NASA Astrophysics Data System (ADS)
Vinogradov, A. P.; Burokur, N.; Zouhdi, S.
2009-06-01
It is shown that the space fluctuations of concentration of conducting inclusions might be responsible for the well-known disagreement between theory and experiment at determining microwave losses in metal-dielectric mixture: the theories (percolation theory, effective medium theory, etc.) predict much lower losses than those measured in experiment. It is demonstrated that if the effective skin depth in the regions occupied by the fluctuation is comparable to the mean diameter of these regions we can expect additional losses.
Density Fluctuations in Liquid Water
NASA Astrophysics Data System (ADS)
English, Niall J.; Tse, John S.
2011-01-01
The density distributions and fluctuations in grids of varying size in liquid water at ambient pressure, both above the freezing point and in the supercooled state, are analyzed from the trajectories obtained from large-scale molecular dynamics simulations. It is found that the occurrence of low- and high-density regions (LDL and HDL) is transient and their respective residence times are dependent on the size of the simulated system. The spatial extent of density-density correlation is found to be within 7 Å or less. The temporal existence of LDL and HDL arises as a result of natural density fluctuations of an equilibrium system. The density of bulk water at ambient conditions is homogenous.
Origin of cosmological density fluctuations
Carr, B.J.
1984-11-01
The density fluctuations required to explain the large-scale cosmological structure may have arisen spontaneously as a result of a phase transition in the early Universe. There are several ways in which such fluctuations may have ben produced, and they could have a variety of spectra, so one should not necessarily expect all features of the large-scale structure to derive from a simple power law spectrum. Some features may even result from astrophysical amplification mechanisms rather than gravitational instability. 128 references.
Quantum density fluctuations in classical liquids.
Ford, L H; Svaiter, N F
2009-01-23
We discuss the density fluctuations of a fluid due to zero point motion, assuming a linear dispersion relation. We argue that density fluctuations in a fluid can be a useful analog model for better understanding fluctuations in relativistic quantum field theory. We calculate the differential cross section for light scattering by the zero point density fluctuations, and find a result proportional to the fifth power of the light frequency. We give some estimates of the relative magnitude of this effect compared to the scattering by thermal density fluctuations, and find that it can be of the order 13% for liquid neon at optical frequencies. This relative magnitude is proportional to frequency and inversely proportional to temperature. Although the scattering by zero point density fluctuation is small, it may be observable.
Multicellular density fluctuations in epithelial monolayers
NASA Astrophysics Data System (ADS)
Zehnder, Steven M.; Wiatt, Marina K.; Uruena, Juan M.; Dunn, Alison C.; Sawyer, W. Gregory; Angelini, Thomas E.
2015-09-01
Changes in cell size often accompany multicellular motion in tissue, and cell number density is known to strongly influence collective migration in monolayers. Density fluctuations in other forms of active matter have been explored extensively, but not the potential role of density fluctuations in collective cell migration. Here we investigate collective motion in cell monolayers, focusing on the divergent component of the migration velocity field to probe density fluctuations. We find spatial patterns of diverging and converging cell groups throughout the monolayers, which oscillate in time with a period of approximately 3-4 h. Simultaneous fluorescence measurements of a cytosol dye within the cells show that fluid passes between groups of cells, facilitating these oscillations in cell density. Our findings reveal that cell-cell interactions in monolayers may be mediated by intercellular fluid flow.
Origin of density fluctuations in extended inflation
NASA Technical Reports Server (NTRS)
Kolb, Edward W.; Salopek, David S.; Turner, Michael S.
1990-01-01
The density fluctuations (both curvature and isocurvature) that arise due to quantum fluctuations in a simple model of extended inflation based upon the Jordan-Brans-Dicke theory are calculated. Curvature fluctuations arise due to quantum fluctuations in the Brans-Dicke field, in general have a nonscale-invariant spectrum, and can have an amplitude that is cosmologically acceptable and interesting without having to tune any coupling constant to a very small value. The density perturbations that arise due to the inflation field are subdominant. If there are other massless fields in the theory, e.g., an axion or an ilion, then isocurvature fluctuations arise in these fields too. Production of gravitational waves and the massless particles associated with excitations of the Brans-Dicke field are also discussed. Several attempts at more realistic models of extended inflation are also analyzed. The importance of the Einstein conformal frame in calculating curvature fluctuations is emphasized. When viewed in this frame, extended inflation closely resembles slow-rollover inflation with an exponential potential and the usual formula for the amplitude of curvature perturbations applies.
Density fluctuations from strings and galaxy formation
NASA Technical Reports Server (NTRS)
Vilenkin, A.; Shafi, Q.
1983-01-01
The spectra of density fluctuations caused by strings in a universe dominated either by baryons, neutrinos, or axions are presented. Realistic scenarios for galaxy formation seem possible in all three cases. Examples of grand unified theories which lead to strings with the desired mass scales are given.
Turbulence velocimetry of density fluctuation imaging data
NASA Astrophysics Data System (ADS)
McKee, G. R.; Fonck, R. J.; Gupta, D. K.; Schlossberg, D. J.; Shafer, M. W.; Holland, C.; Tynan, G.
2004-10-01
Analysis techniques to measure the time-resolved flow field of turbulence are developed and applied to images of density fluctuations obtained with the beam emission spectroscopy diagnostic system on the DIII-D tokamak. Velocimetry applications include measurement of turbulent particle flux, zonal flows, and the Reynolds stress. The flow field of turbulent eddies exhibits quasisteady poloidal flows as well as high-frequency radial and poloidal motion associated with electrostatic potential fluctuations and strongly nonlinear multifield interactions. The orthogonal dynamic programming technique, developed for fluid-based particle and amorphous shape (smoke) flow analysis, is investigated to measure such turbulence flows. Sensitivity and accuracy are assessed and sample results discussed.
Quantum Fluctuations of a Superconductor Order Parameter
NASA Astrophysics Data System (ADS)
Arutyunov, K. Yu; Lehtinen, J. S.
2016-08-01
Tunneling I-V characteristics between very narrow titanium nanowires and "massive" superconducting aluminum were measured. The clear trend was observed: the thinner the titanium electrode, the broader the singularity at eV = Δ1(Al) + Δ2(Ti). The phenomenon can be explained by broadening of the gap edge of the quasi-one-dimensional titanium channels due to quantum fluctuations of the order parameter modulus |Δ2|. The range of the nanowire diameters, where the effect is pronounced, correlates with dimensions where the phase fluctuations of the complex superconducting order parameter Δ = |Δ|eiφ, the quantum phase slips, broadening the R(T) dependencies, have been observed.
Density fluctuations in vibrated granular materials
Nowak, E.R.; Knight, J.B.; Ben-Naim, E.; Jaeger, H.M.; Nagel, S.R.
1998-02-01
We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations, the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity {Gamma}. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In particular, we propose a method to evaluate the compactivity of a powder, first put forth by Edwards and co-workers, that is the analog to temperature for a quasistatic powder. We also propose a stochastic model based on free volume considerations that captures the essential mechanism underlying the slow relaxation. We compare our experimental results with simulations of a one-dimensional model for random adsorption and desorption. {copyright} {ital 1998} {ital The American Physical Society}
Coherent Density Fluctuations in the HSX Stellarator
NASA Astrophysics Data System (ADS)
Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Likin, K. M.; Smoniewski, J.; Talmadge, J. N.
2015-11-01
A multi-channel interferometer system is used to measure equilibrium density profile and its fluctuations in the HSX stellarator. Low-frequency, coherent density fluctuations are observed in certain quasi-helically symmetric (QHS) plasma conditions and has characteristic frequency of 15kHz. The mode is observed for small displacement of the 1st harmonic O-mode ECRH location inward from the magnetic axis. This mode is also observed on magnetic fluctuation signal, using external coils, which shows n =1. When HSX is operated without quasi-helical symmetry (mirror configuration), a coherent electrostatic mode at 28 kHz is observed. While the coherent mode in QHS plasmas shows ballooning effect, the coherent mode in Mirror plasma exhibits an anti-ballooning characteristic. Mode radial structure can be obtained from inversion of interferometer measurement when the m number is known. Under certain Mirror conditions, the coherent modes display strong bi-coherence on Langmuir probe signals. Detailed characterization of the observed coherent modes will be reported and their identification will be explored. Supported by USDOE grants DE-FG03-01ER54615 and DE-FG02-93ER54222.
Exploiting intrinsic fluctuations to identify model parameters.
Zimmer, Christoph; Sahle, Sven; Pahle, Jürgen
2015-04-01
Parameterisation of kinetic models plays a central role in computational systems biology. Besides the lack of experimental data of high enough quality, some of the biggest challenges here are identification issues. Model parameters can be structurally non-identifiable because of functional relationships. Noise in measured data is usually considered to be a nuisance for parameter estimation. However, it turns out that intrinsic fluctuations in particle numbers can make parameters identifiable that were previously non-identifiable. The authors present a method to identify model parameters that are structurally non-identifiable in a deterministic framework. The method takes time course recordings of biochemical systems in steady state or transient state as input. Often a functional relationship between parameters presents itself by a one-dimensional manifold in parameter space containing parameter sets of optimal goodness. Although the system's behaviour cannot be distinguished on this manifold in a deterministic framework it might be distinguishable in a stochastic modelling framework. Their method exploits this by using an objective function that includes a measure for fluctuations in particle numbers. They show on three example models, immigration-death, gene expression and Epo-EpoReceptor interaction, that this resolves the non-identifiability even in the case of measurement noise with known amplitude. The method is applied to partially observed recordings of biochemical systems with measurement noise. It is simple to implement and it is usually very fast to compute. This optimisation can be realised in a classical or Bayesian fashion.
Quantum Fluctuations of a Superconductor Order Parameter.
Arutyunov, K Yu; Lehtinen, J S
2016-12-01
Tunneling I-V characteristics between very narrow titanium nanowires and "massive" superconducting aluminum were measured. The clear trend was observed: the thinner the titanium electrode, the broader the singularity at eV = Δ1(Al) + Δ2(Ti). The phenomenon can be explained by broadening of the gap edge of the quasi-one-dimensional titanium channels due to quantum fluctuations of the order parameter modulus |Δ2|. The range of the nanowire diameters, where the effect is pronounced, correlates with dimensions where the phase fluctuations of the complex superconducting order parameter Δ = |Δ|e(iφ), the quantum phase slips, broadening the R(T) dependencies, have been observed.
Order parameter fluctuations at a buried quantum critical point
Feng, Yejun; Wang, Jiyang; Jaramillo, R.; van Wezel, Jasper; Haravifard, S.; Srajer, G.; Liu, Y.; Xu, Z.-A.; Littlewood, P. B.; Rosenbaum, T. F.
2012-01-01
Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface. PMID:22529348
Order parameter fluctuations at a buried quantum critical point.
Feng, Yejun; Wang, Jiyang; Jaramillo, R; van Wezel, Jasper; Haravifard, S; Srajer, G; Liu, Y; Xu, Z-A; Littlewood, P B; Rosenbaum, T F
2012-05-08
Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe(2) at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface.
Order parameter fluctuations in the holographic superconductor
NASA Astrophysics Data System (ADS)
Plantz, N. W. M.; Stoof, H. T. C.; Vandoren, S.
2017-03-01
We investigate the effect of order parameter fluctuations in the holographic superconductor. In particular, following an introduction to the concept of intrinsic dynamics and its implementation within holographic models, we compute the intrinsic spectral functions of the order parameter in both the normal and the superconducting phase, using a fully backreacted bulk geometry. We also present a vector-like large-N version of the Ginzburg–Landau model that accurately describes our long-wavelength results in both phases. Our results indicate that the holographic superconductor describes a relativistic multi-component superfluid in the universal regime of the BEC–BCS crossover.
Vacuum density fluctuations in extended chaotic inflation
NASA Astrophysics Data System (ADS)
Deruelle, Nathalie; Gundlach, Carsten; Langlois, David
1992-12-01
An inflaton (scalar field) with the potential cσ2n is coupled to gravity within the Jordan-Brans-Dicke theory. The corresponding inflationary model (that is, a flat Friedmann-Robertson-Walker solution with a slowly varying inflaton) is constructed for all values of the coupling β of the inflaton to the dilaton (Brans-Dicke scalar field). The linearized perturbations of the metric, the dilaton, and the inflaton are then quantized within a gauge-invariant formalism. The power spectrum of the vacuum density fluctuations is calculated as a function of c,n, and β. It is the juxtaposition of two powers of the wave number corresponding, respectively, to the contribution of the inflaton and the dilaton. We find the value of β for which the dilaton contribution dominates on observable cosmological scales.
Energy density fluctuations in early universe
Guardo, G. L.; Ruggieri, M.; Greco, V.
2014-05-09
The primordial nucleosinthesys of the element can be influenced by the transitions of phase that take place after the Big Bang, such as the QCD transition. In order to study the effect of this phase transition, in this work we compute the time evolution of thermodynamical quantities of the early universe, focusing on temperature and energy density fluctuations, by solving the relevant equations of motion using as input the lattice QCD equation of state to describe the strongly interacting matter in the early universe plasma. We also study the effect of a primordial strong magnetic field by means of a phenomenological equation of state. Our results show that small inhomogeneities of strongly interacting matter in the early Universe are moderately damped during the crossover.
The Phase Coherence of Interstellar Density Fluctuations
NASA Astrophysics Data System (ADS)
Burkhart, Blakesley; Lazarian, A.
2016-08-01
Studies of MHD turbulence often investigate the Fourier power spectrum to provide information on the nature of the turbulence cascade. However, the Fourier power spectrum only contains the Fourier amplitudes and rejects all information regarding the Fourier phases. Here, we investigate the utility of two statistical diagnostics for recovering information on Fourier phases in ISM column density maps: the averaged amplitudes of the bispectrum and the phase coherence index (PCI), a new phase technique for the ISM. We create three-dimensional density and two-dimensional column density maps using a set of simulations of isothermal ideal MHD turbulence with a wide range of sonic and Alfvénic Mach numbers. We find that the bispectrum averaged along different angles with respect to either the k 1 or k 2 axis is primarily sensitive to the sonic Mach number while averaging the bispectral amplitudes over different annuli is sensitive to both the sonic and Alfvénic Mach numbers. The PCI of density suggests that the most correlated phases occur in supersonic sub-Alfvénic turbulence and near the shock scale. This suggests that nonlinear interactions with correlated phases are strongest in shock-dominated regions, in agreement with findings from the solar wind. Our results suggest that the phase information contained in the bispectrum and PCI can be used to find the turbulence parameters in column density maps.
The Transport of Density Fluctuations Throughout the Heliosphere
NASA Technical Reports Server (NTRS)
Zank, G. P.; Jetha, N.; Hu, Q.; Hunana, P.
2012-01-01
The solar wind is recognized as a turbulent magnetofluid, for which the properties of the turbulent velocity and magnetic field fluctuations are often described by the equations of incompressible magnetohydrodynamics (MHD). However, low-frequency density turbulence is also ubiquitous. On the basis of a nearly incompressible formulation of MHD in the expanding inhomogeneous solar wind, we derive the transport equation for the variance of the density fluctuations (Rho(exp 2)). The transport equation shows that density fluctuations behave as a passive scalar in the supersonic solar wind. In the absence of sources of density turbulence, such as within 1AU, the variance (Rho(exp 2)) approximates r(exp -4). In the outer heliosphere beyond 1 AU, the shear between fast and slow streams, the propagation of shocks, and the creation of interstellar pickup ions all act as sources of density turbulence. The model density fluctuation variance evolves with heliocentric distance within approximately 300 AU as (Rho(exp 2)) approximates r(exp -3.3) after which it flattens and then slowly increases. This is precisely the radial profile for the density fluctuation variance observed by Voyager 2. Using a different analysis technique, we confirm the radial profile for Rho(exp 2) of Bellamy, Cairns, & Smith using Voyager 2 data. We conclude that a passive scalar description for density fluctuations in the supersonic solar wind can explain the density fluctuation variance observed in both the inner and the outer heliosphere.
Density-noise power fluctuations in vibrated granular media
NASA Astrophysics Data System (ADS)
Nowak, E. R.; Grushin, A.; Barnum, A. C.; Weissman, M. B.
2001-02-01
The noise power spectra of the fluctuations in density of a vibrated column of granular material are found to be time dependent. Spectral analysis of these noise power fluctuations shows nontrivial frequency dependences. The noise powers at different frequencies are also found to fluctuate in a partially correlated way. In most instances, the slow variations of the noise are strongly correlated over a broad range of frequencies. These results indicate that highly cooperative interactions exist between fluctuators. In contrast, effects of such strongly coupled fluctuators are absent in the one-dimensional parking-lot-model, one of the simplest systems used to provide a model for recent granular compaction experiments.
Electron cyclotron emission as a density fluctuation diagnostic
Lynn, A.G.; Phillips, P.E.; Hubbard, A.
2004-10-01
A new technique for measuring density fluctuations using a high-resolution heterodyne electron cyclotron emission (ECE) radiometer has been developed. Although ECE radiometry is typically used for electron temperature measurements, the unique viewing geometry of this system's quasioptical antenna has been found to make the detected emission extremely sensitive to refractive effects under certain conditions. This sensitivity gives the diagnostic the ability to measure very low levels of density fluctuations in the core of Alcator C-Mod tokamak. The refractive effects have been modeled using ray-tracing methods, allowing estimates of the density fluctuation magnitude and spatial localization.
Fermion pseudogap from fluctuations of an order parameter
NASA Astrophysics Data System (ADS)
Tchernyshyov, Oleg Vladimirovich
Pseudogap behavior, observed in cuprate superconductors and Peierls chains, is studied using various phenomenological approaches. (1) A work of M. V. Sadovskii on Peierls chains with Gaussian fluctuations of the order parameter is revisited. A more transparent diagrammatic method is given and a serious error is pointed out. The method is applied to a recent work of J. Schmalian, B. Stojkovic and D. Pines on "hot spots". It is shown that, while their model is not affected by Sadovskii's mistake, it predicts no pseudogap in the local density of states. (2) A simple analytical treatment based on the self-consistent t-matrix approach is suggested to describe Cooper pair fluctuations deeply in the pseudogap regime. It is argued that a pronounced depletion of the fermion density of states by the pseudogap suppresses the decay of pairing fluctuations, giving them a propagating, rather than diffusing, nature. In view of an approximate particle-hole symmetry at the Fermi surface, both electron pairs and hole pairs should exist in the pseudogap regime, in addition to gapped fermions. Near 2 dimensions, the condensation temperature of these pairs is linearly proportional to the fermion density (the Uemura scaling). (3) A work of J. R. Schrieffer and A. R. Kampf on the crossover between an antiferromagnetic (AFM) insulator and a Fermi liquid is complemented by an exactly solvable toy model with all essential features intact. Based on that solution, the three bands of Schrieffer and Kampf are reinterpreted as just two AFM bands with a gap slowly varying in time or across the sample.
Interplay between density and superconducting quantum critical fluctuations.
Caprara, S; Bergeal, N; Lesueur, J; Grilli, M
2015-10-28
We consider the case of a density-driven metal-superconductor transition in the proximity of an electronic phase separation. In particular, we investigate the interplay between superconducting fluctuations and density fluctuations, which become quantum critical when the electronic phase separation vanishes at zero temperature into a quantum critical point. In this situation, the critical dynamical density fluctuations strongly affect the dynamics of the Cooper-pair fluctuations, which acquire a more singular character with a z = 3 dynamical critical index. This gives rise to a scenario that possibly rules the disappearance of superconductivity when the electron density is reduced by electrostatic gating at the LaAlO3/SrTiO3 interface.
Modification of Boundary Parameters and Fluctuations by IBW and LHCD in the HT-7 Tokamak
NASA Astrophysics Data System (ADS)
Song, Mei; Wan, Baonian; Xu, Guosheng; Liu, Haiqing; Ling, Bili; Li, Chengfu; Zhou, Liwu
2003-08-01
Measurements of boundary parameters and their fluctuations have been performed in ohmic (OH) plasma and Ion Bernstein Wave (IBW) and Lower Hybrid Current Drive (LHCD) enhanced confinement plasma using a pneumatically driven Langmuir probe array on HT-7 tokamak. In the enhanced confinement plasma, the gradients of electron density and temperature become higher and a transport barrier comes into being in the vicinity of the limiter. The boundary potential shows a clear modification in the same region. The fluctuation levels are significantly depressed and the coherences between fluctuations are reduced evidently in the enhanced plasma. Meanwhile, we obtained the spectral features and the poloidal phase velocity of fluctuations using a two-point correlation technique and found obvious modifications of the turbulence and the poloidal flow. The results suggest that the improved confinement in the IBW and LHCD enhanced plasma is at least partially due to the modification of the boundary parameters and the suppression of the boundary fluctuations and fluctuation induced fluxes.
The power associated with density fluctuations and velocity fluctuations in the solar wind
NASA Technical Reports Server (NTRS)
Intriligator, D. S.
1974-01-01
Direct observations from Pioneer 6 of solar-wind-proton fluctuations have been used to obtain the power spectra associated with solar-wind-proton number density and velocity fluctuations in the frequency range of 0.001 to 0.01 Hz, extending previous analyses by an order of magnitude at the higher frequencies. The slopes of the power spectra associated with the density fluctuations and the velocity fluctuations are similar and are in agreement with the shape of the power spectra found at the lower frequencies. The power spectra indicate that the power-law density spectrum observed at lower frequencies extends to at least 0.01 Hz. This smooth variation in the spectrum at these frequencies is consistent with previous extrapolations of both spacecraft and interplanetary scintillation observations.
Density Fluctuations of Hard-Sphere Fluids in Narrow Confinement
NASA Astrophysics Data System (ADS)
Nygârd, Kim; Sarman, Sten; Hyltegren, Kristin; Chodankar, Shirish; Perret, Edith; Buitenhuis, Johan; van der Veen, J. Friso; Kjellander, Roland
2016-01-01
Spatial confinement induces microscopic ordering of fluids, which in turn alters many of their dynamic and thermodynamic properties. However, the isothermal compressibility has hitherto been largely overlooked in the literature, despite its obvious connection to the underlying microscopic structure and density fluctuations in confined geometries. Here, we address this issue by probing density profiles and structure factors of hard-sphere fluids in various narrow slits, using x-ray scattering from colloid-filled nanofluidic containers and integral-equation-based statistical mechanics at the level of pair distributions for inhomogeneous fluids. Most importantly, we demonstrate that density fluctuations and isothermal compressibilities in confined fluids can be obtained experimentally from the long-wavelength limit of the structure factor, providing a formally exact and experimentally accessible connection between microscopic structure and macroscopic, thermodynamic properties. Our approach will thus, for example, allow direct experimental verification of theoretically predicted enhanced density fluctuations in liquids near solvophobic interfaces.
Measurement of high-frequency, small scale density fluctuations in improved confinement RFP plasmas
NASA Astrophysics Data System (ADS)
Duff, J. R.; Chapman, B. E.; Sarff, J. S.; Carmody, D.; Terry, P. W.; den Hartog, D. J.; Morton, L. A.; Lin, L.; Ding, W. X.; Brower, D. L.; MST Team
2014-10-01
In standard MST RFP plasmas, core transport is governed by magnetic fluctuations associated with global tearing modes. Using pulsed parallel current drive, tearing is significantly reduced and smaller-scale fluctuations are likely important to electron particle and heat transport for these improved confinement plasmas. On MST, an 11-chord FIR laser-based interferometry diagnostic, with ~ 8 cm chord spacing, is used to measure electron density fluctuations with wavenumbers k < 1-2 cm-1. An upgrade underway will allow resolution up to k ~ 15 cm-1. A fast magnetic coil array is employed for magnetic fluctuations. High-frequency (>50 kHz) small-scale (n > 15) density and magnetic fluctuations have been observed in the edge plasma, where density and temperature gradients are largest. These fluctuations are distinct from tearing and have amplitudes that correlate with the density gradient and electron beta. The MST is well suited to explore beta scaling given the large dynamic range (9-26%) found in the device. Correlation of the measured density fluctuations with plasma parameters in high beta plasmas will serve to identify the drive and contribute to validation of gyrokinetic codes. Work supported by DOE and NSF.
MEASUREMENTS OF RAPID DENSITY FLUCTUATIONS IN THE SOLAR WIND
Malaspina, D. M.; Ergun, R. E.; Kellogg, P. J.; Bale, S. D.
2010-03-01
The power spectrum of density fluctuations in the solar wind is inferred by tracking small timescale changes in the electron plasma frequency during periods of strong Langmuir wave activity. STEREO electric field waveform data are used to produce time profiles of plasma density from which the density power spectrum is derived. The power spectra obtained by this method extend the observed frequency range by an order of magnitude while remaining consistent with previous results near a few Hertz. Density power spectral indices are found to be organized by the angle between the local magnetic field and the solar wind direction, indicating significant anisotropy in solar wind high-frequency density turbulence.
Density fluctuation measurements by using the Fraunhofer diffraction method in GAMMA10
NASA Astrophysics Data System (ADS)
Morikawa, Y.; Yoshikawa, M.; Kohagura, J.; Shima, Y.; Hasegawa, Y.; Sakamoto, M.; Imai, T.; Ichimura, M.
2013-12-01
We applied Fraunhofer diffraction (FD) method to GAMMA10 plasma. The FD method can measure the density fluctuation in detail and the wave number of the fluctuation. We successfully obtained the density fluctuation spectra in GAMMA 10. Analyzing the FD method signals of radial fluctuation intensity profile, we can successfully obtain the wave number and the phase velocity of the low frequency density fluctuation.
Shen, Weimin.
1992-08-01
Studies of magnetic fluctuation induced particle transport on Reversed Field Pinch plasmas were done on the Madison Symmetric Torus. Plasma current density and current density fluctuations were measured using a multi-coil magnetic probes. The low frequency (f<50 kHz) current density fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 50 kHz, the magnetic fluctuations were detected to be localized with a radial correlation length of about 1--2 cm. These modes are locally resonant modes since the measured dominant mode number spectra match the local safety factor q. The net charged particle flux induced by magnetic fluctuations was obtained by measuring the correlation term <{tilde j}{sub {parallel}} {tilde B}{sub r}>. The result of zero net charged particle loss was obtained, meaning the flux is ambipolar. The ambipolarity of low frequency global tearing modes is satisfied through the phase relations determined by tearing instabilities. The ambipolarity of high frequency localized modes could be partially explained by the simple model of Waltz based on the radial average of small scale turbulence.
Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas
Sanner, Christian; Su, Edward J.; Keshet, Aviv; Gommers, Ralf; Shin, Yong-il; Huang Wujie; Ketterle, Wolfgang
2010-07-23
We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.
Discriminating the trapped electron modes contribution in density fluctuation spectra
NASA Astrophysics Data System (ADS)
Arnichand, H.; Sabot, R.; Hacquin, S.; Krämer-Flecken, A.; Bourdelle, C.; Citrin, J.; Garbet, X.; Giacalone, J. C.; Guirlet, R.; Hillesheim, J. C.; Meneses, L.
2015-09-01
Quasi-coherent (QC) modes have been reported for more than 10 years in reflectometry fluctuations spectra in the core region of fusion plasmas. They have characteristics in-between coherent and broadband fluctuations as they oscillate at a marked frequency but have a wide spectrum. This work presents further evidences of the link recently established between QC modes and the trapped electron modes (TEM) instabilities (Arnichand et al 2014 Nucl. Fusion 54 123017). In electron cyclotron resonance heated discharges of Tore Supra, an enhancement of QC modes amplitude is observed in a region where TEM cause impurity transport and turbulence. In JET Ohmic plasmas, QC modes disappear during density ramp-up and current ramp-down. This is reminiscent of Tore Supra and TEXTOR observations during transitions from the linear Ohmic confinement (LOC) to the saturated Ohmic confinement (SOC) regimes. Evidencing TEM activity then becomes experimentally possible via analysis of fluctuation spectra.
Baryon number fluctuations at finite temperature and density
NASA Astrophysics Data System (ADS)
Fu, Wei-jie; Pawlowski, Jan M.; Rennecke, Fabian; Schaefer, Bernd-Jochen
2016-12-01
We investigate baryon number fluctuations for finite temperature and density in two-flavor QCD. This is done within a QCD-improved low-energy effective theory in an extension of the approach put forward by Fu and Pawlowski [Phys. Rev. D 92, 116006 (2015), 10.1103/PhysRevD.92.116006 and Phys. Rev. D 93, 091501 (2016), 10.1103/PhysRevD.93.091501]. In the present work, we aim to improve the predictive power of this approach for large temperatures and, in partitular, large densities, that is, for small collision energies. This is achieved by taking into account the full frequency dependence of the quark dispersion. This ensures the necessary Silver Blaze property of finite density QCD for the first time, which so far was only implemented approximately. Moreover, we show that Polyakov-loop fluctuations have a sizeable impact at large temperatures and density. The results for the kurtosis of baryon number fluctuations are compared to previous effective theory results, lattice results, and recent experimental data from STAR.
NASA Astrophysics Data System (ADS)
Deng, C. B.; Brower, D. L.
2012-10-01
The interferometer system on the Helically Symmetric eXperiment (HSX) stellarator uses an expanded beam and linear detector array to realize a multichord measurement. Unlike conventional interferometry which determines the plasma phase shift with respect to a reference, directly evaluating the phase between two adjacent chords can be employed to measure the change in plasma phase with impact parameter. This approach provides a measure of the equilibrium density gradient or the density gradient fluctuations and is referred to as differential interferometry. For central chords, measurements are spatially localized due to a geometrical weighting factor and can provide information on core density gradient fluctuations. The measurement requires finite coherence between fluctuations in the two spatially offset chords. This technique is applied on the HSX stellarator to measure both broadband turbulence and coherent modes. Spatial localization is exploited to isolate core turbulence changes associated with change in magnetic configuration or heating location.
Radial evolution of the energy density of solar wind fluctuations
NASA Technical Reports Server (NTRS)
Zank, G. P.; Matthaeus, W. H.; Smith, C. W.
1995-01-01
On the basis of transport theories appropriate to a radially expanding solar wind, we describe new results for the radial evolution of the energy density in solar wind fluctuations at MHD scales. These models include the effects of 'mixing' and driving as well as the possibility of non-isotropic MHD turbulence. Implications of these results for solar wind heating, cosmic ray diffusion and interstellar pick-up ions will also be addressed.
Amplitude of primeval fluctuations from cosmological mass density reconstructions
NASA Technical Reports Server (NTRS)
Seljak, Uros; Bertschinger, Edmund
1994-01-01
We use the POTENT reconstruction of the mass density field in the nearby universe to estimate the amplitude of the density fluctuation power spectrum for various cosmological models. We find that sigma(sub 8) Omega(sub m sup 0.6) = 1.3(sub -0.3 sup +0.4), almost independently of the power spectrum. This value agrees well with the Cosmic Background Explorer (COBE) normalization for the standard cold dark matter model, while alternative models predict an excessive amplitude compared with COBE. Flat, low Omega(sub m) models and tilted models with spectral index n less than 0.8 are particularly discordant.
Listening to the noise: random fluctuations reveal gene network parameters.
Munsky, Brian; Trinh, Brooke; Khammash, Mustafa
2009-01-01
The cellular environment is abuzz with noise originating from the inherent random motion of reacting molecules in the living cell. In this noisy environment, clonal cell populations show cell-to-cell variability that can manifest significant phenotypic differences. Noise-induced stochastic fluctuations in cellular constituents can be measured and their statistics quantified. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We show that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. This establishes a potentially powerful approach for the identification of gene networks and offers a new window into the workings of these networks.
Spontaneous density fluctuations in granular flow and traffic
NASA Astrophysics Data System (ADS)
Herrmann, Hans J.
It is known that spontaneous density waves appear in granular material flowing through pipes or hoppers. A similar phenomenon is known from traffic jams on highways. Using numerical simulations we show that several types of waves exist and find that the density fluctuations follow a power law spectrum. We also investigate one-dimensional traffic models. If positions and velocities are continuous variables the model shows self-organized criticality driven by the slowest car. Lattice gas and lattice Boltzmann models reproduce the experimentally observed effects. Density waves are spontaneously generated when the viscosity has a non-linear dependence on density or shear rate as it is the case in traffic or granular flow.
Compaction and density fluctuations in vibrated granular media
NASA Astrophysics Data System (ADS)
Barnum, A. C. B.; Ozbay, A.; Nowak, E. R.
2002-03-01
We report measurements of the density of a vibrated granular material as a function of time or taps. The material studied consists of monodisperse spherical glass beads confined to a long, thin cylindrical tube. Changes in vibration intensity are used to induce transitions between two steady state densities that depend on the intensity of the vibrations. We find a complex time evolution similar to previous work on the irreversible relaxation from a loose state toward a steady state. In addition, frequency dependent third order moments of the density fluctuations are measured. The data indicate a coupling between large variations in density on one time scale and noise power over a broad range of higher-frequency scales. This work was partly supported by Petroleum Research Foundation under award No. 35861-G5.
Compaction and Density Fluctuations in Vibrated Granular Media
NASA Astrophysics Data System (ADS)
Barnum, A. C. B.; Ozbay, Arif; Nowak, E. R.
We report measurements of the density of a vibrated granular material as a function of time or taps. The material studied consists of monodisperse spherical glass beads confined to a long, thin cylindrical tube. Changes in vibration intensity are used to induce transitions between two steady state densities that depend on the intensity of the vibrations. We find a complex time evolution similar to previous work on the irreversible relaxation from a loose state toward a steady state. In addition, frequency dependent third order moments of the density fluctuations are measured. The data indicate a coupling between large variations in density on one time scale and noise power over a broad range of higher-frequency scales.
Effect of Heating on Turbulent Density Fluctuations and Noise Generation From High Speed Jets
NASA Technical Reports Server (NTRS)
Panda, Jayanta; Seasholtz, Richard G.; Elam, Kristie A.; Mielke, Amy F.; Eck, Dennis G.
2004-01-01
Heated jets in a wide range of temperature ratios (TR), and acoustic Mach numbers (Ma) were investigated experimentally using far field microphones and a molecular Rayleigh scattering technique. The latter provided density fluctuations measurements. Two sets of operating conditions were considered: (1) TR was varied between 0.84 and 2.7 while Ma was fixed at 0.9; (2) Ma was varied between 0.6 and 1.48, while TR was fixed at 2.27. The implementation of the molecular Rayleigh scattering technique required dust removal and usage of a hydrogen combustor to avoid soot particles. Time averaged density measurements in the first set of data showed differences in the peripheral density shear layers between the unheated and heated jets. The nozzle exit shear layer showed increased turbulence level with increased plume temperature. Nevertheless, further downstream the density fluctuations spectra are found to be nearly identical for all Mach number and temperature ratio conditions. To determine noise sources a correlation study between plume density fluctuations and far field sound pressure fluctuations was conducted. For all jets the core region beyond the end of the potential flow was found to be the strongest noise source. Except for an isothermal jet, the correlations did not differ significantly with increasing temperature ratio. The isothermal jet created little density fluctuations. Although the far field noise from this jet did not show any exceptional trend, the flow-sound correlations were very low. This indicated that the density fluctuations only acted as a "tracer parameter" for the noise sources.
Fluctuation-induced pair density wave in itinerant ferromagnets
NASA Astrophysics Data System (ADS)
Conduit, G. J.; Pedder, C. J.; Green, A. G.
2013-03-01
Magnetic fluctuations near to quantum criticality can have profound effects. They lead to characteristic scaling at high temperature which may ultimately give way to a reconstruction of the phase diagram and the formation of new phases at low temperatures. The ferromagnet UGe2 is unstable to p-wave superconducting order—an effect presaged by the superfluidity in 3He—whereas in CeFePO fluctuations drive the formation of spiral magnetic order. Here we develop a general quantum order-by-disorder description of these systems that encompasses both of these instabilities within a unified framework. This allows us to demonstrate that in fact these instabilities intertwine to form a pair density wave.
Observations of ULF wave related equatorial electrojet and density fluctuations
NASA Astrophysics Data System (ADS)
Yizengaw, E.; Zesta, E.; Moldwin, M.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.
2011-12-01
Global magnetospheric Ultra Low Frequency (ULF) pulsations with frequencies in the Pc 4-5 range (f = 1.0 - 8 mHz) have been observed for decades in space and on Earth. ULF pulsations contribute to magnetospheric particle transport and diffusion and play an important role in magnetospheric dynamics. However, only a few studies have been performed on ionospheric observations of ULF wave-related perturbations in the vicinity of the equatorial region. In this paper we report on Pc5 wave related electric field and thus vertical drift velocity oscillations at the equator as observed by ground magnetometers and radar. We show that the magnetometer estimated equatorial ExB drift oscillate with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. For independent confirmation of the vertical drift velocity fluctuation, we used JULIA 150 km radar drift velocities and found similar fluctuation with the period of 8-10 minutes. We also show ionospheric density fluctuations during the period when we observed ULF wave activities. All these demonstrate that the Pc5 wave can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. Finally, in order to detect the ULF activities both on the ground and in space, we use groundbased magnetometer data from African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Using the WIND spacecraft as the upstream solar wind monitor, we present direct evidence that solar wind number density and ram pressure fluctuations observed far upstream from the terrestrial magnetosphere are the main drivers of ULF wave activity inside the magnetosphere. Finally, we show that the ULF waves in the same frequency range are observed in the magnetosphere by the geosynchronous GOES spacecraft, in the
Penetration and scattering of lower hybrid waves by density fluctuations
Horton, W.; Goniche, M.; Peysson, Y.; Decker, J.; Ekedahl, A.; Litaudon, X.
2014-02-12
Lower Hybrid [LH] ray propagation in toroidal plasma is controlled by a combination of the azimuthal spectrum launched from the antenna, the poloidal variation of the magnetic field, and the scattering of the waves by the density fluctuations. The width of the poloidal and radial RF wave spectrum increases rapidly as the rays penetrate into higher density and scatter from the turbulence. The electron temperature gradient [ETG] spectrum is particularly effective in scattering the LH waves due to its comparable wavelengths and parallel phase velocities. ETG turbulence is also driven by the radial gradient of the electron current density giving rise to an anomalous viscosity spreading the LH-driven plasma currents. The scattered LH spectrum is derived from a Fokker-Planck equation for the distribution of the ray trajectories with a diffusivity proportional to the fluctuations. The LH ray diffusivity is large giving transport in the poloidal and radial wavenumber spectrum in one - or a few passes - of the rays through the core plasma.
Density fluctuation spectrum of two-dimensional correlated fermion systems
NASA Astrophysics Data System (ADS)
Kotani, Akihiro; Hirashima, Dai
2012-12-01
Density fluctuation spectrum of two-dimensional fermions that interact with short-range repulsive interaction is calculated with the self-consistent perturbation theory. The spectrum extends beyond the particle-hole continuum band in the noninteracting case because of the multiparticle excitations. At a large wave vector, a peak develops in the spectrum near the lower threshold of the particle-hole continuum. These results are compared with the recent inelastic neutron scattering experiment on two-dimensional 3He adsorbed on graphite.
Spatial structure of lemming populations (Dicrostonyx groenlandicus) fluctuating in density.
Ehrich, D; Jorde, P E; Krebs, C J; Kenney, A J; Stacy, J E; Stenseth, N C
2001-02-01
The pattern and scale of the genetic structure of populations provides valuable information for the understanding of the spatial ecology of populations, including the spatial aspects of density fluctuations. In the present paper, the genetic structure of periodically fluctuating lemmings (Dicrostonyx groenlandicus) in the Canadian Arctic was analysed using mitochondrial DNA (mtDNA) control region sequences and four nuclear microsatellite loci. Low genetic variability was found in mtDNA, while microsatellite loci were highly variable in all localities, including localities on isolated small islands. For both genetic markers the genetic differentiation was clear among geographical regions but weaker among localities within regions. Such a pattern implies gene flow within regions. Based on theoretical calculations and population census data from a snap-trapping survey, we argue that the observed genetic variability on small islands and the low level of differentiation among these islands cannot be explained without invoking long distance dispersal of lemmings over the sea ice. Such dispersal is unlikely to occur only during population density peaks.
Yun, G S; Lee, W; Choi, M J; Kim, J B; Park, H K; Domier, C W; Tobias, B; Liang, T; Kong, X; Luhmann, N C; Donné, A J H
2010-10-01
The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donné et al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfvén eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.
Yun, G. S.; Lee, W.; Choi, M. J.; Kim, J. B.; Park, H. K.; Domier, C. W.; Tobias, B.; Liang, T.; Kong, X.; Luhmann, N. C. Jr.; Donne, A. J. H.
2010-10-15
The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donneet al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfven eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.
Measurements of Electron Density Profile and Fluctuations on HSX*
NASA Astrophysics Data System (ADS)
Deng, C.; Brower, D. L.; Ding, W. X.; Almagri, A. F.; Anderson, D. T.; Anderson, F. S. B.; Gerhardt, S. P.; Probert, P.; Radder, J.; Talmadge, J. N.
2001-10-01
The 288 GHz interferometer system on the quasi-helical stellarator HSX views the plasma cross section along 9 adjacent chords with 1.5 cm spacing. At this frequency refraction is manageable but requires correction when performing inversions. The interferometer has sensitivity n_edl = 8 x 10^11 cm-2 and frequency response up to 1 MHz. Improved time response permits measurement of high-frequency density fluctuations as well as fast changes to the equilibrium profile. First results from HSX with 2nd harmonic ECH at 28 GHz, using a 5 chord version of the interferometer, indicate that the density profile is quite peaked for both quasi-helically symmetric (QHS) plasmas and those where the quasisymmetry is broken (mirror mode) for ne = 1 x 10^12 cm-3. However, for densities ne = 3 x 10^11 cm-3, the profile for the QHS plasma (high stored energy) is narrower when compared to the mirror mode (low stored energy). Density profile variation with plasma configuration and resonant heating location using the 9 channel interferometer will be described. For high density HSX plasmas, ne > 3 x 10^12 cm-3, coherent oscillations are observed in the line-integrated density traces which are out of phase across the magnetic axis. These m=1 oscillations are observed at frequencies of 1-2 kHz and result in a periodic displacement of the density profile. *Supported by USDOE under grant DE-FG03-01ER-54615, Task III and DE-FG02-93ER54222.
Listening to the Noise: Random Fluctuations Reveal Gene Network Parameters
NASA Astrophysics Data System (ADS)
Munsky, Brian; Trinh, Brooke; Khammash, Mustafa
2010-03-01
The cellular environment is abuzz with noise originating from the inherent random motion of reacting molecules in the living cell. In this noisy environment, clonal cell populations exhibit cell-to-cell variability that can manifest significant prototypical differences. Noise induced stochastic fluctuations in cellular constituents can be measured and their statistics quantified using flow cytometry, single molecule fluorescence in situ hybridization, time lapse fluorescence microscopy and other single cell and single molecule measurement techniques. We show that these random fluctuations carry within them valuable information about the underlying genetic network. Far from being a nuisance, the ever-present cellular noise acts as a rich source of excitation that, when processed through a gene network, carries its distinctive fingerprint that encodes a wealth of information about that network. We demonstrate that in some cases the analysis of these random fluctuations enables the full identification of network parameters, including those that may otherwise be difficult to measure. We use theoretical investigations to establish experimental guidelines for the identification of gene regulatory networks, and we apply these guideline to experimentally identify predictive models for different regulatory mechanisms in bacteria and yeast.
The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe
Li, Rong; Wu, Yongquan Xiao, Junjiang
2014-01-21
We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.
The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe
NASA Astrophysics Data System (ADS)
Li, Rong; Wu, Yongquan; Xiao, Junjiang
2014-01-01
We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.
Plasma density fluctuations observed during Space Shuttle Orbiter water releases
NASA Technical Reports Server (NTRS)
Pickett, J. S.; D'Angelo, N.; Kurth, W. S.
1989-01-01
Observations by the Langmuir probe on the Plasma Diagnostics Package flown as part of the Spacelab 2 mission in the summer of 1985 show a strong increase in the level of turbulence near the Shuttle Orbiter during operations in which liquid water is released. The spectrum of the plasma density fluctuations peaks at the lowest frequencies measured (a few Hz) and extends up to a few kHz, near the lower hybrid frequency. Two potential mechanisms for generating the plasma turbulence are suggested which are both based on the production of water ions as a result of charge exchange with the ambient oxygen ions in the ionosphere. The first mechanism proposed is the ion-plasma instability which arises from the drift of the contaminant with respect to the ambient oxygen ions. The other mechanism proposed is the Ott-Farley instability, which is a result of the ring distribution formed by the 'pick-up' water ions.
NASA Astrophysics Data System (ADS)
Novikov, D. V.; Krasovskiĭ, A. N.; Osmolovskaya, N. A.; Efremov, V. I.
2007-02-01
The specific features of the transformation of a polymer solution into a solid state (film) of an amorphous polymer are investigated using electron microscopy. The correspondence between the characteristics of fractal macromolecular aggregates in a solution and the parameters of the spatial distribution of density fluctuations at the surface of the film is established using a linear atactic poly(styrene) as an example. The correspondence exists under the condition that the packing density of coils does not exceed a critical value at the liquid-solid phase transition point and the polymer concentration in the solution provides the formation of a continuous network of entangled macromolecules.
Density fluctuations at high density in the ergodic divertor configuration of Tore Supra
NASA Astrophysics Data System (ADS)
Devynck, P.; Gunn, J.; Ghendrih, Ph.; Garbet, X.; Antar, G.; Beyer, P.; Boucher, C.; Honore, C.; Gervais, F.; Hennequin, P.; Quémeneur, A.; Truc, A.
2001-03-01
The effect of the ergodic divertor on the plasma edge in Tore Supra is to enhance the perpendicular transport through ergodization of the magnetic field lines [Ph. Ghendrih et al., Contrib. Plasma Phys. 32 (3&4) (1992) 179]. Nevertheless, the hot spots observed on the divertor plates during ergodic divertor operation indicate that the cross-field transport driven by the fluctuations is still playing an important role, although measurements by CO 2 laser scattering and reflectometry show a decrease of the turbulence level [J. Payan, X. Garbet, J.H. Chatenet et al., Nucl. Fusion 35 (1995) 1357; P. Beyer, X. Garbet, P. Ghendrih, Phys. Plasmas 5 (12) (1998) 4271]. In order to gain more understanding, fluctuation level and poloidal velocity have been measured with a reciprocating Langmuir probe biased to collect the ion saturation current ( jsat) and with a CO 2 laser scattering diagnostic. Though the relative fluctuation level behaves as previously observed at low density, a new interesting result is that this picture is gradually modified when the density is increased. Both diagnostics observe an increase of δn/ n with density in the ergodic region, which is not the usual behavior observed in limiter configuration. This increase is detected on both sides of the Er inversion radius and is therefore also affecting the plasma bulk. Finally, the confinement time is found to follow an L-mode law at all densities indicating that the ergodic divertor does not change the global confinement properties of the plasma.
NASA Astrophysics Data System (ADS)
Schunck, M.; Hegmann, M.; Sedlmayr, E.
2007-01-01
We investigate the effects of stochastic density fluctuations on the dust temperatures and the resulting infrared (IR) emission spectra of interstellar clouds as an extension of preceding investigations by Hegmann & Kegel. We consider absorption and scattering by dust grains in spherical clouds which are, on average, homogeneous but have a fluctuating density. The spatial variation of the density is described by means of a Markov process. This clump model introduces two parameters: the correlation length ln and the Gaussian width σn of the density fluctuations. As the intensity Iλ,n inherits the randomness of the density n, the ordinary radiative transfer equation has to be replaced by a generalized transfer equation of Fokker-Planck type. In the first part, we investigate the influence of our model parameters on the radiative transport in the ultraviolet (UV) and use the results to calculate the dust temperature in radiative equilibrium. Afterwards, the IR emission of the dust is modelled for the same set of clump parameters. We find that the presence of clumps decreases the effective extinction and therefore leads to substantial differences in UV illumination and dust temperatures, compared with the homogeneous case. Because of the distribution of dust temperatures, the presence of clumps also affects the IR emission and thus possible observations. In the second part, we use a fit with two blackbody spectra to determine the cloud dust mass from our synthetic IR fluxes. It is shown that in a clumpy environment the overall dust mass is generally underestimated. This effect correlates with the degree of cloud fragmentation.
Collective motion and density fluctuations in bacterial colonies
NASA Astrophysics Data System (ADS)
Zhang, Hepeng; Be'Er, Avraham; Florin, E.-L.; Swinney, Harry L.
2010-03-01
The emergence of collective motion such as in fish schools and swarming bacteria is a ubiquitous self-organization phenomenon. Such collective behavior plays an important role in a range of phenomenon, such as formation and migration of animal or fish groups. To understand the collective motion, tracking of large numbers of individuals is needed, but such measurements have been lacking. Here we examine a microscopic system, where we are able to measure simultaneously the positions, velocities, and orientations of up to a thousand bacteria in a colony. The motile bacteria form closely-packed dynamic clusters within which they move cooperatively. The number of bacteria in a cluster exhibits a power-law distribution truncated by an exponential tail, and the probability of finding large clusters grows markedly as bacterial density increases. Mobile clusters exhibit anomalous fluctuations in bacterial density: the standard deviation (δN) grows with the mean (N) of the number of bacteria as δN˜N^3/4 rather than δN˜N^1/2, as in thermal equilibrium systems.
Collective motion and density fluctuations in swimming bacteria
NASA Astrophysics Data System (ADS)
Zhang, Hepeng
2011-03-01
The emergence of collective motion such as in fish schools, mammal herds, and insect swarms is a ubiquitous self-organization phenomenon. Such collective behavior plays an important role in a range of problems, such as spreading of deceases in animal or fish groups. Current models have provided a qualitative understanding of collective motion, but progress in quantitative modeling in hindered by the lack of experimental data. Here we examine a model microscopic system, where we are able to measure simultaneously the positions, velocities, and orientations of up to a thousand bacteria in a colony. The motile bacteria form closely-packed dynamic clusters within which they move cooperatively. The number of bacteria in a cluster exhibits a power-law distribution truncated by an exponential tail, and the probability of finding large clusters grows markedly as bacterial density increases. Mobile clusters cause anomalous fluctuations in bacterial density as found in mathematical theories and numerical models. Our results demonstrate that bacteria are an excellent system to study general phenomena of collective motion.
Dynamical Selection of the Primordial Density Fluctuation Amplitude
Lehners, Jean-Luc; Steinhardt, Paul J.
2011-02-25
In inflationary models, the predicted amplitude of primordial density perturbations Q is much larger than the observed value ({approx}10{sup -5}) for natural choices of parameters. To explain the requisite exponential fine-tuning, anthropic selection is often invoked, especially in cases where microphysics is expected to produce a complex energy landscape. By contrast, we find examples of ekpyrotic models based on heterotic M theory for which dynamical selection naturally favors the observed value of Q.
Are metastable, precrystallisation, density-fluctuations a universal phenomena?
Heeley, Ellen L; Poh, C Kit; Li, Wu; Maidens, Anna; Bras, Wim; Dolbnya, Igor P; Gleeson, Anthony J; Terrill, Nicolas J; Fairclough, J Patrick A; Olmsted, Peter D; Ristic, Rile I; Hounslow, Micheal J; Ryan, Anthony J
2003-01-01
In-situ observations of crystallisation in minerals and organic polymers have been made by simultaneous, time-resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) techniques. In isotactic polypropylene slow quiescent crystallisation shows the onset of large scale ordering prior to crystal growth. Rapid crystallisations studied by melt extrusion indicate the development of well resolved oriented SAXS patterns associated with long range order before the development of crystalline peaks in the WAXS region. Block copolymers self-assemble into mesophases in polymer melts above a critical chain length (or above a critical temperature) and this self-assembly process is shown to be susceptible to an incipient crystallisation. Mesophase formation is observed at anomalously high temperatures in ethylene-oxide containing block copolymers below the normal melting point of the polyoxy ethylene chains. Formation of calcium carbonate from aqueous solutions of sodium carbonate and calcium nitrate is observed to be a two-stage process and precipitation proceeds by the production of an amorphous metastable phase. This phase grows until it is volume filling and leads to the formation of the two polymorphs Calcite and Vaterite. These three sets of results suggest pre-nucleation density fluctuations, leading to a metastable phase, play an integral role in all three classes of crystallisation. In due course, this phase undergoes transformation to "normal" crystals.
Electron density fluctuation measurements using a multichannel microwave interferometer in GAMMA 10
Yoshikawa, M.; Shima, Y.; Matsumoto, T.; Nakahara, A.; Yanagi, N.; Itakura, A.; Hojo, H.; Kobayashi, T.; Matama, K.; Tatematsu, Y.; Imai, T.; Kohagura, J.; Hirata, M.; Nakashima, Y.; Cho, T.
2006-10-15
Measurement of fluctuation in plasma is important for studying the improvement in plasma confinement by the formation of the plasma confinement potential. The density fluctuation is observed by microwaves by methods such as interferometry, reflectometry and Fraunhofer diffraction method. We have constructed a new multichannel microwave interferometer to measure the plasma density and fluctuation radial profiles in a single plasma shot. We successfully measured the time-dependent density and line-integrated density fluctuation radial profiles in a single plasma shot using the multichannel microwave interferometer. Thus, we have developed a useful tool for studying the improvement in plasma confinement by the formation of plasma confinement potential.
NASA Astrophysics Data System (ADS)
Snicker, Antti; Guidi, Lorenzo; Kohn, Alf; Maj, Omar; Weber, Hannes; Poli, Emanuele
2016-10-01
We present state-of-the-art computations of propagation and absorption of electron cyclotron waves, retaining the effects of scattering due to density fluctuations. In ITER, injected microwaves are foreseen to suppress NTMs by driving current at the resonant surface(s). The good localization of the absorption profile can be spoiled by beam scattering and impair the NTM control capabilities. A novel tool based on the wave kinetic equation has been developed, which retains diffraction, an integral form of the scattering operator assuming the Born scattering approximation, full tokamak geometry and determination of the power absorption profile. This approach has been implemented in the code WKBeam, which has been benchmarked against the beam-tracing code TORBEAM and the full-wave code IPF-FDMC, in particular to verify usage of the Born approximation for ITER parameters. We show that in ITER the radiation transport is diffusive unlike in existing machines. Using WKBeam we demonstrate through parameter scans that the width of the deposition profile in ITER depends on the assumptions on the fluctuations and beam parameters: the effect can be of the order of 100%. A method to quantify mode-to-mode scattering induced by fluctuations has been developed and first results are presented.
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.
Banakh, V A; Smalikho, I N
2014-09-22
Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere have been studied based on numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field by the split-step method. It has been shown that under conditions of strong optical turbulence, the relative variance of energy density fluctuations of pulsed radiation of femtosecond duration becomes much less than the relative variance of intensity fluctuations of continuous-wave radiation. The spatial structure of fluctuations of the energy density with a decrease of the pulse duration becomes more large-scale and homogeneous. For shorter pulses the maximal value of the probability density distribution of energy density fluctuations tends to the mean value of the energy density.
Spatial density fluctuations and selection effects in galaxy redshift surveys
Labini, Francesco Sylos; Tekhanovich, Daniil; Baryshev, Yurij V. E-mail: d.tekhanovich@spbu.ru
2014-07-01
One of the main problems of observational cosmology is to determine the range in which a reliable measurement of galaxy correlations is possible. This corresponds to determining the shape of the correlation function, its possible evolution with redshift and the size and amplitude of large scale structures. Different selection effects, inevitably entering in any observation, introduce important constraints in the measurement of correlations. In the context of galaxy redshift surveys selection effects can be caused by observational techniques and strategies and by implicit assumptions used in the data analysis. Generally all these effects are taken into account by using pair-counting algorithms to measure two-point correlations. We review these methods stressing that they are based on the a-priori assumption that galaxy distribution is spatially homogeneous inside a given sample. We show that, when this assumption is not satisfied by the data, results of the correlation analysis are affected by finite size effects. In order to quantify these effects, we introduce a new method based on the computation of the gradient of galaxy counts along tiny cylinders. We show, by using artificial homogeneous and inhomogeneous point distributions, that this method identifies redshift dependent selection effects and disentangles them from the presence of large scale density fluctuations. We then apply this new method to several redshift catalogs and we find evidence that galaxy distribution, in those samples where selection effects are small enough, is characterized by power-law correlations with exponent γ=0.9 up to 20 Mpc/h followed by a change of slope that, in the range 20–100 Mpc/h, corresponds to a power-law exponent γ=0.25. Whether a crossover to spatial uniformity occurs at ∼ 100 Mpc/h or larger scales cannot be clarified by the present data.
Jacobson, A.R.
1981-04-01
A laser diagnostic scheme is described which facilitates localization of density fluctuations along the line of sight. The method exploits both the generally observed anisotropy of density fluctuations in low-beta plasmas, as well as the twisting of the magnetic field which occurs across the minor diameter of reversed-field pinches, spheromaks, etc. Both interferometric and schlieren variations are discussed.
Density fluctuations and dielectric constant of water in low and high density liquid states
NASA Astrophysics Data System (ADS)
Lascaris, Erik; Zhang, Cui; Galli, Giulia A.; Franzese, Giancarlo; Stanley, H. Eugene
2012-02-01
The hypothesis of a liquid-liquid critical point (LLCP) in the phase diagram of water, though first published many years ago, still remains the subject of a heated debate. According to this hypothesis there exists a critical point near T 244 K, and P 215 MPa, located at the end of a coexistence line between a high density liquid (HDL) and a low density liquid state (LDL). The LLCP lies below the homogenous nucleation temperature of water and it has so far remained inaccessible to experiments. We study a model of water exhibiting a liquid-liquid phase transition (that is a liquid interacting through the ST2 potential) and investigate the properties of dipolar fluctuations as a function of density, in the HDL and LDL. We find an interesting correlation between the macroscopic dielectric constants and the densities of the two liquids in the vicinity of the critical point, and we discuss possible implications for measurements close to the region where the LLCP may be located.
The origin of density fluctuations in the 'new inflationary universe'
NASA Technical Reports Server (NTRS)
Turner, M. S.
1983-01-01
Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.
Additivity, density fluctuations, and nonequilibrium thermodynamics for active Brownian particles
NASA Astrophysics Data System (ADS)
Chakraborti, Subhadip; Mishra, Shradha; Pradhan, Punyabrata
2016-05-01
Using an additivity property, we study particle-number fluctuations in a system of interacting self-propelled particles, called active Brownian particles (ABPs), which consists of repulsive disks with random self-propulsion velocities. From a fluctuation-response relation, a direct consequence of additivity, we formulate a thermodynamic theory which captures the previously observed features of nonequilibrium phase transition in the ABPs from a homogeneous fluid phase to an inhomogeneous phase of coexisting gas and liquid. We substantiate the predictions of additivity by analytically calculating the subsystem particle-number distributions in the homogeneous fluid phase away from criticality where analytically obtained distributions are compatible with simulations in the ABPs.
Non-equilibrium steady states: fluctuations and large deviations of the density and of the current
NASA Astrophysics Data System (ADS)
Derrida, Bernard
2007-07-01
These lecture notes give a short review of methods such as the matrix ansatz, the additivity principle or the macroscopic fluctuation theory, developed recently in the theory of non-equilibrium phenomena. They show how these methods allow us to calculate the fluctuations and large deviations of the density and the current in non-equilibrium steady states of systems like exclusion processes. The properties of these fluctuations and large deviation functions in non-equilibrium steady states (for example, non-Gaussian fluctuations of density or non-convexity of the large deviation function which generalizes the notion of free energy) are compared with those of systems at equilibrium.
NASA Astrophysics Data System (ADS)
Ding, Weixing; Lin, Liang; Duff, J. R.; Brower, D. L.; Sarff, J. S.
2014-10-01
In the MST reversed field pinch (RFP), the evolution of core tearing mode nonlinear evolution is partially determined by the electron current density profile along with nonlinear interactions among multiple tearing modes. Density fluctuations driven by intrinsic magnetic perturbations are usually large, approximately 1%, in RFP plasmas. These density fluctuations can modify the current density profile via the kinetic dynamo effect, defined as the correlated product of parallel electron pressure and radial magnetic field fluctuations, which alters the temporal dynamics of tearing modes in MST. A component of the kinetic dynamo originating from the correlated product of density and radial magnetic fluctuations has been measured using a high-speed, low phase noise polarimetry-interferometry diagnostic. Between sawtooth crashes it is found that the measured kinetic dynamo has finite amplitude that generates an anti-dynamo in the plasma core, which would tend to flatten the current density profile. These measurements suggest that density fluctuations passively driven by magnetic fluctuations can actively alter tearing modes via fluctuation-induced current transport. Work supported by US DOE and NSF.
Wavelet analysis of the parameters of edge plasma fluctuations in the L-2M stellarator
NASA Astrophysics Data System (ADS)
Maslov, S. A.; Vasilkov, D. G.; Kholnov, Yu V.; Skvortsova, N. N.
2016-01-01
Wavelet analysis results are presented for evolution of the spectral fluctuation characteristics of the edge plasma density and potential in the L-2M stellarator for fast and slow transport transitions. The fast transition comes out as a sharp increase of the energy and electron density within ∼0.1ms and the slow one as a weak parameter change during a 0.5 to 1 ms time interval. It is shown that the use of the “Mexican hat” and Morlet wavelets allows one to detect the moment of the fast transition, whereas applying the Haar wavelet adds to this also an estimate of its duration, conforming to the analytical calculations, and reveals the temporal structure of the slow transition.
NASA Technical Reports Server (NTRS)
Huddleston, D. E.; Woo, R.; Neugebauer, M.
1995-01-01
Density fluctuations with periods 10 minutes to 1 hour have been investigated in ISEE 3 plasma measurements of solar wind flows at l AU. Coronal hole, interstream, plasma sheet, coronal mass ejection, and interaction region flow types are considered. The ISEE 3 results support the interpretation of the large-scale variations in density fluctuations observed by Doppler scintillation measurement techniques inside 0.2 AU. The highest absolute and relative density fluctuations occur ahead of and within the plasma from coronal mass ejections, with the maximum values occurring between the associated interplanetary shocks and the driver gas. For the quasi-stationary solar wind, density and relative density fluctuations are highest around the heliospheric current sheet and lowest in the high-speed coronal flow. Superposed epoch analysis shows that the region of enhanced density fluctuations and its abrupt boundaries observed in the vicinity of the heliospheric current sheet near the Sun persists to l AU, providing further support for the filamentary nature of the extensions of coronal streamers. The results of this study confirm the advantages of using density fluctuations rather than density as a tracer of solar wind flows with differing origins at the Sun and as a detector of propagating interplanetary disturbances.
Tarp, Jens M; Angheluta, Luiza; Mathiesen, Joachim; Goldenfeld, Nigel
2014-12-31
Plastic deformation mediated by collective dislocation dynamics is investigated in the two-dimensional phase-field crystal model of sheared single crystals. We find that intermittent fluctuations in the dislocation population number accompany bursts in the plastic strain-rate fluctuations. Dislocation number fluctuations exhibit a power-law spectral density 1/f2 at high frequencies f. The probability distribution of number fluctuations becomes bimodal at low driving rates corresponding to a scenario where low density of defects alternates at irregular times with high populations of defects. We propose a simple stochastic model of dislocation reaction kinetics that is able to capture these statistical properties of the dislocation density fluctuations as a function of shear rate.
DENSITY FLUCTUATIONS UPSTREAM AND DOWNSTREAM OF INTERPLANETARY SHOCKS
Pitňa, A.; Šafránková, J.; Němeček, Z.; Goncharov, O.; Němec, F.; Přech, L.; Chen, C. H. K.; Zastenker, G. N.
2016-03-01
Interplanetary (IP) shocks as typical large-scale disturbances arising from processes such as stream–stream interactions or Interplanetary Coronal Mass Ejection (ICME) launching play a significant role in the energy redistribution, dissipation, particle heating, acceleration, etc. They can change the properties of the turbulent cascade on shorter scales. We focus on changes of the level and spectral properties of ion flux fluctuations upstream and downstream of fast forward oblique shocks. Although the fluctuation level increases by an order of magnitude across the shock, the spectral slope in the magnetohydrodynamic range is conserved. The frequency spectra upstream of IP shocks are the same as those in the solar wind (if not spoiled by foreshock waves). The spectral slopes downstream are roughly proportional to the corresponding slopes upstream, suggesting that the properties of the turbulent cascade are conserved across the shock; thus, the shock does not destroy the shape of the spectrum as turbulence passes through it. Frequency spectra downstream of IP shocks often exhibit “an exponential decay” in the ion kinetic range that was earlier reported at electron scales in the solar wind or at ion scales in the interstellar medium. We suggest that the exponential shape of ion flux spectra in this range is caused by stronger damping of the fluctuations in the downstream region.
Density Fluctuations Upstream and Downstream of Interplanetary Shocks
NASA Astrophysics Data System (ADS)
Pitňa, A.; Šafránková, J.; Němeček, Z.; Goncharov, O.; Němec, F.; Přech, L.; Chen, C. H. K.; Zastenker, G. N.
2016-03-01
Interplanetary (IP) shocks as typical large-scale disturbances arising from processes such as stream-stream interactions or Interplanetary Coronal Mass Ejection (ICME) launching play a significant role in the energy redistribution, dissipation, particle heating, acceleration, etc. They can change the properties of the turbulent cascade on shorter scales. We focus on changes of the level and spectral properties of ion flux fluctuations upstream and downstream of fast forward oblique shocks. Although the fluctuation level increases by an order of magnitude across the shock, the spectral slope in the magnetohydrodynamic range is conserved. The frequency spectra upstream of IP shocks are the same as those in the solar wind (if not spoiled by foreshock waves). The spectral slopes downstream are roughly proportional to the corresponding slopes upstream, suggesting that the properties of the turbulent cascade are conserved across the shock thus, the shock does not destroy the shape of the spectrum as turbulence passes through it. Frequency spectra downstream of IP shocks often exhibit “an exponential decay” in the ion kinetic range that was earlier reported at electron scales in the solar wind or at ion scales in the interstellar medium. We suggest that the exponential shape of ion flux spectra in this range is caused by stronger damping of the fluctuations in the downstream region.
