130,004 research outputs found
Development of new proton conducting materials for intermediate temperature fuel cells
No full textThe work in this thesis mainly focuses on the preparation and characterization of several phosphates and solid oxide systems with the aim of developing new proton conducting materials for intermediate temperature fuel cells (ITFCs). Soft chemical methods such as sol-gel methods and conventional solid state methods were applied for the synthesis of these materials.
Aluminum phosphate obtained by a solution method is single phase and belongs to one of the Al(H₂PO₄)₃ allotropies with hexagonal symmetry. The material is stable up to 200°C and decomposes into Al(PO₃)₃ at a higher temperature. The electrical conductivity of pure Al(H₂PO₄)₃ is on the order of 10⁻⁶-10⁻⁷ S/cm, very close to the value for the known proton conductors AlH₃(PO₄)₂•3H₂O and AlH₂P₃O₁₀•2H₂O. Much higher conductivity is observed for samples containing even a trace amount of excess H₃PO₄. It is likely that the conduction path gradually changes from grain interior to the surface as the acid content increases. The conductivity of Al(H₂PO₄)₃-0.5H₃PO₄ exhibited a good stability over the measured 110 hours.
Although tin pyrophosphate (SnP₂O₇) has been reported to show a significantly high conductivity (~10⁻² S/cm) at 250°C in various atmospheres, we observed large discrepancies in the electrical properties of SnP₂O₇ prepared by different methods. Using an excess amount of phosphorous in the synthetic procedure generally produces SnP₂O₇ with much higher conductivity (several orders of magnitude higher) than samples with stoichiometric Sn:P ratios in their synthetic procedure. Solid state ³¹P NMR confirmed the presence of residual phosphoric acid for samples with excess starting phosphorous. Transmission Electron Microscope (TEM) confirmed an amorphous layer covered the SnP₂O₇ granules which was probably phosphoric acid or condensed phases. Thereby, it is quite likely that the high conductivity of SnP₂O₇ results mainly from the contribution of the residual acid. The conductivity of these samples exhibited a good stability over the measured 80 hours.
Based on the observations for SnP₂O₇, we developed a nano core-shell structure based on BPO₄ and P₂O₅ synthesised by solid state methods. The particle size of BPO₄ using this method varied between 10-20 nm depending on the content of P₂O₅. TEM confirmed the existence of an amorphous layer that is homogeneously distributed. The composite exhibits the highest conductivity of 8.8×10⁻² S/cm at 300°C in air for 20% extra P₂O₅ and demonstrates a good stability during the whole measured 110 hours. Polytetrafluoroethylene (PTFE) was introduced into the composites in order to increase malleability for fabrication. The conductivity and mechanical strength were optimized by adjusting the PTFE and P₂O₅ content. These organic-inorganic composites demonstrate much better stability at elevated temperature (250°C) over
conventional SiC-H₃PO₄-PTFE composites which are common electrolytes for phosphoric acid fuel cells (PAFCs). Fuel cells based on BPO₄-H₃PO₄-PTFE composite as the electrolyte were investigated using pure H₂ and methanol as fuels. A maximum power density of 320 mW/cm² at a voltage of 0.31 V and a maximum current density of 1.9 A/cm² at 200°C were observed for H₂/O₂ fuel cells. A maximum power density of 40 mW/cm² and maximum current of 300 mA/cm² 275°C were observed when 3M methanol was used in the cell.
Phosphoric acid was also introduced into materials with internal open structures such as phosphotungstic acid (H₃PW₁₂O₄₀) and heteropolyacid salt ((NH₄)₃PW₁₂O₄₀), for the purpose of acquiring additional connections. The hybrids obtained have a cubic symmetry with enlarged unit cell volume, probably due to the incorporation of phosphoric acid into the internal structures. Solid state ³¹P NMR performed on H₃PW₁₂O₄₀-xH₃PO₄ (x = 0-3) showed additional peaks at high acid content which could not assigned to phosphorus from the starting materials, suggesting a strong interaction between H₃PW₁₂O₄₀ and H₃PO₄. The conductivity of hybrids was improved significantly compared with samples without phosphoric acid. Fourier transform infrared spectra (FT-IR) suggest the existence of large amount of hydrogen bonds (OH••••O) that may responsible for the high conductivity. A H₂/O₂ fuel cell based on H₃PW₁₂O₄₀-H₃PO₄-PTFE exhibited a peak power density of 2.7 mW/cm² at 0.3 V in ambient temperature.
