed to determine the size and number of air entrainment formed in hydraulic jump at three different Froude numbers and to obtain the relationship between Froude number with the size and number of air entrainment in hydraulic jump. Experiments of hydraulic jump were conducted in a 10 m long and 0.3 m wide Armfield S6MKII glass-sided tilting flume. Hydraulic jumps were produced by flow under sluice gate with varying Froude number. The air entrainment of the hydraulic jump was captured with a Canon Power Shot SX40 HS digital camera in video format at 24 frames per second. Three discharges have been considered, i.e. 0.010 m3/s, 0.011 m3/s, and 0.013 m3/s. For hydraulic jump formed in each discharge, 32 frames were selected for the purpose of analysing the size and number of air entrainment in hydraulic jump. The results revealed that that there is a tendency to have greater range in sizes of air bubbles as Fr1 increases. Experiments with Fr1 = 7.547. 7.707, and 7.924 shown that the number of air bubbles increases exponentially with Fr1 at a relationship of N = 1.3814 e 0.9795Fr1.

Jumping without slipping: leafhoppers (Hemiptera: Cicadellidae) possess special tarsal structures for jumping from smooth surfaces.

PubMed

Clemente, Christofer J; Goetzke, Hanns Hagen; Bullock, James M R; Sutton, Gregory P; Burrows, Malcolm; Federle, Walter

2017-05-01

Many hemipteran bugs can jump explosively from plant substrates, which can be very smooth. We therefore analysed the jumping performance of froghoppers ( Philaenus spumarius, Aphrophoridae) and leafhoppers ( Aphrodes bicinctus/makarovi, Cicadellidae) taking off from smooth (glass) and rough (sandpaper, 30 µm asperity size) surfaces. On glass, the propulsive hind legs of Philaenus froghoppers slipped, resulting in uncontrolled jumps with a fast forward spin, a steeper angle and only a quarter of the velocity compared with jumps from rough surfaces. By contrast, Aphrodes leafhoppers took off without their propulsive hind legs slipping, and reached low take-off angles and high velocities on both substrates. This difference in jumping ability from smooth surfaces can be explained not only by the lower acceleration of the long-legged leafhoppers, but also by the presence of 2-9 soft pad-like structures (platellae) on their hind tarsi, which are absent in froghoppers. High-speed videos of jumping showed that platellae contact the surface briefly (approx. 3 ms) during the acceleration phase. Friction force measurements on individual hind tarsi on glass revealed that at low sliding speeds, both pushing and pulling forces were small, and insufficient to explain the recorded jumps. Only when the tarsi were pushed with higher velocities did the contact area of the platellae increase markedly, and high friction forces were produced, consistent with the observed jumps. Our findings show that leafhoppers have special adhesive footpads for jumping from smooth surfaces, which achieve firm grip and rapid control of attachment/detachment by combining anisotropic friction with velocity dependence. © 2017 The Authors.

Optimal compliant-surface jumping: a multi-segment model of springboard standing jumps.

PubMed

Cheng, Kuangyou B; Hubbard, Mont

2005-09-01

A multi-segment model is used to investigate optimal compliant-surface jumping strategies and is applied to springboard standing jumps. The human model has four segments representing the feet, shanks, thighs, and trunk-head-arms. A rigid bar with a rotational spring on one end and a point mass on the other end (the tip) models the springboard. Board tip mass, length, and stiffness are functions of the fulcrum setting. Body segments and board tip are connected by frictionless hinge joints and are driven by joint torque actuators at the ankle, knee, and hip. One constant (maximum isometric torque) and three variable functions (of instantaneous joint angle, angular velocity, and activation level) determine each joint torque. Movement from a nearly straight motionless initial posture to jump takeoff is simulated. The objective is to find joint torque activation patterns during board contact so that jump height can be maximized. Minimum and maximum joint angles, rates of change of normalized activation levels, and contact duration are constrained. Optimal springboard jumping simulations can reasonably predict jumper vertical velocity and jump height. Qualitatively similar joint torque activation patterns are found over different fulcrum settings. Different from rigid-surface jumping where maximal activation is maintained until takeoff, joint activation decreases near takeoff in compliant-surface jumping. The fulcrum-height relations in experimental data were predicted by the models. However, lack of practice at non-preferred fulcrum settings might have caused less jump height than the models' prediction. Larger fulcrum numbers are beneficial for taller/heavier jumpers because they need more time to extend joints.

Test-retest reliability of jump execution variables using mechanography: a comparison of jump protocols.

PubMed

Fitzgerald, John S; Johnson, LuAnn; Tomkinson, Grant; Stein, Jesse; Roemmich, James N

2018-05-01

Mechanography during the vertical jump may enhance screening and determining mechanistic causes underlying physical performance changes. Utility of jump mechanography for evaluation is limited by scant test-retest reliability data on force-time variables. This study examined the test-retest reliability of eight jump execution variables assessed from mechanography. Thirty-two women (mean±SD: age 20.8 ± 1.3 yr) and 16 men (age 22.1 ± 1.9 yr) attended a familiarization session and two testing sessions, all one week apart. Participants performed two variations of the squat jump with squat depth self-selected and controlled using a goniometer to 80º knee flexion. Test-retest reliability was quantified as the systematic error (using effect size between jumps), random error (using coefficients of variation), and test-retest correlations (using intra-class correlation coefficients). Overall, jump execution variables demonstrated acceptable reliability, evidenced by small systematic errors (mean±95%CI: 0.2 ± 0.07), moderate random errors (mean±95%CI: 17.8 ± 3.7%), and very strong test-retest correlations (range: 0.73-0.97). Differences in random errors between controlled and self-selected protocols were negligible (mean±95%CI: 1.3 ± 2.3%). Jump execution variables demonstrated acceptable reliability, with no meaningful differences between the controlled and self-selected jump protocols. To simplify testing, a self-selected jump protocol can be used to assess force-time variables with negligible impact on measurement error.

