• Wind and Structures
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• v.1 no.2
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• pp.175-181
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• 1998

Torsional flutter occurs at 2D rectangular cylinders with side ratios B/D smaller than about 8 or 10. On the other hand, slender cylinders indicate the occurrence of coupled flutter, which means the coupled derivatives of slender cylinders have more significant role for flutter instability than that of bluffer ones. In this paper, based upon so called "Step-by-step analysis", it is clarified the coupled derivatives stabilize torsional flutter instability of bluffer cylinders (e.x. B/D=5), while they destabilize torsional flutter or coupled flutter instabilities of mores slender cylinders. The boundary of them exists between B/D=5 and 8.

• YAKHAK HOEJI
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• v.43 no.1
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• pp.28-32
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• 1999

Four derivatives of kojic acid were synthesized and their inhibitory activities against tyrosinase were evaluated. The C-2 hydroxymethyl and C-7 hydroxyl of kojic acid were replaced by carboxylate and amine, respectively. These derivatives were coupled to L-phenylalanine, producing two amide compounds. The carboxylate derivative (3), its amide compound (5), and the amine derivative (7) were weak inhibitors. The amide compound (9) where amine derivative (7) coupled to L-phenylalanine showed strong inhibitory activity ($IC_{50}=24.6{\;}{\mu}M$) comparable to kojic acid.

• Journal of Microbiology and Biotechnology
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• v.28 no.2
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• pp.298-304
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• 2018

The single-vessel multienzyme UDP-${\alpha}$-$\text\tiny{D}$-glucose recycling system was coupled with a forward glucosylation reaction to produce novel glucose moiety-conjugated derivatives of different tetracycline antibiotic analogs. Among five tetracycline analogs used for the reaction, four molecules (chlorotetracycline, doxytetracycline, meclotetracycline, and minotetracycline) were accepted by a glycosyltransferase enzyme, YjiC, from Bacillus licheniformis to produce glucoside derivatives. However, the enzyme was unable to conjugate sugar units to rolitetracycline. All glucosides of tetracycline derivatives were characterized by ultraviolet absorbance maxima, ultra-pressure liquid chromatography coupled with photodiode array, and high-resolution quadruple time-of-flight electrospray mass spectrometry analyses. These synthesized glucosides are novel tetracycline derivatives.

• Wind and Structures
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• v.17 no.3
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• pp.275-298
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• 2013

This paper presents a number of approximated analytical formulations for the flutter analysis of long-span bridges using the so-called uncoupled flutter derivatives. The formulae have been developed from the simplified framework of a bimodal coupled flutter problem. As a result, the proposed method represents an extension of Selberg's empirical formula to generic bridge sections, which may be prone to one of the aeroelastic instability such as coupled-mode or single-mode (either dominated by torsion or heaving mode) flutter. Two approximated expressions for the flutter derivatives are required so that only the experimental flutter derivatives of ($H_1^*$, $A_2^*$) are measured to calculate the onset flutter. Based on asymptotic expansions of the flutter derivatives, a further simplified formula was derived to predict the critical wind speed of the cross section, which is prone to the coupled-mode flutter at large reduced wind speeds. The numerical results produced by the proposed formulas have been compared with results obtained by complex eigenvalue analysis and available approximated methods show that they seem to give satisfactory results for a wide range of study cases. Thus, these formulas can be used in the assessment of bridge flutter performance at the preliminary design stage.

• Bulletin of the Korean Chemical Society
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• v.11 no.5
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• pp.383-386
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• 1990

We have synthesized several bicyclic heteroaromatic compounds with bridgehead nitrogen from N-amine salts of heteroaromatic amines. 2-Amino and 2-unsubstituted thiazolo[3,2-b][l,2,4]triazole derivatives 2a-b were prepared by the cyclization reaction from N-amine salts of aminothiazole-5-yl(N-methoxyimino)acetate with cyanogen bromide and formamidine acetic acid salt, respectively. 2-Methylthiazolo[3,2-b][1,2,4]triazole 2c was obtained from N-acetylated N-amine salt of aminothiazole-5-yl(N-methoxyimino)acetate by the cyclization reaction in the presence of polyphosphoric acid (PPA). 2-Substituted and 2-unsubstituted thiazole[3,2-b][1,2,4]triazole derivatives 2a-c were coupled with 7-aminocephalosporanic acid (7-ACA). Coupled cephalosporin derivatives 1a-c did not have good antibacterial activities in vitro.

