In urban environments, radiation energy from the sun becomes a heat load on the human body. The radiation energy can be divided into visible, near-infrared, and far-infrared wavelengths. Far-infrared radiation is re-emitted from structures that have been warmed by the sun. On the other hand, visible and near-infrared light comes directly or reflected from structures. However, previous studies have measured environmental changes using only far-infrared cameras to study urban heat island (UHI) countermeasures. Therefore, it is important to measure the environmental radiation energy at each wavelength region to properly discuss the cause of the heat load. To conduct the measurements, we used three cameras operating at different wavelengths: visible, near-infrared, and far-infrared. In addition, the measurements were conducted in different urban locations, seasons, and weather conditions in the Tokyo area of Japan, an urban metropolis. The results for far-infrared wavelengths show that, in summer when the temperature is high, all structures except the sky have a positive heat load on the human body, while, in winter or cloudy weather when the temperature is low, the heat load on the human body is negative. The results of heat load measurements at visible and near-infrared wavelengths show that the heat load varies greatly depending on the proportion of sky, plants, and buildings, despite the proportion of ground area being the same. These results indicate that the differences in radiation wavelengths need to be considered when considering reducing the heat load on the human body in urban environments. Therefore, the proposed method could contribute to the development of more effective UHI countermeasures by measuring in a various environments and countries.

In the cosmetics industry, fine particles suspended or dispersed in a medium are widely used. Optical properties of the medium can be an indicator for evaluating the performance of cosmetic product, such as the ultraviolet protection capacity of sunscreens and also its appearance. However, the relationship between the optical properties and the appearance of the product has not been clarified. In this study, dispersions of fine particles with titanium dioxide or zinc oxide were used as scattering medium to clarify the relation between their scattering properties and changes in visual perception. For visual perception, sensory tests with human panelists were performed using a custom-designed apparatus to inspect the samples and evaluate the two visual sensory quantities, “glossiness” and “translucency”. The sensory test employed Thurston’s one-pair comparison method, and a total of 18 panelists were asked to evaluate the samples. The sensory tests showed that the translucency became stronger as the scattering coefficient decreased. On the other hand, only the samples in the group with the highest scattering coefficient showed a slightly low glossiness. In contrast, the other samples showed little difference in glossiness due to the difference in scattering coefficients. The results of this study indicate that the appearance of cosmetics products can be influenced by controlling the scattering properties of the medium.

Currently, research related to the visualization of cutaneous vascular changes to heat stress depending on age and gender is limited to methods such as laser Doppler flowmetry and plethysmography, which do not provide any spatially resolved information at high resolution. On the other hand, optical coherence tomography is a real-time, noninvasive, non-contact technique that can visualize internal structures at the level of a few microns and is widely used in ophthalmology to visualize retinal structures, for example. However, the use of OCT in the investigation of skin vasculature heat stress is limited, with no study being conducted with different genders and different age groups. In this study, we propose biospeckle optical coherence tomography (bOCT), which visualizes the structural changes along a temporal scale to visualize the dynamic changes within the skin under heat stress. Heat stress was applied by applying a USB hot pad (40 °C) for five minutes to the palmar forearm of the dominant hand. A swept-source OCT (SS-OCT) operating with a central wavelength of 1310 nm, a bandwidth of 125 nm, and a sweep frequency of 20 kHz was used to obtain OCT structural images at 12.5 fps. From the one hundred OCT structural images recorded for 8 s, the biospeckle image was calculated as a ratio of the standard deviation to the mean of the images. The biospeckle images were obtained before heating, soon after heating, and after 5 min of rest. A total of 20 subjects with an equal number of male and female participants, with 10 in their 20s and the other 10 in their 30s or older, participated in the experiments. The average biospeckle contrast results were compared for significant differences under the three different conditions of before heating, soon after heating, and after rest for different depths, age differences, and genders. With heating, across all subjects at shallow depths within 200 µm or so, possibly in the epidermis–dermis border region, a significant difference was observed in the average contrast between the before-heating and after-rest conditions, with no significant difference seen in the deeper regions. With respect to age groups irrespective of gender, there was only a significant difference in the average contrast between soon after heating and before heating for the younger group, while for the older group, there was significant difference between before heating and soon after heating as well as between before heating and after 5 min of rest. This result suggests that age plays a larger role in the control of vascular dynamics. With respect to gender and irrespective of age, there was significant difference between males and females for both soon after heating and after 5 min of rest, with no significant difference found for before heating. These differences could be explained by hormonal differences that play a larger role in the vascular dynamics of the control of skin under heat stress, though the clear mechanism behind the reason for these gender differences is not clearly understood yet. As for both gender and age, because of the smaller sample size for age and gender combined, more studies are needed to obtain statistically reliable results. In total, our results obtained using bOCT demonstrate that bOCT could be successfully implemented in the study of the environmental effects on skin tissue, and we believe this has potential implications in therapeutic use such warm water immersion.

Photoacoustic tomography (PAT), also known as optoacoustic tomography, has been emerging as a biomedical imaging modality that can provide cross-sectional or three-dimensional (3D) visualization of biological tissues such as blood vessels and lymphatic vessels in vivo at high resolution. The principle behind the visualization involves the light being absorbed by the tissues which results in the generation of ultrasound. Depending on the strength of ultrasound and its decay rate, it could be used to visualize the absorber location. In general, pulsed lasers such as the Q-switched Nd-YAG and OPO lasers that provide high-energy widths in the range of a few nanoseconds operating at low repetition rates are commonly used as a light source in photoacoustic imaging. However, such lasers are expensive and occupy ample space. Therefore, PAT systems that use LED as the source instead of lasers, which have the advantage of being obtainable at low cost and portable, are gaining attention. However, LED light sources have significantly low energy, and the photoacoustic signals generated have a low signal-to-noise ratio (SNR). Therefore, in LED-based systems, one way to strengthen the signal and improve the SNR is to significantly increase the repetition rate of LED pulses and use signal processing, which can be achieved using a high-power LED along M-sequence signal decoding. M-sequence signal decoding is effective, especially under high repetition rates, thus improving the SNR. However, power supplies for high-power LEDs have a circuit jitter, resulting in random temporal fluctuations in the emitted light. Such jitters, in turn, would affect the M-sequence-based signal decoding. Therefore, we propose a new decoding algorithm which compensates for LED jitter in the M-sequence signal processing. We show that the proposed new signal processing method can significantly improve the SNR of the photoacoustic signals.