Jumping without slipping: leafhoppers (Hemiptera: Cicadellidae) possess special tarsal structures for jumping from smooth surfaces

PubMed Central

Bullock, James M. R.

2017-01-01

Many hemipteran bugs can jump explosively from plant substrates, which can be very smooth. We therefore analysed the jumping performance of froghoppers (Philaenus spumarius, Aphrophoridae) and leafhoppers (Aphrodes bicinctus/makarovi, Cicadellidae) taking off from smooth (glass) and rough (sandpaper, 30 µm asperity size) surfaces. On glass, the propulsive hind legs of Philaenus froghoppers slipped, resulting in uncontrolled jumps with a fast forward spin, a steeper angle and only a quarter of the velocity compared with jumps from rough surfaces. By contrast, Aphrodes leafhoppers took off without their propulsive hind legs slipping, and reached low take-off angles and high velocities on both substrates. This difference in jumping ability from smooth surfaces can be explained not only by the lower acceleration of the long-legged leafhoppers, but also by the presence of 2–9 soft pad-like structures (platellae) on their hind tarsi, which are absent in froghoppers. High-speed videos of jumping showed that platellae contact the surface briefly (approx. 3 ms) during the acceleration phase. Friction force measurements on individual hind tarsi on glass revealed that at low sliding speeds, both pushing and pulling forces were small, and insufficient to explain the recorded jumps. Only when the tarsi were pushed with higher velocities did the contact area of the platellae increase markedly, and high friction forces were produced, consistent with the observed jumps. Our findings show that leafhoppers have special adhesive footpads for jumping from smooth surfaces, which achieve firm grip and rapid control of attachment/detachment by combining anisotropic friction with velocity dependence. PMID:28468924

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations.

PubMed

Mermigkis, Panagiotis G; Tsalikis, Dimitrios G; Mavrantzas, Vlasis G

2015-10-28

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, D(eff), of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, D(eff) is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for D(eff) as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on D(eff) (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Determination of the effective diffusivity of water in a poly (methyl methacrylate) membrane containing carbon nanotubes using kinetic Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Mermigkis, Panagiotis G.; Tsalikis, Dimitrios G.; Mavrantzas, Vlasis G.

2015-10-01

A kinetic Monte Carlo (kMC) simulation algorithm is developed for computing the effective diffusivity of water molecules in a poly(methyl methacrylate) (PMMA) matrix containing carbon nanotubes (CNTs) at several loadings. The simulations are conducted on a cubic lattice to the bonds of which rate constants are assigned governing the elementary jump events of water molecules from one lattice site to another. Lattice sites belonging to PMMA domains of the membrane are assigned different rates than lattice sites belonging to CNT domains. Values of these two rate constants are extracted from available numerical data for water diffusivity within a PMMA matrix and a CNT pre-computed on the basis of independent atomistic molecular dynamics simulations, which show that water diffusivity in CNTs is 3 orders of magnitude faster than in PMMA. Our discrete-space, continuum-time kMC simulation results for several PMMA-CNT nanocomposite membranes (characterized by different values of CNT length L and diameter D and by different loadings of the matrix in CNTs) demonstrate that the overall or effective diffusivity, Deff, of water in the entire polymeric membrane is of the same order of magnitude as its diffusivity in PMMA domains and increases only linearly with the concentration C (vol. %) in nanotubes. For a constant value of the concentration C, Deff is found to vary practically linearly also with the CNT aspect ratio L/D. The kMC data allow us to propose a simple bilinear expression for Deff as a function of C and L/D that can describe the numerical data for water mobility in the membrane extremely accurately. Additional simulations with two different CNT configurations (completely random versus aligned) show that CNT orientation in the polymeric matrix has only a minor effect on Deff (as long as CNTs do not fully penetrate the membrane). We have also extensively analyzed and quantified sublinear (anomalous) diffusive phenomena over small to moderate times and correlated them with the time needed for penetrant water molecules to explore the available large, fast-diffusing CNT pores before Fickian diffusion is reached.

Test-retest reliability of jump execution variables using mechanography: a comparison of jump protocols

USDA-ARS?s Scientific Manuscript database

Mechanography during the vertical jump may enhance screening and determining mechanistic causes for functional deficits that reduce physical performance. Utility of jump mechanography for evaluation is limited by scant test-retest reliability data on force-time variables. This study examined the tes...

Increase in Jumping Height Associated with Maximal Effort Vertical Depth Jumps.

ERIC Educational Resources Information Center

Bedi, John F.; And Others

1987-01-01

In order to assess if there existed a statistically significant increase in jumping performance when dropping from different heights, 32 males, aged 19 to 26, performed a series of maximal effort vertical jumps after dropping from eight heights onto a force plate. Results are analyzed. (Author/MT)

Ski jump takeoff performance predictions for a mixed-flow, remote-lift STOVL aircraft

NASA Technical Reports Server (NTRS)

Birckelbaw, Lourdes G.

1992-01-01

A ski jump model was developed to predict ski jump takeoff performance for a short takeoff and vertical landing (STOVL) aircraft. The objective was to verify the model with results from a piloted simulation of a mixed flow, remote lift STOVL aircraft. The prediction model is discussed. The predicted results are compared with the piloted simulation results. The ski jump model can be utilized for basic research of other thrust vectoring STOVL aircraft performing a ski jump takeoff.

Hypohydration Reduces Vertical Ground Reaction Impulse But Not Jump Height

DTIC Science & Technology

2010-01-01

countermovement jump from a 660 9 660 9 60 mm dual force plate plat- form (Leonardo v3.07, Orthometrix, Inc.) connected to a PC for the purpose of collecting... force data and calculating jump height (described below). Subjects stood still on the platform with one foot on each force plate for approxi- mately 10...study examined vertical jump performance using a force platform and weighted vest to determine why hypohydration (~4% body mass) does not improve jump

The Overshoot Phenomenon in Geodynamics Codes

NASA Astrophysics Data System (ADS)

Kommu, R. K.; Heien, E. M.; Kellogg, L. H.; Bangerth, W.; Heister, T.; Studley, E. H.

