Hiroshi Akamine

Imaging of surface spin textures on bulk crystals by scanning electron microscopy

Direct observation of magnetic microstructures is vital for advancing spintronics and other technologies. Here we report a method for imaging surface domain structures on bulk samples by scanning electron microscopy (SEM). Complex magnetic domains, referred to as the maze state in CoPt/FePt alloys, were observed at a spatial resolution of less than 100 nm by using an in-lens annular detector. The method allows for imaging almost all the domain walls in the mazy structure, whereas the visualisation of the domain walls with the classical SEM method was limited. Our method provides a simple way to analyse surface domain structures in the bulk state that can be used in combination with SEM functions such as orientation or composition analysis. Thus, the method extends applications of SEM-based magnetic imaging, and is promising for resolving various problems at the forefront of fields including physics, magnetics, materials science, engineering, and chemistry.

A preliminary study for exploring the luminance ratio of liquid-crystal displays required for display of radiographs

Medical-grade liquid-crystal displays (LCDs) with high contrast ratio (CR) values have recently been developed and become available for soft-copy reading. When the LCD is used under ambient light conditions, the luminance ratio (LR) is a more appropriate indicator than the CR. Our aim was to explore the LR required for LCDs for soft-copy reading by comparing the effective LR values with the LR of the LCD. We defined “the luminance ratio in an image (LRimg)”, the ratio of the maximum to minimum luminance in a radiograph displayed on the LCD, as the effective LR values required for the LCD. The maximum LRimg values in chest radiographs and those in mammograms ranged from 109 to 143 and 372 to 431, respectively. The LR of the LCD was higher than the LRimg values of the radiographs. Our results indicate that currently available medical-grade LCDs have enough LR for display of radiographs.

Effect of fluorescent lighting on the color of liquid-crystal displays

Liquid-crystal displays (LCDs) are used for displaying medical images under various illuminance conditions and with ambient-lighting colors. Our purpose in this study was to understand the variations of the chromaticity in LCDs under different fluorescent lighting conditions. The variation of chromaticity of LCDs at a white point consisting of equivalent pixel value in Red, Green, and Blue was examined under different types of fluorescent lighting. The direction of changes in the chromaticity diagram shifted to the color of each fluorescent lighting. When the differences in chromaticity (∆u′v′) increased, the observers’ confidence levels in distinguishing color differences also increased. When the luminance of the LCD increased, observers’ sensitivities for recognizing differences in chromaticity also increased as compared to observers’ sensitivities at lower luminances. Our results indicate that observers recognized slightly yellowish colors even if ∆u′v′ was less than 0.01; thus, observers could perceive differences in chromaticity. These results could provide important and relevant information with regard to better ambient lighting conditions in an image-reading room.

Rapid Annihilation of the Karman Vortex Street behind a Rectangular Cylinder

The annihilation and reappearance of the Karman vortex street behind a rectangular cylinder are investigated by wind-tunnel experiments, numerical simulations and linear stability analyses. Both experiments and numerical simulations show that the Karman vortex street (primary vortex street) is annihilated at a much shorter distance from the cylinder in the wake of a rectangular cylinder with a small aspect ratio of cross section than in the wake of a circular cylinder, and that another vortex street (secondary vortex street) appears further downstream. The locations where the primary vortex street is annihilated and the secondary one appears are determined numerically, and the mechanism underlying the rapid annihilation of the vortex street is examined on the basis of the linear stability theory. We find that the rapid annihilation of the primary vortex street results from the inherent characteristics of the linear instability mode for the steady symmetric flow.

Effect of ambient lighting on liquid–crystal displays with different types of surface treatment

Liquid–crystal displays (LCDs) with different types of surface treatment have been developed for decreasing the effect of ambient lighting on a displayed image. The effect of ambient lighting on LCDs with different surface treatments, namely, glare (G)-type, anti-glare (AG)-type, and anti-reflection (AR)-coating LCDs, was evaluated quantitatively in this study for appropriate selection. The effect of ambient lighting on diffuse reflection and specular reflection was investigated. The coefficient of diffuse reflection of the AR-coating LCD was smaller than the others. The effect of diffuse reflection on the display function of each LCD was evaluated in terms of the deviation of the contrast response at the lowest luminance level when the illuminance changed from the condition that was used for calibration of the grayscale standard display function. The display function of the AR-coating LCD was affected less by diffuse reflection compared to the others. On the other hand, the coefficient of specular reflection of the AG-type LCD was the smallest until the angle of aperture of the light source was 4.6°. The specular-reflected image on the AG-type LCD had a remarkably broad distribution compared to the others. Our results are merely examples for a limited number of LCDs; however, we clarified quantitatively that the AR-coating and the AG-type LCDs were affected less by diffuse and specular reflection than the G-type LCD.

