A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses

Multipath propagation in the interstellar medium distorts radio pulses, an effect predominant for distant pulsars observed at low frequencies. Typically, broadened pulses are analyzed to determine the amount of propagation-induced pulse broadening, but with little interest in determining the undistorted pulse shapes. In this paper we develop and apply a method that recovers both the intrinsic pulse shape and the pulse broadening function that describes the scattering of an impulse. The method resembles the CLEAN algorithm used in synthesis imaging applications, although we search for the best pulse broadening function, and perform a true deconvolution to recover intrinsic pulse structre. As figures of merit to optimize the deconvolution, we use the positivity and symmetry of the deconvolved result along with the mean square residual and the number of points below a given threshold. Our method makes no prior assumptions about the intrinsic pulse shape and can be used for a range of scattering functions for the interstellar medium. It can therefore be applied to a wider variety of measured pulse shapes and degrees of scattering than the previous approaches. We apply the technique to both simulated data and data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical Journa

Bose-Einstein Condensates in Rotating Lattices

Strongly interacting bosons in 2D in a rotating square lattice are investigated via a modified Bose-Hubbard Hamiltonian. Such a system corresponds to a rotating lattice potential imprinted on a trapped Bose-Einstein condensate. Second-order quantum phase transitions between states of different symmetries are observed at discrete rotation rates. For the square lattice we study, there are four possible ground-state symmetries.Comment: 4 pages, 5 figures, Accepted for publication in PRL v2: Replaced phase winding labels with symmetry eigenstate indices, replaced Gaussian Ansatz with more general treatment and other minor change

Role of pectinolytic yeasts in the degradation of mucilage layer of Coffea robusta cherries

Pectinolytic yeasts, Saccharomyces marxianus, S. bayanus, S. cerevisiae var. ellipsoideus, and Schizosaccharomyces sp., predominated in the natural fermentation of coffee cherries of Coffea robusta variety grown in Chikmagalur district of Mysore State, India. These yeast species were found on the cherry surfaces, and evidence was adduced to show that the natural fermentation of coffee was the result of activity of microflora from the cherry surface itself rather than that of flora of air or water. Incorporation of pure cultures of Saccharomyces species was shown to aid the process when a mixture of all three species was used. An enzyme preparation from the Saccharomyces species was observed to hasten the mucilage-layer degradation

RFI Identification and Mitigation Using Simultaneous Dual Station Observations

RFI mitigation is a critically important issue in radio astronomy using existing instruments as well as in the development of next-generation radio telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA involve multiple stations with spacings of up to a few thousands of kilometers and thus can exploit the drastically different RFI environments at different stations. As demonstrator observations and analysis for SKA-like instruments, and to develop RFI mitigation schemes that will be useful in the near term, we recently conducted simultaneous observations with Arecibo Observatory and the Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and using the mostly uncorrelated RFI between the two sites to excise RFI from several generic kinds of measurements such as giant pulses from Crab-like pulsars and weak HI emission from galaxies in bands heavily contaminated by RFI. This paper presents observations, analysis, and RFI identification and excision procedures that are effective for both time series and spectroscopy applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for publication in Radio Scienc

Monolithic InP-Based Grating Spectrometer for Wavelength-Division Multiplexed Systems at 1.5 μm

A monolithic InP-based grating spectrometer for use in wavelength-division multiplexed systems at 1.5 μm is reported. The spectrometer uses a single etched reflective focusing diffraction grating and resolves >50 channels at 1 nm spacing with a ~0.3nm channel width and at least 19dB channel isolation. Operation is essentially of the state of the input polarisation

A closer look at arrested spinodal decomposition in protein solutions

Concentrated aqueous solutions of the protein lysozyme undergo a liquid solid transition upon a temperature quench into the unstable spinodal region below a characteristic arrest temperature of Tf=15C. We use video microscopy and ultra-small angle light scattering in order to investigate the arrested structures as a function of initial concentration, quench temperature and rate of the temperature quench. We find that the solid-like samples show all the features of a bicontinuous network that is formed through an arrested spinodal decomposition process. We determine the correlation length Xi and demonstrate that Xi exhibits a temperature dependence that closely follows the critical scaling expected for density fluctuations during the early stages of spinodal decomposition. These findings are in agreement with an arrest scenario based on a state diagram where the arrest or gel line extends far into the unstable region below the spinodal line. Arrest then occurs when during the early stage of spinodal decomposition the volume fraction phi2 of the dense phase intersects the dynamical arrest threshold phi2Glass, upon which phase separation gets pinned into a space-spanning gel network with a characteristic length Xi