Search

Photo-induced crawling motion of a crystal of 3,3'-dimethylazobenzene (DMAB) on gold surfaces having different surface properties and various patterns was studied. DMAB crystals crawl continuously when exposed to UV and visible lights simultaneously from different directions. On a gold surface functionalized by a thiol having a hydroxyl group at the terminal (16-hydroxy-1-hexadecanethiol (HOC16SH)), the crystals crawled with a relatively high velocity (ca. 4 μm min-1), and they changed the crystal shape while keeping a distinct crystal face. On a gold surface functionalized by a thiol having an alkyl chain terminal (1-hexadecanethiol (C16SH)), the crawling was observed with a slower velocity (ca. 1.5 μm min-1). However, the shape of the crystals became a droplet-like shape soon after the irradiation started, and the shape persisted during the motion. Light intensity dependence of the crawling velocity of the droplet-like crystal on this surface showed that UV light has stronger dependence for the motion than the visible light. On a substrate with a stripe pattern of alternating C16SH-modified gold and hexadecyltrimethylsilane (HDTMS)-modified glass, crystals crawled only on the surface of the C16SH-modified gold, which may be due to the wettability hysteresis at the surface. On a substrate with a stripe pattern of HOC16SH-modified gold and HDTMS-modified glass, crystals were attracted to the gold side. On a gold substrate with a periodic pattern of different height (ca. 50 nm) but having a uniform treatment with C16SH, crystals crawled up and down the steps without significant disturbance at the boundary of the step. Therefore, wettability of the surface has a greater impact on controlling the motion of the crystal than the surface structure. The present results not only unveil the crawling behavior on various surfaces but also offer a guide to controlling the motion toward applications for novel carriage vehicles to transport molecules/objects on a surface.

Evaluating the anisotropy of transport parameters in rocks is important for various applications, such as reservoir engineering and rock mechanics. Owing to their anisotropic pore structures, the tortuosity, constrictivity, and pore size distribution of rocks are often anisotropic in nature, which in turn affect the permeability and diffusivity. However, it has still not been determined whether the permeability and diffusivity are anisotropic in the same manner. This study used experiments and numerical modeling to examine the effect of the pore structure on the permeability and diffusivity anisotropies of rocks. The experimental results showed a clear difference in the anisotropy ratios of the permeability (k⊥/k‖) and diffusivity (D e ⊥ /D e ‖ ) for Berea sandstone, which is the de facto standard porous sandstone. The analysis results from micro-focus X-ray computed tomography and simulation with the lattice Boltzmann method supported the experimental difference in anisotropy ratios. In the analysis and simulation, the relation between the minimum cross-sectional porosity area and characteristic pressure gradient was estimated. The analysis results suggest that the minimum cross-sectional porosity areas that influence the permeability anisotropy are too large to physically induce anisotropic NaCl diffusion, and thus, the diffusivity of Berea sandstone is nearly isotropic.

Tadashi Iwai, Manabu Hoshi, Naoto Oebisu, Kumi Orita, Akiyoshi Shimatani, Naoki Takada, Hiroaki Nakamura Department of Orthopedic Surgery, Osaka City University Graduate School of Medicine, Osaka, 545-8585, JapanCorrespondence: Tadashi IwaiDepartment of Orthopedic Surgery, Osaka City University Graduate School of Medicine, 1-4-3 Asahi-Machi, Abeno-Ku, Osaka, 545-8585, JapanTel +81-6-6645-3851Fax +81-6-6646-6260Email qq329xpd@opal.ocn.ne.jpPurpose: We aimed to determine if finite element analysis (FEA) provides useful thresholds for bone biopsy practice patterns.Methods: The femoral head compression test was performed on rabbit femurs, using FEA to identify the part of the bone that preferentially fractures (n=15/group). Four types of rectangular biopsy holes were made using finite element (FE) models. These models were divided into control (no defect), defect 1 (10% width), defect 2 (20% width), defect 3 (30% width), and defect 4 (40% width) groups (n=15 each). Three types of rectangular biopsy holes (defect A, 27% length; defect B, 40% length; defect C, 53% length) were also made using FE models (n=15 each). The load to failure was then predicted using FEA.Results: Almost all femurs with no defect were fractured at the femoral shaft in both the femoral head compression test and FEA. The experimental load to failure in intact femurs was predicted well by the FE models (R2=0.74, p< 0.001). There was also a strong linear correlation of stiffness between compression test in femurs with no defect and the FEA (R2=0.68, p< 0.001). Therefore, the femoral shaft was targeted for FEA. The median predicted loads by FEA were significantly higher for defect 1 than for the other types when testing the widths of the rectangular defects, but there were no significant differences among the three types when testing for defect length.Conclusion: The FEA results correlated well with those of the femoral head compression test. A width < 10% of the circumference length in bone biopsy holes helps minimize bone strength reduction using FEA. It may be useful for orthopedic doctors to perform FEA to avoid pathological fractures after bone tumor biopsy.Keywords: femur, orthopedics, bone tumor biopsy, New Zealand white rabbits, finite element analysis

