Nobuo Wakabayashi

Investigation of calcium-iron-silicate glasses by the Mössbauer method

Abstract The oxidation-reduction and coordination of iron atoms in calciumsilicate glasses has been studied as functions of the basic oxide content and partial oxygen pressure on the basis of Mossbauer spectra. It was found that the equilibrium concentration ratio NFe3+/NFe2+ increased as the CaO content or partial oxygen pressure increased. The coordination behavior of iron atoms was complicated. In the glasses containing a large amount of Fe2O3, the Fe2+ ion was always present in the octahedral site, while the Fe3+ ion showed amphoteric behaviour. The ratio in number of tetrahedrally coordinated to octahedrally coordinated ferric ions did not exhibit any remarkable variation for larger partial oxygen pressures (1 and 0.21 atm), but increased slightly with the CaO/SiO2 ratio for the small oxygen pressure (3 × 10−7 atm). In the glasses containing a small amount of Fe2O3, the Fe2+ ion was present in both tetrahedral and octahedral sites. However, the coordination state of the Fe3+ ion was not sufficiently clear in such glasses.

Rotational and boiling motion of speckles in a two-lens imaging system

The motion of speckles produced by a rotating diffuse object with a spatial velocity distribution was investigated. It was shown that speckle motion in a two-lens imaging system depends on the Doppler-shift frequency distribution that is due to the spatial velocity distribution of the diffuse object within the point spread of the optical system used. By measuring the time correlation of speckle intensity fluctuations, the predicted properties of the speckle motion that exhibit a good agreement with the experimental results are presented.

Statistical properties of triggered photocounting distribution

The triggered photocounting distribution (TPCD) of practical fields has been investigated. The moment generating function and the factorial moment are exactly deduced from theory and experimentally justified by the measurement of Gaussian-Lorentzian light. It is found that the first-order factorial moment of the TPCD has the spectral information of incident light corresponding to the second-order factorial moment of ordinary photocounting distribution.

Correlation properties of heterodyned dynamic speckle in a two-lens imaging system and its application to two-dimensional velocity measurements

The space–time correlation function and its space- and time-integration effects of dynamic speckle in a two-lens imaging system superimposed upon a coherent laser light are analytically deduced. From considerations of the specific cases, two methods to perform two-dimensional velocity measurements in real time are proposed: a fringe method and a moment method. As a main result, it was found that the moment method has better spatial resolution than the fringe method.

Real-time measurements of spatial velocity distribution with a laser Doppler imaging system.

A new laser Doppler imaging system with a TV camera has been constructed, which brightly displays 1-D velocity distribution on a monitor. Some characteristics of this system have been experimentally investigated from measurements of simple velocity distribution on a constantly rotating ground glass disk. From an adaptation to fluid flow, it has been shown that the measurements of spatial velocity distribution can be achieved in real time.

Space-time correlation function of spatially and temporally integrated laser speckle intensity in a two-lens imaging optical system

Abstract An analytical form of the cross correlation function in a two-lens imaging optical system has been obtained by calculating the integrated speckle intensity with a gaussian profile approximation for the transmittance of the detection area and the weight function of the sampling time. Adapting the results to a speckle velocimeter, the experimental conditions of the sampling time and the optimal relation between the speckle size and the detection area have been discussed.

Absolute velocity control of a Mossbauer spectrometer by utilizing a laser interferometer

The absolute velocity control of a constant-velocity Mossbauer spectrometer was achieved by detecting the time interval of periodic interference fringes at sampling frequencies above 500 Hz. It was found that the reproducibility and linearity were better than +or-0.001 mm s-1 over the velocity range of 0.16-10.00 mm s-1, and that the stability was +or-0.002 mm s-1 at a velocity of 1.00 mm s-1.

Single-interval statistics of non-Gaussian light in the presence of number fluctuations

By using the basic particle-scattering theory, the high-order moments of non-Gaussian light, including number fluctuations that are due to independent particles, have been deduced for a sampling interval that is much smaller than the characteristic time of the number fluctuations but comparable with that of the interference fluctuations. The results have been compared with experiment by measuring the second- and third-factorial moments.

Measurements of velocity distributions with a laser doppler imaging system

Abstract A laser Doppler imaging system with a TV camera has been constructed and velocity distributions of fluid flow in cross sections of a rectangular channel have been measured. Consequently, it has been found that the system has some advantages in comparison with usual laser Doppler velocimeters, for example, the visualization of flow can be easily achieved.

Simultaneous 2-D velocity measurements using time-averaged contrast of dynamic speckle pattern

Abstract A digital image processing system to detect time-averaged speckle contrast has been constructed. Since the speckle contrast averaged over a finite sampling time decreases as a diffuse object moves rapidly, the present system can display the spatial velocity distribution of the object on a TV monitor in quasi-real time.