2013-12-01

The overshoot phenomenon is a common occurrence in numerical software when a continuous function on a finite dimensional discretized space is used to approximate a discontinuous jump, in temperature and material concentration, for example. The resulting solution overshoots, and undershoots, the discontinuous jump. Numerical simulations play an extremely important role in mantle convection research. This is both due to the strong temperature and stress dependence of viscosity and also due to the inaccessibility of deep earth. Under these circumstances, it is essential that mantle convection simulations be extremely accurate and reliable. CitcomS and ASPECT are two finite element based mantle convection simulations developed and maintained by the Computational Infrastructure for Geodynamics. CitcomS is a finite element based mantle convection code that is designed to run on multiple high-performance computing platforms. ASPECT, an adaptive mesh refinement (AMR) code built on the Deal.II library, is also a finite element based mantle convection code that scales well on various HPC platforms. CitcomS and ASPECT both exhibit the overshoot phenomenon. One attempt at controlling the overshoot uses the Entropy Viscosity method, which introduces an artificial diffusion term in the energy equation of mantle convection. This artificial diffusion term is small where the temperature field is smooth. We present results from CitcomS and ASPECT that quantify the effect of the Entropy Viscosity method in reducing the overshoot phenomenon. In the discontinuous Galerkin (DG) finite element method, the test functions used in the method are continuous within each element but are discontinuous across inter-element boundaries. The solution space in the DG method is discontinuous. FEniCS is a collection of free software tools that automate the solution of differential equations using finite element methods. In this work we also present results from a finite element mantle convection simulation implemented in FEniCS that investigates the effect of using DG elements in reducing the overshoot problem.

Stochastic stability properties of jump linear systems

NASA Technical Reports Server (NTRS)

Feng, Xiangbo; Loparo, Kenneth A.; Ji, Yuandong; Chizeck, Howard J.

1992-01-01

Jump linear systems are defined as a family of linear systems with randomly jumping parameters (usually governed by a Markov jump process) and are used to model systems subject to failures or changes in structure. The authors study stochastic stability properties in jump linear systems and the relationship among various moment and sample path stability properties. It is shown that all second moment stability properties are equivalent and are sufficient for almost sure sample path stability, and a testable necessary and sufficient condition for second moment stability is derived. The Lyapunov exponent method for the study of almost sure sample stability is discussed, and a theorem which characterizes the Lyapunov exponents of jump linear systems is presented.

Efficient global fiber tracking on multi-dimensional diffusion direction maps

NASA Astrophysics Data System (ADS)

Klein, Jan; Köhler, Benjamin; Hahn, Horst K.

2012-02-01

Global fiber tracking algorithms have recently been proposed which were able to compute results of unprecedented quality. They account for avoiding accumulation errors by a global optimization process at the cost of a high computation time of several hours or even days. In this paper, we introduce a novel global fiber tracking algorithm which, for the first time, globally optimizes the underlying diffusion direction map obtained from DTI or HARDI data, instead of single fiber segments. As a consequence, the number of iterations in the optimization process can drastically be reduced by about three orders of magnitude. Furthermore, in contrast to all previous algorithms, the density of the tracked fibers can be adjusted after the optimization within a few seconds. We evaluated our method for diffusion-weighted images obtained from software phantoms, healthy volunteers, and tumor patients. We show that difficult fiber bundles, e.g., the visual pathways or tracts for different motor functions can be determined and separated in an excellent quality. Furthermore, crossing and kissing bundles are correctly resolved. On current standard hardware, a dense fiber tracking result of a whole brain can be determined in less than half an hour which is a strong improvement compared to previous work.

Spatial averaging for small molecule diffusion in condensed phase environments

NASA Astrophysics Data System (ADS)

Plattner, Nuria; Doll, J. D.; Meuwly, Markus

2010-07-01

Spatial averaging is a new approach for sampling rare-event problems. The approach modifies the importance function which improves the sampling efficiency while keeping a defined relation to the original statistical distribution. In this work, spatial averaging is applied to multidimensional systems for typical problems arising in physical chemistry. They include (I) a CO molecule diffusing on an amorphous ice surface, (II) a hydrogen molecule probing favorable positions in amorphous ice, and (III) CO migration in myoglobin. The systems encompass a wide range of energy barriers and for all of them spatial averaging is found to outperform conventional Metropolis Monte Carlo. It is also found that optimal simulation parameters are surprisingly similar for the different systems studied, in particular, the radius of the point cloud over which the potential energy function is averaged. For H2 diffusing in amorphous ice it is found that facile migration is possible which is in agreement with previous suggestions from experiment. The free energy barriers involved are typically lower than 1 kcal/mol. Spatial averaging simulations for CO in myoglobin are able to locate all currently characterized metastable states. Overall, it is found that spatial averaging considerably improves the sampling of configurational space.

Correlation between toe flexor strength and ankle dorsiflexion ROM during the countermovement jump.

PubMed

Yun, Sung Joon; Kim, Moon-Hwan; Weon, Jong-Hyuck; Kim, Young; Jung, Sung-Hoon; Kwon, Oh-Yun

2016-08-01

[Purpose] This study assessed the relationships between peak toe flexor muscle strength, ankle dorsiflexion range of motion, and countermovement jump height. [Subjects and Methods] Eighteen healthy volunteers participated in the study. Each participant completed tests for peak toe flexor muscle strength, ankle dorsiflexion range of motion, and countermovement jump height. [Results] The results showed (1) a moderate correlation between ankle dorsiflexion range of motion and countermovement jump height and (2) a high correlation between peak first toe flexor muscle strength and countermovement jump height. Peak first toe flexor muscle strength and ankle dorsiflexion range of motion are the main contributors to countermovement jump performance. [Conclusion] These findings indicate that the measurement of peak first toe flexor muscle strength and ankle dorsiflexion range of motion may be useful in clinical practice for improving jump performance in athletes training for sports such as volleyball and basketball.

