A novel ultrasonic bone densitometer, prototype LD-100, has been developed to overcome problems inherent in an ultrasonic method and to obtain bone mass density in the unit of mg/cm 3 and bone elasticity in the unit of GPa with a spatial resolution comparable to that of the peripheral quantitative computed tomography (pQCT) system. Bone mass density and bone elasticity are evaluated using ultrasonic parameters based on fast and slow waves in cancellous bone using a modeling of ultrasonic wave propagation path. A good reproducibility of measured values and two-dimensional (2D) imaging of bone density and bone quality are realized by two scannings with an automatic measurement algorithm.

A computationally efficient numerical simulation of a diode-pumped alkali laser (DPAL) has been developed. It considers the thermal lensing effect by a wave-optics optical resonator model coupled with a simplified gas-flow model. The calculation results indicate that the proposed gas-flow model correctly predicts the temperature distribution of the active medium heated by exothermic reactions. As a result, there is good agreement between the calculations and experiments, especially with the output power as a function of the gas-flow velocity. The calculations have shown that the population of the high-lying excited levels of the Cs atom is negligible within a pump power intensity of 10 kW/cm2.

We have developed a numerical simulation method for diode-pumped alkali lasers (DPALs). We previously reported the use of a simplified gas-flow model, whose adaptability was restricted to forced gas-flow DPALs. In the present study, we have employed an incompressible, three-dimensional computational fluid dynamics (CFD) model. The natural convective flow is modeled using a modified Boussinesq approximation. The results of the simulations were found to be in good agreement with those for a compressible CFD model for a heat-induced flow problem. As a result, good agreement with the experimental results was achieved for a sealed DPAL. On the other hand, the results for the forced gas-flow DPAL were the same as those for the simplified gas-flow model, which confirms the validity of the latter model. The dependence of the beam quality on the pump power for the sealed DPAL was consistent with previously reported results.

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