Development of anode material based on La-substituted SrTiO3 perovskites doped with manganese and/or gallium for SOFC

Materials based on La-substituted SrTiO₃ perovskites doped with manganese and/or gallium for SOFC have been studied as novel anodes for solid oxide fuel cell. La₄Sr₈Ti₁₁Mn_1−xGa_xO_38−δ (0 ≤ x ≤ 1) oxides were synthesized by solid state reaction and the influences of the manganese and/or gallium content on the structure, morphology, thermal properties and electrical conductivity of these materials has been investigated. All compounds show cubic structure with a space group Pm-3m. These compounds presented high electrical conductivity values under reducing atmosphere between 7.9 and 6.8 S cm⁻¹ at 900 °C. For the composition x ≥ 0.5, the thermal expansion coefficient in both reducing and oxidizing atmosphere are close to that of SOFC electrolytes (8YSZ, CGD). In general, the substitution of Ga by Mn causes a slight reduction in each of the following, lattice parameter, degree of oxygen loss on reduction, thermal expansion coefficient, and electrical conductivity.     

HEAT TRANSFER FROM A HORIZONTAL BUBBLING SURFACE TO AN OVERLYING WATER POOL†

An experimenl was performed to study the effects of bubbling from a circular, horizontal, fiat plate on the heat transfer to an overlying water pool. The plate had drilled orifices through which nitrogen was injected into an overlying pool of water at atmospheric pressure. For “deep” pools, the heat transfer coefficient was found to increase only about 20% over a range of superficial gas velocities from 0.6 to 8.5cm/s, A turbulent heat transfer model developed by Konsetov was found to agree well with the data from this experiment. This model and the experimental data suggest that under certain conditions the heat transfer coefficient is similar for both horizontal and vertical surfaces. These conditions are, that the bubbles only contribute to the stirring action in the pool and only when the bubbling pool is considered “deep”. When the pool height fell below 60% of its diameter, the heat transfer coefficient decreased almost linearly with pool height. This suggests that there occurs a reduction in the turbulent fluctuations or in the characteristic length scale based on the average turbulent eddy size as the pool height decreases.     

Relative impact of oxidative stress on the functional competence and genomic integrity of human spermatozoa

Reactive oxygen metabolites are known to disrupt sperm-oocyte fusion, sperm movement, and DNA integrity; however, the relative sensitivities of these elements to oxidative stress are unknown. In this study these factors were assessed in human spermatozoa exposed to increasing levels of oxidative stress achieved through the stimulation of endogenous oxidant generation with NADPH or direct exposure to hydrogen peroxide. At low levels of oxidative stress, DNA fragmentation was significantly reduced while the rates of sperm-oocyte fusion were significantly enhanced. As the level of oxidative stress increased, the spermatozoa exhibited significantly elevated levels of DNA damage (p < 0.001) and yet continued to express an enhanced capacity for sperm-oocyte fusion. At the highest levels of oxidative stress, extremely high rates of DNA fragmentation were observed but the spermatozoa exhibited a parallel loss in their capacities for movement and oocyte fusion. These studies emphasize how redox mechanisms can either enhance or disrupt the functional and genomic integrity of human spermatozoa depending on the intensity of the oxidative stimulus. Because these qualities are affected at different rates, spermatozoa exhibiting significant DNA damage are still capable of fertilizing the oocyte. These results may have long-term implications for the safety of assisted conception procedures in cases associated with oxidative stress.     

