Linear Redshift Distortions and Power in the PSCz Survey

We present a state-of-the-art linear redshift distortion analysis of the recently published IRAS Point Source Catalog Redshift Survey (PSCz). The procedure involves linear compression into 4096 Karhunen-Loeve modes culled from a potential pool of about 3 x 10^5 modes, followed by quadratic compression into three separate power spectra, the galaxy-galaxy, galaxy-velocity, and velocity-velocity power spectra. Least squares fitting to the decorrelated power spectra yields a linear redshift distortion parameter beta = Omega_m^0.6/b = 0.41(+0.13,-0.12).Comment: Minor changes to agree with accepted version. Slight changes to power spectrum, including one more point added at large scales, from binning points formerly discarded as too noisy. 5 pages, including 4 embedded PostScript figures. Accepted for publication in MNRAS Letters (pink pages). Power spectrum data available at http://casa.colorado.edu/~ajsh/pscz

Automatic Spatial Calibration of Ultra-Low-Field MRI for High-Accuracy Hybrid MEG--MRI

With a hybrid MEG--MRI device that uses the same sensors for both modalities, the co-registration of MRI and MEG data can be replaced by an automatic calibration step. Based on the highly accurate signal model of ultra-low-field (ULF) MRI, we introduce a calibration method that eliminates the error sources of traditional co-registration. The signal model includes complex sensitivity profiles of the superconducting pickup coils. In ULF MRI, the profiles are independent of the sample and therefore well-defined. In the most basic form, the spatial information of the profiles, captured in parallel ULF-MR acquisitions, is used to find the exact coordinate transformation required. We assessed our calibration method by simulations assuming a helmet-shaped pickup-coil-array geometry. Using a carefully constructed objective function and sufficient approximations, even with low-SNR images, sub-voxel and sub-millimeter calibration accuracy was achieved. After the calibration, distortion-free MRI and high spatial accuracy for MEG source localization can be achieved. For an accurate sensor-array geometry, the co-registration and associated errors are eliminated, and the positional error can be reduced to a negligible level.Comment: 11 pages, 8 figures. This work is part of the BREAKBEN project and has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 68686