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Notes: By applying the HAUP (high-accuracy universal polarimeter) method, [N(CH3)4]2CuCl4 was found to be optically active in its incommensurate phase, e.g., g23=3.9×10−5 at 24 °C. The temperature dependence of g23 was obtained. By making use of the fact that the commensurate phase of [N(CH3)4]2CuCl4 is ferroelastic and centrosymmetric, the temperature dependence of the soliton density in its incommensurate phase was deduced by this optical measurement. It is suggested that the HAUP method will become a new and direct method for measuring soliton densities of incommensurate states.

Notes: Here is presented a computer code "dynamic sasamal,'' which has been developed to simulate the dose dependence of concentration profiles and sputtering yields under ion implantations. The model calculations have been applied for high dose implantations of 50-keV nitrogen into zirconium and aluminum. The results are compared with composition profiles obtained by Rutherford backscattering spectrometry (RBS) and with semiempirical values. In the case of Zr, agreements between calculated composition profiles and experimental profiles obtained by RBS analysis were excellent for all fluences up to 1018 ions/cm2 and the calculated sputtering yield decreased toward the semiempirical value with the increase of the fluence. In the case of Al, for fluences up to 7.5×1017 ions/cm2, the composition profiles obtained by RBS measurements agreed well with the calculated results, but for a fluence of 1×1018 ions/cm2, the measured profile deviated from the calculated one; while the calculations assume a saturation concentration equal to the saturated nitride phase, nitrogen concentrations of 55% were measured within the mean ion range.

Notes: The domain switching of ferroelectric triglycine sulfuric acid and Rochelle salt was studied by observing optical gyration along the ferroelectric axes and measuring rotation of the indicatrices around the same axes. It was established experimentally that the antipolar domains of triglycine sulfuric acid were united by a symmetric twin mechanism and those of Rochelle salt by a hemitrope (rotation twin). It was shown that the high-accuracy universal polarimeter method can become a new general method for distinguishing the twinning mechanism of the ferroelectric domains.

Notes: Recent studies on two aspects of silica glass as a photonic material will be described. Part A of this review will be focused on structural disorder and structural relaxations in silica glass. With regard to the structural disorder, investigations have been made to improve transparency and to shift the optical absorption edge in the ultraviolet towards shorter wavelengths. Remarkable advances have been achieved in the understanding of both light scattering, which is a dominant factor in the optical losses in silica fibers, and the absorption edge. Freezing of the structural disorder was observed, and structural relaxations are found to be important for improving the transparency, whereas for the absorption edge thermal vibration effects seem to be more predominant than the structural disorder. From the results, the present authors have tried to control the structural relaxation for developing silica glass with an ultimate optical transparency, finding that a very tiny amount of the proper impurity species gives rise to structural subrelaxations, which are effective in reducing the Rayleigh scattering. The scattering was reduced by 13% by addition of only 10 wt ppm Na2O, for example. In part B of this review the second-order optical nonlinearity induced in Ge-doped silica glass will be described based on recent experiments carried out by the group of present authors. A large second-order optical nonlinearity has been successfully induced in the glass by simultaneous applications of a high dc electric field and ultraviolet (UV) irradiation, so-called UV poling. The nonlinearity induced by UV poling in bulk and film samples has achieved a magnitude of χ(2), comparable to or even larger than those of LiNbO3 and other crystals. Surprisingly enough, the nonlinearity induced by this method then decays after the UV poling as an exact single-exponential function of time, very much unlike the usual decay processes observed in glasses. Evidence is presented associating the nonlinearity with GeE′ defect centers created from oxygen deficient vacancies through photochemical reactions. The decay or degradation can be made much slower with the addition of proper impurities which work as electron scavengers. In addition, we have found that crystallites are generated in the glass by the UV poling, which leads to an increase in the third-order nonlinearity, χ(3), approximately 15 times larger than before the treatment. As a whole, the evidence strongly suggests that a major origin of the second-order nonlinearity induced in the glass is a combined effect of a large third-order nonlinearity associated with the crystallites and an internal space-charge field, where the charges to build up the field are produced during the formation of GeE′ centers. © 2000 American Institute of Physics.