Development of novel anodes for solid oxide fuel cells

Ni cermet anodes pose considerable problems for SOFC operation in natural gas fuels, particularly with regard to carbon deposition due to hydrocarbon cracking. Oxide anodes offer a good alternative, particularly if a material combining good electronic and ionic transport properties can be utilised. In our search for alternative anode materials, we have investigated fluorite-based systems containing reducible early transition metal dopants. The extent of phase stability has been investigated by solid-state chemical techniques and electrical properties have been investigated by ac impedance techniques as a function of both temperature and oxygen partial pressure. The Nb---Zr---Y---O system has been found to provide a good model system exhibiting reasonable electrical properties. Niobium pentoxide exhibits a wide range of solid solubility in the yttria-zirconia cubic fluorite system and the fluorite structure is retained under reducing conditions. Electronic conductivity increases as niobium concentration increases; however oxide-ionic conductivity decreases with extent of niobium substitution. The defect chemistry of this system, which determines the electrical properties, is dominated by the high concentration of oxide vacancies necessary to stabilise the cubic structure, hence electronic conductivity exhibits a P(O₂)^-1/4 dependence on oxygen partial pressure.     

The homo and copolymerisation of 2-(dimethylamino)ethyl methacrylate in supercritical carbon dioxide

This paper describes the free radical dispersion homopolymerisation of 2-(dimethylamino) ethyl methacrylate (DMA) and copolymerisation of DMA with methyl methacrylate (MMA) in supercritical carbon dioxide (scCO₂). The polymerisations are performed in the presence of two commercially available stabilisers, poly(dimethylsiloxane) monomethacrylate macromonomer (PDMS-mma) and the carboxylic acid terminated perfluoropolyether (Krytox 157FSL). Dry, fine powdered polymer product was produced for the copolymer under optimised conditions, but only aggregated solid is formed for homo poly(DMA). The effect of reaction time, stabiliser, copolymer composition and reaction pressure on the yield, molecular weight and morphology of the copolymers has been investigated.     

Influence of structure and composition upon performance of tin phosphate based negative electrodes for lithium batteries

Tin oxide and amorphous tin borophosphates have recently received significant attention as possible new negative electrode materials for lithium batteries. In this study, we have carefully investigated a number of different well-characterised tin phosphates as electrodes in Li-ion cells, in order to better understand the mode of operation of these materials and how their performance is related to structure and composition. The materials that were investigated were crystalline cubic and layered SnP₂O₇, LiSn₂(PO₄)₃, Sn₂P₂O₇, and Sn₃(PO₄)_2, and amorphous Sn₂BPO₆. Cubic SnP₂O₇ showed the best performance with a reversible specific charge capacity of >360 mA h g⁻¹ and a capacity retention of 96% over 50 cycles when cycled between 0.02 and 1.2 V versus Li_m. The three Sn(IV) materials showed lower initial reversible capacity but better capacity retention than the three Sn(II) materials in the study. Their higher proportion of inert matrix material can partly explain this. However, cubic SnP₂O₇ cycled significantly better than its layered polymorph, which shows that the structure of the starting material is also of great importance. Another important conclusion drawn from the results is that it is not necessary for the starting material to be amorphous, or if crystalline, to have small grain size, to cycle well. The three pyrophosphates all show an initial reduction capacity that corresponds to around 2 Li per P₂O₇⁴⁻ unit more than is predicted by theory. This might be explained by reductive break-up of the POP bond.     

Planar defects in 4H-SiC PiN diodes

Using plan-view transmission electron microscopy (PVTEM), we have identified stacking faults (SFs) and planar defects in 4H-SiC PiN diodes subjected to electrical bias. Our observations suggest that not all planar defects seen in the PiN diodes are SFs. By performing diffraction-contrast imaging experiments using TEM, we can distinguish SFs from other planar defects. In addition, high-resolution TEM (HRTEM) imaging and analytical TEM have revealed that some planar defects consist of a 3-nm-wide SiC amorphous layer. Many of these planar defects are orientated parallel to {1 00} planes, whereas others are roughly parallel to the (0001) plane. The appearance of these planar defects suggests that they are grain boundaries.     

Retinal emboli in patients with mitral valve prolapse

Small fibrin-platelet emboli caused by prolapsed mitral valves may cause retinal occlusive disease with a wide range of ophthalmic manifestations, including amaurosis fugax in young people, retinal or choroidal arteriolar occlusion, and retinal neovascularization (atypical Eales' disease). Six patients with retinal occusive disease underwent extensive noninvasive cardiac and systemic tests and were found to have prolapsed mitral valves. Patients with unexplained ocular emboli should be examined by a cardiologist for possible mitral valve prolapse.     

