Amplitude Of Density Fluctuations Research Articles

The power spectrum and bispectrum of SDSS DR11 BOSS galaxies – I. Bias and gravity

We analyse the anisotropic clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS Data Release 11 sample, which consists of $690 827$ galaxies in the redshift range $0.43 < z < 0.70$ and has a sky coverage of $8 498$ deg$^2$ corresponding to an effective volume of $\sim6\,\rm{Gpc}^3$. We fit the Fourier space statistics, the power spectrum and bispectrum monopoles to measure the linear and quadratic bias parameters, $b_1$ and $b_2$, for a non-linear non-local bias model, the growth of structure parameter $f$ and the amplitude of dark matter density fluctuations parametrised by $\sigma_8$. We obtain $b_1(z_{\rm eff})^{1.40}\sigma_8(z_{\rm eff})=1.672\pm 0.060$ and $b_2^{0.30}(z_{\rm eff})\sigma_8(z_{\rm eff})=0.579\pm0.082$ at the effective redshift of the survey, $z_{\rm eff}=0.57$. The main cosmological result is the constraint on the combination $f^{0.43}(z_{\rm eff})\sigma_8(z_{\rm eff})=0.582\pm0.084$, which is complementary to $f\sigma_8$ constraints obtained from 2-point redshift space distortion analyses. A less conservative analysis yields $f^{0.43}(z_{\rm eff})\sigma_8(z_{\rm eff})=0.584\pm0.051$. We ensure that our result is robust by performing detailed systematic tests using a large suite of survey galaxy mock catalogs and N-body simulations. The constraints on $f^{0.43}\sigma_8$ are useful for setting additional constrains on neutrino mass, gravity, curvature as well as the number of neutrino species from galaxy surveys analyses (as presented in a companion paper).

Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum

X-ray surface brightness fluctuations in the core of the Perseus Cluster are analyzed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 8 to 12 per cent on scales of ~10-30 kpc within radii of 30-160 kpc from the cluster center and from 9 to 7 per cent on scales of ~20-30 kpc in an outer, 60-220 kpc annulus. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km/s on ~20-30 kpc scales and 70-100 km/s on smaller scales ~7-10 kpc. The velocity power spectrum is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the power spectrum of the density fluctuations is lower than 7-8 per cent for radii ~30-220 kpc from the center, leading to a density bias of less than 3-4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density-velocity perturbation relation and further reduce systematic uncertainties in these quantities.

First measurement of the cross-correlation of CMB lensing and galaxy lensing

We measure the cross-correlation of cosmic microwave background lensing convergence maps derived from Atacama Cosmology Telescope data with galaxy lensing convergence maps as measured by the Canada-France-Hawaii Telescope Stripe 82 Survey. The CMB-galaxy lensing cross power spectrum is measured for the first time with a significance of 4.2{\sigma}, which corresponds to a 12% constraint on the amplitude of density fluctuations at redshifts ~ 0.9. With upcoming improved lensing data, this novel type of measurement will become a powerful cosmological probe, providing a precise measurement of the mass distribution at intermediate redshifts and serving as a calibrator for systematic biases in weak lensing measurements.

Intensity of low-latitude nighttime F-region ionospheric density irregularities observed by ROCSAT and ground-based GPS receivers in solar maximum

This study examines the global correlation between the instantaneous total amplitude of ion density fluctuations observed by ROCSAT and the phase fluctuation of the total electron content (TEC) recorded by worldwide ground-based Global Positioning System (GPS) receivers during the high solar activity period of March 1999–December 2002 for Kp<3. The Hilbert–Huang transform (HHT) is applied to compute the instantaneous total amplitude of ROCSAT ion densities. The event-based and climatological comparisons of the total amplitude and occurrence probability of irregularities observed by ROCSAT show that the total amplitude can reveal both the occurrence probability of irregularities and the associated intensity. The noise level of the total amplitude is about 103.5 (near 3000) ions/cm3. The high correlation (correlation coefficient=0.81) between the GPS TEC phase fluctuation index FP and instantaneous total amplitude of ROCSAT electron densities suggests that the total amplitude can be used to globally monitor the intensity of irregularities at equatorial and within the latitude belt of ±15°. The relationship between the ionospheric background ionization and the irregularity intensity is further investigated.