BIOMECHANICS. Jumping on water: Surface tension-dominated jumping of water striders and robotic insects.

PubMed

Koh, Je-Sung; Yang, Eunjin; Jung, Gwang-Pil; Jung, Sun-Pill; Son, Jae Hak; Lee, Sang-Im; Jablonski, Piotr G; Wood, Robert J; Kim, Ho-Young; Cho, Kyu-Jin

2015-07-31

Jumping on water is a unique locomotion mode found in semi-aquatic arthropods, such as water striders. To reproduce this feat in a surface tension-dominant jumping robot, we elucidated the hydrodynamics involved and applied them to develop a bio-inspired impulsive mechanism that maximizes momentum transfer to water. We found that water striders rotate the curved tips of their legs inward at a relatively low descending velocity with a force just below that required to break the water surface (144 millinewtons/meter). We built a 68-milligram at-scale jumping robotic insect and verified that it jumps on water with maximum momentum transfer. The results suggest an understanding of the hydrodynamic phenomena used by semi-aquatic arthropods during water jumping and prescribe a method for reproducing these capabilities in artificial systems. Copyright © 2015, American Association for the Advancement of Science.

Water striders adjust leg movement speed to optimize takeoff velocity for their morphology.

PubMed

Yang, Eunjin; Son, Jae Hak; Lee, Sang-Im; Jablonski, Piotr G; Kim, Ho-Young

2016-12-07

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.

Water striders adjust leg movement speed to optimize takeoff velocity for their morphology

NASA Astrophysics Data System (ADS)

Yang, Eunjin; Son, Jae Hak; Lee, Sang-Im; Jablonski, Piotr G.; Kim, Ho-Young

2016-12-01

Water striders are water-walking insects that can jump upwards from the water surface. Quick jumps allow striders to avoid sudden dangers such as predators' attacks, and therefore their jumping is expected to be shaped by natural selection for optimal performance. Related species with different morphological constraints could require different jumping mechanics to successfully avoid predation. Here we show that jumping striders tune their leg rotation speed to reach the maximum jumping speed that water surface allows. We find that the leg stroke speeds of water strider species with different leg morphologies correspond to mathematically calculated morphology-specific optima that maximize vertical takeoff velocity by fully exploiting the capillary force of water. These results improve the understanding of correlated evolution between morphology and leg movements in small jumping insects, and provide a theoretical basis to develop biomimetic technology in semi-aquatic environments.

The Physics of Equestrian Show Jumping

ERIC Educational Resources Information Center

Stinner, Art

2014-01-01

This article discusses the kinematics and dynamics of equestrian show jumping. For some time I have attended a series of show jumping events at Spruce Meadows, an international equestrian center near Calgary, Alberta, often referred to as the "Wimbledon of equestrian jumping." I have always had a desire to write an article such as this…

DC-Powered Jumping Ring

ERIC Educational Resources Information Center

Jeffery, Rondo N.; Farhang, Amiri

2016-01-01

The classroom jumping ring demonstration is nearly always performed using alternating current (AC), in which the ring jumps or flies off the extended iron core when the switch is closed. The ring jumps higher when cooled with liquid nitrogen (LN2). We have performed experiments using DC to power the solenoid and find similarities and significant…

Role of Vertical Jumps and Anthropometric Variables in Maximal Kicking Ball Velocities in Elite Soccer Players

PubMed Central

Rodríguez-Lorenzo, Lois; Fernandez-del-Olmo, Miguel; Sanchez-Molina, José Andrés

2016-01-01

Abstract Kicking is one of the most important skills in soccer and the ability to achieve ma ximal kicking velocity with both legs leads to an advantage for the soccer player. This study examined the relationship be tween kicking ball velocity with both legs using anthropometric measurements and vertical jumps (a squat jump (SJ); a countermovement jump without (CMJ) and with the arm swing (CMJA) and a reactive jump (RJ)). Anthropome tric measurements did not correlate with kicking ball velocity. Vertical jumps correlated significantly with kicking ball velocity using the dominant leg only (r = .47, r = .58, r = .44, r = .51, for SJ, CMJ, CMJA and RJ, respectively) . Maximal kicking velocity with the dominant leg was significantly higher than with the non-dominant leg (t = 18.0 4, p < 0.001). Our results suggest that vertical jumps may be an optimal test to assess neuromuscular skills involved in kicking at maximal speed. Lack of the relationship between vertical jumps and kicking velocity with the non-dominant leg may reflect a difficulty to exhibit the neuromuscular skills during dominant leg kicking. PMID:28149419

A pulsed jumping ring apparatus for demonstration of Lenz's law

NASA Astrophysics Data System (ADS)

Tanner, Paul; Loebach, Jeff; Cook, James; Hallen, H. D.

2001-08-01

Lenz's law is often demonstrated in classrooms by the use of Elihu Thomson's jumping ring. However, it is ironic that a thorough analysis of the physics of the ac jumping ring reveals that the operation is due mainly to a phase difference, not Lenz's law. A complete analysis of the physics behind the ac jumping ring is difficult for the introductory student. We present a design for a pulsed jumping ring which can be fully described by the application of Lenz's law. Other advantages of this system are that it lends itself to a rigorous analysis of the force balances and energy flow. The simple jumping ring apparatus closely resembles Thomson's, but is powered by a capacitor bank. The jump heights were measured for several rings as a function of energy stored in the capacitors. A simple model describes the data well. Currents in both the drive coil and ring are measured and that of the drive coil modeled to illuminate some properties of the capacitors. An analysis of the energy flow in the system explains the higher jump heights, to 2 m, when the ring is cooled.

