• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.29 no.3
• /
• pp.81-87
• /
• 2015

In order to effectively protect electrical and electronic circuits which are extremely susceptible to lightning surges, multi-stage surge protection circuits are required. This paper presents the operational characteristics of the two-stage hybrid surge protection circuit in extra-low voltage DC power lines. The hybrid surge protective device consists of the gas discharge tube, transient voltage suppressor, and series inductor. The response characteristics of the proposed hybrid surge protective device to combination waves were investigated. As a result, the proposed two-stage surge protective device to combination wave provides the tight clamping level of less than 50V. The firing of the gas discharge tube to lightning surges depends on the de-coupling inductance and the rate-of-change of the current flowing through the transient voltage suppressor. The coordination between the upstream and downstream components of the hybrid surge protective device was satisfactorily achieved. The inductance of a de-coupler in surge protective circuits for low-voltage DC power lines, relative to a resistance, is sufficiently effective. The voltage drop and power loss due to the proposed surge protective device are ignored during normal operation of the systems.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.3
• /
• pp.235-241
• /
• 2014

As a fiber-optic cable is being unwound, it is protected by a tube that is designed to prevent unwinding problems such as tangling and unintentional cutting. In addition, a guide body is separated from the protective tube if a shear pin breaks when the maximum allowable load is exceeded. Therefore, it is important to analyze and predict the unwinding behavior of the protective tube, as well as the load on the shear pin, to enhance the likelihood of a successful operation when laying cables at extreme depths. In this study, the protective tube and the guide body are modeled with particles and are constrained with a constant-length constraint. The load on the shear pin was verified against experimental data, and the unwinding behavior was predicted from the load prediction results.

• Journal of Advanced Marine Engineering and Technology
• /
• v.23 no.2
• /
• pp.150-158
• /
• 1999

The process of designing protective circuits against damage by transient overvoltages requires much work and expensive equipment. However computer simulation using PSpice can overcome these problems. In this paper a gas tube and a ZnO varistor Pspice-model considering the steepness of the wave-front were presented. The effects of various waveforms on the transient behaviors and firing volt-ages of a gas tube were modeled by controlled voltage source E controlled current source G and TABLE function of PSpice. And the nonlinear characteristics of a ZnO varistor were modeled by controlled voltage source E and H. To estimate the characteristics of the models proposed various waveforms specified in IEC Std. 1000310-4-5 were used in the simulation and the actual tests. The simulation results were compared with test results and showed good agreement.

• Corrosion Science and Technology
• /
• v.7 no.1
• /
• pp.13-15
• /
• 2008

Aiming at the corrosion circumstances and corrosion prevention needs of downhole oil tubes, series protective coatings for downhole oil tubes have been developed in the authors' laboratory, including a baked type coating YG-01 and an air curing type coating YG-03, etc. The performance investigation of the coatings has been done for testing their corrosion resistance, mainly including salt fog test, immersion test in oil-field waste water and various acid solutions, high temperature and high pressure test in alkali solution or $H_2S/CO_2$ environment, as well as some other performances. The investigation results show that oil tube anti-corrosion coatings developed here can endure over 4000 hrs salt fog test, over 1000 hrs immersion in various acid solutions at room temperature and in boiling oil-field waste water. In addition, the coatings can keep intact after experiencing test in alkali solution under 70 MPa pressure at $150^{\circ}C$ for 24 hrs, and in simulative sour gas environment under the total pressure of 32 MPa ($P_{H_{2}S}=3.2MPa$, $P_{CO_{2}}=3.2MPa$) at $90^{\circ}C$ for 168 hrs, which show that the coatings can be used for corrosion prevention in downhole environments with specific high temperature and high pressure, such as sour gas wells. The other testing results show the oil tube protective coatings have excellent comprehensive performance.

• Nutrition Research and Practice
• /
• v.7 no.4
• /
• pp.315-325
• /
• 2013

We evaluated folate status of child-bearing age women diagnosed with abnormal pap smear in the US post-folic acid (FA) fortification era and assessed the determinants of NTD-protective and supra-physiologic (SP) concentrations of folate. The distribution of 843 women according to NTD-protective concentrations of RBC folate, plasma folate and SP concentrations of plasma folate were tested in relation to demographic and life-style factors. Logistic regression models specified NTD-protective concentrations of RBC and plasma folate or SP concentrations of plasma folate as dependent variables and demographic and life-style factors as independent predictors of interest. More than 82% reached NTD-protective concentrations of RBC and plasma folate and ~30% reached SP concentrations of plasma folate. FA supplement use was associated with having SP concentrations of plasma folate rather than NTD-protective concentrations of folate. African American (AA) women and smokers were significantly less likely to achieve NTD-protective concentrations of RBC and plasma folate. A large majority of women reached NTD-protective concentrations of folate with the current level of FA fortification without using supplementary FA. Therefore, the remaining disparities in AA women and in smokers should be addressed by targeted individual improvements in folate intake.

