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Sample records for air density fluctuations

  1. Feasibility of measuring temperature and density fluctuations in air using laser-induced O2 fluorescence

    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.

  2. Extracting primordial density fluctuations

    PubMed

    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.

  3. 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.

  4. Simulation of nanoscale density fluctuations

    NASA Astrophysics Data System (ADS)

    Reiss, Howard; Bowles, Richard K.

    2000-11-01

    Problems associated with the simulation of density fluctuations of limited breadth in a small cell are exposed and studied. The fluctuations are viewed as "physical clusters" of the type that might appear in nucleation processes and related phenomena. One of the most important features of the study stems from the fact that the simulation of a small heterogeneity in a macroscopic system presents problems that do not occur in the simulation of a bulk homogeneous property of the system. For example, once having simulated the probability of appearance of the fluctuation in a small cell, how is that result to be "mapped" onto the macrosystem in order to specify the equilibrium number of such fluctuations in that system? This problem is closely associated with the proper separation of the translational and internal degrees of freedom of the system, and has arisen in a number of fields, including the theory of nucleation. There are other problems associated with exponential dependence of cluster probability on the work of formation of the cluster, and also with rareness of some important clusters. In the latter case, simulative "umbrella sampling" does not always solve the entire problem. The present study is confined to clusters that appear in rarefied gases. Such systems are important in a number of scenarios, including nucleation processes. Several cluster models are considered including those consisting of molecules confined to a "container" of fixed volume and those constructed on the center of mass of the cluster. Connections between them are derived and rigorous solutions to the mapping problem are derived. Quantitative measures for the accuracy of approximate solutions, applied to cases in which the cluster is compact, are provided and exact solutions are provided even for the noncompact case. Some surprising results emerge from the study, among which is the fact that a cluster whose location is determined by one of its molecules, does not always have a

  5. 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.

  6. Measurements and comparison of the probability density and covariance functions of laser beam intensity fluctuations in a hot-air turbulence emulator with the maritime atmospheric environment

    NASA Astrophysics Data System (ADS)

    Nelson, C.; Avramov-Zamurovic, S.; Malek-Madani, R.; Korotkova, O.; Sova, R.; Davidson, F.

    2012-10-01

    A hot-air turbulence emulator is employed for generating controlled optical clear air turbulence in the weak fluctuation regime in laboratory conditions. The analysis of the first and second-order statistical moments of the fluctuating intensity of a propagating infra-red (IR) laser beam through the turbulence emulator is made and the results are compared with bi-directional shore-to-ship maritime data collected during two 2009 mid-Atlantic Coast field tests utilizing single-mode adaptive optics terminals at a range of 10.7 km, as well as with a 633 nm Helium Neon laser propagating across land and water at the United States Naval Academy.

  7. Vortex Line Density Fluctuations of Quantum Turbulence

    NASA Astrophysics Data System (ADS)

    Fujiyama, Shoji; Tsubota, Makoto

    2010-02-01

    We investigate vortex line density fluctuations of quantum turbulence generated by an oscillating grid in superfluid 3He- B. The scenario of quantum turbulence experimentally suggested by the Lancaster group is confirmed in the numerical simulation. The spectrum of the vortex line density fluctuations with respect to frequency obeyed a -5/3 power law, which is consistent with the experiment of the Lancaster group. Based on the argument of time scales experienced by vortex rings with different sizes and on the power spectrum, the connection between the self-similar structure of the vortex tangle and the power spectrum is discussed.

  8. 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.

  9. 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.

  10. Density fluctuation spectra in magnetohydrodynamic turbulence

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Brown, M. R.; Matthaeus, W. H.

    1987-01-01

    It is shown that within the framework of nearly incompressible magnetohydrodynamics, but not within that of neutral-fluid hydrodynamics, a k exp -5/3 inertial-range wave number density fluctuation spectrum is to be expected at the same times that k exp -5/3 kinetic energy and magnetic energy cascade spectra are present. A previous discrepancy between theory and observation in the local interstellar medium and solar wind is thereby resolved.

  11. Local density fluctuations and hyperuniformity in quasicrystals

    NASA Astrophysics Data System (ADS)

    Oğuz, Erdal Celal; Torquato, Salvatore

    2015-03-01

    Local density fluctuations in many-body systems are of fundamental importance throughout various scientific disciplines, including physics, materials science, number theory and biology. In a point pattern, let the variance associated with the number of points contained in a spherical window of radius R be denoted by σ2 (R) . Hyperuniform point patterns in d dimensions do not possess infinite-wavelength fluctuations or, equivalently, possess a number variance that grows more slowly than the window volume, i.e., Rd. Hyperuniform systems include all infinite periodic structures, aperiodic quasicrystals, and some special disordered systems. Previous investigations showed that the number variance for large R in hyperuniform systems serves as a useful metric to rank order systems according to the degree to which large-scale density fluctuations are suppressed. In this work, we investigate the number variance of two-dimensional quasicrystals with a variety of different rotational symmetries. We study how the number variance depends on the rotational symmetry and local isomorphism class of the quasicrystal. We compare these results to a number of different periodic systems as well as disordered hyperuniform systems. ECO acknowledges the support from the German Research Foundation (DFG).

  12. Energy density fluctuations in early universe

    SciTech Connect

    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.

  13. Density Fluctuations in Uniform Quantum Gases

    SciTech Connect

    Bosse, J.; Pathak, K. N.; Singh, G. S.

    2011-12-12

    Analytical expressions are given for the static structure factor S(k) and the pair correlation function g(r) for uniform ideal Bose-Einstein and Fermi-Dirac gases for all temperatures. In the vicinity of Bose Einstein condensation (BEC) temperature, g(r) becomes long ranged and remains so in the condensed phase. In the dilute gas limit, g(r) of bosons and fermions do not coincide with Maxwell-Boltzmann gas but exhibit bunching and anti-bunching effect respectively. The width of these functions depends on the temperature and is scaled as {radical}(inverse atomic mass). Our numerical results provide the precise quantitative values of suppression/increase (antibunching and bunching) of the density fluctuations at small distances in ideal quantum gases in qualitative agreement with the experimental observation for almost non-trapped dilute gases.

  14. 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.

  15. Sparse Sampling of Water Density Fluctuations in Interfacial Environments.

    PubMed

    Xi, Erte; Remsing, Richard C; Patel, Amish J

    2016-02-01

    The free energetics of water density fluctuations near a surface, and the rare low-density fluctuations in particular, serve as reliable indicators of surface hydrophobicity; the easier it is to displace the interfacial waters, the more hydrophobic the underlying surface is. However, characterizing the free energetics of such rare fluctuations requires computationally expensive, non-Boltzmann sampling methods like umbrella sampling. This inherent computational expense associated with umbrella sampling makes it challenging to investigate the role of polarizability or electronic structure effects in influencing interfacial fluctuations. Importantly, it also limits the size of the volume, which can be used to probe interfacial fluctuations. The latter can be particularly important in characterizing the hydrophobicity of large surfaces with molecular-level heterogeneities, such as those presented by proteins. To overcome these challenges, here we present a method for the sparse sampling of water density fluctuations, which is roughly 2 orders of magnitude more efficient than umbrella sampling. We employ thermodynamic integration to estimate the free energy differences between biased ensembles, thereby circumventing the umbrella sampling requirement of overlap between adjacent biased distributions. Further, a judicious choice of the biasing potential allows such free energy differences to be estimated using short simulations, so that the free energetics of water density fluctuations are obtained using only a few, short simulations. Leveraging the efficiency of the method, we characterize water density fluctuations in the entire hydration shell of the protein, ubiquitin, a large volume containing an average of more than 600 waters.

  16. Density Fluctuations in Crystallizing Polymers: Fact or Fiction?

    NASA Astrophysics Data System (ADS)

    Baert, Jimmy; Van Puyvelde, Peter

    2008-07-01

    The fact that, in polymer crystallization, nucleation might be accompanied by large scale density fluctuations has been investigated for the flow-induced crystallization of isotactic poly-1-butene (PB-1). Small Angle Light Scattering (SALS) was applied to measure density and orientation fluctuations, whereas complementary results were obtained from optical microscopy. The observations seem to indicate that the detected density fluctuations result from the presence of weakly anisotropic structures, rather than being an indication of densification before the onset of crystallization. In addition, the present work provides a critical review of polymer crystallization studies using SALS.

  17. Recent developments in density, temperature and momentum fluctuation measurement. [in turbulent flow

    NASA Technical Reports Server (NTRS)

    Battle, T. M.; Wang, P. K.; Cheng, D. Y.

    1975-01-01

    Attention is drawn to recent advancements in the fluctuating line-reversal temperature measurement, the development of the two-dimensional drag-sensing probe into a three-dimensional drag-sensing probe, and the fluctuating density gradient cross beam Schlieren technique. An experimental apparatus is explained whereby the temperature fluctuation in a pulsating air-fuel ratio Bunsen burner is measured by means of sodium D-line reversal methods with a new photoelectric circuit to obtain both fluctuating and mean temperature data. The three-D drag probe is made possible by a newly invented differential and total magnetic sensing system that separates signals due to three orthogonal movements so that the vectorial momentum fluctuation can be measured. In the case of the Schlieren technique, the effect of anisotropic density gradients with respect to the angle between the polarization plane and the knife edge of a laser Schlieren system is studied.

  18. 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.

  19. 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.

  20. Charge and spin fluctuations in the density functional theory

    SciTech Connect

    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.

  1. 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.

  2. MEASUREMENTS OF RAPID DENSITY FLUCTUATIONS IN THE SOLAR WIND

    SciTech Connect

    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.

  3. Shock-associated plasma density fluctuations in the interstellar medium

    NASA Technical Reports Server (NTRS)

    Spangler, S. R.

    1989-01-01

    Theories of diffuse shock acceleration of the cosmic rays that predict that there should be regions of intense Alfven waves both upstream and downstream of the shock front are considered. Observations of similar waves near solar system shock waves show that they produce substantial density fluctuations. Such density fluctuations might produce observable scattering of radio waves. Observations which searched for angular broadening or blurring of radio sources whose lines of sight pass close to or through supernova remnants are discussed. No definite cases of remnant-associated scattering are detected. However, the source CL 4, which is viewed through the Cygnus Loop supernova remnant, may be such an object and merits further observation.

  4. Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST

    SciTech Connect

    Shen, Weimin.

    1992-08-01

    Studies of magnetic fluctuation induced particle transport on Reversed Field Pinch plasmas were done on the Madison Symmetric Torus. Plasma current density and current density fluctuations were measured using a multi-coil magnetic probes. The low frequency (f<50 kHz) current density fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 50 kHz, the magnetic fluctuations were detected to be localized with a radial correlation length of about 1--2 cm. These modes are locally resonant modes since the measured dominant mode number spectra match the local safety factor q. The net charged particle flux induced by magnetic fluctuations was obtained by measuring the correlation term <{tilde j}{sub {parallel}} {tilde B}{sub r}>. The result of zero net charged particle loss was obtained, meaning the flux is ambipolar. The ambipolarity of low frequency global tearing modes is satisfied through the phase relations determined by tearing instabilities. The ambipolarity of high frequency localized modes could be partially explained by the simple model of Waltz based on the radial average of small scale turbulence.

  5. Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas

    SciTech Connect

    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.

  6. Backscattering cascade of beam modes off ambient density fluctuations

    NASA Technical Reports Server (NTRS)

    Russell, D. A.; Goldman, M. V.

    1983-01-01

    The effects of a given nonthermal low-frequency density-fluctuation spectrum on the amplification of Langmuir waves by a 'bump-on-tail' beam of electrons are studied. The density-fluctuation spectrum is assumed to contain a uniform distribution of wavelengths ranging from much shorter than the beam mode wavelength to of the same order. This permits multiple large-angle (back) scattering to occur. One-dimensional numerical solutions of the kinetic equations are found which yield criteria for linear saturation of the beam instability of a cascade of backscattering to high wavenumber. The relevant time scales and spectral shapes are also determined in both the stable and unstable regions. Linear damping and Cerenkov emission by a possible nonthermal tail of electrons is taken into account. An application is made to the beam modes observed simultaneously with density fluctuations off the Jovian bow shock. It is shown that the observed level of density fluctuations is sufficient to saturate the unstable Langmuir waves, although nonthermal Landau damping may prevent a cascade to very high wavenumbers.

  7. Density fluctuations in strong Langmuir turbulence - Scalings, spectra, and statistics

    NASA Technical Reports Server (NTRS)

    Robinson, P. A.; Newman, D. L.

    1990-01-01

    A recently developed two-component model of strong Langmuir turbulence is applied to determine the scalings, spectra, and statistics of the associated density fluctuations. The predictions are found to be in excellent agreement with extensive results from numerical solution of the Zakharov equations in two and three dimensions.

  8. Dynamic density functional theory with hydrodynamic interactions and fluctuations.

    PubMed

    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.

  9. Dynamic density functional theory with hydrodynamic interactions and fluctuations

    SciTech Connect

    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.

  10. 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.

  11. 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.

  12. Correlation analysis of magnetic field and density fluctuations in SSX

    NASA Astrophysics Data System (ADS)

    Parks, Holden; Rock, Ariel; Schaffner, David; Brown, Michael; SSX Team

    2015-11-01

    The cross correlation and cross spectrum of magnetic field and density fluctuations of plasmas created by the Swarthmore Spheromak Experiment (SSX) MHD wind tunnel are examined. The SSX MHD wind tunnel produces dynamic magnetized plasma plumes with typical values B ~ 0 . 2 T, n >=1021 m-3, and Ti >= 20 eV. Magnetic field fluctuations of these plasmas are measured with a Ḃ probe and local density fluctuations are measured with a double Langmuir probe inserted radially within 1 mm of the Ḃ probe. The axial distance of both probes from the plasma source is varied to examine plasmas of different ``turbulent ages.'' Linearized MHD theory admits three types of waves - slow, fast, and Alfvén - each with different correlation values between magnetic field and density. By taking the Fourier transforms of B (t) and n (t) time series data, the cross spectrum B~* (f) ñ (f) is calculated, and the correlation between magnetic field and density can be determined as a function of frequency. Preliminary results of SSX data analysis indicate a pressure balanced structure present at 100 kHz, likely in the form of a flux tube, as well as predominately positive correlations in the frequency range 100 kHz to 10 MHz. Work supported by DOE OFES and NSF CMSO.

  13. 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.

  14. Suppression of density fluctuations in a quantum degenerate Fermi gas.

    PubMed

    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.

  15. 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

  16. 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.

  17. 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.

  18. Fluctuating charge-density waves in a cuprate superconductor.

    PubMed

    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

  19. 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.

  20. Study of low density air transportation concepts

    NASA Technical Reports Server (NTRS)

    Webb, H. M.

    1972-01-01

    Low density air transport refers to air service to sparsely populated regions. There are two major objectives. The first is to examine those characteristics of sparsely populated areas which pertain to air transportation. This involves determination of geographical, commercial and population trends, as well as those traveler characteristics which affect the viability of air transport in the region. The second objective is to analyze the technical, economic and operational characteristics of low density air service. Two representative, but diverse arenas, West Virginia and Arizona, were selected for analysis: The results indicate that Arizona can support air service under certain assumptions whereas West Virginia cannot.

  1. Dynamic Density: An Air Traffic Management Metric

    NASA Technical Reports Server (NTRS)

    Laudeman, I. V.; Shelden, S. G.; Branstrom, R.; Brasil, C. L.

    1998-01-01

    The definition of a metric of air traffic controller workload based on air traffic characteristics is essential to the development of both air traffic management automation and air traffic procedures. Dynamic density is a proposed concept for a metric that includes both traffic density (a count of aircraft in a volume of airspace) and traffic complexity (a measure of the complexity of the air traffic in a volume of airspace). It was hypothesized that a metric that includes terms that capture air traffic complexity will be a better measure of air traffic controller workload than current measures based only on traffic density. A weighted linear dynamic density function was developed and validated operationally. The proposed dynamic density function includes a traffic density term and eight traffic complexity terms. A unit-weighted dynamic density function was able to account for an average of 22% of the variance in observed controller activity not accounted for by traffic density alone. A comparative analysis of unit weights, subjective weights, and regression weights for the terms in the dynamic density equation was conducted. The best predictor of controller activity was the dynamic density equation with regression-weighted complexity terms.

  2. 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.

  3. 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.

  4. Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuations

    SciTech Connect

    Yun, G. S.; Lee, W.; Choi, M. J.; Kim, J. B.; Park, H. K.; Domier, C. W.; Tobias, B.; Liang, T.; Kong, X.; Luhmann, N. C. Jr.; Donne, A. J. H.

    2010-10-15

    The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donneet al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfven eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.

  5. 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.

  6. Time-resolved measurements of the density fluctuations in ion phase space

    SciTech Connect

    Diallo, Ahmed; Skiff, Frederick

    2006-05-15

    A two-point correlation function measurement of the ion density fluctuations is presented. Using two laser-induced fluorescence (LIF) detection systems, the density fluctuation is resolved in time, ion parallel velocity, and space (along the magnetic field). The measurements reveal two components of the density fluctuations, one of which is explained by fluid theory. The other component is ion-velocity-dependent and is newly identified. In addition to the density fluctuation measurements, a velocity-resolved estimate of the fluctuation-induced transport flux using correlations between a Langmuir probe and LIF is reported.

  7. Density fluctuations at high density in the ergodic divertor configuration of Tore Supra

    NASA Astrophysics Data System (ADS)

    Devynck, P.; Gunn, J.; Ghendrih, Ph.; Garbet, X.; Antar, G.; Beyer, P.; Boucher, C.; Honore, C.; Gervais, F.; Hennequin, P.; Quémeneur, A.; Truc, A.

    2001-03-01

    The effect of the ergodic divertor on the plasma edge in Tore Supra is to enhance the perpendicular transport through ergodization of the magnetic field lines [Ph. Ghendrih et al., Contrib. Plasma Phys. 32 (3&4) (1992) 179]. Nevertheless, the hot spots observed on the divertor plates during ergodic divertor operation indicate that the cross-field transport driven by the fluctuations is still playing an important role, although measurements by CO 2 laser scattering and reflectometry show a decrease of the turbulence level [J. Payan, X. Garbet, J.H. Chatenet et al., Nucl. Fusion 35 (1995) 1357; P. Beyer, X. Garbet, P. Ghendrih, Phys. Plasmas 5 (12) (1998) 4271]. In order to gain more understanding, fluctuation level and poloidal velocity have been measured with a reciprocating Langmuir probe biased to collect the ion saturation current ( jsat) and with a CO 2 laser scattering diagnostic. Though the relative fluctuation level behaves as previously observed at low density, a new interesting result is that this picture is gradually modified when the density is increased. Both diagnostics observe an increase of δn/ n with density in the ergodic region, which is not the usual behavior observed in limiter configuration. This increase is detected on both sides of the Er inversion radius and is therefore also affecting the plasma bulk. Finally, the confinement time is found to follow an L-mode law at all densities indicating that the ergodic divertor does not change the global confinement properties of the plasma.

  8. Rayleigh Scattering Diagnostic for Measurement of Temperature, Velocity, and Density Fluctuation Spectra

    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.

  9. Collective motion and density fluctuations in swimming bacteria

    NASA Astrophysics Data System (ADS)

    Zhang, Hepeng

    2011-03-01

    The emergence of collective motion such as in fish schools, mammal herds, and insect swarms is a ubiquitous self-organization phenomenon. Such collective behavior plays an important role in a range of problems, such as spreading of deceases in animal or fish groups. Current models have provided a qualitative understanding of collective motion, but progress in quantitative modeling in hindered by the lack of experimental data. Here we examine a model microscopic system, where we are able to measure simultaneously the positions, velocities, and orientations of up to a thousand bacteria in a colony. The motile bacteria form closely-packed dynamic clusters within which they move cooperatively. The number of bacteria in a cluster exhibits a power-law distribution truncated by an exponential tail, and the probability of finding large clusters grows markedly as bacterial density increases. Mobile clusters cause anomalous fluctuations in bacterial density as found in mathematical theories and numerical models. Our results demonstrate that bacteria are an excellent system to study general phenomena of collective motion.

  10. Spatial density fluctuations and selection effects in galaxy redshift surveys

    SciTech Connect

    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.

  11. Fluctuations of energy density of short-pulse optical radiation in the turbulent atmosphere.

    PubMed

    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.

  12. Measuring Air Density in the Introductory Lab

    ERIC Educational Resources Information Center

    Calza, G.; Gratton, L. M.; Lopez-Arias, T.; Oss, S.

    2010-01-01

    The measurement of the mass, or the density, of air can easily be done with very simple materials and offers many interesting phenomena for discussion--buoyancy and its effects being the most obvious but not the only one. Many interesting considerations can be done regarding the behavior of gases, the effect of the external conditions in the…

  13. Parallel-beam correlation technique for measuring density fluctuations in plasmas with strong magnetic shear

    SciTech Connect

    Jacobson, A.R.

    1981-04-01

    A laser diagnostic scheme is described which facilitates localization of density fluctuations along the line of sight. The method exploits both the generally observed anisotropy of density fluctuations in low-beta plasmas, as well as the twisting of the magnetic field which occurs across the minor diameter of reversed-field pinches, spheromaks, etc. Both interferometric and schlieren variations are discussed.

  14. 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.

  15. Measuring Air Density in the Introductory Lab

    NASA Astrophysics Data System (ADS)

    Calzà, G.; Gratton, L. M.; López-Arias, T.; Oss, S.

    2010-03-01

    The measurement of the mass, or the density, of air can easily be done with very simple materials and offers many interesting phenomena for discussion—buoyancy and its effects being the most obvious but not the only one. Many interesting considerations can be done regarding the behavior of gases, the effect of the external conditions in the measurement, and the reason for the choice of the procedure, among others. One of the most widespread approaches makes use of rubber balloons. Such an approach can be misleading if attention is not paid to the effect of the buoyant force on the balloon, exerted by the surrounding air. Air is weightless in an environment full of it. While this fact can usually be neglected in daily, nontechnical weight measurements, it is not the case when we are interested in the weight of air itself. A sketch such as the one depicted in Fig. 1 is often presented in elementary science textbooks, as a demonstration that air has weight. A search of the Internet will reveal that this misleading approach is often presented as the simplest one for this kind of measurement at an elementary level and represents one among other common misconceptions that can be found in K-6 science textbooks as discussed, for instance, in Ref. 2. For a more detailed description of the flaws inherent to the measurement of air's weight with a rubber balloon, see Ref. 3. In this paper we will describe two procedures to measure the density of air: weighing a PET bottle and a vacuum rigid container. There are other interesting ways to estimate the weight of air; see, for instance, the experiment of Zhu and Se-yuen using carbon dioxide and Archimedes' principle.4 We emphasize the experimental implications and the physical reasons for the accuracy and conceptual correctness of each method. It is important not to undervalue the importance of both simplicity and reliability for any experimental measurement made in a didactic context.

  16. Experimental Investigation of Short Scalelength Density Fluctuations in Laser-Produced Plasmas

    SciTech Connect

    Moody, J.D.; MacGowan, B.J.; Glenzer, S.H.; Kirkwood, R.K.; Kruer, W.L.; Williams, E.A.; Stone, G.F.; Montgomery, D.S.; Schmitt, A.J.

    1999-11-01

    The technique of near forward laser. scattering is used to infer characteristics of intrinsic and controlled density fluctuations in laser-produced plasmas. Intrinsic fluctuations are studied in long scalelength plasmas where the fluctuations exhibit scale sizes related to the size of the intensity variations in the plasma forming and interaction beams. Stimulated Brillouin forward scattering and filamentation appear to be the primary mechanism through which these fluctuations originate. The beam spray which results from these fluctuations is important to understand since it can affect symmetry in an inertial confinement fusion (ICF) experiment. Controlled fluctuations are studied in foam and exploding foil targets. Forward scattered light from foam targets shows evidence that the initial target inhomogeneities remain after the target is laser heated. Forward scattered light from an exploding foil plasma shows that a regular intensity pattern can be used to produce a spatially correlated density fluctuation pattern. These results provide data which can be used to benchmark numerical models of beam spray.

  17. Sound Sources Identified in High-Speed Jets by Correlating Flow Density Fluctuations With Far-Field Noise

    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.

  18. The origin of density fluctuations in the 'new inflationary universe'

    NASA Technical Reports Server (NTRS)

    Turner, M. S.

    1983-01-01

    Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.

  19. 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.

  20. 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.

  1. Microwave reflectometry for the study of density fluctuations in tokamak plasmas

    SciTech Connect

    Mazzucato, E.; Nazikian, R.

    1990-12-01

    The effect of small scale density fluctuations on the propagation of electromagnetic waves in an inhomogeneous magnetized plasma in the presence of a cutoff is investigated. It is shown that, provided the fluctuation scale length is greater than the free space wavelength of an incident plane wave, the scattered field is strongly enhanced from fluctuations near the turning point. Numerical results for wave propagation in a tokamak plasma demonstrate the feasibility of reflectometry for the localized measurement of density fluctuations in the range k {sub {perpendicular}} {rho}{sub i} {much lt} 1. 19 refs., 6 figs,

  2. Density fluctuations in solar wind flow types at 1 AU: Comparison to Doppler scintillation measurements

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Woo, R.; Neugebauer, M.

    1995-01-01

    Density fluctuations with periods 10 minutes to 1 hour have been investigated in ISEE 3 plasma measurements of solar wind flows at l AU. Coronal hole, interstream, plasma sheet, coronal mass ejection, and interaction region flow types are considered. The ISEE 3 results support the interpretation of the large-scale variations in density fluctuations observed by Doppler scintillation measurement techniques inside 0.2 AU. The highest absolute and relative density fluctuations occur ahead of and within the plasma from coronal mass ejections, with the maximum values occurring between the associated interplanetary shocks and the driver gas. For the quasi-stationary solar wind, density and relative density fluctuations are highest around the heliospheric current sheet and lowest in the high-speed coronal flow. Superposed epoch analysis shows that the region of enhanced density fluctuations and its abrupt boundaries observed in the vicinity of the heliospheric current sheet near the Sun persists to l AU, providing further support for the filamentary nature of the extensions of coronal streamers. The results of this study confirm the advantages of using density fluctuations rather than density as a tracer of solar wind flows with differing origins at the Sun and as a detector of propagating interplanetary disturbances.

  3. 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.

  4. An observational study of MHD wave-induced density fluctuations upstream of the earth's bow shock

    NASA Technical Reports Server (NTRS)

    Spangler, Steven; Fey, Alan; Anderson, Gregory; Fuselier, Stephen

    1988-01-01

    An investigation of plasma density fluctations upstream of the earth's bow shock and their association with MHD waves is reported. The normalized density fluctuation was 14 percent on a day when the plasma beta was less than unity and the waves were circularly polarized and of relatively low amplitude, and 17 percent on a day when the plasma beta was in excess of unity and the waves were elliptically polarized and of large fractional amplitude. On both days there was a feature of the density power spectrum at the MHD carrier wave frequency attributable to oblique propagation of the waves with propagation angles of a few degrees with respect to the mean field. Ponderomotive effects due to spatial gradient in the MHD wave energy density are proposed as responsible for a correlation betweeen density and transverse wave intensity on both days. Generation of density fluctuations by linear polarized MHD waves is not an important contributor to the observed density fluctuations.

  5. Simple model for an upper bound on density fluctuations in a turbulent pinch

    SciTech Connect

    Jacobson, A.R.

    1980-01-01

    A rough scaling relationship for plasma density fluctuations driven by magnetic field disturbances is derived. The result is found to agree with an earlier theory based on acoustic waves inflating magnetic flux surfaces.

  6. Measurement of density fluctuations in the PDX tokamak using microwave scattering techniques

    SciTech Connect

    Crowley, T.

    1984-01-01

    Density fluctuations in the PDX tokamak were analyzed with the scattering of 2 mm microwaves. The primary focus of the study was the low frequency (fluctuations which are ubiquitous in tokamaks and have the characteristics of drift wave turbulence. In PDX, the mean observed frequencies are about 50 to 100 kHz and the mean wavenumbers are k/sub perpendicular/ approx. 3 cm/sup -1/. It is believed that the drift waves are a possible cause of the anomalous heat transport in tokamaks. Density fluctuations with a narrow frequency spectrum were also observed. The latter include the quasi-coherent fluctuation observed in H-mode plasmas. Several scaling studies of the broad-band turbulence have been carried out. The frequency spectra, k/sub perpendicular/ spectra, and magnitude of the fluctuations were measured and their variation with toroidal field, neutral beam heating power, plasma current, position, and confinement regime in PDX was documented.

  7. Systems evaluation of low density air transportation concepts

    NASA Technical Reports Server (NTRS)

    Bruce, R. W.; Webb, H. M.

    1972-01-01

    Methods were studied for improving air transportation to low-density population regions in the U.S. through the application of new aeronautical technology. The low-density air service concepts are developed for selected regions, and critical technologies that presently limit the effective application of low-density air transportation systems are identified.

  8. Magnetic Fluctuations in Pair-Density-Wave Superconductors.

    PubMed

    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

  9. Mobility of electrons in supercritical krypton: Role of density fluctuations

    NASA Astrophysics Data System (ADS)

    Nishikawa, Masaru; Holroyd, Richard A.; Preses, Jack M.

    2007-07-01

    Excess electrons were generated in supercritical krypton by means of pulsed x-ray irradiation, and the electron transport phenomena were studied. Electron signals immediately after a 30ps pulse showed a distinctive feature characteristic of the presence of the Ramsauer-Townsend minimum in the momentum transfer cross section. The dependence of the drift velocity vD on field strength was found to be concave upward in the low field region and then to go through a maximum with increasing field strength, which is also typical of the presence of a minimum in the scattering cross section at an intermediate field strength. A minimum in the electron mobility was observed at about one-half the critical density. The acoustical phonon scattering model, which successfully explained the mobility change in this density region in supercritical xenon, was again found to account for the mobility in supercritical krypton.

  10. Dynamical Selection of the Primordial Density Fluctuation Amplitude

    SciTech Connect

    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.

  11. Dynamical selection of the primordial density fluctuation amplitude.

    PubMed

    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 (∼10(-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. PMID:21405562

  12. Radial evolution of the intermittency of density fluctuations in the fast solar wind

    SciTech Connect

    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.

  13. Control of an Isolated Table's Fluctuation Caused by Supplied Air Pressure Using a Voice Coil Motor

    NASA Astrophysics Data System (ADS)

    Shirani, Habiburahman; Wakui, Shinji

    Pneumatic type anti-vibration apparatuses are used in the field of semiconductor manufacturing and precision measurement. The variation of the supplied air pressure from the air compressor causes the position fluctuation of the isolated table. A control method using a voice coil motor (VCM) as the actuator is proposed in this study to control the position fluctuation of the isolated table caused by the supplied air pressure. The feedforward compensator control scheme is used to provide a proper controlled signal to the VCM. According to the controlled signal, VCM exerts driving force in the opposite direction of the air spring expansion or compression to suppress the vibration of the isolated table.

  14. Density fluctuations near the liquid-gas critical point of a confined fluid.

    PubMed

    Melnichenko, Y B; Wignall, G D; Cole, D R; Frielinghaus, H

    2004-05-01

    We report the results of an experimental study of the effect of a dilute silica network on liquid-gas critical phenomena in carbon dioxide (CO2). Using small-angle neutron scattering, we measured the correlation length of the density fluctuations in bulk (xi(bulk)) and confined CO2 (xi(conf)) as a function of temperature and average fluid density. We find that quenched disorder induced by an aerogel suppresses density fluctuations: xi(conf) loses the Ising model divergence characteristic of xi(bulk) and does not exceed the size of pores in the homogeneous region.

  15. Thermodynamics versus Local Density Fluctuations in the Metal-Mott-Insulator Crossover

    NASA Astrophysics Data System (ADS)

    Drewes, J. H.; Cocchi, E.; Miller, L. A.; Chan, C. F.; Pertot, D.; Brennecke, F.; Köhl, M.

    2016-09-01

    The crossover between a metal and a Mott insulator leads to a localization of fermions from delocalized Bloch states to localized states. We experimentally study this crossover using fermionic atoms in an optical lattice by measuring thermodynamic and local (on-site) density correlations. In the metallic phase at incommensurable filling we observe the violation of the local fluctuation-dissipation theorem indicating that the thermodynamics of the system cannot be characterized by local observables alone. In contrast, in the Mott insulator we observe the convergence of local and thermodynamic fluctuations indicating the absence of long-range density-density correlations.

  16. Dynamical density fluctuations of superfluids near the critical velocity.

    PubMed

    Kato, Yusuke; Watabe, Shohei

    2010-07-16

    We propose a stability criterion of superfluids in condensed Bose-Einstein systems, which incorporates the spectral function or the autocorrelation function of the local density. Within the Gross-Pitaevskii-Bogoliubov theory, we demonstrate the validity of our criterion for the soliton-emission instability, with use of explicit forms of zero modes of the Bogoliubov equation and a dynamical scaling near the saddle-node bifurcation. We also show that the criterion is applicable to the Landau phonon instability and the Landau roton instability within the single-mode approximation.

  17. Structure, Density and Velocity Fluctuations in Quasi-2D non-Brownian Suspensions of Spheres

    NASA Astrophysics Data System (ADS)

    Rouyer, Florence; Lhuillier, Daniel; Martin, Jérôme; Salin, Dominique

    1999-11-01

    Non-brownian sedimenting suspensions exhibit density and velocity fluctuations. We have performed experiments on a quasi-2D counter-flow stabilized suspension of 2000 spherical particles, namely a liquid-solid fluidized bed in a Hele-Shaw cell. This 2D suspension displays a uniform concentration but the particle radial distribution function and the fluctuations of the particle number in a sub-volume of the suspension suggest that the micostructure is homogeneous but not random. We have also measured the velocity fluctuations of a test-particle and the fluctuation of the mean particle velocity in a sub-volume. It happens that the relation between velocity and concentration fluctuation in a sub-volume can be deduced from a balance between buoyancy and parietal friction forces.

  18. Synergistic influences of phase, density, and climatic variation on the dynamics of fluctuating populations.

    PubMed

    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

  19. Novel Structure and Dynamics of Polymer Thin Films in Supercritical Fluids-Effect of Density Fluctuation

    SciTech Connect

    Koga,T.

    2004-01-01

    Supercritical carbon dioxide (scCO2) is being used increasingly as a green solvent in polymer processing. The major disadvantage thus far is that only a limited class of polymers, such as fluorinated or silicone-based polymers, can be dissolved in CO2. Here I show that large density fluctuations in scCO2 can significantly enhance the solubility of scCO2 in polymer thin films even when the bulk polymers have very poor miscibility with CO2. By using in situ neutron reflectivity, I found that a wide variety of polymer thin films can swell as much as 30-60% when exposed to scCO2 within a narrow temperature and pressure regime, known as the 'density fluctuation ridge', which defines the maximum density fluctuation amplitude in CO2. Furthermore, the swollen structures induced by the density fluctuation could be frozen by a flash evaporation of CO2 via the vitrification process of the polymer without a formation of void structures. X-ray reflectivity clearly showed that the scCO2 process could be used to produce uniform low-density polymer thin films. I also found that other properties of the vitrified films, such as index of refraction, dielectric constant and glass transition, were correlated with the low-density density profile.

  20. The Air Density Explorer Satellite Program

    NASA Technical Reports Server (NTRS)

    Keating, G. M.; Prior, E. J.

    1973-01-01

    Since 1961, four satellites designed specifically for determination of the density and composition variations of the earth's neutral atmosphere at satellite altitudes have been launched: Explorer 9, Explorer 19, Explorer 24, and Explorer 39. Studies of the orbital decay of these satellites have resulted in major revisions in our conception of the upper atmosphere at satellite altitudes. These features include the winter helium bulge detected near 1000 km with its north-south asymmetry, the summer atomic oxygen bulge near 500 km, and the winter enhancement of atomic oxygen near 120 km. The Langley Research Center is now in the process of designing and fabricating the Dual Air Density Explorers. These will be two satellites launched by means of a single Scout rocket in 1975, and they are expected to remain in essentially the same orbital plane throughout the 2-year mission. Each satellite is drag sensitive and uses a mass spectrometer in a unique system which is insensitive to orientation, is highly sensitive to the upper atmosphere, and is capable of in-flight calibration.

  1. Radial electrostatic flux inferred from core measurements of potential and density fluctuations

    SciTech Connect

    Demers, D. R.; Schoch, P. M.; Crowley, T. P.; Connor, K. A.; Ouroua, A.

    2001-04-01

    Broadband potential fluctuations and electrostatic fluctuation induced particle flux have been measured in the core of a medium size tokamak plasma for the first time. Density fluctuations and wave numbers were simultaneously measured. Measurements indicate that radial electrostatic fluctuation induced particle flux in the core region, at the normalized radii of 0.17<{rho}<0.38, due to modes with wave numbers less than 4 cm{sup -1} is small in magnitude, is likely directed inward, and cannot account for particle flux predicted by the continuity equation and particle source codes. Estimates of electrostatic energy flux are also significantly less than values predicted via power balance analysis. Asymmetries in coherent density and potential fluctuation levels on closed flux surfaces are evident. Relative fluctuation levels {tilde n}/n and {tilde {phi}} tend to increase with radius, and the fluctuations are Boltzmann-like in the region 0.17{<=}{rho}{<=}0.38. The direction of mode propagation is in the electron diamagnetic drift direction. Corresponding phase velocities, v{sub ph}{approx}3.5x10{sup 5} cm/s, are similar to drift wave velocities.

  2. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    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.

  3. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    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.

  4. 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.

  5. Poynting vector, energy densities, and pressure of collective transverse electromagnetic fluctuations in unmagnetized plasmas

    SciTech Connect

    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}.

  6. Density fluctuations in the interstellar medium: Evidence for anisotropic magnetogasdynamic turbulence. I - Model and astrophysical sites

    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.

  7. Measurements of Density Fluctuations in the Pdx Tokamak Using Microwave Scattering Techniques.

    NASA Astrophysics Data System (ADS)

    Crowley, Thomas

    Density fluctuations in the PDX tokamak have been analyzed with the scattering of 2 mm microwaves. The primary focus of the study has been the low frequency (< 1MHz), broad band spectrum fluctuations which are ubiquitous in tokamaks and have the characteristics of drift wave turbulence. The fluctuations typically have frequencies and wavelengths characterized by (DELTA)(omega) (TURN) (omega) (TURN) (omega)(,*(,e)) and K(,(PERP))(rho)(,i) of order 1, where (omega)(,*(,e)) is the electron diamagnetic drift frequency and (rho)(,i) is the ion Larmor radius. In PDX, the mean observed frequencies are about 50-100 kHz and the mean wavenumbers are k(,(PERP)) (TURN) 3 cm('-1). It is believed that these waves are a possible cause of the anomalous heat transport in tokamaks. Density fluctuations with a narrow frequency spectrum have also been observed. The latter include the quasi-coherent fluctuation observed in H-mode plasmas. Several scaling studies of the broad band turbulence have been carried out. The frequency spectra, k(,(PERP)) spectra, and magnitude of the fluctuations have been measured and their variation with toroidal field, neutral beam heating power, plasma current, position, and confinement regime in PDX has been documented. Since the turbulence is a possible cause of anomalous heat transport in PDX and other tokamaks, the scaling of the turbulence has been compared with energy confinement scalings. In many cases, increased fluctuation level correlates with decreased energy confinement. In another case, the fluctuation level does not change as the confinement properties of the plasma change. The scaling of the experimental fluctuation levels has also been compared with various drift wave parameters. The fluctuation level scales as the mixing length limit, n/n (TURN) 1/k(,(PERP))L(,n), in some sets of data, but not in other sets. In addition to the broad band frequency spectrum present on all shots, density fluctuations with a narrow frequency spectrum ((DELTA

  8. Scattering of diffracting beams of electron cyclotron waves by random density fluctuations in inhomogeneous plasmas

    NASA Astrophysics Data System (ADS)

    Weber, Hannes; Maj, Omar; Poli, Emanuele

    2015-03-01

    The physics and first results of the new WKBeam code for electron cyclotron beams in tokamak plasmas are presented. This code is developed on the basis of a kinetic radiative transfer model which is general enough to account for the effects of diffraction and density fluctuations on the beam. Our preliminary numerical results show a significant broadening of the power deposition profile in ITER due to scattering from random density fluctuations at the plasma edge, while such scattering effects are found to be negligible in medium-size tokamaks like ASDEX upgrade.

  9. Dispersion relations of electron density fluctuations in a Hall thruster plasma, observed by collective light scattering

    SciTech Connect

    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.

  10. Comparison of density fluctuation measurements between O-mode and X-mode reflectometry on Tore Supra

    SciTech Connect

    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.

  11. Air density measurement with a falling A4 sheet

    NASA Astrophysics Data System (ADS)

    Oladyshkin, Ivan V.; Oladyshkina, Anastasia A.

    2016-09-01

    We propose a simple experiment on the air density measurement which does not require any special equipment: just an A4 sheet of paper, a stopwatch and a ruler. The discussed method uses the most basic air resistance model.

  12. Potential, Pressure and Density Fluctuation Measurements on the Rentor Tokamak Using AN Ion Beam Probe

    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

  13. Short-term variations in gene flow related to cyclic density fluctuations in the common vole.

    PubMed

    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.

  14. 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.

  15. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe

    SciTech Connect

    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.

  16. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe.

    PubMed

    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.

  17. The nucleation process and the roles of structure and density fluctuations in supercooled liquid Fe

    NASA Astrophysics Data System (ADS)

    Li, Rong; Wu, Yongquan; Xiao, Junjiang

    2014-01-01

    We observed homogeneous nucleation process of supercooled liquid Fe by molecular dynamics simulations. Using bond-orientational order parameters together with Voronoi polyhedron method, we characterized local structure, calculated the volume of Voronoi polyhedra of atoms and identified the structure and density fluctuations. We monitored the formation of nucleus and analyzed its inner structure. The birth and growth of the pre-nucleus and nucleus are accompanied with aggregating and disaggregating processes in the time scale of femtosecond. Only the initial solid-like clusters (ISLC), ranging from 1 to 7 atoms, pop up directly from liquid. The relation between the logarithm of number of clusters and the cluster size was found to be linear for ISLCs and was observed to be parabolic for all solid-like clusters (SLC) due to aggregating and disaggregating effects. The nucleus and pre-nuclei mainly consist of body centered cubic (BCC) and hexagonal close packed atoms, while the BCC atoms tend to be located at the surface. Medium-range structure fluctuations induce the birth of ISLCs, benefit the aggregation of embryos and remarkably promote the nucleation. But density fluctuations contribute little to nucleation. The lifetime of most icosahedral-like atoms (ICO) is shorter than 0.7 ps. No obvious relationship was found between structure/density fluctuations and the appearance of ICO atoms.

  18. Characterising density fluctuations in liquid yttria aluminates with small angle x-ray scattering

    SciTech Connect

    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.

  19. Simultaneous Microwave Imaging System for Density and Temperature Fluctuation Measurements on TEXTOR

    SciTech Connect

    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.

  20. The Measurement of Fluctuations of Air Speed by the Hot-Wire Anemometer

    NASA Technical Reports Server (NTRS)

    Dryden, H L; Kuethe, A M

    1930-01-01

    The hot-wire anemometer suggests itself as a promising method for measuring the fluctuating air velocities found in turbulent flow. The only obstacle is the presence of a lag due to the limited energy input which makes even a fairly small wire incapable of following rapid fluctuations with accuracy. This paper gives the theory of the lag and describes an experimental arrangement for compensating for the lag for frequencies up to 100 or more per second when the amplitude of the fluctuation is not too great. An experimental test of the accuracy of compensation and some results obtained with the apparatus in a wind-tunnel air stream are described. While the apparatus is very bulky in its present form, it is believed possible to develop a more portable arrangement. (author)

  1. Finding evidence for density fluctuation effects on electron cyclotron heating deposition profiles on DIII-D

    SciTech Connect

    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.

  2. Stirring Coronal Spaghetti: Exploring Multiple Interactions Between MHD Waves and Density Fluctuations

    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.

  3. Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.

    PubMed

    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.

  4. Wavelike charge density fluctuations and van der Waals interactions at the nanoscale.

    PubMed

    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

  5. Experimental evaluation of fluctuating density and radiated noise from a high temperature jet

    NASA Technical Reports Server (NTRS)

    Massier, P. F.; Parthasarathy, S. P.; Cuffel, R. F.

    1973-01-01

    An experimental investigation has been conducted to characterize the fluctuating density within a high-temperature (1100 K) subsonic jet and to characterize by the noise radiated to the surroundings. Cross correlations obtained by introducing time delay to the signals detected from spatially separated crossed laser beams set up as a Schlieren system were used to determine radial and axial distributions of the convection velocity of the moving noise sources (eddies). In addition, the autocorrelation of the fluctuating density was evaluated in the moving frame of reference of the eddies. Also, the autocorrelation of the radiated noise in the moving reference frame was evaluated from cross correlations by introducing time delay to the signals detected by spatially separated pairs of microphones. Radial distributions of the mean velocity were obtained from measurements of the stagnation temperature, and stagnation and static pressures with the use of probes.

  6. Electron-cyclotron wave scattering by edge density fluctuations in ITER

    SciTech Connect

    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.

  7. Dynamics of sprite streamers in varying air density

    NASA Astrophysics Data System (ADS)

    Qin, Jianqi; Pasko, Victor P.

    2015-03-01

    Similarity laws for streamer discharges, which state that the properties of streamers such as streamer radius, electric field, and electron density should respectively scale as N-1, N1, and N2 in different but uniform air densities N, are important relations that have provided a general understanding of the mesospheric sprite discharges based on existing knowledge of streamers in laboratory conditions. Recent modeling studies, however, show that the properties of sprite streamers in varying air density do not follow exactly or even contradict the similarity relations. We present here simulation results and related analysis of sprite streamers to provide a unified view and resolve these contradictions. Our results indicate that the properties of streamers in varying air density are determined by the physical dimensions of streamers and the reduced electric field E/N, with the varying air density N being only one of the three factors controlling the streamer properties.

  8. Suppression of polarization fluctuations in chromium alloys with commensurate spin-density waves

    NASA Astrophysics Data System (ADS)

    Michel, R. P.; Weissman, M. B.; Ritley, K.; Huang, J. C.; Flynn, C. P.

    1993-02-01

    We compare electrical resistance noise in commensurate and incommensurate phases of the spin-density wave (SDW) in Cr and dilute CrMn alloys. The commensurate phase gives much less polarization fluctuation noise than the incommensurate phase. The incommensurability of the SDW and the lattice in Cr may affect the SDW dynamics through the existence of weak planes in which the induced orbital moment contribution to the SDW is close to zero.

  9. Quasi-Lagrangian measurements of density surface fluctuations and power spectra in the stratosphere

    NASA Technical Reports Server (NTRS)

    Quinn, Elizabeth P.; Holzworth, Robert H.

    1987-01-01

    Pressure and temperature data from eight superpressure balloon flights at 26 km in the southern hemisphere stratosphere are analyzed. The balloons, which float on a constant density surface, travel steadily westward during summer and eastward during winter, as expected from local climatology. Two types of fluctuations are observed: neutral buoyancy oscillations (NBO) of around 4 min, and 0.1- to 1-hour oscillations that are characterized as small-amplitude density surface fluctuations. Lapse rates and densities are calculated and found to agree well with the expected values. Examples of wave damping and simultaneous fluctuation at two nearby balloons are presented. Spectral analysis is performed clearly showing the NBO and that the majority of the power is in the mesoscale range. Spectral slopes of power versus frequency are measured to be on the average -2.18 + or - 0.24 for pressure and -1.72 + or - 0.24 for temperature. These slopes are compared to the predictions of turbulence theories and the theory of a universal gravity wave spectrum.

  10. Interaction between the lower hybrid wave and density fluctuations in the scrape-off layer

    SciTech Connect

    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.

  11. 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.

