Presentations of rings with non-trivial semidualizing modules

Let R be a commutative noetherian local ring. A finitely generated R-module C is semidualizing if it is self-orthogonal and satisfies the condition Hom_R(C,C) \cong R. We prove that a Cohen-Macaulay ring R with dualizing module D admits a semidualizing module C satisfying R\ncong C \ncong D if and only if it is a homomorphic image of a Gorenstein ring in which the defining ideal decomposes in a cohomologically independent way. This expands on a well-known result of Foxby, Reiten and Sharp saying that R admits a dualizing module if and only if R is Cohen--Macaulay and a homomorphic image of a local Gorenstein ring.Comment: 16 pages, uses XY-pic; v.2 reorganized, main theorem revised, examples adde

Decade-scale Nutrient Enrichment Effects on Wetland Plant Community Structure, Function, and Stability

Human activities have increased the supply of nitrogen (N) and phosphorus (P) to coastal waters worldwide, threatening coastal wetlands with excess nutrient loading and subsequent eutrophication. In this dissertation, I present results from two decade-scale fertilization experiments in a Sagittaria lancifolia dominated oligohaline marsh that examined the species-, community-, and ecosystem-level effects of nutrient enrichment. My objectives were to determine (1) which nutrient limits primary production, (2) how increased supply of the limiting nutrient affects plant community structure and function, both above- and belowground, and (3) whether nutrient over-enrichment compromises ecosystem stability. Overall, significant changes in plant growth occurred with N enrichment only. Aboveground, N enrichment stimulated primary production and altered plant tissue nutrient ratios, nutrient resorption efficiencies, and species dominance. Belowground, excess N simultaneously increased live root biomass accumulation in unexploited soil and reduced in situ live root standing crop. The rate of marsh elevation change was unaffected by nutrient enrichment due to an apparent compensatory effect on marsh accretionary processes whereby nutrient-induced shallow subsidence, attributed to reduced live root standing crop, was balanced by nutrient-enhanced soil accretion resulting from greater organic matter accumulation at the soil surface. In addition, the structural integrity of the soil matrix did not deteriorate under elevated nutrient conditions; decomposition rates were similar to control plots, and although root standing crop was reduced, the root system were evidently stronger as soil shear strength tended to increase rather than decrease. Based on these results, I conclude that this oligohaline marsh is N-limited, and that N enrichment beyond the assimilation capacity of the vegetation drives changes in plant community structure and function caused by altered plant nutrient cycling. Eutrophic conditions were both beneficial and detrimental to ecosystem function, and therefore represent an unlikely destabilizing mechanism in this coastal marsh and possibly others due to counterbalancing effects on plant growth above and below the soil surface. However, additional long-term research is required in a diverse range of habitats and environmental settings before broad-based, general conclusions concerning the effects of nutrient enrichment on coastal wetland stability can be made with a high degree of certainty

An Integrative Analysis of Reproduction and Stress in Free-Living Male Cottonmouths, Agkistrodon Piscivorus

I conducted an integrative field study on male cottonmouths (Agkistrodon piscivorus), a common pitviper of the southeastern United States, to investigate the evolution of contrasting mating patterns in North American pitvipers (bimodal and unimodal annual patterns) and resolve conflicting information about the pattern exhibited by the cottonmouth. I determined a unimodal late summer peak of testosterone (T) and a muted unimodal seasonal cycle of the sexual segment of the kidney (a secondary sexual characteristic), both of which were correlated with the single peak of spermatogenesis in late summer. I also conducted a study to determine diel and seasonal variation of corticosterone (CORT), the effect of captive handling on CORT, and the relationship between CORT and T after captive handling, and detected a significant elevation of CORT and a significant decrease of T after capture in male cottonmouths, as well as a significant negative correlation between CORT and T

Diving in Two Marine Lakes in Croatia

We describe the diving methods used for in-situ observations of the scyphozoan medusa, Aurelia sp., in two marine lakes on the island of Mljet, Croatia. Both lakes have a strong pycnocline at approximately 15 m. During this study (May, 2004) surface temperature was about 20o C; bottom temperature about 10o C. Visibility was 15 m to 30 m. Tide and currents were negligible. A dense resident population of Aurelia sp. and a predictable environment made this an ideal study site. Aurelia was most abundant in mid-water around the pycnocline. There were several dive objectives: specimen collection for laboratory analysis, population census, discrete plankton tows and direct observation of flow around swimming medusae. We used several methods for maintaining our orientation underwater including working from an anchor line, towing a tethered buoy, and use of a blue water rig. Because the environment was relatively benign we allowed the rig to drift free while the boat was standing by at a short distance. Often a tether was not required. This plan allowed the most freedom and provided an excellent reference throughout the dive

