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Search Results: 1 - 10 of 1197 matches for " Kentaro Yamauchi "
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The Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic Composite Material  [PDF]
Kentaro Yamauchi, Tsuyoshi Ochiai, Goro Yamauchi
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2015, DOI: 10.4236/jbnb.2015.61001
Abstract: The synergistic antibacterial performance against Escherichia coli (E. coli), Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) of a Cu/WO3-added PTFE (polytetrafluoroethylene) particulate composite was reported in the previous paper. The origin of the synergistic antibacterial performance investigated by evaluating the photocatalytic decomposition of the Cu/WO3-added PTFE particulate composite material is reported in the present paper. Addition of Cu/WO3, visible-light-sensitive photocatalyst, to the PTFE particle dispersed superhydrophobic composite does not deteriorate the superhydrophobic property of the composite. Furthermore the existence of the polytetrafluoroethylene (PTFE) particles dispersed in the composite enhances the antibacterial property caused by the Cu/WO3. The authors call this “The synergistic effect”. In this study, a novel synergistic property of the Cu/WO3-added PTFE particulate composite was investigated by evaluating the degradation of gaseous acetaldehyde on the composite surface using visible light (10,000 lx) and UV-A (1 mW·cm-1) illumination. The 12 wt% Cu/WO3-8 wt% binder-80 wt% PTFE composite shows the synergistic visible-light-sensitive photocatalytic property. But 12 wt% Cu/WO3-44 wt% PTFE-44 wt% binder composite no longer shows the synergistic property of visible-light-sensitive photocatalytic property. The synergetic performance of visible-light-sensitive photocatalytic property appears only when PTFE concentration is larger than the critical point over which superhydrophobic property appears in accordance with the particulate composite model derived by the one of the authors. The hydrophobic surface leads to the low surface free energy derived by the revised Fowkes’s theory, which makes it difficult for bacteria to stick to the hydrophobic surface of the composite. Even if bacteria stick to the surface, they are decomposed by the visible-light-sensitive photocatalyst. This is the reason why the synergistic antibacterial performance against bacteria appears.
Synergistic Antibacterial Performance of a Cu/WO3-Added PTFE Particulate Superhydrophobic Composite under Visible-Light Exposure  [PDF]
Yanyan Yao, Kentaro Yamauchi, Goro Yamauchi, Tsuyoshi Ochiai, Taketoshi Murakami, Yoshinobu Kubota
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2012, DOI: 10.4236/jbnb.2012.34042
Abstract: Addition of TiO2 to a polytetrafluoroethylene (PTFE) particle-dispersed composite contributes to the self-cleaning properties of the water-repellent composite. However, its application is limited to outdoor usage or under ultraviolet (UV) irradiation. In this study, a novel visible-light-sensitive photocatalytic and superhydrophobic material was developed by adding Cu/WO3 to a PTFE particulate composite material to overcome this deficit. A remarkable property of this novel composite material is the synergistic antibacterial performance against Escherichia coli (E. coli), Staphylo-coccus aureus, and methicillin-resistant Staphylococcus aureus compared with the addition of Cu/WO3 without PTFE particles material. During 24-h exposure in visible light at 2000 lx, the number of viable cells of the three strains on the surface of the 8wt% Cu/WO3-added PTFE particulate composite decreased from 2 – 4 × 105 colony-formation units (CFUs) to less than 10, the limit of detection. This bactericidal rate is four times higher than that of 8wt% Cu/WO3 without PTFE particles material, which is attributed to the air trapped in the rough surface of the novel material providing additional oxygen to the photocatalytic reaction. Even for exposure to visible light at 100 lx, the decrease in CFUs of E. coli on the 12wt% Cu/WO3-added PTFE particulate composite reached nearly 2.0 logs. The characterization of the Cu/WO3-added PTFE particulate composite indicated that the composite material containing 80wt% PTFE maintained a superhydrophobic or water-repellent property with a water contact angle >150, although the Cu/WO3 in the composite material remained hydrophilic under visible light. The Cu/WO3-added PTFE particulate composite displayed photo-catalytic reactions to decompose oleic acid adsorbed on its surface and gaseous acetaldehyde under UV-A and visible-light illumination. All results demonstrate that the Cu/WO3-added PTFE particulate composite material may be used in sterilization, as a water repellent, for self-cleaning, and in the oxidative decomposition of volatile organic compounds (VOC) both indoors and outdoors.