The influence of the central region containing residues 19-25 on the aggregation properties and secondary structure of Alzheimer's beta-amyloid peptide

Alzheimer's beta-amyloid peptide (Abeta) is a 39- to 43-amino-acid peptide that is the major component of neuritic plaques found in Alzheimer's disease (AD). The central region of Abeta plays a crucial role in many of its properties, including aggregation, neurotoxicity, proteolytic processing and interactions with other proteins, such as apolipoprotein E. Two mutations in this region, Ala21-->Gly and Glu22-->Gln, give rise to early onset forms of disease. We have studied several peptides based on the central region of Abeta in order to clarify the influence of specific amino acid residues on physicochemical behaviour. To avoid difficulties due to oxidation of Met35, the latter was replaced by the amino acid isostere, norleucine (Ahx), giving [Ahx35]Abeta-(25-35)-amide as a prototype structure. To this prototype, addition of pairs of amino acid residues from the sequence of Abeta, forming the corresponding 23-, 21- and 19-35 derivatives, resulted in peptides that aggregated to form fibrils of diameter 6-10 nm. The rate of aggregation was more rapid as peptide length increased. Circular dichroism spectra of aged solutions of peptides revealed that aggregation was accompanied by a transition from random structure to beta sheet for some, but not all, peptides. The mutation from Ala to Gly at position 21 increased the rate of aggregation and altered the tendency to adopt secondary structure in the direction away from alpha helix and towards beta sheet. In individuals with the Ala21-->Gly mutation, these results would suggest that truncated species with N-termini in the region containing residues 17-20 would be more amyloidogenic than the wild type homologues.     

Distribution of the alpha1 to alpha6 chains of type IV collagen in bovine follicles

During follicular development the proliferative and differentiated state of the epithelioid granulosa cells changes, and the movement of fluid across the follicular basal lamina enables the formation of an antrum. Type IV collagen is an important component of many basal laminae. Each molecule is composed of three alpha chains; however, six different type IV collagen chains have been identified. It is not known which of these chains are present in the follicular basal lamina and whether the type IV collagen composition of the basal lamina changes during follicular development. Therefore, we immunolocalized each of the six chains in bovine ovaries using antibodies directed to the nonconserved non-collagenous (NC) domains. Additionally, dissected follicles were digested with collagenase to release the NC domains, and the NC1 domains were then detected by standard Western immunoblot methods. The follicular basal lamina of almost all primordial and preantral follicles was positive for all type IV collagen alpha chains. Colocalization of type IV collagen and factor VIII-related antigen allowed for discrimination between the follicular and endothelial basal laminae. Type IV collagen alpha1, alpha2, alpha3, alpha4, and alpha5 chains were present within the follicular basal lamina of only a proportion of antral follicles (17 of 22, 20 of 21, 15 of 18, 14 of 28, and 12 of 23, respectively), and staining was less intense than in the preantral follicles. Staining for the alpha1 and alpha2 chains was diffusely distributed throughout the theca in regions not associated with recognized basal laminae. The specificity of this immunostaining for alpha1 and alpha2 chains of type IV collagen was confirmed by Western immunoblots. As well as being detected in the basal lamina of approximately half of the antral follicles examined, type IV collagen alpha4 also colocalized with 3beta-hydroxysteroid dehydrogenase-immunopositive cells in the theca interna. Type IV collagen alpha6 was detected in the basal lamina of only one of the 16 antral follicles examined. Thus, the follicular basal lamina changes in composition during follicular development, with immunostaining levels being reduced for all type IV collagen chains and immunoreactivity for type IV collagen alpha6 being lost as follicle size increases. Additionally, immunoreactivity for alpha1 and alpha2 appears in the extracellular matrix of the theca as it develops.