Electrophoretic Separation on an Origami Paper-Based Analytical Device Using a Portable Power Bank.

The electrophoresis of ampholytes such as amino acids on a paper device is difficult because of the variation of pH distribution in time. On the basis of this observation, we propose a paper-based analytical device (PAD) with origami structure. By folding a filter paper, a low operation voltage of 5 V was achieved, where the power was supplied by a 5 V 1.5 A portable power bank through the USB type A receptacle. As a demonstration, we carried out the electrophoretic separation of pI markers (pI 5.5 and 8.7). The separation was achieved within 4 min before the pH distribution on the paper varied. Though the separation distance was small, it could be increased by expanding the origami structure. This result indicates that our proposed PAD is useful for electrophoretic separation on a paper device.

Impact cratering on a granular bed by hydrogel spheres having intermediate property between solid and liquid.

We investigated the low speed impact on a granular bed by a hydrogel sphere and especially focused on the resultant crater diameter. Though the crater diameter depends only on the impact kinetic energy for the solid sphere impact cratering, it also depends on the elastic energy for the hydrogel sphere. The hydrogel sphere impact cratering is classified into two dynamics: small and large indentation of the sphere. For the small indentation, the crater diameter is proportional to the 1/4 power of the energy for ejecting granular materials, which is calculated by substituting the elastic energy stored in the sphere from the impact kinetic energy. Considering the force balance between the inertial force and the indentation, we derived the relation between the impact kinetic energy, Young's modulus, and the crater diameter. In the large limit of Young's modulus, the relation leads to the 1/4 power law observed in solid sphere impact. The dependency of Young's modulus on the crater diameter for the large indentation of the sphere is larger than the impact with small indentation.

Estimation of diffusive states from single-particle trajectory in heterogeneous medium using machine-learning methods.

We propose a novel approach to analyze random walks in heterogeneous medium using a hybrid machine-learning method based on a gamma mixture and a hidden Markov model. A gamma mixture and a hidden Markov model respectively provide the number and the most probable sequence of diffusive states from the time series position data of particles/molecules obtained by single-particle/molecule tracking (SPT/SMT) method. We evaluate the performance of our proposed method for numerically generated trajectories. It is shown that our proposed method can correctly extract the number of diffusive states when each trajectory is long enough to be frame averaged. We also indicate that our method can provide an indicator whether the assumption of a medium consisting of discrete diffusive states is appropriate or not based on the available amount of trajectory data. Then, we demonstrate an application of our method to the analysis of experimentally obtained SPT data.

Molecular-dynamics study on characteristics of energy and tangential momentum accommodation coefficients.

Gas-surface interaction is studied by the molecular dynamics method to investigate qualitatively characteristics of accommodation coefficients. A large number of trajectories of gas molecules colliding to and scattering from a surface are statistically analyzed to calculate the energy (thermal) accommodation coefficient (EAC) and the tangential momentum accommodation coefficient (TMAC). Considering experimental measurements of the accommodation coefficients, the incident velocities are stochastically sampled to represent a bulk condition. The accommodation coefficients for noble gases show qualitative coincidence with experimental values. To investigate characteristics of these accommodation coefficients in detail, the gas-surface interaction is parametrically studied by varying the molecular mass of gas, the gas-surface interaction strength, and the molecular size of gas, one by one. EAC increases with increasing every parameter, while TMAC increases with increasing the interaction strength, but decreases with increasing the molecular mass and the molecular size. Thus, contradictory results in experimentally measured TMAC for noble gases could result from the difference between the surface conditions employed in the measurements in the balance among the effective parameters of molecular mass, interaction strength, and molecular size, due to surface roughness and/or adsorbed molecules. The accommodation coefficients for a thermo-fluid dynamics field with a temperature difference between gas and surface and a bulk flow at the same time are also investigated.

Polymer-Particle Pressure-Sensitive Paint with High Photostability.

