Search Results

You are looking at 21 - 29 of 29 items for

  • Author or Editor: M. Nakamura x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Phase transition behavior of polyesters derived from 2,7-phenanthrene dicarbonic acid diethylester and alkanediols with even methylene carbon number was investigated by the simultaneous DSC-XRD method. The smectic A phase was observed on cooling from the molten state. The transition entropy from the isotropic state to the smectic A phase was about 9.0 J mol-1 K-1, which depended on the methylene carbon number. The linear expansion coefficients, based on the (001) spacing of the crystalline phase at room temperature, were 1.310-4 K-1 (crystalline phase), 5.710-4 K-1 (crystallization region), 1.710-3 K-1 (smectic A phase) during cooling, and 1.510-4 K-1 (crystalline phase), and 1.010-3K-1(melting region) on heating.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: G. Nakamura, S. Baldochi, V. Mazzocchi, C. Parente, M. Valério, and D. Klimm

Abstract  

The BaF2-YF3 system was partially investigated, with focus given to the BaY2F8 compound and its neighboring phases. In this report, various difficulties that hinder the thermal analysis investigation of this binary fluoride system are described in detail. Samples of various compositions ranging from 58 to 79% YF3 were prepared and subjected to thermal analysis (DTA, TG and DSC) and X-ray diffraction. Diffraction patterns were analyzed through the Rietveld method for the calculation of phase concentrations in samples and determination of the lattice parameters of monoclinic BaY2F8. Thermal results were compared with data from the literature and discrepancies were found.

Restricted access

Abstract  

Concentrations of eighteen trace elements at the sediment-water interface in Biwa Lake were determined by neutron activation analysis. Release of iron, manganese and arsenic from the sediment to the pore water was observed under anoxic conditions. The concentrations of Sb in the pore water as well as Na were nearly constant between the surface and the depth of 40 cm. The behavior of Sb differed from that of As at the sediment-water interface, since the partition coefficient of Sb differed from that of As.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: T. Tanaka, J. Magoshi, Y. Magoshi, S. ichi Inoue, M. Kobayashi, H. Tsuda, M. Becker, and Sh. Nakamura

Abstract  

The thermal properties of liquid silk from domestic and wild silkworms are investigated. Liquid silks obtained from the silk gland of the domesticated silkworm, Bombyx mori and four wild silkworms, Samia cynthia ricini, Dictyoploca japonica, Antheraea pernyi and Antheraea yamamai were used. The DSC curves for the liquid silk from the domestic silkworm have weak endothermic peaks corresponding to the breaking of hydrogen bonds in the β-form or to the untangling of physical network. The DSC curves for the wild silkworm silks, however, show clear exothermic peaks corresponding to a phase transition from the α-helix conformation to the β-form. Liquid silk from all the different silkworms undergoes a characteristic irreversible phase transition.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Suzuki, Y. Oki, M. Numajiri, T. Miura, K. Kondo, N. Oshima, T. Hayashi, H. Nakamura, and Y. Ito

Abstract  

The polymerization process of bisphenol-A dicyanate (BADCy) has been studied using a positron-annihilation lifetime technique (PAL). The polymerization was conducted at 150°C, and the process was followed by PAL. Seven kinds of samples with different curing times were also formed at 150°C, and the relation between the period of the curing time and the degree of polymerization was studied. It has been shown that theo-Ps lifetime increases in samples with a higher polymerization than 85%, which is consistent with measurements of the specific volume of BADCy.

Restricted access

Abstract  

To determine the cross sections of the135Cs(n,γ)136Cs reaction, a sample of135Cs included in a “standardized solution” of137Cs was used as a target and irradiated in a reactor. The ratio of the atom number of135Cs to that of137Cs was determined to be 0.89±0.03 with a quadrupole mass spectrometer. The thermal cross section and the resonance integral measured in this study were determined to be 8.3±0.3 and 38.1±2.6 b respectively.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: T. Iyogi, S. Ueda, S. Hisamatsu, K. Kondo, H. Haruta, H. Katagiri, M. Kurabayashi, Y. Nakamura, and N. Tsuji

Abstract  

To obtain an average dose from 222Rn to the people in Aomori Prefecture where the first Japan"s nuclear fuel cycling facilities are now under construction, we surveyed 222Rn concentrations in 109 dwellings in the Prefecture from 1992 to 1996. The outdoor 222Rn concentrations were also measured in gardens of 15 dwellings. The 222Rn concentrations were measured with passive 222Rn detectors which used a polycarbonate film for counting a-ray and could separate concentrations of 222Rn from 220Rn. Counting efficiencies of the detectors were calibrated with a standard 222Rn chamber in the Environmental Measurement Laboratory in USA and in the National Radiological Protection Board in UK. Geometric means of 222Rn concentration were 13 and 4.4 Bq.m-3 in the dwellings and outdoor, respectively. These values were consistent to nationwide survey results in Japan. The 222Rn concentrations in the dwellings depended on their age. The concentrations were higher in recent dwellings than in older ones. The radiation dose from 222Rn was estimated, taking into account the occupancy factor for inside and outside of dwellings. The annual dose was 0.32 mSv.y-1, and 99% of the dose came from the exposure to 222Rn inside the dwelling.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Oura, R. Watanabe, M. Ebihara, Y. Murakami, Y. Toh, A. Kimura, M. Koizumi, K. Furutaka, M. Oshima, K. Hara, T. Kin, S. Nakamura, and H. Harada

Abstract  

A prompt gamma-ray analysis system using multiple detection method (MPGA system) was constructed at the neutron guide hall of the JRR-3M reactor of the Japan Atomic Energy Agency. We applied MPGA method to geochemical and cosmochemical samples to evaluate its analytical performance on signal to noise (S/N) ratio, sensitivity, and detection limit. The S/N ratio measured by MPGA system was larger than that by normal prompt gamma ray activation analysis (PGAA) at JRR-3M. For some elements, the S/N ratio was improved more than ten times. Several elements that are not detected by PGAA were detected by MPGA. At the present time, concentrations of major elements and trace elements with high neutron capture cross section in geochemical and cosmochemical samples were determined accurately by the MPGA system installed at JRR-3M. It is expected that it will determine a lot of trace elements after appropriate adjustments and modifications.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: T. Tanaka, J. Magoshi, Y. Magoshi, B. Lotz, S.-I. Inoue, M. Kobayashi, H. Tsuda, M. Becker, Zh. Han, and Sh. Nakamura

Abstract  

The crystal structure, thermal properties and growth rates of spherulites of the Tussah silk fibroin, produced upon drying of the silk taken directly from the lumen which is essentially a poly(L-alanine)polypeptide, are investigated. Depending on casting conditions, spherulites with either αhelical chain conformation or β parallel sheet structure are produced. The growth rates display a strong positive temperature coefficient, with an apparent transition, which however cannot be related with the formation of two different crystal structures at this stage.

Restricted access