Processing and microstructure of non-oxide ceramic fibres

Research and development efforts on high-temperature, oxidation-resistant fibres have increased over the past decade due to the demand for light-weight, stiff and strong composite materials in aerospace applications. Varieties of ‘high-performance’, continuous, non-oxide fibres with low-density, high tensile strength and tensile modulus have been developed either from organic precursors or via chemical vapour deposition for fabrication of ceramic matrix composites. Fibres derived from polymer precursors (e.g. Nicalon, Tyranno, HPZ) are small in diameter (compared to CVD monofilaments) and are ideally suited for ceramic composites. Processing, microstructural stability and mechanical properties of these newly developed SiC and Si₃N₄ base fibres are briefly reviewed in this paper.     

Genetic programming of conventional features to detect seizure precursors

This paper presents an application of genetic programming (GP) to optimally select and fuse conventional features (C-features) for the detection of epileptic waveforms within intracranial electroencephalogram (IEEG) recordings that precede seizures, known as seizure precursors. Evidence suggests that seizure precursors may localize regions important to seizure generation on the IEEG and epilepsy treatment. However, current methods to detect epileptic precursors lack a sound approach to automatically select and combine C-features that best distinguish epileptic events from background, relying on visual review predominantly. This work suggests GP as an optimal alternative to create a single feature after evaluating the performance of a binary detector that uses: (1) genetically programmed features; (2) features selected via GP; (3) forward sequentially selected features; and (4) visually selected features. Results demonstrate that a detector with a genetically programmed feature outperforms the other three approaches, achieving over 78.5% positive predictive value, 83.5% sensitivity, and 93% specificity at the 95% level of confidence.     

Effect of Preparation Methods and Condition of Precursors on the Phase Composition of Yttria-Stabilized Zirconia Powders

An yttria-stabilized zirconia powder, free of monoclinic phase, may be prepared by an oxalate method in an ethanol solution at strong acidity. This study demonstrates that the control of pH in the preparation of precursors has a significant effect on the ability of precursors to crystallize and hence plays an important role in determining the formation and fraction of various crystalline phases in the resulting yttria-stabilized zirconia powder. With the increase of pH, a precursor with a certain crystalline form may be transformed into an amorphous precursor, and a monoclinic phase appers in the phase composition of the resulting powder. The results of XRD analysis and Raman spectroscopy are discussed.     

Activity of two lignin biosynthesis enzymes during development of a maize internode

To ascertain the temporal relationships of phcnylpropanoid and lignin pathway enzymes, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol- NADPH dehydrogenase(CAD), with lignin concentration, PAL and CAD activities and lignin concentrations were assessed during progressive development of the 10th internode in maize (Zea mays L). Enzyme activities were quantified and lignin concentrations were determined by the detergent system of fiber fractiona- tion from lower, middle, and upper sections of the elongating internode harvested 3, 5, 7, 9, 11, 13, and 15 days after the internode had reached 10 mm in length. Over 15 days, a coordinated, sequential, and basipetal pattern of enzyme activities and lignin accumulation evolved through the internode, spanning the stages of rapid elongation, cellular differentiation, and secondary cell wall formation. PAL activity was initiated first, rising to peak activity in elongating tissue, and falling basipetally in tissues as they matured. CAD activity rose in fully elongated, maturing internode tissue where PAL activity was waning following its peak activity. Lignin accumulated in tissues with high CAD activity. CAD activity and lignin deposition patterns were similar: simultaneously increasing in activity and deposition over time while activity and deposition also shifting basipetally through the internode, keeping pace with secondary cell wall formation. Lignin concentration correlated significantly with CAD, but not with PAL.     

In-Situ Wet Chemical Composition of Multicomponent Precursors to Blue Emitting Sr2CeO4 Phosphors

Hybrid precursors were assembled with cerium coordination polymers, polyethyl glycohol (PEG), SrCO3 and other functional components using a modified in-situ chemical polymeric gel technology. The hybrid precursors were calcinated to achieve the Sr2CeO4 phosphors, whose particle sizes were in the range of micrometer by XRD and SEM. The photoluminescence spectra indicate that the phosphors present a strong blue emission.     

Effect of Ammonia on the Gas-Phase Hydration of the Common Atmospheric Ion HSO4?

Hydration directly affects the mobility, thermodynamic properties, lifetime and nucleation rates of atmospheric ions. In the present study, the role of ammonia on the formation of hydrogen bonded complexes of the common atmospheric hydrogensulfate (HSO₄⁻) ion with water has been investigated using the Density Functional Theory (DFT). Our findings rule out the stabilizing effect of ammonia on the formation of negatively charged cluster hydrates and show clearly that the conventional (classical) treatment of ionic clusters as presumably more stable compared to neutrals may not be applicable to pre-nucleation clusters. These considerations lead us to conclude that not only quantitative but also qualitative assessment of the relative thermodynamic stability of atmospheric clusters requires a quantum-chemical treatment.     

Ames试验氯化致突变前体物在净水工艺中的去除研究

采用水样比活性作为评价指标，从Ａｍｅｓ试验结果和致突变前体物性质两方面，探讨了不同单元净水工艺对Ａｍｅｓ试验氯化致突变前体物的去除能力，从而为净水工艺的选择提供参考依据     

Post-Translational Modifications of Retroviral HIV-1 Gag Precursors: An Overview of Their Biological Role

Protein post-translational modifications (PTMs) play key roles in eukaryotes since they finely regulate numerous mechanisms used to diversify the protein functions and to modulate their signaling networks. Besides, these chemical modifications also take part in the viral hijacking of the host, and also contribute to the cellular response to viral infections. All domains of the human immunodeficiency virus type 1 (HIV-1) Gag precursor of 55-kDa (Pr55^Gag), which is the central actor for viral RNA specific recruitment and genome packaging, are post-translationally modified. In this review, we summarize the current knowledge about HIV-1 Pr55^Gag PTMs such as myristoylation, phosphorylation, ubiquitination, sumoylation, methylation, and ISGylation in order to figure out how these modifications affect the precursor functions and viral replication. Indeed, in HIV-1, PTMs regulate the precursor trafficking between cell compartments and its anchoring at the plasma membrane, where viral assembly occurs. Interestingly, PTMs also allow Pr55^Gag to hijack the cell machinery to achieve viral budding as they drive recognition between viral proteins or cellular components such as the ESCRT machinery. Finally, we will describe and compare PTMs of several other retroviral Gag proteins to give a global overview of their role in the retroviral life cycle.     

新型组合工艺对微污染原水中有机污染物和消毒副产物前体物的去除

本采用中试试验装置研究了生物陶粒过滤一微絮凝砂滤一活性炭吸附组合工艺，对微污染原水中有机污染物和消毒副产物前体物的去除效果。在原水UV254为0．047～0．065cm^-1，DOC为2．70～4．10mg／L，TOC为3．50～5．00mg／L的条件下，组合工艺对UV254，DOC、TOC平均去除率分别为98．4％、74．1％、69．2％。色-质联机分析结果表明，经组合工艺处理水中有机物由54种降至25种。组合工艺出水中三卤甲烷总含量不及常规工艺出水中该物质含量的五分之一。组合工艺能有效控制和消除水中有机物的污染，提供安全的优质饮用水。     

Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors

Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me₃Si)_0.80((CH₂=CH)MeSi)_1.0(MeHSi)_0.35] _n (VPS) or [MeHSiCH₂] _n (MPCS) with [R₂AlNH₂]₃, where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et₂AlNH₂]₃. In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu₂AlNH₂]₃ yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed.