Driven, underdamped Frenkel-Kontorova model on a quasiperiodic substrate

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

Vanossi, A.; Ro''der, J.; Bishop, A. R.

2001-01-01

We consider the underdamped dynamics of a chain of atoms subject to a dc driving force and a quasiperiodic substrate potential. The system has three inherent length scales which we take to be mutually incommensurate. We find that when the length scales are related by the spiral mean (a cubic irrational) there exists a value of the interparticle interaction strength above which the static friction is zero. When the length scales are related by the golden mean (a quadratic irrational) the static friction is always nonzero. >From considerations based on the connection of this problem to standard map theory, wemore » postulate that zero static friction is generally possible for incommensurate ratios of the length scales involved. However, when the length scales are quadratic irrationals, or have some commensurability with each other, the static friction will be nonzero for all choices of interaction parameters. We also comment on the nature of the depinning mechanisms and the steady states achieved by the moving chain.« less

Temperature gradient scale length measurement: A high accuracy application of electron cyclotron emission without calibration

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

Houshmandyar, S., E-mail: houshmandyar@austin.utexas.edu; Phillips, P. E.; Rowan, W. L.

2016-11-15

Calibration is a crucial procedure in electron temperature (T{sub e}) inference from a typical electron cyclotron emission (ECE) diagnostic on tokamaks. Although the calibration provides an important multiplying factor for an individual ECE channel, the parameter ΔT{sub e}/T{sub e} is independent of any calibration. Since an ECE channel measures the cyclotron emission for a particular flux surface, a non-perturbing change in toroidal magnetic field changes the view of that channel. Hence the calibration-free parameter is a measure of T{sub e} gradient. B{sub T}-jog technique is presented here which employs the parameter and the raw ECE signals for direct measurement ofmore » electron temperature gradient scale length.« less

Electropolishing effect on roughness metrics of ground stainless steel: a length scale study

NASA Astrophysics Data System (ADS)

Nakar, Doron; Harel, David; Hirsch, Baruch

2018-03-01

Electropolishing is a widely-used electrochemical surface finishing process for metals. The electropolishing of stainless steel has vast commercial application, such as improving corrosion resistance, improving cleanness, and brightening. The surface topography characterization is performed using several techniques with different lateral resolutions and length scales, from atomic force microscopy in the nano-scale (<0.1 µm) to stylus and optical profilometry in the micro- and mesoscales (0.1 µm-1 mm). This paper presents an experimental length scale study of the surface texture of ground stainless steel followed by an electropolishing process in the micro and meso lateral scales. Both stylus and optical profilometers are used, and multiple cut-off lengths of the standard Gaussian filter are adopted. While the commonly used roughness amplitude parameters (Ra, Rq and Rz) fail to characterize electropolished textures, the root mean square slope (RΔq) is found to better describe the electropolished surfaces and to be insensitive to scale.

The electrostatic persistence length of polymers beyond the OSF limit.

PubMed

Everaers, R; Milchev, A; Yamakov, V

2002-05-01

We use large-scale Monte Carlo simulations to test scaling theories for the electrostatic persistence length l(e) of isolated, uniformly charged polymers with Debye-Hückel intrachain interactions in the limit where the screening length kappa(-1) exceeds the intrinsic persistence length of the chains. Our simulations cover a significantly larger part of the parameter space than previous studies. We observe no significant deviations from the prediction l(e) proportional to kappa(-2) by Khokhlov and Khachaturian which is based on applying the Odijk-Skolnick-Fixman theories of electrostatic bending rigidity and electrostatically excluded volume to the stretched de Gennes-Pincus-Velasco-Brochard polyelectrolyte blob chain. A linear or sublinear dependence of the persistence length on the screening length can be ruled out. We show that previous results pointing into this direction are due to a combination of excluded-volume and finite chain length effects. The paper emphasizes the role of scaling arguments in the development of useful representations for experimental and simulation data.

Current sheet extension and reconnection scaling in collisionless, hyperresistive, Hall MHD

NASA Astrophysics Data System (ADS)

Sullivan, B. P.; Bhattacharjee, A.; Huang, Y. M.

2009-11-01

We present Sweet-Parker type scaling arguments in the context of collisionless, hyper-resistive, Hall magnetohyrdodynamics (MHD). The predicted steady state scalings are consistent with those found by Chac'on et al. [PRL 99, 235001 (2007)], and Uzdensky, [PoP 16, 040702 (2009)], though our methods differ slightly. As with those studies, no prediction of electron dissipation region length is made. Numerical experiments confirm that both cusp like & extended geometries are realizable. Importantly, the length of the electron dissipation region (taken as a parameter by several recent studies) is found to depend on the level of hyper-resistivity. Although hyper-resistivity can produce modestly extended dissipation regions, the dissipation regions observed here are much shorter than those seen in many kinetic studies. The thickness of the dissipation region scales in a similar way as the length,so that the reconnection rate is not strongly sensitive to the level of hyperresistivity. The length of the electron dissipation region depends on electron inertia as well.The limitations of scaling theories that do not predict the length of the electron dissipation region are emphasized.

Ranges of Applicability for the Continuum-beam Model in the Constitutive Analysis of Carbon Nanotubes: Nanotubes or Nano-beams?

NASA Technical Reports Server (NTRS)

Harik, Vasyl Michael; Bushnell, Dennis M. (Technical Monitor)

2001-01-01

Ranges of validity for the continuum-beam model, the length-scale effects and continuum assumptions are analyzed in the framework of scaling analysis of NT structure. Two coupled criteria for the applicability of the continuum model are presented. Scaling analysis of NT buckling and geometric parameters (e.g., diameter and length) is carried out to determine the key non-dimensional parameters that control the buckling strains and modes of NT buckling. A model applicability map, which represents two classes of NTs, is constructed in the space of non-dimensional parameters. In an analogy with continuum mechanics, a mechanical law of geometric similitude is presented for two classes of beam-like NTs having different geometries. Expressions for the critical buckling loads and strains are tailored for the distinct groups of NTs and compared with the data provided by the molecular dynamics simulations. Implications for molecular dynamics simulations and the NT-based scanning probes are discussed.

A Thermal Model for Carbon Nanotube Interconnects

PubMed Central

Mohsin, Kaji Muhammad; Srivastava, Ashok; Sharma, Ashwani K.; Mayberry, Clay

2013-01-01

In this work, we have studied Joule heating in carbon nanotube based very large scale integration (VLSI) interconnects and incorporated Joule heating influenced scattering in our previously developed current transport model. The theoretical model explains breakdown in carbon nanotube resistance which limits the current density. We have also studied scattering parameters of carbon nanotube (CNT) interconnects and compared with the earlier work. For 1 µm length single-wall carbon nanotube, 3 dB frequency in S12 parameter reduces to ~120 GHz from 1 THz considering Joule heating. It has been found that bias voltage has little effect on scattering parameters, while length has very strong effect on scattering parameters. PMID:28348333

Buckling and postbuckling of size-dependent cracked microbeams based on a modified couple stress theory

NASA Astrophysics Data System (ADS)

Akbarzadeh Khorshidi, M.; Shariati, M.

2017-07-01

The elastic buckling analysis and the static postbuckling response of the Euler-Bernoulli microbeams containing an open edge crack are studied based on a modified couple stress theory. The cracked section is modeled by a massless elastic rotational spring. This model contains a material length scale parameter and can capture the size effect. The von Kármán nonlinearity is applied to display the postbuckling behavior. Analytical solutions of a critical buckling load and the postbuckling response are presented for simply supported cracked microbeams. This parametric study indicates the effects of the crack location, crack severity, and length scale parameter on the buckling and postbuckling behaviors of cracked microbeams.

Role of medium heterogeneity and viscosity contrast in miscible flow regimes and mixing zone growth: A computational pore-scale approach

NASA Astrophysics Data System (ADS)

Afshari, Saied; Hejazi, S. Hossein; Kantzas, Apostolos

2018-05-01

Miscible displacement of fluids in porous media is often characterized by the scaling of the mixing zone length with displacement time. Depending on the viscosity contrast of fluids, the scaling law varies between the square root relationship, a sign for dispersive transport regime during stable displacement, and the linear relationship, which represents the viscous fingering regime during an unstable displacement. The presence of heterogeneities in a porous medium significantly affects the scaling behavior of the mixing length as it interacts with the viscosity contrast to control the mixing of fluids in the pore space. In this study, the dynamics of the flow and transport during both unit and adverse viscosity ratio miscible displacements are investigated in heterogeneous packings of circular grains using pore-scale numerical simulations. The pore-scale heterogeneity level is characterized by the variations of the grain diameter and velocity field. The growth of mixing length is employed to identify the nature of the miscible transport regime at different viscosity ratios and heterogeneity levels. It is shown that as the viscosity ratio increases to higher adverse values, the scaling law of mixing length gradually shifts from dispersive to fingering nature up to a certain viscosity ratio and remains almost the same afterwards. In heterogeneous media, the mixing length scaling law is observed to be generally governed by the variations of the velocity field rather than the grain size. Furthermore, the normalization of mixing length temporal plots with respect to the governing parameters of viscosity ratio, heterogeneity, medium length, and medium aspect ratio is performed. The results indicate that mixing length scales exponentially with log-viscosity ratio and grain size standard deviation while the impact of aspect ratio is insignificant. For stable flows, mixing length scales with the square root of medium length, whereas it changes linearly with length during unstable flows. This scaling procedure allows us to describe the temporal variation of mixing length using a generalized curve for various combinations of the flow conditions and porous medium properties.

Sensitivity of the two-dimensional shearless mixing layer to the initial turbulent kinetic energy and integral length scale

NASA Astrophysics Data System (ADS)

Fathali, M.; Deshiri, M. Khoshnami

2016-04-01

The shearless mixing layer is generated from the interaction of two homogeneous isotropic turbulence (HIT) fields with different integral scales ℓ1 and ℓ2 and different turbulent kinetic energies E1 and E2. In this study, the sensitivity of temporal evolutions of two-dimensional, incompressible shearless mixing layers to the parametric variations of ℓ1/ℓ2 and E1/E2 is investigated. The sensitivity methodology is based on the nonintrusive approach; using direct numerical simulation and generalized polynomial chaos expansion. The analysis is carried out at Reℓ 1=90 for the high-energy HIT region and different integral length scale ratios 1 /4 ≤ℓ1/ℓ2≤4 and turbulent kinetic energy ratios 1 ≤E1/E2≤30 . It is found that the most influential parameter on the variability of the mixing layer evolution is the turbulent kinetic energy while variations of the integral length scale show a negligible influence on the flow field variability. A significant level of anisotropy and intermittency is observed in both large and small scales. In particular, it is found that large scales have higher levels of intermittency and sensitivity to the variations of ℓ1/ℓ2 and E1/E2 compared to the small scales. Reconstructed response surfaces of the flow field intermittency and the turbulent penetration depth show monotonic dependence on ℓ1/ℓ2 and E1/E2 . The mixing layer growth rate and the mixing efficiency both show sensitive dependence on the initial condition parameters. However, the probability density function of these quantities shows relatively small solution variations in response to the variations of the initial condition parameters.

Scaling in Free-Swimming Fish and Implications for Measuring Size-at-Time in the Wild

PubMed Central

Broell, Franziska; Taggart, Christopher T.

2015-01-01

This study was motivated by the need to measure size-at-age, and thus growth rate, in fish in the wild. We postulated that this could be achieved using accelerometer tags based first on early isometric scaling models that hypothesize that similar animals should move at the same speed with a stroke frequency that scales with length-1, and second on observations that the speed of primarily air-breathing free-swimming animals, presumably swimming ‘efficiently’, is independent of size, confirming that stroke frequency scales as length-1. However, such scaling relations between size and swimming parameters for fish remain mostly theoretical. Based on free-swimming saithe and sturgeon tagged with accelerometers, we introduce a species-specific scaling relationship between dominant tail beat frequency (TBF) and fork length. Dominant TBF was proportional to length-1 (r2 = 0.73, n = 40), and estimated swimming speed within species was independent of length. Similar scaling relations accrued in relation to body mass-0.29. We demonstrate that the dominant TBF can be used to estimate size-at-time and that accelerometer tags with onboard processing may be able to provide size-at-time estimates among free-swimming fish and thus the estimation of growth rate (change in size-at-time) in the wild. PMID:26673777

Universality from disorder in the random-bond Blume-Capel model

NASA Astrophysics Data System (ADS)

Fytas, N. G.; Zierenberg, J.; Theodorakis, P. E.; Weigel, M.; Janke, W.; Malakis, A.

2018-04-01

Using high-precision Monte Carlo simulations and finite-size scaling we study the effect of quenched disorder in the exchange couplings on the Blume-Capel model on the square lattice. The first-order transition for large crystal-field coupling is softened to become continuous, with a divergent correlation length. An analysis of the scaling of the correlation length as well as the susceptibility and specific heat reveals that it belongs to the universality class of the Ising model with additional logarithmic corrections which is also observed for the Ising model itself if coupled to weak disorder. While the leading scaling behavior of the disordered system is therefore identical between the second-order and first-order segments of the phase diagram of the pure model, the finite-size scaling in the ex-first-order regime is affected by strong transient effects with a crossover length scale L*≈32 for the chosen parameters.

Investigation of scale effects in the TRF determined by VLBI

NASA Astrophysics Data System (ADS)

Wahl, Daniel; Heinkelmann, Robert; Schuh, Harald

2017-04-01

The improvement of the International Terrestrial Reference Frame (ITRF) is of great significance for Earth sciences and one of the major tasks in geodesy. The translation, rotation and the scale-factor, as well as their linear rates, are solved in a 14-parameter transformation between individual frames of each space geodetic technique and the combined frame. In ITRF2008, as well as in the current release ITRF2014, the scale-factor is provided by Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) in equal shares. Since VLBI measures extremely precise group delays that are transformed to baseline lengths by the velocity of light, a natural constant, VLBI is the most suitable method for providing the scale. The aim of the current work is to identify possible shortcomings in the VLBI scale contribution to ITRF2008. For developing recommendations for an enhanced estimation, scale effects in the Terrestrial Reference Frame (TRF) determined with VLBI are considered in detail and compared to ITRF2008. In contrast to station coordinates, where the scale is defined by a geocentric position vector, pointing from the origin of the reference frame to the station, baselines are not related to the origin. They are describing the absolute scale independently from the datum. The more accurate a baseline length, and consequently the scale, is estimated by VLBI, the better the scale contribution to the ITRF. Considering time series of baseline length between different stations, a non-linear periodic signal can clearly be recognized, caused by seasonal effects at observation sites. Modeling these seasonal effects and subtracting them from the original data enhances the repeatability of single baselines significantly. Other effects influencing the scale strongly, are jumps in the time series of baseline length, mainly evoked by major earthquakes. Co- and post-seismic effects can be identified in the data, having a non-linear character likewise. Modeling the non-linear motion or completely excluding affected stations is another important step for an improved scale determination. In addition to the investigation of single baseline repeatabilities also the spatial transformation, which is performed for determining parameters of the ITRF2008, are considered. Since the reliability of the resulting transformation parameters is higher the more identical points are used in the transformation, an approach where all possible stations are used as control points is comprehensible. Experiments that examine the scale-factor and its spatial behavior between control points in ITRF2008 and coordinates determined by VLBI only showed that the network geometry has a large influence on the outcome as well. Introducing an unequally distributed network for the datum configuration, the correlations between translation parameters and the scale-factor can become remarkably high. Only a homogeneous spatial distribution of participating stations yields a maximally uncorrelated scale-factor that can be interpreted independent from other parameters. In the current release of the ITRF, the ITRF2014, for the first time, non-linear effects in the time series of station coordinates are taken into account. The present work shows the importance and the right direction of the modification of the ITRF calculation. But also further improvements were found which lead to an enhanced scale determination.

Full-Scale Numerical Modeling of Turbulent Processes in the Earth's Ionosphere

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

Eliasson, B.; Stenflo, L.; Department of Physics, Linkoeping University, SE-581 83 Linkoeping

2008-10-15

We present a full-scale simulation study of ionospheric turbulence by means of a generalized Zakharov model based on the separation of variables into high-frequency and slow time scales. The model includes realistic length scales of the ionospheric profile and of the electromagnetic and electrostatic fields, and uses ionospheric plasma parameters relevant for high-latitude radio facilities such as Eiscat and HAARP. A nested grid numerical method has been developed to resolve the different length-scales, while avoiding severe restrictions on the time step. The simulation demonstrates the parametric decay of the ordinary mode into Langmuir and ion-acoustic waves, followed by a Langmuirmore » wave collapse and short-scale caviton formation, as observed in ionospheric heating experiments.« less

Genetic parameters for different growth scales in GIFT strain of Nile tilapia (Oreochromis niloticus).

PubMed

He, J; Gao, H; Xu, P; Yang, R

2015-12-01

Body weight, length, width and depth at two growth stages were observed for a total of 5015 individuals of GIFT strain, along with a pedigree including 5588 individuals from 104 sires and 162 dams was collected. Multivariate animal models and a random regression model were used to genetically analyse absolute and relative growth scales of these growth traits. In absolute growth scale, the observed growth traits had moderate heritabilities ranging from 0.321 to 0.576, while pairwise ratios between body length, width and depth were lowly inherited and maximum heritability was only 0.146 for length/depth. All genetic correlations were above 0.5 between pairwise growth traits and genetic correlation between length/width and length/depth varied between both growth stages. Based on those estimates, selection index of multiple traits of interest can be formulated in future breeding program to improve genetically body weight and morphology of the GIFT strain. In relative growth scale, heritabilities in relative growths of body length, width and depth to body weight were 0.257, 0.412 and 0.066, respectively, while genetic correlations among these allometry scalings were above 0.8. Genetic analysis for joint allometries of body weight to body length, width and depth will contribute to genetically regulate the growth rate between body shape and body weight. © 2015 Blackwell Verlag GmbH.

Adiabatic Coupling Constant of Nitrobenzene- n-Alkane Critical Mixtures. Evidence from Ultrasonic Spectra and Thermodynamic Data

NASA Astrophysics Data System (ADS)

Mirzaev, Sirojiddin Z.; Kaatze, Udo

2016-09-01

Ultrasonic spectra of mixtures of nitrobenzene with n-alkanes, from n-hexane to n-nonane, are analyzed. They feature up to two Debye-type relaxation terms with discrete relaxation times and, near the critical point, an additional relaxation term due to the fluctuations in the local concentration. The latter can be well represented by the dynamic scaling theory. Its amplitude parameter reveals the adiabatic coupling constant of the mixtures of critical composition. The dependence of this thermodynamic parameter upon the length of the n-alkanes corresponds to that of the slope in the pressure dependence of the critical temperature and is thus taken another confirmation of the dynamic scaling model. The change in the variation of the coupling constant and of several other mixture parameters with alkane length probably reflects a structural change in the nitrobenzene- n-alkane mixtures when the number of carbon atoms per alkane exceeds eight.

Nuclear test ban treaty verification: Improving test ban monitoring with empirical and model-based signal processing

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

Harris, David B.; Gibbons, Steven J.; Rodgers, Arthur J.

In this approach, small scale-length medium perturbations not modeled in the tomographic inversion might be described as random fields, characterized by particular distribution functions (e.g., normal with specified spatial covariance). Conceivably, random field parameters (scatterer density or scale length) might themselves be the targets of tomographic inversions of the scattered wave field. As a result, such augmented models may provide processing gain through the use of probabilistic signal sub spaces rather than deterministic waveforms.

Nuclear test ban treaty verification: Improving test ban monitoring with empirical and model-based signal processing

DOE PAGES

Harris, David B.; Gibbons, Steven J.; Rodgers, Arthur J.; ...

2012-05-01

In this approach, small scale-length medium perturbations not modeled in the tomographic inversion might be described as random fields, characterized by particular distribution functions (e.g., normal with specified spatial covariance). Conceivably, random field parameters (scatterer density or scale length) might themselves be the targets of tomographic inversions of the scattered wave field. As a result, such augmented models may provide processing gain through the use of probabilistic signal sub spaces rather than deterministic waveforms.

Angular momentum and Zeeman effect in the presence of a minimal length based on the Kempf-Mann-Mangano algebra

NASA Astrophysics Data System (ADS)

Khosropour, B.

2016-07-01

In this work, we consider a D-dimensional ( β, β^' -two-parameters deformed Heisenberg algebra, which was introduced by Kempf et al. The angular-momentum operator in the presence of a minimal length scale based on the Kempf-Mann-Mangano algebra is obtained in the special case of β^' = 2β up to the first order over the deformation parameter β . It is shown that each of the components of the modified angular-momentum operator, commutes with the modified operator {L}2 . We find the magnetostatic field in the presence of a minimal length. The Zeeman effect in the deformed space is studied and also Lande's formula for the energy shift in the presence of a minimal length is obtained. We estimate an upper bound on the isotropic minimal length.

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

Prinja, A. K.

The Karhunen-Loeve stochastic spectral expansion of a random binary mixture of immiscible fluids in planar geometry is used to explore asymptotic limits of radiation transport in such mixtures. Under appropriate scalings of mixing parameters - correlation length, volume fraction, and material cross sections - and employing multiple- scale expansion of the angular flux, previously established atomic mix and diffusion limits are reproduced. When applied to highly contrasting material properties in the small cor- relation length limit, the methodology yields a nonstandard reflective medium transport equation that merits further investigation. Finally, a hybrid closure is proposed that produces both small andmore » large correlation length limits of the closure condition for the material averaged equations.« less

Comparison of rotator cuff muscle architecture between humans and other selected vertebrate species

PubMed Central

Mathewson, Margie A.; Kwan, Alan; Eng, Carolyn M.; Lieber, Richard L.; Ward, Samuel R.

2014-01-01

In this study, we compare rotator cuff muscle architecture of typically used animal models with that of humans and quantify the scaling relationships of these muscles across mammals. The four muscles that correspond to the human rotator cuff – supraspinatus, infraspinatus, subscapularis and teres minor – of 10 commonly studied animals were excised and subjected to a series of comparative measurements. When body mass among animals was regressed against physiological cross-sectional area, muscle mass and normalized fiber length, the confidence intervals suggested geometric scaling but did not exclude other scaling relationships. Based on the architectural difference index (ADI), a combined measure of fiber length-to-moment arm ratio, fiber length-to-muscle length ratio and the fraction of the total rotator cuff physiological cross-sectional area contributed by each muscle, chimpanzees were found to be the most similar to humans (ADI=2.15), followed closely by capuchins (ADI=2.16). Interestingly, of the eight non-primates studied, smaller mammals such as mice, rats and dogs were more similar to humans in architectural parameters compared with larger mammals such as sheep, pigs or cows. The force production versus velocity trade-off (indicated by fiber length-to-moment arm ratio) and the excursion ability (indicated by fiber length-to-muscle length ratio) of humans were also most similar to those of primates, followed by the small mammals. Overall, primates provide the best architectural representation of human muscle architecture. However, based on the muscle architectural parameters of non-primates, smaller rather than larger mammals may be better models for studying muscles related to the human rotator cuff. PMID:24072803

Effect of artificial length scales in large eddy simulation of a neutral atmospheric boundary layer flow: A simple solution to log-layer mismatch

NASA Astrophysics Data System (ADS)

Chatterjee, Tanmoy; Peet, Yulia T.

2017-07-01

A large eddy simulation (LES) methodology coupled with near-wall modeling has been implemented in the current study for high Re neutral atmospheric boundary layer flows using an exponentially accurate spectral element method in an open-source research code Nek 5000. The effect of artificial length scales due to subgrid scale (SGS) and near wall modeling (NWM) on the scaling laws and structure of the inner and outer layer eddies is studied using varying SGS and NWM parameters in the spectral element framework. The study provides an understanding of the various length scales and dynamics of the eddies affected by the LES model and also the fundamental physics behind the inner and outer layer eddies which are responsible for the correct behavior of the mean statistics in accordance with the definition of equilibrium layers by Townsend. An economical and accurate LES model based on capturing the near wall coherent eddies has been designed, which is successful in eliminating the artificial length scale effects like the log-layer mismatch or the secondary peak generation in the streamwise variance.

Transport regimes spanning magnetization-coupling phase space

NASA Astrophysics Data System (ADS)

Baalrud, Scott D.; Daligault, Jérôme

2017-10-01

The manner in which transport properties vary over the entire parameter-space of coupling and magnetization strength is explored. Four regimes are identified based on the relative size of the gyroradius compared to other fundamental length scales: the collision mean free path, Debye length, distance of closest approach, and interparticle spacing. Molecular dynamics simulations of self-diffusion and temperature anisotropy relaxation spanning the parameter space are found to agree well with the predicted boundaries. Comparison with existing theories reveals regimes where they succeed, where they fail, and where no theory has yet been developed.

An investigation of stress wave propagation in a shear deformable nanobeam based on modified couple stress theory

NASA Astrophysics Data System (ADS)

Akbarzadeh Khorshidi, Majid; Shariati, Mahmoud

2016-04-01

This paper presents a new investigation for propagation of stress wave in a nanobeam based on modified couple stress theory. Using Euler-Bernoulli beam theory, Timoshenko beam theory, and Reddy beam theory, the effect of shear deformation is investigated. This nonclassical model contains a material length scale parameter to capture the size effect and the Poisson effect is incorporated in the current model. Governing equations of motion are obtained by Hamilton's principle and solved explicitly. This solution leads to obtain two phase velocities for shear deformable beams in different directions. Effects of shear deformation, material length scale parameter, and Poisson's ratio on the behavior of these phase velocities are investigated and discussed. The results also show a dual behavior for phase velocities against Poisson's ratio.

Geostatistics and the representative elementary volume of gamma ray tomography attenuation in rocks cores

USGS Publications Warehouse

Vogel, J.R.; Brown, G.O.

2003-01-01

Semivariograms of samples of Culebra Dolomite have been determined at two different resolutions for gamma ray computed tomography images. By fitting models to semivariograms, small-scale and large-scale correlation lengths are determined for four samples. Different semivariogram parameters were found for adjacent cores at both resolutions. Relative elementary volume (REV) concepts are related to the stationarity of the sample. A scale disparity factor is defined and is used to determine sample size required for ergodic stationarity with a specified correlation length. This allows for comparison of geostatistical measures and representative elementary volumes. The modifiable areal unit problem is also addressed and used to determine resolution effects on correlation lengths. By changing resolution, a range of correlation lengths can be determined for the same sample. Comparison of voxel volume to the best-fit model correlation length of a single sample at different resolutions reveals a linear scaling effect. Using this relationship, the range of the point value semivariogram is determined. This is the range approached as the voxel size goes to zero. Finally, these results are compared to the regularization theory of point variables for borehole cores and are found to be a better fit for predicting the volume-averaged range.

The dynamics of oceanic fronts. I - The Gulf Stream

NASA Technical Reports Server (NTRS)

Kao, T. W.

1980-01-01

The establishment and maintenance of the mean hydrographic properties of large-scale density fronts in the upper ocean is considered. The dynamics is studied by posing an initial value problem starting with a near-surface discharge of buoyant water with a prescribed density deficit into an ambient stationary fluid of uniform density; full time dependent diffusion and Navier-Stokes equations are then used with constant eddy diffusion and viscosity coefficients, together with a constant Coriolis parameter. Scaling analysis reveals three independent scales of the problem including the radius of deformation of the inertial length, buoyancy length, and diffusive length scales. The governing equations are then suitably scaled and the resulting normalized equations are shown to depend on the Ekman number alone for problems of oceanic interest. It is concluded that the mean Gulf Stream dynamics can be interpreted in terms of a solution of the Navier-Stokes and diffusion equations, with the cross-stream circulation responsible for the maintenance of the front; this mechanism is suggested for the maintenance of the Gulf Stream dynamics.

Large scale Tesla coil guided discharges initiated by femtosecond laser filamentation in air

NASA Astrophysics Data System (ADS)

Arantchouk, L.; Point, G.; Brelet, Y.; Prade, B.; Carbonnel, J.; André, Y.-B.; Mysyrowicz, A.; Houard, A.

2014-07-01

The guiding of meter scale electric discharges produced in air by a Tesla coil is realized in laboratory using a focused terawatt laser pulse undergoing filamentation. The influence of the focus position, the laser arrival time, or the gap length is studied to determine the best conditions for efficient laser guiding. Discharge parameters such as delay, jitter, and resistance are characterized. An increase of the discharge length by a factor 5 has been achieved with the laser filaments, corresponding to a mean breakdown field of 2 kV/cm for a 1.8 m gap length. Consecutive guided discharges at a repetition rate of 10 Hz are also reported.

Scaling laws in decaying helical hydromagnetic turbulence

NASA Astrophysics Data System (ADS)

Christensson, M.; Hindmarsh, M.; Brandenburg, A.

2005-07-01

We study the evolution of growth and decay laws for the magnetic field coherence length ξ, energy E_M and magnetic helicity H in freely decaying 3D MHD turbulence. We show that with certain assumptions, self-similarity of the magnetic power spectrum alone implies that ξ σm t1/2. This in turn implies that magnetic helicity decays as Hσm t-2s, where s=(ξ_diff/ξH)2, in terms of ξ_diff, the diffusion length scale, and ξ_H, a length scale defined from the helicity power spectrum. The relative magnetic helicity remains constant, implying that the magnetic energy decays as E_M σm t-1/2-2s. The parameter s is inversely proportional to the magnetic Reynolds number Re_M, which is constant in the self-similar regime.

The accuracy of climate models' simulated season lengths and the effectiveness of grid scale correction factors

DOE PAGES

Winterhalter, Wade E.

2011-09-01

Global climate change is expected to impact biological populations through a variety of mechanisms including increases in the length of their growing season. Climate models are useful tools for predicting how season length might change in the future. However, the accuracy of these models tends to be rather low at regional geographic scales. Here, I determined the ability of several atmosphere and ocean general circulating models (AOGCMs) to accurately simulate historical season lengths for a temperate ectotherm across the continental United States. I also evaluated the effectiveness of regional-scale correction factors to improve the accuracy of these models. I foundmore » that both the accuracy of simulated season lengths and the effectiveness of the correction factors to improve the model's accuracy varied geographically and across models. These results suggest that regional specific correction factors do not always adequately remove potential discrepancies between simulated and historically observed environmental parameters. As such, an explicit evaluation of the correction factors' effectiveness should be included in future studies of global climate change's impact on biological populations.« less

Effect of microneedles on transdermal permeation enhancement of amlodipine.

PubMed

Nalluri, Buchi N; Uppuluri, Chandrateja; Devineni, Jyothirmayee; Nayak, Atul; Nair, Karthik J; Whiteside, Benjamin R; Das, Diganta B

2017-06-01

The present study aimed to investigate the effect of microneedle (MN) geometry parameters like length, density, shape and type on transdermal permeation enhancement of amlodipine (AMLO). Two types of MN devices viz. AdminPatch® arrays (ADM) (0.6, 1.2 and 1.5 mm lengths) and laboratory-fabricated polymeric MNs (PM) of 0.6 mm length were employed. In the case of PMs, arrays were applied thrice at different places within a 1.77-cm 2 skin area (PM-3) to maintain the MN density closer to 0.6 mm ADM. Scaling analyses were done using dimensionless parameters like concentration of AMLO (C t /C s ), thickness (h/L) and surface area of the skin (Sa/L 2 ). Microinjection moulding technique was employed to fabricate PM. Histological studies revealed that the PM, owing to their geometry/design, formed wider and deeper microconduits when compared to ADM of similar length. Approximately 6.84- and 6.11-fold increase in the cumulative amount (48 h) of AMLO permeated was observed with 1.5 mm ADM and PM-3 treatments respectively, when compared to passive permeation amounts. Good correlations (R 2  > 0.89) were observed between different dimensionless parameters with scaling analyses. The enhancement in AMLO permeation was found to be in the order of 1.5 mm ADM ≥ PM-3 > 1.2 mm ADM > 0.6 mm ADM ≥PM-1 > passive. The study suggests that MN application enhances the AMLO transdermal permeation and the geometrical parameters of MNs play an important role in the degree of such enhancement.

Correlations between Berg balance scale and gait speed in individuals with stroke wearing ankle-foot orthoses - a pilot study.

PubMed

Kobayashi, Toshiki; Leung, Aaron K L; Akazawa, Yasushi; Hutchins, Stephen W

2016-01-01

The Berg balance scale (BBS) is commonly used to assess balancing ability in patients with stroke. The BBS may be a good candidate for clinical assessment prior to orthotic intervention, if it correlates well with outcome measures such as gait speed. The purpose of this study was to investigate the correlation between the BBS measured prior to walking with an ankle-foot orthosis (AFO) and specific temporal-spatial parameters of gait when walking with an AFO donned. Eight individuals with chronic stroke participated in this study. Balancing ability was assessed using the BBS, while temporal-spatial parameters of gait (gait speed, bilateral step length, stride length and step width) were measured using a three-dimensional motion analysis system. The correlations between the BBS and gait parameters were investigated using a non-parametric Kendall's Tau (τ) correlation analysis. The BBS showed correlations with gait speed (τ = 0.64, p < 0.05), the step length of the affected side (τ = 0.74, p < 0.05), and the stride length (τ = 0.64, p < 0.05). Assessment of the BBS prior to AFO prescription may potentially help clinicians to estimate the gait speed achievable following orthotic intervention in patients with stroke. Implications for Rehabilitation Assessment of the BBS prior to AFO prescription may help orthotists to estimate the gait speed following an orthotic intervention in patients with stroke. Assessment of the BBS prior to AFO prescription may help orthotists to understand overall balance and postural control abilities in patients with stroke. A larger scale multifactorial analysis is warranted to confirm the results of this pilot study.

Scaling of electromagnetic transducers for shunt damping and energy harvesting

NASA Astrophysics Data System (ADS)

Elliott, Stephen J.; Zilletti, Michele

2014-04-01

In order for an electromagnetic transducer to operate well as either a mechanical shunt damper or as a vibration energy harvester, it must have good electromechanical coupling. A simple two-port analysis is used to derive a non-dimensional measure of electromechanical coupling, which must be large compared with unity for efficient operation in both of these applications. The two-port parameters for an inertial electromagnetic transducer are derived, from which this non-dimensional coupling parameter can be evaluated. The largest value that this parameter takes is approximately equal to the square of the magnetic flux density times the length of wire in the field, divided by the mechanical damping times the electrical resistance. This parameter is found to be only of the order of one for voice coil devices that weigh approximately 1 kg, and so such devices are generally not efficient, within the definition used here, in either of these applications. The non-dimensional coupling parameter is found to scale in approximate proportion to the device's characteristic length, however, and so although miniaturised devices are less efficient, greater efficiency can be obtained with large devices, such as those used to control civil engineering structures.

Improved incorporation of strain gradient elasticity in the flexoelectricity based energy harvesting from nanobeams

NASA Astrophysics Data System (ADS)

Zhou, Yarong; Yang, Xu; Pan, Dongmei; Wang, Binglei

2018-04-01

Flexoelectricity, the coupling of strain gradient and polarization, exists in all the dielectric materials and numerous models have been proposed to study this mechanism. However, the contribution of strain gradient elasticity has typically been underestimated. In this work, inspired by the one-length scale parameter model developed by Deng et al. [19], we incorporate three length-scale parameters to carefully capture the contribution of the purely mechanical strain gradients on flexoelectricity. This three-parameter model is more flexible and could be applied to investigate the flexoelectricity in a wide range of complicated deformations. Accordingly, we carry out our analysis by studying a dielectric nanobeam under different boundary conditions. We show that the strain gradient elasticity and flexoelectricity have apparent size effects and significant influence on the electromechanical response. In particular, the strain gradient effects could significantly reduce the energy efficiency, indicating their importance and necessity. This work may be helpful in understanding the mechanism of flexoelectricity at the nanoscale and sheds light on the flexoelectricity energy harvesting.

Device optimization and scaling properties of a gate-on-germanium source tunnel field-effect transistor

NASA Astrophysics Data System (ADS)

Chattopadhyay, Avik; Mallik, Abhijit; Omura, Yasuhisa

2015-06-01

A gate-on-germanium source (GoGeS) tunnel field-effect transistor (TFET) shows great promise for low-power (sub-0.5 V) applications. A detailed investigation, with the help of a numerical device simulator, on the effects of variation in different structural parameters of a GoGeS TFET on its electrical performance is reported in this paper. Structural parameters such as κ-value of the gate dielectric, length and κ-value of the spacer, and doping concentrations of both the substrate and source are considered. A low-κ symmetric spacer and a high-κ gate dielectric are found to yield better device performance. The substrate doping influences only the p-i-n leakage floor. The source doping is found to significantly affect performance parameters such as OFF-state current, ON-state current and subthreshold swing, in addition to a threshold voltage shift. Results of the investigation on the gate length scaling of such devices are also reported in this paper.

Effects of random initial conditions on the dynamical scaling behaviors of a fixed-energy Manna sandpile model in one dimension

NASA Astrophysics Data System (ADS)

Kwon, Sungchul; Kim, Jin Min

2015-01-01

For a fixed-energy (FE) Manna sandpile model in one dimension, we investigate the effects of random initial conditions on the dynamical scaling behavior of an order parameter. In the FE Manna model, the density ρ of total particles is conserved, and an absorbing phase transition occurs at ρc as ρ varies. In this work, we show that, for a given ρ , random initial distributions of particles lead to the domain structure in which domains with particle densities higher and lower than ρc alternate with each other. In the domain structure, the dominant length scale is the average domain length, which increases via the coalescence of adjacent domains. At ρc, the domain structure slows down the decay of an order parameter and also causes anomalous finite-size effects, i.e., power-law decay followed by an exponential one before the quasisteady state. As a result, the interplay of particle conservation and random initial conditions causes the domain structure, which is the origin of the anomalous dynamical scaling behaviors for random initial conditions.

Using electrical impedance tomography to map subsurface hydraulic conductivity

DOEpatents

Berryman, James G.; Daily, William D.; Ramirez, Abelardo L.; Roberts, Jeffery J.

2000-01-01

The use of Electrical Impedance Tomography (EIT) to map subsurface hydraulic conductivity. EIT can be used to map hydraulic conductivity in the subsurface where measurements of both amplitude and phase are made. Hydraulic conductivity depends on at least two parameters: porosity and a length scale parameter. Electrical Resistance Tomography (ERT) measures and maps electrical conductivity (which can be related to porosity) in three dimensions. By introducing phase measurements along with amplitude, the desired additional measurement of a pertinent length scale can be achieved. Hydraulic conductivity controls the ability to flush unwanted fluid contaminants from the surface. Thus inexpensive maps of hydraulic conductivity would improve planning strategies for subsequent remediation efforts. Fluid permeability is also of importance for oil field exploitation and thus detailed knowledge of fluid permeability distribution in three-dimension (3-D) would be a great boon to petroleum reservoir analysts.

Transport regimes spanning magnetization-coupling phase space

DOE PAGES

Baalrud, Scott D.; Daligault, Jérôme

2017-10-06

The manner in which transport properties vary over the entire parameter-space of coupling and magnetization strength is explored in this paper. Four regimes are identified based on the relative size of the gyroradius compared to other fundamental length scales: the collision mean free path, Debye length, distance of closest approach, and interparticle spacing. Molecular dynamics simulations of self-diffusion and temperature anisotropy relaxation spanning the parameter space are found to agree well with the predicted boundaries. Finally, comparison with existing theories reveals regimes where they succeed, where they fail, and where no theory has yet been developed.

Transport regimes spanning magnetization-coupling phase space

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

Baalrud, Scott D.; Daligault, Jérôme

The manner in which transport properties vary over the entire parameter-space of coupling and magnetization strength is explored in this paper. Four regimes are identified based on the relative size of the gyroradius compared to other fundamental length scales: the collision mean free path, Debye length, distance of closest approach, and interparticle spacing. Molecular dynamics simulations of self-diffusion and temperature anisotropy relaxation spanning the parameter space are found to agree well with the predicted boundaries. Finally, comparison with existing theories reveals regimes where they succeed, where they fail, and where no theory has yet been developed.

A method for estimating 2D Wrinkle Ridge Strain from application of fault displacement scaling to the Yakima Folds, Washington

NASA Astrophysics Data System (ADS)

Mège, Daniel; Reidel, Stephen P.

The Yakima folds on the central Columbia Plateau are a succession of thrusted anticlines thought to be analogs of planetary wrinkle ridges. They provide a unique opportunity to understand wrinkle ridge structure. Field data and length-displacement scaling are used to demonstrate a method for estimating two-dimensional horizontal contractional strain at wrinkle ridges. Strain is given as a function of ridge length, and depends on other parameters that can be inferred from the Yakima folds and fault population displacement studies. Because ridge length can be readily obtained from orbital imagery, the method can be applied to any wrinkle ridge population, and helps constrain quantitative tectonic models on other planets.

Approximate scaling properties of RNA free energy landscapes

NASA Technical Reports Server (NTRS)

Baskaran, S.; Stadler, P. F.; Schuster, P.

1996-01-01

RNA free energy landscapes are analysed by means of "time-series" that are obtained from random walks restricted to excursion sets. The power spectra, the scaling of the jump size distribution, and the scaling of the curve length measured with different yard stick lengths are used to describe the structure of these "time series". Although they are stationary by construction, we find that their local behavior is consistent with both AR(1) and self-affine processes. Random walks confined to excursion sets (i.e., with the restriction that the fitness value exceeds a certain threshold at each step) exhibit essentially the same statistics as free random walks. We find that an AR(1) time series is in general approximately self-affine on timescales up to approximately the correlation length. We present an empirical relation between the correlation parameter rho of the AR(1) model and the exponents characterizing self-affinity.

Design and test of a prototype scale ejector wing

NASA Technical Reports Server (NTRS)

Mefferd, L. A.; Alden, R. E.; Bevilacqua, P. M.

1979-01-01

A two dimensional momentum integral analysis was used to examine the effect of changing inlet area ratio, diffuser area ratio, and the ratio of ejector length to width. A relatively wide range of these parameters was considered. It was found that for constant inlet area ratio the augmentation increases with the ejector length, and for constant length: width ratio the augmentation increases with inlet area ratio. Scale model tests were used to verify these trends and to examine th effect of aspect ratio. On the basis of these results, an ejector configuration was selected for fabrication and testing at a scale representative of an ejector wing aircraft. The test ejector was powered by a Pratt-Whitney F401 engine developing approximately 12,000 pounds of thrust. The results of preliminary tests indicate that the ejector develops a thrust augmentation ratio better than 1.65.

Activity-dependent self-regulation of viscous length scales in biological systems

NASA Astrophysics Data System (ADS)

Nandi, Saroj Kumar

2018-05-01

The cellular cortex, which is a highly viscous thin cytoplasmic layer just below the cell membrane, controls the cell's mechanical properties, which can be characterized by a hydrodynamic length scale ℓ . Cells actively regulate ℓ via the activity of force-generating molecules, such as myosin II. Here we develop a general theory for such systems through a coarse-grained hydrodynamic approach including activity in the static description of the system providing an experimentally accessible parameter and elucidate the detailed mechanism of how a living system can actively self-regulate its hydrodynamic length scale, controlling the rigidity of the system. Remarkably, we find that ℓ , as a function of activity, behaves universally and roughly inversely proportional to the activity of the system. Our theory rationalizes a number of experimental findings on diverse systems, and comparison of our theory with existing experimental data shows good agreement.

Equilibrium structure of the plasma sheet boundary layer-lobe interface

NASA Technical Reports Server (NTRS)

Romero, H.; Ganguli, G.; Palmadesso, P.; Dusenbery, P. B.

1990-01-01

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Locking of length scales in two-band superconductors

DOE PAGES

Ichioka, M.; Kogan, Vladimir G.; Schmalian, J.

2017-02-21

Here, a model of a clean two-band s-wave superconductor with cylindrical Fermi surfaces, different Fermi velocities v 1,2, and a general 2×2 coupling matrix V αβ is used to study the order parameter distribution in vortex lattices. The Eilenberger weak coupling formalism is used to calculate numerically the spatial distributions of the pairing amplitudes Δ 1 and Δ 2 of the two bands for vortices parallel to the Fermi cylinders. For generic values of the interband coupling V 12, it is shown that, independently of the couplings V αβ, of the ratio v 1/v 2, of the temperature, and themore » applied field, the length scales of spatial variation of Δ 1 and of Δ 2 are the same within the accuracy of our calculations. The only exception from this single length-scale behavior is found for V 12 << V 11, i.e., for nearly decoupled bands.« less

A laboratory study to estimate pore geometric parameters of sandstones using complex conductivity and nuclear magnetic resonance for permeability prediction

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

Osterman, Gordon; Keating, Kristina; Binley, Andrew

Here, we estimate parameters from the Katz and Thompson permeability model using laboratory complex electrical conductivity (CC) and nuclear magnetic resonance (NMR) data to build permeability models parameterized with geophysical measurements. We use the Katz and Thompson model based on the characteristic hydraulic length scale, determined from mercury injection capillary pressure estimates of pore throat size, and the intrinsic formation factor, determined from multisalinity conductivity measurements, for this purpose. Two new permeability models are tested, one based on CC data and another that incorporates CC and NMR data. From measurements made on forty-five sandstone cores collected from fifteen different formations,more » we evaluate how well the CC relaxation time and the NMR transverse relaxation times compare to the characteristic hydraulic length scale and how well the formation factor estimated from CC parameters compares to the intrinsic formation factor. We find: (1) the NMR transverse relaxation time models the characteristic hydraulic length scale more accurately than the CC relaxation time (R 2 of 0.69 and 0.33 and normalized root mean square errors (NRMSE) of 0.16 and 0.21, respectively); (2) the CC estimated formation factor is well correlated with the intrinsic formation factor (NRMSE50.23). We demonstrate that that permeability estimates from the joint-NMR-CC model (NRMSE50.13) compare favorably to estimates from the Katz and Thompson model (NRMSE50.074). Lastly, this model advances the capability of the Katz and Thompson model by employing parameters measureable in the field giving it the potential to more accurately estimate permeability using geophysical measurements than are currently possible.« less

A laboratory study to estimate pore geometric parameters of sandstones using complex conductivity and nuclear magnetic resonance for permeability prediction

DOE PAGES

Osterman, Gordon; Keating, Kristina; Binley, Andrew; ...

2016-03-18

Here, we estimate parameters from the Katz and Thompson permeability model using laboratory complex electrical conductivity (CC) and nuclear magnetic resonance (NMR) data to build permeability models parameterized with geophysical measurements. We use the Katz and Thompson model based on the characteristic hydraulic length scale, determined from mercury injection capillary pressure estimates of pore throat size, and the intrinsic formation factor, determined from multisalinity conductivity measurements, for this purpose. Two new permeability models are tested, one based on CC data and another that incorporates CC and NMR data. From measurements made on forty-five sandstone cores collected from fifteen different formations,more » we evaluate how well the CC relaxation time and the NMR transverse relaxation times compare to the characteristic hydraulic length scale and how well the formation factor estimated from CC parameters compares to the intrinsic formation factor. We find: (1) the NMR transverse relaxation time models the characteristic hydraulic length scale more accurately than the CC relaxation time (R 2 of 0.69 and 0.33 and normalized root mean square errors (NRMSE) of 0.16 and 0.21, respectively); (2) the CC estimated formation factor is well correlated with the intrinsic formation factor (NRMSE50.23). We demonstrate that that permeability estimates from the joint-NMR-CC model (NRMSE50.13) compare favorably to estimates from the Katz and Thompson model (NRMSE50.074). Lastly, this model advances the capability of the Katz and Thompson model by employing parameters measureable in the field giving it the potential to more accurately estimate permeability using geophysical measurements than are currently possible.« less

Seismic imaging in hardrock environments: The role of heterogeneity?

NASA Astrophysics Data System (ADS)

Bongajum, Emmanuel; Milkereit, Bernd; Adam, Erick; Meng, Yijian

2012-10-01

We investigate the effect of petrophysical scale parameters and structural dips on wave propagation and imaging in heterogeneous media. Seismic wave propagation effects within the heterogeneous media are studied for different velocity models with scale lengths determined via stochastic analysis of petrophysical logs from the Matagami mine, Quebec, Canada. The elastic modeling study reveals that provided certain conditions of the velocity fluctuations are met, strong local distortions of amplitude and arrival times of propagating waves are observed as the degree of scale length anisotropy in the P-wave velocity increases. The location of these local amplitude anomalies is related to the dips characterizing the fabric of the host rocks. This result is different from the elliptical shape of direct waves often defined by effective anisotropic parameters used for layered media. Although estimates of anisotropic parameters suggest weak anisotropy in the investigated models, these effective anisotropic parameters often used in VTI/TTI do not sufficiently describe the effects of scale length anisotropy in heterogeneous media that show such local amplitude, travel time, and phase distortions in the wavefields. Numerical investigations on the implications for reverse time migration (RTM) routines corroborate that mean P-wave velocity of the host rocks produces reliable imaging results. Based on the RTM results, we postulate the following: weak anisotropy in hardrock environments is a sufficient assumption for processing seismic data; and seismic scattering effects due to velocity heterogeneity with a dip component is not sufficient to cause mislocation errors of target structures as observed in the discrepancy between the location of the strong seismic reflections associated to the Matagami sulfide orebody and its true location. Future work will investigate other factors that may provide plausible explanations for these mislocation problems, with the objective of providing a mitigation strategy for incorporation into the seismic data processing sequence when imaging in hardrock settings.

A comprehensive allometric analysis of 2nd digit length to 4th digit length in humans.

PubMed

Lolli, Lorenzo; Batterham, Alan M; Kratochvíl, Lukáš; Flegr, Jaroslav; Weston, Kathryn L; Atkinson, Greg

2017-06-28

It has been widely reported that men have a lower ratio of the 2nd and 4th human finger lengths (2D : 4D). Size-scaling ratios, however, have the seldom-appreciated potential for providing biased estimates. Using an information-theoretic approach, we compared 12 candidate models, with different assumptions and error structures, for scaling untransformed 2D to 4D lengths from 154 men and 262 women. In each hand, the two-parameter power function and the straight line with intercept models, both with normal, homoscedastic error, were superior to the other models and essentially equivalent to each other for normalizing 2D to 4D lengths. The conventional 2D : 4D ratio biased relative 2D length low for the generally bigger hands of men, and vice versa for women, thereby leading to an artefactual indication that mean relative 2D length is lower in men than women. Conversely, use of the more appropriate allometric or linear regression models revealed that mean relative 2D length was, in fact, greater in men than women. We conclude that 2D does not vary in direct proportion to 4D for both men and women, rendering the use of the simple 2D : 4D ratio inappropriate for size-scaling purposes and intergroup comparisons. © 2017 The Author(s).

Multiple-length-scale deformation analysis in a thermoplastic polyurethane

PubMed Central

Sui, Tan; Baimpas, Nikolaos; Dolbnya, Igor P.; Prisacariu, Cristina; Korsunsky, Alexander M.

2015-01-01

Thermoplastic polyurethane elastomers enjoy an exceptionally wide range of applications due to their remarkable versatility. These block co-polymers are used here as an example of a structurally inhomogeneous composite containing nano-scale gradients, whose internal strain differs depending on the length scale of consideration. Here we present a combined experimental and modelling approach to the hierarchical characterization of block co-polymer deformation. Synchrotron-based small- and wide-angle X-ray scattering and radiography are used for strain evaluation across the scales. Transmission electron microscopy image-based finite element modelling and fast Fourier transform analysis are used to develop a multi-phase numerical model that achieves agreement with the combined experimental data using a minimal number of adjustable structural parameters. The results highlight the importance of fuzzy interfaces, that is, regions of nanometre-scale structure and property gradients, in determining the mechanical properties of hierarchical composites across the scales. PMID:25758945

Investigations on the hierarchy of reference frames in geodesy and geodynamics

NASA Technical Reports Server (NTRS)

Grafarend, E. W.; Mueller, I. I.; Papo, H. B.; Richter, B.

1979-01-01

Problems related to reference directions were investigated. Space and time variant angular parameters are illustrated in hierarchic structures or towers. Using least squares techniques, model towers of triads are presented which allow the formation of linear observation equations. Translational and rotational degrees of freedom (origin and orientation) are discussed along with and the notion of length and scale degrees of freedom. According to the notion of scale parallelism, scale factors with respect to a unit length are given. Three-dimensional geodesy was constructed from the set of three base vectors (gravity, earth-rotation and the ecliptic normal vector). Space and time variations are given with respect to a polar and singular value decomposition or in terms of changes in translation, rotation, deformation (shear, dilatation or angular and scale distortions).

Non-Hookean statistical mechanics of clamped graphene ribbons

NASA Astrophysics Data System (ADS)

Bowick, Mark J.; Košmrlj, Andrej; Nelson, David R.; Sknepnek, Rastko

2017-03-01

Thermally fluctuating sheets and ribbons provide an intriguing forum in which to investigate strong violations of Hooke's Law: Large distance elastic parameters are in fact not constant but instead depend on the macroscopic dimensions. Inspired by recent experiments on free-standing graphene cantilevers, we combine the statistical mechanics of thin elastic plates and large-scale numerical simulations to investigate the thermal renormalization of the bending rigidity of graphene ribbons clamped at one end. For ribbons of dimensions W ×L (with L ≥W ), the macroscopic bending rigidity κR determined from cantilever deformations is independent of the width when W <ℓth , where ℓth is a thermal length scale, as expected. When W >ℓth , however, this thermally renormalized bending rigidity begins to systematically increase, in agreement with the scaling theory, although in our simulations we were not quite able to reach the system sizes necessary to determine the fully developed power law dependence on W . When the ribbon length L >ℓp , where ℓp is the W -dependent thermally renormalized ribbon persistence length, we observe a scaling collapse and the beginnings of large scale random walk behavior.

Gate length variation effect on performance of gate-first self-aligned In₀.₅₃Ga₀.₄₇As MOSFET.

PubMed

Mohd Razip Wee, Mohd F; Dehzangi, Arash; Bollaert, Sylvain; Wichmann, Nicolas; Majlis, Burhanuddin Y

2013-01-01

A multi-gate n-type In₀.₅₃Ga₀.₄₇As MOSFET is fabricated using gate-first self-aligned method and air-bridge technology. The devices with different gate lengths were fabricated with the Al2O3 oxide layer with the thickness of 8 nm. In this letter, impact of gate length variation on device parameter such as threshold voltage, high and low voltage transconductance, subthreshold swing and off current are investigated at room temperature. Scaling the gate length revealed good enhancement in all investigated parameters but the negative shift in threshold voltage was observed for shorter gate lengths. The high drain current of 1.13 A/mm and maximum extrinsic transconductance of 678 mS/mm with the field effect mobility of 364 cm(2)/Vs are achieved for the gate length and width of 0.2 µm and 30 µm, respectively. The source/drain overlap length for the device is approximately extracted about 51 nm with the leakage current in order of 10(-8) A. The results of RF measurement for cut-off and maximum oscillation frequency for devices with different gate lengths are compared.

Gate Length Variation Effect on Performance of Gate-First Self-Aligned In0.53Ga0.47As MOSFET

PubMed Central

Mohd Razip Wee, Mohd F.; Dehzangi, Arash; Bollaert, Sylvain; Wichmann, Nicolas; Majlis, Burhanuddin Y.

2013-01-01

A multi-gate n-type In0.53Ga0.47As MOSFET is fabricated using gate-first self-aligned method and air-bridge technology. The devices with different gate lengths were fabricated with the Al2O3 oxide layer with the thickness of 8 nm. In this letter, impact of gate length variation on device parameter such as threshold voltage, high and low voltage transconductance, subthreshold swing and off current are investigated at room temperature. Scaling the gate length revealed good enhancement in all investigated parameters but the negative shift in threshold voltage was observed for shorter gate lengths. The high drain current of 1.13 A/mm and maximum extrinsic transconductance of 678 mS/mm with the field effect mobility of 364 cm2/Vs are achieved for the gate length and width of 0.2 µm and 30µm, respectively. The source/drain overlap length for the device is approximately extracted about 51 nm with the leakage current in order of 10−8 A. The results of RF measurement for cut-off and maximum oscillation frequency for devices with different gate lengths are compared. PMID:24367548

Resilience of Key Biological Parameters of the Senegalese Flat Sardinella to Overfishing and Climate Change.

PubMed

Ba, Kamarel; Thiaw, Modou; Lazar, Najih; Sarr, Alassane; Brochier, Timothée; Ndiaye, Ismaïla; Faye, Alioune; Sadio, Oumar; Panfili, Jacques; Thiaw, Omar Thiom; Brehmer, Patrice

2016-01-01

The stock of the Senegalese flat sardinella, Sardinella maderensis, is highly exploited in Senegal, West Africa. Its growth and reproduction parameters are key biological indicators for improving fisheries management. This study reviewed these parameters using landing data from small-scale fisheries in Senegal and literature information dated back more than 25 years. Age was estimated using length-frequency data to calculate growth parameters and assess the growth performance index. With global climate change there has been an increase in the average sea surface temperature along the Senegalese coast but the length-weight parameters, sex ratio, size at first sexual maturity, period of reproduction and condition factor of S. maderensis have not changed significantly. The above parameters of S. maderensis have hardly changed, despite high exploitation and fluctuations in environmental conditions that affect the early development phases of small pelagic fish in West Africa. This lack of plasticity of the species regarding of the biological parameters studied should be considered when planning relevant fishery management plans.

Asymptotic Expansion Homogenization for Multiscale Nuclear Fuel Analysis

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

Hales, J. D.; Tonks, M. R.; Chockalingam, K.

2015-03-01

Engineering scale nuclear fuel performance simulations can benefit by utilizing high-fidelity models running at a lower length scale. Lower length-scale models provide a detailed view of the material behavior that is used to determine the average material response at the macroscale. These lower length-scale calculations may provide insight into material behavior where experimental data is sparse or nonexistent. This multiscale approach is especially useful in the nuclear field, since irradiation experiments are difficult and expensive to conduct. The lower length-scale models complement the experiments by influencing the types of experiments required and by reducing the total number of experiments needed.more » This multiscale modeling approach is a central motivation in the development of the BISON-MARMOT fuel performance codes at Idaho National Laboratory. These codes seek to provide more accurate and predictive solutions for nuclear fuel behavior. One critical aspect of multiscale modeling is the ability to extract the relevant information from the lower length-scale sim- ulations. One approach, the asymptotic expansion homogenization (AEH) technique, has proven to be an effective method for determining homogenized material parameters. The AEH technique prescribes a system of equations to solve at the microscale that are used to compute homogenized material constants for use at the engineering scale. In this work, we employ AEH to explore the effect of evolving microstructural thermal conductivity and elastic constants on nuclear fuel performance. We show that the AEH approach fits cleanly into the BISON and MARMOT codes and provides a natural, multidimensional homogenization capability.« less

Wetting Transition of Nonpolar Neutral Molecule System on a Neutral and Atomic Length Scale Roughness Substrate

NASA Astrophysics Data System (ADS)

Zhou, Shiqi

2018-03-01

One recently proposed new method for accurately determining wetting temperature is applied to the wetting transition occurring in a single component nonpolar neutral molecule system near a neutral planar substrate with roughness produced by cosinusoidal modulation(s). New observations are summarized into five points: (i) for a planar substrate superimposed with one cosinusoidal modulation, with increasing of the periodicity length or the surface attraction force field, or decreasing of the amplitude, wetting temperature T_W drops accordingly and the three parameters show multiplication effect; moreover, both the periodicity length and amplitude effect curves display pole phenomena and saturation phenomena, and the T_W saturation occurs at small (for case of large amplitude) or large (for case of small amplitude) periodicity length side, respectively. (ii) In the case of the planar substrate superimposed with two cosinusoidal modulations with equal periodicity length, the initial phase difference is critical issue that influences the T_W, which decreases with the initial phase difference. (iii) In the case of the planar substrate superimposed with two cosinusoidal modulations with zero phase difference, change of the T_W with one periodicity length under the condition of another periodicity length unchanged is non-monotonous. (iv) When the parameters are chosen such that the T_W draws ever closer to the bulk critical temperature, wetting transition on the roughness substrate eventually does not occur. (v) The present microscopic calculation challenges traditional macroscopic theory by confirming that the atomic length scale roughness always renders the surface less hydrophilic and whereas the mesoscopical roughness renders the surface more hydrophilic. All of these observations summarized can be reasonably explained by the relative strength of the attraction actually enjoyed by the surface gas molecules to the attraction the gas molecules can get when in bulk.

Angular filter refractometry analysis using simulated annealing [An improved method for characterizing plasma density profiles using angular filter refractometry

DOE PAGES

Angland, P.; Haberberger, D.; Ivancic, S. T.; ...

2017-10-30

Here, a new method of analysis for angular filter refractometry images was developed to characterize laser-produced, long-scale-length plasmas using an annealing algorithm to iterative converge upon a solution. Angular filter refractometry (AFR) is a novel technique used to characterize the density pro files of laser-produced, long-scale-length plasmas. A synthetic AFR image is constructed by a user-defined density profile described by eight parameters, and the algorithm systematically alters the parameters until the comparison is optimized. The optimization and statistical uncertainty calculation is based on a minimization of themore » $$\\chi$$2 test statistic. The algorithm was successfully applied to experimental data of plasma expanding from a flat, laser-irradiated target, resulting in average uncertainty in the density profile of 5-10% in the region of interest.« less

Angular filter refractometry analysis using simulated annealing [An improved method for characterizing plasma density profiles using angular filter refractometry

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

Angland, P.; Haberberger, D.; Ivancic, S. T.

Here, a new method of analysis for angular filter refractometry images was developed to characterize laser-produced, long-scale-length plasmas using an annealing algorithm to iterative converge upon a solution. Angular filter refractometry (AFR) is a novel technique used to characterize the density pro files of laser-produced, long-scale-length plasmas. A synthetic AFR image is constructed by a user-defined density profile described by eight parameters, and the algorithm systematically alters the parameters until the comparison is optimized. The optimization and statistical uncertainty calculation is based on a minimization of themore » $$\\chi$$2 test statistic. The algorithm was successfully applied to experimental data of plasma expanding from a flat, laser-irradiated target, resulting in average uncertainty in the density profile of 5-10% in the region of interest.« less

Nonlinear analysis of 0-3 polarized PLZT microplate based on the new modified couple stress theory

NASA Astrophysics Data System (ADS)

Wang, Liming; Zheng, Shijie

2018-02-01

In this study, based on the new modified couple stress theory, the size- dependent model for nonlinear bending analysis of a pure 0-3 polarized PLZT plate is developed for the first time. The equilibrium equations are derived from a variational formulation based on the potential energy principle and the new modified couple stress theory. The Galerkin method is adopted to derive the nonlinear algebraic equations from governing differential equations. And then the nonlinear algebraic equations are solved by using Newton-Raphson method. After simplification, the new model includes only a material length scale parameter. In addition, numerical examples are carried out to study the effect of material length scale parameter on the nonlinear bending of a simply supported pure 0-3 polarized PLZT plate subjected to light illumination and uniform distributed load. The results indicate the new model is able to capture the size effect and geometric nonlinearity.

Scale-dependent coupling of hysteretic capillary pressure, trapping, and fluid mobilities

NASA Astrophysics Data System (ADS)

Doster, F.; Celia, M. A.; Nordbotten, J. M.

2012-12-01

Many applications of multiphase flow in porous media, including CO2-storage and enhanced oil recovery, require mathematical models that span a large range of length scales. In the context of numerical simulations, practical grid sizes are often on the order of tens of meters, thereby de facto defining a coarse model scale. Under particular conditions, it is possible to approximate the sub-grid-scale distribution of the fluid saturation within a grid cell; that reconstructed saturation can then be used to compute effective properties at the coarse scale. If both the density difference between the fluids and the vertical extend of the grid cell are large, and buoyant segregation within the cell on a sufficiently shorte time scale, then the phase pressure distributions are essentially hydrostatic and the saturation profile can be reconstructed from the inferred capillary pressures. However, the saturation reconstruction may not be unique because the parameters and parameter functions of classical formulations of two-phase flow in porous media - the relative permeability functions, the capillary pressure -saturation relationship, and the residual saturations - show path dependence, i.e. their values depend not only on the state variables but also on their drainage and imbibition histories. In this study we focus on capillary pressure hysteresis and trapping and show that the contribution of hysteresis to effective quantities is dependent on the vertical length scale. By studying the transition from the two extreme cases - the homogeneous saturation distribution for small vertical extents and the completely segregated distribution for large extents - we identify how hysteretic capillary pressure at the local scale induces hysteresis in all coarse-scale quantities for medium vertical extents and finally vanishes for large vertical extents. Our results allow for more accurate vertically integrated modeling while improving our understanding of the coupling of capillary pressure and relative permeabilities over larger length scales.

Lagrangian Formulation of a Magnetostatic Field in the Presence of a Minimal Length Scale Based on the Kempf Algebra

NASA Astrophysics Data System (ADS)

Moayedi, S. K.; Setare, M. R.; Khosropour, B.

2013-11-01

In the 1990s, Kempf and his collaborators Mangano and Mann introduced a D-dimensional (β, β‧)-two-parameter deformed Heisenberg algebra which leads to an isotropic minimal length (\\triangle Xi)\\min = \\hbar √ {Dβ +β '}, \\forall i\\in \\{1, 2, ..., D\\}. In this work, the Lagrangian formulation of a magnetostatic field in three spatial dimensions (D = 3) described by Kempf algebra is presented in the special case of β‧ = 2β up to the first-order over β. We show that at the classical level there is a similarity between magnetostatics in the presence of a minimal length scale (modified magnetostatics) and the magnetostatic sector of the Abelian Lee-Wick model in three spatial dimensions. The integral form of Ampere's law and the energy density of a magnetostatic field in the modified magnetostatics are obtained. Also, the Biot-Savart law in the modified magnetostatics is found. By studying the effect of minimal length corrections to the gyromagnetic moment of the muon, we conclude that the upper bound on the isotropic minimal length scale in three spatial dimensions is 4.42×10-19 m. The relationship between magnetostatics with a minimal length and the Gaete-Spallucci nonlocal magnetostatics [J. Phys. A: Math. Theor. 45, 065401 (2012)] is investigated.

Ultra-fast escape maneuver of an octopus-inspired robot.

PubMed

Weymouth, G D; Subramaniam, V; Triantafyllou, M S

2015-02-02

We design and test an octopus-inspired flexible hull robot that demonstrates outstanding fast-starting performance. The robot is hyper-inflated with water, and then rapidly deflates to expel the fluid so as to power the escape maneuver. Using this robot we verify for the first time in laboratory testing that rapid size-change can substantially reduce separation in bluff bodies traveling several body lengths, and recover fluid energy which can be employed to improve the propulsive performance. The robot is found to experience speeds over ten body lengths per second, exceeding that of a similarly propelled optimally streamlined rigid rocket. The peak net thrust force on the robot is more than 2.6 times that on an optimal rigid body performing the same maneuver, experimentally demonstrating large energy recovery and enabling acceleration greater than 14 body lengths per second squared. Finally, over 53% of the available energy is converted into payload kinetic energy, a performance that exceeds the estimated energy conversion efficiency of fast-starting fish. The Reynolds number based on final speed and robot length is [Formula: see text]. We use the experimental data to establish a fundamental deflation scaling parameter [Formula: see text] which characterizes the mechanisms of flow control via shape change. Based on this scaling parameter, we find that the fast-starting performance improves with increasing size.

An effective medium approach to predict the apparent contact angle of drops on super-hydrophobic randomly rough surfaces.

PubMed

Bottiglione, F; Carbone, G

2015-01-14

The apparent contact angle of large 2D drops with randomly rough self-affine profiles is numerically investigated. The numerical approach is based upon the assumption of large separation of length scales, i.e. it is assumed that the roughness length scales are much smaller than the drop size, thus making it possible to treat the problem through a mean-field like approach relying on the large-separation of scales. The apparent contact angle at equilibrium is calculated in all wetting regimes from full wetting (Wenzel state) to partial wetting (Cassie state). It was found that for very large values of the roughness Wenzel parameter (r(W) > -1/ cos θ(Y), where θ(Y) is the Young's contact angle), the interface approaches the perfect non-wetting condition and the apparent contact angle is almost equal to 180°. The results are compared with the case of roughness on one single scale (sinusoidal surface) and it is found that, given the same value of the Wenzel roughness parameter rW, the apparent contact angle is much larger for the case of a randomly rough surface, proving that the multi-scale character of randomly rough surfaces is a key factor to enhance superhydrophobicity. Moreover, it is shown that for millimetre-sized drops, the actual drop pressure at static equilibrium weakly affects the wetting regime, which instead seems to be dominated by the roughness parameter. For this reason a methodology to estimate the apparent contact angle is proposed, which relies only upon the micro-scale properties of the rough surface.

Generating and controlling homogeneous air turbulence using random jet arrays

NASA Astrophysics Data System (ADS)

Carter, Douglas; Petersen, Alec; Amili, Omid; Coletti, Filippo

2016-12-01

The use of random jet arrays, already employed in water tank facilities to generate zero-mean-flow homogeneous turbulence, is extended to air as a working fluid. A novel facility is introduced that uses two facing arrays of individually controlled jets (256 in total) to force steady homogeneous turbulence with negligible mean flow, shear, and strain. Quasi-synthetic jet pumps are created by expanding pressurized air through small straight nozzles and are actuated by fast-response low-voltage solenoid valves. Velocity fields, two-point correlations, energy spectra, and second-order structure functions are obtained from 2D PIV and are used to characterize the turbulence from the integral-to-the Kolmogorov scales. Several metrics are defined to quantify how well zero-mean-flow homogeneous turbulence is approximated for a wide range of forcing and geometric parameters. With increasing jet firing time duration, both the velocity fluctuations and the integral length scales are augmented and therefore the Reynolds number is increased. We reach a Taylor-microscale Reynolds number of 470, a large-scale Reynolds number of 74,000, and an integral-to-Kolmogorov length scale ratio of 680. The volume of the present homogeneous turbulence, the largest reported to date in a zero-mean-flow facility, is much larger than the integral length scale, allowing for the natural development of the energy cascade. The turbulence is found to be anisotropic irrespective of the distance between the jet arrays. Fine grids placed in front of the jets are effective at modulating the turbulence, reducing both velocity fluctuations and integral scales. Varying the jet-to-jet spacing within each array has no effect on the integral length scale, suggesting that this is dictated by the length scale of the jets.

Estimation of effective aerodynamic roughness with altimeter measurements

NASA Technical Reports Server (NTRS)

Menenti, M.; Ritchie, J. C.

1992-01-01

A new method is presented for estimating the aerodynamic roughness length of heterogeneous land surfaces and complex landscapes using elevation measurements performed with an airborne laser altimeter and the Seasat radar altimeter. Land surface structure is characterized at increasing length scales by considering three basic landscape elements: (1) partial to complete canopies of herbaceous vegetation; (2) sparse obstacles (e.g., shrubs and trees); and (3) local relief. Measured parameters of land surface geometry are combined to obtain an effective aerodynamic roughness length which parameterizes the total atmosphere-land surface stress.

Size effects on miniature Stirling cycle cryocoolers

NASA Astrophysics Data System (ADS)

Yang, Xiaoqin; Chung, J. N.

2005-08-01

Size effects on the performance of Stirling cycle cryocoolers were investigated by examining each individual loss associated with the regenerator and combining these effects. For the fixed cycle parameters and given regenerator length scale, it was found that only for a specific range of the hydrodynamic diameter the system can produce net refrigeration and there is an optimum hydraulic diameter at which the maximum net refrigeration is achieved. When the hydraulic diameter is less than the optimum value, the regenerator performance is controlled by the pressure drop loss; when the hydraulic diameter is greater than the optimum value, the system performance is controlled by the thermal losses. It was also found that there exists an optimum ratio between the hydraulic diameter and the length of the regenerator that offers the maximum net refrigeration. As the regenerator length is decreased, the optimum hydraulic diameter-to-length ratio increases; and the system performance is increased that is controlled by the pressure drop loss and heat conduction loss. Choosing appropriate regenerator characteristic sizes in small-scale systems are more critical than in large-scale ones.

On the structural properties of small-world networks with range-limited shortcut links

NASA Astrophysics Data System (ADS)

Jia, Tao; Kulkarni, Rahul V.

2013-12-01

We explore a new variant of Small-World Networks (SWNs), in which an additional parameter (r) sets the length scale over which shortcuts are uniformly distributed. When r=0 we have an ordered network, whereas r=1 corresponds to the original Watts-Strogatz SWN model. These limited range SWNs have a similar degree distribution and scaling properties as the original SWN model. We observe the small-world phenomenon for r≪1, indicating that global shortcuts are not necessary for the small-world effect. For limited range SWNs, the average path length changes nonmonotonically with system size, whereas for the original SWN model it increases monotonically. We propose an expression for the average path length for limited range SWNs based on numerical simulations and analytical approximations.

Ion kinetic scale in the solar wind observed.

