• The Journal of Engineering Geology
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• v.27 no.3
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• pp.233-244
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• 2017

We conducted hydraulic fracturing experiments on cement samples to investigate the dependency of fracture propagation on the viscosity of injection fluid and the in situ stress state. Ten cubic samples (20 cm side length) were produced using cement that was cured in water for more than one month. Samples were placed in a tri-axial compression apparatus with three independent principal stresses. An injection hole was drilled and the sample was hydraulically fractured under a constant injection rate. We measured injection pressures and acoustic emissions (AE) during the experiments, and investigated the fracture patterns produced by hydraulic fracturing. Breakdown pressures increased exponentially with increasing viscosity of the injection fluid. Fracture patterns were dependent on differential stress (i.e., the difference between the major and minor principal stresses). At low differential stress, multiple fractures oriented sub-parallel to the major principal stress axis propagated from the injection hole, and in some samples the fracture orientation changed during propagation. However, at high differential stress, a single fracture propagated parallel to the major principal stress axis. AE results show similar patterns. At low differential stress, AE source locations were more widespread than at high differential stress, consistent with the fracture pattern results. Our study suggests that hydraulic fracturing during shale gas extraction should be performed parallel to the orientation of minimum differential stress.

• The Korean Journal of Pain
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• v.30 no.4
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• pp.281-286
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• 2017

Background: Magnetic resonance imaging (MRI) of the spine is the preferred diagnostic tool for pathologic conditions affecting the spine. However, in patients receiving epidural corticosteroid injection (ESI) for treatment of spinal diseases, there is a possibility of misreading of MR images because of air or fluid in the epidural space after the injection. Therefore, we defined the characteristics of abnormal changes in MRI findings following an ESI in patients with low back pain. Methods: We reviewed the medical records of 133 patients who underwent MRI of the lumbar spine within 7 days after ESI between 2006 and 2015. All patients were administered an ESI using a 22-gauge Tuohy needle at the lumbar spine through the interlaminar approach. The epidural space was identified by the loss of resistance technique with air. Results: The incidences of abnormal changes in MRI findings because of ESI were 54%, 31%, and 25% in patients who underwent MRI at approximately 24 h, and 2 and 3 days after ESI, respectively. Abnormal MRI findings included epidural air or fluid, needle tracks, and soft tissue changes. Epidural air, the most frequent abnormal finding (82%), was observed in 41% of patients who underwent MRI within 3 days after injection. Abnormal findings due to an ESI were not observed in MR images acquired 4 days after ESI or later. Conclusions: Pain physicians should consider the possibility of abnormal findings in MR images acquired after epidural injection using the interlaminar approach and the loss of resistance technique with air at the lumbar spine.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.75.2-75.2
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• 2012

Turbulence is ubiquitous in astrophysical fluids such as the interstellar medium and intracluster medium. To maintain turbulent motion, energy must be injected into the fluids. In turbulence studies, it is customary to assume that the fluid is driven on a scale, but there can be many different driving mechanisms that act on different scales in astrophysical fluids. We expect different statistical properties of turbulence between turbulence with single driving scale and turbulence with double driving scales. In this work, we perform 3-dimensional incompressible MHD turbulence simulations with energy injection in two ranges, 2${\surd}$12 (large scale) and 15

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.295-300
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• 2016

This paper presents a numerical analysis of the delivery pressure wave in a 210-kW/cyl fuel injection pump (P. Corporation, Changwon-si, Korea) for medium-speed diesel engines using Ansys Fluent R15.0. Results obtained from experiment and from numerical analysis of the fuel delivery pressure wave were compared and found to be similar, thereby confirming the reliability of the numerical analysis of the delivery pressure wave in the fuel injection pump.

• Journal of Biomedical Engineering Research
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• v.26 no.3
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• pp.157-161
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• 2005

Direct injection of a fibrinolytic agent to the intraarterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. In order to calculate the pressure distribution on the clot surface for different jet velocities (1, 3, 5 m/sec) and nozzle arrangements (1, 9, 17 nozzles), computational fluid dynamic methods were used. Thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about $20\%$ increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. The wall shear stress decreased as the number of nozzles increased, and the wall shear stress in most vessel wall was lower than 25 Pa. The results implied that thrombolysis could be accelerated by direct injection of a drug with the moderate velocity without damaging the blood vessel wall.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.5
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• pp.20-27
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• 2000