Improving Estimates Of Phase Parameters When Amplitude Fluctuates
NASA Technical Reports Server (NTRS)
Vilnrotter, V. A.; Brown, D. H.; Hurd, W. J.
1989-01-01
Adaptive inverse filter applied to incoming signal and noise. Time-varying inverse-filtering technique developed to improve digital estimate of phase of received carrier signal. Intended for use where received signal fluctuates in amplitude as well as in phase and signal tracked by digital phase-locked loop that keeps its phase error much smaller than 1 radian. Useful in navigation systems, reception of time- and frequency-standard signals, and possibly spread-spectrum communication systems.
Optimum parameter for estimating phase fluctuations on transionospheric signals at high latitudes
NASA Astrophysics Data System (ADS)
Forte, Biagio; Materassi, Massimo; Alfonsi, Lucilla; Romano, Vincenzo; de Franceschi, Giorgiana; Spalla, Paolo
2011-06-01
Transionospheric radio signals may experience fluctuations in their amplitude and phase due to irregularity in the spatial electron density distribution, referred to as scintillation. Ionospheric scintillation is responsible for transionospheric signal degradation that can affect the performance of satellite based navigation systems. Usually, the scintillation activity is measured by means of indices such as the normalised standard deviation of the received intensity S4 and the standard deviation of the received phase σϕ typically calculated over 1 min of data. Data from a GPS scintillation monitor based on 50 Hz measurements recorded at Dirigibile Italia Station (Ny-Alesund, Svalbard), in the frame of the ISACCO project (De Franceschi et al., 2006) are used to investigate possible adoption of an alternative parameter for the estimate of phase fluctuations: i.e., the standard deviation of the phase rate of change Sϕ. This parameter is shown to better correlate with S4 being much less detrending dependent than σϕ. The couple (S4, Sϕ) should be then considered a more physical proxy of radio scintillation than the couple (S4, σϕ).
Quenching of the beam-plasma instability by 3-D spectra of large scale density fluctuations
NASA Technical Reports Server (NTRS)
Muschietti, L.; Goldman, M. V.; Newman, D.
1984-01-01
A model is presented to explain the highly variable yet low level of Langmuir waves measured in situ by spacecraft when electron beams associated with Type III solar bursts are passing by; the low level of excited waves allows the propagation of such streams from the Sun to well past 1 AU without catastrophic energy losses. The model is based, first, on the existence of large scale density fluctuations that are able to efficiently diffuse small k beam unstable Langmuir waves in phase space, and, second, on the presence of a significantly isotropic nonthermal tail in the distribution function of the background electron population, which is capable of stabilizing larger k modes. The strength of the model lies in its ability to predict various levels of Langmuir waves depending on the parameters. This feature is consistent with the high variability actually observed in the measurements.
Investigation of zonal flows by using the collective scattering measurement of density fluctuations
NASA Astrophysics Data System (ADS)
Shen, H. G.; Yu, Y.; Lan, T.; Li, Y. D.; Liu, A. D.; Xie, J. L.; Liu, W. D.; Yu, C. X.; Zhang, W. Y.; Ti, A.; Li, J. G.
2015-09-01
The poloidal {{E}r}× {{B}\\text{T}} rotation velocities in the core plasma region are studied using the instantaneous frequency method (IFM) with the density fluctuations measured by the CO2 laser collective scattering diagnostics on the HT-7 tokamak. A coherent mode is observed in the fluctuations of poloidal velocities with the mode frequency from 10 to 20 kHz. It is identified as geodesic acoustic mode (GAM) zonal flow with poloidal symmetry (m = 0) and its mode frequency coinciding with the theoretical expected GAM frequency. The nonlinear interactions are investigated by applying the envelope analysis on the density fluctuations. The results confirm that the envelope modulation in the high frequency density fluctuations only comes from the shearing by GAM. The comparison between IFM and envelope analysis is also discussed.
Modeling of Fluctuating Mass Flux in Variable Density Flows
NASA Technical Reports Server (NTRS)
So, R. M. C.; Mongia, H. C.; Nikjooy, M.
1983-01-01
The approach solves for both Reynolds and Favre averaged quantities and calculates the scalar pdf. Turbulent models used to close the governing equations are formulated to account for complex mixing and variable density effects. In addition, turbulent mass diffusivities are not assumed to be in constant proportion to turbulent momentum diffusivities. The governing equations are solved by a combination of finite-difference technique and Monte-Carlo simulation. Some preliminary results on simple variable density shear flows are presented. The differences between these results and those obtained using conventional models are discussed.
Study of Density Fluctuations and Particle Transport at the Edge of I-Mode Plasmas
NASA Astrophysics Data System (ADS)
Dominguez, Arturo
The wide range of plasma parameters available on Alcator C-Mod has led to the accessibility of many regimes of operation. Since its commissioning, C-Mod has accessed the Linear ohmic confinement, Saturated ohmic confinement, L-Mode and ELM-free, ELMy and Enhanced Dalpha H-Mode regimes. Recently, another novel regime, the I-Mode, has been identified. I-modes feature the presence of steep H-Mode-like electron and ion temperature gradients at the edge of the plasma with L-Mode-like density profiles. The I-Mode, in contrast to the H-mode, shows very weak degradation of energy confinement with increased input power, and routinely reaches H 98 > 1 while operating at low edge collisionalities ( n*ped ˜0.1), making it a good candidate for reactor relevant tokamaks. Also relevant for reactors, this regime can be sustained in steady state for more than ˜15 energy confinement times without the need for ELMs to regulate particle and impurity confinement. Changes in edge density, temperature and magnetic field fluctuations accompany the L-mode to I-mode transition, with reduction of fluctuations in the 50--150kHz range as well as the appearance of a Weakly Coherent Mode (WCM) in the 200-300kHz range, analogous to the Quasi-Coherent Mode (QCM) characteristic of the Enhanced D alpha H-mode. Previous work has established a connection between the midrange fluctuation suppression and reduction in the effective thermal diffusivity, chi eff, in the pedestal region. The mechanism in I-mode for maintaining sufficient particle transport to avoid impurity accumulation and instabilities has been unclear. The O-mode reflectometry system has been extensively used for the characterization and detection of the I-mode and the WCM, in part, enhanced by upgrades to the system which enabled the broadband detection of density fluctuations at an array of cutoff locations at the edge of the plasma. Using a novel model, the autopower signals of reflectometry channels detecting the density
Cosmological Inflation with Multiple Fields and the Theory of Density Fluctuations
NASA Astrophysics Data System (ADS)
van Tent, B. J. W.
2002-09-01
Inflation is a stage of extremely rapid expansion in the very early universe. It was proposed to solve a number of problems in the standard Big Bang theory. In particular it others an explanation for the origin of structures like (clusters of) galaxies on the one hand (by generating small density fluctuations that act as gravitational seeds), and for the largescale homogeneity of the universe on the other hand (because of the enormous expansion). Inflation is driven by one or more scalar fields with an appropriate potential. In this thesis we develop an analytical formalism to describe the generation of density fluctuations during inflation with multiple scalar fields. We allow these fields to live on a non-trivial (curved) field manifold, as is often the case in high-energy theories. We also treat the evolution of the fluctuations after inflation, until the time of recombination when the cosmic microwave background radiation was formed. Using our formalism observations of the CMBR can then be used to set constraints on the parameters in (multiple-field) inflation models. In more detail this thesis covers the following topics. After introductory chapters on cosmology in general and single-field inflation, the theory of inflation with multiple fields and a general (non-trivial) field metric is derived. In particular we introduce a basis in field space that is induced by the background dynamics and allows a clear distinction between effectively single-field and truly multiple-field effects. The important slow-roll approximation is generalized to the case of multiple fields. Next we derive how scalar and tensor fluctuations are generated from a quantum origin during multiple-field inflation, paying special attention to the transition that occurs when a perturbation mode crosses the Hubble scale. Using some simplifying assumptions the evolution of both adiabatic and isocurvature perturbation modes after inflation is treated. The final results are expressions for the
Mobility of electrons in supercritical krypton: Role of density fluctuations
Nishikawa, Masaru; Holroyd, Richard A.; Preses, Jack M.
2007-07-07
Excess electrons were generated in supercritical krypton by means of pulsed x-ray irradiation, and the electron transport phenomena were studied. Electron signals immediately after a 30 ps pulse showed a distinctive feature characteristic of the presence of the Ramsauer-Townsend minimum in the momentum transfer cross section. The dependence of the drift velocity v{sub D} on field strength was found to be concave upward in the low field region and then to go through a maximum with increasing field strength, which is also typical of the presence of a minimum in the scattering cross section at an intermediate field strength. A minimum in the electron mobility was observed at about one-half the critical density. The acoustical phonon scattering model, which successfully explained the mobility change in this density region in supercritical xenon, was again found to account for the mobility in supercritical krypton.
NASA Astrophysics Data System (ADS)
Carter, Troy; Martin, Michael; van Compernolle, Bart; Gekelman, Walter; Pribyl, Pat; Vincena, Stephen; Tripathi, Shreekrishna; van Eester, Dirk; Crombe, Kristel
2016-10-01
The LArge Plasma Device (LAPD) at UCLA is a 17 m long, up to 60 cm diameter magnetized plasma column with typical plasma parameters ne 1012 -1013 cm-3, Te 1 - 10 eV, and B 1 kG. A new high-power ( 200 kW) RF system and antenna has been developed for LAPD, enabling the generation of large amplitude fast waves in LAPD. Interaction between the fast waves and density fluctuations is observed, resulting in modulation of the coupled RF power. Two classes of RF-induced density fluctuations are observed. First, a coherent (10 kHz) oscillation is observed spatially near the antenna in response to the initial RF turn-on transient. Second, broadband density fluctuations are enhanced when the RF power is above a threshold a threshold. Strong modulation of the fast wave magnetic fluctuations is observed along with broadening of the primary RF spectral line. Ultimately, high power fast waves will be used for ion heating in LAPD through minority species fundamental heating or second harmonic minority or majority heating. Initial experimental results from heating experiments will be presented along with a discussion of future plans. BaPSF supported by NSF and DOE.
Density fluctuation measurement using motional Stark effect optics in JT-60U
Suzuki, T.; Fujita, T.; Oyama, N.; Isayama, A.; Matsunaga, G.; Oikawa, T.; Asakura, N.; Takechi, M.
2006-10-15
The multichannel motional Stark effect (MSE) diagnostic system in JT-60U has been upgraded to measure density fluctuation profile. A 16-channel fast-sampling digitizer has been added in order to measure photomultiplier-tube signals at measurement frequency of 0.5-1 MHz. The new system works as a MSE and beam emission spectroscopy diagnostic. Spatially resolved electron density fluctuation profile measurement in various operation regimes is presented. In the core plasma, density fluctuation induced by rotation of tearing mode islands was observed. Temporal evolution of the fluctuation frequency agrees with that measured by Mirnov coils (poloidal and toroidal mode numbers: 2 and 1, respectively). The phases of the fluctuations on either side of the q=2 surface are inverted, which is consistent with electron cyclotron emission. These measurements show that the density fluctuation is caused by a rotating magnetic island structure induced by the tearing mode. In the scrape-off layer of a H-mode plasma with edge-localized-mode (ELM), i. e., ELMy H-mode outward propagation of strong intermittent emission corresponding to ELM crash was also observed. The propagation velocity is 0.69-2.2 km/s along the MSE measurement points, the time lag and distance between adjacent channels being 67{+-}35 {mu}s and 70 mm, respectively.
Theory of density fluctuations in strongly radiative plasmas
NASA Astrophysics Data System (ADS)
Cross, J. E.; Mabey, P.; Gericke, D. O.; Gregori, G.
2016-03-01
Derivation of the dynamic structure factor, an important parameter linking experimental and theoretical work in dense plasmas, is possible starting from hydrodynamic equations. Here we obtain, by modifying the governing hydrodynamic equations, a new form of the dynamic structure factor which includes radiative terms. The inclusion of such terms has an effect on the structure factor at high temperatures, which suggests that its effect must be taken into consideration in such regimes.
Measurement of high-frequency density fluctuations in improved confinement RFP plasmas
NASA Astrophysics Data System (ADS)
Duff, J. R.; Chapman, B. E.; Anderson, J. K.; Sarff, J. S.; Lin, L.; Ding, W. X.; Brower, D. L.
2013-10-01
In standard RFP plasmas, transport is dominated by global magnetic tearing modes. For improved-confinement plasmas using inductive current profile control (PPCD), smaller-scale fluctuations at higher frequencies (>50 kHz) may become more important as the global tearing modes are significantly reduced. In particular, drift-wave-like instabilities are theoretically unstable to the higher temperature and density gradients achieved during PPCD discharges. On the MST, an eleven chord Far-Infrared (FIR) laser-based diagnostic system with ~ 8 cm spacing is used to measure electron density fluctuations by interferometry and far-forward collective scattering. The existing diagnostic measures line-integrated density fluctuations within the divergence of the probe beam covering a wavenumber range k-< 1.3 cm-1, corresponding to k-ρs < 1.3 (ρs is the ion-sound Larmor radius). Experimentally, in PPCD plasmas, global tearing modes are reduced while high frequency coherent modes (50 < f < 140 kHz) emerge among broadband fluctuations. Correlations of these modes with sources of free energy, such as temperature and density gradients, will be investigated. Additionally, effects of increased plasma flow from a 1MW tangential NBI on high frequency density fluctuations will also be explored. Work Supported by U.S.D.O.E.
Shock-associated MHD waves - A model for interstellar density fluctuations
NASA Technical Reports Server (NTRS)
Spangler, Steven R.
1988-01-01
The possibility that the density fluctuations responsible for radio scintillations could be due to ion-beam-generated MHD waves near interstellar shock waves is discussed. This suggestion is inspired by spacecraft observations which reveal these phenomena near shocks in the solar system. The model quite naturally accounts for the scale on which these fluctuations occur; it is dictated by the wavelength of the unstable waves.
Nicolaus, Marion; Tinbergen, Joost M; Ubels, Richard; Both, Christiaan; Dingemanse, Niels J
2016-04-01
Heritable personality variation is subject to fluctuating selection in many animal taxa; a major unresolved question is why this is the case. A parsimonious explanation must involve a general ecological process: a likely candidate is the omnipresent spatiotemporal variation in conspecific density. We tested whether spatiotemporal variation in density within and among nest box plots of great tits (Parus major) predicted variation in selection acting on exploratory behaviour (n = 48 episodes of selection). We found viability selection favouring faster explorers under lower densities but slower explorers under higher densities. Temporal variation in local density represented the primary factor explaining personality-related variation in viability selection. Importantly, birds did not anticipate changes in selection by means of adaptive density-dependent plasticity. This study thereby provides an unprecedented example of the key importance of the interplay between fluctuating selection and lack of adaptive behavioural plasticity in maintaining animal personality variation in the wild.
Maps of the little bangs through energy density and temperature fluctuations
Basu, Sumit Chatterjee, Rupa; Nayak, Tapan K.
2016-01-22
Heavy-ion collisions at ultra-relativistic energies are often referred to as little bangs. We propose for the first time to map the heavy-ion collisions at ultra-relativistic energies, similar to the maps of the cosmic microwave background radiation, using fluctuations of energy density and temperature in small phase space bins. We study the evolution of fluctuations at each stage of the collision using an event-by-event hydrodynamic framework. We demonstrate the feasibility of making fluctuation maps from experimental data and its usefulness in extracting considerable information regarding the early stages of the collision and its evolution.
Large-amplitude electron density and Hα fluctuations in the sustained spheromak physics experiment
NASA Astrophysics Data System (ADS)
Wang, Zhehui; Barnes, Cris W.; Wurden, G. A.; Hill, D. N.; Hooper, E. B.; McLean, H. S.; Wood, R. D.; Woodruff, S.
2002-06-01
New types of toroidally rotating fluctuations (toroidal mode numbers n = 1 and n = 2) of line-integrated electron density and Hα emission, with frequencies ranging from 10 to 100 kHz, are observed in the sustained spheromak physics experiment (SSPX). The rotating directions of these fluctuations are the same as the direction determined by E×B, while the E and B directions are determined by the gun voltage and gun magnetic flux polarities, respectively. These results take advantage of one distinctive signature of spheromaks, i.e. it is possible to observe toroidal MHD activity during decay and sustainment at any toroidal angle. A theoretical constraint on line-integrated measurement is proposed and is found to be consistent with experimental observations. Fluctuation analysis in the time and frequency domains indicates that the observed density and Hα fluctuations correlate with magnetic modes. Observation of Hα fluctuations correlating with magnetic fluctuations indicates that, at least in some cases, MHD n = 1 modes are due to the so-called `dough-hook' current paths that connect the coaxial gun to the flux conserver, rather than internal kink instabilities. These results also show that electron density and Hα emission diagnostics complement other tools for spheromak mode study.
Density Fluctuation in Asymmetric Nozzle Plumes and Correlation with Far Field Noise
NASA Technical Reports Server (NTRS)
Panda, J.; Zaman, K. B. M. Q.
2001-01-01
A comparative experimental study of air density fluctuations in the unheated plumes of a circular, 4-tabbed-circular, chevron-circular and 10-lobed rectangular nozzles was performed at a fixed Mach number of 0.95 using a recently developed Rayleigh scattering based technique. Subsequently, the flow density fluctuations are cross-correlated with the far field sound pressure fluctuations to determine sources for acoustics emission. The nearly identical noise spectra from the baseline circular and the chevron nozzles are found to be in agreement with the similarity in spreading, turbulence fluctuations, and flow-sound correlations measured in the plumes. The lobed nozzle produced the least low frequency noise, in agreement with the weakest overall density fluctuations and flow-sound correlation. The tabbed nozzle took an intermediate position in the hierarchy of noise generation, intensity of turbulent fluctuation and flow-sound correlation. Some of the features in the 4-tabbed nozzle are found to be explainable in terms of splitting of the jet in a central large core and 4 side jetlets.
Control of density fluctuations in atomistic-continuum simulations of dense liquids
NASA Astrophysics Data System (ADS)
Kotsalis, E. M.; Walther, J. H.; Koumoutsakos, P.
2007-07-01
We present a control algorithm to eliminate spurious density fluctuations associated with the coupling of atomistic and continuum descriptions for dense liquids. A Schwartz domain decomposition algorithm is employed to couple molecular dynamics for the simulation of the atomistic system with a continuum solver for the simulation of the Navier-Stokes equations. The lack of periodic boundary conditions in the molecular dynamics simulations hinders the proper accounting for the virial pressure leading to spurious density fluctuations at the continuum-atomistic interface. An ad hoc boundary force is usually employed to remedy this situation. We propose the calculation of this boundary force using a control algorithm that explicitly cancels the density fluctuations. The results demonstrate that the present approach outperforms state-of-the-art algorithms. The conceptual and algorithmic simplicity of the method makes it suitable for any type of coupling between atomistic and continuum descriptions of dense fluids.
Control of density fluctuations in atomistic-continuum simulations of dense liquids.
Kotsalis, E M; Walther, J H; Koumoutsakos, P
2007-07-01
We present a control algorithm to eliminate spurious density fluctuations associated with the coupling of atomistic and continuum descriptions for dense liquids. A Schwartz domain decomposition algorithm is employed to couple molecular dynamics for the simulation of the atomistic system with a continuum solver for the simulation of the Navier-Stokes equations. The lack of periodic boundary conditions in the molecular dynamics simulations hinders the proper accounting for the virial pressure leading to spurious density fluctuations at the continuum-atomistic interface. An ad hoc boundary force is usually employed to remedy this situation. We propose the calculation of this boundary force using a control algorithm that explicitly cancels the density fluctuations. The results demonstrate that the present approach outperforms state-of-the-art algorithms. The conceptual and algorithmic simplicity of the method makes it suitable for any type of coupling between atomistic and continuum descriptions of dense fluids.
Anabitarte, E. . Inst. de Energias Renovables); Hanson, G.R.; Harris, J.H.; Wilgen, J.B.; Bell, J.D.; Dunlap, J.L.; Hidalgo, C.; Thomas, C.E.; Uckan, T. )
1990-01-01
A microwave reflectometer system has been installed and operated on the Advanced Toroidal Facility (ATF) to measure density fluctuations. This system consists of two individual reflectometers that use the same antenna system and operate in the 30- to 40-GHz band. This arrangement allows operation at two frequencies along the same radial chord so that radial coherence measurements are possible. During the initial operating period of the reflectometer, a correlation was observed between a change in the edge density fluctuation spectrum and a transition to improved confinement. Recently, local measurements of the density fluctuation spectra in electron-cyclotron-heated (ECH) plasmas has been shown to agree with Langmuir probe measurements at the edge. Furthermore, structure in the spectra has been observed in some ECH plasmas. 4 refs., 3 figs.
Investigation of Density Fluctuations in Supersonic Free Jets and Correlation with Generated Noise
NASA Technical Reports Server (NTRS)
Panda, J.; Seasholtz, R. G.
2000-01-01
The air density fluctuations in the plumes of fully-expanded, unheated free jets were investigated experimentally using a Rayleigh scattering based technique. The point measuring technique used a continuous wave laser, fiber-optic transmission and photon counting electronics. The radial and centerline profiles of time-averaged density and root-mean-square density fluctuation provided a comparative description of jet growth. To measure density fluctuation spectra a two-Photomultiplier tube technique was used. Crosscorrelation between the two PMT signals significantly reduced electronic shot noise contribution. Turbulent density fluctuations occurring up to a Strouhal number (Sr) of 2.5 were resolved. A remarkable feature of density spectra, obtained from the same locations of jets in 0.5< M<1.5 range, is a constant Strouhal frequency for peak fluctuations. A detailed survey at Mach numbers M = 0.95, 1.4 and 1.8 showed that, in general, distribution of various Strouhal frequency fluctuations remained similar for the three jets. In spite of the similarity in the flow fluctuation the noise characteristics were found to be significantly different. Spark schlieren photographs and near field microphone measurements confirmed that the eddy Mach wave radiation was present in Mach 1.8 jet, and was absent in Mach 0.95 jet. To measure correlation between the flow and the far field sound pressure fluctuations, a microphone was kept at a distance of 50 diameters, 30 deg. to the flow direction, and the laser probe volume was moved from point to point in the flow. The density fluctuations in the peripheral shear layer of Mach 1.8 jet showed significant correlation up to the measurement limit of Sr = 2.5, while for Mach 0.95 jet no correlation was measured. Along the centerline measurable correlation was found from the end of the potential core and at the low frequency range (Sr less than 0.5). Usually the normalized correlation values increased with an increase of the jet Mach
Tsikata, S.; Pisarev, V.; Gresillon, D. M.; Lemoine, N.
2009-03-15
Kinetic models and numerical simulations of E-vectorxB-vector plasma discharges predict microfluctuations at the scales of the electron cyclotron drift radius and the ion plasma frequency. With the help of a specially designed collective scattering device, the first experimental observations of small-scale electron density fluctuations inside the plasma volume are obtained, and observed in the expected ranges of spatial and time scales. The anisotropy, dispersion relations, form factor, amplitude, and spatial distribution of these electron density fluctuations are described and compared to theoretical expectations.
NASA Technical Reports Server (NTRS)
Stainback, P. C.; Johnson, C. B.; Basnett, C. B.
1983-01-01
The heat transfer characteristics of a three-wire hot-wire probe operated with a constant temperature anemometer were investigated in the subsonic compressible flow regime. The sensitivity coefficients, with respect to velocity, density and total temperature, were measured and the results were used to calculate the velocity, density, and total temperature fluctuations in the test section of the Langley 0.3-m Transonic Cryogenic Tunnel (TCT). These results were extended to give estimates for fluctuations due to vorticity, sound, and entropy. In addition, attempts were made to determine the major source of disturbances in the 0.3-m TCT.
Comparison of density fluctuation measurements between O-mode and X-mode reflectometry on Tore Supra
Gerbaud, T.; Clairet, F.; Sabot, R.; Sirinelli, A.; Heuraux, S.; Leclert, G.; Vermare, L.
2006-10-15
Reflectometry is a versatile diagnostic which allows both electronic density profile and density fluctuation measurements. Fast sweep heterodyne technique is particularly suitable for precise measurement of the phase of the reflected signal, which records the story of the wave propagation through the plasma up to the cutoff layer, including the density fluctuations. The present article exhibits a comparison of the density fluctuation radial profile measurements between fast sweep frequency technique, both using O-mode and X-mode polarizations, and fixed frequency technique. The correct agreement between all measurements of the relative values of the density fluctuation profiles reinforces the validity of the approximations used.
Gaudillere, J P; Drevon, J J; Bernoud, J P; Jardinet, F; Euvrard, M
1987-01-01
The development of soybean leaves grown at fluctuating photon flux density between 100 and 1500μM m(-2)s(-1) with a period of 160 sec were compared to leaves developed under continuous light with the same mean photon flux density. Number of epidermal cells and stomata, leaf area and specific leaf weight were not affected by the periodic fluctuation of photon flux density. Chloroplastic pigment concentration and chlorophyll fluorescence reveal some photoinhibitory effects of the high photon flux density phase. Stomatal and internal CO2 conductance and the quantum yield were not affected by the light regime. In contrast ribulose 1.5 bisphosphate carboxylase/oxygenase activity before in vitro activation by CO2 and Mg(++) was stimulated by the periodic illumination whereas the total amount of the enzyme and the internal leaf CO2 conductance remained steady. In conclusion, there was no major difference between leaves of plant grown either under a steady or under a periodic fluctuation of the photon flux density except some photoinhibitory symptoms under fluctuating illumination, and a higher in vivo level of activation of the Rubisco.
Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum
NASA Astrophysics Data System (ADS)
Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Allen, S. W.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.
2015-07-01
X-ray surface brightness fluctuations in the core of the Perseus Cluster are analysed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 7 to 12 per cent on scales of ˜10-30 kpc within radii of 30-220 kpc from the cluster centre. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km s-1 on ˜20-30 kpc scales and 70-100 km s-1 on smaller scales ˜7-10 kpc. The velocity power spectrum (PS) is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the PS of the density fluctuations is lower than 7-8 per cent for radii ˜30-220 kpc from the centre, leading to a density bias of less than 3-4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density-velocity perturbation relation and further reduce systematic uncertainties in this analysis.
A molecular Rayleigh scattering setup to measure density fluctuations in thermal boundary layers
NASA Astrophysics Data System (ADS)
Panda, J.
2016-12-01
A Rayleigh scattering-based density fluctuation measurement system was set up inside a low-speed wind tunnel of NASA Ames Research Center. The immediate goal was to study the thermal boundary layer on a heated flat plate. A large number of obstacles had to be overcome to set up the system, such as the removal of dust particles using air filters, the use of photoelectron counting electronics to measure low intensity light, an optical layout to minimize stray light contamination, the reduction in tunnel vibration, and an expanded calibration process to relate photoelectron arrival rate to air density close to the plate surface. To measure spectra of turbulent density fluctuations, a two-PMT cross-correlation system was used to minimize the shot noise floor. To validate the Rayleigh measurements, temperature fluctuations spectra were calculated from density spectra and then compared with temperature spectra measured with a cold-wire probe operated in constant current mode. The spectra from the downstream half of the plate were found to be in good agreement with cold-wire probe, whereas spectra from the leading edge differed. Various lessons learnt are discussed. It is believed that the present effort is the first measurement of density fluctuations spectra in a boundary layer flow.
First in-situ observations of neutral and plasma density fluctuations within a PMSE layer
NASA Technical Reports Server (NTRS)
Lubken, Franz-Josef; Lehmacher, Gerald; Blix, Tom; Hoppe, Ulf-Peter; Thrane, Eivind; Cho, John; Swartz, Wesley
1993-01-01
The NLC-91 rocket and radar campaign provided the first opportunity for high resolution neutral and plasma turbulence measurements with simultaneous observations of PMSE (Polar Mesospheric Summer Echoes). During the flight of the TURBO payload on August 1, 1991, Cornell University Portable Radar Interferometer (CUPRI) and European Incoherent Scattter facility (EISCAT) observed double PMSE layers located at 86 and 88 km altitude, respectively. Strong neutral density fluctuations were observed in the upper layer but not in the lower layer. The fluctuation spectra of the ions and neutrals within the upper layer are consistent with standard turbulence theories. However, we show that there is no neutral turbulence present in the lower layer and that something else must have been operating here to create the plasma fluctuations and hence the radar echoes. Although the in situ measurements of the electron density fluctuations are much stronger in the lower layer, the higher absolute electron density of the upper layer more than compensated for the weaker fluctuations yielding comparable radar echo powers.
First in-situ observations of neutral and plasma density fluctuations within a PMSE layer
NASA Astrophysics Data System (ADS)
Lubken, Franz-Josef; Lehmacher, Gerald; Blix, Tom; Hoppe, Ulf-Peter; Thrane, Eivind; Cho, John; Swartz, Wesley
1993-10-01
The NLC-91 rocket and radar campaign provided the first opportunity for high resolution neutral and plasma turbulence measurements with simultaneous observations of PMSE (Polar Mesospheric Summer Echoes). During the flight of the TURBO payload on August 1, 1991, Cornell University Portable Radar Interferometer (CUPRI) and European Incoherent Scattter facility (EISCAT) observed double PMSE layers located at 86 and 88 km altitude, respectively. Strong neutral density fluctuations were observed in the upper layer but not in the lower layer. The fluctuation spectra of the ions and neutrals within the upper layer are consistent with standard turbulence theories. However, we show that there is no neutral turbulence present in the lower layer and that something else must have been operating here to create the plasma fluctuations and hence the radar echoes. Although the in situ measurements of the electron density fluctuations are much stronger in the lower layer, the higher absolute electron density of the upper layer more than compensated for the weaker fluctuations yielding comparable radar echo powers.
Density matrix of radiation of a black hole with a fluctuating horizon
NASA Astrophysics Data System (ADS)
Iofa, Mikhail Z.
2016-09-01
The density matrix of Hawking radiation is calculated in the model of a black hole with a fluctuating horizon. Quantum fluctuations smear the classical horizon of a black hole and modify the density matrix of radiation producing the off-diagonal elements. The off-diagonal elements may store information on correlations between the radiation and the black hole. The smeared density matrix was constructed by convolution of the density matrix calculated with the instantaneous horizon with the Gaussian distribution over the instantaneous horizons. The distribution has the extremum at the classical radius of the black hole and the width of order of the Planck length. Calculations were performed in the model of a black hole formed by the thin collapsing shell which follows a trajectory that is a solution of the matching equations connecting the interior and exterior geometries.
Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum
Zhuravleva, I.; Churazov, E.; Arevalo, P.; Schekochihin, A. A.; Allen, S. W.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.
2015-05-20
X-ray surface brightness fluctuations in the core of the Perseus Cluster are analysed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 7 to 12 per cent on scales of ~10–30 kpc within radii of 30–220 kpc from the cluster centre. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90–140 km s^{-1} on ~20–30 kpc scales and 70–100 km s^{-1} on smaller scales ~7–10 kpc. The velocity power spectrum (PS) is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the PS of the density fluctuations is lower than 7–8 per cent for radii ~30–220 kpc from the centre, leading to a density bias of less than 3–4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density–velocity perturbation relation and further reduce systematic uncertainties in this analysis.
Ramírez-Hernández, Abelardo; Peters, Brandon L; Schneider, Ludwig; Andreev, Marat; Schieber, Jay D; Müller, Marcus; de Pablo, Juan J
2017-01-07
Coarse grained simulation approaches provide powerful tools for the prediction of the equilibrium properties of polymeric systems. Recent efforts have sought to develop coarse-graining strategies capable of predicting the non-equilibrium behavior of entangled polymeric materials. Slip-link and slip-spring models, in particular, have been shown to be capable of reproducing several key aspects of the linear response and rheology of polymer melts. In this work, we extend a previously proposed multi-chain slip-spring model in a way that correctly incorporates the effects of the fluctuating environment in which polymer segments are immersed. The model is used to obtain the equation of state associated with the slip-springs, and the results are compared to those of related numerical approaches and an approximate analytical expression. The model is also used to examine a polymer melt confined into a thin film, where an inhomogeneous distribution of polymer segments is observed, and the corresponding inhomogeneities associated with density fluctuations are reflected on the spatial slip-spring distribution.
Parameter Fluctuation-Induced Pattern Transition in the Complex Ginzburg-Landau Equation
NASA Astrophysics Data System (ADS)
Ma, Jun; Ja, Ya; Tang, Jun; Chen, Yong
Parameter fluctuation, which is often induced by the noise, temperature, deformation of the media etc., plays an important role in changing the dynamics of the system. In this paper, the problem of parameter fluctuation-induced pattern transition in the Complex Ginzburg-Landau equation (CGLE) is investigated. At first, the perpendicular-gradient initial values are used to generate spiral wave and spiral turbulence under appropriate parameters. At second, the parameter is perturbed with the periodical and/or random signal to simulate the parameter fluctuation, respectively. Then a class of linear error feedback is used to induce transition of the spiral wave and spiral turbulence. It is found that target waves can be induced by the complete feedback forcing, while the local feedback forcing seldom induce a target wave. In the case of spiral turbulence, spiral wave is generated and the spiral turbulence is removed by the new appeared spiral wave as the linear error feedback began to work on the whole media. Finally, the common negative feedback is also used to control the parameter-fluctuated CGLE, and the results are compared with the linear error feedback control, it is found that the whole system become homogeneous when the negative feedback is imposed on the whole media, and the local negative feedback can induce new target wave to remove the spiral wave while it is in vain to generate new target or spiral wave to overcome and eliminate the spiral turbulence.
Propagation of the lower hybrid wave in a density fluctuating scrape-off layer (SOL)
NASA Astrophysics Data System (ADS)
Madi, M.; Peysson, Y.; Decker, J.; Kabalan, K. Y.
2015-12-01
The perturbation of the lower hybrid wave (LH) power spectrum by fluctuations of the plasma in the vicinity of the antenna is investigated by solving the full wave equation in a slab geometry using COMSOL Multiphysics®. The numerical model whose generality allows to study the effect of various types of fluctuations, including those with short characteristic wavelengths is validated against a coupling code in quiescent regimes. When electron density fluctuations along the toroidal direction are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, the power spectrum may be strongly modified from the antenna mouth to the plasma separatrix as the LH wave propagates. The diffraction effect by density fluctuations leads to the appearance of multiple satellite lobes with randomly varying positions and the averaged perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength. This highlights that fast toroidal inhomogeneities with short characteristics length scales in front of the grill may change significantly the initial LH power spectrum used in coupled ray-tracing and Fokker-Planck calculations.
Zero-point fluctuations in naphthalene and their effect on charge transport parameters.
Kwiatkowski, Joe J; Frost, Jarvist M; Kirkpatrick, James; Nelson, Jenny
2008-09-25
We calculate the effect of vibronic coupling on the charge transport parameters in crystalline naphthalene, between 0 and 400 K. We find that nuclear fluctuations can cause large changes in both the energy of a charge on a molecule and on the electronic coupling between molecules. As a result, nuclear fluctuations cause wide distributions of both energies and couplings. We show that these distributions have a small temperature dependence and that, even at high temperatures, vibronic coupling is dominated by the effect of zero-point fluctuations. Because of the importance of zero-point fluctuations, we find that the distributions of energies and couplings have substantial width, even at 0 K. Furthermore, vibronic coupling with high energy modes may be significant, even though these modes are never thermally activated. Our results have implications for the temperature dependence of charge mobilities in organic semiconductors.
Fluctuation-Induced Particle Transport and Density Relaxation in a Stochastic Magnetic Field
NASA Astrophysics Data System (ADS)
Brower, David L.
2009-11-01
Particle transport and density relaxation associated with electromagnetic fluctuations is an unresolved problem of long standing in plasma physics and magnetic fusion research. In toroidal fusion plasmas, magnetic field fluctuations can arise spontaneously from global MHD instabilities, e.g., tearing fluctuations associated with sawtooth oscillations. Resonant magnetic perturbations (RMP) have also been externally imposed to mitigate the effect of edge localized modes (ELMs) by locally enhancing edge transport in Tokamaks. Understanding stochastic-field-driven transport processes is thus not only of basic science interest but possibly critical to ELM control in ITER. We report on the first direct measurement of magnetic fluctuation-induced particle transport in the core of a high-temperature plasma, the MST reversed field pinch. Measurements focus on the sawtooth crash, when the stochastic field resulting from tearing reconnection is strongest, and are accomplished using newly developed, laser-based, differential interferometry and Faraday rotation techniques. The measured electron particle flux, resulting from the correlated product of electron density (δn) and radial magnetic fluctuations (δbr), accounts for density profile relaxation during these magnetic reconnection events. Surprisingly, the electron diffusion is 30 times larger than estimates of ambipolarity-constrained transport in a stochastic magnetic field. A significant ion flux associated with parallel ion flow velocity fluctuations (δvi,//) correlated with δbr appears responsible for transport larger than predictions from the quasi-linear test particle model. These results indicate the need for improved understanding of particle transport in a stochastic magnetic field. Work performed in collaboration with W.X. Ding, W.F. Bergerson, T.F. Yates, UCLA; D.J. Den Hartog, G. Fiksel, S.C. Prager, J.S. Sarff and the MST Group, University of Wisconsin-Madison.
Telloni, D.; Antonucci, E.; Bruno, R.; D'Amicis, R.; Carbone, V.
2009-11-20
This paper investigates the evolution of the plasma density fluctuations of the fast and slow solar wind from the solar corona into the interplanetary space. The study is performed by comparing the low-frequency spectra and the phase correlation of the proton density oscillations, measured in the inner heliosphere with the Helios 2 in situ instrumentation, with those due to the large-scale density perturbations observed with UVCS/SOHO in the outer corona. We find that the characteristics of density fluctuations of the fast solar wind are maintained in the transition from the outer corona to the inner heliosphere, thus suggesting a coronal imprint for the heliospheric large-scale 1/f {sup 2} noise spectrum. In contrast, a quick dynamical evolution is observed in the slow wind, which, starting from large-scale fluctuations with strong phase correlations in the outer corona, gives rise to a Kolmogorov-like spectrum and an accumulation of density structures at small scales at 0.3 AU. This can be explained in the framework of nearly incompressible turbulence.
Two Point Space-Time Correlation of Density Fluctuations Measured in High Velocity Free Jets
NASA Technical Reports Server (NTRS)
Panda, Jayanta
2006-01-01
Two-point space-time correlations of air density fluctuations in unheated, fully-expanded free jets at Mach numbers M(sub j) = 0.95, 1.4, and 1.8 were measured using a Rayleigh scattering based diagnostic technique. The molecular scattered light from two small probe volumes of 1.03 mm length was measured for a completely non-intrusive means of determining the turbulent density fluctuations. The time series of density fluctuations were analyzed to estimate the integral length scale L in a moving frame of reference and the convective Mach number M(sub c) at different narrow Strouhal frequency (St) bands. It was observed that M(sub c) and the normalized moving frame length scale L*St/D, where D is the jet diameter, increased with Strouhal frequency before leveling off at the highest resolved frequency. Significant differences were observed between data obtained from the lip shear layer and the centerline of the jet. The wave number frequency transform of the correlation data demonstrated progressive increase in the radiative part of turbulence fluctuations with increasing jet Mach number.
Characterising density fluctuations in liquid yttria aluminates with small angle x-ray scattering
Greaves, G. Neville; Wilding, Martin C.; Vu Van, Quang; Majerus, Odile; Hennet, Louis
2009-01-29
Small angle x-ray scattering (SAXS) has been measured in the wavevector range 0.01density fluctuations deriving from isothermal compressibility. With decreasing Q a minimum is located close to 0.1 A{sup -1} at the foot of the inter-atomic structure factor, below which SAXS rises, suggesting scatter from longer range fluctuating volumes.
Intermediate-k density and magnetic field fluctuations during inter-ELM pedestal evolution in MAST
NASA Astrophysics Data System (ADS)
Hillesheim, J. C.; Dickinson, D.; Roach, C. M.; Saarelma, S.; Scannell, R.; Kirk, A.; Crocker, N. A.; Peebles, W. A.; Meyer, H.; the MAST Team
2016-01-01
Measurements of local density and magnetic field fluctuations near the pedestal top, conditionally averaged over the edge localized mode (ELM) cycle, have been made in Mega Amp Spherical Tokamak (MAST). A Doppler backscattering (DBS) system installed at MAST was used to measure intermediate-k ≤ft({{k}\\bot}{ρi}≈ 3~\\text{to}~4\\right) density fluctuations at the top of the pedestal. A novel diagnostic technique combining DBS with cross-polarization scattering (CP-DBS) enabled magnetic field fluctuations to also be locally measured at similar wave numbers. Polarization isolation and other effects for CP-DBS are discussed. Both measurements were used in a series of high-β ≤ft({βn}≈ 4.0\\right. -4.5) MAST plasmas with large type-I ELMs with an ˜ 8~\\text{to}~9~\\text{ms} period where microtearing modes (MTMs) had been predicted to be unstable in similar conditions (Dickinson 2012 Phys. Rev. Lett. 108 135002). The measured density fluctuation level increased by a factor of about 4 between 2 and 4 ms after the ELM, which was correlated with the recovery of the density profile while the temperature pedestal height continued to increase slowly. Magnetic field fluctuations showed different temporal behaviors, slowly increasing throughout the ELM cycle as the local β increased. Linear GS2 calculations show both MTM and electron temperature gradient (ETG) modes unstable at similar wave numbers as the measurements (although with more overlap between ETG wave numbers and diagnostic spectral resolution) at the top of the pedestal, along with kinetic ballooning modes are unstable lower in the pedestal (at larger wavelengths). The inferred ratio of fluctuation levels from experiment was ≤ft(δ B/B\\right)/≤ft(δ n/n\\right)≈ 1/20 . The comparable ratios from GS2 were ≤ft(δ B/B\\right)/≤ft(δ n/n\\right)≈ 0.4 for the MTM and ≤ft(δ B/B\\right)/≤ft(δ n/n\\right)≈ 0.02 for the ETG. Both the experimental wave number range and the fluctuation ratio
Simultaneous Microwave Imaging System for Density and Temperature Fluctuation Measurements on TEXTOR
H. Park; E. Mazzucato; T. Munsat; C.W. Domier; M. Johnson; N.C. Luhmann, Jr.; J. Wang; Z. Xia; I.G.J. Classen; A.J.H. Donne; M.J. van de Pol
2004-05-07
Diagnostic systems for fluctuation measurements in plasmas have, of necessity, evolved from simple 1-D systems to multi-dimensional systems due to the complexity of the MHD and turbulence physics of plasmas illustrated by advanced numerical simulations. Using the recent significant advancements in millimeter wave imaging technology, Microwave Imaging Reflectometry (MIR) and Electron Cyclotron Emission Imaging (ECEI), simultaneously measuring density and temperature fluctuations, are developed for TEXTOR. The MIR system was installed on TEXTOR and the first experiment was performed in September, 2003. Subsequent MIR campaigns have yielded poloidally resolved spectra and assessments of poloidal velocity. The new 2-D ECE Imaging system (with a total of 128 channels), installed on TEXTOR in December, 2003, successfully captured a true 2-D images of Te fluctuations of m=1 oscillation (''sawteeth'') near the q {approx} 1 surface for the first time.
Brookman, M. W. Austin, M. E.; Petty, C. C.
2015-12-10
Theoretical work, computation, and results from TCV [J. Decker “Effect of density fluctuations on ECCD in ITER and TCV,” EPJ Web of Conf. 32, 01016 (2012)] suggest that density fluctuations in the edge region of a tokamak plasma can cause broadening of the ECH deposition profile. In this paper, a GUI tool is presented which is used for analysis of ECH deposition as a first step towards looking for this broadening, which could explain effects seen in previous DIII-D ECH transport studies [K.W. Gentle “Electron energy transport inferences from modulated electron cyclotron heating in DIII-D,” Phys. Plasmas 13, 012311 (2006)]. By applying an FFT to the T{sub e} measurements from the University of Texas’s 40-channel ECE Radiometer, and using a simplified thermal transport equation, the flux surface extent of ECH deposition is determined. The Fourier method analysis is compared with a Break-In-Slope (BIS) analysis and predictions from the ray-tracing code TORAY. Examination of multiple Fourier harmonics and BIS fitting methods allow an estimation of modulated transport coefficients and thereby the true ECH deposition profile. Correlations between edge fluctuations and ECH deposition in legacy data are also explored as a step towards establishing a link between fluctuations and deposition broadening in DIII-D.
NASA Astrophysics Data System (ADS)
Brookman, M. W.; Austin, M. E.; Petty, C. C.
2015-12-01
Theoretical work, computation, and results from TCV [J. Decker "Effect of density fluctuations on ECCD in ITER and TCV," EPJ Web of Conf. 32, 01016 (2012)] suggest that density fluctuations in the edge region of a tokamak plasma can cause broadening of the ECH deposition profile. In this paper, a GUI tool is presented which is used for analysis of ECH deposition as a first step towards looking for this broadening, which could explain effects seen in previous DIII-D ECH transport studies [K.W. Gentle "Electron energy transport inferences from modulated electron cyclotron heating in DIII-D," Phys. Plasmas 13, 012311 (2006)]. By applying an FFT to the Te measurements from the University of Texas's 40-channel ECE Radiometer, and using a simplified thermal transport equation, the flux surface extent of ECH deposition is determined. The Fourier method analysis is compared with a Break-In-Slope (BIS) analysis and predictions from the ray-tracing code TORAY. Examination of multiple Fourier harmonics and BIS fitting methods allow an estimation of modulated transport coefficients and thereby the true ECH deposition profile. Correlations between edge fluctuations and ECH deposition in legacy data are also explored as a step towards establishing a link between fluctuations and deposition broadening in DIII-D.
NASA Technical Reports Server (NTRS)
Fletcher, Douglas G.; Mckenzie, R. L.
1992-01-01
Nonintrusive measurements of density, temperature, and their turbulent fluctuation levels were obtained in the boundary layer of an unseeded, Mach 2 wind tunnel flow. The spectroscopic technique that was used to make the measurements is based on the combination of laser-induced oxygen fluorescence and Raman scattering by oxygen and nitrogen from the same laser pulse. Results from this demonstration experiment are compared with previous measurements obtained in the same facility using conventional probes and an earlier spectroscopic technique. Densities and temperatures measured with the current technique agree with the previous surveys to within 3 percent and 2 percent, respectively. The fluctuation amplitudes for both variables agree with the measurements obtained using the earlier spectroscopic technique and show evidence of an unsteady, weak shock wave that perturbs the boundary layer.
Electron-cyclotron wave scattering by edge density fluctuations in ITER
Tsironis, Christos; Peeters, Arthur G.; Isliker, Heinz; Chatziantonaki, Ioanna; Vlahos, Loukas; Strintzi, Dafni
2009-11-15
The effect of edge turbulence on the electron-cyclotron wave propagation in ITER is investigated with emphasis on wave scattering, beam broadening, and its influence on localized heating and current drive. A wave used for electron-cyclotron current drive (ECCD) must cross the edge of the plasma, where density fluctuations can be large enough to bring on wave scattering. The scattering angle due to the density fluctuations is small, but the beam propagates over a distance of several meters up to the resonance layer and even small angle scattering leads to a deviation of several centimeters at the deposition location. Since the localization of ECCD is crucial for the control of neoclassical tearing modes, this issue is of great importance to the ITER design. The wave scattering process is described on the basis of a Fokker-Planck equation, where the diffusion coefficient is calculated analytically as well as computed numerically using a ray tracing code.
Interaction between the lower hybrid wave and density fluctuations in the scrape-off layer
Peysson, Y.; Madi, M.; Kabalan, K.; Decker, J.
2015-12-10
In the present paper, the perturbation of the launched power spectrum of the Lower Hybrid wave at the separatrix by electron density fluctuations in the scrape-off layer is investigated. Considering a slab geometry with magnetic field lines parallel to the toroidal direction, the full wave equation is solved using Comsol Multiphysics® for a fully active multi-junction like LH antenna made of two modules. When electron density fluctuations are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, it is shown that the power spectrum may be strongly modified from the antenna mouth to the plasma separatrix as the wave propagates. The diffraction effect leads to the appearance of multiple satellite lobes with randomly varying positions, a feature consistent with the recently developed model that has been applied successfully to high density discharges on the Tokamak Tore Supra corresponding to the large spectral gap regime [Decker J. et al. Phys. Plasma 21 (2014) 092504]. The perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength.
Interaction between the lower hybrid wave and density fluctuations in the scrape-off layer
NASA Astrophysics Data System (ADS)
Peysson, Y.; Madi, M.; Decker, J.; Kabalan, K.
2015-12-01
In the present paper, the perturbation of the launched power spectrum of the Lower Hybrid wave at the separatrix by electron density fluctuations in the scrape-off layer is investigated. Considering a slab geometry with magnetic field lines parallel to the toroidal direction, the full wave equation is solved using Comsol Multiphysics® for a fully active multi-junction like LH antenna made of two modules. When electron density fluctuations are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, it is shown that the power spectrum may be strongly modified from the antenna mouth to the plasma separatrix as the wave propagates. The diffraction effect leads to the appearance of multiple satellite lobes with randomly varying positions, a feature consistent with the recently developed model that has been applied successfully to high density discharges on the Tokamak Tore Supra corresponding to the large spectral gap regime [Decker J. et al. Phys. Plasma 21 (2014) 092504]. The perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength.
Nonlinear saturation spectra of electric fields and density fluctuations in drift wave turbulence
NASA Technical Reports Server (NTRS)
Kelley, M. C.
1982-01-01
The detection of drift waves in the nonlinear evolution of a space plasma process driven at long wavelengths is considered, adducing measurements of the electric field and density fluctuation power spectra as evidence. Since the driving mechanism is clearly at long wavelengths, the detection of drift waves suggests that they may play an important role in the transfer of wave energy from long to short wavelengths in a low beta plasma. The saturated spectral density is compared with theoretical results in order to estimate the anomalous diffusion rate. The observed spectral form and amplitude is in excellent agreement with drift wave predictions.
NASA Technical Reports Server (NTRS)
Massey, G. A.; Lemon, C. J.
1984-01-01
A tunable line-narrowed ArF laser can selectively excite several rotation al lines of the Schumann-Runge band system of O2 in air. The resulting ultraviolet fluorescence can be monitored at 90 deg to the laser beam axis, permitting space and time resolved observation of density and temperature fluctuations in turbulence. Experiments and calculations show that + or - 1 K, + or - 1 percent density, 1 cu mm spatial, and 1 microsecond temporal resolution can be achieved simultaneously under some conditions.
A new interferometry-based electron density fluctuation diagnostic on Alcator C-Mod.
Kasten, C P; Irby, J H; Murray, R; White, A E; Pace, D C
2012-10-01
The two-color interferometry diagnostic on the Alcator C-Mod tokamak has been upgraded to measure fluctuations in the electron density and density gradient for turbulence and transport studies. Diagnostic features and capabilities are described. In differential mode, fast phase demodulation electronics detect the relative phase change between ten adjacent, radially-separated (ΔR = 1.2 cm, adjustable), vertical-viewing chords, which allows for measurement of the line-integrated electron density gradient. The system can be configured to detect the absolute phase shift of each chord by comparison to a local oscillator, measuring the line-integrated density. Each chord is sensitive to density fluctuations with k(R) < 20.3 cm(-1) and is digitized at up to 10 MS/s, resolving aspects of ion temperature gradient-driven modes and other long-wavelength turbulence. Data from C-Mod discharges is presented, including observations of the quasi-coherent mode in enhanced D-alpha H-mode plasmas and the weakly coherent mode in I-mode.
NASA Technical Reports Server (NTRS)
Mielke, Amy F.; Elam, Kristie A.; Sung, Chih-Jen; Panda, Jayanta
2006-01-01
A molecular Rayleigh scattering technique is developed to measure dynamic gas temperature, velocity, and density in unseeded turbulent flows at sampling rates up to 10 kHz. A high power CW laser beam is focused at a point in a heated air jet plume and Rayleigh scattered light is collected and spectrally resolved. The spectrum of the light, which contains information about the temperature, velocity, and density of the flow, is analyzed using a Fabry-Perot interferometer. The circular interference fringe pattern is divided into four concentric regions and sampled at 1 and 10 kHz using photon counting electronics. Monitoring the relative change in intensity within each region allows for measurement of gas temperature and velocity. Independently monitoring the total scattered light intensity provides a measure of gas density. Power spectral density calculations of temperature, velocity, and density fluctuations, as well as mean and fluctuating quantities are demonstrated for various radial locations in the jet flow at a fixed axial distance from the jet exit plane. Results are compared with constant current anemometry and pitot probe measurements at the same locations.
A new interferometry-based electron density fluctuation diagnostic on Alcator C-Moda)
NASA Astrophysics Data System (ADS)
Kasten, C. P.; Irby, J. H.; Murray, R.; White, A. E.; Pace, D. C.
2012-10-01
The two-color interferometry diagnostic on the Alcator C-Mod tokamak has been upgraded to measure fluctuations in the electron density and density gradient for turbulence and transport studies. Diagnostic features and capabilities are described. In differential mode, fast phase demodulation electronics detect the relative phase change between ten adjacent, radially-separated (ΔR = 1.2 cm, adjustable), vertical-viewing chords, which allows for measurement of the line-integrated electron density gradient. The system can be configured to detect the absolute phase shift of each chord by comparison to a local oscillator, measuring the line-integrated density. Each chord is sensitive to density fluctuations with kR < 20.3 cm-1 and is digitized at up to 10 MS/s, resolving aspects of ion temperature gradient-driven modes and other long-wavelength turbulence. Data from C-Mod discharges is presented, including observations of the quasi-coherent mode in enhanced D-alpha H-mode plasmas and the weakly coherent mode in I-mode.
Three-parameter probability distribution density for statistical image analysis
NASA Astrophysics Data System (ADS)
Schau, H. C.
1980-01-01
Statistical analysis of 2-D image data or data gathered from a scanning radiometer requires that both the non-Gaussian nature and finite sample size of the process be considered. To aid the statistical analysis of this data, a higher moment description density function has been defined, and parameters have been identified with the estimated moments of the data. It is shown that the first two moments may be computed from a knowledge of the Weiner spectrum, whereas all higher moments require the complex spatial frequency spectrum. Parameter identification is carried out for a three-parameter density function and applied to a scene in the IR region, 8-14 microns. Results indicate that a three-parameter distribution density generally provides different probabilities than does a two-parameter Gaussian description if maximum entropy (minimum bias) forms are sought.
NASA Astrophysics Data System (ADS)
Lin, L.; Ding, W. X.; Brower, D. L.
2014-11-01
Combined polarimetry-interferometry capability permits simultaneous measurement of line-integrated density and Faraday effect with fast time response (˜1 μs) and high sensitivity. Faraday effect fluctuations with phase shift of order 0.05° associated with global tearing modes are resolved with an uncertainty ˜0.01°. For physics investigations, local density fluctuations are obtained by inverting the line-integrated interferometry data. The local magnetic and current density fluctuations are then reconstructed using a parameterized fit of the polarimetry data. Reconstructed 2D images of density and magnetic field fluctuations in a poloidal cross section exhibit significantly different spatial structure. Combined with their relative phase, the magnetic-fluctuation-induced particle transport flux and its spatial distribution are resolved.
NASA Astrophysics Data System (ADS)
Antonov, A. N.; Gaidarov, M. K.; Sarriguren, P.; Moya de Guerra, E.
2016-07-01
The volume and surface components of the nuclear symmetry energy (NSE) and their ratio are calculated within the coherent density fluctuation model (CDFM). The estimations use the results of the model for the NSE in finite nuclei based on the Brueckner energy-density functional for nuclear matter. In addition, we present results for the NSE and its volume and surface contributions obtained by using the Skyrme energy-density functional. The CDFM weight function is obtained using the proton and neutron densities from the self-consistent HF+BCS method with Skyrme interactions. We present and discuss the values of the volume and surface contributions to the NSE and their ratio obtained for the Ni, Sn, and Pb isotopic chains, studying their isotopic sensitivity. The results are compared with estimations of other approaches which have used available experimental data on binding energies, neutron-skin thicknesses, excitation energies to isobaric analog states (IAS), and also with results of other theoretical methods.
Bluhm, Christian; Scheu, Stefan; Maraun, Mark
2016-04-01
We investigated the oribatid mite density, community structure and the percentage of parthenogenetic individuals in four different forest types across three regions in Germany in 2008 and once again in 2011. We compared temporal (inter-annual) fluctuations in population densities between sexually and parthenogenetically reproducing species of oribatid mites. We hypothesized that population densities in parthenogenetic oribatid mite species fluctuate more than in sexual ones. Further, we expected species composition and dominance of parthenogenetic species to differ between forest types and regions. Oribatid mite community structure did not differ between years but varied with forest type and region, indicating low species turnover in time. As hypothesized, temporal fluctuations were more pronounced in parthenogenetic as compared to sexual species. The percentage of parthenogenetic individuals was significantly higher in coniferous than in beech forests and significantly higher in Schorfheide-Chorin than in Hainich-Dün and Schwäbische Alb. The results indicate that parthenogenetic species flourish if populations are controlled by density-independent factors and dominate at sites were resources are plentiful and easily available, such as coniferous forests, and in regions with more acidic soils and thick organic layers, such as Schorfheide-Chorin. However, historical factors also may have contributed to the increased dominance of parthenogenetic species in the Schorfheide-Chorin, as this region was more heavily glaciated and this may have favoured parthenogenetic species. Overall, our study supports the hypothesis that parthenogenetic species benefit from the lack of density-dependent population control whereas the opposite is true for sexual species.
Minima of the fluctuations of the order parameter of global seismicity
NASA Astrophysics Data System (ADS)
Sarlis, N. V.; Christopoulos, S.-R. G.; Skordas, E. S.
2015-06-01
It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold Mthres = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.
Minima of the fluctuations of the order parameter of global seismicity.
Sarlis, N V; Christopoulos, S-R G; Skordas, E S
2015-06-01
It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold Mthres = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.
Minima of the fluctuations of the order parameter of global seismicity
Sarlis, N. V. Christopoulos, S.-R. G.; Skordas, E. S.
2015-06-15
It has been recently shown [N. V. Sarlis, Phys. Rev. E 84, 022101 (2011) and N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012)] that earthquakes of magnitude M greater or equal to 7 are globally correlated. Such correlations were identified by studying the variance κ{sub 1} of natural time which has been proposed as an order parameter for seismicity. Here, we study the fluctuations of this order parameter using the Global Centroid Moment Tensor catalog for a magnitude threshold M{sub thres} = 5.0 and focus on its behavior before major earthquakes. Natural time analysis reveals that distinct minima of the fluctuations of the order parameter of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than 8.4. This phenomenon corroborates the recent finding [N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013)] that similar minima of the seismicity order parameter fluctuations had preceded all major shallow earthquakes in Japan. Moreover, on the basis of these minima a statistically significant binary prediction method for earthquakes of magnitude larger than 8.4 with hit rate 100% and false alarm rate 6.67% is suggested.
Planets in other universes: habitability constraints on density fluctuations and galactic structure
NASA Astrophysics Data System (ADS)
Adams, Fred C.; Coppess, Katherine R.; Bloch, Anthony M.
2015-09-01
Motivated by the possibility that different versions of the laws of physics could be realized within other universes, this paper delineates the galactic structure parameters that allow for habitable planets and revisits constraints on the amplitude Q of the primordial density fluctuations. Previous work indicates that large values of Q lead to galaxies so dense that planetary orbits cannot survive long enough for life to develop. Small values of Q lead to delayed star formation, loosely bound galaxies, and compromised heavy element retention. This work generalizes previous treatments in the following directions: [A] We consider models for the internal structure of the galaxies, including a range of stellar densities, and find the fraction of the resulting galactic real estate that allows for stable, long-lived planetary orbits. [B] For high velocity encounters, we perform a large ensemble of numerical simulations to estimate cross sections for the disruption of planetary orbits due to interactions with passing stars. [C] We consider the background radiation fields produced by the galaxies: if a galaxy is too compact, the night sky seen from a potentially habitable planet can provide more power than the host star. [D] One consequence of intense galactic background radiation fields is that some portion of the galaxy, denoted as the Galactic Habitable Zone, will provide the right flux levels to support habitable planets for essentially any planetary orbit including freely floating bodies (but excluding close-in planets). As the value of Q increases, the fraction of stars in a galaxy that allow for (traditional) habitable planets decreases due to both orbital disruption and the intense background radiation. However, the outer parts of the galaxy always allow for habitable planets, so that the value of Q does not have a well-defined upper limit (due to scattering or radiation constraints). Moreover, some Galactic Habitable Zones are large enough to support more
Cao, Qifo; Liu, Yong; Zhao, Hailin; Zhou, Tianfu; Ti, Ang; Hu, Liqun
2016-11-01
A system to simultaneously diagnose the electron temperature and density fluctuations is proposed for Experimental Advanced Superconducting Tokamak device. This system includes a common quasi-optical antenna, a correlation electron cyclotron emission (CECE) system that is used to measure the electron temperature fluctuations and a Doppler backscattering (DBS) system that is used to measure the electron density fluctuations. The frequency range of the proposed CECE system is 108-120 GHz, and this corresponds to a radial coverage of normalized radius ((R - R0)/a, R0 = 1850 mm, a = 450 mm) from 0.2 to 0.67 for the plasma operation with a toroidal magnetic field of 2.26 T. This paper focuses on the design of the quasi-optical antenna and aims at optimizing the poloidal resolution for different frequency bands. An optimum result gives the beam radius for the CECE system of 13-15 mm and this corresponds to a wave number range of kθ < 2.4 cm(-1). The beam radius is 20-30 mm for V band (50-75 GHz) and 15-20 mm for W band (75-110 GHz).
NASA Astrophysics Data System (ADS)
Cao, Qifo; Liu, Yong; Zhao, Hailin; Zhou, Tianfu; Ti, Ang; Hu, Liqun
2016-11-01
A system to simultaneously diagnose the electron temperature and density fluctuations is proposed for Experimental Advanced Superconducting Tokamak device. This system includes a common quasi-optical antenna, a correlation electron cyclotron emission (CECE) system that is used to measure the electron temperature fluctuations and a Doppler backscattering (DBS) system that is used to measure the electron density fluctuations. The frequency range of the proposed CECE system is 108-120 GHz, and this corresponds to a radial coverage of normalized radius ((R - R0)/a, R0 = 1850 mm, a = 450 mm) from 0.2 to 0.67 for the plasma operation with a toroidal magnetic field of 2.26 T. This paper focuses on the design of the quasi-optical antenna and aims at optimizing the poloidal resolution for different frequency bands. An optimum result gives the beam radius for the CECE system of 13-15 mm and this corresponds to a wave number range of kθ < 2.4 cm-1. The beam radius is 20-30 mm for V band (50-75 GHz) and 15-20 mm for W band (75-110 GHz).
Density and magnetic fluctuations at JET: experimental observation and numerical characterization
NASA Astrophysics Data System (ADS)
de Masi, Gianluca; Predebon, Italo; Spagnolo, Silvia; Lupelli, Ivan; Hillesheim, Jon; Meneses, Luis; Maggi, Costanza; Delabie, Ephrem; JET Contributors Team
2016-10-01
Density and magnetic fluctuations have been experimentally observed on JET in the inter ELM phases in low beta discharges.They have been characterized in terms of typical frequency range (60-80 kHz), wavenumber (0.01 <=ky ρi <=0.1), radial localization (pedestal top) and correlation with the relevant kinetic quantities. A linear simulation with gyrokinetic code GENE, matching the experimental edge condition has been performed to gain insight on their possible physical interpretation. ITG modes turn out to be the most unstable modes for 0 <=ky ρi <=1, while microtearing modes (MTMs) are the dominant instabilities for ky ρi <= 0.1.A typical oscillation frequency of about 50-100 kHz is associated to both unstable modes, with opposite propagation direction.Different considerations suggest an interpretation in terms of MTMs for the observed magnetic fluctuations, while density fluctuations appear to be dominated by ITG instabilities. EUROfusion Consortium, JET, Culham Science Centre, Abingdon, OX14 3DB, UK.
Impact of density and environmental factors on population fluctuations in a migratory passerine.
