Characterization of design and economic sensitivity of vapor phase carbon adsorption systems to environmental uncertainties

Vapor phase carbon adsorption systems are used to remove aromatics, aliphatics, and halogenated hydrocarbons. The adsorption capacity of granular activated carbon is reduced when environmental parameters (temperature, pressure, and humidity) interfere with homogeneous surface diffusion and pore distribution dynamics. The purpose of this study was to investigate the effects of parametric uncertainties in adsorption efficiency. ^ Modified versions of the Langmuir isotherm in conjunction with thermodynamic equations described gaseous adsorption of single component influent onto microporous media. Experimental test results derived from Wang et al. (1999) simulated adsorption kinetics while the Myer and monsoon Langmuir constant accounted for isothermal gas compression and energetic heterogeneity under thermodynamic equilibrium conditions. Responsiveness of adsorption capacity to environmental uncertainties was analyzed by statistical sensitivity and modeled by breakthrough curves. Results indicated that extensive fluctuations in adsorption capacity significantly reduced carbon consumption while isothermal variations had a pronounced effect on saturation capacity. ^

An investigation of location effect on trip production using artificial neural networks

As traffic congestion exuberates and new roadway construction is severely constrained because of limited availability of land, high cost of land acquisition, and communities' opposition to the building of major roads, new solutions have to be sought to either make roadway use more efficient or reduce travel demand. There is a general agreement that travel demand is affected by land use patterns. However, traditional aggregate four-step models, which are the prevailing modeling approach presently, assume that traffic condition will not affect people's decision on whether to make a trip or not when trip generation is estimated. Existing survey data indicate, however, that differences exist in trip rates for different geographic areas. The reasons for such differences have not been carefully studied, and the success of quantifying the influence of land use on travel demand beyond employment, households, and their characteristics has been limited to be useful to the traditional four-step models. There may be a number of reasons, such as that the representation of influence of land use on travel demand is aggregated and is not explicit and that land use variables such as density and mix and accessibility as measured by travel time and congestion have not been adequately considered. This research employs the artificial neural network technique to investigate the potential effects of land use and accessibility on trip productions. Sixty two variables that may potentially influence trip production are studied. These variables include demographic, socioeconomic, land use and accessibility variables. Different architectures of ANN models are tested. Sensitivity analysis of the models shows that land use does have an effect on trip production, so does traffic condition. The ANN models are compared with linear regression models and cross-classification models using the same data. The results show that ANN models are better than the linear regression models and cross-classification models in terms of RMSE. Future work may focus on finding a representation of traffic condition with existing network data and population data which might be available when the variables are needed to in prediction.

Effect of arginine and oscillatory calcium ion (II) on vascular response mediated via nitric oxide signaling in normal and salt sensitive hypertensive rat mesenteric arterioles

Hypertension, a major risk factor in the cardiovascular system, is characterized by an increase in the arterial blood pressure. High dietary sodium is linked to multiple cardiovascular disorders including hypertension. Salt sensitivity, a measure of how the blood pressure responds to salt intake is observed in more than 50% of the hypertension cases. Nitric Oxide (NO), as an endogenous vasodilator serves many important biological roles in the cardiovascular physiology including blood pressure regulation. The physiological concentrations for NO bioactivity are reported to be in 0-500 nM range. Notably, the vascular response to NO is highly regulated within a small concentration spectrum. Hence, much uncertainty surrounds how NO modulates diverse signaling mechanisms to initiate vascular relaxation and alleviate hypertension. Regulating the availability of NO in the vasculature has demonstrated vasoprotective effects. In addition, modulating the NO release by different means has proved to restore endothelial function. In this study we addressed parameters that regulated NO release in the vasculature, in physiology and pathophysiology such as salt sensitive hypertension. We showed that, in the rat mesenteric arterioles, Ca2+ induced rapid relaxation (time constants 20.8 ± 2.2 sec) followed with a much slower constriction after subsequent removal of the stimulus (time constants 104.8 ± 10.0 sec). An interesting observation was that a fourfold increase in the Ca 2+ frequency improved the efficacy of arteriolar relaxation by 61.1%. Our results suggested that, Ca2+ frequency-dependent transient release of NO from the endothelium carried encoded information; which could be translated into different steady state vascular tone. Further, Agmatine, a metabolite of L-arginine, as a ligand, was observed to relax the mesenteric arterioles. These relaxations were NO-dependent and occurred via &agr;-2 receptor activity. The observed potency of agmatine (EC50, 138.7 ± 12.1 ± μM; n=22), was 40 fold higher than L-arginine itself (EC50, 18.3 ± 1.3 mM; n = 5). This suggested us to propose alternative parallel mechanism for L-arginine mediated vascular relaxation via arginine decarboxylase activity. In addition, the biomechanics of rat mesentery is important in regulation of vascular tone. We developed 2D finite element models that described the vascular mechanics of rat mesentery. With an inverse estimation approach, we identified the elasticity parameters characterizing alterations in normotensive and hypertensive Dahl rats. Our efforts were towards guiding current studies that optimized cardiovascular intervention and assisted in the development of new therapeutic strategies. These observations may have significant implications towards alternatives to present methods for NO delivery as a therapeutic target. Our work shall prove to be beneficial in assisting the delivery of NO in the vasculature thus minimizing the cardiovascular risk in handling abnormalities, such as hypertension.