  12. Lengthscale-Dependent Solvation and Density Fluctuations in n-Octane.

    PubMed

    Wu, Eugene; Garde, Shekhar

    2015-07-23

    Much attention has been focused on the solvation and density fluctuations in water over the past decade. These studies have brought to light interesting physical features of solvation in condensed media, especially the dependence of solvation on the solute lengthscale, which may be general to many fluids. Here, we focus on the lengthscale-dependent solvation and density fluctuations in n-octane, a simple organic liquid. Using extensive molecular simulations, we show a crossover in the solvation of solvophobic solutes with increasing size in n-octane, with the specifics of the crossover depending on the shape of the solute. Large lengthscale solvation, which is dominated by interface formation, emerges over subnanoscopic lengthscales. The crossover in n-octane occurs at smaller lengthscales than that in water. We connect the lengthscale of crossover to the range of attractive interactions in the fluid. The onset of the crossover is accompanied by the emergence of non-Gaussian tails in density fluctuations in solute shaped observation volumes. Simulations over a range of temperatures highlight a corresponding thermodynamic crossover in solvation. Qualitative similarities between lengthscale-dependent solvation in water, n-octane, and Lennard-Jones fluids highlight the generality of the underlying physics of solvation.

  13. Nonlinear saturation spectra of electric fields and density fluctuations in drift wave turbulence

    NASA Technical Reports Server (NTRS)

    Kelley, M. C.

    1982-01-01

    The detection of drift waves in the nonlinear evolution of a space plasma process driven at long wavelengths is considered, adducing measurements of the electric field and density fluctuation power spectra as evidence. Since the driving mechanism is clearly at long wavelengths, the detection of drift waves suggests that they may play an important role in the transfer of wave energy from long to short wavelengths in a low beta plasma. The saturated spectral density is compared with theoretical results in order to estimate the anomalous diffusion rate. The observed spectral form and amplitude is in excellent agreement with drift wave predictions.

  14. 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.

  15. Adjustments of wingbeat frequency and air speed to air density in free-flying migratory birds.

    PubMed

    Schmaljohann, H; Liechti, F

    2009-11-01

    Birds adjust their flight behaviour to the physical properties of the air. Lift and drag, the two major properties in aerodynamics, are highly dependent on air density. With decreasing air density drag is reduced and lift per wingbeat decreases. According to flight mechanical theory, wingbeat frequency and air speed should increase with decreasing air density, i.e. increasing flight altitude. Although wind tunnel experiments have shed light on many aspects of avian flight, the effect of air density remained ambiguous, because air density could not be adjusted in wind tunnels, until now. By means of radar we recorded tracks of several thousand free-flying individual birds during nocturnal migration. From these tracks we derived wingbeat frequencies and air speeds covering air densities from 0.84 kg m(-3) to 1.13 kg m(-3), corresponding to an altitudinal range of about 3000 m. We demonstrate here with this sample of nocturnal migrants that: (1) wingbeat frequency decreases with air density (which corresponds to an increase in flap-gliding flyers by 0.4 Hz km(-1) and in bounding flyers by 1.1 Hz km(-1)), (2) reducing wingbeat frequency to equivalent sea level values did not abolish the dependency on air density, as expected by flight mechanical theory, and (3) bounding flyers show a higher response in their flight behavioural adjustments to changes in air density than flap-gliding flyers. With respect to air speed flap-gliding flyers increase their air speed by 1.0 m s(-1) km(-1) and bounding flyers by 1.4 m s(-1) km(-1).

  16. Volume and surface contributions to the nuclear symmetry energy within the coherent density fluctuation model

    NASA Astrophysics Data System (ADS)

    Antonov, A. N.; Gaidarov, M. K.; Sarriguren, P.; Moya de Guerra, E.

    2016-07-01

    The volume and surface components of the nuclear symmetry energy (NSE) and their ratio are calculated within the coherent density fluctuation model (CDFM). The estimations use the results of the model for the NSE in finite nuclei based on the Brueckner energy-density functional for nuclear matter. In addition, we present results for the NSE and its volume and surface contributions obtained by using the Skyrme energy-density functional. The CDFM weight function is obtained using the proton and neutron densities from the self-consistent HF+BCS method with Skyrme interactions. We present and discuss the values of the volume and surface contributions to the NSE and their ratio obtained for the Ni, Sn, and Pb isotopic chains, studying their isotopic sensitivity. The results are compared with estimations of other approaches which have used available experimental data on binding energies, neutron-skin thicknesses, excitation energies to isobaric analog states (IAS), and also with results of other theoretical methods.

  17. Rangefinder Corrects for Air Density and Moisture

    NASA Technical Reports Server (NTRS)

    Abshire, J. B.

    1982-01-01

    Proposed distance-measuring instrument compensates for variations in both dry atmospheric density and water-vapor content. Instrument would be expected to be more accurate than previous laser-ranging instruments. New rangefinder sends three signal trains to target: Two trains are at optical frequencies, and one is at a microwave frequency. All three signals are phase-locked.

  18. Spatial correlations of density and structural fluctuations in liquid water: a comparative simulation study.

    PubMed

    Sedlmeier, Felix; Horinek, Dominik; Netz, Roland R

    2011-02-01

    We use large-scale classical simulations employing different force fields to study spatial correlations between local density and structural order for water in the liquid temperature range. All force fields investigated reproduce the main features of the experimental SAXS structure factor S(q), including the minimum at small q, and the recent TIP4P/2005 parametrization yields almost quantitative agreement. As local structural order parameters we consider the tetrahedrality and the number of hydrogen bonds and calculate all pure and mixed spatial two-point correlation functions. Except for the density-density correlation function, there are only weak features present in all other correlation functions, showing that the tendency to form structural clusters is much weaker than the well-known tendency of water to form density clusters (i.e., spatially correlated regions where the density deviates from the mean). In particular, there are only small spatial correlations between local density and structural fluctuations, suggesting that features in density-density correlations (such as measured by the structure factor) are not straightforwardly related to spatial correlations of structure in liquid water.

  19. Quantifying Density Fluctuations in Volumes of All Shapes and Sizes Using Indirect Umbrella Sampling

    NASA Astrophysics Data System (ADS)

    Patel, Amish J.; Varilly, Patrick; Chandler, David; Garde, Shekhar

    2011-10-01

    Water density fluctuations are an important statistical mechanical observable and are related to many-body correlations, as well as hydrophobic hydration and interactions. Local water density fluctuations at a solid-water surface have also been proposed as a measure of its hydrophobicity. These fluctuations can be quantified by calculating the probability, P v ( N), of observing N waters in a probe volume of interest v. When v is large, calculating P v ( N) using molecular dynamics simulations is challenging, as the probability of observing very few waters is exponentially small, and the standard procedure for overcoming this problem (umbrella sampling in N) leads to undesirable impulsive forces. Patel et al. (J. Phys. Chem. B 114:1632, 2010) have recently developed an indirect umbrella sampling (INDUS) method, that samples a coarse-grained particle number to obtain P v ( N) in cuboidal volumes. Here, we present and demonstrate an extension of that approach to volumes of other basic shapes, like spheres and cylinders, as well as to collections of such volumes. We further describe the implementation of INDUS in the NPT ensemble and calculate P v ( N) distributions over a broad range of pressures. Our method may be of particular interest in characterizing the hydrophobicity of interfaces of proteins, nanotubes and related systems.

  20. Quasi-optical design for systems to diagnose the electron temperature and density fluctuations on EAST

    NASA Astrophysics Data System (ADS)

    Cao, Qifo; Liu, Yong; Zhao, Hailin; Zhou, Tianfu; Ti, Ang; Hu, Liqun

    2016-11-01

    A system to simultaneously diagnose the electron temperature and density fluctuations is proposed for Experimental Advanced Superconducting Tokamak device. This system includes a common quasi-optical antenna, a correlation electron cyclotron emission (CECE) system that is used to measure the electron temperature fluctuations and a Doppler backscattering (DBS) system that is used to measure the electron density fluctuations. The frequency range of the proposed CECE system is 108-120 GHz, and this corresponds to a radial coverage of normalized radius ((R - R0)/a, R0 = 1850 mm, a = 450 mm) from 0.2 to 0.67 for the plasma operation with a toroidal magnetic field of 2.26 T. This paper focuses on the design of the quasi-optical antenna and aims at optimizing the poloidal resolution for different frequency bands. An optimum result gives the beam radius for the CECE system of 13-15 mm and this corresponds to a wave number range of kθ < 2.4 cm-1. The beam radius is 20-30 mm for V band (50-75 GHz) and 15-20 mm for W band (75-110 GHz).

  1. Large-scale plasma density fluctuations measured with the HILAT satellite at 830 km altitude

    NASA Astrophysics Data System (ADS)

    Weimer, Daniel R.

    1987-04-01

    Measurements from the plasma monitor on the HILAT satellite have been used to map the distribution of large scale fluctuations in the density of plasma at high latitudes. Digital filtering has been used to separate the original data into three frequency bands. The output from the middle band pass filter has been used to count and map the distribution of large-scale plasma density enhancements. Maps of blob distribution are drawn as a function of magnetic local time and invariant latitude, for both low and high magnetic activity. To serve as a point of reference the same filtering and counting techniques are applied to measurements of the ion drift velocity to show the distribution of electric field fluctuations. Additionally, from the power levels measured at two different frequencies, the average spectral slopes of both the plasma density and electric field have been mapped. The results show that large scale plasma enhancements are created in the auroral zone and are transported away from the production regions by convection. Movement of blobs from the cusp to polar cap is very prominent. The spectral slope of the plasma density is significantly increased in the night side, from 23 to 2 hour magnetic local time. The intermediate scale plasma irregularities appear to be dissipated in this region. Enhanced radio scintillations had been measured with the HILAT radio beacon in the same locations.

  2. Impact of density and environmental factors on population fluctuations in a migratory passerine.

    PubMed

    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

  3. Scaling laws of turbulence and heating of fast solar wind: the role of density fluctuations.

    PubMed

    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

  4. Density fluctuations in irreversible adsorption processes: Hard ellipses in two dimensions

    NASA Astrophysics Data System (ADS)

    Adamczyk, Zbigniew; Weroński, Paweł

    1997-09-01

    Density fluctuations in 2D systems of irreversibly adsorbed particles were studied. Analytical expressions were derived connecting the magnitude of these fluctuations (characterized by the reduced variance σ¯2) with the available surface function φ and the isotropic pair correlation function g0. Limiting expansions in terms of power series of the dimensionless coverage θ were also derived. The range of validity of these expressions was determined by performing numerical simulations based on the random sequential adsorption (RSA) model. Calculations of g0(r), g0(s), φ, and σ¯2 were performed for hard circles and hard ellipses characterized by aspect ratio k=2 and 5. It was deduced that the simulation results can well be accounted for by the theoretical predictions stemming both from the RSA and equilibrium models.

  5. Density fluctuations in saturated phospholipid bilayers increase as the acyl-chain length decreases.

    PubMed Central

    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

  6. Scaling Laws of Turbulence and Heating of Fast Solar Wind: The Role of Density Fluctuations

    SciTech Connect

    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.

  7. 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.

  8. On Static Pressure Fluctuation between Sirocco Fan Blades in a Car Air-Conditioning System

    NASA Astrophysics Data System (ADS)

    Sakai, Yasuhiko; Kato, Takaaki; Moriguchi, Yuu; Sakai, Masaharu; Ito, Kouji; Mitsuishi, Yasushi; Nagata, Kouji; Kubo, Takashi

    In this study, special attention is directed to static pressure fluctuation in a sirocco fan for a car air-conditioning system, because it is expected that there is a close connection between the fluid noise and the pressure fluctuation. The final purpose of this study is to clarify the relationship between the static pressure fluctuation between fan blades and the sound noise emitted to the outside of the fan, and to develop an air-conditioning system with highly low noise level. For this purpose, first of all, a new micro probe for the measurement of static pressure fluctuation has been developed. This new micro probe is composed of an L-type static pressure tube (the outer diameter is 0.5 mm and the inner diameter is 0.34 mm) and a very small pressure transducer. This probe exhibits a flat frequency response until approximately 2,000 Hz, and it is set between the blades of the fan rotating at 1,500 rpm. The measurements of the static pressure fluctuation between the blades have been performed, and the intensity of sound source was quantified from the second derivative of the phase-averaged static pressure fluctuation signals on the basis of Ribner's formula (Ribner 1962). The experiments have been made in two different modes, i.e., the cooling mode (FACE MODE) and the heating mode (FOOT MODE). It is shown that the static pressure increases rapidly as the blade approaches to the nose of the casing. It is also found that the sound source for FACE MODE shows the larger value than that for FOOT MODE as a whole. In particular, the largest intensity of sound source is observed when the blade approaches to the nose. From these results, it is confirmed that the present new static pressure probe is useful to specify the distributions of sound source in a sirocco fan.

  9. Stochastic thermodynamics of fluctuating density fields: Non-equilibrium free energy differences under coarse-graining

    SciTech Connect

    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.

  10. Spacecraft radio scattering observations of the power spectrum of electron density fluctuations in the solar wind

    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.

  11. Propagation of density disturbances in air-water flow

    NASA Technical Reports Server (NTRS)

    Nassos, G. P.

    1969-01-01

    Study investigated the behavior of density waves propagating vertically in an atmospheric pressure air-water system using a technique based on the correlation between density change and electric resistivity. This information is of interest to industries working with heat transfer systems and fluid power and control systems.

  12. Measuring Density Of Air By Ultraviolet Rayleigh Scattering

    NASA Technical Reports Server (NTRS)

    Mckenzie, Robert L.

    1992-01-01

    Report presents theoretical and experimental studies directed toward development of optoelectronic instrument to measure density of air at altitudes from 50 to 90 km and possibly beyond. Instrument mounted in Space Shuttle orbiter and operated during reentry into atmosphere. Data gathered by instrument needed because density of upper atmosphere highly variable in space and time and this variability affects aerodynamic behavior and trajectory of reentering Shuttle. Variations in density also meteorologically significant.

  13. Alternating-Current Equipment for the Measurement of Fluctuations of Air Speed in Turbulent Flow

    NASA Technical Reports Server (NTRS)

    Mock, W C , Jr

    1937-01-01

    Recent electrical and mechanical improvements have been made in the equipment developed at the National Bureau of Standards for measurement of fluctuations of air speed in turbulent flow. Data useful in the design of similar equipment are presented. The design of rectified alternating-current power supplies for such apparatus is treated briefly, and the effect of the power supplies on the performance of the equipment is discussed.

  14. 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.

  15. Collective backscattering of gyrotron radiation by small-scale plasma density fluctuations in large helical device

    SciTech Connect

    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.

  16. 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.

  17. Chaotic density fluctuations in L-mode plasmas of the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Maggs, J. E.; Rhodes, T. L.; Morales, G. J.

    2015-04-01

    Analysis of the time series obtained with the Doppler backscattering system (Hillsheim et al 2009 Rev. Sci. Instrum. 80 0835070) in the DIII-D tokamak (Luxon 2005 Fusion Sci. Technol. 48 828) shows that intermediate wave number plasma density fluctuations in low confinement (L-mode) tokamak plasmas are chaotic. The supporting evidence is based on the shape of the power spectrum; the location of the signal in the complexity-entropy plane (C-H plane) (Rosso et al 2007 Phys. Rev. Lett. 99 154102); and the population of the corresponding Bandt-Pompe (Bandt and Pompe 2002 Phys. Rev. Lett. 88 174102) probability distributions.

  18. Connection between ambient density fluctuations and clumpy Langmuir waves in type III radio sources

    NASA Technical Reports Server (NTRS)

    Robinson, P. A.; Cairns, I. H.; Gurnett, D. A.

    1992-01-01

    A recent stochastic-growth theory of clumpy Langmuir waves in type III sources is shown to imply that the clumps will have the same size distribution as the ambient low-frequency density fluctuations in the solar wind. Spectral analysis of Langmuir-wave time series from the ISEE 3 plasma wave instrument confirms this prediction to within the uncertainties in the spectra. The smallest Langmuir clump size is inferred to be in the range 0.4-30 km in general, and 2-30 km for beam-resonant waves, and it is concluded that the diffusion of waves in the source is anomalous.

  19. Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha)

    NASA Astrophysics Data System (ADS)

    Ding, W. X.; Lin, L.; Duff, J. R.; Brower, D. L.; Sarff, J. S.

    2012-10-01

    The multichannel polarimeter-interferometer system on the MST reversed-field pinch can be utilized to measure far-forward collective scattering from electron density fluctuations. The collective scattering system has 11 viewing chords with ˜8 cm spacing. The source is a 432 μm (694 GHz) far infrared laser and the scattered power is measured using a heterodyne detection scheme. Collective scattering provides a line-integrated measurement of fluctuations within the divergence of the probe beam covering wavenumber range: k⊥ < 1.3 cm-1, corresponding k⊥ρs < 1.3 (ρs is the ion-sound Larmor radius), the region of primary interest for turbulent fluctuation-induced transport. The perpendicular wavenumber consists of toroidal, poloidal, and radial contributions, which vary with chord position. Coherent modes associated with tearing instabilities and neutral-beam driven fast particles are observed along with broadband turbulence at frequencies up to 500 kHz. Changes in frequency are consistent with a Doppler shift due to parallel plasma flow.

  20. Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Xu, B.; Dai, Y. M.; Xiao, H.; Shen, B.; Ye, Z. R.; Forget, A.; Colson, D.; Feng, D. L.; Wen, H. H.; Qiu, X. G.; Lobo, R. P. S. M.

    2016-08-01

    In iron-based superconductors, a spin-density-wave (SDW) magnetic order is suppressed with doping, and unconventional superconductivity appears in close proximity to the SDW instability. The optical response of the SDW order shows clear gap features: substantial suppression in the low-frequency optical conductivity, alongside a spectral weight transfer from low to high frequencies. Here, we study the detailed temperature dependence of the optical response in three different series of the Ba122 system [Ba1 -xKxFe2As2 , Ba (Fe1-xCox) 2As2 , and BaFe2(As1-xPx) 2 ]. Intriguingly, we find that the suppression of the low-frequency optical conductivity and spectral weight transfer appear at a temperature T* much higher than the SDW transition temperature TSDW. Since this behavior has the same optical feature and energy scale as the SDW order, we attribute it to SDW fluctuations. Furthermore, T* is suppressed with doping, closely following the doping dependence of the nematic fluctuations detected by other techniques. These results suggest that the magnetic and nematic orders have an intimate relationship, in favor of the magnetic-fluctuation-driven nematicity scenario in iron-based superconductors.

  1. Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pinch

    SciTech Connect

    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.

  2. Quasi-linear theory of electron density and temperature fluctuations with application to MHD generators and MPD arc thrusters

    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.

  3. Quasi-linear theory of electron density and temperature fluctuations with application to MHD generators and MPD arc thrusters.

    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.

  4. Tangential phase contrast imaging diagnostic for density fluctuation measurement on CDX-U

    NASA Astrophysics Data System (ADS)

    Lo, Ernest P.

    Understanding the nature and effects of turbulence is one of the central efforts in fusion science. Spatially resolved measurement of turbulent fluctuations in the core of hot fusion plasmas would permit the detailed investigation of the relationship between turbulence characteristics and variations in global confinement and local gradients. The tangential CO2 laser phase contrast imaging system was developed on the Current Drive Experiment Upgrade (CDX-U), to allow such measurements to be made. Theoretical work demonstrates that the effect of the plasma on the tangential imaging beam is approximately that of a shift-invariant point-spread function. The result indicates that the recovery of core-localized density fluctuation images using a spatial filter is possible in principle. The imaging process is studied through extensive computer simulations. Results show that a simple step-function phase mirror design provides adequate qualitative image recovery, even in the presence of non-ideal effects in the plasma model, such as a finite k∥ variation along the field lines and significant field line pitch. The instrumental components of the system are characterized and calibrated and the absolute system sensitivity is calculated. Sound waves are used as test phase objects to calibrate the diagnostic. The tests locate the image plane, verify the system magnification, and demonstrate spatial filtering capabilities. Plasma measurements show adequate signal to noise and k spectrum measurement capability. Localization of the measurement is suggested by measurements of sawtooth modes. Full experimental demonstration of image recovery, however, will require further work. Preliminary analyses of the MHD activity and turbulence are done. Analysis of the sawtooth mode measurements indicate a long wavelength structure (kr/leq0.78cm-1) localized to the core, and a density fluctuation amplitude of (3.7/pm0.7)cm-1, yielding /Delta n/n≈(17/pm3)/%. A measurement of the fluctuation k

  5. Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuationsa)

    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.

  6. Characterization of maximally random jammed sphere packings. II. Correlation functions and density fluctuations.

    PubMed

    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

  7. 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.

  8. Characterization of maximally random jammed sphere packings. II. Correlation functions and density fluctuations

    NASA Astrophysics Data System (ADS)

    Klatt, Michael A.; Torquato, Salvatore

    2016-08-01

    In the first paper of this series, we introduced Voronoi correlation functions to characterize the structure of maximally random jammed (MRJ) sphere packings across length scales. In the present paper, we determine a variety of different correlation functions that arise in rigorous expressions for the effective physical properties of MRJ sphere packings and compare them to the corresponding statistical descriptors for overlapping spheres and equilibrium hard-sphere systems. Such structural descriptors arise in rigorous bounds and formulas for effective transport properties, diffusion and reactions constants, elastic moduli, and electromagnetic characteristics. First, we calculate the two-point, surface-void, and surface-surface correlation functions, for which we derive explicit analytical formulas for finite hard-sphere packings. We show analytically how the contact Dirac delta function contribution to the pair correlation function g2(r ) for MRJ packings translates into distinct functional behaviors of these two-point correlation functions that do not arise in the other two models examined here. Then we show how the spectral density distinguishes the MRJ packings from the other disordered systems in that the spectral density vanishes in the limit of infinite wavelengths; i.e., these packings are hyperuniform, which means that density fluctuations on large length scales are anomalously suppressed. Moreover, for all model systems, we study and compute exclusion probabilities and pore size distributions, as well as local density fluctuations. We conjecture that for general disordered hard-sphere packings, a central limit theorem holds for the number of points within an spherical observation window. Our analysis links problems of interest in material science, chemistry, physics, and mathematics. In the third paper of this series, we will evaluate bounds and estimates of a host of different physical properties of the MRJ sphere packings that are based on the

  9. Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Romoli, M.; Poletto, G.; Noci, G.; Kohl, J. L.

    1998-11-01

    In the Letter ``Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind'' by L. Ofman, M. Romoli, G. Poletto, G. Noci, and J. L. Kohl (ApJ, 491, L111 [1997]), there was an error in the data reduction of the polarized brightness (pB). It was assumed that the cadence of the data and the exposure time are equal. However, the correct cadence is30 s longer than the exposure time because of the time it takes the polarizer to change orientation between exposures. This error does not affect the main result of the Letter, i.e., the detection of quasi-periodic density fluctuations in the solar wind. However, the correct cadences of the data in Table 1 are 30 s longer. This correction can be taken into account in Figure 1 by multiplying the times by 1.5 and dividing the frequencies by the same factor. Thus, the highest peak in the power spectrum is at 1.8+/-0.07 mHz (the corresponding period is 9.3+/-0.4 minutes). The correction factor is 1.1 in Figure 2 because of the longer exposure time in this observation.

  10. Scattering from edge density fluctuations on the lower hybrid waves in FTU

    NASA Astrophysics Data System (ADS)

    Calabrò, Giuseppe; Ridolfini, V. Pericoli

    2007-09-01

    Careful measurements of density fluctuations in the scrape-off layer (SOL) of Frascati Tokamak Upgrade (FTU) plasma have been carried out. The analytical model proposed by Andrews and Perkins for the scattering of lower hybrid (LH) waves by density fluctuations will constitute the basis of our discussion. The envelop of the scattering processes occurring on single points sampled along the poloidal profile of the launching antenna at fixed step Δθ is considered. The trajectories and N∥ (LH parallel refraction index) evolution of the corresponding ray bundles are followed using the fast ray tracing code (FRTC), coupled to the transport code ASTRA to infer the radial absorption profile on a given target plasma. Interpretative ASTRA simulations are presented to support the correctness of the scattering model assumed. The current drive (CD) efficiency calculated is then compared with that measured for the shot assumed as reference and with the scaling valid for FTU. Comparison of measured pump frequency spectral broadening on FTU and theoretical prediction is also presented.

  11. Measurements of core electron temperature and density fluctuations in DIII-D and comparison to nonlinear gyrokinetic simulations

    SciTech Connect

    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.

  12. Guiding supersonic projectiles using optically generated air density channels

    NASA Astrophysics Data System (ADS)

    Johnson, Luke A.; Sprangle, Phillip

    2015-09-01

    We investigate the feasibility of using optically generated channels of reduced air density to provide trajectory correction (guiding) for a supersonic projectile. It is shown that the projectile experiences a force perpendicular to its direction of motion as one side of the projectile passes through a channel of reduced air density. A single channel of reduced air density can be generated by the energy deposited from filamentation of an intense laser pulse. We propose changing the laser pulse energy from shot-to-shot to build longer effective channels. Current femtosecond laser systems with multi-millijoule pulses could provide trajectory correction of several meters on 5 km trajectories for sub-kilogram projectiles traveling at Mach 3.

  13. Preliminary Study of the Magnetic Perturbation Effects on the Edge Density Profiles and Fluctuations Using Reflectometers on EAST

    NASA Astrophysics Data System (ADS)

    Gao, Yu; Wang, Yumin; Zhang, Tao; Zhang, Shoubiao; Qu, Hao; Han, Xiang; Wen, Fei; Kong, Defeng; Huang, Canbin; Cai, Jianqing; Sun, Youwen; Liang, Yunfeng; Gao, Xiang; East Team

    2016-09-01

    The resonant magnetic perturbation (RMP) coils have been successfully designed and installed on the Experimental Advanced Superconducting Tokamak (EAST). Using the reflectometer systems, the density profile and the density fluctuations during magnetic perturbations (MPs) phase have been investigated. During the experiments, two different cases are studied separately: steady MPs and rotating MPs. In both cases, a strongly density pump-out has been observed. In the steady MPs cases, an enhancement of the low frequency (<60 kHz) density fluctuations in H-mode phase has been observed. The plasma density boundary out-shifts ~ 5% caused by the MPs. The pedestal density gradient is reduced by 50%, while the radial location nearly stays unchanged. In the rotating MPs, the line-averaged density, the Dα emission at the divertor region and the spectrum of the density fluctuations are modulated. The results suggest that the low frequency (<60 kHz) density fluctuations may contribute to the strong density pump-out. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2014GB106000, 2014GB106003 and 2015GB110001), and National Natural Science Foundation of China (Nos. 11275234, 11305215, 11305208, 11405214 and 11505221)

  14. Extreme atmospheric electron densities created by extensive air showers

    NASA Astrophysics Data System (ADS)

    Rutjes, Casper; Camporeale, Enrico; Ebert, Ute; Buitink, Stijn; Scholten, Olaf; Trinh, Gia

    2016-04-01

    A sufficient density of free electrons and strong electric fields are the basic requirements to start any electrical discharge. In the context of thunderstorm discharges it has become clear that in addition droplets and or ice particles are required to enhance the electric field to values above breakdown. In our recent study [1] we have shown that these three ingredients have to interplay to allow for lightning inception, triggered by an extensive air shower event. The extensive air showers are a very stochastic natural phenomenon, creating highly coherent bursts of extreme electron density in our atmosphere. Predicting these electron density bursts accurately one has to take the uncertainty of the input variables into account. To this end we use uncertainty quantification methods, like in [2], to post-process our detailed Monte Carlo extensive air shower simulations, done with the CORSIKA [3] software package, which provides an efficient and elegant way to determine the distribution of the atmospheric electron density enhancements. We will present the latest results. [1] Dubinova, A., Rutjes, C., Ebert, E., Buitink, S., Scholten, O., and Trinh, G. T. N. "Prediction of Lightning Inception by Large Ice Particles and Extensive Air Showers." PRL 115 015002 (2015) [2] G.J.A. Loeven, J.A.S. Witteveen, H. Bijl, Probabilistic collocation: an efficient nonintrusive approach for arbitrarily distributed parametric uncertainties, 45th AIAA Aerospace Sciences Meeting, Reno, Nevada, 2007, AIAA-2007-317 [3] Heck, Dieter, et al. CORSIKA: A Monte Carlo code to simulate extensive air showers. No. FZKA-6019. 1998.

  15. Light Transmission Fluctuations from Extended Air Showers Produced by Cosmic-Rays and Gamma-Rays

    NASA Astrophysics Data System (ADS)

    Taylor, Stuart

    Cosmic-ray and gamma-ray experiments that use the atmosphere as a calorimeter, such as the High Resolution Fly's Eye (HiRes) and the Telescope Array (TA), require understanding the transmission of the light from the air shower of particles produced by the cosmic-ray or gamma-ray striking the atmosphere. To better understand the scattering and transmission of light to the detectors, HiRes measures light from different calibrated sources. We compare scattered light from laser shots a few kilometers away from the two HiRes detectors with direct light from stable portable light sources placed a few meters in front of the phototubes. We use two HiRes detectors to study and isolate contributions to fluctuations of the measured light. These contributions include fluctuations in the source intensity, the night sky background, scattering and transmission of the laser beam, the phototubes and electronics, and photostatistics. N o rth Mirror Fields of View

  16. Active suppression of air refractive index fluctuation using a Fabry-Perot cavity and a piezoelectric volume actuator

    SciTech Connect

    Banh, Tuan Quoc; Ohkubo, Yuria; Murai, Yoshinosuke; Aketagawa, Masato

    2011-01-01

    Air refractive index fluctuation ({Delta}n{sub air}) is one of the largest uncertainty sources in precision interferometry systems that require a resolution of nanometer order or less. We introduce a method for the active suppression of {Delta}n{sub air} inside a normal air-environment chamber using a Fabry-Perot cavity and a piezoelectric volume actuator. The temporal air refractive index (n{sub air}) at a local point is maintained constant with an expanded uncertainty of {approx}4.2x10{sup -9} (k=2), a sufficiently low uncertainty for precise measurements unaffected by {Delta}n{sub air} to be made inside a chamber.

  17. Impact of fine particulate fluctuation and other variables on Beijing's air quality index.

    PubMed

    Chen, Bo; Lu, Shaowei; Li, Shaoning; Wang, Bing

    2015-04-01

    We analyzed fluctuation in Beijing's air quality over 328 days, based on air quality grades and air quality data from 35 atmospheric monitoring stations. Our results show the air over Beijing is subject to pollution 152 days of the year, or 46.34%. Among all pollutants, fine particulates, solid or liquid, 2.5 μm or less in size (PM2.5), appeared most frequently as the primary pollutant: 249 days, or 76% of the sample year (328 days). Nitrogen dioxide (NO2) and coarse particulates (PM10) cause the least pollution, appearing only 7 and 3 days, or 2 and 1% of the sample year, respectively. In Beijing, fine particulates like PM2.5 vary seasonally: 154.54 ± 18.60 in winter > 145.22 ± 18.61 in spring > 140.16 ± 20.76 in autumn > 122.37 ± 13.42 in summer. Air quality is best in August and worst in December, while various districts in Beijing experience different air quality. To be specific, from south to north and from west to east, air quality tends to improve. Meteorological elements have a constraining effect on air pollutants, which means there is a linear correlation between the air quality index and humidity, rainfall, wind speed, and temperature. Under a typical pollution scenario, the higher the air quality index (AQI) value, the lower the wind speed and the greater the relative humidity; the lower the AQI value, the higher the wind speed and lower the relative humidity. Analysis of influencing factors reveals that the air pollution is mainly particulate matter produced by burning coal, vehicle emissions, volatile oils and gas, fast development of food services, emissions from the surrounding region, and natural dust clouds formed in arid areas to the northwest. Topography affects the distribution of meteorological conditions, in turn varying air quality over the region from one location to another. Human activities also exercise impact on urban air quality with dual functions.

  18. Impact of fine particulate fluctuation and other variables on Beijing's air quality index.

    PubMed

    Chen, Bo; Lu, Shaowei; Li, Shaoning; Wang, Bing

    2015-04-01

    We analyzed fluctuation in Beijing's air quality over 328 days, based on air quality grades and air quality data from 35 atmospheric monitoring stations. Our results show the air over Beijing is subject to pollution 152 days of the year, or 46.34%. Among all pollutants, fine particulates, solid or liquid, 2.5 μm or less in size (PM2.5), appeared most frequently as the primary pollutant: 249 days, or 76% of the sample year (328 days). Nitrogen dioxide (NO2) and coarse particulates (PM10) cause the least pollution, appearing only 7 and 3 days, or 2 and 1% of the sample year, respectively. In Beijing, fine particulates like PM2.5 vary seasonally: 154.54 ± 18.60 in winter > 145.22 ± 18.61 in spring > 140.16 ± 20.76 in autumn > 122.37 ± 13.42 in summer. Air quality is best in August and worst in December, while various districts in Beijing experience different air quality. To be specific, from south to north and from west to east, air quality tends to improve. Meteorological elements have a constraining effect on air pollutants, which means there is a linear correlation between the air quality index and humidity, rainfall, wind speed, and temperature. Under a typical pollution scenario, the higher the air quality index (AQI) value, the lower the wind speed and the greater the relative humidity; the lower the AQI value, the higher the wind speed and lower the relative humidity. Analysis of influencing factors reveals that the air pollution is mainly particulate matter produced by burning coal, vehicle emissions, volatile oils and gas, fast development of food services, emissions from the surrounding region, and natural dust clouds formed in arid areas to the northwest. Topography affects the distribution of meteorological conditions, in turn varying air quality over the region from one location to another. Human activities also exercise impact on urban air quality with dual functions. PMID:25563832

  19. Structure and Function of Intra–Annual Density Fluctuations: Mind the Gaps

    PubMed Central

    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

  20. Structure and Function of Intra-Annual Density Fluctuations: Mind the Gaps.

    PubMed

    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

  1. Density-matrix renormalization-group study of current and activity fluctuations near nonequilibrium phase transitions.

    PubMed

    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

  2. Hyperuniform Density Fluctuations and Diverging Dynamic Correlations in Periodically Driven Colloidal Suspensions

    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.

  3. Vacuum energy density fluctuations in Minkowski and Casimir states via smeared quantum fields and point separation

    NASA Astrophysics Data System (ADS)

    Phillips, Nicholas G.; Hu, B. L.

    2000-10-01

    We present calculations of the variance of fluctuations and of the mean of the energy momentum tensor of a massless scalar field for the Minkowski and Casimir vacua as a function of an intrinsic scale defined by a smeared field or by point separation. We point out that, contrary to prior claims, the ratio of variance to mean-squared being of the order unity is not necessarily a good criterion for measuring the invalidity of semiclassical gravity. For the Casimir topology we obtain expressions for the variance to mean-squared ratio as a function of the intrinsic scale (defined by a smeared field) compared to the extrinsic scale (defined by the separation of the plates, or the periodicity of space). Our results make it possible to identify the spatial extent where negative energy density prevails which could be useful for studying quantum field effects in worm holes and baby universes, and for examining the design feasibility of real-life ``time machines.'' For the Minkowski vacuum we find that the ratio of the variance to the mean-squared, calculated from the coincidence limit, is identical to the value of the Casimir case at the same limit for spatial point separation while identical to the value of a hot flat space result with a temporal point separation. We analyze the origin of divergences in the fluctuations of the energy density and discuss choices in formulating a procedure for their removal, thus raising new questions about the uniqueness and even the very meaning of regularization of the energy momentum tensor for quantum fields in curved or even flat spacetimes when spacetime is viewed as having an extended structure.

  4. Density-dependent life histories in female bank voles from fluctuating populations.

    PubMed

    Tkadlec, E; Zejda, J

    1998-11-01

    Using long-term data sets from two lowland floodplain forest bank vole populations in central Europe, we tested two predictions that with increasing densities: (i) proportions of nonparous females in winter populations would increase; and (ii) age of both nonparous and parous females would increase. These two predictions follow from the assumption that changes in age structure are driven by density-dependent shifts in age at first reproduction. Both populations were sampled by snap trapping between 1956 and 1976. For each year, we examined samples of animals collected between November and April for proportions of females with and without breeding experience and analysed their variation in age relative to the population density. The presence or absence of placental scars was used to discriminate between the parous and nonparous animals. Age was determined by measuring the length of the first mandibular molar (M1 ) roots. Both populations exhibited multi-annual fluctuations in numbers closely resembling those in northern Fennoscandia. The proportion of nonparous females in our total sample was 0.73, suggesting that it is uncommon for parous female bank voles to breed in two successive years and that their life histories are largely designed for breeding in one season only as a major reproductive strategy. Using a logistic-binomial regression model, we found that the probability of females being nonparous or parous at capture varied significantly with time, space and population density. The final model producing the best fit to data predicted that the proportion of nonparous females would be slightly larger over winter and substantially larger after high-density breeding seasons, which is consistent with the tested prediction. With increasing densities during the breeding seasons, both the nonparous and parous females became older at the onset of winter. Again, the field evidence was consistent with the predicted pattern. The age of parous females in the autumn at

  5. Fluctuations of total ozone and their relationship to stratospheric air motions

    NASA Technical Reports Server (NTRS)

    Salby, Murry L.; Callaghan, Patrick F.

    1993-01-01

    The origin of fluctuations of total ozone and the interactions that take place between the distribution of total ozone and the circulation of the troposphere are investigated on the basis of observations of total ozone from Nimbus 7 TOMS together with contemporaneous analyses of the circulation. It is shown that a sizable component of total ozone variability is explained by the quasi-columnar motion of air in the lower stratosphere. The development also suggests that in combination with isentropic analyses, total ozone measurements can provide a detailed picture of air motions in the lower stratosphere. Distributions of ozone column abundance and pressure on the 375-K isentropic surface for the Northern and Southern Hemispheres are illustrated.

  6. Prediction of seasonal water-table fluctuations in La Pampa and Buenos Aires, Argentina

    NASA Astrophysics Data System (ADS)

    Tanco, Raúl; Kruse, Eduardo

    2001-07-01

    The fluctuation of the water table east of La Pampa province and northwest of Buenos Aires province, Argentina, influences agricultural production in the region because it is closely related to the alternation of dry and wet periods. Sea-surface temperature (SST) anomalies have been used as predictors to forecast atmospheric variables in different regions of the world. The objective of this work is to present a simple model to forecast seasonal rainfall using SST distribution in the Pacific Ocean as a predictor. Once the relationship between precipitation and water-table fluctuations was established, a methodology for the prediction of water-table fluctuations was developed. A good agreement between observed and predicted water-table fluctuations was found when estimating water-table fluctuations in the summer and autumn seasons. Résumé. Les fluctuations de la nappe à l'est de la province de La Pampa et au nord-ouest de la province de Buenos Aires (Argentine) influence la production agricole de la région parce qu'elle est étroitement liée à l'alternance de saisons sèches et humides. Les anomalies de la température de surface de l'océan (SST) ont été utilisées comme prédicteurs pour prévoir les variables atmosphériques dans différentes régions du monde. L'objectif de ce travail est de présenter un modèle simple de prévision des précipitations saisonnières en utilisant comme prédicteur la distribution des SST dans l'Océan Pacifique. Une fois que la relation entre les fluctuations des précipitations et celles de la nappe a été établie, une méthodologie de prédiction des variations de la nappe a été mise au point. Un bon accord entre les variations de la nappe observées et celles prédites a été trouvé pour les estimations des variations de nappe en été et en automne. Resumen. La fluctuación del nivel freático al este de la provincia de La Pampa y al nordeste de la de Buenos Aires (Argentina) repercute en la producción agr

  7. A high speed compact microwave interferometer for density fluctuation measurements in Sino-UNIted Spherical Tokamak

    NASA Astrophysics Data System (ADS)

    Zhong, H.; Tan, Y.; Liu, Y. Q.; Xie, H. Q.; Gao, Z.

    2016-11-01

    A single-channel 3 mm interferometer has been developed for plasma density diagnostics in the Sino-UNIted Spherical Tokamak (SUNIST). The extremely compact microwave interferometer utilizes one corrugated feed horn antenna for both emitting and receiving the microwave. The beam path lies on the equatorial plane so the system would not suffer from beam path deflection problems due to the symmetry of the cross section. A focusing lens group and an oblique vacuum window are carefully designed to boost the signal to noise ratio, which allows this system to show good performance even with the small-diameter central column itself as a reflector, without a concave mirror. The whole system discards the reference leg for maximum compactness, which is particularly suitable for the small-sized tokamak. An auto-correcting algorithm is developed to calculate the phase evolution, and the result displays good phase stability of the whole system. The intermediate frequency is adjustable and can reach its full potential of 2 MHz for best temporal resolution. Multiple measurements during ohmic discharges proved the interferometer's capability to track typical density fluctuations in SUNIST, which enables this system to be utilized in the study of MHD activities.

  8. Density nonlinearities in field theories for a toy model of fluctuating nonlinear hydrodynamics of supercooled liquids.

    PubMed

    Yeo, Joonhyun

    2009-11-01

    We study a zero-dimensional version of the fluctuating nonlinear hydrodynamics (FNH) of supercooled liquids originally investigated by Das and Mazenko (DM) [Shankar P. Das and Gene F. Mazenko Phys. Rev. A 34, 2265 (1986)]. The time-dependent density-like and momentum-like variables are introduced with no spatial degrees of freedom in this toy model. The structure of nonlinearities takes the similar form to the original FNH, which allows one to study in a simpler setting the issues raised recently regarding the field theoretical approaches to glass forming liquids. We study the effects of density nonlinearities on the time evolution of correlation and response functions by developing field theoretic formulations in two different ways: first by following the original prescription of DM and then by constructing a dynamical action which possesses a linear time-reversal symmetry as proposed recently. We show explicitly that, at the one-loop order of the perturbation theory, the DM-type field theory does not support a sharp ergodic-nonergodic transition, while the other admits one. The simple nature of the toy model in the DM formulation allows us to develop numerical solutions to a complete set of coupled dynamical equations for the correlation and response functions at the one-loop order. PMID:20364986

  9. A high speed data acquisition and analysis system for transonic velocity, density, and total temperature fluctuations

    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.

  10. Glass transition and density fluctuations in the fragile glass former orthoterphenyl

    SciTech Connect

    Monaco, G.; Fioretto, D.; Comez, L.; Ruocco, G.

    2001-06-01

    High-resolution Brillouin light scattering is used to measure the dynamic structure factor of the fragile glass former orthoterphenyl (OTP) in a wide temperature range around the glass transition region and up to the boiling point. The whole set of spectra is described in terms of a phenomenological generalized hydrodynamic model. In the supercooled phase, we show the contemporary existence of the structural process, whose main features come out to be consistent with the results obtained with other spectroscopies, and of a secondary, activated process, which occurs on the 10{sup {minus}11} s time scale and has a low activation energy (E{sub a}{sup f}=0.28 kcal/mol). This latter process, which is also present in the glassy phase and seems to be insensitive to the glass transition, is attributed to the coupling between the density modes and intramolecular degrees of freedom. In the normal liquid phase, the two processes merge together, and the resulting characteristic time is no longer consistent with those derived with other spectroscopies. The analysis points to the conclusion that, for what concerns the long-wavelength density fluctuations in fragile glass formers such as OTP, the universal dynamical features related to the glass transition come out clearly only in the supercooled phase and at frequencies lower than {approximately}10{sup 6} Hz.

  11. 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

  12. Laser Induced Tunnel Ionization and Electron Density Evolution in Air

    NASA Astrophysics Data System (ADS)

    Tiwari, Pawan K.; Brussaard, G. J. H.; Wiel, M. J. v. d.; Tripathi, V. K.

    2005-08-01

    An indigenously built Ti:sapphire laser system delivering 50 mJ, 100 fs pulses at a repetition rate of 10 Hz, is employed to tunnel ionize air at 1 atm pressure and form a plasma channel. The laser is line focused using a cylindrical lens to a spot size of 20 μm× 1 mm. A folded wave interferometry is used to deduce the radial electron density profile by measuring the phase shift and employing Abel inversion. The maximum value of chord-integrated electron density and radial electron density are estimated to be approximately equal to 3.0× 1016 cm-2 and 4.0× 1018 cm-3 respectively with density scale length of 20 μm. These results have been theoretically interpreted by developing a unified formalism of tunnel ionization. The experimental results are in reasonable agreement with the theory.

  13. Positive streamers in air of varying density: experiments on the scaling of the excitation density

    NASA Astrophysics Data System (ADS)

    Dubrovin, D.; Nijdam, S.; Clevis, T. T. J.; Heijmans, L. C. J.; Ebert, U.; Yair, Y.; Price, C.

    2015-02-01

    Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited molecules in the active streamer front scale as the square of the density of the neutral gas. In this work we estimate the absolute density of nitrogen molecules, excited to the C3Πu state that emit photons in the 2P-N2 band, by radiometrically calibrated short exposure intensified imaging. We test several pressures (100, 200 and 400 mbar) in artificial air at room temperature. Our results provide a first confirmation for the scaling of the density of excited species with the gas density. The method proposed here is particularly suitable to characterize the excitation densities in sprite streamers in the atmosphere.

  14. Fluctuations in air pollution give risk warning signals of asthma hospitalization

    NASA Astrophysics Data System (ADS)

    Hsieh, Nan-Hung; Liao, Chung-Min

    2013-08-01

    Recent studies have implicated that air pollution has been associated with asthma exacerbations. However, the key link between specific air pollutant and the consequent impact on asthma has not been shown. The purpose of this study was to quantify the fluctuations in air pollution time-series dynamics to correlate the relationships between statistical indicators and age-specific asthma hospital admissions. An indicators-based regression model was developed to predict the time-trend of asthma hospital admissions in Taiwan in the period 1998-2010. Five major pollutants such as particulate matters with aerodynamic diameter less than 10 μm (PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) were included. We used Spearman's rank correlation to detect the relationships between time-series based statistical indicators of standard deviation, coefficient of variation, skewness, and kurtosis and monthly asthma hospitalization. We further used the indicators-guided Poisson regression model to test and predict the impact of target air pollutants on asthma incidence. Here we showed that standard deviation of PM10 data was the most correlated indicators for asthma hospitalization for all age groups, particularly for elderly. The skewness of O3 data gives the highest correlation to adult asthmatics. The proposed regression model shows a better predictability in annual asthma hospitalization trends for pediatrics. Our results suggest that a set of statistical indicators inferred from time-series information of major air pollutants can provide advance risk warning signals in complex air pollution-asthma systems and aid in asthma management that depends heavily on monitoring the dynamics of asthma incidence and environmental stimuli.

  15. 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.

  16. Supersonic helium beam diagnostic for fluctuation measurements of electron temperature and density at the Tokamak TEXTOR

    SciTech Connect

    Kruezi, U.; Stoschus, H.; Schweer, B.; Sergienko, G.; Samm, U.

    2012-06-15

    A supersonic helium beam diagnostic, based on the line-ratio technique for high resolution electron density and temperature measurements in the plasma edge (r/a > 0.9) was designed, built, and optimised at TEXTOR (Torus Experiment for Technology Oriented Research). The supersonic injection system, based on the Campargue skimmer-nozzle concept, was developed and optimised in order to provide both a high neutral helium beam density of n{sub 0}= 1.5 Multiplication-Sign 10{sup 18} m{sup -3} and a low beam divergence of {+-}1 Degree-Sign simultaneously, achieving a poloidal resolution of {Delta}{sub poloidal}= 9 mm. The setup utilises a newly developed dead volume free piezo valve for operation in a high magnetic field environment of up to 2 T with a maximum repetition rate of 80 Hz. Gas injections are realised for a duration of 120 ms at a repetition rate of 2 Hz (duty cycle 1/3). In combination with a high sensitivity detection system, consisting of three 32 multi-channel photomultipliers (PMTs), measurements of edge electron temperature and density with a radial resolution of {Delta}{sub radial}= 2 mm and a maximum temporal resolution of {Delta}t Asymptotically-Equal-To 2 {mu}s (470 kHz) are possible for the first time. The diagnostic setup at TEXTOR is presented. The newly developed injection system and its theoretical bases are discussed. The applicability of the stationary collisional-radiative model as basis of the line-ratio technique is shown. Finally, an example of a fluctuation analysis demonstrating the unique high temporal and spatial resolution capabilities of this new diagnostic is presented.

