The aim of this study is to reveal the nature of instability of airflow in the human nasal cavities during sniffing by particle image velocimetry (PIV).The vorticity and the turbulent kinetic energy (TKE) obtained from the fluctuation velocity distribution was calculated from the instantaneous velocity fields. In comparing the result of steady flow and sniffing flow, it revealed the velocity field difference of flow patterns : recirculation flow occurred in the region in front of the left nasal cavity at all inflow conditions, but when Reynolds number is 720, the size was small in the acceleration phase. In addition, TKE revealed instability increased as Reynolds number increased, and there is less instability at the olfactory cleft than at the anterior of the nasal cavity, and TKE became the smallest in the acceleration phase of sniff at many phases in the measured range, so the flow in the nasal cavity is considered to be stable during the acceleration phase of sniff.

Phantoms for ultrasonography have been widely used to improve skills of physicians and techniques of ultrasonic scattering. Several kinds of phantoms for ultrasonography have already been developed using gelatin, Polyacrylamide. In the development of biomodel for ultrasonography that covers human soft tissue, to change the mechanical properties widely is useful. We chose a poly (vinyl alcohol) hydrogel (PVA-H) to mimic human soft tissue. The purpose of this study is to measure the mechanical properties with varieties of concentration of solvent of PVA solution. The ratio of the mixed solution of Dimethyl sulfoxide (DMSO) and water was changed. The measurement of the static viscoelasticity, the dynamic viscoelasticity, and the loss tangent of PVA-H were performed. In addition, we measured the transverse wave velocity for the phantom to which graphite was added. In conclusion, the variety of mechanical properties of PVA-H is shown by the change of solvents, and especially the loss tangent is twice higher than the conventional PVA-H. And the transverse wave velocity has also a relation to the solvents.

This work studied the in-plane tensile characteristic of glass fiber based fabrics structure sheet (GFSS) and for developing a pressure-adjustable fixture of the fabrics structure sheet. In order to reduce or avoid the stress concentration of a liner layer, which was caused by the hard contact between outside hard plates and inside multiple-pins, a corrugated-form-adjustable fixture, which could fasten the single face corrugated specimen with a certain length of fixing span, was developed. Using the proposed fixture, the in-plane tensile test of machine directional and cross-machine directional specimens was investigated. Varying the numbers and diameters of inserted pins, the tensile strength was discussed. As the result, it was found that there were two peak maximum forces during the tensile elongation until reaching the breaking state. The first peak appeared to be the starting of liner layer breaking on one wide, while the second peak was to be the ending of corrugated layer elongation on another side. The peak maximum strength of specimen increased with the numbers of pins and affected by the diameter of pins.

Recently, bone regeneration using a scaffold has been performed instead of autogenous bone grafting as a treatment for a bone defect portion caused by a disease such as osteosarcoma or an accident or the like. The scaffold material should have high strength. However, mechanical properties are poor due to the reduction in strength by porosity and brittleness of β-TCP. In order to solve the problem that the strength is low, we attempted to prepare samples using hydrothermal hot pressing method. - In this study, we prepared the samples by changing the conditions for preparing them, and measured the compressive strength and the porosity of samples. As a result, layer cracking occurred in the samples prepared under conditions of high pressure. Furthermore, cracks were generated after sintering the samples. Therefore, both the compressive strength and the porosity of the samples prepared under conditions of high pressure were lower. In order to reduce layer cracks, we prepared lower pressure to reduce layer cracking. Occurrence of layer cracking could be reduced by prepared at 20 MPa or less. The heating and the cooling rate during sintering was changed from 3 [°C/min] to 2[°C/min]. The temperature distribution of the sample was uniformed to suppress the occurrence of cracks. From the above results, we were succeed in preparing samples which have average compressive strength of 10.0 [MPa] and average porosity of 72.3 [%].

Plasma sterilization of bacteria in cutting fluid was performed under atmospheric pressure and in-liquid, and the tribological properties of the resulting fluid were investigated. The number of bacteria colonies in the fluid sterilized by plasma under atmospheric pressure and in liquid was reduced by more than 90% compared with the untreated fluid. After exposure to ultraviolet light, no comparable reduction was observed. The plasma treated cutting fluids maintained a low friction coefficient 2.4 times longer than the untreated fluid. The study demonstrated that the life of a cutting fluid can be prolonged by this novel plasma treatment with an associated improvement in tribological properties.