Seasonal variability in ichthyoplankton abundance and assemblage composition in the northern Gulf of Mexico off Alabama

Multiyear ichthyoplankton surveys used to monitor larval fish seasonality, abundance, and assemblage structure can provide early indicators of regional ecosystem changes. Numerous ichthyoplankton surveys have been conducted in the northern Gulf of Mexico, but few have had high levels of temporal resolution and sample replication. In this study, ichthyoplankton samples were collected monthly (October 2004–October 2006) at a single station off the coast of Alabama as part of a long-term biological survey. Four seasonal periods were identified from observed and historic water temperatures, including a relatively long (June–October) “summer” period (water temperature >26°C). Fish egg abundance, total larval abundance, and larval taxonomic diversity were significantly related to water temperature (but not salinity), with peaks in the spring, spring–summer, and summer periods, respectively. Larvae collected during the survey represented 58 different families, of which engraulids, sciaenids, carangids, and clupeids were the most prominent. The most abundant taxa collected were unidentified engraulids (50%), sand seatrout (Cynoscion arenarius, 7.5%), Atlantic bumper (Chloroscombrus chrysurus, 5.4%), Atlantic croaker (Micropogonias undulatus, 4.4%), Gulf menhaden (Brevoortia patronus, 3.8%), and unidentified gobiids (3.6%). Larval concentrations for dominant taxa were highly variable between years, but the timing of seasonal occurrence for these taxa was relatively consistent. Documented increases in sea surface temperature on the Alabama shelf may have various implications for larval fish dynamics, as indicated by the presence of tropical larval forms (e.g., fistularids, labrids, scarids, and acanthurids) in our ichthyoplankton collections and in recent juvenile surveys of Alabama and northern Gulf of Mexico seagrass habitats

Efficient syntheses of climate relevant isoprene nitrates and (1R,5S)-(−)-myrtenol nitrate

Here we report the chemoselective synthesis of several important, climate relevant isoprene nitrates using silver nitrate to mediate a ’halide for nitrate’ substitution. Employing readily available starting materials, reagents and Horner–Wadsworth–Emmons chemistry the synthesis of easily separable, synthetically versatile ‘key building blocks’ (E)- and (Z)-3-methyl-4-chlorobut-2-en-1-ol as well as (E)- and (Z)-1-((2-methyl-4-bromobut-2-enyloxy)methyl)-4-methoxybenzene has been achieved using cheap, ’off the shelf’ materials. Exploiting their reactivity we have studied their ability to undergo an ‘allylic halide for allylic nitrate’ substitution reaction which we demonstrate generates (E)- and (Z)-3-methyl-4-hydroxybut-2-enyl nitrate, and (E)- and (Z)-2-methyl-4-hydroxybut-2-enyl nitrates (‘isoprene nitrates’) in 66–80% overall yields. Using NOESY experiments the elucidation of the carbon–carbon double bond configuration within the purified isoprene nitrates has been established. Further exemplifying our ‘halide for nitrate’ substitution chemistry we outline the straightforward transformation of (1R,2S)-(−)-myrtenol bromide into the previously unknown monoterpene nitrate (1R,2S)-(−)-myrtenol nitrate

Omnivory by the Small Cosmopolitan Hydromedusa Aglaura Hemistoma

We investigated the feeding of the small hydromedusa, Aglaura hemistoma (bell diameter \u3c 4 mm), to determine if it occupies a trophic position similar to that of large medusae. Feeding was examined using gut-content analysis of preserved and unpreserved medusae and by analyzing prey-capture events using microvideographic techniques. Analysis of gut contents and prey-capture events revealed that A. hemistoma fed heavily on protistan prey and that it possessed a prey-capture mechanism, specifically a feeding current,that is effective at entraining and capturing protists with low motility. We suggest that many species of small hydromedusae possess prey-capture mechanisms adapted to capture small protistan prey and that many of these small hydromedusae feed omnivorously on microplanktonic prey. The trophic roles of small hydromedusae in different systems are not understood and more studies are needed. However, based on their often high abundances and the cosmopolitan nature, if small hydromedusae are primarily omnivores, they need to be considered when estimating the impact of zooplankton on primary production and, more generally, protistan community dynamics