Characteristics of two favorite injection tools for gasoline direct injection application were compared. An air-assisted fuel injector (AAFI) and a high-pressure swirl injector (HPSI) were designed and fabricated for prototype development, and the characterization strategies and processes for both injection tool have been arranged in parallel. Characterization works were carried out mainly through measurements, and in some cases, computational fluid dynamic analysis was utilized. In this paper, overall characteristics defined as flow rate, spray pattern, penetration, internal spray structure and drop size distribution, was discussed. The AAFI was found to be advantageous in flexibility of fuel flow rate, and the HPSI in stability and precision. Spray shape factor was introduced to describe the development of intermittent sprays from both injectors. Axial penetration appeared to be almost linear in the case of the AAFI while its speed continuously decreased with time in the HPSI.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.835-842
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• 2003

A three dimensional numerical analysis has been conducted for a stoker type incinerator which has the capacity of 1.5 ton/hr. The objective of the present study is to predict the effects of swirl induced by secondary air and to find an optimal operating condition of the incinerator. In this study, combustion characteristics such as distributions of temperature, velocity and concentration of each species have been examined with various injection types of secondary air and with different flow rates of secondary air in the incinerator. It is found that the secondary air injection on the combustion process makes the path of fluid particle longer in the combustor and enhances the mixing between air and combustion gas by arousing a swirl. Therefore, the injection type of secondary air can be an important key in the design process of incinerator.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.62-68
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• 2004

A comprehensive numerical analysis has been carried out for both non-reacting and reacting flows in a scramjet engine combustor with and without a cavity. The theoretical formulation treats the complete conservation equations of chemically reacting flows with finite-rate chemistry of hydrogen-air. Turbulence closure is achieved by means of a k-$\omega$ two-equation model. The governing equations are discretized using a MUSCL-type TVD scheme, and temporally integrated by a second-order accurate implicit scheme. Transverse injection of hydrogen is considered over a broad range of injection pressure. The corresponding equivalence ratio of the overall fuel/air mixture ranges from 0.167 to 0.50. The work features detailed resolution of the flow and flame dynamics in the combustor, which was not typically available in most of the previous studies. In particular, the oscillatory flow characteristics are captured at a scale sufficient to identify the .underlying physical mechanisms. Much of the flow unsteadiness is related not only to the cavity, but also to the intrinsic unsteadiness in the flow-field. The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The roles of the cavity, injection pressure, and heat release in determining the flow dynamics are examined systematically.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.908-914
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• 2019

Fusion power shutdown system (FPSS) is a safety system to stop plasma in case of accidents or incidents. The gas injection system for the FPSS presented in this work is designed to research the flow development in a closed system. As the efficiency of the system is a crucial property, plenty of experiments are executed to get optimum parameters. In this system, the flow is driven by the pressure difference between a gas storage tank and a vacuum vessel with a source pressure. The idea is based on a constant volume system without extra source gases to guarantee rapid response and high throughput. Among them, valves and gas species are studied because their properties could influence the velocity of the fluid field. Then source pressures and volumes are emphasized to investigate the volume flow rate of the injection. The source pressure has a considerable effect on the injected volume. From the data, proper parameters are extracted to achieve the best performance of the FPSS. Finally, experimental results are used as a quantitative benchmark for simulations which can add our understanding of the inner gas flow in the pipeline. In generally, there is a good consistency and the obtained correlations will be applied in further study and design for the FPSS.

• Asian-Australasian Journal of Animal Sciences
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• v.24 no.6
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• pp.818-824
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• 2011

Eight LW${\times}$D crossbred, castrated weanling piglets were used to examine the effect of hyperglycemia by streptozotocin (STZ)-injection on oxidative and anti-oxidative status in circulating fluid. Every two of the eight piglets were intravenously administrated STZ at a dose of 0 (control), 100, 125 or 150 mg/kg BW, respectively, and on 15th day after the STZ-injection, some markers of the oxidative stress in circulating fluid were measured to evaluate oxidative and anti-oxidative status in the piglets. First, piglets with hyperglycemia were selected from the STZ-injected piglets as measured by the levels of fasting plasma glucose (FPG) during 2 weeks after the STZ-injection. Additionally, data obtained from the intravenous glucose tolerance test (IVGTT) on 14th day were analyzed. Secondly, the data obtained in this experiment were divided into the control group and the hyperglycemic (STZ) group, and compared. The FPG level or area under curve (AUC) for plasma glucose during the IVGTT in the STZ-induced diabetic piglets was slightly significantly (FPG, p = 0.070; AUC, p = 0.072) higher compared with the control. On the other hand, the plasma level of lipid peroxidation in the STZ-induced diabetic piglets was significantly (p<0.05) higher compared with the control. These results raise the possibility that STZ-induced diabetic piglets produced in this study can be used as a diabetic animal model to research the pathogenic mechanisms or therapy of complications in diabetic mellitus.