Showing papers by "Pusan National University published in 1989"
01 Jun 1989-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a numerical algorithm for the two-dimensional solidification problem in the twin-roll continuous casting system is presented, which can be applied to general full Navier-Stokes and energy equations.
Abstract: A numerical algorithm for the two-dimensional solidification problem in the twin-roll continuous casting system is presented in this paper Attention is focused on the elucidation of heat transfer and flow characteristics in both the liquid and the solid phases The present mathematical model can be applied to general full Navier-Stokes and energy equations, thereby covering the wide range of twin-roll casting conditions The boundary fixing method (BFM) is adopted to handle the moving boundary, and the resultant transformed governing equations for the solid and liquid regions are solved separately by using a usual explicit-type finite difference method In this paper, a general numerical methodology is presented, and the quantitative relationships between the important control parameters in continuous casting of twin-roll type (such as the roll speed, the roll gap, the initial temperature of molten materials, the material properties, the solidification profile, and the endpoint of solidification) are clarified in detail The present numerical results have been compared with experimental results obtained separately to check the validity of the proposed method
45 citations
TL;DR: Under certain hypotheses, the equivalence between the reachable trajectory set or almost reachably trajectory set of the above system and that of its corresponding linear system is shown.
Abstract: For the abstract delay Volterra control system,
$$x(t) = U(t, 0)\phi (0) + \int_0^t {U(t, s)\{ F(s, x_s (\phi )) + (B\upsilon )(s)\} ds,} $$
we study the trajectory reachable set
$$\begin{gathered} K_\alpha (F) = \{ x( \cdot :\upsilon ) \in C(\alpha , T:X):\} \hfill \\ x( \cdot ) satisfies the above system, \upsilon \in V_{ad} \} , 0< \alpha \leqslant T. \hfill \\ \end{gathered} $$
Under certain hypotheses, we show the equivalence between the reachable trajectory set or almost reachable trajectory set of the above system and that of its corresponding linear system (in caseF≡0).
40 citations
TL;DR: In this paper, the authors analyzed how the supplier can formulate the terms of a quantity-discount pricing schedule, assuming that the buyer always behaves optimally, and derived formulas for price and order size which maximize the economic gain of the supplier resulting from revising prices and order sizes.
Abstract: The purpose of this paper is to analyse how the supplier can formulate the terms of a quantity-discount pricing schedule, assuming that the buyer always behaves optimally. Formulas are derived for price and order size which maximize (1) the economic gain of the supplier resultant from revising price and order size, (2) the gain of the buyer, and (3) the sum of the gains of both parties. It is suggested how the supplier can induce the buyer to a predetermined price and order-size level of mutual benefit by utilizing an all-unit and incremental quantity-discount system.
39 citations
TL;DR: In this paper, the tensile properties and morphology of polyolefin ternary blends of EPDM, polypropylene and high density polyethylene were studied in a laboratory internal mixer.
Abstract: The tensile properties and morphology of the polyolefin ternary blends of ethylenepropylene–diene terpolymer (EPDM), polypropylene and high density polyethylene were studied. Blends were prepared in a laboratory internal mixer where EPDM was cured in the presence of PP and HDPE under shear with dicumyl peroxide (DCP). For comparison, blends were also prepared from EPDM which was dynamically cured alone and blended with PP and HDPE later (cure–blend). The effect of DCP concentration, intensity of the shear mixing, and rubber/plastics composition was studied. The tensile strength and modulus increased with increasing DCP concentration in the blends of EPDM-rich compositions but decreased with increasing DCP concentration in blends of PP-rich compositions. In the morphological analysis by scanning electron microscopy (SEM), the small amount of EPDM acted as a compatibilizer to HDPE and PP. It was also revealed that the dynamic curing process could reduce the domain size of the crosslinked EPDM phase. When the EPDM forms the matrix, the phase separation effect becomes dominant between the EPDM matrix and PP or HDPE domain due to the crosslinking in the matrix.
37 citations
TL;DR: The large piezoelectric and electromechanical anisotropies present in modified PbTiO/sub 3/ ceramics also appear to be an intrinsic property of the material.
Abstract: The dielectric and electromechanical coupling properties of Sm-doped and Mn-doped PbTiO/sub 3/ ceramics were investigated from 4.2 to 300 K. The upper and lower limits of the ceramic dielectric and piezoelectric properties were calculated by averaging the single-domain constants that were determined from a phenomenological theory. Comparisons of the measured and calculated properties were then made. The measured dielectric permittivity epsilon /sup T//sub 33/ and piezoelectric strain coefficient d/sub 33/ appear to be mainly due to the averaging of the intrinsic single-domain response. The large piezoelectric and electromechanical anisotropies present in modified PbTiO/sub 3/ ceramics also appear to be an intrinsic property of the material. The piezoelectric coefficient d/sub 31/, as well as the planar coupling coefficient k/sub p/, was found to have very small values over two temperature regions, from 120 to 170 K and from 240 to 270 K. >
30 citations
TL;DR: Catechin and catechin glycoside named uldavioside A were isolated from the Korean folk medicineUlmus davidiana and their structure has been determined as (+)-catechin-5-O-β-D-apiofuranoside.
