Adaptive SOR methods based on the Wolfe conditions

Numerical Algorithms - Because the expense of estimating the optimal value of the relaxation parameter in the successive over-relaxation (SOR) method is usually prohibitive, the parameter is often...     

On a problem related to the Vandermonde determinant

This short note describes new properties of the elementary symmetric polynomials, and reveals that the properties give an answer to the conjecture raised by El-Mikkawy in [M.E.A. El-Mikkawy, On a connection between the Pascal, Vandermonde and Stirling matrices—II, Appl. Math. Comput. 146 (2003) 759-769].     

Lanczos-type variants of the COCR method for complex nonsymmetric linear systems

Motivated by the celebrated extending applications of the well-established complex Biconjugate Gradient (CBiCG) method to deal with large three-dimensional electromagnetic scattering problems by Pocock and Walker [M.D. Pocock, S.P. Walker, The complex Bi-conjugate Gradient solver applied to large electromagnetic scattering problems, computational costs, and cost scalings, IEEE Trans. Antennas Propagat. 45 (1997) 140–146], three Lanczos-type variants of the recent Conjugate A-Orthogonal Conjugate Residual (COCR) method of Sogabe and Zhang [T. Sogabe, S.-L. Zhang, A COCR method for solving complex symmetric linear systems, J. Comput. Appl. Math. 199 (2007) 297–303] are explored for the solution of complex nonsymmetric linear systems. The first two can be respectively considered as mathematically equivalent but numerically improved popularizing versions of the BiCR and CRS methods for complex systems presented in Sogabe’s Ph.D. Dissertation. And the last one is somewhat new and is a stabilized and more smoothly converging variant of the first two in some circumstances. The presented algorithms are with the hope of obtaining smoother and, hopefully, faster convergence behavior in comparison with the CBiCG method as well as its two corresponding variants. This motivation is demonstrated by numerical experiments performed on some selective matrices borrowed from The University of Florida Sparse Matrix Collection by Davis.     

Synthesis and structure activity relationship studies of benzothieno[3,2-b]furan derivatives as a novel class of IKKbeta inhibitors

As a novel class of IKKbeta inhibitors, a series of tricyclic furan derivatives was designed and synthesized based on the structure of known thiophene IKKbeta inhibitors. Among the various fused furan derivatives synthesized, a benzothieno[3,2-b]furan derivative 13a displayed potent inhibitory activity towards IKKbeta in enzymatic and cellular assays. The potent inhibitory activity originates from an intramolecular non-bonded S...O interaction which was confirmed by the X-ray structure of JNK3 with 16k. The introduction of further substituents on the core structure led to the discovery of the 6-alkoxy derivatives, which possessed a comparable IKKbeta inhibitory activity to 13a and an improved metabolic stability. Among these, appropriately lipophilic compounds 16a, h, i, and 13g (log D>2) were found to possess good oral bioavailability.     

A novel de-O-chloroacetylation reagent: 1-seleonocarbamoylpiperidine

1-Selenocarbamoylpiperidine 2 chemoselectively cleaves the O-chloroacetyl group in the presence of other acyl groups such as acetyl, pivaloyl, and Fmoc without the assistance of a base. The high lipophilicity of 2 allowed us to use 1,4-dioxane, THF, and DMF as reaction solvents, thereby enabling dechloroacetylation at high temperature. A comparative experiment with other dechloroacetyl reagents showed that selenourea 2 has a high potential as a dechloroacetylation reagent.     

Conductive networked polymer gel electrolytes composed of poly(meth)acrylate,lithium salt,and ionic liquid

Self‐standing films of (meth)acrylate‐based polymer gel electrolytes with high ionic liquid content (80 wt %) were prepared by in situ thermally or photo induced radical copolymerization of mono‐functional and di‐functional (meth)acrylates in an ionic liquid in the presence/absence of a lithium salt. Their ionic conductivity, thermal property, mechanical property, and flammability were examined. 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI) or 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) was used as the ionic liquid, and lithium bis(trifluoromethanesulfonyl)imide LiTFSI was used as the lithium salt. The obtained films were semitransparent and flexible with good to moderate thermal stability and mechanical strength with high ionic conductivity. The EMImFSI‐containing gel electrolytes showed higher ionic conductivity than the corresponding EMImTFSI‐containing gel electrolytes. The ionic conductivity in the acrylate‐based gel electrolytes was slightly increased by addition of lithium salt, while that in the corresponding methacrylate‐based electrolytes was decreased significantly. The flame test showed the ionic liquid containing networked polymer gel electrolytes to have low if any flammability and was therefore confirmed to be highly safe. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and properties of methacrylate‐based networked polymers having ionic liquid structures

