THERMAL RADIATION EFFECTS ON THE COMBUSTION BEHAVIOR OF POROUS CHAR PARTICLES

The effects of thermal radiation on the pseudosteady state and transient behavior of porous char particles exposed to an oxygen containing environment are investigated. The numerical simulation results show that particles that do not interchange radiant energy with their environment are characterized by wider ambient temperature regions where multiple steady states exist, higher combustion rates, and lower burning times     

ON THE DYNAMICS OF THE COMBUSTION OF SINGLE CHAR PARTICLES

Diffusion and reaction models of varying complexity are used to study the stability of the combustion of single char particles. In contrast to past studies which have considered only the reaction of carbon with oxygen, both the heterogeneous reactions of carbon with oxygen and carbon dioxide and the homogeneous oxidation of carbon monoxide are taken into account in the formulation of the mathematical models. Emphasis is placed on the investigation of the feasibility of occurrence of oscillatory combustion. Our results show that high rates of the C-O₂ reaction and high concentration of O₂ in the ambient favor the occurrence of multiple steady states and oscillatory solutions, but the appearance of oscillatory instability is suppressed by the homogeneous reaction in the gas phase and the presence of CO and CO₂ in the ambient. The parametric investigation of the problem reveals, in agreement with the results of past studies, that the heat capacity of the porous solid, the Lewis number, and the thickness of the stagnant film are three key parameters for the occurrence of the oscillatory response of the system. Reasonably large values of solid heat capacity practically eliminate the possibility of oscillatory combustion, but an appropriate combination of large values of stagnant film thickness and small Lewis numbers may offset the effect of solid heat capacity     

Circulating antibodies against p53 protein in patients with ovarian carcinoma. Correlation with clinicopathologic features and survival

BACKGROUND: Genetic alterations of the p53 tumor suppressor protein are the most frequent molecular events in human carcinogenesis. For as yet unknown reasons, mutant p53 often acts as an immunogen for autoantibody generation. These autoantibodies can be detected in the serum of cancer patients. The presence of such antibodies has been identified in a subset of patients with ovarian carcinoma, but their clinical significance has not been investigated. METHODS: Serum samples from patients with ovarian carcinoma were quantitatively analyzed for the presence of p53 autoantibodies with a time-resolved immunofluorometric procedure. Tumor p53 overexpression was assessed by immunohistochemical analysis of tissue sections. Kaplan-Meier survival curves were calculated for p53 antibody positive and negative patients, and the Cox model was used to evaluate the strength of the associations between the presence of serum p53 antibodies and cancer relapse or death, and also between the presence of such antibodies and other clinicopathologic features. RESULTS: p53 antibodies were detected in the serum of 41 of 174 patients with ovarian carcinoma (24%). Antibody levels ranged from a few hundred to 9 x 10(6) arbitrary Units/L, and fluctuated during the course of the disease. p53 antibody positive patients tended to have tumors overexpressing p53, but the association between the two parameters was not statistically significant (P = 0.13). There was also no association between the presence of p53 antibodies and clinical stage, tumor histologic type, or overall patient survival. However, these antibodies were more frequently present in patients older than 50 years (P = 0.001), in patients with moderately or poorly differentiated tumors (P = 0.001), and in patients who received chemotherapy (P = 0.015), and who suffered relapse after surgery (P = 0.018). In univariate analysis, p53 antibody positive patients were at an increased risk for relapse but not death. In multivariate analysis, the differences in disease free and overall survival between patients who were p53 antibody positive or negative were not statistically significant. CONCLUSIONS: p53 autoantibodies are found frequently in the serum of patients with ovarian carcinoma. The presence of such autoantibodies was associated with older patient age, more aggressive tumors, and reduced patient disease free survival. In multivariate analysis the prognostic value of p53 autoantibodies was not statistically significant.     

Numerical calculation of diffraction coefficients of genericconducting and dielectric wedges using FDTD

Classical theories such as the uniform geometrical theory of diffraction (UTD) utilize analytical expressions for diffraction coefficient for canonical problems such as the infinite perfectly conducting wedge. We present a numerical approach to this problem using the finite-difference time-domain (FDTD) method. We present results for the diffraction coefficient of the two-dimensional (2-D) infinite perfect electrical conductor (PEC) wedge, the 2-D infinite lossless dielectric wedge, and the 2-D infinite lossy dielectric wedge for incident TM and TE polarization and a 90° wedge angle. We compare our FDTD results in the far-field region for the infinite PEC wedge to the well-known analytical solutions obtained using the UTD. There is very good agreement between the FDTD and UTD results. The power of this approach using FDTD goes well beyond the simple problems dealt with in this paper. It can, in principle, be extended to calculate the diffraction coefficients for a variety of shape and material discontinuities, even in three dimensions     

A variable diffusivity shrinking-core model and its application to the direct sulfation of limestone

A variable diffusivity shrinking-core model that allows for temporal and spatial variation of the effective diffusivity in the solid product layer was developed in this study. The model was used to analyze a set of experimental data for the direct sulfation of three limestones (that is, their reaction with SO2 under noncalcining conditions), and a parameter estimation procedure was formulated for extracting the effective diffusivity as a distributed parameter from the experimental conversion vs. time curves. Very strong effects of temperature, concentration, and depth in the product layer on the effective diffusivity were revealed by the analysis. On the basis of the obtained results, it was concluded that despite being essentially nonporous, uncalcined limestones can react with SO, under noncalcining conditions at rates comparable to those of calcined samples because they present much lower resistance for diffusion of SO2 through the product layer than the latter.     

