Solid oxide fuel cell composite cathodes based on perovskite and fluorite structures

This work presents the results related to the functionally graded fluorite (F)-perovskite (P) nanocomposite cathodes for IT SOFC. Nanocrystalline fluorites (GDC, ScCeSZ) and perovskites (LSrMn, LSrFNi) were synthesized by Pechini method. Nanocomposites were prepared by the ultrasonic dispersion of F and P powders in isopropanol with addition of polyvinyl butyral. Different techniques for deposition and sintering of functionally graded cathode materials were applied including traditional approaches as well as original methods, such as radiation-thermal sintering under electron beam or microwave radiation. Morphology, microstructure and elemental composition of nanocomposites was characterized by XRD and HRTEM/SEM with EDX. Even for dense composites, the sizes of perovskite and fluorite domains remain in the nanorange providing developed P-F interfaces. Oxygen isotope heteroexchange and conductivity/weight relaxation studies demonstrated that these interfaces provide a path for fast oxygen diffusion. The redistribution of the elements between P and F phases in nanocomposites occurs without formation of insulating zirconate phases. Button-size fuel cells with nanocomposite functionally graded cathodes, thin YSZ layers and anode Ni/YSZ cermet (either bulk or supported on Ni-Al foam substrates) were manufactured. For optimized composition and functionally graded design of P-F nanocomposite cathodes, a stable performance in the intermediate temperature range with maximum power density up to 0.5 W cm⁻² at 700 °C in wet H₂/air feeds was demonstrated.     

Evolution of the structure of Co stevensite during its treatment in the air, inert gas flow and flowing hydrogen

Synthetic TOT (2 tetrahedron layers,1 octahedron layer) trioctahedral hydrosilicates (stevensites) of Zn, Mg, Co and Co-Zn were prepared by the deposition–precipitation technique. The evolution of both the structure and spectral properties of the silicates were studied during their treatment in various media. The position of the ν(OH) absorption band and the temperature of crystallization of the anhydrous silicate were found to be useful indicators of the cationic composition of stevensites. The data obtained are used to analyze and to review the earlier data on Co/SiO₂ catalysts. It is concluded that the formation of Co stevensite occurs in the majority of cases when the pH of the maternal solution during the preparation of a catalyst is above four. Received: 27 June 2000 / Reviewed and accepted: 28 June 2000     

Modular Coiled Flow Inverter with Narrow Residence Time Distribution for Process Development and Production

The ideal plug flow reactor is a common model with narrow residence time distribution in reaction engineering. This contribution explains a design strategy of a coiled flow inverter (CFI) with narrow residence time and flexible adjustable process conditions. The design space diagram illustrates the design limits of inner diameter and coil diameter on the base of dimensionless numbers. Standard coil tube diameters allow for rational design of a limited number of devices. The reactor performance diagram enables the facile scale‐up and adaption of new process conditions with the CFI with economic boundary conditions.     

Bacteria in the prostate tissue of men with idiopathic prostatic inflammation

PURPOSE: Although antibiotics represent the first line of treatment for prostatitis syndromes, physicians can document infection in remarkably few cases. We examined the relationship of genitourinary infection to inflammatory prostatitis in 85 subjects without bacteriuria. MATERIALS AND METHODS: Evaluation consisted of cultures of urethra, urine and transperineal prostate biopsies, specifically for commensal and fastidious organisms, and leukocyte counts of expressed prostatic secretions. RESULTS: Men with inflamed expressed prostatic secretions (25) were more likely to have any bacterial isolation (p = 0.01), positive cultures for anaerobic bacteria (p = 0.03), higher total bacterial counts (p = 0.02) and more bacteria, species isolated (p = 0.02) in prostate biopsy cultures than men without expressed prostatic secretion inflammation (60). CONCLUSIONS: Bacterial colonization/invasion of the prostate may be associated with inflammatory prostatitis in some cases.     

Accidents in obstructive sleep apnea patients treated with nasal continuous positive airway pressure: a prospective study. The Working Group ANTADIR, Paris and CRESGE, Lille, France. Association Nationale de Traitement à Domicile des Insuffisants Respiratoires

Many studies have shown a relationship between obstructive sleep apnea (OSA) and accidents, but to our knowledge, none have investigated prospectively the effects of treatment with nasal continuous positive airway pressure (CPAP). CPAP was proposed to 973 patients, of whom 893 patients actually underwent CPAP. These patients were consecutively invited to enter a prospective follow-up study including a questionnaire before treatment and after 6 and 12 months of treatment; 547 patients completed the study (153 left the study, and only partial data were available for 193). The baseline questionnaire included questions concerning accidents in the previous 12 months, asking whether patients had had an accident and, if so, whether they felt that the accident(s) were related to sleepiness, and whether the patients felt that they had had near-miss accidents due to sleepiness. The questionnaires at 6 and 12 months included the same questions referring to the previous 6 months; the accidents reported on each follow-up questionnaire were cumulated and compared with the accidents during the 1-year period before treatment. The number of patients having an accident decreased with treatment for real accidents (from 60 to 36; p<0.01), as well as for near-miss accidents (from 151 to 32; p<0.01). The average number of accidents per patient also decreased, for real accidents (from 1.6+/-1.3 to 1.1+/-0.3; p<0.01) and for near-miss accidents (from 4.5+/-6.5 to 1.8+/-1.4; p<0.01). The cost, in terms of days in hospital related to accidents, decreased from 885 to 84 days. With caution due to the absence of a control group, it is suggested that treatment with CPAP decreases the number of accidents occurring in OSA patients. This result may have important implications in the evaluation of the cost/benefit ratio when treating OSA patients.     

Hierarchical analysis of genetic structure in native fire ant populations: results from three classes of molecular markers

We describe genetic structure at various scales in native populations of the fire ant Solenopsis invicta using two classes of nuclear markers, allozymes and microsatellites, and markers of the mitochondrial genome. Strong structure was found at the nest level in both the monogyne (single queen) and polygyne (multiple queen) social forms using allozymes. Weak but significant microgeographic structure was detected above the nest level in polygyne populations but not in monogyne populations using both classes of nuclear markers. Pronounced mitochondrial DNA (mtDNA) differentiation was evident also at this level in the polygyne form only. These microgeographic patterns are expected because polygyny in ants is associated with restricted local gene flow due mainly to limited vagility of queens. Weak but significant nuclear differentiation was detected between sympatric social forms, and strong mtDNA differentiation also was found at this level. Thus, queens of each form seem unable to establish themselves in nests of the alternate type, and some degree of assortative mating by form may exist as well. Strong differentiation was found between the two study regions using all three sets of markers. Phylogeographic analyses of the mtDNA suggest that recent limitations on gene flow rather than longstanding barriers to dispersal are responsible for this large-scale structure.     

Thermal analysis of ESD-related hot spots [integrated circuits]

The thermal response to a microscopic hot spot, formed by an exponential electrostatic discharge (ESD) pulse, is analyzed and discussed, using a spherically symmetric Gaussian distribution to model the hot spot. A nonsingular solution to the three-dimensional heat equation, applicable to input protection devices in integrated circuits, is obtained. The resulting near-field temperature distribution can be used to study failures related to local silicon melting