Photo-induced crawling motion of a crystal of 3,3′-dimethylazobenzene (DMAB) on a glass substrate having different surface properties was studied. When exposed to UV and visible lights simultaneously from different directions, crystals crawl continuously on a glass surface. On a hydrophilic surface, the crystals crawled faster than those on other surfaces but crystals showed spreading while they moved. On hydrophobic surfaces, on the other hand, the crystals showed little shape change and slower crawling motion. The contact angles of the liquid phase of DMAB on surface-modified glass substrates showed positive correlation with the water contact angles. The interaction of melted azobenzene with glass surfaces plays an important role for the crawling motion. We proposed models to explain the asymmetric condition that leads to the directional motion. Specifically by considering the penetration length of UV and visible light sources, it was successfully shown that the depth of light penetration is different at the position of a crystal. This creates a nonequilibrium condition where melting and crystallization are predominant in the same crystal.

We investigated the enhancement of the capillary effect in a plastic capillary tube using only a nanostructured surface. Since plastic is a hydrophobic material, the capillary effect does not emerge without an additional coating or plasma treatment process. Therefore, capillary effect enhancement by the nanostructure fabrication method is expected to reduce the cost and minimise the contamination produced in the human body. By combining a hydrophilic nylon resin and a nanostructure at the tip of the plastic pipette, we could confirm that the capillary effect was produced solely by the tube fabrication process. The produced capillary effect increased linearly with increasing nanostructure height when a standard solution with a surface tension of 70 mN·m−1 was used. Thus, we can conclude that including the plastic part with nanostructure can be useful for biomedical applications. In addition, we suggest that the proposed method is highly effective in controlling the wetting properties of plastic surfaces, compared to the typical coating or plasma treatment processes.

Digital microfluidics based on electrowetting on dielectric (EWOD) devices has potential as a fundamental technology for the accurate preparation of dangerous reagents, the high-speed dispensing of rapidly deteriorating reagents, and the fine adjustment of expensive reagents, such as the preparation of for positron emission tomography (PET). To allow single substrate type EWODs to be practically used in an automatic operation system, we developed a dimple structure as a key technique for a highly accurate droplet manipulation method. The three-dimensional shape of the dimple structure is embossed onto a disposable thin sheet. In this study, we confirmed that the dimple structure can suppress unintended droplet motion caused by unidentified factors. In addition, the stability of the droplets on the dimple structures was evaluated using a sliding experiment. On a flat substrate, the success rate of a droplet motion was lower than 70.8%, but on the dimple structure, the droplets were able to be moved along the dimple structures correctly without unintended motion caused by several environmental conditions. These results indicated that the dimple structure increased the controllability of the droplets. Hence, the dimple structure will contribute to the practical application of digital microfluidics based on single substrate type EWODs.