  17. Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

    SciTech Connect

    Vukovic, M.; Harper, M.; Breun, R.; Wukitch, S.

    1995-12-31

    Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode converted kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.

  18. Simultaneous measurement of core electron temperature and density fluctuations during electron cyclotron heating on DIII-D

    SciTech Connect

    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.

  19. Climatic Signals from Intra-annual Density Fluctuation Frequency in Mediterranean Pines at a Regional Scale

    PubMed Central

    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

  20. Climatic Signals from Intra-annual Density Fluctuation Frequency in Mediterranean Pines at a Regional Scale.

    PubMed

    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

  1. The THz Spectrum of Density Fluctuations of Water: The Viscoelastic Regime

    SciTech Connect

    Cunsolo, Alessandro

    2015-01-01

    Relevant advances in the knowledge of the water dynamics at mesoscopic scales are reviewed, while mainly focusing on the contribution provided by high resolution inelastic X-ray scattering (IXS). In particular it is discussed how the use of IXS has improved our understanding of viscoelastic properties of water at THz frequencies. This specifically involves some solid-like features such as the onset of shear wave propagation, a sound velocity surprisingly similar to the one of ice, and an anomalously low sound absorption coefficient. All these properties can be explained by assuming the coupling of THz density fluctuations with a structural relaxation process connected to the breaking and forming of hydrogen bonds (HBs). This review also includes more recent IXS results demonstrating that, upon approaching supercritical conditions, relaxation phenomena in water gradually lose their structural character becoming essentially collisional in character. Furthermore, GHz spectroscopy results on supercooled water, suggesting the occurrence of a structural arrest, are discussed. An overview of the new opportunities offered by next generation IXS spectrometers finally concludes this review.

  2. The Effects of the Scattering by Edge Plasma Density Fluctuations on Lower Hyybrid Wave Propagation

    SciTech Connect

    Bertelli, N; Bonoli, P T; Harvey, R W; Smirnov, A P; Baek, S G; Parker, R R; Phillips, C K; Valeo, E J; Wilson, J R; Wright, J C

    2012-08-27

    Scattering effects induced by edge density fluctuations on lower hybrid (LH) wave propagation are investigated. The scattering model used here is based on the work of Bonoli and Ott [Phys. Fluids 25 (1982) 361]. It utilizes an electromagnetic wave kinetic equation solved by a Monte Carlo technique. This scattering model has been implemented in GENRAY , a ray tracing code which explicitly simulates wave propagation, as well as collisionless and collisional damping processes, over the entire plasma discharge, including the scrape-off layer (SOL) that extends from the separatrix to the vessel wall. A numerical analysis of the LH wave trajectories and the power deposition profile with and without scattering is presented for Alcator CMod discharges. Comparisons between the measured hard x-ray emission on Alcator C-Mod and simulations of the data obtained from the synthetic diagnostic included in the GENRAY/CQL3D package are shown, with and without the combination of scattering and collisional damping. Implications of these results on LH current drive are discussed.

  3. Quantification of nanoscale density fluctuations by electron microscopy: probing cellular alterations in early carcinogenesis

    NASA Astrophysics Data System (ADS)

    Pradhan, Prabhakar; Damania, Dhwanil; Joshi, Hrushikesh M.; Turzhitsky, Vladimir; Subramanian, Hariharan; Roy, Hemant K.; Taflove, Allen; Dravid, Vinayak P.; Backman, Vadim

    2011-04-01

    Most cancers are curable if they are diagnosed and treated at an early stage. Recent studies suggest that nanoarchitectural changes occur within cells during early carcinogenesis and that such changes precede microscopically evident tissue alterations. It follows that the ability to comprehensively interrogate cell nanoarchitecture (e.g., macromolecular complexes, DNA, RNA, proteins and lipid membranes) could be critical to the diagnosis of early carcinogenesis. We present a study of the nanoscale mass-density fluctuations of biological tissues by quantifying their degree of disorder at the nanoscale. Transmission electron microscopy images of human tissues are used to construct corresponding effective disordered optical lattices. The properties of nanoscale disorder are then studied by statistical analysis of the inverse participation ratio (IPR) of the spatially localized eigenfunctions of these optical lattices at the nanoscale. Our results show an increase in the disorder of human colonic epithelial cells in subjects harboring early stages of colon neoplasia. Furthermore, our findings strongly suggest that increased nanoscale disorder correlates with the degree of tumorigenicity. Therefore, the IPR technique provides a practicable tool for the detection of nanoarchitectural alterations in the earliest stages of carcinogenesis. Potential applications of the technique for early cancer screening and detection are also discussed. Originally submitted for the special focus issue on physical oncology.

  4. Charge density wave fluctuations, heavy electrons, and superconductivity in KNi2S2

    NASA Astrophysics Data System (ADS)

    Neilson, James R.; McQueen, Tyrel M.; Llobet, Anna; Wen, Jiajia; Suchomel, Matthew R.

    2013-01-01

    Understanding the complexities of electronic and magnetic ground states in solids is one of the main goals of solid-state physics. Materials with the canonical ThCr2Si2-type structure have proved particularly fruitful in this regard, as they exhibit a wide range of technologically advantageous physical properties described by “many-body physics,” including high-temperature superconductivity and heavy fermion behavior. Here, using high-resolution synchrotron x-ray diffraction and time-of-flight neutron scattering, we show that the isostructural mixed valence compound KNi2S2 displays a number of highly unusual structural transitions, most notably the presence of charge density wave fluctuations that disappear on cooling. This behavior occurs without magnetic or charge order, in contrast to expectations based on other known materials exhibiting related phenomena. Furthermore, the low-temperature electronic state of KNi2S2 is found to exhibit many characteristics of heavy-fermion behavior, including a heavy electron state (m*/me˜ 24), with a negative coefficient of thermal expansion, and superconductivity below Tc=0.46(2) K. In the potassium nickel sulfide, these behaviors arise in the absence of localized magnetism, and instead appear to originate in proximity to charge order.

  5. Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for liquid mixtures

    SciTech Connect

    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.

  6. Simultaneous excitation of large-scale geomagnetic field fluctuations and plasma density irregularities by powerful radio waves

    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.

  7. Rapid fluctuations of the air and surface temperature in the city of Bucharest (Romania)

    NASA Astrophysics Data System (ADS)

    Cheval, Sorin; Dumitrescu, Alexandru; Hustiu, Mihaita-Cristinel

    2016-04-01

    Urban areas derive significant changes of the ambient temperature generating specific challenges for society and infrastructure. Extreme temperature events, heat and cold waves affect the human comfort, increase the health risk, and require specific building regulations and emergency preparedness, strongly related to the magnitude and frequency of the thermal hazards. Rapid changes of the temperature put a particular stress for the urban settlements, and the topic has been approached constantly in the scientific literature. Due to its geographical position in a plain area with a temperate climate and noticeable continental influence, the city of Bucharest (Romania) deals with high seasonal and daily temperature variations. However, rapid fluctuations also occur at sub-daily scale caused by cold or warm air advections or by very local effects (e.g. radiative heat exchange, local precipitation). For example, in the area of Bucharest, the cold fronts of the warm season may trigger temperature decreasing up to 10-15 centigrades / hour, while warm advections lead to increasing of 1-2 centigrades / hour. This study focuses on the hourly and sub-hourly temperature variations over the period November 2014 - February 2016, using air temperature data collected from urban sensors and meteorological stations of the national network, and land surface temperature data obtained from satellite remote sensing. The analysis returns different statistics, such as magnitude, intensity, frequency, simultaneous occurrence and areal coverage of the rapid temperature fluctuations. Furthermore, the generating factors for each case study are assessed, and the results are used to define some preliminary patterns and enhance the urban temperature forecast at fine scale. The study was funded by the Romanian Programme Partnership in Priority Domains, PN - II - PCCA - 2013 - 4 - 0509 - Reducing UHI effects to improve urban comfort and balance energy consumption in Bucharest (REDBHI).

  8. Dispersal and air entrainment in unconfined dilute pyroclastic density currents

    NASA Astrophysics Data System (ADS)

    Andrews, Benjamin J.

    2014-09-01

    Unconfined scaled laboratory experiments show that 3D structures control the behavior of dilute pyroclastic density currents (PDCs) during and after liftoff. Experiments comprise heated and ambient temperature 20 μm talc powder turbulently suspended in air to form density currents within an unobstructed 8.5 × 6 × 2.6-m chamber. Comparisons of Richardson, thermal Richardson, Froude, Stokes, and settling numbers and buoyant thermal to kinetic energy densities show good agreement between experimental currents and dilute PDCs. The experimental Reynolds numbers are lower than those of PDCs, but the experiments are fully turbulent; thus, the large-scale dynamics are similar between the two systems. High-frequency, simultaneous observation in three orthogonal planes shows that the currents behave very differently than previous 2D (i.e., confined) currents. Specifically, whereas ambient temperature currents show radial dispersal patterns, buoyancy reversal, and liftoff of heated currents focuses dispersal along narrow axes beneath the rising plumes. The aspect ratios, defined as the current length divided by a characteristic width, are typically 2.5-3.5 in heated currents and 1.5-2.5 in ambient temperature currents, reflecting differences in dispersal between the two types of currents. Mechanisms of air entrainment differ greatly between the two currents: entrainment occurs primarily behind the heads and through the upper margins of ambient temperature currents, but heated currents entrain air through their lateral margins. That lateral entrainment is much more efficient than the vertical entrainment, >0.5 compared to ˜0.1, where entrainment is defined as the ratio of cross-stream to streamwise velocity. These experiments suggest that generation of coignimbrite plumes should focus PDCs along narrow transport axes, resulting in elongate rather than radial deposits.

  9. Battery peak charge voltage monitor for dual air density satellite

    NASA Technical Reports Server (NTRS)

    Shull, T. A.

    1975-01-01

    A battery peak charge voltage monitor was developed for use on the dual air density satellite (DADS). This device retains a reading of the maximum voltage reached by the spacecraft battery during periods of charging, and makes it available during periods of data transmission. The monitor is connected across the battery and operates solely from the battery; it is powered continuously with quiescent input current of only 3 milliamperes. Standard integrated circuits and a thin-film resistor network are utilized. The monitor occupies approximately 40 square centimeters of a printed-circuit board within a larger electronic package.

  10. 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.

  11. Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence

    NASA Technical Reports Server (NTRS)

    Laufer, Gabriel; Mckenzie, Robert L.; Fletcher, Douglas G.

    1990-01-01

    Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be less than 2 percent, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.

  12. A method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence

    NASA Technical Reports Server (NTRS)

    Laufer, Gabriel; Fletcher, Douglas G.; Mckenzie, Robert L.

    1990-01-01

    Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations due to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainty in the temperature and density measurements can be less than 2 and 3 percent, respectively, if the signal uncertainties are dominated by photon-statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.

  13. Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O(2) fluorescence.

    PubMed

    Laufer, G; McKenzie, R L; Fletcher, D G

    1990-11-20

    Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be <2%, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.

  14. Planets in other universes: habitability constraints on density fluctuations and galactic structure

    SciTech Connect

    Adams, Fred C.; Coppess, Katherine R.; Bloch, Anthony M. E-mail: kcoppess@umich.edu

    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

  15. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections.

    PubMed

    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

  16. Low Mach number two-dimensional hydrodynamic turbulence - Energy budgets and density fluctuations in a polytropic fluid

    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.

  17. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections.

    PubMed

    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.

  18. High-Reynolds-number turbulent-boundary-layer wall pressure fluctuations with skin-friction reduction by air injection.

    PubMed

    Winkel, Eric S; Elbing, Brian R; Ceccio, Steven L; Perlin, Marc; Dowling, David R

    2008-05-01

    The hydrodynamic pressure fluctuations that occur on the solid surface beneath a turbulent boundary layer are a common source of flow noise. This paper reports multipoint surface pressure fluctuation measurements in water beneath a high-Reynolds-number turbulent boundary layer with wall injection of air to reduce skin-friction drag. The experiments were conducted in the U.S. Navy's Large Cavitation Channel on a 12.9-m-long, 3.05-m-wide hydrodynamically smooth flat plate at freestream speeds up to 20 ms and downstream-distance-based Reynolds numbers exceeding 200 x 10(6). Air was injected from one of two spanwise slots through flush-mounted porous stainless steel frits (approximately 40 microm mean pore diameter) at volume flow rates from 17.8 to 142.5 l/s per meter span. The two injectors were located 1.32 and 9.78 m from the model's leading edge and spanned the center 87% of the test model. Surface pressure measurements were made with 16 flush-mounted transducers in an "L-shaped" array located 10.7 m from the plate's leading edge. When compared to no-injection conditions, the observed wall-pressure variance was reduced by as much as 87% with air injection. In addition, air injection altered the inferred convection speed of pressure fluctuation sources and the streamwise coherence of pressure fluctuations.

  19. Evaluation of short-term tracer fluctuations in groundwater and soil air in a two year study

    NASA Astrophysics Data System (ADS)

    Jenner, Florian; Mayer, Simon; Aeschbach, Werner; Weissbach, Therese

    2016-04-01

    The application of gas tracers like noble gases (NGs), SF6 or CFCs in groundwater studies such as paleo temperature determination requires a detailed understanding of the dynamics of reactive and inert gases in the soil air with which the infiltrating water equilibrates. Due to microbial gas consumption and production, NG partial pressures in soil air can deviate from atmospheric air, an effect that could bias noble gas temperatures estimates if not taken into account. So far, such an impact on NG contents in groundwater has not been directly demonstrated. We provide the first long-term study of the above mentioned gas tracers and physical parameters in both the saturated and unsaturated soil zone, sampled continuously for more than two years near Mannheim (Germany). NG partial pressures in soil air correlate with soil moisture and the sum value of O2+CO2, with a maximal significant enhancement of 3-6% with respect to atmospheric air during summer time. Observed seasonal fluctuations result in a mass dependent fractionation of NGs in soil air. Concentrations of SF6 and CFCs in soil air are determined by corresponding fluctuations in local atmospheric air, caused by industrial emissions. Arising concentration peaks are damped with increasing soil depth. Shallow groundwater shows short-term NG fluctuations which are smoothed within a few meters below the water table. A correlation between NG contents of soil air and of groundwater is observable during strong recharge events. However, there is no evidence for a permanent influence of seasonal variations of soil air composition on shallow groundwater. Fluctuating NG contents in shallow groundwater are rather determined by variations of soil temperature and water table level. Our data gives evidence for a further temperature driven equilibration of groundwater with entrapped air bubbles within the topmost saturated zone, which permanently occurs even some years after recharge. Local subsurface temperature fluctuations

  20. Experimental triplet and quadruplet fluctuation densities and spatial distribution function integrals for pure liquids

    SciTech Connect

    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.

  1. Local density of states and its mesoscopic fluctuations near the transition to a superconducting state in disordered systems

    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.

  2. Three-dimensional structure of electron density fluctuations in the Hall thruster plasma: ExB mode

    SciTech Connect

    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.

  3. A phase contrast imaging-interferometer system for detection of multiscale electron density fluctuations on DIII-D

    NASA Astrophysics Data System (ADS)

    Davis, E. M.; Rost, J. C.; Porkolab, M.; Marinoni, A.; Van Zeeland, M. A.

    2016-11-01

    Heterodyne interferometry and phase contrast imaging (PCI) are robust, mature techniques for measuring low-k and high-k electron density fluctuations, respectively. This work describes the first-ever implementation of a combined PCI-interferometer. The combined system uses a single 10.6 μm probe beam, two interference schemes, and two detectors to measure electron density fluctuations at large spatiotemporal bandwidth (10 kHz

  4. Characterizing intra-annual density fluctuations using fine-spatial resolution blue intensity profiles

    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

  5. A high speed data acquisition system for the analysis of velocity, density, and total temperature fluctuations at transonic speeds

    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.

  6. Entrainment Rate in Shallow Cumuli: Dependence on Entrained Dry Air Sources and Probability Density Functions

    NASA Astrophysics Data System (ADS)

    Lu, C.; Liu, Y.; Niu, S.; Vogelmann, A. M.

    2012-12-01

    In situ aircraft cumulus observations from the RACORO field campaign are used to estimate entrainment rate for individual clouds using a recently developed mixing fraction approach. The entrainment rate is computed based on the observed state of the cloud core and the state of the air that is laterally mixed into the cloud at its edge. The computed entrainment rate decreases when the air is entrained from increasing distance from the cloud core edge; this is because the air farther away from cloud edge is drier than the neighboring air that is within the humid shells around cumulus clouds. Probability density functions of entrainment rate are well fitted by lognormal distributions at different heights above cloud base for different dry air sources (i.e., different source distances from the cloud core edge). Such lognormal distribution functions are appropriate for inclusion into future entrainment rate parameterization in large scale models. To the authors' knowledge, this is the first time that probability density functions of entrainment rate have been obtained in shallow cumulus clouds based on in situ observations. The reason for the wide spread of entrainment rate is that the observed clouds are affected by entrainment mixing processes to different extents, which is verified by the relationships between the entrainment rate and cloud microphysics/dynamics. The entrainment rate is negatively correlated with liquid water content and cloud droplet number concentration due to the dilution and evaporation in entrainment mixing processes. The entrainment rate is positively correlated with relative dispersion (i.e., ratio of standard deviation to mean value) of liquid water content and droplet size distributions, consistent with the theoretical expectation that entrainment mixing processes are responsible for microphysics fluctuations and spectral broadening. The entrainment rate is negatively correlated with vertical velocity and dissipation rate because entrainment

  7. Spin-density correlations in the dynamic spin-fluctuation theory: Comparison with polarized neutron scattering experiments

    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.

  8. Statistical analysis of polychaete population density: dynamics of dominant species and scaling properties in relative abundance fluctuations

    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.

  9. Spectral density of fluctuations of a double-well Duffing oscillator driven by white noise

    SciTech Connect

    Dykman, M.I.; Mannella, R.; McClintock, P.V.E.; Moss, F.; Soskin, S.M.

    1988-02-15

    The power spectrum of the archetypal fluctuating bistable system, the underdamped double-well Duffing oscillator, is investigated both experimentally, with use of an electronic circuit, and theoretically. The experiment confirms previous analytic results for the structure of the spectrum, including the existence of three distinct peaks within a certain parameter range. The theory is extended to describe analytically the shape of the peak due to intrawell fluctuations for arbitrary noise intensities as well as certain other features of the spectrum. Good quantitative agreement of theory and experiment is demonstrated.

  10. A Concept for Robust, High Density Terminal Air Traffic Operations

    NASA Technical Reports Server (NTRS)

    Isaacson, Douglas R.; Robinson, John E.; Swenson, Harry N.; Denery, Dallas G.

    2010-01-01

    This paper describes a concept for future high-density, terminal air traffic operations that has been developed by interpreting the Joint Planning and Development Office s vision for the Next Generation (NextGen) Air Transportation System and coupling it with emergent NASA and other technologies and procedures during the NextGen timeframe. The concept described in this paper includes five core capabilities: 1) Extended Terminal Area Routing, 2) Precision Scheduling Along Routes, 3) Merging and Spacing, 4) Tactical Separation, and 5) Off-Nominal Recovery. Gradual changes are introduced to the National Airspace System (NAS) by phased enhancements to the core capabilities in the form of increased levels of automation and decision support as well as targeted task delegation. NASA will be evaluating these conceptual technological enhancements in a series of human-in-the-loop simulations and will accelerate development of the most promising capabilities in cooperation with the FAA through the Efficient Flows Into Congested Airspace Research Transition Team.

  11. Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak

    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.

  12. Comparing density, electron temperature, and magnetic fluctuations with gyrokinetic simulations using new synthetic diagnostics

    NASA Astrophysics Data System (ADS)

    Ernst, D. R.; Bergerson, W.; Ennever, P.; Greenwald, M.; Hubbard, A.; Irby, J.; Phillips, P.; Porkolab, M.; Rowan, W.; Terry, J. L.; Xu, P.; Alcator C-Mod Team

    2013-10-01

    Three new synthetic turbulence diagnostics are implemented in GS2 and compared with measurements: phase contrast imaging, polarimetry, and electron-cyclotron (ECE) emission. Our new synthetic diagnostic framework is based on transforming to a real-space annulus in Cartesian coordinates. This allows straightforward convolution with diagnostic point-spread functions, or integration over viewing chords. Wavenumber spectra and fluctuation amplitudes, as well as transport fluxes, are compared with measurements. Both phase contrast imaging and newly observed ECE electron temperature fluctuations, closely follow the electron temperature in an internal transport barrier during on-axis heating pulses, consistent with the role of TEM turbulence. New C-Mod polarimetry measurements, showing strong broadband core magnetic fluctuations, will also be examined against gyrokinetic simulations. The new framework is readily extended to other fluctuation measurements such as two-color interferometry, beam emission spectroscopy, Doppler back-scattering, ECE imaging, and microwave imaging reflectometry. Supported by U.S. DoE awards DE-FC02-08ER54966, DE-FC02-99ER54512, DE-FG03-96ER54373.

  13. On the importance of high-frequency air-temperature fluctuations for spectroscopic corrections of open-path carbon dioxide flux measurements

    NASA Astrophysics Data System (ADS)

    Bogoev, Ivan; Helbig, Manuel; Sonnentag, Oliver

    2015-04-01

    A growing number of studies report systematic differences in CO2 flux estimates obtained with the two main types of gas analyzers: compared to eddy-covariance systems based on closed-path (CP) gas analyzers, systems with open-path (OP) gas analyzers systematically overestimate CO2 uptake during daytime periods with high positive sensible heat fluxes, while patterns for differences in nighttime CO2 exchange are less obvious. These biases have been shown to correlate with the sign and the magnitude of the sensible heat flux and to introduce large uncertainties when calculating annual CO2 budgets. In general, CP and OP gas analyzers commonly used to measure the CO2 density in the atmosphere operate on the principle of infrared light absorption approximated by Beer-Lambert's law. Non-dispersive interference-based optical filter elements are used to select spectral bands with strong attenuation of light transmission, characteristic to the gas of interest. The intensity of the light passing through the optical sensing path depends primarily on the amount of absorber gas in the measurement volume. Besides the density of the gas, barometric pressure and air temperature are additional factors affecting the strength and the half-width of the absorption lines. These so-called spectroscopic effects are accounted for by measuring barometric pressure and air temperature in the sensing path and scaling the light-intensity measurements before applying the calibration equation. This approach works well for CP gas analyzers with an intake tube that acts as a low-pass filter on fast air-temperature fluctuations. Low-frequency response temperature sensors in the measurement cell are therefore sufficient to account for spectroscopic temperature effects. In contrast, OP gas analyzers are exposed to high-frequency air-temperature fluctuations associated with the atmospheric surface-layer turbulent heat exchange. If not corrected adequately, these fast air-temperature variations can cause

  14. Estimation of the radial size and density fluctuation amplitude of edge localized modes using microwave interferometer array

    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.

  15. DENSITY FLUCTUATIONS AND THE ACCELERATION OF ELECTRONS BY BEAM-GENERATED LANGMUIR WAVES IN THE SOLAR CORONA

    SciTech Connect

    Ratcliffe, H.; Bian, N. H.; Kontar, E. P.

    2012-12-20

    Non-thermal electron populations are observed throughout the heliosphere. The relaxation of an electron beam is known to produce Langmuir waves which, in turn, may substantially modify the electron distribution function. As the Langmuir waves are refracted by background density gradients and as the solar and heliospheric plasma density is naturally perturbed with various levels of inhomogeneity, the interaction of Langmuir waves with non-thermal electrons in inhomogeneous plasmas is an important topic. We investigate the role played by ambient density fluctuations on the beam-plasma relaxation, focusing on the effect of acceleration of beam electrons. The scattering of Langmuir waves off turbulent density fluctuations is modeled as a wavenumber diffusion process which is implemented in numerical simulations of the one-dimensional quasilinear kinetic equations describing the beam relaxation. The results show that a substantial number of beam electrons are accelerated when the diffusive timescale in wavenumber space {tau}{sub D} is of the order of the quasilinear timescale {tau}{sub ql}, while when {tau}{sub D} << {tau}{sub ql}, the beam relaxation is suppressed. Plasma inhomogeneities are therefore an important means of energy redistribution for waves and hence electrons, and so must be taken into account when interpreting, for example, hard X-ray or Type III emission from flare-accelerated electrons.

  16. Edge electron density profiles and fluctuations measured by two-dimensional beam emission spectroscopy in the KSTAR

    SciTech Connect

    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.

  17. A real time dynamic data acquisition and processing system for velocity, density, and total temperature fluctuation measurements

    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.

  18. A theory for scattering by density fluctuations based on three-wave interaction

    NASA Technical Reports Server (NTRS)

    Harker, K. J.; Crawford, F. W.

    1973-01-01

    The theory of scattering by charged particle fluctuations of a plasma is developed for the case of zero magnetic field. The source current is derived on the basis of: (1) a three wave interaction between the incident and scattered electromagnetic waves and one electrostatic plasma wave (either Langmuir or ion acoustic), and (2) a synchronous interaction between the same two electromagnetic waves and the discrete components of the charged particle fluctuations. Previous work is generalized by no longer making the assumption that the frequency of the electromagnetic waves in large compared to the plasma frequency. The general result is then applied to incoherent scatter, and to scatter by strongly driven plasma waves. An expansion is carried out for each of those cases to determine the lower order corrections to the usual high frequency scattering formulas.

  19. Fluctuating defect density probed with noise spectroscopy in hydrogenated amorphous silicon

    SciTech Connect

    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}.

  20. Density fluctuations of the leafminer Phyllonorycter strigulatella (Lepidoptera: Gracillariidae) in the impact zone of a power plant.

    PubMed

    Kozlov, M V

    2003-01-01

    Populations of a tiny moth Phyllonorycter strigulatella, whose larvae develop in leaves of Alnus incana, were monitored around a coal fired power plant (annually emitting 11-29 Kt of SO2) near Apatity, northwestern Russia, during 1991-2001. The periodicity in density fluctuation was not affected by pollution; the peak densities of the leafminer in both polluted and clean localities were observed in 1993 and 1999. Densities of P. strigulatella showed no correlation with pollution between the outbreaks but strongly increased near the power plant during the outbreaks. In polluted localities the density increased by a factor of 15-20, whereas in clean localities it increased by a factor of 3-4, relative to the latent density. Mine distribution among individual leaves was more aggregated near the power plant. P. strigulatella demonstrated higher preference of long shoots in the contaminated sites, but mine distributions within a shoot and within a leaf did not change with the distance from the polluter. Thus, moderate contamination by SO2 favoured P. strigulatella, leading to an increase in the intensity of outbreaks (the ratio between outbreak and latent densities) by a factor of five, but did not change either frequency of outbreaks or timing of density increase.

  1. Simultaneous measurement of magnetic and density fluctuations via cross-polarization scattering and Doppler backscattering on the DIII-D tokamak

    NASA Astrophysics Data System (ADS)

    Rhodes, T. L.; Barada, K.; Peebles, W. A.; Crocker, N. A.

    2016-11-01

    An upgraded cross-polarization scattering (CPS) system for the simultaneous measurement of internal magnetic fluctuations B ˜ and density fluctuations ñ is presented. The system has eight radial quadrature channels acquired simultaneously with an eight-channel Doppler backscattering system (measures density fluctuations ñ and flows). 3-D ray tracing calculations based on the GENRAY ray tracing code are used to illustrate the scattering and geometric considerations involved in the CPS implementation on DIII-D. A unique quasi-optical design and IF electronics system allow direct comparison of B ˜ and ñ during dynamic or transient plasma events (e.g., Edge Localized Modes or ELMs, L to H-mode transitions, etc.). The system design allows the interesting possibility of both magnetic-density ( B ˜ -ñ) fluctuation and magnetic-temperature ( B ˜ - T ˜ ) fluctuation cross-phase measurements suitable for detailed tests of turbulence simulations.

  2. Incorporation Of Air Into The Campanian Ignimbrite Pyroclastic Density Current

    NASA Astrophysics Data System (ADS)

    Ort, M. H.; Giordano, G.; Zanella, E.; Isaia, R.

    2015-12-01

    Knowing the temperature of emplacement of an ignimbrite can tell us how much cooling air it incorporated during eruption and transport. Currents that incorporate cool matter (air, water, cold clasts) cool more than those that do not. Lithic fragments record the maximum temperature they reached, up to their maximum unblocking temperature. Studies of large ignimbrites (e.g. Cerro Galan Ignimbrite) emplaced by dense currents show they do not cool very much, with emplacement temperatures often above 580 oC. Smaller currents, such as those from Vesuvius and Colima, lose significant heat in the eruption column, and then lose some, but less, heat as they travel laterally. The amount of atmosphere incorporated by large dilute currents is not known. The ~40 ka Campanian Ignimbrite (CI) erupted from the Campi Flegrei caldera near Naples, Italy, and extends to ~75 km from the caldera. The CI was emplaced from a density-stratified current with a dilute transport system and a denser depositional system that overtopped 1600-m-high ridges, with the depositional system re-forming on the far side. Modeling of dilute currents shows that they can pass over obstacles ~1.5 times their thickness without losing momentum, which implies the CI current was >1 km thick. Much of that dilute current was gas, but how much was atmospheric? Partial thermal demagnetization of lithic clasts allows the identification of the temperature of emplacement. We sampled lithic fragments from the CI in 13 locations from proximal to distal along several azimuths. The current passed over 30-35 km of sea to get to two sites. Partial thermal demagnetization of 10 specimens from each site show that they were heated and deposited above 580 oC, the unblocking temperature of magnetite, implying the temperature of emplacement was at or above this temperature. The CI is poor in lithic clasts (<1% in most places) and evidence of non-magmatic water in the outflow sheet is absent. We suggest the CI current was a large

  3. Marshall N. Rosenbluth Outstanding Doctoral Thesis Award Talk: Simultaneous Measurement of Electron Temperature and Density Fluctuations in the Core of DIII-D Plasmas

    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.

  4. Density fluctuations in the interstellar medium: Evidence for anisotropic magnetogasdynamic turbulence. II - Stationary structures

    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.

  5. Modulation of Core Turbulent Density Fluctuations by Large-Scale Neoclassical Tearing Mode Islands in the DIII-D Tokamak

    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.

  6. Modulation of Core Turbulent Density Fluctuations by Large-Scale Neoclassical Tearing Mode Islands in the DIII-D Tokamak.

    PubMed

    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.

  7. 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.

  8. IPS activity observed as a precursor of solar induced terrestrial activity. [solar wind density fluctuations

    NASA Technical Reports Server (NTRS)

    Cronyn, W. M.; Shawhan, S. D.; Rickard, J. J.; Mitchell, D. G.; Roelof, E. C.; Gotwols, B. L.

    1978-01-01

    A radio telescope designed to exploit the interplanetary scintillation (IPS) technique and locate, map, and track solar wind disturbances which result in geomagnetic disturbances, thereby providing a forecast capability, is described. Preliminary results from operation of the telescope include: (1) evidence for a precursor signal in the IPS activity with a 1-2 day lead time with respect to density enhancements which frequently give rise to geomagnetic activity; (2) detection of a spectral broadening signature which also serves as a precursor of geomagnetic activity; (3) out-of-the-ecliptic plasma density enhancements which were not detected by near-Earth, ecliptic plane spacecraft; (4) detection of 12 corotating density enhancements;(5) detection of over 80 sources which give detectable scintillation of which 45 have been used for detailed synoptic analysis and 9 for spectral analysis; and (6) measurement of 0-lag coefficient of 0.56 between density and IPS activity enhancements.

  9. Local Density Fluctuations Predict Photoisomerization Quantum Yield of Azobenzene-Modified DNA.

    PubMed

    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

  10. Multichannel Microwave Interferometer for Simultaneous Measurement of Electron Density and its Fluctuation on HL-2A Tokamak

    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)

  11. 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 Quantum ESPRESSO distribution, together with a few preliminary results on the magnon dispersions in bulk Fe.

  12. Evidence for selection maintaining MHC diversity in a rodent species despite strong density fluctuations.

    PubMed

    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

  13. Model Of Orbital Density Of Air For Computing Drag

    NASA Technical Reports Server (NTRS)

    Lear, W. M.

    1990-01-01

    Simple, Orbital Density Model for Drag Equations program useful for computing effect of drag over one or more orbits. Mathematical model embodied in program incorporates major changes in density due to solar activity and magnetic activity of Earth. Diurnal (day/night) effects on orbit averaged out. Based on Jacchia daily-average density, evaluated at average time of year. Advantages, right ascension and declination of Sun not needed and computation time much reduced. Written in FORTRAN 77.

  14. Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus ionosphere

    SciTech Connect

    Hoegy, W.R.; Brace, L.H.; Kasprazak, W.T. ); Russell, C.T. )

    1990-04-01

    Pioneer Venus orbiter measurements have shown that coherent small-scale waves exist in the electron density, the electron temperature, and the magnetic field in the lower ionosphere of Venus just downstream of the solar terminator (Brace et al., 1983). The waves become less regular and less coherent at larger solar zenith angles, and Brace et al. suggested that these structures may have evolved from the terminator waves as they are convected into the nightside ionosphere, driven by the day-to-night plasma pressure gradient. In this paper the authors describe the changes in wave characteristics with solar zenith angle and show that the neutral gas also has related wave characteristics, probably because of atmospheric gravity waves. The plasma pressure exceeds the magnetic pressure in the nightside ionosphere at these altitudes, and thus the magnetic field is carried along and controlled by the turbulent motion of the plasma, but the wavelike nature of the thermosphere may also be coupled to the plasma and magnetic structure. They show that there is a significant coherence between the ionosphere, thermosphere, and magnetic parameters at altitudes below about 185 km, a coherence which weakens in the antisolar region. The electron temperature and density are approximately 180{degree} out of phase and consistently exhibit the highest correlation of any pair of variables. Waves in the electron and neutral densities are moderately correlated on most orbits, but with a phase difference that varies within each orbit. The average electron temperature is higher when the average magnetic field is more horizontal; however, the correlation between temperature and dip angle does not extend to individual wave structures observed within a satellite pass, particularly in the antisolar region.

  15. How do climate fluctuations affect persistent organic pollutant distribution in North America? Evidence from a decade of air monitoring.

    PubMed

    Ma, Jianmin; Hung, Hayley; Blanchard, Pierrette

    2004-05-01

    Interannual variations of persistent organic pollutant (POP) air concentrations from the Great Lakes region and the Arctic during the 1990s are strongly associated with atmospheric low-frequency fluctuations, notably the North Atlantic Oscillation (NAO), the El Niño-Southern Oscillation (ENSO), and the Pacific North American (PNA) pattern. This suggests interactions between climate variation and the global distribution of POPs. Atmospheric concentrations of hexachlorocyclohexanes (HCHs), hexachlorobenzene (HCB), and several lighter polychlorinated biphenyls (PCBs) measured around the Great Lakes basin increased during the positive phases of NAO and ENSO in the spring. This implies that anomalous high air temperatures associated with NAO and ENSO enhance volatilization of POPs from reservoirs on the Earth's surface accumulated in the past. These compounds are then available for transport from source regions to more pristine regions such as the Arctic under favorable flow patterns associated with global climate variations.

  16. On the mode-coupling treatment of collective density fluctuations for quantum liquids: para-hydrogen and normal liquid helium.

    PubMed

    Kletenik-Edelman, Orly; Reichman, David R; Rabani, Eran

    2011-01-28

    A novel quantum mode coupling theory combined with a kinetic approach is developed for the description of collective density fluctuations in quantum liquids characterized by Boltzmann statistics. Three mode-coupling approximations are presented and applied to study the dynamic response of para-hydrogen near the triple point and normal liquid helium above the λ-transition. The theory is compared with experimental results and to the exact imaginary time data generated by path integral Monte Carlo simulations. While for liquid para-hydrogen the combination of kinetic and quantum mode-coupling theory provides semi-quantitative results for both short and long time dynamics, it fails for normal liquid helium. A discussion of this failure based on the ideal gas limit is presented. PMID:21280769

  17. On the mode-coupling treatment of collective density fluctuations for quantum liquids: para-hydrogen and normal liquid helium.

    PubMed

    Kletenik-Edelman, Orly; Reichman, David R; Rabani, Eran

    2011-01-28

    A novel quantum mode coupling theory combined with a kinetic approach is developed for the description of collective density fluctuations in quantum liquids characterized by Boltzmann statistics. Three mode-coupling approximations are presented and applied to study the dynamic response of para-hydrogen near the triple point and normal liquid helium above the λ-transition. The theory is compared with experimental results and to the exact imaginary time data generated by path integral Monte Carlo simulations. While for liquid para-hydrogen the combination of kinetic and quantum mode-coupling theory provides semi-quantitative results for both short and long time dynamics, it fails for normal liquid helium. A discussion of this failure based on the ideal gas limit is presented.

  18. Non-Gaussian density fluctuations from entropically generated curvature perturbations in ekpyrotic models

    SciTech Connect

    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.

  19. Analysis of operational requirements for medium density air transportation. Volume 1: Summary

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The medium density air travel market was studied to determine the aircraft design and operational requirements. The impact of operational characteristics on the air travel system and the economic viability of the study aircraft were also evaluated. Medium density is defined in terms of numbers of people transported (20 to 500 passengers per day on round trip routes), and frequency of service ( a minumium of two and maximum of eight round trips per day) for 10 regional carriers. The operational characteristics of aircraft best suited to serve the medium density air transportation market are determined and a basepoint aircraft is designed from which tradeoff studies and parametric variations could be conducted. The impact of selected aircraft on the medium density market, economics, and operations is ascertained. Research and technology objectives for future programs in medium density air transportation are identified and ranked.

  20. Density measurement in air with saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1982-01-01

    Approaches which have the potential to make density measurements in a compressible flow, where one or more laser beams are used as probes, were investigated. Saturation in sulfur hexafluoride iodine and a crossed beam technique where one beam acts as a saturating beam and the other is at low intensity and acts as a probe beam are considered. It is shown that a balance between an increase in fluorescence intensity with increasing pressure from line broadening and the normal decrease in intensity with increasing pressure from quenching can be used to develop a linear relation between fluorescence intensity and number density and lead to a new density measurement scheme. The method is used to obtain a density image of the cross section of an iodine seeded underexpanded supersonic jet of nitrogen, by illuminating the cross section by a sheet of laser light.

  1. 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.

  2. Strong magnetic field fluctuations within filamentary auroral density cavities interpreted as VLF saucer sources

    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.

  3. Fluctuating Pressure Analysis of a 2-D SSME Nozzle Air Flow Test

    NASA Technical Reports Server (NTRS)

    Reed, Darren; Hidalgo, Homero

    1996-01-01

    To better understand the Space Shuttle Main Engine (SSME) startup/shutdown tansients, an airflow test of a two dimensional nozzle was conducted at Marshall Space Flight Center's trisonic wind tunnel. Photographic and other instrumentation show during an SSME start large nozzle shell distortions occur as the Mach disk is passing through the nozzle. During earlier develop of the SSME, this startup transient resulted in low cycle fatigue failure of one of the LH2 feedlines. The two dimensional SSME nozzle test was designed to measure the static and fluctuating pressure environment and color Schlieren video during the startup and shutdown phases of the run profile.

  4. The role of magnetic islands in modifying long range temporal correlations of density fluctuations and local heat transport

    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.

  5. Long-term evolution in the global distribution of solar wind speed and density fluctuations during 1997-2009

    NASA Astrophysics Data System (ADS)

    Tokumaru, Munetoshi; Kojima, Masayoshi; Fujiki, Ken'ichi

    2012-06-01

    Interplanetary scintillation (IPS) observations made with the 327-MHz multistation system of the Solar-Terrestrial Environment Laboratory (STEL) are analyzed to investigate the global distribution of solar wind speed and density fluctuations (ΔNe) and their evolution during 1997-2009. This study aims at elucidating the evolution of ΔNe distribution during the cycle 23 and subsequent extended minimum, which is useful for improving understanding of the heliospheric response to the peculiar solar activity. The computer-assisted tomography (CAT) method is used in the present study to deconvolve the line-of-sight integration of STEL IPS observations. This CAT method enables retrieval of the quasi-stationary large-scale structure of the background solar wind. The results show that the high (low)-latitude region is dominated by reduced (enhanced) ΔNe plasma, being closely associated with the fast (slow) solar wind. The solar wind speed data show a distinct change with solar activity, and an excellent positive (negative) correlation is revealed between the fast (slow) wind area and the polar field strength of the Sun. In contrast, the ΔNe data do not show such a solar cycle variation, but instead reveal a significant increase in the fractional area of low-ΔNe region in 2004 preceded by a constant value with a small amount of fluctuation. This change is observed for all latitudes, distinctly after 2007 for low latitudes. Our finding is consistent with the long-term variation of the solar wind density revealed from in situ measurements at the Earth orbit, if ΔNe ∝ Ne (where Ne is the solar wind electron density), and also consistent with the coronal hole distribution during the last solar cycle. It is found that ΔNe is inversely correlated with the solar wind speed V. We obtain the best fit power law function ΔNe ∝ V-0.36±0.14 for V > 350 km/s, which is basically consistent with our earlier result. This fact suggests that the fractional density fluctuations

  6. Air Density And Wind Retrieval Using GOCE Data

    NASA Astrophysics Data System (ADS)

    Doornbos, E.; Bruinsma, S.; Fritsche, B.; Visser, P.; Van Den IJssel, J.; Encarnacao, J. Teixeira; Kern, M.

    2013-12-01

    In the GOCE+ Theme 3 project, ion thruster activation data from GOCE telemetry has been combined with the accelerometer and star camera data products, to derive a new set of data products on thermosphere neutral density and wind speed. These products can be seen as an ex- tension of the successful accelerometer-derived thermosphere density data sets from CHAMP and GRACE. It is the first time that such data, spanning multiple years, is available at a fixed and very low altitude and at a near constant orientation of the orbit plane with respect to the Sun. The data processing is based on an analysis of the aerodynamic accelerations acting on the satellite, and makes use of data from all instruments onboard the satellite. The following steps are involved: 1) estimation of the bias in the gradiometer common-mode accelerations using GPS tracking data, 2) conversion of ion thruster activation data to accelerations, 3) modelling of radiation pressure accelerations based on orbit and attitude information, 4) removal of radiation pressure and ion thruster accelerations from the common-mode acceleration data, to arrive at the observed aerodynamic accelerations, 5) iterative adjustment of wind direction and density inputs of an aerodynamic model of the satellite, until the modelled aerodynamic accelerations match the observations. The resulting density and wind observations are made available in the form of time series and grids. These data can be applied in investigations of solar-terrestrial physics, as well as for the improvement and validation of models used in space operations.

  7. Human activity under high pressure: A case study on fluctuation scaling of air traffic controller's communication behaviors

    NASA Astrophysics Data System (ADS)

    Wang, Yanjun; Zhang, Qiqian; Zhu, Chenping; Hu, Minghua; Duong, Vu

    2016-01-01

    Recent human dynamics research has unmasked astonishing statistical characteristics such as scaling behaviors in human daily activities. However, less is known about the general mechanism that governs the task-specific activities. In particular, whether scaling law exists in human activities under high pressure remains an open question. In air traffic management system, safety is the most important factor to be concerned by air traffic controllers who always work under high pressure, which provides a unique platform to study human activity. Here we extend fluctuation scaling method to study air traffic controller's communication activity by investigating two empirical communication datasets. Taken the number of controlled flights as the size-like parameter, we show that the relationships between the average communication activity and its standard deviation in both datasets can be well described by Taylor's power law, with scaling exponent α ≈ 0.77 ± 0.01 for the real operational data and α ≈ 0.54 ± 0.01 for the real-time training data. The difference between the exponents suggests that human dynamics under pressure is more likely dominated by the exogenous force. Our findings may lead to further understanding of human behavior.

  8. Density measurement in air with a saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1981-01-01

    Resonantly enhanced scattering from the iodine molecule is studied experimentally for the purpose of developing a scheme for the measurement of density in a gas dynamic flow. A study of the spectrum of iodine, the collection of saturation data in iodine, and the development of a mathematical model for correlating saturation effects were pursued for a mixture of 0.3 torr iodine in nitrogen and for mixture pressures up to one atmosphere. For the desired pressure range, saturation effects in iodine were found to be too small to be useful in allowing density measurements to be made. The effects of quenching can be reduced by detuning the exciting laser wavelength from the absorption line center of the iodine line used (resonant Raman scattering). The signal was found to be nearly independent of pressure, for pressures up to one atmosphere, when the excitation beam was detuned 6 GHz from line center for an isolated line in iodine. The signal amplitude was found to be nearly equal to the amplitude for fluorescence at atmospheric pressure, which indicates a density measurement scheme is possible.

  9. Increase in the Random Dopant Induced Threshold Fluctuations and Lowering in Sub 100 nm MOSFETs Due to Quantum Effects: A 3-D Density-Gradient Simulation Study

    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.

  10. Drought impact on water use efficiency and intra-annual density fluctuations in Erica arborea on Elba (Italy).

    PubMed

    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.

  11. 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.

  12. Drought impact on water use efficiency and intra-annual density fluctuations in Erica arborea on Elba (Italy).

    PubMed

    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

  13. Density measurement in air with a saturable absorbing seed gas

    NASA Technical Reports Server (NTRS)

    Baganoff, D.

    1982-01-01

    A method for making density measurements in a compressible flow by using off resonance laser induced fluorescence is studied. The seed molecule chosen for study is the iodine molecule which is excited with the 514.5 nm line of the argon ion laser whose output is frequency tuned, by as much as 3 GHz, relative to a strong iodine transition using an intracavity etalon. The theory which was developed to analyze the effect will be used in conjunction with two experiments being conducted to further study the method an acoustic resonance tube in which controlled perturbations about a uniform state are produced, and a small supersonic jet in which the conditions of the flow vary widely from point to point.

  14. Measurement of air refractive index fluctuation based on interferometry with two different reference cavity lengths.

    PubMed

    Chen, Qianghua; Luo, Huifu; Wang, Sumei; Wang, Feng; Chen, Xinhua

    2012-09-01

    A measurement method based on interferometry with two different reference cavity lengths is presented and applied in air refractive index measurement in which the two cavity lengths and a laser wavelength are combined to generate two wavelength equivalents of cavity. Corresponding calculation equations are derived, and the optical path configuration is designed, which is inspired by the traditional synthetic wavelength method. Theoretical analyses indicate that the measurement uncertainty of the determined index of refraction is about 2.3×10(-8), which is mainly affected by the length precision of the long vacuum cavity and the ellipticity of polarization components of the dual-frequency laser, and the range of nonambiguity is 3.0×10(-5), which is decided by the length difference of the two cavities. Experiment results show that the accuracy of air refractive index measurement is better than 5.0×10(-8) when the laboratory conditions changes slowly. The merit of the presented method is that the classical refractometry can be also used without evacuation of the gas cavity during the experiment. Furthermore, the application of the traditional synthetic wavelength method may be extended by using the wavelength equivalents of cavity, any value of which can be easily acquired by changing cavity length rather than using actual wavelengths whose number is limited. PMID:22945157

  15. Analysis on the Density Driven Air-Ingress Accident in VHTRs

    SciTech Connect

    Eung Soo Kim; Chang Oh; Richard Schultz; David Petti

    2008-11-01

    Air-ingress following the pipe rupture is considered to be the most serious accident in the VHTRs due to its potential problems such as core heat-up, structural integrity and toxic gas release. Previously, it has been believed that the main air-ingress mechanism of this accident is the molecular diffusion process between the reactor core and the cavity. However, according to some recent studies, there is another fast air-ingress process that has not been considered before. It is called density-driven stratified flow. The potential for density-driven stratified air ingress into the VHTR following a large-break LOCA was first described in the NGNP Methods Technical Program based on stratified flow studies performed with liquid. Studies on densitygradient driven stratified flow in advanced reactor systems has been the subject of active research for well over a decade since density-gradient dominated stratified flow is an inherent characteristic of passive systems used in advanced reactors. Recently, Oh et al. performed a CFD analysis on the stratified flow in the VHTR, and showed that this effect can significantly accelerate the air-ingress process in the VHTRs. They also proposed to replace the original air-ingress scenario based on the molecular diffusion with the one based on the stratified flow. This paper is focusing on the effect of stratified flow on the results of the air-ingress accident in VHTR

  16. In-plane and transverse superconducting fluctuation diamagnetism in the presence of charge-density waves in 2H-NbSe2 single crystals

    NASA Astrophysics Data System (ADS)

    Soto, F.; Berger, H.; Cabo, L.; Carballeira, C.; Mosqueira, J.; Pavuna, D.; Vidal, F.

