• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.453-467
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• 2018

The excavation performance and the cutting tool wear prediction of shield TBM are very important issues for design and construction in TBM tunneling. For hard-rock TBMs, CSM and NTNU model have been widely used for prediction of disc cutter wear and penetration rate. But in case of soft-ground TBMs, the wear evaluation and the excavation performance have not been studied in details due to the complexity of the ground behavior and therefore few testing methods have been proposed. In this study, a new soil abrasion and penetration tester (SAPT) that simulates EPB TBM excavation process is introduced which overcomes the drawbacks of the previously developed soil abrasivity testers. Parametric tests for penetration rate, foam mixing ratio, foam concentration were conducted to evaluate influential parameters affecting TBM excavation and also ripper wear was measured in laboratory. The results of artificial soil specimen composed of 70% illite and 30% silica sand showed TBM additives such as foam play a key role in terms of excavation and tool wear.

• Fire Science and Engineering
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• v.33 no.4
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• pp.41-49
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• 2019

In the present experimental study, based on a real-scale theater, a 1/14 reduced-scale model was constructed, and the effects of natural vent and fire curtain in fire of a theater stage were investigated. The case without fire curtain under the opened natural vent showed lower temperatures in the stage, whereas the case with fire curtain under the opened natural vent showed lower temperatures in the auditorium. On the other hand, through analyzing the starting time of the temperature rise at the point near the proscenium opening in the auditorium, it was found that the opened natural vent condition can delay the starting time of smoke spread from the stage to the auditorium and suppress the temperature rise in the auditorium. Under the present experimental conditions, the fire curtain installation did not affect significantly the velocity and mass flow rate of the outflow through the natural vent of the stage, which might be due to openings in the stage. The present results can be used to examine the effects of natural vent and fire curtain in a real-scale fire of a theater and to check the accuracy of the numerical simulation code.

• Journal of Veterinary Clinics
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• v.33 no.2
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• pp.102-106
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• 2016

More than 20 years after the first report of porcine reproductive and respiratory syndrome virus (PRRSV) in Korea, the disease is still having major impact on domestic pig health and relevant industries. Although ELISA tests are commonly used by veterinarians to guide herd management, data on diagnostic performance of the test in field settings are very limited. The objective of this study was to evaluate two commercially available PRRSV ELISA (IDEXX PRRS X3 ELISA and Bionote PRRSV ELISA 4.0) to detect antibodies against PRRSV on serum samples. To this end, a total of 1,108 sera were recruited from 35 swine farms located in Gyeonggi province and tested at the Gyeonggi Province Veterinary Service Center. All tests were performed according to the manufacturer's instructions, by laboratory technicians who routinely perform PRRS testing on blood samples. Samples were collected from two sources of swine populations with different PRRS prevalence; 60 samples (5.4%) were originated from breeding farms and the remaining 1,048 samples (94.6%) were from farrow-to-finish farms. We applied Bayesian latent class model (LCM) for two-tests in the two-population when the accuracy of the gold standard is not available. The model estimated that Bionote ELISA was a bit more specific but slightly less sensitive. The estimated sensitivity and specificity of the IDEXX ELISA were 99.8% (95% CI 98.1-100%) and 86.4% (95% CI 81.4-96.5%), respectively. Sensitivity, specificity, positive predictive value and negative predictive value for Bionote kit were 98.7% (95% CI 92.8-100%), 89.8% (95% CI 86.2-93.1%), 93.8% (95% CI 91.5-96.0%), and 97.8% (95% CI 87.1-100%), respectively. Based on the Bayesian 95% credible intervals, the sensitivity and specificity of the two ELISAs were not significantly different each other when assuming that two kits were imperfect, indicating that two kits performed equally well in terms of sensitivity and specificity in our filed setting.

• Smart Structures and Systems
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• v.29 no.4
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• pp.625-640
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• 2022

