• Korean Journal of Agricultural Science
• /
• v.47 no.4
• /
• pp.1159-1168
• /
• 2020

The conduits of agricultural reservoirs undergo deterioration over a considerable period of time and this is highly likely to cause structural problems such as cracks. It is therefore important to consider the effects of structural defects on the body from the viewpoint of stability and maintenance of the embankment. In this study, basic data on the effects of the crack location on the stability of the embankment is obtained by identifying, comparing, and analyzing the erosion characteristics and pore water pressure behavior through a large-scale model experiment that involves classifying the location of the conduit cracks. From the results of the experiment, it was confirmed that when a crack occurred, the amount of leakage increased as the location of the crack portion was closer to the water level, and the internal erosion phenomenon accelerated, thereby increasing the possibility of piping. It was also found that an upstream conduit crack affects the erosion and water pressure change of the central and downstream conduit of the embankment, and the conduit crack has a very large effect on the pore water pressure despite the low upstream water level. Therefore, the seepage behavior of the embankment for each conduit crack identified in this study is considered to be useful basic data for preparing a repair and reinforcement plan according to the crack location in the future.

• Smart Structures and Systems
• /
• v.11 no.5
• /
• pp.555-567
• /
• 2013

An Remote Corrosion Monitoring (RCM) system consists of an anode with low potential, the metallic structures against corrosion, an electrode to provide reference potential, and a data-acquisition system to ensure the potential difference for anticorrosion. In more detail, the data-acquisition (DAQ) system monitors the potential difference between the metallic structures and a reference electrode to identify the correct potential level against the corrosion of the infrastructures. Then, the measured data are transmitted to a central office to remotely keep track of the status of the corrosion monitoring (CM) system. To date, the RCM system is designed to achieve low power consumption, so that it can be simply powered by batteries. However, due to memory effect and the limited number of recharge cycles, it can entail the maintenance fee or sometimes cause failure to protect the metallic structures. To address this issue, the low-overhead energy harvesting circuitry for the RCM systems has designed to replenish energy storage elements (ESEs) along with redeeming the leakage of supercapacitors. Our developed energy harvester can scavenge the ambient energy from the corrosion monitoring environments and store it as useful electrical energy for powering local data-acquisition systems. In particular, this paper considers the energy harvesting from potential difference due to galvanic corrosion between a metallic infrastructure and a permanent copper/copper sulfate reference electrode. In addition, supercapacitors are adopted as an ESE to compensate for or overcome the limitations of batteries. Experimental results show that our proposed harvesting schemes significantly reduce the overhead of the charging circuitry, which enable fully charging up to a 350-F supercapacitor under the low corrosion power of 3 mW (i.e., 1 V/3 mA).

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.17 no.2
• /
• pp.265-270
• /
• 2017

4H-SiC has attracted attention for high-power and high-temperature metal-oxide-semiconductor field-effect transistors (MOSFETs) for industrial and automotive applications. The gate oxide in the 4H-SiC MOS system is important for switching operations. Above $1000^{\circ}C$, thermal oxidation initiates $SiO_2$ layer formation on SiC; this is one advantage of 4H-SiC compared with other wide band-gap materials. However, if post-deposition annealing is not applied, thermally grown $SiO_2$ on 4H-SiC is limited by high oxide charges due to carbon clusters at the $SiC/SiO_2$ interface and near-interface states in $SiO_2$; this can be resolved via low-temperature deposition. In this study, low-temperature $SiO_2$ deposition on a Si substrate was optimized for $SiO_2/4H-SiC$ MOS capacitor fabrication; oxide formation proceeded without the need for post-deposition annealing. The $SiO_2/4H-SiC$ MOS capacitor samples demonstrated stable capacitance-voltage (C-V) characteristics, low voltage hysteresis, and a high breakdown field. Optimization of the treatment process is expected to further decrease the effective oxide charge density.

• Journal of the Microelectronics and Packaging Society
• /
• v.11 no.3 s.32
• /
• pp.9-15
• /
• 2004

We investigated the electrical properties of copolymer low-k materials that are compromised of the PMSSQ(Poly Methyl Silsesquioxane)-based matrix with the BTMSE (Bis Tri Methoxy Silyl Ethane) additives. We manufactured MIS-type test samples using the copolymer as the insulator and measured their leakage current and failure time by means of the BTS (bias-temperature-stress) test. The failure time was observed to decrease drastically when the porosity of the copolymer was increased over $30\%$. From the measurement of failure time with respect to temperature. the activation energy of Cu drift through the copolymer was calculated to be 1.51 eV.

