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Analysis of Biological Materials Using a Nuclear Microprobe

Description: The use of nuclear microprobe techniques including: Particle induced x-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) for elemental analysis and quantitative elemental imaging of biological samples is especially useful in biological and biomedical research because of its high sensitivity for physiologically important trace elements or toxic heavy metals. The nuclear microprobe of the Ion Beam Modification and Analysis Laboratory (IBMAL) has been used to study the enhancement in metal uptake of two different plants. The roots of corn (Zea mays) have been analyzed to study the enhancement of iron uptake by adding Fe (II) or Fe (III) of different concentrations to the germinating medium of the seeds. The Fe uptake enhancement effect produced by lacing the germinating medium with carbon nanotubes has also been investigated. The aim of this investigation is to ensure not only high crop yield but also Fe-rich food products especially from calcareous soil which covers 30% of world’s agricultural land. The result will help reduce iron deficiency anemia, which has been identified as the leading nutritional disorder especially in developing countries by the World Health Organization. For the second plant, Mexican marigold (Tagetes erecta), the effect of an arbuscular mycorrhizal fungi (Glomus intraradices) for the improvement of lead-phytoremediation of lead contaminated soil has been investigated. Phytoremediation provides an environmentally safe technique of removing toxic heavy metals (like lead), which can find their way into human food, from lands contaminated by human activities like mining or by natural disasters like earthquakes. The roots of Mexican marigold have been analyzed to study the role of arbuscular mycorrhizal fungi in enhancement of lead uptake from the contaminated rhizosphere.
Date: December 2014
Creator: Mulware, Stephen Juma
Partner: UNT Libraries

UNDERSTANDING THE EFFECTS OF COMPRESSION AND CONSTRAINTS ON WATER UPTAKE OF FUEL-CELL MEMBRANES

Description: Accurate characterization of polymer-electrolyte fuel cells (PEFCs) requires understanding the impact of mechanical and electrochemical loads on cell components. An essential aspect of this relationship is the effect of compression on the polymer membrane?s water-uptake behavior and transport properties. However, there is limited information on the impact of physical constraints on membrane properties. In this paper, we investigate both theoretically and experimentally how the water uptake of Nafion membrane changes under external compression loads. The swelling of a compressed membrane is modeled by modifying the swelling pressure in the polymer backbone which relies on the changes in the microscopic volume of the polymer. The model successfully predicts the water content of the compressed membrane measured through in-situ swelling-compression tests and neutron imaging. The results show that external mechanical loads could reduce the water content and conductivity of the membrane, especially at lower temperatures, higher humidities, and in liquid water. The modeling framework and experimental data provide valuable insight for the swelling and conductivity of constrained and compressed membranes, which are of interest in electrochemical devices such as batteries and fuel cells.
Date: August 24, 2011
Creator: Kusoglu, Ahmet; Kienitz, Briian & Weber, Adam
Partner: UNT Libraries Government Documents Department

Water Uptake in PEMFC Catalyst Layers

Description: Water uptake profiles of proton-exchange-membrane fuel-cell catalyst layers are characterized in the form of capillary-pressure saturation (Pc-S) curves. The curves indicate that the catalyst layers tested are highly hydrophilic and require capillary pressures as low as -80 kPa to eject imbibed water. Comparison of materials made with and without Pt indicates a difference in water ejection and uptake phenomena due to the presence of Pt. The addition of Pt increases the tendency of the catalyst layer to retain water. Dynamic vapor sorption (DVS) is used to characterize the water-vapor sorption onto Nafion, Pt/C, and C surfaces. The DVS results align with the trends found from the Pc-S curves and show an increased propensity for water uptake in the presence of Pt. The effect of the ion in Nafion, sodium or protonated form, is also compared and demonstrates that although the protonation of the Nafion in the catalyst layer also increases hydrophilicity, the effect is not as great as that caused by Pt.
Date: July 1, 2011
Creator: Gunterman, Haluna P.; Kwong, Anthony H.; Gostick, Jeffrey T.; Kusoglu, Ahmet & Weber, Adam Z.
Partner: UNT Libraries Government Documents Department