PubMed

Śafránková, Jana; Němeček, Zdeněk; Přech, Lubomír; Zastenker, Georgy N

2013-01-11

This Letter shows the first results from the solar wind monitor onboard the Spektr-R spacecraft which measures plasma moments with a time resolution of 31 ms. This high-time resolution allows us to make direct observations of solar wind turbulence below ion kinetic length scales. We present examples of the frequency spectra of the density, velocity, and thermal velocity. Our study reveals that although these parameters exhibit the same behavior at the magnetohydrodynamic scale, their spectra are remarkably different at the kinetic scale.

Investigation of Outer Length Scale In Optical Turbulence

DTIC Science & Technology

2003-12-01

experimental situations. This thesis investigated three outer scales of turbulence using experimental data from two instruments: microthermal probes...represents the size of the velocity fluctuations and the boundary thermal convective cell size. The microthermal balloon data had excessive scatter...optical structure parameter C than the microthermal balloon data. The separation of daytime convective thermal plumes was found from the acoustic

Scaling and modeling of turbulent suspension flows

NASA Technical Reports Server (NTRS)

Chen, C. P.

1989-01-01

Scaling factors determining various aspects of particle-fluid interactions and the development of physical models to predict gas-solid turbulent suspension flow fields are discussed based on two-fluid, continua formulation. The modes of particle-fluid interactions are discussed based on the length and time scale ratio, which depends on the properties of the particles and the characteristics of the flow turbulence. For particle size smaller than or comparable with the Kolmogorov length scale and concentration low enough for neglecting direct particle-particle interaction, scaling rules can be established in various parameter ranges. The various particle-fluid interactions give rise to additional mechanisms which affect the fluid mechanics of the conveying gas phase. These extra mechanisms are incorporated into a turbulence modeling method based on the scaling rules. A multiple-scale two-phase turbulence model is developed, which gives reasonable predictions for dilute suspension flow. Much work still needs to be done to account for the poly-dispersed effects and the extension to dense suspension flows.

Lévy-stable two-pion Bose-Einstein correlations in s NN = 200 GeV Au + Au collisions

DOE PAGES

Adare, A.; Aidala, C.; Ajitanand, N. N.; ...

2018-06-14

Here, we present a detailed measurement of charged two-pion correlation functions in 0–30% centrality √ sNN = 200 GeV Au + Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair m T. We find that the positively and the negatively charged pion pairs yield consistent results, andmore » their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(m T) measurements indicate a decrease of the strength of the correlations at low m T. The Lévy length scale parameter R(m T) decreases with increasing m T, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α = 2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.« less

Lévy-stable two-pion Bose-Einstein correlations in s NN = 200 GeV Au + Au collisions

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

Adare, A.; Aidala, C.; Ajitanand, N. N.

Here, we present a detailed measurement of charged two-pion correlation functions in 0–30% centrality √ sNN = 200 GeV Au + Au collisions by the PHENIX experiment at the Relativistic Heavy Ion Collider. The data are well described by Bose-Einstein correlation functions stemming from Lévy-stable source distributions. Using a fine transverse momentum binning, we extract the correlation strength parameter λ, the Lévy index of stability α, and the Lévy length scale parameter R as a function of average transverse mass of the pair m T. We find that the positively and the negatively charged pion pairs yield consistent results, andmore » their correlation functions are represented, within uncertainties, by the same Lévy-stable source functions. The λ(m T) measurements indicate a decrease of the strength of the correlations at low m T. The Lévy length scale parameter R(m T) decreases with increasing m T, following a hydrodynamically predicted type of scaling behavior. The values of the Lévy index of stability α are found to be significantly lower than the Gaussian case of α = 2, but also significantly larger than the conjectured value that may characterize the critical point of a second-order quark-hadron phase transition.« less

Scale effects and morphological diversification in hindlimb segment mass proportions in neognath birds.

PubMed

Kilbourne, Brandon M

2014-01-01

In spite of considerable work on the linear proportions of limbs in amniotes, it remains unknown whether differences in scale effects between proximal and distal limb segments has the potential to influence locomotor costs in amniote lineages and how changes in the mass proportions of limbs have factored into amniote diversification. To broaden our understanding of how the mass proportions of limbs vary within amniote lineages, I collected data on hindlimb segment masses - thigh, shank, pes, tarsometatarsal segment, and digits - from 38 species of neognath birds, one of the most speciose amniote clades. I scaled each of these traits against measures of body size (body mass) and hindlimb size (hindlimb length) to test for departures from isometry. Additionally, I applied two parameters of trait evolution (Pagel's λ and δ) to understand patterns of diversification in hindlimb segment mass in neognaths. All segment masses are positively allometric with body mass. Segment masses are isometric with hindlimb length. When examining scale effects in the neognath subclade Land Birds, segment masses were again positively allometric with body mass; however, shank, pedal, and tarsometatarsal segment masses were also positively allometric with hindlimb length. Methods of branch length scaling to detect phylogenetic signal (i.e., Pagel's λ) and increasing or decreasing rates of trait change over time (i.e., Pagel's δ) suffer from wide confidence intervals, likely due to small sample size and deep divergence times. The scaling of segment masses appears to be more strongly related to the scaling of limb bone mass as opposed to length, and the scaling of hindlimb mass distribution is more a function of scale effects in limb posture than proximo-distal differences in the scaling of limb segment mass. Though negative allometry of segment masses appears to be precluded by the need for mechanically sound limbs, the positive allometry of segment masses relative to body mass may underlie scale effects in stride frequency and length between smaller and larger neognaths. While variation in linear proportions of limbs appear to be governed by developmental mechanisms, variation in mass proportions does not appear to be constrained so.

Scale effects and morphological diversification in hindlimb segment mass proportions in neognath birds

PubMed Central

2014-01-01

Introduction In spite of considerable work on the linear proportions of limbs in amniotes, it remains unknown whether differences in scale effects between proximal and distal limb segments has the potential to influence locomotor costs in amniote lineages and how changes in the mass proportions of limbs have factored into amniote diversification. To broaden our understanding of how the mass proportions of limbs vary within amniote lineages, I collected data on hindlimb segment masses – thigh, shank, pes, tarsometatarsal segment, and digits – from 38 species of neognath birds, one of the most speciose amniote clades. I scaled each of these traits against measures of body size (body mass) and hindlimb size (hindlimb length) to test for departures from isometry. Additionally, I applied two parameters of trait evolution (Pagel’s λ and δ) to understand patterns of diversification in hindlimb segment mass in neognaths. Results All segment masses are positively allometric with body mass. Segment masses are isometric with hindlimb length. When examining scale effects in the neognath subclade Land Birds, segment masses were again positively allometric with body mass; however, shank, pedal, and tarsometatarsal segment masses were also positively allometric with hindlimb length. Methods of branch length scaling to detect phylogenetic signal (i.e., Pagel’s λ) and increasing or decreasing rates of trait change over time (i.e., Pagel’s δ) suffer from wide confidence intervals, likely due to small sample size and deep divergence times. Conclusions The scaling of segment masses appears to be more strongly related to the scaling of limb bone mass as opposed to length, and the scaling of hindlimb mass distribution is more a function of scale effects in limb posture than proximo-distal differences in the scaling of limb segment mass. Though negative allometry of segment masses appears to be precluded by the need for mechanically sound limbs, the positive allometry of segment masses relative to body mass may underlie scale effects in stride frequency and length between smaller and larger neognaths. While variation in linear proportions of limbs appear to be governed by developmental mechanisms, variation in mass proportions does not appear to be constrained so. PMID:24876886

Size-dependent axisymmetric vibration of functionally graded circular plates in bifurcation/limit point instability

NASA Astrophysics Data System (ADS)

Ashoori, A. R.; Vanini, S. A. Sadough; Salari, E.

2017-04-01

In the present paper, vibration behavior of size-dependent functionally graded (FG) circular microplates subjected to thermal loading are carried out in pre/post-buckling of bifurcation/limit-load instability for the first time. Two kinds of frequently used thermal loading, i.e., uniform temperature rise and heat conduction across the thickness direction are considered. Thermo-mechanical material properties of FG plate are supposed to vary smoothly and continuously throughout the thickness based on power law model. Modified couple stress theory is exploited to describe the size dependency of microplate. The nonlinear governing equations of motion and associated boundary conditions are extracted through generalized form of Hamilton's principle and von-Karman geometric nonlinearity for the vibration analysis of circular FG plates including size effects. Ritz finite element method is then employed to construct the matrix representation of governing equations which are solved by two different strategies including Newton-Raphson scheme and cylindrical arc-length method. Moreover, in the following a parametric study is accompanied to examine the effects of the several parameters such as material length scale parameter, temperature distributions, type of buckling, thickness to radius ratio, boundary conditions and power law index on the dimensionless frequency of post-buckled/snapped size-dependent FG plates in detail. It is found that the material length scale parameter and thermal loading have a significant effect on vibration characteristics of size-dependent circular FG plates.

Near-tip dual-length scale mechanics of mode-I cracking in laminate brittle matrix composites

NASA Technical Reports Server (NTRS)

Ballarini, R.; Islam, S.; Charalambides, P. G.

1992-01-01

This paper presents the preliminary results of an on-going study of the near-tip mechanics of mode-I cracking in brittle matrix composite laminates. A finite element model is developed within the context of two competing characteristic lengths present in the composite: the microstructural length (the thickness of the layers) and a macro-length (crack-length, uncracked ligament size, etc.). For various values of the parameters which describe the ratio of these lengths and the constituent properties, the stresses ahead of a crack perpendicular to the laminates are compared with those predicted by assuming the composite is homogeneous orthotropic. The results can be used to determine the conditions for which homogenization can provide a sufficiently accurate description of the stresses in the vicinity of the crack-tip.

Nacre-nanomimetics: Strong, Stiff, and Plastic.

PubMed

De Luca, Francois; Menzel, Robert; Blaker, Jonny J; Birkbeck, John; Bismarck, Alexander; Shaffer, Milo S P

2015-12-09

The bricks and mortar in the classic structure of nacre have characteristic geometry, aspect ratios and relative proportions; these key parameters can be retained while scaling down the absolute length scale by more than 1 order of magnitude. The results shed light on fundamental scaling behavior and provide new opportunities for high performance, yet ductile, lightweight nanocomposites. Reproducing the toughening mechanisms of nacre at smaller length scales allows a greater volume of interface per unit volume while simultaneously increasing the intrinsic properties of the inorganic constituents. Layer-by-layer (LbL) assembly of poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte and well-defined [Mg2Al(OH)6]CO3.nH2O layered double hydroxide (LDH) platelets produces a dense, oriented, high inorganic content (∼90 wt %) nanostructure resembling natural nacre, but at a shorter length scale. The smaller building blocks enable the (self-) assembly of a higher quality nanostructure than conventional mimics, leading to improved mechanical properties, matching those of natural nacre, while allowing for substantial plastic deformation. Both strain hardening and crack deflection mechanisms were observed in situ by scanning electron microscopy (SEM) during nanoindentation. The best properties emerge from an ordered nanostructure, generated using regular platelets, with narrow size dispersion.

Predicting permeability of regular tissue engineering scaffolds: scaling analysis of pore architecture, scaffold length, and fluid flow rate effects.

PubMed

Rahbari, A; Montazerian, H; Davoodi, E; Homayoonfar, S

2017-02-01

The main aim of this research is to numerically obtain the permeability coefficient in the cylindrical scaffolds. For this purpose, a mathematical analysis was performed to derive an equation for desired porosity in terms of morphological parameters. Then, the considered cylindrical geometries were modeled and the permeability coefficient was calculated according to the velocity and pressure drop values based on the Darcy's law. In order to validate the accuracy of the present numerical solution, the obtained permeability coefficient was compared with the published experimental data. It was observed that this model can predict permeability with the utmost accuracy. Then, the effect of geometrical parameters including porosity, scaffold pore structure, unit cell size, and length of the scaffolds as well as entrance mass flow rate on the permeability of porous structures was studied. Furthermore, a parametric study with scaling laws analysis of sample length and mass flow rate effects on the permeability showed good fit to the obtained data. It can be concluded that the sensitivity of permeability is more noticeable at higher porosities. The present approach can be used to characterize and optimize the scaffold microstructure due to the necessity of cell growth and transferring considerations.

Elastic Response and Failure Studies of Multi-Wall Carbon Nanotube Twisted Yarns

NASA Technical Reports Server (NTRS)

Gates, Thomas S.; Jefferson, Gail D.; Frankland, Sarah-Jane V.

2007-01-01

Experimental data on the stress-strain behavior of a polymer multiwall carbon nanotube (MWCNT) yarn composite are used to motivate an initial study in multi-scale modeling of strength and stiffness. Atomistic and continuum length scale modeling methods are outlined to illustrate the range of parameters required to accurately model behavior. The carbon nanotubes yarns are four-ply, twisted, and combined with an elastomer to form a single-layer, unidirectional composite. Due to this textile structure, the yarn is a complicated system of unique geometric relationships subjected to combined loads. Experimental data illustrate the local failure modes induced by static, tensile tests. Key structure-property relationships are highlighted at each length scale indicating opportunities for parametric studies to assist the selection of advantageous material development and manufacturing methods.

Universality of quantum gravity corrections.

PubMed

Das, Saurya; Vagenas, Elias C

2008-11-28

We show that the existence of a minimum measurable length and the related generalized uncertainty principle (GUP), predicted by theories of quantum gravity, influence all quantum Hamiltonians. Thus, they predict quantum gravity corrections to various quantum phenomena. We compute such corrections to the Lamb shift, the Landau levels, and the tunneling current in a scanning tunneling microscope. We show that these corrections can be interpreted in two ways: (a) either that they are exceedingly small, beyond the reach of current experiments, or (b) that they predict upper bounds on the quantum gravity parameter in the GUP, compatible with experiments at the electroweak scale. Thus, more accurate measurements in the future should either be able to test these predictions, or further tighten the above bounds and predict an intermediate length scale between the electroweak and the Planck scale.

Scaling of Transient Storage Parameter Estimates with Increasing Reach Length in a Mountain Headwater Stream

NASA Astrophysics Data System (ADS)

Briggs, M.; Gooseff, M. N.; McGlynn, B.

2006-12-01

. Numerous studies have used the methods of stream tracer experiments and subsequent solute transport modeling to determine transient storage characteristics of streams. Experimental reach length is often determined by site logistics, morphology, specific study goals, etc. Harvey et al. [1996] provided guidance for optimal study reach lengths, based on the Dahmkoler number, as a balance between timescales of advective transport and transient storage. In this study, we investigate the scaling of parameters in a solute transport model (OTIS) with increasing spatial scale of investigation. We conducted 2 6-hour constant rate injections of dissolved NaCl in Spring Park Creek, a headwater stream in the Tenderfoot Creek Experimental Forest, Montana. Below the first injection we sampled 4 reaches ~200m in length, we then moved upstream 640m for the second injection and sampled 3 more ~200 m reaches. Solute transport simulations were conducted for each of these sub-reaches and for combinations of these sub-reaches, from which we assessed estimates of solute velocity, dispersion, transient storage exchange, storage zone size, and Fmed (proportion of median transport time due to storage). Dahmkoler values calculated for each simulation (sub-reaches as well as longer combined reach) were within an order of magnitude of 1, suggesting that our study reach lengths were appropriate. Length-weighted average solute transport and transient storage parameters for the sub-reaches were found to be comparable to their counterparts in the longer reach simulation. In particular the average dispersion found for the sub-reaches (0.43 m2/s) compared very favorably with the value for dispersion calculated for the larger reach (0.40 m2/s). In contrast the weighted average of storage zone size for the sub-reaches was much greater (1.17 m2) than those calculated for the injection reach as a whole (0.09 m2) by a factor of ~13. Weighted average values for transient storage exchange and size for the sub-reaches were both found to be higher than that of the reach as a whole, but only by factors of ~2.5 and 3 respectively. This study indicates that some values of solute transport and transient storage for a particular reach can be reasonably extrapolated from its corresponding component reach values.

Scale Dependence of Statistics of Spatially Averaged Rain Rate Seen in TOGA COARE Comparison with Predictions from a Stochastic Model

NASA Technical Reports Server (NTRS)

Kundu, Prasun K.; Bell, T. L.; Lau, William K. M. (Technical Monitor)

2002-01-01

A characteristic feature of rainfall statistics is that they in general depend on the space and time scales over which rain data are averaged. As a part of an earlier effort to determine the sampling error of satellite rain averages, a space-time model of rainfall statistics was developed to describe the statistics of gridded rain observed in GATE. The model allows one to compute the second moment statistics of space- and time-averaged rain rate which can be fitted to satellite or rain gauge data to determine the four model parameters appearing in the precipitation spectrum - an overall strength parameter, a characteristic length separating the long and short wavelength regimes and a characteristic relaxation time for decay of the autocorrelation of the instantaneous local rain rate and a certain 'fractal' power law exponent. For area-averaged instantaneous rain rate, this exponent governs the power law dependence of these statistics on the averaging length scale $L$ predicted by the model in the limit of small $L$. In particular, the variance of rain rate averaged over an $L \\times L$ area exhibits a power law singularity as $L \\rightarrow 0$. In the present work the model is used to investigate how the statistics of area-averaged rain rate over the tropical Western Pacific measured with ship borne radar during TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean Atmospheric Response Experiment) and gridded on a 2 km grid depends on the size of the spatial averaging scale. Good agreement is found between the data and predictions from the model over a wide range of averaging length scales.

Permeability from complex conductivity: an evaluation of polarization magnitude versus relaxation time based geophysical length scales

NASA Astrophysics Data System (ADS)

Slater, L. D.; Robinson, J.; Weller, A.; Keating, K.; Robinson, T.; Parker, B. L.

2017-12-01

Geophysical length scales determined from complex conductivity (CC) measurements can be used to estimate permeability k when the electrical formation factor F describing the ratio between tortuosity and porosity is known. Two geophysical length scales have been proposed: [1] the imaginary conductivity σ" normalized by the specific polarizability cp; [2] the time constant τ multiplied by a diffusion coefficient D+. The parameters cp and D+ account for the control of fluid chemistry and/or varying minerology on the geophysical length scale. We evaluated the predictive capability of two recently presented CC permeability models: [1] an empirical formulation based on σ"; [2] a mechanistic formulation based on τ;. The performance of the CC models was evaluated against measured permeability; this performance was also compared against that of well-established k estimation equations that use geometric length scales to represent the pore scale properties controlling fluid flow. Both CC models predict permeability within one order of magnitude for a database of 58 sandstone samples, with the exception of those samples characterized by high pore volume normalized surface area Spor and more complex mineralogy including significant dolomite. Variations in cp and D+ likely contribute to the poor performance of the models for these high Spor samples. The ultimate value of such geophysical models for permeability prediction lies in their application to field scale geophysical datasets. Two observations favor the implementation of the σ" based model over the τ based model for field-scale estimation: [1] the limited range of variation in cp relative to D+; [2] σ" is readily measured using field geophysical instrumentation (at a single frequency) whereas τ requires broadband spectral measurements that are extremely challenging and time consuming to accurately measure in the field. However, the need for a reliable estimate of F remains a major obstacle to the field-scale implementation of either of the CC permeability models for k estimation.

Verification of LANDSAT imagery for morphametric and topological studies of drainage basins in a section of the western plateau of Sao Paulo State: Tiete-Aguapei watershed. M.S. Thesis; [Brazil

NASA Technical Reports Server (NTRS)

Parada, N. D. J. (Principal Investigator); Camargo, J. C. G.

1982-01-01

The potential of using LANDSAT MSS imagery for morphometric and topological studies of drainage basins was verified. Using Tiete and Aguapei watershed (Western Plateau) as the test site because of its homogeneous landscape. Morphometric variables collected for ten drainage basins include: circularity index; river density; drainage density; topographic texture; areal and index length; basin parameter; and main river length 1st order and 2nd order channel length. The topographical variables determined were: order; magnitude; bifuraction ratio; weighted bifuraction ratio; number of segments; number of linking; trajectory length; and topological diameter. Data were collected on topographical maps at the scale of 1:250,000 and 1:59,000 and on LANDSAT imagery at the scale of 1:250,000. The results which were summarized on tables for further analysis, show that LANDSAT imagery can supply the lack of topographic charts for drainage studies.

Electrostatic stability of electron-positron plasmas in dipole geometry

NASA Astrophysics Data System (ADS)

Mishchenko, Alexey; Plunk, Gabriel G.; Helander, Per

2018-04-01

The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behaviour. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stability boundaries in parameter space. Landau damping is investigated at scales sufficiently smaller than the Debye length, where instability is absent.

Characteristic Length Scales in Fracture Networks: Hydraulic Connectivity through Periodic Hydraulic Tests

NASA Astrophysics Data System (ADS)

Becker, M.; Bour, O.; Le Borgne, T.; Longuevergne, L.; Lavenant, N.; Cole, M. C.; Guiheneuf, N.

2017-12-01

Determining hydraulic and transport connectivity in fractured bedrock has long been an important objective in contaminant hydrogeology, petroleum engineering, and geothermal operations. A persistent obstacle to making this determination is that the characteristic length scale is nearly impossible to determine in sparsely fractured networks. Both flow and transport occur through an unknown structure of interconnected fracture and/or fracture zones making the actual length that water or solutes travel undetermined. This poses difficulties for flow and transport models. For, example, hydraulic equations require a separation distance between pumping and observation well to determine hydraulic parameters. When wells pairs are close, the structure of the network can influence the interpretation of well separation and the flow dimension of the tested system. This issue is explored using hydraulic tests conducted in a shallow fractured crystalline rock. Periodic (oscillatory) slug tests were performed at the Ploemeur fractured rock test site located in Brittany, France. Hydraulic connectivity was examined between three zones in one well and four zones in another, located 6 m apart in map view. The wells are sufficiently close, however, that the tangential distance between the tested zones ranges between 6 and 30 m. Using standard periodic formulations of radial flow, estimates of storativity scale inversely with the square of the separation distance and hydraulic diffusivity directly with the square of the separation distance. Uncertainty in the connection paths between the two wells leads to an order of magnitude uncertainty in estimates of storativity and hydraulic diffusivity, although estimates of transmissivity are unaffected. The assumed flow dimension results in alternative estimates of hydraulic parameters. In general, one is faced with the prospect of assuming the hydraulic parameter and inverting the separation distance, or vice versa. Similar uncertainties exist, for instance, when trying to invert transport parameters from tracer mean residence time. This field test illustrates that when dealing with fracture networks, there is a need for analytic methods of complexity that lie between simple radial solutions and discrete fracture network models.

Accelerometry-based gait analysis, an additional objective approach to screen subjects at risk for falling.

PubMed

Senden, R; Savelberg, H H C M; Grimm, B; Heyligers, I C; Meijer, K

2012-06-01

This study investigated whether the Tinetti scale, as a subjective measure for fall risk, is associated with objectively measured gait characteristics. It is studied whether gait parameters are different for groups that are stratified for fall risk using the Tinetti scale. Moreover, the discriminative power of gait parameters to classify elderly according to the Tinetti scale is investigated. Gait of 50 elderly with a Tinneti>24 and 50 elderly with a Tinetti≤24 was analyzed using acceleration-based gait analysis. Validated algorithms were used to derive spatio-temporal gait parameters, harmonic ratio, inter-stride amplitude variability and root mean square (RMS) from the accelerometer data. Clear differences in gait were found between the groups. All gait parameters correlated with the Tinetti scale (r-range: 0.20-0.73). Only walking speed, step length and RMS showed moderate to strong correlations and high discriminative power to classify elderly according to the Tinetti scale. It is concluded that subtle gait changes that have previously been related to fall risk are not captured by the subjective assessment. It is therefore worthwhile to include objective gait assessment in fall risk screening. Copyright © 2012 Elsevier B.V. All rights reserved.

A nonlocal strain gradient model for dynamic deformation of orthotropic viscoelastic graphene sheets under time harmonic thermal load

NASA Astrophysics Data System (ADS)

Radwan, Ahmed F.; Sobhy, Mohammed

2018-06-01

This work presents a nonlocal strain gradient theory for the dynamic deformation response of a single-layered graphene sheet (SLGS) on a viscoelastic foundation and subjected to a time harmonic thermal load for various boundary conditions. Material of graphene sheets is presumed to be orthotropic and viscoelastic. The viscoelastic foundation is modeled as Kelvin-Voigt's pattern. Based on the two-unknown plate theory, the motion equations are obtained from the dynamic version of the virtual work principle. The nonlocal strain gradient theory is established from Eringen nonlocal and strain gradient theories, therefore, it contains two material scale parameters, which are nonlocal parameter and gradient coefficient. These scale parameters have two different effects on the graphene sheets. The obtained deflection is compared with that predicted in the literature. Additional numerical examples are introduced to illustrate the influences of the two length scale coefficients and other parameters on the dynamic deformation of the viscoelastic graphene sheets.

Drainage fracture networks in elastic solids with internal fluid generation

NASA Astrophysics Data System (ADS)

Kobchenko, Maya; Hafver, Andreas; Jettestuen, Espen; Galland, Olivier; Renard, François; Meakin, Paul; Jamtveit, Bjørn; Dysthe, Dag K.

2013-06-01

Experiments in which CO2 gas was generated by the yeast fermentation of sugar in an elastic layer of gelatine gel confined between two glass plates are described and analyzed theoretically. The CO2 gas pressure causes the gel layer to fracture. The gas produced is drained on short length scales by diffusion and on long length scales by flow in a fracture network, which has topological properties that are intermediate between river networks and hierarchical-fracture networks. A simple model for the experimental system with two parameters that characterize the disorder and the intermediate (river-fracture) topology of the network was developed and the results of the model were compared with the experimental results.

Charge frustration in complex fluids and in electronic systems

NASA Astrophysics Data System (ADS)

Carraro, Carlo

1997-02-01

The idea of charge frustration is applied to describe the properties of such diverse physical systems as oil-water-surfactant mixtures and metal-ammonia solutions. The minimalist charge-frustrated model possesses one energy scale and two length scales. For oil-water-surfactant mixtures, these parameters have been determined starting from the microscopic properties of the physical systems under study. Thus, microscopic properties are successfully related to the observed mesoscopic structure.

The treatment of uncertainties in reactive pollution dispersion models at urban scales.

PubMed

Tomlin, A S; Ziehn, T; Goodman, P; Tate, J E; Dixon, N S

2016-07-18

The ability to predict NO2 concentrations ([NO2]) within urban street networks is important for the evaluation of strategies to reduce exposure to NO2. However, models aiming to make such predictions involve the coupling of several complex processes: traffic emissions under different levels of congestion; dispersion via turbulent mixing; chemical processes of relevance at the street-scale. Parameterisations of these processes are challenging to quantify with precision. Predictions are therefore subject to uncertainties which should be taken into account when using models within decision making. This paper presents an analysis of mean [NO2] predictions from such a complex modelling system applied to a street canyon within the city of York, UK including the treatment of model uncertainties and their causes. The model system consists of a micro-scale traffic simulation and emissions model, and a Reynolds averaged turbulent flow model coupled to a reactive Lagrangian particle dispersion model. The analysis focuses on the sensitivity of predicted in-street increments of [NO2] at different locations in the street to uncertainties in the model inputs. These include physical characteristics such as background wind direction, temperature and background ozone concentrations; traffic parameters such as overall demand and primary NO2 fraction; as well as model parameterisations such as roughness lengths, turbulent time- and length-scales and chemical reaction rate coefficients. Predicted [NO2] is shown to be relatively robust with respect to model parameterisations, although there are significant sensitivities to the activation energy for the reaction NO + O3 as well as the canyon wall roughness length. Under off-peak traffic conditions, demand is the key traffic parameter. Under peak conditions where the network saturates, road-side [NO2] is relatively insensitive to changes in demand and more sensitive to the primary NO2 fraction. The most important physical parameter was found to be the background wind direction. The study highlights the key parameters required for reliable [NO2] estimations suggesting that accurate reference measurements for wind direction should be a critical part of air quality assessments for in-street locations. It also highlights the importance of street scale chemical processes in forming road-side [NO2], particularly for regions of high NOx emissions such as close to traffic queues.

Scaling theory of topological phase transitions

NASA Astrophysics Data System (ADS)

Chen, Wei

2016-02-01

Topologically ordered systems are characterized by topological invariants that are often calculated from the momentum space integration of a certain function that represents the curvature of the many-body state. The curvature function may be Berry curvature, Berry connection, or other quantities depending on the system. Akin to stretching a messy string to reveal the number of knots it contains, a scaling procedure is proposed for the curvature function in inversion symmetric systems, from which the topological phase transition can be identified from the flow of the driving energy parameters that control the topology (hopping, chemical potential, etc) under scaling. At an infinitesimal operation, one obtains the renormalization group (RG) equations for the driving energy parameters. A length scale defined from the curvature function near the gap-closing momentum is suggested to characterize the scale invariance at critical points and fixed points, and displays a universal critical behavior in a variety of systems examined.

Multiscaling for systems with a broad continuum of characteristic lengths and times: Structural transitions in nanocomposites.

PubMed

Pankavich, S; Ortoleva, P

2010-06-01

The multiscale approach to N-body systems is generalized to address the broad continuum of long time and length scales associated with collective behaviors. A technique is developed based on the concept of an uncountable set of time variables and of order parameters (OPs) specifying major features of the system. We adopt this perspective as a natural extension of the commonly used discrete set of time scales and OPs which is practical when only a few, widely separated scales exist. The existence of a gap in the spectrum of time scales for such a system (under quasiequilibrium conditions) is used to introduce a continuous scaling and perform a multiscale analysis of the Liouville equation. A functional-differential Smoluchowski equation is derived for the stochastic dynamics of the continuum of Fourier component OPs. A continuum of spatially nonlocal Langevin equations for the OPs is also derived. The theory is demonstrated via the analysis of structural transitions in a composite material, as occurs for viral capsids and molecular circuits.

Vertical length scale selection for pancake vortices in strongly stratified viscous fluids

NASA Astrophysics Data System (ADS)

Godoy-Diana, Ramiro; Chomaz, Jean-Marc; Billant, Paul

2004-04-01

The evolution of pancake dipoles of different aspect ratio is studied in a stratified tank experiment. Two cases are reported here for values of the dipole initial aspect ratio alpha_0 = L_v/L_h (where L_v and L_h are vertical and horizontal length scales, respectively) of alpha_0 = 0.4 (case I) and alpha_0 = 1.2 (case II). In the first case, the usual decay scenario is observed where the dipole diffuses slowly with a growing thickness and a decaying circulation. In case II, we observed a regime where the thickness of the dipole decreases and the circulation in the horizontal mid-plane of the vortices remains constant. We show that this regime where the vertical length scale decreases can be explained by the shedding of two boundary layers at the top and bottom of the dipole that literally peel off vorticity layers. Horizontal advection and vertical diffusion cooperate in this regime and the decrease towards the viscous vertical length scale delta = L_hRe(-1/2) occurs on a time scale alpha_0 Re(1/2) T_A, T_A being the advection time L_h/U. From a scaling analysis of the equations for a stratified viscous fluid in the Boussinesq approximation, two dominant balances depending on the parameter R = ReF_h(2) are discussed, where F_h = U/NL_h is the horizontal Froude number and Re = UL_h/nu is the Reynolds number, U, N and nu being, respectively, the translation speed of the dipole, the Brunt Väisälä frequency and the kinematic viscosity. When R≫ 1 the vertical length scale is determined by buoyancy effects to be of order L_b = U/N. The experiments presented in this paper pertain to the case of small R, where viscous effects govern the selection of the vertical length scale. We show that if initially L_v ≤ delta, the flow diffuses on the vertical (case I), while if L_v ≫ delta (case II), vertically sheared horizontal advection decreases the vertical length scale down to delta. This viscous regime may explain results from experiments and numerical simulations on the late evolution of stratified flows where the decay is observed to be independent of the buoyancy frequency N.

A size dependent dynamic model for piezoelectric nanogenerators: effects of geometry, structural and environmental parameters

NASA Astrophysics Data System (ADS)

Sadeghzadeh, Sadegh; Farshad Mir Saeed Ghazi, Seyyed

2018-03-01

Piezoelectric Nanogenerator (PENG) is one of the novel energy harvester systems that recently, has been a subject of interest for researchers. By the use of nanogenerators, it’s possible to harvest different forms of energy in the environment like mechanical vibrations and generate electricity. The structure of a PENG consists of vertical arrays of nanowires between two electrodes. In this paper, dynamic analysis of a PENG is studied numerically. The modified couple stress theory which includes one length scale material parameter is used to study the size-dependent behavior of PENGs. Then, by application of a complete form of linear hybrid piezoelectric—pyroelectric equations, and using the Euler-Bernoulli beam model, the equations of motion has been derived. Generalized Differential Quadrature (GDQ) method was employed to solve the equations of motion. The effect of damping ratio, temperature rise, excitation frequency and length scale parameter was studied. It was found that the PENG voltage maximizes at the resonant frequency of nanowire. The temperature rise has a significant effect on PENG’s efficiency. When temperature increases about 10 {{K}}, the maximum voltage increases about 26%. Increasing the damping ratio, the maximum voltage decreases gradually.

The abundance properties of nearby late-type galaxies. II. The relation between abundance distributions and surface brightness profiles

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

Pilyugin, L. S.; Grebel, E. K.; Zinchenko, I. A.

2014-12-01

The relations between oxygen abundance and disk surface brightness (OH–SB relation) in the infrared W1 band are examined for nearby late-type galaxies. The oxygen abundances were presented in Paper I. The photometric characteristics of the disks are inferred here using photometric maps from the literature through bulge-disk decomposition. We find evidence that the OH–SB relation is not unique but depends on the galactocentric distance r (taken as a fraction of the optical radius R{sub 25}) and on the properties of a galaxy: the disk scale length h and the morphological T-type. We suggest a general, four-dimensional OH–SB relation with themore » values r, h, and T as parameters. The parametric OH–SB relation reproduces the observed data better than a simple, one-parameter relation; the deviations resulting when using our parametric relation are smaller by a factor of ∼1.4 than that of the simple relation. The influence of the parameters on the OH–SB relation varies with galactocentric distance. The influence of the T-type on the OH–SB relation is negligible at the centers of galaxies and increases with galactocentric distance. In contrast, the influence of the disk scale length on the OH–SB relation is at a maximum at the centers of galaxies and decreases with galactocentric distance, disappearing at the optical edges of galaxies. Two-dimensional relations can be used to reproduce the observed data at the optical edges of the disks and at the centers of the disks. The disk scale length should be used as a second parameter in the OH–SB relation at the center of the disk while the morphological T-type should be used as a second parameter in the relation at optical edge of the disk. The relations between oxygen abundance and disk surface brightness in the optical B and infrared K bands at the center of the disk and at optical edge of the disk are also considered. The general properties of the abundance–surface brightness relations are similar for the three considered bands B, K, and W1.« less

Universal dimer–dimer scattering in lattice effective field theory

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

Elhatisari, Serdar; Katterjohn, Kris; Lee, Dean

We consider two-component fermions with short-range interactions and large scattering length. This system has universal properties that are realized in several different fields of physics. In the limit of large fermion–fermion scattering length a ff and zero-range interaction, all properties of the system scale proportionally with a ff. For the case with shallow bound dimers, we calculate the dimer–dimer scattering phase shifts using lattice effective field theory. We extract the universal dimer–dimer scattering length a dd/a ff=0.618(30) and effective range r dd/a ff=-0.431(48). This result for the effective range is the first calculation with quantified and controlled systematic errors. Wemore » also benchmark our methods by computing the fermion–dimer scattering parameters and testing some predictions of conformal scaling of irrelevant operators near the unitarity limit.« less

Universal dimer–dimer scattering in lattice effective field theory

DOE PAGES

Elhatisari, Serdar; Katterjohn, Kris; Lee, Dean; ...

2017-03-14

We consider two-component fermions with short-range interactions and large scattering length. This system has universal properties that are realized in several different fields of physics. In the limit of large fermion–fermion scattering length a ff and zero-range interaction, all properties of the system scale proportionally with a ff. For the case with shallow bound dimers, we calculate the dimer–dimer scattering phase shifts using lattice effective field theory. We extract the universal dimer–dimer scattering length a dd/a ff=0.618(30) and effective range r dd/a ff=-0.431(48). This result for the effective range is the first calculation with quantified and controlled systematic errors. Wemore » also benchmark our methods by computing the fermion–dimer scattering parameters and testing some predictions of conformal scaling of irrelevant operators near the unitarity limit.« less

An algorithm for the design and tuning of RF accelerating structures with variable cell lengths

NASA Astrophysics Data System (ADS)

Lal, Shankar; Pant, K. K.

2018-05-01

An algorithm is proposed for the design of a π mode standing wave buncher structure with variable cell lengths. It employs a two-parameter, multi-step approach for the design of the structure with desired resonant frequency and field flatness. The algorithm, along with analytical scaling laws for the design of the RF power coupling slot, makes it possible to accurately design the structure employing a freely available electromagnetic code like SUPERFISH. To compensate for machining errors, a tuning method has been devised to achieve desired RF parameters for the structure, which has been qualified by the successful tuning of a 7-cell buncher to π mode frequency of 2856 MHz with field flatness <3% and RF coupling coefficient close to unity. The proposed design algorithm and tuning method have demonstrated the feasibility of developing an S-band accelerating structure for desired RF parameters with a relatively relaxed machining tolerance of ∼ 25 μm. This paper discusses the algorithm for the design and tuning of an RF accelerating structure with variable cell lengths.

Investigation of Short Channel Effects on Device Performance for 60nm NMOS Transistor

NASA Astrophysics Data System (ADS)

Chinnappan, U.; Sanudin, R.

2017-08-01

In the aggressively scaled complementary metal oxide semiconductor (CMOS) devices, shallower p-n junctions and low sheet resistances are essential for short-channel effect (SCE) control and high device performance. The SCE are attributed to two physical phenomena that are the limitation imposed on electron drift characteristics in channel and the modification of the threshold voltage (Vth) due to the shortening channel length. The decrement of Vth with decrement in gate length is a well-known attribute in SCE known as “threshold voltage roll-off’. In this research, the Technology Computer Aided Design (TCAD) was used to model the SCE phenomenon effect on 60nm n-type metal oxide semiconductor (NMOS) transistor. There are three parameters being investigated, which are the oxide thickness (Tox), gate length (L), acceptor concentration (Na). The simulation data were used to visualise the effect of SCE on the 60nm NMOS transistor. Simulation data suggest that all three parameters have significant effect on Vth, and hence on the transistor performance. It is concluded that there is a trade-off among these three parameters to obtain an optimized transistor performance.

Theoretical analysis for scaling law of thermal blooming based on optical phase deference

NASA Astrophysics Data System (ADS)

Sun, Yunqiang; Huang, Zhilong; Ren, Zebin; Chen, Zhiqiang; Guo, Longde; Xi, Fengjie

2016-10-01

In order to explore the laser propagation influence of thermal blooming effect of pipe flow and to analysis the influencing factors, scaling law theoretical analysis of the thermal blooming effects in pipe flow are carry out in detail based on the optical path difference caused by thermal blooming effects in pipe flow. Firstly, by solving the energy coupling equation of laser beam propagation, the temperature of the flow is obtained, and then the optical path difference caused by the thermal blooming is deduced. Through the analysis of the influence of pipe size, flow field and laser parameters on the optical path difference, energy scaling parameters Ne=nTαLPR2/(ρɛCpπR02) and geometric scaling parameters Nc=νR2/(ɛL) of thermal blooming for the pipe flow are derived. Secondly, for the direct solution method, the energy coupled equations have analytic solutions only for the straight tube with Gauss beam. Considering the limitation of directly solving the coupled equations, the dimensionless analysis method is adopted, the analysis is also based on the change of optical path difference, same scaling parameters for the pipe flow thermal blooming are derived, which makes energy scaling parameters Ne and geometric scaling parameters Nc have good universality. The research results indicate that when the laser power and the laser beam diameter are changed, thermal blooming effects of the pipeline axial flow caused by optical path difference will not change, as long as you keep energy scaling parameters constant. When diameter or length of the pipe changes, just keep the geometric scaling parameters constant, the pipeline axial flow gas thermal blooming effects caused by optical path difference distribution will not change. That is to say, when the pipe size and laser parameters change, if keeping two scaling parameters with constant, the pipeline axial flow thermal blooming effects caused by the optical path difference will not change. Therefore, the energy scaling parameters and the geometric scaling parameters can really describe the gas thermal blooming effect in the axial pipe flow. These conclusions can give a good reference for the construction of the thermal blooming test system of laser system. Contrasted with the thermal blooming scaling parameters of the Bradley-Hermann distortion number ND and Fresnel number NF, which were derived based on the change of far field beam intensity distortion, the scaling parameters of pipe flow thermal blooming deduced from the optical path deference variation are very suitable for the optical system with short laser propagation distance, large Fresnel number and obviously changed optical path deference.

Effects of finite hot-wire spatial resolution on turbulence statistics and velocity spectra in a round turbulent free jet

NASA Astrophysics Data System (ADS)

Sadeghi, Hamed; Lavoie, Philippe; Pollard, Andrew

2018-03-01

The effect of finite hot-wire spatial resolution on turbulence statistics and velocity spectra in a round turbulent free jet is investigated. To quantify spatial resolution effects, measurements were taken using a nano-scale thermal anemometry probe (NSTAP) and compared to results from conventional hot-wires with sensing lengths of l=0.5 and 1 mm. The NSTAP has a sensing length significantly smaller than the Kolmogorov length scale η for the present experimental conditions, whereas the sensing lengths for the conventional probes are larger than η. The spatial resolution is found to have a significant impact on the dissipation both on and off the jet centreline with the NSTAP results exceeding those obtained from the conventional probes. The resolution effects along the jet centreline are adequately predicted using a Wyngaard-type spectral technique (Wyngaard in J Sci Instr 1(2):1105-1108,1968), but additional attenuation on the measured turbulence quantities are observed off the centreline. The magnitude of this attenuation is a function of both the ratio of wire length to Kolmogorov length scale and the magnitude of the shear. The effect of spatial resolution is noted to have an impact on the power-law decay parameters for the turbulent kinetic energy that is computed. The effect of spatial filtering on the streamwise dissipation energy spectra is also considered. Empirical functions are proposed to estimate the effect of finite resolution, which take into account the mean shear.

Multifractal model of magnetic susceptibility distributions in some igneous rocks

USGS Publications Warehouse

Gettings, Mark E.

2012-01-01

Measurements of in-situ magnetic susceptibility were compiled from mainly Precambrian crystalline basement rocks beneath the Colorado Plateau and ranges in Arizona, Colorado, and New Mexico. The susceptibility meter used measures about 30 cm3 of rock and measures variations in the modal distribution of magnetic minerals that form a minor component volumetrically in these coarsely crystalline granitic to granodioritic rocks. Recent measurements include 50–150 measurements on each outcrop, and show that the distribution of magnetic susceptibilities is highly variable, multimodal and strongly non-Gaussian. Although the distribution of magnetic susceptibility is well known to be multifractal, the small number of data points at an outcrop precludes calculation of the multifractal spectrum by conventional methods. Instead, a brute force approach was adopted using multiplicative cascade models to fit the outcrop scale variability of magnetic minerals. Model segment proportion and length parameters resulted in 26 676 models to span parameter space. Distributions at each outcrop were normalized to unity magnetic susceptibility and added to compare all data for a rock body accounting for variations in petrology and alteration. Once the best-fitting model was found, the equation relating the segment proportion and length parameters was solved numerically to yield the multifractal spectrum estimate. For the best fits, the relative density (the proportion divided by the segment length) of one segment tends to be dominant and the other two densities are smaller and nearly equal. No other consistent relationships between the best fit parameters were identified. The multifractal spectrum estimates appear to distinguish between metamorphic gneiss sites and sites on plutons, even if the plutons have been metamorphosed. In particular, rocks that have undergone multiple tectonic events tend to have a larger range of scaling exponents.

A statistical study of decaying kink oscillations detected using SDO/AIA

NASA Astrophysics Data System (ADS)

Goddard, C. R.; Nisticò, G.; Nakariakov, V. M.; Zimovets, I. V.

2016-01-01

Context. Despite intensive studies of kink oscillations of coronal loops in the last decade, a large-scale statistically significant investigation of the oscillation parameters has not been made using data from the Solar Dynamics Observatory (SDO). Aims: We carry out a statistical study of kink oscillations using extreme ultraviolet imaging data from a previously compiled catalogue. Methods: We analysed 58 kink oscillation events observed by the Atmospheric Imaging Assembly (AIA) on board SDO during its first four years of operation (2010-2014). Parameters of the oscillations, including the initial apparent amplitude, period, length of the oscillating loop, and damping are studied for 120 individual loop oscillations. Results: Analysis of the initial loop displacement and oscillation amplitude leads to the conclusion that the initial loop displacement prescribes the initial amplitude of oscillation in general. The period is found to scale with the loop length, and a linear fit of the data cloud gives a kink speed of Ck = (1330 ± 50) km s-1. The main body of the data corresponds to kink speeds in the range Ck = (800-3300) km s-1. Measurements of 52 exponential damping times were made, and it was noted that at least 21 of the damping profiles may be better approximated by a combination of non-exponential and exponential profiles rather than a purely exponential damping envelope. There are nine additional cases where the profile appears to be purely non-exponential and no damping time was measured. A scaling of the exponential damping time with the period is found, following the previously established linear scaling between these two parameters.

Finite length-scale anti-gravity and observations of mass discrepancies in galaxies

NASA Astrophysics Data System (ADS)

Sanders, R. H.

1986-01-01

The modification of Newtonian attraction suggested by Sanders (1984) contains a repulsive Yukawa component which is characterised by two physical parameters: a coupling constant, α, and a length scale, r0. Although this form of the gravitational potential can result in flat rotation curves for a galaxy (or a point mass) it is not obvious that any modification of gravity associated with a definite length scale can reproduce the observed rotation curves of galaxies covering a wide range of mass and size. Here it is shown that the rotation curves of galaxies ranging in size from 5 to 40 kpc can be reproduced by this modified potential. Moreover, the implied mass-to-light ratios for a larger sample of galaxies are reasonable (one to three) and show no systematic trend with the size of the galaxy. The observed infrared Tully-Fisher law is shown to be consistent with the prediction of this revised gravity. The modified potential permits the X-ray emitting halos observed around elliptical galaxies to be bound without the addition of dark matter.

Beam displacement as a function of temperature and turbulence length scale at two different laser radiation wavelengths.

PubMed

Isterling, William M; Dally, Bassam B; Alwahabi, Zeyad T; Dubovinsky, Miro; Wright, Daniel

2012-01-01

Narrow laser beams directed from aircraft may at times pass through the exhaust plume of the engines and potentially degrade some of the laser beam characteristics. This paper reports on controlled studies of laser beam deviation arising from propagation through turbulent hot gases, in a well-characterized laboratory burner, with conditions of relevance to aircraft engine exhaust plumes. The impact of the temperature, laser wavelength, and turbulence length scale on the beam deviation has been investigated. It was found that the laser beam displacement increases with the turbulent integral length scale. The effect of temperature on the laser beam angular deviation, σ, using two different laser wavelengths, namely 4.67 μm and 632.8 nm, was recorded. It was found that the beam deviation for both wavelengths may be semiempirically modeled using a single function of the form, σ=a(b+(1/T)(2))(-1), with two parameters only, a and b, where σ is in microradians and T is the temperature in °C. © 2012 Optical Society of America

Sound radiation from a subsonic rotor subjected to turbulence

NASA Technical Reports Server (NTRS)

Sevik, M.

1974-01-01

The broadband sound radiated by a subsonic rotor subjected to turbulence in the approach stream has been analyzed. The power spectral density of the sound intensity has been found to depend on a characteristic time scale-namely, the integral scale of the turbulence divided by the axial flow velocity-as well as several length-scale ratios. These consist of the ratio of the integral scale to the acoustic wavelength, rotor radius, and blade chord. Due to the simplified model chosen, only a limited number of cascade parameters appear. Limited comparisons with experimental data indicate good agreement with predicted values.

Relationships of 35 lower limb muscles to height and body mass quantified using MRI.

PubMed

Handsfield, Geoffrey G; Meyer, Craig H; Hart, Joseph M; Abel, Mark F; Blemker, Silvia S

2014-02-07

Skeletal muscle is the most abundant tissue in the body and serves various physiological functions including the generation of movement and support. Whole body motor function requires adequate quantity, geometry, and distribution of muscle. This raises the question: how do muscles scale with subject size in order to achieve similar function across humans? While much of the current knowledge of human muscle architecture is based on cadaver dissection, modern medical imaging avoids limitations of old age, poor health, and limited subject pool, allowing for muscle architecture data to be obtained in vivo from healthy subjects ranging in size. The purpose of this study was to use novel fast-acquisition MRI to quantify volumes and lengths of 35 major lower limb muscles in 24 young, healthy subjects and to determine if muscle size correlates with bone geometry and subject parameters of mass and height. It was found that total lower limb muscle volume scales with mass (R(2)=0.85) and with the height-mass product (R(2)=0.92). Furthermore, individual muscle volumes scale with total muscle volume (median R(2)=0.66), with the height-mass product (median R(2)=0.61), and with mass (median R(2)=0.52). Muscle volume scales with bone volume (R(2)=0.75), and muscle length relative to bone length is conserved (median s.d.=2.1% of limb length). These relationships allow for an arbitrary subject's individual muscle volumes to be estimated from mass or mass and height while muscle lengths may be estimated from limb length. The dataset presented here can further be used as a normative standard to compare populations with musculoskeletal pathologies. © 2013 Published by Elsevier Ltd.

Nonlinear Dynamics and Nucleation Kinetics in Near-Critical Liquids

NASA Technical Reports Server (NTRS)

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

1996-01-01

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

Influence of the length of institutionalization on older adults' postural balance and risk of falls: a transversal study.

PubMed

Batista, Wagner Oliveira; Alves Junior, Edmundo de Drummond; Porto, Flávia; Pereira, Fabio Dutra; Santana, Rosimere Ferreira; Gurgel, Jonas Lírio

2014-01-01

to ascertain the influence of the length of institutionalization on older adults' balance and risk of falls. to evaluate the risk of falls, the Berg Balance Scale and the Timed Get Up and Go test were used; and for measuring postural balance, static stabilometry was used, with acquisition of the elliptical area of 95% and mean velocities on the x and y axes of center of pressure displacement. Parametric and nonparametric measures of association and comparison (α<0.05) were used. there was no significant correlation between the length of institutionalization and the tests for evaluation of risk of falling, neither was there difference between groups and within subgroups, stratified by length of institutionalization and age. In the stabilometric measurements, there was a negative correlation between the parameters analyzed and the length of institutionalization, and difference between groups and within subgroups. this study's results point to the difficulty of undertaking postural control tasks, showing a leveling below the clinical tests' reference scores. In the stabilometric behavior, one should note the reduction of the parameters as the length of institutionalization increases, contradicting the assumptions. This study's results offer support for the development of a multi-professional model for intervention with the postural control and balance of older adults living in homes for the aged.

Brownian dynamics simulation of amphiphilic block copolymers with different tail lengths, comparison with theory and comicelles.

PubMed

Hafezi, Mohammad-Javad; Sharif, Farhad

2015-11-01

Study on the effect of amphiphilic copolymers structure on their self assembly is an interesting subject, with important applications in the area of drug delivery and biological system treatments. Brownian dynamics simulations were performed to study self-assembly of the linear amphiphilic block copolymers with the same hydrophilic head, but hydrophobic tails of different lengths. Critical micelle concentration (CMC), gyration radius distribution, micelle size distribution, density profiles of micelles, shape anisotropy, and dynamics of micellization were investigated as a function of tail length. Simulation results were compared with predictions from theory and simulation for mixed systems of block copolymers with long and short hydrophobic tail, reported in our previous work. Interestingly, the equilibrium structural and dynamic parameters of pure and mixed block copolymers were similarly dependant on the intrinsic/apparent hydrophobic block length. Log (CMC) was, however; proportional to the tail length and had a different behavior compared to the mixed system. The power law scaling relation of equilibrium structural parameters for amphiphilic block copolymers predicts the same dependence for similar hydrophobic tail lengths, but the power law prediction of CMC is different, which is due to its simplifying assumptions as discussed here. Copyright © 2015 Elsevier Inc. All rights reserved.

Image processing for quantifying fracture orientation and length scale transitions during brittle deformation

NASA Astrophysics Data System (ADS)

Rizzo, R. E.; Healy, D.; Farrell, N. J.

2017-12-01

We have implemented a novel image processing tool, namely two-dimensional (2D) Morlet wavelet analysis, capable of detecting changes occurring in fracture patterns at different scales of observation, and able of recognising the dominant fracture orientations and the spatial configurations for progressively larger (or smaller) scale of analysis. Because of its inherited anisotropy, the Morlet wavelet is proved to be an excellent choice for detecting directional linear features, i.e. regions where the amplitude of the signal is regular along one direction and has sharp variation along the perpendicular direction. Performances of the Morlet wavelet are tested against the 'classic' Mexican hat wavelet, deploying a complex synthetic fracture network. When applied to a natural fracture network, formed triaxially (σ1>σ2=σ3) deforming a core sample of the Hopeman sandstone, the combination of 2D Morlet wavelet and wavelet coefficient maps allows for the detection of characteristic scale orientation and length transitions, associated with the shifts from distributed damage to the growth of localised macroscopic shear fracture. A complementary outcome arises from the wavelet coefficient maps produced by increasing the wavelet scale parameter. These maps can be used to chart the variations in the spatial distribution of the analysed entities, meaning that it is possible to retrieve information on the density of fracture patterns at specific length scales during deformation.

Wavepacket dynamics in one-dimensional system with long-range correlated disorder

NASA Astrophysics Data System (ADS)

Yamada, Hiroaki S.

2018-03-01

We numerically investigate dynamical property in the one-dimensional tight-binding model with long-range correlated disorder having power spectrum 1 /fα (α: spectrum exponent) generated by Fourier filtering method. For relatively small α <αc (=2) time-dependence of mean square displacement (MSD) of the initially localized wavepacket shows ballistic spread and localizes as time elapses. It is shown that α-dependence of the dynamical localization length determined by the MSD exhibits a simple scaling law in the localization regime for the relatively weak disorder strength W. Furthermore, scaled MSD by the dynamical localization length almost obeys an universal function from the ballistic to the localization regime in the various combinations of the parameters α and W.

Calculating the sensitivity of wind turbine loads to wind inputs using response surfaces

NASA Astrophysics Data System (ADS)

Rinker, Jennifer M.

2016-09-01

This paper presents a methodology to calculate wind turbine load sensitivities to turbulence parameters through the use of response surfaces. A response surface is a highdimensional polynomial surface that can be calibrated to any set of input/output data and then used to generate synthetic data at a low computational cost. Sobol sensitivity indices (SIs) can then be calculated with relative ease using the calibrated response surface. The proposed methodology is demonstrated by calculating the total sensitivity of the maximum blade root bending moment of the WindPACT 5 MW reference model to four turbulence input parameters: a reference mean wind speed, a reference turbulence intensity, the Kaimal length scale, and a novel parameter reflecting the nonstationarity present in the inflow turbulence. The input/output data used to calibrate the response surface were generated for a previous project. The fit of the calibrated response surface is evaluated in terms of error between the model and the training data and in terms of the convergence. The Sobol SIs are calculated using the calibrated response surface, and the convergence is examined. The Sobol SIs reveal that, of the four turbulence parameters examined in this paper, the variance caused by the Kaimal length scale and nonstationarity parameter are negligible. Thus, the findings in this paper represent the first systematic evidence that stochastic wind turbine load response statistics can be modeled purely by mean wind wind speed and turbulence intensity.

Recapturing Graphite-Based Fuel Element Technology for Nuclear Thermal Propulsion

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

Trammell, Michael P; Jolly, Brian C; Miller, James Henry

ORNL is currently recapturing graphite based fuel forms for Nuclear Thermal Propulsion (NTP). This effort involves research and development on materials selection, extrusion, and coating processes to produce fuel elements representative of historical ROVER and NERVA fuel. Initially, lab scale specimens were fabricated using surrogate oxides to develop processing parameters that could be applied to full length NTP fuel elements. Progress toward understanding the effect of these processing parameters on surrogate fuel microstructure is presented.

Simplification and Validation of a Spectral-Tensor Model for Turbulence Including Atmospheric Stability

NASA Astrophysics Data System (ADS)

Chougule, Abhijit; Mann, Jakob; Kelly, Mark; Larsen, Gunner C.

2018-06-01

A spectral-tensor model of non-neutral, atmospheric-boundary-layer turbulence is evaluated using Eulerian statistics from single-point measurements of the wind speed and temperature at heights up to 100 m, assuming constant vertical gradients of mean wind speed and temperature. The model has been previously described in terms of the dissipation rate ɛ , the length scale of energy-containing eddies L, a turbulence anisotropy parameter Γ, the Richardson number Ri, and the normalized rate of destruction of temperature variance η _θ ≡ ɛ _θ /ɛ . Here, the latter two parameters are collapsed into a single atmospheric stability parameter z / L using Monin-Obukhov similarity theory, where z is the height above the Earth's surface, and L is the Obukhov length corresponding to Ri,η _θ. Model outputs of the one-dimensional velocity spectra, as well as cospectra of the streamwise and/or vertical velocity components, and/or temperature, and cross-spectra for the spatial separation of all three velocity components and temperature, are compared with measurements. As a function of the four model parameters, spectra and cospectra are reproduced quite well, but horizontal temperature fluxes are slightly underestimated in stable conditions. In moderately unstable stratification, our model reproduces spectra only up to a scale ˜ 1 km. The model also overestimates coherences for vertical separations, but is less severe in unstable than in stable cases.

Optimized Kernel Entropy Components.

PubMed

Izquierdo-Verdiguier, Emma; Laparra, Valero; Jenssen, Robert; Gomez-Chova, Luis; Camps-Valls, Gustau

2017-06-01

This brief addresses two main issues of the standard kernel entropy component analysis (KECA) algorithm: the optimization of the kernel decomposition and the optimization of the Gaussian kernel parameter. KECA roughly reduces to a sorting of the importance of kernel eigenvectors by entropy instead of variance, as in the kernel principal components analysis. In this brief, we propose an extension of the KECA method, named optimized KECA (OKECA), that directly extracts the optimal features retaining most of the data entropy by means of compacting the information in very few features (often in just one or two). The proposed method produces features which have higher expressive power. In particular, it is based on the independent component analysis framework, and introduces an extra rotation to the eigen decomposition, which is optimized via gradient-ascent search. This maximum entropy preservation suggests that OKECA features are more efficient than KECA features for density estimation. In addition, a critical issue in both the methods is the selection of the kernel parameter, since it critically affects the resulting performance. Here, we analyze the most common kernel length-scale selection criteria. The results of both the methods are illustrated in different synthetic and real problems. Results show that OKECA returns projections with more expressive power than KECA, the most successful rule for estimating the kernel parameter is based on maximum likelihood, and OKECA is more robust to the selection of the length-scale parameter in kernel density estimation.

Determining Representative Elementary Volume For Multiple Petrophysical Parameters using a Convex Hull Analysis of Digital Rock Data

NASA Astrophysics Data System (ADS)

Shah, S.; Gray, F.; Yang, J.; Crawshaw, J.; Boek, E.

2016-12-01

Advances in 3D pore-scale imaging and computational methods have allowed an exceptionally detailed quantitative and qualitative analysis of the fluid flow in complex porous media. A fundamental problem in pore-scale imaging and modelling is how to represent and model the range of scales encountered in porous media, starting from the smallest pore spaces. In this study, a novel method is presented for determining the representative elementary volume (REV) of a rock for several parameters simultaneously. We calculate the two main macroscopic petrophysical parameters, porosity and single-phase permeability, using micro CT imaging and Lattice Boltzmann (LB) simulations for 14 different porous media, including sandpacks, sandstones and carbonates. The concept of the `Convex Hull' is then applied to calculate the REV for both parameters simultaneously using a plot of the area of the convex hull as a function of the sub-volume, capturing the different scales of heterogeneity from the pore-scale imaging. The results also show that the area of the convex hull (for well-chosen parameters such as the log of the permeability and the porosity) decays exponentially with sub-sample size suggesting a computationally efficient way to determine the system size needed to calculate the parameters to high accuracy (small convex hull area). Finally we propose using a characteristic length such as the pore size to choose an efficient absolute voxel size for the numerical rock.

Clues on the Milky Way disc formation from population synthesis simulations

NASA Astrophysics Data System (ADS)

Robin, A. C.; Reylé, C.; Bienaymé, O.; Fernandez-Trincado, J. G.; Amôres, E. B.

2016-09-01

In recent years the stellar populations of the Milky Way have been investigated from large scale surveys in different ways, from pure star count analysis to detailed studies based on spectroscopic surveys. While in the former case the data can constrain the scale height and scale length thanks to completeness, they suffer from high correlation between these two values. On the other hand, spectroscopic surveys suffer from complex selection functions which hardly allow to derive accurate density distributions. The scale length in particular has been difficult to be constrained, resulting in discrepant values in the literature. Here, we investigate the thick disc characteristics by comparing model simulations with large scale data sets. The simulations are done from the population synthesis model of Besançon. We explore the parameters of the thick disc (shape, local density, age, metallicity) using a Monte Carlo Markov Chain method to constrain the model free parameters (Robin et al. 2014). Correlations between parameters are limited due to the vast spatial coverage of the used surveys (SDSS + 2MASS). We show that the thick disc was created during a long phase of formation, starting about 12 Gyr ago and finishing about 10 Gyr ago, during which gravitational contraction occurred, both vertically and radially. Moreover, in its early phase the thick disc was flaring in the outskirts. We conclude that the thick disc has been created prior to the thin disc during a gravitational collapse phase, slowed down by turbulence related to a high star formation rate, as explained for example in Bournaud et al. (2009) or Lehnert et al. (2009). Our result does not favor a formation from an initial thin disc thickened later by merger events or by secular evolution of the thin disc. We then study the in-plane distribution of stars in the thin disc from 2MASS and show that the thin disc scale length varies as a function of age, indicating an inside out formation. Moreover, we investigate the warp and flare and demonstrate that the warp amplitude is changing with time and the node angle is slightly precessing. Finally, we show comparisons between the new model and spectroscopic surveys. The new model allows to correctly simulate the kinematics, the metallicity, and α-abundance distributions in the solar neighbourhood as well as in the bulge region.

Physical scales in the Wigner–Boltzmann equation

PubMed Central

Nedjalkov, M.; Selberherr, S.; Ferry, D.K.; Vasileska, D.; Dollfus, P.; Querlioz, D.; Dimov, I.; Schwaha, P.

2013-01-01

The Wigner–Boltzmann equation provides the Wigner single particle theory with interactions with bosonic degrees of freedom associated with harmonic oscillators, such as phonons in solids. Quantum evolution is an interplay of two transport modes, corresponding to the common coherent particle-potential processes, or to the decoherence causing scattering due to the oscillators. Which evolution mode will dominate depends on the scales of the involved physical quantities. A dimensionless formulation of the Wigner–Boltzmann equation is obtained, where these scales appear as dimensionless strength parameters. A notion called scaling theorem is derived, linking the strength parameters to the coupling with the oscillators. It is shown that an increase of this coupling is equivalent to a reduction of both the strength of the electric potential, and the coherence length. Secondly, the existence of classes of physically different, but mathematically equivalent setups of the Wigner–Boltzmann evolution is demonstrated. PMID:23504194

Information filtering via a scaling-based function.

PubMed

Qiu, Tian; Zhang, Zi-Ke; Chen, Guang

2013-01-01

Finding a universal description of the algorithm optimization is one of the key challenges in personalized recommendation. In this article, for the first time, we introduce a scaling-based algorithm (SCL) independent of recommendation list length based on a hybrid algorithm of heat conduction and mass diffusion, by finding out the scaling function for the tunable parameter and object average degree. The optimal value of the tunable parameter can be abstracted from the scaling function, which is heterogeneous for the individual object. Experimental results obtained from three real datasets, Netflix, MovieLens and RYM, show that the SCL is highly accurate in recommendation. More importantly, compared with a number of excellent algorithms, including the mass diffusion method, the original hybrid method, and even an improved version of the hybrid method, the SCL algorithm remarkably promotes the personalized recommendation in three other aspects: solving the accuracy-diversity dilemma, presenting a high novelty, and solving the key challenge of cold start problem.

Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

NASA Astrophysics Data System (ADS)

Boella, E.; Fiúza, F.; Stockem Novo, A.; Fonseca, R.; Silva, L. O.

2018-03-01

A numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasi-monoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread (Fiúza et al 2012 Phys. Rev. Lett. 109 215001). In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ions by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.

Uncoupled poroelastic and intrinsic viscoelastic dissipation in cartilage.

PubMed

Han, Guebum; Hess, Cole; Eriten, Melih; Henak, Corinne R

2018-04-26

This paper studies uncoupled poroelastic (flow-dependent) and intrinsic viscoelastic (flow-independent) energy dissipation mechanisms via their dependence on characteristic lengths to understand the root of cartilage's broadband dissipation behavior. Phase shift and dynamic modulus were measured from dynamic microindentation tests conducted on hydrated cartilage at different contact radii, as well as on dehydrated cartilage. Cartilage weight and thickness were recorded during dehydration. Phase shifts revealed poroelastic- and viscoelastic-dominant dissipation regimes in hydrated cartilage. Specifically, phase shift at a relatively small radius was governed by poroviscoelasticity, while phase shift at a relatively large radius was dominantly governed by intrinsic viscoelasticity. The uncoupled dissipation mechanisms demonstrated that intrinsic viscoelastic dissipation provided sustained broadband dissipation for all length scales, and additional poroelastic dissipation increased total dissipation at small length scales. Dehydration decreased intrinsic viscoelastic dissipation of cartilage. The findings demonstrated a possibility to measure poroelastic and intrinsic viscoelastic properties of cartilage at similar microscale lengths. Also they encouraged development of broadband cartilage like-dampers and provided important design parameters to maximize their performance. Copyright © 2018 Elsevier Ltd. All rights reserved.

Implication of Tsallis entropy in the Thomas–Fermi model for self-gravitating fermions

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

Ourabah, Kamel; Tribeche, Mouloud, E-mail: mouloudtribeche@yahoo.fr

The Thomas–Fermi approach for self-gravitating fermions is revisited within the theoretical framework of the q-statistics. Starting from the q-deformation of the Fermi–Dirac distribution function, a generalized Thomas–Fermi equation is derived. It is shown that the Tsallis entropy preserves a scaling property of this equation. The q-statistical approach to Jeans’ instability in a system of self-gravitating fermions is also addressed. The dependence of the Jeans’ wavenumber (or the Jeans length) on the parameter q is traced. It is found that the q-statistics makes the Fermionic system unstable at scales shorter than the standard Jeans length. -- Highlights: •Thomas–Fermi approach for self-gravitatingmore » fermions. •A generalized Thomas–Fermi equation is derived. •Nonextensivity preserves a scaling property of this equation. •Nonextensive approach to Jeans’ instability of self-gravitating fermions. •It is found that nonextensivity makes the Fermionic system unstable at shorter scales.« less

Scalability of the muscular action in a parametric 3D model of the index finger.

PubMed

Sancho-Bru, Joaquín L; Vergara, Margarita; Rodríguez-Cervantes, Pablo-Jesús; Giurintano, David J; Pérez-González, Antonio

2008-01-01

A method for scaling the muscle action is proposed and used to achieve a 3D inverse dynamic model of the human finger with all its components scalable. This method is based on scaling the physiological cross-sectional area (PCSA) in a Hill muscle model. Different anthropometric parameters and maximal grip force data have been measured and their correlations have been analyzed and used for scaling the PCSA of each muscle. A linear relationship between the normalized PCSA and the product of the length and breadth of the hand has been finally used for scaling, with a slope of 0.01315 cm(-2), with the length and breadth of the hand expressed in centimeters. The parametric muscle model has been included in a parametric finger model previously developed by the authors, and it has been validated reproducing the results of an experiment in which subjects from different population groups exerted maximal voluntary forces with their index finger in a controlled posture.

Improved Strength and Damage Modeling of Geologic Materials

NASA Astrophysics Data System (ADS)

Stewart, Sarah; Senft, Laurel

2007-06-01

Collisions and impact cratering events are important processes in the evolution of planetary bodies. The time and length scales of planetary collisions, however, are inaccessible in the laboratory and require the use of shock physics codes. We present the results from a new rheological model for geological materials implemented in the CTH code [1]. The `ROCK' model includes pressure, temperature, and damage effects on strength, as well as acoustic fluidization during impact crater collapse. We demonstrate that the model accurately reproduces final crater shapes, tensile cracking, and damaged zones from laboratory to planetary scales. The strength model requires basic material properties; hence, the input parameters may be benchmarked to laboratory results and extended to planetary collision events. We show the effects of varying material strength parameters, which are dependent on both scale and strain rate, and discuss choosing appropriate parameters for laboratory and planetary situations. The results are a significant improvement in models of continuum rock deformation during large scale impact events. [1] Senft, L. E., Stewart, S. T. Modeling Impact Cratering in Layered Surfaces, J. Geophys. Res., submitted.

Cosmological horizons, uncertainty principle, and maximum length quantum mechanics

NASA Astrophysics Data System (ADS)

Perivolaropoulos, L.

2017-05-01

The cosmological particle horizon is the maximum measurable length in the Universe. The existence of such a maximum observable length scale implies a modification of the quantum uncertainty principle. Thus due to nonlocality of quantum mechanics, the global properties of the Universe could produce a signature on the behavior of local quantum systems. A generalized uncertainty principle (GUP) that is consistent with the existence of such a maximum observable length scale lmax is Δ x Δ p ≥ℏ2/1/1 -α Δ x2 where α =lmax-2≃(H0/c )2 (H0 is the Hubble parameter and c is the speed of light). In addition to the existence of a maximum measurable length lmax=1/√{α }, this form of GUP implies also the existence of a minimum measurable momentum pmin=3/√{3 } 4 ℏ√{α }. Using appropriate representation of the position and momentum quantum operators we show that the spectrum of the one-dimensional harmonic oscillator becomes E¯n=2 n +1 +λnα ¯ where E¯n≡2 En/ℏω is the dimensionless properly normalized n th energy level, α ¯ is a dimensionless parameter with α ¯≡α ℏ/m ω and λn˜n2 for n ≫1 (we show the full form of λn in the text). For a typical vibrating diatomic molecule and lmax=c /H0 we find α ¯˜10-77 and therefore for such a system, this effect is beyond the reach of current experiments. However, this effect could be more important in the early Universe and could produce signatures in the primordial perturbation spectrum induced by quantum fluctuations of the inflaton field.

Multi Length Scale Finite Element Design Framework for Advanced Woven Fabrics

NASA Astrophysics Data System (ADS)

Erol, Galip Ozan

Woven fabrics are integral parts of many engineering applications spanning from personal protective garments to surgical scaffolds. They provide a wide range of opportunities in designing advanced structures because of their high tenacity, flexibility, high strength-to-weight ratios and versatility. These advantages result from their inherent multi scale nature where the filaments are bundled together to create yarns while the yarns are arranged into different weave architectures. Their highly versatile nature opens up potential for a wide range of mechanical properties which can be adjusted based on the application. While woven fabrics are viable options for design of various engineering systems, being able to understand the underlying mechanisms of the deformation and associated highly nonlinear mechanical response is important and necessary. However, the multiscale nature and relationships between these scales make the design process involving woven fabrics a challenging task. The objective of this work is to develop a multiscale numerical design framework using experimentally validated mesoscopic and macroscopic length scale approaches by identifying important deformation mechanisms and recognizing the nonlinear mechanical response of woven fabrics. This framework is exercised by developing mesoscopic length scale constitutive models to investigate plain weave fabric response under a wide range of loading conditions. A hyperelastic transversely isotropic yarn material model with transverse material nonlinearity is developed for woven yarns (commonly used in personal protection garments). The material properties/parameters are determined through an inverse method where unit cell finite element simulations are coupled with experiments. The developed yarn material model is validated by simulating full scale uniaxial tensile, bias extension and indentation experiments, and comparing to experimentally observed mechanical response and deformation mechanisms. Moreover, mesoscopic unit cell finite elements are coupled with a design-of-experiments method to systematically identify the important yarn material properties for the macroscale response of various weave architectures. To demonstrate the macroscopic length scale approach, two new material models for woven fabrics were developed. The Planar Material Model (PMM) utilizes two important deformation mechanisms in woven fabrics: (1) yarn elongation, and (2) relative yarn rotation due to shear loads. The yarns' uniaxial tensile response is modeled with a nonlinear spring using constitutive relations while a nonlinear rotational spring is implemented to define fabric's shear stiffness. The second material model, Sawtooth Material Model (SMM) adopts the sawtooth geometry while recognizing the biaxial nature of woven fabrics by implementing the interactions between the yarns. Material properties/parameters required by both PMM and SMM can be directly determined from standard experiments. Both macroscopic material models are implemented within an explicit finite element code and validated by comparing to the experiments. Then, the developed macroscopic material models are compared under various loading conditions to determine their accuracy. Finally, the numerical models developed in the mesoscopic and macroscopic length scales are linked thus demonstrating the new systematic design framework involving linked mesoscopic and macroscopic length scale modeling approaches. The approach is demonstrated with both Planar and Sawtooth Material Models and the simulation results are verified by comparing the results obtained from meso and macro models.

