• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1863-1870
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• 2000

When an impact stress is applied on the external boundary of double cantilever beam of orthotropic material which crack length is greater than specimen hight and anistropic ratio is very high, dyna mic energy release rate is derived, and the relationship between dynamic energy release rate and crack propagating velocity is studied. Dynamic energy release rate to static energy release rate is decreased with increasment of crack propagating velocity. The relationships between dynamic energy release rate and vertical strain have a similar pattern with those between static energy release rate and vertical strain. When normalized time(Cstla) is greater than or equal to 2, dynamic energy release rate approaches to a constant value.

• Journal of the Korean Society of Safety
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• v.24 no.4
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• pp.96-103
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• 2009

This study was fulfilled to investigate the forest fire risk of forest fuels based on the combustion characteristics of living leaves of coniferous trees and broadleaf trees naturally growing in Youngdong areas of Gangwon Province by using cone calorimeter and smoke density chamber. According to the result, Pinus densiflora and Pinus rigida among coniferous trees released a greater amount of heat release than other kinds. The total smoke release varied depending on the species, whereas Pinus koraiensis showed the largest amount of smoke release. With regard to maximum smoke density, it was much higher in coniferous trees than in broadleaf trees. With regard to smoke temperature, Pinus densiflora showed the lowest compared to other kinds up until 200s from the ignition, but all most trees uniformly maintained constant temperature of about $70^{\circ}C$ after 200s. The concentrations of CO and $CO_2$ release were drastically increased at about 150s and then gradually decreased thereafter. Pinus densiflora showed a bit higher CO release than broadleaf trees, but there was no distinct difference in $CO_2$ release among tress.

• Applied Chemistry for Engineering
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• v.7 no.4
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• pp.735-742
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• 1996

Polymeric matrices were prepared with dextran and silver sulfadiazine by adding glycerine as a plasticiser. Namely, the release rate of the drug from the polymeric matrix formulations in dissolved phases was determined in a phosphate buffer solution. The results were as follows : The drug release time was delayed as drug loading contents increased, whereas it decreased as the glycerine concentration increased. The drug release time was not changed with varying the molecular weight of the dextran. The apparent release rate constant (k) increased as the composition of silver sulfadiazine and glycerine was increased. But the apparent release rate constant (k) was not changed with increasing molecular weight of the dextran.

• Journal of Nutrition and Health
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• v.25 no.7
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• pp.597-607
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• 1992

The present study examined effects of caffeine on coronary circulation myocardial oxygen me-tabolism and calcium release in isolated perfused guinea pig hearts. Intracoronary caffeine({{{{ {10 }^{-5 } }}}}∼{{{{ { 10}^{-3 } }}}}M) was employed for 10 minutes to measure coronary perfusate flow(CF) and coronary vascular sresistance(CVR) at a constant coronary perfusion pressure of 80 cmH2O Perfusate myocardial oxygen consumption(MVO2) and percent oxygen extraction(%EC2) were calcula-ted. In addition calcium contents in both perfusate samples were measured to calculate calcium release in coronary venous effluent. Caffeine significantly decreased CF and increased CVR during 10 minutes of caffeine perfusion regardless of dose of caffeine perfused exhibiting time-response. While % EO2 was significantly enhanced with caffeine MVO2 was markedly reduced. The coronary venous perfusate pH dcreased during the perfusion with caffeine. These changes were consistent with caffeine-induced metabolic acidosis. Calcium release appeared to be dose-dependent and high dose of caffeine greatly increased venous calcium release even 2 minutes after perfusion with carffeine. These finding in dicate that caffeine produced coronary vasoconst-riction with increased calcium release in isolated perfused guinea pig hearts. Additionaly this vasoconstrictor response mignt be due tin part to the direct actions of caffeine.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.221-228
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• 1997

A strong combustion-driven sound from a surface burner made of a perforated metal fiber plate for premixed gas was investigated to clarify the physical mechanism of its generation. A simple model was developed for the acoustic power generation in terms of the heat transfer response function and the acoustic impedance of the burner. The acoustic impedance of the perforated metal fiber placed on the open exit was measured and the heat release response of the burner to the oscillating flow associated with the acoustic disturbance was expressed in terms of a response function. It was found that the power is generated by the heat release in response to the downstream particle velocity, in contrast to the upstream velocity in the case of the Rijke oscillation driven by a heater placed in the lower half of a columm with upstream flow. The measured frequencies of the oscillation were in agreement with the estimated resonance frequencies and their excitation was varied with the combustion conditions. For the same fuel rate, the excited frequency increases with the air ratio if it is low but decreases with the ratio if not so low. Such frequency characteristics were explained by assuming a heat release response function with a time constant and it was shown that the excited frequency decreases as the time constant increases.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.173-184
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• 2002

In order to evaluate the devolatilization models of pulverized coal, various devolatilization models are examined for the numerical analysis of Drop Tube Furnace.The results of analysis are compared with the experimental results. A numerical study was conducted to explore the sensitivities of the predictions to variation of the model parameters. It helps to elucidate the source of the discrepancies. Three different wall temperature conditions of the DTF, 1100, 1300 and $1500^{\circ}C$ were considered in this analysis. Two fuels are U.S.A. Alaska coal and Australia Drayton coal. The results of analysis with constant rate model, single kinetic rate model and two competing rate modes well presented fast volatile matter release in the early devolatilization. However, in the latter devolatilization they did not coincide with experimental results which presented tardy volatile matter release on account of pyrolysis of high molecular substance. On the other hand, the results of analysis with DAEM(Distribute Activation Energy Model) coincided with experiment al results in overall devolatilization.

• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.64-70
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• 2003

For the unconfined vapor cloud explosion(UVCE) accident by the continuous release of gas-liquid flow of various saturated liquids in a vessel at ground level, overpressures were estimated by TNT equivalency model with two estimation methods, such as UVCE I model based on a constant release time and UVCEII model based on a real travel time of vapor by dispersion and analyzed with various release conditions. As a simulation result the simple, easy, and correct method of evaluation of consequences of the UVCE accident was proposed by using consequences of UVCE I model and correlation equations for differences of overpressures between UVCE models, so that this evaluation method could be used easily in the small and medium size enterprises without using the dispersion model.

• Journal of Mechanical Science and Technology
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• v.16 no.6
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• pp.829-838
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• 2002

A constant volume combustion chamber is used to investigate the flame kernel development of gasoline air mixtures under various ignition systems, ignition energies and spark plugs. Three kinds of ignition systems are designed and assembled, and the ignition energy is controlled by the variation of the dwell time. Several kinds of spark plugs are also tested. The velocity of flame propagation is measured by a laser deflection method, and the combustion pressure is analyzed by the heat release rate and the mass fraction burnt. The results represent that as the ignition energy is increased by enlarging either dwell time or spark plug gap, the heat release rate and the mass fraction burnt are increased. The electrodes materials and shapes influence the flame kernel development by changing he transfer efficiency of electrical energy to chemical energy. The diameter of electrodes also influences the heat release rate and the burnt mass fraction.

• Advances in materials Research
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• v.11 no.1
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• pp.41-57
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• 2022

This paper is focused on delamination analysis of a multilayered inhomogeneous viscoelastic beam subjected to linear creep under constant applied stress. The viscoelastic model that is used to treat the creep consists of consecutively connected units. Each unit consists of one spring and two dashpots. The number of units in the model is arbitrary. The modulus of elasticity of the spring in each unit changes with time. Besides, the modulii of elasticity and the coefficients of viscosity change continuously along the thickness, width and length in each layer since the material is continuously inhomogeneous in each layer of the beam. A time-dependent solution to the strain energy release rate for the delamination is derived. A time-dependent solution to the J-integral is derived too. A parametric analysis of the strain energy release rate is carried-out by applying the solution derived. The influence of various factors such as creep, material inhomogeneity, the change of the modulii of elasticity with time and the number of units in the viscoelastic model on the strain energy release rate are clarified.

• Journal of Pharmaceutical Investigation
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• v.35 no.6
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• pp.453-460
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• 2005

4-Aminopyridine (AP) is a potassium channel blocker used in the treatment of neurological disorders such as multiple sclerosis and Alzheimer disease. AP‘s window of therapeutic effect appears to correlate with its plasma halflife (3.5 hours). It demonstrates pH-dependent solubility because of a weakly basic drug. In addition, the resulting release from conventional matrix tablets decreases with increasing pH-milieu of the gastrointestinal tract. The aim of this study is to design sustained release matrix tablet containing AP, overcoming this problem. $Eudragit^{\circledR}$ L 100 (EuL) and sodium alginate were used in an effort to achieve pH independent drug release. The effect of sodium alginate and EuL on drug release from matrix tablet was investigated. The drug release behavior from the different tablets was analyzed by $t_{20%},\;t_{40%},\;t_{60%}$, The exponential diffusion coefficient n, kinetic constant K were calculated according to the Korsmeyer-Peppas equation. The drug release from matrix tablets prepared with sodium alginate was decreased with increasing the content of sodium alginate in pH 7.4 while there is no significant difference in pH 1.2. The exponent n values were determined to be approximately 0.5 and 0.8 respectively, in both pH 1.2 and 7.4. These values indicate diffusion-based anomalous mechanism and erosion-based anomalous mechanism, respectively. The drug release from sodium alginate matrix tablets prepared with solid dispersion of EuL containing drug showed a slow drug release in an acidic medium and a more fast drug release in phosphate medium, compared with sodium alginate matrix tablets prepared with physical mixture. These results may be attributed to the gel forming ability of sodium alginate and pH dependent solubility of EuL. Therefore, sustained-release AP matrix tablets using sodium alginate and EuL were successfully prepared.