Noboru Yamada

A new ferroelectric: La2Ti2o7

Ferroelectricity was observed in a lanthanum titanate single crystal (La2Ti2O7), a monoclinic crystal of the space group C22-P21. The Curie temperature was found to be about 1500°C. It was determined by a D-E hysteresis loop at room temperature that the spontaneous polarization Ps = 5 μC/cm2 and that the coercive field Ec = 45 kV/cm. Ferroelectric domains were observed using a crystal etched by an aqueous solution of nitric acid. The La2Ti2O7crystal showed strong piezoelectric and linear electro-optic effects: electromechanical coupling factor k22 = 0.29; half-wave voltage [E l]δ/2 = 2000 V at a wavelength of 6328 A.

Incommensurately Modulated Structure of K2SeO4

The modulated structure in the incommensurate phase of K 2 SeO 4 has been analyzed at 113 K by X-ray diffractometry based on the concept of four-dimensional space. The final R -factor was 0.046 for all 905 reflections and 0.087 for 326 satellite reflections. The modulation is characterized by the rotation of SeO 4 groups around b -direction and the associated translation of K atoms along c -axis. The eigenvector of the modulation mode was determined from the observed atomic displacement pattern and it is compared with that of Σ 2 soft mode determined by neutron experiment. 1)

Successive Phase Transitions in Cs2CdBr4

X-ray and dielectric measurements were made on Cs 2 CdBr 4 (CCB) crystals, and optical observation was also made. CCB undergoes successive phase transitions at T 1 =-21°C, T 2 =-36°C and T 3 =-65°C. The space groups in all phases have been determined: I: Pnam, II: P Pnam 1ss , III: P2 1 /n and IV: Pbar1. The space group for the incommensurate II-phase is determined on the basis of four-dimensional space group concept. Temperature dependence of the position and the intensity of satellite reflections in the incommensurate phase was measured. Rotation of optical indicatrix was found in III- and IV-phases and its temperature dependence was measured. Ferroelastic activities in III- and IV-phases were found.

Pyroelectric and Dielectric Properties of Rb2Cd2(SO4)3

Pyroelectric and dielectric measurements have been made on Rb 2 Cd 2 (SO 4 ) 3 crystals with the simultaneous optical examination of the domain texture of the specimens. An unusual temperature dependence of the spontaneous polarization was found in the ferroelectric phases, which is similar to that found in (NH 4 ) 2 SO 4 . As the temperature is lowered, the spontaneous polarization appears at the Curie point (-144^° C ), gradually decreases and changes its sign below -160^° C without an appreciable change at the second transition temperature of -170^° C . The reversal in polarization was confirmed to take place by both pyroelectric measurement and optical observation. An abrupt change of dielectric constant e b at the Curie point was revealed by using single domain specimens.

Optical and Dielectric Properties of K2Mn2(SO4)3

Dielectric and birefringence measurements have been made on K 2 Mn 2 (SO 4 ) 3 crystal. Anomalous temperature dependence of the spontaneous birefringences is found in D 4 2 phase (below –80°C). The differences of photoelastic coefficients p 11 - p 12 and p 11 - p 13 are determined by the static method to be both about 0.02 at room temperature. Temperature dependence of the spontaneous birefringence and dielectric susceptibility is analyzed on the basis of thermodynamic potential proposed by Dvořak.

A structural study of the phase transition in (NH4)2BeF4

The crystal structure of (NH4)2BeF4 in the incommensurate phase was analyzed based on the concept of four-dimensional space. The structure is characterized by the modulated ordering of one asymmetric BeF4 group and the translation of NH4 ion along z-axis. The main structural change at the transition from the incommensurate phase to the ferroelectric phase is expressed by the ordering of the other asymmetric BeF4 group.

Experimental observation and numerical simulation of heat island plume in urban surface layer

A peculiar thermal plume is formed over urban areas under urban heat island conditions, which appear owing to huge energy consumption in megacities like Tokyo. In order to clarify the characteristics of this urban heat island phenomenon, the authors made a microscopic analysis for the thermal plume in the urban surface layer, where a lot of various structures including buildings, pavements and other facilities exist. In this article, a simplified experiment and 2-D numerical simulations were conducted by employing a new microscopic modeling for the urban surface layer. The purposes of this microscopic modeling are: (i) to find a similarity between urban building structures and porous media; and (ii) to apply the model of flow in porous media to heat island phenomena, which has been developed in the field of heat transfer. Results of the experimental observations agree well with that of the numerical simulations on the flow pattern of the thermal plume. It is indicated that micro-scale thermal plumes occur in the thermally stable stratified air if clusters of urban structures exist at the lower boundary layer. This means that real atmospheric condition is greatly influenced by this kind of micro-scale thermal plume in the urban surface layer.

A structural study of the phase transition in K2SeO4

Abstract The crystal structure of K2SeO4 has been investigated in incommensurate(INC) and ferroelectric(F) phases by X-ray diffraction technique. Structural change in INC-to-F transition is discussed.

Pyroelectric properties of langbeinite-type K2Zn2(SO4)3

Abstract Pyroelectric measurements have been made on K2Zn2(SO4)3 crystals with simultaneous optical examination of the domain structure of the specimen. The crystal undergoes phase transitions at 136 K and 85 K. Dielectric hysteresis measurement reveals ferroelectricity in the temperature range 85 K < T < 136 K. Anomalous temperature dependence of the spontaneous polarization is observed in the ferroelectric phase. Below 85 K, no pyroelectricity is obtained, and there are found three types of domains, all in parallel extinction. The crystal systems and point groups of the low temperature phases are determined as monoclinic 2 for 85 K < T < 136 K and orthorhombic 222 for T < 85 K.

Mechanisms of Bronchoconstriction after Allergen Ingestion in Sensitized Guinea Pigs

We examined whether oral administration of allergen induced bronchoconstriction in sensitized guinea pigs and investigated the mechanisms of bronchoconstriction. The animals had been immunized intraperitoneally with a mixture of Ascaris suum extract and silica gel, and exposed to ozone. They were then challenged with an oral dose of A. suum extract (6 mg/kg), and respiratory resistance (Rrs) was measured up to 7 h. After oral administration of the allergen, an increase in Rrs was observed. The mean values at 1, 3, 5 and 7 h after oral allergen challenge were 150 +/- 21, 149 +/- 11, 151 +/- 12 and 134 +/- 10% of the baseline value, respectively. When saline instead of the allergen was orally administered, almost no significant increase in Rrs was observed up to 7 h. Moreover, in nonsensitized guinea pigs, oral administration of allergen produced no significant increase in Rrs for up to 7 h. When atropine was administered as an aerosol, the increase in Rrs induced by an oral allergen challenge was attenuated. Three of the five atropine-treated guinea pigs showed temporary increases in Rrs immediately after the oral allergen challenge. The mean values of Rrs in the atropine-treated animals challenged with oral allergen at 1, 3, 5 and 7 h were 106 +/- 3, 106 +/- 5, 115 +/- 5 and 102 +/- 4% of baseline value, respectively. In the animals which received oral allergen, the number of neutrophils in bronchoalveolar lavage fluid (BALF) significantly increased 2.0-fold (p < 0.05), while no significant increase in the number of eosinophils, macrophages, or lymphocytes in BALF was observed.(ABSTRACT TRUNCATED AT 250 WORDS)