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1.
In this paper, we explore the interplay of four different conjectures on certain zero-sum problems in Zp Zp. This study of the inter-relations between these conjectures leads to the conclusion that determining the structure of minimal zero sequences (see below for the precise definition) is crucial. Also, we study the analogous situation in Zn. 相似文献
2.
Critical problems of the present approach of electrolytes for Solid Oxide Fuel Cells (SOFCs) for commercialization are discussed.
Major progress is expected from the development of materials based on the “SEA (Single Element Arrangement)” concept. The
galvanic cell consists in this case basically of a single chemically homogeneous compound, which functions as electrodes at
high and low activity and as electrolyte at intermediate activities of the electroactive component.
In view of the large structural flexibility of the chemical nature of the constitutents, we explored perovskite (ABO3)-type compounds to be used as SEAs for SOFCs. Results of studies on Pr-substituted LSGM and Fe-substituted SrSnO3 perovskite-type oxides are presented. For instance, SrSn1-xFexO3-δ with x=0.1 exhibits p and n-type electronic conduction at the cathode and anode sides of the SOFC, respectively, while oxide
ion conduction prevails at intermediate oxygen partial pressures. The SEA concept is also applicable for other devices in
the field of Ionics. 相似文献
3.
In this paper, we describe the design and synthesis of a novel hybrid foldamer, derived from a conformationally constrained aliphatic-aromatic amino acid conjugate that adopts a well-defined, compact, three-dimensional structure, governed by a combined conformational restriction imposed by the individual amino acids from which the foldamer is composed. Conformational investigations confirmed the prevalence of a unique doubly bent conformation for the foldamer, in both solid and solution states, as evidenced from single crystal X-ray and 2D NOESY studies, respectively. The findings suggest that constrained aliphatic-aromatic amino acid conjugates offer new avenues for the de novo design of hybrid foldamers with distinctive structural architectures. Furthermore, the de novo design strategy disclosed herein has the potential for significantly augmenting the ‘tool-box’ of the modern day peptidomimetic chemist, as well as providing a novel approach to the field of rational design. 相似文献
4.
Oberstrass FC Allain FH Ravindranathan S 《Journal of the American Chemical Society》2008,130(36):12007-12020
RNA recognition by proteins is often accompanied by significant changes in RNA dynamics in addition to conformational changes. However, there are very few studies which characterize the changes in molecular motions in RNA on protein binding. We present a quantitative (13)C NMR relaxation study of the changes in RNA dynamics in the pico-nanosecond time scale and micro-millisecond time scale resulting from interaction of the stem-loop SRE-RNA with the VTS1p-SAM domain. (13)C relaxation rates of the protonated carbons of the nucleotide base and anomeric carbons have been analyzed by employing the model-free formalism, for a fully (13)C/(15)N-labeled sample of the SRE-RNA in the free and protein-bound forms. In the free RNA, the nature of molecular motions are found to be distinctly different in the stem and the loop region. On binding to the protein, the nature of motions becomes more homogeneous throughout the RNA, with many residues showing increased flexibility at the aromatic carbon sites, while the anomeric carbon sites become more rigid. Surprisingly, we also observe indications of a slow collective motion of the RNA in the binding pocket of the protein. The observation of increased motions on binding is interesting in the context of growing evidence that binding does not always lead to motional restrictions and the resulting entropy gain could favor the free energy of association. 相似文献
5.
Thangadurai TD Singh NJ Hwang IC Lee JW Chandran RP Kim KS 《The Journal of organic chemistry》2007,72(14):5461-5464
By linking the urea moiety at the 1,8 positions of the carbazole fragment, we synthesized host systems 1, 2, and 3 having both chromogenic and fluorogenic signaling subunits. The spectral changes in both the signaling subunits could be easily analyzed via a simple 2-dimensional (2D) analytic approach described here, which enables us to differentiate the given set of anions. Structural studies are also reported. 相似文献
6.
We report the effect of donor-doped perovskite-type BaCeO(3) on the chemical stability in CO(2) and boiling H(2)O and electrical transport properties in various gas atmospheres that include ambient air, N(2), H(2), and wet and dry H(2). Formation of perovskite-like BaCe(1-x)Nb(x)O(3±δ) and BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) (x = 0.1; 0.2) was confirmed using powder X-ray diffraction (XRD) and electron diffraction (ED). The lattice constant was found to decrease with increasing Nb in BaCe(1-x)Nb(x)O(3±δ), which is consistent with Shannon's ionic radius trend. Like BaCeO(3), BaCe(1-x)Nb(x)O(3±δ) was found to be chemically unstable in 50% CO(2) at 700 °C, while Zr doping for Ce improves the structural stability of BaCe(1-x)Nb(x)O(3±δ). AC impedance spectroscopy was used to estimate electrical conductivity, and it was found to vary with the atmospheric conditions and showed mixed ionic and electronic conduction in H(2)-containing atmosphere. Arrhenius-like behavior was observed for BaCe(0.9-x)Zr(x)Nb(0.1)O(3±δ) at 400-700 °C, while Zr-free BaCe(1-x)Nb(x)O(3±δ) exhibits non-Arrhenius behavior at the same temperature range. Among the perovskite-type oxides investigated in the present work, BaCe(0.8)Zr(0.1)Nb(0.1)O(3±δ) showed the highest bulk electrical conductivity of 1.3 × 10(-3) S cm(-1) in wet H(2) at 500 °C, which is comparable to CO(2) and H(2)O unstable high-temperature Y-doped BaCeO(3) proton conductors. 相似文献
7.
