• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.201-210
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• 2002

Experiments were done for performance and flow characteristics of a counter-rotating axial flow fan. Performance curves of a counter-rotating axial flow fan were obtained and compared by varying the blade pitch angles. The fan characteristic curves were obtained following the Korean Standard Testing Methods for Turbo Fans and Blowers (KS B 6311). The fan flow characteristics were measured using a five-hole probe and a slanted hot-wire. The velocity profiles between the hub and tip of the fans were measured and analyzed at the peak efficiency point. The peak efficiency of the counter-rotating axial flow fan was improved about 15% respectively, compared with the single rotating axial fan. The single rotating axial flow fan showed relatively law efficiency due to the swirl velocities behind rotor exit which produced pressure losses. The counter-rotating axial flow fan showed that the swirl velocity generated by the front rotor was eliminated by the rear rotor and the associated dynamic pressure is recovered in the from of the static pressure rise.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.7
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• pp.805-810
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• 2012

Determining of the exercise intensity is very important in terms of induction of low fatigue during exercise. Little information is available on the contraction level of the trunk muscles during whole body tilts with and without axial rotation. This study was to investigate the difference muscle activation level according to axial rotation. Twenty subjects were participated. The muscle activities of the five trunk muscles were bilaterally measured at eight axial rotation angles with 12 tilt angles along $15^{\circ}$ intervals. The results showed that tilt with $45^{\circ}$ axial rotation was more balanced in the same tilt angle and was maintained approximately level of 40% MVC at over $60^{\circ}$ tilt angle with respect to co-contraction of abdominal and back muscle. Lumbar stabilization exercise using whole body tilts would be more effective with axial rotation than without axial rotation in terms of muscle co-contraction.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.54.1-54.1
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• 2019

Solar observations often show that interaction of more than one flux rope is involved in solar eruptions. In this regard, Lau and Finn (1996) intensively studied the interaction of two flux ropes, which reside in between two parallel planes each mimicking one polarity region of the solar photosphere. However, this geometry is quite far from the real solar situation, in which all feet of flux tubes are rooted in one surface only. In this paper, we study the interaction of two flux ropes in a semi-infinite region above a plane representing the solar photosphere. Four cases of the flux rope interaction are investigated in our MHD simulation study: (1) parallel axial fields and parallel axial currents (co-helicity), (2) antiparallel axial fields and parallel axial currents (counter-helicity), (3) parallel axial fields and antiparallel axial currents (counter-helicity), and (4) antiparallel axial fields and antiparallel axial currents (co-helicity). Each case consists of four or six subcases according to the background field direction relative to the flux ropes and the relative positions of the flux rope footpoints. In our simulations, all the cases eventually show eruptive behaviors, but their degree of explosiveness and field topological evolutions are quite different. We construct artificial emission measure maps based on the simulations and compare them with images of CME observations, which provides us with information on what field configurations may generate certain eruption features.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.19-28
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• 2013

The longitudinal axial strain in the plastic hinge region of reinforced concrete (RC) columns influences on the structural behavior of RC structures subjected to reversed cyclic loading. This strain decreases the effective compressive strength of concrete and increases the lateral displacements between stories by causing the elongation of member length. This paper investigated the effects of the axial force on the elongation of a RC member by using a sectional analysis of RC members. The analytical and experimental results indicated that the axial force decreased the axial strain in the plastic hinge region of RC columns. In this study, a model was proposed to predict the axial strain of RC columns. The proposed model considering the effects of axial force ratio consisted of three path types ; Path 1-loading region, Path 2-unloading region, and Path 3-reversing cyclic loading region. The axal strains predicted by the proposed model were compared with the test results of RC columns with various axial force ratios, and agreed reasonably with the observed longitudinal strains.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1708-1714
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• 2019

The purpose of the critical evaluation of the spent fuel pool (SFP) is to verify that the maximum effective multiplication factor ($K_{eff}$) is less than the critical safety limit at 100% stored condition of the spent fuel with the maximum reactivity. At nuclear power plants, the storage standard of spent fuel, ie, the loading curve, is established to prevent criticality from being generated in SFP. Here, the loading curve refers to a graph showing the minimum discharged burnup versus the initial enrichment of spent fuel. Recently, US NRC proposed the new critical safety assessment guideline (DSS-ISG-2010-01, Revision 0) of PWR SFPs and most of utilities in US is following it. Of course, the licensed criterion of the maximum effective multiplication factor of SFP remains unchanged and it should be less than 0.95 from the 95% probability and the 95% confidence level. However, the new guideline is including the new evaluation methodologies like the application of the axial burnup profile, the validation of depletion and criticality code, and trend analysis. Among the new evaluation methodologies, the most important factor that affects $K_{eff}$ is the axial burnup profile of spent fuel. US NRC recommends to consider the axial burnup profiles presented in NUREG-6801 in criticality analysis. In this paper, criticality effect was evaluated considering three profiles, respectively: i) Axial burnup profiles presented in NUREG-6801. ii) Representative PWR axial burnup profile. iii) Uniform axial burnup profile. As the result, the case applying the axial burnup profiles presented in NUREG-6801 showed the highest $K_{eff}$ among three cases. Therefore, we need to introduce a new methodology because it can be issued if the axial burnup profiles presented in NUREG/CR-6801 are applied to the domestic nuclear power plants without any other consideration.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.137-149
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• 2021

In engineering design, the axial equivalent elastic modulus of laminated FRP pipe was mostly calculated by the average elastic modulus method or the classical laminated plate theory method, which are based on relatively simplified assumptions, and may be not accurate enough sometimes. A new analytical calculation method for the axial equivalent elastic modulus of laminated FRP pipe was established based on three-dimensional stress state. By comparing the results calculated by this method with those by the above two traditional analytical methods and the finite element method, it is found that this method for the axial equivalent elastic modulus fits well not only for thin-walled pipes with orthotropic layers, but also for thick-walled pipes with arbitrary layers. Besides, the influence of the layer stacking on the axial equivalent elastic modulus was studied with this method. It is found that a proper content of circumferential layer is beneficial for improving the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers, and then can reduce its material quantity under the premise that its axial stiffness remains unchanged. Finally, the meso-mechanical mechanism of this effect was analyzed. The improving effect of circumferential layer on the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers is mainly because that, the circumferential fibers can restrain the rigid body rotations of the oblique fibers, which tend to cause the significant deformations of the pipe wall units and the relatively low axial equivalent elastic modulus of the pipe.

