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Search Results: 1 - 10 of 2295 matches for " Makoto Yuasa "
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Sensitive Electrochemical Detection of Glucose at Glucose Oxidase-Cobalt Phthalocyanine-Modified Boron-Doped Diamond Electrode
Takeshi Kondo,Masaru Horitani,Makoto Yuasa
International Journal of Electrochemistry , 2012, DOI: 10.1155/2012/943957
Abstract: Electrochemical detection of glucose was achieved at a glucose oxidase (GOx)-cobalt phthalocyanine (CoPc)-modified boron-doped diamond (BDD) electrode without any additional electron mediator in the electrolyte solution. The surface of the hydrogen-terminated BDD thin film prepared by microwave plasma-assisted CVD was modified with 4-vinylpyridine (4VP) via photochemical modification. The 4VP-BDD was then immersed in a CoPc solution to obtain CoPc-BDD. A poly(p-phenylenediamine) (PPD) thin film containing GOx was coated on the CoPc-BDD electrode surface via electropolymerization. At the GOx/PPD-CoPc-BDD electrode, anodic current for glucose oxidation was observed with a sigmoidal voltammetric curve, indicating successful electron mediation of H2O2 generated as the result of glucose oxidation at GOx. The signal-to-background ratio for voltammetric current of glucose detection was larger at the GOx/PPD-CoPc-BDD electrode than at the GOx/PPD-modified platinum electrode due to the smaller background current of the modified BDD electrode. 1. Introduction Highly boron-doped diamond (BDD) electrodes have been known to be a promising electrode material for sensitive electroanalysis based on the wide potential window and low background current as well as physical and chemical stability and biocompatibility [1]. Glucose is a compound, whose concentration is one of the most desired to be determined via electrochemical methods in relation to increasing demands for diabetes care [2]. In order to use BDD electrode for glucose detection, one should modify the surface with catalysts or enzymes due to the large overpotential for direct glucose oxidation at unmodified BDD electrodes. For glucose detection at BDD electrodes using electrocatalysts, Cu [3–5] and Ni [6–9] have been used for modification of the surfaces. Immobilization of particles or line patterns of these metals with micrometer or nanometer scale onto BDD surface enables sensitive glucose detection with low background current. On the other hand, BDD electrodes modified with glucose oxidase (GOx) [10–13] are advantageous because of their selectivity and sensitivity of the glucose molecule. In some cases, additional mediators, such as ferrocene carboxylic acid [11], were employed for glucose detection at GOx-modified BDD electrodes. Glucose detection without any additional reagents to samples is possible for simple analysis systems, and especially for monitoring concentration. Hydrogen peroxide is a product of glucose oxidation at GOx and thus can act as an electroactive mediator for electrochemical detection
A Purification Scheme and Entanglement Distillations
Hiromichi Nakazato,Makoto Unoki,Kazuya Yuasa
Physics , 2004,
Abstract: A purification scheme which utilizes the action of repeated measurements on a (part of a total) quantum system is briefly reviewed and is applied to a few simple systems to show how it enables us to extract an entangled state as a target pure state. The scheme is rather simple (e.g., we need not prepare a specific initial state) and is shown to have wide applicability and flexibility, and is able to accomplish both the maximal fidelity and non-vanishing yield.
Preparation and Entanglement Purification of Qubits through Zeno-like Measurements
Hiromichi Nakazato,Makoto Unoki,Kazuya Yuasa
Physics , 2004, DOI: 10.1103/PhysRevA.70.012303
Abstract: A novel method of purification, purification through Zeno-like measurements [H. Nakazato, T. Takazawa, and K. Yuasa, Phys. Rev. Lett. 90, 060401 (2003)], is discussed extensively and applied to a few simple qubit systems. It is explicitly demonstrated how it works and how it is optimized. As possible applications, schemes for initialization of multiple qubits and entanglement purification are presented, and their efficiency is investigated in detail. Simplicity and flexibility of the idea allow us to apply it to various kinds of settings in quantum information and computation, and would provide us with useful and practical methods of state preparation.
Entanglement Purification through Zeno-like Measurements
Kazuya Yuasa,Hiromichi Nakazato,Makoto Unoki
Physics , 2004, DOI: 10.1080/09500340408233616
Abstract: We present a novel method to purify quantum states, i.e. purification through Zeno-like measurements, and show an application to entanglement purification.
Optimization of a Neutron-Spin Test of the Quantum Zeno Effect
Paolo Facchi,Yoichi Nakaguro,Hiromichi Nakazato,Saverio Pascazio,Makoto Unoki,Kazuya Yuasa
Physics , 2003, DOI: 10.1103/PhysRevA.68.012107
Abstract: A neutron-spin experimental test of the quantum Zeno effect (QZE) is discussed from a practical point of view, when the nonideal efficiency of the magnetic mirrors, used for filtering the spin state, is taken into account. In the idealized case the number N of (ideal) mirrors can be indefinitely increased, yielding an increasingly better QZE. By contrast, in a practical situation with imperfect mirrors, there is an optimal number of mirrors, N_opt, at which the QZE becomes maximum: more frequent measurements would deteriorate the performance. However, a quantitative analysis shows that a good experimental test of the QZE is still feasible. These conclusions are of general validity: in a realistic experiment, the presence of losses and imperfections leads to an optimal frequency N_opt, which is in general finite. One should not increase N beyond N_opt. A convenient formula for N_opt, valid in a broad framework, is derived as a function of the parameters characterizing the experimental setup.
