Dune Tunes - Kelly Garcia '07
Abstract: This study reviews literature on the topic of booming sand which investigates the unusual and unexplained acoustical properties of sand known as booming. The sounds (as loud as 110 dB) have been compared to low-flying propeller airplanes. Typical frequencies range from 60 – 100 Hz depending on the sand grain size. The booming contains only the fundamental frequency and the first overtone. It occurs in special types of dunes all over the world: the Sahara, deserts in Morocco, Chile and China. There have been many attempts to replicate the booming dunes in the laboratory. Some researchers have collected sand from these different parts of the world and have had success, while others have instead used glass spheres. These latter studies were neither unsuccessful nor successful: the experiments produced sounds, but these sounds were unlike those found in nature. In the lab, we were unable to make glass spheres boom. This is most likely a result of impurities within the glass spheres. The exact cause for the booming is still undetermined. The most recent notable study in this area has been that of Douady et al (Phys. Rev. Lett. 97, 018002, 2006), which suggests that the booming of sand is not due to resonance within the dune as with wind instruments, nor is it due to “stick-slip motion of grain” as with stringed instruments. That paper claims the sound frequency depends on the shear gradient in the avalanche and that a standing wave resonance is somehow created in the air located within the shear layer. An alternate model is included in which the sand grains themselves act like gas molecules confined in a closed pipe. Computer simulations show that the “sand gas” model may explain the mechanics of this longstanding puzzle.
For more information, contact Dr. Brian Watson
The Arecibo Legacy Fast ALFA Survey (ALFALFA): An Extragalactic Survey for HI - Jamie Lomax '07
Abstract: The Arecibo Legacy Fast ALFA (ALFALFA) Survey is a large-scale blind survey for extragalactic cold neutral hydrogen (HI) utilizing the Arecibo L-Band Feed Array (ALFA) instrument at the Arecibo Observatory. By observing the sky at radio wavelengths near 21 cm it is possible to find dense regions of HI that correspond to galaxies. I studied a 2.4 square degree region of sky centered on right ascension (celestial longitude) 11h48m and declination (celestial latitude) 13° contained in the ALFALFA data to determine the structure of galaxies contained in that section of sky with redshifts ranging from –1600 km/s to +18,000 km/s with 5 km/s resolution. I will discuss the structure of this region and the observing techniques used by the ALFALFA team in detail.
For more information, contact Dr. Aileen O'Donoghue
The Effect of Magnetic Field Variation on Magnetosome Formation in the Magnetotactic Bacterium Magnetospirillum Gryphiswaldense - Ryan Welsh '07
Abstract: Magnetospirillum gryphiswaldense (DSM 6361 obtained from DSMZ) was obtained and cultured effectively in lab using a method emulating the microaerophilic environment in which the bacterium naturally forms magnetosomes. The cells were then grown under variable magnetic fields: low constant field, high constant field, AC field, and 6 Hz oscillating field for 24 hours. The magnetosome chain length for each treatment has been analyzed using the transmission electron microscope (TEM). At the present state of data analysis, no significant difference in magnetosome formation has been seen with the different treatments. However, in preparing for quantitative RT-PCR, marked differences in growth rate seem to have a direct correlation with the treatment. The qRT-PCR part of this experiment, designed to check for changes in regulation of magnetosome gene transcription, is currently underway.
For more information, contact Dr. Catherine Jahncke