Pasinelli, Gilberto; Schaub, Michael; Häfliger, Guido; Frey, Monika; Jakober, Hans; Müller, Mathis; Stauber, Wolfgang; Tryjanowski, Piotr; Zollinger, Jean-Luc; Jenni, Lukas
2011-01-01
1. Populations of plants and animals typically fluctuate because of the combined effects of density-dependent and density-independent processes. The study of these processes is complicated by the fact that population sizes are typically not known exactly, because population counts are subject to sampling variance. Although the existence of sampling variance is broadly acknowledged, relatively few studies on time-series data have accounted for it, which can result in wrong inferences about population processes. 2. To increase our understanding of population dynamics, we analysed time series from six Central European populations of the migratory red-backed shrike Lanius collurio by simultaneously assessing the strength of density dependence, process and sampling variance. In addition, we evaluated hypotheses predicting effects of factors presumed to operate on the breeding grounds, at stopover sites in eastern Africa during fall and spring migration and in the wintering grounds in southern Africa. We used both simple and state-space formulations of the Gompertz equation to model population size. 3. Across populations and modelling approaches, we found consistent evidence for negative density-dependent population regulation. Further, process variance contributed substantially to variation in population size, while sampling variance did not. Environmental conditions in eastern and southern Africa appear to influence breeding population size, as rainfall in the Sahel during fall migration and in the south African wintering areas were positively related to population size in the following spring in four of six populations. In contrast, environmental conditions in the breeding grounds were not related to population size. 4. Our findings suggest negative density-dependent regulation of red-backed shrike breeding populations and are consistent with the long-standing hypothesis that conditions in the African staging and wintering areas influence population numbers of species
NASA Astrophysics Data System (ADS)
Babst, Flurin; Wright, William; Szejner, Paul; Wells, Leon; Belmecheri, Soumaya; Monson, Russell
2016-04-01
Rapidly rising evaporative demand threatens forests in semi-arid areas around the world, but the timing of stem growth response to drought is often coarsely known. This is partly due to a shortage of sub-annual growth records, particularly outside the Mediterranean region where most intra-annual density fluctuation (IADF) chronologies are based. We anticipate that an automated, cost-effective, and easily implementable method to characterize IADFs could foster more widespread development of sub-annual chronologies. Here, we applied a peak detection algorithm to fine-spatial resolution blue intensity (BI) profiles of Ponderosa pine tree rings from two sites located in neighboring mountain ranges in southern Arizona (~300 m elevation difference). This automated procedure proved reliable to isolate and characterize IADFs, thus offering an efficient and objective alternative to visual identification. Out of seven investigated BI parameters, peak height, width, and area showed satisfactory chronology statistics. We assessed the response of these BI and radial growth parameters to six monthly-resolved climate variables and to the onset date of the North American summer monsoon (NAM). The NAM is an atmospheric mode that provides a clear time marker for the termination of a pre-summer drought period (May-June) causing regular IADFs in trees growing near the dry margin of their distribution range. We observed divergent water limitation at the two sites, despite comparable site characteristics. Radial growth at the lower-elevation site depended mainly on winter precipitation, whereas the higher site relied on spring and monsoon precipitation. The pre-summer drought period indeed promoted IADFs in early ring portions at both sites. Yet, IADFs at the higher site were only formed, if spring was sufficiently humid to assume enough radial growth. Late-position IADFs were caused by a weak monsoon and additionally promoted by favorable conditions towards the end of the growing
Scaling laws of turbulence and heating of fast solar wind: the role of density fluctuations.
Carbone, V; Marino, R; Sorriso-Valvo, L; Noullez, A; Bruno, R
2009-08-07
Incompressible and isotropic magnetohydrodynamic turbulence in plasmas can be described by an exact relation for the energy flux through the scales. This Yaglom-like scaling law has been recently observed in the solar wind above the solar poles observed by the Ulysses spacecraft, where the turbulence is in an Alfvénic state. An analogous phenomenological scaling law, suitably modified to take into account compressible fluctuations, is observed more frequently in the same data set. Large-scale density fluctuations, despite their low amplitude, thus play a crucial role in the basic scaling properties of turbulence. The turbulent cascade rate in the compressive case can, moreover, supply the energy dissipation needed to account for the local heating of the nonadiabatic solar wind.
Turbulent small-scale neutral and ion density fluctuations as measured during MAC/Epsilon
NASA Technical Reports Server (NTRS)
Luebken, F.-J.; Hillert, W.; Vonzahn, U.; Blix, T. A.; Thrane, E. V.
1989-01-01
During the MAC/Epsilon campaign (Fall 1987, from Andoya, Northern Norway, 69 N, 16 E) a total of four altitude profiles of neutral gas number densities and six profiles of ion number densities were measured with high spatial resolution in the height range from 60 to 120 km. First results of these rocket-borne experiments are presented with emphasis on small scale turbulent density variations and related turbulent parameter as structure function constants and energy dissipation rates.
NASA Technical Reports Server (NTRS)
Woo, R.; Armstrong, J. W.
1979-01-01
Solar wind electron density power spectra in the solar equatorial region are inferred from observations of phase scintillations and spectral broadening made with the Viking, Helios, and Pioneer spacecraft. The heliocentric distance range covered is 2-215 solar radii and for some observations close to the sun the spectra extend to fluctuation frequencies as high as 100 Hz. For heliocentric distances of about 20 solar radii the equivalent spacecraft-measured one-dimensional density spectrum is well modeled by a single power law in the frequency range 0.0001-0.05 Hz. The flattening of the density spectrum within 20 solar radii is presumably associated with energy deposition in the near-sun region and acceleration of the solar wind.
Lee, Kang Il
2013-11-01
In the present study, correlations of linear and nonlinear ultrasound parameters (speed of sound, normalized broadband ultrasound attenuation, and nonlinear parameter B/A) with bone mineral density and microarchitectural parameters were investigated in 28 bovine femoral trabecular bone samples in vitro. All three ultrasound parameters exhibited relatively high correlation coefficients with the indexes of bone quantity (bone mineral density and bone volume fraction) and lower correlation coefficients with the remaining microarchitectural parameters. These results suggest that B/A, in addition to speed of sound and attenuation, may have potential as an index for the assessment of bone status and osteoporosis.
Theory of small-scale density and electric field fluctuations in the nightside Venus ionosphere
NASA Technical Reports Server (NTRS)
Huba, J. D.
1992-01-01
Recently, it has been reported that small-scale (lambda about 0.1-2 km) density irregularities occur during 100-Hz electric field bursts in the nightside ionosphere of Venus. This paper provides a detailed analysis of the lower-hybrid-drift instability as a mechanism to generate the observed irregularities. A fully electromagnetic theory is developed that is relevant to the finite beta plasma in Venus's ionosphere and includes collisional effects (e.g., electron-ion, electron-neutral, and ion-neutral collisions). The key features of the analysis that favor this instability are the following: (1) it is a flute mode and propagates orthogonal to the ambient magnetic field; (2) it is a relatively short wavelength mode and the Doppler-shifted frequency can be greater than about 100 Hz; (3) it can produce both electric field and density fluctuations, as well as magnetic field fluctuations in a finite beta plasma; and (4) it is most unstable in low-beta plasmas so that it is likely to occur in the low-density, high-magnetic-field ionospheric holes. These features are consistent with observational results.
Communication: Linking the dielectric Debye process in mono-alcohols to density fluctuations
NASA Astrophysics Data System (ADS)
Hecksher, Tina
2016-04-01
This work provides the first direct evidence that the puzzling dielectric Debye process observed in mono-alcohols is coupled to density fluctuations. The results open up for an explanation of the Debye process within the framework of conventional liquid-state theory. The spectral shape of the dynamical bulk modulus of the two studied mono-alcohols, 2-ethyl-1-hexanol and 4-methyl-3-heptanol, is nearly identical to that of their corresponding shear modulus, and thus the supramolecular structures believed to be responsible for the slow dielectric Debye process are manifested in the bulk modulus in the same way as in the shear modulus.
Pradhan, Prabhakar; Damania, Dhwanil; Turzhitsky, Vladimir; Subramanian, Hariharan; Backman, Vadim; Joshi, Hrushikesh M.; Dravid, Vinayak P.; Roy, Hemant K.; Taflove, Allen
2010-12-13
We report a study of the nanoscale mass-density fluctuations of heterogeneous optical dielectric media, including nanomaterials and biological cells, by quantifying their nanoscale light-localization properties. Transmission electron microscope images of the media are used to construct corresponding effective disordered optical lattices. Light-localization properties are studied by the statistical analysis of the inverse participation ratio (IPR) of the localized eigenfunctions of these optical lattices at the nanoscale. We validated IPR analysis using nanomaterials as models of disordered systems fabricated from dielectric nanoparticles. As an example, we then applied such analysis to distinguish between cells with different degrees of aggressive malignancy.
NASA Astrophysics Data System (ADS)
Ding, W. X.; Lin, L.; Duff, J. R.; Brower, D. L.; Sarff, J. S.
2012-10-01
The multichannel polarimeter-interferometer system on the MST reversed-field pinch can be utilized to measure far-forward collective scattering from electron density fluctuations. The collective scattering system has 11 viewing chords with ˜8 cm spacing. The source is a 432 μm (694 GHz) far infrared laser and the scattered power is measured using a heterodyne detection scheme. Collective scattering provides a line-integrated measurement of fluctuations within the divergence of the probe beam covering wavenumber range: k⊥ < 1.3 cm-1, corresponding k⊥ρs < 1.3 (ρs is the ion-sound Larmor radius), the region of primary interest for turbulent fluctuation-induced transport. The perpendicular wavenumber consists of toroidal, poloidal, and radial contributions, which vary with chord position. Coherent modes associated with tearing instabilities and neutral-beam driven fast particles are observed along with broadband turbulence at frequencies up to 500 kHz. Changes in frequency are consistent with a Doppler shift due to parallel plasma flow.
Ding, W. X.; Lin, L.; Brower, D. L.; Duff, J. R.; Sarff, J. S.
2012-10-15
The multichannel polarimeter-interferometer system on the MST reversed-field pinch can be utilized to measure far-forward collective scattering from electron density fluctuations. The collective scattering system has 11 viewing chords with {approx}8 cm spacing. The source is a 432 {mu}m (694 GHz) far infrared laser and the scattered power is measured using a heterodyne detection scheme. Collective scattering provides a line-integrated measurement of fluctuations within the divergence of the probe beam covering wavenumber range: k{sub Up-Tack} < 1.3 cm{sup -1}, corresponding k{sub Up-Tack }{rho}{sub s} < 1.3 ({rho}{sub s} is the ion-sound Larmor radius), the region of primary interest for turbulent fluctuation-induced transport. The perpendicular wavenumber consists of toroidal, poloidal, and radial contributions, which vary with chord position. Coherent modes associated with tearing instabilities and neutral-beam driven fast particles are observed along with broadband turbulence at frequencies up to 500 kHz. Changes in frequency are consistent with a Doppler shift due to parallel plasma flow.
Initial density fluctuation measurements from the NSTX Beam Emission Spectroscopy diagnostic system*
NASA Astrophysics Data System (ADS)
Smith, D. R.; Fonck, R. J.; McKee, G. R.; Schoenbeck, N. L.; Thompson, D.; Uzun-Kaymak, I. U.; Stratton, B. C.
2010-11-01
Density fluctuation measurements on the ion gyroscale have been obtained on NSTX with a newly commissioned beam emission spectroscopy (BES) diagnostic system. The BES system measures red-shifted Dα emission near 660 nm from deuterium neutral beams with high throughput optics and high efficiency detectors. The system presently employs 16 detection channels arranged in radial and poloidal arrays, and an expansion to 32 channels is planned. Radial arrays can measure fluctuations from r/a 0.1 to beyond the last closed flux surface and resolve fluctuations with kρi<=1.5. Initial BES measurements reveal broadband turbulence and coherent modes below 300 kHz for r/a>=0.4. The broadband turbulence appears in high gradient regions and increases at H-L transitions. The frequency characteristics of the coherent modes correlate with Alfvén/energetic particle modes in Mirnov probe measurements, but some coherent modes appear in BES measurements only. *Supported by the U.S. Department of Energy under Contract Nos. DE-FG02-89ER53296, DE-AC02-09CH11466 and DE-SC0001288.
Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors
NASA Astrophysics Data System (ADS)
Xu, B.; Dai, Y. M.; Xiao, H.; Shen, B.; Ye, Z. R.; Forget, A.; Colson, D.; Feng, D. L.; Wen, H. H.; Qiu, X. G.; Lobo, R. P. S. M.
2016-08-01
In iron-based superconductors, a spin-density-wave (SDW) magnetic order is suppressed with doping, and unconventional superconductivity appears in close proximity to the SDW instability. The optical response of the SDW order shows clear gap features: substantial suppression in the low-frequency optical conductivity, alongside a spectral weight transfer from low to high frequencies. Here, we study the detailed temperature dependence of the optical response in three different series of the Ba122 system [Ba1 -xKxFe2As2 , Ba (Fe1-xCox) 2As2 , and BaFe2(As1-xPx) 2 ]. Intriguingly, we find that the suppression of the low-frequency optical conductivity and spectral weight transfer appear at a temperature T* much higher than the SDW transition temperature TSDW. Since this behavior has the same optical feature and energy scale as the SDW order, we attribute it to SDW fluctuations. Furthermore, T* is suppressed with doping, closely following the doping dependence of the nematic fluctuations detected by other techniques. These results suggest that the magnetic and nematic orders have an intimate relationship, in favor of the magnetic-fluctuation-driven nematicity scenario in iron-based superconductors.
Characterization of density fluctuations during ELMs in the DIII-D tokamak
NASA Astrophysics Data System (ADS)
Coda, S.; Porkolab, M.; Burrell, K. H.
2001-12-01
Bursts of turbulence associated with ELMs have been studied systematically in DIII-D with a multichannel phase contrast imaging (PCI) diagnostic, which is sensitive to the long poloidal wavelength components of the density fluctuations in the outer edge of the tokamak. A comparison of the temporal dynamics of the turbulence with the signature Dα signal from the divertor has revealed systematic differences between type I and type III ELMs: even though precursor fluctuations are sometimes seen before type I ELMs, the PCI signal level remains high until the peak in the Dα signal; by contrast, in type III ELMs the fluctuation burst precedes the Dα peak by 0.4-0.6 ms. Type I ELMs can generate `echoes', i.e. secondary bursts, in the scrape-off layer. Coherent modes are observed during type III ELMs only. The radial and temporal correlation structures and the spectral properties of the turbulence during the transient ELM phase have been reconstructed by averaging over multiple ELMs, in order to improve the statistical accuracy. ELM turbulence is found to share many properties with L mode turbulence, including the main qualitative features of radial wavenumber and frequency spectra and radial dispersion relations. However, features unique to ELM turbulence are also identified.
NASA Technical Reports Server (NTRS)
Smith, M.
1972-01-01
Fluctuations in electron density and temperature coupled through Ohm's law are studied for an ionizable medium. The nonlinear effects are considered in the limit of a third order quasi-linear treatment. Equations are derived for the amplitude of the fluctuation. Conditions under which a steady state can exist in the presence of the fluctuation are examined and effective transport properties are determined. A comparison is made to previously considered second order theory. The effect of third order terms indicates the possibility of fluctuations existing in regions predicted stable by previous analysis.
NASA Technical Reports Server (NTRS)
Smith, J. M.
1972-01-01
Fluctuations in electron density and temperature coupled through Ohm's law are studied for an ionizable medium. The nonlinear effects are considered in the limit of a third order quasi-linear treatment. Equations are derived for the amplitude of the fluctuation. Conditions under which a steady state can exist in the presence of the fluctuation are examined and effective transport properties are determined. A comparison is made to previously considered second order theory. The effect of third order terms indicates the possibility of fluctuations existing in regions predicted stable by previous analysis.
Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser
NASA Technical Reports Server (NTRS)
Massey, G. A.
1984-01-01
Noninvasive measurement of density and temperature fluctuations in turbulent air flow was examined. The approach used fluorescence of oxygen molecules which are selectively excited by a tunable vacuum ultraviolet laser beam. The strength of the fluorescence signal and its dependence on laser wavelength vary with the density and temperature of the air in the laser beam. Because fluorescence can be detected at 90 degrees from the beam propagation direction, spatial resolution in three dimensions, rather than path-integrated measurements can be achieved. With spatial resolutions of the order of a millimeter and at supersonic air velocities it is necessary to perform each measurement in a time of the order of a microsecond; this is possible by by using laser pulses of ten nanosecond duration. In this method atmospheric O2 is excited by the emission of a tunable ArF excimer laser, and the fluorescence, which spans the 210 to 420 range, is detected by an ultraviolet phototube.
Critical density fluctuations in lipid bilayers detected by fluorescence lifetime heterogeneity.
Ruggiero, A; Hudson, B
1989-01-01
The heterogeneity of the decay of the fluorescence of transparinaric acid in single-component lipid bilayers at temperatures above their gel/liquid crystalline phase transition is shown to be due to the presence of regions of higher local density and higher acyl chain order than the predominant fluid regions. This conclusion is based on selective excitation behavior and the observation of time-resolved fluorescence anisotropies that increase at long times. The fractional amplitude of the long lifetime component of the fluorescence shows a temperature variation that conforms to conventional descriptions of critical behavior. The critical exponent extracted from this variation is 1.1, close to the value of 1.0 that describes ultrasonic data. We therefore conclude that liquid crystalline lipid bilayers exhibit critical behavior with significant density and order fluctuations. This behavior must be taken into account in the interpretation of fluorescence and other spectroscopic measurements of the properties of bilayers. PMID:2765649
Density fluctuation spectrum of solar wind turbulence between ion and electron scales.
Chen, C H K; Salem, C S; Bonnell, J W; Mozer, F S; Bale, S D
2012-07-20
We present a measurement of the spectral index of density fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be -2.75±0.06, steeper than predictions for pure whistler or kinetic Alfvén wave turbulence but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.
NASA Astrophysics Data System (ADS)
Klatt, Michael A.; Torquato, Salvatore
2016-08-01
In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g2(r ) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the
Rayleigh Scattering Diagnostic Used to Measure Velocity and Density Fluctuation Spectra
NASA Technical Reports Server (NTRS)
Seasholtz, Richard G.; Panda, Jayanta; Elam, Kristie A.
2003-01-01
A new, molecular Rayleigh-scattering-based flow diagnostic developed at the NASA Glenn Research Center has been used for the first time to measure the power spectrum of both gas density and radial velocity components in the plumes of high-speed jets. The objective of the work is to develop an unseeded, nonintrusive dynamic measurement technique for studying turbulent flows in NASA test facilities. This technique provides aerothermodynamic data not previously obtainable. It is particularly important for supersonic flows, where hot wire and pitot probes are difficult to use and disturb the flow under study. The effort is part of the nonintrusive instrumentation development program supporting propulsion research at the NASA Glenn Research Center. In particular, this work is measuring fluctuations in flow velocity, density, and temperature for jet noise studies. These data are valuable to researchers studying the correlation of flow fluctuations with far-field noise. One of the main objectives in jet noise research is to identify noise sources in the jet and to determine their contribution to noise generation. The technique is based on analyzing light scattered from molecules within the jet using a Fabry-Perot interferometer operating in a static imaging mode. The PC-based data acquisition system can simultaneously sample velocity and density data at rates to about 100 kHz and can handle up to 10 million data records. We used this system to interrogate three different jet nozzle designs in a Glenn free-jet facility. Each nozzle had a 25.4-mm exit diameter. One was convergent, used for subsonic flow measurements and to produce a screeching underexpanded jet with a fully expanded Mach number of 1.42. The other nozzles (Mach 1.4 and 1.8) were convergent-divergent types. The radial component of velocity and gas density were simultaneously measured in this work.
Pedestal density fluctuation dynamics during the inter-ELM cycle in DIII-D
Yan, Z.; McKee, G. R.; Groebner, R. J.; Snyder, P. B.; Osborne, T. H.; Burrell, K. H.; Beurskens, M. N.
2011-05-15
Detailed 2D measurements of long-wavelength density fluctuations in the pedestal region with beam emission spectroscopy during the period between edge localized modes (ELMs) indicate two distinct bands of fluctuations propagating in opposite poloidal directions in the plasma frame: one lower frequency band (50-150 kHz) advects in the ion-diamagnetic drift direction (ion mode) and a higher frequency band (200-400 kHz) advects in the electron diamagnetic drift direction (electron mode). The ion mode amplitude is modulated with the ELM cycle: it increases rapidly after an ELM and then saturates, similar to the evolution of the pedestal electron pressure and density gradients. The electron mode, in contrast, has no significant time evolution between ELMs. The decorrelation time of the ion mode is <5 {mu}s[{tau}{sub c}(c{sub s}/c{sub s}aa){<=}1], the radial correlation length is of order 10 {rho}{sub i} and has poloidal wave-number k{sub {theta}{rho}i{approx}}0.1, and the mode advects at near the ion diamagnetic velocity in the plasma frame. These spatiotemporal dynamics are qualitatively similar to features predicted for kinetic ballooning modes.
Pedestal density fluctuation dynamics during the inter-ELM cycle in DIII-D a)
NASA Astrophysics Data System (ADS)
Yan, Z.; McKee, G. R.; Groebner, R. J.; Snyder, P. B.; Osborne, T. H.; Beurskens, M. N.; Burrell, K. H.
2011-05-01
Detailed 2D measurements of long-wavelength density fluctuations in the pedestal region with beam emission spectroscopy during the period between edge localized modes (ELMs) indicate two distinct bands of fluctuations propagating in opposite poloidal directions in the plasma frame: one lower frequency band (50-150 kHz) advects in the ion-diamagnetic drift direction (ion mode) and a higher frequency band (200-400 kHz) advects in the electron diamagnetic drift direction (electron mode). The ion mode amplitude is modulated with the ELM cycle: it increases rapidly after an ELM and then saturates, similar to the evolution of the pedestal electron pressure and density gradients. The electron mode, in contrast, has no significant time evolution between ELMs. The decorrelation time of the ion mode is <5 μs [τc(cs/csa a)≤1], the radial correlation length is of order 10 ρi and has poloidal wave-number kθρi~0.1, and the mode advects at near the ion diamagnetic velocity in the plasma frame. These spatiotemporal dynamics are qualitatively similar to features predicted for kinetic ballooning modes.
Reduced density matrix and order parameters of a topological insulator
NASA Astrophysics Data System (ADS)
Yu, Wing Chi; Li, Yan Chao; Sacramento, P. D.; Lin, Hai-Qing
2016-12-01
It has been recently proposed that the reduced density matrix may be used to derive the order parameter of a condensed matter system. Here we propose order parameters for the phases of a topological insulator, specifically a spinless Su-Schrieffer-Heeger (SSH) model, and consider the effect of short-range interactions. All the derived order parameters and their possible corresponding quantum phases are verified by the entanglement entropy and electronic configuration analysis results. The order parameter appropriate to the topological regions is further proved by calculating the Berry phase under twisted boundary conditions. It is found that the topological nontrivial phase is robust to the introduction of repulsive intersite interactions and can appear in the topological trivial parameter region when appropriate interactions are added.
Measuring long wavelength plasma density fluctuations by CO2 laser scattering (abstract)
NASA Astrophysics Data System (ADS)
Evans, D. E.
1985-05-01
. Asymmetric profiles are frequently encountered in far forward scattering experiments in plasma, and they are attributed either to (1) the volume effect, that is, the finite width of a plasma wave, or (2) a pair of counter-propagating waves, such as poloidal waves in a torus met twice by a probe beam traversing a minor diameter. The first explanation rests on the difference between the multiple order scattering of a two-dimensional grating (Raman-Nath) and the single-order scattering of a three-dimensional crystal (Bragg). In a regime intermediate between these extremes, both +1 and -1 orders are present, but of unequal intensity, therefore giving rise to asymmetry in the beam profile. The Fourier optics treatment can be extended to describe a wave of arbitrary interaction length L, and a controlling parameter Q=κ2L/k (κ and k being wave numbers of the plasma wave and the probe radiation, respectively) which is ≪1 for Raman-Nath and ≫1 for Bragg, determines the precise regime that prevails.7 Calculations describing the counter-propagating waves model have been performed and verified experimentally, again using transducer-driven waves in air.8 Profiles based on this model are currently providing best fits to data recently recorded from tokamak plasmas in TOSCA. A preliminary inspection of the results of these measurements reveals, from the orientation of the beam profile pattern, predominantly poloidal waves. Their maximum intensity is near 100 kHz and they fall away towards higher frequencies as ν-2.5. Evidence for coherent gross modes at lower frequencies is also seen. Wave numbers are in the range 1 cm-1<κ⊥<30 cm-1, bracketing the neighborhood where κ⊥ρi˜1. The strength of the relative density fluctuation ñe/n¯e of a few per cent is consistent with diffusion coefficients D⊥˜104 cm2 s-1, and there is evidence for inverse correlation between ñe/n¯e and confinement time τE.
On the phase shift between electric potential and plasma density fluctuations in the edge turbulence
Shchepetov, S. V. Kholnov, Yu. V.; Vasil'kov, D. G.
2013-02-15
In some cases, the phase shift between fluctuations of the electric potential and plasma density helps to identify the instability that governs the turbulent state. In this paper, the basic experimental and theoretical results that denote the possibility (or impossibility) of such identification are briefly discussed. The experimental data based on measurements of the phase shift between the floating potential and ion saturation current fluctuations in the L-2M stellarator-a system with externally imposed magnetic surfaces-are presented (Shchepetov, Kholnov, Fedyanin, et al., Plasma Phys. Controlled Fusion 50, 045001 (2008)). It is shown that the observed phase shift {Omega} varies in a wide range from {pi} to 0, gradually decreasing with deepening inside the plasma. A number of arguments are presented suggesting that {Omega} Almost-Equal-To {pi} can indicate that the process is nonlocal, i.e., oscillations at a given spatial point are driven and mainly determined by the processes localized outside of the observation point. We note that, within the framework of the magnetohydrodynamic theory, plasma was definitely unstable with respect to resistive interchange modes in all cases under study. It is demonstrated experimentally that the widespread notion that the phase shift {Omega} Almost-Equal-To {pi}/2 is characteristic of only resistive interchange modes is hardly universal. The experimental results are analyzed on the basis of analytical estimates.
Structure and Function of Intra–Annual Density Fluctuations: Mind the Gaps
Battipaglia, Giovanna; Campelo, Filipe; Vieira, Joana; Grabner, Michael; De Micco, Veronica; Nabais, Cristina; Cherubini, Paolo; Carrer, Marco; Bräuning, Achim; Čufar, Katarina; Di Filippo, Alfredo; García-González, Ignacio; Koprowski, Marcin; Klisz, Marcin; Kirdyanov, Alexander V.; Zafirov, Nikolay; de Luis, Martin
2016-01-01
Tree rings are natural archives of climate and environmental information with a yearly resolution. Indeed, wood anatomical, chemical, and other properties of tree rings are a synthesis of several intrinsic and external factors, and their interaction during tree growth. In particular, Intra-Annual Density Fluctuations (IADFs) can be considered as tree-ring anomalies that can be used to better understand tree growth and to reconstruct past climate conditions with intra-annual resolution. However, the ecophysiological processes behind IADF formation, as well as their functional impact, remain unclear. Are IADFs resulting from a prompt adjustment to fluctuations in environmental conditions to avoid stressful conditions and/or to take advantage from favorable conditions? In this paper we discuss: (1) the influence of climatic factors on the formation of IADFs; (2) the occurrence of IADFs in different species and environments; (3) the potential of new approaches to study IADFs and identify their triggering factors. Our final aim is to underscore the advantages offered by network analyses of data and the importance of high-resolution measurements to gain insight into IADFs formation processes and their relations with climatic conditions, including extreme weather events. PMID:27200063
X-ray Fluctuation Power Spectral Density Survey of Six Seyfert 1 Galaxies
NASA Astrophysics Data System (ADS)
Markowitz, A.
2002-05-01
By combining low-density RXTE long- and medium-term monitoring with high-density, short-term monitoring from XMM and Chandra long-looks, we have constructed X-ray fluctuation power spectral densities (PSDs) for six Seyfert 1 galaxies. These PSDs cover unprecedented dynamic ranges, continuously spanning up to or beyond 4 orders of magnitude in temporal frequency. The PSDs of four targets show significant flattening towards lower frequencies and bear remarkable similarity to X-ray Binary PSDs, strengthening the argument that similar emission processes occur in both types of compact accreting systems, spanning a factor of ~106-7 in luminosity and putative black hole mass. Assuming a linear mass-timescale relation, the resulting PSD break frequencies imply black hole masses which generally agree with reverberation-mapped mass estimates. If the geometric origin of the variability is close to the X-ray corona, then the physical timescales associated with thermal and acoustic disk variations may be relevant.
Level density parameters from excitation cross sections of isomeric states
NASA Astrophysics Data System (ADS)
Skakun, E. A.; Batij, V. G.
1992-03-01
Cross section ratios were measured for the production of the isomeric pairs99m,gRh,101m,gRh,102m,gRh,104m,gRh and108m,gIn in the (p,n)-reaction,107m,gIn and109m,gIn in the ( p, γ)-reaction over the energy range up to 9 MeV, and116m,gSb and118m,gSb in the (α, n)-reaction up to 24 MeV. The experimental results for these nuclei as well as for other isometric pairs excited in the ( p, n)-reaction were analysed in the frame of the statistical model for extracting the level density parameter values in the vicinity of closed nucleon shells. The level density parameter behaviour is discussed in the range of nuclear mass numbers under study.
Density fluctuation dynamics in a dissipative self-gravitating dilute gas revisited
NASA Astrophysics Data System (ADS)
Méndez, A. R.; García-Perciante, A. L.
2016-11-01
The analysis of the behavior of density fluctuations in a dissipative self gravitating gas in the linear regime is revisited. A factorization for the dispersion relation given by approximate roots is proposed, which is analogous to the one introduced in the case without gravitational field. The threshold for the onset of a gravitational instability, namely Jeans wavenumber, is found to be unaltered by the presence of thermal and viscous dissipation. However, the behavior of damped modes does not correspond to the usual Rayleigh-Brillouin spectrum when the gravitational field is taken into account. Additional to the usual central Rayleigh peak and Brillouin doublet, both corrected due to the presence of the field, non-Lorentizan terms are included in the structure factor. These terms are larger in the presence of the gravitational field and may lead in principle to relevant differences in the general properties of the spectrum. The possible mathematical origin of these modifications is briefly discussed.
Density fluctuations and topological structures in collective surface motion of microswimmers
NASA Astrophysics Data System (ADS)
Gao, Tong; Shelley, Michael
2014-11-01
Active matter that consists of self-propelled particles, such as bacterial suspensions and assays of self-driven biofilaments, can exhibit collective motions with large-scale complex flows and topological defect dynamics. Using a Doi-Onsager kinetic theory, we study suspensions of microswimmers confined to an air/liquid interface, and identify correlations between particle density fluctuations, defect structures, nematic order, and surface flows. When considering a free-standing liquid film where the microswimmers are distributed on the air/liquid interfaces, we capture hydrodynamic coupling of the two active surface, characterized by synchronization of motile disclination defects. We estimate the effective ``penetration distance'' between the two coupled surfaces through a linear stability analysis.
NASA Astrophysics Data System (ADS)
Phillips, Nicholas G.; Hu, B. L.
2000-10-01
We present calculations of the variance of fluctuations and of the mean of the energy momentum tensor of a massless scalar field for the Minkowski and Casimir vacua as a function of an intrinsic scale defined by a smeared field or by point separation. We point out that, contrary to prior claims, the ratio of variance to mean-squared being of the order unity is not necessarily a good criterion for measuring the invalidity of semiclassical gravity. For the Casimir topology we obtain expressions for the variance to mean-squared ratio as a function of the intrinsic scale (defined by a smeared field) compared to the extrinsic scale (defined by the separation of the plates, or the periodicity of space). Our results make it possible to identify the spatial extent where negative energy density prevails which could be useful for studying quantum field effects in worm holes and baby universes, and for examining the design feasibility of real-life ``time machines.'' For the Minkowski vacuum we find that the ratio of the variance to the mean-squared, calculated from the coincidence limit, is identical to the value of the Casimir case at the same limit for spatial point separation while identical to the value of a hot flat space result with a temporal point separation. We analyze the origin of divergences in the fluctuations of the energy density and discuss choices in formulating a procedure for their removal, thus raising new questions about the uniqueness and even the very meaning of regularization of the energy momentum tensor for quantum fields in curved or even flat spacetimes when spacetime is viewed as having an extended structure.
NASA Astrophysics Data System (ADS)
He, Lianyi
2016-10-01
We present a standard field theoretical derivation of the dynamic density and spin linear response functions of a dilute superfluid Fermi gas in the BCS-BEC crossover in both three and two dimensions. The derivation of the response functions is based on the elegant functional path integral approach which allows us to calculate the density-density and spin-spin correlation functions by introducing the external sources for the density and the spin density. Since the generating functional cannot be evaluated exactly, we consider two gapless approximations which ensure a gapless collective mode (Goldstone mode) in the superfluid state: the BCS-Leggett mean-field theory and the Gaussian-pair-fluctuation (GPF) theory. In the mean-field theory, our results of the response functions agree with the known results from the random phase approximation. We further consider the pair fluctuation effects and establish a theoretical framework for the dynamic responses within the GPF theory. We show that the GPF response theory naturally recovers three kinds of famous diagrammatic contributions: the Self-Energy contribution, the Aslamazov-Lakin contribution, and the Maki-Thompson contribution. We also show that unlike the equilibrium state, in evaluating the response functions, the linear (first-order) terms in the external sources as well as the induced order parameter perturbations should be treated carefully. In the superfluid state, there is an additional order parameter contribution which ensures that in the static and long wavelength limit, the density response function recovers the result of the compressibility (compressibility sum rule). We expect that the f-sum rule is manifested by the full number equation which includes the contribution from the Gaussian pair fluctuations. The dynamic density and spin response functions in the normal phase (above the superfluid critical temperature) are also derived within the Nozières-Schmitt-Rink (NSR) theory.
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.; Smith, S. A.; Tsuda, T.; Sato, T.; Fritts, D. C.
1990-01-01
Results are presented from a six-day campaign to observe velocity fluctuations in the lower atmosphere using the MU radar (Fukao et al., 1985) in Shigaraki, Japan in March, 1986. Consideration is given to the azimuthal anisotropy, the frequency spectra, the vertical profiles of energy density, and the momentum flux of the motion field. It is found that all of the observed azimuthal variations are probably caused by a gravity wave field whose parameters vary with time. The results show significant differences between the mean zonal and meridional frequency spectra and different profiles of mean energy density with height for different frequency bands and for zonal and meridional components.
NASA Astrophysics Data System (ADS)
Nishizawa, Takashi; Craig, D.; den Hartog, D. J.; Nornberg, M. D.
2016-10-01
Passive impurity spectroscopy is used to study high frequency ( 100 kHz) electron density and ion velocity fluctuations in the edge of MST reversed field pinch plasmas. When tearing modes are suppressed, stochastic transport is greatly reduced and microturbulence is anticipated to become important. Gyrokinetic simulations predict unstable trapped electron modes (TEM) in the edge region of these improved-confinement MST plasmas. Interferometry measurements reveal electron density fluctuations with wavenumbers, propagation direction, and a density-gradient threshold in good agreement with predictions for TEMs. These density fluctuations are also observed as emission fluctuations using a recently upgraded Ion Dynamics Spectrometer (IDS II) through edge passive C +2 measurements. The particle transport associated with TEMs will be evaluated directly by correlating the IDS-measured ion velocity and density fluctuations. The measurement is localized to the C +2 emission shell in the edge of the plasma, which is determined by a coronal charge-state balance model using ADAS. We used a large-throughput spectrometer originally developed for fast CHERS measurements and PMTs for light detection to achieve high time resolution. This work is supported by the US DOE.
Evaluating parasite densities and estimation of parameters in transmission systems.
Heinzmann, D; Torgerson, P R
2008-09-01
Mathematical modelling of parasite transmission systems can provide useful information about host parasite interactions and biology and parasite population dynamics. In addition good predictive models may assist in designing control programmes to reduce the burden of human and animal disease. Model building is only the first part of the process. These models then need to be confronted with data to obtain parameter estimates and the accuracy of these estimates has to be evaluated. Estimation of parasite densities is central to this. Parasite density estimates can include the proportion of hosts infected with parasites (prevalence) or estimates of the parasite biomass within the host population (abundance or intensity estimates). Parasite density estimation is often complicated by highly aggregated distributions of parasites within the hosts. This causes additional challenges when calculating transmission parameters. Using Echinococcus spp. as a model organism, this manuscript gives a brief overview of the types of descriptors of parasite densities, how to estimate them and on the use of these estimates in a transmission model.
Density-based penalty parameter optimization on C-SVM.
Liu, Yun; Lian, Jie; Bartolacci, Michael R; Zeng, Qing-An
2014-01-01
The support vector machine (SVM) is one of the most widely used approaches for data classification and regression. SVM achieves the largest distance between the positive and negative support vectors, which neglects the remote instances away from the SVM interface. In order to avoid a position change of the SVM interface as the result of an error system outlier, C-SVM was implemented to decrease the influences of the system's outliers. Traditional C-SVM holds a uniform parameter C for both positive and negative instances; however, according to the different number proportions and the data distribution, positive and negative instances should be set with different weights for the penalty parameter of the error terms. Therefore, in this paper, we propose density-based penalty parameter optimization of C-SVM. The experiential results indicated that our proposed algorithm has outstanding performance with respect to both precision and recall.
Density-Based Penalty Parameter Optimization on C-SVM
Liu, Yun; Lian, Jie; Bartolacci, Michael R.; Zeng, Qing-An
2014-01-01
The support vector machine (SVM) is one of the most widely used approaches for data classification and regression. SVM achieves the largest distance between the positive and negative support vectors, which neglects the remote instances away from the SVM interface. In order to avoid a position change of the SVM interface as the result of an error system outlier, C-SVM was implemented to decrease the influences of the system's outliers. Traditional C-SVM holds a uniform parameter C for both positive and negative instances; however, according to the different number proportions and the data distribution, positive and negative instances should be set with different weights for the penalty parameter of the error terms. Therefore, in this paper, we propose density-based penalty parameter optimization of C-SVM. The experiential results indicated that our proposed algorithm has outstanding performance with respect to both precision and recall. PMID:25114978
NASA Astrophysics Data System (ADS)
Bencze, P.; Illés-Almár, E.; Almár, I.
The study of the high resolution total neutral density measurements of the San Marco V satellite revealed also wave-like fluctuations of the density of amplitude increas- ing with height above a given height. The height at which the amplitude of these fluctuations begins to increase has been found to occur in the height range 300-500 km. Analysis of this phenomenon indicated that this height displays a diurnal varia- tion lower heights occurring by day. On the basis of this findings it is assumed that fluctuations of amplitude increasing with height found in the total neutral density are due to convective instability related to the quasi isothermal state of this part of the thermosphere. Under these conditions an infinitesimal disturbance is enough for the development of instability.
NASA Technical Reports Server (NTRS)
Clukey, Steven J.
1988-01-01
The high speed Dynamic Data Acquisition System (DDAS) is described which provides the capability for the simultaneous measurement of velocity, density, and total temperature fluctuations. The system of hardware and software is described in context of the wind tunnel environment. The DDAS replaces both a recording mechanism and a separate data processing system. The data acquisition and data reduction process has been combined within DDAS. DDAS receives input from hot wires and anemometers, amplifies and filters the signals with computer controlled modules, and converts the analog signals to digital with real-time simultaneous digitization followed by digital recording on disk or tape. Automatic acquisition (either from a computer link to an existing wind tunnel acquisition system, or from data acquisition facilities within DDAS) collects necessary calibration and environment data. The generation of hot wire sensitivities is done in DDAS, as is the application of sensitivities to the hot wire data to generate turbulence quantities. The presentation of the raw and processed data, in terms of root mean square values of velocity, density and temperature, and the processing of the spectral data is accomplished on demand in near-real-time- with DDAS. A comprehensive description of the interface to the DDAS and of the internal mechanisms will be prosented. A summary of operations relevant to the use of the DDAS will be provided.
NASA Astrophysics Data System (ADS)
Zhong, H.; Tan, Y.; Liu, Y. Q.; Xie, H. Q.; Gao, Z.
2016-11-01
A single-channel 3 mm interferometer has been developed for plasma density diagnostics in the Sino-UNIted Spherical Tokamak (SUNIST). The extremely compact microwave interferometer utilizes one corrugated feed horn antenna for both emitting and receiving the microwave. The beam path lies on the equatorial plane so the system would not suffer from beam path deflection problems due to the symmetry of the cross section. A focusing lens group and an oblique vacuum window are carefully designed to boost the signal to noise ratio, which allows this system to show good performance even with the small-diameter central column itself as a reflector, without a concave mirror. The whole system discards the reference leg for maximum compactness, which is particularly suitable for the small-sized tokamak. An auto-correcting algorithm is developed to calculate the phase evolution, and the result displays good phase stability of the whole system. The intermediate frequency is adjustable and can reach its full potential of 2 MHz for best temporal resolution. Multiple measurements during ohmic discharges proved the interferometer's capability to track typical density fluctuations in SUNIST, which enables this system to be utilized in the study of MHD activities.
Zhong, H; Tan, Y; Liu, Y Q; Xie, H Q; Gao, Z
2016-11-01
A single-channel 3 mm interferometer has been developed for plasma density diagnostics in the Sino-UNIted Spherical Tokamak (SUNIST). The extremely compact microwave interferometer utilizes one corrugated feed horn antenna for both emitting and receiving the microwave. The beam path lies on the equatorial plane so the system would not suffer from beam path deflection problems due to the symmetry of the cross section. A focusing lens group and an oblique vacuum window are carefully designed to boost the signal to noise ratio, which allows this system to show good performance even with the small-diameter central column itself as a reflector, without a concave mirror. The whole system discards the reference leg for maximum compactness, which is particularly suitable for the small-sized tokamak. An auto-correcting algorithm is developed to calculate the phase evolution, and the result displays good phase stability of the whole system. The intermediate frequency is adjustable and can reach its full potential of 2 MHz for best temporal resolution. Multiple measurements during ohmic discharges proved the interferometer's capability to track typical density fluctuations in SUNIST, which enables this system to be utilized in the study of MHD activities.
Yeo, Joonhyun
2009-11-01
We study a zero-dimensional version of the fluctuating nonlinear hydrodynamics (FNH) of supercooled liquids originally investigated by Das and Mazenko (DM) [Shankar P. Das and Gene F. Mazenko Phys. Rev. A 34, 2265 (1986)]. The time-dependent density-like and momentum-like variables are introduced with no spatial degrees of freedom in this toy model. The structure of nonlinearities takes the similar form to the original FNH, which allows one to study in a simpler setting the issues raised recently regarding the field theoretical approaches to glass forming liquids. We study the effects of density nonlinearities on the time evolution of correlation and response functions by developing field theoretic formulations in two different ways: first by following the original prescription of DM and then by constructing a dynamical action which possesses a linear time-reversal symmetry as proposed recently. We show explicitly that, at the one-loop order of the perturbation theory, the DM-type field theory does not support a sharp ergodic-nonergodic transition, while the other admits one. The simple nature of the toy model in the DM formulation allows us to develop numerical solutions to a complete set of coupled dynamical equations for the correlation and response functions at the one-loop order.
Temporal evolution of lower hybrid waves in the presence of ponderomotive density fluctuations
Karney, C.F.F.
1980-06-01
The propagation of lower hybrid waves in the presence of ponderomotive density density fluctuations is considered. The problem is treated in two dimensions and, in order to be able to correctly impose the boundary conditions, the waves are allowed to evolve in time. The fields are described by i upsilon/sub tau/ - ..integral.. upsilon/sub xi/d/sub zeta/ + upsilon/sub zeta zeta/ + upsilon//sup 2/ upsilon = 0 where upsilon is proportional to the electric field, tau to time, and zeta and xi measure distances across and along the lower hybrid ray. The behavior of the waves is investigated numerically. If the amplitude of the waves is large enough, the spectrum of the waves broadens and their parallel wavelength becomes shorter. The assumptions made in the formulation preclude the application of these results to the lower hybrid heating experiment on Alcator-A. Nevertheless, there are indications that the physics embodied in this problem are responsible for some of the results of that experiment.
Linear magnetoresistance in n-type silicon due to doping density fluctuations
Porter, Nicholas A.; Marrows, Christopher H.
2012-01-01
We report the observation of a large linear magnetoresistance in the ohmic regime in commonplace commercial n-type silicon wafer with a P dopant density of (1.4±0.1) ×1015 cm–3, and report measurements of it in the temperature range 30–200 K. It arises from the deformation of current paths, which causes a part of the Hall field to be detected at the voltage probes. In short, wide samples we found linear magnetoresistance as large as 4707% in an 8 tesla field at 35 K. Sample geometry effects like these are commonplace in commercial Hall sensors. However, we found that the effect persisted in long, thin samples where the macroscopic current flow should be uniform between the voltage probes: we observed a magnetoresistance of 445% under the same conditions as above. We interpret this result as arising due to spatial fluctuations in the donor density, in the spirit of the Herring model. PMID:22876340
Vukovic, M.; Harper, M.; Breun, R.; Wukitch, S.
1995-12-31
Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode converted kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.
Possibility of determination of the asymptotic level-density parameter
Kudyaev, G.A.; Ostapenko, Y.B.; Svirin, M.I.; Smirenkin, G.N.
1988-02-01
We investigate the sensitivity of the fissility of nuclei to the parameters of the density of excited levels and conclude that the nuclei in the region of Pb are most favorable for an experimental estimate of the asymptotic parameter a-italic-tilde = ..cap alpha..A. The mean value ..cap alpha.. = 0.086 +- 0.009 MeV/sup -1/ is found from analysis of the fission of seven nuclei from /sup 201/Tl to /sup 213/At. This value is in agreement with the phenomenological description of the energy dependence a(U) (..cap alpha.. = 0.093 MeV/sup -1/) and with the theoretical prediction ..cap alpha.. = 0.09 MeV/sup -1/ obtained for a Woods-Saxon potential.
Construct order parameters from the reduced density matrix spectra
Gu, Shi-Jian; Yu, Wing Chi; Lin, Hai-Qing
2013-09-15
In this paper, we try to establish a connection between a quantum information concept, i.e., the mutual information, and the conventional order parameter in condensed matter physics. We show that non-vanishing mutual information between two subsystems separated by a long distance means the existence of long-range orders in the system. By analyzing the spectra of the reduced density matrices that are used to calculate the mutual information, we show how to derive the local order operators that identify various ordered phases in condensed matter physics. -- Highlights: •Discussed the relation between long-range order and the mutual information (MI). •Pointed out how to check the existence of long-range order from MI. •Proposed a scheme to derive the diagonal and off-diagonal order parameter. •Gave three examples to show the effectiveness of the scheme.
White, A. E.; Schmitz, L.; Peebles, W. A.; Rhodes, T. L.; Carter, T. A.; McKee, G. R.; Shafer, M. W.; Staebler, G. M.; Burrell, K. H.; DeBoo, J. C.; Prater, R.
2010-02-15
New measurements show that long-wavelength (k{sub t}hetarho{sub s}<0.5) electron temperature fluctuations can play an important role in determining electron thermal transport in low-confinement mode (L-mode) tokamak plasmas. In neutral beam-heated L-mode tokamak plasmas, electron thermal transport and the amplitude of long-wavelength electron temperature fluctuations both increase in cases where local electron cyclotron heating (ECH) is used to modify the plasma profiles. In contrast, the amplitude of simultaneously measured long-wavelength density fluctuations does not significantly increase. Linear stability analysis indicates that the ratio of the trapped electron mode (TEM) to ion temperature gradient (ITG) mode growth rates increases in the cases with ECH. The increased importance of the TEM drive relative to the ITG mode drive in the cases with ECH may be associated with the increases in electron thermal transport and electron temperature fluctuations.
NASA Astrophysics Data System (ADS)
Nariyuki, Y.; Seough, J.
2015-12-01
It is well known that low-frequency Alfven waves are unstable to parametric instabilities, in which these waves are nonlinearly coupled with density fluctuations [e.g, Nariyuki+Hada, JGR, 2007 and references therein]. In solar wind plasmas, low-frequency fluctuations with non-zero cross-helicity are frequently observed [e.g., Bruno+Carbone, Living Rev. Solar Phys. (2013) and references therein]. When the absolute values of normalized cross helicities are close to the unity, the fluctuations may be composed of uni-directionally (anti-sunward) propagating Alfven waves. The derivative nonlinear Schrodinger equation (DNLS) has been known as the mode of modulational instabilities of unidirectional Alfven waves [Mio et al, JPSJ, 1976; Mjolhus, JPP, 1976]. In the DNLS, the density fluctuations are assumed to be the quasi-static state, which is determined according to the ponderomotive force of envelope-modulated Alfven waves. The DNLS was extended to include the obliquely propagating, compressional component of magnetic field by Mjolhus and Wyller (JPP, 1988). The kinetically modified DNLS (KDNLS) has also been discussed by many authors [Rogister, POF, 1971; Mjolhus and Wyller, Phys. Scr, 1986; JPP, 1988; Spangler, POF B, 1989; 1990; Medvedev+Diamond, POP, 1996; Nariyuki et al, POP, 2013]. On the other hand, ion acoustic modes [Hada, 1993], large scale inhomogeneity of plasmas [Buti et al, APJ, 1999; Nariyuki, POP, 2015] and random density fluctuations [Ruderman, POP, 2002] can also affect nonlinear evolution of Alfven waves. At the present time, combined effects of these effects are not fully understood. In this presentation, we discuss two models: one of them is the model including both ion kinetic effects and ion acoustic mode and another is the model including finite thermal effects and random density fluctuations. In the former case, ion kinetic effects on both longitudinal [Nariyuki+Hada, JPSJ, 2007] and transverse modulational instabilities are discussed, while the
Density profiles of supernova matter and determination of neutrino parameters
Chiu, S.-H.
2007-08-15
The flavor conversion of supernova neutrinos can lead to observable signatures related to the unknown neutrino parameters. As one of the determinants in dictating the efficiency of resonant flavor conversion, the local density profile near the Mikheyev-Smirnov-Wolfenstein (MSW) resonance in a supernova environment is, however, not so well understood. In this analysis, variable power-law functions are adopted to represent the independent local density profiles near the locations of resonance. It is shown that the uncertain matter density profile in a supernova, the possible neutrino mass hierarchies, and the undetermined 1-3 mixing angle would result in six distinct scenarios in terms of the survival probabilities of {nu}{sub e} and {nu}{sub e}. The feasibility of probing the undetermined neutrino mass hierarchy and the 1-3 mixing angle with the supernova neutrinos is then examined using several proposed experimental observables. Given the incomplete knowledge of the supernova matter profile, the analysis is further expanded to incorporate the Earth matter effect. The possible impact due to the choice of models, which differ in the average energy and in the luminosity of neutrinos, is also addressed in the analysis.
Zalloni, Enrica; de Luis, Martin; Campelo, Filipe; Novak, Klemen; De Micco, Veronica; Di Filippo, Alfredo; Vieira, Joana; Nabais, Cristina; Rozas, Vicente; Battipaglia, Giovanna
2016-01-01
Tree rings provide information about the climatic conditions during the growing season by recording them in different anatomical features, such as intra-annual density fluctuations (IADFs). IADFs are intra-annual changes of wood density appearing as latewood-like cells within earlywood, or earlywood-like cells within latewood. The occurrence of IADFs is dependent on the age and size of the tree, and it is triggered by climatic drivers. The variations of IADF frequency of different species and their dependence on climate across a wide geographical range have still to be explored. The objective of this study is to investigate the effect of age, tree-ring width and climate on IADF formation and frequency at a regional scale across the Mediterranean Basin in Pinus halepensis Mill., Pinus pinaster Ait., and Pinus pinea L. The analyzed tree-ring network was composed of P. pinea trees growing at 10 sites (2 in Italy, 4 in Spain, and 4 in Portugal), P. pinaster from 19 sites (2 in Italy, 13 in Spain, and 4 in Portugal), and P. halepensis from 38 sites in Spain. The correlations between IADF frequency and monthly minimum, mean and maximum temperatures, as well as between IADF frequency and total precipitation, were analyzed. A significant negative relationship between IADF frequency and tree-ring age was found for the three Mediterranean pines. Moreover, IADFs were more frequent in wider rings than in narrower ones, although the widest rings showed a reduced IADF frequency. Wet conditions during late summer/early autumn triggered the formation of IADFs in the three species. Our results suggest the existence of a common climatic driver for the formation of IADFs in Mediterranean pines, highlighting the potential use of IADF frequency as a proxy for climate reconstructions with geographical resolution.
Zalloni, Enrica; de Luis, Martin; Campelo, Filipe; Novak, Klemen; De Micco, Veronica; Di Filippo, Alfredo; Vieira, Joana; Nabais, Cristina; Rozas, Vicente; Battipaglia, Giovanna
2016-01-01
Tree rings provide information about the climatic conditions during the growing season by recording them in different anatomical features, such as intra-annual density fluctuations (IADFs). IADFs are intra-annual changes of wood density appearing as latewood-like cells within earlywood, or earlywood-like cells within latewood. The occurrence of IADFs is dependent on the age and size of the tree, and it is triggered by climatic drivers. The variations of IADF frequency of different species and their dependence on climate across a wide geographical range have still to be explored. The objective of this study is to investigate the effect of age, tree-ring width and climate on IADF formation and frequency at a regional scale across the Mediterranean Basin in Pinus halepensis Mill., Pinus pinaster Ait., and Pinus pinea L. The analyzed tree-ring network was composed of P. pinea trees growing at 10 sites (2 in Italy, 4 in Spain, and 4 in Portugal), P. pinaster from 19 sites (2 in Italy, 13 in Spain, and 4 in Portugal), and P. halepensis from 38 sites in Spain. The correlations between IADF frequency and monthly minimum, mean and maximum temperatures, as well as between IADF frequency and total precipitation, were analyzed. A significant negative relationship between IADF frequency and tree-ring age was found for the three Mediterranean pines. Moreover, IADFs were more frequent in wider rings than in narrower ones, although the widest rings showed a reduced IADF frequency. Wet conditions during late summer/early autumn triggered the formation of IADFs in the three species. Our results suggest the existence of a common climatic driver for the formation of IADFs in Mediterranean pines, highlighting the potential use of IADF frequency as a proxy for climate reconstructions with geographical resolution. PMID:27200052
The THz Spectrum of Density Fluctuations of Water: The Viscoelastic Regime
Cunsolo, Alessandro
2015-01-01
Relevant advances in the knowledge of the water dynamics at mesoscopic scales are reviewed, while mainly focusing on the contribution provided by high resolution inelastic X-ray scattering (IXS). In particular it is discussed how the use of IXS has improved our understanding of viscoelastic properties of water at THz frequencies. This specifically involves some solid-like features such as the onset of shear wave propagation, a sound velocity surprisingly similar to the one of ice, and an anomalously low sound absorption coefficient. All these properties can be explained by assuming the coupling of THz density fluctuations with a structural relaxation process connected to the breaking and forming of hydrogen bonds (HBs). This review also includes more recent IXS results demonstrating that, upon approaching supercritical conditions, relaxation phenomena in water gradually lose their structural character becoming essentially collisional in character. Furthermore, GHz spectroscopy results on supercooled water, suggesting the occurrence of a structural arrest, are discussed. An overview of the new opportunities offered by next generation IXS spectrometers finally concludes this review.
NASA Astrophysics Data System (ADS)
Pradhan, Prabhakar; Damania, Dhwanil; Joshi, Hrushikesh M.; Turzhitsky, Vladimir; Subramanian, Hariharan; Roy, Hemant K.; Taflove, Allen; Dravid, Vinayak P.; Backman, Vadim
2011-04-01
Most cancers are curable if they are diagnosed and treated at an early stage. Recent studies suggest that nanoarchitectural changes occur within cells during early carcinogenesis and that such changes precede microscopically evident tissue alterations. It follows that the ability to comprehensively interrogate cell nanoarchitecture (e.g., macromolecular complexes, DNA, RNA, proteins and lipid membranes) could be critical to the diagnosis of early carcinogenesis. We present a study of the nanoscale mass-density fluctuations of biological tissues by quantifying their degree of disorder at the nanoscale. Transmission electron microscopy images of human tissues are used to construct corresponding effective disordered optical lattices. The properties of nanoscale disorder are then studied by statistical analysis of the inverse participation ratio (IPR) of the spatially localized eigenfunctions of these optical lattices at the nanoscale. Our results show an increase in the disorder of human colonic epithelial cells in subjects harboring early stages of colon neoplasia. Furthermore, our findings strongly suggest that increased nanoscale disorder correlates with the degree of tumorigenicity. Therefore, the IPR technique provides a practicable tool for the detection of nanoarchitectural alterations in the earliest stages of carcinogenesis. Potential applications of the technique for early cancer screening and detection are also discussed. Originally submitted for the special focus issue on physical oncology.
NASA Astrophysics Data System (ADS)
Fioretto, D.; Comez, L.; Socino, G.; Verdini, L.; Corezzi, S.; Rolla, P. A.
1999-02-01
Brillouin light scattering is used for studying the spectrum of density fluctuations of the glass-forming epoxy resin diglycidyl ether of bisphenol-A. Spectra at different temperatures ranging from the glassy to the liquid phase are obtained from a direct subtraction of depolarized from polarized spectra. In addition to the structural relaxation, evidence is given of a fast secondary relaxation process, which affects Brillouin spectra also at temperatures lower than that of the glass transition Tg. For the elaboration of isotropic spectra, we exploit the possibility of using the same relaxation function gained from dielectric spectra taken from the same sample. The temperature behavior of the relaxation strength shows the existence of an onset for the structural relaxation, located at a temperature about 93 K higher than Tg, consistent with the results of previous dielectric spectroscopy and depolarized light scattering investigations. The role of secondary relaxations of intramolecular nature in the mode-coupling analysis of real glass formers is also discussed.
COSMOLOGICAL DENSITY FLUCTUATIONS ON 100 Mpc SCALES AND THEIR ISW EFFECT
Papai, Peter; Szapudi, Istvan
2010-12-20
We measure the matter probability distribution function (PDF) via counts in cells in a volume-limited subsample of the Sloan Digital Sky Survey Luminous Red Galaxy Catalog on scales from 30 h {sup -1} Mpc to 150 h {sup -1} Mpc and estimate the linear Integrated Sachs-Wolfe effect produced by supervoids and superclusters in the tail of the PDF. We characterize the PDF by the variance, S{sub 3}, and S{sub 4}, and study in simulations the systematic effects due to finite volume, survey shape, and redshift distortion. We compare our measurement to the prediction of {Lambda}CDM with linear bias and find a good agreement. We use the moments to approximate the tail of the PDF with analytic functions. A simple Gaussian model for the superstructures appears to be consistent with the claim by Granett et al. that density fluctuations on 100 h {sup -1} Mpc scales produce hot and cold spots with {Delta}T {approx} 10 {mu}K on the cosmic microwave background.
Minimum of the order parameter fluctuations of seismicity before major earthquakes in Japan.
Sarlis, Nicholas V; Skordas, Efthimios S; Varotsos, Panayiotis A; Nagao, Toshiyasu; Kamogawa, Masashi; Tanaka, Haruo; Uyeda, Seiya
2013-08-20
It has been shown that some dynamic features hidden in the time series of complex systems can be uncovered if we analyze them in a time domain called natural time χ. The order parameter of seismicity introduced in this time domain is the variance of χ weighted for normalized energy of each earthquake. Here, we analyze the Japan seismic catalog in natural time from January 1, 1984 to March 11, 2011, the day of the M9 Tohoku earthquake, by considering a sliding natural time window of fixed length comprised of the number of events that would occur in a few months. We find that the fluctuations of the order parameter of seismicity exhibit distinct minima a few months before all of the shallow earthquakes of magnitude 7.6 or larger that occurred during this 27-y period in the Japanese area. Among the minima, the minimum before the M9 Tohoku earthquake was the deepest. It appears that there are two kinds of minima, namely precursory and nonprecursory, to large earthquakes.
2015-01-01
Kirkwood-Buff or Fluctuation Solution Theory can be used to provide experimental pair fluctuations, and/or integrals over the pair distribution functions, from experimental thermodynamic data on liquid mixtures. Here, this type of approach is used to provide triplet and quadruplet fluctuations, and the corresponding integrals over the triplet and quadruplet distribution functions, in a purely thermodynamic manner that avoids the use of structure factors. The approach is then applied to binary mixtures of water + methanol and benzene + methanol over the full composition range under ambient conditions. The observed correlations between the different species vary significantly with composition. The magnitude of the fluctuations and integrals appears to increase as the number of the most polar molecule involved in the fluctuation or integral also increases. A simple physical picture of the fluctuations is provided to help rationalize some of these variations. PMID:25747091
Ploetz, Elizabeth A.; Smith, Paul E.
2015-03-07
Kirkwood-Buff or Fluctuation Solution Theory can be used to provide experimental pair fluctuations, and/or integrals over the pair distribution functions, from experimental thermodynamic data on liquid mixtures. Here, this type of approach is used to provide triplet and quadruplet fluctuations, and the corresponding integrals over the triplet and quadruplet distribution functions, in a purely thermodynamic manner that avoids the use of structure factors. The approach is then applied to binary mixtures of water + methanol and benzene + methanol over the full composition range under ambient conditions. The observed correlations between the different species vary significantly with composition. The magnitude of the fluctuations and integrals appears to increase as the number of the most polar molecule involved in the fluctuation or integral also increases. A simple physical picture of the fluctuations is provided to help rationalize some of these variations.
Lande, Russell; Engen, Steinar; Saether, Bernt-Erik
2009-06-12
The evolution of population dynamics in a stochastic environment is analysed under a general form of density-dependence with genetic variation in r and K, the intrinsic rate of increase and carrying capacity in the average environment, and in sigma(e)(2), the environmental variance of population growth rate. The continuous-time model assumes a large population size and a stationary distribution of environments with no autocorrelation. For a given population density, N, and genotype frequency, p, the expected selection gradient is always towards an increased population growth rate, and the expected fitness of a genotype is its Malthusian fitness in the average environment minus the covariance of its growth rate with that of the population. Long-term evolution maximizes the expected value of the density-dependence function, averaged over the stationary distribution of N. In the theta-logistic model, where density dependence of population growth is a function of N(theta), long-term evolution maximizes E[N(theta)]=[1-sigma(e)(2)/(2r)]K(theta). While sigma(e)(2) is always selected to decrease, r and K are always selected to increase, implying a genetic trade-off among them. By contrast, given the other parameters, theta has an intermediate optimum between 1.781 and 2 corresponding to the limits of high or low stochasticity.
NASA Technical Reports Server (NTRS)
Lee, M. C.; Kuo, S. P.
1985-01-01
The physical mechanism of thermal filamentation instability of radio waves whose frequencies can be as low as in the VLF band and as high as in the SHF band are investigated. This instability can excite large-scale magnetic and plasma density fluctuations simultaneously in the ionosphere and magnetosphere. Relevant experiments are reviewed in terms of this instability and other mechanisms.
Identification of craters on Moon using Crater Density Parameter
NASA Astrophysics Data System (ADS)
Vandana, Vandana
2016-07-01
Lunar craters are the most noticeable features on the face of the moon. They take up 40.96% of the lunar surface and, their accumulated area is approximately three times as much as the lunar surface area. There are many myths about the moon. Some says moon is made of cheese. The moon and the sun chase each other across the sky etc. but scientifically the moon are closest and are only natural satellite of earth. The orbit plane of the moon is tilted by 5° and orbit period around the earth is 27-3 days. There are two eclipse i.e. lunar eclipse and solar eclipse which always comes in pair. Moon surface has 3 parts i.e. highland, Maria, and crater. For crater diagnostic crater density parameter is one of the means for measuring distance can be easily identity the density between two craters. Crater size frequency distribution (CSFD) is being computed for lunar surface using TMC and MiniSAR image data and hence, also the age for the selected test sites of mars is also determined. The GIS-based program uses the density and orientation of individual craters within LCCs (as vector points) to identify potential source craters through a series of cluster identification and ejection modeling analyses. JMars software is also recommended and operated only the time when connected with server but work can be done in Arc GIS with the help of Arc Objects and Model Builder. The study plays a vital role to determine the lunar surface based on crater (shape, size and density) and exploring affected craters on the basis of height, weight and velocity. Keywords: Moon; Crater; MiniSAR.
Lehners, Jean-Luc; Steinhardt, Paul J.
2008-03-15
We analyze the non-Gaussian density perturbations generated in ekpyrotic/cyclic models based on heterotic M theory. In this picture, two scalar fields produce nearly scale-invariant entropic perturbations during an ekpyrotic phase that are converted into curvature modes after the ekpyrotic phase is complete and just before the big bang. Both intrinsic nonlinearity in the entropy perturbation and the conversion process contribute to non-Gaussianity. The range of the non-Gaussianity parameter f{sub NL} depends on how gradual the conversion process is and the steepness of the scalar field potential during the ekpyrotic phase. Although a wider range is possible, in principle, natural values of the ekpyrotic parameters combined with a gradual conversion process lead to values of -50 < or approx. f{sub NL} < or approx. +200, typically much greater than slow-roll inflation but within the current observational bounds.
Foroutan, G. R.; Robinson, P. A.; Sobhanian, S.; Moslehi-Fard, M.; Li, B.; Cairns, I. H.