Antibacterial Activity of Hydrophobic Composite Materials Containing a Visible-Light-Sensitive Photocatalyst
Kentaro Yamauchi,Yanyan Yao,Tsuyoshi Ochiai,Munetoshi Sakai,Yoshinobu Kubota,Goro Yamauchi
Journal of Nanotechnology , 2011, DOI: 10.1155/2011/380979
Abstract: The conventional superhydrophobic surface offered by PTFE provides no sterilization performance and is not sufficiently repellent against organic liquids. These limit PTFE's application in the field of disinfection and result a lack of durability. N-doped TiO2 photocatalyst added PTFE composite material was developed to remedy these shortcomings. This paper reports the surface characteristics, and the bactericidal and self-cleaning performance of the newly-developed composite material. The material exhibited a contact angle exceeding 150 degrees consistent with its hydrophobicity despite the inclusion of the hydrophilic N-doped TiO2. The surface free energy obtained for this composite was 5.8?mN/m. Even when exposed to a weak fluorescent light intensity (100 lx) for 24 hours, the viable cells of gram-negative E. coli on the 12% N-doped TiO2-PTFE film were reduced 5 logs. The higher bactericidal activity was also confirmed on the gram-positive MRSA. Compared with the N-doped TiO2 coating only, the inactivation rate of the composite material was significantly enhanced. Utilizing the N-doped TiO2 with the PTFE composite coating could successfully remove, by UV illumination, oleic acid adsorbed on its surface. These results demonstrate the potential applicability of the novel N-doped TiO2 photocatalyst hydrophobic composite material for both indoor antibacterial action and outdoor contamination prevention. 1. Introduction It is well known that the conventional superhydrophobic surface offered by polytetrafluoroethylene (PTFE) provides no sterilization performance and is not sufficiently repellent against organic matters. Thus, there is potential risk for bacteria to adhere to its surface more readily in ambient air, as well as organic matters is considered to reduce the durability of the superhydrophobic performance. To remedy this shortcoming, anatase titanium dioxide (TiO2), a UV light-sensitive photocatalyst added water repellent composite material has been developed in our previous study [1–5]. TiO2 was used to demonstrate the inactivation of various bacteria, such as Escherichia coli (E. coli), methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa (P. aeruginosa), Legionella pneumophila (L. pneumophila) [6–8], and Clostridium difficile spores [8]. The inclusion of TiO2 to the PTFE coating is expected to generate antimicrobial and self-cleaning properties, which would expand its scope of application. Anatase TiO2-added PTFE composite material is not only water-repellent but also exhibits self-cleaning properties. However, because
ZnO Heteroepitaxy on Sapphire Using a Novel Buffer Layer of Titanium Oxide: Crystallographic Behavior  [PDF]
Satoshi Yamauchi, Yoh Imai
Crystal Structure Theory and Applications (CSTA) , 2013, DOI: 10.4236/csta.2013.22006
Abstract: A novel buffer layer consists of titanium oxide grown on a-sapphire by low-pressure chemical vapor deposition using titanum-tetra-iso-propoxide and oxygen gas was used for ZnO epitaxial growth at temperature as low as 340 by plasma-assisted epitaxy using radio-frequency oxygen-gas plasma. XRD and RHEED indicated (0001)Ti2O3 layer in corundum crystal system was epitaxially grown on the substrate in an in-plane relationship of [1-100]Ti2O3// [0001]Al2O3 by uniaxial phase-lock system. Growth behavior of ZnO layer was significantly dependent on the Ti2O3 buffer-layer thickness, for example, dense columnar ZnO-grains were grown on the buffer layer thinner than 10 nm but the hexagonal pyramid-like grains were formed on the thin buffer layers below 2 nm. RHEED observations showed ZnO layer including the pyramid-like grains was epitaxially grown with single-domain on the thin buffer layer of 0.8 nm in the in-plane relationship of [1-100]ZnO//[1-100]Ti2O3//[0001]Al2O3, whereas the multi-domain was included in ZnO layer on the buffer layer above 10 nm.