H-mode transitions and limit cycle oscillations from mean field transport equations

The mean field toroidal and parallel momentum transport equations will be shown to admit both one-step transitions to suppressed transport (L/H) and limit cycle oscillations (LCO). Both types of transitions are driven by the suppression of turbulence by the mean field ExB velocity shear. Using experimental data to evaluate the coefficients of a reduced transport model, the observed frequency of the LCO can be matched. The increase in the H-mode power threshold above and below a minimum density agrees with the trends in the model. Both leading and lagging phase relations between the turbulent density fluctuation amplitude and the ExB velocity shear can occur depending on the evolution of the linear growth rate of the turbulence. The transport solutions match the initial phase of the L/H transition where the poloidal and ExB velocities are observed to change, and the density fluctuations drop, faster than the diamagnetic velocity.

RADIAL DISTRIBUTION OF COMPRESSIVE WAVES IN THE SOLAR CORONA REVEALED BYAKATSUKIRADIO OCCULTATION OBSERVATIONS

Radial variations of the amplitude and the energy flux of compressive waves in the solar corona were explored for the first time using a spacecraft radio occultation technique. By applying wavelet analysis to the frequency time series taken at heliocentric distances of 1.5-20.5 RS (solar radii), quasi-periodic density disturbances were detected at almost all distances. The period ranges from 100 to 2000 s. The amplitude of the fractional density fluctuation increases with distance and reaches ~30% around 5 RS , implying that nonlinearity of the wave field is potentially important. We further estimate the wave energy flux on the assumption that the observed periodical fluctuations are manifestations of acoustic waves. The energy flux increases with distance below ~6 RS and seems to saturate above this height, suggesting that the acoustic waves do not propagate from the low corona but are generated in the extended corona, probably through nonlinear dissipation of Alfven waves. The compressive waves should eventually dissipate through shock generation to heat the corona.

MHD heliosphere with boundary conditions from a tomographic reconstruction using interplanetary scintillation data

AbstractObservations of interplanetary scintillation (IPS) provide a set of data that is used in estimating the solar wind parameters with reasonably good accuracy. Various tomography techniques have been developed to deconvolve the line‐of‐sight integration effects ingrained in observations of IPS to improve the accuracy of solar wind reconstructions. Among those, the time‐dependent tomography developed at the University of California, San Diego (UCSD) is well known for its remarkable accuracy in reproducing the solar wind speed and density at Earth by iteratively fitting a kinematic solar wind model to observations of IPS and near‐Earth spacecraft measurements. However, the kinematic model gradually breaks down as the distance from the Sun increases beyond the orbit of Earth. Therefore, it would be appropriate to use a more sophisticated model, such as a magnetohydrodynamics (MHD) model, to extend the kinematic solar wind reconstruction beyond the Earth's orbit and to the outer heliosphere. To test the suitability of this approach, we use boundary conditions provided by the UCSD time‐dependent tomography to propagate the solar wind outward in a MHD model and compare the simulation results with in situ measurements and also with the corresponding kinematic solution. Interestingly, we find notable differences in proton radial velocity and number density at Earth and various locations in the inner heliosphere between the MHD results and both the in situ data and the kinematic solution. For example, at 1 AU, the MHD velocities are generally larger than the spacecraft data by up to 150 km s−1, and the amplitude of density fluctuations is also markedly larger in the MHD solution. We show that the MHD model can deliver more reasonable results at Earth with an ad hoc adjustment of the inner boundary values. However, we conclude that the MHD model using the inner boundary conditions derived from kinematic simulations has little chance to match IPS and in situ data as well as the kinematic model does unless it too is iteratively fit to the observational data and measurements.

Precision epoch of reionization studies with next-generation CMB experiments

Future arcminute resolution polarization data from ground-based Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near ℓ=1500 in the small angular-scale temperature measurements. Our projections are based on combining expected small-scale E-mode polarization measurements from Advanced ACTPol in the range 300<ℓ<3000 with simulated temperature data from the full Planck mission in the low and intermediate ℓ region, 2<ℓ<2000. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than 1% accuracy. Assuming an efficient cleaning from multi-frequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic Sunyaev-Zel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a 15σ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at ℓ>1500, leading to a measurement of the amplitude of matter density fluctuations, σ8, at 1% precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with σ(zre)=1.1 and σ(Δzre)=0.2. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminute-scale resolution for future CMB surveys.

