Akio Yamagishi

Development of an ultra-high sensitive photon counting system and its application to biomedical measurements

Abstract The sensitivity of the photon counting method for the detection of extra-weak optical intensity was improved on the introduction of the enhanced single photoelectron counting technique incorporated with a selected photomultiplier operated under optimum conditions. With this ultra-high sensitive photon counting system it has been possible to measure the difference between the luminescence of the blood of healthy and diseased human subjects (both have extremely weak values).

Magnetization Measurement of NENP and NINO in High Magnetic Field

Magnetization measurements have been performed on the single crystal samples of Ni(C 2 H 8 N 2 ) 2 NO 2 (ClO 4 ), NENP, and Ni(C 3 H 10 N 2 ) 2 NO 2 (ClO 4 ), NINO in pulsed high magnetic fields. No magnetization appears up to about 10 T reflecting the presence of the Haldane gap and the linear magnetization appears in both compounds above this field. The observed anisotropy of the transition field is explained by the Haldane gap energy E g and the crystalline field constants D and E in the lowest excited triplet. The parameters are estimated as E g =16.8 K, D =-16.1 K, and E =-1.3 K and E g =14.2 K, D =-11.5 K and E =2.1 K for NENP and NINO, respectively.

Diamagnetic Orientation of Clay Mineral Grains

The orientations of diamagnetic mineral grains in magnetic fields are observed, for the first time, in suspensions of clay minerals such as talc, kaolinite and sericite. The minerals consist of two-dimensional crystal layers which produce intrinsic diamagnetic anisotropy, Δχ, in the unit cell. In the case of talc suspension with the average diameter of φ 2.4 µm and the thickness of 0.2 µm, the grains show full orientation in a magnetic field of less than 0.5 T. As the size of the grains becomes smaller, full orientation is achieved with higher fields. This size dependence occurs because the field-induced anisotropic energy of a grain is proportional to N Δχ, where N is the number of unit cells in the grain.

High Field Diamagnetic Susceptibility and the "Curie-Weiss Law" in Organic Liquid

High field diamagnetic susceptibility of organic liquids is measured by means of linear magnetic birefringence (Cotton-Mouton effect) in pulsed high magnetic field up to 400 kOe with special interest in the temperature dependence. It is found that the “Curie-Weiss law” should widely be applied for the high field diamagnetic susceptibility of organic liquids consisted of anisotropic diamagetic molecules. The “Curie-Weiss constant” (varTheta) reflects the intermolecular correlation in liquids and the obtained values are 0, 145 and 165 K for benzene, chlorobenzene and nitrobenzene, respectively.

Magnetization process of haldane materials TMNIN and NINAZ

Magnetization measurements have been performed on the Haldane gap materials (CH 3 ) 4 NNi(NO 2 ) 3 (TMNIN) and Ni(C 3 H 10 N 2 ) 2 N 3 (ClO 4 ) (NINAZ) in pulsed high magnetic fields. TMNIN shows a typical magnetization profile of the Haldane material with the gap energy of 4.1 K. Quenching of the gap appears around 2.7 Tesla(T) and magnetic saturation is obtained above 30 T. In NINAZ, however, the quenching appears at around 30 T reflecting a large Haldane gap energy with the magnitude of 44.3 K.

Excitation of indole acetate in myeloperoxidase-H2O2 system: Possible formation of indole acetate cation radical

Abstract Myeloperoxidase-H 2 O 2 -indole acetate system at pH 7.4 emitted light in visible region. Luminescent spectrum showed a weak peak at or near 480 nm and prominent peaks at or near 550, 580, and 620 nm with deep troughs near 500 and 600 nm. In some cases, no definite peak emissions near 550 and 580 nm, but a prominent broad emission between 550 and 580 nm, is observed. Such spectral patterns in the region of 510 to 620 nm were quite similar to those report for the luminescence of photo-products formed from the indole analogs (tryptophan and indole) in 50% alcohol irradiated by U.V. (365 nm) at 77°K, assuming red shift (20–25 nm) by solvent effect. Possible formation of indole acetate cation radical (a precursor of excited indole acetate) was discussed.

Magnetic Measurements of CuGeO3 by Means of High Magnetic Field.

Magnetic properties of CuGeO 3 single crystal which shows the spin-Peierls transition below T sp =14 K were investigated by means of high field magnetization and susceptibility measurements. The stepwise magnetization was observed in the magnetic fields along the a -, b -, and c -axes up to about 35 T. The magnetization process is different from the case of conventional uniaxially anisotropic antiferromagnets. Such a magnetization process is explained by the crossover model between the ground singlet and the excited magnetic discomensulate state. The main exchange parameter is antiferromagnetic and the estimated value from the high-field magnetization curves is 140 K (97 cm -1 ). A decrease of the critical fields with increasing temperature was observed up to 14 K, the origin of which is considered to be the effect of soft phonons in the spin-Peierls transition.

Two-Dimensional Weak Localization in Electron High-Tc Superconductor Nd2-xCexCuOy under High Magnetic Field

Electron high- T c superconductor Nd 2- x Ce x CuO y single crystals are studied under high magnetic field of up to 20 tesla. The superconducting state is completely destroyed by the field when the field is applied along the c -axis and the normal electrical resistivity is obtained at all temperatures. The temperature dependence of the normal resistivity is plotted down to 1.3 K and a clear resistance minimum is found. The result is understood in terms of the two-dimensional weak localization model and this means that the materials are regarded as the intrinsic two-dimensional conduction system.

Spectral narrowing of a dye laser oscillation using an intracavity vapor prism

Abstract A new method for narrowing the oscillation spectrum of a broad-band dye laser is reported in this paper. The narrowing is achieved by a vapor prism placed inside the laser cavity, which is based on an anomalous dispersion of the atomic vapor so that the narrowing effect occurs only in the vicinity of the absorption line. Using a sodium vapor prism inside a Rhodamine 6G dye laser cavity, an oscillation linewidth less than 0.01 nm was attained at a sodium temperature of 320°C.

Magnetoresistance Measurements of Single-Crystal LnBa2Cu3Oy (Ln=Ho, Dy, Eu and Y) under Pulsed High Magnetic Field

The high-field magnetoresistance of well-characterized LnBa 2 Cu 3 O y (Ln=Ho, Dy, Eu and Y) single crystals has been measured from 4.2 K to 300 K under a pulsed magnetic field up to 60 T. The upper critical field H c2 is well sketched by the usual anisotropic BCS model and the normal resistivity down to liquid helium temperature shows that the system can be regarded as normal metal with positive magnetoresistance. The residual resistivity is between 10 and 50 µΩ cm, reflecting a highly qualified sample preparation. The relations among upper critical field, coherence length and normal resistivity are discussed. It is concluded that the magnetic rare-earth ions Ho and Dy enhance H c2 without affecting T c .