• Journal of the Korean Society of Radiology
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• v.15 no.4
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• pp.437-444
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• 2021

To evaluate the usefulness of Volume Axial Mode by comparing analyzing the exposure dose of the patients and the quality of each images from CT images obtained from high pitch mode using the local phantom or volume axial mode to determine the usefulness of he volume axial mode in diagnosing the head and cervical disease in adults. High Pitch Mode, Helical Mode, and Volume axial Mode as adult phantom were tested according to 70 kVp, 80 kVp, and 100 kVp tube voltages during an adult frontal CT scans. The equipment used was GE's Revolution (GE Healthcare, Wisconsin USA) model and iMED X-ray Phantom. The exposure dose of phantom was compared using the images obtained from each protocol, and the image quality was compared by calculating SNR and CNR by setting ROI on each image. When examined using Volume Axial Mode, the exposure dose of phantom was measured 17.12% lower than Helical Mode, 5.35% lower than High Pitch Mode, and both SNR and CNR were improved. Volume Axial Mode is a useful test that reduces investigation time without table movement using high speed rotary scanner, and in which exposure dose is reduced and image quality is improved by acquiring images in a short time of 0.28 seconds of phantom than using High Pitch Mode and Helical Mode. In addition, the fast testing time of Volume Axial Mode can be seen as the biggest advantage CT scans of emergency patients or patients with physical discomfort.

• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.801-808
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• 2023

In order to minimize radiation exposure and secure diagnostic value images during CT examination of the head of children, the usefulness of volume axial mode is evaluated through comparison and analysis of exposure dose and images of volume axial mode, high pitch mode, and helical mode. Image evaluation and dose evaluation were performed in CT high pitch mode, helical mode, and volume axial mode for infants under the age of 1 according to the voltages of 70, 80, and 100 kVp tubes. The image evaluation was conducted by comparing image quality by setting ROI for each image, calculating SNR and CNR, using ONE-WAY (ANOVA) to evaluated statistical significance, and cross-examining the dose evaluation using DLP values displayed in the Dose Report. When inspected using volume axial mode, DLP values were generally low, and SNR and CNR values differed by ROI and kVp. When volume axial mode evaluated the quality of the image compared to other scan modes, the difference is not uniform. For the reason, certain modes are not considered excellent, but the exposure dose was reduced the most in terms of dose. In addition, the point that the volume axial mode can be examined at its original location, short scanning time and needless of table movement is useful for CT tests for children under 1 year of age with high radiation sensitivity.

• Korean Journal of Radiology
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• v.2 no.4
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• pp.216-221
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• 2001

Objective: To compare, in terms of their demonstration of tears of the anterior glenoid labrum, oblique axial MR arthrography obtained with the patient's shoulder in the abduction and external rotation (ABER) position, with conventional axial MR arthrography obtained with the patient's arm in the neutral position. Materials and Methods: MR arthrography of the shoulder, including additional oblique axial sequences with the patient in the ABER position, was performed in 30 patients with a clinical history of recurrent anterior shoulder dislocation. The degree of anterior glenoid labral tear or defect was evaluated in both the conventional axial and the ABER position by two radiologists. Decisions were reached by consensus, and a three-point scale was used: grade 1=normal; grade 2=probable tear, diagnosed when subtle increased signal intensity in the labrum was apparent; grade 3=definite tear/defect, when a contrast material-filled gap between the labrum and the glenoid rim or deficient labrum was present. The scores for each imaging sequence were averaged and to compare conventional axial and ABER position scans, Student's t test was performed. Results: In 21 (70%) of 30 patients, the same degree of anterior instability was revealed by both imaging sequences. Eight (27%) had a lower grade in the axial position than in the ABER position, while one (3%) had a higher grade in the axial position. Three whose axial scan was grade 1 showed only equivocal evidence of tearing, but their ABER-position scan, in which a contrast material-filled gap between the labrum and the glenoid rim was present, was grade 3. The average grade was 2.5 (SD=0.73) for axial scans and 2.8 (SD=0.46) for the ABER position. The difference between axial and ABER-position scans was statistically significant (p<0.05). Conclusion: MR arthrography with the patient's shoulder in the ABER position is more efficient than conventional axial scanning in revealing the degree of tear or defect of the anterior glenoid labrum. When equivocal features are seen at conventional axial MR arthrography, oblique axial imaging in the ABER position is helpful.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3027-3032
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• 2007

To understand the complex phenomena performed in steam explosion, the fast and global measurement of the steam distribution is imperative for this extremely rapid transient stimulation of the bubble breakup and coalescence due to turbulent eddies and shock waves. TROI, the experimental facility requests more robust sensor system to meet this requirement. In Europe, researchers are prefer a X-ray method but this method is very expensive and has limited measurement range. There is an alternative technology such as ECT. Because of TROI's geometry, however, we need axial tomography method. This paper reviews image reconstruction algorethms for axial tomography, including Tikhonov regularization and iterative Tikhonov regularization. Axial tomography method is examined by simulation and experiment for typical permittivity distributions. Future works in axial tomography technology is discussed.