Reconstructing the linear power spectrum of cosmological mass fluctuations

We describe an attempt to reconstruct the initial conditions for the formation of cosmological large-scale structure. The power spectrum of the primordial fluctuations is affected by bias, nonlinear evolution and redshift-space distortions, but we show how these effects can be corrected for analytically. Using eight independent datasets, we obtain excellent agreement in the estimated linear power spectra given the following conditions. First, the relative bias factors for Abell clusters, radio galaxies, optical galaxies and IRAS galaxies must be in the ratios 4.5:1.9:1.3:1. Second, the data require redshift-space distortion: \Omega^{0.6}/b_{\ss I} = 1.0 \pm 0.2. Third, low values of $\Omega$ and bias are disfavoured. The shape of the spectrum is extremely well described by a CDM transfer function with an apparent value of the fitting parameter $\Omega h =0.25$. Tilted models predict too little power at 100 Mpc wavelengths.Comment: Edinburgh Astronomy Preprint 26/93. Accepted for publication in Monthly Notices of the RAS. 13 pages of LaTeX, plus 10 PostScript figures. You will need the mn.sty style file (from babbage: get mn.sty). The figure .ps files are in the usual self-unpacking unix scrip

Nonlinear evolution of cosmological power spectra

Hamilton et al. have suggested an invaluable scaling formula which describes how the power spectra of density fluctuations evolve into the nonlinear regime of hierarchical clustering. This paper presents an extension of their method to low-density universes and universes with nonzero cosmological constant. We pay particular attention to models with large negative spectral indices, and give a spectrum-dependent fitting formula which is of significantly improved accuracy by comparison with an earlier version of this work. The tendency of nonlinear effects to increase power on small scales is stronger for spectra with more negative spectral indices, and for lower densities. However, for low-density models with a cosmological constant, the nonlinear effects are less strong than for an open universe of the same $\Omega$.Comment: MNRAS in press. 8 pages TeX including Postscript figures. Uses mn.tex and epsf.te

Study of a Renovated Command Module Laboratory and Renovated Command Module. Volume 3 - Subsystems Analysis Final Report

Technical feasibility of renovated command module laboratory and renovated command modul

Ferromagnetically coupled dimers on the distorted Shastry-Sutherland lattice: Application to (CuCl)LaNb2O7

A recent study [Tassel {\it et al.}, Phys. Rev. Lett. {\bf 105}, 167205 (2010)] has proposed a remarkable spin model for (CuCl)LaNb2O7, in which dimers are ferromagnetically coupled to each other on the distorted Shastry-Sutherland lattice. In this model, the intra-dimer exchange coupling J>0 is antiferromagnetic, while the inter-dimer exchange couplings are ferromagnetic and take different values, J_x,J_y<0, in the two bond directions. Anticipating that the highly frustrated character of this model may lead to a wide range of behaviors in (CuCl)LaNb2O7 and related compounds, we theoretically investigate the ground state phase diagram of this model in detail using the following three approaches: a strong-coupling expansion for small J_x and J_y, exact diagonalization for finite clusters, and a Schwinger boson mean field theory. When |J_x|, |J_y| <~ J, the system stays in a dimer singlet phase with a finite spin gap. This state is adiabatically connected to the decoupled-dimer limit J_x=J_y=0. We show that the magnetization process of this phase depends crucially on the spatial anisotropy of the inter-dimer couplings. The magnetization shows a jump or a smooth increase for weak and strong anisotropy, respectively, after the spin gap closes at a certain magnetic field. When |J_x| or |J_y| >~ J, quantum phase transitions to various magnetically ordered phases (ferromagnetic, collinear stripe, and spiral) occur. The Schwinger boson analysis demonstrates that quantum fluctuations split the classical degeneracy of different spiral ground states. Implications for (CuCl)LaNb2O7 and related compounds are discussed in light of our theoretical results and existing experimental data.Comment: 21 pages, 20 figure

Generation of static electricity during fluidisation of polyethylene and its elimination by air ionisation

International audienceStatic electricity is the cause of many problems in the process industries, in particular, when handling powders and granules. The methods usually used to reduce static electricity involve the addition of antistatic agents, the increase of relative humidity or ionisation. But these solutions can give rise to other problems. The purpose of this paper is, first, to study the kinetics of electrostatic charging of polyethylene granules and powders in a fluidised bed and, second, to study the elimination of the static electricity using the same particles with a special supersonic injector producing a neutral cloud of positive and negative ions. The experiments involve taking samples of particles at various times and various locations in the bed and measuring the charge-to-mass ratio by means of a Faraday pail connected to an electrometer. It is found that the electrostatic charge increases during fluidisation up to a limiting value. Concerning the charges elimination, it is shown that ions ejected from the eliminator cannot penetrate into the bulk of particles. Only the particles on the upper surface of the bed are discharged. Thus, the efficiency of the supersonic injector for overall charge neutralisation depends on the movement of the particles in the bed and, in particular, the rate of renewal of the upper surface of the fluidised bed

Shuttle orbiter Ku-band radar/communications system design evaluation

Tasks performed in an examination and critique of a Ku-band radar communications system for the shuttle orbiter are reported. Topics cover: (1) Ku-band high gain antenna/widebeam horn design evaluation; (2) evaluation of the Ku-band SPA and EA-1 LRU software; (3) system test evaluation; (4) critical design review and development test evaluation; (5) Ku-band bent pipe channel performance evaluation; (6) Ku-band LRU interchangeability analysis; and (7) deliverable test equipment evaluation. Where discrepancies were found, modifications and improvements to the Ku-band system and the associated test procedures are suggested