• Clinical and Experimental Pediatrics
• /
• v.55 no.9
• /
• pp.330-336
• /
• 2012

Purpose: Fractional exhaled nitric oxide (FeNO) and forced expiratory flow between 25% and 75% of vital capacity ($FEF_{25-75}$) are not included in routine monitoring of asthma control. We observed changes in FeNO level and $FEF_{25-75}$ after FeNO-based treatment with inhaled corticosteroid (ICS) in children with controlled asthma (CA). Methods: We recruited 148 children with asthma (age, 8 to 16 years) who had maintained asthma control and normal forced expiratory volume in the first second ($FEV_1$) without control medication for ${\geq}3$ months. Patients with FeNO levels >25 ppb were allocated to the ICS-treated (FeNO-based management) or untreated group (guideline-based management). Changes in spirometric values and FeNO levels from baseline were evaluated after 6 weeks. Results: Ninety-three patients had FeNO levels >25 ppb. These patients had lower $FEF_{25-75}$ % predicted values than those with FeNO levels ${\leq}25$ ppb (P<0.01). After 6 weeks, the geometric mean (GM) FeNO level in the ICS-treated group was 45% lower than the baseline value, and the mean percent increase in $FEF_{25-75}$ was 18.7% which was greater than that in other spirometric values. There was a negative correlation between percent changes in $FEF_{25-75}$ and FeNO (r=-0.368, P=0.001). In contrast, the GM FeNO and spirometric values were not significantly different from the baseline values in the untreated group. Conclusion: The anti-inflammatory treatment simultaneously improved the FeNO levels and $FEF_{25-75}$ in CA patients when their FeNO levels were >25 ppb.

• Structural Engineering and Mechanics
• /
• v.70 no.2
• /
• pp.169-178
• /
• 2019

The replacement of damaged components is an important task for long-span bridges. Conventional strategy for component replacement is to close the bridge to traffic, so that the influence of the surrounding environment is reduced to a minimum extent. However, complete traffic interruption would bring substantial economic losses and negative social influence nowadays. This paper investigates traffic control technologies without interruption for component replacement of long-span bridges. A numerical procedure of traffic control technologies is proposed incorporating traffic microsimulation and site-specific data, which is then implemented through a case study of cable replacement of a long-span cable-stayed bridge. Results indicate traffic load effects on the bridge are lower than the design values under current low daily traffic volume, and therefore cable replacement could be conducted without traffic control. However, considering a possible medium or high level of daily traffic volume, traffic load effects of girder bending moment and cable force nearest to the replaced cable become larger than the design level. This indicates a potential risk of failure, and traffic control should be implemented. Parametric studies show that speed control does not decrease but increase the load effects, and flow control using lane closure is not effectual. However, weight control and gap control are very effective to mitigate traffic load effects, and it is recommended to employ a weight control with gross vehicle weight no more than 65 t or/and a gap control with minimum vehicle gap no less than 40 m for the cable replacement of the case bridge.

• Korean Chemical Engineering Research
• /
• v.55 no.6
• /
• pp.767-770
• /
• 2017

Quadruple tank liquid level systems are popular in testing multivariable control systems for multivariable processes with positive or negative zeros. The liquid level system is nonlinear and it will help to illustrate the robustness of control systems. However, due to nonlinearity, it can be cumbersome to obtain process parameters for testing linear control systems. Perturbation sizes are limited for valid linearized process models, requiring level sensors with high precision. A simple method where the outlet orifice is replaced to a long tube is proposed here. The effluent flow rate becomes proportional to the liquid level due to the friction loss of long tube and the liquid level system shows near linear dynamics. It is applied to the quadruple tank system for easier experiments.

