Slope Of Power Spectrum Research Articles

Self-phosphorylation modulates the gating of rat liver gap junction channels: A nonstationary noise analysis

The effect of phosphorylation on the gating of rat liver gap junction hemichannels (Cx 32) has been investigated. It has been shown that self-phosphorylation of rat liver Cx 32 protein reduces the permeability of proteoliposomes as well the current flowing through multichannels in lipid bilayer membrane (BLM). The low frequency power spectral density analyses of nonstationary noise evolved due to the gating of Cx 32 multichannels demonstrated that self-phosphorylation modulated the channel functioning. A clear change in the power spectrum slopes ( α) of the nonstationary noise profiles confirmed the modulation of the channel dynamics due to self-regulation.

The halo mass function from the dark ages through the present day

We use an array of high-resolution N-body simulations to determine the mass function of dark matter haloes at redshifts 10-30. We develop a new method for compensating for the effects of finite simulation volume that allows us to find an approximation to the true 'global' mass function. By simulating a wide range of volumes at different mass resolution, we calculate the abundance of haloes of mass 10 5-12 h -1 M ⊙ . This enables us to predict accurately the abundance of the haloes that host the sources that reionize the Universe. In particular, we focus on the small mass haloes (≥10 5.5-6 h -1 M ⊙ ) likely to harbour Population III stars where gas cools by molecular hydrogen emission, early galaxies in which baryons cool by atomic hydrogen emission at a virial temperature of ∼10 4 K (∼10 7.5-8 h -1 M ⊙ ), and massive galaxies that may be observable at redshift ∼10. When we combine our data with simulations that include high-mass haloes at low redshift, we find that the best fit to the halo mass function depends not only on the linear overdensity, as is commonly assumed in analytic models, but also on the slope of the linear power spectrum at the scale of the halo mass. The Press-Schechter model gives a poor fit to the halo mass function in the simulations at all epochs; the Sheth-Tormen model gives a better match, but still overpredicts the abundance of rare objects at all times by up to 50 per cent. Finally, we consider the consequences of the recently released WMAP 3-yr cosmological parameters. These lead to much less structure at high redshift, reducing the number of z = 10 'mini-haloes' by more than a factor of two and the number of z=30 galaxy hosts by nearly four orders of magnitude. Code to generate our best-fitting halo mass function may be downloaded from http://icc.dur.ac.uk/Research/PublicDownloads/genmf.readme.html.

Cluster‐Supercluster Alignments

We study correlations in spatial orientation between galaxy clusters and their host superclusters using a Hubble Volume N-body realization of a concordance cosmology and an analytic model for tidally-induced alignments. We derive an analytic form for distributions of the alignment angle as functions of halo mass (M), ellipticity (epsilon), distance (r) and velocity (v) and show that the model, after tuning of three parameters, provides a good fit to the numerical results. The parameters indicate a high degree of alignment along anisotropic, collapsed filaments. The degree of alignment increases with M and epsilon while it decreases with r and is independent of v. We note the possibility of using the cluster-supercluster alignment effect as a cosmological probe to constrain the slope of the initial power spectrum.

Power spectrum of HI intensity fluctuations in DDO 210

Abstract We measure the power spectrum of H i intensity fluctuations in the extremely faint (MB∼−10.9) dwarf galaxy DDO 210 using a visibility-based estimator that is well suited to very low signal-to-noise ratio regimes. DDO 210's H i power spectrum is well fitted by a power law PH i(U) = A Uα, with α= −2.75 ± 0.45 over the length-scales 80 pc to 500 pc. We also find that the power spectrum does not change with an increase in the velocity channel width, indicating that the measured fluctuations correspond mainly to density fluctuations. However, Kolmogorov turbulence (with a velocity structure function spectral slope of 2/3) cannot be ruled out from the present observations. The value of the slope α is similar to that obtained in the Milky Way. Compared with the Milky Way, DDO 210 has three orders of magnitude less H i, no spiral arms, and also no measurable ongoing star formation. The fact that the power spectrum slope is nonetheless similar in these two galaxies (and also similar to the values measured for the LMC and SMC) suggests that there is some universal, star-formation-independent phenomenon responsible for producing fine scale structure in the gas.