Aerial Jumping in the Trinidadian Guppy (Poecilia reticulata)

PubMed Central

Soares, Daphne; Bierman, Hilary S.

2013-01-01

Many fishes are able to jump out of the water and launch themselves into the air. Such behavior has been connected with prey capture, migration and predator avoidance. We found that jumping behavior of the guppy Poecilia reticulata is not associated with any of the above. The fish jump spontaneously, without being triggered by overt sensory cues, is not migratory and does not attempt to capture aerial food items. Here, we use high speed video imaging to analyze the kinematics of the jumping behavior P. reticulata. Fish jump from a still position by slowly backing up while using its pectoral fins, followed by strong body trusts which lead to launching into the air several body lengths. The liftoff phase of the jump is fast and fish will continue with whole body thrusts and tail beats, even when out of the water. This behavior occurs when fish are in a group or in isolation. Geography has had substantial effects on guppy evolution, with waterfalls reducing gene flow and constraining dispersal. We suggest that jumping has evolved in guppies as a behavioral phenotype for dispersal. PMID:23613883

Inference of Evolutionary Jumps in Large Phylogenies using Lévy Processes

PubMed Central

Duchen, Pablo; Leuenberger, Christoph; Szilágyi, Sándor M.; Harmon, Luke; Eastman, Jonathan; Schweizer, Manuel

2017-01-01

Abstract Although it is now widely accepted that the rate of phenotypic evolution may not necessarily be constant across large phylogenies, the frequency and phylogenetic position of periods of rapid evolution remain unclear. In his highly influential view of evolution, G. G. Simpson supposed that such evolutionary jumps occur when organisms transition into so-called new adaptive zones, for instance after dispersal into a new geographic area, after rapid climatic changes, or following the appearance of an evolutionary novelty. Only recently, large, accurate and well calibrated phylogenies have become available that allow testing this hypothesis directly, yet inferring evolutionary jumps remains computationally very challenging. Here, we develop a computationally highly efficient algorithm to accurately infer the rate and strength of evolutionary jumps as well as their phylogenetic location. Following previous work we model evolutionary jumps as a compound process, but introduce a novel approach to sample jump configurations that does not require matrix inversions and thus naturally scales to large trees. We then make use of this development to infer evolutionary jumps in Anolis lizards and Loriinii parrots where we find strong signal for such jumps at the basis of clades that transitioned into new adaptive zones, just as postulated by Simpson’s hypothesis. [evolutionary jump; Lévy process; phenotypic evolution; punctuated equilibrium; quantitative traits. PMID:28204787

Jumping to (fatal) conclusions? An analysis of video film on a social networking web site of recreational jumping from height into water.

PubMed

Moran, Kevin

2014-01-01

In high-income countries, death as a consequence of recreational jumping into water from height has not been well investigated partly because it traditionally has been a covert activity within youth culture. An observational study of video recordings posted on the YouTube web site was used to gather data on the nature of jumping activity in New Zealand and Australia. An analytical framework was developed to identify site- participant- social characteristics (10 variables) and online feedback (4 variables). Of the 389 videos recorded in New Zealand (n = 210) and Australia (n = 179), 929 jumpers were observed, and rivers were the most frequently reported site of jumping activity (New Zealand 47%; Australia 35%). One fifth (20%) of the jumps in New Zealand and one third (33%) in Australia were from heights estimated to be more than 12 m. The YouTube website portraying jumps from height were visited almost half a million times (495,686 hits). Ways of reducing recreational jumping risk via targeted education interventions may be best directed at young male adults. Use of social network sites to foster safe behaviours may be an effective way to educate young people of the inherent risks of jumping from height into water.

Drop jumping. II. The influence of dropping height on the biomechanics of drop jumping.

PubMed

Bobbert, M F; Huijing, P A; van Ingen Schenau, G J

1987-08-01

In the literature, athletes preparing for explosive activities are recommended to include drop jumping in their training programs. For the execution of drop jumps, different techniques and different dropping heights can be used. This study was designed to investigate for the performance of bounce drop jumps the influence of dropping height on the biomechanics of the jumps. Six subjects executed bounce drop jumps from heights of 20 cm (designated here as DJ20), 40 cm (designated here as DJ40), and 60 cm (designated here as DJ60). During jumping, they were filmed, and ground reaction forces were recorded. The results of a biomechanical analysis show no difference between DJ20 and DJ40 in mechanical output about the joints during the push-off phase. Peak values of moment and power output about the ankles during the push-off phase were found to be smaller in DJ60 than in DJ40 (DJ20 = DJ60). The amplitude of joint reaction forces increased with dropping height. During DJ60, the net joint reaction forces showed a sharp peak on the instant that the heels came down on the ground. Based on the results, researchers are advised to limit dropping height to 20 or 40 cm when investigating training effects of the execution of bounce drop jumps.

The effect of increasing strength and approach velocity on triple jump performance.

PubMed

Allen, Sam J; Yeadon, M R Fred; King, Mark A

2016-12-08

The triple jump is an athletic event comprising three phases in which the optimal phase ratio (the proportion of each phase to the total distance jumped) is unknown. This study used a planar whole body torque-driven computer simulation model of the ground contact parts of all three phases of the triple jump to investigate the effect of strength and approach velocity on optimal performance. The strength and approach velocity of the simulation model were each increased by up to 30% in 10% increments from baseline data collected from a national standard triple jumper. Increasing strength always resulted in an increased overall jump distance. Increasing approach velocity also typically resulted in an increased overall jump distance but there was a point past which increasing approach velocity without increasing strength did not lead to an increase in overall jump distance. Increasing both strength and approach velocity by 10%, 20%, and 30% led to roughly equivalent increases in overall jump distances. Distances ranged from 14.05m with baseline strength and approach velocity, up to 18.49m with 30% increases in both. Optimal phase ratios were either hop-dominated or balanced, and typically became more balanced when the strength of the model was increased by a greater percentage than its approach velocity. The range of triple jump distances that resulted from the optimisation process suggests that strength and approach velocity are of great importance for triple jump performance. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of drop jump technique on the reactive strength index.