2007-01-15
Gas-dynamic theory is generalized to incorporate the effects of beam-driven Langmuir waves scattering off ambient density fluctuations, and the consequent effects on the propagation of a cloud of hot electrons in an inhomogeneous plasma. Assuming Langmuir scattering as the limit of nonlinear three-wave interactions with fluctuations that are weak, low-frequency, long-wavelength ion-sound waves, the net effect of scattering is equivalent to effective damping of the Langmuir waves. Under the assumption of self-similarity in the evolution of the beam and Langmuir wave distribution functions, gas-dynamic theory shows that the effects of Langmuir scattering on the beam distribution are equivalent to a perturbation in the injection profile of the beam. Analytical expressions are obtained for the height of the plateau of the beam distribution function, wave spectral number density, total wave and particle energy density, and the beam number density. The main results of gas-dynamic theory are then compared with simulation results from numerical solutions of quasilinear equations. The relaxation of the beam in velocity space is retarded in the presence of density fluctuations and the magnitude of the upper velocity boundary is less than that in the absence of fluctuations. There are four different regimes for the height of the plateau, corresponding to different stages of relaxation of the beam in velocity space. Moreover, Langmuir scattering results in transfer of electrons from moderate velocity to low velocity; this effect produces an enhancement in the beam number density at small distances near the injection site and a corresponding decrease at large distances. There are sharp decreases in the profiles of the beam and total wave energy densities, which are related to dissipation of energy at large phase velocities. Due to a slower velocity space diffusion of the beam distribution in the presence of scattering effects, the spatial width of the beam is reduced while its
Battipaglia, Giovanna; DE Micco, Veronica; Brand, Willi A; Saurer, Matthias; Aronne, Giovanna; Linke, Petra; Cherubini, Paolo
2014-02-01
Erica arborea (L) is a widespread Mediterranean species, able to cope with water stress and colonize semiarid environments. The eco-physiological plasticity of this species was evaluated by studying plants growing at two sites with different soil moistures on the island of Elba (Italy), through dendrochronological, wood-anatomical analyses and stable isotopes measurements. Intra-annual density fluctuations (IADFs) were abundant in tree rings, and were identified as the key parameter to understand site-specific plant responses to water stress. Our findings showed that the formation of IADFs is mainly related to the high temperature, precipitation patterns and probably to soil water availability, which differs at the selected study sites. The recorded increase in the (13) C-derived intrinsic water use efficiency at the IADFs level was linked to reduced water loss rather than to increasing C assimilation. The variation in vessel size and the different absolute values of δ(18) O among trees growing at the two study sites underlined possible differences in stomatal control of water loss and possible differences in sources of water uptake. This approach not only helped monitor seasonal environmental differences through tree-ring width, but also added valuable information on E. arborea responses to drought and their ecological implications for Mediterranean vegetation dynamics.
Observation of magnetic fluctuations and rapid density decay of magnetospheric plasma in Ring Trap 1
Saitoh, H.; Yoshida, Z.; Morikawa, J.; Yano, Y.; Mikami, H.; Kasaoka, N.; Sakamoto, W.
2012-06-15
The Ring Trap 1 device, a magnetospheric configuration generated by a levitated dipole field magnet, has created high-{beta} (local {beta} {approx} 70%) plasma by using electron cyclotron resonance heating (ECH). When a large population of energetic electrons is generated at low neutral gas pressure operation, high frequency magnetic fluctuations are observed. When the fluctuations are strongly excited, rapid loss of plasma was simultaneously observed especially in a quiet decay phase after the ECH microwave power is turned off. Although the plasma is confined in a strongly inhomogeneous dipole field configuration, the frequency spectra of the fluctuations have sharp frequency peaks, implying spatially localized sources of the fluctuations. The fluctuations are stabilized by decreasing the hot electron component below approximately 40%, realizing stable high-{beta} confinement.
NASA Technical Reports Server (NTRS)
Panda, Jayanta; Seasholtz, Richard G.
2003-01-01
Noise sources in high-speed jets were identified by directly correlating flow density fluctuation (cause) to far-field sound pressure fluctuation (effect). The experimental study was performed in a nozzle facility at the NASA Glenn Research Center in support of NASA s initiative to reduce the noise emitted by commercial airplanes. Previous efforts to use this correlation method have failed because the tools for measuring jet turbulence were intrusive. In the present experiment, a molecular Rayleigh-scattering technique was used that depended on laser light scattering by gas molecules in air. The technique allowed accurate measurement of air density fluctuations from different points in the plume. The study was conducted in shock-free, unheated jets of Mach numbers 0.95, 1.4, and 1.8. The turbulent motion, as evident from density fluctuation spectra was remarkably similar in all three jets, whereas the noise sources were significantly different. The correlation study was conducted by keeping a microphone at a fixed location (at the peak noise emission angle of 30 to the jet axis and 50 nozzle diameters away) while moving the laser probe volume from point to point in the flow. The following figure shows maps of the nondimensional coherence value measured at different Strouhal frequencies ([frequency diameter]/jet speed) in the supersonic Mach 1.8 and subsonic Mach 0.95 jets. The higher the coherence, the stronger the source was.
Fitting of bone mineral density with consideration of anthropometric parameters
Short, D. F.; Zemel, B. S.; Gilsanz, V.; Kalkwarf, H. J.; Lappe, J. M.; Mahboubi, S.; Oberfield, S. E.; Shepherd, J. A.; Winer, K. K.
2010-01-01
Summary A new model describing normal values of bone mineral density in children has been evaluated, which includes not only the traditional parameters of age, gender, and race, but also weight, height, percent body fat, and sexual maturity. This model may constitute a better comparative norm for a specific child with given anthropometric values. Introduction Previous descriptions of children's bone mineral density (BMD) by age have focused on segmenting diverse populations by race and gender without adjusting for anthropometric variables or have included the effects of anthropometric variables over a relatively homogeneous population. Methods Multivariate semi-metric smoothing (MS2) provides a way to describe a diverse population using a model that includes multiple effects and their interactions while producing a result that can be smoothed with respect to age in order to provide connected percentiles. We applied MS2 to spine BMD data from the Bone Mineral Density in Childhood Study to evaluate which of gender, race, age, height, weight, percent body fat, and sexual maturity explain variations in the population's BMD values. By balancing high adjusted R2 values and low mean square errors with clinical needs, a model using age, gender, race, weight, and percent body fat is proposed and examined. Results This model provides narrower distributions and slight shifts of BMD values compared to the traditional model, which includes only age, gender, and race. Thus, the proposed model might constitute a better comparative standard for a specific child with given anthropometric values and should be less dependent on the anthropometric characteristics of the cohort used to devise the model. Conclusions The inclusion of multiple explanatory variables in the model, while creating smooth output curves, makes the MS2 method attractive in modeling practically sized data sets. The clinical use of this model by the bone research community has yet to be fully established. PMID
NASA Technical Reports Server (NTRS)
Asenov, Asen; Kaya, S.; Davies, J. H.; Saini, S.
2000-01-01
We use the density gradient (DG) simulation approach to study, in 3D, the effect of local oxide thickness fluctuations on the threshold voltage of decanano MOSFETs in a statistical manner. A description of the reconstruction procedure for the random 2D surfaces representing the 'atomistic' Si-SiO2 interface variations is presented. The procedure is based on power spectrum synthesis in the Fourier domain and can include either Gaussian or exponential spectra. The simulations show that threshold voltage variations induced by oxide thickness fluctuation become significant when the gate length of the devices become comparable to the correlation length of the fluctuations. The extent of quantum corrections in the simulations with respect to the classical case and the dependence of threshold variations on the oxide thickness are examined.
NASA Astrophysics Data System (ADS)
Nagayama, Yoshio; Yamaguchi, Soichiro; Tsuchiya, Hayato; Kuwahara, Daisuke; LHD Experimental Team
2016-10-01
Visualization of local electron density fluctuations will be very useful to study the physics of confinement and instabilities in fusion plasma. In the Large Helical Device (LHD), the O-mode microwave imaging reflectometry (O-MIR) has been intensively developed in order to visualize the electron density fluctuations. The frequency is 26 - 34 GHz. This corresponds to the electron density of 0.8 - 1.5 × 1019 m-3. The plasma is illuminated by the Gaussian beam with four frequencies. The imaging optics make a plasma image onto the newly developed 2D (8 × 8) Horn-antenna Millimeter-wave Imaging Device (HMID). In HMID, the signal wave that is accumulated by the horn antenna is transduced to the micro-strip line by using the finline transducer. The signal wave is mixed by the double balanced mixer with the local wave that is delivered by cables. By using O-MIR, electron density fluctuations are measured at the H-mode edge and the ITB layer in LHD. This work is supported by NIFS/NINS under the project of Formation of International Scientific Base and Network, by the NIFS LHD project, by KAKENHI, and by IMS.
Klisz, Marcin; Koprowski, Marcin; Ukalska, Joanna; Nabais, Cristina
2016-01-01
Intra-annual density fluctuations (IADFs) can imprint environmental conditions within the growing season and most of the research on IADFs has been focused on their climatic signal. However, to our knowledge, the genetic influence on the frequency and type of IADFs has not been evaluated. To understand if the genotype can affect the formation of IADFs we have used a common garden experiment using eight families of Larix decidua established in two neighboring forest stands in northern Poland. Four types of IADFs were identified using X-ray density profiles: latewood-like cells within earlywood (IADF-type E), latewood-like cells in the transition from early- to latewood (IADF type E+), earlywood-like cells within latewood (IADF-type L), and earlywood-like cells in the border zone between the previous and present annual ring (IADF-type L+). The influence of explanatory variables i.e., families, sites, and years on identified density fluctuations was analyzed using generalized estimating equations (GEE). We hypothesized that trees from different families will differ in terms of frequency and type of IADFs because each family will react to precipitation and temperature in a different way, depending on the origin of those trees. The most frequent fluctuation was E+ and L types on both sites. The most important factors in the formation of IADFs were the site and year, the last one reflecting the variable climatic conditions, with no significant effect of the family. However, the relation between the formation of IADFs and selected climate parameters was different between families. Although, our results did not give a significant effect of the genotype on the formation of IADFs, the different sensitivity to climatic parameters among different families indicate that there is a genetic influence. PMID:27242883
Karunaweera, Sadish
2015-01-01
Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined. PMID:25637990
Ploetz, Elizabeth A.; Karunaweera, Sadish; Smith, Paul E.
2015-01-28
Fluctuation solution theory has provided an alternative view of many liquid mixture properties in terms of particle number fluctuations. The particle number fluctuations can also be related to integrals of the corresponding two body distribution functions between molecular pairs in order to provide a more physical picture of solution behavior and molecule affinities. Here, we extend this type of approach to provide expressions for higher order triplet and quadruplet fluctuations, and thereby integrals over the corresponding distribution functions, all of which can be obtained from available experimental thermodynamic data. The fluctuations and integrals are then determined using the International Association for the Properties of Water and Steam Formulation 1995 (IAPWS-95) equation of state for the liquid phase of pure water. The results indicate small, but significant, deviations from a Gaussian distribution for the molecules in this system. The pressure and temperature dependence of the fluctuations and integrals, as well as the limiting behavior as one approaches both the triple point and the critical point, are also examined.
Density Fluctuation measurement with Upgraded FIR System on the HSX Stellarator
NASA Astrophysics Data System (ADS)
Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Likin, K. M.; Talmadge, J. N.
2016-10-01
Going forward, a primary physics goal for HSX is to study configuration optimization for reducing turbulence which requires measurement of turbulence with kyρs up to 1. For characteristic HSX parameters (Te 200 eV at r/a 0.5 where the density gradient peaks), this condition corresponds to kyup to 7 cm-1. To accommodate this goal, the 9-chord HSX interferometer/far-forward scattering system (k<2 cm-1) will be upgraded to measure density turbulence at higher k. The existing source (4 mW, 288 GHz) employing frequency modulation will be replaced with two high power (30 mW each, 320 GHz), solid-state sources with fixed frequency offset 4 MHz. This will permit true heterodyne detection, thereby realizing faster measurement time response, increased bandwidth and reduced noise. High power sources and high sensitivity planar-diode mixers will allow us to reduce the aperture of the receiver optics to a few mm thereby increasing the maximum wavenumber to k 15 cm-1. Reconfiguring the interferometer system into a finite-angle collective scattering arrangement is also planned as it will increase the measured k-spectrum up to 18 cm-1 with some spatial resolution (core or edge). Supported by USDOE Grants DE-FG03-01ER54615 and DE-FG02-93ER54222.
Three-dimensional structure of electron density fluctuations in the Hall thruster plasma: ExB mode
Tsikata, S.; Honore, C.; Gresillon, D. M.; Lemoine, N.
2010-11-15
Collective scattering measurements have been conducted on the plasma of a Hall thruster, in which the electron density fluctuations are fully characterized by the dynamic form factor. The dynamic form factor amplitude distribution has been measured depending on the k-vector spatial and frequency components at different locations. Fluctuations are seen as propagating waves. The largest amplitude mode propagates nearly along the cross-field direction but at a phase velocity that is much smaller than the ExB drift velocity. Refined directional analysis of this largest amplitude mode shows a thin angular emission diagram with a mean direction that is not strictly along the ExB direction but at small angles near it. The deviation is oriented toward the anode in the (E,ExB) plane and toward the exterior of the thruster channel in the (B,ExB) plane. The density fluctuation rate is on the order of 1%. These experimentally determined directional fluctuation characteristics are discussed with regard to the linear kinetic theory model and particle-in-cell simulation results.
NASA Astrophysics Data System (ADS)
Burmistrov, I. S.; Gornyi, I. V.; Mirlin, A. D.
2016-05-01
We develop a theory of the local density of states (LDOS) of disordered superconductors, employing the nonlinear sigma-model formalism and the renormalization-group framework. The theory takes into account the interplay of disorder and interaction couplings in all channels, treating the systems with short-range and Coulomb interactions on equal footing. We explore two-dimensional systems that would be Anderson insulators in the absence of interaction and two- or three-dimensional systems that undergo an Anderson transition in the absence of interaction. We evaluate both the average tunneling density of states and its mesoscopic fluctuations which are related to the LDOS multifractality in normal disordered systems. The obtained average LDOS shows a pronounced depletion around the Fermi energy, both in the metallic phase (i.e., above the superconducting critical temperature Tc) and in the insulating phase near the superconductor-insulator transition (SIT). The fluctuations of the LDOS are found to be particularly strong for the case of short-range interactions, especially, in the regime when Tc is enhanced by Anderson localization. On the other hand, the long-range Coulomb repulsion reduces the mesoscopic LDOS fluctuations. However, also in a model with Coulomb interaction, the fluctuations become strong when the systems approach the SIT.
The effect of plasma fluctuations on parallel transport parameters in the SOL
NASA Astrophysics Data System (ADS)
Havlíčková, E.; Fundamenski, W.; Naulin, V.; Nielsen, A. H.; Wiesen, S.; Horacek, J.; Seidl, J.
2011-08-01
The effect of plasma fluctuations due to turbulence at the outboard midplane on parallel transport properties is investigated. Time-dependent fluctuating signals at different radial locations are used to study the effect of signal statistics. Further, a computational analysis of parallel transport in the scrape-off layer (SOL) taking into account these fluctuations is presented. Plasma transport in the SOL along the magnetic field between two targets is calculated by a one-dimensional fluid code in order to estimate the response to transient conditions along the SOL and the attention is given to a comparison of steady-state and time-dependent modelling.
Improving hot region prediction by parameter optimization of density clustering in PPI.
Hu, Jing; Zhang, Xiaolong
2016-11-01
This paper proposed an optimized algorithm which combines density clustering of parameter selection with feature-based classification for hot region prediction. First, all the residues are classified by SVM to remove non-hot spot residues, then density clustering of parameter selection is used to find hot regions. In the density clustering, this paper studies how to select input parameters. There are two parameters radius and density in density-based incremental clustering. We firstly fix density and enumerate radius to find a pair of parameters which leads to maximum number of clusters, and then we fix radius and enumerate density to find another pair of parameters which leads to maximum number of clusters. Experiment results show that the proposed method using both two pairs of parameters provides better prediction performance than the other method, and compare these two predictive results, the result by fixing radius and enumerating density have slightly higher prediction accuracy than that by fixing density and enumerating radius.
NASA Astrophysics Data System (ADS)
Lehmacher, Gerald; Larsen, Miguel; Collins, Richard; Bilen, Sven; Croskey, Charles; Mitchell, John; Luebken, Franz-Josef; Rapp, Markus
In February 2009, a rocket experiment was launched from Alaska entitled: Where is the tur-bopause? Instabilities, generation and development of turbulence in the 100-km region. The salvo of four rockets obtained in situ wind and temperature profiles, neutral and plasma fluctu-ations, and wave and tidal activity from ground based lidar, radar, and other instrumentation. Among the goals are comparisons of turbulent energy dissipation rates measured by spectral analysis and from chemical trail expansion rates. Based on trimethyl aluminum trail diffusion we identified regions of mixing around 90 km, 95 km, and also above 100 km. The lower re-gion coincided with layers of density fluctuations, while the upper region was characterized by strong wind shear and kilometer-size density structures in the lower thermosphere. Rayleigh and sodium lidar observed a dominant 4-hour wave motion in the upper mesosphere.
NASA Technical Reports Server (NTRS)
Clukey, Steven J.; Jones, Gregory S.; Stainback, P. Calvin
1988-01-01
The use of a high-speed Dynamic Data Acquisition System (DDAS) to measure simultaneously velocity, density, and total temperature fluctuations is described. The DDAS is used to automate the acquisition of hot-wire calibration data. The data acquisition, data handling, and data reporting techiques used by DDAS are described. Sample data are used to compare results obtained with the DDAS with those obtained from the FM tape and post-test digitization method.
Order parameter fluctuation and ordering competition in Ba1 -xKxFe2As2
NASA Astrophysics Data System (ADS)
Wang, Jing; Liu, Guo-Zhu; Efremov, Dmitry V.; van den Brink, Jeroen
2017-01-01
The competition among superconductivity, stripe-type magnetic order, and a new type of C4 symmetric magnetic order in Ba1-xKxFe2As2 is theoretically studied, focusing on its impact on the global phase diagram. By carrying out a renormalization group analysis of an effective field theory, we obtain the energy-scale dependent flows of all the model parameters, and then apply the results to understand the observed phase diagram. On the basis of the renormalization group analysis, we show that the critical line of nematic order has a negative slope in the superconducting dome and superconductivity is suppressed near the magnetic quantum critical point, which are both consistent with recent experiments. Moreover, we find that, although the observed C4 symmetric magnetic state could be a charge-spin density wave or a spin-vortex crystal at high temperatures, charge-spin density wave is the only stable C4 magnetic state in the low-temperature regime. Therefore, ordering competition provides a method to distinguish these two candidate C4 magnetic states.
NASA Astrophysics Data System (ADS)
Marinoni, A.; Rost, J. C.; Porkolab, M.; Hubbard, A. E.; Osborne, T. H.; White, A. E.; Whyte, D. G.; Rhodes, T. L.; Davis, E. M.; Ernst, D. R.; Burrell, K. H.
2015-09-01
The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s-1. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations.
Current Fluctuations in One Dimensional Diffusive Systems with a Step Initial Density Profile
NASA Astrophysics Data System (ADS)
Derrida, Bernard; Gerschenfeld, Antoine
2009-12-01
We show how to apply the macroscopic fluctuation theory (MFT) of Bertini, De Sole, Gabrielli, Jona-Lasinio, and Landim to study the current fluctuations of diffusive systems with a step initial condition. We argue that one has to distinguish between two ways of averaging (the annealed and the quenched cases) depending on whether we let the initial condition fluctuate or not. Although the initial condition is not a steady state, the distribution of the current satisfies a symmetry very reminiscent of the fluctuation theorem. We show how the equations of the MFT can be solved in the case of non-interacting particles. The symmetry of these equations can be used to deduce the distribution of the current for several other models, from its knowledge (Derrida and Gerschenfeld in J. Stat. Phys. 136, 1-15, 2009) for the symmetric simple exclusion process. In the range where the integrated current Qt˜sqrt{t} , we show that the non-Gaussian decay exp [- Q {/t 3}/ t] of the distribution of Q t is generic.
Nam, Y. U. Wi, H. M.; Zoletnik, S.; Lampert, M.; Kovácsik, Ákos
2014-11-15
Beam emission spectroscopy (BES) system in Korea Superconducting Tokamak Advanced Research (KSTAR) has recently been upgraded. The background intensity was reduced from 30% to 2% by suppressing the stray lights. This allows acquisition of the relative electron density profiles on the plasma edge without background subtraction from the beam power modulation signals. The KSTAR BES system has its spatial resolution of 1 cm, the temporal resolution of 2 MHz, and a total 32 channel (8 radial × 4 poloidal) avalanche photo diode array. Most measurements were done on the plasma edge, r/a ∼ 0.9, with 8 cm radial measurement width that covers the pedestal range. High speed density profile measurements reveal temporal behaviors of fast transient events, such as the precursors of edge localized modes and the transitions between confinement modes. Low background level also allows analysis of the edge density fluctuation patterns with reduced background fluctuations. Propagation of the density structures can be investigated by comparing the phase delays between the spatially distributed channels.
NASA Astrophysics Data System (ADS)
Happel, T.; Manz, P.; Ryter, F.; Bernert, M.; Dunne, M.; Hennequin, P.; Hetzenecker, A.; Stroth, U.; Conway, G. D.; Guimarais, L.; Honoré, C.; Viezzer, E.; The ASDEX Upgrade Team
2017-01-01
Properties of the I-mode confinement regime on the ASDEX Upgrade tokamak are summarized. A weak dependence of the power threshold for the L-I transition on the toroidal magnetic field strength is found. During improved confinement, the edge radial electric field well deepens. Stability calculations show that the I-mode pedestal is peeling-ballooning stable. Turbulence investigations reveal strongly intermittent density fluctuations linked to the weakly coherent mode in the confined plasma, which become stronger as the confinement quality increases. Across all investigated structure sizes ({{k}\\bot}≈ 5 -12 cm-1, with {{k}\\bot} the perpendicular wavenumber of turbulent density fluctuations), the intermittent turbulence bursts are observed. Comparison with bolometry data shows that they move poloidally toward the X-point and finally end up in the divertor. This might be indicative that they play a role in inhibiting the density profile growth, such that no pedestal is formed in the edge density profile.
NASA Technical Reports Server (NTRS)
Clukey, Steven J.
1991-01-01
The real time Dynamic Data Acquisition and Processing System (DDAPS) is described which provides the capability for the simultaneous measurement of velocity, density, and total temperature fluctuations. The system of hardware and software is described in context of the wind tunnel environment. The DDAPS replaces both a recording mechanism and a separate data processing system. DDAPS receives input from hot wire anemometers. Amplifiers and filters condition the signals with computer controlled modules. The analog signals are simultaneously digitized and digitally recorded on disk. Automatic acquisition collects necessary calibration and environment data. Hot wire sensitivities are generated and applied to the hot wire data to compute fluctuations. The presentation of the raw and processed data is accomplished on demand. The interface to DDAPS is described along with the internal mechanisms of DDAPS. A summary of operations relevant to the use of the DDAPS is also provided.
Constraining cloud parameters using high density gas tracers in galaxies
NASA Astrophysics Data System (ADS)
Kazandjian, M. V.; Pelupessy, I.; Meijerink, R.; Israel, F. P.; Coppola, C. M.; Rosenberg, M. J. F.; Spaans, M.
2016-11-01
Far-infrared molecular emission is an important tool used to understand the excitation mechanisms of the gas in the interstellar medium (ISM) of star-forming galaxies. In the present work, we model the emission from rotational transitions with critical densities n ≳ 104 cm-3. We include 4-3 < J ≤ 15-14 transitions of CO and 13CO , in addition to J ≤ 7-6 transitions of HCN, HNC, and HCO+ on galactic scales. We do this by re-sampling high density gas in a hydrodynamic model of a gas-rich disk galaxy, assuming that the density field of the ISM of the model galaxy follows the probability density function (PDF) inferred from the resolved low density scales. We find that in a narrow gas density PDF, with a mean density of 10 cm-3 and a dispersion σ = 2.1 in the log of the density, most of the emission of molecular lines, even of gas with critical densities >104 cm-3, emanates from the 10-1000 cm-3 part of the PDF. We construct synthetic emission maps for the central 2 kpc of the galaxy and fit the line ratios of CO and 13CO up to J = 15-14, as well as HCN, HNC, and HCO+ up to J = 7-6, using one photo-dissociation region (PDR) model. We attribute the goodness of the one component fits for our model galaxy to the fact that the distribution of the luminosity, as a function of density, is peaked at gas densities between 10 and 1000 cm-3, with negligible contribution from denser gas. Specifically, the Mach number, ℳ, of the model galaxy is 10. We explore the impact of different log-normal density PDFs on the distribution of the line-luminosity as a function of density, and we show that it is necessary to have a broad dispersion, corresponding to Mach numbers ≳30 in order to obtain significant (>10%) emission from n> 104 cm-3 gas. Such Mach numbers are expected in star-forming galaxies, luminous infrared galaxies (LIRGS), and ultra-luminous infrared galaxies (ULIRGS). This method provides a way to constrain the global PDF of the ISM of galaxies from observations of
NASA Astrophysics Data System (ADS)
Rhodes, T. L.; Barada, K.; Peebles, W. A.; Crocker, N. A.
2016-11-01
An upgraded cross-polarization scattering (CPS) system for the simultaneous measurement of internal magnetic fluctuations B ˜ and density fluctuations ñ is presented. The system has eight radial quadrature channels acquired simultaneously with an eight-channel Doppler backscattering system (measures density fluctuations ñ and flows). 3-D ray tracing calculations based on the GENRAY ray tracing code are used to illustrate the scattering and geometric considerations involved in the CPS implementation on DIII-D. A unique quasi-optical design and IF electronics system allow direct comparison of B ˜ and ñ during dynamic or transient plasma events (e.g., Edge Localized Modes or ELMs, L to H-mode transitions, etc.). The system design allows the interesting possibility of both magnetic-density ( B ˜ -ñ) fluctuation and magnetic-temperature ( B ˜ - T ˜ ) fluctuation cross-phase measurements suitable for detailed tests of turbulence simulations.
NASA Astrophysics Data System (ADS)
Vaikuntanathan, Suriyanarayanan; Geissler, Phillip L.
2014-01-01
The physics of air-water interfaces plays a central role in modern theories of the hydrophobic effect. Implementing these theories, however, has been hampered by the difficulty of addressing fluctuations in the shape of such soft interfaces. We show that this challenge is a fundamental consequence of mapping long wavelength density variations onto discrete degrees of freedom. Drawing from studies of surface roughness in lattice models, we account for the resulting nonlinearities simply but accurately. Simulations show that this approach captures complex solvation behaviors quantitatively.
Bardóczi, L; Rhodes, T L; Carter, T A; Bañón Navarro, A; Peebles, W A; Jenko, F; McKee, G
2016-05-27
We report the first observation of localized modulation of turbulent density fluctuations n[over ˜] (via beam emission spectroscopy) by neoclassical tearing modes (NTMs) in the core of the DIII-D tokamak. NTMs are important as they often lead to severe degradation of plasma confinement and disruptions in high-confinement fusion experiments. Magnetic islands associated with NTMs significantly modify the profiles and turbulence drives. In this experiment n[over ˜] was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that n[over ˜] could be dominantly driven by the ion temperature gradient instability.
NASA Astrophysics Data System (ADS)
Woo, K. M.; Yu, S. S.; Barnard, J. J.
2013-06-01
It is well known that the imperfection of pulse power sources that drive the linear induction accelerators can lead to time-varying fluctuation in the accelerating voltages, which in turn leads to longitudinal emittance growth. We show that this source of emittance growth is correctable, even in space-charge dominated beams with significant transients induced by space-charge waves. Two correction methods are proposed, and their efficacy in reducing longitudinal emittance is demonstrated with three-dimensional particle-in-cell simulations.
Thermodynamic theory of equilibrium fluctuations
Mishin, Y.
2015-12-15
The postulational basis of classical thermodynamics has been expanded to incorporate equilibrium fluctuations. The main additional elements of the proposed thermodynamic theory are the concept of quasi-equilibrium states, a definition of non-equilibrium entropy, a fundamental equation of state in the entropy representation, and a fluctuation postulate describing the probability distribution of macroscopic parameters of an isolated system. Although these elements introduce a statistical component that does not exist in classical thermodynamics, the logical structure of the theory is different from that of statistical mechanics and represents an expanded version of thermodynamics. Based on this theory, we present a regular procedure for calculations of equilibrium fluctuations of extensive parameters, intensive parameters and densities in systems with any number of fluctuating parameters. The proposed fluctuation formalism is demonstrated by four applications: (1) derivation of the complete set of fluctuation relations for a simple fluid in three different ensembles; (2) fluctuations in finite-reservoir systems interpolating between the canonical and micro-canonical ensembles; (3) derivation of fluctuation relations for excess properties of grain boundaries in binary solid solutions, and (4) derivation of the grain boundary width distribution for pre-melted grain boundaries in alloys. The last two applications offer an efficient fluctuation-based approach to calculations of interface excess properties and extraction of the disjoining potential in pre-melted grain boundaries. Possible future extensions of the theory are outlined.
Rayleigh Scattering Diagnostic for Measurement of Velocity and Density Fluctuation Spectra
NASA Astrophysics Data System (ADS)
Seasholtz, Richard G.; Panda, Jayanta; Elam, Kristie A.
2002-04-01
A new molecular Rayleigh scattering based flow diagnostic is used for the first time to measure the power spectrum of gas density and radial velocity component in the plumes of high speed jets. The technique is based on analyzing the Rayleigh scattered light with a Fabry-Perot interferometer used in the static, imaging mode. The PC based data acquisition system is capable of simultaneous sampling of velocity and density at rates to 100 kHz and data record lengths to 10 million. Velocity and density power spectra and velocity-density cross spectra are presented for a subsonic jet, an underexpanded screeching jet, and for Mach 1.4 and Mach 1.8 supersonic jets. Software and hardware interfaces were developed to allow computer control of all aspects of the experiment and data acquisition.
Rayleigh Scattering Diagnostic for Measurement of Velocity and Density Fluctuation Spectra
NASA Technical Reports Server (NTRS)
Seasholtz, Richard G.; Panda, Jayanta; Elam, Kristie A.
2002-01-01
A new molecular Rayleigh scattering based flow diagnostic is used for the first time to measure the power spectrum of gas density and radial velocity component in the plumes of high speed jets. The technique is based on analyzing the Rayleigh scattered light with a Fabry-Perot interferometer used in the static, imaging mode. The PC based data acquisition system is capable of simultaneous sampling of velocity and density at rates to 100 kHz and data record lengths to 10 million. Velocity and density power spectra and velocity-density cross spectra are presented for a subsonic jet, an underexpanded screeching jet, and for Mach 1.4 and Mach 1.8 supersonic jets. Software and hardware interfaces were developed to allow computer control of all aspects of the experiment and data acquisition.
Sun, Li-Qiong; Wang, Shu-Yao; Li, Yan-Jing; Wang, Yong-Xiang; Wang, Zhen-Zhong; Huang, Wen-Zhe; Wang, Yue-Sheng; Bi, Yu-An; Ding, Gang; Xiao, Wei
2016-01-01
The present study was designed to determine the relationships between the performance of ethanol precipitation and seven process parameters in the ethanol precipitation process of Re Du Ning Injections, including concentrate density, concentrate temperature, ethanol content, flow rate and stir rate in the addition of ethanol, precipitation time, and precipitation temperature. Under the experimental and simulated production conditions, a series of precipitated resultants were prepared by changing these variables one by one, and then examined by HPLC fingerprint analyses. Different from the traditional evaluation model based on single or a few constituents, the fingerprint data of every parameter fluctuation test was processed with Principal Component Analysis (PCA) to comprehensively assess the performance of ethanol precipitation. Our results showed that concentrate density, ethanol content, and precipitation time were the most important parameters that influence the recovery of active compounds in precipitation resultants. The present study would provide some reference for pharmaceutical scientists engaged in research on pharmaceutical process optimization and help pharmaceutical enterprises adapt a scientific and reasonable cost-effective approach to ensure the batch-to-batch quality consistency of the final products.
Local Density Fluctuations Predict Photoisomerization Quantum Yield of Azobenzene-Modified DNA.
Kingsland, Addie; Samai, Soumyadyuti; Yan, Yunqi; Ginger, David S; Maibaum, Lutz
2016-08-04
Azobenzene incorporated into DNA has a photoisomerization quantum yield that depends on the DNA sequence near the azobenzene attachment site. We use Molecular Dynamics computer simulations to elucidate which physical properties of the modified DNA determine the quantum yield. We show for a wide range of DNA sequences that the photoisomerization quantum yield is strongly correlated with the variance of the number of atoms in close proximity to the outer phenyl ring of the azobenzene group. We infer that quantum yield is controlled by the availability of fluctuations that enable the conformational change. We demonstrate that these simulations can be used as a qualitative predictive tool by calculating the quantum yield for several novel DNA sequences, and confirming these predictions using UV-vis spectroscopy. Our results will be useful for the development of a wide range of applications of photoresponsive DNA nanotechnology.
NASA Astrophysics Data System (ADS)
Laise, T.; Barros, P.; Argolo, C.; Lyra, M. L.
2016-11-01
We study the critical order parameter fluctuations of the absorbing-state phase-transition exhibited by branching and annihilating random walkers performing anomalous diffusion in a linear chain. The diffusion process is considered to follow a power-law distribution of jump lengths with a typical decay exponent α. We focus in the case of parity conserving dynamics for which deviations from the usual directed percolation universality class have been previously demonstrated even for the limiting cases of normal diffusion. Anomalous diffusion induces a continuous change of the critical exponents. By performing a finite-size scaling analysis of simulation data, we show that the critical order parameter moment ratio also varies continuously with α. We unveil that the critical order parameter distribution evolves from a nearly Gaussian to an exponential form as the range of the jump distribution is increased up to the limit α =5/2 on which the active state predominates for any finite branching probability.
Evolution in population parameters: density-dependent selection or density-dependent fitness?
Travis, Joseph; Leips, Jeff; Rodd, F Helen
2013-05-01
Density-dependent selection is one of earliest topics of joint interest to both ecologists and evolutionary biologists and thus occupies an important position in the histories of these disciplines. This joint interest is driven by the fact that density-dependent selection is the simplest form of feedback between an ecological effect of an organism's own making (crowding due to sustained population growth) and the selective response to the resulting conditions. This makes density-dependent selection perhaps the simplest process through which we see the full reciprocity between ecology and evolution. In this article, we begin by tracing the history of studying the reciprocity between ecology and evolution, which we see as combining the questions of evolutionary ecology with the assumptions and approaches of ecological genetics. In particular, density-dependent fitness and density-dependent selection were critical concepts underlying ideas about adaptation to biotic selection pressures and the coadaptation of interacting species. However, theory points to a critical distinction between density-dependent fitness and density-dependent selection in their influences on complex evolutionary and ecological interactions among coexisting species. Although density-dependent fitness is manifestly evident in empirical studies, evidence of density-dependent selection is much less common. This leads to the larger question of how prevalent and important density-dependent selection might really be. Life-history variation in the least killifish Heterandria formosa appears to reflect the action of density-dependent selection, and yet compelling evidence is elusive, even in this well-studied system, which suggests some important challenges for understanding density-driven feedbacks between ecology and evolution.
Fluctuation of Density of States for 1d Schrödinger Operators
NASA Astrophysics Data System (ADS)
Nakano, Fumihiko
2017-03-01
We consider the 1d Schrödinger operator with random decaying potential and compute the 2nd term asymptotics of the density of states, which shows substantial differences between the cases α > 1/2, α < 1/2 and α = 1/2.
NASA Astrophysics Data System (ADS)
Shi, Peiwan; Shi, Zhongbing; Chen, Wei; Zhong, Wulyu; Yang, Zengchen; Jiang, Min; Zhang, Boyu; Li, Yonggao; Yu, Liming; Liu, Zetian; Ding, Xuantong
2016-07-01
A multichannel microwave interferometer system has been developed on the HL-2A tokomak. Its working frequency is well designed to avoid the fringe jump effect. Taking the structure of HL-2A into account, its antennas are installed in the horizontal direction, i.e. one launcher in high field side (HFS) and four receivers in low field side (LFS). The fan-shaped measurement area covers those regions where the magnetohydrodynamics (MHD) instabilities are active. The heterodyne technique contributes to its high temporal resolution (1 μs). It is possible for the multichannel system to realize simultaneous measurements of density and its fluctuation. The quadrature phase detection based on the zero-crossing method is introduced to density measurement. With this system, reliable line-averaged densities and density profiles are obtained. The location of the saturated internal kink mode can be figured out from the mode showing different intensities on four channels, and the result agrees well with that measured by electron cyclotron emission imaging (ECEI). supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB104002, 2013GB107002, 2014GB107001) and National Natural Science Foundation of China (Nos. 11475058, 11475057, 11261140326, 11405049)
Thermal effects on the electron density fluctuation spectra in NIF plasmas
NASA Astrophysics Data System (ADS)
Rozmus, W.; Chapman, T.; Tzoufras, M.; Berger, R.; Brunner, S.; Divol, L.; Michel, P.; Williams, E.; Glenzer, S.
2012-10-01
The high flux model of ignition-scale hohlraum plasmas includes the strong thermal flux from the region of laser beam overlap at the entrance hole of the hohlraum along the directions of the inner cone beams. We have examined results of this large heat flow at the kinetic level using Fokker-Planck codes, which reproduce the temperature profile and corresponding electron distribution functions on the millimeter scale of NIF plasmas. Using the first harmonic of the electron distribution, we have identified contributions from the energetic, heat carrying electrons and the return current component within the bulk of the distribution function. In hot NIF plasmas, the heat-carrying electrons have energies (20-40 keV) that are close to resonance with Langmuir waves produced by SRS. By calculating the plasma dielectric function using distribution functions extracted from Fokker-Planck simulations, we have found a significant reduction in the linear Landau damping for the Langmuir waves propagating in the direction of heat flow, potentially contributing to the onset of backward SRS. This effect was further examined in Vlasov simulations and by calculations of the electrostatic fluctuation levels.
Yadav, Vivek Kumar; Chandra, Amalendu
2013-06-14
A first principles study of the dynamics of supercritical methanol is carried out by means of ab initio molecular dynamics simulations. In particular, the fluctuation dynamics of hydroxyl stretch frequencies, hydrogen bonds, dangling hydroxyl groups, and orientation of methanol molecules are investigated for three different densities at 523 K. Apart from the dynamical properties, various equilibrium properties of supercritical methanol such as the local density distributions and structural correlations, hydrogen bonding aspects, frequency-structure correlations, and dipole distributions of methanol molecules are also investigated. In addition to the density dependence of various equilibrium and dynamical properties, their dependencies on dispersion interactions are also studied by carrying out additional simulations using a dispersion corrected density functional for all the systems. It is found that the hydrogen bonding between methanol molecules decreases significantly as we move to the supercritical state from the ambient one. The inclusion of dispersion interactions is found to increase the number of hydrogen bonds to some extent. Calculations of the frequency-structure correlation coefficient reveal that a statistical correlation between the hydroxyl stretch frequency and the nearest hydrogen-oxygen distance continues to exist even at supercritical states of methanol, although it is weakened with increase of temperature and decrease of density. In the supercritical state, the frequency time correlation function is found to decay with two time scales: One around or less than 100 fs and the other in the region of 250-700 fs. It is found that, for supercritical methanol, the times scales of vibrational spectral diffusion are determined by an interplay between the dynamics of hydrogen bonds, dangling OD groups, and inertial rotation of methanol molecules and the roles of these various components are found to vary with density of the supercritical solvent. Effects
Impact of finite density on spectroscopic parameters of decuplet baryons
NASA Astrophysics Data System (ADS)
Azizi, K.; Er, N.; Sundu, H.
2016-12-01
The decuplet baryons, Δ , Σ*, Ξ*, and Ω-, are studied in nuclear matter by using the in-medium QCD sum rules. By fixing the three-momentum of the particles under consideration at the rest frame of the medium, the negative energy contributions are removed. It is obtained that the parameters of the Δ baryon are more affected by the medium against the Ω- state, containing three strange quarks, whose mass and residue are not considerably affected by the medium. We also find the vector and scalar self-energies of these baryons in nuclear matter. By the recent progresses at the P ¯ ANDA experiment at the FAIR and NICA facility, it may be possible to study the in-medium properties of such states, even the multistrange Ξ* and Ω- systems, in the near future.
NASA Astrophysics Data System (ADS)
Christopoulos, Stavros-Richard G.; Sarlis, Nicholas V.; Skordas, Efthimios S.
2016-04-01
It has been recently shown [1,2] that earthquakes of magnitude M greater or equal to 7 are globally correlated. The identification of this correlation became possible when studying the variance κ1 of natural time which has been proposed as an order parameter for seismicity[3,4]. In the present study, we focus on the behaviour of the fluctuations of κ1 before major earthquakes using the Global Centroid Moment Tensor catalogue for a magnitude threshold Mthres=5.0 as in Ref.[5]. Natural time analysis reveals that distinct minima of the fluctuations κ1of seismicity appear within almost five and a half months on average before all major earthquakes of magnitude larger than M8.4. This phenomenon corroborates the recent finding [6] that similar minima of seismicity order parameter fluctuations had been observed before all major shallow earthquakes in Japan. Finally, we examine the statistical significance of the results by using ROC graphs [7,8] and the proposed prediction method has a p-value to occur by chance well below 0.1%. The hit rate is 100% with a false alarm rate only 6.67%. An attempt to lower the target earthquake magnitude threshold will be also presented. REFERENCES [1] N. V. Sarlis, Phys. Rev. E 84, 022101 (2011). [2] N. V. Sarlis and S.-R. G. Christopoulos, Chaos 22, 023123 (2012) [3] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Practica of Athens Acad. 76, 294 (2001). [4] P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, Phys. Rev. E 66, 011902 (2002). [5] N.V. Sarlis, S.-R. G. Christopoulos, and E. S. Skordas, Chaos 25, 063110 (2015) [6] N. V. Sarlis et al., Proc. Natl. Acad. Sci. U.S.A. 110, 13734 (2013) [7] T. Fawcett, Pattern Recognit. Lett. 27, 861 (2006). [8] N. V. Sarlis and S.-R. G. Christopoulos, Comput. Phys. Commun. 185, 1172 (2014).
NASA Astrophysics Data System (ADS)
Yoon, H.; Hyun, Y.; Lee, K.; Ha, K.; Ko, K.
2012-12-01
Estimation of groundwater level (GWL) fluctuation has been an important and challenging topic in hydrology. In this study, time series models for GWL fluctuation were developed using artificial neural network (ANN) and support vector machine (SVM). This study defines 'prediction' as the estimation of GWL when the model includes past GWL measurements in input components and 'forecast' when it uses past GWL estimated values. In order to reduce model parameter uncertainty for GWL forecast, the classic model building process was modified introducing weighting factors to the objective function. The developed models were applied to rainfall and GWL time series data of 5 groundwater monitoring stations in National Groundwater Monitoring Network (NGMN) of Korea: HC, MH, YH, PC and CS station, in order to compare the models' performance for prediction and forecast of GWL fluctuation and evaluate the impact of the weighting factors on model stability. Results showed that root mean squared error (RMSE) values ranged from 0.05 m to 0.11 m for the GWL prediction and 0.072 m to 0.159 m for the GWL forecast. Correlation coefficient values were over 0.91 and 0.87 for the prediction and forecast, respectively. The ANN model was more frequently selected than SVM for the prediction, whereas vice versa for the forecast. In the present study, FC-TS value was defined as RMSE values in the forecast to testing stage for examining the model parameter uncertainty. The FC-TS values decreased significantly when the weighting factors were utilized, which implies that use of the weighting factors reduced the uncertainty of the developed time series models.
Fluctuation of the charge density wave in TTF-TCNQ under high pressure
NASA Astrophysics Data System (ADS)
Murata, Keizo; Weng, Yufeng; Seno, Yuki; Rani Tamilselvan, Natarajan; Kobayashi, Kensuke; Arumugam, Sonachalam; Takashima, Yusaku; Yoshino, Harukazu; Kato, Reizo
2009-03-01
Temperature dependence of the resistivity of TTF-TCNQ along the b-(1D)- and a-axes was studied under hydrostatic pressure up to 8 GPa. A striking contrast was seen between the b-(1D)- and a-axes in the power-law dependence of resistivity ρ=ρ0Tα in the metallic region as well as the activation energy in the charge density wave (CDW) insulating state. We note that the careful terminal configuration is essentially important to obtain these properties.
Cuny, Jérôme; Sykina, Kateryna; Fontaine, Bruno; Le Pollès, Laurent; Pickard, Chris J; Gautier, Régis
2011-11-21
Solid-state (95)Mo nuclear magnetic resonance (NMR) properties of molybdenum hexacarbonyl have been computed using density functional theory (DFT) based methods. Both quadrupolar coupling and chemical shift parameters were evaluated and compared with parameters of high precision determined using single-crystal (95)Mo NMR experiments. Within a molecular approach, the effects of major computational parameters, i.e. basis set, exchange-correlation functional, treatment of relativity, have been evaluated. Except for the isotropic parameter of both chemical shift and chemical shielding, computed NMR parameters are more sensitive to geometrical variations than computational details. Relativistic effects do not play a crucial part in the calculations of such parameters for the 4d transition metal, in particular isotropic chemical shift. Periodic DFT calculations were tackled to measure the influence of neighbouring molecules on the crystal structure. These effects have to be taken into account to compute accurate solid-state (95)Mo NMR parameters even for such an inorganic molecular compound.
Anisotropic density fluctuations, plasmons, and Friedel oscillations in nodal line semimetal
NASA Astrophysics Data System (ADS)
Rhim, Jun-Won; Kim, Yong Baek
2016-04-01
Motivated by recent experimental efforts on three-dimensional semimetals, we investigate the static and dynamic density response of the nodal line semimetal by computing the polarizability for both undoped and doped cases. The nodal line semimetal in the absence of doping is characterized by a ring-shape zero energy contour in momentum space, which may be considered as a collection of Dirac points. In the doped case, the Fermi surface has a torus shape and two independent processes of the momentum transfer contribute to the singular features of the polarizability even though we only have a single Fermi surface. In the static limit, there exist two independent singularities in the second derivative of the static polarizability. This results in the highly anisotropic Friedel oscillations which show the angle-dependent algebraic power law and the beat phenomena in the oscillatory electron density near a charged impurity. Furthermore, the dynamical polarizability has two singular lines along {\\hslash }ω =γ p and {\\hslash }ω =γ p{sin}η , where η is the angle between the external momentum {p} and the plane where the nodal ring lies. From the dynamical polarizability, we obtain the plasmon modes in the doped case, which show anisotropic dispersions and angle-dependent plasma frequencies. Qualitative differences between the low and high doping regimes are discussed in light of future experiments.
NASA Astrophysics Data System (ADS)
Majumdar, Arun K.; Luna, Carlos E.; Idell, Paul S.
2007-09-01
A new method of reconstructing and predicting an unknown probability density function (PDF) characterizing the statistics of intensity fluctuations of optical beams propagating through atmospheric turbulence is presented in this paper. The method is based on a series expansion of generalized Laguerre polynomials ; the expansion coefficients are expressed in terms of the higher-order intensity moments of intensity statistics. This method generates the PDF from the data moments without any prior knowledge of specific statistics and converges smoothly. The utility of reconstructed PDF relevant to free-space laser communication in terms of calculating the average bit error rate and probability of fading is pointed out. Simulated numerical results are compared with some known non-Gaussian test PDFs: Log-Normal, Rice-Nakagami and Gamma-Gamma distributions and show excellent agreement obtained by the method developed. The accuracy of the reconstructed PDF is also evaluated.
Da Silva-Cadoux, Cécile; Hazemann, Jean-Louis; Testemale, Denis; Proux, Olivier; Rochas, Cyrille
2012-01-28
Synchrotron small angle X-ray scattering measurements on water and alkaline bromine aqueous solutions (XBr, with X = Li, Rb, or Cs) were carried out from ambient to supercritical conditions. The temperature was increased from 300 to 750 K along several isobars between 24 and 35 MPa. The correlation length and the structure factor were extracted from the data following the Ornstein-Zernike formalism. We obtained experimental evidence of the shift of the critical point and isochore and their dependence on the ions concentration (0.33 mol/kg and 1.0 mol/kg). We also observed that the size of the density fluctuations and the structure factor increase with the presence of the ions and that this effect is positively correlated with the atomic number of the cation. These behaviors were compared with ZnBr(2) and NaCl systems from the literature.
NASA Astrophysics Data System (ADS)
Cao, G. M.; Li, Y. D.; Li, Q.; Sun, P. J.; Wu, G. J.; Hu, L. Q.; the EAST Team
2015-08-01
Beta-induced Alfvén eigenmodes (BAEs) during strong tearing modes (TMs) have been frequently observed in fast-electron plasmas of EAST tokamak. The dynamics of the short-scale ({k}\\perp {ρ }s~{1.5-4.3}) density fluctuations during the activity of BAEs with strong TMs has been preliminarily investigated by a tangential CO2 laser collective scattering system. The results suggest the active, but different, response of short-scale density fluctuations to the TMs and BAEs. In the low-frequency (0-10 kHz) part of density fluctuations, there are harmonic oscillations totally corresponding to those of TMs. In the medium-high frequency (10-250 kHz) part of density fluctuations, with the appearance of the BAEs, the medium-high frequency density fluctuations begin to be dominated by several quasi-coherent (QC) modes, and the frequencies of the QC modes seem to be related to the changes of both TMs and BAEs. These results would shed some light on the understanding of the multi-scale interaction physics.
Aliotta, F; Gapiński, J; Pochylski, M; Ponterio, R C; Saija, F; Salvato, G; Vasi, C
2013-02-01
We performed a Brillouin scattering experiment on deeply supercooled water and compared the results with similar literature data obtained both at the same and at higher values of the exchanged wave vector. The whole set of available experimental data can be well reproduced with the use of the generalized hydrodynamic model where all the involved thermodynamic parameters are fixed to their literature values. On the contrary, the model based on the memory function approach generates the wrong estimates for measurables when the same values of the thermodynamic parameters are used. This result confirms our recent criticisms against the utilization of models originating from linear response theory [Phys. Rev. E 84, 051202 (2011)]. The inconsistency between models explains apparent discrepancies between the different conclusions on water acoustic behavior which may be found in the literature. We demonstrate that the observed behavior can be explained by assuming only a single relaxation process that is typical of any viscoelastic system. With all thermodynamics quantities fixed, the hydrodynamic description needs only two parameters to model the experimental data, namely, the relaxation time and the high-frequency limit of the sound velocity. The whole body of the experimental data can be well reproduced when the relaxation time behaves in an Arrhenian manner and the difference between the relaxed and not relaxed sound velocities is a constant. The high-frequency sound velocity is never higher than 2200 m/s. We conclude that, at least from experiments performed within the hydrodynamic regime, there is no indication for a fast sound close to the hypersonic velocity observed in ice.
Probabilistic Analysis and Density Parameter Estimation Within Nessus
NASA Technical Reports Server (NTRS)
Godines, Cody R.; Manteufel, Randall D.; Chamis, Christos C. (Technical Monitor)
2002-01-01
, and 99th percentile of the four responses at the 50 percent confidence level and using the same number of response evaluations for each method. In addition, LHS requires fewer calculations than MC in order to be 99.7 percent confident that a single mean, standard deviation, or 99th percentile estimate will be within at most 3 percent of the true value of the each parameter. Again, this is shown for all of the test cases studied. For that reason it can be said that NESSUS is an important reliability tool that has a variety of sound probabilistic methods a user can employ; furthermore, the newest LHS module is a valuable new enhancement of the program.
NASA Astrophysics Data System (ADS)
Riquelme-Galván, Mauricio; Robledo, Alberto
2017-02-01
We improve on the description of the relationship that exists between critical clusters in thermal systems and intermittency near the onset of chaos in low-dimensional systems. We make use of the statistical-mechanical language of inhomogeneous systems and of the renormalization group (RG) method in nonlinear dynamics to provide a more accurate, formal, approach to the subject. The description of this remarkable correspondence encompasses, on the one hand, the density functional formalism, where classical and quantum mechanical analogues match the procedure for one-dimensional clusters, and, on the other, the RG fixed-point map of functional compositions that captures the essential dynamical behavior. We provide details of how the above-referred theoretical approaches interrelate and discuss the implications of the correspondence between the high-dimensional (degrees of freedom) phenomenon and low-dimensional dynamics.
X-Ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
NASA Technical Reports Server (NTRS)
Markowitz, A.; Edelson, R.; Vaughan, S.; Uttley, P.; George, I. M.; Griffiths, R. E.; Kaspi, S.; Lawrence, A.; McHandy, I.; Nandra, K.
2003-01-01
By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert 1 galaxies. These PSDs span approx. greater than 4 orders of magnitude in temporal frequency, sampling variations on time scales ranging from tens of minutes to over a year. In at least four cases, the PSD shows a "break," a significant departure from a power law, typically on time scales of order a few days. This is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass compact systems with breaks on time scales of seconds. NGC 3783 shows tentative evidence for a doubly-broken power law, a feature that until now has only been seen in the (much better-defined) PSDs of low-state XRBs. It is also interesting that (when one previously-observed object is added to make a small sample of seven), an apparently significant correlation is seen between the break time scale T and the putative black hole mass M(sub BH), while none is seen between break time scale and luminosity. The data are consistent with the linear relation T = M(sub BH) /10(exp 6.5) solar mass; extrapolation over 6-7 orders of magnitude is in reasonable agreement with XRBs. All of this strengthens the case for a physical similarity between Seyfert 1s and XRBs.
NASA Astrophysics Data System (ADS)
Gao, Wang; Chen, Yun; Jiang, Qing
2016-12-01
Discriminating between metallic (M ) and semiconducting (S ) single-walled carbon nanotubes (SWNTs) remains a fundamental challenge in the field of nanotechnology. We address this issue by studying the adsorption of the isotropic atoms Xe, Kr, and a highly anisotropic molecule n heptane on M - and S -SWNTs with density functional theory that includes many-body dispersion forces. We find that the distinct polarizabilities of M - and S -SWNTs exhibit significantly different physisorption properties, which are also strongly controlled by the SWNT's diameter, adsorption site, adsorbate coverage, and the adsorbate's anisotropy. These findings stem from the wavelike nature of charge-density fluctuations in SWNTs. Particularly, these results allow us to rationalize the unusual √{3 }×√{3 }R 3 00 phase of Kr atoms on small gap M -SWNTs and the double desorption peak temperatures of n heptane on M -SWNTs in experiments, and also propose the n heptane as an effective sensor for experimentally discriminating M - and S -SWNTs.
Ultrasonic parameters of renal calculi and gall bladder stones as a function of density.
Agarwal, R
1998-01-01
In this investigation, ultrasonic parameters of complex renal calculi and gall bladder stones, in vitro are measured using a double-probe contact by pulse-echo technique. Due to the variation in the chemical composition of the stones, a large variation in the value of ultrasonic parameters is found. A correlation between ultrasonic parameters and various renal calculi and gall bladder stone pathologies are also discussed. The ultrasonic parameters are found to vary as a function of density of the specimen used.
Wu, J J; Sun, H J; Gao, Z Y
2008-09-01
Detrended fluctuation analysis (DFA) is a useful tool to measure the long-range power-law correlations in 1f noise. In this paper, we investigate the power-law dynamics behavior of the density fluctuation time series generated by the famous Kerner-Klenov-Wolf cellular automata model in road traffic. Then the complexities of spatiotemporal, average speed, and the average density have been analyzed in detail. By introducing the DFA method, our main observation is that the free flow and wide moving jam phases correspond to the long-range anticorrelations. On the contrary, at the synchronized flow phase, the long-range correlated property is observed.
Oprisan, Ana; Oprisan, Sorinel A; Bayley, Brittany; Hegseth, John J; Garrabos, Yves; Lecoutre-Chabot, Carole; Beysens, Daniel
2012-12-01
Large density fluctuations were observed by illuminating a cylindrical cell filled with sulfur hexafluoride (SF(6)), very near its liquid-gas critical point (|T-T(c)|< 300 μK) and recorded using a microscope with 3 μm spatial resolution. Using a dynamic structure factor algorithm, we determined from the recorded images the structure factor (SF), which measures the spatial distribution of fluctuations at different moments, and the correlation time of fluctuations. This method authorizes local measurements in contrast to the classical scattering techniques that average fluctuations over the illuminating beam. We found that during the very early stages of phase separation the SF scales with the wave vector q according to the Lorentzian q(-2), which shows that the liquid and vapor domains are just emerging. The critical wave number, which is related to the characteristic length of fluctuations, steadily decreases over time, supporting a sustained increase in the spatial scale of the fluctuating domains. The scaled evolution of the critical wave number obeys the universal evolution for the interconnected domains at high volume fraction with an apparent power law exponent of -0.35 ± 0.02. We also determined the correlation time of the fluctuations and inferred values for thermal diffusivity coefficient very near the critical point, above and below. The values were used to pinpoint the crossing of T(c) within 13 μK.
Schroeder, C. B.; Esarey, E.; Leemans, W. P.
2012-12-21
The operational plasma density and laser parameters for future colliders based on laser-plasma accelerators are discussed. Beamstrahlung limits the charge per bunch at low plasma densities. Reduced laser intensity is examined to improve accelerator efficiency in the beamstrahlung-limited regime.
NASA Astrophysics Data System (ADS)
Hillesheim, J. C.; Crocker, N. A.; Peebles, W. A.; Meyer, H.; Meakins, A.; Field, A. R.; Dunai, D.; Carr, M.; Hawkes, N.; the MAST Team
2015-07-01
The high-k (7≲ {{k}\\bot}{ρi}≲ 11 ) wavenumber spectrum of density fluctuations has been measured for the first time in MAST (Lloyd et al 2003 Nucl. Fusion 43 1665). This was accomplished with the first implementation of Doppler backscattering (DBS) for core measurements in a spherical tokamak. DBS has become a well-established and versatile diagnostic technique for the measurement of intermediate- k ({{k}\\bot}{ρi}˜ 1 , and higher) density fluctuations and flows in magnetically confined fusion experiments. Previous implementations of DBS for core measurements have been in standard, large aspect ratio tokamaks. A novel implementation with two-dimensional (2D) steering was necessary to enable DBS measurements in MAST, where the large variation of the magnetic field pitch angle presents a challenge. We report on the scattering considerations and ray tracing calculations used to optimize the design and present data demonstrating measurement capabilities. Initial results confirm the applicability of the design and implementation approaches, showing the strong dependence of scattering alignment on the toroidal launch angle and demonstrating that DBS is sensitive to the local magnetic field pitch angle. We also present comparisons of DBS plasma velocity measurements with charge exchange recombination and beam emission spectroscopy measurements, which show reasonable agreement over most of the minor radius, but imply large poloidal flows approaching the magnetic axis in a discharge with an internal transport barrier. The 2D steering is shown to enable high-k measurements with DBS, at {{k}\\bot}>20 cm-1 ({{k}\\bot}{ρi}>10 ) for launch frequencies less than 75 GHz; this capability is used to measure the wavenumber spectrum of turbulence and we find \\mid n≤ft({{k}\\bot}\\right){{\\mid}2}\\propto k\\bot-4.7+/- 0.2 for {{k}\\bot}{ρi}≈ 7 -11, which is similar to the expectation for the turbulent kinetic cascade of \\mid n≤ft({{k}\\bot}\\right){{\\mid}2}\\propto
NASA Technical Reports Server (NTRS)
Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, S.
2000-01-01
In this paper we present a detailed simulation study of the influence of quantum mechanical effects in the inversion layer on random dopant induced threshold voltage fluctuations and lowering in sub 100 nm MOSFETs. The simulations have been performed using a 3-D implementation of the density gradient (DG) formalism incorporated in our established 3-D atomistic simulation approach. This results in a self-consistent 3-D quantum mechanical picture, which implies not only the vertical inversion layer quantisation but also the lateral confinement effects related to current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical dopant fluctuations, is an increase in both threshold voltage fluctuations and lowering. At the same time, the random dopant induced threshold voltage lowering partially compensates for the quantum mechanical threshold voltage shift in aggressively scaled MOSFETs with ultrathin gate oxides.
Opening a nodal gap by fluctuating spin-density wave in lightly doped La2 -xSrxCuO4
NASA Astrophysics Data System (ADS)
Kapon, Itzik; Ellis, David S.; Drachuck, Gil; Bazalitski, Galina; Weschke, Eugen; Schierle, Enrico; Strempfer, Jörg; Niedermayer, Christof; Keren, Amit
2017-03-01
We investigate whether the spin or charge degrees of freedom are responsible for the nodal gap in underdoped cuprates by performing inelastic neutron scattering and x-ray diffraction measurements on La2 -xSrxCuO4 , which is on the edge of the antiferromagnetic phase. We found that a fluctuating incommensurate spin-density wave (SDW) with a bottom part of an hourglass dispersion exists even in this magnetic sample. The strongest component of these fluctuations diminishes at the same temperature where the nodal gap opens. X-ray scattering measurements on the same crystal show no signature of a charge-density wave (CDW). Therefore, we suggest that the nodal gap in the electronic band of this cuprate opens due to fluctuating SDW with no contribution from CDW.
NASA Astrophysics Data System (ADS)
Rosa, Benoit; Brient, Antoine; Samper, Serge; Hascoët, Jean-Yves
2016-12-01
Mastering the additive laser manufacturing surface is a real challenge and would allow functional surfaces to be obtained without finishing. Direct Metal Deposition (DMD) surfaces are composed by directional and chaotic textures that are directly linked to the process principles. The aim of this work is to obtain surface topographies by mastering the operating process parameters. Based on experimental investigation, the influence of operating parameters on the surface finish has been modeled. Topography parameters and multi-scale analysis have been used in order to characterize the DMD obtained surfaces. This study also proposes a methodology to characterize DMD chaotic texture through topography filtering and 3D image treatment. In parallel, a new parameter is proposed: density of particles (D p). Finally, this study proposes a regression modeling between process parameters and density of particles parameter.
Finest light curve details, physical parameters, and period fluctuations of CoRoT RR Lyrae stars
NASA Astrophysics Data System (ADS)
Benkő, J. M.; Szabó, R.; Derekas, A.; Sódor, Á.
2016-12-01
The CoRoT satellite supplied the scientific community with a huge data base of variable stars. Among them the RR Lyrae stars have intensively been discussed in numerous papers in the last few years, but the latest runs have not been checked to find RR Lyrae stars up to now. Our main goal was to fill this gap and complete the CoRoT RR Lyrae sample. We found nine unstudied RR Lyrae stars. Seven of them are new discoveries. We identified three new Blazhko stars. The Blazhko effect shows non-strictly repetitive nature for all stars. The frequency spectrum of the Blazhko star CoRoT 104948132 contains second overtone frequency with the highest known period ratio. The harmonic amplitude and phase declines with the harmonic order were studied for non-Blazhko stars. We found a period dependent but similar shape amplitude decline for all stars. We discovered significant random period fluctuation for one of the two oversampled target, CM Ori. After a successful transformation of the CoRoT band parameters to the Johnson V values we estimated the basic physical properties such as mass, luminosity, metallicity. The sample can be divided into two subgroups with respect to the metallicity but otherwise the physical parameters are in the canonical range of RR Lyrae stars.
NASA Astrophysics Data System (ADS)
McCray, J. E.; Downs, W.; Falta, R. W.; Housley, T.
2005-12-01
DNAPL sources of carbon tetrachloride (CT) vapors are of interest at the Radioactive Waste Management Complex (RWMC) at the Idaho National Engineering and Environmental Laboratory (INEEL). The site is underlain by thick fractured basalt that includes sedimentary interbeds, each are a few meters thick. Daily atmospheric pressure fluctuations serve as driving forces for CT vapor transport in the subsurface. Other important transport processes for vapor movement include gas-phase diffusion and density-driven transport. The objective of this research is to investigate the influence and relative importance of these processes on gaseous transport of CT. Gas pressure and vapor concentration measurements were conducted at various depths in two wells. A numerical multiphase flow model (TOUGH2), calibrated to field pressure data, is used to conduct sensitivity analyses to elucidate the importance of the different transport mechanisms. Results show that the basalt is highly permeable to vertical air flow. The pressure dampening occurs mainly in the sedimentary interbeds. Model-calibrated permeability values for the interbeds are similar to those obtained in a study by the U.S. Geological Survey for shallow sediments, and an order of magnitude higher than column-scale values obtained by previous studies conducted by INEEL scientists. The transport simulations indicate that considering the effect of barometric pressure changes is critical to simulating transport of pollutants in the vadose zone above the DNAPL source. Predicted concentrations can be orders of magnitude smaller than actual concentrations if the effect is not considered. Below the DNAPL vapor source, accounting for density and diffusion alone would yield acceptable results provided that a 20% error in concentrations are acceptable, and that simulating concentrations trends (and not actual concentrations) is the primary goal.
A Cutoff in the X-Ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
NASA Technical Reports Server (NTRS)
Edelson, Rick; Nandra, Kirpal
1999-01-01
During 1997 March-July, RXTE observed the bright, strongly variable Seyfert 1 galaxy NGC 3516 once every approx. 12.8 hr for 4.5 months and nearly continuously (with interruptions due to SAA passage but not Earth occultation) for a 4.2 day period in the middle. These were followed by ongoing monitoring once every approx. 4.3 days. These data are used to construct the first well-determined X-ray fluctuation power density spectrum (PDS) of an active galaxy to span more than 4 decades of usable temporal frequency. The PDS shows no signs of any strict or quasi-periodicity, but does show a progressive flattening of the power-low slope from -1.74 at short time scales to -0.73 at longer time scales. This is the clearest observation to date of the long-predicted cutoff in the PDS. The characteristic variability time scale corresponding to this cutoff temporal frequency is approx. 1 month. Although it is unclear how this time scale may be interpreted in terms of a physical size or process, there are several promising candidate models. The PDS appears similar to those seen for Galactic black hole candidates such as Cyg X-1, suggesting that these two classes of objects with very different luminosities and putative black hole masses (differing by more than a factor of 10(exp 5)) may have similar X-ray generation processes and structures.
