Spectroscopic Evidence for Electron-Boson Coupling in Electron-Doped Sr_{2}IrO_{4}.

The pseudogap, d-wave superconductivity and electron-boson coupling are three intertwined key ingredients in the phase diagram of the cuprates. Sr_{2}IrO_{4} is a 5d-electron counterpart of the cuprates in which both the pseudogap and a d-wave instability have been observed. Here, we report spectroscopic evidence for the presence of the third key player in electron-doped Sr_{2}IrO_{4}: electron-boson coupling. A kink in nodal dispersion is observed with an energy scale of ∼50 meV. The strength of the kink changes with doping, but the energy scale remains the same. These results provide the first noncuprate platform for exploring the relationship between the pseudogap, d-wave instability, and electron-boson coupling in doped Mott insulators.

An automated (novel) algorithm for estimating green vegetation cover fraction from digital image: UIP-MGMEP.

Green vegetation cover fraction (VCF) is an important indicator of vegetation status in ecology and agronomy. Digital image analysis (DIA) has been widely accepted as a new VCF measurement technique. In this study, we present a novel fully automatic threshold segmentation algorithm for VCF measurements, which is named as upper inflection point plus mean gradient magnitude of edge pixels (UIP-MGMEP). The algorithm performs VCF estimation upon the vegetation index Excess Green (EXG). UIP-MGMEP optimizes the EXG threshold by searching the upper inflection point (UIP) of the M-Et curve (mean gradient magnitude of edge pixels (MGMEP) vs. EXG threshold), based on the assumption that EXG variance of the boundary pixels between vegetation and background is larger than the variance of the background. Five typical sample images are used to illustrate how ground complexity reduces the distinctness of the UIP. Three controlled experiments are illustrated to test the robustness of UIP-MGMEP to resolution, exposure, and ground complexity. The results show that UIP-MGMEP is a promising algorithm for automatic VCF estimation upon digital images. Compared to broad-leaved grass, narrow-leaved grass is more sensitive to resolution and exposure. To reduce ground complexity, smaller footprint size while more images to cover the same area may be better than one image with large footprint size. UIP-MGMEP is fully automatic, making it promising for batch processing of VCF measurements that is very difficult in any wide-range field survey in the past. UIP-MGMEP algorithm can only extract green vegetation and is not suitable for non-green (even grayish-green) vegetation, due to the limits of vegetation index EXG. In addition, UIP-MGMEP is not recommended for images with VCF less than 0.5% or greater than 99.5%.

Performance evaluation of a bigrating as a beam splitter.

The design of a bigrating for use as a beam splitter is presented. It is based on a rigorous formulation of plane-wave scattering by a bigrating that is composed of two individual gratings oriented in different directions. Numerical results are carried out to optimize the design of a bigrating to perform 1 x 4 beam splitting in two dimensions and to examine its fabrication and operation tolerances. It is found that a bigrating can be designed to perform two functions: beam splitting and polarization purification.

Diffraction characteristics of surface-relief gratings.

We present a theoretical and experimental study on the diffraction characteristics of gratings, with particular attention focused on the effects of polarization. The goal of our study is to develop multifunctional devices for use in a pickup head for optical storage systems. Experiments and numerical calculations are carried out systematically to determine the effects of the grating parameters of depth, period, and duty cycle and also the effects of the incident-wave parameters of incident angle, wavelength, and polarization. It is shown that, theoretically, the diffraction efficiency can reach 100% for both TE and TM polarizations that are incident at the Bragg angle. The simple dispersion characteristics of the Floquet modes are invoked to explain the different diffraction behaviors between the two polarizations. We conclude that a suitably designed grating may split an incident light beam of mixed polarizations into two beams of the opposite polarizations, each propagating in a different direction. Based on the numerical results, simple criteria are suggested for the design of the grating structures for both polarizing and nonpolarizing beam splitters.

Diffraction of a light beam by doubly periodic structures.

Theoretical and experimental results are presented for the diffraction of light by doubly periodic structures that consist of two gratings separated by a uniform thin film. We observe the appearance of many diffracted beams that are due to the interactions through evanescent fields between the two gratings.

The etiology of hypertrophic scar contracture: another view.

A new theory of hypertrophic scar contracture is proposed which accounts for many hitherto unexplained clinical and microscopic characteristics. The primary motive force is limb flexion with the mucopolysaccharide "glue" locking the buckled collagen in the contractured position. A different role for the myofibroblast is postulated.