• Korean Management Science Review
• /
• v.34 no.3
• /
• pp.1-14
• /
• 2017

This study empirically analyzes the impact of inventory management performance on the energy efficiency in Korean petrochemical companies. The concept of the distance function is used to define the energy efficiency and the estimation of the distance function is performed using the stochastic frontier analysis. The inventory turnover is selected as the variable indicating the inventory management performance of the company. The main results of this study are as follows. First, the inventory turnover has a positive impact on energy efficiency. Second, during the period over 2011~2015, while the gap in energy efficiency among the companies expanded, the average energy efficiency decreased. Third, the average energy efficiency in upstream process companies was greater than downstream process companies and the gap in energy efficiency among downstream process companies was greater than upstream process companies. Fourth, the average marginal effect of inventory turnover on energy efficiency increased gradually from 2011 to 2015. Finally, the average marginal effect of inventory turnover in downstream process companies was greater than upstream process companies, and the gap in the marginal effect of inventory turnover among downstream process companies was greater than upstream process companies. These results together imply the importance of inventory management in terms of energy efficiency.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.20 no.11
• /
• pp.1078-1088
• /
• 2010

In order to analyze the quantitative characteristics of acoustic streaming, experimental setup of 3-D stereoscopic PIV(particle imaging velocimetry) was designed and quantitative ultrasonic flow fields in the gap between the ultrasonic vibrator and heat source were measured. Utilizing acoustic streaming induced by ultrasonic vibration, surface temperature drop of cooling object was also measured. The study on smart cooling method by acoustic streaming induced by ultrasonic vibration was performed due to the empirical relations of flow pattern, average flow velocity, different gaps, and enhancement on cooling rates in the gap. Average velocity fields and maximum acoustic streaming velocity in the open gap between the stationary cylindrical heat source and ultrasonic vibrator were experimentally measured at no vibration, resonance, and non-resonance. It was clearly observed that the enhancement of cooling rates existed owing to the acoustic air flow in the gap at resonance and non-resonance induced by ultrasonic vibration. The ultrasonic wave propagating into air in the gap creates steady-state secondary eddy called acoustic streaming which enhances heat transfer from the heat source to encompassing air. The intensity of the acoustic streaming induced by ultrasonic vibration experimentally depended upon the gap between the heat source and ultrasonic vibrator. The ultrasonic vibration at resonance caused the increase of the acoustic streaming velocity and convective heat transfer augmentation when the flow fields by 3D stereoscopic PIV and temperature drop of the heat source were measured experimentally. The acoustic streaming velocity of air enhancement on cooling rates in the gap is maximal when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which is specifically 12 mm.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.14 no.6
• /
• pp.528-535
• /
• 2004

Ultrasonic Vibrator is designed to achieve the maximum vibration amplitude at 30 kHz by in-cluding a horn (diameter, 40 mm), mechanical vibration amplifier at the top of the ultrasonic vibrator in the system and making the complete system resonate. In addition, it is experimentally visualized by particle imaging velocimetry (PIV) that the acoustic streaming velocity in the gap is at maximum when the gap between the ultrasonic vibrator and stationary plate agrees with the multiples of half-wavelength of the ultrasonic wave. This fact results from the resonance of the sound wave and the theoretical analysis of that is also accomplished and verified by experiment. It is observed that the magnitude of the acoustic streaming dependent upon the gap between the ultrasonic vibrator and stationary plate possibly changes due to the measurement of the average velocity fields of the acoustic streaming induced by the ultrasonic vibration at resonance and non-resonance. There exists extremely small average velocity at non-resonant gaps while the relatively large average velocity exists at resonant gaps compared with non-resonant gaps. It also reveals that there should be larger axial turbulent intensity at the hub region of the vibrator and at the edge of it in the resonant gap where the air streaming velocity is maximized and the flow phenomena is conspicuous than that at the other region. Because the variation of the acoustic streaming velocity at resonant gap is more distinctive than that at non-resonant gap, shear stress increases more in the resonant gap and is also maximized at the center region of the vibrator except the local position of center (r〓0). At the non-resonant gap there should be low values of vorticity distribution, but in contrast to the non-resonant gap, high and negative values of it exist at the center region of the vibrator with respect to the radial direction and in the vicinity of the middle region with respect to the axial direction. Acoustic streaming is noise-free due to the ultrasonic vibration and maintenance-free because of the absence of moving parts. Moreover, the proposed method by acoustic streaming can be utilized to the nano and micro-electro mechanical systems as a driving mechanism in addition to the augmentation of the streaming velocity.

