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 of the reported vortex beam generators with orbital angular momentum (OAM) in the terahertz region only operate in either the reflection mode or the transmission mode, which greatly limits the integration and application in terahertz technology systems. Herein, we propose a full-space vortex beam regulator at two different frequencies. By changing the VO2 phase transition state, the transmission and reflection mode OAM beams can be flexibly controlled by a single metasurface. For the transmission mode, the proposed structure realizes an OAM beam at the topological charges of l = 1 and 2 at 0.6 THz and 1.4 THz. For the reflection mode, our structure generates an OAM beam at the topological charges of l = 1 and 2 at 0.9 THz and 1.5 THz. Based on the superposition theorem and convolution operation principle, the regulation of an OAM vortex beam with a specific deflection angle and a symmetrical deflection OAM vortex beam are realized. The designed metasurface integrates multiple transmitted and reflected vortex beam functions in full space and has potential application in different terahertz systems.

https://www.mdpi.com/1996-1944/15/23/8639/pdf?version=1670294110

Bidirectional Terahertz Vortex Beam Regulator

This paper presents the field measurement results of wind effects on the world’s tallest reinforced concrete building (CITIC Plaza, 391 m high) located in Guangzhou during the passage of typhoon Pabuk on August 10, 2007. The field data such as wind speed, wind direction and acceleration responses were simultaneously and continuously recorded from the tall building by a remote monitoring system. Detailed analysis of the field data was carried out to investigate the wind effects on the super tall building. The characteristics of the typhoon-generated wind including turbulence intensity, gust factor, turbulence integral length scale and power spectral density of fluctuating wind speed were analyzed. The dynamic characteristics of the buildings were determined from the field measurements and comparison with those calculated from the computational model of the building was made. The measured natural frequencies of the two fundamental sway modes of the building were found to be larger than those calculated. The damping ratios of the building were evaluated by random decrement technique, which demonstrated obvious amplitude-dependent characteristics and increased with increasing amplitude of the building during Typhoon Pabuk.

Full-scale measurements of typhoon effects on a super RC tall building based on a remote monitoring system

Long‐standing debates exist over the mechanism of continental lithospheric extension and, more specifically, over the strain distribution across the lithosphere in intraplate settings. The Cretaceous extensional system in South China extends up to ∼800 km inboard of the Paleo‐Pacific convergent margin and enables investigation of the mechanism(s) of intraplate lithospheric extension. Here we use high‐resolution seismic reflection data to image the crustal and upper‐mantle architecture of the central segment of the extensional system. We identify a compositionally stratified upper lithosphere that has undergone depth‐dependent extension, expressed by heterogeneous normal faulting in the upper crust, widely distributed ductile stretching in the lower crust, mantle influx into the crust, a broadly smooth Moho with localized uplift, and mantle shear‐zone generation. We detect, beneath the center of the Ganzhou Rift, the thinnest crust (28–30 km thick) in South China. It spatially correlates with the locus of strong lithospheric thinning and asthenospheric upwelling. We suggest that the generation of the thinnest crust was assisted by lower‐crustal ductile stretching, mantle shearing, and exhumation during depth‐dependent extension. Our study provides insights into the partitioning of depth‐dependent extensional strain into an intraplate stratified lithosphere and the feedback between crustal and mantle processes that shaped the thinnest crust at a position ∼300 km inboard of the convergent margin during continental extension.

The Thinnest Crust in South China Associated With the Cretaceous Lithospheric Extension: Evidence From SINOPROBE Seismic Reflection Profiling

Based on the convolution and superposition theorem, we propose a reflective anisotropic metasurface to realize the functions of deflection and superposition of vortex beams, bifocal focusing, and focusing vortex beam. At frequency of 1.04THz, two deflection vortex beams with topological charges of ( l =-1 and l =+2) and ( l =+1 and l =-2) are generated under x - and y -polarized terahertz wave incidence, respectively. At focal plane, 1200µm from the top layer of the proposed metasurface, one can see that the bifocal focusing along y -axis and x -axis are produced under x - and y -polarized terahertz wave incidence, respectively. Similarly, focusing vortex beams with l =+1 and l =-2 are realized under x - and y -polarized terahertz wave incidence, respectively. The designed metasurface can flexibly manipulate terahertz wave under different polarization waves incidence and has potential application prospects in fields of terahertz communication. 

Qiusheng Li

Papers

Bidirectional Terahertz Vortex Beam Regulator

Full-scale measurements of typhoon effects on a super RC tall building based on a remote monitoring system

The Thinnest Crust in South China Associated With the Cretaceous Lithospheric Extension: Evidence From SINOPROBE Seismic Reflection Profiling

Multifunctional reflection type anisotropic metasurfaces in terahertz band

Large eddy simulation of the characteristics of conical vortex on a flat roof