Abstract: Catechin and catechin glycoside named uldavioside A were isolated from the Korean folk medicineUlmus davidiana. Based on chemical and physicochemical evidences, their structure have been determined as (+)-catechin (1) and (+)-catechin-5-O-β-D-apiofuranoside (2).
26 citations
15 Oct 1989
TL;DR: In this article, the effects of protein denaturants on cloud point and Krafft point of polyoxyl 10 cetyl ether were investigated, and it was shown that the changes in cloud point are due mainly to the interaction of proteins with the hydrated polyoxyethylene shell of the nonionic micelles and that the hydrocarbon core is not involved.
Abstract: The effects of a variety of protein denaturants (seven ureas, three thioureas, acetamide, and guanidinium chloride) on the cloud point and Krafft point ofpolyoxyl 10 cetyl ether were investigated. All additives raised the cloud point in direct proprotion to their concentration in the range 0 to 0.5 m. From 0.5 to 1.0 m, the cloud point increases were less than proportional to additive concentration. Owing to increased micellar solubilization, higher degrees of alkylation of the ureas and thioureas resulted in greater cloud point increases. Urea, methylurea, thiourea, and acetamide did not change the Krafft point, while the more highly alkylated ureas and thioureas produced modest decreases. Cloud point increases and Krafft point decreases represent salting in of the nonionic surfactant. At comparable concentrations, all additives increased the cloud points of polyoxyl 10 cetyl ether and of octoxynol 9 to the same extent, even though octoxynol 9 is more polar owing to the presence of a benzene ring. This indicates that the changes in cloud point are due predominantly to the interaction of the protein denaturants with the hydrated polyoxyethylene shell of the nonionic micelles, and that the hydrocarbon core is not involved. The efficiency of denaturants to salt in nonionic surfactants, as shown by increases in cloud point, was proportional to their efficiency to denature proteins, as shown by reductions in the molar absorption coefficient of the Soret band. This observation documents the similarity between the clouding phenomenon of polyoxyethylated surfactants and the denaturation of proteins.
23 citations
TL;DR: In this article, internal olefins are oxidized selectively to α-chloro ketones in excellent yields from the reaction with chromic anhydride-chlorotrimethylsilane in carbon tetrachloride.
19 citations
TL;DR: It is suggested that in the rabbit TEA transport across the basolateral membranes is driven by an inside-negative potential and that Transport across the brush-border membrane is drivenBy a H+ gradient via an electroneutral H+/TEA antiport system.
Abstract: Transport of [14C]tetraethylammonium (TEA), an organic cation, was studied in brush-border (BBMV) and basolateral (BLMV) membrane vesicles isolated from rabbit kidney cortex. In BBMV, the presence of an outwardly directed H+ gradient induced a marked stimulation of TEA uptake against its concentration gradient (overshoot phenomenon), whereas a valinomycin-induced inside-negative potential had no effect on TEA uptake. In BLMV, TEA uptake was significantly stimulated by the presence of an outwardly directed H+ gradient and by an inside-negative potential, but the effect of H+ gradient was absent when the vesicles were chemically ‘voltage clamped’. In BBMV, internal H+ stimulated TEA uptake in a non-competitive manner by binding at a site with apparent pKa of 6.87. External H+ inhibited TEA uptake through a direct interaction with the putative H+/organic-cation exchanger at a site with apparent pKa of 6.78. Changing external pH while maintaining the pH gradient constant produced a result similar to that obtained by changing external pH alone. Increasing external H+ showed a mixed-type inhibition of TEA uptake. These results suggest that in the rabbit TEA transport across the basolateral membranes is driven by an inside-negative potential and that transport across the brush-border membrane is driven by a H+ gradient via an electroneutral H+/TEA antiport system.
16 citations
TL;DR: From the stem of Cudrania tricuspidata, β-sitosterol and β-sensorol glucoside, arthocarpesin, norarthocarpetin, and 5-O-methyl genistein were isolated and characterized by spectral data as discussed by the authors.
Abstract: From the stem ofCudrania tricuspidata, β-sitosterol, β-sitosterol glucoside, arthocarpesin, norarthocarpetin, and 5-O-methyl genistein were isolated and characterized by spectral data.
14 citations
TL;DR: Results suggest that superoxide-dependent relaxing factor is released from EC differently than the endothelium-derived relaxing factor mediated by acetylcholine, which was not associated with cyclic guanosine 3',5'-monophosphate formation.