Boundary asymptotics for a non-neutral electrochemistry model with small Debye length

NASA Astrophysics Data System (ADS)

Lee, Chiun-Chang; Ryham, Rolf J.

2018-04-01

This article addresses the boundary asymptotics of the electrostatic potential in non-neutral electrochemistry models with small Debye length in bounded domains. Under standard physical assumptions motivated by non-electroneutral phenomena in oxidation-reduction reactions, we show that the electrostatic potential asymptotically blows up at boundary points with respect to the bulk reference potential as the scaled Debye length tends to zero. The analysis gives a lower bound for the blow-up rate with respect to the model parameters. Moreover, the maximum potential difference over any compact subset of the physical domain vanishes exponentially in the zero-Debye-length limit. The results mathematically confirm the physical description that electrolyte solutions are electrically neutral in the bulk and are strongly electrically non-neutral near charged surfaces.

Scale-dependent CMB power asymmetry from primordial speed of sound and a generalized δ N formalism

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

Wang, Dong-Gang; Cai, Yi-Fu; Zhao, Wen

2016-02-01

We explore a plausible mechanism that the hemispherical power asymmetry in the CMB is produced by the spatial variation of the primordial sound speed parameter. We suggest that in a generalized approach of the δ N formalism the local e-folding number may depend on some other primordial parameters besides the initial values of inflaton. Here the δ N formalism is extended by considering the effects of a spatially varying sound speed parameter caused by a super-Hubble perturbation of a light field. Using this generalized δ N formalism, we systematically calculate the asymmetric primordial spectrum in the model of multi-speed inflation by taking intomore » account the constraints of primordial non-Gaussianities. We further discuss specific model constraints, and the corresponding asymmetry amplitudes are found to be scale-dependent, which can accommodate current observations of the power asymmetry at different length scales.« less

CHANG-ES. IX. Radio scale heights and scale lengths of a consistent sample of 13 spiral galaxies seen edge-on and their correlations

NASA Astrophysics Data System (ADS)

Krause, Marita; Irwin, Judith; Wiegert, Theresa; Miskolczi, Arpad; Damas-Segovia, Ancor; Beck, Rainer; Li, Jiang-Tao; Heald, George; Müller, Peter; Stein, Yelena; Rand, Richard J.; Heesen, Volker; Walterbos, Rene A. M.; Dettmar, Ralf-Jürgen; Vargas, Carlos J.; English, Jayanne; Murphy, Eric J.

2018-03-01

Aim. The vertical halo scale height is a crucial parameter to understand the transport of cosmic-ray electrons (CRE) and their energy loss mechanisms in spiral galaxies. Until now, the radio scale height could only be determined for a few edge-on galaxies because of missing sensitivity at high resolution. Methods: We developed a sophisticated method for the scale height determination of edge-on galaxies. With this we determined the scale heights and radial scale lengths for a sample of 13 galaxies from the CHANG-ES radio continuum survey in two frequency bands. Results: The sample average values for the radio scale heights of the halo are 1.1 ± 0.3 kpc in C-band and 1.4 ± 0.7 kpc in L-band. From the frequency dependence analysis of the halo scale heights we found that the wind velocities (estimated using the adiabatic loss time) are above the escape velocity. We found that the halo scale heights increase linearly with the radio diameters. In order to exclude the diameter dependence, we defined a normalized scale height h˜ which is quite similar for all sample galaxies at both frequency bands and does not depend on the star formation rate or the magnetic field strength. However, h˜ shows a tight anticorrelation with the mass surface density. Conclusions: The sample galaxies with smaller scale lengths are more spherical in the radio emission, while those with larger scale lengths are flatter. The radio scale height depends mainly on the radio diameter of the galaxy. The sample galaxies are consistent with an escape-dominated radio halo with convective cosmic ray propagation, indicating that galactic winds are a widespread phenomenon in spiral galaxies. While a higher star formation rate or star formation surface density does not lead to a higher wind velocity, we found for the first time observational evidence of a gravitational deceleration of CRE outflow, e.g. a lowering of the wind velocity from the galactic disk.

Tests of Local Position Invariance Using Continuously Running Atomic Clocks

DTIC Science & Technology

2013-01-22

of the difference in anomalous redshift parameters, β = β1 − β2. (a) Dark data points are previous measurements: (i) neutral strontium optical...and the ratio of the light quark mass to the quantum chromodynamics length scale, mq/ QCD, where mq is the average of the up and down quark masses [17

Relationship between Maternal Language Parameters and the Child's Language Competency and Developmental Condition.

ERIC Educational Resources Information Center

Hooshyar, Nahid T.

Maternal language directed to 21 nonhandicapped, 21 Down syndrome, and 19 language impaired preschool children was examined. The three groups (all Caucasian and middle-class) were matched in mean length of utterance (MLU) and in developmental skills as measured on the Vineland Adaptive Behavior Scale. Mother-child language interaction was…

Homogeneity of small-scale earthquake faulting, stress, and fault strength

USGS Publications Warehouse

Hardebeck, J.L.

2006-01-01

Small-scale faulting at seismogenic depths in the crust appears to be more homogeneous than previously thought. I study three new high-quality focal-mechanism datasets of small (M < ??? 3) earthquakes in southern California, the east San Francisco Bay, and the aftershock sequence of the 1989 Loma Prieta earthquake. I quantify the degree of mechanism variability on a range of length scales by comparing the hypocentral disctance between every pair of events and the angular difference between their focal mechanisms. Closely spaced earthquakes (interhypocentral distance

Temperature and pressure tuneable swollen bicontinuous cubic phases approaching nature's length scales.

PubMed

Barriga, H M G; Tyler, A I I; McCarthy, N L C; Parsons, E S; Ces, O; Law, R V; Seddon, J M; Brooks, N J

2015-01-21

Bicontinuous cubic structures offer enormous potential in applications ranging from protein crystallisation to drug delivery systems and have been observed in cellular membrane structures. One of the current bottlenecks in understanding and exploiting these structures is that cubic scaffolds produced in vitro are considerably smaller in size than those observed in biological systems, differing by almost an order of magnitude in some cases. We have addressed this technological bottleneck and developed a methodology capable of manufacturing highly swollen bicontinuous cubic membranes with length scales approaching those seen in vivo. Crucially, these cubic systems do not require the presence of proteins. We have generated highly swollen Im3m symmetry bicontinuous cubic phases with lattice parameters of up to 480 Å, composed of ternary mixtures of monoolein, cholesterol and negatively charged lipid (DOPS or DOPG) and we have been able to tune their lattice parameters. The swollen cubic phases are highly sensitive to both temperature and pressure; these structural changes are likely to be controlled by a fine balance between lipid headgroup repulsions and lateral pressure in the hydrocarbon chain region.

Impact of polymer film thickness and cavity size on polymer flow during embossing : towards process design rules for nanoimprint lithography.

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

Schunk, Peter Randall; King, William P.; Sun, Amy Cha-Tien

2006-08-01

This paper presents continuum simulations of polymer flow during nanoimprint lithography (NIL). The simulations capture the underlying physics of polymer flow from the nanometer to millimeter length scale and examine geometry and thermophysical process quantities affecting cavity filling. Variations in embossing tool geometry and polymer film thickness during viscous flow distinguish different flow driving mechanisms. Three parameters can predict polymer deformation mode: cavity width to polymer thickness ratio, polymer supply ratio, and Capillary number. The ratio of cavity width to initial polymer film thickness determines vertically or laterally dominant deformation. The ratio of indenter width to residual film thickness measuresmore » polymer supply beneath the indenter which determines Stokes or squeeze flow. The local geometry ratios can predict a fill time based on laminar flow between plates, Stokes flow, or squeeze flow. Characteristic NIL capillary number based on geometry-dependent fill time distinguishes between capillary or viscous driven flows. The three parameters predict filling modes observed in published studies of NIL deformation over nanometer to millimeter length scales. The work seeks to establish process design rules for NIL and to provide tools for the rational design of NIL master templates, resist polymers, and process parameters.« less

Inhibition of Recrystallization of Amorphous Lactose in Nanocomposites Formed by Spray-Drying.

PubMed

Hellrup, Joel; Alderborn, Göran; Mahlin, Denny

2015-11-01

This study aims at investigating the recrystallization of amorphous lactose in nanocomposites. In particular, the focus is on the influence of the nano- to micrometer length scale nanofiller arrangement on the amorphous to crystalline transition. Further, the relative significance of formulation composition and manufacturing process parameters for the properties of the nanocomposite was investigated. Nanocomposites of amorphous lactose and fumed silica were produced by co-spray-drying. Solid-state transformation of the lactose was studied at 43%, 84%, and 94% relative humidity using X-ray powder diffraction and microcalorimetry. Design of experiments was used to analyze spray-drying process parameters and nanocomposite composition as factors influencing the time to 50% recrystallization. The spray-drying process parameters showed no significant influence. However, the recrystallization of the lactose in the nanocomposites was affected by the composition (fraction silica). The recrystallization rate constant decreased as a function of silica content. The lowered recrystallization rate of the lactose in the nanocomposites could be explained by three mechanisms: (1) separation of the amorphous lactose into discrete compartments on a micrometer length scale (compartmentalization), (2) lowered molecular mobility caused by molecular interactions between the lactose molecules and the surface of the silica (rigidification), and/or (3) intraparticle confinement of the amorphous lactose. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association.

Functional Topology of Evolving Urban Drainage Networks

NASA Astrophysics Data System (ADS)

Yang, Soohyun; Paik, Kyungrock; McGrath, Gavan S.; Urich, Christian; Krueger, Elisabeth; Kumar, Praveen; Rao, P. Suresh C.

2017-11-01

We investigated the scaling and topology of engineered urban drainage networks (UDNs) in two cities, and further examined UDN evolution over decades. UDN scaling was analyzed using two power law scaling characteristics widely employed for river networks: (1) Hack's law of length (L)-area (A) [L∝Ah] and (2) exceedance probability distribution of upstream contributing area (δ) [P>(A≥δ>)˜aδ-ɛ]. For the smallest UDNs (<2 km2), length-area scales linearly (h ˜ 1), but power law scaling (h ˜ 0.6) emerges as the UDNs grow. While P>(A≥δ>) plots for river networks are abruptly truncated, those for UDNs display exponential tempering [P>(A≥δ>)=aδ-ɛexp⁡>(-cδ>)]. The tempering parameter c decreases as the UDNs grow, implying that the distribution evolves in time to resemble those for river networks. However, the power law exponent ɛ for large UDNs tends to be greater than the range reported for river networks. Differences in generative processes and engineering design constraints contribute to observed differences in the evolution of UDNs and river networks, including subnet heterogeneity and nonrandom branching.

The coherence length of the peculiar velocity field in the universe and the large-scale galaxy correlation data

NASA Technical Reports Server (NTRS)

Kashlinsky, A.

1992-01-01

This study presents a method for obtaining the true rms peculiar flow in the universe on scales up to 100-120/h Mpc using APM data as an input assuming only that peculiar motions are caused by peculiar gravity. The comparison to the local (Great Attractor) flow is expected to give clear information on the density parameter, Omega, and the local bias parameter, b. The observed peculiar flows in the Great Attractor region are found to be in better agreement with the open (Omega = 0.1) universe in which light traces mass (b = 1) than with a flat (Omega = 1) universe unless the bias parameter is unrealistically large (b is not less than 4). Constraints on Omega from a comparison of the APM and PV samples are discussed.

Physical scales in the Wigner-Boltzmann equation

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

Nedjalkov, M., E-mail: mixi@iue.tuwien.ac.at; Selberherr, S.; Ferry, D.K.

2013-01-15

The Wigner-Boltzmann equation provides the Wigner single particle theory with interactions with bosonic degrees of freedom associated with harmonic oscillators, such as phonons in solids. Quantum evolution is an interplay of two transport modes, corresponding to the common coherent particle-potential processes, or to the decoherence causing scattering due to the oscillators. Which evolution mode will dominate depends on the scales of the involved physical quantities. A dimensionless formulation of the Wigner-Boltzmann equation is obtained, where these scales appear as dimensionless strength parameters. A notion called scaling theorem is derived, linking the strength parameters to the coupling with the oscillators. Itmore » is shown that an increase of this coupling is equivalent to a reduction of both the strength of the electric potential, and the coherence length. Secondly, the existence of classes of physically different, but mathematically equivalent setups of the Wigner-Boltzmann evolution is demonstrated. - Highlights: Black-Right-Pointing-Pointer Dimensionless parameters determine the ratio of quantum or classical WB evolution. Black-Right-Pointing-Pointer The scaling theorem evaluates the decoherence effect due to scattering. Black-Right-Pointing-Pointer Evolution processes are grouped into classes of equivalence.« less

General analysis of group velocity effects in collinear optical parametric amplifiers and generators.

PubMed

Arisholm, Gunnar

2007-05-14

Group velocity mismatch (GVM) is a major concern in the design of optical parametric amplifiers (OPAs) and generators (OPGs) for pulses shorter than a few picoseconds. By simplifying the coupled propagation equations and exploiting their scaling properties, the number of free parameters for a collinear OPA is reduced to a level where the parameter space can be studied systematically by simulations. The resulting set of figures show the combinations of material parameters and pulse lengths for which high performance can be achieved, and they can serve as a basis for a design.

Patching C2n Time Series Data Holes using Principal Component Analysis

DTIC Science & Technology

2007-01-01

characteristic local scale exponent , regardless of dilation of the length examined. THE HURST PARAMETER There are a slew of methods13 available to...fractal dimension D0, which characterises the roughness of the data, and the Hurst parameter, H , which is a measure of the long range dependence (LRD...estimate H . For simplicity, we have opted to use the well known Hurst –Mandelbrot R/S technique, which is also the most elementary. The fitting curve

Influence of Turbulence Parameters, Reynolds Number, and Body Shape on Stagnation-Region Heat Transfer

NASA Technical Reports Server (NTRS)

Vanfossen, G. James; Simoneau, Robert J.; Ching, Chan Y.

1994-01-01

The purpose of the present work was threefold: (1) to determine if a free-stream turbulence length scale existed that would cause the greatest augmentation in stagnation-region heat transfer over laminar levels; (2) to investigate the effect of velocity gradient on stagnation-region heat transfer augmentation by free-stream turbulence; and (3) to develop a prediction tool for stagnation heat transfer in the presence of free-stream turbulence. Heat transfer was measured in the stagnation region of four models with elliptical leading edges that had ratios of major to minor axes of 1:1, 1.5:1, 2.25:1, and 3:1. Five turbulence-generating grids were fabricated; four were square mesh, biplane grids made from square bars. The fifth grid was an array of fine parallel wires that were perpendicular to the model spanwise direction. Heat transfer data were taken at Reynolds numbers ranging from 37 000 to 228 000. Turbulence intensities were in the range of 1.1 to 15.9% while the ratio of integral length scale to leading-edge diameter ranged from 0.05 to 0.30. Stagnation-point velocity gradient was varied by nearly 50%. Stagnation-region heat transfer augmentation was found to increase with decreasing length scale but no optimum length scale was found. Heat transfer augmentation due to turbulence was found to be unaffected by the velocity gradient near the leading edge. A correlation was developed that fit heat transfer data for the square-bar grids to within +/- 4%.

Top down and bottom up engineering of bone.

PubMed

Knothe Tate, Melissa L

2011-01-11

The goal of this retrospective article is to place the body of my lab's multiscale mechanobiology work in context of top-down and bottom-up engineering of bone. We have used biosystems engineering, computational modeling and novel experimental approaches to understand bone physiology, in health and disease, and across time (in utero, postnatal growth, maturity, aging and death, as well as evolution) and length scales (a single bone like a femur, m; a sample of bone tissue, mm-cm; a cell and its local environment, μm; down to the length scale of the cell's own skeleton, the cytoskeleton, nm). First we introduce the concept of flow in bone and the three calibers of porosity through which fluid flows. Then we describe, in the context of organ-tissue, tissue-cell and cell-molecule length scales, both multiscale computational models and experimental methods to predict flow in bone and to understand the flow of fluid as a means to deliver chemical and mechanical cues in bone. Addressing a number of studies in the context of multiple length and time scales, the importance of appropriate boundary conditions, site specific material parameters, permeability measures and even micro-nanoanatomically correct geometries are discussed in context of model predictions and their value for understanding multiscale mechanobiology of bone. Insights from these multiscale computational modeling and experimental methods are providing us with a means to predict, engineer and manufacture bone tissue in the laboratory and in the human body. Copyright © 2010 Elsevier Ltd. All rights reserved.

Estimation of turbulence characteristics of the low-level eyewall and outer-core regions in intense Hurricanes Allen (1980) and Hugo (1989)

NASA Astrophysics Data System (ADS)

Zhang, J. A.; Marks, F. D.; Montgomery, M.; Lorsolo, S.

2010-12-01

Turbulent transport processes in the atmospheric boundary layer play an important role in the intensification and maintenance of a hurricane vortex. However, direct measurement of turbulence in the hurricane boundary layer has been scarce. This study analyzes the flight-level data collected by research aircraft that penetrated the eyewalls of Category 5 Hurricane Hugo (1989) and Category 4 Hurricane Allen (1980) between 1 km and the sea surface. Momentum flux, turbulent kinetic energy (TKE) and vertical eddy diffusivity are estimated before and during the eyewall penetrations. Spatial scales of turbulent eddies are determined through spectral analysis. The turbulence parameters estimated for the eyewall penetration leg are found to be nearly an order of magnitude larger than those for the leg outside the eyewall at similar altitudes. In the low-level intense eyewall region, the horizontal length scale of dominant turbulent eddies is found to be between 500 - 3000 m and the corresponding vertical length scale is approximately 100 - 200 m. The results suggest also that it is unwise to include the eyewall vorticity maximum (EVM) in the turbulence parameter estimation, since the EVMs are likely to be quasi two-dimensional vortex structures that are embedded within the three dimensional turbulence on the inside edge of the eyewall.

The Evolution of the Galactic Thick Disk with the LAMOST Survey

NASA Astrophysics Data System (ADS)

Li, Chengdong; Zhao, Gang

2017-11-01

We select giant stars from LAMOST data release 3 (hereafter DR3) based on their spectral properties and atmospheric parameters in order to detect the structure and kinematic properties of the Galactic thick disk. The spatial motions of our sample stars are calculated. We obtain 2035 thick-disk giant stars by using a kinematic criterion. We confirm the existence of the metal-weak thick disk. The most metal-deficient star in our sample has [{Fe}/{{H}}]=-2.34. We derive the radial and vertical metallicity gradients, which are +0.035 ± 0.010 and -0.164 ± 0.010 dex kpc-1respectively. Then we estimate the scale length and scale height of the thick disk using the Jeans equation, and the results are {h}R=3.0+/- 0.1 {kpc} and {h}Z=0.9+/- 0.1 {kpc}. The scale length of the thick disk is approximately equal to that of the thin disk from several previous works. Finally, we calculate the orbital parameters of our sample stars, and discuss the formation scenario of the thick disk. Our result for the distribution of stellar orbital eccentricity excludes the accretion scenario. We conclude that the thick disk stars are mainly born inside the Milky Way.

Heterogeneity and scaling land-atmospheric water and energy fluxes in climate systems

NASA Technical Reports Server (NTRS)

Wood, Eric F.

1993-01-01

The effects of small-scale heterogeneity in land surface characteristics on the large-scale fluxes of water and energy in land-atmosphere system has become a central focus of many of the climatology research experiments. The acquisition of high resolution land surface data through remote sensing and intensive land-climatology field experiments (like HAPEX and FIFE) has provided data to investigate the interactions between microscale land-atmosphere interactions and macroscale models. One essential research question is how to account for the small scale heterogeneities and whether 'effective' parameters can be used in the macroscale models. To address this question of scaling, three modeling experiments were performed and are reviewed in the paper. The first is concerned with the aggregation of parameters and inputs for a terrestrial water and energy balance model. The second experiment analyzed the scaling behavior of hydrologic responses during rain events and between rain events. The third experiment compared the hydrologic responses from distributed models with a lumped model that uses spatially constant inputs and parameters. The results show that the patterns of small scale variations can be represented statistically if the scale is larger than a representative elementary area scale, which appears to be about 2 - 3 times the correlation length of the process. For natural catchments this appears to be about 1 - 2 sq km. The results concerning distributed versus lumped representations are more complicated. For conditions when the processes are nonlinear, then lumping results in biases; otherwise a one-dimensional model based on 'equivalent' parameters provides quite good results. Further research is needed to fully understand these conditions.

Calculations of High-Temperature Jet Flow Using Hybrid Reynolds-Average Navier-Stokes Formulations

NASA Technical Reports Server (NTRS)

Abdol-Hamid, Khaled S.; Elmiligui, Alaa; Giriamaji, Sharath S.

2008-01-01

Two multiscale-type turbulence models are implemented in the PAB3D solver. The models are based on modifying the Reynolds-averaged Navier Stokes equations. The first scheme is a hybrid Reynolds-averaged- Navier Stokes/large-eddy-simulation model using the two-equation k(epsilon) model with a Reynolds-averaged-Navier Stokes/large-eddy-simulation transition function dependent on grid spacing and the computed turbulence length scale. The second scheme is a modified version of the partially averaged Navier Stokes model in which the unresolved kinetic energy parameter f(sub k) is allowed to vary as a function of grid spacing and the turbulence length scale. This parameter is estimated based on a novel two-stage procedure to efficiently estimate the level of scale resolution possible for a given flow on a given grid for partially averaged Navier Stokes. It has been found that the prescribed scale resolution can play a major role in obtaining accurate flow solutions. The parameter f(sub k) varies between zero and one and is equal to one in the viscous sublayer and when the Reynolds-averaged Navier Stokes turbulent viscosity becomes smaller than the large-eddy-simulation viscosity. The formulation, usage methodology, and validation examples are presented to demonstrate the enhancement of PAB3D's time-accurate turbulence modeling capabilities. The accurate simulations of flow and turbulent quantities will provide a valuable tool for accurate jet noise predictions. Solutions from these models are compared with Reynolds-averaged Navier Stokes results and experimental data for high-temperature jet flows. The current results show promise for the capability of hybrid Reynolds-averaged Navier Stokes and large eddy simulation and partially averaged Navier Stokes in simulating such flow phenomena.

[Analysis of the workload and the use of the nursing resources in an intensive care unit].

PubMed

Valls-Matarín, J; Salamero-Amorós, M; Roldán-Gil, C

2015-01-01

To evaluate and assess the nursing workload (NW) scales by means of three scales and to determine the theoretical and real nurse/patient relationship in a polyvalent ICU. Cross-sectional descriptive study between July 2012 and June 2013 in patients over 18 years old, for which 3 nurses quantified, in randomized days, the NW by the Nursing Activities Score (NAS), Nine Equivalents Manpower Score (NEMS) and Valoración de Cargas de Trabajo y Tiempos de Enfermería (VACTE). Efficiency parameters of nursing resources were calculated: "work utilization ratio" (WUR), "level of care" operative (LOCop) and planned (LOCp). Data on demographics, length of stay and number of nurses were collected. 720 records were collected. The mean age was 64 (13.6) years. 73% were male and the median of length of stay was 3 (1-12) days. 60% were admitted for medical causes. The average total score was: NAS: 696.8 (111.6), NEMS: 311.8 (55.3) and VACTE: 4,978 (897.7). The required number of nurses according to NAS was 7 and 6,7 according to NEMS and VACTE. The actual average was 5.5. On all 3 scales the WUR was >1 and LOCop was 1.6 pacients/nurse. The LOCp was 2 patients/nurse. Assessing NW allows to know the reality of each unit. According to the scales and efficiency parameters of the nursing resources used, there is a shortage of nurses in relation to the work generated. NAS reflects more parameters of NW. Copyright © 2014 Elsevier España, S.L.U. y SEEIUC. All rights reserved.

The impact of atmospheric stability and wind shear on vertical cloud overlap over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Li, Jiming; Lv, Qiaoyi; Jian, Bida; Zhang, Min; Zhao, Chuanfeng; Fu, Qiang; Kawamoto, Kazuaki; Zhang, Hua

2018-05-01

Studies have shown that changes in cloud cover are responsible for the rapid climate warming over the Tibetan Plateau (TP) in the past 3 decades. To simulate the total cloud cover, atmospheric models have to reasonably represent the characteristics of vertical overlap between cloud layers. Until now, however, this subject has received little attention due to the limited availability of observations, especially over the TP. Based on the above information, the main aim of this study is to examine the properties of cloud overlaps over the TP region and to build an empirical relationship between cloud overlap properties and large-scale atmospheric dynamics using 4 years (2007-2010) of data from the CloudSat cloud product and collocated ERA-Interim reanalysis data. To do this, the cloud overlap parameter α, which is an inverse exponential function of the cloud layer separation D and decorrelation length scale L, is calculated using CloudSat and is discussed. The parameters α and L are both widely used to characterize the transition from the maximum to random overlap assumption with increasing layer separations. For those non-adjacent layers without clear sky between them (that is, contiguous cloud layers), it is found that the overlap parameter α is sensitive to the unique thermodynamic and dynamic environment over the TP, i.e., the unstable atmospheric stratification and corresponding weak wind shear, which leads to maximum overlap (that is, greater α values). This finding agrees well with the previous studies. Finally, we parameterize the decorrelation length scale L as a function of the wind shear and atmospheric stability based on a multiple linear regression. Compared with previous parameterizations, this new scheme can improve the simulation of total cloud cover over the TP when the separations between cloud layers are greater than 1 km. This study thus suggests that the effects of both wind shear and atmospheric stability on cloud overlap should be taken into account in the parameterization of decorrelation length scale L in order to further improve the calculation of the radiative budget and the prediction of climate change over the TP in the atmospheric models.

Applications of dewetting in micro and nanotechnology.

PubMed

Gentili, Denis; Foschi, Giulia; Valle, Francesco; Cavallini, Massimiliano; Biscarini, Fabio

2012-06-21

Dewetting is a spontaneous phenomenon where a thin film on a surface ruptures into an ensemble of separated objects, like droplets, stripes, and pillars. Spatial correlations with characteristic distance and object size emerge spontaneously across the whole dewetted area, leading to regular motifs with long-range order. Characteristic length scales depend on film thickness, which is a convenient and robust technological parameter. Dewetting is therefore an attractive paradigm for organizing a material into structures of well-defined micro- or nanometre-size, precisely positioned on a surface, thus avoiding lithographical processes. This tutorial review introduces the reader to the physical-chemical basis of dewetting, shows how the dewetting process can be applied to different functional materials with relevance in technological applications, and highlights the possible strategies to control the length scales of the dewetting process.

Some tests on small-scale rectangular throat ejector. [thrust augmentation for V/STOL aircraft

NASA Technical Reports Server (NTRS)

Dean, W. N., Jr.; Franke, M. E.

1979-01-01

A small scale rectangular throat ejector with plane slot nozzles and a fixed throat area was tested to determine the effects of diffuser sidewall length, diffuser area ratio, and sidewall nozzle position on thrust and mass augmentation. The thrust augmentation ratio varied from approximately 0.9 to 1.1. Although the ejector did not have good thrust augmentation performance, the effects of the parameters studied are believed to indicate probable trends in thrust augmenting ejectors.

Liquid Engine Design: Effect of Chamber Dimensions on Specific Impulse

NASA Technical Reports Server (NTRS)

Hoggard, Lindsay; Leahy, Joe

2009-01-01

Which assumption of combustion chemistry - frozen or equilibrium - should be used in the prediction of liquid rocket engine performance calculations? Can a correlation be developed for this? A literature search using the LaSSe tool, an online repository of old rocket data and reports, was completed. Test results of NTO/Aerozine-50 and Lox/LH2 subscale and full-scale injector and combustion chamber test results were found and studied for this task. NASA code, Chemical Equilibrium with Applications (CEA) was used to predict engine performance using both chemistry assumptions, defined here. Frozen- composition remains frozen during expansion through the nozzle. Equilibrium- instantaneous chemical equilibrium during nozzle expansion. Chamber parameters were varied to understand what dimensions drive chamber C* and Isp. Contraction Ratio is the ratio of the nozzle throat area to the area of the chamber. L is the length of the chamber. Characteristic chamber length, L*, is the length that the chamber would be if it were a straight tube and had no converging nozzle. Goal: Develop a qualitative and quantitative correlation for performance parameters - Specific Impulse (Isp) and Characteristic Velocity (C*) - as a function of one or more chamber dimensions - Contraction Ratio (CR), Chamber Length (L ) and/or Characteristic Chamber Length (L*). Determine if chamber dimensions can be correlated to frozen or equilibrium chemistry.

Influence of the length of institutionalization on older adults' postural balance and risk of falls: a transversal study1

PubMed Central

Batista, Wagner Oliveira; Alves, Edmundo de Drummond; Porto, Flávia; Pereira, Fabio Dutra; Santana, Rosimere Ferreira; Gurgel, Jonas Lírio

2014-01-01

OBJECTIVE: to ascertain the influence of the length of institutionalization on older adults' balance and risk of falls. METHOD: to evaluate the risk of falls, the Berg Balance Scale and the Timed Get Up and Go test were used; and for measuring postural balance, static stabilometry was used, with acquisition of the elliptical area of 95% and mean velocities on the x and y axes of center of pressure displacement. Parametric and nonparametric measures of association and comparison (α<0.05) were used. RESULTS: there was no significant correlation between the length of institutionalization and the tests for evaluation of risk of falling, neither was there difference between groups and within subgroups, stratified by length of institutionalization and age. In the stabilometric measurements, there was a negative correlation between the parameters analyzed and the length of institutionalization, and difference between groups and within subgroups. CONCLUSION: this study's results point to the difficulty of undertaking postural control tasks, showing a leveling below the clinical tests' reference scores. In the stabilometric behavior, one should note the reduction of the parameters as the length of institutionalization increases, contradicting the assumptions. This study's results offer support for the development of a multi-professional model for intervention with the postural control and balance of older adults living in homes for the aged. PMID:25296149

Geometry of an outcrop-scale duplex in Devonian flysch, Maine

USGS Publications Warehouse

Bradley, D.C.; Bradley, L.M.

1994-01-01

We describe an outcrop-scale duplex consisting of 211 exposed repetitions of a single bed. The duplex marks an early Acadian (Middle Devonian) oblique thrust zone in the Lower Devonian flysch of northern Maine. Detailed mapping at a scale of 1:8 has enabled us to measure accurately parameters such as horse length and thickness, ramp angles and displacements; we compare these and derivative values with those of published descriptions of duplexes, and with theoretical models. Shortening estimates based on line balancing are consistently smaller than two methods of area balancing, suggesting that layer-parallel shortening preceded thrusting. ?? 1994.

Confinement and the Glass Transition Temperature in Supported Polymer Films: Molecular Weight, Repeat Unit Modification, and Cooperativity Length Scale Investigations

NASA Astrophysics Data System (ADS)

Mundra, Manish K.

2005-03-01

It is well known that the glass transition temperatures, Tgs, of supported polystyrene (PS) films decrease dramatically with decreasing film thickness below 60-80 nm. However, a detailed understanding of the cause of this effect is lacking. We have investigated the impact of several parameters, including polymer molecular weight (MW), repeat unit structure, and the length scale of cooperatively rearranging regions in bulk. There is no significant effect of PS MW on the Tg-confinement effect over a range of 5,000 to 3,000,000 g/mol. In contrast, the strength of the Tg reduction and the onset of the confinement effect increase dramatically upon changing the polymer from PS to poly(4-tert-butylstyrene) (PTBS), with PTBS exhibiting a Tg reduction relative to bulk at a thickness of 300-400 nm. PTBS also shows a Tg reduction relative to bulk of 47 K in a 21-nm-thick film, more than twice that observed in a PS film of identical thickness. Characterization of the length scale of cooperatively rearranging regions has been done by differential scanning calorimetry but reveals at best a limited correlation with the confinement effect.

Reduced 3d modeling on injection schemes for laser wakefield acceleration at plasma scale lengths

NASA Astrophysics Data System (ADS)

Helm, Anton; Vieira, Jorge; Silva, Luis; Fonseca, Ricardo

2017-10-01

Current modelling techniques for laser wakefield acceleration (LWFA) are based on particle-in-cell (PIC) codes which are computationally demanding. In PIC simulations the laser wavelength λ0, in μm-range, has to be resolved over the acceleration lengths in meter-range. A promising approach is the ponderomotive guiding center solver (PGC) by only considering the laser envelope for laser pulse propagation. Therefore only the plasma skin depth λp has to be resolved, leading to speedups of (λp /λ0) 2. This allows to perform a wide-range of parameter studies and use it for λ0 <<λp studies. We present the 3d version of a PGC solver in the massively parallel, fully relativistic PIC code OSIRIS. Further, a discussion and characterization of the validity of the PGC solver for injection schemes on the plasma scale lengths, such as down-ramp injection, magnetic injection and ionization injection, through parametric studies, full PIC simulations and theoretical scaling, is presented. This work was partially supported by Fundacao para a Ciencia e Tecnologia (FCT), Portugal, through Grant No. PTDC/FIS-PLA/2940/2014 and PD/BD/105882/2014.

Two-length-scale turbulence model for self-similar buoyancy-, shock-, and shear-driven mixing

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

Morgan, Brandon E.; Schilling, Oleg; Hartland, Tucker A.

The three-equation k-L-a turbulence model [B. Morgan and M. Wickett, Three-equation model for the self-similar growth of Rayleigh-Taylor and Richtmyer-Meshkov instabilities," Phys. Rev. E 91 (2015)] is extended by the addition of a second length scale equation. It is shown that the separation of turbulence transport and turbulence destruction length scales is necessary for simultaneous prediction of the growth parameter and turbulence intensity of a Kelvin-Helmholtz shear layer when model coeficients are constrained by similarity analysis. Constraints on model coeficients are derived that satisfy an ansatz of self-similarity in the low-Atwood-number limit and allow the determination of model coeficients necessarymore » to recover expected experimental behavior. The model is then applied in one-dimensional simulations of Rayleigh-Taylor, reshocked Richtmyer-Meshkov, Kelvin{Helmholtz, and combined Rayleigh-Taylor/Kelvin-Helmholtz instability mixing layers to demonstrate that the expected growth rates are recovered numerically. Finally, it is shown that model behavior in the case of combined instability is to predict a mixing width that is a linear combination of Rayleigh-Taylor and Kelvin-Helmholtz mixing processes.« less

Fan noise caused by the ingestion of anisotropic turbulence - A model based on axisymmetric turbulence theory

NASA Technical Reports Server (NTRS)

Kerschen, E. J.; Gliebe, P. R.

1980-01-01

An analytical model of fan noise caused by inflow turbulence, a generalization of earlier work by Mani, is presented. Axisymmetric turbulence theory is used to develop a statistical representation of the inflow turbulence valid for a wide range of turbulence properties. Both the dipole source due to rotor blade unsteady forces and the quadrupole source resulting from the interaction of the turbulence with the rotor potential field are considered. The effects of variations in turbulence properties and fan operating conditions are evaluated. For turbulence axial integral length scales much larger than the blade spacing, the spectrum is shown to consist of sharp peaks at the blade passing frequency and its harmonics, with negligible broadband content. The analysis can then be simplified considerably and the total sound power contained within each spectrum peak becomes independent of axial length scale, while the width of the peak is inversely proportional to this parameter. Large axial length scales are characteristic of static fan test facilities, where the transverse contraction of the inlet flow produces highly anisotropic turbulence. In this situation, the rotor/turbulence interaction noise is mainly caused by the transverse component of turbulent velocity.

Two-length-scale turbulence model for self-similar buoyancy-, shock-, and shear-driven mixing

DOE PAGES

Morgan, Brandon E.; Schilling, Oleg; Hartland, Tucker A.

2018-01-10

The three-equation k-L-a turbulence model [B. Morgan and M. Wickett, Three-equation model for the self-similar growth of Rayleigh-Taylor and Richtmyer-Meshkov instabilities," Phys. Rev. E 91 (2015)] is extended by the addition of a second length scale equation. It is shown that the separation of turbulence transport and turbulence destruction length scales is necessary for simultaneous prediction of the growth parameter and turbulence intensity of a Kelvin-Helmholtz shear layer when model coeficients are constrained by similarity analysis. Constraints on model coeficients are derived that satisfy an ansatz of self-similarity in the low-Atwood-number limit and allow the determination of model coeficients necessarymore » to recover expected experimental behavior. The model is then applied in one-dimensional simulations of Rayleigh-Taylor, reshocked Richtmyer-Meshkov, Kelvin{Helmholtz, and combined Rayleigh-Taylor/Kelvin-Helmholtz instability mixing layers to demonstrate that the expected growth rates are recovered numerically. Finally, it is shown that model behavior in the case of combined instability is to predict a mixing width that is a linear combination of Rayleigh-Taylor and Kelvin-Helmholtz mixing processes.« less

Clinical Analysis of Ocular Parameters Contributing to Intraoperative Pain during Standard Phacoemulsification

PubMed Central

Kim, Myung Jun

2017-01-01

Purpose. To study the correlation between ocular parameters and subjective pain that patients perceived during phacoemulsification. Methods. Medical records of 142 patients who underwent standard phacoemulsification under topical anesthesia between March and August 2016 were retrospectively reviewed. The pain during phacoemulsification and 1 h after surgery was assessed and compared using a visual analog scale. In addition, demographic data, preoperative biometric parameters, and intraoperative surgical parameters were recorded. Results. Mean age of patients was 67.49 ± 12.50 years. The mean pain score was 2.26 ± 0.85 during phacoemulsification and 0.40 ± 0.69 postoperatively. Intraoperative pain was significantly associated with higher preoperative intraocular pressure (β = 0.220, P = 0.016), greater anterior chamber depth (β = 0.210, P = 0.028), and greater axial length (β = 0.181, P = 0.043). Conclusions. To reduce the subjective pain when patients have high preoperative intraocular pressure, large anterior chamber depth, or great axial length, supplementary procedures may be required. PMID:28491473

The association of calcaneal spur length and clinical and functional parameters in plantar fasciitis.

PubMed

Kuyucu, Ersin; Koçyiğit, Figen; Erdil, Mehmet

2015-09-01

Plantar fasciitis (PF)is the most common cause of plantar heel pain. Despite many treatment alternatives for heel spur, the association of calcaneal spur size with clinical and functional parameters is inconclusive. The objective of this study to investigate the correlation of calcaneal spur length with clinical findings and functional status documented with Foot Function Index in patients with plantar fasciitis. We performed power analysis for the sample size estimation. 87 patients with PF were scrutinized to reach the estimated patient number 75. Computer-aided linear measurements were done for spur length from tip to base in milimeters. Perceived pain intensity was evaluated by visual analog scale (VAS). Patients were asked to rate the pain experienced on a 10-cm VAS. Foot function index was applied to the patients to evaluate pain, disability and activity limitation of the patients. Of the 75 participants, 24 were males (32%) and 51 were females (68%). The mean age was 47 ± 10 years (range 30-65 years). The mean calcaneal spur length was 3.86 ± 3.36 mm (range between 0 and 12.2). Calcaneal spur length was significantly correlated with age (p = 0.003), BMI (p = 0.029), symptom duration, (p = 0.001) VAS (p = 0.003), and FFI total score (p < 0.001). Our study demonstrated that length of the calcaneal spur is significantly correlated with age, BMI, symptom duration, perceived pain, FFI pain and disability subscores, and FFI total scores. The size of the calcaneal spur is an important parameter correlated with pain and functional scores in PF. Copyright © 2015 IJS Publishing Group Limited. Published by Elsevier Ltd. All rights reserved.

Revealing the physical insight of a length-scale parameter in metamaterials by exploiting the variational formulation

NASA Astrophysics Data System (ADS)

Abali, B. Emek

2018-04-01

For micro-architectured materials with a substructure, called metamaterials, we can realize a direct numerical simulation in the microscale by using classical mechanics. This method is accurate, however, computationally costly. Instead, a solution of the same problem in the macroscale is possible by means of the generalized mechanics. In this case, no detailed modeling of the substructure is necessary; however, new parameters emerge. A physical interpretation of these metamaterial parameters is challenging leading to a lack of experimental strategies for their determination. In this work, we exploit the variational formulation based on action principles and obtain a direct relation between a parameter used in the kinetic energy and a metamaterial parameter in the case of a viscoelastic model.

Scattering of electromagnetic wave by the layer with one-dimensional random inhomogeneities

NASA Astrophysics Data System (ADS)

Kogan, Lev; Zaboronkova, Tatiana; Grigoriev, Gennadii., IV.

A great deal of attention has been paid to the study of probability characteristics of electro-magnetic waves scattered by one-dimensional fluctuations of medium dielectric permittivity. However, the problem of a determination of a density of a probability and average intensity of the field inside the stochastically inhomogeneous medium with arbitrary extension of fluc-tuations has not been considered yet. It is the purpose of the present report to find and to analyze the indicated functions for the plane electromagnetic wave scattered by the layer with one-dimensional fluctuations of permittivity. We assumed that the length and the amplitude of individual fluctuations as well the interval between them are random quantities. All of indi-cated fluctuation parameters are supposed as independent random values possessing Gaussian distribution. We considered the stationary time cases both small-scale and large-scale rarefied inhomogeneities. Mathematically such problem can be reduced to the solution of integral Fred-holm equation of second kind for Hertz potential (U). Using the decomposition of the field into the series of multiply scattered waves we obtained the expression for a probability density of the field of the plane wave and determined the moments of the scattered field. We have shown that all odd moments of the centered field (U-¡U¿) are equal to zero and the even moments depend on the intensity. It was obtained that the probability density of the field possesses the Gaussian distribution. The average field is small compared with the standard fluctuation of scattered field for all considered cases of inhomogeneities. The value of average intensity of the field is an order of a standard of fluctuations of field intensity and drops with increases the inhomogeneities length in the case of small-scale inhomogeneities. The behavior of average intensity is more complicated in the case of large-scale medium inhomogeneities. The value of average intensity is the oscillating function versus the average fluctuations length if the standard of fluctuations of inhomogeneities length is greater then the wave length. When the standard of fluctuations of medium inhomogeneities extension is smaller then the wave length, the av-erage intensity value weakly depends from the average fluctuations extension. The obtained results may be used for analysis of the electromagnetic wave propagation into the media with the fluctuating parameters caused by such factors as leafs of trees, cumulus, internal gravity waves with a chaotic phase and etc. Acknowledgment: This work was supported by the Russian Foundation for Basic Research (projects 08-02-97026 and 09-05-00450).

Stability of vertical magnetic chains

PubMed Central

2017-01-01

A linear stability analysis is performed for a pair of coaxial vertical chains made from permanently magnetized balls under the influence of gravity. While one chain rises from the ground, the other hangs from above, with the remaining ends separated by a gap of prescribed length. Various boundary conditions are considered, as are situations in which the magnetic dipole moments in the two chains are parallel or antiparallel. The case of a single chain attached to the ground is also discussed. The stability of the system is examined with respect to three quantities: the number of balls in each chain, the length of the gap between the chains, and a single dimensionless parameter which embodies the competition between magnetic and gravitational forces. Asymptotic scaling laws involving these parameters are provided. The Hessian matrix is computed in exact form, allowing the critical parameter values at which the system loses stability and the respective eigenmodes to be determined up to machine precision. A comparison with simple experiments for a single chain attached to the ground shows good agreement. PMID:28293135

Stability of vertical magnetic chains

NASA Astrophysics Data System (ADS)

Schönke, Johannes; Fried, Eliot

2017-02-01

A linear stability analysis is performed for a pair of coaxial vertical chains made from permanently magnetized balls under the influence of gravity. While one chain rises from the ground, the other hangs from above, with the remaining ends separated by a gap of prescribed length. Various boundary conditions are considered, as are situations in which the magnetic dipole moments in the two chains are parallel or antiparallel. The case of a single chain attached to the ground is also discussed. The stability of the system is examined with respect to three quantities: the number of balls in each chain, the length of the gap between the chains, and a single dimensionless parameter which embodies the competition between magnetic and gravitational forces. Asymptotic scaling laws involving these parameters are provided. The Hessian matrix is computed in exact form, allowing the critical parameter values at which the system loses stability and the respective eigenmodes to be determined up to machine precision. A comparison with simple experiments for a single chain attached to the ground shows good agreement.

Microscopic theory of vortex interaction in two-band superconductors and type-1.5 superconductivity

NASA Astrophysics Data System (ADS)

Silaev, Mihail; Babaev, Egor

2011-03-01

In the framework of self-consistent microscopic theory we study the structure and interaction of vortices in two-gap superconductor taking into account the interband Josephson coupling. The asymptotical behavior of order parameter densities and magnetic field is studied analytically within the microscopic theory at low temperature. At higher temperatures, results consistent with Ginzburg-Landau theory are obtained. It is shown that under quite general conditions and in a wide temperature ranges (in particular outside the validity of the Ginzburg-Landau theory) there can exist an additional characteristic length scale of the order parameter density variation which exceeds the London penetration length of magnetic field due to the multi-component nature of superconducting state. Such behavior of order parameter density variation leads to the attractive long-range and repulsive short-range interaction between vortices. Supported by NSF CAREER Award DMR-0955902, Knut and Alice Wallenberg Foundation through the Royal Swedish Academy of Sciences and Swedish Research Council, ''Dynasty'' foundation and Russian Foundation for Basic Research.

Earthquake scaling laws for rupture geometry and slip heterogeneity

NASA Astrophysics Data System (ADS)

Thingbaijam, Kiran K. S.; Mai, P. Martin; Goda, Katsuichiro

2016-04-01

We analyze an extensive compilation of finite-fault rupture models to investigate earthquake scaling of source geometry and slip heterogeneity to derive new relationships for seismic and tsunami hazard assessment. Our dataset comprises 158 earthquakes with a total of 316 rupture models selected from the SRCMOD database (http://equake-rc.info/srcmod). We find that fault-length does not saturate with earthquake magnitude, while fault-width reveals inhibited growth due to the finite seismogenic thickness. For strike-slip earthquakes, fault-length grows more rapidly with increasing magnitude compared to events of other faulting types. Interestingly, our derived relationship falls between the L-model and W-model end-members. In contrast, both reverse and normal dip-slip events are more consistent with self-similar scaling of fault-length. However, fault-width scaling relationships for large strike-slip and normal dip-slip events, occurring on steeply dipping faults (δ~90° for strike-slip faults, and δ~60° for normal faults), deviate from self-similarity. Although reverse dip-slip events in general show self-similar scaling, the restricted growth of down-dip fault extent (with upper limit of ~200 km) can be seen for mega-thrust subduction events (M~9.0). Despite this fact, for a given earthquake magnitude, subduction reverse dip-slip events occupy relatively larger rupture area, compared to shallow crustal events. In addition, we characterize slip heterogeneity in terms of its probability distribution and spatial correlation structure to develop a complete stochastic random-field characterization of earthquake slip. We find that truncated exponential law best describes the probability distribution of slip, with observable scale parameters determined by the average and maximum slip. Applying Box-Cox transformation to slip distributions (to create quasi-normal distributed data) supports cube-root transformation, which also implies distinctive non-Gaussian slip distributions. To further characterize the spatial correlations of slip heterogeneity, we analyze the power spectral decay of slip applying the 2-D von Karman auto-correlation function (parameterized by the Hurst exponent, H, and correlation lengths along strike and down-slip). The Hurst exponent is scale invariant, H = 0.83 (± 0.12), while the correlation lengths scale with source dimensions (seismic moment), thus implying characteristic physical scales of earthquake ruptures. Our self-consistent scaling relationships allow constraining the generation of slip-heterogeneity scenarios for physics-based ground-motion and tsunami simulations.

Scale Effects in the Flow of a Shear-Thinning Fluid in Geological Fractures

NASA Astrophysics Data System (ADS)

Meheust, Y.; Roques, C.; Le Borgne, T.; Selker, J. S.

2017-12-01

Subsurface flow processes involving non-Newtonian fluids play a major role in many engineering applications, from in-situ remediation to enhanced oil recovery. The fluids of interest in such applications (f.e., polymers in remediation) often present shear-thinning properties, i.e., their viscosity decreases as a function of the local shear rate. We investigate how fracture wall roughness impacts the flow of a shear-thinning fluid. Numerical simulations of flow in 3D geological fractures are carried out by solving a modified Navier-Stokes equation incorporating the Carreau viscous-shear model. The numerical fractures consist of two isotropic self-affine surfaces which are correlated with each other above a characteristic scale (thecorrelation length of Méheust et al. PAGEOPH 2003). Perfect plastic closing is assumed when the surfaces are in contact. The statistical parameters describing a fracture are the standard deviation of the wall roughness, the mean aperture, the correlation length, and the fracture length, the Hurst exponent being fixed (equal to 0.8). The objective is to investigate how varying the correlation length impacts the flow behavior, for different degrees of closure, and how this behavior diverges from what is known for Newtonian fluids. The results from the 3D simulations are also compared to 2D simulations based on the lubrication theory, which we have developed as an extension of the Reynolds equation for Newtonian fluids. These 2D simulations run orders of magnitude faster, which allows considering a significant statistics of fractures of identical statistical parameters, and therefore draw general conclusions despite the large stochasticity of the media. We also discuss the implications of our results for solute transport by such flows. References:Méheust, Y., & Schmittbuhl, J. (2003). Scale effects related to flow in rough fractures. Pure and Applied Geophysics, 160(5-6), 1023-1050.

[Geographic variation of seed morphological traits of Picea schrenkiana var. tianschanica in Tianshan Mountains, Xinjiang of Northwest China].

PubMed

Liu, Gui-Feng; Zang, Run-Guo; Liu, Hua; Bai, Zhi-Qiang; Guo, Zhong-Jun; Ding, Yi

2012-06-01

Taking the Picea schrenkiana var. tianschanica forests at three sites with different longitudes (Zhaosu, Tianchi, and Qitai) in Tianshan Mountains as the objects, the cones were collected along an altitudinal gradient to analyze the variation of their seed morphological traits (seed scale length and width, seed scale length/width ratio, seed wing length and width, seed wing length/ width ratio, seed length and width, and seed length/width ratio). All the seed traits except seed width tended to decrease with increasing altitude. The seed traits except seed wing width, seed width, and seed length/width ratio all had significant negative correlations with altitude. Seed scale length and width and seed scale length/width ratio had significant positive correlations with longitude. Seed scale length, seed scale length/width ratio, and seed wing length/width ratio had significant negative correlations with slope degree. No significant correlations were observed between the seed traits except seed wing width and the slope aspect. Altitude was the main factor affecting the seed scale length, seed scale length/width ratio, and seed wing length/width ratio.

Universal relations for range corrections to Efimov features

DOE PAGES

Ji, Chen; Braaten, Eric; Phillips, Daniel R.; ...

2015-09-09

In a three-body system of identical bosons interacting through a large S-wave scattering length a, there are several sets of features related to the Efimov effect that are characterized by discrete scale invariance. Effective field theory was recently used to derive universal relations between these Efimov features that include the first-order correction due to a nonzero effective range r s. We reveal a simple pattern in these range corrections that had not been previously identified. The pattern is explained by the renormalization group for the effective field theory, which implies that the Efimov three-body parameter runs logarithmically with the momentummore » scale at a rate proportional to r s/a. The running Efimov parameter also explains the empirical observation that range corrections can be largely taken into account by shifting the Efimov parameter by an adjustable parameter divided by a. Furthermore, the accuracy of universal relations that include first-order range corrections is verified by comparing them with various theoretical calculations using models with nonzero range.« less

Development of laryngeal video stroboscope with laser marking module for dynamic glottis measurement.

PubMed

Kuo, Chung-Feng Jeffrey; Wang, Hsing-Won; Hsiao, Shang-Wun; Peng, Kai-Ching; Chou, Ying-Liang; Lai, Chun-Yu; Hsu, Chien-Tung Max

2014-01-01

Physicians clinically use laryngeal video stroboscope as an auxiliary instrument to test glottal diseases, and read vocal fold images and voice quality for diagnosis. As the position of vocal fold varies in each person, the proportion of the vocal fold size as presented in the vocal fold image is different, making it impossible to directly estimate relevant glottis physiological parameters, such as the length, area, perimeter, and opening angle of the glottis. Hence, this study designs an innovative laser projection marking module for the laryngeal video stroboscope to provide reference parameters for image scaling conversion. This innovative laser projection marking module to be installed on the laryngeal video stroboscope using laser beams to project onto the glottis plane, in order to provide reference parameters for scaling conversion of images of laryngeal video stroboscope. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effective Debye length in closed nanoscopic systems: a competition between two length scales.

PubMed

Tessier, Frédéric; Slater, Gary W

2006-02-01

The Poisson-Boltzmann equation (PBE) is widely employed in fields where the thermal motion of free ions is relevant, in particular in situations involving electrolytes in the vicinity of charged surfaces. The applications of this non-linear differential equation usually concern open systems (in osmotic equilibrium with an electrolyte reservoir, a semi-grand canonical ensemble), while solutions for closed systems (where the number of ions is fixed, a canonical ensemble) are either not appropriately distinguished from the former or are dismissed as a numerical calculation exercise. We consider herein the PBE for a confined, symmetric, univalent electrolyte and quantify how, in addition to the Debye length, its solution also depends on a second length scale, which embodies the contribution of ions by the surface (which may be significant in high surface-to-volume ratio micro- or nanofluidic capillaries). We thus establish that there are four distinct regimes for such systems, corresponding to the limits of the two parameters. We also show how the PBE in this case can be formulated in a familiar way by simply replacing the traditional Debye length by an effective Debye length, the value of which is obtained numerically from conservation conditions. But we also show that a simple expression for the value of the effective Debye length, obtained within a crude approximation, remains accurate even as the system size is reduced to nanoscopic dimensions, and well beyond the validity range typically associated with the solution of the PBE.

Ultrasound scatter in heterogeneous 3D microstructures: Parameters affecting multiple scattering

NASA Astrophysics Data System (ADS)

Engle, B. J.; Roberts, R. A.; Grandin, R. J.

2018-04-01

This paper reports on a computational study of ultrasound propagation in heterogeneous metal microstructures. Random spatial fluctuations in elastic properties over a range of length scales relative to ultrasound wavelength can give rise to scatter-induced attenuation, backscatter noise, and phase front aberration. It is of interest to quantify the dependence of these phenomena on the microstructure parameters, for the purpose of quantifying deleterious consequences on flaw detectability, and for the purpose of material characterization. Valuable tools for estimation of microstructure parameters (e.g. grain size) through analysis of ultrasound backscatter have been developed based on approximate weak-scattering models. While useful, it is understood that these tools display inherent inaccuracy when multiple scattering phenomena significantly contribute to the measurement. It is the goal of this work to supplement weak scattering model predictions with corrections derived through application of an exact computational scattering model to explicitly prescribed microstructures. The scattering problem is formulated as a volume integral equation (VIE) displaying a convolutional Green-function-derived kernel. The VIE is solved iteratively employing FFT-based con-volution. Realizations of random microstructures are specified on the micron scale using statistical property descriptions (e.g. grain size and orientation distributions), which are then spatially filtered to provide rigorously equivalent scattering media on a length scale relevant to ultrasound propagation. Scattering responses from ensembles of media representations are averaged to obtain mean and variance of quantities such as attenuation and backscatter noise levels, as a function of microstructure descriptors. The computational approach will be summarized, and examples of application will be presented.

Mesoscale mechanics of twisting carbon nanotube yarns.

PubMed

Mirzaeifar, Reza; Qin, Zhao; Buehler, Markus J

2015-03-12

Fabricating continuous macroscopic carbon nanotube (CNT) yarns with mechanical properties close to individual CNTs remains a major challenge. Spinning CNT fibers and ribbons for enhancing the weak interactions between the nanotubes is a simple and efficient method for fabricating high-strength and tough continuous yarns. Here we investigate the mesoscale mechanics of twisting CNT yarns using full atomistic and coarse grained molecular dynamics simulations, considering concurrent mechanisms at multiple length-scales. To investigate the mechanical response of such a complex structure without losing insights into the molecular mechanism, we applied a multiscale strategy. The full atomistic results are used for training a coarse grained model for studying larger systems consisting of several CNTs. The mesoscopic model parameters are updated as a function of the twist angle, based on the full atomistic results, in order to incorporate the atomistic scale deformation mechanisms in larger scale simulations. By bridging across two length scales, our model is capable of accurately predicting the mechanical behavior of twisted yarns while the atomistic level deformations in individual nanotubes are integrated into the model by updating the parameters. Our results focused on studying a bundle of close packed nanotubes provide novel mechanistic insights into the spinning of CNTs. Our simulations reveal how twisting a bundle of CNTs improves the shear interaction between the nanotubes up to a certain level due to increasing the interaction surface. Furthermore, twisting the bundle weakens the intertube interactions due to excessive deformation in the cross sections of individual CNTs in the bundle.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-02-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Simulation and scaling analysis of a spherical particle-laden blast wave

NASA Astrophysics Data System (ADS)

Ling, Y.; Balachandar, S.

2018-05-01

A spherical particle-laden blast wave, generated by a sudden release of a sphere of compressed gas-particle mixture, is investigated by numerical simulation. The present problem is a multiphase extension of the classic finite-source spherical blast-wave problem. The gas-particle flow can be fully determined by the initial radius of the spherical mixture and the properties of gas and particles. In many applications, the key dimensionless parameters, such as the initial pressure and density ratios between the compressed gas and the ambient air, can vary over a wide range. Parametric studies are thus performed to investigate the effects of these parameters on the characteristic time and spatial scales of the particle-laden blast wave, such as the maximum radius the contact discontinuity can reach and the time when the particle front crosses the contact discontinuity. A scaling analysis is conducted to establish a scaling relation between the characteristic scales and the controlling parameters. A length scale that incorporates the initial pressure ratio is proposed, which is able to approximately collapse the simulation results for the gas flow for a wide range of initial pressure ratios. This indicates that an approximate similarity solution for a spherical blast wave exists, which is independent of the initial pressure ratio. The approximate scaling is also valid for the particle front if the particles are small and closely follow the surrounding gas.

Performance of gigabit FDDI

NASA Technical Reports Server (NTRS)

Game, David; Maly, Kurt J.

1990-01-01

Great interest exists in developing high speed protocols which will be able to support data rates at gigabit speeds. Hardware currently exists which can experimentally transmit at data rates exceeding a gigabit per second, but it is not clear as to what types of protocols will provide the best performance. One possibility is to examine current protocols and their extensibility to these speeds. Scaling of Fiber Distributed Data Interface (FDDI) to gigabit speeds is studied. More specifically, delay statistics are included to provide insight as to which parameters (network length, packet length or number of nodes) have the greatest effect on performance.

Experimental evaluation of exhaust mixers for an Energy Efficient Engine

NASA Technical Reports Server (NTRS)

Kozlowski, H.; Kraft, G.

1980-01-01

Static scale model tests were conducted to evaluate exhaust system mixers for a high bypass ratio engine as part of the NASA sponsored Energy Efficient program. Gross thrust coefficients were measured for a series of mixer configurations which included variations in the number of mixer lobes, tailpipe length, mixer penetration, and length. All of these parameters have a significant impact on exhaust system performance. In addition, flow visualization pictures and pressure/temperature traverses were obtained for selected configurations. Parametric performance trends are discussed and the results considered relative to the Energy Efficient Engine program goals.

The pyramid system for multiscale raster analysis

USGS Publications Warehouse

De Cola, L.; Montagne, N.

1993-01-01

Geographical research requires the management and analysis of spatial data at multiple scales. As part of the U.S. Geological Survey's global change research program a software system has been developed that reads raster data (such as an image or digital elevation model) and produces a pyramid of aggregated lattices as well as various measurements of spatial complexity. For a given raster dataset the system uses the pyramid to report: (1) mean, (2) variance, (3) a spatial autocorrelation parameter based on multiscale analysis of variance, and (4) a monofractal scaling parameter based on the analysis of isoline lengths. The system is applied to 1-km digital elevation model (DEM) data for a 256-km2 region of central California, as well as to 64 partitions of the region. PYRAMID, which offers robust descriptions of data complexity, also is used to describe the behavior of topographic aspect with scale. ?? 1993.

Thin film growth studies using time-resolved x-ray scattering

NASA Astrophysics Data System (ADS)

Kowarik, Stefan

2017-02-01

Thin-film growth is important for novel functional materials and new generations of devices. The non-equilibrium growth physics involved is very challenging, because the energy landscape for atomic scale processes is determined by many parameters, such as the diffusion and Ehrlich-Schwoebel barriers. We review the in situ real-time techniques of x-ray diffraction (XRD), x-ray growth oscillations and diffuse x-ray scattering (GISAXS) for the determination of structure and morphology on length scales from Å to µm. We give examples of time resolved growth experiments mainly from molecular thin film growth, but also highlight growth of inorganic materials using molecular beam epitaxy (MBE) and electrochemical deposition from liquids. We discuss how scaling parameters of rate equation models and fundamental energy barriers in kinetic Monte Carlo methods can be determined from fits of the real-time x-ray data.

Thin film growth studies using time-resolved x-ray scattering.

PubMed

Kowarik, Stefan

2017-02-01

Thin-film growth is important for novel functional materials and new generations of devices. The non-equilibrium growth physics involved is very challenging, because the energy landscape for atomic scale processes is determined by many parameters, such as the diffusion and Ehrlich-Schwoebel barriers. We review the in situ real-time techniques of x-ray diffraction (XRD), x-ray growth oscillations and diffuse x-ray scattering (GISAXS) for the determination of structure and morphology on length scales from Å to µm. We give examples of time resolved growth experiments mainly from molecular thin film growth, but also highlight growth of inorganic materials using molecular beam epitaxy (MBE) and electrochemical deposition from liquids. We discuss how scaling parameters of rate equation models and fundamental energy barriers in kinetic Monte Carlo methods can be determined from fits of the real-time x-ray data.

Assessment of effects of neutrals on the power threshold for L to H transitions in DIII-D

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

Owen, L.W.; Carreras, B.A.; Maingi, R.

1997-09-01

To assess the effect of edge neutrals on the low to high confinement transition threshold, a broad range of plasma discharges has been analyzed. From this analysis, the transition power divided by the density, at constant magnetic field, appears to be a function of a single parameter measuring the neutrals` effect, This parameter cannot be uniquely identified. For instance, it may be the radial decay length of the neutral profile or the charge exchange damping rate at about r/a {approx} 0.95. This results suggest that there is a missing parameter linked to the neutrals in the power threshold scaling laws.

Tornado outbreak variability follows Taylor's power law of fluctuation scaling and increases dramatically with severity.

PubMed

Tippett, Michael K; Cohen, Joel E

2016-02-29

Tornadoes cause loss of life and damage to property each year in the United States and around the world. The largest impacts come from 'outbreaks' consisting of multiple tornadoes closely spaced in time. Here we find an upward trend in the annual mean number of tornadoes per US tornado outbreak for the period 1954-2014. Moreover, the variance of this quantity is increasing more than four times as fast as the mean. The mean and variance of the number of tornadoes per outbreak vary according to Taylor's power law of fluctuation scaling (TL), with parameters that are consistent with multiplicative growth. Tornado-related atmospheric proxies show similar power-law scaling and multiplicative growth. Path-length-integrated tornado outbreak intensity also follows TL, but with parameters consistent with sampling variability. The observed TL power-law scaling of outbreak severity means that extreme outbreaks are more frequent than would be expected if mean and variance were independent or linearly related.

Tornado outbreak variability follows Taylor's power law of fluctuation scaling and increases dramatically with severity

PubMed Central

Tippett, Michael K.; Cohen, Joel E.

2016-01-01

Tornadoes cause loss of life and damage to property each year in the United States and around the world. The largest impacts come from ‘outbreaks' consisting of multiple tornadoes closely spaced in time. Here we find an upward trend in the annual mean number of tornadoes per US tornado outbreak for the period 1954–2014. Moreover, the variance of this quantity is increasing more than four times as fast as the mean. The mean and variance of the number of tornadoes per outbreak vary according to Taylor's power law of fluctuation scaling (TL), with parameters that are consistent with multiplicative growth. Tornado-related atmospheric proxies show similar power-law scaling and multiplicative growth. Path-length-integrated tornado outbreak intensity also follows TL, but with parameters consistent with sampling variability. The observed TL power-law scaling of outbreak severity means that extreme outbreaks are more frequent than would be expected if mean and variance were independent or linearly related. PMID:26923210

Tornado outbreak variability follows Taylor's power law of fluctuation scaling and increases dramatically with severity

NASA Astrophysics Data System (ADS)

Tippett, Michael K.; Cohen, Joel E.

2016-02-01

Tornadoes cause loss of life and damage to property each year in the United States and around the world. The largest impacts come from `outbreaks' consisting of multiple tornadoes closely spaced in time. Here we find an upward trend in the annual mean number of tornadoes per US tornado outbreak for the period 1954-2014. Moreover, the variance of this quantity is increasing more than four times as fast as the mean. The mean and variance of the number of tornadoes per outbreak vary according to Taylor's power law of fluctuation scaling (TL), with parameters that are consistent with multiplicative growth. Tornado-related atmospheric proxies show similar power-law scaling and multiplicative growth. Path-length-integrated tornado outbreak intensity also follows TL, but with parameters consistent with sampling variability. The observed TL power-law scaling of outbreak severity means that extreme outbreaks are more frequent than would be expected if mean and variance were independent or linearly related.

Information Filtering via a Scaling-Based Function

PubMed Central

Qiu, Tian; Zhang, Zi-Ke; Chen, Guang

2013-01-01

Finding a universal description of the algorithm optimization is one of the key challenges in personalized recommendation. In this article, for the first time, we introduce a scaling-based algorithm (SCL) independent of recommendation list length based on a hybrid algorithm of heat conduction and mass diffusion, by finding out the scaling function for the tunable parameter and object average degree. The optimal value of the tunable parameter can be abstracted from the scaling function, which is heterogeneous for the individual object. Experimental results obtained from three real datasets, Netflix, MovieLens and RYM, show that the SCL is highly accurate in recommendation. More importantly, compared with a number of excellent algorithms, including the mass diffusion method, the original hybrid method, and even an improved version of the hybrid method, the SCL algorithm remarkably promotes the personalized recommendation in three other aspects: solving the accuracy-diversity dilemma, presenting a high novelty, and solving the key challenge of cold start problem. PMID:23696829

Wavelet phase extracting demodulation algorithm based on scale factor for optical fiber Fabry-Perot sensing.

PubMed

Zhang, Baolin; Tong, Xinglin; Hu, Pan; Guo, Qian; Zheng, Zhiyuan; Zhou, Chaoran

2016-12-26

Optical fiber Fabry-Perot (F-P) sensors have been used in various on-line monitoring of physical parameters such as acoustics, temperature and pressure. In this paper, a wavelet phase extracting demodulation algorithm for optical fiber F-P sensing is first proposed. In application of this demodulation algorithm, search range of scale factor is determined by estimated cavity length which is obtained by fast Fourier transform (FFT) algorithm. Phase information of each point on the optical interference spectrum can be directly extracted through the continuous complex wavelet transform without de-noising. And the cavity length of the optical fiber F-P sensor is calculated by the slope of fitting curve of the phase. Theorical analysis and experiment results show that this algorithm can greatly reduce the amount of computation and improve demodulation speed and accuracy.

Time and length scales within a fire and implications for numerical simulation

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

TIESZEN,SHELDON R.

2000-02-02

A partial non-dimensionalization of the Navier-Stokes equations is used to obtain order of magnitude estimates of the rate-controlling transport processes in the reacting portion of a fire plume as a function of length scale. Over continuum length scales, buoyant times scales vary as the square root of the length scale; advection time scales vary as the length scale, and diffusion time scales vary as the square of the length scale. Due to the variation with length scale, each process is dominant over a given range. The relationship of buoyancy and baroclinc vorticity generation is highlighted. For numerical simulation, first principlesmore » solution for fire problems is not possible with foreseeable computational hardware in the near future. Filtered transport equations with subgrid modeling will be required as two to three decades of length scale are captured by solution of discretized conservation equations. By whatever filtering process one employs, one must have humble expectations for the accuracy obtainable by numerical simulation for practical fire problems that contain important multi-physics/multi-length-scale coupling with up to 10 orders of magnitude in length scale.« less

Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

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

Boella, E.; Fiúza, F.; Novo, A. Stockem

Here, a numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasi-monoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread (Fiúza et al 2012 Phys. Rev. Lett. 109 215001). In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ionsmore » by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Lastly, results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.« less

Some factors influencing radiation of sound from flow interaction with edges of finite surfaces

NASA Technical Reports Server (NTRS)

Hayden, R. E.; Fox, H. L.; Chanaud, R. C.

1976-01-01

Edges of surfaces which are exposed to unsteady flow cause both strictly acoustic effects and hydrodynamic effects, in the form of generation of new hydrodynamic sources in the immediate vicinity of the edge. An analytical model is presented which develops the explicit sound-generation role of the velocity and Mach number of the eddy convection past the edge, and the importance of relative scale lengths of the turbulence, as well as the relative intensity of pressure fluctuations. The Mach number (velocity) effects show that the important paramater is the convection Mach number of the eddies. The effects of turbulence scale lengths, isotropy, and spatial density (separation) are shown to be important in determining the level and spectrum of edge sound radiated for the edge dipole mechanism. Experimental data is presented which provides support for the dipole edge noise model in terms of Mach number (velocity) scaling, parametric dependence on flow field parameter, directivity, and edge diffraction effects.

Ion acceleration in electrostatic collisionless shock: on the optimal density profile for quasi-monoenergetic beams

DOE PAGES

Boella, E.; Fiúza, F.; Novo, A. Stockem; ...

2018-02-01

Here, a numerical study on ion acceleration in electrostatic shock waves is presented, with the aim of determining the best plasma configuration to achieve quasi-monoenergetic ion beams in laser-driven systems. It was recently shown that tailored near-critical density plasmas characterized by a long-scale decreasing rear density profile lead to beams with low energy spread (Fiúza et al 2012 Phys. Rev. Lett. 109 215001). In this work, a detailed parameter scan investigating different plasma scale lengths is carried out. As result, the optimal plasma spatial scale length that allows for minimizing the energy spread while ensuring a significant reflection of ionsmore » by the shock is identified. Furthermore, a new configuration where the required profile has been obtained by coupling micro layers of different densities is proposed. Lastly, results show that this new engineered approach is a valid alternative, guaranteeing a low energy spread with a higher level of controllability.« less

Multi-scale modeling of microstructure dependent intergranular brittle fracture using a quantitative phase-field based method

DOE PAGES

Chakraborty, Pritam; Zhang, Yongfeng; Tonks, Michael R.

2015-12-07

In this study, the fracture behavior of brittle materials is strongly influenced by their underlying microstructure that needs explicit consideration for accurate prediction of fracture properties and the associated scatter. In this work, a hierarchical multi-scale approach is pursued to model microstructure sensitive brittle fracture. A quantitative phase-field based fracture model is utilized to capture the complex crack growth behavior in the microstructure and the related parameters are calibrated from lower length scale atomistic simulations instead of engineering scale experimental data. The workability of this approach is demonstrated by performing porosity dependent intergranular fracture simulations in UO 2 and comparingmore » the predictions with experiments.« less

Multi-scale modeling of microstructure dependent intergranular brittle fracture using a quantitative phase-field based method

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

Chakraborty, Pritam; Zhang, Yongfeng; Tonks, Michael R.

In this study, the fracture behavior of brittle materials is strongly influenced by their underlying microstructure that needs explicit consideration for accurate prediction of fracture properties and the associated scatter. In this work, a hierarchical multi-scale approach is pursued to model microstructure sensitive brittle fracture. A quantitative phase-field based fracture model is utilized to capture the complex crack growth behavior in the microstructure and the related parameters are calibrated from lower length scale atomistic simulations instead of engineering scale experimental data. The workability of this approach is demonstrated by performing porosity dependent intergranular fracture simulations in UO 2 and comparingmore » the predictions with experiments.« less

Nearly constant ratio between the proton inertial scale and the spectrum break length scale in the plasma beta range from 0.2 to 1.4 in the solar wind turbulence

NASA Astrophysics Data System (ADS)

Wang, X.; Tu, C. Y.; He, J.; Wang, L.