    2007-03-01

    The fluctuation-diamagnetism (FD) above the superconducting transition was measured in 2H-NbSe2 single crystals. The moderate uniaxial anisotropy of this compound, and some experimental improvements, allowed us to measure the superconducting fluctuation effects in the two main crystallographic directions. These results reveal that the nonlocal electrodynamic effects on the FD are highly anisotropic, and they also discard a possible contribution to the FD coming from the charge-density waves (CDWs) appearing below TCDW>TC in 2H-NbSe2 , in agreement with a phenomenological estimate.

  17. Air temperature fluctuations in Guadalajara, Mexico, from 1926 to 1994 in relation to urban growth

    NASA Astrophysics Data System (ADS)

    Tereshchenko, I. E.; Filonov, A. E.

    2001-03-01

    Daily, monthly and annual mean air temperatures in Guadalajara, Mexico, were gathered from the time periods: 1926-1994, 1957-1994, 1978-1994. The heat island effect was detected in a trend analysis of the series of minimum temperatures over the period 1926-1994. Also, it was found that the annual mean temperature increased 0.05°C per year. A sharp increase has occurred over the last 20 years because of the abrupt expansion and industrialization of the city of Guadalajara. This study revealed the presence of a cool island in the centre of the metropolitan zone of Guadalajara (MZG) during the wet season. A cross-spectral analysis was used to study the thermal variations with different frequencies. Temperature oscillations in the MZG occurred in time intervals ranging from 3-5 days up to 22 years. The study suggests a relationship between urban growth and temperature variations. The temperature rise relates to urban growth with a correlation co-efficient equal to 0.857.

  18. The origin of the long time correlations of the density fluctuations in the scrape-off layer of the Tore Supra Tokamak

    SciTech Connect

    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.

  19. The origin of the long time correlations of the density fluctuations in the scrape-off layer of the Tore Supra Tokamak

    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.

  20. Using intra annual density fluctuations and d13C to assess the impact of summer drought on Mediterranean ecosystem

    NASA Astrophysics Data System (ADS)

    Battipaglia, G.; Brand, W. A.; Linke, P.; Schaefer, I.; Noetzli, M.; Cherubini, P.

    2009-04-01

    Tree- ring growth and wood density have been used extensively as indicators of climate change, and tree-ring has been commonly applied as a proxy estimate for seasonal integration of temperatures and precipitation with annual resolution (Hughes 2002). While these relationships have been well established in temperate ecosystems (Fritts, 1976; Schweingruber, 1988, Briffa et al., 1998, 2004), in Mediterranean region dendrochronological studies are still scarce (Cherubini et al, 2003). In Mediterranean environment, trees may form intra-annual density fluctuations, also called "false rings" or "double rings" (Tingley 1937; Schulman 1938). They are usually induced by sudden drought events, occurring during the vegetative period, and, allowing intra-annual resolution, they may provide detailed information at a seasonal level, as well as species-specific sensitivity to drought. We investigated the variability of tree- ring width and carbon stable isotopes of a Mediterranean species, Arbutus unedo L., sampled on Elba island, (Tuscany, Italy). The samples were taken at two different sites, one characterized by wet and one by dry conditions. d13C was measured using Laser- Ablation- Combustion -GC-IRMS. Here, we present first results showing the impact of drought on tree growth and on false ring formation at the different sites and we underline the importance of using Laser Ablation to infer drought impact at the intra -annual level. Briffa KR, Schweingruber FH, Jones PD, Osborn TJ, Harris IC, Shiyatov SG, Vaganov EA, Grudd H (1998) Trees tell of past climates: but are they speaking less clearly today? Phil Transact Royal Soc London 353:65-73 Briffa KR, Osborn TJ, Schweingruber FH (2004) Large-scale temperature inferences from tree rings: a review. Glob Panet Change 40:11-26 Cherubini, P., B.L. Gartner, R. Tognetti, O.U. Bräker, W. Schoch & J.L. Innes. 2003. Identification, measurement and interpretation of tree rings in woody species from Mediterranean climates. Biol. Rev

  1. Implications of Air Ingress Induced by Density-Difference Driven Stratified Flow

    SciTech Connect

    Chang Oh; Eung Soo Kim; Richard Schultz; David Petti; C. P. Liou

    2008-06-01

    One of the design basis accidents for the Next Generation Nuclear Plant (NGNP), a high temperature gas-cooled reactor, is air ingress subsequent to a pipe break. Following a postulated double-ended guillotine break in the hot duct, and the subsequent depressurization to nearly reactor cavity pressure levels, air present in the reactor cavity will enter the reactor vessel via density-gradient-driven-stratified flow. Because of the significantly higher molecular weight and lower initial temperature of the reactor cavity air-helium mixture, in contrast to the helium in the reactor vessel, the air-helium mixture in the cavity always has a larger density than the helium discharging from the reactor vessel through the break into the reactor cavity. In the later stages of the helium blowdown, the momentum of the helium flow decreases sufficiently for the heavier cavity air-helium mixture to intrude into the reactor vessel lower plenum through the lower portion of the break. Once it has entered, the heavier gas will pool at the bottom of the lower plenum. From there it will move upwards into the core via diffusion and density-gradient effects that stem from heating the air-helium mixture and from the pressure differences between the reactor cavity and the reactor vessel. This scenario (considering density-gradient-driven stratified flow) is considerably different from the heretofore commonly used scenario that attributes movement of air into the reactor vessel and from thence to the core region via diffusion. When density-gradient-driven stratified flow is considered as a contributing phenomena for air ingress into the reactor vessel, the following factors contribute to a much earlier natural circulation-phase in the reactor vessel: (a) density-gradient-driven stratified flow is a much more rapid mechanism (at least one order of magnitude) for moving air into the reactor vessel lower plenum than diffusion, and consequently, (b) the diffusion dominated phase begins with a

  2. The effect of air pollution and other environmental stressors on leaf fluctuating asymmetry and specific leaf area of Salix alba L.

    PubMed

    Wuytack, Tatiana; Wuyts, Karen; Van Dongen, Stefan; Baeten, Lander; Kardel, Fatemeh; Verheyen, Kris; Samson, Roeland

    2011-10-01

    We aimed at evaluating the effect of low-level air pollution on leaf area fluctuating asymmetry (FAA) and specific leaf area (SLA) of Salix alba L., taking into account other environmental factors. Cuttings were grown in standardized conditions in the near vicinity of air quality measuring stations in Belgium. Variability of SLA and FAA between measuring stations explained 83% and 7.26%, respectively, of the total variability. FAA was not influenced by air pollution or environmental factors such as shading, herbivory, air temperature and humidity. SLA was increased by an increase in shadow, while NO(x) and O(3) concentrations had only a marginal influence. The influence of SO(2) concentration was negligible. Although our data analysis suggests a relationship between SLA and NO(x)/O(3) concentration, the absence of a straightforward relationship between FAA and SLA and air pollution still questions the usefulness of these bio-indicators for monitoring air pollution.

  3. Air Density Measurements in a Mach 10 Wake Using Iodine Cordes Bands

    NASA Technical Reports Server (NTRS)

    Balla, Robert J.; Everhart, Joel L.

    2012-01-01

    An exploratory study designed to examine the viability of making air density measurements in a Mach 10 flow using laser-induced fluorescence of the iodine Cordes bands is presented. Experiments are performed in the NASA Langley Research Center 31 in. Mach 10 air wind tunnel in the hypersonic near wake of a multipurpose crew vehicle model. To introduce iodine into the wake, a 0.5% iodine/nitrogen mixture is seeded using a pressure tap at the rear of the model. Air density was measured at 56 points along a 7 mm line and three stagnation pressures of 6.21, 8.62, and 10.0 MPa (900, 1250, and 1450 psi). Average results over time and space show rho(sub wake)/rho(sub freestream) of 0.145 plus or minus 0.010, independent of freestream air density. Average off-body results over time and space agree to better than 7.5% with computed densities from onbody pressure measurements. Densities measured during a single 60 s run at 10.0 MPa are time-dependent and steadily decrease by 15%. This decrease is attributed to model forebody heating by the flow.

  4. Density Measurements in Air by Optically Exciting the Cordes Bands of I2

    NASA Technical Reports Server (NTRS)

    Balla, R. Jeffrey; Exton, Reginald J.

    2000-01-01

    We describe an optical method based on laser-induced fluorescence for obtaining instantaneous measurements of density along a line in low-density air seeded with I2. The Cordes bands of I2 (D(sup 1)sigma(sup +, sub u)) left arrow X(sup 1)sigma(sup +, sub g)) are excited with a tunable ArF excimer laser. air densities in the range (0.1-6.5) x 10(exp 17) cm(exp -3) are measured over 295-583 K using the density-dependent emission ratio of two emission bands of I2; the 340 nm bands and the diffuse-structured McLennan bands near 320 nm.

  5. The effects of forced air flow and oxygen concentration on flammability, smoke density, and pyrolytic toxicity

    NASA Technical Reports Server (NTRS)

    Sauers, D. G.

    1976-01-01

    The question is posed whether forced air flow should be incorporated into flammability tests as a relevant variable. A test apparatus is described which permits tests to be conducted on small test specimens in a forced flow which is (continuously) variable over flow velocities from zero to 300 feet per minute (1.52 m/s). The effects of air-flow rate and oxygen concentration on flame propagation rate, maximum smoke density, and pyrolytic product toxicity were measured for a single material and were statistically evaluated. Regression analysis was used to graph the resulting relationships. It is concluded that air velocity is an important variable for laboratory flammability testing.

  6. Dynamic density and spin responses of a superfluid Fermi gas in the BCS-BEC crossover: Path integral formulation and pair fluctuation theory

    NASA Astrophysics Data System (ADS)

    He, Lianyi

    2016-10-01

    We present a standard field theoretical derivation of the dynamic density and spin linear response functions of a dilute superfluid Fermi gas in the BCS-BEC crossover in both three and two dimensions. The derivation of the response functions is based on the elegant functional path integral approach which allows us to calculate the density-density and spin-spin correlation functions by introducing the external sources for the density and the spin density. Since the generating functional cannot be evaluated exactly, we consider two gapless approximations which ensure a gapless collective mode (Goldstone mode) in the superfluid state: the BCS-Leggett mean-field theory and the Gaussian-pair-fluctuation (GPF) theory. In the mean-field theory, our results of the response functions agree with the known results from the random phase approximation. We further consider the pair fluctuation effects and establish a theoretical framework for the dynamic responses within the GPF theory. We show that the GPF response theory naturally recovers three kinds of famous diagrammatic contributions: the Self-Energy contribution, the Aslamazov-Lakin contribution, and the Maki-Thompson contribution. We also show that unlike the equilibrium state, in evaluating the response functions, the linear (first-order) terms in the external sources as well as the induced order parameter perturbations should be treated carefully. In the superfluid state, there is an additional order parameter contribution which ensures that in the static and long wavelength limit, the density response function recovers the result of the compressibility (compressibility sum rule). We expect that the f-sum rule is manifested by the full number equation which includes the contribution from the Gaussian pair fluctuations. The dynamic density and spin response functions in the normal phase (above the superfluid critical temperature) are also derived within the Nozières-Schmitt-Rink (NSR) theory.

  7. Nitric oxide density measurements in air and air/fuel nanosecond pulse discharges by laser induced fluorescence

    NASA Astrophysics Data System (ADS)

    Uddi, M.; Jiang, N.; Adamovich, I. V.; Lempert, W. R.

    2009-04-01

    Laser induced fluorescence is used to measure absolute nitric oxide concentrations in air, methane-air and ethylene-air non-equilibrium plasmas, as a function of time after initiation of a single pulse, 20 kV peak voltage, 25 ns pulse duration discharge. A mixture of NO and nitrogen with known composition (4.18 ppm NO) is used for calibration. Peak NO density in air at 60 Torr, after a single pulse, is ~8 × 1012 cm-3 (~4.14 ppm) occurring at ~250 µs after the pulse, with decay time of ~16.5 ms. Peak NO atom mole fraction in a methane-air mixture with equivalence ratio of phiv = 0.5 is found to be approximately equal to that in air, with approximately the same rise and decay rate. In an ethylene-air mixture (also with equivalence ratio of phiv = 0.5), the rise and decay times are comparable to air and methane-air, but the peak NO concentration is reduced by a factor of approximately 2.5. Spontaneous emission measurements show that excited electronic states N2(C 3Π) and NO(A 2Σ) in air at P = 60 Torr decay within ~20 ns and ~1 µs, respectively. Kinetic modelling calculations incorporating air plasma kinetics complemented with the GRI Mech 3.0 hydrocarbon oxidation mechanism are compared with the experimental data using three different NO production mechanisms. It is found that NO concentration rise after the discharge pulse is much faster than predicted by Zel'dovich mechanism reactions, by two orders of magnitude, but much slower compared with reactions of electronically excited nitrogen atoms and molecules, also by two orders of magnitude. It is concluded that processes involving long lifetime (~100 µs) metastable states, such as N2(X 1Σ,v) and O2(b 1Σ), formed by quenching of the metastable N2(A 3Σ) state by ground electronic state O2, may play a dominant role in NO formation. NO decay, in all cases, is found to be dominated by the reverse Zel'dovich reaction, NO + O → N + O2, as well as by conversion into NO2 in a reaction of NO with ozone.

  8. Seasonal fluctuation of different edaphic microarthropod population densities in relation to soil moisture and temperature in a pine, Pinus kesiya Royle plantation ecosystem

    NASA Astrophysics Data System (ADS)

    Reddy, M. Vikram

    1984-03-01

    Seasonal fluctuations of soil and litter microarthropod populations in a pine, Pinus kesiya Royle plantation of North Eastern India were investigated between November 1976 and November 1977. Three major groups were recognized: (a) Collembola, (b) Acarina and (c) miscellaneous. Collembola was the most abundant group and was dominated by Isotoma trispinata (MacGillivray). The total microarthropod density ranged from 26,800 per m2 to 145,200 per m2. Collembola densities ranged from 10,000 to 121,200 per m2, Acarina densities ranged from 8,800 to 41,600 per m2, and the miscellaneous group ranged from 1,200 to 6,400 per m2. Soil moisture was positively correlated with total arthropod, Collembola and Acarina densities. Soil temperature was positively correlated only with Acarina. Densities of Collembola and Acarina were negatively correlated.

  9. Measurement of air-refractive-index fluctuation from laser frequency shift with uncertainty of order 10-9

    NASA Astrophysics Data System (ADS)

    Banh Quoc, Tuan; Ishige, Masashi; Ohkubo, Yuria; Aketagawa, Masato

    2009-12-01

    In the previous work (Ishige et al 2009 Meas. Sci. Technol. 20 084019), we presented a method of measuring the relative air-refractive-index fluctuation (Δnair) from the laser frequency shift with the measurement uncertainty of order 10-8 using a phase modulation homodyne interferometer (Basile et al 1991 Metrologia 28 455), which was supported by an ultralow thermal expansion material (ULTEM) and an external cavity laser diode (ECLD). In this paper, an improvement in the uncertainty of the Δnair measurement is presented. The improvement method is based on a Fabry-Perot cavity constructed on the ULTEM, which has a thermal expansion coefficient of 2 × 10-8 K-1 and an ECLD. The Pound-Drever-Hall method (Drever et al 1983 Appl. Phys. B 31 97) is also used to control the ECLD frequency to track the resonance of the cavity. Δnair can be derived from the ECLD frequency shift. The estimated measurement uncertainty of Δnair for a short time (~150 s) in the experiment is of order 2.5 × 10-9 or less.

  10. Measurements of the cross-phase angle between density and electron temperature fluctuations and comparison with gyrokinetic simulations

    SciTech Connect

    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.

  11. Spatial and temporal variation in the relative contribution of density dependence, climate variation and migration to fluctuations in the size of great tit populations.

    PubMed

    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

  12. Electron density measurements in an atmospheric pressure air plasma by means of infrared heterodyne interferometry

    NASA Astrophysics Data System (ADS)

    Leipold, Frank; Stark, Robert H.; El-Habachi, Ahmed; Schoenbach, Karl H.

    2000-09-01

    An infrared heterodyne interferometer has been used to measure the spatial distribution of the electron density in direct current, atmospheric pressure discharges in air. Spatial resolution of the electron density in the high-pressure glow discharge with characteristic dimensions on the order of 100 µm required the use of a CO2 laser at a wavelength of 10.6 µm. For this wavelength and electron densities greater than 1011 cm-3 the index of refraction of the atmospheric air plasma is mainly determined by heavy particles rather than electrons. The electron contribution to the refractive index was separated from that of the heavy particles by taking the different relaxation times of the two particle species into account. With the discharge operated in a repetitive pulsed mode, the initial rapid change of the refractive index was assumed to be due to the increase in electron density, whereas the following slower rise is due to the decrease in gas density caused by gas heating. By reducing the time between pulses, direct current conditions were approached, and the electron density as well as the gas density, and gas temperature, respectively, were obtained through extrapolation. A computation inversion method was used to determine the radial distribution of the plasma parameters in the cylindrical discharge. For a direct-current filamentary discharge in air, at a current of 10 mA, the electron density was found to be 1013 cm-3 in the centre, decreasing to half of this value at a radial distance of 0.21 mm. Gaussian temperature profiles with σ = 1.1 mm and maximum values of 1000-2000 K in the centre were also obtained with, however, larger error margins than for electron densities.

  13. Body Density Estimates from Upper-Body Skinfold Thicknesses Compared to Air-Displacement Plethysmography

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Technical Summary Objectives: Determine the effect of body mass index (BMI) on the accuracy of body density (Db) estimated with skinfold thickness (SFT) measurements compared to air displacement plethysmography (ADP) in adults. Subjects/Methods: We estimated Db with SFT and ADP in 131 healthy men an...

  14. Generation of High-Density Electrons Based on Plasma Grating Induced Bragg Diffraction in Air

    SciTech Connect

    Shi Liping; Li Wenxue; Wang Yongdong; Lu Xin; Ding Liang'en; Zeng Heping

    2011-08-26

    Efficient nonlinear Bragg diffraction was observed as an intense infrared femtosecond pulse was focused on a plasma grating induced by interference between two ultraviolet femtosecond laser pulses in air. The preformed electrons inside the plasma grating were accelerated by subsequent intense infrared laser pulses, inducing further collisional ionization and significantly enhancing the local electron density.

  15. Studies of velocity fluctuations in the lower atmosphere using the MU radar. I - Azimuthal anisotropy. II - Momentum fluxes and energy densities

    NASA Technical Reports Server (NTRS)

    Vanzandt, T. E.; Smith, S. A.; Tsuda, T.; Sato, T.; Fritts, D. C.

    1990-01-01

    Results are presented from a six-day campaign to observe velocity fluctuations in the lower atmosphere using the MU radar (Fukao et al., 1985) in Shigaraki, Japan in March, 1986. Consideration is given to the azimuthal anisotropy, the frequency spectra, the vertical profiles of energy density, and the momentum flux of the motion field. It is found that all of the observed azimuthal variations are probably caused by a gravity wave field whose parameters vary with time. The results show significant differences between the mean zonal and meridional frequency spectra and different profiles of mean energy density with height for different frequency bands and for zonal and meridional components.

  16. Measurement of Electron Densities in a Pulsed Atmospheric Pressure Air Discharge

    NASA Astrophysics Data System (ADS)

    Leipold, Frank; Stark, Robert H.; Schoenbach, Karl H.

    2000-10-01

    Microhollow cathode discharges have been shown to serve as plasma cathodes for atmospheric pressure air discharges [1]. The high pressure discharges are operated dc at currents from 10 mA up to 30 mA and at average electric fields of 1.25 kV/cm. The electron density in the dc discharge was measured by an interferometrique technique [2]. For a dc filamentary air discharge with a current of 10 mA, the radial electron density distribution was found to be parabolic with a total width of 660 μ m and an electron density of ne = 10^13 cm-3 in the center of the discharge. The diagnostic technique has now also been applied to pulsed discharges. It was found that the method provides electron densities measurements for discharges with durations as low as 5 μ s. The spatial distribution of the index of refraction in the pulsed discharge was obtained by shifting the discharge volume through the laser beam and by using an inversion method to obtain the radial index profile. For the electron density with a assumed parabolic profile, the maximum value was measured as 1.17*10^14 cm-3. (10 mA atmospheric pressure air discharge. The temperature profile was found to be gaussian with a half width of 1.3 mm. Acknowledgement This work was funded by the Air Force Office of Scientific Research in Cooperation with the DDR&E Air Plasma Ramparts MURI Program. References [1] Robert H. Stark and Karl H. Schoenbach, Appl. Phys. Lett. 74, 3770 (1999) [2] Frank Leipold, Robert H. Stark, and Karl H. Schoenbach, to appear in J. Phys. D., Appl. Phys.

  17. The effects of density fluctuations on the partitioning of foreign molecules into lipid bilayers: application to anaesthetics and insecticides.

    PubMed

    Jørgensen, K; Ipsen, J H; Mouritsen, O G; Bennett, D; Zuckermann, M J

    1991-08-26

    An extensive computer-simulation study is performed on a simple but general molecular model recently proposed (Jørgensen et al. (1991) Biochem. Biophys. Acta 1062, 277-238) to describe foreign molecules interacting with lipid bilayers. The model is a multi-state lattice model of the main bilayer transition in which the foreign molecules are assumed to intercalate at interstitial lattice positions. Specific as well as non-specific interactions between the foreign molecules and the lipid acyl chains are considered. Particular attention is paid to the fluctuating properties of the membrane and how the presence of the foreign molecules modulates these fluctuations in the transition region. By means of computer-stimulation techniques, a detailed account is given of the macroscopic as well as microscopic consequences of the fluctuations. The macroscopic consequences of the fluctuations are seen in the thermal anomalies of the specific heat and the passive trans-membrane permeability. Microscopically, the fluctuations manifest themselves in lipid-domain formation in the transition region which implies an effective dynamic membrane heterogeneity. Within the model it is found that certain anaesthetics and insecticides which are characterised by specific interactions with the lipids have a strong effect on the heterogeneity of the membrane inducing regions of locally very high concentration of the foreign molecules. This leads to a broadening of the specific heat peak and a maximum in the membrane/water partition coefficient. These results are in accordance with available experimental data for volatile general anaesthetics like halothane, local anaesthetics like cocain derivatives, and insecticides like lindane.

  18. Simulation of cold atmospheric plasma component composition and particle densities in air

    NASA Astrophysics Data System (ADS)

    Kirsanov, Gennady; Chirtsov, Alexander; Kudryavtsev, Anatoliy

    2015-11-01

    Recently discharges in air at atmospheric pressure were the subject of numerous studies. Of particular interest are the cold streams of air plasma, which contains large amounts of chemically active species. It is their action can be decisive in the interaction with living tissues. Therefore, in addition to its physical properties, it is important to know the component composition and particle densities. The goal was to develop a numerical model of atmospheric pressure glow microdischarge in air with the definition of the component composition of plasma. To achieve this goal the task was divided into two sub-tasks, in the first simulated microdischarge atmospheric pressure in air using a simplified set of plasma chemical reactions in order to obtain the basic characteristics of the discharge, which are the initial approximations in the problem of the calculation of the densities with detailed plasma chemistry, including 53 spices and over 600 chemical reactions. As a result of the model was created, which can be adapted for calculating the component composition of plasma of various sources. Calculate the density of particles in the glow microdischarges and dynamics of their change in time.

  19. Simulation of cold atmospheric plasma component composition and particle densities in air

    NASA Astrophysics Data System (ADS)

    Kirsanov, Gennady; Bekasov, Vladimir; Eliseev, Stepan; Kudryavtsev, Anatoly; Sisoev, Sergey

    2015-11-01

    Recently discharges in air at atmospheric pressure were the subject of numerous studies. Of particular interest are the cold streams of air plasma, which contains large amounts of chemically active species. It is their action can be decisive in the interaction with living tissues. Therefore, in addition to its physical properties, it is important to know the component composition and particle densities. The goal was to develop a numerical model of atmospheric pressure glow microdischarge in air with the definition of the component composition of plasma. To achieve this goal the task was broken down into two sub-tasks, in the first simulated microdischarge atmospheric pressure in air using a simplified set of plasma chemical reactions in order to obtain the basic characteristics of the discharge, which are the initial approximations in the problem of the calculation of the densities with detailed plasma chemistry, including 53 spices and over 600 chemical reactions. As a result of the model was created, which can be adapted for calculating the component composition of plasma of various sources. Calculate the density of particles in the glow microdischarges and dynamics of their change in time.

  20. Nanosecond Enhancements of the Atmospheric Electron Density by Extensive Air Showers

    NASA Astrophysics Data System (ADS)

    Rutjes, C.; Camporeale, E.; Ebert, U.; Buitink, S.; Scholten, O.; Trinh, G. T. N.; Witteveen, J.

    2015-12-01

    As is well known a sufficient density of free electrons and strong electric fields are the basic requirements to start any electrical discharge. In the context of thunderstorm discharges it has become clear that in addition droplets and or ice particles are required to enhance the electric field to values above breakdown. In our recent study [1] we have shown that these three ingredients have to interplay to allow for lightning inception, triggered by an extensive air shower event. The extensive air showers are a very stochastic natural phenomenon, creating highly coherent sub-nanosecond enhancements of the atmospheric electron density. Predicting these electron density enhancements accurately one has to take the uncertainty of the input variables into account. For this study we use the initial energy, inclination and altitude of first interaction, which will influence the evolution of the shower significantly. To this end, we use the stochastic collocation method, [2] to post-process our detailed Monte Carlo extensive air shower simulations, done with the CORSIKA [3] software package, which provides an efficient and elegant way to determine the distribution of the atmospheric electron density enhancements. [1] Dubinova, A., Rutjes, C., Ebert, E., Buitink, S., Scholten, O., and Trinh, G. T. N. "Prediction of Lightning Inception by Large Ice Particles and Extensive Air Showers." PRL 115 015002 (2015)[2] G.J.A. Loeven, J.A.S. Witteveen, H. Bijl, Probabilistic collocation: an efficient nonintrusive approach for arbitrarily distributed parametric uncertainties, 45th AIAA Aerospace Sciences Meeting, Reno, Nevada, 2007, AIAA-2007-317[3] Heck, Dieter, et al. CORSIKA: A Monte Carlo code to simulate extensive air showers. No. FZKA-6019. 1998.

  1. Aeronautical Satellite Data Link System (SDLS) for high-density air-traffic areas

    NASA Technical Reports Server (NTRS)

    Delrieu, Alain; Loisy, Claude; Clinch, Philip; Benhaim, Philippe

    1995-01-01

    The European Space Agency has recently commissioned a study to investigate the feasibility of a low-cost aeronautical Satellite Data Link System (SDLS) to provide for the needs of Air Traffic Services, i.e. safety related communications over continental areas with high air-traffic density. This study is placed in today's context which sees the first generation of Aeronautical Mobile Satellite System (AMSS) being gradually but restrictively put into service in oceanic airspaces with low air-traffic density. This paper first discusses the case of ATS dedicated versus mixed (ATS and commercial) Comms service provision and identifies the specific ATS comms requirements context. Specific emphasis is put on the ICAO (International Civil Aviation Organization) standardization framework for both the ATN (Aeronautical Telecommunication Network) and the SSR (Secondary Surveillance Radar) Mode S specific services. An architectural system and network design for a future SDLS is then proposed, such as to meet the ATS comms requirements within the realm of existing technologies. To minimize development risk and cost, consideration is given to re-use the ESA-developed Land Mobile Communication Technology, known as MSBN (Mobile Satellite Business Network) featuring distinct subnetworks. It is particularly suited to an ATM (Air Traffic Management) decentralized architecture made of independent ATC (Air Traffic Control) Centers. Finally the study follow-on phase is introduced, which is intended to cover system design and development leading to a demonstration program, as a first step towards proposals for international standardization and acceptance.

  2. Analysis of operational requirements for medium density air transportation, volume 2

    NASA Technical Reports Server (NTRS)

    1975-01-01

    The medium density air travel market is examined and defined in terms of numbers of people transported per route per day and frequency of service. The operational characteristics for aircraft to serve this market are determined and a basepoint aircraft is designed from which tradeoff studies and parametric variations can be conducted. The impact of the operational characteristics on the air travel system is evaluated along with the economic viability of the study aircraft. Research and technology programs for future study consideration are identified.

  3. Conduction-electron spin resonance and spin-density fluctuations of CoS2-xSex (x≤0.1)

    NASA Astrophysics Data System (ADS)

    Rivadulla, F.

    2011-10-01

    I report the observation of conduction electron spin resonance (CESR) in the paramagnetic phase of weak itinerant ferromagnet (WIFM) CoS2. The observation of a narrow Lorentzian line above TC is interpreted as a signature of long-wavelength exchange-enhanced spin-density fluctuations, whose amplitude increases up to T* ≈ 2 TC. I propose that this temperature marks a characteristic energy scale below which strong exchange interactions between spin fluctuations determine the spin lifetime. This study shows that the characteristic parameters of CESR are very sensitive to electronic correlations and can be very useful in the study of the spin interactions and relaxation in itinerant electron systems in the intermediate coupling regime.

  4. High-Density, High-Resolution, Low-Cost Air Quality Sensor Networks for Urban Air Monitoring

    NASA Astrophysics Data System (ADS)

    Mead, M. I.; Popoola, O. A.; Stewart, G.; Bright, V.; Kaye, P.; Saffell, J.

    2012-12-01

    Monitoring air quality in highly granular environments such as urban areas which are spatially heterogeneous with variable emission sources, measurements need to be made at appropriate spatial and temporal scales. Current routine air quality monitoring networks generally are either composed of sparse expensive installations (incorporating e.g. chemiluminescence instruments) or higher density low time resolution systems (e.g. NO2 diffusion tubes). Either approach may not accurately capture important effects such as pollutant "hot spots" or adequately capture spatial (or temporal) variability. As a result, analysis based on data from traditional low spatial resolution networks, such as personal exposure, may be inaccurate. In this paper we present details of a sophisticated, low-cost, multi species (gas phase, speciated PM, meteorology) air quality measurement network methodology incorporating GPS and GPRS which has been developed for high resolution air quality measurements in urban areas. Sensor networks developed in the Centre for Atmospheric Science (University of Cambridge) incorporated electrochemical gas sensors configured for use in urban air quality studies operating at parts-per-billion (ppb) levels. It has been demonstrated that these sensors can be used to measure key air quality gases such as CO, NO and NO2 at the low ppb mixing ratios present in the urban environment (estimated detection limits <4ppb for CO and NO and <1ppb for NO2. Mead et al (submitted Aug., 2012)). Based on this work, a state of the art multi species instrument package for deployment in scalable sensor networks has been developed which has general applicability. This is currently being employed as part of a major 3 year UK program at London Heathrow airport (the Sensor Networks for Air Quality (SNAQ) Heathrow project). The main project outcome is the creation of a calibrated, high spatial and temporal resolution data set for O3, NO, NO2, SO2, CO, CO2, VOCstotal, size-speciated PM

  5. Electron density measurements in a pulse-repetitive microwave discharge in air

    SciTech Connect

    Nikolic, M.; Popovic, S.; Vuskovic, L.; Herring, G. C.; Exton, R. J.

    2011-12-01

    We have developed a technique for absolute measurements of electron density in pulse-repetitive microwave discharges in air. The technique is based on the time-resolved absolute intensity of a nitrogen spectral band belonging to the Second Positive System, the kinetic model and the detailed particle balance of the N{sub 2}C{sup 3}{Pi}{sub u} ({nu} = 0) state. This new approach bridges the gap between two existing electron density measurement methods (Langmuir probe and Stark broadening). The electron density is obtained from the time-dependent rate equation for the population of N{sub 2}C{sup 3}{Pi}{sub u} ({nu} = 0) using recorded waveforms of the absolute C{sup 3}{Pi}{sub u}{yields}B{sup 3}{Pi}{sub g} (0-0) band intensity, the forward and reflected microwave power density. Measured electron density waveforms using numerical and approximated analytical methods are presented for the case of pulse repetitive planar surface microwave discharge at the aperture of a horn antenna covered with alumina ceramic plate. The discharge was generated in air at 11.8 Torr with a X-band microwave generator using 3.5 {mu}s microwave pulses at peak power of 210 kW. In this case, we were able to time resolve the electron density within a single 3.5 {mu}s pulse. We obtained (9.0 {+-} 0.6) x 10{sup 13} cm{sup -3} for the peak and (5.0 {+-} 0.6) x 10{sup 13} cm{sup -3} for the pulse-average electron density. The technique presents a convenient, non-intrusive diagnostic method for local, time-defined measurements of electron density in short duration discharges near atmospheric pressures.

  6. Quantification of Pathologic Air Trapping in Lung Transplant Patients Using CT Density Mapping: Comparison with Other CT Air Trapping Measures.

    PubMed

    Solyanik, Olga; Hollmann, Patrick; Dettmer, Sabine; Kaireit, Till; Schaefer-Prokop, Cornelia; Wacker, Frank; Vogel-Claussen, Jens; Shin, Hoen-oh

    2015-01-01

    To determine whether density mapping (DM) is more accurate for detection and quantification of pathologic air trapping (pAT) in patients after lung transplantation compared to other CT air trapping measures. One-hundred forty-seven lung and heart-lung transplant recipients underwent CT-examinations at functional residual capacity (FRC) and total lung capacity (TLC) and PFT six months after lung transplantation. Quantification of air trapping was performed with the threshold-based method in expiration (EXP), density mapping (DM) and the expiratory to inspiratory ratio of the mean lung density (E/I-ratio MLD). A non-rigid registration of inspiration-expiration CT-data with a following voxel-to-voxel mapping was carried out for DM. Systematic variation of attenuation ranges was performed for EXP and DM and correlated with the ratio of residual volume to total lung capacity (RV/TLC) by Spearman rank correlation test. AT was considered pathologic if RV/TLC was above the 95th percentile of the predicted upper limit of normal values. Receiver operating characteristic (ROC) analysis was performed. The optimal attenuation range for the EXP method was from -790 HU to -950 HU (EXP(-790 to -950HU)) (r = 0.524, p<0.001) to detect air trapping. Within the segmented lung parenchyma, AT was best defined as voxel difference less than 80 HU between expiration and registered inspiration using the DM method. DM correlated best with RV/TLC (r = 0.663, p<0.001). DM and E/I-ratio MLD showed a larger AUC (0.78; 95% CI 0.69-0.86; 0.76, 95% CI 0.67-0.85) than EXP(-790 HU to -950 HU) (0.71, 95% CI 0.63-0.78). DM and E/I-ratio MLD showed better correlation with RV/TLC and are more suited quantitative CT-methods to detect pAT in lung transplant patients than the EXP(-790HU to -950HU).

  7. Measurement of Density Correlations in Pseudorapidity via Charged Particle Multiplicity Fluctuations in Au+Au Collisions at sqrt(sNN) = 200 GeV

    SciTech Connect

    Adler, S. S.; Awes, Terry C; Batsouli, Sotiria; Cianciolo, Vince; Efremenko, Yuri; Read Jr, Kenneth F; Silvermyr, David O; Sorensen, Soren P; Stankus, Paul W; Young, Glenn R; Zhang, Chun; PHENIX, Collaboration

    2007-09-01

    Longitudinal density correlations of produced matter in Au+Au collisions at sqrt(s{sub NN})=200 GeV have been measured from the inclusive charged particle distributions as a function of pseudorapidity window sizes. The extracted {alpha}{xi} parameter, related to the susceptibility of the density fluctuations in the long-wavelength limit, exhibits a nonmonotonic behavior as a function of the number of participant nucleons, N{sub part}. A local maximum is seen at N{sub part}{approx}90, with corresponding energy density based on the Bjorken picture of {epsilon}{sub Bj}{tau}{approx}2.4 GeV/(fm{sup 2}c) with a transverse area size of 60 fm2. This behavior may suggest a critical phase boundary based on the Ginzburg-Landau framework.

  8. Simultaneous measurements of temperature and density in air flows using UV laser spectroscopy

    NASA Technical Reports Server (NTRS)

    Fletcher, D. G.; Mckenzie, R. L.

    1991-01-01

    The simultaneous measurement of temperature and density using laser-induced fluorescence of oxygen in combination with Q-branch Raman scattering of nitrogen and oxygen is demonstrated in a low-speed air flow. The lowest density and temperature measured in the experiment correspond to the freestream values at Mach 5 in the Ames 3.5-Foot Hypersonic Wind Tunnel for stagnation conditions of 100 atm and 1000 K. The experimental results demonstrate the viability of the optical technique for measurements that support the study of compressible turbulence and the validation of numerical codes in supersonic and hypersonic wind tunnel flows.

  9. A graphics approach in the design of the dual air density Explorer satellites

    NASA Technical Reports Server (NTRS)

    Mcdougal, D. S.

    1975-01-01

    A computer program was developed to generate a graphics display of the Dual Air Density (DAD) Explorer satellites which aids in the engineering and scientific design. The program displays a two-dimensional view of both spacecraft and their surface features from any direction. The graphics have been an indispensable tool in the design, analysis, and understanding of the critical locations of the various surface features for both satellites.

  10. Effects of rf power on electron density and temperature, neutral temperature, and T{sub e} fluctuations in an inductively coupled plasma

    SciTech Connect

    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.

  11. Does the Genotype Have a Significant Effect on the Formation of Intra-Annual Density Fluctuations? A Case Study Using Larix decidua from Northern Poland

    PubMed Central

    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

  12. Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

    SciTech Connect

    Thiyagarajan, Magesh; Scharer, John

    2008-07-01

    We present measurements and analysis of laser induced plasma neutral densities and temperatures in dry air by focusing 200 mJ, 10 MW high power, 193 nm ultraviolet ArF (argon fluoride) laser radiation to a 30 {mu}m radius spot size. We examine these properties that result from multiphoton and collisional cascade processes for pressures ranging from 40 Torr to 5 atm. A laser shadowgraphy diagnostic technique is used to obtain the plasma electron temperature just after the shock front and this is compared with optical emission spectroscopic measurements of nitrogen rotational and vibrational temperatures. Two-color laser interferometry is employed to measure time resolved spatial electron and neutral density decay in initial local thermodynamic equilibrium (LTE) and non-LTE conditions. The radiating species and thermodynamic characteristics of the plasma are analyzed by means of optical emission spectroscopy (OES) supported by SPECAIR, a special OES program for air constituent plasmas. Core plasma rotational and vibrational temperatures are obtained from the emission spectra from the N{sub 2}C-B(2+) transitions by matching the experimental spectrum results with the SPECAIR simulation results and the results are compared with the electron temperature just behind the shock wave. The plasma density decay measurements are compared with a simplified electron density decay model that illustrates the dominant three-and two-body recombination terms with good correlation.

  13. Experimental investigation of ultraviolet laser induced plasma density and temperature evolution in air

    NASA Astrophysics Data System (ADS)

    Thiyagarajan, Magesh; Scharer, John

    2008-07-01

    We present measurements and analysis of laser induced plasma neutral densities and temperatures in dry air by focusing 200 mJ, 10 MW high power, 193 nm ultraviolet ArF (argon fluoride) laser radiation to a 30 μm radius spot size. We examine these properties that result from multiphoton and collisional cascade processes for pressures ranging from 40 Torr to 5 atm. A laser shadowgraphy diagnostic technique is used to obtain the plasma electron temperature just after the shock front and this is compared with optical emission spectroscopic measurements of nitrogen rotational and vibrational temperatures. Two-color laser interferometry is employed to measure time resolved spatial electron and neutral density decay in initial local thermodynamic equilibrium (LTE) and non-LTE conditions. The radiating species and thermodynamic characteristics of the plasma are analyzed by means of optical emission spectroscopy (OES) supported by SPECAIR, a special OES program for air constituent plasmas. Core plasma rotational and vibrational temperatures are obtained from the emission spectra from the N2C-B(2+) transitions by matching the experimental spectrum results with the SPECAIR simulation results and the results are compared with the electron temperature just behind the shock wave. The plasma density decay measurements are compared with a simplified electron density decay model that illustrates the dominant three-and two-body recombination terms with good correlation.

  14. Increasing the modal density in plates for mono-element focusing in air.

    PubMed

    Etaix, Nicolas; Dubois, Jerôme; Fink, Mathias; Ing, Ros-Kiri

    2013-08-01

    Acoustic focusing experiments usually require large arrays of transducers. It has been shown by Etaix et al. [J. Acoust. Soc. Am. 131, 395-399 (2012)] that the use of a cavity allows reducing this number of transducers. This paper presents experiments with Duralumin plates (the cavities) containing scatterers to improve the contrast of focusing. The use of a scatterer array in the plate allows increasing the modal density at given frequencies. The scatterers used are membranes and buttons that are manufactured in Duralumin plates. Their resonances are studied both experimentally and numerically. Such scatterers present the advantage of having a tunable frequency resonance, which allows controlling the frequencies at which the modal density increases. The dispersion relations of plates with scatterer array show high modal density at given frequencies. Finally acoustic focusing experiments in air, using these plates, are compared to the ones of simple duralumin plates demonstrating the improvement of contrast. Acoustic source localization is also realized using these plates.

  15. Relationship between precipitation and water-table fluctuation in a coastal dune aquifer: northeastern coast of the Buenos Aires province, Argentina

    NASA Astrophysics Data System (ADS)

    Carretero, Silvina C.; Kruse, Eduardo E.

    2012-12-01

    The water-table fluctuation (WTF) method is one of the most widely used means to estimate aquifer recharge. In the northeastern coast of the Buenos Aires province, Argentina, the geomorphological and climatic characteristics, as well as the presence of a shallow, homogeneous unconfined aquifer, make it possible to apply this methodology. The relationship between water-table fluctuations and precipitation in a humid climate, considering its seasonal variations, is assessed. Water tables were measured monthly between February 2008 and September 2010 in a monitoring network; rainfall data were analysed. The water table rises when the accumulated precipitation between measurements is more than 53 mm/month in the dry season and more than 97 mm/month in the rainy season. The index, relating water-table fluctuations and precipitation occurring between measurements, shows that values below 0 suggest no increase in the water reserves, whereas higher values entail an increase. In the study area, where there is a lack of historical data, finding out the relationship between water-table fluctuations and precipitation will constitute a tool for groundwater use and management, and set up an early warning system for dry periods. It could also be extrapolated to other regions with similar hydrological conditions lacking in data.

  16. Fluctuation effects in rotating Bose-Einstein condensates with broken SU(2) and U (1 )×U (1 ) symmetries in the presence of intercomponent density-density interactions

    NASA Astrophysics Data System (ADS)

    Galteland, Peder Notto; Babaev, Egor; Sudbø, Asle

    2015-01-01

    Thermal fluctuations and melting transitions for rotating single-component superfluids have been intensively studied and are well understood. In contrast, the thermal effects on vortex states for two-component superfluids with density-density interaction, which have a much richer variety of vortex ground states, have been much less studied. Here, we investigate the thermal effects on vortex matter in superfluids with U (1 )×U (1 ) broken symmetries and intercomponent density-density interactions, as well as the case with a larger SU (2 ) broken symmetry obtainable from the [U (1 )×U (1 )] -symmetric case by tuning scattering lengths. In the former case we find that, in addition to first-order melting transitions, the system exhibits thermally driven phase transitions between square and hexagonal lattices. Our main result, however, concerns the case where the condensate exhibits SU (2 ) symmetry, and where vortices are not topological. At finite temperature, the system exhibits effects which do not have a counterpart in single-component systems. Namely, it has a state where thermally averaged quantities show no regular vortex lattice, yet the system retains superfluid coherence along the axis of rotation. In such a state, the thermal fluctuations result in transitions between different (nearly) degenerate vortex states without undergoing a melting transition. Our results apply to multicomponent Bose-Einstein condensates, and we suggest how to detect some of these unusual effects experimentally in such systems.

  17. Biexciton state causes photoluminescence fluctuations in CdSe/ZnS core/shell quantum dots at high photoexcitation densities

    NASA Astrophysics Data System (ADS)

    Yoshikawa, N.; Hirori, H.; Watanabe, H.; Aoki, T.; Ihara, T.; Kusuda, R.; Wolpert, C.; Fujiwara, T. K.; Kusumi, A.; Kanemitsu, Y.; Tanaka, K.

    2013-10-01

    The excitation density dependence of photoluminescence (PL) blinking of single CdSe/ZnS quantum dots was studied by means of single-dot PL spectroscopy. As the excitation density increases, an intermediate state appears in addition to the highly emissive (ON) and nonemissive (OFF) states. The systematic study of the excitation density dependence of PL blinking behavior (PL intensity, probabilities of finding these states, time probability distributions, and PL spectra and lifetimes) suggests that the intermediate state can be attributed to a charged exciton (trion) state generated through biexciton generation and charging (ionization) of a quantum dot under a high-density excitation regime. Our results indicate that the biexciton generation is a precursor of the trion state and not of the OFF state.

  18. Correlation and spectral measurements of fluctuating pressures and velocities in annular turbulent flow. [PWR; BWR

    SciTech Connect

    Wilson, R.J.; Jones, B.G.; Roy, R.P.

    1980-02-01

    An experimental study of the fluctuating velocity field, the fluctuating static wall pressure and the in-stream fluctuating static pressure in an annular turbulent air flow system with a radius ratio of 4.314 has been conducted. The study included direct measurements of the mean velocity profile, turbulent velocity field; fluctuating static wall pressure and in-stream fluctuating static pressure from which the statistical values of the turbulent intensity levels, power spectral densities of the turbulent quantities, the cross-correlation between the fluctuating static wall pressure and the fluctuating static pressure in the core region of the flow and the cross-correlation between the fluctuating static wall pressure and the fluctuating velocity field in the core region of the flow were obtained.

  19. Layers of air in the water beneath the floating fern Salvinia are exposed to fluctuations in pressure.

    PubMed

    Mayser, Matthias J; Barthlott, Wilhelm

    2014-12-01

    Superhydrophobic, hierarchically structured, technical surfaces (Lotus-effect) are of high scientific and economic interest because of their remarkable properties. Recently, the immense potential of air-retaining superhydrophobic surfaces, for example, for low-friction transport of fluids and drag-reducing coatings of ships has begun to be explored. A major problem of superhydrophobic surfaces mimicking the Lotus-effect is the limited persistence of the air retained, especially under rough conditions of flow. However, there are a variety of floating or diving plant and animal species that possess air-retaining surfaces optimized for durable water-repellency (Salvinia-effect). Especially floating ferns of the genus Salvinia have evolved superhydrophobic surfaces capable of maintaining layers of air for months. Apart from maintaining stability under water, the layer of air has to withstand the stresses of water pressure (up to 2.5 bars). Both of these aspects have an application to create permanent air layers on ships' hulls. We investigated the effect of pressure on air layers in a pressure cell and exposed the air layer to pressures of up to 6 bars. We investigated the suppression of the air layer at increasing pressures as well as its restoration during decreases in pressure. Three of the four examined Salvinia species are capable of maintaining air layers at pressures relevant to the conditions applying to ships' hulls. High volumes of air per surface area are advantageous for retaining at least a partial Cassie-Baxter-state under pressure, which also helps in restoring the air layer after depressurization. Closed-loop structures such as the baskets at the top of the "egg-beater hairs" (see main text) also help return the air layer to its original level at the tip of the hairs by trapping air bubbles.

