Optimal low-rank approximation to a correlation matrix

AbstractLow-rank approximation of a correlation matrix is a constrained minimization problem that can be translated into a minimization–maximization problem by the method of Lagrange multiplier. In this paper, we solve the inner maximization problems with a single spectral decomposition, and the outer minimization problems with gradient-based descending methods. An in-depth analysis is done to characterize the solutions of the inner maximization problem for the case when they are non-unique. The well-posedness of the Lagrange multiplier problem and the convergence of the descending methods are rigorously justified. Numerical results are presented

Light extraction analysis and enhancement in a quantum dot light emitting diode

We apply a rigorous dipole model to analyze the light outcoupling and angular performance of quantum dot light emitting diode (QLED). To illustrate the design principles, we use a red QLED as an example and compare its performance with an organic light emitting diode (OLED). By combining a high refractive index glass substrate with macroextractors, our simulation results indicate that the light outcoupling efficiency is doubled from similar to 40% to similar to 80%. After analyzing the light emission spectra and angular radiation pattern of the device, we confirm that QLED has a much weaker color shift than OLED

Tuning the correlated color temperature of white LED with a guest-host liquid crystal

We demonstrate an electro-optic method to tune the correlated color temperature (CCT) of white light-emitting-diode (WLED) with a color conversion film, consisting of fluorescent dichroic dye doped in a liquid crystal host. By controlling the molecular reorientation of dichroic dyes, the power ratio of the transmitted blue and red lights of the white light can be accurately manipulated, resulting in different CCT. In a proof-of-concept experiment, we showed that the CCT of a yellow phosphor-converted WLED can be tuned from 3200 K to 4100 K. With further optimizations, the tuning range could be enlarged to 2500 K with fairly good color performance: luminous efficacy of radiation (LER) \u3e 300 lm/W, color rendering index (CRI) \u3e 75, and Duv \u3c 0.005. Besides, the operation voltage is lower than 5 V and good angular color uniformity is achieved with remote-phosphor coating. This approach is promising for next generation smart lighting

High performance liquid crystal displays with a low dielectric constant material

We report high performance liquid crystal displays (LCDs), including fringe field switching (p-FFS) and in-plane switching (p-IPS), with a small average dielectric constant (epsilon) but positive dielectric anisotropy material. Our low e based p-FFS and p-IPS LCDs offer several attractive properties, such as high transmittance, low operation voltage, fast response time (even at -20 degrees C), which is particularly desirable for outdoor applications of mobile or wearable display devices, and suppressed flexoelectric effect. Combining these advantages with the inherent outstanding features, such as wide viewing angle, no grayscale inversion, negligible color shift, and pressure resistance, the low e LC based p-FFS and p-IPS are strong contenders for next-generation mobile displays, and high resolution and high frame rate TVs

Analysis on the Settlement of Adjacent Buildings Caused by the Underpassing Construction of the Biased Tunnel

Through the simulation analysis of the settlement and deformation law of the surface buildings caused by the construction of the biased tunnel, the following points are obtained: (1) The Peak formula is revised, and the influence range of the biased tunnel is predicted based on the formula. (2) It is concluded that when the tunnel is biased, the position of maximum deformation caused by ground settlement is generally in a parallel area 0.5 times the buried depth from the center line of the tunnel. (3) Through the double-layer verification of simulation analysis and monitoring measurement data, prior to the construction of buildings with similar weak foundations, their foundations should be reinforced in advance. (4) In the process of this simulation, the complicated influence of water pressure on tunnel excavation was not considered, which can be further optimized in the later stage

A Spatiotemporal Four-Primary Color Lcd With Quantum Dots

A four-primary liquid crystal display (LCD) by hybrid color processing in spatial and temporal domains is presented. By integrating with quantum dots, the number of LED can be reduced and the emission spectrum optimized. This approach exhibits following advantages over conventional three-primary LCDs: 1) it has 1.5X higher spatial resolution and 2X higher light efficiency; 2) it can achieve 130% color gamut in CIE 1931 and 155% in CIE 1976 color space; and 3) it has a more relaxed LC response time requirement and can be readily integrated into commercial LCD products. © 2005-2012 IEEE