T. Shimizu

National Institute for Materials Science, Tsukuba, Ibaraki, Japan

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Publications (35)59.57 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 11B magic-angle spinning (MAS) NMR experiments are applied to B-doped diamond samples prepared by high-pressure and high-temperature methods. From the spectrum, we show that there are at least four boron signal components and the one at 28.5ppm is ascribed to the substitutional boron in the diamond structure providing the carriers responsible for conductivity. We further apply two-dimensional (2D) NMR to examine 1H dipolar broadening and 11B–11B boron spin diffusion, and candidates purported so far for the excess boron, that is, a boron+hydrogen complex and –B–B– and/or –B–C–B– clusters are negated. Furthermore, we show that 10B MAS NMR is useful to selectively observe the substitutional boron in the diamond structure appearing at 28.5ppm, whose quadrupolar coupling is much smaller than that of the excess boron at 65.5ppm.
    Physica C Superconductivity 12/2010; 470. DOI:10.1016/j.physc.2009.12.002 · 0.94 Impact Factor
  • K. Ota · T. Shimizu · Y. Noda · Y. Katagiri · T. Shirasawa · M. Morita
    Fertility and Sterility 09/2010; 94(4). DOI:10.1016/j.fertnstert.2010.07.585 · 4.59 Impact Factor
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    ABSTRACT: In this work, three boron-doped diamond samples prepared from a high-pressure high-temperature synthesis method with the same starting materials but with different initial ratios for boron are studied. Magnetic susceptibility measurement shows that the increment of the initial amount of boron does not straightforwardly bring lower superconducting transition temperature. In accordance with our previous 11B high-resolution magic-angle spinning (MAS) NMR results, we show that there are at least four boron signal components and the one at 28.5 ppm is ascribed to the substitutional boron in the diamond structure providing the carriers responsible for conductivity. From observed relative intensities of the four signal components, it is suggested that the excess boron, which does not contribute to the conductivity appears as a broad signal at around 65.5 ppm. We apply two-dimensional (2D) NMR to examine 1H dipolar broadening and 11B–11B boron spin diffusion, and candidates purported so far for the excess boron, that is, a boron + hydrogen complex and –B–B– and/or –B–C–B– clusters are negated. From its chemical-shift value, it is suggested that the excess boron exists as trigonally coordinated boron. We further apply 2D nutation NMR to examine the size of its quadrupolar coupling and show that it is not very large. As for a structure that compromises the trigonal coordination invoked from the chemical-shift value and the small quadrupolar coupling, we postulate boron locally in a graphite-like structure but the symmetry of the electric field gradient around it is high. Furthermore, we show that 10B MAS NMR is useful to selectively observe the substitutional boron in the diamond structure appearing at 28.5 ppm, whose quadrupolar coupling is much smaller than that of the excess boron at 65.5 ppm.
    Diamond and Related Materials 10/2009; 18(10-18):1267-1273. DOI:10.1016/j.diamond.2009.05.005 · 1.92 Impact Factor
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    ABSTRACT: The structures of BeO-Al2O3-B2O3 glasses with a range of BeO/Al2O3 ratios at fixed BeO/B2O3 ratios of 1:1·5 and 1:1 have been investigated using 11B and 27Al MAS NMR spectroscopy at ultrahigh magnetic field (21·8 T). These 11B and 27Al MAS NMR spectra are characterised by remarkably superior resolution and thus provide more accurate results for B and Al speciation compared to the low field (11·7 T) NMR results reported in previous studies. All glasses are characterised by a BO3:BO4 ratio of ∼86:14, and approximately 70% of all Al atoms are found to be five- and six-fold coordinated. Such large concentrations of BO3, AlO5 and AlO6 species are consistent with the highest field strength of Be among all alkali and alkaline earth metals. The compositional variation of cation speciation, when combined with bond valence calculations, indicates that most of the oxygens in these glasses would have to be 3-coordinated and shared between BIII-AlVI-BeVI, BIII-BeVI-BeVI, BIV-AlIV-BeVI, AlIV-AlIV-BeVI or AlIV-AlV-BeVI coordination polyhedra. This bonding scenario would be expected to give rise to a dense structure with increased rigidity, consistent with the remarkably high Tg values reported in the literature for these glasses.
    Physics and Chemistry of Glasses 07/2009; 50(4):262-266.
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    ABSTRACT: 11B static/magic-angle spinning (MAS) NMR experiments are applied to four different B-doped diamond samples prepared by either high-pressure and high-temperature (HPHT) or CVD methods with various starting materials. Application of MAS enhances the spectral resolution appreciably and differences of the four B-doped diamond samples are well reflected in the corresponding MAS spectra. From the comparison among the MAS spectra, and also their dependences on the magnetic-field and the pulse-flip angle, it is suggested that at least four kinds of boron including two kinds of impurities exist in B-doped diamond. We further examine 11B spin-lattice relaxation times (T1) for the four components and find that one of them is extremely short (ca. 500 ms) while others are in the range of several seconds. Relation between the component having the short T1 and the super conducting transition temperature (Tc) value is suggested.