  20. Layers of air in the water beneath the floating fern Salvinia are exposed to fluctuations in pressure.

    PubMed

    Mayser, Matthias J; Barthlott, Wilhelm

    2014-12-01

    Superhydrophobic, hierarchically structured, technical surfaces (Lotus-effect) are of high scientific and economic interest because of their remarkable properties. Recently, the immense potential of air-retaining superhydrophobic surfaces, for example, for low-friction transport of fluids and drag-reducing coatings of ships has begun to be explored. A major problem of superhydrophobic surfaces mimicking the Lotus-effect is the limited persistence of the air retained, especially under rough conditions of flow. However, there are a variety of floating or diving plant and animal species that possess air-retaining surfaces optimized for durable water-repellency (Salvinia-effect). Especially floating ferns of the genus Salvinia have evolved superhydrophobic surfaces capable of maintaining layers of air for months. Apart from maintaining stability under water, the layer of air has to withstand the stresses of water pressure (up to 2.5 bars). Both of these aspects have an application to create permanent air layers on ships' hulls. We investigated the effect of pressure on air layers in a pressure cell and exposed the air layer to pressures of up to 6 bars. We investigated the suppression of the air layer at increasing pressures as well as its restoration during decreases in pressure. Three of the four examined Salvinia species are capable of maintaining air layers at pressures relevant to the conditions applying to ships' hulls. High volumes of air per surface area are advantageous for retaining at least a partial Cassie-Baxter-state under pressure, which also helps in restoring the air layer after depressurization. Closed-loop structures such as the baskets at the top of the "egg-beater hairs" (see main text) also help return the air layer to its original level at the tip of the hairs by trapping air bubbles. PMID:24925548

  1. 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).

  2. Density-of-states Fluctuation-induced Negative Out-of-plane Magnetoresistance in Overdoped Bi-2212

    NASA Astrophysics Data System (ADS)

    Usui, Tomohiro; Adachi, Shintaro; Watanabe, Takao; Nishizaki, Terukazu

    We analyzed the in-plane and out -of-plane m agnetoresistance (MR) f or o verdoped B i1.6Pb0.4Sr2CaCu2O8+δ (Bi-2212) s ingle crystals us ing s uperconductive f luctuation t heory, which considers the d ensity-of-states (DOS) contribution i n l ayered superconductors with the conventional s-wave pairing state. The out-of-plane results are well reproduced by the theory, implying that the large, negative out-of-plane MR as well as the sharp increase in the zero-field out-of-plane resistivityρc near the superconducting transition temperature Tc originate from the superconductive DOS fluctuation effect. On the other hand, the in-plane results are better reproduced without the D OS c ontribution (i.e., using only th e Aslamazov-Larkin (AL) contribution), which may be e xplained in terms of the d-wave superconductivity of the layered superconductors.

  3. Application of MODIS GPP to Forecast Risk of Hantavirus Pulmonary Syndrome Based on Fluctuations in Reservoir Population Density

    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.

  4. Air Entrainment and Thermal Evolution of Pyroclastic Density Currents at Tungurahua, Ecuador

    NASA Astrophysics Data System (ADS)

    Benage, M. C.; Dufek, J.; Mothes, P. A.

    2015-12-01

    The entrainment of air into pyroclastic density currents (PDCs) impacts the thermal profile and evolution of the current. However, the associated hazards and opaqueness of PDCs make it difficult to discern internal dynamics and entrainment through direct observations. In this work, we use a three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model, deposit descriptions, and pyroclast field data, such as paleomagnetic and rind thickness, to study the entrainment efficiency and thus the thermal history of PDCs down the Juive Grande quebrada during the August 16-17th 2006 eruption of Tungurahua volcano. We conclude that 1) the efficient entrainment of ambient air cools the nose and upper portion of the PDCs by 30-60% of the original temperature, 2) PDCs with an initial temperature of 727 °C are on average more efficient at entraining ambient air than PDCs with an initial temperature of 327 °C, 3) the channelized PDCs develop a particle concentration gradient with a concentrated bed load region and suspended load region that leads to a large vertical temperature gradient, and 4) observations and pyroclast temperatures and textures suggest that the PDCs had temperatures greater than 327 °C in the bed load region while the upper, exterior portion of the currents cooled down to temperatures less than 100 °C. By combining field data and numerical models, the structure and dynamics of a PDC can be deduced for these relatively common small volume PDCs.

  5. Quenching of the beam-plasma instability by large-scale density fluctuations in 3 dimensions. [Langmuir waves in type 3 solar radio bursts

    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.

  6. Density-fluctuation symbolic computation on the (3+1)-dimensional variable-coefficient Kudryashov-Sinelshchikov equation for a bubbly liquid with experimental support

    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.

  7. Influence of Wind Velocity Fluctuation on Air Temperature Difference between the Fan and Ground Levels and the Effect of Frost Protective Fan Operation

    NASA Astrophysics Data System (ADS)

    Araki, Takuya; Matsuo, Kiyoshi; Miyama, Daisuke; Sumikawa, Osamu; Araki, Shinsuke

    We invested the influence of wind velocity fluctuation on air temperature difference between the fan (4.8 m) and ground levels (0.5 m) and the effect of frost protective fan operation in order to develop a new method to reduce electricity consumption due to frost protective fan operation. The results of the investigations are summarized as follows: (1) Air temperature difference between the fan (4.8 m) and ground levels (0.5 m) was decreased following an increase in wind velocity, and the difference was less than 1°C for a wind velocity more than 3.0 m/s at a height of 6.5 m. (2) When the wind velocity was more than 2-3 m/s, there was hardly any increase in the temperature of the leaves. In contrast, when the wind velocity was less than 2-3 m/s, an increase in the temperature of the leaves was observed. Based on these results, it is possible that when the wind velocity is greater than 2-3 m, it prevents thermal inversion. Therefore, there would be no warmer air for the frost protective fan to return to the tea plants and the air turbulence produced by the frost protective fan would not reach the plants under the windy condition.

  8. Transport, deposition, and liftoff in laboratory density currents composed of hot particles in air

    NASA Astrophysics Data System (ADS)

    Andrews, B. J.; Manga, M.

    2010-12-01

    Understanding the dynamics of transport, deposition, and air entrainment in pyroclastic density currents (PDCs) is required for accurate predictions of future current behaviors and interpretations of ancient deposits, but directly observing the interiors of natural PDCs is effectively impossible. We model PDCs with scaled, hot, particle-laden density currents generated in a 6 m long, 0.6 m wide, 1.8 m tall air-filled tank. Comparison of relevant scaling between our experiments and natural PDCs indicates that we are accurately capturing much of the dynamics of dilute PDCs: * Reynolds numbers of our experiments are lower than natural currents, 10^3 compared to 10^6, but still fully turbulent; * Densimetric and Thermal Richardson numbers are of O(1) in both natural and modeled currents; * Stokes and settling numbers for particles in the experiments fall within the expected range for natural PDCs. Conditions within the tank are monitored with temperature and humidity probes. Experiments are illuminated with sheet lighting, and recorded with high-definition video cameras. In general, currents have average velocities of 10-20 cm/s, initial thicknesses of 10-20 cm (although thickness greatly increases as currents entrain and expand air), and run out or lift off distances of 3-5 m. Large Kelvin-Helmholtz type eddies usually form along the top of the current immediately behind the head; these vortices are similar in size to the total current thickness. In currents that lift off, the distal current end typically retreats with time. Preliminary results suggest that lift off distance decreases with increasing thermal Richardson number. Analysis of turbulent structures indicates that the current heads are dominated by large coherent structures with length scales, L, comparable to the current thickness. Within 5-10 L of the current fronts, sequences of similar large eddies often occur. At greater distances behind the current fronts, turbulent structures become smaller and less

  9. Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints.

    PubMed

    Som, Sanjoy M; Catling, David C; Harnmeijer, Jelte P; Polivka, Peter M; Buick, Roger

    2012-04-19

    According to the 'Faint Young Sun' paradox, during the late Archaean eon a Sun approximately 20% dimmer warmed the early Earth such that it had liquid water and a clement climate. Explanations for this phenomenon have invoked a denser atmosphere that provided warmth by nitrogen pressure broadening or enhanced greenhouse gas concentrations. Such solutions are allowed by geochemical studies and numerical investigations that place approximate concentration limits on Archaean atmospheric gases, including methane, carbon dioxide and oxygen. But no field data constraining ground-level air density and barometric pressure have been reported, leaving the plausibility of these various hypotheses in doubt. Here we show that raindrop imprints in tuffs of the Ventersdorp Supergroup, South Africa, constrain surface air density 2.7 billion years ago to less than twice modern levels. We interpret the raindrop fossils using experiments in which water droplets of known size fall at terminal velocity into fresh and weathered volcanic ash, thus defining a relationship between imprint size and raindrop impact momentum. Fragmentation following raindrop flattening limits raindrop size to a maximum value independent of air density, whereas raindrop terminal velocity varies as the inverse of the square root of air density. If the Archaean raindrops reached the modern maximum measured size, air density must have been less than 2.3 kg m(-3), compared to today's 1.2 kg m(-3), but because such drops rarely occur, air density was more probably below 1.3 kg m(-3). The upper estimate for air density renders the pressure broadening explanation possible, but it is improbable under the likely lower estimates. Our results also disallow the extreme CO(2) levels required for hot Archaean climates. PMID:22456703

  10. Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints.

    PubMed

    Som, Sanjoy M; Catling, David C; Harnmeijer, Jelte P; Polivka, Peter M; Buick, Roger

    2012-04-19

    According to the 'Faint Young Sun' paradox, during the late Archaean eon a Sun approximately 20% dimmer warmed the early Earth such that it had liquid water and a clement climate. Explanations for this phenomenon have invoked a denser atmosphere that provided warmth by nitrogen pressure broadening or enhanced greenhouse gas concentrations. Such solutions are allowed by geochemical studies and numerical investigations that place approximate concentration limits on Archaean atmospheric gases, including methane, carbon dioxide and oxygen. But no field data constraining ground-level air density and barometric pressure have been reported, leaving the plausibility of these various hypotheses in doubt. Here we show that raindrop imprints in tuffs of the Ventersdorp Supergroup, South Africa, constrain surface air density 2.7 billion years ago to less than twice modern levels. We interpret the raindrop fossils using experiments in which water droplets of known size fall at terminal velocity into fresh and weathered volcanic ash, thus defining a relationship between imprint size and raindrop impact momentum. Fragmentation following raindrop flattening limits raindrop size to a maximum value independent of air density, whereas raindrop terminal velocity varies as the inverse of the square root of air density. If the Archaean raindrops reached the modern maximum measured size, air density must have been less than 2.3 kg m(-3), compared to today's 1.2 kg m(-3), but because such drops rarely occur, air density was more probably below 1.3 kg m(-3). The upper estimate for air density renders the pressure broadening explanation possible, but it is improbable under the likely lower estimates. Our results also disallow the extreme CO(2) levels required for hot Archaean climates.

  11. Highly sensitive measurement of liquid density in air using suspended microcapillary resonators.

    PubMed

    Malvar, Oscar; Ramos, Daniel; Martínez, Carmen; Kosaka, Priscila; Tamayo, Javier; Calleja, Montserrat

    2015-03-30

    We report the use of commercially available glass microcapillaries as micromechanical resonators for real-time monitoring of the mass density of a liquid that flows through the capillary. The vibration of a suspended region of the microcapillary is optically detected by measuring the forward scattering of a laser beam. The resonance frequency of the liquid filled microcapillary is measured for liquid binary mixtures of ethanol in water, glycerol in water and Triton in ethanol. The method achieves a detection limit in an air environment of 50 µg/mL that is only five times higher than that obtained with state-of-the-art suspended microchannel resonators encapsulated in vacuum. The method opens the door to novel advances for miniaturized total analysis systems based on microcapillaries with the add-on of mechanical transduction for sensing the rheological properties of the analyzed fluids without the need for vacuum encapsulation of the resonators.

  12. Highly sensitive measurement of liquid density in air using suspended microcapillary resonators.

    PubMed

    Malvar, Oscar; Ramos, Daniel; Martínez, Carmen; Kosaka, Priscila; Tamayo, Javier; Calleja, Montserrat

    2015-01-01

    We report the use of commercially available glass microcapillaries as micromechanical resonators for real-time monitoring of the mass density of a liquid that flows through the capillary. The vibration of a suspended region of the microcapillary is optically detected by measuring the forward scattering of a laser beam. The resonance frequency of the liquid filled microcapillary is measured for liquid binary mixtures of ethanol in water, glycerol in water and Triton in ethanol. The method achieves a detection limit in an air environment of 50 µg/mL that is only five times higher than that obtained with state-of-the-art suspended microchannel resonators encapsulated in vacuum. The method opens the door to novel advances for miniaturized total analysis systems based on microcapillaries with the add-on of mechanical transduction for sensing the rheological properties of the analyzed fluids without the need for vacuum encapsulation of the resonators. PMID:25831083

  13. Air

    MedlinePlus

    ... do to protect yourself from dirty air . Indoor air pollution and outdoor air pollution Air can be polluted indoors and it can ... this chart to see what things cause indoor air pollution and what things cause outdoor air pollution! Indoor ...

  14. Electron densities and energies of a guided argon streamer in argon and air environments

    NASA Astrophysics Data System (ADS)

    Hübner, S.; Hofmann, S.; van Veldhuizen, E. M.; Bruggeman, P. J.

    2013-12-01

    In this study we report the temporally and spatially resolved electron densities and mean energies of a guided argon streamer in ambient argon and air obtained by Thomson laser scattering. The plasma is driven by a positive monopolar 3.5 kV pulse, with a pulse width of 500 ns and a frequency of 5 kHz which is synchronized with the high repetition rate laser system. This configuration enables us to use the spatial and temporal stability of the guided streamer to accumulate a multitude of laser/plasma shots by a triple grating spectrometer equipped with an ICCD camera and to determine the electron parameters. We found a strong initial ne-overshoot with a maximum of 7 × 1019 m-3 and a mean electron energy of 4.5 eV. This maximum is followed by a fast decay toward the streamer channel. Moreover, a 2D distribution of the electron density is obtained which exhibits a peculiar mushroom-like shape of the streamer head with a diameter significantly larger than that of the emission profile. A correlation of the width of the streamer head with the expected pre-ionization channel is found.

  15. A Low Cost High Density Sensor Network for Air Quality at London Heathrow Airport

    NASA Astrophysics Data System (ADS)

    Bright, V.; Mead, M. I.; Popoola, O. A.; Baron, R. P.; Saffell, J.; Stewart, G.; Kaye, P.; Jones, R.

    2012-12-01

    ) resolution data over a 12 month period with data transmitted back to a server every 2 hours. In this paper we present the data capture and storage, data accessibility, data mining and visualisation techniques applied to the measurements of the SNAQ Heathrow high density sensor network, the preliminary results of which provide an insight into the potential use of such networks in characterising air quality, emissions and validating dispersion models on local scales. We also present a web based interface developed for the sensor network that allows users to access archived data and assess meteorological conditions, atmospheric dispersion, pollutant levels and emission rates.

  16. View-Angle Dependent AIRS Cloud Radiances and Fluctuations: Implications of Organized Cloud Structures for Tropical Circulations

    NASA Technical Reports Server (NTRS)

    Wu, Dong L.; Gong, Jie

    2012-01-01

    Interactions between wave dynamics and moisture generate clouds in a wide range of scales. Organized cloud structures produce statistically asymmetric radiances and perturbations in AIRS and AMSU-B measurements. With high resolution (approx.14 km beamwidth) and high-sensitivity instruments, these wave-modulated cloud structures can be readily detected from calibrated Levell radiance data. In this study we analyzed eight-year (2003 - 2010) statistics of AIRS cloud-induced radiances and found that in tropical convective regions the ascending (13:30 LST) measurements reveal higher view-angle asymmetry in cloud radiance than the descending (1:30 LST). The daytime asymmetry suggests 10% more cloudiness when the instrument views east, implying tilted and banded structures in most of the anvil clouds to which AIRS is sensitive. Such banded cloud structures are likely a manifestation of embedded westward propagating gravity waves in tropical convective systems. More importantly, organized cloud structures carry asymmetric momentum fluxes in addition to energy fluxes, which must be taken into account for modeling wave-wave and wave-mean flow interactions in tropical circulations.

  17. The effect of air density on atmospheric electric fields required for lightning initiation from a long airborne object

    NASA Astrophysics Data System (ADS)

    Bazelyan, E. M.; Aleksandrov, N. L.; Raizer, Yu. P.; Konchakov, A. M.

    2007-11-01

    The purpose of the work was to determine minimum atmospheric electric fields required for lightning initiation from an airborne vehicle at various altitudes up to 10 km. The problem was reduced to the determination of a condition for initiation of a viable positive leader from a conductive object in an ambient electric field. It was shown that, depending on air density and shape and dimensions of the object, critical atmospheric fields are governed by the condition for leader viability or that for corona onset. To establish quantitative criteria for reduced air densities, available observations of spark discharges in long laboratory gaps were analyzed, the effect of air density on leader velocity was discussed and evolution in time of the properties of plasma in the leader channel was numerically simulated. The results obtained were used to evaluate the effect of pressure on the quantitative relationships between the potential difference near the leader tip, leader current and its velocity; based on these relationships, criteria for steady development of a leader were determined for various air pressures. Atmospheric electric fields required for lightning initiation from rods and ellipsoidal objects of various dimensions were calculated at different air densities. It was shown that there is no simple way to extend critical ambient fields obtained for some given objects and pressures to other objects and pressures.

  18. The Effect of Air Density on Atmospheric Electric Fields Required for Lightning Initiation from a Long Airborne Object

    NASA Technical Reports Server (NTRS)

    Bazelyan, E. M.; Aleksandrov, N. L.; Raizer, Yu. Pl.; Konchankov, A. M.

    2006-01-01

    The purpose of the work was to determine minimum atmospheric electric fields required for lightning initiation from an airborne vehicle at various altitudes up to 10 km. The problem was reduced to the determination of a condition for initiation of a viable positive leader from a conductive object in an ambient electric field. It was shown that, depending on air density and shape and dimensions of the object, critical atmospheric fields are governed by the condition for leader viability or that for corona onset. To establish quantitative criteria for reduced air densities, available observations of spark discharges in long laboratory gaps were analyzed, the effect of air density on leader velocity was discussed and evolution in time of the properties of plasma in the leader channel was numerically simulated. The results obtained were used to evaluate the effect of pressure on the quantitative relationships between the potential difference near the leader tip, leader current and its velocity; based on these relationships, criteria for steady development of a leader were determined for various air pressures. Atmospheric electric fields required for lightning initiation from rods and ellipsoidal objects of various dimensions were calculated at different air densities. It was shown that there is no simple way to extend critical ambient fields obtained for some given objects and pressures to other objects and pressures.

  19. The effect of reduced air density on streamer-to-leader transition and on properties of long positive leader

    NASA Astrophysics Data System (ADS)

    Bazelyan, E. M.; Raizer, Yu P.; Aleksandrov, N. L.

    2007-07-01

    New results of observations of the leader process in a pressure chamber are presented for reduced air pressures. The analysis of these data and observations of the leader discharge in peak regions shows that the length of the leader tip and some other characteristics vary by several times as pressure decreases from 1 to 0.3 atm, whereas, under the conditions considered, the leader velocity remains almost independent of air density, the leader current being the same. These data are used to extract relationships between discharge parameters. It is shown that, at reduced air densities, electric field in a 'young' section of the leader channel exceeds electric field in the streamer zone. Therefore, transition of the leader process to the final-jump phase is not inevitably followed by a breakdown of the gap for reduced pressures, as opposed to the discharge in atmospheric pressure air. The model suggested previously by the authors for the streamer-to- leader transition at atmospheric pressure is amended to take into account hydrodynamic expansion of the channel and used to simulate the process at a relative air density of 0.3. The calculated results are used to interpret the observations of the leader process at reduced air pressures.

  20. Concentration, temperature, and density in a hydrogen-air flame by excimer-induced Raman scattering

    NASA Technical Reports Server (NTRS)

    Wehrmeyer, Joseph A.; Bowling, John M.; Pitz, Robert W.

    1988-01-01

    Single-pulse, vibrational Raman scattering (VRS) is an attractive laser diagnostic for the study of supersonic hydrogen-air combustion. The VRS technique gives a complete thermodynamic description of the gas mixture at a point in the reacting flow. Single-pulse, vibrational Raman scattering can simultaneously provide independent measurements of density, temperature, and concentration of each major species (H2, H2O, O2 and N2) in a hydrogen/air turbulent combustor. Also the pressure can be calculated using the ideal gas law. However, single-pulse VRS systems in current use for measurement of turbulent combustion have a number of shortcomings when applied to supersonic flows: (1) slow repetition rate (1 to 5 Hz), (2) poor spatial resolution (0.5x0.3x0.3 cu mm), and (3) marginal time resolution. Most of these shortcomings are due to the use of visible wavelength flash-lamp pumped dye lasers. The advent of UV excimer laser allows the possibility of dramatic improvements in the single-pulse, vibrational Raman scattering. The excimer based VRS probe will greatly improve repetition rate (100 to 500 Hz), spatial resolution (0.1x0.1x0.1 cu mm) and time resolution (30ns). These improvements result from the lower divergence of the UV excimer, higher repetition rate, and the increased Raman cross-sections (15 to 20 times higher) at ultra-violet (UV) wavelengths. With this increased capability, single-pulse vibrational Raman scattering promises to be an ideal non-intrusive probe for the study of hypersonic propulsion flows.

  1. Excess of ²¹⁰polonium activity in the surface urban atmosphere. Part (1) fluctuation of the ²¹⁰Po excess in the air.

    PubMed

    Długosz-Lisiecka, Magdalena

    2015-02-01

    The concentrations of (210)Pb, (210)Bi, and (210)Po in the urban atmosphere of Lodz city were measured from February 2010 to May 2010 and from May 2011 to April 2012. The seasonal changes in the activity ratios for (210)Po/(210)Pb and (210)Bi/(210)Pb indicated that the observed fluctuations were independent of the concentration of tropospheric (210)Pb and its decay products, particularly (210)Po. A simple calculation method was proposed for the estimation of the excess of (210)Po in urban aerosols in relation to the fraction of its activity formed from (210)Pb. On the basis of the results obtained, it was concluded that a substantial part of the (210)Po in urban air did not come from the decay of atmospheric (222)Rn, but rather it was from artificial sources. The highest levels of measured total (210)Po activity were observed during the winter period. This observation suggests that the main source of (210)Po in the investigated region could be related to anthropogenic emissions from domestic heating systems and local coal power plants, rather than from other sources, such as soil resuspension or stratospheric air intrusion as usually suggested in the literature.

  2. Excess of ²¹⁰polonium activity in the surface urban atmosphere. Part (1) fluctuation of the ²¹⁰Po excess in the air.

    PubMed

    Długosz-Lisiecka, Magdalena

    2015-02-01

    The concentrations of (210)Pb, (210)Bi, and (210)Po in the urban atmosphere of Lodz city were measured from February 2010 to May 2010 and from May 2011 to April 2012. The seasonal changes in the activity ratios for (210)Po/(210)Pb and (210)Bi/(210)Pb indicated that the observed fluctuations were independent of the concentration of tropospheric (210)Pb and its decay products, particularly (210)Po. A simple calculation method was proposed for the estimation of the excess of (210)Po in urban aerosols in relation to the fraction of its activity formed from (210)Pb. On the basis of the results obtained, it was concluded that a substantial part of the (210)Po in urban air did not come from the decay of atmospheric (222)Rn, but rather it was from artificial sources. The highest levels of measured total (210)Po activity were observed during the winter period. This observation suggests that the main source of (210)Po in the investigated region could be related to anthropogenic emissions from domestic heating systems and local coal power plants, rather than from other sources, such as soil resuspension or stratospheric air intrusion as usually suggested in the literature. PMID:25567523

  3. Reconstruction of air shower muon densities using segmented counters with time resolution

    NASA Astrophysics Data System (ADS)

    Ravignani, D.; Supanitsky, A. D.; Melo, D.

    2016-09-01

    Despite the significant experimental effort made in the last decades, the origin of the ultra-high energy cosmic rays is still largely unknown. Key astrophysical information to identify where these energetic particles come from is provided by their chemical composition. It is well known that a very sensitive tracer of the primary particle type is the muon content of the showers generated by the interaction of the cosmic rays with air molecules. We introduce a likelihood function to reconstruct particle densities using segmented detectors with time resolution. As an example of this general method, we fit the muon distribution at ground level using an array of counters like AMIGA, one of the Pierre Auger Observatory detectors. For this particular case we compare the reconstruction performance against a previous method. With the new technique, more events can be reconstructed than before. In addition the statistical uncertainty of the measured number of muons is reduced, allowing for a better discrimination of the cosmic ray primary mass.

  4. The behavior of high-purity, low-density air plasma sprayed thermal barrier coatings

    SciTech Connect

    Helminiak, Yanar NM

    2009-12-01

    Research on the behavior of high-purity, low-density (85%) air plasma sprayed (APS) thermal barrier coatings (TBC) with NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying is described. The microstructure of the APS topcoats is one variable in this study intended to maximize the coating thicknesses that can be applied without spallation and to minimize the thermal conduction through the YSZ layer. The specimens were evaluated using cyclic oxidation tests and important properties of the TBCs, such as resistance to sintering and phase transformation, were determined. The high purity resulted in top coats which are highly resistant to sintering and transformation from the metastable tetragonal phase to the equilibrium mixture of monoclinic and cubic phases. The porous topcoat microstructure also resulted in significant durability during thermal cycling. The actual failure mechanisms of the APS coatings were found to depend on topcoat thickness, CTE of the superalloy substrate and the nature of the thermal exposure.

  5. Analysis of Mexico City urban air pollution using nitrogen dioxide column density measurements from UV/Visible spectroscopy

    NASA Astrophysics Data System (ADS)

    Garcia Payne, D. G.; Grutter, M.; Melamed, M. L.

    2010-12-01

    The differential optical absorption spectroscopy method (DOAS) was used to get column densities of nitrogen dioxide (NO2) from the analysis of zenith sky UV/visible spectra. Since the optical path length provides critical information in interpreting NO2 column densities, in conjunction with NO2 column densities, the oxygen dimer (O4) column density was retrieved to give insight into the optical path length. We report observations of year round NO2 and O4 column densities (from august 2009 to september 2010) from which the mean seasonal levels and the daily evolution, as well as the occurrence of elevated pollution episodes are examined. Surface nitric oxide (NO) and NO2 from the local monitoring network, as well as wind data and the vertical aerosol density from continuous Lidar measurements are used in the analysis to investigate specific events in the context of local emissions from vehicular traffic, photochemical production and transport from industrial emissions. The NO2 column density measurements will enhance the understanding Mexico City urban air pollution. Recent research has begun to unravel the complexity of the air pollution problem in Mexico City and its effects not only locally but on a regional and global scale as well.

  6. Critical Slowing of Density Fluctuations Approaching the Isotropic-Nematic Transition in Liquid Crystals: 2D IR Measurements and Mode Coupling Theory.

    PubMed

    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.

  7. Temporal Changes in Local Functional Connectivity Density Reflect the Temporal Variability of the Amplitude of Low Frequency Fluctuations in Gray Matter

    PubMed Central

    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

  8. Critical Slowing of Density Fluctuations Approaching the Isotropic-Nematic Transition in Liquid Crystals: 2D IR Measurements and Mode Coupling Theory.

    PubMed

    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

  9. Validations of CFD Code for Density-Gradient Driven Air Ingress Stratified Flow

    SciTech Connect

    Chang H. Oh; Eung S. Kim; Richard Schultz; David Petti

    2010-05-01

    Air ingress into a very high temperature gas-cooled reactor (VHTR) is an important phenomena to consider because the air oxidizes the reactor core and lower plenum where the graphite structure supports the core region in the gas turbine modular helium reactor (GTMHR) design, thus jeopardizing the reactor’s safety. Validating the computational fluid dynamics (CFD) code used to analyze the air ingress phenomena is therefore an essential part of the safety analysis and the ultimate computation required for licensing

  10. [Daily observations (1970-1992) of fluctuations in frequency of occurrence of a sector structure in bacterial colonies selected from open air and from S. aureus cultures].

    PubMed

    Faraone, P

    1995-01-01

    The frequencies of sector structure occurrence in different bacteria colonies (SSC) denuded from open air every day in period from 1970 to 1982 years and also in laboratory cultures Staphylococcus Aureus from 1984 to 1992 were investigated. The value SSC was expressed in percents to general number of colonies. Variations of average SSC is found out distinctly expressed opposition to 11-years cycle of Solar activity for the same period of time. The year cycle SSC was registered also with local maxima in June, August and November and global minimum in March. SSC also were observed on level of sea, on height about 1000 m over the level of sea and in gallery under the rock of thickness 1400 m (Gran Cacco, National laboratory, Assergi). The value of SSC has its maximum on height 1000 M and its minimum in gallery under the rock; it is possible, SSC depends on the intensity of space galactic rays. The results of experience, executed in April-July 1992 on cultures S.aureus have compared with average (on ten-day time periods) values for the same months of 1984-1991. Good correlation of these two curves of SSC was received. Array of measurements received from 1970 to 1992 and made conclusions can be used for long-term forecasts of cosmophysical fluctuating phenomena at least on latitude between Rome and Milano.

  11. Failure of thick, low density air plasma sprayed thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Helminiak, Michael Aaron

    This research was directed at developing fundamental understandings of the variables that influence the performance of air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBC). Focus was placed on understanding how and why each variable influenced the performance of the TBC system along with how the individual variables interacted with one another. It includes research on the effect of surface roughness of NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying, the interdiffusion behavior of bond coats coupled to commercial superalloys, and the microstructural and compositional control of APS topcoats to maximize the coating thicknesses that can be applied without spallation. The specimens used for this research were prepared by Praxair Surface Technologies and have been evaluated using cyclic oxidation and thermal shock tests. TBC performance was sensitive to bond coat roughness with the rougher bond coats having improved cyclic performance than the smoother bond coats. The explanation being the rough bond coat surface hindered the propagation of the delamination cracks. The failure mechanisms of the APS coatings were found to depend on a combination of the topcoat thickness, topcoat microstructure and the coefficient of thermal expansion (CTE) mismatch between the superalloy and topcoat. Thinner topcoats tended to fail at the topcoat/TGO interface due to bond coat oxidation whereas thicker topcoats failed within the topcoat due to the strain energy release rate of the thicker coating exceeding the fracture strength of the topcoat. Properties of free-standing high and conventional purity YSZ topcoats of both a lowdensity (LD) and dense-vertically fissure (DVF) microstructures were evaluated. The densification rate and phase evolution were sensitive to the YSZ purity and the starting microstructure. Increasing the impurity content resulted in enhanced sintering and phase decomposition rates, with the exception of the

  12. Cell Volume Fluctuations in MDCK Monolayers

    PubMed Central

    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

  13. Dependence with air density of the response of the PTW SourceCheck ionization chamber for low energy brachytherapy sources

    SciTech Connect

    Tornero-López, Ana M.; Guirado, Damián; Ruiz-Arrebola, Samuel; Perez-Calatayud, Jose; Simancas, Fernando; Lallena, Antonio M.; Gazdic-Santic, Maja

    2013-12-15

    Purpose: Air-communicating well ionization chambers are commonly used to assess air kerma strength of sources used in brachytherapy. The signal produced is supposed to be proportional to the air density within the chamber and, therefore, a density-independent air kerma strength is obtained when the measurement is corrected to standard atmospheric conditions using the usual temperature and pressure correction factor. Nevertheless, when assessing low energy sources, the ionization chambers may not fulfill that condition and a residual density dependence still remains after correction. In this work, the authors examined the behavior of the PTW 34051 SourceCheck ionization chamber when measuring the air kerma strength of {sup 125}I seeds.Methods: Four different SourceCheck chambers were analyzed. With each one of them, two series of measurements of the air kerma strength for {sup 125}I selectSeed{sup TM} brachytherapy sources were performed inside a pressure chamber and varying the pressure in a range from 747 to 1040 hPa (560 to 780 mm Hg). The temperature and relative humidity were kept basically constant. An analogous experiment was performed by taking measurements at different altitudes above sea level.Results: Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization chamber they are undercorrected. At a typical atmospheric situation of 933 hPa (700 mm Hg) and 20 °C, this undercorrection turns out to be 1.5%. Corrected measurements show a residual linear dependence on the density and, as a consequence, an additional density dependent correction must be applied. The slope of this residual linear density dependence is different for each SourceCheck chamber investigated. The results obtained by taking measurements at different altitudes are compatible with those obtained with the pressure chamber.Conclusions: Variations of the altitude and

  14. Non-Gaussian eccentricity fluctuations

    NASA Astrophysics Data System (ADS)

    Grönqvist, Hanna; Blaizot, Jean-Paul; Ollitrault, Jean-Yves

    2016-09-01

    We study the fluctuations of the anisotropy of the energy density profile created in a high-energy collision at the LHC. We show that the anisotropy in harmonic n has generic non-Gaussian fluctuations. We argue that these non-Gaussianities have a universal character for small systems such as p+Pb collisions, but not for large systems such as Pb+Pb collisions where they depend on the underlying non-Gaussian statistics of the initial density profile. We generalize expressions for the eccentricity cumulants ɛ2{4 } and ɛ3{4 } previously obtained within the independent-source model to a general fluctuating initial density profile.

  15. Two-photon absorption laser induced fluorescence measurement of atomic oxygen density in an atmospheric pressure air plasma jet

    NASA Astrophysics Data System (ADS)

    Conway, J.; Gogna, G. S.; Gaman, C.; Turner, M. M.; Daniels, S.

    2016-08-01

    Atomic oxygen number density [O] is measured in an air atmospheric pressure plasma jet (APPJ) using two-photon absorption laser induced fluorescence (TALIF). Gas flow is fixed at 8 slpm, the RF power coupled into the plasma jet varied between 5 W and 20 W, and the resulting changes in atomic oxygen density measured. Photolysis of molecular oxygen is employed to allow in situ calibration of the TALIF system. During calibration, O2 photo-dissociation and two-photon excitation of the resulting oxygen atoms are achieved within the same laser pulse. The atomic oxygen density produced by photolysis is time varying and spatially non-uniform which needs to be corrected for to calibrate the TALIF system for measurement of atomic oxygen density in plasma. Knowledge of the laser pulse intensity I 0(t), wavelength, and focal spot size allows correction factors to be determined using a rate equation model. Atomic oxygen is used for calibration and measurement, so the laser intensity can be increased outside the TALIF quadratic laser power dependence region without affecting the calibration reliability as the laser power dependence will still be the same for both. The atomic O density results obtained are not directly benchmarked against other known density measurement techniques. The results show that the plasma jet atomic oxygen content increases as the RF power coupled into the plasma increases.

  16. Morphing Surfaces Enable Acoustophoretic Contactless Transport of Ultrahigh-Density Matter in Air

    NASA Astrophysics Data System (ADS)

    Foresti, Daniele; Sambatakakis, Giorgio; Bottan, Simone; Poulikakos, Dimos

    2013-11-01

    The controlled contactless transport of heavy drops and particles in air is of fundamental interest and has significant application potential. Acoustic forces do not rely on special material properties, but their utility in transporting heavy matter in air has been restricted by low power and poor controllability. Here we present a new concept of acoustophoresis, based on the morphing of a deformable reflector, which exploits the low reaction forces and low relaxation time of a liquid with enhanced surface tension through the use of thin overlaid membrane. An acoustically induced, mobile deformation (dimple) on the reflector surface enhances the acoustic field emitted by a line of discretized emitters and enables the countinuos motion of heavy levitated samples. With such interplay of emitters and reflecting soft-structure, a 5 mm steel sphere (0.5 grams) was contactlessly transported in air solely by acoustophoresis.

  17. Morphing Surfaces Enable Acoustophoretic Contactless Transport of Ultrahigh-Density Matter in Air

    PubMed Central

    Foresti, Daniele; Sambatakakis, Giorgio; Bottan, Simone; Poulikakos, Dimos

    2013-01-01

    The controlled contactless transport of heavy drops and particles in air is of fundamental interest and has significant application potential. Acoustic forces do not rely on special material properties, but their utility in transporting heavy matter in air has been restricted by low power and poor controllability. Here we present a new concept of acoustophoresis, based on the morphing of a deformable reflector, which exploits the low reaction forces and low relaxation time of a liquid with enhanced surface tension through the use of thin overlaid membrane. An acoustically induced, mobile deformation (dimple) on the reflector surface enhances the acoustic field emitted by a line of discretized emitters and enables the countinuos motion of heavy levitated samples. With such interplay of emitters and reflecting soft-structure, a 5 mm steel sphere (0.5 grams) was contactlessly transported in air solely by acoustophoresis. PMID:24212104

  18. Enhanced oxidation of air contaminants on an ultra-low density UV-accessible aerogel photocatalyst

    SciTech Connect

    Dreyer, M.; Newman, G.K.; Lobban, L.; Kersey, S.J.; Wang, R.; Harwell, J.H.

    1997-12-31

    This research developed new forms of photocatalysts that could potentially move photocatalytic degradation of air contaminants into the main stream of industrially used remediation technologies. Tests of the photocatalytic activity of the TiO{sub 2} aerogel catalysts have been carried out using both acetone and methane as the air contaminant. For comparison, the same tests were carried out on a standard (non-aerogel) anatase powder. Despite having very low crystallinity, the aerogel decontaminates the air far more effectively than an equal volume of the anatase powder which indicates that a much larger fraction of the aerogel is activated by the UV light. Experimental data were used to determine adsorption equilibrium constants for acetone, and to determine reaction rate constants assuming a Langmuir-Hinshelwood type rate expression.

  19. Modeled Seasonal Variations of Firn Density Induced by Steady State Surface Air Temperature Cycle

    NASA Technical Reports Server (NTRS)

    Jun, Li; Zwally, H. Jay; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    Seasonal variations of firn density in ice-sheet firn layers have been attributed to variations in deposition processes or other processes within the upper firn. A recent high-resolution (mm scale) density profile, measured along a 181 m core from Antarctica, showed small-scale density variations with a clear seasonal cycle that apparently was not-related to seasonal variations in deposition or known near-surface processes (Gerland and others 1999). A recent model of surface elevation changes (Zwally and Li, submitted) produced a seasonal variation in firn densification, and explained the seasonal surface elevation changes observed by satellite radar altimeters. In this study, we apply our 1-D time-dependent numerical model of firn densification that includes a temperature-dependent formulation of firn densification based on laboratory measurements of grain growth. The model is driven by a steady-state seasonal surface temperature and a constant accumulation rate appropriate for the measured Antarctic ice core. The modeled seasonal variations in firn density show that the layers of snow deposited during spring to mid-summer with the highest temperature history compress to the highest density, and the layers deposited during later summer to autumn with the lowest temperature history compress to the lowest density. The initial amplitude of the seasonal difference of about 0.13 reduces to about 0.09 in five years and asymptotically to 0.92 at depth, which is consistent with the core measurements.

  20. Traffic air pollution and risk of death from gastric cancer in Taiwan: petrol station density as an indicator of air pollutant exposure.

    PubMed

    Chiu, Hui-Fen; Tsai, Shang-Shyue; Chen, Pei-Shih; Liao, Yen-Hsiung; Liou, Saou-Hsing; Wu, Trong-Neng; Yang, Chun-Yuh

    2011-01-01

    To investigate the relationship between air pollution and risk of death attributed to gastric cancer, a matched cancer case-control study was conducted using deaths that occurred in Taiwan from 2004 through 2008. Data for all eligible gastric cancer deaths were obtained and compared to a control group consisting of individuals who died from causes other than neoplasms and diseases that were associated with gastrointestinal (GIT) disorders. The controls were pair-matched to the cancer cases by gender, year of birth, and year of death. Each matched control was randomly selected from the set of possible controls for each cancer case. Data for the number of petrol stations in study municipalities were collected from two major petroleum supply companies. The petrol station density (per square kilometer) (PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in ambient evaporative losses of petrol or to air emissions from motor vehicles. The exposed individuals were subdivided into three categories (≤25th percentile; 25th-75th percentile; >75th percentile) according to PSD in the residential municipality. Results showed that individuals who resided in municipalities with the highest PSD were at an increased risk of death attributed to gastric cancer compared to those subjects living in municipalities with the lowest PSD. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of gastric cancer.

  1. A Portable Low-Cost High Density Sensor Network for Air Quality at London Heathrow Airport

    NASA Astrophysics Data System (ADS)

    Popoola, Olalekan; Mead, Iq; Bright, Vivien; Baron, Ronan; Saffell, John; Stewart, Gregor; Kaye, Paul; Jones, Roderic

    2013-04-01

    Outdoor air quality and its impact on human health and the environment have been well studied and it has been projected that poor air quality will surpass poor sanitation as the major course of environmental premature mortality by 2050 (IGAC / IGBP, release statement, 2012). Transport-related pollution has been regulated at various levels by enactment of legislations at local, national, regional and global stages. As part of the mitigation measures, routine measurements of atmospheric pollutants such as carbon monoxide (CO), nitric oxide (NO) and nitrogen dioxide (NO2) have to be established in areas where air quality problems are identified. In addition, emission inventories are also generated for different atmospheric environments including urban areas and airport environments required for air quality models. Whilst recognising that most of the existing sparse monitoring networks provide high temporal measurements, spatial data of these highly variable pollutants are not captured, making it difficult to adequately characterise the highly heterogeneous air quality. Spatial information is often obtained from model data which can only be constrained using measurements from the sparse monitoring networks. The work presented here shows the application of low-cost sensor networks aimed at addressing this missing spatial information. We have shown in previous studies the application of low-cost electrochemical sensor network instruments in monitoring road transport pollutants including CO, NO and NO2 in an urban environment (Mead et. al. 2012, accepted Atmospheric Environment). Modified versions of these instruments which include additional species such as O3, SO2, VOCs and CO2 are currently deployed at London Heathrow Airport (LHR) as part of the Sensor Network for Air Quality (SNAQ) project. Meteorology data such as temperature, relative humidity, wind speed and direction are also measured as well as size-speciated particulates (0.38 to 17.4 µm). A network of 50

  2. 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.

  3. Study of Stable Cathodes and Electrolytes for High Specific Density Lithium-Air Battery

    NASA Technical Reports Server (NTRS)

    Hernandez-Lugo, Dionne M.; Wu, James; Bennett, William; Ming, Yu; Zhu, Yu

    2015-01-01

    Future NASA missions require high specific energy battery technologies, greater than 400 Wh/kg. Current NASA missions are using "state-of-the-art" (SOA) Li-ion batteries (LIB), which consist of a metal oxide cathode, a graphite anode and an organic electrolyte. NASA Glenn Research Center is currently studying the physical and electrochemical properties of the anode-electrolyte interface for ionic liquid based Li-air batteries. The voltage-time profiles for Pyr13FSI and Pyr14TFSI ionic liquids electrolytes studies on symmetric cells show low over-potentials and no dendritic lithium morphology. Cyclic voltammetry measurements indicate that these ionic liquids have a wide electrochemical window. As a continuation of this work, sp2 carbon cathode and these low flammability electrolytes were paired and the physical and electrochemical properties were studied in a Li-air battery system under an oxygen environment.

  4. Performance of a local electron density trigger to select extensive air showers at sea level

    NASA Technical Reports Server (NTRS)

    Abbas, T.; Madani, J.; Ashton, F.

    1985-01-01

    Time coincident voltage pulses in the two closely space (1.6m) plastic scintillators were recorded. Most of the recorded events are expeted to be due to electrons in cosmic ray showers whose core fall at some distance from the detectors. This result is confirmed from a measurement of the frequency distribution of the recorded density ratios of the two scintillators.

  5. Manganese concentrations in the air of the Montreal (Canada) subway in relation to surface automobile traffic density.

    PubMed

    Boudia, Nacéra; Halley, Renée; Kennedy, Greg; Lambert, Jean; Gareau, Lise; Zayed, Joseph

    2006-07-31

    Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organic derivative of manganese (Mn), used since 1976 in Canadian gasoline as an octane enhancer. Its combustion leads to the emission of Mn particles. Several studies carried out by our research group have established a correlation between atmospheric Mn concentrations and automobile traffic density, suggesting that MMT in gasoline could play a significant role. This study aims to measure Mn concentrations in the air of the underground subway in Montreal (Canada) and to examine the relation with nearby surface automobile traffic density and, by extension, with the use of MMT in gasoline. Three subway stations were chosen for their location in different microenvironments with different traffic densities. Respirable (MnR<5 microm) and total Mn (MnT) were sampled over two weeks, 5 days/week, 12 h/day. For the station located in the lower traffic density area, relatively low levels of MnR and MnT were found, with averages of 0.018 and 0.032 microg/m(3), respectively. These concentrations are within the range of the background levels in Montreal. For the other two stations, the average concentrations of MnR were twice as high and exceeded the US EPA reference concentration of 0.05 microg/m(3). Although there may be several sources of Mn from different components of the subway structure and vehicles, no correlation was found between subway traffic and atmospheric Mn in the subway. Since the air in the underground subway is pumped directly from outside without filtration, our findings strongly suggest that the combustion of MMT in automobiles is an important factor. PMID:16297437

  6. Dual-channel heterodyne measurements of atmospheric phase fluctuations.

    PubMed

    Ridley, Kevin D; Jakeman, Eric; Bryce, David; Watson, Stephen M

    2003-07-20

    A dual-channel fiber-coupled laser heterodyne system operating at a 1.55-microm wavelength is used to investigate phase fluctuations induced on a laser beam by propagation through turbulent air. Two receivers are used to characterize spatial and temporal variations produced by a turbulent layer of air in the laboratory. The system is also used for measurements through extended turbulence along an 80-m outdoor atmospheric path. Phase structure functions, power spectral densities, and cross correlations are presented. PMID:12921273

  7. Dynamics of an intense relativistic electron beam injected into full density air. Memorandum report

    SciTech Connect

    Fiorito, R.B.; Fordham, E.W.; Greig, J.R.; Pechacek, R.E.; Sethian, J.D.

    1981-09-21

    We have injected an intense relativistic electron beam (about 1 Mev, 16 kA, 25 ns) into the atmosphere and observed the beam in visible light caused by direct beam excitation of air molecules. The emitted visible light was primarily emission in the 2nd positive system of N2 which was delayed with respect to the beam current by about 6 ns but had the same duration (FWHM) as the beam current. Streak photographs of the beam in this visible light were taken with an Imacon 790 camera at various axial positions with a camera time resolution of about 1 ns. These photographs show that the beam remained a single current filament which oscillated about its initial direction as it propagated through the atmosphere, and that while the 'body' of the beam was pinched to a radius of < or = 5 cm the 'nose' was expanded to give the characteristic trumpet-like shape. Beam and net current monitors were used to determine the beam current and the plasma return current whose peak value was > or = 60% of the peak beam current. Comparison of the measured net current to that predicted from the calculated air conductivity and a simple circuit model to represent the beam propagating in the atmosphere showed good agreement provided a transmission line model including the capacitance of the beam in the ionized atmosphere was used.

  8. Traffic air pollution and lung cancer in females in Taiwan: petrol station density as an indicator of disease development.