We propose a novel fast-responding and paintable pressure-sensitive paint (PSP) based on polymer particles, i.e. polymer-particle (pp-)PSP. As a fast-responding PSP, polymer-ceramic (PC-)PSP is widely studied. Since PC-PSP generally consists of titanium (IV) oxide (TiO2) particles, a large reduction in the luminescent intensity will occur due to the photocatalytic action of TiO2. We propose the usage of polymer particles instead of TiO2 particles to prevent the reduction in the luminescent intensity. Here, we fabricate pp-PSP based on the polystyrene particle with a diameter of 1 µm, and investigate the pressure- and temperature-sensitives, the response time, and the photostability. The performances of pp-PSP are compared with those of PC-PSP, indicating the high photostability with the other characteristics comparable to PC-PSP.

Faster Convergence of Diffusion Anisotropy Detection by Three-Step Relation of Single-Particle Trajectory.

We focus on the issue of limited number of samples in the single particle tracking (SPT) when trying to extract the diffusion anisotropy that originates from the particle asymmetry. We propose a novel evaluation technique of SPT making use of the relation of the consecutive three steps. More specifically, the trend of the angle comprised of the three positions and the displacements are plotted on a scatter diagram. The particle anisotropy dependence of the shape of the scatter diagram is examined through the data from the standard numerical model of anisotropic two-dimensional Brownian motion. Comparison with the existing method reveals the faster convergence in the evaluation. In particular, our proposed method realizes the detection of diffusion anisotropy under the conditions of not only less number of data but also larger time steps. This is of practical importance not only when the abundant data is hard to achieve but also when the rotational diffusion is fast compared to the frame rate of the camera equipment, which tends to be more common for smaller particles or molecules of interest.

Electric conductive pattern element fabricated using commercial inkjet printer for paper-based analytical devices.

Herein, we proposed the addition of an inkjet-printed conductive pattern to paper-based analytical devices (PADs) in order to expand their applications. An electric conductive pattern was easily, quickly, and inexpensively fabricated using a commercial inkjet printer. The addition of a printed electric element will enhance the applications of PADs without the loss of properties such as cost efficiency, disposability, and portability. In this study, we applied an inkjet-printed heater to a piece of paper and investigated its characteristics. The use of the heater as a valve, concentrator, and heat source for chemical reactions on PADs was investigated. Previously, these functions were difficult to realize with PADs. The inkjet-printed heater was used as a valve and concentrator through evaporation of the working fluid and solvent, and was also found to be useful for providing heat for chemical reactions. Thus, the combination of printed electric circuits and PADs has many potential applications.

Unsteady pressure-sensitive paint measurement based on the heterodyne method using low frame rate camera.

The pressure-sensitive paint technique based on the heterodyne method was proposed for the precise pressure measurement of unsteady flow fields. This measurement is realized by detecting the beat signal that results from interference between a modulating illumination light source and a pressure fluctuation. The beat signal is captured by a camera with a considerably lower frame rate than the frequency of the pressure fluctuation. By carefully adjusting the frequency of the light and the camera frame rate, the signal at the frequency of interest is detected, while the noise signals at other frequencies are eliminated. To demonstrate the proposed method, we measured the pressure fluctuations in a resonance tube at the fundamental, second, and third harmonics. The pressure fluctuation distributions were successfully obtained and were consistent with measurements from a pressure transducer. The proposed method is a useful technique for measuring unsteady phenomena.

Organic electroluminescent sensor for pressure measurement.

We have proposed a novel concept of a pressure sensor called electroluminescent pressure sensor (ELPS) based on oxygen quenching of electroluminescence. The sensor was fabricated as an organic light-emitting device (OLED) with phosphorescent dyes whose phosphorescence can be quenched by oxygenmolecules, and with a polymer electrode which permeates oxygen molecules. The sensor was a single-layer OLED with Platinum (II) octaethylporphine (PtOEP) doped into poly(vinylcarbazole) (PVK) as an oxygen sensitive emissive layer and poly(3,4-ethylenedioxythiophene) mixed with poly(styrenesulfonate) (PEDOT:PSS) as an oxygen permeating polymer anode. The pressure sensitivity of the fabricated ELPS sample was equivalent to that of the sensor excited by an illumination light source. Moreover, the pressure sensitivity of the sensor is equivalent to that of conventional pressure-sensitive paint (PSP), which is an optical pressure sensor based on photoluminescence.