Low cation coordination in oxide melts.

The complete set of partial pair distribution functions for a rare earth oxide liquid are measured by combining aerodynamic levitation, neutron and x-ray diffraction on Y2O3, and Ho2O3 melts at 2870 K. The average Y-O (or Ho-O) coordination of these isomorphic melts is measured to be 5.5(2), which is significantly less than the octahedral coordination of crystalline Y2O3 (or Ho2O3). Investigation of La2O3, ZrO2, and Al2O3 melts by x-ray diffraction and molecular dynamics simulations also show lower-than-crystal cation-oxygen coordination. These measurements suggest a general trend towards lower coordination compared to their crystalline counterparts. It is found that the coordination drop is larger for lower field strength, larger radius cations and is negligible for high field strength (network forming) cations, such as SiO2. These findings have broad implications for predicting the local structure and related physical properties of metal-oxide melts and oxide glasses.

A time resolved high energy X-ray diffraction study of cooling liquid SiO2.

The evolution of the X-ray structure factor and corresponding pair distribution function of SiO2 has been measured upon cooling from the melt using high energy X-ray diffraction combined with aerodynamic levitation. Small changes in the position of the average Si-O bond distance and peak width are found to occur at ~1500(100) K in the region of the calorimetric glass transition temperature, T(g) and the observed density minima. At higher temperatures deviations from linear behavior are seen in the first sharp diffraction peak width, height and area at around 1750(50) K, which coincides with the reported density maximum around 1.2T(g).

Structure of molten CaSiO3: neutron diffraction isotope substitution with aerodynamic levitation and molecular dynamics study.

We have performed neutron diffraction isotopic substitution experiments on aerodynamically levitated droplets of CaSiO(3), to directly extract intermediate and local structural information on the Ca environment. The results show a substantial broadening of the first Ca-O peak in the pair distribution function of the melt compared to the glass, which comprises primarily of 6- and 7-fold coordinated Ca-polyhedra. The broadening can be explained by a redistribution of Ca-O bond lengths, especially toward longer distances in the liquid. The first order neutron difference function provides a test of recent molecular dynamics simulations and supports the MD model which contains short chains or channels of edge shared Ca-octahedra in the liquid state. It is suggested that the polymerization of Ca-polyhedra is responsible for the fragile viscosity behavior of the melt and the glass forming ability in CaSiO(3).

Whole, submandibular, and parotid saliva-mediated aggregation of Pseudomonas aeruginosa in cystic fibrosis.

The aggregation of mucoid and nonmucoid Pseudomonas aeruginosa by submandibular, parotid, and whole saliva from patients with cystic fibrosis (CF) and non-CF subjects was investigated. There were significant differences (P less than 0.01) in aggregation of mucoid and nonmucoid variants of P. aeruginosa by submandibular and whole saliva from CF patients and non-CF subjects. However, the differences in the parotid secretion were not as pronounced. Patients with CF who were colonized with P. aeruginosa demonstrated a significantly higher (P less than 0.05) percent aggregation of the mucoid variants by the submandibular secretion and of both mucoid and nonmucoid variants by whole saliva, compared with corresponding secretions from patients with CF not colonized with this pathogen. The parotid saliva aggregation activity was not markedly different for the two groups with CF. From patients with CF, whole saliva demonstrated a higher percent P. aeruginosa aggregation than did the submandibular saliva. In non-CF subjects, however, the percent aggregation of P. aeruginosa by submandibular saliva was higher than that by whole saliva. Our results indicate that the sero-mucous products of the submandibular gland have a more significant role in P. aeruginosa aggregation than the serous secreting parotid cells and that the submandibular secretion is possibly responsible for the differences in oral colonization by this pathogen in subjects with and without CF.

Role of sialic acid in saliva-mediated aggregation of Pseudomonas aeruginosa isolated from cystic fibrosis patients.

The mechanism of saliva-mediated aggregation of Pseudomonas aeruginosa in subjects with and without cystic fibrosis (CF) was investigated. Virtually all saliva from CF patients that we tested strongly agglutinated the Pseudomonas cells and was heat stable to 56 degrees C, whereas saliva from subjects without CF had a decreased aggregating ability and was heat sensitive. When saliva was treated with neuraminidase and proteases, and also when P. aeruginosa cells were treated with mixed gangliosides, there was a decrease in aggregating activities. However, neither the addition of the acid-hydrolyzed ganglioside nor the treatment of the P. aeruginosa cells by sugars had any effect on subsequent aggregating activities. Therefore, the release of sialic acid by enzymatic treatments of saliva, as well as the blockage of the sialic acid-binding sites on the cell wall by mixed gangliosides, resulted in the parallel loss of saliva-mediated aggregating activity of P. aeruginosa. The level of free sialic acid released by endogenous neuraminidase was higher in the saliva from CF patients than in that from the non-CF subjects examined. The increased aggregation of P. aeruginosa mediated by saliva from patients with CF seems to be directly related to the sialic acid content present, suggesting that this acid molecule acts as the salivary receptor for P. aeruginosa.

Characterization by pyocine typing and serotyping of oral and sputum strains of Pseudomonas aeruginosa isolated from cystic fibrosis patients.

Oral and sputum isolates of Pseudomonas aeruginosa in patients with cystic fibrosis were investigated. Of the 17 patients studied, 12 patients (71%) yielded both mucoid and nonmucoid variants of Pseudomonas aeruginosa from sputum and (or) various oral ecological sites, such as buccal mucosa, tongue dorsum, dental plaques, and saliva. A total of 51 strains of mucoid and nonmucoid Pseudomonas aeruginosa were isolated from these patients and were phenotypically characterized by both pyocine typing and serotyping. Five patients (42%) were colonized or infected by a single strain of Pseudomonas aeruginosa, whereas 7 patients (58%) were cocolonized or coinfected by two or more phenotypically different strains of Pseudomonas aeruginosa. To understand the mechanisms involved in Pseudomonas aeruginosa colonization, it may be necessary to identify multiple isolates of Pseudomonas aeruginosa not only from the sputum but also from the various oral ecological sites and to further explore the role of the oral cavity in this colonization.