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College of Sciences

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School of Biological Sciences

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School of Chemistry and Biochemistry

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School of Earth and Atmospheric Sciences

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School of Mathematics

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School of Physics

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Publication Search Results

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Native parasite combating an invasive species: an oomycete vs. Echinogammarus ischnus

(Georgia Institute of Technology, 2010-12-20) van Rensburg, Karla

In the context of invasions in ecology, parasites can play an important role in mediating the outcomes of competition between the native and invasive species. For example, a native parasite in the upper St. Lawrence River area has been found infecting both native and non-native gammarid amphipods, Gammarus fasciatus and Echinogammarus ischnus, respectively. Usually when the non-native species invades an area, the native amphipod is rapidly replaced by the non-native species. However, in this specific region the native amphipod was not replaced by the non-native species, and the non-native species was observed to be infected by a parasite. To determine infection rates in the native and non-native hosts, DNA was extracted from both species of amphipods and specific primers for the 18S rRNA gene were created to generate quantitative analysis of the incidence of the parasite in the amphipods. These data indicate that the effect of the parasite on the native and non-native amphipods could be the mechanism preventing the dominance of the non-native species in this specific area for the past ten years, since the parasite was found to infect the non-native amphipod more frequently and at a higher level than the native amphipod.
The effect of a pathogen on the population dynamics and reproductive method of Asplanchna girodi

(Georgia Institute of Technology, 2010-12-20) Reynolds, Abigial Nicole

Studies show that the abundance of Asplanchna girodi can be affected by many factors including food density, temperature and pH. One such aspect not yet explored is the effect that parasitism has on Asplanchna girodi populations. During weekly samplings of a local lake, a parasitic oomycete was discovered to frequently infect the Asplanchna girodi population. Based on multi-year sampling data, this study supports recent work showing that parasitism of a zooplankton has the potential to have reproductive and evolutionary consequences. I show that epidemics of this parasite, Pythium, occur frequently and that an increased number of males in the population can be correlated to the presence of the parasite. Sexual reproduction involving males provides for Asplanchna girodi's only means of genetic recombination and production of diapausing eggs that overwinter. This study shows that there is a correlation between the rate of infection by Pythium and the density of males in the Asplanchna girodi population. By increasing the number of males in a population, the rate of diapause egg production is also increased. Infection by this parasite could therefore be associated with increased sexual reproduction and genetic recombination of A. girodi populations.
Zooplankton population dynamics in Clayton County Water Authority reservoirs

(Georgia Institute of Technology, 2010-12-20) Ahmed, Tamanna

Reservoirs supply most of Georgia s drinking water, and plankton dynamics can greatly influence the water quality of these reservoirs. Therefore, understanding the dynamics of zooplankton as well as phytoplankton is necessary. Unlike reservoirs in the northern United States, zooplankton dynamics in reservoirs in the South remain largely uncharacterized. Samples were collected from the Clayton County Water Authority reservoirs to study correlations between zooplankton taxa distribution and environmental variables. Population count data has demonstrated that the zooplankton dynamics in southern lakes vary from the dynamics typically seen in northern lakes. While temperature noticeably shaped seasonal densities in some species, other species had variable dynamics and seemed to not be affected by this environmental factor or other taxa of zooplankton, suggesting additional factors may regulate population composition and abundance.
Uranyl phosphate minerals as long term sink in uranium bioremediation

(Georgia Institute of Technology, 2010-12-20) Saad, Emily Marie

US Department of Energy nuclear fuel and weapon production has resulted in uranium contaminated soils and groundwater. As the magnitude of this environmental issue requires an in situ remediation strategy, bioreduction of soluble U(VI) to insoluble U(IV) has been investigated. However, site specific conditions prevent the effectiveness of this remediation technique requiring instead a redox independent method. The biomineralization of the water soluble U(VI) species is presented as a remediation alternative, and the role of different organophosphate species and bacterial strains in this process continues to be studied. However, the stability of these uranyl phosphate minerals must also be examined to evaluate their role as long term sinks for uranium. This study seeks to quantify uranyl phosphate stability in environmentally relevant conditions by examining the effect of Na+, Ca2+, SO42-, and HCO3- present in typical subsurface environments, and uranium phosphate biomineralization in the presence of carbonates. The results of the study suggest that the uranyl phosphate species biomineralized by the facultative anaerobe, Rahnella sp.Y9602, isolated from soils at the DOE Oak Ridge Field Research Center (ORFRC) as a model organism, is preferred even in the presence of the competing carbonate species. Furthermore, even in the presence of cations and anions, uranyl phosphate minerals may be exploited as an alternative remediation reservoir.
T-Shaped Fluorophores Towards the Development of Novel Fluorescent Architectures