NASA Astrophysics Data System (ADS)
Khrennikov, Andrei
2010-05-01
Prequantum classical statistical field theory (PCSFT) is a new attempt to consider quantum mechanics (QM) as an emergent phenomenon, cf. with De Broglie's "double solution" approach, Bohmian mechanics, stochastic electrodynamics (SED), Nelson's stochastic QM and its generalization by Davidson, `t Hooft's models and their development by Elze. PCSFT is a comeback to a purely wave viewpoint on QM, cf. with early Schrödinger. There is no quantum particles at all, only waves. In particular, photons are simply wave-pulses of the classical electromagnetic field, cf. SED. Moreover, even massive particles are special "prequantum fields": the electron field, the neutron field and so on. PCSFT claims that (soon or later) people will be able to measure components of these fields: components of the "photonic field" (the classical electromagnetic field of low intensity), electronic field, neutronic field and so on. However, at the moment (in this paper) we restrict our efforts to reproduce "simply" predictions of QM in the classical field framework. We will show that correlations of entangled systems can be obtained from fluctuations of the prequantum field. We consider the most general case: in QM the state is given by the density operator.
NASA Astrophysics Data System (ADS)
Rueter, Keiti; Novikov, Ivan
2016-09-01
Parameters of a nuclear density distribution for an exotic nuclei with halo or skin structures can be determined from the experimentally measure interaction cross-section. In the presented work, to extract parameters for a halo and core, we compare experimental data on interaction cross section with reaction cross-sections calculated using expressions obtained in the Glauber Model and its optical approximation. These calculations are performed using Markov Chain Monte Carlo algorithm. In addition, we discuss the accuracy of the Monte Carlo approach to calculating the interaction and reaction cross-sections. The dependence of the accuracy of the density parameters of various exotic nuclei on the ``quality'' of the random numbers chains (here, ``quality'' is defined by lag-1 autocorrelation time of a sequence of random numbers) is obtained for the Gaussian density distribution for a core and the Gaussian density distribution for a halo. KY NSF EPSCoR Research Scholars Program.
NASA Astrophysics Data System (ADS)
Duff, James; Chapman, Brett; Sarff, John; Ding, Weixing; Brower, David; Lin, Liang
2012-10-01
In standard RFP plasmas, transport is governed by magnetic fluctuations associated with global tearing modes. For improved-confinement plasmas using inductive current profile control (PPCD), smaller-scale fluctuations at higher frequencies might become important for transport, especially drift-wave-like instabilities which may be theoretically unstable for the larger temperature gradients achieved. On the MST-RFP, an 11-chord laser-based diagnostic with ˜8 cm chord spacing is and frequency 694 GHz used to measure electron density fluctuations both interferometrically and by far-forward collective scattering. The existing diagnostic configuration measures the line-integrated fluctuations within the divergence of the probe beam covering a wavenumber range k<1.3 cm-1, corresponding to kρs <1.3 (ρs is the ion-sound Larmor radius). Of particular interest is comparing fluctuations in standard and PPCD plasmas. Relative to standard plasmas, tearing mode and higher frequency broadband fluctuations (up to 600 kHz) are suppressed with PPCD. This suppression in PPCD plasmas corresponds to the improved confinement. A diagnostic upgrade, in progress, will improve sensitivity and cover shorter wavelengths. Work supported by U.S.D.O.E.
Quantiles, parametric-select density estimation, and bi-information parameter estimators
NASA Technical Reports Server (NTRS)
Parzen, E.
1982-01-01
A quantile-based approach to statistical analysis and probability modeling of data is presented which formulates statistical inference problems as functional inference problems in which the parameters to be estimated are density functions. Density estimators can be non-parametric (computed independently of model identified) or parametric-select (approximated by finite parametric models that can provide standard models whose fit can be tested). Exponential models and autoregressive models are approximating densities which can be justified as maximum entropy for respectively the entropy of a probability density and the entropy of a quantile density. Applications of these ideas are outlined to the problems of modeling: (1) univariate data; (2) bivariate data and tests for independence; and (3) two samples and likelihood ratios. It is proposed that bi-information estimation of a density function can be developed by analogy to the problem of identification of regression models.
Terrier, Philippe; Turner, Vincent; Schutz, Yves
2005-02-01
During free walking, gait is automatically adjusted to provide optimal mechanical output and minimal energy expenditure; gait parameters, such as cadence, fluctuate from one stride to the next around average values. It was described that this fluctuation exhibited long-range correlations and fractal-like patterns. In addition, it was suggested that these long-range correlations disappeared if the participant followed the beep of metronome to regulate his or her pace. Until now, these fractal fluctuations were only observed for stride interval, because no technique existed to adequately analyze an extended time of free walking. The aim of the present study was to measure walking speed (WS), step frequency (SF) and step length (SL) with high accuracy (<1 cm) satellite positioning method (global positioning system or GPS) in order to detect long-range correlations in the stride-to-stride fluctuations. Eight participants walked 30 min under free and constrained (metronome) conditions. Under free walking conditions, DFA (detrended fluctuation analysis) and surrogate data tests showed that the fluctuation of WS, SL and SF exhibited a fractal pattern (i.e., scaling exponent alpha: 0.5 < alpha < 1) in a large majority of participants (7/8). Under constrained conditions (metronome), SF fluctuations became significantly anti-correlated (alpha < 0.5) in all participants. However, the scaling exponent of SL and WS was not modified. We conclude that, when the walking pace is controlled by an auditory signal, the feedback loop between the planned movement (at supraspinal level) and the sensory inputs induces a continual shifting of SF around the mean (persistent anti-correlation), but with no effect on the fluctuation dynamics of the other parameters (SL, WS).
NASA Astrophysics Data System (ADS)
Devynck, P.; Ghendrih, P.; Sarazin, Y.
2005-05-01
It is shown that intermittent density bursts observed in the scrape-off layer of Tore Supra [J. Jacquinot, Nucl. Fusion 43, 1583 (2003)] are detected in packs on the probe. In such a pack, typically two to three bursts are separated by time intervals smaller than the mean separation time. The long tails above 50μs observed on the autocorrelation function of the density fluctuations are found to be the temporal correlation between the individual bursts within their pack. Packs of density bursts can be detected in two limiting states of the turbulence: when the coupling between density and potential is strong and large density bursts split during their radial propagation or at the opposite when the coupling is weak so that different density bursts can propagate radially along the potential valleys. The lack of spatial resolution of the diagnostic does not allow to discriminate between the two mechanisms.
Devynck, P.; Ghendrih, P.; Sarazin, Y.
2005-05-15
It is shown that intermittent density bursts observed in the scrape-off layer of Tore Supra [J. Jacquinot, Nucl. Fusion 43, 1583 (2003)] are detected in packs on the probe. In such a pack, typically two to three bursts are separated by time intervals smaller than the mean separation time. The long tails above 50 {mu}s observed on the autocorrelation function of the density fluctuations are found to be the temporal correlation between the individual bursts within their pack. Packs of density bursts can be detected in two limiting states of the turbulence: when the coupling between density and potential is strong and large density bursts split during their radial propagation or at the opposite when the coupling is weak so that different density bursts can propagate radially along the potential valleys. The lack of spatial resolution of the diagnostic does not allow to discriminate between the two mechanisms.
Arora, Bhavna; Mohanty, Binayak P.; McGuire, Jennifer T.
2013-01-01
Soil and crop management practices have been found to modify soil structure and alter macropore densities. An ability to accurately determine soil hydraulic parameters and their variation with changes in macropore density is crucial for assessing potential contamination from agricultural chemicals. This study investigates the consequences of using consistent matrix and macropore parameters in simulating preferential flow and bromide transport in soil columns with different macropore densities (no macropore, single macropore, and multiple macropores). As used herein, the term“macropore density” is intended to refer to the number of macropores per unit area. A comparison between continuum-scale models including single-porosity model (SPM), mobile-immobile model (MIM), and dual-permeability model (DPM) that employed these parameters is also conducted. Domain-specific parameters are obtained from inverse modeling of homogeneous (no macropore) and central macropore columns in a deterministic framework and are validated using forward modeling of both low-density (3 macropores) and high-density (19 macropores) multiple-macropore columns. Results indicate that these inversely modeled parameters are successful in describing preferential flow but not tracer transport in both multiple-macropore columns. We believe that lateral exchange between matrix and macropore domains needs better accounting to efficiently simulate preferential transport in the case of dense, closely spaced macropores. Increasing model complexity from SPM to MIM to DPM also improved predictions of preferential flow in the multiple-macropore columns but not in the single-macropore column. This suggests that the use of a more complex model with resolved domain-specific parameters is recommended with an increase in macropore density to generate forecasts with higher accuracy. PMID:24511165
NASA Astrophysics Data System (ADS)
Battipaglia, G.; Brand, W. A.; Linke, P.; Schaefer, I.; Noetzli, M.; Cherubini, P.
2009-04-01
Tree- ring growth and wood density have been used extensively as indicators of climate change, and tree-ring has been commonly applied as a proxy estimate for seasonal integration of temperatures and precipitation with annual resolution (Hughes 2002). While these relationships have been well established in temperate ecosystems (Fritts, 1976; Schweingruber, 1988, Briffa et al., 1998, 2004), in Mediterranean region dendrochronological studies are still scarce (Cherubini et al, 2003). In Mediterranean environment, trees may form intra-annual density fluctuations, also called "false rings" or "double rings" (Tingley 1937; Schulman 1938). They are usually induced by sudden drought events, occurring during the vegetative period, and, allowing intra-annual resolution, they may provide detailed information at a seasonal level, as well as species-specific sensitivity to drought. We investigated the variability of tree- ring width and carbon stable isotopes of a Mediterranean species, Arbutus unedo L., sampled on Elba island, (Tuscany, Italy). The samples were taken at two different sites, one characterized by wet and one by dry conditions. d13C was measured using Laser- Ablation- Combustion -GC-IRMS. Here, we present first results showing the impact of drought on tree growth and on false ring formation at the different sites and we underline the importance of using Laser Ablation to infer drought impact at the intra -annual level. Briffa KR, Schweingruber FH, Jones PD, Osborn TJ, Harris IC, Shiyatov SG, Vaganov EA, Grudd H (1998) Trees tell of past climates: but are they speaking less clearly today? Phil Transact Royal Soc London 353:65-73 Briffa KR, Osborn TJ, Schweingruber FH (2004) Large-scale temperature inferences from tree rings: a review. Glob Panet Change 40:11-26 Cherubini, P., B.L. Gartner, R. Tognetti, O.U. Bräker, W. Schoch & J.L. Innes. 2003. Identification, measurement and interpretation of tree rings in woody species from Mediterranean climates. Biol. Rev
Shelukhin, D.A.; Vershkov, V.A.; Razumova, K.A.
2005-12-15
In experiments on off-axis electron-cyclotron resonance heating in the T-10 tokamak, a steep gradient of the electron temperature was observed to form for a short time at a relative radius of {rho} {approx_equal} 0.25 after the heating power was switched off. Small-scale fluctuations of the electron density were studied with the help of correlation reflectometry. It was found that, in a narrow region near {rho} {approx_equal} 0.25, the amplitude of the density fluctuations was two times lower than that in the ohmic heating phase. Quasi-coherent fluctuations were suppressed over a period of time during which the steep temperature gradient existed. Measurements of the poloidal rotation velocity of turbulent fluctuations show that there is no velocity shear after the heating is switched off. An analysis of the linear growth rates of instabilities shows that the ion-temperature-gradient mode is unstable at {rho} {approx_equal} 0.25 throughout the entire discharge phase. The effect observed can be explained by an increase in the distance between the rational surfaces near the radius at which the safety factor is q = 1 due to the temporary flattening of the q profile after the off-axis electron-cyclotron resonance heating is switched off.
Sensitivity of the NMR density matrix to pulse sequence parameters: a simplified analytic approach.
Momot, Konstantin I; Takegoshi, K
2012-08-01
We present a formalism for the analysis of sensitivity of nuclear magnetic resonance pulse sequences to variations of pulse sequence parameters, such as radiofrequency pulses, gradient pulses or evolution delays. The formalism enables the calculation of compact, analytic expressions for the derivatives of the density matrix and the observed signal with respect to the parameters varied. The analysis is based on two constructs computed in the course of modified density-matrix simulations: the error interrogation operators and error commutators. The approach presented is consequently named the Error Commutator Formalism (ECF). It is used to evaluate the sensitivity of the density matrix to parameter variation based on the simulations carried out for the ideal parameters, obviating the need for finite-difference calculations of signal errors. The ECF analysis therefore carries a computational cost comparable to a single density-matrix or product-operator simulation. Its application is illustrated using a number of examples from basic NMR spectroscopy. We show that the strength of the ECF is its ability to provide analytic insights into the propagation of errors through pulse sequences and the behaviour of signal errors under phase cycling. Furthermore, the approach is algorithmic and easily amenable to implementation in the form of a programming code. It is envisaged that it could be incorporated into standard NMR product-operator simulation packages.
NASA Astrophysics Data System (ADS)
Sohn, Kee-Sun; Han, Su Cheol; Park, Woon Bae; Pyo, Myoungho
2016-03-01
Despite extensive effort during the past few decades, a comprehensive understanding of the key variables governing the electrochemical properties of cathode materials in Li-ion batteries is still far from complete. To elucidate the critical parameters affecting energy density (ED) and capacity (Q) retention in layer and spinel cathodes, we data-mine the existing experimental data via confirmatory factor analysis (CFA) based on a structural equation model (SEM), which is a proven, versatile tool in understanding complex problems in the social science. The data sets are composed of 18 and 15 parameters extracted from 38 layer and 33 spinel compounds, respectively. CFA reveals the irrelevance of Q retention to all the parameters we adopt, but it also reveals the sensitive variations of ED with specific parameters. We validate the usefulness of CFA in material science and pinpointed critical parameters for high-ED cathodes, hoping to suggest a new insight in materials design.
Excitation energy dependence of the level density parameter close to the doubly magic 208Pb
NASA Astrophysics Data System (ADS)
Roy, Pratap; Banerjee, K.; Bhattacharya, C.; Pandey, R.; Sen, A.; Manna, S.; Kundu, S.; Rana, T. K.; Ghosh, T. K.; Mukherjee, G.; Roy, T.; Dhal, A.; Dey, A.; Meena, J. K.; Saha, A. K.; Pandit, Deepak; Mukhopadhyay, S.; Bhattacharya, S.
2016-12-01
Neutron evaporation spectra have been measured from 4He+208Pb and 4He+209Bi reactions by using 4He-ion beams of several bombarding energies. Excitation-energy dependence of the level density parameter has been studied for the two systems in the excitation energy range of ˜18 -50 MeV. For both the reactions an overall reduction of the asymptotic level density parameter with increasing excitation energy (temperature) is observed. The trend of the data was compared with the Thomas-Fermi model predictions and found to be in reasonable agreement. The value of the shell damping parameter has been extracted from the lowest-energy data in the case of Po,211210 and At,212211 nuclei close to the Z =82 and N =126 shell closure, and it was found to be consistent with the recent measurement in the vicinity of doubly magic 208Pb nucleus.
NASA Astrophysics Data System (ADS)
Uspensky, M. V.; Janhunen, P.; Koustov, A. V.; Kauristie, K.
2011-06-01
Norway and Finland STARE radar measurements in the eastward auroral electrojet are combined with EISCAT CP-1 measurements of the electron density and electric field vector in the common scattering volume to investigate the variation of the auroral radar volume cross section (VCS) with the flow angle of observations (radar look direction with respect to the E×B electron drift). The data set available consists of ~6000 points for flow angles of 40-85° and electron drifts between 500 and 2000 m s-1. The EISCAT electron density N(h)-profile data are used to estimate the effective electron density, aspect angle and thickness of the backscattering layer. It is shown that the flow angle variation of the VCS is rather weak, only ~5 dB within the range of the considered flow angles. The VCS values themselves respond almost linearly to the square of both the electron drift velocity magnitude and the effective electron density. By adopting the inferred shape of the VCS variation with the flow angle and the VCS dependence upon wavelength, the relative amplitude of electrostatic electron density fluctuations over all scales is estimated. Inferred values of 2-4 percent react nearly linearly to the electron drift velocity in the range of 500-1000 m s-1 but the rate of increase slows down at electron drifts >1000 m s-1 and density fluctuations of ~5.5 percent due to, perhaps, progressively growing nonlinear wave losses.
Key Parameters Governing the Energy Density of Rechargeable Li/S Batteries.
Gao, Jie; Abruña, Héctor D
2014-03-06
Rechargeable lithium-sulfur batteries have high theoretical capacity and energy density. However, their volumetric energy density has been believed to be lower than that of conventional lithium ion batteries employing metal oxide cathodes like LiCoO2. Here, we study the effects of sulfur loading percentage, develop a simple model and calculate the gravimetric and volumetric energy densities based on the total composition of electrodes in a lithium-sulfur cell, and compare those results with a typical graphite/LiCoO2 cell. From the model output, we have identified and established key parameters governing the energy density of rechargeable Li/S batteries. We find that the sulfur loading percentage has a much higher impact on the volumetric energy density than on the gravimetric energy density. A lithium-sulfur cell can exceed a lithium ion cell's volumetric energy density but only at high sulfur loading percentages (ca. 70%). We believe that these findings may attract more attention of lithium-sulfur system studies to high sulfur loading levels.
Two-parameter Fermi function fits to experimental charge and point-proton densities for 208Pb
NASA Astrophysics Data System (ADS)
Jones, Adam B.; Brown, B. Alex
2014-12-01
We use the model-independent experimental charge density for 208Pb to determine a model-independent point-proton density. An improved two-parameter Fermi function representation for the this point-proton density provides input for the analysis of experiments for the neutron density interpreted in terms of neutron skin and halo properties of 208Pb.
Shell energy and the level-density parameter of hot nuclei
Nerlo-Pomorska, Bozena; Pomorski, Krzysztof; Bartel, Johann
2006-09-15
Macroscopic-microscopic calculations have been performed with the Yukawa folded mean field for 134 spherical even-even nuclei and 6 deformed ones at temperatures 0{<=}T{<=}5 MeV and elongations ranging from oblate shapes to the scission configuration of fissioning nuclei. The Strutinsky type free-energy shell corrections for this sample of nuclei and their temperature and deformation dependence are found by a folding procedure in particle-number space. The average dependence of the single-particle level-density parameter on mass number A and isospin I is determined and compared with previous estimates obtained using the relativistic mean-field theory, the Hartree-Fock approximation with the Skyrme effective interaction, and the phenomenological Thomas-Fermi approach adjusted to experimental data. The estimates for the level-density parameter obtained for different deformations are fitted by a liquid-drop type expression.
Typical density of states as an order parameter for the Anderson localization
NASA Astrophysics Data System (ADS)
Tam, Ka-Ming; Moore, Conrad; Moreno, Juana; Jarrell, Mark
2015-03-01
The typical medium theory and its recently proposed extensions for models with off-diagonal disorder and multiple bands are significant progress towards the study of localization phenomenon in real materials. The fundamental assumption of these methods is that the typical density of states can be treated as an order parameter. However, its justifications in lattice model is largely lacking. This is predominantly due to two factors. First, the lattice sizes amenable for exact diagonalization is rather limited. Second, the small lattice sizes lead to a very sensitive dependence on the broadening factor. In this work, we use the kernel polynomial method to perform simulation for large system sizes. By adapting the method for the study of criticality, we find that the typical density of states has a well defined finite size scaling behavior. In particular, from the kurtosis, Binder ratio, of the distribution of the density of states for different lattice sizes, we find a clear crossing to identify the critical point. This provides further support that the typical density of states can be used as an order parameter for the localization transition.
Effect of Microstructural Parameters on the Relative Densities of Metal Foams
NASA Technical Reports Server (NTRS)
Raj, S. V.; Kerr, Jacob A.
2010-01-01
A detailed quantitative microstructural analyses of primarily open cell FeCrAlY and 314 stainless steel metal foams with different relative densities and pores per inch (p.p.i.) were undertaken in the present investigation to determine the effect of microstructural parameters on the relative densities of metal foams. Several elements of the microstructure, such as longitudinal and transverse cell sizes, cell areas and perimeters, ligament dimensions, cell shapes and volume fractions of closed and open cells, were measured. The cross-sections of the foam ligaments showed a large number of shrinkage cavities, and their circularity factors and average sizes were determined. The volume fractions of closed cells increased linearly with increasing relative density. In contrast, the volume fractions of the open cells and ligaments decreased with increasing relative density. The relative densities and p.p.i. were not significantly dependent on cell size, cell perimeter and ligament dimensions within the limits of experimental scatter. A phenomenological model is proposed to rationalize the present microstructural observations.
NASA Astrophysics Data System (ADS)
Jug, Giancarlo; Ziegler, Klaus
1997-10-01
We present a calculation for the second moment of the local density of states in a model of a two-dimensional quantum dot array near the quantum Hall transition. The quantum dot array model is a realistic adaptation of the lattice model for the quantum Hall transition in the two-dimensional electron gas in an external magnetic field proposed by Ludwig, Fisher, Shankar, and Grinstein. We make use of a Dirac fermion representation for the Green's functions in the presence of fluctuations for the quantum dot energy levels. A saddle-point approximation yields nonperturbative results for the first and second moments of the local density of states, showing interesting fluctuation behavior near the quantum Hall transition. To our knowledge we discuss here one of the first analytic characterizations of chaotic behavior for a two-dimensional mesoscopic structure. The connection with possible experimental investigations of the local density of states in the quantum dot array structures (by means of NMR Knight-shift or single-electron-tunneling techniques) and our work is also established.
NASA Astrophysics Data System (ADS)
Yamanashi, Yuki; Masubuchi, Kota; Yoshikawa, Nobuyuki
2016-11-01
The relationship between the timing margin and the error rate of the large-scale single flux quantum logic circuits is quantitatively investigated to establish a timing design guideline. We observed that the fluctuation in the set-up/hold time of single flux quantum logic gates caused by thermal noises is the most probable origin of the logical error of the large-scale single flux quantum circuit. The appropriate timing margin for stable operation of the large-scale logic circuit is discussed by taking the fluctuation of setup/hold time and the timing jitter in the single flux quantum circuits. As a case study, the dependence of the error rate of the 1-million-bit single flux quantum shift register on the timing margin is statistically analyzed. The result indicates that adjustment of timing margin and the bias voltage is important for stable operation of a large-scale SFQ logic circuit.
Camparo, James; Fathi, Gilda
2009-05-15
Atomic clocks that fly on global-navigation satellites such as global positioning system (GPS) and Galileo employ light from low-temperature, inductively coupled plasmas (ICPs) for atomic signal generation and detection (i.e., alkali/noble-gas rf-discharge lamps). In this application, the performance of the atomic clock and the capabilities of the navigation system depend sensitively on the stability of the ICP's optical emission. In order to better understand the mechanisms that might lead to instability in these rf-discharge lamps, and hence the satellite atomic clocks, we studied the optical emission from a Rb/Xe ICP as a function of the rf power driving the plasma. Surprisingly, we found that the electron density in the plasma was essentially independent of increases in rf power above its nominal value (i.e., 'rf-power gain') and that the electron temperature was only a slowly varying function of rf-power gain. The primary effect of rf power was to increase the temperature of the neutrals in the plasma, which was manifested by an increase in Rb vapor density. Interestingly, we also found evidence for electron temperature fluctuations (i.e., fluctuations in the plasma's high-energy electron content). The variance of these fluctuations scaled inversely with the plasma's mean electron temperature and was consistent with a simple model that assumed that the total electron density in the discharge was independent of rf power. Taken as a whole, our results indicate that the electrons in alkali/noble-gas ICPs are little affected by slight changes in rf power and that the primary effect of such changes is to heat the plasma's neutral species.
Draijer, Matthijs J; Hondebrink, Erwin; Larsson, Marcus; van Leeuwen, Ton G; Steenbergen, Wiendelt
2010-10-11
Scattering fluid flux can be quantified with coherent light, either from the contrast of speckle patterns, or from the moments of the power spectrum of intensity fluctuations. We present a theory connecting these approaches for the general case of mixed static-dynamic patterns of boiling speckles without prior assumptions regarding the particle dynamics. An expression is derived and tested relating the speckle contrast to the intensity power spectrum. Our theory demonstrates that in speckle contrast the concentration of moving particles dominates over the contribution of speed to the particle flux. Our theory provides a basis for comparison of both approaches when used for studying tissue perfusion.
Methane dissociation on Pt(111): Searching for a specific reaction parameter density functional
Nattino, Francesco Migliorini, Davide; Kroes, Geert-Jan; Bonfanti, Matteo
2016-01-28
The theoretical description of methane dissociating on metal surfaces is a current frontier in the field of gas-surface dynamics. Dynamical models that aim at achieving a highly accurate description of this reaction rely on potential energy surfaces based on density functional theory calculations at the generalized gradient approximation. We focus here on the effect that the exchange-correlation functional has on the reactivity of methane on a metal surface, using CHD{sub 3} + Pt(111) as a test case. We present new ab initio molecular dynamics calculations performed with various density functionals, looking also at functionals that account for the van der Waals (vdW) interaction. While searching for a semi-empirical specific reaction parameter density functional for this system, we find that the use of a weighted average of the PBE and the RPBE exchange functionals together with a vdW-corrected correlation functional leads to an improved agreement with quantum state-resolved experimental data for the sticking probability, compared to previous PBE calculations. With this semi-empirical density functional, we have also investigated the surface temperature dependence of the methane dissociation reaction and the influence of the rotational alignment on the reactivity, and compared our results with experiments.
NASA Astrophysics Data System (ADS)
Zupan, Ales; Burke, Kieron; Ernzerhof, Matthias; Perdew, John P.
1997-06-01
We analyze the electron densities n(r) of atoms, molecules, solids, and surfaces. The distributions of values of the Seitz radius rs=(3/4πn)1/3 and the reduced density gradient s=|∇n|/(2(3π2)1/3n4/3) in an electron density indicate which ranges of these variables are significant for physical processes. We also define energy-weighted averages of these variables, , from which local spin density (LSD) and generalized gradient approximation (GGA) exchange-correlation energies may be estimated. The changes in these averages upon rearrangement of the nuclei (atomization of molecules or solids, stretching of bond lengths or lattice parameters, change of crystal structure, etc.) are used to explain why GGA corrects LSD in the way it does. A thermodynamic-like inequality (essentially d/>d
SCAN-based hybrid and double-hybrid density functionals from models without fitted parameters
NASA Astrophysics Data System (ADS)
Hui, Kerwin; Chai, Jeng-Da
2016-01-01
By incorporating the nonempirical strongly constrained and appropriately normed (SCAN) semilocal density functional [J. Sun, A. Ruzsinszky, and J. P. Perdew, Phys. Rev. Lett. 115, 036402 (2015)] in the underlying expression of four existing hybrid and double-hybrid models, we propose one hybrid (SCAN0) and three double-hybrid (SCAN0-DH, SCAN-QIDH, and SCAN0-2) density functionals, which are free from any fitted parameters. The SCAN-based double-hybrid functionals consistently outperform their parent SCAN semilocal functional for self-interaction problems and noncovalent interactions. In particular, SCAN0-2, which includes about 79% of Hartree-Fock exchange and 50% of second-order Møller-Plesset correlation, is shown to be reliably accurate for a very diverse range of applications, such as thermochemistry, kinetics, noncovalent interactions, and self-interaction problems.
Permeability parameter as a function of population density in classical infiltration equation
NASA Astrophysics Data System (ADS)
Abidin, Nor Hafizah; Ahmad, Rohanin; Nordin, Syarifah Zyurina
2014-12-01
Rapid development of urban areas has caused many problems especially related to water issues. The increase in urban development also means the increase in impervious surfaces due to expansion of buildings, roads, parking lots to name a few. Impervious surfaces have low water permeability compared to pervious surfaces. Also, infiltration capacity is dependent on the permeability of the area and subsequently permeability is dependent on the surface conditions. In this paper, we study the infiltration capacity with the assumption that permeability parameter can be described in the term of the population density of the area. The modified model is based on the original form of Green-Ampt equation. The new model with population density is able to describe permeability, hence the infiltration capacity of an area.
Hirotani, Hiroshi; Yu, Ma; Yamada, Takeshi
2013-01-01
Fluctuation of bacteriophage and Escherichia coli densities in naturally developed riverbed biofilms were investigated for a 1-year period. E. coli ranged from 1,500 to 15,500 most probable number (MPN)/100 mL and from 580 to 18,500 MPN/cm(2) in the main channel in the river water and biofilms, respectively. However, the fluctuations were much greater in the tributary, ranging from 0.8 to 100 MPN/100 mL and from 0.3 to 185 MPN/cm(2) in water and biofilms, respectively. The fluctuations of coliphages were also greater in the tributary than in the main channel. FRNA phage serotyping results indicated no significant differences in the source type of the fecal contamination in the main channel and tributary sampling stations. Significant correlations between phage groups in biofilms and water were found at both main channel and tributary. It was assumed that natural biofilms developed in the streambed captured and retained somatic phages in the biofilms for a certain period of time in the main channel site. At the location receiving constant and heavy contamination, the usage of phage indicators may provide additional information on the presence of viruses. In the small tributary it may be possible to estimate the virus concentration by monitoring the E. coli indicator.
Level density inputs in nuclear reaction codes and the role of the spin cutoff parameter
Voinov, A. V.; Grimes, S. M.; Brune, C. R.; Burger, A.; Gorgen, A.; Guttormsen, M.; Larsen, A. C.; Massey, T. N.; Siem, S.
2014-09-03
Here, the proton spectrum from the ^{57}Fe(α,p) reaction has been measured and analyzed with the Hauser-Feshbach model of nuclear reactions. Different input level density models have been tested. It was found that the best description is achieved with either Fermi-gas or constant temperature model functions obtained by fitting them to neutron resonance spacing and to discrete levels and using the spin cutoff parameter with much weaker excitation energy dependence than it is predicted by the Fermi-gas model.
Level density inputs in nuclear reaction codes and the role of the spin cutoff parameter
Voinov, A. V.; Grimes, S. M.; Brune, C. R.; ...
2014-09-03
Here, the proton spectrum from the 57Fe(α,p) reaction has been measured and analyzed with the Hauser-Feshbach model of nuclear reactions. Different input level density models have been tested. It was found that the best description is achieved with either Fermi-gas or constant temperature model functions obtained by fitting them to neutron resonance spacing and to discrete levels and using the spin cutoff parameter with much weaker excitation energy dependence than it is predicted by the Fermi-gas model.
Mullender, M G; Huiskes, R; Versleyen, H; Buma, P
1996-11-01
The species-specific relationships between trabecular morphology and osteocyte density were investigated in the femoral heads of 30 adult animals of five mammalian species (rat, rabbit, Rhesus monkey, pig, and cow). Our hypothesis is that osteocytes are mechanosensory cells and are involved in the regulation of bone remodeling. According to the predictions from a simulation model, this hypothesis implies that the influencing distance of osteocytes, together with the magnitude of the mechanical loads, determines the thickness of trabeculae and that the number of osteocytes primarily affects the rate of bone remodeling. The number of osteocytes per bone volume ranged from 93,200 mm-3 in rat to 31,900 mm-3 in bovine cancellous bone. Osteocyte density was inversely related to the size of the species. Since basal metabolic output is related to body mass, we speculate that osteocyte density may be related to metabolic rates. Trabecular thickness was larger in the cow than in the other species, but the range of variation between species was relatively small. This agrees with the hypothesis that trabecular thickness is limited by the domain that can be regulated by an osteocyte and that this domain is of similar size regardless of the species. Only in the rat was trabecular thickness considerably smaller than in the other species. This is probably due to the presence of the cartilaginous growth plate in the femoral head of the rat. The relationships with species are different for osteocyte density than for morphometric parameters. Hence, our data support our hypothesis that osteocyte density is not directly associated with the macroscopic trabecular architecture.
Yoshida, Koh; Baluja, Shipra; Inaba, Akira; Koga, Yoshikata
2011-06-07
Using a differential pressure perturbation calorimetry developed by us recently [K. Yoshida, S. Baluja, A. Inaba, K. Tozaki, and Y. Koga, "Experimental determination of third derivative of G (III): Differential pressure perturbation calorimetry (II)," J. Solution Chem. (in press)], we experimentally determined the partial molar S-V cross fluctuation density of solute B, (SV)δ(B) , in binary aqueous solutions for B = 1-propanol (1P) and glycerol (Gly). This third derivative of G provides information about the effect of solute B on the S-V cross fluctuation density, (SV)δ, in aqueous solution as the concentration of B varies. Having determined (SV)δ(B) by better than 1% uncertainty, we evaluated for the first time the fourth derivative quantity (SV)δ(B-B) = N(∂(SV)δ(B) ∕∂n(B)) for B = 1P and Gly graphically without resorting to any fitting functions within several percent. This model-free quantity gives information about the acceleration of the effect of solute B on (SV)δ. By comparing fourth derivative quantities, (SV)δ(B-B) , among B = 1P, Gly, and 2-butoxyethanol obtained previously, the distinction of the effect of solute on H(2)O becomes clearer than before when only the third derivative quantities were available.
NASA Astrophysics Data System (ADS)
Yoshida, Koh; Baluja, Shipra; Inaba, Akira; Koga, Yoshikata
2011-06-01
Using a differential pressure perturbation calorimetry developed by us recently [K. Yoshida, S. Baluja, A. Inaba, K. Tozaki, and Y. Koga, "Experimental determination of third derivative of G (III): Differential pressure perturbation calorimetry (II)," J. Solution Chem. (in press)], we experimentally determined the partial molar S-V cross fluctuation density of solute B, SVδB, in binary aqueous solutions for B = 1-propanol (1P) and glycerol (Gly). This third derivative of G provides information about the effect of solute B on the S-V cross fluctuation density, SVδ, in aqueous solution as the concentration of B varies. Having determined SVδB by better than 1% uncertainty, we evaluated for the first time the fourth derivative quantity SVδB-B = N(∂SVδB /∂nB) for B = 1P and Gly graphically without resorting to any fitting functions within several percent. This model-free quantity gives information about the acceleration of the effect of solute B on SVδ. By comparing fourth derivative quantities, SVδB-B, among B = 1P, Gly, and 2-butoxyethanol obtained previously, the distinction of the effect of solute on H2O becomes clearer than before when only the third derivative quantities were available.
NASA Astrophysics Data System (ADS)
Young, D. L.; Coutts, T. J.; Kaydanov, V. I.
2000-02-01
A novel machine has been developed to measure transport coefficients in the temperature range of 50-350 K of thin films deposited on electrically insulating substrates. The measured coefficients—resistivity, Hall, Seebeck, and Nernst—are applied to solutions of the Boltzmann transport equation to give information about the film's density-of-states effective mass, the Fermi energy level, and an energy-dependent scattering parameter. The machine is designed to eliminate or compensate for simultaneously occurring transport phenomena that would interfere with the desired measured quantity, while allowing for all four coefficients to be measured on the same sample. An average density-of-states effective mass value of 0.29±0.04me was measured on the transparent conductive oxide, cadmium stannate (CTO), over a carrier concentration range of 2-7×1020cm-3. This effective mass value matched previous results obtained by optical and thermoelectric modeling. The measured scattering parameter indicates that neutral impurities or a mixture of scattering mechanisms may inhibit the transport of carriers in CTO.
Galactic rotation curve and spiral density wave parameters from 73 masers
NASA Astrophysics Data System (ADS)
Bobylev, V. V.; Bajkova, A. T.
2013-12-01
Based on kinematic data on masers with known trigonometric parallaxes and measurements of the velocities of HI clouds at tangential points in the inner Galaxy, we have refined the parameters of the Allen-Santillan model Galactic potential and constructed the Galactic rotation curve in a wide range of Galactocentric distances, from 0 to 20 kpc. The circular rotation velocity of the Sun for the adopted Galactocentric distance R 0 = 8 kpc is V 0 = 239 ± 16 km s-1. We have obtained the series of residual tangential, Δ V θ , and radial, V R , velocities for 73 masers. Based on these series, we have determined the parameters of the Galactic spiral density wave satisfying the linear Lin-Shu model using the method of periodogram analysis that we proposed previously. The tangential and radial perturbation amplitudes are f θ = 7.0±1.2 km s-1 and f R = 7.8±0.7 km s-1, respectively, the perturbation wave length is λ = 2.3±0.4 kpc, and the pitch angle of the spiral pattern in a two-armed model is i = -5.2° ±0.7°. The phase of the Sun ζ ⊙ in the spiral density wave is -50° ± 15° and -160° ± 15° from the residual tangential and radial velocities, respectively.
NASA Astrophysics Data System (ADS)
Schmidt, Denise; Gimeno Garcia, Sebastian; Schreier, Franz; Lichtenberg, Gunter
2015-11-01
Among the various input data required for the retrieval of atmospheric state parameters from infrared remote sensing observations molecular spectroscopy line data have a central role, because their quality is critical for the quality of the final product. Here we discuss the impact of the line parameters on vertical column densities (VCD) estimated from short wave infrared nadir observations. Using BIRRA (the Beer InfraRed Retrieval Algorithm) comprising a line-by-line radiative transfer code (forward model) and a separable nonlinear least squares solver for inversion we retrieve carbon monoxide from observations of SCIAMACHY aboard Envisat. Retrievals using recent versions of HITRAN und GEISA have been performed and the results are compared in terms of residual norms, molecular density scaling factors, their corresponding errors, and the final VCD product. The retrievals turn out to be quite similar for all three databases, so a definite recommendation in favor of one of these databases is difficult for the considered spectral range around 2.3 μm. Nevertheless, HITRAN 2012 appears to be advantageous when evaluating the different quality criteria.
Density of voltage-gated potassium channels is a bifurcation parameter in pyramidal neurons
Robinson, Hugh P. C.; Århem, Peter
2014-01-01
Several types of intrinsic dynamics have been identified in brain neurons. Type 1 excitability is characterized by a continuous frequency-stimulus relationship and, thus, an arbitrarily low frequency at threshold current. Conversely, Type 2 excitability is characterized by a discontinuous frequency-stimulus relationship and a nonzero threshold frequency. In previous theoretical work we showed that the density of Kv channels is a bifurcation parameter, such that increasing the Kv channel density in a neuron model transforms Type 1 excitability into Type 2 excitability. Here we test this finding experimentally, using the dynamic clamp technique on Type 1 pyramidal cells in rat cortex. We found that increasing the density of slow Kv channels leads to a shift from Type 1 to Type 2 threshold dynamics, i.e., a distinct onset frequency, subthreshold oscillations, and reduced latency to first spike. In addition, the action potential was resculptured, with a narrower spike width and more pronounced afterhyperpolarization. All changes could be captured with a two-dimensional model. It may seem paradoxical that an increase in slow K channel density can lead to a higher threshold firing frequency; however, this can be explained in terms of bifurcation theory. In contrast to previous work, we argue that an increased outward current leads to a change in dynamics in these neurons without a rectification of the current-voltage curve. These results demonstrate that the behavior of neurons is determined by the global interactions of their dynamical elements and not necessarily simply by individual types of ion channels. PMID:25339708
Dutra, José Diogo L.; Lima, Nathalia B. D.; Freire, Ricardo O.; Simas, Alfredo M.
2015-01-01
We advance the concept that the charge factors of the simple overlap model and the polarizabilities of Judd-Ofelt theory for the luminescence of europium complexes can be effectively and uniquely modeled by perturbation theory on the semiempirical electronic wave function of the complex. With only three adjustable constants, we introduce expressions that relate: (i) the charge factors to electronic densities, and (ii) the polarizabilities to superdelocalizabilities that we derived specifically for this purpose. The three constants are then adjusted iteratively until the calculated intensity parameters, corresponding to the 5D0→7F2 and 5D0→7F4 transitions, converge to the experimentally determined ones. This adjustment yields a single unique set of only three constants per complex and semiempirical model used. From these constants, we then define a binary outcome acceptance attribute for the adjustment, and show that when the adjustment is acceptable, the predicted geometry is, in average, closer to the experimental one. An important consequence is that the terms of the intensity parameters related to dynamic coupling and electric dipole mechanisms will be unique. Hence, the important energy transfer rates will also be unique, leading to a single predicted intensity parameter for the 5D0→7F6 transition. PMID:26329420
NASA Astrophysics Data System (ADS)
Jensen, Robert K.; Fletcher, P.; Abraham, C.
1991-04-01
The segment mass mass proportions and moments of inertia of a sample of twelve females and seven males with mean ages of 67. 4 and 69. 5 years were estimated using textbook proportions based on cadaver studies. These were then compared with the parameters calculated using a mathematical model the zone method. The methodology of the model was fully evaluated for accuracy and precision and judged to be adequate. The results of the comparisons show that for some segments female parameters are quite different from male parameters and inadequately predicted by the cadaver proportions. The largest discrepancies were for the thigh and the trunk. The cadaver predictions were generally less than satisfactory although the common variance for some segments was moderately high. The use ofnon-linear regression and segment anthropometry was illustrated for the thigh moments of inertia and appears to be appropriate. However the predictions from cadaver data need to be examined fully. These results are dependent on the changes in mass and density distribution which occur with aging and the changes which occur with cadaver samples prior to and following death.
Zeng, Zhiping; Chen, Xuanze; Wang, Hening; Huang, Ning; Shan, Chunyan; Zhang, Hao; Teng, Junlin; Xi, Peng
2015-02-10
Previous stochastic localization-based super-resolution techniques are largely limited by the labeling density and the fidelity to the morphology of specimen. We report on an optical super-resolution imaging scheme implementing joint tagging using multiple fluorescent blinking dyes associated with super-resolution optical fluctuation imaging (JT-SOFI), achieving ultra-high labeling density super-resolution imaging. To demonstrate the feasibility of JT-SOFI, quantum dots with different emission spectra were jointly labeled to the tubulin in COS7 cells, creating ultra-high density labeling. After analyzing and combining the fluorescence intermittency images emanating from spectrally resolved quantum dots, the microtubule networks are capable of being investigated with high fidelity and remarkably enhanced contrast at sub-diffraction resolution. The spectral separation also significantly decreased the frame number required for SOFI, enabling fast super-resolution microscopy through simultaneous data acquisition. As the joint-tagging scheme can decrease the labeling density in each spectral channel, thereby bring it closer to single-molecule state, we can faithfully reconstruct the continuous microtubule structure with high resolution through collection of only 100 frames per channel. The improved continuity of the microtubule structure is quantitatively validated with image skeletonization, thus demonstrating the advantage of JT-SOFI over other localization-based super-resolution methods.
Robert, Clélia; Conan, Jean-Marc; Michau, Vincent; Renard, Jean-Baptiste; Robert, Claude; Dalaudier, Francis
2008-02-01
Scintillation effects are not negligible in the stratosphere. We present a model based on a 3D model of anisotropic and isotropic refractive index fluctuations spectra that predicts scintillation rates within the so-called small perturbation approximation. Atmospheric observations of stellar scintillation made from the AMON-RA (AMON, Absorption par les Minoritaires Ozone et NO(x); RA, rapid) balloon-borne spectrometer allows us to remotely probe wave-turbulence characteristics in the stratosphere. Data reduction from these observations brings out values of the inner scale of the anisotropic spectrum. We find metric values of the inner scale that are compatible with space-based measurements. We find a major contribution of the anisotropic spectrum relative to the isotropic contribution. When the sight line plunges into the atmosphere, strong scintillation occurs as well as coupled chromatic refraction effects.
Accuracy of estimated geometric parameters of trees depending on the LIDAR data density
NASA Astrophysics Data System (ADS)
Hadas, Edyta; Estornell, Javier
2015-04-01
The estimation of dendrometric variables has become important for spatial planning and agriculture projects. Because classical field measurements are time consuming and inefficient, airborne LiDAR (Light Detection and Ranging) measurements are successfully used in this area. Point clouds acquired for relatively large areas allows to determine the structure of forestry and agriculture areas and geometrical parameters of individual trees. In this study two LiDAR datasets with different densities were used: sparse with average density of 0.5pt/m2 and the dense with density of 4pt/m2. 25 olive trees were selected and field measurements of tree height, crown bottom height, length of crown diameters and tree position were performed. To determine the tree geometric parameters from LiDAR data, two independent strategies were developed that utilize the ArcGIS, ENVI and FUSION software. Strategy a) was based on canopy surface model (CSM) slicing at 0.5m height and in strategy b) minimum bounding polygons as tree crown area were created around detected tree centroid. The individual steps were developed to be applied also in automatic processing. To assess the performance of each strategy with both point clouds, the differences between the measured and estimated geometric parameters of trees were analyzed. As expected, the tree height were underestimated for both strategies (RMSE=0.7m for dense dataset and RMSE=1.5m for sparse) and tree crown height were overestimated (RMSE=0.4m and RMSE=0.7m for dense and sparse dataset respectively). For dense dataset, strategy b) allows to determine more accurate crown diameters (RMSE=0.5m) than strategy a) (RMSE=0.8m), and for sparse dataset, only strategy a) occurs to be relevant (RMSE=1.0m). The accuracy of strategies were also examined for their dependency on tree size. For dense dataset, the larger the tree (height or crown longer diameter), the higher was the error of estimated tree height, and for sparse dataset, the larger the tree
Soulis, Johannes V.; Fytanidis, Dimitrios K.; Lampri, Olga P.; Giannoglou, George D.
2016-01-01
Background The temporal variation of the hemodynamic mechanical parameters during cardiac pulse wave is considered as an important atherogenic factor. Applying non-Newtonian blood molecular viscosity simulation is crucial for hemodynamic analysis. Understanding low density lipoprotein (LDL) distribution in relation to flow parameters will possibly spot the prone to atherosclerosis aorta regions. Methods The biomechanical parameters tested were averaged wall shear stress (AWSS), oscillatory shear index (OSI) and relative residence time (RRT) in relation to the LDL concentration. Four non-Newtonian molecular viscosity models and the Newtonian one were tested for the normal human aorta under oscillating flow. The analysis was performed via computational fluid dynamic. Results Tested viscosity blood flow models for the biomechanical parameters yield a consistent aorta pattern. High OSI and low AWSS develop at the concave aorta regions. This is most noticeable in downstream flow region of the left subclavian artery and at concave ascending aorta. Concave aorta regions exhibit high RRT and elevated LDL. For the concave aorta site, the peak LDL value is 35.0% higher than its entrance value. For the convex site, it is 18.0%. High LDL endothelium regions located at the aorta concave site are well predicted with high RRT. Conclusions We are in favor of using the non-Newtonian power law model for analysis. It satisfactorily approximates the molecular viscosity, WSS, OSI, RRT and LDL distribution. Concave regions are mostly prone to atherosclerosis. The flow biomechanical factor RRT is a relatively useful tool for identifying the localization of the atheromatic plaques of the normal human aorta. PMID:28197271
NASA Astrophysics Data System (ADS)
Loehman, R.; Heinsch, F. A.; Mills, J. N.; Wagoner, K.; Running, S.
2003-12-01
Recent predictive models for hantavirus pulmonary syndrome (HPS) have used remotely sensed spectral reflectance data to characterize risk areas with limited success. We present an alternative method using gross primary production (GPP) from the MODIS sensor to estimate the effects of biomass accumulation on population density of Peromyscus maniculatus (deer mouse), the principal reservoir species for Sin Nombre virus (SNV). The majority of diagnosed HPS cases in North America are attributed to SNV, which is transmitted to humans through inhalation of excretions and secretions from infected rodents. A logistic model framework is used to evaluate MODIS GPP, temperature, and precipitation as predictors of P. maniculatus density at established trapping sites across the western United States. Rodent populations are estimated using monthly minimum number alive (MNA) data for 2000 through 2002. Both local meteorological data from nearby weather stations and 1.25 degree x 1 degree gridded data from the NASA DAO were used in the regression model to determine the spatial sensitivity of the response. MODIS eight-day GPP data (1-km resolution) were acquired and binned to monthly average and monthly sum GPP for 3km x 3km grids surrounding each rodent trapping site. The use of MODIS GPP to forecast HPS risk may result in a marked improvement over past reflectance-based risk area characterizations. The MODIS GPP product provides a vegetation dynamics estimate that is unique to disease models, and targets the fundamental ecological processes responsible for increased rodent density and amplified disease risk.
Partnering dispersion corrections with modern parameter-free double-hybrid density functionals.
Sancho-García, J C; Brémond, É; Savarese, M; Pérez-Jiménez, A J; Adamo, C
2017-03-09
The PBE-QIDH and SOS1-PBE-QIDH double-hybrid density functionals are merged with a pair of dispersion corrections, namely the pairwise additive D3(BJ) and the non-local correlation functional VV10, leading to the corresponding dispersion-corrected models. The parameters adjusting each of the dispersion corrections to the functionals are obtained by fitting to well-established energy datasets (e.g. S130) used as a benchmark, giving rise to functionals spanning covalent and non-covalent binding forces. The application of the models to challenging systems out of the training set, like those comprising the L7 database of large supramolecular complexes, or the S66x8 dataset of stretched and elongated intermolecular distances, reveals the high accuracy of the coupling.
Hydration shell parameters of aqueous alcohols: THz excess absorption and packing density.
Matvejev, V; Zizi, M; Stiens, J
2012-12-06
Solvation in water requires minimizing the perturbations in its hydrogen bonded network. Hence solutes distort water molecular motions in a surrounding domain, forming a molecule-specific hydration shell. The properties of those hydration shells impact the structure and function of the solubilized molecules, both at the single molecule and at higher order levels. The size of the hydration shell and the picoseconds time-scale water dynamics retardation are revealed by terahertz (THz) absorption coefficient measurements. Room-temperature absorption coefficient at f = 0.28 [THz] is measured as a function of alcohol concentration in aqueous methanol, ethanol, 1,2-propanol, and 1-butanol solutions. Highly diluted alcohol measurements and enhanced overall measurement accuracy are achieved with a THz absorption measurement technique of nL-volume liquids in a capillary tube. In the absorption analysis, bulk and interfacial molecular domains of water and alcohol are considered. THz ideal and excess absorption coefficients are defined in accordance with thermodynamics mixing formulations. The parameter extraction method is developed based on a THz excess absorption model and hydrated solute molecule packing density representation. First, the hydration shell size is deduced from the hydrated solute packing densities at two specific THz excess absorption nonlinearity points: at infinite alcohol dilution (IAD) and at the THz excess absorption extremum (EAE). Consequently, interfacial water and alcohol molecular domain absorptions are deduced from the THz excess absorption model. The hydration shell sizes obtained at the THz excess absorption extremum are in excellent agreement with other reports. The hydration shells of methanol, ethanol, 1- and 2-propanol consist of 13.97, 22.94, 22.99, and 31.10 water molecules, respectively. The hydration shell water absorption is on average 0.774 ± 0.028 times the bulk water absorption. The hydration shell parameters might shed light on
NASA Astrophysics Data System (ADS)
Trevelyan, Alexander; Corwin, Eric
2014-03-01
We explore the response of a model statistical system to strong, non-linear perturbations to its state variables. Specifically, we work with a tunable model of Johnson-Nyquist noise, designed to permit a driving of both the drift and diffusion terms in the associated White Noise Langevin Equation. We achieve a simultaneous measurement of both sides of the Fluctuation Dissipation Theorem (FDT) by driving the circuit with digitally generated white noise and measuring the output. This allows us to calculate a frequency-dependent effective temperature for the driven system, which for an equilibrium system should be set by the energy scale of the input white noise. Comparison of the two sides of FDT-the circuit's transfer function and the power spectral density of the voltage fluctuations-across frequency-space proves non-trivial, and methods are discussed for achieving the most reliable estimate. After comparing the response for a series of functional signals, we find that FDT, measured in this simultaneous fashion, remains intact even while the system is being actively driven out of equilibrium.
NASA Astrophysics Data System (ADS)
Yoshimura, Shinji; Terasaka, Kenichiro; Tanaka, Eiki; Aramaki, Mitsutoshi; Tanaka, Masayoshi Y.
An intermittent behavior of local electron flux in a laboratory ECR plasma is statistically analyzed by means of probability density functions (PDFs). The PDF constructed from a time series of the floating potential signal on a Langmuir probe has a fat tail in the negative value side, which reflects the intermittency of the local electron flux. The PDF of the waiting time, which is defined by the time interval between two successive events, is found to exhibit an exponential distribution, suggesting that the phenomenon is characterized by a stationary Poisson process. The underlying Poisson process is also confirmed by the number of events in given time intervals that is Poisson distributed.
NASA Astrophysics Data System (ADS)
Henríquez, Paula; Donoso, Denise S.; Grez, Audrey A.
2009-11-01
Habitat fragmentation results in new environmental conditions that may stress resident populations. Such stress may be reflected in demographical or morphological changes in the individuals inhabiting those landscapes. This study evaluates the effects of fragmentation of the Maulino forest on population density, sex ratio, body size, and fluctuating asymmetry (FA) of the endemic carabid Ceroglossus chilensis. Individuals of C. chilensis were collected during 2006 in five locations at Los Queules National Reserve (continuous forest), in five forest fragments and in five areas of surrounding pine plantations (matrix). In each location, once a season, 40 pitfall traps (20 in the centre, 20 in the edge), were opened for 72 h. Population density of C. chilensis was higher in the small fragments than in the pine matrix, with intermediate densities in the continuous forest; sex ratio did not differ significantly from 1:1 in the three habitats. Individuals from the centre of fragments were smaller than those from the centre of continuous forest, and FA did not vary significantly among habitats. These results suggest that small forest fragments maintain dense populations of C. chilensis and therefore they must be considered in conservation strategies. Although the decrease of the body size suggests that small remnants should be connected by managing the structure of the surrounding matrix, facilitating the dispersion of this carabid across the landscape and avoiding possible antagonistic interactions inside small fragments.
Hansen, T F; Stenseth, N C; Henttonen, H; Tast, J
1999-02-02
A 3- to 5-year cycle of vole abundances is a characteristic phenomenon in the ecology of northern regions, and their explanation stands as a central theoretical challenge in population ecology. Although many species of voles usually coexist and are in severe competition for food and breeding space, the role of interspecific competition in vole cycles has never been evaluated statistically. After studying community effects on the population dynamics of the gray-sided vole (Clethrionomys rufocanus) in the subarctic birch forest at Kilpisjärvi, Finland, we report statistical results showing that both interspecific and intraspecific effects are important in the direct year-to-year density dependence. However, interspecific effects are not detectable in the 2-year delayed density dependence that is crucial for generating the characteristic cycles. Furthermore, we show that most of the competition takes place during the winter. The results are evaluated against two models of community dynamics. One assumes that the delayed effects are caused by an interaction with a specialist predator, and the other assumes that they are caused by overgrazing food plants. These statistical results show that vole cycles may be generated by a species-specific trophic interaction. The results also suggest that the gray-sided vole may be the focal species in the birch-forest community, as field voles may be in the taiga and as lemmings may be on the tundra.
NASA Astrophysics Data System (ADS)
Gao, Xin-Yi
2016-06-01
Liquids with gas bubbles are commonly seen in medical science, natural science, daily life and engineering. Nonlinear-wave symbolic computation on the (3+1)-dimensional variable-coefficient Kudryashov-Sinelshchikov model for a bubbly liquid is hereby performed. An auto-Bäcklund transformation and with some solitonic solutions are obtained. With respect to the density fluctuation of the bubble-liquid mixture, both the auto-Bäcklund transformation and solitonic solutions depend on the bubble-liquid-viscosity, transverse-perturbation, bubble-liquid-nonlinearity and bubble-liquid-dispersion coefficient functions. We note that some shock waves given by our solutions have been observed by the gas-bubble/liquid-mixture experiments. Effects on a bubbly liquid with respect to the bubble-liquid-viscosity, transverse-perturbation, bubble-liquid-nonlinearity and bubble-liquid-dispersion coefficient functions might be detected by the future gas-bubble/liquid-mixture experiments.
Puc, Małgorzata
2012-01-01
Pollen grains are one of the most important groups of atmospheric biological particles that originate allergic processes. Knowledge of intradiurnal variation of the atmospheric pollen may be useful for the treatment and prevention of pollen allergies. Intradiurnal fluctuation of hourly pollen counts in 24 h are related to the daily rhythm of anther opening, and modified by various interacting factors. Flowering and pollen production of individual species are influenced by genetic, phenological, ecological, meteorological and climatic factors. Estimation of the intradiurnal variability in the pollen count permits evaluation of the threat posed by allergens over a given area. Measurements performed in Szczecin over a period of 7 years (2006-2012) permitted analysis of hourly variation of the pollen count of birch (Betula) and ash (Fraxinus) in 24 h, and evaluation of the impact of weather conditions and the concentration of gas air pollutants on the intradiurnal patterns of both taxa. Aerobiological monitoring was conducted using a Hirst volumetric trap (Lanzoni VPPS 2000). Consecutive phases during the day were defined as 1, 5, 25, 50, 75, 95, 99% of annual total pollen. The analysis revealed that 50% of total daily pollen was noted at 14:00 for Betula and Fraxinus. The hourly distribution of birch pollen count skewed to the left and the majority of pollen of this taxon appears in the air in the first 12 hours of the day. However, for ash, the hourly distribution of pollen count skewed to the right. Statistically significant correlation was noted between the Betula and Fraxinus pollen concentration and the mean air temperature, relative humidity, wind speed, air pressure, total radiation and nitrogen oxides (NO(x)).
Wang, Xifu; Bai, Renju; Li, Yajun; Zhao, Jinkun
2013-01-01
We evaluated the correlation between computed tomography (CT) perfusion parameters and markers of angiogenesis in adrenal adenomas and non-adenomas to determine if perfusion CT can be used to distinguish between them. Thirty-four patients with pathologically-confirmed adrenal tumors (17 adenomas, 17 non-adenomas) received CT perfusion imaging before surgery. CT perfusion parameters (blood flow [BF], blood volume [BV], mean transit time [MTT], and permeability surface area product [PS]) were calculated. Tumor tissue sections were examined with immunohistochemical methods for vascular endothelial growth factor (VEGF) expression and microvessel density (MVD). The mean age of the 34 patients was 43 years. The median BV was significantly higher in adenomas than in non-adenomas [12.3 ml/100 g, inter-quartile range (IQR): 10.4 to 16.5 ml/100 g vs. 8.8 ml/100 g, IQR: 3.3 to 9.4 ml/100 g, p = 0.001]. Differences in BF, MTT, and PS parameter values between adenomas and non-adenomas were not significant (p>0.05). The mean MVD was significantly higher in adenomas compared to non-adenomas (98.5±28.5 vs. 53.5±27.0, p<0.0001). Adenomas also expressed significantly higher median VEGF than non-adenomas (65%, IQR: 50 to 79% vs. 45%, IQR: 35 to 67%, p = 0.02). A moderately strong correlation between BF and VEGF (r = 0.53, p = 0.03) and between BV and MVD among adenomas (r = 0.57, p = 0.02) exist. Morphology, MVD, and VEGF expression in adenomas differ significantly from non-adenomas. Of the CT perfusion parameters examined, both BF and BV correlate with MVD, but only BF correlates with VEGF, and only in adenomas. The significant difference in BV suggests that BV may be used to differentiate adenomas from non-adenomas. However, the small difference in BV shows that it may only be possible to use BV to identify adenomas vs. non-adenomas at extreme BV values. PMID:24260316
NASA Astrophysics Data System (ADS)
Novikov, Ivan; Rueter, Keiti
2016-09-01
Parameters of density distribution of exotic nuclei with halo structure were extracted from the experimental data on the interaction cross-section using exact expressions obtained in the Glauber theory. Generally, to do so measured interaction cross-section is compared with a reaction cross-section calculated in optical approximation or using exact expressions of the Glauber theory. It was shown before that the parameters of nuclear density distribution depends on chosen density model (Gaussian, harmonic oscillator or Woods-Saxon) and on the used approximation of the Glauber theory (i.e. optical or rigid target). In the presented paper, we discuss the difference between reaction and interaction cross-sections calculated in various approximations, and how this difference affects the accuracy of the nuclear density parameters determination. As an example, we provide results of the analyzes of experimental data on interaction cross-section of 11Li, 16C and 31Ne nuclei on 12C target.
On Predicting Mössbauer Parameters of Iron-Containing Molecules with Density-Functional Theory
2014-01-01
The performance of six frequently used density functional theory (DFT) methods (RPBE, OLYP, TPSS, B3LYP, B3LYP*, and TPSSh) in the prediction of Mössbauer isomer shifts(δ) and quadrupole splittings (ΔEQ) is studied for an extended and diverse set of Fe complexes. In addition to the influence of the applied density functional and the type of the basis set, the effect of the environment of the molecule, approximated with the conducting-like screening solvation model (COSMO) on the computed Mössbauer parameters, is also investigated. For the isomer shifts the COSMO-B3LYP method is found to provide accurate δ values for all 66 investigated complexes, with a mean absolute error (MAE) of 0.05 mm s–1 and a maximum deviation of 0.12 mm s–1. Obtaining accurate ΔEQ values presents a bigger challenge; however, with the selection of an appropriate DFT method, a reasonable agreement can be achieved between experiment and theory. Identifying the various chemical classes of compounds that need different treatment allowed us to construct a recipe for ΔEQ calculations; the application of this approach yields a MAE of 0.12 mm s–1 (7% error) and a maximum deviation of 0.55 mm s–1 (17% error). This accuracy should be sufficient for most chemical problems that concern Fe complexes. Furthermore, the reliability of the DFT approach is verified by extending the investigation to chemically relevant case studies which include geometric isomerism, phase transitions induced by variations of the electronic structure (e.g., spin crossover and inversion of the orbital ground state), and the description of electronically degenerate triplet and quintet states. Finally, the immense and often unexploited potential of utilizing the sign of the ΔEQ in characterizing distortions or in identifying the appropriate electronic state at the assignment of the spectral lines is also shown. PMID:25821417
León, Gabriel; Sudarsky, Daniel E-mail: sudarsky@nucleares.unam.mx
2015-06-01
The statistical properties of the primordial density perturbations has been considered in the past decade as a powerful probe of the physical processes taking place in the early universe. Within the inflationary paradigm, the properties of the bispectrum are one of the keys that serves to discriminate among competing scenarios concerning the details of the origin of cosmological perturbations. However, all of the scenarios, based on the conventional approach to the so-called ''quantum-to-classical transition'' during inflation, lack the ability to point out the precise physical mechanism responsible for generating the inhomogeneity and anisotropy of our universe starting from and exactly homogeneous and isotropic vacuum state associated with the early inflationary regime. In past works, we have shown that the proposals involving a spontaneous dynamical reduction of the quantum state provide plausible explanations for the birth of said primordial inhomogeneities and anisotropies. In the present manuscript we show that, when considering within the context of such proposals, the characterization of the spectrum and bispectrum turn out to be quite different from those found in the traditional approach, and in particular, some of the statistical features, must be treated in a different way leading to some rather different conclusions.
NASA Astrophysics Data System (ADS)
Wickramarachchi, P. N.; Kawamoto, K.; Hamamoto, S.; Nagamori, M.; Moldrup, P.; Komatsu, T.
2011-12-01
Landfill sites have been emerging in greenhouse warming scenarios as a significant source of atmospheric methane (CH4). Until recently, landfill management strategies have mainly addressed the problem of preventing groundwater contamination and reduction of leachate generation. Being one of the largest sources of anthropogenic CH4 emission, the final cover system should also be designed for minimizing the greenhouse gases migration into the atmosphere or the areas surrounding the landfill while securing the hydraulic performance. Compared to the intensive research efforts on hydraulic performances of landfill final cover soil, few studies about gas transport characteristics of landfill cover soils have been done. However, recent soil-gas studies implied that the effects of soil physical properties such as bulk density (i.e., compaction level), soil particle size are key parameters to understand landfill gaseous performance. The gas exchange through the final cover soils is controlled by advective and diffusive gas transport. Air permeability (ka) governs the advective gas transport while the soil-gas diffusion coefficient (Dp) governs diffusive gas transport. In this study, the effects of compaction level and particle size fraction effects on ka and Dp for landfill final cover soil was investigated. The disturbed soil samples were taken from landfill final cover in Japan. A compaction tests were performed for the soil samples with two different size fractions (< 35 mm and < 2.0 mm). In the compaction tests at field water content , the soil samples were repacked into soil cores (i.d. 15-cm, length 12-cm, 2120 cm3) at two different compaction levels [(MP):2700 kN/m2 and (SP):600 kN/m2]. After the compaction tests, ka and Dp were measured and then samples were saturated and subsequently drained at different soil-water matric potential of 0.98, 2.94, 9.81, 1235 kPa and with air-dried and oven-dried conditions. Results showed that measured Dp and ka values for the
NASA Astrophysics Data System (ADS)
Rowland, D. E.; Pfaff, R. F.; Uribe, P.; Burchill, J.
