We demonstrate a method for measuring liquid plug volumes in a rectangular cross-junction microchannel using two-camera phase retrieval holographic microscopy. Our approach employs two in-line hologram recordings acquired simultaneously with a pair of cameras, thereby enabling non-contact quantification of moving transparent plugs in microfluidic devices. As an experimental validation, we formed liquid plugs of a 38 wt% glycerol solution dispersed in 1 cSt silicone oil in a cross-junction channel. The continuous and dispersed phases had refractive indices of n_c = 1.3808 and n_d = 1.3802, respectively, and were supplied at Q_c = 20 μL/min and Q_d = 1 μL/min. The reconstruction process yielded quantitative phase maps to resolve the plug volume and motion. The use of the reconstructed phase enabled direct quantification of the volume of individual translating plugs. Furthermore, tracking-based plug-wise temporal averaging enhanced measurement repeatability, thereby reducing the coefficient of variation from 6.7% to 3.0% for a sample size of N = 37 plugs while maintaining the mean virtually unchanged.

Stair descent carries an increased risk of serious falls, which can cause injuries resulting in the need for long-term care or, in the most severe cases, death. In this study, we report the measurement of tensile force and moment acting on the handrail during stair descent, and we estimate the load-acting position based on these data. To perform experiments on stair descent, we designed and implemented a measurement system integrated into the stair handrail. The participants were five healthy men. The results showed that the average gripping time for all participants was 1.28±0.27 s. In the analysis of normalized time and normalized gripping force (relative to individual maximum), participants exhibited an average gripping force ratio of 31.1%. The highest gripping force ratio recorded was 62.5%, and the lowest was 24.2%. The average maximum path length in the positive X-axis direction was 2.49 mm, whereas that in the negative direction was -8.16 mm. Corresponding values in the positive and negative Y-axis directions were 13.6 mm and -22.3 mm, respectively. When examining the path length shapes during descent, five major characteristics were observed. We quantified the mechanical loads and moments acting on the handrail in each direction and implemented a standardization approach based on individual maximum grip strength in this study.

Snake-like robots offer high adaptability for diverse environments; however, efficient locomotion across varying fluid viscosities remains challenging. While existing models are often specialized for water, our previous high-viscosity model exhibited limited accuracy in low-viscosity environments. To address this, this study proposes a unified fluid force model applicable across a wide viscosity range, incorporating a biological reactive force term alongside pressure resistance and frictional drag. Validation through multi-objective optimization and experiments with an 8-link robot in water and oils showed that the model accurately reproduces results, highlighting the necessity of reactive forces for high-speed swimming. Notably, optimization revealed that the robot can achieve higher maximum speeds in high-viscosity oil than in water―a counter-intuitive phenomenon confirmed experimentally. Furthermore, the optimized motion maintained a universal non-dimensional tail amplitude (0.1–0.3) independent of viscosity, consistent with biological swimmers.

The rise behavior of a single air bubble with an equivalent diameter of about 3.8 mm in distilled stagnant water, Polyoxyethylene sorbitan monooleate (Tween-80) (non-ionic) and Sodium dodecyl sulfate (SDS) (anionic) surfactants were experimentally studied to assess the role of nature of surfactants (non-ionic vs ionic) on bubble rise dynamics. A single air bubble was generated using a high precision syringe pump fitted with a fine needle of 0.51 mm inner diameter (ID). The bubble motion was captured using a high-speed camera operating at 4000 fps. Digital image analysis allowed for the quantification of velocity (U), trajectory, and aspect ratio (χ) of the bubble. In distilled water, the bubble attained a terminal velocity (Uₜ) of about 0.31 m/s and exhibited strong shape oscillations with the aspect ratio fluctuating between approximately 1.5 and 2.7 with an unstable zigzag motion. Tween-80 reduced the terminal velocity to 0.21 m/s, suppressed the deformations to about 1.1–1.2 and stabilized the trajectory of the bubble at high concentration. A transient deceleration stage for the bubble was also observed using Tween-80 solutions. SDS induced similar deceleration of the bubble but required much higher concentrations due to electrostatic repulsion occurring at the bubble interface caused by the ionic nature of surfactant. Overall, the results demonstrate that impact of non-ionic vs ionic surfactant character has a critical role in controlling interfacial mobility, bubble shape, stability and rise dynamics of the bubble.

In our previous studies, dam-break-type hydraulic experiments and CFD simulations were conducted on buildings with upstream obstructions. In contrast, tsunami forces in the presence of a downstream obstruction have been assumed comparable to the isolated case, as pressure on the front face is expected to be same significantly. However, the downstream obstruction can increase rear water depth, generating a counteracting force from downstream to upstream and reducing the net tsunami force. This effect has not been considered previously and suggests potential reductions in overestimated design loads. In this study, two types of hydraulic experiments were conducted to examine tsunami forces on building structures with downstream obstruction. The results suggest that the design tsunami loads can be reduced for structures with downstream obstruction located at distances approximately two to three times the building width.

