• Journal of Biomedical Engineering Research
• /
• v.39 no.5
• /
• pp.220-228
• /
• 2018

The internal resistance of microbial fuel cell (MFC) using stainless steel skein for oxidizing electrode was investigated and the factors affecting the voltage generation were identified. We also investigated the effect of power management system (PMS) on the usability for MFC and the removal efficiency of organic pollutants. The performance of a stack microbial fuel cell connected with (PMS) or PMS+LED was analyzed by the voltage generation and organic matter reduction. The maximum power density of the unit cells was found to be $5.82W/m^3$ at $200{\Omega}$. The maximum current density was $47.53A/m^3$ without power overshoot even under $1{\Omega}$. The ohmic resistance ($R_s$) and the charge transfer resistance ($R_{ct}$) of the oxidation electrode using stainless steel skein electrode, were $0.56{\Omega}$ and $0.02{\Omega}$, respectively. However, the sum of internal resistance for reduction electrode using graphite felts loaded Pt/C catalyst was $6.64{\Omega}$. Also, in order to understand the internal resistance, the current interruption method was used by changing the external resistance as $50{\Omega}$, $300{\Omega}$, $5k{\Omega}$. It has been shown that the ohm resistance ($R_s$) decreased with the external resistance. In the case of a series-connected microbial fuel cell, the reversal phenomenon occurred even though two cells having the similar performance. However, the output of the PMS constantly remained for 20 hours even when voltage reversal occurred. Also the removal ability of organic pollutants (SCOD) was not reduced. As a result of this study, it was found that buffering effect for a certain period of time when the voltage reversal occurred during the operation of the microbial fuel cell did not have a serious effect on the energy loss or the operation of the microbial fuel cell.

• Journal of Advanced Navigation Technology
• /
• v.18 no.3
• /
• pp.215-222
• /
• 2014

In this paper, parafoil airdrop system has been designed and analyzed. 6-degrees of freedom (6-DOF) model of the parafoil system is set up. Nonlinear model predictive control (NMPC) and Proportion integration differentiation (PID) methods were separately applied to adjust the flap yaw angle. Compared the results of setting time and overshoot time of yaw angle, it is found that the of yaw angle is more stable by using PID method. Then, trajectory following controller was designed based on the simulation results of trajectory following effects, which was carried out by using MATLAB. The lateral offset error of parafoil trajectory can be eliminated by its lateral deviation control. The later offset deviation reference was obtained by the interpolation of the current planning path. Moreover, using the designed trajectory, the trajectory following system was simulated by adding the wind disturbances. It is found that the simulation result is highly agreed with the designed trajectory, which means that wind disturbances have been eliminated with the change of yaw angle controlled by PID method.

• Journal of IKEEE
• /
• v.8 no.1 s.14
• /
• pp.96-107
• /
• 2004

In this paper, a new integral variable structure regulation controller(IVSRC) is designed by using a special integral sliding surface and a disturbance observer for the improved regulation control of highly nonlinear robot manipulators with prescribed output performance. The sliding surface having the integral state with a special initial condition is employed in this paper to exactly predetermine the ideal sliding trajectory from a given initial condition to origin without any reaching phase. And a continuous sliding mode input using the disturbance observer is also introduced in oder to effectively follow the predetermined sliding trajectory within the prescribed accuracy without large computation burden. The performance of the prescribed tracking accuracy to the predetermined sliding trajectory is clearly investigated in detail through the two theorems together with the closed loop stability. The design of the proposed IVSRC is separated into the performance design and robustness design in each independent link. The usefulness of the algorithm has been demonstrated through simulation studies on the regulation control of a two link manipulator under parameter uncertainties and payload variations, in view of no reaching phase, no overshoot, predetermined response with prescribed accuracy, easy change of output performance, separation of design phase, and so on.