• Journal of Korean society of Dental Hygiene
• /
• v.10 no.3
• /
• pp.531-540
• /
• 2010

Objectives : In this study, following the cavity restorations with low copper conventional alloy, high copper admixed one and high copper unicompositional one, which are used the most frequently in a clinical setting at the present, to experiment the time-dependent changes of strength, bubbles were examined. Besides, to examine the detrimental effects of mercury contained in dental amalgam, the amount of mercury release was evaluated. Methods : As dental amalgams which were used herein, [BESTALOY], [Hi-Aristaloy 21] and [Sybraloy] were selected for a low-copper conventional amalgam, a high-copper admixed one and a high-copper unicompositional one in the corresponding order. The formation of bubbles and the weight ratio of mercury release were evaluated using a field emission scanning electron microscope (FE-SEM). Thus, the following results were obtained: Results : 1. The time-dependent amount of mercury release reached a statistical significance in three types of alloys, which was shown in such a descending order as [BESTALOY], [Hi-Aristaloy 21] and [Sybraloy]. 2. A low-copper conventional type, BESTALOY is a cutting type and it was found to have an increased formation of fine bubbles. In the remaining two types, [Hi-Aristaloy 21] (a high-copper admixed alloy) and [Sybraloy] (a high-copper unicompositional alloy), the time-dependent changes in the formation of bubbles was negligible. Conclusions : Accordingly, this type of mercury release from amalgam alloy denotes the difference in the weight ratio of total constituents between after 24 hours and after two weeks. But further studies are warranted to examine the amount of mercury release which is detrimental to human bodies. Besides, a low-copper conventional alloy is a cutting type and it was characterized by the abundant formation of bubbles in a time-dependent manner. This implies that the strength of amalgam is impaired, which should be considered in selecting the appropriate amalgam alloy in a clinical setting.

• Korean Journal of Agricultural Science
• /
• v.41 no.2
• /
• pp.75-83
• /
• 2014

Recently, a quick drop of air temperature in plastic film houses by adverse weather conditions leads to the occurrence of low temperature damages to growing crops. Chilling injury, defined as a variety of growth restriction occurring below the optimal temperature, is one of environmental factors strongly affecting crop growth and yield. Low temperature causes the restricted evapotranspiration, reduced mineral uptake (P > K > $NO_3{^-}$), and an increase in electrolyte leakage such as K. Despite being different with plant species, an accumulation of soluble carbohydrates such as glucose, fructose, sucrose and starch under chilling condition is well known. A variety of environmental stresses are known to cause oxidative damage to plants either directly or indirectly by triggering an increased level of production of reactive oxygen species (ROS), and, to combat the oxidative damage, plants have the antioxidant defense systems comprising of enzymes, SOD, POD, CAT, GPX and APX, and non-enzymes, ascorbate, gluthathione, ${\alpha}$-tocopherol, phenolic compounds, carotenoid and flavonoids. The aim of this review is to provide basic information to build chilling-indicators and optimal nutrition management under adverse temperature conditions as broadly considering mineral uptake, carbohydrate metabolism and antioxidative defense system.

• Advances in pediatric surgery
• /
• v.7 no.2
• /
• pp.112-117
• /
• 2001

With the advances in neonatal intensive care, pediatric surgeons experience very low birth weight infants, weighing <1,500 g, more frequently. We report our 14 cases of very low birth weight infants with intestinal perforations without congenital causes, at the Asan Medical Center during the 11-year period from 1989 to 2000. The average birth weight was 919 g(563-1,490), and average gestational age was 206 days(161-286). There were nine males and five females, Operation was performed at an average age of 14.0 days(3-38). Ten neonates with symptomatic PDA were given indomethacin in an attempt to close the ductus. Bowel perforation involved the jejunum in two and ileum in twelve. At laparotomy, there were seven focal intestinal perforations, five typical NEC, one intussusception, and an unknown cause, Four neonates underwent resection and anastomosis of the bowel, and nine underwent exteriorization. One underwent resection and anastomosis after peritoneal drainage. Four patients had postoperative complications; two leakage of anastomosis, one stoma necrosis, and one internal herniation. Seven of fourteen patients survived(50.0 %). Seven patients died of septic complication. There was a significant difference in the birth weight and gestational age in survivors compared with those who died(p<0.05). There was an increased risk of bowel perforation in indomethacin treatment for PDA. Careful clinical observation and keen judgment are essential for this particular group of infants.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.1075-1080
• /
• 2015