    PubMed

    Chang, Chih-Ching; Tsai, Shang-Shyue; Chiu, Hui-Fen; Wu, Trong-Neng; Yang, Chun-Yuh

    2009-01-01

    To investigate the relationship between traffic air pollution exposure and development of lung cancer in females, studies were conducted using a matched cancer case-control model into deaths that occurred in Taiwan from 1997 through 2006. Data on all eligible lung cancer deaths in females were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. The control group consisted of women who died from causes other than neoplasms or diseases that were associated with respiratory problems. The controls were pair matched to the cancer cases by year of birth and year of death. Each matched control was selected randomly from the set of possible controls for each case. Data on the number of petrol stations in study municipalities were collected from the two major petroleum supply companies, Chinese Petroleum Corporation (CPC) and Formosa Petrochemical Corporation (FPCC). The petrol station density (per square kilometer; PSD) for study municipalities was used as an indicator of a subject's exposure to benzene and other hydrocarbons present in ambient evaporative losses of petrol or to air emissions from motor vehicles. The subjects were divided into tertiles according to PSD in their residential municipality. The results showed that there was a significant exposure-response relationship between PSD and risk of lung cancer in females after controlling for possible confounders. The findings of this study warrant further investigation of the role of traffic air pollution exposure in the etiology of lung cancer. PMID:19308850

  9. A dynamic urban air pollution population exposure assessment study using model and population density data derived by mobile phone traffic

    NASA Astrophysics Data System (ADS)

    Gariazzo, Claudio; Pelliccioni, Armando; Bolignano, Andrea

    2016-04-01

    A dynamic city-wide air pollution exposure assessment study has been carried out for the urban population of Rome, Italy, by using time resolved population distribution maps, derived by mobile phone traffic data, and modelled air pollutants (NO2, O3 and PM2.5) concentrations obtained by an integrated air dispersion modelling system. More than a million of persons were tracked during two months (March and April 2015) for their position within the city and its surroundings areas, with a time resolution of 15 min and mapped over an irregular grid system with a minimum resolution of 0.26 × 0.34 Km2. In addition, demographics information (as gender and age ranges) were available in a separated dataset not connected with the total population one. Such BigData were matched in time and space with air pollution model results and then used to produce hourly and daily resolved cumulative population exposures during the studied period. A significant mobility of population was identified with higher population densities in downtown areas during daytime increasing of up to 1000 people/Km2 with respect to nigh-time one, likely produced by commuters, tourists and working age population. Strong variability (up to ±50% for NO2) of population exposures were detected as an effect of both mobility and time/spatial changing in pollutants concentrations. A comparison with the correspondent stationary approach based on National Census data, allows detecting the inability of latter in estimating the actual variability of population exposure. Significant underestimations of the amount of population exposed to daily PM2.5 WHO guideline was identified for the Census approach. Very small differences (up to a few μg/m3) on exposure were detected for gender and age ranges population classes.

  10. A passive measurement of dissociated atom densities in atmospheric pressure air discharge plasmas using vacuum ultraviolet self-absorption spectroscopy

    SciTech Connect

    Laity, George; Fierro, Andrew; Dickens, James; Neuber, Andreas; Frank, Klaus

    2014-03-28

    We demonstrate a method for determining the dissociation degree of atmospheric pressure air discharges by measuring the self-absorption characteristics of vacuum ultraviolet radiation from O and N atoms in the plasma. The atom densities are determined by modeling the amount of radiation trapping present in the discharge, without the use of typical optical absorption diagnostic techniques which require external sources of probing radiation into the experiment. For an 8.0 mm spark discharge between needle electrodes at atmospheric pressure, typical peak O atom densities of 8.5 × 10{sup 17} cm{sup −3} and peak N atom densities of 9.9 × 10{sup 17} cm{sup −3} are observed within the first ∼1.0 mm of plasma near the anode tip by analyzing the OI and NI transitions in the 130.0–132.0 nm band of the vacuum ultraviolet spectrum.

  11. Quantum lattice fluctuations in a 1-dimensional charge-density-wave material: Luminescence and resonance Raman studies of an MX solid

    SciTech Connect

    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

  12. Current fluctuations in stochastic lattice gases.

    PubMed

    Bertini, L; De Sole, A; Gabrielli, D; Jona-Lasinio, G; Landim, C

    2005-01-28

    We study current fluctuations in lattice gases in the macroscopic limit extending the dynamic approach for density fluctuations developed in previous articles. More precisely, we establish a large deviation theory for the space-time fluctuations of the empirical current which include the previous results. We then estimate the probability of a fluctuation of the average current over a large time interval. It turns out that recent results by Bodineau and Derrida [Phys. Rev. Lett. 92, 180601 (2004)

  13. Fluctuations in densities of the invasive gill parasite Centrocestus formosanus (Trematoda: Heterophyidae) in the Comal River, Comal County, Texas, U.S.A.

    PubMed

    Johnson, Matthew S; Bolick, Anne; Alexander, Mara; Huffman, David; Oborny, Ed; Monroe, Allen

    2012-02-01

    Centrocestus formosanus (Trematoda: Heterophyidae) is an invasive fish parasite in the Comal River, Texas, and is considered a threat to the federally endangered fountain darter, Etheostoma fonticola . Monitoring densities of C. formosanus cercariae is crucial to determining levels of infection pressure. We sampled 3 sites in the Comal River during 2 sampling periods, the first during 2006-2007, and again during 2009-2010. Two of the sites were located in the upstream reach of Landa Lake, sites HS and LA, and the third site was located downstream of Landa Lake in the old channel of the river. Cercariae densities were highest at the downstream most site (EA), followed by sites LA and HS, during both sampling periods, but a significant decline in cercariae density was observed between the first and second sampling periods. Several abiotic factors were monitored, including total stream discharge, wading discharge, temperature, and dissolved oxygen, but no river-wide trends were observed. Therefore, we speculate that these factors do not adequately explain the observed long-term decline in cercariae density. We propose that the decline is simply a reflection of a typical pattern followed by most invasive species as they gradually become integrated into the local community following an initial explosive growth in population size. Although cercariae densities may be abating, fountain darters in the Comal River are still threatened by the parasite, and conservation efforts must focus on reducing levels of infection pressure from the parasite whenever possible.

  14. The study of aluminium anodes for high power density Al/air batteries with brine electrolytes

    NASA Astrophysics Data System (ADS)

    Nestoridi, Maria; Pletcher, Derek; Wood, Robert J. K.; Wang, Shuncai; Jones, Richard L.; Stokes, Keith R.; Wilcock, Ian

    Aluminium alloys containing small additions of both tin (∼0.1 wt%) and gallium (∼0.05 wt%) are shown to dissolve anodically at high rates in sodium chloride media at room temperatures; current densities >0.2 A cm -2 can be obtained at potentials close to the open circuit potential, ∼-1500 mV versus SCE. The tin exists in the alloys as a second phase, typically as ∼1 μm inclusions (precipitates) distributed throughout the aluminium structure, and anodic dissolution occurs to form pits around the tin inclusions. Although the distribution of the gallium in the alloy could not be established, it is also shown to be critical in the formation of these pits as well as maintaining their activity. The stability of the alloys to open circuit corrosion and the overpotential for high rate dissolution, both critical to battery performance, are shown to depend on factors in addition to elemental composition; both heat treatment and mechanical working influence the performance of the alloy. The correlation between alloy performance and their microstructure has been investigated.

  15. High cell density cultivation of Pseudomonas putida KT2440 using glucose without the need for oxygen enriched air supply.

    PubMed

    Davis, Reeta; Duane, Gearoid; Kenny, Shane T; Cerrone, Federico; Guzik, Maciej W; Babu, Ramesh P; Casey, Eoin; O'Connor, Kevin E

    2015-04-01

    High Cell Density (HCD) cultivation of bacteria is essential for the majority of industrial processes to achieve high volumetric productivity (g L(-1) h(-1) ) of a bioproduct of interest. This study developed a fed batch bioprocess using glucose as sole carbon and energy source for the HCD of the well described biocatalyst Pseudomonas putida KT2440 without the supply of oxygen enriched air. Growth kinetics data from batch fermentations were used for building a bioprocess model and designing feeding strategies. An exponential followed by linearly increasing feeding strategy of glucose was found to be effective in maintaining biomass productivity while also delaying the onset of dissolved oxygen (supplied via compressed air) limitation. A final cell dry weight (CDW) of 102 g L(-1) was achieved in 33 h with a biomass productivity of 3.1 g L(-1) h(-1) which are the highest ever reported values for P. putida strains using glucose without the supply of pure oxygen or oxygen enriched air. The usefulness of the biomass as a biocatalyst was demonstrated through the production of the biodegradable polymer polyhydroxyalkanoate (PHA). When nonanoic acid (NA) was supplied to the glucose grown cells of P. putida KT2440, it accumulated 32% of CDW as PHA in 11 h (2.85 g L(-1) h(-1) ) resulting in a total of 0.56 kg of PHA in 18 L with a yield of 0.56 g PHA g NA(-1) .

  16. The Effect of Air Density on Sand Transport Structures and the Adobe Abrasion Profile: A Field Wind-Tunnel Experiment Over a Wide Range of Altitude

    NASA Astrophysics Data System (ADS)

    Han, Qingjie; Qu, Jianjun; Dong, Zhibao; Zu, Ruiping; Zhang, Kecun; Wang, Hongtao; Xie, Shengbo

    2013-11-01

    Aeolian sand transport results from interactions between the surface and the airflow above. Air density strongly constrains airflow characteristics and the resulting flow of sand, and therefore should not be neglected in sand transport models. In the present study, we quantify the influence of air density on the sand flow structure, sand transport rate, adobe abrasion profiles, and abrasion rate using a portable wind-tunnel in the field. For a given wind speed, the flow's ability to transport sand decreases at low air density, so total sand transport decreases, but the saltation height increases. Thus, the damage to human structures increases compared with what occurs at lower altitudes. The adobe abrasion rate by the cloud of blowing sand decreases exponentially with increasing height above the surface, while the wind erosion and dust emission intensity both increase with increasing air density. Long-term feedback processes between air density and wind erosion suggest that the development of low-altitude areas due to long-term deflation plays a key role in dust emission, and will have a profound significance for surface Aeolian processes and geomorphology.

  17. A method to determine true air temperature fluctuations in clouds with liquid water fraction and estimate water droplet effect on the calculations of the spectral structure of turbulent heat fluxes in cumulus clouds based on aircraft data

    NASA Astrophysics Data System (ADS)

    Strunin, Alexander M.; Zhivoglotov, Dmitriy N.

    2014-03-01

    Liquid water droplets could distort aircraft temperature measurements in clouds, leading to errors in calculated heat fluxes and incorrect flux distribution pattern. The estimation of cloud droplet effect on the readings of the high-frequency aircraft thermometer employed at the Central Aerological Observatory (CAO) was based on an experimental study of the sensor in a wind tunnel, using an air flow containing liquid water droplets. Simultaneously, calculations of the distribution of speed and temperature in a flow through the sensitive element of the sensor were fulfilled. This permitted estimating the coefficient of water content effect on temperature readings. Another way of estimating cloud droplet effect was based on the analysis of data obtained during aircraft observations of cumulus clouds in a tropical zone (Cuba Island). As a result, a method of correcting air temperature and recovering true air temperature fluctuations inside clouds was developed. This method has provided consistent patterns of heat flux distribution in a cumulus area. Analysis of the results of aircraft observations of cumulus clouds with temperature correction fulfilled has permitted investigation of the spectral structure of the fields of air temperature and heat fluxes to be performed in cumulus zones based on wavelet transformation. It is shown that mesoscale eddies (over 500 m in length) were the main factor of heat exchange between a cloud and the ambient space. The role of turbulence only consisted in mixing inside the cloud.

  18. Quantum lattice fluctuations in a 1-dimensional charge-density-wave material: Luminescence and resonance Raman studies of an MX solid

    SciTech Connect

    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.

  19. Effect of climate change on annual fluctuations in the population density of the brown marmorated stink bug (Hemiptera: Pentatomidae) in northern Japan.

    PubMed

    Funayama, Ken

    2013-10-01

    The relationship between the population density of overwintering adults of the brown marmorated stink bug and the temperatures of each month during the preceding November to April was investigated in Akita Prefecture, northern Japan, from 1999 to 2012. The number of adults entering traps for overwintering at the monitored hibernation site differed considerably among years. There was a significant negative correlation between the increase ratio (the ratio of the number collected in the current year to the number collected in the previous year) and the mean daily maximum temperature of the preceding March and April. These results suggest that the proportion of surviving adult brown marmorated stink bug may be higher when temperatures in early spring (March and April) are lower, as the postoverwintering adults may need to survive without food for a shorter period of time.

  20. Effect of climate change on annual fluctuations in the population density of the brown marmorated stink bug (Hemiptera: Pentatomidae) in northern Japan.

    PubMed

    Funayama, Ken

    2013-10-01

    The relationship between the population density of overwintering adults of the brown marmorated stink bug and the temperatures of each month during the preceding November to April was investigated in Akita Prefecture, northern Japan, from 1999 to 2012. The number of adults entering traps for overwintering at the monitored hibernation site differed considerably among years. There was a significant negative correlation between the increase ratio (the ratio of the number collected in the current year to the number collected in the previous year) and the mean daily maximum temperature of the preceding March and April. These results suggest that the proportion of surviving adult brown marmorated stink bug may be higher when temperatures in early spring (March and April) are lower, as the postoverwintering adults may need to survive without food for a shorter period of time. PMID:24224257

  1. Concentration, size, and density of total suspended particulates at the air exhaust of concentrated animal feeding operations.

    PubMed

    Yang, Xufei; Lee, Jongmin; Zhang, Yuanhui; Wang, Xinlei; Yang, Liangcheng

    2015-08-01

    Total suspended particulate (TSP) samples were seasonally collected at the air exhaust of 15 commercial concentrated animal feeding operations (CAFOs; including swine finishing, swine farrowing, swine gestation, laying hen, and tom turkey) in the U.S. Midwest. The measured TSP concentrations ranged from 0.38 ± 0.04 mg m⁻³ (swine gestation in summer) to 10.9 ± 3.9 mg m⁻³ (tom turkey in winter) and were significantly affected by animal species, housing facility type, feeder type (dry or wet), and season. The average particle size of collected TSP samples in terms of mass median equivalent spherical diameter ranged from 14.8 ± 0.5 µm (swine finishing in winter) to 30.5 ± 2.0 µm (tom turkey in summer) and showed a significant seasonal effect. This finding affirmed that particulate matter (PM) released from CAFOs contains a significant portion of large particles. The measured particle size distribution (PSD) and the density of deposited particles (on average 1.65 ± 0.13 g cm⁻³) were used to estimate the mass fractions of PM10 and PM2.5 (PM ≤ 10 and ≤ 2.5 μm, respectively) in the collected TSP. The results showed that the PM10 fractions ranged from 12.7 ± 5.1% (tom turkey) to 21.1 ± 3.2% (swine finishing), whereas the PM2.5 fractions ranged from 3.4 ± 1.9% (tom turkey) to 5.7 ± 3.2% (swine finishing) and were smaller than 9.0% at all visited CAFOs. This study applied a filter-based method for PSD measurement and deposited particles as a surrogate to estimate the TSP's particle density. The limitations, along with the assumptions adopted during the calculation of PM mass fractions, must be recognized when comparing the findings to other studies.

  2. POPULATION DYNAMICS OF CHAFF SCALE, PARLATORIA PERGANDII COMSTOCK IN COMPARATIVE ANALYSIS OF FLUCTUATING POPULATION DENSITIES ON THREE CITRUS VARIETIES IN EL-BEHEIRA GOVERNORATE, EGYPT.

    PubMed

    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

  3. Sound Source Identification Through Flow Density Measurement and Correlation With Far Field Noise

    NASA Technical Reports Server (NTRS)

    Panda, J.; Seasholtz, R. G.

    2001-01-01

    Sound sources in the plumes of unheated round jets, in the Mach number range 0.6 to 1.8, were investigated experimentally using "casuality" approach, where air density fluctuations in the plumes were correlated with the far field noise. The air density was measured using a newly developed Molecular Rayleigh scattering based technique, which did not require any seeding. The reference at the end provides a detailed description of the measurement technique.

  4. The influence of meteorological conditions and anthropogenic activities on the seasonal fluctuations of BTEX in the urban air of the Hanseatic city of Gdansk, Poland.

    PubMed

    Marć, Mariusz; Bielawska, Michalina; Wardencki, Waldemar; Namieśnik, Jacek; Zabiegała, Bożena

    2015-08-01

    The results of studies conducted in Gdansk in the period from January to December 2013 and focused on the determination of BTEX in the atmospheric air are presented. At the stage of the isolation and/or enrichment of analytes from the gaseous medium, a passive sampling technique-Radiello® diffusive passive samplers, was applied. The time-weighted average annual concentration of benzene, toluene, ethylbenzene, and total xylenes determined in the monitored area was as follows: 0.66 ± 0.32, 1.63 ± 0.94, 0.67 ± 0.61, and 2.9 ± 2.7 μg/m(3). As a result of the research, the potential emission sources of BTEX, which activity has a significant impact on the concentration of these compounds in the atmosphere in the Gdansk area, were identified. A comparison of the accuracy and precision of the results of benzene concentrations in the atmosphere obtained by the BTEX automatic analyzer and passive techniques was performed. Moreover, a significant influence of meteorological conditions, such as air temperature, intensity of solar radiation, velocity and direction of wind, humidity, and rainfall on the benzene content in ambient air was shown. Additionally, in order to determine the conditions in the area covered by the monitoring, information about atmospheric stability and the height of the mixing layer was presented. PMID:25869437

  5. Metal-Air Electric Vehicle Battery: Sustainable, High-Energy Density, Low-Cost Electrochemical Energy Storage – Metal-Air Ionic Liquid (MAIL) Batteries

    SciTech Connect

    2009-12-21

    Broad Funding Opportunity Announcement Project: ASU is developing a new class of metal-air batteries. Metal-air batteries are promising for future generations of EVs because they use oxygen from the air as one of the battery’s main reactants, reducing the weight of the battery and freeing up more space to devote to energy storage than Li-Ion batteries. ASU technology uses Zinc as the active metal in the battery because it is more abundant and affordable than imported lithium. Metal-air batteries have long been considered impractical for EV applications because the water-based electrolytes inside would decompose the battery interior after just a few uses. Overcoming this traditional limitation, ASU’s new battery system could be both cheaper and safer than today’s Li-Ion batteries, store from 4-5 times more energy, and be recharged over 2,500 times.

  6. Absolute OH density measurements in an atmospheric pressure dc glow discharge in air with water electrode by broadband UV absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Xiong, Qing; Yang, Zhiqiang; Bruggeman, Peter J.

    2015-10-01

    Spatially resolved absolute OH radical density measurements are performed in an atmospheric pressure glow discharge generated in ambient air with water electrode by broadband UV absorption spectroscopy. The radial distributions of OH density and gas temperature are obtained for the positive column, anode and cathode regions both for water-cathode and water-anode discharges. It is found that for both polarities of the water electrode the radial profiles of the ground state OH density and gas temperature are significantly broader than the total discharge emission intensity and the emission intensity originating from OH(\\text{A}{}2{{\\text{ }Σ\\text{ }}+} ) only. Exceptional large OH densities exceeding 1023 m-3 are found. The OH kinetics are discussed in detail.

  7. Rapidity Density Fluctuations in Hadron-Nucleus Interactions: Spikes, Intermittency, and Fractal Properties of Multiple Production in Silver, Gold, and Magnesium Targets with Proton, Antiproton, Positive Pion, and Negative Pion Projectiles at 100 and 320 Gev/c

    NASA Astrophysics Data System (ADS)

    Mattingly, Margarita Claudia Krieghoff

    The space-time development of hadron-nucleus interactions is examined using bubble chamber and downstream particle identifier data from the hybrid spectrometer of Fermilab experiment E597. 5583 events representing 12 interactions are studied with conventional and fractal techniques. Comparisons are made to simulated events from the Lund Monte Carlo FRITIOF 1.6. Multiplicities are studied conventionally. Negative binomial descriptions of produced particle multiplicities are interpreted in terms of clusters and cascading and in terms of partial stimulated emission; forward-backward correlations, in terms of short- and long-range correlations and multiple scattering. Multiplicities are consistent with a multiple collision view of multiparticle production mechanisms and are investigated in terms of the number of collisions nu. Rapidity density fluctuations are studied fractally. The possibility of new dynamics is considered on the basis of event-by-event studies of spike phenomena, intermittency, and fractal dimensions. Results from these exploratory studies are consistent with predictions made for quark-gluon plasma transitions. 131 spike events are analyzed; intermittency is investigated with normalized factorial moments and cumulants; and fractal dimensions and correlations dimensions are calculated. Seagull effects and production region sizes from Bose-Einstein pion interferometry are also considered.

  8. An ab initio molecular dynamics study of the liquid-vapor interface of an aqueous NaCl solution: inhomogeneous density, polarity, hydrogen bonds, and frequency fluctuations of interfacial molecules.

    PubMed

    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.

  9. Naphthalene contamination of sterilized milk drinks contained in low-density polyethylene bottles. Part 2. Effect of naphthalene vapour in air.

    PubMed

    Lau, O W; Wong, S K; Leung, K S

    1995-04-01

    A survey on naphthalene vapour in air was conducted, revealing that the ambient atmosphere contained concentrations of naphthalene in the range of 0.005-0.100 mg m-3. The level of naphthalene vapour in air increased to 0.35 and 4.00 mg m-3 in places exposed to lacquer paint and naphthalene-based moth-repellent, respectively. The effect of naphthalene vapour in air on milk drinks contained in low-density polyethylene (LDPE) bottles was assessed. A mathematical model was suggested to describe the migration of naphthalene from the atmosphere into milk. The model was proved to be valid for milk drinks exposed to naphthalene-based moth-repellent during storage. Moreover, the extent of migration was found to increase with the fat content of foods, which might be ascribed to an increase in diffusion, in addition to the kinetic factor, that affects naphthalene migration.

  10. Absolute OH density measurements in the effluent of a cold atmospheric-pressure Ar-H2O RF plasma jet in air

    NASA Astrophysics Data System (ADS)

    Verreycken, Tiny; Mensink, Rob; van der Horst, Ruud; Sadeghi, Nader; Bruggeman, Peter J.

    2013-10-01

    Absolute OH densities are obtained in a radio-frequency-driven Ar-H2O atmospheric-pressure plasma jet by laser-induced fluorescence (LIF), calibrated by Rayleigh scattering and by UV broadband absorption. The measurements are carried out in ambient air and the effect of air entrainment into the Ar jet is measured by analyzing the time-resolved fluorescence signals. The OH densities are obtained for different water vapor concentrations admixed to the Ar and as a function of the axial distance from the nozzle. A sensitivity analysis to deduce the accuracy of the model-calculated OH density from the LIF measurement is reported. It is found that the UV absorption and the LIF results correspond within experimental accuracy close to the nozzle and deviate in the far effluent. The possible reasons are discussed. The OH densities found in the plasma jet are in the range (0.1-2.5) × 1021 m-3 depending on the water concentration and plasma conditions.

  11. Traffic density and stationary sources of air pollution associated with wheeze, asthma, and immunoglobulin E from birth to age 5 years among New York City children.

    PubMed

    Patel, Molini M; Quinn, James W; Jung, Kyung Hwa; Hoepner, Lori; Diaz, Diurka; Perzanowski, Matthew; Rundle, Andrew; Kinney, Patrick L; Perera, Frederica P; Miller, Rachel L

    2011-11-01

    Exposures to ambient air traffic-related pollutants and their sources have been associated with respiratory and asthma morbidity in children. However, longitudinal investigation of the effects of traffic-related exposures during early childhood is limited. We examined associations of residential proximity and density of traffic and stationary sources of air pollution with wheeze, asthma, and immunoglobulin (Ig) E among New York City children between birth and age 5 years. Subjects included 593 Dominican and African American participants from the Columbia Center for Children's Environmental Health cohort. Prenatally, through age 5 years, residential and respiratory health data were collected every 3-6 months. At ages 2, 3, and 5 years, serum IgE was measured. Spatial data on the proximity and density of roadways and built environment were collected for a 250 m buffer around subjects' homes. Associations of wheeze, asthma, total IgE, and allergen-specific IgE with prenatal, earlier childhood, and concurrent exposures to air pollution sources were analyzed using generalized estimating equations or logistic regression. In repeated measures analyses, concurrent residential density of four-way intersections was associated significantly with wheeze (odds ratio: 1.26; 95% confidence interval [CI]: 1.01, 1.57). Age 1 exposures also were associated with wheeze at subsequent ages. Concurrent proximity to highway was associated more strongly with total IgE (ratio of the geometric mean levels: 1.25; 95% CI: 1.09, 1.42) than were prenatal or earlier childhood exposures. Positive associations also were observed between percent commercial building area and asthma, wheeze, and IgE and between proximity to stationary sources of air pollution and asthma. Longitudinal investigation suggests that among Dominican and African American children living in Northern Manhattan and South Bronx during ages 0-5 years, residence in neighborhoods with high density of traffic and industrial

  12. Colloid Mobilization and Transport during Capillary Fringe Fluctuations

    NASA Astrophysics Data System (ADS)

    Aramrak, Surachet; Flury, Markus

    2016-04-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead filled column. Confocal images showed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively-charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively-charged colloids did not attach to static air-bubbles, but hydrophobic negatively-charged and hydrophilic positively-charged colloids did.

  13. The effect of collisional quenching of the O 3p 3PJ state on the determination of the spatial distribution of the atomic oxygen density in an APPJ operating in ambient air by TALIF

    NASA Astrophysics Data System (ADS)

    Zhang, S.; van Gessel, A. F. H.; van Grootel, S. C.; Bruggeman, P. J.

    2014-04-01

    The spatial profile of the absolute atomic oxygen density is obtained by two-photon absorption laser-induced fluorescence (TALIF) in an Ar+2% air cold atmospheric pressure plasma jet (APPJ) operating in ambient air. The varying air concentration in the jet effluent which contributes to the collisional quenching of the O 3p 3PJ state, pumped by the laser, strongly influences the recorded TALIF signal under the present experimental conditions. The spatially resolved air densities obtained from Raman scattering measurements have been reported in our previous work (van Gessel et al 2013 Appl. Phys. Lett. 103 064103). These densities allow us to calculate the spatially dependent collisional quenching rate for the O 3p 3PJ state and reconstruct the spatial O density profile from the recorded TALIF signal. Significant differences between the TALIF intensity profile and the actual O density profile for the investigated experimental conditions are found.

  14. Coupled Quantum Fluctuations and Quantum Annealing

    NASA Astrophysics Data System (ADS)

    Hormozi, Layla; Kerman, Jamie

    We study the relative effectiveness of coupled quantum fluctuations, compared to single spin fluctuations, in the performance of quantum annealing. We focus on problem Hamiltonians resembling the the Sherrington-Kirkpatrick model of Ising spin glass and compare the effectiveness of different types of fluctuations by numerically calculating the relative success probabilities and residual energies in fully-connected spin systems. We find that for a small class of instances coupled fluctuations can provide improvement over single spin fluctuations and analyze the properties of the corresponding class. Disclaimer: This research was funded by ODNI, IARPA via MIT Lincoln Laboratory under Air Force Contract No. FA8721-05-C-0002. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of ODNI, IARPA, or the US Government.

  15. Laser-based air data system for aircraft control using Raman and elastic backscatter for the measurement of temperature, density, pressure, moisture, and particle backscatter coefficient.

    PubMed

    Fraczek, Michael; Behrendt, Andreas; Schmitt, Nikolaus

    2012-01-10

    Flight safety in all weather conditions demands exact and reliable determination of flight-critical air parameters. Air speed, temperature, density, and pressure are essential for aircraft control. Conventional air data systems can be impacted by probe failure caused by mechanical damage from hail, volcanic ash, and icing. While optical air speed measurement methods have been discussed elsewhere, in this paper, a new concept for optically measuring the air temperature, density, pressure, moisture, and particle backscatter is presented, being independent on assumptions on the atmospheric state and eliminating the drawbacks of conventional aircraft probes by providing a different measurement principle. The concept is based on a laser emitting laser pulses into the atmosphere through a window and detecting the signals backscattered from a fixed region just outside the disturbed area of the fuselage flows. With four receiver channels, different spectral portions of the backscattered light are extracted. The measurement principle of air temperature and density is based on extracting two signals out of the rotational Raman (RR) backscatter signal of air molecules. For measuring the water vapor mixing ratio-and thus the density of the moist air-a water vapor Raman channel is included. The fourth channel serves to detect the elastic backscatter signal, which is essential for extending the measurements into clouds. This channel contributes to the detection of aerosols, which is interesting for developing a future volcanic ash warning system for aircraft. Detailed and realistic optimization and performance calculations have been performed based on the parameters of a first prototype of such a measurement system. The impact and correction of systematic error sources, such as solar background at daytime and elastic signal cross talk appearing in optically dense clouds, have been investigated. The results of the simulations show the high potential of the proposed system for

  16. Laser-based air data system for aircraft control using Raman and elastic backscatter for the measurement of temperature, density, pressure, moisture, and particle backscatter coefficient.

    PubMed

    Fraczek, Michael; Behrendt, Andreas; Schmitt, Nikolaus

    2012-01-10

    Flight safety in all weather conditions demands exact and reliable determination of flight-critical air parameters. Air speed, temperature, density, and pressure are essential for aircraft control. Conventional air data systems can be impacted by probe failure caused by mechanical damage from hail, volcanic ash, and icing. While optical air speed measurement methods have been discussed elsewhere, in this paper, a new concept for optically measuring the air temperature, density, pressure, moisture, and particle backscatter is presented, being independent on assumptions on the atmospheric state and eliminating the drawbacks of conventional aircraft probes by providing a different measurement principle. The concept is based on a laser emitting laser pulses into the atmosphere through a window and detecting the signals backscattered from a fixed region just outside the disturbed area of the fuselage flows. With four receiver channels, different spectral portions of the backscattered light are extracted. The measurement principle of air temperature and density is based on extracting two signals out of the rotational Raman (RR) backscatter signal of air molecules. For measuring the water vapor mixing ratio-and thus the density of the moist air-a water vapor Raman channel is included. The fourth channel serves to detect the elastic backscatter signal, which is essential for extending the measurements into clouds. This channel contributes to the detection of aerosols, which is interesting for developing a future volcanic ash warning system for aircraft. Detailed and realistic optimization and performance calculations have been performed based on the parameters of a first prototype of such a measurement system. The impact and correction of systematic error sources, such as solar background at daytime and elastic signal cross talk appearing in optically dense clouds, have been investigated. The results of the simulations show the high potential of the proposed system for

  17. Influence of population density and temporal variations in emissions on the air duality benefits of NOx emission trading.

    PubMed

    Nobel, Carolyn E; McDonald-Buller, Elena C; Kimura, Yosuke; Lumbley, Katherine E; Allen, David T

    2002-08-15

    Ozone formation is a complex function of local hydrocarbon and nitrogen oxide emissions. Therefore, trading of NOx emissions among geographically distributed facilities can lead to more or less ozone formation than across-the-board reductions. Monte Carlo simulations of trading scenarios involving 51 large NOx point sources in eastern Texas were used in a previous study by the authors to assess the effects of trading on air quality benefits, as measured by changes in ozone concentrations. The results indicated that 12% of trading scenarios would lead to greater than a 25% variation from conventional across-the-board reductions when air quality benefits are based only on changes in ozone concentration. The current study found that when benefits are based on a metric related to population exposure to ozone, two-thirds of the trading scenarios lead to changes in air quality benefits of approximately 25%. Variability in air quality benefits is not as strongly dependent on the temporal distribution of NOx emissions.

  18. [Spatiotempaoral distribution patterns of photosynthetic photon flux density, air temperature, and relative air humidity in forest gap of Pinus koraiensis-dominated broadleaved mixed forest in Xi-ao Xing' an Mountains].

    PubMed

    Li, Meng; Duan, Wen-biao; Chen, Li-xin

    2009-12-01

    A continuous measurement of photosynthetic photon flux density (PPFD), air temperature, and relative air humidity was made in the forest gap in primary Pinus koraiensis-dominated broadleaved mixed forest in Xiao Xing' an Mountains to compare the spatiotemporal distribution patterns of the parameters. The diurnal maximum PPFD in the forest gap appeared between 11:00 and 13:00 on sunny and overcast days. On sunny days, the maximum PPFD during various time periods did not locate in fixed locations, the diurnal maximum PPFD occurred in the canopy edge of northern part of the gap; while on overcast days, it always occurred in the center of the gap. The mean monthly PPFD in the gap was the highest in June and the lowest in September, with the largest range observed in July. The maximum air temperature happened between 9:00 and 15:00 on sunny days, between 15:00 and 19:00 on overcast days, the locations were 8 m in the southern part of gap center both on sunny and overcast days. From 5:00 to 9:00, the air temperature at measured positions in the gap was higher on overcast days than on sunny days; but from 9:00 to 19:00, it was opposite. The mean monthly air temperature was the highest in June, and the lowest in September. The maximum relative humidity appeared between 5:00 and 9:00 on sunny and overcast days, and occurred in the canopy border of western part of the gap, with the relative air humidity on overcast days being always higher than that on sunny days. The mean monthly relative humidity was the highest in July, and the lowest in June. The heterogeneity of PPFD was higher on sunny days than on overcast days, but the heterogeneities of air temperature and relative humidity were not obvious. The maximum PPFD, air temperature, and relative humidity were not located in the same positions among different months during growing season. For mean monthly PPFD and air temperature, their variation gradient was higher in and around the center of gap; while for mean monthly

  19. The concept of fitness in fluctuating environments.

    PubMed

    Sæther, Bernt-Erik; Engen, Steinar

    2015-05-01

    Fitness is a central concept in evolutionary biology, but there is no unified definition. We review recent theoretical developments showing that including fluctuating environments and density dependence has important implications for how differences among phenotypes in their contributions to future generations should be quantified. The rate of phenotypic evolution will vary through time because of environmental stochasticity. Density dependence may produce fluctuating selection for large growth rates at low densities but for larger carrying capacities when population sizes are large. In general, including ecologically realistic assumptions when defining the concept of fitness is crucial for estimating the potential of evolutionary rescue of populations affected by environmental perturbations such as climate change. PMID:25843273

  20. Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

    NASA Astrophysics Data System (ADS)

    Marchal, F.; Yousfi, M.; Merbahi, N.; Wattieaux, G.; Piquemal, A.

    2016-03-01

    Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave (MW) resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence (TALIF) using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy (OES). In this case, we compared the spectra intensities of a specific atomic oxygen line (844 nm) and the closest wavelength xenon line (823 nm). The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon (1% Xe) of this chemically inert gas inside the air while a further small quantity of H2 (2%) is also added in the mixture in order to collect OH(A-X) and NH(A-X) spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09×1017±0.2×1017 cm-3. This is in very good agreement with the TALIF measurement, which is equal to 2.0×1017 cm-3.

  1. K/pi Fluctuations at relativistic energies.

    PubMed

    Abelev, B I; Aggarwal, M M; Ahammed, Z; Anderson, B D; Arkhipkin, D; Averichev, G S; Balewski, J; Barannikova, O; Barnby, L S; Baudot, J; Baumgart, S; Beavis, D R; Bellwied, R; Benedosso, F; Betancourt, M J; Betts, R R; Bhasin, A; Bhati, A K; Bichsel, H; Bielcik, J; Bielcikova, J; Biritz, B; Bland, L C; Bombara, M; Bonner, B E; Botje, M; Bouchet, J; Braidot, E; Brandin, A V; Bruna, E; Bueltmann, S; Burton, T P; Bystersky, M; Cai, X Z; Caines, H; de la Barca Sánchez, M Calderón; Catu, O; Cebra, D; Cendejas, R; Cervantes, M C; Chajecki, Z; Chaloupka, P; Chattopadhyay, S; Chen, H F; Chen, J H; Chen, J Y; Cheng, J; Cherney, M; Chikanian, A; Choi, K E; Christie, W; Clarke, R F; Codrington, M J M; Corliss, R; Cormier, T M; Cosentino, M R; Cramer, J G; Crawford, H J; Das, D; Das, S; Dash, S; Daugherity, M; De Silva, L C; Dedovich, T G; DePhillips, M; Derevschikov, A A; de Souza, R Derradi; Didenko, L; Djawotho, P; Dogra, S M; Dong, X; Drachenberg, J L; Draper, J E; Dunlop, J C; Mazumdar, M R Dutta; Edwards, W R; Efimov, L G; Elhalhuli, E; Elnimr, M; Emelianov, V; Engelage, J; Eppley, G; Erazmus, B; Estienne, M; Eun, L; Fachini, P; Fatemi, R; Fedorisin, J; Feng, A; Filip, P; Finch, E; Fine, V; Fisyak, Y; Gagliardi, C A; Gaillard, L; Gangadharan, D R; Ganti, M S; Garcia-Solis, E J; Geromitsos, A; Geurts, F; Ghazikhanian, V; Ghosh, P; Gorbunov, Y N; Gordon, A; Grebenyuk, O; Grosnick, D; Grube, B; Guertin, S M; Guimaraes, K S F F; Gupta, A; Gupta, N; Guryn, W; Haag, B; Hallman, T J; Hamed, A; Harris, J W; He, W; Heinz, M; Heppelmann, S; Hippolyte, B; Hirsch, A; Hjort, E; Hoffman, A M; Hoffmann, G W; Hofman, D J; Hollis, R S; Huang, H Z; Humanic, T J; Huo, L; Igo, G; Iordanova, A; Jacobs, P; Jacobs, W W; Jakl, P; Jena, C; Jin, F; Jones, C L; Jones, P G; Joseph, J; Judd, E G; Kabana, S; Kajimoto, K; Kang, K; Kapitan, J; Keane, D; Kechechyan, A; Kettler, D; Khodyrev, V Yu; Kikola, D P; Kiryluk, J; Kisiel, A; Klein, S R; Knospe, A G; Kocoloski, A; Koetke, D D; Kopytine, M; Korsch, W; Kotchenda, L; Kouchpil, V; Kravtsov, P; Kravtsov, V I; Krueger, K; Krus, M; Kuhn, C; Kumar, L; Kurnadi, P; Lamont, M A C; Landgraf, J M; LaPointe, S; Lauret, J; Lebedev, A; Lednicky, R; Lee, C-H; Lee, J H; Leight, W; LeVine, M J; Li, C; Li, N; Li, Y; Lin, G; Lindenbaum, S J; Lisa, M A; Liu, F; Liu, J; Liu, L; Ljubicic, T; Llope, W J; Longacre, R S; Love, W A; Lu, Y; Ludlam, T; Ma, G L; Ma, Y G; Mahapatra, D P; Majka, R; Mall, O I; Mangotra, L K; Manweiler, R; Margetis, S; Markert, C; Matis, H S; Matulenko, Yu A; McDonald, D; McShane, T S; Meschanin, A; Milner, R; Minaev, N G; Mioduszewski, S; Mischke, A; Mohanty, B; Morozov, D A; Munhoz, M G; Nandi, B K; Nattrass, C; Nayak, T K; Nelson, J M; Netrakanti, P K; Ng, M J; Nogach, L V; Nurushev, S B; Odyniec, G; Ogawa, A; Okada, H; Okorokov, V; Olson, D; Pachr, M; Page, B S; Pal, S K; Pandit, Y; Panebratsev, Y; Pawlak, T; Peitzmann, T; Perevoztchikov, V; Perkins, C; Peryt, W; Phatak, S C; Pile, P; Planinic, M; Pluta, J; Plyku, D; Poljak, N; Poskanzer, A M; Potukuchi, B V K S; Prindle, D; Pruneau, C; Pruthi, N K; Pujahari, P R; Putschke, J; Raniwala, R; Raniwala, S; Redwine, R; Reed, R; Ridiger, A; Ritter, H G; Roberts, J B; Rogachevskiy, O V; Romero, J L; Rose, A; Roy, C; Ruan, L; Russcher, M J; Sahoo, R; Sakrejda, I; Sakuma, T; Salur, S; Sandweiss, J; Sarsour, M; Schambach, J; Scharenberg, R P; Schmitz, N; Seger, J; Selyuzhenkov, I; Seyboth, P; Shabetai, A; Shahaliev, E; Shao, M; Sharma, M; Shi, S S; Shi, X-H; Sichtermann, E P; Simon, F; Singaraju, R N; Skoby, M J; Smirnov, N; Snellings, R; Sorensen, P; Sowinski, J; Spinka, H M; Srivastava, B; Stadnik, A; Stanislaus, T D S; Staszak, D; Strikhanov, M; Stringfellow, B; Suaide, A A P; Suarez, M C; Subba, N L; Sumbera, M; Sun, X M; Sun, Y; Sun, Z; Surrow, B; Symons, T J M; de Toledo, A Szanto; Takahashi, J; Tang, A H; Tang, Z; Tarini, L H; Tarnowsky, T; Thein, D; Thomas, J H; Tian, J; Timmins, A R; Timoshenko, S; Tlusty, D; Tokarev, M; Tram, V N; Trattner, A L; Trentalange, S; Tribble, R E; Tsai, O D; Ulery, J; Ullrich, T; Underwood, D G; Van Buren, G; van Leeuwen, M; Molen, A M Vander; Vanfossen, J A; Varma, R; Vasconcelos, G M S; Vasilevski, I M; Vasiliev, A N; Videbaek, F; Vigdor, S E; Viyogi, Y P; Vokal, S; Voloshin, S A; Wada, M; Walker, M; Wang, F; Wang, G; Wang, J S; Wang, Q; Wang, X; Wang, X L; Wang, Y; Webb, G; Webb, J C; Westfall, G D; Whitten, C; Wieman, H; Wissink, S W; Witt, R; Wu, Y; Xie, W; Xu, N; Xu, Q H; Xu, Y; Xu, Z; Yang, P; Yepes, P; Yip, K; Yoo, I-K; Yue, Q; Zawisza, M; Zbroszczyk, H; Zhan, W; Zhang, S; Zhang, W M; Zhang, X P; Zhang, Y; Zhang, Z P; Zhao, Y; Zhong, C; Zhou, J; Zoulkarneev, R; Zoulkarneeva, Y; Zuo, J X

    2009-08-28

    We report K/pi fluctuations from Au + Au collisions at sqrt[s(NN)]= 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. K/pi fluctuations in central collisions show little dependence on incident energy and are on the same order as those from NA49 at the Super Proton Synchrotron in central Pb + Pb collisions at sqrt[s(NN)]=12.3 and 17.3 GeV. We report results for the collision centrality dependence of K/pi fluctuations and results for charge-separated fluctuations. We observe that the K/pi fluctuations scale with the charged particle multiplicity density. PMID:19792791

  2. Proteins, fluctuations and complexity

    SciTech Connect

    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.

  3. The impacts of replacing air bubbles with microspheres for the clarification of algae from low cell-density culture.

    PubMed

    Ometto, Francesco; Pozza, Carlo; Whitton, Rachel; Smyth, Beatrice; Gonzalez Torres, Andrea; Henderson, Rita K; Jarvis, Peter; Jefferson, Bruce; Villa, Raffaella

    2014-04-15

    Dissolved Air Flotation (DAF) is a well-known coagulation-flotation system applied at large scale for microalgae harvesting. Compared to conventional harvesting technologies DAF allows high cell recovery at lower energy demand. By replacing microbubbles with microspheres, the innovative Ballasted Dissolved Air Flotation (BDAF) technique has been reported to achieve the same algae cell removal efficiency, while saving up to 80% of the energy required for the conventional DAF unit. Using three different algae cultures (Scenedesmus obliquus, Chlorella vulgaris and Arthrospira maxima), the present work investigated the practical, economic and environmental advantages of the BDAF system compared to the DAF system. 99% cells separation was achieved with both systems, nevertheless, the BDAF technology allowed up to 95% coagulant reduction depending on the algae species and the pH conditions adopted. In terms of floc structure and strength, the inclusion of microspheres in the algae floc generated a looser aggregate, showing a more compact structure within single cell alga, than large and filamentous cells. Overall, BDAF appeared to be a more reliable and sustainable harvesting system than DAF, as it allowed equal cells recovery reducing energy inputs, coagulant demand and carbon emissions.

  4. Evaluation of High Density Air Traffic Operations with Automation for Separation Assurance, Weather Avoidance and Schedule Conformance

    NASA Technical Reports Server (NTRS)

    Prevot, Thomas; Mercer, Joey S.; Martin, Lynne Hazel; Homola, Jeffrey R.; Cabrall, Christopher D.; Brasil, Connie L.

    2011-01-01

    In this paper we discuss the development and evaluation of our prototype technologies and procedures for far-term air traffic control operations with automation for separation assurance, weather avoidance and schedule conformance. Controller-in-the-loop simulations in the Airspace Operations Laboratory at the NASA Ames Research Center in 2010 have shown very promising results. We found the operations to provide high airspace throughput, excellent efficiency and schedule conformance. The simulation also highlighted areas for improvements: Short-term conflict situations sometimes resulted in separation violations, particularly for transitioning aircraft in complex traffic flows. The combination of heavy metering and growing weather resulted in an increased number of aircraft penetrating convective weather cells. To address these shortcomings technologies and procedures have been improved and the operations are being re-evaluated with the same scenarios. In this paper we will first describe the concept and technologies for automating separation assurance, weather avoidance, and schedule conformance. Second, the results from the 2010 simulation will be reviewed. We report human-systems integration aspects, safety and efficiency results as well as airspace throughput, workload, and operational acceptability. Next, improvements will be discussed that were made to address identified shortcomings. We conclude that, with further refinements, air traffic control operations with ground-based automated separation assurance can routinely provide currently unachievable levels of traffic throughput in the en route airspace.

  5. Stress fluctuations in drying polymer dispersions.

    PubMed

    König, Alexander M; Johannsmann, Diethelm

    2010-06-15

    Drying polymer dispersions usually experience tensile stress, induced by the reduction in volume and by the rigid substrate. Due to edge-in drying, the stress is usually heterogeneous over the film. Stress peaks play a decisive role in the formation of cracks. This work relies on membrane bending, a technique that provides spatially resolved stress maps. In the experiments reported here, stress fluctuations on the order of 10% on the time scale of a few seconds were found. The stress fluctuations occur coherently over the entire drying front. Fluctuations go back to slight fluctuations in humidity of the environment (as opposed to local stress relaxations due to reorganizations of the particle network). The stress fluctuations disappear when covering the sample with a lid. They can be enhanced by blowing humid or dry air across the sample surface. Modeling builds on the assumption that all stresses go back to capillary pressure created at the menisci in between different spheres at the film-air interface. The local radius of curvature changes in response to slight variations in ambient humidity according to the Kelvin equation. The fluctuations are observed under a wide variety of drying conditions and should be included in film formation models.

  6. Fluctuation relations for spintronics.

    PubMed

    López, Rosa; Lim, Jong Soo; Sánchez, David

    2012-06-15

    Fluctuation relations are derived in systems where the spin degree of freedom and magnetic interactions play a crucial role. The form of the nonequilibrium fluctuation theorems relies on the assumption of a local balance condition. We demonstrate that in some cases the presence of magnetic interactions violates this condition. Nevertheless, fluctuation relations can be obtained from the microreversibility principle sustained only at equilibrium as a symmetry of the cumulant generating function for spin currents. We illustrate the spintronic fluctuation relations for a quantum dot coupled to partially polarized helical edge states.

  7. Strange fluctuations at RHIC

    NASA Astrophysics Data System (ADS)

    Abdel Aziz, Mohamed; Gavin, Sean

    2004-01-01

    Net charge fluctuations measured by the STAR experiment at RHIC agree with hadronic event generators, suggesting that more sensitive fluctuation observables are needed to extract information on collision dynamics. Important information on isospin fluctuations can be extracted from K0SK± measurements. Gavin and Kapusta proposed that disoriented chiral condensate can produce extraordinary isospin fluctuations in both strange and non-strange mesons. However, even in the absence of such a contribution, we argue that this observable is very sensitive to the collision dynamics.