• KDI Journal of Economic Policy
• /
• v.14 no.4
• /
• pp.27-49
• /
• 1992

This paper stresses the role of market fundamentals rather than bubbles in explaining Korea's recent experience of large fluctuations of stock and real estate prices. The bubble story that emphasizes the self-fulfilling prophecies of investors seems to be inappropriate to explain the recent changes of assets prices in Korea. Those who argue for bubble phenomenon in Korea tend to interpret the volatile movements of assets prices as some form of bubbles, but without implementing a rigorous test on the presence of bubbles. Even when some bubble tests are carried out, such studies exhibit various econometric problems in testing. More seriously, they suffer from the misspecification problems in setting up a market model. This paper has shown that Korea's recent changes in assets prices could be explained by changes in market fundamentals according to the emergence and the subsequent fading of 'three lows'. First, it tried to explain changes in assets prices by changes in such market fundamentals as real interest rates and economic growth. Second, it showed that the real estate prices overshoot when the liquidity and exchange rates change, using the two-sector general equilibrium portfolio balance model. It is argued that the rapid rise in real estate prices during 1986-89 stems from Yen's and Won's appreciation $vis-{\grave{a}}-vis$ the U.S. dollar and liquidity expansion (or decreases in real interest rates), while the downturn in real estate prices since 1990 is associated with Yen's and Won's depreciation $vis-{\grave{a}}-vis$ the U.S. dollar and rises in real interest rates in reflection of the excess demand for liquidity.

• The Journal of the Korean Society for Microbiology
• /
• v.13 no.1
• /
• pp.55-62
• /
• 1978

Adult mice were injected with a single sublethal dose of cyclophosphamide. Effects of the drug on the body weight, spleen weight, and morphology of the peripheral lymphoid system have been analysed. The body weights of the mice given cyclophosphamide(300mg/kg body weight) decreased slightly and returned to normal quickly. Spleen weights, however, changed greatly by keeping the process of decrease, recovery, overshoot, and gradual return to normal only by 20 days. Histologic examinations of spleen and popliteal lymph node showed that follicles disappeared 1 to 2 days before periarteriolar lymphatic sheath or paracortex. At the peak of splenomegaly, the architectures of spleen and lymph node were replaced with the interstitial tissue composed of dense and uniform layer of lymphoid cells. With the return of spleen weight to normal range, the architecturles returned to normal. Our results clearly indicated that cyclophosphamide affected not only B cells but also T cells. These results seemed to suggest that augmentation of delayed-type hypersensitivity by cyclophosphamide may be due to the eliminateion of the suppressor T cells.

• Investigative Magnetic Resonance Imaging
• /
• v.13 no.1
• /
• pp.15-21
• /
• 2009

Purpose : A method to estimate a real k-space trajectory based on a circuit model of the gradient system is proposed for spiral imaging. The estimated k-space trajectory instead of the ideal trajectory is used in the reconstruction to improve the image quality in the spiral imaging. Materials and Methods : Since the gradient system has self resistance, capacitance, and inductance, as well as the mutual inductance between the magnet and the gradient coils, the generated gradient fields have delays and transient responses compared to the input waveform to the gradient system. The real gradient fields and their trajectory in k-space play an important role in the reconstruction. In this paper, the gradient system is modeled with R-L-C circuits, and real gradient fields are estimated from the input to the model. An experimental method to determine the model parameters (R, L, C values) is also suggested from the quality of the reconstructed image. Results : The gradient fields are estimated from the circuit model of the gradient system at 1.5 Tesla MRI system. The spiral trajectory obtained by the integration of the estimated gradient fields is used for the reconstruction. From experiments, the reconstructed images using the estimated trajectory show improved uniformity, reduced overshoots near the edges, and enhanced resolutions compared to those using the ideal trajectory without model. Conclusion : The gradient system was successfully modeled by the R-L-C circuits. Much improved reconstruction was achieved in the spiral imaging using the trajectory estimated by the proposed model.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2004.05b
• /
• pp.506-510
• /
• 2004