Influence of water activity on acoustic emission of flat extruded bread

Flat extruded wheat bread and rye bread were subjected to three-point breaking test with simultaneous registration of generated vibrations. Piezoelectric sensor was used to detect vibrations and amplitude–time records were analyzed. It was found that breaking of flat extruded bread generated vibrations in whole audible spectrum. Acoustic emission signal energy expressed in arbitrary units was more dependent on water activity in low frequencies region than those in high frequencies. Transformation of amplitude–time records from time domain to frequency domain showed that regions with high level of power spectrum occurred. Dominating power spectra were in 1–3 and 7–15 kHz. It was proposed to use a ratio between those power spectra as a measure of acoustic activity of the investigated material. This descriptor was called partition power spectrum slope– β. The slope was doubled in the water activity range 0–0.5 and at higher water activities it increased sharply with increasing wetness of the material. Special software was developed to analyze amplitude–time records and detect single acoustic emission events. Majority of acoustic emission events lasted 68.1 μs, and their energy statistically was not dependent on water activity. However, number of acoustic emission events depended strongly on water activity and decreased almost 20 fold in the a w range from 0.03 to 0.75. Analysis of acoustic activity of extruded breads in both time and frequency domains suggested that it originated from simultaneous disintegration and structure microdislocations. Breaking of air cell walls caused large displacements and generated vibrations with low frequencies. Deformation of substructures, splitting of fibers, vibrations and dislocations of macromolecules in the network of the solid matrix could be responsible for generation of high frequency vibrations. It was also noted that both breads were alike when acoustic emission was analyzed in frequency domain, but they were different in the time domain. Combining both frequency and time domains showed that the breads, from the acoustic point of view, are different.

Analysis of concentration patterns in volcanic rocks: Insights into dynamics of highly explosive volcanic eruptions

In this contribution we present new data resulting from the analysis of concentration patterns of mixed juvenile fragments ejected by a highly explosive volcanic eruption that occurred on Salina Island (Aeolian Islands, Italy) and our aim is to identify the fluid-dynamic regime characterizing the magma mixing process. Concentration patterns are studied by calculating the power spectrum of concentration variability along transects crossing the magma mixing structures. Results indicate that the slope of power spectrum has an average value of about −5/3, according to Kolmogorov law of turbulence, and suggest that the magma mixing process, in the studied conditions, can be approximated by considering the passive scalar mixing hypothesis in homogeneous isotropic turbulent flow. These results represent a first step towards a better understanding of magma mixing processes associated to highly explosive volcanic eruptions and this first step is taken by studying concentration patterns in volcanic rocks by coupling petrological and non-linear dynamics methods.

Microrheological assessment of the viscoelastic properties of the endothelial glycocalyx in cremasteric capillaries of living mice

The endothelial glycocalyx forms a gel-like compartment inside the vasculature, of which the glycosaminoglycan hyaluronan (HA) forms a major constituent. We used microrheology to measure the viscoelastic properties of the glycocalyx in vivo. With an optical tweezers intravital microscopic setup we were able to trap platelets inside mouse cremaster capillaries, and with laser-interferometry to measure the frequency behavior of their Brownian motion. The slope of power spectra taken in the center of the capillary lumen (−1.97 [SD 0.03] V^2/Hz^2) is consistent with the behavior a purely viscous fluid (slope = −2). In contrast, the greater slope of power spectra in the glycocalyx (−1.87 [SD 0.04], n=4, p < 0.05), is representative of an elastic component near the vessel wall (slope > −2). Light dye (LD) induced damage of the glycocalyx reversed the slopes of near wall power spectra to −1.96 (SD 0.02), indicating normalized viscous behavior of plasma in the absence of the glycocalyx. An in vitro HA concentration higher than 1 mg/ml was needed to simulate a viscoelastic behavior comparable to that of the glycocalyx, which is at least a 1000 times higher than physiological plasma HA levels. In conclusion, this study reports for the first time on the microrheological properties of the glycocalyx in capillaries of living mice and demonstrates that its viscoelastic behavior resembles that of a relatively high hyaluronan concentration. Financial support by the Royal Netherlands Academy of Arts and Sciences (Fellowship to HV) and The Netherlands Heart Foundation (Established Investigatorship 2005T037 to HV) is greatly appreciated.