Abstract: In the present work, an experimental system was designed to study superoxide anion radical, implicated as the cause of vascular dilatation. To circumvent its direct effect, we employed a two-bath system. When the endothelial cells (EC) were exposed to electrical field stimulation (EFS) or to a hypoxanthine-xanthine oxidase system in bath A plus its physiological buffer solution suffused on a helical strip of cat basilar artery in bath B, the contraction to 5-hydroxytryptamine (5-HT) was depressed to approximately 40-50% of the control value. The reduction was not elicited on EFS in a state of calcium deficiency or in the absence of EC. The depression could be prevented by pretreatment with superoxide dismutase (SOD), but not with an effective dose of catalase, dimethyl sulfoxide (DMSO), mannitol, or indomethacin. The percent depression of contraction was paralleled by an increase in SOD-inhibitable cytochrome c reduction, which was not associated with cyclic guanosine 3',5'-monophosphate formation. These results suggest that superoxide-dependent relaxing factor is released from EC differently than the endothelium-derived relaxing factor mediated by acetylcholine.
TL;DR: In this article, a replacement policy for a system in which minimal repair cost increases in system age is considered, where the mean cost rate is used as a criterion for optimization, and it is shown that the optimal replacement policy minimizing the mean rate is finite and unique.
TL;DR: Cotton xanthate, which was obtained by treating cotton with carbon disulfide in alkaline solution, was treated with the solution of polyvalent metal ions to produce cotton xanthates-metal chelates, and antimicrobial agents with suitable structures could subsequently be coupled to the chelate with ease at moderate pH values and in aqueous solution.
Abstract: Cotton xanthate, which was obtained by treating cotton with carbon disulfide in alkaline solution, was treated with the solution of polyvalent metal ions to produce cotton xanthate-metal chelates. This chelation reaction was readily and simply achieved, and antimicrobial agents with suitable structures could subsequently be coupled to the chelate with ease at moderate pH values and in aqueous solution. Metal ions used in present work include Cu(II), Zn(II) and Fe(III). Tetracycline, streptomycin, neomycin and pyrithion were used as antimicrobial/antifungal agents. Antibacterial activities were measured employing ditch plate method against G(+)Staphylococcus aureus, Streptococcus faecalis, and G(−)Escherichia coli, Enterobacter aerogenes, and the fungus,Aspergillus niger. All the cotton xanthate-metal-antimicrobial agent chelates exhibited activities whereas the cotton xanthate-metal chelates themselves were inactive. Considering the extensive washing procedures and results from control experiments, possibility of the involvement of physical adsorption for the binding of drugs could be excluded.
TL;DR: Release of a vascular-inhibitory factor from endothelial cells (EC), different from endothelium-derived relaxant factor (EDRF), was identified through use of a two-bath system that precluded the effects of oxygen-free radicals when electrical field stimulation is directly imposed on detector muscle.
Abstract: Release of a vascular-inhibitory factor from endothelial cells (EC), different from endothelium-derived relaxant factor (EDRF), was identified through use of a two-bath system. This two-bath system precluded the effects of oxygen-free radicals that appear when electrical field stimulation (EFS) is directly imposed on detector muscle.
TL;DR: In this paper, the authors describe the preparation of copolymeres de styrene and of vinyl naphtalene and of melanges of ces copolymres avec des poly(methyl vinyl ethers).
Abstract: Preparation de copolymeres de styrene et de vinyl naphtalene et de melanges de ces copolymeres avec des poly(methyl vinyl ethers). Mesure de la transparence optique, de la temperature de transition vitreuse, analyse par spectroscopie IR et correlation avec la miscibilite des melanges. Relation etroite entre la miscibilite du melange et la composition du copolymere et la concentration du melange: augmentation de la miscibilite avec la proportion du styrene dans le copolymere
TL;DR: In this paper, it was shown that the spectral mapping theorems such as exp(tσ(Z)) ⊂ σ(Tt) for everyt ≥ 0 hold.
Abstract: LetZ be a generator of an exponentially boundedC-semigroup {St}t≥0 in a Banach space and letTt=C−1St. We show that the spectral mapping theorems such as exp(tσ(Z)) ⊂ σ(Tt) and exp(tσp(Z)) ⊂ tσp(Tt) ⊂ exp(tσp(Z)) ⋃ {0} for everyt≥0 hold.
TL;DR: In this article, the problem of determining the optimal number of redundant units in a standby system is considered and the expected cost rate is obtained, and the number of redundancy units minimizing the expected costs is shown to be finite and unique.
TL;DR: In this paper, an exact numerical solution to the 2D laminar boundary-layer equations of power-law non-newtonian fluids is obtained using a finite difference technique, no limitation has been imposed on the flow behavior index(n) or generalized Prandli number.