Effect of angular performance on the chromaticity of grayscale images displayed on medical liquid-crystal displays

Although variation of chromaticity in medical liquid-crystal displays (LCDs) has created interest in the quality assurance and quality control of display devices for medical use, it is unknown how chromaticity varies with the viewing angle. Our aims in this study were to investigate the variations of chromaticity in grayscale images displayed on medical LCDs depending on viewing angles, and to examine color discrimination at different viewing angles. Variations in chromaticity, Δu′v′, between 0° and each viewing angle (−60° to +60°) were investigated. The chromaticity of each LCD varied as the viewing angle changed. We examined confidence levels of color discrimination at different viewing angles by rotating the LCD for ten observers. When the viewing angle and variation in chromaticity increased, the confidence levels of color discrimination increased. Our results indicated that observers, such as radiologists and radiological technologists, could recognize variation in chromaticity at different viewing angles.

Developments of coal-fired power plants: Microscopy study of Fe-Ni based heat-resistant alloy for efficiency improvement

Anthropogenic emissions of greenhouse gases are one of the possible reasons for the global warming. Coal consumption is predicted to be increased over several decades due to increasing demands in some countries. In the medium-term energy strategy, coal-fired power plants thus need to be developed. For this purpose, developments of new heat-resistant alloys that can stand severe steam conditions in advanced power plants are essential. A potential alloy was studied, which revealed that hardness of the alloy is related to the distribution of precipitates. The development of the alloy is also vital to make the power plants more economically competitive.

Visual assessment method of angular performance in medical liquid-crystal displays by use of the ANG test pattern: Effect of ambient illuminance and effectiveness of modified scoring

A visual assessment method of the angular performance in medical liquid–crystal displays (LCDs) by use of the “ANG test pattern” was proposed by Badano and the International Electrotechnical Commission. Our goals were to examine the effect of ambient illuminance on the visual assessment, and to investigate whether our modified visual assessment (with the ANG test pattern) can be used instead of the conventional assessment based on luminance measurements. As the ambient illuminance increased, the original scores obtained with the visual assessment decreased. The modified score of the visual assessment was in reasonable agreement with the results of the luminance-based assessment. We conclude that the visual assessment with the ANG test pattern should be performed in a room with constant ambient illuminance, and the modified visual assessment could have the potential to be used instead of the luminance-based assessment for quality assurance of medical LCDs.

SU‐E‐I‐16: Comparison of the Blue Part of the Spectral Power Distribution in a Medical Liquid‐Crystal Display for Different Color Temperature Settings

PURPOSE The effects of blue light exposure on visual fatigue have received much attention in recent years. There have been attempts to reduce the blue part of the spectral power distribution in a displays output by using commercial films and glasses. However, reducing the blue part of the spectral power distribution in medical liquid-crystal displays (LCDs) by changing the color temperature settings may prove to be a simpler solution. Our study aimed to quantitatively compare the blue part of the spectral power distribution of a medical LCD in different color temperature settings. MATERIALS AND METHODS We used two color LCDs (RadiForce RX340, 400 cd/m2 , EIZO). The spectral power distribution, chromaticity, and correlated color temperature were measured for LCDs with different color temperature settings (6500, 7500, and 8500 K). The default color temperature setting of the medical LCDs used in this study was 7500 K. A spectroradiometer (CS-2000, KONICA MINOLTA) and original gray-scale test patterns with 18 different luminance levels were used for the measurements. RESULTS The blue parts of the spectral power distribution (380-495 nm) were different for each color temperature setting. The integrated power values over the blue of the spectral power distribution decreased by 9% from 8500 to 7500 K and 13% and from 7500 to 6500 K. The correlated color temperature changed by approximately 1000 K depending on the color temperature setting. The difference in the chromaticity was 0.011 between 8500 and 7500 K and between 7500 and 6500 K. CONCLUSION Our results quantitatively indicate that the blue part of the spectral power distribution of the medical LCDs tested varies for different settings of color temperature.

Domain Wall Dynamics in Ginzburg–Landau-Type Equations with Conservative Quantities

In the Ginzburg–Landau equation, there are domain walls connecting two metastable states. The dynamics of domain walls has been intensively studied, but there remain still unsolved but crucial problems even for a single domain. We study the domain wall dynamics in three different Ginzburg–Landau-type equations satisfying conservation laws. In a modified ϕ4 model satisfying the law of energy conservation and the Lorentz invariance, the motion of a domain wall is accelerated and the velocity approaches its maximum. In a one-dimensional model of eutectic growth, the order parameter is conserved and a domain wall connecting a metastable uniform state and a spatially periodic pattern appears. We try to find a selection rule for the wavelength of a spatially periodic pattern. In a model equation for martensitic transformation, a domain wall connecting a uniform metastable state and a zigzag structure appears which propagates at a high velocity.