Quantifying advective and nonstationary effects on eddy fluxes in the AmeriFlux network

Description: Our goal was to study the flows within and above of a forested area and assess the degree to which horizontal subcanopy motions transport significant amounts of CO2. This process can explain why ecosystem respiration appears to be underestimated on calm nights. It is essential to understand the physical and biological mechanisms that determine relevant processes that occur on these ‘suspect’ nights.
Date: December 19, 2012
Creator: Fitzjarrald, David R.
Partner: UNT Libraries Government Documents Department

A preliminary study on the effect of selective serotonin reuptake inhibitors on peripheral and lower brainstem auditory processing.

Description: This study compared auditory behavioral and physiologic measures in normal control subjects and subjects prescribed with a selective serotonin reuptake inhibitor (SSRI) who were yet to take the drug and those currently taking an SSRI. Test measures used were pure tone averages (PTA), acoustic reflex thresholds, uncomfortable loudness levels (UCL), otoacoustic emissions, masking level difference, temporal integration, amplitude resolution, and Beck Depression Inventory-II (BDI-II) scores. Results indicated that there was a significant difference in the amplitude resolution of the unmedicated group when compared to the medicated and the control group. There was also a significant positive correlation between dynamic range (difference between UCL and PTA) and amplitude resolution. The BDI-II revealed a significant difference between the scores of the unmedicated and the control group as well as the medicated and the control group. Although other test measures indicated differences between the groups, the differences were not statistically significant.
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Date: May 2001
Creator: Carney, Lara E.
Partner: UNT Libraries

Comparative Phyto-uptake Across Distribution Coefficients of Pharmaceutical Compounds and Aquatic Macrophytes: Carbamazepine and Amiodarone Uptake in Lemna Spp

Description: Few studies have been conducted on the effectiveness of phytoremediation of pharmaceutical compounds, although the persistent and non-acutely toxic nature of many of these compounds in today's water bodies may yield an ideal application for this practice. To quantify the potential effectiveness of plant uptake, kinetic and proportional bioconcentration factors (BCFk, and BCFp, respectively) in nanograms (ng) carbamazepine and amiodarone per gram (g) wet weight plant tissue for Lemna spp. were determined utilizing a 14-day continuous flow-through study. Samples were analyzed using isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) running in positive ion mode. Kinetic BCF was estimated at 0.538, while proportional BCF was estimated at 0.485. Kinetic BCF for the amiodarone study was estimated at 23.033, whereas proportional BCF was estimated at 41.340. Possible contamination of the C18 column and peristaltic pump failure may have impacted uptake results. In light of variability and current lack of research in the field, this work should be considered exploratory rather than conclusive.
Date: August 2013
Creator: Woodard, Jennifer Kristin
Partner: UNT Libraries

The Effects of Selective Serotonin Reuptake Inhibitors (SSRI) on Auditory Measures in Women

Description: This study examined the relationship between selective serotonin reuptake inhibitor (SSRI) medication and auditory measures in clinically depressed women. Experimental subjects were tested in both a medicated and unmedicated condition. Experimental subjects were compared to a normal control group; additionally intrasubject comparison was made within the experimental group. Test measures included: audiometry, tympanometry, otoacoustic emissions, uncomfortable loudness level, masking level difference, SCAN-A, Synthetic Sentence Identification (SSI), and the low predictability section of the Revised Speech in noise (RSPIN). The unmedicated group scored significantly less favorably than the control group on the following tests; SCAN-A (composite, filtered words, and auditory figure ground), R-SPIN (0MCR condition in both the right and left ears). Additionally, the unmedicated group scored significantly less favorably than the medicated group on the SSI (-20MCR condition right ear only) and of the R-SPIN (0MCR condition right ear only). Other test measures indicated consistent trends but did reach significance.
Date: May 2002
Creator: Briley, Kelly Anne
Partner: UNT Libraries