Abstract: An exact numerical solution to the 2-D(Two-Dimensional) laminar boundary-layer equations of power-law non-newtonian fluids is obtained using a finite difference technique. No limitation has been imposed on the flow behavior index(n) or generalized Prandli number As a test case, velocity and temperature fields around a circular cylinder in crossflow were calculated The result clearly indicated that heat transfer of power-law materials is governed by shear dependent viscosity.
TL;DR: In this paper, a new nonlinear controller design method called the QLQG/LTR method is proposed, which is related to the use of statistical linearization, LQG, and IRIDF methods.
Abstract: A new nonlinear controller design method called the QLQG/LTR method is proposed This method is related to the use of statistical linearization, LQG/LTR, and IRIDF methods It is applied to a position servo with Coulomb friction The computer simulation results show that the QLQG/LTR control system can adapt automatically to changes in input magnitude
TL;DR: In this paper, the QLQG/LTR control method is applied to a nonlinear system with Coulomb friction, which has a non-Gaussian nature, and a modified model based compensator is proposed.
Abstract: The QLQG/LTR control method is applied to a nonlinear system with Coulomb friction which has a non-Gaussian nature. It is shown that the non-Gaussian nature degrades the effectiveness of the QLQG/LTR design method. Thus, a method for alleviating this problem is proposed. It is the QLQG/LTR control method with a modified model based compensator which can consider the non-Gaussian nature of nonlinear systems. The computer simulation results show that the responses of this nonlinear control system are relatively insensitive to the imput magnitude even if there exist a hard nonlinearity and a non-Gaussian nature in the plant.
TL;DR: In this article, the binding sites of piroxicam and HMBDC to the metal ions were suggested and the stability constants of the complexes were determined at μ → 0. The thermodynamic parameters for the complex formations have also been calculated from the Gibbs-Helmholtz plot.
TL;DR: On etudie les possibilites d'addition de Cd 5 (PO 4 ) 3 Cl afin d'elever le domaine de temperature applicable for des ceramiques piezoelectriques de BaTiO 3
Abstract: On etudie les possibilites d'addition de Cd 5 (PO 4 ) 3 Cl afin d'elever le domaine de temperature applicable pour des ceramiques piezoelectriques de BaTiO 3
TL;DR: In this paper, the free objects in the n-abelian groups of Levi are described in terms of the nabelian group of free objects of the Fibonacci varieties.
Abstract: Fibonacci varieties were introduced by one of us in 1978 and a natural generalisation was studied shortly afterwards. We carry this investigation one stage further by giving a description of the free objects in these varieties. This is done in terms of the n-abelian groups of Levi.
TL;DR: The authors found that full voicing is generally independent of the variation in the oral closure interval of a lax stop: full voicing will not necessarily occur for the shortest lax stop closures of short duration.
TL;DR: It is suggested that B-HT 920 inhibits vagally induced gastric acid secretion by activation of presynaptic α-adrenoceptors located on the vagally stimulated pathways in the gastric wall and this effect of B- HT 920 is more related to α1- adrenOceptors than α 1-adRenocepters.
Abstract: Effects of B-HT 920 on the vagally stimulated gastric acid secretion were studied in anesthetized and gastric fistula rats. When the gastric acid secretion was increased by stimulation of the vagus nerve, B-HT 920 significantly inhibited the vagally induced gastric acid secretion. This inhibitory effect of B-HT 920 was partially attenuated by prazosin, α1-adrenoceptor antagonist and virtually abolished by yohimbine, α2-adrenoceptor antagonist. On the other hand, when the gastric acid secretion was increased by the infusion of bethanechol, a muscarinic parasympathetic stimulant, B-HT 920 had no effect on the bethanechol-induced gastric acid secretion. These results suggest that B-HT 920 inhibits vagally induced gastric acid secretion by activation of presynaptic α-adrenoceptors located on the vagally stimulated pathways in the gastric wall and this effect of B-HT 920 is more related to α1-adrenoceptors than α1-adrenoceptors.
01 Aug 1989
TL;DR: In this paper, cyclic and acyclic chiral ketones were resolved as oxime 3,5-dinitrophenyl carbamates on a chiral stationary phase derived from (S)-1-(6,7-direthyl-1-naphthyl)isobutylamine.
Abstract: Cyclic and acyclic chiral ketones have been resolved as their oxime 3,5-dinitrophenyl carbamates on a chiral stationary phase derived from (S)-1-(6,7-direthyl-1-naphthyl)isobutylamine.
TL;DR: In this article, internal olefins are oxidized selectively to α-chloro ketones in excellent yields from the reaction with chromic anhydride-chlorotrimethylsilane in carbon tetrachloride.
Abstract: Disubstituted internal olefins are oxidized selectively to α-chloro ketones in excellent yields from the reaction with chromic anhydride-chlorotrimethylsilane in carbon tetrachloride.