Volume 6 Issue 2 September 2007

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https://doi.org/10.33697/ajur.2007.011

Guest Opinion: Undergraduate Research Assistants

https://doi.org/10.33697/ajur.2007.012

Author(s):

Barbara Hetrick

Affiliation:

Department of Biology, University of Northern Iowa, Cedar Falls, Iowa 50614-0421 USA


Acoustic Imaging of Sound Sources with a Student-Designed Acoustic Camera

https://doi.org/10.33697/ajur.2007.013

Author(s):

Joachim Sigl and René Scheucher

Affiliation:

Department of Automotive Engineering, FH Joanneum University of Applied Sciences, Alte Poststr. 149, A-8020 Graz, AUSTRIA

ABSTRACT:

An acoustic camera consists of a microphone array, a data recorder and sound analysis- and -visualization software. It creates a color-coded sound map that displays the sound sources overlaid on the visual image of the recorded object. The sound maps are usually produced by analyzing the phase differences of the signals measured by the array microphones. Delay-and-sum beamformer and multiple signal classification (MUSIC) techniques are used in this work for the localization of sound sources. Beamformers are able to determine the amplitude of incident sound, but suffer from poor resolution and from ghost images. MUSIC, on the other hand, is an established technique for efficient and accurate noise source location, which can provide high-resolution source maps, but does not provide any information about the sound level. The combination of both methods gives comprehensive information about the acoustic emission of the system under investigation.


Electrostriction Effects During Defibrillation

https://doi.org/10.33697/ajur.2007.014

Authors and Affiliations:

Michelle M. Fritz
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 USA

Phil W. Prior and Bradley J. Roth
Department of Physics, Oakland University, Rochester, Michigan 48309 USA

ABSTRACT:

Background—The electric field applied to the heart during defibrillation causes mechanical forces (electrostriction), and as a result the heart deforms. This paper analyses the physical origin of the deformation, and how significant it is. Methods—We represent the heart as an anisotropic cylinder. This simple geometry allows us to obtain analytical solutions for the potential, current density, charge, stress, and strain. Results—Charge induced on the heart surface in the presence of the electric field results in forces that deform the heart. In addition, the anisotropy of cardiac tissue creates a charge density throughout the tissue volume, leading to body forces. These two forces cause the tissue to deform in a complicated manner, with the anisotropy suppressing radial displacements in favor of tangential ones. Quantitatively, the deformation of the tissue is small, although it may be significant when using some imaging techniques that require the measurement of small displacements. Conclusions—The anisotropy of cardiac tissue produces qualitatively new mechanical behavior during a strong, defibrillation-strength electric shock.


Analysis of the Ferromagnetic Transition in Melt-Spun Gadolinium Nanocrystals

https://doi.org/10.33697/ajur.2007.015

Authors and Affiliations:

J.G. Bohnet and P. M. Shand
Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614-0150 USA

J. Goertzen and J.E. Shield
Department of Mechanical Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 USA

D. Schmitter, G. Shelburne and D. L. Leslie-Pelecky
Department of Physics & Astronomy and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588 USA

ABSTRACT:

Magnetic materials are present in rewriteable disk drives, electric motors and generators, and signal transformers/receivers. To improve the performance of these and other devices, much research in magnetism continues to be done. In particular, materials that are disordered on the atomic and nanometer scales have recently been the subject of extensive research, as the arrangement of atoms and the interactions between them significantly affect a material’s magnetic properties. We have prepared a disordered pure gadolinium (Gd) system using a melt-spinning technique. This resulted in a system of Gd crystals on the order of 160 nm in size embedded in an amorphous Gd matrix. The structure was identified using X-ray analysis and transmission electron microscopy. AC susceptibility and DC magnetization measurements at various temperatures (280 -350 K) and DC bias fields (0 – 3 kOe) were performed on a sample of the nanocrystalline Gd. Using modified Arrott-Noakes plots and scaling ideas for a second-order phase transition, critical exponents and the Curie temperature (TC) for the ferromagnetic transition in the nanocrystalline Gd system were obtained. TC was found to be 289.70 K, and the critical exponents had shift away from those of bulk Gd and toward those of the Heisenberg model with short-range interactions, indicating that melt-spinning suppressed the interactions present in bulk Gd.