The Linear Theory Power Spectrum from the Lyα Forest in the Sloan Digital Sky Survey

We analyze the SDSS Lyα forest PF(k, z) measurement to determine the linear theory power spectrum. Our analysis is based on fully hydrodynamic simulations, extended using hydro-particle-mesh simulations. We account for the effect of absorbers with damping wings, which leads to an increase in the slope of the linear power spectrum. We break the degeneracy between the mean level of absorption and the linear power spectrum without significant use of external constraints. We infer linear theory power spectrum amplitude Δ(kp = 0.009 s km-1, zp = 3.0) = 0.452 and slope neff(kp, zp) = -2.321 (possible systematic errors are included through nuisance parameters in the fit: a factor ≳5 smaller errors would be obtained on both parameters if we ignored modeling uncertainties). The errors are correlated and not perfectly Gaussian, so we provide a χ2 table to accurately describe the results. The result corresponds to σ8 = 0.85, n = 0.94 for a ΛCDM model with Ωm = 0.3, Ωb = 0.04, and h = 0.7 but is most useful in a combined fit with the CMB. The inferred curvature of the linear power spectrum and the evolution of its amplitude and slope with redshift are consistent with expectations for ΛCDM models, with the evolution of the slope, in particular, being tightly constrained. We use this information to constrain systematic contamination, e.g., fluctuations in the UV background. This paper should serve as a starting point for more work to refine the analysis, including technical improvements such as increasing the size and number of the hydrodynamic simulations and improvements in the treatment of the various forms of feedback from galaxies and quasars.

Three‐dimensional Numerical Simulations of Thermal‐Gravitational Instability in the Protogalactic Halo Environment

We study thermal-gravitational instability in simplified models of protogalactic halos using three-dimensional hydrodynamic simulations. The simulations started with isothermal density perturbations of various power spectra and followed the evolution of gas with radiative cooling down to T = 104 K, background heating, and self-gravity for up to ~20 cooling times. Then cooled and condensed clouds were identified and their physical properties were examined in detail. In our models, the cooling timescale is several times shorter than the gravitational timescale. Hence, during the early stage clouds start to form around initial density peaks as a result of thermal instability. Small clouds appear first, and they are pressure-bound. Subsequently, the clouds grow through compression by the background pressure, as well as through gravitational infall. During the late stage, cloud-cloud collisions become important, and clouds grow mostly through gravitational merging. Gravitationally bound clouds with mass Mc 6 × 106 M☉ are found in the late stage. They are approximately in virial equilibrium and have radii Rc 150-200 pc. Those clouds have gained angular momentum through tidal torque, as well as merging, so they have large angular momentum with a spin parameter ~ 0.3. The clouds formed in a denser background tend to have smaller spin parameters, since self-gravity, compared to radiative cooling, is relatively less important at higher density. H2 cooling to below T = 104 K does not drastically change the evolution and properties of clouds, since it is much less efficient than the H Lyα cooling. The slope of the initial density power spectrum affects the morphology of the cloud distribution, but the properties of individual clouds do not sensitively depend on it. We point out limitations of our study and mention briefly the implications of our results for the formation of protoglobular cluster clouds in protogalactic halos.

Density Power Spectrum of Compressible Hydrodynamic Turbulent Flows

Turbulent flows are ubiquitous in astrophysical environments, and understanding density structures and their statistics in turbulent media is of great importance in astrophysics. In this paper, we study the density power spectra, $P_{\rho}$, of transonic and supersonic turbulent flows through one and three-dimensional simulations of driven, isothermal hydrodynamic turbulence with root-mean-square Mach number in the range of $1 \la M_{\rm rms} \la 10$. From one-dimensional experiments we find that the slope of the density power spectra becomes gradually shallower as the rms Mach number increases. It is because the density distribution transforms from the profile with {\it discontinuities} having $P_{\rho} \propto k^{-2}$ for $M_{\rm rms} \sim 1$ to the profile with {\it peaks} having $P_{\rho} \propto k^0$ for $M_{\rm rms} \gg 1$. We also find that the same trend is carried to three-dimension; that is, the density power spectrum flattens as the Mach number increases. But the density power spectrum of the flow with $M_{\rm rms} \sim 1$ has the Kolmogorov slope. The flattening is the consequence of the dominant density structures of {\it filaments} and {\it sheets}. Observations have claimed different slopes of density power spectra for electron density and cold H I gas in the interstellar medium. We argue that while the Kolmogorov spectrum for electron density reflects the {\it transonic} turbulence of $M_{\rm rms} \sim 1$ in the warm ionized medium, the shallower spectrum of cold H I gas reflects the {\it supersonic} turbulence of $M_{\rm rms} \sim$ a few in the cold neutral medium.

