Modeling iron binding to organic matter

The aim of the present work is to model iron speciation during its interaction with natural organic matter. Experimental data for iron speciation were achieved with an insolubilised humic acid used as an organic matter analogue for 30microM to 1.8 mM total iron concentrations and 2< or = pH< or = 5.5. IHA was found to be able to impose its redox potential to the solution and therefore the Fe(ll)/Fe(lll) ratio. Model VI and the NICA-Donnan model have been adjusted to experimental results of acid-base titrations, total iron measurements, and redox speciation in solution. They both describe well pH and concentration dependence of iron adsorption. For high iron concentration, Fe(lll) solution activity is limited by precipitation of a poorly ordered Fe oxyhydroxide with a higher solubility (log Ks = 5.6-5.7) than ferryhydrite described in the litterature.     

Management practices from questionnaire surveys in herds with very low somatic cell score through a national mastitis program in France

French dairy herds (n = 534) were enrolled in the National 'Zero Mastitis Objective' Program to highlight management practices characterizing very low somatic cell score (SCS) herds. The herds studied were stratified into 2 groups. The first group (LOW) included herds within the first 5 percentiles and the second group (MED) herds within the 50 to 55 percentiles of herds on the basis of mean SCS for the 36 mo preceding the program. Potential explanatory variables, collected through questionnaire surveys, were analyzed using multistep logistic regression models. Twenty-six variables were significant factors in the final models, in which 18 were considered as primary factors for very low SCS. The probability for a herd belonging to the LOW group was associated with: (1) regular use of teat spraying; (2) herdsman precise in his techniques; (3) less than 1 person-year used at activities other than dairy herd; (4) teat dipping after mammary infusion at dry off; (5) heifers kept in a calving pen around parturition; (6) cows locked in feed-line lockups after milking; (7) dry cows with prepartum Ca restriction; (8) heifers on a nondamp pasture; (9) cows culled when at least one damaged teat; (10) heifers at pasture not drinking water from a river; and (11) disinfecting teat ends with alcohol before intramammary infusion at dry off. The probability for a herd belonging to the MED group was associated with: (1) milking cows housed in a straw yard; (2) checking heifers for mastitis only beginning at 2-wk prepartum; (3) no mastitis treatment when at least one clot was observed in milk at successive milkings; (4) distance of herdsman's house to cowshed >300 m; (5) only dirty teats washed before milking; (6) free access of cows from pasture to cowshed during bad weather; and (7) more than 18% of spring calvings. The variables associated with very low SCS should be applied as part of a thorough mastitis-control program adapted to each herd.     

An EXAFS study of the interaction of different reactant gases over nanometer scale Pt clusters deposited on γ-Al2O3

Face to the difficulty to find an efficient catalyst in the reduction of NO by hydrocarbon in diesel exhaust gases, we have examined the interaction of some concerned reactant gases, NO, C₃H₆ and O₂, with a catalyst constituted of nanometer scale platinum particles deposited on alumina. Indeed, in order to understand the catalytic process, it seems essential to have information on the adsorption process and on the evolution of the structural parameters of the particles when submitted to such gases. This work has been performed on a 1% Pt/Al₂O₃ catalyst by using in situ EXAFS measurements. We have concentrated our study, on the one hand, on the influence of NO, C₃H₆ in the presence or not of an excess of oxygen and, on the other hand, on the influence of the total mixture. The most striking result is the growth of the platinum particles under NO. Moreover, when the catalyst is submitted either to a mixture of NO + O₂ or C₃H₆ + O₂, the particles are not fully oxidised. With the total mixture, the particles both grow and are oxidised.     

NO Adsorption on ZnAl2O4/Al2O3 Powder: A NEXAFS Study at the Nitrogen K Edge

In order to understand the mechanism of the selective catalysis of nitrogen oxide reduction by hydrocarbons on a ZnAl₂O₄/Al₂O₃ catalyst, the NO adsorption step has been studied as a function of the surface state of the catalyst by using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K edge. The role of oxygen, whose presence is essential for the reaction to occur, is examined. In absence of a preliminary surface oxidation, nitric oxide was found not to be adsorbed on the ZnAl₂O₄/Al₂O₃ surface. After this preliminary treatment, we observed that the nitrogen atom of the NO molecule was linked to a surface oxygen with an adsorption mode parallel or slightly tilted with respect to the catalyst surface. Through these experiments we clearly demonstrate the advantages of soft X-ray experiments in catalysis research even in the case of practical application to real materials.     