    Diamond and Related Materials 11/2008; 17(11):1835-1839. DOI:10.1016/j.diamond.2008.04.013 · 1.92 Impact Factor
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    ABSTRACT: Senile plaques in the brain of patients with Alzheimer's disease mainly consist of aggregates of amyloid beta peptides (Abeta42, Abeta40). Abeta42 is more neurotoxic than Abeta40. This review describes recent findings from a structural analysis of Abeta42 aggregates and discusses their relevance to neurotoxicity through the formation of radicals.
    Mini Reviews in Medicinal Chemistry 11/2007; 7(10):1001-8. · 2.90 Impact Factor
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    ABSTRACT: 23Na- and 27Al- NMR spectra between 300 and 4K of a potassium-loaded low silica X zeolite which shows ferrimagnetism are obtained. For 23Na, positively shifted components are observed on the spectrum other than an unshifted one. We consider that those shifted components are given by the hyperfine interaction between the magnetic electrons in cages and 23Na nuclei, which are located at several sites inside of the cages. On the other hand, like the case of zeolite A with Rb cluster, 27Al shows symmetrically widened spectrum but gives no apparent shift. We consider that this feature is revealed by the coupling only through the dipolar interaction between the magnetic electrons and the 27Al nuclei.
    Journal of Magnetism and Magnetic Materials 03/2007; 310(2). DOI:10.1016/j.jmmm.2006.10.243 · 1.97 Impact Factor
  • M. Igarashi · T. Kodaira · T. Shimizu · A. Goto · K. Hashi · T. Nakano · Y. Nozue
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    ABSTRACT: Anomalous temperature dependence of T2 for 27Al NMR in dehydrated zeolite A is found. T2 of the satellite transition shows a minimum around 75K and a rapid decrease below 140K, in spite that T2 of the central transition changes gradually. Since T1 shows monotonous dependence on temperature for both transitions below 140K, the anomaly of T2 cannot be caused by the fluctuation of the local magnetic field. Some lattice dynamics which reveal coherence only among the satellite transitions, such as an alternation of the electrical field gradient, may be an origin of those behaviors.
    Chemical Physics Letters 02/2007; 436(1):80-83. DOI:10.1016/j.cplett.2006.12.033 · 1.90 Impact Factor
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    ABSTRACT: Temperature and frequency dependences of T1* of 27Al in K-Al- and Rb-Al-priderite were measured at three frequencies of 20.8, 104.2 and 130.3 MHz in the temperature range from 20 K to 909 K. The temperature dependence of K-Al-priderite is divided into three regions: region 1 below 30 K, region 2 from 30 K to 170 K where T1* is dominated by the ionic motion over the intrinsic barriers, and region 3 above 170 K where T1* is dominated by the ionic motion over the impurity barriers. The temperature and frequency dependence of T1* in the region 2 is well described by a trial function of J(omega, tau) which has the T1* ∝ omega1.0 dependence in the low temperature limit. But in the case of Rb-Al-priderite, the frequency dependence measured in a temperature range which corresponds to the region 2 of K-Al-priderite showed an intermediate dependence between omega1.5 and omega2 dependence. These frequency dependences are compared with Ishii's calculation result of S(omega) of hopping ions in one-dimensional random lattice based on his relaxation mode theory. ENMR obtained from the slope of the straight line in the log(T1*) .vs. 1/T plot in the region 2 of both samples showed a tendency that ENMRmeasured at low frequency has a little smaller value. It means that ENMR is dependent on the frequency.
  • K. Hashi · T. Shimizu · T. Fujito · A. Goto · S. Ohki
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    ABSTRACT: Trial measurements of magic-angle-spinning (MAS) NMR at 30T have been performed with a hybrid magnet of National Institute for Materials Science. A MAS-NMR probe was modified for a top-loading usage with the hybrid magnet. Speed of MAS ranges up to 15.5 KHz. In order to examine effects of inhomogeneity of the field on spectra, MAS-NMR measurements were performed using 4 mm sample holders with different sample size. A pipe of aluminum metal was used as a shield for the field fluctuations. A fourier-transformed 79Br-MAS-NMR spectrum of KBr was obtained from a single shot measurement of a freeinduction- decay (FID) signal. The spectrum shows a spinning-side-band structure demonstrating a high resolution measurement.