Plasma-Assisted Chemical Vapor Deposition of TiO2 Thin Films for Highly Hydrophilic Performance  [PDF]
Satoshi Yamauchi, Yoh Imai
Crystal Structure Theory and Applications (CSTA) , 2013, DOI: 10.4236/csta.2013.21001
Abstract: Titanium-oxide layer was grown on glass substrate by plasma-assisted chemical vapor deposition (PCVD) using oxygen gas plasma excited by radio-frequency power at 13.56 MHz in the pressure as low as 3mtorr at relatively low temperature below 400oC, and studied on the crystallographic properties with the hydrophilic behavior comparing to the layer deposited by low-pressure chemical vapor deposition (LPCVD). Raman spectra indicated anatase-phase TiO2 layer without amorphous-phase could be formed above 340oC by simultaneous supply of plasma-cracked and non-cracked titanium-tetra-iso-propoxide (TTIP) used as preliminary precursor. Surface Scanning Electron Microscope images indicated the PCVD-layer consists of distinct nanometer-size plate-like columnar grains, in contrast to rugged micrometer-size grains in the LPCVD-layer. Extremely small water contact angle about 5o in dark and the quick conversion to super-hydrophilicity by UV-irradiation with a light-power density as low as 50 W/cm2 were observed on the PCVD- layer grown at 380oC, while the large initial contact angle was above 40o and the response for the UV-irradiation was gradual on the LPCVD-layer.
ZnO Heteroepitaxy on Sapphire Using a Novel Buffer Layer of Titanium Oxide: Optoelectronic Behavior  [PDF]
Satoshi Yamauchi, Yoh Imai
Crystal Structure Theory and Applications (CSTA) , 2013, DOI: 10.4236/csta.2013.23014
Abstract:

Optoelectronic property of ZnO epitaxial layer grown by plasma-assisted epitaxy at temperature as low as 340°C using Ti2O3 buffer layer on a-sapphire were studied by low temperature photoluminescence at 10 K comparing to the layers on c-sapphire and a-sapphire without the buffer layer. The near band-edge emission consisting of free-exciton emissions and neutral-donor bound exciton emissions was significantly dependent on the buffer thickness and dominated by the free-exciton emissions in the layer grown on the very thin buffer layer about 0.8 nm, whereas the intense emissions by neutral-donor bound excitons were observed in the ZnO layer on c-sapphire. The structural behavior indicated the donor was originated from the three-dimensional growth of ZnO layer and details of the optoelectronic feature suggested the residual donors were Al and interstitial-Zn.

Effects of Curing Conditions and Formulations on Residual Monomer Contents and Temperature Increase of a Model UV Gel Nail Formulation  [PDF]
Kentaro Taki, Tomomi Nakamura
Journal of Cosmetics, Dermatological Sciences and Applications (JCDSA) , 2011, DOI: 10.4236/jcdsa.2011.14017
Abstract: Recently, the application of ultraviolet (UV) curable monomers to human nails, (also known as UV gel nails) has become a popular decoration technique for women’s nails. However, the unreacted layer, the depletion of residual monomers from the cured UV gel nails, which can cause allergy and asthma, and the increase in temperature during curing process, are major concerns. In this study, the thickness of the unreacted layer, the increase in temperature, and the residual contents in cured film of UV gel nail treatment were measured for the first time. The results of this study indicated that the thickness of unreacted layer was not affected by the cast thickness; however, the intensity of UV light and the photoinitiator concentration had significant effect on the thickness of the unreacted layer. To reduce the thickness of the unreacted layer, the intensity of the UV light and the photoinitiator concentration should be increased. However, the maximum temperature observed during the curing of UV gel nails increases with an increase in the intensity of the UV light and the photoinitiator concentration. A suitable cast thickness range (21 ~ 150 μm), which resulted in the formation of a cured film and without producing temperatures that exceed that of the human body, was identified. The mass fraction of the residuals in the cured layer decreased with an increase in the exposure time, the UV intensity, and the photoinitiator concentration.