In this study, we proposed a hologram calculation method for light-in-flight recording by holography (LIF holography). First, we simulated the behavior of ultrashort pulsed light on the diffuser plate using the two-dimensional finite-difference time-domain method. Second, we calculated the light propagation from the diffuser plate to the recording material and generated a hologram based on the calculation model of LIF holography. We reconstructed moving pictures of pulsed-light propagation from the calculated hologram. Because the behavior of the pulsed light in the moving pictures agreed well with that obtained from the reported optical experiment, the proposed method was successfully validated.

The applicability of a numerical method is preliminarily examined to determine its suitability for simulations of microscopic immiscible liquid-liquid motion on solid walls, which is used for evaluating fluidic devices with heterogeneously wettable and textured surfaces. The method adopts a conservation-modified Allen-Cahn equation for calculations of diffuse-interface advection and formation based on a phase-field model, and a lattice-Boltzmann method is employed as numerical scheme for solving the two-phase fluid-dynamics equations. The simulations demonstrate the ability of the method to successfully capture the shape and motion of a droplet, not only on flat and grooved surfaces in a stagnant liquid under an external force, but also in a liquid flow inside a rectangular microchannel.

To improve the productivity of electronic devices, it is imperative to develop screen-printing techniques that can form finer wires with a higher-aspect ratio. The electric characteristics of conductive wires formed by the proposed screen-printing process combined with an imprinting technique were evaluated. Fine wires with a high-aspect ratio can be realised, owing to the capillary force of parallel-walled structures (PWSs) on polymer films. With the proposed process, printed wires with a line width of only 7.0 µm and an aspect ratio of up to 8.6 were obtained. To optimise the shape of the PWS, the dependence of the shape of PWSs was evaluated electrically. They compared the electric resistance of wires with a width of 10 µm formed using the proposed process to that of 81 µm wires formed using a conventional process. The measured resistance was almost the same, at around 54 kΩ/mm, despite the fact that the proposed process realised wires that were an eighth of the width. By controlling the printing conditions, they confirmed that capillary-effect-based screen-printing is also feasible using highly conductive ink. The resistance of a 13 µm wide printed wire achieved 3.0 Ω/mm.

For development of next-generation light control, a simple manufacturing technology to produce flexible metamaterials is a key component. Here, we report development of a printing method involving combination of a thermal nanoimprint method and a squeegeeing method, and demonstrate printed optical metamaterials made of commercially available ink consisting of silver nanoparticles. Optical evaluations of printed dipole resonators indicate dipole resonances corresponding to the structure lengths; these resonances are observed at wavelengths of 765-1346 nm. In particular, we report the important finding that, in metamaterials strongly affected by their constituent materials, a metamaterial structure made of the ink exhibits optical properties comparable to those produced by a vacuum deposition process.

In the advancement of printed electronics industry, the development of screen-printing techniques in order to form finer wires with a higher aspect ratio is an important task. To this end, we evaluate electrical characteristics of conductive wires formed by the screen-printing process combined with an imprinting technique. We show that fine and high-aspect-ratio wires are realized by the capillary force of parallel-walled structures (PWSs) on polymer films. A printed wire with a line width of 8.4 µm and an aspect ratio of 7.9 is obtained. The printed wires act as conductive wires according to the electrical evaluation. Moreover, the electric resistances of the wires formed by the proposed process keep low values compared with the increasing trend of resistance by the conventional process. At the height of PWS from 40 to 80 µm, the average resistances are gradually decreased from 228 to 87 kΩ/mm with an increase of the height. When the height is increased from 80 to 140 µm, on the other hand, since the decrease of the resistance cannot be observed, we confirm that there is a limit to form a high-aspect-ratio wire using the screen-printing condition. The printing condition needs to be further improved in future to produce an effect on the proposed screen-printing process.

To reduce particulate matter (PM) including soot in diesel exhaust gas, a diesel particulate filter (DPF) has been developed. Since it is difficult to observe the phenomena in a DPF experimentally, we have conducted a lattice Boltzmann simulation. In this study, we simulated the flow in a metallic filter. An X-ray computed tomography (CT) technique was applied to obtain its inner structure. The processes of soot deposition and oxidation were included for a continuously regenerating diesel filter. By comparing experimental data, a parameter of soot deposition probability in the numerical model was determined.