2017-12-01

The spectrum break at the ion scale of the solar wind magnetic fluctuations are considered to give important clue on the turbulence dissipation mechanism. Among several possible mechanisms, the most notable ones are the two mechanisms that related respectively with proton thermal gyro-radius and proton inertial length. However, no definite conclusion has been given for which one is more reasonable because the two parameters have similar values in the normal plasma beta range. Here we do a statistical study for the first time to see if the two mechanism predictions have different dependence on the solar wind velocity and on the plasma beta in the normal plasma beta range in the solar wind at 1 AU. From magnetic measurements by Wind, Ulysses and Messenger, we select 60 data sets with duration longer than 8 hours. We found that the ratio between the proton inertial scale and the spectrum break scale do not change considerably with both varying the solar wind speed from 300km/s to 800km/s and varying the plasma beta from 0.2 to 1.4. The average value of the ratio times 2pi is 0.46 ± 0.08. However, the ratio between the proton gyro-radius and the break scale changes clearly. This new result shows that the proton inertial scale could be a single factor that determines the break length scale and hence gives a strong evidence to support the dissipation mechanism related to it in the normal plasma beta range. The value of the constant ratio may relate with the dissipation mechanism, but it needs further theoretical study to give detailed explanation.

Arms race between weevil rostrum length and camellia pericarp thickness: Geographical cline and theory.

PubMed

Iseki, Naoyuki; Sasaki, Akira; Toju, Hirokazu

2011-09-21

The geographical cline of the coevolving traits of weevil rostrum (mouthpart) length and camellia pericarp (fruit coat) thickness provides an opportunity to test the arms race theory of defense (pericarp thickness) and countermeasure (rostrum length) between antagonistically interacting species. By extending the previous model for the coevolution of quantitative traits to introduce nonlinear costs for exaggerated traits, the generation overlap, and density-dependent regulation in the host, we studied the evolutionarily stable (ES) pericarp thickness in the Japanese camellia (Camellia japonica) and the ES rostrum length in the camellia-weevil (Curculio camelliae). The joint monomorphic ES system has a robust outcome with nonlinear costs, and we analyzed how the traits of both species at evolutionary equilibrium depend on demographic parameters. If camellia demographic parameters vary latitudinally, data collected over the geographical scale of rostrum length and pericarp thickness should lie on an approximately linear curve with the slope less than that of the equiprobability line A/B of boring success, where A and B are coefficients for the logistic regression of boring success to pericarp thickness and rostrum length, respectively. This is a robust prediction as long as the cost of rostrum length is nonlinear (accelerating). As a result, boring success should be lower in populations with longer rostrum length, as reported in the weevil-camellia system (Toju, H., and Sota, T., 2006a. Imbalance of predator and prey armament: Geographic clines in phenotypic interface and natural selection. American Naturalist 167, 105-117). The nonlinearity (exponent) for the cost of rostrum length estimated from the geographical cline data for the weevil-camellia system was 2.2, suggesting nonlinearity between quadratic and cubic forms. Copyright © 2011 Elsevier Ltd. All rights reserved.

Validation of Born Traveltime Kernels

NASA Astrophysics Data System (ADS)

Baig, A. M.; Dahlen, F. A.; Hung, S.

2001-12-01

Most inversions for Earth structure using seismic traveltimes rely on linear ray theory to translate observed traveltime anomalies into seismic velocity anomalies distributed throughout the mantle. However, ray theory is not an appropriate tool to use when velocity anomalies have scale lengths less than the width of the Fresnel zone. In the presence of these structures, we need to turn to a scattering theory in order to adequately describe all of the features observed in the waveform. By coupling the Born approximation to ray theory, the first order dependence of heterogeneity on the cross-correlated traveltimes (described by the Fréchet derivative or, more colourfully, the banana-doughnut kernel) may be determined. To determine for what range of parameters these banana-doughnut kernels outperform linear ray theory, we generate several random media specified by their statistical properties, namely the RMS slowness perturbation and the scale length of the heterogeneity. Acoustic waves are numerically generated from a point source using a 3-D pseudo-spectral wave propagation code. These waves are then recorded at a variety of propagation distances from the source introducing a third parameter to the problem: the number of wavelengths traversed by the wave. When all of the heterogeneity has scale lengths larger than the width of the Fresnel zone, ray theory does as good a job at predicting the cross-correlated traveltime as the banana-doughnut kernels do. Below this limit, wavefront healing becomes a significant effect and ray theory ceases to be effective even though the kernels remain relatively accurate provided the heterogeneity is weak. The study of wave propagation in random media is of a more general interest and we will also show our measurements of the velocity shift and the variance of traveltime compare to various theoretical predictions in a given regime.

Low to high confinement transition theory of finite-beta drift-wave driven shear flow and its comparison with data from DIII-D

NASA Astrophysics Data System (ADS)

Guzdar, P. N.; Kleva, R. G.; Groebner, R. J.; Gohil, P.

2004-03-01

Shear flow stabilization of edge turbulence in tokamaks has been the accepted paradigm for the improvement in confinement observed in high (H) confinement mode plasmas. Results on the generation of zonal flow and fields in finite β plasmas are presented. This theory yields a criterion for bifurcation from low to high (L-H) confinement mode, proportional to Te/√Ln , where Te is the electron temperature and Ln is the density scale-length at the steepest part of the density gradient. When this parameter exceeds a critical value (mostly determined by the strength of the toroidal magnetic field), the transition occurs. The predicted threshold based on this parameter shows good agreement with edge measurements on discharges undergoing L-H transitions in DIII-D [J. L. Luxon, R. Anderson, F. Batty et al., in Proceedings of the 11th Conference on Plasma Physics and Controlled Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter due to the differences in the density gradient scale-lengths in the edge. The theory also provides a possible explanation for lowered threshold power, pellet injection H modes in DIII-D, thereby providing a unified picture of the varied observations on the L-H transition.

Damage evolution analysis of coal samples under cyclic loading based on single-link cluster method

NASA Astrophysics Data System (ADS)

Zhang, Zhibo; Wang, Enyuan; Li, Nan; Li, Xuelong; Wang, Xiaoran; Li, Zhonghui

2018-05-01

In this paper, the acoustic emission (AE) response of coal samples under cyclic loading is measured. The results show that there is good positive relation between AE parameters and stress. The AE signal of coal samples under cyclic loading exhibits an obvious Kaiser Effect. The single-link cluster (SLC) method is applied to analyze the spatial evolution characteristics of AE events and the damage evolution process of coal samples. It is found that a subset scale of the SLC structure becomes smaller and smaller when the number of cyclic loading increases, and there is a negative linear relationship between the subset scale and the degree of damage. The spatial correlation length ξ of an SLC structure is calculated. The results show that ξ fluctuates around a certain value from the second cyclic loading process to the fifth cyclic loading process, but spatial correlation length ξ clearly increases in the sixth loading process. Based on the criterion of microcrack density, the coal sample failure process is the transformation from small-scale damage to large-scale damage, which is the reason for changes in the spatial correlation length. Through a systematic analysis, the SLC method is an effective method to research the damage evolution process of coal samples under cyclic loading, and will provide important reference values for studying coal bursts.

Planar Two-Plasmon-Decay Experiments at Polar-Direct-Drive Ignition-Relevant Scale Lengths at the National Ignition Facility

NASA Astrophysics Data System (ADS)

Rosenberg, M. J.; Solodov, A. A.; Seka, W.; Myatt, J. F.; Regan, S. P.; Hohenberger, M.; Epstein, R.; Collins, T. J. B.; Turnbull, D. P.; Ralph, J. E.; Barrios, M. A.; Moody, J. D.

2015-11-01

Results from the first experiments at the National Ignition Facility (NIF) to probe two-plasmon -decay (TPD) hot-electron production at scale lengths relevant to polar-direct-drive (PDD) ignition are reported. The irradiation on one side of a planar CH foil generated a plasma at the quarter-critical surface with a predicted density gradient scale length of Ln ~ 600 μm , a measured electron temperature of Te ~ 3 . 5 to 4.0 keV, an overlapped laser intensity of I ~ 6 ×1014 W/cm2, and a predicted TPD threshold parameter of η ~ 4 . The hard x-ray spectrum and the Kα emission from a buried Mo layer were measured to infer the hot-electron temperature and the fraction of total laser energy converted to TPD hot electrons. Optical emission at ω/2 correlated with the time-dependent hard x-ray signal confirms that TPD is responsible for the hot-electron generation. The effect of laser beam angle of incidence on TPD hot-electron generation was assessed, and the data show that the beam angle of incidence did not have a strong effect. These results will be used to benchmark simulations of TPD hot-electron production at conditions relevant to PDD ignition-scale implosions. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Stochastic analysis of particle movement over a dune bed

USGS Publications Warehouse

Lee, Baum K.; Jobson, Harvey E.

1977-01-01

Stochastic models are available that can be used to predict the transport and dispersion of bed-material sediment particles in an alluvial channel. These models are based on the proposition that the movement of a single bed-material sediment particle consists of a series of steps of random length separated by rest periods of random duration and, therefore, application of the models requires a knowledge of the probability distributions of the step lengths, the rest periods, the elevation of particle deposition, and the elevation of particle erosion. The procedure was tested by determining distributions from bed profiles formed in a large laboratory flume with a coarse sand as the bed material. The elevation of particle deposition and the elevation of particle erosion can be considered to be identically distributed, and their distribution can be described by either a ' truncated Gaussian ' or a ' triangular ' density function. The conditional probability distribution of the rest period given the elevation of particle deposition closely followed the two-parameter gamma distribution. The conditional probability distribution of the step length given the elevation of particle erosion and the elevation of particle deposition also closely followed the two-parameter gamma density function. For a given flow, the scale and shape parameters describing the gamma probability distributions can be expressed as functions of bed-elevation. (Woodard-USGS)

Influence of Sub-Daily Variation on Multi-Fractal Detrended Fluctuation Analysis of Wind Speed Time Series

PubMed Central

Li, Weinan; Kong, Yanjun; Cong, Xiangyu

2016-01-01

Using multi-fractal detrended fluctuation analysis (MF-DFA), the scaling features of wind speed time series (WSTS) could be explored. In this paper, we discuss the influence of sub-daily variation, which is a natural feature of wind, in MF-DFA of WSTS. First, the choice of the lower bound of the segment length, a significant parameter of MF-DFA, was studied. The results of expanding the lower bound into sub-daily scope shows that an abrupt declination and discrepancy of scaling exponents is caused by the inability to keep the whole diel process of wind in one single segment. Additionally, the specific value, which is effected by the sub-daily feature of local meteo-climatic, might be different. Second, the intra-day temporal order of wind was shuffled to determine the impact of diel variation on scaling exponents of MF-DFA. The results illustrate that disregarding diel variation leads to errors in scaling. We propose that during the MF-DFA of WSTS, the segment length should be longer than 1 day and the diel variation of wind should be maintained to avoid abnormal phenomena and discrepancy in scaling exponents. PMID:26741491

Experimental test of scaling of mixing by chaotic advection in droplets moving through microfluidic channels

PubMed Central

Song, Helen; Bringer, Michelle R.; Tice, Joshua D.; Gerdts, Cory J.; Ismagilov, Rustem F.

2006-01-01

This letter describes an experimental test of a simple argument that predicts the scaling of chaotic mixing in a droplet moving through a winding microfluidic channel. Previously, scaling arguments for chaotic mixing have been described for a flow that reduces striation length by stretching, folding, and reorienting the fluid in a manner similar to that of the baker’s transformation. The experimentally observed flow patterns within droplets (or plugs) resembled the baker’s transformation. Therefore, the ideas described in the literature could be applied to mixing in droplets to obtain the scaling argument for the dependence of the mixing time, t~(aw/U)log(Pe), where w [m] is the cross-sectional dimension of the microchannel, a is the dimensionless length of the plug measured relative to w, U [m s−1] is the flow velocity, Pe is the Péclet number (Pe=wU/D), and D [m2s−1] is the diffusion coefficient of the reagent being mixed. Experiments were performed to confirm the scaling argument by varying the parameters w, U, and D. Under favorable conditions, submillisecond mixing has been demonstrated in this system. PMID:17940580

Swelling of biological and semiflexible polyelectrolytes.

PubMed

Dobrynin, Andrey V; Carrillo, Jan-Michael Y

2009-10-21

We have developed a theoretical model of swelling of semiflexible (biological) polyelectrolytes in salt solutions. Our approach is based on separation of length scales which allowed us to split a chain's electrostatic energy into two parts that describe local and remote electrostatic interactions along the polymer backbone. The local part takes into account interactions between charged monomers that are separated by distances along the polymer backbone shorter than the chain's persistence length. These electrostatic interactions renormalize chain persistence length. The second part includes electrostatic interactions between remote charged pairs along the polymer backbone located at distances larger than the chain persistence length. These interactions are responsible for chain swelling. In the framework of this approach we calculated effective chain persistence length and chain size as a function of the Debye screening length, chain degree of ionization, bare persistence length and chain degree of polymerization. Our crossover expression for the effective chain's persistence length is in good quantitative agreement with the experimental data on DNA. We have been able to fit experimental datasets by using two adjustable parameters: DNA ionization degree (α = 0.15-0.17) and a bare persistence length (l(p) = 40-44 nm).

Non-local damage rheology and size effect

NASA Astrophysics Data System (ADS)

Lyakhovsky, V.

2011-12-01

We study scaling relations controlling the onset of transiently-accelerating fracturing and transition to dynamic rupture propagation in a non-local damage rheology model. The size effect is caused principally by growth of a fracture process zone, involving stress redistribution and energy release associated with a large fracture. This implies that rupture nucleation and transition to dynamic propagation are inherently scale-dependent processes. Linear elastic fracture mechanics (LEFM) and local damage mechanics are formulated in terms of dimensionless strain components and thus do not allow introducing any space scaling, except linear relations between fracture length and displacements. Generalization of Weibull theory provides scaling relations between stress and crack length at the onset of failure. A powerful extension of the LEFM formulation is the displacement-weakening model which postulates that yielding is complete when the crack wall displacement exceeds some critical value or slip-weakening distance Dc at which a transition to kinetic friction is complete. Scaling relations controlling the transition to dynamic rupture propagation in slip-weakening formulation are widely accepted in earthquake physics. Strong micro-crack interaction in a process zone may be accounted for by adopting either integral or gradient type non-local damage models. We formulate a gradient-type model with free energy depending on the scalar damage parameter and its spatial derivative. The damage-gradient term leads to structural stresses in the constitutive stress-strain relations and a damage diffusion term in the kinetic equation for damage evolution. The damage diffusion eliminates the singular localization predicted by local models. The finite width of the localization zone provides a fundamental length scale that allows numerical simulations with the model to achieve the continuum limit. A diffusive term in the damage evolution gives rise to additional damage diffusive time scale associated with the structural length scale. The ratio between two time scales associated with damage accumulation and diffusion, the damage diffusivity ratio, reflects the role of the diffusion-controlled delocalization. We demonstrate that localized fracturing occurs at the damage diffusivity ratio below certain critical value leading to a linear scaling between stress and crack length compatible with size effect for failures at crack initiation. A subseuqent quasi-static fracture growth is self-similar with increasing size of the process zone proportional to the fracture length. At a certain stage, controlled by dynamic weakening, the self-similarity breaks down and crack velocity significantly deviates from that predicted by the quasi-static regime, the size of the process zone decreases, and the rate of crack growth ceases to be controlled by the rate of damage increase. Furthermore, the crack speed approaches that predicted by the elasto-dynamic equation. The non-local damage rheology model predicts that the nucleation size of the dynamic fracture scales with fault zone thickness distance of the stress interraction.

Arbitrary amplitude nucleus-acoustic solitons in multi-ion quantum plasmas with relativistically degenerate electrons

NASA Astrophysics Data System (ADS)

Sultana, S.; Schlickeiser, R.

2018-02-01

A three component degenerate relativistic quantum plasma (consisting of relativistically degenerate electrons, nondegenerate inertial light nuclei, and stationary heavy nuclei) is considered to model the linear wave and also the electrostatic solitary waves in the light nuclei-scale length. A well-known normal mode analysis is employed to investigate the linear wave properties. A mechanical-motion analog (Sagdeev-type) pseudo-potential approach, which reveals the existence of large amplitude solitary excitations, is adopted to study the nonlinear wave properties. Only the positive potential solitary excitations are found to exist in the plasma medium under consideration. The basic properties of the arbitrary amplitude electrostatic acoustic modes in the light nuclei-scale length and their existence domain in terms of soliton speed (Mach number) are examined. The modifications of solitary wave characteristics and their existence domain with the variation of different key plasma configuration parameters (e.g., electrons degeneracy parameter, inertial light nuclei number density, and degenerate electron number density) are also analyzed. Our results, which may be helpful to explain the basic features of the nonlinear wave propagation in multi-component degenerate quantum plasmas, in connection with astrophysical compact objects (e.g., white dwarfs) are briefly discussed.

Multi-scale modeling of diffusion-controlled reactions in polymers: renormalisation of reactivity parameters.

PubMed

Everaers, Ralf; Rosa, Angelo

2012-01-07

The quantitative description of polymeric systems requires hierarchical modeling schemes, which bridge the gap between the atomic scale, relevant to chemical or biomolecular reactions, and the macromolecular scale, where the longest relaxation modes occur. Here, we use the formalism for diffusion-controlled reactions in polymers developed by Wilemski, Fixman, and Doi to discuss the renormalisation of the reactivity parameters in polymer models with varying spatial resolution. In particular, we show that the adjustments are independent of chain length. As a consequence, it is possible to match reactions times between descriptions with different resolution for relatively short reference chains and to use the coarse-grained model to make quantitative predictions for longer chains. We illustrate our results by a detailed discussion of the classical problem of chain cyclization in the Rouse model, which offers the simplest example of a multi-scale descriptions, if we consider differently discretized Rouse models for the same physical system. Moreover, we are able to explore different combinations of compact and non-compact diffusion in the local and large-scale dynamics by varying the embedding dimension.

Bayesian Modal Estimation of the Four-Parameter Item Response Model in Real, Realistic, and Idealized Data Sets.

PubMed

Waller, Niels G; Feuerstahler, Leah

2017-01-01

In this study, we explored item and person parameter recovery of the four-parameter model (4PM) in over 24,000 real, realistic, and idealized data sets. In the first analyses, we fit the 4PM and three alternative models to data from three Minnesota Multiphasic Personality Inventory-Adolescent form factor scales using Bayesian modal estimation (BME). Our results indicated that the 4PM fits these scales better than simpler item Response Theory (IRT) models. Next, using the parameter estimates from these real data analyses, we estimated 4PM item parameters in 6,000 realistic data sets to establish minimum sample size requirements for accurate item and person parameter recovery. Using a factorial design that crossed discrete levels of item parameters, sample size, and test length, we also fit the 4PM to an additional 18,000 idealized data sets to extend our parameter recovery findings. Our combined results demonstrated that 4PM item parameters and parameter functions (e.g., item response functions) can be accurately estimated using BME in moderate to large samples (N ⩾ 5, 000) and person parameters can be accurately estimated in smaller samples (N ⩾ 1, 000). In the supplemental files, we report annotated [Formula: see text] code that shows how to estimate 4PM item and person parameters in [Formula: see text] (Chalmers, 2012 ).

Tunable resonances due to vacancies in graphene nanoribbons

NASA Astrophysics Data System (ADS)

Bahamon, D. A.; Pereira, A. L. C.; Schulz, P. A.

2010-10-01

The coherent electron transport along zigzag and metallic armchair graphene nanoribbons in the presence of one or two vacancies is investigated. Having in mind atomic scale tunability of the conductance fingerprints, the primary focus is on the effect of the distance to the edges and intervacancies spacing. An involved interplay of vacancies sublattice location and nanoribbon edge termination, together with the spacing parameters lead to a wide conductance resonance line-shape modification. Turning on a magnetic field introduces a new length scale that unveils counterintuitive aspects of the interplay between purely geometric aspects of the system and the underlying atomic scale nature of graphene.

Surface Morphology of Liquid and Solid Thin Films via X-Ray Reflectivity.

NASA Astrophysics Data System (ADS)

Shindler, Joseph Daniel

X-ray reflectivity can be used to measure the spatial variations in the electron density on length scales from Angstroms to microns. It is sensitive to atomic scale roughness, interdiffusion in buried layers, the thickness of multilayer stacks, and in-plane correlations in each of these cases. We have pioneered the use of a high intensity, moderate resolution configuration for x-ray reflectivity which utilizes a bent crystal graphite monochromator. With this technique we can obtain a beam intensity one hundred times greater than is possible using the high resolution rotating anode configuration, while we have shown that the resulting instrumental resolution is appropriate for the vast majority of thin film work. For all of the systems studied, we were able to measure the weak diffuse scattering signal to probe the in-plane length scales of interfacial roughness, a measurement which had previously only been attempted at synchrotron sources. Studied systems include thin films and surfaces with a wide range of structural order and surface morphologies. Interest in liquid films has been of a fundamental nature. Theories on the expected film evolution with changing thickness and temperature are currently being tested with scattering experiments. We have pursued the issues of film/substrate wetting and conformality, focussing on the temperature dependence of these phenomena near the triple point. Despite the heterogeneity of the substrate potential, we see a very sharp wetting transition at or near the triple point, although below the triple point the film is still smooth, consistent with a uniform layer. We also see a loss of conformality as the fluid films thicken; this is consistent with theory and with other recent experiments. The properties of a multilayer solid film depend not only on the magnitude of the roughness of each interface, but also on the conformality between interfaces and the length scales of the roughness--i.e., whether the roughness is on the atomic lengths of interdiffusion, crystalline order lengths of faceting, or even longer lengths due to other processes. In a joint project with Alcoa, we combined the methods of x-ray Bragg diffraction and small angle reflectivity to probe aluminum thin films as precursors to true multilayer films, correlating grain size and orientation with the magnitude and length-scales of surface roughness. We also correlated all film properties with such parameters as the deposition method, substrate roughness, and film thickness.

A semi-phenomenological model to predict the acoustic behavior of fully and partially reticulated polyurethane foams

NASA Astrophysics Data System (ADS)

Doutres, Olivier; Atalla, Noureddine; Dong, Kevin

2013-02-01

This paper proposes simple semi-phenomenological models to predict the sound absorption efficiency of highly porous polyurethane foams from microstructure characterization. In a previous paper [J. Appl. Phys. 110, 064901 (2011)], the authors presented a 3-parameter semi-phenomenological model linking the microstructure properties of fully and partially reticulated isotropic polyurethane foams (i.e., strut length l, strut thickness t, and reticulation rate Rw) to the macroscopic non-acoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity ϕ, airflow resistivity σ, tortuosity α∝, viscous Λ, and thermal Λ' characteristic lengths). The model was based on existing scaling laws, validated for fully reticulated polyurethane foams, and improved using both geometrical and empirical approaches to account for the presence of membrane closing the pores. This 3-parameter model is applied to six polyurethane foams in this paper and is found highly sensitive to the microstructure characterization; particularly to strut's dimensions. A simplified micro-/macro model is then presented. It is based on the cell size Cs and reticulation rate Rw only, assuming that the geometric ratio between strut length l and strut thickness t is known. This simplified model, called the 2-parameter model, considerably simplifies the microstructure characterization procedure. A comparison of the two proposed semi-phenomenological models is presented using six polyurethane foams being either fully or partially reticulated, isotropic or anisotropic. It is shown that the 2-parameter model is less sensitive to measurement uncertainties compared to the original model and allows a better estimation of polyurethane foams sound absorption behavior.

A review and analysis of boundary layer transition data for turbine application

NASA Technical Reports Server (NTRS)

Gaugler, R. E.

1985-01-01

A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information. The data were analyzed by using a version of the STAN5 two-dimensional boundary layer code. The transition starting and ending points were determined by adjusting parameters in STAN5 until the calculations matched the data. The results are presented as a table of the deduced transition location and length as functions of the test parameters. The data sets reviewed cover a wide range of flow conditions, from low-speed, flat-plate tests to full-scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free-stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Numerical investigation of the influence of elevated turbulence levels on the cooling effectiveness of an anti-vortex hole geometry

NASA Astrophysics Data System (ADS)

Repko, Timothy William

A novel film cooling hole geometry for use in gas turbine engines has been investigated numerically by solving the Reynolds Averaged Navier-Stokes equations in a commercial CFD code (STAR-CCM+) with varying turbulence intensity and length scale using the k-o SST turbulence model. Both steady and unsteady results were considered in order to investigate the effects of freestream turbulence intensity and length scale on this novel anti-vortex hole (AVH) concept. The AVH geometry utilizes two side holes, one on each side of the main hole, to attempt to mitigate the vorticity from the jet from the main hole. The AVH concept has been shown by past research to provide a substantial improvement over conventional film cooling hole designs. Past research has been limited to low turbulence intensity and small length scales that are not representative of the turbulent flow exiting the combustor. Three turbulence intensities (Tu = 5, 10 and 20%) and three length scales normalized by the main cooling hole diameter (Λ x/dm = 1, 3, 6) were considered in this study for a total of nine turbulence conditions. The highest intensity, largest length scale turbulence case (Tu = 20, Λx/dm = 6) is considered most representative of engine conditions and was shown to have the best cooling performance. Results show that the turbulence in the hot gases exiting the combustor can aid in the film cooling for the AVH geometry at high blowing ratios (BR = 2.0), where the blowing ratio is essentially the ratio of the jet-to-mainstream mass flux ratios. Length scale was shown to have an insignificant effect on the cooling performance at low turbulence intensity and a moderate effect at higher turbulence intensities. The adiabatic film cooling effectiveness was shown to increase as the turbulence intensity was elevated. The convective heat transfer coefficient was also shown to increase at the turbulence intensity was elevated. An increase in the heat transfer coefficient is a deleterious effect and must be weighed against the improvements in the adiabatic cooling effectiveness. The net heat flux reduction (NHFR) is the parameter used to quantify the net benefit of film cooling. As a general trend, the NHFR was shown to increase with the turbulence intensity in all cases.

Scaling of Myocardial Mass to Flow and Morphometry of Coronary Arteries

PubMed Central

Choy, Jenny Susana; Kassab, Ghassan S.

2009-01-01

There is no doubt that scaling relations exist between myocardial mass and morphometry of coronary vasculature. The purpose of this study is to quantify several morphological (diameter, length, and volume) and functional (flow) parameters of the coronary arterial tree in relation to myocardial mass. Eight normal porcine hearts of 117-244 g (mean of 177.5±32.7) were used in this study. Various coronary sub-trees of the Left Anterior Descending (LAD), Right Coronary (RCA) and Left Circumflex (LCX) arteries were perfused at pressure of 100 mmHg with different colors of a polymer (Microfil) in order to obtain rubber casts of arterial trees corresponding to different regions of myocardial mass. Volume, diameter and cumulative length of coronary arteries were reconstructed from casts to analyze their relationship to the perfused myocardial mass. Volumetric flow was measured in relationship with perfused myocardial mass. Our results show that arterial volume is linearly related to regional myocardial mass, whereas the sum of coronary arterial branch lengths, vessel diameters and volumetric flow show an approximately 3/4, 3/8 and 3/4 power-law relationship, respectively, in relation to myocardial mass. These scaling laws suggest fundamental design principles underlying the structure-function relationship of the coronary arterial tree that may facilitate diagnosis and management of diffuse coronary artery disease. PMID:18323461

Scaling of myocardial mass to flow and morphometry of coronary arteries.

PubMed

Choy, Jenny Susana; Kassab, Ghassan S

2008-05-01

There is no doubt that scaling relations exist between myocardial mass and morphometry of coronary vasculature. The purpose of this study is to quantify several morphological (diameter, length, and volume) and functional (flow) parameters of the coronary arterial tree in relation to myocardial mass. Eight normal porcine hearts of 117-244 g (mean of 177.5 +/- 32.7) were used in this study. Various coronary subtrees of the left anterior descending, right coronary, and left circumflex arteries were perfused at pressure of 100 mmHg with different colors of a polymer (Microfil) to obtain rubber casts of arterial trees corresponding to different regions of myocardial mass. Volume, diameter, and cumulative length of coronary arteries were reconstructed from casts to analyze their relationship to the perfused myocardial mass. Volumetric flow was measured in relationship with perfused myocardial mass. Our results show that arterial volume is linearly related to regional myocardial mass, whereas the sum of coronary arterial branch lengths, vessel diameters, and volumetric flow show an approximately 3/4, 3/8, and 3/4 power-law relationship, respectively, in relation to myocardial mass. These scaling laws suggest fundamental design principles underlying the structure-function relationship of the coronary arterial tree that may facilitate diagnosis and management of diffuse coronary artery disease.

Length distributions of nanowires: Effects of surface diffusion versus nucleation delay

NASA Astrophysics Data System (ADS)

Dubrovskii, Vladimir G.

2017-04-01

It is often thought that the ensembles of semiconductor nanowires are uniform in length due to the initial organization of the growth seeds such as lithographically defined droplets or holes in the substrate. However, several recent works have already demonstrated that most nanowire length distributions are broader than Poissonian. Herein, we consider theoretically the length distributions of non-interacting nanowires that grow by the material collection from the entire length of their sidewalls and with a delay of nucleation of the very first nanowire monolayer. The obtained analytic length distribution is controlled by two parameters that describe the strength of surface diffusion and the nanowire nucleation rate. We show how the distribution changes from the symmetrical Polya shape without the nucleation delay to a much broader and asymmetrical one for longer delays. In the continuum limit (for tall enough nanowires), the length distribution is given by a power law times an incomplete gamma-function. We discuss interesting scaling properties of this solution and give a recipe for analyzing and tailoring the experimental length histograms of nanowires which should work for a wide range of material systems and growth conditions.

Studying flow close to an interface by total internal reflection fluorescence cross-correlation spectroscopy: Quantitative data analysis

NASA Astrophysics Data System (ADS)

Schmitz, R.; Yordanov, S.; Butt, H. J.; Koynov, K.; Dünweg, B.

2011-12-01

Total internal reflection fluorescence cross-correlation spectroscopy (TIR-FCCS) has recently [S. Yordanov , Optics ExpressOPEXFF1094-408710.1364/OE.17.021149 17, 21149 (2009)] been established as an experimental method to probe hydrodynamic flows near surfaces, on length scales of tens of nanometers. Its main advantage is that fluorescence occurs only for tracer particles close to the surface, thus resulting in high sensitivity. However, the measured correlation functions provide only rather indirect information about the flow parameters of interest, such as the shear rate and the slip length. In the present paper, we show how to combine detailed and fairly realistic theoretical modeling of the phenomena by Brownian dynamics simulations with accurate measurements of the correlation functions, in order to establish a quantitative method to retrieve the flow properties from the experiments. First, Brownian dynamics is used to sample highly accurate correlation functions for a fixed set of model parameters. Second, these parameters are varied systematically by means of an importance-sampling Monte Carlo procedure in order to fit the experiments. This provides the optimum parameter values together with their statistical error bars. The approach is well suited for massively parallel computers, which allows us to do the data analysis within moderate computing times. The method is applied to flow near a hydrophilic surface, where the slip length is observed to be smaller than 10nm, and, within the limitations of the experiments and the model, indistinguishable from zero.

Nanoscale phase transition behavior of shape memory alloys — closed form solution of 1D effective modelling

NASA Astrophysics Data System (ADS)

Li, M. P.; Sun, Q. P.

2018-01-01

We investigate the roles of grain size (lg) and grain boundary thickness (lb) on the stress-induced phase transition (PT) behaviors of nanocrystalline shape memory alloys (SMAs) by using a Core-shell type "crystallite-amorphous composite" model. A non-dimensionalized length scale lbarg(=lg /lb) is identified as the governing parameter which is indicative of the energy competition between the crystallite and the grain boundary. Closed form analytical solutions of a reduced effective 1D model with embedded microstructure length scales of lg and lb are presented in this paper. It is shown that, with lbarg reduction, the energy of the elastic non-transformable grain boundary will gradually become dominant in the phase transition process, and eventually bring fundamental changes of the deformation behaviors: breakdown of two-phase coexistence and vanishing of superelastic hysteresis. The predictions are supported by experimental data of nanocrystalline NiTi SMAs.

Laboratory studies of the coronal heating problem

NASA Astrophysics Data System (ADS)

Savin, Daniel Wolf; Bose, Sayak; Hahn, Michael; Vincena, Steve; Gekelman, Walter; Carter, Troy; Tripathi, Shreekrishna

2018-06-01

The solar corona, the outer atmosphere of the Sun at 106 K, is ~ 200 times hotter than the underlying visible surface. Incompressible Alfvén waves excited by convective motions at the surface of the Sun are posited to transport energy to the corona. Strong gradients in Alfvén speed at low heights in the corona are believed to be responsible for wave-driven heating of the plasma. These gradients may cause reflection of the incident waves, enabling the generation of turbulence due to nonlinear interaction between the counter propagating waves and subsequent dissipation of the wave energy at smaller length scales. We are studying propagation of Alfvén waves in the laboratory using scaled plasma parameters to approximate the solar corona. The experiments are conducted using the Large Plasma Device (LAPD) at the University of California, Los Angeles. We have explored the effectiveness of the longitudinal gradients in the Alfvén speed at reducing the energy of the Alfvén waves propagating through it in the linear regime. Our results show that the energy of the transmitted Alfvén waves decreases as the inhomogeneity parameter λA/LA increases. Here, λA is the wavelength of the Alfvén wave and LA is the Alfvén speed scale length. The inhomogeneity parameter is changed in two ways. In the first set of the experiments, it is changed by varying λA, while holding LA constant. In the second set, λA/LA is changed by varying LA, while holding λA constant. The decrease in transmittance of the wave energy with increase in λA/LA, for both the above cases, are found to be agreement with each other.

MULTI-WAVELENGTH OBSERVATIONS OF THE SPATIO-TEMPORAL EVOLUTION OF SOLAR FLARES WITH AIA/SDO. I. UNIVERSAL SCALING LAWS OF SPACE AND TIME PARAMETERS

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

Aschwanden, Markus J.; Zhang, Jie; Liu, Kai, E-mail: aschwanden@lmsal.com, E-mail: jzhang7@gmu.edu

2013-09-20

We extend a previous statistical solar flare study of 155 GOES M- and X-class flares observed with AIA/SDO to all seven coronal wavelengths (94, 131, 171, 193, 211, 304, and 335 Å) to test the wavelength dependence of scaling laws and statistical distributions. Except for the 171 and 193 Å wavelengths, which are affected by EUV dimming caused by coronal mass ejections (CMEs), we find near-identical size distributions of geometric (lengths L, flare areas A, volumes V, and fractal dimension D{sub 2}), temporal (flare durations T), and spatio-temporal parameters (diffusion coefficient κ, spreading exponent β, and maximum expansion velocities v{submore » max}) in different wavelengths, which are consistent with the universal predictions of the fractal-diffusive avalanche model of a slowly driven, self-organized criticality (FD-SOC) system, i.e., N(L)∝L {sup –3}, N(A)∝A {sup –2}, N(V)∝V {sup –5/3}, N(T)∝T {sup –2}, and D{sub 2} = 3/2, for a Euclidean dimension d = 3. Empirically, we find also a new strong correlation κ∝L {sup 0.94±0.01} and the three-parameter scaling law L∝κ T {sup 0.1}, which is more consistent with the logistic-growth model than with classical diffusion. The findings suggest long-range correlation lengths in the FD-SOC system that operate in the vicinity of a critical state, which could be used for predictions of individual extreme events. We find also that eruptive flares (with accompanying CMEs) have larger volumes V, longer flare durations T, higher EUV and soft X-ray fluxes, and somewhat larger diffusion coefficients κ than confined flares (without CMEs)« less

Temperature fluctuations and the thermodynamic determination of the cooperativity length in glass forming liquids.

PubMed

Chua, Y Z; Zorn, R; Holderer, O; Schmelzer, J W P; Schick, C; Donth, E

2017-03-14

The aim of this paper is to decide which of the two possible thermodynamic expressions for the cooperativity length in glass forming liquids is the correct one. In the derivation of these two expressions, the occurrence of temperature fluctuations in the considered nanoscale subsystems is either included or neglected. Consequently, our analysis gives also an answer to the widely discussed problem whether temperature fluctuations have to be generally accounted for in thermodynamics or not. To this end, the characteristic length-scales at equal times and temperatures for propylene glycol were determined independently from AC calorimetry in both the above specified ways and from quasielastic neutron scattering (QENS), and compared. The result shows that the cooperative length determined from QENS coincides most consistently with the cooperativity length determined from AC calorimetry measurements for the case that the effect of temperature fluctuations is incorporated in the description. This conclusion indicates that-accounting for temperature fluctuations-the characteristic length can be derived by thermodynamic considerations from the specific parameters of the liquid at glass transition and that temperature does fluctuate in small systems.

Temperature fluctuations and the thermodynamic determination of the cooperativity length in glass forming liquids

NASA Astrophysics Data System (ADS)

Chua, Y. Z.; Zorn, R.; Holderer, O.; Schmelzer, J. W. P.; Schick, C.; Donth, E.

2017-03-01

The aim of this paper is to decide which of the two possible thermodynamic expressions for the cooperativity length in glass forming liquids is the correct one. In the derivation of these two expressions, the occurrence of temperature fluctuations in the considered nanoscale subsystems is either included or neglected. Consequently, our analysis gives also an answer to the widely discussed problem whether temperature fluctuations have to be generally accounted for in thermodynamics or not. To this end, the characteristic length-scales at equal times and temperatures for propylene glycol were determined independently from AC calorimetry in both the above specified ways and from quasielastic neutron scattering (QENS), and compared. The result shows that the cooperative length determined from QENS coincides most consistently with the cooperativity length determined from AC calorimetry measurements for the case that the effect of temperature fluctuations is incorporated in the description. This conclusion indicates that—accounting for temperature fluctuations—the characteristic length can be derived by thermodynamic considerations from the specific parameters of the liquid at glass transition and that temperature does fluctuate in small systems.

Nanoparticle Superlattice Engineering with DNA

NASA Astrophysics Data System (ADS)

Macfarlane, Robert J.; Lee, Byeongdu; Jones, Matthew R.; Harris, Nadine; Schatz, George C.; Mirkin, Chad A.

2011-10-01

A current limitation in nanoparticle superlattice engineering is that the identities of the particles being assembled often determine the structures that can be synthesized. Therefore, specific crystallographic symmetries or lattice parameters can only be achieved using specific nanoparticles as building blocks (and vice versa). We present six design rules that can be used to deliberately prepare nine distinct colloidal crystal structures, with control over lattice parameters on the 25- to 150-nanometer length scale. These design rules outline a strategy to independently adjust each of the relevant crystallographic parameters, including particle size (5 to 60 nanometers), periodicity, and interparticle distance. As such, this work represents an advance in synthesizing tailorable macroscale architectures comprising nanoscale materials in a predictable fashion.

exocartographer: Constraining surface maps orbital parameters of exoplanets

NASA Astrophysics Data System (ADS)

Farr, Ben; Farr, Will M.; Cowan, Nicolas B.; Haggard, Hal M.; Robinson, Tyler

2018-05-01

exocartographer solves the exo-cartography inverse problem. This flexible forward-modeling framework, written in Python, retrieves the albedo map and spin geometry of a planet based on time-resolved photometry; it uses a Markov chain Monte Carlo method to extract albedo maps and planet spin and their uncertainties. Gaussian Processes use the data to fit for the characteristic length scale of the map and enforce smooth maps.

Multi-length-scale Material Model for SiC/SiC Ceramic-Matrix Composites (CMCs): Inclusion of In-Service Environmental Effects

NASA Astrophysics Data System (ADS)

Grujicic, M.; Galgalikar, R.; Snipes, J. S.; Ramaswami, S.

2016-01-01

In our recent work, a multi-length-scale room-temperature material model for SiC/SiC ceramic-matrix composites (CMCs) was derived and parameterized. The model was subsequently linked with a finite-element solver so that it could be used in a general room-temperature, structural/damage analysis of gas-turbine engine CMC components. Due to its multi-length-scale character, the material model enabled inclusion of the effects of fiber/tow (e.g., the volume fraction, size, and properties of the fibers; fiber-coating material/thickness; decohesion properties of the coating/matrix interfaces; etc.) and ply/lamina (e.g., the 0°/90° cross-ply versus plain-weave architectures, the extent of tow crimping in the case of the plain-weave plies, cohesive properties of the inter-ply boundaries, etc.) length-scale microstructural/architectural parameters on the mechanical response of the CMCs. One of the major limitations of the model is that it applies to the CMCs in their as-fabricated conditions (i.e., the effect of prolonged in-service environmental exposure and the associated material aging-degradation is not accounted for). In the present work, the model is upgraded to include such in-service environmental-exposure effects. To demonstrate the utility of the upgraded material model, it is used within a finite-element structural/failure analysis involving impact of a toboggan-shaped turbine shroud segment by a foreign object. The results obtained clearly revealed the effects that different aspects of the in-service environmental exposure have on the material degradation and the extent of damage suffered by the impacted CMC toboggan-shaped shroud segment.

The Effects of Earth's Outer Core's Viscosity on Geodynamo Models

NASA Astrophysics Data System (ADS)

Dong, C.; Jiao, L.; Zhang, H.

2017-12-01

Geodynamo process is controlled by mathematic equations and input parameters. To study effects of parameters on geodynamo system, MoSST model has been used to simulate geodynamo outputs under different outer core's viscosity ν. With spanning ν for nearly three orders when other parameters fixed, we studied the variation of each physical field and its typical length scale. We find that variation of ν affects the velocity field intensely. The magnetic field almost decreases monotonically with increasing of ν, while the variation is no larger than 30%. The temperature perturbation increases monotonically with ν, but by a very small magnitude (6%). The averaged velocity field (u) of the liquid core increases with ν as a simple fitted scaling relation: u∝ν0.49. The phenomenon that u increases with ν is essentially that increasing of ν breaks the Taylor-Proudman constraint and drops the critical Rayleigh number, and thus u increases under the same thermal driving force. Forces balance is analyzed and balance mode shifts with variation of ν. When compared with former studies of scaling laws, this study supports the conclusion that in a certain parameter range, the magnetic field strength doesn't vary much with the viscosity, but opposes to the assumption that the velocity field has nothing to do with the outer core viscosity.

[Evaluation of social demographic aspect of life quality of coal extraction workers in Kouzbass enterprises].

PubMed

Ivoĭlov, V M; Semenikhin, V A; Odintseva, O V; Shternis, T A

2014-01-01

For assessing influence of social factors on life quality of workers in coal extraction enterpirses of Kemerovo region, the authors used questionnaire SF-36. Life quality parameters of workers engaged into coal extraction in Kemerovo region appeared to lower with age from 20 to 64 years. Life quality parameters on scales of pain, physical functioning and general health are invertedly correlated with age and length of service in hazardous work conditions for coal extraction workers. Life quality of the miners is influenced by the following factors: marital status, educational level and income level of the workers.

The influence of idealized surface heterogeneity on virtual turbulent flux measurements

NASA Astrophysics Data System (ADS)

De Roo, Frederik; Mauder, Matthias

2018-04-01

The imbalance of the surface energy budget in eddy-covariance measurements is still an unsolved problem. A possible cause is the presence of land surface heterogeneity, which affects the boundary-layer turbulence. To investigate the impact of surface variables on the partitioning of the energy budget of flux measurements in the surface layer under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, which allows the determination of advection by the mean flow, flux-divergence and storage terms of the energy budget at the virtual measurement site, in addition to the standard turbulent flux. We focus on the heterogeneity of the surface fluxes and keep the topography flat. The surface fluxes vary locally in intensity and these patches have different length scales. Intensity and length scales can vary for the two horizontal dimensions but follow an idealized chessboard pattern. Our main focus lies on surface heterogeneity of the kilometer scale, and one order of magnitude smaller. For these two length scales, we investigate the average response of the fluxes at a number of virtual towers, when varying the heterogeneity length within the length scale and when varying the contrast between the different patches. For each simulation, virtual measurement towers were positioned at functionally different positions (e.g., downdraft region, updraft region, at border between domains, etc.). As the storage term is always small, the non-closure is given by the sum of the advection by the mean flow and the flux-divergence. Remarkably, the missing flux can be described by either the advection by the mean flow or the flux-divergence separately, because the latter two have a high correlation with each other. For kilometer scale heterogeneity, we notice a clear dependence of the updrafts and downdrafts on the surface heterogeneity and likewise we also see a dependence of the energy partitioning on the tower location. For the hectometer scale, we do not notice such a clear dependence. Finally, we seek correlators for the energy balance ratio in the simulations. The correlation with the friction velocity is less pronounced than previously found, but this is likely due to our concentration on effectively strongly to freely convective conditions.

Structural heritage, reactivation and distribution of fault and fracture network in a rifting context: Case study of the western shoulder of the Upper Rhine Graben

NASA Astrophysics Data System (ADS)

Bertrand, Lionel; Jusseaume, Jessie; Géraud, Yves; Diraison, Marc; Damy, Pierre-Clément; Navelot, Vivien; Haffen, Sébastien

2018-03-01

In fractured reservoirs in the basement of extensional basins, fault and fracture parameters like density, spacing and length distribution are key properties for modelling and prediction of reservoir properties and fluids flow. As only large faults are detectable using basin-scale geophysical investigations, these fine-scale parameters need to be inferred from faults and fractures in analogous rocks at the outcrop. In this study, we use the western shoulder of the Upper Rhine Graben as an outcropping analogue of several deep borehole projects in the basement of the graben. Geological regional data, DTM (Digital Terrain Model) mapping and outcrop studies with scanlines are used to determine the spatial arrangement of the faults from the regional to the reservoir scale. The data shows that: 1) The fault network can be hierarchized in three different orders of scale and structural blocks with a characteristic structuration. This is consistent with other basement rocks studies in other rifting system allowing the extrapolation of the important parameters for modelling. 2) In the structural blocks, the fracture network linked to the faults is linked to the interplay between rock facies variation linked to the rock emplacement and the rifting event.

Prediction of scaling physics laws for proton acceleration with extended parameter space of the NIF ARC

NASA Astrophysics Data System (ADS)

Bhutwala, Krish; Beg, Farhat; Mariscal, Derek; Wilks, Scott; Ma, Tammy

2017-10-01

The Advanced Radiographic Capability (ARC) laser at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is the world's most energetic short-pulse laser. It comprises four beamlets, each of substantial energy ( 1.5 kJ), extended short-pulse duration (10-30 ps), and large focal spot (>=50% of energy in 150 µm spot). This allows ARC to achieve proton and light ion acceleration via the Target Normal Sheath Acceleration (TNSA) mechanism, but it is yet unknown how proton beam characteristics scale with ARC-regime laser parameters. As theory has also not yet been validated for laser-generated protons at ARC-regime laser parameters, we attempt to formulate the scaling physics of proton beam characteristics as a function of laser energy, intensity, focal spot size, pulse length, target geometry, etc. through a review of relevant proton acceleration experiments from laser facilities across the world. These predicted scaling laws should then guide target design and future diagnostics for desired proton beam experiments on the NIF ARC. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the LLNL LDRD program under tracking code 17-ERD-039.

Heat transfer, fluid flow and mass transfer in laser welding of stainless steel with small length scale

NASA Astrophysics Data System (ADS)

He, Xiuli

Nd: YAG Laser welding with hundreds of micrometers in laser beam diameter is widely used for assembly and closure of high reliability electrical and electronic packages for the telecommunications, aerospace and medical industries. However, certain concerns have to be addressed to obtain defect-free and structurally sound welds. During laser welding, Because of the high power density used, the pressures at the weld pool surface can be greater than the ambient pressure. This excess pressure provides a driving force for the vaporization to take place. As a result of vaporization for different elements, the composition in the weld pool may differ from that of base metal, which can result in changes in the microstructure and degradation of mechanical properties of weldments. When the weld pool temperatures are very high, the escaping vapor exerts a large recoil force on the weld pool surface, and as a consequence, tiny liquid metal particles may be expelled from the weld pool. Vaporization of alloying elements and liquid metal expulsion are the two main mechanisms of material loss. Besides, for laser welds with small length scale, heat transfer and fluid flow are different from those for arc welds with much larger length scale. Because of small weld pool size, rapid changes of temperature and very short duration of the laser welding process, physical measurements of important parameters such as temperature and velocity fields, weld thermal cycles, solidification and cooling rates are very difficult. The objective of the research is to quantitatively understand the influences of various factors on the heat transfer, fluid flow, vaporization of alloying elements and liquid metal expulsion in Nd:YAG laser welding with small length scale of 304 stainless steel. In this study, a comprehensive three dimensional heat transfer and fluid flow model based on the mass, momentum and energy conservation equations is relied upon to calculate temperature and velocity fields in the weld pool, weld thermal cycle, weld pool geometry and solidification parameters. Surface tension and buoyancy forces were considered for the calculation of transient weld pool convection. Very fine grids and small time steps were used to achieve accuracy in the calculations. The calculated weld pool dimensions were compared with the corresponding measured values to validate the model. (Abstract shortened by UMI.)

Can the scaling behavior of electric conductivity be used to probe the self-organizational changes in solution with respect to the ionic liquid structure? The case of [C8MIM][NTf2].

PubMed

Paluch, Marian; Wojnarowska, Zaneta; Goodrich, Peter; Jacquemin, Johan; Pionteck, Jürgen; Hensel-Bielowka, Stella

2015-08-28

Electrical conductivity of the supercooled ionic liquid [C8MIM][NTf2], determined as a function of temperature and pressure, highlights strong differences in its ionic transport behavior between low and high temperature regions. To date, the crossover effect which is very well known for low molecular van der Waals liquids has been rarely described for classical ionic liquids. This finding highlights that the thermal fluctuations could be dominant mechanisms driving the dramatic slowing down of ion motions near Tg. An alternative way to analyze separately low and high temperature dc-conductivity data using a density scaling approach was then proposed. Based on which a common value of the scaling exponent γ = 2.4 was obtained, indicating that the applied density scaling is insensitive to the crossover effect. By comparing the scaling exponent γ reported herein along with literature data for other ionic liquids, it appears that γ decreases by increasing the alkyl chain length on the 1-alkyl-3-methylimidazolium-based ionic liquids. This observation may be related to changes in the interaction between ions in solution driven by an increase in the van der Waals type interaction by increasing the alkyl chain length on the cation. This effect may be related to changes in the ionic liquid nanostructural organization with the alkyl chain length on the cation as previously reported in the literature based on molecular dynamic simulations. In other words, the calculated scaling exponent γ may be then used as a key parameter to probe the interaction and/or self-organizational changes in solution with respect to the ionic liquid structure.

Geometric scaling of artificial hair sensors for flow measurement under different conditions

NASA Astrophysics Data System (ADS)

Su, Weihua; Reich, Gregory W.

2017-03-01

Artificial hair sensors (AHSs) have been developed for prediction of the local flow speed and aerodynamic force around an airfoil and subsequent application in vibration control of the airfoil. Usually, a specific sensor design is only sensitive to the flow speeds within its operating flow measurement region. This paper aims at expanding this flow measurement concept of using AHSs to different flow speed conditions by properly sizing the parameters of the sensors, including the dimensions of the artificial hair, capillary, and carbon nanotubes (CNTs) that make up the sensor design, based on a baseline sensor design and its working flow condition. In doing so, the glass fiber hair is modeled as a cantilever beam with an elastic foundation, subject to the distributed aerodynamic drag over the length of the hair. Hair length and diameter, capillary depth, and CNT height are scaled by keeping the maximum compressive strain of the CNTs constant for different sensors under different speed conditions. Numerical studies will demonstrate the feasibility of the geometric scaling methodology by designing AHSs for aircraft with different dimensions and flight conditions, starting from the same baseline sensor. Finally, the operating bandwidth of the scaled sensors are explored.

Isotope Mass Scaling of Turbulence and Transport

NASA Astrophysics Data System (ADS)

McKee, George; Yan, Zheng; Gohil, Punit; Luce, Tim; Rhodes, Terry

2017-10-01

The dependence of turbulence characteristics and transport scaling on the fuel ion mass has been investigated in a set of hydrogen (A = 1) and deuterium (A = 2) plasmas on DIII-D. Normalized energy confinement time (B *τE) is two times lower in hydrogen (H) plasmas compare to similar deuterium (D) plasmas. Dimensionless parameters other than ion mass (A) , including ρ*, q95, Te /Ti , βN, ν*, and Mach number were maintained nearly fixed. Matched profiles of electron density, electron and ion temperature, and toroidal rotation were well matched. The normalized turbulence amplitude (ñ / n) is approximately twice as large in H as in D, which may partially explain the increased transport and reduced energy confinement time. Radial correlation lengths of low-wavenumber density turbulence in hydrogen are similar to or slightly larger than correlation lengths in the deuterium plasmas and generally scale with the ion gyroradius, which were maintained nearly fixed in this dimensionless scan. Predicting energy confinement in D-T burning plasmas requires an understanding of the large and beneficial isotope scaling of transport. Supported by USDOE under DE-FG02-08ER54999 and DE-FC02-04ER54698.

Submicron scale tissue multifractal anisotropy in polarized laser light scattering

NASA Astrophysics Data System (ADS)

Das, Nandan Kumar; Dey, Rajib; Chakraborty, Semanti; Panigrahi, Prasanta K.; Meglinski, Igor; Ghosh, Nirmalya

2018-03-01

The spatial fluctuations of the refractive index within biological tissues exhibit multifractal anisotropy, leaving its signature as a spectral linear diattenuation of scattered polarized light. The multifractal anisotropy has been quantitatively assessed by the processing of relevant Mueller matrix elements in the Fourier domain, utilizing the Born approximation and subsequent multifractal analysis. The differential scaling exponent and width of the singularity spectrum appear to be highly sensitive to the structural multifractal anisotropy at the micron/sub-micron length scales. An immediate practical use of these multifractal anisotropy parameters was explored for non-invasive screening of cervical precancerous alterations ex vivo, with the indication of a strong potential for clinical diagnostic purposes.

Channeling of multikilojoule high-intensity laser beams in an inhomogeneous plasma

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

Ivancic, S.; Haberberger, D.; Habara, H.

Channeling experiments were performed that demonstrate the transport of high-intensity (>10¹⁸ W/cm²), multikilojoule laser light through a millimeter-sized, inhomogeneous (~300-μm density scale length) laser produced plasma up to overcritical density, which is an important step forward for the fast-ignition concept. The background plasma density and the density depression inside the channel were characterized with a novel optical probe system. The channel progression velocity was measured, which agrees well with theoretical predictions based on large scale particle-in-cell simulations, confirming scaling laws for the required channeling laser energy and laser pulse duration, which are important parameters for future integrated fast-ignition channeling experiments.

Impact of incomplete metal coverage on the electrical properties of metal-CNT contacts: A large-scale ab initio study

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

Fediai, Artem, E-mail: artem.fediai@nano.tu-dresden.de; Ryndyk, Dmitry A.; Center for Advancing Electronics Dresden, TU Dresden, 01062 Dresden

2016-09-05

Using a dedicated combination of the non-equilibrium Green function formalism and large-scale density functional theory calculations, we investigated how incomplete metal coverage influences two of the most important electrical properties of carbon nanotube (CNT)-based transistors: contact resistance and its scaling with contact length, and maximum current. These quantities have been derived from parameter-free simulations of atomic systems that are as close as possible to experimental geometries. Physical mechanisms that govern these dependences have been identified for various metals, representing different CNT-metal interaction strengths from chemisorption to physisorption. Our results pave the way for an application-oriented design of CNT-metal contacts.

Connecting the large- and the small-scale magnetic fields of solar-like stars

NASA Astrophysics Data System (ADS)

Lehmann, L. T.; Jardine, M. M.; Mackay, D. H.; Vidotto, A. A.

2018-05-01

A key question in understanding the observed magnetic field topologies of cool stars is the link between the small- and the large-scale magnetic field and the influence of the stellar parameters on the magnetic field topology. We examine various simulated stars to connect the small-scale with the observable large-scale field. The highly resolved 3D simulations we used couple a flux transport model with a non-potential coronal model using a magnetofrictional technique. The surface magnetic field of these simulations is decomposed into spherical harmonics which enables us to analyse the magnetic field topologies on a wide range of length scales and to filter the large-scale magnetic field for a direct comparison with the observations. We show that the large-scale field of the self-consistent simulations fits the observed solar-like stars and is mainly set up by the global dipolar field and the large-scale properties of the flux pattern, e.g. the averaged latitudinal position of the emerging small-scale field and its global polarity pattern. The stellar parameters flux emergence rate, differential rotation and meridional flow affect the large-scale magnetic field topology. An increased flux emergence rate increases the magnetic flux in all field components and an increased differential rotation increases the toroidal field fraction by decreasing the poloidal field. The meridional flow affects the distribution of the magnetic energy across the spherical harmonic modes.

Pattern formation in individual-based systems with time-varying parameters

NASA Astrophysics Data System (ADS)

Ashcroft, Peter; Galla, Tobias

2013-12-01

We study the patterns generated in finite-time sweeps across symmetry-breaking bifurcations in individual-based models. Similar to the well-known Kibble-Zurek scenario of defect formation, large-scale patterns are generated when model parameters are varied slowly, whereas fast sweeps produce a large number of small domains. The symmetry breaking is triggered by intrinsic noise, originating from the discrete dynamics at the microlevel. Based on a linear-noise approximation, we calculate the characteristic length scale of these patterns. We demonstrate the applicability of this approach in a simple model of opinion dynamics, a model in evolutionary game theory with a time-dependent fitness structure, and a model of cell differentiation. Our theoretical estimates are confirmed in simulations. In further numerical work, we observe a similar phenomenon when the symmetry-breaking bifurcation is triggered by population growth.

Effect of beam types on the scintillations: a review

NASA Astrophysics Data System (ADS)

Baykal, Yahya; Eyyuboglu, Halil T.; Cai, Yangjian

2009-02-01

When different incidences are launched in atmospheric turbulence, it is known that the intensity fluctuations exhibit different characteristics. In this paper we review our work done in the evaluations of the scintillation index of general beam types when such optical beams propagate in horizontal atmospheric links in the weak fluctuations regime. Variation of scintillation indices versus the source and medium parameters are examined for flat-topped-Gaussian, cosh- Gaussian, cos-Gaussian, annular, elliptical Gaussian, circular (i.e., stigmatic) and elliptical (i.e., astigmatic) dark hollow, lowest order Bessel-Gaussian and laser array beams. For flat-topped-Gaussian beam, scintillation is larger than the single Gaussian beam scintillation, when the source sizes are much less than the Fresnel zone but becomes smaller for source sizes much larger than the Fresnel zone. Cosh-Gaussian beam has lower on-axis scintillations at smaller source sizes and longer propagation distances as compared to Gaussian beams where focusing imposes more reduction on the cosh- Gaussian beam scintillations than that of the Gaussian beam. Intensity fluctuations of a cos-Gaussian beam show favorable behaviour against a Gaussian beam at lower propagation lengths. At longer propagation lengths, annular beam becomes advantageous. In focused cases, the scintillation index of annular beam is lower than the scintillation index of Gaussian and cos-Gaussian beams starting at earlier propagation distances. Cos-Gaussian beams are advantages at relatively large source sizes while the reverse is valid for annular beams. Scintillations of a stigmatic or astigmatic dark hollow beam can be smaller when compared to stigmatic or astigmatic Gaussian, annular and flat-topped beams under conditions that are closely related to the beam parameters. Intensity fluctuation of an elliptical Gaussian beam can also be smaller than a circular Gaussian beam depending on the propagation length and the ratio of the beam waist size along the long axis to that along the short axis (i.e., astigmatism). Comparing against the fundamental Gaussian beam on equal source size and equal power basis, it is observed that the scintillation index of the lowest order Bessel-Gaussian beam is lower at large source sizes and large width parameters. However, for excessively large width parameters and beyond certain propagation lengths, the advantage of the lowest order Bessel-Gaussian beam seems to be lost. Compared to Gaussian beam, laser array beam exhibits less scintillations at long propagation ranges and at some midrange radial displacement parameters. When compared among themselves, laser array beams tend to have reduced scintillations for larger number of beamlets, longer wavelengths, midrange radial displacement parameters, intermediate Gaussian source sizes, larger inner scales and smaller outer scales of turbulence. The number of beamlets used does not seem to be so effective in this improvement of the scintillations.

Effect of rhythmic auditory stimulation on gait kinematic parameters of patients with multiple sclerosis.

PubMed

Shahraki, M; Sohrabi, M; Taheri Torbati, H R; Nikkhah, K; NaeimiKia, M

2017-01-01

Purpose: This study aimed to examine the effect of rhythmic auditory stimulation on gait kinematic parameters of patients with multiple sclerosis. Subjects and Methods: In this study, 18 subjects, comprising 4 males and 14 females with Multiple Sclerosis with expanded disability status scale of 3 to 6 were chosen. Subjects were selected by available and targeted sampling and were randomly divided into two experimental (n = 9) and control (n = 9) groups. Exercises were gait with rhythmic auditory stimulation by a metronome device, in addition to gait without stimulation for the experimental and control groups, respectively. Training was carried out for 3 weeks, with 30 min duration for each session 3 times a week. Stride length, stride time, double support time, cadence and gait speed were measured by motion analysis device. Results: There was a significant difference between stride length, stride time, double support time, cadence and gait speed in the experimental group, before and after the training. Furthermore, there was a significant difference between the experimental and control groups in the enhancement of stride length, stride time, cadence and gait speed in favor of the experimental group. While this difference was not significant for double support time. Conclusion: The results of this study showed that rhythmic auditory stimulation is an effective rehabilitation method to improve gait kinematic parameters in patients with multiple sclerosis.

Thermodynamic scaling of glassy dynamics and dynamic heterogeneities in metallic glass-forming liquid

NASA Astrophysics Data System (ADS)

Hu, Yuan-Chao; Shang, Bao-Shuang; Guan, Peng-Fei; Yang, Yong; Bai, Hai-Yang; Wang, Wei-Hua

2016-09-01

A ternary metallic glass-forming liquid is found to be not strongly correlating thermodynamically, but its average dynamics, dynamic heterogeneities including the high order dynamic correlation length, and static structure are still well described by thermodynamic scaling with the same scaling exponent γ. This may indicate that the metallic liquid could be treated as a single-parameter liquid. As an intrinsic material constant stemming from the fundamental interatomic interactions, γ is theoretically predicted from the thermodynamic fluctuations of the potential energy and the virial. Although γ is conventionally understood merely from the repulsive part of the inter-particle potentials, the strong correlation between γ and the Grüneisen parameter up to the accuracy of the Dulong-Petit approximation demonstrates the important roles of anharmonicity and attractive force of the interatomic potential in governing glass transition of metallic glassformers. These findings may shed light on how to understand metallic glass formation from the fundamental interatomic interactions.

Make dark matter charged again

NASA Astrophysics Data System (ADS)

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa; Scholtz, Jakub

2017-05-01

We revisit constraints on dark matter that is charged under a U(1) gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large, a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.

Particle dynamics in a viscously decaying cat's eye: The effect of finite Schmidt numbers

NASA Astrophysics Data System (ADS)

Newton, P. K.; Meiburg, Eckart

1991-05-01

The dynamics and mixing of passive marker particles for the model problem of a decaying cat's eye flow is studied. The flow field corresponds to Stuart's one-parameter family of solutions [J. Fluid Mech. 29, 417 (1967)]. It is time dependent as a result of viscosity, which is modeled by allowing the free parameter to depend on time according to the self-similar solution of the Navier-Stokes equations for an isolated point vortex. Particle diffusion is numerically simulated by a random walk model. While earlier work had shown that, for small values of time over Reynolds number t/Re≪1, the interval length characterizing the formation of lobes of fluid escaping from the cat's eye scales as Re-1/2, the present study shows that, for the case of diffusive effects and t/Pe≪1, the scaling follows Pe-1/4. A simple argument, taking into account streamline convergence and divergence in different parts of the flow field, explains the Pe-1/4 scaling.

Multi-scale Material Parameter Identification Using LS-DYNA® and LS-OPT®

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

Stander, Nielen; Basudhar, Anirban; Basu, Ushnish

2015-09-14

Ever-tightening regulations on fuel economy, and the likely future regulation of carbon emissions, demand persistent innovation in vehicle design to reduce vehicle mass. Classical methods for computational mass reduction include sizing, shape and topology optimization. One of the few remaining options for weight reduction can be found in materials engineering and material design optimization. Apart from considering different types of materials, by adding material diversity and composite materials, an appealing option in automotive design is to engineer steel alloys for the purpose of reducing plate thickness while retaining sufficient strength and ductility required for durability and safety. A project tomore » develop computational material models for advanced high strength steel is currently being executed under the auspices of the United States Automotive Materials Partnership (USAMP) funded by the US Department of Energy. Under this program, new Third Generation Advanced High Strength Steel (i.e., 3GAHSS) are being designed, tested and integrated with the remaining design variables of a benchmark vehicle Finite Element model. The objectives of the project are to integrate atomistic, microstructural, forming and performance models to create an integrated computational materials engineering (ICME) toolkit for 3GAHSS. The mechanical properties of Advanced High Strength Steels (AHSS) are controlled by many factors, including phase composition and distribution in the overall microstructure, volume fraction, size and morphology of phase constituents as well as stability of the metastable retained austenite phase. The complex phase transformation and deformation mechanisms in these steels make the well-established traditional techniques obsolete, and a multi-scale microstructure-based modeling approach following the ICME [0]strategy was therefore chosen in this project. Multi-scale modeling as a major area of research and development is an outgrowth of the Comprehensive Test Ban Treaty of 1996 which banned surface testing of nuclear devices [1]. This had the effect that experimental work was reduced from large scale tests to multiscale experiments to provide material models with validation at different length scales. In the subsequent years industry realized that multi-scale modeling and simulation-based design were transferable to the design optimization of any structural system. Horstemeyer [1] lists a number of advantages of the use of multiscale modeling. Among these are: the reduction of product development time by alleviating costly trial-and-error iterations as well as the reduction of product costs through innovations in material, product and process designs. Multi-scale modeling can reduce the number of costly large scale experiments and can increase product quality by providing more accurate predictions. Research tends to be focussed on each particular length scale, which enhances accuracy in the long term. This paper serves as an introduction to the LS-OPT and LS-DYNA methodology for multi-scale modeling. It mainly focuses on an approach to integrate material identification using material models of different length scales. As an example, a multi-scale material identification strategy, consisting of a Crystal Plasticity (CP) material model and a homogenized State Variable (SV) model, is discussed and the parameter identification of the individual material models of different length scales is demonstrated. The paper concludes with thoughts on integrating the multi-scale methodology into the overall vehicle design.« less

Bounds on neutrino mass in viscous cosmology

NASA Astrophysics Data System (ADS)

Anand, Sampurn; Chaubal, Prakrut; Mazumdar, Arindam; Mohanty, Subhendra; Parashari, Priyank

2018-05-01

Effective field theoretic description of dark matter fluid on large scales predicts viscosity of the order 10‑6 H0 MP2. Recently, it has been shown that the same magnitude of viscosity can resolve the discordance between large scale structure observations and Planck CMB data in the σ8-Ωm0 and H0-Ωm0 parameters space. On the other hand, massive neutrinos suppresses the matter power spectrum on the small length scales similar to the viscosities. Therefore, it is expected that the viscous dark matter setup along with massive neutrinos can provide stringent constraint on neutrino mass. In this article, we show that the inclusion of effective viscosity, which arises from summing over non linear perturbations at small length scales, indeed severely constrains the cosmological bound on neutrino masses. Under a joint analysis of Planck CMB and different large scale observation data, we find that upper bound on the sum of the neutrino masses, at 2-σ level, decreases respectively from ∑ mν <= 0.396 eV (for normal hierarchy) and ∑ mν <= 0.378 eV (for inverted hierarchy) to ∑ mν <= 0.267 eV (for normal hierarchy) and ∑ mν <= 0.146 eV (for inverted hierarchy).

Is Fish Response related to Velocity and Turbulence Magnitudes? (Invited)

NASA Astrophysics Data System (ADS)

Wilson, C. A.; Hockley, F. A.; Cable, J.

2013-12-01

Riverine fish are subject to heterogeneous velocities and turbulence, and may use this to their advantage by selecting regions which balance energy expenditure for station holding whilst maximising energy gain through feeding opportunities. This study investigated microhabitat selection by guppies (Poecilia reticulata) in terms of the three-dimensional velocity structure generated by idealised boulders in an experimental flume. Velocity and turbulence influenced intra-species variation in swimming behaviour with respect to size, sex and parasite intensity. With increasing body length, fish swam further and more frequently between boulder regions. Larger guppies spent more time in the high velocity and low turbulence region, whereas smaller guppies preferred the low velocity and high shear stress region directly behind the boulders. Male guppies selected the region of low velocity, indicating a possible reduced swimming ability due to hydrodynamic drag imposed by their fins. With increasing parasite (Gyrodactylus turnbulli) burden, fish preferentially selected the region of moderate velocity which had the lowest bulk measure of turbulence of all regions and was also the most spatially homogeneous velocity and turbulence region. Overall the least amount of time was spent in the recirculation zone which had the highest magnitude of shear stresses and mean vertical turbulent length scale to fish length ratio. Shear stresses were a factor of two greater than in the most frequented moderate velocity region, while mean vertical turbulent length scale to fish length ratio were six times greater. Indeed the mean longitudinal turbulent scale was 2-6 times greater than the fish length in all regions. While it is impossible to discriminate between these two turbulence parameters (shear stress and turbulent length to fish length ratio) in influencing the fish preference, our study infers that there is a bias towards fish spending more time in a region where both the bulk measure of turbulence and shear stress magnitude are low. These findings highlight the importance of heterogeneous flow conditions in river channel design due to behavioural variability within a species in terms of size and health status in response to velocity and turbulence.

Multi Scale Modeling of Continuous Aramid Fiber Reinforced Polymer Matrix Composites Used in Ballistic Protection Applications

DTIC Science & Technology

2014-11-16

related to identification of the type and the extent of data generated at a finer length scale to the adjacent coarser length scale, as well as seamless ...data generated at a finer length scale to the adjacent coarser length scale, as well as seamless integration of different length scales into a unified...composite laminate consisting of 32 laminae and impacted (at a 0° obliquity angle and an incident velocity of 500 m/s) by a 0.30 caliber steel

Thermodynamic scaling of dynamics in polymer melts: predictions from the generalized entropy theory.

PubMed

Xu, Wen-Sheng; Freed, Karl F

2013-06-21

Many glass-forming fluids exhibit a remarkable thermodynamic scaling in which dynamic properties, such as the viscosity, the relaxation time, and the diffusion constant, can be described under different thermodynamic conditions in terms of a unique scaling function of the ratio ρ(γ)∕T, where ρ is the density, T is the temperature, and γ is a material dependent constant. Interest in the scaling is also heightened because the exponent γ enters prominently into considerations of the relative contributions to the dynamics from pressure effects (e.g., activation barriers) vs. volume effects (e.g., free volume). Although this scaling is clearly of great practical use, a molecular understanding of the scaling remains elusive. Providing this molecular understanding would greatly enhance the utility of the empirically observed scaling in assisting the rational design of materials by describing how controllable molecular factors, such as monomer structures, interactions, flexibility, etc., influence the scaling exponent γ and, hence, the dynamics. Given the successes of the generalized entropy theory in elucidating the influence of molecular details on the universal properties of glass-forming polymers, this theory is extended here to investigate the thermodynamic scaling in polymer melts. The predictions of theory are in accord with the appearance of thermodynamic scaling for pressures not in excess of ~50 MPa. (The failure at higher pressures arises due to inherent limitations of a lattice model.) In line with arguments relating the magnitude of γ to the steepness of the repulsive part of the intermolecular potential, the abrupt, square-well nature of the lattice model interactions lead, as expected, to much larger values of the scaling exponent. Nevertheless, the theory is employed to study how individual molecular parameters affect the scaling exponent in order to extract a molecular understanding of the information content contained in the exponent. The chain rigidity, cohesive energy, chain length, and the side group length are all found to significantly affect the magnitude of the scaling exponent, and the computed trends agree well with available experiments. The variations of γ with these molecular parameters are explained by establishing a correlation between the computed molecular dependence of the scaling exponent and the fragility. Thus, the efficiency of packing the polymers is established as the universal physical mechanism determining both the fragility and the scaling exponent γ.

Laboratory Study of Homogeneous and Isotropic Turbulence at High Reynolds Number

NASA Astrophysics Data System (ADS)

Pecenak, Zachary; Dou, Zhongwang; Yang, Fan; Cao, Lujie; Liang, Zach; Meng, Hui

2013-11-01

To study particle dynamics modified by isotropic turbulence at high Reynolds numbers and provide experimental data for DNS validation, we have developed a soccer-ball-shaped truncated icosahedron turbulence chamber with 20 adjoining hexagon surfaces, 12 pentagon surfaces and twenty symettrically displaced fans, which form an enclosed chamber of 1m diameter. We use Particle Image Velocimetry (PIV) technique to characterize the base turbulent flow, using different PIV set ups to capture various characteristic scales of turbulence. Results show that the stationary isotropic turbulence field is a spherical domain with diameter of 40 mm with quasi-zero mean velocities. The maximum rms velocity is ~1.5 m/s, corresponding to a Taylor microscale Re of 450. We extract from the PIV velocity field the whole set of turbulent flow parameters including: turbulent kinetic energy, turbulent intensity, kinetic energy dissipation rate, large eddy length and time scales, the Kolmogorov length, time and velocity scales, Taylor microscale and Re, which are critical to the study of inter-particle statistics modified by turbulence. This research is funded by an NSF grant CBET-0967407.