Ion Transport through Diffusion Layer Controlled by Charge Mosaic Membrane
Akira Yamauchi
International Journal of Chemical Engineering , 2012, DOI: 10.1155/2012/417179
Abstract: The kinetic transport behaviors in near interface of the membranes were studied using commercial anion and cation exchange membrane and charge mosaic membrane. Current-voltage curve gave the limiting current density that indicates the ceiling of conventional flux. From chronopotentiometry above the limiting current density, the transition time was estimated. The thickness of boundary layer was derived with conjunction with the conventional limiting current density and the transition time from steady state flux. On the other hand, the charge mosaic membrane was introduced in order to examine the ion transport on the membrane surface in detail. The concentration profile was discussed by the kinetic transport number with regard to the water dissociation (splitting) on the membrane surface. 1. Introduction It is well known that electrodialysis using ion exchange membrane makes drinking water or table salt from sea water.In Japan especially it is popular to use this electrodialysis in various fields such as food, medical pharmacy and ultrapure water [1–3]. However, the more efficient and improved electrodialysis have been required for pure water production because conventional system costs much of electric power at present. One of the main problems originates from the limiting current density that restricts the direct current for supplying through the system and depends on the thickness of diffusion layers. In this study, the way to see the thickness of the depleted solution layer was examined in order to improve the efficiency on the electrodialysis from fundamental standpoint. As mentioned above, the aim will be focused on the ionic behavior of ion transport from bulk solution to membrane surface. In addition, so far developed charge mosaic membrane [4–6] is introduced into electrodialysis model system and the ion transport mechanism is investigated. As experimental strategies, electrical methods were mainly adopted, and 4 kinds of membrane systems were selected to study: cation exchange membrane system (CMV), anion exchange membrane system (AMV), charge mosaic membrane and cation exchange membrane system (MM?+?CMV), and anion exchange membrane and charge mosaic membrane system (AMV?+?MM). The potentiometry was also used on the same membrane systems to elucidate the diffusion layer. The chronopotentiometry has been carried out to obtain the transition time [7–9]. The technique was adopted for 4 membrane arrangements to examine the contribution to the boundary layer of the charge mosaic membrane. The kinetic parameter about the boundary layer was noticed
Life Span of Positive Solutions for the Cauchy Problem for the Parabolic Equations
Yusuke Yamauchi
International Journal of Differential Equations , 2012, DOI: 10.1155/2012/417261
Abstract: Since 1960's, the blow-up phenomena for the Fujita type parabolic equation have been investigated by many researchers. In this survey paper, we discuss various results on the life span of positive solutions for several superlinear parabolic problems. In the last section, we introduce a recent result by the author. 1. Introduction 1.1. Fujita Type Results We first recall the result on the Cauchy problem for a semilinear heat equation: where , is the -dimensional Laplacian, and . Let be a bounded continuous function on . In pioneer work [1], Fujita showed that the exponent plays the crucial role for the existence and nonexistence of the solutions of (1.1). Let denote the Gaussian heat kernel: . Theorem 1.1 (see [1]). Suppose that and that its all derivatives are bounded.(i)Let . Then there is no global solution of (1.1) satisfying that?? for?? and .(ii)Let . Then for any there exists with the following property: if then there exists a global solution of (1.1) satisfying for and . In [2], Hayakawa showed first that there is no global solution of (1.1) in the critical case when or 2. Theorem 1.2 (see [2]). In case of , or , , (1.1) has no global solutions for any nontrivial initial data. In genaral space dimensions, Kobayashi et al. [3] consider the following problem: where and . Let be a bounded continuous function on . Theorem 1.3 (see [3]). Suppose that satisfies the following three conditions:(a) is a locally Lipschitz continuous and nondecreasing function in with?? and for ,(b) for some ,(c)there exists a positive constant such that Then each positive solution of (1.5) blows up in finite time. Remark 1.4. (i) We remark that the proofs of the theorems in [2, 3] are mainly based on the iterated estimate from below obtained by the following integral equation: (ii) The critical nonlinearity of power type satisfies the assumptions (a), (b), and (c) in [3]. Weissler proved the nonexistence of global solution in -framework in [4]. The proof is quite short and elegant. Theorem 1.5 (see [4]). Suppose and that in ? is not identically zero. Then there is no nonnegative global solution to the integral (1.7) with initial value . The outline of the proof is as follows. First we assume that there is a global solution. From the fact that the solution for some , we can obtain that . This contradicts the boundedness of for large . Hence the solution is not global. Existence and nonexistence results for time-global solutions of (1.1) are summarized as follows.(i)Let . Then every nontrivial solution of (1.1) blows up in finite time.(ii)Let . Then (1.1) has a time-global
Effective mass anomalies in strained Si thin films and crystals
Jun Yamauchi
Physics , 2007, DOI: 10.1109/LED.2007.914096
Abstract: Effective mass anomalies due to the geometrical effects are investigated in silicon nanostructures using first-principles calculations for the first time. In \{111\} and \{110\} biaxially strained Si, it is found that longitudinal effective mass is extraordinarily enhanced for both thin films and crystals. This mass enhancement is caused by the change of the band structure with double minima into that with a single minimum due to strain and confinement. At the transition point, it is analytically shown that the effective mass diverges. The dependences of the confinement thickness on the anomalies are qualitatively explained by an extension of the effective mass approximation.
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