The significance of ammonium adsorption on lower laguna madre (texas) sediments

The work presented in this dissertation focuses on + 4 NH in marine sediments and attempts to elucidate some of the specific pathways and processes affecting + 4 NH in coastal marine regions. The majority of work was conducted in the Laguna Madre estuary. A major feature of the estuary is the Gulf Intracoastal Waterway (GIWW) connecting the Lower Laguna Madre to Baffin Bay. Establishment of the GIWW has altered the hydrodynamics of the estuary, reduced seagrass coverage and increased sediment mobility resulting in frequent maintenance by the U.S. Army Corp of Engineers. GIWW sediment relocation associated with dredging is investigated to determine potential influence of + 4 NH release during resuspension. GIWW sediments are characterized by extremely high concentrations of porewater and exchangeable + 4 NH as well as reducing ions (millimolar HS-), and significant release hours to days after resuspension was observed during laboratory experiments. Using sediment + 4 NH porewater and exchangeable quantities, release potentials are calculated for a dredging event conducted in 1989 and results indicate that potential release from the dredging event are comparable to monthly inputs from intact GIWW and seagrass sediments. Reducing condition influence on + 4 NH adsorption dynamics was tested through resuspension experiments over a wide range of initial bulk concentrations in laboratory determined redox conditions. Significant increase in + 4 NH adsorption was observed in anoxic conditions. Calculations of the apparent partition coefficient (K*) were determined to be affected as well and implications to diagenetic models is explored. Observations in the laboratory were tested in field monitoring. Analysis of wind measurements established strong potential for interaction with sediments over the collection period. Measurements of water column + 4 NH , total suspended solids, and chlorophyll exhibited highest concentrations and correlation in areas close to the GIWW. Concentration measurements were combined with flux measurements in a model system designed to integrate field observations. Several model cases were considered including and excluding sediment resuspension. Model simulations including sediment resuspension maintained water column concentrations similar to field observations

Humans Optimize Ground Contact Time and Leg Stiffness to Minimize the Metabolic Cost of Running

Trained endurance runners appear to fine-tune running mechanics to minimize metabolic cost. Referred to as self-optimization, the support for this concept has primarily been collated from only a few gait (e.g., stride frequency, length) and physiological (e.g., oxygen consumption, heart rate) characteristics. To extend our understanding, the aim of this study was to examine the effect of manipulating ground contact time on the metabolic cost of running in trained endurance runners. Additionally, the relationships between metabolic cost, and leg stiffness and perceived effort were examined. Ten participants completed 5 × 6-min treadmill running conditions. Self-selected ground contact time and step frequency were determined during habitual running, which was followed by ground contact times being increased or decreased in four subsequent conditions whilst maintaining step frequency (2.67 ± 0.15 Hz). The same self-selected running velocity was used across all conditions for each participant (12.7 ± 1.6 km · h−1). Oxygen consumption was used to compute the metabolic cost of running and ratings of perceived exertion (RPE) were recorded for each run. Ground contact time and step frequency were used to estimate leg stiffness. Identifiable minimums and a curvilinear relationship between ground contact time and metabolic cost was found for all runners (r2 = 0.84). A similar relationship was observed between leg stiffness and metabolic cost (r2 = 0.83). Most (90%) runners self-selected a ground contact time and leg stiffness that produced metabolic costs within 5% of their mathematical optimal. The majority (n = 6) of self-selected ground contact times were shorter than mathematical optimals, whilst the majority (n = 7) of self-selected leg stiffness' were higher than mathematical optimals. Metabolic cost and RPE were moderately associated (rs = 0.358 p = 0.011), but controlling for condition (habitual/manipulated) weakened this relationship (rs = 0.302, p = 0.035). Both ground contact time and leg stiffness appear to be self-optimized characteristics, as trained runners were operating at or close to their mathematical optimal. The majority of runners favored a self-selected gait that may rely on elastic energy storage and release due to shorter ground contact times and higher leg stiffness's than optimal. Using RPE as a surrogate measure of metabolic cost during manipulated running gait is not recommended

The Glial Regenerative Response to Central Nervous System Injury Is Enabled by Pros-Notch and Pros-NFκB Feedback

Organisms are structurally robust, as cells accommodate changes preserving structural integrity and function. The molecular mechanisms underlying structural robustness and plasticity are poorly understood, but can be investigated by probing how cells respond to injury. Injury to the CNS induces proliferation of enwrapping glia, leading to axonal re-enwrapment and partial functional recovery. This glial regenerative response is found across species, and may reflect a common underlying genetic mechanism. Here, we show that injury to the Drosophila larval CNS induces glial proliferation, and we uncover a gene network controlling this response. It consists of the mutual maintenance between the cell cycle inhibitor Prospero (Pros) and the cell cycle activators Notch and NFκB. Together they maintain glia in the brink of dividing, they enable glial proliferation following injury, and subsequently they exert negative feedback on cell division restoring cell cycle arrest. Pros also promotes glial differentiation, resolving vacuolization, enabling debris clearance and axonal enwrapment. Disruption of this gene network prevents repair and induces tumourigenesis. Using wound area measurements across genotypes and time-lapse recordings we show that when glial proliferation and glial differentiation are abolished, both the size of the glial wound and neuropile vacuolization increase. When glial proliferation and differentiation are enabled, glial wound size decreases and injury-induced apoptosis and vacuolization are prevented. The uncovered gene network promotes regeneration of the glial lesion and neuropile repair. In the unharmed animal, it is most likely a homeostatic mechanism for structural robustness. This gene network may be of relevance to mammalian glia to promote repair upon CNS injury or disease

Kin-cohort estimates for familial breast cancer risk in relation to variants in DNA base excision repair, BRCA1 interacting and growth factor genes

BACKGROUND: Subtle functional deficiencies in highly conserved DNA repair or growth regulatory processes resulting from polymorphic variation may increase genetic susceptibility to breast cancer. Polymorphisms in DNA repair genes can impact protein function leading to genomic instability facilitated by growth stimulation and increased cancer risk. Thus, 19 single nucleotide polymorphisms (SNPs) in eight genes involved in base excision repair (XRCC1, APEX, POLD1), BRCA1 protein interaction (BRIP1, ZNF350, BRCA2), and growth regulation (TGFß1, IGFBP3) were evaluated. METHODS: Genomic DNA samples were used in Taqman 5'-nuclease assays for most SNPs. Breast cancer risk to ages 50 and 70 were estimated using the kin-cohort method in which genotypes of relatives are inferred based on the known genotype of the index subject and Mendelian inheritance patterns. Family cancer history data was collected from a series of genotyped breast cancer cases (N = 748) identified within a cohort of female US radiologic technologists. Among 2,430 female first-degree relatives of cases, 190 breast cancers were reported. RESULTS: Genotypes associated with increased risk were: XRCC1 R194W (WW and RW vs. RR, cumulative risk up to age 70, risk ratio (RR) = 2.3; 95% CI 1.3–3.8); XRCC1 R399Q (QQ vs. RR, cumulative risk up to age 70, RR = 1.9; 1.1–3.9); and BRIP1 (or BACH1) P919S (SS vs. PP, cumulative risk up to age 50, RR = 6.9; 1.6–29.3). The risk for those heterozygous for BRCA2 N372H and APEX D148E were significantly lower than risks for homozygotes of either allele, and these were the only two results that remained significant after adjusting for multiple comparisons. No associations with breast cancer were observed for: APEX Q51H; XRCC1 R280H; IGFPB3 -202A>C; TGFß1 L10P, P25R, and T263I; BRCA2 N289H and T1915M; BRIP1 -64A>C; and ZNF350 (or ZBRK1) 1845C>T, L66P, R501S, and S472P. CONCLUSION: Some variants in genes within the base-excision repair pathway (XRCC1) and BRCA1 interacting proteins (BRIP1) may play a role as low penetrance breast cancer risk alleles. Previous association studies of breast cancer and BRCA2 N372H and functional observations for APEX D148E ran counter to our findings of decreased risks. Due to the many comparisons, cautious interpretation and replication of these relationships are warranted

A sectoral perspective on international climate governance: Key findings and research priorities

This concluding article derives six major findings from the contributions to this special issue. First, the barriers and challenges to decarbonisation vary significantly across sectoral systems. Second, and similarly, the need and potential for the five functions of international governance institutions to contribute to effective climate protec- tion also vary widely. Third, while the pattern is uneven, there is a general undersupply of international cli- mate governance. Fourth, the sectoral analyses confirm that the UNFCCC and Paris Agreement play an important overarching role but remain limited in advancing effective sectoral governance. Fifth, while non-environmental institutions may present important barriers to decarbonisation, more synergistic effects are possible. Sixth, our sectoral approach provides a sound basis on which to identify sector-specific policy options. The paper then offers reflections on the merits and limitations of the sectoral approach, before identifying avenues for future research to further advance the agenda