Age, growth, and size of Lake Superior Pygmy Whitefish (Prosopium coulterii)

USGS Publications Warehouse

Stewart, Taylor; Derek Ogle,; Gorman, Owen T.; Vinson, Mark

2016-01-01

Pygmy Whitefish (Prosopium coulterii) are a small, glacial relict species with a disjunct distribution in North America and Siberia. In 2013 we collected Pygmy Whitefish at 28 stations from throughout Lake Superior. Total length was recorded for all fish and weight and sex were recorded and scales and otoliths were collected from a subsample. We compared the precision of estimated ages between readers and between scales and otoliths, estimated von Bertalanffy growth parameters for male and female Pygmy Whitefish, and reported the first weight-length relationship for Pygmy Whitefish. Age estimates between scales and otoliths differed significantly with otolith ages significantly greater for most ages after age-3. Maximum otolith age was nine for females and seven for males, which is older than previously reported for Pygmy Whitefish from Lake Superior. Growth was initially fast but slowed considerably after age-3 for males and age-4 for females, falling to 3–4 mm per year at maximum estimated ages. Females were longer than males after age-3. Our results suggest the size, age, and growth of Pygmy Whitefish in Lake Superior have not changed appreciably since 1953.

A Study of Parameters of the Counterpropagating Leader and its Influence on the Lightning Protection of Objects Using Large-Scale Laboratory Modeling

NASA Astrophysics Data System (ADS)

Syssoev, V. S.; Kostinskiy, A. Yu.; Makalskiy, L. M.; Rakov, A. V.; Andreev, M. G.; Bulatov, M. U.; Sukharevsky, D. I.; Naumova, M. U.

2014-04-01

In this work, the results of experiments on initiating the upward and descending leaders during the development of a long spark when studying lightning protection of objects with the help of large-scale models are shown. The influence of the counterpropagating leaders on the process of the lightning strike of ground-based and insulated objects is discussed. In the first case, the upward negative leader is initiated by the positive downward leader, which propagates from the high-voltage electrode of the "rod-rod"-type Marx generator (the rod is located on the plane and is 3-m high) in the gap with a length of 9-12 m. The positive-voltage pulse with a duration of 7500 μs had an amplitude of up to 3 MV. In the second case, initiation of the positive upward leader was performed in the electric field created by a cloud of negatively charged aerosol, which simulates the charged thunderstorm cell. In this case, all the phases characteristic of the ascending lightnings initiated by the tall ground-based objects and the triggered lightnings during the experiments with an actual thunderstorm cloud were observed in the forming spark discharge with a length of 1.5-2.0 m. The main parameters of the counterpropagating leader, which is initiated by the objects during the large-scale model experiments with a long spark, are shown.

Meiotic gene-conversion rate and tract length variation in the human genome.

PubMed

Padhukasahasram, Badri; Rannala, Bruce

2013-02-27

Meiotic recombination occurs in the form of two different mechanisms called crossing-over and gene-conversion and both processes have an important role in shaping genetic variation in populations. Although variation in crossing-over rates has been studied extensively using sperm-typing experiments, pedigree studies and population genetic approaches, our knowledge of variation in gene-conversion parameters (ie, rates and mean tract lengths) remains far from complete. To explore variability in population gene-conversion rates and its relationship to crossing-over rate variation patterns, we have developed and validated using coalescent simulations a comprehensive Bayesian full-likelihood method that can jointly infer crossing-over and gene-conversion rates as well as tract lengths from population genomic data under general variable rate models with recombination hotspots. Here, we apply this new method to SNP data from multiple human populations and attempt to characterize for the first time the fine-scale variation in gene-conversion parameters along the human genome. We find that the estimated ratio of gene-conversion to crossing-over rates varies considerably across genomic regions as well as between populations. However, there is a great degree of uncertainty associated with such estimates. We also find substantial evidence for variation in the mean conversion tract length. The estimated tract lengths did not show any negative relationship with the local heterozygosity levels in our analysis.European Journal of Human Genetics advance online publication, 27 February 2013; doi:10.1038/ejhg.2013.30.

Differential cross sections in a thick brane world scenario

NASA Astrophysics Data System (ADS)

Pedraza, Omar; Arceo, R.; López, L. A.; Cerón, V. E.

2018-04-01

The elastic differential cross section is calculated at low energies for the elements He and Ne using an effective 4D electromagnetic potential coming from the contribution of the massive Kaluza-Klein modes of the 5D vector field in a thick brane scenario. The length scale is adjusted in the potential to compare with known experimental data and to set bounds for the parameter of the model.

Multi-length scale tomography for the determination and optimization of the effective microstructural properties in novel hierarchical solid oxide fuel cell anodes

NASA Astrophysics Data System (ADS)

Lu, Xuekun; Taiwo, Oluwadamilola O.; Bertei, Antonio; Li, Tao; Li, Kang; Brett, Dan J. L.; Shearing, Paul R.

2017-11-01

Effective microstructural properties are critical in determining the electrochemical performance of solid oxide fuel cells (SOFCs), particularly when operating at high current densities. A novel tubular SOFC anode with a hierarchical microstructure, composed of self-organized micro-channels and sponge-like regions, has been fabricated by a phase inversion technique to mitigate concentration losses. However, since pore sizes span over two orders of magnitude, the determination of the effective transport parameters using image-based techniques remains challenging. Pioneering steps are made in this study to characterize and optimize the microstructure by coupling multi-length scale 3D tomography and modeling. The results conclusively show that embedding finger-like micro-channels into the tubular anode can improve the mass transport by 250% and the permeability by 2-3 orders of magnitude. Our parametric study shows that increasing the porosity in the spongy layer beyond 10% enhances the effective transport parameters of the spongy layer at an exponential rate, but linearly for the full anode. For the first time, local and global mass transport properties are correlated to the microstructure, which is of wide interest for rationalizing the design optimization of SOFC electrodes and more generally for hierarchical materials in batteries and membranes.

Upscaling of Solute Transport in Heterogeneous Media with Non-uniform Flow and Dispersion Fields

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

Xu, Zhijie; Meakin, Paul

2013-10-01

An analytical and computational model for non-reactive solute transport in periodic heterogeneous media with arbitrary non-uniform flow and dispersion fields within the unit cell of length ε is described. The model lumps the effect of non-uniform flow and dispersion into an effective advection velocity Ve and an effective dispersion coefficient De. It is shown that both Ve and De are scale-dependent (dependent on the length scale of the microscopic heterogeneity, ε), dependent on the Péclet number Pe, and on a dimensionless parameter α that represents the effects of microscopic heterogeneity. The parameter α, confined to the range of [-0.5, 0.5]more » for the numerical example presented, depends on the flow direction and non-uniform flow and dispersion fields. Effective advection velocity Ve and dispersion coefficient De can be derived for any given flow and dispersion fields, and . Homogenized solutions describing the macroscopic variations can be obtained from the effective model. Solutions with sub-unit-cell accuracy can be constructed by homogenized solutions and its spatial derivatives. A numerical implementation of the model compared with direct numerical solutions using a fine grid, demonstrated that the new method was in good agreement with direct solutions, but with significant computational savings.« less

Derivation of a hydrodynamic theory for mesoscale dynamics in microswimmer suspensions

NASA Astrophysics Data System (ADS)

Reinken, Henning; Klapp, Sabine H. L.; Bär, Markus; Heidenreich, Sebastian

2018-02-01

In this paper, we systematically derive a fourth-order continuum theory capable of reproducing mesoscale turbulence in a three-dimensional suspension of microswimmers. We start from overdamped Langevin equations for a generic microscopic model (pushers or pullers), which include hydrodynamic interactions on both small length scales (polar alignment of neighboring swimmers) and large length scales, where the solvent flow interacts with the order parameter field. The flow field is determined via the Stokes equation supplemented by an ansatz for the stress tensor. In addition to hydrodynamic interactions, we allow for nematic pair interactions stemming from excluded-volume effects. The results here substantially extend and generalize earlier findings [S. Heidenreich et al., Phys. Rev. E 94, 020601 (2016), 10.1103/PhysRevE.94.020601], in which we derived a two-dimensional hydrodynamic theory. From the corresponding mean-field Fokker-Planck equation combined with a self-consistent closure scheme, we derive nonlinear field equations for the polar and the nematic order parameter, involving gradient terms of up to fourth order. We find that the effective microswimmer dynamics depends on the coupling between solvent flow and orientational order. For very weak coupling corresponding to a high viscosity of the suspension, the dynamics of mesoscale turbulence can be described by a simplified model containing only an effective microswimmer velocity.

Numerical simulation of gas-phonon coupling in thermal transpiration flows.

PubMed

Guo, Xiaohui; Singh, Dhruv; Murthy, Jayathi; Alexeenko, Alina A

2009-10-01

Thermal transpiration is a rarefied gas flow driven by a wall temperature gradient and is a promising mechanism for gas pumping without moving parts, known as the Knudsen pump. Obtaining temperature measurements along capillary walls in a Knudsen pump is difficult due to extremely small length scales. Meanwhile, simplified analytical models are not applicable under the practical operating conditions of a thermal transpiration device, where the gas flow is in the transitional rarefied regime. Here, we present a coupled gas-phonon heat transfer and flow model to study a closed thermal transpiration system. Discretized Boltzmann equations are solved for molecular transport in the gas phase and phonon transport in the solid. The wall temperature distribution is the direct result of the interfacial coupling based on mass conservation and energy balance at gas-solid interfaces and is not specified a priori unlike in the previous modeling efforts. Capillary length scales of the order of phonon mean free path result in a smaller temperature gradient along the transpiration channel as compared to that predicted by the continuum solid-phase heat transfer. The effects of governing parameters such as thermal gradients, capillary geometry, gas and phonon Knudsen numbers and, gas-surface interaction parameters on the efficiency of thermal transpiration are investigated in light of the coupled model.

Transfer effects of fall training on balance performance and spatiotemporal gait parameters in healthy community-dwelling older adults: a pilot study.

PubMed

Donath, Lars; Faude, Oliver; Bridenbaugh, Stephanie A; Roth, Ralf; Soltermann, Martin; Kressig, Reto W; Zahner, Lukas

2014-07-01

This study examined transfer effects of fall training on fear of falling (Falls Efficacy Scale-International [FES-I]), balance performance, and spatiotemporal gait characteristics in older adults. Eighteen community-dwelling older adults (ages 65-85) were randomly assigned to an intervention or control group. The intervention group completed 12 training sessions (60 min, 6 weeks). During pre- and posttesting, we measured FES-I, balance performance (double limb, closed eyes; single limb, open eyes; double limb, open eyes with motor-interfered task), and gait parameters (e.g., velocity; cadence; stride time, stride width, and stride length; variability of stride time and stride length) under single- and motor-interfered tasks. Dual tasks were applied to appraise improvements of cognitive processing during balance and gait. FES-I (p = .33) and postural sway did not significantly change (0.36 < p < .79). Trends toward significant interaction effects were found for step width during normal walking and stride length variability during the motor dual task (p = .05, ηp 2 = .22). Fall training did not sufficiently improve fear of falling, balance, or gait performance under single- or dual-task conditions in healthy older adults.

Investigation of effective impact parameters in electron-ion temperature relaxation via Particle-Particle Coulombic molecular dynamics

NASA Astrophysics Data System (ADS)

Zhao, Yinjian

2017-09-01

Aiming at a high simulation accuracy, a Particle-Particle (PP) Coulombic molecular dynamics model is implemented to study the electron-ion temperature relaxation. In this model, the Coulomb's law is directly applied in a bounded system with two cutoffs at both short and long length scales. By increasing the range between the two cutoffs, it is found that the relaxation rate deviates from the BPS theory and approaches the LS theory and the GMS theory. Also, the effective minimum and maximum impact parameters (bmin* and bmax*) are obtained. For the simulated plasma condition, bmin* is about 6.352 times smaller than the Landau length (bC), and bmax* is about 2 times larger than the Debye length (λD), where bC and λD are used in the LS theory. Surprisingly, the effective relaxation time obtained from the PP model is very close to the LS theory and the GMS theory, even though the effective Coulomb logarithm is two times greater than the one used in the LS theory. Besides, this work shows that the PP model (commonly known as computationally expensive) is becoming practicable via GPU parallel computing techniques.

Validity of the two-level model for Viterbi decoder gap-cycle performance

NASA Technical Reports Server (NTRS)

Dolinar, S.; Arnold, S.

1990-01-01

A two-level model has previously been proposed for approximating the performance of a Viterbi decoder which encounters data received with periodically varying signal-to-noise ratio. Such cyclically gapped data is obtained from the Very Large Array (VLA), either operating as a stand-alone system or arrayed with Goldstone. This approximate model predicts that the decoder error rate will vary periodically between two discrete levels with the same period as the gap cycle. It further predicts that the length of the gapped portion of the decoder error cycle for a constraint length K decoder will be about K-1 bits shorter than the actual duration of the gap. The two-level model for Viterbi decoder performance with gapped data is subjected to detailed validation tests. Curves showing the cyclical behavior of the decoder error burst statistics are compared with the simple square-wave cycles predicted by the model. The validity of the model depends on a parameter often considered irrelevant in the analysis of Viterbi decoder performance, the overall scaling of the received signal or the decoder's branch-metrics. Three scaling alternatives are examined: optimum branch-metric scaling and constant branch-metric scaling combined with either constant noise-level scaling or constant signal-level scaling. The simulated decoder error cycle curves roughly verify the accuracy of the two-level model for both the case of optimum branch-metric scaling and the case of constant branch-metric scaling combined with constant noise-level scaling. However, the model is not accurate for the case of constant branch-metric scaling combined with constant signal-level scaling.

Model of the Dynamic Construction Process of Texts and Scaling Laws of Words Organization in Language Systems

PubMed Central

Li, Shan; Lin, Ruokuang; Bian, Chunhua; Ma, Qianli D. Y.

2016-01-01

Scaling laws characterize diverse complex systems in a broad range of fields, including physics, biology, finance, and social science. The human language is another example of a complex system of words organization. Studies on written texts have shown that scaling laws characterize the occurrence frequency of words, words rank, and the growth of distinct words with increasing text length. However, these studies have mainly concentrated on the western linguistic systems, and the laws that govern the lexical organization, structure and dynamics of the Chinese language remain not well understood. Here we study a database of Chinese and English language books. We report that three distinct scaling laws characterize words organization in the Chinese language. We find that these scaling laws have different exponents and crossover behaviors compared to English texts, indicating different words organization and dynamics of words in the process of text growth. We propose a stochastic feedback model of words organization and text growth, which successfully accounts for the empirically observed scaling laws with their corresponding scaling exponents and characteristic crossover regimes. Further, by varying key model parameters, we reproduce differences in the organization and scaling laws of words between the Chinese and English language. We also identify functional relationships between model parameters and the empirically observed scaling exponents, thus providing new insights into the words organization and growth dynamics in the Chinese and English language. PMID:28006026

Model of the Dynamic Construction Process of Texts and Scaling Laws of Words Organization in Language Systems.

PubMed

Li, Shan; Lin, Ruokuang; Bian, Chunhua; Ma, Qianli D Y; Ivanov, Plamen Ch

2016-01-01

Scaling laws characterize diverse complex systems in a broad range of fields, including physics, biology, finance, and social science. The human language is another example of a complex system of words organization. Studies on written texts have shown that scaling laws characterize the occurrence frequency of words, words rank, and the growth of distinct words with increasing text length. However, these studies have mainly concentrated on the western linguistic systems, and the laws that govern the lexical organization, structure and dynamics of the Chinese language remain not well understood. Here we study a database of Chinese and English language books. We report that three distinct scaling laws characterize words organization in the Chinese language. We find that these scaling laws have different exponents and crossover behaviors compared to English texts, indicating different words organization and dynamics of words in the process of text growth. We propose a stochastic feedback model of words organization and text growth, which successfully accounts for the empirically observed scaling laws with their corresponding scaling exponents and characteristic crossover regimes. Further, by varying key model parameters, we reproduce differences in the organization and scaling laws of words between the Chinese and English language. We also identify functional relationships between model parameters and the empirically observed scaling exponents, thus providing new insights into the words organization and growth dynamics in the Chinese and English language.

Finite-size scaling above the upper critical dimension in Ising models with long-range interactions

NASA Astrophysics Data System (ADS)

Flores-Sola, Emilio J.; Berche, Bertrand; Kenna, Ralph; Weigel, Martin

2015-01-01

The correlation length plays a pivotal role in finite-size scaling and hyperscaling at continuous phase transitions. Below the upper critical dimension, where the correlation length is proportional to the system length, both finite-size scaling and hyperscaling take conventional forms. Above the upper critical dimension these forms break down and a new scaling scenario appears. Here we investigate this scaling behaviour by simulating one-dimensional Ising ferromagnets with long-range interactions. We show that the correlation length scales as a non-trivial power of the linear system size and investigate the scaling forms. For interactions of sufficiently long range, the disparity between the correlation length and the system length can be made arbitrarily large, while maintaining the new scaling scenarios. We also investigate the behavior of the correlation function above the upper critical dimension and the modifications imposed by the new scaling scenario onto the associated Fisher relation.

Generalized scaling of seasonal thermal stratification in lakes

NASA Astrophysics Data System (ADS)

Shatwell, T.; Kirillin, G.

2016-12-01

The mixing regime is fundamental to the biogeochemisty and ecology of lakes because it determines the vertical transport of matter such as gases, nutrients, and organic material. Whereas shallow lakes are usually polymictic and regularly mix to the bottom, deep lakes tend to stratify seasonally, separating surface water from deep sediments and deep water from the atmosphere. Although empirical relationships exist to predict the mixing regime, a physically based, quantitative criterion is lacking. Here we review our recent research on thermal stratification in lakes at the transition between polymictic and stratified regimes. Using the mechanistic balance between potential and kinetic energy in terms of the Richardson number, we derive a generalized physical scaling for seasonal stratification in a closed lake basin. The scaling parameter is the critical mean basin depth that delineates polymictic and seasonally stratified lakes based on lake water transparency (Secchi depth), lake length, and an annual mean estimate for the Monin-Obukhov length. We validated the scaling on available data of 374 global lakes using logistic regression and found it to perform better than other criteria including a conventional open basin scaling or a simple depth threshold. The scaling has potential applications in estimating large scale greenhouse gas fluxes from lakes because the required inputs, like water transparency and basin morphology, can be acquired using the latest remote sensing technologies. The generalized scaling is universal for freshwater lakes and allows the seasonal mixing regime to be estimated without numerically solving the heat transport equations.

Theory based scaling of edge turbulence and implications for the scrape-off layer width

NASA Astrophysics Data System (ADS)

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)] is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database [Zweben et al., Nucl. Fusion 55, 093035 (2015)]. These are compared with theoretical estimates for drift and interchange rates, profile modification saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λq and its scaling. An explicit proportionality of the width λq to the safety factor and major radius (qR) is obtained under these conditions. Quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λq in NSTX, at least for high plasma current discharges.

Theory based scaling of edge turbulence and implications for the scrape-off layer width

DOE PAGES

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database. These are compared with theoretical estimates for drift and interchange rates, profile modificationmore » saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λ q and its scaling. An explicit proportionality of the width λ q to the safety factor and major radius (qR) is obtained under these conditions. Lastly, quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λ q in NSTX, at least for high plasma current discharges.« less

Finite-size scaling analysis on the phase transition of a ferromagnetic polymer chain model

NASA Astrophysics Data System (ADS)

Luo, Meng-Bo

2006-01-01

The finite-size scaling analysis method is applied to study the phase transition of a self-avoiding walking polymer chain with spatial nearest-neighbor ferromagnetic Ising interaction on the simple cubic lattice. Assuming the scaling M2(T,n)=n-2β/ν[Φ0+Φ1n1/ν(T-Tc)+O(n2/ν(T-Tc)2)] with the square magnetization M2 as the order parameter and the chain length n as the size, we estimate the second-order phase-transition temperature Tc=1.784J/kB and critical exponents 2β/ν≈0.668 and ν ≈1.0. The self-diffusion constant and the chain dimensions ⟨R2⟩ and ⟨S2⟩ do not obey such a scaling law.

Effects of a finite outer scale on the measurement of atmospheric-turbulence statistics with a Hartmann wave-front sensor.

PubMed

Feng, Shen; Wenhan, Jiang

2002-06-10

Phase-structure and aperture-averaged slope-correlated functions with a finite outer scale are derived based on the Taylor hypothesis and a generalized spectrum, such as the von Kármán modal. The effects of the finite outer scale on measuring and determining the character of atmospheric-turbulence statistics are shown especially for an approximately 4-m class telescope and subaperture. The phase structure function and atmospheric coherent length based on the Kolmogorov model are approximations of the formalism we have derived. The analysis shows that it cannot be determined whether the deviation from the power-law parameter of Kolmogorov turbulence is caused by real variations of the spectrum or by the effect of the finite outer scale.

Scaling of Directed Dynamical Small-World Networks with Random Responses

NASA Astrophysics Data System (ADS)

Zhu, Chen-Ping; Xiong, Shi-Jie; Tian, Ying-Jie; Li, Nan; Jiang, Ke-Sheng

2004-05-01

A dynamical model of small-world networks, with directed links which describe various correlations in social and natural phenomena, is presented. Random responses of sites to the input message are introduced to simulate real systems. The interplay of these ingredients results in the collective dynamical evolution of a spinlike variable S(t) of the whole network. The global average spreading length s and average spreading time s are found to scale as p-αln(N with different exponents. Meanwhile, S(t) behaves in a duple scaling form for N≫N*: S˜f(p-βqγt˜), where p and q are rewiring and external parameters, α, β, and γ are scaling exponents, and f(t˜) is a universal function. Possible applications of the model are discussed.

Hydraulic Tomography and the Curse of Storativity

NASA Astrophysics Data System (ADS)

Cirpka, O. A.; Li, W.; Englert, A.

2006-12-01

Pumping tests are among the most common techniques for hydrogeological site investigation. Their traditional analysis is based on fitting analytical expressions to measured time series of drawdown. These expressions were derived for homogeneous conditions, whereas all natural aquifers are heterogeneous. The mentioned conceptual inconsistency complicates the hydrogeological interpretation of the obtained coefficients. In particularly, it has been shown that the heterogeneity of transmissivity is aliased to variability in the estimated storativity. In hydraulic tomography, multiple pumping tests are jointly analyzed. The hydraulic parameters to be estimated are allowed to fluctuate in space. For regularization, a geostatistical smoothness criterion may be introduced. Thus, the inversion results in the most likely spatial distribution of parameters that is consistent with the drawdown measurements and follows a predefined geostatistical model. Applying the restricted maximum likelihood approach, the parameters of the prior covariance function (i.e., the prior variance and correlation length) can be inferred from the data as well. We have applied the quasi-linear geostatistical approach of inverse modeling to drawdown measurements of multiple, overlapping pumping tests performed at the test site Krauthausen near Jülich, Germany. To reduce the computational costs, we have characterized the drawdown curves by their temporal moments. In the estimation of the geostatistical parameters, the measurement error of heads turned out to be of vital importance. The less we trust the data, the larger is the estimated correlation length, resulting in a more uniform distribution of transmissivity. Similar to conventional pumping test analysis, the data analysis point to a high variability of storativity although the properties making up storativity are known to be only mildly heterogeneous. We conjecture that the unresolved small-scale spatial variability of conductivity is mapped to variability of storativity. This is rather unfortunate since reliable field data on the variability of storativity are missing. The study underscores that structural information is difficult to extract from hydraulic data alone. Information on length scales and major deterministic features may be gained by geophysical surveying, even if rock-laws directly relating geophysical to hydraulic properties are considered unreliable.

Engineering Digestion: Multiscale Processes of Food Digestion.

PubMed

Bornhorst, Gail M; Gouseti, Ourania; Wickham, Martin S J; Bakalis, Serafim

2016-03-01

Food digestion is a complex, multiscale process that has recently become of interest to the food industry due to the developing links between food and health or disease. Food digestion can be studied by using either in vitro or in vivo models, each having certain advantages or disadvantages. The recent interest in food digestion has resulted in a large number of studies in this area, yet few have provided an in-depth, quantitative description of digestion processes. To provide a framework to develop these quantitative comparisons, a summary is given here between digestion processes and parallel unit operations in the food and chemical industry. Characterization parameters and phenomena are suggested for each step of digestion. In addition to the quantitative characterization of digestion processes, the multiscale aspect of digestion must also be considered. In both food systems and the gastrointestinal tract, multiple length scales are involved in food breakdown, mixing, absorption. These different length scales influence digestion processes independently as well as through interrelated mechanisms. To facilitate optimized development of functional food products, a multiscale, engineering approach may be taken to describe food digestion processes. A framework for this approach is described in this review, as well as examples that demonstrate the importance of process characterization as well as the multiple, interrelated length scales in the digestion process. © 2016 Institute of Food Technologists®

Modeling and analysis of sub-surface leakage current in nano-MOSFET under cutoff regime

NASA Astrophysics Data System (ADS)

Swami, Yashu; Rai, Sanjeev

2017-02-01

The high leakage current in nano-meter regimes is becoming a significant portion of power dissipation in nano-MOSFET circuits as threshold voltage, channel length, and gate oxide thickness are scaled down to nano-meter range. Precise leakage current valuation and meticulous modeling of the same at nano-meter technology scale is an increasingly a critical work in designing the low power nano-MOSFET circuits. We present a specific compact model for sub-threshold regime leakage current in bulk driven nano-MOSFETs. The proposed logical model is instigated and executed into the latest updated PTM bulk nano-MOSFET model and is found to be in decent accord with technology-CAD simulation data. This paper also reviews various transistor intrinsic leakage mechanisms for nano-MOSFET exclusively in weak inversion, like drain-induced barricade lowering (DIBL), gate-induced drain leakage (GIDL), gate oxide tunneling (GOT) leakage etc. The root cause of the sub-surface leakage current is mainly due to the nano-scale short channel length causing source-drain coupling even in sub-threshold domain. Consequences leading to carriers triumphing the barricade between the source and drain. The enhanced model effectively considers the following parameter dependence in the account for better-quality value-added results like drain-to-source bias (VDS), gate-to-source bias (VGS), channel length (LG), source/drain junction depth (Xj), bulk doping concentration (NBULK), and operating temperature (Top).

Small Angle Neutron Scattering Observation of Chain Retraction after a Large Step Deformation

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

Blanchard, A.; Heinrich, M.; Pyckhout-Hintzen, W.

The process of retraction in entangled linear chains after a fast nonlinear stretch was detected from time-resolved but quenched small angle neutron scattering (SANS) experiments on long, well-entangled polyisoprene chains. The statically obtained SANS data cover the relevant time regime for retraction, and they provide a direct, microscopic verification of this nonlinear process as predicted by the tube model. Clear, quantitative agreement is found with recent theories of contour length fluctuations and convective constraint release, using parameters obtained mainly from linear rheology. The theory captures the full range of scattering vectors once the crossover to fluctuations on length scales belowmore » the tube diameter is accounted for.« less

Subcritical crack growth in fibrous materials

NASA Astrophysics Data System (ADS)

Santucci, S.; Cortet, P.-P.; Deschanel, S.; Vanel, L.; Ciliberto, S.

2006-05-01

We present experiments on the slow growth of a single crack in a fax paper sheet submitted to a constant force F. We find that statistically averaged crack growth curves can be described by only two parameters: the mean rupture time τ and a characteristic growth length ζ. We propose a model based on a thermally activated rupture process that takes into account the microstructure of cellulose fibers. The model is able to reproduce the shape of the growth curve, the dependence of ζ on F as well as the effect of temperature on the rupture time τ. We find that the length scale at which rupture occurs in this model is consistently close to the diameter of cellulose microfibrils.

Aspects of noncommutative (1+1)-dimensional black holes

NASA Astrophysics Data System (ADS)

Mureika, Jonas R.; Nicolini, Piero

2011-08-01

We present a comprehensive analysis of the spacetime structure and thermodynamics of (1+1)-dimensional black holes in a noncommutative framework. It is shown that a wider variety of solutions are possible than the commutative case considered previously in the literature. As expected, the introduction of a minimal length θ cures singularity pathologies that plague the standard two-dimensional general relativistic case, where the latter solution is recovered at large length scales. Depending on the choice of input parameters (black hole mass M, cosmological constant Λ, etc.), black hole solutions with zero, up to six, horizons are possible. The associated thermodynamics allows for the either complete evaporation, or the production of black hole remnants.

Hand grip strength and anthropometric characteristics in Italian female national basketball teams.

PubMed

Pizzigalli, Luisa; Micheletti Cremasco, Margherita; LA Torre, Antonio; Rainoldi, Alberto; Benis, Roberto

2017-05-01

The aim of this study was to investigate the influence of hand and body dimensions on hand grip strength and to define a reference scale for talent identification in basketball players. Body and hand anthropometric data and the maximal handgrip strength of 109 female Italian basketball National players (Under14-Seniores) were measured. Handgrip strength and arm length trend increased, raising the statistical significant differences only for players from the age of 19 (U20, Seniores) with respect to sub-elite groups (U14, U15) (P<0.05). Handgrip strength showed low positive correlations with height and Body Mass Index but a positive relationships with arm length (r=0.5; P<0.001). Findings underline training and years of practice have effects on increasing handgrip strength. Data show that to select female basketball players by arm length means selecting by handgrip strength. Thus it is possible to suggest that in addition to height, arm length could also be considered a useful parameter in young female talent identification.

Biodegradation of toluene by a lab-scale biofilter inoculated with Pseudomonas putida DK-1.

PubMed

Park, D W; Kim, S S; Haam, S; Ahn, I S; Kim, E B; Kim, W S

2002-03-01

The biodegradation of toluene by biofiltration inoculated with Pseudomonas putida DK-1 was investigated with variation of the several environmental parameters, such as temperature, bed length, gas flow rate and optimal humidity zone. The optimal temperature range to treat toluene gas was found to be 32-35 degrees C. Increasing the gas flow rate showed an inverse effect on the elimination capacity and the removal efficiency. The optimal gas flow rate was obtained at 65 ml min(-1) from the relation between the removal efficiency and the elimination capacity. The biodegradation rate of the toluene with respect to the bed lengths (3, 6, 9, 12 and 15 cm) increased up to 80 h but was then independent of the bed lengths after 80 h except for the 3 cm bed length. The elimination capacity was improved by about 70% compared with that reported in other literature and was also in agreement with theoretical models.

Characterization and long term operation of a novel superconducting undulator with 15 mm period length in a synchrotron light source

NASA Astrophysics Data System (ADS)

Casalbuoni, S.; Cecilia, A.; Gerstl, S.; Glamann, N.; Grau, A. W.; Holubek, T.; Meuter, C.; de Jauregui, D. Saez; Voutta, R.; Boffo, C.; Gerhard, Th.; Turenne, M.; Walter, W.

2016-11-01

A new cryogen-free full scale (1.5 m long) superconducting undulator with a period length of 15 mm (SCU15) has been successfully tested in the ANKA storage ring. This represents a very important milestone in the development of superconducting undulators for third and fourth generation light sources carried on by the collaboration between the Karlsruhe Institute of Technology and the industrial partner Babcock Noell GmbH. SCU15 is the first full length device worldwide that with beam reaches a higher peak field than what expected with the same geometry (vacuum gap and period length) with an ideal cryogenic permanent magnet undulator built with the best material available PrFeB. After a summary on the design and main parameters of the device, we present here the characterization in terms of spectral properties and the long term operation of the SCU15 in the ANKA storage ring.

Structure and mechanism of maximum stability of isolated alpha-helical protein domains at a critical length scale.

PubMed

Qin, Zhao; Fabre, Andrea; Buehler, Markus J

2013-05-01

The stability of alpha helices is important in protein folding, bioinspired materials design, and controls many biological properties under physiological and disease conditions. Here we show that a naturally favored alpha helix length of 9 to 17 amino acids exists at which the propensity towards the formation of this secondary structure is maximized. We use a combination of thermodynamical analysis, well-tempered metadynamics molecular simulation and statistical analyses of experimental alpha helix length distributions and find that the favored alpha helix length is caused by a competition between alpha helix folding, unfolding into a random coil and formation of higher-order tertiary structures. The theoretical result is suggested to be used to explain the statistical distribution of the length of alpha helices observed in natural protein structures. Our study provides mechanistic insight into fundamental controlling parameters in alpha helix structure formation and potentially other biopolymers or synthetic materials. The result advances our fundamental understanding of size effects in the stability of protein structures and may enable the design of de novo alpha-helical protein materials.

Competition of mesoscales and crossover to theta-point tricriticality in near-critical polymer solutions.

PubMed

Anisimov, M A; Kostko, A F; Sengers, J V; Yudin, I K

2005-10-22

The approach to asymptotic critical behavior in polymer solutions is governed by a competition between the correlation length of critical fluctuations diverging at the critical point of phase separation and an additional mesoscopic length scale, the radius of gyration. In this paper we present a theory for crossover between two universal regimes: a regime with Ising (fluctuation-induced) asymptotic critical behavior, where the correlation length prevails, and a mean-field tricritical regime with theta-point behavior controlled by the mesoscopic polymer chain. The theory yields a universal scaled description of existing experimental phase-equilibria data and is in excellent agreement with our light-scattering experiments on polystyrene solutions in cyclohexane with polymer molecular weights ranging from 2 x 10(5) up to 11.4 x 10(6). The experiments demonstrate unambiguously that crossover to theta-point tricriticality is controlled by a competition of the two mesoscales. The critical amplitudes deduced from our experiments depend on the polymer molecular weight as predicted by de Gennes [Phys. Lett. 26A, 313 (1968)]. Experimental evidence for the presence of logarithmic corrections to mean-field tricritical theta-point behavior in the molecular-weight dependence of the critical parameters is also presented.

Theory of polyelectrolytes in solvents.

PubMed

Chitanvis, Shirish M

2003-12-01

Using a continuum description, we account for fluctuations in the ionic solvent surrounding a Gaussian, charged chain and derive an effective short-ranged potential between the charges on the chain. This potential is repulsive at short separations and attractive at longer distances. The chemical potential can be derived from this potential. When the chemical potential is positive, it leads to a meltlike state. For a vanishingly low concentration of segments, this state exhibits scaling behavior for long chains. The Flory exponent characterizing the radius of gyration for long chains is calculated to be approximately 0.63, close to the classical value obtained for second order phase transitions. For short chains, the radius of gyration varies linearly with N, the chain length, and is sensitive to the parameters in the interaction potential. The linear dependence on the chain length N indicates a stiff behavior. The chemical potential associated with this interaction changes sign, when the screening length in the ionic solvent exceeds a critical value. This leads to condensation when the chemical potential is negative. In this state, it is shown using the mean-field approximation that spherical and toroidal condensed shapes can be obtained. The thickness of the toroidal polyelectrolyte is studied as a function of the parameters of the model, such as the ionic screening length. The predictions of this theory should be amenable to experimental verification.

Numerical Modeling Studies of Wake Vortex Transport and Evolution Within the Planetary Boundary Layer

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Arya, S. Pal; Kaplan, Michael L.; Shen, Shaohua

1998-01-01

In support of the wake vortex effect of the Terminal Area Productivity program, we have put forward four tasks to be accomplished in our proposal. The first task is validation of two-dimensional wake vortex-turbulence interaction. The second task is investigation of three-dimensional interaction between wake vortices and atmospheric boundary layer (ABL) turbulence. The third task is ABL studies. The, fourth task is addition of a Klemp-Durran condition at the top boundary for TASS model. The accomplishment of these tasks will increase our understanding of the dynamics of wake vortex and improve forecasting systems responsible for air safety and efficiency. The first two tasks include following three parts: (a) Determine significant length scale for vortex decay and transport, especially the length scales associated with the onset of Crow instability (Crow, 1970); (b) Study the effects of atmospheric turbulence on the decay of the wake vortices; and (c) Determine the relationships between decay rate, transport properties and atmospheric parameters based on large eddy simulation (LES) results and the observational data. These parameters may include turbulence kinetic energy, dissipation rate, wind shear and atmospheric stratification. The ABL studies cover LES modeling of turbulence structure within planetary boundary layer under transition and stable stratification conditions. Evidences have shown that the turbulence in the stable boundary layer can be highly intermittent and the length scales of eddies are very small compared to those in convective case. We proposed to develop a nesting grid mesh scheme and a modified Klemp-Durran conditions (Klemp and Wilhelmson, 1978) at the top boundary for TASS model to simulate planetary boundary layer under stable stratification conditions. During the past year, our group has made great efforts to carry out the above mentioned four tasks simultaneously. The work accomplished in the last year will be described in the next section.

Changes in Fundus Autofluorescence after Anti-vascular Endothelial Growth Factor According to the Type of Choroidal Neovascularization in Age-related Macular Degeneration.

PubMed

Lee, Ji Young; Chung, Hyewon; Kim, Hyung Chan

2016-02-01

To describe the changes of fundus autofluorescence (FAF) in patients with age-related macular degeneration before and after intravitreal injection of anti-vascular endothelial growth factor according to the type of choroidal neovascularization (CNV) and to evaluate the correlation of FAF with spectral domain optical coherence tomography (SD-OCT) parameters and vision. This was a retrospective study. Twenty-one treatment-naïve patients with neovascular age-related macular degeneration were included. Study eyes were divided into two groups according to the type of CNV. Fourteen eyes were type 1 CNV and seven eyes were type 2 CNV. All eyes underwent a complete ophthalmologic examination, including an assessment of best-corrected visual acuity, SD-OCT, fluorescein angiography, and FAF imaging, before and 3 months after intravitreal anti-vascular endothelial growth factor injection. Gray scales of FAF image for CNV areas, delineated as in fluorescein angiography, were analyzed using the ImageJ program, which were adjusted by comparison with normal background areas. Correlation of changes in FAF with changes in SD-OCT parameters, including CNV thickness, photoreceptor inner and outer segment junction disruption length, external limiting membrane disruption length, central macular thickness, subretinal fluid, and intraretinal fluid were analyzed. Eyes with both type 1 and type 2 CNV showed reduced FAF before treatment. The mean gray scales (%) of type 1 and type 2 CNV were 52.20% and 42.55%, respectively. The background values were 106.72 and 96.86. After treatment, the mean gray scales (%) of type 1 CNV and type 2 CNV were changed to 57.61% (p = 0.005) and 57.93% (p = 0.008), respectively. After treatment, CNV thickness, central macular thickness, and inner and outer segment junction disruption length were decreased while FAF increased. FAF was noted to be reduced in eyes with newly diagnosed wet age-related macular degeneration, but increased after anti-vascular endothelial growth factor therapy regardless of CNV lesion type.

A Multi-Scale Approach to Airway Hyperresponsiveness: From Molecule to Organ

PubMed Central

Lauzon, Anne-Marie; Bates, Jason H. T.; Donovan, Graham; Tawhai, Merryn; Sneyd, James; Sanderson, Michael J.

2012-01-01

Airway hyperresponsiveness (AHR), a characteristic of asthma that involves an excessive reduction in airway caliber, is a complex mechanism reflecting multiple processes that manifest over a large range of length and time scales. At one extreme, molecular interactions determine the force generated by airway smooth muscle (ASM). At the other, the spatially distributed constriction of the branching airways leads to breathing difficulties. Similarly, asthma therapies act at the molecular scale while clinical outcomes are determined by lung function. These extremes are linked by events operating over intermediate scales of length and time. Thus, AHR is an emergent phenomenon that limits our understanding of asthma and confounds the interpretation of studies that address physiological mechanisms over a limited range of scales. A solution is a modular computational model that integrates experimental and mathematical data from multiple scales. This includes, at the molecular scale, kinetics, and force production of actin-myosin contractile proteins during cross-bridge and latch-state cycling; at the cellular scale, Ca2+ signaling mechanisms that regulate ASM force production; at the tissue scale, forces acting between contracting ASM and opposing viscoelastic tissue that determine airway narrowing; at the organ scale, the topographic distribution of ASM contraction dynamics that determine mechanical impedance of the lung. At each scale, models are constructed with iterations between theory and experimentation to identify the parameters that link adjacent scales. This modular model establishes algorithms for modeling over a wide range of scales and provides a framework for the inclusion of other responses such as inflammation or therapeutic regimes. The goal is to develop this lung model so that it can make predictions about bronchoconstriction and identify the pathophysiologic mechanisms having the greatest impact on AHR and its therapy. PMID:22701430

Length scale effects and multiscale modeling of thermally induced phase transformation kinetics in NiTi SMA

NASA Astrophysics Data System (ADS)

Frantziskonis, George N.; Gur, Sourav

2017-06-01

Thermally induced phase transformation in NiTi shape memory alloys (SMAs) shows strong size and shape, collectively termed length scale effects, at the nano to micrometer scales, and that has important implications for the design and use of devices and structures at such scales. This paper, based on a recently developed multiscale model that utilizes molecular dynamics (MDs) simulations at small scales and MD-verified phase field (PhF) simulations at larger scales, reports results on specific length scale effects, i.e. length scale effects in martensite phase fraction (MPF) evolution, transformation temperatures (martensite and austenite start and finish) and in the thermally cyclic transformation between austenitic and martensitic phase. The multiscale study identifies saturation points for length scale effects and studies, for the first time, the length scale effect on the kinetics (i.e. developed internal strains) in the B19‧ phase during phase transformation. The major part of the work addresses small scale single crystals in specific orientations. However, the multiscale method is used in a unique and novel way to indirectly study length scale and grain size effects on evolution kinetics in polycrystalline NiTi, and to compare the simulation results to experiments. The interplay of the grain size and the length scale effect on the thermally induced MPF evolution is also shown in this present study. Finally, the multiscale coupling results are employed to improve phenomenological material models for NiTi SMA.

Structure and dynamics of hyaluronic acid semidilute solutions: a dielectric spectroscopy study.

PubMed

Vuletić, T; Dolanski Babić, S; Ivek, T; Grgicin, D; Tomić, S; Podgornik, R

2010-07-01

Dielectric spectroscopy is used to investigate fundamental length scales describing the structure of hyaluronic acid sodium salt (Na-HA) semidilute aqueous solutions. In salt-free regime, the length scale of the relaxation mode detected in MHz range scales with HA concentration as c(HA)(-0.5) and corresponds to the de Gennes-Pfeuty-Dobrynin correlation length of polyelectrolytes in semidilute solution. The same scaling was observed for the case of long, genomic DNA. Conversely, the length scale of the mode detected in kilohertz range also varies with HA concentration as c(HA)(-0.5) which differs from the case of DNA (c(DNA)(-0.25)). The observed behavior suggests that the relaxation in the kilohertz range reveals the de Gennes-Dobrynin renormalized Debye screening length, and not the average size of the chain, as the pertinent length scale. Similarly, with increasing added salt the electrostatic contribution to the HA persistence length is observed to scale as the Debye length, contrary to scaling pertinent to the Odijk-Skolnick-Fixman electrostatic persistence length observed in the case of DNA. We argue that the observed features of the kilohertz range relaxation are due to much weaker electrostatic interactions that lead to the absence of Manning condensation as well as a rather high flexibility of HA as compared to DNA.

Physics of Majorana modes in interacting helical liquid.

PubMed

Sarkar, Sujit

2016-07-27

As an attempt to understand and search for the existence of Majorana zero mode, we study the topological quantum phase transition and also the nature of this transition in helical liquid system, which appears in different physical systems. We present Majorana-Ising transition along with the phase boundary in the presence of interaction. We show the appearance of Majorana mode under the renormalization of the parameters of the system and also the topological protection of it. We present the length scale dependent condition for the appearance of Majorana edge state and also the absence of edge state for a certain regime of parameter space.

A quasi-crisis

NASA Astrophysics Data System (ADS)

Wang, Ying-Mei; Wang, Wen-Xiu; Chen, He-Sheng; Zhang, Kai; Jiang, Yu-Mei; Wang, Xu-Ming; He, Da-Ren

2002-03-01

A system concatenated by two area-preserving maps may be addressed as "quasi- dissipative," since such a system can display dissipative behaviors^1. This is due to noninvertibility induced by discontinuity in the system function. In such a system, the image set of the discontinuous border forms a chaotic quasi-attractor. At a critical control parameter value the quasi-attractor suddenly vanishes. The chaotic iterations escape, via a leaking hole, to an emergent period-8 elliptic island. The hole is the intersection of the chaotic quasi-attractor and the period-8 island. The chaotic quasi-attractor thus changes to chaotic quasi-transients. The scaling behavior that drives the quasi-crisis has been investigated numerically. It reads: ∝ (p-p_c)^-ν , where is defined as the averaged length of quasi-transients. The scaling exponent ν=1.66 ± 0.04. The critical parameter value equals p_c=-1.0069799. ^1 J. Wang et al., Phys.Rev.E, 64(2001)026202.

On the nonlinear dynamics of trolling-mode AFM: Analytical solution using multiple time scales method

NASA Astrophysics Data System (ADS)

Sajjadi, Mohammadreza; Pishkenari, Hossein Nejat; Vossoughi, Gholamreza

2018-06-01

Trolling mode atomic force microscopy (TR-AFM) has resolved many imaging problems by a considerable reduction of the liquid-resonator interaction forces in liquid environments. The present study develops a nonlinear model of the meniscus force exerted to the nanoneedle of TR-AFM and presents an analytical solution to the distributed-parameter model of TR-AFM resonator utilizing multiple time scales (MTS) method. Based on the developed analytical solution, the frequency-response curves of the resonator operation in air and liquid (for different penetration length of the nanoneedle) are obtained. The closed-form analytical solution and the frequency-response curves are validated by the comparison with both the finite element solution of the main partial differential equations and the experimental observations. The effect of excitation angle of the resonator on horizontal oscillation of the probe tip and the effect of different parameters on the frequency-response of the system are investigated.

Towards an optimal contact metal for CNTFETs.

PubMed

Fediai, Artem; Ryndyk, Dmitry A; Seifert, Gotthard; Mothes, Sven; Claus, Martin; Schröter, Michael; Cuniberti, Gianaurelio

2016-05-21

Downscaling of the contact length Lc of a side-contacted carbon nanotube field-effect transistor (CNTFET) is challenging because of the rapidly increasing contact resistance as Lc falls below 20-50 nm. If in agreement with existing experimental results, theoretical work might answer the question, which metals yield the lowest CNT-metal contact resistance and what physical mechanisms govern the geometry dependence of the contact resistance. However, at the scale of 10 nm, parameter-free models of electron transport become computationally prohibitively expensive. In our work we used a dedicated combination of the Green function formalism and density functional theory to perform an overall ab initio simulation of extended CNT-metal contacts of an arbitrary length (including infinite), a previously not achievable level of simulations. We provide a systematic and comprehensive discussion of metal-CNT contact properties as a function of the metal type and the contact length. We have found and been able to explain very uncommon relations between chemical, physical and electrical properties observed in CNT-metal contacts. The calculated electrical characteristics are in reasonable quantitative agreement and exhibit similar trends as the latest experimental data in terms of: (i) contact resistance for Lc = ∞, (ii) scaling of contact resistance Rc(Lc); (iii) metal-defined polarity of a CNTFET. Our results can guide technology development and contact material selection for downscaling the length of side-contacts below 10 nm.

Revealing Hidden Structural Order Controlling Both Fast and Slow Glassy Dynamics in Supercooled Liquids

NASA Astrophysics Data System (ADS)

Tong, Hua; Tanaka, Hajime

2018-01-01

The dynamics of a supercooled liquid near the glass transition is characterized by two-step relaxation, fast β and slow α relaxations. Because of the apparently disordered nature of glassy structures, there have been long debates over whether the origin of drastic slowing-down of the α relaxation accompanied by heterogeneous dynamics is thermodynamic or dynamic. Furthermore, it has been elusive whether there is any deep connection between fast β and slow α modes. To settle these issues, here we introduce a set of new structural order parameters characterizing sterically favored structures with high local packing capability, and then access structure-dynamics correlation by a novel nonlocal approach. We find that the particle mobility is under control of the static order parameter field. The fast β process is controlled by the instantaneous order parameter field locally, resulting in short-time particle-scale dynamics. Then the mobility field progressively develops with time t , following the initial order parameter field from disorder to more ordered regions. As is well known, the heterogeneity in the mobility field (dynamic heterogeneity) is maximized with a characteristic length ξ4, when t reaches the relaxation time τα. We discover that this mobility pattern can be predicted solely by a spatial coarse graining of the initial order parameter field at t =0 over a length ξ without any dynamical information. Furthermore, we find a relation ξ ˜ξ4, indicating that the static length ξ grows coherently with the dynamic one ξ4 upon cooling. This further suggests an intrinsic link between τα and ξ : the growth of the static length ξ is the origin of dynamical slowing-down. These we confirm for the first time in binary glass formers both in two and three spatial dimensions. Thus, a static structure has two intrinsic characteristic lengths, particle size and ξ , which control dynamics in local and nonlocal manners, resulting in the emergence of the two key relaxation modes, fast β and slow α processes, respectively. Because the two processes share a common structural origin, we can even predict a dynamic propensity pattern at long timescale from the fast β pattern. The presence of such intrinsic structure-dynamics correlation strongly indicates a thermodynamic nature of glass transition.

Forced reptation revealed by chain pull-out simulations.

PubMed

Bulacu, Monica; van der Giessen, Erik

2009-08-14

We report computation results obtained from extensive molecular dynamics simulations of tensile disentanglement of connector chains placed at the interface between two polymer bulks. Each polymer chain (either belonging to the bulks or being a connector) is treated as a sequence of beads interconnected by springs, using a coarse-grained representation based on the Kremer-Grest model, extended to account for stiffness along the chain backbone. Forced reptation of the connectors was observed during their disentanglement from the bulk chains. The extracted chains are clearly seen following an imaginary "tube" inside the bulks as they are pulled out. The entropic and energetic responses to the external deformation are investigated by monitoring the connector conformation tensor and the modifications of the internal parameters (bonds, bending, and torsion angles along the connectors). The work needed to separate the two bulks is computed from the tensile force induced during debonding in the connector chains. The value of the work reached at total separation is considered as the debonding energy G. The most important parameters controlling G are the length (n) of the chains placed at the interface and their areal density. Our in silico experiments are performed at relatively low areal density and are disregarded if chain scission occurs during disentanglement. As predicted by the reptation theory, for this pure pull-out regime, the power exponent from the scaling G proportional, variant n(a) is a approximately 2, irrespective of chain stiffness. Small variations are found when the connectors form different number of stitches at the interface, or when their length is randomly distributed in between the two bulks. Our results show that the effects of the number of stitches and of the randomness of the block lengths have to be considered together, especially when comparing with experiments where they cannot be controlled rigorously. These results may be significant for industrial applications, such reinforcement of polymer-polymer adhesion by connector chains, when incorporated as constitutive laws at higher time/length scales in finite element calculations.

Changes in arctic and boreal ecosystem productivity in response to changes in growing season length

NASA Astrophysics Data System (ADS)

Hmimina, G.; Yu, R.; Billesbach, D. P.; Huemmrich, K. F.; Gamon, J. A.

2017-12-01

Large-scale greening and browning trends have been reported in northern terrestrial ecosystems over the last two decades. The greening is interpreted as an increased productivity in response to increases in temperature. Boreal and arctic ecosystem productivity is expected to increase as the length of growing seasons increases, resulting in a bigger northern carbon sink pool. While evidences of such greening based on the use of remotely-sensed vegetation indices are compelling, analysis over the sparse network of flux tower sites available in northern latitudes paint a more complex story, and raise some issues as to whether vegetation indices based on NIR reflectance at large spatial scales are suited to the analysis of very fragmented landscapes that exhibit strong patterns in snow and standing water cover. In a broader sense, whether "greenness" is a sufficiently good proxy of ecosystem productivity in northern latitudes is unclear. The current work focused on deriving continuous estimates of ecosystem potential productivity and photosynthesis limitation over a network of flux towers, and on analyzing the relationships between potential yearly productivity and the length of the growing season over time and space. A novel partitioning method was used to derive ecophysiological parameters from sparse carbon fluxes measurements, and those parameters were then used to delimit the growing season and to estimate potential yearly productivity over a wide range of ecosystems. The relationships obtained between those two metrics were then computed for each of the 23 studied sites, exhibiting a wide range of different responses to changes in growing season length. While an overall significant increasing productivity trend was found (R²=0.12) suggesting increased productivity, the more northern sites exhibited a consistent decreasing trend (0.11 The attribution of these trends to either changes in potential productivity or productivity limitation by abiotic factors will be discussed, as well as the potential of extending this analysis over space by using remote-sensing data along with flux tower data.

All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect

DOE PAGES

Jungfleisch, Matthias B.; Zhang, Wei; Ding, Junjia; ...

2016-02-03

The understanding of spin dynamics in laterally confined structures on sub-micron length scales has become a significant aspect of the development of novel magnetic storage technologies. Numerous ferromagnetic resonance measurements, optical characterization by Kerr microscopy and Brillouin light scattering spectroscopy and x-ray studies were carried out to detect the dynamics in patterned magnetic antidot lattices. Here, we investigate Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices with different lattice parameters by electrical means. When the system is driven to resonance, a dc voltage across the length of the sample is detected that changes its sign upon field reversal, whichmore » is in agreement with a rectification mechanism based on the inverse spin Hall effect. Furthermore, we show that the voltage output scales linearly with the applied microwave drive in the investigated range of powers. Lastly, our findings have direct implications on the development of engineered magnonics applications and devices.« less

Analytical description of the breakup of liquid jets in air

NASA Technical Reports Server (NTRS)

Papageorgiou, Demetrios T.

1993-01-01

A viscous or inviscid cylindrical jet with surface tension in a vacuum tends to pinch due to the mechanism of capillary instability. Similarity solutions are constructed which describe this phenomenon as a critical time is encountered, for two physically distinct cases: inviscid jets governed by the Euler equations and highly viscous jets governed by the Stokes equations. In both cases the only assumption imposed is that at the time of pinching the jet shape has a radial length scale which is smaller than the axial length scale. For the inviscid case, we show that our solution corresponds exactly to one member of the one-parameter family of solutions obtained from slender jet theories and the shape of the jet is locally concave at breakup. For highly viscous jets our theory predicts local shapes which are monotonic increasing or decreasing indicating the formation of a mother drop connected to the jet by a thin fluid tube. This qualitative behavior is in complete agreement with both direct numerical simulations and experimental observations.

Configurations and Dynamics of Semi-Flexible Polymers in Good and Poor Solvents

NASA Astrophysics Data System (ADS)

Larson, Ronald

We develop coarse-graining procedures for determining the conformational and dynamic behavior of semi-flexible chains with and without flow using Brownian dynamics (BD) simulations that are insensitive to the degree of coarse-graining. In the absence of flow, in a poor solvent, we find three main collapsed states: torus, bundle, and globule over a range of dimensionless ratios of the three energy parameters, namely solvent-polymer surface energy, energy of polymer folds, and polymer bending energy or persistence length. A theoretical phase diagram, confirmed by BD simulations, captures the general phase behavior of a single long chain (>10 Kuhn lengths) at moderately high (order unity) dimensionless temperature, which is the ratio of thermal energy to the attractive interaction between neighboring monomers. We also find converged results for polymer conformations in shear or extensional flow in solvents of various qualities and determine scaling laws for chain dimensions for low, moderate, and high Weissenberg numbers Wi. We also derive scaling laws to describe chains dimensions and tumbling rates in these regimes.

Parameter identification of JONSWAP spectrum acquired by airborne LIDAR

NASA Astrophysics Data System (ADS)

Yu, Yang; Pei, Hailong; Xu, Chengzhong

2017-12-01

In this study, we developed the first linear Joint North Sea Wave Project (JONSWAP) spectrum (JS), which involves a transformation from the JS solution to the natural logarithmic scale. This transformation is convenient for defining the least squares function in terms of the scale and shape parameters. We identified these two wind-dependent parameters to better understand the wind effect on surface waves. Due to its efficiency and high-resolution, we employed the airborne Light Detection and Ranging (LIDAR) system for our measurements. Due to the lack of actual data, we simulated ocean waves in the MATLAB environment, which can be easily translated into industrial programming language. We utilized the Longuet-Higgin (LH) random-phase method to generate the time series of wave records and used the fast Fourier transform (FFT) technique to compute the power spectra density. After validating these procedures, we identified the JS parameters by minimizing the mean-square error of the target spectrum to that of the estimated spectrum obtained by FFT. We determined that the estimation error is relative to the amount of available wave record data. Finally, we found the inverse computation of wind factors (wind speed and wind fetch length) to be robust and sufficiently precise for wave forecasting.

Studies on the dynamic stability of an axially moving nanobeam based on the nonlocal strain gradient theory

NASA Astrophysics Data System (ADS)

Wang, Jing; Shen, Huoming; Zhang, Bo; Liu, Juan

2018-06-01

In this paper, we studied the parametric resonance issue of an axially moving viscoelastic nanobeam with varying velocity. Based on the nonlocal strain gradient theory, we established the transversal vibration equation of the axially moving nanobeam and the corresponding boundary condition. By applying the average method, we obtained a set of self-governing ordinary differential equations when the excitation frequency of the moving parameters is twice the intrinsic frequency or near the sum of certain second-order intrinsic frequencies. On the plane of parametric excitation frequency and excitation amplitude, we can obtain the instability region generated by the resonance, and through numerical simulation, we analyze the influence of the scale effect and system parameters on the instability region. The results indicate that the viscoelastic damping decreases the resonance instability region, and the average velocity and stiffness make the instability region move to the left- and right-hand sides. Meanwhile, the scale effect of the system is obvious. The nonlocal parameter exhibits not only the stiffness softening effect but also the damping weakening effect, while the material characteristic length parameter exhibits the stiffness hardening effect and damping reinforcement effect.

Charged fixed point in the Ginzburg-Landau superconductor and the role of the Ginzburg parameter /κ

NASA Astrophysics Data System (ADS)

Kleinert, Hagen; Nogueira, Flavio S.

2003-02-01

We present a semi-perturbative approach which yields an infrared-stable fixed point in the Ginzburg-Landau for N=2, where N/2 is the number of complex components. The calculations are done in d=3 dimensions and below Tc, where the renormalization group functions can be expressed directly as functions of the Ginzburg parameter κ which is the ratio between the two fundamental scales of the problem, the penetration depth λ and the correlation length ξ. We find a charged fixed point for κ>1/ 2, that is, in the type II regime, where Δκ≡κ-1/ 2 is shown to be a natural expansion parameter. This parameter controls a momentum space instability in the two-point correlation function of the order field. This instability appears at a non-zero wave-vector p0 whose magnitude scales like ˜ Δκ β¯, with a critical exponent β¯=1/2 in the one-loop approximation, a behavior known from magnetic systems with a Lifshitz point in the phase diagram. This momentum space instability is argued to be the origin of the negative η-exponent of the order field.

Patterning at the 10 nanometer length scale using a strongly segregating block copolymer thin film and vapor phase infiltration of inorganic precursors

NASA Astrophysics Data System (ADS)

Choi, Jonathan W.; Li, Zhaodong; Black, Charles T.; Sweat, Daniel P.; Wang, Xudong; Gopalan, Padma

2016-06-01

In this work, we demonstrate the use of self-assembled thin films of the cylinder-forming block copolymer poly(4-tert-butylstyrene-block-2-vinylpyridine) to pattern high density features at the 10 nm length scale. This material's large interaction parameter facilitates pattern formation in single-digit nanometer dimensions. This block copolymer's accessible order-disorder transition temperature allows thermal annealing to drive the assembly of ordered 2-vinylpyridine cylinders that can be selectively complexed with the organometallic precursor trimethylaluminum. This unique chemistry converts organic 2-vinylpyridine cylinders into alumina nanowires with diameters ranging from 8 to 11 nm, depending on the copolymer molecular weight. Graphoepitaxy of this block copolymer aligns and registers sub-12 nm diameter nanowires to larger-scale rectangular, curved, and circular features patterned by optical lithography. The alumina nanowires function as a robust hard mask to withstand the conditions required for patterning the underlying silicon by plasma etching. We conclude with a discussion of some of the challenges that arise with using block copolymers for patterning at sub-10 nm feature sizes.In this work, we demonstrate the use of self-assembled thin films of the cylinder-forming block copolymer poly(4-tert-butylstyrene-block-2-vinylpyridine) to pattern high density features at the 10 nm length scale. This material's large interaction parameter facilitates pattern formation in single-digit nanometer dimensions. This block copolymer's accessible order-disorder transition temperature allows thermal annealing to drive the assembly of ordered 2-vinylpyridine cylinders that can be selectively complexed with the organometallic precursor trimethylaluminum. This unique chemistry converts organic 2-vinylpyridine cylinders into alumina nanowires with diameters ranging from 8 to 11 nm, depending on the copolymer molecular weight. Graphoepitaxy of this block copolymer aligns and registers sub-12 nm diameter nanowires to larger-scale rectangular, curved, and circular features patterned by optical lithography. The alumina nanowires function as a robust hard mask to withstand the conditions required for patterning the underlying silicon by plasma etching. We conclude with a discussion of some of the challenges that arise with using block copolymers for patterning at sub-10 nm feature sizes. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr01409g

Continuous micron-scaled rope engineering using a rotating multi-nozzle electrospinning emitter

NASA Astrophysics Data System (ADS)

Zhang, Chunchen; Gao, Chengcheng; Chang, Ming-Wei; Ahmad, Zeeshan; Li, Jing-Song

2016-10-01

Electrospinning (ES) enables simple production of fibers for broad applications (e.g., biomedical engineering, energy storage, and electronics). However, resulting structures are predominantly random; displaying significant disordered fiber entanglement, which inevitably gives rise to structural variations and reproducibility on the micron scale. Surface and structural features on this scale are critical for biomaterials, tissue engineering, and pharmaceutical sciences. In this letter, a modified ES technique using a rotating multi-nozzle emitter is developed and utilized to fabricate continuous micron-scaled polycaprolactone (PCL) ropes, providing control on fiber intercalation (twist) and structural order. Micron-scaled ropes comprising 312 twists per millimeter are generated, and rope diameter and pitch length are regulated using polymer concentration and process parameters. Electric field simulations confirm vector and distribution mechanisms, which influence fiber orientation and deposition during the process. The modified fabrication system provides much needed control on reproducibility and fiber entanglement which is crucial for electrospun biomedical materials.

Rupture dynamics along bimaterial interfaces: a parametric study of the coupling between interfacial sliding and normal traction perturbation

NASA Astrophysics Data System (ADS)

Scala, Antonio; Festa, Gaetano; Vilotte, Jean-Pierre

2017-04-01

Earthquake ruptures often develop along faults separating materials with dissimilar elastic properties. Due to the broken symmetry, the propagation of the rupture along the bimaterial interface is driven by the coupling between interfacial sliding and normal traction perturbations. We numerically investigate in-plane rupture growth along a planar interface, under slip weakening friction, separating two dissimilar isotropic linearly elastic half-spaces. We perform a parametric study of the classical Prakash-Clifton regularisation for different material contrasts. In particular mesh-dependence and regularisation-dependence of the numerical solutions are analysed in this parameter space. When regularisation involves a slip-rate dependent relaxation time, a characteristic sliding distance is identified below which numerical solutions no longer depend on the regularisation parameter, i.e. they are consistent solutions of the same physical problem. Such regularisation provides an adaptive high-frequency filter of the slip-induced normal traction perturbations, following the dynamic shrinking of the dissipation zone during the acceleration phase. In contrast, regularisation involving a constant relaxation time leads to numerical solutions that always depend on the regularisation parameter since it fails adapting to the shrinking of the process zone. Dynamic regularisation is further investigated using a non-local regularisation based on a relaxation time that depends on the dynamic length of the dissipation zone. Such reformulation is shown to provide similar results as the dynamic time scale regularisation proposed by Prakash-Clifton when slip rate is replaced by the maximum slip rate along the sliding interface. This leads to the identification of a dissipative length scale associated with the coupling between interfacial sliding and normal traction perturbations, together with a scaling law between the maximum slip rate and the dynamic size of the process zone during the rupture propagation. Dynamic time scale regularisation is show to provide mesh-independent and physically well-posed numerical solutions during the acceleration phase toward an asymptotic speed. When generalised Rayleigh wave does not exist, numerical solutions are shown to tend toward an asymptotic velocity higher than the slowest shear wave speed. When generalised Rayleigh wave speed exists, as numerical solutions tend toward this velocity, increasing spurious oscillations develop and solutions become unstable. In this regime regularisation dependent and unstable finite-size pulses may be generated. This instability is associated with the singular behaviour of the slip-induced normal traction perturbations, and of the slip rate at the rupture front, in relation with complete shrinking of the dissipation zone. This phase requires to be modelled either by more complex interface constitutive laws involving velocity-strengthening effects that may stabilize short wavelength interfacial propagating modes or by considering non-ideal interfaces that introduce a new length scale in the problem that may promote selection and stabilization of the slip pulses.

Confirmation of general relativity on large scales from weak lensing and galaxy velocities.

PubMed

Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uros; Baldauf, Tobias; Gunn, James E; Lombriser, Lucas; Smith, Robert E

2010-03-11

Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, E(G), that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to 'galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of E(G) different from the general relativistic prediction because, in these theories, the 'gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that E(G) = 0.39 +/- 0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of E(G) approximately 0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f(R) theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.

Confirmation of general relativity on large scales from weak lensing and galaxy velocities

NASA Astrophysics Data System (ADS)

Reyes, Reinabelle; Mandelbaum, Rachel; Seljak, Uros; Baldauf, Tobias; Gunn, James E.; Lombriser, Lucas; Smith, Robert E.

2010-03-01

Although general relativity underlies modern cosmology, its applicability on cosmological length scales has yet to be stringently tested. Such a test has recently been proposed, using a quantity, EG, that combines measures of large-scale gravitational lensing, galaxy clustering and structure growth rate. The combination is insensitive to `galaxy bias' (the difference between the clustering of visible galaxies and invisible dark matter) and is thus robust to the uncertainty in this parameter. Modified theories of gravity generally predict values of EG different from the general relativistic prediction because, in these theories, the `gravitational slip' (the difference between the two potentials that describe perturbations in the gravitational metric) is non-zero, which leads to changes in the growth of structure and the strength of the gravitational lensing effect. Here we report that EG = 0.39+/-0.06 on length scales of tens of megaparsecs, in agreement with the general relativistic prediction of EG~0.4. The measured value excludes a model within the tensor-vector-scalar gravity theory, which modifies both Newtonian and Einstein gravity. However, the relatively large uncertainty still permits models within f() theory, which is an extension of general relativity. A fivefold decrease in uncertainty is needed to rule out these models.

Ambient temperature effects on growth of milkfish (Chanos chanos) at aquaculture scale in Blanakan, West Java

NASA Astrophysics Data System (ADS)

A'yun, Q.; Takarina, N. D.

2017-07-01

Growth and survival of fishes can be influenced by temperature [1]. Variation among size like weight and length could be the preference how temperature works on growth of fishes [2]. This could be key factor in determining in production as well as market demand since people like heavy and large fishes. The main purpose of this study was to determine the effects of temperature on the growth of milkfish (Chanos Chanos) on weight and length parameters in fish farms Blanakan. This study conducted to assess the optimal temperature for the growth of fish of different sizes to optimize the culture conditions for raising milkfishes in scale cultivation in Blanakan, West Java. Milkfishes were reared in the aquaculture Blanakan ponds because they can adapt very well. The weight and length of milkfishes were measured together with water temperature. The results showed the temperature min (tmin) and max (tmax) were ranged from 29-35 °C. Based on the result, there were significant differences in mean weight (p = 0.00) between temperature with the fish reared in tmax group having the lowest mean weight (99.87±11.51 g) and fish reared in tmin group having the highest mean weight (277.17±33.76 g). Likewise, the significant differences were also observed in mean length (p = 0.00) between temperature with the fish reared in tmax group having the lowest mean length (176.50±12.50 mm) and fish reared in tmin group having the highest mean length (183.60±23.86 mm). Therefore, this paper confirmed the significant effects of temperature on the fish growth reared in aquaculture ponds. More, maintaining aquaculture to lower temperature can be considered as way to keep growth of milkfish well.

On the development and global oscillations of cometary ionospheres

NASA Technical Reports Server (NTRS)

Houpis, H. L. F.; Mendis, D. A.

1981-01-01

Representing the cometary ionosphere by a single fluid model characterized by an average ionization time scale, both the ionosphere's development as a comet approaches the sun and its response to sudden changes in solar wind conditions are investigated. Three different nuclear sizes (small, average, very large) and three different modes of energy addition to the atmosphere (adiabatic, isothermal, suprathermal) are considered. It is found that the crucial parameter determining both the nature and the size of the ionosphere is the average ionization time scale within the ionosphere. Two different scales are identified. It is noted that the ionosphere can also be characterized by the relative sizes of three different scale lengths: the neutral standoff distance from the nucleus, the ion standoff distance from the nucleus, and the nuclear distance at which the ions and the neutrals decouple collisionally.

Simulation of double layers in a model auroral circuit with nonlinear impedance

NASA Technical Reports Server (NTRS)

Smith, R. A.

1986-01-01

A reduced circuit description of the U-shaped potential structure of a discrete auroral arc, consisting of the flank transmission line plus parallel-electric-field region, is used to provide the boundary condition for one-dimensional simulations of the double-layer evolution. The model yields asymptotic scalings of the double-layer potential, as a function of an anomalous transport coefficient alpha and of the perpendicular length scale l(a) of the arc. The arc potential phi(DL) scales approximately linearly with alpha, and for alpha fixed phi (DL) about l(a) to the z power. Using parameters appropriate to the auroral zone acceleration region, potentials of phi (DPL) 10 kV scale to projected ionospheric dimensions of about 1 km, with power flows of the order of magnitude of substorm dissipation rates.

Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene

NASA Astrophysics Data System (ADS)

Rodríguez-González, Rogelio; Rodríguez-Vargas, Isaac; Díaz-Guerrero, Dan Sidney; Gaggero-Sager, Luis Manuel

2016-01-01

We investigate the transmission properties of quasiperiodic or aperiodic structures based on graphene arranged according to the Cantor sequence. In particular, we have found self-similar behaviour in the transmission spectra, and most importantly, we have calculated the scalability of the spectra. To do this, we implement and propose scaling rules for each one of the fundamental parameters: generation number, height of the barriers and length of the system. With this in mind we have been able to reproduce the reference transmission spectrum, applying the appropriate scaling rule, by means of the scaled transmission spectrum. These scaling rules are valid for both normal and oblique incidence, and as far as we can see the basic ingredients to obtain self-similar characteristics are: relativistic Dirac electrons, a self-similar structure and the non-conservation of the pseudo-spin.

Gaussian process based independent analysis for temporal source separation in fMRI.

PubMed

Hald, Ditte Høvenhoff; Henao, Ricardo; Winther, Ole

2017-05-15

Functional Magnetic Resonance Imaging (fMRI) gives us a unique insight into the processes of the brain, and opens up for analyzing the functional activation patterns of the underlying sources. Task-inferred supervised learning with restrictive assumptions in the regression set-up, restricts the exploratory nature of the analysis. Fully unsupervised independent component analysis (ICA) algorithms, on the other hand, can struggle to detect clear classifiable components on single-subject data. We attribute this shortcoming to inadequate modeling of the fMRI source signals by failing to incorporate its temporal nature. fMRI source signals, biological stimuli and non-stimuli-related artifacts are all smooth over a time-scale compatible with the sampling time (TR). We therefore propose Gaussian process ICA (GPICA), which facilitates temporal dependency by the use of Gaussian process source priors. On two fMRI data sets with different sampling frequency, we show that the GPICA-inferred temporal components and associated spatial maps allow for a more definite interpretation than standard temporal ICA methods. The temporal structures of the sources are controlled by the covariance of the Gaussian process, specified by a kernel function with an interpretable and controllable temporal length scale parameter. We propose a hierarchical model specification, considering both instantaneous and convolutive mixing, and we infer source spatial maps, temporal patterns and temporal length scale parameters by Markov Chain Monte Carlo. A companion implementation made as a plug-in for SPM can be downloaded from https://github.com/dittehald/GPICA. Copyright © 2017 Elsevier Inc. All rights reserved.

Evaluation of a clinical dehydration scale in children requiring intravenous rehydration.

