The theory of a transfer function method of measuring normal incident in-duct acoustic properties is presented. In this method, a broadband stationary random acoustic wave in a tube is mathematically decomposed into its incident and reflected components using a simple transfer-function relation between the acoustic pressure at two locations on the tube wall. The wave decomposition leads to the determination of the complex reflection coefficient from which the complex acoustic impedance and the sound absorption coefficient of a material and the transmission loss of a silencer element can be determined. Also presented are the theories of two techniques for improving transfer function estimates: a sensor-switching technique for automatic system calibration and a coherence function technique for signal enhancement.

This paper is the second of two papers describing the transfer function method of measuring in-duct acoustic properties. In the previous paper the theoretical formulae were developed. In this paper experimental results are presented to demonstrate the accuracy and the general utility of the method. Test results of the complex reflection coefficient, the complex acoustic impedance, and the transmission loss are found to agree well with theoretical predictions. The sound absorption coefficient was evaluated with both the new method and the conventional Standing-Wave-Ratio (SWR) method and the accuracy of the two results are found to be comparable. The new method, however, is about 40 times faster than the SWR method. Also included are experimental verifications of two methods for improving the transfer function estimate, namely the use of sensor switching for automatic system calibration and the use of coherence functions for signal enhancement.

Adaptive programmable materials have attracted increasing attention due to their high functionality, autonomous behavior, encapsulation, and site-specific confinement capabilities in various applications. Compared to conventional materials, adaptive programmable materials possess unique single-material architecture that can maintain, respond, and change their shapes and dimensions when they are subjected to surrounding environment changes, such as alternation in temperature, pH, and ionic strength. In this review, the most-recent advances in the design strategies of adaptive programmable materials are presented with respect to different types of architectural polymers, including stimuli-responsive polymers and shape-memory polymers. The diverse functions of these sophisticated materials and their significance in therapeutic agent delivery systems are also summarized in this review. Finally, the challenges for facile fabrication of these materials and future prospective are also discussed.

Hydrogen released from chemical hydride ammonia borane (AB, NH3BH3) can be greatly improved when AB is confined in metal–organic frameworks (MOFs), showing reduced decomposition temperature and suppressed unwanted byproducts. However, it is still debatable whether the mechanism of improved AB dehydrogenation is due to catalysis or nanosize. In this research, selected MOFs (IRMOF-1, IRMOF-10, UiO-66, UiO-67, and MIL-53­(Al)) were chosen to explore both catalytic effect of the metal clusters and the manipulation of pore size for nanoconfinement by variations in ligand length. When AB particle size was restricted by the controlled micropores of MOFs, we observed that the decomposition temperature was not correlated to the MOF catalytic environment, but inversely proportional to the reciprocal of the particle size. The results correspond well with the derived thermodynamic model for AB decomposition considering surface tension of nanoparticles.

The theory of a new method of measuring acoustic intensity is presented. The method uses measurements of the cross spectrum of the pressures at two closely spaced microphones. To eliminate the measurement error due to instrument phase mismatch, a circuit switching procedure is used. The method is applicable to any acoustic field subject to the condition that the product of the wave number and the microphone spacing remains small. The method has been verified by laboratory experiment.