    Journal of Physics Conference Series 11/2006; 51(1):573-575. DOI:10.1088/1742-6596/51/1/130
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    ABSTRACT: Heparan sulfate proteoglycans, which bear long chains of heparan sulfate glycosaminoglycan, play significant roles during embryogenesis, including the formation of the CNS. However, their involvement in nerve regeneration has not yet been clarified. Here, we found that the mRNA expression of EXT2, one of the crucial enzymes for heparan sulfate-glycosaminoglycan synthesis, was markedly up-regulated in injured hypoglossal motor neurons after axotomy. In addition, immunohistochemical staining with an antibody specific for heparan sulfate-glycosaminoglycan chains demonstrated increased expression of heparan sulfate-glycosaminoglycan chains in the injured nucleus. Furthermore, the mRNA expressions of glypican-1 and syndecan-1, which are both well-known heparan sulfate proteoglycans, were prominently up-regulated in injured motor neurons. These results suggest that the biosynthesis of heparan sulfate chains promoted by EXT2 is activated in injured motor neurons, and that glypican-1 and syndecan-1 are potent candidates for heparan sulfate proteoglycans involved in peripheral nerve regeneration.
    Neuroscience 10/2006; 141(4):1961-9. DOI:10.1016/j.neuroscience.2006.05.026 · 3.36 Impact Factor
  • M. Igarashi · T. Kodaira · T. Shimizu · A. Goto · K. Hashi
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    ABSTRACT: NMR property of 27Al in K-loaded LTA-type zeolite with Si/Al=1.5 is reported. The higher frequency side of the monotonous spectrum of not loaded sample is changed as expanded, only at the higher frequency side, to higher frequency direction by loading of external K. Some NMR parameters, T2 and T2*, of the expanded components are different from those of the original one. Since the potential for external atoms is shallower for the case of Si/Al=1.5 than for that of Si/Al=1.0, the origin of the shift may be attributed to Knight shift by Fermi contact interaction between nuclei and electron from adsorbed K.
    Journal of Physics and Chemistry of Solids 05/2006; 67(5):1063-1066. DOI:10.1016/j.jpcs.2006.01.082 · 1.85 Impact Factor
  • K. Hashi · A. Goto · T. Shimizu · T. Iijima · S. Ohki
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    ABSTRACT: Stability of the Bitter-type resistive magnet installed in Tsukuba Magnet Laboratory of National Institute for Materials Science was measured by NMR up to 23.5T in order to check its availability for a solid-state NMR. Time dependence of the magnetic field at 23.5T shows the presence of a fast and a slow fluctuation. The frequency of the fast fluctuation is 50Hz and its amplitude is about 20G. The slower fluctuation has a period of about 40s and an amplitude of about 30G. The amplitude of these fluctuations provides the lower limit of the NMR line width for the NMR measurements with this magnet system.
    Physica B Condensed Matter 04/2004; 346:531-533. DOI:10.1016/j.physb.2004.01.141 · 1.32 Impact Factor
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    ABSTRACT: Evidence for the quasi one-dimensional (1D) antiferromagnetism of CuO is presented in a framework of Heisenberg model. We have obtained an experimental absolute value of the paramagnetic spin susceptibility of CuO by subtracting the orbital susceptibility separately from the total susceptibility through the $^{63}$Cu NMR shift measurement, and compared directly with the theoretical predictions. The result is best described by a 1D $S=1/2$ antiferromagnetic Heisenberg (AFH) model, supporting the speculation invoked by earlier authors. We also present a semi-quantitative reason why CuO, seemingly of 3D structure, is unexpectedly a quasi 1D antiferromagnet. Comment: 7 pages including 4 tables and 9 figures
    Physical review. B, Condensed matter 05/2003; 68(22). DOI:10.1103/PhysRevB.68.224433 · 3.66 Impact Factor
  • T. Shimizu · T. Matsumoto · A. Goto · K. Yoshimura · K. Kosuge
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    ABSTRACT: We present an experimental evidence for systematics to show the bond-angle dependence of the supertransferred hyperfine interaction and of the superexchange interaction in Cu–O–Cu bonds with the bond-angle ranging from 98° to 180°.
    Physica B Condensed Matter 05/2003; 329:765-766. DOI:10.1016/S0921-4526(02)02506-1 · 1.32 Impact Factor
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    M. Igarashi · T. Kodaira · T. Ikeda · M. Itoh · T. Shimizu · A. Goto · Y. Nozue
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    ABSTRACT: The features of 27Al and 87Rb NMR in Rb-loaded LTA-type zeolite are discussed in comparison with K-loaded one. Broadening of 27Al spectrum by magnetic origin is observed and the difference from the K case is pointed out for the shape of spectrum. These facts suggest that the configurations of electrons are not identical in the cases of Rb and K. For 87Rb the mass center of the spectrum shifts clearly to higher frequency side below 10K. The existence of Fermi contact interaction between s electron and Rb nuclei is suggested.
