acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

Cyclooxygenase (COX) isoforms, COX1 and COX2, generate renal prostaglandin E2, prostaglandin I2 and thromboxane A2. Nonselective COX inhibitors decrease prostaglandin vasodilatory influence on total renal and vasa recta blood flow, especially in resistance vessels preconstricted with angiotensin II (AngII). While this signifies prostaglandin regulation of renal blood flow, each COX isoform's regulatory contribution remains unresolved. The significance of each enzyme can potentially be discriminated during conditions that selective regulate isoform expression. Angiotensin converting enzyme (ACE) inhibition selectively increases cortical COX2 and dietary salt restriction differentially increases cortical COX2 while decreasing cortical COX-1 Interestingly, sodium-restricted animals show normal or only slightly lowered renal hemodynamic parameters despite high plasma renin activity. It remains unresolved whether the concurrently augmented COX-2 expression in sodium restricted animals yield vasodilatory influence to maintain renal hemodynamic parameters by opposing or modifying AngII effects. Hence, we tested the hypothesis that COX-2 inhibitor effects on renal hemodynamic and excretory function are increased in proportion to AngII activity Renal clearance experiments were conducted in four groups of anesthetized Sprague-Dawley rats: those characterized by attenuated AngII activity established by acute captopril either (1) alone (aACEi) or (2) in combination with chronic captopril pretreatment (cACEi); in contrast to rats fed (3) normal (NS) or (4) low (LS) sodium diet, respectively. Acute COX-2 inhibition with nimesulide (NMSLD) was thereafter used to investigate the activity of basal or augmented cortical COX-2 expression. NMSLD did not alter mean arterial blood pressure in any group but decreased renal plasma flow(RPF), cortical blood flow (CBF) and glomerular filtration rate (GFR) in the LS and cACEi groups. In contrast, medullary blood flow (MBF) was significantly decreased by COX-2 inhibition in all groups. Absolute (UNalpha) and fractional (FENalpha) sodium excretion rates were unchanged by NMSLD except in the LS group. These results demonstrate an augmented COX-2-mediated vasodilatation that is AngII-independent in contrast to an augmented COX-2-mediated sodium excretion where AngII activity is requisite. Further, COX-2 effects on MBF are neither AngII-dependent nor dependent on changes in cortical microvascular responses. Therefore, COX-2 continually regulates MBF and responsively limits AngII prohypertensinogenic effects on RPF, CBF, GFR, UNalpha and FENalpha / acase@tulane.edu

This study considers the contemporary use of decimal based floating point representations. Because decimal representations do not require conversion of values between decimal and binary based systems, they are preferred over traditional binary systems. Floating point base conversions require considerable computational effort and frequently result in values that cannot be represented finitely within the target representation. The causes of base conversion error between decimal and binary systems are examined and the superiority of the decimal system for modeling arbitrary rational numbers is demonstrated Decimal based systems have, unfortunately, long been considered as deficient in their representational error behavior when compared with binary systems of similar storage size and range. This study proposes an alternative format to the traditional encodings assumed for a base ten floating point implementation. This encoding is termed the Decimal Floating Point (DFP) format. The DFP format is evaluated with the traditional measures of floating point accuracy and compared to a binary system of comparable size and range. Results from McKeeman's Maximum and Average Relative Representational Error (MRRE and ARRE) analyses, Brent's RMS error evaluation, Matula's ratio of significance space and gap functions, and Brown and Richman's exponent range estimates are extended to accommodate the DFP format. The error performance of the DFP format is shown to be equal or superior to that of a comparable binary representation while exponent range achieves 83% that of the binary case Implementation of the DFP system is demonstrated and the impact shown to be confined to the Arithmetic and Logic Unit of a computer CPU / acase@tulane.edu