PubMed

Struzik, Artur; Juras, Grzegorz; Pietraszewski, Bogdan; Rokita, Andrzej

2016-09-01

The basic drill of plyometric training aimed at improving lower limb power and jump height is a drop jump. This exercise can be performed using different techniques, which substantially affects jump variables. Therefore, the aim of this study was to compare the values of the reactive strength index (RSI) for countermovement drop jumps (CDJs) and bounce drop jumps (BDJs). The study was carried out in a group of 8 male youth basketball players. The tests were conducted using the AMTI BP600900 force plate to measure ground reaction forces and the Noraxon MyoMotion system to record kinematic data. Each player performed two CDJs and two BDJs from the height of 15, 30, 45 and 60 cm. The RSI was calculated as a ratio of jump height and contact time. Moreover, the RSI was determined for the amortization and take-off phases separately. Significant differences (p < 0.05) between RSI values for CDJs and BDJs were recorded for jumps from 30, 45 and 60 cm. Differences in RSI values for jumps from 15 cm were not significant. Furthermore, CDJ height values were significantly higher (p < 0.05) than the values recorded for BDJs. Times of contact, amortization and take-off during BDJs were significantly shorter (p < 0.05) than the respective values obtained for CDJs. Therefore, the use of the RSI to monitor plyometric training should be based on the drop jump technique that is commonly performed by basketball players.

Numerical simulations of katabatic jumps in coats land, Antartica

NASA Astrophysics Data System (ADS)

Yu, Ye; Cai, Xiaoming; King, John C.; Renfrew, Ian A.

A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli''s theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli''s theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump.

Effect of drop jump technique on the reactive strength index

PubMed Central

Juras, Grzegorz; Pietraszewski, Bogdan; Rokita, Andrzej

2016-01-01

Abstract The basic drill of plyometric training aimed at improving lower limb power and jump height is a drop jump. This exercise can be performed using different techniques, which substantially affects jump variables. Therefore, the aim of this study was to compare the values of the reactive strength index (RSI) for countermovement drop jumps (CDJs) and bounce drop jumps (BDJs). The study was carried out in a group of 8 male youth basketball players. The tests were conducted using the AMTI BP600900 force plate to measure ground reaction forces and the Noraxon MyoMotion system to record kinematic data. Each player performed two CDJs and two BDJs from the height of 15, 30, 45 and 60 cm. The RSI was calculated as a ratio of jump height and contact time. Moreover, the RSI was determined for the amortization and take-off phases separately. Significant differences (p < 0.05) between RSI values for CDJs and BDJs were recorded for jumps from 30, 45 and 60 cm. Differences in RSI values for jumps from 15 cm were not significant. Furthermore, CDJ height values were significantly higher (p < 0.05) than the values recorded for BDJs. Times of contact, amortization and take-off during BDJs were significantly shorter (p < 0.05) than the respective values obtained for CDJs. Therefore, the use of the RSI to monitor plyometric training should be based on the drop jump technique that is commonly performed by basketball players. PMID:28149403

Effects of Isometric Scaling on Vertical Jumping Performance

PubMed Central

Bobbert, Maarten F.

2013-01-01

Jump height, defined as vertical displacement in the airborne phase, depends on vertical takeoff velocity. For centuries, researchers have speculated on how jump height is affected by body size and many have adhered to what has come to be known as Borelli’s law, which states that jump height does not depend on body size per se. The underlying assumption is that the amount of work produced per kg body mass during the push-off is independent of size. However, if a big body is isometrically downscaled to a small body, the latter requires higher joint angular velocities to achieve a given takeoff velocity and work production will be more impaired by the force-velocity relationship of muscle. In the present study, the effects of pure isometric scaling on vertical jumping performance were investigated using a biologically realistic model of the human musculoskeletal system. The input of the model, muscle stimulation over time, was optimized using jump height as criterion. It was found that when the human model was miniaturized to the size of a mouse lemur, with a mass of about one-thousandth that of a human, jump height dropped from 40 cm to only 6 cm, mainly because of the force-velocity relationship. In reality, mouse lemurs achieve jump heights of about 33 cm. By implication, the unfavourable effects of the small body size of mouse lemurs on jumping performance must be counteracted by favourable effects of morphological and physiological adaptations. The same holds true for other small jumping animals. The simulations for the first time expose and explain the sheer magnitude of the isolated effects of isometric downscaling on jumping performance, to be counteracted by morphological and physiological adaptations. PMID:23936494

Acute Effects of Plyometric Intervention—Performance Improvement and Related Changes in Sprinting Gait Variability.

PubMed

Maćkała, Krzysztof; Fostiak, Marek

2015-07-01

The purpose of this study was to examine the effect of a short high-intensity plyometric program on the improvement of explosive power of lower extremities and sprint performance as well as changes in sprinting stride variability in male sprinters. Fourteen healthy male sprinters (mean ± SD: age: 18.07 ± 0.73 years, body mass: 73 ± 9.14 kg, height: 180.57 ± 8.16 cm, and best 100 m: 10.89 ± 0.23) participated in the experiment. The experimental protocol included vertical jumping such as squat jump, countermovement jump, and horizontal jumps; standing long jump and standing triple jumps to assess lower-body power, maximal running velocity; a 20-m flying start sprint that evaluated variability of 10 running steps and 60-m starting block sprint. All analyzed parameters were obtained using the new technology of OptoJump-Microgate (OptoJump, Italy). The short-term plyometric training program significantly increased the explosive power of lower extremities, both vertical and horizontal jumping improvement. However, the vertical jumps increased much more than the horizontal. The 20-m improvements were derived from an increase of stride frequency from 4.31 to 4.39 Hz because of a decrease of ground contact time from 138 to 133 milliseconds. This did not translate into step length changes. Therefore, the significantly increased frequency of stride (1.8%), which is a specific expression of ground contact time reduction during support phase, resulted in an increase of speed. The training volume of 2 weeks (with 6 sessions) using high-intensity (between 180 and 250 jumps per session) plyometric exercises can be recommended as the short-term strategy that will optimize one's probability of reaching strong improvements in explosive power and sprint velocity performance.

