Browsing by Subject "Carbon"

Now showing 1 - 5 of 5
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    Au nanoparticle assembly on cnts using flash induced solid-state dewetting
    (2015-04-28) Kulkarni, Ameya; Ryu, Jong Eun; Agarwal, Mangilal; Xie, Jian; Cheng, Ruihua
    Carbon Nanotubes (CNTs) are used extensively in various applications where substrate are required to be possessing higher surface area, porosity and electrical and thermal conductivity. Such properties can be enhanced to target a particular gas and biochemical for efficient detection when CNT matrix is functionalized with Nanoparticles (NPs). Conventional functionalization involves harsh oxidation repeated washing, filtration and sonication, which induce defects. The defects lead to hindered mobility of carriers, unwanted doping and also fragmentation of the CNTs in some cases. In this document we demonstrate functionalization of CNT with Au nanoparticles on a macro scale under dry and ambient condition using Xenon ash induced solid-state dewetting. A sputtered thin film was transformed into nanoparticles which were confirmed to be in a state of thermodynamic equilibrium. We worked on 3 nm, 6 nm, 9 nm, 15 nm, 30 nm initial thickness of thin films. Xenon ash parameters of energy, number of pulse, duration of pulse, duration of gap between consecutive pulses were optimized to achieve complete dewetting of Au thin films. 3 nm deposition was in the form of irregular nano-islands which were transformed into stable nanoparticles with a single shot of 10 J/cm2 of 2 ms duration. 6 nm and 9 nm deposition was in form of continues film which was also dewetted into stable nanoparticles with a single pulse but with an increased energy density of 20 J/cm2 and 35 J/cm2 respectively. In case of 15 nm and 30 nm deposition the thin film couldn't be dewetted with a maximum energy density of 50 J/cm2, it was observed that 3 and 4 pulses of 2 ms pulse duration and 2 ms gap duration with an energy density of 50 J/cm2 were required to completely dewet the thicker films. However irregularity was induced in the sizes of the NPs due to Ostwald ripening phenomenon which causes smaller particle within a critical difiusion length to combine and form a larger particle during or after dewetting process. For comparison, the Au thin films were also dewetted by a conventional process involving annealing of samples until the thin film was fully transformed into NPs and the size of NPs seized to grow. Scanning electron microscope (SEM) was used to characterize the samples. Thermodynamic stability of the particles was confirmed with statistical analyses of size distribution after every additional pulse.
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    Carbon and Phosphorus Cycling in Arabian Sea Sediments across the Oxygen Minimum Zone
    (Longdom Publishing, 2017-11-09) Filippelli, Gabriel M.; Cowie, Gregory L.; Earth and Environmental Sciences, School of Science
    Several studies have focused on carbon, oxygen, and phosphorus dynamics across the modern oxygen minimum zone (OMZ) to constrain how signals of modern systems get “locked in” upon burial. In this study, a sequential phosphorus fractionation technique was applied to surficial and sub-surface sediments from stations at depths spanning the OMZ on the Pakistan margin of the Arabian Sea in order to test the oxygen-carbon-phosphorus connection in modern marine sediments. Some early diagenetic loss of phosphorus compared to organic carbon was observed, but a significant portion of the released phosphorus was retained by uptake on oxyhydroxides and by the formation of an authigenic phosphorus-bearing phase. This process is unaffected by station location relative to the OMZ, and results in an effective organic carbon-to-reactive-phosphorus sediment ratio that is close to the average observed for open-ocean sediments, regardless of bottom water oxygen content.
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    Functional Effects of Carbon Nanoparticles on Barrier Epithelial Cell Function
    (2011-12) Banga, Amiraj; Stauffacher, Cynthia; Blazer-Yost, Bonnie; Witzmann, F. A. (Frank A.); Chernoff, Ellen; Belecky-Adams, Teri; Atkinson, Simon
    As mass production of carbon nanoparticles (CNPs) continues to rise, the likelihood of occupational and environmental exposure raises the potential for exposure‐related health hazards. Although many groups have studied the effects of CNPs on biological systems, very few studies have examined the effects of exposure of cells, tissues or organisms to low, physiologically relevant concentrations of CNPs. Three of the most common types of CNPs are single wall nanotubes (SWNT), multi wall nanotubes (MWNT) and fullerenes (C60). We used electrophysiological techniques to test the effects of CNP exposure (40 μg/cm2 – 4 ng/cm2) on barrier function and hormonal responses of well characterized cell lines representing barrier epithelia from the kidney (mpkCCDcl4) and airways (Calu‐3). mpkCCDcl4 is a cell line representing principal cell type that lines the distal nephron in an electrically tight epithelia that aids in salt and water homeostasis and Calu‐3 is one of the few cell lines that produces features of a differentiated, functional human airway epithelium in vivo. These cell lines respond to hormones that regulate salt/water reabsorption (mpkCCDcl4) and chloride secretion (Calu‐3). In mpkCCDcl4 cells, after 48 hour exposure, the transepithelial electrical resistance (TEER) was unaffected by high concentrations (40 – 0.4 μg/cm2) of C60 or SWNT while lower, more relevant levels (< 0.04 μg/cm2) caused a decrease in TEER. MWNT decreased TEER at both high and low concentrations. CNT exposure for 48 hour did not change the transepithelial ion transport in response to anti‐diuretic hormone (ADH). In Calu‐3 cells, after 48 h of exposure to CNPs, fullerenes did not show any effect on TEER whereas the nanotubes significantly decreased TEER over a range of concentrations (4 μg/cm2‐0.004 ng/cm2). The ion transport response to epinephrine was also significantly decreased by the nanotubes but not by fullerenes. To look at the effect of exposure times, airway cells were exposed to same concentrations of CNPs for 24 and 1h. While the 48 h and 24 h exposures exhibited similar effects, there was no effect seen after 1h in terms of TEER or hormonal responses. In both the cell lines the magnitude of the transepithelial resistance change does not indicate a decrease in cellular viability but would be most consistent with more subtle changes (e.g., modifications of the cytoskeleton or changes in the composition of the cellular membrane). These changes in both the cell lines manifested as an inverse relationship with CNP concentration, were further corroborated by an inverse correlation between dose and changes in protein expression as indicated by proteomic analysis. These results indicate a functional impact of CNPs on epithelial cells at concentrations lower than have been previously studied and suggest caution with regard to increasing CNP levels due to increasing environmental pollution.
