Extracting primordial density fluctuations
Gawiser; Silk
1998-05-29
The combination of detections of anisotropy in cosmic microwave background radiation and observations of the large-scale distribution of galaxies probes the primordial density fluctuations of the universe on spatial scales varying by three orders of magnitude. These data are found to be inconsistent with the predictions of several popular cosmological models. Agreement between the data and the cold + hot dark matter model, however, suggests that a significant fraction of the matter in the universe may consist of massive neutrinos. PMID:9603724
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.
Current density fluctuations and ambipolarity of transport
Shen, W.; Dexter, R.N.; Prager, S.C.
1991-10-01
The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center_dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.
Current density fluctuations and ambipolarity of transport
Shen, W.; Dexter, R.N.; Prager, S.C.
1991-10-01
The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.
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.
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. PMID:26672148
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. PMID:27535694
Extremal-point densities of interface fluctuations
Toroczkai; Korniss; Das Sarma S; Zia
2000-07-01
We introduce and investigate the stochastic dynamics of the density of local extrema (minima and maxima) of nonequilibrium surface fluctuations. We give a number of analytic results for interface fluctuations described by linear Langevin equations, and for on-lattice, solid-on-solid surface-growth models. We show that, in spite of the nonuniversal character of the quantities studied, their behavior against the variation of the microscopic length scales can present generic features, characteristic of the macroscopic observables of the system. The quantities investigated here provide us with tools that give an unorthodox approach to the dynamics of surface morphologies: a statistical analysis from the short-wavelength end of the Fourier decomposition spectrum. In addition to surface-growth applications, our results can be used to solve the asymptotic scalability problem of massively parallel algorithms for discrete-event simulations, which are extensively used in Monte Carlo simulations on parallel architectures. PMID:11088461
Density fluctuations in premixed turbulent flames
Namazian, M.; Talbot, L.; Robben, F.
1984-03-01
The simultaneous two-point density fluctuations in a V-shaped turbulent flame are measured using a two-point Rayleigh scattering method. A wrinkle laminar flame model with finite instantaneous flame thickness is developed for the flames studied. The reaction front probability density function (pdf) is both measured directly and also calculated from the measured mean density. An analytical expression for this pdf is given which is derived based on a thin flame model. The mean, rms and correlation coefficients are calculated using the finite reaction front thickness model and the results are compared with the experimental data. The pdf of the intermediate states are shown to be due to the reaction front thickness.
Nearly incompressible fluids: Decay of solar wind density fluctuations
NASA Astrophysics Data System (ADS)
Hunana, P.; Zank, G. P.; Heerikhuisen, J.; Shaikh, D.
2008-11-01
The evolution of density fluctuations throughout the solar wind is investigated as the basis of a newly developed theory of nearly incompressible hydrodynamics for an inhomogeneous flow. The model is explored using two-dimensional numerical simulations. The lowest-order density fluctuations (absent in the original homogeneous nearly incompressible theory) obey a passive scalar evolution equation with an additional source term that results from coupling to the large-scale inhomogeneous mean density gradient. The importance of this source term is explored, and we estimate analytically an upper bound for the maximum possible effect of a source term for nearly incompressible flows with an inhomogeneous background (static and spherically symmetric). For typical solar wind parameters, we show that this effect is rather weak beyond 0.1 AU and that the density fluctuations can be described sufficiently accurately as a pure passive scalar. Our simulations identify the sensitive dependence of density fluctuation evolution on typical initial length-scale ratio of scalar (density) and velocity fields, an effect known from the theory of passive scalar decay and experimentally measured in grid-generated turbulence. It has long been thought that the variance in the density fluctuations (δρ)2 should decay in the manner analogous to the mean background density, implying that with heliocentric distance (δρ)2 ∝ R-4 throughout the heliosphere. Analysis of plasma data obtained by the Voyager spacecraft by Bellamy et al. (2005) showed that the density fluctuations decay much more slowly than R-4 and the decay rate exhibits a flattening between 20-30 AU and a possible rise afterward. A possible mechanism to reduce the decay rate within 30 AU was suggested to be turbulence driven by stream-stream interactions followed by more dominant pickup ion interactions beyond 30 AU. Here we show that the variance in the density fluctuations as described by the inhomogeneous nearly
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.
Nonlinear density fluctuation field theory for large scale structure
NASA Astrophysics Data System (ADS)
Zhang, Yang; Miao, Hai-Xing
2009-05-01
We develop an effective field theory of density fluctuations for a Newtonian self-gravitating N-body system in quasi-equilibrium and apply it to a homogeneous universe with small density fluctuations. Keeping the density fluctuations up to second order, we obtain the nonlinear field equation of 2-pt correlation ξ(r), which contains 3-pt correlation and formal ultra-violet divergences. By the Groth-Peebles hierarchical ansatz and mass renormalization, the equation becomes closed with two new terms beyond the Gaussian approximation, and their coefficients are taken as parameters. The analytic solution is obtained in terms of the hypergeometric functions, which is checked numerically. With one single set of two fixed parameters, the correlation ξ(r) and the corresponding power spectrum P(κ) simultaneously match the results from all the major surveys, such as APM, SDSS, 2dfGRS, and REFLEX. The model gives a unifying understanding of several seemingly unrelated features of large scale structure from a field-theoretical perspective. The theory is worth extending to study the evolution effects in an expanding universe.
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.
Fluctuating charge-density waves in a cuprate superconductor.
Torchinsky, Darius H; Mahmood, Fahad; Bollinger, Anthony T; Božović, Ivan; Gedik, Nuh
2013-05-01
Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and spin ordering whose significance is not fully understood. So far, static charge-density waves (CDWs) have been detected by diffraction probes only at particular doping levels or in an applied external field . However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here we present a method based on ultrafast spectroscopy to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La(1.9)Sr(0.1)CuO4 film (T(c) = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K that decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La(1.84)Sr(0.16)CuO4 film (T(c) = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favouring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials. PMID:23435216
Current-density fluctuations and ambipolarity of transport
Shen, W.; Dexter, R.N.; Prager, S.C. )
1992-03-02
The fluctuation in the plasma current density is measured in the MST reversed-field-pinch experiment. Such fluctuations, ad the measured radial profile of the {ital k} spectrum of magnetic fluctuations, support the view that low-frequency fluctuations ({ital f}{lt}30 kHz) are tearing modes and high-frequency fluctuations (30 kHz{lt}{ital f}{lt}250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., {bold k}{center dot}{bold B}=0). Correlation of current-density and magnetic fluctuations ({l angle}{ital {tilde j}}{sub {parallel}}{ital {tilde B}{ital r}}{r angle}) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.
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.
Order-parameter scaling in fluctuation-dominated phase ordering.
Kapri, Rajeev; Bandyopadhyay, Malay; Barma, Mustansir
2016-01-01
In systems exhibiting fluctuation-dominated phase ordering, a single order parameter does not suffice to characterize the order, and it is necessary to monitor a larger set. For hard-core sliding particles on a fluctuating surface and the related coarse-grained depth (CD) models, this set comprises the long-wavelength Fourier components of the density profile, which capture the breakup and remerging of particle-rich regions. We study both static and dynamic scaling laws obeyed by the Fourier modes Q_{mL} and find that the mean value obeys the static scaling law 〈Q_{mL}〉∼L^{-ϕ}f(m/L) with ϕ≃2/3 and ϕ≃3/5 for Edwards-Wilkinson (EW) and Kardar-Parisi-Zhang (KPZ) surface evolution, respectively, and ϕ≃3/4 for the CD model. The full probability distribution P(Q_{mL}) exhibits scaling as well. Further, time-dependent correlation functions such as the steady-state autocorrelation and cross-correlations of order-parameter components are scaling functions of t/L^{z}, where L is the system size and z is the dynamic exponent, with z=2 for EW and z=3/2 for KPZ surface evolution. In addition we find that the CD model shows temporal intermittency, manifested in the dynamical structure functions of the density and the weak divergence of the flatness as the scaled time approaches 0. PMID:26871034
How plasma parameters fluctuations influence emissive probe measurements
Bousselin, G. Plihon, N.; Lemoine, N.; Heuraux, S.; Cavalier, J.
2015-05-15
Relationship between the floating potential of an emissive probe and plasma potential oscillations is studied in the case of controlled oscillations of plasma parameters. This relationship is compared to a quasi-static model for floating potential oscillations that assumes a constant emission current and includes the fluctuations of plasma parameters (density and electron temperature). Two different plasma regimes are considered. In the first one, the model is coherent with experimental results. In the second, the model does not fulfill one of the assumption due to the evidence of emission current oscillations when the mean emission current exceeds a given threshold. This second regime highlights the importance of taking into account emission current oscillations in the interpretation of emissive probe measurements. Nevertheless, discrepancies are still observed between emissive probe floating potential and plasma potential oscillations.
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.
Time-dependent density fluctuations in liquid water
NASA Astrophysics Data System (ADS)
Waldron, Conor J.; English, Niall J.
2016-04-01
Temporal system-mass-density fluctuation analysis was performed on liquid-water molecular-dynamics simulations at ambient pressure and 200 and 300 K, in three increasingly-large systems. A prominent mode in system-density fluctuations was observed at molecular-librational frequencies of ∼600-800 cm-1 (with pronounced temperature dependence). This mode displayed marked system-size dependence, disappearing for larger systems. Persistent system-density fluctuations were clearly evident at 10-11 cm-1 for all systems and temperatures, with lower-amplitude 'overtones' evident only in larger systems. It is conjectured that this reflects ∼3 ps timescales observed in earlier studies for dissipation of local-density fluctuations in liquid water in this 200-300 K temperature range.
Effect of density fluctuations on ECCD in ITER and TCV
NASA Astrophysics Data System (ADS)
Decker, J.; Peysson, Y.; Coda, S.
2012-09-01
Density fluctuations near the edge of tokamak plasmas can affect the propagation of electron cyclotron (EC) waves. In the present paper, the EC wave propagation in a fluctuating equilibrium is determined using the ray-tracing code C3PO. The evolution of the electron distribution function is calculated self-consistently with the EC wave damping using the 3-D Fokker-Planck solver LUKE. The cumulative effect of fluctuations results in a significant broadening of the current profile combined with a fluctuating power deposition profile. This mechanism improves the simulation of fully non-inductive EC discharges in the TCV tokamaks. Predictive simulations for ITER show that density fluctuations could make the stabilization of NTMs in ITER more challenging.
Effects of stream-associated fluctuations upon the radial variation of average solar wind parameters
NASA Technical Reports Server (NTRS)
Goldstein, B. E.; Jokipii, J. R.
1977-01-01
A numerical MHD model in both spherically symmetric time-dependent and corotating equatorial flow approximations is used to compute the effects of nonlinear fluctuations due to solar wind streams upon radial gradients of average solar wind parameters. Significant effects of correlations between fluctuations on the gradients of azimuthal magnetic field, radial velocity, density, and azimuthal velocity are found. It is found that nonlinear fluctuations are a significant effect in determining the radial gradients of the solar wind at distances as small as 0.2 AU; at distances greater than 1 AU, nonlinear fluctuations dominate the behavior of the radial gradients.
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.
Current density fluctuations, nonlinear coupling, and transport in MST
Prager, S.C.; Almagri, A.F.; Assadi, S.; Cekic, M.; Chapman, B.E.; Crocker, N.; Den Hartog, D.J.; Dexter, R.N.; Fiksel, G.; Fonck, R.J.; Henry, J.S.; Hokin, S.A.; Holly, D.J.; Ji, H.; Rempel, T.D.; Sarff, J.S.; Scime, E.; Shen, W.; Sidikman, K.L.; Sprott, J.C.; Stoneking, M.R.; Watts, C.
1992-09-01
New information on magnetic fluctuations and transport in toroidal devices has been obtained in the MST reversed field pinch through measurement of nonlinear coupling of three waves in k-space, and measurement of current density fluctuations. Measurements of nonlinear coupling of magnetic fluctuations reveals that (1) two poloidal mode number m = 1 modes couple strongly to an m = 2 mode, (2) toroidal mode coupling is broad extending up to n = 20, (3) these features agree with predictions for tearing fluctuations from a nonlinear MHD code, (4) during a sawtooth crash the number of modes involved in nonlinear interactions increases dramatically and the k-spectrum broadens simultaneously. Measurements of current density fluctuations over the outer 20% of the minor radius reveal that (1) low frequency fluctuations are consistent with tearing modes, (2) high frequency fluctuations are localized turbulence which maintains resonance with the equilibrium field as q changes with radius, (3) particle transport from magnetic fluctuations is ambipolar (i.e., <{delta}j{sub {parallel}}B{sub r}> = O).
Density fluctuations of polymers in disordered media
Deutsch, Joshua M.; Olvera de la Cruz, Monica
2011-03-02
We study self-avoiding random walks in an environment where sites are excluded randomly, in two and three dimensions. For a single polymer chain, we study the statistics of the time averaged monomer density and show that these are well described by multifractal statistics. This is true even far from the percolation transition of the disordered medium. We investigate solutions of chains in a disordered environment and show that the statistics cease to be multifractal beyond the screening length of the solution.
Charge and spin fluctuations in the density functional theory
Gyoerffy, B.L.; Barbieri, A. . H.H. Wills Physics Lab.); Staunton, J.B. . Dept. of Physics); Shelton, W.A.; Stocks, G.M. )
1990-01-01
We introduce a conceptual framework which allow us to treat charge and spin fluctuations about the Local density Approximation (LDA) to the Density Functional Theory (DFT). We illustrate the approach by explicit study of the Disordered Local Moment (DLM) state in Fe above the Curie Temperature {Tc} and the Mott insulating state in MnO. 27 refs., 6 figs.
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.
Density fluctuations of polymers in disordered media.
Deutsch, J M; de la Cruz, M Olvera
2011-03-01
We study self-avoiding random walks in an environment where sites are excluded randomly, in two and three dimensions. For a single polymer chain, we study the statistics of the time averaged monomer density and show that these are well described by multifractal statistics. This is true even far from the percolation transition of the disordered medium. We investigate solutions of chains in a disordered environment and show that the statistics cease to be multifractal beyond the screening length of the solution. PMID:21517516
Topological defects and density fluctuations in collectively moving systems
Schaller, Volker; Bausch, Andreas R.
2013-01-01
Ensembles of collectively moving particles like flocks of birds, bacteria, or filamentous polymers show a broad range of intriguing phenomena, yet seem to obey very similar physical principles. These generic principles have been predicted to lead to characteristic density fluctuations, which are in sharp contrast to normal fluctuations determining the properties of ordered systems in thermal equilibrium. Using high-density motility assays of driven filaments, we characterize here the origin and nature of giant fluctuations that emerge in this class of systems. By showing that these unique statistical properties result from the coupling between particle density and the topology of the velocity field of the particles, we provide insight in the physics of collective motion.
Density fluctuation measurements using beam emission spectroscopy on Heliotron J
Kobayashi, S.; Ohshima, S.; Yamamoto, S.; Mizuuchi, T.; Nagasaki, K.; Okada, H.; Minami, T.; Konoshima, S.; Toushi, K.; Sano, F.; Kado, S.; Oishi, T.; Kagawa, T.; Nagae, Y.; Lee, H. Y.; Minami, T.; Harada, T.; Nakamura, Y.; Estrada, T.; Murakami, S.
2012-10-15
This paper describes the measurement of the density fluctuation using beam emission spectroscopy in Heliotron J, having the non-symmetrical helical-magnetic-axis configuration. In order to optimize the sightlines, the numerical calculations are carried out to estimate the spatial resolution and the observation location. When a tangential neutral beam is used as diagnostic one, suitable sightlines from the newly installed diagnostic port are selected whose spatial resolution {Delta}{rho} is less than {+-}0.07 over the entire plasma region. Modification of the interference filter and the detection systems enables us to measure the radial profile of the density fluctuation. Each of the three coherent modes due to the fast-ion-driven magnetohydrodynamic instabilities has different radial structure of the density fluctuation.
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.
NASA Astrophysics Data System (ADS)
Ikawa, Shohei; Tokumasu, Takashi; Tsuboi, Nobuyuki; Nagashima, Hiroki; Tsuda, Shin-Ichi
2014-11-01
In this study, we evaluated the density fluctuation of diatomic fluids around the critical point. We simulated the density fluctuation of 2-Center-Lennard-Jones (2CLJ) fluids, which have molecular elongations as one of the parameters, by Molecular Dynamics (MD) method. We focused on the effect of anisotropy of diatomic fluid on fluctuation structure to evaluate the principle of corresponding state of the density fluctuation. As the evaluation methods, we calculated the dispersion of number of molecules at certain domain and also computed static structure factor. We calculated those values of diatomic fluids which have various molecular elongations to compare the difference of fluctuation structure of fluids. As results, the principle of corresponding state is satisfied because there is no significant difference in the fluctuation structure between fluids which have shorter molecular elongation and longer one. Hereafter, we are going to calculate the intermediate scattering function and dynamic structure factor to evaluate the principle of corresponding state of the density fluctuation in detail. This study has been supported by Grant-in-Aid for Scientific Research (B) (23360380) and the Collaborative Research Project of the Institute of Fluids Science, Tohoku University.
Lin, L.; Ding, W. X.; Brower, D. L.; Bergerson, W. F.; Yates, T. F.
2010-10-15
Differential interferometry employs two parallel laser beams with a small spatial offset (less than beam width) and frequency difference (1-2 MHz) using common optics and a single mixer for a heterodyne detection. The differential approach allows measurement of the electron density gradient, its fluctuations, as well as the equilibrium density distribution. This novel interferometry technique is immune to fringe skip errors and is particularly useful in harsh plasma environments. Accurate calibration of the beam spatial offset, accomplished by use of a rotating dielectric wedge, is required to enable broad application of this approach. Differential interferometry has been successfully used on the Madison Symmetric Torus reversed-field pinch plasma to directly measure fluctuation-induced transport along with equilibrium density profile evolution during pellet injection. In addition, by combining differential and conventional interferometry, both linear and nonlinear terms of the electron density fluctuation energy equation can be determined, thereby allowing quantitative investigation of the origin of the density fluctuations. The concept, calibration, and application of differential interferometry are presented.
Beyond Poisson-Boltzmann: Numerical Sampling of Charge Density Fluctuations.
Poitevin, Frédéric; Delarue, Marc; Orland, Henri
2016-07-01
We present a method aimed at sampling charge density fluctuations in Coulomb systems. The derivation follows from a functional integral representation of the partition function in terms of charge density fluctuations. Starting from the mean-field solution given by the Poisson-Boltzmann equation, an original approach is proposed to numerically sample fluctuations around it, through the propagation of a Langevin-like stochastic partial differential equation (SPDE). The diffusion tensor of the SPDE can be chosen so as to avoid the numerical complexity linked to long-range Coulomb interactions, effectively rendering the theory completely local. A finite-volume implementation of the SPDE is described, and the approach is illustrated with preliminary results on the study of a system made of two like-charge ions immersed in a bath of counterions. PMID:27075231
Bettelheim, F A; Paunovic, M
1979-01-01
Light-scattering intensities in the I parallel and I+ mode were obtained on thin sections of three human lenses. Random density and orientation fluctuation theory, without cross correlation, was employed to evaluate light-scattering parameters. Both the density correlation distances, as well as the orientation correlation distances, were related to structural elements in the lens fiber cell that have been observed by other investigators with different techniques. The magnitude of these fluctuations were evaluated, and it was demonstrated that the density fluctuations are the main contributors to light scattering in normal human lenses. Changes in the light-scattering parameters were evaluated as a function of position within the lens. The changes observed agree with the biochemical data in the literature that reflects that an aging process occurs when one proceeds from the periphery of the lens toward the center. PMID:262413
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.
Particle-density fluctuations and universality in the conserved stochastic sandpile
NASA Astrophysics Data System (ADS)
Dickman, Ronald; da Cunha, S. D.
2015-08-01
We examine fluctuations in particle density in the restricted-height, conserved stochastic sandpile (CSS). In this and related models, the global particle density is a temperaturelike control parameter. Thus local fluctuations in this density correspond to disorder; if this disorder is a relevant perturbation of directed percolation (DP), then the CSS should exhibit non-DP critical behavior. We analyze the scaling of the variance Vℓ of the number of particles in regions of ℓd sites in extensive simulations of the quasistationary state in one and two dimensions. Our results, combined with a Harris-like argument for the relevance of particle-density fluctuations, strongly suggest that conserved stochastic sandpiles belong to a universality class distinct from that of DP.
Particle-density fluctuations and universality in the conserved stochastic sandpile.
Dickman, Ronald; da Cunha, S D
2015-08-01
We examine fluctuations in particle density in the restricted-height, conserved stochastic sandpile (CSS). In this and related models, the global particle density is a temperaturelike control parameter. Thus local fluctuations in this density correspond to disorder; if this disorder is a relevant perturbation of directed percolation (DP), then the CSS should exhibit non-DP critical behavior. We analyze the scaling of the variance Vℓ of the number of particles in regions of ℓd sites in extensive simulations of the quasistationary state in one and two dimensions. Our results, combined with a Harris-like argument for the relevance of particle-density fluctuations, strongly suggest that conserved stochastic sandpiles belong to a universality class distinct from that of DP. PMID:26382328
Scattering of radio frequency waves by density fluctuations
NASA Astrophysics Data System (ADS)
Ram, A. K.; Hizanidis, K.; Ioannidis, Z.; Tigelis, I.
2015-11-01
The scattering of radio frequency waves by density fluctuations in magnetized fusion plasmas is studied theoretically and computationally. For coherent fluctuations, such as filaments in the edge region, we use a full-wave model for which the theory is similar to that for Mie scattering of electromagnetic waves by dielectric objects. The filaments are considered to be cylindrical with their axes aligned along the magnetic field. The results from the theoretical model are compared with numerical simulations using COMSOL. The simulations are extended to plasma conditions that are beyond the scope of the theoretical model, e.g., multiple filaments and filaments with density gradients. For incoherent planar fluctuations, which can be either in the core of the plasma or in the edge region, our theory is based on the Kirchhoff approach in tandem with Huygen's principle. The coherent and incoherent fluctuations scatter the incident plane wave, as well as couple some of the power to different plasma waves. The scattered spectrum is affected by the size of the fluctuations, the frequency, and the direction of propagation of the incident wave.
Dynamic density functional theory with hydrodynamic interactions and fluctuations.
Donev, Aleksandar; Vanden-Eijnden, Eric
2014-06-21
We derive a closed equation for the empirical concentration of colloidal particles in the presence of both hydrodynamic and direct interactions. The ensemble average of our functional Langevin equation reproduces known deterministic Dynamic Density Functional Theory (DDFT) [M. Rex and H. Löwen, "Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps," Phys. Rev. Lett. 101(14), 148302 (2008)], and, at the same time, it also describes the microscopic fluctuations around the mean behavior. We suggest separating the ideal (non-interacting) contribution from additional corrections due to pairwise interactions. We find that, for an incompressible fluid and in the absence of direct interactions, the mean concentration follows Fick's law just as for uncorrelated walkers. At the same time, the nature of the stochastic terms in fluctuating DDFT is shown to be distinctly different for hydrodynamically-correlated and uncorrelated walkers. This leads to striking differences in the behavior of the fluctuations around Fick's law, even in the absence of pairwise interactions. We connect our own prior work [A. Donev, T. G. Fai, and E. Vanden-Eijnden, "A reversible mesoscopic model of diffusion in liquids: from giant fluctuations to Fick's law," J. Stat. Mech.: Theory Exp. (2014) P04004] on fluctuating hydrodynamics of diffusion in liquids to the DDFT literature, and demonstrate that the fluid cannot easily be eliminated from consideration if one wants to describe the collective diffusion in colloidal suspensions. PMID:24952531
Dynamic density functional theory with hydrodynamic interactions and fluctuations
NASA Astrophysics Data System (ADS)
Donev, Aleksandar; Vanden-Eijnden, Eric
2014-06-01
We derive a closed equation for the empirical concentration of colloidal particles in the presence of both hydrodynamic and direct interactions. The ensemble average of our functional Langevin equation reproduces known deterministic Dynamic Density Functional Theory (DDFT) [M. Rex and H. Löwen, "Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps," Phys. Rev. Lett. 101(14), 148302 (2008)], and, at the same time, it also describes the microscopic fluctuations around the mean behavior. We suggest separating the ideal (non-interacting) contribution from additional corrections due to pairwise interactions. We find that, for an incompressible fluid and in the absence of direct interactions, the mean concentration follows Fick's law just as for uncorrelated walkers. At the same time, the nature of the stochastic terms in fluctuating DDFT is shown to be distinctly different for hydrodynamically-correlated and uncorrelated walkers. This leads to striking differences in the behavior of the fluctuations around Fick's law, even in the absence of pairwise interactions. We connect our own prior work [A. Donev, T. G. Fai, and E. Vanden-Eijnden, "A reversible mesoscopic model of diffusion in liquids: from giant fluctuations to Fick's law," J. Stat. Mech.: Theory Exp. (2014) P04004] on fluctuating hydrodynamics of diffusion in liquids to the DDFT literature, and demonstrate that the fluid cannot easily be eliminated from consideration if one wants to describe the collective diffusion in colloidal suspensions.
Dynamic density functional theory with hydrodynamic interactions and fluctuations
Donev, Aleksandar Vanden-Eijnden, Eric
2014-06-21
We derive a closed equation for the empirical concentration of colloidal particles in the presence of both hydrodynamic and direct interactions. The ensemble average of our functional Langevin equation reproduces known deterministic Dynamic Density Functional Theory (DDFT) [M. Rex and H. Löwen, “Dynamical density functional theory with hydrodynamic interactions and colloids in unstable traps,” Phys. Rev. Lett. 101(14), 148302 (2008)], and, at the same time, it also describes the microscopic fluctuations around the mean behavior. We suggest separating the ideal (non-interacting) contribution from additional corrections due to pairwise interactions. We find that, for an incompressible fluid and in the absence of direct interactions, the mean concentration follows Fick's law just as for uncorrelated walkers. At the same time, the nature of the stochastic terms in fluctuating DDFT is shown to be distinctly different for hydrodynamically-correlated and uncorrelated walkers. This leads to striking differences in the behavior of the fluctuations around Fick's law, even in the absence of pairwise interactions. We connect our own prior work [A. Donev, T. G. Fai, and E. Vanden-Eijnden, “A reversible mesoscopic model of diffusion in liquids: from giant fluctuations to Fick's law,” J. Stat. Mech.: Theory Exp. (2014) P04004] on fluctuating hydrodynamics of diffusion in liquids to the DDFT literature, and demonstrate that the fluid cannot easily be eliminated from consideration if one wants to describe the collective diffusion in colloidal suspensions.
Radial evolution of the intermittency of density fluctuations in the fast solar wind
Bruno, R.; D'Amicis, R.; Telloni, D.; Primavera, L.; Sorriso-Valvo, L.; Carbone, V.; Malara, F.; Veltri, P.
2014-05-01
We study the radial evolution of the intermittency of density fluctuations in the fast solar wind. The study is performed by analyzing the plasma density measurements provided by Helios 2 in the inner heliosphere between 0.3 and 0.9 AU. The analysis is carried out by means of a complete set of diagnostic tools, including the flatness factor at different timescales to estimate intermittency, the Kolmogorov-Smirnov test to estimate the degree of intermittency, and the Fourier transform to estimate the power spectral densities of these fluctuations. Density fluctuations within the fast wind are rather intermittent and their level of intermittency, together with the amplitude of intermittent events, decreases with the distance from the Sun, at odds with the intermittency of both magnetic field and all other plasma parameters. Furthermore, the intermittent events are strongly correlated, exhibiting temporal clustering. This indicates that the mechanism underlying their generation departs from a time-varying Poisson process. A remarkable, qualitative similarity with the behavior of plasma density fluctuations obtained from a numerical study of the nonlinear evolution of parametric instability in the solar wind supports the idea that this mechanism has an important role in governing density fluctuations in the inner heliosphere.
Effects of Density Fluctuations on Weakly Nonlinear Alfven Waves: An IST Perspective
NASA Astrophysics Data System (ADS)
Hamilton, R.; Hadley, N.
2012-12-01
The effects of random density fluctuations on oblique, 1D, weakly nonlinear Alfven waves is examined through a numerical study of an analytical model developed by Ruderman [M.S. Ruderman, Phys. Plasmas, 9 (7), pp. 2940-2945, (2002).]. Consistent with Ruderman's application to the one-parameter dark soliton, the effects on both one-parameter bright and dark solitons, the two-parameter soliton as well as pairs of one-parameter solitons were similar to that of Ohmic dissipation found by Hamilton et al. [R. Hamilton, D. Peterson, and S. Libby, J. Geophys. Res 114, A03104,doi:10.1029/2008JA013582 (2009).] It was found in all cases where bright or two-parameter solitons are present initially, that the effects of density fluctuations results in the eventual damping of such compressive wave forms and the formation of a train of dark solitons, or magnetic depressions.
Electronic density fluctuation associated to coherent plasmon excitations
NASA Astrophysics Data System (ADS)
Gervasoni, Juana; Segui, Silvina; Arista, Nestor
2011-10-01
In this work we analyze, in the frame of the coherent states, the fluctuation of the electronic collective modes associated with the wake potential generated by an external particle of charge Ze. This perturbation is described as coherent states of plasmons spatially localized in an average distance of the order of the velocity of the projectile divided by the plasmon frequency of the material. One of the most important features is that in all the cases, for different trajectories of the external particle, and for different structures of the material, the fluctuations are not negligible. In particular, we observe that due to the importance of the surface in nanostructured materials, the fluctuation of density is very sensitive to their geometry and composition, fact that must have taken into account for the nanodevices designs. In this work we analyze, in the frame of the coherent states, the fluctuation of the electronic collective modes associated with the wake potential generated by an external particle of charge Ze. This perturbation is described as coherent states of plasmons spatially localized in an average distance of the order of the velocity of the projectile divided by the plasmon frequency of the material. One of the most important features is that in all the cases, for different trajectories of the external particle, and for different structures of the material, the fluctuations are not negligible. In particular, we observe that due to the importance of the surface in nanostructured materials, the fluctuation of density is very sensitive to their geometry and composition, fact that must have taken into account for the nanodevices designs. Acknowledgements to CNEA and CONICET, Argentina.
Density and temperature of bosons from quantum fluctuations
NASA Astrophysics Data System (ADS)
Zheng, Hua; Giuliani, Gianluca; Bonasera, Aldo
2012-10-01
A method to determine the density and temperature of a system is proposed based on quantum fluctuations typical of bosons in the limit where the temperature T is close to the critical temperature Tc for a Bose-Einstein condensate (BEC) at a given density ρ. Quadrupole and particle multiplicity fluctuations using Landau's theory of fluctuations near the critical point are derived. As an example, we apply our approach to heavy ion collisions using the Constrained Molecular Dynamics model (CoMD) which includes the Fermi statistics. The model shows some clusterization into deuteron (d) and alpha (α) clusters but it is not enough to reproduce available experimental data. We propose a modification of the collision term in the approach to include the possibility of α-α collisions. The relevant Bose-Einstein factor in the collision term is properly taken into account. This approach increases the yields of bosons relative to fermions closer to data. Boson fluctuations become larger than 1 as expected. If they are confirmed a new field of research could open up for a mixture of strongly interacting fermions and bosons which requires novel techniques both theoretically and experimentally.
Density fluctuations as an intrinsic mechanism of pressure profile formation
NASA Astrophysics Data System (ADS)
Vershkov, V. A.; Shelukhin, D. A.; Subbotin, G. F.; Dnestrovskij, Yu. N.; Danilov, A. V.; Melnikov, A. V.; Eliseev, L. G.; Maltsev, S. G.; Gorbunov, E. P.; Sergeev, D. S.; Krylov, S. V.; Myalton, T. B.; Ryzhakov, D. V.; Trukhin, V. M.; Chistiakov, V. V.; Cherkasov, S. V.
2015-06-01
This article provides new insight into previous and new experimental data regarding behaviour of small-scale density fluctuations in T-10 ohmic and electron cyclotron resonance heated (ECRH) discharges. The experiments demonstrate the existence of certain peaked-‘marginal’ normalized plasma pressure profiles in both ohmic and discharges with on-axis ECRH. Strong particle confinement degradation occurred when the normalized plasma pressure gradient exceeded this marginal profile gradient (fast density decay in ohmic, ‘density pump out’ in ECRH). The marginal profile could be achieved either with a flat density and peaked temperature profile or vice versa. Minimal turbulence level did not depend on heating power and was observed with the ‘optimal’ pressure profile, which was slightly broader than the marginal profile. The density fluctuations did not significantly contribute to the heat transport but determined particle fluxes to maintain the pressure profile. The experimental density behaviour could be reasonably described with the modified model of canonical profiles, which includes particle confinement deterioration under marginal pressure profile conditions.
Langmuir turbulence driven by beams in solar wind plasmas with long wavelength density fluctuations
NASA Astrophysics Data System (ADS)
Krafft, C.; Volokitin, A.
2016-03-01
The self-consistent evolution of Langmuir turbulence generated by electron beams in solar wind plasmas with density inhomogeneities is calculated by numerical simulations based on a 1D Hamiltonian model. It is shown, owing to numerical simulations performed with parameters relevant to type III solar bursts' conditions at 1 AU, that the presence of long-wavelength random density fluctuations of sufficiently large average level crucially modifies the well-known process of beam interaction with Langmuir waves in homogeneous plasmas.
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.
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.
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.
Cluster evolution as a probe of primordial density fluctuations
NASA Technical Reports Server (NTRS)
Bond, J. Richard; Myers, Steven T.
1993-01-01
Although COBE's detection of large angle microwave background anisotropies fixes the amplitude of density fluctuations on length scales k exp -1 approximately = (300-6000) h(exp -1)Mpc, what is crucial for the level of large scale clustering is the amplitude of density fluctuations on scales (5-50) h(exp -1)Mpc. The level of dynamical clustering is usually parameterized by the size of the mass fluctuations in 8 h exp -1 Mpc spheres, sigma sub 8. For the cold dark matter model, COBE gives sigma sub 8 approximately = 1, while models with extra large scale power give sigma sub 8 approximately = 1/2. The most massive clusters of galaxies (greater than or approximately = 10 exp 15 solar mass) form from rare 'peak patches' found in the initial mass density distribution. Their abundance as a function of redshift is a sensitive probe of the wave number band k(exp -1) approx. (3-8) h(exp -1)Mpc, hence of sigma sub 8, and so cluster evolution can discriminate among models allowed by the COBE results. We use our Hierarchical Peaks Method, which accurately reproduces the results of P3M N-body simulations, to calculate the evolution of cluster x-ray flux counts, luminosity, and temperature functions as a function of sigma sub 8 for CDM models and those with more large scale power. We find that the EMSS and Edge et al. cluster samples support sigma sub 8 in the range from approx. 0.6-0.9, and that models with more large scale power (and hence flatter fluctuation spectra in the cluster regime) fit the x-ray bright end better.
Observations of ULF wave related equatorial electrojet and density fluctuations
NASA Astrophysics Data System (ADS)
Yizengaw, E.; Zesta, E.; Biouele, C. M.; Moldwin, M. B.; Boudouridis, A.; Damtie, B.; Mebrahtu, A.; Anad, F.; Pfaff, R. F.; Hartinger, M.
2013-10-01
We report on Pc5 wave related electric field and vertical drift velocity oscillations at the equator as observed by ground magnetometers for an extended period on 9 August 2008. We show that the magnetometer-estimated equatorial E×B drift oscillates with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. We also show ionospheric density fluctuations during the period when we observed ULF wave activity. At the same time, we detect the ULF activity on the ground using ground-based magnetometer data from the 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. Upstream solar wind conditions are provided by the ACE spacecraft. We find that the wave power observed on the ground also occurs in the upstream solar wind and in the magnetosphere. All these observations demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. While no direct drift measurements from equatorial radars exist for the 9 August 2008 event, we used JULIA 150 km radar drift velocities observed on 2 May 2010 and found similar fluctuations with the period of 5-8 min, as a means of an independent confirmation of our magnetometer derived drift dynamics.