Solid oxide proton conductors based on yttrium doped BaZrO₃ were investigated by introducing potassium or lanthanum at the A-sites. The materials were prepared by different methods and were obtained as a single phase with space group Pm-3m (221). The unit cell of these samples is slightly smaller than the undoped one. The upper limit of solid solution formation on the A-sites for potassium is between 5 ~ 10% as introducing more K results in the occurrence of a second phase or impurities such as YSZ (yttrium stabilized zirconium). K doped Barium zirconates showed an improved water uptake capability even with 5% K doping, whereas for La doped ones, water uptake is strongly dependent on particle size and synthetic history. The conductivity of K doped BaZrO₃ was improved by a factor of two (2×10⁻³ S/cm) at 600°C compared with undoped material. Fuel cells based on Pt/Ba₀.₉₅K₀.₀₅Zr₀.₈₅Y₀.₁₁Zn₀.₀₄O[subscript(3-δ)]/Pt under humidified 5% H₂/air conditions gave a maximum power density 7.7 mWcm⁻² at 718°C and an interfacial resistance 4 Ωcm⁻². While for La doped samples, the conductivity was comparable with undoped ones; the benefits of introducing lanthanum at A-sites may not be so obvious as deficiency of barium is one factor that leads to the diminishing conductivity
The concept of peace in the Tao Te Ching
Full text linkThis thesis represents a first attempt to analyze Lao Tzu's main method of resolving the social and political problems in Ch'un Ch'iu and Warring States Periods. Lao Tzu, the founder of Taoism, suggested many solutions that could bring an end to the conflicts and to the ending of the disunity of China. Examples of these include the reform or abolishment of some ancient Chinese institutions as well as new principles for the enhancement and preservation of life. All these ideas were to become crystallised in Tao Te Ch'ing, which became an important religious text. In particular, the aspect of Lao Tzu's methods for solving the social and political problems of China in the Warring States Period needs more attention. In each chapter of the Tao Te Ch'ing there was a main emphasis on peace as the main method of developing social cohesion and as a cure to all fundamental human problems. Therefore, Lao Tzu's ideas about peace and his methods of solving the problems of the Warring States period are significant and from the main focus of the thesis
The identification of the Tao-1 kinase as a key regulator of microtubule dynamics
Full text linkIn a multicellular animal, the different functions of cells are dependent on their diversity of shapes. Protein phosphorylation and dephosphorylation play an important role in altering the cell shape in response to internal and
external signals. In this study I focused on all kinases to explore the gene functions and mechanisms underlying the regulation of cell morphology.
Using genomic information I have constructed a Drosophila kinase RNAi library, which was then used to screen six different cell lines from two different tissues of origin for novel genes involved in the generation of cell
form. In doing so, I identified a group of common regulators of cell behaviour and morphology together with a set of cell-type specific kinases.
Importantly, this analysis also revealed that, when considering the kinome, gene expression signatures are a poor measure of cell type specific differences in gene function, measured by comparing with the microarray
data available in our lab. Most significantly, these screens identified a novel role for Mnb/DYRK1A, a kinase associated with Down’s Syndrome, in the regulation of actin-based protrusions in cell lines derived from neuronal lineages.
Furthermore, I identified a single STE20 kinase Drosophila Tao-1 in the core set which was required for the normal morphology of all cell lines examined. The RNAi-mediated depletion of Tao-1 or expression of the kinase-dead protein leads to the stabilisation of microtubules and to the
formation of long microtubule-based protrusions, whereas the
overexpression of Tao-1 destabilizes microtubules. I also showed in this study that Tao-1 acts independently of Par-1 and Tau in this process.
Instead, Tao-1 appears to function together with EB1 in the regulation of microtubule plus end instability at the cell cortex. Two microtubule motor proteins, Khc and Khc-73, interact with Tao-1 in a yeast two hybrid screen,
which hints at a possible role for the transport of Tao-1 along filaments to microtubule plus ends and the cell cortex. Although evidence for a direct role for Tao-1 in the phosphorylation and/or regulation of EB1 has yet to
be established, this is to my knowledge first time a kinase has been found acting at the cell cortex to regulate microtubule plus end stability
JODI J. L. ROWLEY, DAO T. A. TRAN, DUONG T. T. LE, VINH Q. DAU, PEDRO L. V. PELOSO, TRUONG Q. NGUYEN, HUY D. HOANG, TAO T.
No full textanonymous (2016): JODI J. L. ROWLEY, DAO T. A. TRAN, DUONG T. T. LE, VINH Q. DAU, PEDRO L. V. PELOSO, TRUONG Q. NGUYEN, HUY D. HOANG, TAO T. Zootaxa 4105 (4): 400-400, DOI: http://doi.org/10.11646/zootaxa.4105.4.
Taphrocerus tao Zayas 1988
No full text<i>Taphrocerus tao</i> Zayas <p>(Fig. 4)</p> <p> <i>Taphrocerus tao</i> Zayas 1988: 41.</p> <p>Type locality: CUBA: Pinar del Río Province, Viñales. Zayas (1988: 42) cited three syntype specimens from the type locality. The photographed syntype is a male.</p> <p> This species is most similar to <i>Taphrocerus timidus</i> Chevrolat based on the information provided by Fisher (1925) on the Caribbean species, and USNM specimens identified by Fisher as <i>T. timidus</i> (from Cuban localities: C. Jatiponico; Nagua, Oriente; and Cienfuegos, Soledad). The USNM specimens have a slightly angulate lateral pronotal margin and a vaguely defined prehumeral carina at the posterior angle of the pronotum which appear to be shared by <i>T. tao</i>. <i>Taphrocerus tao</i> could be a synonym of <i>T. timidus</i>, but only examination of the actual specimens, including genitalia, in a comparative context, will resolve the identity of <i>T. tao</i> with certainty.</p>Published as part of <i>Barman, E. H., Michat, M. C., Alarie, Y. & Wolfe, G. W., 2007, Figs. 16 – 17. 16 in A Description of the First Instar of Hoperius planatus Fall, 1927 (Coleoptera: Dytiscidae: Colymbetinae: Colymbetini), with Phylogenetic Implications, pp. 334-338 in The Coleopterists Bulletin 24 (3)</i> on page 337, DOI: 10.1649/0010, <a href="http://zenodo.org/record/10110742">http://zenodo.org/record/10110742</a>
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