Combustion of coke deposits in a catalyst pellet

A model of catalyst pellet regeneration is presented that accounts for the separate combustion reactions of the hydrogen and the carbon in the coke. The complete structure of the burn-off time with respect to several system parameters is given. It is shown that there are values of initial coke weight fraction and pellet size that give minimum burn-off time. The model indicates that the combustion of the deposited coke is limited by diffusion at higher temperatures than previously thought, and it predicts relatively high temperature differences between the solid particles and the fluid phase at low levels of conversion for some range of the model parameters.     

Bacterial secretion of the Fab fragment of a mouse monoclonal IgM that reacts with IgG variable regions

In this report, we describe the expression system that enabledus to produce in Escherichia coli the Fab fragment of a mouseIgM that has previously been shown to inhibit the binding ofIgG to autoantigens by interacting with their variable regions.In our system, both light chain and heavy chain fragments wereput under the control of the malE promoter. The light chainwas fused to the MalE signal sequence, while the heavy chainvariable and first constant region were fused to the alkalinephosphatase signal sequence. In this system, after inductionof the promoter with maltose, the Fab fragment could be detectedin a periplasmic extract of the bacteria by Western blottingand also by ELISA. This Fab fragment was purified on a goatanti-mouse immunoglobulin immunoadsorbent and biotinylated.The Fab fragment produced by E.coli reacted with the trinitrophenyl(TNP) hapten and F(ab')₂ fragments of mouse IgG and these reactivitiescould be specifically inhibited by the corresponding solubleantigens. The dissociation constants of this Fab were 1.65 x10^–6 M for TNP and 5 x 10^–6 M for IgG F(ab')₂ fragments,indicating that the affinity of the Fab fragment compared withthat of the whole IgM molecule was similar for TNP but was lowerfor IgG F(ab')₂ fragments     

Isolement de bacteries pathogenes contaminant une eau a l'aide d'immunoadsorbantsIsolation of pathogenic bacteria present in water using immunoabsorbents

The potability of water is indicated by the presence or the absence of bacteria from faecal origin. According to the World Health Organization, water is not considered dangerous in the absence of such bacteria. However, only a water free of true pathogenic bacteria is clearly drinkable. In our laboratory, we have elaborated a method allowing direct isolation from water of the main pathogenic bacteria which are common faecal contaminants. These bacteria include Salmonella typhi-murium, Escherichia coli K 88 and K 99 and Vibrio cholerae of the El Tor biotype. Our method consists of filtering contaminated water through small immunoabsorbant columns packed with polyacrylamide-agarose beads coupled to specific antibodies against bacterial antigenic structures.Antisera were obtained from rabbits immunized with antigenic fractions of the bacterial walls, known as Ch 1 + 2 (V. cholerae) Tm 1 + 2 (S. typhi-murium), Ec 1 + 2 K 88 and K 99 (E. coli K 88 and K 99). Antibodies were then isolated and coupled to glutaraldehyde-activated 3% polyacrylamide 4% agarose beads (AcA 34). 500 ml of contaminated water was filtered through the columns. The water consisted either of artificially contaminated samples from the Oise river (France) or of similarly contaminated saline. After filtration, the beads were recovered from the columns, diluted in hypersaline peptone water (V. cholerae) or saline (S. typhi-murium, E. coli K 88 and K 99) and incubated overnight at 37°C. The growth from the hypersaline peptone or saline broth was then removed, placed onto Petri dishes and the colonies were counted.Water samples containing a mixture of 10³ of each of the four bacteria were filtered through beads coated with the different antibodies. Bacteria retained on the beads were only those against which antibodies were directed (Table 1). On the other hand, we have analysed column effluent waters after passing 10³ bacteria through the relevant columns. No bacteria were detected after filtration, which suggest that most of the bacteria were retained on the beads. Bacteria were found in column effluent waters when the water samples contained more than 10⁵ bacteria.This technique is highly specific and allows the filtration of relatively large quantities of water. We believe the method may prove useful for collecting pathogenic bacteria from water directly, without the need for the usual isolation steps.     

Tire lateral force estimation and grip potential identification using Neural Networks,Extended Kalman Filter,and Recursive Least Squares

This paper presents a novel hybrid observer structure to estimate the lateral tire forces and road grip potential without using any tire–road friction model. The observer consists of an Extended Kalman Filter structure, which incorporates the available prior knowledge about the vehicle dynamics, a feedforward Neural Network structure, which is used to estimate the highly nonlinear tire behavior, and a Recursive Least Squares block, which predicts the road grip potential. The proposed observer was evaluated under a wide range of aggressive maneuvers and different road grip conditions using a validated vehicle model, validated tire model, and sensor models in the simulation environment IPG CarMaker ^®. The results confirm its good and robust performance.