Density fluctuations due to Raman forward scattering in quantum plasma
NASA Astrophysics Data System (ADS)
Kumar, Punit; Singh, Shiv; Rathore, Nisha Singh
2016-05-01
Density fluctuations due Raman forward scattering (RFS) is analysed in the interaction of a high intensity laser pulse with high density quantum plasma. The interaction model is developed using the quantum hydrodynamic (QHD) model which consist of a set of equations describing the transport of charge, density, momentum and energy of a charged particle system interacting through a self-consistent electrostatic potential. The nonlinear source current has been obtained incorporating the effects of quantum Bohm potential, Fermi pressure and electron spin. The laser spectrum is strongly modulated by the interaction, showing sidebands at the plasma frequency. Furthermore, as the quiver velocity of the electrons in the high electric field of the laser beam is quit large, various quantum effects are observed which can be attributed to the variation of electron mass with laser intensity.
Vallée, R A L; Tomczak, N; Vancso, G J; Kuipers, L; van Hulst, N F
2005-03-15
We investigated the nanometer scale mobility of polymers in the glassy state by monitoring the dynamics of embedded single fluorophores. Recently we reported on fluorescence lifetime fluctuations which reflect the segmental rearrangement dynamics of the polymer in the surroundings of the single molecule probe. Here we focus on the nature of these fluorescence lifetime fluctuations. First the potential role of quenching and molecular conformational changes is discussed. Next we concentrate on the influence of the radiative density of states on the spontaneous emission of individual dye molecules embedded in a polymer. To this end we present a theory connecting the effective-medium theory to a cell-hole model, originating from the Simha-Somcynsky free-volume theory. The relation between the derived distributions of free volume and fluorescence lifetime allows one to determine the number of segments involved in the local rearrangement directly from experimental data. Results for two different polymers as a function of temperature are presented. PMID:15836240
Yang, Shanshan; Cai, Suxian; Zheng, Fang; Wu, Yunfeng; Liu, Kaizhi; Wu, Meihong; Zou, Quan; Chen, Jian
2014-10-01
This article applies advanced signal processing and computational methods to study the subtle fluctuations in knee joint vibroarthrographic (VAG) signals. Two new features are extracted to characterize the fluctuations of VAG signals. The fractal scaling index parameter is computed using the detrended fluctuation analysis algorithm to describe the fluctuations associated with intrinsic correlations in the VAG signal. The averaged envelope amplitude feature measures the difference between the upper and lower envelopes averaged over an entire VAG signal. Statistical analysis with the Kolmogorov-Smirnov test indicates that both of the fractal scaling index (p=0.0001) and averaged envelope amplitude (p=0.0001) features are significantly different between the normal and pathological signal groups. The bivariate Gaussian kernels are utilized for modeling the densities of normal and pathological signals in the two-dimensional feature space. Based on the feature densities estimated, the Bayesian decision rule makes better signal classifications than the least-squares support vector machine, with the overall classification accuracy of 88% and the area of 0.957 under the receiver operating characteristic (ROC) curve. Such VAG signal classification results are better than those reported in the state-of-the-art literature. The fluctuation features of VAG signals developed in the present study can provide useful information on the pathological conditions of degenerative knee joints. Classification results demonstrate the effectiveness of the kernel feature density modeling method for computer-aided VAG signal analysis. PMID:25096412
Fluctuation-dissipation theorem density-functional theory
NASA Astrophysics Data System (ADS)
Furche, Filipp; Van Voorhis, Troy
2005-04-01
Using the fluctuation-dissipation theorem (FDT) in the context of density-functional theory (DFT), one can derive an exact expression for the ground-state correlation energy in terms of the frequency-dependent density response function. When combined with time-dependent density-functional theory, a new class of density functionals results that use approximations to the exchange-correlation kernel fxc as input. This FDT-DFT scheme holds promise to solve two of the most distressing problems of conventional Kohn-Sham DFT: (i) It leads to correlation energy functionals compatible with exact exchange, and (ii) it naturally includes dispersion. The price is a moderately expensive O(N6) scaling of computational cost and a slower basis set convergence. These general features of FDT-DFT have all been recognized previously. In this paper, we present the first benchmark results for a set of molecules using FDT-DFT beyond the random-phase approximation (RPA)—that is, the first such results with fxc≠0. We show that kernels derived from the adiabatic local-density approximation and other semilocal functionals suffer from an "ultraviolet catastrophe," producing a pair density that diverges at small interparticle distance. Nevertheless, dispersion interactions can be treated accurately if hybrid functionals are employed, as is demonstrated for He2 and HeNe. We outline constraints that future approximations to fxc should satisfy and discuss the prospects of FDT-DFT.
Listening to the noise: random fluctuations reveal gene network parameters
Munsky, Brian; Khammash, Mustafa
2009-01-01
The cellular environment is abuzz with noise. The origin of this noise is attributed to the inherent random motion of reacting molecules that take part in gene expression and post expression interactions. In this noisy environment, clonal populations of cells exhibit cell-to-cell variability that frequently manifests as significant phenotypic differences within the cellular population. The stochastic fluctuations in cellular constituents induced by noise 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 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. This establishes a potentially powerful approach for the identification of gene networks and offers a new window into the workings of these networks.
Electron density fluctuations in a disturbed ionospheric environment
NASA Astrophysics Data System (ADS)
Huba, J. D.; Ganguli, G.
1988-01-01
Electron density fluctuations in the earth's ionosphere can adversely affect SDIO systems which involve electromagnetic wave propagation, e.g., laser beams. This is particularly true for severely disturbed ionospheric conditions produced by high-altitude nuclear explosions (HANEs). This paper briefly describes, in general terms, the HANE environment and the various plasma instabilities which could generate small-scale electron density irregularities. As an example, an analysis of a single instability, the lower-hybrid-drift instability, which is likely to be excited in the ionosphere following a high altitude burst. Both the linear and nonlinear behavior of this instability are discussed. It is shown how these results can be applied to potential SDIO laser systems in a HANE environment.
Li, Wei; Chen, Xiaolong; Wang, Lin; He, Yuheng; Wu, Zefei; Cai, Yuan; Zhang, Mingwei; Wang, Yang; Han, Yu; Lortz, Rolf W.; Zhang, Zhao-Qing; Sheng, Ping; Wang, Ning
2013-01-01
We demonstrate that fluctuations of the local density of states (LDOS) in strongly disordered graphene play an important role in determining the quantum capacitance of the top-gate graphene devices. Depending on the strength of the disorder induced by metal-cluster decoration, the measured quantum capacitance of disordered graphene can dramatically decrease in comparison with pristine graphene. This is opposite to the common belief that quantum capacitance should increase with disorder. To explain this counterintuitive behavior, we present a two-parameter model which incorporates both the non-universal power law behavior for the ADOS and a lognormal distribution of LDOS. We find excellent quantitative agreements between the model and measured quantum capacitance for three disordered samples in a wide range of Fermi energies. Thus, by measuring the quantum capacitance, we can simultaneously determine the ADOS and its fluctuations. It is the LDOS fluctuations that cause the dramatic reduction of the quantum capacitance.
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.
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.
Scrape-off layer-induced beam density fluctuations and their effect on beam emission spectroscopy
NASA Astrophysics Data System (ADS)
Moulton, D.; Marandet, Y.; Tamain, P.; Dif-Pradalier, G.
2015-07-01
A statistical model is presented to calculate the magnitude of beam density fluctuations generated by a turbulent scrape-off layer (SOL). It is shown that the SOL can induce neutral beam density fluctuations of a similar magnitude to the plasma density fluctuations in the core, potentially corrupting beam emission spectroscopy measurements. The degree of corruption is quantified by combining simulations of beam and plasma density fluctuations inside a simulated measurement window. A change in pitch angle from the separatrix to the measurement window is found to reduce the effect of beam fluctuations, whose largest effect is to significantly reduce the measured correlation time.
Simulation of Density Fluctuation Intermittency in Decaying Kinetic Alfvén Wave Turbulence
NASA Astrophysics Data System (ADS)
Smith, Kurt; Terry, Paul
2006-10-01
We investigate the possibility that the distance-to-source scaling of the temporal width of pulsar signals is caused by intermittency in the turbulent density fluctuations of the interstellar medium. We simulate the small scales near the ion gyroradius where density fluctuations reach equipartition with the turbulent magnetic field in a kinetic Alfvén wave (KAW) cascade^1. Examination of decaying KAW turbulence using a fluid model establishes the presence of strong intermittency in the current fluctuation field, and a profile of Gaussian curvature of magnetic field that supports the theoretical prediction that the intermittent current filaments avoid turbulent mixing by refracting turbulent KAW activity away from filaments. The theory predicts correlated structures in electron density. These are observed but their intermittency is less pronounced. The role of parameter values, including the ratio of resistivity to density diffusivity, and the initial spectrum are explored to determine the effect on intermittency.^ ^1P.W. Terry, et al., Phys. Plasmas 8, 2707 (2001).
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.
Density fluctuations dispersion relationship for a polymer confined to a nanotube
Carpenter, Joshua H.; Karpusenko, Alena; Pan, Junhan; Lim, Shuang Fang; Riehn, Robert
2011-01-01
DNA confined to rigid nanotubes shows density fluctuations around its stretched equilibrium conformation. We report an experimental investigation of the length-scale dependent dynamics of these density fluctuations. We find that for highly elongated molecules a Rouse description is consistent with observations at sufficiently large length scales. We further find that for strongly fluctuating molecules, or short length scales, such Rouse modes cannot be detected due to strong mixing of fluctuation modes. PMID:21772582
Yates, T. F.; Ding, W. X.; Carter, T. A.; Brower, D. L.
2008-10-15
Fluctuations are expected to play an important role in anomalous particle, momentum, and energy transport for magnetic confinement devices. Magnetic and density fluctuations are simultaneously measured using a high-speed laser-based Faraday rotation-interferometry system with a bandwidth of 500 kHz and 8 cm chord spacing. Density fluctuation and magnetic fluctuation profiles are obtained by using a newly developed fitting procedure.
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.
Ion Density Fluctuations at the Kinetic Scale: Experimental Investigations
NASA Astrophysics Data System (ADS)
Nemecek, Z.; Safrankova, J.; Nemec, F.; Chen, C. H. K.
2014-12-01
It is well established that the solar wind undergoes a heating along its path through the solar system but the sources of this heating are still under debate. Among them, a gradual dissipation of large scale discontinuities toward smaller scales and, eventually, to the heat via turbulent cascades is frequently discussed.The contribution presents the analysis of ion density variations that are measured onboard the Spektr R spacecraft with a unique time resolution of 32 ms. The analysis reveals that (1) the mean frequency spectrum of density variations in the MHD range (up to about 0.05 Hz) is steeper than usually discussed -5/3, and (2) this part is followed by a plateau that is terminated near proton kinetic scales. We study the dependence of the slopes of different parts of the frequency spectra on background plasma parameters and discuss the results in view of present theories of Alfvenic turbulence in the solar wind.
Kramer, G.J.; Nazikian, R.; Valeo, E.
2001-02-10
The correlation between O-mode and X-mode reflectometer signals is studied with a 1-D reflectometer model taking into account the influence of finite density fluctuation levels and the upper hybrid resonance. It is found that a high level of O-X correlation can only be achieved for sufficiently small density fluctuation levels (typically much less than 1%) or very low magnetic field strengths. The influence of the upper hybrid resonance on the O-X correlation was found to also degrade the correlation between the O and X mode signals for very low magnetic field strengths or for very short density scale lengths. The extrapolation of these results to reactor-scale parameters indicates that the magnetic field strength can reliably be measured in the core plasma provided the density fluctuation level is typically much less than 1%.
Statistics of beam-driven waves in plasmas with ambient fluctuations: Reduced-parameter approach
Tyshetskiy, Yu.; Cairns, I. H.; Robinson, P. A.
2008-09-15
A reduced-parameter (RP) model of quasilinear wave-plasma interactions is used to analyze statistical properties of beam-driven waves in plasmas with ambient density fluctuations. The probability distribution of wave energies in such a system is shown to have a relatively narrow peak just above the thermal wave level, and a power-law tail at high energies, the latter becoming progressively more evident for increasing characteristic amplitude of the ambient fluctuations. To better understand the physics behind these statistical features of the waves, a simplified model of stochastically driven thermal waves is developed on the basis of the RP model. An approximate analytic solution for stationary statistical distribution of wave energies W is constructed, showing a good agreement with that of the original RP model. The 'peak' and 'tail' features of the wave energy distribution are shown to be a result of contributions of two groups of wave clumps: those subject to either very slow or very fast random variations of total wave growth rate (due to fluctuations of ambient plasma density), respectively. In the case of significant ambient plasma fluctuations, the overall wave energy distribution is shown to have a clear power-law tail at high energies, P(W){proportional_to}W{sup -{alpha}}, with nontrivial exponent 1<{alpha}<2, while for weak fluctuations it is close to the lognormal distribution predicted by pure stochastic growth theory. The model's wave statistics resemble the statistics of plasma waves observed by the Ulysses spacecraft in some interplanetary type III burst sources. This resemblance is discussed qualitatively, and it is suggested that the stochastically driven thermal waves might be a candidate for explaining the power-law tails in the observed wave statistics without invoking mechanisms such as self-organized criticality or nonlinear wave collapse.
Effects of stream-associated fluctuations upon the radial variation of average solar-wind parameters
NASA Technical Reports Server (NTRS)
Goldstein, B. E.; Jokipii, J. R.
1976-01-01
The effects of nonlinear fluctuations due to solar wind streams upon radial gradients of average solar wind parameters are computed, using a numerical MHD model for both spherically symmetric time dependent and corotating equatorial flow approximations. Significant effects of correlations are found between fluctuations upon the gradients of azimuthal magnetic fields, radial velocity, density and azimuthal velocity. Between 400 to 900 solar radii stream interactions have transferred the major portion of the angular momentum flux to the magnetic field; at even greater distances the plasma again carries the bulk of the angular momentum flux. The average azimuthal component of the magnetic field may decrease as much as 10% faster than the Archimedean spiral out to 6 AU due to stream interactions, but this result is dependent upon inner boundary conditions.
Leonard, T.; Lander, B.; Seifert, U.; Speck, T.
2013-11-28
We discuss the stochastic thermodynamics of systems that are described by a time-dependent density field, for example, simple liquids and colloidal suspensions. For a time-dependent change of external parameters, we show that the Jarzynski relation connecting work with the change of free energy holds if the time evolution of the density follows the Kawasaki-Dean equation. Specifically, we study the work distributions for the compression and expansion of a two-dimensional colloidal model suspension implementing a practical coarse-graining scheme of the microscopic particle positions. We demonstrate that even if coarse-grained dynamics and density functional do not match, the fluctuation relations for the work still hold albeit for a different, apparent, change of free energy.
NASA Astrophysics Data System (ADS)
Leonard, T.; Lander, B.; Seifert, U.; Speck, T.
2013-11-01
We discuss the stochastic thermodynamics of systems that are described by a time-dependent density field, for example, simple liquids and colloidal suspensions. For a time-dependent change of external parameters, we show that the Jarzynski relation connecting work with the change of free energy holds if the time evolution of the density follows the Kawasaki-Dean equation. Specifically, we study the work distributions for the compression and expansion of a two-dimensional colloidal model suspension implementing a practical coarse-graining scheme of the microscopic particle positions. We demonstrate that even if coarse-grained dynamics and density functional do not match, the fluctuation relations for the work still hold albeit for a different, apparent, change of free energy.
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.
Hirsch, M.; Hartfuss, H.; Geist, T.; de la Luna, E.
1996-05-01
A broadband heterodyne reflectometer operating in the frequency range 75{endash}110 GHz in extraordinary mode polarization is used at the W7-AS stellarator for both fast density profile determination and density fluctuation studies. The probing signal is amplitude modulated at a frequency 133 MHz using the envelope phase for profile evaluation and the carrier phase to determine the fluctuation information simultaneously. Separate Gaussian beam optics for final signal launch and detection permits a beam waist of about 2 cm at the reflecting layer in the plasma. Amplitude modulated detection is accomplished in the intermediate frequency part by synchronous detection after recovery of the carrier by narrow-band filtering. Voltage controlled solid state oscillators followed by active frequency multiplication allow to scan the full frequency band within less than 1 ms. For typical W7-AS operation the accessible density range is 1{times}10{sup 19} to 6{times}10{sup 19} m{sup {minus}3} for on axis magnetic field of 2.5 T and 4.5{times}10{sup 19} to 10{times}10{sup 19} m{sup {minus}3} for 1.25 T, respectively. The probed radial positions range between 0.2{lt}{ital r}/{ital a}{lt}1.1 depending on plasma conditions ({ital a}{approx_equal}17 cm). {copyright} {ital 1996 American Institute of Physics.}
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. PMID:25321700
Magnetic-Fluctuation-Induced Particle Transport and Density Relaxation in a High-Temperature Plasma
Ding, W. X.; Brower, D. L.; Fiksel, G.; Den Hartog, D. J.; Prager, S. C.; Sarff, J. S.
2009-07-10
The first direct measurement of magnetic-fluctuation-induced particle flux in the core of a high-temperature plasma is reported. Transport occurs due to magnetic field fluctuations associated with global tearing instabilities. The electron particle flux, resulting from the correlated product of electron density and radial magnetic fluctuations, accounts for density profile relaxation during a magnetic reconnection event. The measured particle transport is much larger than that expected for ambipolar particle diffusion in a stochastic magnetic field.
Reflectometer measurements of density fluctuations in tokamak plasmas
Nazikian, R.; Mazzucato, E.
1994-08-01
We show that many anomalous features observed in reflectometer measurements of turbulent fluctuations in tokamak plasmas, such as loss of coherent reflection, large amplitude fluctuations, large angular divergence of the reflected waves and correlation lengths of the order of the free space wavelength of the probe beam, can be explained by modeling the plasma fluctuations as a poloidally varying random phase grating located at the cutoff with a phase magnitude given by 1D geometric optics. A key result of our analysis is that the turbulence spectrum cannot be inferred from phase measurements when large amplitude fluctuations are observed at the receiver. However, the turbulence spectrum may still be recovered from phase measurements by use of imaging optics, and wide angle phase sensitive receivers.
DXA parameters: beyond bone mineral density.
Briot, Karine
2013-05-01
Dual-energy X-ray absorptiometry (DXA) is the reference standard for measuring bone mineral density (BMD) to diagnose osteoporosis. However, BMD measurement alone does not reliably predict the fracture risk. DXA can be used to assess other parameters (e.g. presence of vertebral fractures, bone microarchitecture, bone geometry, and body composition) simultaneously with BMD measurements, to help identify individuals at high fracture risk. Among these parameters, some are suitable for use in clinical practice, whereas others are reserved for research. Vertebral fracture assessment (VFA) is a very low radiation-dose method for detecting thoracic and lumbar vertebral fractures. Compared to standard radiography, VFA can be used in a broader population to detect asymptomatic vertebral fractures. The very good negative predictive value of VFA leads, in one-third of cases, to changes in patient management (drug treatment and prescription of radiographs). The trabecular bone score (TBS) is a noninvasively measured texture parameter that correlates with 3D bone microarchitecture parameters independently from BMD and that can be determined from lumbar-spine DXA images. Several cross-sectional studies and a prospective study established that the TBS was effective in identifying individuals with fractures. Additional studies will have to be performed to determine whether TBS determination can be recommended for everyday practice when treatment decisions are difficult. PMID:23622733
Effect of fluctuations on the onset of density-driven convection in porous media
NASA Astrophysics Data System (ADS)
Bestehorn, Michael; Firoozabadi, Abbas
2012-11-01
We study the dissolution of CO2 in saline aquifers. The long diffusion times can be accelerated by orders of magnitude from mass transfer that origins from convection. Convection occurs at a critical time via a phase transition from the horizontally homogeneous diffusion state. To start the instability, perturbations that break the horizontal translation symmetry are necessary. We start with the basic equations and the boundary conditions, examine the linearized equations around the diffusive time and z-dependent base state and compare different definitions of the critical time found in the literature. Taking a simple model we show the role of fluctuations for delayed instabilities if the control parameter is slowly swept through the bifurcation point. Apart from the critical time we use a "visible" time where convection is manifested in the vertical CO2 transport. We specify the perturbations with respect to their strength and length scale, and compute the critical times for various cases by numerical integration of the basic equations in two spatial dimensions. Fluctuating concentration at the upper boundary, fluctuating porosity as well fluctuating permeability are studied in detail. For the permeability fluctuation, the compressibility of the fluid becomes important and the velocity field cannot be derived from a stream function. Our work also includes non-isothermal conditions with a prescribed vertical geothermal gradient and space dependent thermal conductivity. Temperature fields for different standard configurations are computed numerically and serve as starting condition for density-driven convection. Based on our work, we conclude that the visible time is much larger than the critical time. The visible time is a strong function of strength and length scale of the perturbations.
Lower thermospheric density fluctuations during the time period of Typhoon Dinah
NASA Technical Reports Server (NTRS)
Hung, R. J.; Tsao, Y. D.; Johnson, D. L.; Chen, A. J.; Liu, J. M.
1989-01-01
High frequency Doppler sounder arrays were used to study the thermospheric density fluctuations caused by Typhoon Dinah in August, 1987. The results show that the maximum density fluctuations caused by the typhoon at altitudes of 150 to 350 km were close to + or - 30 percent deviation from the quiet background. The time-dependent density fluctuations were in phase with the horizontal phase velocity of major gravity waves excited by the storm. It is suggested that the study demonstrates the use of HF Doppler sounder measurement of gravity waves, horizontal wind velocity in the direction of gravity wave propagation, and density perturbations at thermospheric heights.
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.
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.
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.
Effects of turbulent fluctuations on density measurements with microwave reflectometry in tokamaks
Mazzucato, E.; Nazikian, R.
1994-08-01
The short-scale turbulence of tokamak plasmas has deleterious effects on the measurement of plasma density with microwave reflectometry. Density fluctuations may lead to large amplitude and phase modulations of the reflected wave which can impair the measurement of the wave group delay, and hence the determination of the plasma density. The role played by different types of turbulent fluctuations and the limitations imposed on microwave reflectometry are discussed in this paper.
Two dimensional density and its fluctuation measurements by using phase imaging method in GAMMA 10.
Yoshikawa, M; Negishi, S; Shima, Y; Hojo, H; Mase, A; Kogi, Y; Imai, T
2010-10-01
Two dimensional (2D) plasma image analysis is useful to study the improvement of plasma confinement in magnetically confined fusion plasmas. We have constructed a 2D interferometer system with phase imaging method for studying 2D plasma density distribution and its fluctuation measurement in the tandem mirror GAMMA 10. 2D profiles of electron density and its fluctuation have been successfully obtained by using this 2D phase imaging system. We show that 2D plasma density and fluctuation profiles clearly depends on the axial confining potential formation with application of plug electron cyclotron heating in GAMMA 10. PMID:21033869
Density fluctuations in thermal inflation and non-Gaussianity
Kawasaki, Masahiro; Takahashi, Tomo; Yokoyama, Shuichiro E-mail: tomot@cc.saga-u.ac.jp
2009-12-01
We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 e-folds after the standard inflation, the time of horizon-exit during inflation corresponding to the present observational scale shifts toward the end of inflation. It generally makes the primordial power spectrum more deviated from a scale-invariant one and hence renders some models inconsistent with observations. We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We show that, by adopting the mechanism, some inflation models can be liberated even in the presence of the thermal inflation. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario.
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.
NASA Astrophysics Data System (ADS)
Dubkov, Alexander A.; Kharcheva, Anna A.
2014-05-01
Two generalized Verhulst equations with non-Gaussian fluctuations of the reproduction rate and the volume of resources are under analytical investigation. For the first model, using the central limit theorem, we find the asymptotic behavior of the probability distribution of population density for an arbitrary non-Gaussian colored noise with nonzero power spectral density at zero frequency. Specifically, we confirm this result in the case of Markovian dichotomous noise and examine the evolution of mean population density. For fluctuating resources with one-sided stable distribution the transient dynamics of probability density function and statistical characteristics in the steady state are obtained. As shown, the scenario of the population's evolution depends on the parameter of nonlinearity in the original stochastic equation.
Measurements of ICRF wave-induced density fluctuations in LHD by a microwave reflectometer
NASA Astrophysics Data System (ADS)
Ejiri, A.; Tokuzawa, T.; Tsujii, N.; Saito, K.; Seki, T.; Kasahara, H.; Kamio, S.; Seki, R.; Mutoh, T.; Yamada, I.; Takase, Y.
2015-12-01
An O-mode microwave reflectometer has been developed to measure ICRF wave induced electron density fluctuations in LHD plasmas. The system has two probing frequencies (28.8 and 30.1 GHz) to measure two spatial points simultaneously. The rms density fluctuation levels are typically 0.01%. The linearity between the measured density fluctuation amplitude and the square root of the RF power is discussed. The decay length of the RF field was estimated to be 1 to 7 m under the operational condition investigated. A typical spatial distance between the two measurement points corresponding to the two probing frequencies is a few centimeters, and the fluctuation amplitudes at the two points are similar in amplitude. The phase difference between the two fluctuations show in-phase relationship on average. Out-of phase relationships, which implies a standing wave structure, are often observed when the wave absorption is expected to be poor.
Power spectral density of velocity fluctuations estimated from phase Doppler data
NASA Astrophysics Data System (ADS)
Jedelsky, Jan; Lizal, Frantisek; Jicha, Miroslav
2012-04-01
Laser Doppler Anemometry (LDA) and its modifications such as PhaseDoppler Particle Anemometry (P/DPA) is point-wise method for optical nonintrusive measurement of particle velocity with high data rate. Conversion of the LDA velocity data from temporal to frequency domain - calculation of power spectral density (PSD) of velocity fluctuations, is a non trivial task due to nonequidistant data sampling in time. We briefly discuss possibilities for the PSD estimation and specify limitations caused by seeding density and other factors of the flow and LDA setup. Arbitrary results of LDA measurements are compared with corresponding Hot Wire Anemometry (HWA) data in the frequency domain. Slot correlation (SC) method implemented in software program Kern by Nobach (2006) is used for the PSD estimation. Influence of several input parameters on resulting PSDs is described. Optimum setup of the software for our data of particle-laden air flow in realistic human airway model is documented. Typical character of the flow is described using PSD plots of velocity fluctuations with comments on specific properties of the flow. Some recommendations for improvements of future experiments to acquire better PSD results are given.
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).
Muneoka, Hitoshi; Urabe, Keiichiro; Stauss, Sven; Terashima, Kazuo
2015-04-01
Experimentally observed electrical breakdown voltages (U(B)) in high-pressure gases and supercritical fluids deviate from classical theories for low-pressure gas discharges, and the underlying breakdown mechanisms for the high-density fluids making the U(B) differ from those in the classical discharges are not yet well understood. In this study, we developed an electrical breakdown model for the high-density fluids taking into account the effects of density fluctuations and ion-enhanced field emission (IEFE). The model is based on the concept that a critical anomaly of the U(B) (local minimum near the critical point) is caused by long mean free electron path leading to a large first Townsend coefficient in locally low-density spatial domains generated by the density fluctuations. Also, a modified Paschen's curve considering the effect of the IEFE on the second Townsend coefficient was used to reproduce the U(B) curve in the high-density fluids. Calculations based on the novel model showed good agreements with the experimentally measured U(B) even near the critical point and it also suggested that the critical anomaly of the U(B) depends on the gap distance. These results indicate that both the density fluctuations and the IEFE have to be considered to comprehend the plasmas in high-density and density-fluctuating fluids. PMID:25974500
NASA Astrophysics Data System (ADS)
Muneoka, Hitoshi; Urabe, Keiichiro; Stauss, Sven; Terashima, Kazuo
2015-04-01
Experimentally observed electrical breakdown voltages (UB) in high-pressure gases and supercritical fluids deviate from classical theories for low-pressure gas discharges, and the underlying breakdown mechanisms for the high-density fluids making the UB differ from those in the classical discharges are not yet well understood. In this study, we developed an electrical breakdown model for the high-density fluids taking into account the effects of density fluctuations and ion-enhanced field emission (IEFE). The model is based on the concept that a critical anomaly of the UB (local minimum near the critical point) is caused by long mean free electron path leading to a large first Townsend coefficient in locally low-density spatial domains generated by the density fluctuations. Also, a modified Paschen's curve considering the effect of the IEFE on the second Townsend coefficient was used to reproduce the UB curve in the high-density fluids. Calculations based on the novel model showed good agreements with the experimentally measured UB even near the critical point and it also suggested that the critical anomaly of the UB depends on the gap distance. These results indicate that both the density fluctuations and the IEFE have to be considered to comprehend the plasmas in high-density and density-fluctuating fluids.
Power Spectral Density of Fluctuations of Bulk and Thermal Speeds in the Solar Wind
NASA Astrophysics Data System (ADS)
Šafránková, J.; Němeček, Z.; Němec, F.; Přech, L.; Chen, C. H. K.; Zastenker, G. N.
2016-07-01
This paper analyzes solar wind power spectra of bulk and thermal speed fluctuations that are computed with a time resolution of 32 ms in the frequency range of 0.001–2 Hz. The analysis uses measurements of the Bright Monitor of the Solar Wind on board the Spektr-R spacecraft that are limited to 570 km s‑1 bulk speed. The statistics, based on more than 42,000 individual spectra, show that: (1) the spectra of bulk and thermal speeds can be fitted by two power-law segments; (2) despite their large variations, the parameters characterizing frequency spectrum fits computed on each particular time interval are very similar for both quantities; (3) the median slopes of the bulk and thermal speeds of the segment attributed to the MHD scale are ‑1.43 and ‑1.38, respectively, whereas they are ‑3.08 and ‑2.43 in the kinetic range; (4) the kinetic range slopes of bulk and thermal speed spectra become equal when either the ion density or magnetic field strength are high; (5) the break between MHD and kinetic scales seems to be controlled by the ion β parameter; (6) the best scaling parameter for bulk and thermal speed variations is a sum of the inertial length and proton thermal gyroradius; and (7) the above conclusions can be applied to the density variations if the background magnetic field is very low.
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.
Quantum dynamics with non-Markovian fluctuating parameters
NASA Astrophysics Data System (ADS)
Goychuk, Igor
2004-07-01
A stochastic approach to the quantum dynamics randomly modulated in time by a discrete state non-Markovian noise, which possesses an arbitrary nonexponential distribution of the residence times, is developed. The formally exact expression for the Laplace-transformed quantum propagator averaged over the stationary realizations of such N -state non-Markovian noise is obtained. The theory possesses a wide range of applications. It includes some previous Markovian and non-Markovian theories as particular cases. In the context of the stochastic theory of spectral line shape and relaxation, the developed approach presents a non-Markovian generalization of the Kubo-Anderson theory of sudden modulation. In particular, the exact analytical expression is derived for the spectral line shape of optical transitions described by a Kubo oscillator with randomly modulated frequency which undergoes jumplike non-Markovian fluctuations in time.
Magnetic Fluctuations in Pair-Density-Wave Superconductors.
Christensen, Morten H; Jacobsen, Henrik; Maier, Thomas A; Andersen, Brian M
2016-04-22
Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d-wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La_{1.905}Ba_{0.095}CuO_{4} [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)]. PMID:27152819
Magnetic Fluctuations in Pair-Density-Wave Superconductors
NASA Astrophysics Data System (ADS)
Christensen, Morten H.; Jacobsen, Henrik; Maier, Thomas A.; Andersen, Brian M.
2016-04-01
Pair-density-wave superconductivity constitutes a novel electronic condensate proposed to be realized in certain unconventional superconductors. Establishing its potential existence is important for our fundamental understanding of superconductivity in correlated materials. Here we compute the dynamical magnetic susceptibility in the presence of a pair-density-wave ordered state and study its fingerprints on the spin-wave spectrum including the neutron resonance. In contrast to the standard case of d -wave superconductivity, we show that the pair-density-wave phase exhibits neither a spin gap nor a magnetic resonance peak, in agreement with a recent neutron scattering experiment on underdoped La1.905 Ba0.095 CuO4 [Z. Xu et al., Phys. Rev. Lett. 113, 177002 (2014)].
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.
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
NASA Astrophysics Data System (ADS)
Ikawa, Shohei; Tokumasu, Takashi; Tsuboi, Nobuyuki; Tsuda, Shinichi
2014-03-01
In this study, we investigated the principle of corresponding state on the density fluctuation around the critical points of non-polar diatomic fluids. We performed the Molecular Dynamics (MD) simulation for the extraction of the fluctuation structure around the critical points of 2-Center-Lennard-Jones (2CLJ) fluids, which have anisotropy depending on the molecular elongations. We estimated the fluctuation structure by two methods. One is the evaluation of the dispersion of the number of molecules at a certain domain, and the other is the calculation of static structure factor. As a result, in 2CLJ fluids that have shorter molecular elongations comparatively, the principle of corresponding state is satisfied because of the small differences in the fluctuation structure extracted in the present two methods. In addition, paying attention to the time variation of the density fluctuation, we confirmed that the characteristic frequency of the fluctuation is clearly lower around the critical point compared with the other conditions. Hereafter, we are going to calculate a dynamic structure factor, further investigating the principle of corresponding state of density fluctuation.
High Speed Digital Holography for Density and Fluctuation Measurements
ThomasJr., C. E.; Baylor, Larry R; Combs, Stephen Kirk; Meitner, Steven J; Rasmussen, David A; Granstedt, E. M.; Majeski, R.; Kaita, R.
2010-01-01
The state of the art in electro-optics has advanced to the point where digital holographic acquisition of wavefronts is now possible. Holographic wavefront acquisition provides the phase of the wavefront at every measurement point. This can be done with accuracy on the order of a thousandth of a wavelength, given that there is sufficient care in the design of the system. At wave frequencies which are much greater than the plasma frequency, the plasma index of refraction is linearly proportional to the electron density and wavelength, and the measurement of the phase of a wavefront passing through the plasma gives the chord-integrated density directly for all points measured on the wavefront. High-speed infrared cameras up to 40 000 fps at 644 pixels with resolutions up to 640512 pixels suitable for use with a CO2 laser are readily available, if expensive.
High speed digital holography for density and fluctuation measurements (invited)
Thomas, C. E. Jr.; Baylor, L. R.; Combs, S. K.; Meitner, S. J.; Rasmussen, D. A.; Granstedt, E. M.; Majeski, R. P.; Kaita, R.
2010-10-15
The state of the art in electro-optics has advanced to the point where digital holographic acquisition of wavefronts is now possible. Holographic wavefront acquisition provides the phase of the wavefront at every measurement point. This can be done with accuracy on the order of a thousandth of a wavelength, given that there is sufficient care in the design of the system. At wave frequencies which are much greater than the plasma frequency, the plasma index of refraction is linearly proportional to the electron density and wavelength, and the measurement of the phase of a wavefront passing through the plasma gives the chord-integrated density directly for all points measured on the wavefront. High-speed infrared cameras (up to {approx}40 000 fps at {approx}64x4 pixels) with resolutions up to 640x512 pixels suitable for use with a CO{sub 2} laser are readily available, if expensive.
NASA Astrophysics Data System (ADS)
Vaikuntanathan, Suriyanarayanan; Geissler, Phillip
2014-03-01
The physics of air-water interfaces plays a central role in modern theories of the hydrophobic effect such as the Lum-Chandler-Weeks (LCW) theory. 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. Specifically, through an analysis of the lattice gas model and related approximations, we identify a narrow parameter regime in which the lattice gas model can optimally be used to describe long wavelength liquid density fluctuations such as the capillary modes at a liquid-vapor interface. Coupling fluctuations in the lattice model to fluctuations on finer molecular scales through the least complicated realization of the LCW perspective, we obtain an effective Hamiltonian for lattice occupation variables in the presence of a hydrophobic solute. We show that this Hamiltonian - with no unknown parameters - in fact suffices to describe quantitatively the the solvation of hydrophobic objects with various shapes and sizes. This model is uniquely well suited for exploring hydrophobic and interfacial phenomena that involve disparate length scales.