2006-12-01
High-accuracy, high-cadence measurements of ionospheric electron density between 100 and a few x 106 / cc and electron temperature from 200 K to a few thousand K are of critical importance for understanding conductivity, Joule heating rates, and instability growth rates. We present results from the development of an impedance probe at NASA GSFC and show its strengths relative to other measurement techniques. Complementary measurement techniques such as Langmuir Probes, while providing extremely high measurement cadence, suffer from uncertainties in calibration, surface contamination effects, and wake/sheath effects. Impedance Probes function by measuring the phase shift between the voltage on a long antenna and the current flowing from the antenna into the plasma as a function of frequency. At frequencies for which the phase shift is zero, a plasma resonance is assumed to exist. These resonances depend on a variety of plasma parameters, including the electron density, electron temperature, and magnetic field strength, as well as the antenna geometry, angle between the antenna and the magnetic field, and sheath / Debye length effects, but do not depend on the surface properties of the antenna. Previous impedance probe designs which "lock" onto the upper hybrid resonance are susceptible to losing lock in low-density environments. Information about other resonances, including the series resonance (which strongly depends on temperature) and other resonances which may occur near the upper hybrid, confounding its identification, are typically not transmitted. The novel features of the GSFC Impedance Probe (PISA) include: 1) A white noise generator that stimulates a wide range of frequencies simultaneously, allowing the instrument to send down the entire impedance frequency spectrum every few milliseconds. This allows identification of all resonance frequencies, including the series resonance which depends on temperature. 2) DC bias voltage stepping to bring the antenna
Koshy, George; Varghese, Ron Thomas; Naik, Dukhabandhu; Asha, Hesargatta Shyamsunder; Thomas, Nihal; Seshadri, Mandalam Subramaniam; Alexander, Mathew; Thomas, Maya; Aaron, Sanjith; Paul, Thomas Vizhalil
2014-01-01
Background: Although there are reports describing the association of alternations of bone and mineral metabolism in epileptic patients with long-term anticonvulsant therapy, there are only limited Indian studies which have looked at this aspect. Objectives: This study was done to compare the prevalence of changes in bone mineral parameters and bone mineral density (BMD) in ambulant individuals on long-term anticonvulsant therapy with age- and body mass index (BMI)-matched healthy controls. Materials and Methods: There were 55 men (on medications for more than 6 months) and age- and BMI-matched 53 controls. Drug history, dietary calcium intake (DCI), and duration of sunlight exposure were recorded. Bone mineral parameters and BMD were measured. Results: The control group had a significantly higher daily DCI with mean ± SD of 396 ± 91 mg versus 326 ± 101 mg (P = 0.007) and more sunlight exposure of 234 ± 81 vs 167 ± 69 min (P = 0.05). BMD at the femoral neck was significantly lower in cases (0.783 ± 0.105 g/cm2) when compared to controls (0.819 ± 0.114 g/cm2). Majority of the patients (61%) had low femoral neck BMD (P = 0.04). There was no significant difference in the proportion of subjects with vitamin D deficiency (<20 ng/mL) between cases (n = 32) and controls (n = 37) (P = 0.234). Conclusions: Vitamin D deficiency was seen in both the groups in equal proportions, highlighting the existence of a high prevalence of this problem in India. Low femoral neck BMD found in cases may stress the need for supplementing calcium and treating vitamin D deficiency in this specific group. However, the benefit of such intervention has to be studied in a larger proportion of epileptic patients. PMID:25221394
Luo, Shezhou; Chen, Jing M; Wang, Cheng; Xi, Xiaohuan; Zeng, Hongcheng; Peng, Dailiang; Li, Dong
2016-05-30
Vegetation leaf area index (LAI), height, and aboveground biomass are key biophysical parameters. Corn is an important and globally distributed crop, and reliable estimations of these parameters are essential for corn yield forecasting, health monitoring and ecosystem modeling. Light Detection and Ranging (LiDAR) is considered an effective technology for estimating vegetation biophysical parameters. However, the estimation accuracies of these parameters are affected by multiple factors. In this study, we first estimated corn LAI, height and biomass (R^{2} = 0.80, 0.874 and 0.838, respectively) using the original LiDAR data (7.32 points/m^{2}), and the results showed that LiDAR data could accurately estimate these biophysical parameters. Second, comprehensive research was conducted on the effects of LiDAR point density, sampling size and height threshold on the estimation accuracy of LAI, height and biomass. Our findings indicated that LiDAR point density had an important effect on the estimation accuracy for vegetation biophysical parameters, however, high point density did not always produce highly accurate estimates, and reduced point density could deliver reasonable estimation results. Furthermore, the results showed that sampling size and height threshold were additional key factors that affect the estimation accuracy of biophysical parameters. Therefore, the optimal sampling size and the height threshold should be determined to improve the estimation accuracy of biophysical parameters. Our results also implied that a higher LiDAR point density, larger sampling size and height threshold were required to obtain accurate corn LAI estimation when compared with height and biomass estimations. In general, our results provide valuable guidance for LiDAR data acquisition and estimation of vegetation biophysical parameters using LiDAR data.
NASA Astrophysics Data System (ADS)
Suhasini, M.; Sailatha, E.; Gunasekaran, S.; Ramkumaar, G. R.
2015-11-01
The Fourier transform infrared (FT-IR) and FT-Raman spectra of Lornoxicam were recorded in the region 4000-450 cm-1 and 4000-50 cm-1 respectively. Density functional theory (DFT) has been used to calculate the optimized geometrical parameters, atomic charges, and vibrational wavenumbers and intensity of the vibrational bands. The computed vibrational wave numbers were compared with the FT-IR and FT-Raman experimental data. The computational calculations at DFT/B3LYP level with 6-31G(d,p) and 6-31++G(d,p) basis sets. The complete vibrational assignments were performed on the basis of the potential energy distribution (PED) of the Vibrational modes calculated using Vibrational Energy Distribution Analysis (VEDA 4) program. The oscillator's strength calculated by TD-DFT and Lornoxicam is approach complement with the experimental findings. The NMR chemical shifts 13C and 1H were recorded and calculated using the gauge independent atomic orbital (GIAO) method. The Natural charges and intermolecular contacts have been interpreted using Natural Bond orbital (NBO) analysis and the HOMO-LUMO energy gap has been calculated. The thermodynamic properties like Entropy, Enthalpy, Specific heat capacity and zero vibrational energy have been calculated. Besides, molecular electrostatic potential (MEP) was investigated using theoretical calculations.
Parameter scaling toward high-energy density in a quasi-steady flow Z-pinch
NASA Astrophysics Data System (ADS)
Hughes, M. C.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Claveau, E. L.; Doty, S. A.; Forbes, E. G.; Kim, B.; Ross, M. P.
2016-10-01
Sheared axial flows are utilized by the ZaP Flow Z-Pinch Experiment to stabilize MHD instabilities. The pinches formed are 50 cm long with radii ranging from 0.3 to 1.0 cm. The plasma is generated in a coaxial acceleration region, similar to a Marshall gun, which provides a steady supply of plasma for approximately 100 us. The power to the plasma is partially decoupled between the acceleration and pinch assembly regions through the use of separate power supplies. Adiabatic scaling of the Bennett relation gives targets for future devices to reach high-energy density conditions or fusion reactors. The applicability of an adiabatic assumption is explored and work is done experimentally to clarify the plasma compression process, which may be more generally polytropic. The device is capable of a much larger parameter space than previous machine iterations, allowing flexibility in the initial conditions of the compression process to preserve stability. This work is supported by DoE FES and NNSA.
High-precision refractive index measurements revealing order parameter fluctuations in KMnF3 and NiO
NASA Astrophysics Data System (ADS)
Schäfer, F. J.; Kleemann, W.
1985-04-01
The temperature dependence of the refractive index n of cubic crystals undergoing phase transitions (PT) is measured with an accuracy of the order δn=10-6 at temperatures between 3.5 and 1000 K with a computer-controlled Jamin-Lebedeff interferometer. Microscopic monitoring for in situ sample orientation and single domain work is provided. Results are presented for KMnF3 (antiferrodistortive PT) and NiO (antiferromagnetic PT) and discussed within the framework of a generalized phenomenological indicatrix perturbation theory. It predicts the proportionality between the order parameter autocorrelation function <δη2> and the refractive index anomaly preceding the PT. Comparison with recent theoretical predictions is performed.
Universal fluctuations of the AEX index
NASA Astrophysics Data System (ADS)
Gonçalves, Rui; Ferreira, Helena; Stollenwerk, Nico; Pinto, Alberto Adrego
2010-11-01
We compute the analytic expression of the probability distributions F and F of the normalized positive and negative AEX (Netherlands) index daily returns r(t). Furthermore, we define the α re-scaled AEX daily index positive returns r( and negative returns (, which we call, after normalization, the α positive fluctuations and α negative fluctuations. We use the Kolmogorov-Smirnov statistical test as a method to find the values of α that optimize the data collapse of the histogram of the α fluctuations with the Bramwell-Holdsworth-Pinton (BHP) probability density function. The optimal parameters that we found are α+=0.46 and α-=0.43. Since the BHP probability density function appears in several other dissimilar phenomena, our result reveals a universal feature of stock exchange markets.
Longitudinal fluctuations in the Berezinskii-Kosterlitz-Thouless phase
NASA Astrophysics Data System (ADS)
Jakubczyk, Pawel; Metzner, Walter
2017-02-01
We analyze the interplay of longitudinal and transverse thermal fluctuations in a U(1 ) symmetric two-dimensional ϕ4 theory. Toward this end, we derive coupled renormalization-group equations for both types of fluctuations obtained from a linear (Cartesian) decomposition of the order-parameter field. Discarding the longitudinal fluctuations, the expected Berezinskii-Kosterlitz-Thouless phase characterized by a finite stiffness and an algebraic decay of order-parameter correlations is recovered. Renormalized by transverse fluctuations, the longitudinal mass scales to zero so that longitudinal fluctuations become increasingly important for small momenta. Within our expansion of the effective action, they generate a logarithmic decrease of the stiffness, in agreement with previous functional renormalization-group calculations. The logarithmic terms imply a deviation from the vanishing β function for the stiffness in the nonlinear σ model describing the phase fluctuations at three-loop order. To gain further insight, we also compute the flow of the parameters characterizing longitudinal and transverse fluctuations from a density-phase representation of the order-parameter field, with a cutoff on phase fluctuations. The power-law flow of the longitudinal mass and other quantities is thereby confirmed, but the stiffness remains finite in this approach. We conclude that the marginal flow of the stiffness obtained in the Cartesian representation is an artifact of the truncated expansion of momentum dependences.
Kosugi, Yoshiko; Matsuo, Naoko
2006-09-01
Seasonal fluctuations in leaf gas exchange parameters were investigated in three evergreen (Quercus glauca Thunb., Cinnamomum camphora Sieb. and Castanopsis cuspidata Schottky) and one deciduous (Quercus serrata Thunb.) co-occurring, dominant tree species in a temperate broad-leaved forest. Dark respiration rate (Rn), maximum carboxylation rate (Vcmax) and stomatal coefficient (m), the ratio of stomatal conductance to net assimilation rate after adjustment to the vapor pressure deficit and internal carbon dioxide (CO2) concentration, were derived inversely from instantaneous field gas exchange data (one-point method). The normalized values of Rn and Vcmax at the reference temperature of 25 degrees C (Rn25, Vcmax25) and their temperature dependencies (Delta Ha(Rn), Delta Ha(Vcmax)) were analyzed. Parameter Vcmax25 ranged from 24.0-40.3 micromol m(-2) s(-1) and Delta Ha(Vcmax) ranged from 29.1- 67.0 kJ mol(-1). Parameter Rn25 ranged from 0.6-1.4 micromol m(-2) s(-1) and Delta Ha(Rn) ranged from 47.4-95.4 kJ mol(-1). The stomatal coefficient ranged from 7.2-8.2. For the three evergreen trees, a single set of Vcmax25 and Rn25 parameters and temperature dependence curves produced satisfactory estimates of carbon uptake throughout the year, except during the period of simultaneous leaf fall and leaf expansion, which occurs in April and May. In the deciduous oak, declines in Vcmax25 were observed after summer, along with changes in Vcmax25 and Rn25 during the leaf expansion period. In all species, variation in m during periods of leaf expansion and drought should be considered in modeling studies. We conclude that the changes in normalized gas exchange parameters during periods of leaf expansion and drought need to be considered when modeling carbon uptake of evergreen broad-leaved species.
THE MOSDEF SURVEY: ELECTRON DENSITY AND IONIZATION PARAMETER AT z ∼ 2.3
Sanders, Ryan L.; Shapley, Alice E.; Kriek, Mariska; Price, Sedona H.; Reddy, Naveen A.; Freeman, William R.; Siana, Brian; Mobasher, Bahram; Shivaei, Irene; Groot, Laura de; Coil, Alison L.
2016-01-01
Using observations from the MOSFIRE Deep Evolution Field survey, we investigate the physical conditions of star-forming regions in z ∼ 2.3 galaxies, specifically the electron density and ionization state. From measurements of the [O ii]λλ3726,3729 and [S ii]λλ6716,6731 doublets, we find a median electron density of ∼250 cm{sup −3} at z ∼ 2.3, an increase of an order of magnitude compared to measurements of galaxies at z ∼ 0. While z ∼ 2.3 galaxies are offset toward significantly higher O{sub 32} values relative to local galaxies at fixed stellar mass, we find that the high-redshift sample follows a similar distribution to the low-metallicity tail of the local distribution in the O{sub 32} versus R{sub 23} and O3N2 diagrams. Based on these results, we propose that z ∼ 2.3 star-forming galaxies have the same ionization parameter as local galaxies at fixed metallicity. In combination with simple photoionization models, the position of local and z ∼ 2.3 galaxies in excitation diagrams suggests that there is no significant change in the hardness of the ionizing spectrum at fixed metallicity from z ∼ 0 to z ∼ 2.3. We find that z ∼ 2.3 galaxies show no offset compared to low-metallicity local galaxies in emission line ratio diagrams involving only lines of hydrogen, oxygen, and sulfur, but show a systematic offset in diagrams involving [N ii]λ6584. We conclude that the offset of z ∼ 2.3 galaxies from the local star-forming sequence in the [N ii] BPT diagram is primarily driven by elevated N/O at fixed O/H compared to local galaxies. These results suggest that the local gas-phase and stellar metallicity sets the ionization state of star-forming regions at z ∼ 0 and z ∼ 2.
NASA Astrophysics Data System (ADS)
de Almeida, A. M.; Li, S. S.
1986-06-01
The p+-gridded MNOS capacitor was fabricated to facilitate the study of the effects of Write/Erase cycling and of varying the processing parameters on the interface-state density in an MNOS nonvolatile memory device. A model is derived for this device, which enables the extraction of the device parameters using the quasi-static C- V (QSCV) technique. The distribution of the interface-state density across the forbidden energy gap of silicon was deduced from QSCV measurements. Interface-state density minima between 1.8 × 10 11 and 9.1 × 10 11eV-1cm-2 near the silicon midgap were obtained. The effects of processing variations on the Si/SiO 2 interface-state density distribution and the retention characteristics of the MNOS were studied.
NASA Astrophysics Data System (ADS)
Sutter, Kiplangat
This thesis illustrates the utilization of Density functional theory (DFT) in calculations of gas and solution phase Nuclear Magnetic Resonance (NMR) properties of light and heavy nuclei. Computing NMR properties is still a challenge and there are many unknown factors that are still being explored. For instance, influence of hydrogen-bonding; thermal motion; vibration; rotation and solvent effects. In one of the theoretical studies of 195Pt NMR chemical shift in cisplatin and its derivatives illustrated in Chapter 2 and 3 of this thesis. The importance of representing explicit solvent molecules explicitly around the Pt center in cisplatin complexes was outlined. In the same complexes, solvent effect contributed about half of the J(Pt-N) coupling constant. Indicating the significance of considering the surrounding solvent molecules in elucidating the NMR measurements of cisplatin binding to DNA. In chapter 4, we explore the Spin-Orbit (SO) effects on the 29Si and 13C chemical shifts induced by surrounding metal and ligands. The unusual Ni, Pd, Pt trends in SO effects to the 29Si in metallasilatrane complexes X-Si-(mu-mt)4-M-Y was interpreted based on electronic and relativistic effects rather than by structural differences between the complexes. In addition, we develop a non-linear model for predicting NMR SO effects in a series of organics bonded to heavy nuclei halides. In chapter 5, we extend the idea of "Chemist's orbitals" LMO analysis to the quantum chemical proton NMR computation of systems with internal resonance-assisted hydrogen bonds. Consequently, we explicitly link the relationship between the NMR parameters related to H-bonded systems and intuitive picture of a chemical bond from quantum calculations. The analysis shows how NMR signatures characteristic of H-bond can be explained by local bonding and electron delocalization concepts. One shortcoming of some of the anti-cancer agents like cisplatin is that they are toxic and researchers are looking for
NASA Astrophysics Data System (ADS)
Hou, Zhishuai; Wen, Haishen; Li, Jifang; He, Feng; Liu, Qun; Wang, Jinhuan; Guan, Biao; Wang, Qinglong
2017-01-01
The primary goal of this study was to assess the effect of varying densities on serum reproductive parameters of immature rainbow trout Oncorhynchus mykiss. Experimental trout were maintained in intensive, pen-reared farms for 300 days in fresh water reservoirs. Initial densities were 4.6, 6.6, and 8.6 kg/m3 (40, 60, 80 ind./m3), indicated as SD1, SD2, SD3, and final densities were 31.1, 40.6, 49.3 kg/m3, respectively. A summary of the ovarian stages were observed by histological examination. Serum E2 (estradiol), T (testosterone) were evaluated by radioimmunoassay and FSH (follicle-stimulating-hormone), LH (luteinizing-hormone), vitellogenin, 17α,20β-P (17α,20βdihydroxy4-pregnen-3-one) were measured by enzyme-linked immunosorbent assay. Our findings demonstrated that ovarian development were retarded (from stage III to stage IV) at highest rearing density (SD3) after 180 days of intensive culture (over 40.6 kg/m3). In addition, we observed an inverse relationship between serum reproductive parameters and rearing density. Furthermore, compared to serum reproductive parameters of SD1, E2, T, FSH, vitellogenin, 17α,20β-P, GSI and LH of two higher density groups decreased firstly and significantly at 60 (over 15.9 kg/m 3 ), 180 (over 31.7 kg/m 3 ), 180 (over 40.6 kg/m3), 240 (over 36 kg/m3), 240 (over 36 kg/m3), 240 (over 45 kg/m3) and 300 (over 49.3 kg/m3) days, respectively. Comparing serum reproductive parameters within the same ovarian development stage of rainbow trout from varying densities revealed that higher population density also led to significantly lower overall serum reproductive parameters. Overall, this study presents the reproductive, endocrinological parameters of juvenile female rainbow trout at high rearing densities and indicates the need for rainbow trout (114.44±5.21 g, 19.69±0.31 cm) that are initially stocked at 6.6 or 8.6 kg/m3 should be classified and subdivided into lower density after 180 days of farming (not over 31.7 kg/m3).
Sepehrband, Farshid; Clark, Kristi A.; Ullmann, Jeremy F.P.; Kurniawan, Nyoman D.; Leanage, Gayeshika; Reutens, David C.; Yang, Zhengyi
2015-01-01
We examined whether quantitative density measures of cerebral tissue consistent with histology can be obtained from diffusion magnetic resonance imaging (MRI). By incorporating prior knowledge of myelin and cell membrane densities, absolute tissue density values were estimated from relative intra-cellular and intra-neurite density values obtained from diffusion MRI. The NODDI (neurite orientation distribution and density imaging) technique, which can be applied clinically, was used. Myelin density estimates were compared with the results of electron and light microscopy in ex vivo mouse brain and with published density estimates in a healthy human brain. In ex vivo mouse brain, estimated myelin densities in different sub-regions of the mouse corpus callosum were almost identical to values obtained from electron microscopy (Diffusion MRI: 42±6%, 36±4% and 43±5%; electron microscopy: 41±10%, 36±8% and 44±12% in genu, body and splenium, respectively). In the human brain, good agreement was observed between estimated fiber density measurements and previously reported values based on electron microscopy. Estimated density values were unaffected by crossing fibers. PMID:26096639
Burton, J. R.; Watson, C. A.; Fitzsimmons, A.; Moulds, V.; Pollacco, D.; Wheatley, P. J.; Littlefair, S. P.
2014-07-10
The close proximity of short-period hot-Jupiters to their parent star means they are subject to extreme tidal forces. This has a profound effect on their structure and, as a result, density measurements that assume that the planet is spherical can be incorrect. We have simulated the tidally distorted surface for 34 known short-period hot-Jupiters, assuming surfaces of constant gravitational equipotential for the planet, and the resulting densities have been calculated based only on observed parameters of the exoplanet systems. Comparing these results to the density values, assuming the planets are spherical, shows that there is an appreciable change in the measured density for planets with very short periods (typically less than two days). For one of the shortest-period systems, WASP-19b, we determine a decrease in bulk density of 12% from the spherical case and, for the majority of systems in this study, this value is in the range of 1%-5%. On the other hand, we also find cases where the distortion is negligible (relative to the measurement errors on the planetary parameters) even in the cases of some very short period systems, depending on the mass ratio and planetary radius. For high-density gas planets requiring apparently anomalously large core masses, density corrections due to tidal deformation could become important for the shortest-period systems.
Zhang, Xiao Dong; Jiang, Xiao Lu; Cheng, Zhen; Zhou, Yan; Xu, Qiang; Zhang, Zhi Qiang; Qi, Rongfeng; Luo, Song; Yun, Yan Su; Chen, Hui Juan; Kong, Xiang; Lu, Guang Ming; Zhang, Long Jiang
2016-08-30
In this study, we seek to explore alterations of coupling between functional connectivity density (FCD) and amplitude of low frequency fluctuation (ALFF) in systemic lupus erythematosus patients without overt neuropsychiatric symptoms (non-NPSLE) by using resting-state functional MR imaging. This study was approved by the institutional ethical review board, and all participants signed written informed consent prior to the study. Twenty six non-NPSLE patients and 35 matched healthy controls underwent resting-state functional MR imaging. The correlation analysis between FCD and ALFF was conducted to assess the imaging coupling. Pearson correlation analysis was performed to correlate imaging variables to clinical and neuropsychological data in non-NPSLE patients. According to the consistent alteration of FCD and ALFF, region of interests were identified including the right inferior temporal gyrus, bilateral hippocampus-parahippocampus (H-PH), left posterior cingulate cortex, superior parietal gyrus, postcentral gyrus, and bilateral precuneus. Across-voxel correlation analysis showed decreased coupling strengths in some brain regions. Correlations between FCD, ALFF, and coupling strength in H-PH and C3/C4/MoCA were found. The imaging coupling between FCD and ALFF was decreased in non-NPSLE patients, indicating brain function alteration in non-NPSLE patients, especially the abnormal coupling between FCD and ALFF of the hippocampus-parahippocampus might be an imaging biomarker of brain dysfunction in non-NPSLE patients.
Testemale, Denis; Coulet, Marie Vanessa; Hazemann, Jean Louis; Simon, Jean Paul; Bley, Françoise; Geaymond, Olivier; Argoud, Roger
2005-05-15
Synchrotron small angle x-ray scattering measurements on water and zinc bromide ZnBr2 aqueous solutions were carried out from ambient to supercritical conditions. For both systems several isobars (between 285 and 600 bars) were followed beyond the critical isochore. The data were analyzed through an Ornstein-Zernike formalism in terms of correlation length and null angle structure factor. The results for pure water are in agreement with previously published values. Solutions of different electrolyte concentrations were studied. In each case, the values of the correlation length and null angle structure factor are larger than those of pure water. This effect is more pronounced for higher concentrations and/or for pressure closer to the critical point of pure water. This is in agreement with the shift of the critical point determined in the literature for NaCl solutions. Comparing these results to previous x-ray absorption measurements carried out on identical samples we propose the following two step sequence for ionic hydration up to supercritical conditions: (1) from ambient to about 300 degrees C, an increase of ion pairing and formation of multi-ionic complexes which can be correlated to the decrease of the dielectric constant; (2) an enhancement of the local solvation shell of ions due to the onset of the thermal density fluctuations at high temperature, leading to a screening effect between ions and inhibiting the ion pairing processes.
Muon fluctuation studies of EAS 10(17) eV
NASA Technical Reports Server (NTRS)
Blake, P. R.; Luksys, M.; Nash, W. F.; Sephton, A. J.
1985-01-01
Fluctuation studies need to compare a parameter which is sensitive to longitudinal fluctuations against a parameter which is insensitive. Cascade calculations indicate that the shower size parameter at Haverah Park, rho (500), and the muon density are insensitive while parameters that significantly reflect the longitudinal development of a particular extensive air shower (EAS) include the muon/water Cerenkov response ratio and the muon arrival time dispersion. This paper presents conclusions based on muon fluctuation studies of EAS measured between 1976 and 1981 at Haverah Park.
Rossiter, H B; Howe, F A; Ward, S A; Kowalchuk, J M; Griffiths, J R; Whipp, B J
2000-10-15
The ATP turnover rate during constant-load exercise is often estimated from the initial rate of change of phosphocreatine concentration ([PCr]) using 31P-magnetic resonance spectroscopy (MRS). However, the phase and amplitude characteristics of the sample-to-sample fluctuations can markedly influence this estimation (as well as that for the time constant (tau) of the [PCr] change) and confound its physiological interpretation especially for small amplitude responses. This influence was investigated in six healthy males who performed repeated constant-load quadriceps exercise of a moderate intensity in a whole-body MRS system. A transmit- receive surface coil was placed under the right quadriceps, allowing determination of intramuscular [PCr]; pulmonary oxygen uptake (VO2) was simultaneously determined, breath-by-breath, using a mass spectrometer and a turbine volume measuring module. The probability density functions (PDF) of [PCr] and VO2 fluctuations were determined for each test during the steady states of rest and exercise and the PDF was then fitted to a Gaussian function. The standard deviation of the [PCr] and VO2 fluctuations at rest and during exercise (sr and sw, respectively) and the peak centres of the distributions (xc(r) and xc(w)) were determined, as were the skewness (gamma1) and kurtosis (gamma2) coefficients. There was no difference between sr and sw for [PCr] relative to the resting control baseline (s(r) = 1.554 %delta (s.d. = 0.44), s(w) = 1.514 %delta (s.d. = 0.35)) or the PDF peak centres (xc(r) = -0.013 %delta (s.d. = 0.09), xc(w) -0.197 %delta (s.d. = 0.18)). The standard deviation and peak centre of the 'noise' in VO2 also did not vary between rest and exercise (sr = 0.0427 l min(-1) (s.d. = 0.0104), s(w) = 0.0640 l min(-1) (s.d. = 0.0292); xc(r) = -0.0051 l min(-1) (s.d. = 0.0069), xc(w) 0.0022 l min(-1) (s.d. = 0.0034)). Our results demonstrate that the intersample 'noise' associated with [PCr] determination by 31P-MRS may be
NASA Astrophysics Data System (ADS)
Taddei, Keith M.
ordering of this phase-separated state will be elucidated and the superconductivity attributed to a pseudo-stable minority phase. Detailed phase diagrams will be constructed for the related BaFe2(As1--xPx) 2 and Sr1--xNaxFe2 As2 compounds leading to a direct comparison of the effects driving of either doping regime. A strong magneto-elastic coupling will be established in both of these materials and a new magnetic phase will be mapped in Sr1--xNaxFe2As2. These observations will lead to a discussion of the role of magnetic fluctuations in the overall behavior of the material. The results of inelastic and elastic diffraction experiments will be combined with the results of the local probe M?ssbauer spectroscopy technique in order to determine magnetic fluctuations as the primary order parameter in the phase evolution of the iron-based superconductors, and therefore their importance in establishment of superconductivity as the ground state of these materials.
Kreutzfeldt, C
1980-10-01
A calculation program is proposed suitable for programmable pocket calculators (e.g. HP series) to estimate s20,w f omega2 dt values from density gradient centrifugation data. The program can be applied to linear or exponential density gradients prepared from sucrose or glycerol solutions spun in zonal rotors or swinging bucket rotors. A wide solute concentration range and temperature range is accounted for. Constants for empirical density calculation of glycerol and sucrose solutions concentrated in % (w/v) are estimated. Experimental verification of the program was carried out.
Hashemzadeh, M.
2015-11-15
The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.
NASA Astrophysics Data System (ADS)
Hashemzadeh, M.
2015-11-01
The effect of q-nonextensive parameter and saturation time on the electron density steepening in electron-positron-ion plasmas is studied by particle in cell method. Phase space diagrams show that the size of the holes, and consequently, the number of trapped particles strongly depends on the q-parameter and saturation time. Furthermore, the mechanism of the instability and exchange of energy between electron-positron and electric field is explained by the profiles of the energy density. Moreover, it is found that the q-parameter, saturation time, and electron and positron velocities affect the nonlinear evolution of the electron density which leads to the steepening of its structure. The q-nonextensive parameter or degree of nonextensivity is the relation between temperature gradient and potential energy of the system. Therefore, the deviation of q-parameter from unity indicates the degree of inhomogeneity of temperature or deviation from equilibrium. Finally, using the kinetic theory, a generalized q-dispersion relation is presented for electron-positron-ion plasma systems. It is found that the simulation results in the linear regime are in good agreement with the growth rate results obtained by the kinetic theory.
Sokolowsky, Kathleen P; Bailey, Heather E; Hoffman, David J; Andersen, Hans C; Fayer, Michael D
2016-07-21
Two-dimensional infrared (2D IR) data are presented for a vibrational probe in three nematogens: 4-cyano-4'-pentylbiphenyl, 4-cyano-4'-octylbiphenyl, and 4-(trans-4-amylcyclohexyl)-benzonitrile. The spectral diffusion time constants in all three liquids in the isotropic phase are proportional to [T*/(T - T*)](1/2), where T* is 0.5-1 K below the isotropic-nematic phase transition temperature (TNI). Rescaling to a reduced temperature shows that the decays of the frequency-frequency correlation function (FFCF) for all three nematogens fall on the same curve, suggesting a universal dynamic behavior of nematogens above TNI. Spectral diffusion is complete before significant orientational relaxation in the liquid, as measured by optically heterodyne detected-optical Kerr effect (OHD-OKE) spectroscopy, and before any significant orientational randomization of the probe measured by polarization selective IR pump-probe experiments. To interpret the OHD-OKE and FFCF data, we constructed a mode coupling theory (MCT) schematic model for the relationships among three correlation functions: ϕ1, a correlator for large wave vector density fluctuations; ϕ2, the orientational correlation function whose time derivative is the observable in the OHD-OKE experiment; and ϕ3, the FFCF for the 2D IR experiment. The equations for ϕ1 and ϕ2 match those in the previous MCT schematic model for nematogens, and ϕ3 is coupled to the first two correlators in a straightforward manner. Resulting models fit the data very well. Across liquid crystals, the temperature dependences of the coupling constants show consistent, nonmonotonic behavior. A remarkable change in coupling occurs at ∼5 K above TNI, precisely where the rate of spectral diffusion in 5CB was observed to deviate from that of a similar nonmesogenic liquid.
Systematic Parameter Estimation of a Density-Dependent Groundwater-Flow and Solute-Transport Model
NASA Astrophysics Data System (ADS)
Stanko, Z.; Nishikawa, T.; Traum, J. A.
2013-12-01
A SEAWAT-based, flow and transport model of seawater-intrusion was developed for the Santa Barbara groundwater basin in southern California that utilizes dual-domain porosity. Model calibration can be difficult when simulating flow and transport in large-scale hydrologic systems with extensive heterogeneity. To facilitate calibration, the hydrogeologic properties in this model are based on the fraction of coarse and fine-grained sediment interpolated from drillers' logs. This approach prevents over-parameterization by assigning one set of parameters to coarse material and another set to fine material. Estimated parameters include boundary conditions (such as areal recharge and surface-water seepage), hydraulic conductivities, dispersivities, and mass-transfer rate. As a result, the model has 44 parameters that were estimated by using the parameter-estimation software PEST, which uses the Gauss-Marquardt-Levenberg algorithm, along with various features such as singular value decomposition to improve calibration efficiency. The model is calibrated by using 36 years of observed water-level and chloride-concentration measurements, as well as first-order changes in head and concentration. Prior information on hydraulic properties is also provided to PEST as additional observations. The calibration objective is to minimize the squared sum of weighted residuals. In addition, observation sensitivities are investigated to effectively calibrate the model. An iterative parameter-estimation procedure is used to dynamically calibrate steady state and transient simulation models. The resulting head and concentration states from the steady-state-model provide the initial conditions for the transient model. The transient calibration provides updated parameter values for the next steady-state simulation. This process repeats until a reasonable fit is obtained. Preliminary results from the systematic calibration process indicate that tuning PEST by using a set of synthesized
Linscheid, A; Sanna, A; Floris, A; Gross, E K U
2015-08-28
We show that the superconducting order parameter and condensation energy density of phonon-mediated superconductors can be calculated in real space from first principles density functional theory for superconductors. This method highlights the connection between the chemical bonding structure and the superconducting condensation and reveals new and interesting properties of superconducting materials. Understanding this connection is essential to describe nanostructured superconducting systems where the usual reciprocal space analysis hides the basic physical mechanism. In a first application we present results for MgB2, CaC6 and hole-doped graphane.
Density matrix spectra and order parameters in the 1D extended Hubbard model
NASA Astrophysics Data System (ADS)
Yu, Wing Chi; Gu, Shi-Jian; Lin, Hai-Qing
2016-09-01
Without any knowledge of the symmetry existing in a system, we derive the exact forms of the order parameters which show long-range correlations in the ground state of the one-dimensional (1D) extended Hubbard model using a quantum information approach. Our work demonstrates that the quantum information approach can help us to find the explicit form of the order parameter, which could not be derived systematically via traditional methods in the condensed matter theory.
Critical parameters and saturated density of trifluoroiodomethane (CF{sub 3}I)
Duan, Y.Y.; Shi, L.; Zhu, M.S.; Han, L.Z.
1999-05-01
The vapor-liquid coexistence curve of trifluoroiodomethane (CF{sub 3}I) was measured by visual observation of the meniscus disappearance in an optical cell. Thirty-two saturated density data points were obtained along the vapor-liquid coexistence curve between 384.5 and 2024.9 kg/m{sup 3} in the temperature range from 301.02 K to the critical temperature. The experimental uncertainties in temperature and density were estimated to be within {+-}10 mK and {+-}0.5%, respectively. Measurements near the critical point were used to determine the critical temperature T{sub c} = 396.44 {+-} 0.01 K and the critical density {rho}{sub c} = 868 {+-} 3 kg/m{sup 3} for trifluoroiodomethane (CF{sub 3}I) on the basis of the meniscus disappearing level as well as the intensity of the critical opalescence. The critical pressure {rho}{sub c} = 3.953 {+-} 0.005 MPa was extrapolated from the existing vapor pressure equation proposed previously using the present {Tc} value. The critical exponent, {beta}, was also determined, and correlations of the saturated liquid and saturated vapor densities of CF{sub 3}I were developed.
NASA Astrophysics Data System (ADS)
Shanta, Shahnoor; Kadirkamanathan, Visakan
2015-02-01
A bootstrap-based methodology is developed for parameter estimation and polyspectral density estimation in the case of the approximating model of the underlying stochastic process being non-minimum phase autoregressive-moving-average (ARMA) type, given a finite realisation of a single time series data. The method is based on a minimum phase/maximum phase decomposition of the system function together with a time reversal step for the parameter and polyspectral confidence interval estimation. Simulation examples are provided to illustrate the proposed method.
NASA Astrophysics Data System (ADS)
Okuducu, Ş.; Akti, N. N.; Saraç, H.; Bölükdemir, M. H.; Tel, E.
In this study the nuclear energy level density based on nuclear collective excitation mechanism has been identified in terms of the low-lying collective level bands near the neutron binding energy. Nuclear level density parameters of some light deformed medical radionuclides used widely in medical applications have been calculated by using different collective excitation modes of observed nuclear spectra. The calculated parameters have been used successfully in estimation of the neutron-capture cross section basic data for the production of new medical radionuclides. The investigated radionuclides have been considered in the region of mass number 40
Malo, M K H; Töyräs, J; Karjalainen, J P; Isaksson, H; Riekkinen, O; Jurvelin, J S
2014-07-01
Ultrasound reflection and backscatter parameters are related to the mechanical and structural properties of bone in vitro. However, the potential of ultrasound reflection and backscatter measurements has not been tested with intact human proximal femurs ex vivo. We hypothesize that ultrasound backscatter can be measured from intact femurs and that the measured backscattered signal is associated with cadaver age, bone mineral density (BMD) and trabecular bone microstructure. In this study, human femoral bones of 16 male cadavers (47.0±16.1 years, range: 21-77 years) were investigated using pulse-echo ultrasound measurements at the femoral neck in the antero-posterior direction and at the trochanter major in the anteroposterior and lateromedial directions. Recently introduced ultrasound backscatter parameters, independent of cortical thickness, e.g., time slope of apparent integrated backscatter (TSAB) and mean of the backscatter difference technique (MBD) were obtained and compared with the structural properties of trabecular bone samples, extracted from the locations of ultrasound measurements. Moreover, more conventional backscatter parameters, e.g., apparent integrated backscatter (AIB) and frequency slope of apparent integrated backscatter (FSAB) were analyzed. Bone mineral density of the intact femurs was evaluated using dual energy X-ray absorptiometry (DXA). AIB and MDB measured from the femoral neck correlated significantly (p<0.01) with the neck BMD (R2=0.44 and 0.45), cadaver age (R2=0.61 and 0.41) and several structural parameters, e.g., bone volume fraction (R2=0.33 and 0.39, p<0.05 and p<0.01), respectively. To conclude, ultrasound backscatter parameters, measured from intact proximal femurs, are significantly related (p<0.05) to structural properties and mineral density of trabecular bone.
NASA Astrophysics Data System (ADS)
Dafflon, B.; Barrash, W.; Cardiff, M.; Johnson, T. C.
2011-12-01
Reliable predictions of groundwater flow and solute transport require an estimation of the detailed distribution of the parameters (e.g., hydraulic conductivity, effective porosity) controlling these processes. However, such parameters are difficult to estimate because of the inaccessibility and complexity of the subsurface. In this regard, developments in parameter estimation techniques and investigations of field experiments are still challenging and necessary to improve our understanding and the prediction of hydrological processes. Here we analyze a conservative tracer test conducted at the Boise Hydrogeophysical Research Site in 2001 in a heterogeneous unconfined fluvial aquifer. Some relevant characteristics of this test include: variable-density (sinking) effects because of the injection concentration of the bromide tracer, the relatively small size of the experiment, and the availability of various sources of geophysical and hydrological information. The information contained in this experiment is evaluated through several parameter estimation approaches, including a grid-search-based strategy, stochastic simulation of hydrological property distributions, and deterministic inversion using regularization and pilot-point techniques. Doing this allows us to investigate hydraulic conductivity and effective porosity distributions and to compare the effects of assumptions from several methods and parameterizations. Our results provide new insights into the understanding of variable-density transport processes and the hydrological relevance of incorporating various sources of information in parameter estimation approaches. Among others, the variable-density effect and the effective porosity distribution, as well as their coupling with the hydraulic conductivity structure, are seen to be significant in the transport process. The results also show that assumed prior information can strongly influence the estimated distributions of hydrological properties.
Quantiles, Parametric-Select Density Estimations, and Bi-Information Parameter Estimators.
1982-06-01
A non- parametric estimation method forms estimators which are not based on parametric models. Important examples of non-parametric estimators of a...raw descriptive functions F, f, Q, q, fQ. One distinguishes between parametric and non-parametric methods of estimating smooth functions. A parametric ... estimation method : (1) assumes a family F8, fo’ Q0, qo’ foQ8 of functions, called parametric models, which are indexed by a parameter 6 = ( l
Can we estimate plasma density in ICP driver through electrical parameters in RF circuit?
Bandyopadhyay, M. Sudhir, Dass Chakraborty, A.
2015-04-08
To avoid regular maintenance, invasive plasma diagnostics with probes are not included in the inductively coupled plasma (ICP) based ITER Neutral Beam (NB) source design. Even non-invasive probes like optical emission spectroscopic diagnostics are also not included in the present ITER NB design due to overall system design and interface issues. As a result, negative ion beam current through the extraction system in the ITER NB negative ion source is the only measurement which indicates plasma condition inside the ion source. However, beam current not only depends on the plasma condition near the extraction region but also on the perveance condition of the ion extractor system and negative ion stripping. Nevertheless, inductively coupled plasma production region (RF driver region) is placed at distance (∼ 30cm) from the extraction region. Due to that, some uncertainties are expected to be involved if one tries to link beam current with plasma properties inside the RF driver. Plasma characterization in source RF driver region is utmost necessary to maintain the optimum condition for source operation. In this paper, a method of plasma density estimation is described, based on density dependent plasma load calculation.
M, Eze Evelyn; Ezeiruaku, F C; Ukaji, D C
2012-06-15
This study examined the experiential relationship between the parasite density and haematological parameters in male patients with Plasmodium falciparum infection in Port Harcourt, Nigeria reporting to malaria clinics. A total of one hundred and thirty-six (136) male patients were recruited. QBC haematological analysis, QBC malaria parasite specie identification and quantification and thin blood film for differential leucocytes count was used. The mean values of the haematological parameters in each quartile of parasite densities were determined using Microsoft Excel statistical package. Regression analysis was employed to model the experiential relationship between parasite density and haematological parameters. All regression relationships were tested and the relationship with the highest coefficient of determination (R2) was accepted as the valid relationship. The relationships tested included linear, polynomial, exponential, logarithmic and power relationships. The X- axis of the regression graphs stand for the parasite density while Y-axis stands for the respective haematological parameters Neutrophil count had a negative exponential relationship with the parasite density and is related to the parasite density by a polynomial equation model: ynm = -7E-07x2 - 0.0003x + 56.685.The coefficient of determination (R2) was 0.6140. This means that the rate of change of the parasitemia will depend on the initial value of the neutrophil. As the neutrophil increases, the parasitemia will tend to decrease in a double, triple and quadruple manner. The relationship between lymphocyte count, monocyte count and eosinophil count and parasite density was logarithmic and expressed by the following linear equation models: ylm = -2.371ln(x) + 37.296, ymm = 0.6965ln(x) + 5.7692 and yem = 0.9334ln(x) + 4.1718 in the same order. Their respective high coefficients of determination (R2) were 0.8027, 0.8867 and 0.9553. This logarithmic relationship means that each doubling of
M., Eze Evelyn; Ezeiruaku, F. C.; Ukaji, D. C.
2012-01-01
This study examined the experiential relationship between the parasite density and haematological parameters in male patients with Plasmodium falciparum infection in Port Harcourt, Nigeria reporting to malaria clinics. A total of one hundred and thirty-six (136) male patients were recruited. QBC haematological analysis, QBC malaria parasite specie identification and quantification and thin blood film for differential leucocytes count was used. The mean values of the haematological parameters in each quartile of parasite densities were determined using Microsoft Excel statistical package. Regression analysis was employed to model the experiential relationship between parasite density and haematological parameters. All regression relationships were tested and the relationship with the highest coefficient of determination (R2) was accepted as the valid relationship. The relationships tested included linear, polynomial, exponential, logarithmic and power relationships. The X- axis of the regression graphs stand for the parasite density while Y-axis stands for the respective haematological parameters Neutrophil count had a negative exponential relationship with the parasite density and is related to the parasite density by a polynomial equation model: ynm = -7E-07x2 - 0.0003x + 56.685. The coefficient of determination (R2) was 0.6140. This means that the rate of change of the parasitemia will depend on the initial value of the neutrophil. As the neutrophil increases, the parasitemia will tend to decrease in a double, triple and quadruple manner. The relationship between lymphocyte count, monocyte count and eosinophil count and parasite density was logarithmic and expressed by the following linear equation models: ylm = -2.371ln(x) + 37.296, ymm = 0.6965ln(x) + 5.7692 and yem = 0.9334ln(x) + 4.1718 in the same order. Their respective high coefficients of determination (R2) were 0.8027, 0.8867 and 0.9553. This logarithmic relationship means that each doubling of monocyte
Fluctuations and disorder in high temperature superconductors
NASA Astrophysics Data System (ADS)
Blatter, Gianni; Ivlev, Boris
1994-02-01
The special material parameters of the oxide superconductors lead to a dramatic increase of the importance of thermal and quantum fluctuations. The latter can be quantified by the Ginzburg number Gi = {[T c/ }/{H 2c(0)ɛξ 3(0)] 2/2 } and the quantum resistance Q u = {(e 2/ }/{h̵}) {[ϱN/}/{ɛξ(0)]}, where H c(0), ξ(0), and ϱ N denote the thermodynamic critical field, the planar coherence length (both linearly extrapolated to zero), and the planar normal resistivity. ɛ 2 = {m/}/{M} < 1 is the anisotropy parameter. In the high Tc's (specifically for YBCO) we have Gi ≅ 10 -2 and Qu ≅ 1 and thus these parameters are by orders of magnitude larger than in conventional low- Tc superconductors. The large fluctuations lead to the melting of the vortex lattice well below the upper critical field line. The inclusion of quenched disorder as parametrized by the critical current density ratio jc/ jo drastically changes the dynamic behavior of the vortex system ( jc and jo denote the depinning and depairing current densities). We discuss the equilibrium statistical mechanics (vortex lattice melting) and the dynamic behavior (creep) of the vortex system with a particular emphasis on the role of quantum fluctuations.
Distribution of crack density parameter in Central Betic Cordillera (Southern Spain)
NASA Astrophysics Data System (ADS)
Serrano, Inmaculada; Torcal, Federico; Morales, José
2014-01-01
In this study we have used high-resolution P- and S-wave velocity results to estimate crack density (ɛ, epsilon) and saturation ratio (ξ, xi) at a depth of 2 km in an intramountain basin and surrounding regions. Detailed observations of gravity, seismic profile and geological data reveal high ɛ consistent with large sedimentary thickness and minimum ɛ coinciding with elevations arising from the basement of the basin. From the distribution of seismic measurements of ξ it is possible to identify the presence of aquifers in detrital sediments, sandstone and dolostone. However, ξ does not show significant changes for the aquifers in geological formations made up also of schists and marbles. A low ξ anomaly in the western part could be associated with Triassic evaporite and clay rocks, and high values of ξ in the southwestern part near thermal springs may be imaging the intricate system of fractures which connect at depth with aquifer rocks.
Dafflon, Baptisite; Barrash, Warren; Cardiff, Michael A.; Johnson, Timothy C.
2011-12-15
Reliable predictions of groundwater flow and solute transport require an estimation of the detailed distribution of the parameters (e.g., hydraulic conductivity, effective porosity) controlling these processes. However, such parameters are difficult to estimate because of the inaccessibility and complexity of the subsurface. In this regard, developments in parameter estimation techniques and investigations of field experiments are still challenging and necessary to improve our understanding and the prediction of hydrological processes. Here we analyze a conservative tracer test conducted at the Boise Hydrogeophysical Research Site in 2001 in a heterogeneous unconfined fluvial aquifer. Some relevant characteristics of this test include: variable-density (sinking) effects because of the injection concentration of the bromide tracer, the relatively small size of the experiment, and the availability of various sources of geophysical and hydrological information. The information contained in this experiment is evaluated through several parameter estimation approaches, including a grid-search-based strategy, stochastic simulation of hydrological property distributions, and deterministic inversion using regularization and pilot-point techniques. Doing this allows us to investigate hydraulic conductivity and effective porosity distributions and to compare the effects of assumptions from several methods and parameterizations. Our results provide new insights into the understanding of variabledensity transport processes and the hydrological relevance of incorporating various sources of information in parameter estimation approaches. Among others, the variable-density effect and the effective porosity distribution, as well as their coupling with the hydraulic conductivity structure, are seen to be significant in the transport process. The results also show that assumed prior information can strongly influence the estimated distributions of hydrological properties.
NASA Technical Reports Server (NTRS)
Szatmary, Steven A.; Gyekenyesi, John P.; Nemeth, Noel N.
1990-01-01
This manual describes the operation and theory of the PC-CARES (Personal Computer-Ceramic Analysis and Reliability Evaluation of Structures) computer program for the IBM PC and compatibles running PC-DOS/MS-DOR OR IBM/MS-OS/2 (version 1.1 or higher) operating systems. The primary purpose of this code is to estimate Weibull material strength parameters, the Batdorf crack density coefficient, and other related statistical quantities. Included in the manual is the description of the calculation of shape and scale parameters of the two-parameter Weibull distribution using the least-squares analysis and maximum likelihood methods for volume- and surface-flaw-induced fracture in ceramics with complete and censored samples. The methods for detecting outliers and for calculating the Kolmogorov-Smirnov and the Anderson-Darling goodness-of-fit statistics and 90 percent confidence bands about the Weibull line, as well as the techniques for calculating the Batdorf flaw-density constants are also described.
Perea, J Darío; Langner, Stefan; Salvador, Michael; Kontos, Janos; Jarvas, Gabor; Winkler, Florian; Machui, Florian; Görling, Andreas; Dallos, Andras; Ameri, Tayebeh; Brabec, Christoph J
2016-05-19
The solubility of organic semiconductors in environmentally benign solvents is an important prerequisite for the widespread adoption of organic electronic appliances. Solubility can be determined by considering the cohesive forces in a liquid via Hansen solubility parameters (HSP). We report a numerical approach to determine the HSP of fullerenes using a mathematical tool based on artificial neural networks (ANN). ANN transforms the molecular surface charge density distribution (σ-profile) as determined by density functional theory (DFT) calculations within the framework of a continuum solvation model into solubility parameters. We validate our model with experimentally determined HSP of the fullerenes C60, PC61BM, bisPC61BM, ICMA, ICBA, and PC71BM and through comparison with previously reported molecular dynamics calculations. Most excitingly, the ANN is able to correctly predict the dispersive contributions to the solubility parameters of the fullerenes although no explicit information on the van der Waals forces is present in the σ-profile. The presented theoretical DFT calculation in combination with the ANN mathematical tool can be easily extended to other π-conjugated, electronic material classes and offers a fast and reliable toolbox for future pathways that may include the design of green ink formulations for solution-processed optoelectronic devices.
Bodart, P.; Brihoum, M.; Cunge, G.; Joubert, O.; Sadeghi, N.
2011-12-01
The dynamic of charged particles in pulsed plasma is relatively well known since the 1990s. In contrast, works reporting on the impact of the plasma modulation frequency and duty cycle on the radicals' densities are scarce. In this work, we analyze the impact of these modulation parameters on the radicals' composition in Cl{sub 2} and HBr plasmas. The radicals' densities are measured by broad-band UV and vacuum-ultraviolet (VUV) absorption spectroscopy and modulated-beam mass spectrometry. We show that pulsing the rf power allows controlling the plasma chemistry and gives access to the plasma conditions that cannot be reached in continuous wave plasmas. In particular, we show that above 500 Hz, the pulsing frequency has no influence on the plasma chemistry, whereas in contrast the duty cycle is an excellent knob to control the fragmentation of the parent gas, thus the chemical reactivity of the discharge. At low duty cycle, a reduced gas fragmentation combined with a large ion flux leads to new etching conditions, compared to cw plasmas and the expected consequences on pulsed-etching processes are discussed.
Fluctuations in strongly coupled cosmologies
Bonometto, Silvio A.; Mainini, Roberto E-mail: mainini@mib.infn.it
2014-03-01
In the early Universe, a dual component made of coupled CDM and a scalar field Φ, if their coupling β > (3){sup 1/2}/2, owns an attractor solution, making them a stationary fraction of cosmic energy during the radiation dominated era. Along the attractor, both such components expand ∝a{sup −4} and have early density parameters Ω{sub d} = 1/(4β{sup 2}) and Ω{sub c} = 2 Ω{sub d} (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding ∝a{sup −3}, breaks such stationary expansion at z ∼ 3–5 × 10{sup 3}, cosmic components gradually acquire densities consistent with observations. This paper, first of all, considers the case that this component is warm. However, its main topic is the analysis of fluctuation evolution: out of horizon modes are then determined; their entry into horizon is numerically evaluated as well as the dependence of Meszaros effect on the coupling β; finally, we compute: (i) transfer function and linear spectral function; (ii) CMB C{sub l} spectra. Both are close to standard ΛCDM models; in particular, the former one can be so down to a scale smaller than Milky Way, in spite of its main DM component being made of particles of mass < 1 keV. The previously coupled CDM component, whose present density parameter is O(10{sup −3}), exhibits wider fluctuations δρ/ρ, but approximately β-independent δρ values. We discuss how lower scale features of these cosmologies might ease quite a few problems that ΛCDM does not easily solve.
2014-01-01
Background A positive association between handgrip strength and bone mineral density was demonstrated, but not all the investigations confirmed these results. We conducted a screening programme for osteoporosis in a large cohort of postmenopausal women to investigate the relationship between handgrip strength, other nutritional parameters and bone density. Methods This investigation involved 1,300 white volunteers. All participants underwent a bone mineral density evaluation at the heel and a handgrip strength measurement. Results The mean T-score value was -1.15 ± 1; a total of 181 participants reported at least one osteoporotic fracture. In the univariate analysis, both handgrip strength and body mass index were associated with the T-score value. Adjustment for confounding factors confirmed this relationship showing, in the multivariate analysis, that the body mass index was positively correlated to the T-score (B = 0.034; p = 0.001) and, in the logistic regression analysis, that handgrip strength was associated with the presence of osteoporosis (P = 0.005). Conclusion Both body mass index and handgrip strength were strongly correlated to bone mineral density, assessed with ultrasound, suggesting a possible key role as bone disease predictors. PMID:24548517
Change of Bone Mineral Density and Relationship to Clinical Parameters in Male Stroke Patients
2016-01-01
Objective To investigate the clinical characteristics that significantly contribute to a decreased bone mineral density (BMD), the BMD changes and clinical characteristics of men who experienced a stroke between the ages of 50 years and 65 years were studied between 3 months and 4 months after the stroke. Methods Subjects had a brain hemorrhage or a cerebral infarction. Only men aged 50 years to 65 years were included to eliminate postmenopausal osteoporosis and to eliminate the influence of senile osteoporosis. All subjects underwent a BMD test between 3 months and 4 months after their strokes. Also, patients with a medication history that might have caused a secondary osteoporosis before a stroke were excluded. Results The BMD for the lumbar spine and hemiplegic side of the femoral neck correlated significantly with the results of the manual muscle test (MMT) of the hemiplegic lower extremity and the Modified Barthel Index (MBI) score. This result suggests that the immobility from the decreased muscle strength and the weakened daily functionality might have reduced the BMD. According to a multiple linear regression analysis, the MBI score is significantly correlated with the lumbar BMD. The BMD of the hemiplegic femoral neck is significantly correlated with the MMT and the MBI score. Conclusion This study showed that BMD monitoring should be considered in male stroke patients, especially for patients with a high dependency in daily functions and a decreased muscle strength in the hemiplegic lower extremity. PMID:28119827
NASA Astrophysics Data System (ADS)
Hudson, Michael J.; Carrick, Jonathan; Turnbull, Stephen J.; Lavaux, Guilhem
2016-10-01
Using redshifts from the 2M++ redshift compilation, we reconstruct the density of galaxies within 200 h -1 Mpc, and compare the predicted peculiar velocities Tully-Fisher and SNe peculiar velocities. The comparison yields a best-fit value of β ≡ Ωm 0.55/b* = 0.431 +/- 0.021, suggesting Ωm 0.55σ8,lin = 0.401 +/- 0.024, in good agreement with other probes. The predicted peculiar velocity of the Local Group from sources within the 2M++ volume is 540 +/- 40 km s-1, towards l = 268° +/- 4°, b = 38° +/- 6°, which is misaligned by only 10° with the Cosmic Microwave Background dipole. To account for sources outside the 2M++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. The external bulk flow has a velocity of 159 +/- 23 km s-1 towards l = 304° +/- 11°, b6° +/- 13°.
NASA Astrophysics Data System (ADS)
Meng, Kai; Wan, Yongjian; Wu, Fan; Shen, Lijun; Wu, Hsing-Yu
2017-02-01
Mid to high spatial frequency error (MSFR and HSFR) should be strictly controlled in modern optical systems. Pitch tool polishing (PTP) is an effective ultra-smoothing surface manufacturing method to control MSFR and HSFR. But it is difficult to control because it is affected by a lot of factors. The present paper describes the pitch tool polishing study based on eighteen well-planned orthogonal experiments (OA18 matrix). Five main process factors (abrasive particle size, slurry concentration, pad rotation speed, acidity and polishing time) in pitch tool polishing process were investigated. In this study, power spectral density (PSD) based on Fourier analysis of surface topography data obtained by white light interferometer was used as the results of orthogonal experiments instead of material removal rate and surface roughness. A normalization method of PSD was proposed as the range analysis rule. Three parts of spatial frequency bandwidth were selected and discussed. Acidity is the most important factor in part 1 and slurry concentration is the most significant one in part 2; while acidity is the least influenced one in part 3. The result in each part was explained by two-step material removal mechanism. At last, suggestions in low and high spatial frequency are given for pitch tool polishing.
NASA Astrophysics Data System (ADS)
Makino, Nobuyoshi; Suto, Yasushi
1993-04-01
We estimated the X-ray gas mass of the clusters in the Shapley Supercluster by improving a previous estimate based on the extrapolation from the Coma data. Our estimate of the X-ray gas mass in the Shapley Supercluster, which depends on h50 and beta (a power-law index characterizing the gas density profile around a cluster), turned out to be a factor of 2-4 times smaller than the previous value. We then considered its implication on the baryon density parameter in the universe. Our estimates from the the Shapley Supercluster region are consistent with the predicted range according to the standard big-bang nucleosynthesis model if the universe is open for h50 = 2.0, or if the universe is flat (Omega(0) = 1.0), but with a substantial fraction of (non-baryonic) dark matter existing in intercluster space for h50 = 1.0.
NASA Astrophysics Data System (ADS)
Carrick, Jonathan; Turnbull, Stephen J.; Lavaux, Guilhem; Hudson, Michael J.
2015-06-01
Peculiar velocity measurements are the only tool available in the low-redshift Universe for mapping the large-scale distribution of matter and can thus be used to constrain cosmology. Using redshifts from the 2M++ redshift compilation, we reconstruct the density of galaxies within 200 h-1 Mpc, allowing for the first time good sampling of important superclusters such as the Shapley Concentration. We compare the predicted peculiar velocities from 2M++ to Tully-Fisher and SNe peculiar velocities. We find a value of β* ≡ Ω m^{0.55}/b^* = 0.431 ± 0.021, suggesting Ω m^{0.55}σ _{8,lin} = 0.401 ± 0.024, in good agreement with other probes. The predicted peculiar velocity of the Local Group arising from the 2M++ volume alone is 540 ± 40 km s-1, towards l = 268° ± 4°, b = 38° ± 6°, only 10° out of alignment with the cosmic microwave background dipole. To account for velocity contributions arising from sources outside the 2M++ volume, we fit simultaneously for β* and an external bulk flow in our analysis. We find that an external bulk flow is preferred at the 5.1σ level, and the best fit has a velocity of 159 ± 23 km s- 1 towards l = 304° ± 11°, b = 6° ± 13°. Finally, the predicted bulk flow of a 50 h-1 Mpc Gaussian-weighted volume centred on the Local Group is 230 ± 30 km s-1, in the direction l = 293° ± 8°, b = 14° ± 10°, in agreement with predictions from Λ cold dark matter.
Williams, G V M; Jurkutat, M; Rybicki, D; Haase, J
2011-02-23
We report the results from a (63)Cu nuclear magnetic resonance (NMR) study of the electron-doped high temperature superconducting cuprate (HTSC) Pr(1.85)Ce(0.15)Cu(1-x)Ni(x)O(4). We find that Ni induces a magnetic broadening of the (63)Cu NMR spectra that can be interpreted in terms of an induced spin density oscillation about the Ni site, similar to that reported from (63)Cu NMR measurements on the hole-doped HTSCs when Zn is partially substituted for Cu. There is also an additional temperature-dependent contribution to the (63)Cu spin-lattice relaxation rate that can be interpreted in terms of an Ni-induced modification of the low energy spin fluctuations. Furthermore, the spin fluctuations are intrinsically spatially inhomogeneous and additional inhomogeneities are induced by Ni.
Rabelo, E; Rezende, R L; Bertics, S J; Grummer, R R
2003-03-01
Forty cows and twenty heifers were used to study the effects of dietary energy density during late gestation and early lactation on lactation performance and ruminal parameters. A 2 x 2 factorial arrangement of treatments was used. During prepartum (-28 d to calving), animals were fed a low energy density diet [DL; 1.58 Mcal of net energy for lactation (NE(L))/kg, 40% neutral detergent fiber (NDF) and 38% nonfiber carbohydrate (NFC)] or a high energy diet (DH; 1.70 Mcal NE(L)/kg, 32% NDF and 44% NFC). After calving, half of the cows from each prepartum treatment group were assigned to a low energy density diet (L; 1.57 Mcal NE(L)/kg, 30% NDF and 41% NFC) or a high energy density diet (H; 1.63 Mcal NE(L)/kg, 25% NDF and 47% NFC) until d 20 postpartum. After d 20, all cows were fed H until d 70. Animals fed DH had 19.8% greater dry matter intake (DMI; % of body weight) and 21.5% greater energy intake than animals fed DL prepartum and the response was greater for cows compared to heifers. Animals fed DH had lower ruminal pH compared to animals fed DL, but no major changes in volatile fatty acid concentrations were observed. Effects of dietary energy density during prepartum on postpartum production responses were dependent on parity. Primiparous cows fed DL had higher 3.5% fat-corrected milk yield and milk fat production and percentage during the first 10 wk of lactation than those fed DH. Prepartum diet did not affect lactation performance of multiparous cows. Cows fed H had higher DMI and energy intake for the first 20 d of lactation compared to cows fed L. Diets did not affect DMI after the third wk of lactation. Milk production increased faster for cows fed H compared to cows fed L. Animals fed DL-L sequence of treatments tended to have the lowest energy intake during the first 10 wk of lactation. Prepartum treatments did not affect ruminal fermentation characteristics postpartum. Cows fed H had lower ruminal pH and higher propionate concentrations than cows fed L
Wickramarachchi, Praneeth; Kawamoto, Ken; Hamamoto, Shoichiro; Nagamori, Masanao; Moldrup, Per; Komatsu, Toshiko
2011-12-01
Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, ρ(b), and particle size fraction on the main soil-gas transport parameters - soil-gas diffusivity (D(p)/D(o), ratio of gas diffusion coefficients in soil and free air) and air permeability (k(a)) - under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting ρ(b) values ranging from 1.40 to 2.10 g cm(-3). Results showed that D(p) and k(a) values for the '+gravel' fraction (<35 mm) became larger than for the '-gravel' fraction (<2mm) under variably-saturated conditions for a given soil-air content (ε), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on D(p) and k(a) was most pronounced for the '+gravel' fraction. Normalized ratios were introduced for all soil-gas parameters: (i) for gas diffusivity D(p)/D(f), the ratio of measured D(p) to D(p) in total porosity (f), (ii) for air permeability k(a)/k(a)(,pF4.1), the ratio of measured k(a) to k(a) at 1235 kPa matric potential (=pF 4.1), and (iii) for soil-air content, the ratio of soil-air content (ε) to total porosity (f) (air saturation). Based on the normalized parameters, predictive power-law models for D(p)(ε/f) and k(a)(ε/f) models were developed based on a single parameter (water blockage factor M for D(p) and P for k(a)). The water blockage factors, M and P, were found to be linearly correlated to ρ(b) values, and the effects of dry bulk density on D(p) and k(a) for both '+gravel' and '-gravel' fractions were well accounted for by the new models.