• International Journal of Precision Engineering and Manufacturing
• /
• v.9 no.3
• /
• pp.22-26
• /
• 2008

The use of electrical discharge machining (EDM) for micro-machining applications requires particular attention to the machined surface roughness and discharge gap distance, as these factors affect the geometrical accuracy of micro-parts. Previous studies of conventional EDM have shown that selected types of semi-conductive and non-conductive powder suspended in the dielectric reduced the surface roughness while ensuring a limited increase in the gap distance. Based on this, an extension of the technique to micro-EDM was studied Such work is necessary since the introduction of nanopowders suspended in the dielectric is not well understood. The experimental results showed that a statistically significant reduction in the surface roughness value was achieved at particular concentrations of the powder additives, depending on the powder material and the machining input energy setting. The average reduction in surface roughness using a powder suspended dielectric was between 14-24% of the average surface roughness generated using a pure dielectric. Furthermore, when these additive concentrations were used for machining, no adverse increase in the gap distance was observed.

• Journal of Technologic Dentistry
• /
• v.41 no.4
• /
• pp.271-278
• /
• 2019

Purpose: To quantify the effect of the crystallization process on lithium disilicate ceramic crowns that are fabricated using a computer-aided design/computer-aided manufacturing(CAD/CAM) system, and to determine whether they are clinically acceptable by comparing values before and after the crystallization process. Methods: The maxillary first molar was selected as the abutment for the experiments. Ten working models were prepared. Marginal and internal gap of 4 groups of lithium disilicate crowns(n=10) fabricated with conventional method. Comparison was performed using the silicone replica technique and 3D superimposition analysis. The marginal and internal gaps of the restoration were measured before and after the crystallization process of this prosthesis. The average value of each part(the average of values measured before and after the crystallization) was statistically analyzed using paired t-test(α=0.05). Results: The results from the second phase of this research, which compared the average value of the gap between the marginal and internal fits of the lithium disilicate single crown before and after the crystallization process, indicated that the marginal gap was larger and the internal gap was smaller after the crystallization process, and this difference was statistically significant (P<0.05) in all the parts evaluated. Conclusion: While the shrinkage that occurs during crystallization does affect the marginal and internal fit of the prosthesis, it cannot be concluded to be a major effect because the resultant distortion was within the clinically acceptable range.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.30 no.6
• /
• pp.1271-1278
• /
• 2020

Deep learning-based profiling side-channel analysis is a powerful analysis method that utilizes the neural network to profile the relationship between the side-channel information and the intermediate value. Since the neural network interprets each point of the signal in a different dimension, jitter makes it much hard that the neural network with dimension-wise weights learns the relationship. This paper shows that replacing the fully-connected layer of the traditional CNN (Convolutional Neural Network) with global average pooling (GAP) allows us to design the inherently robust neural network inherently for jitter. We experimented with the ChipWhisperer-Lite board to demonstrate the proposed method: as a result, the validation accuracy of the CNN with a fully-connected layer was only up to 1.4%; contrastively, the validation accuracy of the CNN with GAP was very high at up to 41.7%.

• Journal of Korean Society of Forest Science
• /
• v.89 no.5
• /
• pp.543-551
• /
• 2000

This study was conducted to understand Pinus densiflora regeneration characteristics from canopy gaps due to disturbance in natural forests located at Mt. Joongwang in Kangwon-do. The line-transect method was adopted to analyze crown architecture of Pinus densiflora. The saplings of Pinus densiflora in the canopy gap showed high adaptation to growth environment at their early regeneration stage, and showed different characteristics in crown architecture. Variation of branching angle in the main branch of Pinus densiflora was small in canopy gap. Primary branch growth showed was high during 4~5 year-old period and slowly low after that period. Average 5 of primary branch were generated from stem in canopy. Average 4 of secondary branch were generated from primary branch in canopy gap. Primary branches generated from the stem were uniformly distributed at all cardinal directions. When canopy gap size is $100{\sim}120m^2$, secondary branches generated from primary branch had mostly high numbers between $S44^{\circ}E$ and $S90^{\circ}W$.