Push-pull air stages combine jet injection and suction to levitate silicon wafers without contact, but a practical relation between levitation pressure and gap height for design has remained unclear. We derive the pressure field in the thin gas film between a levitated flat plate and a perforated lower wall in the Stokes-flow regime. The stage is represented by a periodic unit cell containing a central jet orifice and suction outlets located at the cell corners, with a prescribed wall-normal velocity distribution on the lower wall and an impermeable upper wall. Under lubrication conditions, pressure is uniform across the gap and the in-plane flow in the gas film, with the upper plate assumed to be stationary, yields a Reynolds-type pressure equation with a mass source. This leads to an inverse-cubic dependence of gauge pressure on the gap height, and the area-averaged pressure can be written with a single geometry-dependent coefficient. The Stokes assumption is assessed through an order comparison of inertial and viscous terms. Using standard 300 mm wafer properties, the coefficient is estimated as 0.034, indicating values around 0.01-0.1 and motivating experimental calibration.

This study examines whether short-time-averaged convection velocities improve the estimation of streamwise velocity-gradient intensity from single-component hot-wire time series in isotropic turbulence. Starting from an advection (sweeping) description in which velocity fluctuations are transported by a large-scale sweeping velocity, we derive a relation between the mean-square time derivative and the mean-square streamwise spatial derivative when the convection velocity is obtained by short-time averaging the measured streamwise velocity with an arbitrary normalized window. Assuming Gaussian, locally isotropic fluctuations with exponential temporal correlation and statistical independence between sweeping velocity and small-scale gradients at high Reynolds number, we obtain integral expressions for the bias and its dependence on fluctuation level, averaging duration, and window shape. The analysis shows that changing the averaging width or window function modifies only a minor correction term, whereas the dominant discrepancy originates from sweeping components normal to the mean flow that are inaccessible to single-wire measurements. Short-time averaging can reduce overestimation linked to streamwise advection variability, but the achievable improvement is bounded.

Obtaining reliable reference velocities for calibrating hot-wire anemometers in the low-speed range (≤ 1.0 m/s) is often challenging unless dedicated calibration facilities are employed. This study proposes an in-situ alternative that exploits size-resolved tracking of water droplets settling through a controlled updraft. We measure the joint distribution of droplet diameter and vertical velocity and infer the background updraft speed from the deviation of the measured settling speed from the still-air terminal-velocity relation. To ensure robustness against tracking outliers, the updraft is estimated with a median-based estimator. Two assumptions underlying the inference are explicitly validated: droplets reach dynamical equilibrium before observation and droplet-induced aerodynamic loading on the flow is negligible; this is ensured by selecting sequences with a kinetic-energy ratio below 1%. The inferred reference velocities are then used to calibrate the anemometer, and fitting the calibration data with a modified King's law yields an exponent of n = 0.65. This approach derives reference velocities directly from the experimental system, substantially simplifying low-speed calibration.

Surface topography, which represents the asperities and geometric features of a material surface, has a significant influence on contact conditions between bodies, as well as on wear, friction, lubrication, contact resistance, and heat transfer. For example, in manufacturing processes such as resistance spot welding, where high voltage is applied under pressure, it is well known that the surface topography of the electrode and the sheet material greatly affects the results. However, even in the simple case of pressing two material surfaces together, accurate estimation of the real contact state remains difficult, and related studies continue to be conducted today. In this study, pressure tests were performed using small blocks of pure aluminum, and the height distribution of the contact surfaces before and after testing was measured. Furthermore, a method for estimating the real contact areas from the height distribution was proposed and applied to the tests. By applying the proposed method, it was possible not only to evaluate the contact area ratio as a single metric of the interface, but also to estimate the specific areas that were actually in contact.

Accurate residual stress evaluation is essential for ensuring the structural integrity and reliability of engineering components. Although the hole-drilling method is widely used for estimating residual stress, the influence of strain gauge geometry on the associated calibration coefficients has not been systematically clarified. As specified in ASTM E837, residual stress is estimated from the strain released during drilling using calibration coefficients derived for ASTM-specified strain gauges, including finite element method-based values for thick plates. However, commercially available strain gauges often differ from the ASTM specifications, leading to discrepancies in residual stress estimation. In this study, we performed finite element analyses for both ASTM-specified and commercially available strain gauges to derive corresponding calibration coefficients. The coefficients obtained for the ASTM gauge size agreed closely with the standard values, whereas those for commercially available gauges deviated significantly. These results indicate that strain gauge size and position significantly affect the calibration coefficients. When non-ASTM gauge dimensions are used, the coefficients derived in this study enable more accurate residual stress estimation and provide practical guidance for industrial applications.