Predicting lower body power from vertical jump prediction equations for loaded jump squats at different intensities in men and women.

PubMed

Wright, Glenn A; Pustina, Andrew A; Mikat, Richard P; Kernozek, Thomas W

2012-03-01

The purpose of this study was to determine the efficacy of estimating peak lower body power from a maximal jump squat using 3 different vertical jump prediction equations. Sixty physically active college students (30 men, 30 women) performed jump squats with a weighted bar's applied load of 20, 40, and 60% of body mass across the shoulders. Each jump squat was simultaneously monitored using a force plate and a contact mat. Peak power (PP) was calculated using vertical ground reaction force from the force plate data. Commonly used equations requiring body mass and vertical jump height to estimate PP were applied such that the system mass (mass of body + applied load) was substituted for body mass. Jump height was determined from flight time as measured with a contact mat during a maximal jump squat. Estimations of PP (PP(est)) for each load and for each prediction equation were compared with criterion PP values from a force plate (PP(FP)). The PP(est) values had high test-retest reliability and were strongly correlated to PP(FP) in both men and women at all relative loads. However, only the Harman equation accurately predicted PP(FP) at all relative loads. It can therefore be concluded that the Harman equation may be used to estimate PP of a loaded jump squat knowing the system mass and peak jump height when more precise (and expensive) measurement equipment is unavailable. Further, high reliability and correlation with criterion values suggest that serial assessment of power production across training periods could be used for relative assessment of change by either of the prediction equations used in this study.

The Effects of Caffeine on Vertical Jump Height and Execution in Collegiate Athletes.

PubMed

Bloms, Lucas P; Fitzgerald, John S; Short, Martin W; Whitehead, James R

2016-07-01

Bloms, LP, Fitzgerald, JS, Short, MW, and Whitehead, JR. The effects of caffeine on vertical jump height and execution in collegiate athletes. J Strength Cond Res 30(7): 1855-1861, 2016-Caffeine ingestion elicits a variety of physiological effects that may be beneficial to maximal-intensity exercise performance, although its effectiveness and physical mechanism of action enhancing ballistic task performance are unclear. The purpose of this study was to examine the effects of caffeine ingestion on vertical jump height and jump execution in Division I collegiate athletes. The study used a single-blind, randomized, crossover design. Athletes (n = 25) consumed either caffeine (5 mg·kg) or placebo. After a 60-minute waiting period, athletes performed 3 squat jumps (SJ) and 3 countermovement jumps (CMJ) while standing on a force platform. Jump height and execution variables were calculated from mechanography data. In comparison with placebo, caffeine increased SJ height (32.8 ± 6.2 vs. 34.5 ± 6.7 cm; p = 0.001) and CMJ height (36.4 ± 6.9 vs. 37.9 ± 7.4 cm; p = 0.001). Peak force (p = 0.032) and average rate of force development (p = 0.037) were increased during the CMJ in the caffeine trail compared with the control. Time to half peak force was the only execution variable improved with caffeine (p = 0.019) during the SJ. It seems that caffeine affects both height and execution of jumping. Our data indicate that the physical mechanism of jump enhancement is increased peak force production or rate of force development during jumping depending on technique. The physical mechanism of jump enhancement suggests that the ergogenic effects of caffeine may transfer to other ballistic tasks involving the lower-body musculature in collegiate athletes.

Effect of a prehop on the muscle-tendon interaction during vertical jumps.

PubMed

Aeles, Jeroen; Lichtwark, Glen; Peeters, Dries; Delecluse, Christophe; Jonkers, Ilse; Vanwanseele, Benedicte

2018-05-01

Many movements use stretch-shortening cycles of a muscle-tendon unit (MTU) for storing and releasing elastic energy. The required stretching of medial gastrocnemius (MG) tendinous tissue during jumps, however, requires large length changes of the muscle fascicles because of the lack of MTU length changes. This has a negative impact on the force-generating capacity of the muscle fascicles. The purpose of this study was to induce a MG MTU stretch before shortening by adding a prehop to the squat jump. Eleven well-trained athletes specialized in jumping performed a prehop squat jump (PHSJ) and a standard squat jump (SSJ). Kinematic data were collected using a 3D motion capture system and were used in a musculoskeletal model to calculate MTU lengths. B-mode ultrasonography of the MG was used to measure fascicle length and pennation angle during the jumps. By combining the muscle-tendon unit lengths, fascicle lengths, and pennation angles, the stretch and recoil of the series elastic element of MG were calculated using a simple geometric muscle-tendon model. Our results show less length changes of the muscle fascicles during the upward motion and lower maximal shortening velocities, increasing the moment-generating capacity of the plantar flexors, reflected in the higher ankle joint moment in the PHSJ compared with the SSJ. Although muscle-tendon interaction during the PHSJ was more optimal, athletes were not able to increase their jump height compared with the SSJ. NEW & NOTEWORTHY This is the first study that aimed to improve the muscle-tendon interaction in squat jumping. We effectively introduced a stretch to the medial gastrocnemius muscle-tendon unit resulting in lower maximal shortening velocities and thus an increase in the plantar flexor force-generating capacity, reflected in the higher ankle joint moment in the prehop squat jump compared with the standard squat jump. Here, we demonstrate an effective method for mechanical optimization of the muscle-tendon interaction in the medial gastrocnemius during squat jumping.