(Georgia Institute of Technology, 2010-05-12) Gharakhanian, Eric Gregory

This study reports the synthesis and photophysical characterization of 12 compounds from two new fluorophore architectures, in order to study the photophysics of cruciforms in relation to stilbenes. Therefore, analogues of cruciforms missing a styryl or arylethynyl branch were synthesized. The response of some of these T-shaped fluorophores to metal salts and protons in CH2Cl2 was studied. Likewise, the solvatochromicity of all derivatives was studied. The derivatives lacking a distyrylbenzene moiety were found to be photochemically unstable and possessed characteristics similar to stilbenes. Derivatives containing a distyryl branch were found to be photochemically stable, with responses analogous to cruciforms.
Performance of dynamic decoupling control sequences on trapped ⁴⁰Ca⁺

(Georgia Institute of Technology, 2010-05-12) Wright, Kenneth Earl

One of the fundamental problems of chemistry is the difficulty in determining full quantum mechanical descriptions of molecules. Molecules contain many degrees of freedom and as a result the classical description scales factorially with the number of electrons. One way to overcome this mismatch between quantum and classical pictures is to use one quantum system, a quantum computer, to simulate another. Quantum computation is based upon a two-level system, a qubit, which is analogous to a bit in classical computation. Unlike a classical bit, a qubit can exist in a superposition of quantum states. The interaction between a quantum system and its environment results in the decay of the superposition state of the system into a probability density of classical states [1]. This is known as decoherence. A realistic quantum computer requires qubits with long coherence times; with respect to the achievable gating times, for a formal relation refer to section 1.2.2. The spin echo effect in nuclear magnetic resonance (NMR) offers a way to increase the coherence time of a qubit and has been studied as a way to mitigate decoherence in quantum computation[2][3]. By applying an appropriate Π pulse to a system under the influence of a large external field, as in NMR, the interaction term of the Hamiltonian between the qubit and environment can be eliminated[3][4]. Periodic implementation of such pulses is known as periodic dynamic decoupling (PDD). Similar to PDD, concatenated dynamic decoupling (CDD) is a periodic pulse sequence which removes the interaction term of the Hamiltonian, however in CDD pulse sequences are recursively embedded within the overall pulse train. Such pulse sequences have been shown theoretically to work for model quantum systems such as GaAs quantum dots, and theoretically such pulse sequences vastly improve the coherence time of a qubit [5]. There have been many calculations showing that by progressively increasing the number of concatenated pulse sequences increasingly longer coherence times can be achieved [6][7]. These techniques have not been tested in the laboratory and experimental implementation of these promising techniques motivates current research. There also continues to be extensive work on developing novel pulse sequences which may improve coherence times even further. The goal of this research is to experimentally determine the coherence times which can be achieved with a trapped calcium atom by applying these pulse sequences.
A mannose receptor-like molecule likely serves as the mate recognition pheromone receptor in the male rotifer Brachionus manjavacas

(Georgia Institute of Technology, 2010-05-12) Couser, Laura M.