• Korean Journal of Clinical Pharmacy
• /
• v.3 no.2
• /
• pp.147-155
• /
• 1993

The cardiac effects of PAF antagonist Ginkgolide B(BN 52051) have been investigated on the isolated perfused guinea pig hearts maintained at the constant hydrostatic perfusion pressure of 80 cm water. PDE(Phosphodiesterase) inhibitor KR-30289 was used as a positive control to see the positive inotropic effects on the perfused hearts. In this expriments, Ginkgolide $B(10^{-5}-SM)$ showed negative inotropic effects by decreasing of LVP, LVDP, LV dp/dt, HR and RPP(Rate Pressure Product). Ginkgolide B also decreased the number of extrasystole by $51.9\%(from\;23.75\pm9.22/min\;to\;11.43\pm435/min)$ induced by global ischemia and reperfusion. The rate, [-dp/dt]/[+dp/dt] increased in preischemia but decreased in postischemia. 1n the separated study the injection of 1ml of Ginkgolide B$(10^{-4M})$ on the isolated heart, increased coronary flow(CF) by $11.8\%(from\;7.5\pm7.65ml/min\;to\;8.5\pm0.29ml/min)$ and decreased the number of extrasystole by $47.6\%(from\;21\pm5.92/min\;to\;11\pm5.27/min)$. In conclusion, Ginkgolide B showed antiarrhythmic and protective effects by decreasing the number of extrasystole and by increasing the coronary flow, respectively.

• International Journal of Automotive Technology
• /
• v.8 no.6
• /
• pp.697-704
• /
• 2007

Recently, a variable valve timing system has been widely adopted in internal combustion engine in order to improve the fuel economy and torque at low engine speed. In addition, it is known that varying valve timing according to the various engine operations could reduce exhaust gas, especially NOx, because of residual gas by valve overlap. In this study, to improve the low exhaust gas and fuel economy at part load condition, the residual gas and back flow of exhaust gas due to valve overlap were calculated computationally. Moreover, the characteristics of engine performances and NOx formations were investigated with the experiment of combination of intake and exhaust valve timing condition. Under these various valve operating conditions, the effects of both the positive valve overlap and negative valve overlap(valve underlap) were examined simultaneously. Finally, the characteristics of cyclic THC emission were analyzed by using Fast Response FID(FR-FID) in the cylinder, intake port and exhaust port positions. Besides, the effect of the different gradients of the valve timing change on engine performance was investigated and an optimum control strategy was suggested.

• Smart Structures and Systems
• /
• v.32 no.5
• /
• pp.281-295
• /
• 2023

The purpose of this study is to demonstrate and verify the application of phase-control absolute-acceleration-feedback active tuned mass dampers (PCA-ATMD) to multiple-degree-of-freedom (MDOF) building structures. In addition, servo speed control technique has been developed as a replacement for force control in order to mitigate the negative effects caused by friction and inertia. The essence of the proposed PCA-ATMD is to achieve a 90° phase lag for a structure by implementing the desired control force so that the PCA-ATMD can receive the maximum power flow with which to effectively mitigate the structural vibration. An MDOF building structure with a PCA-ATMD and a real-time filter forming a complete system is modeled using a state-space representation and is presented in detail. The feedback measurement for the phase control algorithm of the MDOF structure is compact, with only the absolute acceleration of one structural floor and ATMD's velocity relative to the structure required. A discrete-time direct output-feedback optimization method is introduced to the PCA-ATMD to ensure that the control system is optimized and stable. Numerical simulation and shaking table experiments are conducted on a three-story steel shear building structure to verify the performance of the PCA-ATMD. The results indicate that the absolute acceleration of the structure is well suppressed whether considering peak or root-mean-square responses. The experiment also demonstrates that the control of the PCA-ATMD can be decentralized, so that it is convenient to apply and maintain to real high-rise building structures.

