Nitrogen dynamics in primary successional soils on the Tanana River of interior Alaska

Thesis (Ph.D.) University of Alaska Fairbanks, 1988As succession determines the patterns of ecosystem development, it also provides a temporal framework in which to investigate the controls of nitrogen-cycling. The object of this study was to examine patterns of nitrogen-cycling within primary successional soils. Estimates of N mineralization, nitrogen fixation, and denitrification were made within open shrub, alder, and white spruce stands, representing early, mid-, and late successional stages, respectively. Net NH\sb4\sp+ mineralization and net nitrification, measured using the polyethylene bag technique, were significantly different between sites and among forest floors and mineral soils. The alder forest floor had the highest observed mineralization rates, $<$1-21 ug N $\cdot$ g dry soil\sp{-1} $\cdot$ d\sp{-1}, with the white spruce forest floor exhibiting rates of $<$1-2 and mineral soils $<$1. Seasonal patterns of N mineralization were more pronounced in the alder forest floor: high net NH\sb4\sp+ mineralization in early summer and high net nitrification in late summer. Immobilization of nitrogen was observed at all sites. Laboratory studies indicate temperature as a limiting factor of N mineralization in early and mid-successional stages, while both temperature and moisture were limiting in later succession. Laboratory studies suggest heterotrophic nitrification may be important in the alder forest floor. Denitrification activity was low to undetectable at all sites, the highest observed rate was in alder forest floor samples, 220 g N $\cdot$ ha\sp{-1} $\cdot$ d\sp{-1}. Potential denitrification was low, the alder forest floor exhibited the highest rate, 3.4 Kg N $\cdot$ ha\sp{-1} $\cdot$ d\sp{-1}. Laboratory studies indicated denitrification was more limited by carbon and NO\sb3\sp- than temperature or moisture. Nonsymbiotic nitrogen fixation was low to undetectable and highly variable. The highest observed nitrogenase activity was associated with alder root nodules, 163 Kg N $\cdot$ ha\sp{-1} $\cdot$ yr\sp{-1}

Sediment nitrification, denitrification, and nitrous oxide production in an arctic lake

Thesis (M.S.) University of Alaska Fairbanks, 198

Mechanistic studies on palladium-catalyzed carbon-nitrogen bond forming reactions

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2005.Vita.Includes bibliographical references (leaves 68-69).Precatalyst species present in a solution of Pd₂(dba)₃ and Xantphos were identified as Pd(Xantphos)(dba) and Pd(Xantphos)₂ by use of ³¹p NMR and independent syntheses. Pd(Xantphos)₂ was found to form at high ligand concentrations. To determine whether the formation of this species affected reaction rates, reaction calorimetry was used to explore the rate of the palladium-catalyzed coupling of 4-t-butylbromobenzene and morpholine using the ligand Xantphos at varying palladium to ligand ratios. It was found that catalyst activity is dramatically dependent on the concentration of ligand relative to palladium, due to formation of Pd(Xantphos)₂. Two plausible hypotheses for the low activity of Pd(Xantphos)₂ as a precatalyst are (1) a slow rate of dissociation of a ligand from the bis-ligated species, and (2) the high degree of insolubility of Pd(Xantphos)₂. Magnetization transfer experiments were used to probe the rate of dissociation of ligand for the bis-ligated species, and reaction calorimetry experiments were performed using the more soluble t-butylXantphos in comparison to Xantphos to determine whether the insolubility of' Pd(Xantphos)₂ causes it to have relatively low activity. It was found that solubility is not the main cause for the low activity of Pd(Xantphos)₂, and evidence was given to support the hypothesis that low activity results from the slow dissociation of a ligand from the bis-ligated species.by Liane M. Klingensmith.S.M

Menarche delay and menstrual irregularities persist in adolescents with type 1 diabetes

