Stratified Markov Chain Monte Carlo Light Transport

Markov chain Monte Carlo (MCMC) sampling is a powerful approach to generate samples from an arbitrary distribution. The application to light transport simulation allows us to efficiently handle complex light transport such as highly occluded scenes. Since light transport paths in MCMC methods are sampled according to the path contributions over the sampling domain covering the whole image, bright pixels receive more samples than dark pixels to represent differences in the brightness. This variation in the number of samples per pixel is a fundamental property of MCMC methods. This property often leads to uneven convergence over the image, which is a notorious and fundamental issue of any MCMC method to date. We present a novel stratification method of MCMC light transport methods. Our stratification method, for the first time, breaks the fundamental limitation that the number of samples per pixel is uncontrollable. Our method guarantees that every pixel receives a specified number of samples by running a single Markov chain per pixel. We rely on the fact that different MCMC processes should converge to the same result when the sampling domain and the integrand are the same. We thus subdivide an image into multiple overlapping tiles associated with each pixel, run an independent MCMC process in each of them, and then align all of the tiles such that overlapping regions match. This can be formulated as an optimization problem similar to the reconstruction step for gradient-domain rendering. Further, our method can exploit the coherency of integrands among neighboring pixels via coherent Markov chains and replica exchange. Images rendered with our method exhibit much more predictable convergence compared to existing MCMC methods.     

A Survey on Gradient‐Domain Rendering

Monte Carlo methods for physically‐based light transport simulation are broadly adopted in the feature film production, animation and visual effects industries. These methods, however, often result in noisy images and have slow convergence. As such, improving the convergence of Monte Carlo rendering remains an important open problem. Gradient‐domain light transport is a recent family of techniques that can accelerate Monte Carlo rendering by up to an order of magnitude, leveraging a gradient‐based estimation and a reformulation of the rendering problem as an image reconstruction. This state of the art report comprehensively frames the fundamentals of gradient‐domain rendering, as well as the pragmatic details behind practical gradient‐domain uniand bidirectional path tracing and photon density estimation algorithms. Moreover, we discuss the various image reconstruction schemes that are crucial to accurate and stable gradient‐domain rendering. Finally, we benchmark various gradient‐domain techniques against the state‐of‐the‐art in denoising methods before discussing open problems.     

Doubly oriented β-form films of poly(vinylidene fluoride)

PVDF sheets, rapidly quenched, were (1) two-step transversely stretched at various temperatures and (2) stretched at various temperatures, rolled at room temperature and then annealed. The orientation patterns of the β-form crystal (which contains the polar b-axis) in these films were analysed on the basis of X-ray diffraction photographs taken with flat and cylindrical cameras. In the case of (1), when both of the two-step transversely stretching temperatures were below 100°C, a doubly oriented film with the plar b-axis oriented parallel to the film surface was obtained. In the case of (2), when the stretching temperature was below 100°C, the sheets then rolled without annealing, another doubly oriented film with the polar b-axis preferentially oriented at 30° to the film surface was obtained. On the other hand, when these films were annealed above 100°C, or the stretching temperatures were above 100°C, orientation patterns in which the polar b-axis was partially rotated through 60° were obtained. The orientation mechanisms of these films are discussed using the measurements of the lattice spacings of the β-form crystal.     

Phase Separation in 12 mol% Ceria-Doped Zirconia Induced by Heat Treatment in H2 and Ar

The phase separation in 12 mol% CeO₂─ZrO₂ ceramic heattreated in a mixture of H₂ and Ar was investigated by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman scattering. After heat treatment at temperatures above 1200°C, the tetragonal solid-solution phase separated into Zr₂Ce₂O₇ and the monoclinic phase. Raman scattering measurements also provided supplementary evidence for the phase separation. XPS showed that the valence change from Ce⁴⁺ to Ce³⁺ predominantly occurred, whereas the reduction from Zr⁴⁺ to Zr³⁺ took place above 1200°C. It is concluded, that in the highly reduced sample, where the valence changes from Ce⁴⁺ (Zr⁴⁺) to Ce³⁺ (Zr³⁺), the phase separation is noticeably promoted. Below 1000°C the phase separation was suppressed because of no appreciable valence change to trigger the phase separation, and the single tetragonal phase was retained.     