Mechanisms of Bicarbonate Use Influence the Photosynthetic Carbon Dioxide Sensitivity of Tropical Seagrasses

The photosynthetic bicarbonate () use properties of three widely distributed tropical seagrasses were compared using a series of laboratory experiments. Photosynthetic rates of Thalassia testudinum, Halodule wrightii, and Syringodium filiforme were monitored in an enclosed chamber while being subjected to shifts in pH and dissolved inorganic carbon. Specific mechanisms of seagrass use were compared by examining the photosynthetic effects of the carbonic anhydrase inhibitor acetazolamide (AZ). All seagrasses increased photosynthetic rates with reduced pH, suggesting a large effect of dissolved aqueous carbon dioxide (CO2(aq)). However, there was considerable interspecific variation in pH response. T. testudinum was highly sensitive, increasing photosynthetic rates by 100% as the pH was reduced from 8.2 to 7.4, whereas rates in H. wrightii and S. filiforme increased by only 20% over a similar range, and displayed prominent photosynthetic plateaus, indicating an increased capacity for use. Additional incubations that manipulated [] under constant [CO2(aq)] support these findings, as only H. wrightii and S. filiforme increased photosynthetic rates with increasing []. T. testudinum responded to AZ addition, indicating that carbonic anhydrase enzymes facilitate limited use. H. wrightii and S. filiforme showed no response to AZ, suggesting alternate, more efficient mechanisms of use. Estimated kinetic parameters, Ks(CO2) and Vmax, revealed interspecific variation and further support these conclusions. Variation in photosynthetic pH responses and AZ sensitivity indicate distinctions in the carbon use properties of seagrasses exposed to similar environmental conditions. These results suggest that not all seagrasses will similarly respond to future increases in CO2(aq) availability. Attention towards potential shifts in competitive interactions within multispecific seagrass beds is warranted.

Effect of Arginine and Oscillatory Ca2+ on Vascular Response Mediated Via Nitric Oxide Signaling in Normal and Salt Sensitive Hypertensive Rat Mesenteric Arterioles

Hypertension, a major risk factor in the cardiovascular system, is characterized by an increase in the arterial blood pressure. High dietary sodium is linked to multiple cardiovascular disorders including hypertension. Salt sensitivity, a measure of how the blood pressure responds to salt intake is observed in more than 50% of the hypertension cases. Nitric Oxide (NO), as an endogenous vasodilator serves many important biological roles in the cardiovascular physiology including blood pressure regulation. The physiological concentrations for NO bioactivity are reported to be in 0-500 nM range. Notably, the vascular response to NO is highly regulated within a small concentration spectrum. Hence, much uncertainty surrounds how NO modulates diverse signaling mechanisms to initiate vascular relaxation and alleviate hypertension. Regulating the availability of NO in the vasculature has demonstrated vasoprotective effects. In addition, modulating the NO release by different means has proved to restore endothelial function. In this study we addressed parameters that regulated NO release in the vasculature, in physiology and pathophysiology such as salt sensitive hypertension. We showed that, in the rat mesenteric arterioles, Ca2+ induced rapid relaxation (time constants 20.8 ± 2.2 sec) followed with a much slower constriction after subsequent removal of the stimulus (time constants 104.8 ± 10.0 sec). An interesting observation was that a fourfold increase in the Ca2+ frequency improved the efficacy of arteriolar relaxation by 61.1%. Our results suggested that, Ca2+ frequency-dependent transient release of NO from the endothelium carried encoded information; which could be translated into different steady state vascular tone. Further, Agmatine, a metabolite of L-arginine, as a ligand, was observed to relax the mesenteric arterioles. These relaxations were NO-dependent and occurred via α-2 receptor activity. The observed potency of agmatine (EC50, 138.7 ± 12.1 µM; n=22), was 40 fold higher than L-arginine itself (EC50, 18.3 ± 1.3 mM; n = 5). This suggested us to propose alternative parallel mechanism for L-arginine mediated vascular relaxation via arginine decarboxylase activity. In addition, the biomechanics of rat mesentery is important in regulation of vascular tone. We developed 2D finite element models that described the vascular mechanics of rat mesentery. With an inverse estimation approach, we identified the elasticity parameters characterizing alterations in normotensive and hypertensive Dahl rats. Our efforts were towards guiding current studies that optimized cardiovascular intervention and assisted in the development of new therapeutic strategies. These observations may have significant implications towards alternatives to present methods for NO delivery as a therapeutic target. Our work shall prove to be beneficial in assisting the delivery of NO in the vasculature thus minimizing the cardiovascular risk in handling abnormalities, such as hypertension.