Phytoplankton–zooplankton dynamics vary with nutrients: a microcosm study with the cyanobacterium Coleofasciculus chthonoplastes and cladoceran Moina micrura

Anti-grazer responses of phytoplankton have been widely documented to vary with external abiotic factors (e. g. nutrient status), suggesting an environment-dependence of phytoplankton-zooplankton dynamics. Here, we examined the trophic interaction between the cyanobacteria Coleofasciculus chthonoplastes and the cladoceran Moina micrura under three nutrient levels from oligotrophic to hypereutrophic conditions (0.3, 3.0 and 100.0 mu M PO43-; molar ratio NO3- : PO43- - 16 : 1) to determine the effect of nutrients on the stability of a phytoplankton-zooplankton system. In the absence of M. micrura, cell density and filament (single-filament) length of C. chthonoplastes were lower at the low nutrient level compared with those at the medium and high nutrient levels. When M. micrura was present, cell density, filament length, colony proportion and size (the mean number of cells per colony) of C. chthonoplastes were highest under the medium nutrient level, corresponding to the lowest amplitude of density fluctuations in M. micrura. Regression analyses revealed that low cell densities of C. chthonoplastes (due to its limited ability to form colonies and long filaments and hence a high consumption rate of M. micrura) at low and high nutrient levels limited the growth of M. micrura adult females, leading to a sharp decline in embryo length, clutch size and population density. In general, our results suggest that the stability of phytoplankton-zooplankton systems varies with nutrients because of the nutrient-dependent morphology in phytoplankton, and imply that extremely low or high nutrient load may destabilize phytoplankton-zooplankton systems.

Minimal fine tuning in supersymmetric Higgs inflation

We investigate characteristic features of realistic parameter choice for primordial inflation with supersymmetric Higgs inflaton as an example of particle physics inflation model. We discuss constraints from observational results and analyze the degree of fine tuning needed to induce slow-roll inflation for wide range of soft supersymmetry breaking scale. The observed amplitude of density fluctuations implies that the minimal fine tuning for the combined electroweak scale and inflaton flatness predicts the spectral index of 0.950--0.965, which includes the central value from observational data.

Elastically cooperative activated barrier hopping theory of relaxation in viscous fluids. I. General formulation and application to hard sphere fluids.

We generalize the force-level nonlinear Langevin equation theory of single particle hopping to include collective effects associated with long range elastic distortion of the liquid. The activated alpha relaxation event is of a mixed spatial character, involving two distinct, but inter-related, local and collective barriers. There are no divergences at volume fractions below jamming or temperatures above zero Kelvin. The ideas are first developed and implemented analytically and numerically in the context of hard sphere fluids. In an intermediate volume fraction crossover regime, the local cage process is dominant in a manner consistent with an apparent Arrhenius behavior. The super-Arrhenius collective barrier is more strongly dependent on volume fraction, dominates the highly viscous regime, and is well described by a nonsingular law below jamming. The increase of the collective barrier is determined by the amplitude of thermal density fluctuations, dynamic shear modulus or transient localization length, and a growing microscopic jump length. Alpha relaxation time calculations are in good agreement with recent experiments and simulations on dense fluids and suspensions of hard spheres. Comparisons of the theory with elastic models and entropy crisis ideas are explored. The present work provides a foundation for constructing a quasi-universal, fit-parameter-free theory for relaxation in thermal molecular liquids over 14 orders of magnitude in time.

Edge transport studies in the edge and scrape-off layer of the National Spherical Torus Experiment with Langmuir probes

Transport and turbulence profiles were directly evaluated using probes for the first time in the edge and scrape-off layer (SOL) of NSTX [Ono et al., Nucl. Fusion 40, 557 (2000)] in low (L) and high (H) confinement, low power (Pin∼ 1.3 MW), beam-heated, lower single-null discharges. Radial turbulent particle fluxes peak near the last closed flux surface (LCFS) at ≈4×1021 s−1 in L-mode and are suppressed to ≈0.2×1021 s−1 in H mode (80%–90% lower) mostly due to a reduction in density fluctuation amplitude and of the phase between density and radial velocity fluctuations. The radial particle fluxes are consistent with particle inventory based on SOLPS fluid modeling. A strong intermittent component is identified. Hot, dense plasma filaments 4–10 cm in diameter, appear first ∼2 cm inside the LCFS at a rate of ∼1×1021 s−1 and leave that region with radial speeds of ∼3–5 km/s, decaying as they travel through the SOL, while voids travel inward toward the core. Profiles of normalized fluctuations feature levels of 10% inside LCFS to ∼150% at the LCFS and SOL. Once properly normalized, the intermittency in NSTX falls in similar electrostatic instability regimes as seen in other devices. The L-H transition causes a drop in the intermittent filaments velocity, amplitude and number in the SOL, resulting in reduced outward transport away from the edge and a less dense SOL.