Human recombinant interleukin-4 (HurIL-4) improves SCID mouse reconstitution with human peripheral blood lymphocytes

The application of human-scid mouse chimera (hu-scid) technology has some limitations, because of the variable amounts and functional heterogeneity of human cells recovered from engrafted mice. Attempts to optimize the construction of hu-scid chimeras with human peripheral blood mononuclear cells (Hu-PBMC) by using in vivo anti-asialo GM1 antibody treatment in mice in order to eliminate natural killer cells have been published by other authors with interesting results. In this study, Hu-PBMC were incubated in vitro with human recombinant interleukin-4 (HurIL-4) or human recombinant interleukin-2 (HurIL-2) for two hours and were intraperitoneally transferred into scid mice. Total human IgM and IgG levels in hu-scid sera, human cell markers in the thymus and in the spleen of grafted mice were considered as parameters of successful engraftment. HurIL-4 significantly enhanced human immunoglobulin production while HurIL-2 did not show any obvious effect. Human cell markers (CD2 and CD19) were significantly higher in the group of HurIL-4 treated Hu-PBMC than in the other groups, despite the high variability in human cell proliferation in the recipients. Thus, HurIL-4 can be used as an adjuvant growth factor which improves successful engraftment of human peripheral blood lymphocytes in scid mice.     

A TIME-DISCRETE APPROACH TO THE MODELLING OF GRINDING MILL MIXING PROPERTIES

When a grinding mill is not operated in open circuit, residence time distributions (RTD) cannot be directly deduced from tracer concentration measurements at the mill discharge using a conventional tracer impulse experiment. Two methods are proposed for RTD determination from an arbitrary set of input and output tracer concentration/time measurements. The first one provides directly the discretized RTD by a direct deconvolution approach. The second one assumes that the RTD is the impulse response of an autoregressive-moving average model (ARMA). The use of each method is demonstrated using industrial data and a comparison to alternative methods is given.     

Quasielastic scattering of 8B and 7Be on 12C at 40 MeV/nucleon

Enteropathogenic Escherichia coli (EPEC) O111:H2, O119:H6, or O142:H6 caused rapid detachment of Chinese hamster ovary (CHO) cell monolayers within 2 to 4 h of cocultivation. CHO cell detachment was not promoted by nonenteropathogenic E. coli (O125:H4, O126:H27, O157:H7, and O26:H11) and could not be attributed to EPEC production of enterohemolysin or Shiga-like toxins. In contrast, EPEC strains did not promote rapid detachment of Lec1, Lec2, or Lec8 CHO cell monolayers. These CHO cell Lec mutants all express abbreviated glycan sequences on membrane glycoproteins and glycolipids. Although EPEC strains failed to alter the adherent properties of Lec2 cells lacking only terminal sialic acid groups, EPEC adherence to the Lec2 mutant was indistinguishable from that observed with wild-type CHO cells. There was also no significant difference in EPEC-induced actin accumulation or invasion of Lec2 cells. In contrast, EPEC localized adherence to Lec1 and Lec8 mutants, lacking sialyllactosamine (Lec1) or sialic acid and galactose (Lec8) sequences, was reduced by 84 and 93%, respectively. Our results suggest that lactosamine sequences [beta Gal(1-4 or 1-3)beta GlcNAc] not containing sialic acid are sufficient for EPEC adherence, actin accumulation, and invasion of CHO cells. Sialic acid groups, however, may be necessary for EPEC-mediated CHO cell detachment.     

Radiologic aspects of infarction of the appendix epiploica

Clinical, US, CT and MR findings were reviewed in 5 patients with primary epiploic appendagitis (3 men, 2 women, mean age 38 years, age range 29-62 years) seen between December 1994 and December 1997. Diagnosis was reached in all cases with CT, with US in 3 and with MR in 1. Follow-up CT was performed in 2 cases and clinical follow-up in 4. One patient underwent surgery. Initial US, CT or MR examinations revealed a fatty oval-shaped nodule located anteriorly or anterolaterally to the left colon. The greater diameter ranged from 20 to 30 mm. Perinodular lesions with strands of periappendicular fat and thickened parietal peritoneum were visualized in all cases without any other inflammatory process in the abdomen. Symptoms resolved within 4 days in all patients. Signs of fatty inflammatory processes resolved in the 2 patients who had follow-up CTs. Primary epiploic appendagitis has characteristic US, CT and MR features which help guide medical treatment.     

Interaction Between Pt(acac)2 and Alumina Surfaces Studied by XAS

The anchoring and decomposition mechanisms of platinum(II) bis-acetylacetonate on alumina surfaces are studied by X-ray absorption spectroscopy at the platinum L_III edge. A distinction is made between highly reactive surfaces which are partially dehydroxylated and exhibit coordinatively unsaturated surface sites, and deactivated surfaces which are covered by a monolayer of OH groups. The samples are studied after three stages of a wet impregnation synthesis: after drying at room temperature, drying at 120 °C and calcination at 350 °C. The XANES signal and the filtered EXAFS signals of the first and second coordination shells around platinum were analyzed. Two different mechanisms are discussed for the two types of supports.