• Atmosphere
• /
• v.27 no.4
• /
• pp.445-453
• /
• 2017

This study investigates turbulent flow around a square cylinder mounted on a flat surface at high Reynolds number using a large-eddy simulation (LES) model, particularly focusing on vortex streets behind the square cylinder. Total 9 simulation cases with different inflow wind directions, inflow wind speeds, and cylinder widths in the x- and y-directions are considered to examine the effects of inflow wind direction, speed, and cylinder widths on turbulent flow and vortex streets. In the control case, the inflow wind parallel to the x-direction has a maximum speed of $5m\;s^{-1}$ and the width and height of the cylinder are 50 m and 200 m, respectively. In all cases, down-drafts in front of the cylinder and updrafts, wakes, and vortex streets behind the cylinder appear. Low-speed flow below the cylinder height and high-speed flow above it are mixed behind the cylinder, resulting in strong negative vertical turbulent momentum flux at the boundary. Accordingly, the magnitude of the vertical turbulent momentum flux is the largest near the cylinder top. In the case of an inflow wind direction of $45^{\circ}$, the height of the boundary is lower than in other cases. As the inflow wind speed increases, the magnitude of the peak in the vertical profile of mean turbulent momentum flux increases due to the increase in speed difference between the low-speed and high-speed flows. As the cylinder width in the y-direction increases, the height of the boundary increases due to the enhanced updrafts near the top of the cylinder. In addition, the magnitude of the peak of the mean turbulent momentum flux increases because the low-speed flow region expands. Spectral analysis shows that the non-dimensional vortex generation frequency in the control case is 0.2 and that the cylinder width in the y-direction and the inflow wind direction affect the non-dimensional vortex generation frequency. The non-dimensional vortex generation frequency increases as the projected width of the cylinder normal to the inflow direction increases.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.5
• /
• pp.1841-1850
• /
• 2013

The various types of fishways are installed at the multi-functional weirs in the four major rivers to minimize the negative effect due to the construction of the transverse structures. The movable weir was installed at the upstream of the ice-harbor type artificial fishway of the Dalseong weir in the Nakdong river, which can control the fishway flowrate regardless of the river flowrate. The incoming flowrate to the artificial fishway is closely related with the hydraulic characteristics that dominate the fish passage efficiency. Thus, it is crucial to find out the weir operation rule for properly sustaining efficient fish-passage, such as the optimized flowrate. In this study, the FLOW-3D was used to analyze and compare the various hydraulic characteristics associated with the passage efficiency, based upon the given different flowrate, and subsequently provide the optimized flowrate for the fishway movable weir to maintain the best efficient flow condition for the fish-passage.

• Journal of Biomedical Engineering Research
• /
• v.21 no.3 s.61
• /
• pp.261-271
• /
• 2000

The present study investigated flow dynamics of a two-dimensional abdominal aortic bifurcation model under sinusoidal flow conditions considering wall motion. impedance phase angle(time delay between pressure and flow waveforms), and non-Newtonian fluid using computational fluid dynamics. The wall shear stress showed large variations in the bifurcated region and the wall motion reduced amplitude of wall shear stress significantly. As the impedance phase angle was changed to more negative values, the mean wall shear stress (time-averaged) decreased while the amplitude (oscillatory) of wall shear stress increased. At the curvature site on the outer wall where the mean wall shear stress approached zero. influence of the phase angle was relatively large. The mean wall shear stress decreased by $50\%$ in the $-90^{\circ}$ phase angle (flow wave advanced pressure wave by a quarter period) compared to the $0^{\circ}$ phase angle while the amplitude of wall shear stress increased by $15\%$. Therefore, hypertensive patients who tend to have large negative phase angles become more vulnerable to atherosclerosis according to the low and oscillatory shear stress theory because of the reduced mean and the increased oscillatory wall shear stresses. Non-Newtonian characteristics of fluid substantially increased the mean wall shear stress resulting in a less vulnerable state to atherosclerosis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.16 no.4
• /
• pp.318-323
• /
• 2004

When a strong electric field is applied between a sharply curved electrode and a blunt surface, the corona may result in a gas movement in the electrode gap which is directed toward the blunt surface. That is called the corona wind. It enhances heat and mass transfer between the surface and the surrounding gas. Moreover such enhancement causes no noise or vibration, which can be applied in complex, isolated geometries, and allows simple control of surface temperatures. This paper examines the relationship between the corona wind and the relative humidity. The facility consists of high voltage power supply thin tungsten wire, plate electrode, multimeter, microammeter and flow meter. Gas velocity is a linear function of voltage, relative humidity and is proportional to the square root of the current. The maximum velocities for the positive and negative corona discharge are 1.9 m/s (2.74 CMM/m), 1.5 m/s(2.15 CMM/m), respectively.