PubMed

Kinlin, Laura M; Freedman, Stephen B

2012-05-01

To evaluate the reliability and validity of a previously derived clinical dehydration scale (CDS) in a cohort of children with gastroenteritis and evidence of dehydration. Participants were 226 children older than 3 months who presented to a tertiary care emergency department and required intravenous rehydration. Reliability was assessed at treatment initiation, by comparing the scores assigned independently by a trained research nurse and a physician. Validity was assessed by using parameters reflective of disease severity: weight gain, baseline laboratory results, willingness of the physician to discharge the patient, hospitalization, and length of stay. Interobserver reliability was moderate, with a weighted κ of 0.52 (95% confidence interval [CI] 0.41, 0.63). There was no correlation between CDS score and percent weight gain, a proxy measure of fluid deficit (Spearman correlation coefficient = -0.03; 95% CI -0.18, 0.12). There were, however, modest and statistically significant correlations between CDS score and several other parameters, including serum bicarbonate (Pearson correlation coefficient = -0.35; 95% CI -0.46, -0.22) and length of stay (Pearson correlation coefficient = 0.24; 95% CI 0.11, 0.36). The scale's discriminative ability was assessed for the outcome of hospitalization, yielding an area under the receiver operating characteristic curve of 0.65 (95% CI 0.57, 0.73). In children administered intravenous rehydration, the CDS was characterized by moderate interobserver reliability and weak associations with objective measures of disease severity. These data do not support its use as a tool to dictate the need for intravenous rehydration or to predict clinical course.

Unifying Rules for Aquatic Locomotion

NASA Astrophysics Data System (ADS)

Saadat, Mehdi; Domel, August; di Santo, Valentina; Lauder, George; Haj-Hariri, Hossein

2016-11-01

Strouhal number, St (=fA/U) , a scaling parameter that relates speed, U, to the tail-beat frequency, f, and tail-beat amplitude, A, has been used many times to describe animal locomotion. It has been observed that swimming animals cruise at 0.2 <=St <=0.4. Using simple dimensional and scaling analyses supported by new experimental evidence of a self-propelled fish-like swimmer, we show that when cruising at minimum hydrodynamic input power, St is predetermined, and is only a function of the shape, i.e. drag coefficient and area. The narrow range for St, 0.2-0.4, has been previously associated with optimal propulsive efficiency. However, St alone is insufficient for deciding optimal motion. We show that hydrodynamic input power (energy usage to propel over a unit distance) in fish locomotion is minimized at all cruising speeds when A* (= A/L), a scaling parameter that relates tail-beat amplitude, A, to the length of the swimmer, L, is constrained to a narrow range of 0.15-0.25. Our analysis proposes a constraint on A*, in addition to the previously found constraint on St, to fully describe the optimal swimming gait for fast swimmers. A survey of kinematics for dolphin, as well as new data for trout, show that the range of St and A* for fast swimmers indeed are constrained to 0.2-0.4 and 0.15-0.25, respectively. Our findings provide physical explanation as to why fast aquatic swimmers cruise with relatively constant tail-beat amplitude at approximately 20 percent of body length, while their swimming speed is linearly correlated with their tail-beat frequency.

Computer modelling of cyclic deformation of high-temperature materials. Technical progress report, 1 September-30 November 1993

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

Duesbery, M.S.

1993-11-30

This program aims at improving current methods of lifetime assessment by building in the characteristics of the micro-mechanisms known to be responsible for damage and failure. The broad approach entails the integration and, where necessary, augmentation of the micro-scale research results currently available in the literature into a macro-sale model with predictive capability. In more detail, the program will develop a set of hierarchically structured models at different length scales, from atomic to macroscopic, at each level taking as parametric input the results of the model at the next smaller scale. In this way the known microscopic properties can bemore » transported by systematic procedures to the unknown macro-scale region. It may mot be possible to eliminate empiricism completely, because some of the quantities involved cannot yet be estimated to the required degree of precision. In this case the aim will be at least to eliminate functional empiricism. Restriction of empiricism to the choice of parameters to be input to known functional forms permits some confidence in extrapolation procedures and has the advantage that the models can readily be updated as better estimates of the parameters become available.« less

Parameter studies on the energy balance closure problem using large-eddy simulation

NASA Astrophysics Data System (ADS)

De Roo, Frederik; Banerjee, Tirtha; Mauder, Matthias

2017-04-01

The imbalance of the surface energy budget in eddy-covariance measurements is still a pending problem. A possible cause is the presence of land surface heterogeneity. Heterogeneities of the boundary layer scale or larger are most effective in influencing the boundary layer turbulence, and large-eddy simulations have shown that secondary circulations within the boundary layer can affect the surface energy budget. However, the precise influence of the surface characteristics on the energy imbalance and its partitioning is still unknown. To investigate the influence of surface variables on all the components of the flux budget under convective conditions, we set up a systematic parameter study by means of large-eddy simulation. For the study we use a virtual control volume approach, and we focus on idealized heterogeneity by considering spatially variable surface fluxes. The surface fluxes vary locally in intensity and these patches have different length scales. The main focus lies on heterogeneities of length scales of the kilometer scale and one decade smaller. For each simulation, virtual measurement towers are positioned at functionally different positions. We discriminate between the locally homogeneous towers, located within land use patches, with respect to the more heterogeneous towers, and find, among others, that the flux-divergence and the advection are strongly linearly related within each class. Furthermore, we seek correlators for the energy balance ratio and the energy residual in the simulations. Besides the expected correlation with measurable atmospheric quantities such as the friction velocity, boundary-layer depth and temperature and moisture gradients, we have also found an unexpected correlation with the temperature difference between sonic temperature and surface temperature. In additional simulations with a large number of virtual towers, we investigate higher order correlations, which can be linked to secondary circulations. In a companion presentation (EGU2017-2130) these correlations are investigated and confirmed with the help of micrometeorological measurements from the TERENO sites where the effects of landscape scale surface heterogeneities are deemed to be important.

The dependence of the strength and thickness of field-aligned currents on solar wind and ionospheric parameters

PubMed Central

Johnson, Jay R.; Wing, Simon

2017-01-01

Sheared plasma flows at the low-latitude boundary layer (LLBL) correlate well with early afternoon auroral arcs and upward field-aligned currents. We present a simple analytic model that relates solar wind and ionospheric parameters to the strength and thickness of field-aligned currents (Λ) in a region of sheared velocity, such as the LLBL. We compare the predictions of the model with DMSP observations and find remarkably good scaling of the upward region 1 currents with solar wind and ionospheric parameters in region located at the boundary layer or open field lines at 1100–1700 magnetic local time. We demonstrate that Λ~nsw−0.5 and Λ ~ L when Λ/L < 5 where L is the auroral electrostatic scale length. The sheared boundary layer thickness (Δm) is inferred to be around 3000 km, which appears to have weak dependence on Vsw. J‖ has dependencies on Δm, Σp, nsw, and Vsw. The analytic model provides a simple way to organize data and to infer boundary layer structures from ionospheric data. PMID:29057194

Online estimation of the wavefront outer scale profile from adaptive optics telemetry

NASA Astrophysics Data System (ADS)

Guesalaga, A.; Neichel, B.; Correia, C. M.; Butterley, T.; Osborn, J.; Masciadri, E.; Fusco, T.; Sauvage, J.-F.

2017-02-01

We describe an online method to estimate the wavefront outer scale profile, L0(h), for very large and future extremely large telescopes. The stratified information on this parameter impacts the estimation of the main turbulence parameters [turbulence strength, Cn2(h); Fried's parameter, r0; isoplanatic angle, θ0; and coherence time, τ0) and determines the performance of wide-field adaptive optics (AO) systems. This technique estimates L0(h) using data from the AO loop available at the facility instruments by constructing the cross-correlation functions of the slopes between two or more wavefront sensors, which are later fitted to a linear combination of the simulated theoretical layers having different altitudes and outer scale values. We analyse some limitations found in the estimation process: (I) its insensitivity to large values of L0(h) as the telescope becomes blind to outer scales larger than its diameter; (II) the maximum number of observable layers given the limited number of independent inputs that the cross-correlation functions provide and (III) the minimum length of data required for a satisfactory convergence of the turbulence parameters without breaking the assumption of statistical stationarity of the turbulence. The method is applied to the Gemini South multiconjugate AO system that comprises five wavefront sensors and two deformable mirrors. Statistics of L0(h) at Cerro Pachón from data acquired during 3 yr of campaigns show interesting resemblance to other independent results in the literature. A final analysis suggests that the impact of error sources will be substantially reduced in instruments of the next generation of giant telescopes.

Stability, intermittency and universal Thorpe length distribution in a laboratory turbulent stratified shear flow

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

Odier, Philippe; Ecke, Robert E.

Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbersmore » $$0.05\\lesssim Ri\\lesssim 1$$. In order to find a stability parameter that allows close comparison with linear theory and with idealized experiments and numerics, we investigate different definitions of$Ri$$. We find that a gradient Richardson number defined on fluid interface sections where there is no overturning at or adjacent to the maximum density gradient position provides an excellent stability parameter, which captures the Miles–Howard linear stability criterion. For small $$Ri$$ the flow exhibits robust Kelvin–Helmholtz instability, whereas for larger $$Ri$$ interfacial overturning is more intermittent with less frequent Kelvin–Helmholtz events and emerging Holmboe wave instability consistent with a thicker velocity layer compared with the density layer. We compute the perturbed fraction of interface as a quantitative measure of the flow intermittency, which is approximately 1 for the smallest $$Ri$$ but decreases rapidly as $$Ri$ increases, consistent with linear theory. For the perturbed regions, we use the Thorpe scale to characterize the overturning properties of these flows. The probability distribution of the non-zero Thorpe length yields a universal exponential form, suggesting that much of the overturning results from increasingly intermittent Kelvin–Helmholtz instability events. Finally, the distribution of turbulent kinetic energy, conditioned on the intermittency fraction, has a similar form, suggesting an explanation for the universal scaling collapse of the Thorpe length distribution.« less

Stability, intermittency and universal Thorpe length distribution in a laboratory turbulent stratified shear flow

DOE PAGES

Odier, Philippe; Ecke, Robert E.

2017-02-21

Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbersmore » $$0.05\\lesssim Ri\\lesssim 1$$. In order to find a stability parameter that allows close comparison with linear theory and with idealized experiments and numerics, we investigate different definitions of$Ri$$. We find that a gradient Richardson number defined on fluid interface sections where there is no overturning at or adjacent to the maximum density gradient position provides an excellent stability parameter, which captures the Miles–Howard linear stability criterion. For small $$Ri$$ the flow exhibits robust Kelvin–Helmholtz instability, whereas for larger $$Ri$$ interfacial overturning is more intermittent with less frequent Kelvin–Helmholtz events and emerging Holmboe wave instability consistent with a thicker velocity layer compared with the density layer. We compute the perturbed fraction of interface as a quantitative measure of the flow intermittency, which is approximately 1 for the smallest $$Ri$$ but decreases rapidly as $$Ri$ increases, consistent with linear theory. For the perturbed regions, we use the Thorpe scale to characterize the overturning properties of these flows. The probability distribution of the non-zero Thorpe length yields a universal exponential form, suggesting that much of the overturning results from increasingly intermittent Kelvin–Helmholtz instability events. Finally, the distribution of turbulent kinetic energy, conditioned on the intermittency fraction, has a similar form, suggesting an explanation for the universal scaling collapse of the Thorpe length distribution.« less

Length-scale dependent mechanical properties of Al-Cu eutectic alloy: Molecular dynamics based model and its experimental verification

NASA Astrophysics Data System (ADS)

Tiwary, C. S.; Chakraborty, S.; Mahapatra, D. R.; Chattopadhyay, K.

2014-05-01

This paper attempts to gain an understanding of the effect of lamellar length scale on the mechanical properties of two-phase metal-intermetallic eutectic structure. We first develop a molecular dynamics model for the in-situ grown eutectic interface followed by a model of deformation of Al-Al2Cu lamellar eutectic. Leveraging the insights obtained from the simulation on the behaviour of dislocations at different length scales of the eutectic, we present and explain the experimental results on Al-Al2Cu eutectic with various different lamellar spacing. The physics behind the mechanism is further quantified with help of atomic level energy model for different length scale as well as different strain. An atomic level energy partitioning of the lamellae and the interface regions reveals that the energy of the lamellae core are accumulated more due to dislocations irrespective of the length-scale. Whereas the energy of the interface is accumulated more due to dislocations when the length-scale is smaller, but the trend is reversed when the length-scale is large beyond a critical size of about 80 nm.

Three-Dimensional Muscle Architecture and Comprehensive Dynamic Properties of Rabbit Gastrocnemius, Plantaris and Soleus: Input for Simulation Studies

PubMed Central

Siebert, Tobias; Leichsenring, Kay; Rode, Christian; Wick, Carolin; Stutzig, Norman; Schubert, Harald; Blickhan, Reinhard; Böl, Markus

2015-01-01

The vastly increasing number of neuro-muscular simulation studies (with increasing numbers of muscles used per simulation) is in sharp contrast to a narrow database of necessary muscle parameters. Simulation results depend heavily on rough parameter estimates often obtained by scaling of one muscle parameter set. However, in vivo muscles differ in their individual properties and architecture. Here we provide a comprehensive dataset of dynamic (n = 6 per muscle) and geometric (three-dimensional architecture, n = 3 per muscle) muscle properties of the rabbit calf muscles gastrocnemius, plantaris, and soleus. For completeness we provide the dynamic muscle properties for further important shank muscles (flexor digitorum longus, extensor digitorum longus, and tibialis anterior; n = 1 per muscle). Maximum shortening velocity (normalized to optimal fiber length) of the gastrocnemius is about twice that of soleus, while plantaris showed an intermediate value. The force-velocity relation is similar for gastrocnemius and plantaris but is much more bent for the soleus. Although the muscles vary greatly in their three-dimensional architecture their mean pennation angle and normalized force-length relationships are almost similar. Forces of the muscles were enhanced in the isometric phase following stretching and were depressed following shortening compared to the corresponding isometric forces. While the enhancement was independent of the ramp velocity, the depression was inversely related to the ramp velocity. The lowest effect strength for soleus supports the idea that these effects adapt to muscle function. The careful acquisition of typical dynamical parameters (e.g. force-length and force-velocity relations, force elongation relations of passive components), enhancement and depression effects, and 3D muscle architecture of calf muscles provides valuable comprehensive datasets for e.g. simulations with neuro-muscular models, development of more realistic muscle models, or simulation of muscle packages. PMID:26114955

Milky Way Mass Models and MOND

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.

2008-08-01

Using the Tuorla-Heidelberg model for the mass distribution of the Milky Way, I determine the rotation curve predicted by MOND (modified Newtonian dynamics). The result is in good agreement with the observed terminal velocities interior to the solar radius and with estimates of the Galaxy's rotation curve exterior thereto. There are no fit parameters: given the mass distribution, MOND provides a good match to the rotation curve. The Tuorla-Heidelberg model does allow for a variety of exponential scale lengths; MOND prefers short scale lengths in the range 2.0 kpc lesssim Rdlesssim 2.5 kpc. The favored value of Rd depends somewhat on the choice of interpolation function. There is some preference for the "simple" interpolation function as found by Famaey & Binney. I introduce an interpolation function that shares the advantages of the simple function on galaxy scales while having a much smaller impact in the solar system. I also solve the inverse problem, inferring the surface mass density distribution of the Milky Way from the terminal velocities. The result is a Galaxy with "bumps and wiggles" in both its luminosity profile and rotation curve that are reminiscent of those frequently observed in external galaxies.

Patterning at the 10 nanometer length scale using a strongly segregating block copolymer thin film and vapor phase infiltration of inorganic precursors

DOE PAGES

Choi, Jonathan W.; Li, Zhaodong; Black, Charles T.; ...

2016-05-04

Here in this work, we demonstrate the use of self-assembled thin films of the cylinder-forming block copolymer poly(4-tert-butylstyrene-block-2-vinylpyridine) to pattern high density features at the 10 nm length scale. This material's large interaction parameter facilitates pattern formation in single-digit nanometer dimensions. This block copolymer's accessible order–disorder transition temperature allows thermal annealing to drive the assembly of ordered 2-vinylpyridine cylinders that can be selectively complexed with the organometallic precursor trimethylaluminum. This unique chemistry converts organic 2-vinylpyridine cylinders into alumina nanowires with diameters ranging from 8 to 11 nm, depending on the copolymer molecular weight. Graphoepitaxy of this block copolymer aligns andmore » registers sub-12 nm diameter nanowires to larger-scale rectangular, curved, and circular features patterned by optical lithography. The alumina nanowires function as a robust hard mask to withstand the conditions required for patterning the underlying silicon by plasma etching. Lastly, we conclude with a discussion of some of the challenges that arise with using block copolymers for patterning at sub-10 nm feature sizes.« less

Patterning at the 10 nanometer length scale using a strongly segregating block copolymer thin film and vapor phase infiltration of inorganic precursors

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

Choi, Jonathan W.; Li, Zhaodong; Black, Charles T.

Here in this work, we demonstrate the use of self-assembled thin films of the cylinder-forming block copolymer poly(4-tert-butylstyrene-block-2-vinylpyridine) to pattern high density features at the 10 nm length scale. This material's large interaction parameter facilitates pattern formation in single-digit nanometer dimensions. This block copolymer's accessible order–disorder transition temperature allows thermal annealing to drive the assembly of ordered 2-vinylpyridine cylinders that can be selectively complexed with the organometallic precursor trimethylaluminum. This unique chemistry converts organic 2-vinylpyridine cylinders into alumina nanowires with diameters ranging from 8 to 11 nm, depending on the copolymer molecular weight. Graphoepitaxy of this block copolymer aligns andmore » registers sub-12 nm diameter nanowires to larger-scale rectangular, curved, and circular features patterned by optical lithography. The alumina nanowires function as a robust hard mask to withstand the conditions required for patterning the underlying silicon by plasma etching. Lastly, we conclude with a discussion of some of the challenges that arise with using block copolymers for patterning at sub-10 nm feature sizes.« less

EXPERIMENTAL INVESTIGATION OF RELATIVE PERMEABILITY UPSCALING FROM THE MICRO-SCALE TO THE MACRO-SCALE

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

JiangTao Cheng; Ping Yu; William Headley

2001-12-01

The principal challenge of upscaling techniques for multi-phase fluid dynamics in porous media is to determine which properties on the micro-scale can be used to predict macroscopic flow and spatial distribution of phases at core- and field-scales. The most notable outcome of recent theories is the identification of interfacial areas per volume for multiple phases as a fundamental parameter that determines much of the multi-phase properties of the porous medium. A formal program of experimental research was begun to directly test upscaling theories in fluid flow through porous media by comparing measurements of relative permeability and capillary-saturation with measurements ofmore » interfacial area per volume. During this reporting period, we have shown experimentally and theoretically that the optical coherence imaging system is optimized for sandstone. The measurement of interfacial area per volume (IAV), capillary pressure and saturation in two dimensional micro-models structures that are statistically similar to real porous media has shown the existence of a unique relationship among these hydraulic parameters. The measurement of interfacial area per volume on a three-dimensional natural sample, i.e., sandstone, has the same length-scale as the values of IAV determined for the two-dimensional micro-models.« less

Determining erosion relevant soil characteristics with a small-scale rainfall simulator

NASA Astrophysics Data System (ADS)

Schindewolf, M.; Schmidt, J.

2009-04-01

The use of soil erosion models is of great importance in soil and water conservation. Routine application of these models on the regional scale is not at least limited by the high parameter demands. Although the EROSION 3D simulation model is operating with a comparable low number of parameters, some of the model input variables could only be determined by rainfall simulation experiments. The existing data base of EROSION 3D was created in the mid 90s based on large-scale rainfall simulation experiments on 22x2m sized experimental plots. Up to now this data base does not cover all soil and field conditions adequately. Therefore a new campaign of experiments would be essential to produce additional information especially with respect to the effects of new soil management practices (e.g. long time conservation tillage, non tillage). The rainfall simulator used in the actual campaign consists of 30 identic modules, which are equipped with oscillating rainfall nozzles. Veejet 80/100 (Spraying Systems Co., Wheaton, IL) are used in order to ensure best possible comparability to natural rainfalls with respect to raindrop size distribution and momentum transfer. Central objectives of the small-scale rainfall simulator are - effectively application - provision of comparable results to large-scale rainfall simulation experiments. A crucial problem in using the small scale simulator is the restriction on rather small volume rates of surface runoff. Under this conditions soil detachment is governed by raindrop impact. Thus impact of surface runoff on particle detachment cannot be reproduced adequately by a small-scale rainfall simulator With this problem in mind this paper presents an enhanced small-scale simulator which allows a virtual multiplication of the plot length by feeding additional sediment loaded water to the plot from upstream. Thus is possible to overcome the plot length limited to 3m while reproducing nearly similar flow conditions as in rainfall experiments on standard plots. The simulator is extensively applied to plots of different soil types, crop types and management systems. The comparison with existing data sets obtained by large-scale rainfall simulations show that results can adequately be reproduced by the applied combination of small-scale rainfall simulator and sediment loaded water influx.

Make dark matter charged again

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

Agrawal, Prateek; Cyr-Racine, Francis-Yan; Randall, Lisa

2017-05-01

We revisit constraints on dark matter that is charged under a U(1) gauge group in the dark sector, decoupled from Standard Model forces. We find that the strongest constraints in the literature are subject to a number of mitigating factors. For instance, the naive dark matter thermalization timescale in halos is corrected by saturation effects that slow down isotropization for modest ellipticities. The weakened bounds uncover interesting parameter space, making models with weak-scale charged dark matter viable, even with electromagnetic strength interaction. This also leads to the intriguing possibility that dark matter self-interactions within small dwarf galaxies are extremely large,more » a relatively unexplored regime in current simulations. Such strong interactions suppress heat transfer over scales larger than the dark matter mean free path, inducing a dynamical cutoff length scale above which the system appears to have only feeble interactions. These effects must be taken into account to assess the viability of darkly-charged dark matter. Future analyses and measurements should probe a promising region of parameter space for this model.« less

Mesoscopic Length Scale Controls the Rheology of Dense Suspensions

NASA Astrophysics Data System (ADS)

Bonnoit, Claire; Lanuza, Jose; Lindner, Anke; Clement, Eric

2010-09-01

From the flow properties of dense granular suspensions on an inclined plane, we identify a mesoscopic length scale strongly increasing with volume fraction. When the flowing layer height is larger than this length scale, a diverging Newtonian viscosity is determined. However, when the flowing layer height drops below this scale, we evidence a nonlocal effective viscosity, decreasing as a power law of the flow height. We establish a scaling relation between this mesoscopic length scale and the suspension viscosity. These results support recent theoretical and numerical results implying collective and clustered granular motion when the jamming point is approached from below.

Mesoscopic length scale controls the rheology of dense suspensions.

PubMed

Bonnoit, Claire; Lanuza, Jose; Lindner, Anke; Clement, Eric

2010-09-03

From the flow properties of dense granular suspensions on an inclined plane, we identify a mesoscopic length scale strongly increasing with volume fraction. When the flowing layer height is larger than this length scale, a diverging Newtonian viscosity is determined. However, when the flowing layer height drops below this scale, we evidence a nonlocal effective viscosity, decreasing as a power law of the flow height. We establish a scaling relation between this mesoscopic length scale and the suspension viscosity. These results support recent theoretical and numerical results implying collective and clustered granular motion when the jamming point is approached from below.

The role of plasma density scale length on the laser pulse propagation and scattering in relativistic regime

NASA Astrophysics Data System (ADS)

Pishdast, Masoud; Ghasemi, Seyed Abolfazl; Yazdanpanah, Jamal Aldin

2017-10-01

The role of plasma density scale length on two short and long laser pulse propagation and scattering in under dense plasma have been investigated in relativistic regime using 1 D PIC simulation. In our simulation, different density scale lengths and also two short and long pulse lengths with temporal pulse duration τL = 60 fs and τL = 300 fs , respectively have been used. It is found that laser pulse length and density scale length have considerable effects on the energetic electron generation. The analysis of total radiation spectrum reveals that, for short laser pulses and with reducing density scale length, more unstable electromagnetic modes grow and strong longitudinal electric field generates which leads to the generation of more energetic plasma particles. Meanwhile, the dominant scattering mechanism is Raman scattering and tends to Thomson scattering for longer laser pulse.

Quasi-Continuum Reduction of Field Theories: A Route to Seamlessly Bridge Quantum and Atomistic Length-Scales with Continuum

DTIC Science & Technology

2016-04-01

AFRL-AFOSR-VA-TR-2016-0145 Quasi-continuum reduction of field theories: A route to seamlessly bridge quantum and atomistic length-scales with...field theories: A route to seamlessly bridge quantum and atomistic length-scales with continuum Principal Investigator: Vikram Gavini Department of...calculations on tens of thousands of atoms, and enable continuing efforts towards a seamless bridging of the quantum and continuum length-scales

Energy-Containing Length Scale at the Base of a Coronal Hole: New Observational Findings

NASA Astrophysics Data System (ADS)

Abramenko, V.; Dosch, A.; Zank, G. P.; Yurchyshyn, V.; Goode, P. R.

2012-12-01

Dynamics of the photospheric flux tubes is thought to be a key factor for generation and propagation of MHD waves and magnetic stress into the corona. Recently, New Solar Telescope (NST, Big Bear Solar Observatory) imaging observations in helium I 10830 Å revealed ultrafine, hot magnetic loops reaching from the photosphere to the corona and originating from intense, compact magnetic field elements. One of the essential input parameters to run the models of the fast solar wind is a characteristic energy-containing length scale, lambda, of the dynamical structures transverse to the mean magnetic field in a coronal hole (CH) in the base of the corona. We used NST time series of solar granulation motions to estimate the velocity fluctuations, as well as NST near-infrared magnetograms to derive the magnetic field fluctuations. The NST adaptive optics corrected speckle-reconstructed images of 10 seconds cadence were an input for the local correlation tracking (LCT) code to derive the squared transverse velocity patterns. We found that the characteristic length scale for the energy-carrying structures in the photosphere is about 300 km, which is two orders of magnitude lower than it was adopted in previous models. The influence of the result on the coronal heating and fast solar wind modeling will be discussed.; Correlation functions calculated from the squared velocities for the three data sets: a coronal hole, quiet sun and active region plage area.

Shafranov shift bifurcation of turbulent transport in the high βp scenario on DIII-D

NASA Astrophysics Data System (ADS)

McClenaghan, J.; Garofalo, A. M.; Staebler, G. M.; Qian, J.; Gong, X.; Ding, S. Y.

2017-10-01

The Shafranov shift stabilization of turbulence creates a bifurcation in transport leading to formation of a large radius internal transport barrier (ITB) in the high βp scenario on DIII-D. The high βp scenario exhibits high confinement at high βN and high bootstrap fraction in the absence of rapid rotation or negative central shear. Spontaneous formation of an ITB at fixed βN is examined. The energy confinement improves following formation of the ITB. The improvement is associated with a decrease in the minimum mid-radius characteristic turbulence parameter associated with the Shafranov shift: α - s , where α =q2 Rdβ / dρ is a measure of the Shafranov shift, and s is the magnetic shear. After ITB formation, α - s > 0 within region of ITB and α - s < 0 outside the ITB. Before ITB formation, α - s < 0 throughout the entire core. TGLF transport simulations show a bifurcation of the transport depending on the electron pressure gradient scale length. Before ITB formation, the experimental scale length is on the high-transport side of bifurcation. After ITB formation, experimental scale length is on the low-transport side of the bifurcation in the region of the ITB. Work supported in part by the US Department of Energy, Office of Science, Office of Fusion Energy Sciences DE-FC02-04ER54698 (Cooperative Agreement #DE-SC0010685), and by the National Magnetic Confinement Fusion Program of China (No. 2015GB102002, 2015GB10.

Pelagic larval duration and settlement size of a reef fish are spatially consistent, but post-settlement growth varies at the reef scale

NASA Astrophysics Data System (ADS)

Leahy, Susannah M.; Russ, Garry R.; Abesamis, Rene A.

2015-12-01

Recent research has demonstrated that, despite a pelagic larval stage, many coral reef fishes disperse over relatively small distances, leading to well-connected populations on scales of 0-30 km. Although variation in key biological characteristics has been explored on the scale of 100-1000 s of km, it has rarely been explored at the scale relevant to actual larval dispersal and population connectivity on ecological timescales. In this study, we surveyed the habitat and collected specimens ( n = 447) of juvenile butterflyfish, Chaetodon vagabundus, at nine sites along an 80-km stretch of coastline in the central Philippines to identify variation in key life history parameters at a spatial scale relevant to population connectivity. Mean pelagic larval duration (PLD) was 24.03 d (SE = 0.16 d), and settlement size was estimated to be 20.54 mm total length (TL; SE = 0.61 mm). Both traits were spatially consistent, although this PLD is considerably shorter than that reported elsewhere. In contrast, post-settlement daily growth rates, calculated from otolith increment widths from 1 to 50 d post-settlement, varied strongly across the study region. Elevated growth rates were associated with rocky habitats that this species is known to recruit to, but were strongly negatively correlated with macroalgal cover and exhibited negative density dependence with conspecific juveniles. Larger animals had lower early (first 50 d post-settlement) growth rates than smaller animals, even after accounting for seasonal variation in growth rates. Both VBGF and Gompertz models provided good fits to post-settlement size-at-age data ( n = 447 fish), but the VBGF's estimate of asymptotic length ( L ∞ = 168 mm) was more consistent with field observations of maximum fish length. Our findings indicate that larval characteristics are consistent at the spatial scale at which populations are likely well connected, but that site-level biological differences develop post-settlement, most likely as a result of key differences in quality of recruitment habitat.

Turbulence scalings in pipe flows exhibiting polymer-induced drag reduction

NASA Astrophysics Data System (ADS)

Zadrazil, Ivan; Markides, Christos

2014-11-01

Non-intrusive laser based diagnostics technique, namely Particle Image Velocimetry, was used to in detail characterise polymer induced drag reduction in a turbulent pipe flow. The effect of polymer additives was investigated in a pneumatically-driven flow facility featuring a horizontal pipe test section of inner diameter 25.3 mm and length 8 m. Three high molecular weight polymers (2, 4 and 8 MDa) at concentrations of 5 - 250 wppm were used at Reynolds numbers from 35000 to 210000. The PIV derived results show that the level of drag reduction scales with different normalised turbulence parameters, e.g. streamwise and spanwise velocity fluctuations, vorticity or Reynolds stresses. These scalings are dependent of the distance from the wall, however, are independent of the Reynolds numbers range investigated.

Finite size scaling analysis on Nagel-Schreckenberg model for traffic flow

NASA Astrophysics Data System (ADS)

Balouchi, Ashkan; Browne, Dana

2015-03-01

The traffic flow problem as a many-particle non-equilibrium system has caught the interest of physicists for decades. Understanding the traffic flow properties and though obtaining the ability to control the transition from the free-flow phase to the jammed phase plays a critical role in the future world of urging self-driven cars technology. We have studied phase transitions in one-lane traffic flow through the mean velocity, distributions of car spacing, dynamic susceptibility and jam persistence -as candidates for an order parameter- using the Nagel-Schreckenberg model to simulate traffic flow. The length dependent transition has been observed for a range of maximum velocities greater than a certain value. Finite size scaling analysis indicates power-law scaling of these quantities at the onset of the jammed phase.

Universality of modulation length and time exponents.

PubMed

Chakrabarty, Saurish; Dobrosavljević, Vladimir; Seidel, Alexander; Nussinov, Zohar

2012-10-01

We study systems with a crossover parameter λ, such as the temperature T, which has a threshold value λ(*) across which the correlation function changes from exhibiting fixed wavelength (or time period) modulations to continuously varying modulation lengths (or times). We introduce a hitherto unknown exponent ν(L) characterizing the universal nature of this crossover and compute its value in general instances. This exponent, similar to standard correlation length exponents, is obtained from motion of the poles of the momentum (or frequency) space correlation functions in the complex k-plane (or ω-plane) as the parameter λ is varied. Near the crossover (i.e., for λ→λ(*)), the characteristic modulation wave vector K(R) in the variable modulation length "phase" is related to that in the fixed modulation length "phase" q via |K(R)-q|[proportionality]|T-T(*)|(νL). We find, in general, that ν(L)=1/2. In some special instances, ν(L) may attain other rational values. We extend this result to general problems in which the eigenvalue of an operator or a pole characterizing general response functions may attain a constant real (or imaginary) part beyond a particular threshold value λ(*). We discuss extensions of this result to multiple other arenas. These include the axial next-nearest-neighbor Ising (ANNNI) model. By extending our considerations, we comment on relations pertaining not only to the modulation lengths (or times), but also to the standard correlation lengths (or times). We introduce the notion of a Josephson time scale. We comment on the presence of aperiodic "chaotic" modulations in "soft-spin" and other systems. These relate to glass-type features. We discuss applications to Fermi systems, with particular application to metal to band insulator transitions, change of Fermi surface topology, divergent effective masses, Dirac systems, and topological insulators. Both regular periodic and glassy (and spatially chaotic behavior) may be found in strongly correlated electronic systems.

Large-scale changes in bloater growth and condition in Lake Huron

USGS Publications Warehouse

Prichard, Carson G.; Roseman, Edward F.; Keeler, Kevin M.; O'Brien, Timothy P.; Riley, Stephen C.

2016-01-01

Native Bloaters Coregonus hoyi have exhibited multiple strong year-classes since 2005 and now are the most abundant benthopelagic offshore prey fish in Lake Huron, following the crash of nonnative AlewivesAlosa pseudoharengus and substantial declines in nonnative Rainbow Smelt Osmerus mordax. Despite recent recoveries in Bloater abundance, marketable-size (>229 mm) Bloaters remain scarce. We used annual survey data to assess temporal and spatial dynamics of Bloater body condition and lengths at age in the main basin of Lake Huron from 1973 to 2014. Basinwide lengths at age were modeled by cohort for the 1973–2003 year-classes using a von Bertalanffy growth model with time-varying Brody growth coefficient (k) and asymptotic length () parameters. Median Bloater weights at selected lengths were estimated to assess changes in condition by modeling weight–length relations with an allometric growth model that allowed growth parameters to vary spatially and temporally. Estimated Bloater lengths at age declined 14–24% among ages 4–8 for all year-classes between 1973 and 2004. Estimates of  declined from a peak of 394 mm (1973 year-class) to a minimum of 238 mm (1998 year-class). Observed mean lengths at age in 2014 were at all-time lows, suggesting that year-classes comprising the current Bloater population would have to follow growth trajectories unlike those characterizing the 1973–2003 year-classes to attain marketable size. Furthermore, estimated weights of 250-mm Bloaters (i.e., a large, commercially valuable size-class) declined 17% among all regions from 1976 to 2007. Decreases in body condition of large Bloaters are associated with lower lipid content and may be linked to marked declines in abundance of the amphipodsDiporeia spp. in Lake Huron. We hypothesize that since at least 1976, large Bloaters have become more negatively buoyant and may have incurred an increasingly greater metabolic cost performing diel vertical migrations to prey upon the opossum shrimp Mysis diluviana and zooplankton.

Asymptotic limits of some models for sound propagation in porous media and the assignment of the pore characteristic lengths.

PubMed

Horoshenkov, Kirill V; Groby, Jean-Philippe; Dazel, Olivier

2016-05-01

Modeling of sound propagation in porous media requires the knowledge of several intrinsic material parameters, some of which are difficult or impossible to measure directly, particularly in the case of a porous medium which is composed of pores with a wide range of scales and random interconnections. Four particular parameters which are rarely measured non-acoustically, but used extensively in a number of acoustical models, are the viscous and thermal characteristic lengths, thermal permeability, and Pride parameter. The main purpose of this work is to show how these parameters relate to the pore size distribution which is a routine characteristic measured non-acoustically. This is achieved through the analysis of the asymptotic behavior of four analytical models which have been developed previously to predict the dynamic density and/or compressibility of the equivalent fluid in a porous medium. In this work the models proposed by Johnson, Koplik, and Dashn [J. Fluid Mech. 176, 379-402 (1987)], Champoux and Allard [J. Appl. Phys. 70(4), 1975-1979 (1991)], Pride, Morgan, and Gangi [Phys. Rev. B 47, 4964-4978 (1993)], and Horoshenkov, Attenborough, and Chandler-Wilde [J. Acoust. Soc. Am. 104, 1198-1209 (1998)] are compared. The findings are then used to compare the behavior of the complex dynamic density and compressibility of the fluid in a material pore with uniform and variable cross-sections.

Bulk critical state and fundamental length scales of superconducting nanocrystalline Nb3Al in Nb-Al matrix

NASA Astrophysics Data System (ADS)

Mondal, Puspen; Manekar, Meghmalhar; Srivastava, A. K.; Roy, S. B.

2009-07-01

We present the results of magnetization measurements on an as-cast nanocrystalline Nb3Al superconductor embedded in Nb-Al matrix. The typical grain size of Nb3Al ranges from about 2-8 nm with the maximum number of grains at around 3.5 nm, as visualized using transmission electron microscopy. The isothermal magnetization hysteresis loops in the superconducting state can be reasonably fitted within the well-known Kim-Anderson critical-state model. By using the same fitting parameters, we calculate the variation in field with respect to distance inside the sample and show the existence of a critical state over length scales much larger than the typical size of the superconducting grains. Our results indicate that a bulk critical current is possible in a system comprising of nanoparticles. The nonsuperconducting Nb-Al matrix thus appears to play a major role in the bulk current flow through the sample. The superconducting coherence length ξ is estimated to be around 3 nm, which is comparable to the typical grain size. The penetration depth λ is estimated to be about 94 nm, which is much larger than the largest of the superconducting grains. Our results could be useful for tuning the current carrying capability of conductors made out of composite materials which involve superconducting nanoparticles.

Unexpected Nonlinear Effects in Superconducting Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Sadleir, John

2016-01-01

When a normal metal transitions into the superconducting state the DC resistance drops from a finite value to zero over some finite transition width in temperature, current, and magnetic field. Superconducting transition-edge sensors (TESs) operate within this transition region and uses resistive changes to measure deposited thermal energy. This resistive transition is not perfectly smooth and a wide range of TES designs and materials show sub-structure in the resistive transition (as seen in smooth nonmonotonic behavior, jump discontinuities, and hysteresis in the devices current-voltage relation and derivatives of the resistance with respect to temperature, bias current, and magnetic field). TES technology has advanced to the point where for many applications this structure is the limiting factor in performance and optimization consists of finding operating points away from these structures. For example, operating at or near this structure can lead to nonlinearity in the detectors response and gain scale, limit the spectral range of the detector by limiting the usable resistive range, and degrade energy resolution. The origin of much of this substructure is unknown. This presentation investigates a number of possible sources in turn. First we model the TES as a superconducting weak-link and solve for the characteristic differential equations current and voltage time dependence. We find:(1) measured DC biased current-voltage relationship is the time-average of a much higher frequency limit cycle solution.(2) We calculate the fundamental frequency and estimate the power radiated from the TES treating the bias leads as an antennae.(3) The solution for a set of circuit parameters becomes multivalued leading to current transitions between levels.(4)The circuit parameters can change the measure resistance and mask the true critical current. As a consequence the TES resistance surface is not just a function of temperature, current, and magnetic field but is also a function of the circuit elements (such as shunt resistor, SQUID inductance, and capacitor values). In other words, same device measured in different electrical circuits will have a different resistive surface in temperature, current, and magnetic field. Next we consider that at the transition temperature of a superconductor both the magnetic penetration depth and coherence length are divergent. As a consequence these important characteristic length scales are changing with operating point. We present measurements on devices showing commensurate behavior between these characteristic lengths and the length scale of added normal metal structures. Reordering of proximity vortices leads to discontinuities and irreversibility of the current-voltage curves. Last we consider a weak-link TES including both thermal activated resistance effects and the effect of the magnetic penetration depth being a function of temperature and magnetic field. We derive its impact on the resistive transition surface and the important device parameters a and b.

Spatiotemporal and Kinematic Parameters Relating to Oriented Gait and Turn Performance in Patients with Chronic Stroke

PubMed Central

Bonnyaud, Céline; Pradon, Didier; Vuillerme, Nicolas; Bensmail, Djamel; Roche, Nicolas

2015-01-01

Background The timed up and go test (TUG) is a functional test which is increasingly used to evaluate patients with stroke. The outcome measured is usually global TUG performance-time. Assessment of spatiotemporal and kinematic parameters during the Oriented gait and Turn sub-tasks of the TUG would provide a better understanding of the mechanisms underlying patients’ performance and therefore may help to guide rehabilitation. The aim of this study was thus to determine the spatiotemporal and kinematic parameters which were most related to the walking and turning sub-tasks of TUG performance in stroke patients. Methods 29 stroke patients carried out the TUG test which was recorded using an optoelectronic system in two conditions: spontaneous and standardized condition (standardized foot position and instructed to turn towards the paretic side). They also underwent a clinical assessment. Stepwise regression was used to determine the parameters most related to Oriented gait and Turn sub-tasks. Relationships between explanatory parameters of Oriented gait and Turn performance and clinical scales were evaluated using Spearman correlations. Results Step length and cadence explained 82% to 95% of the variance for the walking sub-tasks in both conditions. Percentage single support phase and contralateral swing phase (depending on the condition) respectively explained 27% and 56% of the variance during the turning sub-task in the spontaneous and standardized conditions. Discussion and Conclusion Step length, cadence, percentage of paretic single support phase and non-paretic swing phase, as well as dynamic stability were the main parameters related to TUG performance and they should be targeted in rehabilitation. PMID:26091555

Inherent length-scales of periodic solar wind number density structures

NASA Astrophysics Data System (ADS)

Viall, N. M.; Kepko, L.; Spence, H. E.

2008-07-01

We present an analysis of the radial length-scales of periodic solar wind number density structures. We converted 11 years (1995-2005) of solar wind number density data into radial length series segments and Fourier analyzed them to identify all spectral peaks with radial wavelengths between 72 (116) and 900 (900) Mm for slow (fast) wind intervals. Our window length for the spectral analysis was 9072 Mm, approximately equivalent to 7 (4) h of data for the slow (fast) solar wind. We required that spectral peaks pass both an amplitude test and a harmonic F-test at the 95% confidence level simultaneously. From the occurrence distributions of these spectral peaks for slow and fast wind, we find that periodic number density structures occur more often at certain radial length-scales than at others, and are consistently observed within each speed range over most of the 11-year interval. For the slow wind, those length-scales are L ˜ 73, 120, 136, and 180 Mm. For the fast wind, those length-scales are L ˜ 187, 270 and 400 Mm. The results argue for the existence of inherent radial length-scales in the solar wind number density.

A Stochastic Model of Space-Time Variability of Mesoscale Rainfall: Statistics of Spatial Averages

NASA Technical Reports Server (NTRS)

Kundu, Prasun K.; Bell, Thomas L.

2003-01-01

A characteristic feature of rainfall statistics is that they depend on the space and time scales over which rain data are averaged. A previously developed spectral model of rain statistics that is designed to capture this property, predicts power law scaling behavior for the second moment statistics of area-averaged rain rate on the averaging length scale L as L right arrow 0. In the present work a more efficient method of estimating the model parameters is presented, and used to fit the model to the statistics of area-averaged rain rate derived from gridded radar precipitation data from TOGA COARE. Statistical properties of the data and the model predictions are compared over a wide range of averaging scales. An extension of the spectral model scaling relations to describe the dependence of the average fraction of grid boxes within an area containing nonzero rain (the "rainy area fraction") on the grid scale L is also explored.

The island coalescence problem: Scaling of reconnection in extended fluid models including higher-order moments

DOE PAGES

Ng, Jonathan; Huang, Yi -Min; Hakim, Ammar; ...

2015-11-05

As modeling of collisionless magnetic reconnection in most space plasmas with realistic parameters is beyond the capability of today's simulations, due to the separation between global and kinetic length scales, it is important to establish scaling relations in model problems so as to extrapolate to realistic scales. Furthermore, large scale particle-in-cell simulations of island coalescence have shown that the time averaged reconnection rate decreases with system size, while fluid systems at such large scales in the Hall regime have not been studied. Here, we perform the complementary resistive magnetohydrodynamic (MHD), Hall MHD, and two fluid simulations using a ten-moment modelmore » with the same geometry. In contrast to the standard Harris sheet reconnection problem, Hall MHD is insufficient to capture the physics of the reconnection region. Additionally, motivated by the results of a recent set of hybrid simulations which show the importance of ion kinetics in this geometry, we evaluate the efficacy of the ten-moment model in reproducing such results.« less

The desert ant odometer: a stride integrator that accounts for stride length and walking speed.

PubMed

Wittlinger, Matthias; Wehner, Rüdiger; Wolf, Harald

2007-01-01

Desert ants, Cataglyphis, use path integration as a major means of navigation. Path integration requires measurement of two parameters, namely, direction and distance of travel. Directional information is provided by a celestial compass, whereas distance measurement is accomplished by a stride integrator, or pedometer. Here we examine the recently demonstrated pedometer function in more detail. By manipulating leg lengths in foraging desert ants we could also change their stride lengths. Ants with elongated legs ('stilts') or shortened legs ('stumps') take larger or shorter strides, respectively, and misgauge travel distance. Travel distance is overestimated by experimental animals walking on stilts, and underestimated by animals walking on stumps - strongly indicative of stride integrator function in distance measurement. High-speed video analysis was used to examine the actual changes in stride length, stride frequency and walking speed caused by the manipulations of leg length. Unexpectedly, quantitative characteristics of walking behaviour remained almost unaffected by imposed changes in leg length, demonstrating remarkable robustness of leg coordination and walking performance. These data further allowed normalisation of homing distances displayed by manipulated animals with regard to scaling and speed effects. The predicted changes in homing distance are in quantitative agreement with the experimental data, further supporting the pedometer hypothesis.

The Effects of Augmented Reality-based Otago Exercise on Balance, Gait, and Falls Efficacy of Elderly Women.

PubMed

Yoo, Ha-Na; Chung, Eunjung; Lee, Byoung-Hee

2013-07-01

[Purpose] The purpose of this study was to determine the effects of augmented reality-based Otago exercise on balance, gait, and falls efficacy of elderly women. [Subjects] The subjects were 21 elderly women, who were randomly divided into two groups: an augmented reality-based Otago exercise group of 10 subjects and an Otago exercise group of 11 subjects. [Methods] All subjects were evaluated for balance (Berg Balance Scale, BBS), gait parameters (velocity, cadence, step length, and stride length), and falls efficacy. Within 12 weeks, Otago exercise for muscle strengthening and balance training was conducted three times, for a period of 60 minutes each, and subjects in the experimental group performed augmented reality-based Otago exercise. [Results] Following intervention, the augmented reality-based Otago exercise group showed significant increases in BBS, velocity, cadence, step length (right side), stride length (right side and left side) and falls efficacy. [Conclusion] The results of this study suggest the feasibility and suitability of this augmented reality-based Otago exercise for elderly women.

Spatial variability and macro‐scale drivers of growth for native and introduced Flathead Catfish populations

USGS Publications Warehouse

Massie, Danielle L.; Smith, Geoffrey; Bonvechio, Timothy F.; Bunch, Aaron J.; Lucchesi, David O.; Wagner, Tyler

2018-01-01

Quantifying spatial variability in fish growth and identifying large‐scale drivers of growth are fundamental to many conservation and management decisions. Although fish growth studies often focus on a single population, it is becoming increasingly clear that large‐scale studies are likely needed for addressing transboundary management needs. This is particularly true for species with high recreational value and for those with negative ecological consequences when introduced outside of their native range, such as the Flathead Catfish Pylodictis olivaris. This study quantified growth variability of the Flathead Catfish across a large portion of its contemporary range to determine whether growth differences existed between habitat types (i.e., reservoirs and rivers) and between native and introduced populations. Additionally, we investigated whether growth parameters varied as a function of latitude and time since introduction (for introduced populations). Length‐at‐age data from 26 populations across 11 states in the USA were modeled using a Bayesian hierarchical von Bertalanffy growth model. Population‐specific growth trajectories revealed large variation in Flathead Catfish growth and relatively high uncertainty in growth parameters for some populations. Relatively high uncertainty was also evident when comparing populations and when quantifying large‐scale patterns. Growth parameters (Brody growth coefficient [K] and theoretical maximum average length [L∞]) were not different (based on overlapping 90% credible intervals) between habitat types or between native and introduced populations. For populations within the introduced range of Flathead Catfish, latitude was negatively correlated with K. For native populations, we estimated an 85% probability that L∞ estimates were negatively correlated with latitude. Contrary to predictions, time since introduction was not correlated with growth parameters in introduced populations of Flathead Catfish. Results of this study suggest that Flathead Catfish growth patterns are likely shaped more strongly by finer‐scale processes (e.g., exploitation or prey abundances) as opposed to macro‐scale drivers.

Time-calibrated Milankovitch cycles for the late Permian.

PubMed

Wu, Huaichun; Zhang, Shihong; Hinnov, Linda A; Jiang, Ganqing; Feng, Qinglai; Li, Haiyan; Yang, Tianshui

2013-01-01

An important innovation in the geosciences is the astronomical time scale. The astronomical time scale is based on the Milankovitch-forced stratigraphy that has been calibrated to astronomical models of paleoclimate forcing; it is defined for much of Cenozoic-Mesozoic. For the Palaeozoic era, however, astronomical forcing has not been widely explored because of lack of high-precision geochronology or astronomical modelling. Here we report Milankovitch cycles from late Permian (Lopingian) strata at Meishan and Shangsi, South China, time calibrated by recent high-precision U-Pb dating. The evidence extends empirical knowledge of Earth's astronomical parameters before 250 million years ago. Observed obliquity and precession terms support a 22-h length-of-day. The reconstructed astronomical time scale indicates a 7.793-million year duration for the Lopingian epoch, when strong 405-kyr cycles constrain astronomical modelling. This is the first significant advance in defining the Palaeozoic astronomical time scale, anchored to absolute time, bridging the Palaeozoic-Mesozoic transition.

How congestion shapes cities: from mobility patterns to scaling

PubMed Central

Louf, Rémi; Barthelemy, Marc

2014-01-01

The recent availability of data for cities has allowed scientists to exhibit scalings which present themselves in the form of a power-law dependence on population of various socio-economical and structural indicators. We propose here a stochastic theory of urban growth which accounts for some of the observed scalings and we confirm these predictions on US and OECD empirical data. In particular, we show that the dependence on population size of the total number of miles driven daily, the total length of the road network, the total traffic delay, the total consumption of gasoline, the quantity of CO2 emitted and the relation between area and population of cities, are all governed by a single parameter which characterizes the sensitivity to congestion. Our results suggest that diseconomies associated with congestion scale superlinearly with population size, implying that –despite polycentrism– cities whose transportation infrastructure rely heavily on traffic sensitive modes are unsustainable. PMID:24990624

Neonatal stretched penile length: relationship with gestational maturity and anthropometric parameters at birth.

PubMed

Bhakhri, Bhanu Kiran; Meena, Shyam Sundar; Rawat, Mayank; Datta, Vikram

2015-02-01

It is inappropriate to use universal cut-off points to interpret stretched penile length (SPL) measurements in newborns with variable body dimensions. To assess neonatal SPL on the basis of gestational maturity and anthropometric parameters at birth. A cross-sectional observational study of SPL was conducted on stable newborns at a referral teaching hospital in north India between January and June 2012. Gestational maturity, SPL and anthropometric parameters (weight, length, head circumference and foot length) were recorded within 24 hours of birth. Variation of SPL in relation to gestational age and anthropometric parameters were evaluated using multiple linear regression models. The equation using lower confidence limits of 95% confidence intervals for the correlation coefficients provides cut-off points to define a small penis. Data from 1249 newborns demonstrated that penile growth follows the pattern of increase in body dimensions in newborns. SPL can be predicted best in relation to body and foot length taken together. SPL should be interpreted in relation to anthropometric parameters in newborns, particularly body and foot length.

Solute-specific scaling of inorganic nitrogen and phosphorus uptake in streams

NASA Astrophysics Data System (ADS)

Hall, R. O., Jr.; Baker, M. A.; Rosi-Marshall, E. J.; Tank, J. L.; Newbold, J. D.

2013-11-01

Stream ecosystem processes such as nutrient cycling may vary with stream position in the network. Using a scaling approach, we examined the relationship between stream size and nutrient uptake length, which represents the mean distance that a dissolved solute travels prior to removal from the water column. Ammonium (NH4+) uptake length increased proportionally with stream size measured as specific discharge (discharge/stream width) with a scaling exponent = 1.01. In contrast, uptake lengths for nitrate (NO3-) and soluble reactive phosphorus (SRP) increased more rapidly than increases in specific discharge (scaling exponents = 1.19 for NO3- and 1.35 for SRP). Additionally, the ratio of inorganic nitrogen (N) uptake length to SRP uptake length declined with stream size; there was relatively lower demand for SRP compared to N as stream size increased. Finally, we related the scaling of uptake length with specific discharge to that of stream length using Hack's law and downstream hydraulic geometry. Ammonium uptake length increased less than proportionally with distance from the headwaters, suggesting a strong role for larger streams and rivers in regulating nutrient transport.

Pyrotechnic hazards classification and evaluation program. Run-up reaction testing in pyrotechnic dust suspensions

NASA Technical Reports Server (NTRS)

1971-01-01

A preliminary investigation of the parameters included in run-up dust reactions is presented. Two types of tests were conducted: (1) ignition criteria of large bulk pyrotechnic dusts, and (2) optimal run-up conditions of large bulk pyrotechnic dusts. These tests were used to evaluate the order of magnitude and gross scale requirements needed to induce run-up reactions in pyrotechnic dusts and to simulate at reduced scale an accident that occurred in a manufacturing installation. Test results showed that propagation of pyrotechnic dust clouds resulted in a fireball of relatively long duration and large size. In addition, a plane wave front was observed to travel down the length of the gallery.

Still searching for the Holy Grail: on the use of effective soil parameters for Parflow-CLM.

NASA Astrophysics Data System (ADS)

Baroni, Gabriele; Schalge, Bernd; Rihani, Jehan; Attinger, Sabine

2015-04-01

In the last decades the advances in computer science have led to a growing number of coupled and distributed hydrological models based on Richards' equation. Several studies were conducted for understanding hydrological processes at different spatial and temporal scales and they showed promising uses of these types of models also in practical applications. However, these models are generally applied to scales different from that at which the equation is deduced and validated. For this reason, the models are implemented with effective soil parameters that, in principle, should preserve the water fluxes that would have been estimated assuming the finer resolution scale. In this context, the reduction in spatial discretization becomes a trade-off between complexity and performance of the model. The aim of the present contribution is to assess the performance of Parflow-CLM implemented at different spatial scales. A virtual experiment based on data available for the Neckar catchment (Germany) is used as reference at 100x100m resolution. Different upscaling rules for the soil hydraulic parameters are used for coarsening the model up to 1x1km. The analysis is carried out based on different model output e.g., river discharge, evapotranspiration, soil moisture and groundwater recharge. The effects of soil variability, correlation length and spatial distribution over the water flow direction on the simulation results are discussed. Further researches aim to quantify the related uncertainty in model output and the possibility to fill in the model structure inadequacy with data assimilation techniques.

Variability of DTM-derived, morphometric parameters versus cell size. An example of application in Calabria (Southern Italy)

NASA Astrophysics Data System (ADS)

Rago, Valeria; Caloiero, Paola; Pellegrino, Annamaria Daniela; Iovine, Giulio G. R.; Terranova, Oreste G.; Pascale, Stefania

2016-04-01

Applications of DTM-derived morphometry are nowadays common in many fields of land-use planning, including the protection from natural hazards (cf. e.g. Iovine et al. 2013; 2014). For example, the mathematical modelling of physical processes that occur at slope or basin scales makes extensive use of quantitative parameters that describe the shape of Earth surface. Unfortunately, the values of these parameters depend on the detail with which the territory is represented. Therefore, different relationships must be adopted to describe the same physical processes at different scales. In this study, as part of a wide-ranging research aimed at modelling of geo-hydrological processes, a systematic and rigorous assessment of variability of the morphometric parameters against cell sizes is addressed. The study area under consideration is the whole Calabrian territory, extended about 15075 square kilometres. The region has recently been zoned into eleven homogeneous geomorphological sectors (Antronico et al., 2010). For each geomorphological sector, DTMs have been derived from topographic maps at 1:5000 scale, with cell sizes of 5, 10, 20 and 40 m. The following morphometric parameters - among those most frequently used in land management - have then been evaluated for the above DTMs: altitude, steepness of slope, aspect, plan and profile curvatures, slope length, topographical wetness index, stream power index, topographic position index, terrain ruggedness index, slope length factor. The first results show a marked dependence on cell size for some of the considered parameters. In other cases, such dependence seems not significant. Mathematical relationships are proposed between cell size and considered parameters, also taking into account the geomorphological contexts examined. Based on the above relationships, the most suitable scale to be used for modelling physical processes in a given area of interest can be selected. References Antronico L., L. Borselli, R. Coscarelli, G. Gullà, G. Iovine, O. Petrucci, P. Salvador Sanchis, M. Sorriso-Valvo, O. Terranova, D. Torri, V. Bagarello, C. Di Stefano, V. Ferro, G. Buttafuoco, G. Callegari, P. Porto, B. Betrò, A. Bodini, C. Brambilla (2010) - Relazione Finale Contratto Lotto 2 Pericolosità legata ai fenomeni di intensa erosione idrica areale e lineare- POR Calabria 2000-2006, Azione. 1.4c. Rapporto per Autorità di Bacino Regione Calabria. Iovine G., Greco R., Gariano S.L., Pellegrino A.D., Terranova O.G. (2014) - Shallow-landslide susceptibility in the Costa Viola mountain ridge (southern Calabria, Italy) with considerations on the role of causal factors. Natural Hazards, 73(1), pp.111-136. In: G. Iovine & D. Cohen (Eds.), Advanced methods in landslide modelling. Iovine G., Greco R., Gariano S.L., Iaquinta P., Pellegrino A.D., Terranova O.G. (2013) - Shallow-landslide susceptibility in the Costa Viola mountain ridge (Italia). In: Landslide Science and Practice, Claudio Margottini, Paolo Canuti, Kyoji Sassa (Editors), Volume 3: Spatial Analysis and Modelling, pp.81-87. Proc. Second World Landslide Forum, 3-7 October 2011, Rome.

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

Sivak, David; Crooks, Gavin

A fundamental problem in modern thermodynamics is how a molecular-scale machine performs useful work, while operating away from thermal equilibrium without excessive dissipation. To this end, we derive a friction tensor that induces a Riemannian manifold on the space of thermodynamic states. Within the linear-response regime, this metric structure controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties. We discuss the connection to the existing thermodynamic length formalism, and demonstrate the utility of this metric by solving for optimal control parameter protocols in a simple nonequilibrium model.

Multiscale Modeling of Stiffness, Friction and Adhesion in Mechanical Contacts

DTIC Science & Technology

2012-02-29

over a lateral length l scales as a power law: h  lH, where H is called the Hurst exponent . For typical experimental surfaces, H ranges from 0.5 to 0.8...surfaces with a wide range of Hurst exponents using fully atomistic calculations and the Green’s function method. A simple relation like Eq. (2...described above to explore a full range of parameter space with different rms roughness h0, rms slope h’0, Hurst exponent H, adhesion energy

A Search for Mountain Waves in MLS Stratospheric Limb Radiances from the Winter Northern Hemisphere: Data Analysis and Global Mountain Wave Modeling

DTIC Science & Technology

2004-02-11

the general circulation of the middle atmosphere, Philos. Trans. R. Soc. London, Ser. A, 323, 693–705. Anton , H. (2000), Elementary Linear Algebra ...Because the saturated radiances may depend slightly on tangent height as the limb path length decreases, a linear trend (described by parameters a and b...track days and interpolated onto the same limb-track orbits. The color bar scale for radiance variance is linear . (b) Digital elevations of northern

Physical models of polarization mode dispersion

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

Menyuk, C.R.; Wai, P.K.A.

The effect of randomly varying birefringence on light propagation in optical fibers is studied theoretically in the parameter regime that will be used for long-distance communications. In this regime, the birefringence is large and varies very rapidly in comparison to the nonlinear and dispersive scale lengths. We determine the polarization mode dispersion, and we show that physically realistic models yield the same result for polarization mode dispersion as earlier heuristic models that were introduced by Poole. We also prove an ergodic theorem.

Supergranulation, a convective phenomenon

NASA Astrophysics Data System (ADS)

Udayashankar, Paniveni

2015-08-01

Observation of the Solar photosphere through high resolution instruments have long indicated that the surface of the Sun is not a tranquil, featureless surface but is beset with a granular appearance. These cellular velocity patterns are a visible manifestation of sub- photospheric convection currents which contribute substantially to the outward transport of energy from the deeper layers, thus maintaining the energy balance of the Sun as a whole.Convection is the chief mode of transport in the outer layers of all cool stars such as the Sun (Noyes,1982). Convection zone of thickness 30% of the Solar radius lies in the sub-photospheric layers of the Sun. Convection is revealed on four scales. On the scale of 1000 km, it is granulation and on the scale of 8-10 arcsec, it is Mesogranulation. The next hierarchial scale of convection ,Supergranules are in the range of 30-40 arcsec. The largest reported manifestation of convection in the Sun are ‘Giant Cells’or ‘Giant Granules’, on a typical length scale of about 108 m.'Supergranules' is caused by the turbulence that extends deep into the convection zone. They have a typical lifetime of about 20hr with spicules marking their boundaries. Gas rises in the centre of the supergranules and then spreads out towards the boundary and descends.Broadly speaking supergranules are characterized by the three parameters namely the length L, the lifetime T and the horizontal flow velocity vh . The interrelationships amongst these parameters can shed light on the underlying convective processes and are in agreement with the Kolmogorov theory of turbulence as applied to large scale solar convection (Krishan et al .2002 ; Paniveni et. al. 2004, 2005, 2010).References:1) Noyes, R.W., The Sun, Our Star (Harvard University Press, 1982)2) Krishan, V., Paniveni U., Singh , J., Srikanth R., 2002, MNRAS, 334/1,2303) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2004, MNRAS, 347, 1279-12814) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2005, Solar Physics, 231, 1-105) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2010, MNRAS, 402, Issue 1, 424-428

Supergranular Convection

NASA Astrophysics Data System (ADS)

Udayashankar, Paniveni

2015-12-01

Observation of the Solar photosphere through high resolution instruments have long indicated that the surface of the Sun is not a tranquil, featureless surface but is beset with a granular appearance. These cellular velocity patterns are a visible manifestation of sub- photospheric convection currents which contribute substantially to the outward transport of energy from the deeper layers, thus maintaining the energy balance of the Sun as a whole.Convection is the chief mode of transport in the outer layers of all cool stars such as the Sun (Noyes,1982). Convection zone of thickness 30% of the Solar radius lies in the sub-photospheric layers of the Sun. Here the opacity is so large that heat flux transport is mainly by convection rather than by photon diffusion. Convection is revealed on four scales. On the scale of 1000 km, it is granulation and on the scale of 8-10 arcsec, it is Mesogranulation. The next hierarchial scale of convection , Supergranules are in the range of 30-40 arcsec. The largest reported manifestation of convection in the Sun are ‘Giant Cells’or ‘Giant Granules’, on a typical length scale of about 108 m.'Supergranules' is caused by the turbulence that extends deep into the convection zone. They have a typical lifetime of about 20hr with spicules marking their boundaries. Gas rises in the centre of the supergranules and then spreads out towards the boundary and descends.Broadly speaking supergranules are characterized by the three parameters namely the length L, the lifetime T and the horizontal flow velocity vh . The interrelationships amongst these parameters can shed light on the underlying convective processes and are in agreement with the Kolmogorov theory of turbulence as applied to large scale solar convection (Krishan et al .2002 ; Paniveni et. al. 2004, 2005, 2010).References:1) Noyes, R.W., The Sun, Our Star (Harvard University Press, 1982)2) Krishan, V., Paniveni U., Singh , J., Srikanth R., 2002, MNRAS, 334/1,2303) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2004, MNRAS, 347, 1279-12814) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2005, Solar Physics, 231, 1-105) Paniveni , U., Krishan, V., Singh, J., Srikanth, R., 2010, MNRAS, 402, Issue 1, 424-428

The Snakelike Chain Character of Unstructured RNA

PubMed Central

Jacobson, David R.; McIntosh, Dustin B.; Saleh, Omar A.

2013-01-01

In the absence of base-pairing and tertiary structure, ribonucleic acid (RNA) assumes a random-walk conformation, modulated by the electrostatic self-repulsion of the charged, flexible backbone. This behavior is often modeled as a Kratky-Porod “wormlike chain” (WLC) with a Barrat-Joanny scale-dependent persistence length. In this study we report measurements of the end-to-end extension of poly(U) RNA under 0.1 to 10 pN applied force and observe two distinct elastic-response regimes: a low-force, power-law regime characteristic of a chain of swollen blobs on long length scales and a high-force, salt-valence-dependent regime consistent with ion-stabilized crumpling on short length scales. This short-scale structure is additionally supported by force- and salt-dependent quantification of the RNA ion atmosphere composition, which shows that ions are liberated under stretching; the number of ions liberated increases with increasing bulk salt concentration. Both this result and the observation of two elastic-response regimes directly contradict the WLC model, which predicts a single elastic regime across all forces and, when accounting for scale-dependent persistence length, the opposite trend in ion release with salt concentration. We conclude that RNA is better described as a “snakelike chain,” characterized by smooth bending on long length scales and ion-stabilized crumpling on short length scales. In monovalent salt, these two regimes are separated by a characteristic length that scales with the Debye screening length, highlighting the determining importance of electrostatics in RNA conformation. PMID:24314087

Inertial effects in three-dimensional spinodal decomposition of a symmetric binary fluid mixture: a lattice Boltzmann study

NASA Astrophysics Data System (ADS)

Kendon, Vivien M.; Cates, Michael E.; Pagonabarraga, Ignacio; Desplat, J.-C.; Bladon, Peter

2001-08-01

The late-stage demixing following spinodal decomposition of a three-dimensional symmetric binary fluid mixture is studied numerically, using a thermodynamically consistent lattice Boltzmann method. We combine results from simulations with different numerical parameters to obtain an unprecedented range of length and time scales when expressed in reduced physical units. (These are the length and time units derived from fluid density, viscosity, and interfacial tension.) Using eight large (2563) runs, the resulting composite graph of reduced domain size l against reduced time t covers 1 [less, similar] l [less, similar] 105, 10 [less, similar] t [less, similar] 108. Our data are consistent with the dynamical scaling hypothesis that l(t) is a universal scaling curve. We give the first detailed statistical analysis of fluid motion, rather than just domain evolution, in simulations of this kind, and introduce scaling plots for several quantities derived from the fluid velocity and velocity gradient fields. Using the conventional definition of Reynolds number for this problem, Re[phi] = ldl/dt, we attain values approaching 350. At Re[phi] [greater, similar] 100 (which requires t [greater, similar] 106) we find clear evidence of Furukawa's inertial scaling (l [similar] t2/3), although the crossover from the viscous regime (l [similar] t) is both broad and late (102 [less, similar] t [less, similar] 106). Though it cannot be ruled out, we find no indication that Re[phi] is self-limiting (l [similar] t1/2) at late times, as recently proposed by Grant & Elder. Detailed study of the velocity fields confirms that, for our most inertial runs, the RMS ratio of nonlinear to viscous terms in the Navier Stokes equation, R2, is of order 10, with the fluid mixture showing incipient turbulent characteristics. However, we cannot go far enough into the inertial regime to obtain a clear length separation of domain size, Taylor microscale, and Kolmogorov scale, as would be needed to test a recent ‘extended’ scaling theory of Kendon (in which R2 is self-limiting but Re[phi] not). Obtaining our results has required careful steering of several numerical control parameters so as to maintain adequate algorithmic stability, efficiency and isotropy, while eliminating unwanted residual diffusion. (We argue that the latter affects some studies in the literature which report l [similar] t2/3 for t [less, similar] 104.) We analyse the various sources of error and find them just within acceptable levels (a few percent each) in most of our datasets. To bring these under significantly better control, or to go much further into the inertial regime, would require much larger computational resources and/or a breakthrough in algorithm design.

Experimental evidence for two thermodynamic length scales in neutralized polyacrylate gels

NASA Astrophysics Data System (ADS)

Horkay, Ferenc; Hecht, Anne-Marie; Grillo, Isabelle; Basser, Peter J.; Geissler, Erik

2002-11-01

The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about -3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length ξ and a persistence length L.

Investigation of the dependence of joint contact forces on musculotendon parameters using a codified workflow for image-based modelling.

PubMed

Modenese, Luca; Montefiori, Erica; Wang, Anqi; Wesarg, Stefan; Viceconti, Marco; Mazzà, Claudia

2018-05-17

The generation of subject-specific musculoskeletal models of the lower limb has become a feasible task thanks to improvements in medical imaging technology and musculoskeletal modelling software. Nevertheless, clinical use of these models in paediatric applications is still limited for what concerns the estimation of muscle and joint contact forces. Aiming to improve the current state of the art, a methodology to generate highly personalized subject-specific musculoskeletal models of the lower limb based on magnetic resonance imaging (MRI) scans was codified as a step-by-step procedure and applied to data from eight juvenile individuals. The generated musculoskeletal models were used to simulate 107 gait trials using stereophotogrammetric and force platform data as input. To ensure completeness of the modelling procedure, muscles' architecture needs to be estimated. Four methods to estimate muscles' maximum isometric force and two methods to estimate musculotendon parameters (optimal fiber length and tendon slack length) were assessed and compared, in order to quantify their influence on the models' output. Reported results represent the first comprehensive subject-specific model-based characterization of juvenile gait biomechanics, including profiles of joint kinematics and kinetics, muscle forces and joint contact forces. Our findings suggest that, when musculotendon parameters were linearly scaled from a reference model and the muscle force-length-velocity relationship was accounted for in the simulations, realistic knee contact forces could be estimated and these forces were not sensitive the method used to compute muscle maximum isometric force. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Study of the correlation parameters of the surface structure of disordered semiconductors by the two-dimensional DFA and average mutual information methods

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

Alpatov, A. V.; Vikhrov, S. P.; Rybina, N. V., E-mail: pgnv@mail.ru

The processes of self-organization of the surface structure of hydrogenated amorphous silicon are studied by the methods of fluctuation analysis and average mutual information on the basis of atomic-force-microscopy images of the surface. It is found that all of the structures can be characterized by a correlation vector and represented as a superposition of harmonic components and noise. It is shown that, under variations in the technological parameters of the production of a-Si:H films, the correlation properties of their structure vary as well. As the substrate temperature is increased, the formation of structural irregularities becomes less efficient; in this case,more » the length of the correlation vector and the degree of structural ordering increase. It is shown that the procedure based on the method of fluctuation analysis in combination with the method of average mutual information provides a means for studying the self-organization processes in any structures on different length scales.« less

Introduction and application of the multiscale coefficient of variation analysis.

PubMed

Abney, Drew H; Kello, Christopher T; Balasubramaniam, Ramesh

2017-10-01

Quantifying how patterns of behavior relate across multiple levels of measurement typically requires long time series for reliable parameter estimation. We describe a novel analysis that estimates patterns of variability across multiple scales of analysis suitable for time series of short duration. The multiscale coefficient of variation (MSCV) measures the distance between local coefficient of variation estimates within particular time windows and the overall coefficient of variation across all time samples. We first describe the MSCV analysis and provide an example analytical protocol with corresponding MATLAB implementation and code. Next, we present a simulation study testing the new analysis using time series generated by ARFIMA models that span white noise, short-term and long-term correlations. The MSCV analysis was observed to be sensitive to specific parameters of ARFIMA models varying in the type of temporal structure and time series length. We then apply the MSCV analysis to short time series of speech phrases and musical themes to show commonalities in multiscale structure. The simulation and application studies provide evidence that the MSCV analysis can discriminate between time series varying in multiscale structure and length.

Stagnation Region Heat Transfer: The Influence of Turbulence Parameters, Reynolds Number and Body Shape

NASA Technical Reports Server (NTRS)

Vanfossen, G. James; Simoneau, Robert J.

1994-01-01

The effect of velocity gradient on stagnation region heat transfer augmentation by free stream turbulence was investigated. Heat transfer was measured in the stagnation region of four models with elliptical leading edges with ratios of major to minor axes of 1:1, 1.5:1, 2.25:1, and 3:1. Four geometrically similar, square bar, square mesh, biplane grids were used to generate free stream turbulence with different intensities and length. Heat transfer measurements were made for the following ranges of parameters: Reynolds number, based on leading edge diameter, 37,000 to 228,000; dimensionless leading edge velocity gradient, 1.20 to 1.80; turbulence intensity, 1.1 to 15.9%; and length scale to leading edge diameter ratio, 0.05 to 0.30. Stagnation point heat transfer augmentation by free stream turbulence can be predicted using a modified version of a previously developed correlation for a circular leading edge. Heat transfer augmentation was independent of body shape at the stagnation point. The heat transfer distribution down-stream from the stagnation point can be predicted using the normalized laminar heat transfer distribution.