Pressure redistribution is a key feature for foam mattresses to smoothen the pressure of the body surface and consequently to prevent pressure ulcer. We developed a portable device to evaluate the characteristics of pressure redistribution for foam mattresses by placing it on the mattress. This device consists of a circular bottom plate, a protruding shaft, and a load cell which detects the compressive load on the shaft when a load is applied to the mattress through the bottom of the device. We rounded the circumference of bottom plate with a radius of 5 mm and compared the pressure redistribution and a vertical deformation on a polyurethane foam mattress to a case of no rounding. The results shows that rounding caused a larger displacement and a larger load on the shaft when the device had a large amount of load. Effect of rounding is one of the key factors to evaluate the pressure redistribution quantitatively.

One of the major challenges in the field of regenerative medicine is to make a tissue with three dimensional structure. The cells in the center of the 3D-tissue do not have enough access to oxygen and nutrition, which leads to necrosis in the tissue. In this study, a biodegradable, oxygen generating scaffold was made from poly-caprolactone (PCL) and calcium peroxide (CPO) by the use of additive manufacturing technique. Scaffolds were seeded with MIN6-m9 cells, and the result of DNA quantification, live-dead image was compared after 7 days of hypoxia culture. There were no significant change in DNA quantity. However, the distribution of living cells changed. There were more living cells in the center of scaffold with 5% of CPO compared to that without CPO. This result suggests that the oxygen generating scaffold has positive effect to cell survival. Further study of quantification and the simulation of oxygen concentration is under consideration.

In this study, we investigated the resorption behavior for the substrates due to the osteoclasts cultured on the substrates with different elastic moduli in order to investigate the interaction between the metabolic behavior of osteoclasts and the mechanical properties of the substrates. Here, PCL substrates with different elastic moduli were prepared by changing the cooling rate. After osteoclasts were cultured on the prepared substrates, the elastic modulus and yield strength were evaluated by tensile tests. As a result, in the rapidly cooled PCL, the elastic modulus and the yield strength of the substrate decreased due to the resorption behavior by osteoclasts and hydrolysis. On the other hand, the elastic modulus and yield strength of the slowly cooled PCL decreased by hydrolysis, whereas it did not decrease due to resorption behavior of osteoclasts. Based on these results, the mechanism of the interaction between the metabolic behavior of osteoclasts and the dissolution behavior of the substrates was discussed.

At airport in cold climates, low in-service rate of airplane by snow accumulation, has become a problem. Therefore, it is important for evaluating the tribological behavior of airplane tire on snow and ice runway. To estimate the tribological behavior, degree of separation between a rubber and a stainless steel was measured by using an electric conduction method. Vertical and relative movement between the rubber and snow surfaces was also observed by using a laser displacement sensor. By using the electric conduction method, it was found that the separation between rubber and stainless steel at surface roughness level could be measured. In addition, phase change of snow was observed after landing. On drop behavior of rubber as a tire, elastic deformation of rubber was confirmed and drop velocity before landing, was calculated. This research is a fundamental research to provide an international runway friction index, and it is necessary to further research in order to estimate tribological behavior based on various parameters.

A shaft is manufacutred at a high-speed cutting rate by using machine tools. In some cases, the rotating of a shaft reaches at 5,000 rpm by using a NC lathe etc. The high-speed cutting generates heat. A water-soluble cutting fluid is used for removing the heat generated at the high-speed cutting, however, the fluid invades into the live center, which supports the workpiece of a shaft. The invaded fluid makes a deterioration of bearings in the live center, and finally leads to abrupt functional failure of the live center. In order to avoid the ingress of cutting fluid into the bearing parts, Conventional live center has a waterproofing by a labyrinth seal or an oil seal. However, there is a room for discussion about the sealing mechanism, which can prevent ingress of the water-soluble cutting fluid prefectly.
In this study, a new type of waterproof seal system for high-speed rotation has been proposed, in which a PVF (polyvinyl formal) was used as a seal lip. The effectiveness of seal system has also been discussed, based on the durability tests.