Magnification bias as a novel probe for primordial magnetic fields

In this paper we investigate magnetic fields generated in the early Universe. These fields are important candidates at explaining the origin of astrophysical magnetism observed in galaxies and galaxy clusters, whose genesis is still by and large unclear. Compared to the standard inflationary power spectrum, intermediate to small scales would experience further substantial matter clustering, were a cosmological magnetic field present prior to recombination. As a consequence, the bias and redshift distribution of galaxies would also be modified. Hitherto, primordial magnetic fields (PMFs) have been tested and constrained with a number of cosmological observables, e.g. the cosmic microwave background radiation, galaxy clustering and, more recently, weak gravitational lensing. Here, we explore the constraining potential of the density fluctuation bias induced by gravitational lensing magnification onto the galaxy-galaxy angular power spectrum. Such an effect is known as magnification bias. Compared to the usual galaxy clustering approach, magnification bias helps in lifting the pathological degeneracy present amongst power spectrum normalisation and galaxy bias. This is because magnification bias cross-correlates galaxy number density fluctuations of nearby objects with weak lensing distortions of high-redshift sources. Thus, it takes advantage of the gravitational deflection of light, which is insensitive to galaxy bias but powerful in constraining the density fluctuation amplitude. To scrutinise the potentiality of this method, we adopt a deep and wide-field spectroscopic galaxy survey. We show that magnification bias does contain important information on primordial magnetism, which will be useful in combination with galaxy clustering and shear. We find we shall be able to rule out at 95.4% CL amplitudes of PMFs larger than 5 × 10−4 nG for values of the PMF power spectral index nB ∼ 0.

Relating the L–H power threshold scaling to edge turbulence dynamics

Understanding the physics of the L–H transition power threshold scaling dependencies on toroidal field and density is critical to operating and optimizing the performance of ITER. Measurements of long-wavelength (k⊥ρI < 1) turbulent eddy dynamics, characteristics, flows, and flow shear in the near edge region of DIIID plasmas have been obtained during an ion gyroradius scan (varying toroidal field and current) and density scan in a favourable geometry (ion ∇B drifts towards the X-point), in order to determine the underlying mechanisms that influence the macroscopic L–H power threshold scaling relations. It is found that the normalized integrated long wavelength density fluctuation amplitudes (ñ/n) in the pedestal increases with ρ* approaching the L–H transition. The turbulence poloidal flow spectrum evolves from geodesic acoustic mode dominant at lower power to low-frequency zonal flow (LFZF) dominant near the L–H transition, and the effective shearing rate correspondingly increases. An inferred Reynolds stress, , from BES velocimetry (inferring velocity field from imaging) measurements is found to significantly increase near the L–H transition. At lower electron density, a clear increase of the LFZF is observed prior to the L–H transition, which is not evident at higher density. Taken together, these results are qualitatively consistent with the electron density and toroidal field scaling of the L–H transition power threshold.

Unified Theory of Activated Relaxation in Liquids over 14 Decades in Time

We formulate a predictive theory at the level of forces of activated relaxation in hard sphere fluids and thermal liquids that covers in a unified manner the apparent Arrhenius, crossover and deeply supercooled regimes. The alpha relaxation event involves coupled cage-scale hopping and a long range collective elastic distortion of the surrounding liquid, which results in two inter-related, but distinct, barriers. The strongly temperature and density dependent collective barrier is associated with a growing length scale, the shear modulus and density fluctuations. Thermal liquids are mapped to an effective hard sphere fluid based on matching long wavelength density fluctuation amplitudes, resulting in a zeroth order quasi-universal description. The theory is devoid of fit parameters, has no divergences at finite temperature nor below jamming, and captures the key features of the alpha time of molecular liquids from picoseconds to hundreds of seconds.

THE FATE OF PLANETESIMALS IN TURBULENT DISKS WITH DEAD ZONES. I. THE TURBULENT STIRRING RECIPE

Turbulence in protoplanetary disks affects planet formation in many ways. While small dust particles are mainly affected by the aerodynamical coupling with turbulent gas velocity fields, planetesimals and larger bodies are more affected by gravitational interaction with gas density fluctuations. For the latter process, a number of numerical simulations have been performed in recent years, but a fully parameter-independent understanding has not been yet established. In this study, we present simple scaling relations for the planetesimal stirring rate in turbulence driven by magnetorotational instability (MRI), taking into account the stabilization of MRI due to Ohmic resistivity. We begin with order-of-magnitude estimates of the turbulence-induced gravitational force acting on solid bodies and associated diffusion coefficients for their orbital elements. We then test the predicted scaling relations using the results of recent Ohmic-resistive MHD simulations by Gressel et al. We find that these relations successfully explain the simulation results if we properly fix order-of-unity uncertainties within the estimates. We also update the saturation predictor for the density fluctuation amplitude in MRI-driven turbulence originally proposed by Okuzumi & Hirose. Combination of the scaling relations and saturation predictor allows to know how the turbulent stirring rate of planetesimals depends on disk parameters such as the gas column density, distance from the central star, vertical resistivity distribution, and net vertical magnetic flux. In Paper II, we apply our recipe to planetesimal accretion to discuss its viability in turbulent disks.

