• Applied Chemistry for Engineering
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• v.27 no.1
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• pp.110-114
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• 2016

Cr(VI)-pyrazine complex (PZCC) was synthesized by the reaction of pyrazine with chromium (VI) trioxide in 6 M HCl. The structure was characterized using IR spectroscopy and inductively coupled plasma (ICP). The oxidation of benzyl alcohol using PZCC in various solvents showed that the reactivity increased with the increase of the dielectric constant, in the order: N,N'-dimethylform-amide > acetone > chloroform > cyclohexene. In the presence of N,N'-dimethylformamide solvent with an acidic catalyst such as sulfuric acid ($H_2SO_4$ solution), PZCC oxidized benzyl alcohol (H) and its derivatives ($p-OCH_3$, $m-CH_3$, $m-OCH_3$, m-Cl, $m-NO_2$). Electron-donating substituents accelerated the reaction rate, whereas electron acceptor groups retarded the reaction rate. Hammett reaction constant (${\rho}$) was -0.70 (308 K). The observed experimental data were used to rationalize the hydride ion transfer in the rate-determining step.

• Bulletin of the Korean Chemical Society
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• v.32 no.4
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• pp.1165-1169
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• 2011

Second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of 2,4-dinitrophenyl phenyl thionocarbonate 4 with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plot for the reactions of 4 exhibits downward curvature (i.e., ${\beta}_1$ = 0.21 and ${\beta}_2$ = 1.04), indicating that the reactions proceed through a stepwise mechanism with a change in rate-determining step. It has been found that 4 is less reactive than its oxygen analogue, 2,4-dinitrophenyl phenyl carbonate 3, although the thionocarbonate is expected to be more electrophilic than its oxygen analogue. The $pK_a$ at the center of the Br${\o}$nsted curvature, defined as $pK_a^o$, has been analyzed to be 6.6 for the reactions of 4 and 8.5 for those of 3. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that the reactions of 4 result in smaller $k_1$ values but larger $k_2/k_{-1}$ ratios than the corresponding reactions of 3. The larger $k_2/k_{-1}$ ratios have been concluded to be responsible for the smaller $pK_a^o$ found for the reactions of 4.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2593-2597
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-$NO_2$) with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plots exhibit downward curvature (e.g., $\beta_2$ = 0.89 ~ 0.96 when $pK_a$ < 9.5 while $\beta_1$ = 0.38 ~ 0.46 when $pK_a$ > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The ${pK_a}^o$, defined as the $pK_a$ at the center of Br${\o}$nsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that $k_1$ is governed by the electronic nature of the substituent X but the $k_2/k_{-1}$ ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the $k_2/k_{-1}$ ratio.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.648-653
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• 2014

Cr(VI)-heterocyclic complex (2,4'-bipyridinium chlorochromate) was synthesized by the reaction between heterocyclic compound(2,4'-bipyridine) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,4'-bipyridinium chlorochromate in various solvents showed that the reactivity increased with the increase of the dielectric constant (${\varepsilon}$), in the order : N,N-dimet-hylformamide (DMF) > acetone > chloroform > cyclohexene. In the presence of DMF solvent with acidic catalyst such as hydrochloric acid (HCl solution), 2,4'-bipyridinium chlorochromate oxidized benzyl alcohol (H) and its derivatives (p-$CH_3$, m-Br, m-$NO_2$). Electron-donating substituents accelerated the reaction rate, whereas electron acceptor groups retarded the reaction rate. The Hammett reaction constant (${\rho}$) was -0.67 (303 K). The observed experimental data have been rationalize the proton transfer occurred followed the formation of a chromate ester in the rate-determining step.