The influence of synovial fluid on biphasic lubrication property of articular cartilage has not been discussed enough in previous studies. We hypothesized that synovial fluid pressure generated in wedge-film shaped gap just a head of cartilage contact region suppresses the effusion of interstitial fluid in articular cartilage and this leads to enhance biphasic lubrication ability of articular cartilage. In the present study, we performed an experiment to determine average pressure in the wedge-shaped fluid. We also performed a friction analysis to compare the coefficient of friction of standard poroelastic model with that of synovial fluid pressure (SFP) model in which the effusion of interstitial fluid from articular cartilage was regulated. The effusion was driven by the pressure difference between analyzed pressure of surface element and the average pressure of synovial fluid in SFP model. Results revealed that the coefficients of dynamic friction in both SFP model and standard model decreased with the increase of sliding speed. The coefficients of dynamic friction in SFP model were smaller than those in standard model in whole sliding speed range. These results suggested that synovial fluid plays important roles not only in wedge film hydrodynamic lubrication but also in biphasic lubrication by suppressing the effusion of interstitial fluid in articular cartilage.

Pluripotent stem cells have the ability to generate multicellular tissues with cooperative cell differentiation and movement. During such self-organizing process, cells adjust their fates and behaviors depending on mechanical and geometric environment through 2 types of cell adhesion; cell-substrate and cell-cell adhesion. Here we investigated changes in pluripotency of mouse embryonic stem cells cultured on microstructured mesh sheets in LIF-supplemented pluripotency maintenance medium. The mesh sheets, microfabricated using photolithography, have large mesh openings and narrow mesh strands, hence cell-substrate adhesion area is minimized. Upon seeding, cells attached to the strands were able to proliferate, fill the mesh openings and form sheet-like tissues. Immunofluorescence microscopy revealed that the cells expressed pluripotency markers at 3rd day after seeding. Interestingly, the sheet-like tissues spontaneously became thicker and finally generated spherical cyst-like tissues attributable to cell differentiation. Thus, our results suggest that modulating the cell-substrate adhesion induces these self-organizing morphological changes in 2 steps; sheet-like tissues relying on cell-cell adhesion to overcome substrate restriction and spherical cyst-like tissues accompanied by loss of pluripotency. This research may help to build up a new platform for studying pluripotent stem cell self-organization leading to the generation of functional organoids.

Cancer cells are known to have significantly lower cell stiffness than healthy cells. To establish a screening method of cancer cells based on a difference in mechanical properties between healthy and cancer cells, we developed a handier system based on microfluidics to assess the deformability of cells with the aim of clinical application. The tapered microchannel with the width of 15 μm at the tip was fabricated. Cell lines examined were two metastasis B16 melanoma variants (B16-F1 and B16-F10) and fibroblast (L929). The results demonstrated that the deformability of B16-F10 cells was significantly higher than that of B16-F1 and L929 cells, showing that cells with higher metastatic potential have higher cell deformability. These results addressed the utility of the present system to handily screen cancer cells that circulate in blood with other cells.

Pathogenic bacteria are micrometer-scale bioparticles of potential risk to miscellaneous diseases whose rapid diagnosis and medical care requires a sensor for sensitive microbial detections in dilute suspension of physiological media. Integration of solid-state pore sensors and fluidic channels for particle concentration allows high-throughput single-particle detections in a low-concentration particle solution. This paper presents high-throughput particle detection using capillary-driven hydrodynamics in dual-height fluidic channels integrated with the micropore sensor. The device concept is based on a Washburn model to collect over-sized particles at the junctions of dual-height fluidic channels. We achieved up to 880-fold-concentration of microparticles dispersed in buffer using the micropore-integrated dual-height fluidic channels. As this method uses only hydrodynamic flow for particle concentration, it can be applied to essentially any analytes unlikely to be the case for other techniques such as electrophoretic or magnetic manipulation. Integration of micropore sensors and fluidic channels for particle concentration will contribute to high-throughput bioparticle detections in dilute suspension of physiological media.

The present study aims at investigating the response of a type 316LN austenitic stainless steel (the primary structural material for the core components of SFRs) to simultaneous application of LCF and HCF cycles. All the tests were carried out over a wide range of temperature from ambient to 923 K, at three different strain amplitudes (±0.25%, ±0.4 and ±0.6%). One LCF (major) cycle, together with a specific number of superimposed HCF (minor) cycles, is referred to as a ‘block’. Cyclic life was found to be governed by LCF strain amplitude, block size and temperature. For a given strain amplitude, the cyclic life decreased when the block size is increased, due to an increase in the HCF damage. This phenomenon was more prominent with the increase in temperature from 300 to 923 K as multiple damage modes like ratcheting and creep get activated at higher temperatures, apart from LCF. An anomalous behavior in terms of saturation in cyclic life with block size as well as temperature was observed at 823-873 K which is attributed to the strong presence of dynamic strain aging (DSA) in the above temperature range. DSA suppressed stressdependent damage (ratcheting) originating from the HCF cycling within the block, enabling LCF to be the major damage contributor in this case.