Tightening Constraints from the Lyα Forest with the Flux Probability Distribution Function

The analysis of the Lyα forest of absorption lines in quasar spectra has emerged as a potentially powerful technique to constrain the linear matter power spectrum. In most previous work, the amplitude of the ionizing background was fixed by calibrating simulations to match the observed mean transmitted flux in the Lyα forest. This procedure is undesirable in principle, as it requires the estimation of the unabsorbed quasar continuum level, a difficult undertaking subject to various sources of systematic error and bias. We suggest an alternative approach based on measuring the one-point probability distribution function (pdf) of the fluctuations in the flux about the mean, relative to the mean, i.e., the pdf of δf = (f - ⟨f⟩)/⟨f⟩. This statistic, while sensitive to the amplitude of the ionizing background, has the virtue that its measurement does not require an estimate of the unabsorbed continuum level. We present a measurement of the pdf of δf from seven Keck HIRES spectra, spanning a redshift range of z = 2.2-4.4. To illustrate that our method is useful, we compare our measurements of the pdf of δf and measurements of the flux power spectrum from Croft et al. at z = 2.72, with cosmological simulations. From this comparison, we obtain constraints on the mean transmission in the Lyα forest, the slope of the temperature-density relation, as well as the amplitude and slope of the mass power spectrum. Our methodology is useful for obtaining more precise constraints with larger data samples from the Sloan Digital Sky Survey (SDSS).

Power Spectra inVband and Hα of Nine Irregular Galaxies

Fourier transform power spectra of major axis cuts in V and Hα images were made for a sample of nine irregular galaxies. These power spectra reveal structure over a wide range of scales. For six of the galaxies the power spectrum slopes at intermediate scales (10–400 pc) in the V-band images range from -1.3 to -1.5. The similarity of slopes suggests that the same processes are structuring these systems. These slopes are slightly shallower than those observed in other galaxies in H I, molecular emission, dust extinction, and optical light. Three of the galaxies have flat power spectra like sky noise; these three galaxies are relatively indistinct in the direct images. The power spectrum slope for Hα steepens with increasing star formation rate, ranging from a shallow value comparable to the noise at low rates to a steep value with a slope of ~-1.5 at high rates. This change reflects the increasing areal filling factor of Hα emission with increasing star formation rate and an apparently universal slope inside the Hα regions that is comparable to that for Kolmogorov turbulence. The power spectrum of H I in one galaxy has a steeper power law, with a slope of ~-2.9. The fact that the power laws of star formation are about the same for dwarf galaxies and giant spiral galaxies suggests the microscopic processes are the same, independent of spiral density waves and galaxy size.

Joint cosmological parameters forecast from CFHTLS-cosmic shear and CMB data

We present a prospective analysis of a combined cosmic shear and cosmic microwave background data sets, focusing on a Canada France Hawaii Telescope Legacy Survey (CFHTLS) type lensing survey and the current WMAP-1 year and CBI data. We investigate the parameter degeneracies and error estimates of a seven parameter model, for the lensing alone as well as for the combined experiments. The analysis is performed using a Monte Carlo Markov Chain calculation, allowing for a more realistic estimate of errors and degeneracies than a Fisher matrix approach. After a detailed discussion of the relevant statistical techniques, the set of the most relevant 2 and 3-dimensional lensing contours are given. It is shown that the combined cosmic shear and CMB is particularly efficient to break some parameter degeneracies. The principal component directions are computed and it is found that the most orthogonal contours between the two experiments are for the parameter pairs , and , where ns and are, respectively, the slope of the primordial mass power spectrum and the running of the spectral index. It is shown, under the assumption of perfectely controlled systematics, that an improvement of a factor of 2 is expected on the running of the spectral index from the combined data sets. Forecasts for error improvements from a wide field space telescope lensing survey are also given.