Methacrylate‐based networked polymers having ionic liquid structures were prepared by radical copolymerization of methyl methacrylate (MMA) with multifunctional crosslinkers: ethyleneglycol dimethacrylate (EGDMA), trimethylolpropane trimethacrylate (TMPTMA), or triethyleneglycol dimethacrylate (TEGDMA), in the presence of 1‐ethyl‐3‐methylethyl‐1‐imidazolium bis(trifluoromethane)sulfonyl imide (EMImTFSI). The fundamental physical properties of several film samples prepared by varying the monomer composition and ionic liquid content were investigated. The obtained materials became turbid with increasing crosslinker content and ionic liquid content. Their ionic conductivity increased with increasing ionic liquid content, while it was almost independent of the crosslinker content. EGDMA‐derived materials and TMPTMA‐derived materials showed higher ionic conductivity than TEGDMA‐derived materials. TMPTMA‐derived materials showed higher thermal stability than EGDMA or TEGDMA‐derived materials. EGDMA and TMPTMA‐derived materials were stiffer than the TEGDMA‐derived materials. The elastic modulus of the film samples increased but the film became more brittle with the increase of crosslinker content. Scanning electron microscopy and atomic force microscopy observation revealed that phase separation of networked polymers and ionic liquid occurred in the highly crosslinked samples, and the phase separation structures became larger in scale with the increase of crosslinking density. This phase separation was considered to have a strong effect on the mechanical properties of the film samples. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Construction of polymer skeletons with radiation‐scissile groups at predetermined sites

Polymers that can be cleaved at predetermined sites by ionizing radiations have been synthesized by incorporating benzylic esters into their skeletons. Secondary electrons generated by ionizing radiations are captured by the benzylic esters to dissociate into benzylic radicals and carboxyl anions, so that the polymer skeletons are cleaved at predetermined sites. The γ‐irradiation of a three‐armed star polymer, 1,2,4‐tri‐(2‐polystyrene‐2‐methyl‐propyonyloxymethyl)‐benzene, results in the selective scission of the arms, and the resultant radicals neither combine with each other nor graft to the other polymer skeletons to give larger polymer molecules. The irradiation of poly(methyl methacrylate) crosslinked with 4‐methacryloyloxybenzyl methacrylate results in the selective scission at the crosslinking sites with high radiation‐chemical efficiency of 8.5 scissions per 100 eV radiation energy absorbed. These results indicate that the incorporation of benzylic esters into polymer skeletons opens a new way of constructing radiation resists with high sensitivity to ionizing radiations and high resistivity to plasma etching. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1945–1953, 2008     

Crystal structures of Candida albicans N-myristoyltransferase with two distinct inhibitors

Myristoyl-CoA:protein N-myristoyltransferase (Nmt) is a monomeric enzyme that catalyzes the transfer of the fatty acid myristate from myristoyl-CoA to the N-terminal glycine residue of a variety of eukaryotic and viral proteins. Genetic and biochemical studies have established that Nmt is an attractive target for antifungal drugs. We present here crystal structures of C. albicans Nmt complexed with two classes of inhibitor competitive for peptide substrates. One is a peptidic inhibitor designed from the peptide substrate; the other is a nonpeptidic inhibitor having a benzofuran core. Both inhibitors are bound into the same binding groove, generated by some structural rearrangements of the enzyme, with the peptidic inhibitor showing a substrate-like binding mode and the nonpeptidic inhibitor binding differently. Further, site-directed mutagenesis for C. albicans Nmt has been utilized in order to define explicitly which amino acids are critical for inhibitor binding. The results suggest that the enzyme has some degree of flexibility for substrate binding and provide valuable information for inhibitor design.