Ni-base superalloys have been considered as the candidate materials of the high temperature components of advanced ultra supercritical (A-USC) power plant. Those materials are known to form variety types of the precipitates after those exposing to the high temperature environments. The localized oxidation influenced by those precipitates, particularly those of carbides, are sometimes concerned as an acceleration factor to the material degradation. In this study, in order to confirm the long-term reliability of A-USC power plant, oxidation tests in supercritical water (SCW) which simulated the main steam condition of A-USC were carried out using alloy 625. The cross-sectional analyses were performed to examine the elemental distribution in and beneath the oxide film. A laves phase contained Ni, Mo, Nb, and Mo rich carbides were observed along the grain boundaries. The oxidation of the laves phase was not recognized though those were present adjacent to the oxide film. The voids formed beneath the oxide film were observed and those surroundings were enriched in carbon, therefore it was considered that particular carbides influenced to the formation. A large number of pits were confirmed, and those were initiated on the Nb rich carbides. The Nb and Cr rich oxide was continuously formed at the pit and alloy matrix interface, which layer was speculated to play as the protective one. According to the observations, it is considered that further growth of those pits beyond the size of the existed Nb rich carbide was not pronounced.

In this study, combustion character of thermal degraded electrical cable for the nuclear power plant was evaluated. To make aging degradation electrical cables, accelerated thermal ageing tests were carried. The electrical cable combustion tests on a simple cable tray were applied to evaluate combustion character of thermal degraded electrical cable. Temperature of the accelerated thermal ageing tests were 90°C, 80°C, 70°C and period of tests were 10, 20, 40 days respectively. Finally, combustion tests on the simple cable tray was analyzed by FDS (Fire Dynamics simulation). FDS analysis software apply two fire models (one model was based on heat released rate: HRR model, the other was based on chemical reaction: CR model). In this case, the HRR model was applied. Heat released rate calculated by the FDS analysis was similar to it by the electrical cable combustion tests.

Creep-fatigue damage in high-temperature components gradually proceeds at stress concentrate portion during start-steady state-stop operation. Clarification of the damage evolution process under creep-fatigue loading is important to develop life assessment methods. In this study, strain control creep-fatigue tests with one hour hold time were conducted by using round notch bar specimens on CrMoV forging steel and damage condition was observed for test interrupted specimens. Failure lives of the round notch bar specimens were much shorter than those of smooth bar specimens under the same conditions. Microstructure observation of creep-fatigue damaged specimens indicated that a grain boundary crack initiated from notch root and grew toward inside of the specimen with increasing the creep-fatigue damage. It was found that cyclic loading superimposed on creep loading causes reduction of rupture time due to acceleration of crack initiation and growth. Finite element analysis results also indicated that an axial stress after hold time remains the highest at the notch root.

Miniature creep specimens with 1mm diameter were machined from base metal, weld metal and heat affected zone(HAZ) of a long-term used welded pipe. Creep tests of these miniature specimens were performed in inert gas atmosphere. Creep strengths of the base metal and the HAZ in the long-term used welded pipe were similar to those in an undamaged welded joint. On the other hand, creep strain rate of the weld metal in used welded pipe is much faster than that in the undamaged welded joint. Standard size welded joint specimens were taken from near surface and X-shape regions of the welded pipe to understand creep rupture strength. Creep rupture time of the standard welded joint specimens taken from the used welded pipe was much shorter than that of the undamaged welded joint. It was suggested by finite element creep analyses that the highest axial stress occurred at HAZ in the specimen taken from X-region and that occurred at weld metal in the specimen taken from near surface region.

Thermal fatigue cracking may initiate at a tee pipe where high and low temperature fluids flow in. The mixing flow causes temperature fluctuation near the pipe wall and may result in fatigue crack initiation. In this study, flow pattern at the mixing tee pipe was investigated by experiments in order to prevent the thermal fatigue. Visualization of flow was conducted by a test section of transparent acrylic resin and a tracer method. This test section is consisted of a horizontal main pipe with an inner diameter of 150 mm and a vertical branch pipe with an inner diameter of 50 mm. Flow in the main pipe penetrated into the branch pipe. The penetration patterns were categorized by the momentum ration for the flows in the main and branch pipes. The maximum penetration depth was measured from the movement of tracer particles. Relationship between the maximum penetration depth and the momentum ration was investigated.