Phase-space structure of dark matter haloes: scale-invariant probability density function driven by substructure

We present a method for computing the six-dimensional coarse-grained phase-space density f(x, v) in an N-body system, and derive its distribution function v(f). The method is based on Delaunay tessellation, where v(f) is obtained with an effective fixed smoothing window over a wide f range. The errors are estimated, and v(f) is found to be insensitive to the sampling resolution or the simulation technique. We find that in gravitationally relaxed haloes built by hierarchical clustering, v(f) is well approximated by a robust power law, v(f) ∝f−2.5±0.05, over more than four decades in f, from its virial level to the numerical resolution limit. This is tested to be valid in the Λ cold dark matter cosmology for haloes with masses 109–1015 M⊙, indicating insensitivity to the slope of the initial fluctuation power spectrum. By mapping the phase-space density in position space, we find that the high-f end of v(f) is dominated by the ‘cold’ subhaloes rather than the parent-halo central region and its global spherical profile. The value of f in subhaloes near the virial radius is typically >100 times higher than its value at the halo centre, and it decreases gradually from the outside in toward its value at the halo centre. This seems to reflect phase mixing due to mergers and tidal effects involving puffing up and heating. The phase-space density can thus provide a sensitive tool for studying the evolution of subhaloes during the hierarchical build-up of haloes. It remains to be understood why the evolved substructure adds up to the actual universal power law of v(f) ∝f−5/2. It seems that this behaviour results from the hierarchical clustering process and is not a general result of violent relaxation.

Physical effects on the Lyα forest flux power spectrum: damping wings, ionizing radiation fluctuations and galactic winds

We explore several physical effects on the power spectrum of the Lyα forest transmitted flux. The effects we investigate here are not usually part of hydrodynamic simulations and so need to be estimated separately. The most important effect is that of high column density absorbers with damping wings, which add power on large scales. We compute their effect using the observational constraints on their abundance as a function of column density. Ignoring their effect leads to an underestimation of the slope of the linear theory power spectrum. The second effect we investigate is that of fluctuations in the ionizing radiation field. For this purpose we use a very large high-resolution N-body simulation, which allows us to simulate both the fluctuations in the ionizing radiation and the small-scale Lyα forest within the same simulation. We find an enhancement of power on large scales for quasars and a suppression for galaxies. The strength of the effect rapidly increases with increasing redshift, allowing it to be uniquely identified in cases where it is significant. We develop templates that can be used to search for this effect as a function of quasar lifetime, quasar luminosity function and attenuation length. Finally, we explore the effects of galactic winds using hydrodynamic simulations. We find the wind effects on the Lyα forest power spectrum to be degenerate with parameters related to the temperature of the gas that are already marginalized over in cosmological fits. While more work is needed to conclusively exclude all possible systematic errors, our results suggest that, in the context of data analysis procedures, where parameters of the Lyα forest model are properly marginalized over, the flux power spectrum is a reliable tracer of cosmological information. Ke yw ords: galaxies: high-redshift ‐ intergalactic medium ‐ quasars: absorption lines ‐ cosmology: theory ‐ diffuse radiation ‐ large-scale structure of Universe.

Modification of Projected Velocity Power Spectra by Density Inhomogeneities in Compressible Supersonic Turbulence

