Size exclusion chromatographic approach for the evaluation of processes for upgrading heavy petroleum

A new application of size exclusion chromatography for the evaluation of processes for upgrading heavy crudes is described. The comparison of the elution curves of a feedstock of heavy crude, selected for an upgrading process, is made with the resulting products of the process. A quantitative assessment of the extent of the improvement as a result of the hydrogenation in the crude is presented by defining an algorithm which measures the conversion of material up to 550 °C. The defined conversion is correlated with conventional crude properties and there is a linear relation between the conversion obtained by s.e.c. and certain selected properties. The results for a number of products are included and the relation between conversion and process conditions is discussed.     

The role of nickel in hydrodesulphurisation catalysts

The acidity and activity of promoted (with NiO) and unpromoted MoO₃/A1₂O3 catalysts were studied by ammonia adsorption, titration using acid/base colour indicators, and thiophene hydrodesulphurisation. The incorporation of nickel into supported MoO₃ produced significant changes in activity, which was attributed to changes in the number and strength of the acid sites. Specifically, the nickel decreased the concentration of highly acid sites and increased the number of sites with intermediate acidity in the oxide catalyst. At the same time, the nickel markedly increased the steady state catalytic activity but decreased the initial activity. Carbon and sulphur analyses, as well as acid site concentration of used catalysts, suggest that this behaviour may be associated with modifications brought about by nickel on MoS₂ crystallite growth and on deactivation by carbon deposition. These suggestions are found to be consistent with other effects attributed to the promoter, such as hydrogen spill-over and p-semiconductivity.     

Constructing and analyzing the fitness landscape of an experimental evolutionary process

Iterative saturation mutagenesis (ISM) is a promising approach to more efficient directed evolution, especially for enhancing the enantioselectivity and/or thermostability of enzymes. This was demonstrated previously for an epoxide hydrolase (EH), after five sets of mutations led to a stepwise increase in enantioselectivity. This study utilizes these results to illuminate the nature of ISM, and identify the reasons for its operational efficacy. By applying a deconvolution strategy to the five sets of mutations and measuring the enantioselectivity factors (E) of the EH variants, DeltaDeltaG( not equal) values become accessible. With these values, the construction of the complete fitness-pathway landscape is possible. The free energy profiles of the 5!=120 evolutionary pathways leading from the wild-type to the best mutant show that 55 trajectories are energetically favored, one of which is the originally observed route. This particular pathway was analyzed in terms of epistatic effects operating between the sets of mutations at all evolutionary stages. The degree of synergism increases as the stepwise evolutionary process proceeds. When encountering a local minimum in a disfavored pathway, that is, in the case of a dead end, choosing another set of mutations at a previous stage puts the evolutionary process back on an energetically favored trajectory. The type of analysis presented here might be useful when evaluating other mutagenesis methods and strategies in directed evolution.     

The Influence of Surface Anisotropy Crystalline Structure on Wetting of Sapphire by Molten Aluminum

The wetting of sapphire by molten aluminum was investigated by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) at PO₂ <10^?15 Pa under Ar atmosphere. This study focuses on sapphire crystalline structure and its principle to the interface. The planes “a” and “b” are oxygen terminated structures and wet more by Al, whereas the “c” plane is an aluminum terminated structure. A wetting transition at 1273 K (1000 °C) was obtained and a solid surface tension proves the capillarity trends of the couple.     

Finite element Euler computations in three dimensions

An explicit finite element solution procedure for the three dimensional Euler equations is presented. The solution domain is automatically meshed using a tetrahedral mesh generator which is an extension of our previous two dimensional work. Several examples are included to illustrate the performance of the generator and solver. An adaptive mesh regeneration procedure is used for the first time in three dimensions.     

Collecting and Analyzing Data from Distributed Control Programs

This paper describes a set of tools that allows a developer to instrument a C/C++ program to log data at run-time and then analyze that data to verify correct behavior. The logging tools provide the developer with a means to log a variety of different data to a variety of different outputs. They also allow for synchronized logging of data from distributed programs. One logging output option is an SQL database. We have developed a set of analysis tools that retrieve data from the database to answer common developer questions. The analysis tools use an interval temporal logic to frame database queries. The data logging tools are fully implemented and performance results are given in this paper. The data analysis tools are currently being tested on data from real NASA applications.     

Apparent violation of the radiant exposure reciprocity law in interline CCDs

We analyze in detail the apparent violation of the reciprocity law that occurs for an interline CCD array owing to its responsivity that varies with exposure time, and we investigate other parameters having an influence on this variation, such as the numerical aperture of the system or the illumination wavelength. The variation can be explained from a qualitative point of view by the charge leakage that occurs from the sense region to the register region during readout time. This change of the responsivity can be avoided either by using a synchronized external shutter or by limiting the numerical aperture while keeping relatively high exposure times. A detailed characterization for each particular CCD model must be carried out if it is to be employed in low-uncertainty radiometric measurements.     

Case Study: Impact of Reservoir Stratification on Interflow Travel Time

A case study is presented on the relation between interflow travel time and reservoir stratification. A simulation model is calibrated and validated for the Wachusett Reservoir in Massachusetts. The Reservoir has a major controlled inflow which traverses the reservoir as an interflow. The model is used with a range of alternate inflow schedules and the resulting travel time of the interflow is examined. The inflow density is within the range of densities found in the reservoir thermocline and the inflow rate is sufficient to maintain a continuous interflow. Under these conditions it is found that a linear relation exists between the average interflow travel time, as measured by the arrival of a specified fraction of interflow water at the outlet, and the degree of stratification, as measured by the maximum difference in reservoir thermocline temperature, at the initiation of the inflow. The results may be useful for operation of the reservoir under study subject to continued validation of the simulation model used.     

Peroxynitrite increases the degradation of aconitase and other cellular proteins by proteasome

We report that exposure of aconitase to moderate concentrations of peroxynitrite, 3-morpholinosydnonimine (SIN-1; a superoxide- and nitric oxide-liberating substance), or hydrogen peroxide, inhibits the enzyme and enhances susceptibility to proteolytic digestion by the isolated 20 S proteasome. Exposure to more severe levels of oxidative stress, from these same agents, causes further inhibition of the enzymatic activity of aconitase but actually decreases its proteolytic breakdown by proteasome. It should be noted that the superoxide and nitric oxide liberated by SIN-1 decomposition react to form a steady flux of peroxynitrite. S-Nitroso-N-acetylpenicillamine, a compound that liberates nitric oxide alone, causes only a small loss of aconitase activity (25% or less) and has no effect on the proteolytic susceptibility of the enzyme. Proteasome also seems to be the main protease in cell lysates that can degrade aconitase after it has been oxidatively modified by exposure to peroxynitrite, SIN-1, or hydrogen peroxide. Using cell lysates isolated from K562 cells treated for several days with an antisense oligodeoxynucleotide to the initiation codon region of the C2 subunit of proteasome (a treatment which diminishes proteasome activity by 50-60%), the enhanced degradation of moderately damaged aconitase was essentially abolished. Other model proteins as well as complex mixtures of proteins, such as cell lysates, also exhibit enhanced proteolytic susceptibility after moderate SIN-1 treatment. Therefore we conclude that peroxynitrite reacts readily with proteins and that mild modification by peroxynitrite results in selective recognition and degradation by proteasome.