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.
Density fluctuation measurement using motional Stark effect optics in JT-60U
NASA Astrophysics Data System (ADS)
Suzuki, T.; Fujita, T.; Oyama, N.; Isayama, A.; Matsunaga, G.; Oikawa, T.; Asakura, N.; Takechi, M.
2006-10-01
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 0.5-1MHz. 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 0.69-2.2km/s along the MSE measurement points, the time lag and distance between adjacent channels being 67±35μs and 70mm, respectively.
Slow dynamics of ablated zone observed around the density fluctuation ridge of fluid medium
NASA Astrophysics Data System (ADS)
Koizumi, Masato; Kulinich, Sergei A.; Shimizu, Yoshiki; Ito, Tsuyohito
2013-12-01
In-situ shadowgraph images were recorded to follow and study processes during laser ablation of Sn targets in pressurized carbon dioxide medium. The dynamics of the low-density region with a bubble-like structure forming by ablated Sn in CO2 at different pressures was studied. The lifetime of the region is shown to be pressure-dependent, being the longest near the density fluctuation ridge of the medium, i.e., at 8.8 MPa at 40 °C. The present work is to report on the slower dynamics of ablated zone near the medium density fluctuation maximum, which can be used in nanoparticle synthesis and processing.
Analytic Approach to the Cloud-in-Cloud Problem for Non-Gaussian Density Fluctuations
NASA Astrophysics Data System (ADS)
Inoue, Kaiki Taro; Nagashima, Masahiro
2002-07-01
We revisit the cloud-in-cloud problem for non-Gaussian density fluctuations. We show that the extended Press-Schechter (EPS) formalism for non-Gaussian fluctuations has a flaw in describing mass functions regardless of the type of filtering. As an example, we consider non-Gaussian models in which density fluctuations at a point obey a χ2 distribution with ν degrees of freedom. We find that mass functions predicted by using an integral formula proposed by Jedamzik and Yano, Nagashima, and Gouda, properly taking into account correlation between objects at different scales, deviate from those predicted by using the EPS formalism, especially for strongly non-Gaussian fluctuations. Our results for the mass function at large mass scales are consistent with those by Avelino and Viana obtained from numerical simulations.
Goswami, Varun R; Getz, Lowell L; Hostetler, Jeffrey A; Ozgul, Arpat; Oli, Madan K
2011-08-01
Although ecologists have long recognized that certain mammalian species exhibit high-amplitude, often multiannual, fluctuations in abundance, their causes have remained poorly understood and the subject of intense debate. A key contention has been the relative role of density-dependent and density-independent processes in governing population dynamics. We applied capture-mark-recapture analysis to 25 years of monthly trapping data from a fluctuating prairie vole Microtus ochrogaster population in Illinois, USA, to estimate realized population growth rates and associated vital rates (survival and recruitment) and modeled them as a function of vole density and density-independent climatic variation. We also tested for phase dependence and seasonality in the effects of the above processes. Variation in the realized population growth rate was best explained by phase-specific changes in vole density lagged by one month and mean monthly temperatures with no time lags. The underlying vital rates, survival and recruitment, were influenced by the additive and interactive effects of phase, vole density, and mean monthly temperatures. Our results are consistent with the observation that large-scale population fluctuations are characterized by phase-specific changes in demographic and physiological characteristics. Our findings also support the growing realization that the interaction between climatic variables and density-dependent factors may be a widespread phenomenon, and they suggest that the direction and magnitude of such interactive effects may be phase specific. We conclude that density-dependent and density-independent climatic variables work in tandem during each phase of density fluctuations to drive the dynamics of fluctuating populations. PMID:21905434
Spectral density of velocity fluctuations under switching field conditions in graphene
NASA Astrophysics Data System (ADS)
Iglesias, J. M.; Martín, M. J.; Pascual, E.; Rengel, R.
2016-05-01
In this paper we present an analysis of the velocity fluctuations during transient regimes arising from an abrupt shift of the electric field in bulk monolayer graphene. For this purpose a material Ensemble Monte Carlo simulator is used to examine these fluctuations by means of the transient autocorrelation function and power spectral density. The evolution of these quantities as well as the non-stationary phenomena taking place during the transients is explained with a microscopic approach.
Salimullah, M.; Shah, H. A.; Murtaza, G.
2007-11-15
Dust charge fluctuation instability in a dusty plasma in the presence of equilibrium density and external/ambient static magnetic field inhomogeneities has been examined in detail. The plasma ions acquire a uniform drift speed due to the equilibrium magnetic field gradient. For strongly magnetized electrons and ions, the dust charge fluctuation effect is contributed dominantly by ion dynamics. This results in an instability when the ion drift speed exceeds the perpendicular phase velocity of the waves under consideration.
High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V
Werner, S.A.; Fawcett, E.; Elmiger, M.W.; Shirane, G.
1992-11-01
Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.
High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V
Werner, S.A. . Dept. of Physics); Fawcett, E. . Dept. of Physics); Elmiger, M.W.; Shirane, G. )
1992-01-01
Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.
Maps of the little bangs through energy density and temperature fluctuations
NASA Astrophysics Data System (ADS)
Basu, Sumit; Chatterjee, Rupa; Nandi, Basanta K.; Nayak, Tapan K.
2016-01-01
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.
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. PMID:26929092
Schlickeiser, R.
2012-01-15
A systematic calculation of the electromagnetic properties (Poynting vector, electromagnetic energy, and pressure) of the collective transverse fluctuations in unmagnetized plasmas with velocity-anisotropic plasma particle distributions functions is presented. Time-averaged electromagnetic properties for monochromatic weakly damped wave-like fluctuations and space-averaged electromagnetic properties for monochromatic weakly propagating and aperiodic fluctuations are calculated. For aperiodic fluctuations, the Poynting vector as well as the sum of the space-averaged electric and magnetic field energy densities vanish. However, aperiodic fluctuations possess a positive pressure given by its magnetic energy density. This finite pressure density p{sub a} of aperiodic fluctuations has important consequences for the dynamics of cosmic unmagnetized plasmas such as the intergalactic medium after reionization. Adopting the standard cosmological evolution model, we show that this additional pressure changes the expansion law of the universe leading to further deceleration. Negative vacuum pressure counterbalances this deceleration to an accelerating universe provided that the negative vacuum pressure is greater than 1.5p{sub a}, which we estimate to be of the order 2.1 {center_dot} 10{sup -16} dyn cm{sup -2}.
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.
NASA Astrophysics Data System (ADS)
Higdon, J. C.
1984-10-01
A model of anisotropic magnetogasdynamic turbulence is developed in order to investigate quantitatively a turbulent fluid origin for the small spatial scale density fluctuations observed in 1981 by Armstrong, Cordes, and Rickett in the interstellar medium. The anisotropy at these small spatial scales results from the presence of a large-scale approximately uniform magnetic field that is a sum of the steady-state galactic magnetic field and the large-scale turbulent magnetic field fluctuations. The observed density fluctuations are interpreted to be two-dimensional isobaric entropy variations with oppositely directed gradients in temperature and density projected transverse to the local approximately uniform magnetic field. Three possible sites - cloud shell H II regions, diffuse H II regions produced by O stars, and the tenuous intercloud medium - are investigated as possible locations for turbulent flows.
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. PMID:17677596
Impact of parameter fluctuations on RF stability performance of DG tunnel FET
NASA Astrophysics Data System (ADS)
Sivasankaran, K.; Mallick, P. S.
2015-08-01
This paper presents the impact of parameter fluctuation due to process variation on radio frequency (RF) stability performance of double gate tunnel FET (DG TFET). The influence of parameter fluctuation due to process variation leads to DG TFET performance degradation. The RF figures of merit (FoM) such as cut-off frequency (ft), maximum oscillation frequency (fmax) along with stability factor for different silicon body thickness, gate oxide thickness and gate contact alignment are obtained from extracted device parameters through numerical simulation. The impact of parameter fluctuation of silicon body thickness, gate oxide thickness and gate contact alignment was found significant and the result provides design guidelines of DG TFET for RF applications.
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.
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.
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.
Characterisation of SOL density fluctuations in front of the LHCD PAM launcher in Tore
Oosako, T.; Ekedahl, A.; Goniche, M.; Achard, J.; Decker, J.; Peysson, Y.
2011-12-23
The density fluctuations, modified by Lower Hybrid Wave (LHW), is analyzed in Tore Supra with reference to the injected LHW power, density and the gap between LCFS (Last Closed Flux Surface) and the PAM (passive-active-multijunction) launcher. The density fluctuations are measured with RF probes installed at the PAM launcher front. A density scan at nominal toroidal field (3.8 T) shows that the fluctuations rate stays nearly constant ({approx}50%) for
Nanoscale density fluctuations in swift heavy ion irradiated amorphous SiO{sub 2}
Kluth, P.; Giulian, R.; Ridgway, M. C.; Pakarinen, O. H.; Djurabekova, F.; Nordlund, K.; Byrne, A. P.
2011-12-15
We report on the observation of nanoscale density fluctuations in 2 {mu}m thick amorphous SiO{sub 2} layers irradiated with 185 MeV Au ions. At high fluences, in excess of approximately 5 x 10{sup 12} ions/cm{sup 2}, where the surface is completely covered by ion tracks, synchrotron small angle x-ray scattering measurements reveal the existence of a steady state of density fluctuations. In agreement with molecular dynamics simulations, this steady state is consistent with an ion track ''annihilation'' process, where high-density regions generated in the periphery of new tracks fill in low-density regions located at the center of existing tracks.
Mukamel, Shaul
2005-02-01
Time-ordered superoperators are used to develop a unified description of nonlinear density response and spontaneous fluctuations of many-electron systems. The pth-order density response functions are decomposed into 2{sup p+1} non-causal Liouville space pathways. Individual pathways are symmetric to the interchange of their space, time, and superoperator indices and can thus be calculated as functional derivatives. Other combinations of these pathways represent spontaneous density fluctuations and the response of such fluctuations to an external field. The resolution of the causality paradox of time-dependent density-functional theory (TDDFT) is shown to be intimately connected with the nonretarded nature of fluctuations.
NASA Astrophysics Data System (ADS)
Saravia, Eduardo
A Heavy Ion Beam Probe Diagnostic System with dual energy analyzers was used to measure potential, pressure and density fluctuations in RENTOR. The main advantage of the system is the capability to measure directly the correlation length of the fluctuations by varying the primary beam injection conditions. Broadband density and potential spectra obtained in these experiments are characteristics of turbulent plasmas, with most of the power concentrated in the low part of the spectrum, below 100 kHz. The spectra fall off as f^{rm -n}, where the power-index n is approximately 3.5. The density fluctuation levels n/n are about 10% and they are independent of the plasma radius. Pressure and density fluctuations in RENTOR scale approximately like 3rho_ {rm s}/L_{rm p}~ 0.06, except for points near the plasma center. This is in agreement with the scaling observed in other small and medium tokamak experiments. Strong potential fluctuations were measured all across the plasma with levels nearly ten times larger than the corresponding n/n values. These results agree with the prediction that e~{phi }/k_{rm B}T _{rm e} > n/n in the resistive-MHD rippling mode theory developed by Thayer and Diamond. An rms value for the poloidal correlation length l_{rm c} ~sigma_{rm k}^ {-1} of about 5 mm is obtained for sample points in the plasma interior. The total particle flux across the field lines due to electrostatic fluctuations was estimated at 3 times 10 ^{19} particles/sec, which yields an estimate for the particle confinement time of tau_{rm p}~ 2 ms. Similarly, the total heat loss rate due to fluctuations was estimated at 12 times 10 ^{20} eV/sec, which gives an energy confinement time of tau_{rm E}~ 1 ms. The results clearly indicate that the particle and energy losses in RENTOR due to electrostatic fluctuations of the plasma account for a very significant part of the limited plasma confinement. The results of the experiments performed in this thesis have demonstrated the
Short-term variations in gene flow related to cyclic density fluctuations in the common vole.
Gauffre, Bertrand; Berthier, Karine; Inchausti, Pablo; Chaval, Yannick; Bretagnolle, Vincent; Cosson, Jean-François
2014-07-01
In highly fluctuating populations with complex social systems, genetic patterns are likely to vary in space and time due to demographic and behavioural processes. Cyclic rodents are extreme examples of demographically instable populations that often exhibit strong social organization. In such populations, kin structure and spacing behaviour may vary with density fluctuations and impact both the composition and spatial structure of genetic diversity. In this study, we analysed the multiannual genetic structure of a cyclic rodent, Microtus arvalis, using a sample of 875 individuals trapped over three complete cycles (from 1999 to 2007) and genotyped at 10 microsatellite loci. We tested the predictions that genetic diversity and gene flow intensity vary with density fluctuations. We found evidences for both spatial scale-dependant variations in genetic diversity and higher gene flow during high density. Moreover, investigation of sex-specific relatedness patterns revealed that, although dispersal is biased toward males in this species, distances moved by both sexes were lengthened during high density. Altogether, these results suggest that an increase in migration with density allows to restore the local loss of genetic diversity occurring during low density. We then postulate that this change in migration results from local competition, which enhances female colonization of empty spaces and male dispersal among colonies. PMID:24888708
Density fluctuations in a quasi-one-dimensional Bose gas as observed in free expansion
NASA Astrophysics Data System (ADS)
Gawryluk, Krzysztof; Gajda, Mariusz; Brewczyk, Mirosław
2015-10-01
We study, within the framework of the classical-field approximation, the density correlations of a weakly interacting expanding Bose gas for the whole range of temperatures across the Bose-Einstein condensation threshold. We focus on elongated quasi-one-dimensional systems where there is a huge discrepancy between the existing theory and experimental results [A. Perrin et al., Nat. Phys. 8, 195 (2012), 10.1038/nphys2212]. We find that the density correlation function is not reduced for temperatures below the critical one as it is predicted for the ideal gas or for a weakly interacting system within the Bogoliubov approximation. This behavior of the density correlations agrees with the above-mentioned experiment with the elongated system. Although the system was much larger than that studied here, we believe that the behavior of the density correlation function found there is quite generic. Our theoretical study indicates also large density fluctuations in the trap in the quasicondensate regime where only phase fluctuations were expected. We argue that the enhanced density fluctuations can originate in the presence of interactions in the system, or more precisely in the presence of spontaneous dark solitons in the elongated gas at thermal equilibrium.
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.
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.
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.
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
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.
Size scaling effects on the particle density fluctuations in confined plasmas
Vazquez, Federico; Markus, Ferenc
2009-11-15
In this paper, memory and nonlocal effects on fluctuating mass diffusion are addressed in the context of fusion plasmas. Nonlocal effects are included by considering a diffusivity coefficient depending on the size of the container in the transverse direction to the applied magnetic field. It is obtained by resorting to the general formulation of the extended version of irreversible thermodynamics in terms of the higher order dissipative fluxes. The developed model describes two different types of the particle density time correlation function. Both have been observed in tokamak and nontokamak devices. These two kinds of time correlation function characterize the wave and the diffusive transport mechanisms of particle density perturbations. A transition between them is found, which is controlled by the size of the container. A phase diagram in the (L,2{pi}/k) space describes the relation between the dynamics of particle density fluctuations and the size L of the system together with the oscillating mode k of the correlation function.
Field equation of the correlation function of mass-density fluctuations for self-gravitating systems
NASA Astrophysics Data System (ADS)
Zhang, Yang; Chen, Qing
2015-09-01
We study the mass-density distribution of Newtonian self-gravitating systems. Modeling the system as a fluid in hydrostatical equilibrium, we obtain from first principles the field equation and its solution of the correlation function ξ(r) of the mass-density fluctuation itself. We apply this to studies of the large-scale structure of the Universe within a small redshift range. The equation shows that ξ(r) depends on the point mass m and the Jeans wavelength scale λ0, which are different for galaxies and clusters. It explains several long-standing prominent features of the observed clustering: that the profile of ξcc(r) of clusters is similar to ξgg(r) of galaxies, but with a higher amplitude and a longer correlation length, and that the correlation length increases with the mean separation between clusters as a universal scaling r0 ≃ 0.4d. Our solution ξ(r) also shows that the observed power-law correlation function of galaxies ξgg(r) ≃ (r0/r)1.7 is only valid in a range 1
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)
Cranmer, Steven R.
2016-05-01
The solar corona has been revealed in the past few decades to be a highly dynamic nonequilibrium plasma environment. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be strongly turbulent, and models that invoke the dissipation of incompressible Alfvenic fluctuations have had some success in explaining the heating. However, many of these models neglect the mounting evidence that density and pressure variations may play an important role in the mass and energy balance of this system. In this presentation I will briefly review observations of both compressible and incompressible MHD fluctuations in the corona and solar wind, and discuss future prospects with DKIST. I will also attempt to outline the many ways that these different fluctuation modes have been proposed to interact with one another -- usually with an eye on finding ways to enhance their dissipation and heating. One under-appreciated type of interaction is the fact that Alfven waves will undergo multiple reflections and refractions in a "background plasma" filled with localized density fluctuations. It is becoming increasingly clear that models must not only include the effects of longitudinal variability (e.g., magnetoacoustic waves and pulse-like jets) but also transverse "striations" that appear naturally in a structured magnetic field with small-scale footpoint variability. Future off-limb observations, such as those with DKIST's Cryo-NIRSP instrument, will be crucial for providing us with a detailed census of MHD waves and their mutual interactions in the corona.
Quantifying Density Fluctuations in Water at a Hydrophobic Surface: Evidence for Critical Drying
NASA Astrophysics Data System (ADS)
Evans, Robert; Wilding, Nigel B.
2015-07-01
Employing smart Monte Carlo sampling techniques within the grand canonical ensemble, we investigate the properties of water at a model hydrophobic substrate. By reducing the strength of substrate-water attraction, we find that fluctuations in the local number density, quantified by a rigorous definition of the local compressibility χ (z ) , increase rapidly for distances z within one or two molecular diameters from the substrate as the degree of hydrophobicity, measured by the macroscopic contact angle θ , increases. Our simulations provide evidence for a continuous (critical) drying transition as the substrate-water interaction becomes very weak: cos (θ )→-1 . We speculate that the existence of such a transition might account for earlier simulation observations of strongly enhanced density fluctuations.
NASA Technical Reports Server (NTRS)
Gross, K. P.; Mckenzie, R. L.; Logan, P.
1987-01-01
A laser-induced fluorescence method has been developed that provides simultaneous measurements of temperature, density, and their fluctuations owing to turbulence in unheated compressible flows. Pressure and its fluctuations are also deduced using the equation of state. Fluorescence is induced in nitric oxide that has been seeded into a nitrogen flow in concentrations of 100 ppm. Measurements are obtained from each laser pulse, with a spatial resolution of 1 mm and a temporal resolution of 125 ns. The method was applied to a supersonic, turbulent, boundary-layer flow with a free-stream Mach number of 2. For stream conditions in the range from 150-300 K and 0.3-1 atm, temperature is measured with an uncertainty of approximately 1 percent rms, while density and pressure uncertainties are approximately 2 percent rms.
Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.
Ambrosetti, Alberto; Ferri, Nicola; DiStasio, Robert A; Tkatchenko, Alexandre
2016-03-11
Recent experiments on noncovalent interactions at the nanoscale have challenged the basic assumptions of commonly used particle- or fragment-based models for describing van der Waals (vdW) or dispersion forces. We demonstrate that a qualitatively correct description of the vdW interactions between polarizable nanostructures over a wide range of finite distances can only be attained by accounting for the wavelike nature of charge density fluctuations. By considering a diverse set of materials and biological systems with markedly different dimensionalities, topologies, and polarizabilities, we find a visible enhancement in the nonlocality of the charge density response in the range of 10 to 20 nanometers. These collective wavelike fluctuations are responsible for the emergence of nontrivial modifications of the power laws that govern noncovalent interactions at the nanoscale. PMID:26965622
NASA Technical Reports Server (NTRS)
Martin, R. A.
1979-01-01
Scalar density fluctuations were measured nonintrusively in the shear layer of a 5.08-cm (2-in.) cold air jet using a crossed-beam schlieren method. Two statistics, covariance and three-dimensional spectrum function, were estimated for an exit Mach number range of 0.3 to 0.97. The density fluctuation intensity, integral scale, and eddy convection speed were calculated and compared to available data where possible. Spectra were found to change significantly in shape becoming less peaked between 3 and 9 jet diameters downstream from the orifice, but they consistently exhibited a -5/3 power law decay at 3, 6, and 9 diameters for frequencies above the peak.
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.
Density fluctuations and radiated noise for a high-temperature supersonic jet
NASA Technical Reports Server (NTRS)
Parthasarathy, S. P.; Massier, P. F.; Cuffel, R. F.; Radbill, J. R.
1975-01-01
Experimental data on density fluctuations were obtained by the laser Schlieren method in a supersonic jet which at the nozzle exit had a Mach number of 1.43 and a stagnation temperature of about 1090 K. The jet emerged into the ambient atmosphere in an anechoic chamber, correctly expanded from a nozzle which had an exit diameter of 10.8 cm. Using the information on the density fluctuations and the mean shear obtained by probes, the autocorrelation of the radiated noise was calculated by a theory that is suitable for Mach wave emission. This theory is a modification of that developed by Ffowcs Williams and Maidanik (1965). The calculated noise field agrees well with that obtained by using microphones outside the jet.
Space-potential and density fluctuations in the ISX-B tokamak
Hallock, G.A.; Wootton, A.J.; Hickok, R.L.
1987-09-21
The fluctuating plasma potential and electron density has been measured in Ohmic and neutral-beam--heated tokamak discharges. Radial profiles are presented in the outer two-thirds of the plasma, and the E x B transport calculated. The transport is found to be an order of magnitude larger for beam driven plasmas. Measurements indicate the linearized Boltzman equation is satisfied in the interior, but not at the plasma edge.
Tokuzawa, T.; Kawahata, K.; Ejiri, A.
2010-10-15
In order to measure the internal structure of density fluctuations using a microwave reflectometer, the broadband frequency tunable system, which has the ability of fast and stable hopping operation, has been improved in the Large Helical Device. Simultaneous multipoint measurement is the key issue of this development. For accurate phase measurement, the system utilizes a single sideband modulation technique. Currently, a dual channel heterodyne frequency hopping reflectometer system has been constructed and applied to the Alfven eigenmode measurements.
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.
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.
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.
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.
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.
Lin, L. Ding, W. X.; Brower, D. L.
2014-11-15
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)
Li, Y. G.; Zhou, Y.; Li, Y.; Wang, H. X.; Deng, Z. C.; Yi, J.; Ji, X. Q.; HL-2A Team
2016-02-01
Based on the fact that the scattered power is proportional to the square of the electron density fluctuation amplitude, the four-channel formic acid (HCOOH, λ=432.5 um) laser interferometer has been firstly upgraded to measure the far-forward collective scattering (FCS) from the electron density fluctuation (ñe) on HL-2A tokamak in 2014-15 experimental campaign. The HCOOH-FCS system provides the line-integrated measurement of fluctuations covering the wavenumber range: k⊥ <1.6 cm-1 (perpendicular to the magnetic field). A lot of electron density fluctuations have been successfully measured by the HCOOH-FCS. In especial, the high-frequency density fluctuation (up to 500 kHz) induced by the core-localized Alfvénic eigenmode (AE) has been observed by the innermost scattering chord. The HCOOH-FCS system will be extremely helpful for the research of energetic particles instability on HL-2A.
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
NASA Astrophysics Data System (ADS)
Chen, Xiaolong; Li, Wei; Wang, Lin; He, Yuheng; Wu, Zefei; Cai, Yuan; Zhang, Mingwei; Wang, Yang; Han, Yu; Lortz, Rolf W.; Zhang, Zhao-Qing; Sheng, Ping; Wang, Ning
2013-03-01
We demonstrate that local fluctuations of the density of states (DOS) in strongly disordered graphene play an important role in determining the quantum capacitance of the top-gate device geometry. Depending on the strength of the disorder induced by metal-cluster decoration, the measured quantum capacitance of disordered graphene could dramatically decrease in comparison with pristine graphene (previous work on transport of metal-cluster decoration has been published on Phys. Rev. B 84, 045431, 2011). A quantitative model for correlating fluctuations of local density of states with the disorder strength and quantum capacitance is presented and discussed. The DOS of disordered graphene obeys a non-universal power law. By measuring the quantum capacitance of disordered graphene, we simultaneously determined both the DOS and its local fluctuations, which is in agreement with the lognormal distributions reported previously for localized samples. Financial support from the Research Grants Council of Hong Kong (Project Nos. HKUST9/CRF/08, 604112) and technical support of the Raith-HKUST Nanotechnology Laboratory (Project No. SEG_HKUST08) are hereby acknowledged.
Dominguez, Luis Garcia; Nenadovic, Vera; Wennberg, Richard A.
2010-01-01
The identification of epileptic seizure precursors has potential clinical relevance. It is conjectured that seizures may be represented by dynamical bifurcations and that an adequate order parameter to characterize brain dynamics is the phase difference in the oscillatory activity of neural systems. In this study, the critical point hypothesis that seizures, or more generally periods of widespread high synchronization, represent bifurcations is empirically tested by monitoring the growth of fluctuations in the putative order parameter of phase differences between magnetoencephalographic and electroencephalographic signals in nearby brain regions in patients with epilepsy and normal subjects during hyperventilation. Implications of the results with regard to epileptic phenomena are discussed. PMID:22210968
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
Density fluctuations in saturated phospholipid bilayers increase as the acyl-chain length decreases.
Ipsen, J H; Jørgensen, K; Mouritsen, O G
1990-01-01
A systematic computer simulation study is conducted for a model of the main phase transition of fully hydrated saturated diacyl phosphatidylcholine bilayers (DMPC, DPPC, and DSPC). With particular focus on the fluctuation effects on the thermal properties in the transition region, the study yields data for the specific heat, the lateral compressibility, and the lipid-domain size distribution. Via a simple model assumption the transmembrane passive ion permeability is derived from the lipid-domain interfacial measure. A comparative analysis of the various data shows, in agreement with a number of experiments, that the lateral density fluctuations and hence the response functions increase as the acyl-chain length is decreased. Images FIGURE 2 PMID:2291936
Fluctuation effects on the Raman scattering from the charge-density-wave system TTF-TCNQ
NASA Astrophysics Data System (ADS)
Lin, Y.; Eldridge, J. E.
1998-08-01
The resonant Raman spectrum of TTF-TCNQ has been measured from room temperature to 10 K, using a Fourier Raman spectrometer. Only features due to the TCNQ molecule are observed. New Raman lines appear at temperatures below 150 K as the fluctuating charge-density wave (CDW) occurs. The intensity of the new Raman lines increases with decreasing temperature. In addition to the Raman allowed modes, we observe numerous lines originating from the usually infrared-active-only modes, which become Raman active via the Fröhlich interaction in the fluctuating and static CDW phases. The appearance of the strong out-of-plane intramolecular B3u vibrational modes of TCNQ confirms an earlier x-ray study that found that the CDW on the TCNQ chain involved such an out-of-plane distortion of the TCNQ molecule. The condensation of the longitudinal acoustic phonon is also observed in the Raman spectrum.
Quantum Lattice Fluctuations in the Charge Density Wave State beyond the Adiabatic Approximation
NASA Astrophysics Data System (ADS)
Shida, Keisuke; Watanabe, Yuko; Gomi, Hiroki; Takahashi, Akira; Tomita, Norikazu
2015-12-01
We have developed a tractable numerical method in which large-amplitude quantum lattice fluctuations can be described beyond the adiabatic approximation using the coherent state representation of phonons. A many-body wave function is constructed by the superposition of direct products of non-orthogonal Slater determinants for electrons and coherent states of phonons. Both orbitals in all the Slater determinants and the amplitudes of all the coherent states are simultaneously optimized. We apply the method to the one-dimensional Su-Schrieffer-Heeger model with the on-site and nearest-neighbor-site Coulomb interactions. It is shown the lattice fluctuations in doped charge density wave (CDW) systems are described by the translational and vibrational motion of lattice solitons. Such lattice solitons induce bond alternation in the doped CDW system while the lattice becomes equidistant in the half-filled CDW system.
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
2009-08-01
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. PMID:19792547
Scaling Laws of Turbulence and Heating of Fast Solar Wind: The Role of Density Fluctuations
Carbone, V.; Sorriso-Valvo, L.; 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 Alfvenic 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.
Incommensurate charge density fluctuations in underdoped YBCO detected by resonant x-ray scattering
NASA Astrophysics Data System (ADS)
Ghiringhelli, Giacomo
2013-03-01
A key issue in high Tc superconductivity is the short and mid range ordering of spin and charge degrees of freedom when doping disrupts the long range antiferromagnetic order of parent compounds. Cu sites are the main, although not the only, actors in the play. Inelastic and elastic scattering of x rays, when performed at the Cu L3 absorption resonance, can be used to map the spin and charge excitation spectra and, simultaneously, to unveil the presence of spatial modulations in the charge or spin densities. We have used angle-resolved resonant inelastic soft x-ray scattering (RIXS) and resonant elastic soft x-ray scattering (REXS) to identify two-dimensional charge fluctuations with an incommensurate periodicity of ~ 3 . 2 lattice units in the copper oxide planes of the superconductors (Y,Nd)Ba2Cu3O6+x with hole concentrations 0 . 09 < p < 0 . 13 per planar Cu ion [G. Ghiringhelli et al, Science 337, 821 (2012)]. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, Tc; further cooling below Tc abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity. Further measurements on an Ortho III sample have confirmed that the charge fluctuations are independent of the chain ordering [A. J. Achkar et al, Phys. Rev. Lett. 109, 167001 (2012)]. Put into perspective, these results show that often elastic and inelastic x-ray scattering experiments should be ideally performed jointly, to explore with the greatest sensitivity charge and spin fluctuations [L. Braicovich et al, Phys. Rev. Lett. 104, 077002, (2010)].
Large-scale fluctuations in the number density of galaxies in independent surveys of deep fields
NASA Astrophysics Data System (ADS)
Shirokov, S. I.; Lovyagin, N. Yu.; Baryshev, Yu. V.; Gorokhov, V. L.
2016-06-01
New arguments supporting the reality of large-scale fluctuations in the density of the visible matter in deep galaxy surveys are presented. A statistical analysis of the radial distributions of galaxies in the COSMOS and HDF-N deep fields is presented. Independent spectral and photometric surveys exist for each field, carried out in different wavelength ranges and using different observing methods. Catalogs of photometric redshifts in the optical (COSMOS-Zphot) and infrared (UltraVISTA) were used for the COSMOS field in the redshift interval 0.1 < z < 3.5, as well as the zCOSMOS (10kZ) spectroscopic survey and the XMM-COSMOS and ALHAMBRA-F4 photometric redshift surveys. The HDFN-Zphot and ALHAMBRA-F5 catalogs of photometric redshifts were used for the HDF-N field. The Pearson correlation coefficient for the fluctuations in the numbers of galaxies obtained for independent surveys of the same deep field reaches R = 0.70 ± 0.16. The presence of this positive correlation supports the reality of fluctuations in the density of visible matter with sizes of up to 1000 Mpc and amplitudes of up to 20% at redshifts z ~ 2. The absence of correlations between the fluctuations in different fields (the correlation coefficient between COSMOS and HDF-N is R = -0.20 ± 0.31) testifies to the independence of structures visible in different directions on the celestial sphere. This also indicates an absence of any influence from universal systematic errors (such as "spectral voids"), which could imitate the detection of correlated structures.
Void alignment and density profile applied to measuring cosmological parameters
NASA Astrophysics Data System (ADS)
Dai, De-Chang
2015-12-01
We study the orientation and density profiles of the cosmological voids with Sloan Digital Sky Survey (SDSS; Ahn et al.) 10 data. Using voids to test Alcock-Paczynski effect has been proposed and tested in both simulations and actual SDSS data. Previous observations imply that there exist an empirical stretching factor which plays an important role in the voids' orientation. Simulations indicate that this empirical stretching factor is caused by the void galaxies' peculiar velocities. Recently Hamaus et al. found that voids' density profiles are universal and their average velocities satisfy linear theory very well. In this paper, we first confirm that the stretching effect exists using independent analysis. We then apply the universal density profile to measure the cosmological parameters. We find that the void density profile can be a tool to measure the cosmological parameters.
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.
NASA Astrophysics Data System (ADS)
Tadić, Bosiljka; Thurner, Stefan; Rodgers, G. J.
2004-03-01
We study the microscopic time fluctuations of traffic load and the global statistical properties of a dense traffic of particles on scale-free cyclic graphs. For a wide range of driving rates R the traffic is stationary and the load time series exhibits antipersistence due to the regulatory role of the superstructure associated with two hub nodes in the network. We discuss how the superstructure affects the functioning of the network at high traffic density and at the jamming threshold. The degree of correlations systematically decreases with increasing traffic density and eventually disappears when approaching a jamming density Rc. Already before jamming we observe qualitative changes in the global network-load distributions and the particle queuing times. These changes are related to the occurrence of temporary crises in which the network-load increases dramatically, and then slowly falls back to a value characterizing free flow.
Freeze-out parameters from electric charge and baryon number fluctuations: is there consistency?
Borsanyi, S; Fodor, Z; Katz, S D; Krieg, S; Ratti, C; Szabo, K K
2014-08-01
Recent results for moments of multiplicity distributions of net protons and net-electric charge from the STAR Collaboration are compared to lattice QCD results for higher order fluctuations of baryon number and electric charge by the Wuppertal-Budapest Collaboration, with the purpose of extracting the freeze-out temperature and chemical potential. All lattice simulations are performed for a system of 2+1 dynamical quark flavors, at the physical mass for light and strange quarks; all results are continuum extrapolated. We show that it is possible to extract an upper value for the freeze-out temperature, as well as precise baryochemical potential values corresponding to the four highest collision energies of the experimental beam energy scan. Consistency between the freeze-out parameters obtained from baryon number and electric charge fluctuations is found. The freeze-out chemical potentials are now in agreement with the statistical hadronization model. PMID:25126910
Phase Separation, Density Fluctuations, and Boiling Near the Liquid-Gas Critical Point
NASA Astrophysics Data System (ADS)
Hegseth, John; Oprisan, Ana; Roy, Arun; Nikolayev, Vadim; Beysens, Daniel; Garrabos, Yves; Lecoutre-Chabot, Carole
2002-11-01
A pure liquid-gas mixture is one of the simplest examples of a soft-matter system. In fact, when co-existing gas and liquid phases of pure fluid are heated to their critical point, large-scale density fluctuations make the fluid extremely compressible (to external forces), expandable (to heating), slows the diffusive transport, and decreases the surface tension. In principle these properties and others either diverge to infinity or converge to zero at the critical temperature. These properties lead to some very unusual behavior: large density gradients at the laboratory scale, a large mechanical response to heating, and perfect wetting of a solid wall by the liquid phase (zero contact-angle). We have further simplified this system by performing experiments in weightlessness (Mir spaces station). By controlling the fluid's temperature, these properties may be varied over large ranges in a single sample. When the fluid is driven out of equilibrium by a fast temperature quench from the single-phase (supercritical fluid) state into the two-phase state, we have observed universal growth laws of minority domains (gas bubbles) during phase separation. Prior to this quench we have also observed density fluctuations using optical microscopy near the critical point. When heat is applied to a liquid-gas mixture, we have observed a spectacular spreading of a gas bubble along a hot solid wall as well as gas bubble over-heating (where the interior of a gas bubble gains a higher temperature than the heating wall). Although this gas phase over-heating appears to violate the second law, it is really a transient our-of-equilibrium effect. Inside of these unusual bubbles we also have observed unusually large variations in liquid wetting film thickness that often appear to evolve into spreading contact lines on the sapphire wall when heat is applied. We have observed coarsening and growth of minority domains (gas bubbles) in SF6 near its liquid-gas critical point. Phase separation in
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.