A torque transmission system composed of several gears and couplings is flexible. In order to get an exact response of motor, the torsional vibration due to an unexpected change of motor speed must be suppressed. Therefore, it is very important that motor control suppress vibration. Various methods to control it including dual inertia system are proposed. Specially, the method of vibration suppression is that vibration can be suppressed to fee㏈ack the estimated torsion torque via the disturbance observer filter being of normal filter. The suitable Proportional controller and coefficient parameter can be designed using CDM and the torsional vibration also be suppressed, but it has a low degree of adaptability to disturbance. The PID controller can be designed easily, but makes the excessive overshoot and oscillation for system response in the early period. To resolve these problems, simple and practical PID controller with two degree of freedom is proposed recently that it ran improve performance of obeying the reference unconcerned in any disturbance by changing the proportional gain by two degree of freedom parameter. But it has also the defect that parameter a must be changed to obtain the ideal Proportional parameter. On this paper, we design the controller which automatically adjusts parameter u using fuzzy Algorithm to overcome such defects. Also, we compare the proposed method with established one and evaluate them to confirm performance of the designed controller.

• The Korean Journal of Physiology
• /
• v.18 no.1
• /
• pp.19-35
• /
• 1984

Since the first report of Drury and $Szent-Gy{\ddot{o}}rgyi$ in 1929, the inhibitory influences of adenosine on the heart have repeatedly been described by many investigators. These studies have shown that adenosine and adenine nucleotides have overall depressant effects, similar to those of acetylcholine. Heart beats become slow and weak. It is also well known that adenosine is a potent endogenous coronary vasodilator. Many investigations on the working mechanisms of adenosine have been focused mainly on the effects of the coronary blood flow. However, the cellular mechanisms underlying the inhibitory action of adenosine on sinus node are not well understood yet. Thus, this study was undertaken to examine the behavior of rabbit SA node under influence of adenosine. In these series of experiments three kinds of preparations were used: whole atrial pair, left atrial strip, and isolated SA node preparations. The electrical activity of SA node was recorded with conventional glass microelectrodes 30 to 50 $M{\Omega}$. The preparations were superfused with bicarbonate-buffered Tyrode solution of pH 7.35 and aerated with a gas mixture of $3%\;CO_2-97%\;O_2$ at $35^{\circ}C$. In whole atrial pair, adenosine suppressed sinoatrial rhythm in a dose-dependent manner. Effect of adenosine on atrial rate appeared at the concentration of $10^{-5}M$ and was enhanced in parallel with the increase in adenosine concentration. Inhibitory action of adenosine on pacemaker activity was more prominent in the preparation pretreated with norepinephrine, which can steepen the slope of pacemaker potential by increasing permeability of $Ca^{+2}$. Calcium ions in perfusate slowly produced a marked change in sinoatrial rhythm. Elevation of the calcium concentration from 0.3 to 8 mM increased the atrial rate from 132 to 174 beats/min, but over 10 mM $Ca^{+2}$ decreased. The inhibitory effect of adenosine on sinoatrial rhythm developed very rapidly. Atrial rate was recovered promptly from the adenosine-induced suppression by the addition of norepinephrine, but extra $Ca^{+2}$ was less suitable to restore the suppression of atrial rate. Adenosine suppressed also atrial contractility in the same dosage range that restricted pacemaker activity, even in the reserpinized preparation. In isolated SA node preparation, spontaneous firing rate of SA node at $35^{\circ}C$(mean{\pm}SEM, n=16) was $154{\pm}3.3\;beats/min. The parameters of action potentials were: maximum diastolic potential(MDP), $-73{\pm}1.7\;mV: overshoot(OS), $9{\pm}1.4\;mV: slope of pacemaker potential(SPP), $94{\pm}3.0\;mV/sec. Adenosine suppressed the firing rate of SA node in a dose-dependent manner. This inhibitory effect appeared at the concentration of $10^{-6}M$ and was in parallel with the increase in adenosine concentration. Changes in action potential by adenosine were dose-dependent increase of MDP and decrease of SPP until $10^{-4}M$. Above this concentration, however, the amplitude of action potential decreased markedly due to the simultaneous decrease of both MDP and OS. All these effects of adenosine were not affected by pretreatment of atropine and propranolol. Lowering extra $Ca^{2+}$ irom 2 mM to 0.3 mM resulted in a marked decrease of OS and SPP, but almost no change of MDP. However, increase of perfusate $Ca^{2+}$ from 2 mM to 6 or 8 mM produced a prominent decrease of MDP and a slight increase of OS and SPP. Dipyridamole(DPM), which is known to block the adenosine transport across the cell membrane, definately potentiated the action of adenosine. The results of this experiment suggest that adenosine suppressed pacemaker activity and atrial contractility simultaneously and directly, by decreasing $Ca^{2+}-permeability$ of nodal and atrial cell membranes.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.26 no.2
• /
• pp.94-101
• /
• 1989