Sub-second Morphological Changes in Nafion during Water Uptake Detected by Small-Angle X-Ray Scattering

Description: The ability of Nafion® membrane to absorb water rapidly and create a network of hydrated interconnected water domains provides this material with an unmatched ability to conduct ions through a chemically and mechanically robust membrane. The morphology and composition of these hydrated membranes significantly affects their transport properties and performance. This work demonstrates that differences in interfacial interactions between the membranes exposed to vapor or liquid water can cause significant changes in kinetics of water uptake. In-situ small-angle X-ray scattering (SAXS) experiments captured the rapid swelling of the membrane in liquid water with nanostructure rearrangement on the order of seconds. For membranes in contact with water vapor, morphological changes are four-orders-of-magnitude slower than in liquid water, suggesting that interfacial resistance limits the penetration of water into the membrane. Also, upon water absorption from liquid water, a structural rearrangement from a distribution of spherical and cylindrical domains to exclusively cylindrical-like domains is suggested. These differences in water-uptake kinetics and morphology provide a new perspective into Schroeder’s Paradox, which dictates different water contents for vaporand liquid-equilibrated ionomers at unit activity. The findings of this work provide critical insights into the fast kinetics of water absorption of Nafion membrane, which can aid in the design of energy conversion devices that operate under frequent changes in environmental conditions.
Date: September 30, 2011
Creator: Kusoglu, Ahmet; Modestino, Miguel A.; Hexemer, Alexander; Segalman, Rachel A. & Weber, Adam Z.
Partner: UNT Libraries Government Documents Department

Effects of Mineral Salts on Short-Term Incorporation of CarbonDioxide in Chlorella

Description: Although the functions of the essential major elements in plant metabolism have been studied for many years, little work has been done concerning the effect of these elements during short-term incorporation of radioactive carbon dioxide. This may be of some importance as it has been the general custom during photosynthesis studies in this laboratory to suspend algae in various dilute buffer solutions or in distilled water alone assuming that the salt remaining within the cells from the time of growth in nutrient solution are sufficient in quantity for the cells not to become deficient in one or more of the essential elements during the course of the experiment. There are some indications, however, that the addition of salts to algae suspended in distilled water may have a rapid, pronounced effect on some metabolic system within the plant. Thus, Clendenning, Brown and Eyster (1956) have reported that Nostoc muscorum, if rinsed and resuspended in distilled water, loses most of its photosynthetic capacity, which can, however, be completely restored by the addition of potassium ion in concentrations no greater than a few parts per million. Also, K. Baalorud (personal communication) found that the photosynthetic rate of a marine diatom, when suspended in synthetic magnesium-free water, can be greatly increased by the addition of magnesium salts. In view of these observations it appeared worthwhile to investigate the effects of the addition of the essential elements in those photosynthesis experiments in which the cells are kept in distilled water for varying periods of time.
Date: July 1, 1958
Creator: Holm-Hansen, O.; Nishida, K.; Moses, V. & Calvin, M.
Partner: UNT Libraries Government Documents Department

Oxygen Uptake Kinetics in Severe Intensity Exercise

Description: The purpose of this study was to describe mathematically the oxygen uptake kinetics during cycle ergometry, and to examine the effect of intensity on the kinetic responses within the severe domain. Sixteen volunteers performed a series of exercise tests at a range of intensities selected to elicit fatigue in ~3 to 10 min. A simple mono-exponential model effectively described the response across all intensities. There was a positive correlation between the response time and the time to fatigue, demonstrating that the maximal oxygen uptake was achieved faster at higher intensities within the severe domain. Models incorporating two components effectively described the responses only in tests lasting 8 min or more. It was concluded that there is a second, slow component in the oxygen uptake response only at the lower intensities within the severe domain.
Date: May 2000
Creator: Blumoff, Sonja
Partner: UNT Libraries