Wickramarachchi, Praneeth; Kawamoto, Ken; Hamamoto, Shoichiro; Nagamori, Masanao; Moldrup, Per; Komatsu, Toshiko
2011-12-15
Highlights: > The effects of soil physical properties on gas transport parameters were investigated. > Higher values of D{sub p} and k{sub a} exhibited in the '+gravel' than the '-gravel' fraction at same soil-air content ({epsilon}). > Recent power law models for D{sub p} (WLR) and k{sub a} (RPL) were modified. > Model parameters were linearly related to easily measurable dry bulk density ({rho}{sub b}). - Abstract: Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, {rho}{sub b}, and particle size fraction on the main soil-gas transport parameters - soil-gas diffusivity (D{sub p}/D{sub o}, ratio of gas diffusion coefficients in soil and free air) and air permeability (k{sub a}) - under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting {rho}{sub b} values ranging from 1.40 to 2.10 g cm{sup -3}. Results showed that D{sub p} and k{sub a} values for the '+gravel' fraction (<35 mm) became larger than for the '-gravel' fraction (<2 mm) under variably-saturated conditions for a given soil-air content ({epsilon}), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on D{sub p} and k{sub a} was most pronounced for the '+gravel' fraction. Normalized ratios were introduced for all soil-gas parameters: (i) for gas diffusivity D{sub p}/D{sub f}, the ratio of measured D{sub p} to D{sub p} in total porosity (f), (ii) for air permeability k{sub a}/k{sub a,pF4.1}, the ratio of measured k{sub a} to k{sub a} at 1235 kPa matric potential (=pF 4.1), and (iii) for soil-air content, the ratio of soil-air content ({epsilon}) to total porosity (f) (air
Xie, Gan-Sheng; Lyv, Jin-Xing; Li, Gang; Yan, Chun-Yin; Hou, Jian-Quan; Pu, Jin-Xian; Ding, Xiang; Huang, Yu-Hua
2016-01-01
Background: The diagnostic value of current prostate-specific antigen (PSA) tests is challenged by the poor detection rate of prostate cancer (PCa) in repeat prostate biopsy. In this study, we proposed a novel PSA-related parameter named PSA density variation rate (PSADVR) and designed a clinical trial to evaluate its potential diagnostic value for detecting PCa on a second prostate biopsy. Methods: Data from 184 males who underwent second ultrasound-guided prostate biopsy 6 months after the first biopsy were included in the study. The subjects were divided into PCa and non-PCa groups according to the second biopsy pathological results. Prostate volume, PSA density (PSAD), free-total PSA ratio, and PSADVR were calculated according to corresponding formulas at the second biopsy. These parameters were compared using t-test or Mann-Whitney U-test between PCa and non-PCa groups, and receiver operating characteristic analysis were used to evaluate their predictability on PCa detection. Results: PCa was detected in 24 patients on the second biopsy. Mean values of PSA, PSAD, and PSADVR were greater in the PCa group than in the non-PCa group (8.39 μg/L vs. 7.16 μg/L, 0.20 vs. 0.16, 14.15% vs. −1.36%, respectively). PSADVR had the largest area under the curve, with 0.667 sensitivity and 0.824 specificity when the cutoff was 10%. The PCa detection rate was significantly greater in subjects with PSADVR >10% than PSADVR ≤10% (28.6% vs. 6.5%, P < 0.001). In addition, PSADVR was the only parameter in this study that showed a significant correlation with mid-to-high-risk PCa (r = 0.63, P = 0.03). Conclusions: Our results demonstrated that PSADVR improved the PCa detection rate on second biopsies, especially for mid-to-high-risk cancers requiring prompt treatment. PMID:27453228
Turbulent magnetic fluctuations in laboratory reconnection
NASA Astrophysics Data System (ADS)
Von Stechow, Adrian; Grulke, Olaf; Klinger, Thomas
2016-07-01
The role of fluctuations and turbulence is an important question in astrophysics. While direct observations in space are rare and difficult dedicated laboratory experiments provide a versatile environment for the investigation of magnetic reconnection due to their good diagnostic access and wide range of accessible plasma parameters. As such, they also provide an ideal chance for the validation of space plasma reconnection theories and numerical simulation results. In particular, we studied magnetic fluctuations within reconnecting current sheets for various reconnection parameters such as the reconnection rate, guide field, as well as plasma density and temperature. These fluctuations have been previously interpreted as signatures of current sheet plasma instabilities in space and laboratory systems. Especially in low collisionality plasmas these may provide a source of anomalous resistivity and thereby contribute a significant fraction of the reconnection rate. We present fluctuation measurements from two complementary reconnection experiments and compare them to numerical simulation results. VINETA.II (Greifswald, Germany) is a cylindrical, high guide field reconnection experiment with an open field line geometry. The reconnecting current sheet has a three-dimensional structure that is predominantly set by the magnetic pitch angle which results from the superposition of the guide field and the in-plane reconnecting field. Within this current sheet, high frequency magnetic fluctuations are observed that correlate well with the local current density and show a power law spectrum with a spectral break at the lower hybrid frequency. Their correlation lengths are found to be extremely short, but propagation is nonetheless observed with high phase velocities that match the Whistler dispersion. To date, the experiment has been run with an external driving field at frequencies higher than the ion cyclotron frequency f_{ci}, which implies that the EMHD framework applies
Kang, H. K.; Park, S. B.; Kim, S. H.; Kim, C. H.
2016-01-01
The effects of stocking density on the performance, egg quality, leukocyte concentration, blood biochemistry, corticosterone levels, bone mineral density, and noxious gas emission of laying hens were investigated. Eight hundred 34-week-old Hy-Line Brown laying hens (Gallus gallus domesticus) were randomly assigned to one of 4 treatments, each of which was replicated 4 times. Four stocking densities, including 5, 6, 7, and 10 birds/m2, were compared. A commercial-type basal diet was formulated to meet or exceed nutrient recommendations for laying hens from the National Research Council. The diet was fed to the hens ad libitum for 8 wk. Results indicated that hen-day egg production, egg mass, and feed intake were less for (P < 0.01) 10 birds/m2 stock density than other stock densities. Production rate of floor and broken eggs and eggshell strength were greater (P < 0.01) for 10 birds/m2 stock density than other stock densities. There were no significant differences in the level of leukocytes among densities. However, heterophils and the H/L ratio were greater (P < 0.01) for 10 birds/m2 than in stock density of 6 or 7 birds/m2. Serum corticosterone was greater (P < 0.01) 10 birds/m2 than stock density than other stock densities. Litter moisture and gas emission (CO2 and NH3) were greater (P < 0.01) for 10 birds/m2 than stock density than 6 and 7 birds/m2 stock density. Bone mineral content was not influenced by increasing stock density. However, bone mineral density was less (P < 0.05) for 10 m2 stock density than other stock densities. These results indicate that increasing the density beyond 5 birds/m2 elicits some negative effects on laying performance of Hy-Line brown laying hens. PMID:27578881
Kang, H K; Park, S B; Kim, S H; Kim, C H
2016-12-01
The effects of stocking density on the performance, egg quality, leukocyte concentration, blood biochemistry, corticosterone levels, bone mineral density, and noxious gas emission of laying hens were investigated. Eight hundred 34-week-old Hy-Line Brown laying hens (Gallus gallus domesticus) were randomly assigned to one of 4 treatments, each of which was replicated 4 times. Four stocking densities, including 5, 6, 7, and 10 birds/m(2), were compared. A commercial-type basal diet was formulated to meet or exceed nutrient recommendations for laying hens from the National Research Council. The diet was fed to the hens ad libitum for 8 wk. Results indicated that hen-day egg production, egg mass, and feed intake were less for (P < 0.01) 10 birds/m(2) stock density than other stock densities. Production rate of floor and broken eggs and eggshell strength were greater (P < 0.01) for 10 birds/m(2) stock density than other stock densities. There were no significant differences in the level of leukocytes among densities. However, heterophils and the H/L ratio were greater (P < 0.01) for 10 birds/m(2) than in stock density of 6 or 7 birds/m(2) Serum corticosterone was greater (P < 0.01) 10 birds/m(2) than stock density than other stock densities. Litter moisture and gas emission (CO2 and NH3) were greater (P < 0.01) for 10 birds/m(2) than stock density than 6 and 7 birds/m(2) stock density. Bone mineral content was not influenced by increasing stock density. However, bone mineral density was less (P < 0.05) for 10 m(2) stock density than other stock densities. These results indicate that increasing the density beyond 5 birds/m(2) elicits some negative effects on laying performance of Hy-Line brown laying hens.
Ma, Yuntao; Wen, Meiping; Guo, Yan; Li, Baoguo; Cournède, Paul-Henry; de Reffye, Philippe
2008-01-01
Background and Aims Plant population density (PPD) influences plant growth greatly. Functional–structural plant models such as GREENLAB can be used to simulate plant development and growth and PPD effects on plant functioning and architectural behaviour can be investigated. This study aims to evaluate the ability of GREENLAB to predict maize growth and development at different PPDs. Methods Two field experiments were conducted on irrigated fields in the North China Plain with a block design of four replications. Each experiment included three PPDs: 2·8, 5·6 and 11·1 plants m−2. Detailed observations were made on the dimensions and fresh biomass of above-ground plant organs for each phytomer throughout the seasons. Growth stage-specific target files (a description of plant organ weight and dimension according to plant topological structure) were established from the measured data required for GREENLAB parameterization. Parameter optimization was conducted using a generalized least square method for the entire growth cycles for all PPDs and years. Data from in situ plant digitization were used to establish geometrical symbol files for organs that were then applied to translate model output directly into 3-D representation for each time step of the model execution. Key Results The analysis indicated that the parameter values of organ sink variation function, and the values of most of the relative sink strength parameters varied little among years and PPDs, but the biomass production parameter, computed plant projection surface and internode relative sink strength varied with PPD. Simulations of maize plant growth based on the fitted parameters were reasonably good as indicated by the linearity and slopes similar to unity for the comparison of simulated and observed values. Based on the parameter values fitted from different PPDs, shoot (including vegetative and reproductive parts of the plant) and cob fresh biomass for other PPDs were simulated. Three
Critical Parameters for Obtaining Low Particle Densities on a Si Surface in an HF-Last Process
NASA Astrophysics Data System (ADS)
Alay, Josep-Lluís; Verhaverbeke, Steven; Vandervorst, Wilfried; Heyns, Marc
1993-01-01
A study was made on the relation between particle densities and the (remaining) degree of oxidation of a cleaned (100) Si surface following different HF-treatments (HF, HF/IPA, DI-rinse). A detailed comparison between (X-ray photoelectron spectroscopy) XPS and contact angle measurements of a water droplet with the Si surface shows that the latter method is sensitive to less than 1/10 of a SiO2 monolayer on the (100)Si surface. The results obtained with XPS point out that minute amounts of suboxides (a few percentage of a monolayer) are the dominant cause for particles. On the other hand, HF-dipping time and HF bath temperature are found to be the determinant parameters in an HF-last process. In addition the quality of the rinsing water as well as the initial roughness (Si vs polysilicon) play a major role.
NASA Astrophysics Data System (ADS)
Poeplau, Christopher; Vos, Cora; Don, Axel
2017-03-01
Estimation of soil organic carbon (SOC) stocks requires estimates of the carbon content, bulk density, rock fragment content and depth of a respective soil layer. However, different application of these parameters could introduce a considerable bias. Here, we explain why three out of four frequently applied methods overestimate SOC stocks. In soils rich in rock fragments (> 30 vol. %), SOC stocks could be overestimated by more than 100 %, as revealed by using German Agricultural Soil Inventory data. Due to relatively low rock fragments content, the mean systematic overestimation for German agricultural soils was 2.1-10.1 % for three different commonly used equations. The equation ensemble as re-formulated here might help to unify SOC stock determination and avoid overestimation in future studies.
Mueller, M.; Madejski, G.
2009-05-20
The Method of Light Curve Simulations is a tool that has been applied to X-ray monitoring observations of Active Galactic Nuclei (AGN) for the characterization of the Power Density Spectrum (PDS) of temporal variability and measurement of associated break frequencies (which appear to be an important diagnostic for the mass of the black hole in these systems as well as their accretion state). It relies on a model for the PDS that is fit to the observed data. The determination of confidence regions on the fitted model parameters is of particular importance, and we show how the Neyman construction based on distributions of estimates may be implemented in the context of light curve simulations. We believe that this procedure offers advantages over the method used in earlier reports on PDS model fits, not least with respect to the correspondence between the size of the confidence region and the precision with which the data constrain the values of the model parameters. We plan to apply the new procedure to existing RXTE and XMM observations of Seyfert I galaxies as well as RXTE observations of the Seyfert II galaxy NGC 4945.
Vieira, Vasco M. N. C. S.; Engelen, Aschwin H.; Huanel, Oscar R.; Guillemin, Marie-Laure
2016-01-01
Survival is a fundamental demographic component and the importance of its accurate estimation goes beyond the traditional estimation of life expectancy. The evolutionary stability of isomorphic biphasic life-cycles and the occurrence of its different ploidy phases at uneven abundances are hypothesized to be driven by differences in survival rates between haploids and diploids. We monitored Gracilaria chilensis, a commercially exploited red alga with an isomorphic biphasic life-cycle, having found density-dependent survival with competition and Allee effects. While estimating the linear-in-the-parameters survival function, all model I regression methods (i.e, vertical least squares) provided biased line-fits rendering them inappropriate for studies about ecology, evolution or population management. Hence, we developed an iterative two-step non-linear model II regression (i.e, oblique least squares), which provided improved line-fits and estimates of survival function parameters, while robust to the data aspects that usually turn the regression methods numerically unstable. PMID:27936048
Mueller, Martin; Madejski, Greg
2009-07-20
The method of light-curve simulations is a tool that has been applied to X-ray monitoring observations of active galactic nuclei for the characterization of the power density spectrum (PDS) of temporal variability and measurement of associated break frequencies (which appear to be an important diagnostic for the mass of the black hole in these systems as well as their accretion state). It relies on a model for the PDS that is fitted to the observed data. The determination of confidence regions on the fitted model parameters is of particular importance, and we show how the Neyman construction based on distributions of estimates may be implemented in the context of light-curve simulations. We believe that this procedure offers advantages over the method used in earlier reports on PDS model fits, not least with respect to the correspondence between the size of the confidence region and the precision with which the data constrain the values of the model parameters. We plan to apply the new procedure to existing RXTE and XMM-Newton observations of Seyfert I galaxies as well as RXTE observations of the Seyfert II galaxy NGC 4945.
NASA Astrophysics Data System (ADS)
Mueller, Martin; Madejski, Greg
2009-07-01
The method of light-curve simulations is a tool that has been applied to X-ray monitoring observations of active galactic nuclei for the characterization of the power density spectrum (PDS) of temporal variability and measurement of associated break frequencies (which appear to be an important diagnostic for the mass of the black hole in these systems as well as their accretion state). It relies on a model for the PDS that is fitted to the observed data. The determination of confidence regions on the fitted model parameters is of particular importance, and we show how the Neyman construction based on distributions of estimates may be implemented in the context of light-curve simulations. We believe that this procedure offers advantages over the method used in earlier reports on PDS model fits, not least with respect to the correspondence between the size of the confidence region and the precision with which the data constrain the values of the model parameters. We plan to apply the new procedure to existing RXTE and XMM-Newton observations of Seyfert I galaxies as well as RXTE observations of the Seyfert II galaxy NGC 4945.
NASA Astrophysics Data System (ADS)
Kutiev, Ivan; Marinov, Pencho; Fidanova, Stefka; Belehaki, Anna; Tsagouri, Ioanna
2012-12-01
Validation results on the latest version of TaD model (TaDv2) show realistic reconstruction of the electron density profiles (EDPs) with an average error of 3 TECU, similar to the error obtained from GNSS-TEC calculated paremeters. The work presented here has the aim to further improve the accuracy of the TaD topside reconstruction, adjusting the TEC parameter calculated from TaD model with the TEC parameter calculated by GNSS transmitting RINEX files provided by receivers co-located with the Digisondes. The performance of the new version is tested during a storm period demonstrating further improvements in respect to the previous version. Statistical comparison of modeled and observed TEC confirms the validity of the proposed adjustment. A significant benefit of the proposed upgrade is that it facilitates the real-time implementation of TaD. The model needs a reliable measure of the scale height at the peak height, which is supposed to be provided by Digisondes. Oftenly, the automatic scaling software fails to correctly calculate the scale height at the peak, Hm, due to interferences in the receiving signal. Consequently the model estimated topside scale height is wrongly calculated leading to unrealistic results for the modeled EDP. The proposed TEC adjustment forces the model to correctly reproduce the topside scale height, despite the inaccurate values of Hm. This adjustment is very important for the application of TaD in an operational environment.
NASA Astrophysics Data System (ADS)
Sánchez Úbeda, Juan Pedro; Calvache Quesada, María Luisa; Duque Calvache, Carlos; López Chicano, Manuel; Martín Rosales, Wenceslao
2013-04-01
The hydraulic properties of coastal aquifer are essential for any estimation of groundwater flow with simple calculations or modelling techniques. Usually the application of slug test or tracers test are the techniques selected for solving the uncertainties. Other methods are based on the information associated to the changes induced by tidal fluctuation in coastal zones. The Tidal Response Method is a simple technique based in two different factors, tidal efficiency factor and time lag of the tidal oscillation regarding to hydraulic head oscillation caused into the aquifer. This method was described for a homogeneous and isotropic confined aquifer; however, it's applicable to unconfined aquifers when the ratio of maximum water table fluctuation and the saturated aquifer thickness is less than 0.02. Moreover, the tidal equations assume that the tidal signal follows a sinusoidal wave, but actually, the tidal wave is a set of simple harmonic components. Due to this, another methods based in the Fourier series have been applied in earlier studies trying to describe the tidal wave. Nevertheless, the Tidal Response Method represents an acceptable and useful technique in the Motril-Salobreña coastal aquifer. From recently hydraulic head data sets at discharge zone of the Motril-Salobreña aquifer have been calculated transmissivity values using different methods based in the tidal fluctuations and its effects on the hydraulic head. The effects of the tidal oscillation are detected in two boreholes of 132 m and 38 m depth located 300 m to the coastline. The main difficulties for the application of the method were the consideration of a confined aquifer and the variation of the effect at different depths (that is not included into the tidal equations), but these troubles were solved. In one hand, the assumption that the storage coefficient (S) in this unconfined aquifer is close to confined aquifers values due to the hydrogeological conditions at high depth and without
Fluctuating transport in microstructures
Xie, X.
1988-01-01
In this dissertation, we study electronic transport properties of various kinds of quasi-one dimensional (Q1D) systems. The dissertation can be divided into the following categories: (1) Conductance fluctuations and phase coherence in microstructures. We study the conductance fluctuations for three different regimes of electronic transport: ballistic, diffusive and variable-range-hopping (VRH). Various numerical methods are used in the calculations. In the VRH problem, we also examine the possibility of observing the Aharonov-Bohm effect. We develop a technique based on the recursive Kubo formula to study the universal conductance fluctuations in the diffusive regime. Close comparison with relevant experiments is made and good agreement is found. (2) Drude transport properties of quasi-one dimensional systems. In this problem, we calculate the density of states and Drude conductivity for the screened impurity scattering using many body theory. The DOS and conductivity show strong oscillatory behavior as a function of the Fermi-energy. Self-consistency is included in our theory. Good agreement with experiment is found. (3) Transport in quasicrystals. In solving this problem we use the Landauer formula approach. We find that the electrical resistance of a finite 1D Fibonacci-sequence quasicrystal shows strong fluctuations as resonant tunneling occurs through the allowed energy states of the system. Power law localization and self-similarity can be seen in the transport properties. A possible experiment to observe this phenomenon is suggested.
NASA Astrophysics Data System (ADS)
Nooruddin, Hasan A.; Anifowose, Fatai; Abdulraheem, Abdulazeez
2014-03-01
Soft computing techniques are recently becoming very popular in the oil industry. A number of computational intelligence-based predictive methods have been widely applied in the industry with high prediction capabilities. Some of the popular methods include feed-forward neural networks, radial basis function network, generalized regression neural network, functional networks, support vector regression and adaptive network fuzzy inference system. A comparative study among most popular soft computing techniques is presented using a large dataset published in literature describing multimodal pore systems in the Arab D formation. The inputs to the models are air porosity, grain density, and Thomeer parameters obtained using mercury injection capillary pressure profiles. Corrected air permeability is the target variable. Applying developed permeability models in recent reservoir characterization workflow ensures consistency between micro and macro scale information represented mainly by Thomeer parameters and absolute permeability. The dataset was divided into two parts with 80% of data used for training and 20% for testing. The target permeability variable was transformed to the logarithmic scale as a pre-processing step and to show better correlations with the input variables. Statistical and graphical analysis of the results including permeability cross-plots and detailed error measures were created. In general, the comparative study showed very close results among the developed models. The feed-forward neural network permeability model showed the lowest average relative error, average absolute relative error, standard deviations of error and root means squares making it the best model for such problems. Adaptive network fuzzy inference system also showed very good results.
Multiscale Fluctuation Analysis Revisited
NASA Astrophysics Data System (ADS)
Struzik, Zbigniew R.; Kiyono, Ken; Yamamoto, Yoshiharu
2007-07-01
Ubiquitous non-Gaussianity of the probability density of (time-series) fluctuations in many real world phenomena has been known and modelled extensively in recent years. Similarly, the analysis of (multi)scaling properties of (fluctuations in) complex systems has become a standard way of addressing unknown complexity. Yet the combined analysis and modelling of multiscale behaviour of probability density — multiscale PDF analysis — has only recently been proposed for the analysis of time series arising in complex systems, such as the cardiac neuro-regulatory system, financial markets or hydrodynamic turbulence. This relatively new technique has helped significantly to expand the previously obtained insights into the phenomena addressed. In particular, it has helped to identify a novel class of scale invariant behaviour of the multiscale PDF in healthy heart rate regulation during daily activity and in a market system undergoing crash dynamics. This kind of invariance reflects invariance of the system under renormalisation and resembles behaviour at criticality of a system undergoing continuous phase transition — indeed in both phenomena, such phase transition behaviour has been revealed. While the precise mechanism underlying invariance of the PDF under system renormalisation of both systems discussed is not to date understood, there is an intimate link between the non-Gaussian PDF characteristics and the persistent invariant correlation structure emerging between fluctuations across scale and time.
Tangkaratt, Voot; Mori, Syogo; Zhao, Tingting; Morimoto, Jun; Sugiyama, Masashi
2014-09-01
The goal of reinforcement learning (RL) is to let an agent learn an optimal control policy in an unknown environment so that future expected rewards are maximized. The model-free RL approach directly learns the policy based on data samples. Although using many samples tends to improve the accuracy of policy learning, collecting a large number of samples is often expensive in practice. On the other hand, the model-based RL approach first estimates the transition model of the environment and then learns the policy based on the estimated transition model. Thus, if the transition model is accurately learned from a small amount of data, the model-based approach is a promising alternative to the model-free approach. In this paper, we propose a novel model-based RL method by combining a recently proposed model-free policy search method called policy gradients with parameter-based exploration and the state-of-the-art transition model estimator called least-squares conditional density estimation. Through experiments, we demonstrate the practical usefulness of the proposed method.
Kim, Sangdan; Han, Suhee
2010-01-01
Most related literature regarding designing urban non-point-source management systems assumes that precipitation event-depths follow the 1-parameter exponential probability density function to reduce the mathematical complexity of the derivation process. However, the method of expressing the rainfall is the most important factor for analyzing stormwater; thus, a better mathematical expression, which represents the probability distribution of rainfall depths, is suggested in this study. Also, the rainfall-runoff calculation procedure required for deriving a stormwater-capture curve is altered by the U.S. Natural Resources Conservation Service (Washington, D.C.) (NRCS) runoff curve number method to consider the nonlinearity of the rainfall-runoff relation and, at the same time, obtain a more verifiable and representative curve for design when applying it to urban drainage areas with complicated land-use characteristics, such as occurs in Korea. The result of developing the stormwater-capture curve from the rainfall data in Busan, Korea, confirms that the methodology suggested in this study provides a better solution than the pre-existing one.
Velocity fluctuation analysis via dynamic programming
Schlossberg, D. J.; Gupta, D. K.; Fonck, R. J.; McKee, G. R.; Shafer, M. W.
2006-10-15
A new method of calculating one-dimensional velocity fluctuations from spatially resolved density fluctuation measurements is presented. The algorithm uses vector-matching methods of dynamic programming that match structures, such as turbulent fluctuations, in two data sets. The associated time delay between data sets is estimated by determining an optimal path to transform one vector to another. This time-delay-estimation (TDE) method establishes a new benchmark for velocity analysis by achieving higher sensitivity and frequency response than previously developed methods, such as time-resolved cross correlations and wavelets. TDE has been successfully applied to beam emission spectroscopy measurements of density fluctuations to obtain poloidal flow fluctuations associated with such phenomena as the geodesic acoustic mode. The dynamic programming algorithm should allow extension to high frequency velocity fluctuations associated with underlying electrostatic potential and resulting ExB fluctuations.
NASA Astrophysics Data System (ADS)
Polyanskaya, L. M.; Ivanov, K. E.; Zvyagintsev, D. G.
2012-10-01
The role has been studied of Gram-negative bacteria in the destruction of polymers widely spread in soils: chitin and cellulose. The introduction of chitin had no positive effect on the population density of Gram-negative bacteria, but it advanced the date of their appearance: the maximum population density of Gram-negative bacteria was recorded not on the 7th-15th day as in the control but much earlier, on the 3rd-7th day of the experiment. Consequently, the introduction of chitin as an additional source of nutrition promoted revealing of the Gram-negative bacteria already at the early stages of the succession. In the course of the succession, when the fungal mycelium begins to die off, the actinomycetic mycelium increases in length, i.e., Gram-negative bacteria are replaced at this stage with Gram-positive ones, the leading role among which belongs to actinomycetes. The growth rate of Gram-negative bacteria is higher than that of actinomycetes, so they start chitin utilization at the early stages of the succession, whereas actinomycetes dominate at the late stages. The population density of Gram-negative bacteria was lower under the anaerobic conditions as compared with that in the aerobic ones. The population density of Gram-negative bacteria in the lower layer of the A horizon and in the B horizon was slightly higher only in the case of the chitin introduction. When cellulose was introduced into the soil under aerobic conditions, the population density of Gram-negative bacteria in all the layers of the A horizon was maximal from the 14th to the 22nd day of the experiment. Cellulose was utilized in the soil mostly by fungi, and this was suggested by the increase of the length of the fungal mycelium. Simultaneously, an increase in the length of the actinomycetal mycelium was observed, as these organisms also perform cellulose hydrolysis in soils. The Gram-negative bacteria began to develop at the stage of the fungal mycelium destruction, which indirectly
Clusel, Maxime; Fortin, Jean-Yves; Holdsworth, Peter C W
2004-10-01
Order parameter fluctuations for the two-dimensional Ising model in the region of the critical temperature are presented. A locus of temperatures T(*) (L) and a locus of magnetic fields B(*) (L) are identified, for which the probability density function is similar to that for the two-dimensional XY model in the spin wave approximation. The characteristics of the fluctuations along these points are largely independent of universality class. We show that the largest range of fluctuations relative to the variance of the distribution occurs along these loci of points, rather than at the critical temperature itself and we discuss this observation in terms of intermittency. Our motivation is the identification of a generic form for fluctuations in correlated systems in accordance with recent experimental and numerical observations. We conclude that a universality-class-dependent form for the fluctuations is a particularity of critical phenomena related to the change in symmetry at a phase transition.
NASA Astrophysics Data System (ADS)
Pang, Xiao-Feng; Zhang, Huai-Wu; Yu, Jia-Feng; Luo, Yu-Hui
The dynamic behaviors of the new soliton in the improved Davydov model in the protein molecules at biological temperature have been numerically simulated by utilizing the dynamic equations for the bio-energy transport and the Runge-Kutta way. In this simulation the influences of the temperature and structure disorders of the protein molecules on the soliton transporting the bio-energy have been completely considered. We find that the new soliton is quite stable in the cases of motion of a long time of 300 ps and of disorders of the structures of the proteins at biological temperatures of 300 K-320 K. The disorders of the structures contain the disorder of mass sequence of amino acids and the fluctuations of the coupling constant, force constant and dipole- dipole interaction constant and ground state energy of the proteins, designating the features of its structure and interactions between the particles in it. However, the soliton disperses in the cases of higher temperature of 325 K and larger structure disorders. The numerical results show that the new soliton is very robust against the influences of the thermal perturbation and structure disorders at biological temperature 300 K, its lifetime and critical temperature are at least 300 ps at 300 K and 320 K, respectively. These results are also consistent with analytical data.
Statistical interpretation of traveltime fluctuations
NASA Astrophysics Data System (ADS)
Roth, Michael
1997-02-01
A ray-theoretical relation between the autocorrelation functions of traveltime and slowness fluctuations is established for recording profiles with arbitrary angles to the propagation direction of a plane wave. From this relation follows that the variance of traveltime fluctuations is independent of the profile orientation and proportional to the variance, ɛ2, of slowness fluctuations, to the correlation distance, a, and to the propagation distance L. The halfwidth of the autocorrelation function of traveltime fluctuations is proportional to a and decreases with increasing profile angle. This relationship allows us to estimate the statistical parameters ɛ and a from observed traveltime fluctuations. Numerical experiments for spatial isotropic random media characterized by a Gaussian autocorrelation function show that the statistical parameters can be reproduced successfully if L/a ≤ 10 . For larger L/a the correlation distance is overestimated and the standard deviation is underestimated. However, the results of the numerical experiments provide empirical factors to correct for these effects. The theory is applied to observed traveltime fluctuations of the Pg phase on a profile of the BABEL project. For the upper crust east of Øland (Sweden) slowness fluctuations with standard deviation ɛ = 2.2-5% and correlation distance a = 330-600 m are found.
NASA Astrophysics Data System (ADS)
Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.
2014-12-01
On the basis of coupled Ginzburg-Landau equations we study nonhomogeneous states in systems with two order parameters (OPs). Superconductors with a superconducting OP Δ and a charge- or spin-density wave with amplitude W are examples of such systems. When one OP, say Δ , has a form of a topological defect, like, e.g., a vortex or domain wall between the domains with the phases 0 and π , the other OP W is determined by the Gross-Pitaevskii equation and is localized at the center of the defect. We consider in detail the domain-wall defect for Δ and show that the shape of the associated solution for W depends on temperature and doping (or on the curvature of the Fermi surface) μ . It turns out that, provided the temperature or doping level is close to some discrete values Tn and μn, the spatial dependence of the function W (x ) is determined by the form of the eigenfunctions of the linearized Gross-Pitaevskii equation. The spatial dependence of W0 corresponding to the ground state has the form of a soliton, while other possible solutions Wn(x ) have nodes. The inverse situation when W (x ) has the form of a topological defect and Δ (x ) is localized at the center of this defect is also possible. In particular, we predict a surface or interfacial superconductivity in a system where a superconductor is in contact with a material that suppresses W . This superconductivity should have rather unusual temperature dependence existing only in certain intervals of temperature. Possible experimental realizations of such nonhomogeneous states of OPs are discussed.
Spin fluctuations and superconductivity in UPt3
NASA Astrophysics Data System (ADS)
Fay, D.; Appel, J.
1985-11-01
We attempt to assess the importance of spin fluctuations in the heavy-fermion system UPt3, the most unambiguous evidence for which is the T3 lnT term in the specific heat. We investigate whether other contributions, such as that from a peak in the electronic density of states or from the electron-phonon interaction, could account for the experimental data. We conclude that they cannot although the data are consistent with the presence of both a T3 lnT term and a density-of-states peak of width greater than about 60 K. We determine the input parameters for the paramagnon theory with a self-consistent method developed by Boring, Albers, Stewart, and Koelling for UAl2 and we calculate the s- and p-wave pairing interactions. A one-band model favors p-wave pairing, while a two-band model leads to conventional s-wave superconductivity.
Grudzevich, O. T.
2015-12-15
Existing direct and indirect experimental data on level densities in excited nuclei of mass and charge number in the ranges of A = 20–60 and Z = 11–27, respectively, were compiled and analyzed. Contradictions between values extracted from the results of measurements performed by different methods were revealed. Consistent input data were selected, and a systematics of level-density parameters was created on this basis within the generalized model of superfluid nuclei. The effect of the first discrete vibrational levels on extracted parameters was studied.
Ostrovskaya, G. V.; Markov, V. S.; Frank, A. G.
2016-01-15
The influence of the initial parameters of the magnetic field and plasma on the spatial structure of the electric current and electron density in current sheets formed in helium plasma in 2D and 3D magnetic configurations with X-type singular lines is studied by the methods of holographic interferometry and magnetic measurements. Significant differences in the structures of plasma and current sheets formed at close parameters of the initial plasma and similar configurations of the initial magnetic fields are revealed.
Gregorio, Vincent; Büchi, Lucie; Anneville, Orlane; Rimet, Frédéric; Bouchez, Agnès; Chèvre, Nathalie
2012-11-01
Mixture risk assessment predictions have rarely been confronted with biological changes observed in the environment. In this study, long-term monitoring of a European great lake, Lake Geneva, provides the opportunity to assess to what extent the predicted toxicity of herbicide mixtures explains the changes in the composition of the phytoplankton community next to other classical limnology parameters such as nutrients. To reach this goal, the gradient of the mixture toxicity of 14 herbicides regularly detected in the lake was calculated using concentration addition and response addition models. A temporal gradient of toxicity was observed which decreased from 2004 to 2009. Redundancy analysis and partial redundancy analysis showed that this gradient explains a significant portion of the variation in phytoplankton community composition with and without having removed the effect of all other co-variables. Moreover, species that are significantly influenced, positively or negatively, by the decrease of toxicity in the lake over time are highlighted. It can be concluded that the herbicide mixture toxicity is one of the key parameters to explain phytoplankton changes in Lake Geneva.
Liu, Ning He, Miao; Alghamdi, Hisham; Chen, George; Fu, Mingli; Li, Ruihai; Hou, Shuai
2015-08-14
Trapping parameters can be considered as one of the important attributes to describe polymeric materials. In the present paper, a more accurate charge dynamics model has been developed, which takes account of charge dynamics in both volts-on and off stage into simulation. By fitting with measured charge data with the highest R-square value, trapping parameters together with injection barrier of both normal and aged low-density polyethylene samples were estimated using the improved model. The results show that, after long-term ageing process, the injection barriers of both electrons and holes is lowered, overall trap depth is shallower, and trap density becomes much greater. Additionally, the changes in parameters for electrons are more sensitive than those of holes after ageing.
Shi, Pei-Jian; Xu, Qiang; Sandhu, Hardev S; Gielis, Johan; Ding, Yu-Long; Li, Hua-Rong; Dong, Xiao-Bo
2015-10-01
The relationship between spatial density and size of plants is an important topic in plant ecology. The self-thinning rule suggests a -3/2 power between average biomass and density or a -1/2 power between stand yield and density. However, the self-thinning rule based on total leaf area per plant and density of plants has been neglected presumably because of the lack of a method that can accurately estimate the total leaf area per plant. We aimed to find the relationship between spatial density of plants and total leaf area per plant. We also attempted to provide a novel model for accurately describing the leaf shape of bamboos. We proposed a simplified Gielis equation with only two parameters to describe the leaf shape of bamboos one model parameter represented the overall ratio of leaf width to leaf length. Using this method, we compared some leaf parameters (leaf shape, number of leaves per plant, ratio of total leaf weight to aboveground weight per plant, and total leaf area per plant) of four bamboo species of genus Indocalamus Nakai (I. pedalis (Keng) P.C. Keng, I. pumilus Q.H. Dai and C.F. Keng, I. barbatus McClure, and I. victorialis P.C. Keng). We also explored the possible correlation between spatial density and total leaf area per plant using log-linear regression. We found that the simplified Gielis equation fit the leaf shape of four bamboo species very well. Although all these four species belonged to the same genus, there were still significant differences in leaf shape. Significant differences also existed in leaf area per plant, ratio of leaf weight to aboveground weight per plant, and leaf length. In addition, we found that the total leaf area per plant decreased with increased spatial density. Therefore, we directly demonstrated the self-thinning rule to improve light interception.
NASA Astrophysics Data System (ADS)
Zhou, Yunliang; Ma, S. Y.; Xiong, Chao; Luehr, Hermann
The total air mass densities at about 500 km altitude are derived using super-STAR accelerom-eter measurements onboard GRACE satellites for 25 great magnetic storms with minimum Dst less than 100 nT during 2002 to 2006 years. Taking NRLMSISE-00 model-predicted densities without active ap index input as a reference baseline of quiet-time mass density, the storm-time changes in upper thermospheric mass densities are obtained by subtraction for all the storm events and sorted into different grids of latitude by local time sector. The relationships of the storm-time density changes with various interplanetary parameters and magnetospheric ring current index of Sym-H are statistically investigated. The parameters include Akasofu energy coupling function, the merging electric field Em, the magnitude of IMF component in the GSM y-z plane etc. as calculated from OMNI data at 1 AU. It is found that the storm-time changes in the upper thermospheric mass density have the best linear correlation with the Sym-H index in general, showing nearly zero time delay at low-latitudes and a little time ahead at high-latitudes for most cases. Unexpectedly, the magnitude of IMF component in the y-z plane, Byz, shows correlation with storm-time mass density changes better and closer than Akasofu function and even Em. And, the mass density changes lag behind Byz about 1-4 hours for most cases at low-latitudes. The correlations considered above are local time dependent, showing the lowest at dusk sectors. For the largest superstorm of November 2003, the changes in mass density are correlated very closely with Byz, Em, and Sym-H index, showing correlation coefficients averaged over all latitudes in noon sector as high as 0.93, 0.91 and 0.90 separately. The physical factors controlling the lag times between the mass density changes at mid-low-latitudes and the interplanetary parameter variations are also analyzed. The results in this study may pro-vide useful suggestions for establishing
Study of Fluctuations in the CW Penning Surface-Plasma Source of Negative Ions
NASA Astrophysics Data System (ADS)
Belchenko, Yuri; Sanin, Andrey; Savkin, Valery
2011-09-01
Study of current fluctuations for cw Penning SPS with hollow cathode drive was done. The noiseproof measurements of negative ion beam current, current in extracted electrode circuit, discharge current and voltage were carried out by the low-inductive probes in wide frequency range. Spectrum and intensity of fluctuations at various operation modes, parameters and electrode geometry were recorded for two versions of cw Penning SPS. H- beam current and the extracted electrode circuit current had the level of ripples higher, than the ripples in discharge current and voltage signals. Frequency spectrum of beam and discharge fluctuations displayed stable peaks. The main peak had location in the range 0.1÷1.5 MHz and FWHM of about 0.1 MHz. For the basic operational mode the main peak in frequency spectrum was in the range 0.3-0.4 MHz. The fluctuations of current in extracted electrode circuit and in accelerated electrode circuit had the similar structure and correlated with beam current fluctuations. The obtained data show that plasma density oscillations are responsible for the beam current fluctuations. The 0.1÷1.5 MHz fluctuations of plasma density could be produced by oscillations of cathode emissivity and of discharge current distribution between the specific cathode regions.
NASA Astrophysics Data System (ADS)
Seitenzahl, I. R.; Ciaraldi-Schoolmann, F.; Röpke, F. K.
2011-07-01
Delayed detonations of Chandrasekhar mass white dwarfs (WDs) have been very successful in explaining the spectra, light curves and the width-luminosity relation of spectroscopically normal Type Ia supernovae (SNe Ia). The ignition of the thermonuclear deflagration flame at the end of the convective carbon 'simmering' phase in the core of the WD is still not well understood, and much about the ignition kernel distribution remains unknown. Furthermore, the central density at the time of ignition depends on the still uncertain screened carbon fusion reaction rates, the accretion history and cooling time of the progenitor, and the composition. We present the results of 12 high-resolution three-dimensional delayed detonation SN Ia explosion simulations that employ a new criterion to trigger the deflagration to detonation transition (DDT). The simulations fall into three ignition categories: relatively bright SNe with five ignition kernels and a weak deflagration phase (three different central densities); relatively dim SNe with 1600 ignition kernels and a strong deflagration phase (three different central densities) and intermediate SNe with 200 ignition kernels (six different central densities). All simulations trigger our DDT criterion and the resulting delayed detonations unbind the star. We find a trend of increasing iron group element (IGE) production with increasing central density for all three categories. The total 56Ni yield, however, remains more or less constant, even though increased electron captures at high density result in a decreasing 56Ni mass fraction of the IGE material. We attribute this to an approximate balance of 56Ni producing and destroying effects. The deflagrations that were ignited at higher density initially have a faster growth rate of subgrid-scale turbulence. Hence, the effective flame speed increases faster, which triggers the DDT criterion earlier, at a time when the central density of the expanded star is higher. This leads to an
Fluctuation of charge on dust particles in a complex plasma
Sodha, M. S.; Mishra, S. K.; Misra, Shikha; Srivastava, Sweta
2010-07-15
This paper presents an analytical model for the evaluation of the fluctuation of the charge on the dust particles in a complex plasma. In contrast to earlier analyses, which ignored the effect of dust particles on density and temperature of electrons and ions, the present model takes into account the number and energy balance of electrons and ions. Three cases, viz., (i) no emission, (ii) thermionic emission, and (iii) photoelectric emission of electrons from the dust particles, have been considered. The results have been graphically illustrated for typical parameters. It is seen that the plasma parameters, and hence the fluctuations, are considerably affected by the consideration of number and energy balance of electrons and ions. A comparison of the results of the present analysis with those of earlier works has also been made.
Nuclear quantum fluctuations in ice I(h).
Moreira, Pedro Augusto Franco Pinheiro; de Koning, Maurice
2015-10-14
We discuss the role of nuclear quantum fluctuations in ice Ih, focusing on the hydrogen-bond (HB) structure and the molecular dipole-moment distribution. For this purpose we carry out DFT-based first-principles molecular dynamics and path-integral molecular dynamics simulations at T = 100 K. We analyze the HB structure in terms of a set of parameters previously employed to characterize molecular structures in the liquid phase and compute the molecular dipole moments using the maximally-localized Wannier functions. The results show that the protons experience very large digressions driven by quantum fluctuations, accompanied by major rearrangements in the electronic density. As a result of these protonic quantum fluctuations the molecular dipole-moment distribution is substantially broadened as well as shifted to a larger mean value when compared to the results obtained when such fluctuations are neglected. In terms of dielectric constants, the reconciliation between the greater mean dipole moment and experimental indications that the dielectric constant of H2O ice is lower than that of D2O ice would indicate that the topology of the HB network is sensitive to protonic quantum fluctuations.
Weber, Valéry; Tymczak, Christopher J; Challacombe, Matt
2006-06-14
The application of theoretical methods based on density-functional theory is known to provide atomic and cell parameters in very good agreement with experimental values. Recently, construction of the exact Hartree-Fock exchange gradients with respect to atomic positions and cell parameters within the Gamma-point approximation has been introduced. In this article, the formalism is extended to the evaluation of analytical Gamma-point density-functional atomic and cell gradients. The infinite Coulomb summation is solved with an effective periodic summation of multipole tensors. While the evaluation of Coulomb and exchange-correlation gradients with respect to atomic positions are similar to those in the gas phase limit, the gradients with respect to cell parameters needs to be treated with some care. The derivative of the periodic multipole interaction tensor needs to be carefully handled in both direct and reciprocal space and the exchange-correlation energy derivative leads to a surface term that has its origin in derivatives of the integration limits that depend on the cell. As an illustration, the analytical gradients have been used in conjunction with the QUICCA algorithm to optimize one-dimensional and three-dimensional periodic systems at the density-functional theory and hybrid Hartree-Fock/density-functional theory levels. We also report the full relaxation of forsterite supercells at the B3LYP level of theory.
NASA Astrophysics Data System (ADS)
Cho, Won-Hwi; Dang, Jeong-Jeung; Kim, June Young; Chung, Kyoung-Jae; Hwang, Y. S.
2016-02-01
Transverse magnetic filter field as well as operating pressure is considered to be an important control knob to enhance negative hydrogen ion production via plasma parameter optimization in volume-produced negative hydrogen ion sources. Stronger filter field to reduce electron temperature sufficiently in the extraction region is favorable, but generally known to be limited by electron density drop near the extraction region. In this study, unexpected electron density increase instead of density drop is observed in front of the extraction region when the applied transverse filter field increases monotonically toward the extraction aperture. Measurements of plasma parameters with a movable Langmuir probe indicate that the increased electron density may be caused by low energy electron accumulation in the filter region decreasing perpendicular diffusion coefficients across the increasing filter field. Negative hydrogen ion populations are estimated from the measured profiles of electron temperatures and densities and confirmed to be consistent with laser photo-detachment measurements of the H- populations for various filter field strengths and pressures. Enhanced H- population near the extraction region due to the increased low energy electrons in the filter region may be utilized to increase negative hydrogen beam currents by moving the extraction position accordingly. This new finding can be used to design efficient H- sources with an optimal filtering system by maximizing high energy electron filtering while keeping low energy electrons available in the extraction region.
Cho, Won-Hwi; Dang, Jeong-Jeung; Kim, June Young; Chung, Kyoung-Jae; Hwang, Y S
2016-02-01
Transverse magnetic filter field as well as operating pressure is considered to be an important control knob to enhance negative hydrogen ion production via plasma parameter optimization in volume-produced negative hydrogen ion sources. Stronger filter field to reduce electron temperature sufficiently in the extraction region is favorable, but generally known to be limited by electron density drop near the extraction region. In this study, unexpected electron density increase instead of density drop is observed in front of the extraction region when the applied transverse filter field increases monotonically toward the extraction aperture. Measurements of plasma parameters with a movable Langmuir probe indicate that the increased electron density may be caused by low energy electron accumulation in the filter region decreasing perpendicular diffusion coefficients across the increasing filter field. Negative hydrogen ion populations are estimated from the measured profiles of electron temperatures and densities and confirmed to be consistent with laser photo-detachment measurements of the H(-) populations for various filter field strengths and pressures. Enhanced H(-) population near the extraction region due to the increased low energy electrons in the filter region may be utilized to increase negative hydrogen beam currents by moving the extraction position accordingly. This new finding can be used to design efficient H(-) sources with an optimal filtering system by maximizing high energy electron filtering while keeping low energy electrons available in the extraction region.
Cho, Won-Hwi; Dang, Jeong-Jeung; Kim, June Young; Hwang, Y. S.; Chung, Kyoung-Jae
2016-02-15
Transverse magnetic filter field as well as operating pressure is considered to be an important control knob to enhance negative hydrogen ion production via plasma parameter optimization in volume-produced negative hydrogen ion sources. Stronger filter field to reduce electron temperature sufficiently in the extraction region is favorable, but generally known to be limited by electron density drop near the extraction region. In this study, unexpected electron density increase instead of density drop is observed in front of the extraction region when the applied transverse filter field increases monotonically toward the extraction aperture. Measurements of plasma parameters with a movable Langmuir probe indicate that the increased electron density may be caused by low energy electron accumulation in the filter region decreasing perpendicular diffusion coefficients across the increasing filter field. Negative hydrogen ion populations are estimated from the measured profiles of electron temperatures and densities and confirmed to be consistent with laser photo-detachment measurements of the H{sup −} populations for various filter field strengths and pressures. Enhanced H{sup −} population near the extraction region due to the increased low energy electrons in the filter region may be utilized to increase negative hydrogen beam currents by moving the extraction position accordingly. This new finding can be used to design efficient H{sup −} sources with an optimal filtering system by maximizing high energy electron filtering while keeping low energy electrons available in the extraction region.
Biesta-Peters, Elisabeth G; Reij, Martine W; Joosten, Han; Gorris, Leon G M; Zwietering, Marcel H
2010-03-01
Quantitative microbiological models predicting proliferation of microorganisms relevant for food safety and/or food stability are useful tools to limit the need for generation of biological data through challenge testing and shelf-life testing. The use of these models requires quick and reliable methods for the generation of growth data and estimation of growth parameters. Growth parameter estimation can be achieved using methods based on plate counting and methods based on measuring the optical density. This research compares the plate count method with two optical density methods, namely, the 2-fold dilution (2FD) method and the relative rate to detection (RRD) method. For model organism Bacillus cereus F4810/72, the plate count method and both optical density methods gave comparable estimates for key growth parameters. Values for the maximum specific growth rate (mu(max)) derived by the 2FD method and by the RRD method were of the same order of magnitude, but some marked differences between the two approaches were apparent. Whereas the 2FD method allowed the derivation of values for lag time (lambda) from the data, this was not possible with the RRD method. However, the RRD method gave many more data points per experiment and also gave more data points close to the growth boundary. This research shows that all three proposed methods can be used for parameter estimation but that the choice of method depends on the objectives of the research.
Random matter density perturbations and LMA
NASA Astrophysics Data System (ADS)
Reggiani, N.; Guzzo, M. M.; de Holanda, P. C.
There are reasons to believe that mechanisms exist in the solar interior which lead to random density perturbations in the resonant region of the Large Mixing Angle solution to the solar neutrino problem. We find that, in the presence of these density perturbations, the best fit point in the (sin 2 2θ , Δ m2) parameter space moves to smaller values, compared with the values obtained for the standard LMA solution. Combining solar data with KamLAND results, we find a new compatibility region, which we call VERY-LOW LMA, where sin 2 2θ ~ 0.6 and Δm2 2× 10-5 eV2, for random density fluctuations of order 5% < ξ < 8%. We argue that such values of density fluctuations are still allowed by helioseismological observations at small scales of order 10 - 1000 km deep inside the solar core. PACS: 26.65 - 90.60J - 96.60.H
NASA Astrophysics Data System (ADS)
Diéval, C.; Andrews, D. J.; Morgan, D. D.; Brain, D. A.; Gurnett, D. A.
2015-09-01
Enhanced topside electron densities in the dayside Martian ionosphere have been repetitively observed in areas of near-radial crustal magnetic fields, for periods of tens of days, indicating their long-term spatial and temporal stability despite changing solar wind conditions. We perform a statistical study of these density structures using the ionospheric mode of the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express. We estimate the apparent extents of these structures relative to the altitude of the surrounding ionosphere. The apex of the density structures often lies higher than the surrounding ionosphere (median vertical extent of 18 km), which indicates upwellings. These structures are much wider than they are high, with latitudinal scales of several degrees. The radar reflector regions are observed above both moderate and strong magnetic anomalies, and their precise locations and latitudinal extents match quite well with the locations and latitudinal extents of magnetic structures of given magnetic polarity (oblique to vertical fields), which happen to be regions where the field lines are open part of the time. The majority of the density structures occur in regions where ionospheric plasma is dominant, indicating closed field regions shielded from shocked solar wind plasma.
Kaukonen, M; Gulans, A; Havu, P; Kauppinen, E
2012-03-05
Lennard-Jones (LJ) parameters are derived for classical nonpolarizable force fields for carbon nanotubes (CNTs) and for CNT-water interaction from van der Waals (vdW) enhanced density functional calculations. The new LJ parameters for carbon-carbon interactions are of the same order as those previously used in the literature but differ significantly for CNT-water interactions. This may partially originate from the fact that in addition to pure vdW interactions the polarization and other quantum mechanics effects are embedded into the LJ-potential.
Analysis of Fluctuations in a Combustion-Driven Open-Cycle MHD Generator.
NASA Astrophysics Data System (ADS)
Skorska, Malgorzata Bozena
Fluctuations present in MHD generators may cause significant degradation in the generated power. The fluctuations may result from three sources. First, the mass flow rates of the components' input to the combustor vary. Second, the combustor initiates its own variations which are functions of the combustor geometry and injection techniques. Third, the generator action, i.e., flow of plasma in a magnetic field, introduces variations in the plasma variables. The purpose of the study is to investigate the fluctuations of MHD output signals, which may either arise from the combustor fluctuations propagating into a conducting channel, or are inherent in the generator dynamics. The analysis of fluctuations is based on the analytical and empirical models. Both models assume that stochastic processes take place within the MHD plasma, and both models yield results in the form of autocorrelation, crosscorrelation, and power spectral density functions of the system variables. The study showed that fluctuations, whose frequencies exceed 200 Hz, in the plasma density, velocity, pressure, current and voltage variables are acoustic in nature, and are caused by longitudinal standing waves present in the generator. The analysis proved that Hall generators develop fluctuations mainly in the range 700 Hz to 2000 Hz, whereas Faraday and DCW generators are favorable for the low frequency fluctuations. Parametric study of the plasma disclosed that stronger magnetic fields and larger Hall parameters increase the frequency range of fluctuations. Changes in plasma specific heat ratio or in inlet steady-state parameters may increase or decrease the intensities of some odd harmonics of the standing waves. The fluctuations that originate in the combustion chamber also affect the plasma variables. A white noise character of these fluctuations guarantees a fairly uniform distribution of energy in the fluctuations of the plasma variables in the frequency range up to 200 Hz. Future research in
Current Fluctuations in Stochastic Lattice Gases
NASA Astrophysics Data System (ADS)
Bertini, L.; de Sole, A.; Gabrielli, D.; Jona-Lasinio, G.; Landim, C.
2005-01-01
We study current fluctuations in lattice gases in the macroscopic limit extending the dynamic approach for density fluctuations developed in previous articles. More precisely, we establish a large deviation theory for the space-time fluctuations of the empirical current which include the previous results. We then estimate the probability of a fluctuation of the average current over a large time interval. It turns out that recent results by Bodineau and Derrida [Phys. Rev. Lett.922004180601] in certain cases underestimate this probability due to the occurrence of dynamical phase transitions.
NASA Astrophysics Data System (ADS)
Mattingly, Margarita Claudia Krieghoff
The space-time development of hadron-nucleus interactions is examined using bubble chamber and downstream particle identifier data from the hybrid spectrometer of Fermilab experiment E597. 5583 events representing 12 interactions are studied with conventional and fractal techniques. Comparisons are made to simulated events from the Lund Monte Carlo FRITIOF 1.6. Multiplicities are studied conventionally. Negative binomial descriptions of produced particle multiplicities are interpreted in terms of clusters and cascading and in terms of partial stimulated emission; forward-backward correlations, in terms of short- and long-range correlations and multiple scattering. Multiplicities are consistent with a multiple collision view of multiparticle production mechanisms and are investigated in terms of the number of collisions nu. Rapidity density fluctuations are studied fractally. The possibility of new dynamics is considered on the basis of event-by-event studies of spike phenomena, intermittency, and fractal dimensions. Results from these exploratory studies are consistent with predictions made for quark-gluon plasma transitions. 131 spike events are analyzed; intermittency is investigated with normalized factorial moments and cumulants; and fractal dimensions and correlations dimensions are calculated. Seagull effects and production region sizes from Bose-Einstein pion interferometry are also considered.
Huang, Huabing; Gong, Peng; Cheng, Xiao; Clinton, Nick; Li, Zengyuan
2009-01-01
Forest structural parameters, such as tree height and crown width, are indispensable for evaluating forest biomass or forest volume. LiDAR is a revolutionary technology for measurement of forest structural parameters, however, the accuracy of crown width extraction is not satisfactory when using a low density LiDAR, especially in high canopy cover forest. We used high resolution aerial imagery with a low density LiDAR system to overcome this shortcoming. A morphological filtering was used to generate a DEM (Digital Elevation Model) and a CHM (Canopy Height Model) from LiDAR data. The LiDAR camera image is matched to the aerial image with an automated keypoints search algorithm. As a result, a high registration accuracy of 0.5 pixels was obtained. A local maximum filter, watershed segmentation, and object-oriented image segmentation are used to obtain tree height and crown width. Results indicate that the camera data collected by the integrated LiDAR system plays an important role in registration with aerial imagery. The synthesis with aerial imagery increases the accuracy of forest structural parameter extraction when compared to only using the low density LiDAR data.
Ren, Yong; Jiang, Xuan; Pan, Deng; Mao, Hai-Quan
2011-01-01
A series of polyphosphoramidates (PPA) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293 and HepG2 cells). An increase in MW and/or net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for non-viral gene delivery. PMID:21067136
Maximum entropy distribution of stock price fluctuations
NASA Astrophysics Data System (ADS)
Bartiromo, Rosario
2013-04-01
In this paper we propose to use the principle of absence of arbitrage opportunities in its entropic interpretation to obtain the distribution of stock price fluctuations by maximizing its information entropy. We show that this approach leads to a physical description of the underlying dynamics as a random walk characterized by a stochastic diffusion coefficient and constrained to a given value of the expected volatility, in this way taking into account the information provided by the existence of an option market. The model is validated by a comprehensive comparison with observed distributions of both price return and diffusion coefficient. Expected volatility is the only parameter in the model and can be obtained by analysing option prices. We give an analytic formulation of the probability density function for price returns which can be used to extract expected volatility from stock option data.
Kamiński, Radosław; Domagała, Sławomir; Jarzembska, Katarzyna N; Hoser, Anna A; Sanjuan-Szklarz, W Fabiola; Gutmann, Matthias J; Makal, Anna; Malińska, Maura; Bąk, Joanna M; Woźniak, Krzysztof
2014-01-01
A comprehensive analysis of various properties derived from multiple high-resolution X-ray diffraction experiments is reported. A total of 13 charge-density-quality data sets of α-oxalic acid dihydrate (C2H2O4·2H2O) were subject to Hansen-Coppens-based modelling of electron density. The obtained parameters and properties were then statistically analysed yielding a clear picture of their variability across the different measurements. Additionally, a computational approach (CRYSTAL and PIXEL programs) was utilized to support and examine the experimental findings. The aim of the study was to show the real accuracy and interpretation limits of the charge-density-derived data. An investigation of raw intensities showed that most of the reflections (60-70%) fulfil the normality test and the lowest ratio is observed for weak reflections. It appeared that unit-cell parameters are determined to the order of 10(-3) Å (for cell edges) and 10(-2) ° (for angles), and compare well with the older studies of the same compound and with the new 100 K neutron diffraction data set. Fit discrepancy factors are determined within a 0.5% range, while the residual density extrema are about ±0.16 (3) e Å(-3). The geometry is very well reproducible between different data sets. Regarding the multipole model, the largest errors are present on the valence shell charge-transfer parameters. In addition, symmetry restrictions of multipolar parameters, with respect to local coordinate systems, are well preserved. Standard deviations for electron density are lowest at bond critical points, being especially small for the hydrogen-bonded contacts. The same is true for kinetic and potential energy densities. This is also the case for the electrostatic potential distribution, which is statistically most significant in the hydrogen-bonded regions. Standard deviations for the integrated atomic charges are equal to about 0.1 e. Dipole moments for the water molecule are comparable with
2011-12-15
MODFLOW [Harbaugh et al., 2000], MT3DMS [Zheng and Wang, 1999; Zheng, 2005], and SEAWAT [e.g., Guo and Langevin, 2002; Langevin et al., 2003, 2007...which are fully public- domain codes for 3-D flow and variable-density transport modeling. SEAWAT combines a modified version of MODFLOW and MT3DMS...Surv., Reston, Va. Harbaugh, A. W., E. R. Banta, M. C. Hill, and M. G. McDonald (2000), MODFLOW -2000, The U.S. Geological Surv. modular ground-water
Streubel, A; Siepmann, J; Bodmeier, R
2003-01-01
The aim of this study was to develop and physicochemically characterize single unit, floating controlled drug delivery systems consisting of (i). polypropylene foam powder, (ii). matrix-forming polymer(s), (iii). drug, and (iv). filler (optional). The highly porous foam powder provided low density and, thus, excellent in vitro floating behavior of the tablets. All foam powder-containing tablets remained floating for at least 8 h in 0.1 N HCl at 37 degrees C. Different types of matrix-forming polymers were studied: hydroxypropyl methylcellulose (HPMC), polyacrylates, sodium alginate, corn starch, carrageenan, gum guar and gum arabic. The tablets eroded upon contact with the release medium, and the relative importance of drug diffusion, polymer swelling and tablet erosion for the resulting release patterns varied significantly with the type of matrix former. The release rate could effectively be modified by varying the "matrix-forming polymer/foam powder" ratio, the initial drug loading, the tablet geometry (radius and height), the type of matrix-forming polymer, the use of polymer blends and the addition of water-soluble or water-insoluble fillers (such as lactose or microcrystalline cellulose). The floating behavior of the low density drug delivery systems could successfully be combined with accurate control of the drug release patterns.
NASA Astrophysics Data System (ADS)
Griv, Evgeny; Jiang, Ing-Guey; Russeil, Delphine
2015-02-01
This paper is the third in a series of articles devoted to the determination of the Milky Way's spiral density-wave structure from the kinematics of the Galactic objects, using the ordinary Oort equation. The minor effects caused by the Lin-Shu type two-dimensional density waves are also taken into account. The results obtained allow us to conclude that (a) several low-m spiral patterns with different number of spiral arms m and amplitudes of the perturbed gravitational potential may coexist in the Galaxy. (b) the single-armed m=1 spiral mode dominates the pattern. The distribution of stars and gas in outer parts of the system is thus asymmetric (“lopsided”), (c) the phase velocity of spiral waves (or the pattern rotation speed) does not depend on m and therefore each Fourier component of a gravity perturbation rotates with the same angular velocity, (d) the Sun lies between the main trailing spiral-arm segments in Carina-Sagittarius and Perseus, closer to the inner Carina-Sagittarius one. The local Cygnus-Orion arm in which the Sun is located is thus not a part of the main spiral pattern, and finally (e) the Galaxy seems to be more homogeneous and rotating more like a solid body than in the standard m=0 model (i.e. spiral arms not included in the model).
Resonant tunneling of fluctuation Cooper pairs
Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.
2015-02-09
Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, T_{c}, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at T_{c}. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to T_{c}. This striking effect offers an unprecedented tool for direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.
Resonant tunneling of fluctuation Cooper pairs
Galda, Alexey; Mel'nikov, A. S.; Vinokur, V. M.
2015-02-09
Superconducting fluctuations have proved to be an irreplaceable source of information about microscopic and macroscopic material parameters that could be inferred from the experiment. According to common wisdom, the effect of thermodynamic fluctuations in the vicinity of the superconducting transition temperature, Tc, is to round off all of the sharp corners and discontinuities, which otherwise would have been expected to occur at Tc. Here we report the current spikes due to radiation-induced resonant tunneling of fluctuation Cooper pairs between two superconductors which grow even sharper and more pronounced upon approach to Tc. This striking effect offers an unprecedented tool formore » direct measurements of fluctuation Cooper pair lifetime, which is key to our understanding of the fluctuation regime, most notably to nature of the pseudogap state in high-temperature superconductors. Our finding marks a radical departure from the conventional view of superconducting fluctuations as a blurring and rounding phenomenon.« less
Fluctuation Measurements on the Madison Symmetric Torus with a Heavy Ion Beam Probe
NASA Astrophysics Data System (ADS)
Lei, J.; Schoch, P. M.; Demers, D. R.; Shah, U.; Connor, K. A.; Crowley, T. P.
2000-10-01
Measurements of electron density fluctuations (tilden_e) and electrostatic potential fluctuations (tildeφ) on the Madison Symmetric Torus (MST) reversed field pinch (RFP) are undertaken with a newly installed 200keV Heavy Ion beam Probe (HIBP) system. Initial fluctuation signals observed are closely coupled to low frequency MHD activity. tilde φ induced particle transport can be addressed by simultaneous measurements of tildene and tilde φ. Langmuir probes have been used on MST to measure this kind of transport at low plasma current level and at the edge of the plasma. By changing the beam energy and beam injection conditions, the MST-HIBP can provide localized fluctuation measurements at almost all radii for a broad range of plasma parameters, and thus enrich our understanding of turbulent transport in reversed field pinch plasmas. Current working issues include isolating electrostatic fluctuation signals from those caused by magnetic fluctuations, increasing the ion beam intensity to increase signal-to-noise ratios, and looking for the best operational regime (sample volume locations, plasma parameters, etc.) for this diagnostic. *WORK SUPPORTED BY USDOE
Jaworski, Maciej; Pludowski, Pawel
2013-01-01
Dual-energy X-ray absorptiometry (DXA) method is widely used in pediatrics in the study of bone density and body composition. However, there is a limit to how precise DXA can estimate bone and body composition measures in children. The study was aimed to (1) evaluate precision errors for bone mineral density, bone mass and bone area, body composition, and mechanostat parameters, (2) assess the relationships between precision errors and anthropometric parameters, and (3) calculate a "least significant change" and "monitoring time interval" values for DXA measures in children of wide age range (5-18yr) using GE Lunar Prodigy densitometer. It is observed that absolute precision error values were different for thin and standard technical modes of DXA measures and depended on age, body weight, and height. In contrast, relative precision error values expressed in percentages were similar for thin and standard modes (except total body bone mineral density [TBBMD]) and were not related to anthropometric variables (except TBBMD). Concluding, due to stability of percentage coefficient of variation values in wide range of age, the use of precision error expressed in percentages, instead of absolute error, appeared as convenient in pediatric population.
NASA Astrophysics Data System (ADS)
Panda, Sampad Kumar; Haralambous, Haris; Mostafa, Md Golam
2016-07-01
The present study investigates the variations of the bottomside ionospheric electron density profile thickness (B0) and shape (B1) parameters, deduced from the manually scaled digisonde (DPS-4D) ionograms at the lower mid-latitude Cyprus (Geographic 35°N, 33°E) covering the period 2009-2014. The monthly median hourly values of these parameters during different seasons and solar activity conditions are compared with the International Reference Ionosphere model (IRI-2012) estimations using three different options namely: Bil-2000, Gul-1987, and ABT-2009. To ensure the quiet time profile, the ionograms of the geomagnetically disturbed periods are discarded from the datasets and the storm model in the IRI is intentionally turned off. The statistical studies reveal considerable discrepancies in the observed B0 parameters from the model simulations, though the divergences are minimal around the daytime and during the summer solstice seasons. Nevertheless, B0 with the Gul-1987 option apparently shows closer daytime value during the low solar active summer, whereas the ABT-2009 option manifested relatively better agreement during the high solar active summer months. The characteristic morning, evening, as well as nighttime departure in the model derived B0 parameters are conspicuous in all the seasons in spite of unnoticed perturbations in the B1, suggesting that further improvement in the existing model database is essential with additional in-situ experimental data across the lower mid-latitude region. The important extracts from this study may support in the international efforts of determining the best set of profile parameters for the climatological representation of the ionospheric electron density variation across the globe.
NASA Technical Reports Server (NTRS)
Pai, Shantaram S.; Gyekenyesi, John P.
1988-01-01
The calculation of shape and scale parameters of the two-parameter Weibull distribution is described using the least-squares analysis and maximum likelihood methods for volume- and surface-flaw-induced fracture in ceramics with complete and censored samples. Detailed procedures are given for evaluating 90 percent confidence intervals for maximum likelihood estimates of shape and scale parameters, the unbiased estimates of the shape parameters, and the Weibull mean values and corresponding standard deviations. Furthermore, the necessary steps are described for detecting outliers and for calculating the Kolmogorov-Smirnov and the Anderson-Darling goodness-of-fit statistics and 90 percent confidence bands about the Weibull distribution. It also shows how to calculate the Batdorf flaw-density constants by uing the Weibull distribution statistical parameters. The techniques described were verified with several example problems, from the open literature, and were coded. The techniques described were verified with several example problems from the open literature, and were coded in the Structural Ceramics Analysis and Reliability Evaluation (SCARE) design program.
Correlated fluctuations near the QCD critical point
NASA Astrophysics Data System (ADS)
Jiang, Lijia; Li, Pengfei; Song, Huichao
2016-08-01
In this article, we introduce a freeze-out scheme for the dynamical models near the QCD critical point through coupling the decoupled classical particles with the order parameter field. With a modified distribution function that satisfies specific static fluctuations, we calculate the correlated fluctuations of net protons on the hydrodynamic freeze-out surface. A comparison with recent STAR data shows that our model calculations could roughly reproduce energy-dependent cumulant C4 and κ σ2 of net protons through tuning the related parameters. However, the calculated C2 and C3 with both Poisson and binomial baselines are always above the experimental data due to the positive contributions from the static critical fluctuations. To qualitatively and quantitatively describe all the related experimental data, the dynamical critical fluctuations and more realistic noncritical fluctuation baselines should be investigated in the near future.