Thermal barrier coating (TBC) specimens are prepared from an in-service first stage blade of F-class gas turbine. Using the specimens, furnace cycling tests and a thermal cycling test under thermal gradient are performed. The thicknesses of thermally grown oxide (TGO) formed at the boundary between topcoat and bondcoat in the specimens are estimated as at most about 1μm before the tests, based on the microstructural analysis of other areas in the blade. The topcoat delamination occurs at TGO or in its vicinity in the furnace cycling tests. This suggests that the delamination is caused due to the degradation of TGO growth at the boundary. The number of cycles to delamination does not depend on the TGO thickness before the test. As for the thermal cycling test under thermal gradient, TBC sample extracted from the blade is coupled with a base specimen of a Ni-base superalloy by nickel brazing. After the test, vertical cracks in the direction of coating thickness are formed in the topcoat due to topcoat sintering, and transverse cracks formed in topcoat grow in the vicinity of the boundary. The preparation of the TBC specimen is validated since the morphology of the damage is characteristic to the thermal cycling test under thermal gradient.

The structural integrity of a reactor pressure vessel (RPV) is important for the safety of a nuclear power plant. Pressurized thermal shock (PTS) takes place when the emergency core cooling system (ECCS) is operated and the coolant water is injected into the RPV due to a loss-of-coolant accident (LOCA). With the neutron irradiation, PTS loading may lead a RPV to fracture. Therefore, it is necessary to evaluate the performance of RPV during PTS loading to keep the RPV's safety.
In the present study, the deterministic and probabilistic methods are made to investigate the RPV integrity during PTS loading. For the deterministic integrity assessment, 3D-CFD and finite element method (FEM) simulations are performed, and stress intensity factors (SIFs) are obtained as a function of crack position inside the RPV. As to the probabilistic integrity assessment, a more accurate distribution of SIF on the RPV is calculated. By comparing the distribution obtained with the fracture toughness included as a part of the master curve, the probabilistic integrity assessment method which can obtain the fracture probability on the RPV is finally investigated.

A design study of an advanced sodium-cooled fast reactor (Advanced-SFR) has been conducted in Japan Atomic Energy Agency (JAEA). Hot sodium from the fuel subassembly can mix with the cold sodium from the control rod (CR) channel and the blanket assemblies at the bottom of Upper Internal Structure (UIS). Temperature fluctuation due to mixing of the fluids at different temperature between the core outlet and the bottom of the UIS may cause high cycle thermal fatigue on the structure around the bottom of the UIS. A water experiment using a 1/3 scale 60°-sector model simulating the upper plenum of the Advanced-SFR has been conducted to examine countermeasures for the significant temperature fluctuation generated around the bottom of UIS. By the velocity measurement using the particle image velocimetry (PIV), it was known that the swirling flow in vertical direction from the upper to the lower regions of the CIP was formed around the flow-hole of the back-up control rod (BCR) channel. The large intensity of the temperature fluctuations was observed near the cold fluid outlets simulating the BCR channel. The countermeasure to mitigate the temperature fluctuation intensity was applied and its effectiveness was confirmed.

In nuclear power plants, the structural components that are in contact with coolant are susceptible to thermal loads due to the change in the fluid temperature. If the heating and cooling processes are repeated, the structure will endure thermal fatigue that may lead to failure. Thermal stratification is one of the main loads that can lead to high cycle thermal fatigue damage. The Japan Society of Mechanical Engineers (JSME) has published the evaluation guideline for high cycle thermal fatigue. It treats branch pipe due to thermal stratification, however, it does not contain an analysis method for stress evaluation. This study was aimed at evaluating the thermal stress generation under local temperature fluctuation by thermal stratification at an elbow pipe in a nuclear power plant. A Finite Element Analyses was adopted to study the thermal stress characteristics and their mechanics. In addition, the results were compared with an analytical approach based on a frequency response function.