Cosensitization Properties of Glutathione-Protected Au25 Cluster on Ruthenium Dye-Sensitized TiO2 Photoelectrode
Kazuya Nakata,Sho Sugawara,Wataru Kurashige,Yuichi Negishi,Morio Nagata,Satoshi Uchida,Chiaki Terashima,Takeshi Kondo,Makoto Yuasa,Akira Fujishima
International Journal of Photoenergy , 2013, DOI: 10.1155/2013/456583
Abstract: Cosensitization by glutathione-protected Au25 clusters on Ru complex, N719-sensitized TiO2 photoelectrodes is demonstrated. Glutathione-protected Au25 clusters showed no significant changes in properties after adsorption onto TiO2 particles, as confirmed by optical absorption spectroscopy, transmission electron microscopy, and laser desorption/ionization mass spectrometry. Adsorption property of the glutathione-protected Au25 clusters depends on the pH, which affects the incident photon-to-current conversion efficiency (IPCE) of the TiO2 photoelectrode containing Au25 clusters. When pH < 5, the IPCE increases with pH. Conversely, the IPCE decreases with pH when pH > 7. The IPCE of a TiO2 photoelectrode sensitized by both glutathione-protected Au25 clusters and N719 was increased compared with photoelectrodes containing either glutathione-protected Au25 clusters or N719, which suggests that glutathione-protected Au25 clusters act as a coadsorbent for N719 on TiO2 photoelectrodes. This is also supported by the results that the IPCE of N719-sensitized TiO2 photoelectrodes increased upon addition of glutathione. Furthermore, cosensitization by glutathione-protected Au25 clusters on N719-sensitized TiO2 photoelectrodes allows that wavelength of photoelectric conversion was extended to the near infrared (NIR) region. These results suggest that glutathione-protected Au25 clusters act not only as a coadsorbent to increase IPCE but also as an NIR-active sensitizer. 1. Introduction Dye sensitization of wide bandgap semiconductors such as TiO2, ZnO, and SnO2 is an attractive research field with considerable significance for solar energy utilization, including solar cells [1] and water splitting [2]. As wide bandgap semiconductors absorb only ultraviolet (UV) light, by adding dyes which absorb visible (VIS) light, a larger proportion of solar light can be harnessed. To date, a number of organic dyes, such as phthalocyanines [3–6], perylene bisamides [7–9], xanthenes [10, 11], hemicyanines [12–14], and porphyrins [15–18], have been used as dye sensitizers. One typical sensitizing dye is the ruthenium complex di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II), known as N719, which assists in realizing high photoelectric conversion efficiency [19, 20]. There have been many attempts to further increase incident photon-to-current conversion efficiency (IPCE) in dye-sensitized semiconductor photoelectrodes. One methodology is to use infrared (IR-) active dyes. Generally, dyes absorb UV and VIS light and are able to convert
Extraction of an Entanglement by Repetition of the Resonant Transmission of an Ancilla Qubit
Kazuya Yuasa
Physics , 2009, DOI: 10.1088/1751-8113/43/9/095304
Abstract: A scheme for the extraction of entanglement in two noninteracting qubits (spins) is proposed. The idea is to make use of resonant transmission of ancilla qubit through the two fixed qubits, controlled by the entanglement in the scatterers. Repetition of the resonant transmission extracts the singlet state in the target qubits from their arbitrary given state. Neither the preparation nor the post-selection of the ancilla spin is required, in contrast to the previously proposed schemes.
Quantum Coherence of Electrons Field-Emitted from a Superconductor: Correlations and Entanglement
Kazuya Yuasa
Physics , 2009, DOI: 10.1103/PhysRevB.80.104516
Abstract: The correlations of the electrons field-emitted from a superconductor are fully analyzed, both in space and time. It is proposed that a coincidence experiment would reveal a positive correlation between the electrons emitted in opposite directions. The electrons can be entangled and can even violate Bell's inequality. The crucial role played by Andreev's process is scrutinized, analytical formulas are derived for the correlations, and the physics behind the phenomenon is clarified.
Derivation of Master Equations in the Presence of Initial Correlations with Reservoir: Projection Method Revisited
Kazuya Yuasa
Physics , 2006,
Abstract: We discuss the derivation of master equations in the presence of initial correlations with the reservoir. In van Hove's limit, the total system behaves as if it started from a factorized initial condition. A proper choice of Nakajima-Zwanzig's projection operator is crucial and the reservoir should be endowed with the mixing property.
Uniform sets for infinite measure-preserving systems
Hisatoshi Yuasa
Mathematics , 2011,
Abstract: The concept of a uniform set is introduced for an ergodic, measure-preserving transformation on a non-atomic, infinite Lebesgue space. The uniform sets exist as much as they generate the underlying $\sigma$-algebra. This leads to the result that any ergodic, measure-preserving transformation on a non-atomic, infinite Lebesgue space is isomorphic to a minimal homeomorphism on a locally compact metric space which admits a unique, up to scaling, invariant Radon measure.
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