Hybrid-functional and quasi-particle calculations of band structures of Mg2Si, Mg2Ge, and Mg2Sn

We perform hybrid functional and quasi-particle band structure calculations with spin-orbit interaction to investigate the band structures of Mg2Si, Mg2Ge, and Mg2Sn. For all Mg2X materials, where X = Si, Ge, and Sn, the characteristics of band edge states, i.e., band and valley degeneracies, and orbital characters, are found to be conserved, independent of the computational schemes such as density functional generalized gradient approximation, hybrid functionals, or quasi-particle calculations. However, the magnitude of the calculated band gap varies significantly with the computational schemes. Within density-functional calculations, the one-particle band gaps of Mg2Si, Mg2Ge, and Mg2Sn are 0.191, 0.090, and -0.346 eV, respectively, and thus severely underestimated compared to the experimental gaps, due to the band gap error in the density functional theory and the significant relativistic effect on the low-energy band structures. By employing hybrid-functional calculations with a 35% fraction of the exact Hartree-Fock exchange energy (HSE-35%), we overcame the negative band gap issue in Mg2Sn. Finally, in quasi-particle calculations on top of the HSE-35% Hamiltonians, we obtained band gaps of 0.835, 0.759, and 0.244 eV for Mg2Si, Mg2Ge, and Mg2Sn, respectively, consistent with the experimental band gaps of 0.77, 0.74, and 0.36 eV, respectively.Comment: 23 pages, including 84 references, 5 tables, 3 figure

Enhanced blue photoluminescence realized by copper diffusion doping of ZnO thin films

ZnO thin films with blue photoluminescence (PL) have been fabricated through Cu diffusion doping. A CuOx-ZnO mixture, and Cu/ZnO double layer, films were prepared on amorphous SiOx/Si substrates by pulsed laser deposition (PLD), and electron beam (e-beam) deposition, respectively. After sequential oxygen annealing, CuOx-ZnO mixture films exhibited green emission centered at 523 nm. However, Cu/ZnO double layer films differed in producing a blue emission centered at 480 nm. Detailed analysis identified that this blue shift in the emission center resulted from increased blue emissions attributed to Cu dopants in the film by e-beam deposition. Luminescence intensity was increased to 6 cd/m2 for a sample annealed at 700 deg;C. Color points were close to the locus of points following the line of a black-body-radiator on the CIE 1931 XY chromaticity diagram. The present results show that Cu-doped ZnO has strong potential as a cost effective phosphor for use in down converting LEDs. © 2013 Optical Society of America.1

Exploration of New Electroacupuncture Needle Material

Background. Electro Acupuncture (EA) uses the acupuncture needle as an electrode to apply low-frequency stimulation. For its safe operation, it is essential to prevent any corrosion of the acupuncture needle. Objective. The aim of this study is to find an available material and determine the possibility of producing a standard EA needle that is biocompatible. Methods. Biocompatibility was tested by an MTT assay and cytotoxicity testing. Corrosion was observed with a scanning electron microscope (SEM) after 0.5 mA, 60 min stimulation. The straightness was measured using a gap length of 100 mm, and tensile testing was performed by imposing a maximum tensile load. Results. Phosphor bronze, Ni coated SS304, were deemed inappropriate materials because of mild-to-moderate cytotoxicity and corrosion. Ti-6Al-4V and SS316 showed no cytotoxicity or corrosion. Ti-6Al-4V has a 70 times higher cost and 2.5 times lower conductivity than SS316. The results of both straightness and tensile testing confirmed that SS316 can be manufactured as a standard product. Conclusion. As a result, we confirmed that SS316 can be used a new EA electrode material. We hope that a further study of the maximum capacity of low-frequency stimulation using an SS316 for safe operation

Native point defects and low pp-doping efficiency in Mg2(Si,Sn)Mg_2 (Si,Sn) solid solutions: A hybrid-density functional study

We perform hybrid-density functional calculations to investigate the charged defect formation energy of native point defects in $Mg_2 Si$, $Mg_2 Sn$, and their solid solutions. The band gap correction by hybrid-density functional is found to be critical to determine the charged defect density in these materials. For $Mg_2 Si$, $Mg$ interstitials are dominant and provide unintentional $n$-type conductivity. Additionally, as the $Mg$ vacancies can dominate in $Mg$-poor $Mg_2 Sn$, $p$-type conductivity is possible for $Mg_2 Sn$. However, the existence of low formation energy defects such as $Mg_{Sn}^{1+}$ and $I_{Mg}^{2+}$ in $Mg_2 Sn$ and their diffusion can cause severe charge compensation of hole carriers resulting in low $p$-type doping efficiency and thermal degradation. Our results indicate that, in addition to the extrinsic doping strategy, alloying of $Mg_2 Si$ with $Mg_2 Sn$ under $Mg$-poor conditions would be necessary to enhance the $p$-type conductivity with less charge compensation.Comment: Main: 17 pages (including title, abstract, main, references, figure captions. 4 figures). This manuscript is accepted for publication in JALCOM. The article will be published as Gold Open Acces

Ticks Collected from Selected Mammalian Hosts Surveyed in the Republic of Korea During 2008-2009

A tick survey was conducted to determine the relative abundance and distribution of ticks associated with selected mammals in the Republic of Korea (ROK) during 2008-2009. A total of 918 ticks were collected from 76 mammals (6 families, 9 species) captured at 6 provinces and 3 Metropolitan Cities in ROK. Haemaphysalis longicornis (54.4%) was the most frequently collected tick, followed by Haemaphysalis flava (28.5%), Ixodes nipponensis (7.6%), Ixodes pomerantzevi (4.8%), Ixodes persulcatus (4.6%), and Haemaphysalis japonica (0.1%). Adults (57.0%) and nymphs (28.7%) of Ixodes and Haemaphysalis spp. were collected most frequently from medium or large mammals in this survey, while few larvae (14.3%) were collected. Hydropotes inermis was the most frequently captured mammal (52.6%), with a 16.4 tick index and 5 of 6 species of ticks collected during this survey. H. longicornis (69.7%) was the predominant tick collected from H. inermis, followed by H. flava (22.2%), I. persulcatus (6.1%), I. nipponensis (1.8%), and H. japonica (0.2%)

DRAC: Diabetic Retinopathy Analysis Challenge with Ultra-Wide Optical Coherence Tomography Angiography Images

Computer-assisted automatic analysis of diabetic retinopathy (DR) is of great importance in reducing the risks of vision loss and even blindness. Ultra-wide optical coherence tomography angiography (UW-OCTA) is a non-invasive and safe imaging modality in DR diagnosis system, but there is a lack of publicly available benchmarks for model development and evaluation. To promote further research and scientific benchmarking for diabetic retinopathy analysis using UW-OCTA images, we organized a challenge named "DRAC - Diabetic Retinopathy Analysis Challenge" in conjunction with the 25th International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI 2022). The challenge consists of three tasks: segmentation of DR lesions, image quality assessment and DR grading. The scientific community responded positively to the challenge, with 11, 12, and 13 teams from geographically diverse institutes submitting different solutions in these three tasks, respectively. This paper presents a summary and analysis of the top-performing solutions and results for each task of the challenge. The obtained results from top algorithms indicate the importance of data augmentation, model architecture and ensemble of networks in improving the performance of deep learning models. These findings have the potential to enable new developments in diabetic retinopathy analysis. The challenge remains open for post-challenge registrations and submissions for benchmarking future methodology developments