Thermal stress was analyzed when a gas turbine thermal barrier coated structure was subjected to a sudden change in combustion gas temperature. The thermal stress was calculated based on the third kind boundary condition by the Biot number. The numerical calculation showed that the transient thermal stress magnitude was significantly affected by the Biot number, and that it should be distinguished from the steady state thermal stress. The influence of physical properties in TBCs was also examined quantitatively.

Our research team are now trying to develop a novel water cooling device for electrical devices using pulsating flow. In order to increase heat exchange performance of cooling devices while decreasing power consumption of fans and pumps, a novel technique of flow control should be developed. We are investigating an application of pulsating flow to water cooling devices for high-density packaging electronic equipment. In this report, we especially focused on a pulsating wave pattern of supply flow rate. A relationship between the pulsating wave patterns and the heat transfer performance of the combination of the rib and the pulsating flow was investigated through 3D-CFD analysis. Through the analysis, we clarified that the pulsating wave pattern affects the heat transfer performance around the ribs. Especially, it was found that an optimization the transient change of the supply flow rate in the acceleration period may achieve the higher heat transfer performance by the pulsating flow while decreasing the pressure drop around the rib.

This paper describes the evaluation of relationship between thermal contact resistance and load with 3 types of TIM (Thermal Interface Materials), and the evaluation of performance of heat spreader. Experimental study was conducted for evaluation of thermal contact resistance, and the conditions of bare contact surface and TIM (copper paste and solder) in between were evaluated. For detection of spread angle in heat spreader, thermal analysis is performed. Experimental results showed contact thermal resistance with solder in between was lowest thermal contact resistance, and the resistance was not dependent on contact pressure. Numerical results showed that the spread angle is less than 45°, when the thickness of the heat spreader is 3 [mm].

This paper evaluates boiling heat transfer performance on a lotus-type porous copper plate attached onto a grooved heat transfer surface. The experiments are conducted under atmospheric and saturated pool conditions. The lotus copper plate has uni-directional pore structure in a perpendicular direction for the heated surface and the average hydraulic diameter of the pore hole is 0.36 mm. The lotus copper plate of 2.0 mm in thickness is soldered onto the heated surface with grooves. The boiling curves prove that the utilization of the lotus copper plate leads to boiling heat transfer enhancement especially in the beginning of the nucleate boiling regime and that the critical heat flux increases up to 278 W/cm2, which is two times higher than that in the smooth surface case.

The objective of this research is to obtain basic data for miniaturization and saving energy of thermoelectric cooler (Peltier cooler). For that objective, we made three types of experimental thermoelectric coolers which each have a different heat dissipating component on the hot side of thermoelectric module. We evaluated the cooling capacities and energy consumptions of them on various driving conditions (e.g. applied voltage for thermoelectric module and cooling fan). Per these results, we obtained the relation between heat dissipation performances of the hot side and cooling capacities, and some optimum applied voltages for the cooling fan in order to save energy of thermoelectric cooler. These experimental results show a maximum reduction of energy by nearly half compared to the cooling fan driven rated voltage.

Lead free solder material has been widely used in electric or electronic apparatus. In this paper, low cycle fatigue characteristics of the lead free solder Sn-3.0Ag-0.5Cu material with a very sharp V notch were discussed under different strain rates of 1×10^-4 and 1×10^-3, and electron microscopic observation was carried out. And inelastic numerical simulation depending on time was carried out under low cycle fatigue test conditions for lead free solder test piece with V notch. It was found that equivalent depths to predict the life of solder material having stress strain concentration were independent of the load level and strain rate.

Recently, it has been also found that the amplitude and distribution of the residual stress vary drastically depending on the size of the element component and their manufacturing process. A fluctuation of the residual stress should degrade the long term reliability and the performance of the devices, therefore, it is important to monitor and control the change of the local residual stress. In this study, a stress sensor which was embedded in a silicon chip was developed by applying piezoresistance effect of single-crystalline silicon. Static and dynamic changes of the stress in a silicon chip were applied by bending beam test and the resistance change of the sensor gauge were monitored. The fabricated stress sensor responded quickly to the change of the local residual stress and a stress sensitivity was about 50 times higher than the most typical metallic strain gauges.

