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A high power and sensitive gated radio-frequency (rf) measurement system has been used to determine the absorption of compressional waves in air, in the frequency range from 10–20 MHz. The measured absorption, between 80 and 90 kPa and at room temperature (15 °C to 25 °C), has been found to be in good agreement with that predicted, by extrapolation, from low-frequency (below 1 MHz) data for the combination of the classical and rotational loss effects. The measured data fit a classical-plus-rotational absorption loss coefficient (αcr) for a 20 °C value of 1.83×10−11 Np/m. Above 500 kHz at normal atmospheric pressures, this coefficient becomes dominant, and the effects of variation in humidity are insignificant. The bounds for the parameter domain for this relationship to be valid are now pressures between 80 and 90 kPa, temperatures between 15 °C and 25 °C, and frequency/pressure combinations up to 200 Hz Pa−1. The velocity of ultrasound in air in the frequency range from 10–18 MHz has also been measured and is in good agreement with that predicted from theory. For example, at 83.3 kPa (625.5 mm Hg) and 24.4 °C, the measured velocity is 347.6±1 m/s at 10 MHz and that calculated, including the effect of humidity, is 346.4 m/s. Normalized velocity and attenuation data plotted against Knudsen numbers and a rarefaction parameter are in good agreement with those obtained at reduced pressure and lower frequencies.

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To be most useful, evaluation requires detailed observation and effective analysis of a full spectrum of system use. We have developed an approach and architecture for in-depth data collection and analysis of all use of a visualization system. User interface components in a large visualization and analysis platform automatically record user actions, and can restore previous system states on demand. Audio and text annotations are collected and indexed to states, allowing users to find a comment and restore the system state in which they made it; then explore actions before and after. History is visible as data; so a variety of visual displays and analysis techniques may be used to develop insights about the user's experience. States of any part of the interface may be analyzed separately. Actions are categorized in a taxonomy as the user interface is built, allowing comparison of similar patterns in all tools. History data can co-exist with other data during data exploration, supporting further individual or group data exploration.

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