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

The Index of (White) Noises and their Product Systems

(See detailed abstract in the article.) We single out the correct class of spatial product systems (and the spatial endomorphism semigroups with which the product systems are associated) that allows the most far reaching analogy in their classifiaction when compared with Arveson systems. The main differences are that mere existence of a unit is not it sufficient: The unit must be CENTRAL. And the tensor product under which the index is additive is not available for product systems of Hilbert modules. It must be replaced by a new product that even for Arveson systems need not coincide with the tensor product

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