Hecksher, Tina
2016-04-28
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. PMID:27131521
NASA Technical Reports Server (NTRS)
Basu, Sunanda; Mackenzie, E.; Basu, Santimay; Fougere, P. F.; Maynard, N. C.; Coley, W. R.; Hanson, W. B.; Winningham, J. D.; Sugiura, M.; Hoegy, W. R.
1988-01-01
A detailed study is presented of simultaneous density and electric field fluctuation spectra over a large-scale length range seen in association with large structured convective plasma flows, field-aligned currents, and particle precipitation at high latitudes. The data were obtained for two Dynamics Explorer 2 orbits at two different altitudes within the F region and the topside ionosphere. The observations are compared with results of nonlinear simulations of shear flow-driven instabilities and predictions based on two-dimensional turbulence arguments, with particular reference to the Kelvin-Helmholtz process.
Exact analytic solution for non-linear density fluctuation in a ΛCDM universe
NASA Astrophysics Data System (ADS)
Yoo, Jaiyul; Gong, Jinn-Ouk
2016-07-01
We derive the exact third-order analytic solution of the matter density fluctuation in the proper-time hypersurface in a ΛCDM universe, accounting for the explicit time-dependence and clarifying the relation to the initial condition. Furthermore, we compare our analytic solution to the previous calculation in the comoving gauge, and to the standard Newtonian perturbation theory by providing Fourier kernels for the relativistic effects. Our results provide an essential ingredient for a complete description of galaxy bias in the relativistic context.
NASA Astrophysics Data System (ADS)
Ravichandran, S.; Bagchi, Biman
1996-01-01
We have carried out a computer ``experiment'' of orientational relaxation in a spatially random and orientationally disordered dipolar lattice (RDL), generated by quenching only the translational motion of a dense liquid. In the high polarity limit, the orientational relaxation of the RDL is dramatically different from that of the parent liquid, the former exhibits a very slow, nonexponential long time decay of the orientational correlation functions and markedly non-Debye dielectric relaxation. These results clearly demonstrate the importance of spatial density fluctuations in orientational relaxation.
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.
Kharchev, Nikolay; Tanaka, Kenji; Kubo, Shin; Igami, Hiroe; Batanov, German; Petrov, Alexandr; Sarksyan, Karen; Skvortsova, Nina; Azuma, Yoshifumi; Tsuji-Iio, Shunji
2008-10-01
A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (k(s) approximately 34 cm(-1)) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose. PMID:19044538
Kharchev, Nikolay; Batanov, German; Petrov, Alexandr; Sarksyan, Karen; Skvortsova, Nina; Tanaka, Kenji; Kubo, Shin; Igami, Hiroe; Azuma, Yoshifumi; Tsuji-Iio, Shunji
2008-10-15
A version of the collective backscattering diagnostic using gyrotron radiation for small-scale turbulence is described. The diagnostic is used to measure small-scale (k{sub s}{approx_equal}34 cm{sup -1}) plasma density fluctuations in large helical device experiments on the electron cyclotron heating of plasma with the use of 200 kW 82.7 GHz heating gyrotron. A good signal to noise ratio during plasma production phase was obtained, while contamination of stray light increased during plasma build-up phase. The effect of the stray radiation was investigated. The available quasioptical system of the heating system was utilized for this purpose.
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.
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.
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. PMID:22861861
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
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.
NASA Astrophysics Data System (ADS)
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.
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.
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 g_{2}(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
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.
White, A. E.; Schmitz, L.; Peebles, W. A.; Carter, T. A.; Doyle, E. J.; Rhodes, T. L.; Wang, G.; McKee, G. R.; Shafer, M. W.; Holland, C.; Tynan, G. R.; Austin, M. E.; Burrell, K. H.; Candy, J.; DeBoo, J. C.; Prater, R.; Staebler, G. M.; Waltz, R. E.; Makowski, M. A.
2008-05-15
For the first time, profiles (0.3<{rho}<0.9) of electron temperature and density fluctuations in a tokamak have been measured simultaneously and the results compared to nonlinear gyrokinetic simulations. Electron temperature and density fluctuations measured in neutral beam-heated, sawtooth-free low confinement mode (L-mode) plasmas in DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] are found to be similar in frequency and normalized amplitude, with amplitude increasing with radius. The measured radial profile of two fluctuation fields allows for a new and rigorous comparison with gyrokinetic results. Nonlinear gyrokinetic flux-tube simulations predict that electron temperature and density fluctuations have similar normalized amplitudes in L-mode. At {rho}=0.5, simulation results match experimental heat diffusivities and density fluctuation amplitude, but overestimate electron temperature fluctuation amplitude and particle diffusivity. In contrast, simulations at {rho}=0.75 do not match either the experimentally derived transport properties or the measured fluctuation levels.
NASA Astrophysics Data System (ADS)
Zachary, Chase E.; Torquato, Salvatore
2011-05-01
We provide numerical constructions of one-dimensional hyperuniform many-particle distributions that exhibit unusual clustering and asymptotic local number density fluctuations growing more slowly than the volume of an observation window but faster than the surface area. Hyperuniformity, defined by vanishing infinite-wavelength local density fluctuations, provides a quantitative metric of global order within a many-particle configuration and signals the onset of an “inverted” critical point in which the direct correlation function becomes long ranged. By targeting a specified form of the structure factor at small wavenumbers (S(k)~kα for 0<α<1) using collective density variables, we are able to tailor the form of asymptotic local density fluctuations while simultaneously measuring the effect of imposing weak and strong constraints on the available degrees of freedom within the system. This procedure is equivalent to finding the (possibly disordered) classical ground state of an interacting many-particle system with up to four-body interactions. Even in one dimension, the long-range effective interactions induce clustering and nontrivial phase transitions in the resulting ground-state configurations. We provide an analytical connection between the fraction of constrained degrees of freedom within the system and the disorder-order phase transition for a class of target structure factors by examining the realizability of the constrained contribution to the pair correlation function. Our results explicitly demonstrate that disordered hyperuniform many-particle ground states, and therefore also point distributions, with substantial clustering can be constructed. We directly relate the local coordination structure of our point patterns to the distribution of the void space external to the particles, and we provide a scaling argument for the configurational entropy (analogous to spin-frustated system) of the disordered ground states. By emphasizing the intimate
The Effect of Input Torque Ramps on Density Fluctuations Generated in the QH-mode Edge on DIII-D
NASA Astrophysics Data System (ADS)
Rost, Chris; Davis, E. M.; Marinoni, A.; Porkolab, M. A.; Burrell, K. H.
2015-11-01
Recent studies of Quiescent H-mode with varied input torque have exhibited two regimes of edge density turbulence, as observed with the Phase Contrast Imaging (PCI) density fluctuation diagnostic. The PCI is especially sensitive to turbulence in regions of large velocity shear, as seen in the Er well in the H-mode edge. QH-modes were first discovered in discharges with large input torque from neutral beams. Such plasmas possess a deep Er well inside the separatrix and have highly sheared ion-scale turbulence in the outer portion of the well propagating in the electron diamagnetic direction at 50 % of the largest E × B velocity. As input torque decreases, additional sheared turbulence appears which propagates at 2-3 × the largest E × B velocity, coincident with discontinuous changes in the velocity shear in the Er well and the characteristics of the Edge Harmonic Oscillation. Robust performance is observed to continue throughout these qualitative changes in the QH-mode edge parameters and density turbulence. Work supported in part by the US Department of Energy under DE-FG02-94ER54235 and DE-FC02-04ER54698.
NASA Astrophysics Data System (ADS)
Zong, Jing; Wang, Qiang
2013-03-01
How fluctuations change the order-disorder transition (ODT) of symmetric diblock copolymers (DBC) is a classic yet unsolved problem in polymer physics.[1] Taking a model system of discrete Gaussian chains interacting with soft, finite-range repulsions as commonly used in dissipative-particle dynamics simulations we formulate a density-functional theory (DFT) based on the polymer integral equation theories,[2] which includes the system fluctuations and correlations neglected by the mean-field theory (i.e., the widely applied self-consistent field theory) and can be reduced to the latter under the mean-spherical approximation. We then unambiguously reveal the fluctuation/correlation effects on the ODT of symmetric DBC by direct comparisons among the mean-field theory, DFT, and fast off-lattice Monte Carlo simulations,[3] all using exactly the same model system (Hamiltonian) and thus without any parameter-fitting.
Pursuing parameters for critical-density dark matter models
NASA Astrophysics Data System (ADS)
Liddle, Andrew R.; Lyth, David H.; Schaefer, R. K.; Shafi, Q.; Viana, Pedro T. P.
1996-07-01
We present an extensive comparison of models of structure formation with observations, based on linear and quasi-linear theory. We assume a critical matter density, and study both cold dark matter models and cold plus hot dark matter models. We explore a wide range of parameters, by varying the fraction of hot dark matter , the Hubble parameter h and the spectral index of density perturbations n, and allowing for the possibility of gravitational waves from inflation influencing large-angle microwave background anisotropies. New calculations are made of the transfer functions describing the linear power spectrum, with special emphasis on improving the accuracy on short scales where there are strong constraints. For assessing early object formation, the transfer functions are explicitly evaluated at the appropriate redshift. The observations considered are the four-year COBE observations of microwave background anisotropies, peculiar velocity flows, the galaxy correlation function, and the abundances of galaxy clusters, quasars and damped Lyman alpha systems. Each observation is interpreted in terms of the power spectrum filtered by a top-hat window function. We find that there remains a viable region of parameter space for critical-density models when all the dark matter is cold, though h must be less than 0.5 before any fit is found and n significantly below unity is preferred. Once a hot dark matter component is invoked, a wide parameter space is acceptable, including n 1. The allowed region is characterized by 0.35 and 0.60 n 1.25, at 95 per cent confidence on at least one piece of data. There is no useful lower bound on h, and for curious combinations of the other parameters it is possible to fit the data with h as high as 0.65.
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
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
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
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)
Tjhung, Elsen; Berthier, Ludovic
2015-04-01
The emergence of particle irreversibility in periodically driven colloidal suspensions has been interpreted as resulting either from a nonequilibrium phase transition to an absorbing state or from the chaotic nature of particle trajectories. Using a simple model of a driven suspension, we show that a nonequilibrium phase transition is accompanied by hyperuniform static density fluctuations in the vicinity of the transition, where we also observe strong dynamic heterogeneities reminiscent of dynamics in glassy materials. We find that single particle dynamics becomes intermittent and strongly non-Fickian, and that collective dynamics becomes spatially correlated over diverging length scales. Our results suggest that the two theoretical scenarii can be experimentally discriminated using particle-resolved measurements of standard static and dynamic observables.
Gorissen, Mieke; Hooyberghs, Jef; Vanderzande, Carlo
2009-02-01
Cumulants of a fluctuating current can be obtained from a free-energy-like generating function, which for Markov processes equals the largest eigenvalue of a generalized generator. We determine this eigenvalue with the density-matrix renormalization group for stochastic systems. We calculate the variance of the current in the different phases, and at the phase transitions, of the totally asymmetric exclusion process. Our results can be described in the terms of a scaling ansatz that involves the dynamical exponent z . We also calculate the generating function of the dynamical activity (total number of configuration changes) near the absorbing-state transition of the contact process. Its scaling properties can be expressed in terms of known critical exponents. PMID:19391693
Extracting galactic structure parameters from multivariated density estimation
NASA Technical Reports Server (NTRS)
Chen, B.; Creze, M.; Robin, A.; Bienayme, O.
1992-01-01
Multivariate statistical analysis, including includes cluster analysis (unsupervised classification), discriminant analysis (supervised classification) and principle component analysis (dimensionlity reduction method), and nonparameter density estimation have been successfully used to search for meaningful associations in the 5-dimensional space of observables between observed points and the sets of simulated points generated from a synthetic approach of galaxy modelling. These methodologies can be applied as the new tools to obtain information about hidden structure otherwise unrecognizable, and place important constraints on the space distribution of various stellar populations in the Milky Way. In this paper, we concentrate on illustrating how to use nonparameter density estimation to substitute for the true densities in both of the simulating sample and real sample in the five-dimensional space. In order to fit model predicted densities to reality, we derive a set of equations which include n lines (where n is the total number of observed points) and m (where m: the numbers of predefined groups) unknown parameters. A least-square estimation will allow us to determine the density law of different groups and components in the Galaxy. The output from our software, which can be used in many research fields, will also give out the systematic error between the model and the observation by a Bayes rule.
Effects of Malaria Parasite Density on Blood Cell Parameters
Kotepui, Manas; Piwkham, Duangjai; PhunPhuech, Bhukdee; Phiwklam, Nuoil; Chupeerach, Chaowanee; Duangmano, Suwit
2015-01-01
Changes in blood cell parameters are already a well-known feature of malarial infections. To add to this information, the objective of this study was to investigate the varying effects that different levels of parasite density have on blood cell parameters. Patients diagnosed with malaria at Phobphra Hospital, Tak Province, Thailand between January 1st 2009 and January 1st 2012 were recruited as subjects for data collection. Blood cell parameters of 2,024 malaria-infected patients were evaluated and statistically analyzed. Neutrophil and platelet counts were significantly higher, however, RBC count was significantly lower in patients with P. falciparum infection compared to those with P. vivax infection (p<0.0001). Leukocyte counts were also significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia. In terms of differential leukocyte count, neutrophil count was significantly higher in patients with high parasitemia compared to those with low and moderate parasitemia (p<0.0001). On the other hand, both lymphocyte and monocyte counts were significantly lower in patients with high parasitemia (p<0.0001). RBC count and Hb concentration, as well as platelet count were also significantly reduced (p<0.05) and (p<0.0001), respectively. To summarize, patients infected with different malaria parasites exhibited important distinctive hematological parameters, with neutrophil and eosinophil counts being the two hematological parameters most affected. In addition, patients infected with different malarial densities also exhibited important changes in leukocyte count, platelet count and hemoglobin concentration during the infection. These findings offer the opportunity to recognize and diagnose malaria related anemia, help support the treatment thereof, as well as relieve symptoms of severe malaria in endemic regions. PMID:25807235
Consistent parameter fixing in the quark-meson model with vacuum fluctuations
NASA Astrophysics Data System (ADS)
Carignano, Stefano; Buballa, Michael; Elkamhawy, Wael
2016-08-01
We revisit the renormalization prescription for the quark-meson model in an extended mean-field approximation, where vacuum quark fluctuations are included. At a given cutoff scale the model parameters are fixed by fitting vacuum quantities, typically including the sigma-meson mass mσ and the pion decay constant fπ. In most publications the latter is identified with the expectation value of the sigma field, while for mσ the curvature mass is taken. When quark loops are included, this prescription is however inconsistent, and the correct identification involves the renormalized pion decay constant and the sigma pole mass. In the present article we investigate the influence of the parameter-fixing scheme on the phase structure of the model at finite temperature and chemical potential. Despite large differences between the model parameters in the two schemes, we find that in homogeneous matter the effect on the phase diagram is relatively small. For inhomogeneous phases, on the other hand, the choice of the proper renormalization prescription is crucial. In particular, we show that if renormalization effects on the pion decay constant are not considered, the model does not even present a well-defined renormalized limit when the cutoff is sent to infinity.
Interlocking order parameter fluctuations in structural transitions between adsorbed polymer phases.
Martins, Paulo H L; Bachmann, Michael
2016-01-21
By means of contact-density chain-growth simulations of a simple coarse-grained lattice model for a polymer grafted at a solid homogeneous substrate, we investigate the complementary behavior of the numbers of surface-monomer and monomer-monomer contacts under various solvent and thermal conditions. This pair of contact numbers represents an appropriate set of order parameters that enables the distinct discrimination of significantly different compact phases of polymer adsorption. Depending on the transition scenario, these order parameters can interlock in perfect cooperation. The analysis helps understand the transitions from compact filmlike adsorbed polymer conformations into layered morphologies and dissolved adsorbed structures, respectively, in more detail. PMID:26690091
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
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.
Inversion methods for the measurements of MHD-like density fluctuations by Heavy Ion Beam Diagnostic
NASA Astrophysics Data System (ADS)
Malaquias, A.; Henriques, R. B.; Nedzelsky, I. S.
2015-09-01
We report here on the recent developments in the deconvolution of the path integral effects for the study of MHD pressure-like fluctuations measured by Heavy Ion Beam Diagnostic. In particular, we develop improved methods to account for and remove the path integral effect on the determination of the ionization generation factors, including the double ionization of the primary beam. We test the method using the HIBD simulation code which computes the real beam trajectories and attenuations due to electron impact ionization for any selected synthetic profiles of plasma current, plasma potential, electron temperature and density. Simulations have shown the numerical method to be highly effective in ISTTOK within an overall accuracy of a few percent (< 3%). The method here presented can effectively reduce the path integral effects and may serve as the basis to develop improved retrieving techniques for plasma devices working even in higher density ranges. The method is applied to retrieve the time evolution and spatial structure of m=1 and m=2 modes. The 2D MHD mode-like structure is reconstructed by means of a spatial projection of all 1D measurements obtained during one full rotation of the mode. A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics
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.
Direct Measurements of Upper Limits for Transient Density Fluctuations in the Zodiacal Cloud
NASA Astrophysics Data System (ADS)
Olsson, B.
1997-12-01
Questions regarding the density of the local zodiacal clouds have recently become important in many areas. Several planned searches for extrasolar system planets require a better knowledge of the behavior of zodiacal clouds, the solar system zodiacal cloud has been suggested as a driving force for glaciations, and it is becoming clear that discussions regarding prebiotic chemistry must include the flux of interplanetary particles onto Earth. No certain upper limits can today be set for transient density variations in the local zodiacal cloud, nor for fluctuations in the particle-flux onto Earth. Some new results have, however, created a possibility to measure this in the geological record. An interdisciplinary project is described. The goal for the project is to set upper limits for the zodiacal dust-flux onto Earth during passages through IRAS dust-bands during the last 2.5 million years, and use these limits to calculate the maximum density of the bands. We estimate the predicted flux of zodiacal particles onto Earth through orbital modeling., where it is assumed that the source for the IRAS dust-bands are a few Hirayama asteroid families. The orbits of the asteroids and the produced dust are integrated to find the times when Earth revolved within a dust-band. This forms the basis for a geochemical analysis of oceanic sediments, lake sediments, ice-cores and loess-deposits, with the goal to find the signal from a passage through a dust-band. Apart from providing an excellent stratigraphic dating tool, the identification and characterization of such a signal would give important information about the behavior of the zodiacal cloud over shorter times (1-2 My). Some astronomical results are presented and compared with sedimentological observations.
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.
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.
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.
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
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
NASA Astrophysics Data System (ADS)
Ivanova, I. V.; Dmitriev, D. I.; Sirazetdinov, V. S.
2007-02-01
In this paper we analyze some results of natural and numerical experiments on probability density of intensity fluctuations on an axis for 1,06 microns and 0,53 microns laser beams in comparison with theoretical dependences (lognormal, exponential and K-distribution). Beams were propagated in aviation engine exhaust at various angles between the jet and beam axes. It has been shown that for a beam with a wavelength of 0,53 microns experimental data can be approximated as exponential and K-distribution, while for radiation with a wavelength of 1,06 microns good conformity to K-distribution has been observed. Optimum conditions for image registration with CCD-cameras of laser beams distorted by turbulence have been chosen. For this purpose transfer characteristics of several same type samples of CCD-cameras have been studied at various irradiation modes and registration tunings. It has been shown that the dynamic range of the cameras is used to maximum capacity for image recording when gamma-correction is applied.
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.
NASA Astrophysics Data System (ADS)
Pribram-Jones, Aurora; Grabowski, Paul E.; Burke, Kieron
2016-06-01
The van Leeuwen proof of linear-response time-dependent density functional theory (TDDFT) is generalized to thermal ensembles. This allows generalization to finite temperatures of the Gross-Kohn relation, the exchange-correlation kernel of TDDFT, and fluctuation dissipation theorem for DFT. This produces a natural method for generating new thermal exchange-correlation approximations.
Density functional calculations of Hubbard parameter in actinide series
Puri, A.; Sen, K.D.
1993-05-01
The calculations of Hubbard parameter, U, which defines the polar state formation energy of the reaction 2(5f{sup n} 6d{sup 1} 7d{sup 2}) {yields} 5f{sup n-1} 6d{sup 2}7s{sup 2} + 5f{sup n+1} 7s{sup 2} for the actinide atoms, Th-No, have been carried out using the self-interaction-corrected (SIC) quasi-relativistic local spin density (LSD) functional due to Perdew and Zunger. Based on the available bandwidth calculations for the 5f metals and its monotonically decreasing trend with increasing nuclear charge it is predicted that the 5f state is iterent in Th-Np beyond which it becomes localized. These calculations agree with the conclusions drawn earlier by Johansson using the semiempirical data.
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.
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. PMID:23848555
NASA Technical Reports Server (NTRS)
Woo, Richard; Armstrong, J. W.; Bird, M. K.; Patzold, M.
1995-01-01
The first measurements of fractional electron density fluctuations delta-n(sub e)/n(sub e), where delta-n(sub e) is rms electron density fluctuation and n(sub e) is the mean electron density, have been carried out inside 40 R(sub 0) using 1991 Ulysses dual-frequency S- and X-band (13 and 3.6 cm) ranging (time delay) measurements. In the frequency band of approximately 6 x 10(exp -5) - 8 x 10(exp -4) Hz (periods of 20 min to 5 hr), delta-n(sub e)/n(sub e) varies from a high near 20% in the slow wind close to the neutral line to a low of 1% in the fast wind far from the neutral line. For spatial wavenumber K approximately = 1.4 x 10(exp -6)/km (period of 5 hr at 250 km/s), delta-n(sub e)/n(sub e) is essentially independent of heliocentric distance over 0.03-1.0 AU in the slow wind; it is a factor of 30 lower in the fast wind than in the slow wind inside 0.1 AU, but exhibits dramatic growth with heliocentric distance inside 0.3 AU. This latter result reinforces current views of the evolution of MHD turbulence and the association of Alfven waves with high speed streams based on in situ fields and particles measurements beyond 0.3 AU. That regions of enhanced density fluctuations near or above the neutral line coincide with regions of enhanced density confirms previous conclusions that they are the interplanetary manifestation of the heliospheric current sheet and extensions of coronal streamers. While the regions of enhanced density fluctuations lie within those of enhanced density, they have boundaries that are distinctly more abrupt, suggesting the separation of plasma of different nature and origin.
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.
NASA Technical Reports Server (NTRS)
Woo, R.; Yang, F.-C.; Yip, K. W.; Kendall, W. B.
1976-01-01
It is demonstrated that phase-difference scintillations measured with a coherent dual-frequency radio system such as that on Mariner 10 can be used to study the structure of density fluctuations in the solar wind covering a wider range of scale sizes than has ever been possible before. The Mariner 10 observations at solar elongations of 11.5 and 12.6 deg show that the density spectrum in the frequency range from 0.0001 to 0.5 Hz, which corresponds to the spatial wavenumber range of 2 millionths to 0.001 inverse km if the solar wind velocity is assumed to be 350 km/s, is approximately power-law and close to Kolmogorov (spectral index of 11/3). The results are consistent with direct spacecraft observations near earth and provide strong evidence that the density fluctuations are produced by turbulence. The potential and benefits of future extensive measurements are also discussed.
Effects of pairing correlations on the inverse level density parameter of hot rotating nuclei
NASA Astrophysics Data System (ADS)
Thi Quynh Huong, Le; Quang Hung, Nguyen; Thi Quynh Trang, Le
2016-06-01
Angular momentum dependence of the inverse level density parameter K in the excitation-energy region of ∼ 30 – 40 MeV is studied within the finite-temperature Bardeen-Cooper-Schrieffer (FTBCS) theory and the FTBCS theory that includes the effect due to quasiparticle-number fluctuations (FTBCS1). The two theories take into account the noncollective rotation of the nucleus at nonzero values of z-projection M of the total angular momentum. The comparison between the results obtained within the FTBCS and FTBCS1 as well as the case without pairing correlations and the experimental data for two medium-mass even-even nuclei 108Cd and 122Te shows that by including the pairing corrections the FTBCS and FTBCS1 reproduces quite well all the experimental data, whereas the non-pairing case always overestimates the data. Due to the effect of quasiparticle-number fluctuations, the FTBCS1 gaps at different M values do not collapse at critical temperature TC as in the FTBCS ones but monotonously decrease with increasing T and being finite even at high T. As the result, the values of K obtained within the FTBCS1 are always closer to the experimental data than those obtained within the FTBCS.
An edge density fluctuation diagnostic for DIII-D using lithium beams
NASA Astrophysics Data System (ADS)
Thomas, D. M.
1991-12-01
This report covers the research conducted under DOE grant FG03-90ER-081 during the period August 15, 1990 through November 15, 1991. Progress during the period March 15, 1990 through August 15, 1990 was covered in a previous report. Highlights during this period include the development of a compact neutral lithium accelerator capable of producing several mA at up to 30 kV, measurements of intrinsic beam fluctuation levels, and the design and partial completion of the diagnostic installation on the D3-D tokamak. We also had one journal article describing the system published in Reviews of Scientific Instruments, presented a poster on our recent progress at the APS Plasma Physics conference, and submitted an abstract to the 9th Topical Conference on Plasma Diagnostics. The overall objective of this project is to provide detailed information about the behavior of the electron density in the edge region of D3-D, and in particular to examine the local character of the associated degradation in confinement properties. Measurements should provide important data for testing theories of the L-H transition in tokamaks and should help in assessing the role of various instabilities in anomalous transport. The work on this project may be naturally organized according to the following six subareas: Ion source/beam system, neutralizer system, optical system, data acquisition, data analysis, and machine (D3-D) interface. Progress in each of these areas will be discussed briefly. We also briefly discuss our plans for future work on this program.
Yamakawa, Youichi; Kontani, Hiroshi
2015-06-26
We present a microscopic derivation of the nematic charge-density wave (CDW) formation in cuprate superconductors based on the three-orbital d-p Hubbard model by introducing the vertex correction (VC) into the charge susceptibility. The CDW instability at q=(Δ(FS),0), (0,Δ(FS)) appears when the spin fluctuations are strong, due to the strong charge-spin interference represented by the VC. Here, Δ(FS) is the wave number between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is expressed as the "intra-unit-cell orbital order" accompanied by the charge transfer between the neighboring atomic orbitals, which is actually observed by the scanning tunneling microscope measurements. We predict that the cuprate CDW and the nematic orbital order in Fe-based superconductors are closely related spin-fluctuation-driven phenomena. PMID:26197139
NASA Technical Reports Server (NTRS)
Ghosh, S.; Matthaeus, W. H.
1992-01-01
Theory suggests that three distinct types of turbulence can occur in the low Mach number limit of polytropic flow: nearly incompressible flows dominated by vorticity, nearly pure acoustic turbulence dominated by compression, and flows characterized by near statistical equipartition of vorticity and compressions. Distinctions between these kinds of turbulence are investigated here by direct numerical simulation of two-dimensional compressible hydrodynamic turbulence. Dynamical scalings of density fluctuations, examination of the ratio of transverse to longitudinal velocity fluctuations, and spectral decomposition of the fluctuations are employed to distinguish the nature of these low Mach number solutions. A strong dependence on the initial data is observed, as well as a tendency for enhanced effects of compressibility at later times and at higher wave numbers, as suggested by theories of nearly incompressible flows.
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
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
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.
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. PMID:25637990
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
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.
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.
Influence of the fluid density on the statistics of power fluctuations in von Kármán swirling flows
NASA Astrophysics Data System (ADS)
Opazo, A.; Sáez, A.; Bustamante, G.; Labbé, R.
2016-02-01
Here, we report experimental results on the fluctuations of injected power in confined turbulence. Specifically, we have studied a von Kármán swirling flow with constant external torque applied to the stirrers. Two experiments were performed at nearly equal Reynolds numbers, in geometrically similar experimental setups. Air was utilized in one of them and water in the other. With air, it was found that the probability density function of power fluctuations is strongly asymmetric, while with water, it is nearly Gaussian. This suggests that the outcome of a big change of the fluid density in the flow-stirrer interaction is not simply a change in the amplitude of stirrers' response. In the case of water, with a density roughly 830 times greater than air density, the coupling between the flow and the stirrers is stronger, so that they follow more closely the fluctuations of the average rotation of the nearby flow. When the fluid is air, the coupling is much weaker. The result is not just a smaller response of the stirrers to the torque exerted by the flow; the PDF of the injected power becomes strongly asymmetric and its spectrum acquires a broad region that scales as f-2. Thus, the asymmetry of the probability density functions of torque or angular speed could be related to the inability of the stirrers to respond to flow stresses. This happens, for instance, when the torque exerted by the flow is weak, due to small fluid density, or when the stirrers' moment of inertia is large. Moreover, a correlation analysis reveals that the features of the energy transfer dynamics with water are qualitatively and quantitatively different to what is observed with air as working fluid.
NASA Astrophysics Data System (ADS)
Kim, Jaewook; Ghim, Young-Chul; Nuclear Fusion and Plasma Lab Team
2014-10-01
A BES (beam emission spectroscopy) system and an MIR (Microwave Imaging Reflectometer) system installed in KSTAR measure 2D (radial and poloidal) density fluctuations at two different toroidal locations. This gives a possibility of measuring the parallel correlation length of ion-scale turbulence in KSTAR. Due to lack of measurement points in toroidal direction and shorter separation distance between the diagnostics compared to an expected parallel correlation length, it is necessary to confirm whether a conventional statistical method, i.e., using a cross-correlation function, is valid for measuring the parallel correlation length. For this reason, we generated synthetic 3D density fluctuation data following Gaussian random field in a toroidal coordinate system that mimic real density fluctuation data. We measure the correlation length of the synthetic data by fitting a Gaussian function to the cross-correlation function. We observe that there is disagreement between the measured and actual correlation lengths, and the degree of disagreement is a function of at least, correlation length, correlation time and advection velocity of synthetic data. We identify the cause of disagreement and propose an appropriate method to measure correct correlation length.
NASA Astrophysics Data System (ADS)
Melnikov, N. B.; Reser, B. I.; Paradezhenko, G. V.
2016-08-01
To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.
NASA Astrophysics Data System (ADS)
Quiroz-Martinez, B.; Schmitt, F. G.; Dauvin, J.-C.
2012-01-01
We consider here the dynamics of two polychaete populations based on a 20 yr temporal benthic survey of two muddy fine sand communities in the Bay of Morlaix, Western English Channel. These populations display high temporal variability, which is analyzed here using scaling approaches. We find that population densities have heavy tailed probability density functions. We analyze the dynamics of relative species abundance in two different communities of polychaetes by estimating in a novel way a "mean square drift" coefficient which characterizes their fluctuations in relative abundance over time. We show the usefulness of using new tools to approach and model such highly variable population dynamics in marine ecosystems.
Effects of 2D and Finite Density Fluctuations on O-X Correlation Reflectometry
G.J. Kramer; R. Nazikian; E. Valeo
2001-07-05
The correlation between O-mode and X-mode reflectometer signals is studied with a 1D and 2D reflectometer model in order to explore its feasibilities as a q-profile diagnostic. It was found that 2D effects and finite fluctuation levels both decrease the O-X correlation. At very low fluctuation levels, which are usually present in the plasma core, there is good possibility to determine the local magnetic field strength and use that as a constraint for the equilibrium reconstruction.
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.
NASA Technical Reports Server (NTRS)
Muschietti, L.; Goldman, M. V.; Newman, D.
1985-01-01
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 are addressed by a model based on the existence of large scale density fluctuations capable of sufficiently diffusing small-k beam-unstable Langmuir waves in phase space. The model is also informed by the presence of a significant isotropic nonthermal tail in the distribution function of the background electron population, which is capable of stabilizing larger k modes. The model is able to predict various levels of Langmuir waves, depending on the parameters; calculations indicate that, for realistic parameters, the most unstable small k modes are fully stabilized, while some oblique mode with higher k and lower growth rate may remain unstable.
Thomas, D.M.
1994-01-01
The pivotal role played by edge physics in tokamak transport and performance is widely appreciated but not completely understood at this time. The evident bifurcation in transport behavior during the L-to-H transition and the modification of the edge region by edge localized modes (ELMs) are just two examples of this relationship. There is a clear need to understand the role that turbulence plays in the plasma transport problem. Various workers have seen a suppression of both the magnetic and plasma density fluctuations during the transition. It is clear that the turbulence and transport behavior are linked and we are coming to an understanding of the transition evolution, based on a model of shear suppression of the turbulence and the creation of a transport barrier. In the case of the H-mode, this barrier is known to form a short distance radially inside the location of the last closed flux surface. The VH-mode may be thought of as a natural extension of this situation where the transport barrier moves deeper into the core of the discharge. As summarized in the May 1989 report of the DOE Transport Task Force, one of the key issues to be addressed in making progress on the transport question was to characterize the nature of local fluctuations. The objective of our research was to develop and demonstrate the feasibility of one particular measurement technique to determine density fluctuations in the region of interest on the DIII-D tokamak.
NASA Astrophysics Data System (ADS)
Ayub, M. K.; Yun, G. S.; Leem, J.; Kim, M.; Lee, W.; Park, H. K.
2016-03-01
A novel technique to estimate the range of radial size and density fluctuation amplitude of edge localized modes (ELMs) in the KSTAR tokamak plasma is presented. A microwave imaging reflectometry (MIR) system is reconfigured as a multi-channel microwave interferometer array (MIA) to measure the density fluctuations associated with ELMs, while electron cyclotron emission imaging (ECEI) system is used as a reference diagnostics to confirm the MIA observation. Two dimensional full-wave (FWR2D) simulations integrated with optics simulation are performed to investigate the Gaussian beam propagation and reflection through the plasma as well as the MIA optical components and obtain the interferometric phase undulations of individual channels at the detector plane due to ELM perturbation. The simulation results show that the amplitude of the phase undulation depends linearly on both radial size and density perturbation amplitude of ELM. For a typical discharge with ELMs, it is estimated that the ELM structure observed by the MIA system has density perturbation amplitude in the range ~ 7 % to 14 % while radial size in the range ~ 1 to 3 cm.
Nam, Y U; Zoletnik, S; Lampert, M; Kovácsik, Ákos; Wi, H M
2014-11-01
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. PMID:25430341
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)
Kyzyurov, Yu.
Motions of neutral gas play the important role in creating irregularities of different scales in the ionospheric plasma. In particular, experimental data reveal that mid-latitude sporadic-E layer is formed by a vertical shear in the horizontal east-west wind due to tides or gravity waves. Below the homopause level (100-120 km) turbulent motions of neutral gas exhibit an essential influence on the layer. Neutral turbulence is responsible for the many-cloud structure of spread sporadic-E layers. This report is devoted to small-scale electron-density fluctuations produced by the turbulence in sporadic-E. Length-scales of the fluctuations correspond to the inertial range of turbulence and are small compared with the local scale of mean plasma-density gradient. We discuss an expected shape of the 1D fluctuation spectrum that can be measured during rocket experiments. The discussion is based on an analytical expression for the spectrum. The main steps necessary for obtaining the expression within the framework of macroscopic description are outlined too. Possible parabolic trajectories of two rockets which can be used for measurements of the sporadic-E electron-density fluctuations in the mid-latitude ionosphere (a magnetic dip angle of 45°) are chosen for a comparison. Parameters of the hypothetical flights were the following: (1) an apogee hmax=180 km, a distance between start and final points R=280 km; and (2) hmax=125 km, R=67 km. Mean values of characteristics for the sporadic-E and the neutral turbulence were fixed at around 97 km in this consideration. We have chosen the layer with a thickness of 2 km, a maximum electron density of 2\\cdot1010 m-3, and concentration of Fe^+ ions of 80 % (i.e. the mean ion mass is about 51 AMU). The mean rate of the turbulent energy dissipation was about 0.1 m^2s-3. Under these circumstances, the rms level of relative fluctuations in electron density may be about 10 % in the range of length-scales 10-400 m. The shape of
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.