• Steel and Composite Structures
• /
• v.43 no.2
• /
• pp.257-270
• /
• 2022

Recycled aggregate concrete (RAC) is rarely used in load-carrying structural members. To widen its structural application, the compressive behavior of a promising type of composite column, steel-fiber reinforced polymer (FRP) double-tube confined RAC column, has been experimentally and analytically investigated in this study. The objectives are the different performance of such columns from their counterparts using natural aggregate concrete (NAC) and the different mechanisms of the double-tube and single-tube confined concrete. The single-tube confined concrete refers to that in concrete-filled steel tubular (CFST) columns and concrete-filled FRP tubular (CFFT) columns. The test results showed that the use of recycled coarse aggregates (RCA) affected the axial load-strain response in terms of deformation capacity but such effect could be eliminated with the increasing confinement. The composite effect can be triggered by the double confinement of the steel and carbon FRP (CFRP) tubes but not by the steel and polyethylene terephthalate (PET) FRP tubes. The proposed analysis-oriented stress-strain model is capable to capture the load-deformation history of such steel-FRP double-tube confined concrete columns under axial compression.

• Preventive Nutrition and Food Science
• /
• v.5 no.4
• /
• pp.225-229
• /
• 2000

The antioxidative and protective activities of kefir, low-fat dry milk (NFDM) extract and fractions on SFME cells in serum-free medium were investigated. Kefir and low-fat kefir and NFDM extract were made by solubilizing the freeze dried powder forms in deionized water, filtering through glass prefilter, 12 ㎛ and 2 ㎛ membrane, and demineraling with chelating resin. Kefir, low-fat kefir and NFDM extract were fractioned into dialyzate and retentate by dialysis with membrane tube having the molecular cut-off of 3,500 Dalton. An antioxidative activity was analyzed by the in vitro model system using a linoleic acid. In the case of kefir an antioxidative activity was detected only in the retentate of kefir extract. On the other hand NFDM showed an antioxidative activity in extract, demineralized extract, dialyzate and retentate. The retentate of kefir extract had the higher antioxidative activity than that of NFDM extract. Kefir showed the protective effect of SFME cells in serum-free medium in extract, demineralized extract and retentate, but low-fat kefir didn't. NFDM had the similar protective effect on SFME cells as extract, demineralized extract and retentate of kefir.

• Journal of Ginseng Research
• /
• v.30 no.3
• /
• pp.100-105
• /
• 2006

Liver and kidney are specific organs which play an active role in biotransformation and detoxification mechanisms. Ant adverse effect of chemicals or heavy metal can cause the delay or fade in these mechanisms. Present study was designed to find out the protective effect of Panax ginseng extract on renal functions altered by mercuric chloride (heavy metal) in albino rat. Fifty albino rats were divided into 10 groups. Five groups for acute study and five groups for sud-acute study viz. control group (Tween 20 and distilled water), mercuric chloride treated group (0.926 mg/kg body wt. for acute and 0.044 mg/kg body wt. for sub-acute group after calculated $LD_{50}$ (9.26 mg/kg body wt.) by probit analysis (Finney, 1971), Panax ginseng extract treated group (10 mg/kg body wt. for acute and sub-acute sets), mercuric chloride treated followed by Panax ginseng extract and Panax ginseng extract followed by mercuric chloride group. All doses were given orally by gavage tube. The result revealed that the serum urea and creatinine significantly increased in mercuric chloride treated group, while significantly decreased (p<0.01) in Panax ginseng extract group after acute and sub-acute treatment. The biochemical estimation is also confirmed by nephropathological aspect. However, the Panax ginseng extract treated followed by mercuric chloride group is more prominent than the mercuric chloride treated followed by Panax ginseng extract group. It can be concluded that Panax ginseng extract had a protective nature on renal functions against mercuric chloride toxicity in albino rats.

• Textile Coloration and Finishing
• /
• v.26 no.2
• /
• pp.106-113
• /
• 2014

Work-related falls are a major problem in the construction and roofing industries. To avoid serious injury to the worker caused by high decelerations or forces, different systems to absorb the energy of a fall are implemented in personal protective equipment. In this study, shock energy absorber lanyard protection tube was prepared using high tenacity PET fiber, P-aramid fiber, and UHMWPE fiber, respectively. Dynamic load test and static load test, bursting strength test based on the Korea fall protection equipment standard(Korea Occupational Safety & Health Agency standard 2013-13) or conformity European safety test(CE : EN355) were conducted. Especially maximum arrest force by dynamic load test of energy absorber showed below 6,000N.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.11 no.1
• /
• pp.18-30
• /
• 1999

A heat transfer analysis for the two-dimensional (2-D) steady state using finite difference method (FDM) is performed to predict the thermal behavior of the primary first-wall (FW) system of fusion reactor under various geometric and thermo-hydraulic conditions, such as the beryllium (Be) armor thickness, pitch of cooling tube, and coolant velocity. The FW consists of authentic steel (type 316 stainless steel solution annealed) for cooling tubes, Cu for cooling tubes embedding material, and Be for a protective armor, based on the International Thermonuclear Experiment Reactor (ITER) report. The present 2-D analysis, the control volume discretized with hybrid grid (rectangular grid and polar grid) and Gauss-Seidel iteration method are adapted to solve the governing equations. In the present study, geometric and thermo-hydraulic parameters are optimized with consideration of several limitations. Consequently, it is suggested that the adequate pitch of cooling tube is 22-32mm, the beryllium armor thickness is 10-12mm, and that the coolant velocity is 4.5m/s-6m/s for $100^{\circ}C$ of inlet coolant temperature. The cooling tube should locate near beryllium armor. But, it would be better for locating the center of Cu wall, considering problems of material and manufacturing. Also, 2-D analysis neglecting the axial temperature distribution of cooling tube is appropriate, regarding the discretization error in axial direction.