There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

System Identification I

Dynamics of structures

: This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)

/pdf/nonlinear-time-series-analysis-1j3a35n4y3.pdf

Nonlinear Time Series Analysis.


 Most existing metasurface usually has limited channel behavior, which seriously restricts its development and application. In this paper, we proposed a multi-channel terahertz focused beam generator based on shared-aperture metasurface, which consists of a top square metal strip, a middle layer of silica and a metal bottom plate. By changing the position and size of the shared-aperture array, the designed metasurface can generate arbitrary number multi-channel focusing beams at different predicted positions. In addition, the energy intensity of focusing beams can be controlled. The full-wave simulation results show that the metasurface achieve four-channel vortex focused beam generation with different topological charges, and five-, six-, eight-channel focused beam generation with different energy intensities at frequency of 1 THz, which are in good agreement with the theoretically calculated predictions. This work can provide a new idea for the design of terahertz multichannel devices.

Qiusheng Li

Papers

Multi-channel terahertz focused beam generator based on shared-aperture metasurface