Transport properties of 2DEG at AlGaAs/GaAs interface such as average electron energy, flight distance, each valley occupancy ratio, average electron velocity for various fields are investigated by MONTE-CARLO method. As the electric field increases, more electrons transit drastically from (000) valley to (000) upper valley. This phenomenon shows the nonstationary effect such as velocity overshoot. The duration of the transient decreases from about 1.4 psec for electric field E = 7KV/cm to about 0.7 psec for 12KV/cm. The average electron velocity during transient transport in 2DEG is about 8 times the steady-state velocity for E = 12KV/cm at room temperature. In comparison with bulk GaAs the peak velocity in the 2DEG is higher than that in even pure bulk GaAs at electric field E = 7 KV/cm. On the basis of the fact that the electrons in the 2DEG have larger peak velocity and shorter transient time of velocity than those in the bulk GaAs, it is suggested that the device with 2DEG may obtain higher mobility than that with bulk GaAs.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.29 no.3
• /
• pp.466-470
• /
• 2000

The current study was undertaken to determine the prolinged effects of fasting-refecding on the lipoprotein lipase (LPL) activity and lipogenesis of adipose tissus in male Sprague-Dawley rals and to investigate the effects of various degrecs of food restriction during refeeding on the LPL activity and lipogenesis. The control group (n=5) was fed ad libitum and killed in the fed state at the beginning of the experiment. All rats except conteol group were fasted for 2 days (n=50). Five rats were killed at the end of fasting and others (n=45) were refed either ad libitum (ad libitum group) or mildly restricted (20% food restricted group), or esverely restricted diet (40% food restricted group). Rats were killed on the day of 7th, 14th, and 21st of refeeding. Lipogenesis was determined by the amount of glucose converted to the total lipid. Body weight and epididymal adipose tissue weight returned to control states by 5 days in ad libitym group and by 14 days in 20% food restricted group. As expected, in 40% food restriction during refeeding weight and epididymal adipose tissue weight did not rcturn to control states until day 21. On day 21 after refeeding, the serum total cholesterol concentration of ad libitum group was significantly (p<0.05) higher than that of control group. The serum HDL-C concentration of 40% food restricted group during refeeding was significantly (p<0.05) higher than that of control group. However, there were no significant dif-ferences in serum HDL-C/total cholesterol (TC) ratio and trigluceride concentration among the groups. Fasting for 2 days decreased lipogenesis and LPL activity (p<0.05). On day 21 after refecding, the lipogencsis of ad libitum group was significantly (p<0.05) lower than that of control group. The lipogenesis of 40% food restricted group during refeeding was significantly (p<0.05) higher than that of conrtol group. Ad libitum group and 20% food restricted group during refecding allowed heparin-releasable (HR) LPL or total extractable (TE) LPL activity to return to control states. 40% food restricted group during refeeding delayed the return of HR-LOL or TE-LPL activity to return to control states until day 21 of refeeding. These results suggest that food restriction during refeeding can partially or completely prevent the overshoot of LPL activity, and this may influence the rate of lipid accumulation in adipose tissue during refeeding.