Maglev rail joints are vital components serving as connections between the adjacent F-type rail sections in maglev guideway. Damage to maglev rail joints such as bolt looseness may result in rough suspension gap fluctuation, failure of suspension control, and even sudden clash between the electromagnets and F-type rail. The condition monitoring of maglev rail joints is therefore highly desirable to maintain safe operation of maglev. In this connection, an online damage detection approach based on three-dimensional (3D) convolutional neural network (CNN) and time-frequency characterization is developed for simultaneous detection of multiple damage of maglev rail joints in this paper. The training and testing data used for condition evaluation of maglev rail joints consist of two months of acceleration recordings, which were acquired in-situ from different rail joints by an integrated online monitoring system during a maglev train running on a test line. Short-time Fourier transform (STFT) method is applied to transform the raw monitoring data into time-frequency spectrograms (TFS). Three CNN architectures, i.e., small-sized CNN (S-CNN), middle-sized CNN (M-CNN), and large-sized CNN (L-CNN), are configured for trial calculation and the M-CNN model with excellent prediction accuracy and high computational efficiency is finally optioned for multiple damage detection of maglev rail joints. Results show that the rail joints in three different conditions (bolt-looseness-caused rail step, misalignment-caused lateral dislocation, and normal condition) are successfully identified by the proposed approach, even when using data collected from rail joints from which no data were used in the CNN training. The capability of the proposed method is further examined by using the data collected after the loosed bolts have been replaced. In addition, by comparison with the results of CNN using frequency spectrum and traditional neural network using TFS, the proposed TFS-CNN framework is proven more accurate and robust for multiple damage detection of maglev rail joints.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.607-619
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• 2023

This study, it was tried to evaluate the asphalt behavior under tensile loading conditions through indirect Brazilian and direct tensile tests, experimentally and numerically. This paper is important from two points of view. The first one, a new test method was developed for the determination of the direct tensile strength of asphalt and its difference was obtained from the indirect test method. The second one, the effects of particle size and loading rate have been cleared on the tensile fracture mechanism. The experimental direct tensile strength of the asphalt specimens was measured in the laboratory using the compression-to-tensile load converting (CTLC) device. Some special types of asphalt specimens were prepared in the form of slabs with a central hole. The CTLC device is then equipped with this specimen and placed in the universal testing machine. Then, the direct tensile strength of asphalt specimens with different sizes of ingredients can be measured at different loading rates in the laboratory. The particle flow code (PFC) was used to numerically simulate the direct tensile strength test of asphalt samples. This numerical modeling technique is based on the versatile discrete element method (DEM). Three different particle diameters were chosen and were tested under three different loading rates. The results show that when the loading rate was 0.016 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis till coalescence to the model boundary. When the loading rate was 0.032 mm/sec, two tensile cracks were initiated from the left and right of the hole and propagated perpendicular to the loading axis. The branching occurs in these cracks. This shows that the crack propagation is under quasi-static conditions. When the loading rate was 0.064 mm/sec, mixed tensile and shear cracks were initiated below the loading walls and branching occurred in these cracks. This shows that the crack propagation is under dynamic conditions. The loading rate increases and the tensile strength increases. Because all defects mobilized under a low loading rate and this led to decreasing the tensile strength. The experimental results for the direct tensile strengths of asphalt specimens of different ingredients were in good accordance with their corresponding results approximated by DEM software.

• Advances in nano research
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• v.16 no.4
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• pp.375-394
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• 2024

The extensive utilization of concrete has given rise to environmental concerns, specifically concerning the depletion of river sand. To address this issue, waste deposits can provide manufactured-sand (MS) as a substitute for river sand. The objective of this study is to explore the application of machine learning techniques to facilitate the production of manufactured-sand concrete (MSC) containing stone nano-powder through estimating the splitting tensile strength (STS) containing compressive strength of cement (CSC), tensile strength of cement (TSC), curing age (CA), maximum size of the crushed stone (Dmax), stone nano-powder content (SNC), fineness modulus of sand (FMS), water to cement ratio (W/C), sand ratio (SR), and slump (S). To achieve this goal, a total of 310 data points, encompassing nine influential factors affecting the mechanical properties of MSC, are collected through laboratory tests. Subsequently, the gathered dataset is divided into two subsets, one for training and the other for testing; comprising 90% (280 samples) and 10% (30 samples) of the total data, respectively. By employing the generated dataset, novel models were developed for evaluating the STS of MSC in relation to the nine input features. The analysis results revealed significant correlations between the CSC and the curing age CA with STS. Moreover, when delving into sensitivity analysis using an empirical model, it becomes apparent that parameters such as the FMS and the W/C exert minimal influence on the STS. We employed various loss functions to gauge the effectiveness and precision of our methodologies. Impressively, the outcomes of our devised models exhibited commendable accuracy and reliability, with all models displaying an R-squared value surpassing 0.75 and loss function values approaching insignificance. To further refine the estimation of STS for engineering endeavors, we also developed a user-friendly graphical interface for our machine learning models. These proposed models present a practical alternative to laborious, expensive, and complex laboratory techniques, thereby simplifying the production of mortar specimens.

• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.211-221
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• 2003

At Aspo hard rock laboratory in Sweden, an in-situ heater experiment called "$\"{A}"{s}"{p}"{o}$ Pillar Stability Experiment (APSE)" is prepared to assess capability to predict spatting and stability in a rock mass between deposition holes for radioactive waste. To Predict reasonably fracturing process at rock pillar under a planned configuration before testing, a boundary element code FRACOD has been applied for modelling. The code has been improved to simulate explicitly fracture evolution both at rock boundaries and in intact rocks. A new inverse stress reconstruction technique using boundary element has been also developed to transfer stress field by excavation and thermal loading into the FRACOD model. This article presents the results from predictive modelling far the planned in-situ test condition. Excavation induced stresses might cause slight fracturing in the pillar walls. Typical shear fractures have been initiated and propagated near central pillar walls during 120 days of heating, but overall rock mass remained stable under the considered configuration. The effects of pre-existing joints and properties of fractures are also discussed. It is found from the results that FRACOD can properly model essential rock spatting and propagation at deep tunnels and boreholes.at deep tunnels and boreholes.

• The Korean Journal of Pain
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• v.20 no.1
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• pp.15-20
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• 2007

Background: Lipo-prostaglandin E1 (Lipo-$PGE_1$) has vasodilating and platelet aggregation inhibitory characteristics and it has been used as a treatment for patients with blood flow dysfunction disease. Based on the mechanisms of lumbar spinal stenosis, including veno congestion, neuro-ischemia and mechanical compression, we aimed to study whether intravenous Lipo-$PGE_1$ injection has any therapeutic effect on hyperalgesia in a rat foraminal stenosis model. Methods: In this study, twenty male Sprague-Dawley rats were divided into the control (n = 10) and Lipo-$PGE_1$ (n = 10) groups. A small stainless steel rod was inserted into the L5-6 intervertebral foramen to induce intervertebral foramen stenosis and chronic DRG compression. In the Lipo-$PGE_1$ group, $0.15{\mu}g/kg$ of Lipo-$PGE_1$ were injected intravenously via a tail vein for 10 days starting from the $3^{rd}$ day after operation. Behavioral testing for mechanical and thermal hyperalgesia was performed for 3 weeks after the injections. Results: From the $10^{th}$ day after Lipo-$PGE_1$ injection, the rats in the experimental group showed significant recovery of their mechanical threshold, and this effect was maintained for 3 weeks. No significant differences of the thermal hyperalgesia were observed between the two groups. Conclusions: These findings suggest that intravenously injected Lipo-$PGE_1$ may be effective for alleviating neuropathic pain, which isthe main symptom of spinal stenosis, by improving the blood flow dysfunction.

• International Journal of Highway Engineering
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• v.12 no.3
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• pp.79-85
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• 2010

This paper presents a preliminary study of roller types for chip seals based on aggregate retention performance. Chip seal test sections composed of single seals of granite 78M aggregate and CRS-2 emulsion were constructed using three different roller types: the pneumatic tire roller, steel wheel roller, and combination roller. In order to investigate the performance of these rollers effectively, it is critical to test chip seal samples obtained directly from field construction. Therefore, test sections were constructed on New Sandy Hill Church Road near Bailey, North Carolina. Chip seal samples obtained from these sections were used for laboratory testing. The aggregate retention performance was evaluated using the flip-over test (FOT), Vialit test, and the third-scale Model Mobile Loading Simulator (MMLS3). Based on the test results and visual observation, both the pneumatic roller and the combination roller used together are recommended to improve chip seal performance with the sequence of the pneumatic roller rolling first followed by the combination roller.

• Fire Science and Engineering
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• v.32 no.3
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• pp.51-59
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• 2018

Although a fire curtain plays an important role in preventing smoke from spreading to the auditorium in a theater fire, there has been insufficient research on fire curtains. In this study, to check the accuracy of numerical simulation, for previous experiments using a reduced scale model, a numerical simulation was carried out, and the results were compared with previous experimental data. The fire curtain effect was then predicted numerically. A Fire Dynamics Simulator (FDS) was used, and the natural exhaust vent sizes were set to ~10%, ~5%, and ~1% of the stage floor area. The smoke movement was visualized, and the mass flow rates and temperatures were measured and analyzed. In addition, the law of similarity was used to examine the influence of a fire curtain in a real scale theater fire. Without the fire curtain, the present numerical simulation results were in agreement with the previous experimental data within reasonable accuracy. Meanwhile, the fire curtain affects the mass flow rates through the natural exhaust vent and proscenium opening, as well as the start time of soot outflow to the auditorium. Overall, the present results can be used to develop a fire curtain system.