Cavity Heating Experiments Supporting Shuttle Columbia Accident Investigation

NASA Technical Reports Server (NTRS)

Everhart, Joel L.; Berger, Karen T.; Bey, Kim S.; Merski, N. Ronald; Wood, William A.

2011-01-01

The two-color thermographic phosphor method has been used to map the local heating augmentation of scaled idealized cavities at conditions simulating the windward surface of the Shuttle Orbiter Columbia during flight STS-107. Two experiments initiated in support of the Columbia Accident Investigation were conducted in the Langley 20-Inch Mach 6 Tunnel. Generally, the first test series evaluated open (length-to-depth less than 10) rectangular cavity geometries proposed as possible damage scenarios resulting from foam and ice impact during launch at several discrete locations on the vehicle windward surface, though some closed (length-to-depth greater than 13) geometries were briefly examined. The second test series was designed to parametrically evaluate heating augmentation in closed rectangular cavities. The tests were conducted under laminar cavity entry conditions over a range of local boundary layer edge-flow parameters typical of re-entry. Cavity design parameters were developed using laminar computational predictions, while the experimental boundary layer state conditions were inferred from the heating measurements. An analysis of the aeroheating caused by cavities allowed exclusion of non-breeching damage from the possible loss scenarios being considered during the investigation.

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

Mehrez, Loujaine; Ghanem, Roger; Aitharaju, Venkat

Design of non-crimp fabric (NCF) composites entails major challenges pertaining to (1) the complex fine-scale morphology of the constituents, (2) the manufacturing-produced inconsistency of this morphology spatially, and thus (3) the ability to build reliable, robust, and efficient computational surrogate models to account for this complex nature. Traditional approaches to construct computational surrogate models have been to average over the fluctuations of the material properties at different scale lengths. This fails to account for the fine-scale features and fluctuations in morphology, material properties of the constituents, as well as fine-scale phenomena such as damage and cracks. In addition, it failsmore » to accurately predict the scatter in macroscopic properties, which is vital to the design process and behavior prediction. In this work, funded in part by the Department of Energy, we present an approach for addressing these challenges by relying on polynomial chaos representations of both input parameters and material properties at different scales. Moreover, we emphasize the efficiency and robustness of integrating the polynomial chaos expansion with multiscale tools to perform multiscale assimilation, characterization, propagation, and prediction, all of which are necessary to construct the data-driven surrogate models required to design under the uncertainty of composites. These data-driven constructions provide an accurate map from parameters (and their uncertainties) at all scales and the system-level behavior relevant for design. While this perspective is quite general and applicable to all multiscale systems, NCF composites present a particular hierarchy of scales that permits the efficient implementation of these concepts.« less

Scaling Effects on Materials Tribology: From Macro to Micro Scale.

PubMed

Stoyanov, Pantcho; Chromik, Richard R

2017-05-18

The tribological study of materials inherently involves the interaction of surface asperities at the micro to nanoscopic length scales. This is the case for large scale engineering applications with sliding contacts, where the real area of contact is made up of small contacting asperities that make up only a fraction of the apparent area of contact. This is why researchers have sought to create idealized experiments of single asperity contacts in the field of nanotribology. At the same time, small scale engineering structures known as micro- and nano-electromechanical systems (MEMS and NEMS) have been developed, where the apparent area of contact approaches the length scale of the asperities, meaning the real area of contact for these devices may be only a few asperities. This is essentially the field of microtribology, where the contact size and/or forces involved have pushed the nature of the interaction between two surfaces towards the regime where the scale of the interaction approaches that of the natural length scale of the features on the surface. This paper provides a review of microtribology with the purpose to understand how tribological processes are different at the smaller length scales compared to macrotribology. Studies of the interfacial phenomena at the macroscopic length scales (e.g., using in situ tribometry) will be discussed and correlated with new findings and methodologies at the micro-length scale.

Scaling Effects on Materials Tribology: From Macro to Micro Scale

PubMed Central

Stoyanov, Pantcho; Chromik, Richard R.

2017-01-01

The tribological study of materials inherently involves the interaction of surface asperities at the micro to nanoscopic length scales. This is the case for large scale engineering applications with sliding contacts, where the real area of contact is made up of small contacting asperities that make up only a fraction of the apparent area of contact. This is why researchers have sought to create idealized experiments of single asperity contacts in the field of nanotribology. At the same time, small scale engineering structures known as micro- and nano-electromechanical systems (MEMS and NEMS) have been developed, where the apparent area of contact approaches the length scale of the asperities, meaning the real area of contact for these devices may be only a few asperities. This is essentially the field of microtribology, where the contact size and/or forces involved have pushed the nature of the interaction between two surfaces towards the regime where the scale of the interaction approaches that of the natural length scale of the features on the surface. This paper provides a review of microtribology with the purpose to understand how tribological processes are different at the smaller length scales compared to macrotribology. Studies of the interfacial phenomena at the macroscopic length scales (e.g., using in situ tribometry) will be discussed and correlated with new findings and methodologies at the micro-length scale. PMID:28772909

Influence of eye biometrics and corneal micro-structure on noncontact tonometry.

PubMed

Jesus, Danilo A; Majewska, Małgorzata; Krzyżanowska-Berkowska, Patrycja; Iskander, D Robert

2017-01-01

Tonometry is widely used as the main screening tool supporting glaucoma diagnosis. Still, its accuracy could be improved if full knowledge about the variation of the corneal biomechanical properties was available. In this study, Optical Coherence Tomography (OCT) speckle statistics are used to infer the organisation of the corneal micro-structure and hence, to analyse its influence on intraocular pressure (IOP) measurements. Fifty-six subjects were recruited for this prospective study. Macro and micro-structural corneal parameters as well as subject age were considered. Macro-structural analysis included the parameters that are associated with the ocular anatomy, such as central corneal thickness (CCT), corneal radius, axial length, anterior chamber depth and white-to-white corneal diameter. Micro-structural parameters which included OCT speckle statistics were related to the internal organisation of the corneal tissue and its physiological changes during lifetime. The corneal speckle obtained from OCT was modelled with the Generalised Gamma (GG) distribution that is characterised with a scale parameter and two shape parameters. In macro-structure analysis, only CCT showed a statistically significant correlation with IOP (R2 = 0.25, p<0.001). The scale parameter and the ratio of the shape parameters of GG distribution showed statistically significant correlation with IOP (R2 = 0.19, p<0.001 and R2 = 0.17, p<0.001, respectively). For the studied group, a weak, although significant correlation was found between age and IOP (R2 = 0.053, p = 0.04). Forward stepwise regression showed that CCT and the scale parameter of the Generalised Gamma distribution can be combined in a regression model (R2 = 0.39, p<0.001) to study the role of the corneal structure on IOP. We show, for the first time, that corneal micro-structure influences the IOP measurements obtained from noncontact tonometry. OCT speckle statistics can be employed to learn about the corneal micro-structure and hence, to further calibrate the IOP measurements.

Influence of eye biometrics and corneal micro-structure on noncontact tonometry

PubMed Central

Majewska, Małgorzata; Krzyżanowska-Berkowska, Patrycja; Iskander, D. Robert

2017-01-01

Purpose Tonometry is widely used as the main screening tool supporting glaucoma diagnosis. Still, its accuracy could be improved if full knowledge about the variation of the corneal biomechanical properties was available. In this study, Optical Coherence Tomography (OCT) speckle statistics are used to infer the organisation of the corneal micro-structure and hence, to analyse its influence on intraocular pressure (IOP) measurements. Methods Fifty-six subjects were recruited for this prospective study. Macro and micro-structural corneal parameters as well as subject age were considered. Macro-structural analysis included the parameters that are associated with the ocular anatomy, such as central corneal thickness (CCT), corneal radius, axial length, anterior chamber depth and white-to-white corneal diameter. Micro-structural parameters which included OCT speckle statistics were related to the internal organisation of the corneal tissue and its physiological changes during lifetime. The corneal speckle obtained from OCT was modelled with the Generalised Gamma (GG) distribution that is characterised with a scale parameter and two shape parameters. Results In macro-structure analysis, only CCT showed a statistically significant correlation with IOP (R2 = 0.25, p<0.001). The scale parameter and the ratio of the shape parameters of GG distribution showed statistically significant correlation with IOP (R2 = 0.19, p<0.001 and R2 = 0.17, p<0.001, respectively). For the studied group, a weak, although significant correlation was found between age and IOP (R2 = 0.053, p = 0.04). Forward stepwise regression showed that CCT and the scale parameter of the Generalised Gamma distribution can be combined in a regression model (R2 = 0.39, p<0.001) to study the role of the corneal structure on IOP. Conclusions We show, for the first time, that corneal micro-structure influences the IOP measurements obtained from noncontact tonometry. OCT speckle statistics can be employed to learn about the corneal micro-structure and hence, to further calibrate the IOP measurements. PMID:28472178

Cooling thermal parameters and microstructure features of directionally solidified ternary Sn–Bi–(Cu,Ag) solder alloys

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

Silva, Bismarck L., E-mail: bismarck_luiz@yahoo.com.br; Garcia, Amauri; Spinelli, José E.

Low temperature soldering technology encompasses Sn–Bi based alloys as reference materials for joints since such alloys may be molten at temperatures less than 180 °C. Despite the relatively high strength of these alloys, segregation problems and low ductility are recognized as potential disadvantages. Thus, for low-temperature applications, Bi–Sn eutectic or near-eutectic compositions with or without additions of alloying elements are considered interesting possibilities. In this context, additions of third elements such as Cu and Ag may be an alternative in order to reach sounder solder joints. The length scale of the phases and their proportions are known to be themore » most important factors affecting the final wear, mechanical and corrosions properties of ternary Sn–Bi–(Cu,Ag) alloys. In spite of this promising outlook, studies emphasizing interrelations of microstructure features and solidification thermal parameters regarding these multicomponent alloys are rare in the literature. In the present investigation Sn–Bi–(Cu,Ag) alloys were directionally solidified (DS) under transient heat flow conditions. A complete characterization is performed including experimental cooling thermal parameters, segregation (XRF), optical and scanning electron microscopies, X-ray diffraction (XRD) and length scale of the microstructural phases. Experimental growth laws relating dendritic spacings to solidification thermal parameters have been proposed with emphasis on the effects of Ag and Cu. The theoretical predictions of the Rappaz-Boettinger model are shown to be slightly above the experimental scatter of secondary dendritic arm spacings for both ternary Sn–Bi–Cu and Sn–Bi–Ag alloys examined. - Highlights: • Dendritic growth prevailed for the ternary Sn–Bi–Cu and Sn–Bi–Ag solder alloys. • Bi precipitates within Sn-rich dendrites were shown to be unevenly distributed. • Morphology and preferential region for the Ag{sub 3}Sn growth depend on Ag content and Ṫ{sub L}. • Rappaz-Boettinger model reasonably estimated the experimental scatter of λ{sub 2}.« less

Theory of dynamic barriers, activated hopping, and the glass transition in polymer melts

NASA Astrophysics Data System (ADS)

Schweizer, Kenneth S.; Saltzman, Erica J.

2004-07-01

A statistical mechanical theory of collective dynamic barriers, slow segmental relaxation, and the glass transition of polymer melts is developed by combining, and in some aspects extending, methods of mode coupling, density functional, and activated hopping transport theories. A coarse-grained description of polymer chains is adopted and the melt is treated as a liquid of segments. The theory is built on the idea that collective density fluctuations on length scales considerably longer than the local cage scale are of primary importance in the deeply supercooled regime. The barrier hopping or segmental relaxation time is predicted to be a function primarily of a single parameter that is chemical structure, temperature, and pressure dependent. This parameter depends on the material-specific dimensionless amplitude of thermal density fluctuations (compressibility) and a reduced segmental density determined by the packing length and backbone characteristic ratio. Analytic results are derived for a crossover temperature Tc, collective barrier, and glass transition temperature Tg. The relation of these quantities to structural and thermodynamic properties of the polymer melt is established. A universal power-law scaling behavior of the relaxation time below Tc is predicted based on identification of a reduced temperature variable that quantifies the breadth of the supercooled regime. Connections between the ratio Tc/Tg, two measures of dynamic fragility, and the magnitude of the local relaxation time at Tg logically follow. Excellent agreement with experiment is found for these generic aspects, and the crucial importance of the experimentally observed near universality of the dynamic crossover time is established. Extensions of the theory to treat the full chain dynamics, heterogeneity, barrier fluctuations, and nonpolymeric thermal glass forming liquids are briefly discussed.

On the role of hydrogel structure and degradation in controlling the transport of cell-secreted matrix molecules for engineered cartilage.

PubMed

Dhote, Valentin; Skaalure, Stacey; Akalp, Umut; Roberts, Justine; Bryant, Stephanie J; Vernerey, Franck J

2013-03-01

Damage to cartilage caused by injury or disease can lead to pain and loss of mobility, diminishing one's quality of life. Because cartilage has a limited capacity for self-repair, tissue engineering strategies, such as cells encapsulated in synthetic hydrogels, are being investigated as a means to restore the damaged cartilage. However, strategies to date are suboptimal in part because designing degradable hydrogels is complicated by structural and temporal complexities of the gel and evolving tissue along multiple length scales. To address this problem, this study proposes a multi-scale mechanical model using a triphasic formulation (solid, fluid, unbound matrix molecules) based on a single chondrocyte releasing extracellular matrix molecules within a degrading hydrogel. This model describes the key players (cells, proteoglycans, collagen) of the biological system within the hydrogel encompassing different length scales. Two mechanisms are included: temporal changes of bulk properties due to hydrogel degradation, and matrix transport. Numerical results demonstrate that the temporal change of bulk properties is a decisive factor in the diffusion of unbound matrix molecules through the hydrogel. Transport of matrix molecules in the hydrogel contributes both to the development of the pericellular matrix and the extracellular matrix and is dependent on the relative size of matrix molecules and the hydrogel mesh. The numerical results also demonstrate that osmotic pressure, which leads to changes in mesh size, is a key parameter for achieving a larger diffusivity for matrix molecules in the hydrogel. The numerical model is confirmed with experimental results of matrix synthesis by chondrocytes in biodegradable poly(ethylene glycol)-based hydrogels. This model may ultimately be used to predict key hydrogel design parameters towards achieving optimal cartilage growth. Copyright © 2012 Elsevier Ltd. All rights reserved.

On the role of hydrogel structure and degradation in controlling the transport of cell-secreted matrix molecules for engineered cartilage

PubMed Central

Dhote, Valentin; Skaalure, Stacey; Akalp, Umut; Roberts, Justine; Bryant, Stephanie J.; Vernerey, Franck J.

2012-01-01

Damage to cartilage caused by injury or disease can lead to pain and loss of mobility, diminishing one’s quality of life. Because cartilage has a limited capacity for self-repair, tissue engineering strategies, such as cells encapsulated in synthetic hydrogels, are being investigated as a means to restore the damaged cartilage. However, strategies to date are suboptimal in part because designing degradable hydrogels is complicated by structural and temporal complexities of the gel and evolving tissue along multiple length scales. To address this problem, this study proposes a multi-scale mechanical model using a triphasic formulation (solid, fluid, unbound matrix molecules) based on a single chondrocyte releasing extracellular matrix molecules within a degrading hydrogel. This model describes the key players (cells, proteoglycans, collagen) of the biological system within the hydrogel encompassing different length scales. Two mechanisms are included: temporal changes of bulk properties due to hydrogel degradation, and matrix transport. Numerical results demonstrate that the temporal change of bulk properties is a decisive factor in the diffusion of unbound matrix molecules through the hydrogel. Transport of matrix molecules in the hydrogel contributes both to the development of the pericellular matrix and the extracellular matrix and is dependent on the relative size of matrix molecules and the hydrogel mesh. The numerical results also demonstrate that osmotic pressure, which leads to changes in mesh size, is a key parameter for achieving a larger diffusivity for matrix molecules in the hydrogel. The numerical model is confirmed with experimental results of matrix synthesis by chondrocytes in biodegradable poly(ethylene glycol)-based hydrogels. This model may ultimately be used to predict key hydrogel design parameters towards achieving optimal cartilage growth. PMID:23276516

Multiscale Characterization of Engineered Cardiac Tissue Architecture.

PubMed

Drew, Nancy K; Johnsen, Nicholas E; Core, Jason Q; Grosberg, Anna

2016-11-01

In a properly contracting cardiac muscle, many different subcellular structures are organized into an intricate architecture. While it has been observed that this organization is altered in pathological conditions, the relationship between length-scales and architecture has not been properly explored. In this work, we utilize a variety of architecture metrics to quantify organization and consistency of single structures over multiple scales, from subcellular to tissue scale as well as correlation of organization of multiple structures. Specifically, as the best way to characterize cardiac tissues, we chose the orientational and co-orientational order parameters (COOPs). Similarly, neonatal rat ventricular myocytes were selected for their consistent architectural behavior. The engineered cells and tissues were stained for four architectural structures: actin, tubulin, sarcomeric z-lines, and nuclei. We applied the orientational metrics to cardiac cells of various shapes, isotropic cardiac tissues, and anisotropic globally aligned tissues. With these novel tools, we discovered: (1) the relationship between cellular shape and consistency of self-assembly; (2) the length-scales at which unguided tissues self-organize; and (3) the correlation or lack thereof between organization of actin fibrils, sarcomeric z-lines, tubulin fibrils, and nuclei. All of these together elucidate some of the current mysteries in the relationship between force production and architecture, while raising more questions about the effect of guidance cues on self-assembly function. These types of metrics are the future of quantitative tissue engineering in cardiovascular biomechanics.

A numerical study of Coulomb interaction effects on 2D hopping transport.

PubMed

Kinkhabwala, Yusuf A; Sverdlov, Viktor A; Likharev, Konstantin K

2006-02-15

We have extended our supercomputer-enabled Monte Carlo simulations of hopping transport in completely disordered 2D conductors to the case of substantial electron-electron Coulomb interaction. Such interaction may not only suppress the average value of hopping current, but also affect its fluctuations rather substantially. In particular, the spectral density S(I)(f) of current fluctuations exhibits, at sufficiently low frequencies, a 1/f-like increase which approximately follows the Hooge scaling, even at vanishing temperature. At higher f, there is a crossover to a broad range of frequencies in which S(I)(f) is nearly constant, hence allowing characterization of the current noise by the effective Fano factor [Formula: see text]. For sufficiently large conductor samples and low temperatures, the Fano factor is suppressed below the Schottky value (F = 1), scaling with the length L of the conductor as F = (L(c)/L)(α). The exponent α is significantly affected by the Coulomb interaction effects, changing from α = 0.76 ± 0.08 when such effects are negligible to virtually unity when they are substantial. The scaling parameter L(c), interpreted as the average percolation cluster length along the electric field direction, scales as [Formula: see text] when Coulomb interaction effects are negligible and [Formula: see text] when such effects are substantial, in good agreement with estimates based on the theory of directed percolation.

Grizzly Staus Report

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

Spencer, Benjamin; Zhang, Yongfeng; Chakraborty, Pritam

2014-09-01

This report summarizes work during FY 2014 to develop capabilities to predict embrittlement of reactor pressure vessel steel, and to assess the response of embrittled reactor pressure vessels to postulated accident conditions. This work has been conducted a three length scales. At the engineering scale, 3D fracture mechanics capabilities have been developed to calculate stress intensities and fracture toughnesses, to perform a deterministic assessment of whether a crack would propagate at the location of an existing flaw. This capability has been demonstrated on several types of flaws in a generic reactor pressure vessel model. Models have been developed at themore » scale of fracture specimens to develop a capability to determine how irradiation affects the fracture toughness of material. Verification work has been performed on a previously-developed model to determine the sensitivity of the model to specimen geometry and size effects. The effects of irradiation on the parameters of this model has been investigated. At lower length scales, work has continued in an ongoing to understand how irradiation and thermal aging affect the microstructure and mechanical properties of reactor pressure vessel steel. Previously-developed atomistic kinetic monte carlo models have been further developed and benchmarked against experimental data. Initial work has been performed to develop models of nucleation in a phase field model. Additional modeling work has also been performed to improve the fundamental understanding of the formation mechanisms and stability of matrix defects caused.« less

Effect of a spacer on localization of topological states in a Bragg multihelicoidal fiber with a twist defect

NASA Astrophysics Data System (ADS)

Alexeyev, C. N.; Lapin, B. P.; Yavorsky, M. A.

2018-01-01

We have studied the influence of a spacer introduced into a Bragg multihelicoidal fiber with a twist defect on the existence of defect-localized states. We have shown that in the presence of a Gaussian pump the energy of the electromagnetic field stored in topologically charged defect-localized modes essentially depends on the length of the spacer. We have demonstrated that by changing this length on the wavelength scale it is possible to strongly modulate such energy. This property can be used for generation and controlled emission of topologically charged light. We have also shown that if the value of an isotropic spacer’s refractive index deviates from the optimal value defined by the parameters of the multihelicoidal fiber parts the effect of localization disappears.

Dielectric response of Anderson and pseudogapped insulators

NASA Astrophysics Data System (ADS)

Feigel’man, M. V.; Ivanov, D. A.; Cuevas, E.

2018-05-01

Using a combination of analytic and numerical methods, we study the polarizability of a (non-interacting) Anderson insulator in one-, two-, and three-dimensions and demonstrate that, in a wide range of parameters, it scales proportionally to the square of the localization length, contrary to earlier claims based on the effective-medium approximation. We further analyze the effect of electron–electron interactions on the dielectric constant in quasi-1D, quasi-2D and 3D materials with large localization length, including both Coulomb repulsion and phonon-mediated attraction. The phonon-mediated attraction (in the pseudogapped state on the insulating side of the superconductor-insulator transition) produces a correction to the dielectric constant, which may be detected from a linear response of a dielectric constant to an external magnetic field.

Influences of Exciton Diffusion and Exciton-Exciton Annihilation on Photon Emission Statistics of Carbon Nanotubes.

PubMed

Ma, Xuedan; Roslyak, Oleskiy; Duque, Juan G; Pang, Xiaoying; Doorn, Stephen K; Piryatinski, Andrei; Dunlap, David H; Htoon, Han

2015-07-03

Pump-dependent photoluminescence imaging and second-order photon correlation studies have been performed on individual single-walled carbon nanotubes (SWCNTs) at room temperature. These studies enable the extraction of both the exciton diffusion constant and the Auger recombination coefficient. A linear correlation between these parameters is attributed to the effect of environmental disorder in setting the exciton mean free path and capture-limited Auger recombination at this length scale. A suppression of photon antibunching is attributed to the creation of multiple spatially nonoverlapping excitons in SWCNTs, whose diffusion length is shorter than the laser spot size. We conclude that complete antibunching at room temperature requires an enhancement of the exciton-exciton annihilation rate that may become realizable in SWCNTs allowing for strong exciton localization.

Direct measurement of Vorticella contraction force by micropipette deflection.

PubMed

France, Danielle; Tejada, Jonathan; Matsudaira, Paul

2017-02-01

The ciliated protozoan Vorticella convallaria is noted for its exceptionally fast adenosine triphosphate-independent cellular contraction, but direct measurements of contractile force have proven difficult given the length scale, speed, and forces involved. We used high-speed video microscopy to image live Vorticella stalled in midcontraction by deflection of an attached micropipette. Stall forces correlate with both distance contracted and the resting stalk length. Estimated isometric forces range from 95 to 177 nanonewtons (nN), or 1.12 nN·μm -1 of the stalk. Maximum velocity and work are also proportional to distance contracted. These parameters constrain proposed biochemical/physical models of the contractile mechanism. © Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Plasmon-driven acceleration in a photo-excited nanotube

DOE PAGES

Shin, Young -Min

2017-02-21

A plasmon-assisted channeling acceleration can be realized with a large channel, possibly at the nanometer scale. Carbon nanotubes (CNTs) are the most typical example of nano-channels that can confine a large number of channeled particles in a photon-plasmon coupling condition. This paper presents a theoretical and numerical study on the concept of high-field charge acceleration driven by photo-excited Luttinger-liquid plasmons in a nanotube. An analytic description of the plasmon-assisted laser acceleration is detailed with practical acceleration parameters, in particular, with the specifications of a typical tabletop femtosecond laser system. Lastly, the maximally achievable acceleration gradients and energy gains within dephasingmore » lengths and CNT lengths are discussed with respect to laser-incident angles and CNT-filling ratios.« less

How much a galaxy knows about its large-scale environment?: An information theoretic perspective

NASA Astrophysics Data System (ADS)

Pandey, Biswajit; Sarkar, Suman

2017-05-01

The small-scale environment characterized by the local density is known to play a crucial role in deciding the galaxy properties but the role of large-scale environment on galaxy formation and evolution still remain a less clear issue. We propose an information theoretic framework to investigate the influence of large-scale environment on galaxy properties and apply it to the data from the Galaxy Zoo project that provides the visual morphological classifications of ˜1 million galaxies from the Sloan Digital Sky Survey. We find a non-zero mutual information between morphology and environment that decreases with increasing length-scales but persists throughout the entire length-scales probed. We estimate the conditional mutual information and the interaction information between morphology and environment by conditioning the environment on different length-scales and find a synergic interaction between them that operates up to at least a length-scales of ˜30 h-1 Mpc. Our analysis indicates that these interactions largely arise due to the mutual information shared between the environments on different length-scales.

Using Multiple Watershed-scale Dye Tracing Tests to Study Water and Solute Transport in Naturally Obstructed Stream Channels

NASA Astrophysics Data System (ADS)

Jin, L.; Meeks, J. L.; Hubbard, K. A.; Kurian, L. M.; Siegel, D. I.; Lautz, L. K.; Otz, M. H.

2007-12-01

Temporary storage of surface water at channel sides and pools significantly affects water and solute transport downstream in watersheds. Beavers, natural "stream channel engineers", build dams which obstruct stream flow and temporarily store water in small to large ponds within stream channels. These ponds substantially delay water movement and increase the water residence time in the system. To study how water and solutes move through these obstructed stream channels, we did multiple dye tracing tests at Cherry Creek, a main tributary to Red Canyon Creek (Wind River Range, Wyoming). First we surveyed beaver dam distributions in detail within the study reaches. We then introduced dyes four times from July 2nd to 6th, 2007 using a scale-up approach. The observation site was fixed at the mouth of Cherry Creek, and 1.5 grams of Rhodamine WT (RWT) dye was injected sequentially at upstream sites with increasing test reach length. The reach lengths scaled up from 500m to 2.5 km. A field fluorometer recorded RWT concentrations every 15 seconds. The results show non-linear decreases of the peak concentration of the dye tracing cloud as the reach scaled up. Also, the times to 1.) the arrivals of the leading edges (Tl), 2.) the peak concentrations (Tp) and 3.) the tailing edges (Tt) and 4) the durations of the tracer cloud (Td) behaved non-linearly as function of length scale. For example, plots of arrivals of leading edges and tailing edges with scale distance appear to define curves of the form; Tl=27.665e1.07× Distance (r2=0.99) and Tt=162.62e0.8551× Distance (r2=0.99), respectively. The greatest non-linearity occurred for the time of tailing and the least for the time of leading edge. These observations are consistent with what would be expected with greater density of dams and/or storage volumes as the reach length increased upgradient. To come to a first approximation, we are currently modeling the breakthrough curves with the solute transport code OTIS to address the relative differences in average travel velocity, longitudinal dispersion, and storage parameters from the mouth to the headwaters of the creek.

Size-dependent elastic/inelastic behavior of enamel over millimeter and nanometer length scales.

PubMed

Ang, Siang Fung; Bortel, Emely L; Swain, Michael V; Klocke, Arndt; Schneider, Gerold A

2010-03-01

The microstructure of enamel like most biological tissues has a hierarchical structure which determines their mechanical behavior. However, current studies of the mechanical behavior of enamel lack a systematic investigation of these hierarchical length scales. In this study, we performed macroscopic uni-axial compression tests and the spherical indentation with different indenter radii to probe enamel's elastic/inelastic transition over four hierarchical length scales, namely: 'bulk enamel' (mm), 'multiple-rod' (10's microm), 'intra-rod' (100's nm with multiple crystallites) and finally 'single-crystallite' (10's nm with an area of approximately one hydroxyapatite crystallite). The enamel's elastic/inelastic transitions were observed at 0.4-17 GPa depending on the length scale and were compared with the values of synthetic hydroxyapatite crystallites. The elastic limit of a material is important as it provides insights into the deformability of the material before fracture. At the smallest investigated length scale (contact radius approximately 20 nm), elastic limit is followed by plastic deformation. At the largest investigated length scale (contact size approximately 2 mm), only elastic then micro-crack induced response was observed. A map of elastic/inelastic regions of enamel from millimeter to nanometer length scale is presented. Possible underlying mechanisms are also discussed. (c) 2009 Elsevier Ltd. All rights reserved.

Implementation of a flow-dependent background error correlation length scale formulation in the NEMOVAR OSTIA system

NASA Astrophysics Data System (ADS)

Fiedler, Emma; Mao, Chongyuan; Good, Simon; Waters, Jennifer; Martin, Matthew

2017-04-01

OSTIA is the Met Office's Operational Sea Surface Temperature (SST) and Ice Analysis system, which produces L4 (globally complete, gridded) analyses on a daily basis. Work is currently being undertaken to replace the original OI (Optimal Interpolation) data assimilation scheme with NEMOVAR, a 3D-Var data assimilation method developed for use with the NEMO ocean model. A dual background error correlation length scale formulation is used for SST in OSTIA, as implemented in NEMOVAR. Short and long length scales are combined according to the ratio of the decomposition of the background error variances into short and long spatial correlations. The pre-defined background error variances vary spatially and seasonally, but not on shorter time-scales. If the derived length scales applied to the daily analysis are too long, SST features may be smoothed out. Therefore a flow-dependent component to determining the effective length scale has also been developed. The total horizontal gradient of the background SST field is used to identify regions where the length scale should be shortened. These methods together have led to an improvement in the resolution of SST features compared to the previous OI analysis system, without the introduction of spurious noise. This presentation will show validation results for feature resolution in OSTIA using the OI scheme, the dual length scale NEMOVAR scheme, and the flow-dependent implementation.

The effects of intrinsic properties and defect structures on the indentation size effect in metals

NASA Astrophysics Data System (ADS)

Maughan, Michael R.; Leonard, Ariel A.; Stauffer, Douglas D.; Bahr, David F.

2017-08-01

The indentation size effect has been linked to the generation of geometrically necessary dislocations that may be impacted by intrinsic materials properties, such as stacking fault energy, and extrinsic defects, such as statistically stored dislocations. Nanoindentation was carried out at room temperature and elevated temperatures on four different metals in a variety of microstructural conditions. A size effect parameter was determined for each material set combining the effects of temperature and existing dislocation structure. Extrinsic defects, particularly dislocation density, dominate the size effect parameter over those due to intrinsic properties such as stacking fault energy. A multi-mechanism description using a series of mechanisms, rather than a single mechanism, is presented as a phenomenological explanation for the observed size effect in these materials. In this description, the size effect begins with a volume scale dominated by sparse sources, next is controlled by the ability of dislocations to cross-slip and multiply, and then finally at larger length scales work hardening and recovery dominate the effect.

Phase transition in the parametric natural visibility graph.

PubMed

Snarskii, A A; Bezsudnov, I V

2016-10-01

We investigate time series by mapping them to the complex networks using a parametric natural visibility graph (PNVG) algorithm that generates graphs depending on arbitrary continuous parameter-the angle of view. We study the behavior of the relative number of clusters in PNVG near the critical value of the angle of view. Artificial and experimental time series of different nature are used for numerical PNVG investigations to find critical exponents above and below the critical point as well as the exponent in the finite size scaling regime. Altogether, they allow us to find the critical exponent of the correlation length for PNVG. The set of calculated critical exponents satisfies the basic Widom relation. The PNVG is found to demonstrate scaling behavior. Our results reveal the similarity between the behavior of the relative number of clusters in PNVG and the order parameter in the second-order phase transitions theory. We show that the PNVG is another example of a system (in addition to magnetic, percolation, superconductivity, etc.) with observed second-order phase transition.

Breaking the power law: Multiscale simulations of self-ion irradiated tungsten

NASA Astrophysics Data System (ADS)

Jin, Miaomiao; Permann, Cody; Short, Michael P.

2018-06-01

The initial stage of radiation defect creation has often been shown to follow a power law distribution at short time scales, recently so with tungsten, following many self-organizing patterns found in nature. The evolution of this damage, however, is dominated by interactions between defect clusters, as the coalescence of smaller defects into clusters depends on the balance between transport, absorption, and emission to/from existing clusters. The long-time evolution of radiation-induced defects in tungsten is studied with cluster dynamics parameterized with lower length scale simulations, and is shown to deviate from a power law size distribution. The effects of parameters such as dose rate and total dose, as parameters affecting the strength of the driving force for defect evolution, are also analyzed. Excellent agreement is achieved with regards to an experimentally measured defect size distribution at 30 K. This study provides another satisfactory explanation for experimental observations in addition to that of primary radiation damage, which should be reconciled with additional validation data.

Improved Atomistic Monte Carlo Simulations Demonstrate that Poly-L-Proline Adopts Heterogeneous Ensembles of Conformations of Semi-Rigid Segments Interrupted by Kinks

PubMed Central

Radhakrishnan, Aditya; Vitalis, Andreas; Mao, Albert H.; Steffen, Adam T.; Pappu, Rohit V.

2012-01-01

Poly-L-proline (PLP) polymers are useful mimics of biologically relevant proline-rich sequences. Biophysical and computational studies of PLP polymers in aqueous solutions are challenging because of the diversity of length scales and the slow time scales for conformational conversions. We describe an atomistic simulation approach that combines an improved ABSINTH implicit solvation model, with conformational sampling based on standard and novel Metropolis Monte Carlo moves. Refinements to forcefield parameters were guided by published experimental data for proline-rich systems. We assessed the validity of our simulation results through quantitative comparisons to experimental data that were not used in refining the forcefield parameters. Our analysis shows that PLP polymers form heterogeneous ensembles of conformations characterized by semi-rigid, rod-like segments interrupted by kinks, which result from a combination of internal cis peptide bonds, flexible backbone ψ-angles, and the coupling between ring puckering and backbone degrees of freedom. PMID:22329658

Turbulence closure for mixing length theories

NASA Astrophysics Data System (ADS)

Jermyn, Adam S.; Lesaffre, Pierre; Tout, Christopher A.; Chitre, Shashikumar M.

2018-05-01

We present an approach to turbulence closure based on mixing length theory with three-dimensional fluctuations against a two-dimensional background. This model is intended to be rapidly computable for implementation in stellar evolution software and to capture a wide range of relevant phenomena with just a single free parameter, namely the mixing length. We incorporate magnetic, rotational, baroclinic, and buoyancy effects exactly within the formalism of linear growth theories with non-linear decay. We treat differential rotation effects perturbatively in the corotating frame using a novel controlled approximation, which matches the time evolution of the reference frame to arbitrary order. We then implement this model in an efficient open source code and discuss the resulting turbulent stresses and transport coefficients. We demonstrate that this model exhibits convective, baroclinic, and shear instabilities as well as the magnetorotational instability. It also exhibits non-linear saturation behaviour, and we use this to extract the asymptotic scaling of various transport coefficients in physically interesting limits.

Surface correlation behaviors of metal-organic Langmuir-Blodgett films on differently passivated Si(001) surfaces

NASA Astrophysics Data System (ADS)

Bal, J. K.; Kundu, Sarathi

2013-03-01

Langmuir-Blodgett films of standard amphiphilic molecules like nickel arachidate and cadmium arachidate are grown on wet chemically passivated hydrophilic (OH-Si), hydrophobic (H-Si), and hydrophilic plus hydrophobic (Br-Si) Si(001) surfaces. Top surface morphologies and height-difference correlation functions g(r) with in-plane separation (r) are obtained from the atomic force microscopy studies. Our studies show that deposited bilayer and trilayer films have self-affine correlation behavior irrespective of different passivations and different types of amphiphilic molecules, however, liquid like correlation coexists only for a small part of r, which is located near the cutoff length (1/κ) or little below the correlation length ξ obtained from the liquid like and self-affine fitting, respectively. Thus, length scale dependent surface correlation behavior is observed for both types of Langmuir-Blodgett films. Metal ion specific interactions (ionic, covalent, etc.,) in the headgroup and the nature of the terminated bond (polar, nonpolar, etc.,) of Si surface are mainly responsible for having different correlation parameters.

Electric field induced microstructures in thin films on physicochemically heterogeneous and patterned substrates.

PubMed

Srivastava, Samanvaya; Reddy, P Dinesh Sankar; Wang, Cindy; Bandyopadhyay, Dipankar; Sharma, Ashutosh

2010-05-07

We study by nonlinear simulations the electric field induced pattern formation in a thin viscous film resting on a topographically or chemically patterned substrate. The thin film microstructures can be aligned to the substrate patterns within a window of parameters where the spinodal length scale of the field induced instability is close to the substrate periodicity. We investigate systematically the change in the film morphology and order when (i) the substrate pattern periodicity is varied at a constant film thickness and (ii) the film thickness is varied at a constant substrate periodicity. Simulations show two distinct pathway of evolution when the substrate-topography changes from protrusions to cavities. The isolated substrate defects generate locally ordered ripplelike structures distinct from the structures on a periodically patterned substrate. In the latter case, film morphology is governed by a competition between the pattern periodicity and the length scale of instability. Relating the thin film morphologies to the underlying substrate pattern has implications for field induced patterning and robustness of inter-interface pattern transfer, e.g., coding-decoding of information printed on a substrate.

Mitigation of hot electrons from laser-plasma instabilities in high-Z, highly ionized plasmas

NASA Astrophysics Data System (ADS)

Fein, J. R.; Holloway, J. P.; Trantham, M. R.; Keiter, P. A.; Edgell, D. H.; Froula, D. H.; Haberberger, D.; Frank, Y.; Fraenkel, M.; Raicher, E.; Shvarts, D.; Drake, R. P.

2017-03-01

Hard x-ray measurements are used to infer production of hot electrons in laser-irradiated planar foils of materials ranging from low- to high-Z. The fraction of laser energy converted to hot electrons, fhot , was reduced by a factor of 103 going from low-Z CH to high-Z Au, and hot electron temperatures were reduced from 40 to ˜20 keV. The reduction in fhot correlates with steepening electron density gradient length-scales inferred from plasma refraction measurements. Radiation hydrodynamic simulations predicted electron density profiles in reasonable agreement with those from measurements. Both multi-beam two-plasmon decay (TPD) and multi-beam stimulated Raman scattering (SRS) were predicted to be above threshold with linear threshold parameters that decreased with increasing Z due to steepening length-scales, as well as enhanced laser absorption and increased electron plasma wave collisional and Landau damping. The results add to the evidence that SRS may play a comparable or a greater role relative to TPD in generating hot electrons in multi-beam experiments.

Surface energy balance estimates at local and regional scales using optical remote sensing from an aircraft platform and atmospheric data collected over semiarid rangelands

USGS Publications Warehouse

Kustas, William P.; Moran, M.S.; Humes, K.S.; Stannard, D.I.; Pinter, P. J.; Hipps, L.E.; Swiatek, E.; Goodrich, D.C.

1994-01-01

Remotely sensed data in the visible, near-infrared, and thermal-infrared wave bands were collected from a low-flying aircraft during the Monsoon '90 field experiment. Monsoon '90 was a multidisciplinary experiment conducted in a semiarid watershed. It had as one of its objectives the quantification of hydrometeorological fluxes during the “monsoon” or wet season. The remote sensing observations along with micrometeprological and atmospheric boundary layer (ABL) data were used to compute the surface energy balance over a range of spatial scales. The procedure involved averaging multiple pixels along transects flown over the meteorological and flux (METFLUX) stations. Average values of the spectral reflectance and thermal-infrared temperatures were computed for pixels of order 10−1 to 101 km in length and were used with atmospheric data for evaluating net radiation (Rn), soil heat flux (G), and sensible (H) and latent (LE) heat fluxes at these same length scales. The model employs a single-layer resistance approach for estimating H that requires wind speed and air temperature in the ABL and a remotely sensed surface temperature. The values of Rn and G are estimated from remote sensing information together with near-surface observations of air temperature, relative humidity, and solar radiation. Finally, LE is solved as the residual term in the surface energy balance equation. Model calculations were compared to measurements from the METFLUX network for three days having different environmental conditions. Average percent differences for the three days between model and the METFLUX estimates of the local fluxes were about 5% for Rn, 20% for Gand H, and 15% for LE. Larger differences occurred during partly cloudy conditions because of errors in interpreting the remote sensing data and the higher spatial and temporal variation in the energy fluxes. Minor variations in modeled energy fluxes were observed when the pixel size representing the remote sensing inputs changed from 0.2 to 2 km. Regional scale estimates of the surface energy balance using bulk ABL properties for the model parameters and input variables and the 10-km pixel data differed from the METFLUX network averages by about 4% for Rn, 10% for G and H, and 15% for LE. Model sensitivity in calculating the turbulent fluxes H and LE to possible variations in key model parameters (i.e., the roughness lengths for heat and momentum) was found to be fairly significant. Therefore the reliability of the methods for estimating key model parameters and potential errors needs further testing over different ecosystems and environmental conditions.

Interactions between a fractal tree-like object and hydrodynamic turbulence: flow structure and characteristic mixing length

NASA Astrophysics Data System (ADS)

Meneveau, C. V.; Bai, K.; Katz, J.

2011-12-01

The vegetation canopy has a significant impact on various physical and biological processes such as forest microclimate, rainfall evaporation distribution and climate change. Most scaled laboratory experimental studies have used canopy element models that consist of rigid vertical strips or cylindrical rods that can be typically represented through only one or a few characteristic length scales, for example the diameter and height for cylindrical rods. However, most natural canopies and vegetation are highly multi-scale with branches and sub-branches, covering a wide range of length scales. Fractals provide a convenient idealization of multi-scale objects, since their multi-scale properties can be described in simple ways (Mandelbrot 1982). While fractal aspects of turbulence have been studied in several works in the past decades, research on turbulence generated by fractal objects started more recently. We present an experimental study of boundary layer flow over fractal tree-like objects. Detailed Particle-Image-Velocimetry (PIV) measurements are carried out in the near-wake of a fractal-like tree. The tree is a pre-fractal with five generations, with three branches and a scale reduction factor 1/2 at each generation. Its similarity fractal dimension (Mandelbrot 1982) is D ~ 1.58. Detailed mean velocity and turbulence stress profiles are documented, as well as their downstream development. We then turn attention to the turbulence mixing properties of the flow, specifically to the question whether a mixing length-scale can be identified in this flow, and if so, how it relates to the geometric length-scales in the pre-fractal object. Scatter plots of mean velocity gradient (shear) and Reynolds shear stress exhibit good linear relation at all locations in the flow. Therefore, in the transverse direction of the wake evolution, the Boussinesq eddy viscosity concept is appropriate to describe the mixing. We find that the measured mixing length increases with increasing streamwise locations. Conversely, the measured eddy viscosity and mixing length decrease with increasing elevation, which differs from eddy viscosity and mixing length behaviors of traditional boundary layers or canopies studied before. In order to find an appropriate length for the flow, several models based on the notion of superposition of scales are proposed and examined. One approach is based on spectral distributions. Another more practical approach is based on length-scale distributions evaluated using fractal geometry tools. These proposed models agree well with the measured mixing length. The results indicate that information about multi-scale clustering of branches as it occurs in fractals has to be incorporated into models of the mixing length for flows through canopies with multiple scales. The research is supported by National Science Foundation grant ATM-0621396 and AGS-1047550.

A first-principles analytical theory for 2D magnetic reconnection in electron and Hall MHD.

NASA Astrophysics Data System (ADS)

Zocco, A.; Simakov, A. N.; Chacon, L.

2007-11-01

While the relevance of two-fluid effects in fast magnetic reconnection is well-known,ootnotetextJ. Birn et al., J. Geophys. Res., 106 (A3), pp. 3715--3719 (2001) a first-principles theory --akin to Sweet and Parker's in resistive MHD-- has been elusive. Here, we present such a first principles steady-state theory for electron MHD,ootnotetextL. Chac'on, A. N. Simakov, A. Zocco, Phys. Rev. Lett., submitted and its extension to Hall.ootnotetextA. N. Simakov, L. Chac'on, in preparation The theory discretizes the extended MHD equations at the reconnection site, leading to a set of time-dependent ODEs. Their steady-state analysis provides predictions for the scaling of relevant quantities with the dissipation coefficients (e.g, resistivity and hyper-resistivity) and other relevant parameters. In particular, we will show that EMHD admits both elongated and open-X point configurations of the reconnection region, and that the reconnection rate Ez can be shown not to scale explicitly with the dissipation parameters. This analytic result confirms earlier computational work on the possibility of fast (dissipation-independent) magnetic reconnection in EMHD. We have extended the EMHD results to Hall MHD, and have found a general scaling law for the reconnection rate (and associated length scales) that bridges the gap between resistive and EMHD.

Towards Characterization, Modeling, and Uncertainty Quantification in Multi-scale Mechanics of Oragnic-rich Shales

NASA Astrophysics Data System (ADS)

Abedi, S.; Mashhadian, M.; Noshadravan, A.

2015-12-01

Increasing the efficiency and sustainability in operation of hydrocarbon recovery from organic-rich shales requires a fundamental understanding of chemomechanical properties of organic-rich shales. This understanding is manifested in form of physics-bases predictive models capable of capturing highly heterogeneous and multi-scale structure of organic-rich shale materials. In this work we present a framework of experimental characterization, micromechanical modeling, and uncertainty quantification that spans from nanoscale to macroscale. Application of experiments such as coupled grid nano-indentation and energy dispersive x-ray spectroscopy and micromechanical modeling attributing the role of organic maturity to the texture of the material, allow us to identify unique clay mechanical properties among different samples that are independent of maturity of shale formations and total organic content. The results can then be used to inform the physically-based multiscale model for organic rich shales consisting of three levels that spans from the scale of elementary building blocks (e.g. clay minerals in clay-dominated formations) of organic rich shales to the scale of the macroscopic inorganic/organic hard/soft inclusion composite. Although this approach is powerful in capturing the effective properties of organic-rich shale in an average sense, it does not account for the uncertainty in compositional and mechanical model parameters. Thus, we take this model one step forward by systematically incorporating the main sources of uncertainty in modeling multiscale behavior of organic-rich shales. In particular we account for the uncertainty in main model parameters at different scales such as porosity, elastic properties and mineralogy mass percent. To that end, we use Maximum Entropy Principle and random matrix theory to construct probabilistic descriptions of model inputs based on available information. The Monte Carlo simulation is then carried out to propagate the uncertainty and consequently construct probabilistic descriptions of properties at multiple length-scales. The combination of experimental characterization and stochastic multi-scale modeling presented in this work improves the robustness in the prediction of essential subsurface parameters in engineering scale.

The snakelike chain character of unstructured RNA.

PubMed

Jacobson, David R; McIntosh, Dustin B; Saleh, Omar A

2013-12-03

In the absence of base-pairing and tertiary structure, ribonucleic acid (RNA) assumes a random-walk conformation, modulated by the electrostatic self-repulsion of the charged, flexible backbone. This behavior is often modeled as a Kratky-Porod "wormlike chain" (WLC) with a Barrat-Joanny scale-dependent persistence length. In this study we report measurements of the end-to-end extension of poly(U) RNA under 0.1 to 10 pN applied force and observe two distinct elastic-response regimes: a low-force, power-law regime characteristic of a chain of swollen blobs on long length scales and a high-force, salt-valence-dependent regime consistent with ion-stabilized crumpling on short length scales. This short-scale structure is additionally supported by force- and salt-dependent quantification of the RNA ion atmosphere composition, which shows that ions are liberated under stretching; the number of ions liberated increases with increasing bulk salt concentration. Both this result and the observation of two elastic-response regimes directly contradict the WLC model, which predicts a single elastic regime across all forces and, when accounting for scale-dependent persistence length, the opposite trend in ion release with salt concentration. We conclude that RNA is better described as a "snakelike chain," characterized by smooth bending on long length scales and ion-stabilized crumpling on short length scales. In monovalent salt, these two regimes are separated by a characteristic length that scales with the Debye screening length, highlighting the determining importance of electrostatics in RNA conformation. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Effect of rotation on fingering convection in stellar and planetary interiors

NASA Astrophysics Data System (ADS)

Sengupta, Sutirtha; Garaud, Pascale

2018-01-01

We study the effects of global rotation on the growth and saturation of the fingering (double-diffusive) instability at low Prandtl numbers and estimate the compositional transport rates as a function of the relevant non-dimensional parameters - the Taylor number, Ta^* (defined in terms of the rotation rate, Ω, thermal diffusivity κ_T and associated finger length scale d) and density ratio through direct numerical simulations. Within our explored range of parameters, we find rotation to have very little effect on vertical transport apart for an exceptional case where a cyclonic large scale vortex (LSV) is observed at low density ratio and fairly high Taylor number. The LSV leads to significant enhancement in the fingering transport rates by concentrating high composition fluid at its core which moves downward. The formation of such LSVs is of particular interest for solving the missing mixing problem in the astrophysical context of RGB stars though the parameter regime in which we observe the emergence of this LSV seems to be quite far from the stellar scenario. However, understanding the basic mechanism driving such large scale structures as observed frequently in polar regions of planets (e.g. those seen by Juno near the poles of Jupiter) is important in general for studies of rotating turbulence and its applications to stellar and planetary interior studies, and will be investigated in further detail in a forthcoming work.

Multiscale approach to micro/macro fatigue crack growth in 2024-T3 aluminum panel

NASA Astrophysics Data System (ADS)

Sih, G. C.

2014-01-01

When two contacting solid surfaces are tightly closed and invisible to the naked eye, the discontinuity is said to be microscopic regardless of whether its length is short or long. By this definition, it is not sufficient to distinguish the difference between a micro- and macro-crack by using the length parameter. Microcracks in high strength metal alloys have been known to be several centimeters or longer. Considered in this work is a dual scale fatigue crack growth model where the main crack can be micro or macro but there prevails an inherent microscopic tip region that is damaged depending on the irregularities of the microstructure. This region is referred to as the "micro-tip" and can be simulated by a sharp wedge with different angles in addition to mixed boundary conditions. The combination is sufficient to model microscopic entities in the form of voids, inclusions, precipitations, interfaces, in addition to subgrain imperfections, or cluster of dislocations. This is accomplished by using the method of "singularity representation" such that closed form asymptotic solutions can be obtained for the development of fatigue crack growth rate relations with three parameters. They include: (1) the crack surface tightness σ* represented by σ o/ σ ∞ = 0.3-0.5 for short cracks in region I, and 0.1-0.2 for long cracks in region II, (2) the micro/macro material properties reflected by the shear modulus ratio µ* (=µmicro/µmacro varying between 2 and 5) and (3) the most sensitive parameter d* being the micro-tip characteristic length d* (= d/ d o) whose magnitude decreases in the direction of region I→II. The existing fatigue crack growth data for 2024-T3 and 7075-T6 aluminum sheets are used to reinterpret the two-parameter d a/d N= C(Δ K) n relation where Δ K has now been re-derived for a microcrack with surfaces tightly in contact. The contact force will depend on the mean stress σm or mean stress ratio R as the primary parameter and on the stress amplitude σ a as the secondary parameter.

Length-scale dependent mechanical properties of Al-Cu eutectic alloy: Molecular dynamics based model and its experimental verification

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

Tiwary, C. S., E-mail: cst.iisc@gmail.com; Chattopadhyay, K.; Chakraborty, S.

2014-05-28

This paper attempts to gain an understanding of the effect of lamellar length scale on the mechanical properties of two-phase metal-intermetallic eutectic structure. We first develop a molecular dynamics model for the in-situ grown eutectic interface followed by a model of deformation of Al-Al{sub 2}Cu lamellar eutectic. Leveraging the insights obtained from the simulation on the behaviour of dislocations at different length scales of the eutectic, we present and explain the experimental results on Al-Al{sub 2}Cu eutectic with various different lamellar spacing. The physics behind the mechanism is further quantified with help of atomic level energy model for different lengthmore » scale as well as different strain. An atomic level energy partitioning of the lamellae and the interface regions reveals that the energy of the lamellae core are accumulated more due to dislocations irrespective of the length-scale. Whereas the energy of the interface is accumulated more due to dislocations when the length-scale is smaller, but the trend is reversed when the length-scale is large beyond a critical size of about 80 nm.« less

Taming active turbulence with patterned soft interfaces.

PubMed

Guillamat, P; Ignés-Mullol, J; Sagués, F

2017-09-15

Active matter embraces systems that self-organize at different length and time scales, often exhibiting turbulent flows apparently deprived of spatiotemporal coherence. Here, we use a layer of a tubulin-based active gel to demonstrate that the geometry of active flows is determined by a single length scale, which we reveal in the exponential distribution of vortex sizes of active turbulence. Our experiments demonstrate that the same length scale reemerges as a cutoff for a scale-free power law distribution of swirling laminar flows when the material evolves in contact with a lattice of circular domains. The observed prevalence of this active length scale can be understood by considering the role of the topological defects that form during the spontaneous folding of microtubule bundles. These results demonstrate an unexpected strategy for active systems to adapt to external stimuli, and provide with a handle to probe the existence of intrinsic length and time scales.Active nematics consist of self-driven components that develop orientational order and turbulent flow. Here Guillamat et al. investigate an active nematic constrained in a quasi-2D geometrical setup and show that there exists an intrinsic length scale that determines the geometry in all forcing regimes.

How extreme was the October 2015 flood in the Carolinas? An assessment of flood frequency analysis and distribution tails

NASA Astrophysics Data System (ADS)

Phillips, R. C.; Samadi, S. Z.; Meadows, M. E.

2018-07-01

This paper examines the frequency, distribution tails, and peak-over-threshold (POT) of extreme floods through analysis that centers on the October 2015 flooding in North Carolina (NC) and South Carolina (SC), United States (US). The most striking features of the October 2015 flooding were a short time to peak (Tp) and a multi-hour continuous flood peak which caused intensive and widespread damages to human lives, properties, and infrastructure. The 2015 flooding was produced by a sequence of intense rainfall events which originated from category 4 hurricane Joaquin over a period of four days. Here, the probability distribution and distribution parameters (i.e., location, scale, and shape) of floods were investigated by comparing the upper part of empirical distributions of the annual maximum flood (AMF) and POT with light- to heavy- theoretical tails: Fréchet, Pareto, Gumbel, Weibull, Beta, and Exponential. Specifically, four sets of U.S. Geological Survey (USGS) gauging data from the central Carolinas with record lengths from approximately 65-125 years were used. Analysis suggests that heavier-tailed distributions are in better agreement with the POT and somewhat AMF data than more often used exponential (light) tailed probability distributions. Further, the threshold selection and record length affect the heaviness of the tail and fluctuations of the parent distributions. The shape parameter and its evolution in the period of record play a critical and poorly understood role in determining the scaling of flood response to intense rainfall.

A molecular scale perspective: Monte Carlo simulation for rupturing of ultra thin polymer film melts

NASA Astrophysics Data System (ADS)

Singh, Satya Pal

2017-04-01

Monte Carlo simulation has been performed to study the rupturing process of thin polymer film under strong confinement. The change in mean square displacement; pair correlation function; density distribution; average bond length and microscopic viscosity are sampled by varying the molecular interaction parameters such as the strength and the equilibrium positions of the bonding, non-bonding potentials and the sizes of the beads. The variation in mean square angular displacement χθ = [ < Δθ2 > - < Δθ>2 ] fits very well to a function of type y (t) = A + B *e-t/τ. This may help to study the viscous properties of the films and its dependence on different parameters. The ultra thin film annealed at high temperature gets ruptured and holes are created in the film mimicking spinodal dewetting. The pair correlation function and density profile reveal rich information about the equilibrium structure of the film. The strength and equilibrium bond length of finite extensible non-linear elastic potential (FENE) and non-bonding Morse potential have clear impact on microscopic rupturing of the film. The beads show Rouse or repetition motion forming rim like structures near the holes created inside the film. The higher order interaction as dipole-quadrupole may get prominence under strong confinement. The enhanced excluded volume interaction under strong confinement may overlap with the molecular dispersion forces. It can work to reorganize the molecules at the bottom of the scale and can imprint its signature in complex patterns evolved.

Investigation of the structure of human dental tissue at multiple length scales using high energy synchrotron X-ray SAXS/WAXS

NASA Astrophysics Data System (ADS)

Sui, Tan; Landini, Gabriel; Korsunsky, Alexander M.

2011-10-01

High energy (>50keV) synchrotron X-ray scattering experiments were carried out on beamline I12 JEEP at the Diamond Light Source (DLS, Oxford, UK). Although a complete human tooth could be studied, in the present study attention was focused on coupons from the region of the Dentin-Enamel Junction (DEJ). Simultaneous high energy SAXS/WAXS measurements were carried out. Quantitative analysis of the results allows multiple length scale characterization of the nano-crystalline structure of dental tissues. SAXS patterns analysis provide insight into the mean thickness and orientation of hydroxyapatite particles, while WAXS (XRD) patterns allow the determination of the crystallographic unit cell parameters of the hydroxyapatite phase. It was found that the average particle thickness determined from SAXS interpretation varies as a function of position in the vicinity of the DEJ. Most mineral particles are randomly orientated within dentin, although preferred orientation emerges and becomes stronger on approach to the enamel. Within the enamel, texture is stronger than anywhere in the dentin, and the determination of lattice parameters can be accomplished by Pawley refinement of the multiple peak diffraction pattern. The results demonstrate the feasibility of using high energy synchrotron X-ray beams for the characterization of human dental tissues. This opens up the opportunity of studying thick samples (e.g., complete teeth) in complex sample environments (e.g., under saline solution). This opens new avenues for the application of high energy synchrotron X-ray scattering to dental research.

On the response to ocean surface currents in synthetic aperture radar imagery

NASA Technical Reports Server (NTRS)

Phillips, O. M.

1984-01-01

The balance of wave action spectral density for a fixed wave-number is expressed in terms of a new dimensionless function, the degree of saturation, b, and is applied to an analysis of the variations of this quantity (and local spectral level) at wave-numbers large compared to that of the spectral peak, that are produced by variations in the ocean surface currents in the presence of wind input and wave breaking. Particular care is taken to provide physically based representations of wind input and loss by wave breaking and a relatively convenient equation is derived that specifies the distribution of the degree of saturation in a current field, relative to its ambient (undisturbed) background in the absence of currents. The magnitude of the variations in b depends on two parameters, U(o)/c, where U/(o) is the velocity scale of the current and c the phase speed of the surface waves at the (fixed) wave-number considered or sampled by SAR, and S = (L/lambda) (u*/c)(2), where L is the length scale of the current distribution, lambda the wavelength of the surface waves the length scale of the current distribution, lambda the wavelength of the surface waves and u* the friction velocity of the wind.

The Formation and Evolution of Galactic Disks with APOGEE and the Gaia Survey

NASA Astrophysics Data System (ADS)

Li, Chengdong; Zhao, Gang; Zhai, Meng; Jia, Yunpeng

2018-06-01

We explore the structure and evolutionary history of Galactic disks with Apache Point Observatory Galactic Evolution Experiment data release 13 (DR13 hereafter) and Gaia Tycho-Gaia Astrometric Solution data. We use the [α/M] ratio to allocate stars into particular Galactic components to elucidate the chemical and dynamical properties of the thin and thick disks. The spatial motions of the sample stars are obtained in Galactic Cartesian and cylindrical coordinates. We analyze the abundance trends and metallicity and [α/M] gradients of the thick and thin disks. We confirm the existence of metal-weak thick-disk stars in Galactic disks. A kinematical method is used to select the thin- and thick-disk stars for comparison. We calculate the scale length and scale height of the kinematically and chemically selected thick and thin disks based on the axisymmetric Jeans equation. We conclude that the scale length of the thick disk is approximately equal to that of the thin disk via a kinematical approach. For the chemical selection, this disparity is about 1 kpc. Finally, we get the stellar orbital parameters and try to unveil the formation scenario of the thick disk. We conclude that the gas-rich merger and radial migration are more reasonable formation scenarios for the thick disk.

Nanoscale wear as a stress-assisted chemical reaction

NASA Astrophysics Data System (ADS)

Jacobs, Tevis D. B.; Carpick, Robert W.

2013-02-01

Wear of sliding contacts leads to energy dissipation and device failure, resulting in massive economic and environmental costs. Typically, wear phenomena are described empirically, because physical and chemical interactions at sliding interfaces are not fully understood at any length scale. Fundamental insights from individual nanoscale contacts are crucial for understanding wear at larger length scales, and to enable reliable nanoscale devices, manufacturing and microscopy. Observable nanoscale wear mechanisms include fracture and plastic deformation, but recent experiments and models propose another mechanism: wear via atom-by-atom removal (`atomic attrition'), which can be modelled using stress-assisted chemical reaction kinetics. Experimental evidence for this has so far been inferential. Here, we quantitatively measure the wear of silicon--a material relevant to small-scale devices--using in situ transmission electron microscopy. We resolve worn volumes as small as 25 +/- 5 nm3, a factor of 103 lower than is achievable using alternative techniques. Wear of silicon against diamond is consistent with atomic attrition, and inconsistent with fracture or plastic deformation, as shown using direct imaging. The rate of atom removal depends exponentially on stress in the contact, as predicted by chemical rate kinetics. Measured activation parameters are consistent with an atom-by-atom process. These results, by direct observation, establish atomic attrition as the primary wear mechanism of silicon in vacuum at low loads.

Electrostatic bending response of a charged helix

NASA Astrophysics Data System (ADS)

Zampetaki, A. V.; Stockhofe, J.; Schmelcher, P.

2018-04-01

We explore the electrostatic bending response of a chain of charged particles confined on a finite helical filament. We analyze how the energy difference Δ E between the bent and the unbent helical chain scales with the length of the helical segment and the radius of curvature and identify features that are not captured by the standard notion of the bending rigidity, normally used as a measure of bending tendency in the linear response regime. Using Δ E to characterize the bending response of the helical chain we identify two regimes with qualitatively different bending behaviors for the ground state configuration: the regime of small and the regime of large radius-to-pitch ratio, respectively. Within the former regime, Δ E changes smoothly with the variation of the system parameters. Of particular interest are its oscillations with the number of charged particles encountered for commensurate fillings which yield length-dependent oscillations in the preferred bending direction of the helical chain. We show that the origin of these oscillations is the nonuniformity of the charge distribution caused by the long-range character of the Coulomb interactions and the finite length of the helix. In the second regime of large values of the radius-to-pitch ratio, sudden changes in the ground state structure of the charges occur as the system parameters vary, leading to complex and discontinuous variations in the ground state bending response Δ E .

AC electrified jets in a flow-focusing device: Jet length scaling

PubMed Central

García-Sánchez, Pablo; Alzaga-Gimeno, Javier; Baret, Jean-Christophe

2016-01-01

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates. PMID:27375826

AC electrified jets in a flow-focusing device: Jet length scaling.

PubMed

Castro-Hernández, Elena; García-Sánchez, Pablo; Alzaga-Gimeno, Javier; Tan, Say Hwa; Baret, Jean-Christophe; Ramos, Antonio

2016-07-01

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates.

Comparison of a low- to high-confinement transition theory with experimental data from DIII-D.

PubMed

Guzdar, P N; Kleva, R G; Groebner, R J; Gohil, P

2002-12-23

From our recent theory based on the generation of shear flow and field in finite beta plasmas, the criterion for bifurcation from low to high confinement mode yields a critical parameter proportional to T(e)/square root (L(n)), where T(e) is the electron temperature and L(n) is the density scale length. The predicted threshold shows very good agreement with edge measurements on discharges undergoing low-to-high transitions in DIII-D. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter. The theory also provides an explanation for pellet injection H modes in DIII-D, thereby unifying unconnected methods for accomplishing the transition.

Angular filter refractometry analysis using simulated annealing.

PubMed

Angland, P; Haberberger, D; Ivancic, S T; Froula, D H

2017-10-01

Angular filter refractometry (AFR) is a novel technique used to characterize the density profiles of laser-produced, long-scale-length plasmas [Haberberger et al., Phys. Plasmas 21, 056304 (2014)]. A new method of analysis for AFR images was developed using an annealing algorithm to iteratively converge upon a solution. A synthetic AFR image is constructed by a user-defined density profile described by eight parameters, and the algorithm systematically alters the parameters until the comparison is optimized. The optimization and statistical uncertainty calculation is based on the minimization of the χ 2 test statistic. The algorithm was successfully applied to experimental data of plasma expanding from a flat, laser-irradiated target, resulting in an average uncertainty in the density profile of 5%-20% in the region of interest.

Convex hull approach for determining rock representative elementary volume for multiple petrophysical parameters using pore-scale imaging and Lattice-Boltzmann modelling

NASA Astrophysics Data System (ADS)

Shah, S. M.; Crawshaw, J. P.; Gray, F.; Yang, J.; Boek, E. S.

2017-06-01

In the last decade, the study of fluid flow in porous media has developed considerably due to the combination of X-ray Micro Computed Tomography (micro-CT) and advances in computational methods for solving complex fluid flow equations directly or indirectly on reconstructed three-dimensional pore space images. In this study, we calculate porosity and single phase permeability using micro-CT imaging and Lattice Boltzmann (LB) simulations for 8 different porous media: beadpacks (with bead sizes 50 μm and 350 μm), sandpacks (LV60 and HST95), sandstones (Berea, Clashach and Doddington) and a carbonate (Ketton). Combining the observed porosity and calculated single phase permeability, we shed new light on the existence and size of the Representative Element of Volume (REV) capturing the different scales of heterogeneity from the pore-scale imaging. Our study applies the concept of the 'Convex Hull' to calculate the REV by considering the two main macroscopic petrophysical parameters, porosity and single phase permeability, simultaneously. The shape of the hull can be used to identify strong correlation between the parameters or greatly differing convergence rates. To further enhance computational efficiency we note that the area of the convex hull (for well-chosen parameters such as the log of the permeability and the porosity) decays exponentially with sub-sample size so that only a few small simulations are needed to determine the system size needed to calculate the parameters to high accuracy (small convex hull area). Finally we propose using a characteristic length such as the pore size to choose an efficient absolute voxel size for the numerical rock.

A two-concentric-loop iterative method in estimation of displacement height and roughness length for momentum and sensible heat.

PubMed

Zhao, Wenguang; Qualls, Russell J; Berliner, Pedro R

2008-11-01

A two-concentric-loop iterative (TCLI) method is proposed to estimate the displacement height and roughness length for momentum and sensible heat by using the measurements of wind speed and air temperature at two heights, sensible heat flux above the crop canopy, and the surface temperature of the canopy. This method is deduced theoretically from existing formulae and equations. The main advantage of this method is that data measured not only under near neutral conditions, but also under unstable and slightly stable conditions can be used to calculate the scaling parameters. Based on the data measured above an Acacia Saligna agroforestry system, the displacement height (d0) calculated by the TCLI method and by a conventional method are compared. Under strict neutral conditions, the two methods give almost the same results. Under unstable conditions, d0 values calculated by the conventional method are systematically lower than those calculated by the TCLI method, with the latter exhibiting only slightly lower values than those seen under strictly neutral conditions. Computation of the average values of the scaling parameters for the agroforestry system showed that the displacement height and roughness length for momentum are 68% and 9.4% of the average height of the tree canopy, respectively, which are similar to percentages found in the literature. The calculated roughness length for sensible heat is 6.4% of the average height of the tree canopy, a little higher than the percentages documented in the literature. When wind direction was aligned within 5 degrees of the row direction of the trees, the average displacement height calculated was about 0.6 m lower than when the wind blew across the row direction. This difference was statistically significant at the 0.0005 probability level. This implies that when the wind blows parallel to the row direction, the logarithmic profile of wind speed is shifted lower to the ground, so that, at a given height, the wind speeds are faster than when the wind blows perpendicular to the row direction.

Performance of Renormalization Group Algebraic Turbulence Model on Boundary Layer Transition Simulation

NASA Technical Reports Server (NTRS)

Ahn, Kyung H.

1994-01-01

The RNG-based algebraic turbulence model, with a new method of solving the cubic equation and applying new length scales, is introduced. An analysis is made of the RNG length scale which was previously reported and the resulting eddy viscosity is compared with those from other algebraic turbulence models. Subsequently, a new length scale is introduced which actually uses the two previous RNG length scales in a systematic way to improve the model performance. The performance of the present RNG model is demonstrated by simulating the boundary layer flow over a flat plate and the flow over an airfoil.

Multiscale Constitutive Modeling of Asphalt Concrete

NASA Astrophysics Data System (ADS)

Underwood, Benjamin Shane

Multiscale modeling of asphalt concrete has become a popular technique for gaining improved insight into the physical mechanisms that affect the material's behavior and ultimately its performance. This type of modeling considers asphalt concrete, not as a homogeneous mass, but rather as an assemblage of materials at different characteristic length scales. For proper modeling these characteristic scales should be functionally definable and should have known properties. Thus far, research in this area has not focused significant attention on functionally defining what the characteristic scales within asphalt concrete should be. Instead, many have made assumptions on the characteristic scales and even the characteristic behaviors of these scales with little to no support. This research addresses these shortcomings by directly evaluating the microstructure of the material and uses these results to create materials of different characteristic length scales as they exist within the asphalt concrete mixture. The objectives of this work are to; 1) develop mechanistic models for the linear viscoelastic (LVE) and damage behaviors in asphalt concrete at different length scales and 2) develop a mechanistic, mechanistic/empirical, or phenomenological formulation to link the different length scales into a model capable of predicting the effects of microstructural changes on the linear viscoelastic behaviors of asphalt concrete mixture, e.g., a microstructure association model for asphalt concrete mixture. Through the microstructural study it is found that asphalt concrete mixture can be considered as a build-up of three different phases; asphalt mastic, fine aggregate matrix (FAM), and finally the coarse aggregate particles. The asphalt mastic is found to exist as a homogenous material throughout the mixture and FAM, and the filler content within this material is consistent with the volumetric averaged concentration, which can be calculated from the job mix formula. It is also found that the maximum aggregate size of the FAM is mixture dependent, but consistent with a gradation parameter from the Baily Method of mixture design. Mechanistic modeling of these different length scales reveals that although many consider asphalt concrete to be a LVE material, it is in fact only quasi-LVE because it shows some tendencies that are inconsistent with LVE theory. Asphalt FAM and asphalt mastic show similar nonlinear tendencies although the exact magnitude of the effect differs. These tendencies can be ignored for damage modeling in the mixture and FAM scales as long as the effects are consistently ignored, but it is found that they must be accounted for in mastic and binder damage modeling. The viscoelastic continuum damage (VECD) model is used for damage modeling in this research. To aid in characterization and application of the VECD model for cyclic testing, a simplified version (S-VECD) is rigorously derived and verified. Through the modeling efforts at each scale, various factors affecting the fundamental and engineering properties at each scale are observed and documented. A microstructure association model that accounts for particle interaction through physico-chemical processes and the effects of aggregate structuralization is developed to links the moduli at each scale. This model is shown to be capable of upscaling the mixture modulus from either the experimentally determined mastic modulus or FAM modulus. Finally, an initial attempt at upscaling the damage and nonlinearity phenomenon is shown.

Surface-Based 3d measurements of aeolian bedforms on Mars

NASA Astrophysics Data System (ADS)

Balme, Matthew; Robson, Ellen; Barnes, Robert; Huber, Ben; Butcher, Frances; Fawdon, Peter; Gupta, Sanjeev; Paar, Gerhard

2017-04-01

The surface of Mars hosts many different types of aeolian bedforms, from small wind-ripples with cm-scale wavelength, through decametre-scale "Transverse Aeolian Ridges" (TARs), to km-scale dunes. To date, all mobile Mars surface-missions ('Rovers') have encountered aeolian bedforms of one kind or another. Aeolian deposits of loose, unconsolidated material provide hazards to Mars Rovers: sinkage into the aeolian material and enhanced slippage can prevent traction and forward progress, forcing the Rover to backtrack (e.g., MER Opportunity) and can even 'trap' the rover ending the mission (e.g., MER Spirit). Here, we present morphometry measurements of meter-scale ripple-like bedforms on Mars, as observed by the MER Opportunity Rover during its traverse across the Meridiani Planum region of Mars. The aim is to assess whether there is a relationship between bedforms parameters that can be measured from orbit such as length and width, and bedform height, which can only be reliably measured from orbit for larger features such as TARs. If such a relationship can be found, it might allow estimates of ripple-height to be made from remote sensing data alone. This could help understand the formation mechanism and provide a better characterization of the hazard presented by these features. For much of the first 30 km of the traverse, Opportunity travelled across flat plains with meter-scale, ripple-like aeolian bedforms ("plains ripples") superposed upon them. During the traverse, the Rover acquired stereo imaging data of its surroundings using both its scientific Pancam cameras system and the navigational Navcam system. Using these data, and newly developed Pro3D™ and PRoViP™ software from Joanneum Research, we obtained Digital Elevation Models of many areas along the traverse, allowing us to measure the heights, widths and lengths of aeolian bedforms. In addition, the same bedforms were digitized from orbital HiRISE image data (25 cm/pix resolution) in ArcGIS software to check for agreement between the ground-based and space-based measurements. We found that there is a clear correlation between bedform height and bedform length (as measured perpendicular to the bedform ridge crest and thus, by inference, parallel to the bedform forming wind). We find that bedform height is about 1/15th of bedform length (or bedform wavelength where bedforms are "saturated") - in agreement with terrestrial measurements of granule ripples. This relationship, and the distribution of bedforms heights observed for different bedforms lengths, can be used to provide a probabilistic method of determining the height distributions of bedforms in a given area, simply by measuring their lengths from orbit. This will be useful for determining traversability by Rovers, and so is helpful both for landing site selection and strategic planning of Rover routes.