In this study, we propose an experimental-numerical hybrid method for evaluating thermal strains and thermal stresses by combining finite element analysis and digital image correlation. This method utilizes full-field displacement data of a test specimen composed of multiple different materials, enabling the evaluation of its thermal strains and stresses. Based on the principle of superposition, the distribution of temperature change is identified from the measured displacement field. Since this distribution cannot be uniquely determined by ordinary least-squares, a regularized least-squares approach is employed. Thermal strains and stresses are obtained simultaneously with the temperature change and the displacements, allowing reliable evaluation of thermal stresses arising from differences in thermal expansion coefficients.

Deployable structures are useful for lunar habitat modules because they can be compactly stowed during launch and expanded after deployment. This study investigated the applicability of cellulose nanofiber (CNF) materials as structural components for space deployable structures, with a particular focus on strength degradation induced by bending and deployment processes. CNF board specimens were immersed in water to enhance flexibility, bent at various angles, and then deployed. Tensile tests were conducted to evaluate the residual tensile properties, and scanning electron microscopy (SEM) observations were performed to examine microstructural damage. The tensile strength decreased with increasing bending angle, with a significant reduction observed under 180° bending. SEM observations revealed localized damage in the bent region, including micro-buckling, void concentration, and fracture of the tension side layers. This damage promoted premature failure under tensile loading. Introducing a finite bending radius significantly suppressed damage initiation and improved the tensile strength. These results indicate that controlling bending curvature is a critical design requirement for CNF-based deployable structures.

In recent years, bioabsorbable stents have been attracting attention for treating ischemic heart disease by reducing the risk of restenosis. In this study, a mock circulatory test system was developed to simulate conditions in the human body’s arteries to assess the performance of bioabsorbable stents. A flexion device was featured in the system that repeatedly bends the stent, reproducing the movement of the blood vessel. A pressure generator that generates pressure fluctuation was also developed, which successfully simulated the pulsation in the blood vessel. Using the system, the time-dependent degradation behavior of a magnesium alloy bare metal stent was examined under the phosphate-buffered saline flow. Then, the effects of repeated flexion and pressure fluctuation on the degradation behavior of the stent were investigated. The results revealed that pressure fluctuation is the key factor accelerating degradation over time. It was also found that the contact conditions between the tube and the stent were crucial in controlling the degradation behavior of the material.

Digital image correlation has become a widely used experimental technique for measuring full-field displacement and strain distributions in a non-contact manner. The method enables quantitative characterization of deformation fields and has attracted significant attention in experimental fracture mechanics. By utilizing displacement fields measured by digital image correlation, fracture parameters such as stress intensity factors and the J-integral can be evaluated directly from experimental data. This article reviews the fundamental principles of displacement and strain measurement using digital image correlation and describes methods for evaluating fracture mechanics parameters from the measured fields. A least-squares-based approach for determining mixed-mode stress intensity factors from crack-tip displacement fields is introduced. In addition, evaluation methods for the J-integral are discussed, including both numerical integration techniques based on displacement gradients, strains, and stresses, and a simplified approach utilizing the Hutchinson-Rice-Rosengren (HRR) displacement field. Examples of experimental evaluations using displacement fields obtained by digital image correlation are presented to demonstrate the validity of these methods. The approaches discussed in this article enable fracture parameters to be evaluated directly from experimentally measured displacement fields, thereby reducing reliance on numerical simulations such as finite element analysis. These techniques are expected to play an increasingly important role in experimental fracture mechanics and structural integrity assessment of engineering structures.

This study evaluates the pathway of alumina (Al₂O₃) inclusions in molten steel during calcium (Ca) treatment under laboratory conditions. The observed modification mechanism involves sequential phase transformations: Al₂O₃ → CaO·6Al₂O₃ (CA₆) → CaO·2Al₂O₃ (CA₂) → CaO·Al₂O₃ (CA) → 12CaO·7Al₂O₃ (C₁₂A₇) → CA → CA₂. Under the present conditions, a treatment duration of 600 s represents an optimal window, yielding > 90% of liquid-phase―C₁₂A₇ and 3CaO·Al₂O₃ (C₃A)― and near-liquid-phase (CA) inclusions. Prolonged treatment, however, increases the inclusion number density, in contrast with industrial observations dominated by coarse-inclusion flotation and agglomeration. These results suggest that small inclusions around 1µm may increase in number, a factor often overlooked in practice. Furthermore, maintaining steel temperatures above the melting point of CA (1875 K) facilitates inclusion liquefaction, as CA comprises a significant portion (39%) of inclusions. These findings offer valuable guidance for optimizing calcium treatment strategies and preventing nozzle clogging.