Fluctuating defect density probed with noise spectroscopy in hydrogenated amorphous silicon
Verleg, P.A.W.E.; Uca, O.; Dijkhuis, J.I.
1997-07-01
Resistance fluctuations have been studied in hydrogenated amorphous silicon in the temperature range between 300 K and 450 K. The primary noise source has a power spectrum of approximately 1/f and is ascribed to hydrogen motion. Hopping of weakly bound hydrogen is thermally activated at such low temperatures with an average activation energy of 0.85 eV. The attempt rate amounts to 7 {center_dot} 10{sup 12} s{sup {minus}1}.
NASA Astrophysics Data System (ADS)
White, A. E.
2009-11-01
Multi-field fluctuation measurements provide opportunities for rigorous comparison between experiment and nonlinear gyrokinetic turbulence simulations. A unique set of diagnostics on DIII-D allows for simultaneous study of local, long-wavelength (0 < kθρs< 0.5) electron temperature and density fluctuations in the core plasma (0.4 < ρ< 0.8). Previous experiments in L-mode indicate that normalized electron temperature fluctuation levels (40 < f < 400,kHz) increase with radius from ˜0.4% at ρ= 0.5 to ˜2% at ρ=0.8, similar to simultaneously measured density fluctuations. Electron cyclotron heating (ECH) is used to increase Te, which increases electron temperature fluctuation levels and electron heat transport in the experiments. In contrast, long wavelength density fluctuation levels change very little. The different responses are consistent with increased TEM drive relative to ITG-mode drive. A new capability at DIII-D is the measurement of phase angle between electron temperature and density fluctuations using coupled correlation electron cyclotron emission radiometer and reflectometer diagnostics. Linear and nonlinear GYRO runs have been used to design validation experiments that focus on measurements of the phase angle. GYRO shows that if Te and ∇Te increase 50% in a beam-heated L-mode plasma (ρ=0.5), then the phase angle between electron temperature and density fluctuations decreases 30%-50% and electron temperature fluctuation levels increase a factor of two more than density fluctuations. Comparisons between these predictions and experimental results will be presented.
NASA Astrophysics Data System (ADS)
Higdon, J. C.
1986-10-01
A model of anisotropic plasma fluids is developed to examine the origin of the spectra of random, electron-density variations inferred by Armstrong, Cordes, and Rickett from measurements of pulsar radio signals. These electron variations are interpreted as density components of an anisotropic stationary mode of nonlinear magnetogasdynamics-tangetial pressure balances. It is demonstrated that turbulent flows, generated by the disruption of H I clouds in O star H II regions, reproduce well the mean electron spectrum inferred by Armstrong et al., if the relative rms density variation, >(n-n0)2<1/2/n0 is 0.125, where n0 is the mean density.
Pilkiewicz, Kevin R.; Andersen, Hans C.
2014-01-01
A diagrammatic kinetic theory of density fluctuations in simple dense liquids at long times, described in Paper I, is applied to a high density Lennard-Jones liquid to calculate various equilibrium time correlation functions. The calculation starts from the general theory and makes two approximations. (1) The general diagrammatic expression for an irreducible memory kernel is approximated using a one-loop approximation. (2) The generalized Enskog projected propagator, which is required for the calculation, is approximated using a simple kinetic model for the hard sphere memory function. The coherent intermediate scattering function (CISF), the longitudinal current correlation function (LCCF), the transverse current correlation function (TCCF), the incoherent intermediate scattering function (IISF), and the incoherent longitudinal current correlation function are calculated and compared with simulation results for the Lennard-Jones liquid at high density. The approximate theoretical results are in good agreement with the simulation data for the IISF for all wave vectors studied and for the CISF and LCCF for large wave vector. The approximate results are in poor agreement with the simulation data for the CISF, LCCF, and TCCF for small wave vectors because these functions are strongly affected by hydrodynamic fluctuations at small wave vector that are not well described by the simple kinetic model used. The possible implications of this approach for the study of liquids are discussed.
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. PMID:27284662
NASA Astrophysics Data System (ADS)
Bardóczi, L.; Rhodes, T. L.; Carter, T. A.; Bañón Navarro, A.; Peebles, W. A.; Jenko, F.; McKee, G.
2016-05-01
We report the first observation of localized modulation of turbulent density fluctuations n ˜ (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 ˜ was found to be modulated by 14% across the island. Gyrokinetic simulations suggest that n ˜ 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.
NASA Astrophysics Data System (ADS)
Topa, M. E.; De Paola, F.; Giugni, M.; Kombe, W.; Touré, H.
2012-04-01
The dynamic of hydro-climatic processes can fluctuate in a wide range of temporal scales. Such fluctuations are often unpredictable for ecosystems and the adaptation to these represent the great challenge for the survival and the stability of the species. An unsolved issue is how much these fluctuations of climatic variables to different temporal scales can influence the frequency and the intensity of the extreme events, and how much these events can modify the ecosystems life. It is by now widespread that an increment of the frequency and the intensity of the extreme events will represent one of the strongest characteristic of the global climatic change, with the greatest social and biotics implications (Porporato et al 2006). Recent field experiments (Gutshick and BassiriRad, 2003) and numerical analysis (Porporato et al 2004) have shown that the extreme events can generate not negligible consequences on organisms of water-limited ecosystems. Adaptation measures and species and ecosystems answers to the hydro-climatic variations, is therefore srongly interconnected to the probabilistic structure of these fluctuations. Generally the not-linear intermittent dynamic of a state variable z (a rainfall depth or the interarrival time between two storms), at short time scales (for example daily) is described by a probability density function (pdf), p (z|υ), where υ is the parameter of the distribution. If the same parameter υ varies so that the external forcing fluctuates at longer temporal scale, z reaches a new "local" equilibrium. When the temporal scale of the variation of υ is larger than the one of z, the probability distribution of z can be obtained as a overlapping of the temporary equlibria ("Superstatistic" approach), i.e.: p(z) = ∫ p(z|υ)·φ(υ)dυ (1) where p(z|υ) is the conditioned probability of z to υ, while φ(υ) is the pdf of υ (Beck, 2001; Benjamin and Cornell, 1970). The present work, carried out within FP7-ENV-2010 CLUVA (CLimate Change
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. PMID:26850350
NASA Astrophysics Data System (ADS)
White, A. E.; Schmitz, L.; Peebles, W. A.; Carter, T. A.; Rhodes, T. L.; Wang, G.; Doyle, E. J.; Hillesheim, J. C.; Zeng, L.; McKee, G. R.; Shafer, M. W.; Deboo, J. C.; Staebler, G. M.
2008-11-01
An increase in the ratio of the amplitudes of two fluctuating fields, (Te/Te)/(n/n), is observed in DIII-D beam-heated (˜2.5 MW, co-injected) L-mode plasmas during ECH (˜2.5 MW deposited at ρ 0.17). The amplitude of long wavelength temperature fluctuations, Te/Te, measured with a correlation ECE diagnostic (CECE), increases significantly during ECH. In contrast, the amplitude of long wavelength density fluctuations, n/n, measured simultaneously with a BES diagnostic, does not change. Linear stability analysis with the TGLF code shows that during ECH the ratio of the TEM and ITG growth rates increases at long wavelengths in the range relevant for the CECE and BES diagnostics. These TGLF results are found to be more sensitive to changes in the TEM drive term a/Lne compared with changes in a/LTe or a/LTi. Sensitivity scans with TGLF and comparisons with experimental results for the ratio (Te/Te)/(n/n) measured in Ohmic plasmas with ECH will be presented.
White, A. E.; Peebles, W. A.; Rhodes, T. L.; Schmitz, L.; Carter, T. A.; Hillesheim, J. C.; Doyle, E. J.; Zeng, L.; Holland, C. H.; Wang, G.; McKee, G. R.; Staebler, G. M.; Waltz, R. E.; DeBoo, J. C.; Petty, C. C.; Burrell, K. H.
2010-05-15
This paper presents new measurements of the cross-phase angle, alpha{sub n{sub eT{sub e}}}, between long-wavelength (k{sub t}hetarho{sub s}<0.5) density, n-tilde{sub e}, and electron temperature, T-tilde{sub e}, fluctuations in the core of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] tokamak plasmas. The coherency and cross-phase angle between n-tilde{sub e} and T-tilde{sub e} are measured using coupled reflectometer and correlation electron cyclotron emission diagnostics that view the same plasma volume. In addition to the experimental results, two sets of local, nonlinear gyrokinetic turbulence simulations that are performed with the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] are described. One set, called the pre-experiment simulations, was performed prior to the experiment in order to predict a change in alpha{sub n{sub eT{sub e}}} given experimentally realizable increases in the electron temperature, T{sub e}. In the experiment the cross-phase angle was measured at three radial locations (rho=0.55, 0.65, and 0.75) in both a 'Base' case and a 'High T{sub e}' case. The measured cross-phase angle is in good qualitative agreement with the pre-experiment simulations, which predicted that n-tilde{sub e} and T-tilde{sub e} would be out of phase. The pre-experiment simulations also predicted a decrease in cross-phase angle as T{sub e} is increased. Experimentally, this trend is observed at the inner two radial locations only. The second set of simulations, the postexperiment simulations, is carried out using local parameters taken from measured experimental profiles as input to GYRO. These postexperiment simulation results are in good quantitative agreement with the measured cross-phase angle, despite disagreements with transport fluxes. Directions for future modeling and experimental work are discussed.
NASA Astrophysics Data System (ADS)
Kim, Nam Won; Kim, Youn Jung; Chung, Il-Moon; Lee, Jeongwoo
2014-05-01
A novel application of groundwater table fluctuation method is suggested to predict groundwater level by means of groundwater table variation due to recharge and discharge under unsteady condition. This model analyzes transient groundwater characteristics by using reaction factor related with groundwater flow and specific yield related with recharge. The groundwater level varies according to the characteristics and composite materials of aquifer. In this study, specific yield and reaction factor which are the major two hydrogeological parameters in the WTF(Water Table Fluctuation) method were estimated and analyzed their spatial characteristics. 8 groundwater level stations which have enough measuring period and high correlation with rainfall in the Hancheon watershed were used. The results showed that specific yield was randomly distributed and reaction factor showed inverse trend with altitude. If the enough data were collected, reaction factor according to altitude in ungauged points could be estimated by using these parameter characteristics. keywords: Key words : Groundwater level, parameters, reaction factor, specific yield Acknowledgements This research was supported by the Regional Innovative Technology Project 2B from KICTTEP.
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.
Zhang, Yi-Jun; Gao, Song; Su, Ru-Keng Zhang, Yi-Jun Gao, Song Su, Ru-Keng
1997-12-01
Based on thermofield dynamics, the temperature- and density-dependent effective mass and screening mass of {rho} meson have been calculated. The effects of vacuum fluctuation corrections through effective nucleon mass are examined. We have shown that vacuum fluctuations give an important correction to the self-energy of the {rho} meson and lead to a reduction of the {rho}-meson mass in hot and dense matter. The temperature and density dependence of one-{rho}-meson exchange potential with vacuum fluctuation correction is also given. {copyright} {ital 1997} {ital The American Physical Society}
Local Density Fluctuations Predict Photoisomerization Quantum Yield of Azobenzene-Modified DNA.
Kingsland, Addie; Samai, Soumyadyuti; Yan, Yunqi; Ginger, David S; Maibaum, Lutz
2016-08-01
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. PMID:27428569
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)
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)
Modeling Spin Fluctuations and Magnetic Excitations from Time-Dependent Density Functional Theory
NASA Astrophysics Data System (ADS)
Gorni, Tommaso; Timrov, Iurii; Dal Corso, Andrea; Baroni, Stefano
Harnessing spin fluctuations and magnetic excitations in materials is key in many fields of technology, spanning from memory devices to information transfer and processing, to name but a few. A proper understanding of the interplay between collective and single-particle spin excitations is still lacking, and it is expected that first-principle simulations based on TDDFT may shed light on this interplay, as well as on the role of important effects such as relativistic ones and related magnetic anisotropies. All the numerical approaches proposed so far to tackle this problem are based on the computationally demanding solution of the Sternheimer equations for the response orbitals or the even more demanding solution of coupled Dyson equations for the spin and charge susceptibilities. The Liouville-Lanczos approach to TDDFT has already proven to be a valuable alternative, the most striking of its features being the avoidance of sums over unoccupied single-particle states and the frequency-independence of the main numerical bottleneck. In this work we present an extension of this methodology to magnetic systems and its implementation in the
Schuster, Andrea C; Herde, Antje; Mazzoni, Camila J; Eccard, Jana A; Sommer, Simone
2016-07-01
Strong spatiotemporal variation in population size often leads to reduced genetic diversity limiting the adaptive potential of individual populations. Key genes of adaptive variation are encoded by the immune genes of the major histocompatibility complex (MHC) playing an essential role in parasite resistance. How MHC variation persists in rodent populations that regularly experience population bottlenecks remains an important topic in evolutionary genetics. We analysed the consequences of strong population fluctuations on MHC class II DRB exon 2 diversity in two distant common vole (Microtus arvalis) populations in three consecutive years using a high-throughput sequencing approach. In 143 individuals, we detected 25 nucleotide alleles translating into 14 unique amino acid MHC alleles belonging to at least three loci. Thus, the overall allelic diversity and amino acid distance among the remaining MHC alleles, used as a surrogate for the range of pathogenic antigens that can be presented to T-cells, are still remarkably high. Both study populations did not show significant population differentiation between years, but significant differences were found between sites. We concluded that selection processes seem to be strong enough to maintain moderate levels of MHC diversity in our study populations outcompeting genetic drift, as the same MHC alleles were conserved between years. Differences in allele frequencies between populations might be the outcome of different local parasite pressures and/or genetic drift. Further understanding of how pathogens vary across space and time will be crucial to further elucidate the mechanisms maintaining MHC diversity in cyclic populations. PMID:27225422
Yang, Zhong-Zhi; Wang, Jian-Jiang; Zhao, Dong-Xia
2014-09-01
To promote accuracy of the atom-bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc-Zn, Y-Cd, and Lu-Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO-3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. PMID:25042901
Beghi, Alessandro; Belfi, Jacopo; Beverini, Nicolò; Bouhadef, B; Cuccato, D; Di Virgilio, Angela; Ortolan, Antonello
2012-11-01
He-Ne ring-laser gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performance come from the nonlinear dynamics of the laser. Following Lamb semiclassical theory, we find a set of critical parameters affecting the time stability of the system. We propose a method for estimating the long-term drift of the laser parameters and for filtering out the laser dynamics effects from the rotation measurement. The parameter estimation procedure, based on the perturbative solutions of the laser dynamics, allows us to apply Kalman filter theory for the estimation of the angular velocity. Results of a comprehensive Monte Carlo simulation and results of a preliminary analysis on experimental data from the ring-laser prototype G-Pisa are shown and discussed. PMID:23128698
Compensation of the laser parameter fluctuations in large ring-laser gyros: a Kalman filter approach
NASA Astrophysics Data System (ADS)
Beghi, Alessandro; Belfi, Jacopo; Beverini, Nicolò; Bouhadef, B.; Cuccato, D.; Di Virgilio, Angela; Ortolan, Antonello
2012-11-01
He-Ne ring laser gyroscopes are, at present, the most precise devices for absolute angular velocity measurements. Limitations to their performance come from the non--linear dynamics of the laser. Following the Lamb semi-classical theory, we find a set of critical parameters affecting the time stability of the system. We propose a method for estimating the long term drift of the laser parameters and for filtering out the laser dynamics effects from the rotation measurement. The parameter estimation procedure, based on the perturbative solutions of the laser dynamics, allow us to apply Kalman Filter theory for the estimation of the angular velocity. Results of a comprehensive Monte Carlo simulation and results of a preliminary analysis on experimental data from the ring laser prototype G-Pisa are shown and discussed.
NASA Astrophysics Data System (ADS)
Yadav, Vivek Kumar; Chandra, Amalendu
2013-06-01
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
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.
Probabilistic Analysis and Density Parameter Estimation Within Nessus
NASA Astrophysics Data System (ADS)
Godines, Cody R.; Manteufel, Randall D.
2002-12-01
, 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)
Muscatello, C. M.; Domier, C. W.; Luhmann, N. C., Jr.; Ren, X.; Spear, A.; Tobias, B. J.
2012-10-01
An imaging diagnostic capable of measuring simultaneously the poloidal and radial structure of density fluctuations is being developed for DIII-D. The success of electron-cyclotron emission imaging developed by UC Davis for DIII-D is a testament to the powerful utility of microwave imaging diagnostics for tokamaks. Since its first deployment on TEXTOR, the MIR concept has undergone several improvements in optical and electronics design. For example, the shape of the wavefront of the probing beam and the curvature of the cutoff layer strongly affect the integrity of the reflected signal. This is addressed with transmitting optical elements that are designed to control the shape of the probing beam. Advances in microwave electronics make it possible to transmit and detect multiple frequencies simultaneously, permitting fluctuation measurements at multiple radial locations. Interesting physics occurs over the entire poloidal cross-section of the plasma, on disparate spatial scales. MIR is flexible in this respect, allowing a remote user to rapidly tune the individual probing frequencies for a variety of correlation studies. Synthetic diagnostic simulations and extensive laboratory tests corroborate our confidence in a successful implementation of MIR on DIII-D.
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.
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)
Da Silva-Cadoux, Cécile; Hazemann, Jean-Louis; Testemale, Denis; Proux, Olivier; Rochas, Cyrille
2012-01-01
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 ZnBr2 and NaCl systems from the literature.
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. PMID:23496512
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.
The effect of growth parameters on the height and density of carbon nanotube forests
NASA Astrophysics Data System (ADS)
Call, Robert W.
Carbon nanotube forests (CNTFs) are grown using an injection chemical vapor deposition method. Images of CNTFs are taken using a scanning electron microscope and are used to measure their height and density. Growth parameters are systematically varied to determine their effect on the height and density of CNTFs. Investigations of CNTF density as a function of distance from the growth substrate reveal that diffusion can be a limiting factor on CNTF growth. Our findings indicate that height and density are related and that each growth parameter has multi-dimensional effects.
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)
Knudsen, D. J.; Kabirzadeh, R.; Burchill, J. K.; Pfaff, R. F.; Wallis, D. D.; Bounds, S. R.; Clemmons, J. H.; Pinçon, J.-L.
2012-02-01
The Geoelectrodynamics and Electro-Optical Detection of Electron and Suprathermal Ion Currents (GEODESIC) sounding rocket encountered more than 100 filamentary density cavities associated with enhanced plasma waves at ELF (<3 kHz) and VLF (3-10 kHz) frequencies and at altitudes of 800-990 km during an auroral substorm. These cavities were similar in size (˜20 m diameter in most cases) to so-called lower-hybrid cavities (LHCs) observed by previous sounding rockets and satellites; however, in contrast, many of the GEODESIC cavities exhibited up to tenfold enhancements in magnetic wave power throughout the VLF band. GEODESIC also observed enhancements of ELF and VLF electric fields both parallel and perpendicular to the geomagnetic field B0 within cavities, though the VLF E field increases were often not as large proportionally as seen in the magnetic fields. This behavior is opposite to that predicted by previously published theories of LHCs based on passive scattering of externally incident auroral hiss. We argue that the GEODESIC cavities are active wave generation sites capable of radiating VLF waves into the surrounding plasma and producing VLF saucers, with energy supplied by cold, upward flowing electron beams composing the auroral return current. This interpretation is supported by the observation that the most intense waves, both inside and outside cavities, occurred in regions where energetic electron precipitation was largely inhibited or absent altogether. We suggest that the wave-enhanced cavities encountered by GEODESIC were qualitatively different from those observed by earlier spacecraft because of the fortuitous timing of the GEODESIC launch, which placed the payload at apogee within a substorm-related return current during its most intense phase, lasting only a few minutes.
IPS observations at 140 MHz to study solar wind speeds and density fluctuations by MEXART
NASA Astrophysics Data System (ADS)
Chang, Oyuki; Gonzalez-Esparza, J. A.; Mejia-Ambriz, J.
2016-03-01
The interplanetary scintillation (IPS) technique is a remote-sensing method for monitoring the inner heliosphere. These observations supply information on solar wind conditions covering heliocentric ranges that no other technique can provide. The Mexican Array Radio Telescope (MEXART) is a single-station instrument operating at 140 MHz, fully dedicated to performing solar-wind studies employing the IPS technique. We present solar-wind parameters (scintillation indices and solar-wind speeds), using the initial measurements from this array of four IPS sources (3C273, 3C283, 3C286, 3C298) detected during October-December 2014. We report the transit of an IPS radio source (3C298), observed at 140 MHz, from weak- to strong-scattering regions at around 0.36 AU, and sky projection maps of solar wind conditions associated presumably with the passing of one or more Coronal Mass Ejections (CMEs). These results show the progress to operate the full array in the near future. The MEXART observations will complement the solar wind IPS studies using other frequencies, and the tracking of solar wind disturbances by other stations located at different longitudes. These solar wind measurements, provided in real time, can have space-weather forecasting applications.
NASA Astrophysics Data System (ADS)
van Milligen, B. Ph.; Estrada, T.; García, L.; López Bruna, D.; Carreras, B. A.; Xu, Y.; Ochando, M.; Hidalgo, C.; Reynolds-Barredo, J. M.; López Fraguas, A.; the TJ-II Team
2016-01-01
This work explores the relation between magnetic islands, long range temporal correlations and heat transport. A low order rational surface ({\\rlap- \\iota}=3/2 ) was purposely scanned outward through an electron cyclotron resonance heated (ECRH) plasma in the TJ-II stellarator. Density turbulence and the poloidal flow velocity were characterized using a two channel Doppler reflectometer. Simultaneously, the ECRH power was modulated to characterize heat transport, using measurements from a 12 channel electron cyclotron emission diagnostic. A systematic variation of the poloidal velocity was found to be associated with the {\\rlap- \\iota}=3/2 rational surface. Near the rational surface, the Hurst exponent, quantifying the nature of long-range correlations, was reduced below 0.5 (indicating subdiffusion), while at radii smaller than that of the rational surface, it was found to be significantly enhanced (superdiffusion). In the latter region, heat transport was enhanced as well, thus establishing a link between density fluctuations and anomalous heat transport. The observed variation of the Hurst exponent was consistent with a magnetohydrodynamic turbulence simulation.
Parameters of Calcium Metabolism Fluctuated during Initiation or Changing of Antipsychotic Drugs
Stanojevic Pirkovic, Marijana; Zivancevic Simonovic, Snezana; Matovic, Milovan; Djukic Dejanovic, Slavica; Jankovic, Slobodan M.; Ravanic, Dragan; Petronijevic, Milan; Ignjatovic Ristic, Dragana; Mladenovic, Violeta; Jovanovic, Mirjana; Nikolic Labovic, Sandra; Pajovic, Marina; Djokovic, Danijela; Petrovic, Dusan; Janjic, Vladimir
2016-01-01
Objective Serum parameters of calcium homeostasis were measured based on previously published evidence linking osteoporotic fractures and/or bone/mineral loss with antipsychotics. Methods Prospective, four-week, time-series trial was conducted and study population consisted of patients of both genders, aged 35-85 years, admitted within the routine practice, with acute psychotic symptoms, to whom an antipsychotic drug was either introduced or substituted. Serial measurements of serum calcium, phosphorous, magnesium, 25(OH)D, parathyroid hormone, calcitonin, osteocalcin and C-telopeptide were made from patient venous blood samples. Results Calcium serum concentrations significantly decreased from baseline to the fourth week (2.42±0.12 vs. 2.33±0.16 mmol/L, p=0.022, n=25). The mean of all calcemia changes from the baseline was -2.6±5.7% (-24.1 to 7.7) with more decreases than increases (78 vs. 49, p=0.010) and more patents having negative sum of calcemia changes from baseline (n=28) than positive ones (n=10) (p=0.004). There were simultaneous falls of calcium and magnesium from baseline (63/15 vs. 23/26, p<0.001; OR=4.75, 95% CI 2.14-10.51), phosphorous (45/33 vs. 9/40, p<0.001; 6.06, 2.59-14.20) and 25(OH)D concentrations (57/21 vs. 13/35, p<0.001; 7.31, 3.25-16.42), respectively. Calcemia positively correlated with magnesemia, phosphatemia and 25(OH)D values. Parathyroid hormone and C-telopeptide showed only subtle oscillations of their absolute concentrations or changes from baseline; calcitonin and osteocalcin did not change. Adjustment of final calcemia trend (depletion/accumulation) for relevant risk factors, generally, did not change the results. Conclusion In patients with psychotic disorders and several risks for bone metabolism disturbances antipsychotic treatment was associated with the decrease of calcemia and changes in levels of the associated ions. PMID:26766951
Effects of level density parameter on the superheavy production in cold fusion
NASA Astrophysics Data System (ADS)
Pahlavani, M. R.; Alavi, S. A.
2014-12-01
By using semiclassical method and considering Woods-Saxon and Coulomb potentials, the level density parameter a was calculated for three superheavy nuclei 270110, 278112 and 290116. Obtained results showed that the value of level density parameter of these nuclei is near to the simple relation a ≈ A/10. In framework of the dinuclear system model, the effects of level density parameter on the probability of the formation of a compound nucleus, the ratio of neutron emission width and fission width, and evaporation residue cross-section of three cold fusion reactions 62Ni+208Pb, 70Zn+208Pb and 82Se+208Pb, leading to superheavy elements were investigated. The findings indicate that the level density parameter play a significant role in calculations of heavy-ion fusion-fission reactions. The obtained results in the case of a = A/12 have larger values in comparison with calculated level density parameter with Woods-Saxon potential (aWS) and a = A/10. The theoretical results of the evaporation residue cross-section are very sensitive to the choice of level density parameter. The calculated values with aWS are in good agreement with experimental values.
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)
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 1/f 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.
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.
2016-08-01
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 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.
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.
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.
Li, Pengsong; Huang, Jinyang; Luo, Liang; Kuang, Yun; Sun, Xiaoming
2016-09-01
Density gradient ultracentrifugation (DGUC) has recently emerged as an effective nanoseparation method to sort polydispersed colloidal NPs mainly according to their size differences to reach monodispersed fractions (NPs), but its separation modeling is still lack and the separation parameters' optimization mainly based on experience of operators. In this paper, we gave mathematical descriptions on the DGUC separation, which suggested the best separation parameters for a given system. The separation parameters, including media density, centrifuge speed and time, which affected the separation efficiency, were discussed in details. Further mathematical optimization model was established to calculate and yield the "best" (optimized) linear gradient for a colloidal system with given size and density. The practical experiment results matched well with theoretical prediction, demonstrating the DGUC method, an efficient, practical, and predictable separation technique with universal utilization for colloid sorting. PMID:27457445
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
Analysis of current density and related parameters in spinal cord stimulation.
Wesselink, W A; Holsheimer, J; Boom, H B
1998-06-01
A volume conductor model of the spinal cord and surrounding anatomical structures is used to calculate current (and current density) charge per pulse, and maximum charge density per pulse at the contact surface of the electrode in the dorsal epidural space, in the dorsal columns of the spinal cord and in the dorsal roots. The effects of various contact configurations (mono-, bi-, and tripole), contact area and spacing, pulsewidth and distance between contacts and spinal cord on these electrical parameters were investigated under conditions similar to those in clinical spinal cord stimulation. At the threshold stimulus of a large dorsal column fiber, current density and charge density per pulse at the contact surface were found to be highest (1.9.10(5) microA/cm2 and 39.1 microC/cm2.p, respectively) when the contact surface was only 0.7 mm2. When stimulating with a pulse of 500 microseconds, highest charge per pulse (0.92 microC/p), and the largest charge density per pulse in the dorsal columns (1.59 microC/cm2. p) occurred. It is concluded that of all stimulation parameters that can be selected freely, only pulsewidth affects the charge and charge density per pulse in the nervous tissue, whereas both pulsewidth and contact area strongly affect these parameters in the nonnervous tissue neighboring the electrode contacts. PMID:9631328
Matsuo, K.; Uchida, N.; Kawakubo, M.; Iguchi, H.; Okamura, S.; Matsuoka, K.; Akiyama, T.
2008-10-15
A near-infrared laser phase contrast optical system incorporating a folded beam was developed in order to measure the distribution of density fluctuations in a high-temperature plasma. The coherent light source used was an yttrium aluminum garnet laser stabilized by a ring oscillator. The probe beam system separates and reflects the incident and exiting beams with a polarizer and a fully reflective mirror with a waveplate. This system was employed with a compact helical system to detect fluctuations at the plasma edge.
Rasouli, Saifollah; Tavassoly, M Taghi
2006-11-15
There are several methods for measuring ground-level atmospheric turbulence parameters, such as the refractive index profile and its fluctuations, correlations of the fluctuations in space and time, and the atmospheric refractive-index structure constant. These methods are based mainly on the measurement of fluctuations in intensity and location of an image formed by light propagating in the turbulent atmosphere or the fluctuations in impinging points of narrow light beams traversing the ground-level atmosphere. Exploiting the moiré technique, we suggest a high-precision approach for determining fluctuaions in the angle of arrival. When a low-frequency grating (carrier grating) is installed at a suitable distance from a telescope, its image, practically, forms on the focal plane of the telescope objective. Superimposing a physical grating (probe grating) of the same pitch as the image grating on the image forms the moiré pattern. The atmospheric turbulence distorts the image grating. Processing the fluctuations of successive moiré fringes can yield the mentioned parameters across a rather large cross section of the atmosphere with high accuracy, because of the moiré technique's magnifying character and access to a large volume of data, and does so in a comparatively simple and reliable manner. PMID:17072395
Level densities and spin cutoff parameters for 60Co and 62Ni from proton evaporation spectra
NASA Astrophysics Data System (ADS)
Voinov, Alexander; Grimes, Steven; Brune, Carl R.; Burger, Alexander; Gorgen, Andreas; Guttormsen, Magne; Larsen, Ann Cecilie; Massey, Tomas; Siem, Sunniva
2013-10-01
Prediction of reaction cross sections remains a major problem in applications such as data evaluations or/and astrophysics reaction rate calculations. There is big progress in the development of nuclear reaction codes which now include different reaction mechanisms. However, these codes use many input parameters. The variety of input parameters helps us to describe existing experimental data but it creates problems when it comes to predictions. The uncertainties of the level density and the spin cutoff parameter cause the major concern. The proton spectra from α and lithium induced reactions have been measured and analyzed with the Hauser-Feshbach model. Different input level density models have been tested. The level densities and spin cutoff parameters were obtained with Monte-Carlo technique taking into account known spins of discrete low-lying levels of residual nuclei. It was found that the best description is achieved with the Gilbert and Cameron model functions. Excitation energy dependence of spin cutoff parameters was found to be different for 60Co and 62Ni nuclei. It is inconsistent with Fermi-gas model which is usually used to calculate spin cutoff parameters.
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.
Critical fluctuations of the proton density in A+A collisions at 158 A GeV
NASA Astrophysics Data System (ADS)
Anticic, T.; Baatar, B.; Bartke, J.; Beck, H.; Betev, L.; Białkowska, H.; Blume, C.; Bogusz, M.; Boimska, B.; Book, J.; Botje, M.; Bunčić, P.; Cetner, T.; Christakoglou, P.; Chvala, O.; Cramer, J.; Eckardt, V.; Fodor, Z.; Foka, P.; Friese, V.; Gaździcki, M.; Grebieszkow, K.; Höhne, C.; Kadija, K.; Karev, A.; Kolesnikov, V. I.; Kowalski, M.; Kresan, D.; Laszlo, A.; van Leeuwen, M.; Maćkowiak-Pawłowska, M.; Makariev, M.; Malakhov, A. I.; Mateev, M.; Melkumov, G. L.; Mitrovski, M.; Mrówczyński, St.; Pálla, G.; Panagiotou, A. D.; Peryt, W.; Pluta, J.; Prindle, D.; Pühlhofer, F.; Renfordt, R.; Roland, C.; Roland, G.; Rustamov, A.; Rybczyński, M.; Rybicki, A.; Sandoval, A.; Schmitz, N.; Schuster, T.; Seyboth, P.; Siklér, F.; Skrzypczak, E.; Slodkowski, M.; Stefanek, G.; Stock, R.; Ströbele, H.; Susa, T.; Szuba, M.; Varga, D.; Vassiliou, M.; Veres, G. I.; Vesztergombi, G.; Vranić, D.; Włodarczyk, Z.; Wojtaszek-Szwarć, A.; Antoniou, N. G.; Davis, N.; Diakonos, F. K.
2015-12-01
We look for fluctuations expected for the QCD critical point using an intermittency analysis in the transverse momentum phase space of protons produced around midrapidity in the 12.5 % most central C+C, Si+Si and Pb+Pb collisions at the maximum SPS energy of 158 A GeV. We find evidence of power-law fluctuations for the Si+Si data. The fitted power-law exponent φ 2 = 0.96^{+0.38}_{-0.25}{ (stat.)} ± 0.16{ (syst.)} is consistent with the value expected for critical fluctuations. Power-law fluctuations had previously also been observed in low-mass π ^+ π ^- pairs in the same Si+Si collisions.
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.
NASA Astrophysics Data System (ADS)
Yang, Yunxiang; Du, Gang; Han, Ruqi; Liu, Xiaoyan
2011-04-01
The effects of intrinsic parameter fluctuations, including line-edge-roughness (LER), silicon-body thickness variation (STV) and work-function variation (WFV), in 20-nm-gate variable-γ silicon-on-thin-box (SOTB) metal oxide semiconductor field effect transistors (MOSFETs) have been investigated and compared with those of the conventional SOTB. Results show that the variable-γ SOTB offers not only an enhanced Ion but also a reduced Ion fluctuation with a small increase in the active-state Ioff fluctuation. The Vth-roll-off value in the variable-γ SOTB can be reduced by adopting a reverse-biased side gate to optimize the short channel effect, but the variability of the DIBL effect is enlarged. It is expected that a thinner silicon body can be used to reduce the dominant variability sources.
Wang, Hsiao-Hsuan; Grant, W E; Teel, P D; Hamer, S A
2015-12-01
Tick vector systems are comprised of complex climate-tick-host-landscape interactions that are difficult to identify and estimate from empirical observations alone. We developed a spatially-explicit, individual-based model, parameterized to represent ecological conditions typical of the south-central United States, to examine effects of shifts in the seasonal occurrence of fluctuations of host densities on tick densities. Simulated shifts in the seasonal occurrence of periods of high and low host densities affected both the magnitude of unfed tick densities and the seasonality of tick development. When shifting the seasonal densities of all size classes of hosts (small, medium, and large) synchronously, densities of nymphs were affected more by smaller shifts away from the baseline host seasonality than were densities of larval and adult life stages. When shifting the seasonal densities of only a single size-class of hosts while holding other size classes at their baseline levels, densities of larval, nymph, and adult life stages responded differently. Shifting seasonal densities of any single host-class earlier resulted in a greater increase in adult tick density than when seasonal densities of all host classes were shifted earlier simultaneously. The mean densities of tick life stages associated with shifts in host densities resulted from system-level interactions of host availability with tick phenology. For example, shifting the seasonality of all hosts ten weeks earlier resulted in an approximately 30% increase in the relative degree of temporal co-occurrence of actively host-seeking ticks and hosts compared to baseline, whereas shifting the seasonality of all hosts ten weeks later resulted in an approximately 70% decrease compared to baseline. Differences among scenarios in the overall presence of active host-seeking ticks in the system were due primarily to the degree of co-occurrence of periods of high densities of unfed ticks and periods of high densities
Key Parameters Governing the Energy Density of Rechargeable Li/S Batteries.