  8. Air stable n-doping of WSe{sub 2} by silicon nitride thin films with tunable fixed charge density

    SciTech Connect

    Chen, Kevin; Kiriya, Daisuke; Hettick, Mark; Tosun, Mahmut; Ha, Tae-Jun; Madhvapathy, Surabhi Rao; Desai, Sujay; Sachid, Angada; Javey, Ali

    2014-09-01

    Stable n-doping of WSe{sub 2} using thin films of SiN{sub x} deposited on the surface via plasma-enhanced chemical vapor deposition is presented. Positive fixed charge centers inside SiN{sub x} act to dope WSe{sub 2} thin flakes n-type via field-induced effect. The electron concentration in WSe{sub 2} can be well controlled up to the degenerate limit by simply adjusting the stoichiometry of the SiN{sub x} through deposition process parameters. For the high doping limit, the Schottky barrier width at the metal/WSe{sub 2} junction is significantly thinned, allowing for efficient electron injection via tunneling. Using this doping scheme, we demonstrate air-stable WSe{sub 2} n-MOSFETs with a mobility of ∼70 cm{sup 2}/V s.

  9. Creation of the reduced-density region by a pulsing optical discharge in the supersonic air flow

    NASA Astrophysics Data System (ADS)

    Kiseleva, T. A.; Orishich, A. M.; Chirkashenko, V. F.; Yakovlev, V. I.

    2016-10-01

    As a result of optical and pneumometric measurements is defined the flow shock wave structure that is formed by the optical breakdown, due to focused repetitively pulsed CO2 laser radiation when entering perpendicular to a supersonic (M = 1.36, 1.9) air flow direction. The dynamics of the bow shock formation in front of the energy input area is shown, depending on the frequency of energy impulse sequence. A flow structure is defined in the thermal wake behind pulsing laser plasma as well as wake's length with low thermal heterogeneity. A three-dimensional configuration of the energy area is defined in accordance with pneumometric and optical measuring results. It is shown that Pitot pressure decreases in thermal wake at a substantially constant static pressure, averaged flow parameters weakly depend on the energy impulse's frequency in range of 45-150 kHz.

  10. Fluctuations and symmetry energy in nuclear fragmentation dynamics.

    PubMed

    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.

  11. Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations

    NASA Astrophysics Data System (ADS)

    Pokharel, Rajendra; Gavin, Sean; Moschelli, George

    2012-10-01

    Interest in the development of the theory of fluctuating hydrodynamics is growing [1]. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations [2]. That work stimulated an experimental analysis by STAR [3]. We attack this new data along two fronts. First, we compute STAR's fluctuation observable using the NeXSPheRIO code, which combines fluctuating initial conditions from a string fragmentation model with deterministic viscosity-free hydrodynamic evolution. We find that NeXSPheRIO produces a longitudinal narrowing, in contrast to the data. Second, we study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute STAR's observable. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion. [4pt] [1] J. Kapusta, B. Mueller, M. Stephanov, arXiv:1112.6405 [nucl-th].[0pt] [2] S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97, 162302 (2006)[0pt] [3] H. Agakishiev et al., STAR, STAR, Phys. Lett. B704

  12. Note: On the measurement of plasma potential fluctuations using emissive probes

    SciTech Connect

    Bousselin, G. Lemoine, N.; Cavalier, J.; Heuraux, S.; Bonhomme, G.

    2014-05-15

    In this Note, it is pointed out that emissive probes cannot be used to directly and reliably measure plasma potential fluctuations. An experimentally validated model demonstrates indeed that the floating potential fluctuations of an emissive probe which floats at the mean plasma potential depend not only on the plasma potential fluctuations but also on electron density and temperature fluctuations.

  13. Mesoscale Temperature Fluctuations in the Southern Hemisphere Stratosphere

    NASA Technical Reports Server (NTRS)

    Gary, Bruce L.

    2008-01-01

    Isentrope surfaces in the Southern Hemisphere stratosphere reveal that air parcels undergo mesoscale temperature fluctuations that depend on latitude and season. The largest temperature fluctuations occur at high latitude winter, whereas the smallest fluctuations occur at high latitude summer. This is the same pattern found for the Northern Hemisphere stratosphere. However, the amplitude of the seasonal dependence in the Southern Hemisphere is only 37% of the Northern Hemisphere's seasonal amplitude.

  14. Adiabatic fluctuations from cosmic strings in a contracting universe

    SciTech Connect

    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.

  15. Toward a unified picture of the water self-ions at the air-water interface: a density functional theory perspective.

    PubMed

    Baer, Marcel D; Kuo, I-Feng W; Tobias, Douglas J; Mundy, Christopher J

    2014-07-17

    The propensities of the water self-ions, H3O(+) and OH(-), for the air-water interface have implications for interfacial acid-base chemistry. Despite numerous experimental and computational studies, no consensus has been reached on the question of whether or not H3O(+) and/or OH(-) prefer to be at the water surface or in the bulk. Here we report a molecular dynamics simulation study of the bulk vs interfacial behavior of H3O(+) and OH(-) that employs forces derived from density functional theory with a generalized gradient approximation exchange-correlation functional (specifically, BLYP) and empirical dispersion corrections. We computed the potential of mean force (PMF) for H3O(+) as a function of the position of the ion in the vicinity of an air-water interface. The PMF suggests that H3O(+) has equal propensity for the interface and the bulk. We compare the PMF for H3O(+) to our previously computed PMF for OH(-) adsorption, which contains a shallow minimum at the interface, and we explore how differences in solvation of each ion at the interface vs in the bulk are connected with interfacial propensity. We find that the solvation shell of H3O(+) is only slightly dependent on its position in the water slab, while OH(-) partially desolvates as it approaches the interface, and we examine how this difference in solvation behavior is manifested in the electronic structure and chemistry of the two ions.

  16. Spatial fluctuation theorem

    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.

  17. A density functional theory based study of the electron transfer reaction at the cathode-electrolyte interface in lithium-air batteries.

    PubMed

    Kazemiabnavi, Saeed; Dutta, Prashanta; Banerjee, Soumik

    2015-05-01

    The unique properties of ionic liquids such as a relatively wide electrochemical stability window and very low vapor pressure have made them promising candidates as electrolytes for improving the cyclic performance of lithium-air batteries. The local current density, which is an important parameter in determining the performance of lithium-air batteries, is a function of the rate constant of the electron transfer reactions at the surface of the cathode. In this study, a novel method based on Marcus theory is presented to investigate the effect of varying the length of the alkyl side chain of model imidazolium based cations and the operating temperature on the rates of electron transfer reactions at the cathode. The necessary free energies of all the species involved in the multi-step reduction of oxygen into the peroxide ion were calculated using density functional theory (DFT). Our results indicate that the magnitude of the Gibbs free energy for the reduction of oxygen into the superoxide ion and also for the reduction of superoxide into the peroxide ion increases with an increase in the static dielectric constant of the ionic liquid. This trend in turn corresponds to the decrease in the length of the alkyl side chain of the ionic liquid cation. Furthermore, the change in Gibbs free energy decreases with increase in the operating temperature. The inner-sphere reorganization energies were evaluated using Nelsen's four point method. The total reorganization energies of all reduction reactions increase with decrease in the length of the alkyl side chain and increase in the operating temperature. Finally, the rate constants of the electron transfer reaction involved in the reduction of oxygen were calculated. The logarithm of the reaction rate constants decreases with increase in the static dielectric constant and increases with increase in the operating temperature. Our results provide fundamental insight into the kinetics and thermodynamics of the electron transfer

  18. A density functional theory based study of the electron transfer reaction at the cathode-electrolyte interface in lithium-air batteries.

    PubMed

    Kazemiabnavi, Saeed; Dutta, Prashanta; Banerjee, Soumik

    2015-05-01

    The unique properties of ionic liquids such as a relatively wide electrochemical stability window and very low vapor pressure have made them promising candidates as electrolytes for improving the cyclic performance of lithium-air batteries. The local current density, which is an important parameter in determining the performance of lithium-air batteries, is a function of the rate constant of the electron transfer reactions at the surface of the cathode. In this study, a novel method based on Marcus theory is presented to investigate the effect of varying the length of the alkyl side chain of model imidazolium based cations and the operating temperature on the rates of electron transfer reactions at the cathode. The necessary free energies of all the species involved in the multi-step reduction of oxygen into the peroxide ion were calculated using density functional theory (DFT). Our results indicate that the magnitude of the Gibbs free energy for the reduction of oxygen into the superoxide ion and also for the reduction of superoxide into the peroxide ion increases with an increase in the static dielectric constant of the ionic liquid. This trend in turn corresponds to the decrease in the length of the alkyl side chain of the ionic liquid cation. Furthermore, the change in Gibbs free energy decreases with increase in the operating temperature. The inner-sphere reorganization energies were evaluated using Nelsen's four point method. The total reorganization energies of all reduction reactions increase with decrease in the length of the alkyl side chain and increase in the operating temperature. Finally, the rate constants of the electron transfer reaction involved in the reduction of oxygen were calculated. The logarithm of the reaction rate constants decreases with increase in the static dielectric constant and increases with increase in the operating temperature. Our results provide fundamental insight into the kinetics and thermodynamics of the electron transfer

  19. Colloid mobilization and transport during capillary fringe fluctuations.

    PubMed

    Aramrak, Surachet; Flury, Markus; Harsh, James B; Zollars, Richard L

    2014-07-01

    Capillary fringe fluctuations due to changing water tables lead to displacement of air-water interfaces in soils and sediments. These moving air-water interfaces can mobilize colloids. We visualized colloids interacting with moving air-water interfaces during capillary fringe fluctuations by confocal microscopy. We simulated capillary fringe fluctuations in a glass-bead-filled column. We studied four specific conditions: (1) colloids suspended in the aqueous phase, (2) colloids attached to the glass beads in an initially wet porous medium, (3) colloids attached to the glass beads in an initially dry porous medium, and (4) colloids suspended in the aqueous phase with the presence of a static air bubble. Confocal images confirmed that the capillary fringe fluctuations affect colloid transport behavior. Hydrophilic negatively charged colloids initially suspended in the aqueous phase were deposited at the solid-water interface after a drainage passage, but then were removed by subsequent capillary fringe fluctuations. The colloids that were initially attached to the wet or dry glass bead surface were detached by moving air-water interfaces in the capillary fringe. Hydrophilic negatively charged colloids did not attach to static air-bubbles, but hydrophobic negatively charged and hydrophilic positively charged colloids did. Our results demonstrate that capillary fringe fluctuations are an effective means for colloid mobilization.

  20. Neutrino propagation in a fluctuating sun

    SciTech Connect

    Burgess, C.P.; Michaud, D.

    1997-05-01

    We adapt to neutrino physics a general formulation for particle propagation in fluctuating media, initially developed for applications to electromagnetism and neutron optics. In leading approximation this formalism leads to the usual MSW effective Hamiltonian governing neutrino propagation through a medium. Next-to-leading contributions describe deviations from this description, which arise due to neutrino interactions with fluctuations in the medium. We compute these corrections for two types of fluctuations: (i) microscopic thermal fluctuations and (ii) macroscopic fluctuations in the medium{close_quote}s density. While the first of these reproduces standard estimates, which are negligible for applications to solar neutrinos, we find that the second can be quite large, since it grows in size with the correlation length of the fluctuation. We consider two models in some detail. For fluctuations whose correlations extend only over a local region in space of length l, appreciable effects for MSW oscillations arise if ({delta}n/n){sup 2}l{approx_gt}100m or so. Alternatively, a crude model of helioseismic p-waves gives appreciable effects only when ({delta}n/n){approx_gt}1{percent}. In general the dominant effect is to diminish the quality of the resonance, making the suppression of the {sup 7}Be neutrinos a good experimental probe of fluctuations deep within the sun. Fluctuations can also provide a new mechanism for reducing the solar neutrino flux, giving an energy-independent suppression factor of 1/2 away from the resonant region, even for small vacuum mixing angles. {copyright} 1997 Academic Press, Inc.

  1. Fluctuations In Electrohydrodynamic Instability

    NASA Astrophysics Data System (ADS)

    Bianco, Francesco; Lucchesi, Mauro; Capaccioli, Simone; Fronzoni, Leone; Allegrini, Paolo

    2005-11-01

    Electrohydrodynamic Convection in Liquid Crystals (EHC) is a good system for the experimental study of spatio-temporal chaos. Particularly interesting is the behavior of the Nematic in presence of weak turbulence where ordered and disordered states are mixed. In this case, the fluctuations of velocity and electric current, for instance, are typical fluctuations of a system far from equilibrium. Recently some authors have analyzed the amplitude of the fluctuations as function of the applied electric field and they present interesting interpretations provided by some theories. Although important results have been obtained by these authors, many aspects of the dynamical behavior have to be further analyzed as the role of some localized coherences inside the turbulence regions. The direct optical observation allows us to make a correspondence between fluctuations and patterns, providing important information for a theoretical interpretation.

  2. Fluctuation theory of critical phenomena in fluids

    NASA Astrophysics Data System (ADS)

    Martynov, G. A.

    2016-07-01

    It is assumed that critical phenomena are generated by density wave fluctuations carrying a certain kinetic energy. It is noted that all coupling equations for critical indices are obtained within the context of this hypothesis. Critical indices are evaluated for 15 liquids more accurately than when using the current theory of critical phenomena.

  3. Molecular Rayleigh Scattering Diagnostic for Dynamic Temperature, Velocity, and Density Measurements

    NASA Technical Reports Server (NTRS)

    Mielke, Amy R.; Elam, Kristie A.; Sung, Chi-Jen

    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 16 kHz. A high power CW laser beam is focused at a point in an air jet plume and Rayleigh scattered light is collected and spectrally resolved. The spectrum of the light, which contains information about the temperature and velocity 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 16 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. A low speed heated jet is used to validate the measurement of temperature fluctuations and an acoustically excited nozzle flow is studied to validate velocity fluctuation measurements. Power spectral density calculations of the property fluctuations, as well as mean and fluctuating quantities are presented. Temperature fluctuation results are compared with constant current anemometry measurements and velocity fluctuation results are compared with constant temperature anemometry measurements at the same locations.

  4. Microscale Pressure Fluctuations Within a Deciduous Forest

    NASA Astrophysics Data System (ADS)

    Sigmon, John Thomas

    Attempts to evaluate sources of errors in estimates of fluxes from forested surfaces have been thwarted by the lack of an accurate description of the nature of air flow within forest canopies. An important property of any boundary layer flow is the occurrence of pressure fluctuations at the boundary and within the flow. This study was designed to provide an understanding of the microscale pressure fluctuations within a forest canopy and the relationship between these fluctuations and the air flow within and above the forest canopy. Pressure fluctuations were measured using a method similar to that developed by J. A. Elliott in 1972. Measurements were taken at the ground and above a deciduous forest canopy. Time series, spectra, and cross-correlations were calculated under different canopy conditions, and relationships between surface pressure fluctuations and mean windspeeds were determined. Turbulent pressure fluctuations at the forest floor did not contain the higher frequencies found over smooth terrain and were continuously occurring at frequencies greater than 0.5 Hz. Somewhat higher frequencies and larger amplitudes occurred in the pressure fluctuations above the canopy after leaf emergence than at the surface. Horizontal length scales many times larger than the average spacing of the overstory trees were predominant. While both leaf emergence of flow-through from an adjacent field had an effect on the mean windspeed profiles, only the flow-through conditions had an effect on the relationship of mean windspeed above the canopy to pressure fluctuation variance at the surface. Pressure fluctuations at the surface appeared coupled at all times to those above the canopy and were directly related to windspeed above the canopy. Pressure eddies were advected downwind at speeds approximating the mean windspeed 6-8 meters above the canopy. Shapes of the pressure spectra were affected slightly by changes in windspeed, and comparisons of spectra above and below the

  5. Scalar fluctuations in turbulent combustion - An experimental study

    NASA Astrophysics Data System (ADS)

    Ballal, D. R.; Chen, T. H.; Yaney, P. P.

    1986-01-01

    Temperature and velocity fluctuations data were gathered for turbulent premixed combustion to evaluate a model for scalar transport and scalar dissipation. The data were collected using laser Raman spectroscopy and laser Doppler anemometry with a premixed CH4-air flame from a Bunsen burner. Mean temperature profiles were generated and the pdf's temperature fluctuations were calculated. A wrinkled laminar flame structure was noted in the reaction zone, where the scalar field was anisotropic and where the temperature fluctuations exhibited peak values. The Bray, Moss and Libby model (1985) was successful in predicting the temperature fluctuation intensity and the dissipation ratios, the latter reaching peak values in the flame tip region.

  6. On zero frequency magnetic fluctuations in plasmas

    SciTech Connect

    Tajima, T.; Cable, S. . Inst. for Fusion Studies); Kulsrud, R.M. . Dept. of Astrophysical Sciences)

    1992-01-01

    A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy lost'' by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l angle}B{sup 2}{r angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.

  7. On zero frequency magnetic fluctuations in plasmas

    SciTech Connect

    Tajima, T.; Cable, S.; Kulsrud, R.M.

    1992-01-01

    A plasma sustains fluctuations of electromagnetic fields and particle density even in a thermal equilibrium and such fluctuations have a large zero frequency peak. The level of fluctuations in the plasma for a given wavelength and frequency of electromagnetic fields is calculated through the fluctuation-dissipation theorem. The frequency spectrum shows that the energy contained in this peak is complementary to the energy ``lost`` by the plasma cutoff effect. The level of the zero (or nearly zero) frequency magnetic is computed as {l_angle}B{sup 2}{r_angle}{sup 0}/ 8{pi} = 1/2{pi}{sup 3}T({omega}{sub p}/c){sup 3}, where T and {omega}{sub p} are the temperature and plasma frequency. The relation between the nonradiative and radiative fluctuations is elucidated. Both a simple collision model and a kinetic theoretic treatment are presented with essentially the same results. The size of the fluctuations is {lambda} {approximately} (c/{omega}{sub p})({eta}/{omega}){sup {1/2}}, where {eta} and {omega} are the collision frequency and the (nearly zero) frequency of magnetic fields oscillations. Perhaps the most dramatic application of the present theory, however, is to the cosmological plasma of early epoch. Implications of these magnetic fields in the early Universe are discussed. Quantum mechanical calculations are also carried out for degenerate plasmas.

  8. The perfect ash-storm: large-scale Pyroclastic Density Current experiments reveal highly mobile, self-fluidising and air-cushioned flow transport regime

    NASA Astrophysics Data System (ADS)

    Lube, G.; Cronin, S. J.; Breard, E.; Valentine, G.; Bursik, M. I.; Hort, M. K.; Freundt, A.

    2013-12-01

    We report on the first systematic series of large-scale Pyroclastic Density Current (PDC) experiments using the New Zealand PDC Generator, a novel international research facility in Physical Volcanology recently commissioned at Massey University. Repeatable highly energetic and hot PDCs are synthesized by the controlled ';eruption column-collapse' of up to 3500 kg of homogenously aerated Taupo ignimbrite material from a 15 m-elevated hopper onto an instrumented inclined flume. At discharge rates between 250-1300 kg/s and low- to moderate gas injection rates (yielding initial solids concentration of 15-70 vol%) channelized gas-particle mixture flows life-scaled to dense PDCs can be generated. The flow fronts of the currents reach velocities of up to 9.5 m/s over their first 12 m of travel and rapidly develop strong vertical density stratification. The PDCs typically form a highly mobile, <60 cm-thick dense and channel-confined underflow, with an overriding dilute and turbulent ash cloud surge that also laterally escapes the flume boundaries. Depending on the PDC starting conditions underflows with 1-45 vol% solids concentration are formed, while the upper surge contains <<1 vol.% solids. A characteristic feature of the underflow is the occurrence of 'ignitive' front breakouts, producing jetted lobes that accelerate outward from the flow front, initially forming a lobe-cleft structure, followed by segregation downslope into multiple flow pulses. Depending on initial solids concentration and discharge rate, stratified, dune-bedded and inversely graded bedforms are created whose thicknesses are remarkably uniform along the medial to distal runout path characterising highly mobile flow runout. Along with high-speed video footage we present time-series data of basal arrays of load- and gas-pore pressure transducers to characterise the mobile dense underflows. Data shows that the PDCs are comprised of a turbulent coarse-grained and air-ingesting front with particle

  9. Fluctuations in strongly coupled cosmologies

    SciTech Connect

    Bonometto, Silvio A.; Mainini, Roberto E-mail: mainini@mib.infn.it

    2014-03-01

    In the early Universe, a dual component made of coupled CDM and a scalar field Φ, if their coupling β > (3){sup 1/2}/2, owns an attractor solution, making them a stationary fraction of cosmic energy during the radiation dominated era. Along the attractor, both such components expand ∝a{sup −4} and have early density parameters Ω{sub d} = 1/(4β{sup 2}) and Ω{sub c} = 2 Ω{sub d} (field and CDM, respectively). In a previous paper it was shown that, if a further component, expanding ∝a{sup −3}, breaks such stationary expansion at z ∼ 3–5 × 10{sup 3}, cosmic components gradually acquire densities consistent with observations. This paper, first of all, considers the case that this component is warm. However, its main topic is the analysis of fluctuation evolution: out of horizon modes are then determined; their entry into horizon is numerically evaluated as well as the dependence of Meszaros effect on the coupling β; finally, we compute: (i) transfer function and linear spectral function; (ii) CMB C{sub l} spectra. Both are close to standard ΛCDM models; in particular, the former one can be so down to a scale smaller than Milky Way, in spite of its main DM component being made of particles of mass < 1 keV. The previously coupled CDM component, whose present density parameter is O(10{sup −3}), exhibits wider fluctuations δρ/ρ, but approximately β-independent δρ values. We discuss how lower scale features of these cosmologies might ease quite a few problems that ΛCDM does not easily solve.

  10. Fluctuating shells under pressure

    PubMed Central

    Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.

    2012-01-01

    Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558

  11. The effects of high energy electron beam irradiation in air on accelerated aging and on the structure property relationships of low density polyethylene

    NASA Astrophysics Data System (ADS)

    Murray, Kieran A.; Kennedy, James E.; McEvoy, Brian; Vrain, Olivier; Ryan, Damien; Cowman, Richard; Higginbotham, Clement L.

    2013-02-01

    The response of low density polyethylene (LDPE) to high energy electron beam irradiation in air (10 MeV) between 25 and 400 kGy was examined and compared to non-irradiated polyethylene in terms of the mechanical and structural properties. To quantify the degree of crosslinking, swelling studies were performed and from this it was observed that the crosslink density increased as the irradiation dose increased. Furthermore, a reduction was observed in the numerical data for molar mass between adjacent crosslinks and the number of monomeric units between adjacent crosslinks as the irradiation dose was conducted incrementally. Accelerated aging provided evidence that radicals became trapped in the polymer matrix of LDPE and this in turn initiated further reactions to transpire as time elapsed, leading to additional alteration in the structural properties. Fourier transform infrared spectroscopy (FTIR) was implemented to provide insight into this. This technique established that the aging process had increased the oxidative degradation products due to oxygen permeation into the polymer and double bonds within the material. Mechanical testing revealed an increase in the tensile strength and a decrease in the elongation at break. Accelerated aging caused additional modifications to occur in the mechanical properties which are further elucidated throughout this study. Dynamic frequency sweeps investigated the effects of irradiation on the structural properties of LDPE. The effect of varying the irradiation dose concentration was apparent as this controlled the level of crosslinking within the material. Maxwell and Kelvin or Voigt models were employed in this analytical technique to define the reaction procedure of the frequency sweep test with regards to non-crosslinked and crosslinked LDPE.

  12. Fluctuation of heat current in Josephson junctions

    SciTech Connect

    Virtanen, P.; Giazotto, F.

    2015-02-15

    We discuss the statistics of heat current between two superconductors at different temperatures connected by a generic weak link. As the electronic heat in superconductors is carried by Bogoliubov quasiparticles, the heat transport fluctuations follow the Levitov–Lesovik relation. We identify the energy-dependent quasiparticle transmission probabilities and discuss the resulting probability density and fluctuation relations of the heat current. We consider multichannel junctions, and find that heat transport in diffusive junctions is unique in that its statistics is independent of the phase difference between the superconductors.

  13. Density - Velocity Relationships in Explosive Volcanic Plumes

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Kobs-Nawotniak, S. E.

    2015-12-01

    Positively buoyant volcanic plumes rise until the bulk density of the plume is equal to the density of the ambient atmosphere. As ambient air mixes with the plume, it lowers the plume bulk density; thus, the plume is diluted enough to reach neutral density in a naturally stratified atmospheric environment. We produced scaled plumes in analogue laboratory experiments by injecting a saline solution with a tracer dye into distilled water, using a high-pressure injection system. We recorded each eruption with a CASIO HD digital camera and used ImageJ's FeatureJ Edge toolbox to identify individual eddies. We used an optical flow software based off the ImageJ toolbox FlowJ to determine the velocities along the edge of each eddy. Eddy densities were calculated by mapping the dye concentration to the RGB digital color value. We overlaid the eddy velocities over the densities in order to track the behavioral relationship between the two variables with regard to plume motion. As an eddy's bulk density decreases, the vertical velocity decreases; this is a result of decreased mass, and therefore momentum, in the eddy. Furthermore as the density rate of change increases, the eddy deceleration increases. Eddies are most dense at their top and least dense at their bottom. The less dense sections of the eddies have lower vertical velocities than the sections of the eddies with the higher densities, relating to the expanding radial size of an eddy as it rises and the preferential ingestion of ambient air at the base of eddies. Thus the mixing rate in volcanic plumes fluctuates not only as a function of height as described by the classic 1D entrainment hypothesis, but also as a function of position in an eddy itself.

  14. DBD Plasma Actuators for Flow Control in Air Vehicles and Jet Engines - Simulation of Flight Conditions in Test Chambers by Density Matching

    NASA Technical Reports Server (NTRS)

    Ashpis, David E.; Thurman, Douglas R.

    2011-01-01

    Dielectric Barrier Discharge (DBD) Plasma actuators for active flow control in aircraft and jet engines need to be tested in the laboratory to characterize their performance at flight operating conditions. DBD plasma actuators generate a wall-jet electronically by creating weakly ionized plasma, therefore their performance is affected by gas discharge properties, which, in turn, depend on the pressure and temperature at the actuator placement location. Characterization of actuators is initially performed in a laboratory chamber without external flow. The pressure and temperature at the actuator flight operation conditions need to be simultaneously set in the chamber. A simplified approach is desired. It is assumed that the plasma discharge depends only on the gas density, while other temperature effects are assumed to be negligible. Therefore, tests can be performed at room temperature with chamber pressure set to yield the same density as in operating flight conditions. The needed chamber pressures are shown for altitude flight of an air vehicle and for jet engines at sea-level takeoff and altitude cruise conditions. Atmospheric flight conditions are calculated from standard atmosphere with and without shock waves. The engine data was obtained from four generic engine models; 300-, 150-, and 50-passenger (PAX) aircraft engines, and a military jet-fighter engine. The static and total pressure, temperature, and density distributions along the engine were calculated for sea-level takeoff and for altitude cruise conditions. The corresponding chamber pressures needed to test the actuators were calculated. The results show that, to simulate engine component flows at in-flight conditions, plasma actuator should be tested over a wide range of pressures. For the four model engines the range is from 12.4 to 0.03 atm, depending on the placement of the actuator in the engine. For example, if a DBD plasma actuator is to be placed at the compressor exit of a 300 PAX engine, it

  15. Few-layer black phosphorus field-effect transistors with reduced current fluctuation.

    PubMed

    Na, Junhong; Lee, Young Tack; Lim, Jung Ah; Hwang, Do Kyung; Kim, Gyu-Tae; Choi, Won Kook; Song, Yong-Won

    2014-11-25

    We investigated the reduction of current fluctuations in few-layer black phosphorus (BP) field-effect transistors resulting from Al2O3 passivation. In order to verify the effect of Al2O3 passivation on device characteristics, measurements and analyses were conducted on thermally annealed devices before and after the passivation. More specifically, static and low-frequency noise analyses were used in monitoring the charge transport characteristics in the devices. The carrier number fluctuation (CNF) model, which is related to the charge trapping/detrapping process near the interface between the channel and gate dielectric, was employed to describe the current fluctuation phenomena. Noise reduction due to the Al2O3 passivation was expressed in terms of the reduced interface trap density values D(it) and N(it), extracted from the subthreshold slope (SS) and the CNF model, respectively. The deviations between the interface trap density values extracted using the SS value and CNF model are elucidated in terms of the role of the Schottky barrier between the few-layer BP and metal contact. Furthermore, the preservation of the Al2O3-passivated few-layer BP flakes in ambient air for two months was confirmed by identical Raman spectra.

  16. Faraday polarization fluctuations of satellite beacon signals

    NASA Technical Reports Server (NTRS)

    Lee, M. C.; Klobuchar, J. A.

    1988-01-01

    The anisotropic effects of random density irregularities in causing Faraday polarization fluctuations of VHF radio signals are examined, taking both rod-like and sheet-like irregularities into consideration. It is found that the variance of Faraday polarization fluctuations depends on the ratio of perpendicular to parallel correlation lengths. The anisotropic effect of rod-like ionospheric irregularities are shown to be most appreciable for longitudinal propagation. The anisotropic effect of sheet-like ionospheric irregularities, however, is not strongly dependent on the radio propagation angle. During transionospheric propagation at large angles with respect to the geomagnetic field, sheet-like irregularities may cause greater Faraday polarization fluctuations than rod-like irregularities.

  17. Fluctuating Asymmetry and Intelligence

    ERIC Educational Resources Information Center

    Bates, Timothy C.

    2007-01-01

    The general factor of mental ability ("g") may reflect general biological fitness. If so, "g"-loaded measures such as Raven's progressive matrices should be related to morphological measures of fitness such as fluctuating asymmetry (FA: left-right asymmetry of a set of typically left-right symmetrical body traits such as finger lengths). This…

  18. GRADFLEX: Fluctuations in Microgravity

    NASA Technical Reports Server (NTRS)

    Vailati, A.; Cerbino, R.; Mazzoni, S.; Giglio, M.; Nikolaenko, G.; Cannell, D. S.; Meyer, W. V.; Smart, A. E.

    2004-01-01

    We present the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single-component fluid with a temperature gradient. We also describe the experimental apparatus being developed to carry out similar measurement under microgravity conditions.

  19. Extreme fluctuations in stochastic network coordination with time delays

    NASA Astrophysics Data System (ADS)

    Hunt, D.; Molnár, F.; Szymanski, B. K.; Korniss, G.

    2015-12-01

    We study the effects of uniform time delays on the extreme fluctuations in stochastic synchronization and coordination problems with linear couplings in complex networks. We obtain the average size of the fluctuations at the nodes from the behavior of the underlying modes of the network. We then obtain the scaling behavior of the extreme fluctuations with system size, as well as the distribution of the extremes on complex networks, and compare them to those on regular one-dimensional lattices. For large complex networks, when the delay is not too close to the critical one, fluctuations at the nodes effectively decouple, and the limit distributions converge to the Fisher-Tippett-Gumbel density. In contrast, fluctuations in low-dimensional spatial graphs are strongly correlated, and the limit distribution of the extremes is the Airy density. Finally, we also explore the effects of nonlinear couplings on the stability and on the extremes of the synchronization landscapes.

  20. Transition in fluctuation behaviour of normal liquids under high pressures

    NASA Astrophysics Data System (ADS)

    Postnikov, Eugene B.; Chora&zcedildot; ewski, Mirosław

    2016-05-01

    We explore the behaviour of the inverse reduced density fluctuations and the isobaric expansion coefficient using α , ω-dibromoalkanes as an example. Two different states are revealed far from the critical point: the region of exponentially decaying fluctuations near the coexistence curve and the state with longer correlations under sufficiently high pressures. The crossing of the isotherms of the isobaric expansion coefficient occurs within the PVT range of the mentioned transition. We discuss the interplay of this crossing with the changes in molecular packing structure connected with the analysed function of the density, which represents inverse reduced volume fluctuations.

  1. Terrestrial Gravity Fluctuations

    NASA Astrophysics Data System (ADS)

    Harms, Jan

    2015-12-01

    Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10‑23 Hz‑1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of

  2. Towards a unified picture of the water self-ions at the air-water interface: a density functional theory perspective

    SciTech Connect

    Baer, Marcel D.; Kuo, I-F W.; Tobias, Douglas J.; Mundy, Christopher J.

    2014-07-17

    The propensities of the water self ions, H3O+ and OH- , for the air-water interface has implications for interfacial acid-base chemistry. Despite numerous experimental and computational studies, no consensus has been reached on the question of whether or not H3O+ and/or OH- prefer to be at the water surface or in the bulk. Here we report a molecular dynamics simulation study of the bulk vs. interfacial behavior of H3O+ and OH- that employs forces derived from density functional theory with a generalized gradient approximation exchangecorrelation functional (specifically, BLYP) and empirical dispersion corrections. We computed the potential of mean force (PMF) for H3O+ as a function of the position of the ion in a 215-molecule water slab. The PMF is flat, suggesting that H3O+ has equal propensity for the air-water interface and the bulk. We compare the PMF for H3O+ to our previously computed PMF for OH- adsorption, which contains a shallow minimum at the interface, and we explore how differences in solvation of each ion at the interface vs. the bulk are connected with interfacial propensity. We find that the solvation shell of H3O+ is only slightly dependent on its position in the water slab, while OH- partially desolvates as it approaches the interface, and we examine how this difference in solvation behavior is manifested in the electronic structure and chemistry of the two ions. DJT was supported by National Science Foundation grant CHE-0909227. CJM was supported by the U.S. Department of Energy‘s (DOE) Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences. Pacific Northwest National Laboratory (PNNL) is operated for the Department of Energy by Battelle. The potential of mean force required resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DEAC05-00OR22725. The remaining simulations

  3. Molecular Rayleigh Scattering Diagnostic for Measurement of High Frequency Temperature Fluctuations

    NASA Technical Reports Server (NTRS)

    Mielke, Amy F.; Elam, Kristie A.

    2005-01-01

    A novel technique for measurement of high frequency temperature fluctuations in unseeded gas flows using molecular Rayleigh scattering is investigated. The spectrum of laser light scattered from molecules in a gas flow is resolved using a Fabry-Perot interferometer. The width of the spectral peak is broadened by thermal motion of the molecules and hence is related to gas temperature. The interference fringe pattern containing spectral information is divided into four concentric regions using a series of mirrors angled with respect to one another. Light from each of these regions is directed towards photomultiplier tubes and sampled at 10 kHz using photon counting electronics. Monitoring the relative change in intensity within each region allows measurement of gas temperature. Independently monitoring the total scattered intensity provides a measure of gas density. This technique also has the potential to simultaneously measure a single component of flow velocity by monitoring the spectral peak location. Measurements of gas temperature and density are demonstrated using a low speed heated air jet surrounded by an unheated air co-flow. Mean values of temperature and density are shown for radial scans across the jet flow at a fixed axial distance from the jet exit plane. Power spectra of temperature and density fluctuations at several locations in the jet are also shown. The instantaneous measurements have fairly high uncertainty; however, long data records provide highly accurate statistically quantities, which include power spectra. Mean temperatures are compared with thermocouple measurements as well as the temperatures derived from independent density measurements. The accuracy for mean temperature measurements was +/- 7 K.

  4. K/pi Fluctuations at Relativistic Energies

    SciTech Connect

    STAR Collaboration; Abelev, B.I.

    2009-08-24

    We report results for K/{pi} fluctuations from Au+Au collisions at {radical}sNN = 19.6, 62.4, 130, and 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. Our results for K/{pi} fluctuations in central collisions show little dependence on the incident energies studied and are on the same order as results observed by NA49 at the Super Proton Synchrotron in central Pb+Pb collisions at {radical}sNN = 12.3 and 17.3 GeV. We also report results for the collision centrality dependence of K/{pi} fluctuations as well as results for K{sup +}/{pi}{sup +}, K{sup -}/{pi}{sup -}, K{sup +}/{pi}{sup -}, and K{sup -}/{pi}{sup +} fluctuations. We observe that the K/{pi} fluctuations scale with the multiplicity density, dN/d{eta}, rather than the number of participating nucleons.

  5. Conductance fluctuations in hydrogenated amorphous silicon

    SciTech Connect

    Parman, C.E.

    1992-01-01

    Measurements of co-planar resistance fluctuations are reported for n-type doped hydrogenated amorphous silicon over the temperature range 190 < T < 450 K. The spectral density of the fluctuations obey a 1/f frequency dependence over the frequency range 1 < f < 10[sup 3] Hz. The noise power displays a non-linear dependence on the applied DC current, that is that noise power S[sub I] [proportional to] I[sup b], where 1.0 < b < 2.5. Random telegraph switching noise is observed with fluctuations as large as [delta]R/R [approx] 10[sup [minus]2] in samples with volumes of 10[sup [minus]7] cm[sup 3]. Statistical analysis of the noise power spectra show the fluctuations to be strongly non-Gaussian. The noise power magnitude and frequency dependence are both time dependent. These results suggest that cooperative dynamics govern the conductance fluctuations, and are discussed in terms of models for noise in composite and inhomogeneous materials.

  6. Shadowgraph Study of Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

    2002-01-01

    sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical

  7. Physics of fashion fluctuations

    NASA Astrophysics Data System (ADS)

    Donangelo, R.; Hansen, A.; Sneppen, K.; Souza, S. R.

    2000-12-01

    We consider a market where many agents trade different types of products with each other. We model development of collective modes in this market, and quantify these by fluctuations that scale with time with a Hurst exponent of about 0.7. We demonstrate that individual products in the model occasionally become globally accepted means of exchange, and simultaneously become very actively traded. Thus collective features similar to money spontaneously emerge, without any a priori reason.

  8. Inverse scattering problem in turbulent magnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Treumann, Rudolf A.; Baumjohann, Wolfgang; Narita, Yasuhito

    2016-08-01

    We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand-Levitan-Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes advantage of a particular

  9. Fluctuations in Schottky barrier heights

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.

    1984-02-01

    A double Schottky barrier is often formed at the grain boundary in polycrystalline semiconductors. The barrier height is shown to fluctuate in value due to the random nature of the impurity positions. The magnitude of the fluctuations is 0.1 eV, and the fluctuations cause the barrier height measured by capacitance to differ from the one measured by electrical conductivity.

  10. The interpretation of reflectometry measurements of plasma fluctuations

    SciTech Connect

    Bretz, N.

    1991-10-01

    Wave reflections from density fluctuations with magnitudes and frequencies typical of drift waves have been investigated. Both drift waves and the reflected phase and amplitude depend on the density gradient scale length, and this common feature implies that both the angular deviation of a normally propagating wave and the phase change on reflection are of order unity. Thus the surface will always appear rough'' and amplitude variations will always be large. For smaller amplitude waves numerical solutions of the one dimensional full wave equation for the propagation near cutoff frequencies has been used to show how to interpret reflectometry measurements. For density perturbations with wavelengths near the density scale length, the external fluctuating phase can be simply interpreted in terms of a fluctuating density near the cutoff layer. However, the amplitude of the phase response falls substantially as the fluctuation wavelength, {Lambda}, approaches the free space wavelength of the reflected wave, {lambda}{sub o}, and the location of the maximum response moves out in front of the cutoff layer following the wave matching condition k{sub {Lambda}} = 2k {approx} 2{eta}(x)k{sub 0}. Similarly, correlation measurements of density fluctuations from probe waves of different wavelengths are shown to be limited to about four times the average reflected wavelength. 12 refs., 9 figs.

  11. De Sitter Space Without Dynamical Quantum Fluctuations

    NASA Astrophysics Data System (ADS)

    Boddy, Kimberly K.; Carroll, Sean M.; Pollack, Jason

    2016-06-01

    We argue that, under certain plausible assumptions, de Sitter space settles into a quiescent vacuum in which there are no dynamical quantum fluctuations. Such fluctuations require either an evolving microstate, or time-dependent histories of out-of-equilibrium recording devices, which we argue are absent in stationary states. For a massive scalar field in a fixed de Sitter background, the cosmic no-hair theorem implies that the state of the patch approaches the vacuum, where there are no fluctuations. We argue that an analogous conclusion holds whenever a patch of de Sitter is embedded in a larger theory with an infinite-dimensional Hilbert space, including semiclassical quantum gravity with false vacua or complementarity in theories with at least one Minkowski vacuum. This reasoning provides an escape from the Boltzmann brain problem in such theories. It also implies that vacuum states do not uptunnel to higher-energy vacua and that perturbations do not decohere while slow-roll inflation occurs, suggesting that eternal inflation is much less common than often supposed. On the other hand, if a de Sitter patch is a closed system with a finite-dimensional Hilbert space, there will be Poincaré recurrences and dynamical Boltzmann fluctuations into lower-entropy states. Our analysis does not alter the conventional understanding of the origin of density fluctuations from primordial inflation, since reheating naturally generates a high-entropy environment and leads to decoherence, nor does it affect the existence of non-dynamical vacuum fluctuations such as those that give rise to the Casimir effect.

  12. The instability and breakdown of a round variable-density jet

    NASA Astrophysics Data System (ADS)

    Kyle, D. M.; Sreenivasan, K. R.

    1993-04-01

    Results of a study of an investigation of the instability and the subsequent breakdown of axisymmetric jets of helium/air mixtures emerging into ambient air are presented. Two kinds of instability are observed in the near field, depending upon the mean flow parameters. When the ratio of the exiting nozzle fluid density to ambient fluid density is greater than 0.6, shear-layer fluctuations evolve in a fashion similar to that observed in constant-density jets: the power spectrum near the nozzle is determined by weak background disturbances whose subsequent spatial amplification agrees closely with the spatial stability theory. When the density ratio is less than 0.6, an intense oscillatory instability may also arise. The overall behavior of this latter mode is found to be independent of the Reynolds number, within the range of the present experiments. The overall structure of the oscillating mode is found to repeat itself with extreme regularity.

  13. Speckle imaging of spin fluctuations in a strongly interacting Fermi gas.

    PubMed

    Sanner, Christian; Su, Edward J; Keshet, Aviv; Huang, Wujie; Gillen, Jonathon; Gommers, Ralf; Ketterle, Wolfgang

    2011-01-01

    Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

  14. Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas

    SciTech Connect

    Sanner, Christian; Su, Edward J.; Keshet, Aviv; Huang Wujie; Gillen, Jonathon; Gommers, Ralf; Ketterle, Wolfgang

    2011-01-07

    Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

  15. Fluctuations in granular media

    NASA Astrophysics Data System (ADS)

    Howell, Daniel W.; Behringer, R. P.; Veje, C. T.

    1999-09-01

    Dense slowly evolving or static granular materials exhibit strong force fluctuations even though the spatial disorder of the grains is relatively weak. Typically, forces are carried preferentially along a network of "force chains." These consist of linearly aligned grains with larger-than-average force. A growing body of work has explored the nature of these fluctuations. We first briefly review recent work concerning stress fluctuations. We then focus on a series of experiments in both two- and three-dimension [(2D) and (3D)] to characterize force fluctuations in slowly sheared systems. Both sets of experiments show strong temporal fluctuations in the local stress/force; the length scales of these fluctuations extend up to 102 grains. In 2D, we use photoelastic disks that permit visualization of the internal force structure. From this we can make comparisons to recent models and calculations that predict the distributions of forces. Typically, these models indicate that the distributions should fall off exponentially at large force. We find in the experiments that the force distributions change systematically as we change the mean packing fraction, γ. For γ's typical of dense packings of nondeformable grains, we see distributions that are consistent with an exponential decrease at large forces. For both lower and higher γ, the observed force distributions appear to differ from this prediction, with a more Gaussian distribution at larger γ and perhaps a power law at lower γ. For high γ, the distributions differ from this prediction because the grains begin to deform, allowing more grains to carry the applied force, and causing the distributions to have a local maximum at nonzero force. It is less clear why the distributions differ from the models at lower γ. An exploration in γ has led to the discovery of an interesting continuous or "critical" transition (the strengthening/softening transition) in which the mean stress is the order parameter, and the mean

  16. Fluctuating nematic elastomer membranes.

    PubMed

    Xing, Xiangjun; Mukhopadhyay, Ranjan; Lubensky, T C; Radzihovsky, Leo

    2003-08-01

    We study the flat phase of nematic elastomer membranes with rotational symmetry spontaneously broken by an in-plane nematic order. Such a state is characterized by a vanishing elastic modulus for simple shear and soft transverse phonons. At harmonic level, the in-plane orientational (nematic) order is stable to thermal fluctuations that lead to short-range in-plane translational (phonon) correlations. To treat thermal fluctuations and relevant elastic nonlinearities, we introduce two generalizations of two-dimensional membranes in a three-dimensional space to arbitrary D-dimensional membranes embedded in a d-dimensional space and analyze their anomalous elasticities in an expansion about D=4. We find a stable fixed point that controls long-scale properties of nematic elastomer membranes. It is characterized by singular in-plane elastic moduli that vanish as a power law eta(lambda)=4-D of a relevant inverse length scale (e.g., wave vector) and a finite bending rigidity. Our predictions are asymptotically exact near four dimensions. PMID:14524954

  17. Fluctuating nematic elastomer membranes

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun; Mukhopadhyay, Ranjan; Lubensky, T. C.; Radzihovsky, Leo

    2003-08-01

    We study the flat phase of nematic elastomer membranes with rotational symmetry spontaneously broken by an in-plane nematic order. Such a state is characterized by a vanishing elastic modulus for simple shear and soft transverse phonons. At harmonic level, the in-plane orientational (nematic) order is stable to thermal fluctuations that lead to short-range in-plane translational (phonon) correlations. To treat thermal fluctuations and relevant elastic nonlinearities, we introduce two generalizations of two-dimensional membranes in a three-dimensional space to arbitrary D-dimensional membranes embedded in a d-dimensional space and analyze their anomalous elasticities in an expansion about D=4. We find a stable fixed point that controls long-scale properties of nematic elastomer membranes. It is characterized by singular in-plane elastic moduli that vanish as a power law ηλ=4-D of a relevant inverse length scale (e.g., wave vector) and a finite bending rigidity. Our predictions are asymptotically exact near four dimensions.

  18. 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.

  19. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery

    NASA Astrophysics Data System (ADS)

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-09-01

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm‑2. At 1.0 V of cell voltage, a current density of 324 mA cm‑2 is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm‑2, and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

  20. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery.

    PubMed

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-09-20

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

  1. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery

    PubMed Central

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-01-01

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm−2. At 1.0 V of cell voltage, a current density of 324 mA cm−2 is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm−2, and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte. PMID:27646032

  2. Self-assembly formation of Bi-functional Co3O4/MnO2-CNTs hybrid catalysts for achieving both high energy/power density and cyclic ability of rechargeable zinc-air battery.

    PubMed

    Xu, Nengneng; Liu, Yuyu; Zhang, Xia; Li, Xuemei; Li, Aijun; Qiao, Jinli; Zhang, Jiujun

    2016-01-01

    α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte. PMID:27646032

  3. Low-frequency fluctuations in plasma magnetic fields

    SciTech Connect

    Cable, S.; Tajima, T.

    1992-02-01

    It is shown that even a non-magnetized plasma with temperature T sustains zero-frequency magnetic fluctuations in thermal equilibrium. Fluctuations in electric and magnetic fields, as well as in densities, are computed. Four cases are studied: a cold, gaseous, isotropic, non-magnetized plasma; a cold, gaseous plasma in a uniform magnetic field; a warm, gaseous plasma described by kinetic theory; and a degenerate electron plasma. For the simple gaseous plasma, the fluctuation strength of the magnetic field as a function of frequency and wavenumber is calculated with the aid of the fluctuation-dissipation theorem. This calculation is done for both collisional and collisionless plasmas. The magnetic field fluctuation spectrum of each plasma has a large zero-frequency peak. The peak is a Dirac {delta}-function in the collisionless plasma; it is broadened into a Lorentzian curve in the collisional plasma. The plasma causes a low frequency cutoff in the typical black-body radiation spectrum, and the energy under the discovered peak approximates the energy lost in this cutoff. When the imposed magnetic field is weak, the magnetic field were vector fluctuation spectra of the two lowest modes are independent of the strength of the imposed field. Further, these modes contain finite energy even when the imposed field is zero. It is the energy of these modes which forms the non-magnetized zero-frequency peak of the isotropic plasma. In deriving these results, a simple relationship between the dispersion relation and the fluctuation power spectrum of electromagnetic waves if found. The warm plasma is shown, by kinetic theory, to exhibit a zero-frequency peak in its magnetic field fluctuation spectrum as well. For the degenerate plasma, we find that electric field fluctuations and number density fluctuations vanish at zero frequency; however, the magnetic field power spectrum diverges at zero frequency.