<p>Abstract</p> <p>Background</p> <p>Menarche delay has been reported in adolescent females with type 1 diabetes (T1DM), perhaps due to poor glycemic control. We sought to compare age at menarche between adolescent females with T1DM and national data, and to identify factors associated with delayed menarche and menstrual irregularity in T1DM.</p> <p>Methods</p> <p>This was a cross-sectional study and females ages 12- 24 years (n = 228) with at least one menstrual period were recruited during their outpatient diabetes clinic appointment. The National Health and Nutrition Examination Survey (NHANES) 2001-2006 data (n = 3690) for females 12-24 years were used as a control group.</p> <p>Results</p> <p>Age at menarche was later in adolescent females with T1DM diagnosed prior to menarche (12.81 +/- 0.09 years) (mean+/- SE) (n = 185) than for adolescent females diagnosed after menarche (12.17 0.19 years, <it>p = </it>0.0015) (n = 43). Average age of menarche in NHANES was 12.27 +/- 0.038 years, which was significantly earlier than adolescent females with T1DM prior to menarche (<it>p </it>< 0.0001) and similar to adolescent females diagnosed after menarche (<it>p </it>= 0.77). Older age at menarche was negatively correlated with BMI z-score (r = -0.23 <it>p = </it>0.0029) but not hemoglobin A1c (A1c) at menarche (r = 0.01, <it>p </it>= 0.91). Among 181 adolescent females who were at least 2 years post menarche, 63 (35%) reported usually or always irregular cycles.</p> <p>Conclusion</p> <p>Adolescent females with T1DM had a later onset of menarche than both adolescent females who developed T1DM after menarche and NHANES data. Menarche age was negatively associated with BMI z-score, but not A1c. Despite improved treatment in recent decades, menarche delay and high prevalence of menstrual irregularity is still observed among adolescent females with T1DM.</p

Cordon-Bleu Is an Actin Nucleation Factor and Controls Neuronal Morphology

SummaryDespite the wealth of different actin structures formed, only two actin nucleation factors are well established in vertebrates: the Arp2/3 complex and formins. Here, we describe a further nucleator, cordon-bleu (Cobl). Cobl is a brain-enriched protein using three Wiskott-Aldrich syndrome protein homology 2 (WH2) domains for actin binding. Cobl promotes nonbundled, unbranched filaments. Filament formation relies on barbed-end growth and requires all three Cobl WH2 domains and the extended linker L2. We suggest that the nucleation power of Cobl is based on the assembly of three actin monomers in cross-filament orientation. Cobl localizes to sites of high actin dynamics and modulates cell morphology. In neurons, induction of both neurites and neurite branching is dramatically increased by Cobl expression—effects that critically depend on Cobl's actin nucleation ability. Correspondingly, Cobl depletion results in decreased dendritic arborization. Thus, Cobl is an actin nucleator controlling neuronal morphology and development

Soil resources, microbial activity, and primary production across an agricultural ecosystem

Includes bibliographical references (pages 169-170).The degree to which soil resource availability is linked to patterns of microbial activity and plant productivity within ecosystems has important consequences for our understanding of how ecosystems are structured and for the management of systems for agricultural production. We studied this linkage in a 48-ha site in southwest Michigan, USA, that had been cultivated and planted to row crops for decades. Prior to seeding the site to genetically identical soybean plants (Glycine max) in early spring, we removed soil samples from ≈600 locations; plant biomass was harvested from these same locations later in the season. Soil samples were analyzed for physical properties (texture, bulk density), chemical properties (moisture, pH, total C, total N, inorganic N), and biological attributes (microbial biomass, microbial population size, respiration potential, and nitrification and N-mineralization potentials). Plant analyses included biomass and C and N contents. Soil resource variability across this long-cultivated site was remarkably high, as was variability in microbial activity and primary productivity. In almost all cases variability exhibited a strong spatially explicit structure: for most properties and processes > 50% of sample variance was spatially dependent at a scale of 5–60 m. Exceptions included microtopography, soil pH, and inorganic P, which were spatially dependent across the entire 1–1200 m range of separation distances examined in this study, and the culturable-bacteria population, which was not spatially autocorrelated at any scale examined. Both topographic relief and soil pH exhibited strongly nested structures, with autocorrelation occurring within two (topography) or more (pH) distinct ranges. Multiple regression analysis showed surprisingly little correlation between biological processes (soybean productivity, soil N turnover, soil respiration), and static soil properties. The best predictor of soybean biomass at late reproductive stages (r2 = 0.42) was a combination of nitrate N, bulk density, inorganic P, N-mineralization rates, and pH. Overall, results suggest a remarkable degree of spatial variability for a pedogenically homogeneous site that has been plowed and cropped mostly as a single field for > 100 yr. Such variability is likely to be generic to most ecosystems and should be carefully evaluated when making inferences about ecological relationships in these systems and when considering alternative sampling and management strategies