Gao, Jie; Abruña, Héctor D
2014-03-01
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. PMID:26274082
Grøtan, Vidar; Saether, Bernt-Erik; Engen, Steinar; van Balen, Johan H; Perdeck, Albert C; Visser, Marcel E
2009-03-01
1. The aim of the present study is to model the stochastic variation in the size of five populations of great tit Parus major in the Netherlands, using a combination of individual-based demographic data and time series of population fluctuations. We will examine relative contribution of density-dependent effects, and variation in climate and winter food on local dynamics as well as on number of immigrants. 2. Annual changes in population size were strongly affected by temporal variation in number of recruits produced locally as well as by the number of immigrants. The number of individuals recruited from one breeding season to the next was mainly determined by the population size in year t, the beech crop index (BCI) in year t and the temperature during March-April in year t. The number of immigrating females in year t + 1 was also explained by the number of females present in the population in year t, the BCI in autumn year t and the temperature during April-May in year t. 3. By comparing predictions of the population model with the recorded number of females, the simultaneous modelling of local recruitment and immigration explained a large proportion of the annual variation in recorded population growth rates. 4. Environmental stochasticity especially caused by spring temperature and BCI did in general contribute more to annual fluctuations in population size than density-dependent effects. Similar effects of climate on local recruitment and immigration also caused covariation in temporal fluctuations of immigration and local production of recruits. 5. The effects of various variables in explaining fluctuations in population size were not independent, and the combined effect of the variables were generally non-additive. Thus, the effects of variables causing fluctuations in population size should not be considered separately because the total effect will be influenced by covariances among the explanatory variables. 6. Our results show that fluctuations in the
Density dependent B parameter of relativistic stars with anisotropy in pseudo-spheroidal space-time
NASA Astrophysics Data System (ADS)
Chattopadhyay, P. K.; Paul, B. C.
2016-04-01
We present a class of relativistic solutions for compact cold stars with strange matter in a pseudo-spheroidal space-time. Considering strange matter equation of state namely, p = 1/3(ρ -4B), where ρ , p and B are energy density, pressure and MIT Bag parameter respectively, stellar models are obtained. In the presence of anisotropy with a pseudo-spheroidal geometry described by Vaidya-Tikekar, metric stellar models are explored where the Bag parameter varies with the energy density (ρ ) inside the compact object. We determine the density dependence of B at different anisotropy. It is noted that although B varies with anisotropy inside the star, finally at the surface it attains a value which is independent of the anisotropy. The Bag parameter B is found to increase with an increase in anisotropy for a given compactness factor (M/b) and spheroidicity λ . It is also noted that for a star with given mass and radius, the parameter B increases with the increase in λ and finally at large λ , it attains a constant. The equation of state (EoS) obtained here from geometrical consideration with allowed `B' value is found same to that one obtains from micro-physics. The stability of the stellar models for compact stars with anisotropy in hydrostatic equilibrium obtained here is also studied.
Measuring the matter energy density and Hubble parameter from large scale structure
Lee, Seokcheon
2014-02-01
We investigate the method to measure both the present value of the matter energy density contrast and the Hubble parameter directly from the measurement of the linear growth rate which is obtained from the large scale structure of the Universe. From this method, one can obtain the value of the nuisance cosmological parameter Ω{sub m0} (the present value of the matter energy density contrast) within 3% error if the growth rate measurement can be reached z > 3.5. One can also investigate the evolution of the Hubble parameter without any prior on the value of H{sub 0} (the current value of the Hubble parameter). Especially, estimating the Hubble parameter are insensitive to the errors on the measurement of the normalized growth rate fσ{sub 8}. However, this method requires the high z (z > 3.5) measurement of the growth rate in order to get the less than 5% errors on the measurements of H(z) at z ≤ 1.2 with the redshift bin Δz = 0.2. Thus, this will be suitable for the next generation large scale structure galaxy surveys like WFMOS and LSST.
Estimation of dispersion parameters from photographic density measurements on smoke puffs
NASA Astrophysics Data System (ADS)
Yassky, D.
An extension is proposed of methods that use "optical boundaries" of smoke-plumes in order to estimate atmospheric dispersion parameters. Use is made here of some properties of photographic optics and concentration distributions of light absorbing puffs having no multiple scattering. An array of relative photometric densities, measured on a single photograph of a puff, is shown to be of use in numerical estimation of a puff's dispersive parameters. The proposed method's performance is evaluated by means of computer simulation which includes estimates of the influence of photogrammetric and photometric errors. Future experimental validation of the proposed method may introduce fast and inexpensive ways of obtaining extensive atmospheric dispersion data bases.
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.
NASA Astrophysics Data System (ADS)
Karlický, M.; Jiricka, K.
2002-10-01
Using the recent model of the radio zebra fine structures (Ledenev et al. 2001) the magnetic fields, plasma densities, and plasma beta parameters are estimated from high-frequency zebra fine structures. It was found that in the flare radio source of high-frequency (1-2 GHz) zebras the densities and magnetic fields vary in the intervals of (1-4)×1010 cm-3 and 40-230 G, respectively. Assuming then the flare temperature as about of 107K, the plasma beta parameters in the zebra radio sources are in the 0.05-0.81 interval. Thus the plasma pressure effects in such radio sources, especially in those with many zebra lines, are not negligible.
Development of spiral density waves and evaluation of their parameters: a computer experiment
Grivnev, E.M.
1985-07-01
Numerical experiments with a disk of N = 250 interacting test-particles show that the velocity field does manifest development of the spiral density waves predicted by the Lin theory. The parameters of these simulated waves are evaluated in a nonlinear treatment. Similar N-body computer models can be employed to analyze the spiral structure in loosely wound galaxies such as NGC 3310 whose underlying equilibrium state is strongly perturbed.
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.
Radar meteors range distribution model. III. Ablation, shape-density and self-similarity parameters
NASA Astrophysics Data System (ADS)
Pecinová, D.; Pecina, P.
2007-10-01
The theoretical radar meteors Range Distribution of the overdense echoes developed by Pecinová and Pecina (2007 a) is applied here to observed range distributions of meteors belonging to the Quadrantid, Perseid, Leonid, Geminid, γ Draconid (Giacobinid), ζ Perseid and β Taurid streams to study the variability of the shape-density, ablation, and self-similarity parameters of meteoroids of these streams. We have found in accordance with results of photographical observations that ablation parameter σ is higher for members of showers of clearly cometary origin, and is lower for Geminid and daytime shower meteoroids. Levin's self-similarity parameter μ was found to be much greater than the classical value 2/3 for all investigated streams with the exception of Geminids, for which the value found is almost classical, i.e. 0.66 ± 0.01. The method of getting μ by means of fitting the light curve of faint TV meteors is also suggested.
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.
Methane dissociation on Pt(111): Searching for a specific reaction parameter density functional
NASA Astrophysics Data System (ADS)
Nattino, Francesco; Migliorini, Davide; Bonfanti, Matteo; Kroes, Geert-Jan
2016-01-01
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 CHD3 + 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
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.
SCAN-based hybrid and double-hybrid density functionals from models without fitted parameters.
Hui, Kerwin; Chai, Jeng-Da
2016-01-28
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. PMID:26827209
NASA Astrophysics Data System (ADS)
Aichi, M.; Shiokari, M.; Tokunaga, T.
2010-12-01
A new perturbation solution of the Boussinesq equation for tidally induced water table fluctuations in a coastal phreatic aquifer was derived under the condition of multiple tidal constituents. Then, the obtained solution was applied to estimate hydraulic parameters of the Shiro-mama formation at the Niijima Island, Japan, by fitting the solution to the results of continuous measurements of water table fluctuations in the frequency space. The estimated hydraulic transmissivities from both the amplitudes and the phase-shifts were comparable and consistent with the results of analyses based on the Dupuit-Ghyben-Herzberg model, suggesting that the proposed approach performed well and the obtained values, i.e., transmissivity to be 0.12-1.7 m2/s were reasonable.
Hu Ying; Liang Zhaoxin; Hu Bambi
2009-10-15
We investigate a Bose-Einstein condensate (BEC) trapped in a two-dimensional optical lattice in the presence of weak disorder within the framework of the Bogoliubov theory. In particular, we analyze the combined effects of disorder and an optical lattice on quantum fluctuations and superfluid density of the BEC system. Accordingly, the analytical expressions of the ground-state energy and quantum depletion of the system are obtained. Our results show that the lattice still induces a characteristic three-dimensional (3D) to one-dimensional crossover in the behavior of quantum fluctuations, despite the presence of weak disorder. Furthermore, we use the linear response theory to calculate the normal fluid density of the condensate induced by disorder. Our results in the 3D regime show that the combined presence of disorder and lattice induce a normal fluid density that asymptotically approaches 4/3 of the corresponding condensate depletion. Conditions for possible experimental realization of our scenario are also proposed.
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.
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.; Burger, A.; Gorgen, A.; Guttormsen, M.; Larsen, A. C.; Massey, T. N.; Siem, S.
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.
Level Density Inputs in Nuclear Reaction Codes and the Role of the Spin Cutoff Parameter
NASA Astrophysics Data System (ADS)
Voinov, A. V.; Grimes, S. M.; Brune, C. R.; Bürger, A.; Görgen, A.; Guttormsen, M.; Larsen, A. C.; Massey, T. N.; Siem, S.
2014-05-01
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 spacings and to discrete levels and using the spin cutoff parameter with much a weaker excitation energy dependence than predicted by the Fermi-gas model.
NASA Astrophysics Data System (ADS)
Schmidt, Denise; Gimeno Garcia, Sebastian; Schreier, Franz; Lichtenberg, Gunter
2015-06-01
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.
NASA Astrophysics Data System (ADS)
Eo, Yun Suk; Wolgast, Steven; Kurdak, Cagliyan; Sun, Kai; Kim, Dae-Jeong; Fisk, Zachary; Hatnean, Monica Ciomaga; Balakrishnan, Geetha
There is growing interest in studying the conducting surface of SmB6, which is believed to originate from its nontrivial band topology. Up to date, different measurement techniques, including ARPES, dHvA, and Hall bar transport still disagree on important parameters such as the carrier density. In order to find the carrier density (n) and mobility (μ) for the Dirac pockets participating in transport, we measure magnetotransport on Corbino devices fabricated on (100), (110), and (111) surfaces grown by floating zone and flux methods. Our samples do not exhibit Shubnikov-de Haas oscillations at high field pulsed measurements up to 90 Tesla, which provides an upper bound of μ of each channels. Also, angle-dependent magnetotransport up to 35 T allows us to extract an effective n and μ of the combined channels. Together, a parameter space that confines the possible n and μ of each channel is constructed, and appears to be in agreement with ARPES reports. Additionally, the effective n and μ change up to 20 percent when applying magnetic field up to 35 T. We will discuss how the Landau fan diagram can be nonlinear by this effect. This project was funded by NSF Grant #DMR-1006500. This project was performed at the National High Magnetic Field Laboratory, and in the Lurie Nanofabrication Facility.
Ates, C.; Moseley, Ch.; Ziegler, K.
2005-06-15
The characteristic oscillations of the density-density correlation function and the resulting structure factor are studied for a hard-core Bose gas in a one-dimensional lattice. Their wavelength diverges as the system undergoes a continuous transition from an incommensurate to a Mott insulating phase. The transition is associated with a unit static structure factor and a vanishing sound velocity. The qualitative picture is unchanged when a weak confining potential is applied to the system.
Oliveira, Susana Maria; Teixeira, Nuno José; Fernandes, Lisete; Teles, Pedro; Vieira, Guy; Vaz, Pedro
2014-11-01
The MCNPX code was used to calculate the TG-43U1 recommended parameters in water and prostate tissue in order to quantify the dosimetric impact in 30 patients treated with (125)I prostate implants when replacing the TG-43U1 formalism parameters calculated in water by a prostate-like medium in the planning system (PS) and to evaluate the uncertainties associated with Monte Carlo (MC) calculations. The prostate density was obtained from the CT of 100 patients with prostate cancer. The deviations between our results for water and the TG-43U1 consensus dataset values were -2.6% for prostate V100, -13.0% for V150, and -5.8% for D90; -2.0% for rectum V100, and -5.1% for D0.1; -5.0% for urethra D10, and -5.1% for D30. The same differences between our water and prostate results were all under 0.3%. Uncertainties estimations were up to 2.9% for the gL(r) function, 13.4% for the F(r,θ) function and 7.0% for Λ, mainly due to seed geometry uncertainties. Uncertainties in extracting the TG-43U1 parameters in the MC simulations as well as in the literature comparison are of the same order of magnitude as the differences between dose distributions computed for water and prostate-like medium. The selection of the parameters for the PS should be done carefully, as it may considerably affect the dose distributions. The seeds internal geometry uncertainties are a major limiting factor in the MC parameters deduction. PMID:25239870
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
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.
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
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
NASA Astrophysics Data System (ADS)
Croskey, Charles L.; Mitchell, John D.; Goldberg, Richard A.; Blix, Tom A.; Rapp, Markus; Latteck, Ralph; Friedrich, Martin; Smiley, Byron
2004-10-01
The MaCWAVE/MIDAS program for investigating high-latitude mesospheric dynamics has produced an extensive set of charged particle, plasma and neutral density measurements. We report on the results from one rocket salvo involving a MaCWAVE and two MIDAS payloads launched within a one-hour period. Each payload carried probes for evaluating the plasma and charged particle environment, and additionally, neutral density measurements were obtained by the CONE instrument on the MIDAS payloads. With the combination of particle and electron/ion density measurements, regions with and without charged particles have been clearly identified, and the plasma measurements outside the particle layers have proven useful to characterize the turbulent activity of the neutral gas.
Ramdani, Sofiane; Bonnet, Vincent; Tallon, Guillaume; Lagarde, Julien; Bernard, Pierre Louis; Blain, Hubert
2016-08-01
Entropy measures are often used to quantify the regularity of postural sway time series. Recent methodological developments provided both multivariate and multiscale approaches allowing the extraction of complexity features from physiological signals; see "Dynamical complexity of human responses: A multivariate data-adaptive framework," in Bulletin of Polish Academy of Science and Technology, vol. 60, p. 433, 2012. The resulting entropy measures are good candidates for the analysis of bivariate postural sway signals exhibiting nonstationarity and multiscale properties. These methods are dependant on several input parameters such as embedding parameters. Using two data sets collected from institutionalized frail older adults, we numerically investigate the behavior of a recent multivariate and multiscale entropy estimator; see "Multivariate multiscale entropy: A tool for complexity analysis of multichannel data," Physics Review E, vol. 84, p. 061918, 2011. We propose criteria for the selection of the input parameters. Using these optimal parameters, we statistically compare the multivariate and multiscale entropy values of postural sway data of non-faller subjects to those of fallers. These two groups are discriminated by the resulting measures over multiple time scales. We also demonstrate that the typical parameter settings proposed in the literature lead to entropy measures that do not distinguish the two groups. This last result confirms the importance of the selection of appropriate input parameters. PMID:26372426
Age-density relation of Main galaxies at fixed parameters or for different galaxy families
NASA Astrophysics Data System (ADS)
Deng, Xin-Fa; Song, Jun; Chen, Yi-Qing; Jiang, Peng; Ding, Ying-Ping
2015-09-01
Using two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we examine the environmental dependence of galaxy age at fixed parameters or for different galaxy families. Statistical results show that the environmental dependence of galaxy age is stronger for late type galaxies, but can be still observed for the early types: the age of galaxies in the densest regime is preferentially older than that in the lowest density regime with the same morphological type. We also find that the environmental dependence of galaxy age for red galaxies and Low Stellar Mass (LSM) galaxies is stronger, while the one for blue galaxies and High Stellar Mass ( HSM ) galaxies is very weak.
Benchmarking Density Functionals on Structural Parameters of Small-/Medium-Sized Organic Molecules.
Brémond, Éric; Savarese, Marika; Su, Neil Qiang; Pérez-Jiménez, Ángel José; Xu, Xin; Sancho-García, Juan Carlos; Adamo, Carlo
2016-02-01
In this Letter we report the error analysis of 59 exchange-correlation functionals in evaluating the structural parameters of small- and medium-sized organic molecules. From this analysis, recently developed double hybrids, such as xDH-PBE0, emerge as the most reliable methods, while global hybrids confirm their robustness in reproducing molecular structures. Notably the M06-L density functional is the only semilocal method reaching an accuracy comparable to hybrids'. A comparison with errors obtained on energetic databases (including thermochemistry, reaction barriers, and interaction energies) indicate that most of the functionals have a coherent behavior, showing low (or high) deviations on both energy and structure data sets. Only a few of them are more prone toward one of these two properties. PMID:26730741
Reduction of TEM/ETG-scale Density Fluctuations in the Core and Edge of H-mode DIII-D Plasmas
NASA Astrophysics Data System (ADS)
Schmitz, L.
2008-11-01
Improved confinement during H-mode has been linked to ExB shear suppression of large-scale (kθρs<=0.3) turbulence within an edge transport barrier. While larger scale eddies are preferentially suppressed by increased shear flow in this paradigm, the effects on smaller scale (TEM/ETG-scale) turbulence are less certain. Recent results from DIII-D provide the first experimental evidence that intermediate-scale turbulence (1 < kθρs<=3) together with larger-scale electron temperature fluctuations [1] are also reduced promptly at the L-H transition. These reductions are not confined to the edge region. Intermediate-scale density fluctuations obtained via Doppler backscattering, are significantly reduced (30%-50%) over a range of normalized radii (0.5 <=r/a <=0.85) within a few ms of the L-H transition. A larger reduction (>=75%) is observed at the top of the pedestal (r/a ˜0.9) within 0.2 ms. In addition, low-k electron temperature fluctuations (kθρs<=0.3, from correlation ECE) are strongly reduced (>75%) at the L-H mode transition and during QH-mode (r/a ˜0.7). Gyrokinetic simulation results [2] predict that Te fluctuations contribute significantly to L-mode electron heat transport, hence, the observed reduction is likely an important factor in the observed improved H-mode electron heat confinement (χe^QH/χ3^L < 0.25). Doppler backscattering is also utilized to probe time-dependent shear flows (i.e. zonal flows). The results clearly indicate that zonal flow levels are anti-correlated with the amplitude of intermediate-scale density turbulence in L-mode, suggesting that zonal flows play an important role in turbulence/transport regulation. 3pt [1] L. Schmitz et al., Phys. Rev. Lett. 100, 035002 (2008).[2] A.E. White et al., Phys. Plasmas 15, 056116 (2008).
NASA Astrophysics Data System (ADS)
Davis, E. M.; Rost, J. C.; Porkolab, M.; Marinoni, A.; van Zeeland, M. A.
2015-11-01
A combined phase contrast imaging (PCI) and heterodyne interferometer system has been implemented on DIII-D, extending the physics capabilities of the pre-existing PCI and acting as a prototypical fluctuation diagnostic for next-step devices. The combined PCI-interferometer uses a single 10.6 μ m laser beam, two interference schemes, and two detectors to measure ∫ñe dl over a large spatiotemporal bandwidth (10kHz < f < 2MHzand0 <= k <= 20cm-1) , allowing simultaneous measurement of ion- and electron-scale instabilities. Further, time-correlating our interferometer's measurements with those of DIII-D's pre-existing, toroidally separated (Δζ = 45°) interferometer will allow novel studies of low- n Alfvén eigenmodes. The combined diagnostic's small port requirements and minimal access restrictions make it well-suited to the harsh neutron environments and limited port space expected in next-step devices. Measurements from sound wave calibrations and DIII-D operations will be presented. Work supported by US DOE under DE-FG02-94ER54235, DE-FC02-04ER54698, DE-FC02- 99ER54512 and NNSA SSGF.
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.
STAR COUNT DENSITY PROFILES AND STRUCTURAL PARAMETERS OF 26 GALACTIC GLOBULAR CLUSTERS
Miocchi, P.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Pallanca, C.; Sanna, N.; Pasquato, M.; Beccari, G.
2013-09-10
We used an appropriate combination of high-resolution Hubble Space Telescope observations and wide-field, ground-based data to derive the radial stellar density profiles of 26 Galactic globular clusters from resolved star counts (which can be all freely downloaded on-line). With respect to surface brightness (SB) profiles (which can be biased by the presence of sparse, bright stars), star counts are considered to be the most robust and reliable tool to derive cluster structural parameters. For each system, a detailed comparison with both King and Wilson models has been performed and the most relevant best-fit parameters have been obtained. This collection of data represents the largest homogeneous catalog collected so far of star count profiles and structural parameters derived therefrom. The analysis of the data of our catalog has shown that (1) the presence of the central cusps previously detected in the SB profiles of NGC 1851, M13, and M62 is not confirmed; (2) the majority of clusters in our sample are fit equally well by the King and the Wilson models; (3) we confirm the known relationship between cluster size (as measured by the effective radius) and galactocentric distance; (4) the ratio between the core and the effective radii shows a bimodal distribution, with a peak at {approx}0.3 for about 80% of the clusters and a secondary peak at {approx}0.6 for the remaining 20%. Interestingly, the main peak turns out to be in agreement with that expected from simulations of cluster dynamical evolution and the ratio between these two radii correlates well with an empirical dynamical-age indicator recently defined from the observed shape of blue straggler star radial distribution, thus suggesting that no exotic mechanisms of energy generation are needed in the cores of the analyzed clusters.
Cepollaro, C.; Lauretani, F.; Gozzini, A.; Masi, L.; Falchetti, A.; Monte, F.; Carbonell-Sala, S.; Tanini, A.; Corsi, A.M.; Bandinelli, S.; Ferrucci, L.; Brandi, M.L.
2009-01-01
Bone mineral density (BMD) contributes to bone strength, and methods for clinical assessment of bone quality characteristics beyond what can be gathered by BMD are awaited. Peripheral quantitative computed tomography (pQCT) allows for separate assessments of cortical and trabecular bone, providing information on bone geometry. Previous studies examining the relationship between estrogen receptor α (ERα) gene polymorphisms and BMD have been performed in large populations. However, only limited information is available on the possible segregation of ERα gene polymorphisms with bone structural properties. The aim of our study was to evaluate the association of XbaI and PvuII ERα gene polymorphisms with QCT parameters. We studied 900 subjects (541 women, 449 men) participating to the InCHIANTI study. By tibial pQCT we evaluated trabecular volumetric BMD, cortical volumetric BMD, cortical bone area, and cortical thickness (CtTh). Subjects were genotyped for ERα gene PvuII and XbaI polymorphisms. Analysis of variance was used for statistical analysis. Male subjects with PP and XX genotypes had higher geometric parameters, and female subjects with XX and PP genotypes showed higher densitometric parameters than other genotypes; however, the differences did not reach statistical significance. After adjustment for potential confounders, we found a significant (P = 0.002) CtTh difference across PvuII polymorphism in male subjects, with higher CtTh values in PP genotypes with respect to Pp and pp genotypes. These results show a relationship between the presence of the P allele and higher values of CtTh in male subjects, indicating for ERα a role in the control of tibial bone geometry. PMID:17505773
Fluctuations in nuclear fragmentation
Aranda, A.; Dorso, C.O.; Furci, V.; Lopez, J.A.
1995-12-01
Heavy ion collisions can be used to study the thermodynamics of hot and dense nuclear matter only if the initial mass and energy fluctuations that lead to fragmentation are of thermal origin and survive the disassembly process. If this is the case, the observed fragment multiplicity should be directly related to those initial fluctuations and to the conditions of temperature and density causing them. The feasibility of this scenario is demonstrated with a molecular dynamics study of the evolution of mass and energy fluctuations, and fluctuations of the phase-space density. First, it is verified that the fluctuations leading to fragmentation are indeed early ones. Second, it is determined that different initial conditions of density and temperature can indeed produce varying final fragment multiplicities. The {rho}-{ital T} plane is mapped to the fragment multiplicity with good precision. This mapping should be easily reproducible with existing experimental data.
NASA Astrophysics Data System (ADS)
Cathles, L. M.; Hallam, A.
1991-08-01
The stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume (e.g., third- and higher-order Vail sea level variations, continental foundering). We propose that many of these changes can be caused by stress-induced changes in plate density. Stress changes produce significant changes in the density of the crust and lithosphere (a point missed in previous investigations) and propagate across even the largest plates in less than 30,000 years. Lithospheric plates interacting at existing boundaries can produce stress-related density changes sufficient to cause several meters change in plate elevation; these may account for many of the regressions and transgressions seen in the stratigraphic record. The creation of new rifts could increase plate compression enough to cause ˜50 m of plate subsidence. Plate elevation changes of up to -200 m could result from increased plate compression during continental collisions. A particularly enigmatic kind of rapid nonglacial global (NGG) sea level change is a coupled ˜50 m sea level fall (regression) and roughly equal rise (transgression) occurring in less than 106 years. These couplets, associated with black shales and marine extinctions, can be explained by the elastic snapback attending the rapid formation of a new rift. Isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a ˜50 m fall in sea level. Mantle flow restores isostatic equilibrium along the rift axis and erases the fall in ˜60,000 years. Unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales. A rapid drop in global sea levels reduces the area of ocean bottom within the photic zone, causing overpopulation, food exhaustion, and extinctions. The connections between changes in plate stress and density have many implications. Perhaps the most far
Zhou Kezhao; Liang Zhaoxin; Zhang Zhidong; Hu Ying
2010-10-15
We investigate a dilute Bose gas confined in a tight one-dimensional (1D) optical lattice plus a superimposed random potential at zero temperature. Accordingly, the ground-state energy, quantum depletion, and superfluid density are calculated. The presence of the lattice introduces a crossover to the quasi-two-dimensional (2D) regime, where we analyze asymptotically the 2D behavior of the system, particularly the effects of disorder. We thereby offer an analytical expression for the ground-state energy of a purely 2D Bose gas in a random potential. The obtained disorder-induced normal fluid density n{sub n} and quantum depletion n{sub d} both exhibit a characteristic 1/ln(1/n{sub 2D}a{sub 2D}{sup 2}) dependence. Their ratio n{sub n}/n{sub d} increases to 2 compared to the familiar 4/3 in lattice-free three-dimensional (3D) geometry, signifying a more pronounced contrast between superfluidity and Bose-Einstein condensation in low dimensions. The conditions for possible experimental realization of our scenario are also proposed.
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.
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
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
Johnson, LA; Euston, DE; Tatsuno, M; McNaughton, BL
2010-01-01
Spontaneous reactivation of previously stored patterns of neural activity occurs in hippocampus and neocortex during non-rapid eye movement (NREM) sleep. Notable features of the neocortical local field potential during NREM sleep are high amplitude, low frequency thalamocortical oscillations including K-complexes, low-voltage spindles and high-voltage spindles. Using combined neuronal ensemble and local field potential recordings, we show that prefrontal stored-trace reactivation is correlated with the density of down-to-up state transitions of the population of simultaneously recorded cells, as well as K-complexes, and low voltage spindles in the local field potential. This result strengthens the connection between reactivation and learning as these same NREM sleep features have been correlated with memory. Although memory trace reactivation is correlated with low-voltage spindles, it is not correlated with high-voltage spindles, indicating that despite their similar frequency characteristics, these two oscillations serve different functions. PMID:20164349
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
Drew, Simon C; Young, Charles G; Hanson, Graeme R
2007-04-01
The electron paramagnetic resonance spin Hamiltonian parameters of mononuclear thiomolybdenyl complexes based upon the tris(pyrazolyl)borate ligand, together with their molybdenyl analogues, are calculated using density functional theory. The electronic g matrix and 95Mo hyperfine matrix are calculated as second-order response properties from the coupled-perturbed Kohn-Sham equations. The scalar relativistic zero-order regular approximation (ZORA) is used with an all-electron basis and an accurate mean-field spin-orbit operator which includes all one- and two-electron terms. The principal values and relative orientations of the g and A interaction matrices obtained from the experimental spectra in a previous EPR study are compared with those obtained from unrestricted Kohn-Sham calculations at the BP86 and B3LYP level, and the latter are found to be in good quantitative agreement. A quasi-restricted approach is used to analyze the influence of the various molecular orbitals on g and A. In all complexes the ground state magnetic orbital is dX2-Y2-based and the orientation of the A matrix is directly related to the orientation of this orbital. The largest single contribution to the orientation of the g matrix arises from the spin-orbit coupling of the dYZ-based lowest-unoccupied molecular orbital into the ground state. A number of smaller, cumulative charge-transfer contributions augment the d-d contributions. A comparison of the theoretical EPR parameters obtained using both crystallographic and gas-phase geometry-optimized structures of Tp*MoO(bdt) (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, bdt = 1,2-benzenedithiolate) suggests a correspondence between the metal-dithiolate fold angle and the angle of noncoincidence between g and A. PMID:17305330
Ramalho, Teodorico C; Bühl, Michael
2005-02-01
The 15N chemical shifts of metronidazole (1), secnidazole (2), nimorazole (3) and tinidazole (4), radiosensitizers based on the 5-nitroimidazole motif, are reported. A detailed computational study of 1 is presented, calling special attention to the performance of various theoretical methods in reproducing the 13C and 15N data observed in solution. The most sophisticated approach involves density functional-based Car-Parrinello molecular dynamics simulations (CPMD) of 1 in aqueous solution (BP86 level) and averaging chemical shifts over snapshots from the trajectory. In the NMR calculations for these snapshots (performed at the B3LYP level), a small number of discrete water molecules are retained, and the remaining bulk solution effects are included via a polarizable continuum model (PCM). A similarly good accord with experiment is obtained from much less involved, static geometry optimization and NMR computation of pristine 1 employing a PCM approach. Solvent effects on delta(15N), which are of the order of up to 20 ppm, are not due to changes in geometric parameters upon solvation, but arise from the direct response of the electronic wavefunction to the presence of the solvent, which can be represented by discrete molecules and/or the dielectric bulk. PMID:15558660
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.
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. PMID:27410085
Charge density waves or dynamical fluctuations at the Pb/Ge(111) and Sn/Ge(111) interfaces?
NASA Astrophysics Data System (ADS)
Asensio, M. C.
2001-03-01
Critical phenomena are a fascinating area of current research in solid state physics. The complex phenomenology associated to the phase transitions can be analyzed in a simple playground of low-dimensional systems. In particular, Carpinelli et al. (Nature 381(1996)398) have initially reported a temperature-driven phase transition for a Pb or Sn layer deposited on Ge(111). The low temperature 3x3 phase was described as the stabilization of a charge density wave (CDW) in the Pb layer, driven by electron-phonon coupling in the two dimensional Fermi surface. A similar phenomenology has been observed for Sn/Ge(111). This picture, however, was seriously questioned in several aspects by further investigations. First, the experimental Fermi surface exhibits no significant nesting, a crucial point for the proposed CDW model. Second, valence-band photoemission results do not support that electron correlation plays a major role and the surface valence bands in both phases are split, in disagreement with CDW theoretical calculations. Third, Core-level photoemission for Sn/Ge(111) at room and low temperature indicates the existence of two kinds of Sn atoms. All these experimental facts could be rationalized assuming a corrugated Sn or Pb layer, which we have recently confirmed using surface X-R Diffraction and theoretical calculations (Phys. Rev. Lett 82 (1999) 2524 and Phys. Rev. Lett. 82 (1999) 442 ) .We conclude that the origin of this reversible temperature transition is not a CDW. Both phases have a strong rippling of the Sn (Pb) layer ( ~ 0.49 Åwith two well distinctive Sn (or Pb) sites. Hence, the room temperature phase is the result of a vertical flipping of the Sn (or Pb) adatoms, which is frozen at low temperature.
The MOSDEF Survey: Electron Density and Ionization Parameter at z ~ 2.3
NASA Astrophysics Data System (ADS)
Sanders, Ryan L.; Shapley, Alice E.; Kriek, Mariska; Reddy, Naveen A.; Freeman, William R.; Coil, Alison L.; Siana, Brian; Mobasher, Bahram; Shivaei, Irene; Price, Sedona H.; de Groot, Laura
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-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 O32 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 O32 versus R23 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. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W.M. Keck Foundation.
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
2016-04-01
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).
NASA Astrophysics Data System (ADS)
Srinivasan, V.; Hallberg, M. P.; Strykowski, P. J.
2010-02-01
Viscous linear stability calculations are presented for model low-density axisymmetric jet flows. Absolute growth transitions for the jet column mode are mapped out in a parametric space including velocity ratio, density ratio, Reynolds number, momentum thickness, and subtle differences between velocity and density profiles. Strictly speaking, the profiles used in most jet stability studies to date are only applicable to unity Prandtl numbers and zero pressure gradient flows—the present work relaxes this requirement. Results reveal how subtle differences between the velocity and density profiles generally used in jet stability theory can dramatically alter the absolute growth rate of the jet column mode in these low-density flows. The results suggest heating/cooling or mass diffusion at the outer nozzle surface can suppress absolute instability and potentially global instability in low-density jets.
Rossiter, H B; Howe, F A; Ward, S A; Kowalchuk, J M; Griffiths, J R; Whipp, B J
2000-01-01
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 (τ) 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 (V̇O2) was simultaneously determined, breath-by-breath, using a mass spectrometer and a turbine volume measuring module. The probability density functions (PDF) of [PCr] and V̇O2 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 V̇O2 fluctuations at rest and during exercise (sr and sw, respectively) and the peak centres of the distributions (xcr and xcw) were determined, as were the skewness (γ1) and kurtosis (γ2) coefficients. There was no difference between sr and sw for [PCr] relative to the resting control baseline (sr= 1.554%Δ (s.d.= 0.44), sw= 1.514%Δ (s.d.= 0.35)) or the PDF peak centres (xcr=−0.013 %Δ (s.d.= 0.09), xcw−0.197 %Δ (s.d.= 0.18)). The standard deviation and peak centre of the ‘noise’ in V̇O2 also did not vary between rest and exercise (sr= 0.0427 l min−1 (s.d.= 0.0104), sw= 0.0640 l min−1 (s.d.= 0.0292); xcr=−0.0051 l min−1 (s.d.= 0.0069), xcw 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 characterised as a stochastic Gaussian
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.
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.
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. PMID:16161595
NASA Astrophysics Data System (ADS)
Testemale, Denis; Coulet, Marie Vanessa; Hazemann, Jean Louis; Simon, Jean Paul; Bley, Françoise; Geaymond, Olivier; Argoud, Roger
2005-05-01
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 600bars) 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°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.
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.
Density of the concentrates of peach and pome granate juices at elevated state parameters
NASA Astrophysics Data System (ADS)
Magerramov, M. A.
2006-07-01
Investigation of the density of pomegranate and peach juices in the temperature range from 278.15 to 403.15 K at pressures of 0.1 and 5 MPa is carried out. The dependence of the density of the juices on the content of dry substances in them has been studied. The equations of state are written down and the coefficients of thermal expansion are calculated.
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.