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    Microbial nitrogen limitation in the mammalian large intestine
    (Springer Nature, 2018-12) Reese, Aspen T.; Pereira, Fátima C.; Schintlmeister, Arno; Berry, David; Wagner, Michael; Hale, Laura P.; Wu, Anchi; Jiang, Sharon; Durand, Heather K.; Zhou, Xiyou; Premont, Richard T.; Diehl, Anna Mae; O'Connell, Thomas M.; Alberts, Susan C.; Kartzinel, Tyler R.; Pringle, Robert M.; Dunn, Robert R.; Wright, Justin P.; David, Lawrence A.; Otolaryngology -- Head and Neck Surgery, School of Medicine
    Resource limitation is a fundamental factor governing the composition and function of ecological communities. However, the role of resource supply in structuring the intestinal microbiome has not been established and represents a challenge for mammals that rely on microbial symbionts for digestion: too little supply might starve the microbiome while too much might starve the host. We present evidence that microbiota occupy a habitat that is limited in total nitrogen supply within the large intestines of 30 mammal species. Lowering dietary protein levels in mice reduced their faecal concentrations of bacteria. A gradient of stoichiometry along the length of the gut was consistent with the hypothesis that intestinal nitrogen limitation results from host absorption of dietary nutrients. Nitrogen availability is also likely to be shaped by host-microbe interactions: levels of host-secreted nitrogen were altered in germ-free mice and when bacterial loads were reduced via experimental antibiotic treatment. Single-cell spectrometry revealed that members of the phylum Bacteroidetes consumed nitrogen in the large intestine more readily than other commensal taxa did. Our findings support a model where nitrogen limitation arises from preferential host use of dietary nutrients. We speculate that this resource limitation could enable hosts to regulate microbial communities in the large intestine. Commensal microbiota may have adapted to nitrogen-limited settings, suggesting one reason why excess dietary protein has been associated with degraded gut-microbial ecosystems.
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    Nitrogen, Phosphorus and Carbon Dynamics during Storms in a Glaciated Third-Order Watershed in the US Midwest
    (2013-08-22) Johnstone, Joseph A.; Vidon, Philippe G.; Tedesco, Lenore P.; Licht, Kathy J.
    The characterization of the nutrients nitrogen, phosphorus and carbon (NPC) export to streams during storms is an integral part of understanding processes affecting water quality. Despite the fact that excessive levels of these nutrients in the Mississippi River basin adversely affects water quality in the Gulf of Mexico, little research has been conducted on NPC dynamics during storms on larger (>20 km2) agriculturally dominated Midwestern watersheds. This project examined the storm export of nitrate, ammonium, total phosphorus, and dissolved organic carbon (DOC) in the upper Eagle Creek Watershed (UECW) (274 km2) in Central Indiana, USA. Water samples were collected during five winter and spring storms in 2007 and 2008 on the rising and falling limb of the hydrograph, in order to characterize NPC dynamics during storm events. Stream discharge and precipitation was monitored continuously, and major cations were used to examine changes in source water over the duration of the storm and assist in the determination of potential flowpaths. DOC, total P, and TKN (Total Kjeldahl Nitrogen) tended to peak with discharge, while nitrate usually exhibited a slight lag and peaked on the receding limb. Total phosphorus, NH3-, TKN, and DOC appear to be delivered to the stream primarily by overland flow. NO3--N appear to be delivered by a combination of tile drain and macropore flow. Overall UECW displayed smoother nutrient export patterns than smaller previously studied watersheds in the area suggesting that scale may influence nutrient export dynamics. Further research is underway on a 3000 km2 watershed in the area to further examine the role scale may play in nutrient export patterns.