Vertical and Horizontal Asymmetries are Related to Slower Sprinting and Jump Performance in Elite Youth Female Soccer Players.

PubMed

Bishop, Chris; Read, Paul; McCubbine, Jermaine; Turner, Anthony

2018-02-27

Inter-limb asymmetries have been shown to be greater during vertical jumping compared to horizontal jumping. Notable inter-limb differences have also been established at an early age in male youth soccer players. Furthermore, given the multi-planar nature of soccer, establishing between-limb differences from multiple jump tests is warranted. At present, a paucity of data exists regarding asymmetries in youth female soccer players and their effects on physical performance. The aims of this study were to quantify inter-limb asymmetries from unilateral jump tests and examine their effects on speed and jump performance. Nineteen elite youth female soccer players performed a single leg countermovement jump (SLCMJ), single, triple, and crossover hops for distance and a 20 m sprint test. Test reliability was good to excellent (ICC = 0.81-0.99) and variability acceptable (CV = 1.74-5.42%). A one-way ANOVA highlighted larger asymmetries from the SLCMJ compared to all other jump tests (p < 0.05). Pearson's correlations portrayed significant relationships between vertical asymmetries from the SLCMJ and slower sprint times (r = 0.49-0.59). Significant negative relationships were also found between horizontal asymmetries during the triple hop test and horizontal jump performance (r = -0.47 to -0.58) and vertical asymmetries during the SLCMJ and vertical jump performance (r = -0.47 to -0.53). The results from this study highlight that the SLCMJ appears to be the most appropriate jump test for identifying between-limb differences with values ∼12% showing negative associations with sprint times. Furthermore, larger asymmetries are associated with reduced jump performance and would appear to be direction-specific. Practitioners can use this information as normative data to be mindful of when quantifying inter-limb asymmetries and assessing their potential impact on physical performance in youth female soccer players.

High-Intensity Jump Training Is Tolerated during 60 Days of Bed Rest and Is Very Effective in Preserving Leg Power and Lean Body Mass: An Overview of the Cologne RSL Study.

PubMed

Kramer, Andreas; Kümmel, Jakob; Mulder, Edwin; Gollhofer, Albert; Frings-Meuthen, Petra; Gruber, Markus

2017-01-01

Space agencies are looking for effective and efficient countermeasures for the degrading effects of weightlessness on the human body. The aim of this study was to assess the effects of a novel jump exercise countermeasure during bed rest on vitals, body mass, body composition, and jump performance. 23 male participants (29±6 years, 181±6 cm, 77±7 kg) were confined to a bed rest facility for 90 days: a 15-day ambulatory measurement phase, a 60-day six-degree head-down-tilt bed rest phase (HDT), and a 15-day ambulatory recovery phase. Participants were randomly allocated to the jump training group (JUMP, n = 12) or the control group (CTRL, n = 11). A typical training session consisted of 4x10 countermovement jumps and 2x10 hops in a sledge jump system. The training group had to complete 5-6 sessions per week. Peak force for the reactive hops (3.6±0.4 kN) as well as jump height (35±4 cm) and peak power (3.1±0.2 kW) for the countermovement jumps could be maintained over the 60 days of HDT. Lean body mass decreased in CTRL but not in JUMP (-1.6±1.9 kg and 0±1.0 kg, respectively, interaction effect p = 0.03). Resting heart rate during recovery was significantly increased for CTRL but not for JUMP (interaction effect p<0.001). Participants tolerated the near-daily high-intensity jump training and maintained high peak forces and high power output during 60 days of bed rest. The countermeasure was effective in preserving lean body mass and partly preventing cardiac deconditioning with only several minutes of training per day.

Kinematic And Neuromuscular Measures Of Intensity During Plyometric Jumps.

PubMed

Andrade, David Cristóbal; Manzo, Oscar; Beltrán, Ana Rosa; Álvarez, Cristian; Del Rio, Rodrigo; Toledo, Camilo; Moran, Jason; Ramirez-Campillo, Rodrigo

2017-08-15

The aim of this study was to assess jumping performance and neuromuscular activity in lower limb muscles after drop jumps (DJ) from different drop heights (intensity) and during continuous jumping (fatigue), using markers such as reactive strength, jump height, mechanical power and surface electromyography (sEMG). The eccentric (EC) and concentric (CON) sEMG from the medial gastrocnemius (MG), biceps femoris (BF) and rectus (R) muscles were assessed during all tests. In a cross-sectional, randomized study, eleven volleyball players (age 24.4±3.2 years) completed 20 to 90-cm (DJ20 to DJ90) drop jumps and a 60-s continuous jump test. A one-way ANOVA test was used for comparisons, with Sidak post-hoc. The α level was <0.05. Reactive strength was greater for DJ40 compared to DJ90 (p<0.05; ES: 1.27). Additionally jump height was greater for DJ40 and DJ60 compared to DJ20 (p<0.05; ES: 1.26 and 1.27, respectively). No clear pattern of neuromuscular activity appeared during DJ20 to DJ90: some muscles showed greater, lower, or no change with increasing heights for both agonist and antagonist muscles, as well as for eccentric and concentric activity. Mechanical power, but not reactive strength, was reduced in the 60-s jump test (p<0.05; ES: 3.46). No changes were observed in sEMG for any muscle during the eccentric phase nor for the R muscle during the concentric phase of the 60-s jump test. However, for both MG and BF, concentric sEMG was reduced during the 60-s jump test (p<0.05; ES: 5.10 and 4.61, respectively). In conclusion, jumping performance and neuromuscular markers are sensitive to DJ height (intensity), although not in a clear dose-response fashion. In addition, markers such as mechanical power and sEMG are especially sensitive to the effects of continuous jumping (fatigue). Therefore, increasing the drop height during DJ does not ensure a greater training intensity and a combination of different drop heights may be required to elicit adaptations.