The impact of goal orientation, self-reflection and personal characteristics on the acquisition of oral presentation skills

Although many educators help others to develop oral presentation skills, little research is available to direct the instructional design activities of these educators. In the present article an explorative study on university freshman is described, in which goal-setting, self-reflection, and several characteristics of the subjects during oral presentations were analysed. The research results emphasize the critical impact of motivational constructs, such as self-efficacy and goal orientation, next to the topic of the oral presentation on the acquisition of oral presentation skills

High resolution near-field acoustic holography

High resolution Near-field Acoustic Holography (NAH) is not a widely discussed topic in open literature. For instance articles on automotive or naval applications do not discuss resolutions beyond one centimetre. Electronic appliances on the other hand demand a high spatial resolution, since the components of printed circuit boards become smaller and smaller. These applications require a spatial resolution in the order of millimetres. As an example, components such as Surface Mounted Devices (SMDs) carry high frequent switching voltages, which may have a noise generating effect. Even sound power levels as low as 30 dB(A) can be annoying to the customer, requiring a diagnostic tool such as NAH to localise the sound source(s) of relatively low acoustic levels at a high spatial resolution. To obtain high-resolution acoustic images, the acoustic signal processing and measurement set-up have to be tuned carefully. The paper focuses upon the determination of optimal measurement and reconstruction parameters to enable highly accurate source reconstructions, which in this case are limited to stationary, coherent sources only. To illustrate the high-resolution capabilities of Planar Near-field Acoustic Holography (PNAH) a test case is used. The test case is a plate containing three baffled sources, each two millimetre in diameter, half a millimetre apart. The measurements show that the sources are identified with sub-millimetre resolution

Sonic excitation by means of ultrasound; an experimental illustration of acoustic radiation forces

Ultrasonic acoustic waves are known to induce a vibration of particles around an equilibrium position. However, for large acoustic amplitudes, due to non-linear acoustic effects, a rectified, net acoustic radiation force can occur. Experimental work is performed in which the non-linear behavior is exploited to generate a dynamic acoustic radiation force that is used to dynamically excite a small structure at sonic frequencies. The dynamic radiation forces are quantified experimentally in an inverse manner from the structural displacement of the structure being excited by acoustic radiation forces