University of Tsukuba

About: University of Tsukuba is a education organization based out in Tsukuba, Ibaraki, Japan. It is known for research contribution in the topics: Population & Gene. The organization has 36352 authors who have published 79483 publications receiving 1934752 citations. The organization is also known as: Tsukuba daigaku & Tsukuba University.

Symmetry-protected exceptional rings in two-dimensional correlated systems with chiral symmetry

Abstract: Emergence of exceptional points in two dimensions is one of the remarkable phenomena in non-Hermitian systems. We here elucidate the impacts of symmetry on the non-Hermitian physics. Specifically, we analyze chiral symmetric correlated systems in equilibrium where the non-Hermitian phenomena are induced by the finite lifetime of quasiparticles. Intriguingly, our analysis reveals that the combination of symmetry and non-Hermiticity results in topological degeneracies of energy bands which we call symmetry-protected exceptional rings (SPERs). We observe the emergence of SPERs by analyzing a non-Hermitian Dirac Hamiltonian. Furthermore, by employing the dynamical mean-field theory, we demonstrate the emergence of SPERs in a correlated honeycomb lattice model whose single-particle spectrum is described by a non-Hermitian Dirac Hamiltonian. We uncover that the SPERs survive even beyond the non-Hermitian Dirac Hamiltonian, which is related to a zeroth Chern number. The argument of symmetry protection also holds for three dimensions, elucidating the presence of a symmetry-protected exceptional torus.

Ocular Higher-Order Aberrations and Contrast Sensitivity after Conventional Laser In Situ Keratomileusis

Abstract: PURPOSE. To investigate prospectively the relation between induced changes in higher-order aberrations of the eye and changes in contrast sensitivity by conventional laser in situ keratomileusis (LASIK) for myopia. METHODS. In 200 eyes of 110 consecutive patients (mean age, 32.7 8.4 years) undergoing LASIK, ocular aberrations and contrast sensitivity function were determined before and 1 month after surgery. The amount of myopic correction was 5.2 2.8 D (range, 1.0 –13.0). Ocular higher-order aberrations were measured for a 4-mm pupil using the Hartmann-Shack wavefront analyzer (KR-9000PW; Topcon, Tokyo, Japan). The root mean square (RMS) of the third- and fourth-order Zernike coefficients was used to represent coma- and spherical-like aberrations, respectively. Total higher-order aberrations were calculated as the RMS of the third- and fourth-order coefficients. Contrast sensitivity and low-contrast visual acuity were measured. From the contrast sensitivity data, the area under the log contrast sensitivity function (AULCSF) was calculated. RESULTS. LASIK significantly improved logMAR best corrected visual acuity (Wilcoxon signed-rank test, P 0.001), but significantly reduced AULCSF (P 0.001) and low-contrast visual acuity (P 0.007). Total higher-order (P 0.001), coma-like (P 0.001), and spherical-like (P 0.001) aberrations were significantly increased after LASIK. The greater the amount of achieved myopia correction was, the more the changes in contrast sensitivity function and ocular higher-order aberrations were. The induced changes in AULCSF by LASIK showed significant correlations with changes in total higher-order (Pearson r 0.221, P 0.003), coma-like (r 0.205, P 0.006), and spherical-like (r 0.171, P 0.022) aberrations. The changes in logMAR low-contrast visual acuity by surgery significantly correlated with changes in total higher-order (r 0.222, P 0.003), coma-like (r 0.201, P 0.007), and spherical-like (r 0.207, P 0.005) aberrations. CONCLUSIONS. Conventional LASIK significantly increases ocular higher-order aberrations, which compromise the postoperative contrast sensitivity function. (Invest Ophthalmol Vis Sci. 2004; 45:3986 –3990) DOI:10.1167/iovs.04-0629

Reproducibility of retinal and choroidal thickness measurements in enhanced depth imaging and high-penetration optical coherence tomography.

Abstract: PURPOSE. Two optical coherence tomography (OCT) modalities can visualize the choroid: high-penetration OCT (HP-OCT) using a long wavelength, and enhanced depth imaging technique using Heidelberg OCT (EDI-OCT). The purpose of this study was to compare and investigate the agreement among the retinal/choroidal thickness parameters. METHODS. Twenty-four eyes of 12 healthy volunteers were examined simultaneously using the prototype swept-source HP-OCT and EDI-OCT. Six independent examiners measured the central retinal/choroidal thicknesses on horizontal B-scan images. The reliability was evaluated by intraclass correlation coefficient (ICC). Intervisit reproducibility was assessed by examining 10 of the volunteers 4 months later. RESULTS. Using HP-OCT, the average of all measurements was 209.1 12.9 m in the retina and 292.7 77.3 mi n the choroid, and using EDI-OCT, 212.5 13.3 m in the retina and 283.7 84.1 m in the choroid. An intersystem comparison showed that the ICCs were 0.661 (95% confidence interval [CI], 0.535‐0.754) for the retina and 0.921 (95% CI, 0.875‐ 0.948) for the choroid. Using HP-OCT, the interexaminer ICC reproducibility values were 0.630 (95% CI, 0.447‐0.791) for the retinal thickness and 0.912 (95% CI, 0.835‐0.958) for the choroidal thickness; using EDI-OCT, the values for the retinal and choroidal thicknesses were 0.788 (95% CI, 0.607‐0.898) and 0.970 (95% CI, 0.948‐0.985), respectively. The intervisit ICC values for the retinal and choroidal thicknesses were 0.504 (95% CI, 0.376‐0.609) and 0.893 (95% CI, 0.864‐0.916). CONCLUSIONS. The retinal and choroidal thicknesses were wellcorrelated between the instruments. Higher reliability and reproducibility are expected for the choroidal thickness measurements despite with higher morphologic interindividual variations. (Invest Ophthalmol Vis Sci. 2011;52:5536‐5540)