Notes: © 2000 American Institute of Physics.

Notes: Dielectric dispersion in silica glasses with various OH concentrations were investigated from 20 Hz to 1 MHz in the temperature range from 30 to 1000 °C. Dielectric relaxation, which could be attributed to the elementary process of structural secondary relaxation caused by OH motion, has the activation energy between 2.3 and 2.6 eV. ac and dc electrical conductivities and diffusion coefficient of OH have been deduced from the imaginary part of the dielectric constant. The ac electrical conductivity shows the characteristic feature as is usually observed in amorphous solids. The dc electrical conductivity and diffusion coefficient of OH derived therefrom obey the Arrhenius law with the activation energy of 1.0±0.2 eV in the temperature range from 350 to 1000 °C. © 1999 American Institute of Physics.

Notes: Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first-order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a direct abstraction of H atom from H2, and it gives calculated activation energy which is in good agreement with the present experiment.

Notes: It is found that a reversed-field pinch (RFP) dynamo uniformly generates most of the toroidal flux in a RFP plasma with a high magnetic Reynolds (S) number. Hereafter, this is referred to as the global dynamo. The toroidal flux generated by the global dynamo is proportional to the plasma current. The effective inductance in a RFP plasma increases with S number and remains constant against the changing plasma current. This means that the pinch parameter aitch-theta is held constant, that is, the global dynamo has a self-organizing effect sustaining a particular RFP configuration. By comparing simulation results and analysis of magnetic fluctuations, it is confirmed that a global dynamo is generated by the nonlinear evolution of the single-helicity of the m=1 mode alone.

Notes: Ion cyclotron range of frequency (ICRF) heating experiments on the Large Helical Device (LHD) [O. Motojima et al. Fus. Eng. Des. 20, 3 (1993)] achieved significant advances during the third experimental campaign carried out in 1999. They showed significant results in two heating modes; these are modes of the ICH-sustained plasma with large plasma stored energy and the neutral beam injection (NBI) plasma under additional heating. A long-pulse operation of more than 1 minute was achieved at a level of 1 MW. The characteristics of the ICRF heated plasma are the same as those of the NBI heated plasma. The energy confinement time is longer than that of International Stellarator Scaling 95. Three keys to successful ICRF heating are as follows: (1) an increase in the magnetic field strength, (2) the employment of an inward shift of the magnetic axis, (3) the installation of actively cooled graphite plates along the divertor legs. Highly energetic protons accelerated by the ICRF electric field were experimentally observed in the energy range from 30 to 250 keV and the tail temperature depended on the energy balance between the wave heating and the electron drag. The transfer efficiency from the high energy ions to the bulk plasma was deduced from the increase in the energy confinement time due to the high energy ions in the lower density discharge, which agrees fairly well with the result obtained by the Monte Carlo simulation. The transfer efficiency is expected to be 95% at an electron density of more than ne=5.0×1019 m−3 even in the high power heating of 10 MW. The accumulation of impurities, e.g., FeXVI and OV was not observed in high rf power and long pulse operation. The well-defined divertor intrinsic to LHD is believed to be useful in reducing the impurity influx. © 2001 American Institute of Physics.

Notes: The effects of fluorine (F) doping on silica glass structure, structural relaxations, and vacuum ultraviolet (VUV) absorption edge were investigated by the infrared and vacuum ultraviolet absorption measurements. Linewidth of 2260 cm−1 absorption band, which is one of the good indicators of structural disorder, decreases proportionally to the fictive temperature (Tf). On the other hand, it is irrespective of F concentration. Structural relaxations are strongly stimulated by F doping. The transparency near the absorption edge depends on both F concentration and Tf. When Tf is constant, absorption edge shifts to a shorter wavelength proportionally to the F concentration. These results strongly suggest that there are two main factors that control the VUV absorption edge of F-doped silica glass; band gap widening by increasing Si–F bond and reduction of structural disorder. The latter factor is not directly caused by structural change by F doping. F enhances the structural relaxation, and it is easy to obtain samples with lower Tf, resulting in reducing structural disorder. Furthermore, a way to determine Tf of F-doped silica glass is offered. © 2002 American Institute of Physics.