acase@tulane.edu

Sulfated zirconia was prepared using a two-step sol-gel method. The isomerization of n-butane was used as a probe reaction. The formation of coke on sulfated zirconia during the reaction was quantified as a function of time on stream and temperature using a TGA/FTIR technique. The formation of coke was essentially linear with time on stream when the isomerization reaction was performed at 200$\sp\circ$C. When the amount of coke deposited reached 0.04 wt%, the catalytic isomerization activity was observed to decrease to 10% of its initial value. When the reaction temperature was increased, the higher selectivity to cracked products resulted in an increase in coke formation and a higher rate of deactivation. The deactivated sulfated zirconia catalyst could be completely regenerated in O$\sb2$ and in air at 450$\sp\circ$C by selectively burning off the coke. Changes in the surface structure of sulfated zirconia were studied using nitrogen adsorption, XRD, TGA and in-situ DRIFTS following deactivation and regeneration of the catalyst. The physical properties of sulfated sol-gel zirconia were unchanged as a result of reaction and catalyst regeneration. Both Bronsted and Lewis acid sites as determined using pyridine adsorption at 100$\sp\circ$C were observed on sulfated zirconia. Only Lewis acid sites were observed on non-sulfated zirconia. The ratio of Bronsted to Lewis acid sites was found to be strongly dependent on catalyst pretreatment temperature prior to reaction. The Bronsted to Lewis acid ratio was observed to decrease from a value of 0.466 to 0.127 following the removal of the catalytically active surface sulfur. The total catalyst acidity was observed to decrease only slightly following removal of this surface sulfur species. An infrared band, centered at 1370 cm$\sp{-1}$, was observed for the catalytically active material. This band appeared following activation in N$\sb2$ at 375$\sp\circ$C and was assigned to S=O. An in-situ DRIFTS accessory and heatable sample cell was designed and constructed. The cell and accessory are simple, ease to make, and inexpensive. The optical system consists of only one spherical mirror and two flat mirrors. The specular reflectance from the optical lense was excluded by manipulating the mirrors such that reflectance by the window did not enter the detector / acase@tulane.edu

This dissertation is an analysis of Maya ceramics from the Maya 'collapse' (ca. A.D. 800 to 1250) from the Upper Belize River Valley of western Belize. Ceramic assemblages were compared across space and through time in terms of overall assemblage diversity and the style of individual artifacts Terminal Classic and Early Postclassic ceramics were found to be more common at sites of varying sizes than is currently recognized. Monumental architecture was used sparsely in the Terminal Classic-Early Postclassic, but differences in the architectural context of the ceramic samples were not clearly correlated with differences in the number of forms or types present. Similarly, the proportions of elaborate ceramics did not vary substantially between sites. Ceramic assemblage diversity did not increase markedly, suggesting substantial production continuity between the Terminal Classic and Early Postclassic in the Belize Valley Stylistically, however, there are significant changes. Locally-produced ceramics showed hybridization with the styles of adjacent areas rather than the replacement of local styles by foreign ones. Imports were generally rare at all sites in the valley, but due to a shifting of power to the north in the Terminal Classic-Early Postclassic, imports and imitations of Peten ceramics were more common in earlier contexts, whereas Yucatan-influenced types were found in the later ones The ceramics of the Belize Valley suggest that the area experienced subsistence and cuisine changes in the Terminal Classic-Early Postclassic similar to those in other regions (especially the Peten). Vessels were smaller and lighter and new forms (e.g., griddles, chile graters, net sinkers) were introduced. Religious and ideological changes linked to increasing influence from Central Mexico, the Gulf Coast, and Yucatan are discussed. The survival of Belize Valley sites into the Postclassic may have been related to trade and specialized agricultural production, especially the production of cacao. The abandonment of monumental architecture at the end of the Classic and the style and distribution of ritual ceramics and finewares suggest that the Terminal Classic-Early Postclassic was a time of reduced sociopolitical complexity in the Belize Valley, but the period does not represent the collapse of Maya civilization more generally / acase@tulane.edu

acase@tulane.edu

acase@tulane.edu