    Physica B Condensed Matter 03/2003; 327(1):72-78. DOI:10.1016/S0921-4526(02)01704-0 · 1.32 Impact Factor
  • H Yamada · K Ohashi · T Atsumi · H Okabe · T Shimizu · S Nishio · X D Li · K Kosuge · H Watanabe · Y Hara
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    ABSTRACT: We investigated the effects of inhalation of tea catechin on MRSA in the 24 elderly in patients, who were known to carry MRSA in sputum. The patients in the catechin group (N=12) were administered an inhalation of tea catechin extracts (in saline/bromhexine) (3.7 g/L catechins, 43% of them are composed of epigallocatechin gallate), three times daily with hand nebulizer for four weeks. The clinical effects were compared with the control group (N=12) who were given an inhalation of saline/bromhexine alone. After a week of the course, the numbers of the patients with decreased or disappearance of MRSA in their sputum was significantly higher in the catechin group, compared with that in the control group (seven vs. no patients; P<0.05). The number of patients discharged during the study was significantly increased, and the days of hospital stay were significantly decreased in the catechin group compared with those in the control group (six vs. one patient; P<0.05, 51+/-22 vs. 85+/-50 days, mean+/-S.D.;P <0.05, respectively). No adverse effects were observed in any patients during the study. Catechin inhalation seemed to be safe, and at least temporarily effective in the reduction of MRSA and shortening of hospitalization.
    Journal of Hospital Infection 03/2003; 53(3):229-31. DOI:10.1053/jhin.2002.1327 · 2.54 Impact Factor
  • K. Hashi · H. Kitazawa · T. Shimizu · A. Goto · S. Eguchi · S. Ohki
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    ABSTRACT: For an NMR quantum computer, splitting of an NMR spectrum must be larger than a line width. In order to find a best device material for a solid-state NMR quantum computer, we have made a simulation program to calculate the NMR line width due to the nuclear dipole field by the 2nd moment method. The program utilizes the lattice information prepared by commercial software to draw a crystal structure. By applying this program, we can estimate the NMR line width due to the nuclear dipole field without measurements and find a candidate material for a 6-qubit solid-state NMR quantum computer device.
    Superlattices and Microstructures 12/2002; 32(4):309-312. DOI:10.1016/S0749-6036(03)00033-8 · 2.10 Impact Factor
  • T. Shimizu · A Goto · K Hashi · S Ohki
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    ABSTRACT: We propose a method to implement a quantum computer by solid-state NMR. We can use the J-coupling for the quantum gate in CdTe. Both Cd and Te have two isotopes with spin 1/2, then we can have 4-qubits. The decoherence by dipole interaction may be minimized by preparing the isotope superlattice grown in the order of—111Cd–123Te–113Cd–125Te—in the [111] direction and by applying the magnetic field in the direction of [100], the magic angle of the dipole interaction. The optical pumping technique can be used in CdTe to make the initialization of the qubits.
    Superlattices and Microstructures 12/2002; 32(4):313-316. DOI:10.1016/S0749-6036(03)00034-X · 2.10 Impact Factor
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    G Kido · H Shinagawa · K Terai · K Hashi · A Goto · T Yakabe · T Takamasu · S Uji · T Shimizu · H Kitazawa
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    ABSTRACT: In the last five years, we have investigated quantum phenomena of low-dimensional materials and strongly correlated electron systems at high-magnetic fields under the Center of Excellence Development Program (COE project) at the National Research Institute for Metal. The second stage towards the realization of the solid-state quantum devices and measurement of the quantum properties began in April of this year. NMR spectra have been studied in CeP and various lithium fluoride crystals in anticipation of the crystal lattice quantum computer. The magneto-transport effect on tiny aluminum devices fabricated on semiconductors has been studied, and negative magnetoresistance has clearly been observed. An SPM which can be operated at various temperatures in the presence of high-magnetic fields has been developed to construct a magnetic resonance force microscope. The magnetic field effect on the magnetic recording pattern of an HDD was clearly measured up to 7 T.
    Physica B Condensed Matter 04/2001; 298(1-4-298):567-572. DOI:10.1016/S0921-4526(01)00384-2 · 1.32 Impact Factor

Publication Stats

295 Citations
59.57 Total Impact Points


  • 2002–2010
    • National Institute for Materials Science
      • International Center for Materials Nanoarchitectonics (MANA)
      Tsukuba, Ibaraki, Japan
  • 2006
    • Tokyo Metropolitan Institute of Gerontology
      Edo, Tōkyō, Japan
  • 2003
    • Seirei Hamamatsu General Hospital
      Hamamatu, Shizuoka, Japan
  • 1990
    • Kyoto University
      • Division of Chemistry
      Kioto, Kyōto, Japan
  • 1985–1988
    • The University of Tokyo
      • Institute for Solid State Physics
      Edo, Tōkyō, Japan