• Journal of Korea Society of Industrial Information Systems
• /
• v.28 no.1
• /
• pp.27-34
• /
• 2023

The optimal assignment problem between agents and tasks is known as one of the representative problems of combinatorial optimization and an NP-hard problem. This paper covers multi agent-multi task assignment problems with uncertain completion probability. The completion probabilities are generally uncertain due to endogenous (agent or task) or exogenous factors in the system. Assignment decisions without considering uncertainty can be ineffective in a real situation that has volatility. To consider uncertain completion probability mathematically, a mathematical formulation with stochastic programming is illustrated. We also present an algorithm by using the sample average approximation method to solve the problem efficiently. The algorithm can obtain an assignment decision and the upper and lower bounds of the assignment problem. Through numerical experiments, we present the optimality gap and the variance of the gap to confirm the performances of the results. This shows the excellence and robustness of the assignment decisions obtained by the algorithm in the problem with uncertainty.

• The Journal of Advanced Prosthodontics
• /
• v.7 no.3
• /
• pp.257-263
• /
• 2015

PURPOSE. In this study, we aimed to evaluate the amount of marginal gap with two different substructure materials using identical margin preparations. MATERIALS AND METHODS. Twenty stainless steel models with a chamfer were prepared with a CNC device. Marginal gap measurements of the galvano copings on these stainless steel models and Co-Cr copings obtained by a laser-sintering method were made with a stereomicroscope device before and after the cementation process and surface properties were evaluated by scanning electron microscopy (SEM). A dependent t-test was used to compare the mean of the two groups for normally distributed data, and two-way variance analysis was used for more than two data sets. Pearson's correlation analysis was also performed to assess relationships between variables. RESULTS. According to the results obtained, the marginal gap in the galvano copings before cementation was measured as, on average, $24.47{\pm}5.82{\mu}m$ before and $35.11{\pm}6.52{\mu}m$ after cementation; in the laser-sintered Co-Cr structure, it was, on average, $60.45{\pm}8.87{\mu}m$ before and $69.33{\pm}9.03{\mu}m$ after cementation. A highly significant difference (P<.001) was found in marginal gap measurements of galvano copings and a significant difference (P<.05) was found in marginal gap measurements of the laser-sintered Co-Cr copings. According to the SEM examination, surface properties of laser sintered Co-Cr copings showed rougher structure than galvano copings. The galvano copings showed a very smooth surface. CONCLUSION. Marginal gaps values of both groups before and after cementation were within the clinically acceptable level. The smallest marginal gaps occurred with the use of galvano copings.

• Progress in Medical Physics
• /
• v.29 no.2
• /
• pp.66-72
• /
• 2018

The proper position of a multi-leaf collimator (MLC) is essential for the quality of intensity-modulated radiation therapy (IMRT) and volumetric modulated arc radiotherapy (VMAT) dose delivery. Task Group (TG) 142 provides a quality assurance (QA) procedure for MLC position. Our study investigated the QA validation of the mechanical leaf gap measurement and the maintenance procedure. Two $VitalBeam^{TM}$ systems were evaluated to validate the acceptance of an MLC position. The dosimetric leaf gaps (DLGs) were measured for 6 MV, 6 MVFFF, 10 MV, and 15 MV photon beams. A solid water phantom was irradiated using $10{\times}10cm^2$ field size at source-to-surface distance (SSD) of 90 cm and depth of 10 cm. The portal dose image prediction (PDIP) calculation was implemented on a treatment planning system (TPS) called $Eclipse^{TM}$. A total of 20 VMAT plans were used to confirm the accuracy of dose distribution measured by an electronic portal imaging device (EPID) and those predicted by VMAT plans. The measured leaf gaps were 0.30 mm and 0.35 mm for VitalBeam 1 and 2, respectively. The DLG values decreased by an average of 6.9% and 5.9% after mechanical MLC adjustment. Although the passing rates increased slightly, by 1.5% (relative) and 1.2% (absolute) in arc 1, the average passing rates were still within the good dose delivery level (>95%). Our study shows the existence of a mechanical leaf gap error caused by a degenerated MLC motor. This can be recovered by reinitialization of MLC position on the machine control panel. Consequently, the QA procedure should be performed regularly to protect the MLC system.