• Wind and Structures
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• v.22 no.3
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• pp.273-290
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• 2016

The flutter derivatives of bridge decks can be efficiently identified using the experimentally and/or numerically coupled forced vibration method. This paper addresses the issue of inherent requirement for adopting different frequencies of three modes in this method. The aerostatic force components and the inertia of force and moment are mathematically proved to exert no influence on identification results if the signal length (t) is integer (n=1,2,3...) times of the least common multiple (T) of three modal periods. It is one important contribution to flutter derivatives identification theory and engineering practice in this study. Therefore, it is unnecessary to worry about the determination accuracy of aerostatic force and inertia of force and moment. The influences of signal length, amplitude, and frequency ratio on flutter derivative are thoroughly investigated using a bridge example. If the signal length t is too short, the extraction results may be completely wrong, and particular attention should be paid to this issue. The signal length t=nT ($n{\geq}5$) is strongly recommended for improving parameter identification accuracy. The proposed viewpoints and conclusions are of great significance for better understanding the essences of flutter derivative identification through coupled forced vibration method.

• Journal of the Korean Applied Science and Technology
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• v.28 no.4
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• pp.438-448
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• 2011

Chitosan is widely used in cosmetics and medical fields. Special emphasis has been put on the chemical modification of chitosan to explore its full potential. We have described the synthesis and biological activity of novel peptide amino acid derivatives. The polyamino acid derivatives were synthesized by introducing alkylamine functional group on chitosan at C-6. The poor aqueous solubility of chitosan derivatives hinder both pharmacological studies and pharmaceutical development. To make amino acid coupled chitosan derivatives with improved biological effect and solubility, some attempts have been taken to consist of amino peptide group like aspartic acid and phenylalanine-aspartic acid derivatives onto chitosan C-6. The resultingly substituted chitosan was characterized by solubility in various solvents. We measured chitosan derivatives with $^1H$-NMR and $^{13}C$-NMR. Also, We were investigated on the physical properties and biological activities of these products.

• Bulletin of the Korean Chemical Society
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• v.11 no.6
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• pp.497-505
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• 1990

The function exp$(x^2)$erfc(x), which is often encountered in studies of electrode kinetics, is evaluated to an extended precision with 32 significant decimal digits in order to find theoretical relationships used in derivative polarography/voltammetry for a chemically-coupled electrode process. Computations with a lower precision are not successful. Evaluation of the function is accomplished by using three types of expansions for the function. Best ranges of arguments are selected for each equation for particular precisions for efficiencies. The method is successfully applied to calculate higher-order derivatives of the current-potential curves in all potential ranges for a reversible electron transfer reaction coupled with a prior chemical equilibrium (i.e., a CE type process). Various parameters that characterize the peak asymmetry (such as ratios of peak-heights, ratios of half-peak-widths, and separations in peak-potentials) are analyzed to find how kinetic and thermodynamic parameters influence shapes of the derivatives. The results from the CE process is compared with those from an EC process in which a reversible electron transfer is coupled with a follow-up homogeneous chemical reaction. The two processes exibit quite contrasting differences for values of the parameters.

• Bulletin of the Korean Chemical Society
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• v.21 no.6
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• pp.562-566
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• 2000

$\beta-D-Mannopyranosyl$ disaccharides have been obtained from the coupling of 4,6-O-benzylidene derivatives of ethylthio $\alpha-D-mannopyranoside$ employing NIS-TfOH promoter. NIS-TfOH promoted couplings of the corresponding ethylthio $\beta-D-glucopyranoside$ and produced $\alpha-D-glucopyranosyl$ disaccharides. IDCP (iodonium dicollidine perchlorate) was inactive toward the 4,6-O-benzylidenated ethylthio glucopyranosyl donor. However,lDCP coupled the 4,6-O-benzylidenated $ethylthio-\beta-D-galactopyranoside$ to give a-D-galactopyranosyl disaccharides.

• Journal of applied mathematics & informatics
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• v.30 no.5_6
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• pp.773-785
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• 2012

In this paper, we establish sufficient conditions for the existence and uniqueness of solutions to a general class of three-point boundary value problems for a coupled system of nonlinear fractional differential equations. The differential operator is taken in the Caputo fractional derivatives. By using Green's function, we transform the derivative systems into equivalent integral systems. The existence is based on Schauder fixed point theorem and contraction mapping principle. Finally, some examples are given to show the applicability of our results.