https://doi.org/10.33697/ajur.2004.006
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https://doi.org/10.33697/ajur.2004.007
Author(s):
C.C. Chancey
Affiliation:
American Journal of Undergraduate Research, University of Northern Iowa, Cedar Falls, Iowa 50614-0150 USA
https://doi.org/10.33697/ajur.2004.008
Authors and Affiliations:
B. A. Welle, A. C. Hirsch, L. E. Davis
Department of Geology, College of St. Benedict / St. John’s University, Collegeville, Minnesota 56321 USA
A. C. Johnson, G. J. Hunt, and R. L. Eves
Department of Geology, Southern Utah University, Cedar City, Utah 84720 USA
ABSTRACT:
A sedimentological survey of the southwest arm of the Holocene Pigeon Creek tidal lagoon on San Salvador Island, Bahamas was conducted to determine the origin and distribution of calcareous sediments. Transect surveys, surface samples, and sediment cores were collected and examined to determine the abundance and distribution of sediments and sediment producers in the lagoon and associated tidal delta. The study area has three regions: an extensive tidal to shallow, subtidal flat; a tidal channel near the entrance to the lagoon; and a lobate, ebb-dominated tidal delta. Tidal flat sediments were extensively bioturbated and heavily rooted by Thalassia testudinum. Tidal flat sediments ranged from coarse, calcareous sand to calcareous muds, and were rich in gastropod shells, foraminifera, calcareous algae, and pelletal calcareous mud. The tidal flat sediments are assigned to a pellet-lime wackestone to muddy lime packstone lithofacies. Calcareous green algae are the primary producers of calcareous sediments in the lagoon with species of Halimeda and Penicillus being the dominant genera. Surface samples taken from the coarse channel lag of the tidal channel consisted primarily of whole and fragmented bivalves and gastropods. Most of the bivalves were oriented convex upward. Surface samples taken from ripples, mega-ripples, and sand waves of the tidal delta are dominated by well-sorted, well-rounded, and polished sand-size grains (1-2 mm in diameter). This sediment was dominated by bioclasts (bivalves, gastropods, calcareous algae, foraminifera) and minor ooids. Sediments of the tidal channel and tidal delta are assigned to a lime packstone to grainstone lithofacies. The coarsest fraction (> 2 mm) accumulated on the lee slopes and troughs of large, tidal and wave produced ripples. Ripples for both ebb- and flood tides are strongly asymmetrical, but symmetrical ripples are common, indicating that significant migration of the tidal delta does not occur during normal tidal events. A low energy, shallowing upward cycle is well illustrated in the lagoon, and the presence of a depaurperate biofacies and heavily bioturbated and rooted lithofacies typify a carbonate lagoon depositional environment.
https://doi.org/10.33697/ajur.2004.009
Author(s):
D. K. Kosma, J. A. Long, and S. D. Ebb
Affiliation:
Department of Plant Biology, Southern Illinois University Carbondale, Carbondale, Illinois 62901 USA
ABSTRACT:
Yellow foxtail (Setaria glauca L. P. Beauv) growing on a cadmium-contaminated site was sampled to determine the extent of cadmium bioaccumulation in aerial tissues and the impact of cadmium on growth and development. Water-extractable Cd concentrations in the soil ranged from 5.0 to 18.0 mg L-1. Aerial tissues contained elevated concentrations of Cd (16-48 μg g-1 DW), with mean concentration ratios of >3.0. Since foxtail frequently colonizes disturbed sites, the bioaccumulation of Cd in aerial tissues of foxtail suggests that wildlife feeding upon this plant species could be exposed to elevated Cd levels. A significant negative correlation (r2=0.98) was observed between water-extractable Cd in the soil and seed head length in foxtail, indicative of an adverse effect of Cd on reproductive development. This correlation further suggests seed head length as a biomarker for soluble Cd in contaminated soils.
KEYWORDS:
Cadmium, bioaccumulation, biomarker, phytotoxicity
Apollonius’ Problem: A Study of Solutions and Their Connections
https://doi.org/10.33697/ajur.2004.010
Author(s):
David Gisch and Jason M. Ribando
Affiliation:
Department of Mathematics, University Northern Iowa, Cedar Falls, Iowa 50614-0506 USA
ABSTRACT:
In Tangencies Apollonius of Perga showed how to construct a circle that is tangent to three given circles. More generally, Apollonius’ problem asks to construct the circle which is tangent to any three objects that may be any combination of points, lines, and circles. The case when all three objects are circles is the most complicated case since up to eight solution circles are possible depending on the arrangement of the given circles. Within the last two centuries, solutions have been given by J. D. Gergonne in 1816, by Frederick Soddy in 1936, and most recently by David Eppstein in 2001. In this report, we illustrate the solution using the geometry software Cinderella™, survey some connections among the three solutions, and provide a framework for further study.
Physics of Potassium Ion Channel Inactivation in Neurons
https://doi.org/10.33697/ajur.2004.011
Author(s):
Ryan M. W. Collins
Affiliation:
Department of Physics, University of Northern Iowa, Cedar Falls, Iowa 50614-0150 USA
ABSTRACT:
The electrical signaling capabilities of neurons depend on the flows of ions into and out of their axons. Potassium ions exit an axon’s interior through a potassium channel or pore that connects the intracellular region with the extracellular region. The channel opens, or is activated, allowing potassium ions to exit. The channel then undergoes a blocking transition in which the channel is physically open but is blocked by some part of the larger channel molecule. This blocking process is called inactivation, and the physics by which it might occur forms the topic of our investigation. The N-terminus region of the Drosophila shaker potassium ion channel was identified by Hoshi et al as having an important role in channel inactivation. Using the last 19 amino acids in the N-terminus region, a mass and net charge were calculated. We investigated two forces that might affect the motion of this N-terminus mass (tentatively identified as the blocking or inactivation particle): the magnetic field effects due to potassium ion current in the channel, and an electric force due to the decreasing density of potassium ions from the intracellular region. Time-of-flight calculations were calculated for the inactivation particle. These times will be discussed in terms of typical inactivation processes.