• Journal of Soil and Groundwater Environment
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• v.8 no.1
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• pp.48-56
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• 2003

A geophysical conductivity logging technique has been adopted to determine hydraulic constants using a simplified physical model that depicts the borehole condition. An experiment has been made by monitoring the conductivity change within the model hole using borehole environment water and incoming-outgoing water of different salinity, under the state of constant flow rate by maintaining balance between inflow and outflow. Conductivity variation features were observed that depended on flow rate, salinity contrasts between fluid within the hole and incoming-outgoing fluid, and density contrasts between fluid conductivity within the hole and incoming fluid. The results of the experiment show the uniform change of fluid conductivity within the hole with time, a fairly good correlation between the flow rate and the conductivity change rate. The geophysical conductivity logging technique can be an efficient tool for determining hydraulic constants if the model equation is verified by henceforward experiments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.9B
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• pp.808-817
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• 2004

Many researchers are now working in the Low-Rate WPAN environment. Low-Rate WPAN has as its goal the enhancing computer use by making many sensors available throughout the physical environment, but making them effectively invisible to the user. Low-Rate WPAN environment consists of wireless sensor devices that may move often. Movement of hosts results in a change in routes and the need of some mechanism for determining new routes. This paper suggests an approach to utilize location information to improve performance of a routing mechanism for Low-Rate WPAN Environment. Accordingly, we proved that the proposed mechanism results in a significant reduction in a number of routing messages when comparing with existing mechanisms.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2001.11a
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• pp.42-42
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• 2001

The rate of coating consolidation influences the operation of several coating methods and the final quality of the coating layer. The rate of coating consolidation is characterized with a dynamic gloss meter at short times for a thin coating layer applied to the base sheet of interest. During the coating consolidation process, the laser gloss meter response curve exhibits two critical turning points that indicate the two coating immobilization points defined by the traditional methods. Five base sheets with several different coating suspensions are characterized. A model is proposed to estimate the rate of consolidation based on physical properties of the coating suspension, the base paper, and the liquid phase of the coating. The paper properties, especially the contact angle, are found to be an important factor in determining rate of consolidation. The model predicts the correct trends for the different coating suspensions and base sheets. The test method, along the model, can be used to determine the filtercake resistance of the coating layer for a thin and rapidly formed filtercake.

• 연구논문집
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• s.29
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• pp.49-55
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• 1999

Heat release rate used to characterize the fire is an important factor for determining the fire size, the fire growth and the time for suppression and evacuation. The purpose of present work is to review theoretical backgrounds and to introduce equations for estimation of heat release rate with oxygen consumption method in fires. Our work also shows the experimental results of applications for liquid fuels. The oxygen concentration is measured by the analyzer of paramagnetic type. The analyzers of Infra-Red type are used to measure the concentrations of $CO_2$ and CO gas. Time delays of analyzers are ignored.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.11
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• pp.939-945
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• 2002

The rise throughput and the stability in the device fabrication can be obtained by applying chemical mechanical polishing (CMP) process in 0.18 $\mu\textrm{m}$ semiconductor device. However, it still has various problems due to the CMP equipment. Especially, among the CMP components, process variables are very important parameters in determining the removal rate and non-uniformity. In this paper, we studied the DOE (design of experiment) method in order to get the optimized CMP equipment variables. Various process parameters, such as table and head speed, slurry flow rate and down force, have investigated in the viewpoint of removal rate and non-uniformity. Through the above DOE results, we could set-up the optimal CMP process parameters.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.123.2-123
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• 2001

It is difficult to determine the feeding rate of coagulant in the water treatment plant, due to nonlinearity, multivariables and slow response characteristics, etc. To deal with this difficulty, the neuro-fuzzy system and the genetic-fuzzy system were used in determining the feeding rate of the coagulant. The fuzzy system is excellently robust in multi-variables and nonlinear problems. Therefore it uses basic algorithm, but it is difficult to construct of the fuzzy parameter such as the rule table and the membership function, Therefore we made the neuro-fuzzy system and the genetic-fuzzy system with the fusion of learning algorithms and compared the performance of the two fuzzy systems. To apply these algorithms, we made the rule table, membership function from the actual operation data of the water treatment plant. We determined optimized feeding rate of coagulant using the fuzzy operation, and also compared ...