Mate recognition in the male rotifer Brachionus manjavacas is controlled by contact chemoreception, which occurs when the male has a head-on encounter with a conspecific female. The female expresses a glycoprotein, the mate recognition pheromone or MRP, on her body surface that males detect with a receptor located in the male corona. A positive match between signal and receptor causes males to initiate mating behavior. After surveying the female B. manjavacas and male Brachionus plicatilis transcriptomes for all receptor genes, a C-type lectin gene was found which codes for a mannose receptor (MR). This gene is a good candidate for the MRP receptor because the MRP is glycosylated with mannose and mannose receptors recognize mannose/glucose oligosaccharides. Mannose has been found to block the binding of MR antibodies in males. In addition, mannose receptor immunostains show localized binding at the corona of males, but not in females. Mannose has also been shown to block circling, but binding of antibodies for the human mannose receptor does not decrease circling. A Western blot analysis of female rotifers shows that there is an MR in the female proteome; however, Western blots have not demonstrated binding of MR antibodies to male proteins. Mating bioassays showed that mannose is an important inhibitor of male mate recognition. These findings are best explained by the hypothesis that the male MRP receptor is an MR-like molecule that functions as a C-type lectin that is capable of binding of mannose.
Item selection and self-paced study when learning Chinese pictographs: Does the region of proximal learning hypothesis apply to unfamiliar stimuli?

(Georgia Institute of Technology, 2010-05-12) Murray, Rory Gallagher

This experiment examined the order of learning when faced with a time-constrained, difficult, and unfamiliar task by using 36 Chinese-English word pairs. Eighty younger adults (18 to 25 years old) and forty older adults (60 to 80 years old) participated in this experiment. Participants were asked to make an Ease of Learning Judgment (EOL) for each Chinese character. Then, there were two distinct learning trials in which the participants studied the same 36 Chinese-English word pairs in six 2X3 grids. The younger adults had a maximum of 30 seconds of study time allowed per grid. The older adults had 60 seconds per grid. The critical question was whether individuals would focus study on easier items that have not yet been learned, as predicted by Metcalfe s region of proximal learning model, or whether they would simply study all unlearned items with equal emphasis (as predicted by the discrepancy-reduction model (DRM). Both age groups had relatively accurate EOL s corresponding to item complexity. Young adults showed no evidence for RPL predicated effects. Older adults exhibited behavior largely consistent with RPL predictions
Scaler System Testing in the HAWC Experiment

(Georgia Institute of Technology, 2010-05-12) Browning, Tyler

TeV gamma rays probe the non-thermal Universe in ways that are not possible at other wavelengths. The HAWC observatory, under construction in Mexico, will be able to analyze and survey the TeV sky more completely than any competing detectors that use air Cherenkov techniques, and perhaps yield new insight onto the nature of cosmic accelerators responsible for gamma ray bursts, active galactic nuclei flares, and other cataclysmic astrophysical events. Before it's deployment, one of HAWC's electronic data acquisition systems, the scaler system, will be tested using a pulse generator. The pulse generator's capabilities are assessed and documented.
Chemosensation in Blue Crabs and their Reaction to Attractive and Aversive Cues

(Georgia Institute of Technology, 2010-05-12) Mankin, Danielle N.

Blue crabs, Callinectes sapidus, use their olfactory system as their primary sense of environmental perception. These animals, and others such as insects, use a specific type of olfactory system called chemosensation. This system entails having different sensory receptors on different areas of the body. Specifically, blue crabs have two organs, cephalic and thoracic sensory populations. This allows the crab to simultaneously differentiate between odors and allow for more accurate tracking, or finding of food. Some is known about which sensory organs detect which odor, however, it is currently unknown which of these different sensory organs is responsible for detecting predators. This information will help scientists better understand the overall system of chemosensation as well as having implications in such areas as predator-prey dynamics and robotics simulations. Various deafferentation techniques were used to ablate or temporarily remove the sensory receptors of a single organ at a time. The animal was subjected to a food odor, predator odor, and a combination of the two to test their reaction. Results supported previous research by indicating that intact blue crabs typically track a food odor and typically do not track an odor with a predator scent in it, even in combination with food. Also, as supported by previous research, both cephalic and thoracic sensory populations are responsible for detecting food and the deafferentation of one sensory population results in the decreased ability of the crab to successfully track. It was found that when the cephalic sensors were deafferented that crab lost its ability to detect the predator odor and began tracking in a similar manner as a deafferented crab tracking only a food odor. Therefore, this research indicates that the cephalic sensory populations are responsible for detecting predator odors.