Combined Power Spectrum Research Articles

Cosmology from clustering of Lyα galaxies: breaking non-gravitational Lyα radiative transfer degeneracies using the bispectrum

Large surveys for Lyman-alpha emitting (LAE) galaxies have been proposed as a new method for measuring clustering of the galaxy population at high redshift with the goal of determining cosmological parameters. However, Lyman-alpha radiative transfer effects may modify the observed clustering of LAE galaxies in a way that mimics gravitational effects, potentially reducing the precision of cosmological constraints. For example, the effect of the linear redshift-space distortion on the power spectrum of LAE galaxies is potentially degenerate with Lyman-alpha radiative transfer effects owing to the dependence of observed flux on intergalactic medium velocity gradients. In this paper, we show that the three-point function (bispectrum) can distinguish between gravitational and non-gravitational effects, and thus breaks these degeneracies, making it possible to recover cosmological parameters from LAE galaxy surveys. Constraints on the angular diameter distance and the Hubble expansion rate can also be improved by combining power spectrum and bispectrum measurements.

Effect of non-Kolmogorov turbulence on beam spreading in satellite laser communication

In the past half a century, satellite laser communication has caught the attention of scientists due to its distinct advantages in comparison with conventional satellite microwave communication. For ground-to-satellite and satellite-to-ground data links, the atmosphere is a part of the communication channel; thus, atmospheric turbulence severely degrades the performance of satellite laser communication systems. In general, the Kolmogorov turbulence model is used to study the effect of atmosphere turbulence on satellite laser communications since it has been confirmed by numerous direct measurements of temperature and humidity fluctuations in the atmospheric boundary layer. However, increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes inadequate to describe atmospheric statistics properly, in particular, in some domains of the atmosphere. We analyze the joint influence of Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the spot size associated with the uplink and downlink propagation channels for a satellite laser communication system in the geosynchronous orbit, using a power spectrum of non-Kolmogorov turbulence with power law −5 that describes the refractiveindex fluctuations in the atmosphere above 6 km and considering the combined power spectrum of Kolmogorov and non-Kolmogorov turbulence. Before this analysis, we study the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams.

Influence of non-kolmogorov turbulence on intensity fluctuations in laser satellite communication

Satellite laser communication holds the potential for high-bandwidth communication, but the atmosphere can significantly affect the capability of this type of communication systems for satellite-toground and ground-to-satellite data links to transfer information consistently and operate effectively. Usually the influence of atmosphere on satellite laser communication is investigated based on the Kolmogorov turbulence model. However, both increasing experimental evidence and theoretical investigations have shown that the Kolmogorov theory is sometimes incomplete to describe the atmospheric statistics properly, in particular, in some portions of the atmosphere. Considering a non-Kolmogorov turbulent power spectrum with power law −5 that describes the refractive-index fluctuations in the atmosphere above 6 km, we calculate the scintillation index of a lowest-order Gaussian-beam wave under the weak-fluctuation condition. Then, considering a combined power spectrum of refractiveindex fluctuations and using the expression obtained, we analyze the joint influence of the Kolmogorov turbulence from the ground to 6 km and non-Kolmogorov turbulence above 6 km on the scintillation indices of laser beams used in ground-to-satellite and satellite-to-ground laser communication links. We show that the scintillation index in satellite laser communication is equal to the sum of the scintillation indices induced by the Kolmogorov turbulence from ground to 6 km and that caused by the non-Kolmogorov turbulence above 6 km. Also we investigate variations of the scintillation index with the beam radius on the transmitter, wavelength, the radial distance, and zenith angle. Finally, comparing the scintillation index induced by these two turbulences with the conventional results, we show that the scintillation index induced by these two turbulences is a bit smaller than the conventional results.

Structures, energetics, vibrational spectra of NH4+(H2O)n=4,6 clusters: Ab initio calculations and first principles molecular dynamics simulations

Important structural isomers of NH(4) (+)(H(2)O)(n=4,6) have been studied by using density functional theory, Moller-Plesset second order perturbation theory, and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The zero-point energy (ZPE) correction to the complete basis set limit of the CCSD(T) binding energies and free energies is necessary to identify the low energy structures for NH(4) (+)(H(2)O)(n=4,6) because otherwise wrong structures could be assigned for the most probable structures. For NH(4) (+)(H(2)O)(6), the cage-type structure, which is more stable than the previously reported open structure before the ZPE correction, turns out to be less stable after the ZPE correction. In first principles Car-Parrinello molecular dynamics simulations around 100 K, the combined power spectrum of three lowest energy isomers of NH(4) (+)(H(2)O)(4) and two lowest energy isomers of NH(4) (+)(H(2)O)(6) explains each experimental IR spectrum.

Cosmology and the bispectrum

The present spatial distribution of galaxies in the Universe is non-Gaussian, with 40% skewness in $50{h}^{\ensuremath{-}1}\text{ }\text{ }\mathrm{Mpc}$ spheres, and remarkably little is known about the information encoded in it about cosmological parameters beyond the power spectrum. In this work we present an attempt to bridge this gap by studying the bispectrum, paying particular attention to a joint analysis with the power spectrum and their combination with CMB data. We address the covariance properties of the power spectrum and bispectrum including the effects of beat coupling that lead to interesting cross-correlations, and discuss how baryon acoustic oscillations break degeneracies. We show that the bispectrum has significant information on cosmological parameters well beyond its power in constraining galaxy bias, and when combined with the power spectrum is more complementary than combining power spectra of different samples of galaxies, since non-Gaussianity provides a somewhat different direction in parameter space. In the framework of flat cosmological models we show that most of the improvement of adding bispectrum information corresponds to parameters related to the amplitude and effective spectral index of perturbations, which can be improved by almost a factor of 2. Moreover, we demonstrate that the expected statistical uncertainties in ${\ensuremath{\sigma}}_{8}$ of a few percent are robust to relaxing the dark energy beyond a cosmological constant.

Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey

We investigate the density structure of the interstellar medium using new high-resolution maps of the 8, 24, and 70 μm surface brightness toward a molecular cloud in the Gum Nebula, made as part of the Spitzer Space Telescope Galactic First Look Survey. The maps are correlated with 100 μm images measured with IRAS. At 24 and 70 μm, the spatial power spectrum of surface brightness follows a power law with a spectral index of -3.5. At 24 μm, the power-law behavior is remarkably consistent from the ~02 size of our maps down to the ~5'' spatial resolution. Thus, the structure of the 24 μm emission is self-similar even at milliparsec scales. The combined power spectrum produced from Spitzer 24 μm and IRAS 25 μm images is consistent with a change in the power-law exponent from -2.6 at spatial wavenumber k ~ 2 × 10-3 arcsec-1 to -3.5 at k ~ 4 × 10-3 arcsec-1. The decrease may be due to the transition from a two-dimensional to three-dimensional structure. Under this hypothesis, we estimate the thickness of the emitting medium to be 0.3 pc.

Sunyaev--Zel'dovich distortion from early galactic winds

We consider the distortion in the cosmic microwave background (CMB) resulting from galactic winds at high redshift. Winds outflowing from galaxies have been hypothesized to be possible sources of metals in the intergalactic medium, which is known to have been enriched to 10(-2.5)Z(.) at z similar to 3. We model these winds as functions of mass of the parent galaxy and redshift, assuming that they activate at a common initial redshift, z(in), and calculate the mean y-distortion and the angular power spectrum of the distortion in the CMB, We find that the thermal Sunyaev-Zeldovich (SZ) effect resulting from the winds is consistent with previous estimates. The distortion arising from the kinetic SZ (kSZ) effect is, however, found to be more important than the thermal SZ (tSZ) effect. We find that the distortion resulting from galactic winds is an important contribution to the power spectrum of distortion at very small angular scales (l similar to 10(4)). We also find that the power spectrum resulting from clustering dominates the Poisson power spectrum for l less than or equal to (4-5) x 10(5). We show explicitly how the combined power spectrum from wind dominates over that of clusters at 217 GHz, relevant for PLANCK, We also show how these constraints change when the efficiency of the winds is varied.

Erratum: Sunyaev-Zel'dovich distortion from early galactic winds

We consider the distortion in the cosmic microwave background (CMB) due to galactic winds at high redshift. Winds outflowing from galaxies have been hypothesized to be possible sources of metals in the intergalactic medium, which is known to have been enriched to $10^{-2.5}$ Z$_{\odot}$ at $z \sim 3$. We model these winds as functions of mass of the parent galaxy and redshift, assuming they activate at a common initial redshift, $z_{in}$, and calculate the mean $y$ distortion and the angular power spectrum of the distortion in the CMB. We find that the thermal Sunyaev-Zel'dovich (SZ) effect due to the winds to be consistent with previous estimates. The distortion due to the kinetic SZ (kSZ) effect is, however, found to be more important than the thermal SZ (tSZ) effect. We find that the distortion due to galactic winds is an important contribution to the power spectrum of distortion at very small angular scales $(l \sim 10^4)$. We also find that the power spectrum due to clustering dominates the Poisson power spectrum for $l \le 4\hbox{--}5 \times 10^5$. We show explicitly how the combined power spectrum from wind dominates over that of clusters at 217 GHz, relevant for PLANCK. We also show how these constraints change when the efficiency of the winds is varied.

Noise reduction system and device, and a mobile radio station

Known is a combined Zelinski - spectral substraction system (1) for noise reduction in a combined speech signal (a(t)) in which signals are recorded with a plurality of microphones (5, 6, 7), using a Wiener filter (10) for estimation of the combined speech signal (a(t)'). In the known system (1) sums and differences of all combinations of speech signals are formed, it being assumed that the differences comprise noise only. Furthermore, a two-stage estimation process is carried out, giving rise to considerable estimation errors. An alternative combined Zelinski - spectral substraction system (1) is proposed, giving rise to fewer estimation errors and being more efficient from a computational point of view. In the Zelinski system, spectral subtraction is carried out on a combined cross spectrum (Ζcc). Then, on a speech segment by speech segment basis, filter coefficients for the Wiener filter (10) are determined from a combined auto power spectrum (Ζac) and the thus corrected combined cross power spectrum (Ζ)cc'). The spectral subtraction is carried out on a lower part of the frequency range only, thereby not introducing unnecessary artefacts.

Multichannel Fourier analysis of patterns in protein sequences

The multichannel Fourier transform is a powerful new method for detecting weak periodic patterns in the sequences of protein molecules, against a background of noise. The result of the analysis is a combined power spectrum, analogous to a chi-square measure, which automatically extracts the most significant nonrandom features from the transforms of the original amino acids at any given frequency. The channels can be combined with either phased or unphased weights. Their degree of phase coherence is measured in terms of a coherence manx and expressed through two polarization parameters