The scaling of velocity fluctuation ?v as a function of spatial scale L in molecular clouds can be measured from size-line width relations, principal component analysis, or line centroid variation. Differing values of the power-law index of the scaling relation ?v21/2 L in three dimensions are given by these different methods: the first two give ?3D 0.5, while line centroid analysis gives ?3D 0. This discrepancy has previously not been fully appreciated, as the variation of projected velocity line centroid fluctuations (?v1/2 L) is indeed described, in two dimensions, by ?2D ? 0.5. However, if projection smoothing is accounted for, this implies, in three dimensions, that ?3D ? 0. We suggest that a resolution of this discrepancy can be achieved by accounting for the effect of density inhomogeneity on the observed ?2D obtained from velocity line centroid analysis. Numerical simulations of compressible turbulence are used to show that the effect of density inhomogeneity statistically, but not identically, reverses the effect of projection smoothing in the case of driven turbulence, so that velocity line centroid analysis does indeed predict that ?2D ? ?3D ? 0.5. For decaying turbulence, the effect of density inhomogeneity on the velocity line centroids diminishes with time so that at late times, ?2D ? ?3D + 0.5 as a result of projection smoothing alone. Deprojecting the observed line centroid statistics thus requires some knowledge of the state of the flow. This information can be inferred from the spectral slope of the column density power spectrum and a measure of the standard deviation in column density relative to the mean. Using our numerical results, we can restore consistency between line centroid analysis, principal component analysis, and size-line width relations, and we derive ?3D ? 0.5, corresponding to shock-dominated (Burgers) turbulence, which also describes the simulations of driven turbulence at scales on which numerical dissipation is negligible. We find that this consistency requires that molecular clouds are continually driven on large scales or are only recently formed.

Constraining Amplitude and Slope of the Mass Fluctuation Spectrum Using a Cluster Baryon Mass Function

We derive the baryon mass function for a complete sample of low-redshift clusters and argue that it is an excellent proxy for the total mass function if the ratio fb = Mb/Mtot in all clusters is close to its universal value, ?b/?M. Under this assumption, the baryon mass function can be used to constrain the amplitude and slope of the density fluctuation power spectrum on cluster scales. This method does not use observational determinations of the total mass and thus bypasses major uncertainties in the traditional analyses based on the X-ray temperature function. However, it is sensitive to possible systematic variations of the baryon fraction as a function of cluster mass. Adapting a weak dependence fb , suggested by observations and numerical simulations by Bialek et al., we derive ?8 = 0.72 ? 0.04 and the shape parameter ?Mh = 0.13 ? 0.07, in good agreement with a number of independent methods. We discuss the sensitivity of these values to other cosmological parameters and to different assumptions about variations in fb.

Precision cosmology from the Lyman alpha forest: power spectrum and bispectrum

We investigate the promise of the Lya forest for high-precision cosmology in the era of the Sloan Digital Sky Survey using low-order N-point statistics. We show that, with the existing data, one can determine the amplitude, slope and curvature of the slope of the matter power spectrum with a few per cent precision. Higher-order statistics such as the bispectrum provide independent information that can confirm and improve upon the statistical precision from the power spectrum alone. The achievable precision is comparable to that from the cosmic microwave background with upcoming satellites, and complements it by measuring the power spectrum amplitude and shape at smaller scales. Since the data cover the redshift range 2 2.

The effect of (strong) discrete absorption systems on the Lyman α forest flux power spectrum

We demonstrate that the Lyman a forest flux power spectrum of 'randomized' quasi-stellar object (QSO) absorption spectra is comparable in shape and amplitude to the flux power spectrum of the original observed spectra. In the randomized spectra a random shift in wavelength has been added to the observed absorption lines as identified and fitted with VPFIT. At 0.03 s km -1 15 contribute at large scales, k < 0.03 s km -1 . We further show that a fraction of ≥ 15 per cent of the mean flux decrement is contributed by strong absorbers at z ≥ 2.1. Analysis of the flux power spectrum which use numerical simulations with too few strong absorption systems calibrated with the observed mean flux may underestimate the inferred rms fluctuation amplitude and the slope of the initial dark matter power spectrum.

Impact of gas absorption and surface albedo on cloud radiative smoothing

Using visible and near infrared aircraft observations of stratocumulus clouds over land, the impact of gas absorption and surface albedo on cloud radiative smoothing has been studied. Time series of the observed nadir radiances have been converted into Fourier space, and the scale break as well as the large scale and small scale slopes of the resulting spatial power spectrum have been analyzed. An increase in gas absorption leads to a reduction in radiative smoothing due to a decreased likelihood of horizontal photon transport within the cloud. This can be seen both in the derived scale breaks and in the slope of the power spectrum at high spatial wavenumbers which exhibit a high correlation with cloud single scatter albedo. An increase in surface albedo leads to a radiative smoothing of the observed radiance field at scales proportional to the cloud height and to a decrease in the slope of the large scale spatial power spectrum.