Observation of recording pits on phase-change film using a scanning probe microscope

A phase-change film is a key material for optical data storage media such as rewritable compact disks (CD-RW) and digital versatile disk random access memory (DVD-RAM). Data pits are recorded as differences in crystal state (crystallized state vs. amorphous state) on phase-change film. It is very important to distinguish the crystal state difference in a very small area for material research of phase-change film. Measuring size and shape of recorded data pits is also very important for the development to achieve good data reliability and high data density of optical data storage media. The crystal state difference in very small areas of phase-change film is successfully observed by Kelvin probe force microscopy (KFM) and scanning near-field optical/atomic force microscopy (SNOAM). The advantage of KFM and SNOAM for measuring physical property differences in a very small area is demonstrated.     

A method for estimating visceral fat from the elasticity of lumbar subcutaneous fat

Since metabolic syndrome is a cause of lifestyle-related diseases, and its early diagnosis and an evaluation of visceral fat are important, this study proposes a new method of estimating the amount of fat. The goal of this study is to estimate visceral fat from estimation of subcutaneous fat and total fat. The subcutaneous fat is estimated from the elasticity of the lumbar area, and the total fat is estimated from body information such as the abdominal vertical and lateral width, and body weight. Finally, the estimated subcutaneous fat is subtracted from the estimated total fat to calculate the visceral fat. Measurement tests conducted to verify the constructed visceral fat estimation model showed good results, with a correlation of 0.96 between the visceral fat area estimated by the proposed method and the actual measured area. The reproducibility of the estimation model was also verified by the cross validation method.     

Measuring System for Dynamic Characteristics of Semiconductor Switching Elements and Switching Loss of Thyristors

Thyristors today are used in various electrical apparatus where high operational reliability is of prime importance. For better operational reliability, it is essential that thyristors be used most effectively. It especially is important to predict quantitatively the thyristor's internal impedance (dynamic impedance) which varies by time and by switching loss as transiential stress is applied to the thyristor when it is turned-on and -off, and to design a thyristor circuit basing on the predicted dynamic impedance. This article introduces an outline of a measuring system which can be used for quantitative determination of dynamic characteristics of thyristors and discusses switching loss determined with the measuring system. The measuring system consists primarily of two A/D converters. Dynamic characteristics of a thyristor, either of a normal type or high-speed type, can be quantitatively measured in one turn-on or turn-off operation. This article also discusses the effect of variation of the element area of the thyristor on the switching loss.     

Analysis of abnormal grain growth of oriented LiCoO2 prepared by slip casting in a strong magnetic field

The relationship between the development of the crystallographic orientation and the grain growth behavior were studied. The degree of orientations of the green compacts and sintered samples were evaluated by the Lotgering factor. The f(0 0 l) of all the samples were drastically increased with the increasing applied magnetic field strength. The f(0 0 l) of the samples sintered at 1223 K were improved in comparison to those of the green compacts. However, the f(0 0 l) value of the samples sintered at 1273 K were not increased at 4 T or lower. To characterize the grain growth process, these samples were analyzed using electron backscatter diffraction (EBSD). The sintered samples prepared in the magnetic field at 4 T or lower showed abnormal grain growth. The samples with an applied magnetic field of 8 T or higher had no abnormal grain growth. It was revealed that the orientation angle of the particles has an effect on the grain growth.     

Crystallization and electrical characteristics of Ge1Cu2Te3 films for phase change random access memory

Phase change random access memory (PCRAM) requires an advanced phase change material to lower its power consumption and to enhance its data retention and endurance abilities. The present work investigated the crystallization behaviors and electrical properties of Ge₁Cu₂Te₃ compound films with a low melting point of about 500 °C for PCRAM application. Sputter-deposited Ge₁Cu₂Te₃ amorphous films showed a high crystallization temperature of about 250 °C. The Ge₁Cu₂Te₃ amorphous film showed an electrical resistance decrease of over 10²-fold and exhibited a small increase in thickness of 2.0% upon crystallization. The Ge₁Cu₂Te₃ memory devices showed reversible switching behaviors and exhibited a 10% lower power consumption for the reset operation than the conventional Ge₂Sb₂Te₅ memory devices. Therefore, the Ge₁Cu₂Te₃ compound is a promising phase change material for PCRAM application.