Instream Attenuation of Nitrogen and Phosphorus in Non-Point Source Dominated Streams: Hydrologic and Biogeochemical Controls

NASA Astrophysics Data System (ADS)

Bray, E. N.; Chen, X.; Keller, A. A.

2010-12-01

Non-point source inputs of total nitrogen (TN) and total phosphorus (TP) in rivers are the leading causes of water quality degradation in the United States (Turner and Rabalais, 2003; Broussard and Turner, 2009). Yet it remains a challenge to adequately quantify the relative role and influence of physical hydrological processes versus biogeochemical processes on the attenuation of TN and TP for individual river reaches. A watershed-scale study of instream dynamics and attenuation of TN and TP in northeastern U.S. headwater streams demonstrates that physical and hydrological processes exert greater control over nutrient removal than biogeochemical processes. To explore these interactions under various attenuation scenarios, we developed the watershed-scale model (WARMF) for 97 catchments to simulate watershed processes, hydrology, and diffuse source loads of nutrients. We simulated a hypothetical nutrient release at a rate of 1 kg/d of TN (50% as ammonium and 50% as nitrate) and TP (100% as phosphate) to predict response lengths of downstream catchments. Resulting attenuation factors are presented as the change in mean load at a given location, normalized to the change in the catchment in which the load is applied. Results indicate that for most catchments, the TN and TP load increase is attenuated from the stream within a few tens of kilometers. Fifty percent attenuation occurs across length scales ranging from a few hundreds of meters to kilometers if the load is introduced in the headwaters, indicating the most rapid nutrient removal occurs in the smallest headwater streams but generally decreases with distance downstream. There are some differences in the attenuation factors for TN and TP, although the pattern of attenuation is the same. Sensitivity analyses highlight five hydrological parameters of paramount importance to concentrations of N and P, namely precipitation, evaporation coefficients (magnitude and skewness), soil layer thickness, soil saturated moisture and soil hydraulic conductivity. These model parameters have a significant effect on the concentrations of nutrients, with TN exhibiting greater sensitivity. Further, attenuation results suggest that stream depth, flow regime, and density of agriculture in small headwater streams are potentially important controls to nutrient uptake and removal; i.e. during periods of low flow, dilution is reduced, attenuation length increases, and removal processes may be dominated by settling as opposed to biogeochemistry. Instream attenuation and model results can be used to assess 1) the scale and nature of best management practices which must be adopted to result in nutrient reductions, 2) the downstream distance at which load reductions will be effective, and 3) the hydrological characteristics of the river network which exert considerable influence on attenuation lengths and nutrient removal.

The association between the maximum step length test and the walking efficiency in children with cerebral palsy.

PubMed

Kimoto, Minoru; Okada, Kyoji; Sakamoto, Hitoshi; Kondou, Takanori

2017-05-01

[Purpose] To improve walking efficiency could be useful for reducing fatigue and extending possible period of walking in children with cerebral palsy (CP). For this purpose, current study compared conventional parameters of gross motor performance, step length, and cadence in the evaluation of walking efficiency in children with CP. [Subjects and Methods] Thirty-one children with CP (21 boys, 10 girls; mean age, 12.3 ± 2.7 years) participated. Parameters of gross motor performance, including the maximum step length (MSL), maximum side step length, step number, lateral step up number, and single leg standing time, were measured in both dominant and non-dominant sides. Spatio-temporal parameters of walking, including speed, step length, and cadence, were calculated. Total heart beat index (THBI), a parameter of walking efficiency, was also calculated from heartbeats and walking distance in 10 minutes of walking. To analyze the relationships between these parameters and the THBI, the coefficients of determination were calculated using stepwise analysis. [Results] The MSL of the dominant side best accounted for the THBI (R 2 =0.759). [Conclusion] The MSL of the dominant side was the best explanatory parameter for walking efficiency in children with CP.

Control of DNA-Functionalized Nanoparticle Assembly

NASA Astrophysics Data System (ADS)

Olvera de La Cruz, Monica

Directed crystallization of a large variety of nanoparticles, including proteins, via DNA hybridization kinetics has led to unique materials with a broad range of crystal symmetries. The nanoparticles are functionalized with DNA chains that link neighboring functionalized units. The shape of the nanoparticle, the DNA length, the sequence of the hybridizing DNA linker and the grafting density determine the crystal symmetries and lattice spacing. By carefully selecting these parameters one can, in principle, achieve all the symmetries found for both atomic and colloidal crystals of asymmetric shapes as well as new symmetries, and drive transitions between them. A scale-accurate coarse-grained model with explicit DNA chains provides the design parameters, including degree of hybridization, to achieve specific crystal structures. The model also provides surface energy values to determine the shape of defect-free single crystals with macroscopic anisotropic properties, as well as the parameters to develop colloidal models that reproduce both the shape of single crystals and their growth kinetics.

Aerodynamic configuration design using response surface methodology analysis

NASA Technical Reports Server (NTRS)

Engelund, Walter C.; Stanley, Douglas O.; Lepsch, Roger A.; Mcmillin, Mark M.; Unal, Resit

1993-01-01

An investigation has been conducted to determine a set of optimal design parameters for a single-stage-to-orbit reentry vehicle. Several configuration geometry parameters which had a large impact on the entry vehicle flying characteristics were selected as design variables: the fuselage fineness ratio, the nose to body length ratio, the nose camber value, the wing planform area scale factor, and the wing location. The optimal geometry parameter values were chosen using a response surface methodology (RSM) technique which allowed for a minimum dry weight configuration design that met a set of aerodynamic performance constraints on the landing speed, and on the subsonic, supersonic, and hypersonic trim and stability levels. The RSM technique utilized, specifically the central composite design method, is presented, along with the general vehicle conceptual design process. Results are presented for an optimized configuration along with several design trade cases.

Empirical scaling of the length of the longest increasing subsequences of random walks

NASA Astrophysics Data System (ADS)

Mendonça, J. Ricardo G.

2017-02-01

We provide Monte Carlo estimates of the scaling of the length L n of the longest increasing subsequences of n-step random walks for several different distributions of step lengths, short and heavy-tailed. Our simulations indicate that, barring possible logarithmic corrections, {{L}n}∼ {{n}θ} with the leading scaling exponent 0.60≲ θ ≲ 0.69 for the heavy-tailed distributions of step lengths examined, with values increasing as the distribution becomes more heavy-tailed, and θ ≃ 0.57 for distributions of finite variance, irrespective of the particular distribution. The results are consistent with existing rigorous bounds for θ, although in a somewhat surprising manner. For random walks with step lengths of finite variance, we conjecture that the correct asymptotic behavior of L n is given by \\sqrt{n}\\ln n , and also propose the form for the subleading asymptotics. The distribution of L n was found to follow a simple scaling form with scaling functions that vary with θ. Accordingly, when the step lengths are of finite variance they seem to be universal. The nature of this scaling remains unclear, since we lack a working model, microscopic or hydrodynamic, for the behavior of the length of the longest increasing subsequences of random walks.

Smart Photonic Carbon Brush: FBG Length as Sensing Parameter

NASA Astrophysics Data System (ADS)

Morozov, O. G.; Nureev, I. I.; Kuznetsov, A. A.; Artemiev, V. I.

2018-04-01

This article deals with problem of carbon brush’s length measurements. There are many applications where regular inspection is not feasible because of a number of factors including, for example, time, labor, cost and disruptions due to down time. Thus, there is a need for a system that can monitor the brush’s length to calculate it’s wear rate, while the component is in operation or without removing of the component from its operational position. We propose a novel method for characterization of carbon brush’s length. This method based on the usage of advantages of the multiplicative response of FBGs and FBG arrays: spectral parameters depend on several aspects, such as grating’s period, refractive index, it’s physical length and so on. We are the first, in our point of view, who proposed to use third parameter for sensing application and prospectively all three parameters for complex measurement: the change of FBG’s length is used to measure length of the brush and it’s wear rate, grating’s central wavelength shift for temperature (due to refractive index change) and mechanical stress (due to grating’s period variations) measurements. The results of modelling and experiments are presented.

High-resolution simulation of deep pencil beam surveys - analysis of quasi-periodicity

NASA Astrophysics Data System (ADS)

Weiss, A. G.; Buchert, T.

1993-07-01

We carry out pencil beam constructions in a high-resolution simulation of the large-scale structure of galaxies. The initial density fluctuations are taken to have a truncated power spectrum. All the models have {OMEGA} = 1. As an example we present the results for the case of "Hot-Dark-Matter" (HDM) initial conditions with scale-free n = 1 power index on large scales as a representative of models with sufficient large-scale power. We use an analytic approximation for particle trajectories of a self-gravitating dust continuum and apply a local dynamical biasing of volume elements to identify luminous matter in the model. Using this method, we are able to resolve formally a simulation box of 1200h^-1^ Mpc (e.g. for HDM initial conditions) down to the scale of galactic halos using 2160^3^ particles. We consider this as the minimal resolution necessary for a sensible simulation of deep pencil beam data. Pencil beam probes are taken for a given epoch using the parameters of observed beams. In particular, our analysis concentrates on the detection of a quasi-periodicity in the beam probes using several different methods. The resulting beam ensembles are analyzed statistically using number distributions, pair-count histograms, unnormalized pair-counts, power spectrum analysis and trial-period folding. Periodicities are classified according to their significance level in the power spectrum of the beams. The simulation is designed for application to parameter studies which prepare future observational projects. We find that a large percentage of the beams show quasi- periodicities with periods which cluster at a certain length scale. The periods found range between one and eight times the cutoff length in the initial fluctuation spectrum. At significance levels similar to those of the data of Broadhurst et al. (1990), we find about 15% of the pencil beams to show periodicities, about 30% of which are around the mean separation of rich clusters, while the distribution of scales reaches values of more than 200h^-1^ Mpc. The detection of periodicities larger than the typical void size must not be due to missing of "walls" (like the so called "Great Wall" seen in the CfA catalogue of galaxies), but can be due to different clustering properties of galaxies along the beams.

Impact of the plasma geometry on divertor power exhaust: experimental evidence from TCV and simulations with SolEdge2D and TOKAM3X

NASA Astrophysics Data System (ADS)

Gallo, A.; Fedorczak, N.; Elmore, S.; Maurizio, R.; Reimerdes, H.; Theiler, C.; Tsui, C. K.; Boedo, J. A.; Faitsch, M.; Bufferand, H.; Ciraolo, G.; Galassi, D.; Ghendrih, P.; Valentinuzzi, M.; Tamain, P.; the EUROfusion MST1 Team; the TCV Team

2018-01-01

A deep understanding of plasma transport at the edge of magnetically confined fusion plasmas is needed for the handling and control of heat loads on the machine first wall. Experimental observations collected on a number of tokamaks over the last three decades taught us that heat flux profiles at the divertor targets of X-point configurations can be parametrized by using two scale lengths for the scrape-off layer (SOL) transport, separately characterizing the main SOL ({λ }q) and the divertor SOL (S q ). In this work we challenge the current interpretation of these two scale lengths as well as their dependence on plasma parameters by studying the effect of divertor geometry modifications on heat exhaust in the Tokamak à Configuration Variable. In particular, a significant broadening of the heat flux profiles at the outer divertor target is diagnosed while increasing the length of the outer divertor leg in lower single null, Ohmic, L-mode discharges. Efforts to reproduce this experimental finding with both diffusive (SolEdge2D-EIRENE) and turbulent (TOKAM3X) modelling tools confirm the validity of a diffusive approach for simulating heat flux profiles in more traditional, short leg, configurations while highlighting the need of a turbulent description for modified, long leg, ones in which strongly asymmetric divertor perpendicular transport develops.

Nanofluidic rocking Brownian motors

NASA Astrophysics Data System (ADS)

Skaug, Michael J.; Schwemmer, Christian; Fringes, Stefan; Rawlings, Colin D.; Knoll, Armin W.

2018-03-01

Control and transport of nanoscale objects in fluids is challenging because of the unfavorable scaling of most interaction mechanisms to small length scales. We designed energy landscapes for nanoparticles by accurately shaping the geometry of a nanofluidic slit and exploiting the electrostatic interaction between like-charged particles and walls. Directed transport was performed by combining asymmetric potentials with an oscillating electric field to achieve a rocking Brownian motor. Using gold spheres 60 nanometers in diameter, we investigated the physics of the motor with high spatiotemporal resolution, enabling a parameter-free comparison with theory. We fabricated a sorting device that separates 60- and 100-nanometer particles in opposing directions within seconds. Modeling suggests that the device separates particles with a radial difference of 1 nanometer.

Direct numerical simulations of three-dimensional electrokinetic flows

NASA Astrophysics Data System (ADS)

Chiam, Keng-Hwee

2006-11-01

We discuss direct numerical simulations of three-dimensional electrokinetic flows in microfluidic devices. In particular, we focus on the study of the electrokinetic instability that develops when two solutions with different electrical conductivities are coupled to an external electric field. We characterize this ``mixing'' instability as a function of the parameters of the model, namely the Reynolds number of the flow, the electric Peclet number of the electrolyte solution, and the ratio of the electroosmotic to the electroviscous time scales. Finally, we describe how this model breaks down when the length scale of the device approaches the nanoscale, where the width of the electric Debye layer is comparable to the width of the channel, and discuss solutions to overcome this.

Cavitation in Amorphous Solids

NASA Astrophysics Data System (ADS)

Guan, Pengfei; Lu, Shuo; Spector, Michael J. B.; Valavala, Pavan K.; Falk, Michael L.

2013-05-01

Molecular dynamics simulations of cavitation in a Zr50Cu50 metallic glass exhibit a waiting time dependent cavitation rate. On short time scales nucleation rates and critical cavity sizes are commensurate with a classical theory of nucleation that accounts for both the plastic dissipation during cavitation and the cavity size dependence of the surface energy. All but one parameter, the Tolman length, can be extracted directly from independent calculations or estimated from physical principles. On longer time scales strain aging in the form of shear relaxations results in a systematic decrease of cavitation rate. The high cavitation rates that arise due to the suppression of the surface energy in small cavities provide a possible explanation for the quasibrittle fracture observed in metallic glasses.

Space and time renormalization in phase transition dynamics

DOE PAGES

Francuz, Anna; Dziarmaga, Jacek; Gardas, Bartłomiej; ...

2016-02-18

Here, when a system is driven across a quantum critical point at a constant rate, its evolution must become nonadiabatic as the relaxation time τ diverges at the critical point. According to the Kibble-Zurek mechanism (KZM), the emerging post-transition excited state is characterized by a finite correlation length ξˆ set at the time tˆ=τˆ when the critical slowing down makes it impossible for the system to relax to the equilibrium defined by changing parameters. This observation naturally suggests a dynamical scaling similar to renormalization familiar from the equilibrium critical phenomena. We provide evidence for such KZM-inspired spatiotemporal scaling by investigatingmore » an exact solution of the transverse field quantum Ising chain in the thermodynamic limit.« less

Tip vortices in the actuator line model

NASA Astrophysics Data System (ADS)

Martinez, Luis; Meneveau, Charles

2017-11-01

The actuator line model (ALM) is a widely used tool to represent the wind turbine blades in computational fluid dynamics without the need to resolve the full geometry of the blades. The ALM can be optimized to represent the `correct' aerodynamics of the blades by choosing an appropriate smearing length scale ɛ. This appropriate length scale creates a tip vortex which induces a downwash near the tip of the blade. A theoretical frame-work is used to establish a solution to the induced velocity created by a tip vortex as a function of the smearing length scale ɛ. A correction is presented which allows the use of a non-optimal smearing length scale but still provides the downwash which would be induced using the optimal length scale. Thanks to the National Science Foundation (NSF) who provided financial support for this research via Grants IGERT 0801471, IIA-1243482 (the WINDINSPIRE project) and ECCS-1230788.

A global sensitivity analysis of crop virtual water content

NASA Astrophysics Data System (ADS)

Tamea, S.; Tuninetti, M.; D'Odorico, P.; Laio, F.; Ridolfi, L.

2015-12-01

The concepts of virtual water and water footprint are becoming widely used in the scientific literature and they are proving their usefulness in a number of multidisciplinary contexts. With such growing interest a measure of data reliability (and uncertainty) is becoming pressing but, as of today, assessments of data sensitivity to model parameters, performed at the global scale, are not known. This contribution aims at filling this gap. Starting point of this study is the evaluation of the green and blue virtual water content (VWC) of four staple crops (i.e. wheat, rice, maize, and soybean) at a global high resolution scale. In each grid cell, the crop VWC is given by the ratio between the total crop evapotranspiration over the growing season and the crop actual yield, where evapotranspiration is determined with a detailed daily soil water balance and actual yield is estimated using country-based data, adjusted to account for spatial variability. The model provides estimates of the VWC at a 5x5 arc minutes and it improves on previous works by using the newest available data and including multi-cropping practices in the evaluation. The model is then used as the basis for a sensitivity analysis, in order to evaluate the role of model parameters in affecting the VWC and to understand how uncertainties in input data propagate and impact the VWC accounting. In each cell, small changes are exerted to one parameter at a time, and a sensitivity index is determined as the ratio between the relative change of VWC and the relative change of the input parameter with respect to its reference value. At the global scale, VWC is found to be most sensitive to the planting date, with a positive (direct) or negative (inverse) sensitivity index depending on the typical season of crop planting date. VWC is also markedly dependent on the length of the growing period, with an increase in length always producing an increase of VWC, but with higher spatial variability for rice than for other crops. The sensitivity to the reference evapotranspiration is highly variable with the considered crop and ranges from positive values (for soybean), to negative values (for rice and maize) and near-zero values for wheat. This variability reflects the different yield response factors of crops, which expresses their tolerance to water stress.

Modeling of Ceiling Fire Spread and Thermal Radiation.

DTIC Science & Technology

1981-10-01

under a PMMA ceiling and flame lengths under an inert ceiling are found to be in reasonable agreement with full-scale behavior. Although fire spread...5 3 Flame Lengths under Full-Scale Ceilings 12 4 Correlation of Flame Length under Inert Ceilings 16 5 Correlation of Flame Length under No 234 Model...Ceilings 17 6 Correlation of Flame Length under No B8811 Model Ceilings 18 7 Correlation of Flame Length under No. 223 Model Ceilings 19 8

Natural Length Scales Shape Liquid Phase Continuity in Unsaturated Flows

NASA Astrophysics Data System (ADS)

Assouline, S.; Lehmann, P. G.; Or, D.

2015-12-01

Unsaturated flows supporting soil evaporation and internal drainage play an important role in various hydrologic and climatic processes manifested at a wide range of scales. We study inherent natural length scales that govern these flow processes and constrain the spatial range of their representation by continuum models. These inherent length scales reflect interactions between intrinsic porous medium properties that affect liquid phase continuity, and the interplay among forces that drive and resist unsaturated flow. We have defined an intrinsic length scale for hydraulic continuity based on pore size distribution that controls soil evaporation dynamics (i.e., stage 1 to stage 2 transition). This simple metric may be used to delineate upper bounds for regional evaporative losses or the depth of soil-atmosphere interactions (in the absence of plants). A similar length scale governs the dynamics of internal redistribution towards attainment of field capacity, again through its effect on hydraulic continuity in the draining porous medium. The study provides a framework for guiding numerical and mathematical models for capillary flows across different scales considering the necessary conditions for coexistence of stationarity (REV), hydraulic continuity and intrinsic capillary gradients.

Telomere length is an independent prognostic marker in MDS but not in de novo AML.

PubMed

Williams, Jenna; Heppel, Nicole H; Britt-Compton, Bethan; Grimstead, Julia W; Jones, Rhiannon E; Tauro, Sudhir; Bowen, David T; Knapper, Steven; Groves, Michael; Hills, Robert K; Pepper, Chris; Baird, Duncan M; Fegan, Chris

2017-07-01

Telomere dysfunction is implicated in the generation of large-scale genomic rearrangements that drive progression to malignancy. In this study we used high-resolution single telomere length analysis (STELA) to examine the potential role of telomere dysfunction in 80 myelodysplastic syndrome (MDS) and 95 de novo acute myeloid leukaemia (AML) patients. Despite the MDS cohort being older, they had significantly longer telomeres than the AML cohort (P < 0·0001) where telomere length was also significantly shorter in younger AML patients (age <60 years) (P = 0·02) and in FLT3 internal tandem duplication-mutated AML patients (P = 0·03). Using a previously determined telomere length threshold for telomere dysfunction (3·81 kb) did not provide prognostic resolution in AML [Hazard ratio (HR) = 0·68, P = 0·2]. In contrast, the same length threshold was highly prognostic for overall survival in the MDS cohort (HR = 5·0, P < 0·0001). Furthermore, this telomere length threshold was an independent parameter in multivariate analysis when adjusted for age, gender, cytogenetic risk group, number of cytopenias and International Prognostic Scoring System (IPSS) score (HR = 2·27, P < 0·0001). Therefore, telomere length should be assessed in a larger prospective study to confirm its prognostic role in MDS with a view to integrating this variable into a revised IPSS. © 2017 John Wiley & Sons Ltd.

A comparative study on cotton fiber length parameters’ effects on modeling yarn property

USDA-ARS?s Scientific Manuscript database

Fiber length is one of the key properties of cotton and has important influences on yarn production and yarn quality. Various parameters have been developed to characterize cotton fiber length in the past decades. This study was carried out to investigate the effects of these parameters and their ...

Transport-Induced Spatial Patterns of Sulfur Isotopes (δ34S) as Biosignatures

NASA Astrophysics Data System (ADS)

Mansor, Muammar; Harouaka, Khadouja; Gonzales, Matthew S.; Macalady, Jennifer L.; Fantle, Matthew S.

2018-01-01

Cave minerals deposited in the presence of microbes may host geochemical biosignatures that can be utilized to detect subsurface life on Earth, Mars, or other habitable worlds. The sulfur isotopic composition of gypsum (CaSO4·2H2O) formed in the presence of sulfur-oxidizing microbes in the Frasassi cave system, Italy, was evaluated as a biosignature. Sulfur isotopic compositions (δ34SV-CDT) of gypsum sampled from cave rooms with sulfidic air varied from -11 to -24‰, with minor deposits of elemental sulfur having δ34S values between -17 and -19‰. Over centimeter-length scales, the δ34S values of gypsum varied by up to 8.5‰. Complementary laboratory experiments showed negligible fractionation during the oxidation of elemental sulfur to sulfate by Acidithiobacillus thiooxidans isolated from the caves. Additionally, gypsum precipitated in the presence and absence of microbes at acidic pH characteristic of the sulfidic cave walls has δ34S values that are on average 1‰ higher than sulfate. We therefore interpret the 8.5‰ variation in cave gypsum δ34S (toward more negative values) to reflect the isotopic effect of microbial sulfide oxidation directly to sulfate or via elemental sulfur intermediate. This range is similar to that expected by abiotic sulfide oxidation with oxygen, thus complicating the use of sulfur isotopes as a biosignature at centimeter-length scales. However, at the cave room (meter-length) scale, reactive transport modeling suggests that the overall ˜13‰ variability in gypsum δ34S reflects isotopic distillation of circulating H2S gas due to microbial sulfide oxidation occurring along the cave wall-atmosphere interface. Systematic variations of gypsum δ34S along gas flow paths can thus be interpreted as biogenic given that slow, abiotic oxidation cannot produce the same spatial patterns over similar length scales. The expression and preservation potential of this biosignature is dependent on gas flow parameters and diagenetic processes that modify gypsum δ34S values over geological timescales.

Plasma and cold sprayed aluminum carbon nanotube composites: Quantification of nanotube distribution and multi-scale mechanical properties

NASA Astrophysics Data System (ADS)

Bakshi, Srinivasa Rao

Carbon nanotubes (CNT) could serve as potential reinforcement for metal matrix composites for improved mechanical properties. However dispersion of carbon nanotubes (CNT) in the matrix has been a longstanding problem, since they tend to form clusters to minimize their surface area. The aim of this study was to use plasma and cold spraying techniques to synthesize CNT reinforced aluminum composite with improved dispersion and to quantify the degree of CNT dispersion as it influences the mechanical properties. Novel method of spray drying was used to disperse CNTs in Al-12 wt.% Si prealloyed powder, which was used as feedstock for plasma and cold spraying. A new method for quantification of CNT distribution was developed. Two parameters for CNT dispersion quantification, namely Dispersion parameter (DP) and Clustering Parameter (CP) have been proposed based on the image analysis and distance between the centers of CNTs. Nanomechanical properties were correlated with the dispersion of CNTs in the microstructure. Coating microstructure evolution has been discussed in terms of splat formation, deformation and damage of CNTs and CNT/matrix interface. Effect of Si and CNT content on the reaction at CNT/matrix interface was thermodynamically and kinetically studied. A pseudo phase diagram was computed which predicts the interfacial carbide for reaction between CNT and Al-Si alloy at processing temperature. Kinetic aspects showed that Al4C3 forms with Al-12 wt.% Si alloy while SiC forms with Al-23wt.% Si alloy. Mechanical properties at nano, micro and macro-scale were evaluated using nanoindentation and nanoscratch, microindentation and bulk tensile testing respectively. Nano and micro-scale mechanical properties (elastic modulus, hardness and yield strength) displayed improvement whereas macro-scale mechanical properties were poor. The inversion of the mechanical properties at different scale length was attributed to the porosity, CNT clustering, CNT-splat adhesion and Al 4C3 formation at the CNT/matrix interface. The Dispersion parameter (DP) was more sensitive than Clustering parameter (CP) in measuring degree of CNT distribution in the matrix.

Failure analysis of fuel cell electrodes using three-dimensional multi-length scale X-ray computed tomography

NASA Astrophysics Data System (ADS)

Pokhrel, A.; El Hannach, M.; Orfino, F. P.; Dutta, M.; Kjeang, E.

2016-10-01

X-ray computed tomography (XCT), a non-destructive technique, is proposed for three-dimensional, multi-length scale characterization of complex failure modes in fuel cell electrodes. Comparative tomography data sets are acquired for a conditioned beginning of life (BOL) and a degraded end of life (EOL) membrane electrode assembly subjected to cathode degradation by voltage cycling. Micro length scale analysis shows a five-fold increase in crack size and 57% thickness reduction in the EOL cathode catalyst layer, indicating widespread action of carbon corrosion. Complementary nano length scale analysis shows a significant reduction in porosity, increased pore size, and dramatically reduced effective diffusivity within the remaining porous structure of the catalyst layer at EOL. Collapsing of the structure is evident from the combination of thinning and reduced porosity, as uniquely determined by the multi-length scale approach. Additionally, a novel image processing based technique developed for nano scale segregation of pore, ionomer, and Pt/C dominated voxels shows an increase in ionomer volume fraction, Pt/C agglomerates, and severe carbon corrosion at the catalyst layer/membrane interface at EOL. In summary, XCT based multi-length scale analysis enables detailed information needed for comprehensive understanding of the complex failure modes observed in fuel cell electrodes.

Modeling Framework for Fracture in Multiscale Cement-Based Material Structures

PubMed Central

Qian, Zhiwei; Schlangen, Erik; Ye, Guang; van Breugel, Klaas

2017-01-01

Multiscale modeling for cement-based materials, such as concrete, is a relatively young subject, but there are already a number of different approaches to study different aspects of these classical materials. In this paper, the parameter-passing multiscale modeling scheme is established and applied to address the multiscale modeling problem for the integrated system of cement paste, mortar, and concrete. The block-by-block technique is employed to solve the length scale overlap challenge between the mortar level (0.1–10 mm) and the concrete level (1–40 mm). The microstructures of cement paste are simulated by the HYMOSTRUC3D model, and the material structures of mortar and concrete are simulated by the Anm material model. Afterwards the 3D lattice fracture model is used to evaluate their mechanical performance by simulating a uniaxial tensile test. The simulated output properties at a lower scale are passed to the next higher scale to serve as input local properties. A three-level multiscale lattice fracture analysis is demonstrated, including cement paste at the micrometer scale, mortar at the millimeter scale, and concrete at centimeter scale. PMID:28772948

Earthquake nucleation on faults with rate-and state-dependent strength

USGS Publications Warehouse

Dieterich, J.H.

1992-01-01

Dieterich, J.H., 1992. Earthquake nucleation on faults with rate- and state-dependent strength. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 115-134. Faults with rate- and state-dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability. Calculations with a plane-strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch. The dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip. The critical length is a function of normal stress, loading conditions and constitutive parameters which include Dc, the characteristic slip distance. If slip starts on a patch that exceeds the critical size, the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches. Solutions have been obtained for a uniform, fixed-patch model that are in good agreement with results from the plane-strain model. Over a wide range of conditions, above the steady-state stress, the logarithm of the time to instability linearly decreases as the initial stress increases. Because nucleation patch length and premonitory displacement are proportional to Dc, the moment of premonitory slip scales by D3c. The scaling of Dc is currently an open question. Unless Dc for earthquake faults is significantly greater than that observed on laboratory faults, premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods. Excluding the possibility that Dc in the nucleation zone controls the magnitude of the subsequent earthquake, then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch. ?? 1992.

Growth, mortality and reproduction of the blue tilapia Oreochromis aureus (Perciformes: Cichlidae) in the Aguamilpa Reservoir, Mexico.

PubMed

Peña Messina, Emilio; Tapia Varela, Raul; Velázquez Abunader, José Iván; Orbe Mendoza, Alma Araceli; Velazco Arce, Javier Marcial de Jesús Ruiz

2010-12-01

Tilapia production has increased in Aguamilpa Reservoir, in Nayarit, Mexico, in the last few years and represents a good economic activity for rural communities and the country. We determined growth parameters, mortality and reproductive aspects for 2413 specimens of blue tilapia Oreochromis aureus in this reservoir. Samples were taken monthly from July 2000 through June 2001, of which 1 371 were males and 1 042 were females. Standard length (SL) and total weight (TW) were measured in each organism. The SL/TW relationships through power models for sexes were determined. The growth parameters L infinity k, and t0 of the von Bertalanffy equation were estimated using frequency distribution of length through ELEFAN-I computer program. Finally the reproductive cycle and size of first maturity were established using morph chromatic maturity scale. The results suggested that the males and females had negative allometric growth (b < 3). Significant differences were found between SL/TW model for the sexes, suggesting separate models for males and females. Results indicate that there are no differences in growth rates between sexes; the proposed parameters were L infinity = 43.33 cm standard length, k = 0.36/year and t0 = -0.43 years. Natural and fishing mortality coefficients were 0.83/year and 1.10/year, respectively. The estimated exploitation rate (0.57/year) suggested that during the study period the fishery showed signs of overfishing. Blue tilapia reproduces year-round; the highest activity occurs from January through May and size of first maturity was 23 cm SL. We conclude that it is necessary to establish a minimum catch size in this reservoir based on the reproductive behavior of this species.

Abnormal peri-pubertal anthropometric measurements and growth pattern in adolescent idiopathic scoliosis: a study of 598 patients.

PubMed

Siu King Cheung, Catherine; Tak Keung Lee, Warren; Kit Tse, Yee; Ping Tang, Sheng; Man Lee, Kwong; Guo, Xia; Qin, Lin; Chun Yiu Cheng, Jack

2003-09-15

A cross-sectional study of anthropometric parameters in adolescent idiopathic scoliosis (AIS). To compare anthropometric parameters and growth pattern of AIS girls versus normal controls during peri-puberty. Abnormal pattern of growth has been reported in AIS patients. The sequential changes of growth and the correlation with curve severity have not been properly studied. Five hundred ninety-eight AIS girls and 307 healthy girls entered the study. Weight, height, body mass index (BMI), arm span, sitting height, and leg length were determined using standard techniques. Height and sitting height were adjusted by using the greatest Cobb angle to correct for spinal deformity (Bjure's formula). Puberty was graded by Tanner's staging. AIS girls had significantly shorter height (P = 0.001), corrected height (P = 0.005), arm span (P = 0.022), sitting height (P = 0.005) and leg length (P = 0.004) than the controls at pubertal stage I. From pubertal stages II through V, corrected height (P

Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

NASA Astrophysics Data System (ADS)

Ideguchi, Shinsuke; Tashiro, Yuichi; Akahori, Takuya; Takahashi, Keitaro; Ryu, Dongsu

2017-07-01

Faraday tomography allows astronomers to probe the distribution of the magnetic field along the line of sight (LOS), but that can be achieved only after the Faraday spectrum is interpreted. However, the interpretation is not straightforward, mainly because the Faraday spectrum is complicated due to a turbulent magnetic field; it ruins the one-to-one relation between the Faraday depth and the physical depth, and appears as many small-scale features in the Faraday spectrum. In this paper, by employing “simple toy models” for the magnetic field, we describe numerically as well as analytically the characteristic properties of the Faraday spectrum. We show that the Faraday spectrum along “multiple LOSs” can be used to extract the global properties of the magnetic field. Specifically, considering face-on spiral galaxies and modeling turbulent magnetic field as a random field with a single coherence length, we numerically calculate the Faraday spectrum along a number of LOSs and its shape-characterizing parameters, that is, the moments. When multiple LOSs cover a region of ≳(10 coherence length)2, the shape of the Faraday spectrum becomes smooth and the shape-characterizing parameters are well specified. With the Faraday spectrum constructed as a sum of Gaussian functions with different means and variances, we analytically show that the parameters are expressed in terms of the regular and turbulent components of the LOS magnetic field and the coherence length. We also consider the turbulent magnetic field modeled with a power-law spectrum, and study how the magnetic field is revealed in the Faraday spectrum. Our work suggests a way to obtain information on the magnetic field from a Faraday tomography study.

A simulation study of radial expansion of an electron beam injected into an ionospheric plasma

NASA Technical Reports Server (NTRS)

Koga, J.; Lin, C. S.

1994-01-01

Injections of nonrelativistic electron beams from a finite equipotential conductor into an ionospheric plasma have been simulated using a two-dimensional electrostatic particle code. The purpose of the study is to survey the simulation parameters for understanding the dependence of beam radius on physical variables. The conductor is charged to a high potential when the background plasma density is less than the beam density. Beam electrons attracted by the charged conductor are decelerated to zero velocity near the stagnation point, which is at a few Debye lengths from the conductor. The simulations suggest that the beam electrons at the stagnation point receive a large transverse kick and the beam expands radially thereafter. The buildup of beam electrons at the stagnation point produces a large electrostatic force responsible for the transverse kick. However, for the weak charging cases where the background plasma density is larger than the beam density, the radial expansion mechanism is different; the beam plasma instability is found to be responsible for the radial expansion. The simulations show that the electron beam radius for high spacecraft charging cases is of the order of the beam gyroradius, defined as the beam velocity divided by the gyrofrequency. In the weak charging cases, the beam radius is only a fraction of the beam gyroradius. The parameter survey indicates that the beam radius increases with beam density and decreases with magnetic field and beam velocity. The beam radius normalized by the beam gyroradius is found to scale according to the ratio of the beam electron Debye length to the ambient electron Debye length. The parameter dependence deduced would be useful for interpreting the beam radius and beam density of electron beam injection experiments conducted from rockets and the space shuttle.

The notion of snow grain shape: Ambiguous definitions, retrievalfrom tomography and implications on remote sensing

NASA Astrophysics Data System (ADS)

Krol, Q. E.; Loewe, H.

2016-12-01

Grain shape is known to influence the effective physical properties of snow and therefore included in the international classification of seasonal snow. Accordingly, snowpack models account for phenomenological shape parameters (sphericity, dendricity) to capture shape variations. These parameters are however difficult to validate due to the lack of clear-cut definitions from the 3D microstucture and insufficient links to physical properties. While the definition of traditional shape was tailored to the requirements of observers, a more objective definition should be tailored to the requirements of physical properties, by analyzing geometrical (shape) corrections in existing theoretical formulations directly. To this end we revisited the autocorrelation function (ACF) and the chord length distribution (CLD) of snow. Both functions capture size distributions of the microstructure, can be calculated from X-ray tomography and are related to various physical properties. Both functions involve the optical equivalent diameter as dominant quantity, however the respective higher-order geometrical correction differ. We have analyzed these corrections, namely interfacial curvatures for the ACF and the second moment for the CLD, using an existing data set of 165 tomography samples. To unify the notion of shape, we derived various statistical relations between the length scales. Our analysis bears three key practical implications. First, we derived a significantly improved relation between the exponential correlation length and the optical diameter by taking curvatures into account. This adds to the understanding of linking "microwave grain size" and "optical grain size" of snow for remote sensing. Second, we retrieve the optical shape parameter (commonly referred to as B) from tomography images via the moment of the CLD. Third, shape variations seen by observers do not necessarily correspond to shape variations probed by physical properties.

Study of the Vertical Magnetic Field in Face-on Galaxies Using Faraday Tomography

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

Ideguchi, Shinsuke; Ryu, Dongsu; Tashiro, Yuichi

Faraday tomography allows astronomers to probe the distribution of the magnetic field along the line of sight (LOS), but that can be achieved only after the Faraday spectrum is interpreted. However, the interpretation is not straightforward, mainly because the Faraday spectrum is complicated due to a turbulent magnetic field; it ruins the one-to-one relation between the Faraday depth and the physical depth, and appears as many small-scale features in the Faraday spectrum. In this paper, by employing “simple toy models” for the magnetic field, we describe numerically as well as analytically the characteristic properties of the Faraday spectrum. We showmore » that the Faraday spectrum along “multiple LOSs” can be used to extract the global properties of the magnetic field. Specifically, considering face-on spiral galaxies and modeling turbulent magnetic field as a random field with a single coherence length, we numerically calculate the Faraday spectrum along a number of LOSs and its shape-characterizing parameters, that is, the moments. When multiple LOSs cover a region of ≳(10 coherence length){sup 2}, the shape of the Faraday spectrum becomes smooth and the shape-characterizing parameters are well specified. With the Faraday spectrum constructed as a sum of Gaussian functions with different means and variances, we analytically show that the parameters are expressed in terms of the regular and turbulent components of the LOS magnetic field and the coherence length. We also consider the turbulent magnetic field modeled with a power-law spectrum, and study how the magnetic field is revealed in the Faraday spectrum. Our work suggests a way to obtain information on the magnetic field from a Faraday tomography study.« less

CONVECTION THEORY AND SUB-PHOTOSPHERIC STRATIFICATION

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

Arnett, David; Meakin, Casey; Young, Patrick A., E-mail: darnett@as.arizona.ed, E-mail: casey.meakin@gmail.co, E-mail: patrick.young.1@asu.ed

2010-02-20

As a preliminary step toward a complete theoretical integration of three-dimensional compressible hydrodynamic simulations into stellar evolution, convection at the surface and sub-surface layers of the Sun is re-examined, from a restricted point of view, in the language of mixing-length theory (MLT). Requiring that MLT use a hydrodynamically realistic dissipation length gives a new constraint on solar models. While the stellar structure which results is similar to that obtained by Yale Rotational Evolution Code (Guenther et al.; Bahcall and Pinsonneault) and Garching models (Schlattl et al.), the theoretical picture differs. A new quantitative connection is made between macro-turbulence, micro-turbulence, andmore » the convective velocity scale at the photosphere, which has finite values. The 'geometric parameter' in MLT is found to correspond more reasonably with the thickness of the superadiabatic region (SAR), as it must for consistency in MLT, and its integrated effect may correspond to that of the strong downward plumes which drive convection (Stein and Nordlund), and thus has a physical interpretation even in MLT. If we crudely require the thickness of the SAR to be consistent with the 'geometric factor' used in MLT, there is no longer a free parameter, at least in principle. Use of three-dimensional simulations of both adiabatic convection and stellar atmospheres will allow the determination of the dissipation length and the geometric parameter (i.e., the entropy jump) more realistically, and with no astronomical calibration. A physically realistic treatment of convection in stellar evolution will require substantial additional modifications beyond MLT, including nonlocal effects of kinetic energy flux, entrainment (the most dramatic difference from MLT found by Meakin and Arnett), rotation, and magnetic fields.« less

Microgravity Particle Dynamics

NASA Technical Reports Server (NTRS)

Clark, Ivan O.; Johnson, Edward J.

1996-01-01

This research seeks to identify the experiment design parameters for future flight experiments to better resolve the effects of thermal and velocity gradients on gas-solid flows. By exploiting the reduced body forces and minimized thermal convection current of reduced gravity experiments, features of gas-solid flow normally masked by gravitationally induced effects can be studied using flow regimes unattainable under unigravity. This paper assesses the physical scales of velocity, length, time, thermal gradient magnitude, and velocity gradient magnitude likely to be involved in laminar gas-solid multiphase flight experiments for 1-100 micro-m particles.

The Approach to Equilibrium in a Reflex Triode

DTIC Science & Technology

1990-09-24

once to yield dT ±---27yT"= ’, where y = d/A and the prime also denotes d/ de . The damping length scale is now just a parameter that can be obtained from...pressures near K2 which will figure in the gap shorting time, and the boundary condition evolution at the anode. Aside from the steady conduction...phase evolution of 77 to values near the sin- gular point, one finds that (from an operational point of view in fixing 3) all such auxillary physics

Orbital resonances around black holes.

PubMed

Brink, Jeandrew; Geyer, Marisa; Hinderer, Tanja

2015-02-27

We compute the length and time scales associated with resonant orbits around Kerr black holes for all orbital and spin parameters. Resonance-induced effects are potentially observable when the Event Horizon Telescope resolves the inner structure of Sgr A*, when space-based gravitational wave detectors record phase shifts in the waveform during the resonant passage of a compact object spiraling into the black hole, or in the frequencies of quasiperiodic oscillations for accreting black holes. The onset of geodesic chaos for non-Kerr spacetimes should occur at the resonance locations quantified here.

Thermodynamic metrics and optimal paths.

PubMed

Sivak, David A; Crooks, Gavin E

2012-05-11

A fundamental problem in modern thermodynamics is how a molecular-scale machine performs useful work, while operating away from thermal equilibrium without excessive dissipation. To this end, we derive a friction tensor that induces a Riemannian manifold on the space of thermodynamic states. Within the linear-response regime, this metric structure controls the dissipation of finite-time transformations, and bestows optimal protocols with many useful properties. We discuss the connection to the existing thermodynamic length formalism, and demonstrate the utility of this metric by solving for optimal control parameter protocols in a simple nonequilibrium model.

Analysis of data from NASA B-57B gust gradient program

NASA Technical Reports Server (NTRS)

Frost, W.; Lin, M. C.; Chang, H. P.; Ringnes, E.

1985-01-01

Statistical analysis of the turbulence measured in flight 6 of the NASA B-57B over Denver, Colorado, from July 7 to July 23, 1982 included the calculations of average turbulence parameters, integral length scales, probability density functions, single point autocorrelation coefficients, two point autocorrelation coefficients, normalized autospectra, normalized two point autospectra, and two point cross sectra for gust velocities. The single point autocorrelation coefficients were compared with the theoretical model developed by von Karman. Theoretical analyses were developed which address the effects spanwise gust distributions, using two point spatial turbulence correlations.

Inverse energy cascades in three-dimensional turbulence

NASA Technical Reports Server (NTRS)

Hossain, Murshed

1991-01-01

Fully three-dimensional magnetohydrodynamic (MHD) turbulence at large kinetic and low magnetic Reynolds numbers is considered in the presence of a strong uniform magnetic field. It is shown by numerical simulation of a model of MHD that the energy inverse cascades to longer length scales when the interaction parameter is large. While the steady-state dynamics of the driven problem is three-dimensional in character, the behavior has resemblance to two-dimensional hydrodynamics. These results have implications in turbulence theory, MHD power generator, planetary dynamos, and fusion reactor blanket design.

Evaluating the effect of internal aperture variability on transport in kilometer scale discrete fracture networks

DOE PAGES

Makedonska, Nataliia; Hyman, Jeffrey D.; Karra, Satish; ...

2016-08-01

The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer-scale fracture networks has been under debate for a long time, since the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling within large-scale fracture networks. We addressmore » this question by incorporating internal heterogeneity of individual fractures into flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P 32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. The recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate kilometer scale DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time, , and cumulative retention, , are calculated along particles streamlines. As a result, it is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture aperture variability than the tails of travel time distributions, where no significant effect of the in-fracture aperture variations and spatial correlation length is observed.« less

Evaluating the effect of internal aperture variability on transport in kilometer scale discrete fracture networks

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

Makedonska, Nataliia; Hyman, Jeffrey D.; Karra, Satish

The apertures of natural fractures in fractured rock are highly heterogeneous. However, in-fracture aperture variability is often neglected in flow and transport modeling and individual fractures are assumed to have uniform aperture distribution. The relative importance of in-fracture variability in flow and transport modeling within kilometer-scale fracture networks has been under debate for a long time, since the flow in each single fracture is controlled not only by in-fracture variability but also by boundary conditions. Computational limitations have previously prohibited researchers from investigating the relative importance of in-fracture variability in flow and transport modeling within large-scale fracture networks. We addressmore » this question by incorporating internal heterogeneity of individual fractures into flow simulations within kilometer scale three-dimensional fracture networks, where fracture intensity, P 32 (ratio between total fracture area and domain volume) is between 0.027 and 0.031 [1/m]. The recently developed discrete fracture network (DFN) simulation capability, dfnWorks, is used to generate kilometer scale DFNs that include in-fracture aperture variability represented by a stationary log-normal stochastic field with various correlation lengths and variances. The Lagrangian transport parameters, non-reacting travel time, , and cumulative retention, , are calculated along particles streamlines. As a result, it is observed that due to local flow channeling early particle travel times are more sensitive to in-fracture aperture variability than the tails of travel time distributions, where no significant effect of the in-fracture aperture variations and spatial correlation length is observed.« less

The Effect of Contact Area on the Fluid Flow-Fracture Specific Stiffness Relationship

NASA Astrophysics Data System (ADS)

Petrovitch, C.; Pyrak-Nolte, L. J.; Nolte, D. D.

2009-12-01

The integrity of subsurface CO2 sequestration sites can be compromised by the presence of mechanical discontinuities such as fractures, joints and faults. The ability to detect, seismically, and determine whether a discontinuity poses a risk, requires an understanding of the interrelationships among the mechanical, hydraulic and seismic properties of fractures rock. We performed a computational study to investigate the effect of fracture geometry on the relationship between fluid flow and fracture specific stiffness. The form of this relationship and the ability to scale it among different sample sizes provides a key link between the hydraulic and seismic response of fractures. In this study, model fracture topologies were simulated using the stratified continuum percolation method. This method constructs a hierarchical aperture distribution with a tunable spatial correlation length. Fractures with correlated and uncorrelated aperture distributions were used. The contact area across the fracture plane ranged from approximately 5% to 40%. The fracture specific stiffness was calculated by deforming each fracture numerically under a normal load and extracting the stiffness from the displacement-stress curves. Single-phase flow was calculated for each increment of stress by modeling the fracture topology as a network of elliptical pipes and solving the corresponding linear system of equations. We analyzed the relationship between fracture displacement and contact area and found that the correlation length associated with the contact area distribution enables a scaling relationship between displacement and contact area. The collapse of the fluid flow - stress relationship required use of standard percolation functional forms that use average aperture (cubic law), the void area fraction, and the correlation length of the contact area clusters. A final scaling relationship between fluid flow and fracture specific was found for the class of correlated fractures while a separate relationship was found for the uncorrelated fractures. By expanding the scaling parameters to include additional length scales, it may be possible to unify all of the flow-stiffness relationships, independent of geometry. Acknowledgments: The authors wish to acknowledge support of this work by the Geosciences Research Program, Office of Basic Energy Sciences US Department of Energy (DEFG02-97ER14785 08), the GeoMathematical Imaging Group at Purdue University and from the Computer Research Institute At Purdue University.

Thermal, size and surface effects on the nonlinear pull-in of small-scale piezoelectric actuators

NASA Astrophysics Data System (ADS)

SoltanRezaee, Masoud; Ghazavi, Mohammad-Reza

2017-09-01

Electrostatically actuated miniature wires/tubes have many operational applications in the high-tech industries. In this research, the nonlinear pull-in instability of piezoelectric thermal small-scale switches subjected to Coulomb and dissipative forces is analyzed using strain gradient and modified couple stress theories. The discretized governing equation is solved numerically by means of the step-by-step linearization method. The correctness of the formulated model and solution procedure is validated through comparison with experimental and several theoretical results. Herein, the length-scale, surface energy, van der Waals attraction and nonlinear curvature are considered in the present comprehensive model and the thermo-electro-mechanical behavior of cantilever piezo-beams are discussed in detail. It is found that the piezoelectric actuation can be used as a design parameter to control the pull-in phenomenon. The obtained results are applicable in stability analysis, practical design and control of actuated miniature intelligent devices.

Fatigue Damage Assessment Leveraging Nondestructive Evaluation Data

NASA Astrophysics Data System (ADS)

Mazur, K.; Wisner, B.; Kontsos, A.

2018-05-01

Fatigue in materials depends on several microstructural parameters. The length and time scales involved in such processes have been investigated by characterization methods that target microstructural effects or that rely on specimen-level observations. Combinations of in situ and ex situ techniques are also used to correlate microstructural changes to bulk properties. We present herein an effort to directly link local changes with specimen-level fatigue damage assessment. To achieve this goal, grain-scale observations in an aluminum alloy are linked with deformation measurements made by digital image correlation and with acoustic emission monitoring obtained from inside the scanning electron microscope. Damage assessment is attempted using a data-processing framework that involves noise removal, data reduction, and classification. The results demonstrate that nondestructive evaluation combined with small-scale testing can provide a means for fatigue damage assessment applicable to a broad range of materials and testing conditions.

Mesoscale Thermodynamic Analysis of Atomic-Scale Dislocation-Obstacle Interactions Simulated by Molecular Dynamics

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

Monet, Giath; Bacon, David J; Osetskiy, Yury N

2010-01-01

Given the time and length scales in molecular dynamics (MD) simulations of dislocation-defect interactions, quantitative MD results cannot be used directly in larger scale simulations or compared directly with experiment. A method to extract fundamental quantities from MD simulations is proposed here. The first quantity is a critical stress defined to characterise the obstacle resistance. This mesoscopic parameter, rather than the obstacle 'strength' designed for a point obstacle, is to be used for an obstacle of finite size. At finite temperature, our analyses of MD simulations allow the activation energy to be determined as a function of temperature. The resultsmore » confirm the proportionality between activation energy and temperature that is frequently observed by experiment. By coupling the data for the activation energy and the critical stress as functions of temperature, we show how the activation energy can be deduced at a given value of the critical stress.« less

Pore-scale spectral induced polarization (SIP) signaturesassociated with FeS biomineral transformations

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

Slater, Lee; Ntarlagiannis, Dimitrios; Personna, Yves R.

2007-10-01

The authors measured Spectral Induced Polarization (SIP) signatures in sand columns during (1) FeS biomineralization produced by sulfate reducing bacteria (D. vulgaris) under anaerboci conditions, and (2) subsequent biomineral dissolution upon return to an aerobic state. The low-frequency (0.1-10 Hz peak) relaxations produced during biomineralization can be modeled with a Cole-Cole formulation, from which the evolution of the polarization magnitude and relaxation length scale can be estimated. They find that the modeled time constant is consistent with the polarizable elements being biomineral encrused pores. Evolution of the model parameters is consistent with FeS surface area increases and pore-size reduction duringmore » biomineral growth, and subsequent biomineral dissolution (FeS surface area decreases and pore expansion) upon return to the aerobic state. They conclude that SIP signatures are diagnostic of pore-scale geometrical changes associated with FeS biomineralization by sulfate reducing bacteria.« less

Random cascade model in the limit of infinite integral scale as the exponential of a nonstationary 1/f noise: Application to volatility fluctuations in stock markets

NASA Astrophysics Data System (ADS)

Muzy, Jean-François; Baïle, Rachel; Bacry, Emmanuel

2013-04-01

In this paper we propose a new model for volatility fluctuations in financial time series. This model relies on a nonstationary Gaussian process that exhibits aging behavior. It turns out that its properties, over any finite time interval, are very close to continuous cascade models. These latter models are indeed well known to reproduce faithfully the main stylized facts of financial time series. However, it involves a large-scale parameter (the so-called “integral scale” where the cascade is initiated) that is hard to interpret in finance. Moreover, the empirical value of the integral scale is in general deeply correlated to the overall length of the sample. This feature is precisely predicted by our model, which, as illustrated by various examples from daily stock index data, quantitatively reproduces the empirical observations.

Investigating the Complex Chemistry of Functional Energy Storage Systems: The Need for an Integrative, Multiscale (Molecular to Mesoscale) Perspective.

PubMed

Abraham, Alyson; Housel, Lisa M; Lininger, Christianna N; Bock, David C; Jou, Jeffrey; Wang, Feng; West, Alan C; Marschilok, Amy C; Takeuchi, Kenneth J; Takeuchi, Esther S

2016-06-22

Electric energy storage systems such as batteries can significantly impact society in a variety of ways, including facilitating the widespread deployment of portable electronic devices, enabling the use of renewable energy generation for local off grid situations and providing the basis of highly efficient power grids integrated with energy production, large stationary batteries, and the excess capacity from electric vehicles. A critical challenge for electric energy storage is understanding the basic science associated with the gap between the usable output of energy storage systems and their theoretical energy contents. The goal of overcoming this inefficiency is to achieve more useful work (w) and minimize the generation of waste heat (q). Minimization of inefficiency can be approached at the macro level, where bulk parameters are identified and manipulated, with optimization as an ultimate goal. However, such a strategy may not provide insight toward the complexities of electric energy storage, especially the inherent heterogeneity of ion and electron flux contributing to the local resistances at numerous interfaces found at several scale lengths within a battery. Thus, the ability to predict and ultimately tune these complex systems to specific applications, both current and future, demands not just parametrization at the bulk scale but rather specific experimentation and understanding over multiple length scales within the same battery system, from the molecular scale to the mesoscale. Herein, we provide a case study examining the insights and implications from multiscale investigations of a prospective battery material, Fe3O4.

Dynamics of Bottlebrush Networks

NASA Astrophysics Data System (ADS)

Cao, Zhen; Daniel, William; Vatankhah-Varnosfaderani, Mohammad; Sheiko, Sergei; Dobrynin, Andrey

The deformation dynamics of bottlebrush networks in a melt state is studied using a combination of theoretical, computational, and experimental techniques. Three main molecular relaxation processes are identified in these systems: (i) relaxation of the side chains, (ii) relaxation of the bottlebrush backbones on length scales shorter than the bottlebrush Kuhn length (bK) , and (iii) relaxation of the bottlebrush network strands between cross-links. The relaxation of side chains having a degree of polymerization (DP), nsc, dominates the network dynamics on the time scales τ0 < t <=τsc , where τ0 and τsc τ0 (nsc + 1)2 are the characteristic relaxation times of monomeric units and side chains, respectively. In this time interval, the shear modulus at small deformations decays with time as G0BB (t) t - 1 / 2. On time scales t >τsc, bottlebrush elastomers behave as networks of filaments with a shear modulus G0BB (t) (nsc + 1)- 1 / 4t - 1 / 2 . Finally, the response of the bottlebrush networks becomes time independent at times scales longer than the Rouse time of the bottlebrush network strands. In this time interval, the network shear modulus depends on the network molecular parameters as G0BB (t) (nsc + 1)-1N-1 . Analysis of the simulation data shows that the stress evolution in the bottlebrush networks during constant strain-rate deformation can be described by a universal function. NSF DMR-1409710, DMR-1407645, DMR-1624569, DMR-1436201.

Studying time of flight imaging through scattering media across multiple size scales (Conference Presentation)

NASA Astrophysics Data System (ADS)

Velten, Andreas

2017-05-01

Light scattering is a primary obstacle to optical imaging in a variety of different environments and across many size and time scales. Scattering complicates imaging on large scales when imaging through the atmosphere when imaging from airborne or space borne platforms, through marine fog, or through fog and dust in vehicle navigation, for example in self driving cars. On smaller scales, scattering is the major obstacle when imaging through human tissue in biomedical applications. Despite the large variety of participating materials and size scales, light transport in all these environments is usually described with very similar scattering models that are defined by the same small set of parameters, including scattering and absorption length and phase function. We attempt a study of scattering and methods of imaging through scattering across different scales and media, particularly with respect to the use of time of flight information. We can show that using time of flight, in addition to spatial information, provides distinct advantages in scattering environments. By performing a comparative study of scattering across scales and media, we are able to suggest scale models for scattering environments to aid lab research. We also can transfer knowledge and methodology between different fields.

Multiscale multifractal detrended-fluctuation analysis of two-dimensional surfaces

NASA Astrophysics Data System (ADS)

Wang, Fang; Fan, Qingju; Stanley, H. Eugene

2016-04-01

Two-dimensional (2D) multifractal detrended fluctuation analysis (MF-DFA) has been used to study monofractality and multifractality on 2D surfaces, but when it is used to calculate the generalized Hurst exponent in a fixed time scale, the presence of crossovers can bias the outcome. To solve this problem, multiscale multifractal analysis (MMA) was recent employed in a one-dimensional case. MMA produces a Hurst surface h (q ,s ) that provides a spectrum of local scaling exponents at different scale ranges such that the positions of the crossovers can be located. We apply this MMA method to a 2D surface and identify factors that influence the results. We generate several synthesized surfaces and find that crossovers are consistently present, which means that their fractal properties differ at different scales. We apply MMA to the surfaces, and the results allow us to observe these differences and accurately estimate the generalized Hurst exponents. We then study eight natural texture images and two real-world images and find (i) that the moving window length (WL) and the slide length (SL) are the key parameters in the MMA method, that the WL more strongly influences the Hurst surface than the SL, and that the combination of WL =4 and SL =4 is optimal for a 2D image; (ii) that the robustness of h (2 ,s ) to four common noises is high at large scales but variable at small scales; and (iii) that the long-term correlations in the images weaken as the intensity of Gaussian noise and salt and pepper noise is increased. Our findings greatly improve the performance of the MMA method on 2D surfaces.

Slice-push, formation of grooves and the scale effect in cutting.

PubMed

Atkins, A G

2016-06-06

Three separate aspects of cutting are investigated which complement other papers on the mechanics of separation processes presented at this interdisciplinary Theo Murphy meeting. They apply in all types of cutting whether blades are sharp or blunt, and whether the material being cut is 'hard, stiff and strong' or 'soft, compliant and weak'. The first topic discusses why it is easier to cut when there is motion along (parallel to) the blade as well motion across (perpendicular to) the cutting edge, and the analysis is applied to optimization of blade geometries to produce minimum cutting forces and hence minimum damage to cut surfaces. The second topic concerns cutting with more than one edge with particular application to the formation of grooves in surfaces by hard pointed tools. The mechanics are investigated and applied to the topic of abrasive wear by hard particles. Traditional analyses say that abrasive wear resistance increases monotonically with the hardness of the workpiece, but we show that the fracture toughness of the surface material is also important, and that behaviour is determined by the toughness-to-hardness ratio rather than hardness alone. Scaling forms the third subject. As cutting is a branch of elasto-plastic fracture mechanics, cube-square energy scaling applies in which the important length scale is (ER/k (2)), where E is Young's modulus, R is the fracture toughness and k is the shear yield strength. Whether, in cutting, material is removed as ductile ribbons, as semi-ductile discontinuous chips, or by brittle 'knocking lumps out' is shown to depend on the depth of cut relative to this characteristic length parameter. Scaling in biology is called allometry and its relationship with engineering scaling is discussed. Some speculative predictions are made in relation to the action of teeth on food.

Dependence of Lunar Surface Charging on Solar Wind Plasma Conditions and Solar Irradiation

NASA Technical Reports Server (NTRS)

Stubbs, T. J.; Farrell, W. M.; Halekas, J. S.; Burchill, J. K.; Collier, M. R.; Zimmerman, M. I.; Vondrak, R. R.; Delory, G. T.; Pfaff, R. F.

2014-01-01

The surface of the Moon is electrically charged by exposure to solar radiation on its dayside, as well as by the continuous flux of charged particles from the various plasma environments that surround it. An electric potential develops between the lunar surface and ambient plasma, which manifests itself in a near-surface plasma sheath with a scale height of order the Debye length. This study investigates surface charging on the lunar dayside and near-terminator regions in the solar wind, for which the dominant current sources are usually from the pohotoemission of electrons, J(sub p), and the collection of plasma electrons J(sub e) and ions J(sub i). These currents are dependent on the following six parameters: plasma concentration n(sub 0), electron temperature T(sub e), ion temperature T(sub i), bulk flow velocity V, photoemission current at normal incidence J(sub P0), and photo electron temperature T(sub p). Using a numerical model, derived from a set of eleven basic assumptions, the influence of these six parameters on surface charging - characterized by the equilibrium surface potential, Debye length, and surface electric field - is investigated as a function of solar zenith angle. Overall, T(sub e) is the most important parameter, especially near the terminator, while J(sub P0) and T(sub p) dominate over most of the dayside.

Transformation to equivalent dimensions—a new methodology to study earthquake clustering

NASA Astrophysics Data System (ADS)

Lasocki, Stanislaw

2014-05-01

A seismic event is represented by a point in a parameter space, quantified by the vector of parameter values. Studies of earthquake clustering involve considering distances between such points in multidimensional spaces. However, the metrics of earthquake parameters are different, hence the metric in a multidimensional parameter space cannot be readily defined. The present paper proposes a solution of this metric problem based on a concept of probabilistic equivalence of earthquake parameters. Under this concept the lengths of parameter intervals are equivalent if the probability for earthquakes to take values from either interval is the same. Earthquake clustering is studied in an equivalent rather than the original dimensions space, where the equivalent dimension (ED) of a parameter is its cumulative distribution function. All transformed parameters are of linear scale in [0, 1] interval and the distance between earthquakes represented by vectors in any ED space is Euclidean. The unknown, in general, cumulative distributions of earthquake parameters are estimated from earthquake catalogues by means of the model-free non-parametric kernel estimation method. Potential of the transformation to EDs is illustrated by two examples of use: to find hierarchically closest neighbours in time-space and to assess temporal variations of earthquake clustering in a specific 4-D phase space.

Annealed scaling for a charged polymer in dimensions two and higher

NASA Astrophysics Data System (ADS)

Berger, Q.; den Hollander, F.; Poisat, J.

2018-02-01

This paper considers an undirected polymer chain on {Z}d , d ≥slant 2 , with i.i.d. random charges attached to its constituent monomers. Each self-intersection of the polymer chain contributes an energy to the interaction Hamiltonian that is equal to the product of the charges of the two monomers that meet. The joint probability distribution for the polymer chain and the charges is given by the Gibbs distribution associated with the interaction Hamiltonian. The object of interest is the annealed free energy per monomer in the limit as the length n of the polymer chain tends to infinity. We show that there is a critical curve in the parameter plane spanned by the charge bias and the inverse temperature separating an extended phase from a collapsed phase. We derive the scaling of the critical curve for small and for large charge bias and the scaling of the annealed free energy for small inverse temperature. We argue that in the collapsed phase the polymer chain is subdiffusive, namely, on scale \

Cell adhesion on nanotopography

NASA Astrophysics Data System (ADS)

Tsai, Irene; Kimura, Masahiro; Stockton, Rebecca; Jacobson, Bruce; Russell, Thomas

2003-03-01

Cell adhesion, a key element in understanding the cell-biomaterial interactions, underpins proper cell growth, function and survival. Understanding the parameters influencing cell adhesion is critical for applications in biosensors, implants and bioreactors. A gradient surface is used to study the effect of the surface topography on cell adhesion. A gradient surface is generated by block copolymer and homopolymer blends. The two homopolymers will phase separate on the micron scale and gradually decrease to nano-scale by the microphase separation of the diblock. Gradient surfaces offer a unique opportunity to probe lateral variations in the topography and interactions. Using thin films of mixtures of diblock copolymers of PS-b-MMA with PS and PMMA homopolymers, where the concentration of the PS-b-MMA varies across the surface, a gradient in the size scale of the morphology, from the nanoscopic to microscopic, was produced. By UV exposure, the variation in morphology translated into a variation in topography. The extent of cell spreading and cytoskeleton formation was investigated and marked dependence on the length scale of the surface topography was found.

Shear banding leads to accelerated aging dynamics in a metallic glass

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

Küchemann, Stefan; Liu, Chaoyang; Dufresne, Eric M.

Traditionally, strain localization in metallic glasses is related to the thickness of the shear defect, which is confined to the nanometer scale. In this study, using site-specific x-ray photon correlation spectroscopy (XPCS), we reveal significantly accelerated relaxation dynamics around a shear band in a metallic glass at a length scale that is orders of magnitude larger than the defect itself. The relaxation time in the shear-band vicinity is up to ten-times smaller compared to the as-cast matrix, and the relaxation dynamics occurs in a characteristic three-stage aging response that manifests itself in the temperature-dependent shape parameter known from classical stretchedmore » exponential relaxation dynamics of disordered materials. We demonstrate that the time-dependent correlation functions describing the aging at different temperatures can be captured and collapsed using simple scaling functions. Finally, these insights highlight how an ubiquitous nano-scale strain-localization mechanism in metallic glasses leads to a fundamental change of the relaxation dynamics at the mesoscale.« less

Shear banding leads to accelerated aging dynamics in a metallic glass

DOE PAGES

Küchemann, Stefan; Liu, Chaoyang; Dufresne, Eric M.; ...

2018-01-11

Traditionally, strain localization in metallic glasses is related to the thickness of the shear defect, which is confined to the nanometer scale. In this study, using site-specific x-ray photon correlation spectroscopy (XPCS), we reveal significantly accelerated relaxation dynamics around a shear band in a metallic glass at a length scale that is orders of magnitude larger than the defect itself. The relaxation time in the shear-band vicinity is up to ten-times smaller compared to the as-cast matrix, and the relaxation dynamics occurs in a characteristic three-stage aging response that manifests itself in the temperature-dependent shape parameter known from classical stretchedmore » exponential relaxation dynamics of disordered materials. We demonstrate that the time-dependent correlation functions describing the aging at different temperatures can be captured and collapsed using simple scaling functions. Finally, these insights highlight how an ubiquitous nano-scale strain-localization mechanism in metallic glasses leads to a fundamental change of the relaxation dynamics at the mesoscale.« less

Anomalous solute transport in saturated porous media: Relating transport model parameters to electrical and nuclear magnetic resonance properties

USGS Publications Warehouse

Swanson, Ryan D; Binley, Andrew; Keating, Kristina; France, Samantha; Osterman, Gordon; Day-Lewis, Frederick D.; Singha, Kamini

2015-01-01

The advection-dispersion equation (ADE) fails to describe commonly observed non-Fickian solute transport in saturated porous media, necessitating the use of other models such as the dual-domain mass-transfer (DDMT) model. DDMT model parameters are commonly calibrated via curve fitting, providing little insight into the relation between effective parameters and physical properties of the medium. There is a clear need for material characterization techniques that can provide insight into the geometry and connectedness of pore spaces related to transport model parameters. Here, we consider proton nuclear magnetic resonance (NMR), direct-current (DC) resistivity, and complex conductivity (CC) measurements for this purpose, and assess these methods using glass beads as a control and two different samples of the zeolite clinoptilolite, a material that demonstrates non-Fickian transport due to intragranular porosity. We estimate DDMT parameters via calibration of a transport model to column-scale solute tracer tests, and compare NMR, DC resistivity, CC results, which reveal that grain size alone does not control transport properties and measured geophysical parameters; rather, volume and arrangement of the pore space play important roles. NMR cannot provide estimates of more-mobile and less-mobile pore volumes in the absence of tracer tests because these estimates depend critically on the selection of a material-dependent and flow-dependent cutoff time. Increased electrical connectedness from DC resistivity measurements are associated with greater mobile pore space determined from transport model calibration. CC was hypothesized to be related to length scales of mass transfer, but the CC response is unrelated to DDMT.

Jet length/velocity ratio: a new index for echocardiographic evaluation of chronic aortic regurgitation.

PubMed

Güvenç, Tolga Sinan; Karaçimen, Denizhan; Erer, Hatice Betül; İlhan, Erkan; Sayar, Nurten; Karakuş, Gültekin; Çekirdekçi, Elif; Eren, Mehmet

2015-01-01

Management of aortic regurgitation depends on the assessment for severity. Echocardiography remains as the most widely available tool for evaluation of aortic regurgitation. In this manuscript, we describe a novel parameter, jet length/velocity ratio, for the diagnosis of severe aortic regurgitation. A total of 30 patients with aortic regurgitation were included to this study. Severity of aortic regurgitation was assessed with an aortic regurgitation index incorporating five echocardiographic parameters. Jet length/velocity ratio is calculated as the ratio of maximum jet penetrance to mean velocity of regurgitant flow. Jet length/velocity ratio was significantly higher in patients with severe aortic regurgitation (2.03 ± 0.53) compared to patients with less than severe aortic regurgitation (1.24 ± 0.32, P < 0.001). Correlation of jet length/velocity ratio with aortic regurgitation index was very good (r(2) = 0.86) and correlation coefficient was higher for jet length/velocity ratio compared to vena contracta, jet width/LVOT ratio and pressure half time. For a cutoff value of 1.61, jet length/velocity ratio had a sensitivity of 92% and specificity of 88%, with an AUC value of 0.955. Jet length/velocity ratio is a novel parameter that can be used to assess severity of chronic aortic regurgitation. Main limitation for usage of this novel parameter is jet impringement to left ventricular wall. © 2014, Wiley Periodicals, Inc.

The Relationship Between Constraint and Ductile Fracture Initiation as Defined by Micromechanical Analyses

NASA Technical Reports Server (NTRS)

Panontin, Tina L.; Sheppard, Sheri D.

1994-01-01

The use of small laboratory specimens to predict the integrity of large, complex structures relies on the validity of single parameter fracture mechanics. Unfortunately, the constraint loss associated with large scale yielding, whether in a laboratory specimen because of its small size or in a structure because it contains shallow flaws loaded in tension, can cause the breakdown of classical fracture mechanics and the loss of transferability of critical, global fracture parameters. Although the issue of constraint loss can be eliminated by testing actual structural configurations, such an approach can be prohibitively costly. Hence, a methodology that can correct global fracture parameters for constraint effects is desirable. This research uses micromechanical analyses to define the relationship between global, ductile fracture initiation parameters and constraint in two specimen geometries (SECT and SECB with varying a/w ratios) and one structural geometry (circumferentially cracked pipe). Two local fracture criteria corresponding to ductile fracture micromechanisms are evaluated: a constraint-modified, critical strain criterion for void coalescence proposed by Hancock and Cowling and a critical void ratio criterion for void growth based on the Rice and Tracey model. Crack initiation is assumed to occur when the critical value in each case is reached over some critical length. The primary material of interest is A516-70, a high-hardening pressure vessel steel sensitive to constraint; however, a low-hardening structural steel that is less sensitive to constraint is also being studied. Critical values of local fracture parameters are obtained by numerical analysis and experimental testing of circumferentially notched tensile specimens of varying constraint (e.g., notch radius). These parameters are then used in conjunction with large strain, large deformation, two- and three-dimensional finite element analyses of the geometries listed above to predict crack initiation loads and to calculate the associated (critical) global fracture parameters. The loads are verified experimentally, and microscopy is used to measure pre-crack length, crack tip opening displacement (CTOD), and the amount of stable crack growth. Results for A516-70 steel indicate that the constraint-modified, critical strain criterion with a critical length approximately equal to the grain size (0.0025 inch) provides accurate predictions of crack initiation. The critical void growth criterion is shown to considerably underpredict crack initiation loads with the same critical length. The relationship between the critical value of the J-integral for ductile crack initiation and crack depth for SECT and SECB specimens has been determined using the constraint-modified, critical strain criterion, demonstrating that this micromechanical model can be used to correct in-plane constraint effects due to crack depth and bending vs. tension loading. Finally, the relationship developed for the SECT specimens is used to predict the behavior of circumferentially cracked pipe specimens.