  4. Fluctuation effects in grain growth

    NASA Astrophysics Data System (ADS)

    Kim, Seong Gyoon; Park, Yong Bum

    2016-08-01

    In this study, we attempted to clarify the roles of fluctuation effects in grain growth. To capture the persistent nature in both space and time of fluctuations due to variations in the local surroundings of individual grains, we developed a local mean-field model. The fluctuation strength in this model is arbitrarily controlled by employing an artificial number, n , of nearest neighbor grains. Large-scale numerical computations of the model for various n values and initial GSDs were carried out to follow transient behaviors and determine the steady states. This study reveals that, in the classical mean-field model with no fluctuation effects, the steady state is not unique but is strongly dependent upon the initial GSD. However, a small fluctuation drives the mean-field model to reach the Hillert solution, independent of the fluctuation strength and initial GSD, as long as the fluctuation strength is sufficiently small. On the other hand, when the fluctuation is sufficiently strong, the fluctuation pushes the steady state of the mean-field model out of the Hillert solution, and its strength determines a unique steady state independent of the initial GSD. The strong fluctuation makes the GSD more symmetric than the Hillert distribution. Computations designed to mimic actual 2 and 3D grain growth were carried out by taking the number of nearest neighbors of each grain as a function of the scaled grain size. The resultant GSDs in two and three dimensions were compared with the direct simulations of ideal grain growth.

  5. Far-from-equilibrium superconductor in fluctuational regime

    NASA Astrophysics Data System (ADS)

    Petković, A.; Chtchelkatchev, N. M.; Vinokur, V. M.

    2011-08-01

    We derive Ginzburg-Landau-type action for a two-dimensional disordered superconductor under far-from-equilibrium conditions in a fluctuational regime. Then, utilizing it, we calculate fluctuation-induced density of states and Maki-Thomson- and Aslamazov-Larkin-type contributions to the in-plane electrical conductivity. We apply our approach to a thin superconducting film sandwiched between a gate and a substrate, which have different temperatures and different electrochemical potentials.

  6. Detection limit for rate fluctuations in inhomogeneous Poisson processes

    NASA Astrophysics Data System (ADS)

    Shintani, Toshiaki; Shinomoto, Shigeru

    2012-04-01

    Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

  7. Detection limit for rate fluctuations in inhomogeneous Poisson processes.

    PubMed

    Shintani, Toshiaki; Shinomoto, Shigeru

    2012-04-01

    Estimations of an underlying rate from data points are inevitably disturbed by the irregular occurrence of events. Proper estimation methods are designed to avoid overfitting by discounting the irregular occurrence of data, and to determine a constant rate from irregular data derived from a constant probability distribution. However, it can occur that rapid or small fluctuations in the underlying density are undetectable when the data are sparse. For an estimation method, the maximum degree of undetectable rate fluctuations is uniquely determined as a phase transition, when considering an infinitely long series of events drawn from a fluctuating density. In this study, we analytically examine an optimized histogram and a Bayesian rate estimator with respect to their detectability of rate fluctuation, and determine whether their detectable-undetectable phase transition points are given by an identical formula defining a degree of fluctuation in an underlying rate. In addition, we numerically examine the variational Bayes hidden Markov model in its detectability of rate fluctuation, and determine whether the numerically obtained transition point is comparable to those of the other two methods. Such consistency among these three principled methods suggests the presence of a theoretical limit for detecting rate fluctuations.

  8. Fluctuations in complex networks with variable dimensionality and heterogeneity

    NASA Astrophysics Data System (ADS)

    Yoo, H.-H.; Lee, D.-S.

    2016-03-01

    Synchronizing individual activities is essential for the stable functioning of diverse complex systems. Understanding the relation between dynamic fluctuations and the connection topology of substrates is therefore important, but it remains restricted to regular lattices. Here we investigate the fluctuation of loads, assigned to the locally least-loaded nodes, in the largest-connected components of heterogeneous networks while varying their link density and degree exponents. The load fluctuation becomes finite when the link density exceeds a finite threshold in weakly heterogeneous substrates, which coincides with the spectral dimension becoming larger than 2 as in the linear diffusion model. The fluctuation, however, diverges also in strongly heterogeneous networks with the spectral dimension larger than 2. This anomalous divergence is shown to be driven by large local fluctuations at hubs and their neighbors, scaling linearly with degree, which can give rise to diverging fluctuations at small-degree nodes. Our analysis framework can be useful for understanding and controlling fluctuations in real-world systems.

  9. Motion of a mirror under infinitely fluctuating quantum vacuum stress

    NASA Astrophysics Data System (ADS)

    Wang, Qingdi; Unruh, William G.

    2014-04-01

    The actual value of the quantum vacuum energy density is generally regarded as irrelevant in nongravitational physics. However, this paper presents a nongravitational system where this value does have physical significance. The system is a mirror with an internal degree of freedom that interacts with a scalar field. We find that the force exerted on the mirror by the field vacuum undergoes wild fluctuations with a magnitude proportional to the value of the vacuum energy density, which is mathematically infinite. This infinite fluctuating force gives infinite instantaneous acceleration of the mirror. We show that this infinite fluctuating force and infinite instantaneous acceleration make sense because they will not result in infinite fluctuation of the mirror's position. On the contrary, the mirror's fluctuating motion will be confined in a small region due to two special properties of the quantum vacuum: (1) the vacuum friction that resists the mirror's motion and (2) the strong anticorrelation of vacuum fluctuations that constantly changes the direction of the mirror's infinite instantaneous acceleration and thus cancels the effect of infinities to make the fluctuation of the mirror's position finite.

  10. A note on the fluctuation of dissipative scale in turbulence

    NASA Astrophysics Data System (ADS)

    Biferale, L.

    2008-03-01

    We present an application of the multifractal formalism able to predict the whole shape of the probability density function (pdf) of the dissipative scale, η. We discuss both intense velocity fluctuations, leading to dissipative scales smaller than the Kolmogorov scale, where the formalism gives a pdf decaying as a superposition of stretched exponential, and smooth velocity fluctuations, where the formalism predicts a power-law decay. Both trends are found to be in good agreement with recent direct numerical simulations [J. Schumacher, "Sub-Kolmogorov-scale fluctuations in fluid turbulence," Europhys. Lett. 80, 54001 (2007)].

  11. Impact of magnetic fluctuations on lattice excitations in fcc nickel.

    PubMed

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L; Neugebauer, Jörg

    2016-02-24

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  12. Effect of quantum-lattice fluctuations in one-dimensional fluctuating-valence systems

    NASA Astrophysics Data System (ADS)

    Zheng, H.; Avignon, M.

    1994-04-01

    We have developed a variational approach to treat the nonadiabaticity, that is, the quantum-lattice fluctuations, of the electron-phonon interactions in the one-dimensional half-filled spinless Anderson lattice model including Coulomb interaction between both types of electrons. The nonadiabaticity due to finite phonon frequency is treated through a variational polaronic-type wave function, in which two variational parameters δ and τ2 are used to take into account the dynamical distortion and the squeezing effect of phonon modes. We have found that the quantum-lattice fluctuations gradually smoothes the valence transitions when the polaronic level ɛf-v changes. We have shown that conditions somewhat different from those of Hewson and Newns should be satisfied for the occurrence of a significant reduction of the effective hybridization. The effect of the Coulomb repulsion U is to suppress the quantum-lattice fluctuations, that is, to suppress the reduction of the fluctuating-valence frequency and the relaxation shift. We have also discussed the valence-density-wave ordering in the symmetric case. Our results show that the quantum-lattice fluctuations disfavor the ordering and the lattice dimerization parameter decreases with increasing phonon frequency. We have pointed out the possibility of an order-disorder transition in such systems.

  13. Fluctuating multicomponent lattice Boltzmann model

    NASA Astrophysics Data System (ADS)

    Belardinelli, D.; Sbragaglia, M.; Biferale, L.; Gross, M.; Varnik, F.

    2015-02-01

    Current implementations of fluctuating lattice Boltzmann equations (FLBEs) describe single component fluids. In this paper, a model based on the continuum kinetic Boltzmann equation for describing multicomponent fluids is extended to incorporate the effects of thermal fluctuations. The thus obtained fluctuating Boltzmann equation is first linearized to apply the theory of linear fluctuations, and expressions for the noise covariances are determined by invoking the fluctuation-dissipation theorem directly at the kinetic level. Crucial for our analysis is the projection of the Boltzmann equation onto the orthonormal Hermite basis. By integrating in space and time the fluctuating Boltzmann equation with a discrete number of velocities, the FLBE is obtained for both ideal and nonideal multicomponent fluids. Numerical simulations are specialized to the case where mean-field interactions are introduced on the lattice, indicating a proper thermalization of the system.

  14. Fluctuating Thermodynamics for Biological Processes

    NASA Astrophysics Data System (ADS)

    Ham, Sihyun

    Because biomolecular processes are largely under thermodynamic control, dynamic extension of thermodynamics is necessary to uncover the mechanisms and driving factors of fluctuating processes. The fluctuating thermodynamics technology presented in this talk offers a practical means for the thermodynamic characterization of conformational dynamics in biomolecules. The use of fluctuating thermodynamics has the potential to provide a comprehensive picture of fluctuating phenomena in diverse biological processes. Through the application of fluctuating thermodynamics, we provide a thermodynamic perspective on the misfolding and aggregation of the various proteins associated with human diseases. In this talk, I will present the detailed concepts and applications of the fluctuating thermodynamics technology for elucidating biological processes. This work was supported by Samsung Science and Technology Foundation under Project Number SSTF-BA1401-13.

  15. 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

  16. Evaluation of unsaturated zone air permeability through pneumatic tests

    USGS Publications Warehouse

    Baehr, Arthur L.; Hult, Marc F.

    1991-01-01

    Predicting the steady state distribution of air pressure in the unsaturated zone resulting from a pneumatic test provides a method for determining air-phase permeability. This technique is analogous to the inverse problem of well hydraulics; however, air flow is more complicated than ground water flow because of air compressibility, the Klinkenberg effect, variations in air density and viscosity that result from temperature fluctuations in the unsaturated zone and the possibility of inducing water movement during the pneumatic test. An analysis of these complicating factors reveals that, when induced water movement can be neglected, a linear version of the airflow equation can provide an appropriate approximation for the purpose of determining air-phase permeability. Two analytical solutions for steady state, two-dimensional, axisymmetric airflow to a single well partially screened in the unsaturated zone are developed. One solution applies where there is a stratum of relatively low air permeability, separating the stratum in which the well is completed, from the atmosphere. The other solution applies where there is no separating stratum between the domain and atmosphere. In both situations the water table forms the lower horizontal boundary. Applications of both solutions to determine air permeability from data collected during pneumatic tests are presented.

  17. Impact of quantum entanglement on spectrum of cosmological fluctuations

    SciTech Connect

    Kanno, Sugumi

    2014-07-01

    We investigate the effect of entanglement between two causally separated open charts in de Sitter space on the spectrum of vacuum fluctuations. We consider a free massive scalar field, and construct the reduced density matrix by tracing out the vacuum state for one of the open charts, as recently derived by Maldacena and Pimentel. We formulate the mean-square vacuum fluctuations by using the reduced density matrix and show that the scale invariant spectrum of massless scalar field is realized on small scales. On the other hand, we find that the quantum entanglement affects the shape of the spectrum on large scales comparable to or greater than the curvature radius.

  18. Force Fluctuations and Correlations

    NASA Astrophysics Data System (ADS)

    Behringer, Robert

    1998-03-01

    Granular materials exhibit a rich array of dynamic and static phenomena which are only partly understood. Here, I focus on fluctuations in kinetic properties and in forces for slowly sheared granular materials. We have carried out a series of experiments in both 2D and in 3D. For 2D, we use a novel apparatus which allows us to quantify the forces, positions and orientations associated with individual grains. For slow to moderate shear rates, we find rate independence except for small random deviations which are associated with very long time changes in the system. The system evolves to a nearly steady average flow profile in which the velocity falls off approximately exponentially with distance from the shearing surface. The particle rotation shows systematic oscillations near the shearing surface. Velocity profiles show a complicated non-gaussian structure. Force measurements in both the 2D and 3D system are approximately exponentially distributed, but there are also some systematic deviations. Companion calculations by S. Schoellmann, S. Luding and H. Herrmann capture a number of these features. The experimental work has been carried out partially at Duke and partially at the E.S.P.C.I. Paris in collaboration with D. Howell, B. Miller, S. Tennakoon, and C. Veje.

  19. 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.

  20. Fluctuations as stochastic deformation.

    PubMed

    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.

  1. Chemical Applications of Fluctuation Spectroscopy.

    ERIC Educational Resources Information Center

    Green, Michael E.

    1984-01-01

    Examines some of the possibilities for applying the noise spectroscopic technique as well as the origin of noise (or fluctuations) which accompanies transport in physical systems. Indicates that fluctuation techniques are useful in studying liposome and micelle suspensions, liquid-liquid surfaces, semiconductors, and semiconductor devices. (JN)

  2. Waiting for rare entropic fluctuations

    NASA Astrophysics Data System (ADS)

    Saito, Keiji; Dhar, Abhishek

    2016-06-01

    Nonequilibrium fluctuations of various stochastic variables, such as work and entropy production, have been widely discussed recently in the context of large deviations, cumulants and fluctuation relations. Typically one looks at the probability distributions for entropic fluctuations of various sizes to occur in a fixed time interval. An important and natural question is to ask for the time one has to wait to see fluctuations of a desired size. We address this question by studying the first-passage time distribution (FPTD). We derive the general basic equation to get the FPTD for entropic variables. Based on this, the FPTD on entropy production in a driven colloidal particle in the ring geometry is illustrated. A general asymptotic form of the FPTD and integral fluctuation relation symmetry in terms of the first passages are found.

  3. Frequency fluctuations in silicon nanoresonators

    PubMed Central

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C.; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K.; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L.; Jourdan, Guillaume; Hentz, Sébastien

    2016-01-01

    Frequency stability is key to performance of nanoresonators. This stability is thought to reach a limit with the resonator’s ability to resolve thermally-induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature, and found a similar discrepancy. We propose a new method to show this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices. PMID:26925826

  4. Frequency fluctuations in silicon nanoresonators

    NASA Astrophysics Data System (ADS)

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C.; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K.; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L.; Jourdan, Guillaume; Hentz, Sébastien

    2016-06-01

    Frequency stability is key to the performance of nanoresonators. This stability is thought to reach a limit with the resonator's ability to resolve thermally induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature and found a similar discrepancy. We propose a new method to show that this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices.

  5. Fluctuation phenomena in layered superconductors

    SciTech Connect

    Klemm, R.A.

    1996-10-01

    Gaussian fluctuations in layered superconductors have been the subject of study for many years. Although the FD was studied in detail long ago, the FC (fluctuation conductivity) was studied only recently, since the MT and DOS diagrams were previously neglected. Recent comparisons with experiment on YBCO have shown that the DOS diagrams are important and can lead to qualitatively different behaviors for the FC parallel and perpendicular to the layers. In both cases, Gaussian fluctuations fit the data above {Tc} very well, even for YBCO. To date, nearly all calculations of fluctuation quantities were for B{parallel}{cflx c}. Nevertheless, it should be possible to treat an arbitrary B, but the evaluation of the required matrix elements for the fluctuation quantities will be more complicated.

  6. Core fluctuations test. Revision 1

    SciTech Connect

    Betts, W.S.

    1987-06-01

    Fluctuations were first encountered in the Fort St. Vrain reactor early in cycle 1 operation, during the initial rise from 40% to 70% power. Subsequent in-core tests and operation throughout cycles 1 and 2 demonstrated that fluctuations were repeatable, occurring at core pressure drops of between 2.5 psi and 4.0 psi, and that in each instance their characteristics were very similar. Subsequently, tests and analysis were done to understand the core fluctuation phenomenon. These efforts also lead to a design fix which stopped these fluctuations in the FSV reactor core. This fix required that keys be used in addition to the keys in the core support floor which already existed. This report outlines a test plan to validate that core fluctuations will not occur in the MHTGR core. 2 refs., 12 figs., 3 tabs.

  7. Fluctuations of wavefunctions about their classical average

    NASA Astrophysics Data System (ADS)

    Benet, L.; Flores, J.; Hernández-Saldaña, H.; Izrailev, F. M.; Leyvraz, F.; Seligman, T. H.

    2003-02-01

    Quantum-classical correspondence for the average shape of eigenfunctions and the local spectral density of states are well-known facts. In this paper, the fluctuations of the quantum wavefunctions around the classical value are discussed. A simple random matrix model leads to a Gaussian distribution of the amplitudes whose width is determined by the classical shape of the eigenfunction. To compare this prediction with numerical calculations in chaotic models of coupled quartic oscillators, we develop a rescaling method for the components. The expectations are broadly confirmed, but deviations due to scars are observed. This effect is much reduced when both Hamiltonians have chaotic dynamics.

  8. Universal impedance fluctuations in wave chaotic systems.

    PubMed

    Hemmady, Sameer; Zheng, Xing; Ott, Edward; Antonsen, Thomas M; Anlage, Steven M

    2005-01-14

    We experimentally investigate theoretical predictions of universal impedance fluctuations in wave chaotic systems using a microwave analog of a quantum chaotic infinite square well potential. We emphasize the use of the radiation impedance to remove the nonuniversal effects of the particular coupling between the outside world and the scatterer. Specific predictions that we test include the probability density functions (PDFs) of the real and imaginary parts of the universal impedance, the equality of the variances of these PDFs, and the dependence of these PDFs on a single loss parameter.

  9. Core density turbulence in the HSX Stellarator

    SciTech Connect

    Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Briesemeister, Alexis R.; Likin, K. M.

    2015-10-23

    Broadband turbulent density fluctuations are explored in the helically symmetric stellarator experiment (HSX) by investigating changes related to plasma heating power and location. No fluctuation response is observed to occur with large changes in electron temperature and its gradient, thereby eliminating temperature gradient as a driving mechanism. Instead, measurements reveal that density turbulence varies inversely with electron density scale length. This response is consistent with density gradient drive as one might expect for trapped electron mode (TEM) turbulence. In general, the plasma stored energy and particle confinement are higher for discharges with reduced fluctuations in the plasma core. When the density fluctuation amplitude is reduced, increased plasma rotation is also evident suggesting a role is being played by intrinsic plasma flow.

  10. Core density turbulence in the HSX Stellarator

    DOE PAGES

    Deng, C. B.; Brower, D. L.; Anderson, D. T.; Anderson, F. S. B.; Briesemeister, Alexis R.; Likin, K. M.

    2015-10-23

    Broadband turbulent density fluctuations are explored in the helically symmetric stellarator experiment (HSX) by investigating changes related to plasma heating power and location. No fluctuation response is observed to occur with large changes in electron temperature and its gradient, thereby eliminating temperature gradient as a driving mechanism. Instead, measurements reveal that density turbulence varies inversely with electron density scale length. This response is consistent with density gradient drive as one might expect for trapped electron mode (TEM) turbulence. In general, the plasma stored energy and particle confinement are higher for discharges with reduced fluctuations in the plasma core. When themore » density fluctuation amplitude is reduced, increased plasma rotation is also evident suggesting a role is being played by intrinsic plasma flow.« less

  11. Validation of DSMC results for chemically nonequilibrium air flows against measurements of the electron number density in RAM-C II flight experiment

    SciTech Connect

    Shevyrin, Alexander A.; Vashchenkov, Pavel V.; Bondar, Yevgeniy A.; Ivanov, Mikhail S.

    2014-12-09

    An ionized flow around the RAM C-II vehicle in the range of altitudes from 73 to 81 km is studied by the Direct Simulation Monte Carlo (DSMC) method with three models of chemical reactions. It is demonstrated that vibration favoring in reactions of dissociation of neutral molecules affects significantly the predicted values of plasma density in the shock layer, and good agreement between the results of experiments and DSMC computations can be achieved in terms of the plasma density as a function of the flight altitude.

  12. Growth Rate Fluctuations in Phycomyces Sporangiophores 1

    PubMed Central

    Ensminger, Peter A.; Lipson, Edward D.

    1992-01-01

    The growth rate of the Phycomyces sporangiophore fluctuates under constant environmental conditions. These fluctuations underlie the well-characterized sensory responses to environmental changes. We compared growth fluctuations in sporangiophores of unstimulated wild type and behavioral mutants by use of maximum entropy spectral analysis, a mathematical technique that estimates the frequency and amplitude of oscillations in a time series. The mutants studied are believed to be altered near the input (“night-blind”) or output (“stiff” and “hypertropic”) of the photosensory transduction chain. The maximum entropy spectrum of wild type shows a sharp drop-off in spectral density above 0.3 millihertz, several minor peaks between 0.3 and 10 millihertz, and a broad maximum near 10 millihertz. Similar spectra were obtained for a night-blind mutant and a hypertropic mutant. In contrast, the spectra of three stiff mutants, defective in genes madD, madE, or madG, had distinctive peaks near 1.6 mHz and harmonics of this frequency. A madF stiff mutant, which is less stiff than madD, madE, and madG mutants, had a spectrum intermediate between wild type and the three other stiff mutants. Our results indicate that alterations in one or more steps associated with growth regulation output cause the Phycomyces sporangiophore to express a rhythmic growth rate. PMID:16669047

  13. Thermal fluctuations in superconductor/ferromagnet nanostripes

    NASA Astrophysics Data System (ADS)

    Nasti, U.; Parlato, L.; Ejrnaes, M.; Cristiano, R.; Taino, T.; Myoren, H.; Sobolewski, Roman; Pepe, G.

    2015-07-01

    Thermal fluctuations in hybrid superconductor/ferromagnetic NbN /NiCu bilayers, as well as in pure superconducting NbN, two-dimensional (2D), nanostripes, have been investigated in order to understand the origin of dark counts in superconducting nanostripes when operated as single-photon detectors in the temperature range from 4.2 to 8 K . In 2D superconductors, the dynamics of vortex motion play a significant role in the formation of a transient normal state, leading to dark-count events in current-biased nanostripes. By introducing a weak ferromagnetic overlayer on top of pure NbN, we managed to control the vortex dynamics, which subsequently enabled us to differentiate between several proposed theoretical models. In particular, a 6 -nm-thick NiCu film grown on top of 8 -nm-thick NbN nanostripes led to an enhanced critical current density in the resulting nanostructure, as well as significantly lowered fluctuation rates, as compared to pure NbN structures, leading to reduced dark counts. The enhancement of pinning in NbN /NiCu bilayers provided evidence that thermal excitations of single vortices (vortex hopping) near the edge of a 2D nanostripe were the dominant mechanism of the observed dark-count transients. On the other hand, in pure NbN the leading source of thermal fluctuations was the current-assisted thermal unbinding of vortex-antivortex pairs.

  14. Investigation on the Importance of Fast Air Temperature Measurements in the Sampling Cell of Short-Tube Closed-Path Gas Analyzer for Eddy-Covariance Fluxes

    NASA Astrophysics Data System (ADS)

    Kathilankal, J. C.; Fratini, G.; Burba, G. G.

    2014-12-01

    High-speed, precise gas analyzers used in eddy covariance flux research measure gas content in a known volume, thus essentially measuring gas density. The classical eddy flux equation, however, is based on the dry mole fraction. The relation between dry mole fraction and density is regulated by the ideal gas law and law of partial pressures, and depends on water vapor content, temperature and pressure of air. If the instrument can output precise fast dry mole fraction, the flux processing is significantly simplified and WPL terms accounting for air density fluctuations are no longer required. This will also lead to the reduction in uncertainties associated with the WPL terms. For instruments adopting an open-path design, this method is difficult to use because of complexities with maintaining reliable fast temperature measurements integrated over the entire measuring path, and also because of extraordinary challenges with accurate measurements of fast pressure in the open air flow. For instruments utilizing a traditional long-tube closed-path design, with tube length 1000 or more times the tube diameter, this method can be used when instantaneous fluctuations in the air temperature of the sampled air are effectively dampened, instantaneous pressure fluctuations are regulated or negligible, and water vapor is measured simultaneously with gas, or the sample is dried. For instruments with a short-tube enclosed design, most - but not all - of the temperature fluctuations are attenuated, so calculating unbiased fluxes using fast dry mole fraction output requires high-speed, precise temperature measurements of the air stream inside the cell. In this presentation, authors look at short-term and long-term data sets to assess the importance of high-speed, precise air temperature measurements in the sampling cell of short-tube enclosed gas analyzers. The CO2 and H2O half hourly flux calculations, as well as long-term carbon and water budgets, are examined.

  15. Plasma fluctuations in the magnetosheath downstream from Uranus

    NASA Technical Reports Server (NTRS)

    Richardson, John D.; Zhang, Ming; Belcher, John W.; Siscoe, George L.

    1990-01-01

    The Voyager plasma experiment observed large-amplitude plasma fluctuations in the Uranian magnetosheat downstream from the planet. This is a region that has not been well sampled in the earth's magnetosphere. These waves have periods of tens of minutes, are characterized by an anticorrelation between the plasma density and temperature, and are associated with deflections in the flow angle of the plasma. These fluctuations are observed only in regions where the magnetic field is rapidly varying. These waves have time and distance scales placing them in the MHD regime, but their characteristics are not compatible with any known solution of the MHD equations. It is suggested that these fluctuations are produced by the solar wind interaction with the magnetosphere at the bow shock, but the physics governing the production and propagation of these fluctuations is not understood.

  16. Plasma fluctuations in the magnetosheath downstream from Uranus

    NASA Astrophysics Data System (ADS)

    Richardson, J. D.; Zhang, M.; Belcher, J. W.; Siscoe, G. L.

    1990-05-01

    The Voyager plasma experiment observed large-amplitude plasma fluctuations in the Uranian magnetosheat downstream from the planet. This is a region that has not been well sampled in the earth's magnetosphere. These waves have periods of tens of minutes, are characterized by an anticorrelation between the plasma density and temperature, and are associated with deflections in the flow angle of the plasma. These fluctuations are observed only in regions where the magnetic field is rapidly varying. These waves have time and distance scales placing them in the MHD regime, but their characteristics are not compatible with any known solution of the MHD equations. It is suggested that these fluctuations are produced by the solar wind interaction with the magnetosphere at the bow shock, but the physics governing the production and propagation of these fluctuations is not understood.

  17. Recovery of fluctuation spectrum evolution from tomographic shear spectra

    SciTech Connect

    Bonometto, Silvio A.; Mezzetti, Marino E-mail: mezzetti@oats.inaf.it

    2013-05-01

    Forthcoming large angle surveys are planned to obtain high precision tomographic shear data. In principle, they will allow us to recover the spectra of matter density fluctuation, at various redshift, through the inversion of the expressions yielding shear spectra from fluctuation spectra. This was discussed in previous work, where SVD techniques for matrix inversion were also shown to be the optimal tool to this aim. Here we show the significant improvements obtainable by using a 7 bin tomography, as allowed by future Euclid data, and discuss error propagation from shear to fluctuation spectra. We find that the technique is a promising tool, namely for the analysis of baryon physics through high–l shear spectra and to test the consistency between expansion rate and fluctuation growth.

  18. Order parameter fluctuations at a buried quantum critical point

    PubMed Central

    Feng, Yejun; Wang, Jiyang; Jaramillo, R.; van Wezel, Jasper; Haravifard, S.; Srajer, G.; Liu, Y.; Xu, Z.-A.; Littlewood, P. B.; Rosenbaum, T. F.

    2012-01-01

    Quantum criticality is a central concept in condensed matter physics, but the direct observation of quantum critical fluctuations has remained elusive. Here we present an X-ray diffraction study of the charge density wave (CDW) in 2H-NbSe2 at high pressure and low temperature, where we observe a broad regime of order parameter fluctuations that are controlled by proximity to a quantum critical point. X-rays can track the CDW despite the fact that the quantum critical regime is shrouded inside a superconducting phase; and in contrast to transport probes, allow direct measurement of the critical fluctuations of the charge order. Concurrent measurements of the crystal lattice point to a critical transition that is continuous in nature. Our results confirm the long-standing expectations of enhanced quantum fluctuations in low-dimensional systems, and may help to constrain theories of the quantum critical Fermi surface. PMID:22529348

  19. Cell surface fluctuations studied with defocusing microscopy

    NASA Astrophysics Data System (ADS)

    Agero, U.; Monken, C. H.; Ropert, C.; Gazzinelli, R. T.; Mesquita, O. N.

    2003-05-01

    Phase objects can become visible by slightly defocusing an optical microscope, a technique seldom used as a useful tool. We revisited the theory of defocusing and apply it to our optical microscope with optics corrected at infinity. In our approximation, we obtain that the image contrast is proportional to the two-dimensional (2D) Laplacian of the phase difference introduced by the phase object. If the index of refraction of the phase object is uniform the image obtained from defocusing microscopy is the image of curvature (Laplacian of the local thickness) of the phase object, while standard phase-contrast microscopy gives information about the thickness of the object. We made artificial phase objects and measured image contrasts with defocusing microscopy. Measured contrasts are in excellent agreement with our theoretical model. We use defocusing microscopy to study curvature fluctuations (ruffles) on the surface of macrophages (cell of the innate immune system), and try to correlate mechanical properties of macrophage surface and phagocytosis. We observe large coherent propagating structures: Their shape, speed, density are measured and curvature energy estimated. Inhomogeneities of cytoskeleton refractive index, curvature modulations due to thermal fluctuations and/or periodic changes in cytoskeleton-membrane interactions cause random fluctuations in image contrast. From the temporal and spatial contrast correlation functions, we obtain the decay time and correlation length of such fluctuations that are related to their size and the viscoelastic properties of the cytoskeleton. In order to associate the dynamics of cytoskeleton with the process of phagocytosis, we use an optical tweezers to grab a zymosan particle and put it into contact with the macrophage. We then measure the time for a single phagocytosis event. We add the drug cytochalasin D that depolymerizes the cytoskeleton F-actin network: It inhibits the large propagating coherent fluctuations on the

  20. Scale invariant density perturbations from cyclic cosmology

    NASA Astrophysics Data System (ADS)

    Frampton, Paul Howard

    2016-04-01

    It is shown how quantum fluctuations of the radiation during the contraction era of a comes back empty (CBE) cyclic cosmology can provide density fluctuations which re-enter the horizon during the subsequent expansion era and at lowest order are scale invariant, in a Harrison-Zel’dovich-Peebles sense. It is necessary to be consistent with observations of large scale structure.

  1. Net baryon fluctuations from a crossover equation of state

    NASA Astrophysics Data System (ADS)

    Kapusta, J.; Albright, M.; Young, C.

    2016-08-01

    We have constructed an equation of state which smoothly interpolates between an excluded-volume hadron resonance gas at low energy density to a plasma of quarks and gluons at high energy density. This crossover equation of state agrees very well with lattice calculations at both zero and nonzero baryon chemical potential. We use it to compute the variance, skewness, and kurtosis of fluctuations of baryon number, and compare to measurements of proton number fluctuations in central Au-Au collisions as measured by the STAR Collaboration in a beam energy scan at the Relativistic Heavy-Ion Collider. The crossover equation of state can reproduce the data if the fluctuations are frozen out at temperatures well below than the average chemical freeze-out.

  2. Nonequilibrium molecular transport photoinduced by potential energy fluctuations

    NASA Astrophysics Data System (ADS)

    Dekhtyar, Marina L.; Rozenbaum, Viktor M.

    2011-01-01

    The mechanism of directed substrate-parallel motion of molecules caused by photoinduced potential energy fluctuations is investigated. Unlike simplistic models (e.g., an on-off ratchet), the approach suggested implies that the necessary asymmetry of the potential energy can arise not only from the asymmetry of the substrate potential but also from an asymmetric distribution of the fluctuating charge density in the molecule. The thus induced asymmetry of the potential energy governs the direction motion and enables, under certain conditions, its reversal at some frequencies of resonant laser pulses or temperature. These inferences are exemplified by the model charge distributions in the molecule and substrate, and the charge density fluctuations which are obtained by quantum chemical calculations for the realistic molecule of a substituted phenylpyrene compound on a model substrate.

  3. 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.

  4. Transverse Momentum Fluctuations at RHIC

    NASA Astrophysics Data System (ADS)

    Gavin, Sean; Abdel-Aziz, Mohamed

    2004-10-01

    PHENIX and STAR data in Au+Au collisions at RHIC show that transverse momentum fluctuations increase as centrality increases. The approach to local thermal equilibrium can explain the similar centrality dependence of the average transverse momentum and its fluctuations [1]. Alternatively, this dependence can be attributed to jet effects, although the mechanism has not been spelled out in the literature [2]. Certainly both mechanisms play a role at some level. We review the nonequilibrium description of parton thermalization in [1]. We then extend the formulation to account for contributions to fluctuations from the energy loss of the high transverse momentum particles. Calculations are then compared to the measured average transverse momentum and its fluctuations. We then discuss how correlation function measurements may distinguish these effects. [1] Sean Gavin, Phys.Rev.Lett. 92 (2004) 162301. [2] S. S. Adler et al. [PHENIX Collaboration], arXiv:nucl-ex/0310005.

  5. New Fluctuation Phenomena in the H-Mode Regime of Poloidal-Diverter Tokamak Plasmas

    NASA Astrophysics Data System (ADS)

    Slusher, R. E.; Surko, C. M.; Valley, J. F.; Crowley, T.; Mazzucato, E.; McGuire, K.

    1984-08-01

    A new kind of fluctuation is observed near the edge of plasmas in the PDX tokamak operating in the "H-mode" (improved-confinement) regime. These fluctuations are evidenced as vacuum-uv and density-fluctuation bursts at well-defined frequencies (Δωω<~0.1) in the range between 50 and 180 kHz. The bursts are correlated, both in space and in time, with changes in the temperature-density product near the plasma edge where large density and temperature gradients develop during the H mode.

  6. New fluctuation phenomena in the H-mode regime of poloidal-divertor tokamak plasmas

    SciTech Connect

    Slusher, R.E.; Surko, C.M.; Valley, J.F.; Crowley, T.; Mazzucato, E.; McGuire, K.

    1984-08-13

    A new kind of fluctuation is observed near the edge of plasmas in the PDX tokamak operating in the ''H-mode'' (improved-confinement) regime. These fluctuations are evidenced as vacuum-UV and density-fluctuation bursts at well-defined frequencies (..delta omega../..omega..< or approx. =0.1) in the range between 50 and 180 kHz. The bursts are correlated, both in space and in time, with changes in the temperature-density product near the plasma edge where large density and temperature gradients develop during the H mode.

  7. Fluctuation Probes of Quark Deconfinement

    SciTech Connect

    Asakawa, Masayuki; Heinz, Ulrich; Mueller, Berndt

    2000-09-04

    The size of the average fluctuations of net baryon number and electric charge in a finite volume of hadronic matter differs widely between the confined and deconfined phases. These differences may be exploited as indicators of the formation of a quark-gluon plasma in relativistic heavy-ion collisions, because fluctuations created in the initial state survive until freeze-out due to the rapid expansion of the hot fireball. (c) 2000 The American Physical Society.

  8. Principle of minimal work fluctuations

    NASA Astrophysics Data System (ADS)

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality =e-β Δ F , a change in the fluctuations of e-β W may impact how rapidly the statistical average of e-β W converges towards the theoretical value e-β Δ F, where W is the work, β is the inverse temperature, and Δ F is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-β W. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-β W, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-β W. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014), 10.1103/PhysRevE.90.052132].

  9. Principle of minimal work fluctuations.

    PubMed

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality 〈e-βW〉=e-βΔF, a change in the fluctuations of e-βW may impact how rapidly the statistical average of e-βW converges towards the theoretical value e-βΔF, where W is the work, β is the inverse temperature, and ΔF is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-βW. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-βW, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-βW. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014)].

  10. Fluctuations in classical sum rules.

    PubMed

    Elton, John R; Lakshminarayan, Arul; Tomsovic, Steven

    2010-10-01

    Classical sum rules arise in a wide variety of physical contexts. Asymptotic expressions have been derived for many of these sum rules in the limit of long orbital period (or large action). Although sum-rule convergence may well be exponentially rapid for chaotic systems in a global phase-space sense with time, individual contributions to the sums may fluctuate with a width which diverges in time. Our interest is in the global convergence of sum rules as well as their local fluctuations. It turns out that a simple version of a lazy baker map gives an ideal system in which classical sum rules, their corrections, and their fluctuations can be worked out analytically. This is worked out in detail for the Hannay-Ozorio sum rule. In this particular case the rate of convergence of the sum rule is found to be governed by the Pollicott-Ruelle resonances, and both local and global boundaries for which the sum rule may converge are given. In addition, the width of the fluctuations is considered and worked out analytically, and it is shown to have an interesting dependence on the location of the region over which the sum rule is applied. It is also found that as the region of application is decreased in size the fluctuations grow. This suggests a way of controlling the length scale of the fluctuations by considering a time dependent phase-space volume, which for the lazy baker map decreases exponentially rapidly with time.

  11. Generalised tensor fluctuations and inflation

    SciTech Connect

    Cannone, Dario; Tasinato, Gianmassimo; Wands, David E-mail: g.tasinato@swansea.ac.uk

    2015-01-01

    Using an effective field theory approach to inflation, we examine novel properties of the spectrum of inflationary tensor fluctuations, that arise when breaking some of the symmetries or requirements usually imposed on the dynamics of perturbations. During single-clock inflation, time-reparameterization invariance is broken by a time-dependent cosmological background. In order to explore more general scenarios, we consider the possibility that spatial diffeomorphism invariance is also broken by effective mass terms or by derivative operators for the metric fluctuations in the Lagrangian. We investigate the cosmological consequences of the breaking of spatial diffeomorphisms, focussing on operators that affect the power spectrum of fluctuations. We identify the operators for tensor fluctuations that can provide a blue spectrum without violating the null energy condition, and operators for scalar fluctuations that lead to non-conservation of the comoving curvature perturbation on superhorizon scales even in single-clock inflation. In the last part of our work, we also examine the consequences of operators containing more than two spatial derivatives, discussing how they affect the sound speed of tensor fluctuations, and showing that they can mimic some of the interesting effects of symmetry breaking operators, even in scenarios that preserve spatial diffeomorphism invariance.

  12. Quantum fluctuations of radiation pressure

    SciTech Connect

    Wu, Chun-Hsien; Ford, L. H.

    2001-08-15

    Quantum fluctuations of electromagnetic radiation pressure are discussed. We use an approach based on the quantum stress tensor to calculate the fluctuations in velocity and position of a mirror subjected to electromagnetic radiation. Our approach reveals that radiation pressure fluctuations in the case of a coherent state are due to a cross term between vacuum and state dependent terms in a stress tensor operator product. Thus observation of these fluctuations would entail experimental confirmation of this cross term. We first analyze the pressure fluctuations on a single, perfectly reflecting mirror, and then study the case of an interferometer. This involves a study of the effects of multiple bounces in one arm, as well as the correlations of the pressure fluctuations between arms of the interferometer. In all cases, our results are consistent with those previously obtained by Caves using different methods. We argue that the agreement between the different methods supports the reality of the cross term and justifies the methods used in its evaluation.

  13. Critical spectrum of fluctuations for deconfinement at protoneutron star cores

    SciTech Connect

    Lugones, G.; Grunfeld, A. G.

    2011-10-15

    We study the deconfinement of hadronic matter into quark matter in a protoneutron star focusing on the effects of the finite size on the formation of just deconfined color superconducting quark droplets embedded in the hadronic environment. The hadronic phase is modeled by the nonlinear Walecka model at finite temperature including the baryon octet and neutrino trapping. For quark matter we use an SU(3){sub f} Nambu-Jona-Lasinio model including color superconductivity. The finite size effects on the just deconfined droplets are considered in the frame of the multiple reflection expansion. In addition, we consider that just deconfined quark matter is transitorily out of equilibrium respect to weak interaction, and we impose color neutrality and flavor conservation during the transition. We calculate self-consistently the surface tension and curvature energy density of the quark hadron interphase and find that it is larger than the values typically assumed in the literature. The transition density is calculated for drops of different sizes, and at different temperatures and neutrino trapping conditions. Then, we show that energy density fluctuations are much more relevant for deconfinement than temperature and neutrino density fluctuations. We calculate the critical size spectrum of energy density fluctuations that allows deconfinement as well as the nucleation rate of each critical bubble. We find that drops with any radii smaller than 800 fm can be formed at a huge rate when matter achieves the bulk transition limit of 5-6 times the nuclear saturation density.

  14. Estimating the cell density and invasive radius of three-dimensional glioblastoma tumor spheroids grown in vitro

    NASA Astrophysics Data System (ADS)

    Stein, Andrew M.; Nowicki, Michal O.; Demuth, Tim; Berens, Michael E.; Lawler, Sean E.; Chiocca, E. Antonio; Sander, Leonard M.

    2007-08-01

    To gain insight into brain tumor invasion, experiments are conducted on multicellular tumor spheroids grown in collagen gel. Typically, a radius of invasion is reported, which is obtained by human measurement. We present a simple, heuristic algorithm for automated invasive radii estimation (AIRE) that uses local fluctuations of the image intensity. We then derive an analytical expression relating the image graininess to the cell density for a model imaging system. The result agrees with the experiment up to a multiplicative constant and thus describes a novel method for estimating the cell density from bright-field images.

  15. Turbulent Ion Temperature Fluctuation Measurements on DIII-D

    NASA Astrophysics Data System (ADS)

    Uzun-Kaymak, I. U.; Fonck, R. J.; McKee, G. R.

    2012-10-01

    A novel dual-channel, high throughput, high efficiency, charge exchange spectrometer (UF-CHERS) has been developed to measure impurity ion temperature and toroidal velocity fluctuations with 1 μs time resolution. These measurements are primarily needed for identifying underlying instabilities and validation of transport simulation codes. Based on the measured photon flux levels for the entire spectral line, a photon noise floor ˜1% is expected. Statistical averaging over long data records should provide turbulence measurements to 1/5 to 1/10 of the estimated photon noise floor. Correlation measurements in DIII-D plasmas demonstrate broadband ion-temperature fluctuations from 0-150 kHz, while cross-correlation with BES measurements of density fluctuations exhibits cross-power between density and ion temperature fluctuations to 250 kHz in ECH-heated low-collisionality L-mode discharges. The fluctuation level is Ti/Ti˜2%, with correlation lengths in the range of 3-5 cm. A new detector system will provide improved signal-to-noise level and higher frequency measurements.

  16. Combined chiral and diquark fluctuations along QCD critical line and enhanced baryon production with parity doubling

    NASA Astrophysics Data System (ADS)

    Zhang, Zhao; Kunihiro, Teiji

    2016-08-01

    We argue that there should exist the large combined fluctuations of chiral and diquark condensates along the phase boundary of QCD at moderately high density and relatively low temperature. Such fluctuations might lead to anomalous production of nucleons and its parity partner, which we propose to detect at NICA.

  17. Cosmological fluctuation growth in bimetric MOND

    NASA Astrophysics Data System (ADS)

    Milgrom, Mordehai

    2010-08-01

    I begin to look at the growth of weak density inhomogeneities of nonrelativistic matter, in bimetric-MOND (BIMOND) cosmology. Far from making an exhaustive study, I concentrate on one attractive cosmological scenario, which employs matter-twin-matter-symmetric versions of BIMOND, and, furthermore, assumes that, on average, the universe is symmetrically populated in the two sectors. MOND effects are totally absent in an exactly symmetric universe, apart from the significant possible appearance of a cosmological constant, Λ˜(a0/c)2. MOND effects—local and cosmological—do enter when density inhomogeneities that differ in the two sectors appear and develop. MOND later takes its standard form in systems that are islands dominated by pure matter, as are presumably the well scrutinized systems such as galaxies. I derive the nonrelativistic (weak-field-slow-motion) equations governing small-scale fluctuation growth. The equations split into two uncoupled systems, one for the sum, the other for the difference, of the fluctuations in the two sectors. The former is governed strictly by Newtonian dynamics, and describes standard growth of fluctuations. The latter is governed by MOND dynamics, which entails stronger gravity, and nonlinearity even for the smallest of perturbations. These cause the difference to grow faster than the sum, leading to anticorrelated perturbations, conducing to matter-twin-matter segregation (which continues for high overdensities). The nonlinearity also causes interaction between nested perturbations on different scales. Because matter and twin matter (TM) repel each other in the MOND regime, matter inhomogeneities grow not only by their own self-gravity, but also through shepherding by flanking twin matter overdensities (and vice versa). The relative importance of gravity and pressure in the MOND system (analog of the Jeans criterion), depends also on the strength of the perturbation. MOND gravity, which scales as the square root of the

  18. Quantum fluctuations and dynamic clustering of fluctuating Cooper pairs.

    SciTech Connect

    Glatz, A.; Varlamov, A. A.; Vinokur, V. M.

    2011-05-01

    We derive the complete expression for the fluctuation conductivity in two-dimensional superconductors as a function of the temperature and the magnetic field in the whole fluctuation region above the upper critical field H{sub c2}(T). Focusing on the vicinity of the quantum phase transition near zero temperature, we propose that as the magnetic field approaches the line near H{sub c2}(0) from above, a peculiar dynamic state consisting of clusters of coherently rotating fluctuation Cooper pairs forms and estimate the characteristic size and lifetime of such clusters. We find the zero-temperature magnetic-field dependence of the transverse magnetoconductivity above H{sub c2}(0) in layered superconductors.

  19. Density waves in granular flow

    NASA Astrophysics Data System (ADS)

    Herrmann, H. J.; Flekkøy, E.; Nagel, K.; Peng, G.; Ristow, G.

    Ample experimental evidence has shown the existence of spontaneous density waves in granular material flowing through pipes or hoppers. Using Molecular Dynamics Simulations we show that several types of waves exist and find that these density fluctuations follow a 1/f spectrum. We compare this behaviour to deterministic one-dimensional traffic models. If positions and velocities are continuous variables the model shows self-organized criticality driven by the slowest car. We also present Lattice Gas and Boltzmann Lattice Models which reproduce the experimentally observed effects. Density waves are spontaneously generated when the viscosity has a nonlinear dependence on density which characterizes granular flow.

  20. Topics in fluctuating nonlinear hydrodynamics

    SciTech Connect

    Milner, S.T.

    1986-01-01

    Models of fluctuating nonlinear hydrodynamics have enjoyed much success in explaining the effect of long-wavelength fluctuations in diverse hydrodynamic systems. This thesis explores two such problems; in both, the body of hydrodynamic assumptions powerfully constrains the predictions of a well-posed theory. The effects of layer fluctuations in smectic-A liquid crystals are first examined. The static theory (introduced by Grinstein and Pelcovits) is reviewed. Ward identities, resulting from the arbitrariness of the layering direction, are derived and exploited. The static results motivate an examination of dynamic fluctuation effects. A new sound-damping experiment is proposed that would probe singular dependence of viscosities on applied stress. A theory of Procaccia and Gitterman that reaction rates of chemically reacting binary mixtures are drastically reduced near their thermodynamic critical points is analyzed. Hydrodynamic arguments and Van Hove theory are applied, concluding that the PG idea is drastically slowed, and spatially varying composition fluctuations are at best slowed down over a narrow range of wavenumbers.