Home About us Contact
|
Home About us Contact | ||
|
|
||
Distortion Parameters (distortion + parameter)
Selected AbstractsThe 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the UniverseMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2003Ed Hawkins ABSTRACT We present a detailed analysis of the two-point correlation function, ,(,, ,), from the 2dF Galaxy Redshift Survey (2dFGRS). The large size of the catalogue, which contains ,220 000 redshifts, allows us to make high-precision measurements of various properties of the galaxy clustering pattern. The effective redshift at which our estimates are made is zs, 0.15, and similarly the effective luminosity, Ls, 1.4L*. We estimate the redshift-space correlation function, ,(s), from which we measure the redshift-space clustering length, s0= 6.82 ± 0.28 h,1 Mpc. We also estimate the projected correlation function, ,(,), and the real-space correlation function, ,(r), which can be fit by a power law (r/r0), with r0= 5.05 ± 0.26 h,1 Mpc, ,r= 1.67 ± 0.03. For r, 20 h,1 Mpc, , drops below a power law as, for instance, is expected in the popular , cold dark matter model. The ratio of amplitudes of the real- and redshift-space correlation functions on scales of 8,30 h,1 Mpc gives an estimate of the redshift-space distortion parameter ,. The quadrupole moment of ,(,, ,) on scales 30,40 h,1 Mpc provides another estimate of ,. We also estimate the distribution function of pairwise peculiar velocities, f(v), including rigorously the significant effect due to the infall velocities, and we find that the distribution is well fit by an exponential form. The accuracy of our ,(,, ,) measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of ,(r) and the two redshift-space distortion effects parametrized by , and velocity dispersion, a. We find ,= 0.49 ± 0.09 and a= 506 ± 52 km s,1, although the best-fitting values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(,), and find that the shape is consistent with models and simulations. This is the first time that , and f(v) have been estimated from a self-consistent model of galaxy velocities. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that , (L=L*, z= 0) = 0.47 ± 0.08, and that the present-day matter density of the Universe, ,m, 0.3, consistent with other 2dFGRS estimates and independent analyses. [source] Redshift-space distortions in the PSCz galaxy catalogueMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2001A.N. Taylor We apply a spherical harmonic analysis to the Point Source Redshift Survey (PSCz), to compute the real-space galaxy power spectrum and the degree of redshift distortion caused by peculiar velocities. We employ new parameter eigenvector and hierarchical data compression techniques, allowing a much larger number of harmonic modes to be included, and correspondingly smaller error bars. Using 4644 harmonic modes, compressed to 2278, we find that the IRAS redshift-space distortion parameter is and the amplitude of galaxy clustering on a scale of is . Combining these we find the amplitude of mass perturbations is . While this is compatible with results from the cosmic microwave background (CMB), with a small degree of tilt, it disagrees with the amplitude of matter perturbations estimated from the abundance of clusters by a factor of 2, independent of cosmology. A preliminary model fitting analysis combining the CMB with either the PSCz or cluster abundances shows that the cosmological matter density parameter , and the IRAS bias parameter . However, the cluster abundances suggest that and , while the PSCz requires and . Given the physics of galaxy formation is poorly constrained, we conclude that IRAS galaxies and mass are only partially correlated. [source] Geoelectric dimensionality in complex geological areas: application to the Spanish Betic ChainGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2004Anna Martí SUMMARY Rotational invariants of the magnetotelluric impedance tensor may be used to obtain information on the geometry of underlying geological structures. The set of invariants proposed by Weaver et al. (2000) allows the determination of a suitable dimensionality for the modelling of observed data. The application of the invariants to real data must take into account the errors in the data and also the fact that geoelectric structures in the Earth will not exactly fit 1-D, 2-D or simple 3-D models. In this work we propose a method to estimate the dimensionality of geoelectric structures based on the rotational invariants, bearing in mind the experimental error of real data. A data set from the Betic Chain (Spain) is considered. We compare the errors of the invariants estimated by different approaches: classical error propagation, generation of random Gaussian noise and bootstrap resampling, and we investigate the matter of the