A new tactile sensor with the minimum pressure sensitivity less than 10 kPa has been developed by applying MWCNTs (Multi-Walled Carbon Nanotubes). The sensor was embedded into a highly deformable flexible substrate (PDMS: Polydimethylsiloxane) and the obtained gauge factor of the developed sensor was about 5. Since the electronic properties of MWCNTs vary drastically depending on their shape, it is important to make appropriate aspect ratio of MWCNTs. The aspect ratio of MWCNTs is mainly dominated by their growth condition such as the average thickness of catalyst layer, growth temperature, pressure of resource gases and so on. Thus, the optimum growth condition was investigated for making the MWCNTs with high aspect ratio, in other words, high pressure-sensitivity. A thermal CVD synthesis process of MWCNTs was developed by using acetylene gas. After the synthesis of MWCNTs, flexible isolation material (PDMS) was coated around the grown MWCNT. Then, the interconnection film was deposited by sputtering. After that, PDMS was coated again to fabricate an upper protection layer. Finally, the bottom interconnection layer was sputtered and patterned. The change of the electrical resistance of the grown MWCNTs was measured by applying a compression test in the load range from 0 to 10 mN. It was found that the electrical resistance of the MWCNTs increased almost linearly with applied compressive load and this sensor showed the high load sensitivity of 10 mN that is higher than human fingers.

In aging society with fewer children, the development of medical engineering technologies is strongly demanded for keeping enough nursing cares. One of the expected technologies is human motion detection using strain sensor. To detect human motion, a strain sensor must have high sensitivity and high deformability. However, conventional strain sensors don't satisfy these requirements. Recently, large attention has been focused on graphene as a sensing part for next-generation strain sensor with high sensitivity and large deformability. Graphene is a two-dimensional carbon sheet composed of π-conjugated network of sp² carbons, having large deformability, high electron mobility and some outstanding properties. It is well known that graphene nano-ribbon, which is cut from graphene into nano-scale, shows semiconducting properties. Since semiconductor material has high strain sensitivity based on piezoresistive effect, graphene nano-ribbon can be used for highly sensitive and deformable strain sensor. In this study, to fabricate graphene nano-ribbon and measure its I-V characteristics, thermal CVD (chemical vapor deposition) using C₂H₂, metallic electrodes fabrication using EB evaporation and micromachining using EB(electron beam) lithography were employed. The fabrication of graphene nano-ribbon with metallic electrodes and measurement of I-V characteristics were succeeded.

Rapid change in climate and depletion of resources require the development of advanced and more efficient renewable energy devices. Since solar light is a promising abundant resource, the development of an efficient photovoltaic cell is attractive. Since the conventional solar cells consist of a semiconductor material with a fixed band gap, they can use a limited region of the solar light spectrum, and thus, their efficiency is rather low. In order to improve the efficiency of a solar cell, a novel concept of an enhanced photo-sensor for photovoltaic application using area arrayed graphene nano ribbon (GNR) was proposed. Graphene exhibits superconductive properties with zero band gap in its original structure, however, the band gap of graphene starts to open when it is cut into a ribbon with the width thinner than 70 nm, and it shows semiconductive properties. The amplitude of the band gap is a strong function of the width of graphene nano-ribbon (GNR). Using area-arrayed GNRs with different width, it is possible to develop a new photo-sensor with enhanced photosensitivity. The key parameter for this design is the alignment of plural GNRs with different band gap. The possibility of the development of a highly sensitive and enhanced photo-sensor by using the area-arrayed structure was investigated analytically.

Lead-free solder has been used for surface mounting of electronic devices in consideration of the environment. However, there is a concern that the electronic parts may be damaged by heating during bonding because the lead-free solder has a high melting point. Therefore, development of a new bonding technique without heating is required. There are many studies on nanowires because of their unique characteristics which are different from bulk materials. In this paper, we fabricated Cu nanowire surface fasteners and investigated the improvement of strength by changing the diameter ratio of nanowires. Cr and Au films were formed as electrodes on glass substrates by sputtering. According to the template method, the polycarbonate template was fixed on one electrode to fabricate Cu nanowires by electrodepositing in the CuSO₄·5H₂O solution. After removing the template by etching with dichloromethane, the Cu nanowire surface fastener was fabricated. By applying a preload, the Cu nanowire surface fasteners were connected. Thereafter, the adhesion strength of the Cu nanowire surface fastener was evaluated by a tensile test. The highest bonding strength was found to be 162.6 N/cm² while the combination of the nanowire array with the diameter ratio of 1:4. Nanowires intertangling with each other was assumed to be an additional effect on the van der Waals force between nanowires.