Yarahmadi, Peyman; Miandare, Hamed Kolangi; Fayaz, Sahel; Caipang, Christopher Marlowe A
2016-01-01
densities and crowding resulted in the increase in HSP70 gene expression and the levels of selected stress responses in the serum. However, there was down-regulation of immune genes expression and decreased innate immune responses in the fish. The mRNA expression of the genes and immune parameters that were measured in this study could be helpful in monitoring the health status and welfare of the fish in aquaculture systems particularly in relation to increased stocking densities.
Aufderheide, John; Warbritton, Ryan; Pounds, Nadine; File-Emperador, Sharon; Staples, Charles; Caspers, Norbert; Forbes, Valery
2006-01-01
These experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the apple snail, Marisa cornuarietis. The overall objective of the program is to identify suitable husbandry conditions for maintaining multi-generation populations of this species in the laboratory for use in ecotoxicological testing. In this article, we focus on the effects of photoperiod, temperature, and population density on adult fecundity and juvenile growth. Increasing photoperiod from 12 to 16 h of light per day had no effect on adult fecundity or egg hatching and relatively minor effects on juvenile growth and development. Rearing snails at temperatures between 22°C and 28°C did not influence the rates of egg production or egg clutch size. However, the rates of growth and development (of eggs and juveniles) increased with increasing temperature in this range, and when temperatures were reduced to 22°C egg-hatching success was impaired. Juvenile growth and development were more sensitive to rearing density than adult fecundity traits. On the basis of the present results, we conclude that rearing individuals of M. cornuarietis at a temperature of 25°C, a photoperiod of 12L:12D, and a density of <0.8 snails L−1 (with lower densities for juvenile snails) should provide favorable husbandry conditions for maintaining multi-generation populations of this species. PMID:19009043
NASA Astrophysics Data System (ADS)
Kusche, Jürgen; Forootan, Ehsan; Löcher, Anno; Henze, Christina; Börger, Klaus; Schall, Judith
2015-04-01
The aim of this study is to develop an integrated approach, which allows a) to measure the neutral density of the thermosphere using orbit and accelerometer information from various satellite missions and b) to relate them to operational atmospheric models. The satellite missions to be considered will include low-orbit satellites CHAMP, GRACE, GOCE and SWARM; laser-ranging satellites such as LAGEOS; as well as altimetry satellites such as Topex/Poseidon and Jason 1-2. On the other hand different atmospheric models, including Jacchia-Bowman, MSIS 86, MSISE 90, and NRLMSISE-00 models, will be investigated with respect to their sensitivity to geomagnetic activity and sunspot cycle etc. and they will be used to determine a theoretical acceleration due to air drag. Subsequently, we will compare the "computed" atmospheric density with the total mass density ("observed" atmospheric density) retrieved from accelerometer measurements made on board the satellites during their operational period. Based on these results we finally will develop a method - a so called "integrated approach" - that allows the joint determination of thermospherical, instrumental, and gravitational parameters, as well as their respective errors and correlations.
Chemical Measurement and Fluctuation Scaling.
Hanley, Quentin S
2016-12-20
Fluctuation scaling reports on all processes producing a data set. Some fluctuation scaling relationships, such as the Horwitz curve, follow exponential dispersion models which have useful properties. The mean-variance method applied to Poisson distributed data is a special case of these properties allowing the gain of a system to be measured. Here, a general method is described for investigating gain (G), dispersion (β), and process (α) in any system whose fluctuation scaling follows a simple exponential dispersion model, a segmented exponential dispersion model, or complex scaling following such a model locally. When gain and dispersion cannot be obtained directly, relative parameters, GR and βR, may be used. The method was demonstrated on data sets conforming to simple, segmented, and complex scaling. These included mass, fluorescence intensity, and absorbance measurements and specifications for classes of calibration weights. Changes in gain, dispersion, and process were observed in the scaling of these data sets in response to instrument parameters, photon fluxes, mathematical processing, and calibration weight class. The process parameter which limits the type of statistical process that can be invoked to explain a data set typically exhibited 0 < α < 1, with α > 4 possible. With two exceptions, calibration weight class definitions only affected β. Adjusting photomultiplier voltage while measuring fluorescence intensity changed all three parameters (0 < α < 0.8; 0 < βR < 3; 0 < GR < 4.1). The method provides a framework for calibrating and interpreting uncertainty in chemical measurement allowing robust comparison of specific instruments, conditions, and methods.
Laser-Based Faraday-Effect Measurement of Magnetic Fluctuations and Fluctuation-Induced Transport
NASA Astrophysics Data System (ADS)
Lin, L.; Brower, D. L.; Ding, W. X.; Sarff, J. S.
2013-10-01
A multichord far-infrared laser-based Faraday-effect polarimetry diagnostic has been well developed on MST. Combined polarimetry-interferometry capability permits simultaneous measurement of internal structure of density and magnetic field with fast time response (~ 4 μs) and low phase noise (< 0 .01°) . With this diagnostic, the impact on toroidal current profile from a tangentially injected neutral beam is directly measured, allowing evaluation of non-inductive current drive. In addition, 0 .05° Faraday-effect fluctuations associated with global tearing modes are resolved with an uncertainty below 0 .01° . For physics investigations, these Faraday-effect fluctuations are complicated by contributions from both density and magnetic fluctuations. In our analysis, the local density fluctuations are obtained by inverting the line-integrated interferometry data after resolving the mode helicity through correlation techniques. The local magnetic fluctuations are then reconstructed using a parameterized fit of the polarimetry data, accounting for both the density and magnetic contributions. For the same mode, density and radial magnetic fluctuations exhibit very different spatial structure. In this process, their relative phase is also determined, thereby allowing the determination of magnetic-fluctuation-induced transport. Work supported by US DoE.
Nanoscale thermal fluctuation spectroscopy
NASA Astrophysics Data System (ADS)
Garrity, Patrick Louis
The utilization of thermal fluctuations or Johnson/Nyquist noise as a spectroscopic method to determine transport properties in conductors or semiconductors is developed in this paper. The autocorrelation function is obtained from power spectral density measurements thus enabling electronic transport property calculation through the Green-Kubo formalism. This experimental approach is distinct from traditional numerical methods such as molecular dynamics simulations, which have been used to extract the autocorrelation function and directly related physics only. This work reports multi-transport property measurements consisting of the electronic relaxation time, resistivity, mobility, diffusion coefficient, electronic contribution to thermal conductivity and Lorenz number from experimental data. Double validation of the experiment was accomplished through the use of a standard reference material and a standard measurement method, i.e. four-probe collinear resistivity technique. The advantages to this new experimental technique include the elimination of any required thermal or potential gradients, multi-transport property measurements within one experiment, very low error and the ability to apply controlled boundary conditions while gathering data. This research has experimentally assessed the gas pressure and flow effects of helium and argon on 30 nm Au and Cu thin films. The results show a reduction in Au and Cu electronic thermal conductivity and electrical resistivity when subjected to helium and argon pressure and flow. The perturbed electronic transport coefficients, attributed to increased electron scattering at the surface, were so dominant that further data was collected through straight-forward resistance measurements. The resistance data confirmed the thermal noise measurements thus lending considerable evidence to the presence of thin film surface scattering due to elastic and inelastic gas particle scattering effects with the electron ensemble. Keywords
2015-01-01
An unprecedented [4Fe-3S] cluster proximal to the regular [NiFe] active site has recently been found to be responsible for the ability of membrane-bound hydrogenases (MBHs) to oxidize dihydrogen in the presence of ambient levels of oxygen. Starting from proximal cluster models of a recent DFT study on the redox-dependent structural transformation of the [4Fe-3S] cluster, 57Fe Mössbauer parameters (electric field gradients, isomer shifts, and nuclear hyperfine couplings) were calculated using DFT. Our results revise the previously reported correspondence of Mössbauer signals and iron centers in the [4Fe-3S]3+ reduced-state proximal cluster. Similar conflicting assignments are also resolved for the [4Fe-3S]5+ superoxidized state with particular regard to spin-coupling in the broken-symmetry DFT calculations. Calculated 57Fe hyperfine coupling (HFC) tensors expose discrepancies in the experimental set of HFC tensors and substantiate the need for additional experimental work on the magnetic properties of the MBH proximal cluster in its reduced and superoxidized redox states. PMID:26598030
Wiltner, A.; Linsmeier, Ch.; Jacob, T.
2008-08-28
This paper investigates the reactivity of elemental carbon films deposited from the vapor phase with Fe and Ni substrates at room temperature. X-ray photoelectron spectroscopy (XPS) measurements are presented as a method for evaluating kinetic reaction data. Carbon films are deposited on different surface orientations representing geometries from a dense atom packing as in fcc (111) to an open surface structure as in fcc (100). During annealing experiments several reactions are observed (carbon subsurface diffusion, carbide formation, carbide decomposition, and graphite ordering). These reactions and the respective kinetic parameters are analyzed and quantified by XPS measurements performed while annealing at elevated temperatures (620-820 K). The resulting activation barriers for carbon subsurface diffusion are compared with calculated values using the density functional theory. The determined kinetic parameters are used to reproduce the thermal behavior of carbon films on nickel surfaces.
Coleman, M E; Tamplin, M L; Phillips, J G; Marmer, B S
2003-06-15
Foods may differ in at least two key variables from broth culture systems typically used to measure growth kinetics of enteropathogens: initial population density of the pathogen and agitation of the culture. The present study used nine Escherichia coli O157:H7 strains isolated from beef and associated with human illness. Initial kinetic experiments with one E. coli O157:H7 strain in brain-heart infusion (BHI) broth at pH 5.5 were performed in a 2 x 2 x 3 factorial design, testing the effects of a low (ca. 1-10 colony-forming units [CFU]/ml) or high (ca. 1000 CFU/ml) initial population density, culture agitation or no culture agitation, and incubation temperatures of 10, 19, and 37 degrees C. Kinetic data were modeled using simple linear regression and the Baranyi model. Both model forms provided good statistical fit to the data (adjusted r(2)>0.95). Significant effects of agitation and initial population density were identified at 10 degrees C but not at 19 or 37 degrees C. Similar growth patterns were observed for two additional strains tested under the same experimental design. The lag, slope, and maximum population density (MPD) parameters were significantly different by treatment. Further tests were conducted in a 96-well microtiter plate system to determine the effect of initial population density and low pH (4.6-5.5) on the growth of E. coli O157:H7 strains in BHI at 10, 19, and 37 degrees C. Strain variability was more apparent at the boundary conditions of growth of low pH and low temperature. This study demonstrates the need for growth models that are specific to food products and environments for plausible extrapolation to risk assessment models.
Coexistence in a fluctuating environment by the effect of relative nonlinearity: a minimal model.
Szilágyi, András; Meszéna, Géza
2010-12-21
The minimal model of the "relative nonlinearity" type fluctuation-maintained coexistence is investigated. The competing populations are affected by an environmental white noise. With quadratic density dependence, the long-term growth rates of the populations are determined by the average and the variance of the (fluctuating) total density. At most two species can coexist on these two "regulating" variables; competitive exclusion would ensue in a constant environment. A numerical study of the expected time until extinction of any of the two species reveals that the criterion of mutual invasibility predicts the parameter range of long-term coexistence correctly in the limit of zero extinction threshold. However, any extinction threshold consistent with a realistic population size will allow only short-term coexistence. Therefore, our simulations question the biological relevance of mutual invasibility, as a sufficient condition of coexistence, for large density fluctuations. We calculate the average and the variance of the fluctuating density of the coexisting populations analytically via the moment-closure approximation; the results are reasonably close to the simulated behavior. Based on this treatment, robustness of coexistence is studied in the limit of infinite population size. We interpret the results of this analysis in the context of necessity of niche segregation with respect to the regulating variables using a framework theory published earlier.
K/pi Fluctuations at relativistic energies.
Abelev, B I; Aggarwal, M M; Ahammed, Z; Anderson, B D; Arkhipkin, D; Averichev, G S; Balewski, J; Barannikova, O; Barnby, L S; Baudot, J; Baumgart, S; Beavis, D R; Bellwied, R; Benedosso, F; Betancourt, M J; Betts, R R; Bhasin, A; Bhati, A K; Bichsel, H; Bielcik, J; Bielcikova, J; Biritz, B; Bland, L C; Bombara, M; Bonner, B E; Botje, M; Bouchet, J; Braidot, E; Brandin, A V; Bruna, E; Bueltmann, S; Burton, T P; Bystersky, M; Cai, X Z; Caines, H; de la Barca Sánchez, M Calderón; Catu, O; Cebra, D; Cendejas, R; Cervantes, M C; Chajecki, Z; Chaloupka, P; Chattopadhyay, S; Chen, H F; Chen, J H; Chen, J Y; Cheng, J; Cherney, M; Chikanian, A; Choi, K E; Christie, W; Clarke, R F; Codrington, M J M; Corliss, R; Cormier, T M; Cosentino, M R; Cramer, J G; Crawford, H J; Das, D; Das, S; Dash, S; Daugherity, M; De Silva, L C; Dedovich, T G; DePhillips, M; Derevschikov, A A; de Souza, R Derradi; Didenko, L; Djawotho, P; Dogra, S M; Dong, X; Drachenberg, J L; Draper, J E; Dunlop, J C; Mazumdar, M R Dutta; Edwards, W R; Efimov, L G; Elhalhuli, E; Elnimr, M; Emelianov, V; Engelage, J; Eppley, G; Erazmus, B; Estienne, M; Eun, L; Fachini, P; Fatemi, R; Fedorisin, J; Feng, A; Filip, P; Finch, E; Fine, V; Fisyak, Y; Gagliardi, C A; Gaillard, L; Gangadharan, D R; Ganti, M S; Garcia-Solis, E J; Geromitsos, A; Geurts, F; Ghazikhanian, V; Ghosh, P; Gorbunov, Y N; Gordon, A; Grebenyuk, O; Grosnick, D; Grube, B; Guertin, S M; Guimaraes, K S F F; Gupta, A; Gupta, N; Guryn, W; Haag, B; Hallman, T J; Hamed, A; Harris, J W; He, W; Heinz, M; Heppelmann, S; Hippolyte, B; Hirsch, A; Hjort, E; Hoffman, A M; Hoffmann, G W; Hofman, D J; Hollis, R S; Huang, H Z; Humanic, T J; Huo, L; Igo, G; Iordanova, A; Jacobs, P; Jacobs, W W; Jakl, P; Jena, C; Jin, F; Jones, C L; Jones, P G; Joseph, J; Judd, E G; Kabana, S; Kajimoto, K; Kang, K; Kapitan, J; Keane, D; Kechechyan, A; Kettler, D; Khodyrev, V Yu; Kikola, D P; Kiryluk, J; Kisiel, A; Klein, S R; Knospe, A G; Kocoloski, A; Koetke, D D; Kopytine, M; Korsch, W; Kotchenda, L; Kouchpil, V; Kravtsov, P; Kravtsov, V I; Krueger, K; Krus, M; Kuhn, C; Kumar, L; Kurnadi, P; Lamont, M A C; Landgraf, J M; LaPointe, S; Lauret, J; Lebedev, A; Lednicky, R; Lee, C-H; Lee, J H; Leight, W; LeVine, M J; Li, C; Li, N; Li, Y; Lin, G; Lindenbaum, S J; Lisa, M A; Liu, F; Liu, J; Liu, L; Ljubicic, T; Llope, W J; Longacre, R S; Love, W A; Lu, Y; Ludlam, T; Ma, G L; Ma, Y G; Mahapatra, D P; Majka, R; Mall, O I; Mangotra, L K; Manweiler, R; Margetis, S; Markert, C; Matis, H S; Matulenko, Yu A; McDonald, D; McShane, T S; Meschanin, A; Milner, R; Minaev, N G; Mioduszewski, S; Mischke, A; Mohanty, B; Morozov, D A; Munhoz, M G; Nandi, B K; Nattrass, C; Nayak, T K; Nelson, J M; Netrakanti, P K; Ng, M J; Nogach, L V; Nurushev, S B; Odyniec, G; Ogawa, A; Okada, H; Okorokov, V; Olson, D; Pachr, M; Page, B S; Pal, S K; Pandit, Y; Panebratsev, Y; Pawlak, T; Peitzmann, T; Perevoztchikov, V; Perkins, C; Peryt, W; Phatak, S C; Pile, P; Planinic, M; Pluta, J; Plyku, D; Poljak, N; Poskanzer, A M; Potukuchi, B V K S; Prindle, D; Pruneau, C; Pruthi, N K; Pujahari, P R; Putschke, J; Raniwala, R; Raniwala, S; Redwine, R; Reed, R; Ridiger, A; Ritter, H G; Roberts, J B; Rogachevskiy, O V; Romero, J L; Rose, A; Roy, C; Ruan, L; Russcher, M J; Sahoo, R; Sakrejda, I; Sakuma, T; Salur, S; Sandweiss, J; Sarsour, M; Schambach, J; Scharenberg, R P; Schmitz, N; Seger, J; Selyuzhenkov, I; Seyboth, P; Shabetai, A; Shahaliev, E; Shao, M; Sharma, M; Shi, S S; Shi, X-H; Sichtermann, E P; Simon, F; Singaraju, R N; Skoby, M J; Smirnov, N; Snellings, R; Sorensen, P; Sowinski, J; Spinka, H M; Srivastava, B; Stadnik, A; Stanislaus, T D S; Staszak, D; Strikhanov, M; Stringfellow, B; Suaide, A A P; Suarez, M C; Subba, N L; Sumbera, M; Sun, X M; Sun, Y; Sun, Z; Surrow, B; Symons, T J M; de Toledo, A Szanto; Takahashi, J; Tang, A H; Tang, Z; Tarini, L H; Tarnowsky, T; Thein, D; Thomas, J H; Tian, J; Timmins, A R; Timoshenko, S; Tlusty, D; Tokarev, M; Tram, V N; Trattner, A L; Trentalange, S; Tribble, R E; Tsai, O D; Ulery, J; Ullrich, T; Underwood, D G; Van Buren, G; van Leeuwen, M; Molen, A M Vander; Vanfossen, J A; Varma, R; Vasconcelos, G M S; Vasilevski, I M; Vasiliev, A N; Videbaek, F; Vigdor, S E; Viyogi, Y P; Vokal, S; Voloshin, S A; Wada, M; Walker, M; Wang, F; Wang, G; Wang, J S; Wang, Q; Wang, X; Wang, X L; Wang, Y; Webb, G; Webb, J C; Westfall, G D; Whitten, C; Wieman, H; Wissink, S W; Witt, R; Wu, Y; Xie, W; Xu, N; Xu, Q H; Xu, Y; Xu, Z; Yang, P; Yepes, P; Yip, K; Yoo, I-K; Yue, Q; Zawisza, M; Zbroszczyk, H; Zhan, W; Zhang, S; Zhang, W M; Zhang, X P; Zhang, Y; Zhang, Z P; Zhao, Y; Zhong, C; Zhou, J; Zoulkarneev, R; Zoulkarneeva, Y; Zuo, J X
2009-08-28
We report K/pi fluctuations from Au + Au collisions at sqrt[s(NN)]= 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. K/pi fluctuations in central collisions show little dependence on incident energy and are on the same order as those from NA49 at the Super Proton Synchrotron in central Pb + Pb collisions at sqrt[s(NN)]=12.3 and 17.3 GeV. We report results for the collision centrality dependence of K/pi fluctuations and results for charge-separated fluctuations. We observe that the K/pi fluctuations scale with the charged particle multiplicity density.
López-Hernández, Karla M; Pardío-Sedas, Violeta T; Lizárraga-Partida, Leonardo; Williams, José de J; Martínez-Herrera, David; Flores-Primo, Argel; Uscanga-Serrano, Roxana; Rendón-Castro, Karla
2015-02-15
The influence of environmental parameters on the total and pathogenic Vibrio parahaemolyticus seasonal densities in American oysters (Crassostrea virginica) was evaluated for 1 year. Harvesting site A yielded the highest mean densities of V. parahaemolyticus tlh+, tdh+/trh-, tdh-/trh+ and tdh+/trh+ during spring season at 2.57, 1.74, 0.36, and -0.40 log10 MPN/g, respectively, and tdh+/orf8+ during winter season (0.90 log10 MPN/g). V. parahaemolyticus tlh+ densities were associated to salinity (R(2)=0.372, P<0.022), tdh+/trh+ to turbidity (R(2)=0.597, P<0.035), and orf8+ to temperature, salinity, and pH (R(2)=0.964, P<0.001). The exposure to salinity and temperature conditions during winter and spring seasons regulated the dynamics of V. parahaemolyticus harboring potentially pathogenic genotypes within the oyster. The adaptive response of V. parahaemolyticus to seasonal environmental changes may lead to an increase in survival and virulence, threatening the seafood safety and increasing the risk of illness.
Timalsina, Santosh; Gyawali, Prajwal; Bhattarai, Aseem
2016-01-01
Introduction Preeclampsia is a pregnancy-specific complication that significantly contributes to maternal and perinatal morbidity and mortality worldwide, even more so in developing countries such as Nepal. The potential contribution of dyslipidemia and elevated levels of oxidized low-density lipoprotein (oxLDL) in the pathogenesis of preeclamptic pregnancies has been observed in several studies. The aim of this study was to compare the maternal lipid profile parameters and particularly oxLDL between preeclamptic and healthy pregnancies and also correlate oxLDL with other lipid profile parameters. Patients and methods A total of 54 preeclamptic women were selected as cases for this cross-sectional study. Age and gestational week-matched 60 pregnant women were enrolled as controls. Preeclampsia was defined as per Australasian Society Consensus Statement research definition. The serum lipid parameters were measured using automated enzymatic systems and a competitive enzyme-linked immunosorbent assay was used to determine oxLDL concentrations in the serum. Student’s t-test was used to compare oxLDL levels between preeclamptic and healthy pregnancies, and Pearson’s correlation analysis was carried out to assess the relation between oxLDL and other variables. Results The mean values of serum total cholesterol, triglyceride, non-high-density lipoprotein-cholesterol (non-HDL-c) and oxLDL were significantly higher in the preeclamptic cases (P<0.01). However, the levels of low-density lipoprotein cholesterol (LDL-c and HDL-c) did not significantly differ between the two groups. oxLDL had a significant positive correlation (P<0.01) with total cholesterol, triglyceride, LDL-c and non-HDL-c, and a negative correlation with HDL-c. Conclusion The atherogenic type of dyslipidemia and high oxLDL levels are associated with preeclamptic pregnancies. The lipid parameters, however, seem to be poor markers of the severity of preeclampsia. Further prospective studies are needed to
NASA Astrophysics Data System (ADS)
Sachdev, Subir
2014-03-01
The hole-doped cuprate high temperature superconductors enter the pseudogap regime as their superconducting critical temperature, Tc, falls with decreasing hole density. Experiments have probed this regime for over two decades, but we argue that decisive new information has emerged from recent X-ray scattering experiments. The experiments observe incommensurate charge density wave fluctuations whose strength rises gradually over a wide temperature range above Tc, but then decreases as the temperature is lowered below Tc. We propose a theory in which the superconducting and charge-density wave orders exhibit angular fluctuations in a 6-dimensional space. The theory provides a natural quantitative fit to the X-ray data, and is consistent with other observed characteristics of the pseudogap. Results will also be presented on the microscopic origins of these order parameters. Work in collaboration with Lauren Hayward, Roger Melko, David Hawthorn, and Jay Sau.
Collective-field fluctuations around the wall solution of the C hern-Simons theory
NASA Astrophysics Data System (ADS)
Andrić, I.; Bardek, V.; Jonke, L.
We consider a large-N Chern-Simons theory for the attractive bosonic matter (Jackiw-Pi model) in the Hamiltonian collective-field approach based on the 1/N expansion. We show that the dynamics of low-lying density fluctuations around the semiclassical wall solution is governed by the Calogero Hamiltonian . The relationship between the Chern-Simons coupling constant k and the statistical parameter l signalizes some sort of statistical transmutation accompanying the dimensional reduction of the initial problem.
Properties of magnetic field fluctuations in boundary regions of the Earth's magnetosphere
NASA Astrophysics Data System (ADS)
Kozak, Liudmyla; Savin, Sergey; Lui, Anthony Tat Yin; Igor, Gala
Statistical properties of magnetic field fluctuations in boundary regions of the Earth’s magnetosphere at different timescales were considered. Data with high resolution (22,5 Hz) obtained by Cluster mission from 2004 to 2010 were used. As a characteristic of the fluctuations on various time scales, changes in the shape and parameters of the probability density function and wave analysis were studied. In order for investigations of features of the probability density functions of magnetic field fluctuations we analyzed the statistical properties of the absolute value of magnetic field variations in the different regions of near earth space. Amplitude of fluctuations in the magnetosheath just after crossing bow shock exceeds in a few time amplitude of fluctuations for non-perturbed solar wind or the foreshock. The analysis of the height of maximum of the probability density functions and of the kurtosis values have shown the presence of different asymptotic modes which are characterized by different power laws. The use of the technique of probability density function for magnetic fluctuations has shown that at high frequencies the structure of turbulence differs from that in the low-frequency region. The critical scale corresponds to the scales of the Larmor radius of ions. The research of the statistical properties of boundary layers allows to determine the role of turbulent processes in the interaction of plasma flows with the magnetic obstacles, whether these are fields of planets, stars, or laboratory traps, and to reveal the actual mechanisms of the energy transformation in collisionless plasma. The work is done in the frame of complex program of NAS of Ukraine on space researches for 2012-1016, within the framework of the educational program No.2201250 “Education, Training of students, PhD students, scientific and pedagogical staff abroad” launched by the Ministry of Education and Science of Ukraine and under a partial support of the grant No. F 53.2/039.
Gonçalves, Ezequiel M; Sewaybricker, Leticia E; Baptista, Fatima; Silva, Analiza M; Carvalho, Wellington R G; Santos, Allan O; de Mello, Maricilda P; Lemos-Marini, Sofia H V; Guerra, Gil
2014-07-01
The purpose of this study was to verify the performance of quantitative ultrasound (QUS) parameters of proximal phalanges in the evaluation of reduced bone mineral density (BMD) in patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency (21 OHD). Seventy patients with 21 OHD (41 females and 29 males), aged between 6-27 y were assessed. The QUS measurements, amplitude-dependent speed of sound (AD-SoS), bone transmission time (BTT), and ultrasound bone profile index (UBPI) were obtained using the BMD Sonic device (IGEA, Carpi, Italy) on the last four proximal phalanges in the non-dominant hand. BMD was determined by dual energy X-ray (DXA) across the total body and lumbar spine (LS). Total body and LS BMD were positively correlated to UBPI, BTT and AD-SoS (correlation coefficients ranged from 0.59-0.72, p < 0.001). In contrast, when comparing patients with normal and low (Z-score < -2) BMD, no differences were found in the QUS parameters. Furthermore, UBPI, BTT and AD-SoS measurements were not effective for diagnosing patients with reduced BMD by receiver operator characteristic curve parameters. Although the AD-SoS, BTT and UBPI showed significant correlations with the data obtained by DXA, they were not effective for diagnosing reduced bone mass in patients with 21 OHD.
Solar wind thermally induced magnetic fluctuations.
Navarro, R E; Moya, P S; Muñoz, V; Araneda, J A; F-Viñas, A; Valdivia, J A
2014-06-20
A kinetic description of Alfvén-cyclotron magnetic fluctuations for anisotropic electron-proton quasistable plasmas is studied. An analytical treatment, based on the fluctuation-dissipation theorem, consistently shows that spontaneous fluctuations in plasmas with stable distributions significantly contribute to the observed magnetic fluctuations in the solar wind, as seen, for example, in [S. D. Bale et al., Phys. Rev. Lett. 103, 211101 (2009)], even far below from the instability thresholds. Furthermore, these results, which do not require any adjustable parameters or wave excitations, are consistent with the results provided by hybrid simulations. It is expected that this analysis contributes to our understanding of the nature of magnetic fluctuations in the solar wind.
NASA Astrophysics Data System (ADS)
Dioguardi, Fabio; Dellino, Pierfrancesco; Mele, Daniela
2016-04-01
Dilute pyroclastic density currents (DPDCs) are one of the hazardous events that can happen during explosive eruptions. They are ground-hugging turbulent gas-particle flows that move down volcano slopes under the combined action of density contrast and gravity. DPDCs are dangerous for human lives and infrastructures both because they exert a dynamic pressure in their direction of motion and transport volcanic ash particles, which remain in the atmosphere during and after the passage of DPDC until they settle on the ground. Deposits formed by the passage of a DPDC show peculiar characteristics that can be linked to flow field variables. This has been the subject of extensive investigations in the past years leading to the formulation of a sedimentological model (Dellino et al. 2008), which has been used for evaluating the impact parameters of past eruptions on a statistical basis for hazard assessment purposes. The model has been recently translated in a Fortran code (PYFLOW, Dioguardi and Dellino, 2014). Here we present the latest release of this code (PYFLOW_2.0) which, besides significant improvements in the code structure, computation times and the introduction of a user friendly data input method, allows to calculate the deposition time and rate of the ash and lapilli layer formed by a DPDC by linking deposit (e.g. componentry, grainsize) to flow (e.g. flow average density and shear velocity) characteristics as calculated by the aforementioned sedimentological model. The deposition rate is calculated by summing the contributions of each grainsize class of all components constituting the deposit (e.g. juvenile particles, crystals, etc.), which are in turn computed as a function of particle density, terminal velocity, concentration and deposition probability. Here we apply the concept of deposition probability, previously introduced for estimating the deposition rates of turbidity currents (Stow and Bowen, 1980), to DPDCs, although with a different approach, i
Proteins, fluctuations and complexity
Frauenfelder, Hans; Chen, Guo; Fenimore, Paul W
2008-01-01
Glasses, supercooled liquids, and proteins share common properties, in particular the existence of two different types of fluctuations, {alpha} and {beta}. While the effect of the {alpha} fluctuations on proteins has been known for a few years, the effect of {beta} fluctuations has not been understood. By comparing neutron scattering data on the protein myoglobin with the {beta} fluctuations in the hydration shell measured by dielectric spectroscopy we show that the internal protein motions are slaved to these fluctuations. We also show that there is no 'dynamic transition' in proteins near 200 K. The rapid increase in the mean square displacement with temperature in many neutron scattering experiments is quantitatively predicted by the {beta} fluctuations in the hydration shell.
Fluctuation energies in quantum cosmology
NASA Astrophysics Data System (ADS)
Bojowald, Martin
2014-06-01
Quantum fluctuations or other moments of a state contribute to energy expectation values and can imply interesting physical effects. In quantum cosmology, they turn out to be important for a discussion of density bounds and instabilities of initial-value problems in the presence of signature change in loop-quantized models. This paper provides an effective description of these issues, accompanied by a comparison with existing numerical results and an extension to squeezed states. The comparison confirms that canonical effective methods are well suited for computations of properties of physical states. As a side product, an example is found for a simple state in which quantum fluctuations can cancel holonomy modifications of loop quantum cosmology.
Fluctuations in Cerebral Hemodynamics
2007-11-02
Determination of scaling properties Detrended Fluctuations Analysis (see (28) and references therein) is commonly used to determine scaling...pressure (averaged over a cardiac beat) of a healthy subject. First 1000 values of the time series are shown. (b) Detrended fluctuation analysis (DFA...1000 values of the time series are shown. (b) Detrended fluctuation analysis of the time series shown in (a). Fig . 3 Side-by-side boxplot for the
Fransson, Thomas; Saue, Trond; Norman, Patrick
2016-05-10
The influences of group 12 (Zn, Cd, Hg) metal-substitution on the valence spectra and phosphorescence parameters of porphyrins (P) have been investigated in a relativistic setting. In order to obtain valence spectra, this study reports the first application of the damped linear response function, or complex polarization propagator, in the four-component density functional theory framework [as formulated in Villaume et al. J. Chem. Phys. 2010 , 133 , 064105 ]. It is shown that the steep increase in the density of states as due to the inclusion of spin-orbit coupling yields only minor changes in overall computational costs involved with the solution of the set of linear response equations. Comparing single-frequency to multifrequency spectral calculations, it is noted that the number of iterations in the iterative linear equation solver per frequency grid-point decreases monotonously from 30 to 0.74 as the number of frequency points goes from one to 19. The main heavy-atom effect on the UV/vis-absorption spectra is indirect and attributed to the change of point group symmetry due to metal-substitution, and it is noted that substitutions using heavier atoms yield small red-shifts of the intense Soret-band. Concerning phosphorescence parameters, the adoption of a four-component relativistic setting enables the calculation of such properties at a linear order of response theory, and any higher-order response functions do not need to be considered-a real, conventional, form of linear response theory has been used for the calculation of these parameters. For the substituted porphyrins, electronic coupling between the lowest triplet states is strong and results in theoretical estimates of lifetimes that are sensitive to the wave function and electron density parametrization. With this in mind, we report our best estimates of the phosphorescence lifetimes to be 460, 13.8, 11.2, and 0.00155 s for H2P, ZnP, CdP, and HgP, respectively, with the corresponding transition
Fluctuation relations for spintronics.
López, Rosa; Lim, Jong Soo; Sánchez, David
2012-06-15
Fluctuation relations are derived in systems where the spin degree of freedom and magnetic interactions play a crucial role. The form of the nonequilibrium fluctuation theorems relies on the assumption of a local balance condition. We demonstrate that in some cases the presence of magnetic interactions violates this condition. Nevertheless, fluctuation relations can be obtained from the microreversibility principle sustained only at equilibrium as a symmetry of the cumulant generating function for spin currents. We illustrate the spintronic fluctuation relations for a quantum dot coupled to partially polarized helical edge states.
Thomson, Wendy; Boonen, Steven; Borghs, Herman; Vanderschueren, Dirk; Gielen, Evelien; Huhtaniemi, Ilpo T.; Adams, Judith E.; Ward, Kate A.; Bartfai, Gyorgy; Casanueva, Felipe; Finn, Joseph D.; Forti, Gianni; Giwercman, Aleksander; Han, Thang S.; Kula, Krzysztof; Labrie, Fernand; Lean, Michael E. J.; Pendleton, Neil; Punab, Margus; Wu, Frederick C. W.; O'Neill, Terence W.
2011-01-01
Purpose Genome-wide association studies (GWAS) have identified 6q25, which incorporates the oestrogen receptor α gene (ESR1), as a quantitative trait locus for areal bone mineral density (BMDa) of the hip and lumbar spine. The aim of this study was to determine the influence of this locus on other bone health outcomes; calcaneal ultrasound (QUS) parameters, radial peripheral quantitative computed tomography (pQCT) parameters and markers of bone turnover in a population sample of European men. Methods Eight single nucleotide polymorphisms (SNP) in the 6q25 locus were genotyped in men aged 40–79 years from 7 European countries, participating in the European Male Ageing Study (EMAS). The associations between SNPs and measured bone parameters were tested under an additive genetic model adjusting for centre using linear regression. Results 2468 men, mean (SD) aged 59.9 (11.1) years had QUS measurements performed and bone turnover marker levels measured. A subset of 628 men had DXA and pQCT measurements. Multiple independent SNPs showed significant associations with BMD using all three measurement techniques. Most notably, rs1999805 was associated with a 0.10 SD (95%CI 0.05, 0.16; p = 0.0001) lower estimated BMD at the calcaneus, a 0.14 SD (95%CI 0.05, 0.24; p = 0.004) lower total hip BMDa, a 0.12 SD (95%CI 0.02, 0.23; p = 0.026) lower lumbar spine BMDa and a 0.18 SD (95%CI 0.06, 0.29; p = 0.003) lower trabecular BMD at the distal radius for each copy of the minor allele. There was no association with serum levels of bone turnover markers and a single SNP which was associated with cortical density was also associated with cortical BMC and thickness. Conclusions Our data replicate previous associations found between SNPs in the 6q25 locus and BMDa at the hip and extend these data to include associations with calcaneal ultrasound parameters and radial volumetric BMD. PMID:21760950
Fluctuations and symmetry energy in nuclear fragmentation dynamics.
Colonna, M
2013-01-25
Within a dynamical description of nuclear fragmentation, based on the liquid-gas phase transition scenario, we explore the relation between neutron-proton density fluctuations and nuclear symmetry energy. We show that, along the fragmentation path, isovector fluctuations follow the evolution of the local density and approach an equilibrium value connected to the local symmetry energy. Higher-density regions are characterized by smaller average asymmetry and narrower isotopic distributions. This dynamical analysis points out that fragment final state isospin fluctuations can probe the symmetry energy of the density domains from which fragments originate.
NASA Astrophysics Data System (ADS)
Dong, Yanfang; Wang, Jun
2012-12-01
A financial time series model is developed by the percolation system on the Sierpinski carpet lattice fractal. We investigate the fluctuation behaviors of various shuffled return interval series (original, randomly shuffled and by Zipf method) by applying the multifractal detrended fluctuation analysis for the financial model and Shanghai composite index. Numerically we show the fluctuations of the generalized Hurst exponents for different order parameters, the nonlinear dependence of these scaling exponents and the singularity spectrum show that the return intervals possess the multifractality. By comparing the MF-DFA empirical results of the original series to those for the randomly shuffled series, the empirical research exhibits the multifractality is mainly due to the contributions of long-range correlations as well as the broad probability density function. Further we show that the shuffled series by Zipf method exhibits the similar properties for the positive orders.
Statistical regimes of random laser fluctuations
Lepri, Stefano; Cavalieri, Stefano; Oppo, Gian-Luca; Wiersma, Diederik S.
2007-06-15
Statistical fluctuations of the light emitted from amplifying random media are studied theoretically and numerically. The characteristic scales of the diffusive motion of light lead to Gaussian or power-law (Levy) distributed fluctuations depending on external control parameters. In the Levy regime, the output pulse is highly irregular leading to huge deviations from a mean-field description. Monte Carlo simulations of a simplified model which includes the population of the medium demonstrate the two statistical regimes and provide a comparison with dynamical rate equations. Different statistics of the fluctuations helps to explain recent experimental observations reported in the literature.
NASA Astrophysics Data System (ADS)
Dioguardi, Fabio; Dellino, Pierfrancesco
2014-05-01
PYFLOW is a computer code designed for quantifying the hazard related to Dilute Pyroclastic Density Currents (DPDC). DPDCs are multiphase flows that form during explosive volcanic eruptions. They are the major source of hazard related to volcanic eruptions, as they exert a significant stress over buildings and transport significant amounts of volcanic ash, which is hot and unbreathable. The program calculates the DPDC's impact parameters (e.g. dynamic pressure and particle volumetric concentration) and is founded on the turbulent boundary layer theory adapted to a multiphase framework. Fluid-dynamic variables are searched with a probabilistic approach, meaning that for each variable the average, maximum and minimum solutions are calculated. From these values, PYFLOW creates probability functions that allow to calculate the parameter at a given percentile. The code is written in Fortran 90 and can be compiled and installed on Windows, Mac OS X, Linux operating systems (OS). A User's manual is provided, explaining the details of the theoretical background, the setup and running procedure and the input data. The model inputs are DPDC deposits data, e.g. particle grainsize, layer thickness, particles shape factor and density. PYFLOW reads input data from a specifically designed input file or from the user's direct typing by command lines. Guidelines for writing input data are also contained in the package. PYFLOW guides the user at each step of execution, asking for additional data and inputs. The program is a tool for DPDC hazard assessment and, as an example, an application to the DPDC deposits of the Agnano-Monte Spina eruption (4.1 ky BP) at Campi Flegrei (Italy) is presented.
Lagana, Tatiana F.; Zhang Yuying; Reiprich, Thomas H.; Schneider, Peter
2011-12-10
It is believed that the global baryon content of clusters of galaxies is representative of the matter distribution of the universe, and can, therefore, be used to reliably determine the matter-density parameter {Omega}{sub m}. This assumption is challenged by the growing evidence from optical and X-ray observations that the total baryon mass fraction increases toward rich clusters. In this context, we investigate the dependence of stellar and total baryon mass fractions as a function of mass. To do so, we used a subsample of 19 clusters extracted from the X-ray flux-limited sample HIFLUGCS that have available Sloan Digital Sky Survey Data Release 7 data. From the optical analysis we derived the stellar masses. Using XMM-Newton we derived the gas masses. Then, adopting a scaling relation we estimate the total masses. Adding the gas and the stellar mass fractions we obtain the total baryonic content that we find to increase with cluster mass, reaching seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) prediction for clusters with M{sub 500} = 1.6 Multiplication-Sign 10{sup 15} M{sub Sun }. We observe a decrease of the stellar mass fraction (from 4.5% to {approx}1.0%) with increasing total mass where our findings for the stellar mass fraction agree with previous studies. This result suggests a difference in the number of stars formed per unit of halo mass, though with a large scatter for low-mass systems. That is, the efficiency of star formation varies on a cluster scale that lower mass systems are likely to have higher star formation efficiencies. It follows immediately that the dependence of the stellar mass fraction on total mass results in an increase of the mass-to-light ratio from lower to higher mass systems. We also discuss the consequences of these results in the context of determining the cosmic matter-density parameter {Omega}{sub m}.
Bandura, A V; Sofo, J O; Kubicki, J D
2006-04-27
Plane-wave density functional theory (DFT-PW) calculations were performed on bulk SnO2 (cassiterite) and the (100), (110), (001), and (101) surfaces with and without H2O present. A classical interatomic force field has been developed to describe bulk SnO2 and SnO2-H2O surface interactions. Periodic density functional theory calculations using the program VASP (Kresse et al., 1996) and molecular cluster calculations using Gaussian 03 (Frisch et al., 2003) were used to derive the parametrization of the force field. The program GULP (Gale, 1997) was used to optimize parameters to reproduce experimental and ab initio results. The experimental crystal structure and elastic constants of SnO2 are reproduced reasonably well with the force field. Furthermore, surface atom relaxations and structures of adsorbed H2O molecules agree well between the ab initio and force field predictions. H2O addition above that required to form a monolayer results in consistent structures between the DFT-PW and classical force field results as well.
Ersson, Clara; Möller, Lennart
2011-11-01
The single cell gel electrophoresis (comet assay) is a popular method for measuring DNA migration as an estimate of DNA damage. No standardised comet assay protocol exists, which make comparisons between studies complicated. In a previous inter-laboratory validation study of the comet assay, we identified important parameters in the protocol that might affect DNA migration. The aim of this study was to assess how different comet assay protocols affect DNA migration. The results in this study suggest that (i) there is a significant linear dose-response relationship between the agarose gel's density and DNA migration and that damaged cells are more sensitive to the agarose gel's density; (ii) incubation with formamidopyrimidine DNA glycosylase for 10 min is inadequate, whereas 30 min is sufficient; (iii) the typically used 20 min of alkaline treatment might be to short when analysing samples that contain particular alkali-labile sites (ALS) and (iv) the duration of electrophoresis as well as the strength of the electric field applied affects the DNA migration. By using protocol-specific calibration curves, it is possible to reduce the variation in DNA migration caused by differences in comet assay protocols. This does, however, not completely remove the impact of the durations of alkaline treatment and electrophoresis when analysing cells containing ALS that are relatively resistant to high alkaline treatment.
Peng, Y Z; Wang, Y W; Ning, D; Guo, Y M
2013-08-01
This experiment was conducted to investigate the influence of dietary nutrient density on haematic parameters, oxidative status and mitochondrial complex activity in the heart and liver of broilers under low ambient temperature. Eight-day-old male ROSS-308 chickens were randomly divided into two treatments fed with normal (control) and high metabolizable energy (ME) and crude protein density (H) diets. A high nutrient density diet increased body weight gain and reduced the feed conversation ratio during the first 3 weeks. Increased ascites-related mortality (weeks 4 to 6), right ventricle/total ventricle (week 6), blood haemoglobin (weeks 2 and 4) and mean corpuscular haemoglobin (week 2) were observed in treatment H. Levels of malonaldehyde and protein carbonylation were increased at week 4, and activities of glutathione peroxidase at week 4 and CuZn superoxide dismutase and catalase at week 6 were decreased in the heart; only malonaldehyde (week 6) was increased in the liver in treatment H. Relative mRNA expression of hypoxia inducible factor-1 (heart) was increased and heme oxygenase-1 (heart and liver) was decreased at week 4 in broilers fed with high ME and protein diet. Activities of mitochondrial complex III and IV (week 6) in the heart, and complex I (week 6) and complex III and IV (week 4) in the liver were decreased in treatment H. In conclusion, high levels of dietary ME and protein resulted in oxidative stress and high incidence of ascites in broilers under low ambient temperature. Heart dysfunction was primarily attributed to ascites development, in which oxidative injury and inhibition of mitochondrial complex activity were involved.
Wallace
2000-09-01
The current status of the theory of stress fluctuations is marked by two circumstances: no currently available formulas are valid for a metallic system, and a series of contradictory formulas remains unresolved. Here we derive formulas for shear- and isotropic-stress energy fluctuations, in the primary statistical mechanics ensembles. These formulas are valid for a classical monatomic system representing a metal or nonmetal, in cubic crystal, amorphous solid, or liquid phases. Current contradictions in fluctuation formulas are resolved through the following observations. First, the expansion of a dynamical variable A in terms of the fluctuations explicit in a given ensemble distribution, for example deltaA=adeltaN+bdeltaH in the grand canonical ensemble, is correct if and only if deltaA is a function only of deltaN and deltaH. The common use of this expansion has produced incorrect fluctuation formulas. Second, the thermodynamic fluctuations of Landau and Lifshitz do not correspond to statistical mechanics fluctuations, and the two types of fluctuations have essentially different values.
Revisiting detrended fluctuation analysis
Bryce, R. M.; Sprague, K. B.
2012-01-01
Half a century ago Hurst introduced Rescaled Range (R/S) Analysis to study fluctuations in time series. Thousands of works have investigated or applied the original methodology and similar techniques, with Detrended Fluctuation Analysis becoming preferred due to its purported ability to mitigate nonstationaries. We show Detrended Fluctuation Analysis introduces artifacts for nonlinear trends, in contrast to common expectation, and demonstrate that the empirically observed curvature induced is a serious finite-size effect which will always be present. Explicit detrending followed by measurement of the diffusional spread of a signals' associated random walk is preferable, a surprising conclusion given that Detrended Fluctuation Analysis was crafted specifically to replace this approach. The implications are simple yet sweeping: there is no compelling reason to apply Detrended Fluctuation Analysis as it 1) introduces uncontrolled bias; 2) is computationally more expensive than the unbiased estimator; and 3) cannot provide generic or useful protection against nonstationaries. PMID:22419991
Fluctuating hydrodynamics for ionic liquids
NASA Astrophysics Data System (ADS)
Lazaridis, Konstantinos; Wickham, Logan; Voulgarakis, Nikolaos
2017-04-01
We present a mean-field fluctuating hydrodynamics (FHD) method for studying the structural and transport properties of ionic liquids in bulk and near electrified surfaces. The free energy of the system consists of two competing terms: (1) a Landau-Lifshitz functional that models the spontaneous separation of the ionic groups, and (2) the standard mean-field electrostatic interaction between the ions in the liquid. The numerical approach used to solve the resulting FHD-Poisson equations is very efficient and models thermal fluctuations with remarkable accuracy. Such density fluctuations are sufficiently strong to excite the experimentally observed spontaneous formation of liquid nano-domains. Statistical analysis of our simulations provides quantitative information about the properties of ionic liquids, such as the mixing quality, stability, and the size of the nano-domains. Our model, thus, can be adequately parameterized by directly comparing our prediction with experimental measurements and all-atom simulations. Conclusively, this work can serve as a practical mathematical tool for testing various theories and designing more efficient mixtures of ionic liquids.
NASA Astrophysics Data System (ADS)
Chen, Zhipeng; Sun, Yue; Wang, Zhijiang; Yang, Zhoujun; Ding, Yonghua; Zhuang, Ge; J-Text Team
2012-12-01
As the basic of a deeper investigation on the turbulent transport, the fluctuation property in the boundary of the newly-reconstructed Joint Texas Experimental Tokamak (J-TEXT) is studied experimentally using the reciprocating Langmuir four-tip probe, which has been built and operated as the primary diagnostic tool in the boundary of J-TEXT tokamak. In this paper, spatial profiles of the plasma-edge parameters are obtained, such as electron temperature, plasma density, plasma potential, poloidal electric field and their fluctuations. The results indicate the existence of a Er×BT shear layer at the vicinity of last closed flux surface (LCFS), with the fluctuations suppressed in varying degrees. The turbulence-induced particle and energy fluxes can be calculated by the local plasma parameters above. Convection dominates the cross-field turbulent transport in boundary plasma. Electrostatic fluctuations properties are also studied in detail with the help of numerical analysis. Statistical analysis on density fluctuation shows that, the intermittency can affect the turbulence in the scrape-off layer (SOL).
NASA Astrophysics Data System (ADS)
Pérez-Espigares, Carlos; Redig, Frank; Giardinà, Cristian
2015-08-01
For non-equilibrium systems of interacting particles and for interacting diffusions in d-dimensions, a novel fluctuation relation is derived. The theorem establishes a quantitative relation between the probabilities of observing two current values in different spatial directions. The result is a consequence of spatial symmetries of the microscopic dynamics, generalizing in this way the Gallavotti-Cohen fluctuation theorem related to the time-reversal symmetry. This new perspective opens up the possibility of direct experimental measurements of fluctuation relations of vectorial observables.
Hadronic Correlations and Fluctuations
Koch, Volker
2008-10-09
We will provide a review of some of the physics which can be addressed by studying fluctuations and correlations in heavy ion collisions. We will discuss Lattice QCD results on fluctuations and correlations and will put them into context with observables which have been measured in heavy-ion collisions. Special attention will be given to the QCD critical point and the first order co-existence region, and we will discuss how the measurement of fluctuations and correlations can help in an experimental search for non-trivial structures in the QCD phase diagram.
Continuous information flow fluctuations
NASA Astrophysics Data System (ADS)
Rosinberg, Martin Luc; Horowitz, Jordan M.
2016-10-01
Information plays a pivotal role in the thermodynamics of nonequilibrium processes with feedback. However, much remains to be learned about the nature of information fluctuations in small-scale devices and their relation with fluctuations in other thermodynamics quantities, like heat and work. Here we derive a series of fluctuation theorems for information flow and partial entropy production in a Brownian particle model of feedback cooling and extend them to arbitrary driven diffusion processes. We then analyze the long-time behavior of the feedback-cooling model in detail. Our results provide insights into the structure and origin of large deviations of information and thermodynamic quantities in autonomous Maxwell's demons.
Non scale-invariant density perturbations from chaotic extended inflation
NASA Technical Reports Server (NTRS)
Mollerach, Silvia; Matarrese, Sabino
1991-01-01
Chaotic inflation is analyzed in the frame of scalar-tensor theories of gravity. Fluctuations in the energy density arise from quantum fluctuations of the Brans-Dicke field and of the inflation field. The spectrum of perturbations is studied for a class of models: it is non scale-invarient and, for certain values of the parameters, it has a peak. If the peak appears at astrophysically interesting scales, it may help to reconcile the Cold Dark Matter scenario for structure formation with large scale observations.
Non-scale-invariant density perturbations from chaotic extended inflation
Mollerach, S. ); Matarrese, S. )
1992-03-15
Chaotic inflation is analyzed in the frame of scalar-tensor theories of gravity. Fluctuations in the energy density arise from quantum fluctuations of the Brans-Dicke field and of the inflaton field. The spectrum of perturbations is studied for a class of models: it is non-scale-invariant and, for certain values of the parameters, it has a peak. If the peak appears at astrophysically interesting scales it may help to reconcile the cold-dark-matter scenario for structure formation with large-scale observations.
Wooten, Dustin W; Hillmer, Ansel T; Moirano, Jeffrey M; Ahlers, Elizabeth O; Slesarev, Maxim; Barnhart, Todd E; Mukherjee, Jogeshwar; Schneider, Mary L; Christian, Bradley T
2012-08-01
The goal of this work was to characterize the in-vivo behavior of [(18)F]mefway as a suitable positron emission tomography (PET) radiotracer for the assay of 5-hydroxytryptamine(1A) (5-HT(1A)) receptor density (B(max)). Six rhesus monkeys were studied using a multiple-injection (M-I) protocol consisting of three sequential bolus injections of [(18)F]mefway. Injection times and amounts of unlabeled mefway were optimized for the precise measurement of B(max) and specific binding parameters k(off) and k(on) for estimation of apparent K(D). The PET time series were acquired for 180 minutes with arterial sampling performed throughout. Compartmental analysis using the arterial input function was performed to obtain estimates for K(1), k(2), k(off), B(max), and K(Dapp) in the cerebral cortex and raphe nuclei (RN) using a model that accounted for nontracer doses of mefway. Averaged over subjects, highest binding was seen in the mesial temporal and dorsal anterior cingulate cortices with B(max) values of 42±8 and 36±8 pmol/mL, respectively, and lower values in the superior temporal cortex, RN, and parietal cortex of 24±4, 19±4, and 13±2 pmol/mL, respectively. The K(Dapp) of mefway for the 5-HT(1A) receptor sites was 4.3±1.3 nmol/L. In conclusion, these results show that M-I [(18)F]mefway PET experiments can be used for the in-vivo measurement of 5-HT(1A) receptor density.
IRAS galaxies versus POTENT mass - Density fields, biasing, and Omega
NASA Technical Reports Server (NTRS)
Dekel, Avishai; Bertschinger, Edmund; Yahil, Amos; Strauss, Michael A.; Davis, Marc; Huchra, John P.
1993-01-01
A comparison of the galaxy density field extracted from a complete redshift survey of IRAS galaxies brighter than 1.936 Jy with the mass-density field reconstructed by the POTENT procedure from the observed peculiar velocities of 493 objects is presented. A strong correlation is found between the galaxy and mass-density fields; both feature the Great Attractor, part of the Perseus-Pisces supercluster, and the large void between them. Monte Carlo noise simulations show that the data are consistent with the hypotheses that the smoothed fluctuations of galaxy and mass densities at each point are proportional to each other with the 'biasing' factor of IRAS galaxies, b(I), and that the peculiar velocity field is related to the mass-density field as expected according to the gravitational instability theory. Under these hypotheses, the two density fields can be related by specifying b(I) and the cosmological density parameter, Omega.
Kubiessa, Klaus; Boehm, Andreas; Barthel, Henryk; Kluge, Regine; Kahn, Thomas; Sabri, Osama; Stumpp, Patrick
2015-01-01
Objective To demonstrate the feasibility of simultaneous acquisition of 18F-FDG-PET, diffusion-weighted imaging (DWI) and T1-weighted dynamic contrast-enhanced MRI (T1w-DCE) in an integrated simultaneous PET/MRI in patients with head and neck squamous cell cancer (HNSCC) and to investigate possible correlations between these parameters. Methods 17 patients that had given informed consent (15 male, 2 female) with biopsy-proven HNSCC underwent simultaneous 18F-FDG-PET/MRI including DWI and T1w-DCE. SUVmax, SUVmean, ADCmean, ADCmin and Ktrans, kep and ve were measured for each tumour and correlated using Spearman’s ρ. Results Significant correlations were observed between SUVmean and Ktrans (ρ = 0.43; p ≤ 0.05); SUVmean and kep (ρ = 0.44; p ≤ 0.05); Ktrans and kep (ρ = 0.53; p ≤ 0.05); and between kep and ve (ρ = -0.74; p ≤ 0.01). There was a trend towards statistical significance when correlating SUVmax and ADCmin (ρ = -0.35; p = 0.08); SUVmax and Ktrans (ρ = 0.37; p = 0.07); SUVmax and kep (ρ = 0.39; p = 0.06); and ADCmean and ve (ρ = 0.4; p = 0.06). Conclusion Simultaneous 18F-FDG-PET/MRI including DWI and T1w-DCE in patients with HNSCC is feasible and allows depiction of complex interactions between glucose metabolism, microcirculatory parameters and cellular density. PMID:26270054
Cycles and Universality in Sunspot Number Fluctuations
NASA Astrophysics Data System (ADS)
Gonçalves, R.; Pinto, A. A.; Stollenwerk, N.
2009-02-01
We analyze the famous Wolf's sunspot numbers. Surprisingly, we discovered that the distribution of the sunspot number fluctuations for both the ascending and descending phases is close to the universal nonparametric Bramwell-Holdsworth-Pinton (BHP) distribution. Since the BHP probability density function appears in several other physical phenomena, our result reveals a universal feature of the Wolf's sunspot numbers.
Scaling metabolic rate fluctuations
Labra, Fabio A.; Marquet, Pablo A.; Bozinovic, Francisco
2007-01-01
Complex ecological and economic systems show fluctuations in macroscopic quantities such as exchange rates, size of companies or populations that follow non-Gaussian tent-shaped probability distributions of growth rates with power-law decay, which suggests that fluctuations in complex systems may be governed by universal mechanisms, independent of particular details and idiosyncrasies. We propose here that metabolic rate within individual organisms may be considered as an example of an emergent property of a complex system and test the hypothesis that the probability distribution of fluctuations in the metabolic rate of individuals has a “universal” form regardless of body size or taxonomic affiliation. We examined data from 71 individuals belonging to 25 vertebrate species (birds, mammals, and lizards). We report three main results. First, for all these individuals and species, the distribution of metabolic rate fluctuations follows a tent-shaped distribution with power-law decay. Second, the standard deviation of metabolic rate fluctuations decays as a power-law function of both average metabolic rate and body mass, with exponents −0.352 and −1/4 respectively. Finally, we find that the distributions of metabolic rate fluctuations for different organisms can all be rescaled to a single parent distribution, supporting the existence of general principles underlying the structure and functioning of individual organisms. PMID:17578913
García Martínez, A; Teso Vilar, E; García Fraile, A; Martínez-Ruiz, P
2006-06-21
The single-point total energy (E) of several acyclic and cyclic oligomers of N-methylformamide (NMF) was computed by the first time without any geometrical restriction, using the B3LYP6-31G* method of the density functional theory in order to determine the effect of self-association on intramolecular geometrical parameters of cis- and trans-NMF, the intermolecular distances of the hydrogen-bonding chains formed by NMF as well as intermolecular association energies including counterpoise corrections. It is concluded that liquid NMF exists mainly as polymers formed by self-association of trans-NMF units, whereas the cis-NMF isomer occurs as isolated units inserted along the chains. These computational results are in accordance with the experimentally determined predominance (ca. 90%) of trans-NMF population by means of (1)H- NMR and other spectroscopic techniques, but in severe contradiction with a recent interpretation of x-ray diffraction data on liquid NMF, postulating a cyclic trimer of cis-NMF (c-C(3)) as the predominating species. The counterpoise-corrected values of the association energy, DeltaE(CP), calculated for cyclic oligomers, increase with the polymerization degree (n) revealing a high grade of cooperative effect for amidic hydrogen-bonded chains. Noteworthy, the difference between the DeltaE(CP) values of the cyclic cis- and trans-homooligomers of NMF is positive for n=2 and 3 but negative for n > or =4.
NASA Astrophysics Data System (ADS)
Gabovich, Alexander M.; Voitenko, Alexander I.
2016-10-01
The state of the art concerning tunnel measurements of energy gaps in cuprate oxides has been analyzed. A detailed review of the relevant literature is made, and original results calculated for the quasiparticle tunnel current J(V) between a metallic tip and a disordered d-wave superconductor partially gapped by charge density waves (CDWs) are reported, because it is this model of high-temperature superconductors that becomes popular owing to recent experiments in which CDWs were observed directly. The current was calculated suggesting the scatter of both the superconducting and CDW order parameters due to the samples' intrinsic inhomogeneity. It was shown that peculiarities in the current-voltage characteristics inherent to the case of homogeneous superconducting material are severely smeared, and the CDW-related features transform into experimentally observed peak-dip-hump structures. Theoretical results were used to fit data measured for YBa2Cu3O7-δ and Bi2Sr2CaCu2O8+δ. The fitting demonstrated a good qualitative agreement between the experiment and model calculations. The analysis of the energy gaps in high-Tc superconductors is important both per se and as a tool to uncover the nature of superconductivity in cuprates not elucidated so far despite of much theoretical effort and experimental progress.
Fluctuation dynamics in reconnecting current sheets
NASA Astrophysics Data System (ADS)
von Stechow, Adrian; Grulke, Olaf; Ji, Hantao; Yamada, Masaaki; Klinger, Thomas
2015-11-01
During magnetic reconnection, a highly localized current sheet forms at the boundary between opposed magnetic fields. Its steep perpendicular gradients and fast parallel drifts can give rise to a range of instabilities which can contribute to the overall reconnection dynamics. In two complementary laboratory reconnection experiments, MRX (PPPL, Princeton) and VINETA.II (IPP, Greifswald, Germany), magnetic fluctuations are observed within the current sheet. Despite the large differences in geometries (toroidal vs. linear), plasma parameters (high vs. low beta) and magnetic configuration (low vs. high magnetic guide field), similar broadband fluctuation characteristics are observed in both experiments. These are identified as Whistler-like fluctuations in the lower hybrid frequency range that propagate along the current sheet in the electron drift direction. They are intrinsic to the localized current sheet and largely independent of the slower reconnection dynamics. This contribution characterizes these magnetic fluctuations within the wide parameter range accessible by both experiments. Specifically, the fluctuation spectra and wave dispersion are characterized with respect to the magnetic topology and plasma parameters of the reconnecting current sheet.
Measurement of quantum fluctuations in geometry
Hogan, Craig J.
2008-05-15
A particular form for the quantum indeterminacy of relative spacetime position of events is derived from the context of a holographic geometry with a minimum length at the Planck scale. The indeterminacy predicts fluctuations from a classically defined geometry in the form of ''holographic noise'' whose spatial character, absolute normalization, and spectrum are predicted with no parameters. The noise has a distinctive transverse spatial shear signature and a flat power spectral density given by the Planck time. An interferometer signal displays noise due to the uncertainty of relative positions of reflection events. The noise corresponds to an accumulation of phase offset with time that mimics a random walk of those optical elements that change the orientation of a wavefront. It only appears in measurements that compare transverse positions and does not appear at all in purely radial position measurements. A lower bound on holographic noise follows from a covariant upper bound on gravitational entropy. The predicted holographic noise spectrum is estimated to be comparable to measured noise in the currently operating interferometric gravitational-wave detector GEO600. Because of its transverse character, holographic noise is reduced relative to gravitational wave effects in other interferometer designs, such as the LIGO observatories, where beam power is much less in the beam splitter than in the arms.
TOTAL: A new instrument to study turbulent parameters in the mesosphere and lower thermosphere
NASA Astrophysics Data System (ADS)
Luebken, F. J.
1987-08-01
A rocket-borne instrument used to deduce turbulent parameters (e.g., turbulent energy dissipation rates) from in-situ measurements of small scale density fluctuations is presented. The basic item is an ionization gage, which can measure in a pressure range from 0.0000005 to 1 mbar with a total time constant of the order of msec.
Gaussian fluctuations in the two-dimensional BCS-BEC crossover: finite temperature properties
NASA Astrophysics Data System (ADS)
Bighin, G.; Salasnich, L.
2016-02-01
The role of fluctuations is enhanced in lower dimensionality systems: in a two dimensions off- diagonal long-range order is destroyed by the fluctuations at any finite temperature, drastically modifying the critical properties with respect to the three-dimensional counterpart. Recently two-dimensional systems of interacting fermions have been the subject of Montecarlo studies and experimental investigations, in particular an ultracold gas of attractive fermions with a widely tunable interaction due to a Feshbach resonance has been realized and the Berezinskii- Kosterlitz-Thouless transition has been observed. The present work deals with the theoretical description of an ultracold Fermi gas: we discuss the role of Gaussian fluctuations of the order parameter in the equation of state, in particular we take into account the first sound velocity, showing that the inclusion of order parameter fluctuations is needed in order to get the correct composite-boson limit in the strong-coupling regime. The theory is also compared with experimental data. Finally we focus on the superfluid density in the weak-coupling, intermediate and strong-coupling regimes at finite temperature, through which the Berezinskii-Kosterlitz-Thouless critical temperature is obtained.
Fluctuating shells under pressure
Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.
2012-01-01
Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558
Fluctuation of heat current in Josephson junctions
Virtanen, P.; Giazotto, F.
2015-02-15
We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.
Interacting molecular motors: Efficiency and work fluctuations
NASA Astrophysics Data System (ADS)
Slanina, František
2009-12-01
We investigate the model of “reversible ratchet” with interacting particles, presented by us earlier [F. Slanina, EPL 84, 50009 (2008)]. We further clarify the effect of efficiency enhancement due to interaction and show that it is of energetic origin, rather than a consequence of reduced fluctuations. We also show complicated structures emerging in the interaction and density dependence of the current and response function. The fluctuation properties of the work and input energy indicate in detail the far-from-equilibrium nature of the dynamics.
Spin excitations in fluctuating stripe phases of doped cuprate superconductors.
Vojta, Matthias; Vojta, Thomas; Kaul, Ribhu K
2006-09-01
Using a phenomenological lattice model of coupled spin and charge modes, we determine the spin susceptibility in the presence of fluctuating stripe charge order. We assume the charge fluctuations to be slow compared to those of the spins, and combine Monte Carlo simulations for the charge order parameter with exact diagonalization of the spin sector. Our calculations unify the spin dynamics of both static and fluctuating stripe phases and support the notion of a universal spin excitation spectrum in doped cuprate superconductors.