Pressure swing adsorption: Development of an equilibrium theory for gas separations

Two versions of the pressure swing adsorption process are analysed as a means for purification of the light component of a binary feed of arbitrary composition. Local equilibrium with linear, uncoupled isotherms is assumed. The results of the analysis show that a critical pressure ratio must be exceeded before complete purification is possible and that this pressure ratio increases as the light-component content of the feed decreases. When clean up of the light component is complete, pressurization with product leads to higher light-component recoveries than pressurization with feed. This difference becomes large for small separation factors, small fractions of the light component in the feed, and large pressure ratios.     

Perception and Planning Architecture for Autonomous Ground Vehicles

By combining smart sensors and traversability grids with a JAUS-based component and messaging architecture, DARPA Grand Challenge finalist team CIMAR quickly developed a robust autonomous ground vehicle (AGV), a custom-built off-road vehicle. Key components included six smart sensors for detecting environmental conditions and reporting a priori data, a smart arbiter for fusing data from multiple smart sensors, and a reactive driver for providing real-time navigation planning and obstacle avoidance     

The roles of conserved carboxylate residues in IMP dehydrogenase and identification of a transition state analog

IMP dehydrogenase (IMPDH) catalyzes the oxidation of IMP to XMP with the concomitant reduction of NAD+; the enzyme is activated by K+. This reaction is the rate-limiting step in de novo guanine nucleotide biosynthesis. In order to identify functionally important residues in IMPDH, including those involved in substrate and K+ binding, we have mutated 11 conserved Asp and Glu residues to Ala in Escherichia coli IMPDH. The values of kcat, Km, and Ki for GMP, XMP, mizoribine 5'-monophosphate (MMP), and beta-methylene-tiazofurin adenine dinucleotide (TAD) were determined. Five of these mutations caused a significant change (>/=10-fold) in one of these parameters. The Asp248 --> Ala mutation caused 100-fold decrease in the value of kcat and a 25-fold increase in the value of Kii for TAD; these observations suggest that Asp248 is in the NAD+ binding site. The Asp338 --> Ala mutation caused a 600-fold decrease in the value of kcat, but only a 5-10-fold increase in the values of Km for IMP and Kis for IMP analogs, suggesting that Asp338 may be involved in acid-base catalysis as well as IMP binding. The remaining three residues, Asp13, Asp50, and Glu469, appear to be involved in K+ activation; these residues may be ligands at one or more K+ binding sites. Interestingly, changes in the values of Ki for MMP correlate with changes in kcat/KmKm of IMPDH, while no such correlation is observed for GMP, XMP, and TAD. This observation indicates that MMP is a transition state analog for the IMPDH reaction.     

Relationship between the genomic organization and the overlapping embryonic expression patterns of the zebrafish dlx genes

To understand the relationship between the expression and the genomic organization of the zebrafish dlx genes, we have determined the genomic structure of the dlx2 and dlx4 loci. This led to the identification of the zebrafish dlx1 and dlx6 genes, which are closely linked to dlx2 and dlx4, respectively. Therefore, the inverted convergent configuration of Dlx genes is conserved among vertebrates. Analysis of the expression patterns of dlx1 and dlx6 showed striking similarities to those of dlx2 and dlx4, respectively, the genes to which they are linked. Furthermore, the expression patterns of dlx3 and dlx7, which likely constitute a third pair of convergently transcribed genes, are indistinguishable. Thus, the overlapping expression patterns of linked Dlx genes during embryonic development suggest that they share cis-acting sequences that control their spatiotemporal expression. The evolutionary conservation of the genomic organization and combinatorial expression of Dlx genes in distantly related vertebrates suggest tight control mechanisms that are essential for their function during development.     

A case of paraquat poisoning and subsequent fatality presenting to an emergency department

Paraquat (1,1'-dimethyl-4,4'-dipyridylium) is an herbicide associated with both accidental and intentional ingestion, leading to severe and often fatal toxicity. Prognosis is largely dependent on the amount of paraquat absorbed. Rapid identification of the symptoms of paraquat toxicity (burns or ulceration at the site of ingestion or injection, acute respiratory distress, and renal failure) can facilitate early treatment intervention to limit absorption. We report a case of a 71-year-old man with a suicidal ingestion of paraquat 2 days prior to presentation. Serum paraquat levels, time elapsed since ingestion, and clinical symptoms all indicated poor prognosis. The patient developed severe respiratory distress and progressive renal failure, and died 6 days after admission to the hospital.     

Tyrosine kinases: modular signaling enzymes with tunable specificities

Cytoplasmic tyrosine kinases are composed of modular domains; one (SH1) has catalytic activity, the other two (SH2 and SH3) do not. Kinase specificity is largely determined by the binding preferences of the SH2 domain. Attaching the SH1 domain to a new SH2 domain, via protein-protein association or mutation, can thus dramatically change kinase function.     

Subcontinuations

Continuations have proven to be useful for implementing a variety of control structures, including exception handling facilities and breadth-first searching algorithms. However, traditional continuations are not useful in the presence of concurrency, because the notion of the rest of the computation represented by a continuation does not in general make sense. Traditional continuations can also be difficult to use in nonconcurrent settings, since their global nature is sometimes problematic. This article presents a new type of continuation, called asubcontinuation. Just as a traditional continuation represents the rest of a computation ¿from a given point in the computation, a subcontinuation represents the rest of asubcomputation ¿from a given point in the subcomputation. Subcontinuations may be used to control tree-structured concurrency by allowing nonlocal exits to arbitrary points in a process tree and allowing the capture of a subtree of a computation as a composable continuation for later use. In the absence of concurrency the localized control achievable with subcontinuations makes them more useful than traditional continuations.     

COPD: using nutrition to prevent respiratory function decline

Close to three-fourths of patients with chronic obstructive pulmonary disease (COPD) suffer from weight loss. Identifying a single cause for this is difficult, as several factors-including chronic mouth breathing, dyspnea, aerophagia, certain medications, and depression-often act in concert. Malnutrition can exacerbate symptoms of COPD by decreasing ventilatory muscle strength, exercise tolerance, and immunocompetence, and by increasing the risk of depression and anxiety. Goals of nutrition intervention are to prevent or reverse malnutrition without worsening the disease process and to improve respiratory function, thereby reducing morbidity and delaying mortality. Recommendations for intake of fats, carbohydrates, protein, and water must be individualized.     

The number and biodiversity of the parasites from small mammals in the evacuation area of the Chernobyl Nuclear Power Station

The study of the micromammalian parasite complexes in the Belorussian part of the evacuation zone of the Chernobyl nuclear station revealed 13 species of Coccidia and 30 species of ectoparasitic Arthropoda. Total increase of abundance and biodiversity of both parasites and their hosts was observed. The part of ectoparasites being epidemically hazardous was significantly increased. An analysis of a long-term dynamics of parasite abundance reveals their adaptation to new conditions in the Belorussia.