A novel family of metal oxides with a chemical formula of Sr(2)Ce(1-x)Pr(x)O(4) (x = 0, 0.2, 0.5, 0.8, and 1) was developed as mixed oxide ion and electronic conductors for solid oxide fuel cells (SOFCs). All of the investigated samples were synthesized by the ceramic method at 1000 °C in air and characterized by powder X-ray diffraction (PXRD), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and electrochemical impedance spectroscopy (EIS). Ex-situ PXRD reveals that the Sr(2)PbO(4)-type Sr(2)CeO(4) decomposes readily into a mixture of perovskite-type SrCeO(3) and rock-salt-type SrO at 1400 °C in air. Surprisingly, the decomposed products are converted back to the original Sr(2)PbO(4)-type Sr(2)CeO(4) phase at 800 °C in air, as confirmed by in-situ PXRD. Thermal decomposition is highly suppressed in Sr(2)Ce(1-x)Pr(x)O(4) compounds for Pr > 0, suggesting that Pr improves the thermal stability of the compounds. Rietveld analysis of PXRD and SAED supported that both Pr and Ce ions are located on the 2a site in Pbam (space group no. 55). The electrical transport mechanism could be correlated to the reduction of Pr and/or Ce ions and subsequent loss of oxide ions at elevated temperatures, as shown by TGA and in-situ PXRD. Conductivity increases with Pr content in Sr(2)Ce(1-x)Pr(x)O(4). The highest total conductivity of 1.24 × 10(-1) S cm(-1) was observed for Sr(2)Ce(0.2)Pr(0.8)O(4) at 663 °C in air. 相似文献
8.
Natural kaolinitic clay possessing transition metals such as Fe, Ti in its lattice has been found to catalyze efficiently the protection of a variety of alcohols with 2,3-dihydro-4H-pyran (DHP) and hexamethyldisilazane (HMDS) at ambient conditions. 相似文献
9.
Premanand Ramrao Patil K. P. Ravindranathan Kartha 《Journal of carbohydrate chemistry》2013,32(7):411-419
Aryl glycosides have been prepared from a range of readily available glycosyl halides by a solvent-free mechanochemical procedure employing a planetary ball mill in excellent yields. Besides being a solvent-free reaction, the procedure has been successful in eliminating the need for employing any phase-transfer catalyst in the reaction. 相似文献
10.
S. Ramasamy D. J. Smith P. Thangadurai K. Ravichandran T. Prakash K. PAdmaprasad V. Sabarinathan 《Pramana》2005,65(5):881-891
The ultra high vacuum chamber was developed in the Department of Nuclear Physics, University of Madras with the funding from
DST, India. This UHV chamber is used to prepare nanocrystalline materials by inert gas condensation technique (IGCT). Nanocrystalline
materials such as PbF2, Mn2+-doped PbF2, Sn-doped In2O3 (ITO), ZnO, Al2O3, Ag2O, CdO, CuO, ZnSe:ZnO etc., were prepared by this technique and characterized. Results of some of these materials will be
presented in this paper. In solid-state207Pb NMR on PbF2 a separate signal due to the presence of grain boundary has been observed. The structural phase transition pressure during
the phase transformation from the cubic phase to orthorhombic phase under high pressure shows an increase with the decrease
in grain size. Presence of electronic centres in nanocrystalline PbF2 is observed from Raman studies and the same has been confirmed by photoluminescence studies. Al2O3 was prepared and56Fe ions were implanted. After implantation segregation of56Fe ions was examined by SEM. The oxidation properties of ITO were studied by HRTEM. As against the expectation of oxide coating
on individual nanograins of In-Sn alloy, ITO nanograins grew into faceted nanograins on heat treatment in air and O2 atmosphere. The growth of ITO under O2 atmosphere showed pentagon symmetry. The PMN was initially prepared by solid-state reaction. Further, this PMN relaxor material
will be used to convert into nanocrystalline PMN by IGCT with sputtering and will be studied 相似文献