Ultra Large Castings to Produce Low Cost Aluminum Vehicle Structures

Through a cooperative effort with the U.S. Department of Energy (DOE) Office of Heavy Vehicle Technologies (OHVT), Alcoa is developing a casting process to produce ultra large thin wall components. The casting process is a low pressure, metal mold, multiport injection vertical casting process. The specific system for demonstration of the process is located at Alcoa's Technology Center and will be capable of producing parts extending 3 M long, 1.7 M wide and 0.4 M high. For example, single castings of car floor pan frames or side wall aperture structures are candidates for this installation. This shall provide a major opportunity to reduce the cost of lightweight transportation vehicle structures by (a) reducing the components or part count and (b) reducing the cost of assembly. To develop and demonstrate the process, an inner panel of the Chrysler minivan liftgate will be first produced on this system. Through computer analyses, the cast inner panel design was developed to satisfy both structural performance and casting process requirements. Currently, this is an 11 part assembly of steel components. At the time of this abstract, the numerous system components are in various phases of fabrication and site preparation is fully underway, with system shakedown beginning in the second quarter of 1999. Successful demonstration of caster system operation is anticipated to occur during the third quarter and production of a high quality product during the fourth quarter. Although the process is targeted toward reducing the cost of lightweight trucks, buses and autos, consideration is being given to application in the aircraft industry

Pediatric diabetes consortium T1D New Onset ( NeOn ) study: clinical outcomes during the first year following diagnosis

Objective There have been few prospective, multicenter studies investigating the natural history of type 1 diabetes ( T1D ) from the time of diagnosis. The objective of this report from the Pediatric Diabetes Consortium ( PDC ) T1D New Onset ( NeOn ) study was to assess the natural history and clinical outcomes in children during the first year after diagnosis of T1D . Research design and methods: Clinical measures from the first year following diagnosis were analyzed for 857 participants (mean age 9.1 yr, 51% female, 66% non‐Hispanic White) not participating in an intervention study who had a HbA1c result at 12 months. Results Mean HbA1c ± SD was 102 ± 25 mmol/mol (11.4 ± 2.3%) at diagnosis, 55 ± 12 mmol/mol (7.2 ± 1.1%) at 3 months, 56 ± 15 mmol/mol (7.3 ± 1.3%) at 6 months and 62 ± 16 mmol/mol (7.8 ± 1.5%) at 12 months from diagnosis. A severe hypoglycemic ( SH ) event occurred in 31 (4%) participants (44 events, 5.2 events per 100 person‐years). Diabetic ketoacidosis ( DKA ) not including diagnosis occurred in 10 (1%) participants (13 events, 1.5 events per 100 person‐years). Conclusions After onset of T1D , mean HbA1c reaches its nadir at 3–6 months with a gradual increase through 12 months. SH and DKA are uncommon but still occur during the first year with T1D . Data from large cohorts, such as the PDC T1D NeOn study, provide important insights into the course of T1D during the first year following diagnosis, which will help to inform the development of models to target future interventions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/107374/1/pedi12068.pd