threshold value to be used in the determination of dimensionality. We conclude that the errors of the invariants can be properly estimated by classical error propagation, but the generation of random values is better to ensure stability in the errors of strike direction and distortion parameters. The use of a threshold value between 0.1 and 0.15 is recommended for real data of medium to high quality. The results for the Betic Chain show that the general behaviour is 3-D with a disposition of 2-D structures, which may be correlated with the nature of the crust of the region. [source] Theoretical study of electron paramagnetic resonance spectra and local structure of trigonal [Cr(H2O)6]3+ complex in GASH:Cr3+ and AlCl3,·,6H2O:Cr3+ systems at different temperaturesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010Yan-Fang Li Abstract The electron paramagnetic resonance (EPR) parameters and local structure of the octahedral [Cr(H2O)6]3+ complex for Cr3+ doped in GASH and AlCl3,·,6H2O crystals with trigonal symmetry have been studied on the basis of the 120,×,120 complete energy matrices, respectively. By simulating the EPR and optical spectra, the local structure distortion parameters are determined in the temperature range of 4.2,297,K. The calculated results show that the local structure of [Cr(H2O)6]3+ octahedron exhibits an elongated distortion and the value of distortion depends on the temperature. Furthermore, the interrelation between the g -factors and orbit-reduction factor k has been studied, and the influence of the local structure on the EPR parameters has also been discussed. [source] Single-crystal structure refinement of NaTiSi2O6 clinopyroxene at low temperatures (298,<,T,<,100,K)ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2003Günther J. Redhammer The alkali-metal clinopyroxene NaTi3+Si2O6, one of the rare compounds with trivalent titanium, was synthesized at high temperature/high pressure and subsequently investigated by single-crystal X-ray diffraction methods between 298 and 100,K. One main difference between the high- and the low-temperature form is the sudden appearance of two different Ti3+,Ti3+ interatomic distances within the infinite chain of the TiO6 octahedra just below 197 K. This change can be seen as direct evidence for the formation of Ti,Ti singlet pairs in the low-temperature phase. Mean Ti,O bond lengths smoothly decrease with decreasing temperature and the phase transition is associated with a slight jump in the Ti,O bond length. The break in symmetry, however, causes distinct variations, especially with respect to the two Ti,Oapex bond lengths, but also with respect to the four Ti,O bonds in the equatorial plane of the octahedron. The TiO6 octahedron appears to be stretched in the chain direction with a slightly larger elongation in the P low-temperature phase compared with the C2/c high-temperature phase. Polyhedral distortion parameters such as bond-length distortion and octahedral angle variance suggest the TiO6 octahedron in P to be closer to the geometry of an ideal octahedron than in C2/c. Mean Na,O bond lengths decrease with decreasing temperature and the variations in individual Na,O bond lengths are the result of variations in the geometry of the octahedral site. The tetrahedral site acts as a rigid unit, which does not show pronounced changes upon cooling and through the phase transitions. There are neither large changes in bond lengths and angles nor in polyhedral distortion parameters, for the tetrahedral site, when they are plotted. In contrast with the C2/c,P21/c phase transition, found especially in LiMSi2O6 clinopyroxenes, no very large variations are found for the tetrahedral bridging angle. Thus, it is concluded that the main factor inducing the phase transition and controlling the structural variations is the M1 octahedral site. [source] Manganoan rockbridgeite Fe4.32Mn0.62Zn0.06(PO4)3(OH)5: structure analysis and 57Fe Mössbauer spectroscopyACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2006Günther J. Redhammer The structure of the basic iron phosphate rockbridgeite [iron manganese zinc tris(phosphate) pentahydroxide] was reinvestigated with special emphasis on the cation distribution deduced from new X-ray and 57Fe Mössbauer data. Rockbridgeite is orthorhombic, space group Cmcm, and shows three different Fe sites, one with symmetry, another with m symmetry and the third in a general position. One phosphate group has the P atom on a site with m symmetry, while the other has the P atom at a site with mm symmetry. Two Fe sites are fully occupied by ferric iron, while Mn3+ and Fe2+ are situated at a third, principally Fe, site. Structural data, bond-valence sums and polyhedral distortion parameters suggest a new interpretation of the rockbridgeite 57Fe Mössbauer spectrum. [source] | |||||||||||||