Possible indication for non-zero neutrino mass and additional neutrino species from cosmological observations

The constraints on total neutrino mass and effective number of neutrino species based on CMB anisotropy power spectrum, Hubble constant, baryon acoustic oscillations and galaxy cluster mass function data are presented. It is shown that the discrepancies between various cosmological data in Hubble constant and density fluctuation amplitude, measured in standard LCDM cosmological model, can be eliminated if more than standard effective number of neutrino species and non-zero total neutrino mass are considered. This extension of LCDM model appears to be \approx 3 \sigma\ significant when all cosmological data are used. The model with approximately one additional neutrino type, N_eff \approx 4, and with non-zero total neutrino mass, \approx 0.5 eV, provide the best fit to the data. In the model with only one massive neutrino the upper limits on neutrino mass are slightly relaxed. It is shown that these deviations from LCDM model appear mainly due to the usage of recent data on the observations of baryon acoustic oscillations. Larger than standard number of neutrino species is measured mainly due to the comparison of the BAO data with direct measurements of Hubble constant, which was already noticed earlier. As it is shown below, the data on galaxy cluster mass function in this case give the measurement of non-zero neutrino mass.

Turbulence and transport suppression scaling with flow shear on the Large Plasma Device

Continuous control over azimuthal flow and shear in the edge of the Large Plasma Device (LAPD) [W. Gekelman et al., Rev. Sci. Instr. 62, 2875 (1991)] has been achieved using a biasable limiter. This flow control has allowed a careful study of the effect of flow shear on pressure-gradient-driven turbulence and particle transport in LAPD. The combination of externally controllable shear in a turbulent plasma along with the detailed spatial diagnostic capabilities on LAPD makes the experiment a useful testbed for validation of shear suppression models. Motivated by these models, power-law fits are made to the density and radial velocity fluctuation amplitudes, particle flux, density-potential crossphase, and radial correlation length. The data show a break in the trend of these quantities when the shearing rate (γs=∂Vθ/∂r) is comparable to the turbulent decorrelation rate (1/τac). No one model captures the trends in the all turbulent quantities for all values of the shearing rate, but some models successfully match the trend in either the weak (γsτac&amp;lt;1) or strong (γsτac&amp;gt;1) shear limits.

Density fluctuations induced by MARFE on FTU

High density operations on FTU (Frascati Tokamak Upgade) are affected by strong density oscillations due to the so-called MARFE (Multifaceted Asymmetric Radiation From the Edge). An analysis of these oscillations is reported here. The MARFE on FTU occurs at the value of ρ = 0.48 (ρ is ratio between line-averaged density with averaged current density in the plasma); at the MARFE onset, the volume averaged density versus central density is almost constant, corresponding to the value of 0.8. The MARFE is observed to move up and down along the poloidal circumference on FTU. The MARFE movement causes continuous density fluctuations. Amplitude of density fluctuations decreases with edge safety factor and with electron density. The mechanism to cause MARFE movement is discussed. If amplitude exceeds a certain threshold, it may cause poloidal heat flux asymmetry between the edges of the MARFE, which will make the MARFE moving along the poloidal circumference.

Influence of Edge Defects, Vacancies, and Potential Fluctuations on Transport Properties of Extremely Scaled Graphene Nanoribbons

Atomistic quantum transport simulations of a large ensemble of devices are employed to investigate the impact of different sources of disorder on the transport properties of extremely scaled (length of 10 nm and width of 1–4 nm) graphene nanoribbons. We report the dependence of the transport gap, on- and off-state conductances, and on–off ratio on edge-defect density, vacancy density, and potential fluctuation amplitude. For the smallest devices and realistic lattice defect densities, the transport gap increases by up to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim$</tex></formula> 300%, and the on–off ratio reaches almost <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim\!\!\hbox{10}^{6}$</tex> </formula> . We also report a rather high variation of the transport gap and on–off ratio. In contrast, we find that the potential fluctuations have a negligible impact on the transport gap and cause a relatively modest increase of the on–off ratio.