A hybrid electric vehicle (HEV) powertrain has more than one energy source including a high-voltage electric battery. However, for a high voltage electric battery, the average current is relatively low for a given power level. Introduced to increase the voltage of a HEV battery, a compact, high-efficiency boost converter, sometimes called a step-up converter, is a dc-dc converter with an output voltage greater than its input voltage. The inductor occupies more than 30% of the total converter volume making it difficult to get high power density. The inductor should have the characteristics of good thermal stability, low weight, low losses and low EMI. In this paper, Mega Flux^® was selected as the core material among potential core candidates. Different structured inductors with Mega Flux^® were fabricated to compare the performance between the conventional air cooled and proposed potting structure. The proposed inductor has reduced the weight by 75% from 8.8kg to 2.18kg and the power density was increased from 15.6W/cc to 56.4W/cc compared with conventional inductor. To optimize the performance of proposed inductor, the potting materials with various thermal conductivities were investigated. Silicone with alumina was chosen as potting materials due to the high thermo-stable properties. The proposed inductors used potting material with thermal conductivities of 0.7W/m·K, 1.0W/m·K and 1.6W/m·K to analyze the thermal performance. Simulations of the proposed inductor were fulfilled in terms of magnetic flux saturation, leakage flux and temperature rise. The temperature rise and power efficiency were measured with the 40kW boost converter. Experimental results show that the proposed inductor reached the temperature saturation of 107℃ in 20 minutes. On the other hand, the temperature of conventional inductor rose by 138℃ without saturation. And the effect of thermal conductivity was verified as the highest thermal conductivity of potting materials leads to the lowest temperature saturations.

• Korean Journal of Materials Research
• /
• v.16 no.2
• /
• pp.99-105
• /
• 2006

This paper reports an improved bonding method using the IPA (isopropyl alcohol) assisted low-temperature bonding process for the PMMA (polymethylmethacrylate) micro CE (capillary electrophoresis) chip. There is a problem about channel deformations during the conventional processes such as thermal bonding and solvent bonding methods. The bonding test using an IPA showed good results without channel deformations over 4 inch PMMA wafer at $60^{\circ}C$ and 1.3 bar for 10 minutes. The mechanism of IPA bonding was attributed to the formation of a small amount of vaporized acetone made from the oxidized IPA which allows to solvent bonding. To verify the usefulness of the IPA assisted low-temperature bonding process, the PMMA micro CE chip which had a $45{\mu}m$ channel height was fabricated by hot embossing process. A functional test of the fabricated CE chip was demonstrated by the separation of fluorescein and dichlorofluorescein. Any leakage of liquids was not observed during the test and the electropherogram result was successfully achieved. An IPA assisted low-temperature bonding process could be an easy and effective way to fabricate the PMMA micro CE chip and would help to increase the yield.

• Journal of Gastric Cancer
• /
• v.10 no.4
• /
• pp.241-246
• /
• 2010

Purpose: Laparoscopy-assisted gastrectomy (LAG) has become a technically feasible and safe procedure for early gastric cancer treatment. LAG is being increasingly performed in many centers; however, there have been few reports regarding LAG at low-volume centers. The aim of this study was to report our early experience with LAG in patients with gastric cancer at a low-volume center. Materials and Methods: The clinicopathologic data and surgical outcomes of 39 patients who underwent LAG for gastric cancer between April 2007 and March 2010 were retrospectively reviewed. Results: The mean age was 68.3 years. Thirty-one patients had medical co-morbidities. The mean patient ASA score was 2.0. Among the 39 patients, 4 patients underwent total gastrectomy and 35 patients underwent distal gastrectomy. The mean blood loss was 145.4 ml and the mean operative time was 259.4 minutes. The mean time-to-first flatus, first oral intake, and the postoperative hospital stay was 2.8, 3.1, and 9.3 days, respectively. The 30-day mortality rate was 0%. Postoperative complications developed in 9 patients, as follows: anastomotic leakage, 1; wound infection, 1; gastric stasis, 2; postoperative ileus, 1; pneumonia, 1; cerebral infarction, 1; chronic renal failure, 1; and postoperative psychosis, 1. Conclusions: LAG is technically feasible and can be performed safely at a low-volume center, but an experienced surgical team and careful patient selection are necessary. Furthermore, for early mastery of the learning curve for LAG, surgeons need education and training in addition to an accumulation of cases.