Duziński, Kamil; Knecht, Damian; Srodoń, Sebastian
2014-04-01
The objective of the present research was to eliminate seasonal fluctuations in year-round reproductive performance of sows and to improve litter parameters by administration of oxytocin into liquid semen insemination doses. A 2-year experiment was performed on crossbreed sows, Polish Large White × Polish Landrace, which were partitioned into two groups: control, insemination without any modification with 100 mL semen doses and oxytocin, insemination with 100 mL semen doses to which 5 IU of oxytocin was added just before insemination. A total of 10,486 inseminations were made. The farrowing rate and obtained litter parameters, including the effect of season, were analyzed. For each litter, the following factors were defined: average litter size, percentage of fetal death and mummified piglets, average piglet birth weight, percentage of piglet mortality, fecundity index, average number of piglets weaned, weaned piglet weight, and daily gain. Sows presented a positive reaction to the experimental factor. A statistically higher farrowing rate for oxytocin group in summer and autumn seasons was confirmed (P ≤ 0.01). Regardless of the season, a higher average litter size was observed in the oxytocin group with the most evident differences for winter, spring (P ≤ 0.01), and summer (P ≤ 0.05). The effect of oxytocin on the percentage of fetal death and mummified piglets born was not confirmed statistically except for winter. Analyzing the fecundity index, higher values were obtained for the oxytocin group in all seasons (P ≤ 0.01), including the lowest difference between groups for winter (51.43) and the highest for summer (100.61). A higher average birth piglet weight and weaned piglet weight were recorded for the oxytocin group in all seasons. The highest differences in birth piglet weight between groups were noted for spring (0.22 kg; P ≤ 0.01) and winter (0.17 kg; P ≤ 0.05) and in weaned piglet weight for winter and spring (0.58 kg and 0.52 kg; for
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. PMID:27363680
Tomasi, D.; Shokri-Kojori, E.; Volkow, N. D.
2016-01-01
Data-driven functional connectivity density (FCD) mapping is being increasingly utilized to assess brain connectomics at rest in the healthy brain and its disruption in neuropsychiatric diseases with the underlying assumption that the spatiotemporal hub distribution is stationary. However, recent studies show that functional connectivity is highly dynamic. Here we study the temporal variability of the local FCD (lFCD) at high spatiotemporal resolution (2-mm isotropic; 0.72s) using a sliding-window approach and ‘resting-state’ datasets from 40 healthy subjects collected under the Human Connectome Project. Prominent functional connectivity hubs in visual and posterior parietal cortices had pronounced temporal changes in local FCD. These dynamic patterns in the strength of the lFCD hubs occurred in cortical gray matter with high sensitivity (up to 85%) and specificity (> 85%) and showed high reproducibility (up to 72%) across sessions and high test-retest reliability (ICC(3,1) > 0.5). The temporal changes in lFCD predominantly occurred in medial occipitoparietal regions and were proportional to the strength of the connectivity hubs. The temporal variability of the lFCD was associated with the amplitude of the low frequency fluctuations (ALFF). Pure randomness did not account for the probability distribution of lFCD. Shannon entropy increased in proportion to the strength of the lFCD hubs suggesting high average flow of information per unit of time in the lFCD hubs, particularly in medial occipitoparietal regions. Thus, the higher dynamic range of the lFCD hubs is consistent with their role in the complex orchestration of interacting brain networks. PMID:27116610
Tomasi, D; Shokri-Kojori, E; Volkow, N D
2016-01-01
Data-driven functional connectivity density (FCD) mapping is being increasingly utilized to assess brain connectomics at rest in the healthy brain and its disruption in neuropsychiatric diseases with the underlying assumption that the spatiotemporal hub distribution is stationary. However, recent studies show that functional connectivity is highly dynamic. Here we study the temporal variability of the local FCD (lFCD) at high spatiotemporal resolution (2-mm isotropic; 0.72s) using a sliding-window approach and 'resting-state' datasets from 40 healthy subjects collected under the Human Connectome Project. Prominent functional connectivity hubs in visual and posterior parietal cortices had pronounced temporal changes in local FCD. These dynamic patterns in the strength of the lFCD hubs occurred in cortical gray matter with high sensitivity (up to 85%) and specificity (> 85%) and showed high reproducibility (up to 72%) across sessions and high test-retest reliability (ICC(3,1) > 0.5). The temporal changes in lFCD predominantly occurred in medial occipitoparietal regions and were proportional to the strength of the connectivity hubs. The temporal variability of the lFCD was associated with the amplitude of the low frequency fluctuations (ALFF). Pure randomness did not account for the probability distribution of lFCD. Shannon entropy increased in proportion to the strength of the lFCD hubs suggesting high average flow of information per unit of time in the lFCD hubs, particularly in medial occipitoparietal regions. Thus, the higher dynamic range of the lFCD hubs is consistent with their role in the complex orchestration of interacting brain networks. PMID:27116610
NASA Astrophysics Data System (ADS)
Pekdogan, Hakan; Aydin, Abdullah; Hakki Sarpun, Ismail
2015-07-01
In this study, we have investigated the effects of nuclear level density parameters on the cross sections for the 234U(γ,f) reaction up to 20 MeV. The cross sections on 234U(γ,f) reaction were calculated for different level density models using the TALYS 1.6 code. First, it was determined the level density model that was the closest to the experimental data. Secondly, cross sections obtained for different level density parameters of this model were compared with experimental data from the EXFOR database. Thus it was determined the best level density parameter fit to experimental data.
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.
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
2012-07-01
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
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.
Cell Volume Fluctuations in MDCK Monolayers
Zehnder, Steven M.; Suaris, Melanie; Bellaire, Madisonclaire M.; Angelini, Thomas E.
2015-01-01
Cells moving collectively in tissues constitute a form of active matter, in which collective motion depends strongly on driven fluctuations at the single-cell scale. Fluctuations in cell area and number density are often seen in monolayers, yet their role in collective migration is not known. Here we study density fluctuations at the single- and multicell level, finding that single-cell volumes oscillate with a timescale of 4 h and an amplitude of 20%; the timescale and amplitude are found to depend on cytoskeletal activity. At the multicellular scale, density fluctuations violate the central limit theorem, highlighting the role of nonequilibrium driving forces in multicellular density fluctuations. PMID:25606673
Revised Damping Parameters for the D3 Dispersion Correction to Density Functional Theory.
Smith, Daniel G A; Burns, Lori A; Patkowski, Konrad; Sherrill, C David
2016-06-16
Since the original fitting of Grimme's DFT-D3 damping parameters, the number and quality of benchmark interaction energies has increased significantly. Here, conventional benchmark sets, which focus on minimum-orientation radial curves at the expense of angular diversity, are augmented by new databases such as side chain-side chain interactions (SSI), which are composed of interactions gleaned from crystal data and contain no such minima-focused bias. Moreover, some existing databases such as S22×5 are extended to shorter intermolecular separations. This improved DFT-D3 training set provides a balanced description of distances, covers the entire range of interaction types, and at 1526 data points is far larger than the original training set of 130. The results are validated against a new collection of 6773 data points and demonstrate that the effect of refitting the damping parameters ranges from no change in accuracy (LC-ωPBE-D3) to an almost 2-fold decrease in average error (PBE-D3). PMID:27203625
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. PMID:27070101
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.
NASA Astrophysics Data System (ADS)
Rodriguez, Jorge H.
2013-04-01
The use of phenomenological spin Hamiltonians and of spin density functional theory for the analysis and interpretation of Mössbauer spectra of antiferromagnetic or ferromagnetic diiron centers is briefly discussed. The spectroscopic parameters of the hydroxylase component of methane monooxygenase (MMOH), an enzyme that catalyzes the conversion of methane to methanol, have been studied. In its reduced diferrous state (MMOH Red ) the enzyme displays 57Fe Mössbauer and EPR parameters characteristic of two ferromagnetically coupled high spin ferrous ions. However, Mössbauer spectra recorded for MMOH Red from two different bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, display slightly different electric quadrupole splittings (Δ E Q ) in apparent contradiction to their essentially identical active site crystallographic structures and biochemical functions. Herein, the Mössbauer spectral parameters of MMOH Red have been predicted and studied via spin density functional theory. The somewhat different Δ E Q recorded for the two bacteria have been traced to the relative position of an essentially unbound water molecule within their diiron active sites. It is shown that the presence or absence of the unbound water molecule mainly affects the electric field gradient at only one iron ion of the binuclear active sites.
NASA Astrophysics Data System (ADS)
Du, Ai; Zhou, Bin; Shen, Yang; Yu, Qiujie; Shen, Jun
2014-03-01
Aerogels are more and more regarded as a new state of matter nowadays because of its diverse chemical compositions and unique properties which could fill the gap between condensed matter and gas-state matter. Among the properties, the ultralow sound velocity in the aerogels (lower than that in the air) is of great interests. J. Fricke's group studied many kinds of aerogels with different compositions and found that the sound velocity was mainly influenced by the density. Thus they obtained the lowest sound velocity result (~ 100 m/s) in a low-density silica aerogel medium (~ 0.05 g.cm-3) . Here we studied the acoustical properties of the aerogels with the similar high density (about 1.3 g.cm-3) but different skeleton structure (nano-, micro- or nano-/micro- structured) by adjusting the phase separation mode. The sound velocities of all the aerogels are below 300 m.s-1, among which micro-/nano- structured aerogel exhibits lowest longitudinal wave velocity (below 80 m.s-1) . Further structural studies indicated that the hierarchical arrangement of microstructure is the key parameter determining the sound velocity besides the density. This work was supported by the National Natural Science Foundation of China (51102184, 51172163), National High-tech R&D Program of China (863 Program, 2013AA031801) and National Science and Technology Support Program (2013BAJ01B01).
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.
NASA Astrophysics Data System (ADS)
Wang, Qing-Wei; Liu, Da-Yong; Quan, Ya-Min; Zou, Liang-Jian
2016-08-01
We theoretically study the coexistence of spin density wave (SDW) and superconductivity (SC) in ironpnictide superconductors based on a three-orbital model, focusing on the momentum-space and real-space distributions of SDW and SC order parameters in the coexistence region. We show that a SDW-SC coexisting state lies in the T-n phase diagram, in qualitative agreement with those of NaFe1 - xCoxAs and Ba(Fe1 - xCox)2As2. In the SC state the pairing wavefunction has s± symmetry with sx2y2 and sx2+y2 components. In the coexisting state, the SDW and SC order parameters display strong orbital-selective competitions in momentum space, which also result in real-space modulation and spin singlet-triplet mixing in the Cooper pairing amplitude. We expect that the obtained features may be observed in future experiments.
Fluctuations in strongly coupled cosmologies
NASA Astrophysics Data System (ADS)
Bonometto, Silvio A.; Mainini, Roberto
2014-03-01
In the early Universe, a dual component made of coupled CDM and a scalar field Φ, if their coupling β > (3)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 proptoa-4 and have early density parameters Ωd = 1/(4β2) and Ωc = 2 Ωd (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding proptoa-3, breaks such stationary expansion at z ~ 3-5 × 103, 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 Cl 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 Script O(10-3), 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.
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. PMID:21813272
O'Sullivan, Denis B D; Jones, Christopher E; Abdelraheim, Salama R; Brazier, Marcus W; Toms, Harold; Brown, David R; Viles, John H
2009-02-01
Prion diseases are associated with the misfolding of the prion protein (PrP(C)) from a largely alpha-helical isoform to a beta-sheet rich oligomer (PrP(Sc)). Flexibility of the polypeptide could contribute to the ability of PrP(C) to undergo the conformational rearrangement during PrP(C)-PrP(Sc) interactions, which then leads to the misfolded isoform. We have therefore examined the molecular motions of mouse PrP(C), residues 113-231, in solution, using (15)N NMR relaxation measurements. A truncated fragment has been used to eliminate the effect of the 90-residue unstructured tail of PrP(C) so the dynamics of the structured domain can be studied in isolation. (15)N longitudinal (T(1)) and transverse relaxation (T(2)) times as well as the proton-nitrogen nuclear Overhauser effects have been used to calculate the spectral density at three frequencies, 0, omega(N,) and 0.87omega(H). Spectral densities at each residue indicate various time-scale motions of the main-chain. Even within the structured domain of PrP(C), a diverse range of motions are observed. We find that removal of the tail increases T(2) relaxation times significantly indicating that the tail is responsible for shortening of T(2) times in full-length PrP(C). The truncated fragment of PrP has facilitated the determination of meaningful order parameters (S(2)) from the relaxation data and shows for the first time that all three helices in PrP(C) have similar rigidity. Slow conformational fluctuations of mouse PrP(C) are localized to a distinct region that involves residues 171 and 172. Interestingly, residues 170-175 have been identified as a segment within PrP that will form a steric zipper, believed to be the fundamental amyloid unit. The flexibility within these residues could facilitate the PrP(C)-PrP(Sc) recognition process during fibril elongation. PMID:19173221
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
Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal
NASA Astrophysics Data System (ADS)
Parsouzi, Z.; Shamid, S. M.; Borshch, V.; Challa, P. K.; Baldwin, A. R.; Tamba, M. G.; Welch, C.; Mehl, G. H.; Gleeson, J. T.; Jakli, A.; Lavrentovich, O. D.; Allender, D. W.; Selinger, J. V.; Sprunt, S.
2016-04-01
We report a dynamic light-scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (NTB ) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic modes and one hydrodynamic mode in the NTB phase, and a single nonhydrodynamic mode plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-de Gennes expansion of the free-energy density in terms of heliconical director and helical polarization fields that characterize the NTB structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.
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
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
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.
Drift-wave fluctuation in an inviscid tokamak plasma
NASA Astrophysics Data System (ADS)
Yang, Jian-Rong; Mao, Jie-Jian; Tang, Xiao-Yan
2013-11-01
In order to describe the characterization of resistive drift-wave fluctuation in a tokamak plasma, a coupled inviscid two-dimensional Hasegawa—Wakatani model is investigated. Two groups of new analytic solutions with and without phase shift between the fluctuant density and the fluctuant potential are obtained by using the special function transformation method. It is demonstrated that the fluctuant potential shares similar spatio—temporal variations with the density. It is found from the solutions without phase shift that the effect of the diffusion and adiabaticity on the fluctuant density is quite complex, and that the fluctuation may be controlled through the adiabaticity and diffusion. By using the typical parameters in the quasi-adiabatic regime in the solutions with phase shift, it is shown that the density gradient becomes larger as the contours become dense toward the plasma edge and the contours have irregular structures, which reveal the nonuniform distribution in the tokamak edge.
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.
The finite probe size effect in fluctuation measurements; application to dusty plasmas
NASA Astrophysics Data System (ADS)
Tolias, P.; Ratynskaia, S.; de Angelis, U.; Lazzaro, E.
2016-04-01
> The effect of the finite probe size in plasma fluctuation measurements is revisited for dusty plasmas, where it has been argued that dust leads to a significant low-frequency enhancement in the spectral densities of ion density fluctuations, which can constitute the physical basis of a dust diagnostic technique. Theoretical predictions for the spectral modifications are presented and the dust acoustic mode contribution is analysed. The finite probe size effect is treated within the volume average approach, which introduces geometry dependent form factors that are calculated for spherical and cylindrical probes. The volume average approach is compared with the typically employed cutoff wavenumber approximation for various dust and plasma parameters. The contribution of temperature fluctuations to the spectral density of current fluctuations is also evaluated.
Long, F.H.; Love, S.P.; Swanson, B.I.
1993-01-01
Luminescence spectra, both emission and excitation, and the excitation dependence of the resonance Raman (RR) spectra were measured for a 1-dimensional charge-density-wave solid, [Pt(L)[sub 2]Cl[sub 2
NASA Astrophysics Data System (ADS)
Bandyopadhyay, M.; Sudhir, Dass; Chakraborty, A.
2015-03-01
An inductively coupled plasma (ICP) based negative hydrogen ion source is chosen for ITER neutral beam (NB) systems. To avoid regular maintenance in a radioactive environment with high flux of 14 MeV neutrons and gamma rays, invasive plasma diagnostics like probes are not included in the ITER NB source design. While, optical or microwave based diagnostics which are normally used in other plasma sources, are to be avoided in the case of ITER sources due to the overall system design and interface issues. In such situation, alternative forms of assessment to characterize ion source plasma become a necessity. In the present situation, the beam current through the extraction system in the 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 and negative ion stripping. Apart from that, the ICP production region radio frequency (RF) driver region) is placed far (∼30 cm) from the extraction region. Therefore, there are uncertainties involved in linking the beam current with plasma properties inside the RF driver. To maintain the optimum condition for source operation it is necessary to maintain the optimum conditions in the driver. A method of characterization of the plasma density in the driver without using any invasive or non-invasive probes could be a useful tool to achieve that objective. Such a method, which is exclusively for ICP based ion sources, is presented in this paper. In this technique, plasma density inside the RF driver is estimated through the measurements of the electrical parameters in the RF power supply circuit path. Monitoring RF driver plasma through the described route will be useful during the source commissioning phase and also in the beam operation phase.
Boereboom, J. M.; Wijzenbroek, M.; Somers, M. F.; Kroes, G. J.
2013-12-28
Recently, an implementation of the specific reaction parameter (SRP) approach to density functional theory (DFT) was used to study several reactive scattering experiments of H{sub 2} on Cu(111). It was possible to obtain chemical accuracy (1 kcal/mol ≈ 4.2 kJ/mol), and therefore, accurately model this paradigmatic example of activated H{sub 2} dissociation on a metal surface. In this work, the SRP-DFT methodology is applied to the dissociation of hydrogen on a Pd(111) surface, in order to test whether the SRP-DFT approach is also applicable to non-activated H{sub 2}-metal systems. In the calculations, the Born–Oppenheimer static surface approximations are used. A comparison to molecular beam sticking experiments, performed at incidence energies ⩾125 meV, on H{sub 2} + Pd(111) suggested the PBE-vdW [where the Perdew, Burke, and Ernzerhof (PBE) correlation is replaced by van der Waals correlation] functional as a candidate SRP density functional describing the reactive scattering of H{sub 2} on Pd(111). Unfortunately, quantum dynamics calculations are not able to reproduce the molecular beam sticking results for incidence energies <125 meV. From a comparison to initial state-resolved (degeneracy averaged) sticking probabilities it seems clear that for H{sub 2} + Pd(111) dynamic trapping and steering effects are important, and that these effects are not yet well modeled with the potential energy surfaces considered here. Applying the SRP-DFT method to systems where H{sub 2} dissociation is non-activated remains difficult. It is suggested that a density functional that yields a broader barrier distribution and has more non-activated pathways than PBE-vdW (i.e., non-activated dissociation at some sites but similarly high barriers at the high energy end of the spectrum) should allow a more accurate description of the available experiments. Finally, it is suggested that new and better characterized molecular beam sticking experiments be done on H{sub 2} + Pd(111
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.
Nonequilibrium fluctuations in a resistor
NASA Astrophysics Data System (ADS)
Garnier, N.; Ciliberto, S.
2005-06-01
In small systems where relevant energies are comparable to thermal agitation, fluctuations are of the order of average values. In systems in thermodynamical equilibrium, the variance of these fluctuations can be related to the dissipation constant in the system, exploiting the fluctuation-dissipation theorem. In nonequilibrium steady systems, fluctuations theorems (FT) additionally describe symmetry properties of the probability density functions (PDFs) of the fluctuations of injected and dissipated energies. We experimentally probe a model system: an electrical dipole driven out of equilibrium by a small constant current I , and show that FT are experimentally accessible and valid. Furthermore, we stress that FT can be used to measure the dissipated power P¯ =R I2 in the system by just studying the PDFs’ symmetries.
Far-infrared lines from G45.13 + 0.14 A and K3-50 A - Density fluctuations in compact H II regions
NASA Technical Reports Server (NTRS)
Colgan, Sean W. J.; Simpson, J. P.; Rubin, Robert H.; Erickson, Edwin F.; Haas, M. R.; Wolf, Juergen
1991-01-01
Properties of two compact H II regions, K3-50 A and G45.13 + 0.14 A, were investigated by measuring FIR fluxes from forbidden O III 51.8 and 88.4 micron lines, forbidden N III 57.3 micron line, forbidden S III 33.5 micron line, and forbidden Ne III 36.0 micron line of these regions, using a cooled grating spectrometer on NASA's Kuiper Airborne Observatory. For both H II regions, the ratio of the two FIR O(2+) lines indicates an electron density of about 1000/cu cm, which for K3-50 A is a factor of 10 to 100 lower than the density determined from optical line observations of the lower excitation species S(+) and N(+) and than the peak rms density deduced from radio continuum measurements by Turner and Matthews (1984). Detailed spherically symmetric models of the two sources were constructed using all available measurements.
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. PMID:24995917
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.
Ibn Yacoub, Yousra; Amine, Bouchra; Laatiris, Assia; Wafki, Fahd; Znat, Fatima; Hajjaj-Hassouni, Najia
2012-10-01
In this case-control study, our first aim was to evaluate the bone mineral density (BMD) in women with systemic sclerosis (SSc) and its correlates. Secondarily, we aimed to evaluate 25-hydroxyvitamin D3 status and its relationships with disease parameters and BMD. Sixty patients with SSc and 60 age-and gender-matched controls were included in the absence of confounding factors that interfere with bone metabolism. Body mass index, menopausal status, familial history of osteoporosis and/or fractures; personal fracture history; exercise activity and laboratory parameters of bone metabolism were assessed in patients and controls. BMD was measured by using a dual-energy X-ray absorptiometry in lumbar spine (L1-L4) and femoral neck. The 25-hydroxyvitamin D3 was measured in a subgroup of 30 patients and in a subgroup of 30 matched controls. Systemic manifestations of SSc, biological inflammatory parameters, functional disability (scleroderma health assessment questionnaire (S-HAQ)) and immunological status of disease were collected in patients' group. The mean age of patients was 49.44 ± 13.07 years versus 49.55 ± 12.11 in controls. The mean disease duration was 9.63 ± 5.9 years. SSc patients had a significantly earlier age and longer duration of menopause than controls (P = 0.003). Phosphocalcic metabolism parameters were within normal ranges in both groups. BMD was significantly lower in SSc patients than in controls both in lumbar spine (-2.97 ± 0.25 in patients vs. 0.46 ± 0.11 in controls) and femoral neck (-1.93 ± 0.32 in patients vs. -0.81 ± 0.69 in controls) (P < 0.01). Thirty-six (60%) patients versus 15 (25%) controls had osteoporosis and 19 (31.7%) patients versus 13 (21.7%) controls had osteopenia (P < 0.01). In correlation analysis and in multiple regression models, there were significant correlations between BMD and longer duration of SSc, severe joint involvement (severe joint pain and erosive arthropathy), malabsorption syndrome and the positivity of
NASA Astrophysics Data System (ADS)
Omura, Yasuhisa
2013-06-01
This paper proposes a possible unified model for the Hooge parameter by considering the impact of transport dimensionality on the Hooge parameter behavior of various inversion-layer-channel metal-oxide-semiconductor field-effect transistors. Past experiments show that the Hooge parameter has a couple of peculiar behaviors. Based on a phenomenological consideration, the original mobility-based model for the Hooge parameter is shown to provide only a partial understanding of the results. It is also observed that, in contrast to past models, the interpretation of some aspects of the Hooge parameter strongly depends on how the two fluctuation modes, the carrier-density fluctuation and the mobility fluctuation, correlate. The phenomenological model proposed here gives a fundamental physical basis that allows important aspects of the Hooge parameter to be interpreted; the model also introduces three basic parameters (the Hooge parameter elements for the carrier-density fluctuation, the mobility fluctuation, and the cross-correlation component). Theoretical expressions for the three basic Hooge parameters are given by merging the fundamental Hooge model, Handel's theory, statistical physics, and quantum-mechanical transport physics. The gate voltage dependence of the Hooge parameter can be explained reasonably well by stating that the screening length rules the dielectric function and that the mobility fluctuation and carrier density fluctuation are correlated. Finally, the theoretical models are examined against the results of past experiments.
Far-Infrared Lines from G45.13 + 0.14 and K 3-50 A: Density Fluctuations in Compact H 2 Regions
NASA Technical Reports Server (NTRS)
Colgan, Sean W. J.; Simpson, J. P.; Rubin, Robert H.; Erickson, Edwin F.; Haas, M. R.; Wolf, Jurgen
1991-01-01
The far-infrared lines of (O III) 51.8 and 88.4 microns, (N III) 57.3 microns, (S III) 33.5 microns, and (Ne III) 36.0 microns have been measured in the compact H II regions G45.13+0.14 A and K3-50 A. These measurements were made with the facility cooled grating spectrometer on flights of NASA's Kuiper Airborne Observatory. For both sources, the ratio of the two O(++) lines indicates an electron density N(sub e) approx. 10(exp 3)cm(sup -3). For K3-50 A, this is a factor of 10 to a hundred times lower than the density determined from near-infrared and optical line observations of lower excitation species and from radio measurements of the peak continuum emission. A comparison with other far-infrared measurements for both sources shows that the lower excitation, higher critical density S(++) lines originate from higher density material than do the O(++) lines. Detailed, spherically symmetric models for both sources are presented. These models require clumping, different abundances than the Orion Nebula, and an enhancement in the standard Kurucz stellar atmospheres at energies E greater than 41 eV to obtain reasonable agreement with the measurements. The average nitrogen-to-oxygen abundance ratio for these two H II regions is N/O approx. 0.2, in agreement with other far-infrared studies at Galactic radii greater than or equal to 6 kpc.
Axions and inflation: Vacuum fluctuations
NASA Astrophysics Data System (ADS)
Lyth, D. H.
1992-05-01
Cosmological consequences of the Peccei-Quinn field ψ=reiθ/ √2 are explored. It has a Mexican-hat potential W=1/4λ(r2-f2a)2. During inflation the potential may be modified so that fa has a different effective value fa1; it is assumed that r sits in the vacuum at r=fa1. After inflation the temperature is supposed to be less than fa so that r=fa, and the only degree of freedom is the axion field faθ. It has a Gaussian inhomogeneity coming from the vacuum fluctuation of θ during inflation. When the axion mass ma(T) becomes significant at T~1 GeV, θ has dispersion σθ~=(4/2π)(H1/fa1) and some mean θ¯ (in the observable Universe). The axion potential is U(θ)=(79 MeV)4(1-cosNθ), and the ensuing cosmology is determined by the three parameters fa/N, Nθ¯, and Nσθ. The entire domain of parameter space is considered, including the regime where the axion density perturbation is non-Gaussian and the regime where axionic domain walls are produced. Observational constraints on the parameters are established. At the end of the paper the additional assumption is made that during inflation the vacuum is at r=fa. Unless fa/N is near the Planck scale and axions make up only a small fraction of the dark matter, this leads to the bound V1/41<2×1015 GeV, where V1 is the energy density during inflation, at the epoch when the observable Universe leaves the horizon.
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
NASA Astrophysics Data System (ADS)
Bukhanko, F. N.; Bukhanko, A. F.
2013-06-01
The magnetic phase transformations induced by changes of the composition, external magnetic field strength, and temperature in manganites with a nearly half-filled conduction band in the vicinity of the metal-insulator phase transition have been investigated experimentally. It has been found that the substitution of rare-earth ions (Sm) for Nd ions with a larger ionic radius in R 0.55Sr0.45MnO3 manganites leads to a linear decrease in the Curie temperature T C from 270 to 130 K and a transformation of the second-order ferromagnetic (FM) phase transition into a first-order phase transition. The results of measurements of the alternating-current (ac) magnetic susceptibility in the (Nd1 - y Sm y )0.55Sr0.45MnO3 system indicate the existence of a Griffiths-like phase in samples with a samarium concentration y > 0.5 in the temperature range T C < T < T* (where T* ˜ 220 K). For samples with y > 0.5, the magnetization isotherms at temperatures above T C exhibit specific features in the form of reversible metamagnetic phase transitions associated with strong fluctuations of the short-range ferromagnetic order in the system of Mn spins in the high-temperature Griffiths phase consisting of ferromagnetic clusters. According to the results of measurements of the ac magnetic susceptibility in the (Sm1 - y Gd y )0.55Sr0.45MnO3 system for a gadolinium concentration y = 0.5, there is an antiferromagnetic (AFM) phase with an unusually low critical temperature of the spin ordering T N ≊ 48.5 K. An increase in the external static magnetic field at 4.2 K leads to an irreversible induction of the ferromagnetic phase, which is stable in the temperature range 4.2-60 K. In the temperature range 60 K < T < 150 K, there exists a high-temperature Griffiths-like phase consisting of clusters (correlations) with a local charge/orbital ordering. The metastable antiferromagnetic structure is retained in samples with gadolinium concentrations y = 0.6 and 0.7, but it is destroyed with a further
Yiakoumos, Theocharis; Kälble, Tilman; Rausch, Steffen
2015-01-01
Objective: The aim was to determine the prognostic ability of Partin's tables for a patient collective undergoing radical prostatectomy (RP) and to evaluate the association of prostate-specific antigen (PSA) density (PSAD) and postoperative lymph node status. Methods: From 1999 to 2006, 393 consecutive patients underwent RP at our Urology department. Patients with Gleason scores < 6, clinical stages >T2c or neoadjuvant hormonal therapy were excluded. Preoperative PSA, biopsy results, digital rectal examination, and prostate size at transrectal ultrasound were recorded. Risk stratification according to the Partin scoring system was performed. Postoperative results were compared with preoperative risk estimation. Univariate and multivariate statistical analysis about prediction of postoperative lymph node status was performed. Results: Lymph node invasion (LNI) was found in 36 patients (9.16%). Kendall's rank correlation analysis revealed a significant association between the number of removed LN and LNI (P = 0.016). Patients with LNI had a significantly higher preoperative PSA and PSAD. Preoperative Gleason score was a significant predictor of LNI. The Partin tables' prediction of organ confined stages, extraprostatic extension, and seminal vesicle invasion was in line with the pathological findings in our collective. PSAD was a significant predictor of LNI in univariate and multivariate analysis. Conclusion: The most widely used nomogram is of high value in therapy decision-making, although it remains an auxiliary means. Considering the performance of lymph node dissection, surgeons should be aware of the specifics of the applied nomogram. PSAD appears as a useful adjunctive parameter for preoperative prostate risk estimation and warrants further evaluation. PMID:26692660
Froissart bound and gluon number fluctuations
Xiang Wenchang
2010-05-01
We study the effect of gluon number fluctuations (Pomeron loops) on the impact parameter behavior of the scattering amplitude in the fixed coupling case. We demonstrate that the dipole-hadron cross section computed from gluon number fluctuations saturates the Froissart bound and the growth of the radius of the black disk with rapidity is enhanced by an additional term as compared to the single event case. We find that the physical amplitude has a Gaussian impact parameter dependence once the gluon number fluctuations are included. This indicates that the fluctuations may be the microscopic origin for the Gaussian impact parameter dependence of the scattering amplitude.
NASA Astrophysics Data System (ADS)
Grudzevich, O. T.
2015-12-01
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.
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.
Large-Scale Chaos and Fluctuations in Active Nematics
NASA Astrophysics Data System (ADS)
Ngo, Sandrine; Peshkov, Anton; Aranson, Igor S.; Bertin, Eric; Ginelli, Francesco; Chaté, Hugues
2014-07-01
We show that dry active nematics, e.g., collections of shaken elongated granular particles, exhibit large-scale spatiotemporal chaos made of interacting dense, ordered, bandlike structures in a parameter region including the linear onset of nematic order. These results are obtained from the study of both the well-known (deterministic) hydrodynamic equations describing these systems and of the self-propelled particle model they were derived from. We prove, in particular, that the chaos stems from the generic instability of the band solution of the hydrodynamic equations. Revisiting the status of the strong fluctuations and long-range correlations in the particle model, we show that the giant number fluctuations observed in the chaotic phase are a trivial consequence of density segregation. However anomalous, curvature-driven number fluctuations are present in the homogeneous quasiordered nematic phase and characterized by a nontrivial scaling exponent.
Sharma, A; Kumar, P; Rani, V; Ray, N; Ghosh, S
2016-06-15
We study charge transport in molecular organic semiconductors using two terminal and three terminal field effect transistor devices. Using phthalocyanines as examples, we achieve unification of carrier mobility between the different configurations in a Gaussian density of states. We find that the current density-voltage characteristics for two terminal devices can be understood by introducing a concentration dependence of the carrier mobility, as described by Oelerich et al (2012 Phys. Rev. Lett. 108 226403, 2010 Appl. Phys. Lett. 97 143302). Studying the evolution of the activation energy with the carrier density, we find results consistent with a percolation picture and a density dependent transport energy. PMID:27160656
Long, F.H.; Love, S.P.; Swanson, B.I.
1993-02-01
Luminescence spectra, both emission and excitation, and the excitation dependence of the resonance Raman (RR) spectra were measured for a 1-dimensional charge-density-wave solid, [Pt(L){sub 2}Cl{sub 2}][Pt(L){sub 2}](ClO{sub 4}){sub 4} ; L=1, 2-diaminoethane. The luminescence experiments support the existence of tail states in the band gap region, which indicate the presence of disorder. In contrast, the RR measurements conclusively demonstrated that the effects of static structural disorder on the vibrational spectroscopy can be neglected. This apparently paradoxical result can be explained by considering the zero-point motion of the lattice. The experimental results are compared to recent theoretical models.
NASA Astrophysics Data System (ADS)
Poniewierski, A.; Hołyst, Robert; Price, A. C.; Sorensen, L. B.
1999-03-01
In this paper, we study the dynamic density autocorrelation function G(r,t) for smectic-A films in the layer sliding geometry. We first postulate a scaling form for G, and then we show that our postulated scaling form holds by comparing the scaling predictions with detailed numerical calculations. We find some deviations from the scaling form only for very thin films. For thick films, we find a region of a bulklike behavior, where the dynamics is characterized by the same static critical exponent η, which was originally introduced by Caillé [C. R. Acad. Sci. Ser. B 274, 891 (1972)]. In the limit of very large distance perpendicular to the layer normal, or in the limit of very long time, we find that the decay of G is governed by the surface exponent χ=kBTq2z/(4πγ), where γ is the surface tension and the wave-vector component qz satisfies the Bragg condition. We also find an intermediate perpendicular distance regime in which the decay of G is governed by the time-dependent exponent χexp(-t/τ0), where the relaxation time is given by τ0=η3(Ld)/(2γ), where η3 is the layer sliding viscosity, and Ld is the film thickness.
NASA Astrophysics Data System (ADS)
Sharma, A.; Kumar, P.; Rani, V.; Ray, N.; Ghosh, S.
2016-06-01
We study charge transport in molecular organic semiconductors using two terminal and three terminal field effect transistor devices. Using phthalocyanines as examples, we achieve unification of carrier mobility between the different configurations in a Gaussian density of states. We find that the current density–voltage characteristics for two terminal devices can be understood by introducing a concentration dependence of the carrier mobility, as described by Oelerich et al (2012 Phys. Rev. Lett. 108 226403, 2010 Appl. Phys. Lett. 97 143302). Studying the evolution of the activation energy with the carrier density, we find results consistent with a percolation picture and a density dependent transport energy.
NASA Technical Reports Server (NTRS)
Shantaram, S. Pai; Gyekenyesi, John P.
1989-01-01
The calculation of shape and scale parametes 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 using the Weibull distribution statistical parameters. 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.
NASA Astrophysics Data System (ADS)
Liu, Ning; He, Miao; Alghamdi, Hisham; Chen, George; Fu, Mingli; Li, Ruihai; Hou, Shuai
2015-08-01
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.
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.
Moursi Khadiga, S; Abdel Fattah, S; Rasha; Omar, M A A; Mourad, A K
2015-01-01
Investigation throughout the subsequent years of 2011-2012 and 2012-2013 indicated that chaff scale, P. pegandii is an important economic pest on citrus trees in Abou El-Matamer area, El-Beheira Governorate, Egypt. It has been recorded in relatively high rates all over the year on three citrus varieties called Succari, Baladi and Navel oranges. Field observation and recorded data revealed that the common abundance was recorded for chaff scale on Succari oranges followed by Navel oranges then the least abundant on Baladi oranges. Generally, the calculated data on Succari oranges showed that, the population of P. pergandii reached the maximum during July and there were five highly variation periods in both the growing seasons of 2011-2012 and 2012-2013. The maximal percent of pre and adult females was observed during Spring and early Summer and reached 100% of the total counted individuals during October and December in the first year, but in the second one a higher population was recorded during Summer and early Winter months. The adult males were observed during Summer and Autumn months. Results showed also that the relationship between daily mean temperature and population density of chaff scale was weak, insignificantly negative in the two growing seasons (2011-2012 and 2012-2013) and also insignificantly but positive with relative humidity. That relationship with wind speed indicated weak positive significance in the first year and strong in the second season. The relationship between dew point and insect population was weak of positive significance in both growing seasons. PMID:27145572
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. PMID:26668724
Gambling with Superconducting Fluctuations
NASA Astrophysics Data System (ADS)
Foltyn, Marek; Zgirski, Maciej
2015-08-01
Josephson junctions and superconducting nanowires, when biased close to superconducting critical current, can switch to a nonzero voltage state by thermal or quantum fluctuations. The process is understood as an escape of a Brownian particle from a metastable state. Since this effect is fully stochastic, we propose to use it for generating random numbers. We present protocol for obtaining random numbers and test the experimentally harvested data for their fidelity. Our work is prerequisite for using the Josephson junction as a tool for stochastic (probabilistic) determination of physical parameters such as magnetic flux, temperature, and current.
