Gridless Two-dimensional DOA Estimation With L-shaped Array Based on the Cross-covariance Matrix

The atomic norm minimization (ANM) has been successfully incorporated into the two-dimensional (2-D) direction-of-arrival (DOA) estimation problem for super-resolution. However, its computational workload might be unaffordable when the number of snapshots is large. In this paper, we propose two gridless methods for 2-D DOA estimation with L-shaped array based on the atomic norm to improve the computational efficiency. Firstly, by exploiting the cross-covariance matrix an ANM-based model has been proposed. We then prove that this model can be efficiently solved as a semi-definite programming (SDP). Secondly, a modified model has been presented to improve the estimation accuracy. It is shown that our proposed methods can be applied to both uniform and sparse L-shaped arrays and do not require any knowledge of the number of sources. Furthermore, since our methods greatly reduce the model size as compared to the conventional ANM method, and thus are much more efficient. Simulations results are provided to demonstrate the advantage of our methods

Forming Within-site Topical Information Space to Facilitate Online Free-Choice Learning

Locating specific and structured information in the World Wide Web (WWW) is becoming increasingly difficult, because of the rapid growth of the Web and the distributed nature of information. Although existing search engines do a good job in ranking web pages based on topical relevance, they provide limited assistance for free-choice learners to leverage the nonlinear nature of information spaces for knowledge acquisition. We hypothesize that free-choice learners would benefit more from structured topical information spaces than a list of individual pages across multiple websites. We conceptualize a within-site topical information space as a sphere formed by linked pages centering on a web page. In this paper, we investigate techniques and heuristics to form the space. In particular, we propose a hybrid method that relies on not only content-based characteristics and user queries, but also a site\u27s global structure. Experimental results show that consideration of website topology provides good improvement to page relevance estimation, indicating the clustering tendency of relevant pages

Boundedness of some sublinear operators and commutators on Morrey-Herz spaces with variable exponents

summary:We introduce a new type of variable exponent function spaces $M\dot K^{\alpha (\cdot ),\lambda }_{q,p(\cdot )}(\mathbb R^n)$ of Morrey-Herz type where the two main indices are variable exponents, and give some propositions of the introduced spaces. Under the assumption that the exponents $\alpha$ and $p$ are subject to the log-decay continuity both at the origin and at infinity, we prove the boundedness of a wide class of sublinear operators satisfying a proper size condition which include maximal, potential and Calderón-Zygmund operators and their commutators of BMO function on these Morrey-Herz type spaces by applying the properties of variable exponent and BMO norms