To investigate void formation during resin transfer molding (RTM) processes, we developed a numerical code of a multiphase fluid model that employs Navier-Stokes equation including the interfacial tension term and Cahn-Hilliard equation for capturing the resin-air interface. We performed preliminary numerical simulations of microscale resin-air flow around a regular-lattice array of four single filaments. From the analysis, we found that (1) Laplace pressure arisen from the finite curvature of the resin-air interface could drive a capillary-driven flow penetrating into the gap between the two filaments located in longitudinal direction; (2) there was another dual time scale even at the microscale on the determination of flow patters: one was caused by the main flow, and the other by capillary driven transverse flow; (3) voids could be formed when the time scale of the main flow was shorter than that of capillary flow; (4) two modes of void formations were revealed numerically: longitudinal gaps fully capped by the resin-air interface leading to the void formation under a high interfacial tension coefficient; and a small bubble left at the back-step of the filament under a relatively weak interfacial tension coefficient.

For interface-tracking simulation of two-phase flows in various micro-fluidics devices, we examined the applicability of two versions of computational fluid dynamics method, NS-PFM, combining Navier-Stokes equations with phase-field modeling for interface based on the van der Waals-Cahn-Hilliard free-energy theory. Through the numerical simulations, the following major findings were obtained: (1) The first version of NS-PFM gives good predictions of interfacial shapes and motions in an incompressible, isothermal two-phase fluid with high density ratio on solid surface with heterogeneous wettability. (2) The second version successfully captures liquid-vapor motions with heat and mass transfer across interfaces in phase change of a non-ideal fluid around the critical point.

Since diesel exhaust gas has more ambient air pollutants such as NOx and particulate matters (PM) including soot, the special treatment for exhaust emission standards is needed. Recently, a diesel particulate filter (DPF) has been developed to reduce PM in the after-treatment of exhaust gas. However, since the structure of the filter is small and complex, it is impossible to examine the phenomena inside the filter experimentally. In this study, we conduct fluid simulation in the diesel filter. We use the lattice Boltzmann method. The soot accumulation is considered to simulate the PM trap in the filter. For the wall-boundary in the simulation, the inner structure of the filter is obtained by a 3D-CT technique. Results show complex flow pattern in the diesel filter. Due to the soot accumulation, the velocity is changed and the pressure is increased. The pressure drop becomes larger as soot concentration at the inlet is higher.

An interface-tracking method based on a phase-field modeling is evaluated through numerical simulation of thermal liquid-vapor flows with phase change in micro-fluidics devices. In the modeling, the interface with a finite width between phases is autonomously formed while satisfying the free-energy theory. The phase-field method therefore needs no conventional elaborating algorithms for advection and reconstruction of the interfaces. The numerical results of two-dimensional van-der-Waals fluid flows around a critical point prove that the method has a potential to capture liquid-vapor motions in the non-ideal fluid with heat and mass transfer across the interfaces, such as bubble nucleation on a heater and cavitating flows around a solid body.

In this study, using the lattice Boltzmann method, we simulate soot accumulation in porous media to examine the particle trap in a diesel particulate filter (DPF). The porous media are numerically formed for different inner structure with given porosity. The porous structure similar to the real sample, Ni-Cr metal, can be obtained, where the pressure fields in both cases are almost the same. In the simulation of soot accumulation, the velocity field is changed when the soot is attached to the porous wall. The pressure drop is largely increased. Interestingly, the friction factor is smaller than experimentally predicted value by Ergun equation.

Although diesel engines have an advantage of low fuel consumption in comparison with gasoline engines, several problems must be solved. One of the major concerns is that diesel exhaust gas has more particle matters (PM) including soot, which are suspected to be linked to human carcinogen. As one of the key technologies, a diesel particulate filter (DPF) has been developed to reduce PM in the after-treatment of exhaust gas. In this study, we conduct lattice Boltzmann (LB) simulation on combustion in porous media. Results show that the combustion reaction is well simulated to observe the decrease of soot attached to the porous wall. This information is indispensable for the better design of DPF, and LB method can be a good tool for combustion simulation in porous media.

