Decay estimates for variable coefficient wave equations in exterior domains

In this article we consider variable coefficient, time dependent wave equations in exterior domains. We prove localized energy estimates if the domain is star-shaped and global in time Strichartz estimates if the domain is strictly convex.Comment: 15 pages. In the new version, some typos are fixed and a minor correction was made to the proof of Lemma 1

Characterization of the Arabidopsis thaliana acetyl-CoA synthetase putative carboxylate binding pocket

Acetyl-CoA synthetase catalyzes the activation of acetate by the acetylation of the thiol group of Coenzyme A, while hydrolyzing ATP to AMP and pyrophosphate. The Arabidopsis thaliana acetyl-CoA synthetase (atACS) was compared to other acyl-CoA synthetases, and was computationally modeled on the available crystal structures of the Saccharomyces cerevisiae ACS1 and Salmonella enterica ACS. This allowed the identification of the residues that make up the putative carboxylate binding pocket residues. To further understand substrate selectivity and binding within the putative carboxylate binding pocket, selected residues were mutated to resemble the homologous residues in the Pseudomonas chlororaphis isobutyryl-CoA synthetase. Four residues (Ile323, Thr324, Val399, and Trp427) were identified that are proposed to form the carboxylate binding pocket. One residue, Trp427 was found to be the primary residue in determining the chain length of acceptable carboxylate substrates. By combing two mutations (Val399Ala, and Trp427Gly) the enzyme was able to utilize butyrate with a catalytic efficiency similar to the wild-type enzyme with acetate. Circular dichroism (CD) was used to evaluate the secondary structure of the wild-type atACS and the mutated variants. The CD spectra showed no difference between the mutated variants and the wild-type and indicated the enzyme is largely composed of α-helices

Ecological restoration alters nitrogen transformations in a ponderosa pine-bunchgrass ecosystem

Ponderosa pinebunchgrass ecosystems of the western United States were altered following Euro-American settlement as grazing and fire suppression facilitated pine invasion of grassy openings. Pine invasion changed stand structure and fire regimes, motivating restoration through forest thinning and prescribed burning. To determine effects of restoration on soil nitrogen (N) transformations, we replicated (0.25-ha plots) the following experimental restoration treatments within a ponderosa pinebunchgrass community near Flagstaff, Arizona: (1) partial restorationthinning to presettlement conditions, (2) complete restorationremoval of trees and forest floor to presettlement conditions, native grass litter addition, and a prescribed burn, and (3) control. Within treatments, we stratified sampling to assess effects of canopy cover on N transformations. Forest floor net N mineralization and nitrification were similar among treatments on an areal basis, but higher in restoration treatments on a mass basis. In the mineral soil (015 cm), restoration treatments had 23 times greater annual net N mineralization and 35 times greater annual net nitrification than the control. Gross N transformation measurements indicate that elevated net N mineralization may be due to increased gross N mineralization, while elevated net nitrification may be due to decreased microbial immobilization of nitrate. Net N transformation rates beneath relict grassy openings were twice those beneath postsettlement pines. These short-term (1 yr) results suggest that ecological restoration increases N transformation rates and that prescribed burning may not be necessary to restore N cycling processes

Slow carbon and nutrient accumulation in trees established following fire exclusion in the southwestern United States.

Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests

Stand-replacing wildfires increase nitrification for decades in southwestern ponderosa pine forests.

Stand-replacing wildfires are a novel disturbance within ponderosa pine (Pinus ponderosa) forests of the southwestern United States, and they can convert forests to grasslands or shrublands for decades. While most research shows that soil inorganic N pools and fluxes return to pre-fire levels within a few years, we wondered if vegetation conversion (ponderosa pine to bunchgrass) following stand-replacing fires might be accompanied by a long-term shift in N cycling processes. Using a 34-year stand-replacing wildfire chronosequence with paired, adjacent unburned patches, we examined the long-term dynamics of net and gross nitrogen (N) transformations. We hypothesized that N availability in burned patches would become more similar to those in unburned patches over time after fire as these areas become re-vegetated. Burned patches had higher net and gross nitrification rates than unburned patches (P < 0.01 for both), and nitrification accounted for a greater proportion of N mineralization in burned patches for both net (P < 0.01) and gross (P < 0.04) N transformation measurements. However, trends with time-after-fire were not observed for any other variables. Our findings contrast with previous work, which suggested that high nitrification rates are a short-term response to disturbance. Furthermore, high nitrification rates at our site were not simply correlated with the presence of herbaceous vegetation. Instead, we suggest that stand-replacing wildfire triggers a shift in N cycling that is maintained for at least three decades by various factors, including a shift from a woody to an herbaceous ecosystem and the presence of fire-deposited charcoal

Faith Narrative and Ethical Practice in the Literacy Field

What is the intersection between being a person of faith and a literacy teacher? How do educators experience literacy instruction when trying to connect their faith and practice? Using the lens of researchers Clandinin and Connelly (2000) these questions were explored from the perspective and experience of one of the co-authors. Three themes of Christian pedagogy emerged from the results of this narrative inquiry: the power of words, the power of forgiveness, and the power of voice

The Economics-Security Nexus in the US-China Trade Conflict decoupling dilemmas

For more than two decades, China was enmeshed in transnational trade and investment networks. The complex interdependence that characterised the relationship between the United States and China is now threatened by policies that incentivise decoupling, including the partial unwinding of multinational supply chains. Since 2018 the ‘trade war’ between the US and China has taken on elements of a ‘tech war’, in which national security concerns replace economic logic. The area for win–win gains is reduced, as both countries pursue policies of greater technological autonomy. The bilateral rift creates challenges for companies and third parties who have no wish to take sides and complicates APEC’s goal to promote growth and accelerate regional economic integration