Bojan Nikolic

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We describe phase-retrieval holography measurements of the 100-m diameter Green Bank Telescope using astronomical sources and an astronomical receiver operating at a wavelength of 7 mm. We use the technique with parameterization of the aperture in terms of Zernike polynomials and employing a large defocus, as described by Nikolic et al. (2006). Individual(More)
Using high-resolution three-dimensional realisations of turbulent fields, we investigate the limits on achievable performance of atmospheric phase correction using water-vapour ra-diometers arising from following effects: the incoherent measurement of power from water by the radiometers (in contrast to coherent detection of the astronomical signal); the(More)
The success of any ALMA phase-calibration strategy, which incorporates phase transfer , depends on a good understanding of how the atmospheric path delay changes with frequency (e.g. Holdaway & Pardo 2001). We explore how the wet dispersive path delay varies for realistic atmospheric conditions at the ALMA site using the ATM transmission code. We find the(More)
This memo describes the software engineering and technical details of the design and implementation of the wvrgcal program and associated libraries. This program performs off-line correction of atmospheric phase fluctuations in ALMA observations, using the 183 GHz Water Vapour Radiometers (WVRs) installed on the ALMA 12 m dishes. The memo can be used as a(More)
This memo investigates the properties of atmospheric turbulence above the ALMA site using measurements from the Water Vapour Radiometers (WVRs), in particular testing the Kolmogorov turbulence model and searching for evidence of an outer length scale. We fit model power-spectral density (PSD) curves to the measured power spectra for a number of observations(More)
By observing bright and compact astronomical sources while also taking data with the 183 GHz Water Vapour Radiometers, ALMA will be able to measure the 'empirical' relationship between fluctuations in the phase of the astronomical signal and the fluctuations of sky brightness around 183 GHz. Simulations of such measurements assuming only thermal noise in(More)
The irreducible representations of all of the 80 diperiodic groups, being the symmetries of the systems translationally periodical in two directions, are calculated. To this end, each of these groups is factorized as the product of a generalized translational group and an axial point group. The results are presented in the form of the tables, containing the(More)
We present Giant Metrewave Radio Telescope 21-cm HI observations towards a sample of compact radio sources behind galaxy groups, to search for cool HI. The results – from high dynamic range spectra for 8 lines-of-sight through 7 galaxy groups – do not show any evidence for absorption by cool HI. At a resolution of 20 km s −1 , the optical depth upper limits(More)