For interface-tracking simulation of incompressible two-phase fluids with high density ratios, a new numerical method was proposed by combining Navier-Stokes equations with a phase-field model based on a van der Waals-Cahn-Hilliard free-energy theory. The method was applied to several benchmark problems. Major findings are as follows: (1) The volume flux derived from a local chemical potential gradient in the Cahn-Hilliard equation leads to accurate volume conservation, autonomic reconstruction of gas-liquid interface, and reduction of numerical diffusion and oscillation. (2) The proposed method gave good predictions of pressure increase inside a bubble caused by the surface tension force. (3) A single liquid drop falling in stagnant gas and merging into a stagnant liquid film was successfully simulated.

We developed a simple embedded printing method that is capable of forming high-resolution patterns for transparent metal grid conductors. The simple printing method involves embedding conductive ink in a groove structure formed by nanoimprinting. Since this printing utilizes capillary force, conductive ink easily fills groove structures with small widths of several microns to the submicron scale. An embedded pattern with a line width of 300 nm was printed. In addition, a high aspect ratio of 3.1 was achieved with a 1.6 μm embedded pattern. A prototype transparent conductive film was developed with excellent optical and electrical performances: a high transmittance of 82.7% and a low sheet resistance of 5.1 Ω/sq at a grid width of 3.0 μm and a grid pitch of 150 μm. The grid parameters can easily be changed by mold design during the nanoimprint process. The transparent conductive film (TCF) showed excellent bending resistance compared with indium tin oxide.

Ultrasound was applied to a micropipette micromixer to improve dispersion of gas and liquid in a microchannel. Flow visualization using a high-speed camera was performed to examine the effect of ultrasonic irradiation on bubble generation in the microchannel. Basically, nitrogen gas was injected using a (0.5 µm ID) glass micropipette into ethanol flowing in a rectangular (100 µm×200 µm) microchannel on polydimethylsiloxane (PDMS). Gas and liquid flow rates were regulated using mass flow controllers. At aflow condition that is typical of bubbly flow, ultrasound was transmitted into the microchannel using a piezo-electric (PZT) transducer over a range of operating voltages (2 to 200 Vp-p) and frequencies (50 to 60 kHz). Images captured during the action of the PZT transducer indicate that bubble formation is influenced by ultrasound. When subjected to ultrasound above 50 Vp-p and at the resonant frequency of the PZT transducer, bubbles formed that were smaller and closer together, signifying enhanced shearing of the gas at the micropipette tip by the liquid. The observation of gas slugs occurring sooner might be attributed to the coalescence of gas bubbles that became closely spaced.

We have investigated the effect of doping on the electric conductivity of oxides in the systems La3Ni2(1-x)M2x O7 and La4Ni3(1-x)M3x O10, with M = Mo or W, and also in La3(1-x)M'3x Ni2O7 and La4(1-x)M4x Ni3O10 with M' = Sr or Ba. The temperature of the cross-over from semiconductive to metallic conductivity was increased in the case of Mo or W doping, while Sr or Ba had the opposite effect. A similar influence was exercised by heat treatment in reducing or oxidizing treatments, respectively.

The layer structures in bent-shaped liquid crystal dimers mOAM5AMOm (m=6-16) have been investigated by x-ray microbeam diffraction. These liquid crystal molecules have two rodlike mesogens connected with an odd-numbered alkylene spacer and form a bent shape. In these compounds it is found that the structure changes from the single (m=6) to frustrated-layer structures (m=8, 10, and 12) and switchable frustrated-layer structures (m=14 and 16) with increasing terminal chain length. An anticlinic antiferroelectric structure is suggested in the compound with m=16, based on the different electric-field-induced reorientation behavior from those in the other dimers.