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
Propagation of radiation in fluctuating multiscale plasmas. I. Kinetic theory
Tyshetskiy, Yu.; Pal Singh, Kunwar; Thirunavukarasu, A.; Robinson, P. A.; Cairns, Iver H.
2012-11-15
A theory for propagation of radiation in a large scale plasma with small scale fluctuations is developed using a kinetic description in terms of the probability distribution function of the radiation in space, time, and wavevector space. Large scale effects associated with spatial variations in the plasma density and refractive index of the plasma wave modes and small scale effects such as scattering of radiation by density clumps in fluctuating plasma, spontaneous emission, damping, and mode conversion are included in a multiscale kinetic description of the radiation. Expressions for the Stokes parameters in terms of the probability distribution function of the radiation are used to enable radiation properties such as intensity and polarization to be calculated.
Constraining dark energy fluctuations with supernova correlations
Blomqvist, Michael; Enander, Jonas; Mörtsell, Edvard E-mail: enander@fysik.su.se
2010-10-01
We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state w≠−1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.
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.
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. PMID:26932018
RF current drive and plasma fluctuations
NASA Astrophysics Data System (ADS)
Peysson, Yves; Decker, Joan; Morini, L.; Coda, S.
2011-12-01
The role played by electron density fluctuations near the plasma edge on rf current drive in tokamaks is assessed quantitatively. For this purpose, a general framework for incorporating density fluctuations in existing modelling tools has been developed. It is valid when rf power absorption takes place far from the fluctuating region of the plasma. The ray-tracing formalism is modified in order to take into account time-dependent perturbations of the density, while the Fokker-Planck solver remains unchanged. The evolution of the electron distribution function in time and space under the competing effects of collisions and quasilinear diffusion by rf waves is determined consistently with the time scale of fluctuations described as a statistical process. Using the ray-tracing code C3PO and the 3D linearized relativistic bounce-averaged Fokker-Planck solver LUKE, the effect of electron density fluctuations on the current driven by the lower hybrid (LH) and the electron cyclotron (EC) waves is estimated quantitatively. A thin fluctuating layer characterized by electron drift wave turbulence at the plasma edge is considered. The effect of fluctuations on the LH wave propagation is equivalent to a random scattering process with a broadening of the poloidal mode spectrum proportional to the level of the perturbation. However, in the multipass regime, the LH current density profile remains sensitive to the ray chaotic behaviour, which is not averaged by fluctuations. The effect of large amplitude fluctuations on the EC driven current is found to be similar to an anomalous radial transport of the fast electrons. The resulting lower current drive efficiency and broader current profile are in better agreement with experimental observations. Finally, applied to the ITER ELMy H-mode regime, the model predicts a significant broadening of the EC driven current density profile with the fluctuation level, which can make the stabilization of neoclassical tearing mode potentially
NASA Astrophysics Data System (ADS)
Milanesio, D.; Maggiora, R.
2013-04-01
The successful design of an ion cyclotron antenna mainly relies on the capability of accurately predicting its behavior both in terms of input parameters, and therefore power coupled to plasma, and radiated fields. All these features essentially depend on the antenna itself (its geometry, the matching and tuning systems) and, obviously, on the faced loading. In this paper a number of plasma profiles is analysed with the help of the TOPICA code, a predictive tool for the design and optimization of radio frequency (RF) launchers in front of a plasma, in order to understand which plasma parameters have the most significant influence on the coupling performances of a typical IC antenna.
Risco, D; García, A; Serrano, E; Fernandez-Llario, P; Benítez, J M; Martínez, R; García, W L; de Mendoza, J Hermoso
2014-12-01
Porcine brucellosis is a disease caused by Brucella suis, which is characterized by reproductive disorders in pigs. The number of cases of swine brucellosis has risen in many European countries, likely because of the presence of a wild reservoir of B. suis in wild boar. This study aimed at evaluating factors that may influence the probability of infection with Brucella spp. in wild boar and at assessing the impact of a previous contact with Brucella spp. on reproductive parameters of wild boar. Two hundred and four wild boar living in Extremadura (south-western Spain) were studied. The presence of anti-Brucella antibodies was determined using an indirect ELISA, while the presence of living bacteria in genital organs was evaluated through microbiological cultures. Sex, age, density of wild boar in summer and presence of outdoor pigs were selected as possible risk factors for being seropositive for Brucella spp. in wild boar. In addition, reproductive parameters such as breeding status or potential fertility in females and testis weight in males were estimated and related to the presence of anti-Brucella antibodies. A total of 121 animals were seropositive, resulting in a prevalence of 59.3% (95% CI). In addition, seven isolates of B. suis biovar 2 were obtained. Wild boar density in summer, as well as age and sex, was proposed as factors to explain the probability of Brucella seroconversion, although wild boar density in summer was the key factor. Current measures of reproductive parameters were not influenced by a previous contact with Brucella spp. Isolation of B. suis confirms that wild boar could represent a risk to domestic pig health in the study area. Wild boar density seems to have a great influence in the probability of infections with B. suis and suggests that density management could be useful to control Brucella infection in wild boar. PMID:23347330
NASA Astrophysics Data System (ADS)
Nagy, Á.
1990-10-01
The density-functional theory for ensembles of fractional occupation formulated by Gross, Oliveira, and Kohn [Phys. Rev. A 37, 2821 (1988)] has been applied. The excitation energies of several atoms have been determined using a parameter-free exchange potential of Gáspár [Acta Phys. Hung. 35, 213 (1974)]. The calculated excitation energies are in good agreement with the experimental values.
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
Cong, Alexander; Buijs, Jorn Op Den; Dragomir-Daescu, Dan
2010-01-01
Quantitative computed tomography based finite element analysis of the femur is currently being investigated as a method for non-invasive stiffness and strength predictions of the proximal femur. The specific objective of this study was to determine better conversion relationships from QCT-derived bone density to elastic modulus, in order to achieve accurate predictions of the overall femoral stiffness in a fall-on-the-hip loading configuration. Twenty-two femurs were scanned, segmented and meshed for finite element analysis. The elastic moduli of the elements were assigned according to the average density in the element. The femurs were then tested to fracture and force-displacement data was collected to calculate femoral stiffness. Using a training set of nine femurs, finite element analyses were performed and the parameters of the density-elastic modulus relationship were iteratively adjusted to obtain optimal stiffness predictions in a least-squares sense. The results were then validated on the remaining 13 femurs. Our novel procedure resulted in parameter identification of both power and sigmoid functions for density-elastic modulus conversion for this specific loading scenario. Our in situ estimated power law achieved improved predictions compared to published power laws, and the sigmoid function yielded even smaller prediction errors. In the future, these results will be used to further improve the femoral strength predictions of our finite element models. PMID:21030287
Choudhuri, Jyoti Roy; Chandra, Amalendu
2014-11-21
We have presented a first principles simulation study of the structural and dynamical properties of a liquid-vapor interfacial system of a concentrated (5.3 M) aqueous NaCl solution. We have used ab initio molecular dynamics to examine the structural and dynamical properties of the bulk and interfacial regions. The structural aspects of the system that have been considered here include the inhomogeneous density profiles of ions and water molecules, hydrogen bond distributions, orientational profiles, and also vibrational frequency distributions in the bulk and interfacial regions. It is found that the sodium ions are mostly located in the interior, while the chloride anions occupy a significant portion of the interface of the slab. The water dipoles at the interface prefer to orient parallel to the surface. The dynamical aspects of the interfaces are investigated in terms of diffusion, orientational relaxation, hydrogen bond dynamics, and vibrational spectral diffusion. The results of the interfacial dynamics are compared with those of the corresponding bulk region. It is observed that the interfacial molecules exhibit faster diffusion and orientational relaxation with respect to the bulk. However, the interfacial molecules are found to have longer hydrogen bond lifetimes than those of the bulk. We have also investigated the correlations of hydrogen bond relaxation with the vibrational frequency fluctuations of interfacial water molecules. PMID:25416903
Li, Chen-Xi; Tang, Song-Tao; Zhang, Qiu
2015-01-01
To assess the prevalence of osteoporosis in young men with hypogonadotropic hypogonadism (HH) and to investigate the changes of BMD and metabolic parameters, a total of 22 young male patients with HH and 20 healthy controls were enrolled in the study. BMD, biochemical, and hormonal parameters were measured in two groups. Osteoporosis was more prevalent in HH patients (45.45%) than the control subjects (10.00%) (P < 0.001). The patients with HH had lower BMD in lumbar spine 2–4, femoral neck, and total hip (P < 0.001, for all) and higher fasting insulin (P = 0.001), HOMA-IR (P = 0.002), and SHBG (P < 0.001) compared to the controls. After 6 months of pulsatile gonadorelin treatment, BMI (P = 0.021) and BMD in lumbar spine 2–4, femoral neck, and total hip (P = 0.002, P = 0.003, and P = 0.003, resp.) increased dramatically and total cholesterol (P = 0.034), fasting insulin (P = 0.025), HOMA-IR (P = 0.021), and SHBG (P = 0.001) decreased significantly in HH patients. The study shows a higher prevalence of osteoporosis in young men with HH. Long-term pulsatile gonadorelin treatment indicates a positive effect on BMD and metabolic parameters of HH patients. PMID:26417369
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. PMID:12554071
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.
Fitness in fluctuating environments
NASA Astrophysics Data System (ADS)
Tanase Nicola, Sorin; Nemenman, Ilya
2011-03-01
Often environments change faster than the time needed to evolve optimal phenotypes through cycles of mutation and selection. We focus on this case, but assume that environmental oscillations are slower than an individual's lifetime. This is relevant, for example, for bacterial populations confronted with daily environmental changes. We analyze a resource-limited competition between a mutant phenotype and the ancestor. Environmental dynamics is represented by periodically varying, off-phase parameters of the corresponding Lotka-Volterra model. For the very slow dynamics (but still faster than the fixation time scale) the strength and the sign of selection are functions of the birth/death rates averaged over all of the environmental states and independent of the period of the fluctuations. For faster fluctuations, selection depends on the particular sequence of the successive environmental states. In particular, a time reversal of the environmental dynamics can change the sign of the selection. We conclude that the fittest phenotype in a changing environment can be very different from both the optimal phenotype in the average environment, and the phenotype with the largest average fitness.
Jiang, Bin; Guo, Hua
2016-08-01
In search for an accurate description of the dissociative chemisorption of water on the Ni(111) surface, we report a new nine-dimensional potential energy surface (PES) based on a large number of density functional theory points using the RPBE functional. Seven-dimensional quantum dynamical calculations have been carried out on the RPBE PES, followed by site averaging and lattice effect corrections, yielding sticking probabilities that are compared with both the previous theoretical results based on a PW91 PES and experiment. It is shown that the RPBE functional increases the reaction barrier, but has otherwise a minor impact on the PES topography. Better agreement with experimental results is obtained with the new PES, but the agreement is still not quantitative. Possible sources of the remaining discrepancies are discussed. PMID:27436348
NASA Astrophysics Data System (ADS)
Fadin, V. V.; Aleutdinova, M. I.
2016-04-01
Dry sliding of carbon steels under the action of an AC current of a contact density higher than 100 A/cm2 is realized. It is shown that the contact layer is easily deteriorated in high-carbon steels. This becomes evident as lower wear resistance compared to that of low-carbon steels. There are signs of a developing liquid phase on the worn surface. Using the methods of Auger spectroscopy and X-ray diffraction analysis, it is demonstrated that a high content of carbon in the initial steel structure gives rise to formation of a large amount of γ-Fe (and)as well to a high concentration of carbon near the sliding surface.
Hydration force fluctuations in hydrophilic planar systems.
Kanduč, Matej; Netz, Roland R
2016-03-01
Utilizing all-atom simulations with explicit solvent, the authors model hydrophilic surfaces interacting across water at a fixed chemical potential. They extract the hydration forces acting between the surfaces and assess force fluctuations as well as interlamellar water number fluctuations. The trends obtained from the simulations are captured by a continuum-based description with effective model parameters. The significance of fluctuations depends on surface hydrophilicity and rigidity. The authors show that the force fluctuations play an important role in kinetic processes in systems with lateral sizes smaller than several tens of nanometers. PMID:26746163
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.
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.
Yoon, P. H. E-mail: rsch@tp4.rub.de; Schlickeiser, R. E-mail: rsch@tp4.rub.de; Kolberg, U. E-mail: rsch@tp4.rub.de
2014-03-15
Any fully ionized collisionless plasma with finite random particle velocities contains electric and magnetic field fluctuations. The fluctuations can be of three different types: weakly damped, weakly propagating, or aperiodic. The kinetics of these fluctuations in general unmagnetized plasmas, governed by the competition of spontaneous emission, absorption, and stimulated emission processes, is investigated, extending the well-known results for weakly damped fluctuations. The generalized Kirchhoff radiation law for both collective and noncollective fluctuations is derived, which in stationary plasmas provides the equilibrium energy densities of electromagnetic fluctuations by the ratio of the respective spontaneous emission coefficient and the true absorption coefficient. As an illustrative example, the equilibrium energy densities of aperiodic transverse collective electric and magnetic fluctuations in an isotropic thermal electron-proton plasmas of density n{sub e} are calculated as |δB|=√((δB){sup 2})=2.8(n{sub e}m{sub e}c{sup 2}){sup 1/2}g{sup 1/2}β{sub e}{sup 7/4} and |δE|=√((δE){sup 2})=3.2(n{sub e}m{sub e}c{sup 2}){sup 1/2}g{sup 1/3}β{sub e}{sup 2}, where g and β{sub e} denote the plasma parameter and the thermal electron velocity in units of the speed of light, respectively. For densities and temperatures of the reionized early intergalactic medium, |δB|=6·10{sup −18}G and |δE|=2·10{sup −16}G result.
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
Equilibrium fluctuation theorems compatible with anomalous response
NASA Astrophysics Data System (ADS)
Velazquez, L.; Curilef, S.
2010-12-01
Previously, we have derived a generalization of the canonical fluctuation relation between heat capacity and energy fluctuations C = β2langδU2rang, which is able to describe the existence of macrostates with negative heat capacities C < 0. In this work, we extend our previous results for an equilibrium situation with several control parameters to account for the existence of states with anomalous values in other response functions. Our analysis leads to the derivation of three different equilibrium fluctuation theorems: the fundamental and the complementary fluctuation theorems, which represent the generalization of two fluctuation identities already obtained in previous works, and the associated fluctuation theorem, a result that has no counterpart in the framework of Boltzmann-Gibbs distributions. These results are applied to study the anomalous susceptibility of a ferromagnetic system, in particular, the case of the 2D Ising model.
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. PMID:26549176
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.
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
Magnetohydrodynamic and hybrid simulations of broadband fluctuations near interplanetary shocks
Agim, Y.Z.; Vinas, A.F.; Goldstein, M.L.
1995-09-01
We present results of a theoretical study of evolution of a spectrum of finite amplitude right-hand elliptically polarized magnetohydrodynamic (MHD) waves. The analysis includes use of one-and-a-half-dimensional solutions of the equations that describe compressible MHD together with one-and-a-half-dimensional hybrid simulation of the phenomenon. The motivation of the study is to understand the origin and properties of finite amplitude waves often observed in the vicinity of collisionless shocks in the heliosphere. The solutions of the MHD equations are compared with both the results of the hybrid simulations and observations previously reported by Vinas et al. in the vicinity of a quasi-parallel interplanetary shock. The initial conditions of the MHD solutions were constructed to model the observed spectrum of magnetic and velocity fluctuations; plasma parameters were also chosen to replicate the observed parameters. For the typical parameters of {beta} = 0.5, {sigma}B/B{sub 0} = 0.25 and a spectrum of parallel propagating, circularly polarized dispersive waves, initially the density and magnetic energy density correlations grow due to the (nonlinear) ponderomotive effect. The spectral features below the ion cyclotron frequency are established quickly on the Alfvenic timescale but then persist and match closely the observed fluctuations. The parametric decay instabilities that subsequently appear further enhance the density fluctuations and produce a high-frequency magnetic power spectrum consistent with the spacecraft observation. The MHD and hybrid simulations extend the previous picture of wave generation by a beam-driven ion cyclotron instability to the fully nonlinear stage. 64 refs., 24 figs.
Boltzmann equation and hydrodynamic fluctuations.
Colangeli, Matteo; Kröger, Martin; Ottinger, Hans Christian
2009-11-01
We apply the method of invariant manifolds to derive equations of generalized hydrodynamics from the linearized Boltzmann equation and determine exact transport coefficients, obeying Green-Kubo formulas. Numerical calculations are performed in the special case of Maxwell molecules. We investigate, through the comparison with experimental data and former approaches, the spectrum of density fluctuations and address the regime of finite Knudsen numbers and finite frequencies hydrodynamics. PMID:20364972
Near-field magnetophotoluminescence spectroscopy of composition fluctuations in InGaAsN.
Mintariov, A. M.; Kosel, T. H.; Merz, J. L.; Blagnov, P. A.; Vlasov, A. S.; Ustinov, V. M.; Cook, R. E.; Materials Science Division; Univ. of Notre Dame; Ioffe Physico-Technical Inst.
2001-12-31
The localization of excitons on quantum-dot-like compositional fluctuations has been observed in temperature-dependent near-field magnetophotoluminescence spectra of InGaAsN. Localization is driven by the giant bowing parameter of these alloys and manifests itself by the appearance of ultranarrow lines (half-width <1 meV) at temperatures below 70 K. We show how near-field optical scanning microscopy can be used for the estimation of the size, density, and nitrogen excess of individual compositional fluctuations (clusters), thus revealing random versus phase-separation effects in the distribution of nitrogen.
Multiplicity fluctuations due to the temperature fluctuations in high-energy nuclear collisions
Wilk, Grzegorz; Wlodarczyk, Zbigniew
2009-05-15
We investigate the multiplicity fluctuations observed in high-energy nuclear collisions attributing them to intrinsic fluctuations of temperature of the hadronizing system formed in such processes. To account for these fluctuations, we replace the usual Boltzmann-Gibbs (BG) statistics by the nonextensive Tsallis statistics characterized by the nonextensivity parameter q, with |q-1| being a direct measure of fluctuation. In the limit of vanishing fluctuations, q{yields}1 and Tsallis statistics converge to the usual BG. We evaluate the nonextensivity parameter q and its dependence on the hadronizing system size from the experimentally observed collision centrality dependence of the mean multiplicity
A solar wind-based model of geomagnetic field fluctuations at a mid-latitude station
NASA Astrophysics Data System (ADS)
Lotz, S. I.; Cilliers, P. J.
2015-01-01
Anomalous quasi-DC currents known as geomagnetically induced currents (GIC), produced in electric power network infrastructure during geomagnetic storms, pose a risk to reliable power transmission and network integrity. The prediction of a geomagnetic field-derived proxy to GIC provides an attractive mitigation technique that does not require changes to network hardware. In this paper we present the development of two artificial neural network based models tasked with predicting variations in the X (northward) and Y (eastward) components of the geomagnetic field at Hermanus, South Africa, with only solar wind plasma and interplanetary magnetic field (IMF) parameters as input. The models are developed by iteratively selecting the best set of solar wind parameters to predict the fluctuations in X and Y. To predict the variation in X, IMF magnitude, solar wind speed, fluctuation in solar wind proton density and a IMF-BZ derived parameter are selected. To predict the variation in Y, IMF-BZ , solar wind speed, and fluctuation in IMF magnitude are selected. The difference between the sets of selected input parameters are explained by the dependence of eastward perturbations in geomagnetic field at middle latitudes on field aligned currents. Model performance is evaluated during three storms in 2012. The onset and main phases of storms are fairly accurately predicted, but in cases where prolonged southward IMF coincides with solar wind parameters that are slowly varying the model fails to predict the observed fluctuations.
K/π Fluctuations at Relativistic Energies
NASA Astrophysics Data System (ADS)
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.; Silva, L. C. De; 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., Jr.; 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., Jr.; 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.
2009-08-01
We report K/π fluctuations from Au+Au collisions at sNN=19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. K/π 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 sNN=12.3 and 17.3 GeV. We report results for the collision centrality dependence of K/π fluctuations and results for charge-separated fluctuations. We observe that the K/π fluctuations scale with the charged particle multiplicity density.
Soangra, Rahul; Lockhart, Thurmon E
2012-01-01
Prolonged standing has been associated with loss of balance, onset of low back pain symptoms and development of fatigue in lower extremity muscles in working populations. Although so far, it is unknown how individuals postural stability is affected by standing on rigid versus cushioned platform but many industries are opting for anti-fatigue mats at workstations to reduce fall and injury related socio-economic cost. The goal of this study is to test SATECH's anti-fatigue mat for its effects on postural stability. A pilot test with seven healthy subjects (2535 years old) has been conducted with a force plate to obtain kinetics of body when standing on two different platforms. The centers of pressure (COP) position of subjects were determined on rigid and anti-fatigue mats for quiet stance (each trial 60 seconds). In order to understand postural control along with dynamic or stochastic characteristics of the COP, stabilogram diffusion analysis (SDA) and Invariant density analysis methods are used. Subject specific patterns were seen in stabilogram diffusion plots and associated parameters in both conditions. We also found differences in some postural sway SDA parameters with anti-fatigue mats compared to rigid vinyl floor standing with open eyes condition. But no significant differences were found in sway IDA parameters. This work further provides insights whether anti fatigue mats can be helpful to workers involved with prolonged standing tasks. PMID:22846314
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. PMID:24726797
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.
Electrostatic potential fluctuations in a Maxwellian plasma
Hazeltine, R.D.; Lowrey, J.D.
2006-01-15
The spatial correlation function of a Maxwellian plasma with perturbations arising in the electrostatic potential due to random ion density fluctuations is examined. The entropy is found from the one-particle distribution function using the Shannon formula and then, using the Einstein method, the probability distribution for the electrostatic potential fluctuation is determined. This straightforward procedure is demonstrated to be a powerful tool in studying plasma correlation functions when the system entropy can be computed.
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
How to fool cosmic microwave background parameter estimation
Kinney, William H.
2001-02-15
With the release of the data from the Boomerang and MAXIMA-1 balloon flights, estimates of cosmological parameters based on the cosmic microwave background (CMB) have reached unprecedented precision. In this paper I show that it is possible for these estimates to be substantially biased by features in the primordial density power spectrum. I construct primordial power spectra which mimic to within cosmic variance errors the effect of changing parameters such as the baryon density and neutrino mass, meaning that even an ideal measurement would be unable to resolve the degeneracy. Complementary measurements are necessary to resolve this ambiguity in parameter estimation efforts based on CMB temperature fluctuations alone.
Temporal fluctuations of laser beam radiation in atmospheric precipitation
NASA Astrophysics Data System (ADS)
Kabanov, M. V.; Zhukov, A. F.; Tsvyk, R. Sh.
1988-02-01
The present results of experimental investigations of laser beam intensity temporal fluctuations in atmospheric precipitation indicate the difficulty of obtaining a priori intensity fluctuation estimates in a real atmosphere. The few cases in which one can analytically describe the spectrum and intensity fluctuation variance are nevertheless important for practical purposes. By measuring the intensity fluctuation spectra and intensity variance, it is possible to crudely estimate the precipitation and atmospheric turbulence parameters.
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.
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
NASA Astrophysics Data System (ADS)
Sementa, L.; Wijzenbroek, M.; van Kolck, B. J.; Somers, M. F.; Al-Halabi, A.; Busnengo, H. F.; Olsen, R. A.; Kroes, G. J.; Rutkowski, M.; Thewes, C.; Kleimeier, N. F.; Zacharias, H.
2013-01-01
We present new experimental and theoretical results for reactive scattering of dihydrogen from Cu(100). In the new experiments, the associative desorption of H2 is studied in a velocity resolved and final rovibrational state selected manner, using time-of-flight techniques in combination with resonance-enhanced multi-photon ionization laser detection. Average desorption energies and rotational quadrupole alignment parameters were obtained in this way for a number of (v = 0, 1) rotational states, v being the vibrational quantum number. Results of quantum dynamics calculations based on a potential energy surface computed with a specific reaction parameter (SRP) density functional, which was derived earlier for dihydrogen interacting with Cu(111), are compared with the results of the new experiments and with the results of previous molecular beam experiments on sticking of H2 and on rovibrationally elastic and inelastic scattering of H2 and D2 from Cu(100). The calculations use the Born-Oppenheimer and static surface approximations. With the functional derived semi-empirically for dihydrogen + Cu(111), a chemically accurate description is obtained of the molecular beam experiments on sticking of H2 on Cu(100), and a highly accurate description is obtained of rovibrationally elastic and inelastic scattering of D2 from Cu(100) and of the orientational dependence of the reaction of (v = 1, j = 2 - 4) H2 on Cu(100). This suggests that a SRP density functional derived for H2 interacting with a specific low index face of a metal will yield accurate results for H2 reactively scattering from another low index face of the same metal, and that it may also yield accurate results for H2 interacting with a defected (e.g., stepped) surface of that same metal, in a system of catalytic interest. However, the description that was obtained of the average desorption energies, of rovibrationally elastic and inelastic scattering of H2 from Cu(100), and of the orientational dependence of
NASA Astrophysics Data System (ADS)
Taylor, J. W.; Allan, J. D.; Liu, D.; Flynn, M.; Weber, R.; Zhang, X.; Lefer, B. L.; Grossberg, N.; Flynn, J.; Coe, H.
2015-04-01
Black carbon (BC) is the dominant absorbing aerosol in the atmosphere, and plays an important role in climate and human health. The optical properties and cloud condensation nuclei (CCN) activity of soot depend on the amounts (both relative and absolute) of BC and non-refractory material in the particles. Mixing between these two components is often represented in models by a core / shell coated sphere. The single-particle soot photometer (SP2) is one of, if not the only, instrument capable of reporting distributions of both core size and coating thickness. Most studies combine the SP2's incandescence and 1064 nm scattering data to report coating properties, but to date there is no consistency in the assumed values of density and refractive index of the core that are used in these calculations, which can greatly affect the reported parameters such as coating thickness. Given that such data are providing an important constraint for model comparisons and comparison between large data sets, it is important that this lack of consistency is addressed. In this study we explore the sensitivity of the reported coatings to these parameters. An assessment of the coating properties of freshly emitted, thermodenuded ambient particles demonstrated that a core density of 1.8 g cm-3 and refractive index of (2.26-1.26i) were the most appropriate to use with ambient soot in the Los Angeles area. Using these parameters generated a distribution with median shell / core ratio of 1.02 ± 0.11, corresponding to a median absolute coating thickness of 2 ± 8 nm. The main source of statistical error in the single-particle data was random variation in the incandescence signals. Other than the sensitivity to core refractive index, the incandescence calibration was the main source of uncertainty when optically determining the average coatings. The refractive index of coatings was found to have only a minor influence. This work demonstrates that using this technique the SP2 can accurately
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.
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.
Tait Equation Revisited from the Entropic and Fluctuational Points of View
NASA Astrophysics Data System (ADS)
Postnikov, E. B.; Goncharov, A. L.; Melent'ev, V. V.
2014-11-01
We consider the possibilities for prediction of liquid densities under pressure based on the inverse reduced fluctuations parameter, which is directly connected with the isothermal compressibility. This quantity can be determined based on the thermodynamic properties of the saturated liquid, and it consists of only two constant parameters within a relatively wide region close to the melting points. It is confirmed by the comparison with the experimental data on n-alkanes that the derived expression is a quite reasonable estimator without a necessity to fit data along some parts of isotherms for different temperatures. At the same time, the obtained formula (i) can be reduced to the form of the Tait equation and (ii) the resulting Tait parameters in this representation have a clear physical meaning as functions of the excess entropy, which determines the mentioned reduced fluctuations.
Hui, Stanley Sai-Chuen; Xie, Yao Jie; Woo, Jean; Kwok, Timothy Chi-Yui
2015-01-01
Tai Chi and walking are both moderate-intensity physical activity (PA) that can be easily practiced in daily life. The objective of the study was to determine the effects of these two PAs on weight loss, metabolic syndrome parameters, and bone mineral density (BMD) in Chinese adults. We randomized 374 middle-aged subjects (45.8 ± 5.3 years) into 12-week training (45 minutes per day, 5 days per week) of Tai Chi (n = 124) or self-paced walking (n = 121) or control group (n = 129). On average, Tai Chi and walking groups lost 0.50 and 0.76 kg of body weight and 0.47 and 0.59 kg of fat mass after intervention, respectively. The between-group difference of waist circumference (WC) and fasting blood glucose (FBG) was −3.7 cm and −0.18 mmol/L for Tai Chi versus control and −4.1 cm and −0.22 mmol/L for walking versus control. No significant differences were observed regarding lean mass, blood pressure, triglycerides, total cholesterol, high-density and low-density lipoprotein cholesterol, and BMD compared to control. Change in lean mass, not fat mass or total weight loss, was significantly correlated to the change in BMD. Our results suggest that both of these two PAs can produce moderate weight loss and significantly improve the WC and FBG in Hong Kong Chinese adults, with no additional effects on BMD. PMID:26543489
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. PMID:23721102
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.
Fluctuations as stochastic deformation.
Kazinski, P O
2008-04-01
A notion of stochastic deformation is introduced and the corresponding algebraic deformation procedure is developed. This procedure is analogous to the deformation of an algebra of observables like deformation quantization, but for an imaginary deformation parameter (the Planck constant). This method is demonstrated on diverse relativistic and nonrelativistic models with finite and infinite degrees of freedom. It is shown that under stochastic deformation the model of a nonrelativistic particle interacting with the electromagnetic field on a curved background passes into the stochastic model described by the Fokker-Planck equation with the diffusion tensor being the inverse metric tensor. The first stochastic correction to the Newton equations for this system is found. The Klein-Kramers equation is also derived as the stochastic deformation of a certain classical model. Relativistic generalizations of the Fokker-Planck and Klein-Kramers equations are obtained by applying the procedure of stochastic deformation to appropriate relativistic classical models. The analog of the Fokker-Planck equation associated with the stochastic Lorentz-Dirac equation is derived too. The stochastic deformation of the models of a free scalar field and an electromagnetic field is investigated. It turns out that in the latter case the obtained stochastic model describes a fluctuating electromagnetic field in a transparent medium. PMID:18517590
Fluctuations as stochastic deformation
NASA Astrophysics Data System (ADS)
Kazinski, P. O.
2008-04-01
A notion of stochastic deformation is introduced and the corresponding algebraic deformation procedure is developed. This procedure is analogous to the deformation of an algebra of observables like deformation quantization, but for an imaginary deformation parameter (the Planck constant). This method is demonstrated on diverse relativistic and nonrelativistic models with finite and infinite degrees of freedom. It is shown that under stochastic deformation the model of a nonrelativistic particle interacting with the electromagnetic field on a curved background passes into the stochastic model described by the Fokker-Planck equation with the diffusion tensor being the inverse metric tensor. The first stochastic correction to the Newton equations for this system is found. The Klein-Kramers equation is also derived as the stochastic deformation of a certain classical model. Relativistic generalizations of the Fokker-Planck and Klein-Kramers equations are obtained by applying the procedure of stochastic deformation to appropriate relativistic classical models. The analog of the Fokker-Planck equation associated with the stochastic Lorentz-Dirac equation is derived too. The stochastic deformation of the models of a free scalar field and an electromagnetic field is investigated. It turns out that in the latter case the obtained stochastic model describes a fluctuating electromagnetic field in a transparent medium.
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. PMID:25166159
Exciton dynamics in chromophore aggregates with correlated environment fluctuations
Abramavicius, Darius; Mukamel, Shaul
2011-01-01
We study the effects of correlated molecular transition energy fluctuations in molecular aggregates on the density matrix dynamics, and their signatures in the optical response. Correlated fluctuations do not affect single-exciton dynamics and can be described as a nonlocal contribution to the spectral broadening, which appears as a multiplicative factor in the time-domain response function. Intraband coherences are damped only by uncorrelated transition energy fluctuations. The signal can then be expressed as a spectral convolution of a local contribution of the uncorrelated fluctuations and the nonlocal contribution of the correlated fluctuations. PMID:21548696
Joint constraints on galaxy bias and σ8 through the N-pdf of the galaxy number density
NASA Astrophysics Data System (ADS)
Arnalte-Mur, Pablo; Vielva, Patricio; Martínez, Vicent J.; Sanz, José L.; Saar, Enn; Paredes, Silvestre
2016-03-01
We present a full description of the N-probability density function of the galaxy number density fluctuations. This N-pdf is given in terms, on the one hand, of the cold dark matter correlations and, on the other hand, of the galaxy bias parameter. The method relies on the assumption commonly adopted that the dark matter density fluctuations follow a local non-linear transformation of the initial energy density perturbations. The N-pdf of the galaxy number density fluctuations allows for an optimal estimation of the bias parameter (e.g., via maximum-likelihood estimation, or Bayesian inference if there exists any a priori information on the bias parameter), and of those parameters defining the dark matter correlations, in particular its amplitude (σ8). It also provides the proper framework to perform model selection between two competitive hypotheses. The parameters estimation capabilities of the N-pdf are proved by SDSS-like simulations (both, ideal log-normal simulations and mocks obtained from Las Damas simulations), showing that our estimator is unbiased. We apply our formalism to the 7th release of the SDSS main sample (for a volume-limited subset with absolute magnitudes Mr <= -20). We obtain hat b = 1.193 ± 0.074 and σ̂8 = 0.862 ± 0.080, for galaxy number density fluctuations in cells of the size of 30h-1Mpc. Different model selection criteria show that galaxy biasing is clearly favoured.
Adiabatic fluctuations from cosmic strings in a contracting universe
Brandenberger, Robert H.; Takahashi, Tomo; Yamaguchi, Masahide E-mail: tomot@cc.saga-u.ac.jp
2009-07-01
We show that adiabatic, super-Hubble, and almost scale invariant density fluctuations are produced by cosmic strings in a contracting universe. An essential point is that isocurvature perturbations produced by topological defects such as cosmic strings on super-Hubble scales lead to a source term which seeds the growth of curvature fluctuations on these scales. Once the symmetry has been restored at high temperatures, the isocurvature seeds disappear, and the fluctuations evolve as adiabatic ones in the expanding phase. Thus, cosmic strings may be resurrected as a mechanism for generating the primordial density fluctuations observed today.
Fluctuation modes of nanoconfined DNA
Karpusenko, Alena; Carpenter, Joshua H.; Zhou, Chunda; Lim, Shuang Fang; Pan, Junhan; Riehn, Robert
2012-01-01
We report an experimental investigation of the magnitude of length and density fluctuations in DNA that has been stretched in nanofluidic channels. We find that the experimental data can be described using a one-dimensional overdamped oscillator chain with nonzero equilibrium spring length and that a chain of discrete oscillators yields a better description than a continuous chain. We speculate that the scale of these discrete oscillators coincides with the scale at which the finite extensibility of the polymer manifests itself. We discuss how the measurement process influences the apparent measured dynamic properties, and outline requirements for the recovery of true physical quantities. PMID:22312183
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).
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
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.
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.
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.
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.